Artificial leather

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

[Technical field]

[0001] The present invention relates to an artificial leather. [Background technology]

[0002] 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, and is therefore used in a variety of fields, including vehicle interior materials, interior goods, shoes, clothing, etc. When this artificial leather is used for vehicle seats, furniture, etc., it is required to have the properties of shape stability, strength, and durability against friction (abrasion resistance) in addition to a good texture and an appearance quality that gives a sense of luxury.

[0003] Several techniques have been proposed to achieve both high appearance quality and durability in artificial leather. For example, Patent Document 1 proposes a napped leather-like sheet material made of ultrafine fibers and polyurethane, the polyurethane being made using a polymer diol containing a specific amount of polycarbonate diol, and the sheet material contains the specific amount of polyurethane.

[0004] Furthermore, Patent Document 2 proposes a sheet-like material comprising a nonwoven fabric formed by entanglement of ultrafine fibers and an elastic resin binder containing polyurethane as a main component, 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-30579 A [Patent Document 2] International Publication No. 2005 / 095706 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology proposed in Patent Document 1 makes it possible to obtain artificial leather having a certain level of appearance quality and durability such as light resistance. However, it is difficult to achieve both appearance quality and durability by simply adjusting only the content of polyurethane in the artificial leather or the content of polycarbonate diol in the polyurethane. 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.

[0007] On the other hand, the technology proposed in Patent Document 2 is capable of obtaining artificial leather that has both a certain degree of softness and durability by adjusting the gel point of polyurethane using polycarbonate diol. However, there is no particular mention of polyurethane using diol components other than polycarbonate diol, and there is still a demand for a technology that can provide artificial leather that has a good texture and an appearance quality that gives a sense of luxury, and further has shape stability, strength, and abrasion resistance, regardless of the polyurethane.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an artificial leather that combines a soft feel and a luxurious appearance with excellent shape stability, strength, and abrasion resistance. [Means for solving the problem]

[0009] As a result of extensive investigations conducted by the present inventors in order to achieve the above object, it has been found that by making the polyurethane resin constituting 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 combines a good texture and an appearance quality that gives a sense of luxury, as well as shape stability, strength, and abrasion resistance.

[0010] The present invention has been completed based on these findings, and provides the following inventions.

[0011] [1] An artificial leather comprising 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, wherein the polyurethane resin has a urea bond and a weight average molecular weight of 350,000 or more and 600,000 or less.

[0012] [2] The artificial leather described in [1] above, wherein the content of the polyurethane resin is 10% by mass or more and 60% by mass or less.

[0013] [3] The sum of the 30% circular modulus in two perpendicular directions per unit area is 1.20 (N / 2.54 cm) / (g / m 2 ) or more 1.70(N / 2.54cm) / (g / m 2 ) The artificial leather according to the above [1] or [2],

[0014] [4] The artificial leather according to any one of [1] to [3] above, which is colored with a dye. Effect of the Invention

[0015] According to the present invention, an artificial leather can be obtained which has a good texture and an appearance quality that gives a sense of luxury, and further has shape stability, strength and abrasion resistance. [Brief description of the drawings]

[0016] [Figure 1] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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 350000 or more and 600000 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 deviate from the gist of the invention, and various modifications are possible without departing from the gist of the invention.

[0018] [Textile structures] 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.

[0019] As the thermoplastic resin, any resin capable of forming 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. From the viewpoint of durability, particularly mechanical strength and heat resistance, polyester-based resins are preferably used. 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 same applies to "...-based resin."

[0020] Examples of the polyester resin include polyethylene terephthalate, polytrimethylene terephthalate, polytetramethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, and polyethylene-1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate. Among them, polyethylene terephthalate, which is the most widely used, or a polyester copolymer mainly containing ethylene terephthalate units is preferably used.

[0021] 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, from the viewpoint of compatibility of the two or more components, the difference in intrinsic viscosity (IV value) of the polyesters used is preferably 0.50 or less, and more preferably 0.30 or less.

[0022] In the present invention, the intrinsic viscosity is calculated by the following method. (1) Dissolve 0.8 g of the sample polymer in 10 mL of orthochlorophenol. (2) Relative viscosity η measured using an Ostwald viscometer at a temperature of 25°C r Calculate using the formula below and round off to the third decimal place. η r =η / η0=(t×d) / (t0×d0) Intrinsic viscosity (IV value) = 0.0242 η r +0.2634 (Here, η is the viscosity of the polymer solution, η0 is the viscosity of orthochlorophenol, t is the drop time of the solution (sec), and d is the density of the solution (g / cm 3 ), t0 is the fall time of orthochlorophenol (sec), and d0 is the density of orthochlorophenol (g / cm 3 ) respectively.

[0023] 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. When the lower limit of the range of the average single fiber diameter of the ultrafine fibers is 0.1 μm or more, preferably 0.5 μm or more, excellent effects are achieved in color development after dyeing, light fastness and friction fastness, and stability during spinning. On the other hand, when the upper limit of the range is 10.0 μm or less, preferably 8.0 μm or less, 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.

[0024] In the present invention, the average single fiber diameter of ultrafine fibers is calculated by taking a scanning electron microscope (SEM, for example, "VHX-D500 / D510" manufactured by Keyence Corporation) 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.

[0025] From the viewpoint of processing operability, the cross-sectional shape of the ultrafine fibers according to the present invention is preferably a circular cross-section, but it is also possible to adopt cross-sectional shapes of polygonal cross-sections such as ellipse, flattened or triangular, sectoral or cross-shaped, hollow, Y-shaped, T-shaped or U-shaped irregular cross-sectional shapes. In this case, the average single fiber diameter of the ultrafine fibers is determined by first measuring the cross-sectional area of ​​a single fiber and calculating the diameter when the cross-section is regarded as a circle.

[0026] In the present invention, particularly when the artificial leather is to be colored in a deep 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.

[0027] The particle size referred to here is the particle size when black pigment or chromatic fine oxide pigment is present in ultrafine fibers, and is generally called the secondary particle size. * a * b * In color space, saturation C* "Chromatic fine particle oxide pigment" refers to fine particle oxide pigments that exhibit chromatic colors, and does not include white oxide pigments such as zinc oxide and titanium oxide.

[0028] The lower limit of the average particle size range is preferably 0.05 μm or more, 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.

[0029] In the present invention, the above particle size refers to a value measured and calculated by the following method. (1) Prepare ultrathin sections with a thickness of 5 μm to 10 μm in the cross-sectional direction perpendicular to the longitudinal direction of the ultrafine fibers. (2) Observe the cross-section of the fiber in an ultrathin section at 10,000x magnification using a transmission electron microscope (TEM). (3) Using image analysis software, measure the circle equivalent diameter of 20 particles of black pigment (a1) or chromatic fine particle oxide pigment (a2) contained within a 2.3 μm × 2.3 μm visual field of the observed image. If there are fewer than 20 particles of 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 diameter of all particles of 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 the third decimal place.

[0030] 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 based on 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.

[0031] 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 black pigment with a fine particle size and excellent dispersibility in a polymer, it is preferable that the black pigment is carbon black.

[0032] In addition, as the chromatic fine particle oxide pigment according to the present invention, a known pigment close to the target color can be used, for example, 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.), cobalt aluminate (e.g., "TM Blue 3490E" manufactured by Dainichiseika Chemicals Co., Ltd.), etc.

[0033] Furthermore, to the thermoplastic resin constituting the ultrafine fibers, inorganic particles such as titanium oxide particles, lubricants, heat stabilizers, ultraviolet absorbers, conductive agents, heat storage agents, antibacterial agents, and the like can be added as necessary, within the scope not impairing the object of the present invention.

[0034] Examples of the fiber structure used in the present invention include woven fabrics, knitted fabrics, nonwoven fabrics, and fiber entanglements containing these as components, which are made of the ultrafine fibers, and can be appropriately selected depending on the cost and characteristics required for each application and purpose. Among them, when woven fabrics or knitted fabrics are used as the fiber structure, 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 structure, artificial leather with excellent quality due to a rich texture and fine nap can be obtained when the surface is raised.

[0035] In the present invention, the term "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 applies to a "fiber-entangled body containing a woven fabric (or knitted fabric) as a component".

[0036] The nonwoven fabric may be in the form of a long fiber nonwoven fabric mainly composed of filaments, or a short fiber nonwoven fabric mainly composed of fibers of 100 mm or less. The long fiber nonwoven fabric is preferable because it can provide an artificial leather with excellent strength. On the other hand, the short fiber nonwoven fabric can provide a larger amount of fibers oriented in the thickness direction of the artificial leather than the long fiber nonwoven fabric, and can provide a highly dense surface to the artificial leather when raised.

[0037] 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.

[0038] The basis weight of the fiber structure constituting the artificial leather of the present invention is 50 g / m2, as measured according to "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "General nonwoven fabric test method". 2 More than 400g / m 2 The lower limit of the range of the basis weight of the fiber structure is preferably 50 g / m 2 More preferably, 80 g / m 2 By setting the weight per unit area of ​​the fiber structure to 400 g / m or more, an artificial leather having a sense of fullness and excellent texture can be obtained. 2 Less than 300 g / m 2 By satisfying the above condition, it is possible to obtain a flexible artificial leather having excellent moldability.

[0039] The artificial leather of the present invention is preferably a fiber entangled body in which a nonwoven fabric made of ultrafine fibers and a woven fabric are entangled as the fiber structure. Specifically, the woven fabric is laminated inside the nonwoven fabric or on one surface of the nonwoven fabric. This makes the strength and shape stability of the artificial leather excellent.

[0040] In this case, the type of fiber constituting the woven fabric is preferably a filament yarn, a spun yarn, a mixed composite yarn of a filament yarn and a spun yarn, etc., and from the standpoint of durability, particularly mechanical strength, it is more preferable to use a multifilament made of a polyester-based resin or a polyamide-based resin.

[0041] From the viewpoint of mechanical strength etc., it is preferable that the fibers constituting the woven fabric do not contain black pigments or chromatic fine particle oxide pigments.

[0042] 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 can an artificial leather with excellent flexibility be obtained, 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 a 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.

[0043] In the present invention, the average single fiber diameter of the fibers constituting 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 constituting the woven fabric, measuring the single fiber diameter of the selected fibers, calculating the arithmetic average value of the 10 fibers, and rounding off to one decimal place.

[0044] When the fibers constituting the woven fabric are multifilaments, the total fineness of the multifilaments is preferably 30 dtex or more and 170 dtex or less.

[0045] By setting the upper limit of the total fineness 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 of the yarns constituting the woven fabric to 30 dtex or more, not only is the shape stability of the product as an 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.

[0046] The total fineness of the yarns constituting the above-mentioned woven fabric refers to the value measured and calculated according to "8.3 Fineness" of "8.3.1 Correct fineness b) Method B (simplified method)" in "8.3 Fineness" of JIS L1013:2010 "Testing methods for chemical fiber filament yarns."

[0047] 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.

[0048] [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.

[0049] A specific polyurethane resin is preferably a polyurethane 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 may be either a polyurethane resin (organic solvent-based polyurethane resin) obtained by dissolving the diphenylmethane diisocyanate, etc., described later as an organic diisocyanate in an organic solvent and impregnating the fiber structure as described later, or a polyurethane resin (water-dispersed polyurethane resin) obtained by dispersing the diphenylmethane diisocyanate, etc., described later as an organic diisocyanate, in water and impregnating the fiber structure as described later.

[0050] (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.

[0051] The polycarbonate-based diol can be produced by transesterification of an alkylene glycol with a carbonate ester, or by reaction of an alkylene glycol with phosgene or a chloroformate ester, etc. Examples of the alkylene glycol 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 kinds of alkylene glycols can be used.

[0052] Examples of polyester diols include polyester diols obtained by condensing various low molecular weight polyols with polybasic acids.

[0053] 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. Also usable as the low molecular weight polyol are adducts of various alkylene oxides added to bisphenol A.

[0054] 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.

[0055] Examples of the polyether diol used in the present invention include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymer diols obtained by combining these.

[0056] When the molecular weight of the polyurethane resin is constant, the number average molecular weight of the polymer diol is preferably in the range of 500 to 4000. The artificial leather can be made more flexible by setting the lower limit of the number average molecular weight range to preferably 500 or more, more preferably 1500 or more. The polyurethane resin can be made stronger by setting the upper limit of the number average molecular weight range to preferably 4000 or less, more preferably 3000 or less.

[0057] (2) Organic diisocyanates 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; and these can also be used in combination.

[0058] (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.

[0059] (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 reactive points 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 forming crosslinking points more uniformly in the molecular structure of the polyurethane resin and reducing the loss of flexibility.

[0060] As the crosslinking agent, a compound having an isocyanate group, an oxazoline group, a carbodiimide group, an epoxy group, a melamine resin, a silanol group, or the like can be used.

[0061] In addition, the polyurethane resin may contain, as necessary, pigments such as carbon black, dye antioxidants, antioxidants, light resistance agents, antistatic agents, dispersants, softeners, coagulation regulators, flame retardants, antibacterial agents, deodorizers, etc. 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.

[0062] 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, the artificial leather can have excellent shape stability, strength, and abrasion resistance. 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.

[0063] The weight average molecular weight is a value measured and calculated by the following method. (1) From the obtained artificial leather, polyurethane resin is extracted using a solution of lithium chloride in N,N-dimethylformamide (hereinafter sometimes 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 %, to prepare 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: 0.01M lithium chloride in DMF ·Flow rate: 1.0mL / min Column temperature: 40℃ ·Injection volume: 0.05mL Standard sample: polystyrene If the same column is not available, a column with equivalent performance shall be used for the measurement.

[0064] 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.

[0065] In general, the content of polyurethane resin in artificial leather can be appropriately adjusted in consideration of the type of polyurethane resin used or its constituents such as polymer diol, organic diisocyanate, chain extender, etc., the manufacturing method of the polyurethane resin, and the feel and physical properties. In the present invention, 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 bond 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.

[0066] 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.

[0067] [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.

[0068] 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. The lower limit of the nap length range is preferably 200 μm or more, so that the nap on the surface covers the polyurethane resin and suppresses the 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. In addition, 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 the fibers of the woven fabric near the surface of the artificial leather can be sufficiently covered. On the other hand, the upper limit of the nap length range is preferably 500 μm or less, so that an artificial leather with excellent design effect and wear resistance can be obtained.

[0069] In the present invention, the nap length of the artificial leather is measured and calculated by the following method. (1) For surfaces having raised nap, use a lint brush or similar to raise the nap. (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 model). (3) As shown in the example of Figure 1, in the cross section, a layer consisting only of fibers oriented in the thickness direction is defined as the 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 this is measured at 10 points. (4) (3) is repeated for all cross sections, the arithmetic average value of the above-mentioned pile length (μm) is calculated, and the value is rounded off to the first decimal place.

[0070] 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 method" 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 production 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.

[0071] 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. By having a friction fastness and a light fastness of Grade 4 or higher, color fading and staining of clothes, etc. can be prevented during actual use.

[0072] 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 "Testing 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 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. By having a mass loss rate of 1.5% or less, contamination due to fluff falling during actual use can be prevented.

[0073] The mass reduction rate can be adjusted by the weight average molecular weight of the polyurethane resin, and the fiber length, nap length and apparent density of the ultrafine fibers.

[0074] In addition, the artificial leather of the present invention has a tensile strength measured in accordance with "6.3.1 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric test methods" divided by the basis weight of the artificial leather, i.e., a tensile strength per unit basis weight of the artificial leather, which is 0.12 (N / cm) / (g / m 2 ) or more 0.50(N / cm) / (g / m 2 ) or less.

[0075] The lower limit of the range of tensile strength per unit area is preferably 0.12 (N / cm) / (g / m 2 ) or more, more preferably 0.14 (N / cm) / (g / m 2 ) or more, the artificial leather has excellent shape stability and durability, which is preferable. In addition, the upper limit of the range of the tensile strength per unit area is preferably 0.50 (N / cm) / (g / m 2 ) or less, more preferably 0.45 (N / cm) / (g / m 2 ) or less, the artificial leather has excellent moldability.

[0076] 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 woven fabric to be inserted, and the total fineness and number of twists of the yarns constituting the woven fabric.

[0077] In addition, the artificial leather of the present invention has a total value of 30% circular modulus in two perpendicular directions per unit area weight of 1.20 (N / 2.54 cm) / (g / m 2 ) or more 1.70(N / 2.54cm) / (g / m 2 ) or less. Here, 1.00 (N / 2.54 cm) / (g / m 2 ) is 0.39(N / cm) / (g / m 2 ), and the above range corresponds to 0.47 (N / cm) / (g / m 2 ) or more 0.67(N / cm) / (g / m 2This "total value of 30% circular modulus in two perpendicular directions per unit basis weight" is a parameter related to shape stability, and the lower limit of the range of the total value of 30% circular modulus in two perpendicular directions per unit basis weight is 1.20 (N / 2.54 cm) / (g / m 2 ) or more, more preferably 1.25 (N / 2.54cm) / (g / m 2 ) or more, it is possible to obtain an artificial leather having excellent shape stability, and also to suppress deterioration of surface quality due to slippage during stretching. In addition, the upper limit of the range of the total value of the 30% circular modulus in two perpendicular directions per unit area is preferably 1.70 (N / 2.54 cm) / (g / m 2 ) or less, more preferably 1.65 (N / 2.54 cm) / (g / m 2 ) or less, it has high conformability to curved parts when stretched during molding, and the occurrence of wrinkles and sagging can be prevented.

[0078] 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 each test piece. (3) Using an Instron tensile testing machine (for example, Instron Model 3343), measure the modulus (N / 2.54 cm) at 30% elongation 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 on the artificial leather by sampling in each direction that forms an angle 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) The weight per unit area of ​​the artificial leather is measured and calculated. In the present invention, the weight per unit area of ​​the artificial leather refers to a value obtained by randomly taking five 250 mm x 250 mm test pieces 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 methods", and rounding off the calculated value to the nearest whole number. If it is not possible to take a 250 mm x 250 mm test piece, a test piece with the largest possible square shape is taken, and the mass and dimensions of the test piece are measured to determine the mass per unit area (g / m 2 ) is the value obtained by calculating (6) The sum of the arithmetic average values ​​(N / 2.54 cm) calculated in each direction in (4) is calculated as the weight (g / m2) of the artificial leather calculated in (5). 2 ) divided by (N / 2.54cm) / (g / m 2 ) shall be rounded off to the third decimal place.

[0079] In addition, 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, in the case where a woven fabric is inserted, the density of the woven fabric and the elongation properties of the yarns constituting the woven fabric.

[0080] Furthermore, the artificial leather of the present invention may not be colored with a dye depending on the intended use, and the presence or absence of a dye is not limited. However, in order to impart any hue according to 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 a 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 there is any solid remaining, the presence or absence of a dye can be determined.

[0081] The dye used in the present invention may be selected according to the type of fibers contained in the fiber structure, such as the ultrafine fibers, and is 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 the thermoplastic resin is a polyamide-based resin, an acid dye or a metal-containing dye can be used, or a combination of these can be used.

[0082] Of course, the material may or may not be colored with a dye, and may be colored by other methods, such as printing, as will be described later.

[0083] [Manufacturing method of artificial leather] The method for producing the 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 to 10.0 μm and a polyurethane resin having a weight-average molecular weight of 50,000 to 350,000 in a dyebath having a pH of 4.5 to 5.5. The details of this method are described below.

[0084] (A) Formation of a sheet-like product First, a sheet-like material containing a polyurethane resin and a fiber structure containing ultrafine fibers having an average single fiber diameter of 0.1 μm or more and 10.0 μm or less is formed. This sheet-like material is preferably formed by the following steps. Step (1): A step of producing an ultrafine 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. Step (2): A step of producing a fiber structure having ultrafine fiber-developing fibers as a main component. Step (3): A step of 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 mainly composed of ultrafine fiber-developing fibers. Step (4): A step of applying a polyurethane resin to a fiber structure mainly composed of ultrafine fibers or ultrafine fiber-developing fibers. Each step will be described in detail below.

[0085] <Process 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.

[0086] As the ultrafine fiber-producing fiber, an islands-in-sea type composite fiber is used in which thermoplastic resins with different solvent solubilities are used as a sea portion (easily soluble polymer) and an island portion (slightly soluble polymer), and the sea portion is dissolved and removed using a solvent or the like to turn the island portions into ultrafine fibers. The use of islands-in-sea type composite fiber is preferable from the viewpoint of the texture and appearance quality of the artificial leather, because 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.

[0087] As a method for spinning ultrafine fiber-generating fibers having an islands-in-sea type composite structure, a method using a polymer mutual alignment body in which sea parts and island parts are mutually aligned and spun using an islands-in-sea type composite spinneret is preferred from the viewpoint of obtaining ultrafine fibers with uniform single fiber fineness.

[0088] For the sea portion of the islands-in-sea type composite fiber, polyethylene, polypropylene, polystyrene, copolymer polyesters copolymerized with sodium sulfoisophthalic acid, polyethylene glycol, and the like, and polylactic acid can be used. From the viewpoints of spinnability, ease of elution, and the like, polystyrene and copolymer polyesters are preferably used.

[0089] In the method for producing an artificial leather of the present invention, when islands-in-sea type composite fibers are used, it is preferable to use islands-in-sea type composite fibers having an island portion strength of 2.5 cN / dtex or more. The lower limit of the range of the island portion strength is preferably 2.5 cN / dtex or more, more preferably 2.8 cN / dtex or more, and further preferably 3.0 cN / dtex or more, whereby the abrasion resistance of the artificial leather is improved and a decrease in friction fastness due to fiber shedding can be suppressed.

[0090] 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 area from the sample (1), air-dry it. (3) In accordance with JIS L1013:2010 "Test methods for chemical fiber filament yarn", "8.5 Tensile strength and elongation", "8.5.1 Standard time test", the test shall be carried out 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) above shall be rounded off to one decimal place to obtain the strength of the island portion of the islands-in-sea type composite fiber.

[0091] <Process for producing 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.

[0092] As for the form of the nonwoven fabric, either short fiber nonwoven fabric or long fiber nonwoven fabric can be used as described above. However, in the case of short fiber nonwoven fabric, the number of fibers oriented in the thickness direction of the artificial leather is greater than in the case of long fiber nonwoven fabric, and a highly dense feel can be obtained on the surface of the artificial leather when it is brushed.

[0093] When the nonwoven fabric is a staple fiber nonwoven fabric, the obtained ultrafine fiber development type fiber is 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 process and cutting process can be performed by known methods.

[0094] Furthermore, when the fiber structure contains a woven fabric, the nonwoven fabric obtained above is laminated and then entangled and integrated. The nonwoven fabric and the woven fabric can be entangled and integrated by laminating the woven fabric on one or both sides of the nonwoven fabric, or by sandwiching the woven fabric between multiple nonwoven fabric webs and then entangling the fibers of the nonwoven fabric and the woven fabric by needle punching, water jet punching, or the like.

[0095] The apparent density of the nonwoven fabric made of ultrafine fiber-developing fibers after needle punching or water jet punching is 0.15 g / cm 3 More than 0.45g / cm 3 The lower limit of the apparent density range is preferably 0.15 g / cm or less. 3 By setting the apparent density at or above 1.0 g / cm, 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 / cm. 3 By satisfying the above condition, it is possible to maintain a sufficient space for applying the polyurethane resin.

[0096] In order to improve the denseness of the fibers, it is also a preferred embodiment to subject the nonwoven fabric to a heat shrinkage treatment using hot water or steam. In the present invention, "hot water" refers to water heated to 90°C to 100°C.

[0097] Next, the nonwoven fabric can be impregnated with an aqueous solution of a water-soluble resin and dried to impart the water-soluble resin to the nonwoven fabric. By imparting the water-soluble resin to the nonwoven fabric, the fibers are fixed and the dimensional stability is improved.

[0098] <Process for 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.

[0099] The treatment for developing ultrafine fibers can be carried out by immersing a nonwoven fabric made of islands-in-sea type composite fibers in a solvent to dissolve and remove the sea parts of the islands-in-sea type composite fibers.

[0100] When the ultrafine fiber-producing fiber is an islands-in-the-sea type composite fiber, the solvent for dissolving and removing the sea part can be an organic solvent such as toluene or trichloroethylene when the sea part is polyethylene, polypropylene or polystyrene. Also, when the sea part is a copolymer polyester or polylactic acid, an alkaline aqueous solution such as sodium hydroxide can be used. Also, when the sea part is a water-soluble thermoplastic polyvinyl alcohol resin, hot water can be used.

[0101] <Step of adding 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 polyurethane resin, and these methods can be appropriately selected depending on the type of polyurethane resin used.

[0102] As a solvent used when applying the polyurethane resin, N,N-dimethylformamide, dimethylsulfoxide, etc. may be preferably used. In addition, a water-dispersed polyurethane liquid in which the polyurethane resin is dispersed in water as an emulsion may be used.

[0103] The polyurethane resin to be 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 falling off of the composite fibers can be prevented. 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 an increase in the viscosity of the polyurethane liquid can be suppressed and the polyurethane liquid can be uniformly applied to the fiber structure.

[0104] The polyurethane resin may be applied to the fiber structure before ultrafine fibers are generated from the ultrafine fiber-generating fiber, or after ultrafine fibers are generated from the ultrafine fiber-generating fiber.

[0105] <The process of cutting the sheet 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.

[0106] 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.

[0107] When the sheet-like material is to be nap-raised, a lubricant such as a 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.

[0108] (B) Staining In the method for producing an artificial leather of the present invention, it is preferable to dye the sheet-like material obtained in the above steps 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.

[0109] 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.

[0110] Examples of the dyeing method include flow dyeing using a jigger dyeing machine or a flow dyeing machine, dip dyeing such as thermosol dyeing using a continuous dyeing machine, or printing on the napped surface by 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.

[0111] (C) Post-processing In addition, 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 performed. Of course, it is also a preferred embodiment to perform these post-processing treatments on the sheet-like material before dyeing.

[0112] The artificial leather of the present invention obtained by the production method exemplified above has a good texture and an appearance quality that gives a sense of luxury, and further has shape stability, strength, and abrasion resistance, and therefore can be suitably used, for example, for vehicle seats and furniture. EXAMPLES

[0113] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0114] [Measurement method and evaluation processing method] Unless otherwise specified, the measurements of each physical property were carried out according to the above-mentioned methods.

[0115] (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.

[0116] (2) Presence or absence of urea bonds: The polyurethane resin was extracted from the artificial leather using N,N-dimethylformamide, and after the N,N-dimethylformamide was removed by drying, it was dissolved in deuterated dimethyl sulfoxide so that the urethane resin concentration was 0.1 g / 1 mL. 1 The H-NMR spectrum was evaluated. 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.

[0117] (3) Weight average molecular weight of polyurethane resin: The polyurethane resin was extracted from the obtained polyurethane resin-applied sheet or artificial leather using N,N-dimethylformamide (hereinafter sometimes referred to as DMF), the polyurethane resin concentration was adjusted to 1 mass%, and the weight average molecular weight of the polyurethane resin was determined by gel permeation chromatography (GPC) under the following conditions. Equipment: GPC measuring machine HLC-8020 (Tosoh Corporation) Column: TSKgelGMH-XL (Tosoh Corporation).

[0118] (4) pH of dye solution: After adding water, sheet-like material, dye, leveling agent, and pH buffer solution to a jet dyeing machine and mixing them, the pH of the solution before the dyeing temperature was raised was measured using a pH meter "AS600" manufactured by AS ONE Corporation.

[0119] (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.

[0120] (6) The sum of the 30% circular modulus in two perpendicular directions per unit area ((N / cm) / (g / m 2 ), (N / 2.54cm) / (g / m 2 ), which is expressed 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 performed according to the above-mentioned methods.

[0121] (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 performed according to the above-mentioned methods.

[0122] (8) Mass reduction rate (%): The Martindale abrasion tester used was the James H. Heal & Co. "Model 406," and the standard friction cloth was the same company's "ABRASTIVE CLOTH SM25." Measurements and calculations were performed according to the above-mentioned method.

[0123] (9) Pile length (μm): The scanning electron microscope used was a VHX-D500 / D510 model manufactured by Keyence Corporation, and measurements and calculations were performed according to the above-mentioned methods.

[0124] (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: Flexible and good texture Grade 3: Slightly flexible and good texture Grade 2: Slightly tough and poor texture Grade 1: Strong and poor texture.

[0125] (11) Appearance quality of artificial leather (uniformity): Visual evaluation was carried out by a total of 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, and the most common evaluation was determined 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 fabric, but the ground is not exposed and the color tone is generally uniform. · Level 2: A rating between Level 3 and Level 1. Grade 1: The hair is unevenly raised, with parts of the ground exposed and the color tone uneven.

[0126] [Resins used] ·PET: Polyethylene terephthalate with 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.

[0127] [Example 1] (A) Formation of a sheet-like product <Process 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% sea component and 80 mass% island component, 16 islands / 1 filament, and an average single fiber diameter of 20 μm.

[0128] <Process for producing fiber structure> The obtained islands-in-the-sea type composite fiber was cut into staples with a fiber length of 51 mm, and the staples were passed through a card and a cross wrapper to form a fiber web. The fiber web was entangled by needle punching to obtain a fiber weight of 450 g / m2 The thickness is 2.0 mm and the apparent density is 0.23 g / cm 3 This nonwoven fabric was used as a fiber structure.

[0129] <Process for 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 these ultrafine fibers was 4.4 μm.

[0130] <Step of adding 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. The polyurethane resin was then dried for 10 minutes with hot air at a temperature of 110°C to dry solidify the polyurethane resin, thereby obtaining a polyurethane resin-imparted sheet having a thickness of 1.5 mm and a weight average molecular weight of 200,000.

[0131] <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.

[0132] (B) Staining The napped sheet-like material obtained as described above was dyed with a black disperse dye in a dyeing 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, it was dried in a dryer to obtain artificial leather.

[0133] The weight average molecular weight of the polyurethane resin in the obtained artificial leather was 530000. The results are shown in Table 1.

[0134] [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 in the obtained artificial leather was 500,000. The results are shown in Table 1.

[0135] [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 in the obtained artificial leather was 490,000. The results are shown in Table 1.

[0136] [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.

[0137] [Table 1]

[0138] [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 set 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 in the obtained artificial leather was 240,000. The results are shown in Table 2.

[0139] [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.

[0140] [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.

[0141] [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 (polymer diol A, organic diisocyanate B, chain extender D) having no urea bond 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.

[0142] [Comparative Example 5] The fabric 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.

[0143] [Table 2]

[0144] The artificial leathers obtained in Examples 1 to 4 all had a soft feel and a uniform appearance, and were also good in tensile strength, circular modulus, and abrasion weight loss rate.

[0145] On the other hand, the artificial leathers of Comparative Examples 1 to 4 were excellent in soft feel and appearance quality, but had a small weight average molecular weight of the polyurethane resin and were inferior in orthogonal 30% circular modulus per unit weight. [Explanation of symbols]

[0146] 1:Artificial leather 2: Pierrection part 3: Boundary line between the napped part and the other parts (line connecting the intersection of the fibers oriented in the thickness direction and the 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

1. 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.

2. 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 total value of the 30% circular modulus in two perpendicular directions per unit basis weight is 1.20 (N / 2.54 cm) / (g / m ２ ) or more 1.70 (N / 2.54cm) / (g / m ２ 3. The artificial leather according to claim 1 or 2, wherein the viscosity is 100% or less.

4. 3. The artificial leather according to claim 1, which is colored with a dye.

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