JPWO1999011853A1 - Nonwoven fabrics and artificial leather - Google Patents

Abstract

(57) [Abstract] The present invention relates to a nonwoven fabric having a dense, delicate, high-quality appearance, and to an artificial leather having a dense, delicate, high-quality appearance similar to high-quality natural leather.

Description

[Detailed Description of the Invention] Nonwoven Fabric and Artificial Leather Technical Field The present invention relates to a nonwoven fabric having a dense, delicate, high-quality appearance, more specifically a nonwoven fabric suitable for forming artificial leather, and to artificial leather, particularly nubuck-like artificial leather, having a dense, delicate, high-quality appearance similar to high-quality natural leather.

BACKGROUND ART In recent years, the main types of artificial leathers available include suede-like artificial leather with long naps, nubuck-like artificial leather with short naps, grain-like artificial leather with no nap, and grain-like nubuck-like artificial leather with partial short naps. These artificial leathers are primarily made using nonwoven fabrics, and various proposals have been made to mimic the surface appearance of dense, delicate, high-quality natural leather.

For example, with regard to nubuck-like artificial leather, Japanese Patent Publication No. 62-42076 describes a method in which a sheet-like material having nap made of ultrafine fibers is impregnated or coated with a resin to fix the nap, and then the napped surface is pressed with a calender roll to lay down the nap and adhere, and then the napped surface is buffed. Also, Japanese Patent Publication No. 62-42075 describes a method in which a sheet-like material having nap made of ultrafine fibers is pressed with a calender roll to lay down the nap and adhere, and then the base material is impregnated or coated with a resin, and then the napped surface is buffed. JP-B-6-33577 describes a method in which an elastic polymer is applied to a fibrous sheet containing an elastic polymer on an entangled nonwoven fabric of ultrafine fibers having a single fineness of 0.3 de or less, and if necessary, embossing and buffing are performed, followed by an area shrinkage of 10% or more to form a surface having a mixture of napped portions and grain surfaces. JP-A-3-161576 describes a method in which only the surface layer of a nonwoven fabric made of composite fibers that can be made ultrafine is first made into ultrafine fibers, and then the nonwoven fabric is impregnated with an elastic resin, which is solidified, and the fibers inside the nonwoven fabric are dissolved and extracted with a solvent or the like to make them ultrafine, and the outermost surface is raised. Furthermore, Japanese Patent Laid-Open No. 4-136280 discloses a method in which a liquid composition of non-fibrous collagen powder having an average particle size of 10 μm or less and an apparent density of 0.1 to 0.3 g/cm ³ and a polymer mainly composed of polyurethane is applied to the surface of a fibrous sheet containing a fiber assembly containing a polymer mainly composed of an elastic polymer, the sheet is embossed, and the applied surface is then raised. Furthermore, Japanese Patent Laid-Open No. 7-133592 discloses a method in which ultrafine naps continuous with the ultrafine fibers of the base layer are formed on the surface of a smooth-surfaced fibrous base layer consisting of an entangled nonwoven fabric made of ultrafine fibers and/or ultrafine fiber bundles and a dense foam of elastic polymer present in the entangled spaces, and then a resin mainly composed of an elastic polymer is applied to the raised surface to form a porous layer mixed and integrated with the naps, and then a raising treatment is performed to expose part of the ultrafine naps on the sheet surface.

However, while nubuck-like artificial leathers obtained using conventional methods have a short pile and a smooth surface, the amount of fiber on the surface is much smaller than that of natural leather, and they contain a large amount of resinous parts made of elastomeric polymers and voids other than the raised part made of ultrafine fibers. As a result, no nubuck-like artificial leather has yet been proposed that combines the sharp lighting effect achieved by the extremely high pile density of natural leather with the smooth yet sticky feel.

Furthermore, with regard to grain-finish artificial leather, Japanese Patent Publication No. 4-8547 describes a method in which, when a solution of a polymer mainly composed of a polyurethane elastomer is wet-coagulated with a coagulating liquid to obtain a porous sheet, an ethylene oxide adduct of at least one compound selected from higher alkylamines, higher alcohols, sorbitan fatty acid esters, etc. is added and dissolved in the coagulating liquid, and a solution of the polymer not containing the ethylene oxide adduct is coagulated. However, although the grain-finish artificial leather obtained by this method has good surface smoothness, the intervals between the wrinkles generated on the surface are wider than those of natural leather, which has a small wrinkled feel when bent, and the uniform sponge structure results in high resilience and a rubber-like texture. Furthermore, Japanese Patent Laid-Open Publication No. 4-185777 describes a grain-finish artificial leather comprising a substrate layer made of a nonwoven fabric of ultrafine fiber bundles and a microporous urethane binder, the weight ratio of ultrafine fiber bundles to polyurethane being 70/30 to 97/3 and the apparent density being 0.5 to 0.8 g/cm ³ , and a nonporous layer made of a resin having a modulus at 100% elongation of 20 to 150 kg/cm ² and having a thickness of 10 to 100 μm. However, although the grain-finish artificial leather obtained by this method has low resilience and a good feeling of small wrinkles when bent, since a nonwoven fabric having an apparent density of 0.45 g/cm ³ or more is used, its flexibility is limited, even though texture processing such as kneading is carried out. As described above, among the grain-finish artificial leathers obtained using conventional methods, there has yet to be proposed one that has all of the soft texture of natural leather, a very smooth surface, low resilience, and a very delicate feeling of small wrinkles when bent.

Therefore, the object of the present invention is to provide artificial leathers that have a dense, delicate, high-quality appearance not obtainable with conventional artificial leathers and resemble high-quality natural leathers, such as nubuck-look artificial leathers that have the luxurious feel of natural nubuck leather, i.e., a sharp lighting effect and a smooth yet sticky texture, grain-finished nubuck-look artificial leathers with a unique surface feel, and grain-finished artificial leathers that are flexible, have a smooth surface, and have a delicate, wrinkled appearance.

DISCLOSURE OF THE INVENTION The inventors have conducted extensive research to provide artificial leather, particularly nubuck-like artificial leather, with a dense, delicate, high-quality appearance similar to high-quality natural leather in each of these types. As a result, they have completed the nonwoven fabric, artificial leather, and manufacturing methods thereof, as shown in Items 1 through 7 below.

1. A nonwoven fabric comprising ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less, characterized in that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

2. A nubuck-like artificial leather, wherein the nonwoven fabric constituting the artificial leather is made of ultrafine fiber bundles with a monofilament fineness of 0.2 de or less, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

3. A method for producing nubuck-like artificial leather, comprising pressurizing at least one surface of a nonwoven fabric composed of ultrafine fiber bundles with a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers with a single fineness of 0.2 denominations or less, such that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

4. A grain-finished nubuck-look artificial leather, characterized in that the nonwoven fabric constituting the artificial leather is composed of ultrafine fiber bundles with a single fiber fineness of 0.2 de or less, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

5. A method for producing a grain-finished nubuck-look artificial leather, comprising: pressurizing at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less, such that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1)

6. A grain-finish artificial leather, characterized in that the nonwoven fabric constituting the artificial leather is composed of ultrafine fiber bundles with a single fiber fineness of 0.2 de or less, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

7. A method for producing grain-finish artificial leather, comprising pressure-treating at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less, such that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram showing (1) the cutting direction of an ultrafine fiber bundle (perpendicular to the fiber axis direction) and (2) the minimum (minor diameter a) and maximum (major diameter b) diameters of the circumscribed circle of the outermost ultrafine fiber of the ultrafine fiber bundle.

2(1) and 2(2) are schematic diagrams of the cross-sectional surfaces of the nubuck-like artificial leather obtained in Example 1 and a conventional nubuck-like artificial leather with a/b > 0.6, respectively.

3(1) and (2) are schematic cross-sectional surface diagrams of the grain-finished nubuck-like artificial leather obtained in Example 3 and a conventional grain-finished nubuck-like artificial leather having an a/b ratio of >0.6, respectively.

4(1) and (2) are schematic diagrams of the cross-sectional surfaces of the grain-finish artificial leather obtained in Example 4 and a conventional grain-finish artificial leather having an a/b ratio of > 0.6, respectively.

Best Mode for Carrying Out the Invention The present invention will now be described in detail.

The nonwoven fabric of the present invention is made of ultrafine fiber bundles having a single fiber fineness of 0.2 de or less.

Examples of polymers that form ultrafine fibers include polyamides such as nylon 6, nylon 66, and nylon 12, and polyesters such as polyethylene terephthalate and polybutylene terephthalate. The fineness of the ultrafine fibers is 0.2 denominations or less, and preferably 0.1 denominations or less. The fineness may be an average fineness. The ultrafine fibers must be in a bundle, and each bundle preferably contains 10 to 1,000 ultrafine fibers, more preferably 20 to 700 ultrafine fibers.

In a nonwoven fabric made of such ultrafine fiber bundles, the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on at least one surface must be within the range satisfying the following formula (1): 0.1≦a/b≦0.6 (1). Here, the value of a/b may be less than 0.1, but reducing the value of a/b on the surface of the nonwoven fabric to less than 0.1 is difficult from a processing standpoint. Furthermore, if the value of a/b is greater than 0.6, the amount of fiber covering the surface of the nonwoven fabric will be reduced, resulting in an artificial leather with such a nonwoven fabric structure with poor surface smoothness and an appearance similar to that of conventional artificial leathers.

Furthermore, "at least one surface of the nonwoven fabric" refers to one or both surfaces of the nonwoven fabric, and the "surface" refers to the first five layers, preferably the first three layers, of the ultrafine fiber bundles constituting the nonwoven fabric. The minor diameter a and major diameter b of the cross section of the ultrafine fiber bundles and/or the fibers forming the ultrafine fiber bundles are as shown in Figure 1. Here, the fiber bundle cross section of the ultrafine fiber bundle refers to the circumscribed circle of the outermost ultrafine fiber of the ultrafine fiber bundle cut perpendicular to the fiber axis direction of the ultrafine fiber bundle, and the minor diameter a and major diameter b of the fiber bundle cross section of the ultrafine fiber bundle are the minimum diameter of this circumscribed circle, which is the minor diameter a, and the maximum diameter of this circumscribed circle, which is the major diameter b.

The cross section of the ultrafine fiber bundle-forming fiber refers to the elliptical cross section of the ultrafine fiber bundle-forming fiber cut perpendicular to the fiber axis direction of the ultrafine fiber bundle-forming fiber, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundle-forming fiber are defined as the minimum diameter a and the maximum diameter b in this elliptical cross section. In the nonwoven fabric of the present invention, the value of a/b can be determined by arbitrarily cutting the pressure-treated nonwoven fabric, selecting ultrafine fiber bundles cut perpendicular to the fiber axis direction from the cross section of the nonwoven fabric surface, and determining the value of a/b from an enlarged photograph.

Furthermore, whether or not a nonwoven fabric forming a certain artificial leather corresponds to the nonwoven fabric of the present invention can be determined by arbitrarily cutting the artificial leather, selecting ultrafine fiber bundles cut perpendicular to the fiber axis direction from the surface of the nonwoven fabric in a cross section, and then determining the value of a/b from an enlarged photograph of the cut fiber bundles.

The nubuck-like artificial leather of the present invention is made of a nonwoven fabric comprising ultrafine fiber bundles with a single fineness of 0.2 de. The high-molecular polymer forming the ultrafine fibers and the single fineness of the ultrafine fibers can be the same as those used for the nonwoven fabric.

In a nonwoven fabric made from such ultrafine fiber bundles, the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface must be within the range satisfying the following formula (1): 0.1≦a/b≦0.6 (1). Here, the value of a/b may be less than 0.1, but reducing the value of a/b on the surface of the nonwoven fabric to less than 0.1 is difficult from a processing standpoint. Furthermore, if the value of a/b is greater than 0.6, the amount of fibers exposed on the surface of the nonwoven fabric will be reduced, resulting in a lower pile density of the resulting artificial leather, which is undesirable.

Furthermore, "at least one surface of the nonwoven fabric" refers to one or both surfaces of the nonwoven fabric that constitutes the artificial leather, and the "surface" refers to the first five layers, preferably the first three layers, of the ultrafine fiber bundles in the nonwoven fabric that constitutes the artificial leather. The minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are as shown in Figure 1. Here, the cross section of the ultrafine fiber bundle refers to the circumscribed circle of the outermost ultrafine fiber in the ultrafine fiber bundle cut perpendicular to the fiber axis direction of the ultrafine fiber bundle, and the minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are the minimum diameter of this circumscribed circle, and the maximum diameter of this circumscribed circle, respectively. In the production of the nubuck-like artificial leather of the present invention, the a/b value can be determined by arbitrarily cutting the pressure-treated nonwoven fabric, selecting ultrafine fiber bundles cut perpendicular to the fiber axis direction from the cross-sectional surface of the nonwoven fabric, and determining the a/b value from an enlarged photograph of the cut.

Furthermore, whether a certain nubuck-like artificial leather corresponds to the nubuck-like artificial leather of the present invention can be determined by arbitrarily cutting the nubuck-like artificial leather, selecting the ultrafine fiber bundles cut perpendicular to the fiber axis direction from the surface of the nonwoven fabric in the cross section, and determining the value of a/b from an enlarged photograph of the cut ultrafine fiber bundles.

The nubuck-like artificial leather can be produced by a method in which at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less is pressure-treated so that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

Here, "fibers capable of forming ultrafine fiber bundles with a monofilament size of 0.2 denominations or less" refers to fibers that can be subsequently treated with a solvent or split to form ultrafine fiber bundles with a monofilament size of 0.2 denominations or less. Examples of such fibers capable of forming ultrafine fiber bundles include composite fibers made of multi-component high molecular weight polymers. Examples of composite fiber configurations include islands-in-the-sea and bonded types, with the islands-in-the-sea type being preferred. Examples of the high molecular weight polymers that can be used include the polyamides and polyesters mentioned above, as well as polyethylene, polypropylene, high-molecular weight polyethylene glycol, polystyrene, polyacrylate, and the like.

The nubuck-like artificial leather of the present invention is prepared by pressure-treating at least one surface of a nonwoven fabric made of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers so that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the above-mentioned formula (1). Examples of pressure-treating methods include nip treatment with a calendar roll, pressure treatment in an embossing device, and flat plate or roll press. In the manufacturing method of nubuck-like artificial leather, the timing of the pressure treatment is not particularly limited as long as it is performed, for example, after the nonwoven fabric has been impregnated with and coagulated with the high molecular weight elastomeric polymer (A) and before the buffing treatment of the artificial leather substrate. However, in terms of the manufacturing process of artificial leather, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with the high molecular weight elastomeric polymer (A). In the case of using a nonwoven fabric made of ultrafine fiber bundle-forming fibers, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with the high molecular weight elastomeric polymer (A) and before the ultrafine fiber bundle-forming fibers are subjected to the ultrafine fiber treatment.

Here, the method for producing the nubuck-like artificial leather of the present invention will be described with specific examples.

The ultrafine fiber bundle-forming fibers, which are islands-in-the-sea composite fibers, are passed through a conventional carding, random webber, crosslayer, or the like to form a web. The resulting web is needle-punched in the thickness direction, preferably at a barb-penetration number of 500 to 3,000/ ^cm2 , particularly preferably at a barb-penetration number of 800 to 2,000/ ^cm2 , to entangle the ultrafine fiber bundle-forming fibers, producing a nonwoven fabric. A barb-penetration number of less than 500/ ^cm2 results in insufficient entanglement of the nonwoven fabric, resulting in insufficient strength, and the lighting effect of nubuck-like artificial leather produced therefrom is also insufficient, which is undesirable. Furthermore, a barb-penetration number of more than 3,000/ ^cm2 results in excessive needle-punching, which significantly damages the entangled fibers and causes the nonwoven fabric to become worn. Here, the "number of barb-penetrating punches" refers to the number of punches per cm2 when needles having at least ^one barb are used to punch to a depth where the barb at the most distal end penetrates the web in the thickness direction. The resulting nonwoven fabric is preferably heat-treated to soften the sea component of the composite fiber, and then pressure-treated with a calender roll or the like to adjust the thickness, apparent density, and surface smoothness. This adjustment can be set as desired depending on the intended use of the artificial leather. For example, it is preferable that the nonwoven fabric have a thickness of 0.4 to 3.0 mm, an apparent density of 0.25 to 0.45 g/ ^cm3 , and a flat surface. In this case, pressure treatment with a heated calender roll allows heat treatment and pressure treatment to be performed simultaneously, which is particularly preferred.

The nonwoven fabric thus obtained is impregnated with a solution or dispersion of a high molecular weight elastomeric polymer (A) and coagulated to form a substrate. Examples of the high molecular weight elastomeric polymer (A) include polyurethane elastomers, polyurea elastomers, polyurethane-polyurea elastomers, polyacrylic acid resins, acrylonitrile-butadiene elastomers, and styrene-butadiene elastomers. Among these, polyurethane elastomers, such as polyurethane elastomers, polyurea elastomers, and polyurethane-polyurea elastomers, are preferred. These polyurethane elastomers are obtained by reacting one or more polymer glycols selected from polyether glycols, polyester glycols, polyester ether glycols, polycaprolactone glycols, polycarbonate glycols, etc., each having an average molecular weight of 500 to 4000 with an organic diisocyanate such as 4,4'-diphenylmethane diisocyanate, xylylene resin isocyanate, tolyl resin isocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc., and a chain extender selected from low molecular weight glycols, diamines, hydrazines, or hydrazine derivatives such as organic acid hydrazides and amino acid hydrazides.

To impregnate the nonwoven fabric with the elastomeric polymer (A), the elastomeric polymer (A) is typically impregnated into the nonwoven fabric in the form of an organic solvent solution or dispersion (including an aqueous emulsion). Preferred solutions containing the elastomeric polymer (A) include solutions of good solvents for the elastomeric polymer (A), such as dimethylformamide, diethylformamide, dimethylacetamide, and tetrahydrofuran; solutions obtained by mixing these with water, alcohol, methyl ethyl ketone, and the like; and solutions obtained by further mixing these with the elastomeric polymer (A). These solutions containing the elastomeric polymer (A) solvent must partially dissolve or swell the elastomeric polymer (A), so they preferably contain at least 50%, and preferably 70%, of the elastomeric polymer (A) solvent. The concentration of the high molecular weight elastomeric polymer (A) to be impregnated is preferably 8 to 20%, and particularly preferably 12 to 18%, in terms of the softness of the nubuck-like artificial leather, the denseness of the nubuck-like artificial leather surface, and the fiber pile density. A concentration lower than 8% results in a softer texture, but the surface nap becomes coarse, making it difficult to achieve a nubuck-like appearance. On the other hand, a concentration higher than 20% results in an improved dense appearance and a nap closer to the short pile of nubuck, but the texture becomes stiffer. The amount of high molecular weight elastomeric polymer (A) to be impregnated is preferably selected within the range of 15 to 80% by weight of the nonwoven fabric after ultra-fine processing.

The resulting substrate is preferably squeezed to 60 to 95%, and more preferably 65 to 90%, of its thickness. If the squeeze ratio is less than 60%, the amount of elastomeric polymer (A) contained in the substrate will be small, resulting in a nubuck-like artificial leather with long, non-uniform pile. If the squeeze ratio exceeds 95%, the surface of the final sheet will have a resin-like texture, making it difficult to obtain the nubuck-like artificial leather desired by the present invention. By maintaining the squeeze ratio within the above range, the resulting nubuck-like artificial leather will have a high pile density and excellent pile uniformity.

The impregnated elastomeric polymer is then coagulated in the substrate. The coagulation method for the elastomeric polymer (A) may be either a known wet coagulation method or a known dry coagulation method. However, the coagulation state of the elastomeric polymer (A) in the substrate is preferably porous. Alternatively, a thin coating layer of a elastomeric polymer (B) of the same or a different type as the impregnated elastomeric polymer (A) may be provided on the surface of the substrate.

The resulting substrate is pressed between a mirror-finished metal roll heated to 140°C to 200°C and a back-up roll (rubber roll), or between mirror-finished metal rolls heated to 140°C to 200°C, at a substrate compression pressure (roll-to-roll pressure) of 10 kg/cm to 35 kg/cm, to adjust the a/b value on the nonwoven fabric surface to the range defined by formula (1). Depending on the intended use of the resulting nubuck-like artificial leather, pressure treatment may be applied to one or both sides of the substrate to adjust the a/b value on the nonwoven fabric surface to the range defined by formula (1). Alternatively, pressure treatment may be applied to both sides of the substrate, and the substrate may be sliced into two pieces in the thickness direction.

Thereafter, at least one type of high molecular weight polymer from the composite fibers constituting the substrate is dissolved and extracted to produce ultrafine fiber bundles. Using composite fibers as the fibers constituting the nonwoven fabric is preferable due to the manufacturing process advantage of simultaneously ultrafinely thinning the composite fibers and forming ultrafine fiber bundles. When the high molecular weight polymer to be dissolved and removed is polyamide, a dissolving agent such as a mixture of an alkali metal or alkaline earth metal with a lower alcohol, or formic acid can be used. When polyester is used, an aqueous alkali solution such as sodium hydroxide or potassium hydroxide can be used. When polyethylene, polystyrene, polyacrylate, etc. are used, benzene, toluene, xylene, etc. can be used.

A solution containing a solvent for the high molecular weight elastomeric polymers (A) and/or (B) is then applied to the surface of the ultrathin substrate. This method is not particularly limited as long as it is a conventionally known method, and examples include application using a gravure coater or a spray coater. In this process, the solution is preferably applied while lightly nipping the substrate with a gravure roll or the like. Next, a desolvation process is performed to remove the solvent from the solution containing the high molecular weight elastomeric polymers (A) and/or (B) and solidify the high molecular weight elastomeric polymers (A) and/or (B). Examples of such a desolvation process include a dry process using a hot air dryer and a wet process in which the substrate is immersed in a liquid such as water. However, the dry process is preferred because it reduces the amount of the liquid containing the solvent for the high molecular weight elastomeric polymers (A) and/or (B).

It is preferable to repeat the solution application and desolvation treatment at least 2 to 6 times. The more times, the more uniform the surface of the finally obtained nubuck-like artificial leather becomes, but if it is repeated more than 6 times, the surface tends to become hard, which is not preferable. Furthermore, the amount of solution applied to the non-napped surface of the substrate is preferably 5 to 100 g/ ^m2 . If the amount of solution applied is less than 5 g/ ^m2 , the napped fibers on the surface of the finally obtained nubuck-like artificial leather become long, making it difficult to obtain the desired nubuck-like artificial leather. On the other hand, if the amount of solution applied exceeds 100 g/ ^m2 , the surface of the finally obtained nubuck-like artificial leather becomes hard, and it takes a long time to remove the solvent.

A napped surface is formed by buffing the surface of the substrate that has been subjected to an ultra-fine treatment and further coated with a solution containing a solvent for the high molecular weight elastomeric polymers (A) and/or (B). Buffing can be performed using sandpaper, sand cloth, sand net, sand roll, brush, grinding stone, card cloth, etc. However, to obtain the very short nap of a nubuck-like texture, sandpaper is preferred. Furthermore, fine-grained sandpaper is preferred, and light buffing is also preferred. Vigorous buffing using coarse-grained sandpaper will roughen the surface, making it impossible to achieve the desired nubuck-like appearance. Applying a solution containing a solvent for the high molecular weight elastomeric polymers (A) and/or (B) to the buffed surface is not preferred, as it will result in a low amount of napped fibers on the surface of the final nubuck-like artificial leather, an inhomogeneous nap state on the surface, and a low nap density on the surface.

Furthermore, in the manufacturing method of the nubuck-like artificial leather of the present invention, conventional processes such as dyeing, texture processing by kneading, and other finishing processes such as treatment with functional agents such as softeners and water repellents can be applied at any stage as needed.

The grain-finished nubuck-like artificial leather of the present invention is an artificial leather having, on its surface, a napped portion composed of ultrafine fibers with a single fineness of 0.2 denominations or less and a grain portion composed of a composite layer in which ultrafine fibers with a single fineness of 0.2 denominations or less are fixed with a high-molecular-weight elastic polymer (C). Furthermore, the nap length in the napped portion is 40 to 300 μm, the area of the grain portion accounts for 5 to 80% of the total surface area, and the majority of the grain portion is a discontinuous layer with an area of 0.05 to 100 ^mm2 . The nonwoven fabric constituting the grain-finished nubuck-like artificial leather is composed of bundles of ultrafine fibers with a single fineness of 0.2 denominations or less. The high-molecular-weight polymer forming the ultrafine fibers and the single fineness of the ultrafine fibers can be the same as those for the nonwoven fabric.

In a nonwoven fabric made from such ultrafine fiber bundles, the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface must be within the range satisfying the following formula (1): 0.1≦a/b≦0.6 (1). Here, the value of a/b may be less than 0.1, but reducing the value of a/b on the surface of the nonwoven fabric to less than 0.1 is difficult from a processing standpoint. Furthermore, if the value of a/b is greater than 0.6, the amount of fiber exposed to the surface of the nonwoven fabric will be reduced, resulting in a lower nap density in the napped portion of the resulting grain-finished nubuck-like artificial leather. Furthermore, the surface smoothness of the grain portion will be reduced, and wrinkles will be large when folded, which is undesirable.

Furthermore, "at least one surface of the nonwoven fabric" refers to one or both surfaces of the nonwoven fabric that constitutes the artificial leather, and the "surface" refers to the first five layers, preferably the first three layers, of the ultrafine fiber bundles in the nonwoven fabric that constitutes the artificial leather. The minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are as shown in Figure 1. Here, the cross section of the ultrafine fiber bundle refers to the circumscribed circle of the outermost ultrafine fiber in the ultrafine fiber bundle cut perpendicular to the fiber axis direction of the ultrafine fiber bundle, and the minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are the minimum diameter of this circumscribed circle, and the maximum diameter of this circumscribed circle, respectively. In the production of the grain-finished nubuck-like artificial leather of the present invention, the a/b value can be determined by arbitrarily cutting the pressure-treated nonwoven fabric, selecting a section of the ultrafine fiber bundles on the surface of the nonwoven fabric that has been cut perpendicular to the fiber axis, and determining the a/b value from an enlarged photograph of the section.

Furthermore, whether a certain grain-finished nubuck-look artificial leather corresponds to the grain-finished nubuck-look artificial leather of the present invention can be determined by arbitrarily cutting the grain-finished nubuck-look artificial leather, selecting those cut perpendicular to the fiber axis direction from among the ultrafine fiber bundles on the surface of the nonwoven fabric in the cross section, and determining the value of a/b from an enlarged photograph.

The grain-finished nubuck-like artificial leather can be obtained by a method of pressurizing at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less, such that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).

Here, "fibers capable of forming ultrafine fiber bundles with a monofilament size of 0.2 denominations or less" refers to fibers that can be subsequently treated with a solvent or split to form ultrafine fiber bundles with a monofilament size of 0.2 denominations or less. Examples of such fibers capable of forming ultrafine fiber bundles include composite fibers made of multicomponent high molecular weight polymers. Examples of composite fiber configurations include islands-in-the-sea and bonded types, with the islands-in-the-sea type being preferred. Examples of polymers that can be used include the aforementioned polyamides and polyesters, as well as polyethylene, polypropylene, high-molecular weight polyethylene glycol, polystyrene, and polyacrylate.

The grain-finished nubuck-like artificial leather of the present invention is prepared by pressure-treating at least one surface of a nonwoven fabric made of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers so that the minor diameter a and major diameter b of the cross section of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the above-mentioned formula (1). Examples of pressure-treating methods include nip treatment with a calendar roll, pressure treatment in an embossing device, flat plate or roll press, etc.

In the manufacturing process of grain-finished nubuck-like artificial leather, the timing of the pressure treatment is not particularly limited, as long as it is performed after the nonwoven fabric has been impregnated with and coagulated with high molecular weight elastomeric polymer (A), before the buffing treatment of the artificial leather substrate, or before the formation of the grain surface portion composed of high molecular weight elastomeric polymer (C). However, in terms of the artificial leather manufacturing process, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with high molecular weight elastomeric polymer (A). In the case of using a nonwoven fabric composed of ultrafine fiber bundle-forming fibers, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with high molecular weight elastomeric polymer (A) and before the ultrafine fiber bundle-forming fibers are subjected to the ultrafine fiber bundle-forming treatment.

Here, the method for producing the grain-finished nubuck-like artificial leather of the present invention will be explained using a specific example.

The ultrafine fiber bundle-forming fibers, which are islands-in-sea composite fibers, are passed through a conventional carding, random webber, crosslayer, or the like to form a web. The resulting web is needle-punched in the thickness direction, preferably at a barb-penetrating punch count of 500 to 3,000/ ^cm2 , particularly preferably 800 to 2,000/ ^cm2 , to entangle the ultrafine fiber bundle-forming fibers, producing a nonwoven fabric. A barb-penetrating punch count of less than 500/ ^cm2 results in insufficient entanglement of the nonwoven fabric, resulting in insufficient strength, and the lighting effect of the grain-finished nubuck-like artificial leather produced therefrom is also insufficient, which is undesirable. Furthermore, a barb-penetrating punch count of more than 3,000/ ^cm2 is undesirable because excessive needle-punching causes significant damage to the entangled fibers and causes the nonwoven fabric to become worn. Here, the "number of barb-penetration punches" refers to the number of punches per cm2 when needles having at least ^one barb are used to punch to a depth where the barb at the most distal end penetrates the web in the thickness direction. The resulting nonwoven fabric is preferably heat-treated to soften the sea component of the composite fiber, and then pressure-treated with a calender roll or the like to adjust the thickness, apparent density, and surface smoothness. This adjustment can be set as desired depending on the intended use of the artificial leather. For example, the nonwoven fabric preferably has a thickness of 0.4 to 3.0 mm, an apparent density of 0.25 to 0.45 g/ ^cm3 , and a flat surface. In this case, pressure treatment with a heated calender roll is particularly preferred, as it allows heat treatment and pressure treatment to be performed simultaneously.

The nonwoven fabric thus obtained is impregnated with a solution or dispersion of a high molecular weight elastomeric polymer (A), which is then coagulated to form a substrate. Examples of the high molecular weight elastomeric polymer (A) used here include polyurethane elastomers, polyurea elastomers, polyurethane-polyurea elastomers, polyacrylic acid resins, acrylonitrile-butadiene elastomers, and styrene-butadiene elastomers. Of these, polyurethane elastomers such as polyurethane elastomers, polyurea elastomers, and polyurethane-polyurea elastomers are preferred. These polyurethane elastomers are obtained by reacting one or more polymer glycols selected from polyether glycols, polyester glycols, polyester ether glycols, polycaprolactone glycols, polycarbonate glycols, etc., each having an average molecular weight of 500 to 4000 with an organic diisocyanate such as 4,4'-diphenylmethane diisocyanate, xylylresin isocyanate, tolylresin isocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc., and a chain extender selected from low-molecular-weight glycols, diamines, hydrazines, or hydrazine derivatives such as organic acid hydrazides and amino acid hydrazides.

To impregnate the nonwoven fabric with the elastomeric polymer (A), the elastomeric polymer (A) is typically impregnated into the nonwoven fabric in the form of an organic solvent solution or dispersion (including an aqueous emulsion). Preferred solutions containing the elastomeric polymer (A) include solutions of good solvents for the elastomeric polymer (A), such as dimethylformamide, diethylformamide, dimethylacetamide, and tetrahydrofuran; solutions obtained by mixing these with water, alcohol, methyl ethyl ketone, and the like; and solutions obtained by further mixing these with the elastomeric polymer (A). These solutions containing the elastomeric polymer (A) solvent must partially dissolve or swell the elastomeric polymer (A), so they preferably contain at least 50%, and preferably 70%, of the solvent for the elastomeric polymer (A). The concentration of the high molecular weight elastomeric polymer (A) to be impregnated is preferably 8 to 20%, and particularly preferably 12 to 18%, from the viewpoints of the softness of the grain-finished nubuck-like artificial leather, the surface density of the grain-finished nubuck-like artificial leather, and the fiber pile density. A concentration lower than 8% results in a softer texture, but the surface nap becomes coarser, making it difficult to achieve the grain-finished nubuck-like appearance. On the other hand, a concentration higher than 20% results in an improved appearance with a denser texture and a nap closer to the short pile of grain-finished nubuck-like texture, but has the drawback of a stiffer texture. The high molecular weight elastomeric polymer (A) to be impregnated is preferably selected within the range of 15 to 80% by weight of the nonwoven fabric after ultra-fine processing.

The resulting substrate is preferably squeezed to 60 to 95%, and more preferably 65 to 90%, of its thickness. If the squeeze ratio is less than 60%, the amount of high molecular weight elastomeric polymer (A) contained in the substrate will be small, resulting in a grain-finished nubuck-look artificial leather with long, uneven pile. If the squeeze ratio exceeds 95%, the surface of the final sheet will have a resin-like texture, making it difficult to obtain the grain-finished nubuck-look artificial leather desired by the present invention. By controlling the squeeze ratio within the above range, the resulting grain-finished nubuck-look artificial leather will have a high nap density and excellent uniformity in the nap state.

The impregnated elastomeric polymer (A) is then coagulated in the substrate. The coagulation method for the elastomeric polymer (A) may be either a known wet coagulation method or a known dry coagulation method. However, the coagulation state of the elastomeric polymer (A) in the substrate is preferably porous. Alternatively, a thin coating layer of a elastomeric polymer (B) of the same or different type as the impregnated elastomeric polymer (A) may be provided on the surface of the substrate.

The resulting substrate is pressed between a mirror-finished metal roll heated to 140°C to 200°C and a back-up roll (rubber roll), or between mirror-finished metal rolls heated to 140°C to 200°C, at a substrate compression pressure (roll-to-roll pressure) of 10 kg/cm to 35 kg/cm, to adjust the a/b value on the nonwoven fabric surface to the range defined by formula (1). Depending on the intended use of the resulting grain-finished nubuck-like artificial leather, pressure treatment may be applied to one or both sides of the substrate. Alternatively, both sides of the substrate may be pressure-treated, and the substrate may be sliced into two pieces in the thickness direction.

Thereafter, at least one type of high molecular weight polymer from the composite fibers constituting the substrate is dissolved and extracted to produce ultrafine fiber bundles. Using composite fibers as the fibers constituting the nonwoven fabric is preferable due to the manufacturing process advantage of simultaneously ultrafinely thinning the composite fibers and producing ultrafine fiber bundles. When the high molecular weight polymer to be dissolved and removed is polyamide, a dissolving agent such as a mixture of an alkali metal or alkaline earth metal with a lower alcohol or formic acid can be used. When the high molecular weight polymer to be dissolved and removed is polyester, an aqueous alkali solution such as sodium hydroxide or potassium hydroxide can be used. When polyethylene, polystyrene, polyacrylate, etc. are used, benzene, toluene, xylene, etc. can be used.

The ultra-fine substrate can then be processed into the grain-finished nubuck-like artificial leather of the present invention by any conventionally known method.

A typical processing method involves applying a solution containing a solvent for the high molecular weight elastomeric polymer (A) and/or (B) to the surface of the ultrafine-grained substrate. This method is not particularly limited as long as it is a conventionally known method, and examples include application using a gravure coater or spray coater. In this process, the solution is preferably applied while lightly nipping the substrate with a gravure roll or the like. Next, a desolvation process is performed to remove the solvent from the solution containing the high molecular weight elastomeric polymer (A) and/or (B) and solidify the high molecular weight elastomeric polymer (A) and/or (B). Examples of desolvation processes include a dry process using a hot air dryer and a wet process in which the substrate is immersed in a liquid such as water. The dry process is preferred because it reduces the amount of liquid containing the solvent for the high molecular weight elastomeric polymer (A) and/or (B). The solution application and desolvation process are preferably repeated at least 2 to 6 times. The more times this is repeated, the more uniform the surface of the final grain-finished nubuck-like artificial leather becomes. However, repeating it more than six times tends to result in the surface becoming hard, which is undesirable. The amount of the solution applied to the non-napped surface of the substrate is preferably 5 to 100 g/ ^m² . If the amount of solution applied is less than 5 g/ ^m² , the napped fibers on the surface of the final grain-finished nubuck-look artificial leather will be long, making it difficult to obtain the desired grain-finished nubuck-look artificial leather. On the other hand, if the amount of solution applied exceeds 100 g/ ^m² , the surface of the final grain-finished nubuck-look artificial leather will be hard, and it will take a long time to remove the solvent.

The surface of the substrate that has been subjected to an ultrafine treatment and further to application of a solution containing a solvent for the high molecular weight elastomer (A) and/or (B) is buffed to form a napped surface. Buffing can be performed using sandpaper, sand cloth, sand net, sand roll, brush, grindstone, card cloth, etc., but sandpaper is preferred to obtain very short naps with a grain-finished nubuck look. Furthermore, it is preferable to use fine-grained sandpaper, and light buffing is also preferred. Strong buffing with coarse-grained sandpaper will roughen the surface, making it impossible to obtain the desired nubuck look. Applying a solution containing a solvent for the high molecular weight elastomer (A) and/or (B) to the buffed surface is not preferred because the amount of napped fibers on the surface of the final grain-finished nubuck-look artificial leather will be low, the surface nap state will be uneven, and the surface nap density will be low. A high-molecular-weight elastomeric polymer (C), either the same or different from the high-molecular-weight elastomeric polymer (A) or (B), is applied to the artificial leather so that the grain area of the resulting artificial leather occupies 5 to 80 ^% of the total surface area, and the majority of the grain area is a discontinuous layer having an area of 0.05 to 100 mm2. This results in a grain area consisting of a composite layer in which ultrafine fibers with a monofilament fineness of 0.2 de or less are fixed by the high-molecular-weight elastomeric polymer (C), thereby producing a grain-finished nubuck-like artificial leather. The high-molecular-weight elastomeric polymer (C) can be applied by any conventional method. For example, the high-molecular-weight elastomeric polymer (C) can be applied using a print roll. Alternatively, after forming a textured surface by embossing, the high-molecular-weight elastomeric polymer (C) can be applied to the convex portions using a gravure coater, but methods are not limited to these. The coated area is 5 to 80% of the total surface area of the substrate, preferably 10 to 50%. If it is less than 5%, not only will the design obtained from the grain surface be poor, but the amount of fiber exposed on the surface will be so large that the desired grained nubuck appearance will not be obtained.

Furthermore, if it exceeds 80%, the lighting effect of the nubuck texture cannot be obtained, and the surface will have a stiff, tense texture. It is also necessary to form a grain surface layer such that the majority of the grain surface is a discontinuous layer with an area of 0.05 to 100 mm ² , preferably 0.1 to 20 mm ^{2 .} If the coating area of the high molecular weight elastic polymer (C) is less than 0.05 mm ² , the grain surface properties, luster, and abrasion resistance will be insufficient. Furthermore, if it exceeds 100 mm ² , the lighting effect will be weak, and the grained nubuck texture will not be obtained. The area referred to here is the projected area in the normal direction of the substrate surface.

Furthermore, in the method for producing the grain-finished nubuck-like artificial leather of the present invention, it is possible to carry out, at any stage, conventional dyeing, texture treatment such as rubbing, and finishing treatment by applying functional agents such as softeners and water repellents, as needed. Texture treatment such as rubbing, which is carried out to improve the lighting effect of the napped portions, is preferably carried out after the application of the high molecular weight elastomeric polymer (C).

The grain-finish artificial leather of the present invention is an artificial leather having a grain surface layer made of a high-molecular-weight elastomeric polymer (D) on at least one surface, and the nonwoven fabric constituting the artificial leather is composed of ultrafine fiber bundles with a single fineness of 0.2 denominations or less. The high-molecular-weight polymer forming the ultrafine fibers and the single fineness of the ultrafine fibers can be the same as those used for the nonwoven fabric.

The nonwoven fabric made from the ultrafine fiber bundles must have the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface satisfying the following formula (1): 0.1≦a/b≦0.6 (1) More preferably, the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface satisfy the following formula (2): 0.1≦a/b≦0.5 (2) A grain-finish artificial leather that is flexible, has excellent surface smoothness, and has a delicate, finely wrinkled appearance can be obtained.

Here, the value of a/b may be less than 0.1, but it is difficult to reduce the a/b value of the nonwoven fabric surface to less than 0.1 from the viewpoint of processing. Furthermore, if the value of a/b is greater than 0.6, the grained surface will have low surface smoothness and will wrinkle significantly when folded, which is undesirable.

Furthermore, "at least one surface of the nonwoven fabric" refers to one or both surfaces of the nonwoven fabric constituting the artificial leather. In the case of grain-finished artificial leather, the surface refers to the surface layer of the nonwoven fabric of the ultrafine fiber bundles constituting the artificial leather, from the surface layer to the fifth layer, preferably the third layer, of the nonwoven fabric. The minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are as shown in Figure 1. Here, the cross section of the ultrafine fiber bundle refers to the circumscribed circle of the outermost ultrafine fiber of the ultrafine fiber bundle cut perpendicular to the fiber axis direction of the ultrafine fiber bundle. The minor diameter a and major diameter b of the cross section of the ultrafine fiber bundle are the minimum diameter of this circumscribed circle, and the maximum diameter of this circumscribed circle, respectively. During the production of the grain-finish artificial leather of the present invention, the a/b ratio can be determined by arbitrarily cutting the pressure-treated nonwoven fabric, selecting a section of the ultrafine fiber bundles on the surface of the nonwoven fabric that has been cut perpendicular to the fiber axis, and determining the a/b ratio from an enlarged photograph of the cut section.

Whether a certain grain-finish artificial leather corresponds to the grain-finish artificial leather of the present invention can also be determined by arbitrarily cutting the grain-finish artificial leather, selecting ultrafine fiber bundles cut perpendicular to the fiber axis direction from the surface of the nonwoven fabric in the cross section, and determining the value of a/b from an enlarged photograph of the cut ultrafine fiber bundles.

The method for producing the grain-finish artificial leather involves pressurizing at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a monofiber density of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a monofiber density of 0.2 denominations or less, such that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1), and more preferably, such that the following formula (2): 0.1≦a/b≦0.5 (2).

Here, "fibers capable of forming ultrafine fiber bundles with a monofilament size of 0.2 denominations or less" refers to fibers that can be subsequently treated with a solvent or split to form ultrafine fiber bundles with a monofilament size of 0.2 denominations or less. Examples of such fibers capable of forming ultrafine fiber bundles include composite fibers made of multicomponent high molecular weight polymers. Examples of composite fiber configurations include islands-in-the-sea and bonded types, with the islands-in-the-sea type being preferred. Examples of polymers that can be used include the aforementioned polyamides and polyesters, as well as polyethylene, polypropylene, high-molecular weight polyethylene glycol, polystyrene, and polyacrylate.

The grain-finish artificial leather of the present invention is obtained by pressurizing at least one surface of a nonwoven fabric made of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers so that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or the ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the above-mentioned formula (1), and more preferably, the above-mentioned formula (2). Examples of methods for pressurizing include nip treatment with a calendar roll, pressure treatment in an embossing device, and flat plate or roll press. The timing of the pressure treatment is not particularly limited as long as it is performed after the nonwoven fabric has been impregnated and coagulated with the high molecular weight elastomeric polymer (A) in the manufacturing process of grain-finished artificial leather, or before the buffing treatment of the artificial leather substrate or before the formation of the grain surface layer made of the high molecular weight elastomeric polymer (D). However, in terms of the artificial leather manufacturing process, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with the high molecular weight elastomeric polymer (A). In the case of using a nonwoven fabric made of ultrafine fiber bundle-forming fibers, it is preferable to perform the pressure treatment after the nonwoven fabric has been impregnated with the high molecular weight elastomeric polymer (A) and before the ultrafine fiber bundle-forming fibers are subjected to the ultrafine fiber bundle-forming treatment.

The grain-finish artificial leather of the present invention can be produced by impregnating the nonwoven fabric of the present invention with a high molecular weight elastomeric polymer (A) and then successively coating the surface of the impregnated fabric with a high molecular weight elastomeric polymer (D) of the same or a different type as the high molecular weight elastomeric polymer (A). Another method involves coating the surface of the nubuck-finish artificial leather of the present invention, or of a substrate prior to the formation of the napped surface of the nubuck-finish artificial leather, with a high molecular weight elastomeric polymer (D).

Here, a typical manufacturing method among these will be described with a specific example.

The ultrafine fiber bundle-forming fibers, which are islands-in-sea composite fibers, are passed through a conventional card, random webber, crosslayer, or the like to form a web. The resulting web is needle-punched in the thickness direction, preferably at a barb-penetrating punch count of 500 to 3,000/ ^cm2 , ^and particularly preferably at a barb-penetrating punch count of 800 to 2,000/cm2, to entangle the ultrafine fiber bundle-forming fibers, producing a nonwoven fabric. A barb-penetrating punch count of less than 500/ ^cm2 results in insufficient entanglement of the nonwoven fabric, resulting in insufficient strength, and the strength of the grain-finish artificial leather produced therefrom is also insufficient, which is undesirable. Furthermore, a barb-penetrating punch count of more than 3,000/ ^cm2 is undesirable because excessive needle-punching results in significant damage to the entangled fibers, causing the nonwoven fabric to become worn. Here, the number of barb-penetrating punches refers to the number of punches per cm2 when needles having at least one barb are used to punch to a depth where the barb at the most distal end penetrates the web in the thickness direction. The resulting nonwoven fabric is preferably heat-treated to soften the sea component of the composite fiber, and then pressure-treated with a calender roll or the like to adjust the thickness, apparent density, and surface smoothness. This adjustment can be set arbitrarily depending on the intended use of the artificial leather. For example, it is preferable that the nonwoven fabric have a thickness of 0.4 to 3.0 mm, an apparent density of 0.25 to 0.45 g/ ^cm3 , and a flat surface. In this case, pressure treatment with a heated calender roll is particularly preferred, as it allows heat treatment and pressure treatment to be performed simultaneously.

The nonwoven fabric thus obtained is impregnated with a solution or dispersion of a high molecular weight elastomeric polymer (A) and coagulated to form a substrate. Examples of the high molecular weight elastomeric polymer (A) include polyurethane elastomers, polyurea elastomers, polyurethane-polyurea elastomers, polyacrylic acid resins, acrylonitrile-butadiene elastomers, and styrene-butadiene elastomers. Among these, polyurethane elastomers, such as polyurethane elastomers, polyurea elastomers, and polyurethane-polyurea elastomers, are preferred. These polyurethane elastomers are obtained by reacting one or more polymer glycols selected from polyether glycols, polyester glycols, polyester ether glycols, polycaprolactone glycols, polycarbonate glycols, etc., each having an average molecular weight of 500 to 4000 with an organic diisocyanate such as 4,4'-diphenylmethane diisocyanate, xylylene resin isocyanate, tolyl resin isocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc., and a chain extender selected from low-molecular-weight glycols, diamines, hydrazines, or hydrazine derivatives such as organic acid hydrazides and amino acid hydrazides.

To impregnate the nonwoven fabric with the elastomeric polymer (A), the elastomeric polymer (A) is typically impregnated into the nonwoven fabric in the form of an organic solvent solution or dispersion (including an aqueous emulsion). Preferred solutions containing the elastomeric polymer (A) include solutions of good solvents for the elastomeric polymer (A), such as dimethylformamide, diethylformamide, dimethylacetamide, and tetrahydrofuran; solutions obtained by mixing these with water, alcohol, methyl ethyl ketone, and the like; and solutions obtained by further mixing these with the elastomeric polymer (A). These solutions containing the elastomeric polymer (A) solvent must partially dissolve or swell the elastomeric polymer (A), so they preferably contain at least 50%, and preferably 70%, of the elastomeric polymer (A) solvent. The concentration of the high molecular weight elastomeric polymer (A) to be impregnated is preferably 8 to 20%, and particularly preferably 12 to 18%, from the viewpoints of the softness of the grain-finish artificial leather, the surface density of the grain-finish artificial leather, and the fiber nap density. If the concentration is lower than 8%, the texture will be soft, but the surface will be less smooth, making it difficult to achieve the grain-finish appearance. On the other hand, if the concentration is higher than 20%, the surface will be smoother and fine wrinkles will appear when the fabric is bent, but the texture will be harder. The high molecular weight elastomeric polymer (A) to be impregnated is preferably selected in the range of 15 to 80% based on the weight of the nonwoven fabric after ultra-fine processing.

The resulting substrate is preferably squeezed to 60 to 95%, and more preferably 65 to 90%, of its thickness. If the squeeze ratio is less than 60%, the amount of elastomeric polymer (A) contained in the substrate will be small, resulting in a grain-finish artificial leather with poor surface smoothness and unevenness. If the squeeze ratio exceeds 95%, the final sheet surface will be resin-like, making it difficult to obtain the grain-finish artificial leather desired by the present invention. By maintaining the squeeze ratio within the above range, the resulting grain-finish artificial leather will have high surface smoothness and a delicate, finely wrinkled appearance.

The impregnated elastomeric polymer (A) is then coagulated in the substrate. The coagulation method for the elastomeric polymer (A) may be either a known wet coagulation method or a known dry coagulation method. However, the coagulation state of the elastomeric polymer (A) in the substrate is preferably porous. Alternatively, a thin coating layer of a elastomeric polymer (B) of the same or different type as the impregnated elastomeric polymer (A) may be provided on the surface of the substrate.

The resulting substrate is pressed between a mirror-finished metal roll heated to 140°C to 200°C and a back-up roll (rubber roll), or between mirror-finished metal rolls heated to 140°C to 200°C, at a substrate compression pressure (roll-to-roll pressure) of 10 kg/cm to 35 kg/cm, to adjust the a/b value on the nonwoven fabric surface to the range of formula (1), preferably the range of formula (2). Depending on the intended use of the resulting grain-finish artificial leather, pressure treatment may be applied to one or both sides of the substrate to adjust the a/b value on the nonwoven fabric surface to the range of formula (1). Alternatively, pressure treatment may be applied to both sides of the substrate, and the substrate may be sliced into two pieces in the thickness direction.

Thereafter, at least one type of high molecular weight polymer from the composite fibers constituting the substrate is dissolved and extracted to produce ultrafine fiber bundles. Composite fibers are preferred as the fibers constituting the nonwoven fabric. This is because it is possible to simultaneously ultrafine-fine the composite fibers and produce ultrafine fiber bundles, which is advantageous in terms of the manufacturing process. When the high molecular weight polymer to be dissolved and removed is polyamide, a dissolving agent such as a mixture of an alkali metal or alkaline earth metal with a lower alcohol or formic acid can be used. When the high molecular weight polymer to be dissolved and removed is polyester, an aqueous alkali solution such as sodium hydroxide or potassium hydroxide can be used. When polyethylene, polystyrene, polyacrylate, etc. are used, benzene, toluene, xylene, etc. can be used.

Thereafter, a grain surface layer made of a high molecular weight elastomeric polymer (D) of the same or different type as the high molecular weight elastomeric polymer (A) impregnated on the surface of the ultrafine-grained substrate is applied. The grain surface layer applied here may be a porous layer or a solid layer, and may be composed of two or more resin layers.

Furthermore, in the method for producing the grain-finish artificial leather of the present invention, it is possible to carry out finishing processes at any stage, as necessary, such as dyeing, texture processing by kneading, and the like, which are commonly used, as well as processing by adding functional agents such as softeners and water repellents.

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the examples, percentages, parts, and ratios are by weight unless otherwise specified.

Example 1: Nylon-6 (island component) and low-density polyethylene (sea component) were mixed and spun at a 50/50 ratio to obtain islands-in-sea composite fibers with a fineness of 8.0 Degrees. The resulting composite fibers were cut to a cut length of 51 mm to obtain raw cotton. This was formed into a web using a card and cross-layer, needle-punched at 1,400 needles/ ^cm² , heat-treated in a hot air chamber at 150°C, and pressed with a calender roll at 30°C before the substrate cooled to obtain a nonwoven fabric with a basis weight of approximately 570 g/ ^m² , a thickness of 1.6 mm, and an apparent density of 0.36 g/ ^cm³ .

Next, the nonwoven fabric was impregnated with a dimethylformamide solution (15% concentration) of polyurethane elastomer with a nitrogen content based on isocyanate of 4.5%, which was obtained by reacting polybutylene adipate with polytetramethylene ether glycol having a molecular weight of 1,800, 4,4-diphenylmethane diisocyanate, and ethylene glycol. The polyurethane elastomer had a nitrogen content based on isocyanate of 4.5%. The nonwoven fabric was then immersed in a 15% DMF aqueous solution to coagulate the polyurethane elastomer. The polyurethane elastomer was then thoroughly washed in warm water at 40°C and dried in a hot air chamber at 135°C to obtain a substrate impregnated with the polymeric elastomer.

The surface of the substrate was then subjected to a compressive treatment using a mirror-finish smooth metal roll at 175°C and an unheated back-up roll at a substrate compression pressure (pressure between the rolls) of 22 kg/cm.

The substrate was then repeatedly dipped and nipped in toluene at 80°C to dissolve and remove the polyethylene component, resulting in ultrafine composite fibers. The toluene contained in the substrate was then azeotropically removed in warm water at 90°C, and the composite fibers were dried in a hot air chamber at 120°C. The average fineness of the resulting ultrafine fibers was 0.004 de, and the number of ultrafine fibers in the ultrafine fiber bundle was 635.

The surface of the substrate was then brought into contact with a mirror-like smooth metal roll, and dimethylformamide was applied at a rate of 9 g/ ^m2 using a 200-mesh gravure coater. This process of dry heat drying was repeated four times, and then the cross section of the surface was observed under a microscope to measure the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on the surface of the nonwoven fabric. The a/b value was found to be 0.2. One side of the substrate was very lightly buffed four times with 800-mesh sandpaper to form a napped surface, and a nubuck-like artificial leather was obtained.

The nubuck-like artificial leather thus obtained was dyed under the following conditions.

Dyeing Conditions: Bath Ratio 1:30 Dye: 10% owf Dye Blend ・Lanasyn Yellow S-2GL (SANDOZ) 7 parts ・Kayalax Brown GR (Nippon Kayaku Co., Ltd.) 3 parts ・Lanasyn Red S-G (SANDOZ) 2 parts After dyeing and drying, fabric softener and water repellent were added and the fabric was kneaded.

The resulting nubuck-like artificial leather had a very luxurious appearance, with a sharp lighting effect and a smooth yet sticky feel. The results are summarized in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that the temperature of the mirror-like, smooth metal roll used in the pressure treatment in Example 1 was changed to 100°C. The a/b value of the cross section of the ultrafine fiber bundles present on the surface was 0.7. The resulting nubuck-like artificial leather had a short nubuck-like pile, but the pile density on the surface was low, the lighting effect lacked sharpness, and the bare surface of the substrate was visible, resulting in an appearance lacking in luxury. The results are summarized in Table 1.

Example 2: A nonwoven fabric was made of islands-in-sea composite fibers, consisting of a 60/40 polyethylene terephthalate island component and a low-density polyethylene sea component, with 60 island fibers and a fineness of 5.0 De. The composite fibers were cut to a cut length of 51 mm. This was formed into a web using a card and a crosslayer, needle-punched to 1,200 needles/ ^cm² , heat-treated in a hot air chamber at 150°C, and pressed with a calender roll at 30°C before the substrate cooled, to obtain a nonwoven fabric with a basis weight of approximately 610 g/ ^m² , a thickness of 1.7 mm, and an apparent density of 0.36 g/ ^cm³ .

Next, the nonwoven fabric was impregnated with a dimethylformamide solution (15% concentration) of polyurethane elastomer, the nitrogen content of which was 4.5% based on the isocyanate, obtained by reacting polybutylene adipate (molecular weight 1,800), polytetramethylene ether glycol (molecular weight 2,050), 4,4-diphenylmethane diisocyanate, and ethylene glycol. The nonwoven fabric was then immersed in a 15% DMF aqueous solution to coagulate it, followed by thorough washing in warm water at 40°C and drying in a hot air chamber at 135°C to obtain a substrate impregnated with a high molecular weight elastomer.

Next, both sides of this substrate were subjected to a compression treatment using smooth, mirror-finished metal rolls at 160°C with a compression pressure (pressure between the rolls) of 22 kg/cm.

The substrate was repeatedly dipped and nipped in toluene at 80°C to dissolve and remove the polyethylene component, resulting in ultrafine composite fibers. The toluene contained in the substrate was then azeotropically removed in warm water at 90°C, and the composite fibers were dried in a hot air chamber at 120°C. The average single fiber fineness of the obtained ultrafine fibers was 0.05 de, and the number of ultrafine fibers in the ultrafine fiber bundle was 60.

Thereafter, dimethylformamide was applied to the surface of the substrate at a rate of 9 g/ ^m2 using a 200-mesh gravure coater, followed by drying with dry heat. This operation was repeated four times, and then the cross section of the surface was observed under a microscope. The a/b ratio of the cross section of the fiber bundles of the ultrafine fiber bundles present on the surface was found to be 0.4.

Both sides of the obtained substrate were very lightly buffed three times with 600-mesh sandpaper to form naps, and the substrate was sliced into two pieces in the thickness direction to obtain nubuck-like artificial leather.

The nubuck-like artificial leather thus obtained was dyed under the following conditions.

Dyeing conditions: Bath ratio 1:30 Dye content 8% owf Dye blend Yellow (disperse dye) 7.4 Red (disperse dye) 3.2 Black (disperse dye) 0.6 After dyeing and drying, fabric softener and water repellent were added and the fabric was kneaded.

The resulting nubuck-like artificial leather had a very luxurious appearance, with a sharp lighting effect and a smooth yet sticky feel. The results are summarized in Table 1.

Comparative Example 2: A nonwoven fabric was made of islands-in-sea composite fibers, each composed of a 50/50 mix of polyethylene terephthalate for the island component and low-density polyethylene for the sea component, with 16 island fibers and a fineness of 12.0 De. The composite fibers were cut to a cut length of 51 mm. This was then carded and cross-layered into a web, which was needle-punched at 1,200 needles/ ^cm² , heated in a hot air chamber at 150°C, and pressed with a calender roll at 30°C before the base cooled, to obtain a nonwoven fabric with a basis weight of approximately 580 g/ ^m² , a thickness of 1.6 mm, and an apparent density of 0.36 g/ ^cm³ .

The nonwoven fabric was impregnated with a dimethylformamide solution of polyurethane elastomer (concentration: 15%), coagulated, and washed in the same manner as in Example 2 to obtain a substrate impregnated with a high molecular weight elastomer.

Next, both sides of the substrate were subjected to a pressure treatment using mirror-finished, smooth metal rolls at 160°C with a substrate compression pressure (roll-to-roll pressure) of 22 kg/cm. The substrate was repeatedly dipped and nipped in toluene at 80°C to dissolve and remove the polyethylene component, resulting in ultrafine composite fibers. The toluene contained in the substrate was then azeotropically removed in warm water at 90°C, and the substrate was dried in a hot air chamber at 120°C. The average single fineness of the obtained ultrafine fibers was 0.4 de, and the number of ultrafine fibers in the ultrafine fiber bundle was 16. Subsequently, dimethylformamide was applied to the substrate surface at a rate of 9 g/ ^m2 using a 200-mesh gravure coater, and the dry heat drying operation was repeated four times. When the cross section of the surface was observed under a microscope, the a/b ratio of the cross section of the ultrafine fiber bundle present on the surface was 0.3.

Both sides of the obtained substrate were very lightly buffed three times with 600-mesh sandpaper to form naps, and then the substrate was sliced into two pieces in the thickness direction to obtain nub-like artificial leather.

When dyed and finished in the same manner as in Example 2, the pile was long and the appearance was far from that of nubuck. Furthermore, the thickness of the raised fibers resulted in a very low lighting effect. The results are summarized in Table 1.

Example 3: The surface of the nubuck-like artificial leather obtained in Example 1 was pressurized using an embossing roll with a calfskin pore pattern heated to 180°C at a substrate compression pressure (roll-to-roll pressure) of 22 kg/cm to form irregularities on the substrate surface. A 10% polyurethane elastomer solution was then applied to the substrate surface at a rate of 30 g/ ^m² using a 75-mesh gravure coater, with a clearance between the roll and the backup roll of 80% of the substrate thickness. This process was repeated four times, resulting in a grain layer only on the raised areas, yielding a grain-finished nubuck-like artificial leather, which was then further kneaded. The resulting grain-finished nubuck-like artificial leather had a high nap density in the raised areas, excellent writing effect, and very smoothness, with good wrinkles on the grain area when bent. Furthermore, when the surface of the cross section of the grain-finished nubuck-like artificial leather was observed under a microscope, the a/b ratio of the cross section of the ultrafine fiber bundles present on the surface was 0.5.

Comparative Example 3 The same procedure as in Example 3 was carried out, except that the temperature of the mirror-like smooth metal roll used in the pressure treatment in Example 3 was set to 100°C. Microscopic observation of the cross-sectional surface of the resulting grain-finished nubuck-like artificial leather revealed that the a/b ratio of the cross-section of the ultrafine fiber bundles present on the surface was 0.7. This grain-finished nubuck-like artificial leather had low nap density in the raised portion and low surface smoothness in the grain portion, and exhibited significant wrinkles when bent, making it undesirable.

Example 4 The surface of the nubuck-like artificial leather obtained in Example 1 was subjected to a pressure treatment using a mirror-finish smooth metal roll heated to 160°C at a substrate compression pressure (roll pressure) of 22 kg/cm. Next, a 10% polyurethane elastomer solution was applied to the substrate surface at a rate of 30 g/ ^m² using a 75-mesh gravure coater, with a clearance between the roll and the backup roll of 80% of the substrate thickness, and the polyurethane elastomer solution was then dried with dry heat. This procedure was repeated four times. After that, the cross section of the surface was observed under a microscope, and the a/b ratio of the cross section of the ultrafine fiber bundles present on the surface was 0.5. The surface of this substrate was subjected to a pressure treatment using an embossing roll with a kangaroo-like pattern heated to 180°C at a substrate compression pressure (roll pressure) of 22 kg/cm, imparting a natural leather-like pattern to the substrate surface. Furthermore, a finishing agent consisting of a low-modulus polyurethane elastomer with a good surface feel was applied at a rate of 10 g/ ^m² using a 200-mesh gravure coater, with a clearance between the coater and the backup roll of 40% of the substrate thickness, and the polyurethane elastomer solution was then dried with dry heat. This procedure was repeated twice, and then kneaded to obtain a grain-finish artificial leather. The resulting grain-finish artificial leather had an extremely smooth grain-finish surface and was highly flexible, exhibiting delicate wrinkles when bent.

Comparative Example 4: Nylon-6 (island component) and low-density polyethylene (sea component) were mixed and spun at a 50/50 ratio to obtain islands-in-sea composite fibers with a fineness of 8.0 De. The resulting composite fibers were cut to a cut length of 51 mm to obtain raw cotton. This was formed into a web using a card and cross-layer, needle-punched at 1,400 needles/ ^cm² , heat-treated in a hot air chamber at 150°C, and pressed with a calender roll at 30°C before the substrate cooled to obtain a very high-density nonwoven fabric with a basis weight of approximately 870 g/ ^m² , a thickness of 1.7 mm, and an apparent density of 0.51 g/ ^cm³ .

When the above nonwoven fabric was processed in the same manner as in Example 4, the a/b ratio of the cross-sections of the ultrafine fiber bundles present on the surface was 0.4, and the a/b ratio of the cross-sections of the ultrafine fiber bundles present within the substrate was 0.6. The resulting grain-finish artificial leather had an extremely smooth grain-finish surface and exhibited fine wrinkles when bent, resulting in a very high-quality product. However, the density of the grain-finish artificial leather nonwoven fabric was high throughout the entire substrate, and despite texture processing by kneading, flexibility was insufficient.

INDUSTRIAL APPLICABILITY As described above, the nonwoven fabric of the present invention has a dense, delicate, high-quality appearance and is highly suitable for forming artificial leather. Furthermore, the artificial leather of the present invention has a dense, delicate, high-quality appearance and is similar to high-quality natural leather. In particular, the nubuck-like artificial leather has a short, uniform, and dense nap appearance similar to natural leather. This nap appearance gives the nubuck-like artificial leather a sharp lighting effect on its surface and a smooth, yet clingy, textured feel, resulting in a high-quality nubuck-like artificial leather. Furthermore, the grain-finished nubuck-like artificial leather also has a unique surface feel, and even the grain-finished artificial leather has excellent flexibility, surface smoothness, and a delicate, finely wrinkled appearance.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (1)

[Claims] 1. A nonwoven fabric comprising ultrafine fiber bundles having a monofiber density of 0.2 de or less and/or ultrafine fiber bundle-forming fibers having a monofiber density of 0.2 de or less, wherein the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1). 2. A nubuck-like artificial leather comprising a nonwoven fabric comprising ultrafine fiber bundles having a monofiber density of 0.2 de or less, and wherein the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1). 3. 3. A method for producing a nubuck-like artificial leather according to claim 2, characterized in that at least one surface of a nonwoven fabric made of ultrafine fiber bundles having a single fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a single fineness of 0.2 denominations or less is pressure-treated so that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1) A grain-finished nubuck-like artificial leather, characterized in that the nonwoven fabric constituting the artificial leather is composed of ultrafine fiber bundles having a single fiber fineness of 0.2 de or less, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1). 5. 6. A method for producing a grain-finished nubuck-like artificial leather according to claim 4, characterized in that at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a monofilament fineness of 0.2 denominations or less and/or ultrafine fiber bundle-forming fibers having a monofilament fineness of 0.2 denominations or less is pressure-treated so that the minor axis a and major axis b of the cross-section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1) A grain-finish artificial leather, characterized in that the nonwoven fabric constituting the artificial leather is composed of ultrafine fiber bundles having a monofilament fineness of 0.2 de or less, and the minor axis a and major axis b of the cross section of the ultrafine fiber bundles present on at least one surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1). 7. A method for producing a grain-finish artificial leather, characterized in that at least one surface of a nonwoven fabric composed of ultrafine fiber bundles having a monofilament fineness of 0.2 de or less and/or ultrafine fiber bundle-forming fibers having a monofilament fineness of 0.2 de or less is pressure-treated so that the minor axis a and major axis b of the cross section of the ultrafine fiber bundles and/or ultrafine fiber bundle-forming fibers present on the surface of the nonwoven fabric satisfy the following formula (1): 0.1≦a/b≦0.6 (1).