Core sheath composite fiber and method of manufacturing the same and fiber structure

Abstract

The present invention provides a core-sheath composite fiber, a method for manufacturing the same, and a fiber structure. The core-sheath composite fiber comprises a core component (12) comprising a melt-anisotropic aromatic polyester (A polymer) and a sheath component comprising a flexible thermoplastic polymer (B polymer) and a melt-anisotropic aromatic polyester (C polymer). The B polymer forms a sea component, the C polymer forms a sea component, and the fiber structure has a plurality of sea sections (18) formed by the sea component dispersed within a sea section (14) formed by the sea component.

Description

Technology Field

[0001] The present application claims priority to Japanese Patent Application No. 2021-34707 filed in Japan on March 4, 2021, and incorporates the entirety thereof by reference as part of the present application.

[0002] The present invention relates to a core-sheath composite fiber having a melt-anisotropic aromatic polyester as a core component, improved fibrill resistance and excellent wear resistance, a method for manufacturing the same, and a fiber structure. Background Technology

[0003] Although it is known that melt-anisotropic aromatic polyester fibers possess high strength and high modulus of elasticity, there was a problem in that these fibers easily fibrillated by abrasion because their molecular chains are highly oriented along the fiber axis. Therefore, a composite fiber has been proposed that suppresses fibrillation by using melt-anisotropic aromatic polyester as a core component while coating the surroundings with a sheath component.

[0004] For example, Patent Document 1 (Japanese Published Patent Application No. 2002-20932) discloses a composite fiber characterized in that the core component is a melt anisotropic aromatic polyester (A), the sheath component is a flexible polyester (B) containing 0 to 10% of the polymer (A), and the intrinsic viscosity [η] of the polyester (B) is 0.65 dl / g or higher.

[0005] Patent Document 1 describes that by blending a polymer identical to the core component into the wax component, the strength of the wax component is increased and the adhesion to the core component is increased.

[0006] Patent Document 2 (Japanese Published Patent Application No. 2008-255535) discloses a core-sheath composite fiber that satisfies the following conditions: the core component is composed of a molten anisotropic aromatic polyester (A polymer), the sheath component has a sea island structure, and the sheath component ratio is 0.2 to 0.7; the sea component constituting the sheath component is composed of a flexible thermoplastic polymer (B polymer), the island component is composed of a molten anisotropic aromatic polyester (C polymer), and the island component ratio in the sheath component is 0 to 0.25; wherein 0.03 to 2.5 mass% of inorganic fine particles mainly composed of a silicate compound are attached to the surface of the fiber.

[0007] In Patent Document 2, it is described that since polymers that do not have melt anisotropy have low adhesion to melt anisotropic polyesters and are prone to peeling, the initial component is formed as a blend consisting of melt anisotropic polyesters and polymers that do not have melt anisotropy. Prior art literature

[0008] Japanese Published Patent Application No. 2002-20932 Japanese Published Patent Application No. 2008-255535 The problem to be solved

[0009] However, Patent Document 1 rejects increasing the proportion of melt anisotropic aromatic polyester in the initial component because when the proportion of melt anisotropic aromatic polyester in the initial component exceeds 10%, irregularities occur on the fiber surface and spinnability deteriorates.

[0010] In addition, the composite fiber described in Patent Document 2 is described as being able to suppress inter-fiber adhesion and improve fiber disintegration by attaching 0.03 to 2.5 mass% of inorganic fine particles, mainly composed of silicate compounds, to the fiber surface, but regarding the suppression of fiber fibrillation, it is only mentioned that resistance to fibrillation and wear resistance are greatly improved by using a flexible thermoplastic polymer as a disintegration component.

[0011] If a large amount of melted anisotropic polyester can be incorporated into the sheath component of a core-sheath composite fiber, in which melted anisotropic polyester serves as the core component and the surrounding area is coated with a sheath component, without impairing spinnability, the adhesion between the core and the sheath can be made stronger, thereby suppressing sheath delamination and enabling the realization of wear resistance higher than conventional methods. Furthermore, for the same reason, the sheath can be made thinner, and as a result, it is desirable to increase strength derived from the melted anisotropic polyester on the core side.

[0012] Accordingly, the objective of the present invention is to provide a core sheath composite fiber with excellent wear resistance, while increasing the proportion of melt-anisotropic aromatic polyester in the sheath component of the core sheath composite fiber, and at the same time suppressing fibrillation or spinnable deterioration. means of solving the problem

[0013] The inventors of the present invention, as a result of careful consideration to achieve the above objective, found that in a core-sheath composite fiber having a melt-anisotropic aromatic polyester as a core component, (I) if the sheath component is made into a sea-island structure having a sea-island structure made of melt-anisotropic aromatic polyester and the proportion of melt-anisotropic aromatic polyester in the sea-island structure is increased, sheath delamination is prevented by improving the adhesion between the core and the sheath, and the sheath can be made thinner while increasing abrasion resistance and increasing strength derived from the melt-anisotropic aromatic polyester of the core component, (II) on the other hand, the spinning state deteriorates significantly and the sheath component becomes fibrillated due to the high proportion of melt-anisotropic aromatic polyester, and thus made it a new task to improve the spinning state and suppress fibrillation of the sheath component. In addition, (III) by increasing the proportion of molten anisotropic aromatic polyester in the core component and kneading the core component at a specific temperature, and taking out the extruded yarn at a specific draft value, the shape of the core component can be controlled by finely dispersing the core component made of molten anisotropic aromatic polyester with respect to the core component, and as a result, even when the proportion of molten anisotropic aromatic polyester in the core component is high, the fibrillation of the core composite fiber can be suppressed while maintaining a good spinning state, and the wear resistance can be improved even when the core is thinned, thus completing the present invention.

[0014] That is, the present invention may be configured in the following embodiments.

[0015] [Mode 1]

[0016] A core-sheath composite fiber having a sea-island structure in which a core component comprises a melt-anisotropic aromatic polyester (A polymer), a sheath component comprises a flexible thermoplastic polymer (B polymer) and a melt-anisotropic aromatic polyester (C polymer), wherein the B polymer forms a sea component and the C polymer forms a sea component, and a plurality of sea sections formed of the sea component are dispersed within the sea section formed of the sea component.

[0017] The proportion of the do component in the above-mentioned initial component exceeds 10 weight%, and also,

[0018] In a cross-section obtained by cutting this core sheath composite fiber in the fiber length direction, the maximum width (W) of the portion having the greatest width in the fiber vertical direction is 0.65 μm or less (preferably 0.60 μm or less, more preferably 0.55 μm or less, even more preferably 0.50 μm or less), and

[0019] A core sheath composite fiber having the above-mentioned maximum width (W), wherein, in the portion having the above-mentioned maximum width (W), the ratio (L1 / W) of the maximum width (W) of the maximum length of the inclination length (L1) of the portion that overlaps with the diagonal line among the portions that are tangent to the diagonal line in the above-mentioned sheath component, which extends at a predetermined angle of 10° with respect to the above-mentioned fiber length direction from one end to the other end in the fiber length direction, is 5.0 or more (preferably 5.1 or more, more preferably 5.2 or more, even more preferably 5.3 or more, and even more preferably 5.5 or more).

[0020] [Mode 2]

[0021] A core sheath composite fiber as described in Embodiment 1, wherein the maximum length (L1) of the inclination length is 1.0 μm or more (preferably 1.3 μm or more, more preferably 1.5 μm or more, even more preferably 1.7 μm or more).

[0022] [Mode 3]

[0023] A core sheath composite fiber as described in Embodiment 1 or 2, wherein, in a cross-section obtained by cutting the core sheath composite fiber in the fiber length direction, the fiber length (L2) of the sheath component in the fiber length direction is 450 to 1000 μm (preferably 500 to 800 μm, more preferably 550 to 650 μm).

[0024] [Mode 4]

[0025] A core sheath composite fiber as described in any one of embodiments 1 to 3, wherein the thickness of the sheath component is 0.8 to 5.0 μm (preferably 0.9 to 4.0 μm, more preferably 0.9 to 3.8 μm).

[0026] [Mode 5]

[0027] A core sheath composite fiber as described in any one of embodiments 1 to 4, wherein the polymer A and the polymer C are homogeneous melt anisotropic aromatic polyesters.

[0028] [Mode 6]

[0029] A core-sheath composite fiber as described in any one of embodiments 1 to 5, wherein the weight ratio of the core component to the sheath component, the core component / sheath component, is 20 / 80 to 97 / 3 (preferably 50 / 50 to 96 / 4, more preferably 60 / 40 to 95 / 5, even more preferably 70 / 30 to 94 / 6, even more preferably 75 / 25 to 93 / 7, particularly preferably 80 / 20 to 92 / 8, most preferably 82.5 / 17.5 to 90 / 10).

[0030] [Mode 7]

[0031] A heart sheath composite fiber as described in any one of embodiments 1 to 6, wherein the monofilament fineness of the heart sheath composite fiber is 1 to 120 dtex (preferably 2 to 60 dtex, more preferably 2.5 to 30 dtex, even more preferably 3 to 15 dtex).

[0032] [Mode 8]

[0033] A method for manufacturing a core-sheath composite fiber having a sea-island structure in which a core component comprises a melt-anisotropic aromatic polyester (A polymer), a sheath component comprises a flexible thermoplastic polymer (B polymer) and a melt-anisotropic aromatic polyester (C polymer), wherein the B polymer forms a sea component and the C polymer forms a sea component, and a plurality of sea sections formed of the sea component are dispersed within the sea section formed of the sea component.

[0034] A mixing process in which the polymer B and polymer C used for the above-mentioned initial component are mixed using a twin-screw extruder at a temperature of (Mb) °C or higher relative to the melting point (Mb) of polymer B and (Mc - 20) °C or higher relative to the melting point (Mc) of polymer C, but lower than (Mc) °C, and polymer A used for the above-mentioned core component is melted and mixed using an extruder different from the twin-screw extruder used for the above-mentioned initial component; and an extrusion process in which the initial component and core component, respectively mixed in this mixing process, are combined and extruded to obtain discharged sand;

[0035] A method for manufacturing a core sheath composite fiber comprising at least a process of taking out the discharged yarn with a draft value of 13 to 50 (preferably 15 to 45, more preferably 16 to 40, even more preferably 19 to 38, particularly preferably 20 to 35), which is the ratio of the winding speed to the discharge speed.

[0036] [Mode 9]

[0037] A method for manufacturing a core sheath composite fiber as described in Embodiment 8, comprising a heat treatment process for performing heat treatment on the fiber obtained in the extrusion process.

[0038] [Mode 10]

[0039] A fiber structure comprising at least a portion of the heart sheath composite fiber described in any one of embodiments 1 to 7.

[0040] In this specification, "a cross-section obtained by cutting a core sheath composite fiber in the fiber length direction" is equivalent to a cross-section obtained by cutting a core sheath composite fiber in a plane including the fiber length direction, and may be referred to as "fiber longitudinal cross-section" below. Also, "fiber perpendicular direction" means a direction orthogonal to the fiber length direction (or a direction perpendicular to the fiber length direction) in the fiber longitudinal cross-section.

[0041] Additionally, any combination of at least two components disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention. Effects of the invention

[0042] According to the core-sheath composite fiber of the present invention, in a core-sheath composite fiber having a melt-anisotropic aromatic polyester as the core component and a sheath component having a sea-island structure, even if the proportion of the sheath component is increased as a melt-anisotropic aromatic polyester, the aggregation of the sheath component during spinning is suppressed by finely dispersing the sheath component, thereby improving the fibrill resistance of the core-sheath composite fiber and obtaining a fiber with excellent abrasion resistance. Brief explanation of the drawing

[0043] The invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description purposes only and are not intended to define the scope of the invention. The scope of the invention is defined by the appended claims. In the accompanying drawings, the same part number in a plurality of drawings indicates the same part. FIG. 1A is a schematic perspective view of a heart sheath composite fiber related to one embodiment of the present invention. FIG. 1B is a schematic cross-sectional view of a concentric sheath composite fiber cut along the fiber length direction. Figure 2 is an enlarged schematic cross-sectional view showing a partially enlarged sheath component of a concentric sheath composite fiber. FIG. 3 is a schematic cross-sectional view of a concentric sheath composite fiber cut in a plane perpendicular to the fiber length direction. Figure 4 is a schematic cross-sectional view showing the structure of a die used for spinning concentric sheath composite fibers. Specific details for implementing the invention

[0044] The present invention will be described in detail below based on examples. One embodiment of the present invention is a core-sheath composite fiber comprising a core component and a sheath component covering the core component, wherein the sheath component has a sea-island structure comprising a sea component and a sea-island component. The core component comprises a melt-anisotropic aromatic polyester (A polymer), and the sheath component comprises a flexible thermoplastic polymer (B polymer) and a melt-anisotropic aromatic polyester (C polymer), wherein the B polymer forms the sea component and the C polymer forms the sea component.

[0045] (Heart component)

[0046] A melt anisotropic aromatic polyester (Polymer A) used as a core component is a polymer that exhibits optical anisotropy (liquid crystallization) in the molten phase. For example, whether a sample is a melt anisotropic aromatic polyester can be confirmed by placing the sample on a hot stage, heating it under a nitrogen atmosphere, and observing the transmitted light of the sample. The melt anisotropic aromatic polyester of the present invention is composed of repeating constituent units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and as long as the effect of the present invention is not impaired, the constituent units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in their chemical composition. Furthermore, within a range that does not impede the effect of the present invention, the melt anisotropic aromatic polyester may include constituent units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids. For example, desirable constituent units can be given as shown in Table 1.

[0047]

[0048] In the constituent units of Table 1, m is an integer from 0 to 2, and Y in the formula may be, independently, a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc., alkyl groups having 1 to 4 carbon atoms), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group [benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.], an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.).

[0049] More preferred constituent units include the constituent units described in examples (1) to (18) shown in Tables 2, 3, and 4 below. In addition, if a constituent unit in the formula is a constituent unit capable of representing multiple structures, two or more such constituent units may be combined and used as constituent units for the polymer.

[0050]

[0051]

[0052]

[0053] In the constituent units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each constituent unit n = 1, n = 2 may exist alone or in combination, and Y1 and Y2 may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a 1 to 4 C alkyl group such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group [benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.], an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.). Among these, hydrogen atoms, chlorine atoms, bromine atoms, or methyl groups are preferred.

[0054] Also, Z can be a substituent represented by the following formula.

[0055] [Chemical Formula 1]

[0056]

[0057] The melt anisotropic aromatic polyester may preferably be a combination having a naphthalene backbone as a constituent unit. In addition, it is particularly preferable to include both a constituent unit (A) derived from hydroxybenzoic acid (abbreviation: HBA) and a constituent unit (B) derived from hydroxynaphthoic acid (abbreviation: HNA). For example, the following formula (A) may be used as the constituent unit (A) and the following formula (B) may be used as the constituent unit (B). In terms of improving melt moldability, the ratio of constituent unit (A) to constituent unit (B) may preferably be in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and even more preferably 5 / 1 to 1 / 1.

[0058] [Chemical Formula 2]

[0059]

[0060] [Chemical Formula 3]

[0061]

[0062] In addition, the sum of the constituent units of (A) and (B) may, for example, be 65 mol% or more with respect to the total constituent units, more preferably 70 mol% or more, and even more preferably 80 mol% or more. Among the polymers, a melt anisotropic aromatic polyester in which the constituent units of (B) are 4 to 45 mol% is particularly preferred.

[0063] The melting point of the melted anisotropic aromatic polyester preferably used in the present invention is preferably in the range of 250 to 360 ℃, and more preferably 260 to 320 ℃. The melting point referred to here is measured by a test method in accordance with JIS K 7121 and is the peak temperature of the main endothermic peak observed by a differential scanning calorimeter (e.g., Shimadzu Corporation DSC).

[0064] In addition, thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyetheretherketone, and fluoropolymer may be added to the above-mentioned melted anisotropic aromatic polyester to the extent that it does not impede the effects of the present invention. Furthermore, it may contain various additives such as inorganic materials such as titanium oxide, kaolin, silica, and barium oxide, carbon black, coloring agents such as dyes or pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

[0065] (First component)

[0066] The primary component has a seabed structure, a flexible thermoplastic polymer (B polymer) forms the seabed component, and a melt-anisotropic aromatic polyester (C polymer) forms the island component.

[0067] Examples of flexible thermoplastic polymers (B polymers) forming the components include polymers that do not have aromatic rings on the main chain, or polymers that have aromatic rings on the main chain and have four or more atoms on the main chain between the aromatic rings. Specifically, examples include polyolefins; polyamides; polycarbonates; polyphenylene sulfide (abbreviated: PPS); polyesters such as polyethylene terephthalate, modified polyethylene terephthalate, amorphous polyarylate, and polyethylene naphthalate (abbreviated: PEN); polyetheretherketones; fluoropolymers, etc. These flexible thermoplastic polymers may be used alone or in combination of two or more types, or one may be the main thermoplastic polymer (e.g., accounting for 80 weight% or more) and the others added thereto. Among these, it is preferable that PPS or PEN be the main thermoplastic polymers.

[0068] In addition, flexible thermoplastic polymers may contain various additives such as inorganic materials such as titanium oxide, silica, and barium oxide, coloring agents such as carbon black, dyes or pigments, antioxidants, ultraviolet absorbers, light stabilizers, and nucleating agents.

[0069] The melt anisotropic aromatic polyester (C polymer) forming the component may be the melt anisotropic aromatic polyester described in the above A polymer, and may be the same as or different from the A polymer, but from the perspective of affinity, it is preferable that it be a melt anisotropic aromatic polyester with the same main constituent unit. In addition, the A polymer and the C polymer may be polymers of the same type that have the same main constituent unit, and, for example, only differ in the added thermoplastic polymer or additive.

[0070] Also, the melting point (Mc) of the C polymer can be appropriately selected within a range where the C polymer is finely dispersed with respect to the B polymer, for example, the melting point (Mc) of the C polymer may be in the range of (Mb - 10) to (Mb + 80) °C with respect to the melting point (Mb) of the B polymer, or may be in the range of Mb to (Mb + 70) °C.

[0071] In addition, the melt viscosity η of the C polymer may be, for example, 10 to 60 Pa·s from the perspective of spinnability, preferably 20 to 50 Pa·s, and more preferably 25 to 45 Pa·s.

[0072] In addition, the melt viscosity η referred to in the present invention is defined as follows: temperature T (T = (Mc + 10) ℃ if the melting point (Mc) of the C polymer is 290 ℃ or higher, and T = 300 ℃ if the melting point Mc is less than 290 ℃), and a shear rate of 1000 sec. -1 It is the melt viscosity measured at.

[0073] (Method for manufacturing heart core composite fibers)

[0074] The core sheath composite fiber of the present invention can be manufactured by a manufacturing method comprising at least a kneading process and an extrusion process. The manufacturing process may additionally include a heat treatment process.

[0075] In the mixing process, the above B polymer and the above C polymer used for the initial component are melted and mixed using a twin-screw extruder, and the A polymer used for the core component is melted and mixed using an extruder different from the twin-screw extruder used for the initial component.

[0076] In particular, in a twin-screw extruder used for mixing B polymer and C polymer, the set temperature of the mixing section in the twin-screw extruder is set to be (Mb) °C or higher with respect to the melting point (Mb) of B polymer and (Mc - 20) °C or higher with respect to the melting point (Mc) of C polymer and (Mc) °C or lower, and by the rotation of a parallel twin-screw supported to rotate freely in the mixing section, it is possible to achieve fine dispersion of multiple particles in the initial components.

[0077] In addition, the extruder used to melt and knead the above-mentioned polymer A used in the core component may be a single-screw extruder or a twin-screw extruder. Also, when using raw materials in which polymer B and polymer C have been compounded under the above conditions in advance, since it is possible to achieve fine dispersion of multiple parts within the core component, the extruder used for melting and kneading the core component may be a single-screw extruder or a twin-screw extruder.

[0078] In the mixing process, the ratio of core components to sheath components may be, for example, 20 / 80 to 97 / 3, preferably 50 / 50 to 96 / 4, more preferably 60 / 40 to 95 / 5, even more preferably 70 / 30 to 94 / 6, even more preferably 75 / 25 to 93 / 7, particularly preferably 80 / 20 to 92 / 8, and most preferably 82.5 / 17.5 to 90 / 10, from the perspective of promoting the improvement of fibrillation and suppressing the exposure of core components. In particular, it is desirable that the core component is 50% or more, as this can improve the strength of the composite fiber. The weight ratio of core components to sheath components can be determined, for example, by the weight ratio of core components and sheath components fed into each extruder described below during manufacturing.

[0079] The proportion of the peach component in the base component may exceed 10 weight%, preferably 15 weight% or more, and more preferably 20 weight% or more. By increasing the proportion of the peach component, the anchoring effect between the core component and the base component by the peach component can be strengthened. On the other hand, if the proportion of the peach component is excessively high, the likelihood of the peach component aggregating increases, so the peach component may be 40 weight% or less, and preferably 35 weight% or less.

[0080] In the extrusion process, the core and core components, which are each mixed in the mixing process, can be combined and extruded from a die with a structure shown in Fig. 4, for example, to produce a core-sheath composite fiber with a circular cross-section (fiber cross-section).

[0081] The die temperature (spinning temperature) at the time of extrusion may be, for example, (Ma + 10) to (Ma + 60) ℃ with respect to the melting point (Ma) of polymer A, preferably (Ma + 15) to (Ma + 40) ℃, and more preferably (Ma + 20) to (Ma + 35) ℃.

[0082] The shape of the undispersed yarn is controlled by a draft value, and the discharged yarn may be drawn with a draft value of 13 to 50, preferably 15 to 45, more preferably 16 to 40, even more preferably 19 to 38, and particularly preferably 20 to 35. In addition, discharged yarn refers to a yarn that is discharged from a nozzle hole and has not been stretched, that is, a yarn having a fiber diameter approximately equal to the diameter of the nozzle hole, and the draft value refers to the ratio of the winding speed to the discharge speed during spinning.

[0083] Additionally, heat treatment may be performed on the spun fibers. By heat treatment, not only can the degree of orientation crystallization of the B polymer in the core component be increased, but the melt-anisotropic aromatic polyester can also be polymerized in the solid state, thereby improving the strength of the core-sheath composite fiber.

[0084] In the heat treatment, the spun fibers may be heat-treated under atmospheric pressure or reduced pressure in an inert gas atmosphere such as nitrogen, or in an oxygen-containing active gas atmosphere (e.g., air).

[0085] When performing heat treatment, the heat treatment atmosphere is preferably a low-humidity gas with a dew point of -50°C or lower, preferably -60°C or lower, and more preferably -70°C or lower. As for the heat treatment conditions, a temperature pattern can be provided in which the temperature is sequentially increased from (Ma - 20)°C or lower, preferably (Ma - 30)°C or lower, and more preferably (Ma - 40)°C or lower, with respect to the melting point (Ma) of polymer A, up to the melting point of the supercomponent.

[0086] Methods of heat supply include using a gaseous medium, utilizing radiation via heating plates or infrared heaters, and internal heating methods using high frequency. The processing configuration may be roll-to-roll continuous production, coil form, toe form, or batch production by rewinding spun yarn onto a heat treatment bobbin.

[0087] In order to prevent excessive delamination caused by interlocking of the fibers after heat treatment, inorganic fine particles may be applied to the surface of the fibers during or after spinning, or before heat treatment, if necessary. It is preferable that the inorganic fine particles have silicate compounds, including talc and mica, as the main component.

[0088] Unlike Patent Document 2, the present invention has good disintegration properties even without attaching inorganic fine particles, but attachment of inorganic fine particles may be performed to further improve disintegration properties.

[0089] By uniformly attaching inorganic fine particles to the surface of the fibers during or after spinning and before heat treatment, direct contact between the fibers is prevented, thereby avoiding the entanglement of the fibers. In addition, most of the inorganic fine particles, which are mainly composed of silicate compounds, are inert, and even when attached to the fibers, no deterioration in the physical properties of the fibers is observed.

[0090] The method of attaching the above-mentioned inorganic fine particles to the surface of the fiber is not limited at all as long as it is a method of uniformly attaching to the fiber. For example, a method of attaching the inorganic fine particles, which have been stirred and dispersed in a spinning lubricant, using an oiling roller or an ogre is simple and desirable.

[0091] The average particle size of the inorganic fine particles attached to the surface of the core sheath composite fiber may be, for example, in the range of 0.01 to 10 μm, preferably 0.02 to 5 μm, in terms of uniform attachment to the fiber surface. The amount of inorganic fine particles attached to the surface of the core sheath composite fiber may be in the range of 0.03 to 2.5 mass%, preferably 0.1 to 2.3 mass%.

[0092] (Epicanthoplastic complex fibers)

[0093] FIG. 1A is a schematic perspective view of a core sheath composite fiber related to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of a core sheath composite fiber cut along the fiber length direction. The core sheath composite fiber (10) has a core (12) formed of a core component and a sheath (14) formed of a sheath component.

[0094] FIG. 2 is an enlarged cross-sectional view showing a partial enlargement of Part II of FIG. 1B. As shown in FIG. 1B and FIG. 2, in a cross-section (fiber longitudinal section) in which a core sheath composite fiber is cut along the fiber length direction including the fiber central axis, the sheath (14) forms a sea-island structure and forms a plurality of sea-islands (18) within the sea-island (16). The sea-islands are undispersed within the sea-island, and the shape of the sea-islands is controlled.

[0095] In the core sheath composite fiber of the present invention, the proportion of the fiber component among the sea component is increased and the fiber portion is finely dispersed, thereby strengthening the anchoring ability of the sheath portion to the core portion through a large number of fiber portions and suppressing sheath peeling, as well as suppressing fibrillation of the sheath portion.

[0096] The ridges, while undispersed, are basically extended along the fiber length in an approximately elliptical shape. If the diameter of the ridges is large, the irregularities originating from the ridge components on the fiber surface become larger. Since the formation of fibrils originates from the size of these irregularities on the fiber surface, it is desirable for the maximum diameter of the ridges to be small. Furthermore, it is desirable for the ridges to have a shape that extends long along the fiber length, as this allows for the exertion of an anchoring effect. In other words, simply measuring the diameter of the ridges in a single fiber cross-section does not account for the contribution of the anchoring effect caused by the length of the ridges; however, by observing the shape of the ridges along the length in a micrograph of the ridges and evaluating the shape of the ridges by adding not only the width but also the length of the ridges with the greatest width, fibrilability can be evaluated while incorporating the contribution of the anchoring effect of the ridges. To do so, after selecting a section having a maximum width (W), for this section, as shown in FIG. 2, the maximum length (L1) of the inclination length that overlaps with a diagonal line extending from one end of the fiber length direction toward the other end at a predetermined angle α (10°) with respect to the fiber length direction is measured, and by calculating L1 / W, it becomes possible to evaluate the shape of the section with the extension in the fiber length direction.

[0097] First, the section having the maximum width (W) can be selected from an enlarged image of the fiber cross-section. Specifically, the fiber cross-section is observed in the fiber length direction at a distance of 100 μm or more and 1000 μm or less using a scanning probe microscope (SPM) as described later, and the numerical value at the point where the length in the direction perpendicular to the fiber length direction (fiber vertical direction) of the section within the observation range is maximum is taken as the measurement value. However, the observation range does not need to be continuous and can be the sum of multiple randomly extracted fields. For example, in the observation range of the fiber cross-section, a plurality of sections with a relatively large fiber vertical length are extracted from a plurality of sections extending in the fiber length direction, and the section having the maximum width can be determined by comparing the fiber vertical length of the extracted sections as the width of the section. In this example, in the fiber cross-section, only one of the upper or lower parts of the initial component (e.g., the lower part of FIG. 1B) needs to be used as the observation range. In addition, in this example, the maximum width of the cut is determined by observing the fiber cross-section with a scanning probe microscope; however, any means other than a scanning probe microscope may be used as long as the maximum width of the cut can be determined. Furthermore, when cutting the fiber, it is preferable to fix the fiber by embedding it in resin before cutting in order to minimize the effects of stress.

[0098] The maximum width (W) of the cut may be 0.65 μm or less, preferably 0.60 μm or less, more preferably 0.55 μm, and even more preferably 0.50 μm or less. If the maximum width of the cut exceeds the upper limit value, there is a risk that the fibrill resistance will be insufficient. In addition, the maximum width (W) of the cut may be 0.07 μm or more, or 0.1 μm or more.

[0099] After selecting a section having a maximum width (W), the section is continuously observed in the longitudinal direction, and as shown in FIG. 2, the maximum length (L1) of the inclination length is measured, which overlaps with a diagonal line extending at a predetermined angle α (10°) relative to the fiber length direction from one end to the other end in the fiber length direction. When the ratio (L1 / W) of the maximum length (L1) of the inclination length to the maximum width (W) is 5.0 or higher, the core sheath composite fiber can enhance the anchoring effect by the section while suppressing fibrillation. The L1 / W value is preferably 5.1 or higher, more preferably 5.2 or higher, even more preferably 5.3 or higher, and even more preferably 5.5 or higher. There is no particular limit on the upper value of L1 / W, but it may be 10 or lower.

[0100] The maximum length (L1) of the above-mentioned slope length is a value that varies depending on the value of the maximum width (W), but, for example, it may be 1.0 μm or more, preferably 1.3 μm or more, more preferably 1.5 μm or more, and even more preferably 1.7 μm or more. When the maximum length (L1) of the slope length is greater than or equal to the above-mentioned lower limit value, the anchoring effect on the core component tends to increase. Also, the maximum length (L1) of the above-mentioned slope length may be 3.3 μm or less, preferably 3.1 μm or less, and more preferably 2.9 μm or less. When the maximum length (L1) of the slope length is less than or equal to the above-mentioned upper limit value, fibrillation tends to be suppressed.

[0101] In the fiber cross-section above, the fiber length (L2) of the section having the largest width among the shear components may be, for example, 450 to 1000 μm, preferably 500 to 800 μm, and more preferably 550 to 650 μm. The longer L2 is, the greater the anchoring effect on the core component. The fiber length of this section can be obtained from an enlarged image of the fiber cross-section. Alternatively, the fiber length of the section may be obtained using a discharge yarn and calculated as a value obtained by multiplying that value by a draft value.

[0102] The thickness of the sheath component may be, for example, 0.8 to 5.0 μm, preferably 0.9 to 4.0 μm, and more preferably 0.9 to 3.8 μm, from the perspective of preventing exposure of the core component and securing the strength of the fiber.

[0103] As shown in FIG. 3, the thickness of the sheath component can be obtained, for example, from an enlarged image of the cross-section of a core-sheath composite fiber (hereinafter referred to as the "fiber cross-section") by cutting the fiber in a plane perpendicular to the fiber length direction. Specifically, it is possible to obtain the thickness of the sheath component by capturing the fiber cross-section with a scanning microscope or the like, measuring the radial distance from the outer surface of the core component to the outer surface of the sheath component at any three points that divide the outer circumference of the fiber into three equal parts, and averaging the values. Furthermore, when cutting the fiber, it is preferable to fix the fiber by embedding it in resin and then cutting it in order to minimize the influence of stress.

[0104] The single filament fineness of the core sheath composite fiber may be, for example, 1 to 120 dtex, preferably 2 to 60 dtex, more preferably 2.5 to 30 dtex, and even more preferably 3 to 15 dtex. This single filament fineness can be measured, for example, in accordance with JIS L 1013 “Test Method for Chemical Fiber Filament Yarns”. In addition, the core sheath composite fiber may be a monofilament or a multifilament containing two or more monofilaments.

[0105] The tensile strength of the core sheath composite fiber under a 25°C atmosphere may, for example, be 10 cN / dtex or higher, preferably 13 cN / dtex or higher, more preferably 15 cN / dtex or higher, even more preferably 18 cN / dtex or higher, and even more preferably 20 cN / dtex or higher. There is no particular limit on the upper limit of the tensile strength, but it may be 30 cN / dtex or lower. Here, the tensile strength is a value measured by referring to the JIS L 1013 test method. In addition, if the core sheath composite fiber is a multifilament, considering the change in strength due to fiber alignment, one fiber may be taken from the multifilament and measured as a single filament tensile strength.

[0106] The core sheath composite fiber has excellent fibrill resistance, and for this core sheath composite fiber, the fibers under test are each passed through three comb guides alternately arranged at an angle of 120°, and a load of 1 g / dtex is applied to each fiber, and 30,000 reciprocating movements are applied at a stroke length of 3 cm and a speed of 95 times / min, and the average number of lint (average of 5 times) generated per 3 cm length of fiber may be, for example, 1 or less, and preferably 0.5 or less. Here, the lint can be observed as small lint (fibrils) of 1 mm or less, or lint larger than 1 mm, or as fiber delamination when the core sheath composite fiber is magnified 20 times with a camera.

[0107] The core sheath composite fiber of the present invention can be woven or knitted by conventional methods, and can also be dyed by conventional methods depending on the type of flexible thermoplastic polymer. For example, if the flexible polymer is a polyester-based polymer, it can be dyed by a conventional dyeing method for polyester fibers using disperse dyes.

[0108] The core sheath composite fiber of the present invention can preferably be used as various fiber structures, and the fiber structure of the present invention comprises at least a portion of the core sheath composite fiber of the present invention. Examples of fiber structures include one-dimensional structures such as ropes and blended yarns, and two-dimensional structures such as woven fabrics, knitted fabrics, and nonwoven fabrics, which are high-order processed products. The fiber structure may be composed solely of the core sheath composite fiber, or it may include other constituent members to the extent that the effects of the present invention are not impaired. After the fiber structure is formed, the fiber structure may be dyed using the dyeing method described above.

[0109] When the fiber structure is a fabric, the woven structure is not particularly limited and examples include plain weave, skein weave, satin weave, modified plain weave, modified skein weave, modified satin weave, modified weave, pattern weave, double weave, multi-layer weave, warp pile weave, weft pile weave, twisted weave, etc. Also, when the fiber structure is a knitted fabric, the knitted structure is not particularly limited and examples include circular knit, weft knit, warp knit (including tricot knit and Raschel knit), pile knit, flat knit, twill knit, rib knit, smooth knit (double-sided knit), rib knit, pearl knit, Denby weave, cord weave, atlas weave, chain weave, insert weave, etc.

[0110] Examples

[0111] The present invention will be explained in more detail below through examples, but the present invention is not limited in any way by these examples. In addition, in the following examples and comparative examples, various physical properties were measured by the following methods.

[0112] [Seomdo]

[0113] Based on the JIS L 1013:2010 8. 3. 1 A method, a core fiber composite was wound into a 100 m skein using a measuring instrument manufactured by Taiei Science Seikishu Co., Ltd., and its weight (g) was multiplied by 100 and three measurements were taken per level, and the average value of the three measurements was taken as the obtained fineness (dtex).

[0114] [tensile strength]

[0115] In accordance with JIS L 1013, five measurements were taken on one sample using the tensile strength measuring instrument “TENSORAPID5” manufactured by USTER, under conditions of a test length of 20 cm, a tensile speed of 10 cm / min, and an initial load of 0.33 g / dtex, and the average value of the five measurements was taken as the strength (cN / dtex). In addition, when the core sheath composite fiber was multifilament, one sample was taken from the multifilament to measure the single filament tensile strength.

[0116] [Thickness of the first component]

[0117] A core-sheath composite fiber was embedded in an epoxy resin, and a cross-section of the fiber was formed by cutting the embedded fiber in a plane perpendicular to the fiber length direction. In this fiber cross-section, the radial distance from the outer surface of the core to the outer surface of the sheath was measured using a microscope at any three points that divided the outer circumference of the fiber into three equal parts, and the average value was calculated and used as the thickness of the sheath component.

[0118] [Tow length, Tow maximum width]

[0119] A core sheath composite fiber was embedded in an epoxy resin, and the embedded fiber was cut along the fiber length direction using a cross-section polisher (CP) to form a cross-sectional view of the fiber. In this fiber cross-sectional view, observation was performed using a scanning probe microscope (SPM) at a depth of 100 μm or more and 1000 μm or less in the fiber length direction. Within the observation range, among a number of fibers extending along the fiber length direction, a number of fibers with a relatively large length in the fiber vertical direction were extracted, and the fiber vertical length of the extracted fibers was compared as the fiber width to determine the maximum fiber width (W) for the fiber with the largest width. Additionally, the fiber length direction (L2) was measured for the fiber with the maximum fiber width (W).

[0120] [Maximum length of slope of the ditch]

[0121] Next, for a section having a maximum width (W), the longest line segment among the lengths overlapping with a diagonal line extending at a predetermined angle α (10°) relative to the fiber length direction from one end to the other in the fiber length direction was measured as the maximum length (L1) of the inclination length of the section.

[0122] [Wear resistance]

[0123] Using a TM type bonding force tester (model TM-200) manufactured by Taiei Kagaku Seikisakusho, the fibers under test were passed through three comb guides alternately arranged at a 120° angle, and a load of 1 g / dtex was applied to each fiber. 30,000 reciprocating motions were applied at a stroke length of 3 cm and a speed of 95 revolutions / min, and the condition of the lint was checked by magnifying it 20 times with a camera. The above test was performed 5 times, and the presence or absence of lint was observed for each fiber length of 3 cm. In addition, regarding the generated lint, fine lint of 1 mm or less in length and lint larger than 1 mm in length were distinguished and evaluated according to the following criteria.

[0124] (Presence or absence of lint)

[0125] ◎ : No lint was observed in any of the 5 tests.

[0126] ○ : In 5 tests, lint was observed at least once, but lint larger than 1 mm in length was never observed.

[0127] × : In 5 tests, lint was observed at least once, and lint larger than 1 mm in length was observed at least once.

[0128] In addition, for cases where lint was observed at least once in 5 tests, the number of lints was measured and calculated as the average value of the 5 tests.

[0129] [Example 1]

[0130] A core sheath composite fiber was prepared according to the following method.

[0131] For the core component, a melt anisotropic aromatic polyester [melting point (Ma): 278 °C, melt viscosity (MVa): 32.1 Pa·s] with a molar ratio of constituent units (P: HBA) and (Q: HNA) of 73 / 27 was used as polymer A. Also, for the super component, PEN [melting point (Mb): 266.3 °C, melt viscosity (MVb): 100 Pa·s] was used as polymer B forming the solution component, and a melt anisotropic aromatic polyester [melting point (Mc): 278 °C, melt viscosity (MVc): 32.1 Pa·s] identical to polymer A was used as polymer C forming the do component.

[0132] In the mixing process, the core component and the sheath component were melt-mixed using a different extruder. In the mixing process of the sheath component, polymer B and polymer C were mixed such that the ratio of the do component in the sheath component was 30 wt%. After starting the mixing extrusion, the temperature of the mixing section of the twin-screw extruder was set to 266 °C ((Mc - 12) °C) and the mixture was thoroughly mixed (low-temperature mixing process). Then, in the extrusion process, the mixture was spun at a spinning temperature of 310 °C and a draft value of 22.3 times from a die having the structure of Fig. 4, which was controlled so that the sheath component ratio was 0.35 (65 / 35 as the core-sheath ratio (weight ratio)), to obtain a core-sheath composite fiber of 10.3 dtex monofilament. The spinnability was good, and it was possible to collect the fiber without it becoming a single filament.

[0133] Next, as a heat treatment process, the obtained fibers were rewound onto a heat treatment bobbin, and the treatment temperature was increased stepwise to a maximum temperature of 260°C and carried out for 18 hours in a nitrogen gas atmosphere. There were no problems with the tolerance from the heat treatment bobbin, and the obtained heat-treated yarn had the performance shown in Table 5.

[0134] [Examples 2 to 8]

[0135] A core sheath composite fiber was prepared in the same manner as in Example 1, except that the core sheath ratio, the ratio of the fiber component to the core component, the number of filaments, the single filament fineness, and the draft value were changed as shown in Table 5. The results are shown in Table 5. All had good spinnability and could be harvested without single filament formation.

[0136] [Comparative Example 1]

[0137] A core-sheath composite fiber was manufactured by performing spinning and heat treatment in the same manner as in Example 1, except that a chip blend was used by hand-mixing chips of polymer B and polymer C of the core components, polymer B and polymer C were mixed such that the ratio of the core component in the core components was 30 wt%, melt-kneaded at 310°C using a single-screw extruder in a low-temperature kneading process, and spun from a die having the structure of Fig. 4, which was controlled so that the core component ratio was 0.35 (65 / 35 as core-sheath ratio (weight ratio)). The fiber was spun at a spinning temperature of 310°C and a draft value of 9.9 times. The spinnability was poor, and there were cases where the fibers became single. The results are shown in Table 5.

[0138] [Comparative Example 2]

[0139] A core sheath composite fiber was prepared in the same manner as in Comparative Example 1, except that the ratio of the fiber component to the fiber component in the fiber component was mixed to 20% by weight. Spinnability was poor, and there were cases where it became a single filament. The results are shown in Table 5.

[0140] [Comparative Example 3]

[0141] A core-sheath composite fiber was prepared by performing spinning and heat treatment in the same manner as Comparative Example 1, except that the ratio of the peach component to the sheath component was mixed to 5 weight%. As described in Patent Document 1, since the ratio of the peach component to the sheath component was 10 weight% or less, the spinnability was good, and it was possible to harvest without single filaments. The results are shown in Table 5.

[0142] [Comparative Example 4]

[0143] A core sheath composite fiber was prepared in the same manner as in Comparative Example 1, except that the core sheath component ratio was 0.15 (85 / 15 as the core sheath ratio (weight ratio)) and the draft value was 15.5. Spinnability was poor, and there were cases of single filament formation. The results are shown in Table 5.

[0144] [Comparative Example 5]

[0145] A core sheath composite fiber was prepared by performing spinning and heat treatment in the same manner as Comparative Example 1, except that the same low-temperature mixing process as in Example 1 was carried out in the mixing process of the core components. The spinnability was good, and it was possible to harvest the fiber without it becoming a single filament. The results are shown in Table 5.

[0146]

[0147] As shown in Table 5, in Examples 1 to 8, even if the proportion of molten anisotropic aromatic polyester in the primary component is high, high wear resistance and spinnability can be achieved by controlling the shape of the island structure of the primary component.

[0148] Examples 1 to 8 all exhibit excellent wear resistance, as no lint larger than 1 mm was observed in the wear test involving 30,000 reciprocating motions, and no delamination occurred. In particular, in Examples 2 to 3, even minute fibrils smaller than 1 mm were not observed, possibly because the maximum width of the blade was small. Furthermore, in Examples 1 and 4 to 5, although the maximum width of the blade was larger than in Examples 2 to 3, even minute fibrils smaller than 1 mm were not observed, or were observed only once out of five measurements, possibly because the maximum length (L1) / maximum width (W) of the bevel length of the blade could be increased by making the blade width smaller and the blade length longer.

[0149] In particular, in Examples 4 and 5, by controlling the shape of the core component in the wax, wear resistance is maintained even when the wax is thin, and strength is also increased due to the high core component ratio.

[0150] In addition, even Example 6, which has a small single filament fineness, and Examples 7 to 8, which have a large single filament fineness, exhibit better wear resistance than Comparative Examples 1 to 3 by controlling the shape of the blade in the base component.

[0151] On the other hand, Comparative Example 1 did not perform a specific melt-kneading process on the sheath component, so the spinnability was poor and single filaments occurred during spinning. In addition, although Comparative Example 1 has the same core-sheath ratio and the ratio of the sheath component to the sheath component as Example 1, the sheath portion of the obtained core-sheath composite fiber shows that the maximum width of the sheath portion is larger than that of Example 1, indicating a larger sheath portion. Furthermore, perhaps because the maximum length / maximum width of the warp length of the sheath portion is small, the anchoring effect of the sheath component cannot be exerted. When evaluating fluff in the abrasion resistance test, not only did small fluff (fibrils) of 1 mm or less occur, but the number of fluffs was also higher than in Example 1, and fluff larger than 1 mm and sheath delamination also occurred. In addition, regarding fiber strength, it showed a lower value than Example 1.

[0152] In Comparative Example 2, although it has the same core-sheath ratio and the ratio of the fiber component to the fiber component as in Example 2, since a specific melt-kneading process is not performed on the fiber component, it is shown that the maximum width of the fiber section is larger compared to Example 2, and it has a large fiber section. When evaluating fluff in the abrasion resistance test, the number of fluffs is higher than in Example 2, and fluff larger than 1 mm and fiber peeling also occur. In addition, regarding fiber strength, it shows a lower value than in Example 2.

[0153] In Comparative Example 3, although the proportion of melt anisotropic aromatic polyester in the wax component is lower than in Examples 1 and 2, it is shown that the maximum width of the wax is larger compared to Examples 1 and 2, and that it has a large wax. When evaluating lint in the abrasion resistance test, the number of lints is higher than in Examples 1 and 2, and lint larger than 1 mm and wax delamination occur. In addition, regarding fiber strength, it shows lower values ​​than in Examples 1 and 2.

[0154] In Comparative Example 4, the same core ratio and the ratio of the fiber component to the fiber component as in Example 5 are used, but because a specific melt mixing process is not performed on the fiber component, the maximum length / maximum width of the fiber inclination length is small, and fiber peeling greater than 1 mm occurs.

[0155] In Comparative Example 5, the same core ratio and the ratio of the fiber component to the fiber component as in Example 1 are used, and a specific melt mixing process is performed on the fiber component. Therefore, although the maximum width of the fiber component is small, the draft value during spinning is small, so the maximum length / maximum width of the fiber inclination length is small, and lint and fiber peeling greater than 1 mm occur.

[0156] Industrial applicability

[0157] The core sheath composite fiber of the present invention can suppress fibrillation while maintaining high strength and high modulus of elasticity by increasing the proportion of melt anisotropic aromatic polyester in the sheath component, and is therefore utilized in high-grade processed products such as tension members (electric wires, optical fibers, umbilical cables, heater wires, cords of various electrical products such as earphone cords), sailcloth, ropes (marine, mountaineering, cranes, yachts, tags, etc.), ropes, land nets, slings, leashes, fishing lines, sewing threads, netting cords, fishing nets, kite strings, geogrids, protective gloves, protective clothing and outdoor medical ripstops, rider suits, sports rackets, guts, medical catheter reinforcements, sutures, screen threads, filters, foam for printed circuit boards, mesh conveyor belts, papermaking belts, dryer canvases, airships, balloons, airbags, speaker cones, reinforcements for various hoses and pipes, and reinforcements for rubber and plastics such as tires and conveyor belts. In addition, since it can be dyed using general methods, it is particularly well utilized in high-grade processed products such as sailcloth, ropes, land nets, fishing lines, fishing nets, kite strings, ripstop for protective clothing and outdoor medical wear, reinforcing materials for rubber and plastic, and general medical wear.

[0158] As described above, preferred embodiments of the present invention have been explained with reference to the drawings; however, those skilled in the art will readily conceive of various changes and modifications within the obvious scope by looking at this specification. Accordingly, such changes and modifications are interpreted as being within the scope of the invention as defined by the claims.

Claims

Claim 1 A core-sheath composite fiber having a sea-island structure in which a core component comprises a melt-anisotropic aromatic polyester (A polymer), a sheath component comprises a flexible thermoplastic polymer (B polymer) and a melt-anisotropic aromatic polyester (C polymer), wherein the B polymer forms a sea component and the C polymer forms a sea component, and a plurality of sea sections formed by the sea section formed by the sea component are dispersed therein, wherein the ratio of the sea section in the sheath component exceeds 10 weight%, and furthermore, in a cross-section in which the core-sheath composite fiber is cut in the fiber length direction, the maximum width (W) of the sea section is 0.65 μm or less, and in the sea section having the maximum width (W), among the sea sections that are tangent to a diagonal line in the sheath component extending at a predetermined angle of 10° with respect to the fiber length direction as they extend from one end to the other end in the fiber length direction, the ratio (L1) of the maximum length of the diagonal length that overlaps with the diagonal line and the maximum width (W) of the sea section Cardiac sheath complex fibers with a value of 5.0 or higher. Claim 2 A core sheath composite fiber according to claim 1, wherein the maximum length (L1) of the slope length is 1.0 μm or more. Claim 3 A core sheath composite fiber according to claim 1, wherein, in a cross-section cut in the fiber length direction of the core sheath composite fiber, the fiber length (L2) of the fiber length direction of the sheath component is 450 to 1000 μm. Claim 4 A core sheath composite fiber according to claim 1, wherein the thickness of the sheath component is 0.8 to 5.0 μm. Claim 5 In claim 1, the core sheath composite fiber in which the A polymer and the C polymer are composed of melt-anisotropic aromatic polyesters having the same main constituent unit. Claim 6 A core-sheath composite fiber according to claim 1, wherein the weight ratio of the core component to the sheath component, the core component / sheath component, is 20 / 80 to 97 / 3. Claim 7 In claim 1, the heart sheath complex fiber having a monofilament fineness of 1 to 120 dtex. Claim 8 A method for manufacturing a core-sheath composite fiber having a sea-island structure in which a core component comprises a molten anisotropic aromatic polyester (A polymer), a sheath component comprises a flexible thermoplastic polymer (B polymer) and a molten anisotropic aromatic polyester (C polymer), wherein the B polymer forms a sea component and the C polymer forms a sea component, and a plurality of sea sections formed by the sea component are dispersed within the sea section formed by the sea component, comprising: a mixing process in which the B polymer and the C polymer used for the sheath component are mixed using a twin-screw extruder at a temperature of (Mb) °C or higher relative to the melting point (Mb) °C of the B polymer and (Mc - 20) °C or higher relative to the melting point (Mc) °C of the C polymer, and (Mc) °C or lower relative to the melting point (Mc) °C of the C polymer, and the A polymer used for the core component is melted and mixed using an extruder different from the twin-screw extruder used for the sheath component; and an extrusion process in which the sheath component and the core component, respectively mixed in the mixing process, are combined and extruded to obtain a discharged yarn. A method for manufacturing a core sheath composite fiber comprising at least a process and a process for taking out the discharged yarn with a draft value of 13 to 50, which is the ratio of the winding speed to the discharge speed. Claim 9 A method for manufacturing a core sheath composite fiber according to claim 8, comprising a heat treatment process for performing heat treatment on the fiber obtained in the extrusion process. Claim 10 A fiber structure comprising at least a portion of the heart sheath composite fibers described in any one of claims 1 to 7.

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