US3914501A

US3914501A - Porous products and processes therefor

Info

Publication number: US3914501A
Authority: US
Inventors: Walter A Miller; Richard D Jenkinson
Original assignee: Union Carbide Corp
Current assignee: Viskase Corp
Priority date: 1969-06-27
Filing date: 1973-05-17
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21

Abstract

The invention relates to non-woven fiber structures in which the fibers are ultra-fine, and are inter-bonded by fusion at a plurality of points in said structure. Such fibers define open and unfilled pores which are interconnected and extend from surface to surface of the sheet. Such structures are produced by extruding a blend of immiscible, thermoformable, fiber-forming polymers into a shaped article, reducing said shaped article into a sheet structure, heating the sheet structure to a temperature to fuse at least a portion of the ultra-fine fibers therein, and extracting at least a portion of the ultra-fine fibers from the sheet to render it porous. Diverse products are produced such as synthetic leather, apparel fabrics, and the like.

Description

United States Patent [191 Miller et al.

[4 Oct. 21, 1975 POROUS PRODUCTS AND PROCESSES THEREFOR Ill.

[73] Assignee: Union Carbide Corporation, New

York, N.Y.

[22] Filed: May 17, 1973 [21] Appl. No.: 361,149

Related US. Application Data [63] Continuation of Ser. No. 837,302, June 27, 1969,

abandoned.

[56] References Cited UNITED STATES PATENTS 3,016,599 1/1962 Perry, Jr. 161/169 Miller 161/DIG. 2 Fukushima 161/D1G. 2

Primary ExaminerGeorge F. Lesmes Assistant Examiner-Ellis P. Robinson Attorney, Agent, or FirmG. A. Skoler [57] ABSTRACT The invention relates to non-woven fiber structures in which the fibers are ultra-fine, and are inter-bonded by fusion at a plurality of points in said structure. Such fibers define open and unfilled pores which are interconnected and extend from surface to surface of the sheet. Such structures are produced by extruding a blend of immiscible, thermoformable, fiber-forming polymers into a shaped article, reducing said shaped article into a sheet structure, heating the sheet structure to a temperature to fuse at least a portion of the ultra-fine fibers therein, and extracting at least a portion of the ultra-fine fibers from the sheet to render it porous. Diverse products are produced such as synthetic leather, apparel fabrics, and the like.

1 Claim, No Drawings POROUS PRODUCTS AND PROCESSES THEREFOR This is a continuation, of application Ser. No. 837,302 filed June 27, 1969, now abandoned.

This invention is directed to a novel process for making a wide variety of novel porous nonwoven fibrous structures. Moreover, encompassed within such a variety of nonwoven structures is synthetic leather possessing characteristics which are remarkably similar to natural leather.

Nonwoven fabrics can be made by a variety of methods, such as carding, garnetting, air-laying, wet-laying, or melt spinning and exploding mono-filaments or multi-filaments which are layed down in a random pattern to form a mat.

These nonwoven fabrics are relatively useless until the fibers therein are inter-bonded. This may be achieved by frictional engagement of the fibers with one another, such as, is achieved by needle punching or they may be inter-bonded through the use of an adhesive.

In order to provide such nonwoven products with useful tear and tensile strengths, it is necessary to effect a substantial amount of inter-bonding and this results in stiffening the structure so that it lacks the drape, hand, and other tactile properties normally associated with woven and knitted fabrics. As a result, these nonwoven fabrics have not significantly penetrated the markets in which woven and knitted fabrics are employed.

In addition, there are presently in the market place a number of substitute leather materials which are being used for making shoe uppers, as well as gasket materials. These materials are called substitute leather because they have a surface which resembles leather and to the touch of one s finger tips, they feel like leather, much like the leathery feel of expanded vinyl films. However, they do not have the total tactile qualities of leather and when such a substitute material is freely rolled in ones hand, they possess a plastic feel.

These substitute leathers are plastic composites of at least two layers. The bottom layer is typically a relatively costly nonwoven mat of staple fibers and the other layer, typically the surface layer, is made of a microporous film. These microporous films are typically made from solutions or dispersions of a resin and a liquid non-resin. When the non-resin is removed from the resin or nonsolvent for the resin is added, the resin is coagulated, rinsed and dried to produce a microporous film. Such coagulation is believed to produce fused particles of the resin. The resins presently employed are polyurethane elastomers. The surface layer may be directly bonded to the nonwoven bottom layer by applying the solution or dispersion of resin and non-resin to the surface of the nonwoven layer followed by coagulation, rinsing and drying. Another approach involves coating the solution or dispersion on a fabric such as a woven scrim, followed by coagulation and adhesive bonding of the underside of the coated fabric to the bottom layer. As a rule, the non-woven mat layer is separately impregnated with a resin to enhance bonding of the fibers therein. The nonwoven mat may also be needled punched to increase its density and strength. Shrinking the nonwoven mat also increases its density.

The formation of such microporous films is most difficult because it is achieved by the deposition of a liquid resin onto a solid surface followed by the steps of 2 coagulation, rinsing and drying. The resulting product, that is, the dry microporous film, can easily contail craters, pinholes, orange peeling, variations in thickness, streaks on the surface, and many other objectionable characteristics unless considerable, if not extreme, care in manufacture is employed.

There is described also other methods for forming substitute leather products. Though these products are also laminates, their surface layer is relatively thin and provides the aesthetic qualities of leather. The surface layers are formed by incorporating a soluble salt into a polymeric layer followed by leaching the salt out to leave voids in the layer. lf sufficient salt is employed, the layer can be porous to air. However, such layers are difficult to produce in a continuous basis to provide uniform and consistent quality products. lnvariably the surface layer is of uneven uniformity.

Another technique mentioned in the literature involves blending two immiscible polymers and extruding them from an orifice into fibrous structures. Then these fibers are apparently disintegrated in water and lapped on a screen to form a thin film. Then one of the polymers is dissolved with a solvent, which also generally contains a water soluble salt therein, to destroy one of the polymers to convert it into an adhesive to bond the remaining fiber component into a plastic sheet. None of the polymers are removed from the lap so the resulting adhesively bonded lapped sheet contains a substantial amount of the adhesive polymer formed by dissolution by the solvent. By evaporation of the solvent with or without dissolution from the lapped sheet of the soluble salt, there is allegedly formed a porous film. The resulting film should possess a coarse surface and to remove such coarseness, the surface must be heat finished and this will adversely affect the films porosity and give it a plastic appearance. The film is relatively thin but it is stated to possess the tactile qualities of leather. However, though such allegations are magnanimous, they fail to take into consideration that leather for footwear seldom has a thickness less than 20 mils, a thickness beyond the apparant capabilities of this process for producing a uniform, continuous sheet of porous product. This thin film therefore will require lamination to another substrate to provide the thickness and body required for a substitute leather.

These laminated substitute leather products are susceptable to delamination at the interface of the layers or in the proximity of such interface, thus, severly limiting the degree of flexing to which such product can be put. In normal flex tests used by the leather industry, such substitute leathers generally do not compare favorably in flex life with reasonably good quality leather. It is believed that the layered homogeneous nature of leather is the reason for its better flex life.

There are descriptions in the prior art of substitute leathers made from needle punched nonwoven fiber mats. These products have very coarse surfaces which only with great difficulty and expense can be converted to have the appearance, physical and tactile properties of leather. It is believed that these products represent the scheme of an idea which resulted in the laminated structures which are in the market place today but of themselves are not or cannot reasonably be considered a substitute for leather.

Moreover, the needle projections in the nonwoven mat which bind the staple fibers therein serve to create very dense points within the mat. The non-needled sections are significantly less dense. As a result, the product possesses an undesirable flex characteristic in that the roll of the flex is very coarse and irregular. A substantial amount of needling or a lot of resin binder is required in the mat to minimize this effect. This effect is believed to be the cause of internal failure of the nonwoven mat which typically shows up during limited flexing of such type of mats by conventional methods. Thus, a product made from needled nonwoven mat does not possess homogeneity in the mat layer and has an essentially irregular density throughout. Of course, the gross effect of needling, so long as the needle patterns are regular, achieves a regular and relatively uniformly dense structure. However, in use, leather isnot worn throughout its gross structure, but at isolated points, thus, where such irregularities exist in the substitute product, there exists locales wherein fractures occur in the material.

This invention relates to the manufacture of unitized nonwoven fibrous sheet material which can be employed in diverse areas of use ranging from gaskets, dialytic membranes, battery separators, to textile fabrics and synthetic leather. This invention is particularly directed to the manufacture of a porous, fibrous sheet which can be made to possess the tactile qualities of woven and knitted fabrics, the drape and roll of woven and knitted fabrics, and which can be made, on the other hand, to possess the full tactile qualities of leather, such that it can be classed not only a substitute for leather but a synthetic leather. Such a synthetic leather is microporous, in that the pores therein are not visible to the eye but under microscope are visible such as is the case of the polished surface of leather.

This invention is directed to a sheet-like structure containing ultra-fine, thermoformable fibers which are interbonded by fusion at a plurality of points where such fibers contact. These fibers define open and unfilled pores which are inter-connected and extend from surface to surface of the sheet. The ultra-fine, thermoformable fibers desirably have a denier of less than about 0.5, and preferably, these fibers are drawn, most preferably molecularly oriented as well, and possess a cross-sectional diameter normal to their elongated shape of less than about 5 microns.

The fiber characteristics in the sheet-like structure are selected with consideration to the type of product desired. The density of the sheet, the thickness of the sheet, the thickness and length of the fibers, the tensile modulus and other properties, all bear on the eventual properties of the sheet-like structure.

Tensile modulus as employed herein and in the claims is the l per cent (1%) tensile modulus of the polymer employed in the manufacture of the particular ultra-fine fiber in question determined in accordance with ASTM D-638.

The term major amount," as employed herein and in the claims, means that at least fifty per cent (50%), on a weight basis, of that material referred to as being present in such major amount. The term minor amount," as employed herein and in the claims, shall mean that amount less than fifty per cent (50%), on a weight basis, of that referred to as being presentin such minor amount. On a weight basis" means herein and in the claims the total weight in the sheet of the particular class of materials being referred to, such as total weight of ultra-fine fibers, etc.

Herein and in the claims reference shall be made to non-extractable or residual ultra-fine fiber(s) and extractable ultra-fine fiber(s). An extractable ultra- 4 fine fiber shall mean an ultra-fine fiber which is removed from the structure and is not present therein and non-extractable or residual ultra-fine fiber, shall mean those fibers which are contained in the breathable sheet-like structure of this invention.

In the manufacture of sheet-like structures of this invention, the following process, employing the steps recited hereinafter, is employed:

A. a shaped article is made comprising extractable and non-extractable fibers, wherein the non-extractable fibers comprise not more than about the volume of the extractable fibers therein, by extrusion with drawing of an immiscible polymer mixture wherein at least one polymer is converted to the extractable fiber and at least one polymer is converted to the non-extractable fiber and both polymers are thermoformable; this step is described in U.S. Pat. No. 3,099,067, patented July 30, 1963 (assigned to the same assignee hereof), and our copending U.S. application Ser. No. 671,238 filed Sept. 28, 1967.

B. forming the shaped article into a sheet, such as by forming a pulp and shaping the pump into a sheet, this step is described in U.S. Pat. No. 3,097,991, patented July 16, 1963 (assigned to the same assignee hereof) or by weaving, air laying, cross lapping, and the like, the shaped article into a sheet;

C. heating said sheet made in Step (B) to a temperature whereby to fuse at least a portion of the ultra-fine fibers therein; and

D. extracting at least a portion of the extractable ultra-fine fibers from said sheet to render the sheet porous, that is, the sheet exhibits moisture vapor transmission as described herein.

Fusion or inter-fusion as employed herein and in the claims means that condition in which two individual fibers of the same composition are caused to be interbonded through an indefinable interface by application of heat to said fibers. Inter-bonding can be achieved at isolated points on each of said fibers and need not involve the totality of these said fibers though this condition is not excluded by the definition of fusion or interfusion.

GENERAL DESCRIPTION OF TECHNOLOGY Fundamentally, this invention is characterized by a porous fibrous sheet and the process for making it in which the major amount of the fibers in the sheet are ultra-fine, that is, they have a denier of less than 0.5, preferably a crosssectional diameter determined normal to the drawn length of the fiber which is less than about 5 microns. Most preferably, they have a crosssectional diameter ranging from as low as 0.1 micron and below about 2.5 microns. ln the preferred embodiment of the invention, a portion of the fibers in the sheet, generally at least 5 weight per cent thereof, are ultra-fine fibers which have a tensile modulus less than about 25,000 psi, and these fibers are bound in the sheet by being fused together. This class of ultra-fine fibers may be present in the sheet up to per cent by. weight thereof. Preferably at least '10 per cent by weight of the sheet to a 100 per cent by weight of the sheet is made of ultra-fine fibers havin ga tensile modulus below about 25,000 psi. The amount'of these fibers which are present in the sheet determine, to a great extent, the ultimate utility of the sheet.

These ultra-fine fibers which have a tensile modulus below about 25,000 are herein called soft ultra-fine fibers. Ultra-fine fibers which possess a higher tensile modulus are herein called hard ultra-fine fibers.

.When the soft ultra-fine fibers are elastomeric, and at least 50 per cent by weight of the sheet contains such elastomeric soft ultra-fine fibers, then the sheet has such properties that it can be employed as a synthetic leather. When the amount of such soft elastomeric fibers is less than about 20 weight per cent of the fibrous sheet and the remaining are hard ultrafine fibers therein, for example, having a high tensile modulus even in excess of 100,000, such a sheet can range in utilities from a textile fabric to a gasket material depending upon the particular ultra-fine fibers therein. Moreover, the thinner the sheet, the more susceptible it is for textile useage. Also, the measurement of the cross-sectional diameter of the ultra-fine fibers will be a significant factor in the tactility, i.e., hand and drape properties, of the sheetlike structure. Because of the interplay of the various components making up the sheet-like materials in determining particular usages therefor, this invention is definable in terms of the groups of products obtainable, thus allowing for a more specific illustration of each of the various factors necessary to make such products; for example, there will be sections below which refer to the manufacture of syn thetic leathers, textile quality fabrics, and stiff, sheetlike structures suitable for use as gaskets, battery separators, filters, and the like. Prior to these sections are sections of general technology common to the other sections relating to processing techniques involved in the manufacture of the products described herein.

STARTING MATERIALS As mentioned previously, the shaped structure of this invention is predicated upon the manufacture of ultrafine fibers, as characterized in Step (A) above.

There are two types of soft polymer fiber employable in practice of this invention, to wit, elastomeric soft ultra-fine fibers and non-elastomeric soft ultra-fine fibers. The elastomeric soft ultra-fine fibers are characterized as being made up of a polymer having a tensile modulus below about 10,000 determined at 25C., which tensile modulus is preferably above 100, most preferably above 250. It is desirable that it have a tensile strength of at least 50 psi (pounds per square inch), preferably at least 200 psi and most preferably at least 600 psi. The elastomeric ultra-fine fiber, in isolated condition, is capable of at least 100 per cent extension (i.e., stretch) and at least about 50 per cent recovery within minutes when relaxed at room temperature (25C.). In addition, the elastomeric ultra-fine fiber is capable of at least 25 per cent elongation at room temperature. The elastomeric polymer which is employed in making the ultrafine fiber is thermoformable, that is, a polymer which can be shaped to an extremely fine diameter fiber, such as below 5 microns in diameter under pressure and heat.

Particularly illustrative of a thermoformable polymer is a thermoplastic polymer, but the definition of thermoformable is not restricted thereto. A polymer which is not wholly thermoplastic because it contains some cross-linking but is capable of being shaped into the ultra-fine fiber is encompassed by the term thermoformable.

The non-elastomeric, soft ultra-fine fiber is also made of a polymer which is thermoformable. It has a tensile modulus of less than about 25,000. Its tensile modulus is generally above 5,000. As an ultra-fine soft fiber it does not possess the rubbery quality of the elastomeric,

soft ultra-fine fiber as is shown by the fact that it does not recover when relaxed after per cent extension within 10 minutes at room temperature. Though this fiber is soft, it is typically considered somewhat harder and stiffer than the limp elastomeric ultra-fine fiber. The hard ultra-fine fiber, as employed herein and in the claims, is made from a thermoformable polymer which has a tensile modulus in excess of about 25,000, preferably in excess of about 50,000. Its other properties including nonrubbery quality is the same as described above for the soft non-elastomeric ultra-fine fiber.

Included in the definition of raw materials are other inert ingredients which are not critical to the manufacture of porous sheet-like structure. Such materials include, by way of example, fillers, pigments, dyes, plasticizers, and the like. They are called herein inert ingreclients.

Illustrative of non-elastomeric soft polymers which form the soft non-elastomeric ultra-fine fibers are the following: low density polyethylene, resinous polyethylene oxide, polyvinylacetate, partially hydrolyzed polyvinylacetate, nonelastomeric copolymers of ethylene and acrylic acid, nonelastomeric copolymers of ethylene and alkylacrylates such as ethylacrylate, n-butyl acrylate and 2-ethylhexyl acrylate and the like, maleic acid anhydride adducts of pyrolyzed polyethylene, polypropylene, copolymers of ethylene and propylene, polyepsilon-caprolactone, wholly aliphatic polyester and polycarbonate resins, and the like.

Illustrative of elastomeric polymers which produce the soft elastomeric ultra-fine fibers include for example, elastomeric polyurethanes, polyamides, polyesters, polycarbonates, polyalkylacrylates, copolymers of ethylene and ethylacrylate which can be saponified with caustic and the like.

Suitable polyurethane elastomers are the segmented polymers of soft, low-temperature melting hydroxylterminated polymers which have been bonded through urethane linkages to stiff, high-temperature melting urethane, polyamide, polyurea, and/or polyester polymers which have been terminated with isocyanato or groups reactable with polyisocyanates (such as hyroxyl, amino, mercapto, and the like).

The more desirable polyurethanes typically possess at least one, preferably at least two, recurring polyether radical, that is, a polymeric moiety possessing recurring ether linkages i.e., -COC- wherein the carbon atoms adjacent the oxygen are saturated, in the internal chain structure thereof, and/or at least one, preferably at least two, recurring polyester radical, that is, a polymeric moiety possessing recurring ester linkages, i.e.,

in the internal chain structure thereof. The polyether and polyester radicals preferably possess a molecular weight of at least about 500 and not in excess of about 7,000. They are joined to the remainder of the polymer by urethanyl linkages, i.e.,

wherein R may be hydrogen or an organic group such as alkyl of from 1 to about 8 carbon atoms, cycloalkyl of from 5 to 8 carbon atoms, phenyl, or benzyl. The urethanyl linkage is bonded to a carbon atom of the or- 7 ganic residue of an organic diisocyanate which in turn is joined through the nitrogen atom of an amide linkage (i.e.,

to one of the active hydrogen-free (as determined by the well known Zerewitinoff method) residue of, e.g., an organic diol, a polyamine compound or amino to form a urea linkage (i.e.,

The polyether and polyester radicals as described herein and in the claims may also contain urethanyl linkages of the type described above in the chain thereof. Such radicals desirably have a melting point below 150C., and preferably below 60C.

The polyester radical may be formed by the reaction of a dicarboxylic acid with an organic diol or by the condensation polymerization of an alpha-omegahydroxy-carboxylic acid or an alphaomega-lactone. Preferably, these polyesters are hydroxyl end-blocked in that the end groups of the polyester are hydroxyl bonded to noncarbonyl containing carbon atoms. These polyesters are then reacted, if they are of the desired molecular weight, with an organic diisocyanate, most desirably in the ratio of at least 2 moles of diisocyanate to one mole of the polyester, to form a diisocyanato end-block prepolymer. This prepolymer is then reacted with a chain extender such as diol or dithiol chain extenders, diamino chain extenders, or water, to form a substantially linear, solvent-soluble polyurethane. A process for the manufacture of the aforementioned polyurethanes are described in U.S. Pat. No. 3,097,192. Specific illustrations of chain extenders include hydrazine, ethylene diamine, 1,3-propylene diamine, 1,4-butane diamine, 1,6-hexamethylene diamine, 1,4-piperazine, ethylene glycol, 1,2-propylene glycol, 1,4-butane diol, ethanol amine, diethanolamine, urea, dimethylol urea, and the like.

Other suitable polyesters may be formed by the reaction of epsilon caprolactone and/or alkyl-substituted epsilon caprolactone and an active hydrogen containing initiator such as water, ethylene glycol, ethylene diamine, diethylene glycol, dipropylene glycol, or 1,2- propylene glycol, such as described in U.S. Pat. Nos. 3,169,945; 3,186,971; and 3,427,346.

The polyesters possessing hydroxyl end groups and having a molecular weight in excess of 500 and up to 7,000 may then be reacted with an organic diisocyanate to produce a polyurethane prepolymer having a molecular weight of from about 1,000 up to about 10,000. This polyurethane may be isocyanato endblocked for direct reaction with the chain extender or may be hydroxyl end-blocked and is considered a prepolymer for additional reaction with diisocyanate, as described in U.S. Pat. No. 3,186,971.

Another polyurethane which is most suitably employed is that described in U.S. Pat. No. 2,871,218. The polyesterpolyurethane of this patent is made by ad mixing a hydroxyl end-blocked or terminated polyester, formed by the reaction of 1,4-butane diol with adipic acid, with diphenylmethane-p,p-diisocyanate and 1,4-butane diol in essentially exact stoichiometric proportions. The polyester should have a molecular weight of about 800 to 1,200 and for every mole of polyester there is employed from about 1.1 to 3.1 moles of the diisocyanate and from about 0.1 to 2.1 moles of the butane diol. By increasing the mole amount of diisocyanate, it is possible to increase the melting point and hardness of the resulting polyurethane and by reducing the mole amount of diisocyanate, it is possible to decrease the meltingpoint and hardness of the resulting polyurethane.

The polyethers may be characterized in essentially the same manner as the polyester above. They fall in the same melting point ranges, are desirably in the same molecular weight range and are hydroxyl endblocked or terminated. They are formed by the alkaline or acid condensation of alkylene oxides. Such polyethers and their utilization in polyurethanes are described in U.S. Pat. Nos. 2,813,776; 2,818,404; 2,929,800; 2,929,803; 2,929,804; 2,948,707; 3,180,853 and RE 24,691.

Suitable polycarbonate elastomers include the segmented polymers of soft, low-temperature multihydroxyl-terminated polymers which have been bonded through carbonate linkages to stiff, high-temperature multicarbonate polymers.

Such polycarbonate elastomers are illustrated in the following patents:

Canadian Pat. No. 668,153, issued Aug. 6, 1963, note particularly Examples 2, and 3; U.S. Pat. No. 3,030,335, patented Apr. 17, 1962, note Ex. 2 and the disclosure at column 1, lines 56 to 68, inclusive; U.S. Pat. No. 3,161,615, patented Dec. 15, 1964, note particularly Examples 3, 7, 10, 14, 15, 19, 20, 21, 22, 24 and 25; U.S. Pat. No. 3,207,814, patented Sept. 21, 1965, note Examples 1, 2, 5, 7, 9,10 and 11; and U.S. Pat. No. 3,287,442, patented Nov. 22, 1966, note Examples 9,l0,11,13,l6,18, 21, 23, 29 and 30. The method and the components involved in the manufacture of such polycarbonte elastomers suitable for use in the practice of this invention are disclosed in the above patents and the disclosures of these patents are incorporated herein by refernce with respect to their teachings of methods and reactants.

Suitable elastomeric polyesters are described in U.S.

Pat. No. 2,623,031, patented Dec. 23, 1962, note Examples 1, 2, 3, 4, 5 and 6; U.S. Pat. No. 3,023,192, patented Feb. 27, 1962, note all of the Examples therein; and U.S. Pat. No. 3,037,960, patented June 5, 1962, note all of the Examples therein. These elastomeric polyesters are also segmented copolymers in which a soft segment is interbonded to a hard segment by an ester linkage. The hard segment is polyester and the soft segment may be polyester or polyether such as described above with respect to polyurethane elastomers.

Suitable elastomeric polyalkyl acrylates include, by way of example, poly(ethylacrylate), copolymers of ethylacrylate and other alkylacrylates such as n-butylacrylate, 2-ethylhexylacrylate, and the like. Also included are copolymers of ethylene with alkylacrylates (such as ethylacrylate) which can be saponified with caustic such as sodium and/or potassium hydroxide, to produce useable terpolymers of ethylene, alkylacrylate and acrylic acid. Other copolymers of this class include copolymers of ethylene with acrylic acid and/or other alkylacrylates such as 2-ethylhexylacrylate, and the 9 like.

Suitable elastomeric polyamides for use in this invention are described in US. Pat. Nos. 2,929,801; 3,044,987 and 3,044,989.

The hard ultra-fine fibers are obtained from thermoformable polymers, as characterized above, such as high density polyethylene, polypropylene, poly-lbutene, polystyrene, polyalpha-methylstyrene, polyalpha-chlorostyrene, copolymers of vinyl chloride and vinyl acetate, partially hydrolyzed copolymers of vinyl chloride and vinyl acetate, polyvinylpyrrolidone, copolymers of N-vinylpyrrolidone and vinyl acetate, copolymers of vinyl methyl ketone and vinyl chloride, vinyl acetate or N-vinyl pyrrolidone, polymethylmethacrylate, polymethacrolein, diethylacetal of polyacrolein, copolymers of styrene and acrylonitrile, nylon (such as polyhexamethyleneadipate, polytetramethylenesebacamide, poly-epsilon-caprolactam, polypyrrolidone), the polyimidazolines, polyesters (such as polyethyleneterephthalate poly-l ,4-cyclohexyleneterephthalate, and the like), oxymethylene homopolymers and copolymers (the formaldehyde polymers), polycarbonates such as the reaction product of phosgene or monomeric carbonate esters with bis Phenol A [2-bis(4hydroxyphenyl)propane], and the like, polyarylene polyethers such as described in US. Pat. No. 3,264,536, patented Aug. 2, 1966, and the like.

THE PROCESS STEP A This step involves blending two or more thermoformable polymers, melt extrusion of the blend into the shape of a monofilament, multi-filaments, rod, ribbon or film with drawing of the shaped article either during extrusion or thereafter. As stated previously, the shaped article contains at least one extractable and one non-extractable fiber therein. These fibers are derived from the extrusion and drawing of a blend of polymers which are immiscible in each other, that is, they are mutually incompatible in each other either in solid or molten state. Usually, both polymers have molecular weights greater than 10,000. Generally speaking, in combining mutually incompatible polymers prior to extruding them into the shaped article, conventional methods and apparatus are entirely suitable. If the polymers are available as raw materials in powder, pelletized or granular form of sizes substantially uniform and equal as between the two or more polymers, dry blending, e.g., in a conical blender or a ribbon blender, is quite good. However, if the particle sizes of the individual polymers are too dissimilar, poor mixing results from these methods. In this event, hot processing methods may be employed. Fluxing the polymers on a tworoll mill or a Banbury mixer ata temperature dependent on the polymers being handled produces suitable mixtures. Another means of mixing is to dissolve all of the starting materials in a suitable mutual solvent system and then removing the solvent(s) by evaporation.

Still another method, practical when polymers are being used which show little tendency to degrade at double extrusion in which the polymers are fluxed by v fibers ultimately obtained only when very little working of the mixture in molten state is done prior to extrusion through an orifice or slot to form a shaped article such as mono-filament, multi-filament, rod, ribbon or film. If for example, a mixture of two incompatible polymers is charged into a heated cylinder equipped with a piston to force the molten mixture out through a small orifice with a minimum amount of milling of the mass, the dimensions of the fibers comprising the extruded filament can be controlled by correlating the particle size in the dry blend mixture with the dimension of the fibers produced, having set a fixed rate of filament attenuation (drawing or stretch). If there is no milling prior to or during extrusion, a proportional relationship exists between fiber diameter and pre-extrusion particle size.

Normal operation, however, produces ultra-fine fibers such as described above. By normal operation is meant that at some point in the extrusion process the incompatible polymers are fluxed in a plastic state to such an extent that initial particle size of the starting materials is not a factor in determining the dimensions of the fiber in the article. The amount of fluxing required is not great the operation of the feeding screw in a conventional screw type extruder being sufficient. Hot processing of a granulated polymer mixture on a two-roll mill or Banbury mixer before extrusion is sufficient even if a non-milling type ram or plunger extruder is used.

Extrusion conditions, particularly temperature, will vary over a relatively wide range. The conditions depend on the physical and chemical properties of the extruded polymers and thus may even vary for identical compositions according to the preference of the skilled operator. However, the fluxed mixture of the incompatible polymers must obtain a melt fluidity in the extruder such that during the first drawn stage there is a smooth reduction of the diameter as the composite mono-filament, multi-filaments, or film issues from the orifice or slot and elongates while being hot drawn. While the extruded mix, as it issues from the extruder nozzle, does have a fibrous nature, attenuation (or drawing) ensures production of ultra-fine fibers. Such drawing can be achieved in the extruder providing the extruder is machined for this purpose.

It is to be understood that whereas either hot drawing or cold drawing alone may produce fine fibers in a composite shaped article of this invention of the two or more mutually incompatible polymers, each such operation produces unique characteristics in the final ultrafine fiber produced and such result may be achieved by employing both techniques in combination. Hot drawing will, in the main, serve to reduce the diameter in thickness of the extruded article thereby necessarily reducing the diameter of the individual fibers of which it is composed. After hot drawn in the melt, the fibers in the article have little or no molecular orientation in the longitudinal direction.

The amount of hot processing or fluxing of the two or more mutually incompatible granulated polymers will be a factor in determining the diameter of the ultra-fine fibers making up the composite article at the moment it emerges from the extruder die. The difference in diameter between the bore of the extruder and the die orifice or slot causes a certain amount of attenuation which may vary between extruders of for the same extruder depending on the size die that is attached. However, once the fluxing and extruding conditions for a given polymer mixture has been adapted, a single determination of the fiber size produced for a given amount of hot drawing is sufficient to establish approximately the amount draw to produce fibers of a desired diameter. Assuming ideal characteristics for the individual ultra-fine fibers in the shaped article, that is, they are uniform rods, preferably having circular crosssectional areas, and elongate the same extent as the shaped article is elongated, the diameter of a fiber after drawing is equal to the diameter before drawing divided by the square root of the ratio of the new length to the old length.

If desired, cold drawing to induce molecular orientation may be included as an intergral part of the overall process and follow immediately after hot drawing or may be carried out at any time, even after storage of the shaped article.

Cold drawing is primarily for the purpose of inducing the ultra-fine fibers molecular orientation in a longitudinal direction. This stretch orientation, as it is commonly called, is well known in the synthetic fiber art to effect improvement in physical properties such as tensile strength and, in some instances, resistance to a heat aging. The stretching of the shaped article is carried out in the same fashion as it is effected in the prior art. The degree of orientation imparted to the fiber is dependent upon the polymer employed and the uses to which the product will be put. Due to the relationship of the diameter to the length of ultra-fine fiber before and after stretching, cold drawing sufficient to induce orientation to the extent of several hundred percent stretch or elongation does not greatly alter the ultra-fine fibers diameters even when hot drawing had previously reduced it to a range of for example 0.125 microns.

It is preferred in the practice of this invention that the molten immiscible polymer mixture be drawn at least 100 percent either during extrusion or after extrusion to obtain a shaped article most favorably employable in the practice of this invention. This drawing is exhibited or evidenced by a commensurate reduction in the diameter or thickness of the shaped article from the corresponding diameter or thickness of the immiscible polymer mixture from which it is obtained just before its extrusion. Such drawing can be achieved in the extrusion opening or by pulling the article at a great rate as it issues from the opening.

As stated previously, the shaped extruded article described above contains therein a plurality of extremely fine (ultra-fine) fibers. The extruded shaped article, regardless of whether it is a mono-filament, multi-filament, film, etc., contains many such ultra-fine fibers therein, for example, a rod having a one-inch square cross-section can contain one million or more of such fibers laying parallel to the drawing axis of the rod.

STEP B As pointed out in U.S. Pat. No. 3,097,991, referred to above, the shaped article of Step (A) can be readily converted into a paper pulp. Though the aforementioned U.S. patent stresses the manufacture of a shaped article in the form of a mono-filament, multi-filaments or thin sheeting cut into strips can be handled in the same manner to be beaten by conventional means into a pulp from which interfelting is readily accomplished. The first step of the process in forming a felt of the ultra-fine fibers is to make a slush of the shaped article. In the case of a film, ribbon or rod, they are first slit into a predetermined width and thickness then cut in the pre-determined length and deposited in water to form the slush.

- With respect to use of mono-filaments and multi-filaments, they are cut in pre-determined lengths in making the slush according to the amount of beating or refining employed. It is preferred that the cut shaped article containing the ultra-fine fibers have a length not in excess of 12 inches, most preferably not in excess of 8 inches, and preferably not less than one-sixteenth inch when employed in formation of a slush. The thickness and width of any shaped article employed in making the slush should not exceed one-half inch preferably not in excess of one-fourth inch. The slush is nothing more than a dispersion of the cut and/or sliced shaped article.

The slush is thereafter treated to effect mechanical fibrillation, that is, the shaped article is mechanically attavked to effect breakage and splitting thereof whereby the shaped article, which is a unitary bundle of ultra-fine fibers, is fractured into smaller bundles of said ultra-fine fibers and the individual ultra-fine fibers. Such fibrillation causes extremely small bundles of the ultra-fine fiber or the individual ultra-fine fibers to be loosen from the surface of these smaller bundles as fibrils. This may be accomplished by any conventional paper beating or refining technique such as in a Hollander type beater, a Hydrapulper, a Vortex beater, a Sharple pulper, a Dynopulper, a Jordan refiner, a Bauer refiner, a Curlator refiner and the like.

The beating or refining step is important to the process of this invention and will greatly determine some of the significant properties of the resulting product. If beating does not reduce the ultra-fine fiber length or the length of the bundles of ultra-fine fibers to any great extent and the fiber length is in excess of, e.g., one-half inch, the resulting product, that is the breathable product of this invention, will possess superior tear strength, though it is possible in some cases that other properties such as degree of breathability, hand and drape may suffer. In the step of beating or refining, one may employ a minor amount of conventional staple fibers such as cotton, nylon, polyester, acrylic, modacrylic, and the like, to enhance such properties as tear and tensile strengths even though they alone do not lend themselves to the formation of the cohesive sheetlike structure of this process.

One may only partially beat and refine a given slush and thereafter combine it with a slush of another composition such as cellulosic paper pulp or the partially beaten or refined slush made of other ultra-fine fibers, that is, a slush of a fractured shaped article having a different composition. in this way, blends of different fibers can be obtained in a simple manner. As will be pointed out later, variations in the manufacture of a pulp in which there exists different fiber lengths can be of extreme advantage in the manufacture of certain products.

Usually, the beating and refining step reduces the length of the shaped article to no more than about 1 inch, typically less than one-half inch and most usually between about one thirty-second inch and threeeighths inch. The pulp resulting from the beating and refining step is now employable in making the felted sheet described in Step B above. This may be accomplished in any of the known ways by hand or by machine.

If desired, the pulp can be formed by other means such as by ball milling the cut and/or stripped shaped articles with water or by air micronizing or micropul- -verizing and then depositing in water the small fractured fragments containing fibrils extending from their surfaces to form the pulp. The sheet which is formed from any one of these pulps can be accomplished by hand in the conventional way by depositing the pulp onto a screen, squeezing the mass on the screen to form a filtered cake followed by further water removal such as by suction and then heating to remove the water to form a felted sheet. Of course, the most desirable way is to form a felted sheet on machinery such as a Fourdrinier paper machine. Standard paper making techniques are employable to make a very uniform cohesive dry-felted sheet which can be treated in accordance with Step C described herein.

As mentioned previously, the pulp can contain ultrafine fibers from a plurality of different shaped articles defined in Step A, each composed of different fibers, and/or the pulp can contain as well cellulosic paper pulp or pulp of other fibrous matter such as cotton, nylon, polyester, acrylic and modacrylic type fibers. These pulps can be formed in the initial stages of the paper making process such as prior to or in the head box of a Fourdrinier machine. The options available are numerous and are easily within the skill of the operator.

The dry inter-felted sheet containing the ultra-fine fibers is now ready for Step C.

Instead of pulping, forming a slush and felting, the shaped articles can be formed into a sheet by numerous methods including, but not limited thereto: air laying cut staple of the shaped article (in the form of mono and multi-filaments); cross-lapping continuous tapes, films and/or filaments of the immiscible polymers using conventional hand or machine cross-lapping techniques to form a scrim, web or batting; or by weaving tapes or filaments to form a woven fabric. These sheet products are now ready for Step C.

STEP C The dry sheet of Step B is heated to a temperature sufficient enough to fuse at least a portion of the nonextractable ultra-fine fibers in the sheet. The temperature employed is one which under the pressure employed causes sufficient softening of such non-extractable ultra-fine fibers that they are fused together to form a cohesive bond and to interbond together all of the fibers in the sheet. It is very desirable, but not critical to the most broad aspects of the invention, to similarly interfuse the extractable ultra-fine fibers in the sheet. In the usual case, the softening point of the non-extractable ultra-fine fibers is higher than the softening point of the extractable ultra-fine fibers, and hence, these fibers are also fused in the heating step.

In a most significant embodiment of this invention, pressure is applied to the surfaces of the sheetswhile the sheet is being heated. In such case, it is preferred that the temperature applied while the sheet is being pressed be at least as high as the softening temperature of the non-extractable ultra-fine fibers which are being fused, i.e., the softening temperature of the fiber determined at normal temperature pressure (NTP).

It is most preferred that the temperature applied be sufficient to fuse a major amount of the non-extractable ultrafine fibers in the sheet.

This step of the process can be accomplished in a platen press wherein the platens are heated to the desired temperature. It can also be accomplished by passing the sheet of Step (B) through heated calender or nip rolls, typically a series of such rolls, or it can be passed around a large roll and be put under pressure on said roll by an endless belt which circumscribes at least a portion of such roll. The last described apparatus is illustrated by a Rotocure, a machine which is employed for curing rubber sheets. Suitable apparatus for effecting this heating and pressure step of the process is described in copending application Ser. No. 379,268, filed June 30, 1964, assigned to assignee hereof, and in U.S. Pat. No. 2,971,218, patented Feb. 14, l96l. The sheet can be heated dielectrically if desired.

The pressure employed is typically at least 25 pounds per square inch of the felted sheet. As a rule, the amount of pressure is sufficient to effect a degree of compression of the sheet, typically at least 5 percent compression in thickness of the sheet. This compression is permanent in that when pressure is relieved and the sheet is cooled to room temperature, it does not expand to its original thickness. If the ultra-fine fibers in the sheet are stretch oriented, then there is usually a small amount of shrinkage occurring during the heat fusion and pressure step. Such shrinkage may be noted in reductions in the width or length of the sheet or in its thickness or in all three dimensions simultaneously.

STEP D It is this step of the process in which microporosity or breathability is achieved. The fused sheet is transported from the compression step, in the preferred case, to a bath of a liquid which is a solvent for the extractable ultra-fine fiber in the fused sheet but which is essentially a non-solvent for the non-extractable ultra-fine fiber in the sheet. The choice of solvent is important in the manufacture of the desired product and for processing efficiency. The solvent should be readily active in dissolving the extractable ultra-fine fiber and most preferably should be a total non-solvent for the nonextractable ultra-fine fibers. If conventional staple fibers have been incorporated in the fused sheet, it is preferred that the solvent be a non-solvent for such staple fibers. It is preferred in the practice of this invention that essentially all of the extractable ultra-fine fibers be removed from the fused sheet such that the sheet is essentially free of such fibers. It is particularly desirable to preclude the formation of resinous nonfibrous-like materials inside the porous structure and hence, any fiber which is dissolved should be essentially totally removed from the fused sheet. It is in this fashion that there can be obtained a sheet having the most desirable porosity and/or breathability. Also, it is this factor which achieves a uniformly porous sheet.

The extraction step simply involves the immersion of the fused sheet into the bath of solvent. The bath should be essentially free of any liquid therein which is a solvent for the non-extractable fibers. The bath may contain an amount of liquid which is a non-solvent for any of the extractable ultrafine fibers in the fused sheet The solvent employed is typically present in an amount greater, on a volume basis, than the amount of extractable fiber in the sheet. Most desirably, a substantially excess of solvent is employed and multiple baths involving sequential extraction are generally used to insure maximum extraction of the extractable fiber. The resulting leached sheet, after drying, has the desired properties of porosity, hand, drape, tactility, and the like.

If desired, the fused sheet prior to or as part of the treatment of Step (D) may be heat embossed with a calendar embossing roll to impart designs in one or both of the surfaces of the sheet. This embossing step may take place after the extraction step and if it does, it should be recognized that some of the surface pores of the sheet will be compressed and reduced in size thereby reducing the rate of breathability of the sheet.

In addition, one or both of the surfaces of the resulting sheet may be buffed or scoured to effect surface characteristics for particular uses without adversely affecting the porosity of the sheet.

SYNTHETIC LEATHER One of the most significant characteristics of leather is that it does not readily pass liquids but allows moisture vapor to pass through it. This latter quality is characterized as moisture vapor transmission. These are important properties for a shoe upper material.

The synthetic leather of this invention possesses each of these qualities. In addition, the synthetic leather of this invention can exhibit the flexing, hand, and drape properties of leather.

The term moisture vapor transmission is meant herein and in the claims as that weight of moisture determined in grams per square meter per hour which passes through the sheet when evaluated under the following conditions:

a circular disc of the sheet having a known area is sealed with wax at its edge on the top of a cup containing an excess quantity of desiccant (such as calcium chloride). The cup is placed under constant temperature and humidity of 70F. (dry bulb temperature) and 65 percent relative humidity for 16 hours, after which time the cup with the film is weighed;

after the first weighing, the cup is left in the same atmosphere for an additional hour and is weighed again, and this procedure of weighing is repeated until such time as a static or constant moisture vapor transmission determined in grams per square meter per hour, is obtained. The final figure represents the moisture vapor transmission (referred to hereinafter as MVT). The MVT of good quality, finished calfskin typically runs from about 15 to about 60 and higher, though usually the MVT is from about 20 to about 25. The most widely promoted leather substitute today is Corfam, sold by E. I. du Pont de Nemours and Company, which is described as a poromeric material. Samples of it have been found to possess MVTs ranging from as low as 15 and as high as about 35 to 40, depending upon the type of embossment and surface finish.

In addition to MVT requirements, synthetic leather should possess a flex life, drape, body, hand, tactility, workability, tear strength and tensile strength comparable to natural leather. Many of the above characteristics are the subjective evaluation of an expert in the characteristics of leather. The synthetic leather of this invention satisfies such subjective standards and pos- 16 sesses advantages over those products in the market place with respect to physical properties which can be evaluated in accordance with standard tests.

A most significant quality of the synthetic leather of this invention is that it is an extremely homogeneous material, that is, it can be made of essentially single composition and is not a nonwoven laminate. At best, the synthetic leather of this invention does not require any backing fabric because of its extremely good physical properties but in certain circumstances it may be desirable to bond it to a backing fabric, such as a woven or bonded nonwoven fabric for the purposev of giving the synthetic leather added dimensional stability.

The surface of this synthetic leather is most uniform due to the nature of the process employed and in many cases it will not be necessary to finish the surfaces of the synthetic leather with a lacquer or latex coating which is common practice with leather substitutes presently in the marketplace. The surface of the synthetic leather can be embossed to give the product a leather grain appearance, e.g., the appearance of alligator hide, calfskin, and snakeskins. The surface may be brushed in the conventional manner to give a suede effect if such is desired.

In characterizing synthetic leather of this invention, the major amount of the fused ultra-fine fibers in the sheet are elastomeric soft ultra-fine fibers and the remaining ultra-fine fibers in said sheet may be hard or soft ultra-fine fibers. Preferably, at least 60 percent by weight of the porous sheet comprises the elastomeric soft ultra-fine fibers and most preferably at least percent by weight of the porous sheet is made of said ultra-fine fibers. In a significantly preferred embodiment of this invention, hard ultra-fine fibers are not present in the sheet in amounts by weight thereof greater than 10 percent. The most favorable product obtainable for most uses is a sheet in which percent of the ultra-fine fibers therein are soft ultra-fine fibers. In accordance with this most favorable embodiment, the porous sheet may contain up to 25 percent weight percent thereof of soft ultra-fine fibers other than the elastomeric ultra-fine fibers. It is most preferred that all of the ultra-fine fibers in the sheet are elastomeric, soft ultra-fine fibers.

In the manufacture of such a sheet, Step (A) is achieved by forming a shaped article in which the amount by volume of the elastomeric soft ultra-fine fibers therein is not significantly greater than the amount by volume of either non-elastomeric soft or hard ultrafine fibers therein. Preferably, the amount by volume of these elastomeric ultra-fine fibers in the shaped article is not greater than the amount by volume of the nonelastomeric soft or hard ultra-fine fibers in the article. The amount by volume of the elastomeric soft ultrafine fibers may be as little as 20 percent (20%) of the amount by volume of the non-elastomeric hard or soft ultra-fine fibers in the article. In the most desirable embodiment, the amount by volume of the elastomeric soft ultra-fine fibers in the article ranges from 40 percent to 98 percent of the amount by volume of the nonelastomeric hard or soft ultra-fine fibers therein.

The sheet is made in accordance with the procedures in Steps (A) to (D). In the practice of Step (C) it is most desirable that the temperature employed to effect fusion is at least equal to the softening temperature of the elastomeric, soft ultra-fine fibers in the sheet, and it is most desirable that the non-elastomeric hard or soft ultra-fine fibers employed have softening points which are lower than the softening points of the elastomeric,

soft ultra-fine fibers. It is also preferred in the practice of Step (C) that pressure be applied to the surfaces of the sheet during the fusion step sufficient to effect some reduction in the thickness of the sheet being treated.

The use of a large concentration of elastomeric ultrafine fibers in the sheet is important and significant to the manufacture of good synthetic leather. Non-elastomeric ultra-fine fibers, when presentin the sheet in too large a quantity, adversely affect the aforementioned subjective tests which are so important in the characterization of a good quality product.

In this respect, synthetic leather is a distinctive embodiment of this invention, and it is important to appreciate that it typically possesses a thickness greater than the usual fabric, in most cases having a thickness greater than mils, preferably greater than 20 mils and in most cases does not exceed 100 mils. Because of this considerable thickness, the body characteristics of the product become paramount in the evaluation of the product, and it has been found that the presence of large quantities of elastomeric ultra-fine fibers greatly contributes to this characteristic.

NONWOVEN FABRICS The products of this category are distinctive from synthetic leather in many respects. Nonwoven fabrics do not require the employment of elastomeric soft ultra-fine fibers, though they may be employed if desired. Moreover, the sheet which is treated in Steps (C) and (D) need not contain only ultra-fine fibers as is usually the case with synthetic leather. Thus the sheet may also contain therein conventional staple fibers. Moreover, though the ultimate sheet from Step (D) is porous, it need not be microporous, as is the case with synthetic leather. Though it is usual to employ a pulp in the case of synthetic leather in Step (B) wherein the ultra-fine fibers are beaten to a generally uniform length, it can be most beneficial to employ a pulp in the manufacture of nonwoven fabrics wherein the lengths of the ultrafine fibers in the pulp vary greatly, indeed, ranging from as low as one thirty-second of an inch to 1 inch or more in length in any given pulp.

Whereas a synthetic leather, in most cases, should be free of boardiness, some nonwoven fabrics may possess boardiness because such characteristics is desired in a certain marketplace, and in some instances a soft limp nonwoven fabric, which would be wholly unsatisfactory for synthetic leather purposes, will be useful for a given fabric market.

In characterizing nonwoven fabrics one must give consideration to the qualities of hand and feel. They are important subjective standards in this field. There is a hazy demarcation between a soft and a stiff hand. This difference is a product of the modulusof the polymers employed in making the ultra-fine fibers, the cross-sectional diameter of the ultra-fine fibers, the apparent density of the porous sheet and the shape of the ultra-fine fibers in the structure. Thus, in a nonporous, fully densified structure wherein no shape identity of ultra-fine fibers is apparent or characterized, the soft hand of the sheet falls off when the polymer employed in making the ultra-fine fibers has a tensile modulus above about 10,000. By reducing the density of the sheet, as is accomplished in Step (D), a softer hand is achievable even when the tensile modulus of the polymer employed in making the ultra-fine fiber is as high as 50,000. If the sheet is thin, the tensile modulus needed for a soft hand can be greater than 50,000, even as high as 500,000. The more porous, or less dense, is the sheet, the higher the tensile modulus of the polymer making up the ultra-fine fiber can be in order to obtain a product with a soft hand. So it can be seen that many significant variables are available in the manufacture of nonwoven fabrics in accordance with this invention. This is a great advantage because the more variables available to the technician, the greater is his ability to provide a product having the exact qualities desired by the customer.

In the manufacture of nonwoven fabrics, it is desired that the sheet contain not more than 40 percent by weight thereof of staple fibers, preferably not more than 25 percent. The use of staple fibers greatly increases the tear and tensile strengths of the sheet, but it does affect the sheets hand. An alternative approach, and greatly favored here, is to employ two pulps in Step (B), each pulp made from a shaped article as characterized in Step (A) but where one pulp contains fiber lengths not greater than about one half inch and another pulp having greater fiber lengths, typically not greater than about 1 inch. These pulps can be blended in various proportions depending on the type of products desired. The term fiber lengths with respect to pulps refers to the average length of the fibers in the pulp. Thus, ultra-fine fibers of varying lengths can be employed to either improve or reduce the tear and tensile strengths of the ultimate sheet. As the density of the sheet increases, so does the tensile and tear strengths, but there also occurs a falling off in drape and hand unless one insures that the tensile modulus of the fibers in the sheet as defined above, is below about 50,000, preferably below 25,000 and most preferably below 10,000. Higher density sheets made of such fibers of low tensile modulus will not differ significantly in hand.

Another significant factor in the manufacture of nonwoven sheets is that Step (C), where fusion is effected, may be practiced without application of pressure to the surfaces of the sheet. In some cases, particularly where textured effects are desired, it will be most important not to apply pressure to the surfaces of the sheet during the fusion step.

As noted previously, one does not have to rely upon pulping to create the sheet from which the desired fabric is made. For example, the shaped article, preferably in the form of filament(s), slit film, ribbon or tape strips, can be woven into a fabric from which fusion and extraction, as characterized above, there is produced a porous fabric. In addition, monoor multi-filaments of immiscible polymers can be cut into staple fibers which can be air layed into a non-woven sheet from. which fusion and extraction there is produced a porous fabric. Alternatively, mono-oriented films of immiscible polymers may be cross-lapped by well known procedures, such as on a mandrel or on a carding cross-lapper, to produce a sheet which upon fusion and extraction produces the porous fabric. Another technique involves needle punching with barbed needles any of the above sheets or one or more of the aforedefined films superimposed on another to cause blending of bundles of fibrils, followed by fusion and extraction to produce a desirable porous sheet.

The term nonwoven fabrics, as employed herein, is not intended to be exclusive of synthetic leather since the latter is often used in areas normally regarded the domain of fabrics. However, this term is intended to mean a nonwoven cloth-like textile fabric suitable for use in areas normally regarded suitable for woven or knitted fabrics. 7

Moreover, though one may weave or knit a sheet from the aforedefined shaped articles, the final fused and extracted sheet is not to be regarded as woven or knitted, as the case may be. Fusion serves the purpose of destroying the woven or knit structure and the dominant binding force of the fused sheet becomes cohesion between the melt compatible fibrils. On extraction of the extractable fibrils (ultra-fine fibers), the resulting porous sheet shows little, it any, of the woven or knit structure.

STlFF STRUCTURES The stiff and boardy structures can be made by selection of a hard non-extractable fiber alone or in admixture with soft non-extractable fibers or by producing a relatively dense structure (possessing low MVT) from any fiber. The above procedures are employable. The density can be controlled by, e.g., either reducing the amount of extractable fiber in the sheet or the amount of extractable fiber taken from the sheet. Alternatively, essentially all of the extractable fiber can be removed from the sheet and density is controlled by the amount of such fiber in the sheet prior to extraction or by subsequently hot compressing the porous sheet to permanently reduce its density.

These products have good structural stability and can be used as battery separators, insulation medium, building material, gaskets, and the like.

In order to further characterize this invention, reference is made to the examples which follow. These examples serve the sole purpose of further illustrating this invention and they are not intended for the purpose of restricting the scope of this invention.

EXAMPLE 1 This example describes four thermoplastic polyurethane elastomers employed in other examples.

Polyurethane A To a 2,000 milliliter reaction flask equipped with heating mantle, stirrer thermometer, ebulater and vacuum inlet tube is charged 730 grams (0.75 equivalent) of polycaprolactone diol (hereinafter called polyo1). The polyol has a molecular weight of 2,000 and is formed by the reaction of epsiloncaprolactone with diethylene glycol. The polyol is heated to 100C. and is allowed to degas at 100C. for 1 hour under about 0.1 inch mercury to remove moisture and dissolved gasses. A portion of bis(4-isocyanatophenyl) methane (565 grams) is similarly melted and degassed at 50C. The temperature of the polyol is raised to 149C. Vacuum is broken and the heated and degassed polyol is poured into a heated (177C.) steel cylinder mold. To the polyol is added 169 grams (3.75 equivalents) of 1,4- butane diol with stirring, followed by 565 grams of the bis(4-isocyanatophenyl)methane. The mixture is stirred for 1 minute after the addition of the bis(4- isocyanatophenyl)-methane and cured in an air-oven at 177C. for 1 hour. The resulting thermoformable polyurethane elastomer is granulated.

Polyurethane B This elastomer is prepared by the same procedure as polyurethane A, except that the equivalent ratio of bis(4-isocyanatophenyl)methane/polyol/1,4-butane 20 diol is 5:1:4 instead of 6:1:5. Weights and equivalents used are as follows:

Weight- (Grams) Equivalents Polyol 730 0.75 1,4-butane diol 135 .3 3.00 bis(4-isocyanatophenyl )methane 471.6 3.75

Polyurethanes A and B, produced as described above have the following physical properties.

TABLE 1 Hardness Shore D 50 45 100% Modulus, psi 2350 1225 300% Modulus, psi 4850 3250 Tensile Strength, psi 4950 5400 Ultimate Elongation, 305 360 C Tear psi 730 640 B Compression Set, 51 55 Zwick Resilience, 37 47 Polyurethane C This polyurethane is an elastomer which is believed to be produced by the reaction of a hydroxyl endblocked polyethyleneadipate (molecular weight above 700 and believed to be below 2,000) with bis(4- isocyanatophenyl)methane and 1,4-butane diol. This polyurethane is called ESTANE 5701 resin produced by B. F. Goodrich Chemical Company, a division of the B. F. Goodrich Company, 3135 Euclid Avenue, Cleveland, Ohio 441 15. It has the following physical properties:

Polyurethane D This polyurethane is an elastomer which is believed to be produced by the reaction of a hydroxyl end block polyethyleneadipate (molecular weight above 700 and believed to be below 2,000) with bis(4-isocyanatophenyl)methane and 1,4-butane diol. This polyurethane is called ESTANE 5740 X 070 resin produced by B. F. Goodrich Chemical Company, a division of the B. F. Goodrich Company, 3135 Euclid Avenue, Cleveland, Ohio 44115. It has the following physical propertleSI ASTM N0.

Value Specific Gravity 1.20 D12-27 Hardness. Durometer A 95 D-676 Durometer C Durometer D 48 Tensile Strength (psi) (min) 5800 D-412 -continued Value ASTM No.

Modulus at 300% Elongation (psi) 3500 Elongation (min) 450 Grave Tear (lbs/in) 700 D-624 Low-Temperature Brittleness Point (F) 100 D-746 Gehman Low Temperature Freeze Point (F) D-l053 Compression Set Method A* 22 Hours at 158F. ll D-395-55 Taber Abrasion (mg loss) (CS 17 wheel, 1000 gms.

weight, 5000 cycles 3 D1044-49T Processing Stock Temperature 3503 80 Method A uses constant compression stress at constant test temperature.

EXAMPLE 2 A mixture weighing 4,000 grams is made up by combining 1,200 grams of Polyurethane D, 400 grams of film and fiber grade polypropylene resin (melt index of 2-4; density of 0.88) and 2,400 grams of atactic crystal clear polystyrene having a molecular weight of 50,000. The resins are each in approximately Va inch dice form and the mixture is effected by tumble blending the three resins together. The mixture is melted in a 1% inch single screw extruder at 180C. The extruded strand is diced into Vs inch pellets. The 4; inch pellets are mixed and again melted and then extruded through the same extruder into an approximately 1/16 inch diameter strand which is drawn by a Godet from the extruder at the rate of 10 feet per minute. This strand is then passed into a glycerine stretching bath, maintained at 125C. and the strand is there stretched by drawing it out of the bath at 110 feet per minute. This imparts a molecular orientation to the strand that may be expressed as 1 10-10)/ 10 X 100% 1,000% stretch oriented. The strand is cut to staple lengths of from one-half inch to 6 inches and is next fed to a Noble and Wood Cycle Beater with a blade clearance setting of mils. The cut strands are beaten to produce a thoroughly digested pulp of the mixed polymer mono-filaments. I

The pulp is then processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 200 mils thick.

The felt is dried in an air-oven at 70C. After drying the felt is pressed at 165C. and 100 psi in a platen press to produce a full density molded sheet of 120 mils thick. The sheet is then placed in a beaker containing toluene to extract the polystyrene. The sheet after extraction is dried and is a semi-finished leather like product. The sheet is approximately four-tenths of its full density, has porosity comparable to leather, showing a MVT of 15, and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather.

EXAMPLE 3 The process of Example 2 is repeated except that the mix weighs 2,000 grams and is formed by combining 1,000 grams of Polyurethane D with 1,000 grams of atactic, crystal clear polystyrene. The 9% inch melt mixed pellets are extruded into an approximately 1/16 inch diameter strand and drawn by a Godet at 10 feet per minute. -The strand is passed into the glycerine Stretching bath at C. and is drawn out of the bath at 250 feet per minute. The molecular orientation imparted may be expressed as (25025 )/25 X 100% 900% stretch orientation. The strand is arbitrarily cut to staple lengths of from about one-quarter inch to about 4 inches and is next fed to 21 Noble and Wood Cycle Beater with a blade clearance setting of 7 mils. The strand is beaten to produce a pulp of the mixed polymer monofilament.

The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 100 mils thick.

The felt is dried in an air-oven at 65C. After drying the felt is pressed at 170C. and 300 psi in a platen press to produce a full density molded sheet of 60 mils in thickness. The sheet is then placed in a beaker containing toluene to extract the polystyrene. The sheet after extraction is dried and is the semi-finished leather like product. The sheet is approximately one-half of its full density, has porosity comparable to calf skin, showing an MVT of 18, and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather.

EXAMPLE 4 Example 1 is repeated except that the mix weighs 2,000 grams achieved by combining 1,000 grams of the polystyrene of Example 3, 800 grams of Polyurethane D and 200 grams of film and fiber grade polypropylene having a melt index of 2-4 and a density of 0.88. The blended pellets are melt mixed using a 1% inch single screw extruder heated to 200C. The extruded strand is diced into inch pellets. The Vs inch pellets are melt extruded into approximately 1/32 inch diameter strand and drawn by the Godet at 10 feet per minute. The strand is then passed into a hot stretching bath at C. and is drawn out of the bath at 100 feet per minute. This imparted on orientation expressed as 900% stretch. The strand is abritrarily cut to staple lengths of about 1 inch to about 3 inches and is next fed to a Noble and Wood Cycle Beater with a blade clearance setting of 6 mils. The strand is beaten to produce a pulp of the mixed polymer mono-filament.

The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 50 mils thick.

The pressed felt is dried in an air-oven at 50C. After drying the felt is pressed at C. and 50 psi to produce a full density molded sheet having a thickness of 25 mils. The sheet is then placed in a beaker containing toluene to extract the polystyrene. The sheet after extraction is dried and is the semi-finished leather like product. The sheet is approximately one-half of its full density, has porosity comparable to calf skin, showing an MVT of 30, and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather.

EXAMPLE 5 Example 4 is repeated except that the 2,000 grams mixture contains 600 grams of Polyurethane D, 156 grams of Polyurethane C, 244 grams of the polypropylene and 1,000 grams of the polystyrene. The four resins are in approximately Vs inch diced form and tumble 23 blended. The blended pellets are melt mixed in the extruder at 175C. and the extruded strand is diced and re-extruded into an approximately l/32 inch diameter strand which is drawn by the Godet at 20 feet per minute. The strand is then passed into a glycerine stretching bath at 125C. and then drawn out of the bath at 220 feet per minute. There is obtained a molecular orientation expressed as 1,000% stretch. The strand is cut and next fed to a Noble and Wood Cycle Beater with a blade clearance setting of 7 mils. The strand is beaten to produce a pulp of the mixed polymer mono-filament.

The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 35 mils thick.

The pressed felt is dried in an air-oven at 25C. After drying the felt is pressed at 170C. and 100 psi to produce a full density molded sheet having a thickness of 18 mils. The sheet is then placed in toluene to extract the polystyrene. The sheet after extraction is dried. The sheet is approximately one-half of its full density, has porosity comparable to glove leather or a closely woven fabric, and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather as well as the suppleness of a soft woven fabric.

EXAMPLE 6 The process of Example is repeated except that the 2,000 grams mixture is made by combining 1,000 grams of the polystyrene and 1,000 grams of Polyurethane A. The two resins are both in powder form and tumble blended. The blend is melted using a 1% inch single screw extruder at 195C. and then the extruded strand is diced as before. The resulting pellets are again extruded in approximately l/32 inch diameter strand and drawn at 19 feet per minute. The strand is then passed into a glycerine stretching bath at 125C. and drawn out of the bath at 90 feet per minute, thus, imparting a molecular orientation expressed as 370% stretch. The strand is cut and next is fed to a Noble and Wood Cycle Beater with a blade clearance setting of 6 mils. The strand is beaten to produce a pulp of the mixed polymer mono-filament.

The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 17 mils thick.

The pressed felt is dried in an air-oven at 75C. After drying the felt is pressed at 190C. and 50 psi in a platen press to produce a full density molded sheet having a thickness of 7.2 mils. The sheet is then placed in toluene to extract the polystyrene. The sheet after extraction is dried. The sheet is approximately one-half of its full density, has substantial porosity, showing an MVT of 51, and mechanical properties between that of glove leather and a supple woven fabric. It has excellent flex life and abrasion resistance. Furthermore it has the break and tactility of leather.

EXAMPLE 7 A 1000 grams mixture is made by combining 500 grams of the polystyrene of Example 2 and 500 grams of Polyurethane B. The two resins are in approximately Vs inch diced form and tumble blended. The blended pellets are mixed in the melt in a 1% inch single screw extruder at 220C. The extruded strand is diced into /8 inch pellets and the pellets are mixed and again extruded but this time into a strand having a diameter of l/32 inch. The strand is drawn from the extruder by a Godet at 20 feet per minute. The strand is then passed into a glycerine stretching bath at 130C. and is drawn out of the bath at feet per minute, to impart a molecular orientation expressed as 400% stretch. The strand is cut to lengths of one-quarter inch to about 6 inches and next fed to a Noble and Wood Cycle Beater with a blade clearance setting of 6 mils. The strand is beaten to produce a pulp of the mixed polymer monofilament.

The pulp is processed into 12 inches X v12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 123 mils thick.

The pressed felt is dried in an air-oven at 75C. After drying the felt is pressed at 190C. and 50 psi to produce a full density molded sheet having a thickness of 62 mils. The sheet is then placed in toluene to extract the polystyrene. The sheet after extraction is dried and is the semi-finished leather like product. The sheet is approximately one-half of its full density, has porosity comparable to leather and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand" of leather.

EXAMPLE 8 The process of Example 3 is repeated except that the 2,000 grams mixture contains 1,000 grams of the polystyrene, 333 grams of the polypropylene of Example 4 and 666 grams of Polyurethane D. The strand of the reextruded pellets is approximately 1/32 inch diameter and drawn by the Godet at 20 feet per minute. The strand is passed into the glycerine stretching bath and drawn out of the bath a 250 feet per minute to impart a molecular orientation expressed as 1,150% stretch. The strand is cut and next is fed to a Noble and Wood Cycle Beater with a blade clearance setting of 8 mils. The strand is beaten to produce a pulp of the mixed polymer mono-filament.

The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 200 mils thick.

The pressed felt is dried in an air-oven at 55C. After drying the felt is pressed at 165C. and 150 psi to produce a full density molded sheet having a thickness of 125 mils. The sheet is then placed in toluene to extract the polystyrene. The sheet after extraction is dried and is the semi-finished leather like product. The sheet is approximately one-half of its full density, has porosity comparable to leather and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather.

EXAMPLE 9 The process of Example 8 is repeated except that the 2,000 grams mixture is made by combining 756 grams of Polyurethane D, 244 grams of the polypropylene and 1,000 grams of the polystyrene. The strand upon extrusion has a l/64 inch diameter and is drawn by the Godet at 30 feet per minute; then it is passed into the glycerine stretching bath at C. and drawn out of the bath at 330 feet per minute to impart a molecular orientation expressed as 1,000% stretch. The cut strand is next fed to a Noble and Wood Cycle Beater with a 25 blade clearance setting of mils. The strand is beaten -to produce a pulp of the mixed polymer mono-filament.

26 sity sheet of 60 mils thickness. The following are comparative properties characterizing this porous sheet:

5% Bally Thick- Den- Elonga- Tangent Flexo- Satra ness sity Tensile tion Modulus Tear MVT meter Flex mils gm/cc psi psi lb/in. gm/M"/hr cycles cycles Synthetic leather of Example 12 60 0.530 817 93 2,450 216 18 1.6MM 8MM Corfam (Dupont) 62 0.500 1,200 36 2,350 125 19 l00M Aztran (Sold by Bv F. Goodrich Company) 60 0.580 1,380 23 2,100 I83 17 50M lMM Calf Skin perpendicular to Backbone 50 0.630 2,700 44 2,300 216 28 l.6MM 8MM Calf Skin parallel to Backbone 50 0.630 3,800 48 4,000 347 28 1.6MM 8MM 75% relative humidity at 82"Fv Unfinished, not surface coated 1.6MM and 8MM" mean 1.6 million and 8 million, respectively. IO0M" and $0M mean 100 thousand and 50 thousand, respectively.

EXAMPLE 13 The pulp is processed into 12 inches X 12 inches hand sheets using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The felt or paper is 150 mils thick.

The pressed felt is dried in an air-oven at 60C. After drying the felt is pressed at 170C. and 50 psi to produce a full density molded sheet. The sheet is then placed in toluene to extract the polystyrene. The sheet after extraction is dried and is the semi-finished leather like product. The sheet is approximately one-half of its full density, has porosity comparable to leather and mechanical properties similar to leather. It has excellent flex life and abrasion resistance. Furthermore it has the break and hand of leather.

EXAMPLE 10 The process of Example 9 is repeated except that the 2,000 grams mixture contains 1,000 grams of polyvinylacetate, 667 grams of Polyurethane D and 333 grams of the polypropylene. The melt mixing in the single screw extruder is at 170C. and the extruded strand has a diameter of l/32 inch and is drawn by the Godet at feet per minute. The glycerine stretching bath is at a temperature of 120C. and the strand is drawn out of the bath at a rate of 250 feetper minute, thus, imparting a molecular orientation expressed as 900% stretch. Using the procedures of the previous examples, an excellent synthetic leather is produced from a felt of this fiber using toluene to extract the polyvinylacetate fiber therein.

EXAMPLE 1 1 Example 6 is repeated except that the inch melt mix pellets are extruded through a multi-orifice die to produce a 20 filament, continuous filament yarn wherein each filament has a denier of 0.5 and is stretch oriented.

The yarn is woven into a 120 X 120 pick fabric and a 12 inches X 12 inches swatch is pressed at 190C. in a platen press at 50 psi to produce a full density molded sheet having a thickness of about 2 mils. The sheet is then extracted with toluene to remove the polystyrene using the procedure of Example 6 to produce a soft, highly porous sheet which has good strength and considerable elasticity.

EXAMPLE l2 Repeating Example 6, except that the felt is made 123 mils thick and hot pressed at 190C. to a full den- The procedure of Example 2 is repeated by combining equal parts by weight of the polypropylene and polystyrene without adding Polyurethane D. The pulp of polypropylene and polystyrene polymer fibers is processed into a 12 inches X 12 inches hand sheet, 15 mils thick. After hot pressing and extraction with toluene, followed by drying, there is obtained a 5 mil thick p0- rous nonwoven sheet of polypropylene fibers. The sheet is broadly and finds usefulness as a battery separator and as a gasket.

EXAMPLE 14 The procedure of Example 13 is repeated with equal parts by weight of the same polypropylene and polycaprolactam having a molecular weight of 40,000. There is obtained a 2 mil thick porous nylon sheet from extraction with hot toluene of hot pressed 10 mil thick felt. The nonwoven has good hand and drape and can be used in making outerwear.

What is claimed is:

l. A porous sheet-like structure comprising:

A. Forming shaped articles by melt extruding with drawing an immiscible fiber forming polymer mixture, wherein at least one polymer of said mixture is converted to an extractable fiber and at least one other polymer of said mixture is converted to a non-extractable fiber having a cross-sectional diameter normal to its elongated shape of less than about five microns;

B. Forming said shaped articles into an unbonded sheet;

C. Heating said sheet made in (B) to a temperature whereby to interfuse substantially all of the nonextractable fibers therein sufficient to unite all of the fibers in the sheet;

D. Extracting as a solution at least a portion of the extractable fibers from said sheet in an amount sufficient to have said sheet possess moisture vapor transmission; and

E. Separating the solution from the sheet in an amount to produce a porous sheet possessing moisture vapor transmission and containing the ultrafine, thermoformable, molecularly oriented nonextractable fibers therein, which nonextractable fibers are interbounded by fusion at a plurality of points where such nonextractable fibers interconnect, and said fibers define open and unfilled pores which are interconnected and extend from surface to surface of said sheet, and said fibers have a shape end less than about microns.

cross-sectional diameter normal to their elongated 4 Page 1 of 2 UNITED STATES PATENT OFFIQE Patent No:

W. A. Miller and R. 'D. Jenkinson lnventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 2. "contail" should read contain--.

Column 6, line 42, "hyroxyl" should read --hydroxyl--.

Column 10, line 66. "of" should read -or-.

l2 18o "atravked" should read --attacked--.

Column 12, us 24. "loosen" should read --loosened-.

Column 19, line 12. "it" should read --if-.

, Column 19, line 9; "cohesion" should read cohesive Column 24, line 36. "a" should read --at--.

. V Page 2 of 2 UNITED STATES PATENT OFFICE QERTEFIQATE @F CQERECTKQN Patent No. 3,914,501 DatedQ b 21 19B W. A. Miller and Jenkinson Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 25, Footnote 1., "82F" should read -85F--.

Column 26, line 29. "broadly" should read --boardy--.

Signed and [SEAL] RUTH C. MASON Arresting 0 C-MARSHAILIL DAMN Commissioner oflarents and Trademarks twenty-second Day 0 June 1976 l

Claims

1. A POROUS SHEET-LIKE STRUCTURE COMPRISING: A. FORMING SHAPED ARTICLES BY MELT EXTRUDING WITH DRAWING AN IMMISCIBLE FIBER FORMING POLYMER MIXTURE, WHEREIN AT LEAST ONE POLYMER OF SAID MIXTURE IS CONVERTED TO AN EXTRACTABLE FIBER AND AT LEAST ONE OTHER POLYMER OF SAID MIXTURE IS CONVERTED TO A NON-EXTRACTABLE FIBER HAVING A CROSS-SECTIONAL DIAMETER NORMAL TO ITS ELONGATED SHAPE OF LESS THAN ABOUT FIVE MICRONS, B. FORMING SAID SHAPED ARTICLES INTO AN UNBONDED SHEET, C. HEATING SAID SHEET MADE IN (B) TO A TEMPERATURE WHEREBY TO INTERFUSE SUBSTANTIALLY ALL OF THE NON-EXTRACTABLE FIBERS THEREIN SUFFICIENT TO UNITE ALL OF THE FIBERS IN THE SHEET, D. EXTRACTING AS A SOLUTION AT LEAST A PORTION OF THE EXTRACTABLE FIBERS FROM SAID SHEET IN AN AMOUNT SUFFICIENT TO HAVE SAID SHEET POSSES MOISTURE VVAPOUR TRANSMISSION, AND E. SEPARATING THE SOLUTION FROM THE SHEET IN AN AMOUNT TO PRODUCE A POROUS SHEET POSSESSING MOISTURE VVAPOUR TRANSMISSION AND CONTAINING THE ULTRAFINE, THERMOFORMABLE, MOLECURLARLY ORIENTED NONEXTRACTABLE FIBERS THEREIN, WHICH NONEXTRACTABLE FIBERS ARE INTERACTABLE BY FUSION AT A PLURALITY OF POINTS WHERE SUCH NONEXTRACTABLE FIBERS INTERCONNECT AND SAID FIBERS DEFINE OPEN AND UNFILLED PORES WHICH ARE INCONNECTED AND EXTEND FROM SURFACE O SURFACE OF SAID SHEET, AND SAID FIBERS HAVE A CROSS-SECTIONAL DIAMETER NORMAL TO THEIR ELONGATED SHAPE END LESS THAN ABOUT 5 MICRONS.