US3812000A - Soft,absorbent,fibrous,sheet material formed by avoiding mechanical compression of the elastomer containing fiber furnished until the sheet is at least 80%dry - Google Patents

Abstract

A FIBROUS WEB OR SHEET MATERIAL, FORMED BY DEPOSITION FROM AN AQUEOUS SLURRY AND CHARACTERIZED BY UNSUALLY HIGH BULK AND SOFTNESS, ACHIEVED AT LEAST IN PART BY THE ADDITION OF AN ELASTOMERIC BONDING MATERIAL TO THE AQUEOUS SLURRY AND BY THE AVOIDANCE OF MECHANICAL COMPRESSION OF THE WEB UNTIL IT IS AT LEAST 80% DRY, SO THAT THE ELASTOMERIC BONDING MATERIAL CREATES MANY OF THE INTERFIBER BONDS WITHIN THE SHEET MATERIAL. IN SOME INSTANCES THE WEB IS SUBJECTED TO DIFFERENTIAL CREPING TECHNIQUES BY ADHERING IT IN A PRINTED PATTERN TO THE CREPING SURFACE. IN SOME EMBODIMENTS, ADDITIONAL ELASTOMERIC BONDING MATERIAL IS ADDED IN THE PRINTED PATTERN. THE UNSUALLY HIGH BULK OF THE WEB IS DEMONSTRATED BY VERY LOW AVERAGE CALCULATED DENSITY THROUGH ITS THICKNESS UNDER NO LOAD OF LESS THAN 0.3000 GRAMS PER CUBIC CENTIMETER. ANOTHER SIGNIFCANT FEATURE INDICATIVE OF THE BULK AND SOFTNESS OF THE WEB IS DEMONSTRATED BY ITS RELATIVELY HIGH TEA-TO-STIFFNESS RATIO OF GREATER THAN 1.50 X 10==4 A METHOD FOR FORMING SUCH WEBS OR SHEET MATERIAL IS ALSO DISCLOSED. IN WHICH LIGNOCELLULOSIC FIBERS ARE MIXED WITH WATER AND WITH AN ELASTOMERIC BONDING MATERIAL INTO A FIBER FURNISH, WHICH FURNISH IS FORMED INTO A WEB. WATER IS REMOVED FROM THE WEB WITHOUT MECHANICAL COMPRESSION OF THE WEB AND, WHEN THE WEB IS AT LEAST 80% DRY, IT IS ADHERED TO A CREPING SURFACE AND CREPED THEREFROM.

Description

May 21. 9 J. L. SALVUCCI. JR. ETA!- 3,312,000

SOFT, ABSOHBENT. FlBROUS, SHEET MATERIAL FORMED BY AVOIDING MECHANICAL COMPRESSION OF THE ELASTOMER CONTAINING FIBER FURNISH UNTIL THE SHEET IS AT LEAST 87 DRY Filed June 24, 1971 3 Sheets-Sheet 1 INVENTORS JOSEPH L. SALVUCCI BY PETER N- YIANNOS May 21. 1974 J. 1.. SALVUCCI. JR, ETAL 3,812,000

SOFT, ABSORBENT. FIBROUS, SHEET MATERIAL FORMED BY AVOIDING MECHANICAL COMPRESSION OF THE ELASTOMER CONTAINING FIBER FURNISH UNTIL THE SHEET IS AT LEAST 8 DRY Filed June 24, 1971 3 Sheets-Sheet B I l I (CALIPER OF UNPRESSED WEB) WEB CALIPER (MILS) 30 4O 5O 6O 7O 8O 90 I PER CENT WEB DRYNESS BEFORE PRESSED Fig 4 Fig. 2

INVENTORS I JOSEPH L. SALVUCCI BY PETER N. YIANNOS ATTORNEY May 21. 1914 J. L. SALVUCCI. JR.. ETA!- SOFT, ABSORBENT, FIBROUS, SHEET HATERIAL FORMED BY AVOIDING IECHANICAL COMPRESSION OF THE ELASTOHER CONTAINING FIBER FURNISH UNTIL THE SHEET IS AT LEAST 8 7o DRY Filed June 24, 1971 3 Sheets-Sheet S PRIOR ART FIG. 5

FIGB

INVENTORS JOSEPH L. SALVUCCI PETER N. YIANNOS ATTORNE United States Patent SOFT, ABSORBENT, FIBROUS, SHEET MATERIAL FORMED BY AVOIDING MECHANICAL COM- PRESSION OF THE ELASTOMER CONTAINING FIBER FURNISHED UNTIL THE SHEET IS AT LEAST 80% DRY Joseph L. Salvucci, Jr., Drexel Hill, Pa., and Peter N. Yiannos, Wilmington, Del., assignors to Scott Paper Company, Delaware County, Pa.

Filed June 24, 1971, Ser. No. 156,282 Int. Cl. 1331f 1/14; D21f 9/02; D2111 3/64 US. Cl. 162-111 33 Claims ABSTRACT OF THE DISCLOSURE A fibrous web or sheet material, formed by deposition from an aqueous slurry and characterized by unusually high bulk and softness, achieved at least in part by the addition of an elastomeric bonding material to the aqueous slurry and by the avoidance of mechanical compression of the web until it is at least 80% dry, so that the elastomeric bonding material creates many of the interfiber bonds within the sheet material. In some instances, the web is subjected to differential creping techniques by adhering it in a printed pattern to the creping surface. In some embodiments, additional elastomeric bonding material is added in the printed pattern. The unusually high bulk of the web is demonstrated by very low average calculated density through its thickness under no load of less than 0.300 grams per cubic centimeter. Another significant feature indicative of the bulk and softness of the web is demonstrated by its relatively high TEA-to-stiffness ratio of greater than 1.50 A method for forming such webs or sheet material is also disclosed, in which lignocellulosic fibers are mixed with water and with an elastomeric bonding material into a fiber furnish, which furnish is formed into a Web. Water is removed from the web without mechanical compression of the web and, when the web is at least 80% dry, it is adhered to a creping surface and creped therefrom.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to soft, fibrous sheet materials and to a method for forming them. Such sheet materials are useful for sanitary paper products such as tissues, towels and the like. More particularly, the present invention relates to a soft, absorbent, fibrous sheet material, characterized by unusually high bulk, that is, low density, as measured by a calculated average density through its thickness under no load, and by a high TEA-to-stiffness ratio, stemming at least in part from the use of an elastomeric bonding material to supply much of the interfiber bonding strength of the sheet material, and from a unique method for making such sheet material. The present invention also relates to the method of making a web which has the above-mentioned characteristics.

(2) Brief description of the prior art In the past, and recently, there has been extensive activity in the field of papermaking to discover ways of impar-ting softness to paper webs without degrading their strength. Paper webs are conventionally softened by working them in different ways, such as by embossing them, calendering them, or by creping them from an adhering surface with a creping blade. Such processes disrupt and break many of the rather brittle, natural, intenfiber bonds in the paper web which are formed during the drying thereof by the hydrate bonding process associated with papermaking. However, these interfiber bonds are the principal source of strength in an ordinary paper web. Very little strength results from the physical entanglement of the fibers since papermaking fibers have such an extremely short length, generally on the order of inch or less. In addition, they are randomly deposited from an aqueous slurry so that entanglement is not encouraged.

Furthermore, although breakinginterfiber bonds in a previously formed web imparts substantial softness primarily upon the surface of such webs due to loose fiber ends extending therefrom, it does nothing to increase the bulk, compressibility, and flexibility of the product or to lower the density of the product, all of which are characteristics which also subjectively indicate softness to a person, without substantially decreasing the strength of the material. This undesired result becomes more pronounced as efforts to soften the web increase.

Attempts to improve this situation have included the creping of webs in only selected spaced-apart areas over its surface, such as by creping with a notched or serrated creping blade, or creping from a discontinuous surface such as a circumferentially grooved roll, leaving the portions therebetween with substantially all of their strength. However, such creping patterns necessarily created lines of weakness through the sheet so that the ultimate sheet was not very strong at least in certain directions. By creping or embossing the web while it is wet, the reduction in strength is minimized or reduced.

When paper webs are formed by conventional papermaking techniques, they are generally pressed between two opposed surfaces, at least one of which is porous, so that water is removed from the web. It is common to press such Webs on the Fourdrinier wire or other forming surface, as by a pickup roll, or in a press section on a felt between two press rolls, or onto the hard surface of a cast iron Yankee drying drum, which is steam heated to remove moisture from the web and which provides a surface from which the web may be creped. To insure rapid drying of the web, it has been shown to be important for uniform contact to be provided between the Yankee dryer surface and the web. It has been suggested by a number of prior art patents, that paper webs, and particularly those used for sanitary paper products, be formed and partially dried prior to being subjected to mechanical pressure of a type which would compact the structure and bring the fibers into closely contacting engagement with one another. For example, see US. Pat. No. 3,301,746, to Sanford et al. This same patent discloses that such a web be impressed with the knuckle pattern of a wove-n wire or other imprinting fabric onto the Yankee dryer after it is partially dried in order to adhere portions of the web to the surface of the dryer and to effect differential creping when the web is creped from the Yankee dryer. The impressed portions were used to provide areas of extensive interfiber bonding so as to impart strength to the Web. However, in areas between these impressed portions, the web lacks the desired amount of strength, due to the reduced amount of interfiber bonding resulting from the lack of compression during formation. The interfiber bonds which are present are of a hard brittle nature, i.e. hydrogen or hydrate bonds, and deleteriously effect the softness of the web. In addition, the pressures generated by the knuckle pattern of the woven wire are so high as to create hard portions of the web which give a feeling of harshness to the resulting product. In addition, even this form of pressing of the web prior to its being at least dry, results in a loss of bulk in the web, and an increase in density of the web, all of which is undesirable in a sanitary paper product requiring softness and absorbency.

One of the characteristics of a sheet product which gives the semblance of strength is the toughness of the sheet. In essence, this is representative of a combination of the tensile strength of the sheet and the ability of the sheet to stretch. Obviously, if the sheet can absorb some work imposed upon it by stretching so as to avoid firmly resisting thefull force applied, the resulting web' is tougher. It has long been known to crepe webs in various ways to create stretch and, accordingly, to impart toughness. However, even webs which have been creped in one direction, or in several different directions so as to impart universal or isotropic stretch, are weakened by the creping, and accordingly, do not have as much strength as desirable, especiallyif they have relatively low basis weight such as sanitary papers do.

In, the field ofnonwoven webs, which generally include substantial amounts of fibers having a length greater than /,4 inch, it has been common practice to apply bonding material vto spaced portions of the web so that fibers in at least portions, and perhaps in a network across the web, become bonded together to impart strength to the web. However, the fibers in such nonwoven webs are sufiiciently longto enable small amounts of adhesive to impart substantial strength to the web since any two adjacent areas of adhesive application can be quite far apart and yet be, able to bond one fiber into a network.

It has often been thought that to apply bonding material to a paper web to impart strength thereto would result in harsh areas in the sheet which would destroy any feeling of softness which is desirable. In addition, in view of the extremely short length of papermaking fibers, it has been felt that the amount of bonding material required, and the large percentage of the overall area of the sheet which would have to be impregnated to impart any strength to the sheet, would result in a very hard sheet, having little or no stretch and poor softness characteristics. Past applications of adhesives to paper webs have generally been unsatisfactory from the standpoint of forming suitably soft papers for sanitary paper products since such adhesives as were applied made the webs rather hard and heavy.

One form of web which overcomes these problems is described in copending US. patent application, Ser. No. 156,327, continuation-in-part of Ser. No. 27,743, now abandoned, assigned to the same assignee as this application. These webs are made by printing bonding material, and preferably an elastomeric bonding material, onto a previously formed web which has a reduced amount of natural interfiber bonding, and involves the creping of such webs in a manner which softens the bonded web portions which contain the strength-imparting bonding material. However, the Webs described in that application are characterized by a lack of uniform interfiber bonding throughout the web as is often desirable in sanitary products to give them more uniform strength, stretch, and softness. Instead, the bonding material is present in those webs only in spaced areas as a result of such webs being printed in a pattern with the bonding material.

It has quite unexpectedly been discovered that fibrous webs can be formed which have unusually high softness and bulk and yet which have an elastomeric adhesive uniformly distributed at interfiber contact points throughout the web. This is accomplished by. adding the elastomeric patern of bonding material by means of which the web is initially formed, and by substantially drying the web before subjecting it to any mechanical compression so as to create and preserve bulk. Such a Web is even further improved by successive imprinting of such a web with a pattern of bonding material by means of which the web is adhered to a creping surface so that it can be differentially creped to provide even further bulk and softness. It was extremely surprising to discover that such webs possess very low density which is a desirable characteristic in disposable sanitary paper products which are to be soft and absorbent so as to perform wiping functions. In addition, the webs have quite uni-form strength and stretch of a substantial amount, resulting from the elastomeric bonding material providing interfiber bonds uniformly throughout the webs, and from the differential creping operation in the instances where that was ernployed. The webs also have good strength or ability to absorb work without tearing or breaking. One of the unique advantages of these webs is that they are capable of being made on conventional papertnakiug machines with modifications to avoid compression until the webs are at least dry.

Thus, a principal object and advantage of the present invention is to provide uniquely soft, absorbent, creped fibrous webs.

A further object and advantages of the presentinvention is to enable such webs to be made on a modified papermaking machine which can operate at high speed.

SUMMARY OF THE INVENTION I The present invention is a soft, absorbent, creped, fibrous web formed by deposition from an aqueous slurry. The web comprises randomly arranged, contacting lignocellulosic fibers, and an elastomeric bonding material at substantially uniformly distributed contact points between the fibers generally throughout the web so as to impart structural integrity to the web. The web is characterized by having a basis weight of from about 10 to about 30 pounds per 2880 ft a TEA-to-stitfness ratio greater than 1.S0 10-*, and an average calculated density throughout its thickness of no load of less than 0.300 grams per cubic centimeter. In some instances, the web is formed from fibers which have been treated with a debonding agent in order to reduce their natural interfiber bonding capacity. Some embodiments of the web contain additional amounts of an elastomeric bonding material in a predetermined pattern so as to create higher strength web segments spaced apart by lower strength web segments. More preferred embodiments of the fibrous web of the invention has a TEA-to-stiifness ratio greater than 2.0 10

The present invention also is a method for forming the above-described soft, absorbent, creped, fibrous webs or sheet material. In accordance with the method, a fiber furnish is mixed from lignocellulosic fibers, an elastomeric bonding material and water. A web is formed from the fiber furnish by introductoin of the fiber funrish into a drainage zone in which it contacts at least one foraminous support surface which permits the removal of water thereform. Additional water is removed from the web without employing mechanical compression until the web is at least 80% dry. The web is then adhered to a creping surface and removed therefrom by a creping blade. In some embodiments, the web is adhered with an adhesive to the creping surface. The method also includes in some instances the steps of applying an adhesive to selected areas of the web such as by printing, and pressing the web into engagement with the creping surface so that only selected areas of the web are adhered to the creping surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of one form of apparatus for forming the fibrous web of the present invention in accordance with the method of the present invention;

FIG. 2 is a side elevation view of a portion of one'form of apparatus for carrying out one form of the method of the present invention;

FIG. 3 is a side elevation view of a portion ofan alternative form of apparatus for carrying out one 'form'of the method of the present invention;

FIG. 4 is a graph illustrating the manner in which the dryness of a web when pressed effects the caliper of the web after pressing;

FIG. 5 is a photomicrograph, having a linear magnification of 75, of a cross-section of one type of prior art web, formed as described in Example I, and having an outline drawn thereover according to the procedure described for determining its calculated density;

FIG. 6 is a photomicrograph, having a linear magnification of 75, of a cross-section of another type of prior art web, formed as described in Example I, and having an outline drawn thereover according to the procedure described for determining its calculated density;

FIG. 7 is a photomicrograph, having a linear magnification of 75, of a cross-section of a web of the present invention, formed as described in Example I, and having an outline drawn thereover according to the procedure described for determining its calculated density; and

FIG. 8 is a photomicrograph, having a linear magnification of 75, of a cross-section of a web of the present invention, formed as described in Example II, and having an outline drawn thereover according to the procedure described for determining its calculated density.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates one type of papermaking machine which is capable of forming the soft, absorbent, fibrous sheet materials of the present invention and in accordance with the method of the present invention. The papermaking machine has a stock distribution means associated therewith, and indicated generally by reference numeral 10, for delivering an aqueous papermaking slurry or fiber furnish to a Fourdrinier wire 16. The stock distribution means includes a tapered manifold or header 11 which is connected to a source (not shown) of an aqueous papermaking slurry or fiber furnish. A number of branch tubes or laterals 12 connect the tapered manifold 11 to a blending chamber 13 defined by generally parallel upper and lower walls, 14 and 15, respectively. The stock distribution system may be similar to that disclosed in U.S. Pat. 3,298,905, issued on Jan. 17, 1967, to A. C. Spengos et al. The Fourdrinier wire 16 is carried over a suction breast roll 17 and over a plurality of table rolls 18 after which it passes around a wire turning roll 20 and is threaded past three guide rolls 21, 22, and 23, respectively, back to the suction breast roll 17. The assembly of wire 16 and its supporting rolls is driven by drive means (not shown) connected to the wire turning roll 20.

One or more vacuum boxes, hydrofoils or other dewatering or formation assisting devices (none of which are shown in FIG. 1) may be employed in conjunction with the Fourdrinier wire 16. In addition, the configuration of the papermaking machine may vary widely from that described above without having any effect upon the present invention. It is important, however, that the web thus formed on the Fourdrinier wire 16 be maintained free from any mechanical compression or compaction until it is at least 80% dry for reasons set forth subsequently.

At this point, the web formed is transferred substantially free from any compaction or mechanical compression from the upper surface of the Fourdrinier wire 16 to the suface of a foraminous drying fabric 24, which may comprise a woven sheet material, such as made of wire or other filamentary materials, or perforated or foraminous base. The drying fabric 24 is advanced past a position closely adjacent the portion of the Fourdrinier wire 16 running between the wire turning roll 20 and the first guide roll 22. In doing so, it passes over a rotating suction pickup roll 25 or stationary suction pickup shoe and transfer thereto may be assisted if desired by a steam or air jet such as might issue from a header 26, as shown in phantom line in FIG. 1, disposed opposite the Fourdrinier wire 16 and the suction pickup roll 25. The drying fabric 24 carrying the web moves from the suction pickup roll into a drying means, indicated generally by reference numeral 27, and then is carried about guide rolls 28 and 30, and about a pressure roll 31 which presses the Web into engagement with the surface of a creping drum 32. One or more vacuum boxes (not shown) may be disposed behind drying fabric 24 following the pickup roll 25 to 6 remove additional entrained water from the web without compression. The drying fabric 24 continues on about a further guide roll 33 and then returns to the transfer point adjacent pickup roll 25.

The drying means 27 may comprise any means for drying the Web to a point where it has a moisture content of less than 20% by weight, that is, so that it is more than dry. It is important that no mechanical compression or compaction of the web occur prior to its obtaining this dryness level and, therefore, the traditional Yankee drying techniques, wherein the paper web is firmly pressed against the surface of a steam-heated Yankee drying drum, must be avoided when it has a moisture content above 20%. However, various other techniques for drying the web may be employed such as radiant heat lamps, tunnel dryers, or transpiration dryers wherein an preferably heated, is passed through the web. FIG. illustates a typical form of transpiration dryer in which air from a hood 34 is passed through the web and through the drying fabric 24 and through the drum 35 supporting both and hence, removed from the interior of the drum 35 as by another hood 36. A typical form of such drying apparatus is shown in U.S. Pat. No. 3,432,936, issued on Mar. 18, 1969 to R. 1. Cole et a1.

Since the web applied to the surfaceof the creping drum 32 is over 80% dry, it often is necessary to apply a creping adhesive such as starch to the Web surface or to the creping drum 32 by an elongate sprayer 37 such as that shown in phantom line in FIG. 1. This is particularly true where the sheet is dried to a level of or above, since there is insufficient moisture remammg in the web at this point to adhere it to the creping drum and to permit it to be creped therefrom. A creping blade 38 is disposed around it on the opposite side of the creping drum 32 from the pressure roll 31 and is used to remove the web from the creping drum 32. FIGS. 2 and 3 illustrate alternative methods for applying adhesive to the web in order to adhere it to the creping drum 32. Thus, FIG. 2 illustrates a glue application roll 40 which picks up adhesive from a reservoir 41 and transmits it to the surface of the web immediately prior to the web contacting the creping drum 32. FIG. 3 shows and application roll 42 which picks up adhesive from a reservoir 43 and applies it directly to the creping drum 32 after which the web is pressed into contact therewith and adhered.

Each of the embodiments shown in FIGS. 2 and 3 is particularly useful in the practice of the method of the invention where only predetermined portions of the web are adhered to the creping surface in order to obtain differential or patterned creping of the web in order to further increase bulk, softness and strength. For example, where additional strength is to be incorporated into the web, the adhesive which is printed onto the web as shown in FIG. 2 or onto the creping drum as shown in FIG. 3 contains an elastomeric bonding material which accomplishes further interfiber bonding in the portions of the web to which it is applied. The benefits of this will become apparent subsequently.

As stated previously, the method of the present invention comprises a series of steps which result in the formation of the new sheet materials of the present invention. The method includes mixing a fiber furnish from lignocellulosic fibers, an elastomeric bonding material, and water. A web is then formed from the fiber furnish in accordance with any one of a number of different techniques, most of which are standard techniques employed in papermaking. The web is then subjected to treatment to remove water therefrom without mechanically compressing the web. It is important that enough water be removed from the Web in this manner so that it is at least 80% dry before being mechanically compressed. The web is then adhered to the creping surface and creped from the surface with a creping blade.

The mixing step is normally performed in a headbox preceding the flow distribution equipment employed with the papermaking machine. The fibers in the furnish preferably comprise largely relatively short fibers, i.e. those having a length of less than A" and predominately shorter, and substantially all of the fibers are lignocellulosic fibers; that is, those coming from some natural wood fiber source such as wood pulp, so that they form hydrogen bonds of the type associated with papermaking.

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 generally should have an initial Youngs modulus by stretching which is less than 25,000 p.s.i. Typical materials may be of the butadiene acrylonitrile type, or other natural or synthetic rubber latices or dispersions thereof with elastomeric properties, such as butadiene-styrene, neoprene, acrylic copolymers, polyvinyl chloride, vinyl copolymers, or nylon. Elastomeric properties may be obtained by the addition of suitable plasticizers to polymers such as polyvinyl alcohol or carboxy-methyl-cellulose.

Although webs of the present invention may be formed with advantages in a wide range of basis weight, for purposes of forming sanitary paper products, it is preferred that the basis weight be from about to about 30 pounds per ream of 2880 ft. Sheet. products in this particular range of basis weight benefit most from the the method of the present invention since they largely find use in areas where softness and bulk are important. For example, where the product is a wiper, both softness and bulk are important as well as fiuid absorbency and strength. This range of basis weight is one where it is very diflicult to impart to a product the combination of properties achieved by the present invention. As indicated above, the web may be formed by any technique which accomplishes deposition and drainage of the fibrous slurry on a foraminous condenser such as a Fourdrinier wire and, of course, the speed of formation of such webs may vary from several hundred feet per minute to over 5,000 feet per minute.

The steps of the method, in which the web is formed and partially dried without being compressed in any way, are extremely important to the present invention in achieving the formation of a web which has the desired characteristics of high bulk and softness and unusually low density. It has been found from extensive experimentation that when a web is formed by deposition of a fibrous slurry onto a Fourdrinier wire and is dried to at least '80% dry before it is subjected to any mechanical compression such as between two surfaces in a felt or roll nip, that subsequent compression has only a minimal effect upon the subsequent properties such as bulk or caliper unless such compression is sutficiently harsh to cause the breakage of bonds or the chemical transformation of the lignocellulosic material, such as often occurs in an embossing or calendering nip. Thus, after the web has been subjected to water removal techniques to render it 80% dry or more, its ultimate caliper is not significantly eiTected by typical pressing processes such as occurs on papermaking machines in press nips and in the nip between the pressure roll and the Yankee Dryer.

FIG. 4 of the drawings graphically illustrates the results of experimentation in this area. For test purposes, a fiber furnish consisting of 50% Western softwood sulfite pulp and 50% Southern gum craft pulp was formed into hand sheets having a basis weight of 10 pounds per ream of 2880 ft. One of the hand sheets was not subjected to any pressure and was dried. Its caliper was measured and found to be of a level shown in broken line on the graph. Additional hand sheets were dried to give levels of web dryness as indicated by the reference points on the graph. They were then subjected to pressure between surfaces at a level of 40 p.s.i.g. The samples were then dried until they were 95% dry and their caliper was measured. From the resulting graph line joining these experimental points, it can be seen that until the web becomes at least dry, its caliper is substantially reduced when it is pressed below that of an unpressed web. This is known to result in greatly increased numbers of interfiber bonds which is undesirable as mentioned above. It also results in an increased web density which means lower softness.

The values of caliper and basis weight reported herein were determined by the following procedures. Basis weight was measured in accordance with TAPPI Standard T410- 05-61. Caliper, or the thickness of one sheet, was measured with a Federal Micrometer Gauge, Model No. D815, in accordance with TAPPI Standard T-411 M-44. A face area of 1 square inch (pressure of 0.5 p.s.i.) was employed when testing 28 pound per ream sheets instead of the standard 0.25 square inch face area (pressure of 7 to 9 p.s.i.). Caliper is indicated in mils.

The web at this point has fewer hydrogen bonds than would normally be present in a web which is of the same basis weight but which had been subjected to compression prior to being rendered at least 80% dry. This paucity of hydrogen bonds results in unusual softness and compressibility to the web and, of course, the web has greater bulk (lower density) due to the fact that it was not pressed when wet or bonded in the compressed condition.

A more preferred embodiment of the present invention results from an even further reduction in the number of hydrogen bonds of the type used between fibers in papermaking. It is well-known that such bonds are typically quite hard and inelastic and unfortunately impart these same general properties to the resulting web. By treating the fibers, from which the web is formed, with a chemical debonding agent as by adding such a debonder to the fibrous slurry in the headbox, the number of bonding sites along the individual fibers is reduced so that the fibers are less susceptible to interfiber bonding by hydrogen bonding. Debonding agents which may be used for this purpose include, for example, the cationic debonding agents disclosed in U.S. Pat. No. 3,395,708, issued Aug. 6, 1968, to Hervey et al., that is, substances within the class of long chain cationic surfactants, preferably with at least twelve carbon atoms in at least one alkyl chain, such as fatty dialkyl quaternary amine salts, mono fatty alkyl tertiary amine salts, primary amine salts, and unsaturated fatty alkyl amine salts; the cation-active tertiary amine oxides disclosed in U.S. Pat. No. 2,432,- 126, issued Dec. 9, 1947, to Schlosser et al.; and the cation-active amino compounds disclosed in U.S. Pat. No. 2,432,127, issued Dec. 9, 1947, to Schlosser et al.

The elastomeric bonding material which is also added to the fibrous slurry at the headbox substitutes its bonding ability for that of the hydrogen bonding which is prevented by the debonder, and provides sufficient interfiber bonding to give the web structural integrity. In addition, the bonds formed by such elastomeric bonding materials are quite soft and resilient and impart further softness to the web without lessening its absorptivity or its bulk, that is, without increasing its density.

As mentioned above, the apparatus shown in FIGS. 2 and 3 may be utilized to apply adhesive to the web or to the creping surface in order to enhance the bonding of the web to the creping surface so as to promote better dry creping and a softer product. This is particularly important where the moisture content of the web being applied to the creping surface is less than 10%, for example, when the web is dry. The creping adhesive makes up for the lack of moisture which ordinarily is used to attach the web to the dryer surface.

In certain more preferred embodiments of the invention, the mechanism shown in FIGS. 2 and 3 are utilized to print bonding material in predetermined patterns on the web or alternatively on the creping surface in order to selectively adhere the web to the creping surface. However, in addition to the unique creping effects which are achieved in this manner, it has been found desirable to either utilize an elastomeric bonding material as the adhesive between the web and the creping surface or to add elastomeric bonding material to the adhesive so that, when it is ultimately applied to the web by one of the mechanisms shown in FIGS. 2 and 3, it provides supplemental strength to the web. That is, the elastomeric bonding material applied in this way provides areas of greater interfiber bonding and, therefore, areas of greater webs strength than adjacent areas to which no additional adhesive was applied beyond that applied in the headbox to the fibers themselves.

The pattern of bonding material applied to the web can be in any form which leaves a substantial portion of the surface of the web free from extra amounts of bonding material other than that applied during web formation. Most preferably the pattern comprises less than about 35% of the total surface area of the web so as to leave about 65% or more of the surface of the web free from additional bonding material, at least when printed. Thus, any of the patterns taught by US. Pats. 3,047,444; 3,009,- 822; 3,059,313; and 3,009,823 may be advantageously employed for the rolls 40 or 42 which comprise, in this instance, gravure rolls. Some migration of bonding material occurs after printing. Thus, the bonding material penetrates at least partially through the web and in all directions in the plane of the web. However, preferably migration in all directions in the plane of the web is minimized so as to leave areas comprising a substantial portion of the web free from any additional bonding material, other than that applied by the headbox, for purposes which will become apparent subsequently.

It has been found to be particularly desirable to apply the additional bonding material in a reticular pattern so that the additional bonding material forms a net-like web of supplemental strength over the web. Thus, it is wellknown that papermaking fibers generally have a length less than about 4 inch and normally have a predominant fiber length less than about inch in length. Therefore, when additional strength is to be imparted to the sheet by a bonding material, in addition to that added at the headbox, as in this embodiment of the present invention, it is important that there be a continuous interconnection of at least some of the fibers by the additional bonding material throughout the entire web. If the pattern of additional bonding material is in the form of parallel lines, bars, or other forms of discrete areas, the web will lack the additional strength desired beyond that provided by the bonding material added in the headbox, unless such discrete areas are spaced apart by distances less than average fiber lengths or, typically, less than about ,4 inch. However, where the pattern of adhesive is reticular or net-like in configuration, the interconnected lines of bonding material application provide a network of strength even where substantial areas, in many cases much larger than inch in every direction, are defined between the lines of bonding material application as web portions have a lower amount of interfiber bonding.

The creping drum 32 may in some instances comprise a heated pressure vessel such as a Yankee dryer, or in other instances may be a smaller roll and may be unheated. It is characterized by an extremely smooth, polished surface to which the bonding material, applied to the web, adheres. The significance of heating depends upon both the characteristics of the particular bonding material employed and the moisture level in the web. Thus, the bonding material may require drying or curing by heating in which case the creping drum 32 may provide a convenient means to accomplish this. Or, the moisture level of the web being fed to the creping drum 32 may be higher than ultimately desired, and the creping drum 32 may be heated to evaporate some of this moisture.

In each of the embodiments shown in FIGS. 2 and 3, the web is carried on the surface of the creping drum 32 for a distance and then removed therefrom by the action of a creping doctor blade 38. The doctor blade 38 performs a conventional creping operation on the additionally bonded portions of the web, that is, it imparts a series of fine fold lines to portions of the web which are adhered to the creping surface 32. However, since the web in this instance is only adhered to the creping surface 32 in a pattern having either a reticular form or comprising a plurality of spaced discrete areas, the creping blade 38 causes the lesser bonded web portions, which are not attached to the creping drum 32, to puff and arch up to form shaped web portions having excellent softness characteristics.

The bonding material utilized in the above-described embodiment of the present invention must be capable of several functions, one being the ability to bond fibers in the web to one another and the other being the ability to adhere the additionally bonded portions of the web to the surface of the creping drum 32. In general, any material having these two capabilities may be utilized as the bonding material, if the material can be dried or cured to set it. Among the bonding materials which are capable of accomplishing both of these functions and which can be successfully used are acrylate latex rubber emulsion, useful on an unheated creping surface; emulsions of resins such as acrylates, vinyl acetates, vinyl chlorides, and methacrylates, all of which are useful on a heated creping surface; and water soluble resins such as carboxy methyl cellulose, polyvinylalcohol, and polyacrylamide. However, in other instances, the bonding material may comprise a mixture of several materials, one having the ability to accomplish interfiber bonding and the other being utilized to create adherence of the web to the creping surface. However, in either instance, the materials are preferably applied as an integral mixture to the same areas of the web. Such materials may comprise any of the materials listed above mixed with a low molecular weight starch, such as dextrin, or a low molecular weight polymer such as carboxymethyl-cellulose or polyvinylalcohol. Of course, compatible wet strength additives may be used with any of the above materials in order to impart additional wet tensile strength to the resulting sheet material.

It has been found desirable to apply the bonding material to the surface of creping drum 32 just prior to covering that surface with the web, especially where the bonding material contains volatile components or components which set or cure quickly, particularly at elevated temperatures in the event the creping drum 32 is heated. This insures that the bonding material will penetrate the web to the thickness desired and that portions of the web will be adhered to the dryer before the bonding material becomes cured and loses its tackiness.

The sheet materials of the present invention, resulting from treatment with an elastomeric bonding material of webs which are formed by deposition from an aqueous slurry of fibers, water, and preferably, a debonding agent, having been found to be superior, in terms of such properties as softness and wiping ability, to any other prior art sheet material so formed but not subjected to such treatment. These properties may be characterized in many different ways when applied to sheet material used in sanitary paper products such as tissues, towels and the like. This is due to the fact that softness and wiping ability in large measure are subjective impressions one gets from handling the sheet material, and involve an assessment of the combination of thickness or bulk, density, resistance to bending and compression, and other physical properties susceptible to tactile observation.

However, for purposes of measuring the acceptability of these sheet materials of the present invention for use in the above-mentioned sanitary paper products from the general standpoint of softness, two different properties have been found which, in combination, provide a basis 1 1 for accurately distinguishing such materials from those of the prior art. These properties are (l) the TEA-tostifiness ratio of the sheet material and (2) the average calculated density throughout the thickness of the sheet material under no load. These properties, the desired ranges therefor, and the procedures and techniques for determining them are described in detail herein so as to explain the invention and to permit others to clearly ascertain its scope with regard to such sheet materials.

The TEA-to-stiffness ratio is obtained by first measuring the TEA (tensile energy absorption) of a given specimen of sheet material in accordance with TAPPI Test, T494 su-64, in both the machine direction (M.D.) and the cross-machine direction (C.D.) in kilogram meters per square meter, with the exception that a jaw sparing of 2 inches rather than the 8 inches recommended by TAPPI is used because of the particular nature of the products, some of which have lines of perforations which must be avoided. This test method is not a TAPPI standard but is suggested by TAPPI as the most suitable method to date. The stiffness of the product is then measured by subjecting the specimen to the test set forth in TAPPI Standard Test, T451 m-60, in both the machine direction and the cross-machine direction, to determine its effective overhanging length (critical length) denoted as L in centimeters. The stiffness of the product is proportional to the cube of the effective overhanging length and is therefore expressed herein as L Briefly described, the TEA of a product is obtained by clamping a 100010.005 in. (25410.01 cm.) wide specimen in two spaced sets of jaws when they are 2 in. (5.08 cm.) apart, with any noticeable slack being pulled out of the strip before clamping. Strain is applied to the specimen by moving the jaws further apart at a constant rate of 1.001001 in./min. (2.541002 cm./min.) while recording the elongation with an accuracy of 12% of the actual value and the load in either pounds or kilograms with an accuracy of 10.5% until breakage of the specimen. The area under the load-elongation curve is then measured by a planimeter or integrator with an accuracy of 12% The TEA is then calculated using the equation:

TEA: 100A /LW with units of kilogram-meters per square meter where:

A=area under load-elongation curve in kilogram-centimeters L=initial span between clamp lines in centimeters W=initial width of specimen in centimeters.

The stiffness of a product is obtained with a Clark softness Tester by placing the end of a 15 to 50 mm. /3 to 2 inches) wide specimen with parallel edges and of convenient length between the jaws or rollers comprising a clamp mounted on a rotatable spindle. The spindle can be rotated about a horizontal axis parallel to the long axis of the jaws or rollers and perpendicular to the long axis of the paper strip. The overhanging length of the specimen is adjusted by resetting the jaws or turning the rollers until, when the spindle is slowly rotated back and forth through 90", the specimen just falls over at each of the end points of rotation. The overhanging or critical length L is then measured from the line where the edges of the jaws or the rollers grip the specimen to the end of the strip. For purposes of defining the products of the present invention, the stiffness is indicated by the cube of L.

In using the above tests for TEA and stiflness to form a ratio which defines a desired property of a fibrous product of the invention, specimens for each test are taken in both the machine direction (M.D.) and the cross-machine direction (C.D.). Preferably several tests are made with each and the results averaged in order to eliminate errors due to measurement or to formation. The resulting values are then combined in ratio form as follows:

The average calculated density throughout the thickness of the sheet material under no load is determined by the following procedure. An approximately one inch long specimen of the product is oven dried to eliminate moisture therein. The dried specimen is inserted in a small container and is slowly immersed at atmospheric pressure in a solution of butyl methacrylate monomer therein containing a small amount of benzoyl peroxide as a catalyst. The container and the immersed specimen are placed in an oven having an interior temperature of 55 C. for a period of about 16 hours to cause polymerization of the monomer. A small amount of volumetric shrinkage occurs which is insignificant because it is constant for each sample. Cross-sections are cut from the resulting embedded sample using a microtome, the sections having a thickness of 10-l2 microns.

Each section is placed on a glass slide, and covered with mineral oil and a glass cover slip. The section of the specimen is now photographed by transmitted light through a microscope having a 24 mm. objective lens and an eye piece of 125x. The bellows extension is 50 cm. The resulting linear magnification is and the magnified picture is printed in a 5" x 7" format.

The resulting photomicrograph is mounted on a board, and a transparent paper is placed over the photomicrograph. The outline of the resulting cross-section shown in the photomicrograph is now traced onto the transparent paper, care being taken to follow the basic curves and undulations of the cross-sectional outline to an extent sufficient to get inside the outline at least or more of the cross-sectional area including any stray fibers. Certain stray fibers deviating from the outline of the cross-section should be left outside the area in order to obtain truer density values. A planimeter is then used to measure the area within the inside edge of the line defining the crosssectional outline in square inches. Several photographs of each specimen are preferably used and several cross-sectional area measurements are taken, the results being average to obtain a reliable cross-sectional area.

The actual thickness of the sample was obtained by dividing the area by the length of the cross-section outlined and by the linear magnification of 75. The calcula ed density under no load in grams per cubic centimeter was obtained by the equation:

TEA-to-stiffness ratio Basis weight, g./m. Actual tm (in.) 2.54 om. 10,000 cm.

where the basis weight is that of the original sheet material from which the specimen was taken.

All of the sheet materials of this improved form of the invention comprises a web of randomly arranged lignocellulosic fibers, and an elastomeric bonding material, such as that mentioned previously, at some of the contact points between said fibers to impart structural integrity to the sheet material or web. The lignocellulosic fibers may be any of the wood pulp fibers normally used in papermaking. Depending upon the particular fine pattern in which the bonding material is applied to the web, and the amount of migration of such material through the web, the elastomeric bonding material may form bonded web segments spaced apart by unbonded web segments. In a particular embodiment, the bonding material is present in the web in a continuous, predetermined reticular pattern which defines a discontinuous predetermined intermittent pattern of discrete unbonded web segments.

Advantageously, the fibers are treated with a debond- Calculated density, g./cc.=

75 ing agent in an amount sufficient to reduce their inter- Tentative Standard T220 m-60. In this procedure, a pulp sheet having a basis weight (r) in 0 grams per square meter (on a moisture-free basis) is measured to determine its tensile break load (p) in kilograms on a 15- mm. strip. The breaking length in meters is calculated from the equation:

Breaking length=200,000p/3r and is equivalent to the length in meters of a uniformly wide strip of paper which, if held at one end (e.g., freely suspending a coil of that paper by its tab end), would just cause the strip to break under its own weight.

The following examples comparatively illustrate the difference between the sheet materials of the present invention and conventional sheet materials used in the past. This difference is clearly apparent on the basis of the properties measured in accordance with the above procedures and in large measure stems from the use of elastomeric bonding materials therein along with a reduced amount of interfiber bonding due to natural bonds prior to drying of the web. However, any specific enumeration of detail contained therein should not be interpreted as a limitation in the concept or scope of the invention.

EXAMPLE I As an illustration of the prior art, a first webwas formed from a fiber furnish consisting of water and the following conventional papermaking pulps:

Percent Softwood bleached kraft 20 Softwood bleached sulfite 20 Hardwood bleached kraft 40 Mechanical fiber 20 The web was formed on a conventional Fourdrinier-type papermaking machine and was transferred by a felt run to the surface of a Yankee Dryer. The web was creped from the Yankee Dryer when it was about 65% dry, that is, when it contained only about 35% moisture by weight. The web was further dried in an after-dryer section in the form of heated drums until it was more than about 92% dry. The resultant sheet material was one which is typically used in sanitary paper products, such as wet creped bathroom tissue, and possessed the following general properties:

Basis weight 20.8 gms./M. -12.3 lbs/2880 ft.

Bulk 0.081 in./24 sheets (Federal Bulker) Tensile (MD) 12.8 oz./in. (TAPPI Standard, T220 Stretch (MD) 7.9% (TAPPI Standard, T220 m-60) TEA (MD) 0.993 kg.-rn./m. (TAPPI Test, T494 su-64) Tensile (CD) 5.3 oz./in. (TAPPI Standard, T220 m-60) Stretch (CD) 3.3% (TAPPI Standard, T220 m-60) TEA (CD) 0.189 kg.-'m./m. (TAPPI Test, T494 su-64) Lo (MD) 5.5 cm. (Critical lengthTAPPI Standard,

T-45l m-66) Lo (CD) 4.5 cm. (Critical length-TAPPI Standard,

This first web was subjected to the tests described above and was found to have a TEA-to-stiffness ratio of 0.12 l0 and an average calculated density throughout the thickness of the web under no load of 0.441 grams per cubic centimeter. A typical cross-section of this first web photographed with a linear magnification of 75 as described above for determining the average calculated density is shown in FIG. 5. The very appearance of the sheet indicates the closely-packed disposition of the fibers and the relative harshness of the sheet even after creping has occurred. An outline of the crosssection has also been drawn on the photograph to illustrate the manner in which this is done for purposes of determining the area and the average thickness of the cross-section.

EXAMPLE II As another illustration of the prior art, a second web was formed from a fiber furnish consisting of water and the following papermaking pulps:

Percent Softwood bleached kraft 30 Softwood bleached sulfite 25 Hardwood bleached kraft 35 Mechanical fiber 10 The web was formed on a conventional Fourdriniertype papermaking machine and was transferred by a felt run to the surface of a Yankee Dryer. The web was creped from the Yankee Dryer when it was about 94% dry, that is, when it contained only about 6% moisture by weight. The resultant sheet material was one which is typically used in sanitary paper products, such as dry creped bathroom tissue, and possessed the following general properties:

Basis Weight 9.6 lbs./ 2880 ft.

Bulk 0.086 in./ 24 sheets (Federal Bulker) Tensile (MD) 12.6 oz./in. (TAPPI Standard, T220 Stretch (MD) 17.5% (TAPPI Standard, T220 m-60) TEA (MD) 1.29 kg.-m./m. (TAPPI Test, T494 su-64) Tensile (CD) 2.4 oz./in. (TAPPI Standard, T220 m-60) Stretch (CD) 5.6% (TAPPI Standard, T220 m-60) TEA (CD) 0.20 kg.-m./m. (TAPPI Test, T494 su-64) Lo (MD) 3.8 cm. (Critical lengthTAPPI Standard,

Lo (CD) 4.5 cm. (Critical lengthTAPPI Standard,

This second web was subjected to the tests described above and was found to have a TEA-to-stiffness ratio of 0.527 10- and an average calculated density throughout the thickness of the web under no load of 0.466 grams per cubic centimeter. A typical cross-section of this second web photographed with a linear magnification of as described above for determining the average calculated density is shown in FIG. 6. The very appearance of the sheet indicates the closely-packed disposition of the fibers and the relative harshness of the sheet even after creping has occurred. An outline of the cross-section has also been drawn on the photograph to illustrate the manner in which this is done for purposes of determining the area and the average thickness of the cross-section.

EXAMPLE III By comparison, as an illustration of the present invention, a third web was formed from an unrefined fiber furnish consisting of water and the following conventional paper-making pulps:

Percent Softwood bleached kraft Hardwood bleached kraft 20 The following chemicals were added to the papermaking furnish in a percent by weight of the wood pulp:

0.7% Quaker 2000, a debonding agent manufactured by Quaker Chemical Company, Conshohocken, Pa., used to reduce interfiber bonding capacity,

0.085% 8-243 Amine--a cationic polyelectrolyte used for beater deposition of anionic materials, and

5.0% Rhoplex P339-an anionic acrylic latex used as an elastomeric bonding material.

inches mercury for a duration of 15 milliseconds. This reduced the moisture content of the wet web to approximately 70% by weight of the wet web. The web was further dried on the fabric by passing heated air at 260 F. through the web while conveying it on the fabric through a tunnel dryer. The tunnel dryer had sufiicient thermal capacity to reduce the moisture content of the web to less than 10% by weight of the wet web, so that the web was now more than 90% dry.

The conveyed web was then transferred from the fabric to the surface of a creping dryer of 20 inch diameter by means of a press nip formed against the dryer surface by a inch diameter elastomeric roll having a neoprene cover /2 inch thick and having a hardness of 55 Shore A. To insure complete transfer and uniform adhesion of the web to the creping dryer surface, a 1.5% solution of Peter Cooper T6220 creping adhesive was sprayed into the press nip between the web and the creping dryer surface. The amount of adhesive present in the web after spraying is approximately .1% by weight of the web. The nip pressure between the elastomeric roll and creping dryer was maintained at 60 p.s.i. The creping dryer contained electrical heating coils of suflicient capacity to maintain a surface temperature of 200 F., this being sufficient drying to reduce the moisture content of the sprayed web to approximately 6% by weight at the creping blade at a crepting dryer speed of 30 ft./min. The web was creped from the surface of the drying drum by a conventional creping doctor blade set at a creping angle of 5 above the radial line at the point of contact. The creped web or sheet material was wound at a speed of 26 ft./min. resulting in a foreshortening of the web in the machine direction of 15%, that is, the formation of 15% crepe in the resultant sheet material. The web possessed the following general properties:

Basis Weight 22.5 lbs./ 2880 ft. Bulk .232"/ 24 sheets (Federal Bulker) Tensile (MD) 17.0 oz./ in. (TAPPI Standard,

T220 m-60) Stretch (MD) 18.6% (TAPPI Standard, T220 m-60) TEA (MD) 1.286 kg.-m./m. (TAPPI Test, T494 su-64) Tensile (CD) 5.4 oz./in. (TAPPI Standard, T220 m-60) Stretch (CD) 10.5% (TAPPI Standard T220 m-60) TEA (CD) 0.537 kg.-m./m. (TAPPI Test, T494 su-64) Lo (MD) 3.8 cm. (Critical length-TAPPI Standard,

T-451 m60) Lo (CD) 4.26 cm. (Critical length-TAPPI Standard,

T-451 m-60) Elastomeric Bonder Content by analysis 4.0%

This sheet material was subjected to the tests described above and was found to have a TEA-to-stitfness ratio of 1.55 10- and an average calculated density throughout the thickness of the sheet under no load of 0.180 grams per cubic centimeter. A typical cross-section of this third web photographed with a linear magnification of 75 as described above for determining the average calculated density is shown in FIG. 7. It is readily apparent from the appearance of this sheet that the fibers are loosely arranged so as to provide low density and high bulk, both of which are key factors in the softness of a web. An outline of the cross-section has also been drawn on the photograph to indicate the manner in which this is done for purposes of determining the area and the average thickness of the cross-section.

EXAMPLE IV A fourth web was formed from an unrefined fiber furnish consisting of water and the following conventional papermaking pulps:

Percent Softwood bleached kraft 80 Hardwood bleached kraft 20 The following chemicals were added to the papermaking furnish in a percent by weight of the wood pulp:

0.5% Quaker 2000, a debonding agent manufactured by Quaker Chemical Company, Conshohocken, Pa., used to reduce interfiber bonding capacity,

0.03% S-243 Aminea cationic polyelectrolyte used for beater deposition of anionic materials, and

2.0% Rhoplex P339-an anionic acrylic latex used as an elastomeric bonding material.

The web was formed on a conventional Fourdrinier-type papermaking machine and transferred to a synthetic twill fabric of 72 x 60 mesh by means of a suction pickup shoe at a point where the web is carried on a stretch of the Fourdrinier wire running between two support rolls. While being conveyed on the fabric, the web was subjected to vacuum applied to the underside of the fabric of 10-11 inches mercury for a duration of 15 milliseconds. This reduced the moisture content of the wet web to approximately 70% by weight of the wet web. The web was further dried on the fabric by passing heated air at 260 F. through the web while conveying it on the fabric through a tunnel dryer. The tunnel dryer had sufficient thermal capacity to reduce the moisture content of the web to less than 10% by weight of the wet web, so that the web was now more than dry. The web was then fed through apparatus similar to that shown in FIG. 2. Thus, it was printed in a nip formed by a patterned gravure roll having a diameter of 5" and an elastomeric roll having a diameter of 5" and a neoprene cover /2" thick and having a hardness of 65 Shore A durometer. The gravure roll had a reticular pattern of interconnected distorted hexagons having two sides perpendicular to the machine direction and a pattern repeat length of 0.040". The distance from apex to apex in the cross direction was 0.080". The engraved lines of the pattern were 180-190 microns wide and approximately 46 microns deep. The engraved lines of the pattern comprised approximately 27% of the overall surface area.

The bonding material which was applied to the web by the gravure roll comprised an elastomeric bonding material consisting of a mixture of 70% Celanese 6308 and 30% Celanese 5269 by weight. This bonding material is an aqueous emulsion with a solids content of 45% and a viscosity of 250 centipoise at 25 C. as measured on a Brookfield RFV viscometer spindle #3 at 20 r.p.m. The pressure in the printing nip was controlled at p.s.i. average and the average basis weight of the sheet was increased during printing by 12.0%. The printed web was then applied to the surface of a cast iron creping dryer having a diameter of 15 inches by means of the elastomeric roll described above and with an average nip pressure of p.s.i. The creping dryer was oil heated to a surface temperature of F. and the drum surface speed was 20 ft./min. As the web was pressed to the dryer the average dryness was 84%, and upon leaving the drum, the web had an average dryness of about 94%. The web was creped from the surface of the drying drum by a conventional creping doctor blade set at an angle of 6 below the radial line at the point of contact. The creped web or sheet material was wound at a speed of 16.6 ft./min. resulting in a foreshortening in the machine direction of 20%, that is, the formation of 20% crepe in the resultant sheet material. The sheet material possessed the following general properties:

Basis Weight 23.5 lbs./ 2880 ft.

Bulk 0.354 in./24 sheets (Federal Bulker) Tensile (MD) 8.3 oz./in. (TAPPI Standard, T220 m-60) Stretch (MD) 21.8% (TAPPI Standard, T220 m-60) TEA (MD) 3.372 kg.-m./m. (TAPPI Test, T494 su-64) Tensile (CD) 5.8 oz./in. (TAPPI Standard, T220 m-60) Stretch (CD) 16.4% (TAPPI Standard, T220 m-60) TEA (D) 0.779 kg.-m./m. (TAPPI Test, T494 su-64) Lo (MD) 3.8 cm. (Critical length-TAPPI Standard,

17 Lo (CD) 4.6 cm. (Critical length-TAPPI Standard,

T-451 m-60) Elastomeric Bonder Content by analysis Beater addition 1.5% Print-bonding 5.5%

The sheet material was subjected to the tests described above and was found to have a TEA-to-stitfness ratio of 4.9l and an average calculated density throughout the thickness of the sheet under no load of 0.139 grams per cubic centimeter. A typical cross-section of this third web photographed with a linear magnification of 75 as described above for determining the average calculated density is shown in FIG. 8. It is readily apparent from the appearance of this sheet that the fibers are loosely arranged so as to provide low density and high bulk, both of which are key factors in the softness of a web. An outline of the cross-section has also been drawn on the photograph to indicate the manner in which this is done for purposes of determining the area and the average thickness of the cross-section.

The results for the four webs in Examples I and II are set forth in Table I for comparative purposes.

From the above data, it can be seen that a marked product improvement has resulted in the third and fourth webs, which constitute preferred embodiments of the present invention, with respect to properties as described which are believed to be most indicative of the softness and wiping ability of the sheet material of the present invention.

In view of the above description of specificembodiments of the method and products of the present invention, it can be seen that the present invention provides a new and improved form of sheet material which has. a combination of properties heretofore not obtainable in paper Webs. Thus, the sheet materials of the present invention are quite strong as a result of the elastorneric bonding material incorporated therein, but also are extremely soft and bulky as evidenced by the high TEA-tostilfness ratio and the low density. In addition, the sheet material of the present invention has substantial stretch in all directions in its own plane stemming from the elastomeric bonds and, in the instances where differential or patterned creping is employed, from the structure thus formed. One of the surprising features of the method of the present invention is the simplicity by which the products of the invention are formed, especially in view of some of the alternative methods utilized in the past to achieve some of these features individually.

From the above, it will be apparent that various modifications in the method and the products described in detail herein may be made within the scope of the invention. For example, the composition of the bonding material may vary quiet widely as may also the pattern in which the bonding material is applied to the web. Moreover, the particular apparatus utilized to accomplish the method of the invention is not significant. For example, a wide variety ofdiiferent means can be used for drying the web, creping the web, and applying bonding material to the web. Therefore, the invention is not to be limited to the specific details of the method and products described herein except as may be required by the following claims.

We claim:-

1. A method for making a soft, absorbent, creped fibrous sheet material, comprising the steps of mixing a fiber furnish from lignocellulosic fibers, an

elastorneric bonding material, and water,

forming a web from said fiber furnish by introducing said fiber furnish into a drainage zone in which it contacts at least one foraminous support surface which permits the removal of water therefrom, removing additional water from said web without mechanical compression until it is at least dry, adhering said web to a creping surface, and

removing said web from said surface by a creping blade.

2. A method according to claim 1, wherein said web is treated to remove additional water therefrom without mechanical compression until it is at least 95% dry before it is adhered to said creping surface.

3. A method according to clam 2, wherein said creping surface is heated, and including the step of adding moisture to said web immediately before adhering it to said creping surface to render it less than dry, and :vaporating said moisture by heat from said creping surace.

4. A method according to claim 1, including adhering said web to said creping surface with an adhesive.

5. A method according to claim 1, including pressing said web into engagement with said creping surface.

6. A method according to claim 1, including applying an adhesive to one surface of said web, and bringing said one surface into engagement with said creping surface.

7. A method according to claim 6, including pressing said web into engagement with said creping surface.

8. A method according to claim 1, including. applying an adhesive to said creping surface, and bringing said web into engagement with said creping surface.

9. A method according to claim 8, including pressing said web into engagement with said creping surface.

10.A method according to claim 1, wherein said creping surface is heated, and including the step of adding moisture to said web immediately before adhering it to said creping surface, and evaporating said moisture by heat from said creping surface.

11. A method according to claim 1, including the steps of promoting formation of said web and water removal therefrom by applying a partial vacuum to one surface of said web prior to adhering said web toa creping'surface.

12. A method according to claim 1, including applying a partial vacuum to one surface of said web while it is disposed in said drainage zone to remove water therefrom, and applying a partial vacuum to the opposite surface of said web to remove it from contact with said foraminous support surface.

13. A method according to claim 12, including-applying a partial vacuum to one surface of said web after it has been removed from contact with said foraminous support surface.

14. A method according to claim 1, including the step of passing air through said web to remove water therefrom until it is at least 80% dry prior to adhering it to said creping surface.

15. A method according to claim 1, wherein only selected areas of said web are adhered to said creping surface.

16. A method according to claim 1, including the steps of applying an adhesive to selected areas of said web, and pressing said web into engagement with said creping surface, whereby only said selected areas of said web are adhered to said creping surface.

17. A method according to claim 16, wherein said adhesive includes an elastomeric bonding agent which bonds fibers together in said selected areas of said web to a greater degree than in other areas of said web.

an amount which when added to the amount of elasto-' meric bonding agent applied to selected areas of the web is about 7% of the total dry web weight.

19. A method according to claim 1, including the steps of applying an adhesive to selected areas of said creping surface, and pressing said web into engagement with said creping surface, whereby only areas of said web which contact said selected areas are adhered to said creping surface.

20. A method according to claim 19, wherein said adhesive includes an elastomeric bonding agent which bonds fibers together in areas of said web which contact said selected areas of said creping surface to a greater degree than in other areas of said web.

21. A method according to claim 1, including initially an amount of debonding agent to said fiber furnish which is sufiicient to reduce the breaking length of a flat sheet consisting essentially of such fibers to less than800 meters. 24. A method according to claim 1, including mixing a fiber furnish from lignocellulosic fibers, an elastomeric bonding material in the amount of about 5% of the amount of lignocellulosic fibers in said fiber furnish, and water.

25. A soft, absorbent, creped fibrous web formed by deposition from an aqueous slurry, said web comprising randomly arranged, contacting lignocellulosic fibers,

and an elastomeric bonding material at substantially uniformly distributed contact points between said fibers generally throughout said web to impart structural integrity to said web, said web being of uniform density and having a basis weight of from about 10 to about 30 lbs/2880 it, a TEA-to-stitfness ratio greater than 1.50 10- and an average calculated density throughout its thickness under no load of less than 0.300 grams per cubic centimeter. 26. A soft, absorbent, creped fibrous web according to claim 25, wherein said fibers have a natural interfiber bonding capacity, resulting from treatment with a debonding agent, such that a fiat sheet consisting essentially of such fibers has a breaking length of less than 800 meters.

27. A soft, absorbent, creped fibrous web according to 20 mined pattern of higherstrength web segments spaced apart by lower strength web segments.

28. A soft, absorbent, creped fibrous Web according to claim 27, wherein the sum of the amount of elastomeric bonding material substantially uniformly distributed between said fibers and the amount of elastomeric bonding material present in said web in a predetermined pattern is from about 4% to about 7% of the dry web weight.

29. A soft, absorbent, creped fibrous web according to' claim 25, wherein additional amounts of said elastomeric bonding material are present in said web in a continuous I 30. A soft, absorbent, creped fibrous web according to claim 25, wherein said web has a TEA-to-stifi'ness ratio greater than 2.0x10- 31. A soft, absorbent, creped fibrous web according to claim 30, wherein additional amounts of said elastomeric bonding material are present in said web in a predetermined pattern of higher strength web segments spaced apart by lower strength web segments.

32. A soft, absorbent, creped fibrous web according to claim 30, wherein additional amounts of said elastomeric bonding material are present in said web in a continuous predetermined reticular pattern of higher strength web so as to define a discontinued predetermined intermittent pattern of discrete lower strength web segments.

33. A soft, absorbent, creped fibrous web according to claim 25, wherein the amount of elastomeric bonding material distributed between said fibers is from about 4% to about 7% of the dry web weight.

References Cited UNITED STATES PATENTS 2,635,045 4/ 1953 Bixler et al. 162-164 2,765,229 10/1956 McLaughlin 162-168 3,019,134 1/ 1962 Hechtman et al. 117-155 UA 3,059,313 10/1962 Harmon 156-183 3,301,746 1/1967 Sanford et a1 162-362 X 2,650,163 8/1953 'Horsey et al. 162-169 3,310,459 3/1967 Guthrie 162-169 X 3,395,708 8/1968 Hervey et a1 162-179 X p v FOREIGN PATENTS 1,951,099 4/1971 Germany 162-207 ROBERT L. LINDSAY, 1 Primary Ezraminer R. H. TUSHIN, Assistant Examiner US. Cl. x.R.

PO-IOSO (s/es) Patent No.

' Inventor a) Dated May 21, 1974 Joseph L. Salvucci, Jr. Peter N. Yiannos It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

zolumn l, in the title, change "FURNISHED" to FURNISH-;

Column 3, line 59, delete "patern of bonding material by means of" and insert therefor -bonding material to the aqueous slurry from;

Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column.

l3, l3, l4, l4, l5, l5, l5, l6,

line line line line

line

[SEAL] change "advantages" to -advantage-; change "introductoin" to -introduction--; change "and" to -an-; change "weight" to Weights-; delete the period after "Sheet";

change "give" to given-; change "webs" to -web;

change "kg.m./m. to -I g.M./M. change "kg.m./m. to -Kg.M./M. change "kg.m./m. to -Kg.-M./M. change "kg.-m./m. to --Kg.M./M. change "crepting" to --creping; change "kg.m./m. to --Kg.M./M. change "kg.m./m. to --Kg.M./M. change "kg.-m./m. to --Kg.M./M. change "kg.--m./m. to :-Kg.M./M. change "quiet" to --quite-; change "clam" to --claim--.

Signed and Sealed this Fifteenth D f March 1977 Arrest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner oj'lalent: and Trademarks

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