US3817827A

US3817827A - Soft absorbent fibrous webs containing elastomeric bonding material and formed by creping and embossing

Info

Publication number: US3817827A
Application number: US00239539A
Authority: US
Inventors: C Benz
Original assignee: Scott Paper Co
Current assignee: Kimberly Clark Tissue Co
Priority date: 1972-03-30
Filing date: 1972-03-30
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: CA978784A; GB1395447A; BE797145A; DE2314684A1; AU472589B2; JPS497507A; FR2177856A1; IT979971B; FR2177856B1; AU5270073A

Abstract

A SOFT, ABSORBENT CREPED FIBROUS WEB FORMED BY DEPOSITION FROM AN QUAQUEOUS SLURRY AND CONSISTING OF LIGNOCELLULOSIC FIBERS AND ABOUT 3% TO ABOUT 25% ELASTOMERIC BONDING MATERIAL. THE LIGNOCELLULOSIC FIBERS INTERBOUND WITH EACH OTHER TO FORM THE STIFF BONDS ASSOCIATED WITH PAPERMAKING, AND THE ELASTOMERIC BONDING MATERIAL IS UNIFORMLY DISTRIBUTED THROUGHOUT THE WEB (BY ADDITION TO THE SLURRY OF THE BEATER) AND FORMS FLEXIBLE BONDS WHERE IT CONTACTS THE FIBERS. THE WEB HAS BEEN MECHANICALLY WORKED TO PARTIALLY FRACTURE STIFF BONDS IN SELECTED LOCATIONS TO INCREASE THE STRETCH, FLEXIBILITY, AND SOFTNESS OF THE WEB WHILE RETAINING SUFFICIENT STIFF BONDS IN DESIRED LOCATIONS TO MAINTAIN STRENGTH. IN THE PREFERRED PRODUCT OF THE INVENTION, THE MECHANICAL WORKING WHICH PARTIALLY FRACTURE THE CREPED WEB IS CARRIED OUT BY EMBOSSING TO PRODUCE A DISTORTED WEB CONTOUR OF RAISED AREAS AND DEPRESSIONS WHICH INCREASES WEB BULK AND TO CREATE APERTURES UNIFORMLY DISTRIBUTED THROUGHOUT THE WEB. THE APERTURES ARE ELONGATED IN THE MACHINE DIRECTION OF THE WEB AND GREATLY INCREASE CROSS-MACHINE DIRECTION STRETCH OF THE WEB. THE EMBOSSING OPERATION ALLOWS RETENTION OF STIFF BONDS IN SELECTED CRITICAL LOCATIONS WHERE THEY MAINTAIN THE WEB DISTORTIONS AND PRESERVE BULK.

Description

Ju 8, 1974 c. s. BENZ 3,817,827

SOFT, ABSORBENT FlBROUS WEBS CONTAINING ELASTOMERIC BONDING MATERIAL AND FORMED BY CREPING AND EMBOSSING Filed March 30, 1972 L m L g Icaoss MACHINE DIRECTION h (C I3 m m ////////I MACHINE DIRECTION Fig.2

United States Patent U.S. Cl. 162-113 16 Claims ABSTRACT OF THE DISCLOSURE A soft, absorbent creped fibrous web formed by deposition from an aqueous slurry and consisting of lignocellulosic fibers and about 3% to about 25% elastomeric bonding material. The lignocellulosic fibers interbond with each other to form the stiff bonds associated with papermaking, and the elastomeric bonding material is uniformly distributed throughout the web (by addition to the slurry of the beater) and forms flexible bonds where it contacts the fibers. The web has been mechanically worked to partially fracture stiff bonds in selected locations to increase the stretch, flexibility, and softness of the web while retaining sufficient stiff bonds in desired locations to maintain strength. In the preferred product of the invention, the mechanical working which partially fractures the creped web is carried out by embossing to produce a distorted web contour of raised areas and depressions which increases web bulk and to create apertures uniformly distributed throughout the web. The apertures are elongated in the machine direction of the web and greatly increase cross-machine direction stretch of the web. The embossing operation allows retention of stiff bonds in selected critical locations where they maintain the web distortions and preserve bulk.

BACKGROUND OF THE INVENTION (1) Field of the invention The invention relates to soft, absorbent, fibrous webs made primarily from wood pulp, and to a method for forming them. Such webs are useful for sanitary paper products such as tissues, towels and the like. More particularly, the present invention relates to a soft, absorbent, web material characterized by a combination of very good softness, toughness and bulk, making it particularly desirable for use as a towel.

(2) Brief description of the prior art It has long been a goal in the field of papermaking to impart softness to paper webs without excessively degrading their strength. Paper webs are conventionally softened by working them in ways such as embossing, calendering, or creping them from an adhering surface with a creping blade. Such working processes disrupt and break many of the stiff, natural, interfiber bonds in the paper web which are formed during the drying thereof by the dehydrate bonding process associated with papermaking. However, these interfiber bonds are the principle source of strength in an ordinary paper web, because very little strength results from the physical entanglement of fibers since papermaking fibers are extremely short, generally on the order of /8 inch or less. Therefore, such web working processes necessarily result in loss of strength to the web.

Softness, of course, is a desirable characteristic for most sanitary paper products, but products such as towels must also be tough, so that they will maintain their integrity when subjected to the punishing type of work for which they are often used. Toughness is the ability of the web to absorb work energy without being torn apart. It is not a measure of the sheets tensile strength alone,

ice

but rather, it is a combination of the sheets tensile strength and ability to stretch. Therefore it is desirable for paper towel products to have the abiilty to stretch.

It has long been known that crcping a sheet imparts stretch to a sheet. However, creping also reduces tensile strength. Furthermore, in most papermaking operations, creping is limited to only the machine direction of the web, resulting in little or no increase in the sheets ability to stretch in the cross-machine direction. But it is desirable for paper products used as towels to be capable of being worked in all directions, thus having the ability to stretch in the cross-machine direction as well as the machine direction. Although there are known methods of creping which impart stretch in the cross-machine direction of the web, such as described in U.S. Pat. No. 2,610,935, these methods are diflicult to perform and generally do not impart a large amount of cross-machine direction stretch except with excessive strength reduction.

U.S. Pat. No. 2,834,809 discloses a method of working a sheet which imparts cross-machine direction stretch to a paper web. Cross-machine direction stretch is imparted to the web in the method disclosed in that patent by working the web to impart an undulating cross-section thereto and to impart elongated apertures disposed in the machine direction of the paper. While this method imparts cross directional stretch to a paper web, it also considerably reduces the cross directional tensile strength of the web. It has been found that product strength requirements limit the amount of this type of working and thus the amount of stretch which can be imparted to the web in this manner.

Another known method to improve web stretch is to add elastomeric bonding materials to the web. Such a method is disclosed in U.S. Pat. No. 3,622,447, which describes the addition of an aqueous polymer latex to paper fiber sheets. But, the addition alone of elastomeric bonding material to paper fiber sheets does not necessarily add substantial stretch to the sheet, because the elastomeric bonding material added in this manner does not replace stiff paper bonds, but rather supplements them.

There are methods of replacing still? paper bonds with flexible elastomeric bonds. One such method is disclosed in U.S. patent application Ser. No. 108,638, assigned to the same assignee as this application, now abandoned. The method disclosed in that application consists, in essence, of reducing initial forming of stiff paper bonds by the addition of chemical debonding agents to the aqueous slurry of fibers and replacing the strength lost from the reduction of still paper bonds with flexible bonds by the addition of elastomeric bonding material to the aqueous slurry of fibers. This method enables production of a strong paper web having good stretch and softness.

A disadvantage of this method is that substanial strength along with substantial stretch and softness can be imparted to a web only by using a large amount of elastomeric bonding material, thus greatly increasing the product cost. If a paper towel product is to be economically produced by this method, a substantial portion of the stiff paper bonds must be allowed to form in order to obtain satisfactory strength without the use of an excessive amount of expensive elastomeric bonding material. And as already pointed out, forming stiff paper bonds in the web reduces the webs ability to stretch, and thus, its toughness. The stiff paper bonds also reduce softness and flexibility of the web.

Another method of improving web stretch and softness is disclosed in U.S. Patent Application Ser. No. 156,282, assigned to the same assignee as this application. The method disclosed in that application consists of reducing initial forming of stiff paper bonds by avoiding to a large degree pressing the web while it is wet. Elastomeric bonding material is added to the aqueous slurry of fibers to produce the required strength and stretch in the web. The product produced by this method has the same discussed disadvantage as the product disclosed in application Ser. No. 108,638, now abandoned. Either the amount of elastomeric bonding material required for adequate strength is excessive or the sheet has little stretch and softeness. It is to be recognized that additional stretch can readily be imparted to the webs disclosed in both the 156,282" and 108,638" applications by creping, but creping is generally limited to stretch in the machine direction of the web, and is always accompanied by substantial strength loss.

Another method of increasing stretch in a paper web is disclosed in US. Patent Application Ser. No. 156,327, assigned to the same assignee as this application. The method disclosed in that application consists of applying a pattern of elastomeric bonding material to a paper web, adhering only the portions of the web containing the bonding material to a creping surface, and removing the web from the creping surface by a creping blade. If the elastomeric bonding material is applied in the appropriate pattern, a product can be produced with some stretch in the cross-machine direction. This cross direction stretch is primarily a result of contraction or shrinkage of the elastomeric bonded regions of the web upon being creped, causing puckering of the product. However, the stretch imparted to the cross-machine direction of the web is generally less than half of the stretch imparted in the machine direction. In addition the webs are characterized by a lack of uniform fiber bonding throughout the web as is often desirable in towel products to give them more uniform strength, stretch, and softness.

Furthermore, the 156,327" method produces a sheet with a limited amount of bulk, as also do the other discussed methods employing elastomeric bonding material. High bulk is important in a towel product, because the desired body and hand feel depend in large measure upon the bulk. One usual method of increasing the bulk of a web is to distort the web to create an irregular surface contour. Creping can produce a limited amount of bulk as a result of web distortion. Embossing can produce a large amount of bulk as a result of web distortion.

Retention of bulk created by sheet distortion depends in large measure upon some stiffness in the sheet. Thus, a relatively stiff conventional paper web of the prior art would be expected to retain bulk which had been imparted by embossing or by other sheet distortion techniques. On the other hand, a soft flexible web with a large amount of stretch such as might be formed by the 108,638 method would not necessarily be expected to retain a high degree of bulk resulting from sheet distortion. It can be seen that a desirable paper towel product requires two properties which would appear to be mutually exclusive of each other, softness for hand feel and stiffness for bulk retention. If softness is increased, it would seem that it must be done so at the expense of bulk. However, contrary to what would be expected, the preferred product of the invention is capable of maintaining bulk and strength in a soft flexible web having substantial stretch in all directions.

Having described the disadvantages of the prior art, it is an object of the invention to produce a bulky, soft paper web having substantial toughness and stretch in both the machine and cross-machine direction of the web.

BRIEF SUMMARY 'OF THE INVENTION These and other objects are accomplished by producing a web sonsisting of lignocellulosic fibers which are bonded together to form the stiff bonds associated with papermaking and in which elastomeric bonding material is distributed throughout the web to form flexible bonds where the bonding material contacts lignocellulosic fibers. The web while dry is mechanically worked by embossing or by other means to partially fracture portions of the web in a controlled manner which greatly increases the web's ability to stretch without excessively reducing its tensile strength. The preferred product of the invention is also worked to produce uniformly distributed apertures which are elongated in the machine direction of the web, resulting in a web having unusually high stretch in the cross-machine direction. The preferred product of the invention has been worked to also proluce a plurality of raised areas and depressions in each side of the web, the depressions in each side forming the raised areas in the other side. The irregular contour of the web greatly increases the bulk of the web, and sufficient stiff bonds are left unfractured in selected critical locations in the web contour to preserve this bulk.

The mechanical working which partially fractures the web is carried out in a manner which breaks many of the web bonds in the portion being worked, but not so many that the sheet is ruptured all the way through at that location. Partially fracturing the web of the invention greatly increases the webs ability to stretch, and although it also reduces its strength, it surprisingly decreases the strength much less than would be expected from the increase in stretch. It is believed that mechanically working the web of the invention in this manner breaks a larger percentage of the stiff bonds than of the flexible bonds, probably due to the stiff bonds being incapable of substantial flexing or bending.

In its broadest form, the invention is another method of increasing softness and flexibility of an elastomerically bonded web by reducing the number of stiff bonds associated with papermaking. However, in contrast to prior art methods, such as the 108,638" method, the invention allows selective retention of stiff bonds in locations Where they can assist flexible bonds in developing high tensile strength of the web without excessively interfering with the softness, flexibility and stretch of the web. Such selective retention enables production of a tough flexible web with minimum addition of expensive elastomeric bonding material to the web. Furthermore, selective retention of stiff bonds enables production of a soft flexible product which is capable of retaining bulk resulting from sheet distortion, because the stiff bonds are retained in locations where they maintain the distortion of the web.

The reduction of stiff bonds can be controllably confined to locations which produce elasticity in one desired direction without excessively reducing the web strength in other directions. Thus, the invention offers a practical method of greatly increasing the stretch in the cross-machine direction of a web having elastomeric bonding material throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of the web of the invention being passed through a pair of embossing rolls.

FIG. 2 is an enlarged sectional plan view taken along line 22 of FIG. 1.

FIG. 3 is an enlarged plan view of the preferred form of embossed web of the invention.

FIG. 4 is a sectional view of the preferred form of embossed web of the invention taken along line 44 of FIG. 3.

FIG. 5 is a sectional view of the preferred form of the embossed web of the invention taken along line 55 of FIG. 3, further enlarged over FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the invention consists of two distinctive steps, production of a base web and mechanical working of the base web.

(1) Production of the base web The base web of the invention can be formed on most conventional papermaking equipment where an aqueous slurry of lignocellulosic fibers is deposited upon a foraminous surface such as a fourdrinier wire. Upon such deposition, the water is drained and the fibers are brought into close contact with each other to form stiff hydrogen bonds between the hydroxyl groups of adjacent fibers, resulting in the production of a sheet material which owes its strength to this natural fiber-to-fiber bonding. The Web is formed in a manner which produces a basis weight of the dry web within the range of from about 12 to about 60 lbs/2880 ft It is within this range that a web which is particularly suited for a towel product can be produced. Elastomeric bonding material is added to the aqueous slurry at the beater, stock chest, fan pump, headbox or at any other suitable point ahead of the Web forming stage, so that the elastomeric bonding material is substantially uniformly disributed throughout the web.

The elastomeric bonding materials which may be employed in the present invention are basically any materials which are capable of at least 75% elongation at rupture. Such materials should also have an initial Youngs modulus by stretching which is less than 25,000 psi. Typical materials may be of the butadiene acrylonitrile type, or other latices or dispersions thereof with elastomeric properties, such as acrylic, acrylic copolymers, vinyl chloride acrylic, acrylic vinyl acetate, butadiene-styrene or ethylene vinyl acetate. Elastomeric properties may be obtained by the addition of suitable plasticizers to polymers such as polyvinyl alcohol or carboxy-rnethyl-cellulose. These elastomeric bonding materials can be used either alone or in combination with other resins such as those which are commonly used to improve the wet strength of lignocellulosic webs, the urea-formaldehyde and melamine formaldehyde type resins for example. Other wet strength resins which can be used are of the neutral cure type, examples being Kymene 557, available from Hercules, Inc., Wilmington, Del., and Parez 63 ONC, available from American Cyanamid, Wayne, NJ.

Commercially available elastomeric bonding materials which have been found to be particularly useful include Rhoplex K3, a nonionic self-cross-linking acrylic emulsion available from Rohm and Haas Company, Philadelphia, Pa.; Rhoplex P339, an anionic self-crosslinking acrylic emulsion, also available from Rohm and Haas Company; Goodrite 2570 x 15, an anionic, carboxylated styrenebutadiene copolymer available from B. F. Goodrich Chemical Company, Cleveland, Ohio; Hycar 26-00-X92, an acrylic emulsion also available from B. F. Goodrich Chemical Company; and Tylac RB 1118, an anionic, carboxylated styrene-butadiene copolymer containing approximately 50% styrene from Standard Brands Chemical Corporation, Dover, Del. The following anionic, selfcrosslinking, acrylic emulsions available from Rohm and Haas Company have also been found to be particularly useful-Rhoplex E631, Rhoplex E610, and Rhoplex TR407. Other useful, commercially-available resins include Piolite 610, a styrene-butadiene latex from B. F. Goodrich Chemical Company, and Rhoplex E32 a nonionic, self-crosslinking acrylic emulsion from Rohm and Haas Company. An additional resin which has been found to be useful in carrying out the present invention is a cationically dispersed acrylic emulsion comprising about 68 parts ethylacrylate and about 32 parts styrene.

The elastomeric bonding material can be added to the aqueous slurry by methods well-known in the art, including the methods disclosed in U.S. Pat. No. 3,622,447 and in US. Patent Application Ser. No. 108,638, now abandoned. The amount of elastomeric bonding material which is added to the aqueous slurry can be varied over a wide range depending upon the properties desired in the final product, the amount of material desired to be retained on the fibers, and other variables associated with the sheet forming operation. It is preferred to add an amount of elastomeric bonding material to the slurry which will result in about 3% to about 25% of the dry weight of the web. It is especially preferred, for economic and performance reasons, for the elastomeric bonding material con- 6 tent in the web to be from about 7% to about 15% of the dry web weight.

If the elastomeric bonding material selected is not cationic, it may be desirable to add a deposition aid to the aqueous slurry to cause the bonding material to adhere to the anionic lignocellulosic fibers. The deposition aids which have been found to be useful in carrying out the present invention include those compounds which are known to be useful for depositing a water-insoluble polymer onto cellulosic fibers. These compounds include vinyl imidazoline polymers, such as those disclosed in US. Pat. 3,527,719 and in British Pat. 1,052,112, and polyquaternary ammonium compounds, such as those described in US. Pat. 2,765,229. Commercially available compounds which have been found to be particularly useful include Lufax 295, a cationic polyelectrolyte available from Rohm and Haas Company, Philadelphia, Pa.; Resin S243, a cationic solution polymer also available from Rohm and Hass; and Velvetol 2000, a cationic, high molecular weight, quaternized imidazoline available from Quaker Chemical Corporation, Conshohocken, Pa. The Velvetol 2000 can function as both a coupler and a debonder.

The amount of deposition aid employed can be varied over a wide range depending on the type of furnish employed, the amount of elastomeric bonding material to be deposited, and other variables associated with the web forming operation. It is especially preferred to employ an amount equal to from about 0.1% to about 3.0% based on the oven dry weight of the fibers employed.

The base web of the preferred product of the invention can be further treated by adding a chemical debonder to the aqueous slurry to reduce forming of some of the bonds between the lignocellulosic fibers and increase overall softness of the web. The debonders which can be employed in carrying out the present invention include anionic and cationic surface active agents. Especially preferred are cationic quaternary ammonium compounds including imidazolium compounds such as Velvetol 2000 and Velvetol CHR, high molecular weight quaternized imidazolines available from Quaker Chemical Corporation, Conshohocken, Pa. Other preferred cationic quaternary ammonium compounds are the alkyl ammonium salts such as dihydrogenated tallow dimethyl ammonium chloride, available from General Mills, Inc., Chemical Division, Kankakee, Ill. as Aliquat H226; dialkylamide diethyl ammonium sulfate available from Reichold Chemicals, Inc., Conshohocken, Pa. as Rycofax 6-18; and Rycofax 637, an amphoteric quaternary ammonium compound also available from Reichold Chemicals, Inc.

Anionic surface active agents which are also preferred for use as debonders in carrying out the pesent invention include compounds such as sodium tetradecyl sulfate available was Tergitol Anionic 4 from Union Carbide Corporation, New York, N.Y. and the sodium salt of sulfated nonyl phenoxy poly( ethylene oxy) ethanol available as Alipal A8436 from General Aniline and Film Corporation, New York, NW.

The amout of debonder employed can be varied over a wide range depending upon the furnish employed, the properties desired in the final product and other variables associated with the web forming operation. It is especially preferred to employ an amount of debonder equal to from about 0.50% to about 2.0% of the oven dry weight of the fibers employed.

After the base web has been formed on the foraminous surface of a papermaking machine, it is dewatered, creped and dried in a conventional manner. To produce a base web which has suflicient elasticity to be satisfactorily passed through the mechanical working step, it has been found desirable to crepe the web in a manner which results in approximately 18% to 28% stretch in the machine direction of the web. It is also preferable that the web be at least dry before being mechanically worked.

(2) Mechanical working of the base web After the base web has been formed, creped, and dried, it is mechanically worked to partially fracture the web in selected locations to produce a product having the desired properties of softness and flexibility along with toughness and bulk. The mechanical working can be carried out by apparatus mounted at the end of the papermaking machine whereby the complete product is produced in one continuous operation, or the base web can be collected in rolls from the papermaking machine and transported to a separate location for mechanical working in a separate operation.

The term partially fracture" when used in the specification and claims of this application shall mean mechanical working of the web in some locations at least to the degree of breaking some of the bonds holding the fibers to each other, and may include working the sheet to the extent that the web is completely torn in portions of the worked locations to the point of forming apertures in the web. The result of partially fracturing paper webs is that the web is more soft, flexible, and extensible in those 10- cations. The web is also weaker, but by selecting the appropriate locations, weakening can be greatly reduced. While partially fracturing a conventional paper web which has no elastomeric bonding material will produce the desired properties to some degree, performing the same step upon the base web of the invention results in unusually high production of the desired properties, even beyond what one skilled in the art would have expected.

The type of mechanical working which will partially fracture the web is that which will stress in tension the selected area of the web to the point of causing failure of only some of the fiber bonds. Embossing is an example of mechanical work which will partially fracture the web. Creping is another example. Creping does not offer the degree of control of partially fracturing only selected areas required for the preferred product of the invention. Embossing does. A particular form of embossing has been found to offer very good control of partially fracturing selected areas, and it is this form of embossing which is employed to produce the preferred product of the invention. This form of embossing also enables working the sheet to produce apertures distributed uniformly through the web.

FIG. 1 illustrates the preferred embossing operation. The base web 10 of the invention is passed through a pair of mating cylindrical embossing rolls 11 and 12 (partially shown) to produce the embossed web 13 of the invention. The embossing rolls 11 and 12 have

knuckles

14 and 15 which intermesh to distort the web in the desired fashion.

FIG. 2 is an enlarged sectional view taken along line 2-2 and illustrates the intermeshing arrangement of the upper knuckles 14 (shown cross-hatched) with the lower knuckles 15 (shown with broken lines). The distortions produced in the base web 10 by the knuckles are illustrated in FIGS. 3, 4 and 5, where the lower knuckles 15 have produced raised areas 16 and the upper knuckles 14 have produced depressions 17. Of course, if the embossed web 13 is viewed from the underside, the raised areas 16 become depressions, and the depressions 17 become raised areas. Interconnecting ther aised areas 16 and depressions 17 are intermediate portions 18. It is these intermediate portions 18 which have received most of the mechanical working which partially fractures the web.

At locations 19 where the upper knuckles 14 pass very close to the lower knuckles 15, the work applied to the web exceeds the strength of the web and produces apertures in the web. The length of these apertures 20 can be varied vy varying the overlap 21 of upper knuckles 14 and lower knuckles 15. By causing these apertures 20 to be elongated in the machine direction of the web, the cross-direction stretch of the web can be increased substantially more than by partially fracturing the web alone. Furthermore, the flexibility and softness of the web can be greatly increased by these apertures 20. However, as pointed out earlier, this method of increasing stretch and flexibility excessively decreases strength. Therefore, the preferred product of the invention employs well-controlled portions of both apertures and partially fractured regions.

The size and spacing of the knuckles, as well as the depth to which they emboss the web, can be varied over a wide range and produce useful products. Particularly desirable paper products useful for towels can be produced, it the knuckles are within the ranges from about 0.050 inch to aobut 0.100 inch long, from about 0.024 inch to about 0.040 inch wide, and concentrated at about 70 to about 300 per square inch. Of course, the size of the knuckles selected governs to a large extent the spacing and thus concentration of the knuckles.

It has been found that the most desirable towel products are produced by setting the spacing between embossing rolls 11 and 12 to cause the upper knuckles 14 to pass below the lower knuckles 15 a distance within the range of from 0.020 inches to 0.060 inches. Because each knuckle in one of the embossing rolls will create two apertures in the web it embosses, a web embossed by knuckles within the above-stated range will create approximately 140 to 600 apertures per square inch of web. Within the range of spacings stated above for the embossing rolls, the apertures will be of a size within the range from about .010 inch to about .100 inch long.

As stated above, partially fracturing the base web of the invention increases stretch of the web considerably more than would be expected by the amount of decrease in tensile strength. For example, a conventional paper web having no elastomeric bonding material (described as Example 1 below in the specification), when subjected to the preferred embossing operation of the invention (the resulting web is described as Example 2 below in the specification) experienced in the cross-direction of the web 72.9% strength decrease and a stretch increase from 3.8% to 14.4%. In contrast, the base web of the invention (described as Example 3 below in the specification) when subjected to the preferred embossing operation of the invention (the resulting web is described as Example 4 below in the sepcification) experienced in the crossdirection of the web 68.8% strength decrease and a stretch increase from 5.2% to 19.7%.

In order to describe the present invention so that it may be more clearly understood, the following examples are set forth. The physical properties reported herein were obtained using the following test procedures.

Basis weight of the sheets was determined by weighing eight sheets measuring 2% inches x 2% inches and converting the result of pounds/ream (2880 square feet).

Bulk was determined by measuring the thickness of 24 stacked sheets under a weighted pressure of 235 grams per square inch in a Federal Bulker Model 57B-l/Y-7227.

Tensile strength, stretch and energy absoption were determined with a standard Instron Tensile Tester using 1 inch wide test strips, a span of 2 inches and a strain rate of 2 inches per minute. These tests were run in accordance with TAPPI Standard, T220 m-60 and TAPPI Test, T494 su-64. All wet tensiles were from uncured specimens and were measured within a minute of wetting.

Length overhang tests (a measure of stiffness, higher numbers indicating stiffer specimens) were measured by subjecting the specimens to the test set forth in TAPPI Standard Tests, T451 m-60 on a Clark Softness Tester using a degree angle movement.

Fold value and crush value were measured on an apparatus designed to give an indication of the softness of a sheet by measuring the force required to fold the sheet (the' fold value) and the force required to crush the folded sheet (the crush value). A decrease in these values is indicative of a shofter sheet. The apparatus employed to obtain these measurements comprises an inner set of circular platens and an outer set of annular platens. The

platens are arranged so that there is an upper and lower member of each set. The upper circular platen has a diameter of 1.09 inches and a rounded edge having a radius of .062 inches. The lower circular platen has a diameter of 1.43 inches and is located directly below the upper circular platen. The upper annular platen has an inside diameter of 2.125 inches and a rounded inner edge also having a radius of .062 inches. The lower annular platen is of similar size and is located directly below the upper annular platen. The rounded edges of the two sets of platens are separated by a distance of .382 inches. The upper member of each set of platens is attached to means for clamping that set of platens together and the surfaces of all the platens are highly polished.

There is also included, below the space between the two sets of platens a circumferential ring attached to means for moving said ring through said space. The ring has an inner diameter of 1.5 inches, an outer diameter of 1.75 inches and the rounded portion has a radius of .062 inches. Above the space is another annular platen having an inside diameter of 1.16 inches and an outside diameter of 2.062 inches. This platen is also highly polished and is attached to means for moving said platen towards the space.

In operation the sheet to be tested is placed between the upper and lower members of the two sets of platens. The inner circular set of platens is clamped to hold the sheet in place and the distance between the upper and lower members of the outer annular set is adjusted to .065 inches. The distance the circumferential ring will travel is adjusted to .250 inches and a force is applied to said ring causing it to move in an upward direction through that distance folding the sheet as it moves. The maximum force on the ring during this folding operation is recorded in grams and is referred to as the fold value of the sheet.

After the sheet is thus folded the outer annular set of plates is clamped to maintain the sheet in the folded condition. The folded sheet is crushed by, simultaneously, moving the circumferential ring down away from the sheet and moving the annular platen down onto the sheet for a distance of .050 inches. The maximum force on the platen as it moves through this distance is measured in grams and is referred to as the crush value of the sheet.

The following examples are set forth primarily for the purpose of illustration, and any specific enumeration of detail contained therein should not be interpreted as a limitation on the concept of this invention.

EXAMPLE 1 The web of Example 1 is a conventional paper web having no elastomeric bonding material and is described for purposes of comparison only. The web was formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

Percent Bleached Northern Kraft Spruce 30 Bleached Southern hardwood 40 Bleached Western sulfite softwood 30 The following chemicals were added to the papermaking furnish in a percent by weight of the wood pulp:

1.2% melamine formaldehyde, used to increase the wetstrength of the web; and

0.5% Velvetol 2000, a cationic, high molecular weight,

quaternized imidazolines, used to reduce interfiber bonding capacity.

10 The web processed the following properties:

Basis weight 3.1 lbs/2880 ftF. Bulk .240 inches per 24 sheets. Tensile (MD) $9.2 ozs. per inch. Stretch (MD) 19.6%. Tensile (CD) 41.3 ozs. per inch. Stretch (CD) 3.8%. Tensile wet (MD) 18.3 ozs. per inch. Tensile wet (CD) 13.2 ozs. per inch. Fold 562.8. Crush 180.

EXAMPLE 2 The web of Example 2 was produced by passing the web of Example 1 through embossing rolls of the type illustrated in FIG. 1. The size of the knuckles in the embossing rolls used were 0.078 inch long and 0.030 inch wide and concentrated at 98 per square inch. The knuckles of both embossing rolls were identical. The spacing between the embossing rolls was adjusted to produce the product desired cross-direction tensile strength of approximately 11-14 ounces per inch. The spacing required for this strength reduction corresponded to that spacing required to cause the upper knuckles to pass below the lower knuckles a distance within the range from .030 inches to .043 inches.

The web of Example 2, as was the case with Example 1, is described for purposes of comparison only, and possessed the following properties:

Basis weight 32.2 lbs/2880 ft Bulk .431 inches per 24 sheets. Tensile (MD') 31.6 ozs. per inch. Stretch (MD) 12.9%. Tensile (CD) 11.2 ozs. per inch. Stretch (CD) 14.4%. Tensile wet (MD) 9.6 ozs. per inch. Tensile wet (CD) 3.5 ozs. per inch. Fold 246. Crush 101.

EXAMPLE 3 The web was formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

1.5% melamine formaldehyde, used to increase the wetstrength of the web;

0.5% Velvetol 2000, a cationic, high molecular weight, quaternized imidazolines, used to reduce interfiber bonding capacity; and

10% I-lycar 2600-X92, an acrylic emulsion available from B. F. Goodrich Chemical Company (9.5% content in web).

The acrylic emulsion was added to the furnish in discrete particles in accordance with the process described in U.S. Pat. No. 3,622,447 and with apparatus of the type described in U.S. Pat. No. 3,529,936. The web was formed on the same conventional Fourdrinier-type papermaking machine as the web of Example 1 and creped from a Yankee dryer at 70% to dryness and at 20% crepe. The web was then further dried on conventional drying equipment to more than dry.

The web of Example 4 was produced by passing the web of Example 3 through the same embossing rolls used to produce the web of Example 2.

The web possessed the following properties:

Basis weight 36.3 lbs/2880 ftF. Bulk .466 inches per 24 sheets. Tensile (MD) 33.4 ozs. per inch. Stretch (MD) 16.9%. Tensile (CD) 12.6 ozs. per inch. Stretch (CD) 19.7%. Tensile wet (MD) 11.8 ozs. per inch. Tensile wet (CD) 4.8 ozs. per inch. Fold 168. Crush 83.

EXAMPLE 5 The web was formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

1.5% melamine formaldehyde, used to increase the wet strength of the web;

0.7% Velvetol 2000, a cationic, high molecular weight,

quaternized imidazolines, used to reduce interfiber bonding capacity; and

5.5% Hycar 2600-X92, an acrylic emulsion available from B. F. Goodrich Chemical Company (5.0% content in web).

The acrylic emulsion was added to the furnish in discrete particles in accordance with the process described in U.S. Pat. No. 3,622,447 and with apparatus of the type described in U.S. Pat. No. 3,529,936. The web was formed on a conventional Fourdrinier-type papermaking machine and creped from the surface of a Yankee dryer at 70% to 80% dryness to give approximately 20.6% crepe. The web was then further dried until it was more than 90% dry by passing it over a transpiration dryer like that described in U.S. Pat. No. 3,432,936. The web possessed the following properties:

Basis weight 39.5 lbs/2880 ftfi. Bulk .227 inches per 24 sheets. Tensile (MD) 57.1 ozs. per inch. Stretch (MD) 18.5%. Tensile (CD) 42.1 ozs. per inch. Stretch (CD) 5.2%. Tensile wet (MD) 28.9 ozs. per inch. Tensile wet (CD) 16.4 ozs. per inch. Fold 476. Crush 91.

EXAMPLE 6 The web of Example 6 was produced by passing the web of Example 5 through embossing rolls which meet the 12 description of the embossing rolls used to produce the web of Example 2.

The web possessed the following properties:

Basis weight 39.9 lbs/2880 ft."'.

Bulk .509 inches per 24 sheets. Tensile (MD) 33.0 ozs. per inch.

Stretch (MD) 14.5%.

Tensile (CD) 13.0 ozs. per inch.

Stretch (CD) 18.5%.

Tensile wet (MD) 15.8 ozs. per inch.

Tensile wet (CD) 5.8 ozs. per inch.

Fold ..t...... 246.

Crush 118.

3.214 oz.-in./in. 1.833 oz.-in./in.'.

Energy absorption (MD) Energy absorption (CD) Length overhang (MD) 8.0 cm. Length overhang (CD) 6.7 cm.

EXAMPLE 7 The web was formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

1.0% melamine formaldehyde, used to increase the wet strength of the web;

1.0% Velvetol 2000, a cationic, high molecular weight, quaternized imidazolines, used to reduce interfiber bonding capacity; and

8.0% Hycar 2600-)(92, acrylic emulsion available from B. F. Goodrich Chemical Company (7.25% content in web).

The acrylic emulsion was added to the furnish in discrete particles in accordance with the process described in U.S. Pat. 3,622,447 and with apparatus of the type described in U.S. Pat. 3,529,936. The web was formed on a conventional Fourdrinier-type papermaking machine and creped from the surface of a Yankee dryer at 70%-80% dryness to give approximately 14.5% crepe. The web was then further dried until it was more than dry by passing it over a transpiration dryer like that described in U.S. Pat. No. 3,432,936. The web possessed the following properties:

Basis weight 39.4 lbs./ 2880 ft. Bulk 208 inches per 24 sheets. Tensile (MD) 79.1 ozs. per inch. Stretch (MD) 18.9%. Tensile (CD) 41.0 ozs. per inch. Stretch (CD) 4.3%. Tensile wet (MD) 29.7 ozs. per inch. Tensile wet (CD) 15.3 ozs. per inch. Fold 384. Crush 167.

EXAMPLE 8 The web of Example 8 was produced by passing the web of Example 7 through embossing rolls which meet the description of the embossing rolls used to produce the web of Example 2.

The web possessed the following properties:

Basis weight 38.3 lbs/2880 ftF.

Bulk .528 inches per 24 sheets. Tensile (MD) 41.2 02.5. per inch.

Stretch (MD) 11.5%.

Tensile (CD) 13.6 ozs. per inch.

Stretch (CD) 20.7%.

Tensile wet (MD) 13.6 ozs. per inch.

Tensile wet (CD) 4.7 ozs. per inch.

13 TABLE-Continued Fold 227. Crush 132.

Energy absorption (MD) 3.179 oz.-in./in.". Energy absorption (CD) 1.807 oz.-in./in.. Length overhang (MD) 8.6 cm.

Length overhang (CD) 6.4 cm.

\EXAMPLE 9 The web was formed from fiber furnish consisting of water and the following conventional papermaking pulps:

1.35% melamine formaldehyde, used to increase the wetstrength of the web;

10% Hycar 2600-X92, an acrylic emulsion available from B. F. Goodrich Chemical Company (9.0% content in web).

The acrylic emulsion was added to the furnish in discrete particles in accordance with the process described in U.S. Pat. No. 3,622,447 and with apparatus of the type described in U.S. Pat. No. 3,529,936. The web was formed on a conventional Fourdrinicr-type papermaking machine and creped from the surface of a Yankee dryer at 70% to 80% dryness to give'approximately 22.2% crepe. The web was then further dried until it was more than 90% dry by passing it over a transpiration dryer like that described in U.S. Pat. No. 3,432,936. The web possessed the following properties:

The web of Example 10 was produced by passing the web of Example 9 through embossing rolls which meet the description of the embossing rolls used to produce the web of Example 2.

The web possessed the following properties:

Basis weight 36.3 lbs/2880 ft Bulk .472 inches per 24 sheets. Tensile (MD) 38.9 ozs. per inch. Stretch (MD) 18.2%.

Tensile (CD) 13.6 ozs. per inch. Stretch (CD) 24.5%.

Tensile wet (MD) 12.2 ozs. per inch. Tensile wet (CD) 4.8 ozs. per inch. Fold 178.

Crush 95.

4.700 oz.-in./in.. 2.272 oz.-in./in.. 7.5 cm. 6.2 cm.

Energy absorption (MD) Energy absorption (CD) Length overhang (MD) Length overhang (CD) 14 EXAMPLE 11 The web was formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

1.0% wet-strength resin, consisting of 4.5 parts melamine formaldehyde to 1 part urea-formaldehyde;

1.0% Velvetol 2000, a cationic, high molecular weight, quaternized imidazolines, used to reduce interfiber bonding capacity;

10.0% Hycar 2600-X92, an acrylic emulsion available from B. F. Goodrich Chemical Company (9.5% content in web); and

0.5% Lufax 295, a cationic polyelectrolyte available from Rohm and Haas Company, used as a deposition aid.

The chemicals were added to the furnish in accordance with the process described in U.S. Patent Application Ser. No. 108,638, assigned to the same assignee as this application. The web was formed on a conventional Fourdrinier-type papermaking machine and creped from the surface of a Yankee dryer at 70% to dryness to give approximately 17% crepe. The web was then further dried until it was more than dry by passing it over a transpiration dryer like that described in U.S. Pat. No. 3,432,936. The web possessed the following properties:

Basis weight 37.0 lbs/2880 ft). Bulk .211 inches per 24 sheets. Tensile (MD) 51.9 ozs. per inch. Stretch (MD) 17.1%. Tensile (CD) 45.5 ozs. per inch. Stretch (CD) 6.3%. Tensile wet (MD) 25.5 ozs. per inch. Tensile wet (CD) 17.6 ozs. per inch. Fold 410. Crush 87.

EXAMPLE 12 The web of Example 12 was produced by passing the Web of Example 11 through embossing rolls which meet the description of the embossing rolls used to produce the web of Example 2.

The web possessed the following properties:

Basis weight 36.7 lbs/2880 ft. Bulk .455 inches per 24 sheets. Tensile (MD) 31.0 ozs. per inch. Stretch (MD) 13.4%. Tensile (CD) 13.7 ozs. per inch. Stretch (CD) 21.1%. Tensile wet (MD) 12.9 ozs. per inch. Tensile wet (CD) 5.1 ozs. per inch. Fold 208. Crush 104.

What is claimed is:

1. A soft, absorbent, creped fibrous web formed by deposition from an aqueous slurry, comprising:

randomly arranged contacting lignocellulosic fibers forming stilf web bonds in some places where they contact, and an elastomeric bonding material at substantially uniformly distributed contact points between the fibers generally throughout the web forming flexible web bonds where they contact the fibers;

the web having a basis weight of from about 12 to about 60 l=bs./ 2880 ft; and

the web having a plurality of areas where the web is partially fractured, the areas being substantially uni formly distributed throughout the web. 2. A web as recited by claim 1, wherein the web has substantial stretch in all directions in its own plane.

3. A soft, absorbent, creped fibrous web formed by deposition from an aqueous slurry, comprising:

randomly arranged contacting lignocellulosic fibers forming stilt web bonds in some places where they contact and an elastomeric bonding material at substantially uniformly distributed contact points between the fibers generally throughout the web forming flexible web bonds where they contact the fibers;

the web having a basis weight of from about 12 to about 60 lbs/2880 ft;

the web having a plurality of raised areas and depressions in each side, the depressions in each side forming the raised areas in the other side;

the web having intermediate portions intervening raised areas and depressions;

the web being partially fractured in at least some of the intermediate portions; and

the web having substantial stretch in all directions in its own plane.

4. A web as recited by claim 3, wherein the web in at least some of the areas fractured is completely ruptured to form longitudinal apertures in the web generally aligned in the machine direction of the web.

5. A web as recited by claim 4, wherein the web includes a chemical debonder agent to reduce the capacity of the lignocellulosic fibers to form stiff interfiber bonds.

6. A web as recited by claim 4, wherein the apertures are of a size within the range from about .010 inch to about .100 inch and are disposed substantially uniformly throughout the web at a concentration of about 140 to about 600 per square inch of web.

7. A web as recited by claim 6, wherein the amount of elastomeric bonding material is within the range from 3% to 25% by weight of the dry web weight.

8. A web as recited by claim 7, wherein the amount of elastomeric bonding material is within the range from approximately 7% to approximately 15% by weight of the dry web weight.

9. A web as recited by claim 8, wherein the elastomeric bonding material is selected from the group consisting of acrylic, vinyl chloride acrylic, acrylic vinyl acetate, butadiene-styrene, butadiene acrylonitrile, and ethylene vinyl acetate.

10. Method of making a soft, absorbent, fibrous web having substantial stretch in all directions in its own plane, comprising the steps of:

depositing an aqueous slurry on a forming surface of a papermaking machine, the aqueous slurry comprising lignocellulosic fibers, at least one chemical debonder and at least one elastomeric bonding material;

forming the web from the aqueous slurry;

creping the web;

drying the web; and

partially fracturing the dried web in selected predetermined locations.

11. Method as recited in claim 10, wherein the elastomeric bonding material in the aqueous slurry is selected from the group of acrylic, vinyl chloride acrylic, acrylic vinyl acetate, butadiene-styrene, butadiene acrylonitrile, and ethylene vinyl acetate.

12. Method as recited by claim 11, wherein the amount of elastomeric bonding material in the aqueous slurry is selected to produce an amount of elastomeric bonding material in the dried web which is within the range from 7% to 15% by weight of the dry web weight.

13. Method as recited by claim 10, wherein the amount of elastomeric bonding material in the aqueous slurry is selected to produce an amount of elastomeric bonding material in the dried web which is within the range from 3% to 25% by weight of the dry web weight.

14. Method as recited by claim 10, wherein the step of partially fracturing the dried web includes production of apertures in the web.

15. Method as recited by claim 14, wherein the apertures are elongated in the machine direction of the web.

16. Method as recited by claim 15, wherein the elongated dimensions of the apertures are within the range from .010 inch to .100 inch and are substantially uniformly disposed throughout the web at a concentration within the range from to 600 per square inch of web surface.

References Cited UNITED STATES PATENTS 3,455,778 7/1969 Bernardin 1621l3 S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R.