JP7576448B2 - Grain-finish artificial leather and its manufacturing method - Google Patents

Description

The present invention relates to a grain-finished artificial leather that includes a substrate that includes a fiber entanglement and a wet-type polyurethane porous layer, and a method for producing the same.

Grain-finished artificial leathers that have a grain-finished appearance similar to natural leather are known and are used as skin materials for bags, clothing, shoes, etc. Grain-finished artificial leathers that include a substrate that includes a fiber entanglement and a wet-type polyurethane porous layer are known as such grain-finished artificial leathers. Applications of such grain-finished artificial leathers include applications for products that come into contact with the human body. Examples of such applications include clothing materials, shoe upper materials, and backpack linings. Grain-finished artificial leathers used for such applications are required to be less likely to become stuffy when worn. Methods for producing such grain-finished artificial leathers that are less likely to become stuffy have been proposed in the past.

For example, a method has been proposed for forming ventilation holes by mechanically opening holes in the surface of grain-finished artificial leather using a needle.Specifically, the following Patent Document 1 discloses a grain-finished artificial leather comprising a leather-like sheet made of a fine long fiber nonwoven fabric and a polymeric elastomer impregnated therein, and a grain surface layer formed on at least one side of the leather-like sheet, in which 10 to 100 pinholes/cm2 on the grain surface layer surface are formed by piercing the grain surface layer and the leather-like sheet with a needle, the pinholes having a major axis of 30 to 100 μm and ^a minor axis of 3 to 5 μm. The pinhole-processed grain-finished artificial leather is used for the back of a backpack.

For example, a grain-finished artificial leather has been proposed in which ventilation holes are formed by opening holes by laser processing in the surface resin layer that will become the grain surface layer. Specifically, the following Patent Document 2 discloses a grain-finished artificial leather in which a coating made of a polymeric elastomer is present on a substrate made of fibers and a porous polymeric elastomer, the coating having holes penetrating the coating, the inner walls of the holes having pores that connect to the inside of the substrate, and the fibers and the polymeric elastomer being fused to each other on the inner walls of the holes.

Also proposed is a grain-finished artificial leather in which a resin layer, which is a surface layer that becomes a grain surface layer, is formed by fusing fibers to form ventilation holes. Specifically, the following Patent Document 3 discloses a method for producing a leather-like sheet in which a nonwoven fabric made of polyurethane fibers and having a basis weight of 5 to 125 g/ ^m2 is temporarily fixed by point bonding with a polyurethane resin to at least one surface of a base layer made of a fiber-entangled nonwoven fabric and an elastic polymer contained therein, and then the polyurethane fibers are heat-fused and laminated and integrated with the base layer. Also disclosed is a leather-like sheet obtained by such a production method, in which a discontinuous polyurethane layer is present on at least one surface of a base layer made of a fiber-entangled nonwoven fabric and an elastic polymer contained therein, and further a heat-fused layer of a nonwoven fabric made of polyurethane fibers is present thereon.

For example, the following Patent Document 4 discloses a grained leather-like sheet structure in which a film layer having holes is formed using peelable transfer paper with an uneven surface, and such a film layer is adhered to a substrate as a surface layer that becomes a grained surface layer.

For example, Patent Document 5 below discloses a method for producing a grain-finished artificial leather by forming an interconnected porous polyurethane layer on one side of a substrate made of a fibrous material and a polymeric elastomer, and forming a finish polyurethane coating on the surface of the layer, in which a good solvent, a poor solvent, a mixed solvent of a good solvent and a poor solvent, or a mixed solvent of a good solvent and a non-solvent for polyurethane is applied to the surface of the interconnected porous polyurethane layer with a gravure mesh roll to generate open pores with a diameter of 5 to 40 μm on the surface, and then a finish polyurethane coating is formed, so that the open pores in the interconnected porous polyurethane layer also appear as open pores in the finish polyurethane coating. Also disclosed is a grain-finished artificial leather obtained by such a production method, which has 200 or more open pores with a diameter of 0.5 to 35 μm per ^cm2 on the surface, is formed with a finish polyurethane coating covering the pore walls of the open pores and reaching the interior of the interconnected porous polyurethane layer, and has an air permeability of 0.5 L/ ^cm2 ·hr or more and a moisture permeability of 6 mg/ ^cm2 ·hr or more.

JP 2011-214196 A JP 2010-248644 A JP 2000-265378 A JP 2003-27381 A Japanese Patent Application Publication No. 8-041786

In the conventional breathable grain-finished artificial leather described above, although breathability was improved, water could still seep through during rainy weather. In addition, there were other issues such as dirt getting into the pores and becoming easily soiled, difficulty in coloring, and low cost.

For example, in the case of grain-finished artificial leather in which holes are made using a needle as disclosed in Patent Document 1, the holes tend to close after the needle penetrates, making it difficult to obtain sufficient breathability, and if the pinhole is made too large, water tends to pass through and the area around the pinhole tends to become dirty. In addition, in the case of grain-finished artificial leather in which holes are made using laser processing as disclosed in Patent Document 2, there is a problem of high processing costs.

For example, in the case of grain-finished artificial leather in which ventilation holes are formed by fusing fibers to form a resin surface layer that becomes the grain surface layer, as disclosed in Patent Document 3, in order to color the grain surface layer, it is necessary to color the fused fibers, and the degree of freedom in coloring is low.

In addition, for example, in the case of a grained leather-like sheet structure manufactured by forming a film layer with holes using peelable transfer paper with an uneven shape, and adhering such a film layer to a substrate as a surface layer that becomes a grain surface layer, as disclosed in the following Patent Document 4, the shape of the holes formed is limited by the uneven shape of the peelable transfer paper, so there is a problem that the types of surface unevenness are limited and the degree of freedom in design is reduced.

For example, when a good solvent, poor solvent, mixed solvent of good solvent and poor solvent, or mixed solvent of good solvent and non-solvent for polyurethane is applied with a gravure mesh roll to generate open holes of 5 to 40 μm in diameter on the surface as disclosed in Patent Document 5 below, grain-finished artificial leather with ventilation holes formed therein is produced, but because the viscosity of the applied solvent is low, it is difficult to apply a small amount of solvent uniformly, and when a large amount of solvent is applied, open holes with a pore size that is too large are likely to occur, resulting in only products with low water resistance. In addition, the surface coated with the solvent becomes rough, so the surface is easily soiled and has low abrasion resistance.

The present invention aims to provide a grain-finished artificial leather that has a wet-processed polyurethane porous layer that forms a grain surface layer, and that combines high water resistance that makes it difficult for rainwater to pass through, breathability that appropriately suppresses stuffiness, and abrasion resistance by forming open, continuous pores with controlled pore size and number.

After extensive investigations, the present inventors have found that in the manufacture of grain-finished artificial leather that includes a substrate that includes a fiber entanglement body, a wet polyurethane porous layer, and a top coat, if a solvent is simply applied to form air holes in the wet polyurethane porous layer and then a top coat is formed thereon to form open pores on the surface of the wet polyurethane porous layer, the size and number of the air hole openings cannot be controlled, and therefore, although breathability is obtained, grain-finished artificial leather with high water resistance cannot be obtained.

In order to solve the above problems, the present inventors have found that by applying a polyurethane solution containing a solvent with high solubility in polyurethane to the surface of a wet polyurethane porous layer, the wet polyurethane porous layer is made difficult to penetrate by the solvent, thereby forming a first top coat while forming interconnected open pores of controlled size and number, and then embossing the surface of the first top coat with a heated embossing roll to appropriately block the interconnected open pores formed, thereby controlling the size and number of the openings and eliminating surface roughness, and by applying a polyurethane solution containing a solvent with low solubility in polyurethane to the surface of the embossed first top coat to form a second top coat without enlarging the openings, a grain-finished artificial leather can be obtained that combines high water resistance that makes it difficult for rainwater to penetrate, and breathability and abrasion resistance that appropriately suppresses stuffiness, and thus the present invention has been conceived.

That is, one aspect of the present invention includes the steps of preparing a substrate including a fiber-entangled body and a wet-type polyurethane porous layer that is impregnated with and laminated to the fiber-entangled body to be integrated therewith ; gravure-coating a first polyurethane solution in which a first polycarbonate- based polyurethane is dissolved onto a surface of the wet-type polyurethane porous layer to dissolve the wet-type polyurethane porous layer and form open pores that communicate in the thickness direction, followed by drying to form a first top coat; embossing the first top coat with a heated embossing roll having texture; and applying a silicone to the surface of the embossed first top coat. and a step of gravure-coating a second polyurethane solution in which a second polycarbonate-based polyurethane containing a modified polycarbonate-based polyurethane is dissolved, and then drying to form a second top coat, wherein the total thickness of the first top coat and the second top coat is 1 to 5 μm , the first polyurethane solution contains a mixed solvent containing 50 to 80 mass % of N,N-dimethylformamide and 20 to 50 mass % of cyclohexanone, the concentration of the first polycarbonate-based polyurethane is 5 to 10 mass %, the Zahn cup viscosity at 20° C. is 10 to 40 seconds, and the viscosity is 20 to 60 g/m The ^second polyurethane solution contains a mixed solvent containing 10 to 40% by mass of N,N-dimethylformamide, 25 to 35% by mass of cyclohexanone, and 20 to 40% by mass of acetone, the concentration of the second polycarbonate-based polyurethane is 5 to 10% by mass, the Zahn cup viscosity at 20 ° C. is 10 to 40 seconds, and the coating amount is 20 to 60 g / m ² , the water resistance (hereinafter also referred to simply as water resistance) measured in accordance with the water resistance test (hydrostatic pressure method) A method of JIS L 1092 (2009 ) "Testing method for waterproofness of textile products" is 1000 mm or more, and the air permeability (hereinafter also referred to simply as air permeability) measured in accordance with the method specified in the air permeability A method (Fragile type method) of JIS L 1096 (2010) "Testing method for woven and knitted fabrics" is 0 . This is a method for producing a grain-finished artificial leather, in which the opening diameter and number of holes are adjusted in each process so that the grain-finished artificial leather has a grain-finished finish of 10 cm ³ /cm ² ·s or more. According to this method for producing a grain-finished artificial leather, the first polyurethane solution is gravure-coated on the surface of the wet polyurethane porous layer, and the wet polyurethane porous layer is appropriately dissolved with a solvent to form open holes that communicate from the front surface to the back surface. Furthermore, by embossing the surface of the first top coat with a heated embossing roll having texture, some of the openings are blocked or reduced in size, and large openings that reduce water resistance are blocked, while an appropriate number of small openings that maintain breathability are left. Furthermore, the surface of the wet polyurethane porous layer is smoothed by embossing, so that the abrasion resistance is less likely to decrease. And, by forming the second top coat without widening the openings, the surface is smoothed, so that high abrasion resistance can be maintained, and openings that maintain high water resistance and are less likely to seep in during rainy weather can be left. Specifically, the grain-finished artificial leather is obtained by adjusting the opening size and number so that the resulting grain-finished artificial leather has a water resistance of 1000 mm or more and an air permeability of 0.1 ^cm3 / ^cm2 ·s or more. As a result, the grain-finished artificial leather is obtained that combines high water resistance, air permeability that appropriately suppresses stuffiness, and abrasion resistance.

In addition, the first polyurethane solution contains a mixed solvent containing 50 to 80% by mass of N,N-dimethylformamide and 20 to 50% by mass of cyclohexanone, has a first polyurethane concentration of 5 to 10% by mass, has a Zahn cup viscosity at 20°C of 10 to 40 seconds, and is applied in an amount of 20 to 60 g/ ^m2 ; and the second polyurethane solution contains a mixed solvent containing 10 to 40% by mass of N,N-dimethylformamide, 25 to 35% by mass of cyclohexanone, and 20 to 40% by mass of acetone, has a second polyurethane concentration of 5 to 10% by mass, has a Zahn cup viscosity at 20°C of 10 to 40 seconds, and is applied in an amount of 20 to 60 g/ ^m2 . In this way, the solvent contained in the first polyurethane solution forms an appropriate amount of interconnected open pores in the wet polyurethane porous layer, and the solvent contained in the second polyurethane solution does not dissolve the wet polyurethane porous layer excessively. As a result, a grain-finished artificial leather is obtained which has a top coat layer of appropriate thickness and in which the diameter and number of the communicating open pores are adjusted as described above.

Another aspect of the present invention is a grain-finished artificial leather comprising a fiber-entangled body, a wet-type polyurethane porous layer impregnated with and laminated onto the fiber-entangled body to be integrated with it, and a top coat having a thickness of 1 to 5 μm and containing a polycarbonate-based polyurethane, the top coat containing a silicone-modified polycarbonate-based polyurethane, the surface of the top coat being grained and having communicating open pores that communicate from the surface to a back surface of the wet-type polyurethane porous layer, the number of openings having a major axis of 0.5 μm or more and 40 μm or less per ^cm2 of the surface being 100 or more and less than 200, the number of openings having a major axis of more than 20 μm and 40 μm or less being less than 20, and the number of openings having a major axis of more than 40 μm being 0, the water resistance being 1,000 mm or more, and the breathability being 0.10 ^cm3 / ^cm2 ·s or more. Such grain-finished artificial leather can combine high water resistance, breathability that appropriately suppresses stuffiness, and abrasion resistance.

According to the present invention, a grain-finished artificial leather having a wet-type polyurethane porous layer forming a grain surface layer is obtained, which has high water resistance, breathability that appropriately suppresses stuffiness, and abrasion resistance.

FIG. 1 is a schematic cross-sectional view of a grain-finished artificial leather 10 according to an embodiment of the present invention. FIG. 2 is a photograph of the surface of the wet-processed polyurethane porous layer of the grain-finished artificial leather obtained in Example 1, observed under a microscope at a magnification of 45. FIG. 3 is a photograph of the surface of the wet-processed polyurethane porous layer of the grain-finished artificial leather obtained in Comparative Example 1, observed under a microscope at a magnification of 45. FIG. 4 is a photograph of the surface of the wet-processed polyurethane porous layer of the grain-finished artificial leather obtained in Comparative Example 2, observed under a microscope at 100 times.

Hereinafter, one embodiment of the grain-finished artificial leather according to the present invention will be described. The grain-finished artificial leather of this embodiment comprises a fiber-entangled body, a wet polyurethane porous layer impregnated and laminated with the fiber-entangled body to be integrated, and a top coat containing a polycarbonate-based polyurethane and having a thickness of 1 to 5 μm, the top coat containing a silicone-modified polycarbonate-based polyurethane, the surface of which is grained and has open pores that communicate from the surface to the back surface of the wet polyurethane porous layer, the number of openings with a major axis of 0.5 μm to 40 μm per 1 ^cm2 of the surface being 100 to less than 200, the number of openings with a major axis of more than 20 μm and less than 40 μm being less than 20, the number of openings with a major axis of more than 40 μm being 0, and the water resistance of the grain-finished artificial leather being 1000 mm or more and the air permeability of the grain-finished artificial leather being 0.10 ^cm3 / ^cm2.s or more. Hereinafter, the grain-finished artificial leather of this embodiment will be described in detail with reference to the drawings and a representative manufacturing method thereof.

Figure 1 shows a schematic cross-sectional view of a grain-finished artificial leather 10. In Figure 1, 1 is a fiber entanglement body, 2 is a wet polyurethane porous layer impregnated and laminated on the fiber entanglement body 1, and 3 is a polyurethane top coat laminated on the wet polyurethane porous layer. The wet polyurethane porous layer 2 includes a grain surface layer 2a that is not integrated with the fiber entanglement body 1 in the wet polyurethane porous layer 2 and is laminated on the surface of the fiber entanglement body 1, and an impregnated layer 2b that is impregnated into the fiber entanglement body 1 and is integrated with the fiber entanglement body 1 in the wet polyurethane porous layer 2. The wet polyurethane porous layer 2 includes voids v that form a porous structure. A top coat 3 containing polycarbonate-based polyurethane and having a thickness of 1 to 5 μm is further laminated on the surface of the wet polyurethane porous layer 2. The grain-finished artificial leather 10 includes open holes h that communicate from the front surface to the back surface of the wet polyurethane porous layer 2 and open to the surfaces of the wet polyurethane porous layer 2 and the top coat 3. The outer surface of the grained artificial leather is embossed with an embossing roll (not shown).

The manufacturing method for the grain-finished artificial leather according to this embodiment is described below.

In the method for producing the grain-finished artificial leather of this embodiment, first, a substrate is prepared that includes a fiber entanglement and a wet-processed polyurethane porous layer that is impregnated with and laminated to the fiber entanglement and integrated with it.

The fiber structure of the fiber entanglement is not particularly limited, but examples include nonwoven fabric, woven fabric, knitted fabric, and an entanglement of a combination thereof, and preferably includes a nonwoven fabric or an entanglement of a nonwoven fabric and a woven fabric.

The resin that forms the fiber entanglement is not particularly limited. Specifically, for example, polyamide-based resins such as polyamide 6, polyamide 66, polyamide 610, polyamide 10, polyamide 11, polyamide 12, and polyamide 6-12; aromatic polyester-based resins such as polyethylene terephthalate (PET), modified polyethylene terephthalate, polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polytriethylene terephthalate, polyhexamethylene terephthalate, polypropylene terephthalate, and polyethylene naphthalate; polylactic acid, polyethylene succinate, polybutylene succinate, and polybutylene Examples of suitable resins include polyester resins such as aliphatic polyester resins, such as succinate adipate and polyhydroxybutyrate-polyhydroxyvalerate copolymers; polyolefin resins, such as polypropylene, polyethylene, polybutene, polymethylpentene, chlorine-based polyolefins, ethylene-vinyl acetate copolymers, and styrene-ethylene copolymers; modified polyvinyl alcohol resins formed from modified polyvinyl alcohols containing 25 to 70 mol% ethylene units; and crystalline elastomers, such as polyurethane elastomers, polyamide elastomers, and polyester elastomers. Among these, polyamide resins and aromatic polyester resins are preferred because of their excellent balance of various properties.

The fiber fineness and shape are not particularly limited. For example, it may be a regular fiber with an average fineness of more than 1 dtex, or an ultrafine fiber with an average fineness of less than 1 dtex. The fiber shape may be a solid fiber or a fiber with voids such as hollow fiber or lotus root-shaped fiber. Among these, ultrafine fibers with an average fineness of 0.0001 to 0.1 dtex are preferred because they provide an excellent balance between the texture, such as flexibility, and durability. The average fineness is calculated by taking a 3000x magnification image of a cross section parallel to the thickness direction of the grain-finished artificial leather using a scanning electron microscope (SEM) and calculating the average value from 15 evenly selected fiber diameters using the density of the resin that forms the fiber.

The thickness of the fiber entanglement is not particularly limited, but is preferably, for example, 0.3 to 3 mm, and more preferably, 0.5 to 1.5 mm.

The substrate comprises a fiber entanglement and a wet polyurethane porous layer that is impregnated and laminated to the fiber entanglement, forming an integrated structure. Such a substrate can be obtained, for example, by impregnating the fiber entanglement with a polyurethane solution that wet-coagulates (hereinafter referred to as a wet-coagulating polyurethane solution), applying a similar wet-coagulating polyurethane solution to the surface of the fiber entanglement, and then immersing the fiber entanglement in an aqueous coagulating liquid such as water or a mixed solvent of water and DMF to wet-coagulate the porous polyurethane.

Specific examples of polyurethanes contained in the wet coagulation polyurethane solution include polyester glycol-based polyurethanes, polypropylene glycol-based polyurethanes, polytetramethylene glycol-based polyurethanes, polycarbonate-based polyurethanes, and polytetramethylene glycol-polycarbonate copolymer-based polyurethanes, which use polyethylene adipate, polybutylene adipate, polypropylene adipate, polyhexamethylene adipate, polycaprolactone, polymethylvalerolactone, etc. as the polyol component.

The solvent contained in the wet coagulation polyurethane solution is one that has high solubility in polyurethane, such as a mixed solvent consisting mainly of N,N-dimethylformamide (DMF) and water, with cyclohexanone (CHN), tetrahydrofuran (THF), methyl ethyl ketone (MEK), acetone (Ac), dioxane, isopropyl alcohol, toluene, etc., mixed as necessary.

In addition, the wet-coagulated polyurethane solution may contain additives such as coagulation regulators, antioxidants, light resistance agents, and antibacterial agents, in addition to colorants such as pigments.

In the substrate, the fiber entanglement is impregnated with a wet-coagulated polyurethane solution in advance, and then the surface of the fiber entanglement is coated with the wet-coagulated polyurethane solution, after which it is immersed in the coagulation liquid and coagulated to form a polyurethane porous layer that is impregnated and laminated to the fiber entanglement and integrated with it, including an impregnated layer that is impregnated into the interior of the fiber entanglement and integrated with it, and an area that becomes a grain surface layer in which porous polyurethane is laminated alone on the surface of the fiber entanglement, forming an integrated polyurethane porous layer.

The polyurethane porous layer may have a single layer structure formed from the same polyurethane, or a multi-layer structure in which different types of polyurethane are applied in layers and then coagulated by immersion in a coagulating liquid.

The total thickness of the wet polyurethane porous layer is preferably 100 to 600 μm, and more preferably 200 to 400 μm. The thickness of the area of the wet polyurethane porous layer that becomes the silver surface layer laminated on the surface is preferably 50 to 500 μm, and more preferably 100 to 300 μm. The total thickness of the substrate is preferably 800 to 3000 μm, and more preferably 1200 to 2000 μm.

The mass ratio of the fiber entanglement and the wet polyurethane porous layer (fiber entanglement/wet polyurethane porous layer) constituting the grain-finished artificial leather is preferably 40/60 to 70/30, more preferably 50/50 to 60/40, in terms of an excellent balance between texture and shape stability. If the ratio of the wet polyurethane porous layer is too high, the texture tends to be rubber-like, and if the ratio of the fiber entanglement is too high, shape stability tends to decrease.

Next, a first polyurethane solution in which polycarbonate-based polyurethane is dissolved is gravure-coated onto the surface of the wet polyurethane porous layer of the substrate thus prepared, dissolving the wet polyurethane porous layer to form open pores that communicate in the thickness direction, and then drying to form a first top coat. By applying the first polyurethane solution and dissolving the wet polyurethane porous layer with the solvent contained in the first polyurethane solution, it is possible to generate open pores that communicate from the front surface to the back surface.

The first polyurethane solution contains a solvent that is highly soluble in polyurethane and the first polyurethane.

Examples of solvents with high solubility in polyurethane include solvents that are mainly N,N-dimethylformamide (DMF, boiling point 153°C) and, as necessary, are mixed with cyclohexanone (CHN, boiling point 156°C), tetrahydrofuran (THF, boiling point 66°C), methyl ethyl ketone (MEK, boiling point 80°C), dioxane (boiling point 101°C), toluene (boiling point 111°C), isopropyl alcohol (IPA, boiling point 124°C), etc., to adjust the solubility. Among these, mixed solvents containing DMF and CHN, specifically, mixed solvents containing 50 to 80% by mass, or even 60 to 70% by mass, 20 to 50% by mass, or even 25 to 40% by mass, and other polar solvents such as THF as the remainder, are preferred because they are easy to adjust to the appropriate pore size and number. CHN has a boiling point close to that of DMF and is more soluble in polyurethane than DMF, which helps prevent the sudden evaporation of DMF during drying and the sudden formation of a polyurethane film, thereby making it difficult to form large openings.

The first polyurethane forms the first top coat and is blended as a thickener to increase the solution viscosity of the first polyurethane solution. The first polyurethane includes polycarbonate-based polyurethanes such as polycarbonate polyurethane, silicone-modified polycarbonate-based polyurethane, and polytetramethylene glycol-polycarbonate copolymer polyurethane in order to form a first top coat with high abrasion resistance. Silicone-modified polycarbonate-based polyurethane is preferably used because of its particularly excellent abrasion resistance.

The first polyurethane solution may also contain additives such as antioxidants, light fasteners, and antibacterial agents, in addition to colorants such as pigments.

The Zahn cup viscosity of the first polyurethane solution is preferably 10 to 40 seconds, more preferably 15 to 35 seconds, and particularly preferably 20 to 30 seconds. If the Zahn cup viscosity of the first polyurethane solution is too low, it becomes difficult to apply a small amount of the solution uniformly by gravure, and the solution tends to form large, interconnected open pores in a non-uniform manner, resulting in low water resistance. If the Zahn cup viscosity of the first polyurethane solution is too high, the solution also tends to become too viscous to apply a small amount of the solution uniformly by gravure, and to penetrate the wet polyurethane porous layer with difficulty, resulting in insufficient formation of interconnected open pores.

In addition, the concentration of the first polyurethane in the first polyurethane solution is preferably 5 to 10% by mass, more preferably 6 to 9% by mass, and particularly preferably 7 to 8% by mass. If the concentration of the first polyurethane is too low, the first polyurethane solution cannot be adequately thickened, and non-uniform interconnected open pores with large variations in opening diameter are likely to be formed. If the concentration is too high, the viscosity of the first polyurethane solution becomes too high, making it difficult for the solution to penetrate into the wet polyurethane porous layer, and making it difficult to form sufficient interconnected open pores.

The first polyurethane solution is applied to the surface of the wet polyurethane porous layer using a gravure roll. It is preferable for the gravure roll to have cells engraved on the surface of the gravure roll with a size of 65 to 180 mesh, or even 100 to 130 mesh, since this allows an appropriate amount of the first polyurethane solution to be applied uniformly.

The coating amount of the first polyurethane is preferably 20 to 60 g/m ² , more preferably 30 to 50 g/m ² , and particularly preferably 35 to 45 g/m ² . By coating the first polyurethane solution on the surface of the wet polyurethane porous layer in such a coating amount, the wet polyurethane porous layer is dissolved in the solvent in the first polyurethane solution, and continuous open pores are formed that connect the front surface to the back surface of the wet polyurethane porous layer. The solvent is then dried to form a first top coat having openings of continuous open pores. The drying conditions are appropriately adjusted depending on the type of solvent, etc., but for example, drying conditions in a hot air dryer set at 100 to 120° C. for 5 to 30 seconds or until the remaining amount of DMF is about 100 to 10,000 ppm are preferred.

The thickness of the first top coat thus formed is preferably about 1 to 3 μm. In addition, it is preferable that the number of openings on the surface of the first top coat per 1 ^cm2 of the surface be 1000 to 3000 openings with a major axis of 0.5 μm or more and 20 μm or less, the number of openings with a major axis of more than 20 μm and 40 μm or less be 100 to 500, and the number of openings with a major axis of more than 40 μm be 200 or less, from the viewpoint of facilitating the production of a grain-finished artificial leather having openings of the size and number described below.

Next, the surface of the formed first topcoat is embossed with a heated embossing roll. By embossing in this manner, the openings in the surface of the first topcoat tend to be deformed by embossing, large openings tend to be blocked, and small openings tend to remain. In addition, the surface of the first topcoat becomes smooth.

The shape of the embossing roll is not particularly limited, but an embossing roll with a height difference of about 20 to 100 μm is preferably used. The surface temperature of the embossing roll is appropriately selected so that the shape of the embossing can be properly transferred and small openings tend to remain. Specifically, for example, a temperature of 150 to 190°C, or more preferably 160 to 180°C, is preferable. If the surface temperature of the embossing roll is too high, the openings tend to be overly blocked and the overall texture tends to be hard. If the surface temperature of the embossing roll is too low, the shape of the embossing cannot be properly transferred and large openings tend to be difficult to block.

As for the openings on the surface of the first top coat embossed with the embossing roll, the number of openings per 1 ^cm2 of surface having a major axis of 0.5 μm or more and 20 μm or less is preferably 100 to 500, the number of openings having a major axis of more than 20 μm and 40 μm or less is 10 to 100, and the number of openings exceeding 40 μm is 10 or less, from the viewpoint of easily obtaining a grain-finished artificial leather having openings of the size and number described below.

In the production of the grain-finished artificial leather of this embodiment, a second polyurethane solution in which a second polycarbonate-based polyurethane containing a silicone-modified polycarbonate- based polyurethane is dissolved is gravure-coated onto the surface of the embossed first top coat, and then the solution is dried to form a second top coat.

The solvent contained in the second polyurethane solution is preferably less soluble in polyurethane than the solvent contained in the first polyurethane solution. As the solvent contained in the second polyurethane solution, for example, a solvent mainly containing DMF and mixed with a polar solvent such as cyclohexanone (CHN), tetrahydrofuran (THF), dioxane, isopropyl alcohol, and a ketone such as acetone (Ac) or methyl ethyl ketone (MEK) is preferably used to adjust the solubility as necessary. Among these, a mixed solvent of DMF, CHN, and Ac, specifically, a mixed solvent of DMF, CHN, and Ac, with 10 to 40 mass %, or even 15 to 35 mass %, 25 to 35 mass %, or even 30 to 35 mass %, and 20 to 40 mass %, or even 25 to 35 mass %, of Ac, and other solvents such as THF and MEK as the remainder, is preferred in terms of ease of adjusting the openings to the appropriate diameter and number.

The second polyurethane forms a second top coat, closes large openings, and makes it easier for small openings to remain appropriately. As the second polyurethane forming the second top coat, polycarbonate-based polyurethanes such as polycarbonate polyurethane, silicone-modified polycarbonate-based polyurethane, and polytetramethylene glycol-polycarbonate copolymer polyurethane are used because of their excellent abrasion resistance. In addition, silicone-modified polycarbonate-based polyurethanes are included because of their particularly excellent abrasion resistance.

The second polyurethane solution may also contain additives such as antioxidants, light fasteners, antibacterial agents, water and oil repellents, etc., in addition to colorants such as pigments.

The Zahn cup viscosity of the second polyurethane solution is preferably 10 to 40 seconds, and more preferably 15 to 25 seconds. If the Zahn cup viscosity of the second polyurethane solution is too low, the viscosity is too low and the liquid will not be transferred uniformly, so a top coat of sufficient thickness will not be formed. If the Zahn cup viscosity is too high, the top coat will tend to become a continuous film and the openings will tend to be blocked too much.

To adjust the second polyurethane solution to have such a solution viscosity, the concentration of the second polyurethane in the second polyurethane solution is preferably 5 to 10% by mass, more preferably 6 to 9% by mass, and particularly preferably 7 to 8% by mass. If the concentration of the second polyurethane is too low, a top coat of sufficient thickness will not be formed, and if it is too high, the top coat will tend to become a continuous film and the openings will tend to be blocked too much.

The second polyurethane solution is applied to the surface of the first top coat using a gravure roll. It is preferable for the size of the cells engraved on the surface of the gravure roll to be 65 to 180 mesh, or even 100 to 130 mesh, since this allows an appropriate amount of the second polyurethane solution to be applied uniformly.

The amount of the second polyurethane solution applied is preferably 20 to 60 g/m ² , more preferably 30 to 50 g/m ² , and particularly preferably 35 to 45 g/m ² . If the amount of the second polyurethane solution applied is too large, the top coat tends to become a continuous film and the openings tend to be blocked, and if the amount of the second polyurethane solution applied is too small, a top coat of sufficient thickness tends not to be formed. Then, by drying the solvent, a second top coat with an appropriate amount of remaining openings is formed. The drying conditions are appropriately adjusted depending on the type of solvent, etc., but for example, a condition in which drying is performed in a hot air dryer set at 100 to 120° C. for 5 to 30 seconds or until the amount of remaining DMF is 3000 ppm or less is preferable.

In this way, a second topcoat is formed on the surface of the first topcoat that has been embossed by the embossing roll. The thickness of the second topcoat is preferably about 1 to 3 μm.

The total thickness of the first top coat and the second top coat is 1 to 5 μm, and preferably 2 to 4 μm. If the layer thickness of the top coat including the first top coat and the second top coat is less than 1 μm, the effect of improving abrasion resistance will be insufficient, and if it exceeds 5 μm, water resistance and breathability will decrease, the texture will become hard, and bending resistance will deteriorate.

The grain-finished artificial leather of this embodiment can be obtained by the manufacturing method described above. The grain-finished artificial leather obtained by the manufacturing method described above is a grain-finished artificial leather that combines high water resistance and breathability that appropriately suppresses stuffiness.

Specifically, the water resistance of the grain-finished artificial leather of this embodiment is preferably 1000 mm or more in the water resistance test described below, in order to maintain high water resistance.

In addition, the grain-finished artificial leather of this embodiment has an air permeability of 0.1 ^cm3 / ^cm2 ·s or more, and preferably 0.3 ^cm3 / ^cm2 ·s or more, in the air permeability test described later, from the viewpoint of suppressing stuffiness when used in products that come into contact with the human body.

Such a grain-finished artificial leather has open pores that are open on the surface and communicate from the surface to the back surface. The number of openings on the surface of the wet-processed polyurethane porous layer of the grain-finished artificial leather or on the surface of the top coat formed as necessary is preferably less than 200, more preferably from 100 to 200, per ^{1 cm2} of surface, each having a major axis of 0.5 μm or more and 40 μm or less, and more preferably from 100 to 200, more preferably from 10 to 200 , more preferably from 10 to 20 , and more preferably from 0 to ...

The grain-finished artificial leather of this embodiment described above is preferably used as the outer material of products that come into contact with the human body, such as clothing materials, shoe upper materials, and backpack linings.

The present invention will be explained in more detail below with reference to examples. Note that the scope of the present invention is not limited to these examples.

First, we will summarize the evaluation method used in this example.

(Water resistance)
The water resistance test was carried out according to the method specified in the water resistance test (hydrostatic pressure method) method A of JIS L 1092 (2009) "Waterproof test method for textile products". Specifically, five test pieces were cut into 150 mm x 150 mm from the grain-finished artificial leather. Then, in an atmosphere of room temperature 23°C and relative humidity 65%, the test pieces were attached to a specified water resistance test device so that the front side of the test pieces was exposed to water, and the water in the leveling device was raised at a speed of 600 mm/min ± 30 mm/min, and the water level when water came out from three places on the back side of the test pieces was measured in mm units. This water resistance (mm) was measured five times, and the average value was taken as the water resistance of the grain-finished artificial leather.

(Breathability)
The air permeability test was conducted according to the method specified in the Air Permeability A Method (Fragile Method) of JIS L 1096 (2010) "Test Method for Woven and Knit Fabrics". Specifically, five test pieces were cut into 200 mm x 200 mm pieces of silver-finished artificial leather. Then, in an atmosphere of room temperature 23°C and relative humidity 65%, the test pieces were attached to one end of the cylinder of the specified tester, and the suction fan and air hole were adjusted by a rheostat so that the inclined barometer indicated a pressure of 125 Pa, and the pressure indicated by the vertical barometer at that time was measured. From the measured pressure and the type of air hole used, the amount of air passing through the test piece ( ^cm3 / ^cm2 ·s) was calculated using the conversion table attached to the tester. The average value of the five test results was then calculated.

(Measurement of Zahn cup viscosity of polyurethane solution)
The Zahn cup viscosity at 20° C. was measured using Zahn cup No. 4 in accordance with ASTM D4212. The average value of the results of three measurements was taken as the Zahn cup viscosity of the polyurethane solution.

(Topcoat thickness)
An arbitrary cross section parallel to the thickness direction of the grain-finished artificial leather was observed with an SEM at 300x magnification. Then, the film thickness of the top coat was measured at 10 randomly selected points, and the average value was calculated.

(Taber abrasion)
A test piece was prepared by attaching double-sided tape to the back surface of the grain-finished artificial leather and cutting it into a circle with a diameter of 10.6 cm, and then weighed precisely on a specified balance. Next, the test piece was set on a turntable and attached to the vertical drive shaft of a Taber abrasion tester. Then, an arm equipped with an abrasion wheel (H-22 (manufactured by Daito Electron Co., Ltd.)) was lowered onto the measurement surface, and the grain-finished artificial leather was abraded under the conditions of a load of 500 g and a rotation speed of 1000 times. After abrasion up to 1000 rotations, the test piece was removed, the abrasion debris attached to the test piece was thoroughly removed with a brush, and the test piece was weighed precisely on a specified balance, and the abrasion loss (mg) was measured. The abrasion loss was calculated as the difference in weight before and after abrasion. The average value of the results of three measurements was taken as the abrasion loss of the grain-finished artificial leather.

(Counting the number of openings)
The surface of the grain-finished artificial leather was photographed at three random locations using a scanning electron microscope at a magnification of 40 to 50 times, with the area photographed being 5 to 8 ^mm2 , the number of openings was counted, and the total number of openings at the three locations was converted into the number per ^cm2 .

[Example 1]
50 parts by mass of polyethylene (sea component) and 50 parts by mass of polyamide 6 (island component) were melt spun in the same melt system to produce islands-in-sea composite fibers with a fineness of 15 dtex. The islands-in-sea composite fibers were then stretched 2.5 times, crimped, and cut into staple fibers with a fiber length of 51 mm. The staple fibers were then opened by a card and a fiber web was formed by a cross-wrapper weber. The fiber webs were cross-wrapped, overlapped, and needle-punched to obtain a fiber-entangled product with a basis weight of 650 g/ ^m2 .

The fiber-entangled body was then impregnated with a 13% dimethylformamide (DMF) solution of polyester-based polyurethane. The polyester-based polyurethane was a copolymer of polyethylene propylene adipate, 4,4'-diphenylmethane diisocyanate (MDI), and ethylene glycol (EG) and had a 100% modulus of 100 kg/ ^cm2 . Immediately thereafter, a 26% DMF solution of the same polyester-based polyurethane was applied to the surface of the fiber-entangled body at 40 g/ ^m2 and allowed to penetrate. Furthermore, a 20% DMF solution of polycarbonate-based polyurethane was applied to the upper surface at 75 g/ ^m2 . The polycarbonate-based polyurethane was a copolymer whose main components were polyhexacarbonate glycol, polymethylene propylene adipate, and methylene diamine, and further copolymerized with n-hexane diisocyanate, MDI, and EG, and had a 100% modulus of 40 kg/ ^cm2 .

The fiber entanglement impregnated or coated with each polyurethane was then immersed in a coagulation bath (40°C) of DMF/water = 30/70 for 30 minutes to coagulate each polyurethane into a porous form, and then washed with water. The polyethylene in the islands-in-the-sea composite fibers was then extracted and removed with toluene to convert them into ultrafine fibers. In this way, a substrate with a thickness of 1.6 mm was obtained, which included an entanglement of fiber bundles of ultrafine fibers of polyamide 6 with an average fineness of 0.01 dtex and a porous wet polyurethane porous layer. The overall thickness of the wet polyurethane porous layer was 250 μm.

On the other hand, a polyurethane solution containing a mixed solvent of N,N-dimethylformamide (DMF), cyclohexanone (CHN), and tetrahydrofuran (THF) in a mass ratio of 70/25/5 (DMF/CHN/THF), a first polyurethane concentration of 7.5 mass%, and 5 mass% of pigment in the solid content was prepared as the first polyurethane solution. The Zahn cup viscosity of the first polyurethane solution was 20 seconds. The first polyurethane was a polycarbonate-based polyurethane with a 100% modulus of 9 MPa.

As a second polyurethane solution, a polyurethane solution was prepared containing a mixed solvent of DMF, CHN, and acetone (Ac) in a mass ratio of 30/35/35 (DMF/CHN/Ac) and having a second polyurethane concentration of 7.3 mass%. The Zahn cup viscosity of the second polyurethane solution was 15 seconds. The second polyurethane was a silicone-modified polycarbonate-based polyurethane with a 100% modulus of 5 MPa.

The first polyurethane solution was applied to the surface of the porous polyurethane of the substrate with a 110 mesh gravure roll in an amount of 40 g/ ^m2 , and then dried by passing through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this way, a first top coat was formed.

The surface of the dried first top coat was then embossed using an embossing roll having textured projections at a roll temperature of 170° C., a press pressure of 6 kg/cm ² and a processing speed of 2 m/min.

Then, the second polyurethane solution was applied to the embossed surface of the first top coat with a coating amount of 40 g/ ^m2 using a 110 mesh gravure roll, and dried by passing through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this way, a second top coat was formed.

In this way, grain-finished artificial leather was obtained. It was then evaluated according to the above evaluation method. The results are shown in Table 1.

[Example 2]
A grain-finished artificial leather was produced in the same manner as in Example 1, except that the formation of the top coat was changed as follows. A first polyurethane solution was prepared in which the concentration of the first polyurethane was changed to 9% by mass, and the concentration of the pigment in the solid content was changed to 8% by mass. The Zahncup viscosity of the first polyurethane solution was 23 seconds. The first polyurethane was a polycarbonate-based polyurethane with a 100% modulus of 9 MPa.
The first polyurethane solution was then applied to the surface of the porous polyurethane of the substrate with a 110 mesh gravure roll in an amount of 50 g/ ^m2 , and dried by passing through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this manner, a first top coat was formed. Grain-finished artificial leather was then manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]
A grain-finished artificial leather was produced in the same manner as in Example 1, except that the formation of the top coat was changed as follows. A first polyurethane solution was prepared in which the concentration of the first polyurethane was changed to 6% by mass, and the pigment in the solid content was changed to 5% by mass. The Zahncup viscosity of the first polyurethane solution was 18 seconds. The first polyurethane was a polycarbonate-based polyurethane with a 100% modulus of 9 MPa.
The first polyurethane solution was then applied to the surface of the porous polyurethane of the substrate with a 110 mesh gravure roll in an amount of 30 g/ ^m2 , and dried by passing through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this manner, a first top coat was formed. Grain-finished artificial leather was then manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 4]
In Example 1, the fiber-entangled body after needle punching was impregnated with a 13% dimethylformamide (DMF) solution of polyester-based polyurethane. Immediately thereafter, a 26% DMF solution of the same polyester-based polyurethane was applied to the surface of the fiber-entangled body at 40 g/ ^m2 and allowed to penetrate. Furthermore, 75 g/m2 of a 20% DMF solution of polycarbonate-based polyurethane toned to beige by mixing white pigment, yellow pigment, and red pigment was applied to the ^upper surface.

The fiber entanglement impregnated or coated with each polyurethane was then immersed in a coagulation bath (40°C) of DMF/water = 30/70 for 30 minutes to coagulate each polyurethane into a porous form, and then washed with water. The polyethylene in the islands-in-the-sea composite fibers was then extracted and removed with toluene to convert them into ultrafine fibers. In this way, a substrate with a thickness of 1.6 mm was obtained, which contained fiber bundles of ultrafine fibers of polyamide 6 with an average fineness of 0.01 dtex and porous polyurethane.

On the other hand, a polyurethane solution containing a mixed solvent containing DMF, CHN, and THF in a mass ratio of 65/30/5 (DMF/CHN/THF) and a concentration of the first polyurethane of 7.5 mass% was prepared as a first polyurethane solution. The Zahn cup viscosity of the first polyurethane solution was 15 seconds. The first polyurethane was a polycarbonate-based polyurethane with a 100% modulus of 9 MPa.
The first polyurethane solution was then applied to the surface of the porous polyurethane of the substrate with a 110 mesh gravure roll in an amount of 40 g/ ^m2 , and dried by passing through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this way, a first top coat was formed.
Thereafter, grain-finished artificial leather was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 5]
Except for changing the formation of the top coat as follows, the same procedure as in Example 1 was repeated to produce grain-finished artificial leather and evaluate it. The results are shown in Table 1.

As the second polyurethane solution, a polyurethane solution was prepared containing a mixed solvent with a mass ratio of 15/30/15/15/25 (DMF/CHN/THF/methyl ethyl ketone (MEK)/Ac) and a second polyurethane concentration of 7.5 mass%. The Zahn cup viscosity of the second polyurethane solution was 17 seconds. The second polyurethane was a silicone-modified polycarbonate polyurethane with a 100% modulus of 8 MPa.

Then, the second polyurethane solution was applied to the surface of the first top coat embossed in the same manner as in Example 1 with a 110 mesh gravure roll in an amount of 40 g/ ^m2 , and the resultant was dried by passing it through a hot air dryer at 110°C and a speed of 8 m/min for about 10 seconds. In this manner, a second top coat was formed. A grain-finished artificial leather was produced and evaluated. The results are shown in Table 1.

[Comparative Example 1]
A grain-finished artificial leather was produced and evaluated in the same manner as in Example 1, except that the second top coat was not formed. The results are shown in Table 1.

[Comparative Example 2]
In Example 1, instead of the first polyurethane solution, DMF was applied with a 110 mesh gravure roll at a coating weight of 40 g/ ^m2 . The Zahn cup viscosity of DMF was 6 seconds.
Thereafter, a first polyurethane solution in which the same first polyurethane as in Example 1 was dissolved was applied with a 110 mesh gravure roll at a coating amount of 40 g/ ^m2 . The first polyurethane solution contained a mixed solvent containing DMF, cyclohexanone, and tetrahydrofuran in a mass ratio of 65/30/5 (DMF/cyclohexanone/tetrahydrofuran), had a concentration of the first polyurethane of 7.5 mass%, and had a Zahn cup viscosity of 15 seconds. The first polyurethane was a polycarbonate-based polyurethane with a 100% modulus of 9 MPa. Thereafter, embossing was performed in the same manner as in Example 1.

[Comparative Example 3]
The grain-finished artificial leather was produced and evaluated in the same manner as in Comparative Example 2, except that the amount of the second polyurethane solution applied was changed. The results are shown in Table 1.

[Comparative Example 4]
Example 1 was repeated to obtain a grain-finished artificial leather, except that the following polyurethane solution was applied as the first polyurethane solution in Example 1.
The first polyurethane solution contained a mixed solvent containing DMF, cyclohexanone, tetrahydrofuran, methyl ethyl ketone, and acetone in a mass ratio of 15/30/15/15/25 (DMF/cyclohexanone/tetrahydrofuran/methyl ethyl ketone/acetone), had a first polyurethane concentration of 7.5 mass%, had a Zahn cup viscosity of 20 seconds, and contained 6 mass% of pigment in the solid content. The first polyurethane was a silicone-modified polyester polyurethane with a 100% modulus of 8 MPa.

[Comparative Example 5]
In Example 5, after the first polyurethane solution was applied, it was dried in a dryer at 110°C for about 10 seconds, and then the second polyurethane solution was applied, and then embossing was performed. In the same manner as in Example 5, except that, a grain-finished artificial leather was obtained and evaluated.

[Comparative Example 6]
A grain-finished artificial leather was obtained and evaluated in the same manner as in Example 1, except that the first polyurethane solution was applied in an amount of 70 g/ ^m2 using a 55 mesh gravure roll, instead of 30 g/ ^m2 using a 110 mesh gravure roll in Example 3. The grain-finished artificial leather obtained had a lack of surface smoothness and was inferior in quality.

All of the grain-finished artificial leathers obtained in Examples 1 to 5 had high water resistance, breathability that moderately suppresses stuffiness, and abrasion resistance. On the other hand, the grain-finished artificial leather obtained in Comparative Example 1, in which the second polyurethane solution was not applied, had low water resistance and abrasion resistance because the large openings were not fully blocked. Moreover, the grain-finished artificial leathers obtained in Comparative Examples 2 and 3, in which only a solvent was applied instead of applying the viscosity-adjusted first polyurethane solution, also had large openings that were not fully blocked, and although they had excellent breathability, they had low water resistance and low abrasion resistance. Moreover, the grain-finished artificial leather obtained in Comparative Example 4, in which the solubility of the solvent in the first polyurethane solution was too high, had high water resistance but extremely low breathability. Moreover, the grain-finished artificial leather obtained in Comparative Example 5, in which a second top coat was formed and then an embossing roll was applied instead of embossing the first top coat, also had low breathability because the openings were too blocked. Furthermore, the grain-finished artificial leather obtained in Comparative Example 6, in which too much of the first polyurethane solution was applied and too many open interconnecting pores were formed, had excellent abrasion resistance but poor water resistance and breathability.

1 Substrate 2 Wet polyurethane porous layer 2a Laminated region of wet polyurethane porous layer (grain surface layer)
2b Lamination region of wet polyurethane porous layer (impregnated layer)
3 Top coat 10 Grain-finished artificial leather v Void h Communicating open hole

Claims (3)

A step of preparing a substrate including a fiber-entangled body and a wet-type porous polyurethane layer impregnated and laminated to the fiber-entangled body to be integrated therewith;
a step of gravure-coating a first polyurethane solution, in which a first polycarbonate-based polyurethane is dissolved, onto a surface of the wet polyurethane porous layer to dissolve the wet polyurethane porous layer and form open pores communicating in a thickness direction, and then drying the solution to form a first top coat;
embossing the first topcoat with a heated, textured embossing roll;
a step of gravure-coating a second polyurethane solution, in which a second polycarbonate-based polyurethane containing a silicone-modified polycarbonate- based polyurethane is dissolved, on the surface of the embossed first top coat, and then drying the second polyurethane solution to form a second top coat;
the total thickness of the first top coat and the second top coat is 1 to 5 μm ;
The first polyurethane solution contains a mixed solvent containing 50 to 80% by mass of N,N-dimethylformamide and 20 to 50% by mass of cyclohexanone, the concentration of the first polycarbonate-based polyurethane is 5 to 10% by mass, the Zahn cup viscosity at 20°C is 10 to 40 seconds, and the coating amount is 20 to 60 g/ ^m2 ;
The second polyurethane solution contains a mixed solvent containing 10 to 40% by mass of N,N-dimethylformamide, 25 to 35% by mass of cyclohexanone, and 20 to 40% by mass of acetone, the concentration of the second polycarbonate-based polyurethane is 5 to 10% by mass, the Zahn cup viscosity at 20°C is 10 to 40 seconds, and the coating amount is 20 to 60 g/ ^m2 ;
a method for producing a grain-finished artificial leather, characterized in that the opening diameter and number of the open holes are adjusted in each step so that the water resistance measured in accordance with the water resistance test (hydrostatic pressure method) Method A of JIS L 1092 (2009) "Testing methods for waterproofing of textile products" is 1000 mm or more, and the air permeability measured in accordance with the method specified in the air permeability test A (Fragile type method) of JIS L 1096 (2010) "Testing methods for woven and knitted fabrics" is 0.10 ^cm3 / ^cm2 ·s or more. A grain-finished artificial leather comprising: a fiber-entangled body; a wet-processed polyurethane porous layer impregnated with and laminated on the fiber-entangled body to be integrated; and a top coat having a thickness of 1 to 5 μm and containing a polycarbonate-based polyurethane,
The top coat contains a silicone-modified polycarbonate-based polyurethane and has a grained surface.
the wet polyurethane porous layer has open pores extending from the surface to the back surface of the wet polyurethane porous layer ,
the number of openings having a major axis of 0.5 μm or more and 40 μm or less per ^cm2 of the surface is 100 or more and less than 200, the number of openings having a major axis of more than 20 μm and 40 μm or less is 10 or more and less than 20, and the number of openings having a major axis of more than 40 μm is 0,
A grain-finished artificial leather characterized in that the water resistance measured in accordance with the water resistance test (hydrostatic pressure method) Method A of JIS L 1092 (2009) "Testing methods for waterproofness of textile products" is 1,000 mm or more, and the air permeability measured in accordance with the method specified in the air permeability test A (Fragile type method) of JIS L 1096 (2010) "Testing methods for woven and knitted fabrics" is 0.10 ^cm3 / ^cm2.s or more. 3. The grain-finished artificial leather according to claim 2 , wherein the number of openings having a major axis of 0.5 μm or more present per 1 ^cm2 of the surface is less than 200.

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