COMPOSITE FIBER, METHOD FOR PRODUCING SAME, AND FIBER STRUCTURE INCLUDING SAME

Abstract

 The present invention relates to a conjugate fiber that includes a first component containing poly-L-lactic acid with an optical purity of 95% or more, and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid, and a crystallization temperature of the second component during a cooling process is 78°C or higher and a melting heat amount per unit mass of the second component during a second heating process is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber. The conjugate fiber can be produced by melt spinning the first component at a lower temperature than the second component, followed by drawing performed at a temperature of 55°C or higher and 90°C or lower at a drawing ratio of 1.4-fold or more. Thus, it is possible to provide a conjugate fiber capable of being processed into a fiber structure having favorable flexibility and voluminousness, a method for producing the conjugate fiber, and a fiber structure that includes the conjugate fiber.

Description

Technical Field

[0001] The present invention relates to a conjugate fiber that includes a first component containing polylactic acid and a second component containing an aliphatic polyester, a method for producing the same, and a fiber structure that includes the same.

Background Art

[0002] Conjugate fibers that include a low-melting-point resin component and a high-melting-point resin component are widely used as materials of a fiber structure such as a non-woven fabric. In recent years, a biomass-derived resin or a biodegradable resin has been used in conjugate fibers in consideration of the environment. For example, Patent Documents 1 to 4 propose conjugate fibers containing polylactic acid as a core component and polybutylene succinate as a sheath component.

Prior Art Documents

Patent Documents

[0003] 

Patent Document 1: JP 2006-112012A

Patent Document 2: JP 2007-119928A

Patent Document 3: JP 2007-126780A

Patent Document 4: JP 2014-37656A

Disclosure of Invention

Problem to be Solved by the Invention

[0004] However, non-woven fabrics produced using conjugate fibers disclosed in Patent Documents 1 to 4 containing polylactic acid and polybutylene succinate have insufficient flexibility and voluminousness, and a further improvement in the texture thereof is required.

[0005] In order to solve the aforementioned conventional problems, the present invention provides a conjugate fiber capable of being processed into a fiber structure having favorable flexibility and voluminousness, a method for producing the conjugate fiber, and a fiber structure that includes the conjugate fiber.

Means for Solving Problem

[0006] The present invention relates to a conjugate fiber including: a first component containing poly-L-lactic acid with an optical purity of 95% or more; and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid, wherein the second component occupies 50% or more of a surface of the conjugate fiber, and a crystallization temperature of the second component during a cooling process is 78.0°C or higher and a melting heat amount per unit mass of the second component during a second heating process is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[0007] The present invention also relates to a method for producing the conjugate fiber, including: a step of preparing a first component containing poly-L-lactic acid with an optical purity of 95% or more in an amount of 70 mass% or more, and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid in an amount of 70 mass% or more; a step of producing a spun filament by melt spinning the first component and the second component; and a step of drawing the spun filament to obtain a conjugate fiber in which the second component occupies 50% or more of a surface of the conjugate fiber, wherein, in the step of producing a spun filament, the first component is melt extruded at a temperature lower than the second component, and in the drawing step, a drawing temperature is 55°C or higher and 90°C or lower, and a drawing ratio is 1.4-fold or more.

[0008] The present invention also relates to a fiber structure containing the conjugate fiber in an amount of 5 mass% or more.

Effects of the Invention

[0009] The present invention can provide a conjugate fiber capable of being processed into a fiber structure having favorable flexibility and voluminousness.

[0010] The present invention can also provide a fiber structure having favorable flexibility and voluminousness.

[0011] With the producing method of the present invention, a conjugate fiber having favorable flexibility and voluminousness can be obtained.

Brief Description of Drawings

[0012] 

FIG. 1 is a differential scanning calorimetry curve (DSC curve) obtained through differential scanning calorimetry (DSC) performed on a conjugate fiber of Example 8.

FIG. 2 shows a portion corresponding to a first heating process in the DSC curve obtained through differential scanning calorimetry (DSC) performed on a conjugate fiber of Example 8.

FIG. 3 is a schematic diagram illustrating a method for calculating a peak height/half width ratio of a first component during the first heating process in the DSC curve obtained through differential scanning calorimetry (DSC).

Description of Invention

[0013] The inventors of the present invention conducted numerous studies in order to solve the aforementioned conventional problems. As a result, it was found that, regarding a conjugate fiber that includes a first component containing poly-L-lactic acid and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid, a non-woven fabric obtained by processing conventional conjugate fibers through heating has high bending resistance but poor flexibility and voluminousness, but, by configuring the conjugate fiber such that the crystallization temperature of the second component during a cooling process satisfies/is 78°C or higher and the melting heat amount per unit mass of the second component during a second heating process satisfies/is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber and controlling the molten state and the solidified state of the second component to be within the ranges above, the workability of the conjugate fiber during heat processing of the fibers into a non-woven fabric is also improved and thus non-woven fabric having excellent flexibility and voluminousness is obtained.

[0014] Specifically, when the crystallization temperature per unit mass of the second component during the cooling process is 78.0°C or higher, the second component is rapidly cooled during melt spinning due to the high solidification temperature of the melt-extruded second component and can thus be wound up at a high rate, thus making it possible to reduce the fineness of fibers. Also, when the second component present on the surface of the fiber is melted and then cooled in processing of the fibers performed to obtain a non-woven fabric, the second component is solidified at a high temperature, and therefore, the fiber is suitable for high-speed production, and voluminousness is likely to be achieved due to the amount of heat applied to the first component being reduced. Furthermore, when the melting heat amount per unit mass of the second component during the second heating process is 73.5 mJ/mg or less, since the second component has moderate crystallinity, the second component can be easily melted in processing of the fibers performed to obtain a non-woven fabric and also has adhesive strength. In addition, the first component is not excessively heated, and thus non-woven fabric having a favorable texture (voluminousness and fiber adhesiveness) is obtained.

[0015] The inventors of the present invention arrived at the finding that a conjugate fiber that satisfies the above-described requirements is obtained by melt spinning the first component at a lower temperature than the second component, followed by drawing at a predetermined drawing temperature and a predetermined drawing ratio unlike Patent Documents 1 to 4. In general, when conjugate spinning is performed, the melt extrusion temperature of a component having a higher melting point is set to be higher than the melt extrusion temperature of a component having a lower melting point, or the melt extrusion temperatures of a component having a higher melting point and a component having a lower melting point are set to be the same. However, in the present invention, it was surprisingly found that the spinnability of the conjugate fiber is improved and the flexibility and the voluminousness of a non-woven fabric produced using the obtained conjugate fiber are improved by setting the melt extrusion temperature of the first component having a higher melting point to be lower than the melt extrusion temperature of the second component having a lower melting point.

[0016] Also, by configuring the conjugate fiber such that the crystallization temperature of the second component during the cooling process is 78°C or higher and the melting heat amount per unit mass of the second component is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber, fibers that are less prone to adherence (agglutination) during spinning and/or drawing, are less prone to yarn breakage, and have high productivity are likely to be obtained. When the fibers are crimped, a crimp shape is likely to be maintained, and favorable crimpability is likely to be achieved. Furthermore, the fibers can be drawn at a ratio close to the maximum drawing ratio (Vmax), and thus conjugate fibers with smaller fineness can be obtained. The thus obtained conjugate fibers are excellent in terms of formation of a fiber web when being processed into a non-woven fabric, and thus a uniform non-woven fabric can be obtained.

[0017] In the present invention, differential scanning calorimetry (DSC) is performed under the following conditions based on JIS K 7121: 1987.

[0018] The amount of a sample (fiber) is set to 3.0 mg, and the sample is weighed out and filled into a sample holder. Next, the sample filled into the sample holder is heated from an ordinary temperature (23±2°C) to 250°C at a rate of 5°C/minute (first heating process), and a DSC measurement for first melting is performed. After the temperature reaches 250°C, the sample is kept at this temperature for 10 minutes in a molten state and is then cooled from 250°C to 40°C at a rate of 1°C/minute (cooling process), and thus the molten sample is solidified. At this time, DSC during cooling is measured. After the first heating process and the cooling process are finished, the sample is not removed from a DSC measurement apparatus and is kept at 40°C for 10 minutes. Then, the sample is heated again from 40°C to 250°C at a rate of 5°C/minute (second heating process), and a DSC measurement for second melting is performed.

[0019] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the crystallization temperature of the second component during the cooling process is preferably 78.0°C or higher and 115.0°C or lower, more preferably 79.0°C or higher and 105.0°C or lower, even more preferably 80.0°C or higher and 100.0°C or lower, even more preferably 81.0°C or higher and 95.0°C or lower, and particularly preferably 82.0°C or higher and 93.0°C or lower, from the viewpoint of preventing the fibers from fusing to each other. In the present invention, the crystallization temperature of the second component during the cooling process in the DSC curve refers to a temperature at the exothermic peak of the second component in a DSC curve obtained during the cooling process.

[0020] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the melting heat amount per unit mass of the second component during the second heating process is preferably 25.0 mJ/mg or more and 73.5 mJ/mg or less, more preferably 27.0 mJ/mg or more and 72.5 mJ/mg or less, even more preferably 28.5 mJ/mg or more and 71.5 mJ/mg or less, even more preferably 30.0 mJ/mg or more and 70.5 mJ/mg or less, and particularly preferably 32.0 mJ/mg or more and 69.5 mJ/mg or less, from the viewpoint of improving the voluminousness and fiber adhesiveness of a non-woven fabric. In the present invention, the melting heat amount per unit mass of the second component during the second heating process in the DSC curve is calculated by determining the melting heat amount from the endothermic peak of the second component in the DSC curve obtained during the second heating process and converting the obtained melting heat amount into a melting heat amount per 1 mg of the second component.

[0021] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the melting heat amount per unit mass of the second component during the first heating process is preferably 68.0 mJ/mg or less, more preferably 25.0 mJ/mg or more and 68.0 mJ/mg or less, even more preferably 27.0 mJ/mg or more and 67.0 mJ/mg or less, particularly preferably 30.0 mJ/mg or more and 66.0 mJ/mg or less, even more preferably 32.0 mJ/mg or more and 64.0 mJ/mg or less, even more preferably 35.0 mJ/mg or more and 62.0 mJ/mg or less, even more preferably 37.0 mJ/mg or more and 59.0 mJ/mg or less, and particularly preferably 40.0 mJ/mg or more and 55.0 mJ/mg or less, from the viewpoint of further improving the flexibility, voluminousness, and texture of a non-woven fabric. When the melting heat amount per unit mass of the second component during the first heating process is 68.0 mJ/mg or less, the second component present on the surface of the fiber is rapidly melted in processing of the fibers performed to obtain a non-woven fabric, and the fibers adhere to each other in a short period of time, and therefore, high-speed production is possible. In addition, the heat influence on the first component can be minimized, and therefore, the voluminousness of a carded web is maintained, and thus a voluminous non-woven fabric is ultimately obtained. In the present invention, the melting heat amount per unit mass of the second component during the first heating process in the DSC curve is calculated by determining the melting heat amount from the endothermic peak of the second component in the DSC curve obtained during the first heating process and converting the obtained melting heat amount into a melting heat amount per 1 mg of the second component.

[0022] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the crystallization heat amount per unit mass of the second component during the cooling process is preferably 59.5 mJ/mg or less, more preferably 15.0 mJ/mg or more and 59.5 mJ/mg or less, even more preferably 20.0 mJ/mg or more and 56.0 mJ/mg or less, even more preferably 25.0 mJ/mg or more and 53.0 mJ/mg or less, even more preferably 30.0 mJ/mg or more and 50.0 mJ/mg or less, and particularly preferably 35.0 mJ/mg or more and 48.5 mJ/mg or less, from the viewpoint of effectively preventing the fibers from fusing to each other and further improving the flexibility and voluminousness of a non-woven fabric. When the crystallization heat amount per unit mass of the second component during the cooling process is 59.5 mJ/mg or less, the second component present on the surface of the fiber is rapidly solidified after melted and cooled in processing of the fibers performed to obtain a non-woven fabric, and therefore, the non-woven fabric does not lose elasticity. In the present invention, the crystallization heat amount per unit mass of the second component during the cooling process in the DSC curve is calculated by determining the crystallization heat amount from the exothermic peak of the second component in the DSC curve obtained during the cooling process and converting the obtained crystallization heat amount into a crystallization heat amount per 1 mg of the second component.

[0023] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the ratio between the peak (endothermic peak) height and the half width of the first component during the first heating process is preferably 11.0 or less, more preferably 10.5 or less, even more preferably 10.0 or less, even more preferably 9.5 or less, even more preferably 9.0 or less, and particularly preferably 8.5 or less, from the viewpoint of further improving the flexibility and voluminousness of a non-woven fabric. The ratio between the peak (endothermic peak) height and the half width of the first component during the first heating process is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 3.0 or more, even more preferably 3.5 or more, even more preferably 4.0 or more, and particularly preferably 4.5 or more. When the ratio between the peak height and the half width of the first component during the first heating process is within the range above, the endothermic peak (melting peak) of the first component (polylactic acid) included in the core component of the conjugate fiber has a relatively broad shape, and a drawback to polylactic acid, which is generally said to be hard and brittle, is eliminated, thus making it likely to obtain a non-woven fabric having favorable flexibility and voluminousness. In the present invention, the peak half width in a DSC curve is measured based on the half width method according to Japanese Pharmacopoeia.

[0024] In the present invention, the ratio between the peak (endothermic peak) height and the half width of the first component during the first heating process in a DSC curve can be calculated as follows. FIG. 3 is a schematic diagram illustrating a method for calculating the peak height/half width ratio of the first component during the first heating process in a DSC curve obtained through differential scanning calorimetry (DSC).

(1) A perpendicular line L1 is drawn from a peak top St of the endothermic peak to a base line Lb, and the length of the perpendicular line is taken as a peak height (h). Note that, in the case of a double peak, the highest peak is used.

(2) A distance between a point S 1 and a point S2 at which a line drawn from a position Sh located at half the height (h/2) of the peak height of the perpendicular line L1 so as to be orthogonal to the perpendicular line L1 intersects the endothermic peak curve is taken as a half width (Wh).

(3) The peak ratio is calculated using Expression 1 below.

[0025] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the melting heat amount per unit mass of the first component during the first heating process is preferably 30.0 mJ/mg or more, more preferably 30.0 mJ/mg or more and 100.0 mJ/mg or less, even more preferably 35.0 mJ/mg or more and 90.0 mJ/mg or less, even more preferably 40.0 mJ/mg or more and 80.0 mJ/mg or less, even more preferably 42.0 mJ/mg or more and 75.0 mJ/mg or less, and particularly preferably 45.0 mJ/mg or more and 70.0 mJ/mg or less, from the viewpoint of further improving the flexibility and voluminousness of a non-woven fabric. In the present invention, the melting heat amount per unit mass of the first component during the first heating process in the DSC curve is calculated by determining the melting heat amount from the endothermic peak of the first component in the DSC curve obtained during the first heating process and converting the obtained melting heat amount into a melting heat amount per 1 mg of the first component.

[0026] In a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber of the present invention, the crystallization time of the second component during the cooling process is preferably 208 minutes or longer and 228 minutes or shorter, more preferably 210 minutes or longer and 227 minutes or shorter, even more preferably 212 minutes or longer and 226 minutes or shorter, even more preferably 214 minutes or longer and 225 minutes or shorter, and particularly preferably 216 minutes or longer and 224 minutes or shorter, from the viewpoint of preventing the fibers from fusing to each other and improving the workability of a non-woven fabric. In the present invention, the crystallization time of the second component during the cooling process in a DSC curve refers to exothermic peak time of the second component in a DSC curve obtained during the cooling process.

[0027] The first component contains poly-L-lactic acid. The melting point of the poly-L-lactic acid is preferably 160°C or higher, more preferably 165°C or higher, even more preferably 168°C or higher, and particularly preferably 173°C or higher. When the melting point of the poly-L-lactic acid is 160°C or higher, the difference in the melting point between the poly-L-lactic acid and the sheath component does not decrease, the melting point and a processing temperature at which the fibers are processed into a fiber structure such as a non-woven fabric through heating significantly differ from each other, and elasticity is not lost during the heat processing. The upper limit of the melting point of the poly-L-lactic acid is preferably 230°C or lower.

[0028] The first component may also contain a nucleating agent. Any known nucleating agent may be used, and preferable examples thereof include inorganic fillers such as calcium carbonate, talc, silica, and aluminum compounds, fatty acid metal salts such as calcium stearate, phosphate ester metal salts, amide-based compounds, minerals such as mica and wollastonite, and barium sulfate. The nucleating agent may be added in an amount of 0.01 parts by mass or more and 10 parts by mass or less, and preferably 0.05 parts by mass or more and 5 parts by mass or less, with respect to 100 parts by mass of poly-L-lactic acid.

[0029] The optical purity of the poly-L-lactic acid is 95% or more, preferably 98.0% or more, more preferably 98.5% or more, even more preferably 99.0% or more, and particularly preferably 99.5% or more. When the optical purity is 95% or more, elasticity is not lost during heat processing, and volume recovery properties are improved.

[0030] Since the poly-L-lactic acid used in the present invention tends to have high heat resistance and high bending elasticity, a non-woven fabric having low heat shrinkage, a large volume, and excellent volume recovery properties is likely to be obtained.

[0031] Another resin may be mixed in the first component in addition to the poly-L-lactic acid, as long as the effects of the present invention are not inhibited. Examples of the other resin include an aromatic polyester such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate, an aromatic-aliphatic polyester, an aliphatic polyester, and polyolefin. The ratio of the poly-L-lactic acid in the first component is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and most preferably 95 mass% or more.

[0032] The second component contains an aliphatic polyester composed of glycol and dicarboxylic acid. The aliphatic polyester is preferably polyalkylene dicarboxylate, and specific examples thereof include polybutylene succinate, polybutylene adipate, polybutylene sebacate, polyethylene oxalate, polyethylene succinate, polyethylene adipate, polyethylene azelate, polyhexamethylene sebacate, polyneopentyl oxalate, and copolymers thereof. Of these, polybutylene succinate, which is a condensation product of succinic acid with 1,4-butanediol, and/or copolymers thereof are preferable because they have a relatively high melting point of about 110°C, result in excellent fiber productivity, excellent workability during processing performed to obtain a non-woven fabric, and excellent physical properties of a non-woven fabric, and can be made into a biomass raw material.

[0033] The melting point of the aliphatic polyester is preferably 100°C or higher and 130°C or lower, and more preferably 110°C or higher and 125°C or lower. When the melting point is 100°C or higher, a molten resin discharged from a nozzle during melt spinning rapidly solidifies, and thus the occurrence of fused yarn is suppressed. When the melting point is 130°C or lower, there is a big difference in the melting point between the aliphatic polyester and the first component, and elasticity is not lost during heat processing.

[0034] It is preferable that the second component contains a nucleating agent from the viewpoint of improving spinnability. Examples of the nucleating agent include inorganic nucleating agents and organic nucleating agents. Examples of the 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 the organic nucleating agents include fatty acid metal salts, phosphate ester metal salts, and amide-based compounds. The nucleating agent is preferably an organic nucleating agent, and particularly preferably a fatty acid metal salt. Fatty acid metal salts have an effect of improving the heat resistance of a formed fiber because the fatty acid metal salts form uniform minute crystals. 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, zinc montanate, calcium montanate, magnesium montanate, sodium 12-hydroxystearate, lithium 12-hydroxystearate, lead 12-hydroxystearate, nickel 12-hydroxystearate, 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 montanite, sodium octylate, lithium octylate, magnesium octylate, calcium octylate, barium octylate, aluminum octylate, nickel octylate, sodium sebacate, lithium sebacate, magnesium sebacate, calcium sebacate, barium sebacate, aluminum sebacate, thallium sebacate, lead sebacate, 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. It is preferable to use salts of metals having a valency of two or more out of the fatty acid metal salts above. When salts of metals having a valency of two or more are used, a physical cross-linking structure can be easily formed, and the movability of the segments in the polymer chain is limited. Thus, these salts serve as a crystalline nucleus and enable rapid crystallization. Furthermore, from the viewpoint of spinnability, fatty acid metal salts having a melting point higher than the melting point of the resin of the second component are preferable, and metal salts bound to a fatty acid with a high binding force are preferable. Examples of the metal include calcium, magnesium, and zinc, and calcium is particularly preferable. The fatty acid is preferably a saturated fatty acid having a high melting point. The number of carbon atoms in the fatty acid is preferably 12 or greater and 28 or smaller, and more preferably 14 or greater and 20 or smaller. When the number of carbon atoms is within this range, the molecular chain is not excessively long, and the melting point is lower than the melt extrusion temperature of the second component. Therefore, the nucleating agent is uniformly dispersed in the resin. One or more selected from the group consisting of calcium stearate, magnesium stearate, and zinc stearate is particularly preferable.

[0035] From the viewpoint of improving crystallinity and improving spinnability, the second component preferably contains the nucleating agent in an amount of 0.01 parts by mass or more and 20 parts by mass or less, more preferably in an amount of 0.03 parts by mass or more and 10 parts by mass or less, and even more preferably 0.06 parts by mass or more and 5 parts by mass or less, with respect to 100 parts by mass of the aliphatic polyester. When the nucleating agent is an inorganic nucleating agent, the second component preferably contains the inorganic nucleating agent in an amount of 0.1 parts by mass or more and 20 parts by mass or less, more preferably in an amount of 0.5 parts by mass or more and 10 parts by mass or less, and even more preferably 1.0 part by mass or more and 5.0 parts by mass or less, with respect to 100 parts by mass of the aliphatic polyester, from the viewpoint of promoting the crystallization of the resin. When the nucleating agent is an organic nucleating agent, the second component preferably contains the organic nucleating agent in an amount of 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably in an amount of 0.03 parts by mass or more and 4.0 parts by mass or less, and even more preferably 0.06 parts by mass or more and 3.0 parts by mass or less, with respect to 100 parts by mass of the aliphatic polyester, from the viewpoint of promoting the crystallization of the resin.

[0036] Another resin may be mixed in the second component in addition to the aliphatic polyester, as long as the effects of the present invention are not inhibited. Examples of the other resin include polylactic acid, polyhydroxybutyrate, polyhydroxybutyrate-valerate, polycaprolactam, aromatic polyester, polyamide, and polyolefin. The ratio of the aliphatic polyester in the second component is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and most preferably 95 mass% or more.

[0037] There is no particular limitation on the cross-sectional shape of the conjugate fiber, and it is sufficient that the second component occupies 50% or more of the fiber surface. For example, the shape of the first component in the fiber cross section may be a circular shape or non-circular shape such as a semicircular shape, an elliptical shape, a Y-shape, an X-shape, a lattice shape, a polygonal shape, or a star shape, and the shape of the conjugate fiber in the fiber cross section may be a circular shape, or non-circular such as an elliptical shape, a Yshape, an X-shape, a lattice shape, a polygonal shape, or a star shape, or a hollow shape.

[0038] From the viewpoint of strength and voluminousness of a non-woven fabric, it is preferable that the conjugate fiber is a core-sheath conjugate fiber in which the first component is used as a core component and the second component is used as a sheath component, and it is more preferable that the conjugate fiber is a concentric core-sheath conjugate fiber in which the center position of the first component coincides with the center position of the conjugate fiber. The conjugate fiber may also be an eccentric core-sheath conjugate fiber in which the center position of the first component does not coincide with the center position of the conjugate fiber.

[0039] In the conjugate fiber, the conjugate ratio (first component / second component) represented as a mass ratio is preferably 80/20 to 30/70, more preferably 75/25 to 35/65, even more preferably 70/30 to 40/60, even more preferably 65/35 to 50/50, and particularly preferably 60/40 to 55/45. When the conjugate ratio is within the range above, a non-woven fabric is likely to be flexible and also has favorable strength and volume recovery properties.

[0040] The percentage of crimp of the conjugate fiber is preferably 2% or more and 20% or less, and more preferably 4% or more and 15% or less. When the percentage of crimp is 2% or more, the fiber does not have a straight shape, and a voluminous non-woven fabric is likely to be obtained. When the percentage of crimp is 20% or less, favorable fiber loosening properties are achieved, and a carded web and an air laid web that have a favorable texture are likely to be obtained.

[0041] There is no limitation on the crimp shape of the conjugate fiber, and any shape obtained through machine crimping, wave crimping, spiral crimping, and the like may be employed.

[0042] Although there is no particular limitation on the single-fiber strength of the conjugate fiber, the single-fiber strength is preferably 1.0 cN/dtex or more and 5.0 cN/dtex or less and more preferably 1.0 cN/dtex or more and 4.0 cN/dtex or less. When the single-fiber strength is 1.0 cN/dtex or more, the occurrence of fiber breakage in a carding process is suppressed. When the single-fiber strength is 4.0 cN/dtex or less, a fiber structure such as a non-woven fabric has favorable volume recovery properties and flexibility.

[0043] Although there is no particular limitation on the single-fiber fineness of the conjugate fiber, the single-fiber fineness is preferably 0.3 dtex or more and 30 dtex or less, more preferably 1 dtex or more and 20 dtex or less, even more preferably 1.5 dtex or more and 10 dtex or less, even more preferably 1.6 dtex or more and 8 dtex or less, even more preferably 1.7 dtex or more and 6 dtex or less, and particularly preferably 1.8 dtex or more and 3 dtex or less, from the viewpoint of the volume recovery properties of a fiber structure such as a non-woven fabric.

[0044] The conjugate fiber of the present invention can be produced by melt spinning the first component at a lower temperature than the second component, followed by drawing performed under predetermined conditions.

[0045] First, the first component containing poly-L-lactic acid with an optical purity of 95% or more in an amount of 70 mass% or more and the second component containing an aliphatic polyester composed of glycol and dicarboxylic acid in an amount of 70 mass% or more are prepared. The first component preferably contains the poly-L-lactic acid in an amount of 80 mass% or more, more preferably 90 mass% or more, and particularly preferably 95 mass% or more. The second component preferably contains the aliphatic polyester in an amount of 80 mass% or more, more preferably 90 mass% or more, and particularly preferably 95 mass% or more. The poly-L-lactic acid and the aliphatic polyester may be those described above.

[0046] Next, a spun filament in which the second component occupies 50% or more of the fiber surface is produced by melt spinning the first component and the second component (this process is also referred to as a "spinning process" hereinafter). Specifically, a conjugate nozzle with which a predetermined fiber cross section is obtained is attached to a melt spinning machine, and the first component and the second component are melt extruded and spun such that the second component occupies 50% or more of the fiber surface. Thus, a spun filament (i.e., undrawn filament) is obtained. In the spinning process, the first component is melt extruded at a temperature lower than the second component. Thus, cooling of the first component is facilitated, and the first component can be rapidly crystallized, thus making it easy to control the crystallization of the first component. Accordingly, a spun filament with low crystalline orientation and small fineness can be obtained. The spun filament has favorable extensibility, and it is possible to not only produce a fiber with regular crystallinity and orientation by drawing the spun filament but also further reduce the fineness after drawing. Also, a conjugate fiber in which the second component has high crystallinity can be obtained. The first component is preferably melt extruded at a temperature lower than the second component by 1°C or higher or 30°C or lower, more preferably 3°C or higher or 20°C or lower, even more preferably 5°C or higher or 18°C or lower, and particularly preferably 7°C or higher or 16°C or lower. Specifically, the first component and the second component may be melt extruded at a temperature of 200°C or higher and 240°C or lower and a temperature of 220°C or higher and 250°C or lower, respectively, or may be melt extruded at a temperature of 205°C or higher and 235°C or lower and a temperature of 225°C or higher and 245°C or lower, respectively, or may be melt extruded at a temperature of 210°C or higher and 230°C or lower and a temperature of 225°C or higher and 240°C or lower, respectively, or may be melt extruded at a temperature of 215°C or higher and 225°C or lower and a temperature of 225°C or higher and 235°C or lower, respectively.

[0047] Next, a drawn filament (conjugate fiber) is obtained by drawing the spun filament.

[0048] The drawing process may be a process known as single-stage drawing that includes only a single drawing step, or may be multi-stage drawing that includes two or more drawing steps. The single-stage drawing or the first stage of the multi-stage drawing is carried out at a drawing temperature of 55°C or higher and 90°C or lower. When the drawing temperature is 90°C or lower, fusion does not occur during the drawing process. When the drawing temperature is 55°C or higher, a high degree of drawing can be achieved. The drawing temperature is preferably 60°C or higher and 85°C or lower, and more preferably 70°C or higher and 80°C or lower. In the second stage and onwards of the multi-stage drawing, the drawing temperature is preferably 60°C or higher and 100°C or lower, more preferably 70°C or higher and 95°C or lower, and particularly preferably 75°C or higher and 90°C or lower. In the case of multi-stage drawing, the drawing temperature in the second stage and onwards is preferably higher than or equal to that in the first stage. The difference in the temperature between the first stage and the second stage and onwards is preferably 0°C or higher and 30°C or lower, more preferably 0°C or higher and 25°C or lower, even more preferably 1°C or higher and 20°C or lower, and particularly preferably 2°C or higher and 17°C or lower.

[0049] The drawing ratio is 1.4-fold or more. This makes it possible to improve the crystallinity of the first component and the second component, and thus improve the flexibility and voluminousness of a non-woven fabric. The drawing ratio is preferably 1.4-fold or more and 3.8-fold or less, more preferably 1.5-fold or more and 3.5-fold or less, even more preferably 1.6-fold or more and 3.2-fold or less, even more preferably 1.7-fold or more and 2.9-fold or less and particularly preferably 1.8-fold or more and 2.6-fold or less. When the drawing ratio is 1.4-fold or more, yarn breakage does not occur during the drawing process, and the spun filament can be uniformly drawn. The drawing process may be single-stage drawing or multi-stage drawing that includes two or more stages. The second stage and onwards of the multi-stage drawing may be a tensile heating set in which heat treatment is performed with a fiber under tension, or a loose heating set in which heat treatment is performed with a fiber in a loose state. In the case of the tensile heating set, the drawing ratio may be 1.0-fold or more and 1.2-fold or less, or 1.0-fold or more and 1.1-fold or less. In the case of the loose heating set, the drawing ratio may be 0.9-fold or more and less than 1.0-fold, or 0.95-fold or more and less than 1.0-fold. The second stage and onwards of the multi-stage drawing are preferably a tensile heating set. Performing the tensile heating set makes it possible to achieve regular and stable crystallinity of the first component and the second component, and thus workability during subsequent secondary forming processes (e.g., forming of non-woven) is improved. Also, the texture as well as voluminousness of a non-woven fabric is improved due to the regular crystallinity. In the case of multi-stage drawing, the drawing ratio is a product of the drawing ratios of the all stages.

[0050] In the drawing process, the drawing ratio is preferably 60% or more and 99% or less of the maximum drawing ratio (Vmax), more preferably 65% or more and 99% or less, and even more preferably 70% or more and 99% or less. When the drawing ratio is 60% or more and 99% or less of the maximum drawing ratio, a high degree of drawing can be achieved while yarn breakage is suppressed during the drawing process.

[0051] The drawing method may be a wet drawing method or a dry drawing method. Air, vapor, water, or oil such as glycerin can be used as a heat medium as appropriate. In the case of the wet drawing method, drawing can be performed in a liquid while heat is applied. For example, drawing may be performed in hot water or warm water. In the case of the dry drawing method, drawing can be performed in high-temperature gas or on a high-temperature metal roll, etc. while heat is applied. Drawing is preferably performed in warm water. The reason for this is that, in the case where the conjugate fiber is a core-sheath conjugate fiber, when drawing is performed in warm water, the core component and the sheath component are likely to be distorted, and thus a crimp shape with more curved convex portions can be more easily obtained.

[0052] In the present invention, the "maximum drawing ratio (V_max)" is measured as follows. Melt spinning is performed using a core-sheath conjugate nozzle, and obtained spun filaments (undrawn fiber bundle) are subjected to wet drawing in warm water at a predetermined temperature. At this time, the feeding speed (V₁) of a roll for feeding the undrawn fiber bundle is set to 10 m/minute, and the take-up speed (V₂) of a metal roll on a take-up side is gradually increased from 10 m/minute. Then, the take-up speed of the metal roll on the take-up side when the undrawn fiber bundle breaks is taken as the maximum drawing speed, a ratio (V₂/V₁) between the maximum drawing speed and the feeding speed of the roll for feeding the undrawn fiber bundle is determined, and the obtained speed ratio is taken as the maximum drawing ratio (V_max).

[0053] In the case of a process known as single-stage drawing in which a drawing process is performed once, and the case where a drawing process is performed a plurality of times using the same drawing method at the same drawing temperature, the maximum drawing ratio can be measured using the same method as that used in the drawing process, at the same temperature as that in the drawing process. In the case where a spun filament is drawn through a process known as multi-stage drawing in which a drawing process is performed a plurality of times, and the drawing processes are performed at different temperatures, the maximum drawing ratio is measured using the same drawing method as that used in the drawing method performed at a higher temperature, at the same drawing temperature as that in such a drawing process.

[0054] In the case where a spun filament is drawn through a process known as multi-stage drawing in which a drawing process is performed a plurality of times, and the drawing processes are performed at the same temperature but using different drawing methods, the maximum drawing ratios are measured using both of the methods, and a larger maximum drawing ratio is taken as the maximum drawing ratio for these production conditions.

[0055] A predetermined amount of a fiber treatment agent is attached to the obtained drawn filament as needed, and furthermore, the drawn filament is subjected to machine crimping using a crimper (crimp imparting apparatus) as needed. When treated with the fiber treatment agent, fibers can be easily dispersed in water or the like in the case where a non-woven fabric is produced using a wet paper-making method. Also, when fibers to which the fiber treatment agent is attached are impregnated with the fiber treatment agent by applying an external force (this external force is, for example, a force applied when crimp is imparted by the crimper) onto the fiber surfaces of the fibers, the dispersibility of the fibers in water or the like is improved.

[0056] The drawn filament to which the fiber treatment agent is attached (or to which the fiber treatment agent is not attached but that is in a wet state) is dried at a temperature of 80°C or higher and 110°C or lower for several seconds to about 30 minutes, and thus a dry fiber is obtained. The drying process may be omitted according to the circumstances. Thereafter, the drawn filament is cut such that the fiber length is preferably 1 mm or more and 100 mm or less, and more preferably 2 mm or more and 70 mm or less.

[0057] In the case where the conjugate fiber is a core-sheath conjugate fiber, the poly-L-lactic acid in the core component and the aliphatic polyester in the sheath component are highly compatible with each other, and therefore, the core and the sheath are unlikely to be separated from each other, thus making it possible to obtain a thermal bonded non-woven fabric with high strength. Furthermore, the aliphatic polyester in the sheath component has excellent adhesiveness to a polyester other than polylactic acid and poly-L-lactic acid and cellulose, thus making it possible to obtain a non-woven fabric with firmer adhering points.

[0058] The conjugate fiber of the present invention can be used for a fiber structure such as yarn, a non-woven fabric, a woven fabric, and a knitted fabric. The fiber structure may contain the conjugate fiber in an amount of 5 mass% or more and 10 mass% or more. In particular, in the case where the conjugate fiber of the present invention is used for a non-woven fabric, it is preferable that the non-woven fabric contains the conjugate fiber in an amount of 5 mass% or more, and the fibers included in the non-woven fabric are thermally bonded to each other due to the second component of the conjugate fiber being melted. The non-woven fabric may contain the conjugate fiber in an amount of 20 mass% or more, 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, or 95 mass% or more, or 100 mass%. In the case where the non-woven fabric contains another fiber, examples of the other fiber include a natural fiber, a regenerated fiber, and a synthetic fiber. Examples of the natural fiber include cotton, silk, wool, hemp, pulp, and kapok. Examples of the regenerated fiber include rayon, cupra, and polynosic. Examples of the synthetic fiber include an acrylic fiber, a polyester fiber, a polyamide fiber, a polyolefin fiber, and a polyurethane fiber. As the other fiber, one type or a plurality of types of fibers can be selected from the above-described fibers as appropriate in accordance with the application or the like.

[0059] Examples of the form of a fiber web included in the non-woven fabric of the present invention 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 paper web. The fiber web exhibits its effects due to adhesion of the second component caused by heat treatment. The fiber web may be subjected to needle-punching treatment or hydroentangling treatment as needed. There is no particular limitation on the heat treatment measures as long as the functions of the conjugate fiber of the present invention are sufficiently exhibited, and it is preferable to use a heat treatment machine that applies little pressure (e.g., little wind pressure), such as a hot-air penetration heat treatment machine, an upper-and-lower hot-air blast heat treatment machine, or an infrared heat treatment machine.

[0060] From the viewpoint of excellent initial volume, the specific volume of the non-woven fabric is preferably 20 cm³/g or more, and more preferably 30 cm³/g or more and 100 cm³/g or less, when measured at a load of 2.96 N/cm³. From the viewpoint of excellent volume recovery properties, the specific volume of the non-woven fabric is preferably 10 cm³/g or more, and more preferably 15 cm³/g or more and 40 cm³/g or less, when measured at a load of 19.6 N/cm³.

[0061] From the viewpoint of excellent voluminousness and flexibility, the bending resistance in the machine direction (MD direction) of the non-woven fabric is preferably 100 mN·mm or less, and more preferably 15 mN·mm or more and 50 mN·mm or less, when the non-woven fabric has a basis weight of about 20 g/m² (specifically, 20±3 g/m²). The bending resistance in the MD direction is preferably 250 mN·mm or less, and more preferably 30 mN·mm or more and 200 mN·mm or less, when the non-woven fabric has a basis weight of about 40 g/m² (specifically, 40±3 g/m²). Here, the machine direction refers to a direction in which the fibers are oriented. From the viewpoint of excellent voluminousness and flexibility, the bending resistance in the orthogonal direction (CD direction) to the machine direction of the non-woven fabric is preferably 30 mN·mm or less, and more preferably 5 mN·mm or more and 20 mN·mm or less, when the non-woven fabric has a basis weight of about 20 g/m² (specifically, 20±3 g/m²). The bending resistance in the CD direction is preferably 50 mN·mm or less, and more preferably 15 mN·mm or more and 45 mN·mm or less, when the non-woven fabric has a basis weight of about 40 g/m² (specifically, 40±3 g/m²).

[0062] From the viewpoint of excellent water resistance and heat resistance, the decreasing rate of tensile strength of the non-woven fabric is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less, when measured through the water resistance and heat resistance test below. The decreasing rate may also be 0% or more. When the decreasing rate is within this range, the non-woven fabric has appropriate strength even when used in an environment where it is always heated and in an environment where it is impregnated with a liquid, while having biodegradability.

Decreasing Rate of Tensile Strength (Water Resistance and Heat Resistance Test)

[0063] A fiber web is produced using a parallel carding machine, and a non-woven fabric (basis weight: about 40 g/m², specifically 40±3 g/m²) is produced by heating this fiber web at 128°C for 10 seconds using a hot-air penetration heat treatment machine, and then the non-woven fabric is impregnated with ion-exchanged water at 45°C for 7 weeks. The tensile strength of the non-woven fabric before the impregnation and the tensile strength of the non-woven fabric after 7 weeks are measured through a tensile test performed in conformity with JIS L 1913: 2010 6.3 using a constant-speed tension-type tensile tester under conditions of a test piece width of 5 cm, a grip interval of 10 cm, and a tension rate of 30±2 cm/min, and a load value at the time of breakage (tensile strength) is measured. The decreasing rate of the tensile strength is calculated using Expression 2 below.

[0064] The non-woven fabric of the present invention can be used as at least a portion of a cushioning material. Examples of the cushioning material include interior materials for domestic chairs, vehicle seats, and the like, hygienic materials for diapers, sanitary napkins, and the like, cosmetic materials for filters, cosmetic puffs, and the like, and molded articles such as brassiere pads.

Examples

[0065] Hereinafter, the present invention will be described in more detail using examples and comparative examples. Note that the present invention is not limited to the following examples.

Evaluation Methods

[0066] 

(1) Differential scanning calorimetry: Differential scanning calorimetry was performed under the following conditions based on JIS K 7121: 1987 using a differential scanning calorimeter (manufactured by Hitachi High-Tech Corporation).
The amount of a sample (fiber) was set to 3.0 mg, and the sample was weighed out and filled into a sample holder. Next, the sample filled into the sample holder was heated from an ordinary temperature (23±2°C) to 250°C at a rate of 5°C/minute (first heating process), and a DSC measurement for first melting was performed. After the temperature reached 250°C, the sample was kept at this temperature for 10 minutes in a molten state and was then cooled from 250°C to 40°C at a rate of 1°C/minute (cooling process), and thus the molten sample was solidified. At this time, DSC during cooling was measured. After the first heating process and the cooling process were finished, the sample was not removed from the DSC measurement apparatus and was kept at 40°C for 10 minutes. Then, the sample was heated again from 40°C to 250°C at a rate of 5°C/minute (second heating process), and a DSC measurement for second melting was performed.

(2) Fiber physical properties: The Single-fiber fineness, the single-fiber strength (breaking strength), the elongation (elongation at break), and the Young's modulus were measured in conformity with JIS L 1015: 2021.

(3) Percentage of crimp: The percentage of crimp was measured in conformity with JIS L 1015: 2021.

(4) Basis weight: The basis weight of a non-woven fabric was measured based on JIS L 1913: 2010 6.2.

(5) Specific volume: The thickness of a non-woven fabric in a state where a load of 2.96 N/cm³ or 19.6 N/cm³ is being applied was measured using a thickness measurement apparatus (product name "THICKNESS GAUGE", model "CR-60A", manufactured by Daiei Kagaku Seiki MFG. Co., Ltd.), and the specific volume was calculated from the basis weight and the thickness of the non-woven fabric.

(6) Bending resistance: The bending resistance was measured in conformity with the 41.5° cantilever method of JIS L 1913: 2010.

(7) Decreasing rate of tensile strength (water resistance and heat resistance test): A fiber web was produced using a parallel carding machine, and a non-woven fabric (basis weight: about 40 g/m², specifically 40±3 g/m²) was produced by heating this fiber web at 128°C for 10 seconds using a hot-air penetration heat treatment machine, and then the non-woven fabric was impregnated with ion-exchanged water at 45°C for 7 weeks. The tensile strength of the non-woven fabric before the impregnation and the tensile strength of the non-woven fabric after 7 weeks were measured through a tensile test performed in conformity with JIS L 1913: 2010 6.3 using a constant-speed tension-type tensile tester under conditions of a test piece width of 5 cm, a grip interval of 10 cm, and a tension rate of 30±2 cm/min, and a load value at the time of breakage (tensile strength) was measured. The decreasing rate of the tensile strength was calculated using Expression 2 below.

Examples 1 to 18, Comparative Examples 1 and 2

[0067] Specific conditions are shown in Tables 1 to 4.

(1) Resin

(i) Poly-L-lactic acid (also referred to as "PLA" hereinafter)

A: L-130, optical purity of 99% or more, melting point of 175°C, manufactured by Total-Corbion PLA

B: Ingeo3251D, optical purity of 98.5%, melting point of 155 to 170°C, manufactured by Nature Works

(ii) Aliphatic polyester
C: Polybutylene succinate (also referred to as "PBS" hereinafter), FZ71 PM, melting point of 115°C, manufactured by PTT MCC Biochem

(iii) Nucleating agent (added to a sheath component; the blend amounts of the nucleating agent shown in Tables are those in the sheath component)

D: Talc (manufactured by Nippon Talc Co., Ltd., product name "MICRO ACE P-S")

E: Calcium stearate (manufactured by NOF Corporation, product name "CALCIUM STEARATE S")

(2) Resins for core component and sheath component

Core component: Tables 1 to 4

Sheath component: C

(3) Take-up speed: 926 m/minute (410 m/minute only in Comparative Example 1)

(4) Cross section: concentric circles

(5) Drawing method: wet (warm water), two-stage drawing

(6) Oil (fiber treatment agent) concentration: 5 mass%

(7) Drying temperature: 85°C

(8) Cut length: 51 mm (Examples 1 to 14, Examples 16 to 18, Comparative Examples 1 and 2), 5 mm (Example 15)

(9) A non-woven fabric was produced using a hot-air penetration heat treatment machine to heat a fiber web produced using a parallel carding machine. In Examples 1 to 10, Comparative Example 1, and Examples 13 to 18, heat treatment was performed at 128°C for 10 seconds, and in Examples 11 and 12 and Comparative Example 2, heat treatment was performed at 115°C for 100 seconds.

[0068] In the examples and the comparative examples, the conjugate fiber and the non-woven fabric were evaluated using the above-described evaluation methods. Tables 1 to 5 below show the results. In Tables 1 to 5 below, "- (minus)" in the column of "PBS crystallization heat amount" means crystallization.

Table 1

Ex.		1	2	3		4	5
Composition	PLA type	A			B
	Nucleating agent type	D			D
	Nucleating agent blend amount (mass%)	1.3			1.3
	Conjugate ratio (mass ratio) core : sheath	58:42			58:42
Spinning conditions	PLA melt extrusion temperature (°C)	220			220
	PBS melt extrusion temperature (°C)	235			235
Undrawn yarn	Fineness (dtex)	4.1			4.22
Drawing Conditions	Vmax (fold)	2	2.1	1.7		1.8	1.9
	Drawing ratio (fold)	1.9	2.05	1.6		1.7	1.8
	First drawing ratio (fold)	1.9	2.05	1.6		1.7	1.8
	Second drawing ratio (fold)	1	1	1		1	1
	First drawing tank temperature (°C)	70	80	60		70	80
	Second drawing tank temperature (°C)	85	85	85		85	85
Drawn yarn	Fineness (dtex)	3.1	2.59	3.16		3.18	2.82
	Strength (cN/dtex)	2.14	2.4	2.22		2.29	2.35
	Elongation (%)	37.52	35.72	41.14		40.37	39.3
	Young's modulus (cN/dtex)	25.8	28.9	31.9		33.7	33.1
	Percentage of crimp (%)	8.9	9.9	6.8		7.7	7.4
DSC / first heating process	PBS melting temperature (°C)	114.9	114.9	114.8		114.8	114.3
	PBS melting heat amount (mJ/mg)	64.0	58.6	61.8		59.3	57.9
	(Low temperature) PLA melting temperature (°C)	173.3	172.5	164.3		164.9	165.6
	(High temperature) PLA melting temperature (°C)	None	174.2	170.3		170.6	170.3
	PLA melting heat amount (mJ/mg)	57.8	55.5	57.7		50.6	51.0
	Peak height / half width	7.2	7.7	9.6		8.9	14.1
DSC/ cooling process (crystal)	PBS / crystallization temperature (°C)	78.9	84.5	86.8		86.3	86.2
	PBS / crystallization time (minutes)	227.6	223.0	219.7		220.1	220.4
	PBS / crystallization heat amount (mJ/mg)	-52.3	-45.7	-54.9		-49.5	-48.2
DSC/ second heating process	PBS melting temperature (°C)	111.8	111.8	112.1		111.6	111.2
	PBS melting heat amount (mJ/mg)	67.0	54.0	58.5		58.0	55.7
Non-woven fabric	Specific volume (cm3/g) (2.96 cN/cm3 load)	55.6	66.3	44.7		55.7	60.3
	Specific volume (cm3/g) (19.6 cN/cm3 load)	21.5	21.7	16.7		20.7	20.7
	Basis weight (g/m2) / MD	39.5	42.1	41.1		40.0	38.9
	Basis weight (g/m2) / CD	41.6	41.1	42.1		38.4	39.5
	MD bending resistance (mN·mm)	105.7	60.1	231.0		181.2	161.2
	CD bending resistance (mN·mm)	30.2	28.7	35.7		33.0	31.2

Table 2

Ex.		6	7	8	9	10
Composition	PLA type	A
	Nucleating agent type	E
	Nucleating agent blend amount (mass%)	0.125
	Conjugate ratio (mass ratio) core: sheath	58:42
Spinning conditions	PLA melt extrusion temperature (°C)	220
	PBS melt extrusion temperature (°C)	235
Undrawn yarn	Fineness (dtex)	4.6
Drawing Conditions	Vmax (fold)	2.1	2.3	2.3	2.3	2.3
	Drawing ratio (fold)	1.9	2	2	2	2
	First drawing ratio (fold)	1.9	2	2	2	2
	Second drawing ratio (fold)	1	1	1	1	1
	First drawing tank temperature (°C)	70	75	80	83	86
	Second drawing tank temperature (°C)	85	85	85	85	85
Drawn yarn	Fineness (dtex)	2.69	2.55	2.57	2.4	2.79
	Strength (cN/dtex)	2.58	2.73	2.74	3.06	3.28
	Elongation (%)	40.3	39.7	38.6	36.3	39.6
	Young's modulus (cN/dtex)	28.2	29	28.8	33	33.4
	Percentage of crimp (%)	9.9	8.1	11.4	8.7	5.3
DSC / first heating process	PBS melting temperature (°C)	115.8	115.8	115.8	115.7	115.6
	PBS melting heat amount (mJ/mg)	50.8	48.2	49.4	50.4	48.6
	(Low temperature) PLA melting temperature (°C)	172.6	172.8	172.8	172.8	172.6
	(High temperature) PLA melting temperature (°C)	None	None	None	174.8	174.5
	PLA melting heat amount (mJ/mg)	50.6	50.2	48.6	50.9	49.9
	Peak height / half width	7.3	9.2	10.0	8.7	8.0
DSC / cooling process (crystal)	PBS / crystallization temperature (°C)	86.8	86.8	87.9	87.1	88.0
	PBS / crystallization time (minute)	219.6	218.9	218.6	219.2	218.5
	PBS / crystallization heat amount (mJ/mg)	-46.3	-46.8	-46.7	-47.9	-49.6
DSC / second heating process	PBS melting temperature (°C)	113.2	113.2	113.0	112.9	113.0
	PBS melting heat amount (mJ/mg)	43.9	41.0	38.7	44.3	41.8
Non-woven fabric	Specific volume (cm3/g) (2.96 cN/cm3 load)	57.8	53.3	63.8	66.4	62.6
	Specific volume (cm3/g) (19.6 cN/cm3 load)	19.4	17.5	17.8	21.2	17.6
	Basis weight (g/m2) / MD	21.2	21.6	21.4	23.1	19.4
	Basis weight (g/m2) / CD	19.9	20.2	21.9	21.1	20.1
	MD bending resistance (mN·mm)	33.1	29.8	30.3	32.7	29.5
	CD bending resistance (mN·mm)	9.0	8.5	7.9	7.0	8.9

Table 3

Ex./Comp. Ex.		Comp. Ex. 1	Ex. 11	Ex. 12	Comp. Ex. 2
Composition	PLA type	A
	Nucleating agent type	E
	Nucleating agent blend amount (mass%)	0.125
	Conjugate ratio (mass ratio) core: sheath	50:50	58:42		58:42
Spinning conditions	PLA melt extrusion temperature (°C)	240	220		220
	PBS melt extrusion temperature (°C)	210	235		235
Undrawn yarn	Fineness (dtex)	8.66	4.23		3.62
Drawing Conditions	Vmax (fold)	1.9	2.2	2.2	2
	Drawing ratio (fold)	1.75	2	2	1.8
	First drawing ratio (fold)	1.75	2	2	1.8
	Second drawing ratio (fold)	1	1	1	1
	First drawing tank temperature (°C)	50	80	80	80
	Second drawing tank temperature (°C)	80		85
Drawn yarn	Fineness (dtex)	5.39	2.61	2.33	2.08
	Strength (cN/dtex)	3.36	3.32	3.53	3.49
	Elongation (%)	47.36	39.23	40.56	39.88
	Young's modulus (cN/dtex)	28.8	27.8	34.0	32.9
	Percentage of crimp (%)	6.8	4.5	6	6.7
DSC / first heating process	PBS melting temperature (°C)	115.8	116.0	115.9	115.8
	PBS melting heat amount (mJ/mg)	68.2	63.3	62.4	57.4
	(Low temperature) PLA melting temperature (°C)	171.1	171.5	171.8	171.3
	(High temperature) PLA melting temperature (°C)	None	None	None	None
	PLA melting heat amount (mJ/mg)	61.1	61.7	61.9	56.7
	Peak height / half width	11.4	8.9	10.5	8.3
DSC/ cooling process (crystal)	PBS / crystallization temperature (°C)	81.3	82.0	82.4	77.9
	PBS / crystallization time (minute)	225.5	224.4	224.1	228.4
	PBS / crystallization heat amount (mJ/mg)	-59.6	-58.1	-57.5	-51.8
DSC / second heating process	PBS melting temperature (°C)	112.6	112.6	112.5	112.2
	PBS melting heat amount (mJ/mg)	73.8	62.1	66.0	64.3
Non-woven fabric	Specific volume (cm3/g) (2.96 cN/cm3 load)	The conjugate fiber has poor card passing properties, and thus a non-woven fabric cannot be produced.	58.9	62.3	57.8
	Specific volume (cm3/g) (19.6 cN/cm3 load)		19.2	20.1	17.1
	Basis weight (g/m2) / MD		38.9	37.9	40.0
	Basis weight (g/m2) / CD		38.9	40.0	38.9
	MD bending resistance (mN·mm)		114.7	92.1	198.1
	CD bending resistance (mN·mm)		43.7	43.3	58.2

Table 4

Ex.		13	14	15	16	17	18
Composition	PLA type	A
	Nucleating agent type	E
	Nucleating agent blend amount (mass%)	0.125
	Conjugate ratio (mass ratio) core: sheath	58:42	58:42	58:42	58:42	50:50	42:58
Spinning conditions	PLA melt extrusion temperature (°C)	230	225	220	220	220	220
	PBS melt extrusion temperature (°C)	235	235	235	235	235	235
Undrawn yarn	Fineness (dtex)	4.32	4.53	4.81	4.35	5.2	5.14
Drawing Conditions	Vmax (fold)	2.25	2.3	2.2	2.7	3	3
	Drawing ratio (fold)	2	2	2	2.2	2.3	2.5
	First drawing ratio (fold)	2	2	2	2.2	2.3	2.5
	Second drawing ratio (fold)	1	1	1	1	1	1
	First drawing tank temperature (°C)	75	75	70	75	75	75
	Second drawing tank temperature (°C)	85	85	85	85	85	85
Drawn yarn	Fineness (dtex)	2.26	2.63	2.56	2.54	2.62	2.49
	Strength (cN/dtex)	2.5	2.32	2.5	2.16	2.02	1.9
	Elongation (%)	33.6	38.9	38.3	43.15	40.87	43.36
	Young's modulus (cN/dtex)	28.47	26.98	32.17	18.18	19.38	20.76
	Percentage of crimp (%)	9	8.9	Not measured	8.8	11.7	10.7
DSC / first heating process	PBS melting temperature (°C)	115.1	115.3	116.0	115.2	115.3	115.3
	PBS melting heat amount (mJ/mg)	68.3	65.1	61.1	66.8	61.7	63.3
	(Low temperature) PLA melting temperature (°C)	171.0	170.3	171.5	170.4	171.0	171.1
	(High temperature) PLA melting temperature (°C)	174.9	172.3	173.8	None	None	None
	PLA melting heat amount (mJ/mg)	60.7	57.4	54.8	60.2	59.9	61.0
	Peak height / half width	4.6	5.3	6.3	7.0	6.5	6.3
DSC/ cooling process (crystal)	PBS / crystallization temperature (°C)	83.4	90.6	84.3	86.2	81.9	82.5
	PBS / crystallization time (minute)	222.2	214.8	221.4	219.5	223.7	223.2
	PBS / crystallization heat amount (mJ/mg)	-65.6	-63.3	-58.9	-62.3	-59.7	-59.8
DSC/ second heating process	PBS melting temperature (°C)	112.8	113.1	112.6	112.8	113.1	113.2
	PBS melting heat amount (mJ/mg)	64.8	50.2	58.2	59.0	64.1	65.1
Non-woven fabric	Specific volume (cm3/g) (2.96 cN/cm3 load)	68.4	73.1	Not measured	62.0	43.7	39.4
	Specific volume (cm3/g) (19.6 cN/cm3 load)	21.4	27.0	Not measured	21.2	18.1	15.9
	Basis weight (g/m2) / MD	40.0	38.9	Not measured	40.5	38.5	39.2
	Basis weight (g/m2) / CD	40.0	40.0	Not measured	40.0	38.9	38.9
	MD bending resistance (mN·mm)	111.9	100.2	Not measured	115.8	130.2	160.1
	CD bending resistance (mN·mm)	39.4	39.2	Not measured	37.7	38.0	45.1

Table 5

	Ex. 2	Ex. 13	Ex. 14
Basis weight of non-woven fabric (g/m2)	41.2	39.9	40.8
Decreasing rate of tensile strength (%)	43.2	25.4	18.4

[0069] FIGS. 1 and 2 show DSC curves of the conjugate fiber of Example 8. The conjugate fiber of Example 8 contains calcium stearate.

[0070] As is clear from Tables 1 to 4 above, in the case of the conjugate fibers of the examples, the crystallization temperature of the second component during the cooling process was 78°C or higher and the melting heat amount per unit mass of the second component during the second heating process was 73.5 mJ/mg or less in the DSC curve.

[0071] The non-woven fabrics of Examples 1 to 5 and 11 to 18 having a basis weight of about 40 g/m² obtained using these conjugate fibers had an MD bending resistance of 250 mN·mm or less, and had excellent flexibility and voluminousness. The non-woven fabrics of Examples 6 to 10 having a basis weight of about 20 g/m² had an MD bending resistance of 100 mN·mm or less, and had excellent flexibility and voluminousness.

[0072] The non-woven fabrics of the examples had a specific volume of 20 cm³/g or more at a load of 2.96 N/cm³ and had a large initial volume. They had a specific volume of 10 cm³/g or more at a load of 19.6 N/cm³g and had favorable volume retaining properties.

[0073] In the case of the conjugate fiber of Comparative Example 1, the melting heat amount per unit mass of the second component during the second heating process exceeded 73.5 mJ/mg in the DSC curve. The conjugate fiber had poor card passing properties, and thus a non-woven fabric could not be obtained.

[0074] In the case of the conjugate fiber of Comparative Example 2, the crystallization temperature of the second component (PBS) during the cooling process was lower than 78.0°C in the DSC curve of the conjugate fiber. Spinning draft occurred due to the low crystallization temperature, and thus undrawn yarn with high orientation was obtained. Accordingly, the extensibility was low, and a sufficient amount of crystals were not formed in the fiber. Therefore, the texture of the non-woven fabric was prone to be hard compared with Examples 11 and 12 in which the heat treatment conditions for the production of a non-woven fabric were the same as those in Comparative Example 2.

[0075] As is clear from Table 5 above, in the case of non-woven fabrics produced using the fibers of Examples 2, 13, and 14 in an amount of 100 mass%, the decreasing rate of the tensile strength of the non-woven fabric after the water resistance and heat resistance test was 50% or less, and it can be said that these non-woven fabrics had water resistance and heat resistance. In particular, in the case where calcium stearate serving as a nucleating agent was blended in the second component, excellent water resistance and heat resistance were exhibited. Accordingly, biodegradability can be controlled by adding a nucleating agent to the second component, and furthermore, crystallinity is made uniform by using a fatty acid metal salt, which contributes to water resistance and heat resistance.

[0076] The present invention includes at least embodiments below.

[1] A conjugate fiber including:

a first component containing poly-L-lactic acid with an optical purity of 95% or more; and

a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid,

wherein the second component occupies 50% or more of a surface of the conjugate fiber, and

a crystallization temperature of the second component during a cooling process is 78°C or higher and a melting heat amount per unit mass of the second component during a second heating process is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[2] The conjugate fiber according to [1], wherein a melting heat amount per unit mass of the second component during a first heating process is 68.0 mJ/mg or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[3] The conjugate fiber according to [1] or [2], wherein a crystallization heat amount per unit mass of the second component during the cooling process is 59.5 mJ/mg or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[4] The conjugate fiber according to any one of [1] to [3], wherein a ratio between a peak height and a half width of the first component during a first heating process is 11.0 or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[5] The conjugate fiber according to any one of [1] to [4], wherein a melting heat amount per unit mass of the first component during a first heating process is 30.0 mJ/mg or more in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

[6] The conjugate fiber according to any one of [1] to [5], wherein the aliphatic polyester is polybutylene succinate and/or a copolymer of polybutylene succinate.

[7] The conjugate fiber according to any one of [1] to [6], wherein the second component contains a nucleating agent.

[8] The conjugate fiber according to [7], wherein the second component contains the nucleating agent in an amount of 0.01 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the aliphatic polyester.

[9] The conjugate fiber according to [7], wherein the nucleating agent is a fatty acid metal salt.

[10] The conjugate fiber according to [9], including the fatty acid metal salt in an amount of 0.01 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the aliphatic polyester.

[11] A method for producing the conjugate fiber according to any one of [1] to [10], including:

a step of preparing a first component containing poly-L-lactic acid with an optical purity of 95% or more in an amount of 70 mass% or more, and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid in an amount of 70 mass% or more;

a step of producing a spun filament by melt spinning the first component and the second component; and

a step of drawing the spun filament to obtain a conjugate fiber in which the second component occupies 50% or more of a surface of the conjugate fiber,

wherein, in the step of producing a spun filament, the first component is melt extruded at a temperature lower than the second component, and

in the drawing step, a drawing temperature is 55°C or higher and 90°C or lower, and a drawing ratio is 1.4-fold or more.

[12] A fiber structure including the conjugate fiber according to any one of [1] to [10] in an amount of 5 mass% or more.

Industrial Applicability

[0077] The conjugate fiber of the present invention is suitable for a non-woven fabric having excellent voluminousness and flexibility, and the non-woven fabric produced using this conjugate fiber can be used for, for example, hygienic materials for diapers, sanitary napkin members, and the like, filters, wipers, agricultural materials, food wrappings, garbage bags, and automobile materials.

Claims

1. A conjugate fiber comprising:

a first component containing poly-L-lactic acid with an optical purity of 95% or more; and

a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid,

wherein the second component occupies 50% or more of a surface of the conjugate fiber, and

a crystallization temperature of the second component during a cooling process is 78°C or higher and a melting heat amount per unit mass of the second component during a second heating process is 73.5 mJ/mg or less in a DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

2. The conjugate fiber according to claim 1,
wherein a melting heat amount per unit mass of the second component during a first heating process is 68.0 mJ/mg or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

3. The conjugate fiber according to claim 1 or 2,
wherein a crystallization heat amount per unit mass of the second component during the cooling process is 59.5 mJ/mg or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

4. The conjugate fiber according to any one of claims 1 to 3,
wherein a ratio between a peak height and a half width of the first component during a first heating process is 11.0 or less in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

5. The conjugate fiber according to any one of claims 1 to 4,
wherein a melting heat amount per unit mass of the first component during a first heating process is 30.0 mJ/mg or more in the DSC curve obtained through differential scanning calorimetry (DSC) performed on the conjugate fiber.

6. The conjugate fiber according to any one of claims 1 to 5,
wherein the aliphatic polyester is polybutylene succinate and/or a copolymer of polybutylene succinate.

7. The conjugate fiber according to any one of claims 1 to 6,
wherein the second component contains a nucleating agent.

8. The conjugate fiber according to claim 7,
wherein the second component contains the nucleating agent in an amount of 0.01 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the aliphatic polyester.

9. The conjugate fiber according to claim 7,
wherein the nucleating agent is a fatty acid metal salt.

10. The conjugate fiber according to claim 9,
wherein the second component contains the fatty acid metal salt in an amount of 0.01 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the aliphatic polyester.

11. A method for producing the conjugate fiber according to any one of claims 1 to 10, comprising:

a step of preparing a first component containing poly-L-lactic acid with an optical purity of 95% or more in an amount of 70 mass% or more, and a second component containing an aliphatic polyester composed of glycol and dicarboxylic acid in an amount of 70 mass% or more;

a step of producing a spun filament by melt spinning the first component and the second component; and

a step of drawing the spun filament to obtain a conjugate fiber in which the second component occupies 50% or more of a surface of the conjugate fiber,

wherein, in the step of producing a spun filament, the first component is melt extruded at a temperature lower than the second component, and

in the drawing step, a drawing temperature is 55°C or higher and 90°C or lower, and a drawing ratio is 1.4-fold or more.

12. A fiber structure comprising the conjugate fiber according to any one of claims 1 to 10 in an amount of 5 mass% or more.

Drawing