Liquid crystal polyester fiber and method of manufacturing the same

Abstract

The present invention provides a liquid crystal polyester fiber having excellent tensile strength and compressive strength, and excellent disk fatigue resistance. The liquid crystal polyester fiber has a melting point of 335°C or higher and less than 360°C as measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10°C / min, a degree of crystallization of 45 to 60%, and a total number of unmelted material and voids with a major axis of 5 μm or more per 5 cm of single filament is 3 or less. For example, the liquid crystal polyester fiber may have a degree of orthorhombicity of 20% or more in its crystalline component.

Description

Technology Field

[0001] The present application claims priority to Japanese patent application 2022-199789 filed in Japan on December 14, 2022, and incorporates the entirety thereof as part of the present application by reference.

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

[0003] Liquid crystal polyester fibers are fibers made from liquid crystal polyester, which has a rigid molecular structure. It is known that the highest strength among synthetic fibers obtained by melt spinning is achieved by highly orienting molecular chains along the fiber axis direction during melt spinning and performing heat treatment at high temperatures for a long time. Additionally, it is known that liquid crystal polyester fibers improve heat resistance and dimensional stability as their molecular weight increases and their melting point rises through heat treatment. Therefore, they can be used for general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and protection applications. For example, mechanical properties are required for reinforcing material applications, and for electronic component applications such as substrate materials for circuit boards, heat resistance capable of withstanding thermal processing during component mounting is required in addition to the mechanical properties required for reinforcing materials.

[0004] Patent Document 1 (International Publication No. 2019 / 142692) describes that by heat-treating a liquid crystal polyester fiber having a longitudinal orientation degree of 89% or more and 95% or less at a temperature of 250°C or higher, a liquid crystal polyester fiber with a tensile strength of 25 cN / dtex or more and 30 cN / dtex or less can be obtained.

[0005] Patent document 2 (Japanese Published Patent Application No. 2010-43380) discloses a material for manufacturing fibers comprising a liquid crystal polyester having, as repeating units, a structural unit derived from an aromatic hydroxycarboxylic acid, a structural unit derived from an aromatic dicarboxylic acid, and a structural unit derived from an aromatic diol, wherein 40 mol% or more of these structural units are 2,6-naphthalenediyl groups, and a flow initiation temperature of 280 to 320°C, and it is described that a liquid crystal polyester fiber having high heat resistance can be obtained.

[0006] Patent Document 3 (Japanese Published Patent Application No. 2022-6590) describes a manufacturing method in which liquid crystal polyester is processed into a fibrous form by a melt spinning method and heated at a temperature of 330°C or higher, wherein the maximum crystallite size is 120 × 10 -10 A liquid crystal polyester fiber with a length of m or more and improved heat resistance is described. Prior art literature

[0007] International Publication No. 2019 / 142692, Japanese Published Patent Application No. 2010-43380, Japanese Published Patent Application No. 2022-6590 The problem to be solved

[0008] However, while liquid crystal polyester fibers are strong against tensile stress, they are relatively weak against compressive stress, requiring further improvement in mechanical properties depending on the application. For example, regarding reinforcing fibers used in rubber materials such as tires, timing belts, and rubber hoses, high strength and fatigue resistance are required against stress in both directions because forces are applied to the fiber axis in both the tensile and compressive directions.

[0009] In Patent Document 1, regarding the mechanical properties of liquid crystal polyester fibers, it is described that tensile strength is improved, but there is room for further improvement regarding tensile strength, and compressive strength and fatigue resistance are not described.

[0010] Patent Document 2 describes that by lowering the viscosity of the liquid crystal polyester during melt spinning, it can be easily fiberized, thereby enabling the production of fibers with high heat resistance. Although the yarnability of the liquid crystal polyester is evaluated, the physical properties of the obtained fibers are not evaluated, and mechanical properties are not described.

[0011] Patent Document 3 describes raising the melting point of liquid crystal polyester fibers, but does not describe the mechanical properties of the liquid crystal polyester fibers actually obtained.

[0012] The present invention aims to solve the above problem by providing a liquid crystal polyester fiber that not only has excellent tensile strength and compressive strength, but also has excellent fatigue resistance against tensile and compressive deformation. means of solving the problem

[0013] The inventors of the present invention, as a result of careful consideration to achieve the above objective, discovered that depending on the raw materials of the liquid crystal polyester used and the conditions during melt spinning of the liquid crystal polyester fibers, unmelted materials and voids occur in the fibers, and the presence of these materials causes a deterioration in the mechanical properties of the fibers. Furthermore, as a result of further research, it was discovered that by using a liquid crystal polyester having a specific weight average molecular weight and melting point, and by adjusting the conditions inside the extruder and the spinning temperature conditions to apply shear to the molten resin through melt mixing and spinning, the occurrence of unmelted materials and voids can be suppressed, and high orientation can be achieved. In addition, by heat-treating the highly oriented spun yarn, which has fewer unmelted materials and voids, the melting point and degree of crystallinity can be increased, thereby obtaining a liquid crystal polyester fiber that not only has sufficient tensile strength and compressive strength but also has excellent fatigue resistance in a disk fatigue test in which tensile strain and compressive strain are alternately applied (hereinafter referred to as disk fatigue resistance), and thus the completion of the present invention was achieved.

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

[0015] [Mode 1]

[0016] A liquid crystal polyester fiber having a melting point of 335°C or higher and less than 360°C (preferably 337°C or higher and less than 358°C, more preferably 340°C or higher and less than 355°C) as measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10°C / min, a degree of crystallization of 45 to 60% (preferably 46 to 58%, more preferably 48 to 55%), and a total number of unmelted material and voids with a major axis of 5 μm or more per 5 cm of single filament of 3 or fewer (preferably 2 or fewer, more preferably 1 or fewer).

[0017] [Mode 2]

[0018] A liquid crystal polyester fiber as described in Embodiment 1, wherein the degree of orthorhombicity in the crystalline component is 20% or more (preferably 26% or more, more preferably 27% or more).

[0019] [Mode 3]

[0020] A liquid crystal polyester fiber as described in Embodiment 1 or 2, wherein the degree of orientation in the fiber axis direction in the crystalline component is 97% or more and less than 100%.

[0021] [Mode 4]

[0022] A liquid crystal polyester fiber as described in any one of embodiments 1 to 3, having a tensile strength of 27 cN / dtex or more (preferably 28 cN / dtex or more, more preferably 30 cN / dtex or more).

[0023] [Mode 5]

[0024] A liquid crystal polyester fiber as described in any one of embodiments 1 to 4, wherein the compressive strength of the staple fiber is 0.70 cN / dtex or higher (preferably 0.75 cN / dtex or higher, more preferably 0.80 cN / dtex or higher).

[0025] [Mode 6]

[0026] A liquid crystal polyester fiber as described in any one of embodiments 1 to 5, wherein the staple fiber fineness is 7 dtex or less, and the coefficient of variation of the staple fiber fineness is 7% or less (preferably 6% or less, more preferably 5% or less).

[0027] [Mode 7]

[0028] A fiber structure composed of at least a portion of a liquid crystal polyester fiber described in any one of embodiments 1 to 6.

[0029] [Mode 8]

[0030] A composite material comprising a liquid crystal polyester fiber described in any one of embodiments 1 to 6 as a reinforcing fiber.

[0031] [Mode 9]

[0032] A method for manufacturing a liquid crystal polyester fiber as described in any one of embodiments 1 to 6,

[0033] A liquid crystal polyester having a weight average molecular weight in polystyrene equivalent in GPC of 50,000 or more and 160,000 or less (preferably 60,000 or more and 150,000 or less, more preferably 80,000 or more and 130,000 or less), and also a melting point Mp0 of 300 ℃ or higher (preferably 300 to 340 ℃, more preferably 305 to 330 ℃) measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10 ℃ / min, is described in the following (1) to (3):

[0034] (1) Extruder temperature: Mp0+15 ℃ to Mp0+35 ℃ (preferably Mp0+16 ℃ to Mp0+30 ℃, more preferably Mp0+17 ℃ to Mp0+25 ℃)

[0035] (2) Screw peripheral speed of the extruder: 10 to 40 m / min (preferably 15 to 35 m / min, more preferably 17 to 25 m / min)

[0036] (3) Spinning die temperature: Extruder temperature -15 ℃ ~ Extruder temperature -5 ℃

[0037] A process for obtaining spun yarn by spinning under conditions satisfying, and

[0038] A process of heat treating the obtained spun yarn

[0039] A method for manufacturing liquid crystal polyester fibers, comprising at least [ ].

[0040] [Mode 10]

[0041] A method for manufacturing liquid crystal polyester fibers as described in Embodiment 9, wherein the extruder is a twin-screw extruder.

[0042] [Mode 11]

[0043] A method for manufacturing liquid crystal polyester fibers as described in Embodiment 9 or 10, wherein the heat treatment temperature is 250 to 350 ℃ (preferably 255 to 320 ℃, more preferably 260 to 315 ℃, even more preferably 280 to 310 ℃).

[0044] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form including “at least one” unless the content clearly indicates otherwise. As used herein, the terms “and / or,” “at least one,” and “one or more” include any and all combinations of the related enumerated items.

[0045] Additionally, any combination of at least two components disclosed in the claims and / or specification is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention. Effects of the invention

[0046] The liquid crystal polyester fiber of the present invention has excellent tensile strength and compressive strength, and excellent disk fatigue resistance. Specific details for implementing the invention

[0047] [Liquid Crystal Polyester Fiber]

[0048] The liquid crystal polyester fiber of the present invention comprises a liquid crystal polyester. The liquid crystal polyester is composed of constituent units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and as long as the effects of the present invention are not impaired, the constituent units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in their chemical composition. Furthermore, within a range that does not impede the effects of the present invention, the liquid crystal polyester may also include constituent units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids. For example, preferred constituent units may be those shown in Table 1.

[0049]

[0050] In the constituent units of Table 1, m is an integer from 0 to 2, and Y in the formula may be, independently, a hydrogen atom, a halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), an alkyl group (e.g., methyl group, ethyl group, isopropyl group, t-butyl group, etc., alkyl groups having 1 to 4 carbon atoms), an alkoxy group (e.g., methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), an aryl group (e.g., phenyl group, naphthyl group, etc.), an aralkyl group (e.g., benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., phenoxy group, etc.), an aralkyloxy group (e.g., benzyloxy group, etc.).

[0051] More preferred constituent units include the constituent units described in examples (1) to (20) shown in Tables 2, 3, and 4 below. In addition, if a constituent unit in the formula is a constituent unit capable of representing multiple structures, two or more such constituent units may be combined and used as constituent units for the polymer.

[0052]

[0053]

[0054]

[0055] In the constituent units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each constituent unit n=1 or n=2 may exist alone or in combination, and Y1 and Y2 may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a 1 to 4 C alkyl group such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.). Among these, hydrogen atoms, chlorine atoms, bromine atoms, or methyl groups are preferred.

[0056] Also, Z can be a substituent represented by the following formula.

[0057] [Chemical Formula 1]

[0058]

[0059] The liquid crystal polyester may preferably include at least one constituent unit selected from the group consisting of a constituent unit represented by the following formula (I) (constituent unit (I)), a constituent unit represented by the following formula (II) (constituent unit (II)), a constituent unit represented by the following formula (III) (constituent unit (III)), and a constituent unit represented by the following formula (IV) (constituent unit (IV)).

[0060]

[0061] (during food, Ar 1 It is at least one selected from the group consisting of silver, phenylene groups, naphthylene groups, and biphenyllylene groups, and Ar 2 , Ar 3 and Ar 4 Each is independently at least one selected from the group consisting of a phenylene group, a naphthylene group, a biphenyllylene group, and a diphenyletherdiyl group, and Ar 1 , Ar 2 , Ar 3 and Ar 4 The hydrogen atoms of the aromatic ring may each 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.

[0062] The constituent unit (I) is a constituent unit derived from an aromatic hydroxycarboxylic acid, and Ar 1 The 1,4-phenylene group constituent unit (a constituent unit derived from 4-hydroxybenzoic acid), and the 2,6-naphthylene group constituent unit (a constituent unit derived from 6-hydroxy-2-naphthoic acid) are preferred.

[0063] The constituent unit (II) is a constituent unit derived from an aromatic dicarboxylic acid, and Ar 2 a. A 1,4-phenylene group constituent unit (a constituent unit derived from terephthalic acid), a 1,3-phenylene group constituent unit (a constituent unit derived from isophthalic acid), a 2,6-naphthylene group constituent unit (a constituent unit derived from 2,6-naphthalenedicarboxylic acid), and a diphenyl ether-4,4'-diyl group constituent unit (a constituent unit derived from diphenyl ether-4,4'-dicarboxylic acid) are preferred.

[0064] The constituent unit (III) is a constituent unit derived from an aromatic diol, and Ar 3The 1,4-phenylene group constituent unit (constituent unit derived from hydroquinone), the 4,4'-biphenylylene group constituent unit (constituent unit derived from 4,4'-dihydroxybiphenyl), the phenyl-1,4-phenylene group constituent unit (constituent unit derived from phenylhydroquinone), and the diphenyl ether-4,4'-diyl group constituent unit (constituent unit derived from 4,4'-dihydroxydiphenyl ether) are preferred.

[0065] Constituent unit (IV) is a constituent unit derived from an aromatic hydroxyamine, and Ar 4 a. A 1,4-phenylene group constituent unit (a constituent unit derived from 4-aminophenol), and a 4,4'-biphenylylene group constituent unit (a constituent unit derived from 4-amino-4'-hydroxybiphenyl) are preferred.

[0066] The content of the constituent unit (I) in the liquid crystal polyester may be 20 to 80 mol% with respect to the total amount of all constituent units, preferably 30 to 75 mol%, and more preferably 40 to 70 mol%.

[0067] The content of the constituent unit (II) in the liquid crystal polyester may be 10 to 40 mol% with respect to the total amount of all constituent units, preferably 12.5 to 35 mol%, and more preferably 15 to 30 mol%.

[0068] The total content of constituent units (III) and (IV) in the liquid crystal polyester may be 10 to 40 mol% with respect to the total amount of all constituent units, preferably 12.5 to 35 mol%, and more preferably 15 to 30 mol%.

[0069] The molar ratio of the content of constituent unit (II) and the total content of constituent units (III) and (IV) may be (II) / [(III)+(IV)], which makes it easier to increase the molecular weight of the liquid crystal polyester and improves mechanical properties, and may be 90 / 100 to 100 / 90, preferably 95 / 100 to 100 / 95, more preferably 98 / 100 to 100 / 98, and even more preferably 100 / 100.

[0070] Among the liquid crystal polyesters, each constituent unit (I) to (IV) may contain two or more types. The above content of each constituent unit represents the content of all constituent units corresponding to each constituent unit, and for example, the content of constituent unit (I) represents the total content of constituent units (I) when two or more types of constituent unit (I) are included in the liquid crystal polyester.

[0071] The liquid crystal polyester may have a total content of constituent units (I) to (IV) of at least 90 mol% with respect to the total amount of all constituent units, for example, preferably at least 95 mol%, more preferably at least 99 mol%, and even more preferably at least 100 mol%.

[0072] For liquid crystal polyester, a combination having a naphthalene backbone as a constituent unit is preferable from the perspective of increasing the melting point and degree of crystallinity by having a structure with high crystallinity. For example, the total content of constituent units containing a 2,6-naphtylene group in the liquid crystal polyester may be 40 mol% or more, preferably 50 mol% or more, more preferably 65 mol% or more, even more preferably 68 mol% or more, even more preferably 70 mol% or more, and may be 90 mol% or less, preferably 85 mol% or less, more preferably 83 mol% or less, and even more preferably 80 mol% or less. As for constituent units containing a 2,6-naphtylene group, Ar1 This 2,6-naphthylene group constituent unit (I) (constituent unit derived from 6-hydroxy-2-naphthoic acid) and Ar 2 A constituent unit (II) that is a 2,6-naphthylene group (a constituent unit derived from 2,6-naphthalenedicarboxylic acid) is preferred.

[0073] In addition, the liquid crystal polyester fiber may include thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyetheretherketone, and fluoropolymer, to the extent that it does not impede the effects of the present invention. Furthermore, it may include various additives such as inorganic materials such as titanium oxide, kaolin, silica, and barium oxide, carbon black, coloring agents such as dyes or pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

[0074] The liquid crystal polyester fiber of the present invention may contain 50 weight% or more of liquid crystal polyester, preferably 80 weight% or more, more preferably 90 weight% or more, even more preferably 95 weight% or more, and even more preferably 99.9 weight% or more.

[0075] The liquid crystal polyester fiber of the present invention has a melting point of 335°C or higher and less than 360°C, measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10°C / min. The liquid crystal polyester fiber of the present invention has a high melting point and excellent heat resistance. The melting point of the liquid crystal polyester fiber may preferably be 337°C or higher and 358°C or lower, and more preferably 340°C or higher and 355°C or lower. In addition, the melting point of the liquid crystal polyester fiber is a value measured by the method described in the examples described below.

[0076] The liquid crystal polyester fiber of the present invention has a degree of crystallization of 45 to 60%. Since the degree of crystallization of the liquid crystal polyester fiber of the present invention is within a specific range, the mechanical properties are excellent. If the degree of crystallization is excessively low, the orientation along the fiber axis is reduced, and the tensile strength and compressive strength tend to decrease. Also, if the degree of crystallization is excessively high, toughness is impaired, and the compressive strength or disk fatigue tends to deteriorate. The degree of crystallization of the liquid crystal polyester fiber may preferably be 46 to 58%, and more preferably 48 to 55%. In this specification, the degree of crystallization of the liquid crystal polyester fiber is calculated from the diffraction peaks originating from each crystal of the X-ray diffraction profile obtained by wide-angle X-ray diffraction measurement (e.g., diffraction peaks appearing around the diffraction angle 2θ = 19 to 21° and around 2θ = 27°, etc.) and is a value measured by the method described in the examples below.

[0077] The liquid crystal polyester fiber of the present invention has a total number of unmelted particles and voids of a major axis of 5 μm or more per 5 cm of single filament, which is 3 or less. In this specification, unmelted particles refer to microcrystalline particles derived from liquid crystal polyester that remain unmelted during spinning and have an orientation different from that of crystals generally oriented in the direction of the fiber axis, and can be confirmed by observation with a polarized light microscope. In addition, voids refer to bubbles remaining from decomposition gases generated from the resin during spinning or bubbles generated due to poor melt mixing, and can be confirmed by observation with a microscope using transmitted light.

[0078] The liquid crystal polyester fiber of the present invention has excellent mechanical properties because it not only has a degree of crystallization within a specific range but also has minimal unmelted material and voids. If unmelted material or voids are present in the fiber, those points are localized weak defect areas; therefore, when a force is applied in the tensile direction, these points become the starting points for fracture, and the tensile strength decreases. Furthermore, it is known that liquid crystal polyester fibers experience a decrease in strength when a force is applied in the compressive direction due to buckling deformation known as kink bands. Since kink bands originating from unmelted material or voids are prone to forming, the compressive strength is consequently lowered. Additionally, since unmelted material and voids are defects that occur during spinning, the presence of such defects (particularly voids) makes it easy for the single fiber fineness to change, and the uniformity of the resulting fiber is easily compromised.

[0079] Since mechanical properties or fiber uniformity are prone to deterioration when these unmelted materials and voids are included in a predetermined size, in the present invention, unmelted materials and voids with a major diameter (maximum diameter) of 5 μm or more are used as measurement targets. The total number of unmelted materials and voids with a major diameter of 5 μm or more included per 5 cm of single fiber may preferably be 2 or fewer, and more preferably 1 or fewer. The total number of unmelted materials and voids is a value measured by the method described in the examples described below. In addition, when targeting short fibers of liquid crystal polyester fibers with a fiber length of less than 5 cm, the total number of unmelted materials and voids with a major diameter of 5 μm or more included per 5 cm can be measured by observing multiple short fibers that add up to 5 cm and counting the number of unmelted materials and voids with a major diameter of 5 μm or more in those multiple short fibers.

[0080] The liquid crystal polyester fiber of the present invention may have a degree of orthorhombicity of 20% or more in its crystalline components. Liquid crystal polyesters have crystalline components such as orthorhombic or hexagonal crystals, but if the degree of orthorhombicity in their crystalline components is high, heat resistance and mechanical properties tend to be further improved. The degree of orthorhombicity can be adjusted by the composition of the liquid crystal polyester used, manufacturing conditions such as spinning conditions and heat treatment conditions, etc. The degree of orthorhombicity may preferably be 26% or more, and more preferably 27% or more. In addition, the upper limit of the degree of orthorhombicity is not particularly limited, but, for example, may be 35% or less. In the present specification, the degree of orthorhombicity of the liquid crystal polyester fiber is calculated from the diffraction peaks originating from the orthorhombic and hexagonal X-ray diffraction profile obtained by wide-angle X-ray diffraction measurement (e.g., diffraction peaks appearing around the diffraction angle 2θ = 19 to 21°, etc.) and is a value measured by the method described in the examples described below.

[0081] The liquid crystal polyester fiber of the present invention may have a degree of orientation in the fiber axis direction of the crystalline component of 97% or more and less than 100%. The degree of orientation is an indicator of how much the crystalline component is oriented in the fiber axis direction, and the higher the degree of orientation, the more mechanical properties can be improved. In this specification, the degree of orientation of the liquid crystal polyester fiber is a value calculated from an azimuth profile obtained by wide-angle X-ray diffraction measurement and measured by the method described in the examples below.

[0082] The liquid crystal polyester fiber of the present invention may have a tensile strength of 27 cN / dtex or higher, preferably 28 cN / dtex or higher, and more preferably 30 cN / dtex or higher. In addition, the upper limit of the tensile strength is not particularly limited, but may be, for example, about 40 cN / dtex. The tensile strength of the liquid crystal polyester fiber is a value measured by the method described in the examples described below.

[0083] The liquid crystal polyester fiber of the present invention may have a compressive strength of 0.70 cN / dtex or higher, preferably 0.75 cN / dtex or higher, and more preferably 0.80 cN / dtex or higher. In addition, the upper limit of the compressive strength is not particularly limited, but, for example, may be approximately 1.5 cN / dtex. The compressive strength of the liquid crystal polyester fiber is a value measured by the method described in the examples described below.

[0084] The liquid crystal polyester fiber of the present invention may have a strength retention rate of 50% or more in a disk fatigue test by the method described in the examples below, preferably 55% or more, and more preferably 60% or more.

[0085] The liquid crystal polyester fiber of the present invention may appropriately select the short fiber fineness according to the application, etc. For example, the short fiber fineness may be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. However, from the perspective of responding to miniaturization for electronic component applications, it is preferable to have a fine fineness, for example, 7 dtex or less. In addition, the lower limit of the short fiber fineness is not particularly limited, but for example, it may be about 0.01 dtex. The short fiber fineness is a value measured by the method described in the examples described below.

[0086] The liquid crystal polyester fiber of the present invention may have a coefficient of variation of single fiber fineness of 7% or less, preferably 6% or less, and more preferably 5% or less. In applications such as electronic components, thinning of fibers or fabrics is required along with the miniaturization of products, but since fiber uniformity is particularly required when the single filament diameter is thinner, it is desirable that the non-uniformity of single fiber fineness be small even at fine fineness. The coefficient of variation of single fiber fineness can be calculated as standard deviation of single fiber fineness (σ) / single fiber fineness (average value) (x) × 100, and is a value measured by the method described in the examples described below.

[0087] The liquid crystal polyester fiber of the present invention may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be appropriately selected according to 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.

[0088] The liquid crystal polyester fiber of the present invention may appropriately select a total fineness depending on the application, etc., and for example, the total fineness may be 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 2,000 dtex or less, and even more preferably 600 dtex or less. From the perspective of responding to miniaturization for electronic component applications, it is preferable to have a fine fineness, for example, 300 dtex or less. In addition, the lower limit of the total fineness is not particularly limited, but for example, it may be about 1 dtex.

[0089] [Method for manufacturing liquid crystal polyester fibers]

[0090] The method for manufacturing liquid crystal polyester fibers of the present invention is,

[0091] A liquid crystal polyester having a weight average molecular weight equivalent to polystyrene in GPC of 50,000 or more and 160,000 or less, and a melting point Mp0 of 300 ℃ or higher measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10 ℃ / min, is described below (1) to (3):

[0092] (1) Extruder temperature: Mp0+15 ℃ ~ Mp0+35 ℃

[0093] (2) Extruder screw peripheral speed: 10 to 40 m / min

[0094] (3) Spinning die temperature: Extruder temperature -15 ℃ ~ Extruder temperature -5 ℃

[0095] A process for obtaining spun yarn by spinning under conditions satisfying, and

[0096] At least a process for heat treating the obtained spun yarn may be provided.

[0097] In the present invention, by using a liquid crystal polyester having a specific weight average molecular weight and melting point as a raw material resin, it is easy to increase the degree of crystallization during the spinning process and heat treatment process, so it is possible to obtain a liquid crystal polyester fiber with a high degree of crystallization and melting point as a fiber after heat treatment.

[0098] Meanwhile, the inventors of the present invention have discovered that such liquid crystal polyesters are prone to the occurrence of unmelted material and voids. Specifically, liquid crystal polyesters, which have a high melting point relative to a specific weight-average molecular weight range, tend to have low melt viscosity. Consequently, shearing is difficult to apply during melt mixing, and unmelted material remains as an impurity without being completely melted. Furthermore, if the melt mixing temperature is set high to reduce unmelted material, decomposition gas is generated, resulting in the formation of voids. The occurrence of these unmelted material and / or voids causes single filaments to bundle during spinning, making it difficult to stably obtain uniform fibers, and can also be a cause that hinders the improvement of the fiber's crystallinity. Additionally, it has been discovered that because the liquid crystal polyester has low melt viscosity, extrusion is unstable and non-uniformity of fineness is likely to occur. Moreover, since shearing is difficult to apply during extrusion, it is difficult to achieve high orientation, making it difficult to increase the crystallinity.

[0099] Therefore, in the present invention, by adjusting the temperature and the peripheral speed of the screw in the extruder, shearing is applied at a temperature where decomposition gas is not generated and the liquid crystal polyester is not degraded, thereby promoting melting and suppressing the generation of unmelted material and voids. In addition, by adjusting the temperature of the spinneret to be lower than the temperature of the extruder on the upstream side in a specific relationship, the viscosity of the liquid crystal polyester is increased to stabilize the discharge and suppress non-uniformity of fineness, and at the same time, shearing is applied during discharge to orient the material and promote crystallization. Thus, in the present invention, even when using a liquid crystal polyester having a specific weight average molecular weight and melting point as a raw material, it is possible to obtain the liquid crystal polyester fiber described above by adjusting the spinning conditions to reduce unmelted material and voids and heat-treating the spun yarn with adjusted crystallinity.

[0100] The weight average molecular weight of the liquid crystal polyester used in the present invention is preferably 50,000 or more and 160,000 or less, more preferably 60,000 or more and 150,000 or less, and even more preferably 80,000 or more and 130,000 or less. Liquid crystal polyester having such a weight average molecular weight has high molecular chain mobility, and when heat treated, the molecular chains are densely packed, making it easy for the degree of crystallization to increase. In this specification, the weight average molecular weight is calculated as the weight average molecular weight in polystyrene equivalent in gel permeation chromatography (GPC) and is a value measured by the method described in the examples below.

[0101] The melting point of the liquid crystal polyester used in the present invention (hereinafter referred to as Mp0) is preferably 300°C or higher, more preferably 300°C to 340°C, and even more preferably 305°C to 330°C. By using a liquid crystal polyester having such a melting point as a raw material, the melting point of the liquid crystal polyester fiber after heat treatment can be improved, thereby improving heat resistance. In this specification, the melting point is the temperature of the main absorption peak observed by measuring with a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of the sample is taken into a DSC device and sealed in an aluminum pan, and 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 raised from room temperature (e.g., 25°C) to 10°C / min. If a clear peak does not appear in the 1st run of the DSC measurement depending on the type of polymer, the temperature can be raised at a rate of 50 ℃ / min to a temperature 50 ℃ higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then lowered to 50 ℃ at a rate of 80 ℃ / min, and then the endothermic peak can be measured at a rate of 10 ℃ / min.

[0102] The liquid crystal polyester used in the present invention has, for example, a shear rate of 1216 sec at Mp0 + 15 ℃. -1 The melt viscosity at may be 3 to 28 Pa·s, preferably 4 to 25 Pa·s, and more preferably 5 to 20 Pa·s. The melt viscosity is a value measured by the method described in the examples described below.

[0103] The liquid crystal polyester used in the present invention may be a liquid crystal polyester having the constituent units described above. From the perspective of obtaining liquid crystal polyester fibers with further improved heat resistance and mechanical properties, a combination having a naphthalene backbone as a constituent unit is preferred, and more preferably, the liquid crystal polyester may be one in which the total content of constituent units including 2,6-naphtylene groups is 40 mol% or more relative to the total amount of all constituent units.

[0104] Liquid crystal polyesters can be synthesized by known polycondensation methods. As monomers provided for polycondensation, various aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids, aromatic diols, and aromatic hydroxyamines may be used, and acylated compounds of hydroxyl groups with activated ends of these monomers, esterified compounds of carboxyl groups, acid halides, acid anhydrides, and other carboxylic acid derivatives may also be used.

[0105] Polycondensation may be carried out in the presence of various polymerization catalysts, examples of which include organotin-based catalysts (dialkyltin oxide, etc.), antimony-based catalysts (antimony trioxide, etc.), titanium-based catalysts (titanium dioxide, etc.), alkali metal salts or alkaline earth metal salts of carboxylic acids (potassium acetate, etc.), Lewis salts (BF3, etc.).

[0106] In addition, the thermoplastic polymer described above or various additives may be added to the liquid crystal polyester to the extent that it does not impede the effects of the present invention.

[0107] In the spinning process, the liquid crystal polyester is fed into an extruder and melted and kneaded by the rotation of a screw while being heated inside the extruder. Afterward, the melted mixture is metered by a gear pump, transported to a spinning head, and discharged through a spinning die. By winding the obtained yarn, a spun yarn can be obtained.

[0108] In the extruder, heating can be performed by known heating means such as a heater, and the extruder temperature may be Mp0 + 15°C to Mp0 + 35°C with respect to the melting point Mp0 of the liquid crystal polyester, preferably Mp0 + 16°C to Mp0 + 30°C, and more preferably Mp0 + 17°C to Mp0 + 25°C. By adjusting to such a temperature range, melting can be promoted within a range where decomposition gas is not generated and the liquid crystal polyester is not degraded. Furthermore, in this specification, the extruder temperature refers to the maximum temperature inside the extruder.

[0109] In addition, in addition to heat transfer from the heating means of the extruder, shear is applied between the screw and the inner wall of the cylinder (barrel) or between the screws by the rotation of the screw. The peripheral speed of the screw may be 10 to 40 m / min, preferably 15 to 35 m / min, and more preferably 17 to 25 m / min. By adjusting to such a peripheral speed, mechanical energy can be applied within a range where the liquid crystal polyester does not deteriorate, thereby promoting the melting of the liquid crystal polyester. That is, if the screw peripheral speed is above the above lower limit, sufficient mixing is possible and melting can be promoted, making it difficult for unmelted material to remain. If the screw peripheral speed is below the above upper limit, it is difficult for bubbles to be trapped in the mixed resin, making it difficult for voids to remain; furthermore, since the heat generated by shear does not become excessively large, it is difficult to cause the generation of decomposition gases or resin deterioration.

[0110] The total residence time in the device from the time the liquid crystal polyester is fed into the extruder until it is discharged from the spinneret may be 60 minutes or less, preferably 40 minutes or less, and more preferably 30 minutes or less, from the perspective of suppressing resin degradation or decomposition.

[0111] Since bubbles may be included during melt mixing due to the generation of gas by decomposition or the entrapment of air within the extruder, it is desirable to degas the material by reducing the pressure inside the extruder, for example, by installing a vent in the extruder and connecting a pressure reducing pump, in order to suppress the generation of voids. For example, the vacuum level may be 100 kPa or less in absolute pressure, preferably 80 kPa or less, and more preferably 60 kPa or less.

[0112] As for the extruder, known extruders such as single-screw extruders and multi-screw extruders (two or more axes) can be used, and a two-screw extruder is preferred in terms of improving mixing and degassing properties.

[0113] A molten mixture obtained by melting and kneading in an extruder is supplied to a spinning head and extruded from a spinneret at a specific temperature. The spinneret temperature may be from the extruder temperature - 15°C to the extruder temperature - 5°C. By adjusting the spinneret temperature to be lower than the temperature in the extruder upstream of the spinneret and to have a specific relationship, the viscosity of the liquid crystal polyester at the time of extrusion can be increased to stabilize the extrusion, and at the same time, shear can be applied to promote orientation crystallization. Additionally, the spinneret temperature may be from Mp0 + 5°C to Mp0 + 15°C relative to the melting point Mp0 of the liquid crystal polyester.

[0114] Melt spinning can be carried out by known or conventional methods, and a spun yarn can be obtained by extruding a molten mixture from a spinning die having the specific temperature and winding it by a godet roller, etc.

[0115] By performing heat treatment on the spun yarn, solid-state polymerization of the liquid crystal polyester proceeds, the melting point rises from the melting point (Mp) of the spun yarn, and the degree of crystallinity is improved. In the heat treatment process, the method of heat treatment is not particularly limited; for example, it may be a batch heat treatment or a continuous heat treatment by conveying. In addition, the melting point (Mp) of the spun yarn can be measured by the same method as the melting point of the liquid crystal polyester fiber.

[0116] For example, in the heat treatment of a batch process, the heat treatment may be performed in a packaged state on a bobbin, a spool, or a fiber bundle, for example; however, it is preferable to perform the treatment in a packaged state as this simplifies the equipment and improves productivity. The bobbin needs to withstand the temperature of solid-state polymerization, and it is preferable that it be made of a metal such as aluminum, brass, iron, or stainless steel.

[0117] In the case of continuous heat treatment by conveying, the conveying method may be carried out using either contact conveying (e.g., a conveyor system, a support roll system, or a heat treatment method on heated rollers) or non-contact conveying (roll-to-roll system). Furthermore, the processing path does not have to be a straight line, and heat treatment may be performed by appropriately changing the length, angle, curvature, etc., of the processing path by placing return rollers or guides within the device.

[0118] For the heat treatment process, known methods may be used, such as atmospheric heating or contact heating. As the atmosphere, air, an inert gas (e.g., nitrogen, argon), or a combination thereof is preferably used. Furthermore, there is no problem at all if the heat treatment is performed under reduced pressure.

[0119] In the heat treatment process, the heat treatment temperature may be 250 to 350 ℃, preferably 255 to 320 ℃, more preferably 260 to 315 ℃, and even more preferably 280 to 310 ℃. By setting the temperature to such a range, the degree of crystallization can be appropriately increased. In addition, the heat treatment temperature may be below the melting point (Mp) of the spun yarn provided to the heat treatment process to prevent melting, and for example, in the range of 250 to 350 ℃, it may be Mp-50 ℃ or higher and less than Mp ℃, preferably Mp-40 ℃ or higher and less than Mp ℃, and more preferably Mp-30 ℃ or higher and less than Mp ℃. In the heat treatment process, since the melting point of the liquid crystal polyester fiber increases with the progress of solid-state polymerization, the initial heat treatment temperature in the heat treatment process may be lower than the melting point (Mp) of the spun yarn, and from the perspective of efficient strength improvement, the heat treatment temperature may be increased stepwise according to the progress of solid-state polymerization, and heat treatment may be performed at a temperature exceeding the melting point (melting point of the spun yarn) at the time of providing the heat treatment process.

[0120] The heat treatment time of the heat treatment process can be appropriately set according to the heat treatment method or heat treatment temperature. For example, it can be set from a range of 15 minutes to 30 hours, preferably 2 to 24 hours, more preferably 3 to 20 hours, and the heat treatment time here refers to the holding time at a predetermined heat treatment temperature (e.g., maximum temperature).

[0121] In the method for manufacturing liquid crystal polyester fibers according to the present invention, the strength ratio of the liquid crystal polyester fibers before and after the heat treatment process 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 fibers before and after the heat treatment process is not particularly limited, but, for example, may be 10 times or less. Here, the strength ratio before and after the heat treatment process refers to the value obtained by dividing the tensile strength of the liquid crystal polyester fiber after the heat treatment process by the tensile strength of the liquid crystal polyester fiber (spun yarn) before the heat treatment process.

[0122] In the method for manufacturing liquid crystal polyester fibers of the present invention, for example, a known emulsion may be applied before the heat treatment process to improve the fiber's cohesiveness or to prevent fusion during heat treatment.

[0123] [Fiber structure]

[0124] The liquid crystal polyester fiber of the present invention can be used as a reinforcing fiber for manufacturing a composite material. When used as a reinforcing fiber, a fiber structure comprising at least a portion of the liquid crystal polyester fiber can be used as an intermediate material for manufacturing the composite material.

[0125] The fiber structure comprising the liquid crystal polyester fiber of the present invention can be used in any fiber form such as staple fiber, short-cut fiber, filament yarn, spun yarn, cord-shaped material, rope, etc., and can also be used as various fabrics such as nonwoven fabric, woven fabric, and knitted fabric using the liquid crystal polyester fiber. Such fibers or fabrics can be manufactured using the liquid crystal polyester fiber by a known method.

[0126] The fiber structure of the present invention may be a combination of liquid crystal polyester fibers and other fibers, provided that it does not impede the effects of the present invention. For example, a composite fiber using liquid crystal polyester fibers and other fibers (e.g., a blended yarn in which liquid crystal polyester fibers and other fibers are blended) may be used. In addition, a composite fabric using liquid crystal polyester fibers and other fibers may be used (e.g., a blended fabric in which liquid crystal polyester fibers and other fibers are blended, or a laminate of a fabric made of liquid crystal polyester fibers and a fabric made of other fibers). When the fiber structure is used in the manufacture of a composite material, the fiber structure may be a composite fiber or a composite fabric that includes a fused fiber forming the matrix of the composite material as the other fiber.

[0127] The liquid crystal polyester fiber of the present invention can be used in the form of various fiber structures for various purposes, such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and protective materials. For example, it can be used as various fiber products such as tension members (electric wires, optical fibers, etc.), heater wire cores, cords for various electrical products such as earphone cords, ropes, sling belts, ropes, lifelines, fishing lines, fishing nets, kite lines, land nets (safety nets, golf driving range nets, etc.), catheters, reinforcing materials for plastics, concrete, or rubber, foam for printed circuit boards, sail cloths, protective clothing, and protective gloves. In particular, liquid crystal polyester fibers with fine denier (e.g., a single fiber denier of 7 dtex or less) can be used for electronic components such as foam for printed circuit boards.

[0128] [Composite]

[0129] In the present invention, the composite material may be one that can be obtained by using liquid crystal polyester fibers as reinforcing fibers and molding a matrix resin. The liquid crystal polyester fibers can be molded using the fiber structure.

[0130] As the matrix resin, a resin generally used in composites may be used, and a thermosetting resin or a thermoplastic resin may be used. For example, thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, bismaleimide resins, phenolic resins, urea resins, melamine resins, thermosetting polyimide resins, thermosetting polyurethane resins, benzoxazine resins, etc. As for the thermoplastic resin, the type is not particularly limited as long as the softening temperature is lower than the melting point of the liquid crystal polyester fiber of the present invention, but for example, vinyl resins (polymers or derivatives composed of monomers having vinyl groups CH2=CH- or vinylidene groups CH2=C<); Examples include polyamide resins such as aliphatic polyamide resins (polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612, etc.) and semi-aromatic polyamide resins; polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; fluorine resins such as polytetrafluoroethylene resin; polysulfone resins such as polysulfone resin and polyethersulfone resin; polyetherketone resins such as polyetherketone resin, polyetheretherketone resin, and polyetherketoneketone resin; polycarbonate resin; polyphenylene ether resin; amorphous polyarylate resin; liquid crystal polyester resins such as fully aromatic polyester resin.

[0131] Examples

[0132] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto. In addition, in the following examples and comparative examples, various physical properties were measured by the following methods.

[0133] (Weight-average molecular weight)

[0134] A mixed solvent of pentafluorophenol / chloroform = 1 / 2 (weight ratio) was used as the solvent, and the liquid crystal polyester was dissolved in the solvent to a concentration of 0.03 wt% to prepare a sample for GPC measurement. This was measured under the following conditions using a high-speed GPC measuring device (manufactured by Tosho Corporation, “HLC-8420GPC”), and the weight-average molecular weight was calculated by converting to standard polystyrene.

[0135] Column: TSK gel guardcolumn SuperH-L 4.6 mm × 3.5 cm 1 piece,

[0136] TSKgel SuperH2000 6.0 mm ID × 15 cm 1 piece,

[0137] TSKgel SuperHM-H 6.0 mm ID × 15 cm 2 pieces

[0138] Detector: RI detector

[0139] Temperature: 40 ℃

[0140] Flow rate: 0.6 mL / min

[0141] Injection volume: 100 μL

[0142] (Melting point of resin chips (granular molded bodies) and fibers)

[0143] In accordance with JIS K 7121, measurements were taken using a differential scanning calorimeter (DSC; "DSC60A Plus" manufactured by Shimadzu Corporation), and the temperature of the observed main absorption peak was set as the melting point. Specifically, 4 to 6 mg of the sample was placed in an aluminum pan using the above DSC apparatus, and nitrogen was flowed as a carrier gas at a flow rate of 200 mL / min. The endothermic peak originating from the liquid crystal polyester was measured when the temperature was increased from 25 ℃ to 10 ℃ / min.

[0144] (Melting viscosity of resin chips (granular molded bodies))

[0145] The melt viscosity of the raw resin was measured using a melt viscosity measuring device (Capilograph 1C manufactured by Toyo Seiki Co., Ltd.). Resin chips were filled into the device cylinder, and using a 1.00 mmφ × 10 mm capillary, a shear rate of 1216 sec was measured under each temperature condition of Mp0 + 15 ℃ relative to the melting point Mp0 of the liquid crystal polyester (the melting point of the liquid crystal polyester of the resin chip measured above). -1 The melt viscosity at was measured.

[0146] (Degree of crystallization)

[0147] A liquid crystal polyester fiber was mounted in a fiber-dedicated holder, and X-rays were incident in a direction orthogonal to the fiber axis using the transmission method under the following measurement conditions, and wide-angle X-ray diffraction (WAXD) measurements were performed.

[0148] Measuring device: Bruker "D8 Discover IμS"

[0149] Detector: 2D PSPC·VANTEC-500

[0150] X Source: Cu

[0151] Current: 1 mA

[0152] Voltage: 50 kV

[0153] Exposure time: 10 minutes

[0154] Collimator diameter: 0.5 mm

[0155] Camera length: 17 cm

[0156] Detector position (2θ): 20°

[0157] Sample position (ω): 10°

[0158] Angle of elevation (Ψ): 90°

[0159] Measurement temperature: Room temperature (approx. 25 ℃)

[0160] Under the following conditions, an X-ray diffraction profile was obtained with the horizontal axis being the diffraction angle (2θ) and the vertical axis being the intensity.

[0161] Integration range: 2θ = 5 ∼ 35°, γ (azimuth) = 250 ∼ 290°

[0162] Step width: 0.05° (diffraction angle)

[0163] In the obtained X-ray diffraction profile, a baseline was established by connecting the values ​​of 2θ = 5° and 35° with a straight line. Based on this newly established baseline, the difference in intensity along the vertical axis from the measured data to the baseline was converted into profile data with the new intensity.

[0164] For the profile data after baseline correction, a pseudopoite function (ratio of Lorentz function: α=0) was used to fit the non-finite peak with peak height, peak top position, σ, and asymmetry parameter as variables. At this time, the initial value of the peak top position of the fitting function was set to approximately 20.6°. The peak area of ​​this fitting function was calculated as the non-finite (D).

[0165] For peaks A (peak top position around 19°), B (peak top position around 20.5°), and C (peak top position around 27°) of the profile data after baseline correction, the determination peaks were fitted using the following function with peak height, peak top position, and σ as variables. All determination peaks were made symmetric.

[0166] Peak A: Pseudopoite function (α=1)

[0167] Peak B: Pseudopoite function (α=0)

[0168] Peak C: Pseudopoite function (α=0.5)

[0169] In addition, fitting was performed using the least squares method, including the fitting function of the previously obtained non-normal peak, so that the difference between the sum of all fitting functions and the profile data after baseline correction was minimized. The peak areas of these fitting functions were calculated as the determined amounts (A), (B), and (C), respectively.

[0170] Using the above non-quantitative and quantified amounts, the degree of crystallization was calculated from the following formula.

[0171] Degree of crystallinity (%) = {(A) + (B) + (C)} / {(A) + (B) + (C) + (D)} × 100

[0172] (Four Directions Correction Diagram)

[0173] The degree of orthorhombic crystallization was calculated using the amount of crystallization of peak A originating from hexagonal crystallization (A) and the amount of crystallization of peak B originating from orthorhombic crystallization (B), calculated from the X-ray diffraction profile (profile data after baseline correction) as a measure of the degree of crystallization above, from the following formula.

[0174] Orthorhombicity (%) = (B) / {(A)+(B)}×100

[0175] (Orientation)

[0176] In the wide-angle X-ray diffraction measurement under the above crystallinity measurement conditions, an azimuth profile was obtained under the following conditions, with the horizontal axis representing the azimuth (γ) and the vertical axis representing the intensity.

[0177] Integration range: γ=225 ∼ 315°, 2θ=19.0 ∼ 21.0°

[0178] Step width: 0.5°

[0179] In the obtained azimuth profile, a baseline was established by connecting the values ​​of γ=225° and 315° with a straight line. Based on this newly established baseline, the difference in intensity along the vertical axis from the actual measurement data to the baseline was converted into profile data with the new intensity.

[0180] In the profile data after baseline correction, the full width at half maximum of the identified peak was calculated. Using the full width at half maximum of the peak, the degree of orientation (%) was calculated from the following formula.

[0181] Orientation (%) = (180 - Half-width) / 180 × 100

[0182] (Number of voids)

[0183] One staple fiber was taken from a liquid crystal polyester fiber (multifilament), and microscopic observation by transmitted illumination was performed using a microscope (Eclipse Ci-E manufactured by Nikon Inc.) over a length of 5 cm, and the number of voids with a major axis (maximum diameter) of 5 μm or more was counted. The number of voids was counted for 5 staple fibers, and the average number was taken as the number of voids with a major axis of 5 μm or more contained per 5 cm of staple fiber.

[0184] (Number of beauty products)

[0185] Polarized light microscopy (cross-Nicole) was performed on the same sample as the void measurement above. Specifically, using the same microscope, a polarizer "Sensitive Color Polarizer Unit C-TP" and an analyzer "Sensitive Color Polarizer Unit C-IA" were set on the upper and lower parts of the microscope stage, and the sample was observed in a state where the transmission axes of the polarizer and the analyzer were orthogonal to each other (cross-Nicole). Since liquid crystal polyester fibers are highly oriented and possess optical anisotropy (birefringence), the entire fiber can be observed in a bright field state when viewed from any angle. When the stage is rotated 45° from this state to observe the fiber in a dark field state where the entire fiber is darkened, if unmelted material is present, that part glows, allowing for identification. By this method, the number of unmelted materials with a major axis (maximum diameter) of 5 μm or more was counted within a fiber length range of 5 cm. For 5 staple fibers, the number of unmelted particles was counted, and the average number was defined as the number of unmelted particles with a major diameter of 5 μm or more contained per 5 cm of staple fiber.

[0186] (Total fiber fineness, single fiber fineness)

[0187] Based on the JIS L 1013:2010 8.3.1 A method, liquid crystal polyester fibers were wound onto a spool of 1 m × 100 m (total 100 m) using a measuring instrument "Wrap Reel by Motor Driven" manufactured by Daiei Kagaku Seiki Co., Ltd., and the weight (g) was multiplied by 100 and two measurements were taken per level, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fibers. In addition, the quotient obtained by dividing this value by the number of filaments was taken as the staple fiber fineness (dtex).

[0188] (tensile strength)

[0189] Referring to JIS L 1013:2010 8.5.1, eight tensile tests were performed on one sample of threads using the Autograph "AGS-100B" manufactured by Shimadzu Corporation under conditions of a test length of 20 cm and a tensile speed of 10 cm / min, and the average tensile strength (cN) was divided by the total denier (dtex) measured by the method described above to calculate the tensile strength (cN / dtex).

[0190] (Compressive strength)

[0191] A single fiber was extracted from a liquid crystal polyester fiber (multifilament), placed on a glass plate so that it protruded from its end, and secured with an adhesive. A focused ion beam (FIB) device was used to cut the fiber at a position 1.5 times the fiber diameter away from the end of the glass plate where the fiber protruded. This produced a sample for measuring the compression strength of a single fiber, having a cross-section that is precisely orthogonal to the fiber axis. Using a single fiber compression tester (model B20-049 manufactured by THK Precision Co., Ltd.), an indenter was applied to the cut surface of the sample at a speed of 200 nm / sec, and a pressure-strain curve was acquired. This measurement was performed on each of the five samples, and the average value of the pressure at the yield point of the pressure-strain curves obtained from the five tests was calculated. The average pressure was divided by the short fiber fineness measured by the method described above to calculate the compressive strength (cN / dtex) of the short fiber.

[0192] (Coefficient of variation in staple fiber fineness)

[0193] Fifteen staple fibers were extracted from liquid crystal polyester fibers (multifilaments). Using a "Denier Computer DC-11" manufactured by Search Control Electric Co., Ltd., the staple fiber fineness was measured under conditions where an initial load of 0.1 g per 0.9 dtex was applied to staple fibers with a measurement length of 50 mm. The standard deviation of the 15 measured staple fiber fineness values ​​was divided by the mean and multiplied by 100 to calculate the coefficient of variation (%) of the staple fiber fineness.

[0194] (Disc fatigue test)

[0195] Six liquid crystal polyester fibers with a total denier of 280 dtex were combined (10 fibers were combined in the case of a total denier of 170 dtex; combined so that the total denier becomes approximately 1700 dtex) and a 328 T / m Z twist was applied, and three of the Z twisted fibers were combined and a 268 T / m S twist was applied to produce a cord.

[0196] The following dipping process was performed on this to obtain the deep code.

[0197] 1st time :

[0198] Dipping treatment was performed using a dip solution mixed with 1 wt% of Mapo Masse (70%; manufactured by Matsumoto Yuji Pharmaceutical Co., Ltd.), 4 wt% of Denacol EX313 (manufactured by Nagase Chemtex Co., Ltd.), 0.3 wt% of an aqueous sodium hydroxide solution (10%), and 94.7 wt% of water. Afterward, the product was dried at 150°C for 30 seconds and then heat-treated at 240°C for 30 seconds.

[0199] 2nd time :

[0200] Dipping treatment was performed using the RFL liquid as a dip liquid. Afterward, the sample was dried at 150°C for 30 seconds and then heat-treated at 240°C for 30 seconds. Additionally, the RFL liquid was prepared as follows. Liquid A, a mixture of 3.3 wt% resorcinol, 2.46 wt% formaldehyde (37%), 1.4 wt% sodium hydroxide aqueous solution (10%), and 32.2 wt% water, was aged at a temperature of 25°C for 6 hours. Liquid B, a mixture of 52.86 wt% VP latex (JSR-0650; 40%; manufactured by JSR Corporation) and 7.78 wt% water, was mixed with the aged Liquid A and aged at a temperature of 25°C for 16 hours to obtain the RFL liquid.

[0201] A rubber composite test specimen was prepared by embedding the prepared dip cord in rubber (SBR : NR = 1 : 1) and vulcanizing it at 150°C for 30 minutes. Referring to JIS L 1017 : 2002, a disc fatigue test was performed by the Goodrich method under the following conditions.

[0202] Device: Disc fatigue testing machine (Manufactured by Maize Testing Machine Co., Ltd.)

[0203] Disk spacing: 24.5 mm

[0204] Deformation: 2% (elongation, compression)

[0205] Rotation speed: 2500 rpm

[0206] Temperature: 100 ℃

[0207] Count: 300,000

[0208] For the dip cords taken from rubber composite test specimens before and after the disc fatigue test, six tensile tests were performed on one sample using the Autograph "AGS-100B" manufactured by Shimadzu Corporation in reference to JIS L 1013:2010 8.5.1, under conditions of a test length of 20 cm and a tensile speed of 10 cm / min, and the average tensile strength was measured as the tensile strength (N) of the dip cords before and after the disc fatigue test. The strength retention rate (%) was calculated from the following formula.

[0209] Strength Retention Rate (%) = (Tensile Strength of Deep Code after Disk Fatigue Test) / (Tensile Strength of Deep Code before Disk Fatigue Test) × 100

[0210] [Reference Example 1]

[0211] 20.66 g (60 mol%) of 6-hydroxy-2-naphthoic acid, 7.91 g (20 mol%) of 2,6-naphthalenedicarboxylic acid, 3.02 g (15 mol%) of hydroquinone, 1.70 g (5 mol%) of 4,4'-dihydroxybiphenyl, 20.55 g of acetic anhydride, and 3.77 mg of potassium acetate as a polymerization catalyst were added to a reaction vessel, and after acetylation (160 °C, reflux for about 2 hours) under a nitrogen atmosphere, the temperature was maintained at 280 °C for 0.5 hours, 320 °C for 1 hour, and 360 °C for 1 hour, followed by reduced pressure treatment (100 Pa) until it was confirmed that foaming had stopped (30 to 120 minutes), and then nitrogen was substituted to obtain a liquid crystal polyester. The obtained liquid crystal polyester had a weight-average molecular weight of 109,000 and a melting point of 309 ℃.

[0212] [Reference Example 2]

[0213] 19.74 g (60 mol%) of 6-hydroxy-2-naphthoic acid, 7.56 g (20 mol%) of 2,6-naphthalenedicarboxylic acid, 0.96 g (5 mol%) of hydroquinone, 4.88 g (15 mol%) of 4,4'-dihydroxybiphenyl, 19.64 g of acetic anhydride, and 3.77 mg of potassium acetate as a polymerization catalyst were added to a reaction vessel, and after acetylation (160 °C, reflux for about 2 hours) under a nitrogen atmosphere, the temperature was maintained at 280 °C for 0.5 hours, 320 °C for 1 hour, and 360 °C for 2 hours, followed by reduced pressure treatment (100 Pa) until it was confirmed that foaming had stopped (30 to 120 minutes), and then nitrogen was substituted to obtain a liquid crystal polyester. The obtained liquid crystal polyester had a weight-average molecular weight of 91,000 and a melting point of 302 ℃.

[0214] [Reference Example 3]

[0215] A liquid crystal polyester was obtained in the same manner as Reference Example 1, except that the maximum temperature during the polymerization reaction was changed to 365 ℃. The obtained liquid crystal polyester had a weight average molecular weight of 167,000 and a melting point of 320 ℃.

[0216] [Reference Example 4]

[0217] 22.64 g (73 mol%) of 4-hydroxybenzoic acid, 11.41 g (27 mol%) of 6-hydroxy-2-naphthoic acid, 23.38 g of acetic anhydride, and 3.77 mg of potassium acetate were added to a reaction vessel and acetylated under a nitrogen atmosphere (160 °C, reflux for about 2 hours), then maintained at 250 °C for 0.5 hours, 280 °C for 1 hour, and 320 °C for 1 hour, followed by reduced pressure treatment (100 Pa) for 30 minutes. After confirming that foaming had stopped, nitrogen was substituted to obtain a liquid crystal polyester. The obtained liquid crystal polyester had a weight average molecular weight of 159,000 and a melting point of 278 °C.

[0218] [Example 1]

[0219] The liquid crystal polyester chip (granular molded body) obtained in Reference Example 1 was hot-air dried at 120°C for at least 4 hours. Afterward, it was fed into a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd., “KZW15TW-45MG-NH(-700)”), melt-kneaded at a heater temperature of 330°C and a screw peripheral speed of 18 m / min, and the melt-kneaded material was supplied to the spinning head while metering with a gear pump. At this time, a pressure reduction pump (dry pump manufactured by Orion Machinery Co., Ltd., “KRF40A-V-01B”) was connected through a metal pipe from the vent section in the middle of the twin-screw extruder, and the pressure was reduced to 50 kPa in the resin-non-filled space inside the twin-screw extruder. In addition, the temperature setting from the extruder outlet to the spinning head was set to 330°C, and the spinneret temperature setting was set to 315°C. The spinning head was equipped with a spinning die having a hole diameter of 0.10 mmφ, a land length of 0.14 mm, and 50 holes, and a molten kneaded material was extruded at an extrusion rate of 28 g / min and wound onto a bobbin at a winding speed of 1000 m / min to obtain a spun yarn of liquid crystal polyester fiber. At this time, an aqueous solution of 2 wt% sodium dodecyl phosphate (manufactured by Fujifilm Wako Junyaku Kogyo Co., Ltd., Wako Grade 1) was applied to the spun yarn from an oiling guide placed directly below the spinning die. The amount of this aqueous solution applied was 1.4 g / min, and the attachment ratio of sodium dodecyl phosphate to the spun yarn was calculated to be 0.1 wt%.

[0220] Next, 500 m of the spun yarn obtained here was rewound onto an aluminum bobbin to achieve a winding density of 0.6 g / cm³, and using a sealed oven under a nitrogen atmosphere, the temperature was gradually increased from room temperature. After reaching 300 ℃, heat treatment was performed at 300 ℃ for 8 hours to obtain a heat-treated liquid crystal polyester filament yarn. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 5.

[0221] [Example 2]

[0222] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the liquid crystal polyester obtained in Reference Example 2 was used, the heater temperature of the extruder during spinning and the temperature setting from the extruder outlet to the spinning head were set to 320 ℃, and the spinneret temperature setting was set to 310 ℃.

[0223] [Example 3]

[0224] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.08 mmφ, a land length of 0.11 mm, and 100 holes was used, and the discharge rate during spinning was 17 g / min.

[0225] [Example 4]

[0226] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the screw peripheral speed of the extruder during spinning was set to 15 m / min, the heater temperature of the extruder and the temperature setting from the extruder outlet to the spinning head were set to 325 ℃, and the spinneret temperature setting was set to 315 ℃.

[0227] [Example 5]

[0228] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the spinneret temperature setting during spinning was set to 320 ℃.

[0229] [Example 6]

[0230] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the spun yarn was heat-treated at 330°C for 8 hours.

[0231] [Comparative Example 1]

[0232] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the screw peripheral speed of the extruder during spinning was set to 7 m / min.

[0233] [Comparative Example 2]

[0234] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the screw peripheral speed of the extruder during spinning was set to 45 m / min.

[0235] [Comparative Example 3]

[0236] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the heater temperature of the extruder during spinning and the temperature setting from the extruder outlet to the spinning head were set to 320 ℃, and the spinning die temperature setting was set to 310 ℃.

[0237] [Comparative Example 4]

[0238] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the spinneret temperature setting during spinning was set to 340 ℃.

[0239] [Comparative Example 5]

[0240] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the heater temperature of the extruder during spinning and the temperature setting from the extruder outlet to the spinning head were set to 360 ℃, and the spinning die temperature setting was set to 350 ℃.

[0241] [Comparative Example 6]

[0242] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the liquid crystal polyester obtained in Reference Example 3 was used, the heater temperature of the extruder during spinning and the temperature setting from the extruder outlet to the spinning head were set to 340 ℃, and the spinning die temperature setting was set to 325 ℃.

[0243] [Comparative Example 7]

[0244] A spun yarn was obtained in the same manner as in Example 1, except that the liquid crystal polyester obtained in Reference Example 4 was used, the heater temperature of the extruder during spinning and the temperature setting from the extruder outlet to the spinning head were set to 310 ℃, and the spinneret temperature setting was set to 310 ℃. Next, a liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the obtained spun yarn was heat-treated at 270 ℃ for 5 hours.

[0245] [Comparative Example 8]

[0246] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the spun yarn was heat-treated at 245°C for 8 hours.

[0247] [Comparative Example 9]

[0248] A liquid crystal polyester fiber was obtained in the same manner as in Example 1, except that the spun yarn was heat-treated at 355°C for 8 hours.

[0249]

[0250] As shown in Table 5, in Examples 1 to 6, a specific liquid crystal polyester is used as the raw material resin, and melt mixing and melt spinning are performed under specific conditions, so unmelted material and voids can be reduced, and the melting point and degree of crystallinity are adjusted to a specific range. Therefore, the liquid crystal polyester fibers of Examples 1 to 6 have excellent tensile strength and compressive strength, excellent disk fatigue resistance, and excellent uniformity of short fiber fineness.

[0251] Meanwhile, in Comparative Examples 1 to 5, although the same raw resin of liquid crystal polyester as in Examples 1 and 3 to 6 was used, the temperature in the extruder, the screw peripheral speed, or the spinneret temperature were not within a specific range, so a large amount of unmelted material or voids occurred. Consequently, the liquid crystal polyester fibers of Comparative Examples 1 to 5 have lower tensile strength and compressive strength compared to Examples 1 to 6, and their disk fatigue properties are inferior, resulting in a large coefficient of variation of single fiber fineness and causing non-uniformity.

[0252] In addition, in Comparative Example 6, because the weight-average molecular weight of the liquid crystal polyester in the raw resin was large, it was difficult to melt in the extruder, and unmelted material remained. Also, perhaps due to the low mobility of the molecular chains, the molecular chains could not be packed densely during heat treatment, and the degree of crystallinity could not be improved. Consequently, the liquid crystal polyester fibers of Comparative Example 6 had lower tensile strength and compressive strength compared to Examples 1 to 6, and the disk fatigue properties were inferior, resulting in a large coefficient of variation of the single fiber fineness and causing non-uniformity.

[0253] In addition, in Comparative Example 7, since the melting point of the liquid crystal polyester of the raw resin is low, the melting point could not be sufficiently raised even if the spun yarn was heat-treated. Therefore, the liquid crystal polyester fiber of Comparative Example 7 has lower heat resistance compared to Examples 1 to 6.

[0254] In addition, in Comparative Examples 8 and 9, although there are few unmelted materials or voids, the degree of crystallization deviates from a specific range. Therefore, the liquid crystal polyester fibers of Comparative Examples 8 and 9 have lower tensile strength and compressive strength compared to Examples 1 to 6, and their disk fatigue properties are inferior.

[0255] Industrial applicability

[0256] The liquid crystal polyester fiber of the present invention can be used for various purposes, such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and protection, and, for example, can be used as a reinforcing fiber for composite materials.

[0257] As described above, preferred embodiments of the present invention have been explained, but various additions, changes, or deletions are possible without departing from the spirit of the present invention, and such additions, changes, or deletions are also included within the scope of the present invention.

Claims

Claim 1 A liquid crystal polyester fiber having a melting point of 335°C or higher and less than 360°C as measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10°C / min, a degree of crystallinity of 45 to 60%, and a total number of unmelted material and voids with a major axis of 5 μm or more per 5 cm of single filament, which is 3 or less. Claim 2 A liquid crystal polyester fiber having a degree of orthorhombicity of 20% or more in the crystalline component, according to claim 1. Claim 3 A liquid crystal polyester fiber according to claim 1 or 2, wherein the degree of orientation in the fiber axis direction in the crystalline component is 97% or more and less than 100%. Claim 4 A liquid crystal polyester fiber having a tensile strength of 27 cN / dtex or more, according to claim 1 or 2. Claim 5 A liquid crystal polyester fiber according to claim 1 or 2, wherein the compressive strength of the staple fiber is 0.70 cN / dtex or higher. Claim 6 A liquid crystal polyester fiber according to claim 1 or 2, wherein the staple fiber fineness is 7 dtex or less and the coefficient of variation of the staple fiber fineness is 7% or less. Claim 7 A fiber structure composed of at least a portion of the liquid crystal polyester fibers described in claim 1 or 2. Claim 8 A composite material comprising the liquid crystal polyester fiber described in claim 1 or 2 as a reinforcing fiber. Claim 9 A method for manufacturing a liquid crystal polyester fiber according to claim 1 or 2, comprising at least a process of obtaining a spun yarn by spinning a liquid crystal polyester, wherein the weight average molecular weight in GPC equivalent to polystyrene is 50,000 or more and 160,000 or less, and the melting point Mp0 measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10 ℃ / min is 300 ℃ or more, and the following (1) to (3): (1) extruder temperature: Mp0+15 ℃ to Mp0+35 ℃ (2) extruder screw peripheral speed: 10 to 40 m / min (3) spinneret temperature: extruder temperature-15 ℃ to extruder temperature-5 ℃, and a process of heat treating the obtained spun yarn. Claim 10 A method for manufacturing liquid crystal polyester fibers according to claim 9, wherein the extruder is a twin-screw extruder. Claim 11 A method for manufacturing liquid crystal polyester fibers according to claim 9, wherein the heat treatment temperature is 250 to 350 ℃.

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