Fibers and non-woven fabric

Abstract

The present invention provides fibers that contain a poly(3-hydroxyalkanoate) resin that includes a 3-hydroxybutyrate unit, the poly(3-hydroxyalkanoate) resin–containing fibers making it possible for fusion to be suppressed during production of the fibers but for thermal fusion to be achieved at a low temperature when the fibers are thermally processed. The present invention provides fibers that have a core / sheath structure that includes a core part and a sheath part. Both the core part and the sheath part contain a poly(3-hydroxyalkanoate) resin that includes a 3-hydroxybutyrate unit. The average molar 3-hydroxybutyrate unit content of the poly(3-hydroxyalkanoate) resin of the core part is greater than the average molar 3-hydroxybutyrate unit content of the poly(3-hydroxyalkanoate) resin of the sheath part.

Description

Fibers and nonwoven fabrics

[0001] The present invention relates to fibers and nonwoven fabrics.

[0002] In recent years, plastic waste has become a major problem that causes a significant burden on the global environment, including impacts on ecosystems, the generation of harmful gases when burned, and global warming due to the large amount of heat generated by combustion. As a solution to these problems, biodegradable plastics have been actively developed.

[0003] Among these biodegradable plastics, those made from plant-derived raw materials emit carbon dioxide when burned, which was originally present in the air and does not increase the amount of carbon dioxide in the atmosphere. This is called carbon neutrality, and is considered important under the Kyoto Protocol, which imposed carbon dioxide reduction targets, and active use of such plastics is desired.

[0004] Recently, from the viewpoints of biodegradability and carbon neutrality, aliphatic polyester resins, and in particular polyhydroxyalkanoate resins, have been attracting attention as biodegradable plastics that are produced by microorganisms using plant-derived raw materials as a carbon source.

[0005] Patent Document 1 discloses a biodegradable composite fiber having a core component of poly(β-hydroxyalkanoate) or a copolymer thereof and a sheath component of poly-ε-caprolactone and / or poly-β-propiolactone. Patent Document 2 discloses a foamed, defibrated molding containing the following copolymer (A) and copolymer (B). (A) A copolymer containing the following structural units (a1) and (a2) in the following ratios (the total of (a1) and (a2) is 100 mol %): (a1) 3-hydroxybutyrate structural units: 92 mol % or more and 98 mol % or less; (a2) structural units represented by [—O—R1-CO—]: 2 mol % or more and 8 mol % or less (R1 represents a linear or branched alkyl group having from 3 to 17 carbon atoms). (However, structural units (a2) do not include 3-hydroxybutyrate structural units.) (B) A copolymer containing the following structural units (b1) and (b2) in the following ratios (the total of (b1) and (b2) is 100 mol %): (b1) 3-hydroxybutyrate structural units: 85 mol % or more and less than 92 mol %; (b2) structural units represented by [—O—R2-CO—]: more than 8 mol % and 15 mol % or less. (R2 represents a linear or branched alkyl group having 3 to 17 carbon atoms.) (However, the structural unit (b2) does not include a 3-hydroxybutyrate structural unit.)

[0006] JP 5-93318 A JP 2023-49669 A

[0007] However, conventional fibers tend to fuse together during production, or are not sufficiently heat-fused at low temperatures during heat processing, making them difficult to heat process.

[0008] Therefore, an object of the present invention is to provide a fiber containing a poly(3-hydroxyalkanoate)-based resin containing a 3-hydroxybutyrate unit, which fiber is inhibited from fusing during fiber production and can be heat-fused at low temperatures during thermal processing of the fiber, and a nonwoven fabric comprising the fiber.

[0009] The present invention relates to a fiber having a core-sheath structure including a core and a sheath, wherein the core and sheath each contain a poly(3-hydroxyalkanoate) resin containing 3-hydroxybutyrate units, and the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the core is greater than the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the sheath. The present invention also relates to a method for producing the fiber, in which the fiber is obtained by melt-spinning a raw material composition for the core and a raw material composition for the sheath using a core-sheath multi-component spinning nozzle. The present invention also relates to a nonwoven fabric comprising the fiber.

[0010] According to the present invention, there are provided fibers containing a poly(3-hydroxyalkanoate)-based resin containing a 3-hydroxybutyrate unit, which fibers are inhibited from fusing during fiber production and can be heat-fused at low temperatures during thermal processing of the fibers, and a nonwoven fabric comprising the fibers.

[0011] 1 is a schematic diagram of a cross section of a single fiber of the fiber according to the present embodiment. FIG.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] <Fiber According to the Present Embodiment> The fiber according to the present embodiment has a core-sheath structure including a core and a sheath. The core and sheath each contain a poly(3-hydroxyalkanoate)-based resin containing 3-hydroxybutyrate units (hereinafter also referred to as "P3HA-based resin," "P3HA," "poly(3-hydroxybutyrate)-based resin," or "P3HB-based resin"). The average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate)-based resin of the core is greater than the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate)-based resin of the sheath. By having such a structure, the fiber according to the present embodiment becomes a poly(3-hydroxyalkanoate)-based resin-containing fiber that is suppressed from fusing during fiber production and can be heat-fused at low temperatures during thermal processing of the fiber.

[0014] The fiber according to this embodiment may be a multifilament having a plurality of single fibers, or a monofilament having a single fiber, but a multifilament is preferred from the viewpoint of flexibility and softness, and of being usable for nonwoven fabrics and the like.

[0015] The single fiber is a sheath-core composite fiber. FIG. 1 is a schematic diagram of a cross section (a cross section perpendicular to the longitudinal direction of the single fiber) of a single fiber 1 that is a sheath-core composite fiber according to this embodiment. As shown in FIG. 1, the single fiber 1 that is a sheath-core composite fiber includes a core 10 and a sheath 20. In the cross section (a cross section perpendicular to the longitudinal direction of the sheath-core composite fiber) of the sheath-core composite fiber, it is preferable that the core is located inside the sheath. Furthermore, in the cross section (a cross section perpendicular to the longitudinal direction of the sheath-core composite fiber), the sheath-core composite fiber may have a concentric structure in which the center position of the core coincides with the center position of the sheath-core composite fiber, or an eccentric structure in which the center position of the core does not coincide with the center position of the sheath-core composite fiber and is eccentric. The cross-sectional shapes of the single fiber 1 that is a sheath-core composite fiber and the core 10 are not particularly limited and may be, for example, circular or an irregular shape other than circular. Examples of irregular shapes include an ellipse, a cross-circular shape, a cocoon shape, a potbelly shape, a dogbone shape, and a ribbon shape. The cross-sectional shape of the sheath-core composite fiber and the cross-sectional shape of the core may be the same (similar shapes) or different. In this embodiment, the long axis direction of the cross section of the single fiber coincides with the long axis direction of the cross section of the core. In the embodiment shown in Figure 1, the cross-sectional shape of the single fiber 1 that is the sheath-core composite fiber and the cross-sectional shape of the core 10 are both circular, and the core 10 is arranged concentrically with the single fiber 1 that is the sheath-core composite fiber. The cross-sectional shapes of the single fiber and the core that are the sheath-core composite fiber can be controlled by using a sheath-core composite spinning nozzle having a nozzle hole with a shape similar to the desired cross-sectional shape when producing fibers using the sheath-core composite spinning nozzle described below.

[0016] The core-sheath ratio (ratio of core 10 to sheath 20) in the cross section of the fiber according to this embodiment (cross section perpendicular to the longitudinal direction of the fiber, i.e., cross section perpendicular to the longitudinal direction of a single fiber) is not particularly limited, but an area ratio of the core 10 to the sheath 20 in the range of 1:9 to 9:1 is preferred from the viewpoints of the development of a complex appearance, spinning, cross-sectional stability, etc., more preferably 2:8 to 8:2, and even more preferably 3:7 to 7:3. In other words, the area ratio of the core 10 to the sheath 20 in the cross section of the fiber is preferably core / sheath = 9 / 1 to 1 / 9, more preferably core / sheath = 8 / 2 to 2 / 8, and even more preferably core / sheath = 7 / 3 to 3 / 7. The core-sheath ratio can be determined by the method described in the Examples below.

[0017] The fiber according to this embodiment contains a polymer component. The polymer component contains a poly(3-hydroxyalkanoate)-based resin containing a 3-hydroxybutyrate unit. The polymer component may also contain other polymers in addition to the poly(3-hydroxyalkanoate)-based resin.

[0018] The poly(3-hydroxyalkanoate) resin is a biodegradable polymer. In this embodiment, "biodegradable" refers to the property of being decomposed into low molecular weight compounds by microorganisms in nature. Specifically, biodegradability can be determined based on tests suitable for each environment, such as ISO 14855 (compost) and ISO 14851 (activated sludge) under aerobic conditions, and ISO 14853 (aqueous phase) and ISO 15985 (solid phase) under anaerobic conditions. Microbial decomposition in seawater can be evaluated by measuring biochemical oxygen demand. The poly(3-hydroxyalkanoate) resin is a concept that includes homopolymers and copolymers. The poly(3-hydroxyalkanoate) resin is preferably a copolymer.

[0019] Examples of the poly(3-hydroxyalkanoate) resins include P3HB, P3HB3HH, P3HB3HV, P3HB4HB, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Here, P3HB refers to poly(3-hydroxybutyrate) as a homopolymer. P3HB3HH refers to poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), also known as a (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin. P3HB3HV refers to poly(3-hydroxybutyrate-co-3-hydroxyvalerate). P3HB4HB refers to poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0020] Since P3HB has the function of promoting the crystallization of P3HB itself and poly(3-hydroxyalkanoate) resins other than P3HB, the poly(3-hydroxyalkanoate) resin preferably contains P3HB.

[0021] From the viewpoint of achieving both excellent biodegradability and moldability, the poly(3-hydroxyalkanoate) resin is preferably, but not limited to, P3HB, P3HB3HH, P3HB3HV, P3HB4HB, etc. Furthermore, from the viewpoint of increasing the strength and moldability of the fiber according to this embodiment, the poly(3-hydroxyalkanoate) resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH).

[0022] The average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the core is greater than the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the sheath. In the present application, the "average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin" is also referred to as the "average molar content of 3HB in the P3HA resin." The difference between the average molar content of 3HB in the P3HA resin of the core and the average molar content of 3HB in the P3HA resin of the sheath is preferably 0.2 to 9.0 mol%, more preferably 0.4 to 7.0 mol%, even more preferably 0.5 to 4.5 mol%, particularly preferably 1.0 to 4.0 mol%, and most preferably 1.5 to 3.5 mol%, from the viewpoint of further suppressing fusion during fiber production while enabling heat fusion at an even lower temperature during thermal processing of the fiber. The difference between the average molar content of 3HB in the P3HA-based resin of the core and the average molar content of 3HB in the P3HA-based resin of the sheath is the value obtained by subtracting the average molar content of 3HB in the P3HA-based resin of the sheath from the average molar content of 3HB in the P3HA-based resin of the core. In the fiber according to this embodiment, the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate)-based resin of the core is greater than the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate)-based resin of the sheath. This suppresses fusion during fiber production and enables heat fusion at low temperatures when the fiber is thermally processed.

[0023] From the viewpoint of further suppressing fusion during fiber production while enabling heat fusion at an even lower temperature when the fiber is thermally processed, the fiber according to this embodiment preferably contains a copolymer (A) in which the molar ratio of monomers of 3-hydroxybutyrate units and other hydroxyalkanoate units is 3-hydroxybutyrate units / other hydroxyalkanoate units=99 / 1 to 93 / 7, and a copolymer (B) in which the molar ratio of monomers of 3-hydroxybutyrate units and other hydroxyalkanoate units is 3-hydroxybutyrate units / other hydroxyalkanoate units=92 / 8 to 76 / 24.

[0024] In the copolymer (A), the molar ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units is 3-hydroxybutyrate units / other hydroxyalkanoate units=99 / 1 to 93 / 7, preferably 98 / 2 to 93 / 7, and more preferably 97 / 3 to 93 / 7.

[0025] In the copolymer (B), the molar ratio of the 3-hydroxybutyrate unit to the other hydroxyalkanoate unit monomers is 3-hydroxybutyrate unit / other hydroxyalkanoate unit=92 / 8 to 76 / 24, preferably 91 / 9 to 80 / 20, and more preferably 90 / 10 to 85 / 15.

[0026] The average molar content of 3-hydroxybutyrate units in a poly(3-hydroxyalkanoate) resin and the molar ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units (3-hydroxybutyrate units / other hydroxyalkanoate units) in a poly(3-hydroxyalkanoate) resin can be determined as follows. First, 20 mg of dried P3HA resin is added to a sample containing 2 mL of a mixture of sulfuric acid and methanol (volume of sulfuric acid:volume of methanol=15:85) and 2 mL of chloroform. The sample is sealed and heated in a sealed state at 100°C for 140 minutes to obtain a first reaction solution containing methyl esters, which are decomposition products of the P3HA resin. The first reaction solution is then cooled, and 1.5 g of sodium bicarbonate is added little by little to neutralize the cooled first reaction solution. The mixture is then left to stand until carbon dioxide generation ceases to yield a second reaction solution. Furthermore, the second reaction solution is thoroughly mixed with 4 mL of diisopropyl ether to obtain a mixture. The mixture is then centrifuged to obtain a supernatant. The monomer unit composition of the decomposition product in the supernatant is then analyzed by capillary gas chromatography under the following conditions to determine the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin and the molar ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units in the poly(3-hydroxyalkanoate) resin (3-hydroxybutyrate units / other hydroxyalkanoate units). Gas chromatograph: GC-17A manufactured by Shimadzu Corporation. Capillary column: NEUTRA BOND-1 manufactured by GL Sciences (column length: 25 m, column inner diameter: 0.25 mm, liquid film thickness: 0.4 μm). Carrier gas: He. Column inlet pressure: 100 kPa. Sample amount: 1 μL.

[0027] From the viewpoint of further suppressing fusion during fiber production and enabling heat fusion at an even lower temperature when the fiber is thermally processed, the fiber according to this embodiment contains preferably 5 to 40% by weight, more preferably 10 to 35% by weight, and even more preferably 12 to 30% by weight of the copolymer (B) relative to 100% by weight of the poly(3-hydroxyalkanoate) resin.

[0028] From the viewpoint of enabling heat fusion at an even lower temperature when thermally processing the fiber, the sheath preferably contains the copolymer (B). Furthermore, from the viewpoint of enabling heat fusion at an even lower temperature when thermally processing the fiber while further suppressing fusion during fiber production, the sheath more preferably contains the copolymer (A) and the copolymer (B).

[0029] From the viewpoint of further suppressing fusion during fiber production, the core preferably contains the copolymer (A).

[0030] The fiber according to this embodiment contains preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more of a poly(3-hydroxyalkanoate)-based resin. The fiber according to this embodiment also contains preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more of a copolymer (A) and a copolymer (B).

[0031] The other polymer is preferably biodegradable.

[0032] Examples of other biodegradable polymers include polycaprolactone, polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polyethylene succinate, polyvinyl alcohol, polyglycolic acid, unmodified starch, modified starch, cellulose acetate, chitosan, and poly(4-hydroxyalkanoate)-based resins. The polycaprolactone is a polymer obtained by ring-opening polymerization of ε-caprolactone. The polymer component may contain one or more other polymers.

[0033] The fiber according to this embodiment contains a biodegradable polymer, and therefore, even if discarded in the environment, it is easily decomposed in the environment, thereby reducing the burden on the environment.

[0034] The fiber according to the present embodiment may further contain additives, such as nucleating agents, lubricants, plasticizers, spinning oils, stabilizers (antioxidants, ultraviolet absorbers, etc.), colorants (dyes, pigments, etc.), inorganic fillers, organic fillers, and antistatic agents.

[0035] In order to promote the crystallization of the poly(3-hydroxyalkanoate)-based resin, the fiber according to this embodiment preferably contains a crystal nucleating agent. The crystal nucleating agent is a compound that has the effect of promoting the crystallization of the poly(3-hydroxyalkanoate)-based resin. The crystal nucleating agent has a higher melting point than the poly(3-hydroxyalkanoate)-based resin. Examples of the crystal nucleating agent include inorganic substances (boron nitride, titanium oxide, talc, layered silicates, calcium carbonate, sodium chloride, metal phosphates, etc.); sugar alcohol compounds derived from natural products (pentaerythritol, erythritol, galactitol, mannitol, arabitol, etc.); polyvinyl alcohol; chitin; chitosan; polyethylene oxide; aliphatic carboxylates; aliphatic alcohols; aliphatic carboxylate esters; dicarboxylic acid derivatives (dimethyl adipate, dibutyl adipate, diisodecyl adipate, dibutyl stearate, etc.); Examples of suitable poly(3-hydroxyalkanoate) resins include cyclic compounds having C═O and a functional group selected from NH, S, and O in the molecule (such as indigo, quinacridone, and quinacridone magenta); sorbitol derivatives (such as bisbenzylidene sorbitol and bis(p-methylbenzylidene)sorbitol); compounds containing a nitrogen-containing heteroaromatic nucleus (such as a pyridine ring, triazine ring, and imidazole ring) (such as pyridine, triazine, and imidazole); phosphate ester compounds; bisamides of higher fatty acids; metal salts of higher fatty acids; and branched polylactic acid. Furthermore, the poly(3-hydroxyalkanoate) resin P3HB can also be used as a crystal nucleating agent. These may be used alone or in combination of two or more.

[0036] As the crystal nucleating agent, from the viewpoint of the effect of improving the crystallization rate of the poly(3-hydroxyalkanoate) resin and from the viewpoint of compatibility and affinity with the poly(3-hydroxyalkanoate) resin, sugar alcohol compounds, polyvinyl alcohol, chitin, and chitosan are preferred. Among the sugar alcohol compounds, pentaerythritol is preferred.

[0037] The nucleating agent preferably has a crystalline structure at room temperature (25°C). The nucleating agent having a crystalline structure at room temperature (25°C) has the advantage of further accelerating the crystallization of the poly(3-hydroxyalkanoate) resin. Furthermore, the nucleating agent having a crystalline structure at room temperature (25°C) is preferably in a powder form at room temperature (25°C). Furthermore, the average particle size of the nucleating agent in a powder form at room temperature (25°C) is preferably 10 μm or less.

[0038] The content of the nucleating agent in the fiber according to this embodiment is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. Having a content of the nucleating agent in the fiber according to this embodiment of 0.05 parts by weight or more per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin has the advantage of further promoting crystallization of the poly(3-hydroxyalkanoate)-based resin. Furthermore, the content of the nucleating agent in the fiber according to this embodiment is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and even more preferably 5 parts by weight or less, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. By having the content of the nucleating agent in the fiber according to this embodiment be 10 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) resin, the viscosity of the molten material can be reduced when the fiber is produced from the molten material by the melt spinning method described below, which has the advantage of facilitating the production of the fiber. Note that P3HB is a poly(3-hydroxyalkanoate) resin and can also function as a nucleating agent, so when the fiber contains P3HB, the amount of P3HB is included in both the amount of the poly(3-hydroxyalkanoate) resin and the amount of the nucleating agent.

[0039] The fiber according to the present embodiment may contain a lubricant. Examples of the lubricant include a compound having an amide bond. The compound having an amide bond preferably includes one or more compounds selected from the group consisting of lauric acid amide, myristic acid amide, stearic acid amide, behenic acid amide, and erucic acid amide.

[0040] The content of the lubricant in the fiber according to this embodiment is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and even more preferably 0.5 parts by weight or more, relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. Having the content of the lubricant in the fiber according to this embodiment be 0.05 parts by weight or more, relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin, offers the advantage of excellent lubrication of the single fiber. Furthermore, the content of the lubricant in the fiber according to this embodiment is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and most preferably 5 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. Having the content of the lubricant in the fiber according to this embodiment be 12 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin, offers the advantage of suppressing bleeding of the lubricant onto the surface of the fiber.

[0041] The single fiber fineness of the fiber according to this embodiment is preferably 1 to 15 dtex, more preferably 2 to 13 dtex, and even more preferably 3 to 12 dtex. Having a single fiber fineness of 15 dtex or less provides the fiber according to this embodiment with the advantage that it can be used for a variety of applications. For example, the fiber according to this embodiment can be used as a material for producing spun yarn. Having a single fiber fineness of 1 dtex or more provides the fiber according to this embodiment with the advantage that it has increased strength. When the fiber according to this embodiment is a multifilament, the single fiber fineness of the fiber means the average value of the finenesses of the single fibers contained in the fiber. When the fiber according to this embodiment is a monofilament, the single fiber fineness of the fiber means the fineness of the fiber itself. The single fiber fineness can be measured by the method described in the Examples below.

[0042] When the fiber according to this embodiment is a multifilament having a plurality of single fibers, it preferably has 30 or more single fibers, more preferably 30 to 300,000 single fibers, and even more preferably 50 to 300,000 single fibers.

[0043] The weight average molecular weight of the fiber according to this embodiment is preferably 2.0 × 10 from the viewpoint of excellent processability when processing the fiber to obtain a processed product. ５ ~6.0 x 10 ５ , more preferably 2.3 × 10 ５ ~4.0 x 10 ５ is.

[0044] The weight average molecular weight in this embodiment refers to a value measured from the polystyrene equivalent molecular weight distribution using gel permeation chromatography (GPC) with a chloroform eluent. A column suitable for measuring the molecular weight may be used as the column in the GPC. For example, the weight average molecular weight in this embodiment can be measured under the following conditions. Measuring apparatus: Shimadzu 20A manufactured by Shimadzu Corporation Column: Shodex K-806M manufactured by Showa Denko Detector: RI detector Standard material: polystyrene Eluent: chloroform (HPLC grade) Flow rate: 1 mL / min Temperature: 40°C

[0045] The fibers according to this embodiment may be used as they are in the form of threads. Alternatively, the fibers may be cut to obtain staples having a length of 20 cm or less. Alternatively, the staples may be used as they are in the form of threads. Alternatively, textile products (fibrous bodies) may be produced using the fibers and / or staples. The textile products may be formed into various shapes (e.g., nonwoven fabrics, etc.). The fibers, staples, and textile products can be suitably used for conventionally known applications. The fibers, staples, and textile products can be suitably used in fields such as agriculture (e.g., horticulture), fisheries, forestry, the medical industry, and the food industry. Examples of the textile products include clothing, curtains, carpets, bags, shoes, wiping materials, sanitary products, automotive components, building materials, and filtration materials (filters).

[0046] <Nonwoven Fabric According to the Present Embodiment> The nonwoven fabric according to the present embodiment includes the fiber according to the present embodiment. Examples of the nonwoven fabric according to the present embodiment include a thermally bonded nonwoven fabric, a needle-punched nonwoven fabric, a chemically bonded nonwoven fabric, an air-laid nonwoven fabric, and a wet-laid nonwoven fabric. The fiber according to the present embodiment can be thermally fused at a low temperature during thermal processing, and is therefore suitable for use in producing a thermally bonded nonwoven fabric.

[0047] <Method for producing fibers according to this embodiment> The method for producing fibers according to this embodiment uses a core-sheath composite spinning nozzle to melt-spin a raw material composition for the core and a raw material composition for the sheath to obtain the fibers. For example, the method for producing fibers according to this embodiment includes a spinning step in which a raw material composition is melted to obtain a melt and then spun to obtain an undrawn yarn by a melt spinning method, and a drawing step in which the undrawn yarn is drawn. The raw material composition includes a raw material composition for the core and a raw material composition for the sheath separately. The raw material composition contains a poly(3-hydroxyalkanoate)-based resin. The weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin in the raw material composition is preferably 3.0 x 10 ５ ~7.0 x 10 ５ , more preferably 3.5 × 10 ５ ~7.0 x 10 ５ , and more preferably 4.0 × 10 ５ ~7.0 x 10 ５ , most preferably 4.5×10 ５ ~6.5 x 10 ５ The weight average molecular weight of the poly(3-hydroxyalkanoate) resin in the raw material composition is 3.0 × 10 ５ When the weight average molecular weight of the poly(3-hydroxyalkanoate) resin in the raw material composition is 7.0 × 10 or more, it becomes easy to increase the weight average molecular weight of the poly(3-hydroxyalkanoate) resin in the fiber, and as a result, it becomes easy to increase the strength of the fiber. ５ By satisfying the above condition, it becomes easier to form the fibers.

[0048] In the spinning process, the core raw material composition is supplied to a core extruder, and the sheath raw material composition is supplied to a sheath extruder, and the core raw material composition and the sheath raw material composition are melted to obtain a molten core material and a molten sheath material. The molten core material and the molten sheath material are then extruded from a core-sheath multi-component spinning nozzle and wound up on a take-up roll to obtain one or more undrawn yarns.

[0049] In the drawing step, one or more undrawn yarns are taken up from the take-up roll section by a take-up roll section, drawn by a drawing roll section, and wound up by a heat treatment roll section to obtain a fiber.

[0050] 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.

[0051] For example, in this embodiment, one or more undrawn yarns are drawn to form a fiber, but in the present invention, one or more undrawn yarns may also be used as a fiber.

[0052] Disclosure Items Each of the following items is a disclosure of a preferred embodiment.

[0053] [Item 1] A fiber having a core-sheath structure including a core and a sheath, wherein the core and sheath each contain a poly(3-hydroxyalkanoate) resin containing 3-hydroxybutyrate units, and wherein the average molar content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the core is greater than the average molar content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the sheath. [Item 2] The fiber according to item 1, comprising: a copolymer (A) in which the molar ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units is 3-hydroxybutyrate units / other hydroxyalkanoate units of 99 / 1 to 93 / 7; and a copolymer (B) in which the molar ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units is 3-hydroxybutyrate units / other hydroxyalkanoate units of 92 / 8 to 76 / 24. [Item 3] The fiber according to item 2, wherein the copolymer (B) accounts for 5 to 40% by weight of 100% by weight of the poly(3-hydroxyalkanoate)-based resin. [Item 4] The fiber according to item 2 or 3, wherein the sheath portion comprises the copolymer (B). [Item 5] The fiber according to item 4, wherein the sheath portion comprises the copolymer (A) and the copolymer (B). [Item 6] The fiber according to any one of items 1 to 5, wherein the area ratio of the core portion to the sheath portion in the cross section of the fiber is core / sheath = 8 / 2 to 2 / 8. [Item 7] The fiber according to any one of items 1 to 6, wherein the poly(3-hydroxyalkanoate)-based resin is poly-(3-hydroxybutyrate-co-3-hydroxyhexanoate). [Item 8] The fiber according to any one of items 1 to 7, wherein the single fiber fineness is 1 to 15 dtex. [Item 9] A method for producing a fiber, comprising melt-spinning a core raw material composition and a sheath raw material composition using a core-sheath type composite spinning nozzle to obtain the fiber according to any one of items 1 to 8. [Item 10] A nonwoven fabric comprising the fiber according to any one of items 1 to 8.

[0054] Next, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples. The measurement methods and evaluation methods used in the examples and comparative examples are as follows.

[0055] Example 1 First, the following materials were dry blended in the following proportions, and melt-kneaded at 150° C. in an extruder to obtain pellets of a core raw material composition and a shell raw material composition.

[0056] <Core Raw Material Composition> A (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit molar content (3HB ratio): 94.0 mol%, 3-hydroxyhexanoate unit molar content (3HH ratio): 6 mol%, melting point: 145°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (A1)): 100 parts by mass; erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass; behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass; and pentaerythritol (PETL) as a crystal nucleating agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 part by mass.

[0057] <Sheath Raw Material Composition> 50 parts by mass of (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit molar content (3HB ratio): 94.0 mol %, 3-hydroxyhexanoate unit molar content (3HH ratio): 6 mol %, melting point: 145°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (A1)) as a poly(3-hydroxyalkanoate) resin (copolymer (A)). Poly(3-hydroxyalkanoate)-based resin (copolymer (B)) (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (molar content of 3-hydroxybutyrate units (3HB ratio): 89.0 mol%, molar content of 3-hydroxyhexanoate units (3HH ratio): 11.0 mol%, melting point: 108 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (B1)): 50 parts by mass Erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass Behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass Crystal nucleating agent Pentaerythritol (PETL) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 part by mass

[0058] The molar content of 3-hydroxybutyrate units (3HB ratio), the molar content of 3-hydroxyhexanoate units (3HH ratio), and the weight average molecular weight (Mw) were determined by the methods described above.

[0059] The melting point was defined as the temperature at the point where the endotherm was maximum (the apex of the endothermic peak) in the DSC curve obtained by differential scanning calorimetry (DSC). The differential scanning calorimetry (DSC) was a method in accordance with JIS K7122 (1987) "Method for measuring the heat of transition of plastics." Specifically, the measurement was carried out under the following conditions: Apparatus: Differential scanning calorimeter DSC6200 manufactured by Seiko Instruments Inc. Sample amount: 4 to 10 mg Measurement temperature range: 30°C to 200°C Heating rate: 10°C / min

[0060] The crystallization temperature (Tc) was measured in accordance with JIS K7121-1987 "Method for measuring transition temperatures of plastics." Specifically, a differential scanning calorimeter (e.g., a differential scanning calorimeter DSC25 manufactured by TA Instruments) was used. Approximately 6.0 mg of the poly(3-hydroxyalkanoate) resin sample was filled into a measurement container, and the sample was heated and cooled between -30°C and 180°C at a heating and cooling rate of 10°C / min under a nitrogen gas flow rate of 50 ml / min. The temperature at the top of the exothermic peak during the second cooling was taken as the crystallization temperature. When there were two or more exothermic peaks, the temperature at the top of the exothermic peak with the largest peak area was taken as the crystallization temperature.

[0061] <Spinning Step> Next, pellets of the core raw material composition were fed to a core extruder, and pellets of the sheath raw material composition were fed to a sheath extruder, and the core raw material composition and the sheath raw material composition were melted to obtain a molten core material and a molten sheath material. The molten core material and the molten sheath material were then extruded from a concentric core-sheath type composite spinning nozzle (200 holes, 0.5 mm diameter) set at 175°C and taken up on a take-up roll at a speed of 250 to 300 m / min, to obtain 200 undrawn core-sheath composite fibers with a core-to-sheath area ratio in the cross section (core:sheath) (hereinafter simply referred to as the "core-sheath ratio") of 7:3.

[0062] <Sheath-core ratio> At room temperature, fibers were bundled and fixed with a shrink tube to prevent the fiber bundle (total fineness 2200 dtex) from shifting, and then sliced ​​with a cutter to prepare a fiber bundle for cross-section observation. This fiber bundle was photographed at 500x magnification with a laser microscope (Keyence Corporation, "VK-9500"), and the core-sheath ratio was determined based on the obtained fiber cross-section photograph.

[0063] <Drawing step> The obtained 200 undrawn yarns were taken up from the take-up roll section by a take-up roll section (55.5 m / min, 30°C), drawn by a drawing roll section (110 m / min, 90°C), and taken up by a heat treatment roll section (100 m / min) to obtain a fiber (a multifilament having 200 single fibers that were core-sheath composite fibers having the cross-sectional shape shown in Figure 1) (single fiber fineness 5.5 dtex, core-sheath ratio 7:3). The draw ratio was 2.0 times, and the relaxation rate was 10%. The take-up roll section, drawing roll section, and heat treatment roll section each consisted of two rolls operating at the same speed and temperature.

[0064] <Single Fiber Fineness> Measurement was carried out using an auto-blow type fineness measuring instrument "DENIER COMPUTER Type DC-11" (manufactured by Search Co.), and the average value of the measured values ​​of 10 samples was calculated to be the single fiber fineness.

[0065] Example 2 A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) (single fiber fineness 6.1 dtex, core-sheath ratio 5:5) was obtained in the same manner as in Example 1, except that the core-sheath ratio of the undrawn yarn was set to 5:5.

[0066] Example 3 A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) (single fiber fineness: 5.8 dtex) was obtained in the same manner as in Example 1, except that the raw material composition for the sheath portion was blended in the following proportions: 30 parts by mass of a (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit content: 94.0 mol %, 3-hydroxyhexanoate unit content: 6 mol %, melting point: 145°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (A1)) as a poly(3-hydroxyalkanoate)-based resin (copolymer (A)): Poly(3-hydroxyalkanoate)-based resin (copolymer (B)) (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit content: 89.0 mol%, 3-hydroxyhexanoate content: 11.0 mol%, melting point: 108 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (B1)): 70 parts by mass Erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass Behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass Pentaerythritol (PETL) as a crystal nucleating agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 part by mass

[0067] Example 4 A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) was obtained in the same manner as in Example 1, except that the single fiber fineness was set to 11.0 dtex.

[0068] (Example 5) A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) (single fiber fineness 4.5 dtex) was obtained in the same manner as in Example 1, except that the raw material composition for the core was blended in the following blending ratio, the raw material composition for the sheath was blended in the following blending ratio, the core-sheath ratio of the undrawn yarn was set to 5:5, and the drawing step was not performed.

[0069] <Raw Material Composition for Core Portion> A (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit molar content (3HB ratio): 97.0 mol %, 3-hydroxyhexanoate unit molar content (3HH ratio): 3 mol %, melting point: 152°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 390,000) (P3HB3HH) (copolymer (A2)): 100 parts by mass; erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass; behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass; and pentaerythritol (PETL) as a crystal nucleating agent (Neuriser P, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.): 1.0 part by mass. <Raw Material Composition for Sheath Portion> Poly(3-hydroxyalkanoate)-based resin (copolymer (A)) (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (molar content of 3-hydroxybutyrate units (3HB ratio): 94.0 mol%, molar content of 3-hydroxyhexanoate units (3HH ratio): 6 mol%, melting point: 145°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 582,936) (P3HB3HH) (copolymer (A1)): 50 parts by mass Poly(3-hydroxyalkanoate)-based resin (copolymer (B)) (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (molar content of 3-hydroxybutyrate units (3HB ratio): 89.0 mol%, molar content of 3-hydroxyhexanoate units (3HH ratio): 11.0 mol%, melting point: 108 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 220,000) (P3HB3HH) (copolymer (B2)): 50 parts by mass Erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass Behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass Pentaerythritol (PETL) as a crystal nucleating agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 part by mass

[0070] (Example 6) A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) (single fiber fineness 4.5 dtex) was obtained in the same manner as in Example 1, except that the raw material composition for the core was blended in the following blending ratio, the raw material composition for the sheath was blended in the same manner as in Example 5, the core-sheath ratio of the undrawn yarn was set to 5:5, and the drawing step was not performed.

[0071] <Core Raw Material Composition> 50 parts by mass of (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit molar content (3HB ratio): 97.0 mol %, 3-hydroxyhexanoate unit molar content (3HH ratio): 3 mol %, melting point: 152°C, crystallization temperature (Tc): 60°C, weight average molecular weight (Mw): 390,000) (P3HB3HH) (copolymer (A2)) as a poly(3-hydroxyalkanoate) resin (copolymer (A)). Poly(3-hydroxyalkanoate)-based resin (copolymer (B)) (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (molar content of 3-hydroxybutyrate units (3HB ratio): 89.0 mol%, molar content of 3-hydroxyhexanoate units (3HH ratio): 11.0 mol%, melting point: 108 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 310,000) (P3HB3HH) (copolymer (B3)): 5 parts by mass Poly(3-hydroxybutyrate) (P3HB) as a homopolymer of poly(3-hydroxyalkanoate)-based resin (melting point: 180 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 310,000): 45 parts by mass Erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass Behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass Pentaerythritol (PETL) as a crystal nucleating agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 parts by mass

[0072] Comparative Example 1 A fiber (a multifilament having 200 single fibers that are core-sheath composite fibers) (single fiber fineness 5.6 dtex) was obtained in the same manner as in Example 1, except that the raw material composition for the sheath portion was blended in the following blending ratio. Poly(3-hydroxyalkanoate)-based resin (copolymer (A)) as a (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3-hydroxybutyrate unit content: 94.0 mol%, 3-hydroxyhexanoate content: 6 mol%, melting point: 145 ° C., crystallization temperature (Tc): 60 ° C., weight average molecular weight (Mw): 582,936) (P3HB3HH): 100 parts by mass Erucic acid amide (EA) as a lubricant having an amide bond: 0.5 parts by mass Behenic acid amide (BA) as a lubricant having an amide bond: 0.5 parts by mass Pentaerythritol (PETL) as a crystal nucleating agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Neuraizer P): 1.0 part by mass

[0073] Comparative Example 2 A fiber (a multifilament having 400 single fibers that are single-layer fibers) (single fiber fineness 5.8 dtex) was obtained in the same manner as in Example 1, except that only the core raw material composition of Example 1 was used, and a single-layer spinning nozzle was used instead of a concentric core-sheath type composite spinning nozzle.

[0074] (Comparative Example 3) A fiber (a multifilament having 400 single fibers that are single-layer fibers) (single fiber fineness 6.0 dtex) was obtained in the same manner as in Example 1, except that only the raw material composition for the sheath portion of Example 1 was used, and a single-layer spinning nozzle was used instead of a concentric core-sheath type composite spinning nozzle.

[0075] (Fusion Rate) The fusion rate was determined as follows. First, a multifilament fiber was cut in a plane perpendicular to the longitudinal direction of the fiber, thereby cutting all of the single fibers contained in the fiber. Next, the cut surface of the multifilament was observed using a scanning electron microscope (SEM), and the total number of single fibers contained in the multifilament at the cut surface and the number of single fibers fused to other single fibers at the cut surface (this number is also calculated by subtracting the number of single fibers not fused to other single fibers from the total number of single fibers contained in the multifilament) were counted. The fusion rate was then determined using the following formula: Fusion rate (%) = (number of single fibers fused to other single fibers at the cut surface / total number of single fibers contained in the multifilament at the cut surface) x 100

[0076] (Heat Fusion Temperature) Eight fiber bundles of approximately 3 cm each were cut out, and four bundles were arranged in a lattice pattern. The bundles were sandwiched between iron plates heated to 60 to 120°C and left to stand for 1 minute, then removed. The temperature at which the overlapping portions in the lattice pattern fused together was taken as the heat fusion temperature.

[0077]

[0078] As shown in Table 1, Examples 1 to 6, which are within the scope of the present invention, had lower heat-fusion temperatures than Comparative Example 1 (poly(3-hydroxyalkanoate)-based resin: copolymer (A) only), in which the average molar content of 3-hydroxybutyrate units was the same between the core and sheath, and Comparative Example 2 (poly(3-hydroxyalkanoate)-based resin: copolymer (A) only), in which the fiber did not have a core-sheath structure. Furthermore, Examples 1 to 6, which are within the scope of the present invention, had lower fusion rates than Comparative Example 3 (poly(3-hydroxyalkanoate)-based resin: copolymer (A) and copolymer (B)), in which the fiber did not have a core-sheath structure. Therefore, it can be seen that the present invention can provide a poly(3-hydroxyalkanoate)-based resin-containing fiber that contains a poly(3-hydroxyalkanoate)-based resin containing 3-hydroxybutyrate units, which is inhibited from fusion during fiber production and can be heat-fused at low temperatures during thermal processing of the fiber.

[0079] 1: Single fiber, 10: Core, 20: Sheath

Claims

1. A fiber having a core-sheath structure including a core and a sheath, wherein the core and sheath each contain a poly(3-hydroxyalkanoate) resin containing 3-hydroxybutyrate units, and the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the core is greater than the average molar content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin of the sheath.

2. The fiber according to claim 1, comprising: a copolymer (A) having a molar ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units of 99 / 1 to 93 / 7; and a copolymer (B) having a molar ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units of 92 / 8 to 76 / 24.

3. The fiber according to claim 2, wherein the fiber contains 5 to 40% by weight of the copolymer (B) relative to 100% by weight of the poly(3-hydroxyalkanoate) resin.

4. The fiber according to claim 2 or 3, wherein the sheath portion contains the copolymer (B).

5. The fiber according to claim 4, wherein said sheath portion comprises said copolymer (A) and said copolymer (B).

6. The fiber according to any one of claims 1 to 3, wherein the area ratio of the core to the sheath in the cross section of the fiber is core / sheath = 8 / 2 to 2 / 8.

7. The fiber according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

8. The fiber according to any one of claims 1 to 3, wherein the single fiber fineness of the fiber is 1 to 15 dtex.

9. A method for producing a fiber, comprising melt-spinning a raw material composition for a core portion and a raw material composition for a sheath portion using a core-sheath type composite spinning nozzle to obtain the fiber according to any one of claims 1 to 3.

10. A nonwoven fabric comprising the fibers according to any one of claims 1 to 3.