JP2024051372A - Artificial leather and its manufacturing method - Google Patents

Abstract

[Problem] To provide an artificial leather having good quality and excellent texture, and furthermore, little change in texture and abrasion resistance over time, and a method for producing the same. [Solution] An artificial leather containing, as components, a fibrous base material including a nonwoven fabric made of ultrafine fibers having an average single fiber diameter of 0.1 μm to 10.0 μm, and a polyurethane resin, wherein the content of the fibrous base material in the entire artificial leather is 40.0 mass % to 60.0 mass %, the polyurethane resin has an isocyanurate structure, and the elution rate of the polyurethane resin in N,N-dimethylformamide is 30 mass % or less of the total mass of the polyurethane resin. [Selected Figures] None

Description

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

Artificial leather, which is made primarily of fibrous base materials such as nonwoven fabric and polyurethane, has excellent characteristics that natural leather does not have, such as excellent durability and ease of dyeing. In particular, artificial leather made with a fibrous base material made of ultrafine fibers has excellent surface quality and touch, and is being used more and more every year for clothing, miscellaneous goods, and automotive interior materials.

When producing such artificial leather, it is required that the leather changes little over time so that it can be used for long periods of time. In the method disclosed in Patent Document 1, it is reported that by subjecting artificial leather consisting of a polymeric elastomer having hydrophilic groups and a fibrous base material to a moist heat treatment under specific conditions, a certain amount of voids are generated between the fibers and the polymeric elastomer, resulting in artificial leather that is flexible and does not easily change in texture or shape over time.

JP 2022-27451 A

However, in the method disclosed in Patent Document 1, a crosslinking agent is used in combination with the polyurethane when it solidifies, and hydrolysis is likely to occur at the crosslinking points of the polyurethane. This hydrolysis of the polyurethane progresses over time, and as a result, the long-term stability of the polyurethane itself is insufficient, resulting in a problem of reduced abrasion resistance over time.

In view of the above background of the prior art, the object of the present invention is to provide an artificial leather that has good quality and excellent texture, and furthermore, exhibits little change in texture and abrasion resistance over time, and a method for producing the same.

The present invention was completed as a result of extensive research to achieve the above-mentioned objective, and provides the following inventions:

[1] An artificial leather comprising, as its constituent elements, a fibrous base material containing a nonwoven fabric made of ultrafine fibers with an average single fiber diameter of 0.1 μm or more and 10.0 μm or less, and polyurethane, wherein the content of the fibrous base material in the entire artificial leather is 40.0% by mass or more and 60.0% by mass or less, the polyurethane has an isocyanurate structure, and the elution rate of the polyurethane in N,N-dimethylformamide is 30.0% by mass or less of the total mass of the polyurethane.

[2] The artificial leather described in [1] above, in which the ultrafine fibers form fiber bundles consisting of 5 to 100 fibers, and the ratio of the fiber bundles in which half or more of the periphery is covered with polyurethane to the total number of the fiber bundles observed within the observation range of a scanning electron microscope photograph of a cross section cut perpendicular to the surface of the artificial leather is 20% to 70%.

[3] The artificial leather according to [1] or [2], wherein the polyurethane has a hydrophilic group.

[4] A method for producing the artificial leather according to [1] or [2],
A step of forming a fibrous substrate comprising a nonwoven fabric made of ultrafine fiber-developing composite fibers;
an impregnation step of impregnating the fibrous base material with a solution or aqueous dispersion containing a polyurethane precursor and a heat-sensitive coagulant as main components of a solute or dispersoid;
A drying step of performing drying at a temperature of 100° C. or more and 180° C. or less;
a step of expressing the ultrafine fibers from the ultrafine fiber-expressing composite fibers in the polyurethane-coated nonwoven fabric obtained after the drying step,
The impregnation step and the drying step are repeated two to five times.
A method for manufacturing artificial leather.

The present invention provides artificial leather that has good quality and excellent texture, and furthermore, changes in texture and abrasion resistance over time are minimal.

The artificial leather of the present invention contains as its components a fibrous base material containing a nonwoven fabric made of ultrafine fibers and a polyurethane resin.

[Ultrafine fibers]
Resins that can be used for the ultrafine fibers include, for example, polyester-based resins and polyamide-based resins from the viewpoint of excellent durability, particularly mechanical strength, heat resistance, and light resistance. Specific examples of polyester-based resins include polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. Polyester-based resins can be obtained, for example, from dicarboxylic acid and/or its ester-forming derivative and diol.

Examples of the dicarboxylic acid and/or its ester-forming derivative used in the polyester resin include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid and its ester-forming derivative. The ester-forming derivative in the present invention is a lower alkyl ester of a dicarboxylic acid, an acid anhydride, an acyl chloride, etc. Specifically, methyl ester, ethyl ester, hydroxyethyl ester, etc. are preferably used. A more preferred embodiment of the dicarboxylic acid and/or its ester-forming derivative used in the present invention is terephthalic acid and/or its dimethyl ester.

Diols used in the polyester resin include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and cyclohexanedimethanol. Of these, ethylene glycol is preferably used.

Examples of the polyamide-based resin that can be used include polyamide 6, polyamide 66, polyamide 56, polyamide 610, polyamide 11, polyamide 12, and copolymer polyamide.

The resin used in the ultrafine fibers can contain inorganic particles such as titanium oxide particles, lubricants, pigments, heat stabilizers, UV absorbers, conductive agents, heat storage agents, antibacterial agents, etc., depending on various purposes.

When a pigment is added to the ultrafine fibers for the purpose of coloring the fibers, it is preferable that the area ratio of the pigment to the cross-sectional area of one ultrafine fiber is 2% or more and 15% or less. When the area ratio is 2% or more, preferably 2.4% or more, the fibers are sufficiently colored and the deterioration of the surface quality over time due to color fading can be suppressed. Furthermore, when the area ratio is 15% or less, preferably 13% or less, the strength of the ultrafine fibers can be maintained at a level that can withstand practical use.

The area ratio of the pigment to the cross-sectional area of one ultrafine fiber is calculated by the following method. That is, a cross section of the artificial leather cut in the thickness direction is observed with a transmission electron microscope (TEM). For any 10 ultrafine fiber cross sections within the observation surface, the area of each ultrafine fiber cross section and the total area of the pigment present in one ultrafine fiber cross section are calculated. The total area of the pigment present in one ultrafine fiber cross section is divided by the area of each ultrafine fiber cross section, and the result multiplied by 100 is the area ratio of the pigment to the cross-sectional area of one ultrafine fiber.

It is also preferable that the resin used in the ultrafine fibers contains components derived from biomass resources.

As the biomass resource-derived component of the polyester resin, a biomass resource-derived component may be used as the constituent dicarboxylic acid or its ester-forming derivative, or a biomass resource-derived component may be used as the diol. From the viewpoint of reducing the environmental load, it is preferable to use biomass resource-derived components for both the dicarboxylic acid or its ester-forming derivative and the diol.

As the biomass resource-derived components of the polyamide resin, for example, polyamide 56, polyamide 610, and polyamide 11 are preferably used, because the raw materials derived from biomass resources can be obtained economically advantageously and because of the physical properties of the fibers.

The cross-sectional shape of the ultrafine fibers may be either round or irregular. Specific examples of irregular cross-sections include ovals, flats, polygons such as triangles, sectors, and crosses.

The average single fiber diameter of the ultrafine fibers is 0.1 μm or more and 10.0 μm or less. By making the average single fiber diameter of the ultrafine fibers 10.0 μm or less, preferably 7.0 μm or less, more preferably 5.0 μm or less, the artificial leather can be made more flexible. In addition, the quality of the nap can be improved. On the other hand, by making the average single fiber diameter of the ultrafine fibers 0.1 μm or more, preferably 0.3 μm or more, more preferably 0.7 μm or more, the artificial leather can have excellent color development after dyeing. In addition, when performing a nap raising process by buffing, the ease of dispersion and handling of the ultrafine fibers present in a bundle can be improved.

The average single fiber diameter in the present invention is measured by the following method.
(1) A cross section of an artificial leather cut in the thickness direction is observed using a scanning electron microscope (SEM).
(2) The fiber diameters of 50 random ultrafine fibers within the observation plane are measured in three directions on the cross section of each ultrafine fiber. However, when ultrafine fibers with a modified cross section are used, the cross-sectional area of a single fiber is first measured, and the diameter of a circle having the cross-sectional area is calculated by the following formula. The diameter thus obtained is the single fiber diameter of the single fiber.
Single fiber diameter (μm)=(4×(cross-sectional area of single fiber (μm ² ))/π) ^1/2
(3) Calculate the arithmetic mean value (μm) of the total 150 points obtained, and round off to the first decimal place.

[Fiber base material]
The fibrous base material includes a nonwoven fabric made of the ultrafine fibers. It is acceptable for the fibrous base material to contain a mixture of ultrafine fibers made of different raw materials.

Specific forms of the nonwoven fabric include those in which the ultrafine fibers are entangled with each other and those in which fiber bundles of ultrafine fibers are entangled. Among these, those in which fiber bundles of ultrafine fibers are entangled are preferably used from the viewpoint of the strength and texture of the artificial leather. From the viewpoint of flexibility and texture, it is particularly preferable to use a nonwoven fabric in which the ultrafine fibers forming the fiber bundles of ultrafine fibers are appropriately spaced apart and have voids. In this way, a nonwoven fabric in which fiber bundles of ultrafine fibers are entangled can be obtained, for example, by entangling ultrafine fiber-expressing fibers in advance and then expressing the ultrafine fibers. In addition, a nonwoven fabric in which the ultrafine fibers forming the fiber bundles of ultrafine fibers are appropriately spaced apart and have voids can be obtained, for example, by using sea-island composite fibers in which the sea component can be removed to form voids between the island components.

The nonwoven fabric is preferably a short-fiber nonwoven fabric made of ultra-fine fibers having a certain fiber length. By using a short-fiber nonwoven fabric, the texture and quality of the artificial leather can be further improved. In addition, the fibers oriented in the thickness direction of the fibrous substrate are more numerous than in a long-fiber nonwoven fabric, and a high sense of density can be obtained on the surface of the fibrous substrate when it is raised.

Specifically, the average fiber length of the ultrafine fibers is preferably in the range of 25 mm or more and 90 mm or less. By making the average fiber length 25 mm or more, more preferably 35 mm or more, and even more preferably 40 mm or more, the ultrafine fibers are sufficiently entangled, resulting in an artificial leather with better abrasion resistance. In addition, by making the average fiber length 90 mm or less, more preferably 80 mm or less, and even more preferably 70 mm or less, the artificial leather has better texture and quality.

In the present invention, the average fiber length of the ultrafine fibers is calculated by the following method. That is, cuts are made with scissors at three random locations on the artificial leather, and tears are made by hand. From the cross section of each tear that was not cut with scissors, 10 ultrafine fibers are extracted with tweezers and the fiber lengths are measured. The number average (mm) of the measured fiber lengths of the 30 fibers is rounded off to the first decimal place to obtain the average fiber length of the ultrafine fibers.

For the purpose of improving the strength of the fibrous substrate, a woven or knitted fabric may be inserted, laminated, or lined inside the nonwoven fabric. The average single fiber diameter of the fibers constituting the woven or knitted fabric is preferably 0.3 μm or more and 10.0 μm or less in order to suppress damage during needle punching and maintain strength.

The fibers constituting the woven or knitted fabrics can be, for example, polyesters such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polylactic acid; synthetic fibers such as polyamides such as nylon 6 and nylon 66; regenerated fibers such as cellulose-based polymers; and natural fibers such as cotton and hemp.

It is important that the content of the fibrous base material in the artificial leather is 40.0% by mass or more and 60.0% by mass or less. By having the content of the fibrous base material be 40.0% by mass or more, preferably 43.0% by mass or more, and more preferably 45.0% by mass or more, the artificial leather can have a strength that can withstand practical use. In addition, by having the content of the fibrous base material be 60.0% by mass or less, preferably 57.0% by mass or less, and more preferably 55.0% by mass or less, the fibrous base material can have a moderate amount of voids, making it easier for the fiber bundles to assume a structure coated with the polyurethane resin, and the fibrous base material is firmly held by the polyurethane resin, so that shape changes such as twisting and wrinkles can be suppressed. Furthermore, since the proportion of the polyurethane resin in the entire artificial leather is increased, the effects of hydrolysis of polyurethane can be reduced.

The content of fibrous substrate in artificial leather can be calculated by the following method. That is, in order to remove the fibrous substrate contained in the artificial leather, it is subjected to immersion extraction with hexafluoroisopropanol (HFIP), and then separated into soluble and insoluble matter by filtration. The mass of the soluble matter is taken as the mass of the fibrous substrate, and the mass of the soluble matter is divided by the mass of the entire artificial leather, multiplied by 100, and the value obtained by rounding off to one decimal place (%) is taken as the proportion of the mass of the fibrous substrate in the artificial leather.

[Polyurethane resin]
It is important for the artificial leather of the present invention that the polyurethane resin has an isocyanurate structure. By having the polyurethane resin have an isocyanurate structure, the hydrolysis resistance of the polyurethane is improved, and deterioration over time of the texture and abrasion resistance of the artificial leather due to hydrolysis of the polyurethane can be suppressed.

The polyurethane resin preferably has a hydrophilic group. When the polyurethane resin has a hydrophilic group, an artificial leather with excellent solvent resistance can be obtained. Furthermore, when the polyurethane resin has a hydrophilic group, the polyurethane resin can be handled as an aqueous dispersion in which the polyurethane resin is dispersed in water, eliminating the need to use an organic solvent as a solvent for the polyurethane resin, and reducing harmfulness to humans and the environment.

In the present invention, "having a hydrophilic group" refers to the fact that the polyurethane has a hydrophilic group having active hydrogen in the main chain or side chain, and the "hydrophilic group" here refers to a functional group that has a high affinity for water. Specific examples of hydrophilic groups include hydroxyl groups, carboxyl groups, sulfonic acid groups, and amino groups.

It is preferable that the polyurethane resin does not have amide bonds or ester bonds other than urethane bonds. These bonds are likely to be the starting point of hydrolysis, so by having polyurethane that does not have these bonds other than urethane bonds, the occurrence of hydrolysis can be suppressed, and the change over time in the texture and abrasion resistance of the artificial leather can be suppressed.

The presence or absence of amide bonds and ester bonds other than the urethane bonds can be confirmed by infrared spectroscopy using, for example, a Fourier transform infrared spectrophotometer.

As the polyurethane, a resin obtained by reacting a polymer polyol having a number average molecular weight of preferably 500 to 5000, an organic polyisocyanate, and a chain extender is preferably used. In order to increase the stability of the polyurethane aqueous dispersion, it is preferable to use a hydrophilic group-containing active hydrogen component described later in combination. By making the number average molecular weight of the polymer polyol 500 or more, more preferably 1500 or more, it is possible to easily prevent the texture from becoming hard. In addition, by making the number average molecular weight 5000 or less, more preferably 4000 or less, it is possible to easily maintain the strength of the polyurethane resin as a binder.

The following describes the case where a polyurethane resin having hydrophilic groups is used as the polyurethane resin.

(1) Reaction Components of Polyurethane Resin Having a Hydrophilic Group First, the reaction components of the polyurethane resin having a hydrophilic group will be described.

(1-1) Polymer Polyol Examples of the polymer polyol include polyether polyols, polyester polyols, and polycarbonate polyols.

The polyether polyols include polyols obtained by addition polymerization of monomers such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, and cyclohexylene using polyhydric alcohols or polyamines as initiators, and polyols obtained by ring-opening polymerization of the monomers using protonic acids, Lewis acids, cationic catalysts, etc. as catalysts. Specific examples include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene ether glycol, etc., and copolymer polyols that combine these.

Examples of the polyester polyol include polyester polyols obtained by condensing various low molecular weight polyols with polybasic acids, and polyols obtained by open polymerization of lactones.

Examples of the low molecular weight polyol include 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. In addition, adducts obtained by adding various alkylene oxides to bisphenol A can also be used as low molecular weight polyols.

The polybasic acid may be, for example, 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.

The polycarbonate-based polyols include compounds obtained by reacting polyols with carbonate compounds such as dialkyl carbonates and diaryl carbonates.

As the polyols used as raw materials for producing polycarbonate polyols, the polyols listed as raw materials for producing polyester polyols can be used. As the dialkyl carbonates, dimethyl carbonate, diethyl carbonate, etc. can be used, and as the diaryl carbonates, diphenyl carbonate, etc. can be used.

In the artificial leather of the present invention, it is preferable that the polyurethane resin having a hydrophilic group contains polyether diol as a constituent component. In this specification, "containing as a constituent component" means containing as a monomer component or oligomer component that constitutes polyurethane. Polyether diol has a high degree of freedom of its ether bond, so that the glass transition temperature is low and the cohesive force is weak, making it easier to obtain a polyurethane resin with excellent flexibility.

(1-2) Organic Diisocyanate Examples of the organic diisocyanate include aromatic diisocyanates having 6 to 20 carbon atoms (excluding carbons in NCO groups, the same applies below), aliphatic diisocyanates having 2 to 18 carbon atoms, alicyclic diisocyanates having 4 to 15 carbon atoms, araliphatic diisocyanates having 8 to 15 carbon atoms, modified products of these diisocyanates (carbodiimide modified products, urethane modified products, urethodione modified products, etc.), and mixtures of two or more of these.

Specific examples of the aromatic diisocyanates having 6 to 20 carbon atoms include 1,3- and/or 1,4-phenylene diisocyanate, 2,4- and/or 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.

Specific examples of the aliphatic diisocyanates having 2 to 18 carbon atoms include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl)carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexaate.

Specific examples of the alicyclic diisocyanates having 4 to 15 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.

Specific examples of the aromatic aliphatic diisocyanates having 8 to 15 carbon atoms include m- and/or p-xylylene diisocyanate and α,α,α',α'-tetramethylxylylene diisocyanate.

Among these, the preferred organic diisocyanates are alicyclic diisocyanates. The most preferred organic diisocyanate is dicyclohexylmethane-4,4'-diisocyanate.

(1-3) Chain extender Examples of the chain extender 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 isophorone diamine,
Aromatic diamines such as 4,4-diaminodiphenylmethane,
aromatic aliphatic diamines such as xylylene diamine;
Alkanolamines such as ethanolamine,
Hydrazine,
Dihydrazides such as adipic dihydrazide;
And mixtures of two or more of these are also included.

Among these, preferred chain extenders are water, low molecular weight diols, and aromatic diamines, and more preferred are water, ethylene glycol, 1,4-butanediol, 4,4'-diaminodiphenylmethane, and mixtures of two or more of these.

(1-4) Catalyst for Isocyanate Trimerization Reaction In order to form an isocyanurate structure in the polyurethane resin, it is preferable to use a catalyst (trimerization catalyst) that promotes the trimerization reaction of isocyanate. For example, potassium salts and quaternary ammonium salts can be used as the trimerization catalyst.

(2) Heat-sensitive coagulant As described later, it is preferable to add a heat-sensitive coagulant to a solution or aqueous dispersion containing a polyurethane precursor having a hydrophilic group (polyurethane in a state before solidification). As the heat-sensitive coagulant, a monovalent cation-containing inorganic salt is preferable.

(3) Component that causes polyurethane to contain hydrophilic group In the polyurethane having the hydrophilic group, a component that causes polyurethane to contain a hydrophilic group can be, for example, a hydrophilic group-containing active hydrogen compound. Examples of the hydrophilic group-containing active hydrogen compound include compounds that contain a nonionic group, an anionic group, a cationic group, or a combination thereof, and active hydrogen.

Examples of compounds having a nonionic group and active hydrogen include compounds that contain two or more active hydrogen components or two or more isocyanate groups and have a polyoxyethylene glycol group with a molecular weight of 250 to 9000 on the side chain, and triols such as trimethylolpropane and trimethylolbutane.

Examples of compounds 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 derivatives thereof; sulfonic acid group-containing compounds such as 1,3-phenylenediamine-4,6-disulfonic acid and 3-(2,3-dihydroxypropoxy)-1-propanesulfonic acid, and derivatives thereof; and salts of these compounds neutralized with a neutralizing agent.

Examples of compounds 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.

The hydrophilic group-containing active hydrogen compound can also be used in the form of a salt neutralized with a neutralizing agent.

As the hydrophilic group-containing active hydrogen compound, it is preferable to use 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and neutralized salts thereof from the viewpoint of the mechanical strength and dispersion stability of the polyurethane resin having a hydrophilic group.

Polyurethane resins can contain pigments such as titanium oxide and carbon black, dyes, anti-mold agents, UV absorbers such as benzophenones and benzotriazoles, various stabilizers such as hindered phenols such as 4,4-butylidene-bis(3-methyl-6-1-butylphenol), antioxidants such as organic phosphites such as triphenyl phosphite and trichloroethyl phosphite, light resistance agents such as light stabilizers, flame retardants, lubricants, water repellents, surfactants such as antistatic agents, fillers such as cellulose, inorganic fillers such as calcium carbonate, inorganic particles such as silica and titanium oxide, etc.

[Artificial leather]
In the artificial leather of the present invention, the ultrafine fibers preferably form a fiber bundle of 5 to 200 fibers. The ultrafine fibers forming the fiber bundle are preferably 5 or more, more preferably 8 or more, and even more preferably 10 or more, so that the ultrafine fiber-generating fibers can have a fiber diameter suitable for entanglement. The ultrafine fibers forming the fiber bundle are preferably 200 or less, more preferably 130 or less, and even more preferably 100 or less, so that the dispersion of the ultrafine fibers can be improved, and an artificial leather having a good touch can be obtained. In addition, in the observation of the artificial leather, a collection of multiple ultrafine fibers that can be regarded as facing in the same direction can be regarded as a fiber bundle. In addition, in the present invention, the fact that the ultrafine fibers can be regarded as facing in the same direction means that the cross sections of the ultrafine fibers can be regarded as having substantially the same shape. For example, if ultrafine fibers having the same circular cross section (which can also be said to be an ellipse with an aspect ratio of 0) are gathered in the vicinity of 10 fibers in the cross section of the artificial leather, the collection can be said to be a fiber bundle formed of 10 ultrafine fibers.

The number of ultrafine fibers forming a fiber bundle, which can be counted from observing the artificial leather, is calculated by the following method. That is, 10 images of a cross section of the artificial leather cut in the thickness direction are taken with a scanning electron microscope (SEM, for example, Keyence Corporation's "VHX-D500/D510") at a magnification of 1200 to 1700 times so that the total number of ultrafine fiber cross sections facing the observation surface that are present in the observation range are 200 or more. Then, for each of the 10 images, the number of ultrafine fibers forming what can be considered a "fiber bundle" is counted, and the average number (number of fibers) per fiber bundle is rounded off to the first decimal place to determine the number of ultrafine fibers forming the fiber bundle.

In the artificial leather of the present invention, it is important that the elution rate of the polyurethane resin by DMF is 30.0 mass% or less of the total mass of the polyurethane resin. By making the elution rate of the polyurethane resin by DMF 30.0 mass% or less, preferably 25.0 mass% or less, the artificial leather has excellent chemical resistance and is less susceptible to elution of the polyurethane resin due to wetting or adhesion of chemicals, and as a result, the change over time in the texture and abrasion resistance of the artificial leather can be suppressed.

In the present invention, the elution rate of polyurethane resin by DMF is calculated by the following method.

That is, the artificial leather sample is immersed in hexafluoroisopropanol (HFIP) to extract the fibrous base material, and then separated into soluble and insoluble matter by filtration. The mass of the insoluble matter is taken as the mass of polyurethane resin, and the mass of the insoluble matter is divided by the mass of the sample before immersion to obtain the polyurethane resin content in the artificial leather.

In addition, another sample of the same artificial leather is immersed in DMF at 25°C for 15 hours to dissolve the polyurethane resin, then washed with water and dried, and the masses before and after are compared to calculate the mass of polyurethane resin dissolved in DMF. The mass of the dissolved polyurethane resin is divided by the mass of the sample before immersion in DMF to obtain the percentage of polyurethane resin dissolved in DMF in the artificial leather.

Next, the percentage of polyurethane resin dissolved into DMF in the artificial leather is divided by the content of polyurethane resin in the artificial leather, multiplied by 100, and the resulting value (mass%) is rounded off to the second decimal place to obtain the percentage of polyurethane resin dissolved into DMF.

The above elution rate can be set within the above range by adjusting, for example, each reactive component of the polyurethane resin, the weight average molecular weight, or the number of repetitions of the impregnation process in which a solution or aqueous dispersion in which the polyurethane precursor and the heat-sensitive coagulant are the main components of the solute or dispersoid is impregnated and the drying process. As an example, by increasing the weight average molecular weight of the polyurethane, it is possible to make the polyurethane less soluble in DMF.

In the artificial leather of the present invention, the ratio of the fiber bundles having at least half of their circumference covered with polyurethane resin to the total number of the fiber bundles, as observed within the observation range of a scanning electron microscope photograph of a cross section cut perpendicular to the surface of the artificial leather, is preferably 20.0% or more and 70.0% or less. When the ratio of the fiber bundles is preferably 20.0% or more, more preferably 30.0% or more, and even more preferably 35.0% or more, the fiber bundles are firmly held by the polyurethane resin, and shape changes such as twisting and wrinkles can be suppressed. In addition, when the ratio of the fiber bundles is preferably 70.0% or less, more preferably 65.0% or less, and even more preferably 60.0% or less, an artificial leather with a good touch and a feeling of raised nap can be obtained.

The ratio of the fiber bundles is calculated as follows:
(1) A cross section of the artificial leather cut in the thickness direction is observed using a scanning electron microscope (SEM, for example, "VHX-D500/D510" manufactured by Keyence Corporation). The conditions for the observation range are to satisfy the following (a) to (c).
(a) The total number of ultrafine fiber bundles facing the observation surface within the observation area is 100 or more.
(b) If the sheet surface is napped, the napped portion should not be included in the observation range.
(c) If a woven or knitted fabric is inserted inside the nonwoven fabric, the cross-section of the fibers that make up the woven or knitted fabric should not be included in the observation range.
(2) Count the number of fiber bundles present within the observation range. Note that "present within the observation range" means that the entire periphery of the fiber bundle is contained within the observation range.
(3) Among the fiber bundles present within the observation range, the number of fiber bundles having half or more of their outer circumference covered with polyurethane resin is counted. Note that, when a fiber bundle is in contact with other fiber bundles without polyurethane resin, if half or more of the combined outer circumference of all the fiber bundles in contact is covered with polyurethane resin, all of these fiber bundles are counted as the number of fiber bundles having half or more of their outer circumference covered with polyurethane resin.
(4) Calculate the percentage of fiber bundles in which more than half of the outer circumference of the fiber bundle is covered with polyurethane resin according to the following formula 1, and round off the obtained value (%) to one decimal place.
Percentage (%) of fiber bundles the half or more of whose periphery is covered with polyurethane resin = 100 × (number of fiber bundles the half or more of whose periphery is covered with polyurethane resin) / (number of fiber bundles the entire periphery of which is contained within the observation range) ... (Equation 1).

The ratio of the fiber bundles can be set within the above range by adjusting the drying time after impregnation with polyurethane resin and the number of times the impregnation and drying steps are repeated. By extending the drying time after impregnation with polyurethane resin, the thermal movement of the polyurethane resin improves the adhesive strength between the fibers and the polyurethane resin, making it easier to obtain a structure in which the fiber bundles are covered with polyurethane resin. In addition, by increasing the number of times the impregnation and drying steps are repeated, the amount of polyurethane resin applied to the fibrous base material can be increased, making it easier to obtain a structure in which the fiber bundles are covered with polyurethane resin.

In the abrasion resistance test of the artificial leather of the present invention, specified in "8.19.5 E method (Martindale method)" of "8.19 Abrasion resistance and friction discoloration" of JIS L1096:2010 "Test methods for woven and knitted fabrics," and performed under conditions of a pressing load of 12.0 kPa and 20,000 abrasion cycles, it is preferable that the abrasion loss after 10 weeks of jungle testing at 70°C and 95% is 0% or more and 30% or less compared to the abrasion loss before the jungle test. By having the abrasion loss change rate be 30% by mass or less, preferably 25% by mass or less, the artificial leather can be made to have little change in abrasion resistance over time.

[Manufacturing method of artificial leather]
The method for producing an artificial leather of the present invention includes a step of forming a fibrous base material containing a nonwoven fabric made of ultrafine fiber-developing composite fibers.

As the ultrafine fiber-producing fiber, it is preferable to use an island-in-sea composite fiber in which the sea component and island component are made of two thermoplastic resin components with different solvent solubility (two or three components if the island fiber is a core-sheath composite fiber), and the sea component is dissolved and removed using a solvent or the like to turn the island components into ultrafine fibers, because appropriate gaps can be provided between the island components, i.e., between the ultrafine fibers inside the fiber bundle, when the sea component is removed. This is because this can provide appropriate gaps between the island components, i.e., between the ultrafine fibers inside the fiber bundle, when the sea component is removed. This is preferable from the perspective of the texture and surface quality of the artificial leather.

As for the islands-in-the-sea composite fiber, a method using a polymer mutual alignment body in which two components, a sea component and an island component (three components if the island fiber is a core-sheath composite fiber), are mutually aligned and spun using an islands-in-the-sea composite spinneret is preferred from the viewpoint of obtaining ultrafine fibers with a uniform single fiber diameter.

As the sea component, polyethylene, polypropylene, polystyrene, copolymer polyesters copolymerized with sodium sulfoisophthalic acid or polyethylene glycol, and polylactic acid can be used, but polystyrene and copolymer polyesters are preferably used from the viewpoints of spinnability and ease of elution.

The mass ratio of the sea component to the island components, sea component/island component, is preferably within the range of 10/90 to 80/20. When the mass ratio of the sea component is 10% by mass or more, more preferably 20% by mass or more, the island components are easily and sufficiently finely divided. When the mass ratio of the sea component is 80% by mass or less, more preferably 70% by mass or less, the proportion of eluted components is small, thereby improving productivity.

When a staple fiber nonwoven fabric is used as the fiber entanglement, the obtained ultrafine fiber-developing fiber is preferably subjected to a crimping process and cut to a predetermined length to obtain raw cotton. The crimping and cutting processes can be carried out by known methods.

Next, the obtained raw cotton is made into a fiber web using a cross wrapper or the like, and then entangled to obtain a staple fiber nonwoven fabric. Methods for entangling the fiber web to obtain a staple fiber nonwoven fabric include needle punching and water jet punching.

When stacking and integrating staple fiber nonwoven fabric and woven fabric, the woven fabric can be stacked on one or both sides of the staple fiber nonwoven fabric, or the woven fabric can be sandwiched between multiple staple fiber nonwoven fabric webs, and then the fibers of the staple fiber nonwoven fabric and the woven fabric can be entangled and integrated by needle punching, water jet punching, etc.

The apparent density of the short fiber nonwoven fabric made of ultrafine fiber development type fibers after needle punching or water jet punching is preferably 0.15 g/ ^cm3 or more and 0.45 g/ ^cm3 or less. By setting the apparent density to preferably 0.15 g/ ^cm3 or more, the fibrous substrate can obtain sufficient shape stability and dimensional stability. On the other hand, by setting the apparent density to preferably 0.45 g/ ^cm3 or less, sufficient space for applying the polyurethane resin can be maintained.

From the viewpoint of densification, the nonwoven fabric obtained in this manner is preferably shrunk by dry heat, wet heat, or both to further increase the density. The nonwoven fabric can also be compressed in the thickness direction by calendaring or the like.

The method for producing the artificial leather of the present invention involves an impregnation step in which a fibrous substrate containing a nonwoven fabric made of the ultrafine fiber-developing composite fiber is impregnated with a solution or aqueous dispersion containing a polyurethane precursor and a heat-sensitive coagulant as the main components of the solute or dispersoid (hereinafter also referred to as a "precursor solution" or "precursor dispersion"). By applying a polyurethane resin to the nonwoven fabric made of the ultrafine fiber-developing fibers, the ultrafine fibers tend to remain as fiber bundles even after the ultrafine fibers are developed, making it possible to produce an artificial leather with little change in shape.

When applying polyurethane resin to a fibrous substrate, it is done by impregnating it with the precursor solution or the precursor dispersion. The term "polyurethane precursor" here refers to polyurethane in a state before it is solidified by means of coagulation or solidification, which will be described later. Hereinafter, it may be simply called "precursor". The precursor solution or precursor dispersion can be used according to the characteristics of the polyurethane. As the solvent and dispersion medium for the precursor solution and the precursor dispersion, water or a water-miscible organic solvent such as N,N-dimethylformamide can be used, but since organic solvents are generally highly harmful to the environment, it is preferable to use water.

From the viewpoint of storage stability of the precursor solution or the precursor dispersion, the concentration of the precursor solution or the precursor dispersion (the content relative to the precursor solution or the precursor dispersion) is preferably 5% by mass or more and 50% by mass or less, and more preferably 8% by mass or more and 40% by mass or less.

As the polyurethane precursor, it is preferable to use a polyurethane having a weight average molecular weight of 1,000,000 or more and 2,000,000 or less. By making the weight average molecular weight of the polyurethane 1,000,000 or more, preferably 1,100,000 or more, it is possible to reduce the elution rate in DMF and other organic solvents, and when made into artificial leather, the artificial leather has excellent chemical resistance and is less susceptible to elution of polyurethane resin due to wetting or adhesion of chemicals, and as a result, it is possible to suppress the change over time in the texture and abrasion resistance of the artificial leather. In addition, from the viewpoint of viscosity stability and workability, it is preferable that the weight average molecular weight of the polyurethane is 2,000,000 or less, preferably 1,900,000 or less.

The heat-sensitive coagulant is preferably an inorganic salt containing a monovalent cation. By adding an inorganic salt containing a monovalent cation, it is possible to impart heat-sensitive coagulability to the polyurethane precursor in the dispersion. In the present invention, heat-sensitive coagulability refers to the property that when the precursor solution or the precursor dispersion is heated, the fluidity of the precursor solution or the precursor dispersion decreases and the polyurethane coagulates when a certain temperature (heat-sensitive coagulation temperature) is reached.

By imparting heat-sensitive coagulation properties to the polyurethane precursor, it is possible to suppress the occurrence of migration, a phenomenon in which the polyurethane precursor migrates to the sheet surface as moisture evaporates.

The monovalent cation-containing inorganic salt is preferably sodium chloride and/or sodium sulfate. In conventional methods, inorganic salts having divalent cations such as magnesium sulfate and calcium chloride have been suitably used as heat-sensitive coagulants. However, even a small amount of these inorganic salts significantly affects the stability of the solution or aqueous dispersion, so that depending on the type of precursor, it is difficult to precisely control the heat-sensitive gelation temperature by adjusting the amount of addition, and there are also issues such as concerns about gelation during preparation and storage of the precursor solution or precursor dispersion. On the other hand, inorganic salts containing monovalent cations with a small ionic valence have little effect on the stability of the precursor solution or precursor dispersion, and by adjusting the amount of addition, it is possible to strictly control the heat-sensitive coagulation temperature while ensuring the stability of the precursor solution or precursor dispersion.

The thermosensitive coagulation temperature of the precursor solution or the precursor dispersion is preferably 55°C or higher and 80°C or lower. By setting the thermosensitive coagulation temperature at 55°C or higher, more preferably 60°C or higher, the stability of the precursor solution or the precursor dispersion during storage is improved, and adhesion of the polyurethane resin having hydrophilic groups to the inside of the manufacturing equipment during operation can be suppressed. In addition, by setting the thermosensitive coagulation temperature at 80°C or lower, more preferably 70°C or lower, the migration phenomenon of the polyurethane resin to the surface layer of the fibrous substrate can be suppressed, and further, by allowing the precursor to proceed to coagulate before the water evaporates from the fibrous substrate, a structure similar to that in the case of wet coagulation of a solvent-based polyurethane precursor, that is, a structure in which the polyurethane resin does not strongly bind the ultrafine fibers, can be formed. As a result, an artificial leather that is more flexible and has a resilient feel can be obtained.

In the impregnation step, it is also preferable to perform nipping in the precursor dispersion, generation of a liquid flow by stirring, spraying of the precursor solution or the precursor dispersion onto the sheet by injection, etc. By adopting the above-mentioned method, it is possible to make it easier to impregnate the precursor solution or the precursor dispersion into the fibrous substrate, even if the impregnation and drying of the precursor solution or the precursor dispersion into the fibrous substrate is performed multiple times, as described below.

In the method for producing the artificial leather of the present invention, the impregnation step is followed by a drying step. That is, in the drying step, a dry heat coagulation method is performed to coagulate the polyurethane precursor. This dry heat coagulation method is a very simple method in which a sheet impregnated with the precursor solution or precursor dispersion is heat-treated with a hot air dryer or the like, and is a method with excellent processability without the risk of the polyurethane resin falling off.

The temperature in the drying process is 100°C or higher and 180°C or lower. By setting the heating temperature to 100°C or higher, and preferably 120°C or higher, the polyurethane precursor is quickly solidified to form polyurethane, and it is possible to prevent the polyurethane resin from being unevenly distributed on the underside of the artificial leather due to its own weight during processing. Furthermore, by setting the heating temperature to 180°C or lower, and preferably 160°C or lower, it is possible to prevent thermal deterioration of the polyurethane precursor or polyurethane resin.

The drying time for each drying step is preferably 10 minutes or more and 30 minutes or less. By setting the drying time to 10 minutes or more, preferably 15 minutes or more, and more preferably 18 minutes or more, the thermal movement of the polyurethane resin improves the adhesive strength between the fiber and the polyurethane resin, making it easier to form a structure in which the fiber bundle is covered with the polyurethane resin. On the other hand, by setting the drying time to 30 minutes or less, preferably 25 minutes or less, and more preferably 22 minutes or less, the thermal degradation of the polyurethane resin can be suppressed, and the durability can be made practical when used as artificial leather.

In the method for producing artificial leather of the present invention, it is important to repeat the impregnation step and the drying step two or more times and up to five or less times. By repeating the steps two or more times, the amount of polyurethane resin applied to the fibrous base material can be increased, making it easier for the fiber bundles to assume a structure coated with polyurethane resin, and making it possible to produce artificial leather with excellent shape stability. In addition, by repeating the steps five or less times, it is possible to prevent too much polyurethane resin from adhering near the surface layer, making it possible to produce artificial leather with good quality and texture.

The precursor solution or the precursor dispersion may contain the additives described above, antiblocking agents such as silica or titanium oxide, viscosity adjusters, antifoaming agents such as silicone, penetrants, coagulation adjusters, etc.

When an island-in-sea composite fiber is used as the ultrafine fiber-producing fiber, the ultrafine fiber processing (sea-removal processing) can be carried out, for example, by immersing the island-in-sea composite fiber in a solvent and squeezing the liquid out. As a solvent for dissolving the sea component, when the sea component is polyethylene, polypropylene, or polystyrene, an organic solvent such as toluene or trichloroethylene can be used. When the sea component is a copolymer polyester or polylactic acid, an alkaline aqueous solution such as sodium hydroxide or hot water can be used.

For the process of producing ultrafine fibers, equipment such as a continuous dyeing machine, a vibro washer type seaweed removal machine, a liquid flow dyeing machine, a winch dyeing machine, and a jigger dyeing machine can be used.

After the ultrafine fiber development process, it is preferable to carry out a thorough washing process after the alkali treatment. By going through the washing process, the artificial leather can be processed without leaving any alkali or inorganic salts containing monovalent cations on the sheet, and can be processed without affecting the production equipment. It is preferable to use water as the washing liquid, taking into consideration environmental and safety aspects.

The drying temperature after washing is preferably 80°C or higher and 200°C or lower. By setting the drying temperature at 80°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher, drying can be performed efficiently in a short time. In addition, by setting the drying temperature at 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower, thermal decomposition of polyurethane can be suppressed.

In the present invention, at least one surface of the artificial leather may be subjected to a nap raising treatment to form nap on the surface. The method for forming nap is not particularly limited, and various methods commonly used in the field, such as buffing with sandpaper, can be used. If the nap length is too short, it is difficult to obtain an elegant appearance, and if it is too long, pilling tends to occur easily, so the nap length is preferably 0.2 mm or more and 1 mm or less.

Also, before the raising process, silicone or the like may be applied as a lubricant to the artificial leather. By applying a lubricant, raising by surface grinding becomes easy and the surface quality becomes very good, which is preferable. Also, an antistatic agent may be applied before the raising process. By applying an antistatic agent, grinding powder generated from the artificial leather by grinding is less likely to accumulate on the sandpaper, which is preferable.

Artificial leather can be dyed. For this dyeing process, various methods commonly used in this field can be used, such as flow dyeing using a jigger dyeing machine or flow dyeing machine, dip dyeing such as thermosol dyeing using a continuous dyeing machine, or printing on the napped surface using roller printing, screen printing, inkjet printing, sublimation printing, vacuum sublimation printing, etc. Among these, it is preferable to use a flow dyeing machine, since it is possible to soften the unbrushed artificial leather or artificial leather by imparting a kneading effect at the same time as dyeing the unbrushed artificial leather or artificial leather. In addition, various resin finishing processes can be applied after dyeing, if necessary.

The dyeing temperature depends on the type of fiber, but is preferably 80°C or higher and 150°C or lower. By setting the dyeing temperature at 80°C or higher, and more preferably at 110°C or higher, the fiber can be dyed efficiently. On the other hand, by setting the dyeing temperature at 150°C or lower, and more preferably at 130°C or lower, deterioration of the polyurethane can be prevented.

The dyes used in the present invention may be selected according to the type of fiber that constitutes the fibrous substrate, and are not particularly limited. For example, disperse dyes can be used for polyester fibers, and acid dyes or metal-containing dyes can be used for polyamide fibers, or combinations of these can be used. When dyeing with disperse dyes, reduction cleaning may be performed after dyeing.

It is also a preferred embodiment to use dyeing auxiliaries during dyeing. By using dyeing auxiliaries, the uniformity and reproducibility of the dyeing can be improved. In addition, finishing treatments can be performed using softeners such as silicone, antistatic agents, water repellents, flame retardants, light fasteners, and antibacterial agents in the same bath as dyeing or after dyeing.

In the present invention, from the viewpoint of manufacturing efficiency, it is also a preferred embodiment to cut the film in half in the thickness direction, regardless of whether it is before or after the dyeing process.

Furthermore, in one embodiment of the present invention, the surface can be given a design, if necessary. For example, post-processing such as perforation, embossing, laser processing, pinsonic processing, and printing can be performed.

Next, the artificial leather of the present invention will be described in more detail using examples. However, the present invention is not limited to these examples. In addition, unless otherwise specified, the measurements of each physical property were performed according to the above-mentioned method.

[Evaluation method]
(1) Dissolution rate of polyurethane resin by DMF A sample of artificial leather was immersed in hexafluoroisopropanol (HFIP) to extract the fibrous base material, and the fibrous base material was separated into soluble and insoluble matter by filtration. The mass of the insoluble matter was taken as the mass of polyurethane resin, and the mass of the insoluble matter was divided by the mass of the sample before immersion to obtain the content of polyurethane resin in the artificial leather.

In addition, another sample of the same artificial leather was immersed in DMF at 25°C for 15 hours to dissolve the polyurethane resin, then washed with water and dried, and the masses before and after were compared to calculate the mass of polyurethane resin dissolved in DMF. The mass of the dissolved polyurethane resin was divided by the mass of the sample before immersion in DMF to obtain the percentage of polyurethane resin dissolved in DMF in the artificial leather.

Next, the percentage of polyurethane resin dissolved into DMF in the artificial leather was divided by the content of polyurethane resin in the artificial leather and multiplied by 100 to obtain the percentage of polyurethane resin dissolved into DMF.

(2) Presence or absence of isocyanurate structure in polyurethane resin The polyurethane resin separated from the artificial leather was subjected to infrared spectroscopic analysis using a Fourier transform infrared spectrophotometer (FT/IR 4000 series manufactured by JASCO Corporation) to confirm the presence or absence of an isocyanurate structure.

(3) Average fiber length of ultrafine fibers (mm)
According to the above-mentioned method, 10 ultrafine fibers were extracted from each of three randomly selected locations of the artificial leather using tweezers, and the fiber lengths were measured, and the number average of the fiber lengths of the 30 fibers measured was calculated.

(4) Number of ultrafine fibers forming the fiber bundle (number of fibers)
A cross section of the artificial leather cut in the thickness direction was photographed at a magnification of 1500 times using a scanning electron microscope (SEM) (VHX-D500/D510 manufactured by Keyence Corporation) so as to satisfy the above-mentioned conditions of the observation range. The number of ultrafine fibers constituting the fiber bundle was counted for each of the 10 images, and the average value was calculated.

(5) Surface quality Evaluation was performed by a sensory test conducted by 11 subjects. Evaluation was performed as follows, and the level evaluated by the greatest number of people was determined as the surface quality of the artificial leather. In the case of an equal number of evaluations, the higher evaluation was determined as the surface quality of the artificial leather. In the present invention, A and B were determined as acceptable levels.
A: Very uniform surface quality.
B: The surface quality is uniform.
C: The surface quality is non-uniform.
D: The surface quality is very non-uniform.

(6) Texture Evaluation was performed by a sensory test with 11 subjects. Evaluation was performed as follows, and the level given by the largest number of people was determined to be the texture of the artificial leather. In the case of a tie, the higher rating was determined to be the texture of the artificial leather. In the present invention, A and B were determined to be acceptable levels.
A: Very soft feel.
B: Soft texture.
C: Hard texture.
D: Very hard texture.

(7) Change in texture over time Evaluation was performed by a sensory test conducted by 11 subjects. The texture of the artificial leather before the jungle test was conducted and the texture of the artificial leather after 10 weeks of exposure to the jungle test at 70°C and 95% humidity as a forced deterioration environment were compared and evaluated as described below, and the level evaluated by the largest number of people was determined as the change in texture over time of the artificial leather. In the present invention, A and B were determined as acceptable levels.
A: The texture is the same and there is no noticeable change over time.
B: The texture is roughly the same, and changes over time are not noticeable.
C: The texture is slightly different, and changes due to aging can be felt.
D: The texture is extremely different, and changes due to aging are clearly noticeable.

(8) Change in Abrasion Resistance over Time The artificial leather of the present invention was subjected to an abrasion resistance test specified in "8.19.5 E Method (Martindale Method)" of "8.19 Abrasion Resistance and Discoloration by Friction" of JIS L1096:2010 "Testing Methods for Woven and Knitted Fabrics" under conditions of a pressing load of 12.0 kPa and 20,000 abrasion cycles. The abrasion loss in a state where the jungle test was not conducted was compared with the abrasion loss after 10 weeks of exposure to a jungle test at 70°C and 95% humidity as a forced deterioration environment. A change in the abrasion loss of 0% or more and 30% or less was deemed to pass.

[Example 1]
(Nonwoven fabric)
A copolymer polyester copolymerized with 8 mol % of 5-sodium sulfoisophthalate (SSIA) was used as the sea component, and polyethylene terephthalate was used as the island component, to obtain an islands-in-sea type composite fiber with a composite ratio of 20 mass % of the sea component and 80 mass % of the island component, 37 islands/1 filament, and an average single fiber diameter of 16 μm. The obtained islands-in-sea type composite fiber was cut into a fiber length of 51 mm to form staples, which were passed through a card and a cross wrapper to form a fiber web, and a nonwoven fabric was obtained by needle punching. The obtained nonwoven fabric was immersed in hot water at a temperature of 98° C. for 2 minutes to cause it to shrink, and then dried at a temperature of 100° C. for 5 minutes.

(Precursor Dispersion)
A polyurethane precursor having an isocyanurate structure and a carboxyl group and a weight average molecular weight of 1,200,000, sodium sulfate as a heat-sensitive coagulant, and water were mixed to prepare a precursor dispersion containing 11% by mass of the precursor and 5% by mass of the heat-sensitive coagulant relative to the precursor dispersion.

(Impregnation process/Drying process)
The nonwoven fabric was impregnated with the precursor dispersion and then dried for 20 minutes with hot air at a temperature of 120° C. This impregnation and drying process was repeated four times to obtain a polyurethane-added nonwoven fabric in which polyurethane was added in an amount of 52.6 mass % relative to the total mass.

(Ultrafine fiber production treatment)
The nonwoven fabric with polyurethane was immersed in a 50 g/L aqueous sodium hydroxide solution heated to 95° C. for 5 minutes to remove the sea component of the islands-in-sea composite fibers (sea-removal), thereby forming ultrafine fibers. The sodium hydroxide aqueous solution adhering to the nonwoven fabric was then immersed in water for 30 minutes to wash, and dried in a dryer at 160° C. for 30 minutes to obtain a post-sea-removal sheet made of ultrafine fibers and polyurethane having hydrophilic groups.

(dyeing and finishing)
The sheet after the sea-removal was cut in half perpendicular to the thickness direction, and the opposite side of the half-cut surface was ground with endless sandpaper of sandpaper size 180 to obtain a sheet with a napped surface.

The resulting sheet was dyed with a black dye at 120°C using a jet dyeing machine, and then dried in a dryer to obtain artificial leather.

The results are shown in Table 1. The artificial leather obtained had good quality and excellent texture. The average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 47.4 mass%, and the elution rate of polyurethane by DMF was 20.0%. No change in texture was felt over time, and the change in abrasion resistance test over time was only 21.8%, which was little change.

[Example 2]
The impregnation and drying steps were repeated five times, except for the above, in the same manner as in Example 1, to produce an artificial leather.

The results are shown in Table 1. The artificial leather obtained had an average single fiber diameter of ultrafine fibers of 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 43.1 mass%, and the elution rate of polyurethane by DMF was 24.9%. In addition, the change in texture over time was not noticeable, and the change in the abrasion resistance test over time was only 20.1%, which was a small change.

[Example 3]
The impregnation and drying steps were repeated three times, but otherwise the same procedure was followed as in Example 1 to produce an artificial leather.

The results are shown in Table 1. The artificial leather obtained had an average single fiber diameter of ultrafine fibers of 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 56.5 mass%, and the elution rate of polyurethane by DMF was 20.5%. The change in texture over time was not noticeable, and the change in the abrasion resistance test over time was only 22.6%, which was a small change.

[Example 4]
In the production of the nonwoven fabric, the number of islands in the sea-island type composite fiber was set to 12 islands/filament, but otherwise the same procedure as in Example 1 was repeated to produce an artificial leather.

The results are shown in Table 1. The artificial leather obtained had good quality and excellent texture. The average single fiber diameter of the ultrafine fibers was 4.4 μm, the mass of the fibrous base material in the entire artificial leather was 46.5 mass%, and the elution rate of polyurethane by DMF was 24.1%. There was no noticeable change in the texture over time, and the change in the abrasion resistance test over time was only 20.4%, which was little change.

[Example 5]
In the production of the nonwoven fabric, the number of islands in the sea-island type composite fiber was set to 52 islands/1 filament, but otherwise the same procedure as in Example 1 was repeated to produce an artificial leather.

The results are shown in Table 1. The artificial leather obtained had an average single fiber diameter of ultrafine fibers of 3.0 μm, the mass of the fibrous base material in the entire artificial leather was 45.5 mass%, and the elution rate of polyurethane by DMF was 22.1%. The change in texture over time was not noticeable, and the change in the abrasion resistance test over time was only 28.4%, which was a small change.

[Example 6]
In the preparation of the precursor dispersion, the concentration of the precursor was set to 8% by mass. In addition, the impregnation step and the drying step were repeated 5 times. An artificial leather was produced in the same manner as in Example 1 except for the above.

The results are shown in Table 1. The artificial leather obtained had good quality and excellent texture. In addition, the average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 50.1 mass%, and the elution rate of polyurethane by DMF was 23.3%. There was no noticeable change in the texture over time, and the change in the abrasion resistance test over time was only 28.1%, which was little change.

[Example 7]
In the preparation of the precursor dispersion, the concentration of the precursor was set to 15 mass %, but otherwise the same procedure as in Example 1 was repeated to produce an artificial leather.

The results are shown in Table 1. The artificial leather obtained had an average single fiber diameter of ultrafine fibers of 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 46.2 mass%, and the elution rate of polyurethane by DMF was 21.1%. There was no noticeable change in the texture over time, and the change in the abrasion resistance test over time was only 20.3%, which was a small change.

[Comparative Example 1]
In the preparation of the precursor dispersion, the concentration of the precursor was set to 15% by mass. In addition, the impregnation step and the drying step were repeated 5 times. An artificial leather was produced in the same manner as in Example 1 except for the above.

The results are shown in Table 2. The artificial leather obtained was of non-uniform quality and had a hard texture. The average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 36.4 mass%, and the elution rate of polyurethane by DMF was 18.9%. There was no noticeable change in the texture over time, and the change in the abrasion resistance test over time was only 18.2%, which was little change.

[Comparative Example 2]
The impregnation step and the drying step were each carried out once without being repeated, but otherwise in the same manner as in Example 1, an artificial leather was produced.

The results are shown in Table 2. The artificial leather obtained had an excellent texture. The average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 78.1 mass%, and the elution rate of polyurethane by DMF was 29.8%. The texture changed over time, and the change in the abrasion resistance test was 54.1%, showing a large change.

[Comparative Example 3]
In preparing the precursor dispersion, a polyurethane precursor having an isocyanurate structure, a carboxyl group, and a weight average molecular weight of 500,000 was used. Except for this, an artificial leather was produced in the same manner as in Example 1.

The results are shown in Table 2. The artificial leather obtained had good quality and excellent texture. The average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 45.7 mass%, and the elution rate of polyurethane by DMF was 44.0%. The texture changed over time, and the change in the abrasion resistance test was 36.0%, which was a large change.

[Comparative Example 4]
In preparing the precursor dispersion, a polyurethane precursor having no isocyanurate structure, but having a carboxyl group, and a weight average molecular weight of 1,200,000 was used. Except for this, an artificial leather was produced in the same manner as in Example 1.

The results are shown in Table 2. The artificial leather obtained had good quality and excellent texture. The average single fiber diameter of the ultrafine fibers was 3.3 μm, the mass of the fibrous base material in the entire artificial leather was 42.3 mass%, and the elution rate of polyurethane by DMF was 20.1%. The texture changed over time, and the change in the abrasion resistance test was 45.0%, showing a large change.

The artificial leathers of Examples 1 to 7 use polyurethane with an isocyanurate structure, and by increasing the proportion of polyurethane in the artificial leather, it was possible to obtain artificial leathers that exhibit little change in texture and abrasion resistance over time.

On the other hand, the artificial leather of Comparative Example 1 had a low ratio of fibrous base material to the entire artificial leather, and had too much polyurethane, resulting in an artificial leather with a hard texture.

The artificial leather of Comparative Example 2 had a high ratio of fibrous base material to the entire artificial leather, so the ultrafine fibers were not adequately held by the polyurethane, resulting in an artificial leather that changed significantly in texture and abrasion resistance over time.

The artificial leather of Comparative Example 3 used polyurethane with a high elution rate in DMF, which resulted in a large amount of polyurethane falling off over time, resulting in an artificial leather with significant changes in texture and abrasion resistance over time.

The artificial leather of Comparative Example 4 used polyurethane not having an isocyanurate structure, and therefore the polyurethane had low hydrolysis resistance, resulting in an artificial leather that suffered significant changes in texture and abrasion resistance over time.

Claims (4)

An artificial leather comprising as its components a fibrous base material containing a nonwoven fabric made of ultrafine fibers with an average single fiber diameter of 0.1 μm to 10.0 μm, and polyurethane, wherein the content of the fibrous base material in the entire artificial leather is 40.0% by mass to 60.0% by mass, the polyurethane has an isocyanurate structure, and the elution rate of the polyurethane in N,N-dimethylformamide is 30.0% by mass or less of the total mass of the polyurethane. The artificial leather according to claim 1, wherein the ultrafine fibers form fiber bundles consisting of 5 to 100 fibers, and the ratio of the fiber bundles having at least half of their circumference covered with polyurethane to the total number of the fiber bundles observed within the observation range of a scanning electron microscope photograph of a cross section cut perpendicular to the surface of the artificial leather is 20% to 70%. The artificial leather according to claim 1 or 2, wherein the polyurethane has a hydrophilic group. A method for producing the artificial leather according to claim 1 or 2,
A step of forming a fibrous substrate comprising a nonwoven fabric made of ultrafine fiber-developing composite fibers;
an impregnation step of impregnating the fibrous base material with a solution or aqueous dispersion containing a polyurethane precursor and a heat-sensitive coagulant as main components of a solute or dispersoid;
A drying step of performing drying at a temperature of 100° C. or more and 180° C. or less;
a step of expressing the ultrafine fibers from the ultrafine fiber-expressing composite fibers in the polyurethane-coated nonwoven fabric obtained after the drying step,
The impregnation step and the drying step are repeated two to five times.
A method for manufacturing artificial leather.