Liquid crystal polyester fiber and method for producing same

Abstract

Provided is a liquid crystal polyester fiber having excellent liquid absorbing ability. The liquid crystal polyester fiber has a fatty acid metal salt having nine or more carbon atoms adhered to the surface thereof. For example, the arithmetic average height Sa of the fiber surface of the liquid crystal polyester fiber as measured in accordance with ISO 25178 may be 7.5 nm or less. In addition, the liquid crystal polyester fiber may have a strength of at least 20 cN / dtex. In addition, the amount of the fatty acid metal salt adhered to the liquid crystal polyester fiber may be 0.01-2.0 wt%.

Description

Liquid crystal polyester fiber and its manufacturing method Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2023-221579, filed on December 27, 2023, the entire contents of which are incorporated herein by reference.

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

[0003] Liquid crystal polyester fibers are composed of polymers with rigid molecular structures, and due to the highly oriented molecular chains, they have high strength, high elastic modulus, and excellent heat resistance and dimensional stability. Therefore, they are expected to be used in a variety of 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 2006-336147 A) discloses a melt-anisotropic aromatic polyester fiber having 0.05 to 2 mass % of inorganic fine particles having an average particle size of 0.001 to 1 μm attached to the surface of a single fiber, and having a single fiber fineness of 0.01 to 1.5 dtex and a strength after heat treatment of 15 cN / dtex or more.

[0005] Patent Document 2 (JP 2016-169464 A) discloses a liquid crystal polyester monofilament, which is made of a liquid crystal polyester and has fine irregularities on the fiber surface, the surface roughness (Ra) of the fine irregularities on the fiber surface being 0.015 μm or more and 0.100 μm or less, and the maximum thinning rate being 8.0% or less.

[0006] Patent Document 3 (JP 2013-133576 A) discloses a liquid crystal polyester multifilament characterized by being composed of a liquid crystal polyester containing 0.01 to 1% by weight of a metal soap when the weight of the entire fiber is taken as 100% by weight.

[0007] JP 2006-336147 A JP 2016-169464 A JP 2013-133576 A

[0008] However, while liquid crystalline polyester fibers have high mechanical properties, they have low liquid absorbency due to the hydrophobicity and high orientation of the liquid crystalline polyester. This has led to problems such as poor comfort when used in clothing applications such as protective clothing, and poor adhesion to matrix resins when used as a reinforcing material in composite applications.

[0009] Patent Document 1 describes that by attaching inorganic fine particles to the surface of fused anisotropic aromatic polyester fibers, adhesion between single yarns is suppressed and single yarn separation is improved, resulting in a good texture when made into clothing; however, it was difficult to improve liquid absorbency by simply attaching inorganic fine particles to the fiber surface.

[0010] In Patent Document 2, fine irregularities are formed by cutting the molecular chains of the liquid crystalline polyester on the fiber surface with a phosphoric acid compound, but even if a conventional oil agent such as a phosphoric acid compound is added or the shape of the fiber surface is modified, the liquid absorbency is not improved.

[0011] In Patent Document 3, a specific amount of metal soap is contained inside the fiber by mixing the metal soap with a liquid crystalline polyester and melt-spinning the mixture, but simply containing the metal soap inside the fiber does not improve the properties of the fiber surface, and does not lead to an improvement in liquid absorbency.

[0012] Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystalline polyester fiber having excellent liquid absorption properties and a method for producing the same.

[0013] As a result of intensive research to achieve the above object, the inventors of the present invention have found that liquid absorption can be improved by attaching a fatty acid metal salt having a specific carbon number to the surface of a liquid crystalline polyester fiber, and have thus completed the present invention.

[0014] That is, the present invention can be configured in the following aspects. [Aspect 1] A liquid crystal polyester fiber having a metal salt of a fatty acid having 9 or more carbon atoms (preferably 10 to 20, more preferably 10 to 18) attached to the fiber surface. [Aspect 2] A liquid crystal polyester fiber according to Aspect 1, wherein the arithmetic mean height Sa of the fiber surface measured in accordance with ISO 25178 is 7.5 nm or less (preferably 0.1 to 6.0 nm, more preferably 1.0 to 5.0 nm, and even more preferably 2.0 to 5.0 nm). [Aspect 3] A liquid crystal polyester fiber according to Aspect 1 or 2, wherein the tenacity is 20 cN / dtex or more (preferably 22 cN / dtex or more, more preferably 24 cN / dtex or more). [Aspect 4] The liquid crystal polyester fiber according to any one of Aspects 1 to 3, wherein the amount of the fatty acid metal salt attached is 0.01 to 2.0% by weight (preferably 0.03 to 1.5% by weight, more preferably 0.1 to 1.0% by weight, even more preferably 0.1 to 0.9% by weight, and still more preferably 0.1 to 0.8% by weight). [Aspect 5] The liquid crystal polyester fiber according to any one of Aspects 1 to 4, wherein the amount of inorganic particles attached is 100 ppm by weight or less (preferably 10 ppm by weight or less, 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 the value of the maximum height difference P-V of the fiber surface measured in accordance with ISO 25178 is 1 to 80 nm (preferably 10 to 60 nm, and more preferably 20 to 40 nm). [Aspect 7] The liquid crystalline polyester fiber according to any one of Aspects 1 to 6, having a unit circumferential liquid absorption of 5.0% / μm or more (preferably 5.0 to 20% / μm, more preferably 6.0 to 15% / μm, and even more preferably 7.0 to 10% / μm). [Aspect 8] The liquid crystalline polyester fiber according to any one of Aspects 1 to 7, having a metal-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 at least partially comprising the liquid crystalline polyester fiber according to any one of Aspects 1 to 8. [Aspect 10] A method for producing a liquid crystalline polyester fiber, comprising a step of applying a metal salt of a fatty acid having 9 or more carbon atoms (preferably 10 to 20, more preferably 10 to 18) to the surface of a liquid crystalline polyester fiber. [Aspect 11] The method for producing a liquid crystalline polyester fiber according to Aspect 10, further comprising a step of heat-treating a raw spinning yarn of the liquid crystalline polyester fiber, wherein the applying step is carried out before and / or after the heat-treating step. [Aspect 12] The method for producing a liquid crystalline polyester fiber according to Aspect 11, wherein the applying step is carried out at least before the heat-treating step.

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

[0016] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification is included in the present invention, and in particular any combination of two or more of the claims described in the claims is included in the present invention.

[0017] The liquid crystal polyester fiber of the present invention has excellent liquid absorbency.

[0018] [Liquid Crystal Polyester Fiber] The liquid crystal polyester fiber includes a liquid crystal polyester. The liquid crystal polyester is composed of, for example, structural units derived from aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in chemical structure as long as the effects of the present invention are not impaired. Furthermore, the liquid crystal polyester may be a liquid crystal polyester amide containing structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids, as long as the effects of the present invention are not impaired. For example, preferred structural units include the examples shown in Table 1.

[0019]

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

[0021] More preferred structural units include the structural units described in Examples (1) to (20) shown in the following Tables 2, 3, and 4. When the structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

[0022]

[0023]

[0024]

[0025] In the structural units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n=1 and n=2 may exist alone or in combination; Y １ and Y ２ may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), 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.

[0026] Examples of Z include substituents represented by the following formulas.

[0027]

[0028] In one embodiment, the liquid crystal polyester may contain a structural unit derived from a hydroxycarboxylic acid as a main component. The liquid crystal polyester may preferably contain a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) may be a structural unit derived from 4-hydroxybenzoic acid (formula (A) below), and the structural unit (B) may be a structural unit derived from 6-hydroxy-2-naphthoic acid (formula (B) below). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural 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.

[0029]

[0030]

[0031] The liquid crystal polyester may contain a structural unit derived from 4-hydroxybenzoic acid, and when it contains both the structural unit (A) and the structural unit (B), the content of the structural unit derived from 4-hydroxybenzoic acid may be 50 mol% or more, preferably 53 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, and even more preferably 70 mol% or more, relative to the total amount of all structural units. The upper limit of the content of the structural unit derived from 4-hydroxybenzoic acid in the liquid crystal polyester is not particularly limited, but 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 contain a structural unit derived from 6-hydroxy-2-naphthoic acid, and when it contains both the structural unit (A) and the structural unit (B), the content of the structural unit derived from 6-hydroxy-2-naphthoic acid may be 4 to 45 mol% relative to the total amount of all structural units.

[0033] Furthermore, the total content of the structural unit (A) and the structural unit (B) relative to the total amount of all structural units may be, for example, 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more.

[0034] In another embodiment, the liquid crystal polyester may contain at least one structural unit selected from the group consisting of a structural unit represented by the following formula (I) (structural unit (I)), a structural unit represented by the following formula (II) (structural unit (II)), 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)): -O-Ar １ -CO- (I) -CO-Ar ２ -CO- (II) -O-Ar ３ -O- (III) -O-Ar ４ -NH- (IV) (wherein, Ar １ is at least one selected from the group consisting of a phenylene group, a naphthylene group, and a biphenylylene group, and Ar ２ , Ar３ and Ar ４ are each independently at least one selected from the group consisting of a phenylene group, a naphthylene group, a biphenylylene group, and a diphenyletherdiyl group, and Ar １ , Ar ２ , Ar ３ and Ar ４ Each hydrogen atom in the aromatic ring 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 Ar １ However, structural units which are 1,4-phenylene groups (structural units derived from 4-hydroxybenzoic acid) and structural units which are 2,6-naphthylene groups (structural units derived from 6-hydroxy-2-naphthoic acid) are preferred.

[0036] The structural unit (II) is a structural unit derived from an aromatic dicarboxylic acid, and Ar ２ However, preferred are structural units which are 1,4-phenylene groups (structural units derived from terephthalic acid), 1,3-phenylene groups (structural units derived from isophthalic acid), 2,6-naphthylene groups (structural units derived from 2,6-naphthalenedicarboxylic acid), and diphenylether-4,4'-diyl groups (structural units derived from diphenylether-4,4'-dicarboxylic acid).

[0037] The structural unit (III) is a structural unit derived from an aromatic diol, and Ar ３ However, preferred are structural units which are 1,4-phenylene groups (structural units derived from hydroquinone), structural units which are 4,4'-biphenylylene groups (structural units derived from 4,4'-dihydroxybiphenyl), structural units which are phenyl-1,4-phenylene groups (structural units derived from phenylhydroquinone), and structural units which are diphenylether-4,4'-diyl groups (structural units derived from 4,4'-dihydroxydiphenyl ether).

[0038] The structural unit (IV) is a structural unit derived from an aromatic hydroxyamine, and Ar ４ However, a structural unit which is a 1,4-phenylene group (a structural unit derived from 4-aminophenol) and a structural unit which is a 4,4'-biphenylylene group (a structural unit derived from 4-amino-4'-hydroxybiphenyl) are preferred.

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

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

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

[0042] The molar ratio of the content of structural unit (II) to the total content of structural units (III) and (IV), expressed as (II) / [(III)+(IV)], may be from 90 / 100 to 100 / 90, preferably from 95 / 100 to 100 / 95, more preferably from 98 / 100 to 100 / 98, and even more preferably 100 / 100.

[0043] The liquid crystal polyester may contain two or more of each of the structural units (I) to (IV). The content of each structural unit represents the content of all structural units corresponding to that structural unit. For example, when the liquid crystal polyester contains two or more types of structural unit (I), the content of the structural unit (I) represents the total content thereof.

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

[0045] The liquid crystal polyester is preferably a combination having a naphthalene skeleton as a structural unit. For example, the total content of structural units containing 2,6-naphthylene groups in the liquid crystal polyester may be 28 mol% or more, preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 55 mol% or more, particularly preferably 60 mol% or more, especially more preferably 65 mol% or more, and especially more preferably 70 mol% or more, based on the total amount of all structural units. Furthermore, from the viewpoint of improving melt moldability, the total content of structural units containing 2,6-naphthylene groups in the liquid crystal polyester may be 95 mol% or less, preferably 90 mol% or less, more preferably 85 mol% or less, based on the total amount of all structural units. Examples of structural units containing 2,6-naphthylene groups include structural units derived from 6-hydroxy-2-naphthoic acid (structural unit (B) represented by the above formula (B)), Ar １ is a 2,6-naphthylene group) and a structural unit derived from 2,6-naphthalenedicarboxylic acid (Ar ２ is a 2,6-naphthylene group).

[0046] The melting point of the liquid crystal polyester (hereinafter referred to as Mp ０The melting point (sometimes referred to as "melting point") is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, even more preferably 260 to 360°C, even more preferably 260 to 340°C, and particularly preferably 260 to 330°C. In this specification, the melting point is the main absorption peak temperature observed when measured using a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of a sample is placed in an aluminum pan and sealed in a DSC apparatus. Then, nitrogen is flowed as a carrier gas at a flow rate of 200 mL / min, and the endothermic peak is measured when the temperature is increased from room temperature (e.g., 25°C) at a rate of 10°C / min. If a clear peak does not appear in the first run of DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50°C / min to a temperature 50°C higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50°C at a rate of 80°C / min, and then the endothermic peak should be measured at a heating rate of 10°C / min.

[0047] The liquid crystal polyester may be mixed with a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, fluororesin, etc., within the range that does not impair the effects of the present invention. Furthermore, various additives such as inorganic substances such as titanium oxide, kaolin, silica, barium oxide, etc., colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers may also be mixed.

[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 a liquid crystal polyester with the above-mentioned thermoplastic polymer and various additives, or a conjugate spun fiber obtained by simultaneously spinning different components, the liquid crystal polyester and the above-mentioned thermoplastic polymer, from separate spinnerets. The liquid crystal polyester fiber may be a non-conjugate spun fiber or a conjugate spun fiber. In particular, it is preferable that the liquid crystal polyester is present on the fiber surface, and it is preferable that a fatty acid metal salt described below is attached to the surface of the fiber composed of the liquid crystal polyester.

[0049] The liquid crystal polyester fiber may contain 50% by weight or more of liquid crystal polyester, preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and still more preferably 98% by weight or more.

[0050] A liquid crystal polyester fiber has a fatty acid metal salt having 9 or more carbon atoms attached to its surface. In this case, the liquid crystal polyester fiber is composed of a fiber main body portion mainly composed of liquid crystal polyester and a surface attachment portion formed to cover the fiber main body and containing a fatty acid metal salt having 9 or more carbon atoms. In the present invention, it has been discovered that adhering a fatty acid metal salt having a specific number of carbon atoms to the surface of a liquid crystal polyester fiber improves liquid absorption. It is presumed that when an amphipathic oil agent is attached to the surface of a liquid crystal polyester fiber, the hydrophobic portion of the oil agent faces the hydrophobic surface side of the liquid crystal polyester fiber and the hydrophilic portion faces outward, thereby improving hydrophilicity and liquid absorption. While amphipathic oil agents such as metal salts other than carboxylic acid-based oil agents, such as phosphoric acid-based oil agents, and fatty acid metal salts with relatively short carbon chains, are unable to fully exhibit the effect of improving liquid absorption, it has been discovered that a fatty acid metal salt having a specific number of carbon atoms can improve liquid absorption, possibly due to the interaction of its long carbon chain and carboxyl group with the liquid crystal polyester molecules.

[0051] The fatty acid in the metal salt of a fatty acid having 9 or more carbon atoms may be either saturated or unsaturated, or may be a hydroxy fatty acid containing a hydroxy group. Examples 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 used alone or in combination of two or more. The number of carbon atoms of the fatty acid may be preferably 10 to 20, more preferably 10 to 18, from the viewpoints of improving the liquid absorption property of the liquid crystalline polyester fiber, imparting solubility or dispersibility in water, and making it easy to apply as an oil agent.

[0052] Examples of metal salts of fatty acids having 9 or more carbon atoms include lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, barium salts, aluminum salts, and zinc salts. Among these metal salts, alkali metal salts such as lithium salts, sodium salts, and potassium salts are preferred, with potassium salts being more preferred due to their high water solubility and ease of application as an oil. Examples of metal salts of fatty acids 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 may contain components other than the metal salts of fatty acids having 9 or more carbon atoms (e.g., amphiphilic compounds other than the metal salts of fatty acids, metal salts of fatty acids having 8 or less carbon atoms, etc.) as long as the effects of the present invention are not impaired.

[0053] From the viewpoint of improving the liquid absorption, the liquid crystal polyester fiber may have an adhesion amount of the fatty acid metal salt of 0.01 wt % or more, preferably 0.03 wt % or more, and more preferably 0.1 wt % or more. The adhesion amount of the fatty acid metal salt may be 2.0 wt % or less, preferably 1.5 wt % or less. From the viewpoint of reducing the arithmetic mean height Sa of the fiber surface, it may be more preferably 1.0 wt % or less, even more preferably 0.9 wt % or less, and even more preferably 0.8 wt % or less. In this specification, the adhesion amount of the fatty acid metal salt refers to the ratio of the adhesion amount of the fatty acid metal salt to the weight of the entire fiber including the adhesion on the fiber surface, and is a value measured by the method described in the Examples below.

[0054] The liquid crystal polyester fiber may have a unit circumferential liquid absorption 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 unit circumferential liquid absorption is not particularly limited, but may be, for example, 20% / μm or less. In applications where absorbency needs to be controlled, the unit circumferential liquid absorption is preferably 15% / μm or less, and more preferably 10% / μm or less. In this specification, the unit circumferential liquid absorption refers to the liquid absorption (water absorption) rate based on the circumference of the cross section of a single fiber calculated from the single fiber fineness, assuming that the fiber cross section is a perfect circle, and is measured by the method described in the Examples below.

[0055] The liquid crystal polyester fiber may have an arithmetic mean height Sa of the fiber surface of 7.5 nm or less. The arithmetic mean height Sa of the fiber surface is affected by the state of the surface attachment portion. However, when a fatty acid metal salt having a specific carbon number is attached, the long carbon chain and carboxyl groups of the fatty acid metal salt interact with the liquid crystal polyester molecules on the fiber surface, causing the fatty acid metal salt to migrate and uniformly cover the fiber surface, thereby reducing the unevenness of the fiber surface. This can be achieved when a fatty acid metal salt having a specific carbon number is used. However, fatty acid metal salts having 8 or fewer carbon atoms tend not to sufficiently reduce the arithmetic mean height Sa of the fiber surface, possibly due to insufficient interaction with the liquid crystal polyester molecules. Controlling the arithmetic mean height Sa of the fiber surface within a specific range reduces the coefficient of friction with the friction target and provides excellent wear resistance. The arithmetic mean height Sa of the fiber surface may be preferably 6.0 nm or less, more preferably 5.0 nm or less, or may be 0.1 nm or more, preferably 1.0 nm or more, and more preferably 2.0 nm or more. The arithmetic mean height Sa represents the average of the absolute values ​​of the differences in height at each point relative to the average plane of the surface in a defined area, measured in accordance with ISO 25178. In this specification, the arithmetic mean height Sa is measured by the method described in the examples below.

[0056] The liquid crystal polyester fiber may have an arithmetic mean roughness Ra of 20 nm or less on the fiber surface. The arithmetic mean roughness Ra of the fiber surface may be preferably 14 nm or less, more preferably 12 nm or less, and even more preferably 10 nm or less, or may be 0.1 nm or more, preferably 1.0 nm or more, and even 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 even more 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 is expressed as the average of the absolute values ​​of the deviations from the mean line to the roughness curve for a reference length. In this specification, the arithmetic mean roughness Ra is measured from the profile curve of the surface in the fiber axis direction of a single fiber, using the method described in the Examples below.

[0057] The liquid crystal polyester fiber may have a maximum height difference (PV) of 80 nm or less, preferably 60 nm or less, more preferably 40 nm or less, or may have a maximum height difference (PV) of 1 nm or more, preferably 10 nm or more, more preferably 20 nm or more. The maximum height difference (PV) of the fiber surface may be 1 to 80 nm, preferably 10 to 60 nm, more preferably 20 to 40 nm. The maximum height difference (PV) represents the sum of the maximum peak height and the maximum valley depth of the profile curve over a reference length, as measured in accordance with ISO 25178. In this specification, the maximum height difference (PV) is measured by the method described in the Examples below.

[0058] From the viewpoint of adjusting the surface roughness and achieving low friction, the liquid crystal polyester fiber may have an adhesion amount of inorganic particles of 100 ppm by weight or less, preferably 10 ppm by weight or less, and more preferably 1 ppm by weight or less. In this specification, the adhesion amount of inorganic particles refers to the ratio of the adhesion amount of inorganic particles to the weight of the entire fiber including adhesions on the fiber surface.

[0059] The liquid crystal polyester fiber may have a metal-fiber kinetic 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-fiber kinetic friction coefficient is not particularly limited, but may be, for example, 0.10 or more. In this specification, the metal-fiber kinetic friction coefficient is measured by the method described in the Examples below.

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

[0061] The single fiber fineness of the liquid crystal polyester fiber can be appropriately selected depending on the application, etc. For example, the single fiber fineness may be 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, but may be, for example, about 0.01 dtex. The single fiber fineness is a value measured by the method described in the examples below.

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

[0063] The total fineness of the liquid crystal polyester fiber can be appropriately selected 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 even more preferably 2,000 dtex or less. The lower limit of the total fineness is not particularly limited, but may be, for example, about 1 dtex.

[0064] [Method for producing liquid crystal polyester fiber] The method for producing a liquid crystal polyester fiber includes a step of applying a metal salt of a fatty acid having 9 or more carbon atoms to the surface of a liquid crystal polyester fiber. In the present invention, it has been found that the liquid absorbency can be improved by applying a metal salt of a fatty acid having a specific number of carbon atoms to the surface of a liquid crystal polyester fiber.

[0065] In the step of applying the fatty acid metal salt, the above-mentioned fatty acid metal salt can be used, and the form of the fatty acid metal salt when applied to the liquid crystal polyester fiber may be an oil solution in which the fatty acid metal salt is dissolved in a medium, or an oil dispersion in which the fatty acid metal salt is dispersed in a medium. The application method is not particularly limited, and examples thereof include known application methods such as impregnation treatment, discharge treatment, coating treatment, and immersion 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 or a glass nozzle.

[0066] The method for producing a liquid crystal polyester fiber may further include a step of heat-treating the raw spinning yarn of the liquid crystal polyester fiber. By subjecting the raw spinning yarn of the liquid crystal polyester fiber to heat treatment, solid-state polymerization of the liquid crystal polyester proceeds, thereby improving the strength of the fiber.

[0067] When a heat treatment step is included, the step of applying a fatty acid metal salt may be carried out before and / or after the heat treatment step. Before the heat treatment step, the fatty acid metal salt may be applied to the raw spun yarn of the liquid crystal polyester fiber. For example, the fatty acid metal salt may be applied while the spun raw spun yarn is being wound, or may be applied when the raw spun yarn that has been spun and wound is being rewound. After the heat treatment step, the fatty acid metal salt may be applied to the heat-treated yarn of the liquid crystal polyester fiber. For example, the fatty acid metal salt may be applied as a finishing oil to the heat-treated yarn.

[0068] From the viewpoint of improving liquid absorption, it is preferable that the step of applying a fatty acid metal salt is carried out at least before the heat treatment step. Although the mechanism of action is unclear, when a fatty acid metal salt having a specific carbon number is applied to the raw spun yarn and then heat treatment is carried out, the fatty acid metal salt applied as an aqueous solution or the like becomes bone dry and is therefore more likely to absorb moisture, thereby improving liquid absorption.

[0069] In the fatty acid metal salt application step, from the viewpoint of improving the liquid-crystal polyester fiber's liquid-crystal absorbency, the fatty acid metal salt may be applied so that its adhesion amount is 0.01 wt % or more, preferably 0.03 wt % or more, and more preferably 0.1 wt % or more. Furthermore, when the fatty acid metal salt application step is performed before the heat treatment step, if the adhesion amount of the fatty acid metal salt on the liquid-crystal polyester fiber subjected to the heat treatment is too large, the progress of solid-state polymerization during the heat treatment may be inhibited, and strength tends to be insufficiently improved. Therefore, from the viewpoint of not inhibiting the progress of solid-state polymerization during the heat treatment, the fatty acid metal salt may be applied so that its adhesion amount is 2.0 wt % or less, preferably 1.5 wt % or less, more preferably 1.0 wt % or less, even more preferably 0.9 wt % or less, and even more preferably 0.8 wt % or less. By applying a fatty acid metal salt having a specific carbon number among the fatty acid metal salts in such an adhesion amount, strength can be sufficiently improved in the subsequent heat treatment, thereby achieving both liquid-absorbency and strength. On the other hand, in the case of fatty acid metal salts having 8 or fewer carbon atoms, the balance of amphiphilicity affects the morphology when applied to the fiber surface, and this may be because the solid-phase polymerization of the liquid crystalline polyester is inhibited, and therefore the strength tends not to be sufficiently improved by heat treatment.

[0070] The heat treatment method is not particularly limited, and may be, for example, a batch-type heat treatment or a continuous heat treatment by conveyance. In the batch-type heat treatment, for example, the heat treatment may be performed in a state where the material is wound around a bobbin in a packaged form, or in a reel-like or tow-like form, and it is preferable to perform the heat treatment in a packaged form from the viewpoint of simplifying the equipment and improving productivity. In the case of continuous heat treatment by conveyance, the conveyance method may be either contact conveyance (for example, a conveyor system, a support roll system, or a heat treatment system using a heated roller) or non-contact conveyance (a roll-to-roll system).

[0071] The heat treatment can be carried out by a known method, such as atmospheric heating or contact heating. The atmosphere is preferably air, an inert gas (e.g., nitrogen, argon), or a combination thereof. The heat treatment may also be carried out under reduced pressure.

[0072] The heat treatment temperature may be 230°C or higher, and from the viewpoint of efficient strength improvement, it may be preferably 240°C or higher, more preferably 250°C or higher. Furthermore, the heat treatment temperature may be lower than the melting point (Mp) of the raw spun yarn subjected to the heat treatment step to prevent melting. For example, within the range of 230°C or higher, it may be Mp-50°C or higher and lower than Mp°C, preferably Mp-40°C or higher and lower than Mp°C, more preferably Mp-30°C or higher and lower than Mp°C. In the heat treatment step, the melting point of the liquid crystalline polyester fiber increases as the solid-state polymerization progresses, so the initial heat treatment temperature in the heat treatment step may be set lower than the melting point (Mp) of the raw spun yarn. From the viewpoint of efficient strength improvement, the heat treatment temperature may be increased stepwise depending on the progress of the solid-state polymerization, and the heat treatment may be performed at a temperature higher than the melting point (melting point of the raw spun yarn) at the time of subjecting the fiber to the heat treatment step.

[0073] The heat treatment time can be appropriately set depending on the heat treatment method and heat treatment temperature, for example, in the range of 15 minutes to 30 hours, preferably 2 to 24 hours, and more preferably 3 to 20 hours. The heat treatment time here refers to the holding time at a predetermined heat treatment temperature.

[0074] In the method for producing a liquid crystal polyester fiber, the strength ratio of the liquid crystal polyester fiber before and after the heat treatment 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 treatment step is not particularly limited, but may be, for example, 10 times or less. Here, the strength ratio before and after the heat treatment step refers to the value obtained by dividing the strength of the liquid crystal polyester fiber after the heat treatment step by the strength of the liquid crystal polyester fiber (raw spinning yarn) before the heat treatment step.

[0075] [Textile Structure] The liquid crystal polyester fiber can be used in various applications as a fiber structure containing at least a part of the fiber. The fiber structure containing the liquid crystal polyester fiber can be used in any fiber form, such as staple fiber, short-cut fiber, filament yarn, spun yarn, string-like material, rope, etc. Furthermore, the liquid crystal polyester fiber can be used as various fabrics, such as nonwoven fabrics, woven fabrics, and knitted fabrics. Such fibers and fabrics can be produced using the liquid crystal polyester fiber by known methods.

[0076] The fiber structure may be a combination of liquid crystal polyester fiber and other fibers as long as the effects of the present invention are not impaired. For example, a composite fiber using liquid crystal polyester fiber and other fibers (e.g., a mixed yarn in which liquid crystal polyester fiber is mixed with other fibers) can be used. Also, composite fabrics using liquid crystal polyester fiber and other fibers (e.g., a mixed fabric in which liquid crystal polyester fiber is mixed with other fibers, or a laminate of a fabric made of liquid crystal polyester fiber and a fabric made of other fibers) can be used.

[0077] Liquid crystal polyester fibers can be used in the form of various fiber structures for a variety of applications, such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products. For example, they can be used in advanced processed products such as tension members (electric wires, optical fibers, umbilical cables, heater wire core threads, earphone cords, and other electrical cords), sailcloth, ropes (marine, mountain climbing, crane, yacht, tug, and other), ropes, land nets (safety nets, golf driving range nets, and other), slings, lifelines, fishing lines, sewing threads, screen cords, fishing nets, longlines, geogrids, protective gloves, ripstop protective clothing and outdoor clothing, rider suits, sports rackets, guts, reinforcing materials for medical catheters, sutures, screen gauze, filters, base fabrics for printed circuit boards, exterior materials for electronic devices, mesh conveyor belts, papermaking belts, dryer canvas, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses and pipes, and reinforcing materials for rubber and plastic materials such as tires and conveyor belts.

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, various physical properties were measured by the following methods.

[0079] (Melting Point of Resin Chips (Granular Molded Body)) Measurement was performed using a differential scanning calorimeter (DSC; "DSC60A Plus" manufactured by Shimadzu Corporation) in accordance with JIS K 7121, and the observed main absorption peak temperature was taken as the melting point. Specifically, 4 to 6 mg of a sample was placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen was then flowed as a carrier gas at a flow rate of 200 mL / min, and the endothermic peak derived from the liquid crystal polyester was measured when the temperature was raised from 25°C at a rate of 10°C / min.

[0080] (Total fineness, single fiber fineness) Based on JIS L 1013:2010 8.3.1 A method, a 10 m reel of liquid crystal polyester fiber was taken using a measuring instrument "Wrap Reel by Motor Driven" manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd., and its weight (g) was multiplied by 1000 to perform measurements three times per level, and the average value of the three measurements was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber. In addition, the quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

[0081] (Arithmetic mean height Sa and maximum height difference P-V) A single fiber was taken out of the liquid crystal polyester fiber (multifilament), and the fiber surface was measured using a scanning probe microscope ("Environmental Control Unit E-sweep" manufactured by Hitachi High-Tech Science Corporation) under the following conditions: Measurement mode: DFM mode Cantilever: SI-DF20 (made of silicon) Scanning range: 2 μm × 2 μm Number of pixels: 256 × 256 pixels Measurement environment: 23°C, 40% RH, in air

[0082] The obtained image data was subjected to third-order tilt correction, and then the arithmetic mean height Sa and the maximum height difference P-V were calculated from the corrected image. Measurements were performed on five single fibers, and the average values ​​of the arithmetic mean height Sa and the maximum height difference P-V were calculated.

[0083] (Arithmetic mean roughness Ra) A single fiber was taken out from the liquid crystal polyester fiber (multifilament), and the fiber surface was measured using a scanning probe microscope ("Environmental Control Unit E-sweep" manufactured by Hitachi High-Tech Science Corporation) under the following conditions: Measurement mode: DFM mode Cantilever: SI-DF20 (made of silicon) Scanning range: 10 μm × 10 μm Number of pixels: 256 × 256 pixels Measurement environment: 23°C, 40% RH, in air

[0084] After third-order tilt correction, the image data was subjected to a third-order gradient correction, and a line was drawn at the center of the fiber so as to be parallel to the longitudinal direction of the fiber, and the arithmetic mean roughness Ra was calculated. Measurement was performed on five single fibers, and the average value of the arithmetic mean roughness Ra was calculated.

[0085] (Amount of fatty acid metal salt attached) 10 g of a liquid crystal polyester fiber sample and 1 mg of an internal standard substance were extracted with 100 mL of methanol for 24 hours, and the methanol phase was concentrated using an evaporator. The resulting residue was measured using a gas chromatograph (Shimadzu Corporation's "Gas Chromatograph GC-8A" and "CR-6A Chromatopack") under conditions of an injection temperature of 340°C, an FID detector, a detector temperature of 340°C, and a temperature increase rate of 15°C / min from 60°C to 340°C, and the ratio of the peak area of ​​the internal standard substance to that of the fatty acid metal salt was calculated. The content of the fatty acid metal salt was calculated from the peak area of ​​the fatty acid metal salt / the peak area of ​​the internal standard substance x the content (1 mg) of the internal standard substance. The ratio of the content of the fatty acid metal salt to 10 g of the liquid crystal polyester fiber sample was calculated as the amount of fatty acid metal salt attached (wt%).

[0086] (Amount of inorganic particles attached) The amount of inorganic particles attached to the liquid crystal polyester fiber was measured by the Soxhlet extraction method. Specifically, 5 g of liquid crystal polyester fiber to which an oil solution containing a fatty acid metal salt and inorganic particles had been applied was placed in a Soxhlet extractor, and the extraction solvent, methanol and zeolite, were placed in a flat-bottom flask, followed by extraction in a 10 L water bath (100 ° C) for 1.5 hours. Thereafter, the methanol was evaporated, and the weight of the oil solution after extraction was weighed. The oil solution adhesion rate was calculated by a gravimetric method from the weight of the liquid crystal polyester fiber before extraction. The amount of inorganic particles attached to the fiber was calculated from the obtained oil solution adhesion rate and the ratio of fatty acid metal salt to inorganic particles in the oil solution.

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

[0088] (Liquid absorption rate per unit circumference) A liquid crystal polyester fiber (multifilament) was divided into 10 single fibers, and each 20 cm long single fiber was collected and collected on a pre-tared vinyl sheet, and the total weight A of the 10 single fibers was measured. Each single fiber was immersed in water and allowed to stand for 1 minute, and then the total weight B of the 10 single fibers was measured. From these measurement results, the liquid absorption rate (%) per single fiber was calculated using the following formula. This measurement was performed three times, and the average value C was calculated. Liquid absorption rate (%) per single fiber = (B - A) / (A x 10) x 100

[0089] Assuming that the fiber cross section is a perfect circle, the circumference D (μm) of the cross section of the single fiber was calculated from the single fiber fineness (dtex) measured by the above-mentioned method, and the unit circumference liquid absorption was calculated using the following formula: Unit circumference liquid absorption (% / μm) = C / D

[0090] (Metal-fiber kinetic friction coefficient) Using a radar method fiber friction coefficient measuring device (manufactured by Aoi Seiki Research Institute), the metal-fiber kinetic friction coefficient was measured using a liquid crystal polyester fiber and an abrading test piece (φ8 mm chrome-plated matte finish) under conditions of 25°C, 40% RH, a load of 500 g, and a speed of 0.1 cm / min. The measurement was performed for two pieces, and the average value was calculated as the metal-fiber kinetic friction coefficient.

[0091] [Example 1] A liquid crystal polyester (Mp) composed of 4-hydroxybenzoic acid-derived structural units and 6-hydroxy-2-naphthoic acid-derived structural units at a ratio of 73 / 27 (mol%) ０ Chips (granular molded bodies) of 1000 kJ / min (278°C) were dried with hot air at 120°C for 4 hours or more. Thereafter, melt extrusion was performed using a single-screw extruder, and the molten mixture was supplied to a spinning head while being metered using a gear pump. In the spinning head, the molten mixture was filtered using a metal nonwoven fabric filter, and the molten mixture was discharged from a spinneret with a hole diameter of 0.10 mmφ, a land length of 0.14 mm, and 40 holes at a discharge rate of 17.6 g / min. An aqueous solution of potassium caprate with a concentration of 1.6 wt% was applied as a spinning oil to the discharged filamentous material from an oiling guide arranged directly below the spinneret. The material was taken up by a first godet roll, passed through a second godet roll, and then wound into a cheese shape using a winder via a dancer roller at 800 m / min to obtain a 220 dtex / 40 filament spun yarn.

[0092] The obtained spun raw yarn was unwound in the longitudinal direction (perpendicular to the fiber circumferential direction) using a rewinder and rewound onto a stainless steel bobbin with a perforated nonwoven fabric to obtain a bobbin package for heat treatment. The obtained package was heat-treated at 275°C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of liquid crystalline polyester fiber. The heat-treated yarn was then unwound in the transverse direction (horizontal to the fiber circumferential direction) using a rewinder and rewound, during which a finishing oil mainly composed of coconut oil was applied. The analysis results of the obtained liquid crystalline polyester fiber are shown in Table 5.

[0093] Example 2 Liquid crystal polyester fibers were obtained in the same manner as in Example 1, except that the 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 the spinning oil.

[0095] [Example 4] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that a molten mixture was discharged at a discharge rate of 4.48 g / min using a spinneret having a hole diameter of 0.10 mmφ, a land length of 0.14 mm, and 10 holes to obtain a spinning raw yarn of 56 dtex / 10 filaments.

[0096] [Example 5] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that a molten mixture was discharged at a discharge rate of 64.0 g / min using a spinneret with a hole diameter of 0.10 mmφ, a land length of 0.14 mm, and 300 holes to obtain a spinning raw yarn of 1670 dtex / 300 filaments.

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

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

[0099] [Example 8] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that a molten mixture was discharged at a discharge rate of 64.0 g / min using a spinneret with a hole diameter of 0.08 mmφ, a land length of 0.112 mm, and 600 holes to obtain a spinning raw yarn of 1670 dtex / 600 filaments.

[0100] Example 9 A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that an aqueous solution of sodium dodecyl phosphate was used as the spinning oil and an aqueous solution of potassium caprate was used as the finishing oil.

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

[0102] Comparative Example 2 A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that an aqueous solution of sodium dodecyl phosphate was used as the spinning oil. The amount of sodium dodecyl phosphate attached was 0.62% by weight.

[0103]

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

[0105] Furthermore, in Examples 1 to 6, 8, and 9, a fatty acid metal salt having a specific carbon number was used as the oil to be applied, and inorganic particles were not applied, so the arithmetic mean height Sa could be adjusted to a relatively low value. Similarly, the arithmetic mean roughness Ra and the maximum height difference P-V could also be adjusted to a relatively low value. Therefore, the coefficient of dynamic friction between the metal and the fiber was low, and the wear resistance was excellent.

[0106] In Examples 1 to 5, 7 and 8, the amount of fatty acid metal salt used as the spinning oil was adjusted, so that the strength could be sufficiently improved by the subsequent heat treatment.

[0107] On the other hand, Comparative Example 1, which uses a fatty acid metal salt with a small number of carbon atoms, has a lower unit circumference liquid absorption rate and inferior liquid absorption properties compared to Examples 1 to 9. Furthermore, Comparative Example 1 has a larger arithmetic mean height Sa than Examples 1 and 3, which use fatty acid metal salts with different carbon numbers, a higher metal-fiber dynamic friction coefficient, and inferior wear resistance. Furthermore, Comparative Example 1 has significantly lower strength than Examples 1 and 3, which have the same or greater amount of fatty acid metal salt attached, and does not have sufficient strength.

[0108] Furthermore, in Comparative Example 2, in which sodium dodecyl phosphate was used as the oil agent, the unit circumference liquid absorption rate was lower than in Examples 1 to 9, and the liquid absorbency was poor.

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

[0110] As described above, the preferred embodiment of the present invention has been described, but various additions, modifications, or deletions can be made without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention.

Claims

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

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

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

4. The liquid crystal polyester fiber according to claim 1 or 2, wherein the adhesion amount of the fatty acid metal salt is 0.01 to 2.0% by weight.

5. The liquid crystal polyester fiber according to claim 1 or 2, wherein the adhesion amount of inorganic particles is 100 ppm by weight or less.

6. The liquid crystal polyester fiber according to claim 1 or 2, wherein the value of the maximum height difference P - V of the fiber surface measured according to ISO 25178 is 1 to 80 nm.

7. The liquid crystal polyester fiber according to claim 1 or 2, having a unit circumferential liquid absorption rate of 5.0% / μm or more.

8. The liquid crystal polyester fiber according to claim 1 or 2, having a metal - fiber dynamic friction coefficient of 0.18 or less.

9. A fiber structure comprising at least a part of the liquid crystal polyester fiber according to claim 1 or 2.

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

11. The production method according to claim 10, further comprising a step of heat - treating the spinning dope of the liquid crystal polyester fiber, and the applying step is performed before and / or after the heat - treating step.

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

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