GB1576449A - Leatherlike material - Google Patents

Description

(54) LEATHER-LIKE MATERIAL (71) We, KURARAY CO. LTD., a Japanese body corporate, of 1621 Sakazu, Kurashiki-city, Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to the production of leather-like sheet material.

Leather-like sheet consisting of a fibrous material and a polymer material based on an elastomeric polymer is known as synthetic leather, simulated leather, artificial leather or (preferably) leather-like material, and has been widely used as a substitute for genuine or natural leather in footwear, carrying bags, clothing and interior materials. Heretofore, such a leather-like sheet has been manufactured by fabricating a porous substrate from a fibrous material and a polymer material based on an elastomer, applying a coloration layer comprising a pigment and a polymer component to the substrate and embossing the assembly. The conventional leather-like sheet obtained in the above manner has serious disadvantages in comparison with genuine leather.Thus, such sheet is not only inferior to genuine leather in the brightness of color and the delicacy of appearance but also lacks the flexibility and solid feeling of genuine leather. Notwithstanding the advantages of such a leather-like sheet, such as greater resistance to water, greater ease with which it may be cleaned when soiled, greater ease with which it may be fabricated into end-use products at higher yields, and lesser fluctuations in supply, the aforesaid disadvantages have put such leather-like sheet at a considerable disadvantage as compared to genuine leather. Thus, while genuine leather is almost exclusively used in expensive quality products, leather-like material is used only in medium-priced and low-priced products, thus creating a general impression that articles such as footwear, bags and interior materials made of leather-like sheet are low-quality products.

It is an essential prerequisite, therefore, to overcome the above disadvantages in order that, on the market, leather-like sheet may attain a status equal to that of genuine leather.

To accomplish bright shades, it has heretofore been proposed to superimpose a polymeric layer with a satisfactory dye receptivity on a porous substrate, in lieu of providing a coloration layer comprising a pigment and a polymer (hereinafter such a product will sometimes be referred to as a pigmented product), and then dyeing it by a jigger or pad dyeing method.

However, despite the obvious improvement in the brightness of shades over the more conventional pigmented products, the leather-like sheets obtained by the above procedures also have serious disadvantages. Thus, for example, it is difficult to attain a delicate appearance and the product has a harsh or stiffened feeling.

To attain a delicate appearance, the sheet has been embossed with a heating calender or roller engraved with the grained pattern of genuine leather or crumpled under heating on a sanforizing or equivalent machine, which is widely used for the shrink-proofing of fabrics.

Adapted to impart "grain" to the sheet by the application of an external physical force at a high temperature near the softening point of the elastomer used, thus taking advantage of the thermoplasticity of the material, these methods have the advantage that regular surface patterns may be created. However, the methods are disadvantageous in that the products tend to look artificial and in that, because the elastomer layer is subjected to elevated temperature and pressure during the process, the air-permeability, flexibility and feeling of the products are adversely affected.

There also are known procedures for improving the so-called feeling of the sheet through a chemical treatment, with a softening agent, or a mechanical flexing or crumpling procedure.

However, in the chemical method, while certain softening agents result in desired softness, also result in a rubber-like feeling. Moreover, in use of the leather-like sheet, such softening agents migrate onto the surface of the product to cause discoloration, color fading and other defects in addition to the comparatively higher cost of production. In the case of the latter mechanical method, the hitherto-proposed procedure is such that a leather-like sheet is crumpled under a given tension, under dry or wet conditions, but generally it is not only difficult to accomplish an adequate graining (crumpling) effect (soft feeling) but the disadvantage is encountered that it produces unnecessary wrinkles characteristic of mechanical crumpling. Furthermore, mechanical crumpling as such could result in reduced strength, if carried out to an excessive degree.

Extensive research undertaken by us has shown that a selection of the proper materials and the application to them of crumpling (flexing) and drying procedures under selected conditions give rise to products that have surface creases completely like those of genuine leather, and apparent softness and feeling comparable to those of genuine leather, with considerable improvements in rubber-like or paper-like properties, which are associated with leather-like sheets and which it has previously been thought to be impossible to eliminate, and, yet, without impairing the original strength of the sheet.

In accordance with the present invention, there is provided a method of producing a leather-like sheet in which a leather-like sheet comprising a porous substrate consisting of a porous layer of elastomer and a substrate of fibrous material and one or more nonporous coating layers of elastomer on the surface of said porous substrate, the total thickness of the nonporous layer(s) being in the range 0.5 to 50 ,u, is crumpled under a maximum tension of 0.3 kg per 1.5 mm of thickness per 25.4 mm width in a liquid medium and, then dried at a temperature not exceeding 100"C under minimum tension as hereinafter defined.

By proceeding in accordance with this invention, leather-like sheet that is soft in appearance and flexible and yet has a solid feeling can be produced, as will appear from the description of certain preferred embodiments below. Moreover, a brightly colored leatherlike sheet that both looks and feels like genuine leather can be produced.

The term 'porous substrate' as used throughout this specification means a flexible sheet material made up of a porous layer of elastomer and fibrous material and containing continuous micro or macro pores all of which can be detected by the eye looking through a microscope at a magnification of 50. The interfiber spaces in a nonwoven fabric and the micropores produced by the wet-coagulation of an elastomer are typical of the porosity of the substrate used according to this invention. It is necessary, for the purpose of this invention, that the percentage of voids in the porous substrate (void ratio) be not less than 10 percent, preferably 30 to 70 percent.

The high void ratio not only ensures adequate flexure characteristics of the porous substrate but also leads to the formation of appropriate grain-like creases in the nonporous surface layer during the crumpling operation in a liquid, which will hereinafter be described in detail. When the void ratio is in excess of 90 percent, the resultant grains will be undesirably coarse. The effects of the invention are most pronounced with a product consisting of a porous substrate, particularly a porous elastomer layer based on a nonwoven fabric having a void ratio of 40 to 80%, preferably 60 to 80%. In the above case, the thickness of the porous layer is not less than 50 ,u, preferably not less than 100 ,u. The thickness of the porous substrate is normally within the range of 0.5 to 3 mm.

The aforesaid fibrous substrate is a sheet-form material based on a fibrous material such as a nonwoven fabric, woven fabric or knitted fabric, which is preferably impregnated and cured or coagulated with a polymeric binder. The aforesaid fibrous material may be any ordinary kind of fiber, thus including cotton, linen, wool, spun rayon, rayon staple, acetate, nylon, polyester, polyacrylonitrile, vinylon and polyolefin, as well as the corresponding mix-spun or composite fibers.

The binder may be any of the binding agents that are generally used in the production of simulated leather and other materials. Thus, for example, natural rubber, acrylic resin, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polyvinyl chloride, polyurethane and other synthetic rubbers and mixtures of such materials may be mentioned.

Such binders are applied in any appropriate forms, e.g. as solutions, emulsions and other forms, by such procedures as dipping, coating and spray-coating. The amount of binder so used is normally within the range not exceeding 150 percent based on the fiber.

The elastomer layer applied to at least one side of the fibrous substrate forms a layer corresponding to the so-called grain side of an ordinary genuine leather, being a porous layer obtainable by wet, dry (primarily by foaming) or semi-dry coagulation. The elastomers include polyurethane and acrylonitrile-butadiene copolymer, although polyurethane elastomers are preferred.The polyurethane elastomers particularly preferred for the purposes of this invention are those elastomers obtainable from a soft segment having a molecular weight of 500 to 4000 such as polyethylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyethylene adipate glycol, polybutylene adipate glycol, polyhexamethylene adipate glycol and polycaprolactone glycol, a chain-extending agent such as ethylene glycol, butanediol, hexanediol, ethanolamine, hydrazine of 4 ,4'-methylenebis(2-chloroaniline), and a diisocyanate or a mixture of diisocyanates such as diphenylmethane-4, 4'-diisocyanate, tolylene diisocyanate or hexamethylene diisocyanate.If necessary, there may be incorporated in said elastomer such additives as filler, softening agent, stabilizer, antistatic agent, pigment, dyestuff, foaming agent or coagulation-regulator, as well as polymers having good compatibility with the elastomer, such as nitrocellulose, polyvinyl chloride, polyvinyl formal, poly methyl acrylate and vinylidene chloride-acrylonitrile copolymer. The elastomer is applied to the fibrous substrate, preferably by coating or spraying. It is also possible to prepare a self-supporting layer of the elastomer and to laminate it to the fibrous substrate.

The porous elastomer layer thus produced, as such, is a porous substrate usable for the purpose of this invention.

By imparting a thin nonporous coating layer to the porous substrate thus produced, there is obtained a leather-like sheet, which is then subjected to said the specific crumpling treatment in a liquid, which is a feature of this invention. In accordance with this invention, the selection of the starting material is as important as the conditions of the specific crumpling, which are described hereinafter, for a maximum realization of the effects of this invention. The elastomer layer used according to this invention is a nonporous coating layer of total thickness 0.5 to 50,u and preferably has a double-layer structure consisting of a hiding layer and a dye-receptive layer.For the purpose of preventing color unevenness, i.e. uneven coagulation which is liable to result, owing to unevenness of the air or bath flow, temperature and other causes in the course of coagulation of the elastomer solution the hiding layer is generally formed as a very thin layer, 0.5 to 10 E.L, of the elastomer containing 10 to 300 weight percent of a pigment based on the polymer, on the surface of the elastomer layer constituting the porous substrate. Where the uneven coagulation will not be conspicuous in the final product, said hiding layer may be dispensed with, but it is essential for the unmistakable development of creases resembling those of genuine leather (a certain finely embossed pattern) by the specific crumpling and final drying according to this invention.With a pigment in amounts less than 10 weight percent, it is difficult to cover up the uneven coagulation fully, while when the pigment is used in a proportion exceeding 300 weight percent, no adequate bond with the porous substrate is obtained, nor is it possible to realize a uniform pattern of creases even by the specific cumpling according to this invention. The uneven coagulation cannot be fully covered up when the coating amount (thickness) of said polymer is less than 0.5 ij while where the thickness of the coating part of the non-porous layer is in excess of 10 ,a, not only does deterioration take place in crease and grain characteristics, feeling and flexure fatigue, but other disadvantages result as well.Thus when the coating amount of the polymer exceeds the above range, it is not only difficult to establish the conditions of specific treatment within a preferred range but the entire balance between the dye-receptive layer and porous substrate is disturbed to interfere with the development of well-defined creases (similar to embossed patterns) resembling those of genuine leather which, in accordance with this invention, are obtainable without literal embossing.

In accordance with one embodiment of this invention, a dye-receptive (easily dyeable) layer is superimposed on said hiding layer, the thickness of said dye-receptive layer being from 0.5 to 10 ,u . The dye-receptive layer is so designated in the hope that the final product will be attractively dyed (colored), but the thickness of such a layer is dictated by conditions favorable not only to the development of a brilliant color but also to the development of satisfactory bending strength, crease and grain characteristics, as well as those soft feeling and crease-characteristics resembling those of genuine leather which are major characteristics of the invention.

In accordance with a preferred embodiment of this invention, there may also be disposed a nonporous intermediate layer, in addition to said hiding and dye-receptive layers, either beneath said hiding layer or between said hiding and dye-receptive layers. However, if such elastic nonporous layers have a total thickness that is too great, the creases obtainable by the liquid crumpling (flexing) treatment of this invention will be undesirably coarse and harsh.

Therefore, the thickness of such a nonporous top-layer structure, inclusive of said hiding and dye-receptive layers, must not exceed 50 E.L. Generally, the thickness of such nonporous elastomer coating layer(s) should be in the range 0.5 to 20 IL and, particularly when the porous substrate consists of a fibrous base material on which is disposed a porous elastomer layer, the thickness of the nonporous layer(s) is most desirably in the range 1 to 10 E.L.

The polymer to be used for the formation of such a nonporous elastomer layer may be the elastomer used in the formation of the porous elastomer layer superimposed on the porous substratum, and is preferably a polyurethane elastomer. Where it is used for the formation of the hiding layer or said intermediate or under layer, the polyurethane elastomer may be of almost any kind. However, in order to effectively develop a brilliant shade and desirable grain-like creases, the dye-receptive layer is preferably made of polymers which are predominantly made up of polyurethane elastomers in which polyethylene glycol constitutes a component of its soft segment.

Preferably Total Weight of Total Weight of Polyurethane Polyethylene Containing Polyethylene Glycol Glycol in Soft Segment x x = 0.02 Total Weight of Total Weight of Soft Segment Polymer It is not certain why, when a polyurethane containing polyethylene glycol in its soft segment is used as the dye-receptive layer (to be disposed as substantially the uppermost layer of the leather-like sheet), the surface has an exceedingly soft feeling. However, it is presumably because this polyurethane has an extraordinary affinity for the medium water in the course of specific liquid crumpling.

When selecting a polyurethane for the formation of the dye-receptive layer, the nitrogen content, based on the diisocyanate component, of the polyurethane elastomer also has an influence upon the dyeability of the dye-receptive layer as well as upon such characteristics as flexure fatigue, crease, bending crimp and grain characteristics, and is preferably within the range 3 to 7 weight percent.

It is desirable that, in this dye-receptive layer, a dyestuff should have previously been incorporated in an amount up to 150 weight percent.

The dye used in the dye-receptive layer may be any dyestuff soluble in the solvent for said polyurethane elastomer but where it is necessary that the dye remain in the final product, a metal complex salt dye is optimum in view of properties such as light fastness and resistance to migration which it provides, and where such a dye is required only for covering up flaws in the application of the dye-receptive layer and must be removed before the dyeing step, it is most desirable to use a dye that has no dyeing affinity for the polyurethane elastomer and that is soluble in water, for example one of certain acid dyestuffs.Furthermore, to preclude the formation of color unevenness spots, which are liable to be produced in the dyeing step, it is possible to apply a small amount of a polyurethane elastomer-based polymer material which, as such, has few dyeing seats and is poorly dyeable on top of the dye-receptive layer.

As to the procedure of applying thin elastomer layers (hiding and dye-receptive layers) to the surface of said porous substrate, the elastomeric polymer may be applied by the gravure printing method or by spray-coating and evaporating the solvent from the coat. Therefore, the layers are nonporous. Moreover, the leather-like sheet obtained in the above manner may be embossed as desired, either before or after the liquid crumpling treatment.

The porous sheet obtained in the above manner is then submerged in a liquid and, under intense stirring but under minimum tension (which term is used, throughout the specification and claims, to mean a tension not exceeding 0.3 kg per 1.5 mm thickness per 25.4 mm width), subjected to random flexing (liquid crumpling treatment).

If a tension force greater than the specified minimum is applied to the porous sheet or the sheet is held stationary, not only will the product have an inferior feeling but the desired creases will not be produced, thus failing to give a soft appearance.

In the present invention, it is essential that the medium used for the crumpling operation be a liquid. The high resistance of the liquid contributes to a greater crumpling effect under minimum tension. The pronounced crumpling effect of this invention cannot be realized when the medium is a gas such as air even assuming that an identical equipment is used. The most effective medium for the purposes of this invention is water, although other liquids such as alcohols (eg methanol or ethanol) and inert lower hydrocarbons as well as mixutres of such liquids may also be employed. When an organic solvent is used as the crumpling medium, it must be inert to the constituents of the leather-like sheet. If desired, a dye, softening agent or/and other additives may be incorporated in the liquid medium. When a dye has been added, the drying effect is accomplished concurrently with the graining effect and, therefore, the entire production process is simplified. When a softening agent or other additive is used, care should be exercised in the selection of such an agent, for certain additives could adversely affect the effect of this invention (e.g. soft feeling). Among preferred softening agents are sorbitan ester activators, low molecular-weight polyoxyalkylene alkyl esters and turkey red oil. The liquid medium containing such additives may be a solution, an emulsion or any other appropriate form.The crumpling operation is conducted in a plant which may for example be an apparatus resembling a laundering machine equipped with a revolving screw member within a tank, a device adapted so that a liquid is compressed by a pump and forced into a tank to generate a vortex of liquid jets, or a bowl or drum-type apparatus equipped with a baffle member on its internal wall for an improved agitation of liquid and adapted so that the bowl or drum as a whole or an inner member thereof may freely revolve. It is most desirable to use an apparatus such that its tank as a whole or an inner member thereof is rotatable in a vertical plane so that the material to be processed may fall only under its own weight to create a random flexing action, for no external force will then be acting upon the material which will thus be flexed under a minimum of tension.

The substrate sheet may be in any shape as it is subjected to the crumpling operation of this invention, although an excessively large sheet will prove undesirable for the purposes of this invention. For example, when the sheet is more than 20 m long, the use of said apparatus resembling a laundering machine might create an uneven tension within the sheet so that no sufficient flexing action could be obtained. This invention is generally applied to sheets not exceeding 10 m in length, normally to sheets within the range 0.5 to 5 meters in length.

The operating temperature of said liquid medium is preferably within the range 20 to 70"C in consideration of the magnitude of each flexure crease.

The dye to be used in conjunction with the practice of this invention is most desirably a metal complex salt dye in view of its high light fastness and migration resistance, among others. The softening agent is desirably a substance that has a maximum of softening action and a minimum of decolorizing action.

Normally prior to dyeing, premoisturizing is carried out to prevent uneven dyeing or remove the dye used for covering flaws in the application of the dye-receptive layer. The temperature of premoisturizing water is also preferably 20 to 700C as is the case with aforesaid dyeing and softening treatment.

The porous sheet that has undergone the dyeing and/or softening treatment described above is finally subjected to the low-temperature drying operation under minimum tension as hereinbefore defined. The selection of the proper drying temperature and tension is essential to the objects of this invention. The drying of a conventional wet sheet is performed in a hot air current within the temperature range of about 140 to 1500C for commercial purposes and by means of a pin tentering machine (which normally gives a tension about. 0.5 to 2 kg per linear inch per 1.5 mm thickness) or the like for shape-retension purposes.However, in accordance with this invention, the drying is effected at a temperature not exceeding 100"C, preferably within the range of 10 to 700C and under minimum tension (less than 0.3 kg or, preferably 0.1 kg to substantial zero per 1.5 mm thickness per 25.4 mm width). If the drying temperature is higher than the above range or an excessive tension is applied, the feeling and apparent softness are sacrificed and no neat flexure creases can be obtained.

The leather-like sheet thus obtained is finished by a conventional finishing technique available and used for leather-like sheets within the scope in which the effects of this invention will not be adversely affected. Especially, in many instances, a coloration layer composed of a polymer and a colorant is applied to the sheet. The polymer used for this purpose may be a polyurethane elastomer similar to that mentioned in connection with said porous substrate layer or a polymer compatible with said elastomer. As in the case of dyeing, the dyestuff is most desirably a metal complex salt dye.

The leather-like sheet obtained in the described manner has fine flexure creases which give rise to an apparent softness as well as a good feeling due to its excellent hand and bright shade.

The invention will be further described by way of the following examples in which all percentages are by weight.

Example 1 A nonwoven polyester web, 150 cm wide, was impregnated with a solution comprising 15% of a polyurethane elastomer (nitrogen content 4%) of polyethylene adipate glycol, ethylene glycol and diphenylmethane-4,4'-diisocyanate, 1% of brown pigment, 2% of water and 82% of dimethylformamide. Then, the same solution as above was further layered onto the web at a rate of 100 g/ m2 on- a solids basis. The web was immersed in a coagulation bath of 30% dimethylformamide and 70% water at 35"C for 30 minutes, after which time the web was treated to remove the solvent and dried to obtain a porous substrate. The thickness of the surface coat was about 300 CL, with the void ratio being 70%.In view of the fairly extensive uneven coagulation on this porous substrate, the surface was covered up by coating with a solution of 5%of the same polyurethane elastomer as above, 7%of brown pigment, 22% of dimethylformamide and 66 % of methyl ethyl ketone (hiding layer, 1.5 gsolids/m2). Thereafter, the substrate was further coated, on top of said hiding layer, with a solution comprising 7% of a polyurethane elastomer (nitrogen content 5.5%) of polyethylene glycol, ethylene glycol and diphenylmethane-4,4'-diisocyanate, 1 % of KayanoSMilling Brown 4 GW(an acid dyestuff available from Nihon Kayaku K.K.),21 of dimethylformamide and 71% of methyl ethyl ketone at a rate of 2.5 g solids/m2 (dye-receptive layer).The surface was then embossed to a coarse-weave design and cut to 1 m lengths. Thereafter, the product was premoisturized in an apparatus comprising a drum-shaped tank equipped with baffle-plates on its internal wall and capable of revolving it (12 revolutions per min. about a vertical axis using warm water at 50"C for 30 minutes. The product was further treated with an aqueous dispersion containing 1.5% of polypropylene glycol adipate ester at 40"C for 10 minutes. Throughout the above operations, the porous sheet was allowed to move and to flex freely within the vessel under minimum external tension force. After the liquid content of the sheet had been adjusted to 130%, the sheet was left standing at room temperature to dry under minimum tension.

Yellowish brown metal complex dye 3% owf Bath ratio 1:50 Bath temperature 60"C Finally, the sheet was coated with a solution containing 7% of a polyurethane elastomer (nitrogen content 5.5No) of polyethylene glycol, polybutylene adipate glycol (2/1), 1,4butanediol and diphenylmethane-4,4'-diisocyanate, 3 %of brown metal complex dye, 21 % of dimethylformamide and 69% of methyl ethyl ketone at a rate of 1 g solids per m2 (coloration layer) to produce a leather-like sheet product (A). This leather-like sheet (A) had an apparent softness due to the presence of tiny flexure creases similar to those of genuine leather, a bright shade and an exquisite feeling, thus being of high commercial value.

The production conditions of the above leather-like sheet (A) were partially modified to manufacture control sheets (B) to (F). The conditions used and the results obtained are summarized in Table 1. As a test of flexibility, the Gurley stiffness of each sheet was determined according to JIS-L-1079-1976. As to the brightness of shade, apparent softness and feeling of each sample sheet, a panel of judges, who were engaged in the development or sale of leather-like material, was requested to score the samples and an average of the scores for each evaluation item was recorded on a five-point scale. The relative marketability or commercial value of those leather sheets was also recorded on a 5-point scale. The larger values represented higher quality evaluations.

Leather-like sheets (B) & (C) A control test was performed for evaluating the effects of tension and flexure during the liquid-flexing crumpling treatment.

A jigger-type machine was used in lieu of the drum machine to manufacture a leather-like sheet (B). This sheet, in turn, was crumpled by means of a conventional mechanical crumpling apparatus as disclosed in U.S.P. 3695801 to manufacture a leather-like sheet (C). Since not only the jigger machine applied a tension to the porous sheet but the movement of the sheet was considerably restricted, no crumpling effect could be obtained in the leather sheet (B). Despite its bright shade, this sample (B) was also inferior in feeling and other features, being completely identical with the prior art product. The leather-like sheet (C) produced by the mechanical flexing of the leather-like sheet (B) had a slightly improved flexibility but had no adequate flexure creases. In addition, this sheet (C) was somewhat inferior even to (B) in the brightness of shade.

Leather-like sheet (D) A control test was also carried out to evaluate the influence of tension during the drying process. A leather-like sheet (D) was manufactured in the same manner as in the above description except that, instead of drying in the air, the tenter dryer (which exerted a tension of about 2 kg per inch width and 1.5 mm thickness) was used. The sheet (D) had a sufficient brightness of shade but substantially no flexure creases. Thus, the sheet had no soft appearance and lacked overall flexibility.

Leather-like sheet (E) This control test was performed to evaluate the influence of the temperature in the drying process.

A leather-like sheet (E) was.manufactured under the same conditions, except that the drying operation was carried out at 1500 C in lieu of room temperature. This sheet (E) had no fine creases such as those found in sheet (A), thus having a stiff feeling.

Leather-like sheet (F) This control test was carried out to evaluate the relative advantage of a liquid and a gas as the flexing medium. A cut substrate web was immersed in an aqueous dispersion containing 1.5% of polypropylene glycol adipate ester at 40"C for 10 minutes, adjusted to a liquid content of 130% and subjected to random flexing in a dye-free empty drum for 40 minutes.

Thereafter, the web was treated in the same manner as the sheet (A) to manufacture a leather-like sheet (F).

Although this sheet (F) of course had no bright shade because it had not been dyed, no adequate flexure effects and, hence, no flexibility could be obtained.

Leather-like Brightness Aparent Stiffness Overall sheet of shade softness Hand (Gurley, mg) score A 5 5 5 2600 5 B-Jigger 5 1 1 5200 1 C - Jigger & 4 2 2 4600 2 mechanical flexing D - Tenter 5 3 2-3 4800 2 drying E - 1500C 5 3 2 5000 2 F-Air 1 3 3 3800 3* * This elevation was made in disregard of the brightness of shade.

Example 2 A polyethylene sheet embossed to a kip tone was coated with a solution consisting of 9 % of a polyurethane elastomer composed of polycaprolactone glycol, ethanolamine and diphenylmethane-4,4'-diisocyanate (nitrogen content based on diisocyanate: 4.2it), 1.5% of polyvinyl chloride, 1.5%of titanium oxide and 88 % of dimethylacetamide at a rate of 60 g solids per m2 and the resultant coating layer was immersed in a coagulation bath of 40% dimethylacetamide-60% H20 at 400C. Thereafter, the sheet was treated to remove the solvent and dried to obtain a porous film having a thickness of about 200 IL This sheet was bonded to a 1 m-wide woven polyester fabric to manufacture a porous substrate.In view of some evidence of uneven coagulation on this porous substrate, the surface of the substrate was coated with a solution consisting of 6% of a polyurethane elastomer of the same type as above,12 of titanium oxide, 20% of dimethylacetamide, 32% of tetrahydrofuran and 30% of cyclohexanone at a rate of 2 g solids per m2 (about 2 IL thick). Then, the surface was further coated with a solution consisting of 7% of the same polyurethane elastomer as that used in Example 1 for the formation of the coloration layer of leather-like sheet A, 22% of dimethylacetamide, 41%oftetrahydrofuran and 30%ofcyclohexanone at a rate of 3 g solids per m2 (about 3 CL thick).The sheet was cut into 1 m lengths, which were dyed in a launderer-type apparatus provided with an internal revolving screw using the following conditions and under minimum tension so that each porous sheet would be completely free to move. The sheet was then dried at 300C to obtain a leather-like sheet (G).

Yellow metal complex salt dye 1.5% owf Bath ratio 1:100 Bath temperature & dyeing time 70"C, 20 minutes This product had not only a bright shade but also delicate flexure creases completely identical with those of genuine leather on the surface. Thus, having an excellent feeling and an apparent softness, this sheet gave an impression of being real leather. As controls, a leather substitute produced by coating a 100 thick nonporous layer of polyvinyl chloride on a woven polyester fabric and another leather substitute produced by coating a 100 ,thick nonporous layer of nylon on a similar fabric were each subjected to the same treatments as described in Example 2.The resultant leather-like sheets (H and I) had surface creases which, however, were by far coarser than the creases of leather-like sheet (G), and were inferior to (G) in overall soft feeling as well. The leather like sheet (H) had not been dyed and had a poor appearance.

Example 3 A porous substrate similar to that used in Example 2 was coated with a solution consisting of 2.5% of a polyurethane elastomer of the same type as that used in Example 1 for the formation of the dye-receptive layer of leather-like sheet (A), 5% of a polyurethane elastomer of the same type as that used in Example 1 for the formation of the substrate layer, 4.5 % of Lanyl Brown 3R (a metal complex salt dye available from Sumitomo Kagaku Kogyo K. K.). 25%ofdimethylformamide, 33%oftetrahydrofuran and 30%ofcyclohexanone ata rate of 4.2 g of solids per m2. Thus, upon drying, there was produced a nonporous coating film as thick as about 4.2 it. The surface of the sheet was then embossed to a kid grain.Using a drum-shaped apparatus similar to that used in Example 1, the sheet was treated with an aqueous solution containing 2% of Turkey red oil at 500 for 30 minutes. Then, the sheet was dried at 500C and under minimum tension to obtain a leather-like sheet (J). This sheet was also satisfactory in the brightness of shade, hand and apparent softness, having an overall good feeling. The above procedure was repeated except that the thickness of the nonporous coat was altered to obtain leather-like sheets (K) and (L). It was found that as the thickness of the nonporous layer was increased, both the surface crease pattern and feeling of the product were adversely affected. The results evaluated by the same scoring procedure as described in Example 1 are given below in Table 2.

Table 2 Thickness of Gurley Leather- nonporous Brightness Apparent stiffness Overall like sheet layer (,u) of shade softness Hand (mg) score (J) 4.2 5 4 5 2700 4 (K) 14 5 4 4 2800 4 (L) 91 5 2 3 3100 2-3 WHAT WE CLAIM IS: 1. A method of producing a leather-like sheet in which a leather-like sheet comprising a porous substrate consisting of a porous layer of elastomer and a substrate of fibrous material and one or more nonporous coating layers of elastomer on the surface of said porous substrate, the total thickness of the nonporous layer(s) being in the range 0.5 to 50 ,ufl is crumpled under a maximum tension of 0.3 hg per 1.5 mm thickness per 25.4 mm width in a liquid medium and then dried at a temperature not exceeding 100"C under minimum tension as hereinbefore defined.

2. A method according to claim 1 including the step of applying the porous layer of elastomer to the fibrous material constituting the porous substrate.

3. A method according to claim 1 in which the polymer forming the porous layer of elastomer and the polymer forming the nonporous coating layer(s) of elastomer are based on a polyurethane elastomer.

4. A method according to claim 2 in which the nonporous coating layers of elastomer consist of (a) a hiding layer having a thickness of 0.5 to 10 IL and containing a pigment in a proportion of 10 to 300 weight percent based on the elastomer and (b) a dye-receptive layer having a thickness of 0.5 to 10 CL and containing a dye in a proportion not exceeding 150 weight percent based on the elastomer.

5. A method to claim 4 in which the elastomer forming the dye-receptive layer is a polyurethane elastomer containing polyethylene glycol in its soft segment.

6. A method to claim in which the quantity Total Weight of Total Weight of Polyurethane Polyethylene Containing Polyethylene Glycol Glycol in Soft Segment x Total Weight of Total Weight of Soft Segment Polymer is not less than 0.02.

7. A method according to claim 2 in which the porous substrate consists of a fibrous substrate comprising a nonwoven fabric and an elastomer, together with a porous layer coated on the substrate and having a void ratio of 40 ta 80 percent.

8. A method of producing a leather-like sheet, substantially as hereinbefore described in the foregoing Examples with reference to the sheets designated (A), (G) and (J).

9. A leather-like sheet produced by a method according to any one of the preceding

Claims (1)

1. claims.