Thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber

Abstract

Provided are: a thermoplastic polyurethane resin composition which exhibits good spinnability during melt spinning and has excellent heat resistance and stretchability when processed into a fiber; and an elastic fiber. A thermoplastic polyurethane resin composition according to the present invention contains a resin which is composed of a hard segment comprising an active hydrogen-containing compound and a diisocyanate compound and a soft segment comprising a long-chain polyol and a diisocyanate compound, and has the following characteristics: (a) the number average molecular weight of the hard segment is 800 to 2400 inclusive, the number average molecular weight of the soft segment is 1900 to 4800 inclusive, and the Mh fraction is 15% to 40% inclusive; (b) Mw is 100,000 to 300,000 inclusive, and Mw / Mn is 1.5 to 3.0 inclusive; (c) the distance between hard domains as measured by SAXS is 8 nm to 25 nm inclusive; and (d) the rate of change in the distance between hard domains when heated at 140°C is 30% or less.

Description

Thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber

[0001] This invention relates to thermoplastic polyurethane resin compositions and thermoplastic polyurethane elastic fibers.

[0002] Polyurethane elastic fibers used as gathers in the waist and leg areas of sanitary materials such as disposable diapers are typically dry-spun polyurethane urea elastic fibers (dry-spun polyurethane elastic fibers) using organic solvents as the spinning solution. However, in recent years, from the perspectives of environmental impact, safety, and energy costs, thermoplastic polyurethane urethane elastic fibers (hereinafter referred to as molten polyurethane elastic fibers) spun using a melt-spinning method that does not use organic solvents have been sought. However, molten polyurethane elastic fibers have a problem in the manufacturing process of the gathers: they frequently break when hot melt, heated to 140°C to 180°C (generally 140°C to 160°C), is applied to the elastic fibers while they are under a certain tension.

[0003] As a method to improve this problem, Patent Document 1 describes increasing the hard segment molar content (hard fraction) to increase the number of hard segment repeats and thereby increase the cohesive force, thereby improving heat resistance. However, if the hard fraction is too high, the tightening force becomes too strong, causing it to dig into the skin and leave marks, and it does not stretch sufficiently, making it difficult to put on diapers, so it is not suitable for elastic fibers used in disposable diapers. Furthermore, thermoplastic polyurethane resins obtained by continuous polymerization as described in Patent Document 1 require polymerization at high temperatures, and localized reactions tend to cause uneven polymer quality, and when made into granular resin, unevenness in shape is likely to occur.

[0004] Patent Document 2 below proposes a method for improving the heat resistance of polyurethane elastic fibers by adding a polyisocyanate compound to molten thermoplastic polyurethane resin and performing intermolecular crosslinking. However, in the method described in Patent Document 2, gels are generated due to the side reactions of the polyisocyanate compound before spinning, resulting in the formation of urea, biuret, allophanate, and other bonds, which cause frequent yarn breakage during spinning, and thus spinning stability cannot be ensured.

[0005] Thus, a thermoplastic polyurethane elastic fiber that achieves both heat resistance in the disposable diaper manufacturing process and the elasticity of disposable diapers, and a thermoplastic polyurethane resin composition that can produce the aforementioned thermoplastic polyurethane elastic fiber stably over the long term, have yet to be found.

[0006] Japanese Unexamined Patent Publication No. 7-33846 Special Publication No. 2006-522862

[0007] In view of the aforementioned level of prior art, the problem that the present invention aims to solve is to provide a thermoplastic polyurethane resin composition that enables stable production of elastic fibers for disposable diapers that possess excellent heat resistance and elasticity. Furthermore, it aims to provide thermoplastic polyurethane fibers that do not break during the disposable diaper manufacturing process (hot melt coating process) and exhibit the elasticity required for gather fibers in disposable diapers.

[0008] The inventors of the present invention have discovered that by controlling the microphase separation structure of a thermoplastic polyurethane resin composition, i.e., the hard domain size and its distribution, it is possible to provide elastic fibers that possess excellent spinning stability and excellent heat resistance and elasticity, leading to the present invention. Furthermore, the inventors have discovered that by using the thermoplastic polyurethane resin composition of the present invention as a raw material and controlling the molecular orientation during the melt spinning process to reconstruct the microphase separation structure of the raw material resin composition, it is possible to achieve excellent heat resistance and elasticity, which is an important practical performance of disposable diapers, in the disposable diaper manufacturing process (hot melt coating process), thus completing the present invention.

[0009] In other words, the present invention is as follows: [1] A thermoplastic polyurethane resin composition comprising a thermoplastic polyurethane resin composed of a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, characterized by the following features: (a) The number average molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the number average molecular weight of the soft segment is 1900 to 4800, and the proportion of the hard segment (Mh fraction) is 15% to 40%; (b) The weight average molecular weight (Mw) is 150,000 to 500,000, and the molecular weight distribution (Mw / Mn (number average molecular weight)) is 1.5 to 3.0; (c) The interdomain distance between hard domains measured by a small-angle X-ray scattering device (SAXS) is 5 nm to 20 nm; and (d) The rate of change of the interdomain distance between hard domains when heated at 140°C is 30% or less. [2] The thermoplastic polyurethane resin composition according to [1], wherein the rate of change of the distance between hard domains when heated to 160°C is 50% or less. [3] The thermoplastic polyurethane resin composition according to [1] or [2], wherein the hydrogen bonding rate obtained by 13C-NMR measurement is 51% or more and 80% or less. [4] The thermoplastic polyurethane resin composition according to any one of [1] to [3], wherein the crystallization peak temperature measured by DSC (differential calorimetry) is 60°C or more and 100°C or less. [5] The thermoplastic polyurethane resin composition according to [4], wherein the difference between the crystallization start temperature and the crystallization end temperature measured by DSC is 40°C or more and 75°C or less. [6] The thermoplastic polyurethane resin composition according to any one of [1] to [5], wherein the thermoplastic polyurethane resin composition exhibits the form of granular resin, the weight of the granular resin is 10 mg or more and 100 mg or less, and the coefficient of variation is 50% or less. [7] The thermoplastic polyurethane resin composition according to any one of [1] to [6], wherein the thermoplastic polyurethane resin composition exhibits a form in which fine powder is attached to the surface of a granular resin, and the weight of the fine powder is 10 wt% or less of the weight of the granular resin.[8] A thermoplastic polyurethane elastic fiber comprising a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, characterized in the following ways: (a) The number average molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the number average molecular weight of the soft segment is 1900 to 4800, and the proportion of the hard segment (Mh fraction) is 15% to 40%; (b) The weight average molecular weight (Mw) is 100,000 to 300,000, and the molecular weight distribution (Mw / Mn (number average molecular weight)) is 1.5 to 3.0; (c) The inter-hard domain distance measured by a small-angle X-ray scattering device (SAXS) is 8 nm to 25 nm; and (d) The rate of change of the inter-hard domain distance when heated at 140°C is 30% or less. [9] The thermoplastic polyurethane elastic fiber according to [8], wherein the rate of change of the distance between hard domains when heated to 160°C is 50% or less.

[10] The thermoplastic polyurethane elastic fiber according to [8] or [9], wherein the hydrogen bonding rate obtained by 13C-NMR measurement is 51% or more and 80% or less.

[11] The thermoplastic polyurethane elastic fiber according to any one of [8] to

[10] , wherein the total fineness is 160 dtex or more and 2000 dtex or less.

[12] The thermoplastic polyurethane elastic fiber according to

[11] , wherein the single filament fineness is 5 dtex or more and 100 dtex or less.

[13] The thermoplastic polyurethane elastic fiber according to any one of [8] to

[11] , wherein the tanδ value at 25°C obtained by viscoelasticity measurement is 0.01 or more and 0.10 or less, and the tanδ value at 160°C is 0.05 or more and 0.20 or less.

[0010] The thermoplastic polyurethane resin composition according to the present invention enables the stable production of elastic fibers for disposable diapers, possessing excellent heat resistance and elasticity, over long periods of time without the use of organic solvents. The thermoplastic polyurethane fibers according to the present invention do not experience thread breakage during the disposable diaper manufacturing process (hot melt coating process), thus not impairing the productivity of disposable diapers. Furthermore, the thermoplastic polyurethane elastic fibers of the present invention can exhibit the elasticity required for elastic fibers used in disposable diapers.

[0011] This diagram illustrates the distance between hard domains. This diagram illustrates the change in the distance between hard domains due to heating.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. One embodiment of the present invention is a thermoplastic polyurethane resin composition comprising a thermoplastic polyurethane resin composed of a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, characterized by the following features: (a) the number average molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the number average molecular weight of the soft segment is 1900 to 4800, and the proportion (Mh fraction) of the hard segment is 15% to 40%; (b) the weight average molecular weight (Mw) is 150,000 to 500,000, and the molecular weight distribution (Mw / Mn (number average molecular weight)) is 1.5 to 3.0; (c) the inter-hard domain distance measured by a small-angle X-ray scattering device (SAXS) is 5 nm to 20 nm; and (d) the rate of change of the inter-hard domain distance when heated at 140°C is 30% or less.

[0013] In this embodiment, the thermoplastic polyurethane resin contained in the thermoplastic polyurethane resin composition is a copolymer of hard segments and soft segments, and is known to adopt a microphase separation structure at room temperature. The glass transition temperature of the soft segments is below room temperature, and the hard domains act as physical crosslinking points to exhibit rubber elasticity. The soft segments are composed of a polymer of a diisocyanate compound and a long-chain polyol, and the hard segments are composed of a polymer of a chain extender consisting of a diisocyanate compound and an active hydrogen-containing compound, and the primary structure is represented by the following general formula. {In the formula, R' is an aliphatic, alicyclic, or aromatic hydrocarbon derived from a diisocyanate compound, R １ R is an alkyl group (C2-C10) derived from an active hydrogen-containing compound, ２ is a polyether group, polyester group, or polycarbonate group derived from a long-chain polyol, l is an integer from 1 to 10, m is an integer from 12 to 42, and n is an integer from 1 to 7.

[0014] As described above, the thermoplastic polyurethane resin of this embodiment is a polymer of a long-chain polyol, a diisocyanate compound, and an active hydrogen-containing compound. The long-chain polyol is preferably polyalkylene ether diol, polyester diol, or polycarbonate diol, which are commonly used in the polymerization of thermoplastic polyurethane resins, and is particularly preferably polyalkylene ether diol. Examples of polyalkylene ether diol include those in which the alkylene group is a tetramethylene group, or those in which a tetramethylene group is a linear or branched alkylene group having 1 to 8 carbon atoms. Specifically, polytetramethylene ether diol (PTMG), copolymer poly(tetramethylene / neopentylene) ether diol, and copolymer poly(tetramethylene / 2-methylbutylene) ether diol are preferred. The above long-chain polyol may be used alone or as a mixture of two or more types.

[0015] As diisocyanate compounds, for example, all aliphatic, alicyclic, and aromatic diisocyanates that are soluble or liquid under reaction conditions can be used, specifically methylene-bis(4-phenylisocyanate), methylene-bis(3-methyl-4-phenylisocyanate), 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, m- and p-xylylenediisocyanate, α,α,α',α'-tetramethyl-xylylenediisocyanate, m- and p-phenylenediisocyanate, 4,4'-dimethyl-1,3-xylylenediisocyanate, 1-alkylphenylene-2,4- and 2,6-diisocyanate, 3-(α-isocyanate) Examples include ethyl)phenyl isocyanate, 2,6-diethylphenylene-1,4-diisocyanate, diphenyl-dimethylmethane-4,4-diisocyanate, diphenyl ether-4,4'-diisocyanate, naphthylene-1,5-diisocyanate, 1,6-hexamethylene diisocyanate, methylene-bis(4-cyclohexyl isocyanate), 1,3- and 1,4-cyclohexylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc., with methylene-bis(4-phenyl isocyanate) (MDI) being particularly preferred. The above diisocyanate compounds may be used individually or as a mixture of two or more.

[0016] Examples of active hydrogen-containing compounds (chain extenders) include low molecular weight glycols commonly used in the polymerization of thermoplastic polyurethane resins. Specifically, these include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, hexamethylene glycol, diethylene glycol, 1,10-decanediol, 1,3-dimethylolcyclohexane, or 1,4-dimethylolcyclohexane. Alkanolamines such as 2-amino-1-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, and 5-amino-1-pentanol can also be used. Among the active hydrogen-containing compounds that react with the isocyanate group, 1,4-butanediol (BDO) is particularly preferred. The above active hydrogen-containing compounds may be used individually or in combination of two or more.

[0017] The number-average molecular weight of the hard segments of the thermoplastic polyurethane resin composition of this embodiment, as measured by 1H nuclear magnetic resonance spectroscopy (hereinafter referred to as "1H-NMR"), is 800 or more and 2400 or less. By controlling the number-average molecular weight of the hard segments of the resin composition as a fiber raw material to 800 or more and 2400 or less, it becomes possible to exhibit both heat resistance and elasticity in thermoplastic polyurethane elastic fibers, and to spin them stably for a long time without yarn breakage during the melt spinning process. That is, when the number-average molecular weight of the hard segments is 800 or more, hydrogen bonding between hard segments increases, and the cohesive force of the hard domains improves, thereby exhibiting both heat resistance and elasticity simultaneously. On the other hand, when the number-average molecular weight of the hard segments exceeds 2400, the hard domains become coarser and less likely to melt, causing yarn breakage due to unmelted material (components that remain unmelted when the polymer melts) during melt spinning. From the viewpoint of improving the heat resistance and elasticity of thermoplastic polyurethane elastic fibers and spinning stability, the number-average molecular weight of the hard segments of the thermoplastic polyurethane resin composition is preferably 1000 or more and 2000 or less, and more preferably 1100 or more and 1800 or less.

[0018] The thermoplastic polyurethane resin composition of this embodiment has a number-average molecular weight of soft segments measured by 1H-NMR of 1900 to 4800. A number-average molecular weight of 1900 or more allows the composition to exhibit the elasticity required for disposable diapers when fiberized. On the other hand, a number-average molecular weight of 4800 or less facilitates the self-assembly of soft domains, leading to the development of a microphase separation structure. That is, the interface between hard domains and soft domains becomes clearer, reducing the mixed region and enabling the development of the necessary heat resistance. From the viewpoint of improving the heat resistance and elasticity of thermoplastic polyurethane elastic fibers, the number-average molecular weight of the soft segments measured by 1H-NMR is preferably 2500 to 4500, more preferably 3000 to 4000, and most preferably 3200 to 3500.

[0019] The thermoplastic polyurethane resin composition of this embodiment has a hard segment ratio (denoted as Mh fraction) of 15% or more and 40% or less. The Mh fraction (%) is calculated by the following formula: Mh fraction (%) = (number average molecular weight of hard segments (Mh)) / {(number average molecular weight of hard segments (Mh)) + (number average molecular weight of soft segments (Ms))} × 100 By controlling the Mh fraction of the resin composition to 15% or more and 40% or less as a fiber raw material, it is possible to suppress thermal decomposition in the spinning process and to achieve both heat resistance and elasticity in the resulting thermoplastic polyurethane elastic fibers. If the Mh fraction is less than 15%, a significant decrease in molecular weight occurs due to thermal decomposition in the spinning process, and furthermore, the thermoplastic polyurethane elastic fibers have low hydrogen bonding strength between urethane bonds and cannot achieve the heat resistance required in the hot melt process. On the other hand, if the Mh fraction of the resin composition exceeds 40%, the tightening force of the resulting thermoplastic polyurethane elastic fiber becomes too strong (the stress during contraction becomes too strong), leaving marks on the skin when wearing a disposable diaper, and reducing the responsiveness during contraction (it does not follow the body's movements). From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, it is preferably 20% to 30%, and more preferably 22% to 28%.

[0020] The thermoplastic polyurethane resin composition of this embodiment has a hard domain distance of 5 nm to 20 nm, as measured in a room temperature (25°C) atmosphere using a small-angle X-ray scattering device (hereinafter referred to as "SAXS"), and the rate of change of the hard domain distance in a 140°C atmosphere compared to the hard domain distance in a room temperature atmosphere measured by a heated in-situ measurement method using SAXS is 30% or less. Since the thermoplastic polyurethane resin composition exhibits fluidity when the hard domains that form a microphase separation structure melt, it is presumed that the melt spinning stability of the thermoplastic polyurethane resin composition and the heat resistance of the resulting elastic fibers are influenced by the size of the hard domains (hard domain size) and the uniformity of their size. However, it is technically difficult to directly measure the hard domain size and its uniformity. The inventors of the present invention hypothesized that "hard domain size correlates with the distance between hard domains measured under room temperature conditions" and "uniformity of hard domain size correlates with the rate of change of the distance between hard domains measured under heated conditions." As a result of diligent research, they found that by controlling the distance between hard domains of a thermoplastic polyurethane resin composition at room temperature to between 5 nm and 20 nm, and the rate of change of the distance between hard domains between room temperature and a 140°C atmosphere to 30% or less, stable continuous spinning is possible, and the resulting elastic fibers can exhibit heat resistance in the hot melt coating process and elasticity as gathers.

[0021] The details are explained below. First, as shown in Figure 1-a), for example, a short hard domain distance (x) measured in a thermoplastic polyurethane resin composition under room temperature conditions at the same hard fraction indicates that there are many small hard domains per unit volume. In the melt spinning process, even if the hard domain size of the thermoplastic polyurethane resin composition is relatively small, molecular orientation promotes the growth (aggregation) of hard domains in the fibers. However, the inventors have found that when the hard domain distance (x) of the thermoplastic polyurethane resin composition is less than 5 nm, hard domain growth (aggregation) does not occur in the melt spinning process, and as a result, a fiber structure is formed in which small hard domains (hard domain distance of less than 8 nm in elastic fibers, which is another aspect of the present invention) are finely dispersed. It has been found that in elastic fibers with such a structure, soft domains and hard domains are compatible at low temperatures below 140°C. On the other hand, in order to achieve heat resistance that can withstand a typical hot-melt coating process, it is necessary to form large hard domains, that is, to increase the distance between hard domains. However, as shown in Figure 1-b), if the distance between hard domains (x') exceeds 20 nm, melting becomes difficult and unmelted material remains, impairing the long-term productivity of the fiber. Therefore, in order to provide an elastic fiber that enables stable spinning over a long period of time and exhibits the heat resistance required in the hot-melt coating process, (x'') must be between 5 nm and 20 nm, preferably between 7 nm and 18 nm, and more preferably between 8 nm and 15 nm (Figure 1-c).

[0022] On the other hand, the hard domain distance measured under room temperature conditions is the average distance between hard domains per unit volume, as described above, but in reality, there is variation in the hard domain distance (hard domain size). For example, even if the hard domain distance measured under room temperature conditions is the same (5 nm to 20 nm), if there is a large variation in hard domain size, as shown in Figure 2-a), the hard domain distance will increase as smaller hard domains melt during heating. However, this change does not represent the growth of hard domain size, but rather the disappearance of hard domains that serve as binding points between soft domains, and the resulting material cannot withstand the heat and tension of the hot melt coating process where a fume hood is applied. Therefore, by controlling the structure of a thermoplastic polyurethane resin composition so that the hard domain distance measured under room temperature conditions is between 5 nm and 20 nm, and the rate of change in the hard domain distance between room temperature and 140°C is 30% or less (see Figure 2-b), hard domains that serve as binding points between soft domains remain, and an elastic fiber that can withstand the heat and tension of the hot melt coating process can be provided. On the other hand, while a small change in the distance between hard domains at room temperature and 140°C is desirable, it is practically impossible to form perfectly uniform hard domains that do not undergo any structural change in a 140°C atmosphere. Therefore, the lower limit of the change in the distance between hard domains at room temperature and 140°C is 1%. Accordingly, from the viewpoint of melt spinnability and the heat resistance of the resulting elastic fiber, the change in the distance between hard domains at room temperature and 140°C is preferably 1% to 30%, more preferably 5% to 25%, and even more preferably 5% to 20%.

[0023] The thermoplastic polyurethane resin composition of this embodiment preferably has a rate of change of the hard domain distance under a 160°C atmosphere compared to the hard domain distance under a room temperature atmosphere of 50% or less, more preferably 45% or less, and even more preferably 40% or less. As mentioned above, the temperature of the hot melt applied in the hot melt coating process of diaper manufacturing is generally between 140°C and 160°C. By making the rate of change of the hard segment distance when the thermoplastic polyurethane resin composition of the present invention is heated to 160°C 50% or less, it is possible to provide elastic fibers that do not break during the high-temperature hot melt coating process.

[0024] The weight-average molecular weight (Mw) of the thermoplastic polyurethane resin composition in this embodiment is 150,000 or more and 500,000 or less. In order to suppress thread breakage in the hot-melt coating process of diaper manufacturing (heat reception of 140°C or more under constant tension), as described later, it is necessary for the thermoplastic polyurethane elastic fiber to have a well-developed microphase separation structure as a higher-order structure (hard domain size of 8 nm to 25 nm), and furthermore, to have an appropriate entanglement of molecular chains (weight-average molecular weight of 100,000 or more and 300,000 or less). Since thermal decomposition occurs at a certain rate in the melt-spinning process of the thermoplastic polyurethane resin composition, the weight-average molecular weight (Mw) of the raw material thermoplastic polyurethane resin composition must be at least 150,000. If it is less than 150,000, it is difficult to obtain thermoplastic polyurethane elastic fibers with a weight-average molecular weight (Mw) of 100,000 or more. On the other hand, thermoplastic polyurethane resin compositions with a weight-average molecular weight (Mw) exceeding 500,000 have very high melt viscosity, and the spinning temperature must be raised to adjust the melt viscosity to a suitable level for melt spinning. As a result, a significant decrease in molecular weight occurs, making it difficult to obtain thermoplastic polyurethane elastic fibers with a weight-average molecular weight (Mw) of 100,000 or more. Furthermore, while it is possible to spin thermoplastic polyurethane resin compositions with a weight-average molecular weight (Mw) exceeding 500,000 within a temperature range that controls the yarn molecular weight to 100,000 or more, the fibers spun under these conditions have strong tightening force and are unsuitable as gather fibers for diapers. From the viewpoint of heat resistance and elasticity of thermoplastic polyurethane elastic fibers, the lower limit of the weight-average molecular weight (Mw) of the thermoplastic polyurethane resin composition is preferably 200,000 or more, and the upper limit is preferably 450,000, more preferably 400,000, due to ease of control.

[0025] The molecular weight distribution (Mw / Mn (number-average molecular weight)) of the thermoplastic polyurethane resin composition in this embodiment is 1.5 or more and 3.0 or less. If the molecular weight distribution of the thermoplastic polyurethane resin composition is 1.5 or more, the variation in molecular chain length is small, which makes it easier for molecular chains to orient themselves regularly, promoting the growth of hard domains, and thus enabling the heat resistance required for diaper gather fibers to be achieved. Furthermore, if the molecular weight distribution of the thermoplastic polyurethane resin composition is 3.0 or less, the proportion of microphase mixed regions is small when the microphase separation structure is reformed in the melt spinning process, and the amount of minute hard domains mixed in the soft domains is small, so the elongation of the soft domains is less likely to be inhibited, and the elasticity required for diaper gather fibers to be achieved. From the viewpoint of heat resistance and elasticity of thermoplastic polyurethane elastic fibers, the molecular weight distribution of the thermoplastic polyurethane resin composition is preferably 1.7 or more and 2.5 or less, and more preferably 1.8 or more and 2.2 or less.

[0026] The thermoplastic polyurethane resin composition of this embodiment preferably has a hydrogen bonding rate of 51% or more and 80% or less, as measured by 13C nuclear magnetic resonance spectroscopy (hereinafter referred to as "13C-NMR"). As mentioned above, controlling the number-average molecular weight of hard segments by 1H-NMR affects heat resistance and elasticity, but it is preferable to form even higher density hard domains, and to achieve this, increasing the intermolecular hydrogen bonding rate is effective. On the other hand, it is technically difficult to directly measure hydrogen bonding force. The inventors hypothesized that "hydrogen bonding force correlates with the ratio of urethane bonds derived from hard segments to the total amount of urethane bonds (hereinafter referred to as the hydrogen bonding rate)," and after diligent research, they found that if the hydrogen bonding rate measured by 13C-NMR is 51% or more, the density of hard domains is high, and the rate of change in the distance between hard domains during heating can be further suppressed. If the hydrogen bonding rate by 13C-NMR exceeds 80%, high-density and coarse hard domains are formed, making it difficult to melt and hindering the stable production of elastic fibers. The hydrogen bonding rate of the thermoplastic polyurethane resin composition as determined by 13C-NMR is preferably 53% to 75%, and more preferably 55% to 70%.

[0027] In this embodiment, the thermoplastic polyurethane resin composition preferably has a crystallization peak temperature of 60°C or higher and 100°C or lower, as measured by a differential scanning calorimeter (hereinafter referred to as "DSC"). If the crystallization peak temperature is 60°C or higher, the obtained thermoplastic polyurethane elastic fiber undergoes microphase separation more easily as it is stretched and oriented before reaching the crystallization temperature during the spinning process, making it easier to exhibit elasticity. On the other hand, if the crystallization peak temperature exceeds 100°C, crystallization is rapid, resulting in a smaller hard domain size formed during the melt spinning process, and the growth of hard domains due to molecular orientation is also less likely to occur. As a result, the hard domain size and the rate of change in the distance between hard domains during heating of the thermoplastic polyurethane elastic fiber, which is another embodiment of the present invention, fall outside the range defined in the present invention, making it difficult to exhibit the heat resistance required for diaper gather fibers. From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, the crystallization peak temperature measured by DSC is preferably 60°C or higher and 95°C or lower, and more preferably 65°C or higher and 90°C or lower.

[0028] In this embodiment, the thermoplastic polyurethane resin composition preferably has a difference between the crystallization start temperature and the crystallization end temperature measured by DSC of 40°C or more and 75°C or less. When the crystallization temperature difference of the thermoplastic polyurethane resin composition is 40°C or more, hard domains are formed in the melt spinning process, and the growth of hard domains due to molecular orientation is also likely to occur, making it easier to control the hard domain size and the rate of change of the distance between hard domains during heating of the thermoplastic polyurethane elastic fiber, which is another embodiment of the present invention, within the range defined in the present invention. On the other hand, when the crystallization temperature difference of the thermoplastic polyurethane resin composition exceeds 75°C, variations tend to occur in the hard domain size formed in the melt spinning process. From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, the difference between the crystallization start temperature and the crystallization end temperature measured by DSC is preferably 45°C or more and 70°C or less, and more preferably 45°C or more and 60°C or less.

[0029] The thermoplastic polyurethane resin composition of this embodiment can be in the form of granular resin, and the granular resin refers to individual solid resin particles obtained by granulating the thermoplastic polyurethane resin composition through a granulation process. In the present specification, the granular resin has a particle size (for example, diameter or side length) of 1 mm or more and 20 mm or less, and it can be angular (for example, die-shaped) or round (for example, cylindrical, spherical, etc.). From the perspective of preventing blocking in the hopper during raw material storage in the spinning process and achieving stable raw material supply over a long period, it is preferable that the weight of one granular resin particle is 10 mg or more and 100 mg or less. Also, it is preferable that the coefficient of variation (CV value) indicating the variation in the weight distribution is 50% or less. Within such a range, the uniformity of the weight of the granular resin is high, and the deviation in the filling rate in the hopper is small, so blocking at the lower part can be prevented. Also, if the weight of one particle is 10 mg or more, the bulk density of the granular resin is large, and the fluidity of the granular resin in the hopper is good. If it is 100 mg or less, the biting-in at the resin input part of the extruder is stable, and the continuous productivity is high. The weight of one granular resin particle is preferably 20 mg or more and 80 mg or less, more preferably 20 mg or more and 60 mg or less. Furthermore, if the CV value is 50% or less, the variation in the weight of the granular resin is small, and uniform raw material supply is possible, which also contributes to the stability in the spinning process and the uniformity of product quality. The CV value is preferably 40% or less, more preferably 30% or less.

[0030] In this embodiment, the thermoplastic polyurethane resin composition preferably has a fine powder content of 10 wt% or less of the chip's weight, from the viewpoint of reducing the amount of dirt adhering around the holes of the spinneret discharge section during the spinning process and achieving stable production over long periods of time. The fine powder includes, but is not limited to, resin powder generated during cutting during granulation in the polymerization process of thermoplastic polyurethane, and additives or their components that have bled out from the thermoplastic polyurethane resin composition. In this specification, fine powder refers to powdery material with a particle size (e.g., diameter or side length) of 500 μm or less. Fine powder melts more easily than chips in the extruder during the spinning process, and has low viscosity because it receives relatively more heat and undergoes thermal decomposition. Therefore, it is preferable to have less fine powder, as it tends to seep out in liquid form around the holes during discharge and easily contaminates the holes, so it is preferably 10 wt% or less, more preferably 8.0 wt% or less, and even more preferably 5.0 wt% or less.

[0031] In this embodiment, when the melt viscosity of the thermoplastic polyurethane resin composition is measured using a flow tester and plotted on a semi-logarithmic graph with temperature on the x-axis and melt viscosity on a logarithmic scale on the y-axis, the slope of the melt viscosity with respect to temperature is preferably -0.20 Pa·s / °C or more and -0.10 Pa·s / °C or less, more preferably -0.18 Pa·s / °C or more and -0.12 Pa·s / °C or less, even more preferably -0.17 Pa·s / °C or more and -0.14 Pa·s / °C or less, and most preferably -0.16 Pa·s / °C or more and -0.14 Pa·s / °C or less. When the slope is -0.20 Pa·s / °C or more, the change in melt viscosity during heating is small, the material is less affected by the spinning environment during the melt spinning process, and the spinning stability is high. On the other hand, if the viscosity is -0.1 Pa·s / °C or lower, the variation in melt viscosity is small, and the variation in cohesive force during heating is small. As a result, the tensile stress in the length direction of the yarn during heating is uniform, localized stress concentration is less likely to occur, and the frequency of yarn breakage due to heat absorption during the gathering process is reduced.

[0032] The proportion of the low molecular weight component having a weight average molecular weight of 10,000 or less contained in the thermoplastic polyurethane resin composition of the present embodiment is not particularly limited, but from the viewpoint of preventing spinneret fouling caused by the low molecular weight component during melt spinning and realizing stable spinning for a long time, it is preferably 1.00% or less.

[0033] The thermoplastic polyurethane resin composition of the present embodiment may contain other additives, for example, a stabilizer, an anti-blocking agent, and a plasticizer, if necessary. Examples of the stabilizer include compounds commonly used in polyurethane resins, such as an ultraviolet absorber, an antioxidant, a light stabilizer, a heat stabilizer, a gas resistance stabilizer, and an antistatic agent. Further, a plasticizer and an anti-blocking agent can be added if necessary. Examples of the antioxidant include a radical scavenger, a radical chain initiation inhibitor, and a peroxide decomposer. Examples of the radical scavenger in the present invention include hindered phenol, semi-hindered phenol, and hindered amine.

[0034] Examples of the hindered phenol include 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate, bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionic acid](2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diyl)bis(2,2-dimethyl-2,1-ethanediyl), bis(3-t-butyl-4-hydroxy-5-methylbenzene propanoic acid)ethylene bis(oxyethylene), a mono-hindered phenol compound having at least one mono-hindered hydroxyphenyl group and having a molecular weight of about 300 or more, a polymer of p-cresol and divinylbenzene, a polymer of p-cresol and dicyclopentadiene, a polymer of p-chloromethylstyrene and p-cresol, and the like.

[0035] The semi-hindered phenol is preferably a compound that contains at least two hindered hydroxyphenyl groups and has a skeleton selected from bisesters and alkylidenes. Furthermore, the alkyl group located at the ring position adjacent to the hydroxyl group in the hydroxyphenyl group is preferably a tertiary butyl group, and it is even more preferable that the equivalent weight of the hydroxyl group is 600 or less. Examples of semi-hindered phenol compounds include ethylene-1,2-bis(3,3-bis[3-t-butyl-4-hydroxyphenyl]butyrate), in which a semi-hindered hydroxyphenyl group is covalently bonded to a bisester skeleton, and 1,1-bis(2-methyl-5-t-butyl-4-hydroxyphenyl)butane, 1,1,3-tris(2-methyl-5-t-butyl-4-hydroxyphenyl)butane, and 1,1,3-tris(2-methyl-5-t-butyl-4-hydroxyphenyl)butane, in which a unihindered hydroxyphenyl group is covalently bonded to an alkylidene skeleton.

[0036] Hindered amines include 4-oxo-2,2,6,6-tetramethylpiperidine, 1,3,8-triaza-2,4-dioxo-3-stearyl-7,7,9,9-tetramethyl-spiro(4,5)decane, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6 Examples include 6-tetramethyl-4-piperidyl)hexamethylene-1,6-dicarbamate, 1,3,8-triaza-2-oxo-3-phenyl-4-imino-7,7,9,9-tetramethyl-spiro[4,5]decane, and 1,3,8-triaza-2,4-dioxo-3-n-octyl-7,7,9,9-tetramethyl-8-benzyl-spiro(4,5)decane.

[0037] Examples of radical chain initiation inhibitors include benzotriazoles and benzophenones. Benzotriazoles include 2-(2'-hydroxy-5'-methylphenyl)benztriazole, 2-(2'-hydroxy-5'-t-butylphenyl)benztriazole, 2(2'-hydroxy-3',5'-di-t-butylphenyl)benztriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorbenztriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorbenztriazole. Examples include 2-(2'-hydroxy-3',5'-diisoamylphenyl)benztriazole, 2-(2-hydroxy-3,5-(1,1-dimethyl-1-phenylmethyl)phenyl)benztriazole, 2-[2-hydroxy-5-(1,1,3,3-tetramethylbutyl)phenyl]benztriazole, and condensates of methyl-3-(3-t-butyl-5(2H-benzotriazole-2-yl)-4-hydroxyphenyl)propionate and polyethylene glycol.

[0038] Benzophenones include 2-hydroxy-4-methoxybenzophenone, 2-hydroxybenzophenone, 2-hydroxy-4-n-oxybenzophenone, 2-hydroxy-4-isooxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-butoxybenzophenone, 2-hydroxy-3,5-dimethylbenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-5-chlorbenzophenone, and 2,2'-dihydroxybenzophenone.

[0039] Examples of peroxide decomposing agents include phosphates and phosphonites. Examples of phosphates include tris(2,4-di-t-butylphenyl) phosphite, tris(nonylphenyl) phosphite, tris(isooctylphenyl) phosphite, tris(2,6-dimethylphenyl) phosphite, distearyl-pentaerythrityl phosphite, ditridicate phosphite, triallyl phosphite, and phenyldi-tridecyl phosphite.

[0040] Examples of phosphonates include distearyl pentaerythritol diphosphonite, tris(di-tert-butylphenyl)phosphonite, diactyl palmitylphosphonite, tris(2,4-di-tert-butylphenyl)phosphonite, diisodecylphenylphosphonite, and phosphonite dioxide.

[0041] As plasticizers, phthalate esters such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate, diisodecyl phthalate, diundecyl phthalate, and diisononyl phthalate; phosphate esters such as tricresyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, trimethylhexyl phosphate, tris-chloroethyl phosphate, and tris-dichloropropyl phosphate; octyl trimellitate, isodecyl trimellitate, and trimellitate esters. Examples include fatty acid esters such as dipentaerythritol esters, dioctyl adipate, dimethyl adipate, di-2-ethylhexyl azelate, dioctyl azelate, dioctyl sebacate, di-2-ethylhexyl sebacate, and methylacetyl ricinocate; pyromellitic acid esters such as octyl pyromellitic acid ester; epoxy plasticizers such as epoxidized soybean oil, epoxidized linseed oil, and epoxidized alkyl fatty acid esters; polyether plasticizers such as adipate ether esters and polyethers; liquid rubbers such as liquid NBR, liquid acrylic rubber, and liquid polybutadiene; and non-aromatic paraffin oils.

[0042] Examples of anti-adhesion agents include saturated fatty acid metal salts and / or saturated fatty acid amides. A saturated fatty acid metal salt refers to a saturated fatty acid that is ionically bonded to a metal. A saturated fatty acid amide refers to an amide compound formed by the condensation of a saturated fatty acid and an amine. As saturated fatty acids constituting saturated fatty acid metal salts and saturated fatty acid amides, saturated fatty acids having 12 to 20 carbon atoms are preferred, with lauric acid, palmitic acid, stearic acid, arachidic acid, etc., being examples, but stearic acid is particularly preferred. As metals constituting saturated fatty acid metal salts, examples include magnesium, calcium, aluminum, zinc, etc., but magnesium is preferred. As amines constituting saturated fatty acid amides, they can be monoamines or diamines. Examples of monoamines include monomethylamine, dimethylamine, monoethylamine, diethylamine, monoethanolamine, diethanolamine, etc., and examples of diamines include ethylenediamine, hexamethylenediamine, etc., but ethylenediamine is preferred. In other words, magnesium stearate is preferred as a saturated fatty acid metal salt, and ethylenebisstearamide is preferred as a saturated fatty acid amide.

[0043] The polyurethane resin composition of this embodiment can be manufactured using known polyurethaneization reaction techniques. Both the one-shot method (OS method) and the prepolymer method (PPo method) are applicable, but the one-shot method is preferred from the viewpoint of controlling the molecular weight of the hard segments. The manufacturing method using the one-shot method will be described below.

[0044] In the production of the thermoplastic polyurethane resin composition of this embodiment, polyalkylene ether diols, particularly polytetramethylene ether diol (PTMG), are preferred as the long-chain polyol. The number average molecular weight of PTMG is preferably 900 to 3000. If it is 900 or higher, hydrogen bonding between urethane bonds increases, allowing for appropriate control of the distance between hard domains. On the other hand, if it is 3000 or lower, the self-assembly of soft domains is enhanced, a microphase separation structure develops, and elasticity suitable for disposable diaper applications can be achieved. More preferably, it is 1500 to 3000, and even more preferably 1800 to 2500.

[0045] The molecular weight distribution of PTMG is preferably 2.5 or less. By using PTMG with a molecular weight of 2.5 or less, the uniformity of the hard segment molecular weight is increased, the distance between hard domains can be controlled to be between 5 nm and 20 nm, and the rate of change during heating can also be controlled within the scope of the present invention. There is no particular limit to the lower limit of the PTMG molecular weight distribution, but it is 1.0 or more for ease of procurement. More preferably it is 1.0 or more and 2.0 or less, and even more preferably 1.1 or more and 1.8 or less.

[0046] The moisture content of PTMG is preferably 500 ppm or less. By using PTMG with a moisture content of 500 ppm or less, deactivation of isocyanate groups due to side reactions with moisture during polymerization is less likely to occur, making it possible to increase the molecular weight and control the weight-average molecular weight of the thermoplastic polyurethane resin composition to 150,000 or more and 500,000 or less. More preferably 300 ppm or less, and even more preferably 200 ppm or less.

[0047] Methylene-bis(4-phenylisocyanate) (MDI) is preferred as the diisocyanate compound. The content of MDI isomers (2,2'-MDI, 2,4'-MDI, 4,4'-MDI) is preferably 5.0% or less. A low isomer content promotes the regular arrangement of molecular chains and increases the uniformity of hard segment molecular weight, so that the hydrogen bonding rate measured by 13C-NMR can be controlled to 51% or more and 80% or less. More preferably 3.0% or less, and even more preferably 2.0% or less.

[0048] The content of MDI dimers is preferably 5.0% or less. A content of 5.0% or less makes it less likely for molecular weight to decrease due to dimer decomposition during polymerization, making it easier to obtain a polyurethane resin with high molecular weight and a uniform molecular weight distribution. This allows for control of the weight-average molecular weight between 150,000 and 500,000. Furthermore, the molecular weight distribution can be controlled between 1.5 and 3.0. More preferably, it is 3.0% or less, and even more preferably 2.0% or less.

[0049] As the active hydrogen-containing compound, 1,4-butanediol (BDO) is preferred. The water content of the BDO is also preferably 500 ppm or less, which suppresses side reactions (urea biuret formation) during hard segment formation and increases the uniformity of the hard segment molecular weight, so that the hydrogen bonding rate measured by 13C-NMR can be controlled to 51% or more and 80% or less. More preferably 300 ppm or less, and even more preferably 200 ppm or less.

[0050] The total number of moles (OH / NCO ratio) of the active hydrogen-containing compound (mainly 1,4-butanediol) and the long-chain polyol (mainly PTMG) is preferably 0.95 or more and 1.10 or less. If it is 0.95 or more, the formation of gel due to side reactions (allophanate) is suppressed, and if it is 1.10 or less, the reactivity of the urethane bond is increased, so that the weight-average molecular weight and molecular weight distribution of the thermoplastic polyurethane resin composition can be controlled within the range of the present invention. More preferably it is 0.99 or more and 1.05 or less, and even more preferably 1.00 or more and 1.01 or less.

[0051] In the polymerization process, the supply tank temperature for each raw material (PTMG, BDO, MDI, etc.), the piping temperature, and the mixer temperature are preferably in the range of 30°C to 80°C. PTMG and BDO are heated and maintained at 40°C to 60°C, and MDI at 50°C to 70°C, and the raw materials are measured and supplied while matching their respective viscosities. After uniformly mixing these in the mixer section, they are continuously fed into the reaction section, such as a twin-screw extruder. By allowing the melting, kneading, and reaction of the raw materials to proceed in a stepwise and uniform manner, localized reactions of chain extenders such as BDO and the generation of unmelted material can be suppressed, resulting in a uniform hard segment structure and a high hydrogen bonding rate.

[0052] Various stirring methods can be used in the polymerization process, including mixers, static mixers, dynamic mixers, propeller-type stirrers, paddle-type stirrers, and screw stirring of twin-screw extruders. Among these, mixers (especially high-speed dynamic mixers) are the most preferred. Mixers excel at uniform mixing of raw materials and temperature uniformity, and can suppress localized reactions and the generation of unmelted material in the initial stages of the reaction. The rotation speed of the mixer should preferably be between 500 rpm and 4000 rpm for medium-high speed stirring. Within this range, raw materials such as PTMG, BDO, and MDI can be uniformly mixed in a short time, and the molecular weight of the hard segment, the molecular weight of the soft segment, and the hard fraction can be precisely controlled within the scope of the present invention. At speeds of 500 rpm or higher, temperature and concentration unevenness are less likely to occur, and the dispersion of raw materials becomes uniform, while at speeds of 4000 rpm or lower, excessive shearing can suppress the cleavage of PTMG molecular chains.

[0053] To ultimately produce a thermoplastic polyurethane resin composition with a controlled range of hard segment molecular weight, hard domain distance, and heating rate, it is important to measure the hard segment molecular weight and hydrogen bonding rate immediately after stirring during the polymerization process and adjust process conditions such as reaction temperature, raw material supply ratio, stirring speed, and vacuum level accordingly. Methods for measuring the hard segment molecular weight and hydrogen bonding rate immediately after stirring include analyzing a sample taken from the raw material mixture stirred in a mixer using 1H-NMR or 13C-NMR as described herein. Furthermore, analytical methods such as GPC, FT-IR, and DSC can be used in combination as needed to confirm the reaction progress and the uniformity of the segment structure.

[0054] The oxygen concentration inside the piping is preferably in the range of 10% or less. Within this range, side reactions with moisture inside the piping are suppressed, and the generation of foreign substances such as urea and biuret is reduced, making it easier to form uniform hard domains, allowing the distance between hard domains to be controlled to 5 nm to 20 nm, and the rate of change during heating to be controlled within the range of the present invention. More preferably, it is 8.0% or less, and even more preferably 5.0% or less.

[0055] In the production of the thermoplastic polyurethane resin composition of this embodiment, various reaction devices can be used to ensure that the melting, kneading, and reaction of the raw materials proceed in a stepwise and uniform manner. Examples include batch reactors, continuous reactors, reaction kneaders, and extruders, and it is possible to optimize temperature control and mixing conditions according to each device. Among these, twin-screw extruders are particularly preferred because they can process the entire process from raw material supply to reaction and granulation in a continuous manner, contributing to the realization of a uniform hard segment structure, a high hydrogen bonding rate, and a uniform granular resin shape. When using a twin-screw extruder, it is preferable to set the cylinder temperature stepwise for each element (zone) from the upstream (raw material input section) to the downstream (just before the die). For example, in a five-zone configuration, a temperature gradient is created by setting a temperature difference of 10 to 30°C for each zone, such as 130 to 150°C for the first zone (raw material input area), 150 to 170°C for the second zone, 170 to 190°C for the third zone, 190 to 210°C for the fourth zone, and 200 to 220°C for the fifth zone (immediately before die). This temperature setting is effective in suppressing localized reactions of chain extenders such as BDO and the generation of unmelted material, thereby achieving uniform hard segment molecular weight control. Furthermore, twin-screw extruders have high kneading performance, which also contributes to improving the dispersibility of raw materials and the uniformity of the reaction.

[0056] In a twin-screw extruder, it is preferable to introduce a vacuum degassing process to efficiently remove by-products and unreacted components and to precisely control the molecular weight of hard segments and the molecular weight distribution of the polyurethane resin composition. It is practical and effective to perform the degassing process at a vacuum level between 200 Pa and 1000 Pa. Vacuum degassing allows for control of BDO evaporation within the extruder, thereby controlling reactivity and enabling the Mh fraction to be controlled within the desired range.

[0057] Various granulation methods are available to obtain granular resin, including the strand cutting method, die cutting method, and underwater cutting method. Among these, the strand cutting method is the most preferred. The strand cutting method involves extruding molten resin as a water-cooled strand, and then cutting it to a certain length after cooling. Because it is cut after sufficient cooling, it offers excellent uniformity in chip shape and weight, and suppresses the generation of fine powder, thus contributing to the stability of raw material supply during spinning and preventing blocking in the hopper.

[0058] When using the strand cutting method, the resin temperature during cutting is preferably in the range of 10°C to 100°C. The strands extruded from the extruder have sufficient shape retention within this temperature range, and a uniform chip shape can be obtained when cutting, so that the weight of the granular resin can be controlled to 10 mg to 100 mg and the coefficient of variation of the weight to 50% or less. Furthermore, by controlling the resin temperature during cutting to 10°C to 100°C, deformation and adhesion during cutting are suppressed, so there is less polymer residue adhering to the blade, and the weight of fine powder adhering to the surface of the granular resin can be controlled to 10 wt% or less of the weight of the granular resin. More preferably, it is 20°C to 80°C, and even more preferably 30°C to 70°C.

[0059] The method of cooling the strand is not particularly limited, but water cooling at 10°C to 60°C is preferred. Within this range, the occurrence of cracks due to rapid cooling is suppressed, and the strand surface solidifies quickly, so that the amount of fine powder generated during cutting and the fine resin fragments produced during cutting are reduced, and the weight of fine powder adhering to the surface of the granular resin can be controlled to 10 wt% or less of the weight of the granular resin. More preferably, the temperature is 15°C to 50°C, and even more preferably 20°C to 40°C.

[0060] Solid-phase polymerization can be performed as needed. Solid-phase polymerization is a process in which the polyurethane resin obtained after melt polymerization is processed into granules and then heat-treated for a certain period of time in the range of 40°C to 100°C to increase the molecular weight and improve the crystallinity of the hard segments. If the treatment temperature is 40°C or higher, molecular motion becomes possible, and the crystallinity of the hard domains is enhanced. The crystallinity peak temperature measured by DSC can be controlled to be between 60°C and 100°C, and the difference between the crystallinity start temperature and the crystallinity end temperature can be controlled to be between 40°C and 75°C. Furthermore, if the temperature is below 100°C, the crystallinity of the hard segments can be improved while suppressing thermal degradation and decomposition of the soft segments. The treatment time is preferably between 30 minutes and 24 hours, and it is desirable to perform the treatment under an inert gas atmosphere such as nitrogen to prevent oxidation. Solid-phase polymerization is particularly effective when high molecular weight or improved blocking prevention performance is required.

[0061] Another embodiment of the present invention is a thermoplastic polyurethane elastic fiber comprising a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, characterized by the following features: (a) the molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the molecular weight of the soft segment is 1900 to 4800, and the proportion of the hard segment (Mh fraction) is 15% to 40%; (b) the weight-average molecular weight (Mw) is 100,000 to 300,000, and the molecular weight distribution (Mw / Mn (number-average molecular weight)) is 1.5 to 3.0; (c) the hard domain distance measured by a small-angle X-ray scattering device (SAXS) is 8 nm to 25 nm; and (d) the rate of change of the hard domain distance when heated to 140°C is 30% or less.

[0062] The number-average molecular weight of the hard segments of the thermoplastic polyurethane elastic fiber measured by 1H-NMR in this embodiment is 800 to 2400. By controlling the number-average molecular weight of the hard segments of the elastic fiber to 800 to 2400, it is possible to achieve both heat resistance and elasticity. That is, when the number-average molecular weight of the hard segments is 800 or more, hydrogen bonding between hard segments increases, and the cohesive force of the hard domains improves, thereby enabling the simultaneous expression of heat resistance and elasticity. On the other hand, if the number-average molecular weight of the hard segments is 2400 or less, the hard domains are less likely to coarseen, and uneven elongation is less likely to occur when a draft is applied during the hot melt coating process, thus reducing the likelihood of thread breakage due to localized stress concentration. From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, and the manufacturing stability of disposable diapers, the number-average molecular weight of the hard segments of the thermoplastic polyurethane elastic fiber is preferably 1000 to 2000, and more preferably 1100 to 1800.

[0063] The number-average molecular weight of the soft segments of the thermoplastic polyurethane elastic fiber in this embodiment, as measured by 1H-NMR, is 1900 to 4800, from the viewpoint of heat resistance and elasticity development. When the number-average molecular weight of the soft segments is 1900 or more, the soft segments stretch sufficiently, enabling the elasticity required for disposable diapers. On the other hand, when the number-average molecular weight of the soft segments is 4800 or less, the self-assembly of the soft domains increases, leading to the development of a microphase separation structure. That is, the interface between hard domains and soft domains becomes clearer, and the mixed region decreases, enabling the development of the necessary heat resistance. From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, a number-average molecular weight of 2500 to 4500 is preferred, more preferably 3000 to 4000, and most preferably 3200 to 3500.

[0064] The thermoplastic polyurethane elastic fiber of this embodiment has a hard segment ratio of 15% to 40%. The Mh fraction (%) is calculated by the following formula: Mh fraction (%) = (number average molecular weight of hard segments (Mh)) / {(number average molecular weight of hard segments (Mh)) + (number average molecular weight of soft segments (Ms))} × 100 By controlling the Mh fraction of the elastic fiber to 15% to 40%, both heat resistance and elasticity can be achieved. When the Mh fraction is 15% or more, hydrogen bonding between urethane bonds increases, the distance between hard domains falls within the aforementioned range, and heat resistance and elasticity are improved. On the other hand, when the Mh fraction is 40% or less, the tightening force becomes too strong (the stress during contraction becomes too strong), leaving marks on the skin when wearing a disposable diaper, and the responsiveness during contraction decreases (it does not follow the body's movements). The Mh fraction of the elastic fiber is preferably 20% to 30%, and more preferably 22% to 28%.

[0065] The thermoplastic polyurethane elastic fiber of this embodiment has a hard domain distance of 8 nm to 25 nm as measured by SAXS in a room temperature (25°C) atmosphere, and the rate of change of the hard domain distance in a 140°C atmosphere compared to the hard domain distance in a room temperature atmosphere measured by the SAXS heating in-situ measurement method is 30% or less. By controlling the hard domain distance to 8 nm or more, the hard domains are less likely to melt when heated, and the heat resistance of the elastic fiber required in the hot melt coating process of disposable diaper manufacturing can be satisfied. On the other hand, by controlling the hard domain distance to 25 nm or less, coarse hard domains are less likely to be generated and the elongation of soft domains is not inhibited, so the elasticity required for disposable diapers can be achieved. The hard domain distance must be 8 nm to 25 nm, preferably 9 nm to 20 nm, and more preferably 10 nm to 18 nm.

[0066] By controlling the structure so that the rate of change in the distance between hard domains under a 140°C atmosphere compared to the distance under a room temperature atmosphere is 30% or less, hard domains that serve as binding points between soft domains remain, making it possible to provide elastic fibers that can withstand the heat and tension of the hot melt coating process. On the other hand, since it is practically impossible to form perfectly uniform hard domains that do not undergo any structural change under a 140°C atmosphere, the lower limit of the rate of change in the distance between hard domains between room temperature and 140°C is 1%. Therefore, from the viewpoint of heat resistance and elasticity of the elastic fiber, the rate of change in the distance between hard domains between room temperature and 140°C is 1% or more and 30% or less, more preferably 5% or more and 25% or less, and even more preferably 5% or more and 20% or less.

[0067] The thermoplastic polyurethane elastic fiber of this embodiment has a rate of change of the hard domain distance under a 160°C atmosphere of 50% or less compared to the hard domain distance under a room temperature atmosphere. As mentioned above, the temperature of the hot melt applied in the hot melt application process of diaper manufacturing is generally between 140°C and 160°C. Since the rate of change of the hard segment distance when the thermoplastic polyurethane elastic fiber of the present invention is heated to 160°C is 50% or less, it is possible to provide an elastic fiber that does not break during the high-temperature hot melt application process. The rate of change of the hard domain distance under a 160°C atmosphere is preferably 45% or less, and more preferably 40% or less.

[0068] The weight-average molecular weight (Mw) of the thermoplastic polyurethane elastic fiber in this embodiment is 100,000 or more and 300,000 or less. If Mw is 100,000 or more, the cohesive force at high temperatures is less likely to decrease due to entanglement of molecular chains, and an elastic fiber that does not break during the high-temperature hot melt coating process can be provided. On the other hand, if Mw is 300,000 or less, the cohesive force is appropriate, the stress during elongation does not become too high, the tightening force when wearing a disposable diaper does not become too strong, and it is less likely to leave marks on the skin. From the viewpoint of heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, the molecular weight distribution of the thermoplastic polyurethane elastic fiber is preferably 120,000 or more and 250,000 or less, and more preferably 140,000 or more and 220,000 or less.

[0069] The molecular weight distribution (Mw / Mn (number-average molecular weight)) of the thermoplastic polyurethane elastic fiber in this embodiment is 1.5 or more and 3.0 or less. If the molecular weight distribution of the thermoplastic polyurethane elastic fiber is less than 1.5, the molecular chains become too uniform, making it difficult to disperse stress during elongation, and thus it cannot exhibit the elasticity required for diaper gather fibers. Furthermore, if the molecular weight distribution of the thermoplastic polyurethane elastic fiber exceeds 3.0, the amount of low molecular weight components increases, making it impossible to maintain cohesive force due to entanglement of molecular chains during heating, and thus it cannot exhibit the heat resistance required for diaper gather fibers. From the viewpoint of heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, the molecular weight distribution of the thermoplastic polyurethane elastic fiber is preferably 1.7 or more and 2.5 or less, and more preferably 1.8 or more and 2.2 or less.

[0070] The thermoplastic polyurethane elastic fiber of this embodiment has a hydrogen bonding rate of 51% to 80% as measured by 13C-NMR. If the hydrogen bonding rate by 13C-NMR is 51% or higher, the density of hard domains is high, and the decrease in cohesive force due to heat is less likely to occur, thus improving heat resistance. If the hydrogen bonding rate by 13C-NMR is 80% or lower, high-density and coarse hard segments are not formed, the uniformity of microphase separation is high, and the fluidity of soft segments is not restricted, so sufficient elasticity can be achieved. From the viewpoint of improving the heat resistance and elasticity of the thermoplastic polyurethane elastic fiber, a hydrogen bonding rate by 13C-NMR of 53% to 75% is preferred, and more preferably 55% to 70%.

[0071] The total fineness of the thermoplastic polyurethane elastic fiber in this embodiment is preferably 160 dtex or more and 2000 dtex or less. The total fineness referred to here is calculated from a certain amount of yarn mass after winding. If the total fineness is 160 dtex or more, the tightening force in the gathered portion is sufficient, and the disposable diaper is less likely to slip down. On the other hand, if the total fineness is less than 2000 dtex, stiffness in the gathered portion is less likely to occur. The total fineness is more preferably 200 dtex or more and 1000 dtex or less, and even more preferably 300 dtex or more and 700 dtex or less.

[0072] The thermoplastic polyurethane elastic fiber of this embodiment can be a multifilament, and the single filament fineness is preferably 5 dtex or more and 100 dtex or less. When the single filament fineness is 5 dtex or more, the heat of the hot melt is not easily transferred during the gathering manufacturing process, and yarn breakage due to heat is less likely to occur. On the other hand, when the single filament fineness is 100 dtex or less, cooling is more effective during spinning and the orientation of the single filaments is easier to achieve, so it is easier to obtain an elastic fiber that exhibits sufficient tightening force when wearing a disposable diaper. The single filament fineness is preferably 10 dtex or more and 45 dtex or less, and more preferably 20 dtex or more and 40 dtex or less.

[0073] In this embodiment, the tanδ of the thermoplastic polyurethane elastic fiber at 25°C is preferably 0.01 to 0.10 from the viewpoint of elasticity. When the tanδ at 25°C is 0.01 or higher, there is less energy loss during fiber elongation, and elastic deformation is efficient, improving the ratio of elongation stress to recovery stress (R / S) in the repeated elongation-recovery test. On the other hand, when the tanδ at 25°C is 0.10 or lower, the molecular chains are strongly entangled, and due to the synergistic effect with the cohesive force due to hydrogen bonding of the hard segments, the recovery stress during elongation is high, the tightening force in the gathered portion is sufficient, and the disposable diaper is less likely to slip down. The tanδ at 25°C is preferably 0.02 to 0.09, and more preferably 0.03 to 0.08.

[0074] In this embodiment, the tanδ of the thermoplastic polyurethane elastic fiber at 160°C is preferably 0.05 to 0.20 from the viewpoint of heat resistance. When the tanδ at 160°C is 0.05 or higher, the cohesive force due to the entanglement of molecular chains does not become too strong, the stress does not become too high during heating and stretching in the gathering manufacturing process, and heat resistance can be maintained. On the other hand, when the tanδ at 150°C is 0.20 or lower, the molecular motion during heating is suppressed by the entanglement of molecular chains, and the decrease in cohesive force during heating is small, thus improving heat resistance. The tanδ at 160°C is preferably 0.08 to 0.15, and more preferably 0.10 to 0.13.

[0075] The storage modulus E' of the thermoplastic polyurethane elastic fiber in this embodiment at 25°C is preferably 1 MPa to 10 MPa from the viewpoint of elasticity. When E' at 25°C is 1 MPa or higher, the molecular chains are strongly entangled, and the recovery stress during elongation can be increased due to the synergistic effect of the cohesive force due to hydrogen bonding and the intermolecular forces, resulting in sufficient tightening force in the gathered portion and making it difficult for the disposable diaper to slip down. When E' at 25°C is 10 MPa or lower, the energy loss during fiber elongation is small, and elastic deformation is efficient, so the R / S ratio is improved. When E' at 25°C is preferably 1 MPa to 7 MPa, more preferably 1 MPa to 5 MPa, and even more preferably 1 MPa to 3 MPa.

[0076] In viscoelasticity measurements, the thermoplastic polyurethane elastic fiber exhibits a plateau region where the strain stress is constant at temperatures above 90°C, and then decreases as the temperature rises. From the viewpoint of heat resistance, the temperature at which the strain stress decreases by 10% (with the plateau region being 100%) is preferably between 130°C and 230°C. When the strain stress decrease temperature is above 130°C, molecular motion during heating is suppressed by the entanglement of molecular chains, resulting in less reduction of cohesive force during heating, thus improving heat resistance. On the other hand, when the strain stress decrease temperature is below 230°C, the stress does not become too high during heating and stretching in the hot-melt coating process of disposable diaper manufacturing, thus maintaining heat resistance. The strain stress decrease temperature is preferably between 140°C and 200°C, and more preferably between 150°C and 180°C.

[0077] The elongation at break of the thermoplastic polyurethane elastic fiber of the present invention is preferably 300% or more and 900% or less. If the elongation is 300% or more, thread breakage due to insufficient elongation is less likely to occur during the disposable diaper manufacturing process. The elongation is preferably 400% or more, and more preferably 500% or more.

[0078] In the 200% stretch-recovery repeated test of the thermoplastic polyurethane elastic fiber of this embodiment, the ratio R / S (%) of the stress at 90% stretch (S) to the stress at 90% recovery (R) in the second cycle is preferably 60% or more and 85% or less. If R / S is 60% or more, the tightening force when wearing a disposable diaper is sufficient, and the diaper is less likely to slip down or urine leakage will occur. On the other hand, if R / S is 85% or less, marks on the skin due to excessive tightening are less likely to be left. R / S is preferably 65% ​​or more and 80% or less, and more preferably 70% or more and 78% or less.

[0079] The spinning method for the thermoplastic polyurethane elastic fiber in this embodiment is not particularly limited as long as the desired physical properties can be obtained. For example, in addition to the method of putting granular resin of the polyurethane resin composition into an extruder, heating it, and melt spinning it, other methods include melting the granular resin of the polyurethane resin composition, mixing it with a polyisocyanate compound, and then spinning it, and adding a reaction product of the isocyanate group prepolymer and an active hydrogen compound to the isocyanate group prepolymer at both ends, and spinning it continuously without going through chipping.

[0080] In the method for producing thermoplastic polyurethane elastic fibers of this embodiment, it is preferable to use the thermoplastic polyurethane resin composition of the present invention. The moisture content of the raw material resin of the thermoplastic polyurethane resin composition is preferably 500 ppm or less. If it is 500 ppm or less, the isocyanate groups formed when the urethane bonds are temporarily detached during the melt-kneading of the polyurethane will not be deactivated by moisture, and the weight-average molecular weight can be controlled to 100,000 to 300,000 when the urethane is recombined. The moisture content is preferably 400 ppm or less, and more preferably 200 ppm or less.

[0081] The spinning process for thermoplastic polyurethane elastic fibers involves feeding a thermoplastic polyurethane resin composition into an extruder, measuring it with a metering pump, and introducing it into a spinning head. If necessary, foreign matter is removed within the spinning head by filtration using wire mesh or glass beads, after which the fiber is discharged from the die, air-cooled in a cold air chamber, treated with a processing agent, and then wound up via a godet roll.

[0082] In the spinning process, the die temperature, cooling start point, cold air velocity, cold air temperature, cooling length, focusing position, and spinning speed are adjusted to precisely control the fiber's temperature profile, spinning tension, and crystallinity. The temperature from the extruder to the spinning head is preferably between 150°C and 230°C. The lower the temperature within this range, the more effectively the decrease in molecular weight and the increase in molecular weight distribution can be suppressed. Furthermore, it is preferable to lower the temperature in areas of the melting line where the residence time is long, making it easier to control within the range of the present invention. The cooling method used is a general method for melt spinning, such as applying cold air perpendicular to the direction of yarn travel from directly below the spinneret. The cooling start point is preferably 20 mm to 200 mm, the cold air velocity is preferably 0.2 m / s to 2.0 m / s, the cold air temperature is preferably 5°C to 20°C, the cooling length is preferably 200 mm to 2000 mm, the convergence position is preferably 500 mm to 3000 mm, and the spinning speed is preferably 400 m / min to 2000 m / min. By combining these methods and stretching and oriented the thermoplastic polyurethane resin composition near its crystallization temperature, hard domains can be grown, and the inter-hard domain distance of the thermoplastic polyurethane elastic fiber and the rate of change of inter-domain distance during heating can be controlled within the scope of the present invention.

[0083] In a method for producing thermoplastic polyurethane elastic fibers, the method for controlling the hard domain distance at room temperature, the rate of change of the hard domain distance during heating, and the hydrogen bonding rate within a specific range is not particularly limited. Examples include methods for controlling the cohesiveness of hard segments and methods for developing a microphase separation structure to promote the growth of hard domains. Specifically, to control the cohesiveness of hard segments, methods include using the thermoplastic polyurethane resin composition, including isocyanate isomer ratios within the hard segments within the aforementioned range, including low molecular weight components within the aforementioned range, and adding nucleating agents.

[0084] Effective methods for developing a microphase separation structure and promoting hard domain growth include extending the time it takes for the polymer temperature to reach the phase separation temperature after the polymer is extruded from the spinneret, and methods such as attaching a heat-retaining cylinder or heating cylinder of 10 mm to 500 mm in height to heat the area directly below the spinneret to 100°C to 200°C, lowering the height of the cold air outlet to lower the starting point of cooling to 50 mm to 500 mm directly below the spinneret, narrowing the pore pitch to 2 mm to 5 mm to make cooling more difficult, increasing the fineness of the single filament to reduce the yarn elongation rate, and blowing warm air from below toward the spinneret.

[0085] Methods to promote hard domain growth include increasing the tensile stress after the start of cooling to orient the hard segments and enhance hydrogen bonding strength by rapidly cooling using cold air at temperatures between 0°C and 15°C, or by using cold air containing mist, and by increasing the number of filaments to increase the cooling surface area of ​​the fiber.

[0086] In the method for producing thermoplastic polyurethane elastic fibers of this embodiment, the method for controlling the viscoelasticity (tanδ, E', strain stress reduction temperature) to a specific range is not particularly limited, but examples include methods for maintaining the entanglement of molecular chains and methods for reducing main chain breakage of polyurethane. Specifically, examples include using the thermoplastic polyurethane resin composition, reducing the shear rate by designing the screw of the extruder, lowering the temperature of the extruder, and lowering the temperature and pressure of the compression section of the extruder. When implementing each of these methods, the viscosity inside the extruder may become too high, and the original purpose of the extruder, which is to melt and knead the resin, may not be achieved. Therefore, viscosity can also be adjusted by appropriately adding plasticizers, adjusting the isomer ratio of isocyanates in the hard segment to a specific range, or including low molecular weight components in a specific concentration range. Other examples include lowering the L / D ratio of the spindle, shortening the flow path in the spindle pack to reduce residence time, using stabilizers as additives, and reducing the tensile stress after spindle extrusion. Methods to reduce tensile stress include attaching a heater to a heat-retaining tube or the spindle surface to warm the spindle after spindle extrusion, blowing hot air, lowering the cooling start point, and raising the convergence position.

[0087] In this embodiment, the thermoplastic polyurethane elastic fiber is characterized by the fact that the polyurethane main chain of the thermoplastic polyurethane resin composition used as a raw material is broken by heat absorption during spinning, and the rate of breakage is preferably 10% or less from the viewpoint of heat resistance. The rate of breakage of the polyurethane main chain is calculated from the specific peak intensities obtained by measuring the FT-IR of the raw material polyurethane resin composition and the thermoplastic polyurethane elastic fiber obtained by spinning, using the following formula: Main chain breakage rate (%) = 100 - {Rm2 / Ra2} / {Rm1 / Ra1} × 100 {wherein Rm1 is approximately 2850 cm ―１ The C-H symmetric stretch peak of the thermoplastic polyurethane resin composition appearing in the vicinity is Ra1, which is approximately 1600 cm. ―１ The aromatic C=C stretch peak of the thermoplastic polyurethane resin composition appearing in the vicinity is approximately 2850 cm². ―１The C-H symmetrical stretch peak of thermoplastic polyurethane elastic fibers appears in the vicinity, and Ra2 is approximately 1600 cm. ―１ This is the aromatic C=C stretch peak of thermoplastic polyurethane elastic fibers appearing in the vicinity.

[0088] If the cleavage rate of the polyurethane main chain is 10% or less, molecular motion during heating is suppressed due to the entanglement of molecular chains, and the decrease in cohesive force during heating is small, thus improving heat resistance. The cleavage rate of the polyurethane main chain is more preferably 8% or less, and even more preferably 5% or less. On the other hand, there is no particular lower limit to the cleavage rate of the polyurethane main chain, but if it is 1% or more, the cohesive force due to the entanglement of molecular chains does not become too strong, and the stress does not become too high during heating and stretching in the manufacturing process of disposable diapers (hot melt coating process), thus maintaining heat resistance. The lower limit to the cleavage rate of the polyurethane main chain is more preferably 2% or more, and even more preferably 3% or more.

[0089] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measured values ​​in the examples were obtained by the measurement methods described below. In this example, the thermoplastic polyurethane resin composition is a manufactured granular resin, and the thermoplastic polyurethane elastic fiber is sampled from a manufactured wound yarn. However, if the sampling described below is not possible due to constraints such as sample size, a reasonable sampling method and measurement method may be adopted as appropriate.

[0090] (1) A hard domain distance thermoplastic polyurethane resin composition was set on a sample stage. In the case of thermoplastic polyurethane elastic fibers, the sample stage was set such that the fiber axis was perpendicular to the ground. X-rays were irradiated from a direction perpendicular to the fiber axis (long axis), and SAXS measurement was performed under the following conditions. Measurement apparatus: NANOPIX manufactured by Rigaku Corporation Incident X-ray wavelength λ: 0.154 nm Detector: Two-dimensional detector "Hypix-6000" Measurement time: 15 minutes Camera length: 1312 mm Measurement temperature: 25°C Optical system: Point collimation: 1st slit: 0.55 mmφ, guard slit: 0.35 mmφ High Resolution Mode Beam stopper: 2 mmφ

[0091] With the 12 o'clock direction of the two-dimensional SAXS pattern I(2θ, φ) obtained by the two-dimensional detector defined as 0°, the azimuth angle θ was defined clockwise, and the following formula I: {In the formula, φ ｓ : -10°, φ ｅ : 10°, θ: Bragg angle}, the fan-shaped average scattering intensity I(2θ) with respect to the yarn length direction was calculated. The obtained fan-shaped average scattering intensity I(2θ) was calculated by the following formula II: {In the formula, I ｃ (2θ): Scattering intensity corrected for the empty cell, I ｓａｍｐｌｅ (2θ): Scattering intensity of the sample, I ｅｍｐｔｙ (2θ): Scattering intensity of the empty cell, t ｓａｍｐｌｅ : Measurement time of the sample, t ｅｍｐｔｙ : Measurement time of the empty cell measurement, T: Transmittance, C: Apparatus constant}, the empty cell scattering correction was performed, and the one-dimensional scattering intensity I ｃ was calculated.

[0092] Next, the peak position q ｍａｘ obtained by fitting the vicinity of the peak of the fan-shaped average one-dimensional SAXS profile obtained by formula I and formula II with a Gaussian function was used to calculate the hard domain distance. Note that q is the absolute value of the scattering vector. {In the formula, θ: Bragg angle, λ: Incident X-ray wavelength}.

[0093] (2) Hard domain distance when heated at 140°C (heated In-Situ measurement) The thermoplastic polyurethane resin composition was set on the sample stage, and in the case of thermoplastic polyurethane elastic fibers, the fiber axis was set on the sample stage so that it was perpendicular to the ground. Both ends of the thread were fixed to the sample stage. The sample stage was placed in a dedicated heating furnace heated to 140°C, and after 5 minutes, X-ray irradiation was performed while still heated, and the hard domain distance was measured using SAXS.

[0094] (3) Hard domain distance when heated to 160°C (heated In-Situ measurement) The thermoplastic polyurethane resin composition was set on the sample stage, and in the case of thermoplastic polyurethane elastic fibers, the fiber axis was set on the sample stage so that it was perpendicular to the ground. Both ends of the thread were fixed to the sample stage. The sample stage was placed in a dedicated heating furnace heated to 160°C, and after 5 minutes, X-ray irradiation was performed while still heated, and the hard domain distance was measured using SAXS.

[0095] (4) Qualitative determination of components of thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber and measurement of molecular weight of hard segment by 1H-NMR measurement Samples taken from thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber, along with predetermined amounts of internal standard dimethyl sulfoxide, were measured and 1H-NMR was performed under the following conditions to identify the structure and molar ratio of long-chain polyols, active hydrogen-containing compounds, and diisocyanate compounds. The structures of diisocyanate compounds and active hydrogen-containing compounds can be determined from the peak positions obtained by NMR measurement. Measurement device: Bruker Biospin Avance 600 Measurement nucleus: １ H Resonance frequency: 600 MHz Number of cumulative measurements: 256 Measurement temperature: Room temperature Solvent: Deuterated dimethylformamide Measurement concentration: 1.5% by weight Chemical shift standard: Dimethylformamide (8.0233 ppm)

[0096] The molecular weights of the thermoplastic polyurethane resin composition and the hard segments of the thermoplastic polyurethane elastic fibers are calculated by solving the following simultaneous equations (1) and (2): Mh = {Mda(N1-1) + Mdi × N0} / (N1 - N0-1) + 2Mdi …Equation (1) N0 = 0.03806N1 ４-0.03997N1 ３ +1.617N1 ２ -2.144N １ +0.8795 …Equation (2) Mda: Molecular weight of the active hydrogen-containing compound (number average molecular weight if two or more types are used in a mixture) Mdi: Molecular weight of the isocyanate compound N0: Molar ratio of unreacted isocyanate compound to long-chain polyol N1: Molar ratio of isocyanate compound to long-chain polyol Mh: Molecular weight of the hard segment N1 can be calculated from the integral value obtained from 1H-NMR, but when 4,4'-diphenylmethane diisocyanate is used as the isocyanate compound and polytetramethylene ether diol is used as the long-chain polyol, it is calculated by the following equation (3). N1 = (Mdim × 2) / Mdom ...Equation (3) In the equation, Mdim is the peak integral value of the methylene group of the isocyanate compound (around 3.82 ppm to 3.88 ppm) and Mdom is the peak integral value of the methylene group adjacent to the urethane bond of the long-chain polyol (around 4.10 ppm to 4.13 ppm). If the peak derived from the long-chain polyol overlaps with the peak of the active hydrogen-containing compound, the point where the data between the peaks is minimized is separated by a perpendicular line, and the peak integral value is calculated.

[0097] (5) Method for determining the ratio of the molecular weight of the soft segment to the hard segment (Mh fraction) The Mh fraction of the thermoplastic polyurethane resin composition and the thermoplastic polyurethane elastic fiber is given by the following equations (4) to (7): Ms = {Mdo + Mdi(N1-N0)} / (N1-N0-1) - 2Mdi ...Equation (4) Mh = {Mda(N1-1) + Mdi × N0} / (N1-N0-1) + 2Mdi ...Equation (5) N0 = 0.03806N1 ４ -0.3997N1 ３ +1.617N1 ２ -2.144N1 １+0.8795 …Equation (6) Mh fraction (%) = {Mh / (Ms + Mh)} × 100 …Equation (7) This is calculated by solving the simultaneous equations. In the equations, Ms: number average molecular weight of the soft segment Mdo: number average molecular weight of the long-chain polyol Mdi: molecular weight of the isocyanate compound N1: molar ratio of the isocyanate compound to the long-chain polyol N0: molar ratio of the unreacted isocyanate compound to the long-chain polyol Mh: number average molecular weight of the hard segment Mda: molecular weight of the active hydrogen-containing compound (number average molecular weight of the compound if two or more are mixed and used). Mdo can be calculated from the integral value obtained from 1H-NMR, but if polytetramethylene etherdiol is used as the long-chain polyol, it is calculated by the following equation (8). Mdo: 72 × {(Mdom + MdoM + Mdomc + MdomC) / (Mdom + MdoM)} + 18 ...Equation (8) In the equation, MdoM: Methylene group two positions away from the urethane bond of the long-chain polyol (around 1.65 ppm to 1.70 ppm) Mdomc: Methylene group adjacent to the O atom of the long-chain polyol (around 3.32 ppm to 3.42 ppm) MdomC: Methylene group of the long-chain polyol (around 1.50 ppm to 1.65 ppm). Also, if the peak derived from the long-chain polyol overlaps with the peak of the active hydrogen-containing compound, the point where the data between the peaks is minimized is demarcated with a perpendicular line, and the peak integral value is calculated.

[0098] (6) Measurement of hydrogen bonding rate of thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber by 13C-NMR measurement Samples taken from thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fiber, along with predetermined amounts of internal standard dimethyl sulfoxide, were measured, and 13C-NMR was measured under the following conditions to calculate the hydrogen bonding rate. Measurement device: Bruker 400 UltraShield Measurement nucleus: １３ C. Resonance frequency: 100 MHz; Number of cumulative measurements: 18,000; Measurement temperature: Room temperature; Solvent: Deuterated dimethylformamide; Measurement concentration: 5.0% by weight; Chemical shift standard: Dimethylformamide (162.66 ppm)

[0099] The hydrogen bonding rate between a thermoplastic polyurethane resin composition and thermoplastic polyurethane elastic fibers is calculated by solving the following equation (9): Hydrogen bonding rate = (Ndd + Ndi) / (Ndd + Ndi + Nip + Npp) × 100 ...Equation (9) In the equation, Ndd: Peak integral value derived from the isocyanate compound when the active hydrogen-containing compound is urethane bonded to both terminal groups of the isocyanate compound Ndi: Peak integral value derived from the isocyanate compound on the active hydrogen-containing compound side when the active hydrogen-containing compound and the long-chain polyol are urethane bonded to one terminal group each of the isocyanate compound Nip: Peak integral value derived from the isocyanate compound on the long-chain polyol side when the active hydrogen-containing compound and the long-chain polyol are urethane bonded to one terminal group each of the isocyanate compound Npp: Peak integral value derived from the isocyanate compound when the long-chain polyol is urethane bonded to both terminal groups of the isocyanate compound. When 4,4'-diphenylmethanediisocyanate is used as the isocyanate compound, 1,4-butanediol as the active hydrogen-containing compound, and polytetramethylene etherdiol as the long-chain polyol, the hard segment molecular weight can be calculated by using the peak integral values ​​at the following positions: Ndd: around 137.8 ppm to 138 ppm Ndi: around 138 ppm to 138.1 ppm Nip: around 135.9 ppm to 136.5 ppm Npp: around 136.0 ppm to 136.2 ppm. If the peaks overlap, the point where the data between the peaks is minimum is separated by a perpendicular line, and the peak integral value is calculated.

[0100] (7) Measurement of the slope of melt viscosity Using a Shimadzu flow tester CFT-500D (manufactured by Shimadzu Corporation), under the conditions of a sample amount of 1.5 g, a die (nozzle) diameter of 0.5 mm, and a thickness of 1.0 mm, an extrusion load of 49 N is applied, preheating for 240 seconds at an initial temperature of 120 °C, and then heating is increased at a constant rate of 3 °C / min. The plunger stroke-temperature curve drawn at that time is obtained and converted into a melt viscosity-temperature curve. When the temperature is plotted on the horizontal axis and the melt viscosity on the vertical axis on a logarithmic scale is plotted on a semi-logarithmic graph, the slope of the straight line of melt viscosity with respect to temperature is obtained.

[0101] (8) Measurement of Elongation at Breaking (%) The measurement is performed using a Shimadzu AGS-500NG AUTOGRAPH tester under conditions of a temperature of 20°C and a humidity of 65%. The elongation at breaking is measured when an elastic thread with a gripping length of 5 cm is stretched at a speed of 500 mm / min. Five samples are taken at 5 m intervals, and the elongation at breaking is measured for each, and the average value is calculated.

[0102] (9) Measurement of stress at 200% elongation in the first cycle, stress at 90% elongation and stress at 90% recovery in the second cycle, and method for evaluating elasticity A thermoplastic polyurethane elastic fiber is set in a tensile testing machine (Shimadzu AGS-500NG AUTOGRAPH) at 20°C and a 65% RH atmosphere with an initial length of 5 cm, and the stress at 200% mod (cN) at 200% elongation during the first elongation up to 200% elongation at a speed of 500% / min, and the stress at 90% elongation during the second elongation and the stress at 90% elongation during the second recovery are measured. [Method for Evaluating Elasticity R / S] Using the stress S at 90% elongation during the second stretch and the stress R at 90% elongation during the second recovery, obtained by the method described above, the elasticity R / S was calculated using the following formula (10): Elasticity R / S (%) = Stress R (cN) at 90% elongation during stretch / Stress S (cN) at 90% elongation during recovery × 100 …Formula (10) The elasticity R / S was then evaluated using the following five-level evaluation criteria. (Evaluation Criteria) 5: R / S was 70% or higher. 4: R / S was 65% or higher and less than 70%. 3: R / S was 60% or higher and less than 65%. 2: R / S was 50% or higher and less than 60%. 1: R / S was less than 50%.

[0103] (10) Measurement of Fineness The polyurethane elastic fiber was peeled from the winding without tension, and a length of 1 m was measured and cut off in a tension-free and taut state. Its weight was measured and the fineness was calculated using the following formula (11): Fineness (dt) = 10000 × weight per meter (g) ... formula (11). The measurement was performed five times, and the average value was taken as the fineness. The total fineness was measured for one multifilament using the above method, and the single filament fineness was taken by dividing the total fineness by the number of filaments.

[0104] (11) Measurement of Molecular Weight and Molecular Weight Distribution (Mw / Mn) A thermoplastic polyurethane resin composition or thermoplastic polyurethane elastic fiber is dissolved in a dimethylacetamide solution containing 0.02 mol / L of LiBr to a solid content concentration of 0.25% by weight, and this is used as the measurement sample. The prepared sample is measured using a Shodex GPC-101 under the conditions shown below. The molecular weight of the thermoplastic polyurethane elastic fiber refers to the number average molecular weight (Mn) and weight average molecular weight (Mw) calculated from a calibration curve obtained by measuring all samples of a Shodex polystyrene standard sample (SM-105) from the peak top molecular weight. The polydispersity of the molecular weight refers to the weight average molecular weight divided by the number average molecular weight (Mw / Mn). [GPC Measurement Conditions] Column: (Sample side) → KD-G → KD-806M → KD-806M → KD-802.5 → KD-801 × 3 → RI-71S (Detector) (All of the above are manufactured by Shodex) Column oven temperature: 60℃ Flow rate: 1.0 ml / min Eluent: Dimethylacetamide solution containing LiBr at a concentration of 0.02 mol / L

[0105] (12) Measurement of viscoelasticity (storage modulus E', tanδ, strain stress) A thermoplastic polyurethane elastic fiber with a total fineness of 620 dtex was cut to 5 cm and measured using a TA Instruments RSA-G2 under the following conditions. [Viscoelasticity measurement conditions] Measurement frequency: 1 Hz Measurement strain: 2% Heating rate: 5°C / min Measurement atmosphere: Nitrogen Measurement start temperature: 20°C Measurement end temperature: 180°C

[0106] (13) Measurement of crystallization peak temperature, crystallization start temperature, and crystallization end temperature A thermoplastic polyurethane resin composition or thermoplastic polyurethane elastic fiber was placed in an aluminum pan to the extent of 3 to 10 mg to be used as a measurement sample. The prepared sample was heated to 240°C at a heating rate of 10°C / min using a Hitachi High-Tech Analysis DSC7000X, held at 240°C for 5 minutes, and then the crystallization temperature was measured under the following conditions. The crystallization peak temperature, crystallization start temperature, and crystallization end temperature were calculated on a DSC curve with heat flow per unit weight (mW / mg) on ​​the vertical axis and temperature on the horizontal axis. The crystallization peak temperature refers to the peak top temperature of the exothermic peak during the cooling process. The crystallization start temperature is the start temperature of the exothermic peak during the cooling process, and refers to the temperature at which it begins to change from the baseline. The crystallization end temperature is the end temperature of the exothermic peak during the cooling process, and refers to the temperature at which it returns to the baseline. [DSC Measurement Conditions] Measurement atmosphere: Nitrogen Cooling rate: 30°C / min Measurement start temperature: 240°C Measurement end temperature: -60°C

[0107] (14) The 2,4'-MDI content in the MDI used as the raw material for measuring the isomer concentration of MDI was determined by gas chromatography (GC). A sample was prepared by dissolving 500 mg of MDI in 10 mL of toluene beforehand. The GC was measured using the prepared sample under the following conditions to determine the 2,4'-MDI content. [GC measurement conditions] Measuring device: Hewlett-Packard 5890A Column: Fused silica capillary column 0.3 mmφ × 25 m, Cross-linked capillary silicone (ULTRA #1) Detector: Flame ionization detector (FID) Column temperature: 150°C → 20°C / min → 340°C Injection port temperature: 340°C Injection volume: 1 μL

[0108] (15) Method for calculating the 2,4'-MDI content in MDI The 2,4'-MDI content in the MDI used as raw material was calculated using the corresponding peak area value obtained by GC measurement, using the following formula (12): 2,4'-MDI content (%) = {P1 / (P1 + P2)} × 100 …Formula (12) P1: Peak area of ​​2,4'-MDI appearing when the retention time (hereinafter referred to as RT) is around 4.5 to 4.6 min P2: Peak area of ​​4,4'-MDI appearing when the RT is around 4.8 to 5.0 min

[0109] (16) Quantitative method for determining the main chain break rate of thermoplastic polyurethane The main chain break rate of thermoplastic polyurethane elastic fibers was calculated using the following formula (13) by measuring the FT-IR of the granular resin of the thermoplastic polyurethane resin composition used as a raw material and the thermoplastic polyurethane elastic fibers peeled from the wound yarn, and using the detected peak intensity. Main chain break rate (%) = 100 - {Rm2 / Ra2} / {Rm1 / Ra1} × 100 ...Formula (13) Rm1: Approximately 2850 cm ―１ The C-H symmetric stretch peak Ra1 of the thermoplastic polyurethane resin composition appearing in the vicinity is approximately 1600 cm. ―１ Aromatic C=C stretching peak Rm2 of thermoplastic polyurethane resin composition appearing in the vicinity: approximately 2850 cm ―１ The C-H symmetrical stretch peak of thermoplastic polyurethane elastic fibers appearing in the vicinity, Ra2: approximately 1600 cm. ―１ Aromatic C=C stretch peaks of thermoplastic polyurethane elastic fibers appearing in the vicinity. [FT-IR measurement conditions] Measurement device: Carry620 (Agilent) Measurement method: ATR method Resolution: 4 cm ―１ Total number of times: 16

[0110] (17) Measurement of the particle shape of thermoplastic polyurethane resin composition A digital microscope (Olympus DSX-1000) was used to measure the particle shape of the granular resin of the thermoplastic polyurethane resin composition. 100 granules of the granular resin to be measured were randomly selected and photographed on a flat black background so that the granules did not touch each other. The captured images were processed using image analysis software to extract the longest length of each granular resin. Here, the longest length refers to the longest straight-line distance in the outer shape of the granular resin. For round granular resin, the maximum diameter was defined as the longest diameter, and for square granular resin, the longest side length or diagonal length was defined as the longest length. The mean and standard deviation were calculated from the measured longest lengths of the 100 obtained granules.

[0111] (18) Measurement of the weight of fine powder adhering to the surface of thermoplastic polyurethane granular resin A granular resin of thermoplastic polyurethane resin composition was randomly selected, and 100 g of the granular resin was prepared. This was washed with pure water at room temperature to separate the fine powder adhering to the surface of the granular resin into the water. Washing was performed by gently stirring the granular resin in water to prevent dissolution or damage to the granular resin itself. After washing, the granular resin was removed, and the remaining water was recovered by filtration or centrifugation, and the obtained water was completely dried in a dryer. Drying was carried out in a vacuum dryer at 60°C for more than 4 hours to confirm that there was no residual moisture. The weight of the fine powder obtained after drying was measured using a precision balance, and the ratio of the weight of fine powder to the weight of granular resin (wt%) was calculated using the following formula: Weight of fine powder (wt%) = (Weight of fine powder after drying / 100 g) × 100 …Formula (14)

[0112] (19) Method for evaluating heat resistance A test thread with an initial length of 7 cm was stretched by 200% to 21 cm, and pressed against a cylindrical heating element with a diameter of 6 cm and a surface temperature of 160°C (contact area of ​​1 cm). The number of seconds until it was cut was measured and evaluated according to the following five evaluation criteria: (Evaluation criteria) 5: The number of seconds until it was cut was 900 seconds or more. 4: The number of seconds until it was cut was 600 seconds or more and less than 900 seconds. 3: The number of seconds until it was cut was 300 seconds or more and less than 600 seconds. 2: The number of seconds until it was cut was 5 seconds or more and less than 300 seconds. 1: The number of seconds until it was cut was less than 5 seconds.

[0113] (20) Yarn breakage The number of yarn breaks was recorded when the elastic fiber was spun for 72 hours using the above method. Based on the obtained data, the yarn breakage frequency (number of yarn breaks / 24 hours) was calculated. If necessary, multiple tests were conducted and the average was calculated.

[0114] [Example 1] 20.00 kg of polytetramethylene ether diol with a number average molecular weight of 2000 and a molecular weight distribution of 1.2 and 1.62 kg of 1,4-butanediol were stirred under a dry nitrogen atmosphere to obtain a mixture. 90 g of ADEKA AO-60 as an antioxidant and 90 g of ADEKA LA-24 as an ultraviolet absorber were added to this mixture. Meanwhile, 7.00 kg of 4,4'-diphenylmethane diisocyanate (MDI) with an isomer concentration of 1%, melted at 40°C under a dry nitrogen atmosphere, was prepared in a storage tank. The mixture was injected from each tank at a rate of 2.16 kg / hour and the MDI at a rate of 0.70 kg / hour into a high-speed mixer using a metering pump, stirred at 2000 rpm, and then continuously supplied to a twin-screw extruder through piping. Immediately before injection into the twin-screw extruder, the material was passed through a 15-stage static mixer heated to 60°C, and then injected into a 45φ extruder for polymerization. Intermediate polymer samples were also extracted before injection into the twin-screw extruder, and the hydrogen bonding rate was checked using 13C-NMR while adjusting the supply rate, mixer speed, and temperature. A five-zone twin-screw extruder was used, with temperatures set to 140°C, 160°C, 180°C, 200°C, and 220°C in order from the first zone (raw material supply port), with a temperature gradient of 20°C per zone. The screw rotation speed was 100 rpm, the average residence time was 4 minutes, and the resin was discharged from three holes at the extruder tip. Stable granular resin was obtained by strand cutting. The resin temperature at cutting was 40°C. Next, this granular resin was dehydrated and solid-phase polymerization was carried out under vacuum at 80°C for 16 hours. Afterward, it was dried to a moisture content of 100 ppm or less. The obtained dried granular resin was melt-kneaded using a 30φ extruder at an extrusion temperature of 210°C, weighed and pressurized using a gear pump installed in the head, filtered through a 60μm filter, and then extruded at a die temperature of 210°C from a 0.5 mm diameter, 20-hole nozzle at a discharge rate of 43 g / min. A cold air chamber with a length of 500 mm was placed 50 mm directly below the spinneret, and cold air with a wind speed of 0.6 m / s and a cold air temperature of 12°C was blown out and applied perpendicularly to the fibers. After converging at a position of 2000 mm directly below the spinneret using a false twister installed 5 m below, the fibers were wound at a speed of 700 m / min while applying a treatment agent mainly composed of polydimethylsiloxane, obtaining polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex.The yarn temperature at the convergence point was 30°C, and the application rate of the treatment agent to the thermoplastic polyurethane elastic fiber was 1 part by mass. The performance evaluations of various machines are shown in Tables 1 to 5 below. There were no yarn breaks during 72 hours of spinning, and all evaluations for heat resistance and elasticity were rated 5 points, resulting in a thermoplastic polyurethane resin composition and elastic fiber with excellent spunability, heat resistance, and elasticity.

[0115] [Examples 2-6] Thermoplastic polyurethane resin compositions of Examples 2-6 were obtained in the same manner as in Example 1, except that the amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol were adjusted and the Mh fraction was adjusted. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin compositions and elastic fibers are shown in Table 1 below.

[0116] [Examples 7-9] Thermoplastic polyurethane resin compositions of Examples 7-9 were obtained in the same manner as in Example 1, except that the amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol were adjusted and the OH / NCO ratio was adjusted. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin compositions and elastic fibers are shown in Table 1 below.

[0117] [Examples 10 and 11] Thermoplastic polyurethane resin compositions of Examples 10 and 11 were obtained in the same manner as in Example 1, except that the molecular weight distribution of polytetramethylene ether diol was changed to adjust the molecular weight distribution of the resin. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Tables 1 and 2 below.

[0118] [Example 12] The thermoplastic polyurethane resin composition of Example 12 was obtained in the same manner as in Example 1, except that the liquid was supplied to a twin-screw extruder using the following prepolymerization method. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below. 20.0 kg of polytetramethylene ether diol with a number average molecular weight of 2000 and a molecular weight distribution of 1.2 and 6.93 kg of 4,4'-diphenylmethane diisocyanate with an isomer concentration of 1% were reacted under a dry nitrogen atmosphere at 60°C for 5 hours with stirring to obtain a polyurethane prepolymer capped with terminal isocyanates. 90 g of ADEKA AO-60 as an antioxidant and 90 g of ADEKA LA-24 as an ultraviolet absorber were mixed into this reaction solution. Meanwhile, 1,4-butanediol (1,4-BD) was prepared as an active hydrogen-containing compound in a storage tank at 80°C. From each tank, the prepolymer was injected at a rate of 2.69 kg / hour and 1,4-butanediol at a rate of 0.16 kg / hour into a high-speed mixer using a metering pump. After stirring at 2000 rpm, the mixture was continuously supplied through piping to a twin-screw extruder.

[0119] [Example 13] The thermoplastic polyurethane resin composition of Example 13 was obtained in the same manner as in Example 1, except that the temperature of solid-phase polymerization was changed. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the stress 200% mod of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below.

[0120] [Examples 14 and 15] Thermoplastic polyurethane resin compositions of Examples 14 and 15 were obtained in the same manner as in Example 1, except that the temperature of the twin-screw extruder, the temperature gradient for each zone, and the temperature of solid-phase polymerization were changed. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the stress 200% mod of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below.

[0121] [Examples 16 and 17] Thermoplastic polyurethane resin compositions of Examples 16 and 17 were obtained in the same manner as in Example 1, except that the molecular weight distribution of polytetramethylene etherdiol, the temperature gradient for each zone of the twin-screw extruder, and the temperature and time of solid-phase polymerization were changed. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the stress 200% mod of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below.

[0122] [Examples 18 and 19] Thermoplastic polyurethane resin compositions of Examples 18 and 19 were obtained in the same manner as in Example 1, except that the strand cutting speed was changed and the granular resin weight was adjusted. Furthermore, polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below.

[0123] [Example 20] The thermoplastic polyurethane resin composition of Example 20 was obtained in the same manner as in Example 1, except that the amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol, and the resin temperature during cutting were changed to adjust the amount of fine powder adhering to the surface of the granular resin. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 2 below.

[0124] [Examples 21 and 22] Thermoplastic polyurethane elastic fibers of Examples 21 and 22 were obtained in the same manner as in Example 1, except that the extrusion temperature, die temperature, cold air velocity, and focusing position were changed to adjust the Mw of the elastic fibers. The results of various performance evaluations of the thermoplastic polyurethane elastic fibers are shown in Table 3 below.

[0125] [Example 23] Using the resin from Example 9, thermoplastic polyurethane elastic fibers of Example 23 were obtained in the same manner as in Example 1, except that the extrusion temperature, die temperature, and focusing position were changed. The results of various performance evaluations of the thermoplastic polyurethane elastic fibers are shown in Table 3 below.

[0126] [Example 24] Using the resin from Example 4, thermoplastic polyurethane elastic fibers of Example 24 were obtained in the same manner as in Example 1, except that the cold air velocity, cold air temperature, cooling start point, cooling length, and spinning rate were changed. The results of various performance evaluations of the thermoplastic polyurethane elastic fibers are shown in Table 3 below.

[0127] [Example 25] Using the resin from Example 4, thermoplastic polyurethane elastic fibers of Example 25 were obtained in the same manner as in Example 1, except that the cold air velocity, cold air temperature, cooling start point, and spinning speed were changed. The results of various performance evaluations of the thermoplastic polyurethane elastic fibers are shown in Table 3 below.

[0128] [Example 26] Using the resin from Example 8, thermoplastic polyurethane elastic fibers of Example 26 were obtained in the same manner as in Example 1, except that the cold air velocity, cold air temperature, cooling start point, and spinning speed were changed. The results of various performance evaluations of the thermoplastic polyurethane elastic fibers are shown in Table 3 below.

[0129] [Example 27] Using the resin from Example 1, the drying time was adjusted so that the resin moisture content was approximately 200 ppm, and a 200 mm long heating cylinder set to 150°C was attached directly below the spindle to change the bundling position. Except for these changes, the procedure was the same as in Example 1 to obtain the thermoplastic polyurethane elastic fiber of Example 27. The results of various performance evaluations of the thermoplastic polyurethane elastic fiber are shown in Table 3 below.

[0130] [Example 28] Using the resin from Example 1, the drying time was adjusted so that the resin moisture content was approximately 200 ppm, and 1 wt% of the antioxidant AO-60 was added to the resin composition during spinning. Except for these differences, the thermoplastic polyurethane elastic fiber of Example 28 was obtained in the same manner as in Example 1. The results of various performance evaluations of the thermoplastic polyurethane elastic fiber are shown in Table 3 below.

[0131] [Comparative Example 1] A thermoplastic polyurethane resin composition of Comparative Example 1 was obtained in the same manner as in Example 1, except that the amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol were changed and the Mh fraction was adjusted. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 4 below.

[0132] [Comparative Example 2] A thermoplastic polyurethane resin composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that the number-average molecular weight of polytetramethylene ether diol was changed, the blending amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol were adjusted, and the Mh fraction was adjusted. However, the viscosity was low, and granular resin could not be collected due to its stickiness, and it could not be formed into fibers. The results of various performance evaluations of the thermoplastic polyurethane resin composition are shown in Table 4 below.

[0133] [Comparative Examples 3-6] Thermoplastic polyurethane resin compositions of Comparative Examples 3-6 were obtained in the same manner as in Example 1, except that the number-average molecular weight of polytetramethylene ether diol was changed and the blending amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol were changed. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin compositions and elastic fibers are shown in Table 4 below.

[0134] [Comparative Examples 7 and 8] Thermoplastic polyurethane resin compositions of Comparative Examples 7 and 8 were obtained in the same manner as in Example 1, except that the amounts of polytetramethylene ether diol, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol and the solid-phase polymerization temperature were changed. Furthermore, thermoplastic polyurethane elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin compositions and elastic fibers are shown in Table 4 below.

[0135] [Comparative Examples 9 and 10] Thermoplastic polyurethane resin compositions for Comparative Examples 9 and 10 were obtained in the same manner as in Example 1, except that the molecular weight distribution of polytetramethylene ether diol was changed. Furthermore, while fine-tuning the spinning conditions so that the 200% mod stress of the elastic fibers obtained using this resin composition was equivalent to that of Example 1, thermoplastic polyurethane resin compositions and elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained. The results of various performance evaluations of the thermoplastic polyurethane resin compositions and elastic fibers are shown in Table 4 below.

[0136] [Comparative Example 11] A thermoplastic polyurethane resin composition of Comparative Example 11 was obtained in the same manner as in Example 12, except that the molecular weight distribution of polytetramethylene ether diol was changed, the liquid was delivered to a twin-screw extruder using the prepolymerization method, and the temperature gradient of the twin-screw extruder and the temperature and time of solid-phase polymerization were changed. Furthermore, a thermoplastic polyurethane resin composition and elastic fibers with a single filament fineness of 31 dtex and a total fineness of 620 dtex were obtained by finely adjusting the spinning conditions so that the stress 200% mod of the elastic fibers obtained using this resin composition was equivalent to that of Example 1. The results of various performance evaluations of the thermoplastic polyurethane resin composition and elastic fibers are shown in Table 4 below.

[0137] [Comparative Example 12] A thermoplastic polyurethane elastic fiber of Comparative Example 12 was obtained in the same manner as in Example 1, except that the cold air velocity, cold air temperature, cooling start point, and spinning speed were changed using the resin of Comparative Example 5. The results of various performance evaluations of the thermoplastic polyurethane elastic fiber are shown in Table 5 below.

[0138] [Comparative Example 13] A thermoplastic polyurethane elastic fiber of Comparative Example 13 was obtained in the same manner as in Example 1, except that the resin of Comparative Example 7 was used and the extrusion temperature, die temperature, and focusing position were changed. The results of various performance evaluations of the thermoplastic polyurethane elastic fiber are shown in Table 5 below.

[0139]

[0140]

[0141]

[0142]

[0143]

[0144] This invention relates to thermoplastic polyurethane elastic fibers with excellent heat resistance and elasticity, and a thermoplastic polyurethane resin composition suitable therefor. Furthermore, the thermoplastic polyurethane resin composition according to the present invention exhibits good spinnability during melt spinning, which is expected to improve productivity. Due to these properties, there is no thread breakage due to heat during hot melt application in the disposable diaper manufacturing process, and it has excellent tightening force in disposable diapers, making it suitably usable as a gathered part or elastic component in sanitary materials such as disposable diapers.

Claims

1. A thermoplastic polyurethane resin composition comprising a thermoplastic polyurethane resin composed of a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, wherein the composition has the following characteristics: (a) The number average molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the number average molecular weight of the soft segment is 1900 to 4800, and the proportion of the hard segment (Mh fraction) is 15% to 40%; (b) The weight average molecular weight (Mw) is 150,000 to 500,000, and the molecular weight distribution (Mw / Mn (number average molecular weight)) is 1.5 to 3.0; (c) The inter-hard domain distance measured by a small-angle X-ray scattering device (SAXS) is 5 nm to 20 nm; and (d) The rate of change of the inter-hard domain distance when heated at 140°C is 30% or less.

2. The thermoplastic polyurethane resin composition according to claim 1, wherein the rate of change of the distance between hard domains when heated to 160°C is 50% or less.

3. The thermoplastic polyurethane resin composition according to claim 1 or 2, wherein the hydrogen bonding rate obtained by 13C-NMR measurement is 51% or more and 80% or less.

4. The thermoplastic polyurethane resin composition according to claim 1 or 2, wherein the crystallization peak temperature measured by DSC (differential calorimetry) is 60°C or higher and 100°C or lower.

5. The thermoplastic polyurethane resin composition according to claim 4, wherein the difference between the crystallization start temperature and the crystallization end temperature measured by DSC is 40°C or more and 75°C or less.

6. The thermoplastic polyurethane resin composition according to claim 1 or 2, wherein the thermoplastic polyurethane resin composition exhibits the form of granular resin, the weight of the granular resin is 10 mg or more and 100 mg or less, and the coefficient of variation is 50% or less.

7. The thermoplastic polyurethane resin composition according to claim 1 or 2, wherein the thermoplastic polyurethane resin composition exhibits a form in which fine powder is attached to the surface of a granular resin, and the weight of the fine powder is 10 wt% or less of the weight of the granular resin.

8. A thermoplastic polyurethane elastic fiber comprising a hard segment consisting of an active hydrogen-containing compound and a diisocyanate compound, and a soft segment consisting of a long-chain polyol and a diisocyanate compound, having the following characteristics: (a) The number average molecular weight of the hard segment obtained by ¹H-NMR measurement is 800 to 2400, the number average molecular weight of the soft segment is 1900 to 4800, and the proportion of the hard segment (Mh fraction) is 15% to 40%; (b) The weight average molecular weight (Mw) is 100,000 to 300,000, and the molecular weight distribution (Mw / Mn (number average molecular weight)) is 1.5 to 3.0; (c) The inter-hard domain distance measured by a small-angle X-ray scattering device (SAXS) is 8 nm to 25 nm; and (d) The rate of change of the inter-hard domain distance when heated at 140°C is 30% or less.

9. The thermoplastic polyurethane elastic fiber according to claim 8, wherein the rate of change of the distance between hard domains when heated to 160°C is 50% or less.

10. The thermoplastic polyurethane elastic fiber according to claim 8 or 9, wherein the hydrogen bonding rate obtained by 13C-NMR measurement is 51% or more and 80% or less.

11. The thermoplastic polyurethane elastic fiber according to claim 8 or 9, wherein the total fineness is 160 dtex or more and 2000 dtex or less.

12. The thermoplastic polyurethane elastic fiber according to claim 11, wherein the single filament fineness is 5 dtex or more and 100 dtex or less.

13. The thermoplastic polyurethane elastic fiber according to claim 8 or 9, wherein the tanδ value at 25°C obtained by viscoelasticity measurement is 0.01 or more and 0.10 or less, and the tanδ value at 160°C is 0.05 or more and 0.20 or less.

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