Artificial leather and method for producing artificial leather

Abstract

A problem to be solved by the present invention is to provide artificial leather excellent in hand, surface abrasion resistance, and pilling resistance, and a method for producing the artificial leather. The artificial leather of the present invention includes ultrafine fibers, in which in a cut surface cut at a depth of 0.3 mm from a surface, a maximum area of cut surfaces of an ultrafine fiber bundle is 4500 µm2 or more, and a number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm2 or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle.

Description

Technical Field

[0001] The present invention relates to artificial leather and a method for producing artificial leather.Background Art

[0002] A leather-like sheet such as artificial leather has flexibility and functionality not found in natural leather, and thus is used in various applications such as a clothing and material.

[0003] In addition, artificial leather is required to meet not only sensory requirements such as appearance (a surface texture more similar to that of natural leather), hand (a soft hand feeling combined with appropriate plumpness and fullness), and color development (vividness and depth of color) but also physical property requirements such as light resistance, pilling resistance, and abrasion resistance all at a high level. Various proposals have been made to address the problem.

[0004] For example, PTL 1 describes a leather-like sheet including an ultrafine fiber entangled body formed from an ultrafine fiber bundle and a polymer elastic body applied to the inside of the ultrafine fiber entangled body, in which the ultrafine fiber bundle is formed from ultrafine single fibers having an average cross-sectional area of 0.1 to 30 µm 2< , the average cross-sectional area of the ultrafine fiber bundle is 40 to 400 µm 2< , the ultrafine fiber bundle is present at a density of 600 to 4000 cross-sections per 1 mm 2< in an arbitrary cross-section parallel to a thickness direction of the ultrafine fiber entangled body. It is indicated that the leather-like sheet has luxurious appearance, exhibits good quality stability such as robustness and surface abrasion properties, and is excellent in practicality.

[0005] In addition, for example, PTL 2 describes a base material for artificial leather formed from an unwoven fabric structure of an ultrafine long fiber bundle, in which the ultrafine long fiber bundle has a cross-sectional area of 170 to 700 µm 2< and a flatness ratio of 4.0 or less, and the number of cross-sections of the ultrafine fiber bundle present in an arbitrary cross-section parallel to a thickness direction of the unwoven fabric structure falls within a range of 1500 to 3000 per 1 mm 2< . It is indicated that the base material for artificial leather mentioned above achieves, at high levels, both sensory performance and physical performance which have been heretofore considered mutually incompatible properties.Citation ListPatent Literature

[0006] PTL 1: WO2007 / 040144 PTL 2: JP2008-308784 A Summary of InventionTechnical Problem

[0007] Artificial leather is generally produced, for example, by a method in which staple fibers are obtained from multicomponent fibers spun from two kinds of polymers differing in solubility and degradability, the staple fibers are formed into a web having a desired weight using a carding machine, a cross-lapper, a random weber, or the like, the web is then formed into entangled unwoven fabric by entangling fibers each other by needle punching, water jetting, or the like, a solution or emulsion of a polymer elastic body as typified by polyurethane is subsequently applied to the entangled unwoven fabric and solidified, and thereafter one component in the multicomponent fibers is removed or the weight thereof is reduced to provide ultrafine fibers, or by a method in which the step of impregnation and solidification of the polymer elastic body and the step of making the multicomponent fibers into the ultrafine fibers are carried out in reverse order in the above-described method, as described in PTLs 1 and 2.

[0008] Although the techniques described in PTLs 1 and 2 improve the quality of artificial leather, there remain, for example, the following problems: fibers easily pull out, and abrasion resistance, pilling resistance, and the like of surfaces are not always sufficient; accordingly, there has been a demand for artificial leather capable of meeting sensory and physical requirements at higher levels.

[0009] In addition, although application of an organic solvent, a polymer elastic body, or the like to a surface of artificial leather can suppress pullout of fibers and improve abrasion resistance and pilling resistance of the surface to some extent, a higher cost is incurred, and there has been the following problem: when an organic solvent is used, human bodies and environment are adversely affected.

[0010] The present invention solves the above-described problems, and an object thereof is to provide artificial leather excellent in hand, surface abrasion resistance, and pilling resistance, and a method for producing the artificial leather.Solution to Problem

[0011] As a result of various studies, the present inventors have found that the above-described problems can be solved when, in a cut surface cut at a depth of 0.3 mm from a surface, a maximum area of cut surfaces of an ultrafine fiber bundle is a predetermined value or more, and a number ratio of the ultrafine fiber bundle is a predetermined value or more, and the present invention has been achieved. That is, the present invention encompasses the following aspects. [1] Artificial leather including ultrafine fibers, in which in a cut surface cut at a depth of 0.3 mm from a surface, a maximum area of cut surfaces of an ultrafine fiber bundle is 4500 µm 2< or more, and a number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle. [2] The artificial leather according to item [1] above, in which a total area of the ultrafine fiber bundle in the cut surface is 50000 µm 2< / mm 2< or more. [3] The artificial leather according to item [1] or [2] above, in which an average diameter of the ultrafine fibers is 7.5 µm or less. [4] The artificial leather according to any of items [1] to [3] above, in which an average fineness of the ultrafine fibers is 0.5 dtex or less. [5] The artificial leather according to any of items [1] to [4] above, in which the ultrafine fibers are long fibers. [6] The artificial leather according to any of items [1] to [5] above, including 45% by mass or less of a polymer elastic body. [7] A method for producing the artificial leather according to any of items [1] to [6] above, the method including: preparing a fiber web formed from ultrafine fiber-generating fibers; subjecting the fiber web to a crimping treatment to form a crimped fiber web; stacking a plurality of layers of the crimped fiber web to form a web laminate; entangling the web laminate to form an entangled fiber sheet; and removing at least one component from the ultrafine fiber-generating fibers. [8] The artificial leather production method according to items [7] above, further including impregnating the entangled fiber sheet with the polymer elastic body. Advantageous Effects of Invention

[0012] According to the present invention, artificial leather excellent in hand, surface abrasion resistance, and pilling resistance, and a method for producing the artificial leather can be provided. In addition, according to the present invention, artificial leather exhibiting the above-described effects can be obtained without applying an organic solvent or a polymer elastic body to a surface of the artificial leather.Brief Description of Drawings

[0013] [Fig. 1]Fig. 1 is an image obtained by capturing at a magnification of 100 a scanning electron microscope (SEM) photograph of a cut surface on the remaining side, when a piece of artificial leather according to the present invention is sliced off at a position at a depth of 0.3 mm from a surface using a single edged razor blade. [Fig. 2]Fig. 2 is an image (left-right reversed image of Fig. 1) obtained by printing the image of Fig. 1, placing the printed surface on a flat panel light, illuminating the image from the printed surface side to transmit the image through to the back surface, and blackening and transferring a cut surface portion of an ultrafine fiber bundle present in the cut surface from the back surface side. Description of Embodiments

[0014] Artificial leather according to an embodiment of the present invention and a method for producing artificial leather according to an embodiment of the present invention (hereinafter, also referred to as "the artificial leather of the present embodiment" and "the method for producing artificial leather of the present embodiment") will be described below.[Artificial leather]

[0015] The artificial leather of the present embodiment is artificial leather including ultrafine fibers, in which in a cut surface cut at a depth of 0.3 mm from a surface, the maximum area of cut surfaces of an ultrafine fiber bundle is 4500 µm 2< or more, and the number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle.

[0016] The artificial leather in which the maximum area of cut surfaces of the ultrafine fiber bundle is a predetermined value or more and the number ratio of the ultrafine fiber bundle is a predetermined value or more in a cut surface cut at a depth of 0.3 mm from a surface can be artificial leather excellent in hand, surface abrasion resistance, and pilling resistance.

[0017] Note that the artificial leather of the present invention refers to artificial leather that is artificially produced and has hand similar to that of natural leather, and includes napped artificial leather with a raised surface, grained artificial leather, and the like. Furthermore, the napped artificial leather includes suede-like leather, velour-like leather, nubuck-like leather, and the like as variations depending on the raised surface state.

[0018] In the present description, the "cut surface cut at a depth of 0.3 mm from a surface" means, in a case of the napped artificial leather, a cut surface obtained by slicing the napped artificial leather at a position at which the difference between the thickness of the napped artificial leather and the thickness from the surface opposite to the fiber napped surface to the cut surface is 0.3 mm, and means, in a case of the grained artificial leather, a cut surface obtained by slicing the grained artificial leather at a position at which the difference between the thickness of a fiber layer forming the grained artificial leather and the thickness from the surface opposite to the surface in contact with a resin layer of the fiber layer to the cut surface is 0.3 mm. Note that, the cut surface is a plane parallel to the plane direction of the artificial leather and is a plane perpendicular to the thickness direction.

[0019] In addition, in the present description, "excellent hand " refers to hand similar to that of natural leather, for example, being excellent in denseness, flexibility, and the like and having good tactile sensation.

[0020] Although the thickness of the artificial leather of the present embodiment is not particularly limited, from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, the thickness is preferably 0.1 to 2.0 mm, more preferably 0.3 to 1.5 mm, and still more preferably 0.5 to 1.2 mm.

[0021] Note that the "thickness" described above is a value measured in accordance with JIS L 1096(2010) (method A).

[0022] Although the apparent density of the artificial leather of the present embodiment is not particularly limited, from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, the apparent density is preferably 0.1 to 1.0 g / cm 3< , more preferably 0.2 to 0.9 g / cm 3< , and still more preferably 0.3 to 0.8 g / cm 3< .

[0023] Note that the "apparent density" described above is a value measured in accordance with JIS L 1096(2010) (method A).

[0024] Although the basis weight of the artificial leather of the present embodiment is not particularly limited, from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, the basis weight is preferably 100 to 1000 g / m 2< , more preferably 150 to 800 g / m 2< , and still more preferably 200 to 600 g / m 2< .

[0025] Note that the "basis weight" described above is a value measured in accordance with JIS L 1096(2010) (method A).

[0026] The artificial leather of the present embodiment is preferably napped artificial leather with a napped surface from the viewpoint of more readily achieving the effects of the present invention, but is not particularly limited thereto.<Ultrafine fibers>

[0027] The ultrafine fibers included in the artificial leather of the present embodiment are fibers fined by removing at least one component from multicomponent fibers (composite fibers) formed from at least two or more spinnable polymers having different chemical or physical properties. In addition, the ultrafine fiber bundle herein reefers to a bundle in which a plurality of the ultrafine fibers is gathered, and to an assembly of the ultrafine fibers in which three or more of the ultrafine fibers are gathered in proximity to each other, with distances between ultrafine fibers being 6 µm or less, and the total area of cut surfaces of the gathered ultrafine fibers is 60 µm 2< or more.

[0028] The ultrafine fibers of the present embodiment are preferably long fibers from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance.

[0029] In the present description, the "long fibers" refer to continuous fibers which are not short fibers intentionally cut after spinning. More specifically, for example, the "long fibers" refer to filaments or continuous fibers which are not short fibers intentionally cut to have a fiber length of about 3 to 80 mm. The fiber length of sea-island type composite fibers before being made into the ultrafine fibers described later is preferably 100 mm or more and more preferably 200 mm or more. As long as the fibers can be technically produced and are not unavoidably cut during production steps, the above-described long fibers may be continuous fibers which have a fiber length of several meters, several hundred meters, several kilometers, or even longer, are produced, for example, by a spunbond method, and are continuously spun. Note that some of the long fibers may be unavoidably cut into short fibers during a production step due to needle punching for entanglement or surface buffing.

[0030] Examples of a resin constituting the ultrafine fibers of the present embodiment include fibers of aromatic polyesters such as polyethylene terephthalate (hereinafter, sometimes referred to as "PET"), modified PET such as isophthalic acid-modified PET, sulfoisophthalic acid-modified PET, and cationic dye-dyeable PET, polybutylene terephthalate, and polyhexamethylene terephthalate; aliphatic polyesters such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polyhydroxybutyrate-polyhydroxyvalerate resins; nylons such as nylon 6, nylon 66, nylon 10, nylon 11, nylon 12, and nylon 6-12; and polypropylene, polyethylene, polybutene, polymethylpentene, and chlorine-based polyolefin. Note that the modified PET is PET in which at least a part of an ester-forming dicarboxylic acid-based monomer unit or diol-based monomer unit of unmodified PET is replaced with a substitutable monomer unit. Specific examples of a modification monomer unit for substituting the dicarboxylic acid-based monomer unit include units derived from isophthalic acid, sodium sulfoisophthalate, sodium sulfonaphthalenedicarboxylate, adipic acid, and the like for substituting the terephthalic acid unit. In addition, specific examples of a modification monomer unit for substituting the diol-based monomer unit include units derived from a diol such as butanediol or hexanediol substituting an ethylene glycol unit.

[0031] Among these, from the viewpoint of obtaining artificial leather excellent in colorability, surface abrasion resistance, and pilling resistance, a polyester-based resin such as an aromatic polyester or an aliphatic polyester is preferable. In addition, from the viewpoint of productivity in spinning, mechanical strength, and the like, aromatic polyesters such as polyethylene terephthalate (PET), modified PET such as isophthalic acid-modified PET, sulfoisophthalic acid-modified PET, and cationic dye-dyeable PET, polybutylene terephthalate, and polyhexamethylene terephthalate; aliphatic polyesters such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polyhydroxybutyrate-polyhydroxyvalerate resins; nylons such as nylon 6, nylon 66, nylon 10, nylon 11, nylon 12, and nylon 6-12; and polyolefins such as polypropylene, polyethylene, polybutene, polymethylpentene, and chlorine-based polyolefin are preferable.

[0032] The resin constituting the ultrafine fibers of the present embodiment may include various additives within a range not impairing the effects of the present invention. Examples of the additives include a catalyst, a coloring agent, a heat resistant agent, a flame retardant, a lubricant, an antifouling agent, a fluorescent brightener, a flatting agent, a gloss improver, an antistatic agent, a fragrance, a deodorant, an antibacterial agent, a mite repellent, and inorganic fine particles.

[0033] In the artificial leather of the present embodiment, the maximum area of cut surfaces of the ultrafine fiber bundle in a cut surface cut at a depth of 0.3 mm from a surface is 4500 µm 2< or more.

[0034] The maximum area of the cut surfaces of the ultrafine fiber bundle is preferably 5000 µm 2< or more, more preferably 5500 µm 2< or more, and still more preferably 6000 µm 2< or more from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, and is preferably 30000 µm 2< or less, more preferably 25000 µm 2< or less, and still more preferably 20000 µm 2< or less from the viewpoints of ease of production and obtaining artificial leather having excellent appearance. That is, the maximum area of the cut surfaces of the ultrafine fiber bundle is preferably 5000 to 30000 µm 2< , more preferably 5500 to 25000 µm 2< , and still more preferably 6000 to 20000 µm 2< .

[0035] Note that the "maximum area of cut surfaces of an ultrafine fiber bundle" described above is a value calculated on the basis of a photograph of a cut surface cut at a depth of 0.3 mm from a surface of the artificial leather captured using a scanning electron microscope (SEM) at a magnification of 100, and is specifically measured by the procedure described in the examples.

[0036] In the artificial leather of the present embodiment, the number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle in a cut surface cut at a depth of 0.3 mm from a surface.

[0037] The number ratio of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more with respect to the total number of the cut surfaces of the ultrafine fiber bundle is preferably 61% or more, more preferably 63% or more, and still more preferably 65% or more from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, and is preferably 95% or less, more preferably 93% or less, and still more preferably 90% or less from the viewpoint of deterioration in appearance due to a base material visually observed through gaps between napped fibers when the artificial leather has a fiber napped surface. That is, the above-described number ratio is preferably 61% to 95%, more preferably 63% to 93%, and still more preferably 65% to 90%.

[0038] Note that the "number ratio of cut surfaces of an ultrafine fiber bundle having an area of 500 µm 2< or more with respect to the total number of cut surfaces of the ultrafine fiber bundle" described above is a value calculated on the basis of a photograph of a cut surface cut at a depth of 0.3 mm from a surface of the artificial leather captured using a scanning electron microscope (SEM) at a magnification of 100, and is specifically measured by the procedure described in the examples.

[0039] The total area (a value obtained by converting the total value of areas of cut surfaces of the ultrafine fiber bundle to a value per 1 mm 2< ) of cut surfaces of the ultrafine fiber bundle in a cut surface cut at a depth of 0.3 mm from a surface is preferably 25000 µm 2< / mm 2< or more, more preferably 40000 µm 2< / mm 2< or more, and still more preferably 50000 µm 2< / mm 2< or more from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, and is preferably 200000 µm 2< / mm 2< or less, more preferably 180000 µm 2< / mm 2< or less, and still more preferably 150000 µm 2< / mm 2< or less from the viewpoints of ease of production and obtaining artificial leather having good tear strength. That is, the total area of the cut surfaces of the ultrafine fiber bundle is preferably 25000 to 200000 µm 2< / mm 2< , more preferably 40000 to 180000 µm 2< / mm 2< , and still more preferably 50000 to 150000 µm 2< / mm 2< .

[0040] Note that the "total area of cut surfaces of an ultrafine fiber bundle" is a value calculated on the basis of a photograph of a cut surface cut at a depth of 0.3 mm from a surface of the artificial leather captured using a scanning electron microscope (SEM) at a magnification of 100, and is specifically measured by the procedure described in the examples.

[0041] The average diameter of the ultrafine fibers of the present embodiment is preferably 7.5 µm or less, more preferably 6.0 µm or less, still more preferably 5.5 µm or less, and yet still more preferably 5.0 µm or less from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance. The lower limit is not particularly limited, but is, for example, 1.0 µm or more or 1.5 µm or more from the viewpoints of ease of production and color development. In other words, the average diameter of the ultrafine fibers of the present embodiment is preferably 1.0 to 7.5 µm and more preferably 1.5 to 6.0 µm.

[0042] The average fineness of the ultrafine fibers of the present embodiment is preferably 0.50 dtex or less, more preferably 0.40 dtex or less, and still more preferably 0.30 dtex or less from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance. The lower limit is not particularly limited, but is, for example, 0.01 dtex or more or 0.02 dtex or more from the viewpoints of ease of production and color development. In other words, the average fineness of the ultrafine fibers of the present embodiment is preferably 0.01 to 0.50 dtex and more preferably 0.01 to 0.40 dtex.

[0043] Note that the "average diameter" and the "average fineness" described above are values calculated on the basis of measured cross-sectional areas of randomly selected multiple ultrafine fibers in an enlarged photograph of a cross-section of the ultrafine fibers, and are specifically measured by the procedure described in the examples.<Polymer elastic body>

[0044] The artificial leather of the present embodiment may include a polymer elastic body.

[0045] Any polymer elastic body heretofore used in artificial leather can be employed as the polymer elastic body, and specific examples thereof include a polyurethane elastomer, an acrylonitrile elastomer, an olefin elastomer, a polyester elastomer, and an acrylic elastomer, and a polyurethane elastomer and an acrylic elastomer are preferable.

[0046] Examples of the polyurethane elastomer include various polyurethane elastomers obtained by combining as main components: at least one polymer polyol having an average molecular weight of 500 to 3000 selected from a polyester diol, a polyether diol, a polyether ester diol, a polycarbonate diol, a polycarbonate ether diol, a polycarbonate ester diol, and the like; and at least one polyisocyanate selected from an aromatic diisocyanate, an alicyclic diisocyanate, an aliphatic diisocyanate, and the like, such as 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate, further combining at least one low molecular weight compound having two or more active hydrogen atoms such as ethylene glycol and ethylenediamine at a predetermined molar ratio, and subjecting same to a polymerization reaction in one step or in multiple steps using a melt polymerization method, a bulk polymerization method, a solution polymerization method, or the like.

[0047] The content of the polymer polyol component in the polyurethane elastomer is preferably 15% to 90% by mas.

[0048] In addition, examples of the acrylic elastomer include various acrylic elastomers obtained by subjecting, to a polymerization reaction, a monomer which exhibits a glass transition temperature within a range of -90°C to -5°C when polymerized into a homopolymer and which is preferably a non-crosslinkable monomer, such as at least one soft component selected from the group consisting of methyl acrylate, n-butyl acrylate, isobutyl acrylate, isopropyl acrylate, n-hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; a monomer which exhibits a glass transition temperature within a range of 50°C to 250°C when polymerized into a homopolymer and which is preferably a non-crosslinkable monomer, such as at least one hard component selected from the group consisting of methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, and (meth)acrylic acid; and a monofunctional or polyfunctional ethylenically unsaturated monomer unit capable of forming a cross-linked structure, or a compound capable of reacting with an ethylenically unsaturated monomer unit introduced into a polymer chain to form a cross-linked structure, such as an ethylenically unsaturated monomer including at least one cross-link forming component selected from the group consisting of ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate.

[0049] Artificial leather obtained by employing the polyurethane elastomer as the main polymer elastic body is excellent in balance of hand and mechanical properties, and is also preferable from the point of excellent balance including durability when the kind is appropriately selected. In addition, artificial leather obtained by employing the acrylic elastomer is not suitable for forming napped artificial leather, since the acrylic elastomer has lower adhesion to the ultrafine fiber bundle compared to the polyurethane elastomer and thus provides poor napped fiber fixation effect when napped fibers are formed; however, since the degree of hand hardening relative to the content is suppressed, the acrylic elastomer is particularly preferable when grained artificial leather is formed.

[0050] Different types of the polymer elastic body may be mixed and contained, or different types of the polymer elastic body may be added in multiple steps, and the polymer elastic body may also be contained as a polymer elastic body composition to which a polymer elastic body such as synthetic rubber is added as necessary in addition to the main polymer elastic body such as the polyurethane elastomer, the acrylonitrile elastomer, the olefin elastomer, and the polyester elastomer, and the acrylic elastomer as described above.

[0051] The content of the polymer elastic body in the artificial leather is preferably 5% to 45% by mass, more preferably 7% to 40% by mass, and still more preferably 8% to 30% by mass from the viewpoint of obtaining artificial leather excellent in hand.<Other components>

[0052] The artificial leather of the present embodiment may include a component other than the ultrafine fibers and the polymer elastic body or may include no other components. Examples of such other components include the same components as those included in the ultrafine fibers described above and various additives which may be added to the polymer elastic body liquid described later in relation to step (4). The above-mentioned other components may be contained in at least one of the ultrafine fibers and the polymer elastic body.

[0053] The content of each of the other components is preferably 0.5% to 10.0% by mass, more preferably 1.0% to 5.0% by mass, and still more preferably 1.5% to 3.0% by mass with respect to the mass of the artificial leather from the viewpoint of facilitating expression of intended effects of the above-described other components and the viewpoints of water absorbency, water repellency, stain resistance, and the like.[Method for producing artificial leather]

[0054] The artificial leather according to the present embodiment is preferably produced by a production method including the following steps (1) to (4) and (6). Step (1): a step of preparing a fiber web formed from ultrafine fiber-generating fibers Step (2): a step of subjecting the fiber web to a crimping treatment to form a crimped fiber web Step (3): a step of stacking a plurality of layers of the crimped fiber web to form a web laminate Step (4): a step of entangling the web laminate to form an entangled fiber sheet Step (6): a step of removing at least one component from the ultrafine fiber-generating fibers

[0055] In addition, from the viewpoint of imparting hand similar to that of natural leather, morphological stability, and the like, the following step (5) may be provided, and from the viewpoint of providing more excellent hand, the following step (7) may be provided. Step (5): a step of impregnating the entangled fiber sheet with the polymer elastic body Step (7): a step of dyeing the artificial leather

[0056] The step (5) is preferably carried out between the step (4) and the step (6), and the step (7) is preferably carried out after the step (6).

[0057] When the production method according to the present embodiment includes the step (2), artificial leather in which in a cut surface cut at a depth of 0.3 mm from a surface, the maximum area of cut surfaces of the ultrafine fiber bundle is 4500 µm 2< or more, and the number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle is easily obtained. As a result, artificial leather excellent in hand, surface abrasion resistance, and pilling resistance is easily obtained.

[0058] Each step will be described below.<Step (1)>

[0059] The step (1) is a step of preparing a fiber web formed from ultrafine fiber-generating fibers.

[0060] As described above, the ultrafine fibers are fined by removing at least one component from multicomponent fibers (composite fibers) formed from at least two or more spinnable polymers having different chemical or physical properties, and the multicomponent fibers generating the ultrafine fibers are the ultrafine fiber-generating fibers. Representative examples of the ultrafine fiber-generating fibers include sea-island type composite fibers, multilayer laminated composite fibers, and radial laminated composite fibers obtained by using a method such as a chip blending (blend spinning) method or a composite spinning method. Among these, sea-island type composite fibers are preferable from the viewpoints of enhancing productivity because of high-speed spinning and obtaining artificial leather excellent in surface abrasion resistance and pilling resistance, and it is preferable that the sea-island type composite fibers be subjected melt spinning to obtain the fiber web from the same viewpoints.

[0061] In the case where the ultrafine fiber-generating fibers are the sea-island type composite fibers, an island component is dispersed in a sea component to be a matrix in a fiber cross-section, and the ultrafine fibers in a fiber bundle state are generated by removing the sea component.

[0062] A method for obtaining the fiber web by using the sea-island type composite fibers as the ultrafine fiber-generating fibers and subjecting the sea-island type composite fibers to melt spinning is described in more detail below.

[0063] Examples of a resin included in the sea-island type composite fibers as the island component to be the ultrafine fibers later include resins similar to those for the resin constituting the ultrafine fibers in the "ultrafine fibers" described above.

[0064] As a resin included in the sea-island type composite fibers as the sea component to be removed by extraction, decomposition, or the like, a resin having solubility or degradability different from that of the resin for the island component and having low compatibility with the resin for the island component is preferably used. It is preferable that such a resin be appropriately selected according to the kind and production method of the resin for the island component.

[0065] Examples of the resin for the sea component include resins that are dissolved in an organic solvent and can be removed by an organic solvent through dissolution, such as olefin-based resins such as polyethylene, polypropylene, ethylene-propylene copolymers, and ethylene-vinyl acetate copolymers, polystyrenes, styrene-acrylic copolymers, and styrene-ethylene copolymers. Examples thereof also include resins capable of being removed by a treatment using only water without using any solvents, such as polyvinyl alcohol-based resins, water-soluble polyester resins, modified polyester resins easily decomposed by an alkali, polyacrylamide resins, and carboxymethyl cellulose resins. Among these, polyethylene or a polyvinyl alcohol-based resin is preferably used from the viewpoints of melt spinnability, water solubility, and fiber physical properties (fiber strength), and polyethylene and a modified polyvinyl alcohol are more preferable.

[0066] As the kinds of copolymer monomers used in the modified polyvinyl alcohol, α-olefins having 4 or less carbon atoms such as ethylene, propylene, 1-butene, and isobutene; and vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether are preferable from the viewpoints of copolymerizability, melt spinnability, and water solubility of fibers.

[0067] The content of the copolymer unit in the polyvinyl alcohol is preferably 1 to 20 mol%, more preferably 4 to 15 mol%, and still more preferably 6 to 13 mol%.

[0068] Furthermore, an ethylene-modified polyvinyl alcohol is more preferable since the fiber physical properties are enhanced when the copolymer unit is ethylene. The ethylene unit content in the ethylene-modified polyvinyl alcohol is preferably 4 to 15 mol% and more preferably 6 to 13 mol%.

[0069] The mass ratio between the sea component and the island component in the sea-island type composite fibers is not particularly limited but preferably falls within the range in which sea component:island component = 5:95 to 80:20, for example. When the sea component polymer ratio in the sea-island type composite fibers is 5% by mass or more, spinning stability of the sea-island type fibers is hardly reduced, and industrial productivity is easily ensured. In addition, when the polymer elastic body is applied, a void with a necessary size is easily formed between the ultrafine fiber bundle and the polymer elastic body after removing the sea component; as a result, plumpness, fullness, dense surface texture, and the like are easily obtained. On the other hand, when the sea component polymer ratio is 60% by mass or less, the shape and distribution state of the island component in a cross-section of the sea-island type fibers are stabilized, and deterioration of quality stability is easily prevented.

[0070] As a method for producing the fiber web, a method in which the ultrafine fiber-generating fibers melt-spun using by a so-called spunbond method are collected on a net without being cut, thereby forming a fiber web of long fibers, which are continuous fibers, is preferably employed.

[0071] Specifically, a melt strand of sea-island type composite fibers is continuously discharged at a predetermined discharge rate from a spinning nozzle using a composite spinning spinneret having a plurality of nozzle holes arranged in a predetermined pattern, a high-speed airflow is applied using a suction device such as an air-jet nozzle described later, while substantially cooling and solidifying the strand with cooling air at any point between directly below the nozzle holes and the suction device to uniformly draw and fine the composite fibers so that the composite fibers have a desired diameter or fineness.

[0072] The high-speed airflow is applied such that the average spinning speed corresponding to the mechanical take-up speed in normal spinning falls within the range of 1000 to 6000 m / min. Furthermore, a fiber web of long fibers can be produced by a spunbond method in which, depending on the formation of the fiber web obtained, the composite fibers are spread by a collision plate, an air current, or the like, and are simultaneously collected and deposited on a collecting plane such as a conveyer belt-like mobile net while being suctioned from the opposite side of the net, thereby forming the fiber web. In addition, the fiber web may be subjected to hot-pressing to impart morphological stability, and the fiber web may be fused accordingly.

[0073] When the basis weight or thickness of the obtained fiber web is insufficient, the fiber web is adjusted to achieve a desired basis weight and thickness by wrapping (supplying a single layer of the fiber web from a direction perpendicular to the direction in which the process flows and folding the fiber web substantially in the widthwise direction (transverse direction), or folding the web supplied from a direction parallel to the direction in which the process flows in the length direction (longitudinal direction)) or by layering (stacking a plurality of layers of the fiber web). When morphological stability, fiber denseness, orientation in the thickness direction of the sea-island type fibers, and the like are adjusted, mechanical entanglement processing is performed by a known method such as a needle punching method. Fibers constituting the fiber web, in particular, fibers between adjacent layers of the layered fiber web obtained by wrapping or layering are three-dimensionally entangled with each other as a result.

[0074] When the entanglement processing is performed by a needle punching method, various processing conditions such as the needle type (including the shape and gauge of a needle, the shape and depth of a barb, and the number and arrangement of barbs), the number of needle punches (needle punching processing density per unit area calculated by multiplying the density of needles embedded in a needle board by the number of strokes of the board applied to the fiber web per unit area), and the needle punching depth (depth to which the needle penetrates the fiber web) are appropriately selected and implemented.

[0075] An example of the entanglement processing is a method in which needle punching or high-pressure water stream treatment is performed under conditions where at least one or more barbs penetrate from both sides either simultaneously or alternately. In addition, the punching density in the needle punching processing is preferably 1500 to 5500 punches per 1 cm 2< and further preferably 2000 to 5000 punches per 1 cm 2< from the point of easily obtaining high abrasion resistance. When the punching density falls within the above ranges, insufficient entanglement is suppressed, thereby preventing a surface of the artificial leather from becoming a rough surface due to fiber fraying, and breakage of the fibers is also suppressed, thereby preventing a decrease in the degree of entanglement.<Step (2)>

[0076] The step (2) is a step of subjecting the fiber web to a crimping treatment to form a crimped fiber web.

[0077] Examples of the crimping treatment include physical mechanical crimping methods such as a method of passing the fiber web between two gears, a method of using a forced feeding roller (forced feed crimping), a method of bending and rubbing the fiber web against a knife edge, a method of jetting air, and a method of twisting yarn; a latent crimping method using multicomponent fibers, hollow fibers, or the like with different heat shrinkage properties; and a method of combining these methods. The crimping treatment is preferably a physical mechanical method capable of stably subjecting fibers to crimping across a wide range, and forced feed crimping is more preferable from the viewpoint of imparting an appropriate crimp ratio to fibers. Among forced feed crimping methods, forced feed crimping carried out by pressing with a roller on which an uneven shape is formed is preferable from the viewpoint of obtaining artificial leather with good process passability and more excellent in hand, surface abrasion resistance, and pilling resistance. The uneven shape is preferably a periodic uneven shape from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, and an average height difference between a concave portion and a convex portion is preferably 1 to 30 mm, more preferably 1.5 to 25 mm, and still more preferably 2 to 20 mm. A distance between concave portions and a distance between convex portions are preferably 1 to 30 mm, more preferably 1.5 to 25 mm, and still more preferably 2 to 20 mm.

[0078] The crimp ratio in subjecting the fiber web to the crimping treatment by pressing the fiber web with a roller on which a periodic uneven shape is formed is preferably 120% or more, more preferably 150% or more, and still more preferably 170% or more from the viewpoint of obtaining artificial leather more excellent in hand, surface abrasion resistance, and pilling resistance, and is preferably 300% or less, more preferably 250% or less, and still more preferably 220% or less from the viewpoint of ease of production. That is, the crimp ratio is preferably 120% to 300%, more preferably 150% to 250%, and still more preferably 170% to 220%.

[0079] Note that the "crimp ratio" described above is a ratio (length along uneven shape of uneven roller / length of fiber web before crimping treatment × 100 (%)) between the length along the uneven shape of the uneven roller described above and the length of the fiber web before the crimping treatment.

[0080] Furthermore, after the crimping treatment, a spray-applied oil or a finishing oil may be applied to the crimped fiber web as long as no adverse effects are caused.<Step (3)>

[0081] The step (3) is a step of stacking a plurality of layers of the crimped fiber web to form a web laminate.

[0082] As a method of stacking a plurality of layers of the crimped fiber web, layers of the crimped fiber web may be stacked with the crimping directions of all of the crimped fiber web aligned in the same direction, or layers of the crimped fiber web may be stacked in a cross-lapping manner by changing the conveying direction of the crimped fiber web by 90 degrees and folding the crimped fiber web back while stacking. The method of stacking the plurality of layers of the crimped fiber web is preferably cross-lapping lamination from the viewpoints of easily adjusting the width of the entangled fiber sheet to an arbitrary width and being capable of suppressing occurrence of irregularity in the width direction of the entangled fiber sheet, that is, from the viewpoint of suppressing unevenness of basis weight.

[0083] The number of layers of the fiber web stacked is not particularly limited but is preferably two layers or more and more preferably three layers or more from the viewpoints of reducing basis weight irregularity of the entangled fiber sheet and mechanical strength, and is preferably 30 layers or less and more preferably 25 layers or less from the viewpoint of ease of production. That is, the number of layers of the fiber web stacked is preferably 2 to 30 layers and more preferably 3 to 25 layers.<Step (4)>

[0084] The step(4) is a step of entangling the web laminate to form an entangled fiber sheet.

[0085] In the step (4), fibers constituting the fiber web, in particular, fibers between adjacent layers of the layered fiber web obtained by wrapping or layering are three-dimensionally entangled with each other by subjecting the web laminate to mechanical entanglement processing using a known method such as a needle punching method or high-pressure water stream treatment.

[0086] When the entanglement processing is performed by a needle punching method, various processing conditions such as the needle type (including the shape and gauge of a needle, the shape and depth of a barb, and the number and arrangement of barbs), the number of needle punches (needle punching processing density per unit area calculated by multiplying the density of needles embedded in a needle board by the number of strokes of the board applied to the fiber web per unit area), and the needle punching depth (depth to which the needle penetrates the fiber web) are appropriately selected and implemented.

[0087] When the web laminate in which crimped fiber web layers are laminated is used and subjected to the entanglement processing using a needle punching method, the crimped fiber web catches on a barb, and the fibers drag along many surrounding fibers as the fibers move, the amount of fibers oriented in the thickness direction increases, and the degree of entanglement increases. As a result, pullout of fibers caused by surface friction is suppressed, and abrasion resistance and pilling resistance are improved. Therefore, the entanglement processing is preferably performed by a needle punching method using the web laminate in which the crimped fiber web layers are laminated.

[0088] The punching density in the needle punching processing is preferably 1500 to 5500 punches per 1 cm 2< and further preferably 2000 to 5000 punches per 1 cm 2< from the viewpoint of easily obtaining high abrasion resistance. When the punching density falls within the above ranges, insufficient entanglement is suppressed, thereby preventing a surface of the artificial leather from becoming a rough surface due to fiber fraying, and breakage of the fibers is also suppressed, thereby preventing a decrease in the degree of entanglement.

[0089] In addition, at any stage from the spinning of the sea-island type composite fibers to the entangling processing, an oil agent or an antistatic agent may be applied to the ultrafine fiber-generating fibers, fiber web, crimped fiber web, web laminate, entangled fiber sheet, and the like. Furthermore, as necessary, a shrinkage treatment may be performed by immersing the ultrafine fiber-generating fibers, fiber web, crimped fiber web, web laminate, entangled fiber sheet, and the like in hot water at about 70°C to 150°C to preliminarily densify the entangled state.

[0090] The basis weight of the entangled fiber sheet obtained through entanglement preferably falls within the range of about 100 to 2000 g / m 2< . Furthermore, the entangled fiber sheet may be subjected to a treatment in which the fiber density and degree of entanglement are further increased through heat shrinkage, as necessary. In addition, for the purpose of further densifying the entangled fiber sheet that has been densified by the heat shrinkage treatment as well as fixing the morphology of the entangled fiber sheet, smoothening the surface of the entangled fiber sheet, and the like, the fiber density may be further increased by performing a hot-pressing treatment, as necessary.<Step (5)>

[0091] The step (5) is a step of impregnating the entangled fiber sheet with the polymer elastic body.

[0092] In the step (5), the entangled fiber sheet is impregnated with the polymer elastic body in at least one stage among: a stage before removal of the sea component; and a stage after removal of the sea component.

[0093] In the artificial leather production of the present embodiment, it is preferable that the entangled fiber sheet be impregnated with the polymer elastic body before removal of the sea component in order to impart hand similar to that of natural leather and morphological stability and also impart flexibility.

[0094] By imparting the polymer elastic body through impregnation before removal of the sea component in this manner, a void formed through removal of the sea component is formed between the ultrafine fibers forming the fiber bundle after the removal of the sea component. As a result, the ultrafine fibers inside the fiber bundle are less likely to be constrained by the polymer elastic body, that is, the ultrafine fiber bundle is less likely to be affected by the polymer elastic body, and artificial leather with excellent flexibility is easily obtained. Note that when the polymer elastic body is imparted, through impregnation, to the ultrafine fibers forming the fiber bundle after the sea component is removed from the sea-island type composite fibers, through penetration of the polymer elastic body into the void of the fiber bundle, the ultrafine fibers forming the fiber bundle are constrained by the polymer elastic body to provide artificial leather having stiff hand.

[0095] When the polymer elastic body is applied to the entangled fiber sheet, a non-aqueous polymer elastic body liquid in which the polymer elastic body is dissolved or dispersed in a solvent may be used, or an aqueous polymer elastic body liquid in which the polymer elastic body is dispersed in an aqueous medium with a dispersant as necessary may be used. In the former case, a uniform polymer elastic body liquid is easily obtained, and in the latter case, the amount of an organic solvent used can be more easily reduced.

[0096] The concentration of the polymer elastic body liquid, that is, the content of the polymer elastic body in the polymer elastic body liquid is preferably 0.1% to 60% by mass.

[0097] Various additives including a coloring agent such as a dye or a pigment, a solidification modifier, an antioxidant, an ultraviolet absorber, a fluorescent agent, an antifungal agent, a penetrant, a defoaming agent, a lubricant, a water repellent, an oil repellent, a thickener, an extender, a curing accelerator, a foaming agent, and a water-soluble polymer compound such as polyvinyl alcohol or carboxymethyl cellulose may be appropriately added to the polymer elastic body liquid, within a range not impairing properties of artificial leather finally obtained.

[0098] The details of the polymer elastic body used in the step (5) are as described in the above section titled "polymer elastic body."

[0099] The polymer elastic body may be fixed into the entangled fiber sheet by impregnating the entangled fiber sheet with the polymer elastic body, and then solidifying the polymer elastic body using a conventionally known dry or wet method. The dry method herein refers generally to a method of fixing the polymer elastic body within the fiber sheet structure by removing a solvent, a dispersant, and the like through drying or the like. In addition, the wet method herein refers generally to a method of temporarily or completely fixing the polymer elastic body within the entangled fiber sheet structure prior to removal of the dispersant by treating the entangled fiber sheet structure impregnated with the polymer elastic body liquid using a non-solvent or a coagulating agent for the polymer elastic body or by subjecting the entangled fiber sheet after impregnation to a thermal treatment or the like using the aqueous polymer elastic body liquid to which a thermosensitive gelling agent or the like is added.<Step (6)>

[0100] The step (6) is a step of removing at least one component from the ultrafine fiber-generating fibers. The one component is preferably a resin of the sea component included in the sea-island type composite fibers. The ultrafine fiber-generating fibers can be converted into the fiber bundle of the ultrafine fibers by removing the sea component.

[0101] Examples of a method of removing the resin of the sea component include a removal method using a solvent or decomposing agent capable of selectively removing only the resin of the sea component.

[0102] When the sea component is a water-soluble resin such as a polyvinyl alcohol-based resin, a water-soluble polyester resin, a modified polyester resin readily decomposable by alkali, a polyacrylamide resin, or a carboxymethyl cellulose resin, the sea component can be removed by water.

[0103] When the sea component is not soluble in water but soluble in an organic solvent and the resin for the island component is a polyamide-based resin or a polyester-based resin, examples of the organic solvent for dissolving and removing the sea component include toluene, trichloroethylene, and tetrachloroethylene.

[0104] In the present embodiment, it is preferable to use water from the viewpoint of environmental compatibility, and it is preferable to use toluene, which has high resin dissolving power, for resins that are poorly soluble in water.

[0105] A dip-nip treatment is preferably performed in parallel when removing the sea component.

[0106] In addition, between the melt spinning of the sea-island type composite fibers to obtain a web and the removal of the sea component, a heat shrinkage treatment (fiber shrinkage treatment) with steam, hot water, dry heat, or the like may be performed to densify the fibers.<Step (7)>

[0107] The step (7) is a step of dyeing the artificial leather.

[0108] The step (7) may be executed at any stage after the sea-island type fibers have been converted into the ultrafine fiber bundle.

[0109] In the step (7), any dyeing method using a known dyeing machine heretofore commonly used for dyeing artificial leather such as a padder dyeing machine, a jigger dyeing machine, a circular dyeing machine, or a winch dyeing machine can be adopted, using a dye based on a disperse dye, a reactive dye, an acid dye, a metal complex dye, a sulfur dye, a sulfur vat dye, or the like appropriately selected depending on the type of the fibers.

[0110] In addition, besides dyeing, a finishing treatment such as a mechanical crumpling treatment in a dry state, a relaxation treatment in a wet state using a dyeing machine, a washing machine, or the like, a softening agent treatment, a functionality imparting treatment with a flame retardant, an antibacterial agent, a deodorant, a water / oil repellent, or the like, tactile modifier imparting treatment with a silicone-based resin, a silk protein-containing treatment agent, a grip property imparting resin, or the like, or a design imparting treatment of applying a resin other than the above-described resins, such as a coloring agent or an enamel-like coating resin may also be performed as necessary.

[0111] The artificial leather of the present embodiment may be sliced into a plurality of pieces in the thickness direction as necessary, and the thickness may be adjusted by, for example, grinding the surface serving as a back surface, or a solvent capable of dissolving or swelling the polymer elastic body or the ultrafine fiber bundle may be applied to the surface serving as the back surface, as in conventional artificial leather production.

[0112] The artificial leather of the present embodiment may have a fiber napped surface.

[0113] Any known method such as a buffing treatment with sandpaper, wire cloth, or the like, or a brushing treatment can be used for forming a fiber napped surface. In addition, either before or after such a raising treatment, a solvent capable of dissolving or swelling the polymer elastic body or the ultrafine fiber bundle, for example, a treatment liquid containing dimethylformamide (DMF) or the like, a treatment liquid containing a phenolic compound such as resorcinol, or the like in the case where the polymer elastic body is a polyurethane elastomer may be applied to the surface to be subjected to the raising treatment. Consequently, it is possible to finely adjust the constraint state of the ultrafine fiber bundle due to adhesion of the polymer elastic body and the ultrafine fiber bundle, the length of the napped ultrafine fibers of the artificial leather, the surface friction durability, and the like.

[0114] In addition, dyed artificial leather may be obtained by carrying out the above-described step (7) after performing the raising treatment described above.Examples

[0115] The present invention will be described more specifically with reference to examples below. Note that the scope of the present invention is not limited at all by the contents of the examples.

[0116] First, measurement and evaluation methods used in Examples and Comparative Examples described later will be summarized and described below.<Average diameter>

[0117] The average diameter of polyester fibers was measured as follows.

[0118] A scanning electron microscope (SEM) photograph of a cross-section of artificial leather was captured at a magnification of 3000. Then, 10 cross-sections of the fibers were randomly selected from the SEM photograph, and the cross-sectional areas thereof were measured. An arithmetic mean value of the cross-sectional areas was calculated, and a value calculated based on the following formula (1) was taken as an average diameter of the fibers. average diameter = average cross - sectional area / π 1 / 2 × 2<Average fineness>

[0119] The average fineness of polyester fibers was measured as follows.

[0120] A scanning electron microscope (SEM) photograph of a cross-section of artificial leather was captured at a magnification of 3000. Then, 10 cross-sections of the fibers were randomly selected from the SEM photograph, the cross-sectional areas thereof were measured, and an arithmetic mean value of the cross-sectional areas was calculated. Then, the average value of the cross-sectional areas was converted to the average fineness using the density of the resin.<Content of polymer elastic body>

[0121] The mass C of artificial leather cut to be a size having a mass of 1 g or more was measured. When the polymer elastic body was dissolved in N,N-dimethyl formamide (DMF), the artificial leather was immersed in 300 mL of DMF at room temperature for 5 hours, DMF was then removed by compression, DMF obtained by compression was poured into water, and the process from immersion in DMF to compression was repeated while replacing DMF under the same conditions until water was no longer turbid to remove the polymer elastic body from the artificial leather. The polyester fibers remaining after the polymer elastic body had been removed from the artificial leather were dried to remove DMF, and the mass D of the dried polyester fibers was measured. Then, the content of the polymer elastic body in the artificial leather was determined based on the following formula (2). content of polymer elastic body = C - D / C × 100

[0122] When the polymer elastic body was not dissolved in DMF, the artificial leather was immersed in 300 mL of hexafluoro-2-propanol (HFIP) at room temperature (25°C) for 12 hours to dissolve the polyester fibers, the remaining solid content was taken out through filtration, washed with HFIP, subsequently dried to remove HFIP, and the mass E of the obtained solid was measured. Then, the content of the polymer elastic body in the artificial leather was determined based on the following formula (3). content mass % of polymer elastic body = E / C × 100

[0123] Note that the "solid content" means a component excluding solvents and liquid dispersants. That is, the "solid content" means a component excluding liquids.<Thickness, basis weight, and apparent density>

[0124] In accordance with JIS L 1096(2010) (method A), using a thickness measuring device (gauge diameter: 10 mm), the thickness (mm) and the basis weight (g / m 2< ) of the obtained artificial leather were measured under a constant pressure of 23.5 kPa applied for 5 seconds, and the apparent density (g / cm 3< ) of the artificial leather was calculated from these values.<Measurement of area and number of ultrafine fiber bundle cross sections>

[0125] A piece of artificial leather was prepared, and the back side (the side on which neither napped fibers nor a resin layer was formed) thereof was fixed to a base using double-sided adhesive tape. The artificial leather piece was sliced at a position at a depth of 0.3 mm from the surface of the artificial leather using a single edged razor blade to remove the surface side, and a scanning electron microscope (SEM) photograph of the cut surface on the remaining side was captured at a magnification of 100. The photograph was printed (see Fig. 1), the printed surface was placed on a flat panel light and illuminated from the printed surface side to transmit the image through to the back surface, a cut surface portion of the ultrafine fiber bundle present in the cut surface was blackened from the back surface side (see Fig. 2), and the area of cut surfaces of the ultrafine fiber bundle and the number of cut surfaces of the ultrafine fiber bundle were measured using Image-Pro Premier ver. 9.1 (manufactured by NIPPON ROPER KK). The maximum value of the areas of the cut surfaces of the ultrafine fiber bundle was taken as the maximum area of the cut surfaces of the ultrafine fiber bundle. In addition, the total value of the areas of the cut surfaces of the ultrafine fiber bundle was converted into a value per 1 mm 2< and taken as the total ultrafine fiber bundle are. Further, the ratio of the number of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more to the total number of the cut surfaces of the ultrafine fiber bundle was calculated.<20% Strength>

[0126] A specimen was prepared by cutting the obtained artificial leather to have a size of 16 cm in length and 2.5 cm in width. The specimen was placed between grips of a tensile tester adjusted to provide a gauge length of 10 cm so that the artificial leather was extended in the longitudinal direction (process flow direction in the step (3)), and an S-S curve was measured using an autograph at a tensile speed of 100 mm / min. The above procedure was carried out three times. From the obtained S-S curve, the strength at 20% elongation was read, and the average value of the three measurements was taken as the 20% strength (kgf / 2.5 cm) in the longitudinal direction.

[0127] In addition, the 20% strength (kgf / 2.5 cm) in the transverse direction was calculated in the same manner as described above except that the specimen was placed between the grips of the tensile tester so that the artificial leather was extended in the transverse direction (direction at 90° to the process flow direction in the step (3)) perpendicular to the longitudinal direction of the artificial leather.<Abrasion loss>

[0128] In accordance with JIS L 1096 (2020) (8.19.5, method E, Martindale method), a Martindale abrasion tester was used to conduct a test under conditions of a pressing load of 12 kPa (gf / cm 2< ) and 35,000 abrasion cycles, and the abrasion loss of the surface of the artificial leather was calculated.<Pilling>

[0129] In accordance with JIS L 1096 (2020) (8.19.5, method E, Martindale method), a Martindale abrasion tester was used to conduct a test with the abrasion cycle number shown in Table 1 under a pressing load of 12 kPa (gf / cm 2< ), and the surface pilling of the artificial leather after the test was determined based on visual observation and tactile assessment according to the following criteria. A: No aggregated fiber pill is observed, and the tactile sensation is smooth and pleasant. B: Although fiber aggregation is slightly observed, no pill is detected, and the tactile sensation is slightly rough. C: Aggregated fiber pills are observed, and the tactile sensation is rough. <Hand>

[0130] The hand of the obtained artificial leather after bending was determined by visual observation and tactile assessment according to the following criteria. A: Hand with fullness and excellent flexibility without buckling wrinkles (generation of creases due to buckling). B: Hand corresponding to one or more of: lack of fullness; occurrence of buckling (generation of creases due to buckling), and stiff. <Appearance>

[0131] The appearance of the obtained artificial leather was visually observed and determined according to the following criteria. A: The fibers are finely separated and have a uniform length without aggregation and formation of clumps. B: The fibers are aggregated, loosely separated, and have non-uniform lengths. [Example 1]

[0132] A fiber web including sea-island type composite fibers having an average fineness of 2.95 dtex was obtained by discharging, at 270°C from a spinneret for conjugate melt spinning (the number of islands: 25 islands / fiber), a water-soluble thermoplastic polyvinyl alcohol-based resin as a sea component and isophthalic acid-modified polyethylene terephthalate (polyethylene terephthalate modified at 6 mol% with isophthalic acid) as an island component so that the sea component / island component ratio became 25 / 75 (mass ratio), and performing spinning at a spinning speed of 3500 m / min.

[0133] Thereafter, the fiber web was hot-pressed with a calender roll, and subsequently pressed with a roll having an uneven shape to impart an uneven shape (apply a crimping treatment) to the fiber web in the width direction so that the crimp ratio reached 200%.

[0134] Thereafter, the fiber web having been subjected to the crimping treatment was folded in the longitudinal direction and laminated in a cross-lapping manner such that seven layers of the fiber web overlapped each other to form a laminated web. The laminated web was then subjected to needle punching processing using 1-barb and 6-barb needles at a punching density of 3500 punches per 1 cm 2< , thereby forming an entangled fiber sheet having a basis weight of 385 g / m 2< and crimped in the longitudinal direction.

[0135] Thereafter, the entangled fiber sheet was subjected to a steam treatment under conditions of 110°C and 23.5% RH. Then, after drying in an oven at 90°C to 110 °C, the sheet was further hot-pressed at 120°C to obtain a hot-pressed fiber sheet having a basis weight of 755 g / m 2< , a specific gravity of 0.65 g / cm 3< , and a thickness of 1.16 mm.

[0136] Thereafter, the hot-pressed fiber sheet was impregnated at 52% pick-up with an emulsion obtained by adding, to an emulsion of polycarbonate-based non-yellowed polyurethane (polyurethane (1)) as a polymer elastic body, 1.5 parts by mass of a carbodiimide-based crosslinking agent and 2.7 parts by mass of ammonium sulfate with respect to 100 parts by mass of the polymer elastic body so that the solid content of the polymer elastic body became 16% by mass, and the solid content of the polymer elastic body was adjusted to be 10% by mass with respect to the total of polyester fibers and the polymer elastic body in the heat-shrunk fiber sheet. The emulsion-impregnated hot-pressed fiber sheet was then subjected to a moist-heat treatment in an environment at 110°C and 29% RH and further subjected to a drying treatment at 150°C to obtain a hot-pressed fiber sheet to which the polymer elastic body had been imparted.

[0137] Then, the heat-pressed fiber sheet to which the polymer elastic body had been imparted was immersed in hot water at 95°C for 10 minutes while subjecting the sheet to a dip-nip treatment and a high-pressure water stream treatment, thereby dissolving and removing the water-soluble thermoplastic polyvinyl alcohol-based resin serving as the sea component of the sea-island type composite fibers to form ultrafine fibers of isophthalic acid-modified polyethylene terephthalate having an average diameter of 3.02 µm and an average fineness of 0.1 dtex. Then, after drying, the back surface was ground using #320 sandpaper, and the main surface was ground using #320 sandpaper and #400 sandpaper to form a napped fiber surface, thereby obtaining artificial leather having the napped fiber surface.

[0138] The obtained artificial leather was dyed at 120°C using a disperse dye to obtain dyed artificial leather having a basis weight of 439 g / m 2< , an apparent density of 0.499 g / cm 3< , and a thickness of 0.88 mm. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 2]

[0139] Dyed artificial leather was obtained in the same manner as in Example 1 except that the crimping treatment was performed so that the crimp ratio reached 175%. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 3]

[0140] Dyed artificial leather was obtained in the same manner as in Example 1 except that the artificial leather was produced to have a thickness of 0.68 mm. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 4]

[0141] Dyed artificial leather was obtained in the same manner as in Example 3 except that the crimping treatment was performed so that the crimp ratio reached 175%. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 5]

[0142] Dyed artificial leather was obtained in the same manner as in Example 3 except that the laminated web was formed by stacking, in the advancing direction (process flow direction) of the entangled fiber sheet, fiber web layers that had been subjected to the crimping treatment in the width direction, thereby forming an entangled fiber sheet crimped in the transverse direction. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 6]

[0143] Dyed artificial leather was obtained in the same manner as in Example 1 except that polyethylene was used as the sea component, an entangled web sheet having been subjected to heat shrinkage treatment was obtained by shrinking an entangled fiber sheet in hot water at 90°C and pressing same with a cooled roll, a DMF solution (solid content: 18.5% by mass) of polycarbonate-based polyurethane (polyurethane (2)) was used as the polymer elastic body, the solid content of the polymer elastic body was adjusted to 30% by mass with respect to the total of the polyethylene terephthalate fibers and the polymer elastic body in the hot-pressed fiber sheet, toluene was used to dissolve and remove the polyethylene serving as the sea component, and the thickness was adjusted to 0.78 mm. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 7]

[0144] Dyed artificial leather was obtained in the same manner as in Example 6 except that the crimping treatment was performed so that the crimp ratio reached 175%. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Example 8]

[0145] Dyed artificial leather was obtained in the same manner as in Example 7 except that a DMF solution (solid content: 18.5% by mass) of ether-based polyurethane (polyurethane (3)) was used as the polymer elastic body. Measurement and evaluation results of the obtained artificial leather are shown in Table 1.[Comparative Example 1]

[0146] Dyed artificial leather was obtained in the same manner as in Example 1 except that no crimping treatment was applied. Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Comparative Example 2]

[0147] Dyed artificial leather was obtained in the same manner as in Example 3 except that no crimping treatment was applied. Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Comparative Example 3]

[0148] Dyed artificial leather was obtained in the same manner as in Example 5 except that no crimping treatment was applied, and the thickness was set to 0.80 mm. Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Comparative Example 4]

[0149] Dyed artificial leather was obtained in the same manner as in Example 6 except that no crimping treatment was applied. Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Comparative Example 5]

[0150] Sea-island type composite fibers were obtained in the same manner as in Example 6 except that spinning was conducted at a spinning speed of 800 m / min, and the sea-island type composite fibers were then drawn at a draw ratio of 2.7 in a hot water bath to obtain sea-island type composite fibers having a fineness of 4.0 dtex. An uneven shape was subsequently imparted (crimping treatment was applied) to the sea-island type composite fibers having a fineness of 4.0 dtex using a crimper so that the crimp ratio reached 9.0%, and a fiber web formed from the sea-island type composite fibers having been subjected to a crimping treatment was then produced by using a carding machine.

[0151] Thereafter, the fiber web was folded in the longitudinal direction and laminated in a cross-lapping manner such that seven layers of the fiber web overlapped each other to form a laminated web. Then, the laminated web was subjected to needle punching processing using a 1-barb needle at a punching density of 2500 punches per 1 cm 2< , thereby forming an entangled fiber sheet having a basis weight of 1128 g / m 2< .

[0152] Subsequently, in the same manner as in Example 6, a hot-pressed fiber sheet was obtained, and application of the polymer elastic body to the hot-pressed fiber sheet, dissolution and removal of the sea component of the sea-island type composite fibers, and formation of a napped fiber surface were performed to obtain artificial leather having a napped fiber surface. Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Comparative Example 6]

[0153] In Comparative Example 5, when the obtained fiber web formed from short fibers was hot-pressed with a calender roll, and subsequently pressed with a roll to which an uneven shape was imparted to impart an uneven shape (apply a crimping treatment) to the fiber web in the width direction so that the crimp ratio reached 200%, the short fiber web was torn, and subsequent process could not be carried out.[Comparative Example 7]

[0154] Dyed artificial leather was obtained in the same manner as in Example 3 except that the punch density in the needle punching processing was increased to 5900 punches per 1 cm 2< . Measurement and evaluation results of the obtained artificial leather are shown in Table 2.[Table 1]

[0155] Table 1Example No.Example 1Example 2Example 3Example 4Sea componentTypeModified polyvinyl alcoholModified polyvinyl alcoholModified polyvinyl alcoholModified polyvinyl alcoholIsland componentTypePolyesterPolyesterPolyesterPolyesterUltrafine fiber average diameter (µm)3.022.943.163.02Ultrafine fiber average fineness (dtex)0.1000.0950.1100.100Fiber lengthLong fiberLong fiberLong fiberLong fiberCrimp ratio (%)200175200175Crimping directionLongitudinalLongitudinalLongitudinalLongitudinalPolymer elastic bodyTypePolyurethane (1)Polyurethane (1)Polyurethane (1)Polyurethane (1)Content ratio (mass%)10101010Ultrafine fiber bundleTotal area (µm 2< / mm 2< ) *1< 1325951122596462671393Maximum area (µm 2< ) *2< 18144770583884576Number ratio (%)* 3< 70.464.373.770.7Thickness (mm)0.880.920.680.66Apparent density (g / cm 3< )0.4990.4850.4590.45620% Strength (kgf / 2.5 cm)Longitudinal9.98.210.812.2Transverse3.24.22.51.3Abrasion loss (35,000 cycles) (mg)25.221.926.127.4Pilling2,000 cyclesAAAA5,000 cyclesAAAA35,000 cyclesAAAAHandAAAAAppearanceAAAA Table 1 (continued) Example No.Example 5Example 6Example 7Example 8Sea componentTypeModified polyvinyl alcoholPolyethylenePolyethylenePolyethyleneIsland componentTypePolyesterPolyesterPolyesterPolyesterUltrafine fiber average diameter (µm)2.864.574.574.77Ultrafine fiber average fineness (dtex)0.0900.2300.2300.250Fiber lengthLong fiberLong fiberLong fiberLong fiberCrimp ratio (%)200200175200Crimping directionTransverseLongitudinalLongitudinalLongitudinalPolymer elastic bodyTypePolyurethane (1)Polyurethane (2)Polyurethane (2)Polyurethane (3)Content ratio (mass%)10293032Ultrafine fiber bundleTotal area (µm 2< / mm 2< ) *1< 110062590292691260105Maximum area (µm 2< )* 2< 8911670472476658Number ratio (%)* 3< 72.563.366.761.0Thickness (mm)0.680.780.780.79Apparent density (g / cm 3< )0.4740.4060.4050.40820% Strength (kgf / 2.5 cm)Longitudinal14.15.58.45.0Transverse0.93.43.53.8Abrasion loss (35,000 cycles) (mg)27.025.324.324.0Pilling2,000 cyclesAAAA5,000 cyclesABBB35,000 cyclesAAAAHandAAAAAppearanceAAAA *1: A value obtained by converting the total value of the areas of the cut surfaces of the ultrafine fiber bundle to an area per 1 mm 2< . *2: The maximum value of the areas of the cut surfaces of the ultrafine fiber bundle. *3: The number ratio of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more with respect to the total number of cut surfaces of the ultrafine fiber bundle. [Table 2]

[0156] Table 2Example No.Comparative Example 1Comparative Example 2Comparative Example 3Comparative Example 4Sea componentTypeModified polyvinyl alcoholModified polyvinyl alcoholModified polyvinyl alcoholPolyethyleneIsland componentTypePolyesterPolyesterPolyesterPolyesterUltrafine fiber average diameter (µm)3.163.023.024.67Ultrafine fiber average fineness (dtex)0.1100.1000.1000.240Fiber lengthLong fiberLong fiberLong fiberLong fiberCrimp ratio (%)0000Crimping direction----Polymer elastic bodyTypePolyurethane (1)Polyurethane (1)Polyurethane (1)Polyurethane (1)Content ratio (mass%)10101031Ultrafine fiber bundleTotal area (µm 2< / mm 2< ) *1< 35824286607546311607Maximum area (µm 2< )* 2< 4470229374482882Number ratio (%)* 3< 66.768.355.956.3Thickness (mm)0.930.660.800.78Apparent density (g / cm 3< )0.4910.4550.4640.40320% Strength (kgf / 2.5 cm)Longitudinal20.217.313.78.0Transverse2.12.910.03.1Abrasion loss (35,000 cycles) (mg)37.255.436.724.0Pilling2,000 cyclesCCCC5,000 cyclesBCCA35,000 cyclesABAAHandBBBAAppearanceBBBB Table 2 (continued) Example No.Comparative Example 5Comparative Example 6Comparative Example 7Sea componentTypePolyethylenePolyethyleneModified polyvinyl alcoholIsland componentTypePolyesterPolyesterPolyesterUltrafine fiber average diameter (µm)4.264.263.16Ultrafine fiber average fineness (dtex)0.2000.2000.110Fiber lengthShort fiberShort fiberLong fiberCrimp ratio (%)02000Crimping direction-Longitudinal-Polymer elastic bodyTypePolyurethane (2)-Polyurethane (1)Content ratio (mass%)20-10Ultrafine fiber bundleTotal area (µm 2< / mm 2< ) *1< 26371-89072Maximum area (µm 2< )* 2< 915-6414Number ratio (%) *3< 0.6-2.9Thickness (mm)0.71-0.71Apparent density (g / cm 3< )0.466-0.46320% Strength (kgf / 2.5 cm)Longitudinal11.0-13.1Transverse3.6-2.8Abrasion loss (35,000 cycles) (mg)36.2-15.5Pilling2,000 cyclesC-A5,000 cyclesC-A35,000 cyclesA-AHandA-BAppearanceB-B *1: A value obtained by converting the total value of the areas of the cut surfaces of the ultrafine fiber bundle to an area per 1 mm 2< . *2: The maximum value of the areas of the cut surfaces of the ultrafine fiber bundle. *3: The number ratio of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more with respect to the total number of cut surfaces of the ultrafine fiber bundle.

[0157] From Table 1, it has been found that the artificial leather obtained in each of Examples 1 to 8 is excellent in hand, surface abrasion resistance, and pilling resistance.

[0158] On the other hand, it has been found that the artificial leather (Comparative Examples 1, 2, and 4), in which the maximum area of the cut surfaces of the ultrafine fiber bundle in the cut surface cut at a depth of 0.3 mm from the surface is less than 4500 µm 2< , does not achieve the combination of excellent hand, excellent surface abrasion resistance, and pilling resistance.

[0159] In addition, it has been found that even when the maximum area is 4500 µm 2< or more, the artificial leather (Comparative Example 3), in which the number ratio of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more with respect to the total number of cut surfaces of the ultrafine fiber bundle is less than 60%, has inferior hand.

[0160] In addition, it has been found that the number ratio of the cut surfaces of the ultrafine fiber bundle having an area of 500 µm 2< or more is less than 60% in the artificial leather (Comparative Example 7), in which the degree of entanglement of the fiber web was increased by increasing the punching density to 5900 punches per 1 cm 2< in the needle punching processing without subjecting the fiber web to a crimping treatment, and the hand and appearance quality are poor.

Claims

1. Artificial leather comprising ultrafine fibers, wherein in a cut surface cut at a depth of 0.3 mm from a surface, a maximum area of cut surfaces of an ultrafine fiber bundle is 4500 µm2 or more, and a number ratio of cut surfaces of the ultrafine fiber bundle having an area of 500 µm2 or more is 60% or more with respect to the total number of cut surfaces of the ultrafine fiber bundle.

2. The artificial leather according to claim 1, wherein a total area of the ultrafine fiber bundle in the cut surface is 50000 µm2 / mm2 or more.

3. The artificial leather according to claim 1 or 2, wherein an average diameter of the ultrafine fibers is 7.5 µm or less.

4. The artificial leather according to any of claims 1 to 3, wherein an average fineness of the ultrafine fibers is 0.5 dtex or less.

5. The artificial leather according to any of claims 1 to 4, wherein the ultrafine fibers are long fibers.

6. The artificial leather according to any of claims 1 to 5, comprising 45% by mass or less of a polymer elastic body.

7. A method for producing the artificial leather according to any of claims 1 to 6, the method comprising: preparing a fiber web formed from ultrafine fiber-generating fibers; subjecting the fiber web to a crimping treatment to form a crimped fiber web; stacking a plurality of layers of the crimped fiber web to form a web laminate; entangling the web laminate to form an entangled fiber sheet; and removing at least one component from the ultrafine fiber-generating fibers.

8. The artificial leather production method according to claim 7, further comprising impregnating the entangled fiber sheet with the polymer elastic body.

Images