Thermoplastic polyurethane elastic fiber

Abstract

The present invention addresses the problem of providing a thermoplastic polyurethane elastic fiber having excellent NOx gas-induced yellowing resistance and heat resistance. The present invention relates to a thermoplastic polyurethane elastic fiber characterized by comprising 0.05 wt% to 5.00 wt% of at least one metal compound selected from the group consisting of a metal hydroxide, a metal carbonate, and a metal oxide, wherein the metal compound includes an alkali metal or an alkaline earth metal.

Description

[Technical Field]

[0001] The present invention relates to thermoplastic polyurethane elastic fibers. [Background technology]

[0002] Polyurethane elastic fibers are generally used in clothing and sanitary materials. They are required to be resistant to yellowing and heat. Patent Document 1 below discloses that polyurethane elastic fibers obtained by adding a hindered amine compound and dry spinning the fibers can have improved resistance to yellowing due to NOx gases. Patent Document 2 below discloses that the NOx gas yellowing resistance of polyurethane resins can be improved by using a phenolic antioxidant, a hindered amine light stabilizer, a polyester compound, and a benzotriazole light stabilizer in combination. Patent Document 3 listed below discloses that the heat resistance of polyurethane elastic fibers can be improved by melt-spinning a thermoplastic polyurethane resin obtained by reacting a prepolymer having isocyanate groups at both ends, which is obtained by reacting a polyol with a diisocyanate, and a prepolymer having hydroxyl groups at both ends, which is obtained by reacting a polyol with a diisocyanate and a low-molecular-weight diol. Patent Document 4 below discloses that the heat resistance of polyurethane elastic fibers can be improved by using an oil agent made of polydimethylsiloxane in combination with a phenolic antioxidant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-342448 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-19062 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-307409 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-20521 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the cited documents 1 to 4 do not disclose thermoplastic polyurethane elastic fibers that are resistant to NOx gas yellowing and heat resistance.

[0005] In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a thermoplastic polyurethane elastic fiber having excellent resistance to yellowing by NOx gases and heat resistance. [Means for solving the problem]

[0006] As a result of extensive research and experimentation to solve the above-mentioned problems, the inventors of the present application unexpectedly discovered that the above-mentioned problems can be solved by a thermoplastic polyurethane elastic fiber containing at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt% to 5.00 wt%, and characterized in that the metal compound contains an alkali metal or an alkaline earth metal, and thus completed the present invention.

[0007] That is, the present invention is as follows. [1] A thermoplastic polyurethane elastic fiber comprising at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt% to 5.00 wt%, and wherein the metal compound contains an alkali metal or alkaline earth metal. [2] The thermoplastic polyurethane elastic fiber according to [1], wherein the metal compound contains an alkaline earth metal. [3] The thermoplastic polyurethane elastic fiber according to [2] above, wherein the alkaline earth metal is magnesium. [4] The thermoplastic polyurethane elastic fiber according to any one of [1] to [3] above, wherein the metal compound is magnesium hydroxide. [5] The thermoplastic polyurethane elastic fiber according to any one of [1] to [4], wherein the polyurethane constituting the thermoplastic polyurethane elastic fiber is a polyurethane polymerized from a polymer polyol, a diisocyanate, and a chain extender comprising an active hydrogen compound. [6] The thermoplastic polyurethane elastic fiber according to [5], wherein the chain extender is a diol having a molecular weight of 60 or more and 120 or less. [7] The thermoplastic polyurethane elastic fiber according to [5] or [6], wherein the diisocyanate is 4,4'-diphenylmethane diisocyanate (MDI). [8] The thermoplastic polyurethane elastic fiber according to any one of [5] to [7], wherein the proportion of hard segments consisting of the chain extender and the diisocyanate (Mh fraction) is 20% or more and 40% or less. [9] The thermoplastic polyurethane elastic fiber according to any one of [5] to [8], wherein the total number of moles of the chain extender and the polymer polyol is 1.001 to 1.100 times the number of moles of the diisocyanate.

[10] The thermoplastic polyurethane elastic fiber according to any one of [1] to [9] above, having a total fineness of 160 dtex or more and 2000 dtex or less.

[11] The thermoplastic polyurethane elastic fiber according to any one of [1] to

[10] above, which is a multifilament fiber.

[12] The thermoplastic polyurethane elastic fiber according to any one of [1] to

[11] above, wherein the coefficient of variation of fineness unevenness in the length direction of the fiber is 3.0% or more and 10.0% or less.

[13] The thermoplastic polyurethane elastic fiber according to any one of [1] to

[12] above, wherein the difference between the maximum fineness and the minimum fineness in the length direction of the fiber is 10 dtex or more and 150 dtex or less.

[14] The thermoplastic polyurethane elastic fiber according to any one of [1] to

[13] , wherein the flow initiation temperature of the thermoplastic polyurethane elastic fiber measured with a flow tester is 150°C or higher and 220°C or lower. [Effects of the Invention]

[0008] The thermoplastic polyurethane elastic fiber according to one embodiment of the present invention has the above-described structure, and is therefore a thermoplastic polyurethane elastic fiber having excellent resistance to NOx gas yellowing and heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The present invention is not limited to the following embodiment, and can be modified and implemented within the scope of the gist thereof.

[0010] [Metal compounds] The thermoplastic polyurethane elastic fiber of this embodiment is characterized by containing at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt% to 5.00 wt%, preferably 0.10 wt% to 1.00 wt%, and more preferably 0.30 wt% to 0.50 wt%. By containing at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt% to 5.00 wt%, excellent resistance to NOx gas yellowing and heat resistance are achieved. The reason why the inclusion of at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt% to 5.00 wt% improves NOx gas yellowing resistance and heat resistance is not yet clear, but the inventors speculate as follows. By incorporating at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides at 0.05 wt% or more, effective resistance to NOx gas yellowing is achieved, and by incorporating at most 5.00 wt%, the polymer ratio in the polyurethane elastic fiber does not decrease too much, allowing heat resistance to be maintained.

[0011] The metal element of the metal compound preferably contains an alkali metal or an alkaline earth metal. It is more preferable that the metal compound contains an alkaline earth metal. The alkaline earth metal is preferably calcium or magnesium, and more preferably magnesium. If the metal element is an alkali metal or alkaline earth metal, the effect of improving NOx gas yellowing resistance is further enhanced. The reason why NOx gas yellowing resistance can be improved by using an alkaline earth metal as the metal element of the metal compound is not yet clear, but the inventors speculate as follows: Because alkaline earth metals have a large charge, they easily adsorb NOx gas, suppressing the attack of NOx gas on the thermoplastic polyurethane elastic fiber, thereby improving the NOx gas yellowing resistance of the thermoplastic polyurethane elastic fiber.

[0012] It is particularly preferable that the metal compound be magnesium hydroxide, since this further enhances the effect of improving resistance to NOx gas yellowing. The reason why using magnesium hydroxide as the metal compound can improve resistance to NOx gas yellowing is not yet clear, but the inventors speculate as follows: Magnesium hydroxide is a solid base with high basic strength and easily reacts with acidic NOx gas, which is why it is speculated that this improves resistance to NOx gas yellowing.

[0013] [Thermoplastic polyurethane] In this embodiment, the thermoplastic polyurethane constituting the thermoplastic polyurethane elastic fiber is not particularly limited as long as it has a structure polymerized from, for example, diisocyanate, polymer polyol, diol, diamine, etc. and has thermoplasticity. Furthermore, the polymerization method is also not particularly limited. The thermoplastic polyurethane may be, for example, polyurethane polymerized from diisocyanate, polymer polyol, and low-molecular-weight diamine as a chain extender composed of an active hydrogen compound, or polyurethane polymerized from diisocyanate, polymer polyol, and low-molecular-weight diol as a chain extender composed of an active hydrogen compound (hereinafter also referred to as "polyurethane urethane"). Glycols and isocyanates with three or more functionalities may be used as long as they do not interfere with the desired effects of the present invention. In this specification, "thermoplastic" means that the material can be melted by heating below its decomposition temperature, exhibits plastic flow while in the molten state, and has the reversible property of solidifying upon cooling. Generally, polyurethane resins begin to decompose at temperatures above 230°C.

[0014] [Polymer polyol] Examples of polymer polyols include, but are not limited to, polyether-based diols, polyester-based diols, polycarbonate-based diols, etc. From the viewpoint of hydrolysis resistance, the polymer polyol is preferably a polyether-based polyol.

[0015] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, copolymer diols that are copolymers of tetrahydrofuran (THF) and neopentyl glycol, and copolymer diols that are copolymers of THF and 3-methyltetrahydrofuran. These polyether polyols may be used alone or in combination of two or more. Furthermore, from the viewpoint of easily obtaining elastic fibers that are excellent in elongation, stretch recovery, and heat resistance, it is preferable that the number-average molecular weight of the polymer diol be 1,000 or more and 8,000 or less. From the viewpoint of light embrittlement resistance, it is preferable that the polyether polyol be polytetramethylene ether glycol, copolymer diols that are copolymers of THF and neopentyl glycol, or polyols that are blends of these.

[0016] [Diisocyanate] Examples of diisocyanates include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates. Examples of aromatic diisocyanates include, but are not limited to, diphenylmethane diisocyanate (hereinafter also referred to as "MDI"), tolylene diisocyanate, 1,4-diisocyanate benzene, xylylene diisocyanate, and 2,6-naphthalene diisocyanate. Examples of alicyclic diisocyanates and aliphatic diisocyanates include methylenebis(cyclohexylisocyanate) (hereinafter also referred to as "H12MDI"), isophorone diisocyanate, methylcyclohexane 2,4-diisocyanate, methylcyclohexane 2,6-diisocyanate, cyclohexane 1,4-diisocyanate, hexahydroxylylene diisocyanate, hexahydrotolylene diisocyanate, and octahydro-1,5-naphthalene diisocyanate. These diisocyanates may be used alone or in combination of two or more. In particular, from the viewpoint of the stretch recovery of elastic fibers, the diisocyanate is preferably an aromatic diisocyanate, and more preferably MDI. Furthermore, by using MDI, a cyclic structure is introduced into the polymer skeleton, thereby increasing rigidity and improving heat resistance.

[0017] [Chain extender] The chain extender consisting of an active hydrogen compound is preferably at least one selected from the group consisting of low molecular weight diamines and low molecular weight diols. The chain extender may also be one having both a hydroxyl group and an amino group in the molecule, such as ethanolamine. From the viewpoint of obtaining a thermoplastic polyurethane suitable for melt spinning, the active hydrogen compound is preferably a low molecular weight diol.

[0018] Examples of low-molecular-weight diamines as chain extenders comprising active hydrogen compounds include hydrazine, ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 2-methyl-1,5-pentanediamine, 1,2-diaminobutane, 1,3-diaminobutane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,2-dimethyl-1,3-diaminopropane, 1,3-diamino-2,2-dimethylbutane, 2,4-diamino-1-methylcyclohexane, 1,3-pentanediamine, 1,3-cyclohexanediamine, bis(4-aminophenyl)phosphine oxide, hexamethylenediamine, 1,3-cyclohexyldiamine, hexahydrometaphenylenediamine, 2-methylpentamethylenediamine, and bis(4-aminophenyl)phosphine oxide.

[0019] Examples of low molecular weight diols as chain extenders made of active hydrogen compounds include ethylene glycol, 1,3-propanediol, 1,4-butanediol, bishydroxyethoxybenzene, bishydroxyethylene terephthalate, 1-methyl-1,2-ethanediol, 1,6-hexanediol, 1,8-octanediol, etc. These low molecular weight diols may be used alone or in combination of two or more.

[0020] From the viewpoint of improving the stretch recovery property of the elastic fiber and the heat resistance and resistance to NOx gas yellowing, the chain extender is preferably a diol having a molecular weight of 60 or more and 120 or less. The active hydrogen compound which is a diol having a molecular weight of 60 or more and 120 or less is preferably ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, or 1,8-octanediol, more preferably 1,3-propanediol, 1,4-butanediol, or 1,6-hexanediol, and most preferably 1,4-butanediol.

[0021] [Method for synthesizing thermoplastic polyurethane] Thermoplastic polyurethane can be obtained using a known polyurethane reaction technique, and may be produced by either a one-shot method or a prepolymer method. In the case of the prepolymer method, a polymer polyol and a diisocyanate are added to a reaction tank equipped with a nitrogen purge, a hot water jacket, and a stirrer in a molar ratio of preferably 1.0:1.8 to 3.0, more preferably 1.0:1.8 to 3.0. By adding them in a ratio of 1.0:2.0-2.5 and reacting them, the prepolymer with isocyanate groups at both ends is formed. A polymer is obtained. Next, a chain extender is added to this prepolymer having isocyanate groups at both ends, and a chain extension reaction is carried out. Thereafter, solid-state polymerization is carried out to obtain a polyurethane of a predetermined molecular weight. After uniformly mixing the prepolymer and the chain extender, a polymer may be obtained continuously or semi-continuously using a cylindrical pipe or twin-screw extruder, and then solid-state polymerization may be carried out.

[0022] It is preferable that the total number of moles of the chain extender and polymer polyol be 1.001 to 1.100 times the number of moles of the diisocyanate, since this allows both heat resistance and resistance to NOx gas yellowing to be achieved. The reason why NOx gas yellowing resistance and heat resistance can be improved by having the total number of moles of the chain extender and polymer polyol be 1.001 to 1.100 times the number of moles of the diisocyanate is not yet clear, but the inventors speculate as follows: If the total number of moles of the chain extender and polymer polyol is 1.001 or more times the number of moles of the diisocyanate, the amount of diisocyanate-derived structures in the molecule that easily adsorb NOx gas can be reduced, thereby improving NOx gas yellowing resistance. On the other hand, if the total number of moles of the chain extender and polymer polyol is 1.100 times or less the number of moles of the diisocyanate, ligand exchange between the hydroxyl groups of the thermoplastic polyurethane and the metal salt is less likely to occur, and the metal salt is more likely to exhibit its NOx gas yellowing resistance, thereby improving NOx gas yellowing resistance.Furthermore, if the total number of moles of the chain extender and polymer polyol is 1.001 times or more the number of moles of the diisocyanate, the molecular weight of the thermoplastic polyurethane is more likely to increase, thereby improving heat resistance.

[0023] [Method of manufacturing thermoplastic polyurethane elastic fiber] The spinning method is not particularly limited as long as the desired physical properties can be obtained. Examples include a method in which thermoplastic polyurethane chips are fed into an extruder, heated, and melt-spinned, a method in which the chips are melted and then mixed with a polyisocyanate compound for spinning, and a method in which a reaction product of a prepolymer having isocyanate groups at both ends and an active hydrogen compound is added to a prepolymer having isocyanate groups at both ends, and the reaction is continuously spun without going through chipping.

[0024] The polyurethane fed into the extruder is metered by a metering pump and introduced into the spinning head. If necessary, foreign matter is removed by filtration using a wire mesh or glass beads in the spinning head, and the polyurethane is then discharged from the spinneret, air-cooled in a cold air chamber, treated with a treatment agent, and wound up on a godet roll.

[0025] During the spinning process, the die temperature, cold air speed, cold air temperature, focusing position, and spinning speed are adjusted to precisely control the fiber temperature profile and spinning tension. The die temperature is preferably 180°C to 220°C, more preferably 200°C to 210°C. A typical melt spinning cooling method, such as applying cold air directly below the spinneret perpendicular to the yarn running direction, is used. The cold air speed is preferably 0.2 m / s to 2.0 m / s, more preferably 0.5 m / s to 1.2 m / s, and the cold air temperature is preferably 5°C to 20°C, more preferably 7°C to 15°C. One method for bundling multifilaments is to install a false twister between the spinneret and the godet roll, and by varying the strength of the twist, propagate the twist from below, converge the filaments, and control the height of the convergence point. Conventional methods can be used for false twisting, such as air false twisting using an air nozzle or a ring false twister in contact with a rotating ring.

[0026] The method for incorporating at least one metal compound selected from a metal hydroxide, a metal carbonate, and a metal oxide in an amount of 0.05 wt % to 5.00 wt % in the thermoplastic polyurethane elastic fiber of this embodiment is not particularly limited, but examples include adding the compound when raw materials are charged before the prepolymer reaction between a polymer polyol and a diisocyanate, adding the compound during the chain extension reaction between a prepolymer and an active hydrogen compound, and adding a masterbatch containing the metal compound during spinning.

[0027] The thermoplastic polyurethane elastic fiber of the present embodiment may contain polymers other than polyurethane, or additives such as antioxidants, light fasteners, ultraviolet absorbers, gas discoloration inhibitors, dyes, activators, delustering agents, pigments, lubricants, etc., to the extent that the desired effects of the present invention are not lost.

[0028] The thermoplastic polyurethane elastic fiber of this embodiment may contain a treatment agent such as an oil agent from the viewpoint of reelability, processability, etc. Examples of the treatment agent include, but are not limited to, silicone-based oils such as dimethyl silicone, mineral oils, and combinations thereof. The method for applying the treatment agent is not particularly limited, and examples include application using an oiling roller or the like.

[0029] In the thermoplastic polyurethane elastic fiber of this embodiment, the proportion of hard segments composed of a chain extender and a diisocyanate (hereinafter referred to as the Mh fraction) is preferably 20% to 40%, more preferably 20% to 35%, and even more preferably 22% to 30%. An Mh fraction of 20% to 40% can improve both heat resistance and NOx gas yellowing resistance. The reason why an Mh fraction of 20% to 40% can improve NOx gas yellowing resistance and heat resistance is not yet clear, but the inventors speculate as follows: An Mh fraction of 20% or more increases the number of hydrogen bonds between urethane bonds, improving heat resistance, and also increases the presence of metal salts around the hard segments, improving NOx gas yellowing resistance. On the other hand, an Mh fraction of 40% or less improves NOx gas yellowing resistance when the diisocyanate contains an aromatic ring, reducing the amount of aromatic rings that yellow upon NOx gas adsorption. A detailed calculation method for the Mh fraction will be described later.

[0030] The total fineness of the polyurethane elastic fiber of this embodiment is preferably 160 dtex or more and 2000 dtex or less, more preferably 300 dtex or more and 1500 dtex or less, and even more preferably 600 dtex or more and 1000 dtex or less.

[0031] The polyurethane elastic fiber of this embodiment may be either a monofilament or a multifilament, but is preferably a multifilament. When the polyurethane elastic fiber is a multifilament, the number of single threads is preferably 14 or more and 140 or less.

[0032] The coefficient of variation of fineness unevenness in the length direction of the thermoplastic polyurethane elastic fiber of this embodiment is preferably 3.0% to 10.0%, more preferably 3.0% to 9.5%, and even more preferably 3.5% to 9.0%. A coefficient of variation of fineness unevenness of 3% to 10% can improve both NOx gas yellowing resistance and heat resistance. The reason why a coefficient of variation of fineness unevenness of 3.0% to 10.0% improves NOx gas yellowing resistance and heat resistance is not yet clear, but the inventors speculate as follows. A coefficient of variation of fineness unevenness of 3.0% or more facilitates diffuse reflection of light on the fiber surface, making the fiber appear opaque and making yellowing inside the fiber less visible, and the yellowing appears faint. A coefficient of variation of fineness unevenness of 10.0% or less can suppress yarn breakage due to heat exposure at fine fiber portions, improving heat resistance. The method for controlling the coefficient of variation of fineness unevenness is not particularly limited as long as the desired physical properties can be obtained. Examples of the method include a method of enlarging the diameter of the spinneret used in melt spinning to generate draw resonance, a method of increasing the discharge rate to generate sharkskin or melt fracture, and a method of changing the cooling intensity during the spinning process to cause yarn sway.

[0033] The difference between the maximum fineness and the minimum fineness in the length direction of the thermoplastic polyurethane elastic fiber of this embodiment is preferably 10 dtex to 150 dtex, more preferably 15 dtex to 100 dtex, and even more preferably 20 dtex to 80 dtex. When the difference between the maximum fineness and the minimum fineness is 10 dtex to 150 dtex, both NOx gas yellowing resistance and heat resistance can be improved. The reason why the difference between the maximum fineness and the minimum fineness is 10 dtex to 150 dtex and improves NOx gas yellowing resistance and heat resistance is not yet clear, but the inventors speculate as follows. When the difference between the maximum fineness and the minimum fineness is 10 dtex or more, light is easily diffused on the fiber surface, making the fiber appear opaque, making yellowing inside the fiber less visible, and the yellowing appears faint. When the difference between the maximum fineness and the minimum fineness is 150 dtex or less, yarn breakage due to heat exposure at thin fineness points can be suppressed, improving heat resistance. The method for controlling the difference in fineness is not particularly limited as long as the desired physical properties can be obtained, and examples thereof include a method of enlarging the diameter of the spinneret used in melt spinning to generate draw resonance, a method of increasing the discharge rate to generate sharkskin or melt fracture, and a method of changing the cooling intensity during the spinning process to cause yarn swaying.

[0034] From the viewpoint of improving heat resistance and resistance to NOx gas yellowing, the thermoplastic polyurethane elastic fiber of this embodiment preferably has an outflow start temperature measured by a flow tester of 150°C or more and 220°C or less, more preferably 150°C or more and 200°C or less. The reason why the heat resistance and resistance to NOx gas yellowing can be improved by setting the outflow start temperature to 150°C or more and 220°C or less is not yet clear, but the inventors speculate as follows: Setting the outflow start temperature to 150°C or more reduces structural changes in the thermoplastic polyurethane due to exposure to heat, thereby improving heat resistance. On the other hand, setting the outflow start temperature to 220°C or less reduces the viscosity during melting, improving wettability and allowing the metal salt to be dispersed uniformly, thereby improving resistance to NOx gas yellowing. [Example]

[0035] The present invention will be specifically explained with reference to the following examples and comparative examples, but the scope of the present invention is not limited to these examples. First, the methods for evaluating physical properties and the like used in the examples and comparative examples will be described.

[0036] <Quantitative analysis of thermoplastic polyurethane components> The structures of the chain extender, which is made of an active hydrogen compound that constitutes the thermoplastic polyurethane contained in the thermoplastic polyurethane elastic fiber, and the diisocyanate were identified using NMR. Specifically, NMR was measured under the following conditions to identify the structures of the diisocyanate and chain extender. The structures of the diisocyanate and chain extender can be determined from the peak positions in the NMR measurement. Measurement device: Bruker Biospin Avance600 Measurement nuclei: 1 H Resonance frequency: 600MHz Number of times accumulated: 256 Measurement temperature: room temperature Solvent: deuterated dimethylformamide Measured concentration: 1.5% by weight Chemical shift reference: dimethylformamide (8.0233 ppm)

[0037] <How to calculate the ratio of the total number of moles of chain extender and polymer polyol to the number of moles of diisocyanate (hereinafter referred to as OH / NCO)> The OH / NCO ratio of thermoplastic polyurethane elastic fibers is calculated by the integral value of the corresponding peak in NMR measurement according to the following formula (1): OH / NCO={(Hh+Hs) / 4} / (Hi / x) …Equation (1) It was calculated by: During the ceremony, Hh: Integral value derived from the methylene group of active hydrogen compounds adjacent to the urethane bond Hs: Integral value derived from methylene groups of polymer polyol adjacent to urethane bond Hi: Integral value derived from hydrogen compounds in diisocyanates x: total number of hydrogen atoms in the diisocyanate is.

[0038] <Method for quantifying the hard segment ratio (Mh fraction)> The Mh fraction of the thermoplastic polyurethane elastic fiber is calculated by the following formulas (2) to (5): Ms={Mdo+Mdi(N1-N0)} / (N1-N0-1)-2Mdi...Equation (2) Mh={Mda(N1-1)+Mdi×N0} / (N1-N0-1)+2Mdi...Equation (3) N0=0.03806N1 4 -0.3997N1 3 +1.617N1 2 -2.144N1 1 +0.8795 …Equation (4) Mh fraction (%)={Mh / (Ms+Mh)}×100...Equation (5) It is calculated by solving the following simultaneous equations: During the ceremony, Ms: number average molecular weight of the soft segment Mdo: number average molecular weight of polymer polyol Mdi: Molecular weight of isocyanate N1: Molar ratio of isocyanate to polymer polyol N0: Molar ratio of unreacted isocyanate to polymer polyol Mh: Number average molecular weight of the hard segment Mda: molecular weight of chain extender (number average molecular weight when two or more types are used in combination) Mdi: Molecular weight of isocyanate is.

[0039] <Method for identifying and quantifying metal compounds> Thermoplastic polyurethane elastic fibers are wrapped around a glass plate and analyzed using an XRD (Rigaku Ultima-IV). The chemical composition of the metal compounds contained can be identified by comparing the analyzed spectrum with database data. Once the metal compounds have been identified using XRD, a sample is prepared by tightly wrapping the thermoplastic polyurethane elastic fibers around a perforated PP film at the center. This sample is then analyzed using an XRF (Rigaku ZSX-100e). The metal compound content can be quantified based on the detected intensity of the elements that make up the metal compound. If necessary, a calibration curve using the same metal compound as the contained metal compound can be used for quantification.

[0040] <Measurement of flow start temperature of thermoplastic polyurethane elastic fiber> The flow start temperature of the thermoplastic polyurethane elastic fiber is measured using a flow tester CFT-500D (Shimadzu Corporation). The thermoplastic polyurethane elastic fiber is not pre-treated, such as by removing processing agents such as oils, and 1.5 g of sample is measured for each measurement. A die (nozzle) with a diameter of 0.5 mm and a thickness of 1.0 mm is used. An extrusion load of 49 N is applied, and after 240 seconds of preheating at an initial temperature of 120°C, the temperature is raised uniformly to 250°C at a rate of 3°C / min. The stroke length (mm) vs. temperature curve is obtained. As the temperature rises, the polymer in the toner heats up, and the polymer begins to flow out of the die. The temperature at this point is the flow start temperature.

[0041] <Method for measuring coefficient of variation of fineness unevenness> The coefficient of variation of fineness unevenness is measured by adjusting the rotation speed of two godet rolls so that the thermoplastic polyurethane elastic fiber is stretched twice, and setting the following device between the godet rolls. The outer diameter of the elastic fiber is measured using a laser from two mutually perpendicular directions, and the ratio of the average deviation of the diagonal length calculated using Pythagoras' theorem to the average value is taken as the coefficient of variation of fineness unevenness. The measurement data used is the average value of 50,000 data points measured at 160 points / second. Measuring device: LS9006D (Keyence Corporation) Measurement type: Outer diameter Minimum display unit: 0.0001mm Number of measurement points: 50,000 Accumulation cycle: ×100

[0042] <Method for measuring fineness> The fineness was measured by cutting the thermoplastic polyurethane elastic fiber vertically, observing the cross section of the fiber using the following equipment and conditions, calculating the total cross-sectional area of ​​the fiber by automatic area measurement, and calculating the fineness per unit length using the following formula (6): d = D × 1.1 (g / cm 3 ) x 10 6 ...Formula (6) {where d is the fineness (dtex), D is the total cross-sectional area of ​​the yarn (cm 2 )} was calculated using Measuring device: VHX-7000 (Keyence Corporation) Lens used: VH-Z100R Magnification: 500x Measurement: Automatic area measurement Extraction Method: Brightness <Method for measuring the difference between the maximum and minimum fineness of polyurethane elastic fibers> The difference between the maximum and minimum finenesses was measured by cutting the thermoplastic polyurethane elastic fiber vertically, observing the cross section of the fiber using the following equipment and conditions, calculating the total cross-sectional area of ​​the fiber using automatic area measurement, and calculating the fineness per unit length from the difference between the maximum and minimum finenesses at 10 points at 5 mm intervals in the fiber length direction using the above formula (6). Measuring device: VHX-7000 (Keyence Corporation) Lens used: VH-Z100R Magnification: 500x Measurement: Automatic area measurement Extraction Method: Brightness

[0043] <Heat resistance evaluation method> Thermoplastic polyurethane elastic fiber was stretched twice and held in that state, and the time it took for the fiber to break when pressed against a heat source at 110°C (number of seconds until thermal breakage) was evaluated as an index of heat resistance.

[0044] <Evaluation method for NOx gas yellowing resistance> 1. ΔYI value Using thermoplastic polyurethane elastic fibers, yellowing was evaluated in accordance with JIS-L-0855, a test method for color fastness to nitrogen oxide gas, and a weak test method. The yellowness index YI value measured by a Macbeth colorimeter (manufactured by Macbeth Co., Ltd.) was compared with the YI0 value of an untreated sample according to the following formula (7): ΔYI=YI-YI0…Equation (7) The evaluation was based on the ΔYI value calculated by the following formula. The smaller the ΔYI value, the less likely the film is to yellow, and the larger the ΔYI value, the more likely the film is to yellow.

[0045] 2. Yellowing visibility The thermoplastic polyurethane elastic fiber yellowed by method 1 above was compared with the color code and given an evaluation score on a 10-point scale. Specifically, a total of 18 people, 10 people in their 20s and 2 people each in their 30s to 60s, were asked to select the color code that most closely matched the color of the yellowed thermoplastic polyurethane elastic fiber, and the average score was used as the evaluation score for yellowing visibility. The color code and evaluation scores used are as follows, with a higher evaluation score indicating less yellowing. #FFD500:1 point #FFD91A: 2 points #FFDD33: 3 points #FFE14D: 4 points #FFE666: 5 points #FFEA80: 6 points #FFEE99:7 points #FFF2B3: 8 points #FFF7CC: 9 points #FFFBE6:10 points

[0046] Both the ΔYI value and yellowing visibility are evaluations of resistance to NOx gas yellowing. The ΔYI value is not affected by human visibility, whereas yellowing visibility is affected by human visibility. Therefore, by comparing the yellowing visibility of samples with the same ΔYI value, it is possible to evaluate resistance to NOx gas yellowing based on human visibility.

[0047] [Example 1] <Synthesis of Thermoplastic Polyurethane Resin> 2400 g of polytetramethylene ether diol with a number average molecular weight of 1800 and 750.78 g of 4,4'-diphenylmethane diisocyanate were reacted under a dry nitrogen atmosphere at 60°C for 3 hours with stirring to obtain a polyurethane prepolymer capped with terminal isocyanate. 151.20 g of 1,4-butanediol was added to this polyurethane prepolymer and stirred for 15 minutes to obtain a polyurethane with a viscosity of 2000 poise (30°C). Thereafter, the mixture was poured onto a Teflon (registered trademark) tray, and the polyurethane was annealed in a hot air oven at 110°C for 16 hours while still in the tray to obtain a thermoplastic polyurethane resin.

[0048] <Masterbatch production> The thermoplastic polyurethane resin thus obtained was crushed into powder of approximately 3 mm using a UG-280 crusher manufactured by Horai Co., Ltd. The crushed chips were dried in a dehumidifying dryer at 110°C to a moisture content of 100 ppm, after which polyurethane resin powder and magnesium hydroxide were added to a hopper in a specified ratio, melted in an extruder to form strands, cooled in a water bath at 20°C, and pelletized using an SCF-100 plastic processing machine manufactured by Isuzu Chemical Engineering Co., Ltd. to obtain a masterbatch of magnesium hydroxide with an active ingredient of 10 wt%.

[0049] <Preparation of thermoplastic polyurethane elastic fiber> A magnesium hydroxide-containing polyurethane resin powder, a mixture of thermoplastic polyurethane resin powder and a magnesium hydroxide masterbatch in a weight ratio of 95:5, was metered and pressurized using a gear pump attached to the head, filtered, and then extruded at a die temperature of 210°C from a 0.23 mm diameter, 60-hole nozzle at a discharge rate of 620 dtex. The fibers were then melt-spun by blowing cold air perpendicularly from a cold air chamber adjusted to a cold air temperature of 15-17°C and a cold air speed of 0.8-1.0 m / s. The multifilament fibers were then twisted using a ring-type false twister. A treatment agent primarily composed of polydimethylsiloxane and mineral oil was applied, and the fibers were wound onto a paper tube to obtain a 620 dtex / 60 filament thermoplastic polyurethane elastic fiber wound body. The thermoplastic polyurethane elastic fiber contained 0.50 wt% magnesium hydroxide, an Mh fraction of 24%, a fineness unevenness coefficient of variation of 4.0%, an OH / NCO ratio of 1.010, a thermal cutting time of 600 seconds or more, a ΔYI value of 8 for the thermoplastic polyurethane elastic fiber, a difference between the maximum and minimum fineness of 30 dtex, an outflow starting temperature of 160°C, and a yellowing visibility rating of 10 points. The results are also shown in Table 1 below.

[0050] [Examples 2 to 6] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide contained in the polyurethane elastic fibers was increased or decreased by adjusting the ratio of polyurethane resin to masterbatch. The results are shown in Table 1 below.

[0051] [Examples 7 to 12] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the metal compound was changed to magnesium carbonate (Example 7), magnesium oxide (Example 8), calcium hydroxide (Example 9), calcium carbonate (Example 10), sodium carbonate (Example 11), or potassium carbonate (Example 12). The results are shown in Table 1 below.

[0052] [Examples 13 to 17] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the chain extender consisting of an active hydrogen compound was changed to ethylene glycol (Example 13), 1,3-propanediol (Example 14), 1,6-hexanediol (Example 15), 1,8-octanediol (Example 16), or 1,10-decanediol (Example 17). The results are shown in Table 1 below.

[0053] [Examples 18 and 19] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that methylenebis(cyclohexyl isocyanate) (H12MDI) (Example 18) and 1,6-hexamethylene diisocyanate (HDI) (Example 19) were used instead. The results are shown in Table 1 below.

[0054] [Examples 20 to 26] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the Mh fraction of the thermoplastic polyurethane elastic fibers was increased or decreased by adjusting the molar ratio of polymer polyol to diisocyanate. The results are shown in Table 1 below.

[0055] [Table 1]

[0056] [Examples 27 to 33] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the OH / NCO ratio of the thermoplastic polyurethane elastic fibers was changed by adjusting the molar ratio of the polymer polyol, diisocyanate, and diol. The results are shown in Table 2 below.

[0057] [Examples 34 to 41] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the coefficient of variation of fineness unevenness of the thermoplastic polyurethane elastic fibers was changed by adjusting the spinning temperature, spinning nozzle diameter, throughput rate, cooling conditions, and winding conditions during spinning. The results are shown in Table 2 below.

[0058] [Examples 42 to 49] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the difference in fineness (maximum fineness - minimum fineness) of the thermoplastic polyurethane elastic fibers was changed by adjusting the spinning temperature, spinning nozzle diameter, throughput rate, cooling conditions, and winding conditions during spinning. The results are shown in Table 2 below.

[0059] [Table 2]

[0060] [Examples 50 to 54] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the molecular weight of the thermoplastic polyurethane was adjusted by adjusting the molecular weight of the polymer polyol, and the flow initiation temperature of the thermoplastic polyurethane elastic fibers was changed. The results are shown in Table 3 below.

[0061] [Comparative Example 1] Except for not adding the metal compound, thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1. The results are shown in Table 3 below.

[0062] Comparative Example 2 Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide contained in the polyurethane elastic fibers was changed to 10.0 wt% by adjusting the amount of masterbatch added. The results are shown in Table 3 below.

[0063] [Comparative Examples 3 to 6] Thermoplastic polyurethane elastic fibers were obtained in the same manner as in Example 1, except that the metal compound was changed to magnesium stearate (Comparative Example 3), calcium stearate (Comparative Example 4), zinc oxide (Comparative Example 5), or aluminum hydroxide (Comparative Example 6). The results are shown in Table 3 below.

[0064] [Table 3] [Industrial Applicability]

[0065] The thermoplastic polyurethane elastic fiber according to the present invention can be suitably used in clothing such as innerwear, stockings, and compression wear, as well as in sanitary materials such as gathering members and diapers.

Claims

1. A thermoplastic polyurethane elastic fiber, characterized in that it contains at least one metal compound selected from the group consisting of metal hydroxides, metal carbonates, and metal oxides in an amount of 0.05 wt % to 5.00 wt %, and the metal compound contains an alkali metal or an alkaline earth metal, and the coefficient of variation of fineness unevenness in the yarn length direction is 3.0% to 10.0%, and the difference between the maximum fineness and the minimum fineness in the yarn length direction is 10 dtex to 150 dtex.

2. The thermoplastic polyurethane elastic fiber of claim 1 , wherein the metal compound comprises an alkaline earth metal.

3. The thermoplastic polyurethane elastic fiber of claim 2 , wherein the alkaline earth metal is magnesium.

4. The thermoplastic polyurethane elastic fiber according to any one of claims 1 to 3, wherein the metal compound is magnesium hydroxide.

5. The thermoplastic polyurethane elastic fiber according to any one of claims 1 to 3, wherein the polyurethane constituting the thermoplastic polyurethane elastic fiber is a polyurethane polymerized from a polymer polyol, a diisocyanate, and a chain extender comprising an active hydrogen compound.

6. The thermoplastic polyurethane elastic fiber according to claim 5 , wherein the chain extender is a diol having a molecular weight of 60 or more and 120 or less.

7. The thermoplastic polyurethane elastic fiber according to claim 5, wherein the diisocyanate is 4,4'-diphenylmethane diisocyanate (MDI).

8. 6. The thermoplastic polyurethane elastic fiber according to claim 5, wherein the proportion of hard segments formed from the chain extender and the diisocyanate (Mh fraction) is 20% or more and 40% or less.

9. The thermoplastic polyurethane elastic fiber according to claim 5 , wherein the total number of moles of the chain extender and the polymer polyol is 1.001 times or more and 1.100 times or less the number of moles of the diisocyanate.

10. The thermoplastic polyurethane elastic fiber according to any one of claims 1 to 3, wherein the total fineness of the thermoplastic polyurethane elastic fiber is 160 dtex or more and 2000 dtex or less.

11. The thermoplastic polyurethane elastic fiber according to any one of claims 1 to 3, which is a multifilament fiber.

12. The thermoplastic polyurethane elastic fiber according to any one of claims 1 to 3, wherein the flow initiation temperature of the thermoplastic polyurethane elastic fiber measured with a flow tester is 150°C or higher and 220°C or lower.

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