Artificial leather base material and method for manufacturing artificial leather base material

Abstract

Provided is a polyamide fiber-containing artificial leather base material having excellent morphological stability when wetted with water, said artificial leather base material comprising polyamide fibers and a polymer elastomer, said artificial leather base material being obtained by drying the artificial leather base material at 100 DEG C for 10 minutes, then transferring the dried artificial leather base material to a gas atmosphere having a temperature of 22 DEG C and a relative humidity of 45%, and drying the dried artificial leather base material in the atmosphere. When the mass of the artificial leather base material 40 seconds after the movement is denoted as A, the mass when the artificial leather base material is further left to stand in the gas atmosphere and the mass change does not occur is denoted as B, and the ratio of the mass of the polymeric elastomer to the total mass of the polyamide fiber and the polymeric elastomer is denoted as X mass%, X mass% is less than X mass%. The equilibrium moisture regain calculated by the following formula (1) is 1.80% or less: equilibrium moisture regain (%) = {(B-A) / [A * (100-X) / 100]} * 100.

Description

Technical Field

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

[0002] Conventionally, there are known artificial leathers in which the surface of an artificial leather substrate impregnated with polyurethane is napped to a suede or nubuck-like texture, and grained artificial leathers in which a polyurethane layer is laminated on the surface of the artificial leather substrate. Such artificial leathers are widely used as raw materials for clothing, shoes, furniture, car seats, sundry goods, and the like.

[0003] In recent years, concerns have been raised about the potential adverse effects of organic solvents on the human body and the environment, leading to a desire to establish a solvent-free manufacturing process for artificial leather. To address this demand, for example, ultrafine fiber-producing fibers for fiber entanglements have been studied, in which extractive components are removed using aqueous solutions to produce ultrafine fibers. Furthermore, aqueous dispersions of polymer elastomers have been studied as resins to be impregnated within the fiber entanglements. Among these, extensive research has focused on nonwoven fabrics made from long fibers, which have the advantage of not requiring a series of large-scale equipment such as a raw cotton supply device, fiber opening device, and carding machine, and are also stronger than short-fiber nonwovens.

[0004] For example, Patent Document 1 discloses a method for producing a leather sample sheet containing a long fiber web composed of ultrafine fiber-forming fibers that are a water-soluble thermoplastic polyvinyl alcohol-based resin and a thermosensitive gelling emulsion.

[0005] Patent Document 2 discloses an artificial leather substrate comprising ultrafine long fiber bundles, wherein the artificial leather substrate satisfies the following conditions: 8 to 70 ultrafine long fibers having a substantially circular cross-sectional shape are bundled together, and the cross-sectional area is 170 to 700 μm. 2 The flatness is below 4.0, and the cross section of the ultra-fine long fiber bundle is 1500~3000 / mm 2 In any cross section parallel to the thickness direction of the nonwoven fabric structure, the gap size between the ultrafine long fiber bundles is 70 μm or less.

[0006] Patent Document 3 discloses a leather-like sheet comprising a fiber entanglement body composed of fibers having an average single fiber fineness of 0.001 to 10 dtex, and a polymeric elastomer contained therein. Patent Document 3 further discloses that the fiber entanglement body comprises at least one of ultrafine fiber bundles and hollow fibers; the polymeric elastomer is formed by curing a polyurethane resin composition comprising a water-soluble polyoxyalkylene compound, an organic acid ammonium salt or an inorganic acid ammonium salt, and a self-emulsifying aqueous polyurethane resin self-emulsified with anionic groups; and the average distance between the peripheral fibers of the ultrafine fiber bundles or the hollow fibers and the polymeric elastomer is 1 μm or greater.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-002288

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-308784

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2014-065979 Summary of the Invention

[0012] Technical problem solved by the invention

[0013] Among the environmentally responsive artificial leathers proposed in the past, although polyester ultrafine long fibers are relatively easy to obtain good quality, the actual situation is that polyamide ultrafine long fibers cannot necessarily ensure satisfactory quality.

[0014] For example, in Patent Documents 1 and 2, when leather samples or artificial leather substrates are produced using a water-soluble thermoplastic resin as a sea component and nylon 6, if the melting point of the water-soluble thermoplastic resin is not at least 30°C lower than that of nylon 6, the tension during spinning tends to be less likely to act on the nylon 6. Consequently, the crystal orientation of the resin as the sea component is low, and even increasing the spinning speed is difficult to eliminate this phenomenon. Therefore, for example, a stretching treatment is required after spinning to modify the crystal orientation and crystal structure. Furthermore, if such measures are not taken, the ultrafine nylon 6 fibers will significantly elongate when wetted with water, resulting in a problem in which the leather samples or artificial leather substrates described above lack morphological stability when wetted with water.

[0015] Furthermore, the leather sample described in Patent Document 3 can be expected to improve its appearance and feel by controlling the structure of the polymer elastomer. However, if a resin with a melting point not lower than 30°C or more than that of nylon 6 is selected as the sea component resin and no post-spinning stretching treatment is performed, this system also suffers from a lack of morphological stability when wetted with water.

[0016] Performing the above-mentioned stretching treatment after spinning increases the number of manufacturing steps, which is disadvantageous in terms of productivity. In addition, when using a sea component with a melting point sufficiently lower than that of nylon 6, the degree of freedom in resin selection is reduced. Therefore, even when using fibers made of polyamide resins such as nylon 6, an artificial leather base material with excellent shape stability when wetted with water is required.

[0017] An object of the present invention is to solve the above-mentioned problems and to provide an artificial leather substrate comprising polyamide fibers which is excellent in morphological stability when wetted with water.

[0018] Technical means to solve the problem

[0019] The present inventors have conducted extensive research and have discovered that by setting the average number of carbon atoms of the polyamide resin constituting the polyamide fiber to a predetermined value or above, or by using a predetermined hydrophobic component together with the polyamide resin, the equilibrium moisture regain of the artificial leather substrate can be controlled. This solves the above-mentioned technical problems and has led to the completion of the present invention. Specifically, the present invention includes the following inventions.

[0020] [1] An artificial leather substrate comprising polyamide fiber and a polymer elastomer, wherein:

[0021] The artificial leather substrate is dried at 100° C. for 10 minutes and then transferred to an atmosphere at a temperature of 22° C. and a relative humidity of 45%. The mass of the artificial leather substrate 40 seconds after the transfer is defined as A. The mass of the artificial leather substrate when no mass change occurs after further standing in the atmosphere is defined as B. When the ratio of the mass of the polymer elastic body to the total mass of the polyamide fiber and the polymer elastic body is defined as X mass%, the equilibrium moisture regain calculated by the following formula (1) is 1.80% or less.

[0022] Equilibrium regain (%) = {(BA) / [A×(100-X) / 100]}×100···Formula (1).

[0023] [2] The artificial leather substrate according to [1] above, wherein the polyamide fiber has an average diameter of 7.5 μm or less.

[0024] [3] The artificial leather substrate according to [1] or [2] above, wherein the average fineness of the polyamide fiber is 0.50 dtex or less.

[0025] [4] The artificial leather substrate according to any one of [1] to [3] above, wherein the polyamide fiber contains a polyamide resin and an olefin-maleic anhydride resin, and the content of the olefin-maleic anhydride resin in the polyamide fiber exceeds 0% by mass and is 30% by mass or less.

[0026] [5] The artificial leather substrate according to any one of [1] to [4] above, wherein the polyamide resin contained in the polyamide fiber is a polyamide resin having an average carbon number of 8 or more between amide bonds.

[0027] [6] The artificial leather substrate according to any one of [1] to [5] above, wherein the content of the polymeric elastomer is 5 to 45% by mass relative to the total mass of the polyamide fiber and the polymeric elastomer.

[0028] [7] A napped artificial leather obtained by subjecting the surface of the artificial leather substrate according to any one of [1] to [6] to napping treatment.

[0029] [8] A method for producing an artificial leather substrate, wherein the artificial leather substrate is the artificial leather substrate described in any one of [1] to [6], the method comprising:

[0030] A process for spinning ultrafine fibers using a water-soluble thermoplastic resin and a polyamide resin to which an olefin-maleic anhydride resin is added to produce a type fiber;

[0031] a step of preparing a fiber web formed of the ultrafine fiber-generating fibers;

[0032] a step of forming an entangled fiber sheet using the fiber web;

[0033] a step of impregnating the entangled fiber sheet with a polymer elastic body; and

[0034] A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after the impregnation with the polymeric elastic body.

[0035] [9] A method for producing an artificial leather substrate, wherein the artificial leather substrate is the artificial leather substrate described in any one of [1] to [6], the method comprising:

[0036] A process for spinning ultrafine fibers using a water-soluble thermoplastic resin and a polyamide resin having an average carbon number of 8 or more between amide bonds to produce a type fiber;

[0037] a step of preparing a fiber web formed of the ultrafine fiber-generating fibers;

[0038] a step of forming an entangled fiber sheet using the fiber web;

[0039] a step of impregnating the entangled fiber sheet with a polymer elastic body; and

[0040] A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after the impregnation with the polymeric elastic body.

[0041] Effects of the Invention

[0042] According to the present invention, an artificial leather substrate comprising polyamide fibers having excellent morphological stability when wetted with water can be obtained. DETAILED DESCRIPTION

[0043] Hereinafter, an artificial leather substrate according to an embodiment of the present invention and methods for producing artificial leather substrates according to the first and second embodiments of the present invention (hereinafter sometimes referred to as "artificial leather substrate according to the present embodiment" or "method for producing artificial leather substrate according to the present embodiment") will be described.

[0044] [Artificial leather base material]

[0045] An artificial leather substrate comprising polyamide fibers and a polymeric elastomer is dried at 100°C for 10 minutes and then transferred to an atmosphere at a temperature of 22°C and a relative humidity of 45%. The mass of the artificial leather substrate 40 seconds after the transfer is defined as A. The artificial leather substrate is further allowed to stand in the atmosphere until no mass change occurs, and the equilibrium moisture regain calculated by the following formula (1) is 1.80% or less when the ratio of the mass of the polymeric elastomer to the total mass of the polyamide fibers and the polymeric elastomer is defined as X mass%. It should be noted that the mass B can be measured, for example, after 20 minutes or more.

[0046] Equilibrium regain (%) = {(BA) / [A×(100-X) / 100]}×100···Formula (1)

[0047] The artificial leather substrate having the above-mentioned configuration can be made into an artificial leather substrate having excellent morphological stability when wetted with water.

[0048] The present inventors conducted various studies and found that by using a polyamide resin having an average number of carbon atoms of 8 or more between amide bonds as the polyamide resin contained in the polyamide fiber, or by using a specific hydrophobic component when obtaining the polyamide fiber, the equilibrium moisture regain can be reduced to a given value or less while maintaining the surface feel.

[0049] In this specification, the "equilibrium moisture regain" is a value calculated by the following formula (1) when the artificial leather substrate is dried at 100°C for 10 minutes, then transferred to a gas atmosphere at a temperature of 22°C and a relative humidity of 45%, the mass of the artificial leather substrate 40 seconds after the transfer is defined as A, the mass of the artificial leather substrate when no mass change occurs after further standing in the above gas atmosphere is defined as B, and the ratio of the mass of the polymer elastic body to the total mass of the polyamide fiber and the above polymer elastic body is defined as X mass %.

[0050] Equilibrium regain (%) = {(BA) / [A×(100-X) / 100]}×100···Formula (1)

[0051] More specifically, the equilibrium moisture regain is measured according to the procedure described in Examples.

[0052] The equilibrium moisture regain is a physical property that indicates the maximum amount of water that an artificial leather substrate can absorb in a standard artificial leather substrate usage environment. A larger equilibrium moisture regain value indicates that the artificial leather substrate more readily absorbs water, while a smaller value indicates that it less readily absorbs water. It should be noted that the equilibrium moisture regain does not indicate the degree of swelling of the artificial leather substrate upon absorbing water, and therefore does not necessarily change in the same manner as the area swelling rate of the water-absorbing surface, described later.

[0053] From the perspective of improving morphological stability when wetted with water, the equilibrium moisture regain is preferably 1.80% or less, more preferably 1.78% or less, even more preferably 1.75% or less, even more preferably 1.73% or less, and particularly preferably 1.70% or less. The lower limit of the equilibrium moisture regain is not particularly limited; for example, it may be 0.60% or 0.70% from the perspective of flexibility and ease of manufacture. In other words, the equilibrium moisture regain of the artificial leather substrate is preferably 0.60 to 1.80%.

[0054] <Polyamide fiber>

[0055] The polyamide fibers may be polyamide short fibers, or may be polyamide long fibers from the viewpoint of excellent physical properties.

[0056] As used herein, "long fibers" refer to continuous fibers, not short fibers that are intentionally cut after spinning. More specifically, for example, these refer to filaments or continuous fibers that are not intentionally cut into short fibers with a fiber length of approximately 3 to 80 mm. Furthermore, as used herein, "short fibers" refer to fibers that are intentionally cut after spinning, for example, fibers with a fiber length of approximately 3 to 80 mm.

[0057] The fiber length of the island-in-the-sea composite fibers, described below, prior to microfiberization, is preferably 100 mm or longer, more preferably 200 mm or longer. The long fibers can be continuous fibers, such as those produced by a spunbond process and continuously spun to a length of several meters, hundreds of meters, or even kilometers, as long as they are technically feasible and are not inevitably cut during the manufacturing process. It should be noted that needle punching during entangling or surface polishing may inevitably cause the long fibers to partially cut during the manufacturing process, resulting in short fibers.

[0058] The polyamide fibers are preferably used in the form of a nonwoven fabric formed from these polyamide fibers. This nonwoven fabric can be produced by shrinking a fiber web entangled sheet formed from a laminate of fiber webs in hot water or a moist, hot air atmosphere, as needed, then tentering the sheet in a direction perpendicular to the conveyance direction as needed, and drying the sheet by moving it in the conveyance direction. The following describes the details of the nonwoven fabric formed from polyamide fibers, along with its production method.

[0059] Nonwoven fabrics comprising entangled microfibers are formed from bundles of microfibers, each composed of multiple microfibers. Such nonwoven fabrics can be obtained by, for example, entangling and then microfiberizing microfibers, such as island-in-the-sea (matrix-domain) composite fibers. The following details an example using island-in-the-sea composite fibers.

[0060] Methods for producing nonwoven fabrics of entangled ultrafine fibers include melt-spinning island-in-the-sea composite fibers to produce a fiber web, subjecting the fiber web to an entanglement treatment, and then selectively removing the sea component from the island-in-the-sea composite fibers to form the ultrafine fibers. Furthermore, in any of the steps from removing the sea component of the island-in-the-sea composite fibers to forming the ultrafine fibers, the island-in-the-sea composite fibers may be densified by undergoing a fiber shrinkage treatment such as heat shrinkage using steam, hot water, or dry heat.

[0061] The ultrafine fiber-generating fibers are, for example, fibers that are formed into fibers with a small fineness by melt spinning and then subjected to chemical or physical post-treatment. Specific examples of the ultrafine fiber-generating fibers include island-in-the-sea composite fibers and splittable composite fibers.

[0062] In the case of island-in-the-sea composite fibers, the fiber cross-section has island components dispersed within a sea component, which serves as the matrix. The sea component is removed to produce bundles of ultrafine fibers. Separable and splittable composite fibers, on the other hand, have multiple resins alternately arranged around the periphery to form a petal or overlapping shape. These different resins are then physically separated and split, producing bundles of ultrafine fibers.

[0063] The ultrafine fiber-forming fibers may be subjected to a stretching treatment as needed after spinning. The stretching treatment may be performed, for example, while heating.

[0064] By including a polyamide resin in the ultrafine fibers, a soft surface feel and an excellent hand feel can be obtained.

[0065] The polyamide resin is not particularly limited as long as it has an amide bond, and examples thereof include polyamide 6, polyamide 6,6, polyamide 6,10, polyamide 10,10, polyamide 11, and polyamide 12.

[0066] The polyamide resin contained in the polyamide fiber is preferably one having an average carbon number of 8 or more between amide bonds. Polyamide resins having an average carbon number of 8 or more between amide bonds tend to have reduced water absorption due to their relatively long methylene chains, and this tendency becomes more pronounced as the methylene chains become longer. Therefore, by using a polyamide resin having an average carbon number of 8 or more between amide bonds, the water absorption of the artificial leather substrate can be suppressed to a certain extent, even when a hydrophobic component is low or absent. As a result, the equilibrium moisture regain of the artificial leather substrate can be easily adjusted to the above-mentioned numerical range.

[0067] As the polyamide resin included in the polyamide fiber, a polyamide resin having an average carbon number of 7 or less between amide bonds, which is relatively readily available and has a proven track record of use in a wide range of applications, can also be used. Specific examples of polyamide resins having an average carbon number of 7 or less between amide bonds include polyamide 6 and polyamide 6,6. However, since polyamide resins having an average carbon number of 7 or less between amide bonds generally tend to have increased water absorption, when using a polyamide resin having an average carbon number of 7 or less between amide bonds, it is preferably used in combination with a hydrophobic component, as described below.

[0068] It should be noted that the number of carbon atoms between amide bonds varies depending on the polyamide resin, and sometimes two types of carbon atoms are repeated alternately. Therefore, in this specification, when two types of carbon atoms are repeated alternately, the average carbon number is the arithmetic mean of the carbon atoms of the two carbon atoms between the three amide bonds arranged in sequence. Based on this, for example, the average carbon number of polyamide 4 is 4, the average carbon number of polyamide 6 is 6, the average carbon number of polyamide 6,6 is 6, the average carbon number of polyamide 6,10 is 8, the average carbon number of polyamide 10,10 is 10, the average carbon number of polyamide 11 is 11, and the average carbon number of polyamide 12 is 12.

[0069] The polyamide resins may be used alone or in combination. When used alone, the ease of manufacture is improved, and desired physical properties are easily exhibited. When used in combination of two or more types, the physical properties of the polyamide fiber can be easily controlled, and various physical properties can be easily imparted to the artificial leather substrate.

[0070] When two or more polyamide resins are used, for example, a polyamide resin having an average number of carbon atoms between amide bonds of 7 or less and a polyamide resin having an average number of carbon atoms between amide bonds of 8 or more may be used in combination. In this case, from the viewpoint of ease of production, the ratio of the mass of the polyamide resin having an average number of carbon atoms between amide bonds of 7 or less to the mass of the polyamide resin having an average number of carbon atoms between amide bonds of 8 or more is preferably 99 / 1 to 50 / 50, more preferably 90 / 10 to 60 / 40, and even more preferably 80 / 20 to 70 / 30.

[0071] It is preferred to add a hydrophobic component to the polyamide resin from the viewpoint of easily adjusting the equilibrium moisture regain of the artificial leather substrate to the above range and from the viewpoint of easily suppressing the water absorption of the polyamide resin.

[0072] Examples of the hydrophobic component include olefin resins, fluororesins, silicone resins, etc. From the perspective of environmental protection and chemical resistance, olefin resins are preferably used, and more preferably, the terminals of the olefin resins are modified with maleic anhydride.

[0073] In other words, the polyamide fiber preferably contains a polyamide resin and an olefin-maleic anhydride resin obtained by modifying the terminal of an olefin resin with maleic anhydride.

[0074] Maleic anhydride reacts with the terminal amino groups and amide bond sites of polyamide resins to form bonds. Therefore, the use of maleic anhydride-modified olefin resins can improve the compatibility of olefin resins with polyamide resins. In addition, the use of maleic anhydride-modified olefin resins can easily ensure spinning stability during melt spinning.

[0075] From the viewpoint of easily suppressing the water absorption of the polyamide resin to a certain extent, the content of the hydrophobic component in the polyamide fiber is preferably greater than 0% by mass and 30% by mass or less, more preferably 1.0 to 25% by mass, further preferably 1.5 to 20% by mass, and even more preferably 2.0 to 20% by mass.

[0076] From the viewpoint of easily reducing the equilibrium moisture regain of the artificial leather substrate or easily obtaining morphological stability when wetted with water, the content of the olefin-maleic anhydride resin in the polyamide fiber is preferably greater than 0% by mass and 30% by mass or less, more preferably 1.0 to 25% by mass, further preferably 1.5 to 20% by mass, and even more preferably 2.0 to 20% by mass.

[0077] From the viewpoint of easily adjusting the morphological stability when wetted with water, the amount of modification of the olefin-maleic anhydride resin with maleic anhydride is preferably 1 to 15 mol %, more preferably 1.5 to 10 mol %, and even more preferably 2 to 7.5 mol %.

[0078] The modification amount of the olefin-maleic anhydride resin with maleic anhydride can be measured by infrared spectroscopy, and specifically by the method described in Examples.

[0079] From the viewpoint of improving kneading properties when melt-mixed with the polyamide resin, the melting point of the olefin-maleic anhydride resin is preferably 80 to 120° C., a temperature at which the polyamide resin can melt before melting.

[0080] From the viewpoint of facilitating adjustment of the morphological stability when wetted with water, the olefin-maleic anhydride resin may be modified with a third component different from maleic anhydride.

[0081] Examples of the third component for modifying the olefin-maleic anhydride resin include methyl acrylate, butyl acrylate, and ethyl acrylate.

[0082] When the melting point of the olefin-maleic anhydride resin is within the above range, the olefin-maleic anhydride resin may or may not be modified with a third component different from maleic anhydride.

[0083] The polyamide resin constituting the above-mentioned polyamide fiber may contain other components as needed, such as colored pigments such as carbon black; white pigments such as zinc white, lead white, zinc lithopone, titanium dioxide, precipitated barium sulfate and barite powder; dyes; fillers; mildew inhibitors; antioxidants; light stabilizers such as ultraviolet absorbers and light stabilizers; additives such as flame retardants; mildew inhibitors; anti-hydrolysis agents; lubricants; microparticles; and friction resistance regulators.

[0084] Hereinafter, a method of using the island-in-the-sea composite fiber as the ultrafine fiber-producing fiber will be described in more detail.

[0085] As described above, the ultrafine fiber-generating fibers may be short fibers or long fibers.

[0086] On the other hand, in order to cope with environmental concerns, the thermoplastic resin used to form the sea component of the island-in-the-sea composite fiber needs to be removable using only water without using a solvent.

[0087] Specific examples of thermoplastic resins for the sea component include polyvinyl alcohol resins, water-soluble polyester resins, alkali-degradable modified polyester resins, polyacrylamide resins, and carboxymethylcellulose resins. Among these, polyvinyl alcohol resins are preferred, and modified polyvinyl alcohol is more preferred, due to their biodegradability, reduced environmental impact from post-extraction handling, melt spinnability, water solubility, and fiber properties.

[0088] As the type of comonomer used in the modified polyvinyl alcohol, from the viewpoint of copolymerizability, melt spinnability and water solubility of the fiber, preferably α-olefins having less than 4 carbon atoms such as ethylene, propylene, 1-butene, isobutylene; and vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether.

[0089] The copolymerization unit content in the polyvinyl alcohol is preferably 1 to 20 mol %, more preferably 4 to 15 mol %, and even more preferably 6 to 13 mol %.

[0090] Furthermore, when the copolymerized units are ethylene, the fiber properties are improved, so ethylene-modified polyvinyl alcohol is particularly preferred. The ethylene unit content in the ethylene-modified polyvinyl alcohol is preferably 4 to 15 mol%, more preferably 6 to 13 mol%.

[0091] The mass ratio of the sea component to the island component of the island-in-sea composite fiber is not particularly limited, and is preferably in the range of 5:95 to 80:20. If the sea component polymer ratio in the island-in-sea composite fiber is 5% by mass or more, the spinning stability of the island-in-sea fiber is not easily reduced, and it is easy to ensure industrial productivity. In addition, when a high molecular weight elastomer is imparted, it is easy to form a gap of the necessary size between the ultrafine fiber bundle and the high molecular weight elastomer after removing the sea component, resulting in a sense of expansion, fullness, and a dense surface feel. On the other hand, if the sea component polymer ratio is 80% by mass or less, the shape and distribution state of the island component in the cross section of the island-in-sea fiber are stable, which makes it easy to prevent a decrease in quality stability.

[0092] The island-in-the-sea composite fibers can be converted into ultrafine fibers having a finer fineness than that of the island-in-the-sea composite fibers by subsequently performing an ultrafine fiberization treatment.

[0093] When the ultrafine fibers are formed from island-in-sea composite fibers, the number of ultrafine fibers constituting a single ultrafine fiber bundle is 8 or more from the perspectives of the flexibility of the ultrafine fiber bundle, i.e., the ease of entangling within the nonwoven fabric structure, and the flexibility of the resulting artificial leather substrate. From the perspectives of the flexibility of the ultrafine fiber bundle, the deformability of the cross-sectional shape, and the color development of the resulting artificial leather substrate, the number of ultrafine fibers is 70 or less. Furthermore, the number of ultrafine fibers is preferably 10 to 60, and more preferably 12 to 45.

[0094] If the number of fine fibers is 8 or more, the flexibility of the ultrafine fiber bundle is ensured, and when the nonwoven fabric structure contains a polymeric elastomer, the constraint fiber ratio (i.e., the proportion of fibers arranged at the outermost periphery to the total number of fibers in the ultrafine fiber bundle) is prevented from increasing. The polymeric elastomer is less likely to impair the flexibility of the ultrafine fiber bundle, and even if the polymeric elastomer is included, the hand feel is less likely to become hard. Therefore, unevenness in the inclusion of the polymeric elastomer is less likely to manifest as noticeable unevenness in the hand feel of the artificial leather substrate, making it easier to verify its value as an industrial product. On the other hand, it is believed that if the number of ultrafine fibers is 70 or less, the increased contact area between the ultrafine fibers within the ultrafine fiber bundle can be avoided, thereby preventing a decrease in flexibility.

[0095] Next, a fiber web is produced using the ultrafine fiber-generating fibers described above.

[0096] When long fibers are used, a fiber web can be produced by collecting ultrafine fiber-generating fibers melt-spun by a so-called spunbond method on a web without cutting them to form a fiber web of continuous long fibers.

[0097] Specifically, a spinneret for composite spinning having a plurality of nozzle holes arranged in a given pattern is used, so that the molten strands of the island-in-sea composite fiber are continuously ejected from the spinning nozzle at a given ejection speed, and are substantially cooled and solidified by cooling air at any stage between directly below the nozzle hole and the suction device described later, and a suction device such as an air jet nozzle is used to apply the action of high-speed airflow so that the composite fiber is uniformly pulled and refined in such a manner that it has a target diameter or fineness.

[0098] The high-speed airflow is applied to achieve an average spinning speed equivalent to the mechanical take-off speed in conventional spinning, ranging from 1000 to 6000 m / min. Furthermore, depending on the texture of the resulting fiber web, the composite fibers are spread by a collision plate, airflow, or the like, while being sucked from the opposite side of the web onto a collection surface of a conveyor-like moving net, etc., and then collected and accumulated to form a fiber web. This spunbonding method can produce a fiber web of long fibers. Furthermore, the fiber web can be subjected to heat pressing to impart morphological stability, and the web can be melt-bonded in conjunction with this process.

[0099] If the weight per unit area or thickness of the resulting fiber web is insufficient, adjustments are made by folding (feeding a single fiber web from a direction perpendicular to the process direction and folding it approximately in the width direction, or folding a fiber web fed from a direction parallel to the process direction in its length direction) or stacking (overlaying multiple fiber webs) to achieve the desired weight per unit area and thickness. If the morphological stability and fiber density of the nonwoven fabric structure formed of island-in-sea fibers are insufficient, or if the orientation of the nonwoven fabric structure toward the island-in-sea fibers in the thickness direction is to be adjusted, mechanical entanglement treatment is performed using known methods such as needle punching. This allows the fibers constituting the fiber web, particularly the fibers between adjacent layers of the folded and stacked layered fiber web, to be three-dimensionally entangled.

[0100] When the bonding treatment is performed by acupuncture, various treatment conditions are appropriately selected, such as the type of needle (needle shape, number, hook shape, depth, number of hooks, position, etc.), the number of needle punches (the density of needle punching treatment per unit area obtained by multiplying the density of needles embedded in the needle plate by the number of strokes of the plate acting on the fiber web per unit area), and the depth of needle penetration (the depth at which the needle acts on the fiber web).

[0101] As the entanglement treatment, there are methods such as needle punching or high-pressure water jet treatment under conditions where at least one hook is simultaneously or alternately penetrated from both sides of the net having a desired weight per unit area and thickness. In addition, the needle punch density of the needle punching treatment is preferably 1500 to 5500 needle punches / cm from the viewpoint of easily obtaining high wear resistance. 2 , more preferably 2000~5000 needle punches / cm 2 If the needle punching density is within the above range, insufficient cohesion can be suppressed, preventing the surface of the artificial leather substrate from becoming rough due to the spreading of fibers, and can also suppress the cutting of fibers and prevent the reduction of cohesion.

[0102] In addition, the fiber web may be provided with an oil or antistatic agent at any stage from the spinning process to the entanglement treatment of the island-in-the-sea composite fiber. Furthermore, if necessary, the entanglement of the fiber web may be made dense in advance by performing a shrinkage treatment by immersing the fiber web in warm water at about 70 to 150°C. The weight per unit area of ​​the entangled web obtained by entanglement of the fiber webs is preferably 100 to 2000 g / m 2 The fiber density and degree of cohesion can be further increased by heat shrinking the entangled web as needed. Furthermore, in order to further densify the entangled fiber sheet densified by the heat shrinkage treatment, fix the shape of the entangled fiber sheet, or smooth the surface, a heat press treatment can be performed as needed to further increase the fiber density.

[0103] To easily produce napped artificial leather with an elegant appearance and a good hand, the average diameter of the polyamide fibers is preferably 7.5 μm or less, more preferably 6.0 μm or less, even more preferably 5.5 μm or less, and even more preferably 4.5 μm or less. The lower limit is not particularly limited, but from the perspectives of ease of manufacture, durability, and color development, it is, for example, 1.0 μm or 1.5 μm. In other words, the average diameter of the polyamide fibers is preferably 1.0 μm or more and 7.5 μm or less, and more preferably 1.0 to 6.0 μm.

[0104] From the perspective of easily obtaining a napped artificial leather with an elegant appearance and a good hand, the average fineness of the polyamide fiber is preferably 0.50 dtex or less, more preferably 0.40 dtex or less, even more preferably 0.30 dtex or less, and even more preferably 0.20 dtex or less. The lower limit is not particularly limited, but from the perspectives of ease of manufacture, durability, and color rendering, it is, for example, 0.01 dtex or 0.02 dtex or greater. In other words, the average fineness of the polyamide fiber is preferably 0.01 dtex or greater and 0.50 dtex or less, and more preferably 0.01 to 0.40 dtex.

[0105] The “average diameter” and “average fineness” are values ​​calculated based on the cross-sectional areas of a plurality of randomly selected fibers in an enlarged photograph of a cross section of a polyamide fiber, and can be specifically measured according to the procedures described in the Examples.

[0106] <Polymer Elastomer>

[0107] The above-mentioned polymer elastomer can be any polymer elastomer conventionally used for artificial leather substrates. Specific examples include polyurethane elastomers, acrylonitrile elastomers, olefin elastomers, polyester elastomers, and acrylic elastomers, with polyurethane elastomers and acrylic elastomers being preferred.

[0108] Examples of polyurethane elastomers include various polyurethane elastomers obtained by combining at least one polymer polyol having an average molecular weight of 500 to 3000 selected from polyester diols, polyether diols, polyether ester diols, polycarbonate diols, polycarbonate ether diols, and polycarbonate ester diols as main components with at least one polyisocyanate selected from aromatic, alicyclic, and aliphatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate, and further combining at least one low molecular weight compound having two or more active hydrogen atoms such as ethylene glycol and ethylenediamine in a predetermined molar ratio, and subjecting these to a polymerization reaction in one or more steps by melt polymerization, bulk polymerization, solution polymerization, or the like.

[0109] The content of the polymer polyol component in the polyurethane elastomer is preferably 15 to 90% by mass.

[0110] Examples of acrylic elastomers include various acrylic elastomers obtained by polymerizing a soft component, a hard component, and a monofunctional or polyfunctional ethylenically unsaturated monomer unit capable of forming a crosslinked structure, or a compound capable of reacting with an ethylenically unsaturated monomer unit introduced into a polymer chain to form a crosslinked structure (for example, an ethylenically unsaturated monomer composed of at least one crosslinking-forming component selected from ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate). The hard component is a monomer having a homopolymer glass transition temperature in the range of -90 to -5°C, preferably a non-crosslinking monomer, for example, at least one selected from methyl acrylate, n-butyl acrylate, isobutyl acrylate, isopropyl acrylate, n-hexyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, and the hard component is a monomer having a homopolymer glass transition temperature in the range of 50 to 250°C, preferably a non-crosslinking monomer, for example, at least one selected from methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate and (meth)acrylic acid.

[0111] Artificial leather substrates using polyurethane elastomers as the main polymeric elastomer are preferred because they offer an excellent balance between feel and mechanical properties, as well as excellent balance in durability. Meanwhile, artificial leather substrates using acrylic elastomers have lower adhesion to ultrafine fiber bundles than polyurethane elastomers, resulting in insufficient nap-fixing effect during nap formation. Therefore, acrylic elastomers are not suitable for napped artificial leather. However, acrylic elastomers suppress the hardening of the feel relative to the content, making them particularly preferred for grain-finished artificial leather.

[0112] As the polymer elastomer, different types may be mixed or contained in multiple batches. In addition, in addition to the above-mentioned polymer elastomers such as polyurethane elastomers, acrylonitrile elastomers, olefin elastomers, polyester elastomers, acrylic elastomers, etc. as the main body, polymer elastomers other than polymer elastomers such as synthetic rubber and polyester elastomer may be added as needed and contained as a polymer elastomer composition.

[0113] From the viewpoint of easily obtaining the feel of artificial leather, the content of the elastic polymer relative to the total mass of the polyamide fiber and the elastic polymer is preferably 5 to 45 mass %, more preferably 7 to 40 mass %, and even more preferably 8 to 30 mass %.

[0114] <Other ingredients>

[0115] The artificial leather substrate may or may not contain components other than the polyamide fiber and the polymeric elastomer. Examples of such other components include the same components as those contained in the polyamide resin and the various additives that can be added to the polymeric elastomer liquid described in step (4) below. The other components may be encapsulated in at least one of the polyamide fiber and the polymeric elastomer.

[0116] From the viewpoint of easily exhibiting the effects of the other components and easily ensuring the shape stability of the artificial leather substrate when wetted with water, the content of the other components is preferably 0.5 to 10.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 1.5 to 3.0% by mass, relative to the mass of the artificial leather substrate.

[0117] The total content of the polyamide fiber and the polymeric elastomer in the artificial leather substrate is preferably 90.0 to 99.5% by mass, more preferably 95.0 to 99.0% by mass, and even more preferably 97.0 to 98.5% by mass based on the mass of the artificial leather substrate.

[0118] [Method for producing artificial leather base material]

[0119] The method for producing an artificial leather substrate according to the first embodiment of the present invention (hereinafter also referred to as "the first method for producing an artificial leather substrate") comprises the following step (1A) and steps (2) to (5).

[0120] Step (1A): A step of spinning ultrafine fiber-forming fibers using a water-soluble thermoplastic resin and a polyamide resin to which an olefin-maleic anhydride resin is added.

[0121] Step (2): a step of preparing a fiber web formed of the ultrafine fiber-generating fibers.

[0122] Step (3): a step of forming an entangled fiber sheet using the fiber web.

[0123] Step (4): a step of impregnating the entangled fiber sheet with a polymer elastic body.

[0124] Step (5): A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after impregnation with the elastic polymer.

[0125] The method for producing an artificial leather substrate according to the second embodiment of the present invention (hereinafter also referred to as "the method for producing a second artificial leather substrate") comprises the following step (1B) and steps (2) to (5).

[0126] Step (1B): a step of spinning ultrafine fiber-forming fibers using a water-soluble thermoplastic resin and a polyamide resin having an average carbon number of 8 or more between amide bonds.

[0127] Step (2): a step of preparing a fiber web formed of the ultrafine fiber-generating fibers.

[0128] Step (3): a step of forming an entangled fiber sheet using the fiber web.

[0129] Step (4): a step of impregnating the entangled fiber sheet with a polymer elastic body.

[0130] Step (5): A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after impregnation with the elastic polymer.

[0131] In step (1A) of the first method for producing an artificial leather base material, ultrafine fiber-forming fibers are spun using a water-soluble thermoplastic resin and a polyamide resin to which an olefin-maleic anhydride resin is added. Furthermore, in step (1B) of the second method for producing an artificial leather base material, ultrafine fiber-forming fibers are spun using a water-soluble thermoplastic resin and a polyamide resin having an average carbon number of 8 or more between amide bonds. Therefore, in step (5) of the first and second methods for producing artificial leather base materials, the water-soluble thermoplastic resin can be removed from the ultrafine fiber-forming fibers using an aqueous solution.

[0132] Furthermore, by preparing an entangled fiber sheet in steps (1A) to (3) or steps (1B) to (3), and impregnating the entangled fiber sheet with a polymeric elastomer in step (4), the polyamide fiber can be made to contain the polymeric elastomer. Therefore, at least for removing the sea component, no organic solvent is required, making it possible to achieve an environmentally friendly production method. Furthermore, when an aqueous polymeric elastomer that can form an emulsion with an aqueous solvent such as water as a dispersion medium is used as the polymeric elastomer, it can achieve an even more environmentally friendly production method.

[0133] Furthermore, in step (1A), an olefin-maleic anhydride resin, which is a hydrophobic component and has excellent compatibility with the polyamide resin, is added to the polyamide resin. This makes it easier to ensure spinning stability, and the polyamide resin constituting the polyamide fiber tends to have a large amount of γ-type crystal structure, thereby making it easier to achieve an equilibrium moisture regain of 1.80% or less as defined by the above-mentioned formula (1). As a result, an artificial leather substrate having excellent morphological stability when wetted with water can be obtained. Furthermore, in step (1B), a polyamide resin having a relatively long methylene chain and an average number of carbon atoms between amide bonds of 8 or more is used, thereby making it easier to suppress water absorption, and thus an artificial leather substrate having excellent morphological stability when wetted with water can be obtained.

[0134] Hereinafter, each step included in the method for producing the artificial leather substrate will be described.

[0135] <Step (1A)>

[0136] As described above, step (1A) is a step of spinning ultrafine fiber-forming fibers using a water-soluble thermoplastic resin and a polyamide resin to which an olefin-maleic anhydride resin is added.

[0137] The specific steps of the above step (1A) are as described in the above-mentioned "polyamide fiber" column.

[0138] <Step (1B)>

[0139] As described above, step (1B) is a step of spinning ultrafine fiber-forming fibers using a water-soluble thermoplastic resin and a polyamide resin having an average carbon number of 8 or more between amide bonds.

[0140] The specific steps of the above step (1B) are as described in the above "polyamide fiber" column.

[0141] <Process (2)>

[0142] As described above, step (2) is a step of preparing a fiber web formed of ultrafine fiber-generating fibers.

[0143] The other specific steps of the above process (2) are as described in the above "polyamide fiber" column.

[0144] <Process (3)>

[0145] As described above, step (3) is a step of forming an entangled fiber sheet using the fiber web.

[0146] The other specific steps of the above process (3) are as described in the above "polyamide fiber" column.

[0147] <Step (4)>

[0148] As described above, step (4) is a step of imparting a polymeric elastic body to the entangled fiber sheet.

[0149] In the production of napped artificial leather, a polymer elastomer is applied to an entangled fiber sheet formed by entangled sea-island composite fibers before the sea component is removed, for example, by impregnation, in order to impart morphological stability and a sense of fullness. Thus, by impregnating the entangled fiber sheet formed by entangled sea-island composite fibers before the sea component is removed with a polymer elastomer, gaps formed by the removal of the sea component can be formed between the ultrafine fibers that form the fiber bundles after the sea component is removed. As a result, the ultrafine fibers are not constrained by the polymer elastomer, thereby obtaining a napped artificial leather with a soft hand. It should be noted that when a nonwoven fabric containing ultrafine fibers formed into fiber bundles after the sea component is removed from the sea-island composite fibers is impregnated with a polymer elastomer, the polymer elastomer penetrates the gaps in the fiber bundles, thereby constraining the ultrafine fibers forming the fiber bundles by the polymer elastomer, resulting in a napped artificial leather with a firm hand.

[0150] At least one of the steps before and after the removal of the sea component, the entangled fiber sheet is impregnated with a polymeric elastomer liquid, such as a polymeric elastomer dispersion, and then the polymeric elastomer is coagulated by a conventionally known dry or wet method to thereby fix the polymeric elastomer within the entangled fiber sheet. The dry method herein refers to any method that fixes the polymeric elastomer within the fiber sheet structure by removing the solvent or dispersant by drying, etc. Furthermore, the wet method herein refers to any method that temporarily or completely fixes the polymeric elastomer within the nonwoven fabric structure before removing the dispersant by treating the entangled fiber sheet structure impregnated with the polymeric elastomer liquid with a non-solvent or coagulant for the polymeric elastomer, or by heating the impregnated nonwoven fabric structure with an aqueous polymeric elastomer liquid containing a heat-sensitive gelling agent, etc.

[0151] When applying the polymeric elastomer to the entangled fiber sheet, a non-aqueous polymeric elastomer liquid prepared by dissolving or dispersing the polymeric elastomer in a solvent may be used, or an aqueous polymeric elastomer liquid prepared by dispersing the polymeric elastomer and, if necessary, a dispersant in an aqueous medium may be used. The former facilitates obtaining a uniform polymeric elastomer liquid, while the latter facilitates reducing the amount of organic solvent used.

[0152] In order to completely fix the solidified elastic polymer, it is preferable to perform a curing treatment such as a heat treatment after removing the solvent or the dispersant.

[0153] The concentration of the polymeric elastomer liquid, that is, the content of the polymeric elastomer in the polymeric elastomer liquid, is preferably 0.1 to 60% by mass.

[0154] Various additives conventionally contained in polymeric elastomer liquids for artificial leather base materials, such as colorants such as dyes and pigments, coagulation regulators, antioxidants, ultraviolet absorbers, fluorescent agents, mildew inhibitors, penetrants, defoamers, lubricants, water repellents, oil repellents, thickeners, extenders, curing accelerators, foaming agents, and water-soluble polymer compounds such as polyvinyl alcohol and carboxymethyl cellulose, may be appropriately added to the polymeric elastomer liquid, within a range that does not impair the properties of the final artificial leather base material.

[0155] The details of the polymeric elastic body used in the above step (4) are as described in the above-mentioned "polymeric elastic body" section.

[0156] <Step (5)>

[0157] Step (5) is a step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time from before to after the impregnation with the polymeric elastic body.

[0158] As a method for removing the sea component polymer from the island-in-sea type fibers constituting the entangled fiber sheet structure before or after containing the polymer elastomer, a method can be adopted in which the non-woven fabric structure is treated with a liquid that is a non-solvent or non-degradant for the island component polymer. In the case of removal after containing the polymer elastomer, the liquid is a non-solvent or non-degradant for the polymer elastomer and a solvent or degradant for the sea component polymer.

[0159] For example, when polyvinyl alcohol, a water-soluble thermoplastic resin as described above, is used as the sea component polymer, it can be removed in warm water at a temperature at which the polymer is soluble. Alternatively, when a modified polyester readily alkali-degradable by copolymerization of a compound containing an alkali metal sulfonic acid salt as described above is used as the sea component polymer, it can be removed using an aqueous solution of an alkaline decomposing agent such as an aqueous sodium hydroxide solution at an appropriate temperature. By such a sea component polymer removal treatment, the island-in-the-sea fibers are converted into ultrafine fiber bundles composed of the island component polymer, thereby obtaining a fiber having a density of preferably 300 to 1800 g / m². 2 A substrate for artificial leather having a weight per unit area of ​​.

[0160] <Step (6)>

[0161] The above-mentioned first and second methods for producing artificial leather substrates preferably further comprise a step of dyeing the artificial leather substrate (step (6)). Step (6) can be carried out at any stage after the island-in-sea fibers are converted into ultrafine fiber bundles.

[0162] In step (6), any dyeing method using a known dyeing machine commonly used for dyeing artificial leather in the past, such as a padder, a jigger, a circular dyeing machine, a rope dyeing machine, etc., can be adopted, using a dye mainly composed of disperse dyes, reactive dyes, acid dyes, metal complex dyes, sulfur dyes, sulfur-reducing dyes, etc., which is appropriately selected according to the type of fiber.

[0163] In addition to dyeing, it is also preferred to perform finishing treatments such as mechanical kneading treatment in a dry state, relaxation treatment in a wet state using a dyeing machine, washing machine, etc., softener treatment, flame retardant, antibacterial agent, deodorant, waterproof and oil-proof agent and other functional imparting treatments, silicone resin, silk protein-containing treatment agent, grip-imparting resin and other touch modifier imparting treatments, coloring agent, enamel-style coating resin and other resins other than the above-mentioned resins to impart design.

[0164] [Raised nap artificial leather]

[0165] The napped artificial leather according to an embodiment of the present invention is obtained by napping the surface of any of the above-mentioned artificial leather substrates. Such a napped artificial leather has excellent morphological stability when wetted with water and can combine a soft surface feel with excellent napped appearance and mechanical properties.

[0166] The above-mentioned napped artificial leather is manufactured in the same manner as conventional artificial leather. The artificial leather substrate obtained by the above-mentioned method for manufacturing an artificial leather substrate is sliced ​​into multiple slices along the thickness direction as needed. The back surface is then ground to adjust the thickness. The back surface and the front surface are then treated with a liquid containing a polymer elastomer and a solvent for the ultrafine fiber bundles. Subsequently, at least the front surface is raised by a method such as sanding to form a napped surface composed primarily of ultrafine fibers. This produces a napped artificial leather having a suede-like or nubuck-like texture.

[0167] The formation of the fiber nap surface can be achieved by any of the known methods such as polishing with sandpaper, needle cloth, etc., brushing, etc. In addition, before or after such a napping treatment, a solvent that can dissolve or swell the polymer elastomer or the ultrafine fiber bundle, for example, a treatment liquid containing dimethylformamide (DMF) when the polymer elastomer is a polyurethane elastomer, or a treatment liquid containing phenolic compounds such as resorcinol when the ultrafine fiber bundle is a polyamide resin, can be applied to the surface to be napped. In this way, the constraint state of the ultrafine fiber bundle based on the bonding of the polymer elastomer and the ultrafine fiber bundle, the nap length of the ultrafine fiber of the napped artificial leather, the surface friction durability, etc. can be fine-tuned.

[0168] Alternatively, the step (6) may be performed after the napping treatment to produce a dyed napped artificial leather.

[0169] Thus, the napped artificial leather of this embodiment can be obtained. As described above, when the average diameter of the polyamide fibers contained in the napped artificial leather is 7.5 μm or less, or the average fineness is 0.50 dtex or less, a beautiful napped appearance can be easily obtained. As a result, a napped artificial leather having a beautiful napped appearance, morphological stability when wetted with water, and a soft surface feel can be obtained.

[0170] Example

[0171] The present invention will be described in more detail below with reference to the following examples. However, it should be noted that the scope of the present invention is not limited by the contents of the examples.

[0172] First, the evaluation methods used in the examples and comparative examples described below will be summarized and described below.

[0173] <Average diameter>

[0174] The average diameter of the polyamide fiber is determined as follows. A scanning electron microscope (SEM) photograph of a cross section of a napped artificial leather is taken at 3000x magnification. Ten fiber cross sections are then randomly selected from the SEM photograph and their cross-sectional areas are measured. The arithmetic mean of these cross-sectional areas is calculated, and the value calculated using the following formula (2) is used as the average diameter of the polyamide fiber.

[0175] Average diameter = (average cross-sectional area / π) 1 / 2 ×2···Formula (2)

[0176] <Average fineness>

[0177] The average fineness of polyamide fibers is determined as follows. A scanning electron microscope (SEM) photograph of a cross section of a pile artificial leather is taken at 3000x magnification. Ten fiber cross sections are then randomly selected from the SEM photograph, and the cross-sectional area is measured. The arithmetic mean of these cross-sectional areas is then calculated. The average cross-sectional area is then converted to the average fineness using the density of the polyamide resin.

[0178] <Polymer Elastomer Content>

[0179] The mass C of the artificial leather substrate cut into a size having a mass of 1 g or more is measured.

[0180] After the polymer elastomer was dissolved in N,N-dimethylformamide (DMF), the artificial leather substrate was immersed in 300 mL of DMF at room temperature for 5 hours, then squeezed to remove the DMF. The squeezed DMF was then placed in water, and the process of immersing in DMF and squeezing was repeated again under the same conditions, while replacing the DMF, until the water became turbid. The polymer elastomer was removed from the artificial leather substrate. The remaining component after removing the polymer elastomer from the artificial leather substrate, namely the polyamide fiber, was dried to remove the DMF, and the mass D of the dried polyamide fiber was measured. The polymer elastomer content in the artificial leather substrate was then calculated based on the following formula (3).

[0181] Elastomer content (mass %) = (CD) / C × 100···Formula (3)

[0182] In the case where the polymeric elastomer is insoluble in DMF, the artificial leather substrate was immersed in 300 mL of hexafluoro-2-propanol (HFIP) at room temperature for 12 hours to dissolve the polyamide fiber. The remaining solid content was filtered, washed with HFIP, and then dried to remove HFIP. The mass E of the resulting solid was measured. Then, the content of the polymeric elastomer in the artificial leather substrate was calculated based on the following formula (4).

[0183] Elastomer content (mass %) = E / C × 100 ···Formula (4)

[0184] <Apparent density>

[0185] The obtained artificial leather substrate was cut into pieces of 16 cm × 16 cm in size (256 cm 2 The mass (g) of the artificial leather after cutting was measured, and the weight per unit area (g / m2) of the artificial leather substrate after cutting was calculated by the following formula (5): 2 ).

[0186] Weight per unit area = mass / 256×10000···Formula (5)

[0187] The thickness (mm) of the cut artificial leather substrate was measured using a thickness gauge (diameter of the gauge: 10 mm) at a constant pressure of 23.5 kPa for 5 seconds in accordance with JIS L1096 (2010) (Method A). The apparent density (g / cm2) of the artificial leather substrate was calculated using the following formula (6) in accordance with JIS K6505 (1995) 5.2.2: 3 ).

[0188] Apparent density = weight per unit area / thickness / 1000 ···Formula (6)

[0189] Melting point

[0190] The melting point of the resin was determined using a thermal analyzer "DSC-60A" manufactured by Shimadzu Corporation. The temperature was raised to 400° C. at a heating rate of 10° C. / min in a nitrogen atmosphere, and the exothermic peak temperature was defined as the melting point.

[0191] <Tear Strength>

[0192] Test pieces measuring 10 cm long by 4 cm wide were cut from the resulting artificial leather substrate. A 5 cm slit was then cut into the center of the short side of the test piece, parallel to the long side. Each piece was then clamped to the chuck of a tensile testing machine and the SS curve was measured at a tensile speed of 10 cm / min. Three test pieces were measured in the longitudinal direction and in the transverse direction perpendicular to the longitudinal direction of the artificial leather substrate, and the average value was calculated as the tear strength.

[0193] <Water Absorption Area Swelling Ratio>

[0194] A test piece measuring 5 cm in length and 5 cm in width was cut from the obtained artificial leather substrate. The test piece was then immersed in water and pressed so that the water pickup rate (liquid squeeze rate) was 50%. The longitudinal dimension G (cm) and the transverse dimension H (cm) were measured, and the water absorption area swelling ratio was calculated using the following formula (7).

[0195] Water absorption area swelling rate (%) = [G × H - 5 × 5] / [5 × 5] × 100 ··· Formula (7)

[0196] <Balanced moisture regain>

[0197] A test piece measuring 5 cm in length and 5 cm in width was cut from the artificial leather substrate. The test piece was dried in a dryer at 100°C for 10 minutes, removed from the dryer, and transferred to an atmosphere at a temperature of 22°C and a relative humidity of 45%. The mass of the test piece 40 seconds after transfer was defined as A. The mass of the test piece when it remained in an atmosphere at a temperature of 22°C and a relative humidity of 45% for a predetermined period without undergoing a mass change was defined as B. The ratio of the mass of the polymeric elastomer, determined by the method for determining the content of the polymeric elastomer, to the total mass of the polyamide fiber and the polymeric elastomer was defined as X mass %, and the equilibrium moisture regain was calculated using the following formula.

[0198] Equilibrium regain (%) = {(BA) / [(A×(100-X) / 100)]}×100···Formula (1)

[0199] <Surface feel>

[0200] The touch of the surface of the obtained napped artificial leather was evaluated based on the following criteria.

[0201] A: The surface feels smooth and soft when you touch it.

[0202] B: The surface feels smooth when touched, but is less soft than "A".

[0203] <Modification Amount>

[0204] The measurement was performed by Fourier transform infrared spectroscopy (FTIR) based on the wave number 1780 cm-1 assigned to the carbonyl group. -1 The modified amount of the olefin-maleic anhydride resin was calculated based on the peak intensity of .

[0205] [Example 1]

[0206] A water-soluble thermoplastic resin, i.e., a modified polyvinyl alcohol-based resin, as the sea component, and polyamide 6, as the island component, were ejected from a melt composite spinning spinneret (number of islands: 25 islands / fiber) at 260°C in a sea component / island component ratio of 30 / 70 (mass ratio), and spun at a spinning speed of 3500 m / min to obtain a fiber web comprising sea-island type composite fibers having an average fineness of 2.71 dtex. The polyamide 6 was added with an olefin-maleic anhydride resin (Lotarder 5500, maleic anhydride modification amount 2.8 mol%, melting point 80°C, methyl acrylate modification amount 20 mol%) (manufactured by SK GeoCentric Co., Ltd.) in a manner to achieve 10% by mass of the total.

[0207] Next, the fiber webs were stacked to form a stacked web. Then, using a needle with 1 hook and 6 hooks, the fibers were cut at 3500 P / cm 2 The laminated web was needle punched with a needle punching density of 600 g / m2, thereby forming a unit area weight of 620 g / m2. 2 of cohesive fiber sheets.

[0208] The entangled fiber sheet was then steamed at 110°C and 23.5% RH. After drying in an oven at 90-110°C, it was hot-pressed at 120°C to obtain a sheet with a unit weight of 625 g / m2. 2 Specific gravity 0.50g / cm 3 , hot-pressed fiber sheet with a thickness of 1.25mm.

[0209] Next, 1.5 parts by mass of a carbodiimide crosslinking agent and 2.7 parts by mass of ammonium sulfate were added to an emulsion of a polycarbonate-based non-yellowing polyurethane emulsion as the polymer elastomer, relative to 100 parts by mass of the polymer elastomer. The emulsion, which had a solid content of 15% by mass of the polymer elastomer, was impregnated into the hot-pressed fiber sheet at a pickup rate of 52%. The solid content of the polymer elastomer was adjusted to 15% by mass relative to the total of the polyamide fibers and the polymer elastomer in the hot-pressed fiber sheet. The hot-pressed fiber sheet impregnated with the emulsion was then dried at 115°C and 25% RH, and further dried at 150°C to obtain a hot-pressed fiber sheet to which the polymer elastomer had been applied.

[0210] The hot-pressed fiber sheet, imbued with a high-molecular-weight elastomer, was then subjected to an immersion nip treatment, a high-pressure water jet treatment, and then immersed in 95°C hot water for 10 minutes. This dissolved and removed the water-soluble thermoplastic polyvinyl alcohol resin, the sea component of the island-in-the-sea composite fiber, to form ultrafine polyamide 6 fibers with an average diameter of 2.6 μm. The sheet was then dried to obtain an artificial leather substrate. The back surface of the artificial leather substrate was then ground with #320 paper, and the main surface was ground with #320 and #400 papers to form a napped surface.

[0211] Then, the artificial leather substrate with the fiber napped surface formed thereon was dyed at 90°C using a gold-containing dye to obtain a napped artificial leather having a fiber napped surface. The obtained napped artificial leather had a basis weight of 262 g / m 2 , the apparent density is 0.471g / cm 3 , thickness is 0.61mm, and the equilibrium moisture regain of the pile artificial leather is 1.73%.

[0212] The napped artificial leather of Example 1 can be produced by a method that does not use a solvent. Its water absorption area swelling ratio was 8.2%, significantly lower than the water absorption area swelling ratio of 18.8% for artificial leather composed solely of polyamide 6 described in Comparative Example 1 described below. Furthermore, mechanical properties were not impaired, and the surface felt smooth and soft, resulting in an A rating. These results are shown in Table 1 below.

[0213] [Example 2]

[0214] As shown in Table 1, in Example 1, except that (i) the island component was changed to polyamide 6,10 to which no olefin-maleic anhydride resin was added, and (ii) the emulsion of a polycarbonate-based non-yellowing polyurethane as the polymer elastomer was adjusted to a solid content of 15% by mass of the polymer elastomer, and then the emulsion was impregnated into the hot-pressed fiber sheet so that the emulsion was 10% by mass relative to the total of the polyamide fiber and the polymer elastomer, a napped artificial leather was obtained in the same manner. The results are shown in Table 1.

[0215] [Example 3]

[0216] As shown in Table 1, in Example 1, except that (i) the island component was changed to polyamide 10,10 to which no olefin-maleic anhydride resin was added, and (ii) the emulsion of a polycarbonate-based non-yellowing polyurethane as the polymer elastomer was adjusted to a solid content of 15% by mass of the polymer elastomer, and then the emulsion was impregnated into the hot-pressed fiber sheet so that the emulsion was 10% by mass relative to the total of the polyamide fiber and the polymer elastomer, a napped artificial leather was obtained in the same manner. The results are shown in Table 1.

[0217] [Example 4]

[0218] As shown in Table 1, in Example 1, (i) an olefin-maleic anhydride resin (Lotarder 4210, maleic anhydride modification level 3.6 mol%, melting point 105°C, butyl acrylate modification level 6.5 mol%) (manufactured by SK Geo Centric) was added to a mixture of polyamide 6 and polyamide 10,10 (mass ratio (polyamide 6 / polyamide 10,10) = 70 / 30) as the island component to provide 5% by mass of the total, and the spinning speed was set at 1400 m / min. Furthermore, (ii) a polycarbonate-based non-yellowing polyurethane emulsion, as the polymer elastomer, was adjusted to a solid content of 10% by mass of the polymer elastomer and then impregnated into the hot-pressed fiber sheet with this emulsion. A napped artificial leather was obtained in the same manner. The results are shown in Table 1.

[0219] [Example 5]

[0220] As shown in Table 1, in Example 1, a napped artificial leather was obtained in the same manner except that (i) an olefin-maleic anhydride resin (Lotarder 4210) (manufactured by SK Geo Centric) was added to the mixture of polyamide 6 and polyamide 10,10 (mass ratio (polyamide 6 / polyamide 10,10) = 80 / 20) as the island component so as to account for 5% by mass of the total, and the spinning speed was set to 1400 m / min. Furthermore, (ii) an emulsion of a polycarbonate-based non-yellowing polyurethane was adjusted to have a solid content of 10% by mass of the elastomer, and the emulsion was then impregnated into the hot-pressed fiber sheet. The results are shown in Table 1.

[0221] [Example 6]

[0222] As shown in Table 1, in Example 2, napped artificial leather was obtained in the same manner except that the island component was changed to polyamide 11 to which no olefin-maleic anhydride resin was added.

[0223] [Example 7]

[0224] As shown in Table 2, in Example 1, polyamide 6 (island component) and polyvinyl alcohol resin (sea component) were conjugated in a polyamide / polyvinyl alcohol resin ratio of 50 / 50, the elastomer was replaced with a DMF solution of polyester polyurethane (solids content 13.5% by mass), and the solids content of the elastomer was adjusted to 41% by mass relative to the total of the polyamide fibers and the elastomer in the hot-pressed fiber sheet. A napped artificial leather was obtained in the same manner. The results are shown in Table 2.

[0225] [Example 8]

[0226] As shown in Table 2, in Example 1, polyamide 6 (island component) and polyvinyl alcohol resin (sea component) were conjugated in a polyamide / polyvinyl alcohol resin ratio of 50 / 50, the elastomer was replaced with a DMF solution of polyether polyurethane (solids content 13.5% by mass), and the solids content of the elastomer was adjusted to 42% by mass relative to the total of the polyamide fibers and the elastomer in the hot-pressed fiber sheet. A napped artificial leather was obtained in the same manner. The results are shown in Table 2.

[0227] [Example 9]

[0228] A water-soluble thermoplastic resin, i.e., a modified polyvinyl alcohol-based resin, as a sea component and polyamide 6 as an island component were ejected from a melt composite spinning spinneret (number of islands: 64 islands / fiber) at 260°C in a sea component / island component ratio of 30 / 70 (mass ratio), and spun at a spinning speed of 800 m / min. The unstretched sea-island type fiber obtained was dry-heat stretched at a stretching temperature of 100°C at a stretching ratio of 3.6 times, thereby obtaining a stretched sea-island type composite fiber with a diameter of 20.8 μm (fineness 3.67 dtex). The polyamide 6 was added with an olefin-maleic anhydride resin (Lotarder 5500) (manufactured by SK Geo Centric) in a manner to achieve 10% by mass of the total. Subsequently, the stretched sea-island type composite fiber was crimped and cut to obtain a short fiber with a fiber length of 51 mm. The short fiber was combed, overlapped, and needle-punched to form a fiber with a unit area weight of 620 g / m 2 of cohesive fiber sheets.

[0229] The entangled fiber sheet was then steamed at 110°C and 23.5% RH, dried in an oven at 90-110°C, and then hot-pressed at 120°C to obtain a hot-pressed fiber sheet.

[0230] To an emulsion of a polycarbonate-based non-yellowing polyurethane emulsion as a polymeric elastomer, 1.5 parts by mass of a carbodiimide crosslinking agent and 2.7 parts by mass of ammonium sulfate were added per 100 parts by mass of the polymeric elastomer. The emulsion, having a solid content of 15% by mass of the polymeric elastomer, was impregnated into the hot-pressed fiber sheet at a pickup rate of 52%. The solid content of the polymeric elastomer was adjusted to 10% by mass relative to the total of the polyamide fibers and the polymeric elastomer in the hot-pressed fiber sheet. The hot-pressed fiber sheet impregnated with the emulsion was then dried at 115°C and 25% RH, and further dried at 150°C to obtain a hot-pressed fiber sheet to which the polymeric elastomer had been applied.

[0231] The hot-pressed fiber sheet, imbued with a high-molecular-weight elastomer, was then subjected to an immersion nip treatment, a high-pressure water jet treatment, and then immersed in 95°C hot water for 10 minutes. This dissolved and removed the water-soluble thermoplastic polyvinyl alcohol resin, the sea component of the island-in-the-sea composite fiber, to form ultrafine polyamide 6 fibers with an average diameter of 2.01 μm and an average fineness of 0.036 dtex. The resulting sheet was then dried to obtain an artificial leather substrate. The artificial leather substrate was then cut in half at the center of the thickness direction, and the cut surface was ground with #320 paper. The main surface of the artificial leather substrate was then ground with #320 and #400 papers to form a napped surface.

[0232] Then, the artificial leather substrate with the fiber napped surface formed thereon was dyed at 90°C using a gold-containing dye to obtain a napped artificial leather having a fiber napped surface. The obtained napped artificial leather had a basis weight of 270 g / m 2 , the apparent density is 0.450g / cm 3 , thickness is 0.60mm, and the equilibrium moisture regain of the pile artificial leather is 1.78%.

[0233] The napped artificial leather of Example 9 was produced by a method that did not use a solvent. Its water absorption area swelling ratio was 5.0%, a sufficiently low value. Furthermore, mechanical properties were not impaired, and the surface felt smooth and soft, resulting in an A rating. These results are shown in Table 2 below.

[0234] [Comparative Example 1]

[0235] As shown in Table 2, in Example 1, except that (i) the island component was changed to polyamide 6 to which no olefin-maleic anhydride resin was added, and (ii) the emulsion of a polycarbonate-based non-yellowing polyurethane as the polymer elastomer was adjusted to a solid content of 10% by mass of the polymer elastomer, and then the emulsion was impregnated into the hot-pressed fiber sheet, a napped artificial leather was obtained in the same manner. The results are shown in Table 2.

[0236] [Comparative Example 2]

[0237] As shown in Table 2, in Example 1, except that polyethylene was used as the sea component, (i) polyamide 6 to which no olefin-maleic anhydride resin (Lotarder 4210) (manufactured by SK Geo Centric) was added was used as the island component, (ii) the polyamide 6 (island component) and polyethylene (sea component) were mixed and spun at a polyamide / polyethylene ratio of 50 / 50 (mass ratio) before stretching, and (iii) the solid content of the polymer elastomer was changed to 46% by mass, napped artificial leather was obtained in the same manner. The results are shown in Table 2.

[0238] [Comparative Example 3]

[0239] As shown in Table 2, a napped artificial leather was obtained in the same manner as in Example 1 except that polyethylene terephthalate (hereinafter referred to as PET) to which no olefin-maleic anhydride resin (Lotarder 4210) (manufactured by SK Geo Centric) was added was used as the island component.

[0240]

[0241]

[0242] As shown in Tables 1 and 2, the area swelling ratio of the napped artificial leathers obtained in Examples 1 to 9 when wetted with water was less than 10%, and they had excellent morphological stability and the smooth and soft surface feel unique to polyamide resins.

[0243] On the other hand, in Comparative Example 1 using polyamide 6 without olefin-maleic anhydride resin, the equilibrium moisture regain exceeded 1.80%, and the area swelling ratio when wetted with water exceeded 18%, indicating a lack of morphological stability.

[0244] It can also be seen that for Comparative Example 2, in which the sea component is polyethylene and the island component is polyamide 6, the mixed spinning is performed, and then the stretching treatment is performed, although the area swelling rate when wetted with water is low and the morphological stability is excellent, a solvent must be used to remove the sea component, which lacks environmental friendliness.

[0245] Furthermore, it can be seen that Comparative Example 3 using PET as the resin constituting the island component has an area swelling ratio of 0% when wetted with water, and has excellent morphological stability, but the surface feel is different from the softness unique to polyamide and is inferior to that of the examples.

[0246] Industrial Applicability

[0247] The artificial leather of the present invention has excellent morphological stability when wetted with water. Furthermore, since it contains polyamide fibers, it has a soft surface and an excellent hand feel. Therefore, it can be suitably used in products such as automotive parts, information equipment-related parts, home appliance-related parts, optical parts, luxury goods, and shoe parts. It is particularly suitable for products used in environments exposed to moisture and for applications requiring morphological stability when wetted with water.

[0248] It should be noted that this application is based on the Japanese patent application (Japanese Patent Application No. 2023-017646) filed on February 8, 2023, the entirety of which is incorporated by reference.

Claims

1. An artificial leather substrate comprising polyamide fiber and a polymer elastomer, wherein: The artificial leather substrate is dried at 100° C. for 10 minutes and then transferred to an atmosphere at a temperature of 22° C. and a relative humidity of 45%. The mass of the artificial leather substrate 40 seconds after the transfer is defined as A. The mass of the artificial leather substrate when no mass change occurs after further standing in the atmosphere is defined as B. When the ratio of the mass of the polymer elastic body to the total mass of the polyamide fiber and the polymer elastic body is defined as X mass%, the equilibrium moisture regain calculated by the following formula (1) is 1.80% or less. Equilibrium regain (%) = {(BA) / [A×(100-X) / 100]}×100···Formula (1).

2. The artificial leather substrate according to claim 1, wherein The average diameter of the polyamide fiber is 7.5 μm or less.

3. The artificial leather substrate according to claim 1, wherein The average fineness of the polyamide fiber is less than 0.50 dtex.

4. The artificial leather substrate according to claim 1, wherein The polyamide fiber contains a polyamide resin and an olefin-maleic anhydride resin, and the content of the olefin-maleic anhydride resin in the polyamide fiber exceeds 0% by mass and is 30% by mass or less.

5. The artificial leather substrate according to claim 1, wherein The polyamide resin contained in the polyamide fiber is a polyamide resin having an average carbon number of 8 or more between amide bonds.

6. The artificial leather substrate according to claim 1, wherein The content of the polymeric elastomer is 5 to 45% by mass relative to the total mass of the polyamide fiber and the polymeric elastomer. 7 . A napped artificial leather, wherein the surface of the artificial leather substrate according to claim 1 is subjected to a napping treatment.

8. A method for producing an artificial leather substrate, wherein the artificial leather substrate is the artificial leather substrate according to any one of claims 1 to 6, the method comprising: A process for spinning ultrafine fibers using a water-soluble thermoplastic resin and a polyamide resin to which an olefin-maleic anhydride resin is added to produce a type fiber; a step of preparing a fiber web formed of the ultrafine fiber-generating fibers; a step of forming an entangled fiber sheet using the fiber web; a step of impregnating the entangled fiber sheet with a polymer elastic body; and A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after the impregnation with the polymeric elastic body.

9. A method for producing an artificial leather substrate, wherein the artificial leather substrate is the artificial leather substrate according to any one of claims 1 to 6, the method comprising: A process for spinning ultrafine fibers using a water-soluble thermoplastic resin and a polyamide resin having an average carbon number of 8 or more between amide bonds to produce a type fiber; a step of preparing a fiber web formed of the ultrafine fiber-generating fibers; a step of forming an entangled fiber sheet using the fiber web; a step of impregnating the entangled fiber sheet with a polymer elastic body; and A step of removing the water-soluble thermoplastic resin from the ultrafine fiber-forming fibers at any time between before and after the impregnation with the polymeric elastic body.

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