GB2099030A - A simulated leather sheet material and a method of forming the same - 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

1 GB 2 099 030 A 1

SPECIFICATION A simulated leather sheet material and a method of forming the same

This invention relates to simulated leather sheet material and to methods of forming the 70 same.

Resin impregnated sheet materials such as cloth, batts, water-leaves, etc. are well known in the art. These resin impregnated sheet materials are useful for a plurality of purposes including imitation leather in the form of vinyls etc., structural sheet materials such as conveyor belts and similar products.

Prior art methods of impregnating a particular web involve the impregnation or coating of a porous material with a polymeric resin such as a polyurethane, vinyl or a similar material.

Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexibility and chemical resistance. In impregnating the porous sheet material with a polymeric resin several techniques have been employed. One such prior art method involves the use of the polymeric resin in an organic solvent system wherein the sheet material is dipped in the solution and the solvent is removed therefrom. These solvent systems are undesirable since the solvent, in many cases, is toxic and must either be recovered for re-use or discarded. These solvent systems are expensive and do not necessarily provide a desirable product since upon evaporation of the solvent from the impregnated porous sheet material the resin tends to migrate to provide a non-homogeneous impregnation of the porous sheet material resulting in resin richness toward the surface of the sheet material rather then uniform impregnation.

in order to alleviate the problems with solvent systems, certain aqueous polymeric systems have been proposed. In forming impregnated sheet materials by impregnation with aqeuous polymers the aqueous portion must be removed. Again heat is required and migration of the polymer to the surfaces of the impregnated sheet material is encountered.

In one method of combining polyurethane solution with porous substrates the polymer is applied in an organic solvent to a substrate, such as a needle punched polyester batt. The polymersubstrate composite is subsequently bathed with a mixture of organic solvent for the polymer and a non-solvent for the polymer that is at least partially miscible with the solvent until the layer is 120 coagulated into a cellular structure of interconnected micropores. The solvent is removed from the coating layer along with the non-soivent to produce a solvent free microporous layer. Although this process yields acceptable properties for a polyurethane impregnated fabric, it has the disadvantage of an organic solvent system partially when high performance polyurethanes are utilized which require relatively toxic and high boiling solvents. An example of this method is disclosed in U.S. Patent Specification No. 3,208,875.

In another method, polyurethane dispersions in organic vehicles have been proposed and used to coat porous substrates such as is disclosed in U.S. Patent Specification No. 3,100,721. In this system, a dispersion is applied to a substrate, and coagulated by further addition of a nonsolvent. Although this approach has been used with some success, it involves two major limitations: (1) the vehicle of the dispersion is substantially organic since relatively small amounts of non- solvent, preferably water, are needed to form a dispersion; and (2) there is a narrow useful range of added non-solvent so that reproducible results are difficult to obtain.

One particularly useful method of preparing composite sheet material by impregnating a porous substrate is disclosed in U.S. Patent Specification No. 4,171,391. In this system a porous sheet material is impregnated with an aqueous ionic dispersion of a polyurethane and the impregnant is coagulated therein. The composite is then dried to form a composite sheet go material. The present invention is an improvement over this basic process and in some instances is broader in scope.

Impregnated porous substrates and similar materials have been proposed as leather substitutes with the goal of preparing a product having the same characteristics as natural leather.

Natural leather, appropriately finished, is valued for its durability and aesthetic characteristics for a plurality of uses. Due to the scarcity of leather and the increased cost of processing leather for particular applications, economics have dictated that synthetic materials be substituted in certain applications where leather goods had been used. Such synthetic materials have been proposed and used in the areas of shoe uppers, upholstery, clothing, luggage making, book binding and similar applications. Because these various applications require differing physical, chemical, and aesthetic qualities, different processes using different materials must be used to obtain an acceptable product which is comparable to natural leather; although in most instances these synthetics are readily distinguishable from natural leather.

Natural leather from animal hides is composed of two surfaces: one surface defining the grain layer, which in most instances is the most aesthetically desirable and the opposing surface defining the split layer. The grain layer is the epidermis of the animal and is very smooth whereas the split layer in most instances is rough and fibrous.

One method of preparing a synthetic as a substitute for leather involves impregnating and/or coating of porous material, for example, cloth, with a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide 2 GB 2 D99 030 A 2 variation in chemical and physical properties, particularly their flexibility and chemical resistance.

Objectives in preparing the synthetic substitutes for leather are that they provide: (1) sheets especially suitable for leather-like and upholstery uses; (2) sheets of uniform width as commonly used in the textile industry (unlike natural products which sustain substantial weight and area losses in cutting and finishing); (3) end use versatility, for example, under a vareity of exposure conditions where certain chemical treatments will assist maintenance and useful lifetime of properties; and most importantly, (4) a product with the strength, hand, drape and 80 softness comparable to natural leather.

Further, a simulated leather sheet material when used for shoe uppers should be characterised by a leather appearance, with no undesirable fabric show through, good water vapour permeation into the uncoated side of the upper, and a leather grain break (minimal gross wrinkling). -Leather-like grain break", as recognised in leather and upholstery industries, is manifested in the behaviour of well finished leather when folded or crumpled. The leather fold is characterised by a smooth curved contour, frequently with numerous fine wrinkles in the compressed region of the fold area. This is contrasted with sharp creases or gross wrinkles formed when papers or films are folded; this kind of undesirable appearance is known as "pin wrinkling---.

The "hand" of leather is highly distinctive and synthetics normally have a rubbery feel which is 100 contrasted with leather.

Polyurethane polymers as coatings or impregnants for fabric to provide substitutes for leather have long been recognised. For example, polyurethanes can be made which are highly resistant to solvents and abrasion, conferring dry cleanability and outstanding durability to coated fabrics. The basic chemistry of polyurethanes, involving reactions between the isocyanate groups and molecules with multiply reactive hydrogen, such as polyols and polyamines, afford great versatility and variability in final chemical and physical properties by the selection of intermediates to achieve processibility and the desired balance of end use performance 115 requirements.

There are various methods for applying polyurethane solutions or other post curable liquid polymers to porous substrates which are well known to those skilled in the art. An article in Joumal of CoatedFabrics, Vol. 7 (July 1977), pages 43 through 57 describe some of the commercial coating systems, e.g. reverse roll coating, pan fed coater, gravure and the like.

Brushing and spraying may also be used to coat polyurethane on porous substrates. These polyurethane solutions, after impregnation or coating on the porous substrate, are dried or cured by a method such as heated air, infra-red radiation and the like. Characteristic of these processes is the deposition of a polymer and a film-like layer which tends to produce a coated fabric which folds in undesirable sharp creases rather than leather-like grain break. Other methods of combining polymeric solutions and particularly polyurethane solutions with porous substrates are exemplified by U.S. Patent Specification No. 3,208,875 and U.S. Patent Specification No. 3,100,721. 75 An improved process for impregnating fabrics is disclosed in U.S. Patent Specification No. 4,171,391 which includes certain steps which are necessary in forming simulated leather sheet material in accordance with the invention. The present invention seeks to provide a simulated leather sheet material which has the appearance and properties of natural leather and further has certain physical similarities therewith. According to one aspect of the present invention there is provided a simulated leather sheet material comprising: 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 go 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.

According to another aspect of the present invention there is provided a method of forming a simulated leather sheet material comprising: uniformly impregnating a fibrous mass with a polymer to form a porous sheet material; heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has been applied, the grain layer having a bulk density equal to the actual density, and a split layer having a bulk density less than its actual density, the 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.

"Bulk density" as used herein means and refers to the density of the material including air space. "actual density" as used herein means and refers to the density of the material not including air space, i.e. specific gravity.

The fibrous mass useful in the practice of the present invention include woven and knit fabrics, felt and non-wovens, such as spun bonded sheets, needled batts and waterleaves. Suitable substrate fibres are the natural fibres, particularly cotton and wool; synthetic fibres such as polyester, nylon, acrylics, modacrylics, and rayon.

Most preferably, the fibrous mass is needled fibrous batts formed of such natural and synthetic fibres. Preferably, the fibres have a denier of 1 to 5 and a length which is suitable for carding which is typically 2.54 to 15.24 cm (1 to 6 inches) and more preferably 2.54 to 7.62 cm (1 1 to 3 inches). T 4 3 1 GB 2 099 030 A 3 The needled fibrous batts can be either of high, intermediate or low density. The high density batts have a maximum density of 0.5 grams/cc.

These high density batts are typically composed of wool. When synthetic fibres are used in forming the batts, the high density batts are up to 0.25 grams/cc. Preferably in the practice of the invention, the fibrous batts have a density of 0.08 grams/cc to 0.5 grams/cc. The thickness of the batts may be up to 1.27 em (0.5 inch) and 75 preferably between 0.30 em (0. 12 inch) and 1.02 em (0.4 inch) with a minimum thicness of 0.076 em (0.030 inch). Additionally, the batts are characterized as "saturating batts- which have high integrity due to the needle punching 80 operation as opposed to lightly bonded batts having few needle punches with little or no integrity.

The polymeric resins useful in the practice of the invention are preferably those polymeric resins which are capable of solubilization, dispersion, or emulsification in water and subsequent coagulation from the water system with an ionic coagulating agent.

A preferred polymer system is one which is synthesized from acrylic monomers such as the alkyl acrylates and methylacrylates, acrylonitrile, methylacrylonitrile and other well known acrylic monomers. These acrylic monomers may be polymerized by emulsion polymerization to form a latex or by other free radical polymerization 90 mechanisms and subsquently solubilized or emulsified in water. The emulsification or solubilizing system must be such that when the emulsion is contacted with concentrated acid or base the polymer coagulates from the aqueous system and is rendered substantially insoluble.

Most preferably, emulsified or aqueously dispersed polyurethanes are utilized. Exemplary of the emulsified polyurethanes are those disclosed in U.S. Patent Specification No. 2,968,575 prepared and dispersed in water with the aid of detergents under the action of powerful shearing forces. When these polyurethane emulsions are formed, the emulsifying agent or detergent must be one which is ionic in nature so that a counter ion may be added to the aqueous system to coagulate the polymer. Most preferably, the polyurethanes useful in the practice of the invention are those recognised in the art as ionically water dispersible.

The preferred system for preparing ionic aqueous polyrrethane dispersions is to prepare polymers that have free acid groups, preferably carboxylic acid groups covalently bonded to the polymer backbone. Neutralization of these carboxyl groups with an amine, preferably a water soluble mono-amine, affords water dilutability. Careful selection of the compound bearing the carboxylic group must be made because isocyanates, necessary components in any polyurethane system, are generally reactive with carboxylic groups. However, as disclosed in U.S. Patent Specification No. 3,412,054, incorporated herein by reference, 2,2-hydroxyrn ethy]substituted carboxylic acids can be reacted with organic polyisocyanates without significant reaction between the acid and isocyanate groups due to the stearic hinderance of the carboxyl by the adjacent alkyl groups. This approach provides the desired carboxyl containing polymer with the carboxylic groups being neutralized with the tertiary mono-amine to provide an internal quaternary ammonium salt and hence, water dilutability.

Suitable carboxyUc acids and preferably the stearically hindered carboxylic acids, are well known and readily available. For example, they may be prepared from an aldehyde that contains at least two hydrogens in the alpha position which are reacted in the presence of a base with two equivalents of formaldehyde to form a 2,2hydroxymethyl aldehyde. The aldehyde is then oxidized to the acid by procedures known to those skilled in the art. Such acids are represented by the structural formula, CH20H 1 R-C-COOF1 1 CH20H wherein R represents hydrogen, or alkyl of up to 20 carbon atoms, and preferably, up to eight carbon atoms. A preferred acid is 2,2- di(hydroxymethyl) propionic acid. The polymers with the pendant carboxyl groups are characterised as anionic polyurethane polymers.

Further, in accordance with the present invention, an alternate route to confer water dilutability is to use a cationic polyurethane having pendant amino groups. Such cationic polyurethanes are disclosed in U.S. Patent Specification No. 4,066,591 incorporated herein by reference, and particularly, in Example XVII. In the context of the present invention it is preferred that the anionic polyurethane be used.

The polyurethanes useful in the practice of the invention more particularly involve the reaction of di-or polyisocyanates and compounds with multiple reactive hydrogens suitable for the preparation of polyurethanes. Such diisocyanates and reactive hydrogen compounds are more fully disclosed in U.S. Patent Specification Nos.

3,412,034 and 4,046,729. Further, the processes to prepare such polyurethanes are well recognised as exemplified by the aforementioned patents. In accordance with the present invention, aromatic, aliphatic and cyclo-aliphatic diisocyanates or mixtures thereof can be used in forming the polymer. Such diisocyanates, for example, are tolyiene-2,4-di-isocyanate; tolylene2,6-diisocyanate; meta-phenylene diisocyanate; biphenylene-4,4'- diisocyanate; methylene-bis(4- phenyl isocyanate); 4-chloro-1,3,-phenylene diisocyanate; naphthylene-1,5diisocyanate; tetra m ethylene- 1,4-d i isocya nate; hexa methylene- 1,6d iisocyanate; deca methylene- 1, 10-diisocyanate; 4 GB 2 099 030 A 4 cyclohexylene-1,4-diisocyanate; methylene-bis(4 cyclohexyl isocyanate); tetrahydronaphthylene diisocyanate; isophorone diisocyanate and the like. Preferably, the arylene and cyclo-aliphatic diisocyanates are used most advantageously in the practice of the invention.

Characteristically, the arylene diisocyanates encompass those in which the isocyanate group is attached to the aromatic ring. The most preferred isocyanates are the 2,4 and 2,6 isomers of tolylene diisocyanate and mixtures thereof, due to their ready availability and their reactivity.

Further, the cyclo-aliphatic dilsocyanates used most advantageously in the practice of the present invention are 4,4'-methylene bis(cyclohexyl isocyanate) and isophorone 80 diisocyanate.

Selection of the aromatic or allphatic diisocyanates is predicated upon the final end use of the particular material. As is well recognised by those skilled in the art, the aromatic isocyanates may be used where the final product is not excessively exposed to ultraviolet radiation which tends to yellow such polymeric compositions; whereas the aliphatic diisocyanates may be more advantageously used in exterior applications and have less tendency to yellow upon exposure to ultraviolet radiation. Although these principles form a general basis for the selection of the particular isocyanate to be used, the aromatic dilsocyanates may be further stabilized by well known ultraviolet stabilizers to enhance the final properties of the polyurethane impregnated sheet material. In addition, antioxidants may be added in art recognised levels to improve the characteristics of the final product. Typical anti oxidants are the thloethers and phenolic antioxidants such as 4-4-butylidine bismeta cresol and 2,6-dilLIert-butyl-para-cresol.

The isocyanate is reacted with the multiple reactive hydrogen compounds such as diols, diamines, or triols. In the case of diols or triols, they are typically either polyalkylene ether or polyester polyols. A polyalkylene ether polyol is the preferred active hydrogen containing polymeric material for formulation of the polyurethane. The most useful polyglycols have a molecular weight of 50 to 10,000 and in the context of the present invention, the most preferred is from about 400 to 7,000. Further, the polyether polyols improve flexibility proportionally with the increase in their molecular weight.

Examples of the polyether polyols are, but not limited to, polyethylene ether glycol, polypropylene-ether glycol, polytetram ethylene ether glycol, polyhexamethylene ether glycol, polyocta methylene ether glycol, po lydeca methylene ether glycol, polydodeca methylene ether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain, such as, for 125 example, the compound HO(CH20C21-140),,H wherein n is an integer greater than one, can also be used.

The polyol may also be a hydroxy terminated or hydroxy pendant polyester which can be used instead or in combination with the polyalkylene ether glycols. Exemplary of such polyesters are thus formed by reacting acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols such as ethylene, propylene, tetramethylene or decamethylene glycol; substituted methylene glycols such as 2,2- dimethyi-l -3,-propane diol, cyclic glycols such as cyclohexanediol and aromatic glycols. Aliphatic glycols are generally preferred when flexibility is desired. These glycols are reacted with aliphatic, cyclo- aliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester forming derivatives to produce relatively low molecular weight polymers, preferably having a melting point of less than about 700C, and a molecular weight like those indicated for the polyalkylene ether glycols.

Acids for preparing such polyesters are, for example, phthalic, maleic, succinic, adipic, suberic, sebacic, terephathalic and hexahydrophthalic acids and the alkyl and halogen substituted derivatives of these acids. In addition, polycaprolactone terminated with hydroxyl groups may also be used.

One particularly useful polyurethane system is the cross-linked polyurethane system which is more fully disclosed in U.S. Patent Application Serial No. 947,544, filed October 2,1978 of Andrea Russiello entitled--- Crosslinked Polyurethane Dispersions-.

When used herein, 1onic dispersing agent" means an lonizable acid or base capable of forming a salt with the solubilizing agent. These 1onic dispersing agents- are amines and preferably water soluble amines such as triethylamine, tripropylamine, Wethyl piperidine, and the like; also, acid and preferably water soluble acids such as acetic, propionic, lactic, and the like. Naturally, an acid or amine will be selected contingent on the solubilizing group pendant on the polymer chain.

The desired elastomeric behaviour would generally require about 25-80% by weight of long chain polyol (Le. 700 to 2,000 eq. wt.) in the polymer. The degree of elongation and elasticity may vary widely from product to product depending upon the desired properties of the final product.

In forming the polyurethanes useful in the practice of the invention, the polyol and a molar excess of diisocyanate are reacted to form isocyanate terminated polymer. Although suitable reaction conditions and reaction times and temperatures are variable within the context of the particular isocyanate and polyol utilized, those skilled in the art well recognise these variations. Such skilled artisans recognise that reactivity of the ingredients involved requires the balance of reaction rate with undesirable secondary reactions leading to colour and molecular weight degradation. Typically, the reaction is carried out 1 GB 2 099 030 A 5 with stirring at about 501C, to about 1200C, for about one to four hours. To provide pendant carboxyl groups the isocyanate terminated polymer is reacted with a molar deficiency of dihydroxy acid, for one to four hours at 501C. to 1201 C. to form isocyanate terminated prepolymer. The acid is desirably added as a solution, for example, in Wrn ethyl- 1,2-pyrrol idone or N-N-dimethyiformamide. The solvent for the acid will typically be no more than about 5% of the total charge in order to minimize the organic solvent concentration in the polyurethane composition. After the dihydroxy acid is reacted into the polymer chain, the pendant carboxyl groups are neutralized with an amine at about 580-750C. for about twenty minutes and chain extension and dispersion are accomplished by addition to water with stirring. A water soluble diamine may be added to the water as an additional chain extender. The chain extension involves the reaction of the remaining isocyanate groups with water to form urea groups and further polymerize the polymeric material with the result that all the isocyanate groups are reacted by virtue of the addition to a large stoichiometric excess of water. It is to be noted that the polyurethanes of the invention are thermoplastic in nature, i.e. not capable of extensive further curing after formation except by the addition of an external curing agent. Preferably, no such curing agent is added to form the composite sheet material.

Sufficient water is used to disperse the polyurethane at a concentration of about 10 40% by weight solids and a dispersion viscosity in 100 the range of 0.0 1 to 1 Pas (10-1,000 centipoise). Viscosity may be adjusted in accordance with the particular impregnation properties desired and by the particular dispersion composition which are all dictated by the final 105 product characteristics. It should be noted that no emulsifiers or thickeners are required for the stability of the dispersions.

Those of ordinary skill in the art recognize ways to modify the primary polyurethane dispersion according to end product uses, for example, by the addition of coloring agents, compatible vinyl polymer dispersions, ultraviolet filtering compounds, stabilizers against oxidation and the like.

The characterization of the dispersions prepared in accordance with the invention is done by measurements of non-volatile content, particle size, viscosity measurements and by stress strain properties on strips of cast film.

The concentration range useful in the practice of the invention is governed by the desirable percent add on of polymer into the needled batt.

The dispersion viscosity is generally in the range from 0.0 1 to 1 Pas (10-1,000 centipoise). 125 The low viscosity, relative to that of identical polymers at the same solids level in organic solvent polymer solutions, assists rapid and complete penetration of the aqueous dispersion and subsequent penetration of the coagulant. 130 Useful solutions of polyurethanes will, in contrast, generally have viscosities of several thousand centipoise, ranging as high as 50 Pas (50, 000 centipoise) at concentrations of 20-30%.

The polymers should be impregnated into the fibrous batt at a level of at least 70 percent by weight add on based upon the weight of the fibrous batt and up to about 400 percent by weight. Preferably, the polymeric resin is impregnated at a level of about 200 to 300 percent by weight add on based upon the weight of the fibrous batt.

Coagulation is accomplished by contacting the impregnated substrata with an aqueous solution of an ionic media designed to ionically replace the solubilizing ion. In theory, although not intended to be bound by such theory, in the case of an anionically solubilized polymer, the amine which neutralizes the carboxyl containing polyurethane is replaced with a hydrogen ion which reverts the anionic carboxyl ion thus reverting the polymer to its original, "non-dilutable" condition. This causes coagulation of the polymer within the substrata structure.

In the case of the anionic polymer, aqueous acetic acid solutions at concentrations of 0.5% to about 75% are suitable ionic coagulant for the anionic dispersions and are preferred over stronger acids because of the relative ease of handling, low corrosion potential and disposability.

-Salting out- to coagulate the dispersion by the addition of the natural salt is feasible but is not favoured because of the large amounts of salt needed, about 10 times the concentration of acid, and attendant problems of product contamination.

in impregnating the needled batt with the polymeric resin as contemplated herein, the batt is immersed in an aqueous ionic emulsion or dispersion at a concentration level sufficient to provide an add on of at least 70% by weight.

Upon immersion of the batt in the aqueous emulsion or dispersion, the batt may be squeezed to remove air to provide full impregnation of the emulsion or dispersion within the batt. The batt, now fully impregnated with the aqueous dispersion or emulsion, is passed through wiping rolls or the like to remove excess dispersion or emulsion on the surface of the impregnated batt. The batt is then immersed in a bath containing the counter ion toprovide coagulation with the counter ion containing material permeating the batt through diffusion and providing coagulation of the resin within the fibrous structure. After coagulation, the batt is squeezed to remove excess water and dried to form the impregnated web.

This process is a further improvement over the process described in U.S. Patent Specification No. 4,171,391 in respect of providing particular products. The differences between the referenced patent and the present process is that the batt is fully saturated, i.e. no retained air space with the aqueous dispersion or emulsion providing an

6 GB 2 099 030 A 6 ultimate add on of at least 70 percent by weight of polymeric resin based upon the weight of the batt. Because of these differences, a novel structure is obtained wherein the batt has a uniform density throughout and the bulk density 70 of the web is less than the actual density of the web.

After the impregnated web has been formed, a density gradient is imported hereto to form a simulated leather sheet material. When forming the simulated leather sheet material the impregnant for the web is preferably polymers which in particulate form are capable of fusion with themselves under conditions of heat and pressure. Normally, these polymers are thermoplastic; however, some cross-linked polymers capable of coalescense may also be used. More particularly, polyurethanes described in U.S. Patent Application Serial No. 947,544 referred to above have been found to be particularly useful in the practice of the invention to develop the desired density gradient through the thickness of the material.

The characterizing features of the simulated sheet material in accordance with the invention are primarily physical features wherein a density gradient is provided from one side of the sheet material to the opposing side of the sheet material. Preferably, the density gradient is uniform. One surface of the impregnated fibrous mass defines a grain layer with this grain layer having an actual density equal to its bulk density.

This grain layer closely simulates the grain layer of natural leather. On the opposing side of the sheet material, there is a surface which Subsequent to formation, the simulated leather defines the split layer which has a bulk density 100 maybe buffed, coated or further processed in less than its actual density with there being a accordance with known leather finishing preferably uniform density gradient throughout techniques.

the material. The split layer is somewhat fibrous In still another process, grain layer and simulates the split layer of natural leather. development may be accomplished on unwound The polymer is present in the simulated leather 105 strips of impregnated non-woven starting sheet material at a level of at least 70% by weight material unwound from packages and passed add on based upon the weight of the fibrous through a pair of rolls in a calendering operation.

Preferably one of the rolls is metal, heated to 149 to 2040C (300 to 400OF), smooth or suitably embossed; and the other roll is a softer, resilient material, such as rubber. The grain layer will be developed on the metal roll side of the sheet.

Effective calendering may be accomplished generally with a load of 5-15 tons/yard width of the sheet passing through the rolls. Wetting the sheet, prior to calendering, to 50 to 100 percent by weight added water may assist calendering.

The structures of the impregnated web and simulated leather sheet material are more fully shown in the accompanying drawings which are merely by way of example, and which are photo micrographs of cross sections of an impregnated web and simulated leather sheet material prepared in accordance with the present invention.

Figure 1 is a plan view of the resin impregnated web prepared in accordance with Example 1 prior to splitting, Figure 2 is a photomicrograph taken through to itself within the impregnant at the surfaces of the material, but yet insufficient to completely fuse the polymer at the interior of the sheet material. This process develops a density gradient from the interior of the non-woven sheet material to the two exterior surfaces. The dimensions of the gauge of the heated and pressed sheet material can be regulated by the pressure applied during the heating and pressing operations or by the insertion of spacers between the press plates or by use of a dead load press.

Further, the plates of the press can be embossed to provide a specific surface finish design to 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 process for forming the simulated leather sheet material, the impregnated non- woven starting material previously discussed can be placed in a press with only one of the plates hebted to form the grain layer while having the opposing side on the cool plate forming the split layer.

go In yet another process for forming the simulated leather sheet material, two pieces of the impregnated non-woven starting material previously discussed can be mounted upon each other in a press and heat and pressure applied sufficient to fuse the polymer to itself within the impregnant at the outer surface of each piece. After pressing, the individual pieces are separated resulting in two sheets of simulated leather.

mass.

Typically, the split layer is up about 75% of the density of the grain layer to provide a porous grain 110 layer simulating the grain layer of leather. Also it must be noted that the polymer is uniformly distributed throughout the fibrous mass in a manner wherein the ratio of fibre to polymer is uniform throughout.

The simulated leather sheet material is produced by processing the impregnated fibrous mass and preferably an impregnated non-woven sheet material as previously described.

Most preferably, the polymer used as the impregnant is one of those or of the type disclosed in U.S. Patent Application Serial No.

947,544.

In one method of processing, the impregnated non-woven sheet material to form the simulated leather sheet, the impregnated non-woven sheet material is placed in a press and heat and pressure are applied to both sides thereof. The heat and pressure is sufficient to fuse the polymer 4 q 7 _ GB 2 099 030 A 7 the thickness of the web of Figure 1 through the 65 11-11 line.

Figure 3 is a 100x photornicrograph of the III section of Figure 2, Figure 4 is a 1 00x photomicrograph of the IV section of Figure 2, 70 Figure 5 is a 1 00x photomicrograph of the V section of Figure 2, Figure 6 is a 1 00x photomicrograph of a resin impregnated batt prepared in accordance with Example I after splitting, and Figure 7 is a 1 00x photomicrograph of a cross section through the thickness of a simulated leather sheet material produced from the batt of Figure 6.

Referring now to Figures 1 to 5, wherein like reference numerals refer to like parts there is shown a resin impregnated web 10 prepared in accordance with Example 1. More particularly, Figures 2-5 show a cross section through the thickness of the web 10. The web 10 is composed of a top surface 12 and a bottom surface 14. Throughout the web 10 there are a substantial number of uncoated fibers 16, concentrations of resin 20, voids 18 and resin coated fibres 22. The structure and hence its bulk density is substantially uniform throughout the thickness of the material, although on a microscopic scale, the structure is non homogeneous.

The structure shown in Figures 2 to 5, is believed to be attributable to the full impregnation of the needled batt with the aqueous emulsion or dispersion with subsequent coagulation of the polymer while the batt is fully impregnated with the aqueous resin system.

Referring now to Figure 6 which is a I 00x photo microg ra ph, there is shown a split impregnated needled batt 24 having a uniform density throughout such as is shown in Figures 1 to 5. The impregnated batt 24 has a substantial amount of uncoated fibres 26, masses of polymer 28, coated fibres 32, and voids 30. It is to be 105 noted that although the impregnated batt is non homogeneous on a microscopic scale it has a uniform bulk density throughout.

Referring now to Figure 7 which is a 1 00x photomicrograph, there is shown the simulated leather sheet material 32 in accordance with Example IV. The material 32 has a grain layer 34 which has minimal void space and the bulk density at the grain layer 34 is equal to the actual density. At the grain layer 34, there is formed a composite 36 of fibres in a continuous resin matrix as a result of the application of heat and pressure. Moving along the A direction, it is shown that the voids 30 increase along the direction approaching the split layer 38. At the split layer 38, there are a substantial number of voids 30, uncoated fibres 26, and masses of polymer 28. The structure at the split layer 38 approximates the structure shown in Figure 6.

The following examples are illustrative of the 125 products prepared in accordance with the present invention.

Example 1

A needled batt which was heat set and had a density of 1,200 grams/sq. meter composed of polyester, polypropylene and rayon fibres and a thickness of 0.76 cm (0.3 inch) with a bulk density of 0. 16 gra MS/CM3 was immersed in a polyurethene prepared in accordance with Example Ill of U.S. Patent Application Serial No. 947,544 previously mentioned. The polymeric dispersion had a 22% total solids content to provide an add on of 120 percent based upon the weight of the batt. The batt was immersed in the polyurethane dispersion for 10 minutes at room temperature until all of the air was expelled from within the batt and the batt was fully impregnated. The surface of the batt was wiped with a straight edge on both sides to remove excess aqueous dispersion and immersed in a 10 percent acetic acid bath for 10 minutes at room temperature. Immersion in the acid completely coagulated the polyurethane within the fibre structure. The excess acetic acid was washed from the batt and the resin impregnated batt was squeezed to remove excess water. The resin impregnated batt was split into four slices through its thickness and each split was dried at 149 to 1770C (300 to 350OF), in a circulating air oven to form four resin impregnated webs having a bulk density of 0.41 g/CM3. The final product had a photomicrograph as shown in the drawings.

Example 11

Example 1 was repeated except that a 100 percent polyester batt having a density of 0. 13 grams/cc and 0.51 em (0.2 inch) thick was impregnated with 22 percent solids dispersion of Example 1. The resulting impregnated web had a uniform density throughout, high integrity and a bulk density of 0.38 grams/cm3.

Example Ill

Example 1 was repeated except that a 100% polyester needled batt of 0.56 cm (0.22 inch) thickness and a density of 0.23 graMS/CM2 was impregnated with 32 percent solids dispersion to form a needled impregnated resin fibrous web having a bulk density of 0. 56 grams/cm3. The product in accordance with Example Ill was used as a polishing pad and had toughness, high tear strength, resilience and complete recovery upon compression.

Thus the process and product in accordance with the invention provides an impregnated fibrous web of high integrity and useful as a product in and of itself and useful in forming other products. Further, the impregnated fibrous web may be buffed to provide a desirable finish.

Example IV

Two 0.18 cm (0.07 inch) thick splits of the non-woven impregnated web prepared in accordance with Example I were superposed upon 8 GB 2 099 030 A 8 each other and placed between plates of a press heated to 249'C (3000F) at a pressure of 2441 kg/M2 (500 psi) for 30 seconds. The two splits were then peeled apart, thus obtaining two sheets of simulated leather sheet material. The grain layer of the sheets correspond to the surfa, ces which were in contact with the hot press plates.

The interior sides of the sheets retained their fibrous texture similar to the unpressed sheet.

Microscopic examination showed that the simulated leather sheet material had a density gradient from the grain layer to the split layer as is shown in Figure 7.

The simulated leather sheet material, subsequent to formation can be post treated with other polymers for surface finishing in accordance 60 with known techniques.

Claims (14)

Claims

1. A simulated leather sheet material comprising: 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.

2. A sheet material as claimed in claim 1 in which the fibrous mass is a needled batt.

3. A sheet material as claimed in claim 1 or 2 in which said fibrous mass is impregnated with a polyurethane.

4. A sheet material as claimed in claim 3 in which said polyurethane is crosslinked.

5. A sheet material as claimed in any preceding claim in which said fibrous mass is impregnated with a polymer present at a level of at least 75% by weight add on based upon the weight of said fibrous mass.

6. A sheet material as claimed in claim 5 in which said polymer is present at a level of up to 400% by weight based upon the weight of said fibrous mass.

7. A sheet material as claimed in claim 6 in which said polymer is present at a level of 200 to 300% by weight add on based upon the weight of said fibrous mass.

8. A sheet material as claimed in any preceding claim in which the split layer is up to 75% of the density of the grain layer.

9. A sheet material as claimed in any preceding claim in which the fibrous mass is impregnated with a polymer substantially uniformly distributed throughout said fibrous mass.

10. A sheet material as claimed in any preceding claim in which the density of said sheet material has a uniform gradient from the split side to the grain side.

11. A method of forming a simulated leather sheet material comprising: uniformly impregnating a fibrous mass with a polymer to form a porous sheet material; heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has been applied, the grain layer having a bulk density equal to the actual density, and a split layer having a bulk density less than its actual density, the 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.

12. A method as claimed in claim 11 in which heat and pressure is applied to both surfaces of said sheet material to develop a density gradient from the exterior of said sheet material to the interior of said sheet material and splitting the sheet material in half, the exterior surfaces forming the grain layer and the interior surfaces forming the split layers.

13. A simulated leather sheet material substantially as herein described with reference to and as shown in the accompanying drawings.

14. A method of forming a simulated leather sheet material substantially as herein described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office. 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.

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