Liquid crystal polyester fiber and method for producing same

Abstract

Provided is a liquid crystal polyester fiber excellent in liquid absorption. The liquid crystal polyester fiber includes a fatty acid metal salt having 9 or more carbon atoms attached to a fiber surface. For example, the liquid crystal polyester fiber may an arithmetical mean height Sa of the fiber surface of 7.5 nm or less measured in accordance with ISO 25178. The liquid crystal polyester fiber may have a tenacity of 20 cN / dtex or more. The liquid crystal polyester fiber may have an amount of the fatty acid metal salt attached of 0.01 to 2.0 wt%.

Description

LIQUID CRYSTAL POLYESTER FIBER AND METHOD FOR PRODUCING SAME CROSS REFERENCE TO THE RELATED APPLICATION

[0001] This application is based on and claims Convention priority to Japanese patent application No. 2023-221579, filed December 27, 2023. FIELD OF THE INVENTION

[0002] The present invention relates to a liquid crystal polyester fiber and a method for producing the same. BACKGROUND OF THE INVENTION

[0003] A liquid crystal polyester fiber is formed of a polymer having a rigid molecular structure, and has high strength and high elastic modulus and is excellent in heat resistance and dimensional stability due to high orientation of molecular chains. Therefore, such a fiber is expected to be used for various applications such as general industrial materials, civil engineering and construction materials, reinforcing materials, electrical and electronic component materials, and protective clothing.

[0004] For example, Patent Document 1 (JP Laid-open Patent Publication No. 2006-336147) discloses a melt-anisotropic aromatic polyester fiber including 0.05 to 2 mass% of inorganic fine particles having an average particle size of 0.001 to 1 μm attached to a surface of a single fiber, having a single fiber fineness of 0.01 to 1.5 dtex, and having a tenacity of 15 cN / dtex or more after heat treatment.

[0005] Patent Document 2 (JP Laid-open Patent Publication No. 2016- 169464) discloses a liquid crystal polyester monofilament being a monofilament made of a liquid crystal polyester, having fine roughness on a fiber surface, having a surface roughness (Ra) of the fine roughness on the fiber surface of 0.015 µm or more and 0.100 µm or less, and having a maximum diameter reduction proportion of 8.0% or less.

[0006] Patent Document 3 (JP Laid-open Patent Publication No. 2013- 133576) discloses a liquid crystal polyester multifilament formed of a liquid crystal polyester containing 0.01 to 1 wt% of a metallic soap when a total weight of a fiber is 100 wt%. 5 CONVENTIONAL ART DOCUMENT PATENT DOCUMENT

[0007] [Patent Document 1] JP Laid-open Patent Publication No. 2006- 336147 [Patent Document 2] JP Laid-open Patent Publication No. 2016- [Patent Document 3] JP Laid-open Patent Publication No. 2013- 133576 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, while a liquid crystal polyester fiber has high mechanical properties, the liquid crystal polyester fiber has low liquid absorption due to hydrophobicity and high orientation of the liquid crystal polyester. Therefore, for example, there have been the problem that the comfort in clothing applications such as protective clothing is not good and the problem that the liquid crystal polyester fiber is poor in adhesiveness to a matrix resin where it is used as a reinforcing material in composite material applications.

[0009] Patent Document 1 describes that attaching inorganic fine particles to a surface of a melt-anisotropic aromatic polyester fiber suppresses adhesion between single fibers to improve separability to single fibers, and thus texture of clothing made using such a fiber is good. However, it has been difficult to improve liquid absorption only by attaching the inorganic fine particles to the fiber surface.

[0010] In Patent Document 2, fine roughness is formed by the scission of the liquid crystal polyester molecular chain on the fiber surface by a phosphate compound. However, even if a conventional oil agent such as a phosphate compound is applied or the shape of the fiber surface is modified, liquid absorption has not been improved.

[0011] In Patent Document 3, a specific amount of a metallic soap is contained inside the fiber by mixing the metallic soap with a liquid crystal polyester and melt-spinning the mixture. However, it has not been possible to improve the properties of the fiber surface only by containing the metallic soap inside the fiber, and the liquid absorption has not been improved.

[0012] Therefore, an object of the present invention is to solve the above problems and to provide a liquid crystal polyester fiber having excellent liquid absorption and a method for producing the same. MEANS FOR SOLVING THE PROBLEMS

[0013] As a result of intensive studies to achieve the above object, the inventors of the present invention have found that attaching a fatty acid metal salt having a specific number of carbon atoms to a surface of a liquid crystal polyester fiber improves liquid absorption, leading to the completion of the present invention.

[0014] That is, the present invention may include the following aspects. [Aspect 1] A liquid crystal polyester fiber, including a fatty acid metal salt having 9 or more carbon atoms (preferably 10 to 20, and more preferably 10 to 18) attached to a fiber surface. [Aspect 2] The liquid crystal polyester fiber according to aspect 1, wherein an arithmetical mean height Sa of the fiber surface is 7.5 nm or less (preferably 0.1 to 6.0 nm, more preferably 1.0 to 5.0 nm, and further preferably 2.0 to 5.0 nm) measured in accordance with ISO 25178. [Aspect 3] The liquid crystal polyester fiber according to aspect 1 or 2, having a tenacity of 20 cN / dtex or more (preferably 22 cN / dtex or more, and more preferably 24 cN / dtex or more). [Aspect 4] The liquid crystal polyester fiber according to any one of aspects 1 to 3, wherein an amount of the fatty acid metal salt attached is 0.01 to 2.0 wt% (preferably 0.03 to 1.5 wt%, more preferably 0.1 to 1.0 wt%, further preferably 0.1 to 0.9 wt%, and even more preferably 0.1 to 0.8 wt%). [Aspect 5] The liquid crystal polyester fiber according to any one of aspects 1 to 4, wherein an amount of inorganic particles attached is 100 ppm by weight or less (preferably 10 ppm by weight or less, and more preferably 1 ppm by weight or less). [Aspect 6] The liquid crystal polyester fiber according to any one of aspects 1 to 5, wherein a maximum height difference P-V of the fiber surface is 1 to 80 nm (preferably 10 to 60 nm, and more preferably 20 to 40 nm) measured in accordance with ISO 25178. [Aspect 7] The liquid crystal polyester fiber according to any one of aspects 1 to 6, having a liquid absorption rate per unit circumference of 5.0% / µm or more (preferably 5.0 to 20% / μm, more preferably 6.0 to 15% / μm, and further preferably 7.0 to <semantics>10% / μm<annotation encoding="application / x-tex">10\% / \mu m< / annotation>< / semantics>). [Aspect 8] The liquid crystal polyester fiber according to any one of aspects 1 to 7, having a metal to fiber dynamic friction coefficient of 0.18 or less (preferably 0.17 or less, and more preferably 0.16 or less). [Aspect 9] A fiber structure including the liquid crystal polyester fiber according to any one of aspects 1 to 8 in at least a part of the fiber structure. [Aspect 10] A method for producing a liquid crystal polyester fiber, including applying a fatty acid metal salt having 9 or more carbon atoms (preferably 10 to 20, and more preferably 10 to 18) to a surface of a liquid crystal polyester fiber. [Aspect 11] The method according to aspect 10, further including heat-treating an as- spun fiber of the liquid crystal polyester fiber, wherein the applying is performed before and / or after the heat-treating. [Aspect 12] The method according to aspect 11, wherein the applying is performed at least before the heat-treating.

[0015] As used in the present specification, the singular forms "a", "an", and "the" are intended to include the plural forms including "at least one", unless the content clearly indicates otherwise. As used in the present specification, the terms "and / or", "at least one", and "one or more" include any and all combinations of the relevant listed items.

[0016] Any combination of at least two constructions, disclosed in the appended claims and / or the specification should be construed as included within the scope of the present invention. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention. EFFECT OF THE INVENTION

[0017] The liquid crystal polyester fiber according to the present invention is excellent in liquid absorption. DESCRIPTION OF EMBODIMENT

[0018] [Liquid Crystal Polyester Fiber] The liquid crystal polyester fiber includes a liquid crystal polyester. The liquid crystal polyester includes structural units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc. As long as the effect of the present invention is not impaired, the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not limited to a specific chemical composition. The liquid crystal polyester may be a liquid crystal polyester amide including structural units derived from aromatic diamines, aromatic hydroxy amines, or aromatic aminocarboxylic acids as long as the effect of the present invention is not impaired. For example, preferable structural units may include units shown in Table 1.

[0019] [Table 1] [Image disponible dans le document PDF, Image available in the PDF document] In the formula, X is selected from the following [Image disponible dans le document PDF, Image available in the PDF document] 1 m is an integer from 0 to 2, Y is a substituent selected from hydrogen atom, halogen atoms, alkyl groups, aryl groups, aralkyl groups, alkoxy groups, aryloxy groups, aralkyloxy groups.

[0020] In the structural units in Table 1, m is an integer from 0 to 2, and Y in the formula independently represents, as from one substituent to the number of substituents in the range of the replaceable maximum number of aromatic ring, a hydrogen atom, a halogen atom (for example, fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group and t-butyl group, etc.), an alkoxy group (for example, methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), an aryl group (for example, phenyl group, naphthyl group, etc.), an aralkyl group [for example, benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.], an aryloxy group (for example, phenoxy group, etc.), an aralkyloxy group (for example, benzyloxy group, etc.), and others.

[0021] As more preferable structural units, there may be mentioned structural units as described in Examples (1) to (20) shown in the following Tables 2, 3, and 4. It should be noted that where the structural unit in the formula is a structural unit which can show a plurality of structures, combination of two or more types may be used as structural units for a polymer. [Image disponible dans le document PDF, Image available in the PDF document] - • _ . [Image disponible dans le document PDF, Image available in the PDF document] 4 . . • [Table 4] [Image disponible dans le document PDF, Image available in the PDF document] . .

[0025] In the structural units shown in Tables 2, 3, and 4, n is an integer of 1 or 2, among each of the structural units, <semantics>n=1<annotation encoding="application / x-tex">n = 1< / annotation>< / semantics> and <semantics>n=2<annotation encoding="application / x-tex">n = 2< / annotation>< / semantics> may independently exist, or may exist in combination; each of the Y1 and Y2 independently represents, a hydrogen atom, a halogen atom (for example, fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group, and t-butyl group, etc.), an alkoxy group (for example, methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), an aryl group (for example, phenyl group, naphthyl group, etc.), an aralkyl group [for example, benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.], an aryloxy group (for example, phenoxy group, etc.), an aralkyloxy group (for example, benzyloxy group, etc.), and others. Among these, the preferable one may include a hydrogen atom, a chlorine atom, a bromine atom, and a methyl group.

[0026] Z may include substitutional groups denoted by following formulae.

[0027] [Chem. 1] [Image disponible dans le document PDF, Image available in the PDF document]

[0028] In one embodiment, the liquid crystal polyester may include a structural unit derived from a hydroxycarboxylic acid as a main component. The liquid crystal polyester may preferably include a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxy naphthoic acid. For example, the structural unit (A) may have a structural unit derived from 4- hydroxybenzoic acid (the following formula (A)), and the structural unit (B) may have a structural unit derived from 6-hydroxy-2-naphthoic acid (the following formula (B)). In order to improve melt-formability, the ratio of the structural unit (A) and the structural unit (B) may preferably be in a range of former / latter of 9 / 1 to <semantics>1 / 1<annotation encoding="application / x-tex">1 / 1< / annotation>< / semantics>, more preferably from <semantics>7 / 1<annotation encoding="application / x-tex">7 / 1< / annotation>< / semantics> to <semantics>1 / 1<annotation encoding="application / x-tex">1 / 1< / annotation>< / semantics>, and further preferably from <semantics>5 / 1<annotation encoding="application / x-tex">5 / 1< / annotation>< / semantics> to <semantics>1 / 1<annotation encoding="application / x-tex">1 / 1< / annotation>< / semantics>.

[0029] [Chem. 2] [Image disponible dans le document PDF, Image available in the PDF document]

[0030] [Chem. 3] [Image disponible dans le document PDF, Image available in the PDF document]

[0031] The liquid crystal polyester may include the structural unit derived from 4-hydroxybenzoic acid. In the case where the liquid crystal polyester includes both the structural unit (A) and the structural unit (B), a content of the structural unit derived from 4-hydroxybenzoic acid based on a total content of all the structural units may be 50 mol% or more, preferably 53 mol% or more, more preferably 60 mol% or more, further preferably 65 mol% or more, and even more preferably 70 mol% or more. The upper limit of the content of the structural unit derived from 4-hydroxybenzoic acid in the liquid crystal polyester is not particularly limited to a specific value, and may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0032] The liquid crystal polyester may include the structural unit derived from 6-hydroxy-2-naphthoic acid. In the case where the liquid crystal polyester includes both the structural unit (A) and the structural unit (B), a content of the structural unit derived from 6-hydroxy-2-naphthoic acid based on the total content of all the structural units may be 4 to 45 mol%.

[0033] Furthermore, a total content of the structural unit (A) and the structural unit (B) based on the total content of all the structural units may be, for example, 65 mol% or more, more preferably 70 mol% or more, and further preferably 80 mol% or more.

[0034] In another embodiment, the liquid crystal polyester may include a structural unit represented by the following formula (I) (structural unit (I)), a structural unit represented by the following formula (II) (structural unit (II)), and at least one structural unit selected from the group consisting of a structural unit represented by the following formula (III) (structural unit (III)) and a structural unit represented by the following formula (IV) (structural unit (IV)). [Image disponible dans le document PDF, Image available in the PDF document] (I) [Image disponible dans le document PDF, Image available in the PDF document] (II) [Image disponible dans le document PDF, Image available in the PDF document] (III) [Image disponible dans le document PDF, Image available in the PDF document] (IV) (wherein Ar1 represents at least one group selected from the group consisting of a phenylene group, a naphthylene group, and a biphenylylene group, each of Ar2, Ar3, and Ar4 independently represents at least one group selected from the group consisting of a phenylene group, a naphthylene group, a biphenylylene group, and a diphenyl ether diyl group, and hydrogen atoms in each aromatic ring in Ar1, Ar2, Ar3, and Ar4 may be independently substituted with a halogen atom, an alkyl group, an alkoxy group, an aryl group, an aralkyl group, an aryloxy group, or an aralkyloxy group)

[0035] The structural unit (I) is a structural unit derived from an aromatic hydroxycarboxylic acid, and may be preferably a structural unit in which Ar1 is a 1,4-phenylene group (structural unit derived from 4-hydroxybenzoic acid) and a structural unit in which Ar1 is a 2,6-naphthylene group (structural unit derived from 6-hydroxy-2-naphthoic acid).

[0036] The structural unit (II) is a structural unit derived from an aromatic dicarboxylic acid, and may be preferably a structural unit in which Ar2 is a 1,4- phenylene group (structural unit derived from terephthalic acid), a structural unit in which Ar2 is a 1,3-phenylene group (structural unit derived from isophthalic acid), a structural unit in which Ar2 is a 2,6-naphthylene group (structural unit derived from 2,6-naphthalenedicarboxylic acid), and a structural unit in which Ar2 is a diphenyl ether-4,4'-diyl group (structural unit derived from diphenyl ether- 4,4'-dicarboxylic acid).

[0037] The structural unit (III) is a structural unit derived from an aromatic diol, and may be preferably a structural unit in which Ar3 is a 1,4-phenylene group (structural unit derived from hydroquinone), a structural unit in which Ar3 is a 4,4'- biphenylylene group (structural unit derived from 4,4'-dihydroxybiphenyl), a structural unit in which Ar3 is a phenyl-1,4-phenylene group (structural unit derived from phenylhydroquinone), and a structural unit in which Ar3 is a diphenyl ether-4,4'-diyl group (structural unit derived from 4,4'-dihydroxydiphenyl ether).

[0038] The structural unit (IV) is a structural unit derived from an aromatic hydroxy amine, and may be preferably a structural unit in which Ar4 is a 1,4- phenylene group (structural unit derived from 4-aminophenol) and a structural unit in which Ar4 is a 4,4'-biphenylylene group (structural unit derived from 4-amino- 4'-hydroxybiphenyl).

[0039] A content of the structural unit (I) in the liquid crystal polyester based on a total content of all the structural units may be 20 to 80 mol%, preferably 30 to 75 mol%, and more preferably 40 to 70 mol%.

[0040] A content of the structural unit (II) in the liquid crystal polyester based on a total content of all the structural units may be 10 to 40 mol%, preferably 12.5 to 35 mol%, and more preferably 15 to 30 mol%.

[0041] A total content of the structural units (III) and (IV) in the liquid crystal polyester based on a total content of all the structural units may be 10 to 40 mol%, preferably 12.5 to 35 mol%, and more preferably 15 to 30 mol%.

[0042] A molar ratio of the content of the structural unit (II) to the total content of the structural units (III) and (IV), as <semantics>(II) / [(III)+(IV)]<annotation encoding="application / x-tex">(II) / [(III) + (IV)]< / annotation>< / semantics>, may be <semantics>90 / 100<annotation encoding="application / x-tex">90 / 100< / annotation>< / semantics> to <semantics>100 / 90<annotation encoding="application / x-tex">100 / 90< / annotation>< / semantics>, preferably 95 / 100 to 100 / 95, more preferably 98 / 100 to 100 / 98, and further preferably 100 / 100.

[0043] The liquid crystal polyester may include two or more types of each of the structural units (I) to (IV). The content of each structural unit represents the total content of all structural units corresponding to the structural unit, and for example, in the case where the liquid crystal polyester includes two or more types of the structural unit (I), the content of the structural unit (I) represents the total content of these types.

[0044] In the liquid crystal polyester, the total content of the structural units (I) to (IV) based on the total content of all the structural units may be, for example, 90 mol% or more, preferably 95 mol% or more, more preferably 99 mol% or more, and further preferably 100 mol%.

[0045] The liquid crystal polyester preferably has a combination including a structural unit having a naphthalene skeleton. For example, a total content of a structural unit including a 2,6-naphthylene group in the liquid crystal polyester based on the total content of all the structural units may be 28 mol% or more, preferably 30 mol% or more, more preferably 40 mol% or more, further preferably 50 mol% or more, even more preferably 55 mol% or more, particularly preferably 60 mol% or more, more particularly preferably 65 mol% or more, and further particularly preferably 70 mol% or more. Furthermore, from the viewpoint of improving melt-formability, the total content of the structural unit including the 2,6-naphthylene group in the liquid crystal polyester based on the total content of all the structural units may be 95 mol% or less, preferably 90 mol% or less, and more preferably 85 mol% or less. As the structural unit including the 2,6- naphthylene group, a structural unit derived from 6-hydroxy-2-naphthoic acid (the structural unit (B) represented by the above formula (B), a structural unit (I) in which Ar1 is a 2,6-naphthylene group) and a structural unit derived from 2,6- naphthalenedicarboxylic acid (a structural unit (II) in which Ar2 is a 2,6- naphthylene group) are preferable.

[0046] The liquid crystal polyester may preferably have a melting point (hereinafter sometimes referred to as Mp0) in the range of from 250 to 380°C, more preferably from 255 to 370°C, further preferably from 260 to 360°C, even more preferably from 260 to 340°C, and particularly preferably from 260 to 330°C. In the present specification, the melting point refers to a main endothermic peak temperature determined and observed using a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of a sample is encapsulated in an aluminum pan and taken into the DSC device. Then, the temperature is elevated at a rate of 10°C / min from room temperature (e.g., 25°C) while supplying nitrogen as a carrier gas at a flow rate of 200 mL / min to measure an endothermic peak. Depending on the type of polymer, some polymers may not show a clear peak in the 1st run of DSC measurement. If no clear peak appears in the 1st run of DSC measurement, the sample is heated up to a temperature 50°C higher than the expected flow temperature in a temperature elevation rate of 50°C / min. After keeping the temperature for 3 minutes so as to make the sample completely molten, the sample is cooled at a cooling rate of 80°C / min to 50°C, and then is elevated at 10°C / min to measure the endothermic peak thereof.

[0047] It should be noted that the liquid crystal polyester may be mixed with thermoplastic polymers, such as a polyethylene terephthalate, a modified- polyethylene terephthalate, a polyolefin, a polycarbonate, a polyamide, a polyphenylene sulfide, a polyether ether ketone, and a fluoro-resin, as long as the effects of the present invention are not impaired. In addition, the liquid crystal polyester may be mixed with various additives including: inorganic substances such as titanium oxide, kaolin, silica, and barium oxide; carbon black; a colorant such as dyes and paints; an antioxidant; an ultraviolet-ray absorbent; a light stabilizer; etc.

[0048] As long as the effects of the present invention are not impaired, the liquid crystal polyester fiber may be a mixed spun fiber obtained by mixing and spinning the liquid crystal polyester with the above-described thermoplastic polymer and various additives, or may be a composite spun fiber obtained by simultaneously spinning the liquid crystal polyester and different components of the above-described thermoplastic polymer from separate spinnerets. The liquid crystal polyester fiber may be a non-composite spun fiber or may be a composite spun fiber. In particular, it is preferable that the liquid crystal polyester be present on the fiber surface, and it is preferable that a fatty acid metal salt described below be attached to the fiber surface formed of the liquid crystal polyester.

[0049] The liquid crystal polyester fiber may contain the liquid crystal polyester in an amount of 50 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, further preferably 95 wt% or more, and even more preferably 98 wt% or more.

[0050] The liquid crystal polyester fiber includes a fatty acid metal salt having 9 or more carbon atoms attached to a fiber surface. In this case, the liquid crystal polyester fiber includes a fiber body part mainly containing the liquid crystal polyester, and a surface-attached part that is formed so as to cover the fiber body and contains the fatty acid metal salt having 9 or more carbon atoms. In the present invention, it has been found that attaching the fatty acid metal salt having the specific number of carbon atoms to the surface of the liquid crystal polyester fiber improves liquid absorption. It is presumed that where an amphiphilic oil agent is attached to the surface of the liquid crystal polyester fiber, the hydrophobic part of the oil agent is directed toward the surface side of the hydrophobic liquid crystal polyester fiber, and the hydrophilic part is directed outward, so that the hydrophilicity is improved and the liquid absorption is improved. The present inventors have found that, while an amphiphilic oil agent such as a metal salt (e.g., a phosphate oil agent) other than a carboxylate salt and a fatty acid metal salt having a relatively short carbon chain cannot sufficiently exhibit the effect of improving the liquid absorption, the fatty acid metal salt having the specific number of carbon atoms can improve the liquid absorption probably because a long carbon chain and a carboxy group interact with the liquid crystal polyester molecules.

[0051] A fatty acid in the fatty acid metal salt having 9 or more carbon atoms may be either a saturated or unsaturated fatty acid, and may be a hydroxy fatty acid having a hydroxy group. Examples thereof include pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, heneicosylic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, lauroleic acid, myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, gadoleic acid, eicosenoic acid, arachidonic acid, erucic acid, hydroxystearic acid, and ricinoleic acid. These fatty acids may be included singly or in combination of two or more. The number of carbon atoms of the fatty acid may be preferably 10 to 20, and more preferably 10 to 18, from the viewpoint of improving the liquid absorption of the liquid crystal polyester fiber, as well as imparting solubility or dispersibility in water in order to facilitate application of an oil agent.

[0052] Examples of a metal salt in the fatty acid metal salt having 9 or more carbon atoms include a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a calcium salt, a barium salt, an aluminum salt, and a zinc salt. Among these metal salts, alkali metal salts such as a lithium salt, a sodium salt, and a potassium salt are preferable, and a potassium salt is more preferable from the viewpoint of imparting high water solubility in order to facilitate application of an oil agent. Examples of the fatty acid metal salt having 9 or more carbon atoms include potassium caprate, potassium laurate, potassium myristate, potassium palmitate, potassium stearate, potassium oleate, and potassium linoleate. The liquid crystal polyester fiber includes the fatty acid metal salt having 9 or more carbon atoms attached to the fiber surface, and may include a component other than the fatty acid metal salt having 9 or more carbon atoms (for example, amphiphilic compounds other than fatty acid metal salts, fatty acid metal salts having 8 or less carbon atoms, and the like) as long as the effects of the present invention are not impaired.

[0053] In the liquid crystal polyester fiber, an amount of the above-described fatty acid metal salt attached may be 0.01 wt% or more, preferably 0.03 wt% or more, and more preferably 0.1 wt% or more from the viewpoint of improving the liquid absorption. The amount of the above-described fatty acid metal salt attached may be 2.0 wt% or less, preferably 1.5 wt% or less, and from the viewpoint of reducing an arithmetical mean height Sa of the fiber surface, the amount may be more preferably 1.0 wt% or less, further preferably 0.9 wt% or less, and even more preferably 0.8 wt% or less. In the present specification, the amount of the fatty acid metal salt attached refers to a ratio of the amount of the fatty acid metal salt attached based on the total weight of the fiber including the attached materials on the fiber surface, and is a value measured by the method described in Examples below.

[0054] The liquid crystal polyester fiber may have a liquid absorption rate per unit circumference of 5.0% / µm or more, preferably 6.0% / µm or more, and more preferably 7.0% / µm or more. The upper limit of the liquid absorption rate per unit circumference is not particularly limited to a specific one, and may be, for example, 20% / µm or less, and in the case of applications in which the liquid absorption is required to be controlled, may be preferably 15% / µm or less, and more preferably 10% / µm or less. In the present specification, the liquid absorption rate per unit circumference refers to a liquid absorption rate (water absorption rate) based on the circumference of the cross section of a single fiber calculated from a single fiber fineness assuming that the cross section of the fiber is a perfect circle, and is measured by the method described in Examples below.

[0055] The liquid crystal polyester fiber may have an arithmetical mean height Sa of the fiber surface of 7.5 nm or less. Although the arithmetical mean height Sa of the fiber surface is affected by the state of the surface-attached part, where the fatty acid metal salt having the specific number of carbon atoms is attached to the fiber surface, the unevenness of the fiber surface can be reduced, probably because the long carbon chain and the carboxy group of the fatty acid metal salt interact with the liquid crystal polyester molecules on the fiber surface, and the fatty acid metal salt moves to cover the fiber surface and makes the fiber surface uniform. This can be achieved where the fatty acid metal salt having the specific number of carbon atoms is used, and in the case of a fatty acid metal salt having 8 or less carbon atoms, there is the tendency that the arithmetical mean height Sa of the fiber surface cannot be made sufficiently small, probably because the interaction with the liquid crystal polyester molecules is not sufficient. By adjusting the arithmetical mean height Sa of the fiber surface within a specific range, the coefficient of friction between the fiber and the object subjected to friction can be reduced, and the fiber is excellent in abrasion resistance. The arithmetical mean height Sa of the fiber surface may be preferably 6.0 nm or less, and more preferably 5.0 nm or less, and may be 0.1 nm or more, preferably 1.0 nm or more, and more preferably 2.0 nm or more. The arithmetical mean height Sa is measured in accordance with ISO 25178, and represents the average value of absolute values of differences in height of each point from the mean plane of the surface within the definition area. In the present specification, the arithmetical mean height Sa is measured by the method described in Examples below.

[0056] The liquid crystal polyester fiber may have an arithmetic mean roughness Ra of the fiber surface of 20 nm or less. The arithmetic mean roughness Ra of the fiber surface may be preferably 14 nm or less, more preferably 12 nm or less, and further preferably 10 nm or less, and may be 0.1 nm or more, preferably 1.0 nm or more, and more preferably 3.0 nm or more. The arithmetic mean roughness Ra of the fiber surface may be 0.1 to 20 nm, preferably 0.1 to 14 nm, more preferably 1.0 to 12 nm, and further preferably 3.0 to 10 nm. The arithmetic mean roughness Ra is an index of roughness in the height direction measured in accordance with JIS B 0601: 2001, and represents the unevenness state of a section in a roughness profile of a sampling length as the average value of the absolute values of deviations from a mean line to the roughness profile. In the present specification, the arithmetic mean roughness Ra is measured from a profile of a surface of a single fiber in a fiber axis direction, and is measured by the method described in Examples below.

[0057] The liquid crystal polyester fiber may have a maximum height difference P-V of the fiber surface of 80 nm or less, preferably 60 nm or less, and more preferably 40 nm or less, and 1 nm or more, preferably 10 nm or more, and more preferably 20 nm or more. The maximum height difference P-V of the fiber surface may be 1 to 80 nm, preferably 10 to 60 nm, and more preferably 20 to 40 nm. The maximum height difference P-V is measured in accordance with ISO 25178, and represents the sum of the maximum value of the peak height and the maximum value of the valley depth in a profile of a sampling length. In the present specification, the maximum height difference P-V is measured by the method described in Examples below.

[0058] In the liquid crystal polyester fiber, an amount of inorganic particles attached may be 100 ppm by weight or less, preferably 10 ppm by weight or less, and more preferably 1 ppm by weight or less from the viewpoint of adjusting the surface roughness and achieving low friction. In the present specification, the amount of the inorganic particles attached refers to a ratio of the amount of the inorganic particles attached based on the total weight of the fiber including the attached materials on the fiber surface.

[0059] The liquid crystal polyester fiber may have a metal to fiber dynamic friction coefficient of 0.18 or less, preferably 0.17 or less, and more preferably 0.16 or less. The lower limit of the metal to fiber dynamic friction coefficient is not particularly limited to a specific one, and may be, for example, 0.10 or more. In the present specification, the metal to fiber dynamic friction coefficient is measured by the method described in Examples below.

[0060] The liquid crystal polyester fiber may have a tenacity of 20 cN / dtex or more, preferably 22 cN / dtex or more, and more preferably 24 cN / dtex or more. The upper limit of the tenacity is not particularly limited to a specific one, and may be, for example, about 40 cN / dtex. In the present specification, the tenacity of the liquid crystal polyester fiber refers to tensile strength, and is a value measured by the method described in Examples below.

[0061] The liquid crystal polyester fiber may have an adjusted single fiber fineness depending on the application, etc. The single fiber fineness may be, for example, 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. The lower limit of the single fiber fineness is not particularly limited to a specific one, and may be, for example, about 0.01 dtex. The single fiber fineness is a value measured by the method described in Examples below.

[0062] The liquid crystal polyester fiber may be a monofilament or a multifilament. In the case of multifilament, the number of filaments may be adjusted depending on the application, etc. For example, the number of filaments may be 2 to 5,000 filaments, preferably 3 to 4,000 filaments, and more preferably 5 to 3,000 filaments.

[0063] The total fineness of the liquid crystal polyester fiber can be adjusted depending on the application, etc. For example, the total fineness may be 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 5,000 dtex or less, and further preferably 2,000 dtex or less. The lower limit of the total fineness is not particularly limited to a specific one, and may be, for example, about 1 dtex.

[0064] [Method for Producing Liquid Crystal Polyester Fiber] A method for producing a liquid crystal polyester fiber includes applying a fatty acid metal salt having 9 or more carbon atoms to a surface of a liquid crystal polyester fiber. In the present invention, it has been found that attaching a fatty acid metal salt having the specific number of carbon atoms to the surface of the liquid crystal polyester fiber improves liquid absorption.

[0065] In the step of applying the fatty acid metal salt, the fatty acid metal salt described above can be used, and as an embodiment of applying the fatty acid metal salt to the liquid crystal polyester fiber, an oil agent solution in which the fatty acid metal salt is dissolved in a medium or an oil agent dispersion in which the fatty acid metal salt is dispersed in a medium may be used. An application method is not particularly limited to a specific one, and examples thereof include known application methods such as an impregnation treatment, a discharge treatment, a coating treatment, and a dipping and squeezing treatment, and it is preferable to apply the fatty acid metal salt to the running liquid crystal polyester fiber using an oiling guide such as an oiling roller and a ruling pen.

[0066] The method for producing the liquid crystal polyester fiber may further include heat-treating an as-spun fiber of the liquid crystal polyester fiber. By performing heat treatment on the as-spun fiber of the liquid crystal polyester fiber, solid-phase polymerization of the liquid crystal polyester can be advanced to improve the tenacity of the fiber.

[0067] In the case of including the heat-treating step, the step of applying the fatty acid metal salt may be performed before and / or after the heat-treating step. In the case of applying before the heat-treating step, the fatty acid metal salt is applied to the as-spun fiber of the liquid crystal polyester fiber, and for example, the fatty acid metal salt may be applied while the as-spun fiber is wound, or may be applied when the as-spun fiber which is once wound by spinning is unwound. In the case of applying after the heat-treating step, the fatty acid metal salt is applied to a heat-treated fiber of the liquid crystal polyester fiber, and for example, the fatty acid metal salt may be applied to the heat-treated fiber as a finishing oil agent.

[0068] The step of applying the fatty acid metal salt is preferably performed at least before the heat-treating step from the viewpoint of improving the liquid absorption. Although the mechanism of action is not clear, where the heat- treating is performed after the fatty acid metal salt having the specific number of carbon atoms is applied to the as-spun fiber, the liquid absorption can be improved probably because the fatty acid metal salt applied as an aqueous solution or the like is in an absolutely dry state due to the heat-treating and moisture can be easily absorbed.

[0069] The step of applying the fatty acid metal salt may be performed so that the amount of the fatty acid metal salt attached is 0.01 wt% or more, preferably 0.03 wt% or more, and more preferably 0.1 wt% or more from the viewpoint of improving the liquid absorption of the liquid crystal polyester fiber. Furthermore, where the step of applying the fatty acid metal salt is performed before the heat- treating step, if the amount of the fatty acid metal salt attached to the liquid crystal polyester fiber to be subjected to the heat treatment is too large, the tenacity tends not to be sufficiently improved, probably because the progress of solid phase polymerization in the heat treatment is inhibited. Therefore, from the viewpoint of not inhibiting the progress of solid phase polymerization in the heat treatment, the fatty acid metal salt may be applied so that the amount of the fatty acid metal salt attached is 2.0 wt% or less, preferably 1.5 wt% or less, more preferably 1.0 wt% or less, further preferably 0.9 wt% or less, and even more preferably 0.8 wt% or less. Where the fatty acid metal salt having the specific number of carbon atoms among fatty acid metal salts is applied in such an application amount, the tenacity can be sufficiently improved in the subsequent heat treatment, so that both the liquid absorption and the tenacity can be achieved. On the other hand, in the case of a fatty acid metal salt having 8 or less carbon atoms, there is a tendency that the tenacity cannot be sufficiently improved by the heat treatment, probably because the balance of amphiphilicity affects the morphology when the fatty acid metal salt is applied to the fiber surface, inhibiting solid phase polymerization of the liquid crystal polyester.

[0070] The method of the heat treatment is not particularly limited to a specific one, and may be, for example, a batch-type heat treatment or a continuous heat treatment by conveyance. For example, the batch-type heat treatment may be carried out in a state where the as-spun fiber is wound onto a bobbin in the form of a package, or in a state of hank as well as tow. The heat treatment may be preferably carried out in a package from the viewpoint of simpler equipment and improved productivity. In the case of the continuous heat treatment by conveyance, the conveyance method may be either contact conveyance (for example, a conveyor type, a support roll type, a heated roller type), or non-contact conveyance (a roll-to-roll type).

[0071] For the heat treatment, a publicly known method can be used, and examples thereof include atmosphere heating, contact heating, and other heating procedures. As the atmosphere, air, an inert gas (for example, nitrogen and argon), a combined atmosphere thereof, or the like is suitably used. In addition, there is no problem even if the heat treatment is carried out under vacuum.

[0072] A heat treatment temperature may be 230°C or higher, and from the viewpoint of efficient strength improvement, the heat treatment temperature may be preferably 240°C or higher, and more preferably 250°C or higher. In order to prevent heat-treated fibers from being fused during heat treatment, the heat treatment temperature may be lower than the melting point (Mp) of the as-spun fiber to be subjected to the heat-treating step, and may be, for example, in the range of 230°C or higher, Mp – 50°C or higher and lower than Mp°C, preferably Mp – <semantics>40∘<annotation encoding="application / x-tex">40^{\circ}< / annotation>< / semantics>C or higher and lower than Mp°C, and more preferably Mp <semantics>−30∘<annotation encoding="application / x-tex">-30^{\circ}< / annotation>< / semantics>C or higher and lower than Mp°C. In the heat-treating step, since the melting point of the liquid crystal polyester fiber increases with the progress of solid phase polymerization, it is sufficient to carry out the heat-treating step at a first heat treatment temperature of lower than the melting point (Mp) of the as-spun fiber. From the viewpoint of efficient strength improvement, the heat treatment temperature may be step-wisely raised according to the progress of solid phase polymerization, so that the heat treatment may be performed at a temperature beyond the melting point (melting point of as-spun fiber) at the time of starting the heat-treating step.

[0073] Depending on the heat treatment method and / or the heat treatment temperature, a heat treatment period may be set as appropriate. For example, the heat treatment period may be set in the range of 15 minutes to 30 hours, and may be preferably 2 to 24 hours, and more preferably 3 to 20 hours. Here, the heat treatment period refers to a retention time at a predetermined heat treatment temperature.

[0074] In the method for producing the liquid crystal polyester fiber, a strength ratio of the liquid crystal polyester fiber before and after the heat-treating step may be 1.5 times or more, preferably 1.8 times or more, and more preferably 2.0 times or more. The upper limit of the strength ratio of the liquid crystal polyester fiber before and after the heat-treating step is not particularly limited to a specific one, and may be, for example, 10 times or less. Here, the strength ratio before and after the heat-treating step refers to a value obtained by dividing a tenacity of the liquid crystal polyester fiber after the heat-treating step by a tenacity of the liquid crystal polyester fiber (as-spun fiber) before the heat-treating step.

[0075] [Fiber Structure] The liquid crystal polyester fiber can be used for various applications as a fiber structure at least partially including the liquid crystal polyester fiber. The fiber structure including the liquid crystal polyester fiber can be used as various fiber configurations such as staple fibers, short-cut fibers, filament yarns, spun yarns, cordage, and ropes. Further, the fiber structure can also be used as various fabrics such as nonwoven fabrics, woven fabrics, and knitted fabrics, using the liquid crystal polyester fibers. Such fibers and fabrics can be produced using the liquid crystal polyester fibers by known methods.

[0076] The fiber structure may be made by combining the liquid crystal polyester fibers with other fibers as long as the effects of the present invention are not impaired. The fiber structure may be, for example, a combined yarn using the liquid crystal polyester fibers and other fibers (e.g., a commingled yarn made from the liquid crystal polyester fibers and other fibers, or the like). The fiber structure may also be a blend fabric using the liquid crystal polyester fibers and other fibers (e.g., a combined fabric in which the liquid crystal polyester fibers and other fibers are used in combination, a layered material in which a fabric of the liquid crystal polyester fibers and a fabric of other fibers are used in combination, or others).

[0077] The liquid crystal polyester fiber can be used in various forms of fiber structures for various applications such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various fiber products. For example, the liquid crystal polyester fiber can be used for highly processed products such as tension members (electric cables, optical fibers, umbilical cables, heater wire core yarns, cords for various electrical products such as earphone cords, etc.), sailcloth, ropes (marine ropes, mountaineering ropes, crane ropes, yacht ropes, tug ropes, etc.), climbing ropes, land nets (safety nets, nets of golf practice range, etc.), slings, life lines, fishing lines, sewing threads, cords for screen doors and screen windows, fishing nets, longlines, geogrids, protective gloves, ripstop for protective clothing and outdoor clothing, rider suits, sports rackets, guts, medical catheter reinforcing materials, sutures, screen gauzes, filters, base cloth for printed circuit boards, exterior materials for electronic devices, mesh-like conveyor belts, paper-making belts, dryer canvas, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses and pipes, and reinforcing materials for rubbers and plastics such as tires and conveyor belts EXAMPLES

[0078] Hereinafter, the present invention will be demonstrated by way of some examples that are presented only for the sake of illustration, which are not to be construed as limiting the scope of the present invention. It should be noted that in the following Examples and Comparative Examples, various properties were evaluated in the following manners.

[0079] (Melting Point of Resin Chip (Granular Molded Body)) In accordance with the JIS K 7121, a melting point was determined as a main endothermic peak temperature observed in measurement using a differential scanning calorimeter (DSC; "DSC60A Plus", manufactured by SHIMADZU CORPORATION). Specifically, 4 to 6 mg of a sample was encapsulated in an aluminum pan and taken into the DSC device. Then, the temperature was elevated at a rate of 10°C / min from 25°C while supplying nitrogen as a carrier gas at a flow rate of 200 mL / min to measure an endothermic peak attributed to the liquid crystal polyester.

[0800] (Total Fineness and Single Fiber Fineness) In accordance with 8.3.1 Method A in JIS L 1013: 2010, the liquid crystal polyester fiber was reeled into a hank of 10 m using a sizing reel "Wrap Reel by Motor Driven" manufactured by DAIEI KAGAKU SEIKI MFG. Co., Ltd., to measure the weight of the liquid crystal polyester fibers. The measurement was conducted three times. Each of the weights (g) was multiplied by 1000, and the average of the three measurements was regarded as a total fineness (dtex) of the obtained liquid crystal polyester fibers. Thus-obtained total fineness was divided by the number of filaments in the liquid crystal polyester fibers so as to give a single fiber fineness (dtex).

[0081] (Arithmetical Mean Height Sa and Maximum Height Difference P-V) One single fiber was taken out from the liquid crystal polyester fibers (multifilament), and the fiber surface was measured under the following conditions using a scanning probe microscope ("Environment Control Unit E-sweep" manufactured by Hitachi High-Tech Science Corporation). Measurement mode: DFM mode Cantilever: SI-DF20 (made of silicon) Scanning range: <semantics>2μm×2μm<annotation encoding="application / x-tex">2 \mu m \times 2 \mu m< / annotation>< / semantics> Number of pixels: <semantics>256×256<annotation encoding="application / x-tex">256 \times 256< / annotation>< / semantics> pix Measurement environment: 23°C, 40% RH, in air

[0082] After the third-order tilt correction was performed on the obtained image data, the arithmetical mean height Sa and the maximum height difference P-V were calculated from the corrected image. The measurement was performed on each of five single fibers, and the average values of the arithmetical mean height Sa and the maximum height difference P-V were determined.

[0083] (Arithmetic Mean Roughness Ra) One single fiber was taken out from the liquid crystal polyester fibers (multifilament), and the fiber surface was measured under the following conditions using a scanning probe microscope ("Environment Control Unit E-sweep" manufactured by Hitachi High-Tech Science Corporation). Measurement mode: DFM mode Cantilever: SI-DF20 (made of silicon) Scanning range: <semantics>10μm×10μm<annotation encoding="application / x-tex">10 \mu m \times 10 \mu m< / annotation>< / semantics> Number of pixels: <semantics>256×256<annotation encoding="application / x-tex">256 \times 256< / annotation>< / semantics> pix Measurement environment: 23°C, 40% RH, in air

[0084] After the third-order tilt correction was performed on the obtained image data, the arithmetic mean roughness Ra was calculated by targeting the fiber central part which is parallel to the longitudinal direction of the fiber. The measurement was performed on each of five single fibers, and the average value of the arithmetic mean roughness Ra was determined.

[0085] (Amount of Fatty Acid Metal Salt Attached) With 100 mL of methanol, 10 g of a liquid crystal polyester fiber sample and 1 mg of an internal standard were extracted for 24 hours, and then the methanol phase was concentrated using an evaporator. The obtained residue was measured using a gas chromatograph ("Gas chromatograph GC-8A" and "CR-6A" Chromatopac" manufactured by SHIMADZU CORPORATION) under the conditions of an injection temperature of 340°C, an FID detector, a detector temperature of 340°C, and temperature rising from 60°C to 340°C at a temperature rising rate of 15°C / min, and the ratio between the peak areas of the internal standard and the fatty acid metal salt was calculated. The content of the fatty acid metal salt was determined from the following formula: peak area of fatty acid metal salt / peak area of internal standard × content of internal standard (1 mg). The ratio of the content of the fatty acid metal salt to 10 g of the liquid crystal polyester fiber sample was determined as an amount (wt%) of the fatty acid metal salt attached.

[0086] (Amount of Inorganic Particles Attached) An amount of inorganic particles attached to the liquid crystal polyester fiber was measured by the Soxhlet extraction method. Specifically, 5 g of a liquid crystal polyester fiber to which an oil agent containing the fatty acid metal salt and inorganic particles had been applied was put in a Soxhlet extractor, methanol as an extraction solvent and zeolite were put in a flat-bottom flask, and the mixture was extracted in a 10-L water bath (100°C) for 1.5 hours. Thereafter, methanol was evaporated, the oil agent after the extraction was weighed, and the oil agent attachment ratio was calculated from the weight of the liquid crystal polyester fiber before extraction by the gravimetric method. From the obtained oil agent attachment ratio and the ratio between the fatty acid metal salt and the inorganic particles in the oil agent, the amount of the inorganic particles attached to the fiber was determined by calculation.

[0087] (Tenacity) With reference to JIS L 1013: 2010 8.5.1, using a strength and elongation measuring machine "TENSORAPID5" manufactured by USTER Technologies AG, a tensile test was carried out under the conditions of a test sample length of 30 cm, a tensile speed of 15 cm / min, and an initial load of 0.33 g / dtex 5 times for each sample to obtain an average tensile strength (cN). The average tensile strength (cN) of the five tests was divided by the total fineness (dtex) measured by the above-described method to calculate a tensile strength (cN / dtex).

[0088] (Liquid Absorption Rate Per Unit Circumference) From the liquid crystal polyester fibers (multifilament), 10 single fibers each having a length of 20 cm were separated and collected in a pre-tared vinyl sheet, and a total weight A of 10 single fibers was weighed. Each single fiber was immersed in water and allowed to stand for 1 minute, and then a total weight B of 10 single fibers was weighed. From these measurement results, the liquid absorption rate (%) per single fiber was calculated by the following formula. This measurement was performed three times, and the average value C was calculated. Liquid absorption rate per single fiber (%) = <semantics>(B−A) / (A×10)×100<annotation encoding="application / x-tex">(B - A) / (A \times 10) \times 100< / annotation>< / semantics>

[0089] Assuming that the cross section of the fiber was a perfect circle, a circumference D (µm) of the cross section of the single fiber was calculated from the single fiber fineness (dtex) measured by the above-described method, and a liquid absorption rate per unit circumference was calculated from the following formula. Liquid absorption rate per unit circumference (<semantics>% / μm<annotation encoding="application / x-tex">\% / \mu m< / annotation>< / semantics>) = C / D

[0090] (Metal to Fiber Dynamic Friction Coefficient) A metal to fiber dynamic friction coefficient was measured in an atmosphere of 25°C and 40% RH under conditions of a load of 500 g and a speed of 0.1 cm / min using the liquid crystal polyester fiber and an abrasion test piece (chromium-plated matte finished test piece having a diameter of <semantics>φ<annotation encoding="application / x-tex">\varphi< / annotation>< / semantics>8 mm) using a Roeder fiber friction coefficient tester (manufactured by Aoi Seiki Co., Ltd.). The measurement was performed on two fibers, and the average value thereof was determined as the metal to fiber dynamic friction coefficient.

[0091] [Example 1] Chips (granular molded bodies) of a liquid crystal polyester (Mp0: 278°C) having a structural unit derived from 4-hydroxybenzoic acid and a structural unit derived from 6-hydroxy-2-naphthoic acid at a ratio of 73 / 27 (mol%) were dried by hot air at 120°C for at least 4 hours. Then, the chips were melt-extruded using a single screw extruder, and the melt-kneaded material was fed to a spinning head while being measured with a gear pump. In the spinning head, the melt-kneaded material was filtered with a metal nonwoven fabric filter, and was discharged at a discharge rate of 17.6 g / min from a spinneret having 40 holes each having a hole diameter of 0.10 mm and a land length of 0.14 mm. An aqueous solution containing a potassium caprate at a concentration of 1.6 wt% was applied as a spinning oil agent to the discharged yarn through an oiling guide placed directly below the spinneret, and the yarn was taken up by a first godet roll, passed through a second godet roll, and then wound onto a winder in the form of a cheese through a dancer roller at a winding rate of 800 m / min to obtain as-spun fibers with 220 dtex / 40 filaments.

[0092] The obtained as-spun fibers were unwound in the longitudinal direction (direction perpendicular to the circumferential direction of the fiber) using a rewinder, and rewound onto a stainless steel perforated bobbin wound with a nonwoven fabric to obtain a bobbin package for a heat treatment. The obtained package was subjected to the heat treatment at 275°C for 16 hours under a nitrogen atmosphere to obtain heat-treated fibers of the liquid crystal polyester fibers. Thereafter, the heat-treated fibers were unwound in the horizontal direction (horizontal direction to the circumferential direction of the fiber) using a rewinder and rewound, and at that time, a finishing oil agent containing coconut oil as a main component was applied. The analysis results of the obtained liquid crystal polyester fibers are shown in Table 5.

[0093] [Example 2] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous potassium caprate solution was applied so as to increase the amount of potassium caprate attached.

[0094] [Example 3] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous potassium stearate solution was used as a spinning oil agent.

[0095] [Example 4] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that a melt-kneaded material was discharged at a discharge rate of 4.48 g / min using a spinneret having 10 holes each having a hole diameter of 0.10 mmφ and a land length of 0.14 mm to obtain as-spun fibers with 56 dtex / 10 filaments.

[0096] [Example 5] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that a melt-kneaded material was discharged at a discharge rate of 64.0 g / min using a spinneret having 300 holes each having a hole diameter of 0.10 mm<semantics>φ<annotation encoding="application / x-tex">\varphi< / annotation>< / semantics> and a land length of 0.14 mm to obtain as-spun fibers with 1,670 dtex / 300 filaments.

[0097] [Example 6] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous potassium caprate solution was applied so as to increase the amount of potassium caprate attached.

[0098] [Example 7] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that a spinning oil agent containing 1.6 wt% of potassium caprate and 0.13 wt% of mica was used. The amount of mica attached to the obtained liquid crystal polyester fibers was 0.11 wt%.

[0099] [Example 8] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that a melt-kneaded material was discharged at a discharge rate of 64.0 g / min using a spinneret having 600 holes each having a hole diameter of 0.08 mm<semantics>φ<annotation encoding="application / x-tex">\varphi< / annotation>< / semantics> and a land length of 0.112 mm to obtain as-spun fibers with 1,670 dtex / 600 filaments

[0100] [Example 9] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous sodium dodecyl phosphate solution was used as a spinning oil agent, and an aqueous potassium caprate solution was used as a finishing oil agent.

[0101] [Comparative Example 1] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous potassium caprylate solution was used as a spinning oil agent.

[0102] [Comparative Example 2] Liquid crystal polyester fibers were obtained in the same manner as in Example 1 except that an aqueous sodium dodecyl phosphate solution was used as a spinning oil agent. The amount of sodium dodecyl phosphate attached was 0.62 wt%.

[0103] [Table 5] [Image disponible dans le document PDF, Image available in the PDF document] [Table 5-continued] [Image disponible dans le document PDF, Image available in the PDF document]

[0104] As shown in Table 5, in Examples 1 to 9, since the fatty acid metal salt having the specific number of carbon atoms is attached to the liquid crystal polyester fiber as the oil agent, the liquid absorption rate per unit circumference is high and the liquid absorption is excellent.

[0105] In Examples 1 to 6, 8, and 9, since the fatty acid metal salt having the specific number of carbon atoms is used as the oil agent to be attached, and any inorganic particles are not attached, the arithmetical mean height Sa is adjusted to be relatively low. In addition, the arithmetic mean roughness Ra and the maximum height difference P-V are similarly adjusted to be relatively low. Therefore, the metal to fiber dynamic friction coefficient is low and abrasion resistance is excellent.

[0106] In Examples 1 to 5, 7, and 8, since the amount of the fatty acid metal salt attached used as the spinning oil is adjusted, the tenacity can be sufficiently improved by the subsequent heat treatment.

[0107] On the other hand, in Comparative Example 1 in which the fatty acid metal salt having the small number of carbon atoms is used, the liquid absorption rate per unit circumference is lower and the liquid absorption is inferior, as compared with Examples 1 to 9. Further, in Comparative Example 1, the arithmetical mean height Sa is larger than those in Examples 1 and 3 in which the numbers of carbon atoms of the fatty acid metal salt are different, the metal to fiber dynamic friction coefficient is high and the abrasion resistance is poor. Furthermore, in Comparative Example 1, the tenacity is significantly lower than those in Examples 1 and 3 in which the amounts of the fatty acid metal salt attached are equal to or more than that in Comparative Example 1, and the strength is not sufficient.

[0108] In Comparative Example 2 in which sodium dodecyl phosphate is used as the oil agent, the liquid absorption rate per unit circumference is lower and the liquid absorption is inferior, as compared with Examples 1 to 9. INDUSTRIAL APPLICABILITY

[0109] The liquid crystal polyester fiber can be used for various applications such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various fiber products.

[0110] Although the preferred embodiments of the present invention have been described, various additions, modifications, or deletions may be made without departing from the scope of the present invention. Accordingly, such variants are included within the scope of the present invention.

Claims

1. A liquid crystal polyester fiber, comprising a fatty acid metal salt having 9 or more carbon atoms attached to a fiber surface.

2. The liquid crystal polyester fiber according to claim 1, wherein an arithmetical mean height Sa of the fiber surface is 7.5 nm or less measured in accordance with ISO 25178.

3. The liquid crystal polyester fiber according to claim 1 or 2, having a tenacity of 20 cN / dtex or more.

4. The liquid crystal polyester fiber according to any one of claims 1 to 3, wherein an amount of the fatty acid metal salt attached is 0.01 to 2.0 wt%.

5. The liquid crystal polyester fiber according to any one of claims 1 to 4, wherein an amount of inorganic particles attached is 100 ppm by weight or less.

6. The liquid crystal polyester fiber according to any one of claims 1 to 5, wherein a maximum height difference P-V of the fiber surface is 1 to 80 nm measured in accordance with ISO 25178.

7. The liquid crystal polyester fiber according to any one of claims 1 to 6, having a liquid absorption rate per unit circumference of 5.0% / µm or more.

8. The liquid crystal polyester fiber according to any one of claims 1 to 7, having a metal to fiber dynamic friction coefficient of 0.18 or less.

9. A fiber structure comprising the liquid crystal polyester fiber according to any one of claims 1 to 8 in at least a part of the fiber structure.

10. A method for producing a liquid crystal polyester fiber, comprising applying a fatty acid metal salt having 9 or more carbon atoms to a surface of a liquid crystal polyester fiber.

11. The method according to claim 10, further comprising heat-treating an as-spun fiber of the liquid crystal polyester fiber, wherein the applying is performed before and / or after the heat-treating.

12. The method according to claim 11, wherein the applying is performed at least before the heat-treating.