GB2077142A

GB2077142A - Artificial leather and process for producing the same

Info

Publication number: GB2077142A
Application number: GB8113549A
Authority: GB
Original assignee: Toray Textiles Inc
Current assignee: Toray Textiles Inc
Priority date: 1980-05-07
Filing date: 1981-05-01
Publication date: 1981-12-16
Also published as: DE3117894A1; GB2077142B; FR2482144A1; JPS56159368A

Abstract

An artificial leather having a natural leather-like appearance and touch and an enhanced draping property, comprises a fibrous fabric substrate, a superficial layer formed on a surface of the substrate and comprising a synthetic polymer resin, and a back layer formed on the other surface of the substrate and comprising fine fibers derived from natural leather.

Description

SPECIFICATION Artificial leather and process for producing the same FIELD OF THE INVENTION The present invention relates to an artificial leather, resembling closely a natural leather in appearance and hand, and a process for producing the same. More particularly, the present invention provides a natural leather-like artificial leather suitable for use in the field of clothing.

BACKGROUND OF THE INVENTION It is known, heretofore, that an artificial leather can be prepared in such a manner that a synthetic polymer resin layer such as polyurethane is laminated on one surface of a substrate consisting of a knitted, woven or non-woven fabric; or that the substrate is impregnated with a solution of a synthetic polymer resin in a solvent, the impregnated substrate is dried with heat or wet-coagulated, and a synthetic resin polymer layer is laminated on one surface of the resultant substrate. However, in the case of the artificial leather prepared by the former process, the back surface of the artificial leather exhibits a texture of the knitted, woven or non-woven fabric itself which makes it possible to distinguish the resultant artificial leather from natural leather at a glance.On the other hand, also in the case of the artificial leather prepared from the impregnated substrate by the latter process, the appearance of the artificial leather can be clearly distinguished from that of natural leather. In addition, these artificial leathers are unsatisfactory in their draping property. Therefore, the above mentioned artificial leathers are far removed from natural leather.

It is also known that an air-permeable artificial leather can be prepared in such a process that: one surface of a substrate is coated with ah adhesive; short fibers such as natural Lather powder are spread on the adhesivecoated surface of the substrate; the resultant substrate is subjected to a rolling procedure to press the short fibers into an adhesive layer, and; the rolled substrate is dried by heating.

However, this type of artificial leather has a back surface exhibiting a texture of the substrate itself which makes it possible to distinguish the artificial leather from natural leather at a glance. Moreover, the short fiber-bonded surface of the artificial leather exhibits a quite different feel and appearance, as compared with that of the surface of the natural leather.

Therefore, this type of artificial leather is limited in its use.

SUMMARY OF THE INVENTION An object of the present invention is to provide an artificial leather resembling closely natural leather in both appearance and feel of not only the superficial surface but also, the back surface of the artificial leather, and a process for producing the same.

Another object of the present invention is to provide an artificial leather resembling closely natural leather and having an enhanced softness and draping property, and a process for producing the same, which is suitable for use in the field of clothing.

The above-mentioned objects can be attained by the artificial leather of the present invention which comprises (1) a substrate comprising a fibrous fabric; (2) a superficial layer formed on a surface of the substrate and comprising a synthetic polymer resin, and; (3) a back layer formed on the other surface of the substrate and comprising fine fibers derived from natural leather.

The above-mentioned artificial leather can be produced by the process of the present invention which comprises the steps of: (1) bonding fine fibers derived from natural leather onto a surface of a substrate comprising a fibrous fabric with an adhesive; (2) buffing the resultant bonded fine fibers layer, and; (3) laminating a layer of a synthetic polymer resin on the other surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing shows an explanatory cross-sectional profile of an embodiment of the artificial leather of the present invention.

DETAILED DESCRIPTION OF THE INVEN TION In one aspect of the present invention, there is provided an artificial leather comprising a substrate, such as knitted, woven or non-woven fabrics, one surface of which has been covered by fine fibers provided by finely dividing natural leather and the other surface of which has laminated thereon a superficial layer made of a synthetic polymer resin.

In the present invention, it is preferable that the superficial layer of a synthetic resin is composed of a porous under layer corresponding to the reticulate layer of the natural leather and a non-porous upper layer corresponding to the grain of natural leather. More preferably, the superficial layer of the synthetic polymer resin has an embossed design similar to a design on the superficial surface of animal leathers.

In a second aspect of the present invention, there is provided a process for producing the above-mentioned artificial leather. In this process, dyed or undyed fine fiber (particles) of natural leather are bonded on a surface of a dyed or undyed substrate consisting of a knitted, woven or non-woven fabric; the bonded fine fiber layer on the surface of the substrate is buffed before or after the fine fiber layer and/or the substrate is dyed, and the other surface of the substrate is laminated with a superficial layer made of a synthetic polymer resin.

The substrate usable for the present invention may be selected from knitted, woven or non-woven fabrics. The substrate has preferably a number of fluffs on the surface thereof.

This is because the fluffs are effective for attaining a uniform lamination of the synthetic polymer resin layer or a uniform distribution of the natural fine leather fibers. In addition, the fluffs are effective for causing the natural leather fine fibers to be firmly embedded in the surface of the substrate so that the fine fibers are prevented from falling off from the surface and is effective for ensuring a firm bonding between the synthetic polymer resin layer and the surface of the substrate so that the polymer resin layer is prevented from separating from the surface.

The fluffed surface of the substrate may be obtained by raising the surface of the substrate, or by making the substrate from fluffed yarns or spun yarns, or by embedding short fibers in the surface of the substrate: In the case where both surfaces of the substrate are fluffed, the fluffing operation may be carried out in such a manner that the surface on which the natural leather fine fiber layer is laminated has a lower fluff density than that on the other surface of the substrate.

In order to ensure that the artificial leather of the present invention exhibits an excellent draping property, a thin fabric having a low weight basis is preferably used as the substrate. The most preferable substrate is a knitted fabric made from synthetic fibers, for example, polyester fibers or polyamide fibers.

In accordance with the present invention, the fine fibers prepared by finely dividing natural leather are bonded onto one surface of the substrate with an adhesive. In the case where the substrate is a thin fabric, it is preferable that the fabric is rendered waterrepellent so as to avoid an excessive penetration of the adhesive thereinto before it is subjected to a fine fiber-bonding procedure.

The natural fine leather fibers usable for the present invention may be prepared by various methods. For example, typical methods for preparing the fine fibers are.

(1) shaving of an oxhide or cowhide are impregnated with water, the water-impregnated shavings are pulverized in a pulverizer and the pulverized mass is screened to separate the finely divided particles therefrom; (2) an oxhide or cowhide is ground by means of a grinder, and; (3) an oxhide or cowhide is dry-pulverized at a temperature of 50"C or less, the pulverized mass is treated with an aqueous solution containing sodium salts of higher alcohol sulfuric esters and polyoxyethlene nonyl-phenol ethers, the treated mass is dehydrated, and, then, dried at a low temperature.

The natural fine leather fibers thus obtained are treated with a flocking promotor, and, then, bonded onto a surface of dyed or undyed substrate. Before treating with the flocking promotor, the natural fine leather fibers may be dyed. In the bonding procedure, a conventional adhesive, such as poluyrethane type adhesive, polyacryl type adhesive or synthetic rubber adhesive, is first applied on one surface of the substrate, and, then, the natural leather fine fibers are spread on the adhesiveapplied surface of these fine fibers are electrostatically flocked on the adhesive-applied surface. If a deeply colored artificial leather is desired, the substrate and the natural fine leather fibers are previously dyed and after the bonding procedure, the resultant product is again dyed. This two-step dyeing is also effective for increasing the shade depth of the resultant artificial leather.

The natural leather fine fibers usable for the present invention have preferably a particle size of from 10 to 90 meshes. The above mentioned particle size range is effective for attaining a fine texture of the resultant artificial leather. In order to attain a uniform distribution of the natural fine leather fibers on the surface of the substrate, the natural fine leather fibers to be bonded should have a moisture content of 35 + 5%. After the bonding procedure is complete, the fine fiberbonded surface is subjected to a buffing procedure and, then, if necessary, to a dyeing procedure. Thus, a natural suede-like surface having a deep shade is obtained. This surface forms a back surface of the artificial leather of the present invention.

In the other hand, the other surface of the substrate, is laminated with a superficial layer made of a synthetic resin so as to provide a superficial surface of the artificial leather of the present invention. The superficial synthetic polymer resin layer may be porous so that it corresponds to the reticulate structure of the natural leather. The porous superficial layer may be formed by a so-called wet type micropore-forming method, dry type micropore-forming method or vinyl chloride type micropore-forming method.

The wet type micropore-forming method may be carried out as follows. A solution of a polymer consisting mainly of a polyurethane elastomer in a solvent is applied on the surface of the substrate to a predetermined thickness, the solution-applied substrate is immersed in a coagulating liquid which is not capable of dissolving the polymer and compatible with the solvent for the polymer, so as to coagulate the layer of the polymer solution into a uniform microporous layer while removing the solvent from the layer of the polymer solution, and, then, the resultant microporous layer is dried.

The dry type micropore-forming method may be carried out as follows. A foamable polyurethane preopolymer liquid which is prepared by partially reacting an organic polyisocyanate with an active hydrogen atom-containing compound, in applied on a release sheet, the liquid-applied sheet is placed in a thermoand humidistat maintained at a constant temperature and relative humidity so as to effect a complete reaction of the polyisocyanate with the active hydrogen atom, thereby forming a microporous layer consisting of so-called polyurethane foam, the resultant composite sheet is laminated on the surface of the substrate while the polyurethane foam retains some degree of tackiness, the resultant laminate is heated for a certain period of time so as to cause the polyurethane foam to interact with the substrate, and, then, the release sheet is separated from the laminate.

The dry type micropore-forming method may also be carried out by applying a socalled mechanical foam, which has been prepared by blowing air into an emulsion of a synthetic polymer such as polyurethane, polyacrylic ester or synthetic rubber, on the surface of the substrate, and, then, by drying the foam on the substrate at an elevated temperature. The microporous layer may be formed by another method so that the mechanical foam is applied on a release sheet. the resultant sheet is dried by heating, the dried sheet is laminated on the surface of the substrate, and, then, the release sheet is separated from the laminate so as to form the microporous superficial layer.

The vinyl chloride type micropore-forming method can be carried out by coating the surface of the substrate with a vinyl chloride composition containing a thermally decomposable foaming agent, and by heating the coating substrate at a predetermined elevated temperature so as to cause the foaming agent to be thermably decomposed, whereby a microporous superficial layer is formed.

In the aritifical leather of the present invention, for the purpose of attaining a superficial surface more closely resembling the grain surface of natural leather, the above mentioned microporous layer is further laminated with a non-porous upper layer made of a synthetic polymer resin. The thus prepared superficial surface corresponding to the grain surface of natural leather may be provided with the same design as that of natural leather by means of an embossing processing as described hereinafter.

The upper layer may be made of any synthetic polymer resin conventionally used for the formation of a superficial layer of an artificial leather, such as polyurethane resins, polyamide resins, poiyamino acid resins and polyurethane-modified polyamino acid resins.

The upper layer may be provided by dissolving a synthetic polymer resin in a solvent together with any additive such as coloring matters and stabilizers and: by applying the resultant solution on the microporous under layer, and; drying the upper layer of the polymer resin solution formed on the microporous under layer. Otherwise, the upper layer may be formed by dissolving a synthetic polymer resin in a solvent together with any additive such as coloring matters and stabilizers; by applying the resultant solution on a release sheet; by partially drying the applied solution layer; by laminating the partially dried sheet on the microporous layer, and; by separating the release sheet T'rnm the laminate after the complete drying of the applied solution layer.

As the release sheet, use may be made of a sheet coated with silicones on the surface thereof, or a sheet laminated with a synthetic polymer resin film such as polyethylene films and plypropylene films. The synthetic polymer resin layer may be subjected to a printing procedure or a surface treating procedure, as required. The surface of the synthetic polymer resin superficial layer may also be provided with a rugged design formed by means of the use of a release sheet having the corresponding rugged design, an embossing roll or a high frequency embossing apparatus.In addition, if a metal plate on which a natural surface design of animals and plants or an artifical design is formed, is hot stamped on the synthetic polymer resin superficial layer, a high quality-imaged artifical leather exhibiting a natural leaaher-lil:e appearance which could never by obtained by the conventional processes, is obtained.

Referring to the accompanying drawing, the aritifical leahter of the present invention comprises a substrate 1; a microporous under layer 2 laminated on a surface of the substrate 1; a non-porous upper layer 3 a laminated on the under layer 2, and made of a synthetic polymer resin, and; a natural fine leather fiber layer 4 formed on the other surface of the substrate 1. The synthetic polymer resins upper layer 3 exhibits the grain appearance of natural leather, while the natural fine leather fiber layer 4 exhibits a buckskin appearance of natural leather. Accordingly, the artificial leather of the present invention, as a whole, exhibits an appearance and a feel which resemble closely these of natural leather. In addition, the artificial leather of the present invention exhibits a very excellent draping property because a thin fabric is used as the substrate.

In a particular embodiment of the artificial leather of the present invention, a substrate whose front surface has a high fluft density and whose back surface has a low fluff density is used. Then, natural fine leather fibers are spread on an adhesive layer formed on the back surface and the spread fine fibers are lightly pressed into the adhesive layer by means of a pair of pressing rolls. The fine fiber layer is dried and, then, subjected to a buffing operation. As a result of the buffing procedure, the natural leather fine fibers penetrate into spaces formed between the fluffs on the substrate, and the buffed portion of the natural fine leather fibers and the fluffs of the substrate are exposed to the outside so as to form a pile layer. Such a back layer is substantially similar to the back skin of the natural leather in respect of touch, feel and appearance.

The present invention will be illustrated in more detail by the folloiwng examples.

Example 1 A nylon yarn having a yarn count of 75 denier/36 filaments and a nylon yarn having a yarn count of 1 5 denier/monofilament were crossknitted by using a 28 gauge tricot knitting machine to prepare a substrate. Both the surfaces of the substrate was subjected to a raising procedure so that the front surface of the substrate had a high fluff density, while the back surface thereof had a low fluff density. Then, the raised substrate was subjected to a conventional water repellence-imparting process such that the degree of repellency thereof was 95 or more.

Subsequently, a polyurethane type adhesive was applied on the back surface of the substrate. Natural fine leather fibers having a particle mesh size of 60 and a moisture content of 40%, were electrostatically flocked in the adhesive layer at a speed of the substrate 3 m/min by using a drop type electrostatic flocking machine. The natural fine leather fibers were prepared by impregnating shavings of cattle leather with water and by finely dividing the water-impregnated shavings by using a pulverizer. Also, the fine fibers were impregnated with a flocking promotor before they were subjected to the bonding procedure. As a result of the bonding procedure, a uniform and dense distribution of the fine fibers in the back surface was attained.

After being buffed, the fine fiber-bonded surface was dyed in brown by using a winch dyeing machine, washed with water, and, then, dried. Thus, a natural fine leather fiber layer was formed on the back surface of the substrate to form a back layer of an artificial leather.

Then, the other surface of the substrate opposite to the fine fiber layer was coated with a brown-colored solution of a polyurethane elastomer in DMF (dimethylformamide) at a coverage of about 700 g/m2. The elastomer coated substrate was immersed in water at room temperature, and, then, hot water having a temperature of 60 C, so as to effect a thorough removal of the DMF from the elastomer layer by extracting it into the water.

Subsequently, the elastomer layer was dried to form a microporous under layer.

Thereafter, a one-pack type polyurethane resin solution dyed with the same color as that of the microporous under layer was applied on a release sheet which had been previously prepared. The resultant release sheet was heat dried to a degree so as to form a tacky polyurethane layer thereon. Subsequently, the dried release sheet was laminated on the microporous superficial layer of the substrate and the tacky polyurethane resin layer was thoroughly dried. After the release sheet was separated from the laminate, the resultant polyurethane upper layer was coated with a surface treating agent by using a gravure coater and, then, dried. Then, a grain pattern was formed on the dried resin surface layer by using embossing rolls. Thus, an artificial leather was obtained. The resultant artificial leather was substantially similar to natural leather in respect of feel, touch and appearance.Also, the resultant artificial leather could be subjected to a skinning process without separation of the superficial and back layers from the substrate. The artificial leather could be conveniently used in various fields of clothing, furniture, bags, shoes and the like.

Example 2 A twin yarn made of spun rayon yarns having a metric count of 40 was converted to a twill fabric. The same raising procedure and water repellence-imparting processing as those described in Example 1 were applied to the twill fabric. A cattls leather was dry pulverized at a temperature of 50"C or less. The resultant fine leather fibers having a particle mesh size of 70 were treated with an aqueous solution containing a sodium salt of a higher alcohol sulfuric ester and a polyoxyethylene nonylphenol ether. The treated leather fine fibers were dehydrated and dried at a low temperature. The resultant fine leather fibers had a moisture content of 40%.The fine leather fibers thus prepared were bonded to a surface the substrate with an adhesive at a speed of the substrate of 4 m/min by using the drop type electrostatic flocking machine.

The fine fiber-bonded surface was heat set at a temperature of 1 50 C for 10 minutes. After being buffed, the fine fiber-bonded surface was dyed black by using a liquid stream type dyeing machine, washed with water and dried. Thus, a fine leather fiber layer was formed on the back surface of the substrate.

Separately, a foamable urethane prepolymer composition liquid colored black was coated on a release sheet. The coated sheet was placed in a thermo- and humidistat so as to completely polymerize the urethane prepolym-er while causing it to foam. The resultant sheet was laminated on the other surface of the substrate while the foamed polyurethane layer is tacky. Then, the resultant laminate was heated so as to cause the foamed polyurethane layer to be firmly bonded to the substrate and, thereafter, the release sheet was separated from the laminate. Thus, a microporous under layer consisting of the foamed polyurethane was formed on the substrate.

Further, a polyurethane resin colored in the same color as that of the microporous superficial layer was directly applied on the microporous under layer and dried; to form an upper layer.

Finally, a metal plate having an ostrich design thereon was hot-stamped on the surface of the polyurethane upper layer. Thus, an artificial leather resembling dlosely a natural ostrich leather was obtained.

Claims

1. An artificial leather comprising: (1) a substrate comprising a fibrous fabric; (2) a superficial layer formed on a surface of said substrate and comprising a synthetic polymer resin, and; (3) a back layer formed on the other surface of said substrate and comprising fine fibers derived from natural leather.

2. An artificial leather as claimed in claim 1, wherein said superficial synthetic polymer resin layer is porous.

3. An artificial leather as claimed in claim 1, wherein said superficial synthetic polymer resin layer is composed of a microporous synthetic polymer resin under layer formed on the surface of said substrate and a non-porous synthetic polymer resin upper layer laminated on said under layer.

4. An artificial leather as claimed in claim 1, wherein said synthetic polymer resin comprises at least one member selected from the group consisting of polyurethanes polyamides, polyamino acids, polyurethane-modified polyamino acids.

5. An artificial leather as claimed in claim 1, wherein said fine fibers of said natural leather have a 10 to 90 mesh size.

6. An artificial leather as claimed in claim 1, said fine fibers of said natural leather are bonded to the surface of said substrate with an adhesive by means of a electrostatic flocking method.

7. An artificial leather as claimed in claim 1, wherein said superficial synthetic polymer resin layer has a predetermined embossed pattern.

8. A process for producing an artificial leather comprising the steps of: (1) bonding fine fibers derived from natural leather onto a surface of a substrate comprising a fibrous fabric with an adhesive; (2) buffing said bonded fine fiber layer, and; (3) laminating a layer of a synthetic polymer resin on the other surface of said substrate.

9. A process as claimed in claim 8, wherein after said buffing procedure (2) but before said laminating procedure (3), said substrate and/or said natural leather fine fibers are dyed.

1 0. A process as claimed in claim 8, wherein after said bonding procedure (1) but before said buffing procedure (2), said substrate and/or said natural leather fine fibers are dyed.

11. A process as claimed in claim 8, wherein said natural fine leather fibers to be bonded, contain 35 + 5% by weights of moisture.

1 2. A process as claimed in claim 8, wherein before said bonding procedure (1), said substrate is treated with a water-repellent agent.

1 3. A process as claimed in claim 8, wherein both surfaces of said substrate have a number of fluffs.

14. A process as claimed in claim 13, wherein the surface of said substrate on which said natural leather fine fiber layer is laminated, has a lower density of the fluffs than that on the other surface of said substrate.

1 5. An artificial leather as claimed in claim 8, wherein said superficial synthetic polymer resin layer is prepared by coating a solution of said synthetic polymer resin in a solvent on the surface of said substrate and, by coagulating said synthetic polymer resin solution layer with a coagulating liquid to form a microporous synthetic polymer resiri layer.

16. An artificial leather as claimed in claim 8, wherein said superficial synthetic polymer resin layer is prepared by forming a layer of a foaming polyurethane prepolymer on a release sheet, by heating said layer to allow said prepolymer to be foamed, and, then, by transferring said foamed polyurethane layer onto the surface of said substrate, thereby forming a microporous superficial layer.

1 7. An artificial leather as claimed in claim 1, wherein said superficial synthetic polymer resin layer is prepared by blowing air into an emulsion of a synthetic polymer resin to form a mechanical foam, by coating said mechanical foam onto the surface of said substrate, and by drying said coated mechanical foam layer at an elevated temperature, whereby a microporous superficial layer is formed.

1 8. An artificial leather as claimed in claim 1, wherein said superficial synthetic polymer resin layer is prepared by blowing air into an emulsion of a synthetic polymer resin to form a mechanical foam, by coating said mechanical foam onto a surface of a release sheet, by drying said coated mechanical foam layer at an elevated temperature and, finally, transferring said dried foam layer onto the surface of said substrate, whereby a microporous superficial layer is formed.

1 9. An artificial leather as claimed in claim 8, wherein said superficial synthetic polymer resin layer is prepared by coating a polyvinyl chloride composition containing a thermally decomposable foaming agent, onto the surface of said substrate and, by heating said coated layer at a temperature at which said foaming agent is thermally decomposed to allow the coated layer to be foamed, whereby a microporous superficial layer is formed.

20. A process as claimed in claim 8, wherein said superficial layer of said synthetic polymer resin is embossed in a predetermined pattern.