NO854228L - STIMULATED, SHEET-SHORTED MATERIALS, AND PROCEDURES FOR MANUFACTURING SUCH A PRODUCT - Google Patents

Description

The invention relates to a simulated, sheet-like leather material, as well as a method for producing such a product.

Resin-impregnated sheet materials, such as cloth,

wadding, water-sedimented articles and the like are well known.

These resin-impregnated sheet materials are common for a variety of purposes, including imitation leather in the form of vinyl and the like, sheet construction materials such as conveyor belts and similar products.

Known methods for impregnating a special web involve impregnating or coating a porous material with a polymer resin, e.g. a polyurethane, a polyvinyl compound or a similar material. Polyurethanes have largely gained acceptance as coating or impregnation preparations due to their ability to greatly vary in chemical and physical properties, especially their flexibility and chemical

ke resistance. When impregnating the porous, sheet-like material with a polymer resin, different techniques have been used. A known method involves the use of a polymeric resin in a system of organic solvent, whereby the sheet-like material is dipped in the solution and the solvent is removed from there. These solvent systems are not desirable, as the solvent is in many cases toxic and must either be removed before new use or it must be discarded. These solvent systems are expensive and do not necessarily give a desirable product, as the resin, upon evaporation of the solvent from the impregnated, porous, sheet-like material, tends to migrate, forming a non-homogeneous impregnation of the porous, sheet-like material, which leads to resin enrichment at the surface of the sheet material instead of a uniform impregnation.

To reduce the solvent system problem, certain aqueous polymeric systems have been proposed. When forming impregnated, sheet-like material by impregnation with water-containing polymers, the water-containing part must be removed. Again cre-

is heated, and migration of the polymer towards the surfaces of the impregnated, sheet-like material occurs.

In a method that involves combining polyurethane solutions with porous substrates, the polymer is placed in an organic solvent on a substrate such as e.g. a needle-stitched polyester wadding. The composite product of polymer substrate is then bathed with a mixture of organic solvent for the polymer and a non-solvent for the polymer, which is at least partially miscible with the solvent, until the layer coagulates into a cellular structure with interconnected micropores. The solvent is removed from the coating layer together with the non-solvent so that a solvent-free, microporous layer is formed. Although this method provides acceptable properties for a polyurethane-impregnated fabric, it has the disadvantage of an organic solvent system, especially when high-performance polyurethanes are used, which require relatively toxic and high-boiling solvents. An example of this method is described in US patent 3,280,875.

In another method, polyurethane dispersions in organic carriers have been proposed and used for coating porous substrates, as described in US patent 3,100,721. In this system, a suspension is placed on a substrate and coagulated by further addition of a non-solvent . Although this problem solution has been used with some success, it involves two main limitations: (1) the carrier in the dispersion is essentially organic, after which relatively small amounts of non-solvent, preferably water, are required for the formation of a dispersion, and (2) ) there is a narrow applicable interval for added non-solvent, so that it is difficult to achieve reducible results.

A particularly valuable method for the production of sheet-like composite materials by impregnation of a porous substrate is described in US patent 4,171,391, to which reference is hereby made. In this system, a porous, sheet-like material is impregnated with an aqueous, ionic dispersion of a polyurethane, and the impregnating agent is coagulated in this. The composite material is then dried to form a sheet-like composite material. The present invention constitutes an improvement of this basic method•

Impregnated, porous substrates and similar materials have been proposed as leather substitutes with the aim of producing a

product with the same properties as natural leather.

Natural leather, suitably surface-treated, is valued for its durability and for its aesthetic qualities for a variety of applications. Due to the scarcity of leather and the increased price of treating leather for special applications, the economy is managed so that synthetic materials are used within certain application areas where leather goods have been used. Such synthetic materials have been proposed and used in the areas of shoe uppers, furniture upholstery, clothing, travel effects, bookbinding and similar areas of application. While these different areas of application require different physical, chemical and aesthetic properties, different methods using different materials must be used to obtain an acceptable product comparable to natural leather, although these synthetic materials are in most cases easily distinguishable from natural leather.

Natural leather from animal skins is composed of two surfaces: a surface that defines the grain layer, which in most cases is the most aesthetically desirable, and the opposite surface that defines the split layer. The grain layer is the animal's epidermis and is very smooth, while the split layer is in most cases rough and fibrous.

A method of producing a synthetic material as a substitute for leather involves impregnation and/or coating of porous material, e.g. fabric, with a polyurethane, a polyvinyl compound or a similar material. Polyurethane has largely been accepted as a coating or impregnation preparation due to its ability to vary greatly in chemical and physical properties, especially in terms of flexibility and chemical resistance.

The purpose of producing synthetic substitutes for leather is that such provide: (1) sheets which are particularly suitable for leather-like applications and upholstery, (2) sheets of uniform width which are usually used in the textile industry (as opposed to natural products which undergo significant weight and surface loss during cutting and surface treatment); (3) mutuality in end use, e.g. under a wide range of exposure conditions, where certain chemical treatments will aid in the maintenance and useful life of the properties; and, most significantly, (4) a product with strength, grip, fall and softness comparable to natural leather.

An imitated, sheet-like leather material should further, when used for shoe uppers, be characterized by a leather appearance without any undesirable cloth appearance, good water vapor permeability into the uncoated side of the upper, and a leather-grain break (minimal total wrinkling). "Leather-like grain breakage", as understood in the leather and upholstery industry, manifests itself in the behavior of well-surfaced leather when curling or crumpling. The leather fold is characterized by a smooth, bent contour, often with numerous fine folds in corresponding areas of the folded area. This is in contrast to sharp folds or overall wrinkles that form when paper or film is folded; this type of undesirable appearance is termed "needle curling".

The "grip" of leather is highly distinctive, and synthetic material normally has a rubber-like grip that contrasts with leather. Polyurethane polymers as a coating or impregnating agent for cloth to provide substitute material for leather have long been known. For example, polyurethanes can be produced that are highly resistant to solvents and abrasion, which give the coated materials unusual strength and cleaning ability when chemically cleaned. The basic chemistry of polyurethanes, which involves reactions between isocyanate groups and molecules with multiple reactive hydrogen, such as polyols and polyamines, provides great versatility and variability in the final chemical and physical properties when choosing intermediate products to achieve processability and the desired balance with the end-use's performance requirements.

There are various methods for applying polyurethane solutions or other later curable, liquid polymers to porous substrates, which are well known to those skilled in the art. An article in the Journal of Coated Fabrics, vol. 7 (July 1977), pp.43-57 describes some of the commercial coating systems, e.g. reverse roller coating, container feeder coating device, engraving and the like. Brushing and spraying can also be used for coating polyurethanes on porous substrates. These polyurethane solutions are dried or cured after impregnation or coating on the porous substrate by a method such as e.g. with heated air, infrared radiation, etc. Characteristic of these methods is the deposition of a polymer and a film-like layer, which tends to form a coated fabric that folds into undesirable sharp folds rather than learning grain fractures. Other methods for combining polymeric solutions and especially polyurethane solutions with porous substrates are shown, for example. in US Patents 3,208,875 and 3,100,721.

An improved method for impregnating cloth is described in US patent 4,171,391, which includes certain steps which are necessary for the formation of simulated, sheet-like leather material according to the invention.

A method for impregnating porous, sheet-like materials and especially needle-punched wadding, whereby uniform impregnation is provided in an aqueous system while forming a product with high tear strength and integrity, is described in application no. 81.3123.

There is also described an impregnated fiber web having a new and unusual, valuable structure adapted for use in the formed state or subsequently processed to provide additional benefits.

According to the present invention, a simulated sheet-like leather material is provided which has the appearance and properties of natural leather and which also has certain physical similarities to it.

A resin-impregnated fiber web is composed of a needle-punched, fibrous wadding and a polymer resin which is distributed in the wadding. The density of the impregnated web is completely uniform, whereby the spatial density of the web is less than the real density of the web, as the web is porous. The impregnated web has filaments that are both coated and uncoated with the polymer resin. A method of forming the impregnated fiber web is also described.

A simulated, sheet-like leather material is produced from the impregnated web. The simulated, sheet-like leather material is composed of a polymer-impregnated fiber mass with a grain layer that forms one surface, and a gap layer that forms the opposite surface. The grain layer has a real density that is equal to its spatial density, and the gap layer has a spatial density that is less than its real density. The sheet material has a density that decreases from the grain layer to the gap layer.

"Space density" shall here mean the density of the material including air space. "Actual density" shall here mean the density of the material without air spaces, i.e. the density (specific weight).

The fibrous mass which is applicable in the implementation of the invention includes woven and knitted fabrics, felt and non-woven material, such as spunbond cloth, needle wool and water-sedimented material. Suitable substrate fibers are natural fibers, especially cotton and wool, synthetic fibers, e.g. . polyesters, nylon, acrylic, modacrylic and rayon. The fiber mass is preferably needle-punched fiber wool which is formed from such natural and synthetic fibres. The fibers preferably have a denier number of 1-5 and a length which is suitable for carding, and which is typically 2.5-15 cm, preferably 38-76 mm.

The needle-punched fiber batting can either have high, medium or low density. High-density wadding has a maximum density of 0.5 g/cm-<*>. Such a high-density wadding is typically composed of wool. When synthetic fibers are used in the formation of wadding, a high-density wadding has a density of up to 0.25 g/cm^. When practicing the invention, fiber wadding preferably has a density of 0.08-0.5 g/cm"<*>. The thickness of the wadding can be up to 0.5 mm and is preferably between 3 and 10 cm, with a minimum thickness at 7.5 mm-in Vatten is also distinguished by being "saturating wadding" that has high integrity due to the needle treatment, in contrast to lightly bundled wadding with a few needle punctures with little or no integrity.

Polymer resins that can be used in the practice of the invention are preferably such polymer resins that have the ability to solubilize, disperse or emulsify in water with subsequent coagulation from the water system with an ionic coagulant.

A suitable polymer system is one that is synthesized from acrylic monomers, e.g. alkyl acrylate and methacrylate, acrylonitrile, methacrylonitrile and other well-known acrylic monomers.

These acrylic monomers can be polymerized by emulsion polymerization to form a latex, or by other free radical polymerization mechanisms and then solubilized or emulsified in water. The emulsifying or solubilizing system must be such that when the emulsion is brought into contact with concentrated acid or base, the polymer coagulates from the water-containing system and is made essentially insoluble.

Emulsified or aqueous dispersed polyurethanes are preferably used. Examples of emulsified polyurethanes are those described in US patent 2,968,575, which are produced and dispersed in water using synthetic detergents under the influence of strong shearing forces. When these polyurethane emulsions are formed, the emulsifier or synthetic detergent must be ionic in nature so that a counterion can be added to the aqueous system for coagulation of the polymer. Polyurethanes which are valuable in the practice of the invention are preferably those which are considered to be ionically water dispersible.

A suitable system for producing ionic aqueous polyurethane dispersions is to produce polymers with free acid groups, preferably carboxylic acid groups, which are covalently bound to the polymer skeleton. Neutralization of these carboxyl groups with an amine, preferably a water-soluble monoamine, provides water dilutability. Exact selection of the compound bearing the carboxyl group must take place, while isocyanate, which are necessary components in any polyurethane system, are generally reactive with carboxyl groups. However, as described in US patent 3,412,054, to which reference is made here, 2,2-hydroxymethyl-substituted carboxylic acids can be made to react with organic polyisocyanate without any significant reaction between acid and isocyanate groups, due to the steric hindrance of the carboxyl group by adjacent acrylic groups. This solution to the problem provides the desired carboxyl-containing polymer, whereby the carboxyl groups are neutralized with the tertiary monoamine to provide an internal quaternary ammonium salt and consequently water dilutability.

Suitable carboxylic acids and preferably the sterically hindered carboxylic acids are well known and readily available. They can, for example, be produced from an aldehyde containing at least two hydrogen atoms in the a-position, which is reacted in the presence of a base with two equivalents of formaldehyde to form a 2,2-hydroxymethylaldehyde. The aldehyde is then oxidized to acid by methods known in the art. Such acids can be illustrated by the following structural formula:

where R denotes hydrogen or alkyl with up to 20 carbon atoms, preferably up to 8 carbon atoms. A suitable acid is 2,2-dihydroxymethylpropionic acid. Polymers with pendant carboxyl groups are characterized as anionic polyurethane polymers.

According to the present invention, an alternative way of providing water dilutability is to use a cationic polyurethane with pendant amino groups. Such cationic polyurethanes are described in US patent 4,066,591, to which reference is hereby made, and especially in example XVII. In connection with the present invention, it is convenient to use anionic polyurethane.

Polyurethanes which are valuable in the practice of the present invention involve in particular the reaction of di- or polyisocyanate and compounds with several reactive hydrogen atoms, which are suitable for the production of polyurethanes. Such diisocyanates and reactive hydrogen compounds are described more fully in US Patents 3,412,034 and 4,046,729. The method for producing such polyurethanes is also well known, as exemplified in the specified patents. According to the present invention, aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used when forming the polymer. Such diisocyanates are, for example, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, m-phenylene-diisocyanate, biphenylene-4,4'-diisocyanate, methylene-bis(4-phenyl-isocyanate), 4 -chloro-1,3-phenylenediisocyanate, naphthylene-1,5-diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, decamethylene-1,10-diisocyanate, cyclohexylene-1,4-diisocyanate, methylene -bis(4-cyclohexyl isocyanate), tetrahydronaphthylene diisocyanate, isophorone diisocyanate, etc. Preferably, the arylene and cycloaliphatic diisocyanates are used most advantageously in practicing the invention.

The arylene diisocyanate characteristically includes those where the isocyanate group is bound to the aromatic ring. The most suitable isocyanates are the 2,4- and 2,6-isomers of tolylene diisocyanate and mixtures thereof because of their easy availability and because of their reactivity. Cycloaliphatic diisocyanates that are suitably used in the practice of the present invention are further 4,4<1->methylene bis(cyclohexyl isocyanate) and isophorone diisocyanate.

The selection of the aromatic or aliphatic diisocyanates is dictated by the end use of the particular material. As is well known to those skilled in the art, the aromatic isocyanates can be used where the end product is not exposed to a strong degree to ultraviolet radiation, which tends to cause such polymeric products to turn yellow; while the aliphatic diisocyanates can more appropriately be used outdoors and have less of a tendency to yellow when exposed to ultraviolet radiation. While these principles form a general basis for the selection of the particular isocyanate to be used, the aromatic diisocyanates can be further stabilized with well-known ultraviolet stabilizers to improve the finishing properties of the polyurethane-impregnated sheet material. Antioxidants can also be added in known levels to improve the final product's properties - Typical antioxidants are thioethers and phenolic antioxidants, e.g. 4,4'-butyl-idine-bis-m-cresol and 2,6-di-t-butyl-p-cresol.

The isocyanate is caused to react with the multiple reactive hydrogen compounds, such as diols, diamines or triols. If diols or triols are used, they are typically either polyalkylene ether or polyester polyols. A polyalkylene ether polyol is the suitable active, hydrogen-containing polymer material for making the polyurethane. The most applicable polyglycols have a molecular weight of 50-10,000, and in connection with the present invention, the most advantageous is 400-7,000. Polyether polyols further improve flexibility in proportion to the increase in their molecular weight.

Examples of polyether polyols include, but are not limited to. polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol. polyhexamethylene ether glycol, polyoctamethylene ether glycol, polydecamethylene ether glycol, polydodecamethylene ether glycol and mixtures thereof. Polyglycols that contain several different groups in the molecular chain, e.g. the compound HO(CH2OC2H40)nH, where n denotes a larger whole number than 1, can also be used.

The polyol can also be a polyester with hydroxyl in the terminal position or with a pendant hydroxyl, and such a polyester can be used instead of or in combination with the polyalkylene ether glycols. Examples of such polyesters are those formed by reacting acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols, e.g. ethylene, propylene, tetramethylene or decamethylene glycol; substituted methylene glycols, such as 2,2-dimethyl-1,3-propanediol, cyclic glycols, such as cyclohexanediol, and aromatic glycols. Aliphatic glycols are generally most suitable when flexibility is desired. These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester-forming derivatives to form polymers of relatively low molecular weight, preferably with lower melting points than approx. 70°C and a molecular weight similar to those indicated for the polyalkylene ether glycols. Acids for the production of such polyesters are e.g. phthalic acid, maleic acid, succinic acid, adipic acid. suberic acid, sebacic acid, terephthalic acid and hexahydrophthalic acid and alkyl- and halogen-substituted derivatives of these acids. In addition, polycaprolactone with hydroxyl groups in the terminal position can also be used.

A particularly useful polyurethane system is the crosslinked polyurethane system, which is more fully described in US Patent Application 947,544, filed October 2, 1978 by Andrea Russiello entitled "Crosslinked Polyurethane Dispersions", which is hereby incorporated by reference.

The term "ionic dispersant" shall mean an ionizable acid or base capable of forming a salt with the solubilizing agent. These "ionic dispersants" are amines and preferably water-soluble amines, e.g. triethylamine, tripropylamine, N-ethylpiperidine and the like; likewise acid and preferably water-soluble acids, e.g. acetic acid, propionic acid, lactic acid etc. Naturally, the acid or amine must be selected depending on the solubilizing group attached to the polymer chain.

The desired elastomer performance will generally require approx. 25-80 wt% long chain polyol (ie 700-2000 equivalent weight)

in the polymer. The degree of stretch and elasticity may vary

within wide limits from one product to another depending

of the final product's desired properties.

In the production of polyurethanes which are applicable in practicing the invention, the polyol and a molar excess of diisocyanate are reacted to form polymer with isocyanate in the end position. While suitable reaction conditions and reaction times and temperatures are variable in connection with the particular isocyanate and the particular polyol used, the person skilled in the art will appreciate these variations well. Those skilled in the art realize that the reactivity of the ingredients in question requires a balance of reaction rate with undesirable secondary reactions leading to coloration and molecular weight degradation. In a typical manner, the reaction is carried out with stirring at approx. 50-approx. 120°C for approx. 1-4 hours. To provide pedantic carboxyl groups, the isocyanate-terminated polymer is reacted with a molar deficit of dihydroxy acid for 1-4 hours at 50-120°C to form the isocyanate-terminated prepolymer. The acid is added appropriately as a solution, e.g. in N-methyl-1,2-pyrrolidone or N-N-dimethylformamide. The solvent for the acid will typically not be more than approx. 5% of the two-figure investment for reducing the concentration of organic solvent in the polyurethane product. After the dihydroxy acid has reacted into the polymer chain, the pendant carboxyl groups are neutralized with an amine at approx. 58-75°C for approx. 20 minutes, and chain extension and dispersion are carried out by addition to water while stirring. A water-soluble diamine can be added to the water as a further chain extender. The chain extension involves reaction between remaining isocyanate groups with water to form urea groups and further polymerization of the polymer material with the result that all isocyanate groups react due to the addition of a large stoichiometric excess of water. It should be observed that the polyurethanes according to the present invention are thermoplastic in nature,

i.e. that they are not particularly capable of further hardening after formation without the addition of an external hardening agent. Preferably, no such hardening agent is added for the formation of sheet-like composite material.

A sufficient amount of water is used to disperse the polyurethane at a concentration of approx. 10-40% by weight dry matter and a dispersion viscosity in the range 10-1000 cP. The viscosity can be set according to the special, desired impregnation properties and by the special dispersing mixture, all of this being controlled by the end product properties. It should be observed that no emulsifiers or thickeners are necessary for the stability of the dispersions.

The person skilled in the art realizes ways of modifying the primary polyurethane dispersion according to the end product application, e.g. by adding coloring agents, combinable vinyl polymer dispersions, UV filtering compounds, stabilizers against oxidation and the like.

The characterization of dispersions produced according to the invention takes place by measurements of the content of non-volatile material, particle size, viscosity and by the stretch/stress properties of strips of cast film.

The concentration range applicable to the practice of the invention is controlled by the desired percentage addition of polymer into the needle-punched cotton wool.

The dispersion viscosity is generally in the range of 10-1000 cP. The low viscosity compared to that of identical polymers at the same dry matter level in polymer solutions in organic solvent is helpful for rapid and complete penetration of the aqueous dispersion and subsequent penetration of the coagulant. Usable polyurethane solutions, on the other hand, generally have viscosities of several thousand cP and are as high as 50,000 cP at concentrations of 20-30%.

The polymers should be impregnated into the fiber wadding at a level of at least 70% by weight addition, calculated on the weight of the fiber wadding, and up to approx. 400% by weight. Preferably, the polymer resin is impregnated at a level of approx. 200-300% by weight addition, calculated on the weight of fiber wadding.

Coagulation is provided by the impregnated substrate being brought into contact with an aqueous solution of an ionic medium intended in an ionic manner to replace the solubilizing ion.

Although the invention is not intended to be bound by any theory, in the case of an anionic solubilized polymer, the amine that neutralizes the carboxyl-containing polyurethane is replaced by a hydrogen ion that restores the anionic carboxyl ion, thus restoring the polymer to its original, "non-dilutable" state . This provides coagulation of

the polymer in the substrate structure.

In the case of anionic polymer, aqueous acetic acid solutions in concentrations of 0.5 - approx. 75% suitable ionic coagulant for the anionic dispersions and is more suitable than stronger acids due to its relative ease of handling, low corrosion potential and availability.

"Salting out" for coagulation of the dispersion by addition of neutral salt is possible, but is not successful because of the necessary large amounts of salt, approx. 10 times the concentration of acid, as well as accompanying problems with product contamination.

When impregnating the needle-punched wadding with the polymer resin, as contemplated here, the wadding is immersed in an aqueous, ionic emulsion or dispersion at a concentration level sufficient to provide an addition of at least 70% by weight. Upon immersion of the water in the aqueous emulsion or dispersion, the water may be pressed to remove air to provide full impregnation of the emulsion or dispersion in the water. The wadding, which is now completely impregnated with the aqueous dispersion or emulsion, is made to pass through drying rollers or the like to remove excess dispersion or emulsion on the surface of the impregnated wadding. Water is then immersed in a bath containing cations to provide coagulation, whereby the cation-containing material penetrates the water by diffusion and causes coagulation of the resin in the fiber structure. After coagulation, the water is pressed to remove excess water and dried to form the impregnated web.

This method is a further improvement of the method described in US patent 4,171,391,

which concerns the manufacture of special products. The differences between the specified patent and the present method are that the water is completely saturated, i.e. no air space is left, whereby the water-containing dispersion or emulsion provides a final addition of at least 70% by weight of polymer resin, calculated on the weight of the water. Because of these differences, a new structure is obtained, in which the water has a uniform density throughout and where the web's spatial density is less than the web's real density.

After the impregnated web is formed, it is given a density gradient to form a simulated, sheet-like leather material. In the formation of the simulated, sheet-like leather material, the impregnation agent for the web is preferably polymers, which in particle form have the ability to fuse with themselves under conditions of heat and pressure. These polymers are normally thermoplastic; however, certain cross-linked polymers with the ability to fuse can also be used. In particular, polyurethanes which are described in US application 947,544, filed on October 2, 1978 by Andrea Russiello with the title "Crosslinked PolyurethanesDispersions", have been shown to be particularly useful in the practice of the invention for producing the desired density gradient through the thickness of the material.

The characterizing features of the simulated, sheet-like material according to the invention are primarily physical characteristics, whereby a density gradient is provided from one side of the sheet-like material to the opposite side thereof. Preferably, the density gradient is uniform. A surface of the impregnated fiber mass delimits a grain layer, whereby this grain layer has a real density which is equal to its spatial density.

This grain layer strongly imitates the grain layer of natural leather. On the opposite side of the sheet-like material there is one

surface that delimits the gap layer, which has a lower spatial density than the real density, whereby there is a preferably uniform density gradient through the material. The split layer is somewhat fibrous and imitates the split layer of natural leather.

The polymer is present in the simulated sheet leather material at a level of at least 70% addition by weight based on the weight of the fibrous pulp.

The gap layer typically has up to 75% of the density of the grain layer to provide a porous grain layer that mimics the grain layer of leather. One must also observe that the polymer is uniformly distributed throughout the fiber mass in such a way that the ratio between fiber and polymer is uniform throughout.

The simulated sheet-like leather material is produced by treating the impregnated fiber mass and preferably an impregnated, non-woven cloth material, as described earlier.

The polymer used as an impregnating agent is preferably one of such or of the type described in US application 947 544, to which reference is made above.

In one treatment method, the impregnated, non-woven cloth material that is to form the simulated leather sheet is used in a

press, and heat and pressure are applied to both sides of it. The heat and pressure are sufficient for fusion of the polymer itself in the impregnating agent at the material's surfaces, but still insufficient for complete fusion of the polymer with the interior of the cloth material. This method produces a density gradient from the interior of the non-woven fabric material to the two outer surfaces. The thickness dimensions of the heated and pressed cloth material can be regulated by means of the pressure applied during the heating and pressing treatments, or by inserting spacers between the press plates or by using a press with a resting load.

The pressed plates can also be in relief to provide a specific surface pattern on the material. After pressing, the sheet material is split down the middle to provide two simulated leather sheets each having a grain layer and a split layer.

In another method of forming the simulated leather sheet material, the impregnated non-woven starting material discussed above can be placed in a press with only one of the plates heated, so that the grain layer is formed, while the opposite side to the cold plate forms the gap layer.

In a further method of forming the simulated leather sheet material, two pieces of impregnated non-woven starting material, as discussed above, can be placed on top of each other in a press and heat and pressure applied to an extent sufficient to fuse the polymer itself into the impregnating agent at the outer surface of each piece. After pressing, the individual pieces are separated, resulting in two sheets of simulated leather.

After formation, the simulated leather can be poked, coated or further processed according to known leather finishing techniques.

In yet another method, grain layer development can be provided on non-wound strips of impregnated, non-woven starting material which are unwound from packages, and which are made to pass through a pair of rollers in a calendering process. Preferably, one of the rollers is made of metal heated to 150-205°C and is smooth or suitably embossed, and the other roller is of a softer, yielding material, e.g. rubber. The grain layer will be developed on the side of the sheet facing the metal roller. Effective calendering can generally be carried out with a load of 5.5-16.5 tonnes/m width of sheet passing through the rollers. Wetting the sheet before calendering to 50-100% by weight of added water can be helpful during calendering.

The structures of the impregnated web and the simulated sheet-shaped leather material are shown more fully in the attached figures which are photomicrographs of cross-sections of an impregnated web and a simulated sheet-shaped leather material produced according to the invention. Fig. 1 shows a plan view of a resin-impregnated web produced according to Example 1, before cleavage; Fig. 2 shows a photomicrograph taken through the thickness of the web according to fig. 1 after the line II-II; Fig. 3 shows a lOOx photomicrograph of section III according to fig. 2; Fig. 4 shows a lOOx photomicrograph of section IV according to fig. 2; Fig. 5 shows a 100x photomicrograph of section <. According to fig. 2; Fig. 6 shows a 100x photomicrograph of a resin-impregnated wadding made according to Example 1 after cleavage, and Fig. 7 shows a 100x photomicrograph of a cross-section through the thickness of a simulated sheet leather material made from the wadding according to Fig. 6.

In fig. 1-5t where like reference numbers refer to like parts, a resin-impregnated web 10 is shown, produced according to example 1. In particular, fig. 2-5 a cross section through the thickness of the web 20. The web 10 is composed of an upper surface 12 and a lower surface 14. Throughout the web 10 there are a substantial number of uncoated fibers 16, resin concentrations 20, voids 18 and resin coated fibers 22. The structure and consequently its space density is essentially uniform throughout the entire material thickness, even if the microscale structure is not homogeneous.

The one in fig. The structure shown in 2-5 is considered to be attributable to the needle-punched wadding with full impregnation with an aqueous emulsion or dispersion and subsequent coagulation of the polymer, while the wadding is completely impregnated with the aqueous

resin system.

In fig. 6, which shows a 100 x photomicrograph, shows a split, impregnated needle-punched wadding 24 of uniform density throughout, as shown in FIG. 1-5. The impregnated wadding 24

has a significant amount of uncoated fibers 26,

polymer masses 28, coated fibers 32 and hollow

room 30. It should be observed that although the impregnated wadding is non-homogeneous on a micro scale, it has a uniform room density throughout.

In fig. 7, which shows a 100 x photomicrograph, shows the simulated sheet-like leather material 32 according to Example 4. The material 32 has a grain layer 34 which has a minimal void content, and the space density at the grain layer 34 is equal to the real density. At the grain layer 34, a composite material 36 is formed of fibers in a continuous resin matrix as a result of the application of heat and pressure. Upon displacement in the direction A, it is shown that the cavity 30 increases along the direction approaching the gap layer 38. At the gap layer 38, there is a significant number of cavities 30, uncoated fibers 26 and polymer masses 28. The structure at the gap layer 38 approaches that in fig. 6 showed structure.

The following examples illustrate products that have been produced

according to the invention.

EXAMPLE 1

A needle punched wadding which was heat cured and had a density of 1200 g/m 2 consists of polyester, polypropylene and rayon fibers and had a thickness of 7.6 mm with a bulk density of 0.16 g/cm<3> was immersed in a polyurethane which was prepared according to Example III of US Application 947,544 (Andrea Russiello), which is discussed above. The polymer dispersion had a total content of 22% dry matter to provide 120%, calculated on the weight of the water. Water was immersed in the polyurethane dispersion for 10 min. at room temperature, until all air was expelled from the water and the water was completely impregnated. The surface of the water was wiped with a straight edge on both sides to remove excess aqueous dispersion and was immersed in a bath of 10% acetic acid for 10 min. at room temperature. The immersion in the acid coagulated the polyurethane completely in the fiber structure. Excess acetic acid was washed away from the cotton wool, and the resin-impregnated cotton wool was pressed to remove excess water. The resin-impregnated wadding was split into four slices through the thickness and each split product was dried at 150-175°C in an air circulation oven to form four resin-impregnated webs with a bulk density of 0.45 g/cm 2 . The final product had an appearance that can be seen from the attached photomicrographs.

EXAMPLE 2

Example 1 was repeated, except that a wadding of 100% polyester with a density of 0.13 g/cm 3 and a thickness of 5.0 mm was impregnated with a dispersion with 22% solids according to Example 1. The impregnated web had throughout uniform density, high integrity and a room density of 0.38 g/cm 3.

EXAMPLE 3

Example 1 was repeated, except that a needle-stitched batting of 100% polyester with a thickness of 5.6 mm and a density of 0.23 g/cm<3>

was impregnated with a dispersion with 32% solids to produce a needle punched, resin-impregnated fiber web with a bulk density of 0.56 g/cm . The product according to example 3 was used as a polishing pad and had toughness, high tear strength, flexibility and complete recyclability when compressed.

The method described here thus provides an impregnated fiber web with high integrity and which is usable as a product in itself and which is valuable from other products. The impregnated fiber web can further be polished to provide a desirable surface.

EXAMPLE 4

Two 1.8 mm thick slit products of the non-woven impregnated web prepared according to Example 1 were superimposed and placed between the plates in a press heated to 150°C at a pressure of 3.5 MPa for 30 sec. The two cleavage products were then separated, whereby two sheets of simulated leather sheet material were obtained. The grain layer in the sheets corresponds to the surfaces that were in contact with the hot press plates. The inner sides of the sheets retained their fiber structure in the same way as the unpressed sheet. Microscopic examination showed that the simulated, sheet-like material had a density gradient from the grain layer to the gap layer as shown in fig. 7.

After formation, the simulated, sheet-like leather material can be post-treated with other polymers for surface treatment according to known techniques.

Although the invention is described with reference to special materials and by special methods, the invention is only limited to the extent that appears from the patent claims.

Claims (8)

IN 1. Simulated, sheet-like leather material, characterized by J eri polymer-impregnated fiber mass with a grain layer that forms a surface, whereby the grain layer has a real density equal to its spatial density, and a gap layer that forms the opposite surface, whereby the gap layer has a lower spatial density than its real density, whereby the sheet-like material has a density that decreases from the grain layer to the gap layer, and where the ratio between fiber and polymer is uniform throughout the sheet-like material. 2. Sheet-like material as stated in claim 1, characterized in that the fiber mass is a needle-stitched wadding. 3. Sheet material as stated in claim 1 or 2, characterized in that the polymer is a polyurethane, e.g. a cross-linked polyurethane. 4. Sheet material as set forth in any of claims 1 to 3, characterized in that the polymer is present at a level of at least 75% by weight addition, preferably up to 400% by weight addition, e.g. 200-300% by weight addition, calculated on the weight of the fiber mass. i 5. Sheet material as stated in any of claims 1 to 4, characterized in that the gap layer has a density of up to 75% of the grain layer and that preferably the density of the sheet material has a uniform gradient from the gap side to the grain side. 6. Sheet material as stated in any one of claims 1 to 5, characterized in that the polymer is uniformly distributed throughout the fibrous mass. 7. Method for producing a simulated, sheet-like leather material, characterized in that a fiber mass is uniformly impregnated with a polymer to form a porous sheet-like material, that the porous sheet-like material is heated under heat and pressure, whereby the heat and pressure is applied to at least one surface thereof, to produce a simulated, sheet-like leather material with a grain layer on the surface on which the heat is applied, whereby the grain layer has a space density which is equal to the real density, and a gap layer with a lower spatial density than its real density, whereby the sheet-like material has a density that decreases from the grain layer to the gap layer, and whereby the ratio between fiber and polymer is uniform throughout the sheet material. 8. Method as stated in claim 7, characterized in that heat and pressure are applied to the two surfaces of the sheet-shaped material to induce a density gradient from the outside of the sheet-shaped material to its interior, and that the sheet-shaped material is split in the middle, whereby the outer surfaces form the grain layer and the inner surfaces the gap layer.