Artificial leather base material, and method for producing artificial leather base material

Abstract

An artificial leather base material contains a polyamide fiber (a), wherein the polyamide fiber (a) contains polyamide fibers (a) formed using recycled polyamide resin, the content of an impurity element other than the titanium element in the polyamide fiber (a) is 0-950 mass ppm, and the average yarn diameter of the polyamide fibers (a) is 0.1-5.0 μm.

Description

Artificial leather substrate and method for manufacturing artificial leather substrate

[0001] The present invention relates to an artificial leather substrate and a method for producing an artificial leather substrate.

[0002] Conventionally, artificial leathers containing nonwoven fabrics with polyamide fibers as an ultrafine fiber component have been highly acclaimed as materials with a texture similar to that of natural leather, such as being softer and having a superior crease texture, compared to those containing nonwoven fabrics with polyester fibers as an ultrafine fiber component or those containing nonwoven fabrics with normal fineness fibers. Furthermore, the polyamide fibers contained in artificial leathers are required to satisfy high levels of physical properties such as abrasion resistance and aesthetic requirements such as texture (soft feel). Various proposals have been made to address these issues.

[0003] For example, Patent Document 1 describes a nylon hollow fiber made of nylon having a relative viscosity of 2.9 to 4.0, having a hollow portion with a hollow ratio of 10 to 30%, and containing a specific amount of a specific diamide compound. It also describes that the nylon hollow fiber improves the softness of the fabric without impairing the abrasion resistance.

[0004] Japanese Patent Application Laid-Open No. 2006-9178

[0005] In recent years, research into recycling and sustainable materials has been actively conducted to realize a sustainable society. As part of this research, it has been discovered that when artificial leather substrates are produced from recycled polyamide resins, which form polyamide fibers such as nylon, the tensile strength of the artificial leather substrates decreases, resulting in a problem of decreased tensile strength of the artificial leather itself.

[0006] The present invention aims to solve the above-mentioned problems and to provide an artificial leather substrate that has excellent tensile strength despite containing polyamide fibers formed using recycled polyamide resin, and a method for producing the same.

[0007] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by adjusting the content of impurity elements other than titanium in the polyamide fiber (A) contained in the artificial leather substrate to 0 to 950 ppm by mass, and have arrived at the present invention.

[0008] [1] An artificial leather substrate comprising polyamide fibers (A), wherein the polyamide fibers (A) comprise polyamide fibers (a) formed using recycled polyamide resin, wherein the content of impurity elements other than titanium in the polyamide fibers (A) is 0 to 950 mass ppm, and the average fiber diameter of the polyamide fibers (A) is 0.1 to 5.0 μm. [2] The artificial leather substrate according to [1] above, wherein the content of magnesium among the impurity elements is 30 mass% or less. [3] The artificial leather substrate according to [1] or [2] above, comprising a polymeric elastomer. [4] A method for producing an artificial leather substrate comprising polyamide fibers (A), wherein the polyamide fibers (A) comprise polyamide fibers (a) formed using a recycled polyamide resin, the polyamide fibers (A) have a content of impurity elements other than titanium of 0 to 950 ppm by mass, and the polyamide fibers (A) have an average fiber diameter of 0.1 to 5.0 μm, the method comprising the following steps (1) to (3): step (1): melt-spinning ultrafine fiber-generating fibers containing a thermoplastic resin and a recycled polyamide resin to prepare a fiber web formed from the ultrafine fiber-generating fibers, step (2): forming an entangled fiber sheet using the fiber web, and step (3): removing the thermoplastic resin from the ultrafine fiber-generating fibers. [5] A method for producing an artificial leather substrate according to the above item [4], comprising the following step (4): step (4): impregnating a polymer elastomer. [6] A method for producing an artificial leather substrate according to the above item [4] or [5], comprising the following step (5): Step (5): Dyeing step

[0009] According to the present invention, it is possible to provide an artificial leather substrate that has excellent tensile strength despite containing polyamide fibers formed using recycled polyamide resin, and a method for producing the same.

[0010] The following describes an artificial leather substrate according to an embodiment of the present invention and a method for manufacturing an artificial leather substrate according to an embodiment of the present invention (hereinafter sometimes referred to as "artificial leather substrate according to the present embodiment" or "method for manufacturing an artificial leather substrate according to the present embodiment").

[0011] [Artificial Leather Substrate] The artificial leather substrate of this embodiment is an artificial leather substrate comprising polyamide fibers (A), wherein the polyamide fibers (A) comprise polyamide fibers (a) formed using recycled polyamide resin, the content of impurity elements other than titanium in the polyamide fibers (A) being 0 to 950 ppm by mass, and the average fiber diameter of the polyamide fibers (A) being 0.1 to 5.0 μm. In this specification, "impurity elements other than titanium" has the following meaning. When the artificial leather substrate does not contain a polymeric elastomer, "impurity elements other than titanium" means elements other than carbon, hydrogen, oxygen, nitrogen, and titanium. In other words, "impurity elements other than titanium" does not include carbon, hydrogen, oxygen, nitrogen, or titanium. Specific examples of "impurity elements other than titanium" include calcium, sodium, magnesium, silicon, aluminum, boron, barium, cadmium, cobalt, chromium, copper, iron, potassium, lithium, manganese, molybdenum, nickel, phosphorus, lead, antimony, vanadium, and zinc. These elements are elements other than titanium that can be measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy: ICP-AES, ICP-OES). When the artificial leather substrate contains a polymeric elastomer, "impurity elements other than titanium" means elements other than carbon, hydrogen, oxygen, nitrogen, and titanium. In other words, "impurity elements other than titanium" does not include carbon, hydrogen, oxygen, nitrogen, or titanium. Specific examples of "impurity elements other than titanium" include calcium, sodium, magnesium, silicon, aluminum, boron, barium, cadmium, cobalt, chromium, copper, iron, potassium, lithium, manganese, molybdenum, nickel, phosphorus, lead, antimony, vanadium, and zinc, as in the case where the artificial leather substrate does not contain a polymeric elastomer.These elements are elements other than titanium that can be measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy: ICP-AES, ICP-OES). In this specification, the content of impurity elements other than titanium in polyamide fiber (A) is a value determined by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy: ICP-AES, ICP-OES) and is the content in elemental terms. Specifically, it can be determined by the method described in the examples below.

[0012] The artificial leather substrate of this embodiment, having the above-described configuration, exhibits excellent tensile strength despite containing polyamide fiber (a) formed using recycled polyamide resin. While the details of the reason for this are unclear, it is presumed to be due to the following reasons. Generally, when producing polyamide fibers, additives such as magnesium compounds are added to polyamide resins to improve productivity, such as by reducing thread breakage and improving spinnability. Furthermore, during the process of producing polyamide resins or polyamide fibers, impurities such as cleaning agents for the production equipment or contaminants may be mixed into the polyamide resins or polyamide fibers. These impurities may be mixed in if the impurity removal process is insufficient, whether through chemical recycling or material recycling. When spinning is performed using raw materials containing these impurities (including additives), the impurities accelerate degradation of the polyamide fibers due to heating during spinning. As a result, the stretchability of the spun raw yarn deteriorates, making it difficult for crimping to occur, reducing the entanglement of the entangled fiber sheet, and presumably reducing the tensile strength of the artificial leather substrate.

[0013] The thickness of the artificial leather substrate of this embodiment is not particularly limited, but from the viewpoint of achieving both good texture and processability, it is preferably 0.1 mm or more, more preferably 0.3 mm or more, even more preferably 0.5 mm or more, and preferably 3.0 mm or less, more preferably 2.0 mm or less, and even more preferably 1.0 mm or less. That is, from the viewpoint of achieving both good texture and processability, the thickness of the artificial leather substrate of this embodiment is preferably 0.1 to 3.0 mm, more preferably 0.3 to 2.0 mm, and even more preferably 0.5 to 1.0 mm. In this specification, the "thickness of the artificial leather substrate" refers to the thickness measured in accordance with JIS L 1913:2010 (Method A).

[0014] The basis weight of the artificial leather substrate of this embodiment is not particularly limited, but from the viewpoint of the transportability of the fiber web and the impregnation of the polymeric elastomer, it is preferably 100 g / m ２ More preferably, 150 g / m ２ More preferably, 180 g / m ２ or more, preferably 1000 g / m ２ or less, more preferably 500 g / m ２ More preferably 250 g / m or less ２ That is, the basis weight of the artificial leather substrate of this embodiment is preferably 100 to 1000 g / m from the viewpoint of the transportability of the fiber web and the impregnation of the polymeric elastomer. ２ , more preferably 150 to 500 g / m ２ , more preferably 180 to 250 g / m ２ In this specification, the term "basis weight of the artificial leather substrate" refers to the mass per unit area measured in accordance with JIS L 1913:2010.

[0015] The apparent density of the artificial leather substrate of the present embodiment is not particularly limited, but from the viewpoint of achieving both high tensile strength and high stretchability, it is preferably 0.10 g / cm ３ More preferably, 0.15 g / cm ３ More preferably, 0.20 g / cm ３ or more, preferably 1.00 g / cm ３or less, more preferably 0.80 g / cm ３ More preferably, 0.60 g / cm ３ That is, from the viewpoint of achieving both high tensile strength and high stretchability, the apparent density of the artificial leather substrate of this embodiment is preferably 0.10 to 1.00 g / cm ３ , more preferably 0.15 to 0.80 g / cm ３ , more preferably 0.20 to 0.60 g / cm ３ In this specification, the "apparent density of the artificial leather substrate" is a value calculated by subtracting the "thickness of the artificial leather substrate" from the "basis weight of the artificial leather substrate."

[0016] <Polyamide fiber (A)> The polyamide fiber (A) of the present embodiment includes a polyamide fiber (a) formed using a recycled polyamide resin, the content of impurity elements other than titanium in the polyamide fiber (A) is 0 to 950 ppm by mass, and the average fiber diameter of the polyamide fiber (A) is 0.1 to 5.0 μm.

[0017] In the present invention, the term "recycled polyamide resin" refers to a polyamide resin derived from recycled waste. The recycled waste is not limited to recovered polyamide products discarded after actual use, but also includes recovered polyamide products that were manufactured but discarded without actually being used. Recycling methods include material recycling (mechanical recycling) and chemical recycling (feedstock recycling) as described in ISO 15270:2008.

[0018] The polyamide fiber (A) of this embodiment may be composed of polyamide fiber (a), or may contain polyamide fibers other than polyamide fiber (a). That is, the polyamide fiber (A) of this embodiment may contain polyamide fibers that are not formed using recycled polyamide resin. The content of polyamide fiber (a) in polyamide fiber (A) is not limited as long as the content of impurity elements other than titanium in the polyamide fiber (A) is 0 to 950 ppm by mass and the average fiber diameter of the polyamide fiber (A) is 0.1 to 5.0 μm. However, from the viewpoint of meeting sustainable demand and increasing the recycling rate, the content of polyamide fiber (a) in polyamide fiber (A) may be 30% by mass or more, 50% by mass or more, 70% by mass or more, 90% by mass or more, or even 100% by mass. That is, the content of the polyamide fiber (a) in the polyamide fiber (A) may be 30 to 100 mass%, 50 to 100 mass%, 70 to 100 mass%, 90 to 100 mass%, or 100 mass%.

[0019] When the polyamide fiber (A) of the present embodiment includes a polyamide fiber that is not formed using a recycled polyamide resin, the polyamide fiber may be the same type of polyamide fiber as the polyamide fiber (a) or a different type of polyamide fiber.

[0020] The amount of impurity elements other than titanium in polyamide fiber (A) can be adjusted based on the amount of impurity elements other than titanium contained in recycled polyamide resins and non-recycled polyamide resins used to form polyamide fiber (a) of polyamide fiber (A) and polyamide fibers other than polyamide fiber (a). Polyamide fiber (a) may be formed using only recycled polyamide resins having an impurity content of 0 to 950 ppm by mass other than titanium, or may be formed by combining recycled polyamide resins having an impurity content of more than 950 ppm by mass other than titanium with recycled polyamide resins having an impurity content of less than 950 ppm by mass other than titanium, or non-recycled raw materials having an impurity content of less than 950 ppm by mass other than titanium.

[0021] The average thread diameter of the polyamide fiber (A) of this embodiment is preferably 0.2 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more, from the viewpoint of both high tensile strength and suitable elongation, and is preferably 4.5 μm or less, more preferably 4.0 μm or less, and even more preferably 3.5 μm or less, from the viewpoint of texture. That is, the average thread diameter of the polyamide fiber (A) of this embodiment is preferably 0.2 to 4.5 μm, more preferably 0.4 to 4.0 μm, and even more preferably 0.6 to 3.5 μm. In the present invention, the "average thread diameter of the polyamide fiber (A)" refers to the average diameter of 10 fibers randomly selected from an SEM photograph of the cross section of an artificial leather substrate taken at 5000x magnification using a scanning electron microscope (SEM). Specifically, it can be determined by the method described in the Examples below.

[0022] The average fineness of the polyamide fiber (A) of this embodiment is preferably 0.0010 dtex or more, more preferably 0.0050 dtex or more, and even more preferably 0.0100 dtex or more, from the viewpoint of both high tensile strength and suitable elongation, and is preferably 1.0000 dtex or less, more preferably 0.5000 dtex or less, and even more preferably 0.1000 dtex or less, from the viewpoint of texture. That is, the average fineness of the polyamide fiber (A) of this embodiment is preferably 0.0010 to 1.0000 dtex, more preferably 0.0050 to 0.5000 dtex, and even more preferably 0.0100 to 0.1000 dtex. In the present invention, the "average fineness of the polyamide fiber (A)" refers to a value calculated from the following formula (2), and specifically, can be determined by the method described in the Examples below. Average fineness (dtex) of polyamide fiber (A) = d × (r / 2) ２ ×π×10 －２ (2) r: average fiber diameter (μm) d: density of polyamide fiber (A) (g / cm ３ )

[0023] Examples of polyamide resins constituting the polyamide fiber (A) include polyamide 6, polyamide 66, polyamide 610, polyamide 1010, polyamide 11, and polyamide 12. Among these, from the viewpoint of easy availability, polyamide 6 and polyamide 66 are preferred, and polyamide 6 is more preferred. The above polyamide resins may be used alone or in combination of two or more.

[0024] The polyamide resin constituting the polyamide fiber (A) of this embodiment may contain various additives within the range that does not impair the effects of the present invention, such as catalysts, colorants, heat stabilizers, flame retardants, lubricants, stain-proofing agents, fluorescent brighteners, delustering agents, gloss improvers, antistatic agents, fragrances, deodorizers, antibacterial agents, anti-mite agents, and inorganic fine particles.

[0025] From the viewpoint of tensile strength, the polyamide fiber (A) of this embodiment is preferably a polyamide long fiber. In this specification, "long fiber" refers to a continuous fiber that is not a short fiber intentionally cut after spinning. More specifically, it refers to a filament or continuous fiber that is not a short fiber intentionally cut to a fiber length of about 3 to 80 mm. The fiber length of the islands-in-sea type composite fiber before being converted into ultrafine fibers, as described below, is preferably 100 mm or more, more preferably 200 mm or more. As long as it is technically producible and is not inevitably cut during the production process, the long fiber may be a continuous fiber having a fiber length of several meters, several hundred meters, several kilometers, or even longer, produced by, for example, a spunbonding method and continuously spun. Note that, during the production process, needle punching or surface buffing during entanglement may unavoidably cut a portion of the long fiber to produce a short fiber.

[0026] The polyamide fiber (A) of this embodiment is preferably an ultrafine fiber, from the viewpoint of reducing the rigidity of the fiber and making it easier to obtain a soft texture. In the present invention, the term "ultrafine fiber" refers to a fiber that has been made ultrafine by removing at least one component from a multicomponent fiber (composite fiber) made of at least two or more spinnable polymers having different chemical or physical properties.

[0027] From the viewpoint of stretchability, the content of polyamide fiber (A) in the artificial leather substrate is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, or may be 100% by mass. That is, the content of polyamide fiber (A) in the artificial leather substrate may be 70 to 100% by mass, 80 to 100% by mass, 90 to 100% by mass, or 100% by mass.

[0028] (Polyamide fiber (a)) The polyamide fiber (a) of the present embodiment is formed using a recycled polyamide resin. Examples of the polyamide resin constituting the polyamide fiber (a) include the same polyamide resins as those constituting the polyamide fiber (A).

[0029] The amount of ash obtained by pyrolysis of the recycled polyamide resin used to form the polyamide fiber (a) (hereinafter sometimes referred to as "recycled polyamide resin") is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and may even be 0% by mass, relative to 100% by mass of the recycled polyamide resin subjected to pyrolysis. That is, the amount of ash obtained by pyrolysis of the recycled polyamide resin is preferably 0 to 5% by mass, more preferably 0 to 3% by mass, even more preferably 0 to 1% by mass, and may even be 0% by mass, relative to 100% by mass of the recycled polyamide resin subjected to pyrolysis.

[0030] The weight-average molecular weight of the recycled polyamide resin is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more, from the viewpoint of tensile strength, and is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 70,000 or less, from the viewpoint of drawability during spinning and drawing. That is, the weight-average molecular weight of the recycled polyamide resin is preferably 10,000 to 100,000, more preferably 20,000 to 80,000, and even more preferably 30,000 to 70,000. In the present invention, the "weight-average molecular weight" refers to the molecular weight in terms of polymethyl methacrylate (PMMA) determined by gel permeation chromatography (GPC) measurement, and can be determined specifically by the method described in the Examples below.

[0031] The number average molecular weight of the recycled polyamide resin is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 11,000 or more, from the viewpoint of tensile strength, and is preferably 50,000 or less, more preferably 30,000 or less, and even more preferably 20,000 or less, from the viewpoint of drawability during spinning and drawing. That is, the number average molecular weight of the recycled polyamide resin is preferably 5,000 to 50,000, more preferably 8,000 to 30,000, and even more preferably 11,000 to 20,000. In the present invention, the "number average molecular weight" refers to the molecular weight in terms of polymethyl methacrylate (PMMA) determined by gel permeation chromatography (GPC) measurement, and specifically can be determined by the method described in the examples below.

[0032] The relative viscosity of the recycled polyamide resin is preferably 1.5 or more, more preferably 1.8 or more, and even more preferably 2.0 or more, from the viewpoint of both high tensile strength and suitable elongation, and is preferably 5.0 or less, more preferably 4.7 or less, and even more preferably 4.5 or less, from the viewpoint of spinnability. That is, the relative viscosity of the recycled polyamide resin is preferably 1.5 to 5.0, more preferably 1.8 to 4.7, and even more preferably 2.0 to 4.5. In the present invention, the "relative viscosity" is a value determined by measuring the flow time of a polymer solution, and specifically, can be determined by the method described in the examples below.

[0033] Recycled polyamide resin before and after heat treatment at 150°C for 2 hours ＊ Amount of change in value Δb ＊ From the viewpoint of tensile strength, b is preferably 20 or less, more preferably 17 or less, further preferably 15 or less, and may be 0. That is, b before and after heat treatment of recycled polyamide resin at 150°C for 2 hours ＊ Amount of change in value Δb ＊ is preferably 0 to 20, more preferably 0 to 17, and even more preferably 0 to 15, and may be 0. ＊ "Value" refers to the CIE 1976 (L ＊ a ＊ b＊ ) b defined by the color system ＊ The value is measured by the method described in the Examples below. ＊ If the value of is negative, the value is considered to be 0.

[0034] <Impurity Elements Other Than Titanium> The content of impurity elements other than titanium in the polyamide fiber (A) of this embodiment is 0 to 950 ppm by mass. From the viewpoint of tensile strength, the content of impurity elements other than titanium in the polyamide fiber (A) is preferably 840 ppm by mass or less, more preferably 830 ppm by mass or less, and even more preferably 820 ppm by mass or less. From the viewpoint of tensile strength, a lower content of impurity elements other than titanium is preferable, but from the viewpoint of recyclability, the content may be 10 ppm by mass or more, 20 ppm by mass or more, or 30 ppm by mass or more. That is, the content of impurity elements other than titanium in the polyamide fiber (A) of this embodiment is preferably 10 to 840 ppm by mass, more preferably 20 to 830 ppm by mass, and even more preferably 30 to 820 ppm by mass.

[0035] From the viewpoint of suppressing deterioration of the polyamide fiber (A) and obtaining an artificial leather substrate having excellent tensile strength, the lower the content of magnesium element among the impurity elements other than titanium element, the more preferable. The content of magnesium element among the impurity elements other than titanium element is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and may even be 0% by mass. That is, the content of magnesium element among the impurity elements other than titanium element is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, even more preferably 0 to 10% by mass.

[0036] When using a polyamide resin derived from recycled materials, the content of impurity elements other than titanium in the polyamide fiber (A) can be adjusted by the following (i) to (v): (i) adjusting the content of impurity elements other than titanium in the polyamide fiber (A) by selecting and using a polyamide resin derived from recycled materials having a content of impurity elements other than titanium of 0 to 950 ppm by mass; (ii) adjusting the content of impurity elements other than titanium in the polyamide fiber (A) by selecting a polyamide resin derived from recycled materials having a content of impurity elements other than titanium of 0 to 950 ppm by mass and using this polyamide resin in combination with a polyamide resin not derived from recycled materials; (iii) adjusting the content of impurity elements other than titanium in the polyamide fiber (A) by using recycled waste (polyamide resin) after washing it during the material recycling process to reduce the content of impurity elements other than titanium so that the content of impurity elements other than titanium in the polyamide fiber (A) in the final artificial leather substrate is 0 to 950 ppm by mass. (iv) During the material recycling process, the waste (polyamide resin) subjected to recycling is washed to reduce the content of impurity elements other than titanium in the polyamide fiber (A) in the finally obtained artificial leather substrate so that the content of impurity elements other than titanium in the polyamide fiber (A) is 0 to 950 ppm by mass, and further, a polyamide resin not derived from recycling is used in combination to adjust the content of impurity elements other than titanium in the polyamide fiber (A). (v) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by using in combination a polyamide resin derived from material recycling having a content of impurity elements other than titanium of more than 950 ppm by mass with a polyamide resin derived from material recycling having a content of impurity elements other than titanium of less than 950 ppm by mass, or a polyamide resin not derived from recycling.The polyamide resin derived from material recycling and having a content of impurity elements other than titanium of more than 950 mass ppm may be unwashed or may be washed to reduce the content of impurity elements other than titanium.

[0037] When a polyamide resin derived from chemical recycling is used, the content of impurity elements other than titanium in the polyamide fiber (A) can be adjusted by the following (vi) to (x): (vi) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by selecting and using a polyamide resin derived from chemical recycling having a content of impurity elements other than titanium of 0 to 950 ppm by mass; (vii) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by using a combination of a polyamide resin derived from chemical recycling having a content of impurity elements other than titanium of 0 to 950 ppm by mass and a polyamide resin not derived from recycling. (viii) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by reducing the content of impurity elements other than titanium by washing or purifying the recycled waste (polyamide resin) during the chemical recycling process so that the content of impurity elements other than titanium in the polyamide fiber (A) in the finally obtained artificial leather substrate is 0 to 950 ppm by mass. (ix) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by washing or purifying the recycled waste (polyamide resin) during the chemical recycling process so that the content of impurity elements other than titanium in the polyamide fiber (A) in the finally obtained artificial leather substrate is 0 to 950 ppm by mass, and further a polyamide resin not derived from recycling is used in combination to adjust the content of impurity elements other than titanium in the polyamide fiber (A). (x) The content of impurity elements other than titanium in the polyamide fiber (A) is adjusted by using a combination of a polyamide resin derived from chemical recycling having a content of impurity elements other than titanium of more than 950 ppm by mass and a polyamide resin derived from chemical recycling having a content of impurity elements other than titanium of less than 950 ppm by mass, or a polyamide resin not derived from recycling.The polyamide resin derived from chemical recycling and having a content of impurity elements other than titanium of more than 950 mass ppm may be one that has not been washed or purified, or one in which the content of impurity elements other than titanium has been reduced by washing or purification.

[0038] Unless the recycled polyamide resin used in the production of an artificial leather substrate is intentionally selected and subjected to washing, purification, and other operations to reduce the content of impurity elements other than titanium, it is difficult to achieve a content of impurity elements other than titanium in the polyamide fiber (A) contained in the artificial leather substrate of 0 to 950 ppm by mass. Note that the content of impurity elements other than titanium in polyamide fibers formed using only non-recycled polyamide resins is 0 to 950 ppm by mass.

[0039] The content of impurity elements other than titanium in the polyamide fiber (A) is not particularly limited as long as it can be measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy: ICP-AES, ICP-OES). When the artificial leather substrate of this embodiment contains a non-aqueous polymer elastomer, the content of impurity elements other than titanium in the polyamide fiber (A) may be determined by immersing the artificial leather substrate in a solvent that dissolves the polymer elastomer, such as DMF (N,N-dimethylformamide), dissolving the polymer elastomer in the solvent, separating it, and then measuring the content of impurity elements other than titanium contained in both the separated polymer elastomer and the artificial leather substrate, and calculating the content of impurity elements other than titanium in the polyamide fiber (A) from the measured values. Furthermore, when the artificial leather substrate of this embodiment contains a water-based polymer elastomer, the artificial leather substrate may be immersed in a solvent such as HFIP (hexafluoroisopropanol) that dissolves the polyamide fiber (A) but not the polymer elastomer, and the polymer elastomer present as a solid may be separated. Thereafter, the content of impurity elements other than titanium contained in the separated polymer elastomer and the artificial leather substrate may be measured, and the content of impurity elements other than titanium contained in the polyamide fiber (A) may be calculated from the measured values.

[0040] <Polymer elastomer> The artificial leather substrate of this embodiment may or may not contain a polymer elastomer. Any polymer elastomer conventionally used in artificial leather substrates can be used, and specific examples include polyurethane elastomers, acrylonitrile elastomers, olefin elastomers, polyester elastomers, and acrylic elastomers, with polyurethane elastomers and acrylic elastomers being preferred. Examples of polyurethane elastomers include various polyurethane elastomers obtained by combining, as the main component, at least one polymer polyol having an average molecular weight of 500 to 3,000 selected from polyester diols, polyether diols, polyether ester diols, polycarbonate diols, polycarbonate ether diols, polycarbonate ester diols, etc., 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 or ethylenediamine, in a predetermined molar ratio, and polymerizing these in one or multiple stages by melt polymerization, bulk polymerization, solution polymerization, or the like. The content of the polymer polyol component in the polyurethane elastomer is preferably 15 to 90% by mass.

[0041] The acrylic elastomer may be a mixture of at least one soft component selected from the group consisting of a monomer whose homopolymer has a glass transition temperature in the range of −90 to −5° C. and is preferably non-crosslinkable, such as methyl acrylate, n-butyl acrylate, isobutyl acrylate, isopropyl acrylate, n-hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and a monomer whose homopolymer has a glass transition temperature in the range of 50 to 250° C. and is preferably non-crosslinkable, such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, and cyclohexyl methacrylate. and (meth)acrylic acid, and a monofunctional or polyfunctional ethylenically unsaturated monomer unit capable of forming a crosslinked structure, or a compound capable of forming a crosslinked structure by reacting with an ethylenically unsaturated monomer unit introduced into a polymer chain, such as an ethylenically unsaturated monomer comprising at least one crosslink-forming component selected from the group consisting of ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate.

[0042] Artificial leather substrates obtained using polyurethane elastomers as the main polymeric elastomer are preferred because they offer an excellent balance of texture and mechanical properties, and if the appropriate type is selected, they also offer an excellent balance, including durability. Artificial leather substrates obtained using acrylic elastomers are unsuitable for forming napped artificial leathers because the acrylic elastomers have lower adhesion to ultrafine fiber bundles than polyurethane elastomers and are less effective at fixing the nap during nap formation. However, they are particularly preferred for forming grain-finish artificial leathers because the degree of hardening of the texture relative to the content is suppressed. Different types of polymeric elastomers may be mixed or added multiple times. In addition to the aforementioned main polymeric elastomers such as polyurethane elastomers, acrylonitrile elastomers, olefin elastomers, polyester elastomers, and acrylic elastomers, polymeric elastomers such as synthetic rubbers may also be added as needed to form polymeric elastomer compositions.

[0043] When the artificial leather substrate of the present embodiment contains a polymeric elastomer, the content thereof in the artificial leather substrate is preferably 5 to 45% by mass, more preferably 7 to 40% by mass, and even more preferably 8 to 30% by mass, from the viewpoint of obtaining an artificial leather substrate having excellent texture.

[0044] <Other Components> The artificial leather substrate of this embodiment may or may not contain components other than the polyamide fibers (A) and the polymeric elastomer. Examples of such other components include fibers other than the polyamide fibers (A), the other components contained in the polyamide fibers (A), and additives similar to those that can be added to the polymeric elastomer liquid used to impregnate the polymeric elastomer. The other components may be encapsulated in at least one of the polyamide fibers (A) and the polymeric elastomer. 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, from the viewpoints of facilitating the desired effects of the other components and of water absorbency, water repellency, stain resistance, etc.

[0045] [Method for manufacturing artificial leather substrate] From the viewpoint of obtaining an artificial leather substrate excellent in tensile strength, the artificial leather substrate according to this embodiment is preferably manufactured by a manufacturing method comprising the following steps (1) to (3): Step (1): A step of melt-spinning ultrafine fiber-generating fibers containing a thermoplastic resin and a recycled polyamide resin to prepare a fiber web formed from the ultrafine fiber-generating fibers; Step (2): A step of forming an entangled fiber sheet using the fiber web; Step (3): A step of removing the thermoplastic resin from the ultrafine fiber-generating fibers.

[0046] <Step (1)> Step (1) is a step of spinning ultrafine fiber-generating fibers containing a thermoplastic resin and a recycled polyamide resin, and preparing a fiber web formed from the ultrafine fiber-generating fibers. As described above, ultrafine fibers are ultrafine fibers obtained by removing at least one component from a multicomponent fiber (composite fiber) made of at least two or more spinnable polymers with different chemical or physical properties. The multicomponent fiber that generates these ultrafine fibers is the ultrafine fiber-generating fiber. Typical examples of ultrafine fiber-generating fibers include islands-in-sea composite fibers, multilayer laminated composite fibers, and radial laminated composite fibers, which are obtained using methods such as chip blending (mixed spinning) and composite spinning. Among these, islands-in-sea composite fibers are preferred from the viewpoints of increasing productivity through high-speed spinning and of obtaining an artificial leather substrate that is excellent in surface abrasion resistance and pilling resistance. From the same viewpoint, it is preferred to melt-spin the islands-in-sea composite fiber to spin ultrafine fiber-generating fibers, and obtain a fiber web formed from the ultrafine fiber-generating fibers. When the ultrafine fiber-forming fiber is an islands-in-sea type composite fiber, island components are dispersed in a sea component that serves as a matrix in the fiber cross section, and ultrafine fibers in the form of fiber bundles are generated by removing the sea component. Hereinafter, a method for using islands-in-sea type composite fiber as the ultrafine fiber-forming fiber, melt-spinning the islands-in-sea type composite fiber, and obtaining a fiber web formed from the islands-in-sea type composite fiber will be described in more detail.

[0047] The island component fibers contained in the islands-in-sea composite fiber and later to become ultrafine fibers contain at least a recycled polyamide resin, i.e., the polyamide resin constituting the polyamide fiber (a). The island component fibers may contain a resin other than the recycled polyamide resin. That is, they may contain a polyamide resin that is not recycled. Examples of the polyamide resin constituting the island component fibers include the same polyamide resins as those constituting the polyamide fiber (A) and the polyamide fiber (a). Examples of the resin other than the polyamide resin constituting the island component fibers include modified PET such as polyethylene terephthalate (hereinafter sometimes referred to as "PET"), isophthalic acid-modified PET, sulfoisophthalic acid-modified PET, and PET dyeable with cationic dyes; aromatic polyesters such as polybutylene terephthalate and polyhexamethylene terephthalate; and aliphatic polyesters such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polyhydroxybutyrate-polyhydroxyvalerate resin. In this specification, polyester resins such as the aromatic polyester and aliphatic polyester contain dicarboxylic acid monomer units and diol monomer units, and modified PET is PET in which at least a portion of the ester-forming dicarboxylic acid monomer units or diol monomer units of unmodified PET have been replaced with substitutable monomer units. Specific examples of modifying monomer units that replace dicarboxylic acid monomer units include units derived from isophthalic acid, sodium sulfoisophthalic acid, sodium sulfonaphthalenedicarboxylic acid, adipic acid, etc., which replace terephthalic acid units. Specific examples of modifying monomer units that replace diol monomer units include units derived from diols such as butanediol and hexanediol, which replace ethylene glycol units.

[0048] The sea component contained in the islands-in-sea type composite fiber and removed by extraction, decomposition, or the like is a thermoplastic resin, and it is preferable to use a resin that has a different solubility or decomposability from the island component resins and has low compatibility with them. It is preferable to select such a thermoplastic resin appropriately depending on the type of island component resin and the production method. Examples of the thermoplastic resin for the sea component include olefin-based resins such as polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer, as well as resins that are soluble in organic solvents and can be dissolved and removed by organic solvents, such as polystyrene, styrene-acrylic copolymer, and styrene-ethylene copolymer. Other examples include resins that can be removed with water alone without using a solvent, such as polyvinyl alcohol-based resins, modified polyvinyl alcohol-based resins, water-soluble polyester resins, easily alkali-decomposable modified polyester resins, polyacrylamide resins, and carboxymethyl cellulose resins. Among these, polyethylene is preferable from the viewpoints of melt spinnability and the tensile strength of the islands-in-sea type composite fiber.

[0049] As the type of copolymerization monomer used in the modified polyvinyl alcohol-based resin, from the viewpoints of copolymerizability and melt spinnability, preferred are α-olefins having 4 or less carbon atoms, such as ethylene, propylene, 1-butene, and isobutene; and vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether. The content of copolymerization units in the polyvinyl alcohol is preferably 1 to 20 mol%, more preferably 4 to 15 mol%, and even more preferably 6 to 13 mol%. Furthermore, since the tensile strength of the islands-in-sea type composite fiber increases when the copolymerization units are ethylene, ethylene-modified polyvinyl alcohol is more preferred. The content of ethylene units in the ethylene-modified polyvinyl alcohol is preferably 4 to 15 mol%, and more preferably 6 to 13 mol%.

[0050] The mass ratio of the sea part to the island parts in the islands-in-sea type composite fiber is not particularly limited, but preferably falls within the range of 5:95 to 80:20 (sea part:island part). When the sea part polymer ratio in the islands-in-sea type composite fiber is 5% by mass or more, the spinning stability of the islands-in-sea type composite fiber is less likely to decrease, and industrial productivity is easily ensured. Furthermore, when a polymeric elastomer is added, voids of a required size are more likely to be formed between the ultrafine fiber bundles and the polymeric elastomer after the sea part is removed, and as a result, a fluffy feel, a solid feel, a dense surface feel, and the like are more likely to be obtained. On the other hand, when the sea part polymer ratio is 60% by mass or less, the shape and distribution of the island parts in the cross section of the islands-in-sea type composite fiber are stable, and a decrease in quality stability is easily prevented.

[0051] The islands-in-sea type composite fibers are subsequently subjected to an ultrafine fiber treatment to be converted into ultrafine fibers having a fineness lower than that of the islands-in-sea type composite fibers.

[0052] As a method for melt-spinning ultrafine fiber-generating fibers (islands-in-sea type composite fibers) and producing a fiber web formed from the ultrafine fiber-generating fibers, it is preferable to employ a method in which melt-spinning is performed using a so-called spunbond method, and the ultrafine fiber-generating fibers thus obtained are collected on a conveyor belt without being cut, to form a fiber web of long fibers that are continuous fibers.

[0053] Specifically, a conjugate spinning die having a large number of nozzle holes arranged in a predetermined pattern is used to continuously extrude molten strands of islands-in-sea composite fibers from a spinning nozzle at a predetermined extrusion rate. The strands are substantially cooled and solidified by cooling air at some stage between directly below the nozzle holes and the suction device described below. A high-speed air stream is applied using a suction device such as an air jet nozzle, and the conjugate fibers are uniformly pulled and attenuated to a desired diameter or fineness. The high-speed air stream is applied so that the average spinning speed, which corresponds to the mechanical take-up speed in normal spinning, falls within the range of 1,000 to 6,000 m / min. Furthermore, depending on the texture of the resulting fiber web, the islands-in-sea composite fibers are opened by a collision plate or air stream, and then collected and deposited on a collecting surface such as a conveyor belt-like moving net while being suctioned from the opposite side of the net, thereby forming a long-fiber web. The web may be subjected to a heat press treatment to impart shape stability, and the web may be fusion-bonded accordingly.

[0054] <Step (2)> Step (2) is a step of forming an entangled fiber sheet using the fiber web. Step (2) is a step of obtaining an entangled fiber sheet in which fibers are entangled in the thickness direction by performing an entanglement treatment such as needle punching or hydroentanglement treatment.

[0055] The fiber web obtained in step (1) may be superimposed in multiple layers. The method for superimposing multiple fiber webs may involve superimposing the fiber webs all in the same direction, or may involve changing the conveying direction of the fiber web to a 90° angle and superimposing the fiber web while folding it back, using a cross-lapping method. The method for superimposing multiple fiber webs may be cross-lap lamination, which makes it easy to adjust the width of the entangled fiber sheet as desired and can suppress the occurrence of unevenness in the width direction of the fiber web, i.e., can suppress non-uniformity in basis weight. The number of layers of the superimposed webs is not particularly limited, but is preferably 4 or more, more preferably 8 or more, from the viewpoint of mechanical strength, and preferably 20 or less, more preferably 16 or less, from the viewpoint of ease of production.

[0056] A multi-layered fiber web is subjected to a mechanical entanglement treatment by a known method such as needle punching or high-pressure water jet treatment, thereby three-dimensionally entangling the fibers constituting the fiber web, particularly the fibers between adjacent layers of a wrapped or stacked layered fiber web. When entanglement is performed by needle punching, various treatment conditions are appropriately selected, such as the type of needle (needle shape and count, barb shape and depth, number and position of barbs, etc.), needle punch count (needle punch treatment density per unit area obtained by multiplying the density of needles implanted in a needle board by the number of strokes the board applies to per unit area of ​​the fiber web), and needle punch depth (depth at which the needles apply to the fiber web). When the component to be removed from the ultrafine fiber-generating fiber is a water-soluble polymer, the entanglement is preferably performed by needle punching, from the viewpoint of suppressing the elution of the water-soluble polymer during the entanglement treatment.

[0057] The punch density of the needle punching process is 1500 to 5500 punches / cm ２ , and further, 2000 to 5000 punches / cm ２ If the punch density is within the above range, insufficient entanglement is suppressed, preventing the surface of the artificial leather substrate from becoming rough due to fraying of the fibers, and also preventing fiber breakage from occurring, preventing a decrease in the degree of entanglement.

[0058] In addition, an oil or an antistatic agent may be applied to the ultrafine fiber-generating fiber, the fiber web, the fiber web laminate, the entangled fiber sheet, or the like at any stage from the melt spinning of the islands-in-sea type composite fiber to the entanglement treatment.

[0059] The weight of the entangled fiber sheet is 100 to 1000 g / m ２ In addition, for the purpose of fixing the shape of the entangled fiber sheet, smoothing the surface, etc., the fiber density may be further increased by performing a heat press treatment as necessary.

[0060] <Step (3)> Step (3) is a step of removing the thermoplastic resin, which is the sea component resin, from the ultrafine fiber-forming fibers. By removing the thermoplastic resin, the ultrafine fiber-forming fibers can be converted into a fiber bundle of ultrafine fibers.

[0061] Examples of methods for removing the thermoplastic resin, which is the sea component resin, include methods using a solvent or decomposing agent that can selectively remove only the thermoplastic resin. When the thermoplastic resin is a water-soluble resin such as a polyvinyl alcohol resin, a water-soluble polyester resin, an easily alkali-decomposable modified polyester resin, a polyacrylamide resin, or a carboxymethyl cellulose resin, the thermoplastic resin can be removed with water. When the thermoplastic resin is insoluble in water but soluble in an organic solvent, examples of organic solvents that can dissolve and remove the thermoplastic resin include toluene, trichloroethylene, and tetrachloroethylene. In this embodiment, it is preferable to use toluene, which has a high dissolving power for thermoplastic resins. Furthermore, when removing the thermoplastic resin, a dip-nip treatment may be performed in parallel.

[0062] <Step (4)> The method for producing an artificial leather substrate according to this embodiment may further include step (4), which is a step of impregnating the substrate with a polymeric elastomer, from the viewpoint of imparting texture and dimensional stability similar to those of natural leather. Step (4) may be performed between steps (2) and (3), or may be performed after step (3). In producing the artificial leather substrate according to this embodiment, in order to impart texture and dimensional stability similar to those of natural leather as well as flexibility, it is preferable to perform step (4) between steps (2) and (3). That is, it is preferable to impregnate the entangled fiber sheet with a polymeric elastomer before removing the thermoplastic resin. By impregnating the entangled fiber sheet with a polymeric elastomer before removing the thermoplastic resin, voids formed by removing the thermoplastic resin are formed between the ultrafine fibers that form the fiber bundles after removing the thermoplastic resin. As a result, the ultrafine fibers within the fiber bundles are less likely to be restrained by the polymeric elastomer, i.e., the ultrafine fiber bundles are less susceptible to the influence of the polymeric elastomer, making it easier to obtain an artificial leather substrate with excellent flexibility. In addition, when the ultrafine fibers forming the fiber bundles after the thermoplastic resin, which is the sea component, has been removed from the islands-in-sea type composite fibers are impregnated with a polymeric elastomer, the polymeric elastomer penetrates into the voids in the fiber bundles, and the ultrafine fibers forming the fiber bundles are bound by the polymeric elastomer, making it easier to obtain an artificial leather substrate with a hard texture.

[0063] When applying the polymeric elastomer to the entangled fiber sheet, a non-aqueous polymeric elastomer liquid in which the polymeric elastomer is dissolved or dispersed in a solvent may be used, or an aqueous polymeric elastomer liquid in which the polymeric elastomer is dispersed in an aqueous medium, optionally together with a dispersant, may be used. In the former case, a uniform polymeric elastomer liquid is easily obtained, while in the latter case, the amount of organic solvent used can be easily reduced.

[0064] The concentration of the polymeric elastomer body fluid, i.e., the content of the polymeric elastomer in the polymeric elastomer body fluid, is preferably 0.1 to 60% by mass. The polymeric elastomer body fluid may contain various additives, such as colorants such as dyes and pigments, coagulation regulators, antioxidants, ultraviolet absorbers, fluorescent agents, antifungal agents, penetrating agents, antifoaming agents, lubricants, water repellents, oil repellents, thickeners, bulking agents, hardening accelerators, foaming agents, and water-soluble polymer compounds such as polyvinyl alcohol and carboxymethyl cellulose, within the range that does not impair the properties of the final artificial leather.

[0065] Details of the polymeric elastomer used in step (4) are as explained above in the section "polymeric elastomer."

[0066] The polymeric elastomer may be fixed in the entangled fiber sheet by impregnating the entangled fiber sheet with the polymeric elastomer and then coagulating the polymeric elastomer by a conventionally known dry or wet method. The dry method here refers to any method for fixing the polymeric elastomer in a fiber sheet structure by removing the solvent, dispersant, etc. by drying or the like. The wet method here refers to any method for temporarily or completely fixing the polymeric elastomer in the entangled fiber sheet structure prior to removing the dispersant by treating the entangled fiber sheet structure impregnated with a polymeric elastomer liquid with a non-solvent or coagulant for the polymeric elastomer, or by subjecting the impregnated entangled fiber sheet to a heat treatment or the like using an aqueous polymeric elastomer liquid containing a thermosensitive gelling agent or the like.

[0067] <Step (5)> The method for producing an artificial leather substrate according to this embodiment may further include a dyeing step (5). Step (5) can be performed at any stage after the ultrafine-generating fibers have been converted into ultrafine fiber bundles, i.e., after step (3).

[0068] In step (5), any dyeing method using a known dyeing machine typically used for dyeing conventional artificial leather substrates such as padder, jigger, circular, or wince, can be employed, using a dye selected appropriately depending on the type of fiber and mainly consisting of disperse dyes, reactive dyes, acid dyes, metal complex dyes, sulfur dyes, sulfur vat dyes, etc. In addition to dyeing, it is also preferable to perform finishing treatments such as mechanical kneading in a dry state, relaxation treatment in a wet state using a dyeing machine or washing machine, softener treatment, functionality-imparting treatment such as a flame retardant, antibacterial agent, deodorizer, or water / oil repellent, treatment to impart a tactile feel such as a silicone resin, a silk protein-containing treatment, or a grip-imparting resin, or design-imparting treatment in which a resin other than the above-mentioned resins is applied, such as a colorant or an enamel-like coating resin.

[0069] In addition to the above steps (1) to (5), finishing treatments such as mechanical kneading treatment in a dry state, relaxation treatment in a wet state using a dyeing machine or washing machine, treatment with a softener, treatment to impart functionality such as a flame retardant, antibacterial agent, deodorizer, or water / oil repellent, treatment to impart a texture modifier such as a silicone resin, a silk protein-containing treatment agent, or a grip-imparting resin, and design imparting treatment by applying a resin other than the above-mentioned resins such as a colorant or an enamel-like coating resin may be performed as needed.

[0070] The artificial leather substrate of this embodiment may be sliced ​​into multiple pieces in the thickness direction as required, and the thickness may be adjusted by grinding the surface that will become the back surface, or a solvent that can dissolve or swell the polymer elastomer or ultrafine fiber bundles may be applied to the surface that will become the back surface, as in the production of conventional artificial leather substrates.

[0071] The artificial leather substrate of this embodiment may have a napped surface. Formation of the napped surface can be achieved by any known method, such as buffing with sandpaper or card cloth, or brushing. Furthermore, before or after such nap-raising treatment, a solvent capable of dissolving or swelling the polymeric elastomer or ultrafine fiber bundles, such as a treatment solution containing dimethylformamide (DMF) or a treatment solution containing a phenolic compound such as resorcinol, may be applied to the surface to be napped. This allows for fine adjustment of the restraint state of the ultrafine fiber bundles due to adhesion of the polymeric elastomer or ultrafine fiber bundles, the nap length of the ultrafine fibers of the artificial leather substrate, and the surface friction durability. Furthermore, the above-mentioned step (5) may be performed after the nap-raising treatment.

[0072] The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to the contents of the examples.

[0073] [Measurement and Evaluation Methods] Various physical properties were measured by the following methods.

[0074] <Δb ＊ The polyamide resins used in the Examples, Comparative Examples, and Reference Examples were subjected to heat treatment at 150°C for 2 hours. ＊ Amount of change in value Δb ＊ was measured using a spectrophotometer "UH3900S" (manufactured by Hitachi, Ltd.) with a D65 light source, reflection mode, geometric condition c (di: 8°, de: 8°), diffuse illumination: 8° receiving light, measurement mode SCI, and measurement diameter = φ20 mm. ＊ After the measurement, the polyamide resin was heat-treated at 150°C for 2 hours using a constant temperature dryer "NDO-600ND" (manufactured by Tokyo Rikakikai Co., Ltd.), and the b value of the polyamide resin after the heat treatment was measured under the same conditions as above. ＊ The values ​​were measured. ＊ From the value, Δb ＊ was calculated.

[0075] <Relative Viscosity> The relative viscosity of the polyamide resins used in the Examples, Comparative Examples, and Reference Examples was determined in accordance with JIS K6920-2:2009 as follows. 25 mL of sulfuric acid (96% sulfuric acid (special grade, manufactured by Kanto Chemical Co., Inc.)) was added to 0.25 g of polyamide resin, and the mixture was completely dissolved at room temperature to prepare a sample solution. The solution was then filtered through a 1 μm membrane filter. The filtered sample solution was poured into a viscometer (Ubbelohde Viscometer "No. 2," manufactured by Shibata Scientific Co., Ltd.) and allowed to stand in a thermostatic water bath "TV-55" (manufactured by Thomas Chemical Instruments Co., Ltd.) at 25°C for at least 20 minutes, after which the average vulcanization time of the sample solution was measured. Furthermore, sulfuric acid (96% sulfuric acid (special grade, manufactured by Kanto Chemical Co., Inc.)) was poured into the viscometer and allowed to stand in the thermostatic water bath at 25°C for at least 20 minutes, after which the average flow time of the sulfuric acid was measured. From the measurement results, the relative viscosity was calculated using the following formula (1): Relative viscosity = t / t ０ (1) t: average vulcanization time of the sample solution (s) t ０ : Average flow time (s) of sulfuric acid (96% sulfuric acid (special grade reagent, manufactured by Kanto Chemical Co., Ltd.))

[0076] <Ash Content> The ash content of the polyamide resins used in the Examples, Comparative Examples, and Reference Examples was determined as follows: 10.0 g of polyamide resin was placed in a crucible and heated in an electric furnace "RKC CB900" (manufactured by Koyo Corporation) at 400°C for 90 minutes, at 600°C for 90 minutes, and at 800°C for 120 minutes in this order, and the ash content was calculated using the following formula: Ash content = W / W ｏ × 100 (%) W: mass of polyamide resin after combustion (g) W ｏ : mass of polyamide resin before combustion (g)

[0077] <Weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn)> The weight-average molecular weight and number-average molecular weight of the polyamide resins used in the Examples, Comparative Examples, and Reference Examples were measured by gel permeation chromatography (GPC) using a measurement solution under the following conditions. The molecular weight distribution was calculated from the obtained weight-average molecular weight and number-average molecular weight. Apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Eluent: hexafluoroisopropanol with sodium trifluoroacetate added to a concentration of 20 mM Column: two "GMHHR-H(S)" manufactured by Tosoh Corporation Column temperature: 40°C Detector: RI Flow rate: 0.2 mL / min The measurement solution was prepared by adding 3 mg of polymethyl methacrylate (PMMA) and 3 mg of polyamide resin as standard samples to 5 mL of hexafluoroisopropanol (HFIP) with sodium trifluoroacetate added to a concentration of 20 mM, stirring the mixture at 40°C for 2 hours, and then filtering it using a 0.45 μm filter.

[0078] <Original Yarn Tensile Strength> The tensile strength of an undrawn islands-in-sea type composite fiber was measured and used as the original yarn tensile strength in accordance with JIS L 1013: 2010. Specifically, the tensile strength was measured using a precision universal testing machine "Autograph AG-X plus" (manufactured by Shimadzu Corporation) by elongating the fiber at a gripping distance of 10 cm and a head speed of 20 cm / min.

[0079] <Original Yarn Tensile Elongation> The tensile elongation of an undrawn islands-in-sea type composite fiber was measured and defined as the original yarn tensile elongation with reference to JIS L 1013: 2010. Specifically, using a precision universal testing machine "Autograph AG-X plus" (manufactured by Shimadzu Corporation), the fiber was stretched at a gripping distance of 10 cm and a head speed of 20 cm / min, and the elongation was measured, which was defined as the original yarn tensile elongation.

[0080] <Contents of Impurities Other Than Titanium (Impurity Element Content) and Magnesium Element Content in Polyamide Fiber (A), and Magnesium Element Content Among the Impurities> The artificial leather substrates obtained in the Examples, Comparative Examples, and Reference Examples were immersed in DMF (N,N-dimethylformamide) to dissolve the polycarbonate-based polyurethane contained in the artificial leather substrates in DMF, and the DMF solution containing the dissolved polycarbonate-based polyurethane was then separated. Water was added to the separated DMF solution to coagulate the polycarbonate-based polyurethane, and the DMF and water were separated to obtain a polycarbonate-based polyurethane. Subsequently, 0.1 g of the artificial leather substrates obtained in the Examples, Comparative Examples, and Reference Examples was mixed with 8 ml of nitric acid to prepare Mixed Solution 1. Furthermore, 0.1 g of the polycarbonate-based polyurethane separated from the artificial leather substrates obtained in the Examples, Comparative Examples, and Reference Examples was mixed with 8 ml of nitric acid to prepare Mixed Solution 2. The mixed solutions 1 and 2 were subjected to microwave decomposition using a microwave decomposition apparatus "Multiwave 5000" (manufactured by Anton Paar) at a decomposition temperature of 220°C for a decomposition time of 70 minutes, thereby obtaining decomposition solutions 1 and 2. Pure water was added to each of the decomposition solutions 1 and 2 to make a total volume of 100 ml, and the solution was filtered through a filter with a pore size of 0.45 μm to obtain measurement samples 1 and 2. Measurement samples 1 and 2 were each subjected to ICP-AES measurement three times using an inductively coupled plasma optical emission spectrometer "iCAP-6500Duo" (manufactured by Thermo Fisher Scientific), and the contents of impurity elements other than titanium and magnesium were calculated. The average values ​​of the results of the three measurements were used for each content. The magnesium content in the impurity elements was calculated from the contents of impurity elements other than titanium and magnesium. The content of impurity elements other than titanium in polyamide fiber (A) was calculated using the following formula (i):Content (ppm by mass) of impurity elements other than titanium in polyamide fiber (A) = (content (ppm by mass) of impurity elements other than titanium in artificial leather substrate - content (ppm by mass) of impurity elements other than titanium in polycarbonate-based polyurethane separated from artificial leather substrate x content (% by mass) of polycarbonate-based polyurethane in artificial leather substrate) / content (% by mass) of polyamide fiber in artificial leather substrate (i) The "content of polyamide fiber in the artificial leather substrate" was calculated based on the mass of the artificial leather substrate and the "polymer elastomer content" described below.

[0081] <Average Yarn Diameter> The yarn diameters of 10 randomly selected polyamide fibers were measured from an SEM photograph of the cross section of the artificial leather substrate taken at 5000x magnification using a scanning electron microscope (SEM), and the average value was taken as the average yarn diameter (μm).

[0082] <Average Fineness> The value calculated from the following formula (2) was taken as the average fineness (dtex) of the polyamide fiber. Average fineness (dtex) of the polyamide fiber = d × (r / 2) 2 ×π×10 -2 (2) r: average fiber diameter (μm) d: density of polyamide fiber (g / cm ３ The density of polyamide fiber is 1.14 g / cm 3 (density of polyamide 6).

[0083] <Polymer elastomer content> The polymer elastomer content in the obtained artificial leather substrate was calculated from the following formula (3): Polymer elastomer content (mass %) = [C x E / 100 x F / 100] / [C x D / 100 + C x E / 100 x F / 100] (3) where C: mass C of entangled fiber sheet (i) (size: 10 cm x 10 cm), D: mass ratio D of polyamide resin (A) in the ultrafine fiber-forming fiber, E: concentration E (mass %) of polymer elastomer solution, F: pickup rate F (mass %) when impregnated into the entangled fiber sheet. Note that the "pickup rate" refers to the adhesion rate (mass %) of the polymer elastomer solution to the entangled fiber sheet. For example, a pickup rate of 100 mass % means that the same mass of polymer elastomer solution is adhered to the entangled fiber sheet.

[0084] <Thickness, basis weight and apparent density> The thickness (mm) and basis weight (g / m2) of the obtained artificial leather substrate were measured in accordance with JIS L 1913:2010. ２ ) was measured, and from these values, the apparent density (g / cm ３ ) was calculated.

[0085] <Tensile Strength> Using 16 cm x 2.5 cm test pieces cut from the artificial leather substrate, stress-strain curves were obtained in accordance with JIS L 1096:2010 8.14.1 "Tensile Strength Test." Specifically, stress-strain curves were measured at a tensile speed of 10 cm / min. Three test pieces were cut out of the artificial leather substrate with their long sides aligned along the longitudinal direction, and three test pieces were cut out with their long sides aligned along the transverse direction. The stress at break was read from the stress-strain curve obtained using each test piece, and the average stress values ​​for the three test pieces cut out with their long sides aligned along the longitudinal direction and the three test pieces cut out with their long sides aligned along the transverse direction were calculated to obtain the tensile strength of each test piece.

[0086] [Materials] Details of the polyamide resins (i) to (vi) used in the examples and comparative examples and the measurement results of their physical properties are shown in Table 1. Note that the polyamide resins (i) to (iii) are polyamide resins derived from material recycling of film scraps, the polyamide resin (iv) is a polyamide resin derived from chemical recycling of fishing nets, and the polyamide resins (v) and (vi) are polyamide resins not derived from recycling.

[0087]

[0088] Example 1 A polyamide resin blended with low-density polyethylene (chip form) as a sea component and a polyamide resin (i) derived from recycled materials and a polyamide resin (vi) not derived from recycled materials in a mass ratio of 60 / 40 was extruded from a melt conjugate spinning die (number of islands: 600 / fiber) at 275°C so that the sea component / island component ratio was 50 / 50 in mass ratio, and spun at a spinning speed of 285 m / min to obtain a fiber web containing islands-in-sea composite fibers having an average diameter of 35 µm and an average fineness of 10 dtex. The obtained fiber web containing islands-in-sea composite fibers was stretched 2.6 times in a warm water bath at a stretching temperature of 84°C to obtain a drawn fiber web containing islands-in-sea composite fibers having an average diameter of 25 µm and an average fineness of 5 dtex. Next, the drawn islands-in-sea type composite fiber was mechanically buckled using a pair of push rollers and a stuffer box to impart crimps, and then cut to obtain staple fibers with a fiber length of 51 mm. The staple fibers were carded, stacked, and needle-punched to obtain a fiber weight of 630 g / m. ２ An entangled fiber sheet of 190 g / m2 was produced. This entangled fiber sheet was immersed in a dimethylformamide solution containing 14% by mass of polycarbonate-based polyurethane (elastomer), and the polycarbonate-based polyurethane solution was impregnated into the entangled fiber sheet at a pickup rate of 69% by mass. Next, the entangled fiber sheet impregnated with polycarbonate-based polyurethane was immersed in a dimethylformamide / water mixed solution to wet-coagulate the polycarbonate-based polyurethane. After washing with water, the low-density polyethylene sea component was extracted and removed using toluene at 90°C. Thereafter, the sheet was sliced ​​completely in two, and one side was buffed with sandpaper to perform a nap raising treatment, resulting in a basis weight of 195 g / m2. ２ The measurement results of the obtained raw yarn (undrawn islands-in-sea type composite fiber) and the obtained artificial leather substrate are shown in Table 2.

[0089] Example 2 Low-density polyethylene (in chip form) as the sea component and polyamide resin (ii) derived from recycled materials as the island component were extruded from a melt conjugate spinning die (number of islands: 300 / fiber) at 285°C so that the sea component / island component ratio was 50 / 50 (mass ratio), and spun at a spinning speed of 285 m / min to obtain a fiber web containing islands-in-sea composite fibers with an average diameter of 35 μm and an average fineness of 10 dtex. The fiber web containing the obtained islands-in-sea composite fibers was stretched 2.4 times in a warm water bath at a stretching temperature of 84°C to obtain a drawn fiber web containing islands-in-sea composite fibers with an average diameter of 25 μm and an average fineness of 5 dtex. The drawn islands-in-sea composite fibers were then mechanically buckled using a pair of push rollers and a stuffer box to impart crimps, and then cut to obtain staple fibers with a fiber length of 51 mm. The staples were carded, overlapped and needle-punched to a basis weight of 673 g / m ２ An entangled fiber sheet of 1000 g was produced. This entangled fiber sheet was immersed in a dimethylformamide solution containing 14% by mass of polycarbonate-based polyurethane (polymeric elastomer), and the polycarbonate-based polyurethane solution was impregnated into the entangled fiber sheet at a pickup rate of 74% by mass. Next, the entangled fiber sheet impregnated with polycarbonate-based polyurethane was immersed in a dimethylformamide / water mixed solution to wet-coagulate the polycarbonate-based polyurethane. After washing with water, the low-density polyethylene sea component was extracted and removed using toluene at 90°C. Thereafter, the sheet was sliced ​​completely in two, and one side was buffed with sandpaper to perform a nap raising treatment, resulting in a basis weight of 204 g / m. ２ The measurement results of the obtained raw yarn (undrawn islands-in-sea type composite fiber) and the obtained artificial leather substrate are shown in Table 2.

[0090] Example 3 Low-density polyethylene (in chip form) as the sea component and chemically recycled polyamide resin (iv) as the island component were extruded from a melt conjugate spinning die (number of islands: 300 / fiber) at 285°C so that the sea component / island component ratio was 50 / 50 (mass ratio), and spun at a spinning speed of 285 m / min to obtain a fiber web containing islands-in-sea composite fibers with an average diameter of 35 μm and an average fineness of 10 dtex. The obtained fiber web containing islands-in-sea composite fibers was stretched 2.4 times in a warm water bath at a stretching temperature of 84°C to obtain a drawn fiber web containing islands-in-sea composite fibers with an average diameter of 25 μm and an average fineness of 5 dtex. The drawn islands-in-sea composite fibers were then mechanically buckled using a pair of push rollers and a stuffer box to impart crimps, and then cut to obtain staple fibers with a fiber length of 51 mm. The staples were carded, overlapped and needle-punched to a basis weight of 673 g / m ２ An entangled fiber sheet of 1000 g was produced. This entangled fiber sheet was immersed in a dimethylformamide solution containing 14% by mass of polycarbonate-based polyurethane (polymeric elastomer), and the polycarbonate-based polyurethane solution was impregnated into the entangled fiber sheet at a pickup rate of 74% by mass. Next, the entangled fiber sheet impregnated with polycarbonate-based polyurethane was immersed in a dimethylformamide / water mixed solution to wet-coagulate the polycarbonate-based polyurethane. After washing with water, the low-density polyethylene sea component was extracted and removed using toluene at 90°C. Thereafter, the sheet was sliced ​​completely in two, and one side was buffed with sandpaper to perform a nap raising treatment, resulting in a basis weight of 206 g / m. ２ The measurement results of the obtained raw yarn (undrawn islands-in-sea type composite fiber) and the obtained artificial leather substrate are shown in Table 2.

[0091] Comparative Example 1 A polyamide resin blended with low-density polyethylene (chip form) as a sea component and a polyamide resin (iii) derived from recycled materials and a polyamide resin (vi) not derived from recycled materials in a ratio of polyamide resin (i) / polyamide resin (v) = 60 / 40 was extruded from a melt conjugate spinning die (number of islands: 600 / fiber) at 275°C so that the sea component / island component ratio was 50 / 50 (mass ratio) and spun at a spinning speed of 285 m / min to obtain a fiber web containing islands-in-sea type composite fibers having an average diameter of 35 µm and an average fineness of 10 dtex. The obtained fiber web containing islands-in-sea type composite fibers was stretched 2.6 times in a warm water bath at a stretching temperature of 84°C to obtain a drawn fiber web containing islands-in-sea type composite fibers having an average diameter of 25 µm and an average fineness of 5 dtex. Next, the drawn islands-in-sea type composite fiber was mechanically buckled using a pair of push rollers and a stuffer box to impart crimps, and then cut to obtain staple fibers with a fiber length of 51 mm. The staple fibers were carded, stacked, and needle-punched to obtain a fiber weight of 630 g / m. ２ An entangled fiber sheet of 198 g / m2 was produced. This entangled fiber sheet was immersed in a dimethylformamide solution containing 14% by mass of polycarbonate-based polyurethane (polymeric elastomer), and the polycarbonate-based polyurethane solution was impregnated into the entangled fiber sheet at a pickup rate of 69% by mass. Next, the entangled fiber sheet impregnated with polycarbonate-based polyurethane was immersed in a dimethylformamide / water mixed solution to wet-coagulate the polycarbonate-based polyurethane. After washing with water, the low-density polyethylene sea component was extracted and removed using toluene at 90°C. Thereafter, the sheet was sliced ​​completely in two, and one side was buffed with sandpaper to perform a nap raising treatment, resulting in a basis weight of 198 g / m2. ２ The measurement results of the obtained raw yarn (undrawn islands-in-sea type composite fiber) and the obtained artificial leather substrate are shown in Table 2.

[0092] Reference Example 1 Spinning was carried out in the same manner as in Example 1, except that polyamide resin (v) was used as the island component, to obtain a fiber web containing islands-in-sea type composite fibers with an average diameter of 35 μm and an average fineness of 10 dtex. The resulting lower fiber web containing islands-in-sea type composite fibers was stretched 2.6 times in a warm water bath at a stretching temperature of 84°C to obtain a drawn fiber web containing islands-in-sea type composite fibers with an average diameter of 25 μm and an average fineness of 5 dtex. The drawn islands-in-sea type composite fibers were then mechanically buckled using a pair of push rollers and a stuffer box to impart crimps, and then cut to obtain staple fibers with a fiber length of 51 mm. The staple fibers were carded, overlapped, and needle-punched to obtain a fiber web with a basis weight of 630 g / m ２ An entangled fiber sheet of 190 g / m2 was produced. This entangled fiber sheet was immersed in a dimethylformamide solution containing 14% by mass of polycarbonate-based polyurethane (elastomer), and the polycarbonate-based polyurethane solution was impregnated into the entangled fiber sheet at a pickup rate of 69% by mass. Next, the entangled fiber sheet impregnated with polycarbonate-based polyurethane was immersed in a dimethylformamide / water mixed solution to wet-coagulate the polycarbonate-based polyurethane. After washing with water, the low-density polyethylene sea component was extracted and removed using toluene at 90°C. Thereafter, the sheet was sliced ​​completely in two, and one side was buffed with sandpaper to perform a nap raising treatment, resulting in a basis weight of 190 g / m2. ２ The measurement results of the obtained raw yarn (undrawn islands-in-sea type composite fiber) and the obtained artificial leather substrate are shown in Table 2.

[0093]

[0094] As shown in Table 2, the artificial leather substrates obtained in Examples 1 to 3, in which the content of impurity elements other than titanium in the polyamide fiber (A) was 0 to 950 ppm by mass, were excellent in tensile strength, regardless of whether the polyamide resin contained in the polyamide fiber (A) was a polyamide resin derived from material recycling or a polyamide resin derived from chemical recycling. On the other hand, the artificial leather substrate obtained in Comparative Example 1, which did not have the configuration of the present invention, was inferior in tensile strength.

Claims

1. An artificial leather substrate comprising polyamide fibers (A), wherein the polyamide fibers (A) comprise polyamide fibers (a) formed using recycled polyamide resin, the content of impurity elements other than titanium in the polyamide fibers (A) is 0 to 950 ppm by mass, and the average fiber diameter of the polyamide fibers (A) is 0.1 to 5.0 μm.

2. The artificial leather substrate according to claim 1, wherein the content of magnesium element among the impurity elements is 30 mass % or less.

3. The artificial leather substrate according to claim 1 or 2, which contains a polymeric elastomer.

4. A method for producing an artificial leather substrate comprising polyamide fiber (A), wherein the polyamide fiber (A) comprises polyamide fiber (a) formed using recycled polyamide resin, the content of impurity elements other than titanium in the polyamide fiber (A) is 0 to 950 mass ppm, and the average fiber diameter of the polyamide fiber (A) is 0.1 to 5.0 μm, and the method for producing an artificial leather substrate comprises the following steps (1) to (3): Step (1): melt-spinning ultrafine fiber-generating fibers containing a thermoplastic resin and a recycled polyamide resin to prepare a fiber web formed from the ultrafine fiber-generating fibers, Step (2): forming an entangled fiber sheet using the fiber web, and Step (3): removing the thermoplastic resin from the ultrafine fiber-generating fibers.

5. A method for producing an artificial leather substrate according to claim 4, comprising the following step (4): Step (4): Impregnating a polymeric elastomer.

6. A method for producing an artificial leather substrate according to claim 4 or 5, comprising the following step (5): Step (5): Dyeing step

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