WO2001034534A2

WO2001034534A2 - Gypsum wallboard and method of making same

Info

Publication number: WO2001034534A2
Application number: PCT/US2000/042127
Authority: WO
Inventors: Gopalakrishnan Sethuraman; Ronald S. Finkelstein
Original assignee: National Gypsum Properties Llc
Priority date: 1999-11-12
Filing date: 2000-11-09
Publication date: 2001-05-17
Also published as: AU3439001A; WO2001034534A3

Abstract

A method of preparation and use of high-strength gypsum wallboard, as well as a core composition suitable for use therein, are disclosed. The core composition includes a slurry of calcium sulfate hemihydrate (stucco), water and a fluorosurfactant. The composition and method provide a wallboard having increased nail pull resistance, increased core compressive strength, and increased paper-to-core bonding.

Description

GYPSUM WALLBOARD AND METHOD OF MAKING SAME

BACKGROUND OF THE INVENTION Field of the Invention

The invention generally relates to the production of gypsum- containing products and, more specifically, the invention relates to an improved method and composition for producing gypsum wallboard and related products.

Brief Description of Related Technology

A common method of constructing walls and barriers includes the use of inorganic wallboard panels or sheets, such as gypsum wallboard, often referred to simply as "wallboard" or "drywall." Wallboard can be formulated for interior, exterior, and wet applications. The use of wallboard, as opposed to conventional boards made from wet plaster methods, is desirable because the installation of wallboard is ordinarily less costly and less cumbersome than installation of conventional plaster walls.

Generally, wallboard is produced by enclosing a core composition including an aqueous slurry of calcined gypsum and other materials ("core composition") between two large sheets of board cover paper. Various types of cover paper are known in the art, including high-impact cover paper. After the core composition has set (i.e., reacted with water present in the aqueous slurry) and dried, the formed sheet is cut into standard sizes. Methods for the production of gypsum wallboard generally are described, for example, by T. Michelsen, "Building Materials (Survey)," Encyclopedia of Chemical Technology, (1992 4th ed.), vol. 21, pp. 621-24, the disclosure of which is hereby incorporated herein by reference.

Gypsum wallboard is manufactured utilizing commercial processes that are capable of operation under continuous, high-speed conditions. A conventional process for manufacturing the core composition of gypsum wallboard initially includes the premixing of dry ingredients in a highspeed mixing apparatus. The dry ingredients can include calcium sulfate hemihydrate, an accelerator, and a binder (e.g., starch). The dry ingredients are mixed together with a "wet" (aqueous) portion of the core composition in a pin mixer apparatus. The wet portion can include a first component, commonly referred to as a "paper pulp solution," that includes a mixture of water, paper pulp, and, optionally, one or more fluidity-increasing agents, and a set retarder. The paper pulp solution provides a major portion of the water that forms the gypsum slurry of the core composition. A second wet component can include a mixture of foam and other conventional additives, if desired. Together, the aforementioned dry and wet portions comprise an aqueous gypsum slurry that forms a wallboard core composition.

A major ingredient of the gypsum wallboard core composition is calcium sulfate hemihydrate, commonly referred to as "calcined gypsum," "stucco," or "plaster of Paris." Stucco has a number of desirable physical properties including, but not limited to, its fire resistance, thermal and hydrometric dimensional stability, compressive strength, and neutral pH. Typically, stucco is prepared by drying, grinding, and calcining natural gypsum rock (i.e., calcium sulfate dihydrate). The drying step of stucco manufacture includes passing crude gypsum rock through a rotary kiln to remove any free moisture present in the rock from rain or snow, for example. The dried rock then is passed through a roller mill (or impact mill types of pulverizers), wherein the rock is ground or comminuted to a desired fineness. The degree of comminution is determined by the ultimate use. The dried, fine-ground gypsum can be referred to as "land plaster" regardless of its intended use. The land plaster is used as feed to calcination processes for conversion to stucco.

The calcination (or dehydration) step in the manufacture of stucco is performed by heating the land plaster, and generally can be described by the following chemical equation which shows that heating calcium sulfate dihydrate yields calcium sulfate hemihydrate (stucco) and water vapor:

CaSO₄-2H₂O + heat → CaSO₄-'/2H₂O + VΛ H₂O. This calcination process step is performed in a "calciner," of which there are several types known by those of skill in the art.

Uncalcined calcium sulfate (i.e., land plaster) is the "stable" form of gypsum. However, calcined gypsum, or stucco, has the desirable property of being chemically reactive with water, and will "set" rather quickly when the two are mixed together. This setting reaction is actually a reversal of the above-described chemical reaction performed during the calcination step. The setting reaction proceeds according to the following chemical equation which shows that the calcium sulfate hemihydrate is rehydrated to its dihydrate state:

CaSO₄-'/₂H₂O + VA H₂O → CaSO₄-2H₂O + heat. The actual time required to complete the setting reaction generally depends upon the type of calciner and the type of gypsum rock that are used to produce the gypsum, and can be controlled within certain limits by the use of additives such as retarders, set accelerators, and/or stabilizers, for example. Generally, the rehydration time period can be in a range of about two minutes to about eight hours depending on the amount and quality of retarders, set accelerators, and/or stabilizers present.

After the aqueous gypsum slurry is prepared, the slurry and other desired ingredients are combined to form a core composition that is continuously deposited to form a wallboard core between two continuously- supplied moving sheets of board cover paper. The two cover sheets generally comprise a pre-folded face paper and a backing paper. As the core composition is deposited onto the face paper, the backing paper is brought down atop the deposited core composition and bonded to the pre-folded edges of the face paper. The whole assembly then is sized for thickness utilizing a roller bar or forming plate. The deposited core composition is then allowed to set between the two cover sheets, thereby forming a gypsum wallboard. The continuously- produced board is cut into panels of a desired length and then passed through a drying kiln where excess water is removed to form a strong, dry, and rigid building material. The cover sheets used in the process typically are multi-ply paper manufactured from re-pulped newspapers and/or other grades of recycled papers. The face paper has an unsized inner ply which contacts the core composition such that gypsum crystals can grow up to (or into) the inner ply— this, along with the starch, is the principal form of bonding between the core composition and the cover sheet. The middle plies are sized and an outer ply is more heavily sized and treated to control absorption of paints and sealers. The backing paper is also a similarly constructed multi-ply sheet. Both cover sheets must have sufficient permeability to allow for water vapor to pass therethrough during the downstream board drying step(s).

Standardized sheets (or panels) of wallboard typically are cut and trimmed to dimensions of about four feet (about 1.2 meters) wide and about 8 feet to about 16 feet (about 2.4 meters to about 4.9 meters) in length (ASTM-C36). Sheets typically are available in thicknesses varying in a range of about 'Λ inch to about one inch (about 0.635 centimeters (cm) to about 2.54 cm) in about ¹/β inch (about 0.3175 cm) increments. Standardized sheets of wallboard typically have a density in a range of about 1,600 pounds (lbs) to about 1,700 lbs per thousand square feet (lbs/MSF) (about 7,800 kilograms (kg) to about 8,300 kg per thousand square meters (m²)) of about one-half inch (1.27 cm) board.

The time at which the board may be cut, or in other words, the speed of the conveyor and the consequent rate of production of the gypsum board, is generally controlled by the setting time of the calcined gypsum slurry. Thus, conventional adjuvants to the calcined gypsum slurry in the mixer generally include set time control agents, particularly accelerators. These and other additives, such as pregenerated foam to control final density of the board, paper cover sheet bond promoting agents, fibrous reinforcements, consistency reducers and the like typically constitute less than 5%, and usually less than 2%, of the weight of the finished board core. Walls and ceilings made with gypsum wallboard panels typically are constructed by securing, e.g., with nails or screws, the wallboard panels to structural members, such as vertically- and horizontally-oriented pieces of steel or wood often referred to as "studs."

To provide satisfactory strength, commercially-available gypsum wallboard generally requires a density of about 1 ,600 lbs/MSF to about 1 ,700 lbs/MSF (about 7,800 kg per 1 ,000 m² to about 8,300 kg per 1 ,000 m²) of about one-half inch (1.27 cm) board. Heavy or high-density gypsum wallboards are more costly and difficult to manufacture, transport, store, and manually install at job sites, compared to lighter or low-density boards. It is possible to formulate wallboard having reduced densities through the inclusion of lightweight fillers and foams, for example. Often, however, where wallboard is formulated to have a density less than about 1,600 lbs/MSF (about 7,800 kg per 1,000 m²) of about one-half inch (1.27 cm) board, the resulting strength is unacceptable for commercial sale. Because high-density or heavy gypsum wallboard generally is not desirable, various attempts have been made to reduce board weight and density without sacrificing board strength.

However, while lighter and less dense wallboard products can be produced, many of the wallboard products may be of a quality ill-suited for commercial use.

One type of gypsum wallboard panel product failure occurs when a fastener head, such as a nail head, is pulled through the gypsum wallboard panel. The strength measure of a gypsum wallboard panel for this type of failure is known as nail pull resistance. Standardized tests to measure nail pull resistance (e.g. ASTM C 473-99), typically measure the ability of a gypsum wallboard panel to resist pull-through of a standard size nail head through the product.

Another measure of gypsum wallboard panel strength is its compressive strength, which is its ability to resist compressive forces. Compressive strength also is an indirect measure of other strength properties such as transverse load strengths, sag resistance, 90° pull force resistance, and core tensile strength, for example. In view of the foregoing, it would be desirable to produce high-strength gypsum wallboard having weights and densities generally equal to or slightly less than those produced by conventional methods. Reduced weight and density boards, however, should meet industry standards and have strengths similar to, or greater than, conventional wallboard. Such wallboard also should be able to be manufactured using high-speed manufacturing apparatus and not suffer from other negative side-effects. For example, such high-strength wallboard should be able to set and dry within a reasonable period of time.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more of the problems described above.

Thus, one aspect of the invention is a composition for use in the manufacture of gypsum construction materials, wherein the composition includes calcium sulfate hemihydrate, a fluorosurfactant, and sufficient water to form a slurry including at least about 30 weight percent calcium sulfate hemihydrate.

Another aspect of the invention is a method of making a composition for use in gypsum board manufacturing processes. The method generally includes the steps of forming a slurry including water, a fluorosurfactant, and at least about 30 weight percent calcium sulfate hemihydrate, based on the weight of the slurry, and mixing the slurry.

Yet another aspect of the invention is a wallboard panel which includes a first cover sheet, a second cover sheet, and a core disposed between the cover sheets. Preferably, the core includes calcium sulfate dihydrate and a fluorosurfactant.

Still another aspect of the invention is a method of producing gypsum wallboard. The method generally includes the step of forming a slurry containing water, calcium sulfate hemihydrate, and a fluorosurfactant. The method also includes the steps of mixing the slurry, and depositing the slurry on a cover sheet. Further aspects and advantages of the invention may become apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a complete understanding of the invention, reference should be made to the following detailed description, examples, and accompanying drawings wherein like reference numbers designate the same or similar elements in the various drawing figures. Figure 1 is a Scanning-Electron Micrograph (SEM) of calcium sulfate dihydrate crystals in the core of a gypsum wallboard of the prior art. Figure 2 is a SEM of calcium sulfate dihydrate crystals in the core of a gypsum wallboard of the invention, which was made from a core composition including about 0.01 wt. % fluorosurfactant, based on the weight of stucco added to the core composition.

While the invention is susceptible of embodiment in various forms, there are illustrated in the drawing figures and will hereafter be described specific embodiments of the invention, with the understanding that the disclosure is intended to be illustrative, and is not intended to limit the invention to the specific embodiments described and illustrated herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally, the invention is directed to a composition for use in the manufacture of gypsum construction materials. The composition comprises calcium sulfate hemihydrate, a fluorosurfactant, and sufficient water to form a slurry including at least about 30 weight percent calcium sulfate hemihydrate. The invention also is directed to gypsum wallboard panels and methods of making said composition and said gypsum wallboard panels.

The compositions of the invention provide improvements in properties of the final wallboard core and wallboard product, such as increased strength and improved paper-core interface bonding. The final products have improved nail pull resistance and increased compressive strength over known products.

The ingredients of a preferred wallboard core composition of the invention will now be described in more detail. One dry ingredient present in the wallboard core composition of the invention is calcium sulfate hemihydrate, or stucco (CaSO₄ ^#1/2H₂0). Preferably, the β-hemihydrate form of calcium sulfate hemihydrate is used in the invention, however, either the α- or β- form may be used. The core composition includes at least about 30 wt. % calcium sulfate hemihydrate, preferably about 30 wt. % to about 70 wt. %, more preferably about 35 wt. % to about 55 wt. %, and even more preferably about

40 wt. % to about 55 wt. %, for example about 48 wt. % calcium sulfate hemihydrate based on the total weight of the core composition. The calcium sulfate hemihydrate can be produced by a dry calcination method, such as kettle, calcidyne, holoflyte, rotary kiln, impmill, or caludis peter calcination. Other dry ingredients may be included in the core composition, including an accelerator, which can be used to control the crystal growth rate and set time of the stucco. Examples of suitable accelerators, some of which also are available liquid form, include, but are not limited to, ball mill accelerators ("BMA") and metallic salts that provide cations, such as aluminum sulfate, potassium sulfate, calcium sulfate, ferrous sulfate, and ferric chloride supplied, for example, by the J.T. Baker Chemical Company of Philadelphia, New Jersey.

Wet ingredients used to make the core composition preferably include an aqueous slurry or solution of pulp including water and paper fibers ("paper pulp"), and may also include corn starch and/or potash. The paper pulp solution provides a major portion of the water that forms the gypsum slurry of the core composition. The water supplied in the wet portion of the composition should include sufficient water for the setting reaction of the gypsum, plus an additional amount sufficient to decrease the consistency of the slurry during the manufacturing process. The paper fibers in the pulp solution serve to enhance the flexibility of the gypsum wallboard. Gypsum wallboard made without fibers is typically very brittle and more susceptible to breakage during handling. The paper fibers aid in evenness of drying during manufacture, and enhance the ability of the final wallboard product to accept and hold nails during installation.

A set retarder optionally may be included in the paper pulp solution and can be used in conjunction with the aforementioned accelerator in order to tailor the set time of the core composition. Retarding agents are typically used in the invention at very low concentrations such as, for example, about 0.0007 wt. %, based on the weight of the core composition.

The pulp solution can be prepared by blending or mixing the above ingredients with water in a blending apparatus. Alternatively, a concentrated pulp solution using only a small volume of water can be produced. In this case, the remainder of the core mix water requirement is made up with a separate water source. Typically, about 75 weight parts water are used per 100 weight parts stucco. Preferably, high shear mixing "pulps" the material, forming a homogenous solution or slurry. The pulp solution can be transferred to a holding vessel, from which it can be continuously added to the core composition mix.

Wet ingredients used to make the core composition preferably include a component that incorporates a foaming agent. Foam introduces air voids into the core through the use of a foaming agent that contains very little solid material, but is resilient enough to resist substantial breakdown in the mixing operation. In this manner, the density of the core can be controlled.

Known foaming agents may be supplied in either liquid or flake (powdered) form, and may be produced from soaps known in the art. A suitable foaming agent for the invention is sold under the trade name CEDEPAL FA-406, by the Stepan Company of Northfield, Illinois. An antidessicant such as starch also can be included in the core composition to prevent the dehydration of calcium sulfate dihydrate crystals -Informed during setting of the core composition. A suitable starch for the invention is Wallboard Binder Starch, CAS #65996-63-6, which is sold by A.E. Staley Manufacturing Co., of Decatur, IL. In some products, lightweight aggregates (e.g., expanded perlite or vermiculite) also can be included. "Water-reducing" additives may be included in the core composition to improve its fluidity while allowing the use of reduced levels of water. Reduction in water usage brings reduced costs in the form of reduced water and energy demands, as less water will have to be removed during the drying step(s). Reduction of water usage also provides environmental benefits. Various commercially-available fluidity-enhancing and/or water-reducing agents are known in the art for various applications. Materials used as fluidity-enhancing and or water-reducing agents include "lignosulfonates" which are commercially available either in liquid or powder form. Fluidity-enhancing and/or water-reducing agents supplied in liquid form can be either incorporated in the pulp solution or added directly to the mixing operation. A suitable water-reducing agent for the invention is sold under the trade name DILOFLO GW, by the Henkel Corporation of Ambler, Pennsylvania. The use of condensation products of naphthalene sulfonic acid and formaldehyde is also known. See also U.S. Patent No. 4,184,887, the disclosure of which is hereby incorporated herein by reference.

Water-reducing agents are described in "The Gypsum Industry and Flue Gas Desulfurization (FGD) Gypsum Utilization: A Utility Guide," New York State Electric & Gas Corp. and ORTECH, pp. 3-38 (1994), the disclosure of which is hereby incorporated herein by reference. The use of higher molecular weight anionic condensation products such as melamine formaldehyde modified with sulfite alkylaryl sulfonates and lignin sulfonates, preferably calcium lignosulfonate, ammonium lignosulfonate, sodium lignosulfonate, and naphthalene sulfonate is also known. Gypsum wallboard can be adapted for wet and exterior applications, in addition to use in constructing interior walls and ceilings. In -l ithe production of exterior sheathing and moisture-resistant board cores, various materials can be incorporated into the core composition to impart increased absorption resistance to the board. Useful materials include silicone and other water repellents, waxes, and asphalt emulsions. These materials are typically supplied as water emulsions to facilitate ease of incorporation into the board core. These materials can be added directly into the mixing apparatus or incorporated into the pulp solution prior to addition to the mixing apparatus.

A fluorosurfactant is also included in the wallboard core composition of the invention. The fluorosurfactant preferably is anionic, but may also be cationic or non-ionic. Generally, the fluorosurfactant is present in an amount sufficient to provide increased strength in the wallboard product of the invention over known wallboard products. Preferably, the fluorosurfactant is present in an amount up to about five wt. %, based on the weight of stucco in the core composition. More preferably, the fluorosurfactant is about 0.001 wt. % to about two wt.%, even more preferably, about 0.005 wt. % to about 0.25 wt. %, most preferably about 0.01 wt. % to about 0.1 wt.%, for example about 0.05 wt. %, based on the weight of stucco in the core composition.

Generally, surfactants contain an insoluble moiety, which is inherently insoluble in the liquid in which it is useful, combined with a solubilizing group, such as a hydrophilic group. Such surfactants can be divided into three major chemical classes: hydrocarbons, silicones, and fluorochemicals. This classification describes the insoluble portion of the surfactant molecule. Thus, fluorosurfactants have an insoluble fluorocarbon moiety and a solubilizing group. A suitable anionic fluorosurfactant for the invention is sold under the trade name ZONYL FSJ fluorosurfactant by DuPont Chemicals of Wilmington, Delaware, the material data safety sheets of which are hereby incorporated herein by reference. ZONYL FSJ fluorosurfactant is a water- soluble, anionic surfactant material including a blend of a fluorosurfactant and a nonfluorinated hydrocarbon surfactant having the following formula,

(R_rCH₂CH₂O)_xP(O)(ONH₄)_y*, wherein R_f is F(CF₂CF₂)_Z, x is 1 or 2, y is 1 or 2, x+y=3, z is 1 to about 7, and * represents a nonfluorinated hydrocarbon surfactant. The fluorosurfactant is sold as a liquid including about 40 wt.% surfactants, about 45 wt. % water, and about 15 wt. % isopropyl alcohol, based on the total weight of the ZONYL FSJ fluorosurfactant. Other fluorosurfactants are sold under the trade name

FLUORAD by 3M of St. Paul, Minnesota.

The above-described fluorosurfactants may be included in the gypsum core composition by addition at any advantageous point in the gypsum board-forming process. Preferably, however, the fluorosurfactant is injected into one or more pin mixer feedstock lines, or directly into the pin mixer itself.

More preferably, the fluorosurfactant is added with the paper pulp solution wet component or the foam wet component.

The invention is not limited to any order or manner of mixing the ingredients described above. General ranges of ingredients used in gypsum wallboard are shown in Table I below, wherein the wt. % of an ingredient is based on the total weight of the core composition used to make the wallboard product, unless otherwise indicated.

Table I

Ingredient Exemplary Range stucco about 48 wt. % to about 55 wt. % accelerator about 0.04 wt. % to about 0.25 wt. % starch about 0.12 wt. % to about 0.32 wt. % retarder about 0 to about 0.2 wt. % paper pulp about 0.06 wt. % to about 0.33 wt. % pulp water about 36 wt. % to about 44 wt. % foam solution (including water) about 4 wt. % to about 12 wt. % A preferred process for manufacturing the core composition and wallboard of the invention initially includes the premixing of dry ingredients in a mixing apparatus. The dry ingredients preferably include calcium sulfate hemihydrate (stucco), an optional accelerator, and an antidessicant (e.g., starch), as described below in greater detail. The dry ingredients are preferably mixed together with one or more "wet" (aqueous) portions of the core composition in a pin mixer apparatus.

As noted above, a fluorosurfactant may be incorporated into the core composition at any advantageous point in the manufacturing process. Preferably, the fluorosurfactant is injected into one or more pin mixer feedstock lines, or directly into the pin mixer itself. More preferably, a fluorosurfactant is injected into the gauging water feed line, the foam line, or the pulp solution line of the gypsum core manufacturing process. However, the invention is not limited to the order and manner of mixing the ingredients described above. The core composition thus produced is deposited between paper cover sheets to form a sandwich. The core composition is allowed to cure or set, whereby calcium sulfate hemihydrate is converted to calcium sulfate dihydrate. The product then preferably is dried by exposing the product to heat, in order to remove excess water not consumed in the reaction forming the calcium sulfate dihydrate.

The setting reaction produces gypsum crystals, which are interwoven to contribute strength to the dried wallboard core. The strength of the crystal-to-crystal interaction contributes to the final strength of the gypsum wallboard product. The gypsum crystals also preferably bond with paper fibers protruding from the surface or cover papers, thus providing a stronger bond between the paper cover sheets and the wallboard core. This bonding or interaction also increases the strength of the wallboard product.

Although the invention is not to be limited by any particular mechanism or theory, it is believed that the fluorosurfactant generally influences the crystal morphology of gypsum. The fluorosurfactant may also interact with calcium sulfate hemihydrate to provide a nucleating site for calcium sulfate dihydrate crystal growth. Figure 1 depicts the crystal morphology of a gypsum wallboard of the prior art. As shown in Figure 1, the calcium sulfate dihydrate crystals in the prior art wallboard are generally long, slender, hexagonal crystals that often aggregate in flat sheets or rosettes. Figure 2 depicts the crystal morphology of a gypsum wallboard of the invention made with about 0.01 wt. % of a fluorosurfactant, based on the weight of stucco added to the core composition. As shown in Figure 2, the calcium sulfate dihydrate crystals in the wallboard of the invention generally appear cylindrical, having rounded ends, and aggregate in interlocking structures. It is believed that the fluorosurfactant' s influence on the gypsum crystal morphology results in increased wallboard strength.

It is also believed that the ionic nature of ionic fluorosurfactants stabilizes the foam used in gypsum board. Furthermore, it is believed that the fluorosurfactant enhances the binding of the core composition to the board cover paper. The fluorosurfactant may also enhance binding between gypsum crystals and paper fragments in the core of the wallboard product.

In order to demonstrate the advantageous results of the invention, comparative testing has been performed.

EXAMPLES

The following examples are provided to illustrate some of the benefits of the invention, but are not intended to limit the scope of the invention.

Example I

Control sample wallboards were prepared from core compositions made in accordance with the invention, but without a fluorosurfactant. Test sample wallboards were prepared from core compositions in accordance with the invention. Table II summarizes the compositions of the core compositions and the corresponding characteristics of the final control and test sample wallboards at an ambient temperature of 70 T (21 -C):

Table II - Wallboard Composition

The wt. % fluorosurfactant added to each sample is based on the weight of stucco. In samples la-3a and lb-3b, the fluorosurfactant was added to the pulp solution, which caused foaming to occur. In sample 4a, the fluorosurfactant was added to the foam solution. All control and test samples were made using a standard wallboard cover paper.

Nail pull tests were conducted on the samples described in Table II according to ASTM C 473-99, Method B, the disclosure of which is hereby incorporated herein by reference. Results are tabulated below in Table III. Table m - Nail Pull Strength (lb-force)

Compressive strength tests also were conducted on samples la- 4a described in Table H The tests were performed using an Instron model 4486-standard, manufactured by Instron of Canton, Massachusetts, by methods known in the art. The samples measured three inches by three inches square. Results are tabulated below in Table IV:

Table IV - Compressive Strength (lb/in²)

Example II

Control and test sample wallboards were prepared as described above in Example I, but with high-impact cover paper sheets. Table V summarizes the compositions of the core compositions and the corresponding characteristics of the final control and test sample wallboards at an ambient temperature of 70 °F (21 °C):

Table V - Wallboard Composition (High-Impact Cover Paper Samples)

In samples one through three, the fluorosurfactant was added to the pulp solution, which caused foaming to occur. Nail pull tests were conducted on the samples described in Table TV according to ASTM C 473-99, Method B. Results are tabulated below in Table VI:

Table VI - Nail Pull Strength (lb-force) (High-Impact Cover Paper Samples)

Compressive strength tests also were conducted on the samples described in Table VI. The tests were performed as described above in Example I. Results are tabulated below in Table VII:

Table VII - Compressive Strength (lb/in²) (High-Impact Cover Paper Samples)

The results of Examples I and II demonstrate that a fluorosurfactant, when added to either the pulp water or foam solution water when forming a core composition used to make a gypsum wallboard product, increases the nail-pull strength and compressive strength of standard gypsum wallboard and gypsum wallboard made with high-impact cover paper. Other properties of the wallboard product can also be benefitted by use of the inventive methods and compositions, including transverse load strengths, sag resistance, 90 ° pull force resistance, and core tensile strength. In addition, the inventive compositions and methods may advantageously provide these strengths over substantial periods of time. The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the invention may be apparent to those having ordinary skill in the art.

Claims

What is claimed is:

1. A composition for use in the manufacture of gypsum construction materials, the composition comprising:

(a) calcium sulfate hemihydrate;

(b) a fluorosurfactant; and,

(c) sufficient water to form a slurry comprising at least about 30 weight percent (wt. %) said calcium sulfate hemihydrate, based on the total weight of the slurry.

2. The composition of claim 1, wherein the fluorosurfactant is included at up to about two weight percent, based on the weight of the calcium sulfate hemihydrate.

3. The composition of claim 2, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.25 wt. %, based on the weight of the calcium sulfate hemihydrate.

4. The composition of claim 3, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.1 wt. %, based on the weight of the calcium sulfate hemihydrate.

5. The composition of claim 4, wherein the fluorosurfactant is present in the composition in an amount of about 0.01 wt. % to about 0.1 wt. %.

6. The composition of claim 1, wherein the fluorosurfactant is anionic.

7. The composition of claim 1, wherein the slurry comprises about 30 wt. % to about 70 wt. % calcium sulfate hemihydrate.

8. The composition of claim 1 further comprising at least one of a starch, a foam, paper pulp, a slip agent, and a water-reducing agent.

9. A method of making a composition for use in gypsum board manufacturing processes, the method comprising the steps of:

(a) forming a slurry comprising water, a fluorosurfactant, and at least about 30 wt. % calcium sulfate hemihydrate, based on the total weight of the slurry; and,

(b) mixing said slurry.

10. The method of claim 9 wherein the fluorosurfactant is present in the composition in an amount of up to about two wt. %, based on the weight of the calcium sulfate hemihydrate.

11. The method of claim 10 wherein the fluorosurfactant is present in the composition in an amount of up to about 0.25 wt. %, based on the weight of the calcium sulfate hemihydrate.

12. The method of claim 11 wherein the fluorosurfactant is present in the composition in an amount of up to about 0.1 wt. %, based on the weight of the calcium sulfate hemihydrate.

13. The method of claim 12 wherein the fluorosurfactant is present in the composition in an amount of about 0.01 wt. % to about 0.1 wt. %, based on the weight of the calcium sulfate hemihydrate.

14. The method of claim 9 wherein the fluorosurfactant is anionic.

15. The method of claim 9, wherein the slurry comprises about 30 wt. % to about 70 wt. % calcium sulfate hemihydrate, based on the total weight of the slurry.

16. A wallboard panel comprising:

(a) a first cover sheet;

(b) a second cover sheet; and,

(c) a core disposed between the cover sheets (a) and (b), the core comprising calcium sulfate dihydrate and a fluorosurfactant.

17. The wallboard panel of claim 16, wherein the fluorosurfactant is present in the composition in an amount of up to about two wt. %, based on the weight of the calcium sulfate dihydrate.

18. The wallboard panel of claim 17, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.25 wt. %, based on the weight of the calcium sulfate dihydrate.

19. The wallboard panel of claim 18, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.1 wt. %, based on the weight of the calcium sulfate dihydrate.

20. The wallboard panel of claim 19, wherein the fluorosurfactant is present in an amount of about 0.01 wt. % to about 0.1 wt. %, based on the weight of the calcium sulfate dihydrate.

21. The wallboard panel of claim 16 wherein the fluorosurfactant is anionic.

22. The wallboard panel of claim 16 further comprising at least one of a starch, a foam, paper pulp, a slip agent, and a water-reducing agent.

23. A method of producing gypsum wallboard, the method comprising the steps of:

(a) forming a slurry comprising (i) water, (ii) calcium sulfate hemihydrate, and (iii) a fluorosurfactant;

(b) mixing said slurry; and,

(c) depositing said slurry on a cover sheet.

24. The method of claim 23, wherein the fluorosurfactant is present in the composition in an amount of up to about two wt. %, based on the weight of the calcium sulfate hemihydrate.

25. The method of claim 24, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.25 wt. %, based on the weight of the calcium sulfate hemihydrate.

26. The method of claim 25, wherein the fluorosurfactant is present in the composition in an amount of up to about 0.1 wt. %, based on the weight of the calcium sulfate hemihydrate.

27. The method of claim 26, wherein the fluorosurfactant is present in an amount of about 0.01 wt. % to about 0.1 wt. %, based on the weight of the calcium sulfate hemihydrate.

28. The method of claim 21 wherein the fluorosurfactant is anionic.

29. The method of claim 23, wherein the slurry comprises about 30 wt. % to about 70 wt. % calcium sulfate hemihydrate, based on the total weight of the slurry.

30. The gypsum wallboard produced by the method of claim 23.