Polyurethane elastic fiber and its manufacturing method

Abstract

The present invention provides a material recycled polyurethane elastic fiber that uses a recovered fabric containing polyurethane fiber and a final product as raw materials, and a method for producing the same. The material recycled polyurethane elastic fiber uses a recovered fabric containing polyurethane fiber, and a component separated by wet specific gravity separation of the fabric is used as at least a part of the raw material, and the method for producing the same.

Description

[Technical field]

[0001] The present invention relates to a polyurethane elastic fiber, and more particularly to a polyurethane elastic fiber using recycled polyurethane fiber as at least a part of the raw material, and a method for producing the same. [Background technology]

[0002] In recent years, there has been a demand for contributions to the Sustainable Development Goals (SDGs), and recycling resource utilization is a top priority issue for all industrial products. For example, for polyurethane elastic fibers, there is a known technology for recovering and recycling fiber waste generated during the manufacturing process and necessary fibers from used products. As shown in Patent Documents 1 and 2, the technology for dissolving and recycling fiber waste has been known for a long time. In addition, as shown in Patent Documents 3 and 4, a technology for producing cascade-type recycled yarn in which polyurethane material is broken down as a raw material and then dissolved using a solvent has been discovered in recent years.

[0003] However, in the horizontal recycling of polyurethane elastic fiber to polyurethane elastic fiber, there are problems specific to polyurethane elastic fiber. For example, although there was a concept of recovering polyurethane from a wound polyurethane elastic fiber in the process, there was no concept of recovering polyurethane from fabrics containing polyurethane elastic fiber. This is because the content of polyurethane elastic fiber in fabrics is small, and the concept of recovery was not reached. In addition, the conventional thinking was that dissolution is essential to effectively recover polyurethane (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 56-122836 [Patent Document 2] Special Publication No. 57-42657 [Patent Document 3] Publication number CN101096781 [Patent Document 4] Special Publication No. 2002-538314 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a polyurethane elastic fiber containing polyurethane by material recycling. More specifically, the object of the present invention is to provide a material recycled polyurethane elastic fiber and a manufacturing method thereof that enable efficient fiber-to-fiber recycling in which recovered fabrics and final products containing polyurethane fibers are used as raw materials and reused for the same material and application as horizontal recycling. [Means for solving the problem]

[0006] When polyurethane is recovered from a recovered fabric containing polyurethane elastic fiber itself as a raw material, it is necessary to separate the polyurethane from other fibers such as nylon and polyester. In addition, if chemical recycling or material recycling is performed on the remaining recovered fabric after polyurethane recovery, it is desirable that the polyurethane in the recovered fabric is recovered at as high a recovery rate as possible and that no polyurethane remains in the remaining recovered fabric. In response to these problems, the present inventors have found that by using a wet specific gravity separation method, polyurethane can be easily separated from fibers other than polyurethane and polyurethane can be obtained at a high recovery rate. They have also found that by blending polyurethane recovered with high accuracy with a virgin polymer, it is possible to obtain polyurethane elastic fiber containing recycled polyurethane, which also enables horizontal recycling of polyurethane elastic fiber.

[0007] That is, the present invention has the following configuration. (1) A material recycled polyurethane elastic fiber in which recovered fabric containing polyurethane fibers is used, and a component separated by wet specific gravity separation of the fabric is used as at least a part of the raw material. (2) The polyurethane elastic fiber according to (1), wherein the fabric is pulverized to a size of 0.005 mm or more and 0.5 mm or less and then subjected to the wet specific gravity separation. (3) The polyurethane elastic fiber according to (1) or (2), wherein a surfactant is used in the wet specific gravity separation. (4) The polyurethane elastic fiber according to (3), wherein the surfactant is an ionic surfactant that is liquid at room temperature. (5) The polyurethane elastic fiber according to (3) or (4), wherein the concentration of the surfactant is in the range of 0.1% by mass or more and 50% by mass or less. (6) The polyurethane elastic fiber according to any one of (1) to (5), wherein ultrasonic waves are used in the wet specific gravity separation. (7) The polyurethane elastic fiber according to (6), wherein the intensity of the ultrasonic waves is in the range of 20 W or more and 2000 W or less per 1 kg of the heavy liquid for wet specific gravity separation in which the fabric is immersed, and the frequency of the ultrasonic waves is in the range of 20 kHz or more and 100 kHz or less. (8) The polyurethane elastic fiber according to any one of (1) to (7), wherein the specific gravity of the heavy liquid in the wet specific gravity separation is in the range of 1.10 or more and 2.40 or less. (9) The polyurethane elastic fiber according to any one of (1) to (8), wherein the liquor ratio (mass of heavy liquid:mass of fabric) in the wet specific gravity separation is in the range of 20:1 to 500:1. (10) The polyurethane elastic fiber according to any one of (1) to (9), wherein the heavy liquid in the wet specific gravity separation is an aqueous calcium chloride solution. (11) A polyurethane elastic fiber according to any one of (1) to (10), wherein the polyurethane contained in the fabric has a number average molecular weight based on gel permeation chromatography (GPC) of 20,000 or more and 120,000 or less, and the detection intensity curve based on the GPC has no peak or shoulder in a region where the molecular weight is 30,000 or less. (12) AνC=O 1730 based on the infrared spectrum (IR) of the polyurethane fiber contained in the fabric -1 / AνC=O 1710 -1 The polyurethane elastic fiber according to any one of (1) to (11), wherein the value is 1.05 or more and 1.50 or less. (13) The polyurethane elastic fiber according to any one of (1) to (12), wherein the fabric is used for producing clothing products that are washed frequently. (14) The polyurethane elastic fiber according to (13), wherein the fabric is used for underwear. (15) A method for producing material recycled polyurethane elastic fibers using recovered fabrics containing polyurethane fibers, comprising using at least a component separated by wet specific gravity separation of the fabric as a raw material. (16) The method for producing a polyurethane elastic fiber according to (15), wherein the fabric is pulverized to a size of 0.005 mm or more and 0.5 mm or less and then subjected to the wet specific gravity separation. (17) The method for producing recycled polyurethane elastic fibers according to (15) or (16), wherein a surfactant is used in the wet specific gravity separation. (18) The method for producing polyurethane elastic fibers according to (17), wherein the surfactant is an ionic surfactant that is liquid at room temperature. (19) The method for producing a polyurethane elastic fiber according to (17) or (18), wherein the concentration of the surfactant is in the range of 0.1% by mass or more and 50% by mass or less. (20) The method for producing a polyurethane elastic fiber according to any one of (15) to (19), wherein ultrasonic waves are used in the wet specific gravity separation. (21) The method for producing a polyurethane elastic fiber according to (20), wherein the intensity of the ultrasonic waves is in the range of 20 W or more and 2000 W or less per 1 kg of the heavy liquid for wet specific gravity separation in which the fabric is immersed, and the frequency of the ultrasonic waves is in the range of 20 kHz or more and 100 kHz or less. (22) The method for producing a polyurethane elastic fiber according to any one of (15) to (21), wherein the specific gravity of the heavy liquid in the wet specific gravity separation is in the range of 1.10 or more and 2.40 or less. (23) The method for producing a polyurethane elastic fiber according to any one of (15) to (22), wherein the bath ratio (mass of heavy liquid:mass of fabric) in the wet specific gravity separation is within the range of 20:1 to 500:1. (24) The method for producing a polyurethane elastic fiber according to any one of (15) to (23), wherein the heavy liquid in the wet specific gravity separation is an aqueous calcium chloride solution. Effect of the Invention

[0008] According to the present invention, a high recovery rate of polyurethane can be achieved by performing wet specific gravity separation using a recycled fabric containing polyurethane fiber as a raw material. In addition, even if the polyurethane elastic fiber contains a large amount of recycled polyurethane, it is possible to provide a polyurethane elastic fiber that has sufficient functionality as a polyurethane elastic fiber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below with reference to the embodiments. First, the polyurethane used as the main component in the polyurethane elastic fiber of the present invention will be described. Here, the main component is a component contained in the polyurethane elastic fiber in an amount of more than 50% by mass.

[0010] The polyurethane used in the present invention may be any polyurethane having a structure starting from a polymer diol and a diisocyanate, and is not particularly limited. The synthesis method is also not particularly limited. That is, for example, it may be a polyurethane urea consisting of a polymer diol, a diisocyanate, and a low molecular weight diamine as a chain extender, or it may be a polyurethane urethane consisting of a polymer diol, a diisocyanate, and a low molecular weight diol as a chain extender. It may also be a polyurethane urea using a compound having a hydroxyl group and an amino group in the molecule as a chain extender. It is also preferable to use a polyfunctional glycol or isocyanate having three or more functionalities within a range that does not interfere with the effects of the present invention. Furthermore, the processing method is not particularly limited. That is, the polyurethane may be recycled through remolding and re-spinning.

[0011] The polymer diol is preferably a polyether-based diol, a polyester-based diol, a polycarbonate diol, etc. In particular, it is preferable to use a polyether-based diol from the viewpoint of imparting flexibility and elongation to the yarn.

[0012] As the polyether diol, for example, polyethylene oxide, polyethylene glycol, a derivative of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol (hereinafter sometimes abbreviated as PTMG), modified PTMG which is a copolymer of tetrahydrofuran (hereinafter sometimes abbreviated as THF) and 3-methyltetrahydrofuran, modified PTMG which is a copolymer of THF and 2-methyltetrahydrofuran, modified PTMG which is a copolymer of THF and 2,3-dimethylTHF, polyols having side chains on both sides as disclosed in Japanese Patent No. 2615131, random copolymers in which THF and ethylene oxide and / or propylene oxide are irregularly arranged, etc. may be preferably used. These polyether diols may be used alone or in a mixture or copolymer of two or more kinds.

[0013] From the viewpoint of obtaining abrasion resistance and light resistance as a polyurethane elastic fiber, polyester diols such as butylene adipate, polycaprolactone diol, and polyester polyols having side chains disclosed in JP-A-61-26612 and polycarbonate diols disclosed in JP-B-2-289516 are preferably used.

[0014] Moreover, such polymer diols may be used alone, or two or more kinds may be mixed or copolymerized for use.

[0015] From the viewpoint of obtaining elongation, strength, heat resistance, etc. when made into a thread, the molecular weight of the polymer diol is preferably a number average molecular weight of 1,000 or more and 8,000 or less, and more preferably 1,500 or more and 6,000 or less. By using a polyol with a molecular weight in this range, an elastic thread excellent in elongation, strength, elastic recovery force, and heat resistance can be easily obtained.

[0016] Next, as diisocyanates, aromatic diisocyanates such as diphenylmethane diisocyanate (hereinafter sometimes abbreviated as MDI), tolylene diisocyanate, 1,4-diisocyanate benzene, xylylene diisocyanate, and 2,6-naphthalene diisocyanate are particularly suitable for synthesizing polyurethanes with high heat resistance and strength. Furthermore, as alicyclic diisocyanates, for example, methylene bis(cyclohexyl isocyanate), isophorone diisocyanate, methylcyclohexane 2,4-diisocyanate, methylcyclohexane 2,6-diisocyanate, cyclohexane 1,4-diisocyanate, hexahydroxylylene diisocyanate, hexahydrotolylene diisocyanate, and octahydro 1,5-naphthalene diisocyanate are preferred. Alicyclic diisocyanates can be used effectively, particularly when suppressing yellowing of polyurethane elastic yarn. These diisocyanates may be used alone or in combination of two or more.

[0017] The chain extender used in synthesizing polyurethane is preferably at least one of low molecular weight diamines and low molecular weight diols, although those having both a hydroxyl group and an amino group in one molecule, such as ethanolamine, may also be used.

[0018] Examples of preferred low molecular weight diamines include ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, hexamethylenediamine, p-phenylenediamine, p-xylylenediamine, m-xylylenediamine, p,p'-methylenedianiline, 1,3-cyclohexyldiamine, hexahydrometaphenylenediamine, 2-methylpentamethylenediamine, and bis(4-aminophenyl)phosphine oxide. It is preferable to use one or more of these. Ethylenediamine is particularly preferred. By using ethylenediamine, it is possible to easily obtain threads that are excellent in elongation, elastic recovery, and heat resistance. A triamine compound capable of forming a crosslinked structure, such as diethylenetriamine, may be added to these chain extenders to an extent that the effect is not lost.

[0019] Representative examples of low molecular weight diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, bishydroxyethoxybenzene, bishydroxyethylene terephthalate, and 1-methyl-1,2-ethanediol. It is preferable to use one or more of these. Ethylene glycol, 1,3-propanediol, and 1,4-butanediol are particularly preferable. When these are used, the heat resistance of the diol-extended polyurethane is increased, and a stronger thread can be obtained.

[0020] In the present invention, the molecular weight of the polyurethane is preferably in the range of 30,000 to 150,000 in terms of number average molecular weight, from the viewpoint of obtaining polyurethane elastic fibers having high durability and strength. The molecular weight is measured by GPC and converted into polystyrene.

[0021] It is also preferable to use one or more kinds of terminal blocking agents in combination for the polyurethane. Examples of the terminal blocking agent include monoamines such as dimethylamine, diisopropylamine, ethylmethylamine, diethylamine, methylpropylamine, isopropylmethylamine, diisopropylamine, butylmethylamine, isobutylmethylamine, isopentylmethylamine, dibutylamine, and diamylamine, monools such as ethanol, propanol, butanol, isopropanol, allyl alcohol, and cyclopentanol, and monoisocyanates such as phenylisocyanate.

[0022] In the material recycled polyurethane elastic fiber according to the present invention, the polyurethane elastic fiber made of polyurethane having the above basic structure is constituted as a polyurethane elastic fiber using recycled polyurethane elastic fiber as at least a part of the raw material, and in the present invention, in particular, it is constituted as a polyurethane elastic fiber using recovered fabric containing polyurethane fiber as at least a part of the raw material. Here, the material recycled polyurethane elastic fiber includes those recovered from the form of fabric, those recovered from general consumer products such as underwear, and those recovered from repeated recycling. There is no particular limitation on the recovery method, and recycled polyurethane elastic fiber recovered by any method is included.

[0023] In the present invention, material recycling refers to reusing the polyurethane of recovered polyurethane elastic fibers as a raw material for new polyurethane elastic fibers without reducing the molecular weight or converting the polyurethane into monomers.

[0024] The polyurethane elastic fiber of the present invention, in which the recycled polyurethane fiber-containing fabric is used as at least a part of the raw material, has a first feature that the recycled polyurethane fiber as the raw material is recovered by wet specific gravity separation. The wet specific gravity separation of the present invention is a method in which recovered fabric or general consumer products such as underwear are crushed into fine fiber waste using a crusher, and then the fibers are separated by the difference in specific gravity using a heavy liquid to selectively recover the polyurethane fibers.

[0025] The fabric may be composed of polyurethane fibers alone, because wet gravity separation can be used to obtain recycled polyurethane fibers that are a more refined, high-quality raw material.

[0026] In the present invention, the pulverization of a fabric means, for example, in the case of an apparel product, cutting the apparel product itself and subjecting it to wet specific gravity separation.

[0027] The size of the fibers at the time of crushing depends on the size of the openings in the crusher screen. For example, a size of 0.5 mm or less means that the fibers are crushed and discharged through 0.5 mm openings in the crusher screen.

[0028] In addition, the fabric in the present invention mainly refers to a mixed fabric with any fiber, regardless of the content of polyurethane. However, it may be a fabric composed only of polyurethane fibers. Examples of fibers other than polyurethane in the mixed fabric include, for example, representative synthetic fibers such as polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate, polytetramethylene glycol terephthalate, or polyester fibers obtained from polyester resins mainly composed of these structural units and copolymerized with other copolymerization components, and polyethylene terephthalate fibers are preferred, that is, fibers whose main polymer is polyethylene terephthalate or copolymerized polyethylene terephthalate. For example, fibers made of polyethylene terephthalate, polybutylene terephthalate, or ethylene terephthalate units as the main repeating components (specifically, 90 mol% or more of the repeating units), butylene terephthalate units as the main repeating components (specifically, 90 mol% or more of the repeating units), etc. can be preferably used. Among them, fibers made of polyesters containing 90 mol% or more of ethylene terephthalate units as repeating components are preferred, and fibers made of polyesters containing 95 mol% or more of ethylene terephthalate units as repeating components are more preferred. Fibers made of polyesters containing 100 mol% of ethylene terephthalate units as repeating components (i.e., polyethylene terephthalate) are even more preferred. These polyethylene terephthalate-based fibers have good texture and luster, and are easy to care for, such as wrinkle resistance, and are suitable as fiber materials for constituting elastic fabrics. In addition, polyethylene terephthalate-based fibers are suitable when used in combination with polyurethane urea-based elastic yarns, which are preferably used in the present invention, and can be used to make good stretch fabrics. Representative examples of semi-synthetic and natural fibers include cellulose fibers. Examples of the cellulose fibers include natural cellulose fibers such as cotton and hemp, regenerated cellulose fibers such as rayon, semi-synthetic cellulose fibers, and so-called non-designated fibers (lyocell, cupra).

[0029] Furthermore, the number of types of fibers to be mixed is preferably as small as possible, preferably 6 or less, more preferably 3, and most preferably 2. For example, a fabric made of a mixture of two types of fibers, polyurethane elastic fiber and polyester fiber.

[0030] In order to recover polyurethane fibers with a higher yield when performing the above-mentioned wet specific gravity separation, the bath ratio (specific gravity liquid mass: pulverized material mass) is preferably in the range of 20:1 to 500:1. More preferably, it is in the range of 30:1 to 300:1. Even more preferably, it is in the range of 40:1 to 250:1. In addition, a heavy liquid is required when performing wet specific gravity separation, and examples of solutes for preparing the heavy liquid include sodium chloride, calcium chloride, sodium polytungstate, bromoform, tetrabromoethane, and methylene iodide. More preferably, sodium chloride, calcium chloride, and sodium polytungstate, which have a relatively small environmental load, are used from the viewpoint of safety to the body and environmental consideration. In addition, it is preferable that the solvent of the heavy liquid does not dissolve the fibers to be put in as much as possible. More specifically, water-soluble solvents such as water, alcohol, and ketone are also preferable, and a non-water-soluble solvent may be used by suspending it together with a surfactant if it is a small amount.

[0031] In carrying out the above-mentioned wet specific gravity separation, the specific gravity of the heavy liquid used is preferably in the range of 1.10 to 2.40. More preferably, the specific gravity is in the range of 1.10 to 2.00, since the specific gravities of typical fibers to be separated, such as polyurethane and polyester, are in the range of 1.0 to 2.0. Still more preferably, the specific gravity is in the range of 1.20 to 1.40.

[0032] The temperature at which the heavy liquid gravity separation is carried out is preferably in the range of 20°C to 70°C, more preferably in the range of 30°C to 45°C, from the viewpoint of the solubility of the solute.

[0033] To further improve the recovery rate of polyurethane fibers in wet gravity separation, a surfactant may be used as an additive. The surfactant adsorbs to the fiber surface and reduces friction between the fiber surfaces, which eliminates entanglement between fibers and significantly improves the recovery rate of polyurethane. In addition to significantly improving the recovery rate, the surfactant can also reduce the effects of metal soaps that accumulate during recycling. When the surfactant content in the yarn is in the range of 0.003% by mass or more and 0.5% by mass or less, practically preferable properties of polyurethane elastic fiber, particularly preferable wound yarn shape and breaking strength and elongation, are ensured.

[0034] More specifically, examples of the surfactant to be used include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. More preferably, from the viewpoint of easy attachment to each fiber, ionic surfactants that are liquid at room temperature, such as anionic surfactants and cationic surfactants, are desirable.

[0035] Examples of the nonionic surfactant used in the present invention include polyoxyethylene alkyl ether, alkyl monoglyceryl ether, polyoxyethylene alkylamine, fatty acid sorbitan ester, fatty acid diethanolamide, etc. Among these, the so-called hydrophilic part (Hydrophil) of the surfactant is preferably an ether type, for example, at least one of ethylene oxide polymer, propylene oxide polymer, and copolymer of ethylene oxide and propylene oxide. By containing at least one of terminal modified derivatives of ethylene oxide polymer, terminal modified derivatives of propylene oxide polymer, and terminal modified derivatives of copolymer of ethylene oxide and propylene oxide as the nonionic surfactant, it is possible to improve the spinnability while, for example, improving the antibacterial property. The so-called hydrophobic portion of the surfactant is the aforementioned terminal modified structure, and is preferably an alkyl group, a phenyl group, or a styrenated phenyl group. Specific examples of nonionic surfactants include polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene ethylphenol ether, polyoxyethylene propylphenol ether, polyoxyethylene styrenated phenyl ether, and polyoxyethylene sorbitol tetraoleate. More preferred is polyoxyethylene styrenated phenyl ether, including polyoxyethylene oxypropylene tristyrenated phenyl ether, polyoxyethylene oxypropylene distyrenated phenyl ether, polyoxyethylene oxypropylene monostyrenated phenyl ether, polyoxyethylene oxypropylene-2,4,6-tris(α,α-dimethylbenzyl)phenyl ether, polyoxyethylene oxypropylene-2,4-bis(α,α-dimethylbenzyl)phenyl ether, polyoxyethylene oxypropylene-2-mono(α,α-dimethylbenzyl)phenyl ether, polyoxyethylene oxypropylene-4-mono(α,α-dimethylbenzyl)phenyl ether, etc. Most preferred is when the number of moles of these styrene groups added has a distribution and a mixture of these is used.

[0036] Examples of the ionic surfactants used in the present invention include anionic surfactants such as alkylbenzene sulfonates, such as sodium dodecylbenzene sulfonate; dialkyl sulfosuccinates, such as sodium di-2-ethylhexyl sulfosuccinate and sodium diisotridecyl sulfosuccinate; dipolyoxyethylene alkyl ether sulfosuccinates, such as sodium di(polyoxyethylene 2-ethylhexyl ether) sulfosuccinate and sodium di(polyoxyethylene isotridecyl ether) sulfosuccinate; polyoxyalkylene alkyl ether sulfates, such as sodium polyoxyethylene lauryl ether sulfate and sodium polyoxyethylene myristyl ether sulfate; alkyl sulfates, such as sodium lauryl sulfate, higher alcohol sulfate, triethanolamine lauryl sulfate and ammonium lauryl sulfate; and fatty acid salts, such as potassium oleate, sodium oleate and sodium semi-hardened beef tallow fatty acid.

[0037] Examples of cationic surfactants include alkyltrimethylammonium salts such as lauryltrimethylammonium chloride, cetyltrimethylammonium bromide, and stearyltrimethylammonium chloride; and alkyldimethylbenzylammonium salts such as stearyldimethylbenzylammonium chloride, benzalkonium chloride, and lauryldimethylbenzylammonium chloride.

[0038] The concentration of the surfactant in the heavy liquid used in the wet gravity separation is preferably in the range of 0.1% by mass to 50% by mass. More preferably, from the viewpoint of controlling the specific gravity of the heavy liquid, the concentration is in the range of 0.1% by mass to 30% by mass. Even more preferably, the concentration is in the range of 0.1% by mass to 10% by mass. In addition, from the viewpoint of easily controlling the concentration of the surfactant, it is also preferable that the surfactant is in the form of a liquid at room temperature.

[0039] In order to further improve the recovery rate of polyurethane fibers in the wet specific gravity separation, ultrasonic waves may be used during the wet specific gravity separation. As a device for generating ultrasonic waves, an ultrasonic homogenizer, an ultrasonic cleaner, or other device may be used. The shape of the horn for generating ultrasonic waves is not particularly limited. The strength of the ultrasonic waves used is preferably in the range of 20 W to 2000 W, more preferably 50 W to 1200 W, per 1 kg of the heavy liquid of the wet specific gravity separation in which the fabric is immersed. In addition, the frequency is preferably in the range of 20 kHz to 100 kHz.

[0040] In the present invention, the polyurethane fiber recovered by the wet specific gravity separation is preferably washed with water from the viewpoint of suppressing deterioration of the properties of the recycled polyurethane elastic fiber due to adhesion of salt in the heavy liquid. By washing with water, solutes and surfactants in the heavy liquid can be removed, so that changes in the properties of the recycled polyurethane elastic fiber can be prevented. From the viewpoint of solubility in water, the temperature for washing with water is preferably in the range of 20°C to 80°C.

[0041] When the polyurethane elastic fiber of the present invention contains a surfactant, it is preferable that the surfactant content is 0.003% by mass or more and 3.0% by mass or less. The surfactant can reduce the effect of metal soap that accumulates due to recycling, and the surfactant has an appropriate sustained release property and accumulates only slightly while the polyurethane elastic fiber is used. When the surfactant content is within this range, the properties of the polyurethane elastic fiber that are practically preferable, particularly the wound yarn shape and the breaking strength and elongation, are ensured. The surfactant content is more preferably in the range of 0.03% by mass or more and 2.5% by mass or less, and even more preferably in the range of 0.3% by mass or more and 2.0% by mass or less.

[0042] The surfactant content of the recycled polyurethane elastic fiber recovered and used as a raw material is preferably in the range of 0.003% by mass to 0.5% by mass. When the surfactant content of the recycled polyurethane elastic fiber is within this range, the surfactant content contained in the polyurethane elastic fiber finally produced can be easily controlled to the desired surfactant content described above. The surfactant content of the recycled polyurethane elastic fiber is more preferably in the range of 0.03% by mass to 0.25% by mass, and even more preferably in the range of 0.05% by mass to 0.2% by mass.

[0043] In the present invention, when a cationic surfactant, a quaternary ammonium salt, is used in combination, the antibacterial activity differs depending on the chain length of the alkyl group in the ammonium ion, and a quaternary ammonium salt with a strong antibacterial activity is desirable. However, from the viewpoint of suppressing thermal decomposition due to heat exposure during the production of polyurethane elastic yarn, it is preferable to select a chain type such as an alkyl group, such as an alkyl group with a large chain length, i.e., an alkyl group with a large number of carbon atoms. In addition, it is preferable to contain an antibacterial agent from the viewpoint of hygiene, for recycling from old clothes, etc. From this viewpoint, particularly preferred ammonium ions are didecyl dimethyl ammonium ion, oleyl trimethyl ammonium ion, etc. These are usually supplied by inorganic salts such as chlorides, bromides, and iodides, and organic salts such as sulfonates, carboxylates, and phosphates. Among them, sulfonates and carboxylates are preferred from the viewpoint of stability such as discoloration and heat resistance.

[0044] Specific examples of salts having the above structure include didecyldimethylammonium trifluoride methylsulfonate, di-n-decyldimethylammonium trifluoromethanesulfonate, di-n-decyldimethylammonium pentafluoroethanesulfonate, n-hexadecyltrimethylammonium trifluoromethanesulfonate, and benzyldimethylcocoalkylammonium pentafluoroethanesulfonate.

[0045] From the viewpoint of exerting antibacterial properties and maintaining a balance between discoloration and stretch properties, the quaternary ammonium salt-based antibacterial agent is preferably contained in an amount of 0.1% by mass to 5% by mass based on the total mass of the polyurethane elastic yarn.

[0046] When the polyurethane elastic fiber of the present invention contains an antioxidant, the content is preferably 0.002% by mass or more and 5.0% by mass or less. When the content of the antioxidant is within this range, the properties of the polyurethane elastic fiber are practically preferable, and a particularly preferred antioxidant is a hindered phenol compound, such as a phenol compound generally known as an antioxidant.For example, 3,5-di-t-butyl-4-hydroxy-toluene, n-octadecyl-β-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, 1,3,5-trimethyl-2,4,6'-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, calcium (3,5-di-t-butyl-4-hydroxy-benzyl-monoethyl-phosphate), triethylene glycol-bis[3-( 3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 3,9-bis[1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane, tocopherol, 2,2'-ethylidenebis(4,6-di-t-butylphenol), N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2'-oxamidebis[ethyl-3-(3,5-di-t-butyl- 4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, ethylene-1,2-bis(3,3-bis[3-t-butyl-4-hydroxyphenyl]butyrate), ethylene-1,2-bis(3-[3-t-butyl-4-hydroxyphenyl]butyrate), 1,1-bis(2-methyl-5-t-butyl-4-hydroxyphenyl)butane, 1,1,3-tris(2-methyl-5-t-butyl-4-hydroxyphenyl)butane, 1,3,5-tris(3',5'-di-t Also suitable are 1,3,5-tris(3'-t-butyl-4'-hydroxybenzyl)-S-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(3'-t-butyl-4'-hydroxy-5-methylbenzyl)-S-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and furthermore high molecular weight hindered phenol compounds which are known as antioxidants for polyurethane elastic yarns.

[0047] Specific preferred examples of such high molecular weight hindered phenol compounds include addition polymers of divinylbenzene and cresol, addition polymers of dicyclopentadiene and cresol, isobutylene adducts, and polymers of chloromethylstyrene and compounds such as cresol, ethylphenol, and t-butylphenol. Here, divinylbenzene and chloromethylstyrene may be p- or m-. Cresol, ethylphenol, and t-butylphenol may be any of o-, m-, and p-.

[0048] Among them, from the viewpoint of stabilizing the viscosity of the raw material spinning solution of polyurethane yarn, suppressing the volatilization loss during spinning, and obtaining good spinnability, it is preferable to use a compound having a molecular weight of 300 or more. Furthermore, in order to efficiently exhibit a high spinning speed, heat resistance during dyeing, resistance to unsaturated fatty acids, and resistance to heavy metals, it is preferable to use any one of 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], ethylene-1,2-bis(3,3-bis[3-t-butyl-4-hydroxyphenyl]butyrate), and an adduct of divinylbenzene and p-cresol having a repeat number of 6 to 12, or a combination of them. Among them, 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione is particularly preferred. In addition, when triazine compounds are selected as compound (a) and compound (c), a particularly high synergistic effect can be obtained in terms of heat resistance during dyeing. Among them, it is particularly preferred that compound (a) is 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione and compound (c) is 2,4-di(2',4'-dimethylphenyl)-6-(2"-hydroxy-4"-alkoxyphenyl)-1,3,5-triazine.

[0049] Furthermore, the polyurethane elastic fiber of the present invention preferably contains a singly hindered phenol compound from the viewpoint of suppressing deterioration of properties due to recycling, particularly from the viewpoint of suppressing breaking strength / elongation and discoloration. The singly hindered phenol compound is preferably a compound containing at least two singly hindered hydroxyphenyl groups and having a skeleton selected from bisester and alkylidene. Here, it is more preferable that the alkyl group present at the ring position adjacent to the hydroxyl group in the hydroxyphenyl group is a tertiary butyl group, and it is even more preferable that the equivalent weight of the hydroxyl group is 600 or less.

[0050] Furthermore, the phenol compound in the present invention is preferably a singly hindered phenol compound. For example, a singly hindered phenol compound is preferably ethylene-1,2-bis(3,3-bis[3-t-butyl-4-hydroxyphenyl]butyrate) (chemical formula 1 below) having a structure in which a singly hindered hydroxyphenyl group is covalently bonded to a bisester skeleton.

[0051] [ka]

[0052] By including the above-mentioned single hindered phenol compound, the effect of suppressing the deterioration of properties due to recycling can be enhanced. This type of hindered phenol compound is effective in the case of underwear and the like, which is washed and bleached frequently, because it specifically contributes to suppressing the molecular weight of polyurethane constituting the polyurethane elastic fiber. In order to ensure this effect sufficiently and not to adversely affect the physical properties of the fiber, the single hindered phenol compound is preferably included in the polyurethane elastic yarn at 0.15 to 4 mass %. It is more preferable to include 0.5 to 3.5 mass %, and the breaking strength and elongation, composite durability, yellowing resistance, and light resistance in some cases are ensured. The content of the antioxidant is more preferably in the range of 0.2 mass % to 3.0 mass %. It is even more preferable to include 0.5 mass % to 2.0 mass %.

[0053] The content of the antioxidant in the recycled polyurethane elastic fiber recovered and used as a raw material is preferably in the range of 0.1% by mass to 5.0% by mass. When the content of the antioxidant in the recycled polyurethane elastic fiber is within this range, the content of the antioxidant contained in the polyurethane elastic fiber finally produced can be easily controlled to the above-mentioned desired content of the antioxidant. The content of the antioxidant in the recycled polyurethane elastic fiber is more preferably in the range of 0.2% by mass to 3.0% by mass, and even more preferably in the range of 0.5% by mass to 2.0% by mass.

[0054] The antioxidant contained is more specifically a hindered phenol compound having a molecular weight of 1000 or more, and a hindered phenol compound having a molecular weight of 1,000 or more, which is known as an antioxidant for polyurethane elastic yarn, is preferably used. There is no particular restriction other than the relatively high molecular weight of 1,000 or more, and preferred examples of such high molecular weight hindered phenol compounds include addition polymers of divinylbenzene and cresol, addition polymers of dicyclopentadiene and cresol, isobutylene adducts, and polymers of chloromethylstyrene and compounds such as cresol, ethylphenol, and t-butylphenol. Here, divinylbenzene and chloromethylstyrene may be p- or m-. Cresol, ethylphenol, and t-butylphenol may be any of o-, m-, and p-.

[0055] Among them, from the viewpoint of stabilizing the viscosity of the raw material spinning solution for polyurethane yarn and obtaining good spinnability, a polymer hindered phenol compound derived from cresol is preferable. Furthermore, in order to efficiently exhibit a high spinning speed, heat resistance during dyeing, resistance to unsaturated fatty acids, and resistance to heavy metals, it is preferable to contain a certain amount of the high molecular weight hindered phenol compound. However, from the viewpoint of obtaining better basic physical properties as a polyurethane yarn, it is preferable that the amount is not too much.

[0056] When the polyurethane elastic fiber of the present invention contains a tertiary amine compound, the content is preferably 0.2% by mass or more and 5.0% by mass or less. When the content of the tertiary amine compound is within this range, the properties of the polyurethane elastic fiber that are practically preferable, such as spinnability, dyeability, durability, and yellowing resistance, are improved.

[0057] The tertiary amine compound used in the present invention is not particularly limited as long as it has an amino group in its structure. However, from the viewpoint of the chlorine deterioration resistance and yellowing of the polyurethane elastic yarn, it is particularly preferable to use a compound having only a tertiary amino group in the molecule among the primary to tertiary amino groups.

[0058] If the number average molecular weight of the tertiary amine compound is less than 2,000, the water repellency is deteriorated due to the fact that the compound falls off due to rubbing against guides or knitting needles during knitting of polyurethane elastic yarn, or flows out during processing in a bath such as dyeing. Therefore, the number average molecular weight must be 2,000 or more. In consideration of the solubility in the polyurethane spinning dope, the number average molecular weight is preferably in the range of 2,000 to 10,000. More preferably, the number average molecular weight is in the range of 2,000 to 4,000.

[0059] By including a tertiary amine compound, the recyclability, particularly the yellowing prevention performance, of the polyurethane elastic yarn can be improved. In order to obtain this effect sufficiently and not to adversely affect the physical properties of the fiber, the tertiary amine compound is preferably included in an amount of 0.2% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 4.0% by mass or less, based on the fiber mass. The content of the tertiary amine compound is more preferably in the range of 0.5% by mass or more and 3.0% by mass or less. The range of 0.5% by mass or more and 2.0% by mass or less is even more preferably.

[0060] More specifically, the tertiary amine compound contained therein may be a linear polymeric compound having a number average molecular weight of 2000 or more obtained by reacting t-butyldiethanolamine with methylene-bis-(4-cyclohexylisocyanate), polyethyleneimine, or a high molecular weight compound having a branched structure containing a primary amino group, a secondary amino group, and a tertiary amino group in the molecular skeleton.

[0061] As a typical example, in the case of recycling in which non-standard fibers for industrial products due to some defect immediately after production, i.e., waste yarn, are blended at a high concentration, if this is repeated, the breaking strength and elongation decrease significantly. In order to avoid such a decrease in properties, it is effective to blend a polyurethane source containing a high molecular weight tertiary amine compound, its decomposition product, a high molecular weight antioxidant, and a low content of its decomposition product, as described above, to reduce the concentration of additives contained. As an index, it is preferable to blend a polyurethane having a number average molecular weight based on gel permeation chromatography (GPC) of 20,000 to 120,000 and no peak or shoulder in the detection intensity curve in the region of the molecular weight based on GPC of 30,000 or less. In consideration of the breaking strength and elongation of polyurethane elastic fiber, the number average molecular weight is preferably in the range of 30,000 to 100,000. More preferably, it is in the range of 40,000 to 80,000. The detection intensity curve is a differential molecular weight distribution curve (the horizontal axis is molecular weight, and the vertical axis is the value obtained by differentiating the concentration fraction by the logarithm of the molecular weight), and the shoulder is the shoulder peak.

[0062] In the present invention, the molecular weight of the polyurethane elastic fiber using the recycled polyurethane elastic fiber as a part of the raw material may be in the range of 10,000 to 50,000 in terms of number average molecular weight when a tertiary amine compound having a number average molecular weight in the range of 2,000 to 10,000 or a preferably used antioxidant having a molecular weight of 1,000 or more is blended. The molecular weight is measured by GPC and converted into polystyrene.

[0063] Furthermore, the absorbance of the carbonyl stretching vibration of the urethane bond based on the infrared spectrum (IR) of the recycled polyurethane elastic fiber, AνC=O 1730cm -1 and AνC=O 1710cm -1 About AνC=O 1730cm -1 AνC=O 1710cm -1 Ratio, i.e., AνC=O 1730 cm -1 / AνC=O 1710 cm -1 It is more preferable to compound a polyurethane having a value of 1.05 or more and 1.50 or less.

[0064] Such a source of recycled polyurethane raw material is more preferable when the application is achieved in clothing products that are washed frequently. In many cases, this can be achieved by using used underwear, i.e., undergarments, collected from the city. The reason for this is that they are repeatedly washed with anionic surfactants, which makes them suitable for use as raw materials for recycled polyurethane elastic fibers. EXAMPLES

[0065] (Examples 1 to 17, Comparative Examples 1 to 8) The production and evaluation of polyurethane elastic fibers obtained by recovering polyurethane from recovered fabrics and adding recycled polyurethane fibers will be described below for Examples 1 to 17 and Comparative Examples 1 to 8 shown in Table 1.

[0066] <Production of dry-spun polyurethane elastic fibers> In Comparative Example 1, a N,N'-dimethylacetamide (hereinafter abbreviated as DMAc) solution (35% by mass) of polyurethane composed of tetramethylene ether glycol having a molecular weight of 2,000, bis-(p-isocyanatephenyl)-methane and ethylenediamine was polymerized to obtain a polymer solution PUU1.

[0067] Next, a 1:1 (mass ratio) mixture of polyurethane (DuPont's "Methachlor" (registered trademark) 2462) produced by the reaction of t-butyldiethanolamine with methylene-bis-(4-cyclohexylisocyanate) and a condensation polymer of p-cresol and divinylbenzene (DuPont's "Methachlor" (registered trademark) 2390) was used as an antioxidant, and a DMAc solution (35 mass%) of this mixture was prepared and used as additive solution (B).

[0068] The above solution PUU1, additive solution (B), and ethylenediamine (C) were uniformly mixed at 99 mass %, 1.0 mass %, and 0.1 mass %, respectively, to obtain a spinning solution (D).

[0069] The spinning solution thus obtained was dry-spun at a dry nitrogen temperature of 300°C or higher so that the DMAc in the spinning solution and the floating ethylenediamine were 1 / 100 or less of the spinning solution content. At this time, the speed ratio of the godet roller and the winder was set to 1:1.20, and a multifilament polyurethane elastic fiber of 22 dtex / 3fil was spun. A treatment agent (oil agent) described later was applied by a preliminary winding oiling roller, and the fiber was wound using a surface drive winder at a winding speed of 600 m / min on a cylindrical paper tube of 58 mm in length through a traverse guide that gave a winding width of 38 mm. 500 g of wound yarn was obtained as a dry-spun polyurethane elastic fiber. The obtained polyurethane elastic fiber was a fused yarn in which three filaments were fused together.

[0070] In Example 1, a knitted fabric (shirt-like underwear sewn from a circular knitted fabric that had been repeatedly washed) with a PU (polyurethane) content of 10% was used as a raw material, and the fabric was pulverized to a size of 0.5 mm using a three-blade helical cutting type pulverizer. Then, a heavy liquid with a specific gravity of 1.3 was prepared using an aqueous calcium chloride solution, and the pulverized material was added thereto at a bath ratio (heavy liquid mass: fabric mass) of 200:1 and stirred for 5 minutes. The aqueous solution was then left to stand for 6 hours, and after confirming that the fibers had separated into layers, polyurethane fibers were recovered. The recovered polyurethane fibers were washed with water at 60°C and air-dried. The recovered polyurethane fibers were then dissolved in DMAc to obtain a polyurethane recovery solution, which was then added to the spinning solution (D) so that the recycled polymer content in the yarn was 20%. This was used as a spinning stock solution, and spun in the same manner as in Comparative Example 1.

[0071] In Example 2, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, 1% by mass of an ionic surfactant (didecyldimethylammonium sulfonate) was added to the heavy liquid in the wet specific gravity separation step.

[0072] In Examples 3 to 10, polyurethane elastic fibers as shown in Table 1 were obtained in the same manner as in Example 1.

[0073] In Example 11, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, in the wet specific gravity separation step, after stirring the heavy liquid and before leaving it to stand, ultrasonic waves with an ultrasonic output of 100 W and an ultrasonic frequency of 20 kHz were irradiated for 5 minutes using an ultrasonic generator.

[0074] In Examples 12 to 15, polyurethane elastic fibers as shown in Table 1 were obtained in the same manner as in Example 1.

[0075] In Example 16, polyurethane elastic fiber was obtained as shown in Table 1 in the same manner as in Example 1. However, the polyurethane elastic fiber was obtained so that the yarn content of a 1:1 (mass ratio) mixture of polyurethane ("Methachlor" (registered trademark) 2462 manufactured by DuPont) produced by the reaction of t-butyldiethanolamine with methylene-bis-(4-cyclohexylisocyanate) and a condensation polymer of p-cresol and divinylbenzene ("Methachlor" (registered trademark) 2390 manufactured by DuPont) as an antioxidant was 6%.

[0076] In Example 17, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, the heavy liquid in the wet specific gravity separation process was prepared using sodium polytungstate, which is expensive but uneconomical, as the solute.

[0077] In Comparative Example 2, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, the size of the pulverized material was 12 mm.

[0078] In Comparative Example 3, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, the size of the pulverized material was 2.5 mm.

[0079] In Comparative Example 4, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, the specific gravity in the heavy liquid in the wet specific gravity separation step was 1.05.

[0080] In Comparative Example 5, polyurethane elastic fibers were obtained as shown in Table 1 in the same manner as in Example 1. However, the specific gravity in the heavy liquid in the wet specific gravity separation step was 2.45.

[0081] In Comparative Examples 6 to 8, polyurethane elastic fibers as shown in Table 1 were obtained.

[0082] In Table 1, the content is a value relative to 100 parts by mass of the polymer solid content in the spinning dope. In Table 1, the recycled polymer is a polymer having a number average molecular weight of 63,000 based on GPC, no peak or shoulder in the detection intensity curve in the region of the molecular weight of 30,000 or less based on GPC, and an AνC=O of 1730 cm based on IR. -1 / AνC=O 1710 cm -1 The polyurethane fiber used is recycled, with a viscosity coefficient of 1.48, and is made from recycled polyurethane fibers extracted from used circular knitted underwear that has been washed frequently.

[0083] Next, the dry-spun polyurethane elastic fiber obtained above (hereinafter, sample yarn) was subjected to the following evaluations.

[0084] <Elongation at break, strength at break, permanent set rate> The breaking elongation, breaking strength, permanent set rate and stress relaxation rate were measured by subjecting the polyurethane elastic yarn to a tensile test using an Instron 5564 tensile tester, and each property was evaluated according to the following criteria. A sample with a length of 5 cm (L1) was stretched 300% five times at a tensile speed of 50 cm / min. The stress at 300% stretch was defined as (G1). The length of the sample was then held at 300% stretch for 30 seconds. The stress after 30 seconds was defined as (G2). The sample was then restored to its original length, and the length of the sample when the stress became 0 was defined as (L2). This cycle of 300% stretching, holding, and recovery was repeated until the sample broke at the sixth stretch. The stress at break was defined as (G3), and the length of the sample at break was defined as (L3). The above properties are calculated using the following formulas below. Breaking strength (cN) = (G3) 20 or more: ◎, 17~20: 〇, 14~17: △, 14 or less: × Breaking elongation (%) = 100 × ((L3)-(L1)) / (L1) 480 or more: ◎, 460~480: 〇, 430~460: △, 430 or less: × Permanent distortion rate (%)=100×((L2)-(L1)) / (L1) 20 or less: ◎, 20~22: 〇, 22~24: △, 24 or more: ×

[0085] <Amount of water used> The amount of water used to recover polyurethane fiber by wet specific gravity separation in the present invention was evaluated. The main amounts used include the amount of aqueous solution used in wet specific gravity separation and the amount used for washing. The amount of water affects the size of the equipment, so it is desirable to keep it as small as possible. The amount of water used to recover 1 kg of recovered polyurethane fiber was determined as follows. 100L or less: 〇, 100L~250L: △, 250L or more: ×

[0086] The molecular weight measurement by GPC was carried out under the following conditions. Column: Showa Denko SHODEX KF-806M (2 pieces) Solvent: N,N-dimethylacetamide 1ml / min Temperature: 40℃ Detector: Differential refractometer (RI detector)

[0087] The IR spectrum was measured by the KBr pellet method using an FT / IR7300 infrared spectrometer manufactured by JASCO Corporation.

[0088] In Table 1, the overall evaluations of ◎, ○, and △ were considered to be pass, and × was considered to be fail. The weighting in the overall evaluation was mainly based on the PU recovery rate (%) (40%), elastic fiber properties (40%), and the amount of water used (20%).

[0089] [Table 1]

Claims

1. A material recycled polyurethane elastic fiber made from recovered fabric containing polyurethane fibers, in which components separated by wet specific gravity separation of the fabric are used as at least part of the raw material.

2. 2. The polyurethane elastic fiber according to claim 1, wherein the fabric is pulverized to a size of 0.005 mm or more and 0.5 mm or less and then subjected to the wet gravity separation.

3. The polyurethane elastic fiber according to claim 1 , wherein a surfactant is used in the wet gravity separation.

4. The polyurethane elastic fiber according to claim 3 , wherein the surfactant is an ionic surfactant that is liquid at room temperature.

5. 4. The polyurethane elastic fiber according to claim 3, wherein the concentration of the surfactant is in the range of 0.1% by mass to 50% by mass.

6. The polyurethane elastic fiber according to claim 1 , wherein ultrasonic waves are used for the wet specific gravity separation.

7. 7. The polyurethane elastic fiber according to claim 6, wherein the ultrasonic intensity is in the range of 20 W or more and 2000 W or less per kg of heavy liquid for wet gravity separation in which the fabric is immersed, and the ultrasonic frequency is in the range of 20 kHz or more and 100 kHz or less.

8. 2. The polyurethane elastic fiber according to claim 1, wherein the specific gravity of the heavy liquid in the wet gravity separation is in the range of 1.10 to 2.

40.

9. 2. The polyurethane elastic fiber according to claim 1, wherein the bath ratio (mass of heavy liquid:mass of fabric) in the wet gravity separation is in the range of 20:1 to 500:

1.

10. 2. The polyurethane elastic fiber according to claim 1, wherein the heavy liquid in the wet gravity separation is an aqueous calcium chloride solution.

11. 2. The polyurethane elastic fiber according to claim 1, wherein the polyurethane contained in the fabric has a number average molecular weight of 20,000 or more and 120,000 or less based on gel permeation chromatography (GPC), and the detection intensity curve has no peak or shoulder in the region where the molecular weight based on GPC is 30,000 or less.

12. AνC=O 1730 based on the infrared spectrum (IR) of the polyurethane fiber contained in the fabric -1 / AνC=O 1710 -1 2. The polyurethane elastic fiber according to claim 1, wherein the tensile strength is 1.05 or more and 1.50 or less.

13. The polyurethane elastic fiber according to any one of claims 1 to 12, wherein the fabric is used for clothing products that are washed frequently.

14. The polyurethane elastic fiber according to claim 13, wherein the fabric is used for underwear.

15. A method for producing material recycled polyurethane elastic fibers using recovered fabric containing polyurethane fibers, in which components separated by wet gravity separation of the fabric are used as at least part of the raw materials.

16. The method for producing polyurethane elastic fibers according to claim 15, wherein the fabric is pulverized to a size of 0.005 mm or more and 0.5 mm or less and then subjected to the wet gravity separation.

17. The method for producing recycled polyurethane elastic fibers according to claim 15, wherein a surfactant is used in the wet gravity separation.

18. The method for producing polyurethane elastic fibers according to claim 17, wherein the surfactant is an ionic surfactant that is liquid at room temperature.

19. The method for producing polyurethane elastic fibers according to claim 17, wherein the concentration of the surfactant is in the range of 0.1% by mass or more and 50% by mass or less.

20. The method for producing polyurethane elastic fibers according to claim 15, wherein ultrasonic waves are used in the wet specific gravity separation.

21. 21. The method for producing polyurethane elastic fibers according to claim 20, wherein the ultrasonic intensity is in the range of 20 W or more and 2000 W or less per kg of heavy liquid for wet gravity separation in which the fabric is immersed, and the ultrasonic frequency is in the range of 20 kHz or more and 100 kHz or less.

22. The method for producing polyurethane elastic fibers according to claim 15, wherein the specific gravity of the heavy liquid in the wet gravity separation is in the range of 1.10 to 2.

40.

23. The method for producing polyurethane elastic fibers according to claim 15, wherein the bath ratio (mass of heavy liquid:mass of fabric) in the wet gravity separation is 20:1 to 500:

1.

24. The method for producing polyurethane elastic fibers according to any one of claims 15 to 23, wherein the heavy liquid in the wet gravity separation is an aqueous calcium chloride solution.