Core-sheath composite fibers and fiber structures

Abstract

A core-sheath composite fiber and a fiber structure are provided. 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), wherein the B polymer constitutes a sea component, the C polymer constitutes an island component, and the sheath component has a sea-island structure in which a plurality of islands constituted from the island component are dispersed in a sea (14) constituted from the sea component, the proportion of the B-polymer component in the core-sheath composite fiber being 20 wt% or less.

Description

Related Application

[0001] This application claims the priority of Japanese Patent Application No. 2021-34708 filed on March 4, 2021, and the entire content thereof is incorporated herein by reference and made a part of this application.

Technical Field

[0002] The present invention relates to core-sheath composite fibers and fibrous structures having a melt anisotropic aromatic polyester as a core component, which have improved fibrillation resistance, excellent abrasion resistance, and excellent dimensional stability.

Background Art

[0003] Although melt anisotropic aromatic polyester fibers are known to have high strength and high elastic modulus, these fibers have a problem that they are easily fibrillated by abrasion because the molecular chains are highly oriented in the fiber axis direction. Therefore, composite fibers have been proposed in which a melt anisotropic aromatic polyester is used as a core component and the periphery is coated with a sheath component to suppress fibrillation.

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

[0005] Patent Document 1 describes that by blending the same polymer as the core component into the sheath component, the strength of the sheath component is increased and at the same time the adhesiveness with the core component is increased.

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

[0007] Patent Document 2 describes that polymers without melt anisotropy have poor adhesion to melt anisotropic polyesters and are easily peeled off, therefore the sheath component is formed from a blend consisting of melt anisotropic polyester and a polymer without melt anisotropy. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2002-20932 [Patent Document 2] Japanese Patent Publication No. 2008-255535 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, Patent Document 1 denies that the ratio of the sheath component containing flexible polyester should be reduced, stating that the core component is more likely to be exposed when the ratio of the sheath component containing flexible polyester is less than 0.2. Furthermore, it denies increasing the proportion of fused anisotropic aromatic polyester in the sheath component, stating that if the proportion of fused anisotropic aromatic polyester in the sheath component exceeds 10%, irregularities will occur on the fiber surface and spinnability will deteriorate. Thus, reducing the proportion of flexible polyester (B polymer) in core-sheath composite fibers is denied.

[0010] Furthermore, even if the ratio of island components in the sheath component is set to the maximum value of 0.25, following the description in Patent Document 2, it is estimated that the B polymer component (sea component) will still be abundant, and the properties derived from the B polymer component will become more pronounced.

[0011] Therefore, the object of the present invention is to provide a technology that improves fibril resistance and abrasion resistance in core-sheath composite fibers while also providing excellent dimensional stability. [Means for solving the problem]

[0012] The inventors of the present invention, after diligent research to achieve the above objective, found that in a core-sheath composite fiber having molten anisotropic aromatic polyester as the core component, (I) the sheath component has a sea-island structure with island portions made of molten anisotropic aromatic polyester and sea portions made of flexible thermoplastic polymer, and by increasing the proportion of flexible thermoplastic polymer in the core-sheath composite fiber, abrasion resistance can be improved due to the properties of the flexible thermoplastic polymer (i.e., fibrillation can be prevented). However, (II) on the other hand, dimensional stability decreases due to the high proportion of flexible thermoplastic polymer. Therefore, the inventors made it a new challenge to achieve both improved abrasion resistance and improved dimensional stability, which are in a trade-off relationship. Then, (III) they found that by setting the proportion of flexible thermoplastic polymer in the core-sheath composite fiber within a predetermined range, and by kneading the sheath component in a specific way and drawing the discharged yarn at a specific draft value, it is possible to improve both the abrasion resistance and dimensional stability of the core-sheath composite fiber, thus completing the present invention.

[0013] In other words, the present invention may be configured in the following embodiments. [Aspect 1] A core-sheath composite fiber having a sea-island structure in which the core component comprises a fused anisotropic aromatic polyester (polymer A), and the sheath component comprises a flexible thermoplastic polymer (polymer B) and a fused anisotropic aromatic polyester (polymer C), wherein the polymer B forms a sea component, the polymer C forms an island component, and a plurality of island components are dispersed within the sea component, Core-sheath composite fiber in which the proportion of B polymer component in the core-sheath composite fiber is 20% by weight or less (preferably 18% by weight or less, more preferably 16% by weight or less, even more preferably less than 15% by weight, even more preferably 14% by weight or less, particularly preferably 12% by weight or less, and most preferably 11% by weight or less). [Aspect 2] A core-sheath composite fiber according to Embodiment 1, wherein the proportion of the B polymer component in the core-sheath composite fiber is 5% by weight or more (preferably 10% by weight or more). [Aspect 3] A core-sheath composite fiber according to embodiment 1 or 2, wherein the maximum width W of the island portion having the greatest width in the direction perpendicular to the fiber, in a cross-section obtained by cutting the core-sheath composite fiber in the longitudinal direction of the fiber, is 0.65 μm or less (preferably 0.60 μm or less, more preferably 0.55 μm or less, and even more preferably 0.50 μm or less). [Aspect 4] A core-sheath composite fiber according to any one of embodiments 1 to 3, wherein in a cross-section obtained by cutting the core-sheath composite fiber in the longitudinal direction of the fiber, in the island portion having the maximum width W, the ratio L1 / W of the maximum diagonal length L1 that overlaps with the diagonal line in the sheath component extending at a predetermined angle of 10° with respect to the longitudinal direction of the fiber from one end to the other in the longitudinal direction of the fiber to the maximum width W of the island portion 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). [Aspect 5] A core-sheath composite fiber according to any one embodiment of embodiments 1 to 4, wherein the thickness of the sheath component in the fiber radial direction is 0.8 to 5.0 μm (preferably 0.9 to 4.0 μm, more preferably 0.9 to 3.0 μm, and particularly preferably 1.0 to 2.5 μm). [Aspect 6] A core-sheath composite fiber according to any one of embodiments 1 to 5, wherein the A polymer and the C polymer are melt-isotropic aromatic polyesters having the same main constituent units. [Aspect 7] The core-sheath composite fiber according to any one of aspects 1 to 6, wherein the weight ratio of the core component to the sheath component, core component / sheath component, is 65 / 35 to 97 / 3 (preferably 70 / 30 to 95 / 5, more preferably 75 / 25 to 90 / 10). [Aspect 8] The core-sheath composite fiber according to any one of aspects 1 to 7, wherein the fineness of a single fiber of this core-sheath composite fiber is 1 to 120 dtex (preferably 2 to 60 dtex, more preferably 2.5 to 30 dtex, still more preferably 3 to 15 dtex). [Aspect 9] A fiber structure comprising at least a part of the core-sheath composite fiber according to any one of aspects 1 to 8.

[0014] In this specification, the cross-section of the core-sheath composite fiber cut along the fiber longitudinal direction so as to include the fiber central axis may be referred to as the "fiber longitudinal cross-section". Further, the fiber perpendicular direction means the direction orthogonal (or perpendicular) to the fiber longitudinal direction in the fiber longitudinal cross-section.

[0015] In addition, 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.

Advantages of the Invention

[0016] According to the core-sheath composite fiber of the present invention, in the core-sheath composite fiber having a molten anisotropic aromatic polyester as the core component and a sea-island structure for the sheath component, the sea component and the island component of the sheath component are respectively a flexible thermoplastic polymer and a molten anisotropic aromatic polyester, and further, by setting the ratio of the flexible thermoplastic polymer in the core-sheath composite fiber within a predetermined range and kneading the sheath component by a specific method, the wear resistance of the core-sheath composite fiber can be improved, fibrillation can be prevented, and the dimensional stability can be highly improved.

Brief Description of the Drawings

[0017] This 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 illustrative and explanatory purposes only and should not be used to define the scope of this invention. The scope of this invention is determined by the appended claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts. [Figure 1A] It is a schematic perspective view of a core-sheath composite fiber according to an embodiment of the present invention. [Figure 1B] It is a schematic cross-sectional view of the concentric core-sheath composite fiber cut in the fiber longitudinal direction. [Figure 2] It is an enlarged view of part II in Fig. 1B. [Figure 3] It is a schematic cross-sectional view of the concentric core-sheath composite fiber cut in a plane perpendicular to the fiber longitudinal direction. [Figure 4] It is a schematic cross-sectional view showing the structure of a spinneret used for spinning the concentric core-sheath composite fiber.

Mode for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in detail based on examples. One aspect of the present invention is a core-sheath composite fiber including a core component and a sheath component covering the core component, and the sheath component has a sea-island structure including a sea component and an island component. The core component includes a melt anisotropic aromatic polyester (A polymer), the sheath component includes a flexible thermoplastic polymer (B polymer) and a melt anisotropic aromatic polyester (C polymer), the B polymer forms the sea component, and the C polymer forms the island component. The proportion of the flexible thermoplastic polymer (B polymer) in the core-sheath composite fiber is 20% by weight or less.

[0019] (Core component) The fused anisotropic aromatic polyester (polymer A) used as the core component is a polymer that exhibits optical anisotropy (liquid crystallinity) in the molten phase. For example, by placing a sample on a hot stage, heating it under a nitrogen atmosphere, and observing the transmitted light from the sample, it is possible to determine whether or not it is a fused anisotropic aromatic polyester. The fused anisotropic aromatic polyester of the present invention consists of repeating structural units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and the chemical composition of the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids is not particularly limited as long as it does not impair the effects of the present invention. Furthermore, the fused anisotropic aromatic polyester may also contain structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids, to the extent that it does not hinder the effects of the present invention. For example, preferred structural units are shown in Table 1.

[0020] [Table 1]

[0021] In the constituent units of Table 1, m is an integer from 0 to 2, and Y in the formula can be independently a hydrogen atom, halogen atoms (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl groups (e.g., alkyl groups with 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group, t-butyl group, etc.), alkoxy groups (e.g., methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), aryl groups (e.g., phenyl group, naphthyl group, etc.), aralkyl groups [benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.], aryloxy groups (e.g., phenoxy group, etc.), aralkyloxy groups (e.g., benzyloxy group, etc.), etc.).

[0022] More preferred structural units include those shown in Examples (1) to (18) in Tables 2, 3, and 4 below. If a structural unit in a formula can exhibit multiple structures, two or more such structural units may be combined and used as structural units to constitute the polymer.

[0023] [Table 2]

[0024] [Table 3]

[0025] [Table 4]

[0026] In the constituent units of Tables 2, 3, and 4, n is an integer of 1 or 2, and each constituent unit n=1 and n=2 may exist alone or in combination. Y1 and Y2 may independently be a hydrogen atom, a halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), an alkyl group (e.g., a C1 to C4 alkyl group such as a methyl group, ethyl group, isopropyl group, t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), an aryl group (e.g., a phenyl group, naphthyl group, etc.), an aralkyl group [benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.], an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.). Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0027] Furthermore, Z can be represented by the substituent shown in the following formula.

[0028] [ka]

[0029] The molten anisotropic aromatic polyester may preferably be a combination having a naphthalene skeleton as a constituent unit. It is particularly preferable to include both a constituent unit (A) derived from hydroxybenzoic acid (abbreviated as HBA) and a constituent unit (B) derived from hydroxynaphthoic acid (abbreviated as HNA). For example, the following formula (A) is an example of constituent unit (A), and the following formula (B) is an example of constituent unit (B). From the viewpoint 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.

[0030] [ka]

[0031] [ka]

[0032] Furthermore, the sum of the constituent units of (A) and (B) may be, for example, 65 mol% or more of the total constituent units, more preferably 70 mol% or more, and even more preferably 80 mol% or more. A melt anisotropic aromatic polyester in which the constituent units of (B) are particularly concentrated in 4 to 45 mol% of the polymer is preferred.

[0033] The melting point of the molten anisotropic aromatic polyester preferably used in the present invention is in the range of 250 to 360°C, and more preferably 260 to 320°C. 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 with a differential scanning calorimetry (e.g., Shimadzu Corporation DSC).

[0034] Furthermore, the above-mentioned fused anisotropic aromatic polyester may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, to the extent that the effects of the present invention are not impaired. It may also contain various additives such as inorganic substances such as titanium dioxide, kaolin, silica, and barium oxide, carbon black, colorants such as dyes and pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

[0035] (sheath component) The sheath component has a sea-island structure, with flexible thermoplastic polymers (B polymers) forming the sea components and melt-isotropic aromatic polyesters (C polymers) forming the island components. Examples of flexible thermoplastic polymers (B polymers) that form the marine component 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 polyesters such as polyolefins, polyamides, polycarbonates, polyphenylene sulfide (abbreviated as PPS), polyethylene terephthalate, modified polyethylene terephthalate, amorphous polyarylate, and polyethylene naphthalate (abbreviated as PEN), as well as polyether ether ketones and fluororesins. These flexible thermoplastic polymers may be used alone or in combination of two or more, with one being the main thermoplastic polymer (for example, accounting for 80% or more by weight) and the others being added thermoplastic polymers. Among these, it is preferable that PPS and PEN be the main thermoplastic polymer. Furthermore, the flexible thermoplastic polymer may contain various additives such as inorganic substances like titanium dioxide, silica, and barium oxide, colorants such as carbon black, dyes, or pigments, antioxidants, ultraviolet absorbers, light stabilizers, and nucleating agents.

[0036] The fused anisotropic aromatic polyester (C polymer) that forms the island component can be the fused anisotropic aromatic polyester described in the description of polymer A, and may be the same as or different from polymer A. However, from the viewpoint of affinity, it is preferable that it be the same type of fused anisotropic aromatic polyester, for example, that it is the same type of fused anisotropic aromatic polyester with the same main constituent units. Furthermore, polymer A and polymer C may be the same type of polymer with the same main constituent units, and only differ, for example, in the thermoplastic polymer or additives added.

[0037] Furthermore, the melting point (Mc) of polymer C can be appropriately selected within a range that allows for fine dispersion of polymer C relative to polymer B. For example, the melting point (Mc) of polymer C may be in the range of (Mb-10) to (Mb+80)°C, or in the range of Mb to (Mb+70)°C, relative to the melting point (Mb) of polymer B.

[0038] Furthermore, the melt viscosity η of the C polymer may be, for example, 10 to 60 Pa·s, preferably 20 to 50 Pa·s, and more preferably 25 to 45 Pa·s, from the viewpoint of spinnability. In this invention, the melt viscosity η is defined as temperature T (T = Mc + 10°C if the melting point (Mc) of the C polymer is 290°C or higher, and T = 300°C if the melting point Mc is less than 290°C) and shear rate 1000 sec. -1 This is the melt viscosity measured using [the specified method].

[0039] (Method for manufacturing core-sheath composite fibers) The core-sheath composite fiber of the present invention can be manufactured by a manufacturing method comprising at least a kneading step and an extrusion step. The manufacturing step may further include a heat treatment step.

[0040] In the kneading process, the B polymer and the C polymer used for the sheath component are melted and kneaded using a twin-screw extruder, while the A polymer used for the core component is melted and kneaded using a different extruder than the twin-screw extruder used for the sheath component.

[0041] In particular, in a twin-screw extruder used for kneading B polymer and C polymer, the temperature of the kneading section in the twin-screw extruder is set to be (Mb)°C or higher relative to the melting point (Mb) of the B polymer, and (Mc-20)°C or higher and (Mc)°C or lower relative to the melting point (Mc) of the C polymer. Furthermore, by rotating the parallel twin-screws rotatably supported in the kneading section, it becomes possible to achieve fine dispersion of multiple island portions within the sheath component. In the present invention, when reducing the proportion of B polymer, it is conceivable to (i) increase the proportion of the core component and / or (ii) increase the proportion of the island component. However, in the case of (i), the thickness of the sheath component becomes thinner, and in the case of (ii), the proportion of the island component increases, so it is important to achieve fine dispersion of multiple island portions. Furthermore, the extruder used to melt and knead the A polymer may be a single-screw extruder or a twin-screw extruder. Also, when using raw materials in which the B polymer and C polymer have been compounded in advance under the above conditions, since the multiple island portions in the sheath component have already been finely dispersed, the extruder used to melt and knead the sheath component may be a single-screw extruder or a twin-screw extruder.

[0042] In the mixing process, the ratio of core component to sheath component may be, from the viewpoint of reducing the proportion of B polymer, a weight ratio of core component to sheath component (hereinafter sometimes simply referred to as the core-sheath ratio), for example, 65 / 35 to 97 / 3, preferably 70 / 30 to 95 / 5, and more preferably 75 / 25 to 90 / 10. The weight ratio of core component to sheath component can be determined, for example, by the weight ratio of core component to sheath component fed into each extruder described later during manufacturing.

[0043] The proportion of island components in the sheath component may exceed, for example, 10% by weight, preferably 15% by weight or more, and more preferably 20% by weight or more. Increasing the proportion of island components can strengthen the anchoring effect between the core component and the sheath component. On the other hand, if the proportion of island components is too high, the likelihood of aggregation of island components increases, so the proportion of island components may be 45% by weight or less, preferably 40% by weight or less.

[0044] In the extrusion process, the sheath component and core component, which were kneaded in the kneading process, are combined and extruded from a die with a structure like the one shown in Figure 4, for example, to spin a core-sheath composite fiber with a circular cross-section (fiber cross-section). In the heat treatment process, the fibers obtained in the extrusion process are subjected to a heat treatment in which the processing temperature is increased in stages, making it possible to more reliably satisfy the required quality.

[0045] The spinneret temperature (spinning temperature) during extrusion may be, for example, (Ma+10) to (Ma+60)°C relative to the melting point (Ma) of polymer A, preferably (Ma+15) to (Ma+40)°C, and more preferably (Ma+20) to (Ma+35)°C. The shape of the finely dispersed islands is controlled by the draft value, and the discharged yarn is taken up at a draft value of 13 to 50, preferably 15 to 45, more preferably 16 to 40, even more preferably 19 to 38, and especially preferably 20 to 35. The draft value refers to the ratio of the winding speed to the discharge speed during spinning.

[0046] Furthermore, the spun fibers may be subjected to heat treatment. Heat treatment not only increases the degree of orientation and crystallinity of the B polymer in the sheath component, but also enables solid-phase polymerization of the molten anisotropic aromatic polyester, thereby improving the strength of the core-sheath composite fiber.

[0047] In 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). When heat treatment is performed, the heat treatment atmosphere is preferably a low-humidity environment 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 is used in which the temperature is gradually increased from (Ma-20)°C or lower, preferably (Ma-30)°C or lower, and more preferably (Ma-40)°C or lower, to below the melting point of the sheath component, relative to the melting point (Ma) of polymer A. Methods for supplying heat include using a gaseous medium, utilizing radiation through heating plates or infrared heaters, and internal heating using high-frequency waves. The processing configuration may be continuous roll-to-roll production, or batch production by winding yarn onto hank-type, tow-type, or heat-treatment bobbins.

[0048] From the viewpoint of preventing sheath peeling due to yarn adhesion after heat treatment, inorganic fine particles may be applied to the surface of the fibers during or after spinning, or before heat treatment, as needed. The inorganic fine particles are preferably those mainly composed of silicate compounds such as talc and mica.

[0049] Unlike Patent Document 2, the present invention has good decomposition properties even without attaching inorganic fine particles, but inorganic fine particles may be attached to further improve decomposition properties. By uniformly attaching inorganic microparticles to the surface of fibers during or after spinning, before heat treatment, direct contact between fibers can be prevented, thus avoiding fiber adhesion. Furthermore, most inorganic microparticles, primarily composed of silicate compounds, are inert, and their attachment to fibers does not degrade the fiber's properties.

[0050] The method for attaching the inorganic fine particles to the surface of the fibers is not limited in any way, as long as it can be attached uniformly to the fibers. For example, a simple and preferred method is to attach a mixture of inorganic fine particles dispersed in a spinning oil using an oiling roller or a crow's nozzle.

[0051] 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, from the viewpoint 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% by mass, preferably 0.1 to 2.3% by mass.

[0052] (Core-sheath composite fiber) Figure 1A is a schematic perspective view of a core-sheath composite fiber according to one embodiment of the present invention, and Figure 1B is a schematic cross-sectional view of the same core-sheath composite fiber when cut in the longitudinal direction of the fiber. The core-sheath composite fiber 10 has a core portion 12 formed of a core component and a sheath portion 14 formed of a sheath component.

[0053] Figure 2 is an enlarged cross-sectional view showing a partial enlargement of part II of Figure 1B. As shown in Figures IB and 2, in a cross-section (fiber longitudinal section) obtained by cutting a core-sheath composite fiber in the longitudinal direction of the fiber including its central axis, the sheath portion 14 forms a sea-island structure, forming multiple island portions 18 within the sea portion 16. The island portions are finely dispersed in the sea component.

[0054] In the core-sheath composite fiber of the present invention, the proportion of the sea portion (i.e., flexible thermoplastic polymer) 16 in the core-sheath composite fiber is 20% by weight or less, preferably 18% by weight or less, more preferably 16% by weight or less, even more preferably less than 15% by weight, even more preferably 14% by weight or less, particularly preferably 12% by weight or less, and most preferably 11% by weight or less. As long as the sheath portion can form a sea-island structure, the lower limit of the proportion (by weight) of the sea portion (i.e., flexible thermoplastic polymer) 16 in the core-sheath composite fiber is not particularly limited, but for example it may be 5% by weight or more, preferably 7% by weight or more, and more preferably 10% by weight or more.

[0055] Thus, the core-sheath composite fiber of the present invention can improve both the abrasion resistance and dimensional stability of the core-sheath composite fiber. Specifically, the sheath component containing a flexible thermoplastic polymer can impart abrasion resistance to the core-sheath composite fiber, derived from the properties of the flexible thermoplastic polymer. At the same time, reducing the content of the flexible thermoplastic polymer can suppress the decrease in dimensional stability derived from the flexible thermoplastic polymer, thereby improving the dimensional stability of the core-sheath composite fiber. Therefore, by optimizing the content of the flexible thermoplastic polymer in the core-sheath composite fiber of the present invention, it is possible to achieve both improved abrasion resistance and improved dimensional stability, which are in a trade-off relationship.

[0056] The island portions, while finely dispersed, are basically approximately elliptical in shape and extend in the longitudinal direction of the fiber. A larger island diameter results in greater irregularities on the fiber surface originating from the island components. Since fibril formation is due to the size of these irregularities on the fiber surface, it is preferable for the maximum diameter of the island portions to be small. Furthermore, it is preferable for the island portions to extend long in the longitudinal direction of the fiber, as this allows them to exert an anchoring effect. In other words, simply measuring the maximum width of the island portions in a single fiber cross-section does not take into account the contribution of the anchoring effect caused by the length of the island portions. However, by observing the shape of the island portions in the longitudinal direction in a micrograph of the sheath components and measuring the width of the island portion with the largest width, taking into account not only the width of the island portion but also its length, it is possible to evaluate the fibril resistance while taking into account the contribution of the anchoring effect of the island portions. To achieve this, for example, after selecting an island having the maximum width W, the shape of the island may be evaluated by measuring the maximum diagonal length L1 of the length that overlaps with a diagonal line extending from one end to the other in the longitudinal direction of the fiber at a predetermined angle α (10°) with respect to the longitudinal direction of the fiber, as shown in Figure 2, or by calculating L1 / W.

[0057] The island with the maximum width can be selected from a magnified image of the fiber longitudinal section. Specifically, the fiber longitudinal section is observed using a scanning probe microscope (SPM), as described later, at a distance of 100 μm to 1000 μm in the fiber longitudinal direction, and the value of the point where the length of the island in the direction perpendicular to the fiber longitudinal direction (fiber perpendicular direction) is maximum within that observation range is taken as the measured value. However, the observation range does not need to be continuous; it can be the sum of multiple randomly extracted fields. For example, within the observation range of the fiber longitudinal section, several islands with relatively large lengths in the fiber perpendicular direction can be extracted from among many islands extending in the fiber longitudinal direction, and the island with the maximum width can be determined by comparing the fiber perpendicular lengths of the extracted islands as the width of the islands. In this example, in the fiber longitudinal section, only the upper or lower part of the sheath component (for example, the lower part of Figure 1B) needs to be used as the observation range. In this example, the maximum width of the island portion is determined by observing the longitudinal section of the fiber with a scanning probe microscope, but other means may be used as long as they can determine the maximum width of the island portion. Furthermore, when cutting the fibers, it is preferable to embed them in resin to fix them in place and minimize the effects of stress.

[0058] The maximum width W of the island portion 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 island portion exceeds 0.65 μm, the fibril resistance may be insufficient. Also, the maximum width W of the island portion may be 0.07 μm or more, or 0.1 μm or more.

[0059] After selecting an island having the maximum width W, this island is continuously observed in the longitudinal direction, and as shown in Figure 2, the maximum length L1 of the diagonal length that overlaps with a diagonal line extending from one end to the other in the longitudinal direction of the fiber at a predetermined angle α (10°) with respect to the longitudinal direction of the fiber is measured.

[0060] The maximum length L1 of the diagonal length is a value that changes 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 diagonal length is greater than or equal to the lower limit value, the anchoring effect on the core component tends to increase. Also, the maximum length L1 of the diagonal 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 diagonal length is less than or equal to the upper limit value, fibrillation tends to be suppressed.

[0061] Furthermore, from the viewpoint of suppressing fibrillation while improving the anchoring effect by the island portion, the ratio L1 / W of the maximum length L1 of the diagonal length to the maximum width W may be, for example, 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. There is no particular upper limit to L1 / W, but it may be 10 or less.

[0062] In the longitudinal section of the fiber, the length L2 in the longitudinal direction of the island portion having the largest width within the sheath component may be, for example, 450 to 1000 μm, preferably 500 to 800 μm, and more preferably 550 to 650 μm. The longer the length, the greater the anchoring effect on the core component. This length in the longitudinal direction of the island portion can be determined from an enlarged image of the longitudinal section of the fiber. Alternatively, the length in the longitudinal direction of the island portion may be determined using the discharged yarn, and this value may be calculated by multiplying it by the draft value.

[0063] The thickness of the sheath component may be, for example, 0.8 to 5.0 μm, preferably 0.9 to 4.0 μm, more preferably 0.9 to 3.0 μm, and particularly preferably 1.0 to 2.5 μm, from the viewpoint of spinning the core and ensuring the strength of the fiber.

[0064] As shown in Figure 3, the thickness of the sheath component can be determined, for example, from a magnified image of a cross-section (hereinafter sometimes referred to as the "fiber cross-section") obtained by cutting a core-sheath composite fiber in a plane perpendicular to the fiber's longitudinal direction. Specifically, it is possible to image the fiber cross-section with a scanning microscope, measure the radial distance from the outer surface of the core component to the outer surface of the sheath component at three arbitrary points that divide the outer circumference of the fiber into three equal parts, and determine the thickness of the sheath component from the average value. When cutting the fiber, it is preferable to fix the fiber by embedding it in resin in order to minimize the influence of stress.

[0065] 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 Yarn". The core-sheath composite fiber may be a monofilament or a multifilament containing two or more monofilaments.

[0066] The core-sheath composite fiber may have a tensile strength of, for example, 10 cN / dtex or more in a 25°C atmosphere, preferably 13 cN / dtex or more, more preferably 15 cN / dtex or more, even more preferably 18 cN / dtex or more, and even more preferably 20 cN / dtex or more. There is no particular upper limit to the tensile strength, but it may be 30 cN / dtex or less. Here, the tensile strength is a value measured with reference to the JIS L 1013 test method. In the case of a multifilament core-sheath composite fiber, considering the change in strength due to the alignment of the fibers, one fiber may be taken from the multifilament and measured as the tensile strength of a single filament.

[0067] Core-sheath composite fibers have extremely high dimensional stability, and their dry heat shrinkage rate at 250°C may be 0.01% or less, preferably 0.01% or less. Here, the dry heat shrinkage rate is a value measured by the method described in the examples below.

[0068] Furthermore, when the core-sheath composite fiber is subjected to a test by passing each fiber through three comb guides arranged alternately at a 120° angle, applying a load of 1 g / dtex to each fiber, and performing 30,000 reciprocating motions at a stroke length of 3 cm and a speed of 95 times / min, the average number of fluffs (average of 5 trials) generated per 3 cm of fiber length may be, for example, 1 or less, and preferably 0.5 or less. Here, the fluff can be observed as small fluffs (fibrils) of 1 mm or less, or fluffs or sheath peeling larger than 1 mm, when the core-sheath composite fiber is magnified 20 times with a camera.

[0069] The core-sheath composite fiber of the present invention can be woven and 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 polymer, it can be dyed using conventional dyeing methods for polyester fibers with disperse dyes.

[0070] The core-sheath composite fiber of the present invention can be suitably used as various fiber structures, and the fiber structures of the present invention contain 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, as well as other processed products. The fiber structure may be composed solely of the core-sheath composite fiber, or it may contain other components to the extent that the effects of the present invention are not hindered. After forming the fiber structure, the fiber structure may be dyed using the dyeing method described above.

[0071] When the fiber structure is a woven fabric, the weave structure is not particularly limited and includes, for example, plain weave, twill weave, satin weave, modified plain weave, modified twill weave, modified satin weave, stylized weave, patterned weave, single-layer weave, double weave, multi-layer weave, warp pile weave, weft pile weave, and leno weave. Also, when the fiber structure is a knitted fabric, the knit structure is not particularly limited and includes, for example, circular knit, weft knit, warp knit (including tricot knit and raschel knit), pile knit, plain knit, jersey knit, rib knit, smooth knit (double-sided knit), rib knit, pearl knit, denby weave, cord weave, atlas weave, chain weave, and insert weave. [Examples]

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. In the following examples and comparative examples, various physical properties were measured by the methods described below.

[0073] [Fineness] Based on JIS L 1013:2010 8.3.1 Method A, a 100m skein of core-sheath composite fiber was taken using a measuring instrument manufactured by Daiei Kagaku Seiki Seisakusho, and its weight (g) was multiplied by 100. Three measurements were taken for each level, and the average of these three measurements was used as the obtained fineness (dtex).

[0074] [Tensile strength] In accordance with JIS L 1013, a USTER TENSORAPID5 strength and elongation measuring instrument was used to perform five measurements per sample under the following conditions: test length 20 cm, tensile speed 10 cm / min, and initial load 3.3 g / dtex. The average of these five measurements was defined as the strength (cN / dtex). In the case of a core-sheath composite fiber being a multifilament, a single filament was taken from the multifilament and its single-fiber tensile strength was measured.

[0075] [Sheath thickness] Core-sheath composite fibers were embedded in epoxy resin, and the fiber cross-section was obtained by cutting the embedded material with a plane perpendicular to the fiber's longitudinal direction. At 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 three arbitrary points that divide the outer circumference of the fiber into three equal parts. The average value of these measurements was calculated and used as the thickness of the sheath component.

[0076] [Island length, maximum island width] Core-sheath composite fibers were embedded in epoxy resin, and the embedded material was cut longitudinally using a cross-section polisher (CP) to obtain a cross-sectional view of the fiber. The longitudinal fiber section was observed using a scanning probe microscope (SPM) at a depth of 100 μm to 1000 μm in the longitudinal direction of the fiber. Within the observed range, several islands with relatively large lengths in the longitudinal direction of the fiber were extracted from among the numerous islands extending in the longitudinal direction of the fiber. The lengths of the extracted islands in the longitudinal direction were compared as the width of the islands, and the maximum width W of the island with the largest width was determined. In addition, the length L2 in the longitudinal direction of the fiber was measured for the island with the maximum width W.

[0077] [Maximum diagonal length of the island section] Next, for the island portion having the maximum width W, the longest line segment that overlaps with a diagonal line extending from one end to the other in the longitudinal direction of the fiber at a predetermined angle α (10°) with respect to the longitudinal direction of the fiber was measured as the maximum diagonal length L1 of the island portion.

[0078] [Abrasion resistance] Using a TM-type plicating force tester (model TM-200) manufactured by Daiei Kagaku Seiki Seisakusho, the fibers to be tested were passed through three comb guides arranged alternately at a 120° angle. A load of 1 g / dtex was applied to each fiber, and a reciprocating motion was performed 30,000 times at a stroke length of 3 cm and a speed of 95 cycles / minute. The state of fluffing was checked by magnifying the image 20 times with a camera. The above test was performed five times, and the presence or absence of fluffing was observed for each 3 cm length of fiber. The fluffing that occurred was distinguished into minute fluffs of 1 mm or less in length and fluffs of 1 mm or more in length, and evaluated according to the following criteria. (Presence or absence of lint) ◎: No fluff was observed in any of the 5 tests. ○: Although fluff was observed at least once in 5 tests, no fluff larger than 1 mm in length was observed. ×: Fuzz was observed at least once in 5 tests, and fuzz larger than 1 mm in length was observed at least once. Furthermore, for samples where fluffing was observed at least once in five tests, the number of fluff particles was measured and calculated as the average value obtained from five of the above tests.

[0079] [Dry heat shrinkage rate] The fiber length (Y cm) obtained after cutting fibers to X cm and holding them in an air-temperature bath maintained at 250°C for 30 minutes with a load of 0.5 mg / d applied to the yarn was calculated using the following formula. Dry heat shrinkage rate (%)=<X―Y / X> ×100

[0080] [Example 1] Core-sheath composite fibers were manufactured according to the following method. For the core component, polymer A was a molten anisotropic aromatic polyester with a molar ratio of constituent units (P:HBA) to (Q:HNA) of 73 / 27 [melting point (Ma): 278°C, melt viscosity (MVa): 32.1 Pa·s]. For the sheath component, PEN [melting point (Mb): 266.3°C, melt viscosity (MVb): 100 Pa·s] was used as polymer B to form the sea component, and a molten anisotropic aromatic polyester [melting point (Mc): 278°C, melt viscosity (MVc): 32.1 Pa·s] similar to polymer A was used as polymer C to form the island component.

[0081] In the compounding process, the core component and sheath component were melt-mixed using separate extruders. In the sheath component compounding process, B polymer and C polymer were mixed so that the island component ratio in the sheath component was 30% by weight. After the compounding extrusion start, the compounding section temperature of the twin-screw extruder was set to 266°C ((Mc-12)°C) and the mixture was thoroughly compounded (low-temperature compounding process). In the discharge process, the sheath component ratio was controlled to 0.35 (core-sheath ratio (weight ratio) of 65 / 35). The material was spun at a spinning temperature of 310°C and a draft value of 21.6 times using a die with the structure shown in Figure 4, and obtained a 14.0 dtex filament fiber (16f). The spinnability was good, and it was possible to harvest the fiber without breakage. The proportion of the B polymer component in this core-sheath composite fiber was 0.105 (10.5% by weight).

[0082] Next, as a heat treatment step, the obtained fibers were wound onto a heat treatment bobbin, and the treatment temperature was gradually increased until a maximum temperature of 260°C was reached, followed by heat treatment in a nitrogen gas atmosphere for 18 hours. There were no problems with unwinding from the heat treatment bobbin, and the obtained heat-treated yarn had the performance shown in Table 5.

[0083] [Examples 2-4] Core-sheath composite fibers were manufactured in the same manner as in Example 1, except that the core-sheath ratio, the proportion of island components in the sheath component, the single fiber fineness, the number of filaments, and the draft value were changed as shown in Table 5. The results are shown in Table 5. In all cases, the spinnability was good, and it was possible to harvest the fibers without breaking them.

[0084] [Comparative Example 1] Using a chip blend obtained by hand-mixing chips of sheath components B polymer and C polymer, B polymer and C polymer were mixed so that the island component ratio in the sheath component was 20% by weight. In a low-temperature kneading process, the mixture was melt-kneaded using a single-screw extruder, and the sheath component ratio was controlled to 0.35 (core-sheath ratio (weight ratio) of 65 / 35). Spinning and heat treatment were carried out in the same manner as in Example 1, except that the spinning temperature was 310°C and the draft value was 9.9 times. Core-sheath composite fibers were produced. The spinnability was poor, and breakage occurred in some cases. The results are shown in Table 5.

[0085] [Comparative Example 2] Core-sheath composite fibers were manufactured in the same manner as in Comparative Example 1, except that the island component in the sheath component was mixed to a ratio of 20% by weight. Spinning properties were poor, and filament breakage sometimes occurred. The results are shown in Table 5.

[0086] [Comparative Example 3] Except for mixing the island components in the sheath components to a ratio of 5% by weight, spinning and heat treatment were carried out in the same manner as in Comparative Example 1 to produce a core-sheath composite fiber. As described in Patent Document 1, since the ratio of island components in the sheath components was 10% by weight or less, the spinnability was good and it was possible to harvest without breaking the fibers. The results are shown in Table 5.

[0087] [Table 5]

[0088] As shown in Table 5, the proportion of the B polymer component in the core-sheath composite fiber was reduced, resulting in a dry heat shrinkage rate of 0.00% in Examples 1-4, demonstrating extremely high dimensional stability. Furthermore, in all Examples 1-4, no fluff larger than 1 mm was observed in the abrasion test involving 30,000 reciprocating motions, indicating no sheath delamination and excellent abrasion resistance. In particular, in Examples 1 and 2, neither fluff nor even minute fibrils smaller than 1 mm were observed. Moreover, Example 3 showed better abrasion resistance than Comparative Examples 1-3 despite having a small single-fiber fineness. Similarly, even in the case of a thicker single-fiber fineness, as in Example 4, better abrasion resistance was shown than Comparative Examples 1-3.

[0089] On the other hand, because the proportion of B polymer component in the core-sheath composite fiber is high, the dry heat shrinkage in Comparative Examples 1-3 is 0.05%-0.1%, which is lower than that of Examples 1-4, and thus the high level of dimensional stability is not achieved. Furthermore, in Comparative Examples 1-3, the conventional chip blending method does not allow for fine mixing of LCP, resulting in the generation of fibrils larger than 1 mm in the abrasion resistance test. As a result, not only is the number of fibrils larger than 1 mm generated, but the number of fibrils is also higher than in Example 1, and fibrils larger than 1 mm and sheath peeling occur. In addition, the fiber strength is also lower than that of Example 1. [Industrial applicability]

[0090] The core-sheath composite fiber of the present invention has improved fibril resistance and excellent abrasion resistance, while also having excellent dimensional stability. Therefore, it can be used in advanced processed products such as tension members (electric wires, optical fibers, umbilical cables, heater wire cores, earphone cords and other cords for various electrical products), sailcloth, ropes (marine, mountaineering, cranes, yachts, tugs, etc.), climbing ropes, land nets, slings, safety lines, fishing lines, sewing threads, screen door cords, fishing nets, longlines, geogrids, protective gloves, ripstop for protective clothing and outdoor wear, rider suits, sports rackets, strings, medical catheter reinforcement materials, sutures, screen mesh, filters, printed circuit board base fabrics, mesh conveyor belts, papermaking belts, dryer canvases, airships, balloons, airbags, speaker cones, reinforcement materials for various hoses and pipes, and reinforcement materials for rubber and plastics such as tires and conveyor belts. It is particularly well utilized in printed circuit board base fabrics. Furthermore, because it can be dyed using common methods, it is particularly well utilized in high-end processed products such as sailcloth, ropes, land nets, fishing lines, fishing nets, longlines, ripstop for protective clothing and outdoor wear, reinforcing materials such as rubber and plastic, and general clothing.

[0091] As described above with reference to the drawings, preferred embodiments of the present invention have been explained. However, those skilled in the art will readily anticipate various changes and modifications within the obvious scope by reviewing this specification. Therefore, such changes and modifications will be interpreted as falling within the scope of the invention as defined by the claims.

Claims

1. A core-sheath composite fiber having a sea-island structure in which the core component comprises a fused anisotropic aromatic polyester (polymer A), and the sheath component comprises a flexible thermoplastic polymer (polymer B) and a fused anisotropic aromatic polyester (polymer C), wherein the polymer B forms a sea component, the polymer C forms an island component, and a plurality of island components are dispersed within the sea component, The proportion of the B polymer component in the core-sheath composite fiber is 5% by weight or more and 20% by weight or less. A core-sheath composite fiber in which, when the core-sheath composite fiber is cut in the longitudinal direction of the fiber, the maximum width of the island having the widest width in the direction perpendicular to the fiber is defined as the maximum width W, and in the island having the maximum width W, the ratio L1 / W of the maximum diagonal length L1 that overlaps with the diagonal line in the sheath component that extends at a predetermined angle of 10° with respect to the longitudinal direction of the fiber from one end to the other in the longitudinal direction of the fiber, to the maximum width W of the island is 5.0 or more.

2. A core-sheath composite fiber according to claim 1, wherein the maximum width W is 0.65 μm or less.

3. A core-sheath composite fiber according to claim 1 or 2, wherein the thickness of the sheath component in the fiber radial direction is 0.8 to 5.0 μm.

4. A core-sheath composite fiber according to any one of claims 1 to 3, wherein the polymer A and the polymer C are melt-isotropic aromatic polyesters having the same main constituent units.

5. A core-sheath composite fiber according to any one of claims 1 to 4, wherein the weight ratio of the core component to the sheath component, i.e., the core component / sheath component, is 65 / 35 to 97 / 3.

6. A core-sheath composite fiber according to any one of claims 1 to 5, wherein the single filament fineness of the core-sheath composite fiber is 1 to 120 dtex.

7. A fiber structure comprising at least a portion of the core-sheath composite fiber described in any one of claims 1 to 6.

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