Composite fiber, its manufacturing method, and fiber structure containing the same

Abstract

The present invention relates to a composite fiber containing a first component and a second component, wherein: the first component contains poly-L-lactic acid; the second component contains a biodegradable resin different from the poly-L-lactic acid; the first component and / or the second component is divided into two or more segments when viewed from a cross-section of the fiber; a part of the first component and a part of the second component are exposed on the surface of the composite fiber; and in a DSC curve, at least one of the following (1) to (4) is satisfied, or in X-ray diffraction measurement, the crystallite size of poly-L-lactic acid is 92-122 Å. (1) The heat of fusion per unit mass of the poly-L-lactic acid in a first heating process is 62.0 mJ / mg or greater. (2) The crystallization temperature of the poly-L-lactic acid in a cooling process is 90°C or higher. (3) The heat of fusion per unit mass of the poly-L-lactic acid in a second heating process is 51.0 mJ / mg or greater. (4) The heat of fusion per unit mass of the biodegradable resin in the second heating process is 60.5 mJ / mg or greater.

Description

[Technical Field]

[0001] The present invention relates to a conjugated fiber containing a first component containing an aliphatic polyester, more specifically poly-L-lactic acid, and a second component containing various biodegradable resins such as aliphatic polyesters, a method for producing the same, and a fiber structure containing the same. [Background technology]

[0002] Splittable conjugate fibers are widely used to make fibers finer. In recent years, biomass-derived resins or biodegradable resins have been used in conjugate fibers in consideration of the environment. For example, Patent Document 1 describes a splittable conjugate fiber made of polylactic acid and crystalline polybutylene succinate. Patent Document 2 describes a splittable conjugate fiber in which an amorphous polylactic acid component is roughly split into two or more parts by a polybutylene succinate component, which is a crystalline biodegradable polymer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-183592 [Patent Document 2] Japanese Patent Application Publication No. 9-41223 Summary of the Invention [Problem to be solved by the invention]

[0004] However, splittable conjugate fibers in which resins having similar resin properties are combined as described in Patent Documents 1 and 2, specifically, splittable conjugate fibers in which aliphatic polyesters having similar structures and resin physical properties, such as biodegradability, are combined, have the problem of poor splittability due to physical impact.

[0005] In order to solve the above-mentioned problems of the related art, the present invention provides a conjugated fiber having good splittability, which contains a first component containing an aliphatic polyester, more specifically poly-L-lactic acid, and a second component containing various biodegradable resins such as aliphatic polyesters, a method for producing the same, and a fiber structure containing the same. [Means for solving the problem]

[0006] The present invention provides a conjugated fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; The second component is different from the poly-L-lactic acid. and has a lower melting point than the poly-L-lactic acid. Contains biodegradable resin, When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, The composite fiber is a composite fiber that satisfies at least one of the following (1) to (4) in a DSC curve obtained by differential scanning calorimetry (DSC): (1) The heat of fusion per unit mass of the poly-L-lactic acid during the first temperature rise process is 62.0 mJ / mg or more. (2) The crystallization temperature of the poly-L-lactic acid during the temperature drop is 90°C or higher. (3) The heat of fusion per unit mass of the poly-L-lactic acid during the second heating process is 51.0 mJ / mg or more. (4) The heat of fusion per unit mass of the biodegradable resin during the second heating process is 60.5 mJ / mg or more.

[0007] The present invention also provides a conjugated fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; The second component is different from the poly-L-lactic acid. and has a lower melting point than the poly-L-lactic acid. Contains biodegradable resin, When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, The present invention relates to a composite fiber in which, in an X-ray diffraction measurement of the composite fiber, the crystallite size calculated based on the peak of the poly-L-lactic acid within the diffraction angle range of 2θ=16.5±0.3° is 92 Å or more and 122 Å or less.

[0008] The present invention also relates to a fiber structure containing 5% by mass or more of the composite fiber.

[0009] The present invention also provides a method for producing a conjugated fiber comprising a first component and a second component, the method comprising: A first component containing poly-L-lactic acid and a second component containing poly-L-lactic acid different from the poly-L-lactic acid and has a lower melting point than the poly-L-lactic acid. providing a second component comprising a biodegradable resin; melt-spinning the first component and the second component to produce a spun filament; and drawing the spun filaments; In the step of producing the spun filament, the first component is melt-spun at a lower temperature than the second component, In the stretching step, the stretching temperature is higher than 60°C and lower than 90°C, and the stretching ratio is 1.4 times or more, The present invention relates to a method for producing a composite fiber in which the first component and / or the second component are divided into two or more segments when viewed from the cross section of the obtained composite fiber, and a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber. [Effects of the Invention]

[0010] The present invention can provide a conjugated fiber having good splittability, which comprises a first component containing an aliphatic polyester, more specifically poly-L-lactic acid, and a second component containing various biodegradable resins such as aliphatic polyesters. According to the manufacturing method of the present invention, it is possible to obtain a composite fiber having good splittability, which contains a first component containing an aliphatic polyester, more specifically, poly-L-lactic acid, and a second component containing various biodegradable resins such as aliphatic polyesters. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing a cross section of a conjugate fiber according to an embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view showing a cross section of a conjugate fiber according to an embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view showing a cross section of a conjugate fiber according to an embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional view showing a cross section of a conjugate fiber according to an embodiment of the present invention. [Figure 5] 1 is a differential scanning calorimetry (DSC) curve obtained by DSC of the composite fiber of Example 1. [Figure 6] 1 is a graph showing the results of X-ray diffraction measurement of the composite fiber (drawn filament) of Example 1. [Figure 7] 1 is a graph showing the results of X-ray diffraction measurement of spun filaments (undrawn filaments) in Example 1. [Figure 8] 1 is a graph showing the results of X-ray diffraction measurement of the composite fiber (drawn filament) of Comparative Example 1. [Figure 9] 1 is a graph showing the results of X-ray diffraction measurement of spun filaments (undrawn filaments) in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present inventors have conducted extensive research to solve the above-mentioned problems of the prior art. As a result, they have discovered that in a splittable conjugate fiber comprising a first component containing poly-L-lactic acid and a second component containing a biodegradable resin different from the poly-L-lactic acid, the first component and / or the second component are divided into two or more segments when viewed from the fiber cross section, and a part of the first component and a part of the second component are exposed on the surface of the conjugate fiber, the conjugate fiber has, in a DSC curve obtained by differential scanning calorimetry (DSC), (1) a 100% or less mass fraction of the poly-L-lactic acid in the first heating process; It has been found that the divisibility can be improved by satisfying one or more of the following requirements (hereinafter also referred to as DSC requirements): (1) the heat of fusion of the poly-L-lactic acid is 62.0 mJ / mg or more, (2) the crystallization temperature of the poly-L-lactic acid during the temperature-lowering process is 90°C or more, (3) the heat of fusion of the poly-L-lactic acid per unit mass during the second temperature-raising process is 51.0 mJ / mg or more, and (4) the heat of fusion of a biodegradable resin other than the poly-L-lactic acid per unit mass during the second temperature-raising process is 60.5 mJ / mg or more.

[0013] Alternatively, in a splittable composite fiber comprising a first component containing poly-L-lactic acid and a second component containing a biodegradable resin different from the poly-L-lactic acid, wherein the first component and / or the second component are divided into two or more segments when viewed from the fiber cross section, and a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, when the composite fiber is subjected to X-ray diffraction measurement, the crystallite size calculated based on the peak of the poly-L-lactic acid within the diffraction angle 2θ=16.5±0.3° range is 92 Å or more and 122 Å or less (hereinafter also referred to as XRD requirement), and it has been found that splittability is improved.

[0014] Unlike Patent Documents 1 and 2, the present application has found that a conjugate fiber that satisfies the DSC and / or XRD requirements can be obtained by melt-spinning the first component at a lower temperature than the second component and drawing it at a predetermined drawing temperature and draw ratio. Typically, in conjugate spinning, the spinning temperature of the component with a higher melting point is higher than that of the component with a lower melting point, or the spinning temperatures of the components with a higher and lower melting points are the same. However, in the present invention, it has surprisingly been found that by lowering the spinning temperature of the first component containing poly-L-lactic acid with a higher melting point than that of the second component, the cooling efficiency of the first component is improved and crystallization of the poly-L-lactic acid after spinning (undrawn) is promoted, resulting in a conjugate fiber with high crystallinity in the first and second components after drawing, and the splittability of the resulting conjugate fiber is improved.

[0015] (composite fiber) In this specification, differential scanning calorimetry (DSC) is performed based on JIS K 7121:1987 under the following conditions. 5.0 mg of composite fiber is weighed and used as a sample. First, the sample is loaded into a sample holder. Next, the sample loaded into the sample holder is heated from room temperature (23±2°C) to a temperature at least 30°C higher than the melting point of the thermoplastic resin with the highest melting point among the thermoplastic resins contained in the composite fiber (for example, if the melting point of poly-L-lactic acid contained in the first component is the highest among the thermoplastic resins contained in the composite fiber and its melting point is 175°C, the temperature is raised to 205°C or higher. In the present example, the temperature is raised to 210°C). At this time, a DSC measurement is performed during the first melting. After reaching the maximum temperature set under the above conditions (a temperature at least 30°C higher than the melting point of the thermoplastic resin with the highest melting point among the thermoplastic resins contained in the composite fiber), the temperature is maintained for 2 minutes, and then the temperature is lowered from the maximum temperature to room temperature (23±2°C) at a rate of 5°C / min (temperature lowering process), allowing the molten sample to solidify. At this time, a DSC measurement is performed during the temperature lowering process. After the first heating and cooling processes are completed, the sample is not removed from the DSC measurement device, but is kept at room temperature (23±2°C) for 2 minutes, and then the temperature is raised again from room temperature (23±2°C) to the maximum temperature (a temperature that is at least 30°C higher than the melting point of the thermoplastic resin with the highest melting point among the thermoplastic resins contained in the composite fiber) at a rate of 5°C / min (second heating process), and DSC measurement is performed during the second melting.

[0016] In a DSC curve obtained by differential scanning calorimetry (DSC) of the conjugated fiber of the present invention, the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating process is preferably 62.0 mJ / mg or more. A large heat of fusion of poly-L-lactic acid indicates high crystallinity of the poly-L-lactic acid. High crystallinity of the first component poly-L-lactic acid after drawing increases the splittability of the conjugated fiber, and the conjugated fiber can be stably split by subjecting the conjugated fiber or a web containing the conjugated fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. From the viewpoint of further improving divisibility, the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating step is more preferably 62.0 mJ / mg to 80.0 mJ / mg, even more preferably 63.0 mJ / mg to 75.0 mJ / mg, even more preferably 64.0 mJ / mg to 72.0 mJ / mg, and particularly preferably 65.0 mJ / mg to 70.0 mJ / mg. In this specification, the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating step on the DSC curve is calculated by determining the heat of fusion from the endothermic peak of the first component poly-L-lactic acid in the DSC curve obtained during the first heating step, and converting the determined heat of fusion to the heat of fusion per 1 mg of the first component poly-L-lactic acid.

[0017] In the DSC curve obtained by differential scanning calorimetry (DSC) of the conjugated fiber of the present invention, the crystallization temperature of the first component poly-L-lactic acid during the temperature-lowering process is preferably 90°C or higher, from the viewpoint of improving splitting properties. A high crystallization temperature (fast crystallization rate) of poly-L-lactic acid indicates high crystallinity of the poly-L-lactic acid. High crystallinity of the first component poly-L-lactic acid after stretching improves splitting properties of the conjugated fiber, and the conjugated fiber can be stably split by subjecting the conjugated fiber or a web containing the conjugated fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. From the viewpoint of further improving splitting properties, the crystallization temperature of the first component poly-L-lactic acid during the temperature-lowering process is more preferably 90°C or higher and 110°C or lower, even more preferably 92°C or higher and 107°C or lower, even more preferably 95°C or higher and 104°C or lower, and particularly preferably 98°C or higher and 101°C or lower. In this specification, the crystallization temperature of the first component poly-L-lactic acid in the temperature-lowering process of the DSC curve refers to the temperature at the exothermic peak of the first component poly-L-lactic acid in the DSC curve obtained in the temperature-lowering process.

[0018] In the DSC curve obtained by differential scanning calorimetry (DSC) of the conjugated fiber of the present invention, from the viewpoint of improving splittability, the heat of fusion per unit mass of the first component poly-L-lactic acid in the second heating process is preferably 51.0 mJ / mg or more. A large heat of fusion of poly-L-lactic acid indicates high crystallinity of the poly-L-lactic acid. High crystallinity of the first component poly-L-lactic acid after drawing increases the splittability of the conjugated fiber, and the conjugated fiber can be stably split by subjecting the conjugated fiber or a web containing the conjugated fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. From the viewpoint of further improving divisibility, the heat of fusion per unit mass of the poly-L-lactic acid during the second heating step is more preferably 51.0 mJ / mg to 70.0 mJ / mg, even more preferably 52.0 mJ / mg to 65.0 mJ / mg, even more preferably 53.0 mJ / mg to 60.0 mJ / mg, and particularly preferably 54.0 mJ / mg to 58.0 mJ / mg. In this specification, the heat of fusion per unit mass of the first component poly-L-lactic acid during the second heating step on the DSC curve is calculated by determining the heat of fusion from the endothermic peak of the first component poly-L-lactic acid in the DSC curve obtained during the second heating step, and converting the determined heat of fusion to the heat of fusion per 1 mg of the first component poly-L-lactic acid.

[0019] In the DSC curve obtained by differential scanning calorimetry (DSC) of the composite fiber of the present invention, from the viewpoint of improving splittability, the heat of fusion per unit mass of the biodegradable resin of the second component during the second heating process is preferably 60.5 mJ / mg or more. A large heat of fusion of the biodegradable resin of the second component indicates high crystallinity of the biodegradable resin. Higher crystallinity of the biodegradable resin of the second component after drawing improves splittability of the composite fiber, and the composite fiber can be stably split by subjecting the composite fiber or a web containing the composite fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. From the viewpoint of further improving divisibility, the heat of fusion per unit mass of the biodegradable resin of the second component during the second heating process is more preferably 60.5 mJ / mg to 75.0 mJ / mg, even more preferably 60.7 mJ / mg to 70.0 mJ / mg, even more preferably 60.9 mJ / mg to 65.0 mJ / mg, and particularly preferably 61.0 mJ / mg to 63.0 mJ / mg. In this specification, the heat of fusion per unit mass of the biodegradable resin of the second component during the second heating process of the DSC curve is calculated by determining the heat of fusion from the endothermic peak of the biodegradable resin of the second component in the DSC curve obtained during the second heating process, and converting the determined heat of fusion to the heat of fusion per 1 mg of the biodegradable resin of the second component.

[0020] In order to further enhance splittability, the DSC curve obtained by differential scanning calorimetry (DSC) of the conjugated fiber of the present invention preferably has a melting peak temperature of 165°C or higher during the first heating step. The melting peak temperature refers to the temperature at the maximum height of the melting peak in the DSC curve obtained during the first heating step, and is the melting point of the poly-L-lactic acid, the first component, in the conjugated fiber. A high melting peak temperature of poly-L-lactic acid indicates high crystallinity of the poly-L-lactic acid. High crystallinity of poly-L-lactic acid after stretching increases the splittability of the conjugated fiber, and the conjugated fiber can be stably split by subjecting the conjugated fiber or a web containing the conjugated fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. From the viewpoint of further improving divisibility, the melting peak temperature of the first component poly-L-lactic acid in the first heating process is more preferably 165°C or higher and 180°C or lower, even more preferably 166°C or higher and 178°C or lower, even more preferably 167°C or higher and 177°C or lower, even more preferably 168°C or higher and 176°C or lower, and particularly preferably 169°C or higher and 175°C or lower.

[0021] In X-ray diffraction analysis of the composite fiber of the present invention, the crystallite size of the first component poly-L-lactic acid, calculated based on peaks within the diffraction angle 2θ=16.5±0.3° range, is preferably 92 Å to 122 Å. In this specification, crystallite size refers to the size of a crystallite, which is the smallest unit of a crystal grain that can be considered a single crystal. When the crystallite size of the first component poly-L-lactic acid is within the above-mentioned range, the crystallinity of the first component poly-L-lactic acid is enhanced, thereby improving the splitting ability of the composite fiber. The composite fiber can be stably split by subjecting the composite fiber or a web containing the composite fiber to physical impacts such as needle punching, high-pressure water jet treatment, and pulper agitation. The crystallite size of the first component poly-L-lactic acid is more preferably 100 Å to 120 Å, even more preferably 105 Å to 119 Å, and even more preferably 110 Å to 118 Å. In this specification, the crystallite size of the first component poly-L-lactic acid can be measured and calculated as described in the Examples. When two or more peaks are observed within the range of the diffraction angle 2θ=16.5±0.3°, the peak with the narrower full width at half maximum is used.

[0022] In X-ray diffraction measurement of the composite fiber of the present invention, the full width at half maximum (FWHM) of the first component poly-L-lactic acid, calculated based on peaks within a diffraction angle range of 2θ = 16.5 ± 0.3°, is preferably 0.50° to 0.85°. The FWHM indicates the broadening of the diffraction line width and refers to the width of the diffraction line at half the height of the diffraction line intensity. When the FWHM of the first component poly-L-lactic acid is within the above-mentioned range, the crystallinity of the first component poly-L-lactic acid is enhanced, thereby improving the splitting ability of the composite fiber. The composite fiber can be stably split by subjecting the composite fiber or a web containing the composite fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. The FWHM is more preferably 0.60° to 0.80°, even more preferably 0.65° to 0.77°, and even more preferably 0.68° to 0.75°. In this specification, the full width at half maximum of poly-L-lactic acid can be measured and calculated as described in the Examples. If two or more peaks are observed within the diffraction angle 2θ=16.5±0.3° range, the peak with the narrower full width at half maximum is used.

[0023] In X-ray diffraction measurement of the composite fiber of the present invention, the integral width of the first component poly-L-lactic acid, calculated based on peaks within the diffraction angle range of 2θ = 16.5 ± 0.3°, is preferably 0.85° to 1.10°. The integral width indicates the broadening of the diffraction line and refers to the ratio of the integrated intensity of the diffraction line to the peak intensity. When the integral width of the first component poly-L-lactic acid is within the above-mentioned range, the crystallinity of the first component poly-L-lactic acid is enhanced, thereby improving the splitting ability of the composite fiber. The composite fiber can be stably split by subjecting the composite fiber or a web containing the composite fiber to physical impacts such as needle punching, high-pressure water jet treatment, and stirring with a pulper. The integral width is more preferably 0.87° to 1.05°, even more preferably 0.89° to 1.03°, and even more preferably 0.90° to 1.00°. Herein, the integral width of the first component poly-L-lactic acid can be measured and calculated as described in the Examples. When two or more peaks are observed within the range of the diffraction angle 2θ=16.5±0.3°, the peak with the narrower full width at half maximum is used.

[0024] The optical purity of the first component poly-L-lactic acid is preferably 95.0% or more, more preferably 98.0% or more, even more preferably 99.0% or more, and particularly preferably 99.5% or more. When the optical purity of the first component poly-L-lactic acid is within the above range, the splitting ability of the composite fiber is improved.

[0025] The first component may contain a nucleating agent. Any known nucleating agent can be used as appropriate and is not particularly limited. Preferred examples include inorganic fillers such as calcium carbonate, talc, silica, and aluminum compounds; minerals such as mica and wollastonite; and inorganic nucleating agents such as barium sulfate; as well as organic nucleating agents such as metal salts of fatty acids such as calcium stearate, metal salts of phosphate esters, and amide compounds. The nucleating agent may be contained in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of poly-L-lactic acid.

[0026] In addition to the poly-L-lactic acid, other resins may be mixed into the first component as long as the effects of the present invention are not impaired. Examples of other resins include aromatic polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate, aromatic aliphatic polyesters, aliphatic polyesters, and polyolefins. The proportion of poly-L-lactic acid in the first component is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The first component may consist of 100% by mass of poly-L-lactic acid.

[0027] In the second component, the biodegradable resin different from the poly-L-lactic acid contained in the first component is not particularly limited, but for example, an aliphatic polyester can be suitably used. The aliphatic polyester is not particularly limited, and examples thereof include poly(α-hydroxy acid), poly(β-hydroxyalkanoate), poly(ω-hydroxyalkanoate), and aliphatic polyesters composed of glycol and dicarboxylic acid. Examples of poly(α-hydroxy acid)s include polyglycolic acid and poly-L-lactic acid having a lower melting point than the poly-L-lactic acid of the first component. Examples of poly(β-hydroxyalkanoate)s include poly(β-hydroxybutyric acid). Examples of poly(ω-hydroxyalkanoate)s include poly-ε-caprolactone. The aliphatic polyester composed of glycol and dicarboxylic acid is preferably a polyalkylene dicarboxylate, and specific examples of the polyalkylene dicarboxylate include polybutylene succinate, polybutylene adipate, polybutylene sebacate, polyethylene oxalate, polyethylene succinate, polyethylene adipate, polyethylene azelate, polyhexamethylene sebacate, polyneopentyl oxalate, and copolymers thereof. Among these, polybutylene succinate, which is a condensation product of succinic acid and 1,4-butanediol, and / or a copolymer of polybutylene succinate is preferred because it has a relatively high melting point of about 110°C, is excellent in fiber productivity, nonwoven fabric processability, and nonwoven fabric physical properties, and can be converted into a biomass raw material.

[0028] In the second component, the biodegradable resin different from the poly-L-lactic acid contained in the first component may be a biodegradable resin other than an aliphatic polyester. Examples of biodegradable resins other than aliphatic polyesters include poly(butylene succinate / carbonate), poly(ethylene terephthalate / succinate), poly(ethylene terephthalate / co-succinate), poly(butylene adipate / terephthalate), poly(tetramethylene adipate / terephthalate), and polyvinyl alcohol. Among these, poly(ethylene terephthalate / succinate), poly(ethylene terephthalate / co-succinate), poly(butylene adipate / terephthalate), and poly(tetramethylene adipate / terephthalate) are preferred because they are not only readily available, but also highly spinnable and easily formed into fibers. Furthermore, they are also biodegradable thermoplastic resins like the poly-L-lactic acid contained in the first component, allowing the entire composite fiber to be biodegradable.

[0029] When the second component contains an aliphatic polyester different from the poly-L-lactic acid and the melting point of the aliphatic polyester (the melting peak temperature of the aliphatic polyester during the first heating process) is lower than that of the poly-L-lactic acid, and when the melting point of the poly-L-lactic acid of the first component in the composite fiber is Tm1f and the melting point of the aliphatic polyester in the composite fiber is Tm2f, [Tm1f - Tm2f] is preferably 45°C to 75°C, more preferably 47°C to 70°C, even more preferably 50°C to 70°C, and particularly preferably 50°C to 65°C. More specifically, when the second component contains an aliphatic polyester different from the poly-L-lactic acid and the melting point of the aliphatic polyester is lower than that of the poly-L-lactic acid, the melting point of the aliphatic polyester is preferably 100°C to 130°C, more preferably 110°C to 125°C. If the melting point is 100°C or higher, the molten resin discharged from the nozzle during melt spinning solidifies quickly, suppressing the formation of fused threads. If the melting point is 130°C or lower, the difference in melting point between the first component and the second component is large, and the resin does not deteriorate during thermal processing.

[0030] The second component preferably contains a nucleating agent from the viewpoint of improving spinnability. Examples of nucleating agents include inorganic nucleating agents and organic nucleating agents. Examples of inorganic nucleating agents include inorganic fillers such as calcium carbonate, talc, silica, and aluminum compounds, minerals such as mica and wollastonite, and barium sulfate. Examples of organic nucleating agents include fatty acid metal salts, phosphate ester metal salts, and amide compounds.

[0031] The nucleating agent is preferably an organic nucleating agent, and particularly preferably a fatty acid metal salt, which can produce uniform, fine crystals and therefore has the effect of improving heat resistance after fiber formation. Examples of the fatty acid metal salts include sodium laurate, potassium laurate, potassium hydrogen laurate, magnesium laurate, calcium laurate, zinc laurate, sodium myristate, potassium hydrogen myristate, magnesium myristate, calcium myristate, zinc myristate, silver myristate, aluminum myristate, potassium palmitate, magnesium palmitate, calcium palmitate, zinc palmitate, copper palmitate, lead palmitate, sodium oleate, potassium oleate, magnesium oleate, calcium oleate, zinc oleate, lead oleate, copper oleate, nickel oleate, sodium stearate, calcium stearate, magnesium stearate, zinc stearate, barium stearate, aluminum stearate, thallium stearate, lead stearate, nickel stearate, sodium 12-hydroxystearate, lithium 12-hydroxystearate, lead 12-hydroxystearate, and Nickel phosphate, zinc 12-hydroxystearate, calcium 12-hydroxystearate, magnesium 12-hydroxystearate, barium 12-hydroxystearate, potassium isostearate, magnesium isostearate, calcium isostearate, aluminum isostearate, zinc isostearate, nickel isostearate, sodium behenate, potassium behenate, magnesium behenate, calcium behenate, zinc behenate, nickel behenate, sodium montanate, potassium montanate, magnesium montanate, calcium montanate, aluminum montanate, zinc montanate, nickel montanate, sodium octoate, lithium octoate, magnesium octoate, calcium octoate, barium octoate, aluminum octoate, nickel octoate, sodium sebacate, lithium sebacate, magnesium sebacate, calcium sebacate, barium sebacate, aluminum sebacate, thallium sebacate, lead sebacateExamples of suitable metal salts include nickel sebacate, sodium undecylenate, lithium undecylenate, magnesium undecylenate, calcium undecylenate, barium undecylenate, aluminum undecylenate, lead undecylenate, nickel undecylenate, beryllium undecylenate, sodium ricinoleate, lithium ricinoleate, magnesium ricinoleate, calcium ricinoleate, barium ricinoleate, aluminum ricinoleate, thallium ricinoleate, lead ricinoleate, nickel ricinoleate, and beryllium ricinoleate. Among these, it is preferable to use a divalent or higher metal salt. The use of a divalent or higher metal salt facilitates the formation of a physically crosslinked structure, restricting the mobility of polymer chain segments and allowing them to form crystal nuclei, facilitating rapid crystallization. Furthermore, from the viewpoint of spinnability, fatty acid metal salts exhibiting a melting point higher than that of the second component aliphatic polyester are preferred, and metal salts with strong binding strength to fatty acids are preferred. Examples include calcium, magnesium, and zinc, with calcium being particularly preferred. The fatty acid is preferably a saturated fatty acid with a high melting point. The number of carbon atoms of the fatty acid is preferably 12 to 28, more preferably 14 to 20. Within this range, the molecular chain is not too long and the melting point is lower than the spinning temperature of the second component, so that the nucleating agent is uniformly dispersed in the resin. Particularly preferred is one or more selected from the group consisting of calcium stearate, magnesium stearate, and zinc stearate.

[0032] From the viewpoint of increasing crystallinity and improving spinnability, the second component preferably contains 0.01 to 20 parts by mass of a nucleating agent per 100 parts by mass of the biodegradable resin (such as an aliphatic polyester different from the poly-L-lactic acid of the first component), more preferably 0.03 to 10 parts by mass, and even more preferably 0.06 to 5 parts by mass. If the nucleating agent is an inorganic nucleating agent, from the viewpoint of promoting resin crystallization, the inorganic nucleating agent is preferably contained in an amount of 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 1.0 to 5.0 parts by mass per 100 parts by mass of the biodegradable resin. If the nucleating agent is an organic nucleating agent, from the viewpoint of promoting crystallization of the resin, it is preferable that the organic nucleating agent is contained in an amount of 0.01 to 5.0 parts by mass, more preferably 0.03 to 4.0 parts by mass, and even more preferably 0.06 to 3.0 parts by mass, per 100 parts by mass of the biodegradable resin.

[0033] In addition to the biodegradable resin (such as an aliphatic polyester different from the poly-L-lactic acid of the first component), other resins may be mixed into the second component as long as the effects of the present invention are not impaired. Examples of other resins include aromatic polyesters, polyamides, and polyolefins. The proportion of the biodegradable resin in the second component is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0034] In the cross section of the composite fiber, the first component and / or the second component are divided (divided) into two or more segments, and a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber. The cross-sectional shape and the number of divisions are not particularly limited. From the viewpoint of productivity, the fiber cross section is preferably circular or elliptical. The number of divisions of the composite fiber (the total number of segments of the first and second components) can be determined depending on the fineness of the composite fiber and the fineness of the desired fine fibers after division. For example, it is preferably 4 to 36, more preferably 5 to 30, even more preferably 6 to 24, and particularly preferably 7 to 20. The composite fiber tends to be more easily divisible as the number of divisions decreases, but if the interface between the first and second components is too small, it tends to be difficult to obtain fine fibers. Furthermore, if the number of divisions is too small, the fineness of the composite fiber must be reduced to obtain ultrafine fibers of the desired fineness, which may result in poor fiber productivity or difficulty in spinning. A large number of divisions increases the number of interfaces between the first and second components, making it easier to obtain finer fibers. The number of divisions (number of segments) of the first component and the number of divisions (number of segments) of the second component may be the same or different, but from the viewpoint of increasing the number of interfaces between the first and second components, it is preferable that the number of divisions is the same. It is more preferable that the first component and the second component have a plurality of divisions, and that the segments of the first component and the segments of the second component are arranged alternately, and it is more preferable that the segments of the first component and the segments of the second component are arranged alternately and radially.

[0035] The composite fiber may or may not have a hollow portion in the fiber cross section. When the composite fiber has a hollow portion, the contact area between adjacent first and second component segments is smaller than when the composite fiber does not have a hollow portion. This reduces the adhesiveness between the resin segments, making the composite fiber more likely to split when a fiber web containing the composite fiber is subjected to physical impact, such as when the composite fiber is agitated in water using a pulper, when a web containing the composite fiber is entangled with a high-pressure water stream, or when a needle-punched web is entangled. This reduces the likelihood of unsplit composite fibers remaining in the nonwoven fabric. Furthermore, this tends to help prevent yarn breakage during spinning of the composite fiber. When the composite fiber is a so-called hollow splittable composite fiber having a hollow portion in the fiber cross section, the position of the hollow portion is not particularly limited. The hollow portion may be located at the center of the fiber when viewed from the fiber cross section, or the hollow portion may be located at a position offset from the center of the fiber when viewed from the fiber cross section (eccentric from the center of the fiber). Considering the spinnability (productivity) and ease of splitting of hollow splittable conjugate fibers, the hollow portion is preferably located in the center of the fiber when viewed from the fiber cross section.

[0036] When the composite fiber has a hollow portion, the hollow ratio can be determined depending on the splitting ratio and the cross-sectional shape of the ultrafine fibers after splitting. In this specification, the hollow ratio is the ratio of the area of ​​the hollow portion to the fiber cross section. When the composite fiber has a hollow portion, the hollow ratio is preferably, for example, about 1% to 50%, and more preferably about 5% to 40%. More specifically, when the number of splits of the composite fiber is 6 to 10, the hollow ratio is preferably 5% to 30%, more preferably 10% to 25%, and particularly preferably 10% to 20%. When the number of splits is 12 to 20, the hollow ratio is preferably 5% to 40%, more preferably 7% to 30%, and particularly preferably 10% to 25%. A hollow ratio of about 1% to 50% is preferable because it makes it easier to obtain the effects of providing hollow portions and makes the composite fiber less likely to split during the manufacturing process, making it easier to handle.

[0037] 1 is a schematic cross-sectional view showing the cross section of an example of a composite fiber. Composite fiber 10 has a circular cross-sectional shape and contains a first component 1 and a second component 2. It is an eight-segment composite fiber in which first component 1 is divided into four first segments and second component 2 is divided into four second segments, and first component 1 and second component 2 are arranged adjacent to each other, with a portion of first component 1 and a portion of second component 2 exposed on the surface of composite fiber 10. The four first segments and four second segments are arranged alternately and radially.

[0038] 2 is a schematic cross-sectional view showing the cross section of another example of a composite fiber. The composite fiber 20 has a circular cross-sectional shape and includes a first component 11 and a second component 12. The first component 11 is divided into four first segments, and the second component 12 is divided into eight second segments, resulting in a 16-segment composite fiber. The first component 11 and the second component 12 are arranged adjacent to each other, and a portion of the first component 11 and a portion of the second component 12 are exposed on the surface of the composite fiber 20. The eight first segments and the eight second segments are arranged alternately and radially.

[0039] 3 is a schematic cross-sectional view showing the cross section of another example of a conjugate fiber. Similar to conjugate fiber 10, conjugate fiber 30 has a circular cross-sectional shape except for having a hollow portion 3 located at the center of the fiber cross section, and contains a first component 1 and a second component 2. It is an eight-segment conjugate fiber in which first component 1 is divided into four first segments and second component 2 is divided into four second segments, and first component 1 and second component 2 are arranged adjacent to each other, with a portion of first component 1 and a portion of second component 2 exposed on the surface of conjugate fiber 10. The four first segments and four second segments are arranged alternately and radially.

[0040] 4 is a schematic cross-sectional view showing the cross section of another example of a conjugate fiber. Similar to the conjugate fiber 20, the conjugate fiber 40 has a circular cross-sectional shape except for having a hollow portion 13 located at the center of the fiber cross section, and contains a first component 11 and a second component 12. The first component 11 is divided into four first segments, and the second component 12 is divided into eight second segments, resulting in a 16-segment conjugate fiber. The first component 11 and the second component 12 are arranged adjacent to each other, and a portion of the first component 11 and a portion of the second component 12 are exposed on the surface of the conjugate fiber 20. The eight first segments and the eight second segments are arranged alternately and radially.

[0041] In the composite fiber, from the viewpoint of fiber splitting and processability, the composite ratio (first component / second component) is preferably 80 / 20 to 20 / 80 by mass, more preferably 75 / 25 to 25 / 75, even more preferably 70 / 30 to 30 / 70, still more preferably 65 / 35 to 35 / 65, and particularly preferably 60 / 40 to 40 / 60.

[0042] The single fiber fineness of the conjugated fiber is not particularly limited, but from the viewpoints of spinning stability and ease of thinning the fibers after splitting, it is preferably from 0.1 dtex to 30 dtex, more preferably from 0.2 dtex to 25 dtex, even more preferably from 0.3 dtex to 20 dtex, even more preferably from 0.4 dtex to 15 dtex, still more preferably from 0.5 dtex to 10 dtex, and particularly preferably from 0.6 dtex to 7.0 dtex.

[0043] The tensile strength (also referred to as strength) of the conjugated fiber is not particularly limited, but from the viewpoint of handleability during nonwoven fabric production, it is preferably 0.5 cN / dtex or more and 10 cN / dtex or less, more preferably 1.0 cN / dtex or more and 5.0 cN / dtex or less, even more preferably 1.2 cN / dtex or more and 4.0 cN / dtex or less, and particularly preferably 1.5 cN / dtex or more and 3.0 cN / dtex or less.

[0044] The elongation percentage (also referred to as elongation rate) of the composite fiber is not particularly limited, but from the viewpoint of ease of handling during nonwoven fabric production, it is preferably 10% or more and 150% or less, more preferably 15% or more and 100% or less, even more preferably 20% or more and 80% or less, and particularly preferably 25% or more and 50% or less.

[0045] The initial tensile resistance (also referred to as Young's modulus) of the conjugated fiber is not particularly limited, but from the viewpoint of handleability during nonwoven fabric production and of obtaining a bulky nonwoven fabric, it is preferably 5.0 cN / dtex or more and 45 cN / dtex or less, more preferably 10 cN / dtex or more and 35 cN / dtex or less, preferably 12 cN / dtex or more and 30.0 cN / dtex or less, and more preferably 14 cN / dtex or more and 25 cN / dtex or less.

[0046] The crimp rate of the composite fiber is not particularly limited, but from the viewpoint of the texture and bulkiness of the nonwoven fabric, it is preferably 2.0% or more and 30% or less, more preferably 4.0% or more and 25% or less, even more preferably 6.0% or more and 22% or less, and even more preferably 8.0% or more and 20% or less.

[0047] (Method of manufacturing composite fiber) The conjugate fiber of the present invention can be produced preferably by melt-spinning the first component at a temperature lower than that of the second component, and drawing the resultant fiber under predetermined conditions.

[0048] First, a first component containing poly-L-lactic acid and a second component containing a biodegradable resin different from the poly-L-lactic acid of the first component are prepared. The first component preferably contains 70% by mass or more of poly-L-lactic acid, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The first component may be composed of 100% by mass of poly-L-lactic acid. The second component preferably contains 70% by mass or more of a biodegradable resin different from the poly-L-lactic acid of the first component, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The poly-L-lactic acid of the first component and the biodegradable resin different from the poly-L-lactic acid of the first component may be those described above.

[0049] Next, the first component and the second component are melt-spun so that the first component and / or the second component are divided into two or more segments in the cross section of the spun filament, and a portion of the first component and a portion of the second component are exposed on the surface of the spun filament, thereby producing a spun filament (hereinafter also referred to as the "spinning process").

[0050] Specifically, the spinning process preferably includes a step of supplying the first component and the second component to a composite spinning nozzle and melt-extruding them, and a step of cooling the molten first component and second component extruded from the composite spinning nozzle directly below the composite spinning nozzle with an air flow supplied from a forced cooling device.

[0051] As the composite spinning nozzle, a split composite spinning nozzle can be appropriately used, which produces spun filaments in which the first component and / or the second component are divided into two or more segments in the fiber cross section and a portion of the first component and a portion of the second component are exposed on the surface of the fiber.

[0052] In the spinning process, the first component is melt-spun at a lower temperature than the second component. Specifically, in the melt-extrusion process, the first component is melt-extruded at a lower temperature than the second component. In the spinning process, melt-spinning the first component at a lower temperature than the second component facilitates cooling of the first component containing poly-L-lactic acid, allowing poly-L-lactic acid to crystallize quickly, making it easier to control the crystallization of the poly-L-lactic acid. This allows for the production of spun filaments with less crystalline orientation of poly-L-lactic acid and finer fineness. The spun filaments have good drawability, and not only do they become fibers with well-ordered crystallinity and orientation during drawing, but they can also be further refined after drawing. In addition, composite fibers with highly crystalline biodegradable resin contained in the second component can be obtained. Specifically, when the second component contains an aliphatic polyester different from the poly-L-lactic acid and the melting point (Tm2p) of the aliphatic polyester before spinning is lower than the melting point (Tm1p) of the poly-L-lactic acid before spinning, it is preferable to melt-spin the first component at a temperature 1°C to 30°C lower than that of the second component, more preferably at a temperature 3°C to 25°C lower, even more preferably at a temperature 5°C to 22°C lower, and particularly preferably at a temperature 7°C to 20°C lower. More specifically, the first component may be melt spun at a temperature of [Tm1p + 25°C] or more and [Tm1p + 65°C] or less, and the second component may be melt spun at a temperature of [Tm1p + 30°C] or more and [Tm1p + 75°C] or less; the first component may be melt spun at a temperature of [Tm1p + 30°C] or more and [Tm1p + 60°C] or less, and the second component may be melt spun at a temperature of [Tm1p + 35°C] or more and [Tm1p + 70°C] or less; or the first component may be melt spun at a temperature of [Tm1p + 40°C] or more and [Tm1p + 50°C] or less, and the second component may be melt spun at a temperature of [Tm1p + 45°C] or more and [Tm1p + 60°C] or less.More specifically, the first component may be melt spun at a temperature of 200°C or higher and 240°C or lower, and the second component may be melt spun at a temperature of 220°C or higher and 250°C or lower; the first component may be melt spun at a temperature of 205°C or higher and 235°C or lower, and the second component may be melt spun at a temperature of 225°C or higher and 245°C or lower; the first component may be melt spun at a temperature of 210°C or higher and 230°C or lower, and the second component may be melt spun at a temperature of 225°C or higher and 240°C or lower; or the first component may be melt spun at a temperature of 215°C or higher and 225°C or lower, and the second component may be melt spun at a temperature of 225°C or higher and 235°C or lower. The melting point of resins such as poly-L-lactic acid and aliphatic polyester before spinning refers to the melting peak temperature in the first heating process in the DSC curve obtained by differential scanning calorimetry (DSC), and can be determined by performing differential scanning calorimetry (DSC) in the same way as for composite fibers, except that resins are used as samples.

[0053] In the spinning step, although not particularly limited, from the viewpoint of stably obtaining spun filaments, the take-up speed is preferably 150 m / min or more and 2500 m / min or less, more preferably 200 m / min or more and 2300 m / min or less, and even more preferably 250 m / min or more and 2100 m / min or less.

[0054] In the cooling process, the molten first and second components (hereinafter also referred to simply as molten resins) extruded from the composite spinning nozzle are cooled directly below the composite spinning nozzle by an air flow supplied from a forced cooling device, thereby imparting a certain degree of crystallinity to the first component of the spun filament (undrawn filament), and further improving the splittability of the drawn filament (composite fiber) obtained by subsequent drawing.

[0055] In the production method of the present invention, rapid cooling directly below the conjugate spinning nozzle means cooling at a position close to the conjugate spinning nozzle. By adjusting the position of the forced cooling device and the volume of the air flow (cooling air) supplied from the forced cooling device, the first and second components in a molten state extruded from the conjugate spinning nozzle can be cooled at a position close to the conjugate spinning nozzle. From the viewpoint of promoting crystallization of poly-L-lactic acid having a crystalline phase and making it easier to obtain undrawn filaments with high crystallinity, it is preferable to adjust the volume of the cooling air. Specifically, from the viewpoint of quickly transitioning from a molten state to a crystalline state and obtaining fibers with a fairly high crystallinity during spinning, the volume of the cooling air is set to 0.10 m 3 / s or more 0.60m 3 / s or less is preferable, and 0.15m 3 / s or more 0.55m 3 / s or less is more preferable, and 0.20m 3 / s or more 0.50m 3 / s or less is more preferable, and 0.25m 3 / s or more 0.45m 3 / s or less, and even more preferably 0.30 m 3 / s or more 0.40m 3 When the proportion of poly-L-lactic acid in the first component is 99.0% or more, the flow rate of the cooling air is thought to particularly improve the cooling efficiency and further increase the crystallinity of the composite fiber, thereby contributing to further improvement of splittability.

[0056] The cooling method of the forced cooling device is not particularly limited. It may be a uniflow-type cooling device that cools the melt-extruded and stretched undrawn filaments from one direction, or a circular-type cooling device that blows cooling air onto the molten resin or undrawn filaments from the inside to the outside, or onto the molten resin or undrawn filaments from the outside to the inside. The gas used for the cooling air is not particularly limited, but rare gases such as argon and helium, which are stable (very low reactivity) at room temperature, nitrogen, or air are preferably used. Among these, nitrogen or air, which can be supplied inexpensively, is particularly preferred. The speed of the cooling air is preferably 0.2 m / s or more and 5 m / s or less, and more preferably 0.3 m / s or more and 3 m / s or less. The temperature of the cooling air is preferably low to ensure uniform cooling, but considering the cost of adjusting the temperature, it may be 40°C or less, or 15°C or more and 35°C or less.

[0057] The single fiber fineness of the obtained undrawn filament is not particularly limited, but from the viewpoint of productivity that can be produced using ordinary equipment, it is preferably 0.5 dtex or more and 50 dtex or less, more preferably 1.0 dtex or more and 40 dtex or less, even more preferably 1.5 dtex or more and 30 dtex or less, particularly preferably 2.0 dtex or more and 20 dtex or less, and most preferably 3.0 dtex or more and 15 dtex or less.

[0058] In the undrawn filaments, the first component poly-L-lactic acid preferably contains a crystalline phase to some extent. This makes it easier for the drawn filaments (composite fibers) obtained by drawing the undrawn filaments to be split by physical impact. The state in which the first component poly-L-lactic acid contains a crystalline phase to some extent in the undrawn filaments can be confirmed by subjecting the undrawn filaments to X-ray diffraction (XRD) measurement and measuring and calculating the crystallite size and integral width of the first component poly-L-lactic acid based on peaks within the diffraction angle 2θ=16.5±0.3° range. Specifically, from the viewpoint of improving the splitting ability of the composite fiber, the undrawn filaments preferably have a crystallite size of the first component poly-L-lactic acid of 30 Å or more and 250 Å or less, more preferably 50 Å or more and 220 Å or less, even more preferably 70 Å or more and 200 Å or less, and particularly preferably 100 Å or more and 180 Å or less, calculated based on peaks within the diffraction angle 2θ=16.5±0.3° range in X-ray diffraction measurement. Alternatively, from the viewpoint of improving the splittability of the composite fiber, the undrawn filament preferably has a full width at half maximum (FWHM) of the first component poly-L-lactic acid calculated based on peaks within the diffraction angle 2θ=16.5±0.3° range in X-ray diffraction measurement of 0.20° or more and 3.50° or less, more preferably 0.25° or more and 2.50° or less, even more preferably 0.30° or more and 1.50° or less, and particularly preferably 0.35° or more and 1.00° or less. Alternatively, from the viewpoint of improving the splittability of the composite fiber, the undrawn filament preferably has an integral width of the first component poly-L-lactic acid calculated in X-ray diffraction measurement based on peaks within a diffraction angle 2θ range of 16.5±0.3° of 0.30° or more and 3.70° or less, more preferably 0.35° or more and 3.00° or less, even more preferably 0.40° or more and 2.00° or less, and particularly preferably 0.50° or more and 1.00° or less. When two or more peaks are observed within the range of the diffraction angle 2θ=16.5±0.3°, the peak with the narrower full width at half maximum is used.

[0059] Next, the spun filament is drawn to obtain a drawn filament (composite fiber).

[0060] The stretching process may be a so-called one-stage stretching process having only one stretching step, or a multi-stage stretching process having two or more stretching steps. The stretching temperature is set to more than 60°C and less than 90°C. When the stretching process is a one-stage stretching process, or when the stretching process is a multi-stage stretching process, the stretching temperature in the first stretching step is preferably set to more than 60.0°C and less than 85.0°C. When the stretching temperature is less than 85.0°C, no fusion occurs during the stretching process. When the stretching temperature is more than 60.0°C, a high degree of stretching is possible. The stretching temperature is preferably 65.0°C or more and 80.0°C or less, and more preferably 67.0°C or more and 78.0°C or less. In the second stage and thereafter of multistage drawing, the drawing temperature is preferably more than 60.0°C and less than 90.0°C, more preferably from 65.0°C to 89.0°C, and particularly preferably from 70.0°C to 88.0°C. In the case of multistage drawing, the drawing temperature in the second stage and thereafter is preferably the same as or higher than that in the first stage. The temperature difference between the first stage and the second stage and thereafter is preferably more than 0°C and less than 30.0°C, more preferably from 1.0°C to 25.0°C, even more preferably from 3.0°C to 23.0°C, and particularly preferably from 5.0°C to 20.0°C.

[0061] The draw ratio is 1.4 times or more. This can increase the crystallinity of the poly-L-lactic acid contained in the first component and the biodegradable resin contained in the second component, thereby improving the splittability of the composite fiber against physical impact. The draw ratio is preferably 1.4 times or more and 6.0 times or less, more preferably 1.5 times or more and 5.0 times or less, even more preferably 1.6 times or more and 4.0 times or less, even more preferably 1.7 times or more and 3.0 times or less, and particularly preferably 1.8 times or more and 2.8 times or less. A draw ratio of 1.4 times or more can prevent yarn breakage during the drawing process and allow the spun filaments to be drawn uniformly. The drawing treatment may be a single-stage drawing or a multi-stage drawing with two or more stages. Furthermore, the second and subsequent stages of the multi-stage drawing may be a tension heat set in which the filaments are heat-treated in a tensioned state, or a relaxation heat set in which the filaments are heat-treated in a relaxed state. When the second or subsequent stage is tension heat setting, the stretching ratio in the first stage is preferably 1.4 times or more and 6.0 times or less, more preferably 1.5 times or more and 5.0 times or less, even more preferably 1.6 times or more and 4.0 times or less, even more preferably 1.7 times or more and 3.0 times or less, and particularly preferably 1.8 times or more and 2.8 times or less, and the stretching ratio in the second or subsequent stage may be 1.0 times or more and 1.2 times or less, or may be 1.0 times or more and 1.1 times or less. When the second or subsequent stage is relaxation heat set, the draw ratio in the first stage is preferably 1.4 to 6.0 times, more preferably 1.5 to 5.0 times, even more preferably 1.6 to 4.0 times, even more preferably 1.7 to 3.0 times, and particularly preferably 1.8 to 2.8 times. The draw ratio in the second or subsequent stage may be 0.9 to less than 1.0 times, or may be 0.95 to less than 1.0 times. The second or subsequent stage of multi-stage drawing is preferably tension heat set. Tension heat set can adjust and stabilize the crystallinity of the poly-L-lactic acid contained in the first component and the biodegradable resin contained in the second component, thereby improving processability during subsequent secondary molding (e.g., molding into a nonwoven fabric). In the case of multi-stage drawing, the draw ratio is calculated by multiplying the draw ratios in each stage.

[0062] In the drawing step, the draw ratio is preferably 60% to 100% of the maximum draw ratio (Vmax), more preferably 70% to 99%, even more preferably 80% to 99%, and particularly preferably 85% to 99%. When the draw ratio is 60% to 99% of the maximum draw ratio, high drawing can be achieved while suppressing yarn breakage during the drawing step.

[0063] The stretching method may be either a wet stretching method or a dry stretching method. As the heat medium, air, steam, water, oils such as glycerin, etc. can be used as appropriate. In the wet stretching method, stretching can be performed while heating in a liquid, for example, stretching may be performed in hot water or warm water. In the dry stretching method, stretching can be performed while heating in a high-temperature gas or with a high-temperature metal roll, etc. It is preferable to perform stretching in warm water.

[0064] In this specification, the maximum stretching ratio (V max )" is measured as follows. Melt spinning is performed using a split composite nozzle, and the resulting undrawn filament is wet drawn in warm water at a predetermined temperature. During this process, the feed speed (V1) of the roll that feeds the undrawn filament is set to 10 m / min, and the take-up speed (V2) of the metal roll on the take-up side is gradually increased from 10 m / min. The take-up speed of the metal roll on the take-up side when the undrawn filament breaks is defined as the maximum draw speed, and the ratio (V2 / V1) of the maximum draw speed to the feed speed of the roll that feeds the undrawn filament is calculated. The obtained speed ratio is used as the maximum draw ratio (V max )

[0065] In the case of a single drawing process, i.e., one-stage drawing, or in the case of a plurality of drawing processes at the same drawing temperature using the same drawing method, the maximum draw ratio can be measured using the same method and temperature as in the drawing process. In the case of a multi-stage drawing process, i.e., a plurality of drawing processes, where the drawing temperatures are different in different drawing stages, the maximum draw ratio is measured using the same drawing method and temperature as in the drawing stage where the drawing temperature is higher.

[0066] When the spun filaments are drawn by a so-called multi-stage drawing process in which drawing treatment is performed multiple times, and the drawing temperature is the same in each drawing stage but the drawing method is different, the maximum draw ratio is measured by each method, and the larger maximum draw ratio is taken as the maximum draw ratio.

[0067] A predetermined amount of fiber treatment agent may be applied to the obtained drawn filaments as needed, and further, mechanical crimping may be performed using a crimper (crimping device) as needed. When a nonwoven fabric is produced using a wet papermaking method, the fiber treatment agent can easily disperse the fibers in water, etc. Furthermore, if an external force is applied to the fiber surface to which the fiber treatment agent has been applied (for example, the force applied when crimping using a crimper) to impregnate the fiber treatment agent into the fibers, dispersibility in water, etc. is further improved. When crimping is performed, the obtained drawn filaments are dried by a predetermined method described below and cut to obtain composite fibers. When not crimping, the obtained drawn filaments are dried by a predetermined method described below and cut to obtain composite fibers.

[0068] The drawn filaments after application of the fiber treatment agent (or in a wet state without application of the fiber treatment agent) are dried, as needed, at a temperature in the range of 80°C to 110°C for several seconds to about 30 minutes to dry the fibers. The drying process may be omitted in some cases. The drawn filaments are then preferably cut to lengths of 1 mm to 100 mm, more preferably 2 mm to 70 mm. For example, when used for papermaking (wet nonwoven fabrics) or air-laid nonwoven fabrics, the filaments are cut to lengths of 20 mm or less, more specifically 2 mm to 20 mm. When used for dry nonwoven fabrics such as hydroentangled nonwoven fabrics, needle-punched nonwoven fabrics, and air-through nonwoven fabrics, the filaments are cut to lengths greater than 20 mm, more specifically 20 mm to 70 mm, more preferably 24 mm to 65 mm.

[0069] The conjugated fiber of the present invention can be used in fiber structures such as yarns, nonwoven fabrics, and woven and knitted fabrics. The fiber structure may contain 5% by mass or more of the conjugated fiber, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or even 100% by mass. When other fibers are contained, examples of the other fibers that can be used include natural fibers, recycled fibers, and synthetic fibers. Examples of natural fibers include cotton, silk, wool, hemp, pulp, and kapok. Examples of recycled fibers include rayon, cupro, and polynosic. Examples of synthetic fibers include acrylic fibers, polyester fibers, polyamide fibers, polyolefin fibers, and polyurethane fibers. As the other fibers, one or more types of fibers can be appropriately selected from the above-mentioned fibers depending on the intended use and the like.

[0070] When the fiber structure is a nonwoven fabric, examples of the form of the fiber web constituting the nonwoven fabric include a parallel web, a semi-random web, a random web, a cross-lay web, a crisscross web, an air-laid web, and a wet-laid web. When the fibers of these webs are entangled by a needle punching method or a high-pressure water jet method before and / or after heat treatment, the highly splittable conjugate fiber of the present invention can be easily split by the physical impact given to the conjugate fiber, thereby producing fine fibers. The heat treatment can be carried out as described below.

[0071] The conditions for the needle punching method can be appropriately selected depending on the type and basis weight of the fiber web. 2 More than 100g / m 2 In the case of the following card web, the fibers are opened with a semi-random card to produce a card web with a predetermined basis weight, and then the penetration number (number of needles per unit area) is set to 60 / cm. 2 Over 200 strands / cm2 A needle-punched nonwoven fabric can be produced by needle-punching on both sides at a needle depth of 3 mm to 15 mm.

[0072] The conditions for the high-pressure water jet method can be appropriately selected depending on the type and basis weight of the fiber web. 2 More than 100g / m 2 In the case of the following wetlaid paper web, airlaid web, or carded web, the fiber web can be placed on a support such as a plain weave structure of approximately 70 mesh or more and 100 mesh or less, and a columnar water stream with a water pressure of 1 MPa or more and 20 MPa or less is sprayed onto the front and back of the fiber web from a nozzle having orifices with a hole diameter of 0.05 mm or more and 0.5 mm or less, spaced 0.5 mm or more apart at intervals of 0.5 mm or more and 1.5 mm or less, once to 10 times.

[0073] Even when the fiber structure is a yarn or a woven or knitted fabric, the highly splittable conjugated fiber of the present invention can be easily split and split into fine fibers by applying a physical impact. Methods for splitting and splitting include a high-pressure water jet method, a method of passing the fiber through a liquid jet dyeing machine, and a buckling method.

[0074] In a fiber web or a nonwoven fabric in which fibers are entangled by needle punching or high-pressure water jetting, a portion of the first component or a portion of the second component melts and softens upon heat treatment, and the melted and softened first component or second component functions as an adhesive component, thermally bonding the constituent fibers together. The heat treatment temperature is not particularly limited as long as it melts and softens either the first component or the second component. For example, when Tm is the melting point of the thermoplastic resin with the lowest melting point among the poly-L-lactic acid contained in the first component and the biodegradable resin contained in the second component, the heat treatment temperature may be from [Tm + 5°C] to [Tm + 80°C] or from [Tm + 10°C] to [Tm + 50°C]. More specifically, the heat treatment temperature may be from [100°C to 200°C] or from 110°C to 180°C. When the second component contains an aliphatic polyester different from the poly-L-lactic acid contained in the first component, and the melting point (Tm2p) of the aliphatic polyester is lower than the melting point (Tm1p) of the poly-L-lactic acid contained in the first component, the heat treatment temperature may be [Tm2p - 5°C] or higher [Tm2p + 40°C] or higher [Tm2p + 25°C] or higher, more specifically, 103°C or higher and 140°C or lower, or 105°C or higher and 135°C or lower. The heat treatment time is not particularly limited as long as it allows the second component to melt and soften, but may be, for example, 3.0 seconds or higher and 40.0 seconds or lower, or 8.0 seconds or higher and 35.0 seconds or lower. The heat treatment method is not particularly limited, and examples include a hot air penetration heat treater, a hot air up / down blowing heat treater, and an infrared heat treater.

[0075] The air permeability of the nonwoven fabric can be measured and used as an index of the splitting property of the composite fiber. For example, the air permeability of the nonwoven fabric is measured using only the composite fiber at 60 g / m using a parallel carding machine. 2 As described in the examples, the nonwoven fabric produced under the conditions of condition (1) had an air permeability of 100 cm as measured by the Frazier method. 3 / cm 2 / s or less, 90cm 3 / cm 2 / s or less, 80cm 3 / cm 2 The nonwoven fabric may have an air permeability of 0 cm / s or less as measured by a Frazier method. 3 / cm 2 / s, and may be greater than 1.0 cm 3 / cm 2 If the breathability of the nonwoven fabric is within the above range, it can be said that the composite fibers are split.

[0076] The fiber structures such as nonwoven fabrics can be used for various purposes, and can be suitably used alone or in combination with paper, other nonwoven fabrics, films, sheets, or the like, for example, as surface materials for various sanitary articles such as masks, disposable diapers for babies, disposable diapers for adults, sanitary napkins, vaginal discharge absorbent sheets (panty liners), and incontinence pads, sheets to be placed between the surface material and the absorbent, and sheets for absorbent articles such as backing materials, skin covering sheets (face masks, base fabrics for patches), human wipers (sweat wipe sheets, makeup remover sheets, etc.), wiping sheets for various animals, object wipers (for wiping floors, kitchens, toilets, bathtubs, furniture, walls, screen doors, window glass, etc.), cushioning materials, wet towels, filters (cartridge filters, laminated filters, etc.), etc. [Example]

[0077] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0078] [Evaluation method] (1) Differential scanning calorimetry Based on JIS K 7121:1987, a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation) was used under the following conditions. 5.0 mg of composite fiber was weighed and used as a sample. First, the sample was loaded into a sample holder. Next, the sample loaded into the sample holder was heated from room temperature (23±2°C) to 210°C at a rate of 5°C / min (first heating process), and a DSC measurement was performed during the first melting. After reaching 210°C, the temperature was held for 2 minutes and then cooled from 210°C to room temperature (23±2°C) at a rate of 5°C / min (heating process), allowing the molten sample to solidify. At this time, a DSC measurement was performed during the temperature drop. After the first heating and cooling processes were completed, the sample was not removed from the DSC measurement device but was held at room temperature (23±2°C) for 2 minutes. It was then heated again from room temperature (23±2°C) to 210°C at a rate of 5°C / min (second heating process), and a DSC measurement was performed during the second melting. In the case of resin, DSC measurement was carried out in the same manner as in the case of composite fiber, except that 5.0 mg of resin was weighed and used as the sample. (2) X-ray diffraction (XRD) analysis A drawn filament (composite fiber) or a spun filament (undrawn filament) was cut to the same length as the short side of an aluminum sample holder for X-ray diffraction and used as a sample. The sample was attached and fixed to one side of the aluminum sample holder so that it was perpendicular to the direction of incidence of the X-rays, and wide-angle X-ray diffraction was performed. The measurement conditions were as follows: X-ray diffraction equipment: Rigaku Corporation "SmartLab 9kW" X-ray source: CuKα ray (1.5418Å) Output: Tube voltage 45kV, tube current 200mA Slit system: IS is 1 / 2°, RS1 is 20mm, RS2 is 20mm Measurement direction: Fiber diameter scan Scan axis: 2θ / θ Scanning Method: Continuous Scan Measurement range: 2θ=5~40° Step: 0.01° Scan speed: 10° / min From the diffraction peak profile obtained by X-ray diffraction (XRD) analysis using Cu kα radiation, the half-width of the diffraction line from the (hkl) = (110) plane observed around 2θ = 16.5 ± 0.3° was measured, and the crystallite size of poly-L-lactic acid was calculated using the Scherrer equation. Note that the proportionality constant in the Scherrer equation was k = 0.94. Data analysis was performed using Rigaku Data Analysis Software_PDXL2 manufactured by Rigaku Corporation. Specifically, background processing was performed, and profile fitting was performed using a split pseudo-Voigt function for optimization, and peak height, full width at half maximum (FWHM), integrated intensity, integrated width, and crystallite size were calculated. (3) Fiber properties: According to JIS L 1015:2010, the single fiber fineness, tensile strength (strength), elongation (elongation), initial tensile resistance (Young's modulus) and crimp rate of the drawn filament were measured. (4) Basis weight: The basis weight of the nonwoven fabric was measured based on JIS L 1913:2010 6.2. (5) Specific volume: Using a thickness gauge (product name "THICKNESS GAUGE", model "CR-60A", manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd.), the thickness of the nonwoven fabric was measured under a load of 296 Pa or 1.96 kPa, and the specific volume was calculated based on the basis weight and thickness of the nonwoven fabric. (6) Tensile strength: In accordance with JIS L 1913:2010 6.3, a tensile test was performed on a nonwoven fabric specimen using a constant-speed tension tensile tester under the conditions of a width of 5 cm, a gripping distance of 10 cm, and a pulling speed of 30±2 cm / min, and the load value at break was measured and used as the tensile strength. (7) Dividability: As described in the Examples, the nonwoven fabrics prepared under conditions (1) and (2) were cut in the thickness direction. The cut nonwoven fabrics were tightly packed into a cylinder with a diameter of 1.42 mm and a thickness of 1.00 mm so that the cut surface was exposed. The cut surface was then examined under an electron microscope at 300x magnification to determine the diameter of the nonwoven fabric. 2 The area was photographed. If even a portion of the interface between the first and second components was peeled off, it was counted as a split fiber, and if the interface between the first and second components was not peeled off, it was counted as an unsplit fiber. Note that, assuming that the fiber cross section is circular, if the total area of ​​a single fiber was less than 50%, it was excluded from the count. The total cross-sectional area of ​​all fibers to be counted and the total cross-sectional area of ​​unsplit fibers were calculated, and the splitting rate was calculated using the following formula. In the nonwoven fabric produced under condition (1), if the split ratio is 10.0% or more, it means that the composite fiber is split, and in the nonwoven fabric produced under condition (2), if the split ratio is 30.0% or more, it means that the composite fiber is split. Splitting rate (%) = {(total cross-sectional area of ​​all fibers - total cross-sectional area of ​​unsplit fibers) ÷ total cross-sectional area of ​​all fibers} × 100

[0079] (Examples 1 to 6, Comparative Examples 1 to 5) The specific conditions are shown in Tables 1 and 2. (1) Resin (i) Poly-L-lactic acid (hereinafter also referred to as PLA) A: L-130, optical purity 99% or more, melting point 175°C, manufactured by Total-Corbion B: Ingeo 3251D, optical purity 98.5%, melting point 155-170°C, manufactured by Nature Works C: LX-530, optical purity 98%, melting point 165°C, manufactured by Total-Corbion (ii) Aliphatic polyester D: Polybutylene succinate (hereinafter also referred to as PBS), melting point 115°C, FZ71 PM, manufactured by PTT MCC Biochem (iii) Nucleating agent (0.125 parts by weight added per 100 parts by weight of the second component) E: Calcium stearate (manufactured by NOF Corporation, trade name "Calcium Stearate S") (2) Resins of the first and second components First component: Table 1 and Table 3 Second component: D (3) Take-up speed: 827 m / min for Examples 1 to 4; 1460 m / min for Examples 5 and 6; 1100 m / min for Comparative Examples 1 to 4; 1023 m / min for Comparative Example 5 (4) Cross section: Examples 1 to 4 and Comparative Examples 1 to 5 have the cross section shown in FIG. 1, a circular cross section, and a solid 8-division structure; Examples 5 and 6 have the cross section shown in FIG. 4, a circular cross section, and a hollow 16-division structure. (5) Cooling air: airflow, temperature 29.6℃, speed 0.24~0.35m / s (6) Stretching method: Examples 1 to 6 are wet (hot water), two-stage stretching; Comparative Examples 1 to 5 are wet (hot water), one-stage stretching (7) Oil concentration: 5% by mass (8) Drying temperature: 85℃ (9) Cut length: 51.0 mm for water-entangled nonwoven fabric; 5 mm for wet-laid nonwoven fabric (10) Hydroentangled nonwoven fabric is made using a parallel carding machine at 60 g / m 2 The card webs were prepared and subjected to hydroentanglement treatment under the following conditions. Condition (1): A carded web was placed on a 90-mesh plain-weave support and, while transported at a speed of 4 m / min, a water stream of 3.0 MPa was sprayed once onto the front side of the carded web, followed by a water stream of 3.0 MPa sprayed once onto the back side of the carded web, for hydroentanglement. The nozzle used for the hydroentanglement treatment was a nozzle with orifices of 0.12 mm diameter spaced 0.6 mm apart, and the distance between the nozzle and the fiber web during treatment was 20 mm. Condition (2): A hydroentanglement treatment was performed by placing a carded web on a 90-mesh plain-weave support and transporting it at a speed of 4 m / min. The front surface of the carded web was sprayed with water at pressures of 2.0 MPa, 3.0 MPa, and 3.0 MPa three times, one each, and then the back surface of the carded web was sprayed with water at pressures of 2.0 MPa, 3.0 MPa, and 3.0 MPa three times. The nozzle used for the hydroentanglement treatment had orifices with a hole diameter of 0.12 mm spaced 0.6 mm apart, and the distance between the nozzle and the fiber web during treatment was 20 mm. (11) The wet-laid nonwoven fabric is made of splittable composite fibers with a fiber length (cut length) of 5 mm and a basis weight of 40 g / m 2 The wet-laid nonwoven fabric was obtained by drying the wet-laid nonwoven fabric under the following conditions. Condition (1): Splittable composite fiber for producing a wetlaid nonwoven fabric was weighed out to 2.50 g in bone dry condition. The weighed splittable conjugate fibers were placed in 1 L of tap water to form a slurry, and the slurry was stirred with a pulper at a rotation speed of 1000 rpm for 120 seconds to uniformly disperse the splittable conjugate fibers in the water. Tap water was added to the slurry that had been stirred with a pulper to make 16 L of slurry. The slurry diluted to 16 L was poured into a 250 mm square frame covered with a metal mesh (200 mesh), and wet-pressed to a size of 250 mm length x 250 mm width, with a dry basis weight of 40 g / cm. 2 The wet papermaking web was as follows. The obtained wet-laid paper web was sandwiched between filter papers and subjected to a pressure of 3.5 kg / cm 2 The pressure was applied for 30 seconds to perform dehydration. The dewatered wetlaid web was transported on a transport support while being dried in a cylinder dryer having a metal roll set at a predetermined temperature, to obtain a wetlaid nonwoven fabric. Condition (2): Splittable composite fiber for producing a wetlaid nonwoven fabric was weighed out to 2.50 g in an absolutely dry state. The weighed splittable conjugate fibers were placed in 1 L of tap water to form a slurry, and the slurry was stirred with a pulper at a rotation speed of 1500 rpm for 30 seconds to uniformly disperse the splittable conjugate fibers in the water. Tap water was added to the slurry that had been stirred with a pulper to make 16 L of slurry. The slurry diluted to 16 L was poured into a 250 mm square frame covered with a metal mesh (200 mesh), and wet-pressed to a size of 250 mm length x 250 mm width, with a dry basis weight of 40 g / cm. 2 The wet papermaking web was as follows. The obtained wet-laid paper web was sandwiched between filter papers and subjected to a pressure of 3.5 kg / cm 2 The pressure was applied for 30 seconds to perform dehydration. The dewatered wetlaid web was transported on a transport support while being dried in a cylinder dryer having a metal roll set at a predetermined temperature, to obtain a wetlaid nonwoven fabric. In the method for producing a wetlaid nonwoven fabric described in the conditions (1) and (2), the heat treatment in the cylinder dryer was performed on the wetlaid web for 45 seconds. When producing a wetlaid nonwoven fabric, if the split ratio is to be measured using the obtained wetlaid nonwoven fabric, the temperature of the metal roll surface of the cylinder dryer is set to 80°C for drying. When producing a wetlaid nonwoven fabric for measuring physical properties other than the split ratio, the temperature of the metal roll surface of the cylinder dryer is set to 140°C for drying.

[0080] In the examples and comparative examples, the physical properties of the composite fibers and nonwoven fabrics were evaluated by the above-mentioned evaluation methods, and the results are shown in the following Tables 1 to 5. In the following Tables 1 and 2, "- (minus)" in the PBS crystallization heat column means crystallization.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] Figure 5 shows the DSC curve of the composite fiber of Example 1. Figures 6 and 7 show the results of X-ray diffraction measurement of the composite fiber (drawn filament) of Example 1 and the spun filament (undrawn filament) of Example 1, respectively. Figures 8 and 9 show the results of X-ray diffraction measurement of the composite fiber (drawn filament) of Comparative Example 1 and the spun filament (undrawn filament) of Example 1.

[0087] As can be seen from Tables 1, 2, and 5, the DSC curves of the conjugated fibers of the Examples showed that the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating process was 62.0 mJ / mg or more. Furthermore, the DSC curves of the conjugated fibers of the Examples showed that the crystallization temperature of the first component poly-L-lactic acid during the heating process was 90°C or higher. Furthermore, the DSC curves of the conjugated fibers of the Examples showed that the heat of fusion per unit mass of the first component poly-L-lactic acid during the second heating process was 51.0 mJ / mg or more. Furthermore, the DSC curves of the conjugated fibers of the Examples showed that the heat of fusion per unit mass of the second component aliphatic polyester during the second heating process was 60.5 mJ / mg or more. In addition, in X-ray diffraction measurement, the composite fibers of the Examples had a crystallite size of the first component poly-L-lactic acid of 92 Å or more and 122 Å or less, calculated based on peaks within the diffraction angle 2θ=16.5±0.3° range. In the Examples, in the step of producing spun filaments, the first component was melt-spun at a temperature lower than that of the second component, and in the drawing step, the first component was drawn at a temperature higher than 60°C and lower than 90°C at a draw ratio of 1.4 or more, thereby enabling the production of composite fibers with the above-mentioned properties. The composite fibers of the examples were excellent in splitting properties and were split by physical impacts such as high-pressure water flow and stirring with a pulper in water during the production of nonwoven fabric.

[0088] On the other hand, as can be seen from Tables 2 and 4, in Comparative Examples 1 to 4, which reproduce the examples described in Patent Document 1, the first component and the second component were melt-spun at the same temperature in the process of producing the spun filaments. However, in the DSC curve of the obtained composite fiber, the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating process was less than 62.0 mJ / mg, and no peak for the first component poly-L-lactic acid was observed during the heating process. The heat of fusion per unit mass of the first component poly-L-lactic acid during the second heating process was less than 51.0 mJ / mg, and the heat of fusion per unit mass of the second component aliphatic polyester during the second heating process was less than 60.5 mJ / mg. In X-ray diffraction measurement, the crystallite size of the first component poly-L-lactic acid calculated based on peaks within the diffraction angle 2θ = 16.5 ± 0.3 ° was less than 92 Å. Therefore, the composite fiber had poor splitting properties and could not be split by the physical impact of high-pressure water jets during the production of nonwoven fabric. Furthermore, as can be seen from Tables 2 and 4, in Comparative Example 5, which reproduced the example described in Patent Document 2, in the process of producing the spun filament, the first component and the second component were melt-spun at the same temperature and drawn at 90°C. However, in the DSC curve of the obtained composite fiber, the heat of fusion per unit mass of the first component poly-L-lactic acid during the first heating process was less than 62.0 mJ / mg, and no peak for the first component poly-L-lactic acid was observed during the heating process. The heat of fusion per unit mass of the first component poly-L-lactic acid during the second heating process was less than 51.0 mJ / mg, and the heat of fusion per unit mass of the second component aliphatic polyester during the second heating process was less than 60.5 mJ / mg. In X-ray diffraction measurement, the crystallite size of the first component poly-L-lactic acid calculated based on peaks within a diffraction angle 2θ = 16.5 ± 0.3° range exceeded 122 Å. It is believed that if the crystallite size is too large, the crystallites tend to stack together, making them difficult to split. The composite fiber had poor splitting properties and could not be split by the physical impact of the high-pressure water stream during the production of the nonwoven fabric.

[0089] The present invention is not particularly limited, but may include at least the following embodiments. [1] A composite fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; the second component contains a biodegradable resin different from the poly-L-lactic acid, When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, A composite fiber in which a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, and the composite fiber satisfies at least one of the following (1) to (4) in a DSC curve obtained by differential scanning calorimetry (DSC): (1) The heat of fusion per unit mass of the poly-L-lactic acid during the first temperature rise process is 62.0 mJ / mg or more. (2) The crystallization temperature of the poly-L-lactic acid during the temperature drop is 90°C or higher. (3) The heat of fusion per unit mass of the poly-L-lactic acid during the second heating process is 51.0 mJ / mg or more. (4) The heat of fusion per unit mass of the biodegradable resin during the second heating process is 60.5 mJ / mg or more. [2] A composite fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; the second component contains a biodegradable resin different from the poly-L-lactic acid, When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, A composite fiber in which a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, and in an X-ray diffraction measurement of the composite fiber, the crystallite size calculated based on the peak of the poly-L-lactic acid within a diffraction angle range of 2θ=16.5±0.3° is 92 Å or more and 122 Å or less. [3] The composite fiber according to [1] or [2], wherein in the DSC curve obtained by differential scanning calorimetry (DSC) of the composite fiber, the melting peak temperature of the poly-L-lactic acid in the first heating process is 165°C or higher. [4] The conjugated fiber according to any one of [1] to [3], wherein the optical purity of the poly-L-lactic acid is 99.0% or more. [5] The conjugated fiber according to any one of [1] to [4], wherein the biodegradable resin contains an aliphatic polyester made of glycol and dicarboxylic acid. [6] The composite fiber according to [5], wherein the aliphatic polyester composed of a glycol and a dicarboxylic acid is polybutylene succinate and / or a copolymer of polybutylene succinate. [7] The composite fiber according to any one of [1] to [6], wherein the second component contains a nucleating agent. [8] A fiber structure containing 5% by mass or more of the composite fiber according to any one of [1] to [7]. [9] The fiber structure according to [8], wherein the fiber structure is a nonwoven fabric.

[10] A method for producing a composite fiber containing a first component and a second component, A step of preparing a first component containing poly-L-lactic acid and a second component containing a biodegradable resin different from the poly-L-lactic acid; The method includes melt-spinning the first component and the second component to produce a spun filament, and drawing the spun filament; In the step of producing the spun filament, the first component is melt-spun at a lower temperature than the second component, In the stretching step, the stretching temperature is higher than 60°C and lower than 90°C, and the stretching ratio is 1.4 times or more, A method for producing a composite fiber, wherein the first component and / or the second component are divided into two or more segments when viewed from the cross section of the obtained composite fiber, and a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber.

[11] The step of producing the spun filament comprises: feeding the first component and the second component into a multi-component spinning nozzle; and cooling the molten first and second components extruded from the conjugate spinning nozzle directly below the conjugate spinning nozzle with an air flow supplied from a forced cooling device; In the cooling step, the volume of the cooling air is 0.10 m 3 / s or more 0.60m 3 / s or less.

[12] The method for producing a composite fiber according to

[10] or

[11] , wherein, in an X-ray diffraction measurement of the spun filament, the crystallite size calculated based on peaks within the diffraction angle range of 2θ = 16.5 ± 0.3° of the poly-L-lactic acid is 30 Å or more and 250 Å or less, and / or the integral width is 0.30° or more and 3.70° or less. [Explanation of symbols]

[0090] 1, 11 First component 2, 12 Second component 3, 13 Hollow part 10, 20, 30, 40 composite fiber

Claims

1. A composite fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; the second component includes a biodegradable resin different from the poly-L-lactic acid and having a melting point lower than that of the poly-L-lactic acid; When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, The composite fiber satisfies at least one of the following (1) to (4) in a DSC curve obtained by differential scanning calorimetry (DSC): (1) The heat of fusion per unit mass of the poly-L-lactic acid during the first temperature rise process is 62.0 mJ / mg or more. (2) The crystallization temperature of the poly-L-lactic acid during the temperature drop is 90°C or higher. (3) The heat of fusion per unit mass of the poly-L-lactic acid during the second temperature increase process is 51.0 mJ / mg or more. (4) The heat of fusion per unit mass of the biodegradable resin during the second temperature rise process is 60.5 mJ / mg or more.

2. A composite fiber comprising a first component and a second component, the first component comprises poly-L-lactic acid; the second component includes a biodegradable resin different from the poly-L-lactic acid and having a melting point lower than that of the poly-L-lactic acid; When viewed from the fiber cross section, the first component and / or the second component are divided into two or more segments, a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber, In X-ray diffraction measurement of the composite fiber, the crystallite size calculated based on the peak of the poly-L-lactic acid within the range of a diffraction angle 2θ=16.5±0.3° is 92 Å or more and 122 Å or less.

3. 3. The composite fiber according to claim 1, wherein in a DSC curve obtained by differential scanning calorimetry (DSC) of the composite fiber, the melting peak temperature of the poly-L-lactic acid in the first heating process is 165°C or higher.

4. The composite fiber according to claim 1 or 2, wherein the optical purity of the poly-L-lactic acid is 99.0% or more.

5. The composite fiber according to claim 1 or 2, wherein the biodegradable resin includes an aliphatic polyester made of a glycol and a dicarboxylic acid.

6. 6. The conjugated fiber according to claim 5, wherein the aliphatic polyester composed of a glycol and a dicarboxylic acid is polybutylene succinate and / or a copolymer of polybutylene succinate.

7. The bicomponent fiber of claim 1 or 2, wherein the second component comprises a nucleating agent.

8. A fiber structure comprising 5% by mass or more of the conjugate fiber according to claim 1 or 2.

9. The fibrous structure of claim 8 , wherein the fibrous structure is a nonwoven fabric.

10. A method for producing a conjugated fiber comprising a first component and a second component, preparing a first component containing poly-L-lactic acid and a second component containing a biodegradable resin different from the poly-L-lactic acid and having a melting point lower than that of the poly-L-lactic acid; melt spinning the first component and the second component to produce a spun filament; and drawing the spun filaments; In the step of producing the spun filament, the first component is melt-spun at a lower temperature than the second component, In the stretching step, the stretching temperature is higher than 60°C and lower than 90°C, and the stretching ratio is 1.4 times or more, A method for producing a composite fiber, wherein the first component and / or the second component are divided into two or more segments when viewed from the cross section of the obtained composite fiber, and a portion of the first component and a portion of the second component are exposed on the surface of the composite fiber.

11. The step of producing the spun filament comprises: feeding the first component and the second component into a multi-component spinning nozzle; and cooling the molten first and second components extruded from the conjugate spinning nozzle directly below the conjugate spinning nozzle with an air flow supplied from a forced cooling device; In the cooling step, the volume of the cooling air is 0.10 m 3 / s or more 0.60m 3 The method for producing a composite fiber according to claim 10, wherein the fiber strength is 1 / s or less.

12. The method for producing a composite fiber according to claim 10 or 11, wherein, in X-ray diffraction measurement of the spun filaments, the crystallite size calculated based on peaks of the poly-L-lactic acid within a diffraction angle range of 2θ=16.5±0.3° is 30 Å or more and 250 Å or less, and / or the integral width is 0.30° or more and 3.70° or less.

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