EP4613930A1

EP4613930A1 - Artificial leather and method for manufacturing same

Info

Publication number: EP4613930A1
Application number: EP23885604.1A
Authority: EP
Inventors: Shunichi Kimura; Makoto Yamashina; Satoshi Yanagisawa
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2022-10-31
Filing date: 2023-10-25
Publication date: 2025-09-10
Also published as: JPWO2024095846A1; WO2024095846A1; CN119895095A

Abstract

Artificial leather including: a fibrous base material including polyester ultrafine fibers having an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less; and a polyurethane having a hydrophilic group, the fibrous base material and the polyurethane being constituents of the artificial leather, wherein a content rate of the polyurethane having a hydrophilic group in the artificial leather is 15 mass% or more and 25 mass% or less, after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the polyurethane having a hydrophilic group has a mass retention ratio of 50 mass% or more and 80 mass% or less, and after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, a component dissolved in the N,N-dimethylformamide has a weight average molecular weight of 50000 or more and 100000 or less. Artificial leather is provided that achieves both a supple texture and excellent durability while obtained by an environmentally friendly process without using an organic solvent, and a method for manufacturing the artificial leather is provided.

Description

TECHNICAL FIELD

The present invention relates to artificial leather and a method for manufacturing the artificial leather.

BACKGROUND ART

Artificial leather mainly including a fibrous base material such as a nonwoven fabric and a polyurethane has excellent characteristics that natural leather does not have, and the range of use of artificial leather has been widened year by year to use in clothing, furniture, automobile interior materials, and the like. For manufacture of such artificial leather, a more environmentally friendly method has been considered in which a water-dispersible polyurethane prepared by dispersing a polyurethane resin into water is used, instead of a method in which a conventional organic solvent-based polyurethane is used.
For obtaining such artificial leather, several methods have been proposed so far.
For example, Patent Document 1 proposes a method in which a specific amount of polyvinyl alcohol having a specific degree of saponification and a specific degree of polymerization is added to a fibrous base material, then a water-dispersible polyurethane is added, and then the polyvinyl alcohol is removed. Patent Document 1 describes that a sheet-shaped article can be obtained, with this method, that achieves an elegant appearance and a supple texture and further has good abrasion resistance.
Patent Document 2 proposes a method including a polymer elastic body impregnating step of impregnating a fibrous base material including ultrafine fiber-generating fibers with an aqueous dispersion containing a specific polymer elastic body, a specific amount of an inorganic salt containing a monovalent cation, and a crosslinking agent and then performing a heating treatment at a specific temperature, an ultrafine fiber generating step, a drying step, and a nap raising step, in this order. Patent Document 2 describes that a sheet-shaped article having both a supple texture and excellent light resistance is obtained with this method.
Patent Document 3 proposes a method in which before and after removing a sea component from a sea-island composite fiber, the sea-island composite fiber is impregnated with a polyurethane of an aqueous emulsion and the polyurethane is fixed to the sea-island composite fiber. Patent Document 3 describes that this method enables manufacture of a suede leather type ultrafine fibrous nonwoven fabric having optimum physical mechanical properties, optimum abrasion resistance, and an optimum appearance.
Patent Document 4 proposes a method including, before and after an ultrafine fiber generating step, a polymer elastic body impregnating step of impregnating a fibrous base material including ultrafine fiber-generating fibers with an aqueous dispersion containing a specific polymer elastic body, a specific amount of an inorganic salt containing a monovalent cation, and a crosslinking agent and then performing a heating treatment at a specific temperature. Patent Document 4 describes that a sheet-shaped article excellent in flexibility, chemical resistance, and dyeing resistance is obtained with this method.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: International Publication No. 2014-042241
Patent Document 2: International Publication No. 2021-125032
Patent Document 3: Japanese Patent Laid-open Publication No. 2003-306878
Patent Document 4: International Publication No. 2021-125029

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

In the method disclosed in Patent Document 1, the adhesion state between the polyurethane and the ultrafine fibers is appropriately adjusted to achieve both a supple texture and durability, but the method requires a polyvinyl alcohol elution treatment, and thus has room for improvement in manufacturing efficiency.
Also in the method disclosed in Patent Document 2, the adhesion state between the polyurethane and the ultrafine fibers is moderately relaxed, and a supple texture is achieved without adding polyvinyl alcohol. However, there is room for improvement from the viewpoint of durability including abrasion resistance.
In the methods disclosed in Patent Documents 3 and 4, the polyurethane is added twice to achieve both a supple texture and durability. However, since the polyurethane is added in two stages, there is room for improvement in manufacturing efficiency.
Therefore, in view of the above problems, an object of the present invention is to provide artificial leather that achieves both a supple texture and excellent durability while obtained by an environmentally friendly process without using an organic solvent, and a method for manufacturing the artificial leather.

SOLUTIONS TO THE PROBLEMS

As a result of intensive studies by the present inventors to achieve the above object, it has been found that both the flexibility and the abrasion resistance of artificial leather can be achieved at a high level by using a polyurethane having a hydrophilic group as a water-dispersible polyurethane in the artificial leather and adjusting the mass retention ratio of the polyurethane having a hydrophilic group after immersion in N,N-dimethylformamide (hereinafter, sometimes abbreviated as DMF) and the weight average molecular weight of a component dissolved in DMF within specific ranges. In addition, it has been found that artificial leather has higher durability in a case where the degree of entanglement of fibers in a fibrous base material is increased to a specific range in a manufacturing process.
The present invention has been completed on the basis of these findings, and according to the present invention, the following inventions are provided.

[1] Artificial leather including:
- a fibrous base material including polyester ultrafine fibers having an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less; and
- a polyurethane having a hydrophilic group,
- the fibrous base material and the polyurethane being constituents of the artificial leather, wherein
- a content rate of the polyurethane having a hydrophilic group in the artificial leather is 15 mass% or more and 25 mass% or less,
- after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the polyurethane having a hydrophilic group has a mass retention ratio of 50 mass% or more and 80 mass% or less, and
- after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, a component dissolved in the N,N-dimethylformamide has a weight average molecular weight of 50000 or more and 100000 or less.
[2] The artificial leather according to [1], having an apparent density of 0.30 g/cm³ or more and 0.40 g/cm³ or less.
[3] The artificial leather according to [1] or [2], wherein the polyurethane having a hydrophilic group includes a constituent component derived from a polyester polyol.
[4] The artificial leather according to [3], wherein the polyurethane having a hydrophilic group further includes a constituent component derived from a polycarbonate polyol.
[5] The artificial leather according to any one of [1] to [4], wherein the polyurethane having a hydrophilic group has an N-acylurea bond and/or an isourea bond.
[6] A method for manufacturing the artificial leather according to any one of [1] to [5], the method including steps (1) to (4) described below in order, the steps (1) to (4) of:
1. (1) subjecting a nonwoven fabric including ultrafine fiber-generating fibers to a treatment for entanglement so that the nonwoven fabric has a ratio of density change before and after entanglement of 2.5 times or more and 3.5 times or less to form a fibrous base material;
2. (2) impregnating the fibrous base material with an aqueous dispersion, the aqueous dispersion containing a polyurethane precursor having a weight average molecular weight of 50000 or more and 100000 or less and a crosslinking agent, and then performing a heating and drying treatment to form an impregnated sheet including, as constituents, a fibrous base material and a polyurethane having a hydrophilic group;
3. (3) generating polyester ultrafine fibers from ultrafine fiber-generating fibers of the impregnated sheet to form a sheet before heat treatment including, as constituents, a fibrous base material including polyester ultrafine fibers, and the polyurethane having a hydrophilic group; and
4. (4) subjecting the sheet before heat treatment to a heat treatment at an atmospheric temperature of 150°C or more and 200°C or less for 5 minutes or more and 20 minutes or less.
[7] The method according to [6], wherein the crosslinking agent is a carbodiimide-based crosslinking agent.
[8] The method according to [6] or [7], wherein the step (1) includes adding 0.01 mass% or more and 3 mass% or less of silicone with respect to a mass of the ultrafine fiber-generating fibers.

EFFECTS OF THE INVENTION

According to the present invention, artificial leather having both a supple texture and excellent abrasion resistance is obtained.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a conceptual sectional view for explanation of a method of measuring the average nap length of the artificial leather of the present invention.

EMBODIMENTS OF THE INVENTION

The artificial leather of the present invention is artificial leather including a fibrous base material including polyester ultrafine fibers having an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less and a polyurethane having a hydrophilic group as constituents, the content rate of the polyurethane having a hydrophilic group in the artificial leather is 15 mass% or more and 25 mass% or less, and after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the polyurethane having a hydrophilic group has a mass retention ratio of 50 mass% or more and 80 mass% or less, and after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, a component dissolved in the N,N-dimethylformamide has a weight average molecular weight of 50000 or more and 100000 or less.
Hereinafter, the constituents will be described in detail, but the present invention is not limited to the scope described below without departing from the gist of the present invention, and various modifications can be made without departing from the gist of the present invention.

[Polyester Ultrafine Fibers]

The artificial leather of the present invention includes the fibrous base material as a constituent including the polyester ultrafine fibers having an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less. The term "polyester ultrafine fibers" refers to ultrafine fibers including a polyester-based resin described below, and the ultrafine fibers refer to "fibers having a single-fiber diameter of 0.1 µm or more and 10.0 µm or less" measured and calculated with a method described below.
In the present invention, the term "polyester-based resin" refers to a resin including repeating units having a mole fraction of polyester units of 80 mol% to 100 mol%. The same applies to those described as "···-based resin" unless otherwise specified. The polyester-based resin can be formed into artificial leather excellent in heat resistance, light resistance, and the like, and specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and mixtures and copolymers of these polyester resins. The polyester-based resin can be obtained, for example, using a dicarboxylic acid and/or its ester-forming derivative and a diol as raw materials.
Examples of the dicarboxylic acid and/or its ester-forming derivative used in the polyester-based resin include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, and ester-forming derivatives thereof. Note that the ester-forming derivatives referred in the present invention include lower alkyl esters of a dicarboxylic acid, acid anhydrides, and acyl chlorides. Specifically, methyl esters, ethyl esters, hydroxyethyl esters, and the like are preferably used. A more preferable aspect of the dicarboxylic acid and/or its ester-forming derivative used in the present invention is terephthalic acid and/or its dimethyl ester.
Examples of the diol used in the polyester-based resin include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and cyclohexanedimethanol. Among them, ethylene glycol is preferably used.
The polyester-based resin can contain inorganic particles such as titanium oxide particles, a lubricant, a pigment, a thermal stabilizer, an ultraviolet absorber, an electrically conductive agent, a heat storage agent, an antibacterial agent, and the like to meet various purposes.
The polyester-based resin can contain a component other than the polyester-based resin at a content of preferably 3 mass% or less, and more preferably 1.5 mass% or less in the polyester-based resin. If the content of the component other than the polyester-based resin is 3 mass% or less, a decrease in the strength of the polyester ultrafine fibers can be suppressed, and artificial leather excellent in abrasion resistance can be obtained.
As for a cross-sectional shape of the polyester ultrafine fibers, either a round cross section or a modified cross section can be adopted. Specific examples of the shape of the modified cross section include an elliptical shape, a flat shape, a polygonal shape such as a triangular shape, a sector shape, and a cross shape.
In the present invention, the polyester ultrafine fibers have an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less. If the average single-fiber diameter of the polyester ultrafine fibers is 10.0 µm or less, preferably 7.0 µm or less, and more preferably 5.0 µm or less, the artificial leather can be suppler. Furthermore, the quality of the nap can be improved. Meanwhile, if the average single-fiber diameter of the polyester ultrafine fibers is 0.1 µm or more, preferably 0.3 µm or more, and more preferably 0.7 µm or more, artificial leather can be obtained that is excellent in color developability after dyeing in the case of performing dyeing. Furthermore, at the time of nap raising by buffing, the bundled polyester ultrafine fibers can be improved in ease of dispersion and ease of handling.
The single-fiber diameter and the average single-fiber diameter of the polyester ultrafine fibers in the present invention are measured and calculated with the following method.

(1) The cross section obtained by cutting the obtained artificial leather in the thickness direction is observed with a scanning electron microscope (SEM, for example, "VHX-D500/D510" manufactured by KEYENCE CORPORATION) at a magnification of 1000 times.
(2) The single-fiber diameter of each of any 50 polyester ultrafine fibers in the observation plane is measured in 3 directions in each polyester ultrafine fiber cross section. Note that in the case of utilizing polyester ultrafine fibers having a modified cross section, first, the cross-sectional area of a single fiber is measured, and the diameter of a circle having the cross-sectional area is calculated with the following formula. The obtained diameter is regarded as the single-fiber diameter of the single fiber. Single-fiber diameter (µm) = (4 × (cross-sectional area (µm²) of single fiber)/π)^1/2
(3) The arithmetic average (µm) of the total 150 single-fiber diameters obtained as described above is calculated, rounded off to one decimal place, and regarded as the average single-fiber diameter (µm) of the polyester ultrafine fibers.

[Fibrous Base Material]

The fibrous base material used in the present invention includes the polyester ultrafine fibers. The fibrous base material is allowed to include mixed ultrafine fibers made from different raw materials.
As a specific form of the fibrous base material, a nonwoven fabric including the polyester ultrafine fibers entangled with each other or a nonwoven fabric including polyester ultrafine fiber bundles entangled with each other can be used. Among them, a nonwoven fabric including polyester ultrafine fiber bundles entangled with each other is preferably used, from the viewpoint of the strength and the texture of the artificial leather. From the viewpoint of flexibility and a texture, a nonwoven fabric is particularly preferably used in which polyester ultrafine fibers constituting polyester ultrafine fiber bundles are appropriately spaced from each other to form gaps of 1 µm to 100 µm. As described above, the nonwoven fabric including polyester ultrafine fiber bundles entangled with each other can be obtained, for example, by entangling ultrafine fiber-generating fibers in advance and then generating polyester ultrafine fibers. The nonwoven fabric in which polyester ultrafine fibers constituting polyester ultrafine fiber bundles are appropriately spaced from each other to form gaps can be obtained, for example, by using sea-island composite fibers in which gaps can be formed between island components by removing a sea component.
The nonwoven fabric may be either a staple fiber nonwoven fabric or a filament fiber nonwoven fabric, and from the viewpoint of the texture and the quality of the artificial leather, a staple fiber nonwoven fabric is more preferably used. The staple fiber nonwoven fabric refers to a nonwoven fabric in which fibers have a fiber length of less than 1000 mm.
In the case of using a staple fiber nonwoven fabric, the fiber length of the fibers included in the staple fiber nonwoven fabric is preferably in a range of 25 mm or more and 90 mm or less. If the fiber length is 25 mm or more, more preferably 35 mm or more, and still more preferably 40 mm or more, artificial leather excellent in abrasion resistance is easily obtained by entanglement. If the fiber length is 90 mm or less, more preferably 80 mm or less, and still more preferably 70 mm or less, artificial leather more excellent in texture and quality can be obtained.
In the present invention, in the case of using a nonwoven fabric as the fibrous base material, a woven fabric or a knitted fabric may be inserted into or stacked on the nonwoven fabric, or the nonwoven fabric may be lined with a woven fabric or a knitted fabric, for the purpose of improvement in strength, or the like. The average single-fiber diameter of the fibers constituting the woven fabric or the knitted fabric is preferably 0.3 µm or more and 10 µm or less, because damage at the time of entanglement can be suppressed and the strength can be maintained.
In a case where the fibers constituting the woven fabric or the knitted fabric are multifilaments, the multifilaments preferably have a total fineness of 30 dtex or more and 170 dtex or less. If the total fineness of the multifilaments constituting the woven fabric or the like is 170 dtex or less, and more preferably 150 dtex or less, artificial leather excellent in flexibility is obtained. Meanwhile, if the total fineness is 30 dtex or more, not only the form stability of a product as artificial leather is improved, but also the fibers constituting the woven fabric or the like are less likely to be exposed on the surface of the artificial leather at the time of entangling and integrating the nonwoven fabric and the woven fabric or the like by needle punching or the like, and therefore such a total fineness is preferable. At this time, in the woven fabric, the multifilaments of the warp and the weft may have the same total fineness or different total finenesses.
In the present invention, the total fineness of the multifilaments refers to a value measured and calculated in accordance with "8.3.1 Fineness based on corrected mass b) Method B (simplified method)" in "8.3 Fineness" in JIS L 1013: 2010 "Testing methods for man-made filament yarns".
As the fibers constituting the woven fabric or the knitted fabric, it is possible to use a polyester such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, or polylactic acid, a synthetic fiber such as a polyamide such as polyamide 6 or polyamide 66, a regenerated fiber such as a cellulose-based polymer, or a natural fiber such as cotton or hemp.
In the artificial leather of the present invention, the fibrous base material preferably has an apparent density of 0.25 g/cm³ or more and 0.30 g/cm³ or less. If the lower limit of the range of the apparent density of the fibrous base material is 0.25 g/cm³ or more, and more preferably 0.26 g/cm³ or more, the artificial leather is excellent in abrasion resistance. Meanwhile, if the upper limit of the range is 0.30 g/cm³ or less, and more preferably 0.28 g/cm³ or less, the polyurethane having a hydrophilic group is uniformly added, and artificial leather excellent in resilience can be obtained. In the present invention, the apparent density of the fibrous base material is calculated with the following formula.
Apparent density (g/cm³) of fibrous base material = apparent density (g/cm³) of artificial leather × ratio (%) of fibrous base material in artificial leather
Here, the ratio (%) of the fibrous base material in the artificial leather refers to the ratio of a mass decreased by extraction when only the polyester ultrafine fibers of the artificial leather are extracted with a solvent, assuming that the mass of the artificial leather is 100%.

[Polyurethane Having Hydrophilic Group]

Next, the artificial leather of the present invention includes the polyurethane having a hydrophilic group as a constituent. Hereinafter, this detail will be further described.

(1) Polyurethane having hydrophilic group

First, in the present invention, the term "hydrophilic group" refers to a "group having active hydrogen". Specific examples of the group having active hydrogen include a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group. A hydroxyl group or a carboxyl group is preferable from the viewpoint of reactivity with a crosslinking agent having a carbodiimide group described below.
The polyurethane having a hydrophilic group can be obtained by reacting a crosslinking agent with a polyurethane precursor obtained by reacting a polymeric polyol described below, an organic diisocyanate, and an active hydrogen component-containing compound having a hydrophilic group to form a hydrophilic prepolymer and then adding and reacting a chain extender. Hereinafter, these will be described in detail.

(1-1) Polymeric polyol

Examples of the polymeric polyol preferably used in the present invention include polyether-based polyols, polyester-based polyols, and polycarbonate-based polyols.
Examples of the polyether-based polyols include polyols obtained by addition and polymerization of a monomer such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, or cyclohexylene using a polyhydric alcohol or a polyamine as an initiator, and polyols obtained by ring-opening polymerization of the monomer using a protic acid, a Lewis acid, a cationic catalyst, or the like as a catalyst. Specific examples thereof include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymerized polyols obtained by combining these glycols.
Next, examples of the polyester-based polyols include polyester polyols obtained by condensing various low-molecular-weight polyols with a polybasic acid, and polyols obtained by ring-opening polymerization of lactones.
Examples of the low-molecular-weight polyols used in the polyester-based polyols include one or more selected from linear alkylene glycols such as "ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol", branched alkylene glycols such as "neopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 2-methyl-1,8-octanediol", alicyclic diols such as 1,4-cyclohexanediol, and aromatic dihydric alcohols such as 1,4-bis(β-hydroxyethoxy)benzene. Adducts obtained by adding various alkylene oxides to bisphenol A can also be used as low-molecular-weight polyols.
Examples of the polybasic acid used in the polyester-based polyols include one or more selected from the group consisting of succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, and hexahydroisophthalic acid.
Examples of the polycarbonate-based polyols include compounds obtained by a reaction between a polyol and a carbonate compound, such as a polyol and a dialkyl carbonate or a polyol and a diaryl carbonate.
As the polyol used in the polycarbonate-based polyols, the low-molecular-weight polyols used in the polyester-based polyols can be used. Meanwhile, as the dialkyl carbonate, dimethyl carbonate, diethyl carbonate, or the like can be used, and as the diaryl carbonate, diphenyl carbonate or the like can be used.
The polymeric polyol preferably used in the present invention preferably has a number average molecular weight of 500 or more and 5000 or less. If the number average molecular weight of the polymeric polyol is 500 or more, and more preferably 1500 or more, the texture of the artificial leather can be easily prevented from stiffening. if the number average molecular weight is 5000 or less, and more preferably 4000 or less, the strength of the polyurethane having a hydrophilic group serving as a binder can be easily maintained.

(1-2) Organic diisocyanate

Examples of the organic diisocyanate used in the present invention include aromatic diisocyanates having 6 or more and 20 or less carbon atoms (excluding a carbon atom in an NCO group; the same applies to the following), aliphatic diisocyanates having 2 or more and 18 or less carbon atoms, alicyclic diisocyanates having 4 or more and 15 or less carbon atoms, aroaliphatic diisocyanates having 8 or more and 15 or less carbon atoms, modified products of these diisocyanates (such as carbodiimide-modified products, urethane-modified products, and uretdione-modified products), and mixtures of two or more kinds thereof.
Specific examples of the aromatic diisocyanates having 6 or more and 20 or less carbon atoms include 1,3- and/or 1,4-phenylene diisocyanate, 2,4- and/2,6-tolylene diisocyanate, 2,4'- and/or 4,4'-diphenylmethane diisocyanate (hereinafter, abbreviated as MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane, and 1,5-naphthylene diisocyanate, and among them, MDI, which is excellent in flexibility when used in the polyurethane having a hydrophilic group, is preferably used.
Specific examples of the aliphatic diisocyanates having 2 or more and 18 or less carbon atoms include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate, bis(2-isocyanatoethyl) carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexaate.
Specific examples of the alicyclic diisocyanates having 4 or more and 15 or less carbon atoms include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexylene-1,2-dicarboxylate, and 2,5- and/or 2,6-norbornane diisocyanate. Among them, dicyclohexylmethane-4,4'-diisocyanate, which is excellent in durability when used as the polyurethane having a hydrophilic group, is preferably used.
Specific examples of the aroaliphatic diisocyanates having 8 or more and 15 or less carbon atoms include m- and/or p-xylylene diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

(1-3) Active hydrogen component-containing compound having hydrophilic group

Examples of the active hydrogen component-containing compound having a hydrophilic group preferably used in the present invention include compounds containing one or more groups selected from nonionic groups, anionic groups, and cationic groups and active hydrogen. These active hydrogen component-containing compounds can also be used in the form of a salt neutralized with a neutralizer. Using the active hydrogen component-containing compound having a hydrophilic group can enhance the stability of the aqueous dispersion used in the method for manufacturing artificial leather described below.
Examples of the compound having a nonionic group and active hydrogen include compounds containing two or more active hydrogen components or two or more isocyanate groups and including a side chain having a polyoxyethylene glycol group with a molecular weight of 250 to 9000 or the like, and triols such as trimethylol propane and trimethylol butane.
Examples of the compound having an anionic group and active hydrogen include carboxyl group-containing compounds such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and 2,2-dimethylolvaleric acid and their derivatives, sulfonic acid group-containing compounds such as 1,3-phenylenediamine-4,6-disulfonic acid and 3-(2,3-dihydroxypropoxy)-1-propanesulfonic acid and their derivatives, and salts obtained by neutralizing these compounds with a neutralizer.
Examples of the compound containing a cationic group and active hydrogen include tertiary amino group-containing compounds such as 3-dimethylaminopropanol, N-methyldiethanolamine, and N-propyldiethanolamine and their derivatives.

(1-4) Chain extender

Examples of the chain extender used in the present invention include water, low-molecular-weight diols such as "ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, and neopentyl glycol", alicyclic diols such as "1,4-bis(hydroxymethyl)cyclohexane", aromatic diols such as "1,4-bis(hydroxyethyl)benzene", aliphatic diamines such as "ethylenediamine", alicyclic diamines such as "isophoronediamine", aromatic diamines such as "4,4-diaminodiphenylmethane", aroaliphatic diamines such as "xylenediamine", alkanolamines such as "ethanolamine", hydrazine, dihydrazides such as "adipic acid dihydrazide", and mixtures of two or more kinds thereof.
Among them, a preferred chain extender is selected from water, low-molecular-weight diols, and aromatic diamines, and a more preferred chain extender is selected from water, ethylene glycol, 1,4-butanediol, 4,4'-diaminodiphenylmethane, and mixtures of two or more kinds thereof.

(1-5) Structure of polyurethane resin

As described above, the polyurethane precursor used in the present invention is prepared by reacting the polymeric polyol, the organic diisocyanate, and the active hydrogen component-containing compound having a hydrophilic group described above to form a hydrophilic prepolymer, and then adding and reacting a chain extender.

(1-6) Crosslinking agent

As the crosslinking agent used in the present invention, a crosslinking agent can be used that has two or more reactive groups, in one molecule, capable of reacting with a reactive group introduced into the polyurethane precursor. Specific examples of the crosslinking agent include polyisocyanate-based crosslinking agents such as water-soluble isocyanate compounds and blocked isocyanate compounds, melamine-based crosslinking agents, and carbodiimide-based crosslinking agents. The crosslinking agents may be used singly or in combination of two or more kinds thereof.
The water-soluble isocyanate-based compound has two or more isocyanate groups in one molecule, and examples of the compound include the organic diisocyanate compounds described above. Examples of the commercially available product include "Bayhydur" (registered trademark) series and "Desmodur" (registered trademark) series manufactured by Bayer MaterialScience.
The blocked isocyanate-based compound has two or more blocked isocyanate groups in one molecule. The blocked isocyanate group means a group of the organic polyisocyanate compound blocked with a blocking agent such as an amine, a phenol, an imine, a mercaptan, a pyrazole, an oxime, or an active methylene. Examples of the commercially available product include "ELASTRON" (registered trademark) series manufactured by DKS Co. Ltd., "DURANATE" (registered trademark) series manufactured by Asahi Kasei Corp., and "TAKENATE" (registered trademark) series manufactured by Mitsui Chemicals, Inc.
Examples of an oxazoline-based crosslinking agent include compounds having two or more oxazoline groups (oxazoline skeletons) in one molecule. Examples of the commercially available product include "EPOCROS" (registered trademark) series manufactured by NIPPON SHOKUBAI CO., LTD.
Examples of the carbodiimide-based crosslinking agent include compounds having two or more carbodiimide groups in one molecule. Examples of the commercially available product include "CARBODILITE" (registered trademark) series manufactured by Nisshinbo Chemical Inc.
Among them, the carbodiimide-based crosslinking agent is particularly preferably used because the polyurethane having a hydrophilic group obtained after the reaction has particularly excellent durability and flexibility.

(1-7) Structure of polyurethane having hydrophilic group

The polyurethane having a hydrophilic group preferably includes a constituent component derived from a polyether-based polyol from the viewpoint of flexibility. If the polyurethane having a hydrophilic group includes the constituent component derived from a polyether-based polyol, a water-dispersible polyurethane can be obtained that has a low glass transition temperature due to the high degree of freedom of the ether bond and is excellent in flexibility because of the weak cohesive force.
The polyurethane having a hydrophilic group preferably further includes a constituent component derived from a polycarbonate-based polyol from the viewpoint of durability. If the polyurethane having a hydrophilic group includes the constituent component derived from a polycarbonate-based polyol, a polyurethane having a hydrophilic group can be obtained that is excellent in water resistance, heat resistance, weather resistance, and mechanical properties due to the high cohesive force of the carbonate group.
In a method of confirming the constituent components of the polyurethane having a hydrophilic group, polyester ultrafine fibers constituting the artificial leather are eluted from the artificial leather, and the insoluble matter (polyurethane having a hydrophilic group) is analyzed by infrared spectroscopic analysis (using, for example, "FT/IR 4000 series" manufactured by JASCO Corporation, as an analytical instrument) and pyrolysis GC/MS analysis (using, for example, "GCMS-QP5050A" manufactured by SHIMADZU CORPORATION, as an analytical instrument), and thus it can be confirmed that the polyurethane having a hydrophilic group includes a constituent component derived from a polyester polyol and a constituent component derived from a polycarbonate polyol. As a solvent capable of eluting polyester ultrafine fibers constituting the artificial leather, m-cresol or hexafluoroisopropanol can be used, and hexafluoroisopropanol, which can be handled at room temperature, is preferably used.
The polyurethane having a hydrophilic group used in the present invention preferably has an N-acylurea bond and/or an isourea bond. The N-acylurea bond and/or the isourea bond is formed by a reaction between the hydrophilic group and the crosslinking agent having a carbodiimide group to form a crosslinked structure in the polyurethane having a hydrophilic group, and thus the durability of the polyurethane having a hydrophilic group can be enhanced.
The presence of the N-acylurea group or the isourea group in the polyurethane having a hydrophilic group can be analyzed by, for example, mapping processing such as time-of-flight secondary ion mass spectrometry (TOF-SIMS analysis) (using, for example, "TOF.SIMS 5" manufactured by IONTOF, as an analytical instrument) or infrared spectroscopic analysis (using, for example, "FT/IR 4000 series" manufactured by JASCO Corporation, as an analytical instrument) of the cross section of the artificial leather.

[Artificial Leather]

The artificial leather of the present invention is artificial leather including the fibrous base material and the polyurethane having a hydrophilic group as constituents. In the artificial leather of the present invention, the content rate of the polyurethane having a hydrophilic group in the artificial leather is 15 mass% or more and 25 mass% or less, and after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the polyurethane having a hydrophilic group has a mass retention ratio of 50 mass% or more and 80 mass% or less, and after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the component dissolved in the N,N-dimethylformamide has a weight average molecular weight of 50000 or more and 100000 or less. Only when all of these three conditions are satisfied, artificial leather can be obtained that has a supple texture and is less likely to undergo an appearance change by, for example, breakage, perforation, or pilling even after an extremely high-load abrasion test.
First, in the artificial leather of the present invention, the content rate of the polyurethane having a hydrophilic group is 15 mass% or more and 25 mass% or less. If the content rate of the polyurethane having a hydrophilic group is 15 mass% or more, and preferably 18 mass% or more, artificial leather excellent in abrasion resistance is obtained. Meanwhile, if the content rate is 25 mass% or less, and preferably 22 mass% or less, artificial leather having a supple texture can be obtained.
In the present invention, the content rate of the polyurethane having a hydrophilic group is measured and calculated with the following method.

(1) A test piece of 5 cm × 5 cm is cut out from the artificial leather, and the mass (M_X) of the test piece is measured.
(2) The test piece is immersed in hexafluoroisopropanol to elute polyester ultrafine fibers from the artificial leather.
(3) The insoluble component (polyurethane having a hydrophilic group) in (2) is dried with a dryer at 100°C, the mass (M_A) is measured, and the content rate of the polyurethane having a hydrophilic group in the artificial leather is calculated with the following formula. Content rate (%) of polyurethane having hydrophilic group = (M_A/M_X) × 100.

In the artificial leather of the present invention, the mass retention ratio of the polyurethane having a hydrophilic group after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours (hereinafter, sometimes simply abbreviated as "mass retention ratio of the polyurethane having a hydrophilic group") is 50 mass% or more and 80 mass% or less. The mass retention ratio of the polyurethane having a hydrophilic group correlates with the durability and the flexibility of the polyurethane having a hydrophilic group. If the lower limit is 50 mass% or more, preferably 55 mass% or more, and more preferably 60 mass% or more, artificial leather is obtained that is excellent in durability including abrasion resistance due to a component undissolved in N,N-dimethylformamide and having a high molecular weight and excellent durability in the polyurethane having a hydrophilic group. Meanwhile, if the upper limit of the mass retention ratio of the polyurethane having a hydrophilic group is 80 mass% or less, preferably 75 mass% or less, and more preferably 70 mass% or less, artificial leather is obtained that has a supple and excellent texture due to a component dissolved in N,N-dimethylformamide and having a low molecular weight and an excellent texture in the polyurethane having a hydrophilic group.
In the present invention, the mass retention ratio of the polyurethane having a hydrophilic group is measured and calculated with the following method.

(1) A test piece of 5 cm × 5 cm is cut out from the artificial leather.
(2) The test piece is immersed in hexafluoroisopropanol to elute polyester ultrafine fibers from the artificial leather.
(3) The insoluble component (polyurethane having a hydrophilic group) in (2) is dried with a dryer at 100°C, the mass (M_α) is measured, then the insoluble component is immersed in N,N-dimethylformamide at 25°C for 24 hours and dried with a dryer at 100°C, then the mass (M_β) is measured, and the mass retention ratio after immersion in N,N-dimethylformamide for 24 hours is calculated with the following formula. Mass retention ratio (%) after immersion in N,N-dimethylformamide for 24 hours = (M_β/M_α) × 100
(4) The measurement was performed three times, and the arithmetic average (%) of the obtained values is calculated and rounded off to one decimal place.

The mass retention ratio of the polyurethane having a hydrophilic group can be adjusted by the weight average molecular weight or the degree of crosslinking of the used polyurethane having a hydrophilic group. For example, the weight average molecular weight of the polyurethane having a hydrophilic group can be adjusted by the weight average molecular weight of the used polyurethane precursor, the atmospheric temperature of the heat treatment, and the treatment time. As the weight average molecular weight increases, the mass retention ratio tends to increase, and as the degree of crosslinking of the polyurethane having a hydrophilic group increases, the mass retention ratio tends to increase.
In the artificial leather of the present invention, after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the weight average molecular weight of a component dissolved in the N,N-dimethylformamide (hereinafter, sometimes simply abbreviated as "weight average molecular weight of a dissolved component") is 50000 or more and 100000 or less. The dissolved component is a component having a relatively low molecular weight in the polyurethane having a hydrophilic group and being a constituent of the artificial leather, and the "weight average molecular weight of the dissolved component" substantially corresponds to the weight average molecular weight of the polyurethane precursor used to obtain the polyurethane having a hydrophilic group and being a constituent of the artificial leather. If the lower limit of the range of the weight average molecular weight of the dissolved component is 50000 or more, and more preferably 60000 or more, the strength and the durability of the polyurethane having a hydrophilic group can be enhanced. If the upper limit of the range is 100000 or less, more preferably 90000 or less, and still more preferably 80000 or less, artificial leather having a supple texture can be obtained.
In the present invention, the weight average molecular weight of the dissolved component can be determined by gel permeation chromatography (GPC) after immersing the artificial leather in N,N-dimethylformamide at 25°C for 24 hours and then drying the component dissolved in N,N-dimethylformamide, and is measured under the following conditions.

Instrument: For example, "HLC-8220" manufactured by Tosoh Corporation
Column: For example, "TSKgel α-M" manufactured by Tosoh Corporation
Solvent: N,N-dimethylformamide (DMF)
Temperature: 40°C
Standard sample for calibration: Polystyrene (for example, "TSK standard POLYSTYRENE" manufactured by Tosoh Corporation)

The weight average molecular weight of the dissolved component can be adjusted by the weight average molecular weight of the used polyurethane having a hydrophilic group, the atmospheric temperature of the heat treatment, and the heat treatment time.
The artificial leather of the present invention preferably has an apparent density of 0.30 g/cm³ or more and 0.40 g/cm³ or less. If the artificial leather has an apparent density of 0.30 g/cm³ or more, more preferably 0.32 g/cm³ or more, and still more preferably 0.34 g/cm³ or more, the artificial leather is excellent in abrasion resistance. Meanwhile, if the apparent density is 0.40 g/cm³ or less, and preferably 0.38 g/cm³ or less, artificial leather having a supple texture can be obtained.
In the present invention, the apparent density of the artificial leather is calculated using the following formula by measuring the thickness and the mass per unit area of the artificial leather using the method specified in JIS L 1913: 2010 "Test methods for nonwovens" 6.1.1 (Thickness A method) and 6.2 (Mass per unit area).
Apparent density of artificial leather (g/cm³) = mass per unit area of artificial leather (g/cm²)/thickness of artificial leather (cm).
The artificial leather of the present invention preferably has a nap of 150 µm or more and 400 µm or less at least on one surface. If the length of the nap (hereinafter, sometimes simply abbreviated as "nap length") is 150 µm or more, and preferably 200 µm or more, artificial leather having an elegant suede-like appearance can be obtained. Meanwhile, if the nap length is 400 µm or less, and preferably 350 µm or less, entry of dirt into the inside of the nap can be suppressed, and artificial leather can be obtained that is less likely to be contaminated even when actually used for a long time and is excellent in appearance.
In a case where the artificial leather has a nap, the nap length is calculated with the following method.

(1) The cross section of the artificial leather in a state where the nap is raised using a lint brush or the like is photographed with a scanning electron microscope (SEM, for example, "VHX-D500/D510" manufactured by KEYENCE CORPORATION) at a magnification of 50 to 100 times.
(2) In the taken SEM image, in accordance with the schematic view of the cross section of the artificial leather shown in Fig. 1, 10 perpendicular lines are drawn, at intervals of 200 µm, on a line (L_A in Fig. 1) parallel to the bottom surface (L_B in Fig. 1) of the artificial leather.
(3) Points P₁ to P₁₀ are marked on intersections of a boundary line (L₀) between a nap portion (1 in the drawing) and a base portion (2 in the drawing), which is a portion other than the nap portion, and the perpendicular lines.
(4) Points Q₁ to Q₁₀ are marked at which the perpendicular lines passing through the points P₁ to P₁₀ respectively intersect with the edge of the nap layer.
(5) R₁ is defined as distance between the points P₁ and Q₁. Similarly, R₂ to R₁₀ are determined, and the average (arithmetic average) of R₁ to R₁₀ is calculated and regarded as the nap length in the present invention.

The artificial leather of the present invention preferably has an abrasion loss of 30 mg or less measured when the number of abrasion times is 50000 in the Martindale abrasion test specified in "8.19.5 Method E (Martindale method)" in "8.19 Abrasion resistance and change in colour due to abrasion" in JIS L 1096: 2005 "Testing methods for woven and knitted fabrics". The abrasion loss is more preferably 25 mg or less from the viewpoint of suppressing deterioration of the appearance of the artificial leather.
The abrasion loss can be adjusted by setting the content rate of the polyurethane having a hydrophilic group in the artificial leather, the mass retention ratio of the polyurethane having a hydrophilic group after immersing the artificial leather in N,N-dimethylformamide at 25°C for 24 hours, and the ratio of density change before and after entanglement of the nonwoven fabric including the ultrafine fiber-generating fibers to the described preferable ranges.
The artificial leather obtained according to the present invention can be suitably used in interior materials having a very elegant appearance as surface materials of furniture, chairs, walls, seats in vehicles including automobiles, trains, and aircraft, ceilings, interior decorations, and the like; clothing materials used in shirts, jackets, uppers and trim and the like of shoes including casual shoes, sports shoes, men's shoes, and ladies' shoes, bags, belts, wallets, and the like, and a part thereof; and industrial materials such as wiping cloths, abrasive cloths, and CD curtains.

[Method for Manufacturing Artificial Leather]

The method for manufacturing artificial leather of the present invention preferably includes the following steps (1) to (4) in this order.

(1) The step of subjecting a nonwoven fabric including ultrafine fiber-generating fibers to a treatment for entanglement so that the nonwoven fabric has a ratio of density change before and after entanglement of 2.5 times or more and 3.5 times or less to form a fibrous base material.
(2) The step of impregnating the fibrous base material with an aqueous dispersion, the aqueous dispersion containing a polyurethane precursor having a weight average molecular weight of 50000 or more and 100000 or less and a crosslinking agent, and then performing a heating and drying treatment to form an impregnated sheet including, as constituents, a fibrous base material and a polyurethane having a hydrophilic group.
(3) The step of generating polyester ultrafine fibers from ultrafine fiber-generating fibers of the impregnated sheet to form a sheet before heat treatment including, as constituents, a fibrous base material including polyester ultrafine fibers, and the polyurethane having a hydrophilic group.
(4) The step of subjecting the sheet before heat treatment to a heat treatment at an atmospheric temperature of 150°C or more and 200°C or less for 5 minutes or more and 20 minutes or less.

The details thereof will be described below.

In this step, a nonwoven fabric including ultrafine fiber-generating fibers is subjected to a treatment for entanglement so that the nonwoven fabric has a ratio of density change before and after entanglement of 2.5 times or more and 3.5 times or less to form a fibrous base material.
As the ultrafine fiber-generating fibers, sea-island composite fibers are preferably used in which two components (two or three components in a case where the island fibers are core-sheath composite fibers) of thermoplastic resins having different solvent solubility are used as a sea component and an island component and the sea component is dissolved and removed using a solvent or the like to form island components as ultrafine fibers, from the viewpoint of the texture and the surface appearance of the artificial leather, because appropriate gaps can be added between the island components, that is, between the ultrafine fibers inside the fiber bundle when the sea component is removed.
The sea-island composite fibers are preferably obtained by a method of using a sea-island composite spinneret and using a mutually aligned polymer array in which two components of a sea component and an island component (three components in a case where the island fibers are core-sheath composite fibers) are arranged and spun, from the viewpoint of obtaining ultrafine fibers having a uniform single-fiber diameter.
As the sea component of the sea-island composite fibers, polyethylene, polypropylene, polystyrene, a copolymerized polyester obtained by copolymerizing sodium sulfoisophthalic acid, polyethylene glycol, or the like, polylactic acid, or the like can be used, and from the viewpoints of a yarn-making property, easy elution, and the like, polystyrene or a copolymerized polyester is preferably used.
The mass ratio between the sea component and the island component in the sea-island composite fibers used in the present invention is preferably in a range of sea component : island component = 10 : 90 to 80 : 20. If the mass ratio of the sea component is 10 mass% or more, the island component tends to be sufficiently ultrafine. If the mass ratio of the sea component is 80 mass% or less, the proportion of the eluted component is small and therefore the productivity is improved. The mass ratio between the sea component and the island component is more preferably in a range of sea component : island component = 20 : 80 to 70 : 30.
As the nonwoven fabric constituting the fibrous base material, either a staple fiber nonwoven fabric or a filament fiber nonwoven fabric can be used as described above, and a staple fiber nonwoven fabric is preferably used because the number of fibers oriented in the thickness direction of the artificial leather is larger than that in the case of using a filament fiber nonwoven fabric and thus highly fine feel can be obtained on the surface of the napped artificial leather.
In the case of using a staple fiber nonwoven fabric as the fibrous base material, the obtained ultrafine fiber-generating fibers are preferably crimped and cut into a predetermined length to obtain raw stock. The crimping and the cutting can be performed using known methods.
Next, the obtained raw stock is formed into a nonwoven fabric with a cross lapper or the like. Then, the obtained nonwoven fabric is entangled so that the ratio of apparent density change before and after entanglement is 2.5 times or more and 3.5 times or less to obtain a fibrous base material. If the ratio of apparent density change before and after entanglement is 2.5 times or more, and more preferably 2.7 times or more, entanglement between fibers becomes sufficient to improve the durability. Meanwhile, if the ratio of apparent density change is 3.5 times or less, and more preferably 3.2 times or less, a sufficient space can be maintained for adding the polyurethane having a hydrophilic group between fibers. As the method of entangling a nonwoven fabric to obtain a fibrous base material, needle punching, water jet punching, or the like can be used, and needle punching, which has high entanglement efficiency, is preferably performed in order to set the ratio of apparent density change before and after entanglement within the above range.
The ratio of apparent density change before and after entanglement is an index representing the degree of entanglement of the fibrous base material, and can be determined with the following formula. Ratio of apparent density change before and after entanglement (times) = apparent density of fibrous base material after entanglement (g/cm³)/apparent density of nonwoven fabric before entanglement (g/cm³)
Here, the apparent densities (g/cm³) of a fiber web before entanglement and after entanglement are calculated using the following formula by measuring the thickness and the mass per unit area of the fiber web using the method specified in "6.1.1 Method A" and "6.2 Mass per unit area (ISO method)" in "6.1 Thickness (ISO method)" in JIS L 1913: 2010 "Test methods for nonwovens". Here, the fiber web includes both the nonwoven fabric before entanglement and the fibrous base material after entanglement.
Apparent density of fiber web (g/cm³) = mass per unit area of fiber web (g/cm²) /thickness of fiber web (cm).
As the method of entangling a nonwoven fabric to obtain a fibrous base material, needle punching, water jet punching, or the like can be used, and needle punching, which has high entanglement efficiency, is preferably performed in order to set the ratio of apparent density change before and after entanglement within the above range.
In the case of using needle punching for entanglement, an aspect is also preferable in which 0.01 to 3 mass% of silicone is added to the raw stock before entanglement in order to improve the smoothness of the raw cotton and improve the entanglement efficiency. If the amount of the added silicone is 0.01 mass% or more, and preferably 0.05 mass% or more, the entanglement efficiency can be enhanced. Meanwhile, if the amount is 3 mass% or less, and more preferably 1 mass% or less, the fibrous base material largely elongates during processing and thus deterioration of the quality of the artificial leather can be suppressed.
In the case of using needle punching for entanglement, needle punching is preferably performed at a punching density of 2000 punches/cm² or more and 4000 punches/cm² or less using a needle having a barb (notch) capable of gripping 5 to 15 fibers, in order to set the ratio of apparent density change before and after entanglement to the above value.
The fibrous base material including the composite fibers after the treatment for entanglement (ultrafine fiber-generating fibers) preferably has an apparent density of 0.20 g/cm³ or more and 0.30 g/cm³ or less. If the apparent density is 0.20 g/cm³ or more, and more preferably 0.23 g/cm³ or more, the fibrous base material has sufficient form stability and dimensional stability. Meanwhile, if the apparent density is 0.30 g/cm³ or less, and more preferably 0.28 g/cm³ or less, a sufficient space can be maintained for adding the polyurethane having a hydrophilic group.
From the viewpoint of fineness, an aspect is also preferable in which the fibrous base material thus obtained is contracted by dry heat, wet heat, or both dry heat and wet heat to further increase the density.

In this step, the fibrous base material is impregnated with an aqueous dispersion containing a polyurethane precursor having a weight average molecular weight of 50000 or more and 100000 or less and a crosslinking agent, and then a heating and drying treatment is performed to form an impregnated sheet including, as constituents, a fibrous base material and a polyurethane having a hydrophilic group.
The concentration of the polyurethane precursor in the aqueous dispersion (the content of the polyurethane precursor in 100 mass% of the aqueous dispersion) is preferably 3 mass% or more and 30 mass% or less. If the concentration of the polyurethane precursor is 3 mass% or more, and more preferably 5 mass% or more, the polyurethane precursor can be uniformly added to the fibrous base material even in a case where the polyurethane precursor is added in a small amount. Meanwhile, if the concentration is 30 mass% or less, and more preferably 15 mass% or less, the storage stability of the aqueous dispersion can be enhanced.
It is important that the polyurethane precursor used in the present invention has a weight average molecular weight of 50000 or more and 100000 or less. If the weight average molecular weight is 50000 or more, and more preferably 60000 or more, the strength and the durability of the polyurethane having a hydrophilic group can be enhanced. If the weight average molecular weight is 100000 or less, more preferably 90000 or less, and still more preferably 80000 or less, artificial leather having a supple texture can be obtained.
In the present invention, the weight average molecular weight of the polyurethane precursor can be measured with the same method as the weight average molecular weight of the dissolved component described above.
After the fibrous base material is impregnated with the aqueous dispersion, the aqueous dispersion can be coagulated using a coagulation method usually used in the art, such as a dry coagulation method or an in-liquid coagulation method. In the case of using a dry coagulation method, the aqueous dispersion is added to the fibrous base material and then dry-coagulated by a heat treatment at a temperature of 120°C or more and 180°C or less, and thus a polyurethane having a hydrophilic group is preferably added to the fibrous base material. In the case of using an in-liquid coagulation method, a coagulation method can be used such as an acid coagulation method in which a coagulation treatment is performed with a coagulation solvent having a pH of 1 or more and 3 or less, or a hot water coagulation method in which a coagulation treatment is performed with hot water having a temperature of 80°C or more and 100°C or less.
In the method for manufacturing artificial leather of the present invention, the aqueous dispersion can contain an inorganic salt in the case of using a dry coagulation method. If the aqueous dispersion contains an inorganic salt, thermosensitive coagulability can be imparted to the aqueous dispersion. In the present invention, the thermosensitive coagulability refers to a property of decreasing the fluidity of the aqueous dispersion and coagulating at a certain temperature (thermosensitive coagulation temperature) reached when the aqueous dispersion is heated.
The aqueous dispersion preferably has a thermosensitive coagulation temperature of 55°C or more and 80°C or less. If the thermosensitive coagulation temperature is 55°C or more, and more preferably 60°C or more, gelation can be suppressed at the time of preparation or storage of the aqueous dispersion. Meanwhile, if the thermosensitive coagulation temperature is 80°C or less, and more preferably 70°C or less, coagulation of the polyurethane precursor proceeds before moisture evaporation from the fibrous base material, and thus a structure can be formed that is similar to a structure obtained by wet coagulation of a solvent-based polyurethane, that is, a structure in which a polyurethane does not bind fibers strongly, so that good flexibility and resilience can be achieved.
In the present invention, in the case of using an inorganic salt as a thermosensitive coagulant, a monovalent cation-containing inorganic salt is preferably used. The monovalent cation-containing inorganic salt is preferably sodium chloride and/or sodium sulfate. The monovalent cation-containing inorganic salt, which has a small ionic valence, has a small influence on the stability of the aqueous dispersion, so that adjustment of the amount of the added monovalent cation-containing inorganic salt enables strict control of the thermosensitive coagulation temperature while the stability of the aqueous dispersion is ensured.
In the present invention, the content of the monovalent cation-containing inorganic salt in the aqueous dispersion is preferably 10 mass% or more and 50 mass% or less with respect to the polyurethane precursor. If the content is 10 mass% or more, more preferably 20 mass% or more, and still more preferably 30 mass% or more, ions present in a large amount in the aqueous dispersion uniformly act on the polyurethane precursor particles, so that coagulation can be quickly completed at a specific thermosensitive coagulation temperature. Thus, a more remarkable effect can be obtained on progress of coagulation of the polyurethane precursor in a state where the fibrous base material contains a large amount of moisture as described above. As a result, a structure can be formed that is very similar to that obtained by wet coagulation of a solvent-based polyurethane, and thus good flexibility and resilience can be achieved. Furthermore, if the amount of the added monovalent cation-containing inorganic salt is set as described above, the inorganic salt serves as an inhibitor of fusion of the polyurethane precursor particles, and can suppress hardening of the polyurethane precursor caused by continuous film formation. Meanwhile, if the content is 50 mass% or less, an appropriate continuous film structure of the polyurethane precursor can remain to suppress deterioration of physical properties. The stability of the aqueous dispersion can also be maintained.
In the method for manufacturing artificial leather of the present invention, it is important that the aqueous dispersion contains a crosslinking agent. If a three-dimensional network structure is introduced into the polyurethane precursor with a crosslinking agent, physical properties such as abrasion resistance can be improved.
The concentration of the crosslinking agent in the aqueous dispersion is preferably 1 mass% or more and 10 mass% or less with respect to the mass of the polyurethane precursor. If the concentration of the crosslinking agent in the aqueous dispersion is 1 mass% or more, and more preferably 2 mass% or more, a larger amount of three-dimensional network structures can be introduced into the polyurethane precursor with the crosslinking agent, and artificial leather can be obtained that is excellent in abrasion resistance and the like. Meanwhile, if the concentration of the crosslinking agent is 10 mass% or less, and more preferably 7 mass% or less, it is suppressed that, at the time of forming the polyurethane precursor, the excessive crosslinking agent inhibits coagulation of the polyurethane precursor, and thus deterioration of physical properties such as abrasion resistance is easily suppressed.
The crosslinking agent according to the method for manufacturing artificial leather of the present invention is preferably a carbodiimide-based crosslinking agent and/or a blocked isocyanate crosslinking agent. Thus, a three-dimensional crosslinked structure can be added by an N-acylurea bond and/or an isourea bond, which is excellent in physical properties such as light resistance, heat resistance, and abrasion resistance and flexibility, into a molecule of the polymer elastic body in the artificial leather, and the physical properties such as durability and abrasion resistance can be dramatically improved while the flexibility of the artificial leather is maintained.
Then, after impregnation with the aqueous dispersion, a heating and drying treatment is performed to form an impregnated sheet including, as constituents, a fibrous base material and a polyurethane having a hydrophilic group.
The temperature of the heating and drying treatment after impregnation with the aqueous dispersion is preferably 110°C or more, and more preferably 120°C or more. If the temperature of the heating and drying treatment is 110°C or more, not only the drying efficiency of the sheet can be enhanced, but also the progress of the crosslinking reaction can be promoted, and the physical properties such as durability and abrasion resistance of the artificial leather can be further enhanced. Meanwhile, if the temperature of the heating and drying treatment is 180°C or less, or 170°C or less, thermal deterioration of the polyurethane having a hydrophilic group can be suppressed.
The time of the heating and drying treatment is preferably 5 minutes or more and 30 minutes or less. The heating for 5 minutes or more, and more preferably 10 minutes or more can promote the progress of the crosslinking reaction. If the heating time is 30 minutes or less, and preferably 25 minutes or less, thermal deterioration of the polyurethane having a hydrophilic group due to excessive heating can be suppressed.

In this step, polyester ultrafine fibers are generated from ultrafine fiber-generating fibers of the impregnated sheet to form a sheet before heat treatment including, as constituents, a fibrous base material including polyester ultrafine fibers, and the polyurethane having a hydrophilic group.
An ultrafine fiber-forming treatment (disolution treatment) in the case of using sea-island composite fibers as the ultrafine fiber-generating fibers can be performed with a method in which, for example, the sea-island composite fibers are immersed in a solvent and then a heat treatment is performed. The solvent in which the sea component is dissolved can be appropriately selected according to the kind of the sea component. In a case where the sea component is a copolymerized polyester, an aqueous alkali solution such as an aqueous sodium hydroxide solution can be used.
In the case of using an aqueous alkali solution as the solvent for the disolution treatment, the molar concentration of the aqueous alkali solution is preferably 3 mol/L or less in order to prevent excessive deterioration of the polyurethane having a hydrophilic group.

In this step, the sheet before heat treatment is subjected to a heat treatment at an atmospheric temperature of 150°C or more and 200°C or less for 5 minutes or more and 20 minutes or less.
This heat treatment is performed after the sheet before heat treatment is obtained, and is preferably performed immediately after the ultrafine fiber-forming treatment in order to suppress deterioration of the quality caused by elongation in the step.
In the heat treatment method, a hot air dryer is preferably used such as a floater dryer, a drum dryer, or a pin tenter.
In this heat treatment, it is important that the atmospheric temperature is 150°C or more and 200°C or less and the heating time is 5 minutes or more and 20 minutes or less. Thus, the adhesiveness between the ultrafine fibers and the polyurethane having a hydrophilic group is improved to improve the strength and the abrasion resistance of the artificial leather, and the molecular weight is reduced in a part of the polyurethane having a hydrophilic group to soften the artificial leather, so that the artificial leather can achieve both a supple texture and excellent abrasion resistance.
First, it is important that the atmospheric temperature is 150°C or more and 200°C or less. If the temperature is 150°C or more, and more preferably 155°C or more, not only the adhesiveness between the ultrafine fibers and the polyurethane having a hydrophilic group can be improved to improve the strength and the abrasion resistance of the artificial leather, but also the molecular weight can be reduced in a part of the polyurethane having a hydrophilic group to enhance the flexibility of the artificial leather. Meanwhile, if the temperature is 200°C or less, preferably 190°C or less, and more preferably 180°C or less, the molecular weight can be gradually reduced in a part of the polyurethane having a hydrophilic group.
Next, it is important that the heating time is 5 minutes or more and 20 minutes or less. If the heating time is 5 minutes or more, and preferably 6 minutes or more, the adhesiveness between the ultrafine fibers and the polyurethane having a hydrophilic group is improved, and the strength and the abrasion resistance of the artificial leather can be improved. Meanwhile, if the heating time is 20 minutes or less, preferably 15 minutes or less, and more preferably 12 minutes or less, it is possible to prevent deterioration of physical properties of the artificial leather caused by excessive reduction in molecular weight of the polyurethane having a hydrophilic group.

Also in the method for manufacturing artificial leather of the present invention, various finishing steps are preferably performed as in manufacture of general artificial leather.
First, the method for manufacturing artificial leather of the present invention preferably includes a dyeing step of dyeing artificial leather. As the dyeing method, various methods usually used in the art can be adopted. Examples of the usable method include jet dyeing in which a jigger dyeing machine or a jet dyeing machine is used, dip dyeing such as thermosol dyeing in which a continuous dyeing machine is used, and textile printing on a nap surface by roller textile printing, screen textile printing, inkjet textile printing, sublimation textile printing, vacuum sublimation textile printing, or the like. Among them, a method is preferable in which a jet dyeing machine is used, because such a method can soften non-napped artificial leather or artificial leather by dyeing non-napped artificial leather or artificial leather and simultaneously giving a kneading effect. Furthermore, various resin finishing can be performed as necessary after dyeing.
In the dyeing bath or after dyeing, a finishing agent treatment can be performed using, for example, a softener such as silicone, an antistatic agent, a water repellent, a flame retardant, a light resisting agent, or an antimicrobial agent.
In the present invention, an aspect is preferable in which half-cut in the thickness direction is performed before or after the dyeing step, from the viewpoint of manufacturing efficiency.
The method for manufacturing artificial leather of the present invention also preferably includes a nap raising step of forming a nap before or after the dyeing step. The method of forming a nap is not particularly limited, and various methods usually performed in the art, such as buffing with sandpaper or the like, can be used.
In a case where nap raising is performed, a lubricant such as a silicone emulsion can be applied to the surface of the artificial leather before the nap raising. If an antistatic agent is further applied before the nap raising, a buffing powder generated from the artificial leather by buffing is less likely to deposit on the sandpaper. Thus, artificial leather is formed.
In the method for manufacturing artificial leather of the present invention, as necessary, the artificial leather can be further subjected to post-processing including drilling such as perforation, embossing, laser processing, pinsonic processing, and print processing.

EXAMPLES

The artificial leather of the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

[Evaluation Method]

An evaluation method used in Examples and its measurement conditions will be described. Unless otherwise described, each physical property was measured on the basis of the above-described method.

(1) Average single-fiber diameter (µm):
The average single-fiber diameter (µm) was measured and calculated with the above-described method using "VHX-D500/D510" manufactured by KEYENCE CORPORATION as a scanning electron microscope (SEM).
(2) Weight average molecular weight (unitless) of polyurethane precursor and dissolved component:
The weight average molecular weight of the polyurethane precursor or the dissolved component was measured and calculated with the above-described method using the following apparatus under the following conditions.
- Instrument: HLC-8020 (manufactured by Tosoh Corporation)
- Column: TSKgel GMH-XL (manufactured by Tosoh Corporation)
- Solvent: N,N-dimethylformamide (DMF)
- Temperature: 40°C
- Standard sample for calibration: Polystyrene ("TSK standard POLYSTYRENE" manufactured by Tosoh Corporation)
- Flow rate: 1.0 ml/minute
(3) Confirmation of fact that polyurethane having hydrophilic group has N-acylurea bond and/or isourea bond:
"FT/IR 4600" manufactured by JASCO Corporation was used as a measuring apparatus for infrared spectroscopic analysis, and the fact was confirmed with the following method. A test piece of 5 cm × 5 cm was cut out from the artificial leather, and the test piece was immersed in hexafluoroisopropanol to elute polyester ultrafine fibers from the artificial leather. Next, the insoluble component (polyurethane having a hydrophilic group) was dried with a dryer at 100°C and then subjected to infrared spectroscopic analysis, and in a case where a peak of C=O stretching vibration derived from an N-acylurea bond and/or an isourea bond, which is observed in the vicinity of 1650 cm^-1, was observed, it was determined that the polyurethane having a hydrophilic group had an N-acylurea bond and/or an isourea bond.
(4) Content rate (mass%) of polyurethane having hydrophilic group:
The content rate (mass%) of the polyurethane having a hydrophilic group was measured and calculated with the above-described method.
(5) Mass retention ratio (%) of polyurethane having hydrophilic group:
The mass retention ratio (%) of the polyurethane having a hydrophilic group was measured and calculated with the above-described method.
(6) Apparent density (g/cm³) of artificial leather:
The apparent density (g/cm³) of the artificial leather was measured and calculated with the above-described method using "DIAL THICKNESS GAUGE Model H" manufactured by OZAKI MFG. CO., LTD. as a thickness meter.
(7) Nap length (µm):
The nap length was measured and calculated with the above-described method using "VHX-D500/D510" manufactured by KEYENCE CORPORATION as a scanning electron microscope (SEM).
(8) Abrasion loss (mg) of artificial leather:
In measurement and calculation of the abrasion loss (mg) of the artificial leather, "Model 406" manufactured by James H. Heal & Co. Ltd. was used as a Martindale abrasion tester, and "ABRASTIVE CLOTH SM25" manufactured by James H. Heal & Co. Ltd. was used as a standard friction cloth. A load of 12 kPa was applied to the artificial leather, and the number of times of abrasion was set to 50000 times. The abrasion loss was calculated with the following formula using the masses of the artificial leather before and after abrasion. Abrasion loss (mg) = mass before abrasion (mg) - mass after abrasion (mg) A value obtained by rounding to the nearest whole number was regarded as the abrasion loss (mg).
(9) Texture of artificial leather
The texture of the artificial leather was evaluated to A, B, or C described below by 20 healthy adults serving as evaluators, and the most frequent evaluation was taken as the feel of touch of the artificial leather. A satisfactory level in the present invention is "A or B".
1. A: Being soft without resistance at the time of grip.
2. B: Being soft with slight resistance at the time of grip.
3. C: Being hard with large resistance at the time of grip.

[Polyurethane Precursor]

The polyurethane precursors used in Examples and Comparative Examples are as follows.
PU-A: A polyurethane precursor having a weight average molecular weight of 80000 in which polytetramethylene glycol is used as a polymeric polyol, MDI is used as an organic diisocyanate, 2,2-dimethylolpropionic acid is used as an active hydrogen component-containing compound having a hydrophilic group, and ethylene glycol is used as a chain extender.
PU-B: A polyurethane precursor having a weight average molecular weight of 55000 in which polytetramethylene glycol is used as a polymeric polyol, MDI is used as an organic diisocyanate, 2,2-dimethylolpropionic acid is used as an active hydrogen component-containing compound having a hydrophilic group, and ethylene glycol is used as a chain extender.
PU-C: A polyurethane precursor having a weight average molecular weight of 90000 in which polytetramethylene glycol is used as a polymeric polyol, MDI is used as an organic diisocyanate, 2,2-dimethylolpropionic acid is used as an active hydrogen component-containing compound having a hydrophilic group, and ethylene glycol is used as a chain extender.
PU-D: A polyurethane precursor having a weight average molecular weight of 80000 in which a polyol obtained by copolymerizing polytetramethylene glycol and polyhexamethylene carbonate at a molar ratio of 3 : 1 is used as a polymeric polyol, MDI is used as an organic diisocyanate, 2,2-dimethylolpropionic acid is used as an active hydrogen component-containing compound having a hydrophilic group, and ethylene glycol is used as a chain extender.
PU-E: A polyurethane precursor having a weight average molecular weight of 110000 in which polytetramethylene glycol is used as a polymeric polyol, MDI is used as an organic diisocyanate, 2,2-dimethylolpropionic acid is used as an active hydrogen component-containing compound having a hydrophilic group, and ethylene glycol is used as a chain extender.

[Example 1]

A polyester obtained by copolymerizing 8 mol% of sodium 5-sulfoisophthalate was used as a sea component, polyethylene terephthalate having an intrinsic viscosity of 0.73 was used as an island component, and melt spinning was performed using a sea-island composite spinneret having 16 islands per hole under the conditions of a spinning temperature of 285°C, an island/sea mass ratio of 80/20, a discharge rate of 1.6 g/min·hole, and a spinning speed of 1100 m/min. Next, the obtained fibers were stretched 3.7 times in an oil solution bath, dimethylsilicone was added in an amount of 0.5 mass% with respect to the fiber mass (hereinafter, described that the "amount of silicone added to raw stock" was 0.5 mass%), and then the fibers were cut into a length of 51 mm to obtain raw stock of sea-island composite fibers having a single-fiber fineness of 3.8 dtex. Then, using the raw stock of sea-island composite fibers, carding and cross-lapping were performed to form a laminated web having an apparent density of 0.09 g/cm³. The laminated web was needle-punched at a punching density of 3500 punches/cm² using a needle having a barb capable of gripping up to 10 pieces of raw stock (hereinafter, described that the "maximum number of pieces gripped by a needle barb" was 10) to obtain a fibrous base material having a basis weight of 700 g/m², a thickness of 2.6 mm, and an apparent density of 0.27 g/cm³ (a ratio of density change before and after entanglement of 3.0 times). The obtained fibrous base material was immersed and contracted in hot water at a temperature of 98°C for 2 minutes and then dried at a temperature of 100°C for 5 minutes to obtain a fibrous base material including a nonwoven fabric of sea-island composite fibers.

As a polyurethane precursor, an aqueous dispersion was prepared that contained 11 parts by mass of "PU-A", 1 part by mass of a crosslinking agent A (carbodiimide-based crosslinking agent, "CARBODILITE-V-02-L2" manufactured by Nisshinbo Chemical Inc.), 5 parts by mass of sodium sulfate, and 83 parts by mass of water. The fibrous base material was impregnated with the aqueous dispersion, then squeezed with a mangle so that the pick-up rate of the aqueous dispersion was 200%, and further heated with hot air at 120°C for 20 minutes to coagulate the polyurethane precursor and form a crosslinked structure including an N-acylurea bond and/or an isourea bond, and thus an impregnated sheet was obtained that included a nonwoven fabric of sea-island composite fibers and a polyurethane having a hydrophilic group.

The obtained impregnated sheet was immersed in a 5% aqueous sodium hydroxide solution, then squeezed with a mangle so that the pick-up rate of the aqueous sodium hydroxide solution was 100%, and further heated with steam at 95°C for 10 minutes to cause alkali-decomposition of the sea component of the sea-island composite fibers, and then excess sodium hydroxide and sodium sulfate were washed with water to obtain a sheet before heat treatment.

The sheet before heat treatment after washing with water was heated for 10 minutes with a pin tenter in which the atmospheric temperature was raised to 160°C, and thus a sheet was obtained that included a fibrous base material including ultrafine fibers and a polyurethane having a hydrophilic group.

The obtained sheet was half-cut in a direction perpendicular to the thickness direction, and the side opposite from the half-cut surface was buffed with endless sandpaper with a sandpaper grit number of 120 to obtain a napped sheet having a thickness of 0.70 mm.
The napped sheet was dyed black using a disperse dye with a jet dyeing machine under a temperature condition of 120°C. The dyed napped sheet was dried with a dryer to obtain artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group. The obtained artificial leather had a supple texture and excellent durability. Table 1 shows the results.

[Example 2]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the polyurethane precursor was changed to "PU-B" in <Step of Forming Impregnated Sheet>. The obtained artificial leather had a supple texture and excellent durability. Table 1 shows the results.

[Example 3]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the polyurethane precursor was changed to "PU-C" in <Step of Forming Impregnated Sheet>. The obtained artificial leather showed slight resistance, but had a supple texture and excellent durability. Table 1 shows the results.

[Example 4]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 18 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the pick-up rate of the aqueous dispersion was changed to 150% in <Step of Forming Impregnated Sheet>. The obtained artificial leather had a supple texture and excellent durability. Table 1 shows the results.

[Example 5]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the polyurethane precursor was changed to "PU-D" in <Step of Forming Impregnated Sheet>. The obtained artificial leather showed slight resistance, but had a supple texture and excellent durability. Table 1 shows the results.

[Example 6]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the atmospheric temperature of the heat treatment was changed to 180°C in <Step of Performing Heat Treatment>. The obtained artificial leather had a supple texture and excellent durability. Table 1 shows the results.

[Example 7]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the heat treatment time was changed to 15 minutes in <Step of Performing Heat Treatment>. The obtained artificial leather had a supple texture and excellent durability. Table 2 shows the results.

[Example 8]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the atmospheric temperature of the heat treatment was changed to 150°C in <Step of Performing Heat Treatment>. The obtained artificial leather showed slight resistance, but had a supple texture and excellent durability. Table 2 shows the results.

[Example 9]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that no dimethylsilicone was added to the raw stock in <Step of Forming Fibrous Base Material>. The obtained artificial leather had a supple texture and excellent durability. Table 2 shows the results.

[Example 10]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that no dimethylsilicone was added to the raw stock and needle punching was performed at 3000 punches/cm² in <Step of Forming Fibrous Base Material>. The obtained artificial leather had a supple texture and excellent durability. Table 2 shows the results.

[Comparative Example 1]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the heat treatment time was changed to 30 minutes in <Step of Performing Heat Treatment>. The obtained artificial leather had a supple texture, but was significantly poor in durability. Table 3 shows the results.

[Comparative Example 2]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the polyurethane precursor was changed to "PU-E" in <Step of Forming Impregnated Sheet>. The obtained artificial leather had excellent durability, but had a hard texture. Table 3 shows the results.

[Comparative Example 3]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 13 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the pick-up rate of the aqueous dispersion was changed to 110% in <Step of Forming Impregnated Sheet>. The obtained artificial leather had a supple texture, but was significantly poor in durability. Table 3 shows the results.

[Comparative Example 4]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 29 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 1 except that the pick-up rate of the aqueous dispersion was changed to 250% in <Step of Forming Impregnated Sheet>. The obtained artificial leather had excellent durability, but had a hard texture. Table 3 shows the results.

[Comparative Example 5]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Comparative Example 1 except that no dimethylsilicone was added to the raw stock and needle punching was performed at 2500 punches/cm² in <Step of Forming Fibrous Base Material>. The obtained artificial leather had a supple texture, but was significantly poor in durability. Table 4 shows the results.

[Comparative Example 6]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Comparative Example 5 except that a needle in which the "maximum number of pieces gripped by a needle barb" was 6 was used as a needle used in needle punching in <Step of Forming Fibrous Base Material>. The obtained artificial leather had a supple texture, but was significantly poor in durability. Table 4 shows the results.

[Comparative Example 7]

Artificial leather including ultrafine fibers having an average single-fiber diameter of 4.4 µm and 23 mass% of a polyurethane having a hydrophilic group was obtained in the same manner as in Example 2 except that the heat treatment time was changed to 3 minutes in <Step of Performing Heat Treatment>. The obtained artificial leather had a supple texture, but was significantly poor in durability. Table 4 shows the results.

[Table 1]

	Example 1	Example 2	Example 3	Example 4	Example 5
Average single-fiber diameter [µm]	4.4	4.4	4.4	4.4	4.4
Amount of silicone added to raw stock [mass%]	0.5	0.5	0.5	0.5	0.5
Maximum number of fibers gripped by needle barb [fibers]	10	10	10	10	10
Punching density [punches/cm²]	3500	3500	3500	3500	3500
Ratio of apparent density change before and after entanglement [-]	3.0	3.0	3.0	3.0	3.0
Kind of polyurethane precursor	PU-A	PU-B	PU-C	PU-A	PU-D
Weight average molecular weight of polyurethane precursor [-]	80000	55000	90000	80000	80000
Kind of crosslinking agent	A	A	A	A	A
Presence [Y] or absence [N] of polyester polyol included as constituent component in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Presence [Y] or absence [N] of polycarbonate polyol further included as constituent component in polyurethane having hydrophilic group	N	N	N	N	Y
Presence [Y] or absence [N] of N-acylurea bond in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Presence [Y] or absence [N] of isourea bond in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Content rate [mass%] of polyurethane having hydrophilic group	23	23	23	18	23
Atmospheric temperature [°C] in step of performing heat treatment	160	160	160	160	160
Heat treatment time [min] in step of performing heat treatment	10	10	10	10	10
Mass retention ratio [%] of polyurethane having hydrophilic group	72	65	76	72	72
Weight average molecular weight of dissolved component [-]	84000	60000	95000	84000	84000
Apparent density [g/cm³] of artificial leather	0.37	0.37	0.37	0.36	0.37
Nap length [µm]	280	330	290	320	220
Abrasion loss [mg] of artificial leather	20	22	18	24	15
Texture of artificial leather	A	A	B	A	B

[Table 2]

	Example 6	Example 7	Example 8	Example 9	Example 10
Average single-fiber diameter [µm]	4.4	4.4	4.4	4.4	4.4
Amount of silicone added to raw stock [mass%]	0.5	0.5	0.5	0	0
Maximum number of fibers gripped by needle barb [fibers]	10	10	10	10	10
Punching density [punches/cm²]	3500	3500	3500	3500	3000
Ratio of apparent density change before and after entanglement [-]	3.0	3.0	3.0	2.6	2.5
Kind of polyurethane precursor	PU-A	PU-A	PU-A	PU-A	PU-A
Weight average molecular weight of polyurethane precursor [-]	80000	80000	80000	80000	80000
Kind of crosslinking agent	A	A	A	A	A
Presence [Y] or absence [N] of polyester polyol included as constituent component in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Presence [Y] or absence [N] of polycarbonate polyol further included as constituent component in polyurethane having hydrophilic group	N	N	N	N	N
Presence [Y] or absence [N] of N-acylurea bond in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Presence [Y] or absence [N] of isourea bond in polyurethane having hydrophilic group	Y	Y	Y	Y	Y
Content rate [mass%] of polyurethane having hydrophilic group	23	23	23	23	23
Atmospheric temperature [°C] in step of performing heat treatment	180	160	150	160	160
Heat treatment time [min] in step of performing heat treatment	10	15	10	10	10
Mass retention ratio [%] of polyurethane having hydrophilic group	63	66	78	72	72
Weight average molecular weight of dissolved component [-]	86000	85000	89000	84000	84000
Apparent density [g/cm³] of artificial leather	0.37	0.37	0.37	0.33	0.30
Nap length [pm]	260	270	290	320	360
Abrasion loss [mg] of artificial leather	29	28	35	32	36
Texture of artificial leather	A	A	B	A	A

[Table 3]

	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4
Average single-fiber diameter [µm]	4.4	4.4	4.4	4.4
Amount of silicone added to raw stock [mass%]	0.5	0.5	0.5	0.5
Maximum number of fibers gripped by needle barb [fibers]	10	10	10	10
Punching density [punches/cm²]	3500	3500	3500	3500
Ratio of apparent density change before and after entanglement [-]	3.0	3.0	3.0	3.0
Kind of polyurethane precursor	PU-A	PU-E	PU-A	PU-A
weight average molecular weight of polyurethane precursor [-]	80000	110000	80000	80000
Kind of crosslinking agent	A	A	A	A
Presence [Y] or absence [N] of polyester polyol included as constituent component in polyurethane having hydrophilic group	Y	Y	Y	Y
Presence [Y] or absence [N] of polycarbonate polyol further included as constituent component in polyurethane having hydrophilic group	N	N	N	N
Presence [Y] or absence [N] of N-acylurea bond in polyurethane having hydrophilic group	Y	Y	Y	Y
Presence [Y] or absence [N] of isourea bond in polyurethane having hydrophilic group	Y	Y	Y	Y
Content rate [mass%] of polyurethane having hydrophilic group	23	23	13	29
Atmospheric temperature [°C] in step of performing heat treatment	160	160	160	160
Heat treatment time [min] in step of performing heat treatment	30	10	10	10
Mass retention ratio [%] of polyurethane having hydrophilic group	47	86	72	72
Weight average molecular weight of dissolved component [-]	93000	115000	84000	84000
Apparent density [g/cm³] of artificial leather	0.37	0.37	0.35	0.39
Nap length [pm]	250	250	340	250
Abrasion loss [mg] of artificial leather	47	18	55	17
Texture of artificial leather	A	C	A	C

[Table 4]

	Comparative Example 5	Comparative Example 6	Comparative Example 7
Average single-fiber diameter [µm]	4.4	4.4	4.4
Amount of silicone added to raw stock [mass%]	0	0	0.5
Maximum number of fibers gripped by needle barb [fibers]	10	8	10
Punching density [punches/cm²]	2500	2500	3500
Ratio of apparent density change before and after entanglement [-]	2.2	2.0	3.0
Kind of polyurethane precursor	PU-A	PU-A	PU-B
Weight average molecular weight of polyurethane precursor [-]	80000	80000	55000
Kind of crosslinking agent	A	A	A
Presence [Y] or absence [N] of polyester polyol included as constituent component in polyurethane having hydrophilic group	Y	Y	Y
Presence [Y] or absence [N] of polycarbonate polyol further included as constituent component in polyurethane having hydrophilic group	N	N	N
Presence [Y] or absence [N] of N-acylurea bond in polyurethane having hydrophilic group	Y	Y	Y
Presence [Y] or absence [N] of isourea bond in polyurethane having hydrophilic group	Y	Y	Y
Content rate [mass%] of polyurethane having hydrophilic group	23	23	23
Atmospheric temperature [°C] in step of performing heat treatment	160	160	160
Heat treatment time [min] in step of performing heat treatment	30	30	3
Mass retention ratio [%] of polyurethane having hydrophilic group	45	46	24
Weight average molecular weight of dissolved component [-]	92000	92000	46000
Apparent density [g/cm³] of artificial leather	0.33	0.31	0.37
Nap length [µm]	270	280	290
Abrasion loss [mg] of artificial leather	54	62	53
Texture of artificial leather	A	A	A

DESCRIPTION OF REFERENCE SIGNS

1:: Nap portion
2:: Base portion

Claims

Artificial leather comprising:
a fibrous base material including polyester ultrafine fibers having an average single-fiber diameter of 0.1 µm or more and 10.0 µm or less; and

a polyurethane having a hydrophilic group,

the fibrous base material and the polyurethane being constituents of the artificial leather, wherein

a content rate of the polyurethane having a hydrophilic group in the artificial leather is 15 mass% or more and 25 mass% or less,

after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, the polyurethane having a hydrophilic group has a mass retention ratio of 50 mass% or more and 80 mass% or less, and

after the artificial leather is immersed in N,N-dimethylformamide at 25°C for 24 hours, a component dissolved in the N,N-dimethylformamide has a weight average molecular weight of 50000 or more and 100000 or less.
The artificial leather according to claim 1, having an apparent density of 0.30 g/cm³ or more and 0.40 g/cm³ or less.
The artificial leather according to claim 1 or 2, wherein the polyurethane having a hydrophilic group includes a constituent component derived from a polyester polyol.
The artificial leather according to claim 3, wherein the polyurethane having a hydrophilic group further includes a constituent component derived from a polycarbonate polyol.
The artificial leather according to claim 1 or 2, wherein the polyurethane having a hydrophilic group has an N-acylurea bond and/or an isourea bond.
A method for manufacturing the artificial leather according to claim 1, the method comprising steps (1) to (4) described below in order, the steps (1) to (4) of:
(1) subjecting a nonwoven fabric including ultrafine fiber-generating fibers to a treatment for entanglement so that the nonwoven fabric has a ratio of density change before and after entanglement of 2.5 times or more and 3.5 times or less to form a fibrous base material;

(2) impregnating the fibrous base material with an aqueous dispersion, the aqueous dispersion containing a polyurethane precursor having a weight average molecular weight of 50000 or more and 100000 or less and a crosslinking agent, and then performing a heating and drying treatment to form an impregnated sheet including, as constituents, a fibrous base material and a polyurethane having a hydrophilic group;

(3) generating polyester ultrafine fibers from ultrafine fiber-generating fibers of the impregnated sheet to form a sheet before heat treatment including, as constituents, a fibrous base material including polyester ultrafine fibers, and the polyurethane having a hydrophilic group; and

(4) subjecting the sheet before heat treatment to a heat treatment at an atmospheric temperature of 150°C or more and 200°C or less for 5 minutes or more and 20 minutes or less.
The method according to claim 6, wherein the crosslinking agent is a carbodiimide-based crosslinking agent.
The method according to claim 6 or 7, wherein the step (1) includes adding 0.01 mass% or more and 3 mass% or less of silicone with respect to a mass of the ultrafine fiber-generating fibers.