WO2016209942A1

WO2016209942A1 - Composite gypsum board and methods related thereto

Info

Publication number: WO2016209942A1
Application number: PCT/US2016/038737
Authority: WO
Inventors: Alfred C. Li; Weixin D. Song; Yijun SANG; Gregg G. DIEFENBACHER; Annamaria VILINSKA; Brian J. CHRIST; Frederick T. Jones; Bradley W. TODD
Original assignee: United States Gypsum Company
Priority date: 2015-06-24
Filing date: 2016-06-22
Publication date: 2016-12-29

Abstract

Disclosed is a composite gypsum board comprising a board core and a concentrated layer of substantial thickness (e.g., at least about 0.02 inches). The concentrated layer includes a higher weight percentage of an enhancing additive than the board core. The board core has a thickness greater than the thickness of the concentrated layer and forms the bulk of the board volume. The concentrated layer has a higher density (e.g., at least about 1.1 times greater) than the density of the board core. Also disclosed is a method of preparing a composite gypsum board.

Description

COMPOSITE GYPSUM BOARD AN D M ETHODS RELATED THERETO

CROSS-REFERENCE TO R ELATED APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application Nos. 62/1 84,060, filed June 24, 2015, and 62/290,361 , filed February 2, 2016, and U.S.

Patent Application Nos. 15/186,176, filed June 1 7, 2016, 1 5/1 86,212, filed June 17, 2016, 15/186,232, filed June 17, 2016, and 1 5/186,257, filed June 17, 201 6, which are incorporated by reference.

BACKGROUND

[0002] Set gypsum (i.e., calcium sulfate dihydrate) is a well-known material that is used in many products, including panels and other products for building construction and remodeling. One such panel (often referred to as gypsum board) is in the form of a set gypsum core sandwiched between two cover sheets (e.g.. paper-faced board) and is commonly used in drywall construction of interior walls and ceilings of buildings. One or more dense layers, often referred to as "skim coats" may be included on either side of the core, usually at the paper-core interface.

[0003] During manufacture of the board, stucco (i.e., calcined gypsum in the form of calcium sulfate hemihydrate and/or calcium sulfate anhydrite), water, and other ingredients as appropriate are mixed, typically in a pin mixer as the term is used in the art. A slurry is formed and discharged from die mixer onto a moving conveyor carrying a cover sheet with one of the skim coats (if present) already applied (often upstream of the mixer). The slurry is spread over die paper (with skim coat optionally included on the paper). Another cover sheet, with or without skim coat, is applied onto the slurry to form die sandwich structure of desired thickness with the aid of e.g., a forming plate or the like. The mixture is cast and al lowed to harden to form set (i.e., rehydrated) gypsum by reaction of die calcined gypsum with water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is the desired hydration of die calcined gypsum that enables the formation of the interlocking matrix of set gypsum crystals, thereby imparting strength to the gypsum structure in the product. Heat is required (e.g., in a kiln) to drive off the remaining free (i.e., unreacted) water to yield a dry product. 10004 J The excess water thai is driven off represents inefficiency in the system. Energy input is required to remove the water, and the manufacturing process is slowed to

accommodate the drying step. However, reducing the amount of water in the system has proven to be very difficult without compromising other critical aspects of gypsum hoard, e.g., commercial gypsum board product, including board weight and strength.

[0005] Another challenge is reducing the weight of gypsum board while maintaining strength. One measure of the strength of board is "nail pull resistance," sometimes simply referred to as "nail pull." To reduce the weight of the board, foaming agent can be introduced into the slurry to form air voids in the final product. Replacing solid mass with air in the gypsum board envelope reduces weight, but that loss of solid mass can also result in less strength. Compensating for loss in strength is a significant obstacle in weight reduction efforts in the art.

[0006] It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art nor as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some regards and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached cl ims, and not by the ability of the claimed invention to solve any specific problem noted herein.

BRIEF SUMMARY

[0007] In one aspect, the disclosure provides a composite gypsum board. The composite board comprises a board core comprising set gypsum formed from at least water, stucco, and optionally, an enhancing additive. The board core defines first and second core faces in opposing relation and a concentrated layer. The concentrated layer is disposed in bonding relation to the first core lace. The concentrated layer is formed from the enhancing additive, water, and. e.g., a eementitious material, such as stucco, to form a bydrated cementitious material such as set gypsum in a continuous crystalline matrix. The enhancing additive is preferably more concentrated (by weight percentage) in the concentrated layer than in the board core. As used herein, any reference to the enhancing additive being "more

concentrated" (or variants of the term) in die slurry for forming the concentrated layer than i the slurry for forming board core includes the situations where (a) both the concentrated layer and the board core are formed from enhancing additive, and (b) the concentrated layer is formed from the enhancing addiiive but the board core contains zero, or no, enhancing additive.

[0008] The concentrated layer has a density of at least about 1 , 1 times higher than a density of the board core and has a thickness of from about 0.02 inches (about 0.05 cm) to about 0.2 inches (about 0.5 era) in some embodiments. The board core preferably has a thickness greater than the thickness of the concentrated layer, The enhancing addiiive includes a strength -imparting additive as described herein that helps produce desired strength properties as described herein.

[0009] Board formed from a concentrated layer slurry containing higher weight percentage of the enhancing additive than contained in the board core slurry allows for one or more efficiencies or process benefits. For example, the overall use of enhancing additive in the board can be reduced by focusing the enhancing additive in forming a smaller weight section of smaller thickness (i.e., the concentrated layer) and using less or no enhancing additive in forming a larger weight section of larger thickness (i.e., the board core).

Surprisingly and unexpectedly, the concentrated layer, formed from a higher weight percentage of the enhancing additive, is able to distribute the desired resulting properties throughout the board core, such that the board exhibits the strength properties. As a result, the board core can be made with less overall enhancing additive, and in some embodiments can be lighter and less dense than conventional board cores, in turn, overall board weight can be reduced as the density in a large weight section of the board (i.e., the core) is reduced. 10010] In the case of some enhancing additives, such as certain pregeiatinized starches, they can require water in a slurry, i.e., they increase water demand. By reducing the amount of the enhancing additive in the slurry for forming the board core, the water demand in the slurry for forming the core can be reduced in some embodiments. Thus, for example, overall water usage in preparing the board can be reduced, which further can improve efficiencies as less water is used in the system such that less water is required to be driveii off by heating in the kiln. As a result, manufacturing line speed can be improved and drying costs can be reduced.

1001 1 The composite gypsum board can be within a range of desired densities. In some embodiments, the board can be made at ultra-light weights, such as at a board density of about 33 pcf or less. It will be understood that board weight is a function of density and thickness. Thus, density can be used as a measure of board weight as will be understood in the art. Such ultra-light weights can be achieved without compromising desired strength properties. For example, in some embodiments, the composite gypsum board can. exhibit a nail pull resistance of at least about 65 lbs of feree (e.g., at least about 72 lbs of force, at least about 77 lbs of feree, etc.) according to ASTM C473-10, Method B.

[0012] in another aspect, the disclosure provides a method of making composite gypsum hoard. The method comprises preparing a concentrated layer slurry comprising water and the enhancing additive. The concentrated layer slurry can also include a base material to impart, e.g., a primary source of mass and density, such as a cernentitious material, e.g., stucco that can hydrate to form an interlocking matrix of set gypsum. The concentrated layer slurry is applied in a bonding relation to a first cover sheet to form a concentrated layer having a first face and a second face. The first face of the concentrated layer faces the first cover sheet. The method also comprises mixing at least water, stucco, and optionally the enhancing additive, to form a hoard core slurry. The board core slurry is applied in a bonding relation to the concentrated layer to form a board core. The board core has a first face and a second face, wherein the first board core face faces the concentrated layer second face. A second cover sheet is applied in bonding relation to the second board core face to form a board precursor. The hoard precursor is dried to form the board. When the board core slurry contains enhancing additive, the concentrated layer slurry contains a higher weight percentage of the enhancing slurry than the board core slurry. In some embodiments, the concentrated layer has a thickness of from about 0.02 inches (about 0.05 cm) to about 0.2 inches (about 0.5 cm). When dried, the hoard core has a thickness greater than the thickness of the concentrated layer.

[0013] In another aspect, the disclosure provides another method of making composite gypsum board. The method comprises preparing a concentrated layer slurry comprising water and the enhancing additive. The concentrated layer slurry can also include a base material to impart, e.g., a primary source of mass and density, such as a cernentitious material, e.g., stucco that can hydrate to form an interlocking matrix of set gypsum. The concentrated layer slurry is applied in a bonding relation to a first cover sheet to form a concentrated layer having a first face and a second face. The first face of the concentrated layer faces the first cover sheet. The method also comprises mixing at least water, stucco, and optionally the enhancing additive, to form a board core slurry. The board core slurry is applied in a bonding relation to the concentrated layer to form a board core. The board core has a first face and a second face, wherein the first board core face faces the concentrated layer second face. A second cover sheet is applied in bonding relation to the second hoard core face to form a board precursor. The board precursor is dried to form die board. When the board core slurry contains enhancing additive, the concentrated layer slurry contains a higher weight percentage of the enhancing slurry than the board core slurry. When dried, the board core has a thickness greater than the thickness of the concentrated layer.

[0014] Processes according to the disclosure can be used to produce composite board at any suitable density. In some embodiments, the board can be made at ultra-light weights, such as at a board density of about 33 pcf (about 530 kg m³) or less. Such ultra-light weights can be achieved without compromising desired strength properties. For example, in some embodiments, the composite gypsum board can exhibit a nail pull resistance of at least about 65 lbs of feree (e.g., at least about 72 lbs of feree, at least about 77 lbs of force, etc.) according to ASTM C473-10, Method B. Other aspects and embodiments will be apparent from the full description herein.

BR I EF DESCR IPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] FIG. 1 is a schematic sectional view of a composite gypsum board constructed in accordance with principles of the present disclosure.

[0016] FIG. 2 illustrates schematic flow diagrams of three alternate process arrangements

(labeled A, B. and C) that illustrate steps for preparing slurries for the board core and the concentrated layer in accordance with principles of the present disclosure,

[00.17] FIG. 3 is an illustration depicting a slurry head upstream of a roller used in forming a concentrated layer on a manufacturing line for gypsum vvallboard in a trial as discussed in Example 3 herein, wherein the slurry is absent glass fiber,

[0018] FIG. 4 is an il lustration depicting a slurry head upstream of a roller used in forming a concentrated layer on a manufacturing line for gypsum wall board in a trial as discussed in Example 3 herein, wherein the slurry contains glass fiber.

[0019] FIG. 5 is an illustration depicting the slurry forming an edge around the roller of the trial depicted in FIG. 3 as discussed in Example 3 herein, wherein the slurry is absent glass fiber.

[0020] FIG. 6 is an illustration depicting the slurry forming an edge around the roller of the trial depicted in FIG. 4 as discussed in Example 3 herein, wherein the slurry contains glass fiber. DETAILED DESCR IPTION

[0021 ] Embodiments of the disclosure provide a novel construction for a composite board (e.g., gypsum board, such as wallboard) and a method of making such board. As used herein, gypsum wallboard (often referred to as drywali), can encompass such board used not only for walls but also for ceilings and other locations as understood in the art. In one aspect, the composite board contains multiple layers which contain dilferent cementitious compositions, e.g., in the form of a continuous crystalline matrix of set gypsum in the final product. One layer forms the board core and another layer forms a concentrated layer of substantial thickness (e.g., at least about 0.02 inches, or about 0.05 cm). The board core is generally thicker than the concentrated layer in preferred embodiments and makes up the bulk (e.g., over about 60%, such as over about 70%, over about 75%, etc) of the volume of the board' s envelope. Typically, the board also includes top (face) and bottom (back) cover sheets.

[0022] The board core and the concentrated layer are both formed from cementitious material and water. In accordance with preferred embodiments of the disclosure, the concentrated layer is formulated to have a higher density than the board core has (e.g., at least about 1.1 times higher). To formulate a lower density board core, foaming agents as known in the art can be used in the board core, although other materials for reducing density can be included in the slurry for forming the board core, as an alternative or additional ingredient, such as lightweight filler including, tor example, lightweight aggregate or perlite, particularly if the additional expense can be accepted. The concentrated layer can include less or no foaming agent and/or less or no lightweight filler in order to achieve the desired higher density in that layer.

[0023] While not wishing to be bound by any particular theory, it is believed that the compositions of, and inter-relationships between, the respective layers in the composite board impart surprising and unexpected properties in the product. In particular, it is believed that the targeted use of enhancing additive- in the concentrated layer can be used to impart desired board properties, and enhance process efficiencies as desired, hi addition, in some embodiments, aspects such as (a) the thickness, density, and/or strength of the concentrated layer, and/or (b) the properties of the concentrated layer relative to the paper and the board core, respectively, can be used to optimize board properties as desired. Based at least in part on these aspects, it is believed that desired properties from the concentrated layer can be distributed and directed throughout the board, to thereby facilitate production of a composite board while maintaining physical properties into the board core as desired. [0024] In accordance with some embodiments, the dry concentrated layer has a stiffness value that is closer to a stiffness value of the top cover sheet to which it is generally adjacent, The concentrated layer has a higher stiffness value than the board core in some embodiments, Tims, the concentrated layer can be disposed between a material with relatively good stiffness and strength (i.e., the top cover sheet) and a material with less stiffness and strength (i.e., the board core) in some embodiments. It will be understood that stiffness value can be measured according to Young's modulus as known in the art.

[0025] While not wishing to be bound by any particular theory, it is believed that including a higher weight percentage of enhancing additive, which imparts desired strength properties, in the concentrated layer results in effective desired strength properties. The concentrated layer is disposed between a top cover sheet and a preferably lighter and weaker board core. Surprisingly and unexpectedly, the concentrated layer serves to absorb energy from a load and more uniformly distribute the load into the board core and throughout the board such that the load desirably will more readily attenuate and dissipate. As such, the inventive composite gypsum board will demonstrate good strength properties and allow for lower weiglii board to be produced by targeting enhanced strength in the concentrated layer where the property can be distributed into the board core. For example, this advantage can be illustrated via good results on a nail pull resistance and flexura! strength tests in some embodiments, as is understood in the art in accordance with ASTM 473-10, Method B.

Composition of Board Core and Concentrated Layer

[0026] In accordance with some embodiments of the disclosure, the composite gypsum board is tailored to include an enhancing additive in a higher concentration than the enhancing additive is included (if at all) in the board core. The resulting board can be formed to achieve a composite gypsum board with desired strength properties,

[9027] In accordance with some embodiments, it has been surprisingly and unexpectedly found drat the higher concentration of the enhancing additive in the concentrated layer relative to the board core results in efficient board performance with respect to desired strength properties, e.g., nail pull resistance, compressive strength, flexura! strength, etc. As such, the present inventors have found thai, the usage of the enhancing additives can be optimized in accordance with preferred embodiments by tailoring the formulations of the compositions of the respective board core and concentrated layers to include enhancing additives where their effect can provide more of an impact to achieve desired strength properties (i.e., in a higher weight percentage in the concentrated layer than in the board core), and a lower overall water demand. This discovery imparts a considerable advantage including, but not limited to, reducing overall enhancing additive usage and, hence, cost of the raw material, enhancing manufacturing efficiency, and enhancing product strength, e.g., allowing for lower weight product with sufficient strength properties.

[0028] In some embodiments, the slurry for forming the concentrated layer contains at least about 1 .2 times the concentration of the enhancing additive as compared with the slurry for forming board core, such as, for example, at least about 1 ,5 times, at least about 1.7 times, at least about 2 times, at least about 2.5 times, at least about 3 times, at least about 3.5 times, at least about 4 times, at least about 4.5 times, at least about 5 times, at least about 6 times, etc., wherein each of these ranges can ha ve any suitable upper limit as appropriate, such as, for example, about 60, about 50, about 40, about 30, about 20, about 10, about 9, about 8, about 7, about 6.5, about 6, about 5.5, about 5, about 4.5, about 4, about 3.5, about 3, about 2.5, about 2, about 1.5, etc. It will be understood that "higher concentration," as used herein, refers to relative amounts of an enhancing additive (by weight of the stucco), as opposed to gross amounts of ingredients. Since the board core provides a higher bulk volume and thickness contribution to the board, as compared with such contribution by the concentrated layer, it is possible that any particular additive may be provided in a higher total gross amount in the board core slurry, e.g., in pounds or kilograms, yet be provided in a lower weight concentration as compared with the slurry for the concentrated layer, i.e., in a lower relative amount, e.g., in weight percentage (wt.%),

[0029] Surprisingly and unexpectedly, some embodiments of the disclosure are effective in reducing the overall water usage in making the composite gypsum board. In this regard, by tailoring the respective compositions of the concentrated layer and the board core, the total amount of water used to make the board can be reduced such that water usage is optimized since the water is present in a higher concentration where it is needed more (e.g., in the concentrated layer) and reduced where it is needed less (e.g., in the board core),

[0030] It will be understood that, since set gypsum is formed from a stucco slurry (sometimes cal led a gypsum slurry) containing water and stucco, a water-to-stucco ratio ("WSR") can be observed. In some embodiments, the board core, which can form the bulk of the board volume, can be formed from a lower WSR as compared with the WSR used to form the concentrated layer. Thus, the overall water usage and WSR in the composite gypsum board as a whole can advantageously be brought down in some embodiments since the contribution to the overall board volume by the concentrated layer is less than the contribution to the overall board volume by the bo'ard core.

[0031] The board core and concentrated layer can be formed from any suitable WSR, in some embodiments, the concentrated layer is formed from slurry having a WSR that is higher than the WSR of the slurry used to form the board core. For example, in some embodiments, the concentrated layer is formed from a slurry having a WSR that is at least about 1.2 times higher than the WSR of the slurry used to form the board core (e.g., at least about 1 ,5 times higher, at least about 1.7 times higher, at least about 2 times higher, at least about 2.2 times higher, at least about 2.5 times higher, at least about 2.7 times higher, at least about 3 times higher, at least about 3.2 times higher, at least about 3.5 times higher, at least about 3.7 times higher, at least about 4 times higher etc., wherein each of these ranges can have any suitable upper limit as appropriate, such as, for example, about 7, about 6.5, about 6, about 5.5, about 5, about 4.5, about 4, about 3,5, about 3, about 2,5, about 2, about 1 ,5, etc,)

[0032] In some embodiments, the board core is formed from stucco slurry having a water-stucco ratio from about 0.3 to about 1.3, e.g., from about 0.3 to about 1.2, from about 0.3 to about 1.2, from about 0,3 to about 1.2, from about 0.3 to about 1.2, from about 0.3 to about 1.1 , from about 0.3 to about 1 , from about 0.3 to about 0.9, from about 0.4 to about 1.3, from, about 0.4 to about 1.2, from about 0.4 to about 1 ,1 , from about 0.4 to about 1 , from about 0.4 to about 0.9, from about 0.5 to about 1.3, from about 0.5 to about 1.2, from about 0.5 to about. 1 , 1 , from about 0,5 to about 1 , from about 0.5 to about. 0,9, from about 0.6 to about 1.3, from about 0.6 to about 1.2, from about 0,6 to about 1.1 , from about 0.6 to about 1 , from about 0.6 to about 0.9, from about 0.6 to about 0,8, or from about 0.6 to about 0.7.

[0033] In some embodiments, lower water-stucco ratios are preferred, e.g., from about 0.3 to about 0,8, such as, for example, from about 0.3 to about 0.7, from about 0.3 to about 0.6, from about. 0.3 to about 0.5, from about 0.3 to about 0.4, from about 0.4 to about 0.8, from about 0.4 to about 0.7, from about 0.4 to about 0.6, from about 0,4 to about 0.5, from about 0.5 to about 0,8, from about 0,5 to about 0.7, from about 0.5 to about 0.6, from about 0.6 to about 0,8, from about 0.6 to about 0.7, etc.

[0034] In some embodiments, the concentrated layer is formed from a slurry having a water-stucco ratio from about 0.7 to about 2, such as, for example, from about 0.7 to about 1.7, from about 0.7 to about 1.4, from about 0.7 to about 1.2, from about 0,7 to about 1 , from about 0.8 to about 2, from about 0.8 to about 1 .7, from about 0.8 to about 1.4, from about 0.8 to about 1.2, from about 0.8 to about 1 , from about 1 to about 2, from about 1 to about 1.7, from about 1 to about 1.4, from about 1 to about 1.2, from about 1.2 to about 2, from about 1 ,2 to about 1.7. from about 1.2 to about 1 .4, from about 1 ,4 to about 2, from about 1 ,4 to about 1.7, etc. The concentrated layer can have a higher water content to satisfy the water demand of enhancing additives. Since the enhancing additive content is more concentrated in the concentrated layer in some embodiments, the higher water demand can be more isolated to the concentrated layer, thereby allowing for a lower WSR in the board core, and, advantageously, a lower water usage overall, particularly in view of the board core's large contribution to the volume bulk of the composite board.

Composite Board Density

[0035] The composite gypsum board according to embodiments of the disclosure has utility in a variety of desired densities for gypsum board, i.e.,, drywall or wallboard (which can encompass such board used not only for walls but also for ceilings and other locations as understood in the art). As noted herein, board weight is a function of thickness. Since boards are commonly made at varying thicknesses (e.g., 3/8 inch, ½ inch, ¾ inch, one inch, etc.), board density is used herein as a measure of board weight. The advantages of the composite gypsum board in accordance with embodiments of the disclosure can be seen at a range of dry densities, including up to heavier board densities, e.g., about 43 pef (about 690 kg m³) or less, such as from about 18 pcf (about 290 kg m^"") to about 43 pet, from about 20 pef (about 320 kg m³) to about 43 pcf, from about 20 pcf to about 40 pcf (about 640 kg/nr'), from about 24 pcf (about 380 kg m³) to about 43 pcf, from about 27 pef (about 430 kg m³) to about 43 pcf, from about 20 pcf to about 38 pcf (about 610 kg/m³), from about 24 pcf to about 40 pcf, from about 27 pcf to about 40 pcf, from about 20 pef to about. 37 pef (about 600 kg/m ), from about 24 pcf to about 37 pcf, from about 27 pef to about 37 pcf. from about 20 pcf to about 35 pcf (about 560 kg/m"), from about 2.4 pcf to about 35 pet, from about 27 pcf to about 35 pcf, etc.

[0036] As noted herein, removing solid mass from gypsum wallboard can lead to considerable difficulty in compensating for the concomitant loss in strength. Some embodiments of the disclosure surprisingly and unexpectedly enable the use of lower weight board with good strength, lower water demand, and efficient use of enhancing additive. For example, in some embodiments, dry board density can be from about 16 pcf to about 33 pef, e.g., from about 16 pcf to about 27 pcf, from about 16 pcf to about 24 pcf, from about 18 pcf to about 33 pef (about 530 kg πΓ), from about 18 pet to about 31 pcf, from about 18 pet to about 30 pcf, from about ! 8 pcf to about 27 pcf, from about 1 8 pcf to about 24 pcf, from about 20 pcf to about 33 pcf, from about 20 pcf to about 32 pcf (about 510 kg/m^J), from about 20 pcf to about. 31 pcf (about 500 kg/^'m³), from about 20 pcf to about 30 pcf (about 480 kg/m^'' ), from about 20 pcf to about 30 pcf, from about 20 pcf to about 29 pcf (about 460 kg/m^), from about 20 pcf to about 28 pcf (about 450 kg/m ³ ), from about 21 pcf (about 340 kg m^"5) to about 33 pcf, from about 21 pcf to about 32 pc from about 21 pcf to about 33 pcf, from about 21 pcf to about 32 pci, from about. 21 pcf to about 31 pcf, from about 21 pcf to about. 30 pcf, from about 21 pcf to about 29 pcf, from about 21 pcf to about 28 pcf, from about 21 pcf to about 29 pcf, from about 24 pcf to about 33 pcf, from about 24 pcf to about 32 pcf, from about 24 pcf to about 31 pcf, from about 24 pcf to about 30 pcf, from about 24 pcf to about 29 pcf, from about 24 pcf to about 28 pel, or from about 24 pcf to about 27 pcf.

Composite Board Structure and Assembly

[0( 37] To illustrate an embodiment of the disclosure, reference is made to FIG, 1 , which shows a schematic cross-sectional view of a composite gypsum board 10, A face paper 12 serves as a top cover sheet. The face paper 12 has a first face 14 and a second face 16. A concentrated layer 18 is in bonding relation to face paper 12. The concentrated layer 18 has a first face 20 and a second face 22. A board core 24 has a first face 26 and a second face 28. A back paper 30 serves as a bottom cover sheet. The back paper 30 has a first face 32 and a second face 34.

[0038] As seen in FIG. I , the composite gypsum board 10 is arranged such that face 16 of the face paper 12 faces the first face 20 of the concentrated layer 18 and the second face 22 of the concentrated layer 18 faces the first face 26 of the core 24. The second face 28 of the core 24 faces the first face 32 of the back paper 30.

[0039] It will be understood that composite gypsum board in accordance with some embodiments can be constructed and used in an assembly as will be understood in the art. Generally, as will be understood, the composite boards can be affixed in any suitable arrangement to studs formed of any suitable material such as wood, metal or the like. The top or face cover sheet of the board faces out and is generally decorated (e.g., with paint, texture, wallpaper, etc.) in use while the bottom or back cover sheet faces the studs, A cavity is normally present behind the stud, facing the back paper, in use. If desired, insulation material as known in the art optionally can be placed in the cavity, in one embodiment, the assembly comprises two composite boards connected by studs with a cavity there between, facing the bottom cover sheets of the respective boards.

Board Core

[0040] The board core forms the majority of the volume of the composite gypsum board, In some embodiments, the board core forms at least about 60% of the board volume, e.g., at least about 70% of the board volume, at least about 80% of th board volume, at least about 90% of the board volume, at least about 92%, at least about 95%, at least about 97%, etc. While the concentrated layer has substantial thickness, the board core can be considerably thicker. For example, in some embodiments, the dry board core can be from about 2.5 times to about 35 times as thick as the dry concentrated layer, e.g., from about 2.5 times to about 30 times, from about 2.5 times to about 25 times, from about 2.5 times to about 20 times, from about 2.5 times to about 1 5 times, from about 2.5 times to about 10 times, from about 2.5 times to about 5 times, from about 2.8 times to about 35 times, from about 2,8 times to about 30 times, from about 2.8 times to about 25 times, from about 2,8 times to about 20 times, from about 2.8 times to about 15 times, from about 2.8 times to about 10 times, from about 2.8 times to about 5 times, from about 5 times to about 35 times, from about 5 times to about 30 times, from about 5 times to about 25 times, from about 5 times to about 20 times, from about 5 times to about 1.5 times, or from about 5 times to about 10 times as thick as the concentrated layer.

[0041 ] In some embodiments, the board core is from about 8 times to about 16 times as thick as the concentrated layer, e.g., from about 8 times to about 12 times, from about 9 times to about 16 times, from about 9 times to about 1 times, from about 9 times to about 12 times, from about 10 times to about 16 times, from about 10 times to about 14 times as thick as the concentrated layer, etc,

[0042] The board core is formed from at least water and stucco. As referred to herein throughout, stucco can be in the form of calcium sulfate alpha hemihydrate, calcium sulfate beta hemihydrate, and/or calcium sulfate anhydrite. The stucco can be fibrous or non-fibrous, in addition to the stucco and water, the board core is formed from an agent that contributes to its lower density, such as a low density filler (e.g., perlite, low density aggregate or the like), or foaming agents. Various foaming agent regimes are well known in the art. Foaming agent can be included to form an air void distribution within the continuous crystalline matrix of set gypsum. In some embodiments, the foaming agent comprises a major weight portion of unstable component, and a minor weight portion of stable component (e.g., where unstable and blend of stable/unstable are combined). The weight ratio of unstable component to stable component is effective to form an air void distribution within the set gypsum core. See, e.g., U.S. Patents 5,643,510; 6,342,284; and 6,632,550. in some embodiments, the foaming agent comprises an alkyl sulfate surfactant.

[0043] Many commercially known foaming agents are available and can be used in accordance with embodiments of the disclosure, such as the HYONIC line (e.g., 25AS) of soap products from GEO Specialty Chemicals, Ambler, PA. Other commercially available soaps include the Polystep B25, from Stepan Company, Northfleld, Illinois. The foaming agents described herein can be used alone or in combination with other foaming agents. The foam can be pregenerated and then added to the stucco slurry. The pregeneration can occur by inserting air into the aqueous foaming agent. Methods and apparatus for generating foam are well known. See, e.g., U.S. Patents 4,518,652; 2,080,009; and 2,017,022.

[0044] In some embodiments, the foaming agent, comprises, consists of, or consists essentially of at least one alkyl sulfate, at least one alkyl ether sulfate, or any combination thereof but is essentially free of an olefin (e.g., olefin sulfate) and/or alkyne, Essentially free of olefin or alkyne means that the foaming agent contains either (i) 0 wt.% based on the weight of stucco, or no olefin and/or alkyne, or (ii) a ineffective or (iii) an immaterial amount of olefin and/or alkyne. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using olefin and/or alkyne foaming agent, as one of ordinary skill in the art will appreciate. An immaterial amount may be, e.g., below about 0.001 wt.%, such as below about 0.0005 wt.%, below about 0,001 wt.%, below about O.OOOOl wt.%, etc., based on the weight of stucco, as one of ordinary skill in the art will appreciate.

[0045] Some types of unstable soaps, in accordance with embodiments of the disclosure, are alkyl sulfate surfactants with varying chain length and varying cations. Suitable chain lengths, can be, for example, Cg-C^, e.g., Cg-Cjo, or C(o-C; 2. Suitable cations include, for example, sodium, ammonium, magnesium, or potassium. Examples of unstable soaps include, for example, sodium dodecyl sulfate, magnesium dodecyl sulfate, sodium decyl sulfate, ammonium dodecyl sulfate, potassium dodecyl sulfate, potassium decyl sulfate, sodium octyl sulfate, magnesium decyl sulfate, ammonium decyl sulfate, blends thereof, and any combination thereof. [0046] Some types of stable soaps, in accordance with embodiments of the disclosure, are a!koxylaied (e.g., ethoxylated) alkyl sulfate surfactants with varying (generally longer) chain length and varying cations. Suitable chain lengths, can be, for example, CIO-CH, e.g., Cj₂- Cj.i, or C[o-C i2. Suitable cations include, for example, sodium, ammonium, magnesium, or potassium. Examples of stable soaps include, for example, sodium laureih sulfate, potassium laureih sulfate, magnesium laureih sulfate, ammonium laureth sulfate, blends thereof, and any combination thereof. In some embodiments, any combination of stable and unstable soaps from these lists can be used.

[0047] Examples of combinations of foaming agents and their addition in preparation of foamed gypsum products are disclosed in U.S. Patent 5,643,510, herein incorporated by reference. For example, a first foaming agent which forms a stable foam and a second foaming agent which forms an unstable foam can be combined, hi some embodiments, the first foaming agent is soap, e.g., with an alkoxylated alkyl sulfate soap with an alkyl chain length of 8-12 carhon atoms and an alkoxy (e.g., ethoxy) group chain length of 1-4 units, The second foaming agent is optionally an unalkoxylated (e.g., unethoxylated) alkyl sulfate soap with an alkyl chain length of 6-20 carbon atoms, e.g., 6-18 or 6-16 carbon atoms. Regulating the respective amounts of these two soaps, in accordance with some embodiments, is believed to allow for control of the board foam structure until about 100% stable soap or about 100% unstable soap is reached.

[0048] In some embodiments, a fatty alcohol optionally can be included with th foaming agent, e.g., in a pre-mix to prepare the foam. This can result in an improvement in the stability of the foam, thereby allowing better control of foam (air) void size and distribution. The fatty alcohol can be any suitable aliphatic fatty alcohol. It will be understood that, as defined herein throughout, "aliphatic" refers to alkyl, alkenyl, or alkynyl, and can be substituted or unsubstituted. branched or unhranehed, and saturated or unsaturated, and in relation to some embodiments, is denoted by the carbon chains set forth herein, e.g., C_x-C_y, where x and y are integers. The term aliphatic thus also refers to chains with heteroatom substitution that preserves the hydrophobicity of the group. The fatty alcohol can be a single compound, or can be a combination of two or more compounds.

(0049] In some embodiments, the optional fatty alcohol is a C6-C20 fatty alcohol (e.g., ,-

C|g,€ C: ] 6, C-6- :4, Q,-C[2, &-Cio, Ce- g, Cs-Cjf,, g~C] 4, Cg-Ci2, Cg-C;o, C:o-C;,¾, C|G-C j4,

Cio-C i2 , Ci2-C :/„ Ci2-C j4, or C 14-C16 aliphatic fatty alcohol, etc.). Examples include octanol, nonanol, decano⁾, undecano⁾, dodecanol, or any combination thereof. The C ;o~C₂o fatty alcohol comprises a linear or branched C ,~Oji} carbon chain and at least one hydroxyl group. The hydroxyl group can be attached at any suitable position on the carbon chain but is preferably at or near either terminal carbon. In certain embodiments, the hydroxyl group can be attached at the α-, β-, or γ-position of the carbon chain, for example, the C -Cao fatty

'¾>"^'"" ^"'Ύ"^"

alcohol can comprise the following structural subunits: ^"'-'·^■ ^ , OH _?: or

- 1 hus, examples of. a desired optional tatty alcohol in accordance with some embodiments are 1 -dodecanol, 1 -undeeanol, 1 -deeanol, 1 -nonanol, 1 -octanol, or any combination thereof.

[ΘΘ50] In some embodiments, the optional foam stabilizing agent comprises the fatty alcohol and is essentially free of fatty acid alkyloamides or carboxylie acid taurides. In some embodiments, the optional foam stabilizing agent is essentially free of a glycol, although glycols can be included in some embodiments, e.g., to allow for higher surfactant content. Essentially free of any of the aforementioned ingredients means that the foam stabilizer contains either (i) 0 wt.% based on the weight of any of these ingredients, or (ii) an ineffective or (iii) an immaterial amount of any of these ingredients. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using any of these ingredients, as one of ordinary skill in the art will appreciate. An immaterial amount may be, e.g., below about 0.0001 wt.%, such as below about 0.00005 wt.%, below about 0.00001 wt.%, below about 0.000001 wt.%, etc, based on the weight of stucco, as one of ordinary skill in the art will appreciate.

[0051 J ft has been found that suitable void distribution and wall thickness

(independently) can be effective to enhance strength, especially in lower density board (e.g., below about 35 pel). See, e.g., US 2007/0048490 and US 2008/0090068. Evaporative water voids, generally having voids of about 5 pm or less in diameter, also contribute to the total void distribution along with the aforementioned air (foam) voids, in some embodiments, the volume ratio of voids with a pore size greater than about 5 microns to the voids with a pore size of about 5 microns or less, is from about 0.5: 1 to about 9: 1 , such as, for example, from about 0.7: 1 to about 9: 1 , from about 0.8: 1 to about 9: 1 , from about 1 .4: 1 to about 9: 1 , from about 1 .8: 1 to about 9: 1 , from about 2.3 : 1 to about 9: 1 , from about 0.7: 1 to about 6: 1 , from about 1 .4: 1 to about 6: 1 , from about 1 .8: 1 to about 6: 1 , from about (5.7: 1 to about 4: 1 , from about 1 .4: 1 to about 4: 1 , from about 1 .8: 1 to about 4: 1 , from about 0.5: 1 to about 2.3 : 1 . from

1 "> about 0.7: 1 to about 2.3 : 1 , from about 0,8: 1 to about 2.3 : 1 , from about 1 .4: 1 to about 2,3 : 1 , from about 1.8: 1 to about 2.3 : 1 , etc.

[0052 ] As used herein, a void size is calculated from the largest diameter of an individual void in the core. The largest diameter is the same as the Feret diameter. The largest diameter of each defined void can be obtained from an image of a sample, images can be taken using any suitable technique, such as scanning electron microscopy (SEM), which provides two- dimensional images. A large number of pore sizes of voids can be measured in an SEM image, such that the randomness of the cross sections (pores) of the voids can provide the average diameter. Taking measurements of voids in multiple images randomly situated throughout the eore of a sample can improve this calculation. Additionally, building a three- dimensional si ereological model of the core based on several two-dimensional SEM images can also improve the calculation of the void sizes. Another technique is X-ray CT-scanning analysis (XMT), which provides a three-dimensional image. Another technique is optical microscopy, where light contrasting can be used to assist in determining, e.g., the depth of voids. The voids can be measured either manually or by using image analysis software, e.g., ImageJ, developed by N1H. One of ordinary skill in the art will appreciate that manual determination of void, sizes and distribution from the images can be determined by visual observation of dimensions of each void. The sample can be obtained by sectioning a gypsum board,

[0053] The foaming agent can be included in the core slurry in any suitable amount, e.g., depending on the desired density. In some embodiments, the foaming agent is present in the slurry for forming the board core, e.g., in an amount of less than about 0.5% by weight of the stucco such as about 0.01% to about 0.5%, about 0.01 % to about 0.4%, about 0.01 % to about 0.3%, about 0.01 % to about 0.25%, about 0.01 % to about 0.2%, about 0.01 % to about 0, 15% , about 0.01 % to about 0.1 %, about 0.02% to about 0.4%, about 0.02% to about 0.3%, about 0.02% to about 0.2%, etc., all by weight of the stucco. Since the concentrated layer has a higher density, the slurry for forming the concentrated layer can be made with less (or no) foam, e.g., in an amount from about 0,0001 % to about 0.05% by weight of the stucco, e.g., from about 0.0001 % to about 0.025% by weight of the stucco, from about 0,0001 % to about 0.02% by weight of the stucco, or from about 0.001 % to about 0.015% by weight of the stucco.

[0054] The fatty alcohol can be present, if included, in the core slurry in any suitable amount, in some embodiments, the fatty alcohol is present in the core slurry in an amount of from about 0.0001 % to about 0.03% by weight of the stucco, e.g., from about 0.0001% to about 0.025% by weight of the stucco, from about 0.0001 % to about 0.02% by weight of the stucco, or from about 0.0001% to about 0,01 % by weight of the stucco. Since the

concentrated layer slurry can have less or no foam, the fatty alcohol is not required in the concentrated layer, or else can be included in a lower amount, such as from about 0.0001% to about 0.004% by weight of the stucco, e.g., from about 0.00001% to about 0,003% by weight of the stucco, from about 0,00001 % to about 0.00.15% by weight of the stucco, or from about 0.00001 % to about 0.001 % by weight of the stucco.

[0055] Enhancing agent for imparting strength properties as described herein can also optionally be included in the slurry for forming the board core. Other ingredients as known in the art can also be included in the board, core slurry, including, for example, accelerators, retarders, etc. Accelerator can be in various forms (e.g., wet gypsum accelerator, heat resistant accelerator, and climate stabilized accelerator). See, e.g., U.S. Patents 3,573,947 and 6,409,825. In some embodiments where accelerator and/or retarder are included, the accelerator and/or retarder each can be in the stucco slurry for forming the board core in an amount on a solid basis of, such as, from, about 0% to about 10% by weight of the stucco (e.g., about 0.1 % to about 10%), such as, for example, from about 0% to about 5% by weight of the stucco (e.g., about 0.1 % to about 5%).

[0056] hi addition, the board core and/or concentrated layer can be further formed from at least one dispersant to enhance fluidity in some embodiments, The dispersants may be included in a dry form with other dry ingredients and/or in a liquid form with other liquid ingredients in stucco slurry. Examples of dispersants include naphthalenesulfonates, such as polynaphthalenesulfonic acid and its salts (polynaphthalenesu!fonates) and derivatives, which are condensation products of naphtha] enesulfonic acids and formaldehyde; as well as polycarboxylate dispersants, such as polycarboxylic ethers, for example, PCE21 1 , PCE1 1 1 , 1641 , 164 I F, or PCE 2641 -Type Dispersants, e.g., MELFLUX 264 IF, MELFLUX 265 I F, M ELF LUX 1641 F, MELFLUX 2500L dispersants (BASF), and COATEX EthacryJ M, available from Coatex, inc.; and/or lignosuifonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers, byproducts from the production of wood pulp using sulfite pulping. One example of a lignin useful in the practice of principles of embodiments of the present disclosure is Marasperse€-21 available from Reed Lignin Inc.

[00571 Lower molecular weight dispersants are generally preferred. For

naphthaienesuifonatc dispersants, in some embodiments, they are selected, to have molecular weights from about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000). in some embodiments, higher water demand naphthalenesulfonates can be used, e.g., having molecular weights above 10,000. As another illustration, for PCE21 1 type dispersants, in some embodiments, the molecular weight can be from about 20,000 to about 60,000, which exhibit less retardation than dispersants having molecular weight above 60,000.

[0058] One example of a naphthalenesulfonate is D!LOFLO, available from GEO Specialty Chemicals. DiLOFLO is a 45% naphthalenesulfonate solution in water, although other aqueous solutions, for example, in the range of about 35% to about 55% by weight solids content, are also readily available. Naphthalenesulfonates can be used in dry solid or powder fomi, such as LOMAR D, available from GEO Specialty Chemicals, for example. Another example of naphthalenesulfonate is DAXAD, available from GEO Specialty Chemicals, Ambler, PA.

[0059] If included, the dispersant can be provided in any suitable amount. In sorne embodiments, for example, the dispersant can be present in the concentrated layer slurry in an amount, for example, from about 0.05% to about 0,5%, e.g., about 0.1 % to about 0,2% by weight of the stucco, and can be present in the board core slurry in an amount, for example, from about 0% to about 0.7%, e.g., 0% to about 0.4% by weight of the stucco.

[0060] in some embodiments, the board core and/or concentrated laver can be further formed from at least one phosphate-containing compound, if desired, to enhance green strength, dimensional stability, and/or sag resistance. For example, phosphate-containing components useful in sorne embodiments include water-soluble components and can be in the form of an ion, a salt, or an acid, namely, condensed phosphoric acids, each of which comprises two or more phosphoric acid units; salts or ions of condensed phosphates, each of which composes two or more phosphate units; and monobasic salts or monovalent ions of orthophosphates as well as water-soluble acyclic polyphosphate salt. See, e.g., U.S. Patents 6,342,284; 6,632,550; 6,815,049; and 6,822,033.

[0061 [ Phosphate compositions if added in some embodiments can enhance green strength, resistance to permanent deformation (e.g., sag), dimensional stability, etc. Green strength refers to the strength of the board while still wet during manufacture. Due to the rigors of the manufacturing process, without sufficient green strength, a board precursor can become damaged on a manufacturing line.

[0062] Tnmetaphosphate compounds can be used, including, for example, sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium frimetaphosphate. Sodium trimetaphosphate (STMP) is preferred, although other phosphates may be suitable, including for example sodium tetrametaphosphate, sodium

bexameiaphosphate having from about 6 to about 27 repeating phosphate units and having the molecular formula Na_n.₍.2P_n0_3rt<-i wherein n^::::6-27, teirapotassium pyrophosphate having the molecular formula K4P2O7, trisodium dipotassium tripolyphosphate having the molecular formula

sodium tripolyphosphate having the molecular formula

tetrasodium pyrophosphate having the molecular formula Na^i^O_?, aluminum

trimetaphosphate having the molecular formula AlfPC)?)*, sodium acid pyrophosphate having the molecular formula

ammonium polyphosphate having 1 ,000-3,000 repeating phosphate units and having the molecular formula (NH4)_ir¾P_riQ ii+i wherein n= 1,000-3 ,000, or polyphosphorie acid having two or more repeatin phosphoric acid units and having the molecular formula

wherein n is two or more.

[0063] If included, the polyphosphate can be present in any suitable amount. To illustrate, in some embodiments, the polyphosphate can be present in the concentrated layer slurry in an amount, for example, from about 0.1% to about 1 %, e.g., about. 0.2% to about 0.4% by weight of the stucco, and is present in the board core slurry in an amount, for example, from about 0% to about 0.5%, e.g., from about 0% to about 0,2% by weight of the stucco. Tims, the dispersant and polyphosphate optionally can be in any suitable amount in the core slurry and/or in the concentrated layer slurry, such that in some embodiments, the core slurry contains a higher weight percentage of the dispersant and/or polyphosphate than the concentrated layer slurry. In alternate embodiments, the dispersant and/or polyphosphate are included in higher weight percentage in the concentrated layer slurry than in the core slurry (including core slurries with zero dispersant and/or polyphosphate) (with or without the enhancing additive being more concentrated in the concentrated layer).

{006 ] The hoard core can have any suitable density useful in contributing to a desired total composite board density, such as, for example, a core density of from about 16 pcf {about 260 kg m³) to about 40 pcf e.g., from about 18 pcf to about 40 pcf, 18 pcf to about 38 pcf, 18 pcf to about 36 pcf, 18 pcf to about 32 pcf, 20 pcf io about 40 pel, 20 pcf to about 36 pcf, 20 pcf to about 32 pel^', 22 pcf to about 40 pcf, 22 pcf to about 36 pcf, 22 pcf to about 32 pcf, 26 pcf to about 40 pcf, 26 pcf to about 36 pcf, or 26 pcf to about 32 pcf. In some embodiments, the board core has an even lower density, e.g.. about 30 pcf or less, about 29 pcf (about 460 kg nv') or less, about 28 pcf or less, about 27 pcf (about 430 kg^'m³) or less, about 26 pcf or less, etc. For example, in some embodiments, the core density is from about 12 pcf (about 190 kgbrr') to about 30 pcf, from about 14 pcf (about 220 kg/m^J) to about 30 pcf 16 pcf to about 30 pcf, 16 pcf to about 28 pcf, 16 pcf to about 26 pcf, 16 pcf to about 22 pcf (about 350 k.g/rrf ), 18 pcf to about 30 pcf, 18 pcf to about 28 pcf, 18 pcf to about 26 pcf 18 pcf to about 24 pcf, 20 pcf to about 30 pcf, 20 pcf to about 28 pcf, 20 pcf to about 26 pcf, 20 pcf to about 24 pcf, 22 pcf to about 28 pcf, etc.

Concentrated Layer

[0065] The concentrated layer is "concentrated" in some embodiments because of the presence of an enhancing additive in the concentrated layer slurry in an amount that is more concentrated than the amount by weight, if any, of the same enhancing additive in the board core slurry. In some embodiments, the concentrated layer has a density that is at least about 1.1 times higher than the density of the board core, and/or has substantial thickness, such as at least about 0.02 inches (about 0,05 cm).

[0066] The concentrated layer is formed from slurry comprising water and eementitioiis material, such as stucco, which hydrates to form a set hydrated material, e.g., continuous crystalline matrix of set gypsum, in the final product, in preferred embodiments, the eementitious material is stucco, and the slurry for forming the concentrated layer is a stucco slurry. As noted, the slurry for forming the concentrated layer further comprises an enhancing additive in a higher relative weight concentration than the concentration of the enhancing additive in the slurry for forming the board core. The slurry for forming the concentrated layer can optionally include foaming agent or other lightweight agent as described herein to produce the desired density for the concentrated layer, If included, in some embodiments the foaming or other lightweight agent will be present in a lower amount in the slurry for forming the concentrated layer, or the foaming agent can be '^''beaten out" to at least some extent to reduce the population of foam voids as known in the art in order to achieve the desired higher density than the density of the board core. Thus, the formation of the concentrated layer to the desired density through an effective (or no) amount of foaming agent or other lightweight agent can be achieved as described herein and through the ordinary skill in the art. Other ingredients such as accelerator and retarder can optionally be included in the concentrated layer as desired as described herein.

[0067] Fibers can further be included in the concentrated layer as an optional additive to improve the process of preparing gypsum board. In this regard, as explained herein, the concentrated layer slurry can be applied to the paper, e.g., at a high rate of speed and with the use of a roller or other spreading means, which forms a head of slurry that accumulates upstream of the roller before it is applied evenly to the paper downstream of the roller (and whereby board edges are typically formed around the ends of the roller from the concentrated layer slurry). The environment in which the concentrated layer is applied is transient with three-dimensional oscillation, leading to scalloping in the slurry, whereby relatively large ah entrain ents can occur, which can cause a rough, uneven slurry that can lead to defects in the board if not addressed. Such defects can include the formation of large air pockets which are referred to as voids or blisters, as well as del animation of the paper, soft and/or hard edges, etc.

[0068] There are a variety of mechanical and other treatments available for addressing the scalloping in the flow induced by the unsteady environment in the process, including the use of mechanical pieces to break up air pockets as known in the art, such as vibrators on the line, as well as slurry spreaders, various mixer discharge treatments, as well as forrrmlation adjustments, including water/stucco ratio, viscosity of the slurry, etc. However, the inventors have discovered another optional technique, which is the addition of fiber to the concentrated layer slurry as a way to form a smoother slurry, for example, at the head where the concentrated layer is applied (e.g., upstream of a roller in a preferred embodiment), with less scalloping and less large air pockets. While not wishing to be bound by any particular theory, it is believed that the fibers advantageously improve the rheology of the slurry in order to ensure a smoother flow. It is also believed that the fibers improve the hydrodynamic properties of the slurry such that viscosity, rheology and the balance of iriterpartiele forces of the slurry are improved, the slurry is more evenly distributed on the application roller, and undesirable entrained air is more easily released from the slurry.

0069] The fibers can he in the form of any suitable fibers. In some embodiments, the fibers can be in the form of one or more of glass fibers, mineral fibers, carbon fibers, paper fibers, and mixtures of such fibers, as well as other comparable fibers providing comparable benefits to the process and/or end product. In some embodiments, glass fibers are

incorporated in the concentrated layer slurry and resulting crystalline core structure. Glass fibers are preferred because they do not absorb water.

10070] hi the case of some fi bers, such as glass fibers, it can be useful in some

embodiments to optionally treat the fibers with sizing agent additive to improve their properties and handling. For example, sizing agents can allow tor sizing of individual fibers in order to, e.g., change surface coating and properties and typically be in the form of one or more of organofunctionalized silanes, forming agents, surfactants, defoamers, lubricants and/or stabilizers. As one of ordinary skill i the art will appreciate, the precise selection of each ingredient can vary depending on fiber properties and the desired application. For example, the silanes can be, e.g.. amino based, such as for, example,

aramopropyltriethoxysilane or aminoethylaminopropyltrimethoxysiiane, vinyl based such as for example, vinyltrimethoxysilane or vinyltriacetoxysiiane, alkyl based such as

methyltrimethoxysilane or memyltriethoxysilane, or any combination thereof.

100711 Forming agents are often polymers and can be hydrophobic to provide desired wetting characteristics and protection from fiber-to-fiber damage, live forming agents can be in the form of, for example, polyurethanes, polyvinyl acetates, polyesters, polyalkenes and epoxies. Cationic lubricants can optionally be added and can be in the form of aliphatic ethanolamides such as stearic efhanol amide, or polyethyleneimine poiyamides,

alkylamidoaikyi sultaines or polyethylene oxide, or any combination thereof. Surfactants can optionally be included to emulsify the forming agent, e.g., when the forming agent is hydrophobic. In some embodiments, the surfactant if included is nonionie or slightly cationic, and can be in the form of an amide or other suitable form, e.g., polyoxyethylene glycol alkyl esters, copolymers of polyethylene glycol and polypropylene glycol, cocamide monoethanolarnme, or any combination thereof. Defoarners can provide benefit because they control foam formation with glass fiber, and any suitable defoamer can be used. For example, suitable defoarners can be siloxane based, oil based or polymer based, such as, but not limited to mineral oil, waxes, ethylene bis stearamide, silicone oil, polyethylene glycol and polypropylene glycol copolymers based defoarners, or any combination thereof. Stabilizers provide the benefit of stabilizing the sizing fonmilation and any suitable stabilizer can be used. In some embodiments, additive such as lubricant provides a positive surface charge which is believed to further improve slurry flow.

[0072] If included, the sizing agent can be provided in any suitable amount in the slurry for forming the concentrated layer. For example, the sizing agent can be provided in an amount of from about 0.02 wt.% to about 2 wt.% of the fibers, such as from about 0.05 wt.,% to about I wt.%, or from about 0.1 wt.% to about 1.5 wt.% of the fibers. For the weight percentages of ingredients provided herein in relation to either the board core slurry or concentrated layer slurry, in some embodiments, the concentrated layer and/or board core in the board product can contain the recited ingredient in an amount within the recited ranges, [0073] The fibers (e.g., glass fiber) can have any suitable length. For example, in some embodiments, the fibers can have an average length of from about 0.125 inch (about 0.32 cm) to about 1 mch (about 2,54 cm), such as, for example, from about 0, 125 inch to about 0.75 inch (about 1 .9 cm), from about 0.125 inch to about 0.5 inch (about 1 .3 cm), from about 0.125 inch to about 0.375 inch (about 1 em), from about 0.125 inch to about 0.25 inch (about 0.6 cm), from about 0.25 inch to about 3 inch, from about 0.25 inch to about 0.75 inch, from about 0.25 inch to about 0,5 inch, from about 0.25 inch to about 0.375 inch, from about 0.375 inch to about I inch, from about 0.375 inch to about 0.75 inch, from about 0.375 inch to about 0.5 inch, from about 0. 5 inch to about 1 inch, from about 0.5 inch to about 0.75 inch, or from about 0.75 inch to about 1 inch.

[0074] The fibers (e.g., glass fiber) can have any suitable average diameter. For example, in some embodiments the fibers can have an average diameter of from about 5 microns to about 20 microns, from about 10 microns to about 15 microns, from about 10 microns to about 20 microns, from about 8 microns to about 18 microns, from about 5 microns to about 25 microns, from about 9 microns to about 20 microns, from about 10 microns to about 18 microns, from about 7 microns to about 18 microns, from about 10 microns to about 25 microns, a diameter of about 1 1 to about 17 microns, or a diameter of from about 15 microns to about 17 microns,

[0075] In some embodiments, such glass fibers can have an average length of about 0.5 to about 0.675 inches (about 1.7 cm) and a diameter of about 13 to about 16 microns, an average length of about 0.5 to about 0.75 inches and a diameter of about 11 to about 17 microns, or an average fiber length of 0.5 inch and an average diameter of from about 1 5,24 microns to about 16.51 microns.

[0076] The aspect ratio of the fibers refers to the length divided by the diameter and in practice is believed to influence the slurry flow characteristics. To make the units consistent, the length in inches can be converted into microns such that the values are unitless. n some embodiments, the preferred aspect ratio is from about 200 to about 2000, such as from about 400 to about 1300, e.g., from about 800 to about 1500, from about 250 to about 1000, from about 500 to about 1500, or from about 700 to about 1 600, from about 800 to about 1400. (0 77J If included, fibers, such as glass fibers, are present in the slurry for forming the concentrated layer in any suitable amount, such as, from about 0.1% to about 3%, e.g., from about 0.13% to about 2,5%, or from about 0.5% to about 1 % by weight of the stucco, and is present in the board core in any suitable amount, such as from about 0% to about 1 %, e.g., from 0% to about 0.5% by weight of the stucco, if desired, the fiber (and the aforementioned associated additives such as sizing agent, etc) can also be included in the core in any suitable amount such as these enumerated weight percentages.

10078 J The concentrated layer desirably has substantial thickness. In some embodiments, the dry concentrated layer has a substantial thickness of at least about 0.02 inches (about 0.05 cm), such as from about 0.02 inches to about 0.2 inches (about 0.5 cm). For example, in various embodiments, the concentrated layer has a substantial thickness with a minimum thickness of at least about 0.025 inches (about 0,06 cm), at least about 0.03 inches (about 0.075 cm), at least about 0.035 inches (about 0.09 cm), at least about 0.04 inches (about 0,1 cm), at least about 0.045 inches (about 0.1 1 cm), at least about 0.05 inches (about 0.13 cm), at least about 0.055 inches (about 0.14 cm), at least about 0.06 inches (about 0.15 cm), at least about 0.065 inches (about 0.17 cm), at least about 0.07 inches (about 0.18 cm), at least about 0.075 inches (about 0.19 cm), at least about 0.08 inches (about 0.2 cm), at least about 0.085 inches (about 0.22 cm), at least about 0.09 inches (about 0.23 cm), at least about 0.095 inches (about 0.24 em), at least about 0.1 inch (about 0,254 cm), at least about 0.11 inch (about 0.28 cm), at least about 0.12 inch (about 0.3 cm), at least about 0.13 inch (about 0.33 em), at least about 0.14 inch (about 0,36 cm), at least about 0, 15 inch (about 0.38 cm), or at least about 0.16 inch (about 0.41 cm); wherein each of these ranges has a suitabl e upper limit as mathematically appropriate, such as, for example, about 0.2 inches, about 0, 185 inches (about 0.47 cm), about 0.175 inches (about 0.45 cm), about 0.16 inches, about 0.15 inches (about 0.38 cm), about 0.145 inches (about (3.37 cm), about 0.13 inches, about 0,12 inches (about 0.3 cm), 0.1 inch, about 0.09 inches (0.23 cm), about 0.08 inches, about 0.07 inches, about 0.06 inches, about 0.055 inches, about 0.05 inches, about 0.045 inches, about 0.04 inches, about 0.035 inches, etc.).

f 0079] To illustrate, but not by way of any limitation, the dry concentrated layer can have a thickness from about 0,02 inches to about 0.175 inches, e.g., from about 0.02 inches to about 0.1 5 inches, from about 0,02 inches to about 0, 12 inches, from about 0.02 inches to about 0.1 inches, from about 0.02 inches to about 0.08 inches, from abou 0.02 inches to about 0,055 inches, from about 0.02 inches to about 0.05 inches, from about 0.02 inches to about 0.04 inches, front about 0.02 inches to about 0,03 inches, from about 0.03 inches to about 0.2 inches, from about 0.03 inches to about 0.175 inches, from about 0.03 inches to about 0.1 5 inches, from about 0,03 inches to about 0, 12 inches, from about 0.03 inches to about 0.1 inches, from about 0.03 inches to about 0.08 inches, from about 0.03 inches to about 0.055 inches, from about 0.03 inches to about 0.05 inches, from about 0.04 inches to about 0.2 iiiches, from about 0.04 inches to about 0.175 inches, from about 0.04 inches to about 0.15 inches, from about 0,04 inches to about 0.12 inches, from about 0.04 iiiches to about 0.1 inches, from about 0.04 inches to about 0.08 inches, from about 0.04 inches to about 0.055 inches, from about 0.04 inches to about 0.05 inches, from about 0.05 inches to about 0,2 inches, from about 0.05 inches to about 0.175 inches, from about 0.05 inches to about 0.15 inches, from about 0.05 inches to about 0,12 inches, from about 0,05 inches to about 0.1 inches, from about 0,05 inches to about 0.8 inches, from about 0,06 inches to about 0.2 inches, from about 0.06 inches to about 0,175 inches, from about 0,06 inches to about 0, 15 inches, from about 0.06 iiiches to about 0.12 inches, from about 0.06 inches to about 0.1 inches, from about 0.06 inches to about 0.8 inches, etc.

[0080] The concentrated layer preferably has a higher dry density and/or dry strength than the density of the board core. For example, in some embodiments, the concentrated layer has a density that is at least about 1 , 1 times greater than the density of the board core, e.g., at least about 1.2 times greater, at least about 1.3 times greater, at least about 1.4 times greater, at least about 1.5 times greater, at least about 1 .6 times greater, at least, about 1.7 times greater, at least about 1.8 times greater, at least about 1.9 times greater, at least about 2 times greater, etc, wherein each of these ranges has a suitable upper limit, as mathematically appropriate, such as, for example, about 3 times greater, about 2.9 times greater, about 2,8 times greater, abou 2.7 times greater, about 2,6 times greater, about 2,5 times greater, about 2.4 times greater, about 2.3 times greater, about 2.2 times greater, about 2,1 times greater, about 2 times greater, about 1 ,9 times greater, about 1 .8 times greater, about 1 .7 times greater, about 1 .6 times greater, about 1.5 times greater, about 1.4 times greater, about 1.3 times greater, and about 1 ,2 times greater.

[0081] Thus, for example, the concentrated layer can have a dry density that is from about 1.1 to about 3 times the density of the board core, e.g., from about 1.1 to about 3 times, from about 1.1 to about 2.7 times, from about 1 .1 to about 2.5 times, from about 1.1 to about 2.2 times, from about 1.1 to about 2 times, from about 1.1 to about 1.7 times, from about 1 .1 to about 1.5 times, from about 1 .1 to about 1 ,4 times, from about 1 ,1 to about 1.3 times, from about 1 ,2 to about 3 times, from about 1 .2 to about 2.5 times, from about 1.2 to about 2.2 times, from about 1.2 to about 2 times, from about 1 ,2 to about 1 ,7 times, from about 1.2 to about 1.5 times, from about 1 .2 to about 1 .4 times, from about 1.2 to about 1 ,3 times, from about 1.3 to about 3 times, from about 1 ,3 to about 2.5 times, from about 1.3 to about 2 times, from about 1 .3 to about 1 ,7 times, from about 1 .3 to about 1 .5 times, from about 1.3 to about 1 .4 times, from about 1 .4 to about 3 times, from about 1 ,4 to about 2.5 times, from about 1 .4 to about 2.5 times, from about 1.4 to about 2 times, from about 1.4 to about 1.7 times, from about 1 .4 to about 1 ,6 times, from about 1.4 to about 1.5 times, from about 1 ,5 to about 3 times, from about 1.5 to about 2.5 times, from about 1 .5 to about 2 times, from about 1 .5 to about 1 .8 times, from about 1 .5 to about 1.7 times, from about 1.5 to about 1 .6 times, from about 1 .6 to about 3 times, from about 1 ,6 to about. 2.5 times, from about 1.6 to about 2 times, from about 1.1 to about 1 .8 times, from about 1.7 to about 3 times, from about 1.7 to about

2.5 times, from about 1 .7 to about 2.2 times, from about 1.7 to about 2 times, from about 1 .7 to about 1 .9 times, from about 1.8 to about 3 times, from about 1.8 to about 2.7 times, from about 1 .8 to about 2.5 times, from about 1.8 to about 2.2 times, from about 1.8 to about 2 times, from about 1.9 to about 3 times, from about 1.9 to about 2,7 times, from about 1 .9 to about 2.5 times, from about 1 .9 to about 2.2 times, from about 2 to about 3 times, etc.

[0082] The composite gypsum board can be designed to demonstrate any suitable dry- density differential between the concentrated layer and the board core, In some

embodiments, the density differential between the concentrated layer and the board core can be at least about 8 pcf (about 1 30 kg/m³). For example, in some embodiments, the dry density differential between the concentrated layer and the bonding layer can be at least about 10 pci^", at least about 12 pcf, at least about 14 pcf, at least about 16 pcf, at least about 1 8 pcf, at least about 20 pcf, etc. In some embodiments, the density differential between the concentrated layer and the board core is from about 8 pcf to about 50 pcf, such as about 8 pcf to about 45 pcf (about 720 kg/m³), about 8 pcf to about 40 pcf, about 8 pcf to about 35 pcf, 8 pcf to about 30 pcf, about 8 pcf to about 25 pcf (about 400 kg m"), about 8 pcf to about 20 pcf, about 8 pcf to about 15 pcf (about 240 kg/m³), about 8 pcf to about 12 pcf, about 10 pcf (about 160 kg-'m³) to about 50 pcf, about 10 pcf to about 45 pcf, about 10 pcf to about 40 pcf, about 1 0 pcf to about 35 pcf, about 10 pcf to about 30 pcf, about 10 pcf to about 25 pcf, about 10 pcf to about 20 pcf, about ! O pcf to about 1 5 pcf, about 15 pcf to about 50 pcf (about 800 kg m³), about 1 5 pcf to about 45 pcf, about 15 pcf to about 40 pcf, about 1 pcf to about 35 pcf, about 15 pcf to about 30 pcf, about 1 5 pcf to about 25 pcf, about 15 pcf to about 20 pcf, about 20 pcf to about 50 pcf, about 20 pcf to about 45 pcf, about 20 pcf to about 40 pcf, about 20 pcf to about 35 pcf, about 20 pcf to about 30 pcf, about 20 pcf to about 25 pcf, about 25 pcf to about 35 pcf about 25 pcf to about 30 pcf, etc.

(0083] The concentrated layer can have any suitable dry density to fit within the desired parameters of embodiments described herein. In some embodiments, the concentrated layer has a dry density of from about 28 pcf to about 70 pcf (about 1 120 kg/m³), such as from about 28 pcf to about 65 pcf (about 1040 kg m^J), from about 28 pcf to about 60 pcf (about 960 kg/m^J), from about 28 pcf to about 55 pcf (about 880 kg/rrf ), from about. 28 pcf to about 50 pcf, from about 28 pcf to about 45 pcf, from about 28 pcf to about 40 pcf, from about 28 pcf to about 35 pcf, from about 34 pcf to about 70 pcf, from about 34 pcf to about 65 pcf, from about 34 pcf to about 60 pcf, fronvabout 34 pcf to about 55 pcf from about 34 pcf to about 50 pcf. from about 34 pcf to about 45 pcf, from about 34 pcf to about 40 pcf from, about 38 pcf to about 70 pcf, from about 38 pcf to about 65 pcf, from about 38 pcf to about 60 pcf, from about 38 pcf to about 55 pcf from about 38 pcf to about 50 pcf, from about 38 pcf to about 45 pcf, from about 40 pcf to about 70 pcf, from about 40 pcf to about. 65 pcf, from about 40 pcf to about 60 pcf, from about. 40 pcf to about 55 pcf, from about 40 pcf to about 50 pcf. from about 40 pcf to about 45 pcf, from about 36 pcf to about 38 pcf etc.

10084] The concentrated layer generally has a dry stiffness value that is greater than the dry stiffness value of the board core. As noted, Young's modulus of elasticity can be used as a measure of dry stiffness herein, In some embodiments, the dry concentrated layer has a Young's modulus that is at least about 1.5 times as high, as the Young's modulus of the board core, e.g., 2 times as high as the Young's modulus of the board core, such as. for example, from about 2 times to about 10 times, from about 2 times to about 8 times, from about 2 times to about 6 times, from about 2 times to about 4 times, from about 3 times to about 10 times, from about 3 times to about 8 times, from about 3 times to about 6 times, from about 3 times to about 5 times, from about 4 times to about 10 times, from about 4 times to about 8 times, from about 4 times to about 6 times, from about 5 times to about 10 times, from about 5 times to about 8 times, from about 6 times to about 10 times, from about 6 times to about 8 times, etc. n some embodiments, the concentrated layer has a stiffness value thai, is closer to a stiffness value of the top and/or bottom cover sheet than a stiffness of the board core, when each stiffness value is measured according to Young's modulus. In some embodiments, the concentrated layer has a stiffness value according to Young's modulus that is from about 0.3 to about 0.5 of the Young^'s modulus for at least one of the cover sheets,

Co ver Sheets

[0085] The cover sheets can be in any suitable form. It will be understood that, with respect to cover sheets, the terms "face" and "top^"' sheets are used interchangeably herein, while the terms "back" and '"bottom" are likewise used interchangeably herein. For example, the cover sheets may comprise cellulosic fibers, glass fibers, ceramic fibers, mineral wool, or a combination of the aforementioned materials. One or both of the sheets may comprise individual sheets or multiple sheets. In preferred embodiments, the cover sheets comprise a cellulosic fiber. For example, paper sheet, such as Manila paper or kraft paper, can be used as the back sheet. Useful cover sheet paper includes Manila 7-piy and News-Line 3 ply, or 7 ply available from United States Gypsum Corporation, Chicago, IL,; Grey-Back 3-ply and Manila Ivory 3-ply, available from International Paper, Newport, IN: and Manila heavy paper and Mil Manila HT (high tensile) paper, available from United States Gypsum Corporation, Chicago, IL. An exemplary cover sheet paper is 5-pIy Newsline. In some embodiments, the back sheet can optionally define perforations, e.g., pin-holes, therein. Such perforations assist with drying in a kiln to provide an outlet for any steam formed during the heating process.

[0086] In addition, the paper (e.g., cellulosic) can comprise any other material or combination of materials. For example, one or both sheets, particularly the face (top) sheet can include polyvinyl alcohol, boric acid, or polyphosphate as described herein (e.g.. sodium trimetaphosphate) to enhance the strength of the paper. In some embodiments, the paper can be contacted with a solution of one or more of polyvinyl alcohol, boric acid, and/or polyphosphate so that the paper is at least partially wetted. The paper can be at least partially saturated in some embodiments. The polyvinyl alcohol, boric acid and/or boric acid can penetrate the fibers in the paper in some embodiments. The solution of polyvinyl alcohol, boric acid, and/or polyphosphate can be in any suitable amount and can be applied in any suitable manner as will be appreciated in the art. For example, the solution can be in the form of from about 1% to about 5% solids by weight in water of each ingredient present between the polyvinyl alcohol, the boric acid and/or polyphosphate, which can be added in one solution or if desired in multiple solutions.

(0087) In some embodiments, one or both sheets can comprise glass fibers, ceramic fibers, mineral wool, or a combination of the aforementioned materials. One or both sheets in accordance with the present disclosure can be generally hydrophilic, meaning that the sheet is at least partially capable of adsorbing water molecules onto the surface of the sheet and/or absorbing water molecules into the sheet.

[0088] In other embodiments, the cover sheets can be "substantially free" of glass fibers ceramic fibers, mineral wool, or a mixture thereof, which means that the cover sheets contain either (i) 0 wt.% based on the weight of the sheet, or no such glass fibers ceramic fibers, mineral wool, or a mixture thereof, or (ii) an ineffective or (iii) an immaterial amount of glass fibers ceramic fibers, mineral wool, or a mixt ure thereof. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using glass fibers ceramic fibers, mineral wool, or a mixture thereof, as one of ordinary skill in the art will appreciate. An immaterial amount may be, e.g., below about 5 wt.%, such as below about 2 wt.%. below about 1 wt.%, below about 0.5 wt.%, below about 0.2 wt.%, below about 0. 1 wt,%, or below about 0.01 wt.% based on the weight stucco as one of ordinary skill in the art will appreciate. However, if desired in alternative embodiments, such ingredients can be included in the cover sheets.

[0089] In some embodiments, the thermal conductivity of the top and/or bottom sheet is less than about 0, 1 w/(m.k.). For example, the thermal conductivity of the top and/or bottom sheet is less than about 0.05 w (m.k.).

100901 If desired, in some embodiments, one or both cover sheets can optionally include any suitable amount of inorganic compound or mixture of inorganic compo unds that adequately imparts greater fire endurance where such properties are sought. Examples of suitable inorganic compounds include aluminum trihydrate and magnesium hydroxide. For example, the cover sheets can comprise any inorganic compound or mixture of inorganic- compounds with high crystallized water content, or any compound that releases water upon heating, hi some embodiments, the amount of inorganic compound or the total mixture of inorganic compounds in the sheet ranges from about 0.1 % to about 30% by weight of the sheet. The inorganic compound or inorganic compounds used in the sheet may be of any suitable particle size or suitable particle size distribution.

[9091] Aluminum trihydrate (ATH), also known as alumina trihydrate and hydratcd alumina, can increase fire resistance due to its crystallized or compound water content. In some embodiments, ATH can be added in an amount from about 5% to about 30% by total weight of the sheet. ATH typically is very stable at room temperature. Above temperatures between about 1 80 °C and 205 °C, ATH typically undergoes an endotherrnic decomposition releasing water vapor. The heat of decomposition for such ATH additives is greater than about 1 00 Joule/grarn, and in one embodiment is about 1 170 Joule/ gram. Without being bound by theory, it is believed that the ATH additive decomposes to release approximately 35% of the water of crystallization as water vapor when heated above 205 °C in accordance with the fol lowing equation: AUQH) -→ Al- 0₃ + 3H₂0.

[0092 j A cover sheet comprising inorganic particles of high water content, such as ATH, can increase fire endurance of the composite board. The inorganic compound or mixture of compounds is incorporated into the sheet in some embodiments. A cover sheer such as paper comprising ATH can be prepared by first diluting cellulosic fiber in water at about 1% consistency, then mixing with ATH particles at a predetermined ratio. The mixture can be poured into a mold, the bottom of which can have a wire mesh to drain off water, After draining, fiber and ATH particles are retained on the wire. The wet sheet can he transferred to a blotter paper and dried at about 200-360°F.

[ΘΘ93] In some embodiments, as described for inclusion in the cover sheet or in a stucco slurry, e.g., ATH particles of less than about 20 μηι are preferred, but any suitable source or grade of ATH can be used. For example, ATH can be obtained from commercial suppliers such as Huber under the brand names SB 432 (10 prn) or Hydra!^® 710 (Ι μηϊ).

[0094] In some embodiments, the cover sheet may comprise magnesium hydroxide. In these embodiments, the magnesium hydroxide additive preferably has a heat of

decomposition greater than about 1000 Joule/gram, such as about 1350 Joule/gram, at or above 180° C to 205° C, In such embodiments, any suitable magnesium hydroxide can he used, such as that commercially available from suppliers, including Akrochem Corp. of Akron, Ohio.

[0095] In other embodiments, the cover sheets can be "substantially free" of inorganic compounds such as ATH, magnesium hydroxide, or a mixture thereof, which means that the cover sheets contain either (i) 0 wt.% based on the weight of the sheet, or no such inorganic compounds such as ATH, magnesium hydroxide, or a mixture thereof, or (it) an ineffective or (hi) an immaterial amount of inorganic compounds such as ATH, magnesium hydroxide, or a mixture thereof, An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using inorganic compounds such as ATH, magnesium hydroxide, or a mixture thereof, as one of ordinary skill m the art will appreciate. An immaterial amount may be, e.g., below about 5 wt.%, such as below about 2 wt.%, below about 1 wt.%, below about 0.5 wt.%, below about 0.1 wt.%, below about 0.05 wt.%, below about 0.01 wt.%, etc.

[0096] The cover sheets can also have any suitable total thickness, in some

embodiments, at least one of the cover sheets has a relatively high thickness, e.g., a thickness of at least about 0.014 inches. In some embodiments, it is preferred that there is an even higher thickness, e.g., at least about 0.0 i 5 inches, at least about 0.016 inches, at least about 0.017 inches, at least about 0.018 inches, at least about 0.019 inches, at least about 0.020 inches, at least about 0,021 inches, at least about 0.022 inches, or at least about 0.023 inches. Any suitable upper limit for these ranges can be adopted, e.g., an upper end of the range of about 0.030 inches, about 0.027 inches, about 0.025 inches, about 0.024 inches, about 0.023 inches, about 0.022 inches, about 0.021 inches, about 0,020 inches, about 0.039 inches, about 0.018 inches, etc. The total sheet thickness refers to the sum of the thickness of each sheet attached to the gypsum board.

[0097] The cover sheets can have any suitable density. In some embodiments, at least one of the cover sheets, e.g., the top (face) cover sheet, has a density that is equal to or greater than the density of the concentrated layer. For example, in some embodiments, at least one or both of the cover sheets has a density of at least about 36 pcf, e.g., from about 36 pcf to about 46 pcf, such as from about 36 pcf to about 44 pcf, from about 36 pcf to about 42 pcf, from about 36 pcf to about 40 pcf, from about 38 pcf to about 46 pcf, from about 38 pcf to about 44 pcf. from about 38 pcf to about 42 pcf, etc.

[0098] The cover sheet can have any suitable weight. For example, in some

embodiments, lower basis weight cover sheets (e.g., formed from paper) such as, for example, at least about 33 Ibs/MSF (about 160 g m'), e.g., from about 33 Ibs/MSF to about

65 Ibs/MSF (about 320 g/m²), from about 33 Ibs/MSF to about 60 Ibs/MSF (about 290 g/m²),

33 Ibs/MSF to about 58 Ibs/MSF (about 280 g/m²), from about 33 Ibs/MSF to about

55 Ibs/MSF (about 270 g/m²), from about 33 Ibs/MSF to about 50 Ibs/MSF^' (about 240 g m²), from about 33 Ibs/MSF to about 45 Ibs/MSF (abou 220 g-'ra"), etc. or less than about

45 Ibs/MSF, can be utilized in some embodiments. In other embodiments, one or both cover sheets has a basis weight from about 38 Ibs/MSF (about 190 g/m⁴') to about 65 Ibs/MSF, from about 38 Ibs/MSF to about 60 Ibs/MSF, from about 38 Ibs/MSF to about 58 Ibs/MSF, from about 38 Ibs/MSF to about 55 Ibs/MSF, from about 38 Ibs/MSF to about 50 Ibs/MSF, or from about 38 lbs/MSI to about 5 Ibs/MSF.

[009 However, if desired, in some embodiments, even heavier basis weights can be used, e.g., to further enhance nail pull resistance or to enhance handling, e.g., to facilitate desirable "feel" characteristics for end-users. Thus, one or both of the cover sheets can have a basis weight of, for example, at least about 45 Ibs/MSF (e.g., from about 45 Ibs/MSF to about 65 Ibs/MSF, from about 45 Ibs/MSF to about 60 Ibs/MSF, from about 45 Ibs/MSF to about 55 Ibs/MSF, from about^' 50 Ibs/MSF to about 65 Ibs/MSF, from about 50 Ibs/MSF to about 60 Ibs/MSF, etc.). If desired, in some embodiments, one cover sheet (e.g., the "face" paper side when installed) can have the aforementioned higher basis weight, e.g.. to enhance nail pull resistance and handling, while the other cover sheet (e.g., the ''back" sheet when the board is installed) can have somewhat lower weight basis if desired (e.g., weight basis of less than about 45 Ibs/MSF, e.g., from about 33 Ibs/MSF to about 45 Ibs/MSF or from about 33 ibs/MSF to about 40 Ibs/MSF).

Enhancing Additive

[00100] The enhancing additive provides desired strength properties. In preferred embodiments, the enhancing additive is more concentrated in the concentrated layer slurry than in the board core slurry (and/or the resulting layers in the board product), as discussed herein. Examples of suitable enhancing additives help provide strength, such as starch, polyvinyl alcohol, boric acid, gypsum-cement, nano-cellulose, micro-cellulose, or any combination thereof The use of the singular term enhancing additive herein is used for convenience but will be understood to encompass the plural, i.e., more than one enhancing additive in combination, as one of ordinary skill in the art will readily appreciate. Thus, an enhancing additive may comprise one or more of starch, polyvinyl alcohol, boric acid, gypsum-cement, nano-cellulose, and/or micro-cellulose.

[00101 j In some embodiments, the enhancing additive comprises an ingredient, such as starch, that is effective to increase the dry strength of the composite gypsum board relative to the sirength of the composite board without the ingredient such as starch (e.g., via increased compressive strength, nail pull resistance, fiexural strength, core hardness, or other strength parameter). With respect to starch, any suitable strength enhancing starch can be used, including hydroxyalkylated starches such as hydroxyethy!ated or hydroxypropylaied starch, or a combination thereof, uncooked starches, or pregela inized starches, which are generally preferred over acid-modifying migrating starches which generally provide paper-core bond enhancement but not core strength enhancement. However, if desired, the acid-modifying migrating starch can be included with the enhancing additive in some embodiments.

[0100] The starch can be cooked or uncooked. Uncooked starches are characterized as being cold water insoluble and having a semi-crystalline structure. Typically, uncooked starches are obtained by wet milling and are not modified by heating wet starch as in the case of cooked starches. Cooked starches are characterized by being cold water soluble and having a non-crystalline structure. Cooked starches are prepared by heating wet starch, and can be prepared, e.g., by extrusion techniques. See, e.g., co-pending U.S. patent applications 14/494,547; 14/044,582; and 13/835,002, which extrusion techniques are incorporated by reference. [0101] Cooked starches are sometimes referred to as pregeSatinized starches, because the crystalline structure of the starch granules melts, and results in starch geiatinization, which is characterized by the disappearance of the birefringence under a microscope with a polarized light. Preferred starches, whether cooked or uncooked, are different than acid-modified migratory starches which do not confer the same strength properties and are used in the art for paper-core bond enhancement as they migrate to the paper-core interface due to their smaller chain lengths. The acid-modified migratory starches have minimal molecular weight, typically below about 6,000 Daltons. in some embodiments, preferred starches in accordance with embodiments of the disclosure have higher molecular weights, e.g.. at least about 30,000 Daltons.

|0102] For example, in some embodiments, the starch added to the concentrated layer slurry can have a molecular weight of from about 30,000 Daltons to about 150.000.000 Dalions, e.g., from about 30,000 Daltons to about 1 50,000,000 Daltons, from about 30,000 Daltons to about 100,000,000 Daltons, from about 30,000 Daltons to about 50,000,000 Daltons, from about 30,000 Daltons to about 10,000,000 Daitons, from about 30,000 Daitons to about 5,000,000 Daltons, from about 30,000 Daltons to about 1 ,000,000 Daltons, from about 30,000 Daltons to about 500,000 Daltons, from about 30,000 Dalions to about 100,000 Daltons, from about 50,000 Daltons to about 150,000,000 Daltons, from about 50,000 Daltons to about 100,000,000 Daltons, from about 50,000 Daitons to about 50,000,000 Dalions, from about 50,000 Daltons to about 10,000,000 Daltons, from about 50,000 Daltons to about 5,000,000 Daltons, from about 50,000 Daltons to about 1 ,000,000 Daltons, from about 50,000 Daltons to about 500,000 Daltons, from about 50,000 Daltons to about 100,000 Daltons, from about 100,000 Daltons to about 1 50,000,000 Daltons, from about 1 00,000 Daltons to about 1 00,000,000 Daltons, from about 100,000 Daltons to about 50,000,000 Daltons, from about 100,000 Daltons to about 10,000,000 Daltons, from about 100,000 Daltons to about 5,000,000 Daitons, from about 1 00,000 Daltons to about 1 ,000,000 Daltons, from about 100,000 Daltons to about 500,000 Daltons, or from about 100,000 Daltons to about 100,000 Daltons, etc.

[0103] Properties of uncooked starches include having low viscosity in cold water (i.e., at a temperature of 77 °¥ (25 °C)), while properties of pregelatinized starches include having instant high viscosity in cold water. Uncooked starches tend to have a viscosity of about 10 eentipoise or less in cold water (e.g., from about 1 centipoise to about 1 0 centipoise, such as from about 3 centipoise to about 7 centipoise), as measured according to a modified rapid viscosity analyzer method. The rapid viscosity analyzer method is explained in the text, Deffenbangh, L.B. and Walker, C.E., "Comparison of Starch Pasting Properties in the Brabender Viscoamylograph and the Rapid Visco- Analyzer,'^" Cereal Chemistry, Vol. 66, No. 6, pp. 493-499 (1989), and modified as defined herein with respect to sample preparation and testing profile as follows. Starch (20 g, dry) is added into water (180 g) in a Waring blender (model 31 BL92) while mixing at low speed for 1 5 seconds. Starch solution (28 g) is weighed into a measuring cup. The paddle speed of the rapid viscosity analyzer is set at 160 rpm. The testing profile is set with an initial temperature of 25°C for 10 min. Heat to 93°C at a heating rate of 15°C/min. Keep the temperature at 93 °C for 5 min. Cool to 50°C at a cooling rate of - 15°C/min; and keep at 50°C for 1 min. The viscosity value measured at 30 seconds is used as the viscosity of the starch.

[0104] The pregelatinized starches have "instant" high viscosity in cold water because the starch tends to instantly dissolve in water. Cooked or pregelatinized starches tend to have a cold water viscosity of at least about 100 centipoise (e.g., from about 50 ceniipoise to about ].()()() centipoise. such as from about 350 ceniipoise to about 1000 centipoise) as measured according to the modified rapid viscosity analyzer method.

[01 OS] In some embodiments, uncooked starches are selected because they are easy to mix with water. This is because of their low viscosity in water. Pregelatinized starches can sometimes cause '"fish eye," which is a condition that is characterized by one or more large lumps that form in the water soiution during mixing. While not wishing to be bound by any particular theory, during the mixing process, the large lumps are believed to be caused by fast water absorption of the starch, forming a viscous film on the surface of the lump, which prevents water penetration of the lump. Uncooked starches are believed to avoid the fish eye condition because of their cold water insolubility, which results in the separation of starch granules. However, it will be understood that pregelatinized starches can be used in accordance with embodiments of the disclosure inasmuch as they are desirable for the exposure of functional groups which allows for hydrogen bonding between starch and gypsum crystals.

S 0106J Examples of suitable uncooked starches include, but are not limited to. one or more of native cereal starches, native root starches, native tuber starches, and/or chemically modified starches, with specific representative examples including, e.g., corn starch (normal, waxy, and/or high-amylose), A type wheat starch, B type wheat starch, pea starch, acid modified starches with a molecular weight of at least about 30,000 Daltons, substituted starches having substituted groups (such as acetate, phosphate, hydroxyethyl, hydrox propyl) on starch hydroxyl groups, or any combination thereof, In some embodiments, the uncooked starch excludes pea starch.

[0107] Any suitable pregelatinized starch can be included in the enhancing additive, as described m US 2014/01 13124 Al and US 2015/0010767-A1 , which include methods of preparation thereof and desired viscosity ranges described therein. If included, the pregelatinized starch can exhibit any suitable viscosity. In some embodiments, the pregelatinized starch is a mid-range viscosity starch as measured according to the VMA method as known in the art and as set forth in, e.g., US 2014/01 13124 AL which VMA method is hereby incorporated by reference,

[0108] Desirable pregelatinized starches in accordance with some embodiments can have a mid-range viscosity, e.g., measured in a 15 wt.% solution of starch in water, of from about 20 centipoise to about 700 centipoise, e.g., from about from about 20 centipoise to about 600 centipoise, from about 20 centipoise to about 500 centipoise, from about 20 centipoise to about 400 centipoise, from about 20 centipoise to about 300 centipoise,^" from about 20 eentipoise to about 200 centipoise, from about 20 centipoise to about 100 centipoise, from about 30 centipoise to about 700 eentipoise, from about 30 centipoise to about 600 centipoise, from about 30 centipoise to about 500 centipoise, from about 30 centipoise to about 400 centipoise, from about 30 eentipoise to about 300 centipoise, from about 30 centipoise to about 200 centipoise, from about 30 eentipoise to about 100 centipoise, from about 50 eentipoise to about 700 centipoise, from about 50 eentipoise to about 600 centipoise, from about 50 centipoise to about 500 centipoise, from about 50 eentipoise to about 400 centipoise, from about 50 eentipoise to about 300 centipoise, from about 50 centipoise to about 200 centipoise, from about 50 centipoise to about 100 centipoise, irom about 70 centipoise to about 700 eentipoise, from about 70 centipoise to about 600 centipoise, from about 70 centipoise to about 500 centipoise, from about 70 centipoise to about 400 centipoise, from about 70 centipoise to about 300 centipoise, from about 70 centipoise to about 200 centipoise, from about 70 centipoise to about 100 eentipoise, from about 100 centipoise to about 700 eentipoise, irons about 100 centipoise to about 600 centipoise, from about 1 00 centipoise to about 500 centipoise. from about 100 eentipoise to about 400 centipoise, from about 100 centipoise to about 300 centipoise, from about 100 centipoise to about 200 centipoise, etc, [0109] In accordance with some embodiments, the pregelatinized starch can he prepared as an extruded starch, e.g., where starch is prepared by pregelai.inizat.ion and acid- modification in one step in an extruder as described in US 2015/0010767-A1 , which extrusion method is hereby incorporated by reference. Briefly, any suitable extruder can be used, such as a single-screw extruder (e.g., the Advantage 50 available from American Extrusion international, located in South Beloit, ίΐ,) or a twin-screw extruder (e.g., the Wenger TX52 available from Wenger located in Sahetha, KS). in general, in some embodiments: (a) a precursor to pregelatinized starch, i.e., non-pregelatinized starch, (b) an acid in the form of a weak acid, that substantially avoids chelating calcium ions, and/or a strong acid in a small amount, and (c) water, are mixed and fed into the extruder. In some embodiments, additional water may be added to the extruder, in some embodiments, for example, aluminum sulfate (alum) is an appropriate weak acid to use in preparing the wet starch since it substantially avoids chelating calcium ions.

[0110] For example, in some embodiments, weak acid is included in an amount of from about 0,5 wt.% to about 5 wt.% based on the weight of the starch. The amount of strong acid is relatively small, such as about 0.05 wt.% or less by weight of the starch, e.g., from about 0.0001 wt.% to about 0.05 wt.%. The amounts of strong acid used in accordance with some embodiments of the disclosure are considerably smaller than what were included in conventional systems which used, e.g., at least about 2 g of sulfuric acid for 35 g of starch, in some embodiments, the strong acid in small amounts as described above can be used in combination with a weak acid that does not chelate calcium ions, such as alum, as described herein.

[0111] While in the extruder, a combination of heating elements and mechanical shearing melts and prege latinizes the starch, and the weak acid partially hydrolyzes the starch to a desired molecular weight indicated by viscosity as desirable as described herein. For example, the wet starch can be pregelatinized and acid-modified in an extruder having a die at a temperature of from about 150°C (about 300°F) to about 21 0°C (about 410°F). Pressure inside the extruder is determined by the raw material being extruded, moisture content, die temperature, and screw speed, which will be recognized by one of ordinary skill in the art. For example, the pressure in the extruder can be at least about 2,000 psi (about 13,800 kPa), e.g., from about 2,000 psi to about 5.000 psi (34,500 kPa). The conditions in the extruder, because of the mechanical energy, will also cause the starch molecules to degrade, which partially produces the same effect of acid-modification. It is believed that because the conditions in an extruder (e.g., high reaction temperature and high pressure) in accordance with some embodiments facilitate this chemical reaction, a weak acid and or low amounts of a strong acid can be used.

[0.1.121 Cold water solubility relates to a pregelatinized starch having any amount of solubility in water at room temperature (about 25°C). In some embodiments, the

pregelatinized starch is partially hydrolyzed and can have, desired cold water solubility of from about 70% to about 100%, from about 75% to about 100%, from about 80% to about 100%, from about 85% to about 100%, from about 90% to about 100%, from about 95% to about 100%, from about 70% to about 99%, etc, from about 75% to about. 99%, from about 80% to about 99%, from about. 85% to about. 99%, from about 90% to about 99%, from about 95% to about 99%. In some embodiments, the pregelatinized starch has a cold water viscosity (10% solids, 25°C) of from about 10 BU to about 120 BU, measured according to the Brabender method where viscosity is measured using a C.W. Brabender Viscograph, e.g., a Viscograph-E thai uses reaction torque for dynamic measurement. For example, the cold water viscosity can be, e.g., from about 20 BU to about 1 10 BU, from about 30 BU to about 100 BU, from about 40 BU to about 90 BU. from about 50 BU to about 80 BU, or from about 60 BU to about 70 BU. It is to be noted that, as defined herein, the Brabender units are measured using a sample cup size of 16 ft. oz (about 500 cc), with a 700 cmg cartridge at an RPM of 75. One of ordinary skill in the art also will readily recognize that the Brabender units can be converted to other viscosity measurements, such as centi poises (e.g., cP ^::: BLJ X 2,1 , when the measuring cartridge is 700 cmg) or Krebs units.

[0113] In some embodiments, the starch has a cold water viscosity of al.0% slurry of the starch in water when measured at 25 °C of from about 60 cP to about 160 cP, as measured with a Brookfield viscometer with #2 spindle and at a rotation, speed of 30 rpm. For example, the cold water viscosity of a 10% slurry of the starch in water when measured at 25 °C can be from about 60 cP to about 150 cP, from about 60 cP to about 120 cP, from about 60 cP to about 100 cP, from about 70 cP to about 150 cP, from about 70 cP to about 120 cP, from about 70 cP to about 100 cP, from about 80 cP to about 150 cP from about 80 cP to about 120 cP, from about 80 cP to about 100 cP, from about 90 cP to about 150 cP, from about 90 cP to about 120 cP, from about 100 cP to about 150 cP, or from about 100 cP to about 120 cP. |0114] If included, the starch of any type described herein as enhancing additive can be present in any suitable amount. Irs some embodiments, the starch is present in the

concentrated layer in an amount from about 5% to about 40%, by weight of the stucco, e.g., from about 5% to about 35% by weight, of the stucco, from about 5% to about 30% by weight of the stucco, from about 5% to about 25%, from about 5% to about 20%, from about 5% to about 15%, from about 5% to about 10%, from about 1 0% to about 30%, from about 10% to about 2.5%, from about 1 % to about 20%, from about 10% to about 15%, etc. The starch can be present in the board core in an amount, from about 0% to about 4% by weight of the stucco, e.g., from about 0.1 % to about 4% by weight of the stucco, from about 0.1 % to about 3% by weight of the stucco, from about 0.1% to about 2% by weight of the stucco, from about 0.1% to about 1 % by weight of the stucco, from about 1 % to about 4% by weight of the stucco, from about 1 % to about 3% by weight of the stucco, from about 1 % to about 2% by weight of the stucco, etc.

[011 ] In some embodiments, with or without starch, the enhancing additive can include polyvinyl alcohol and/or boric acid to enhance strength. In some embodiments, polyvinyl alcohol, boric acid, and starch are all present. While not wishing to be bound by theory, it is believed that the boric acid acts as a cross-linker for the polyvinyl alcohol and starch to further enhance st arch. In some embodiments, the concentration of polyvinyl alcohol and/or boric acid in the concentrated layer is believed to positively impact strength in the face paper; diis can be compounded by penetrating the face paper with polyvinyl alcohol and/or boric acid as described herein.

[0116] If included, the polyvinyl alcohol and boric acid can be present in any suitable amounts. For example, in some embodiments, the polyvinyl alcohol can be present in the concentrated layer in an amount from about 1 % to about 5% by weight of the stucco. n addition, the polyvinyl alcohol can be present in the board core in an amount from about 0% to about 1% by weight of the stucco. The boric acid can be present in the concentrated layer in an amount from about 0.1% to about 1% by weight of the stucco, and can be present in the board core in an amount from about 0% to about 0.1 % by weight of the stucco.

[0117] In some embodiments, the enhancing additive optionally comprises nano- cellulose, micro-cellulose, or any combination thereof in order to enhance strength, e.g., nail pull resistance or other strength parameter. If included, the nano-cellulose, micro-cellulose, or combination thereof can be present in any suitable amount such as, for example, in the concentrated layer slurry in an amount, for example, from about 0.01 % to about 2%. e.g., from about 0.05% to about 1 % by weight of the stucco, and in the board core slurry in an amount, for example, from about 0% to about 0.5%, e.g., from 0% to about 0,01 % by weight of the stucco. [01 IS] The enhancing additive can comprise gypsum-cement in order to enhance strength, e.g., nail pull resistance or other strength parameter, in some embodiments. The gypsum-cement is optional and can be present in any suitable amount. For example, in some embodiments, it can be included in the concentrated layer in an amount of from about 5% to about 30% by weight of the stucco, and can be present in the board core in an amount from about 0% to about 10% by weight of the stucco.

Board Strength

1011.9] In some embodiments, composite board made according to the disclosure meets test protocols according to ASTM Standard C473- 10. For example, in some embodiments, when the board is cast at a thickness of 1 /2 inch, the dry board has a nail pull resistance of at least about 65 ib_f (pounds force) as determined according to ASTM C473- 10 (method B), e.g., at least about 68 Ibf, at least about 70 ib_f. at least about 72 Ibf, at least about 74 Ibf, at least about 75 Ibf, at least about 76 Ibf, at least about 77 Ibf, etc. In various embodiments, the nail pull resistance can be from about 65 Ibf to about 100 Ibf, from about 65 Ib_f to about

95 Ibf, from about 65 Ib_f to about 90 Ibf, from about 65 ibf to about 85 ib_f, from about 65 Ibf to about 80 Ibr, from about 65 Ibf to about 75 Ibf, from about 68 Ibf to about 100 Ib_f, from about

68 Ibf to about 95 Ibf, from about 68 Ib_f to about 90 ib_f, from about 68 lb_/ to about 85 Ibf. from about 68 lb? to about 80 lb-, from about 70 Ib_f to about 100 Ibf, from about 70 ibf to abou

95 Ibf, from about 70 lb_t- to about 90 Ibf, from about 70 Ib_f to about 85 Ibf, from about 70 Ibf to about 80 Ibf, from about 72 Ibf to about 100 ibf, from about 72 Ibf to about 95 Ibf, from about

72 Ibf to about 90 Ibf, from about 72 Ibf to about 85 ib_f, from about 72 Ibf to about 80 Ibf, from about 72 ibf to about 77 Ib_f, from about 72 Ibf to about 75 Ibf, from about 75 ibf to about

100 Ib_f, from about 75 Ibf to about 95 Ib_f, from about 75 Ib_f to about 90 ibf, from about 75 ibf to about 85 ibf, from about 75 Ibr to about 80 ibf, from about 75 ibf to about 77 Ib_f, from about

77 ib_f to about 100 Ibf, from about 77 Ibf to about 95 Ib_f, from about 77 lb; to about 90 ibf, from about 77 Ibf to about 85 Ibr, or from about 77 Ib_f to about 80 Ibf.

[0120] In some embodiments, board can have an average core hardness of at least about

1 1 Ib_f, e.g., at least about 12 Ibf, at least about 13 ib_f, at least about 14 Ib_f, at least about 15 Ibf, at least about 16 Ibf, at least about 1 7 Ibf, at least about 18 lb--, at least about 1 Ib_f, at least about 20 Ibf, at least about 21 Ib_f, or at least about 22 ib_f, as determined according to ASTM

€473-1 0, method B. in some embodiments, board can have a core hardness of from about

1 1 Ib_f to about 25 Ibr, e.g., from about 1 1 ibf to about 22 ¾, from about 1 1 Ibf to about 21 lb--, from about 1 1 Ib_f to about 20 ibf, from about ] 1 Ibf to about 19 ib_f, from about i i ibf to about 1 8 Ib_f, from about 1 1 Ibr to about 17 Ib_f. from about 1 1 lb-- to about 16 Ibf, from about 1 1 ib_f to about 15 Ib_f, from about I I Ibf to about 14 Ib_f, from about 1 1 Ibf to about 13 Ibf, from about

1 1 Ib_f to about 12 Ib_f, from about 12 Ib_f to about 25 ib_f, from about 12 Ib_f to about 22 Ibf, from about 12 Ib_f to about 21 Ibf, from about 12 Ib_f to about 20 Ibf, from about 12 Ibf to about

1 9 ib_f, from about 12 ib_f to about 1 8 Ibf, from about 12 Ibf to about 17 ibf, from about 12 ibf to about 16 Ibf, from about 12 ibf to about 15 Ibf, from about 12 ibf to about 14 Ibf, from about

12 Ibf to about 1 3 Ib_f, from about 13 Ibf to about 25 ibf, from about 13 ibr to about 22 Ibf, from about 13 Ib_f to about 21 Ibf, from about 13 ibf to about 20 Ibf, from about 13 Ibf to about

1 9 Ib_f, from about 13 Ibf to about 1 8 Ibf, from about 13 Ibf to about 17 Ibf, from about 13 ibf to about 16 Ibf, from about 13 Ibf to about 15 Ibf, from about 13 ibf to about 14 Ibf, from about

14 Ibf to about 25 ib_f, from about 14 ib_f to about 22 Ibf, from about 14 Ibf to about 21 Ibf, from about 14 Ib_f to about 20 Ibf, from about 14 Ibf to about 19 Ibf, from about 14 Ibf to about

18 Ibf, from about 14 Ibf to about 17 Ibf, from about 14 Ibf to about 16 Ibf, from about 14 Ibf to about 15 Ibf, from about 1 5 ib_f to about 25 Ibf, from about 1 5 Ibf to about 22 Ib_f, from about

15 Ib_f to about. 21 Ibf, from about 15 Ibf to about 20 Ibf, from about 15 Ibf to about 19 Ibf, from about 1 5 I bf to about 18 Ibf, from about 1 5 ibf to about 17 Ibf, from about 15 Ibf to about

16 Ib_f, from about 16 Ibf to about 25 Ibf, from about 16 Ibf to about 22 Ibf, from about 16 Ibf to about 21 Ib_f, from about 1 6 Ibf to about 20 Ib_f, from about 1 6 Ibf to about 19 Ibf, from about 16 Ib_f to about 18 Ibf, from about 16 Ibf to about 17 Ibf, from about 17 Ibf to about 25 Ib_f, from about 17 ib_f to about 22 Ibf, from about 1 7 ibf to about 21 Ibf, from about 17 Ibf to about

20 Ib_f, from about 17 Ibf to about 19 Ibf, from about 17 Ibf to about 18 ibf, from about 18 Ib_f to about 25 Ib_f, from about 1 8 i bf to about 22 Ibf, from about 1 8 ibf to about 21 lb;, from about

18 Ibf to about 20 Ibf, from about 1 8 lb-- to about 19 Ib_f, from about 19 ib_f to about 25 Ibf, from about 1 9 ib_f to about 22 Ibf, from about 1 9 Ibf to about 21 Ibf, from about 19 Ibf to about 20 Ib_f, from about 21 ibf to about 25 Ibr, from about 21 Ibf to about 22 Ibf, or from about 22 Ibf to about 25 lb_r.

[0121 ] in some embodiments, the concentrated layer has an average, dry core hardness that is at least about 1 .5 times greater than the average dry core hardness of the board core, wherein the average core hardness is measured according to ASTM C-473- 10, e.g., at least about 2 times greater, 2.5 times greater, 3 times greater, 3.5 times greater, 4 times greater, 4.5 times greater, etc, wherein each of these ranges can have any mathematically appropriate upper limit, such as, for example, 8, 7, 6, 5, 4, 3, or 2, [0122] With respect to fiexurai ^'strength, in some embodiments, when cast in a board of ¼ inch thickness, the dry board has a fiexurai strength of at least about 36 Ibf in a machine direction (e.g. , at least about 38 Ibf, at least about 40 ib_f, etc.) and/or at least about 107 Ibf (e.g., at least about 1 10 ibf, at least about 1 12 Ib_f, etc) in a cross-machine direction as determined according io the ASTM standard C473-10. in various embodiments, the board can have a .fiexurai strength in a machine direction of from about 36 Ibf to about 60 Ibf, e.g., from about 36 Ibf to about 55 Ibf, from about 36 Ibf to about 50 Ibf, from about 36 Ibf to about 45 Ibf, from about 36 Ibf to about 40 ibf, from about 36 Ibf to about 38 ib_f, frorn about 38 !b_;- to about 60 Ibf, from about 38 Ibf to about 55 Ibf, from about 38 lb,- to about 50 ibf, from about 38 Ib_f to about. 45 ibf, ixom about 38 Ibf to about 40 Ibf, from about 40 Ibf to about 60 Ibf, from about 40 lb-- to about 55 Ibf, from about 40 Ibf to about 50 Ibf, or from about 40 ibf to about 45 Ibf. In various embodiments, the board can have a fiexurai strength in a cross-machine direction of from about 107 Ibf to about 130 Ibf, e.g., from about 107 Ibf to about 125 Ibf, from about 107 ibf to about 120 Ibf, from about 107 Ib_f to about 1 15 ibf, from about 107 Ibf to about. 1 12 Ibf, from about 107 Ibf to about 1 10 ibf, from about. 1 1 0 Ib to about 130 Ibf, from about 1 10 Ibf to about 125 Ib_f, from about 1 10 Ibf to about 1.20 lb--, from about 1 10 Ibf to about 1 15 ibf, from about 1 ] 0 Ibf to about. 1 12 Ibf, from about 1 12 Ibf to about 1 30 Ibf, from about 1 12 Ib_f to about .125 Ibf, from about 1 1 2 Ibf to about 120 Ibf, or from about. 1 12 Ib_f to about 1 15 Ibf.

|0123] Advantageously, in various embodiments at various board densities as described herein, the dry gypsum board can have a compressive strength of at. least about 170 psi ( 1 ,1 70 kPa), eg., from about 1 70 psi to about 1 ,000 psi (6,900 kPa), from about 170 psi to about 900 psi (6,200 kPa), from about 170 psi to about 800 psi (5,500 kPa), from about 170 psi to about 700 psi (4,800 kPa), from about 1 70 psi to about 600 psi (4, 100 kPa), from about 170 psi to about 500 psi (3,450 kPa), from about 170 psi to about 450 psi (3.1 00 kPa), from about 170 psi to about 400 psi (2,760 kPa), from about 1 0 psi to about 350 psi (2,410 kPa), from about 1 70 psi to about .300 psi (2,070 kPa), or from about 170 psi to about 250 psi ( 1 ,720 kPa). In some embodiments, the board has a compressive strength of at least about 450 psi

(3, 100 kPa), at least about 500 psi (3,450 kPa), at least about 550 psi (3,800 kPa), at least about 600 psi (4, 1 00 kPa), at least about 650 psi (4,500 kPa), at [east about 700 psi

(4,800 kPa), at least about 750 psi (5,200 kPa), at least about 800 psi (5,500 kPa), at least about 850 psi (5,850 kPa), at least about 900 psi (6,200 kPa), at least, about 950 psi

(6,550 kPa), or at least about 1 ,000 psi (6,900 kPa), In addition, in some embodiments, the compressive strength can be bound by any two of the foregoing points. For example, the compressive strength can be between about 450 psi and about 1 ,000 psi (e.g., between about 500 psi and about 900 psi, between about 600 psi and about 800 psi, etc.). The compressive strength can be measured using a materials testing system commercially available as ATS machine model 1.610, from Applied Test Systems in Butler, P A. The load is applied continuously and without a shock at speed of 1 mch/'min.

[0124] Due at least in part to the concentrated layer and the benefits thereof, surprisingly and unexpectedly, these standards (e.g., nail pull resistance, flexurai strength, and core hardness) can be met even with respect to ultra light density board (e.g., about 33 pcf or less, such as about 32 pcf or less, 31 pcf or less, 30 pcf or less, 29 pcf or less, 28 pcf or less, 27 pcf or less, 26 pcf or less, etc.), as described herein. Furthermore, these standards surprisingly can be met in some embodiments while using less overall enhancing additive and with a lighter, weaker, and/or softer core, and/or with lower overall water usage such that embodiments of the disclosure provide manufacturing efficiencies.

Process of Preparing Composite Gypsum Board

[0125] Composite gypsum board according to embodiments of the disclosure can be made on typical gypsum waliboard manufacturing lines. For example, board manufacturing techniques are described in, for example, U.S. Patent 7,364,676 and U.S. Patent Application Publication 2010/0247937. Briefly, the process typically involves discharging a cover sheet onto a moving conveyor. Since gypsum board is normally formed "face down," this cover sheet is the "face" cover sheet in such embodiments,

[0126] In accordance with aspects of the disclosure, two separate slurries are formed. One slurry is a stucco slurry used to form the board core, and the other slurry is used to form the concentrated layer. The concentrated layer can be formed from any suitable material, including a cemencitious material, such as stucco, that hydrates to a set material, e.g., set gypsum. Thus, in various embodiments, slurries containing a desired cementitious material can be prepared. As described herein, in some embodiments where both the board core and the concentrated layer are formed from stucco slurries, the stucco slurry for forming the board core can have a lower WSR than the VV SR of the stucco slurry used for making the concentrated layer in some embodiments.

[0127] As noted herein, foaming agent (or other lightweight material) is generally more prevalent in the board core slurry to provide its lower density, although some foam or lightweight material can be included in the concentrated layer slurry so long as the density parameters are achieved. In some embodiments, the concentration of the enhancing agent can be greater in the concentrated layer and some enhancing agent may not even be present in the board core slurry in accordance with some embodiments. Accordingly, the feed lines to the respective mixers can be adjusted accordingly, which is well within the level of ordinary skill.

[0128] The two slurries can be formed in any suitable manner. For example, two separate mixers can be used, where the raw materials are agitated to form the respective slurries. The mixers can be in series or unconnected. Alternatively, one mixer can be used to develop both slurry streams, FIG. 2 illustrates three alternate schematic flow diagrams showing examples ' of how the slurries can be formed in accordance with the present disclosure. As seen in depiction A of FIG. 2, a single mixer can be used, whereas in depictions B and C, the two slurries are formed in separate mixers, e.g., in the form of "pin mixers^"' or '''pin-less mixers'" as desired. As seen in flow diagrams B and C, if desired for efficiency, the mixer used for the concentrated layer can have a smaller mixing volume capacity in some embodiments since the amount of slurry needed to be applied for the concentrated layer is less than the amount of slurry that is applied to form the board core. The "main" mixer (i.e., for forming the board core slurry) comprises a main body and a discharge conduit (e.g., a gate-canister-boot arrangement as known in the art, or a modified outlet design (MOD) arrangement as described in U.S. Patents 6,494,609 and 6,874,930). As seen in all three depictions A-C, foaming agent can be added in the discharge conduit of the mixer (e.g., in the gate as described, for example, in U.S. Patents 5,683,635 and 6,494,609).

[0129] Diagram A illustrates an embodiment where the steps occur using one mixer, i.e., the main mixer 100. Stucco 102 and water 104 are inserted into the main mixer 100, while foam 106 is inserted downstream in the discharge conduit 108 which can include a modified outlet design or canister, meaning that foam is not inserted in the body of the main mixer 100. A portion of the slurry 1 10, which is essentially foamless, is diverted from the mixer 100 from an exit port, e.g.. generally away from the discharge conduit 108 to form the

concentrated layer slurry 1 1 2, The main mixer 100 acts as a pump to drive the unfoamed slurry 1 10 out the smaller discharge port for the concentrated layer slurry which flows through the pressurized slurry line. Additives, particularly, the enhancing additive, in wet form 1 14 are injected into the pressurized slurry line through injection ports. The inventors have found that the line is desirably long enough, which can be determined within the level of ordinary skill, to allow for uniform mixing of slurry including enhancing additive. There is no need for separate introduction- of stucco or water. As seen in depi ction A, edge slurry streams 1 16 and 1 1 S can also be diverted from the main mixer 100 without foam so that they have the desired hardness for their use on the edges as known in the art.

[0130] In diagram B, it can be seen that the two mixers 200 and 202 are connected in series. Stucco 204 and water 206 are added to the main mixer 200, The foam 208 is added downstream of the body of the main mixer 200 in the discharge conduit 210 (which can contain a modified outlet design or canister). Thus, fbamless slurry 212 can exit the mixer 200 through an exit port and inserted into the smaller secondary mixer 202 for the

concentrated layer, where dry and wet additives 214 (e.g., via separate lines), including enhancing additive, can be separately added to provide the concentrated effect as desired. Edge slurry streams 214 and 216 are also shown as exiting from a port separate from the main discharge 210 to minimize foam therein and provide their desired hardness.

10331] In diagram C, it can be seen that there are two mixers 300 and 302 but the slurries are made separately, with each mixer having its own inputs for stucco and water as desired. Particularly, stucco 304 and water 306 are added into the main mixer 300. Foam 308 is added downstream of the body of the main mixer 300 in the discharge conduit 3 ί 0 (which can contain a canister or modified outlet design as described in U.S. Patents 6,494,609 and 6,8^*74,930), Edge slurry streams 312 and 314 can exit from a port separate from the main discharge 310 to minimize foam therein and provide their desired hardness. n a secondary mixer 302 for forming the concentrated layer slurry 316, stucco and water 318, 320 can he added and mixed. Dry and wet additives (e.g., via separate lines), including enhancing additive as described herein, can be inserted into the concentrated layer mixer 302. As such, the concentrated layer slurry 316 is prepared separately from the core slurry formed in the main mixer 300.

{0132] in some embodiments, the edge slurries can be extracted from the concentrated layer mixer, instead of from the main mixer, as desired. The edges can he denser than the board core in some embodiments and, e.g., can have the same density as the concentrated layer. For example, as the concentrated layer is laid down, a portion of the concentrated layer slurry can How around the ends of the roller to form edges of the ultimate product, as seen in FIGS. 5 and 6 with respect to one end. The length of the roller can be configured (e.g., to be shorter than the width of the paper) to accommodate the formation of edges in d ss manner. 10133] In some embodiments, it will be understood that the discharge conduit can include^' a slurry distributor with either a single feed inlet or multiple feed inlets, such as those described in U.S. Patent Application Publication 2012/0168527 Al (Application No.

13/341 ,016) and U.S. Patent Application Publication 2012/0170403 Al (Application No, 13/341 ,209), for example. In those embodiments, using a slurry distributor with multiple feed inlets, the discharge conduit can include a suitable flow splitter, such as those described in U.S. Patent Application Publication 2012/0170403 Al .

[0134] Board is formed in a sandwich structure, normally concurrently and continuously, as will be understood in the art. The face cover sheet travels as a continuous ribbon on a conveyor. After being discharged from its mixer, the concentrated layer slurry is applied to the moving face cover sheet. Also, hard edges, as known in the art, can be formed, e.g., from the same slurry stream forming the concentrated layer for convenience, if desired.

[0135] The board core slurry is then applied over the moving face paper bearing the concentrated layer slurry, and covered with a second cover sheet (typically the "back" cover sheet) to form a wet assembly in the form of a sandwich structure that is a board precursor to the final product. The back (bottom) cover sheet may optionally bear a skim coat, which can be formed from the same or different gypsum slurry as for the concentrated layer. The cover sheets may be formed from paper, fibrous mat or other type of material (e.g., foil, plastic, glass mat, non-woven material such as blend of cellulosic and inorganic filler, etc.). In some embodiments, the concentrated layer is applied on both major sides of the board, i.e., in bonding relation to both the top and bottom sheets,

[0136] The wet assembly thereby provided is conveyed to a forming station where the product is sized to a desired thickness (e.g., via forming plate), and to one or more knife sections where it is cut to a desired length. The wet assembly is allowed to harden to form the interlocking crystalline matrix of set gypsum, and excess water is removed using a drying process (e.g., by transporting the assembly through a kiln). Surprisingly and unexpectedly, it has been found that board prepared according to the disclosure requires significantly less time in a drying process because of the low water demand characteristic of the board arrangement and composition. This is advantageous because it reduce energy costs.

|0137] it also is common in the manufacture of gypsum board to use vibration in order to eliminate large voids or air pockets from the deposited slurry. Each of the above steps, as well as processes and equipment for performing such steps, are known in the art. [0138] The following example(s) further illustrate the invention but, of course, should not be construed as in any way limiting its scope.

EXAMPLE 1

[0139] This example demonstrates strength characteristics of different types of board samples in accordance with principles of the present disclosure,

0140] In particular, three different boards were tested. Board 1 was a comparative board, absent a concentrated layer. Boards 2 and 3 were composite gypsum boards where each contained a concentrated layer and board core in accordance with principles of the disclosure. Each board was prepared at a thickness of about one-half inch with a composite density, not including the face and back paper, of about 26 pcf

[0141] Each board was produced as a 6 inch by 6 inch laboratory sample following the genera] arrangement shown in FIG. 1 . Each hoard contained a face paper having a basis weight of 48 Ibs/MSF and a back paper having a basis weight of 42 Ibs/MSF (MSF ^:::= 1 000 if"). The respective thickness and density for the concentrated layer (if present) and board core for each board is provided in Tables i A and IB.

[0142] The enhancing additive was a pregelatinized com starch having a viscosity of 773 centipoise determined according to the VMA method. In Boards 2 and 3, it can be seen in Tables 1 A and I B that the enhancing additive was more concentrated in the concentrated layer than in the board core.

[0.1 3] Nai 1 pull resistance was tested in accordance with ASTM 473-10, Method B. The nail pull values are reported in Table 1 C.

Table 1 A

Table I B

Table 1 C

As can be seen from Table 1C, the comparative sample (Board 1 ) had a low nail pull resistance value, whereas both of Composite Boards 2 and 3 exhibited improved nail pull resistance. Thus, this Example illustrates that an improved composite design in accordance with the present disclosure enhances nail pull resistance by incorporating a concentrated layer adjacent to the face paper. This concentrated layer contributes to the desirable nail pull resistance with a considerable thickness in accordance with principles of the present disclosure.

EXAMPLE 2

[0145] This example demonstrates the effect of various starches on strength in gypsum disks representative of a concentrated layer. Each cornposition included the ingredients set forth in Table 2, although the type of starch varied as shown in Table 3. Particularly, composition 2A was a comparative composition inasmuch as it included no starch.

Composition 2B included a cooked starch in the form of a pregelatmized starch having a viscosity of 80 cP, as measured according to the VMA Method, as set forth in US

2014/01 1 3124 A L Compositions 2C-20 included one of various uncooked starches as shown in Table 3 ,

Table 1

(0146) The disks were prepared from separate slurry compositions 2A-20. In comparative composition 2A, the total weight was 799.8 g as there was no starch. Each composition was prepared from dry and wet mixes that were combined. Each wet mix was prepared by weighing the water, dispersant, retard er 1% solution, dispersant, and sodium trimeiaphosphate .10% solution in a mixing bowl of a Waring blender (model CBI 5), commercially available from Conair Corp. (East Windsor, New Jersey). The sodium trimeiaphosphate 10% solution was prepared by dissolving 10 parts (weight) of sodium trimetaphosphate in 90 parts (weight) of water, while the retarder 1% solution was composed of an aqueous solution of the pentasodium salt of di ethyl enetriaminepentaacetic acid (Versenex™ 80, commercially available from DOW Chemical Company, Midland, MI), and prepared by mixing 1 part (weight) of Versenex™ 80 with 99 parts (weight) of water. The remaining ingredients, particularly, the stucco, heat resistant accelerator, and starch (if present), were weighed and prepared in a dry mix. The heat resistant accelerator was composed of ground up land piaster and dextrose. The dry mix was poured into the blender with the wet ingredients, and soaked for 5 seconds and then mixed at high speed for 15 seconds.

[0147] Foam was added in order to reduce disk density (and hence weight). For foam preparation, a 0.5% solution of Hyonic™ PFM-33 soap (available from GEO Specialty Chemicals, Ambler, PA) was formed and then mixed with air to make the air foam. The air foam was added to the slurry using a foam generator. The foam generator was operated at a rate sufficient to obtain a density of the final dried disk of 38 pcf.

[0148] After foam addition, the slurry was immediately poured into a ring (4" inside diameter and 0.5" thick) type of mold which was suited for forming a disk sample. The surface of the molds had previously been sprayed with lubricant in the form of WD40™, commercially available from WD-40 Company, San Diego, CA. The slurry was poured to a point slightly above the top of the ring of the molds. The excess slurry was scraped as soon as the plaster was set. After the disks hardened in the mold, the disks were removed from the moid, and heated at 300 °F (149°C) for 60 min, then dried at 1 10°F (43°C) for about 48 hours until a constant weight was reached. Following removal from the oven, the disks were allowed to cool at room temperature for one hour. The final disks had dimensions of a diameter of 4 inches (10.16 em), and a thickness of 0.5 inches (1 .27 cm).

[0149] Strength was tested by measuring compressive strength and nail pull resistance. The nail pull resistance was tested in accordance with ASTM 473-10, Method B. The compressive strength was measured using the materials testing system commercially available as SATEC™ E/M Systems from MTS Systems Corp. (Eden Prairie, MN). The load was applied continuously and without a shock at speed of 0.04 ineh/min (with a constant rate between 1 5 to 40 psi/s). The results are shown in Table 3.

Table 3

[0150] In embodiments where starches are used in the concentrated layer, this example illustrates thai both cooked and uncooked starches have benefit as enhancing additive for improving strength as shown by the improvement in performance on strength. As seen from Table 3, the uncooked and cooked starches showed considerable improvement in strength over the comparative composition without the starch, with many of the values being more than about 50% higher than the strength of the control without starch, more than about 75% higher than the strength of the control without starch, or more than about 100% more than the strength of the control without starch.

[0151 ] The improvement in strength seen in the disks shown from both cooked and uncooked starches, in accordance with various embodiments of the invention, indicates the utili ty of these starches in the concentrated layer of a gypsum wallboard in accordance with some embodiments because the desired starches provides extra bonding between gypsum crystals for strength improvement. The starches were effective to improve strength, thereby suggesting lack of migration, contrary to the case with a migratory acid-modified starch. Therefore, the example shows that the starches would be effective in a concentrated layer.

EXAMPLE. 3

[0.152] This example demonstrates the optional use of fibers in the concentrated layer. In particular, two types of slurries were prepared. Each slurry was then used to form a concentrated layer in separate production boards prepared and trialed on the wet end of a manufacturing line. One type of slurry (composition 3 A) did not contain any fi ber, while the other type of slurry (composition 3B) contained glass fiber having a fiber length of 0.5 inch (25,400 μηα) and diameter of 15.24 -· 16.51 μιτι, thereby having an aspect ratio of about 1540 to about 1670 (length divided by diameter). The glass fiber was in the form of DuraCore™ SF+ 1/2M300 pre-chopped strands, commercially available from Johns Manviile Inc., (Denver, CO).

[0153] A general representative range of formulation for illustrative purposes only for the concentrated layer is provided in Table 4, where low and high columns are provided to indicate an example of desired ranges of ingredients therebetween (inclusive) in accordance with an embodiment. Other representative formulations and embodiments will be easily ascertained from the full description herein, including the ranges for ingredients provided. The triaied formulations are provided in Tables 5A and 5B. Aside from the differences in glass fiber, the two formulations were the same, as can be seen in Tables 5A and 5B.

Table 4

Dry Density (pcf) I Dry Density (pcf) |

Density 25 1 65

Table 5 A - Composition 3 A

[0154] The heat resistant accelerator was composed of ground land plaster and dextrose. Each slurry composition was prepared from dry and wet ingredients that were combined in a secondary mixer dedicated for the concentrated layer, separate from the main mixer for preparing the core. The sodium trimeiaphosphate, retarder, and dispersani were added in liquid form. The retarder was in the form of pentasodium salt of

dieihylenetriaminepentaacetic acid (Versenex™ 80, commercially available from DOW Chemical Company, Midland, Ml). The dispersant was in the form of a poly naphthalene sulfonate calcium salt (DURASAR™ commercially from Ruetgers Polymers, Candiae, (Canada). A 3 urn can optionally be included to modify the gypsum hydration rate, if desired, j OlSS] Foam was included in the concentrated layer, and the density of the concentrated layer produced from both slurries was 36 pcf on a dry basis. For foam preparation, a solution of a mixture of STEOL™ CS230 and Polystep 25 foaming agents (available from Stepan Co., Nortbfteld, IL) was formed and then mixed with air to make the air foam using a foam generator. The air foam was added to the slurry at the secondary mixer. The amount of foam added was 1 % by weight foaming agent. The foaming agent (1 % solution) was prepared by dissol ving 1 parts (weight) of foaming agent in 1(50 parts (weight) of water.

[Θ156] In order to prepare trial board on a manufacturing line, paper was released on a continuous roll onto a conveyor as commonly known in the art. The concentrated layer slurry was discharged from the secondary mixer and laid on the paper as it traveled along the conveyor at high speed (over 6(50 feet/rnin). A driven roller was positioned transverse to the paper and was used to spread the concentrated slurry across the paper, The roller typically rotates in the direction opposite the direction the paper travels. The length of the roller was slightly less than the width of the paper so that the slurry was allowed to travel around the ends of the roller over the edges of the paper to ultimately form the edges of the finished board product. The roller normally works with a second roller under the paper with a sufficient gap between the rollers to permit the thickness of the paper to travel therebetween. f01S?S As the roller obstructs the forward progress of the slurry, a slurry head forms behind, and just upstream, from the roller, controlled primarily by tangential speed of the rotating roller. The head is an inventory of slurry that helps decelerate the incoming material, providing spread, which allows for proper amount, of slurry to form the concentrated layer and the edges. The slurry is wiped from the head and carried by the roller to the downstream side of the roller and re-deposited on the paper and spread to lay what becomes the concentrated layer o the board. Optionally, a laser can be used to control the head in order to regulate the volume of slurry by varying the amount of soap or foam air used which then changes the density of slurry contained within the head, as known in the art. Downstream, the core slurry is deposited from the main mixer over the concentrated layer and the board process is completed using understood techniques. [0158] FIGS. 3-6 illustrate images depicting the slurry head (FIGS. 3-4) and the formation of an edge around the roller (FIGS. 5-6) from the manufacturing trials using ihe slurries without the glass fiber (composition 3 A; FIGS. 3 and 5), and with optional glass fiber (composition 3B; FIGS. 4 and 6). The same trial run using composition 3A was carried out to illustrate the conditions shown in FIGS. 3 and 5. while the same trial run using

composition 3B was carried out to illustrate the conditions shown in FIGS, 4 and 6.

[0159] As seen in FIGS. 3-4, the concentrated layer slurry was applied by a roller 400 or 500 to a paper cover sheet 402 or 502, The slurry without glass fiber shown in FIG. 3 was deposited on paper 402 upstream of roller 400 and the deposited slurry traveled toward the roller 400 in a line of slurry 404 that was choppy and uneven. The slurry without glass fiber resulted in a more scalloped slurry head 406, with livdrodynamic instability 408 resulting in undesired air entraimnent. On the other hand, the slurry with glass fiber shown in FIG. 4 was deposited on paper 502 upstream of roller 500 and the deposited slurry traveled in a line of slurry 504 that was stable and calmer. The slurry with glass fiber resulted in less scalloping and a more even, smooth head 506 with a more stable slurry 508 as a result of a change in rheologieal properties. The head 406 containing scalloping tends to create unstable flow dynamics in various length and time scales and thereby can result in defects such as voids, blisters, or paper delamination once the product is kiln dried.

[0160 FIG. 5 corresponds with the trial shown in FIG. 3, and FIG. 6 corresponds with the trial shown in FIG. 4. Particularly, FIGS. 5-6 show an edge 410 or 510 of the roller 400 or 500. An edge slurry 12 or 512 is formed around the edge 410 or 510 of the roller 400 or 500 to ultimately form an edge of the board to be produced. The slurry without glass fiber resulted in a more variable edge which can cause voids, blisters, paper delamination, soft and/or hard edges, and general disruption to the edge formation and manufacturing process, as seen in FIG. 5. As seen in FIG. 5, there is undesirable splashing 414 of the edge slurry over an edge of the paper 402, Due to flow variation, wave 416 formation can occur as the slurry is partially lifted onto the roller 400, such that as wave 416 reaches the edge, splashing is undesirably caused. As seen in FIG. 6, the slurry edge 512 is more controlled and does not splash over the paper 502. The slurry with glass fiber had less edge variation, resulting in better control, reducing the opportunity for defects such as voids, blisters, paper

delamination, soft and/or hard edges, and other disruptions to the manufacturing process, as seen in FIG. 6. [0161] Ιΐ will be appreciated that fiber such as glass fiber is not required in the concentrated layer. Defects including blisters, voids, delamination, poor edges, etc., can be controlled by other means, including by a variety of mechanical or other means well known in ie art. For example, mechanical vibrators can be used under the conveyor to remove large air pockets in the slurry. In addition, other mechanical or other process adjustments will be appreciated, including the use of slurry spreaders, slurry distributors, head control means, and adjustments to mixer discharge, line speed, and formulation viscosity, etc. These examples of mechanical and other techniques can be used alone or in combination with glass to provide acceptable results.

EXAMPLES 4-10

[0162] In the following Examples 4-10, slurry compositions were prepared as follows. Each slurry composition was prepared from dry and wet ingredients that were combined in a mixer (i.e., a main mixer for the core slurries, and a secondary mixer dedicated for the concentrated layer .slurries). The water, sodium trimetaphosphate, retarder, dispersant, and alum were added in liquid form. The retarder was in the form of pentasodium salt of diethylenetriaminepentaaeetie acid (Versenex™ 80, commercially available from DOW Chemical Company, Midland, MI). The dispersant was in the form of a poly naphthalene sulfonate calcium salt (DU ASAR™ commercially from Ruetgers Polymers, Candiac, Canada). The stucco, heat resistant accelerator, glass fiber, and dextrose were added in solid form. Alum was optionally included to modify the gypsum hydration rate, if desired. The heat resistant accelerator was composed of ground land-plaster and dextrose. Additional dextrose was added in some instances to improve bonding with the back (news-line) paper cover sheet.

[0163] Foam was included in the core slurries and concentrated layer slurries. For foam preparation, a solution of a mixture of STTEOL™ CS230 and Polystep 25 foaming agent (available from Stepan Co., Northfield, IL) was formed and then mixed with air to make the air foam using a foam generator. The air foam density was approximately 4.5 lbs per cubic foot. The air foam was added to core slurry in a discharge conduit of the main mixer and added to the concentrated slurry at the secondary mixer. The weight percentage of a specific ingredient is based on its own weight, versus the total composition of the wet slurry (thus, excluding paper). Any inconsistencies in the totals are due to rounding of values of individual ingredients, e.g., due to effective limits of readings from equipment such as pumps and flow meters, as will be understood by those skilled in the art. EXAMPLE 4

[0164] This example demonstrates a benefit of including a concentrated layer in gypsum board. The example shows that the concentrated layer enhances nail pull performance. Two boards were prepared. Board 4A and Board 4B. Board 4A did not contain a coneentrated layer. Board 4B did. The slurry compositions for preparing boards 4A and 4B are set forth in Tables 6 and 7, respectively.

Table 6 - Composition for Board 4A

Table 7 - Composition for Board 4B

j^; Core Concentrated Layer

Weight :i _W: _% Weight

Ingredients j _Wt o/

(3bs/MISF) j (Ibs/MSF) 1

Stucco 896.3 j 54% 99.7 1 41 % Accelerator

Foaming Agent 0.78 0.05% 0.04 0.02%

Pregeiaiinized 13.5 1 % 14.5 6%

Starch

Sodium 1 .07 0.06% 0.10 0.04% Trimetaphosphate

Retarder 0.46 0.03% 0.04 0.01 %

Dispersani 0.8 0.05% 0.16 0.07%

Alum 0.8 0.05% 0.04 0.01 %

Glass Fiber 0 0% 0 0%

Dextrose 1 0.06% 0.1 1 0.05%

Water 729.7 44% 125. 1 ! 52%

Total: 1662 100% 242 100%

[0165] Boards 4A and 4B were each prepared on a high speed (over 600 ft/min) board manufacturing line (machine) using a main pin mixer to combine wet and dry ingredients in a continuous process to form a continuous ribbon of board precursor, with a core slurry deposited between two sheets of paper, as described in Example 3. The concentrated layer- was used in preparing Board 4B with the aid of a secondary board, mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit from the main mixer. The precursors were processed and kiln dried to form the final Boards, 4A and 4B.

Properties and dimensions of the boards are set forth in Table 8.

Table 8

Board 4B 0.5 1 289 86.9 1 0.025 1 39.4

[0166] This example shows a benefit of the concentrated layer in enhancing strength of the board product. As seen in Table 8, Board 4B, which included the concentrated layer, resulted in an increased nail pull (resistance) value. It will be understood that the term ^'"nail pull" herein refers to nail pull resistance as mea ured according to ASTM 473 - 10 Method B, unless otherwise stated. Such nail pull improvement is beneficial in providing strength and enhancing peribraiance in the field of.the board. Advantageously, increasing nail pull with the aid of concentrated layer can be used to reduce board weight and the cost of

manufacturing wallboard products,

EXAMPLE 5

[0167] This example demonstrates a benefit of using a concentrated layer in gypsum board. In particular, tailoring ingredients in the slurry for forming the concentrated layer can be beneficial The rate in which a concentrated layer stiffens can be optionally modulated to effect the washout of the concentrated layer as the main (core) slurry meets the concentrated layer slurry during the board manufacturing process. Washout refers to the removal of the concentrated layer which can occur when the core slurry is distributed over the concentrated layer during the continuous manufacturing process. Washout undesirably can result in product non-uniformity and reduced nail pull. Two boards were prepared. Boards 5A and 5B. The compositions for preparing Boards 5 A and 5 B are set forth in Tables 9 and 10, respecti ely.

[0168] The stiffening rate of stucco slurry (sometimes called gypsum slurry) in this example was modified using alum and retard er. The amount of al um was decreased in Board 5B to decrease the rate of setting, while retarder was added to Board 5B to also decrease the rate of setting.

^'"(^"able 9 - Composition for Board 5 A

Alum 0.8 0.06% 0.06 I 0.03%

Glass fiber 0 0% 0 6.66%

Dextrose i 1.2 0.08% 0.12 |^: 0.05%

W ater 601 42% 1 15.3 | 51.87%

Total: 1440 100% 99 100%

Table 10 - Composition for Board 5B

Core Concentrated Layer

[0169] Boards 5A and Mix 5B were each, prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards 5A and 5B with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit from the main mixer. The precursors were processed and kiln dried to form the final boards 5A and 5B. Properties and dimensions of the boards are set forth in Table 1 1. [0170] Washout was measured utilizing a density profiiimeier machine which utilizes X- Ray technology (i.e., QDP-01X Density Profiler, commercially available from Quintek Measurement Systems, inc., noxville, TN) to determine the density gradient throughout the sample. One inch samples taken from Boards 5A and 5B were prepared and cut in the cross direction of the board so a density profile could be assembled to represent the entire width and thickness of each board.

Table 1 1

Board 5B 1 0.5 1134 0.02 J 0.025 28-32

[0171] This example shows a benefit of using a concentrated layer, as both Boards 5A and 5B were effective. Board 5A was more preferred because it exhibited less washout. Reducing the stiffening rate led to more preferred board. As seen in Table 1 1 , Board 5A demonstrated an increased ability to resist washout from the main slurry from contacting the concentrated layer during the manufacturing process as compared with Board 5B. in this regard, Board 5 A differed from Board 5B in that Board 5A was prepared using less retarder and more alum resulting in less washout, while Board 5B was prepared using more retarder but included less alum. The results shown in Table 1 1 indicate a 50% reduction in washout for Board 5A as compared with Board 5B, although both boards were useful products.

EXAMPLE 6

[0172] This example demonstrates a benefit of including a concentrated layer in a gypsum board. Particularly, the slurry composition for forming the concentrated layer can be tailored to include enhancing additives. As this example shows, starch concentration can be used to decrease the washout of the concentrated layer as the main (core) slurry meets the concentrated layer slurry during the board manufacturing process. Two boards were prepared, Boards 6A and 6B. The slurry compositions for preparing Boards 6A and 6B are set forth in Tables 12 and 13, respectively. Table 12 - Composition for Board 6A

Table 33 - Composition for Board 6B

Dextrose 1.2 0.08% 0.12 0.05% 1 Water 601 j 41.7% j 121 j 52%

1 Total: 1440 ; 100% j 234 j 100%

[0173] Boards 6A and 6B were each prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards 6 A and 6B with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit from the main mixer. The precursors were processed and kiln dried to form the final Boards, 6A and 6B. Properties of the boards are set forth in Table 14.

Washout was measured as described in Example 5.

Table 14

1_.0174] This example illustrates a benefit of having a concentrated layer. Particularly, it can be seen that having a higher concentration of pregeiatinized starch in the concentrated layer slurry, as compared with the core slurry, was beneficial. As seen in Table 14, Board 6 A demonstrated more washout as compared with Board 6B. In this regard, Board 6A differed from Board 6B in that Board 6A was prepared using less pregeiatinized starch, resulting in more washout, while Board 6B included more pregelaniinized starch in the slurry. The results shown in Table ,14 indicate washout was reduced by 75% in Board 6B as compared with Board 6A. Use of more enhancing additive, e.g., pregeiatinized starch, in the concentrated layer can be less costly and more efficient as the additive is more highly located where the most benefit is seen, i.e., in the concentrated layer.

EXAMPLE 7

[0175] This example demonstrates a benefit of including a concentrated layer in a gypsum board. In particular, it is shown that density of a concentrated layer can be used to improve nail pull. Density was modified by changing the amount of foam contained in the concentrated layer. Two boards were prepared, Boards 7A and 7B. The slurry compositions for preparing Boards 7A and 7B are set forth in Tables 15 and 16, respectively.

Table 1 5 - Composition for Board 7 A

Total: 1446 100% 219.5 I 100%

Table 16 - - Composition for Board 7B

Alum 0.8 1 0.06% 0.045 0.02%

! Glass Fiber 2 0.14% 0.2 0.09% i Dextrose 1.2 0.08% 0.12 [ 0.05% ^;

I Water 610.6 42.18% 1 1 3.7 1 52%

1 Total; 1448 100% 219 j Ϊ00%

[01.76] Boards 7A and 7B were each prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards 7A and 7B with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge from the main mixer. The precursors were processed and kiln dried to form the final boards 7 A and 7B. Properties and dimensions of the boards are set forth in Table

17.

Table 17

[0177] This example shows benefit and efficiency of using a concentrated layer.

Focusing strength additive and density in the concentrated layer provides an overall strength benefit efficiently, Both boards exhibited effective nail. pull. As seen in Table 1 7, Board 7 A demonstrated decreased nail pull as compared with Board 7B. in this regard, Board 7 A differed from Board 7B in that Board 7 A was prepared using more foaming agent in the concentrated layer slurry, resulting in lower density, while Board 7B included less foam in the concentrated layer slurry, resulting in higher density. But the results were similar as Board 7B was prepared with a higher weight percentage of starch. The results shown in fable 1 7 indicate that concentrating increased density in the concentrated layer and increasing enhancing additive dosage (by weight percentage) in the concentrated layer slurry are effective at increasing nail pull in an efficient manner.

EXAMPLE 8

[0178] This example demonstrates a benefit of including a concentrated layer in gypsum board. Starcii concentration in the concentrated layer can be used to improve nail pull. Two boards were prepared, Boards 8A and 8B. In this instance, since washout was more prevalent under test conditions, the nail pull difference was measured along the machine direction side of the board (the non-code side) where washout was not prevalent. The slurry compositions for preparing Boards 8A and 8B are set forth in Tables 18 and 19, respectively.

Table 18 - Composition for Board 8A

Total: 1432 i ()0% 247 100%

Table 19 - Composition for Board 8B

Total: 1432 100% 271 100%

[0179] Boards SA and 8B were each prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards 8A and 8B with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit from the main mixer. The precursors were processed and kiln dried to form the final Boards, 8 A. and SB. Properties and dimensions of the boards are set forth in Table 20.

Table 20

[0180] This example shows a benefit of using a concentrated layer. Both boards demonstrated good nail pull with higher concentration of starch in the concentrated layer. Adding a higher concentration of pregelatinized starch in the concentrated layer resulted in better strength. As seen in Table 20, Board 8A demonstrated lower nail pull as compared with Board 8B. In this regard, Board 8A differed from Board 8B in that the concentrated layer of Board 8 A was prepared using less pregelaiinized starch, resulting in lower nail pull, while the concentrated layer slurry of Board 8B included more starch, resulting in higher nail pull. The results shown in Table 20 indicate starch concentration in the concentrated layer can be used to modify the nail pull result.

EXAMPLE 9

[0181] This example illustrates a benefit of including a concentrated layer in gypsum board. Representative thickness of the concentrated layer for achieving improved nail pull is shown. Other thickness as described throughout herein can be used. Two boards were prepared. Boards 9 A and 9B. Thickness was modified by increasing the speed of the application roller and narrowing the spread of the concentrated layer, thereby making it thicker. The compositions used in preparing 9 A and 9B are set forth in Tables 21 and 22, respectively.

Table 21 - Composition for E toard 9A

Table 22 - Composition for Board 9B

[0182] Boards 9A and 9B were each prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards 9A and B with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit from the main, mixer . The precursors were processed and kiln dried to form the final boards, 9.4 and 9B. Properties and dimensions of the boards are set forth in Table 23.

Table 23

Board Overal l Board Details

I Board Nai l Pull Actual

Board Weight

1 Thickness Result Thickness

( Ibs/MSF)

! ΟΌ ( lbs force) (pet)

Board A i: 0.5 1 1 1 0 75.6 0.035 ! Board 9B J 0.5 j 1 109 | 80.2 | 0.04

This example shows a benefit of using a concentrated l ayer. Increasing the thickness of the concentrated layer enhanced strength, although both Boards 9A and 9B were sufficiently strong and effective. Both boards contained higher concentration of enhancing additive (starch) in. the concentrated layer. As seen in Table 23, Board 9A demonstrated lower nail pull as compared with Board 9B. n this regard, Board 9 A differed from Board 9B in that Board 9 A was prepared using a lower speed on the application roller, resulting in a thinner concentrated layer, while Board 9B was prepared using a higher speed on the application roller, resulting in a thicker concentrated layer. The results shown in Table 23 indicate that increased starch concentration in the concentrated layer, as well as concentrated layer thickness can be used to modify nail pull results.

EXAMPLE 10

[0183] This example demonstrates that the concentrated layer enhances nail pull performance at a board weight target of 1.100 Ibs/MSF (about 5370 g/m²). Two boards were prepared, Board 10A and Board 10B. Board IOB did not contain a concentrated layer, while Board 10A did. The slurry compositions for preparing Boards 10A and IOB are set forth in Tables 24 and 25, respectively. The compositions were prepared as described in Example 3, Table 24 - Composition for Board 10A

Water 585 41.20% 1 14 48.4%

^ ₄₂₀

Totah 100% 236 100%

Table 25 - Composition tor Board 1 0B

Total; 1541 100%) N/A N/A

{0184] Boards 10A and 10B were each prepared on a high speed machine using a main pin mixer to combine wet and dry ingredients in a continuous process, as described in Example 3, to form a continuous ribbon of board precursor, with core slurry deposited between two sheets of paper. A concentrated layer was used to prepare Boards i OA with the aid of a secondary board mixer to blend wet and dry ingredients. This concentrated layer slurry was applied to the face paper using an application roller, with the core slurry deposited thereon from a discharge conduit, from the main mixer. The precursors were processed and kiln dried to form the final boards, 10A and 10B. Properties and dimensions of the boards are set forth in Table 26.

Table 26

Board Board Nail Pull Formulated

Dry Density Thickness Weight Result Thickness

(pel) (in) (lbs/MSP) (lbs force) (in)

Board 1GA 0.5 .. 1098 76.4 [ 0.035 41

Board ! OB [ 0.5 1096 70.Γ^{" "} /A N/A

[0185] This example shows a benefit of using a concentrated layer. As seen in Table 26, Board I DA demonstrated a higher nail pull as compared with Board 10B. in this regard, Board lOA differed from Board 10B in that Board 10A was prepared using a concentrated layer slurry that included higher concentrations of pregelatinized starch compared to the core slurry, resulting in higher nail pull, while Board 10B did not contain a concentrated layer. The results shown in Table 26 indicate a concentrated layer containing high concentrations of pregelatinized starch can be used to increase nail pull,

[0186] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein,

[0187] The use of the terms "a" and "an" and "the" and "at least one" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context, The use of the term "at least one" followed by a list of one or more items (for example, "at least one of A and B") is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly

contradicted by context. As used herein, it will be understood that the term "bonding relation" does not necessarily mean that two layers are in immediate contact. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Also, everywhere "comprising" (or its equivalent) is recited, the "comprising" is considered to incorporate "consisting essentially of and "consisting of." Thus, an embodiment

"comprising" (an) element(s) supports embodiments "consisting essentially of and

"consisting of the recited element(s). Everywhere "consisting essentially of is recited is considered to incorporate "consisting of." Thus, an embodiment "consisting essentially of (an) elements) supports embodiments "consisting of the recited element(s). Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value failing within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The term "exemplary" refers to an example and is not intended io suggest the best example. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless othenvise claimed. No language in the specification should be constmed as indicating any non-claimed element as essential to the practice of the invention.

[0.188J Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

CLAIM(S)

1 , A composite gypsum board comprising:

(a) a board core composing set gypsum formed from at least water, stucco, and optionally, an enhancing additive, the core having a dry density and dry thickness, the core defining first and second core faces in opposing relation; and

(b) a concentrated layer formed from, at least water, stucco, and the enhancing additive, the concentrated layer disposed in bonding relation to the first core face, the concentrated layer having a dry density of at least about 1 ,1 times higher than the dry density of the board core; wherein:

(i) when the enhancing additive is present in forming the core, the enhancing additive is included in a higher concentration in forming the concentrated layer than in torming the board core, and

(ii) the board core dry thickness is greater than the dry thickness of the concentrated ayer.

2, The composite gypsum board of claim 1 , wherein:

the concentrated layer defines first and second concentrated layer faces,

the board further comprises a top cover sheet, the first concentrated layer face facing the top cover sheet, and

the second concentrated layer face faces the first core face.

3, The composite gypsum board of claim 1 or 2, wherein the board further comprises a bottom cover sheet, the second core face facing the bottom cover sheet.

4. The composite gypsum board of claim 2 or 3, wherein the top and/or bottom cover sheet has a thickness of at least about 0.014 inches (about 0.036 cm).

5. The composite gypsum board of any one of claims 2-4, wherein the top and/or bottom cover sheet is formed from paper and has a paper basis weight from about 38 Ibs/MSF (about 185 g/m²) to about 58 Ibs/MSF (about 283 g nr).

6. The composite gypsum board of any one of claims 2-5, wherein the top and/or bottom cover sheet has a density from about 38 pcf (about 610 kg m^J) to about 42 pcf (about 670 kg/m

7. The composite gypsum board of any one of claims 1 -6, wherein the dry- density of the concentrated layer is from about 36 pcf (about 580 kg m³) to about 45 pcf (about 720 kg^'m³).

8. The composite gypsum board of any one of claims 1-7, wherein the dry thickness of the concentrated layer is from about 0.035 inches (about 0,09 cm) to about 0.05 inches (about 0.13 cm).

9. The composite gypsum board of any one of claims 1-8, wherein the density of the board core is from about 24 pcf (about 380 kg/rrr^') to about 40 pcf (about 640 kg/m^").

10. The composite gypsum board of any one of claims 1-9, wherein the thickness of the board core is from about 9 times to about 14 times thicker than the thickness of the concentrated layer.

1 1. The composite gypsum board of any one of claims 1 -10, wherein the enhancing additive comprises starch.

12. The composite gypsum board of claim 1 1 , wherein the starch includes hydroxyethylated or hydroxypropylated starch, or a combination thereof.

13. The composite gypsum board of claim 1 1 or .12, wherein the starch includes pregelatinized starch.

14. The composite gypsum board of claim 13, the pregelatinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method.

15. The composite gypsum board of claim 14, the pregelatinized starch having a viscosity of from about 30 centipoise to about 200 centipoise according to the VMA method.

36. The composite gypsum board of any one of claims 1 1-15, wherein the starch is included in forming the concentrated 3 aver in an amount of from about 5% to about 40% by weight of the stucco and is included in forming the board core in an amount of from about 0% to about 4% by weight of the siucco.

17. The composite gypsum board of any one of claims 1 -16, wherein the enhancing additive comprises polyvinyl alcohol and/or boric acid.

1 8. The composite gypsum board of claim 17, wherein the enhancing additive includes polyvinyl alcohol and die polyvinyl alcohol is present in the concentrated layer in an amount from about 1 % to about 5% by weight of the stucco, and is present in the board core in an amount from about 0% to about 1 % by weight of the stucco.

19. The composite gypsum board of claim 17, wherein the enhancing additive includes boric acid, and the boric acid is present in the concentrated layer in an amount of from about 0.1 % to about 1 % by weight of the stucco, and is present in the board core in an amount from about 0% to about 0.1 % by weight of the stucco.

20. The composite gypsum board of any one of claims 1-19, wherein the enhancing additive comprises nano-eeliulose, micro-cellulose, or any combination thereof.

21. The composite gypsum board of claim 20, wherein the nano-cellulose, micro- cellulose, or any combination thereof is present in the concentrated layer in an amount from about 0.05% to about 1 % by weight of the stucco, and is present in the in the board core in an amount from about 0% to about 0.01 % by weight of the stucco.

22 , The composite gypsum board of any one of claims 1 -21 , wherein the enhancing additive comprises gypsum-cement.

23. The composite gypsum board of claim 22, wherein the gypsum-cement is included in forming the concentrated layer in an amount of from about 5% to about 30% by weight of the stucco, and is included in forming the board core in an amount of from about 0% to about 10% by weight of the stucco.

24. The composite gypsum board of any one of claims 3 -23. wherein the core and/or the concentrated layer is further formed from a polyphosphate.

25. The composite gypsum board of claim 24, wherein the polyphosphate is sodium trimetaphosphate, potassium trimetaphosphate, ammonium trimetaphosphate, lithium trimetaphosphate or any combination thereof.

26. The composite gypsum board of claim 24 or 25, wherein the polyphosphate is included in forming the concentrated layer in an amount of from about 0,2% to about 0.4% by weight of the stucco, and is included in forming the board core in an amount of from about 0% to about 0.2% by weight of the stucco.

27. The composite gypsum board of any one of claims 1-26, wherein the core a3 d/or the concentrated layer is further formed from a dispersant.

28. The composite gypsum board of claim 27, wherein the dispersant is a naphihalenesulfonate, polycarboxylate, iignosulfonate, sulfonated lignin, or any combination thereof.

29. The composite gypsum board of claim 27 or 28, wherein the dispersant is included in forming the concentrated layer in an amount from about 0.1% to about 0.2% by weight of the stucco, and is included in forming the board core in an amount of from about 0% to about 0.4% by weight of the stucco.

30. The composite gypsum board of any one of claims 1 -29, wherein the board has a nail pull resistance according to AST^'M C'473- ί 0, Method B of at least about 68 lbs of force.

31. The composite gypsum board of any one of claims 1-30, wherein the concentrated layer has an average core hardness that is at least about 4 times greater than the average core hardness of the board core, wherein the average core hardness is measured according to ASTM C-473-10.

32. The composite gypsum board of any one of claims 1 -31 , wherein the water and stucco for forming the board core are in a water-stucco ratio of from about 0.3 to about 0.7.

33. The composite gypsum hoard of any one of claims 1-32, wherein the water and stucco for forming the concentrated layer are in a water-stucco ratio of frorn about 0.7 to about 2.0.

34. The composite, gypsum board of any one of claims 1 -33, wherein the board has a density of from about 24 pcf (about 380 kg/ra³) to about 33 per {about 530 kg/^'nr ).

35. The composite gypsum board of any one of claims 1 -33, wherein the board has a density of from about 24 pcf (about 380 kg ) to about 29 pcf (about 460 kg'm³).

36. The composite gypsum board of any one of claims 1-35, wherein the enhancing additive comprises at least two of the following: starch, polyvinyl alcohol, boric acid, nano-celluiose, micro-cellulose, and gypsum cement.

37. The composite gypsum hoard of claim 36, wherein the enhancing additive comprises pregelantinized starch having a viscosity from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method, polyvinyl alcohol, and boric acid.

38. The composite gypsum board of claim 36 or 37, wherein the enhancing additive comprises (i) pregelantinized starch having a a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method, and (ii) micro-cellulose and/or nano-cellulose.

39. The composite gypsum board of any one of claims 36-38, wherein the enhancing additive comprises pregelantinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured wh le the starch is subjected to conditions according to the VMA method, and gypsum cement.

40. The composite gypsum board any one of claims 36-39, wherein the enhancing additive comprises pregelantinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to VMA method, and the core and/or the concentrated layer is further formed from polyphosphate and dispersant.

41. The composite gypsum board of claim 40, wherein the polyphosphate is sodium trimetaphosphate and the dispersant is a napthalenesulfonate,

42. The composite gypsum board of any one of claims 2-41 , wherein the board further comprises a bonding layer disposed between the top cover sheet and the board core and/or between the bottom cover sheet and the board core, wherein the bonding layer has a thickness of from about 0.01 inches (about 0.03 cm) to about 0.(315 inches (about 0.04 cm).

43. The composite gypsum board of any one of claims 1 -42, wherein the concentrated layer is further formed from fiber.

44. The composite gypsum hoard of claim 43. wherein the fiber includes a sizing agent,

45. The composite gypsum board of any one of claims 1-44, wherein the enhancing additive comprises an uncooked starch having a molecular weight of at least about 30,000 Daltons.

46. A composite gypsum board comprising:

(a) a board core comprising set gypsum formed from a first slurry at least water, stucco, and optional Sy, an enhancing additive, the first slurry having a first water-stucco ratio, the core having a first density, the core defining first and second core faces in opposing relation; and

(b) a concentrated layer formed from a second slurry comprising at least water, stucco, and the enhancing additive, the second slurry having a second water-stucco ratio, the concentrated layer disposed in bonding relation to the first core face, the concentrated layer having a density of at least about 1.1 times higher than the density of the board core; wherein;

(i) when the enhancing additive is present in the first slurry, the

enhancing additive is included in a higher concentration in the second slurry than in the first slurry,

(ii) the board core has a thickness greater than the thickness of Ore

concentrated layer, and

(iii) the second water-stucco ratio is at least about 1.2 times higher than the first water-stucco ratio.

47. The composite gypsum board of claim 46, wherein:

the concentrated layer defines first and second concentrated layer faces,

the second concentrated layer face faces the first core face.

48. The composite gypsum board of claim 47, wherein the board further comprises a bottom cover sheet, the second core face lacing the bottom cover sheet.

49. The composite gypsurn board of any of claims 46-48, wherein the second water-stucco ratio is at least about 1.4 times higher than the first water-stucco ratio.

50. The composite gypsum board of airy of claims 46-49, wherein the

concentrated layer has an average core hardness that is at least about 1.5 times greater than the average core hardness of the board core,

51. The composite gypsum board of any one of claims 46-50, wherein the board core has a dry density of about 30 pcf or less.

52. The composite gypsum hoard of any one of claims 46-51 , wherein the board core has a dry density of about 27 pcf or less.

53. The composite gypsum board of any one of claims 46-52, wherein the concentrated layer is formed from at least about 1.2 times the enhancing additive used in forming the board core.

54. The composite gypsum board of any one of claims 46-53. wherein the board h a density of about 33 pcf (about 5.30 kg'm³) or less, and the board has a nail pull resistance according to ASTM C473-10, Method B of at least about 68 lbs of force.

55. The composite gypsum board of any one of claims 46-54, wherein the enhancing additive comprises starch.

56. The composite gypsurn board of claim 55, wherein the starch comprises a pregelatinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method.

57. A composite gypsum board comprising:

(a) a board core comprising set gypsum formed from at least water, stucco, and optionally, an enhancing additive, the core having a density, the core defining a first core face; and

(b) a concentrated layer formed from at least water, stucco, and the enhancing additive, the concentrated layer disposed in bonding relation to the. first core face: wherein; (i) when the enhancing additive is present in forming the core, the

enhancing additive is included in a higher concentration in forming the concentrated layer than in forming the board core,

(ii) the board core having a dry density of about 30 pcf or less, and

(iii) the concentrated layer having a higher dry density than the board core dry density.

58. The composite gypsum board of claim 57, wherein a density differential between die concentrated layer and the board core is at least about 8 pcf (about 130 kg-'nr),

59. The composite gypsum board of claim 57 or 58, wherein the concentrated layer has an average core hardness that is at least about 1.5 times greater than the average core hardness of the board core.

60. The composite gypsum board of any one of claims 57-59, wherein the concentrated layer is formed from at least about 1 .2 times the enhancing additive used in forming the hoard core.

61. The composite gypsum board of any one of claims 57-60, wherein the board has a density of about 33 pcf (about 530 kg m^J) or less, and the board has a nail pull resistance according to ASTM C473-1 G, Method B of at least about 68 lbs of feree.

62. The composite gypsum board of any one of claims 57-61 , wherein the enhancing additive comprises starch.

63. A composite gypsum board comprising:

(a) a board core comprising set gypsum formed from at least water, stucco, and optionally, an enhancing additive, the core having a density, the core defining a first core face: and

(b) a concentrated layer fomied frorn at least water, stucco, and the enhancing additive, the concentrated layer disposed in bonding relation to the first core face, the concentrated layer having a density of at least about 1 , 1 times higher than the density of the board core: wherein: (i) when the enhancing additive is present in forming the core, the

(ii) the concentrated layer has a Yonng's modulus that is at least about 1.5 times higher than a Young's modulus of the board core, and

64. The composite gypsum board of claim 63, wherein the enhancing additive comprises starch.

65. The composite gypsum board of any claim 63 or 64, wherein the concentrated layer has an average core hardness that is at least about 1.5 times greater than the average core hardness of the board core.

66. The composite gypsum board of any one of claims 63-65, wherein the concentrated layer is formed from at least about 1.2 times the enhancing additive used in forming the board core,

67. The composite gypsum board of any one of claims 63-66, wherein the board has a density of about 33 pcf (about 530 kg/m^J) or less, and the board has a nail pull resistance according to ASTM C473-10, Method B of at least about 68 lbs of force.

68. A composite gypsum board comprising:

(a) a board core comprising set gypsum formed from at least water, stucco, and optionally, an enhancing additive, the core defining a first core face; and

(b) a concentrated layer formed from at least water, stucco, and the enhancing additive, the concentrated layer disposed in bonding relation to the first core face; wherein:

(i) when the enhancing additive is included in forming the board core, the enhancing additive is included in a higher concentration in forming the concentrated layer than in forming the board core,

(ii) the board core has a thickness greater than the thickness of the

concentrated layer, and (lii) the concentrated layer has an average core hardness that is at least

about 1.5 times greater than the average core hardness of the board core,

69. The composite gypsum board of claim 68, wherein the concentrated layer is formed from at least about 1 ,2 times the enhancing additive used in forming the board core.

70. The composite gypsum board of claim 68 or 69, wherein the board has a density of about 33 pcf (about 530 kg/m³) or less, and the board has a nail pud resistance according to ASTM C473-10, Method B of at least about 68 lbs of feree.

71 . The composite gypsum board of any one of claims 68-70, wherein the enhancing additive comprises starch,

72. The composite gypsum board of claim 71 , wherein the starch comprises a pregelatinized starch-having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method,

73. The composite gypsum board of any one of claims 68-72, wherein the board core has a dry density of about 30 pcf or less.

74. The composite gypsum board of any one of claims 68-73, wherein the concentrated layer has a Young^' s modulus that is at least about 1.5 times higher than a Young's modulus of the board core

75. A composite gypsum board comprising:

(a) a board core comprising set gypsum formed from at least water, stucco, and optionally, an enhancing additive, the core having a dry density, the core defining first and second core faces in opposing relation; and

(i) when the enhancing additive is present in forming the core, the

concentrated layer is formed from at least about 1.2 times the enhancing additive used in forming the board core,

(ii ) the board core has a dry density of about 30 pcf or less, and (i i) the concentrated layer has a higher dry density than the board core dry density.

76. The composite gypsum board of claim 75, wherein the board has a density of about 33 pcf (about 530 kg m³) or [ess, and the board has a nail pull resistance according to ASTM C473-10, Method B of at least about 68 lbs of feree.

77. The composite gypsum board of claim 75 or 76, wherein the enhancing additive comprises starch.

78. The composite gypsum board of claim 77, wherein the starch comprises a pregelatinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method,

79. The composite gypsum board of any one of claims 75-78, wherein the hoard core has a dry density of about 30 pcf or less.

80. The composite gypsum board of any one of claims 75-79, wherein the concentrated layer has a Young's modulus that is at least about 1.5 times higher than a Young's modulus of the board core.

81. The composite gypsum board of any one of claims 75-80, wherein the density differential between the concentrated layer and the board core is at least about 8 pcf (about 130 kg- ).

82. A composite gypsu n board comprising:

(a) a board core comprising set. gypsum formed from at least water, stucco, and optionally, one or both of dispersant and/or polyphosphate, the core having a dry density, the core defining first and second core faces in opposing relation; and

(h) a concentrated layer formed from at least water, stucco, and one or both of polyphosphate and dispersant, the concentrated layer disposed in bonding relation to the first core face; wherein:

(i) when the polyphosphate and/or dispersant is present in form ng the core, the polyphosphate and/or dispersant is included in a higher concentration in forming the concentrated layer than in forming the board core, and

(ii) the concentrated layer has a higher dry density than the board core dry density,

83. The composite gypsum board of claim 82, wherein the concentrated layer is further from enhancing additive, and the board core is optionally further formed from enhancing additive, and wherein when the enhancing additive is included in forming the board core, the enhancing additive is included in a higher concentration in forming the concentrated layer than in forming the board core.

84. The composite gypsum board of claim 82 or 83, wherein the board core has a dry density of about 30 pcf or less.

85. The composite gypsum board of any one of claims 82-84, wherein the board h a density of about 33 pcf (about 530 kg m³) or less, and the board has a nail pull resistance according to ASTM C47.3-10, Method B of at least about 68 lbs of feree,

86. The composite gypsum hoard of any one of claims 82-85, wherein the enhancing additive comprises starch,

87. The composite gypsum board of claim 86, wherein the starch comprises a pregelalinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method.

88. A method of making composite gypsum hoard, the method comprising:

(a) preparing a first slurry comprising stucco, water and enhancing additive;

(b) applying the first slurry in a bonding relation to a first cover sheet to form a concentrated layer, the concentrated layer having a first face and a second face, wherein the first concentrated layer face faces the first cover sheet;

(c) mixing at least water, stucco, and optionally the enhancing additive to form a second slurry;

(d) applying the second slurry in a bonding relation to the concentrated layer to form a board core having a first face and a second face, the first board core face facing the second concentrated layer face; (e) applying a second cover sheet in bonding relation to the second board core lace to form a board precursor; and

(f) drying the board precursor to form a board; wherein:

i, when the second slurry contains the enhancing additive, the enhancing

additive is more concentrated in the first slurry than the second slurry, and ii, when dried, the board core has a thickness greater than the thickness of the concentrated layer,

89. The method of claim 88, wherein, when dried, the concentrated layer has a density of at least about i . l times higher than a density of the board core.

90. The method of claim 88 or 89, wherein a density differential between the concentrated layer and the board core is at least about 8 pcf (about 130 kg/m³).

91. The method of any one of claims 88-90, wherein the board has a density from about 24 pcf (about 380 kg/nr⁵) to about 33 pcf (about 530 kg/nr).

92. The method of any one of claims 88-91, wherein the board has a density from about 24 pcf (about 380 kg m³) to about 29 pcf (about 460 kg/m³).

93. The method of any one of claims 88-92, wherein the board has a density of about 33 pcf or less, and a nail pull resistance aecording to ASTM C473-10, Method B of at least about 68 lbs of force,

94. The method of any one of claims 88-93, wherein the board has a nail pull resistance according to ASTM C473-10. Method B of at least about 72 lbs of force.

95. The method of any one of claims 88-94, wherein the second slurry further comprises stucco,

96. The method of claim 95, wherein the first slurry is mixed in a first mixer and the second slurry is mixed in a second mixer.

97. The method of any one of claims 88-96, wherein the enhancing additive comprises starch.

98. The method of claim 97, wherein the starch comprises a pregeiatinized starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method.

99. The method of any one of claims 88-98, wherein, when dried, the conceiitrated layer has a thickness of from about 0.02 inches (about 0.05 cm) to about 0.2 inches (about 0.5 cm).

100. The method of any one of claims 88-100, wherein first slurry contains at least about 1.2 times the enhancing additive contained in the second slurry.

101 . The method of any one of claims 88- 100, wherein, when dried, the concentrated layer has an average core hardness that is at least about 1.5 times greater than the average core hardness of the board core.

102. A method of making composite gypsum board, the method comprising:

(a) mixing at least water, stucco and enhancing additive to form a first slurry having a water-stucco ratio of from about 0.7 to about 2;

(b) applying the first slurry in a bonding relation, to a first cover sheet to form a concentrated layer having a first face and a second face;

(c) mixing at least water, stucco, and optionally the enhancing additive to form a second slurry having a water-stucco ratio of from about 0.3 to about 1.1 ;

(d) applying the second slurry in a bonding relation to the concentrated layer to form a board core having a iirst density, the board core having a first face and a second face, wherein the first board core face faces the concentrated layer first face and the second concentrated layer face faces the first cover sheet;

(e) applying a second cover sheet in bonding relation to the second core face to form a board; and

(f) drying the board; wherein:

i, when the second slurry contains the enhancing additive, the enhancing additive is more concentrated in the first slurry than the second slurry, and ii. when dried, the board core has a thickness greater than the thickness of the concentrated layer.

103. The method of claim 102, wherein, when dried, the concentrated layer has a density of at least about 1.1 times higher than a density of the board core.

104. The method of claim 102 or 103, wherein, when dried, the concentrated layer has a thickness of from about 0.02 inches (about 0.05 cm) to about 0.2 inches (about 0,5 cm).

105. The method of any one of claims 102-104, wherein the first slurry is mixed in a first mixer and the second slurry is mixed in a second mixer.

106. The method of claim 105, wherein the second mixer has a higher mixing volume capacity than the first mi er,

107. The method of any of any one of claims 102-106, further comprising applying a bonding layer between the second cover sheet and the board core.

108. The method of any of claims 102- 107, wherein the board has a density from about 24 pcf (about 380 kg/m^J) to about: 33 pcf (about 530 kg nv⁵).

109. The method of any one of claims 102-108, wherein the hoard has a density from about 24 pcf (about 380 kg/m^") to about 29 pcf (about 460 kg<m^J).

1 10. The method of any one of claims 102-109, wherein the hoard has a density of about 33 pcf (about 530 kg m³) or less, and a nail pull resistance of at least about 68 lbs of force according to AST C473-10, Method B.

1 1 1 . The method of any one of claims 102-1 10, wherein the board has a nail pull resistance according to ASTM C473-10, Method B of at least about 72 lbs of force.

1 12. The method of any one of claims 1 2- 1 1 1 , wherein the enhancing additive comprises starch.

1 13. The method of claim 1 12, wherein the starch comprises a pregelatimzed starch having a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured while the starch is subjected to conditions according to the VMA method.

1 14, The method of any one of claims 102-1 3, wherein, when dried, the

concentrated layer has an average core hardness thai is at least about 1.5 times greater than the average core hardness of the board core.