Resin composition for poly(3-hydroxyalkanoate)-based fiber, fiber, and method for manufacturing same

Abstract

The present invention provides a resin composition for a poly(3-hydroxyalkanoate)-based fiber for producing a poly(3-hydroxyalkanoate)-based resin-containing fiber having excellent toughness. The present invention is a resin composition for a poly(3-hydroxyalkanoate)-based fiber, the resin composition containing a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000-700,000, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000-1,400,000, wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is larger than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A) by at least 200,000, and the content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B).

Description

Poly(3-hydroxyalkanoate)-based fiber resin composition, fiber, and method for producing the same

[0001] The present invention relates to a poly(3-hydroxyalkanoate)-based resin composition for fibers, as well as fibers and a method for producing the same.

[0002] In recent years, plastic waste has become a burden on the global environment, affecting ecosystems, emitting harmful gases when burned, and contributing to global warming due to the large amount of heat generated by combustion. There has been active development of biodegradable plastics as a material that can solve these problems.

[0003] Among biodegradable plastics, biodegradable plastics produced by microorganisms using plant-derived raw materials as a carbon source, particularly aliphatic polyester-based resins, have attracted attention from the viewpoints of biodegradability and carbon neutrality. Among these, poly(3-hydroxyalkanoate)-based resins, such as poly(3-hydroxybutyrate) homopolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer resin, have attracted attention.

[0004] Patent Document 1 discloses a meltblown nonwoven fabric formed from fibers containing a poly(3-hydroxyalkanoate) resin, and Patent Document 2 discloses a poly(3-hydroxyalkanoate) composition used in a molding method such as melt spinning.

[0005] International Publication No. 2023 / 106231 Japanese Patent Application Laid-Open No. 2004-331757

[0006] Incidentally, fibers are sometimes required to have excellent toughness, but poly(3-hydroxyalkanoate)-based fiber resin compositions for producing poly(3-hydroxyalkanoate)-based resin-containing fibers with excellent toughness have not been sufficiently studied to date.

[0007] Therefore, an object of the present invention is to provide a poly(3-hydroxyalkanoate)-based fiber resin composition for producing poly(3-hydroxyalkanoate)-based resin-containing fibers having excellent toughness, and fibers containing the poly(3-hydroxyalkanoate)-based fiber resin composition.

[0008] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that excellent toughness can be achieved by incorporating into fibers a poly(3-hydroxyalkanoate) resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less and a poly(3-hydroxyalkanoate) resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less in predetermined content ratios, and by making the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (B) larger than the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (A) by at least a predetermined amount, thereby completing the present invention.

[0009] That is, the present invention relates to a poly(3-hydroxyalkanoate)-based resin composition for fibers, which comprises a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less, wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A), and the content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B). The present invention also relates to a fiber comprising a poly(3-hydroxyalkanoate)-based resin composition for fibers, the poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less, wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A), and the content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B). The present invention also relates to a method for producing fibers by melt spinning, the method comprising: step (A) of discharging a melt of the poly(3-hydroxyalkanoate)-based resin composition for fibers from a discharge hole to obtain a raw yarn; step (B) of cooling the raw yarn; and step (C) of drawing the cooled raw yarn to obtain the fiber.

[0010] According to the present invention, it is possible to provide a poly(3-hydroxyalkanoate)-based fiber resin composition for producing a poly(3-hydroxyalkanoate)-based resin-containing fiber having excellent toughness, and a fiber containing the poly(3-hydroxyalkanoate)-based fiber resin composition.

[0011] An embodiment of the present invention will be described below.

[0012] [Poly(3-hydroxyalkanoate)-Based Fiber Resin Composition] First, the poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment will be described. The poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment contains a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less. The weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A). The content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B). The poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment has such a constitution, and is therefore a resin composition for producing poly(3-hydroxyalkanoate)-based resin-containing fibers that have excellent toughness.

[0013] <Poly(3-hydroxyalkanoate)-based resins (A) and (B)> The poly(3-hydroxyalkanoate)-based resins (A) and (B) are biodegradable aliphatic polyesters (preferably polyesters not containing aromatic rings) and are resins having at least one or two or more types of 3-hydroxyalkanoate units (also referred to as "3-hydroxyalkanoic acid units"). In the present application, the poly(3-hydroxyalkanoate)-based resin is also referred to as P3HA.

[0014] The poly(3-hydroxyalkanoate) resin (A) and / or (B) preferably contains a 3-hydroxyalkanoic acid unit represented by the following formula (1): [—CHR—CH ２ —CO—O—] (1) In the formula (1), R is C ｐ H ２ｐ＋１where p is an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably an integer of 1 to 10, and more preferably an integer of 1 to 8.

[0015] As the poly(3-hydroxyalkanoate) resin (A) and / or (B), a poly(3-hydroxyalkanoate) resin produced by a microorganism is particularly preferred. In the poly(3-hydroxyalkanoate) resin produced by a microorganism, all of the 3-hydroxyalkanoate units are contained as (R)-3-hydroxyalkanoate units.

[0016] The poly(3-hydroxyalkanoate) resin (A) and / or (B) preferably contains 3-hydroxyalkanoate units (particularly units represented by the above formula (1)) in an amount of 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the total structural units (monomer units). The poly(3-hydroxyalkanoate) resin may contain only one or more types of 3-hydroxyalkanoate units as structural units of the polymer, or may contain one or more types of 3-hydroxyalkanoate units as well as other units (e.g., 4-hydroxyalkanoate units).

[0017] The poly(3-hydroxyalkanoate) resins (A) and / or (B) preferably contain 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units, and more preferably are copolymers containing 3-hydroxybutyrate units and other hydroxyalkanoate units. The 3-hydroxybutyrate units are preferably all (R)-3-hydroxybutyrate units.

[0018] The other hydroxyalkanoate units may be 3-hydroxyalkanoate units other than 3HB units, or may be hydroxyalkanoate units other than 3-hydroxyalkanoate units (for example, 4-hydroxyalkanoate units). Only one type of other hydroxyalkanoate unit may be included, or two or more types may be included.

[0019] Specific examples of the poly(3-hydroxyalkanoate) resins (A) and / or (B) include homopolymers such as poly(3-hydroxybutyrate) (abbreviation: P3HB), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxy). Examples of suitable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB) include poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), and poly(3-hydroxybutyrate-co-3-hydroxyundecanoate). In particular, from the viewpoints of productivity and mechanical properties of the resin composition, P3HB3HH or P3HB4HB is preferred, with P3HB3HH being particularly preferred.

[0020] P3HA can be produced by microorganisms. Such microbially produced P3HA is usually P3HA composed only of D-form (R-form) hydroxyalkanoic acid repeating units. Among microbially produced P3HAs, P3HB, P3HB3HH, P3HB3HV, P3HB3HV3HH, and P3HB4HB are preferred in terms of ease of industrial production, with P3HB, P3HB3HH, P3HB3HV, and P3HB4HB being more preferred, and P3HB3HH being particularly preferred. P3HA (A) and P3HA (B) may be the same resin, or may be resins with different monomer species.

[0021] The microorganism that produces P3HA is not particularly limited as long as it has the ability to produce P3HA. For example, the first P3HB-producing bacterium was Bacillus megaterium, discovered in 1925. Other known natural microorganisms include Cupriavidus necator (formerly classified as Alcaligenes eutrophus, Ralstonia eutropha) and Alcaligenes latus. In these microorganisms, P3HB accumulates intracellularly.

[0022] Known examples of bacteria that produce copolymers of 3HB with other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, with regard to P3HB3HH, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), into which genes encoding P3HA synthases have been introduced, is preferred. Microbial cells obtained by culturing such microorganisms under appropriate conditions and allowing P3HA to accumulate within the cells are used. In addition to the above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may be used depending on the P3HA to be produced, or culture conditions, including the type of substrate, may be optimized.

[0023] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (A) is in the range of 200,000 or more and 700,000 or less. By making the weight-average molecular weight of P3HA (A) 200,000 or more, fibers exhibiting good physical properties can be formed by melt spinning. Furthermore, by using P3HA (A) in combination with P3HA (B), which will be described later, crystallization after melt spinning of the resin composition is promoted, allowing for the production of fibers with excellent toughness. On the other hand, by making the weight-average molecular weight of P3HA (A) 700,000 or less, processability is further improved, making fiber production easier. The weight-average molecular weight of P3HA (A) is preferably 400,000 to 670,000, and more preferably 500,000 to 650,000.

[0024] The weight-average molecular weight of P3HA can be determined as the molecular weight in terms of polystyrene using gel permeation chromatography (GPC) (Shimadzu Corporation's "High Performance Liquid Chromatograph 20A System"), a polystyrene gel (Showa Denko K.K.'s "K-G 4A" or "K-806M") as a column, and chloroform as a mobile phase. In this case, a calibration curve is prepared using polystyrenes with weight-average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. As the column for the GPC, a column appropriate for measuring the molecular weight may be used.

[0025] The poly(3-hydroxyalkanoate) resin (A) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) resin (A) is preferably 60 / 40 to 99.5 / 0.5 (mol % / mol %), more preferably 65 / 45 to 99 / 1 (mol % / mol %), and even more preferably 70 / 30 to 98 / 2 (mol % / mol %). By having this average molar ratio within this range, the poly(3-hydroxyalkanoate) resin composition for fibers can achieve both flexibility and rigidity, and productivity can also be improved.

[0026] The monomer composition ratio in P3HA can be measured by gas chromatography or the like, for example, by the method described in the Examples.

[0027] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (B) is in the range of 400,000 to 1,400,000, and is at least 200,000 greater than the weight-average molecular weight of the aforementioned P3HA (A). By using P3HA (B) having a weight-average molecular weight of 400,000 or greater and at least 200,000 greater than that of P3HA (A), the molecular chains of this high molecular weight component are more likely to be oriented by melt spinning, thereby inducing crystallization. This promotes crystallization by melt spinning, allowing for the production of fibers with excellent toughness. By setting the weight-average molecular weight of P3HA (B) to 1,400,000 or less, processability is further improved, making fiber production easier. The weight-average molecular weight of P3HA (B) is preferably 500,000 to 1,300,000, more preferably 600,000 to 1,200,000, and even more preferably 700,000 to 1,100,000.

[0028] By using P3HA(B) having a weight-average molecular weight 200,000 or more greater than that of P3HA(A), it is possible to achieve the crystallization-promoting effect of melt spinning. If the difference in weight-average molecular weight between P3HA(B) and P3HA(A) is less than 200,000, the crystallization-promoting effect of using P3HA(B) cannot be fully achieved. The difference in weight-average molecular weight between P3HA(B) and P3HA(A) is preferably 220,000 or more, more preferably 250,000 or more.

[0029] The poly(3-hydroxyalkanoate) resin (B) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) resin (B) is preferably 85 / 15 to 99.5 / 0.5 (mol % / mol %), more preferably 93 / 7 to 99 / 1 (mol % / mol %), and even more preferably 93 / 7 to 98 / 2 (mol % / mol %). By having this average molar ratio within this range, the poly(3-hydroxyalkanoate) resin composition for fibers can achieve both flexibility and rigidity, and productivity can also be improved.

[0030] The content of the poly(3-hydroxyalkanoate) resin (A) is greater than the content of the poly(3-hydroxyalkanoate) resin (B). The weight ratio of the content of the poly(3-hydroxyalkanoate) resin (A) to the content of the poly(3-hydroxyalkanoate) resin (B) (P3HA (A) content / P3HA (B) content) is preferably 95 / 5 to 70 / 30, more preferably 93 / 7 to 75 / 25, and even more preferably 91 / 9 to 80 / 20. By having the P3HA (A) content greater than the P3HA (B) content, fibers with excellent toughness can be produced.

[0031] The poly(3-hydroxyalkanoate)-based resin composition for fibers according to this embodiment contains a total of P3HA (A) and P3HA (B) in an amount of preferably 50 to 100% by weight, more preferably 60 to 100% by weight, even more preferably 80 to 100% by weight, and particularly preferably 90 to 99% by weight.

[0032] The poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate)-based fiber resin composition is preferably 80 / 20 to 95 / 5 (mol % / mol %), more preferably 83 / 17 to 92 / 7 (mol % / mol %), and even more preferably 85 / 15 to 90 / 10 (mol % / mol %). By having this average molar ratio within this range, the poly(3-hydroxyalkanoate)-based fiber resin composition can achieve both flexibility and rigidity, and productivity can also be improved.

[0033] The poly(3-hydroxyalkanoate)-based resin composition for fibers according to this embodiment may contain, in addition to P3HA (A) and P3HA (B), optionally at least one selected from the group consisting of other resins, crystal nucleating agents, and lubricants.

[0034] <Other Resins> The poly(3-hydroxyalkanoate)-based fiber resin composition may contain another resin that does not fall under either P3HA(A) or P3HA(B). There are no particular limitations on the other resin, but it is preferable that the other resin does not significantly reduce the compatibility or processability when producing fibers from the poly(3-hydroxyalkanoate)-based fiber resin composition, or the mechanical properties of the resulting fibers. Furthermore, when the resulting fibers are used in applications requiring biodegradability, the other resin is preferably a biodegradable resin.

[0035] Examples of the other resins include aliphatic polyesters having a structure obtained by polycondensation of an aliphatic diol and an aliphatic dicarboxylic acid, and aliphatic-aromatic polyesters having both an aliphatic compound and an aromatic compound as monomers. Examples of the former include polyethylene succinate, polybutylene succinate (PBS), polyhexamethylene succinate, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polybutylene succinate adipate (PBSA), polyethylene sebacate, and polybutylene sebacate. Examples of the latter include poly(butylene adipate-co-butylene terephthalate) (PBAT), poly(butylene sebacate-co-butylene terephthalate), poly(butylene azelate-co-butylene terephthalate), and poly(butylene succinate-co-butylene terephthalate) (PBST). The other resins may be used singly or in combination of two or more.

[0036] When the poly(3-hydroxyalkanoate)-based fiber resin composition contains the other resin, the content of the other resin is preferably 250 parts by weight or less, more preferably 100 parts by weight or less, even more preferably 50 parts by weight or less, and particularly preferably 20 parts by weight or less, per 100 parts by weight of the total of P3HA(A) and P3HA(B). Alternatively, the content may be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less. There is no particular lower limit for the content of the other resin, and it may even be 0 parts by weight.

[0037] <Crystal Nucleating Agent> The poly(3-hydroxyalkanoate)-based fiber resin composition may further contain a crystal nucleating agent. By including a crystal nucleating agent in the poly(3-hydroxyalkanoate)-based fiber resin composition, crystallization of the resin component can be further promoted, and tensile strength, productivity, etc. can be improved.

[0038] The crystal nucleating agent is not particularly limited, and conventionally known ones can be used. Examples of the crystal nucleating agent include sugar alcohol compounds derived from natural products (pentaerythritol, erythritol, galactitol, mannitol, arabitol, etc.); inorganic substances (boron nitride, titanium oxide, talc, layered silicates, calcium carbonate, sodium chloride, metal phosphates, etc.); polyvinyl alcohol; chitin; chitosan; polyethylene oxide; aliphatic carboxylates; aliphatic alcohols; aliphatic carboxylate esters; dicarboxylic acid derivatives (dimethyl adipate, dibutyl adipate, diisopropyl methyl ... Examples of suitable crystal nucleating agents include siladipate and dibutyl sebacate; cyclic compounds having C═O and a functional group selected from NH, S, and O in the molecule (indigo, quinacridone, quinacridone magenta, etc.); sorbitol derivatives (bisbenzylidene sorbitol, bis(p-methylbenzylidene)sorbitol, etc.); compounds containing a nitrogen-containing heteroaromatic nucleus (pyridine ring, triazine ring, imidazole ring, etc.) (pyridine, triazine, imidazole, etc.); phosphate ester compounds; bisamides of higher fatty acids; metal salts of higher fatty acids; and branched polylactic acid. These crystal nucleating agents may be used alone or in combination of two or more.

[0039] The content of the nucleating agent is not particularly limited as long as it can promote the crystallization of the resin component, but the poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment preferably contains 0.1 to 10 parts by weight, and more preferably 0.5 to 8 parts by weight, of the nucleating agent (particularly, pentaerythritol) per 100 parts by weight of the poly(3-hydroxyalkanoate)-based fiber resin composition. When the content of the nucleating agent is within the above range, the molten state and the degree of crystallization during fiber production are appropriately maintained, and the effect of the nucleating agent can be obtained while suppressing deterioration of the physical properties of the fiber and bleed-out of the nucleating agent.

[0040] <Lubricant> The poly(3-hydroxyalkanoate)-based resin composition for fibers according to this embodiment may further contain a lubricant. By containing a lubricant, the surface smoothness of the resulting fiber can be improved. The lubricant is not particularly limited, but it is preferable to contain at least one selected from the group consisting of behenamide, stearamide, erucamide, and oleamide. By containing these lubricants, the resulting fiber can have good lubricity (particularly external lubricity). Among these, it is preferable to contain behenamide and / or erucamide from the viewpoint of improving processability and productivity.

[0041] The lubricant may be behenamide, stearamide, erucamide, oleamide, or a combination of two or more of these. It may also be a combination of behenamide, stearamide, erucamide, or oleamide with a lubricant other than these (hereinafter referred to as "other lubricants"). Examples of other lubricants include, but are not limited to, alkylene fatty acid amides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; polyethylene wax, oxidized polyester wax, glycerin monofatty acid esters such as glycerin monostearate, glycerin monobehenate, and glycerin monolaurate; organic acid monoglycerides such as succinic acid saturated fatty acid monoglycerides; sorbitan fatty acid esters such as sorbitan behenate, sorbitan stearate, and sorbitan laurate; polyglycerin fatty acid esters such as diglycerin stearate, diglycerin laurate, tetraglycerin stearate, tetraglycerin laurate, decaglycerin stearate, and decaglycerin laurate; and higher alcohol fatty acid esters such as stearyl stearate. The other lubricants may be used alone or in combination of two or more.

[0042] The content of the lubricant (when multiple lubricants are used, the total content) is not particularly limited as long as it can impart lubricity to the fiber, but is preferably 0.01 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, even more preferably 0.5 to 10 parts by weight, even more preferably 0.5 to 5 parts by weight, and particularly preferably 0.7 to 4 parts by weight, relative to 100 parts by weight of the total of P3HA(A) and P3HA(B). When the content of the lubricant is within the above range, it is possible to obtain the effect as a lubricant while avoiding bleeding out of the lubricant onto the fiber surface.

[0043] <Other Components> The poly(3-hydroxyalkanoate)-based fiber resin composition may contain other components such as plasticizers; inorganic fillers; antioxidants; ultraviolet absorbers; colorants such as dyes and pigments; and antistatic agents, within the range that does not impair the functionality of the resulting molded article.

[0044] The plasticizer is not particularly limited, but examples thereof include modified glycerin-based compounds such as glycerin diacetomonolaurate, glycerin diacetomonocaprylate, and glycerin diacetomonodecanoate; adipate-based compounds such as diethylhexyl adipate, dioctyl adipate, and diisononyl adipate; polyether ester-based compounds such as polyethylene glycol dibenzoate, polyethylene glycol dicaprylate, and polyethylene glycol diisostearate; benzoate-based compounds; epoxidized soybean oil; epoxidized fatty acid 2-ethylhexyl; and sebacic acid monoesters. These may be used alone or in combination of two or more. Among the above plasticizers, modified glycerin-based compounds and polyether ester-based compounds are preferred in terms of ease of availability and high effectiveness. These may be used alone or in combination of two or more.

[0045] The inorganic filler is not particularly limited, but examples thereof include clay, synthetic silicon, carbon black, barium sulfate, mica, glass fiber, whisker, carbon fiber, calcium carbonate, magnesium carbonate, glass powder, metal powder, kaolin, graphite, molybdenum disulfide, zinc oxide, etc. These may be used alone or in combination of two or more.

[0046] The antioxidant is not particularly limited, but examples thereof include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, etc. These may be used alone or in combination of two or more.

[0047] The ultraviolet absorber is not particularly limited, and examples thereof include benzophenone-based compounds, benzotriazole-based compounds, triazine-based compounds, salicylic acid-based compounds, cyanoacrylate-based compounds, nickel complex salt-based compounds, etc. These may be used alone or in combination of two or more.

[0048] The colorants such as pigments and dyes are not particularly limited, and examples thereof include inorganic colorants such as titanium oxide, calcium carbonate, chromium oxide, cuprous oxide, calcium silicate, iron oxide, carbon black, graphite, titanium yellow, and cobalt blue, soluble azo pigments such as lake red, lithol red, and brilliant carmine, insoluble azo pigments such as dinitrian orange and fast yellow, phthalocyanine pigments such as monochlorophthalocyanine blue, polychlorophthalocyanine blue, and polybromophthalocyanine green, condensed polycyclic pigments such as indigo blue, perylene red, isoindolinone yellow, and quinacridone red, and dyes such as oracet yellow. These may be used alone or in combination of two or more.

[0049] The antistatic agent is not particularly limited, but examples thereof include low molecular weight antistatic agents such as fatty acid ester compounds, aliphatic ethanolamine compounds, and aliphatic ethanolamide compounds; polymeric antistatic agents; etc. These may be used alone or in combination of two or more.

[0050] The content of each of the other components described above is not particularly limited as long as the effects of the invention are achieved, and can be appropriately determined by a person skilled in the art.

[0051] [Method for producing poly(3-hydroxyalkanoate)-based fiber resin composition] The poly(3-hydroxyalkanoate)-based fiber resin composition according to this embodiment can be produced by a known method. Specific examples include a method in which P3HA (A), P3HA (B), and other optional components are melt-kneaded using an extruder, kneader, Banbury mixer, kneading roll, or the like. When melt-kneading, it is preferable to mix them while taking care to avoid a decrease in molecular weight due to thermal decomposition. Alternatively, the poly(3-hydroxyalkanoate)-based fiber resin composition can also be produced by dissolving each component in a soluble solvent and then removing the solvent.

[0052] When produced by melt kneading, each component may be charged separately into an extruder, etc., or each component may be mixed in advance and then charged into an extruder, etc. When melt kneaded using an extruder, the resulting poly(3-hydroxyalkanoate)-based resin composition for fibers may be extruded into a strand shape and then cut, thereby processing it into particle shapes such as a bar shape, a cylindrical shape, an elliptical cylinder shape, a sphere shape, a cube shape, a rectangular parallelepiped shape, etc.

[0053] The resin temperature during melt-kneading cannot be generally defined because it depends on the melting point and melt viscosity of the resin used. However, from the viewpoint of achieving good dispersibility while avoiding thermal decomposition of P3HA(A) and P3HA(B), the temperature is preferably 140 to 200°C, more preferably 150 to 195°C, and even more preferably 160 to 190°C.

[0054] [Fibers] The fibers according to this embodiment contain the poly(3-hydroxyalkanoate)-based fiber resin composition. Specifically, the fibers according to this embodiment contain a poly(3-hydroxyalkanoate)-based fiber resin composition containing a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less. The weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A). The content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B). The fiber according to the present embodiment preferably contains 50 to 100% by weight, more preferably 60 to 100% by weight, even more preferably 80 to 100% by weight, and particularly preferably 90 to 100% by weight, of the poly(3-hydroxyalkanoate)-based resin composition for fibers, and may contain 100% by weight. The fiber according to the present embodiment may be a multifilament having a plurality of single yarns, or a monofilament that is a single fiber (also referred to as a "single yarn"). In other words, the fiber according to the present embodiment may be either a multifilament or a monofilament, depending on the application. The single fiber contains the poly(3-hydroxyalkanoate)-based resin composition for fibers. When the fiber according to the present embodiment is a multifilament, the single fineness is preferably 0.5 to 15 dtex, more preferably 1.0 to 10 dtex, from the viewpoint of excellent tensile strength, fineness, and toughness. When the fiber according to the present embodiment is a monofilament, from the viewpoint of excellent tensile strength, fineness, and toughness, the single fiber fineness is preferably 50 to 3,000 dtex, more preferably 100 to 500 dtex. The fiber length of the single fiber is preferably 5 times or more, more preferably 10 times or more, the maximum diameter of the single fiber.

[0055] [Method for producing fibers] The method for producing fibers according to this embodiment is a method for producing fibers by melt spinning. The method for producing fibers according to this embodiment includes the steps of: (A) discharging a melt of the poly(3-hydroxyalkanoate)-based resin composition for fibers through a discharge hole to produce a raw yarn; (B) cooling the raw yarn; and (C) drawing the cooled raw yarn to produce the poly(3-hydroxyalkanoate)-based fiber.

[0056] In the step (A), the poly(3-hydroxyalkanoate)-based fiber resin composition is introduced into an extruder and melted to obtain a melt, which is then extruded from a spinning nozzle to obtain a raw yarn.

[0057] In the step (B), the raw yarn obtained in the step (A) is cooled. The cooling method may be a method of blowing cooling air onto the raw yarn or a method of passing the raw yarn through a water tank.

[0058] In the step (C), the raw yarn cooled in the step (B) is taken up with a take-up roll and stretched with a stretching roll to obtain the fiber. After being taken up with the take-up roll and before being stretched with the stretching roll, the raw yarn may be warmed with hot water.

[0059] From the viewpoint of increasing the strength and toughness of the fiber, the draw ratio in step (C) is preferably 6.0 times or more, more preferably 7.0 times or more, more preferably 8.0 times or more, and even more preferably 9.0 times or more when the fiber is a monofilament, and is preferably 1.5 times or more, more preferably 1.7 times or more, and even more preferably 1.8 times or more when the fiber is a multifilament. When the fiber is a monofilament, the draw ratio is, for example, 12 times or less, more specifically 10 times or less, and when the fiber is a multifilament, it is, for example, 3.0 times or less, more specifically 2.0 times or less. The draw ratio can be calculated by the following formula: Draw ratio = draw roll speed (m / min) / take-up roll speed (m / min)

[0060] The poly(3-hydroxyalkanoate)-based resin composition for fibers, or fibers containing the composition, can be suitably used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, the food industry, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

[0061] It should be noted that the present invention is not limited to the above-described embodiment. Furthermore, the present invention is not limited to the above-described effects. Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention.

[0062] [Disclosure items]

[0063] The following items are preferred embodiments of the present disclosure, but the present invention is not limited to them. [Item 1] A poly(3-hydroxyalkanoate) fiber comprising a poly(3-hydroxyalkanoate) resin composition for fibers, the poly(3-hydroxyalkanoate) resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate) resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less, wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin (A), and the content of the poly(3-hydroxyalkanoate) resin (A) is greater than the content of the poly(3-hydroxyalkanoate) resin (B). [Item 2] The poly(3-hydroxyalkanoate) fiber according to Item 1, wherein the weight ratio of the content of the poly(3-hydroxyalkanoate) resin (A) to the content of the poly(3-hydroxyalkanoate) resin (B) is 95 / 5 to 70 / 30. [Item 3] The poly(3-hydroxyalkanoate) fiber according to Item 1 or 2, wherein the poly(3-hydroxyalkanoate) resin (A) and / or the poly(3-hydroxyalkanoate) resin (B) contains a 3-hydroxyalkanoic acid unit represented by the following formula (1): [-CHR-CH ２ —CO—O—] (1) (In the formula (1), R is C ｐ H ２ｐ＋１and p represents an alkyl group represented by the formula (I) and represents an integer of 1 to 15.) [Item 4] The poly(3-hydroxyalkanoate)-based fiber according to Item 3, wherein the poly(3-hydroxyalkanoate)-based resin (A) and / or the poly(3-hydroxyalkanoate)-based resin (B) is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate). [Item 5] The poly(3-hydroxyalkanoate) fiber according to Item 4, wherein the poly(3-hydroxyalkanoate) resin (A) and / or the poly(3-hydroxyalkanoate) resin (B) is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). [Item 6] The poly(3-hydroxyalkanoate) fiber according to any one of Items 1 to 5, wherein the poly(3-hydroxyalkanoate) fiber resin composition contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units / other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) fiber resin composition is 80 / 20 to 95 / 5 (mol % / mol %). [Item 7] The poly(3-hydroxyalkanoate) fiber according to any one of Items 1 to 6, wherein the poly(3-hydroxyalkanoate) resin (B) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units / other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) resin (B) is 93 / 7 to 99 / 1 (mol % / mol %).[Item 8] The poly(3-hydroxyalkanoate)-based fiber according to any one of Items 1 to 7, wherein the poly(3-hydroxyalkanoate)-based fiber resin composition contains 0.1 to 10 parts by weight of pentaerythritol per 100 parts by weight of the poly(3-hydroxyalkanoate)-based fiber resin composition. [Item 9] A poly(3-hydroxyalkanoate)-based resin composition for fibers, comprising: a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less; and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less; wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A); and the content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B). [Item 10] The poly(3-hydroxyalkanoate)-based resin composition for fibers according to Item 9, wherein the weight ratio of the content of the poly(3-hydroxyalkanoate)-based resin (A) to the content of the poly(3-hydroxyalkanoate)-based resin (B) is 95 / 5 to 70 / 30. [Item 11] A production method for obtaining fibers by melt spinning, comprising: step (A) of discharging a melt of the poly(3-hydroxyalkanoate)-based resin composition for fibers according to Item 9 or 10 from a discharge hole to obtain a raw yarn; step (B) of cooling the raw yarn; and step (C) of drawing the cooled raw yarn to obtain the fiber. [Item 12] The method for producing fibers according to Item 11, wherein the draw ratio in step (C) is 5.0 times or more.

[0064] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0065] The substances used in the examples and comparative examples are shown below.

[0066] <Poly(3-hydroxyalkanoate)-based resin (P3HA)> P3HB3HH (A-1): P3HB3HH (average molar ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%), weight average molecular weight = 660,000 g / mol) The P3HB3HH (A-1) was produced in accordance with the method described in Example 2 of WO 2019 / 142845. P3HB3HH (A-2): P3HB3HH (average molar ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight average molecular weight = 660,000 g / mol) The P3HB3HH (A-2) was produced in accordance with the method described in Example 9 of WO 2019 / 142845. - P3HB3HH (A-3): P3HB3HH (average molar ratio 3HB / 3HH = 94.0 / 6.0 (mol% / mol%), weight average molecular weight = 660,000 g / mol) The P3HB3HH (A-3) was produced in accordance with the method described in Example 1 of WO 2019 / 142845. - P3HB3HH (B-1): P3HB3HH (average molar ratio 3HB / 3HH = 94.0 / 6.0 (mol% / mol%), weight average molecular weight = 900,000 g / mol) The P3HB3HH (B-1) was produced in accordance with the method described in Example 1 of WO 2019 / 142845. P3HB3HH (B-2): P3HB3HH (average molar ratio 3HB / 3HH = 89.0 / 11.0 (mol% / mol%), weight average molecular weight = 900,000 g / mol) The P3HB3HH (B-2) was produced in accordance with the method described in Example 5 of WO 2019 / 142845. P3HB3HH (C-1): P3HB3HH (average molar ratio 3HB / 3HH = 94.0 / 6.0 (mol% / mol%), weight average molecular weight = 400,000 g / mol) The P3HB3HH (C-1) was produced in accordance with the method described in Example 1 of WO 2019 / 142845.

[0067] <Monomer Composition Ratio of P3HA> The monomer composition ratio of P3HB3HH, a P3HA having a 3-hydroxyhexanoate unit, was determined as follows. Approximately 20 mg of P3HA was added to 1 mL of a sulfuric acid-methanol mixture (15:85) and 1 mL of chloroform, sealed, and heated at 100°C for 140 minutes to obtain the methyl ester of the P3HB3HH decomposition product. After cooling, 0.5 mL of deionized water was added and mixed thoroughly, and the mixture was allowed to stand until the aqueous and organic layers separated. The monomer unit composition of the P3HA decomposition product in the separated organic layer was then analyzed by capillary gas chromatography. The average molar ratio of 3-hydroxybutyrate (3HB) to other hydroxyalkanoate units (3-hydroxyhexanoate (3HH) in the Examples and Comparative Examples) was calculated from the obtained peak areas.

[0068] <Measurement of Weight-Average Molecular Weight of P3HA> The weight-average molecular weight of P3HA was measured by first dissolving the resin to be measured in chloroform and heating it in a hot water bath at 60°C for 0.5 hours, filtering the soluble matter through a disposable PTFE filter with a 0.45 μm pore size, and then using the filtrate to perform GPC measurement under the following conditions to determine the weight-average molecular weight. GPC measurement device: High-performance liquid chromatograph 20A system manufactured by Shimadzu Corporation Column: K-G 4A (1 column), K-806M (2 columns) manufactured by Showa Denko K.K. Sample concentration: 1 mg / ml Free liquid: chloroform solution Free liquid flow rate: 1.0 ml / min Sample injection amount: 100 μL Analysis time: 30 minutes Standard sample: standard polystyrene

[0069] <Additives> Additive 1: Pentaerythritol (manufactured by Mitsubishi Chemical: Neuraizer P) Additive 2: Behenic acid amide (manufactured by Nippon Fine Chemicals: BNT-22H) Additive 3: Erucic acid amide (manufactured by Nippon Fine Chemicals: Neutron S)

[0070] Example 1 Preparation of Pellet-Form Poly(3-hydroxyalkanoate)-Based Fiber Resin Composition Pellet-Form P3HA Blend of 90 wt% (content of all P3HA components) of P3HB3HH (A-3) and 10 wt% (content of all P3HA components) of P3HB3HH (B-1) was further blended with 1.0 part by weight (content relative to 100 parts by weight of all P3HA components) of Additive 1, 0.5 part by weight (content relative to 100 parts by weight of all P3HA components) of Additive 2, and 0.5 part by weight (content relative to 100 parts by weight of all P3HA components) of Additive 3 to obtain a resin mixture. The resin mixture was fed into a 40 mm diameter co-rotating twin-screw extruder with the cylinder and extrusion nozzle temperatures set to 150°C, and a strand was discharged from the extruder. The strand was passed through a water bath filled with warm water at 40°C to solidify it, and then cut into pellets using a pelletizer to obtain a poly(3-hydroxyalkanoate)-based fiber resin composition in the form of pellets. In Example 1, P3HB3HH(A-3) corresponds to P3HA(A), and P3HB3HH(B-1) corresponds to P3HA(B). The average molar ratio of 3HB / 3HH in the resin composition was 94.0 / 6.0 (mol% / mol%).

[0071] [Preparation of Monofilament Fibers] In step (A), the pelletized poly(3-hydroxyalkanoate)-based fiber resin composition was introduced into a single-screw extruder (screw diameter: 30 mm) with the cylinder and spinning nozzle temperatures set to 165°C, and melted to obtain a molten material. The molten material was then extruded from a spinning nozzle having five circular nozzle holes with a diameter of 1.5 mm to obtain five raw yarns. In step (B), the raw yarns were cooled by passing them through a water bath. In step (C), the cooled raw yarns were taken up with a take-up roll (speed: 5.0 m / min), and subsequently passed through a 3-m-long hot water bath filled with hot water. The raw yarns were drawn with a drawing roll (speed: 45.0 m / min) to obtain five monofilament fibers. The draw ratio was 9.0 times.

[0072] Example 2 A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 1, except that P3HB3HH(B-2) was used instead of P3HB3HH(B-1). In Example 2, P3HB3HH(A-3) was P3HA(A), and P3HB3HH(B-2) was P3HA(B). The average molar ratio of 3HB / 3HH in the resin composition was 93.5 / 6.5 (mol % / mol %).

[0073] Example 3 A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 1, except that pentaerythritol, the additive 1, was not used. In Example 3, P3HB3HH(A-3) was P3HA(A), and P3HB3HH(B-1) was P3HA(B). The average molar ratio of 3HB / 3HH in the resin composition was 94.0 / 6.0 (mol % / mol %).

[0074] Example 4 A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 1, except that a P3HA blend containing 35% by weight of P3HB3HH (A-1), 35% by weight of P3HB3HH (A-2), 20% by weight of P3HB3HH (A-3), and 10% by weight of P3HB3HH (B-2) was used, and the draw ratio was set to 8.5 times. The average molar ratio of 3HB / 3HH in the resin composition was 86.8 / 13.2 (mol% / mol%).

[0075] Example 5 Preparation of pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition was obtained in the same manner as in Example 1. The average molar ratio of 3HB / 3HH contained in the resin composition was 94.0 / 6.0 (mol % / mol %).

[0076] [Production of Multifilament Fibers] In step (A), the pelletized poly(3-hydroxyalkanoate)-based fiber resin composition was introduced into a single-screw extruder (screw diameter: 25 mm) with the cylinder and spinning nozzle temperatures set to 180°C, and melted to obtain a melt. The melt was then extruded from a spinning nozzle having 128 circular nozzle holes with a diameter of 0.65 mm to obtain 128 raw yarns. In step (B), the raw yarns were cooled with cooling air at 6°C. In step (C), the raw yarns cooled in step (B) were taken up with a take-up roll (speed: 450 m / min) heated to 40°C, and then continuously drawn with a drawing roll at 810 m / min to obtain a multifilament fiber (single yarns: 128). The draw ratio was 1.8 times.

[0077] Example 6 A pellet-shaped poly(3-hydroxyalkanoate)-based resin composition for fibers and a multifilament fiber were prepared in the same manner as in Example 5, except that P3HB3HH(B-2) was used instead of P3HB3HH(B-1) and the draw ratio was 1.9 times. In Example 6, P3HB3HH(A-3) was P3HA(A), and P3HB3HH(B-2) was P3HA(B). The average molar ratio of 3HB / 3HH in the resin composition was 93.5 / 6.5 (mol% / mol%).

[0078] Comparative Example 1 A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 3, except that only P3HB3HH (A-3) was used as P3HA and the draw ratio was 8.5. The average molar ratio of 3HB / 3HH in the resin composition was 94.0 / 6.0 (mol% / mol%).

[0079] (Comparative Example 2) A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 1, except that a P3HA blend containing 30% by weight of P3HB3HH (A-1), 30% by weight of P3HB3HH (A-2), 10% by weight of P3HB3HH (A-3), and 30% by weight of P3HB3HH (C-1) was used. In Comparative Example 2, P3HB3HH (A-1), P3HB3HH (A-2), and P3HB3HH (A-3) represent P3HA (B), and P3HB3HH (C-1) represents P3HA (A). The average molar ratio of 3HB / 3HH in the resin composition was 88.3 / 11.7 (mol% / mol%).

[0080] (Comparative Example 3) A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a multifilament fiber were produced in the same manner as in Example 1, except that P3HA was a blend of 38 wt% P3HB3HH (A-1), 38 wt% P3HB3HH (A-2), and 24 wt% P3HB3HH (A-3) and that the draw ratio was 5.0 times. The average molar ratio of 3HB / 3HH in the resin composition was 86.8 / 13.2 (mol% / mol%).

[0081] Comparative Example 4 A pellet-shaped poly(3-hydroxyalkanoate)-based fiber resin composition and a monofilament fiber were prepared in the same manner as in Example 5, except that only P3HB3HH (A-3) was used as P3HA. The average molar ratio of 3HB / 3HH in the resin composition was 94.0 / 6.0 (mol% / mol%).

[0082] <Single Yarn Fineness of Fiber> The single yarn fineness of the fiber was measured by an autobibroscopic method. The single yarn fineness (also simply referred to as "fineness") is shown in Table 1 below.

[0083] <Tensile Strength and Breaking Elongation of Fiber Single Yarn> The tensile strength and breaking elongation of fiber single yarn were measured at an initial length of 20 mm and a speed of 20 mm / min in accordance with JIS L 1015:2021 "Testing Methods for Chemical Fiber Staples." The tensile strength of the single yarn was specifically determined as follows. First, using a tensile measuring device Autograph AG-I (manufactured by Shimadzu Corporation), the load (cN) at the time of breaking of the single yarn was measured under the following conditions: Initial length of each single fiber: 20 mm Pulling speed: 20 mm / min Load cell: Load cell with a rated capacity of 5 N Then, using the fineness of the single yarn measured by the autobibroscope method, the tensile strength of each single yarn was determined according to the following formula. Tensile strength of single yarn (cN / dtex) = Load at break of single yarn (cN) / Fineness of single yarn The fineness of single yarn (also simply referred to as "fineness") and the tensile strength of single yarn (also simply referred to as "tensile fineness") are shown in Table 1 below.

[0084] <Toughness> The toughness (tenacity) of a single fiber yarn was calculated using the following formula in accordance with the description of JP 2019-136348 A: Toughness = Tensile strength (unit: N / dtex) × (Elongation at break (unit: %)) １／２ The toughness is shown in Table 1 below.

[0085]

[0086] As shown in Table 1, in Examples 1 to 3 within the scope of the present invention, fibers with similar single filament fineness were produced, and the toughness of the single filament was higher than that of Comparative Example 1, which did not use P3HA(B). Furthermore, when fibers with similar single filament fineness were produced with the poly(3-hydroxyalkanoate)-based fiber resin composition of Example 4, which is within the scope of the present invention, the toughness of the single filament was higher than that of Comparative Example 2, which contains a smaller amount of P3HA(A), and Comparative Example 3, which does not use P3HA(B). Furthermore, when fibers with similar single filament fineness were produced with the poly(3-hydroxyalkanoate)-based fiber resin compositions of Examples 5 and 6, which are within the scope of the present invention, the toughness of the single filament was higher than that of Comparative Example 4, which does not use P3HA(B). Thus, it can be seen that the present invention can provide a poly(3-hydroxyalkanoate)-based fiber resin composition for producing poly(3-hydroxyalkanoate)-based resin-containing fibers with excellent toughness.

[0087] Furthermore, with regard to the monofilament, Examples 1 to 3 had higher toughness than Example 4, in which the fineness of the single filament of the fiber was as large as about 1000 dtex.

Claims

1. A poly(3-hydroxyalkanoate) fiber comprising a resin composition for poly(3-hydroxyalkanoate) fibers, the resin composition comprising a poly(3-hydroxyalkanoate) resin (A) having a weight average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate) resin (B) having a weight average molecular weight of 400,000 or more and 1,400,000 or less, wherein the weight average molecular weight of the poly(3-hydroxyalkanoate) resin (B) is 200,000 or more greater than the weight average molecular weight of the poly(3-hydroxyalkanoate) resin (A), and the content of the poly(3-hydroxyalkanoate) resin (A) is greater than the content of the poly(3-hydroxyalkanoate) resin (B).

2. The poly(3-hydroxyalkanoate) fiber according to claim 1, wherein the weight ratio of the content of the poly(3-hydroxyalkanoate) resin (A) to the content of the poly(3-hydroxyalkanoate) resin (B) is 95 / 5 to 70 / 30.

3. The poly(3-hydroxyalkanoate)-based fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin (A) and / or the poly(3-hydroxyalkanoate)-based resin (B) contains a 3-hydroxyalkanoic acid unit represented by the following formula (1): [-CHR-CH ２ —CO—O—] (1) (In the above formula (1), R is C ｐ H ２ｐ＋１ and p is an integer of 1 to 15.

4. The poly(3-hydroxyalkanoate)-based fiber according to claim 3, wherein the poly(3-hydroxyalkanoate)-based resin (A) and / or the poly(3-hydroxyalkanoate)-based resin (B) is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

5. The poly(3-hydroxyalkanoate) fiber according to claim 4, wherein the poly(3-hydroxyalkanoate) resin (A) and / or the poly(3-hydroxyalkanoate) resin (B) is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

6. The poly(3-hydroxyalkanoate) fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate) fiber resin composition contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units / other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) fiber resin composition is 80 / 20 to 95 / 5 (mol % / mol %).

7. The poly(3-hydroxyalkanoate) fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate) resin (B) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average molar ratio of 3-hydroxybutyrate units / other hydroxyalkanoate units contained in the poly(3-hydroxyalkanoate) resin (B) is 93 / 7 to 99 / 1 (mol % / mol %).

8. The poly(3-hydroxyalkanoate)-based fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based fiber resin composition contains 0.1 to 10 parts by weight of pentaerythritol per 100 parts by weight of the poly(3-hydroxyalkanoate)-based fiber resin composition.

9. A poly(3-hydroxyalkanoate)-based fiber resin composition comprising a poly(3-hydroxyalkanoate)-based resin (A) having a weight-average molecular weight of 200,000 or more and 700,000 or less, and a poly(3-hydroxyalkanoate)-based resin (B) having a weight-average molecular weight of 400,000 or more and 1,400,000 or less, wherein the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (B) is 200,000 or more greater than the weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A), and the content of the poly(3-hydroxyalkanoate)-based resin (A) is greater than the content of the poly(3-hydroxyalkanoate)-based resin (B).

10. The poly(3-hydroxyalkanoate)-based fiber resin composition according to claim 9, wherein the weight ratio of the content of the poly(3-hydroxyalkanoate)-based resin (A) to the content of the poly(3-hydroxyalkanoate)-based resin (B) is 95 / 5 to 70 / 30.

11. A method for producing fibers by melt spinning, comprising the steps of: (A) obtaining a raw yarn by discharging a melt of the poly(3-hydroxyalkanoate)-based fiber resin composition according to claim 9 or 10 from a discharge hole; (B) cooling the raw yarn; and (C) drawing the cooled raw yarn to obtain the fiber.

12. The method for producing a fiber according to claim 11, wherein the draw ratio in step (C) is 5.0 times or more.

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