US3440131A

US3440131A - Strong fibrous sheet material and method of making the same

Info

Publication number: US3440131A
Application number: US382626A
Authority: US
Inventors: Shu-Tung Tu
Original assignee: United Shoe Machinery Corp
Current assignee: United Shoe Machinery Corp
Priority date: 1964-07-14
Filing date: 1964-07-14
Publication date: 1969-04-22
Anticipated expiration: 1986-04-22
Also published as: GB1112252A; DE1570179A1

Description

United States Patent Int. Cl. B32b 27/06 US. Cl. 161-53 Claims ABSTRACT OF THE DISCLOSURE A strong fibrous sheet is formed by assembling a primary mat of intermeshed fibers with a second mat of intermeshed fibers, penetrating the thickness of both of the mats with an aqueous suspension of distinct, swollen collagen fibers of microscopic size and removing the swelling water from the collagen to reaggregate the collagen fibers into a larger collagen fiber structure holding the primary mat and second mat of fibers firmly together and reinforcing the intermeshed fibers in each of the mats against displacement. The second mat may be either woven or nonwoven and provides a fiber structure resisting lengthwise and widthwise forces and providing superior surface character.

This invention relates to an improvement in strong fibrous sheet material and to a method of making the same.

In the co-pending application of Shu-Tung Tu, Ser. No. 356,067, filed Mar 31, 1964, now US. Patent 3,362,- 849, entitled Manufacture of Strong Fibrous Material there is disclosed the manufacture of a leather-like material in which lightly tanned collagen suspended in an aqueous medium as distinct, slightly swollen fibers of microscopic size is caused to penetrate an intermeshed fibrous mass, Thereafter, by altering the conditions the fibers are deswelled and associated with each other as a larger collagen fiber structure extending through the fibrous mass and associated with the fibers of the mass to reinforce them against displacement. The reinforced fiber masses so produced are strong and possess many of the characteristics of leather. However, it has been found that unless special precautions are observed, an undesirable surface character may develop in a finished surface of such a fibrous mass when the mass is subjected to stretching.

It is an object of the present invention to provide an improved leather-like sheet material possessing superior surface characteristics and a novel method of making same.

To these ends and in accordance with a feature of the present invention, a special fiber relation is provided at at least one surface of the intermeshed fiber mat, and a suspension of slightly swollen collagen fibers is caused to penetrate the inter-fiber spaces of the intermeshed fiber mat. It is found that on altering the conditions to desWell the fibers and associate them as a larger collagen fiber structure, the intermeshed fibers are firmly held as a unitary strong sheet.

In accordance with a further feature of the invention the special fiber relation at the surface of the mat is provided by disposing a separate mat or layer of intermeshed fibers on a surface of the primary mat and penetrating interfiber spaces with collagen fiber. It is found that the collagen fiber structure extending through both mats is effective to hold the mats firmly together so that the special characteristics of one cooperate with and aug- 3,440,131 Patented Apr. 22, 1969 "ice ment the properties of the other intermeshed fiber mat.

Superior surface character is obtained according to the present. invention by providing fibers, preferably fine denier fibers, at least at and adjacent one surface of the intermeshed fiber mat extending substantially parallel to the surface and oriented to resist lengthwise and widthwise forces exerted on the mat. Needling, commonly employed to give dimensional stability and delamination resistance to mats of nonwoven fibers, disrupts the surfaceparallel relation of the fibers and it has been found important that the surface fibers be in unneedled, or at most very lightly needled relation. This relation can be used in the present situation because of the desirable fiber holding action of the collagen structure formed in the mat which resists delamination.

Intermeshed fiber mats which can be employed include single unneedled or very lightly needled mats which may be laid down by carding, air laying or otherwise depositing fibers in essentially surface parallel relation. Preferably, however, two or more mats are laid up in face to face relation. This provides greater flexibility and convenience in operation. The primary or base mat may be of different character from the fiber layer forming the surface and difiiculties arising where the mat is needled are in large measure compensated for by an unneedled fiber layer forming the surface.

The intermeshed fiber mats, usually in sheet form may be selected from a wide variety of woven or nonwoven fibrous materials. Ordinarily, a nonwoven fiber mat is preferred for the first or base layer of intermeshed fiber because of the great variety of thicknesses, densities and openness to penetration by collagen fiber suspensions which are obtainable in such nonwoven mats. These mats may be composed of various fibers or mixtures of fibers, usually textile fibers, including nylon, polyacrylic ester fibers (Orlon), polyester fibers (Dacron), polypropylene fibers, wool, extruded cellulosic fibers such as viscose or cellulose acetate and others. For special purposes, a mat of longer collagen fibrous material which has been treated, for example by chrome tanning or other treatment to decrease its affinity for water may be used. Cotton fiber mats, preferably treated to decrease the affinity of the cotton for water are also usable. As discussed at greater length in the copending application above-referred to the intermeshed fiber material used in the first or base layer may have relatively large interstitial spaces between fibers. Optionally, the fibers in the mat may be in the relation produced by needling in which fibers are forced in a direction transverse to the plane of the mat to improve resistance to delamination.

Unneedled fiber mats, particularly mats of crimped fibers appear to offer special advantages as a first or base layer of mat. The mat takes up collagen fiber from suspension with great uniformity because of the absence of the irregularities created by needling; and crimped fibers resist excessive compaction of the mat by the pressure of the collagen fiber suspension being forced into the mat. Also it appears that the crimped fiber has a more effective collagen fiber entrapping action than uncrimped fiber so that a high collagen content product is obtained. Also the collagen fiber entrapped in such a mat has a superior mechanical locking action on the crimped fiber so that the product has greater integrity. It appears that a rate of crimping corresponding to at least about 5 crimps per inch is elfective to give this result and higher crimped fiber is useful.

Without regard to whether the mat is crimped or uncrimped fiber, it is noted that because of its water content, the volume occupied by collagen fiber after removal of the water is much less than occupied by the penetrating fiber suspension so that in the relatively large openings created in a needled mat by the action of the needles, there is a tendency for development of fiber poor or fiberfree spaces within the needle craters after removal of water, while the unneedled fiber mat is free from such void spaces. A still further advantage is that since in a needled mat fibers are displaced in a direction normal to the mat by the action of the needles and these displaced fibers resist compression of the mat, when a needled mat is dried with resultant loss in volume of the collagen, the mat cannot be compacted in the areas surrounding the needle holes and further voids develop.

Satisfactory fiber density and relation have been found in nylon fiber mats having densities of the order of 4 oz. per sq. yd. at a thickness of 0.15" and 6 oz. per sq. yd. at a thickness of 0.175". Another highly satisfactory mate-rial is a polypropylene fiber mat having densities of 7 oz. per sq. yd. and a thickness of 0.2". It is preferred that the fibers be relatively fine, e.g. in the range of from 1 to denier with 3 denier being satisfactory.

The second intermeshed fiber layer may be a woven or nonwoven sheet. The fibers in this layer may be up to 5 denier, but for best surface appearance it is preferred to use finer denier, suitably 0.5 to 3 denier, than the fibers in the base layer. Because of the high strength available with minimum thickness it is often desirable that this layer be composed of continuous threads either of twisted staple fibers or monofilaments with threads disposed in line with expected stresses to be applied to the finished material. A simple weave comparable to the weave of a batiste fabric providing threads extending at right angles to each other has proved satisfactory. However, a comparable result can be obtained using a sheet of fibers lying generally parallel to the faces of the sheet and oriented to provide strength both lengthwise and widthwise of the sheet as in random orientation or with one set or layer of fibers, e.g. a carded layer extending in one direction and another set or layer of fibers extending in a direction, suitably 90 away from the direction of the first set or layer of fibers.

Although the fine woven fabric offers a high degree of strength with a minimum thickness, special advantages are also obtainable through the use as a second layer of a nonwoven, preferably unneedled mat, suitably of different fibers from the first or base mat. Thus, as indicated above, the second layer may be composed of fibers of finer denier such as 0.5 to 3.0, or the fibers may be of a material cooperating more effectively with a finish to be applied to the final sheet. For example, nylon fibers may be more compatible with various finishes than would, for example polypropylene fibers where the base is composed of polypropylene fibers.

It has been found that simply associating the base mat with a second layer of intermeshed fibers is all that is required and it is not necessary that adhesives or mechanical fastening such as a needling treatment be used to secure the base sheet and second sheet together. Also more than two layers of intermeshed fibers may be assembled in face to face relationship and the layer of fibers lying generally parallel to the faces of the sheet may be a layer other than one of the surface layers.

The suspension if microscopic lightly tanned collagen fibers used in the present process may be that described in greater detail in the application of Tu referred to above. Briefly, the suspension is prepared by beating in water the collagen source, for example skin or hide, under conditions which limit swelling of the collagen to reduce it to fibers of microscopic size suspended in the water in a manner allowing the fibers relatively free movement in the suspension. The condition is markedly different from that referred to as colloidal in which collagen is reduced to a swollen viscous mass. In the preferred suspension, the collagen material is lightly tanned, for example to an extent comparable to l/ 10% to preferably not over 3% of combined aldehyde such as formaldehyde o-r glyoxal based on the dried weight of the skin materia and the resulting suspension is adjusted to a pH relative to the isoelectric range of the collagen fibers of the suspension. It is noted that according to a recent discovery certain additives appear to be effective to allow at least some impregnation of the collagen fiber suspension even in the isoelectric range although penetration ability falls off sharply as the range is approached or entered. For impregnation, the suspension comprises preferably from about 1% to about 5% by weight of fiber solids based on the weight of the suspension, and the collagen fibers are distinct and noncolloidal with a length of from about 0.001 mm. to not over about 4 mm. and preferably not over about 1 mm.

Because of the wide variation in properties of collagen source material and the nature of the fibers in suspension resulting from the beating operation, the suspension after adjustment to a pH ordinarily either above or below the isoelectric range may be calibrated for cooperation with the combined fiber sheets to be used by filtration through a trial mat of the intermeshed fibers. In general it is preferred that the relation of the suspension and the fiber mat be such that 600 ml. of the suspension will pass through a 6" diameter circular section in from A minute to about 2 minutes under a vacuum of about 10" of mercury.

Penetration ability increases as the pH departs from the isoelectric range so that a suspension having inadequate penetration characteristics, for example requiring over about two minutes for penetration may be able to be brought to a desired penetration value by adjusting its pH to a point farther removed from the isoelectric range. Conversely, a suspension having a high penetration ability and inadequate or undesirably low retention within the fiber sheet may be improved as to these latter properties by adjusting the pH to a point closer to the isoelectric range. Also the rate of penetration is greater with lower concentrations of fibers in the suspension, and penetration may be improved by diluting the suspension. After adjustment of the suspension to a pH and concentration giving a desired penetration value for the selected fiber mat, penetration of the mat for making of the final product is begun. This penetration is preferably effected by using vacuum or pressure for forcing the suspension into the assembled fibers as supported on a screen. In this penetration step, where there are two mats, the mat presenting surface fibers parallel to the surface may be either above or below the base sheet. That is, it may be on the side to which the collagen fiber suspension is applied or it may be on the side opposite that to which the collagen fiber suspension is supplied. In either case, the collagen fibers are caused to impregnate the assembly of sheets to provide a substantial concentration of collagen fiber slurry at least at the interface between the two sheets and in the sections of the base sheet and second sheet adjacent the interface. Optionally, the assembly of intermeshed fiber sheets may be treated more than one time with a collagen fiber suspension. For example, a collagen fiber suspension having good penetrating ability may be used for a first treatment and thereafter the assembly may be treated with a suspension having a lower penetration ability. If desired the collagen fiber suspension may be applied from alternating sides.

Deswelling of the collagen fibers within the intermeshed fiber mass may be effected by reducing the acid or alkali content of a collagen fiber material. This action may be secured by extracting the fibrous mass with distilled water or with a water-miscible volatile organic solvent such as acetone or other ketones and lower alcohols such as methanol, ethanol and isopropanol. Alternatively, the fiber base may be treated with an aqueous solution of a buffer salt such as an acetate or phosphate buffered system to bring the pH to a value, for example in the range of about 3.5 to about 6, at which reaggregation of the collagen microscopic fibers will occur. Reaggregation may also be effected by treating the fiber batt with a aqueous ammonium sulfate solution which effects a deswelling of the fibers.

The fiber mat assembly is compacted and reduced in thickness in the course of penetration by the suspension and reaggregation of the collagen material so that, for example, starting with a mat assembly having an initial thickness of 0.19, after penetration by suspension and reaggregation of the collagen material, the thickness may have reduced to about .03. This reduction in thickness is due in considerable measure to the action of the suspension in being forced into the mat assembly. A further action which influences the reduction in thickness is the pulling together of the collagen material by water bonding; and this factor may range from very slight where water is extracted from the sheet by solvent to relatively large where a substantial portion of the water is removed by evaporation.

The sheet material is preferably subjected to tanning with mineral tanning agents such as chrome tanning liquors or with vegetable tanning agents or with combination tanning agents. Because of the collagen deswelling action of mineral tanning agents such as chrome tanning agents it is possible to effect both reaggregation and tanning with such agents. Conventional leather tanning procedures may be used and the tanning may be carried out either in an aqueous tanning medium or a solvent type tanning medium.

After tanning the sheet material will be washed and manually pressed to remove excess water. Ordinarily the sheet is subjected to a treatment to introduce a plasticizing or softening agent into it as by fat liquoring or pref erably by immersing it in an acetone solution containing for example, 4% by weight of oleic acid. After this treatment, the sheet is dried in air and may be subjected to various finishing treatments including fat liquoring, resin treatments, staking and so on.

For use, the surface of the sheet may be coated with leather finishes or resinous and/or waxy material. One finish for the sheet material involves the application to the surface of the sheet of certain soluble, 800 type, nylons (which are alkoxy derivatives of type 66 nylon) which are believed to contain groups reactive with certain groups of the collagen material. Formation of this coating may involve a deposition as by spraying of a solution of a suitable nylon in a 70% isopropanol solution, this solution suitably containing pigment to give the desired color. After the solution is applied the sheet may be dried, subjected to a needling treatment, and thereafter embossed or plated. The surface so obtained is a soft, strong and flexible film closely resembling the grain surface of leather and firmly adherent to the sheet.

The following examples are given to aid in understanding the invention and it is to be understood that the invention is not restricted to the particular materials or conditions set forth in the examples.

EXAMPLE I A needle loomed nonwoven 3 denier polypropylene fiber mat having a weight of 7.5 ounces per square yard was laid up in face to face relation with a nonwoven cotton fiber mat having a weight of about 2 ounces per square yard. The associated fiber mats were disposed on a filter bed provided with means for applying suctionfthe cotton fiber mat being uppermost.

An aqueous dispersion of collagen fibers of microscopic size was prepared by tanning hide material with formaldehyde to give a formaldehyde content of about 0.20% by weight and beating the hide material together with water in a beater similar to a paper beater at a pH of about 5. The collagen fibers thus produced had a length of about 0.2 to 1 mm. The suspension was diluted to bring the 6 solids content to about 1% and the pH was adjusted to 3.5.

A quantity of the above-prepared fiber suspension was deposited on the associated fiber mat on the filter bed as a layer of uniform thickness and suction was applied to pull the suspension into the associated mat fiber structure. The vacuum applied was 29 inches and after one minute the associated fiber structure of the mat was filled with the suspension.

The mat with collagen fiber in it was removed from the filter bed and replaced with the cotton fiber side down. A further quantity of the same collagen fiber suspension at pH 2.5 was deposited on the mat and pulled in by suction. Two portions of acetone were applied successively to the sheet on the filter bed and sucked through to remove water and effect reaggregation of the collagen fiber in the mat.

The resulting sheet material after removal from the filter bed and evaporation of the acetone had a collagen content of about 43.3% by weight based on the total weight of mat fibers and collagen.

The impregnated mat then was placed in a chrome tanning bath containing 1% by weight chromium calculated as Cr O and 2% by weight of sodium formate. After standing overnight in this tanning bath, the sheet was removed, washed in warm tap water for six hours, pressed between filter paper to remove further water and disposed in a fat liquor bath. After fat liquoring the sheet was removed and air dried. The sheet resembled a chrome tanned leather in which the surface on which the cotton fiber mat was disposed had a fine uniform appearance resembling a grain layer.

EXAMPLE II A needle loomed nonwoven 3 denier polypropylene fiber mat having a weight of 6.6 ounces per square yard was laid up in face to face relation with a square woven cotton fiber cloth (Batiste) having a thread count x 98. The fiber mat and the cloth were disposed on a filter bed provided with means for applying suction, the 3 denier fiber mat being uppermost.

An aqueous disperson of collagen fibers of microscopic size was prepared by tanning hide material with formaldehyde to give a formaldehyde content of about 0.15% and beating the hide material in a heater similar to a .paper beater. The collagen fibers thus produced had a length of about 0.2 to 1 mm. The suspension was diluted to bring the solids content to about 2% and and the pH was adjusted to 3.18.

A quantity of the above-prepared fiber suspension was deposited on the associated fiber mat and cloth on the filter bed as a layer of uniform thickness and suction was applied to pull the suspension into the associated mat fiber structure. The vacuum applied was 25 inches and the associated fiber structure of the mat was filled with the suspension.

After impregnation, the impregnated associated mat was removed from the filter bed and while still wet with water was placed in a chrome tanning bath containing 1% by weight chromium calculated as Cr O and 2% by weight of sodium formate, the bath having a pH of about 4.2. After standing 6 hours in this tanning bath, the sheet was removed, washed in warm tap water for 6 hours, pressed between sheets of filter paper to remove further water and disposed in a fat liquor bath. After fat liquoring the sheet was removed and air dried. The sheet resembled a chrome tanned leather in which the surface on which the cloth was disposed had a fine uniform appearance resembling a grain layer.

EXAMPLE III A needle loomed nonwoven 3 denier polypropylene fiber mat having a weight of 7.5 ounces per square yard was laid up in face to face relation with a nonwoven 1.5 denier polypropylene fiber mat having a weight of 1.48

ounces per square yard. The associated fiber mats were disposed on a filter bed provided with means for applying suction, the 3 denier fiber mat being uppermost.

An aqueous dispersion of collagen fibers of microscopic size was prepared by tanning hide material with formaldehyde to give a formaldehyde content of about 0.2% and beating the hide material in a beater similar to a paper beater. The collagen fibers thus produced had a length of about 0.2 to 1 mm. The suspension was diluted to bring the solids content to about 1% and the pH was adjusted to 3.34.

A quantity of the above-prepared fiber suspension was deposited on the associated fiber mat on the filter bed as a layer of uniform thickness and suction was applied to pull the suspension into the associated mat fiber structure. The vacuum applied was 29 inches and after about minutes the associated fiber structure of the mat was filled with the suspension.

After impregnation, the impregnated associated mats were removed from the filter bed and dehydrated by immersion in acetone. At this stage the sheet was found to have a collagen content of 47% by weight based on the combined weight of the mat fibers and collagen fibers. The sheet was placed in a chrome tanning bath containing 5% by weight chromium calculated as Cr O and 1% by weight of sodium formate, the bath having a pH of about 4.0. After standing 2 hours in this tanning bath, the sheet was removed, drained and allowed to stand overnight. The sheet was washed in tap water for two hours, pressed between filter paper to remove further water and disposed in a fat liquor bath. After fat liquoring the sheet was removed and air dried. The sheet resembled a chrome tanned leather in which the surface on which the 1 denier fiber mat was disposed had a fine uniform appearance resembling a grain layer.

EXAMPLE IV A nonwoven unneedled mat of 1 /2 denier polypropylene fiber having about crimps to the inch and weigh ing about 5.66 ounces per square yard was disposed on a filter bed provided with means for applying suction. An aqueous dispersion of collagen fibers of microscopic size as in Example II was diluted to bring the solids content to about 2% and the pH was adjusted to about 3.2. A quantity of the fiber suspension was deposited on the fiber mat and suction was applied to pull the suspension into the mat fiber structure.

After impregnation, the impregnated mat was treated while on the filter bed with a chrome tanning bath containing 1% by weight chromium calculated as Cr O and 2% by Weight of sodium formate, the bath having a pH of about 4.2. After the treatment of the mat with the tanning agent, the sheet was allowed to stand overnight, removed from the filter bed, washed in warm tap water for six hours and thereafter fat liquored and dried. The sheet had properties comparable to a chrome tanned leather material and had a fine uniform appearance resistant to the development of surface irregularities when stripped, On analysis it was found that the product had about a 65% collagen content based on the combined weight of polypropylene fiber and collagen fiber.

EXAMPLE V A needle loomed nonwoven 3 denier polypropylene fiber mat having a Weight of about 7 ounces per square yard was disposed on a filter bed provided with means for applying suction. On the exposed face of this fiber mat there was laid a mat of unneedled 4.6 denier nylon uncrimped fiber having a weight of about 1 ounce per square yard. An 80 mesh polypropylene fiber screen was disposed over the surface of the unneedled mat and a quantity of the fiber suspension described in Example IV was deposited on the surface of the screen covering the associated fiber mats on the filter bed. Suction was applied to pull the suspension into the associated mat fiber structure.

After impregnation, dried acetone was supplied to the surface of the mat in successive portions to dry the mat. At this stage the sheet was found to have a collagen content of 50% by weight based on the combined weight of the mat fibers and collagen fibers. The associated mat and screen were removed from the filter bed and placed in a chrome tanning bath containing 1% by weight chrome calculated as Cr O and 2% by weight of sodium formate, the bath having a pH of about 4.2. The polypropylene screen was stripped from the sheet and the sheet allowed to stand overnight in the tanning bath. Thereafter, the sheet was removed, washed in warm tap water for six hours, pressed between sheets of filter paper to remove further water and disposed in a fat liquor bath. After fat liquoring the sheet was removed and air dried. The sheet had properties comparable to a chrome tanned leather and was resistant to the development of surface irregularities on the surface corresponding to the unneedled fiber layer.

EXAMPLE VI An unneedled nonwoven 2.3 denier uncrimped nylon fiber mat having a weight of 1 oz. per square yard was laid up in face to face relation with an unneedled mat of a blend of 3 denier high crimp nylon fiber and 3 denier polypropylene fiber, the fibers being employed in the ratio of 70 parts by weight of nylon to 30 parts by weight of polypropylene and the mat having a weight of about 4 ounces per square yard. The associated fiber mats were disposed on a filter bed provided with means for applying suction with the 1 ounce per square yard mat uppermost; and an mesh polypropylene fiber screen was disposed over the exposed surface of the associated mats.

An aqueous dispersion of collagen fibers of microscopic size was prepared by tanning hide materal with formaldehyde to give a formaldehyde content of about 0.4% by weight and beating the hide material together with Water in a beater similar to a paper beater at a pH of about 5. The collagen fibers thus produced had a length of from about 0.2 to about 1 mm. The suspension was diluted to a solids content of about 1% and the pH was adjusted by addition of sulfuric acid to about 2.6.

A quantity of the fiber suspension was deposited on the screen-covered surface of the fiber mats and suction was applied to pull the suspension into the associated mat fiber structure.

After impregnation, dried acetone was supplied to the surface of the mat in successive portions to dry the mat. At this stage the sheet was found to have a collagen content of 52% by weight based on the combined weight of the mat fibers and collagen fibers. The associated mat and screen were removed from the filter bed and tanned as in Example V, the polypropylene screen being stripped from the sheet. Thereafter, the sheet was removed from the tanning bath, washed in warm tap water for six hours, pressed to remove further water and disposed in a fat liquor bath. After fat liquoring the sheet was removed and air dried. The sheet had properties comparable to a chrome tanned leather and was resistant to the development of surface irregularities when stretched.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. The process of forming a strong fibrous sheet material which comprises the steps of providing a primary mat of intermeshed fibers disposing a second mat of intermeshed fibers on a surface of said primary intermeshed mat, penetrating the thickness of both of said mats of intermeshed fibers with an aqueous suspension of distinct swollen collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

2. The process of forming a strong fibrous sheet material which comprises the steps of providing a primary mat of intermeshed fibers, disposing a second mat of intermeshed fibers on a surface of said primary mat, the fibers of said second mat at least at and adjacent the free surface of said mat being arranged substantially parallel to said free surface and oriented to resist lengthwise and widthwise forces exerted on said mat, penetrating the thickness of both of said mats of intermeshed fibers with an aqueous suspension of distinct swollen collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

3. The process of forming a strong fibrous sheet material which comprises the steps of providing a primary mat of intermeshed textile fibers, disposing a layer of interwoven textile fibers on a surface of said primary intermeshed mat, penetrating the thickness of both said primary mat and said layer of interwoven fibers with an aqueous suspension of distinct swollen collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said layer of interwoven fibers firmly together in face to face relation and reinforcing the fibers in each of said mats against displacement.

4. The process of forming a strong fibrous sheet material which comprises the steps of providing a primary mat of intermeshed textile fibers of from 1 to denier, said fibers being crimped at least to the extent of about 5 crimps per linear inch and said mat being substantially free from textile fibers and portions of textile fibers oriented normal to the surface of said mat, but being oriented to resist lengthwise and widthwise forces exerted on said mat, disposing a second mat of intermeshed textile fibers of from 0.5 to 3 denier on the surface of said primary mat, the fibers of said second mat at least at and adjacent the free surface of said mat being arranged substantially parallel to said free surface and oriented to resist lengthwise and widthwise forces exerted on said mat, said second mat being substantially free from fibers and portions of fibers oriented normal to the surface of said mat, penetrating the thickness of both of said mats of intermeshed fibers with an aqueous suspension containing from about 1% to about 5% by weight of distinct swollen collagen fibers of microscopic size, said collagen fibers having a content of combined formaldehyde of from about 0.1% to about 3.0% based on the dry weight of said fibers, said collagen fiber suspension being caused to penetrate said mats in quantity sufficient to associate with said mat at least about 50% of collagen by weight based on the combined weight of the collagen and mat fibers, and removing the swelling Water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

5. The process of forming a strong fibrous sheet which comprises the steps of providing a primary mat of intermeshed fibers of from 1 to 5 denier, said fibers being crimped at least to the extent of about 5 crimps per linear inch and said mat being substantially free from fibers and portions of fibers oriented normal to the surface of said mat, but being oriented to resist lengthwise and widthwise forces exerted on said mat, disposing a layer of interwoven textile fibers on a surface of said intermeshed mat, penetrating the thickness of said primary mat and said layer of interwoven textile fibers with an aqueous suspension of distinct swollen collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said layer of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in said mat and layer against displacement.

6. The process of forming a strong fibrous sheet which comprises the steps of providing a primary mat of intermeshed fibers of from 1 to 5 denier, said fibers being crimped at least to the extent of about 5 crimps per linear inch and said mat being substantially free from fibers and portions of fibers oriented normal to the surface of said mat, but being oriented to resist lengthwise and widthwise forces exerted on said mat, disposing a layer of interwoven textile fibers on a surface of said intermeshed mat, penetrating the thickness of said primary mat and said layer of interwoven textile fibers with an aqueous suspension containing from about 1% to about 5% by weight of distinct swollen collagen fibers of microscopic size, said collagen fibers having a content of combined formaldehyde from about 0.1% to about 3.0% based on the dry weight of said fibers, said collagen fiber suspension being caused to penetrate said mat and said layer in quantity sufiicient to associate with said mat and layer at least about 50% of collagen by weight based on the combined weight of the collagen and the fibers of said mat and layer, and removing the swelling water from said collagen to reaggregate said collagen fibers into a larger collagen fiber structure holding said primary mat of fibers and said layer of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in said mat and layer against displacement.

7. A strong fibrous sheet material which comprises a primary mat of intermeshed textile fibers, a second mat of intermeshed textile fibers on a surface of said primary mat and a collagen fiber structure extending through the thickness of both of said mats of intermeshed fibers holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

8. A strong fibrous sheet material comprising a primary mat of intermeshed fibers, a second mat of intermeshed fibers on a surface of said primary mat, the fibers of said second mat at least at and adjacent the free surface of said mat being arranged substantially parallel to said free surface and oriented to resist lengthwise and widthwise forces exerted on said mat and a collagen fiber structure extending through the thickness of both of said mats of intermeshed fibers holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

9. A strong fibrous sheet material which comprises a primary mat of intermeshed textile fibers of from 1 to 5 denier, said fibers being crimped at least to the extent of about 5 crimps per linear inch and said mat being substantially free from textile fibers and portions of textile fibers oriented normal to the surface of said mat, but being oriented to resist lengthwise and widthwise forces exerted on said mat, a second mat of intermeshed textile fibers of from 0.5 to 3 denier on a surface of said primary mat, the fibers of said second mat at least at and adjacent the free surface of said mat being arranged substantially parallel to said free surface and oriented to resist lengthwise and widthwise forces exerted on said mat, and a collagen fiber structure extending through the thickness of both of said mats of intermeshed fibers holding said primary mat of fibers and said second mat of fibers firmly together in face to face relation and reinforcing the intermeshed fibers in each of said mats against displacement.

10. A strong fibrous sheet material which comprises a primary mat of intermeshed textile fibers of from 1 to 5 11 12 denier, said fibers being crimped at least to the extent References Cited of about 5 crimps per linear inch and said mat being UNITED STATES PATENTS substantially free from fibers and aoruons of fibers 2,802,767 8/1957 Mightonl orlented normal to the surface of sa1d mat, but being 2908 O6 4 10/1959 Lauterback et a1 28 72 oriented to resist lengthwise and widthwise forces exerted 5 3:223:551 12/1965 Tu on said mat, a layer of interwoven textile fibers on a surface of said primary intermeshed mat holding said ROBERT F. BURNETT, Primary Examiner.

primary mat of fibers and said layer of interwoven textile WILLIAM POWELL, Assistant Examiner.

fibers firmly together in face to face relation and reinl0 forcing the intermeshed fibers in said mat and layer US. Cl. X.R.

against displacement 161-81, s2, 88, 154, 155, 156, 59; 117-440; 156148