CS241488B2 - Resin impregnated fibrous flat formation - Google Patents

Abstract

A simulated leather sheet material comprises: a polymer impregnated fibrous mass with a grain layer forming one surface, the grain layer having an actual density equal to its bulk density and a split layer forming the opposing surface, the split layer having a bulk density less than its actual density, said sheet material having a density decreasing from the grain layer to the split layer, the ratio of fibre to polymer being substantially uniform throughout said sheet material. There is also disclosed a method of forming such simulated leather sheet material.

Description

The invention relates to fibrous sheet structures impregnated with artificial resin, in particular to units having the same specific gravity throughout their volume, as well as products made therefrom.

Synthetic resin impregnated fabrics, such as fabrics, textile webs, waterleave webs, etc., are used for a variety of purposes, including imitation leather in the form of vinyl products, etc., technical sheets such as conveyor belts and the like Ware.

Methods known in the art for impregnating a sheet of a kind include impregnating or coating a porous material with a polymeric resin, such as polyurethane, vinyl, or the like. Polyurethanes have found widespread use as coating or impregnating agents for a wide range of their chemical and physical properties, particularly in terms of flexibility and chemical resistance. Several different working techniques are used to impregnate porous sheets with polymeric resin. One known method consists in using a polymer in an organic solvent, wherein the sheet is immersed in solution and the solvent is then removed therefrom. Such solvent systems are disadvantageous since the solvent is in many cases toxic and must either be recovered for reuse or> disposed of. Moreover, such systems are expensive and do not always produce the desired product, since when solvent evaporates from the impregnated porous sheet, the resin tends to migrate, resulting in an inhomogeneous impregnation of the porous sheet, resulting in excess resin at the surface of the sheet. and vice versa a lack of remaining volume.

Some aqueous polymer systems have been proposed to alleviate the problems associated with solvent systems. When forming sheets impregnated with aqueous polymers, the aqueous component must be removed. This again requires heat, and again the polymer migrates to the surface of the impregnated sheet.

According to one method of combining polyurethane solutions with porous substrates, the polymer in an organic solvent is applied to the substrate, e.g., a needled polyester fiber web. The assembly is then treated with a bath containing a mixture of organic solvent for the polymer and a non-solvent-containing substance that is at least partially miscible with the solvent until the layer coagulates to a cellular consistency with interconnected micropores. The solvent is removed from the coating layer together with the non-solvent to form a solvent-free microporous layer.

This process imparts acceptable properties to polyurethane impregnated materials, but its disadvantage resides in the organic solvent system, since in the case of high quality polyurethanes, relatively toxic high boiling solvents have to be used. This method is described, for example, in US Pat. No. 3,208 · 875.

According to another method, it is proposed to use polyurethane dispersions in organic carriers to coat porous substrates, as is known from U.S. Pat. No. 3,100,721. In this method, the dispersion is applied to the substrate and allowed to coagulate by additional addition of a non-solvent. Although this method has met with some success, it has two major drawbacks: (1) the dispersion carrier is essentially organic because only a small proportion of the non-solvent, preferably water, is required to form the dispersion; (2) there is only a narrow selection of non-solvents, making it difficult to obtain reproducible results.

One particularly effective method of preparing composite sheets by impregnating a porous substrate is described in US Pat. No. 4,171,391.

According to this method, the porous sheet is impregnated with an aqueous ionic polyurethane dispersion and the impregnating agent is allowed to coagulate therein. The resulting product is then dried to form a composite sheet. The purpose of the present invention is to improve this basic process and, in some cases, to extend its scope.

Impregnated porous substrates and similar materials have been proposed as · skin substitutes in order to produce a product with the characteristics of natural leather.

Properly treated natural leather is highly rated in a wide range of industries for its durability and aesthetic properties. Due to the scarcity of natural leather and the relatively high cost of processing it for certain uses, economic aspects have necessitated its replacement by synthetic materials in some fields. For example, it has been proposed to use synthetic materials for the manufacture of shoe uppers, upholstery, clothing, luggage, bookbinding.

Since these different applications require different physical, chemical and aesthetic properties, it was necessary to use different processes and different materials to achieve a satisfactory product comparable to natural leather products, although in most cases these synthetic materials clearly distinguish them from natural leather.

Natural leather from animal leather shows both the face side, which in most cases is most desirable for its aesthetic appearance, and the reverse side - the so-called split leather. The cheek layer represents the epidermis of the animal and is very smooth, while the glaze layer is in most cases coarse and fibrous.

One method of preparing the synthetic material as a skin substitute comprises impregnating and / or coating a porous material, e.g., a fabric, polyurethane, vinyl, or a similar chemical substance. P, ro · A wide range of chemical and physical properties, particularly in terms of flexibility and chemical resistance, have gained great popularity as a coating or impregnation material.

Synthetic materials for use as a substitute for natural leather must provide (1) planar formations which are particularly suitable for use in the manufacture of classic leather goods, (2) planar formations of standard widths customary in the textile industry (unlike cd natural products which are cut and (3) the versatility of the end use, for example, when subjected to a variety of chemical processing conditions to impart easy maintenance and durability characteristics to these products; and (4) a product with its strength, feel natural, smooth and smooth

Should the skin substitute for use in the manufacture of uppers of shoes, have a skin-like appearance without undesirable characteristic vapor as in the fabric, show a satisfactory degree of water vapor permeability to the uncoated side of the uppers, ie, the minimum rough corrugability). 'Leather quarry' - as the term commonly used in the leather and upholstery industry - is manifested in the behavior of well-groomed leather when folded or creased. The skin depot is characterized by a smooth curved contour often showing numerous fine wrinkles in the compressed area of the depot area. This contrasts with sharp stock or coarse wrinkles manifested in folded paper, film or foil; this property of undesirable appearance is known as pin wrinkling.

The feel of the leather is very typical and differs considerably from that of synthetic materials, which is unlike rubber-like leather.

Polyurethane polymers used as materials for coating and impregnating textiles for the manufacture of leather substitutes have long been known. For example, polyurethanes that are highly resistant to solvents and which give coated fabrics certain important properties such as dry cleaning and excellent durability can be prepared. The basic chemistry of polyurethanes involving reactions between isocyanate groups and multiple reactive hydrogen molecules - such as polyols and polyamines - gives these substances great versatility and variability in the resulting chemical and physical properties by appropriate selection of intermediates to achieve workability and desired balance of performance requirements .

There are various ways of applying polyurethane solutions or post-coagulable liquid polymers to porous substrates. These methods are well known to those skilled in the art. Article in Journal of Coated Fabrics, vol. 7 (July 1977), pp. 43-57, discloses some of the commercial coating systems, such as a rotary cylinder device, a wading cylinder, an engraved cylinder, and the like. Brush and spray systems can also be used to apply polyurethanes to porous substrates.

These polyurethane solutions, after impregnating or coating the porous substrates, are either dried or cured in a variety of ways such as warm air, infrared radiation and the like. A characteristic feature of these processes is the deposition of the polymer in a very thin layer, thereby forming a coated formation which, when folded, is said to create undesirable sharp folds and not a typical leather face fracture. Other methods of combining polymeric solutions, especially polyurethane solutions, with porous substrates are described, for example, in US Pat. No. 3,208,875 and 3,100,721.

An improved method of impregnating textiles which is the subject of US Pat. No. 4,171,391, includes some of the operations necessary to form a skin replacement sheet according to the present invention.

The present invention relates to a resinous fiber impregnated sheet having a specific gravity of 0.4 to 0.75 g / cm @ ³ , consisting of an iron fiber web having a bulk density of not more than 0.5 g / cm @ ³ and a thickness of at least 0.75 mm. of non-meltable fibers uniformly impregnated with a water-dispersible resin, characterized in that the needled fiber web is impregnated with a weight of 70 to 400% polymer resin based on the weight of the needled web, the density of the needled fiber web being uniform; specific gravity, the shape is porous and the impregnated fibrous web comprises polymer resin coated and uncoated fibers. Preferably, the fibrous needled web comprises from 200 to 300% by weight of polyurethane based on the weight of the fibrous web.

According to the invention, the fiber sheet is produced by thoroughly saturating the needled fibrous web with an aqueous dispersion or emulsion of a polymeric resin, contacting it with a coagulating agent, and drying it after the coagulation of the resin. Preferably, the dispersion or emulsion comprises 5 to 60% by weight of solid polymeric resin.

The impregnated fibrous web of the present invention exhibits a novel and unusually useful structure that is suitable after processing to obtain further advantages.

Further, according to the invention, a sheet material is substituted which substitutes the skin and which has the appearance and properties of natural skin as well as other skin-like physical features.

The resin-impregnated fibrous web consists of a needle-bonded fibrous web and poles of the resin dispersed in the material. The bulk density of the impregnated web in the entire volume of the sheet is less than the actual density of the web, or the web is porous. The impregnated web comprises resin-coated fibers as well as uncoated fibers.

The skin replacing the sheet is made of impregnated fleece. This formation consists of a polymer-impregnated fibrous mass with a facing layer and a split layer which forms the reverse side. The density of the facing layer is equal to its density, while the density of the split layer is lower than its density. The total volume density of the sheet decreases from the mating layer to the chipboard layer.

The term "bulk density" refers to the weight of the material, including the volume of air contained therein. On the other hand, the term "specific weight" refers to the weight of the material without this air volume.

The sheet formation which can be used in the practice of the present invention includes spunbonded, needled webs and papermaking webs of water suspension. Suitable fibrous materials are natural fibers, in particular cotton and wool, synthetic fibers such as polyester, nylon, acrylic and so-called modacrylic fibers, and fibers of regenerated cellulose. They are best suited to this; For this purpose, a suitable pulp in the form of a needle-punched web made of said natural and synthetic fibers. Preferred are denier fibers of 1 to 5 denier and staple or staple lengths suitable for carding; between 2.5 and 15.2 mm or more, preferably between 3.8 and 7.6 mm.

High, medium and low density fiber webs of up to 0.5 g / cm ^{@ 3} are suitable for the purposes of the invention. These high-weight webs are generally made of wool. When synthetic fibers are used to prepare the web, the specific gravity is up to 0.25 g / cm ³ . For the purposes of the invention, the specific weight of the needled needles in the range of 0.08 to 0.5 g / cm ³ is preferred. The thickness of the web can be up to 12.7 mm, preferably in the range 3.0 to 10.0 mm, but at least 0.8 mm. On. In contrast to the relatively loosely bonded, sparse needles which have little or no cohesion, the nonwoven webs for carrying out the method according to the invention are also distinguished by a suitable needling, high compactness or coherence.

Polymeric resins suitable for the invention are preferably of the type which is soluble, emulsifiable or dispersible in water and which is capable of subsequent coagulation from the aqueous system by using ^one ionic coagulant.

The preferred polymer is a polymer prepared synthetically from acrylic monomers such as alkyl acrylates and methacrylates, acrylonitrile, methacrylonitrile and other well known acrylic monomers. These acrylic monomers can be polymerized by emulsion polymerization to form latex, or other free radical polymerization reactions, followed by solubilization and emulsification in water. The emulsification or solubilization system must be such that when the emulsion is contacted with a concentrated acid or base, the polymer coagulates from the aqueous system and becomes substantially insoluble.

Most preferably, emulsified and water dispersed polyurethanes are used for this purpose. The emulsified polyurethanes described, for example, in US Pat. No. 2,968,575 are prepared and dispersed in water by detergents under the influence of considerable shear forces. In forming these polyurethane emulsions, the emulsifier or detergent must be ionic in nature so that the ion added to the aqueous system will induce coagulation of the polymer. The most effective polyurethanes for the purposes of the invention are polyurethanes known in the art to be ionically dispersible in water.

In order to obtain ionogenic aqueous polyurethane dispersions, it is preferable to prepare polymers containing free acid groups, preferably carboxylic acids, which are covalently bonded to the backbone of the poles; meru. Neutralization of these carboxyl groups with an amine, preferably a water-soluble _λ monoamine, makes it possible to dilute with water. Care should be exercised in selecting the compound with the presence of a carboxyl group, since isocyanates, which are an essential component of any polyurethane system, generally react with carboxyl groups. However, as disclosed in U.S. Pat. No. 3,412,054, 2,2-hydroxymethyl substituted carboxylic acids react with organic polyisocyanates without appreciable reaction between the acid and the isocyanate groups due to stear inhibition of the carboxyl by adjacent alkyl groups. In this way, a polymer containing carboxyl groups can be obtained which are neutralized with a tertiary monoamine, thereby forming a quaternary ammonium salt and, consequently, dilutability with water.

Suitable carboxylic acids, preferably stearically inhibited carboxylic acids, are well known and readily available. For example, they can be prepared from an aldehyde that contains at least two α-position hydrogens that react in the presence of a base with two equivalents of formaldehyde to 2,2-hydroxymethylaldehyde.

This aldehyde is then oxidized to. acid according to a method known in the art. Such acids have a structural formula

CH ₂ OH

R = C-COOH

CH 2 OH wherein R is hydrogen or alkyl of up to about 20, preferably up to 8, carbon atoms. Preferred for this purpose is 2,2-di- (hydroxymethyl) -propionic acid, and polymers with attached carboxyl groups are referred to as anionic polyurethane polymers.

Alternatively, water dilutability according to the invention can be obtained using cationic polyurethane and linked amine groups. Similar cationic polyurethanes are described in US Pat. No. 4,066,591, especially in Example 17. Anionic polyurethane is preferred in the context of the present invention.

The preparation of polyurethanes suitable for carrying out the invention involves, in particular, the reaction of di- or polyisocyanates with compounds with multiply reactive hydrogens which are suitable for the preparation of polyurethanes. Such diisocyanates and reactive hydrogen compounds are described in detail in US Pat. Nos. 3,412,034 and 4,046,729. In addition, these processes describe, by way of example, methods for preparing these polyurethanes. According to the invention, aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used to prepare the polymer. These diisocyanates include, for example, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, metaphenylene diisocyanate, diphenylene 4,4'-diisocyanate, methylene bis (4-phenylisocyanate),

4-coior-1,3-phenelenediisocyanate, naphthylene-1,5-diisocyanate, tetramethylene-1,4-diisocyanate, hexamethyley-1,6-diisocyanate, decamethyl ethyl-1,1-diisocyanate, cyclohexylene-1, 4-diisocyanate, methylene-bis (4-cyclohexylsocyanato), tetrahydronaphthylenediisocyanate, iso-ortho-diisocyanate and the like.

Arylene and cycloaliphatic diisocyanates have proved to be the most suitable for the practical application of the invention.

Arylene diisocyanates can be characterized in that their isocyanate group is attached to the aromatic nucleus. The most preferred isocyanates are the 2,4- and 2,6-isomers of tolylene diisocyanate and mixtures thereof, for their ease of availability and reactivity. Furthermore, cycloaliphatic diisocyanates (in particular 4,4-methylene-bis (cyclohexylisocyanate) and isophorone diisocyanate) are highly preferred for carrying out the invention.

The choice of aromatic or aliphatic diisocyanates is divided by the end use of the material. As is known in the art, aromatic isocyanates can be used wherever the end product is not exposed to excessive ultraviolet radiation which causes yellowing of these polymer systems. Conversely, aliphatic diisocyanates are most suitable for outdoor applications since their tendency to yellow when exposed to ultraviolet radiation is less. Although this fundamental difference can be taken as a criterion in the choice of the appropriate isocyanate, the aromatic diisocyanates can be further stabilized by known stabilizers against the effects of ultraviolet radiation in order to improve the final properties of the polyurethane-impregnated sheet. In addition, anti-oxidants can be added in an amount known in the art, again improving the properties of the final product. Typical antioxidants for this purpose are thioethers and phenolic antioxidants such as 4,4'-butylidin-bis-metacresol and 2,6-di-tert-butyl-p-cresol.

The isocyanate is reacted with compounds containing multiple reactive hydrogen such as diols, diamines or triols. In the case of diols or trioles, typical representatives are either polyalkylene ether or polyester polyols. The polyalkylene ether polyol is a suitable polymer containing active hydrogen for the formation of polyurethane. Most preferred polyglycols have a molecular weight of 50 to 10,000, with a molecular weight in the range of 400 to 7,000 being most suitable for the purposes of the invention. Polyether glycols further improve flexibility in proportion to their molecular weight growth.

Non-limiting examples of polyether glycols include polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol, polyoctamethylene ether glycol, polydecamethylene ether glycol, polydodecamethylene ether glycol, and mixtures thereof. It is also possible to use polyglycols containing several different radicals in the molecular chain, such as HOJCH2OC2.H4O J _n H, in which n is an integer greater than 1.

The polyol may also be a terminal OH-bonded or polyester which can be used either instead or in combination with polyalkylene ether glycols. Examples of these polyesters are reactive acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols such as ethylene, propylene, tetramethylene or decamethylene glycol; further substituted methylene glycols such as 2,2-dimethyl-1,3-propanediol, cyclic glycols such as cyclohexadiol and aromatic glycols.

In general, aliphatic glycols are preferred when flexibility is desired. These glycols react with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl ethers or ester-forming esters to form low molecular weight polymers having a melting point of preferably less than about 70 ° C and a molecular weight corresponding to the weight of the polyalkylene ether glycols. Acids suitable for the preparation of such polyesters are, for example, phthalic, maleic, succinic, adipic, suberic (cork), terephthalic and hexahydrophthalic acids, as well as alkyl- and halogen-substituted derivatives of these acids. In addition, hydroxyl-terminated polycaprolactam may be used.

Particularly suitable is the cross-linked polyurethane system described in U.S. Pat. No. 212,711 (01/10/79) entitled "Crosslinked Polyurethane Dispersions" (Andrea Russiello).

As used herein, the term "ionic dispersant" refers to an ionizable acid or base capable of forming a salt with a solubilizing agent. These dispersants include amines, preferably water-soluble amines such as triethylamine, tripropylamine, N-ethylpiperidine, as well as acids, preferably acetic acid, propionic acid, lactic acid, etc. The acid or amine must be selected appropriately to the solubilizing group attached to the polymer chain .

The desirable elastomeric nature generally requires about 20 to 80 wt% of the long chain polyol (i.e., 700 to 2000 eq) in the polymer. The degree of elongation and elasticity can vary widely from product to product, since it depends on the desired properties of the final material.

The preparation of polyurethanes suitable for carrying out the invention consists in reacting the polyol and diisocyanate in a molar excess to form an isocyanate-terminated polymer. Although suitable reaction conditions, reaction times and temperatures vary greatly depending on the isocyanate and polyol employed in the reaction, these variations are well known in the art. It will be appreciated by those skilled in the art that the reactivity of substances entering the reaction requires that the reaction rate be adjusted with respect to undesirable side reactions resulting in degradation of color and molecular weight. Typically, the reaction may be carried out with stirring at 50 to 120 ° C for one to four hours. To obtain bound carboxyl groups, the isocyanate-terminated polymer is reacted with a dihydroxylic acid-deficient molar for one to four hours at 50 to 120 ° C to form an isocyanate-terminated prepolymer.

It is recommended to add the acid, preferably in the form of a solution, for example in N-methyl-1,2-pyrrolidone or N-N-dimethylformamide.

Typically, the amount of acid solvent should not be more than about 5% of the total charge to minimize the concentration of the organic solvent in the polyurethane composition. Once the dicarboxylic acid enters the polymer chain, the carboxyl groups are neutralized with an amine for about 20 minutes at a temperature of 58-75 ° C, whereupon the chain extension and dispersion are achieved by adding water with stirring. Water-soluble diamine may be added to the water as an additive to extend the chain.

Chain elongation involves reacting the remaining isocyanate groups with water to form urea groups and further polymerize the polymeric material so that all isocyanate groups are reacted by adding a significant stoichiometric excess of water. It is to be appreciated that the polyurethanes of the invention are thermoplastic in nature, which means that they cannot be cured after formation without an additional hardener. Preferably, no such hardener is added when forming the composite sheet.

Sufficient water must be added to disperse the polyurethane to a concentration of about 10 to 40% by weight, a solids and a viscosity in the range of 10 to 1000 mPa s. The viscosity can be adjusted according to the impregnation conditions by means of a suitable dispersion composition, which is largely determined by the desired properties of the final product. It should be emphasized that it is not necessary to use any emulsifiers or dies to achieve the stability of the dispersions.

Those skilled in the art are familiar with ways to modify the primary polyurethane dispersion with respect to the end-use application, for example by adding colorants, compatible vinyl polymer dispersions, ultraviolet filter additives, antioxidant stabilizers.

The dispersions prepared according to the invention can be characterized by determining the non-volatile fraction, particle size, viscosity and mechanical properties of the strips of the cast film.

In practice, the concentration value of the process of the invention is governed by the desired percentage of the composition added to the needled web.

The viscosity of the dispersion is usually in the range of 10 to 1000 mPa. The low viscosity - due to the viscosity of the same polymers at the same solids value in the polymer solutions in the organic solvent - promotes rapid and perfect penetration of the aqueous dispersion and subsequent penetration of the coagulant. In contrast, the polyurethane solutions used usually have a viscosity of several thousand, often up to 50,000 mPa. s at concentrations of 20 to 30%.

The fibrous web should be impregnated with polymers in an amount of from 70 to 400% by weight, calculated on the weight of the web.

A preferred range is 200 to 300 wt.

The coagulation is carried out by contacting the impregnated substrate with an aqueous solution of an ionogerm medium intended to replace the solubilizing ion. In theory, although the invention is not based on this theory, in the case of an anionically solubilized polymer, the amine that neutralizes the carboxyl-containing polyurethane is replaced by a hydrogen ion, which reverses the anionic carboxyl and thus returns the polymer to its "undiluted" state. This causes the polymer to coagulate within the substrate structure.

In the case of the anioinactive polymer, a suitable ionogenic coagulant is an aqueous solution of acetic acid at a concentration of 0.5 to 75%, which is preferred to stronger acid solutions for relatively easy handling, low corrosion potential and disposal.

Salting out ,, ^u to coagulate by addition of a neutral salt is indeed feasible but not used due к having substantial amounts of salt, desirably about tenfold к acid concentration а к problems associated with contamination of the product.

When impregnating the needle web with a polymeric resin of the above type, the web is immersed in an aqueous ionic emulsion or dispersion having a concentration sufficient to receive at least 70% by weight of the bath, calculated on the weight of the web. Immediately prior to immersion in the aqueous emulsion or dispersion, the web should be compressed to remove air to achieve complete impregnation. The fleece impregnated with the aqueous dispersion or emulsion is passed between the scraper rollers or the like to remove excess dispersion or emulsion on the surface of the impregnated fleece.

Thereafter, the web is immersed in a bath containing a counter-ion, thereby coagulating with a material containing the counter ion, which diffuses through the web and induces coagulation of the resin in the fibrous structure. After coagulation, the fleece is squeezed to remove excess water and dried to form an impregnated sheet.

This process represents a further refinement of the process described in US Pat. No. 4171391 and its purpose is to achieve specific products. The differences between the two processes are that according to the present invention, the web is perfectly saturated with an aqueous dispersion or emulsion, which means that upon receipt of at least 70% by weight of polymeric resin (calculated from the weight of the web) virtually no air. a new web structure is obtained which has the same specific gravity throughout the mass and whose bulk density is less than the actual specific gravity of the sheet.

After the impregnated sheet has been formed, the mass gradient required to produce a material to replace the natural skin is induced. In the formation of a skin substitute, polymers are preferably used as impregnating agents for the sheet and are capable of fusing in particulate form when exposed to heat and pressure. Normally, these polymers are thermoplastic; however, some cross-linked coalescence polymers can also be used. In practice, the polyurethanes disclosed in Czechoslovak Patent No. 212,711 (October 2, 1978 to Andrea Russiello) have been shown to be particularly suitable for practicing the present invention for their ability to produce the desired weight gradient in the thickness of the material.

The characteristics of the skin substitute according to the invention are primarily of a physical nature, since a weight gradient is induced in the material from one side to the other side of the sheet. This gradient is preferably uniform, with one surface of the impregnated fibrous material representing a face layer in which the actual density is equal to the density.

This cheek layer imitates the cheek layer of natural skin. On the other side of the sheet, there is an area which represents a split layer whose bulk density is less than the actual density, and the material as a whole exhibits a uniform weight gradient. The split layer is somewhat fibrous in nature and mimics the split layer of natural leather.

The polymer is present in the leather substitute in an amount of at least 70% calculated on the weight of the fibrous mass.

Typically, the split layer achieves approximately 75% of the specific weight of the facing layer, thereby providing a porous facing layer imitating the natural skin facing layer. It is understood that the polymer is uniformly distributed throughout the fibrous mass in such a way that the ratio of fiber to polymer is uniform throughout its volume.

The skin substitute sheet is produced by treating the impregnated fibrous material, preferably the nonwoven sheet fibrous formation as described above.

As the impregnating agent, one of the polymers described in the above-mentioned Czechoslovak patent is most suitable.

According to one method of processing an impregnated nonwoven fibrous sheet to a leather substitute, the sheet is placed in a press and subjected to heat and pressure on both sides. This heat and pressure is sufficient to induce the fusion of polymer particles in the impregnating agent on the surface of the material, but they are insufficient to fully bond the polymer within the sheet. This process induces the formation of a mass gradient advancing from the interior of the nonwoven to its two surfaces. The resulting dimensions (i.e., thickness) of the heated and molded sheet can be controlled by the amount of pressure exerted in the process or by inserting the stop elements between the sheet plates, or by using a fixed pressure press.

In addition, an embossed pattern press can be used to achieve a specific surface finish of the sheet. After molding, the material is split in the middle of the thickness, so that two sheets are obtained, each having a face and a split layer.

According to another method of making a skin substitute according to the invention, the impregnated nonwoven starting material described above is placed in a press having only one heated plate to form a facing layer while the other side of the material is in contact with the cold plate to form a split layer.

Another method of making a skin substitute according to the invention is that the two pieces of impregnated nonwoven starting material described above are stacked and subjected to heat and pressure in a press sufficient to bond the polymer particles in the impregnating composition to the surface facing both pieces. to heated press plates. After pressing, the individual pieces are separated from each other again, thereby obtaining two planar shapes replacing the natural skin.

The leather substitute thus produced can then be polished, coated or further processed according to known leather coating technology.

According to another method, the facing layer can be formed on strips of impregnated nonwoven starting material unwound from coils by passing between a pair of calender rolls. One of them is preferably a metal smooth or embossed pattern roller, heated to a temperature of 149 to 205 ° C, while the other has a coating of soft, flexible material, such as rubber. The face layer is formed on the surface of the belt facing the metal cylinder. For the purpose of the invention, a suitable calendering process is usually carried out at a pressure of approximately 5 to 15 tonnes per meter of width of the strip passing between the rolls. Calendering can be facilitated by wetting the web with water in an amount of about 50 to 100 wt.

The structure of the impregnated sheet and skin substitute is illustrated more clearly in the accompanying drawing, in which is a plan view of the sheet produced according to Example 1 below, prior to splitting.

Referring to FIG. 1, a resin-impregnated sheet 10 manufactured according to Example 1 is shown.

The sheet 10 has an upper surface and a lower surface. Within the formation 10 there is a significant proportion of uncoated fibers, as well as resin agglomeration, voids, and resin coated fibers. The structure and consequently the bulk density of the sheet 10 is substantially uniform throughout the thickness of the material, although its structure on a microscopic scale is inhomogeneous.

The following examples illustrate several exemplary embodiments of the articles of the invention, as well as methods for their preparation.

Example 1

Heat-fixed needle-punched nonwoven fabric with a basis weight of 1200 g. m ² consisting of polyester, polypropylene and viscose fibers, the reagent thickness of which was 7.62 mm at a density of 0.16 g / cm ³ , was immersed in a polyurethane prepared according to Example 3 of the aforementioned Czechoslovak patent specification 212,711 ( Andrea Russiello). The polymer dispersion contained 22% solids and represented 120% by weight of the web. The web was immersed in a polyurethane dispersion for 10 minutes at room temperature, with all of the air contained therein expelled and the web was completely impregnated. The fleece surface was wiped on both sides with a flat spatula to remove excess aqueous dispersion and then immersed in a 10% acetic acid bath for 10 minutes at room temperature. By immersion in acid, the polyurethane is completely coagulated in the fiber structure. Excess acetic acid was washed from the web and the impregnated web was squeezed to remove excess water. The resin-impregnated web was split into four layers and each was then dried at a temperature of 149-177 ° C in an air circulation oven to produce four sheets each having a density of 0.41 g / cm ³ .

Example 2

The procedure described in Example 1 was repeated except that a web of 100% polyester fiber having a specific weight of 0.13 g.cm &^lt; ³ > and a thickness of 5.1 mm was used and was impregnated with the dispersion of Example 1 with 22% solids. The resulting impregnated sheet exhibited uniform weight, high cohesiveness and bulk density of 0.38 g / cm 3 throughout the volume.

Example 3

The procedure described in Example 1 was repeated except that a needle web of 100% polyester fiber 5.6 mm thick and a bulk density of 0.23 g.cm 3 was used, impregnated with a dispersion of 32% solids to form resin - impregnated fibrous sheet with a density of 0,56 g / cm ³ . The product prepared according to Example 3 was used as a polishing aid. It was tough, exhibited high tear strength, below 221488 integrity and shape recovery after crease.

The method of manufacture and the product produced according to the invention provide an impregnated fibrous sheet of high cohesiveness which is usable as the product itself or for the production of other products. The impregnated fibrous sheet can be further polished to give it the desired finish.

Example 4

Two 1.8 mm thick layers formed by the splitting of the nonwoven impregnated sheeting prepared in accordance with Example 1 were stacked, sandwiched between the press plates heated to 149 ° C and subjected to a pressure of 3.5 MPa for 30 seconds. The two layers were then peeled off again, yielding two layers replacing the natural skin.

The surfaces of the two sheets which had previously been in contact with the hot plates of the press corresponded to the cheek layer of the leather substitute. For both inner surfaces of both formations, a fibrous character was preserved, which corresponded to the surface of unpressed formations. Microscopic observation revealed that the skin-replacing material exhibited a density gradient, respectively. weight from the face to the split surface.

This skin substitute may be post-treated with other polymers by known methods to obtain the desired surface finish.

Claims (4)

OBJECT OF THE INVENTION A resin-impregnated fibrous sheet having a specific gravity of 0.4 to 0.75 g. Cm * ³ , consisting of a needled fibrous web having a density not exceeding 0.5 g. cm * ³ and a thickness of at least 0.75 mm of non-meltable fibers, uniformly impregnated with a water-dispersible resin, characterized in that the needle web is impregnated with 70 to 400% polymer resin by weight of the web, it is uniform, its bulk density is less than the density, the formation is porous and the impregnated fibrous web comprises polymer resin coated and uncoated fibers. 2. A fibrous sheet according to claim 1, characterized in that the needled fibrous web comprises from 200 to 300% by weight of polyurethane, based on the weight of the needled fibrous web. 3. A method according to claim 1, wherein the needled fiber web is completely saturated with an aqueous dispersion or emulsion of polymeric resin, contacted with a coagulating agent, and dried after the coagulation of the resin. 4. A method according to claim 3, characterized in that the fibrous needled web is impregnated with an aqueous dispersion or emulsion containing 5 to 60% by weight of solid polymeric resin.