JP2024065002A - Artificial leather - Google Patents

Abstract

To provide an artificial leather achieving soft feeling and high-class appearance quality, excellent morphological stability, strength, and abrasion resistance.SOLUTION: An artificial leather contains a fiber structure including ultra fine fibers that have an average single fiber diameter of 0.1 μm or more and 10.0 μm or less and are made of thermoplastic resin, and polyurethane resin. The polyurethane resin has a urea bond. The weight average molecular weight of the polyurethane resin is 350,000 or more and 600,000 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to artificial leather.

Artificial leather, which mainly contains a fiber structure containing ultrafine fibers and a polymer elastomer, is more durable than natural leather and can be made of uniform quality, so it is used in a variety of fields, including vehicle interior materials, interior goods, shoes, and clothing. When this artificial leather is used for vehicle seats, furniture, etc., in addition to a good texture and an appearance that gives a sense of luxury, the properties required include shape stability, strength, and durability against friction (abrasion resistance).

Several proposals have been made so far as a technique for achieving both high appearance quality and durability in this artificial leather. For example, Patent Document 1 proposes a napped leather-like sheet material made of ultrafine fibers and polyurethane, in which the polyurethane is made using a polymer diol containing a specific amount of polycarbonate diol, and the sheet material contains a specific amount of the polyurethane.

Patent Document 2 also proposes a sheet-like material made of a nonwoven fabric formed by entanglement of ultrafine fibers and an elastic resin binder whose main component is polyurethane, in which the polyurethane is a polycarbonate-based polyurethane having a polycarbonate skeleton with a specific structure, and the gel point of the polyurethane is within a specific range.

JP 2002-30579 A International Publication No. 2005/095706

The technology proposed in Patent Document 1 makes it possible to obtain artificial leather that has a certain level of appearance quality and durability, such as light resistance. However, simply adjusting the content of polyurethane in the artificial leather or the content of polycarbonate diol in that polyurethane makes it difficult to achieve both appearance quality and durability. For example, if the content of polycarbonate diol in the polyurethane is excessive, the texture tends to be hard, and conversely, if the content is too low, the durability tends to be insufficient.

On the other hand, the technology proposed in Patent Document 2 is capable of obtaining artificial leather that combines a certain degree of softness and durability by adjusting the gel point of polyurethane using polycarbonate diol. However, there is no specific mention of polyurethane using diol components other than polycarbonate diol, and there is still a demand for technology that can provide artificial leather that combines a good texture and a high-quality appearance, regardless of the polyurethane, and that also has shape stability, strength, and abrasion resistance.

The present invention was made in consideration of the above circumstances, and its purpose is to provide artificial leather that combines a soft feel and a luxurious appearance with excellent shape stability, strength, and abrasion resistance.

As a result of extensive research conducted by the inventors in order to achieve the above object, it was discovered that by making the polyurethane resin that constitutes the artificial leather have specific bonds and by setting the weight-average molecular weight of the polyurethane resin within a specific range, it is possible to obtain artificial leather that has a good texture and an appearance that gives a sense of luxury, and further has shape stability, strength, and abrasion resistance.

The present invention has been completed based on these findings, and provides the following:

[1] An artificial leather containing a fiber structure including ultrafine fibers made of a thermoplastic resin and having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less, and a polyurethane resin, the polyurethane resin having a urea bond and a weight average molecular weight of 350,000 or more and 600,000 or less.

[2] The artificial leather described in [1] above, in which the content of the polyurethane resin is 10% by mass or more and 60% by mass or less.

[3] The artificial leather according to [1] or [2], wherein the total value of 30% circular modulus in two perpendicular directions per unit area is 1.20 (N/2.54 cm)/(g/ ^m2 ) or more and 1.70 (N/2.54 cm)/(g/ ^m2 ) or less.

[4] The artificial leather described in any one of [1] to [3] above, which is colored with a dye.

The present invention provides artificial leather that has both a good texture and a high-quality appearance, as well as shape stability, strength, and abrasion resistance.

FIG. 1 is a cross-sectional view of an artificial leather for illustrating and explaining a method for measuring and calculating nap length related to the artificial leather.

The artificial leather of the present invention is an artificial leather containing a fiber structure including ultrafine fibers made of a thermoplastic resin and having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less, and a polyurethane resin, the polyurethane resin having a urea bond and a weight average molecular weight of 350,000 or more and 600,000 or less. These components are described in detail below, but the present invention is not limited to the scope described below as long as it does not exceed the gist of the invention, and various modifications are possible within the scope of the invention.

[Textile structure]
First, the fiber structure according to the artificial leather of the present invention contains ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less, and made of a thermoplastic resin.

As the thermoplastic resin, any resin that can be formed into a fiber form can be used, such as polyester-based resins such as "polyethylene terephthalate, polybutylene terephthalate, and polyester elastomers," polyamide-based resins such as "polyamide 6, polyamide 66, and polyamide elastomers," polyurethane-based resins, polyolefin-based resins, and acrylonitrile-based resins. However, polyester-based resins are preferably used from the viewpoints of durability, particularly mechanical strength and heat resistance. In this invention, "polyester-based resin" refers to a resin in which the molar fraction of the polyester unit in the repeating unit is 80 mol % to 100 mol %. Unless otherwise specified, the term "...-based resin" is used in the same sense.

Examples of the polyester resin include polyethylene terephthalate, polytrimethylene terephthalate, polytetramethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, and polyethylene-1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate. Among these, polyethylene terephthalate, which is the most widely used, or a polyester copolymer mainly containing ethylene terephthalate units is preferably used.

As the polyester-based resin, a single polyester or two or more different polyesters may be used. When two or more different polyesters are used, the difference in intrinsic viscosity (IV value) of the polyesters used is preferably 0.50 or less, and more preferably 0.30 or less, from the viewpoint of compatibility of the two or more components.

In the present invention, the intrinsic viscosity is calculated by the following method.
(1) Dissolve 0.8 g of a sample polymer in 10 mL of orthochlorophenol.
(2) Using an Ostwald viscometer at a temperature of 25°C, calculate the relative viscosity _ηr using the following formula and round off to two decimal places: _ηr = η/ _η0 = (t x d)/( _t0 x _d0 )
Intrinsic viscosity (IV value) = 0.0242 η _r + 0.2634
(Here, η represents the viscosity of the polymer solution, η ₀ represents the viscosity of orthochlorophenol, t represents the falling time of the solution (seconds), d represents the density of the solution (g/cm ³ ), t ₀ represents the falling time of orthochlorophenol (seconds), and d ₀ represents the density of orthochlorophenol (g/cm ³ ).

The ultrafine fibers according to the present invention have an average single fiber diameter of 0.1 μm or more and 10.0 μm or less. By setting the lower limit of the range of the average single fiber diameter of the ultrafine fibers to 0.1 μm or more, and preferably 0.5 μm or more, excellent effects are achieved in terms of color development after dyeing, light fastness and friction fastness, and stability during spinning. On the other hand, by setting the upper limit of the above range to 10.0 μm or less, preferably 8.0 μm or less, and more preferably 6.0 μm or less, an artificial leather with excellent surface quality that is dense and soft to the touch can be obtained.

In the present invention, the average single fiber diameter of ultrafine fibers is calculated by taking a scanning electron microscope (SEM, for example, Keyence Corporation's "VHX-D500/D510 type") photograph of the cross section of the artificial leather, randomly selecting 10 ultrafine fibers that are circular or elliptical and close to circular, measuring the single fiber diameter, calculating the arithmetic average value of the 10 fibers, and rounding off to one decimal place.

From the viewpoint of processing operability, the cross-sectional shape of the ultrafine fibers according to the present invention is preferably a round cross-section, but it is also possible to adopt irregular cross-sectional shapes such as oval, flat, triangular, and other polygonal, sectoral, cross, hollow, Y-shaped, T-shaped, and U-shaped cross-sections. In this case, the average single fiber diameter of the ultrafine fibers is determined by first measuring the cross-sectional area of the single fiber and then calculating the diameter when the cross-section is regarded as a circle.

In the present invention, particularly when the artificial leather is to be colored in a dark color, it is preferable that the thermoplastic resin constituting the ultrafine fibers contains a black pigment or a chromatic fine particle oxide pigment having an average particle size of 0.05 μm or more and 0.20 μm or less.

The particle size referred to here is the particle size when the black pigment or the chromatic fine oxide pigment is present in the ultrafine fiber, and is generally referred to as the secondary particle size. In addition, "chromatic color" refers to a color with a chroma C ^* of 10 or more in the CIELAB1976L ^* a ^* b ^* color space, and "chromatic fine oxide pigment" refers to fine oxide pigments that exhibit chromatic colors, and does not include white oxide pigments such as zinc oxide and titanium oxide.

The lower limit of the average particle size range is preferably 0.05 μm or more, and more preferably 0.07 μm or more, so that the black pigment or chromatic fine oxide pigment is held inside the ultrafine fibers and is prevented from falling off from the ultrafine fibers. On the other hand, the upper limit of the average particle size range is preferably 0.20 μm or less, more preferably 0.18 μm or less, and even more preferably 0.16 μm or less, so that the stability during spinning and the yarn strength are excellent.

In the present invention, the above particle size refers to a value measured and calculated by the following method.
(1) An ultrathin section having a thickness of 5 μm to 10 μm is prepared in the cross-sectional direction perpendicular to the longitudinal direction of the ultrafine fiber.
(2) Observe the cross section of the fiber in the ultrathin section at 10,000x magnification using a transmission electron microscope (TEM).
(3) Using image analysis software, measure the circle-equivalent particle diameters of 20 points of the black pigment (a1) or chromatic fine-particle oxide pigment (a2) particles contained within a 2.3 μm × 2.3 μm visual field of the observed image. When there are fewer than 20 particles of the black pigment (a1) or chromatic fine-particle oxide pigment (a2) contained within a 2.3 μm × 2.3 μm visual field, measure the circle-equivalent particle diameters of all the particles of the black pigment (a1) or chromatic fine-particle oxide pigment (a2) present.
(4) Calculate the arithmetic mean value (μm) of the particle diameters measured at the 20 points, and round off to two decimal places.

The content of black pigment or chromatic fine oxide pigment contained in the thermoplastic resin forming the ultrafine fibers is preferably 0.5% by mass or more and 2.0% by mass or less relative to the mass of the ultrafine fibers. The lower limit of the pigment content range is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, and even more preferably 0.9% by mass or more, so that the color development of dark colors is excellent. On the other hand, the upper limit of the pigment content range is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.6% by mass or less, so that the artificial leather has high physical properties such as strength and elongation.

The black pigment used in the present invention may be a carbon-based black pigment such as carbon black or graphite, or an oxide-based black pigment such as triiron tetroxide or a composite oxide of copper and chromium. From the viewpoints of easily obtaining a fine particle size and excellent dispersibility in polymers, it is preferable that the black pigment is carbon black.

As the chromatic fine particle oxide pigment according to the present invention, known pigments close to the target color can be used, such as iron oxyhydroxide (e.g., "TM Yellow 8170" manufactured by Dainichiseika Chemicals Co., Ltd.), iron oxide (e.g., "TM Red 8270" manufactured by Dainichiseika Chemicals Co., Ltd.), and cobalt aluminate (e.g., "TM Blue 3490E" manufactured by Dainichiseika Chemicals Co., Ltd.).

In addition, inorganic particles such as titanium oxide particles, lubricants, heat stabilizers, ultraviolet absorbers, conductive agents, heat storage agents, antibacterial agents, etc. can be added to the thermoplastic resin that constitutes the ultrafine fibers, as necessary, within the scope that does not impair the object of the present invention.

The fiber structures used in the present invention include woven fabrics, knitted fabrics, nonwoven fabrics, and fiber entanglements containing these as components, all of which are made of the ultrafine fibers described above. They can be used appropriately depending on the cost and properties required for each application or purpose. In particular, when woven fabrics or knitted fabrics are used as the fiber structures, artificial leather with excellent uniformity in thickness and quality can be obtained. Furthermore, when nonwoven fabrics or fiber entanglements containing nonwoven fabrics as components are used as the fiber structures, artificial leather with a rich texture and excellent quality due to fine nap can be obtained when the surface is raised.

In the present invention, "a fiber-entangled body containing a nonwoven fabric as a component" refers to an embodiment in which the fiber-entangled body is a nonwoven fabric, an embodiment in which a nonwoven fabric and a woven fabric are entangled and integrated as described below, and an embodiment in which a fiber-entangled body is entangled and integrated with a nonwoven fabric and a substrate other than a woven fabric. The same is true for "a fiber-entangled body containing a woven fabric (or knitted fabric) as a component".

Nonwoven fabrics are available in the form of long fiber nonwoven fabrics mainly made up of filaments, and short fiber nonwoven fabrics mainly made up of fibers of 100 mm or less. Long fiber nonwoven fabrics are preferred because they produce artificial leather with excellent strength. On the other hand, short fiber nonwoven fabrics can have more fibers oriented in the thickness direction of the artificial leather than long fiber nonwoven fabrics, and the artificial leather can have a denser surface when raised.

When using a short fiber nonwoven fabric, the fiber length of the ultrafine fibers is preferably 25 mm or more and 90 mm or less. The upper limit of the fiber length range is preferably 90 mm or less, more preferably 80 mm or less, and even more preferably 70 mm or less, which results in good quality and texture. On the other hand, the lower limit of the fiber length range is preferably 25 mm or more, more preferably 35 mm or more, and even more preferably 40 mm or more, which results in an artificial leather with excellent abrasion resistance.

The basis weight of the fiber structure constituting the artificial leather according to the present invention is preferably in the range of 50 g/ ^m2 or more and 400 g/ ^m2 or less, as measured by "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "General nonwoven fabric test method". The lower limit of the basis weight range of the fiber structure is preferably 50 g/ ^m2 or more, more preferably 80 g/ ^m2 or more, so that the artificial leather has a solid feel and excellent texture. On the other hand, the upper limit of the basis weight range of the fiber structure is preferably 400 g/ ^m2 or less, more preferably 300 g/ ^m2 or less, so that the artificial leather has excellent moldability and is flexible.

The artificial leather of the present invention is preferably a fiber entanglement body in which a nonwoven fabric made of ultrafine fibers is entangled with a woven fabric as the fiber structure. Specifically, the woven fabric is laminated inside the nonwoven fabric or on one surface of the nonwoven fabric. This provides the artificial leather with excellent strength and shape stability.

In this case, the type of fiber that constitutes the woven fabric is preferably filament yarn, spun yarn, or a composite yarn made of filament yarn and spun yarn, and from the standpoint of durability, particularly mechanical strength, it is more preferable to use a multifilament made of polyester resin or polyamide resin.

In addition, from the standpoint of mechanical strength, etc., it is preferable that the fibers constituting the above-mentioned woven fabric do not contain black pigments or chromatic fine particle oxide pigments.

The average single fiber diameter of the fibers constituting the woven fabric is preferably 1 μm or more and 50 μm or less. By setting the upper limit of the average single fiber diameter range of the fibers to preferably 50 μm or less, more preferably 15 μm or less, and even more preferably 13 μm or less, not only is it possible to obtain an artificial leather with excellent flexibility, but even if the fibers of the woven fabric are exposed on the surface of the artificial leather, the hue difference with the ultrafine fibers containing the pigment after dyeing is small, so that the uniformity of the hue of the surface is not impaired. On the other hand, by setting the lower limit of the average single fiber diameter range of the fibers constituting the woven fabric to 1 μm or more, more preferably 8 μm or more, and even more preferably 9 μm or more, the shape stability of the product as an artificial leather is improved.

In the present invention, the average single fiber diameter of the fibers that make up the woven fabric is calculated by taking a scanning electron microscope (SEM) photograph of the cross section of the artificial leather, randomly selecting 10 fibers that make up the woven fabric, measuring the single fiber diameters of the selected fibers, calculating the arithmetic average of the 10 fibers, and rounding off to one decimal place.

When the fibers constituting the woven fabric are multifilament, it is preferable that the total fineness of the multifilament is 30 dtex or more and 170 dtex or less.

By setting the upper limit of the total fineness range of the yarns constituting the woven fabric to 170 dtex or less, an artificial leather with excellent flexibility can be obtained. On the other hand, by setting the lower limit of the total fineness range of the yarns constituting the woven fabric to 30 dtex or more, not only is the shape stability of the product as artificial leather improved, but also, when the nonwoven fabric and the woven fabric are entangled and integrated by needle punching or the like, the fibers constituting the woven fabric are less likely to be exposed on the surface of the artificial leather, which is preferable. In this case, it is preferable that the total fineness of the warp and weft multifilaments is the same.

The total fineness of the yarns constituting the above-mentioned woven fabric refers to the value measured and calculated according to "8.3 Fineness" and "8.3.1 Correct fineness b) Method B (simplified method)" in "8.3 Fineness" of JIS L1013:2010 "Test methods for chemical fiber filament yarns."

Furthermore, the number of twists of the yarns constituting the woven fabric is preferably 1000 T/m or more and 4000 T/m or less. The upper limit of the range of the number of twists of the yarns constituting the woven fabric is preferably 4000 T/m or less, more preferably 3500 T/m or less, and even more preferably 3000 T/m or less, so that an artificial leather with excellent flexibility can be obtained. On the other hand, the lower limit of the range of the number of twists of the yarns constituting the woven fabric is preferably 1000 T/m or more, more preferably 1500 T/m or more, and even more preferably 2000 T/m or more, so that when the nonwoven fabric and the woven fabric are entangled and integrated by needle punching or the like, damage to the fibers constituting the woven fabric can be prevented, and the mechanical strength of the artificial leather is excellent, which is preferable.

[Polyurethane resin]
Next, the artificial leather of the present invention contains a polyurethane resin from the viewpoint of flexibility and cushioning. The polyurethane resin has a urea bond. This "polyurethane resin has a urea bond" means that a peak attributable to a urea bond is present when the polyurethane resin is extracted from the artificial leather using N,N-dimethylformamide, the N,N-dimethylformamide is removed by drying, and then a solution of the polyurethane resin in deuterated dimethyl sulfoxide is subjected to proton nuclear magnetic resonance spectroscopy (hereinafter sometimes referred to as NMR) and carbon nuclear magnetic resonance spectroscopy.

Specific examples of polyurethane resins that are preferred include polyurethanes obtained by reacting a polymer diol, an organic diisocyanate, and a chain extender. Each will be described in detail below. The polyurethane resin according to the present invention can be either a polyurethane resin (organic solvent-based polyurethane resin) obtained by dissolving the diphenylmethane diisocyanate, etc., described below, in an organic solvent and impregnating the fiber structure as described below, or a polyurethane resin (water-dispersed polyurethane resin) obtained by dispersing the 4,4'-dicyclohexylmethane diisocyanate, etc., described below, in water and impregnating the fiber structure as described below.

(1) Polymer diol As the above-mentioned polymer diol, for example, polycarbonate-based diol, polyester-based diol, polyether-based diol, silicone-based diol can be adopted, and copolymers of these can also be used.Among them, it is preferable to use polycarbonate-based diol from the viewpoint of hydrolysis resistance and abrasion resistance, and it is preferable to use polyether-based diol from the viewpoint of hydrolysis resistance and flexibility.

The polycarbonate-based diols can be produced by transesterification of alkylene glycols with carbonates, or by reactions of phosgene or chloroformates with alkylene glycols. Examples of these alkylene glycols include linear alkylene glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 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, aromatic diols such as bisphenol A, glycerin, trimethylolpropane, and pentaerythritol. In the present invention, either a polycarbonate-based diol obtained from a single alkylene glycol or a copolymer polycarbonate-based diol obtained from two or more types of alkylene glycols can be used.

An example of a polyester diol is a polyester diol obtained by condensing various low molecular weight polyols with polybasic acids.

The low molecular weight polyol may be, for example, one or more selected from ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol. In addition, adducts of various alkylene oxides added to bisphenol A can also be used as low molecular weight polyols.

Examples of polybasic acids include one or more selected from 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 polyether diols used in the present invention include, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymer diols that combine these.

The number average molecular weight of the polymer diol is preferably in the range of 500 to 4000 when the molecular weight of the polyurethane resin is constant. The lower limit of the number average molecular weight range is preferably 500 or more, more preferably 1500 or more, so that the artificial leather can be made more flexible. The upper limit of the number average molecular weight range is preferably 4000 or less, more preferably 3000 or less, so that the polyurethane resin can have higher strength.

(2) Organic Diisocyanate Examples of the organic diisocyanate used in the present invention include aliphatic diisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and norborane diisocyanate; and aromatic diisocyanates such as diphenylmethane diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,5-naphthylene diisocyanate, and xylylene diisocyanate. These can also be used in combination.

(3) Chain extender In the present invention, a polyurethane resin having a urea bond can be obtained by using an amine-based chain extender. As the amine-based chain extender, ethylenediamine, methylenebisaniline, etc. are preferably used. In addition, a polyamine obtained by reacting polyisocyanate with water can also be used as the chain extender.

(4) Other Additives, etc. A crosslinking agent can be used in combination with the polyurethane resin according to the present invention in order to improve water resistance, abrasion resistance, hydrolysis resistance, etc. The crosslinking agent may be an external crosslinking agent added to the polyurethane resin as a third component, or an internal crosslinking agent that introduces a reactive point that will become a crosslinked structure in advance into the molecular structure of the polyurethane resin can also be used. It is preferable to use an internal crosslinking agent from the viewpoint of being able to form crosslinking points more uniformly in the molecular structure of the polyurethane resin and to reduce the decrease in flexibility.

As a crosslinking agent, a compound having an isocyanate group, an oxazoline group, a carbodiimide group, an epoxy group, a melamine resin, a silanol group, etc. can be used.

In addition, pigments such as carbon black, dye antioxidants, antioxidants, light resistance agents, antistatic agents, dispersants, softeners, coagulation regulators, flame retardants, antibacterial agents, and deodorizers can be added to the polyurethane resin as needed. In particular, when the artificial leather is to be colored in a deep color, it is more preferable that the polyurethane resin used contains a black pigment.

In the present invention, the weight-average molecular weight of the polyurethane resin is 350,000 or more and 600,000 or less. By setting the lower limit of the weight-average molecular weight range to 350,000 or more, preferably 400,000 or more, an artificial leather with excellent shape stability, strength, and abrasion resistance can be obtained. By setting the upper limit of the weight-average molecular weight range to 600,000 or less, preferably 550,000 or less, the flexibility and moldability of the artificial leather can be maintained.

The weight average molecular weight is a value measured and calculated by the following method.
(1) A polyurethane resin is extracted from the obtained artificial leather using a solution of lithium chloride in N,N-dimethylformamide (hereinafter, may be referred to as DMF) adjusted to a concentration of 0.01 M, and the amount of N,N-dimethylformamide is adjusted so that the polyurethane resin concentration is 1 mass %, thereby preparing a polyurethane resin solution.
(2) The polyurethane resin solution is measured by gel permeation chromatography (GPC, for example, "HLC-8020" manufactured by Tosoh Corporation) using an RI detector as a detector under the following conditions.
Eluent: 0.01 M lithium chloride solution in DMF Flow rate: 1.0 mL/min Column temperature: 40° C.
Injection volume: 0.05 mL
- Standard sample: polystyrene. If the same column is not available, a column with equivalent performance shall be used for the measurement.

The weight average molecular weight of the polyurethane resin can be adjusted by the weight average molecular weight of the polymer diol used, the mixing ratio of the chain extender in the polyurethane resin, and the pH of the dye solution.

In general, the content of polyurethane resin in artificial leather can be appropriately adjusted taking into consideration the type of polyurethane resin used or its constituents such as polymer diol, organic diisocyanate, and chain extender, the manufacturing method of the polyurethane resin, and the texture and physical properties. In the present invention, however, the content of polyurethane resin in artificial leather is preferably 10% by mass or more and 60% by mass or less based on the mass of the artificial leather. The lower limit of the content range of the polyurethane resin is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 18% by mass or more, so that the bonding between the fibers by the polyurethane resin can be strengthened and the abrasion resistance of the artificial leather can be improved. On the other hand, the upper limit of the content range of the polyurethane resin is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, so that the artificial leather can be made more flexible.

In the present invention, the content (mass %) of polyurethane resin in the artificial leather is calculated from the percentage of the difference in mass between the artificial leather before extraction and the residue after extraction, relative to the mass of the artificial leather before extraction, after immersing the artificial leather in N,N-dimethylformamide to extract and remove the polyurethane resin. If the polyurethane resin is not soluble in N,N-dimethylformamide, the content is measured and calculated by immersing the artificial leather in a mixture of phenol and tetrachloroethane, dissolving the ultrafine fibers, filtering, and collecting and weighing the residual polyurethane resin.

[Artificial leather]
The artificial leather of the present invention is an artificial leather containing the above-mentioned fiber structure and a polyurethane resin. The artificial leather of the present invention preferably has nap on the surface. The nap may be present on only one surface of the artificial leather, or it is acceptable to have it on both surfaces. In the case where the surface has nap, the nap shape preferably has a nap length and directional flexibility to the extent that a mark is left when the surface is traced with a finger, that is, the nap direction changes when the surface is traced with a finger, and the nap length and directional flexibility are sufficient to leave a so-called finger mark, from the viewpoint of design effect.

More specifically, the nap length on the surface is preferably 200 μm or more and 500 μm or less, and more preferably 250 μm or more and 450 μm or less. With regard to the nap length range, the lower limit is preferably 200 μm or more, so that the nap on the surface covers the polyurethane resin and suppresses exposure of the polyurethane resin to the surface of the artificial leather, thereby making it possible to obtain an artificial leather with uniform color development. Furthermore, when a woven fabric is integrated with the nonwoven fabric constituting the artificial leather, it is preferable to set the nap length on the surface within the above range, since it is possible to sufficiently cover the fibers of the woven fabric near the surface of the artificial leather. On the other hand, with regard to the nap length range, the upper limit is preferably 500 μm or less, so that an artificial leather with excellent design effect and abrasion resistance can be obtained.

In the present invention, the nap length of the artificial leather is measured and calculated by the following method.
(1) For a surface having nap, use a lint brush or the like to make the nap stand up.
(2) With the nap raised, two images of the cross section of the artificial leather are taken at 120x magnification using a scanning electron microscope (SEM: for example, Keyence Corporation's VHX-D500/D510 type).
(3) As shown in FIG. 1, a layer consisting only of fibers oriented in the thickness direction in the cross section is defined as a napped portion, and the length from the intersection of the fibers oriented in the thickness direction and the fibers oriented in the surface direction of the artificial leather to the tip of the nap is defined as the nap length (μm), and 10 points are measured.
(4) Repeat step (3) for all cross sections, calculate the arithmetic average value of the nap length (μm), and round off to the first decimal place.

The artificial leather of the present invention preferably has a thickness measured by "6.1.1 A method" of "6.1 Thickness (ISO method)" of JIS L1913:2010 "General nonwoven fabric test methods" in a range of 0.2 mm to 1.2 mm. The lower limit of the thickness range of the artificial leather is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.4 mm or more, so that the artificial leather not only has excellent processability during manufacturing but also has a rich feel and excellent texture. On the other hand, the upper limit of the thickness range of the artificial leather is preferably 1.2 mm or less, more preferably 1.1 mm or less, and even more preferably 1.0 mm or less, so that the artificial leather has excellent moldability and flexibility.

The artificial leather of the present invention preferably has a friction fastness measured by "9.1 Friction Tester Type I (Crockmeter) Method" of JIS L0849:2013 "Test Method for Color Fastness to Friction" and a light fastness measured by "7.2 Exposure Method a) First Exposure Method" of JIS L0843:2006 "Test Method for Color Fastness to Xenon Arc Lamp Light" of Grade 4 or higher. Having a friction fastness and light fastness of Grade 4 or higher can prevent color fading and staining of clothes, etc. during actual use.

In addition, in an abrasion resistance test of the artificial leather of the present invention measured by "8.19.5 E method (Martindale method)" of "8.19 Abrasion resistance and discoloration due to friction" of JIS L1096:2010 "Test methods for woven and knitted fabrics", the artificial leather is preferably abraded 15,000 times with a pressing load of 12.0 kPa, and the mass loss rate of the artificial leather (percentage of the weight difference of the test cloth before and after the abrasion test relative to the weight of the test cloth before the abrasion test) is 1.5% or less, more preferably 1.3% or less, and even more preferably 1.1% or less. A mass loss rate of 1.5% or less can prevent contamination due to fluff shedding during actual use.

The mass reduction rate can be adjusted by the weight average molecular weight of the polyurethane resin, the fiber length, nap length, and apparent density of the ultrafine fibers.

Furthermore, the artificial leather of the present invention preferably has a value obtained by dividing the tensile strength measured in accordance with "6.3.1 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics" by the basis weight of the artificial leather, i.e., the tensile strength per unit basis weight, in any measurement direction of 0.12 (N/cm)/(g/ ^m2 ) or more and 0.50 (N/cm)/(g/ ^m2 ) or less.

The range of tensile strength per unit area weight is preferably 0.12 (N/cm)/(g/ ^m2 ) or more, more preferably 0.14 (N/cm)/(g/ ^m2 ) or more, since the artificial leather has excellent shape stability and durability. The range of tensile strength per unit area weight is preferably 0.50 (N/cm)/(g/ ^m2 ) or less, more preferably 0.45 (N/cm)/(g/ ^m2 ) or less, since the artificial leather has excellent moldability.

The tensile strength per unit area can be adjusted by the weight average molecular weight and apparent density of the polyurethane resin, the density of the inserted fabric, and the total fineness and twist of the yarns that make up the fabric.

The artificial leather of the present invention preferably has a total value of 30% circular modulus in two perpendicular directions per unit area of 1.20 (N/2.54 cm)/(g/ ^m2 ) to 1.70 (N/2.54 cm)/(g/ ^m2 ). Here, 1.00 (N/2.54 cm)/(g/ ^m2 ) corresponds to 0.39 (N/cm)/(g/ ^m2 ), and the above range can be expressed as 0.47 (N/cm)/(g/ ^m2 ) to 0.67 (N/cm)/(g/ ^m2 ). This "total value of 30% circular modulus in two orthogonal directions per unit basis weight" is a parameter related to shape stability, and by setting the lower limit of the range of the total value of 30% circular modulus in two orthogonal directions per unit basis weight to 1.20 (N/2.54 cm)/(g/ ^m2 ) or more, more preferably 1.25 (N/2.54 cm)/(g/ ^m2 ) or more, an artificial leather with excellent shape stability can be obtained, and deterioration of surface quality due to slip-through during stretching can be suppressed. Furthermore, by setting the upper limit of the range of the total value of 30% circular modulus in two orthogonal directions per unit basis weight to preferably 1.70 (N/2.54 cm)/(g/ ^m2 ) or less, more preferably 1.65 (N/2.54 cm)/(g/ ^m2 ) or less, the leather can have high conformability to bends and the like when stretched during molding, and can prevent the occurrence of wrinkles and sagging.

The above-mentioned total value of 30% circular modulus in two perpendicular directions per unit area refers to a value measured and calculated by the following method.
(1) Cut a circular test piece of 300 mm diameter from the artificial leather.
(2) Mark one reference point per 200 mm in the center of the test piece.
(3) Using an Instron tensile tester (for example, Instron Model 3343), the modulus at 30% elongation (N/2.54 cm) is measured with a gripping distance of 200 mm and a tensile speed of 200 mm/min.
(4) The measurements of (1) to (3) are carried out by sampling in each direction forming angles of 0 degrees and 90 degrees with respect to a reference line drawn arbitrarily on the artificial leather, and the arithmetic mean value (N/2.54 cm) of the values measured for three or more samples is calculated in each direction.
(5) Measure and calculate the weight per unit area of the artificial leather. In the present invention, the weight per unit area of the artificial leather refers to a value obtained by randomly taking five test pieces of 250 mm x 250 mm from the artificial leather, measuring them in accordance with "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "General nonwoven fabric test method", and rounding the calculated value to the nearest whole number. Here, if it is not possible to take a test piece of 250 mm x 250 mm, take a test piece in the largest possible square shape, measure the mass and dimensions of the test piece, and calculate the mass per unit area (g/m ² ).
(6) The sum of the arithmetic average values (N/2.54 cm) calculated in each direction in (4) is divided by the basis weight (g/ ^m2 ) of the artificial leather calculated in (5) to obtain (N/2.54 cm)/(g/ ^m2 ), and rounded off to two decimal places.

The total value of the 30% circular modulus in two perpendicular directions per unit area can be adjusted by the weight average molecular weight and apparent density of the polyurethane resin, and, if a woven fabric is inserted, the density of the woven fabric and the elongation properties of the threads that make up the woven fabric.

Furthermore, the artificial leather of the present invention does not have to be colored with a dye depending on the intended use, and there is no restriction on whether or not it contains a dye. However, in order to impart any hue to suit the intended use or design, it is more preferable that the artificial leather of the present invention is colored with a dye. The presence or absence of dye can be determined by immersing the artificial leather in methanol and squeezing it several times to obtain a methanol extract, and evaporating and removing the methanol, and if any solid remains, it can be determined that the artificial leather contains a dye.

The dyes used in the present invention may be selected according to the type of fibers contained in the fiber structure, such as the ultrafine fibers described above, and are not particularly limited. For example, if the thermoplastic resin of the ultrafine fibers is a polyester-based resin, a disperse dye can be used, and if it is a polyamide-based resin, an acid dye or a metal-containing dye can be used, or a combination of these can be used.

Of course, it may or may not be colored with dyes, and may be colored by other methods, such as printing, as described below.

[Manufacturing method of artificial leather]
The method for producing an artificial leather of the present invention preferably includes a step of dyeing a sheet-like material containing a fiber structure including ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less and a polyurethane resin having a weight-average molecular weight of 50,000 or more and 350,000 or less, in a dyebath having a pH of 4.5 or more and 5.5 or less. The details of this method are described below.

(A) Formation of a sheet-like product First, a sheet-like product is formed containing a fiber structure including ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less and a polyurethane resin. This sheet-like product is preferably formed by the following steps.
Step (1): A process for producing ultrafine fiber-developing fiber having an islands-in-sea composite structure in which islands made of a thermoplastic resin are formed and a soluble polymer forms the sea.Step (2): A process for producing a fiber structure having ultrafine fiber-developing fiber as a main component.Step (3): A process for forming ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less from a fiber structure having ultrafine fiber-developing fiber as a main component.Step (4): A process for applying a polyurethane resin to ultrafine fibers or a fiber structure having ultrafine fiber-developing fiber as a main component. Each step is described in detail below.

<Step for producing ultrafine fiber-developing fiber>
In this step, an ultrafine fiber-forming fiber having an islands-in-sea composite structure in which islands made of a thermoplastic resin are formed and a sea part is formed of a readily soluble polymer is produced.

As an ultrafine fiber-producing fiber, an islands-in-sea type composite fiber is used, in which thermoplastic resins with different solvent solubility are used as a sea portion (easily soluble polymer) and an island portion (poorly soluble polymer), and the sea portion is dissolved and removed using a solvent or the like to turn the island portion into ultrafine fibers. By using islands-in-sea type composite fiber, it is possible to provide appropriate gaps between the island portions, i.e., between the ultrafine fibers inside the fiber bundle, when removing the sea portion, which is preferable from the viewpoint of the texture and appearance quality of the artificial leather.

As a method for spinning ultrafine fiber-generating fibers having an island-in-sea composite structure, a method using a polymer mutual alignment body in which the sea part and the island part are mutually aligned and spun using an island-in-sea composite spinneret is preferred from the viewpoint of obtaining ultrafine fibers with uniform single fiber fineness.

For the sea portion of islands-in-the-sea composite fibers, 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 preferred from the viewpoints of spinnability and ease of elution.

In the method for producing artificial leather of the present invention, when islands-in-the-sea composite fibers are used, it is preferable to use islands-in-the-sea composite fibers whose island strength is 2.5 cN/dtex or more. The lower limit of the range of island strength is preferably 2.5 cN/dtex or more, more preferably 2.8 cN/dtex or more, and even more preferably 3.0 cN/dtex or more, which improves the abrasion resistance of the artificial leather and suppresses the decrease in friction fastness due to fiber shedding.

In the present invention, the strength of the island parts of the islands-in-sea type composite fiber is calculated by the following method.
(1) Ten islands-in-the-sea composite fibers, each 20 cm long, are bundled together.
(2) After dissolving and removing the sea portion from the sample (1), dry it in air.
(3) According to JIS L1013:2010 "Test methods for chemical fiber filament yarn", "8.5 Tensile strength and elongation", "8.5.1 Standard time test", the test is performed 10 times under the conditions of a grip length of 5 cm, a pulling speed of 5 cm/min, and a load of 2 N (N=10).
(4) The arithmetic mean value (cN/dtex) of the test results obtained in (3) is rounded off to one decimal place, and the value obtained is the strength of the island parts of the islands-in-sea type composite fiber.

<Step of producing a fiber structure>
In this process, a fiber structure containing ultrafine fiber as a main component is produced. More preferably, the spun ultrafine fiber is opened and then formed into a fiber web by a cross wrapper or the like, and entangled to obtain a nonwoven fabric, which is a fiber structure. As a method for entangling the fiber web to obtain a nonwoven fabric, a needle punching process, water jet punching process, or the like can be used.

As mentioned above, either short fiber nonwoven fabric or long fiber nonwoven fabric can be used as the nonwoven fabric, but with short fiber nonwoven fabric, there are more fibers oriented in the thickness direction of the artificial leather than with long fiber nonwoven fabric, and the surface of the artificial leather can have a high degree of density when raised.

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

Furthermore, when the fiber structure includes a woven fabric, the nonwoven fabric and the woven fabric obtained above are laminated and then entangled and integrated. To entangle the nonwoven fabric and the woven fabric, the woven fabric can be laminated on one or both sides of the nonwoven fabric, or the woven fabric can be sandwiched between multiple nonwoven fabric webs, and then the fibers of the nonwoven fabric and the woven fabric can be entangled by needle punching, water jet punching, or the like.

The apparent density of the 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. The lower limit of the apparent density range is preferably 0.15 g/ ^cm3 or more, so that the artificial leather can have sufficient shape stability, dimensional stability, and abrasion resistance. On the other hand, the upper limit of the apparent density range is preferably 0.45 g/ ^cm3 or less, so that a sufficient space for applying the polyurethane resin can be maintained.

It is also a preferred embodiment of the nonwoven fabric to subject it to a heat shrink treatment using hot water or steam in order to improve the denseness of the fibers. In the present invention, "hot water" refers to water heated to 90°C to 100°C.

Next, the nonwoven fabric can be impregnated with an aqueous solution of the water-soluble resin and dried to impart the water-soluble resin. By imparting the water-soluble resin to the nonwoven fabric, the fibers are fixed and dimensional stability is improved.

<Step of forming ultrafine fibers>
In this step, the obtained fiber structure is treated with a solvent to produce ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less.

The ultrafine fiber development process can be carried out by immersing a nonwoven fabric made of islands-in-the-sea composite fibers in a solvent to dissolve and remove the sea portion of the islands-in-the-sea composite fibers.

When the ultrafine fiber-producing fiber is an islands-in-the-sea type composite fiber, the solvent for dissolving and removing the sea portion can be an organic solvent such as toluene or trichloroethylene when the sea portion is polyethylene, polypropylene, or polystyrene. Also, when the sea portion is a copolymer polyester or polylactic acid, an alkaline aqueous solution such as sodium hydroxide can be used. Also, when the sea portion is a water-soluble thermoplastic polyvinyl alcohol resin, hot water can be used.

<Step of applying polyurethane resin>
In this process, a fiber structure mainly composed of ultrafine fibers or ultrafine fiber-developing fibers is impregnated with a polyurethane resin solution and solidified to provide the polyurethane resin. Methods for fixing the polyurethane resin to the fiber structure include a method of impregnating the fiber structure with a polyurethane resin solution and then wet coagulating or dry coagulating the solution, and these methods can be appropriately selected depending on the type of polyurethane resin used.

Preferably, the solvent used when applying the polyurethane resin is N,N-dimethylformamide or dimethyl sulfoxide. Alternatively, a water-dispersed polyurethane liquid in which the polyurethane resin is dispersed in water as an emulsion may be used.

The polyurethane resin applied to the fiber structure preferably has a weight average molecular weight of 50,000 or more and 400,000 or less. The lower limit of the weight average molecular weight range is preferably 50,000 or more, more preferably 100,000 or more, and even more preferably 150,000 or more, so that the strength of the artificial leather can be maintained and the composite fibers can be prevented from falling off. The upper limit of the weight average molecular weight range is preferably 400,000 or less, more preferably 350,000 or less, and even more preferably 300,000 or less, so that the viscosity increase of the polyurethane liquid can be suppressed and it can be applied uniformly to the fiber structure.

The polyurethane resin may be applied to the fiber structure before generating ultrafine fibers from the ultrafine fiber generating fiber, or after generating ultrafine fibers from the ultrafine fiber generating fiber.

<Step of cutting the sheet-like material in half and polishing it>
From the viewpoint of production efficiency, it is also a preferred embodiment that the sheet-like material to which the polyurethane resin has been imparted (polyurethane resin-imparted sheet) obtained after completing the above steps is cut in half in the thickness direction to form two sheet-like materials.

Furthermore, the surface of the sheet-like material to which the polyurethane resin has been applied or the surface of the sheet-like material cut in half can be subjected to a nap raising treatment. The nap raising treatment can be performed by a method such as grinding using sandpaper or a roll sander. The nap raising treatment can be performed on only one surface of the sheet-like material or on both surfaces.

When performing nap raising, a lubricant such as silicone emulsion can be applied to the surface of the sheet-like material before the nap raising process. Also, by applying an antistatic agent before the nap raising process, grinding powder generated from the sheet-like material during grinding is less likely to accumulate on the sandpaper.

(B) Dyeing In the method for producing an artificial leather of the present invention, the sheet-like material obtained in the above steps is preferably dyed in a dyeing solution having a pH of 4.5 to 5.5. If it is not necessary to color the sheet-like material, it is not necessary to add a dye to the dye bath. By setting the pH of the dyeing solution within the above range, not only can deterioration of the fiber structure of the artificial leather and the polyurethane resin due to dyeing be suppressed, but also the weight average molecular weight of the polyurethane resin can be increased by dyeing, thereby improving the shape stability, strength, and abrasion resistance of the obtained artificial leather.

The pH of the staining solution can be controlled by a pH buffer solution. Examples of pH buffer solutions include acetate buffer solution, citrate buffer solution, malate buffer solution, phthalate buffer solution, carbonate buffer solution, and phosphate buffer solution. Among these, acetate buffer solution and malate buffer solution are preferably used because of their high buffering capacity in the acidic range.

Examples of dyeing methods include flow dyeing using a jigger dyeing machine or a flow dyeing machine, immersion 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, flow dyeing using a flow dyeing machine is preferred in terms of obtaining a soft texture and quality and grade.

(C) Post-processing The artificial leather obtained by the above method can be given a design on its surface as necessary. For example, post-processing such as perforation, embossing, laser processing, pinsonic processing, and printing can be given. Of course, it is also preferable to perform these post-processing treatments on the sheet-like material before dyeing.

The artificial leather of the present invention obtained by the above-mentioned manufacturing method has a good texture and a high-quality appearance, and further has shape stability, strength, and abrasion resistance, so it can be used for vehicle seats and furniture, for example.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Measurement method and evaluation processing method]
Unless otherwise specified, the measurements of each physical property were carried out according to the above-mentioned methods.

(1) Average single fiber diameter of ultrafine fibers (μm):
A scanning electron microscope (SEM) "VHX-D500/D510" manufactured by Keyence Corporation was used, and the average single fiber diameter was calculated according to the above method.

(2) Presence or absence of urea bonds:
The polyurethane resin was extracted from the artificial leather using N,N-dimethylformamide, and the N,N-dimethylformamide was removed by drying. The polyurethane resin was then dissolved in deuterated dimethyl sulfoxide to a urethane resin concentration of 0.1 g/1 mL, and ^{the 1} H-NMR spectrum was evaluated using a JNM-ECZ400S manufactured by JEOL Ltd. In the obtained spectrum, the peak appearing at 8.0 to 8.6 ppm was assigned to urea bonds, and the presence or absence of urea bonds was determined.

(3) Weight average molecular weight of polyurethane resin:
From the obtained polyurethane resin-applied sheet or artificial leather, the polyurethane resin was extracted using N,N-dimethylformamide (hereinafter, sometimes referred to as DMF), and the polyurethane resin concentration was adjusted to 1 mass %, and the weight average molecular weight of the polyurethane resin was determined by measurement using gel permeation chromatography (GPC) under the following conditions.
・Equipment: GPC measuring machine HLC-8020 (manufactured by Tosoh Corporation)
Column: TSKgel GMH-XL (manufactured by Tosoh Corporation).

(4) pH of dye solution:
Water, a sheet-like material, a dye, a leveling agent, and a pH buffer solution were charged into a jet dyeing machine and mixed, and then the pH of the solution before the dyeing temperature was raised was measured using a pH meter "AS600" manufactured by AS ONE Corporation.

(5) Polyurethane resin content (mass%):
The artificial leather was immersed in N,N-dimethylformamide to extract and remove the polyurethane resin, and the calculation was performed according to the above method.

(6) Total value of 30% circular modulus in two perpendicular directions per unit area ((N/cm)/(g/m ² ), (N/2.54 cm)/(g/m ² ), represented as “total value of modulus per unit area” in Tables 1 and 2):
The tensile tester used was an Instron Model 3343, and measurements and calculations were carried out according to the above-mentioned method.

(7) Tensile strength per unit area (N/cm)/(g/m ² ):
The tensile tester used was an Instron Model 3343, and measurements and calculations were carried out according to the above-mentioned method.

(8) Mass reduction rate (%):
The Martindale abrasion tester used was a Model 406 manufactured by James H. Heal & Co., and the standard friction cloth was ABRASTIVE CLOTH SM25 manufactured by the same company, and measurements and calculations were performed according to the above-mentioned method.

(9) Pile length (μm):
The scanning electron microscope used was a VHX-D500/D510 model manufactured by Keyence Corporation, and measurements and calculations were carried out according to the above-mentioned methods.

(10) Texture of artificial leather:
A total of 20 healthy adult males and females, 10 each, conducted a sensory evaluation. The artificial leather was cut into 300 mm squares and evaluated as follows based on the feel when held in the palm of the hand, with the most common evaluation being taken as the texture of the artificial leather. In the case of a tie in the number of evaluations, the higher evaluation was taken as the texture of the artificial leather. In the present invention, a good level is "Grade 3 or 4."
Grade 4: Soft and good texture; Grade 3: Slightly soft and good texture; Grade 2: Slightly hard and poor texture; Grade 1: Hard and poor texture.

(11) Appearance quality (uniformity) of artificial leather:
Visual evaluation was carried out by 20 people, 10 healthy adult males and 10 healthy adult females. Artificial leathers with a size of 300 mm square or more were evaluated on a 5-point scale as shown below, with the most common evaluation being regarded as the appearance quality. In the present invention, a good level is "grade 3 to grade 5."
Grade 5: The entire surface of the artificial leather is covered with uniform nap and has a uniform color tone.
・Level 4: A rating between Level 5 and Level 3.
Grade 3: There is some variation in the standing condition of the hair, but the ground is not exposed and the color tone is generally uniform.
・Level 2: An evaluation between Level 3 and Level 1.
Grade 1: The hair is unevenly raised, with parts of the ground exposed and the color tone uneven.

[Resins used, etc.]
PET: polyethylene terephthalate having an intrinsic viscosity (IV value) of 0.72; Polymer diol A: polytetramethylene glycol; Organic diisocyanate B: diphenylmethane diisocyanate; Chain extender C: methylene bisaniline; Chain extender D: ethylene glycol.

[Example 1]
(A) Formation of a sheet-like material <Step for producing ultrafine fiber-developing fiber>
Using polystyrene as the sea component and the above-mentioned PET as the island component, an islands-in-sea type composite fiber was obtained with a conjugation ratio of 20 mass % of the sea component and 80 mass % of the island component, with 16 islands/1 filament and an average single fiber diameter of 20 μm.

<Step of producing a fiber structure>
The obtained islands-in-the-sea composite fibers were cut into staples with a fiber length of 51 mm, and then passed through a card and a cross wrapper to form a fiber web. The fiber web was entangled by needle punching to obtain a nonwoven fabric with a basis weight of 450 g/ ^m2 , a thickness of 2.0 mm, and an apparent density of 0.23 g/ ^cm3 . This nonwoven fabric was used as a fiber structure.

<Step of forming ultrafine fibers>
The obtained fiber structure was immersed in trichloroethylene and squeezed with a mangle five times to obtain a sheet of ultrafine fibers from which the sea component of the islands-in-sea type composite fibers had been removed. The average single fiber diameter of the ultrafine fibers was 4.4 μm.

<Step of applying polyurethane resin>
The sheet made of ultrafine fibers obtained as described above was immersed in a DMF solution of polyurethane resin, the main component of which was an organic solvent-based polyurethane resin having urea bonds (polymer diol A, organic diisocyanate B, chain extender C), adjusted to a solid content concentration of 12% by mass, and then the polyurethane resin was solidified in an aqueous solution with a DMF concentration of 30% by mass. Thereafter, the polyurethane resin was dry-solidified by drying for 10 minutes with hot air at a temperature of 110°C, to obtain a polyurethane resin-imparted sheet having a thickness of 1.5 mm and a weight average molecular weight of the polyurethane resin of 200,000.

<The process of cutting in half and raising the nap>
The polyurethane resin-imparted sheet obtained as described above was cut in half in the thickness direction to obtain a half-cut sheet having a thickness of 0.75 mm. The surface formed by cutting in half (half-cut surface) was ground with endless sandpaper having a sandpaper size of 180 to obtain a sheet-like material having a thickness of 0.45 mm and a nap length of 390 μm.

(B) Dyeing The napped sheet-like material obtained as described above was dyed with a black disperse dye in a dye solution of pH 4.8 (pH buffer: acetate buffer) at a temperature of 120°C using a liquid jet dyeing machine, and then reduced and washed. After that, the sheet was dried in a dryer to obtain an artificial leather.

The weight average molecular weight of the polyurethane resin in the resulting artificial leather was 530,000. The results are shown in Table 1.

[Example 2]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, the pH of the dyeing solution was set to 5.0 by adjusting the composition ratio of acetic acid and sodium acetate in the acetate buffer. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 500,000. The results are shown in Table 1.

[Example 3]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, the pH of the dyeing solution was adjusted to 5.2 by adjusting the composition ratio of acetic acid and sodium acetate in the acetate buffer. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 490,000. The results are shown in Table 1.

[Example 4]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, no dye was added and the pH of the dyeing solution was set to 4.6. The weight average molecular weight of the polyurethane resin in the obtained artificial leather was 540,000. The results are shown in Table 1.

[Comparative Example 1]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, the pH of the dyeing solution was adjusted to 3.0 by adjusting the composition ratio of acetic acid and sodium acetate in the acetate buffer. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 240,000. The results are shown in Table 2.

[Comparative Example 2]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, the pH of the dyeing solution was set to 5.7 by adjusting the composition ratio of acetic acid and sodium acetate in the acetate buffer. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 230,000. The results are shown in Table 2.

[Comparative Example 3]
An artificial leather was obtained in the same manner as in Example 1, except that in the dyeing step, the pH of the dyeing solution was set to 6.5 by adjusting the composition ratio of acetic acid and sodium acetate in the acetate buffer. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 120,000. The results are shown in Table 2.

[Comparative Example 4]
An artificial leather was obtained in the same manner as in Example 2, except that in the step of applying the polyurethane resin, a DMF solution of polyurethane mainly composed of an organic solvent-based polyurethane resin not having a urea bond (polymer diol A, organic diisocyanate B, chain extender D) was used. The weight average molecular weight of the polyurethane resin of the obtained artificial leather was 200,000. The results are shown in Table 2.

[Comparative Example 5]
The fiber structure was produced in the same manner as in Example 2, except that in the step of applying the polyurethane resin, the weight average molecular weight of the polyurethane resin was set to 500,000. However, when the fiber structure was impregnated with the polyurethane solution, the viscosity of the polyurethane solution was high, and the polyurethane did not penetrate into the fiber structure, resulting in poor processability. The results are shown in Table 2.

The artificial leathers obtained in Examples 1 to 4 all had a soft feel and uniform appearance, and also had good tensile strength, circular modulus, and abrasion weight loss rate.

On the other hand, the artificial leathers of Comparative Examples 1 to 4 had excellent softness and appearance quality, but the weight-average molecular weight of the polyurethane resin was small and the orthogonal 30% circular modulus per unit area was poor.

1: Artificial leather 2: Raised portion 3: Boundary between raised portion and other portions (line connecting intersections of fibers oriented in the thickness direction and fibers oriented in the surface direction of the artificial leather)
4: Arrow indicating the distance from the intersection of the fiber oriented in the thickness direction and the fiber oriented in the surface direction of the artificial leather to the tip of the nap

Claims (4)

An artificial leather comprising a fiber structure including ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less and made of a thermoplastic resin, and a polyurethane resin,
The polyurethane resin has a urea bond,
The weight average molecular weight of the polyurethane resin is 350,000 or more and 600,000 or less.
Artificial leather. The artificial leather according to claim 1, wherein the content of the polyurethane resin is 10% by mass or more and 60% by mass or less. 3. The artificial leather according to claim 1, wherein the total value of 30% circular modulus in two perpendicular directions per unit area is 1.20 (N/2.54 cm)/(g/ ^m2 ) or more and 1.70 (N/2.54 cm)/(g/ ^m2 ) or less. 3. The artificial leather according to claim 1 or 2, which is colored with a dye.