Melt anisotropic aromatic polyester fiber machine and manufacturing method thereof

Abstract

Provided is a melt anisotropic aromatic polyester fiber having excellent creep characteristics. The degree of orthorhombic crystallization of the crystal component of the melt anisotropic aromatic polyester fiber is 15.0% or more. For example, the melt anisotropic aromatic polyester fiber may have a density of 1.4080 g / cm3 or more as determined by a density gradient tube. The melt anisotropic aromatic polyester fiber may contain a melt anisotropic aromatic polyester having a structural unit derived from 4-hydroxybenzoic acid in an amount of 50 mol% or more.

Description

[0001] Related Application

[0002] This application claims the priority of Japanese Patent Application No. 2022-199790 filed in Japan on December 14, 2022, and the entire content thereof is incorporated herein by reference as part of this application. Technical Field

[0003] The present invention relates to a molten anisotropic aromatic polyester fiber and a method for manufacturing the same. Background Art

[0004] General fibers such as general polyester fibers are widely used in tensile members. However, in order to miniaturize electrical products, it is required to reduce the wire diameters of cables and cords. Therefore, super fibers that have sufficient strength despite their small wire diameters have attracted attention. In addition, in applications such as optical cables, since even a slight elongation of the optical fiber can significantly reduce the communication speed, liquid crystal polymer fibers (molten anisotropic aromatic polyester fibers, aramid fibers, etc.) with high dimensional stability are used. It is known that a molten anisotropic aromatic polyester fiber can obtain a spun yarn that is highly oriented along the fiber axis by spinning, and then the spun yarn is heat-treated for solid-phase polymerization to increase the crystallinity, so the dimensional stability is excellent.

[0005] For example, regarding the crystallinity of a molten anisotropic aromatic polyester fiber, Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-150694) discloses a liquid crystal polyester fiber characterized in that in wide-angle X-ray diffraction measurement using CuKα rays as the radiation source, the half-value width of the maximum peak in the equatorial direction at 18 to 22° is 3.5° or more.

[0006] In addition, regarding the method for manufacturing a molten anisotropic aromatic polyester fiber, Patent Document 2 (Japanese Patent Application Laid-Open No. 3-227407) discloses a method for spinning a molten anisotropic aromatic polyester, characterized in that when extruding and spinning the molten anisotropic aromatic polyester using an extruder with vent holes, the vent hole part is depressurized to 100 to 760 mmHg, the front-end pressure of the extruder is adjusted to 5 to 30 kg / cm 2 and then boosted to 40 to 200 kg / cm by a gear pump with a volumetric efficiency of 50 to 90% 2 and passed through a filter for spinning.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-150694

[0010] Patent Document 2: Japanese Patent Laid-Open No. 3-227407

[0011] Content of the Invention

[0012] Problems to be Solved by the Invention

[0013] However, in order to increase the lifespan for various applications such as electrical products, compared with existing melt anisotropic aromatic polyester fibers, further improvement in dimensional stability is required, and creep characteristics need to be improved. However, the improvement of creep characteristics is not described in Patent Documents 1 and 2.

[0014] Therefore, in order to solve the above problems, an object of the present invention is to provide melt anisotropic aromatic polyester fibers having excellent creep characteristics.

[0015] Means for Solving the Problems

[0016] In order to achieve the above object, the inventors of the present invention conducted in-depth research and found that when the kneading conditions of melt spinning are changed, there are differences in the creep characteristics of melt anisotropic aromatic polyester fibers obtained by subsequently heat-treating the spun raw yarn.

[0017] Moreover, when considering the relationship with creep characteristics and focusing on the crystal structure of melt anisotropic aromatic polyester fibers, it was found that the melt anisotropic aromatic polyester fibers having more excellent creep characteristics have a high orthorhombic crystallinity.

[0018] Further research was repeatedly conducted, and as a result, it was found that in melt spinning, by using a twin-screw extruder to knead the melt anisotropic aromatic polyester at a low temperature, shear can be applied in a high-viscosity state, and a spun raw yarn having a more uniform microcrystalline structure can be obtained. Therefore, by heat-treating such a spun raw yarn, the molecular chains can be densely stacked during solid-phase polymerization, and the proportion of orthorhombic crystals as a denser crystal structure can be increased, thus completing the present invention.

[0019] That is, the present invention can be configured in the following manner.

[0020] 〔Aspect 1〕

[0021] A melt anisotropic aromatic polyester fiber, wherein

[0022] the orthorhombic crystallinity of the crystalline component is 15.0% or more (preferably 16.0% or more, more preferably 17.0% or more, further preferably 18.0% or more, and 25.0% or less, preferably 24.0% or less, more preferably 23.0% or less).

[0023] 〔Aspect 2〕

[0024] The melt anisotropic aromatic polyester fiber according to Method 1 has a density of 1.4080 g / cm 3 or more.

[0025] 〔Method 3〕

[0026] The melt anisotropic aromatic polyester fiber according to Method 1 or 2 contains a melt anisotropic aromatic polyester having 50 mol% or more (preferably 53 mol% or more, more preferably 60 mol% or more, further preferably 65 mol% or more, and still further preferably 70 mol% or more) of structural units derived from 4-hydroxybenzoic acid.

[0027] 〔Method 4〕

[0028] The melt anisotropic aromatic polyester fiber according to any one of Methods 1 to 3 has a melting point of 260 to 380 °C (preferably 270 to 360 °C, more preferably 275 to 340 °C, and further preferably 275 to 330 °C) as measured by a differential scanning calorimeter at a heating rate of 10 °C / minute in a nitrogen atmosphere.

[0029] 〔Method 5〕

[0030] A fiber structure comprising, at least in part, the melt anisotropic aromatic polyester fiber according to any one of Methods 1 to 4.

[0031] 〔Method 6〕

[0032] A method for producing a melt anisotropic aromatic polyester fiber, which at least includes:

[0033] In the case where the melting point of the melt anisotropic aromatic polyester measured by a differential scanning calorimeter at a heating rate of 10 °C / minute in a nitrogen atmosphere is Mp0, a step of melt-kneading the melt anisotropic aromatic polyester using a twin-screw extruder under the condition that the barrel temperature from the resin supply section to the outlet of the kneading section is lower than the melting point Mp0 (preferably Mp0 - 5 °C or lower, more preferably Mp0 - 10 °C or lower, and further preferably Mp0 - 15 °C or lower);

[0034] A step of spinning the melt-kneaded product to obtain a spun yarn; and

[0035] A step of heat-treating the obtained spun yarn.

[0036] 〔Method 7〕

[0037] According to the method for producing a melt anisotropic aromatic polyester fiber described in Method 6, wherein

[0038] The melt-kneading is carried out under the condition that the residence time in the kneading section of the twin-screw extruder is 10 seconds or more (preferably 15 seconds or more, more preferably 20 seconds or more).

[0039] When used in this specification, unless the content is clearly indicated otherwise, the singular forms "a", "an", and "the" each refer to the plural form including "at least one". When used in this specification, the terms "and / or", "at least one", and "one or more" include any and all combinations of the relevant listed items.

[0040] It should be noted that any combination of at least two constituent elements disclosed in the claims and / or the specification and / or the drawings is also included in the present invention. In particular, any combination of two or more claims recited in the claims is also included in the present invention.

[0041] Effects of the Invention

[0042] The melt anisotropic aromatic polyester fiber of the present invention has excellent creep characteristics. In addition, in the manufacturing method of the present invention, a melt anisotropic aromatic polyester fiber with a high orthorhombic crystallinity can be manufactured. Brief Description of the Drawings

[0043] The present invention can be more clearly understood by describing the following preferred embodiments with reference to the accompanying drawings. However, the embodiments and the drawings are only for illustration and description, and are not used to limit the scope of the present invention. The scope of the present invention is defined by the accompanying claims. The drawings are not necessarily drawn to scale and are exaggerated on the basis of showing the principle of the present invention.

[0044] Figure 1 It is a schematic diagram for explaining the manufacturing method of the melt anisotropic aromatic polyester fiber according to an embodiment of the present invention.

[0045] Symbol Description

[0046] 100 ··· Twin-screw extruder

[0047] 11 ··· Hopper

[0048] 12 ··· Barrel

[0049] 13 ··· Screw

[0050] 13a, 13b, 13c ··· Screw elements

[0051] 14 ··· Vent hole

[0052] 21 ··· Resin supply section

[0053] 22 ··· Kneading section

[0054] 23 ··· Conveyor section

[0055] X ··· Travel direction Detailed implementation mode

[0056] [Melted anisotropic aromatic polyester fiber]

[0057] The melted anisotropic aromatic polyester fiber of the present invention contains melted anisotropic aromatic polyester. As the melted anisotropic aromatic polyester, for example, it is formed from structural units derived from aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc. As long as the effects of the present invention are not impaired, there are no particular restrictions on the chemical composition of the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids. In addition, within the range that does not impair the effects of the present invention, the melted anisotropic aromatic polyester may contain structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids. For example, as preferred structural units, the examples shown in Table 1 can be cited.

[0058] [Table 1]

[0059]

[0060] (wherein, X in the formula is selected from the following structures)

[0061]

[0062] (wherein, m = 0 to 2, and Y = a substituent selected from hydrogen, halogen atom, alkyl group, aryl group, aralkyl group, alkoxy group, aryloxy group, aralkyloxy group)

[0063] Among the structural units in Table 1, m is an integer of 0 to 2, and for Y in the formula, examples can include hydrogen atoms, halogen atoms (for example, fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl groups (for example, alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group, tert-butyl group, etc.), alkoxy groups (for example, methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), aryl groups (for example, phenyl group, naphthyl group, etc.), alkoxy groups (for example, benzyl (benzyl group), phenethyl (phenylethyl group), etc.), aryloxy groups (for example, phenoxy group, etc.), aralkyloxy groups (for example, benzyloxy group, etc.) that are each independent within the range from 1 to the maximum number of substituents.

[0064] As more preferred structural units, examples can include the structural units described in Examples (1) to (18) shown in the following Tables 2, 3, and 4. It should be noted that in the case where the structural unit in the formula is a structural unit capable of representing multiple structures, two or more such structural units can be combined and used as the structural units constituting the polymer.

[0065] [Table 2]

[0066]

[0067] [Table 3]

[0068]

[0069] [Table 4]

[0070]

[0071] In the structural units of Table 2, Table 3, and Table 4, n is an integer of 1 or 2, and the structural units with n = 1 and n = 2 can exist alone or in combination. Y1 and Y2 can 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 tert-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, a n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an alkoxyalkyl group (e.g., a benzyl (phenylmethyl) group, a phenyethyl (phenyl ethyl) group, etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.), etc. Among them, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0072] In addition, as Z, a substituent represented by the following formula can be cited.

[0073] [Chemical formula 1]

[0074]

[0075] The molten anisotropic aromatic polyester can preferably have a combination of naphthalene skeletons as structural units. It is particularly preferred to contain both the structural unit (A) derived from hydroxybenzoic acid and the structural unit (B) derived from hydroxynaphthoic acid. For example, as the structural unit (A), the following formula (A) can be cited, and as the structural unit (B), the following formula (B) can be cited. From the viewpoint of improving the melt moldability, the ratio of the structural unit (A) to the structural unit (B) can preferably be in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and further preferably 5 / 1 to 1 / 1.

[0076] [Chemical formula 2]

[0077]

[0078] [Chemical formula 3]

[0079]

[0080] In addition, with respect to all the structural units, the total of the structural units of (A) and the structural units of (B) can be, for example, 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more. In the polymer, a melt anisotropic aromatic polyester in which the structural units of (B) are particularly preferably 4 to 45 mol% is preferred.

[0081] The melt anisotropic aromatic polyester may contain structural units derived from 4-hydroxybenzoic acid, and preferably contains 50 mol% or more, more preferably 53 mol% or more, even more preferably 60 mol% or more, still more preferably 65 mol% or more, and particularly preferably 70 mol% or more. The upper limit of the content of the structural units derived from 4-hydroxybenzoic acid in the melt anisotropic aromatic polyester is not particularly limited, and can be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0082] The melting point (hereinafter sometimes referred to as Mp0) of the melt anisotropic aromatic polyester used in the present invention can preferably be in the range of 250 to 380 °C, more preferably 255 to 370 °C, even more preferably 260 to 360 °C, and still more preferably 260 to 330 °C. In this specification, the melting point is the main absorption peak temperature observed by measurement using a differential scanning calorimeter (DSC) according to the JIS K 7121 test method. Specifically, in the DSC apparatus, 4 to 6 mg of the sample is weighed and sealed in an aluminum pan, and then nitrogen gas as the carrier gas is allowed to flow at a flow rate of 200 mL / min, and the endothermic peak is measured when the temperature is raised from room temperature (for example, 25 °C) at a rate of 10 °C / min. Depending on the type of polymer, when no clear peak appears in the first operation (1st run) in the DSC measurement, the temperature is raised at a rate of 50 °C / min to a temperature 50 °C higher than the expected flow temperature, and after completely melting at this temperature for 3 minutes, the temperature is lowered to 50 °C at a rate of 80 °C / min, and then the endothermic peak is measured at a rate of 10 °C / min.

[0083] It should be noted that within the range not impairing the effects of the present invention, the melt anisotropic aromatic polyester fiber may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin. In addition, it may also contain inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, coloring agents such as carbon black, dyes or pigments, and various additives such as antioxidants, ultraviolet absorbers, and light stabilizers.

[0084] The melt anisotropic aromatic polyester fiber of the present invention may contain 50% by weight or more of the melt anisotropic aromatic polyester, preferably 80% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, and even more preferably 99.9% by weight or more.

[0085] The orthorhombic crystallinity of the crystalline component of the melt anisotropic aromatic polyester fiber of the present invention is 15.0% or more. The melt anisotropic aromatic polyester has crystalline components such as orthorhombic and hexagonal crystal systems. Since the orthorhombic crystal has a crystalline structure in which molecular chains are stacked more densely, the melt anisotropic aromatic polyester fiber with increased crystallinity, orientation degree, and the proportion of orthorhombic crystals in the crystalline component will have excellent creep properties due to its dense crystalline structure. The orthorhombic crystallinity can preferably be 16.0% or more, more preferably 17.0% or more, and further preferably 18.0% or more. In addition, the orthorhombic crystallinity can be, for example, 25.0% or less, preferably 24.0% or less, and more preferably 23.0% or less. In this specification, the orthorhombic crystallinity of the melt anisotropic aromatic polyester fiber can be calculated based on the diffraction peaks from orthorhombic and hexagonal crystals in the X-ray diffraction pattern obtained by wide-angle X-ray diffraction (for example, diffraction peaks appearing near a diffraction angle 2θ = 19 - 21°), and is a value measured by the method described in the examples below.

[0086] The melt anisotropic aromatic polyester fiber of the present invention has a high proportion of orthorhombic crystals in which molecular chains are densely stacked, so it has a high density. For example, the density obtained by a density gradient tube can be 1.4080 g / cm 3 or more. The upper limit value of the density is not particularly limited and also depends on the composition of the melt anisotropic aromatic polyester, etc. For example, it can be 1.4200 g / cm 3 or less. In this specification, the density of the melt anisotropic aromatic polyester fiber is a value measured by the method described in the examples below.

[0087] The melting point of the melt anisotropic aromatic polyester fiber of the present invention can be 260 - 380 °C, preferably 270 - 360 °C, more preferably 275 - 340 °C, and further preferably 275 - 330 °C. Through solid-phase polymerization, the melting point of the melt anisotropic aromatic polyester fiber rises from the melting point (Mp) of the spinning dope. It should be noted that the melting point of the melt anisotropic aromatic polyester fiber is a value measured by the method described in the examples below.

[0088] The tensile strength of the melt anisotropic aromatic polyester fiber of the present invention can be 20 cN / dtex or more, preferably 24 cN / dtex or more, and more preferably 25 cN / dtex or more. In addition, the upper limit value of the tensile strength is not particularly limited. For example, it can be about 40 cN / dtex. The tensile strength of the melt anisotropic aromatic polyester fiber is the value measured by the method described in the following examples.

[0089] For the melt anisotropic aromatic polyester fiber of the present invention, in the creep test based on the method described in the following examples, the time until the fiber breaks can be 30 hours or more, preferably 60 hours or more, and more preferably 68 hours or more.

[0090] The single fiber fineness of the melt anisotropic aromatic polyester fiber of the present invention can be appropriately selected according to the use and the like. For example, the single fiber fineness can be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. From the viewpoint of coping with the miniaturization of electrical product applications and the like, a fine fineness is preferred. For example, it can be 7 dtex or less. In addition, the lower limit of the single fiber fineness is not particularly limited. For example, it can be about 0.01 dtex. The single fiber fineness is the value measured by the method described in the following examples.

[0091] The melt anisotropic aromatic polyester fiber of the present invention can be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be appropriately selected according to the use and the like. For example, the number of filaments can be 2 to 5000, preferably 3 to 4000, and more preferably 5 to 3000.

[0092] The total fineness of the melt anisotropic aromatic polyester fiber of the present invention can be appropriately selected according to the use and the like. For example, the total fineness can be 50000 dtex or less, preferably 10000 dtex or less, more preferably 2000 dtex or less, and further preferably 1000 dtex or less. In addition, the lower limit of the total fineness is not particularly limited. For example, it can be about 1 dtex.

[0093] [Manufacturing method of melt anisotropic aromatic polyester fiber]

[0094] The manufacturing method of the melt anisotropic aromatic polyester fiber of the present invention at least includes:

[0095] In the case where the melting point of the melt anisotropic aromatic polyester measured by a differential scanning calorimeter in a nitrogen atmosphere at a heating rate of 10 °C / minute is Mp0, a step of melt-kneading the melt anisotropic aromatic polyester using a twin-screw extruder under the condition that the barrel temperature from the resin supply part to the outlet of the kneading part is lower than the melting point Mp0;

[0096] A step of spinning a melt-kneaded product to obtain a spun yarn; and

[0097] A step of heat-treating the obtained spun yarn.

[0098] In the present invention, a twin-screw extruder is used to improve the kneadability of the molten anisotropic aromatic polyester, and the kneading section in the twin-screw extruder is set to a low temperature below the melting point and kneaded in a high-viscosity state, whereby shear can be efficiently applied to the molten anisotropic aromatic polyester. Generally, melting is promoted by heating to a temperature above the melting point of the resin to be introduced, but for the conditions of the present invention described above, the temperature condition is opposite to the usual one with respect to the melting point of the resin, and this point should be particularly noted.

[0099] Next, by spinning the melt-kneaded product to which shear has been applied by kneading at a low temperature in this way, a spun yarn having a more uniform microcrystalline structure can be obtained. Therefore, in this spun yarn, molecular chains can be densely stacked in solid-phase polymerization based on heat treatment, and the proportion of orthorhombic crystals as a denser crystal structure can be increased.

[0100] In addition, compared with the case of heating to a temperature above the melting point of the resin as in the past, more mechanical energy can be applied by applying shear by kneading at a low temperature than its thermal energy. Therefore, compared with the conventional melt-kneading conditions, its melting can be further promoted. As a result, in addition to the formation of the crystal structure, the remaining of unmelted matter can be reduced. Therefore, the filter provided for removing foreign matters is not easily clogged, and the occurrence of thread breakage during spinning can also be suppressed.

[0101] It should be noted that it is generally known to use a single-screw extruder in the melt spinning method. However, if the extruder temperature is set below the melting point as described above in the single-screw extruder for extrusion, poor resin entrapment, pressure fluctuations, and increased torque will occur, and stable spinning cannot be performed. It is considered that this is because, compared with the idea of melting the resin by heat generation caused by high shear in the twin-screw extruder, the contribution of heat transfer from the extruder barrel during melting is large in the single-screw extruder. Therefore, the same effect cannot be obtained by using a single-screw extruder in the present invention.

[0102] Hereinafter, with reference to Figure 1 A method for manufacturing a molten anisotropic aromatic polyester fiber will be described. Figure 1 FIG. is a schematic view showing the internal structure of a twin-screw extruder 100 used for manufacturing a molten anisotropic aromatic polyester fiber according to an embodiment of the present invention as viewed from the side. As Figure 1As shown, the above-mentioned twin-screw extruder 100 includes a hopper 11 for feeding and melting an anisotropic aromatic polyester, a barrel 12, a screw 13 rotating in the barrel 12, and a vent hole 14. Inside the barrel 12, there are a resin supply section 21, a kneading section 22, and a conveying section 23 from the upstream side to the downstream side. The resin supply section 21, the kneading section 22, and the conveying section 23 have respective screw elements 13a, 13b, 13c of the screw 13. It should be noted that the screw 13 (screw elements 13a, 13b, 13c) represents one screw in the twin-screw extruder 100. Figure 1 In [description], for the purpose of explaining the method for manufacturing the molten anisotropic aromatic polyester fiber of the present invention, a simple structure is illustrated, and a plurality of various devices can be provided as needed. In addition, in addition to the illustrated devices, the twin-screw extruder can also be equipped with devices commonly used in twin-screw extruders.

[0103] In Figure 1 In [description], the solid molten anisotropic aromatic polyester fed from the hopper 11 is conveyed in the barrel 12 along the X direction as the traveling direction by the rotation of the screw 13, and is heated by a known heating device such as a heater provided in the barrel 12. In addition to the heat transfer from the heating device, shear is applied between the inner wall of the barrel 12 and the screw 13 and between the screws 13, so that the solid molten anisotropic aromatic polyester melts as it progresses along the X direction. It should be noted that a resin composition containing the molten anisotropic aromatic polyester, the above-mentioned thermoplastic polymer, various additives, etc. can be prepared and fed into the twin-screw extruder 100.

[0104] In the resin supply section 21, the solid molten anisotropic aromatic polyester supplied from the hopper 11 is compacted while being kept in a solid state by the rotation of the screw 13 and moves in the X direction. At the same time, it slowly melts through the heat transfer caused by the heating device of the barrel 12 and the shear applied by the rotation of the screw 13. As the screw element 13a used in the resin supply section 21, for example, a full-thread screw can be used.

[0105] In the kneading section 22, kneading can be promoted by using a shear-applying screw element represented by a kneading disk or the like as the screw element 13b, which can promote the melting of the molten anisotropic aromatic polyester containing the solid conveyed from the resin supply section 21. In Figure 1 One kneading section 22 is provided, and multiple kneading sections can also be provided.

[0106] In the conveying section 23, the viscosity can be adjusted when conveying the molten kneaded product obtained in the kneading section 22 to the spinning head. As the screw element 13c used in the conveying section 23, for example, a full-thread screw can be used.

[0107] In the present invention, by setting the temperatures of the resin supply section 21 and the kneading section 22 in the barrel 12 to a low temperature below the melting point Mp0 of the molten anisotropic aromatic polyester to be fed into the twin-screw extruder 100, shear can be efficiently applied to the molten anisotropic aromatic polyester in a high-viscosity state. The temperature of the barrel 12 from the resin supply section 21 to the outlet of the kneading section 22 can preferably be Mp0 - 5°C or lower, more preferably Mp0 - 10°C or lower, and further preferably Mp0 - 15°C or lower. Additionally, from the perspective of promoting melting by heating, it can be Mp0 - 100°C or higher, preferably Mp0 - 90°C or higher, and more preferably Mp0 - 80°C or higher. In the manufacturing method of the present invention, when there are multiple kneading sections, the barrel temperature from the resin supply section to the outlet of the kneading section refers to the barrel temperature up to the outlet of the lowermost kneading section adjacent to the conveying section.

[0108] The heating device provided in the barrel 12 can perform different temperature controls on each region along the traveling direction from the upstream side to the downstream side, and preferably adjusts the temperature of the barrel 12 from the resin supply section 21 to the outlet of the kneading section 22 in a manner of slowly increasing within the above temperature range.

[0109] In the present invention, it is only necessary to adjust the temperatures of the resin supply section 21 and the kneading section 22 in the barrel 12 to within the above temperature range. From the perspective of viscosity adjustment during spinning, the temperature of the barrel 12 of the subsequent conveying section 23 can be Mp0 or higher, preferably Mp0 + 10°C or higher, and more preferably Mp0 + 20°C or higher. Additionally, from the perspective of suppressing the decomposition of the molten anisotropic aromatic polyester, it can be 400°C or lower, preferably 370°C or lower, and more preferably 350°C or lower.

[0110] From the perspective of efficiently applying shear to the molten anisotropic aromatic polyester and improving spinnability, the residence time in the kneading section 22 can be 10 seconds or longer, preferably 15 seconds or longer, and more preferably 20 seconds or longer. Additionally, from the perspective of suppressing the deterioration of the molten anisotropic aromatic polyester, it can be 300 seconds or shorter, preferably 180 seconds or shorter, and more preferably 130 seconds or shorter. The residence time in the kneading section can be calculated by the following formula based on the volume of the kneading section and the discharge amount.

[0111] (Void in barrel [cm 3 ) = (Volume in the kneading section barrel [cm 3 ) - (Volume of the kneading section screw [cm 3 )

[0112] (Residence time in the kneading section [s]) = (Void in barrel [cm 3 ) / (Volume discharge amount [cm 3 / s])

[0113] The capacity, ratio, arrangement, etc. of the resin supply section, kneading section, and conveying section, the shape of the screw, the clearance between screws, etc. can be appropriately designed according to the type of the molten anisotropic aromatic polyester, the spinning conditions, etc. In addition, in addition to screw elements such as full-thread screws and kneading disks, screw elements that return in the opposite direction along the traveling direction from the upstream side to the downstream side can also be arranged, for example, a back kneading disc, etc. In addition, for the purpose of retaining the resin in the kneading section with good efficiency and improving the sealing performance of the upstream part of the vent hole, a sealing ring can also be used for the element at the outlet of the kneading section.

[0114] In the twin-screw extruder 100, due to the entrainment of air, etc., bubbles may be contained during melt-kneading. Therefore, for example, it is preferable to provide a vent hole 14 in the twin-screw extruder 100 and connect a vacuum pump or the like, and degas by reducing the pressure inside the twin-screw extruder 100. For example, the degree of vacuum can be 100 kPa or less in terms of absolute pressure, and can preferably be 80 kPa or less, more preferably 60 kPa or less.

[0115] The melt-kneaded product obtained by melt-kneading in the twin-screw extruder 100 is then metered by a gear pump (not shown) in the conveying section 23 and conveyed to the spinning head. In order to avoid the mixing of impurities such as unmelted matter contained in the melt-kneaded product, a filter can be provided before or after the gear pump after being conveyed from the twin-screw extruder 100. In the present invention, the residue of unmelted matter can be reduced by melt-kneading in the twin-screw extruder, so the filter is not likely to be clogged, and stable spinning can be achieved.

[0116] After being conveyed to the spinning head, the melt-kneaded product can be ejected through a nozzle at a given spinning temperature, and the obtained filament can be wound up by a godet roller or the like, thereby manufacturing a spinning raw yarn of the molten anisotropic aromatic polyester fiber. With respect to the melting point Mp0 of the molten anisotropic aromatic polyester, the spinning temperature (spinning nozzle temperature) can be, for example, Mp0 - 30 to Mp0 + 60 °C, and can preferably be Mp0 - 25 °C to Mp0 + 50 °C, more preferably Mp0 - 20 °C to Mp0 + 45 °C. In addition, the spinning temperature can be the barrel temperature of the kneading section + 10 °C to the barrel temperature of the kneading section + 120 °C, and can preferably be the barrel temperature of the kneading section + 15 °C to the barrel temperature of the kneading section + 100 °C, more preferably the barrel temperature of the kneading section + 20 °C to the barrel temperature of the kneading section + 90 °C, and further preferably the barrel temperature of the kneading section + 30 °C to the barrel temperature of the kneading section + 80 °C. When the spinning temperature (spinning nozzle temperature) is below the above upper limit value, the resin deterioration near the nozzle can be suppressed, and the processability defect caused by thread breakage and the yellowing of the product are not likely to occur.

[0117] Since a more uniform microcrystalline structure is formed in the spinning dope, solid-phase polymerization of the molten anisotropic aromatic polyester can be carried out by subjecting the spinning dope to heat treatment, the melting point rises from the melting point (Mp) of the spinning dope, and the orthorhombic crystallinity of the fiber after heat treatment is increased. In the heat treatment step, the heat treatment method is not particularly limited. For example, it can be a batch-type heat treatment or a continuous heat treatment by conveyance. It should be noted that the melting point (Mp) of the spinning dope can be measured by the same method as the melting point of the molten anisotropic aromatic polyester fiber.

[0118] For example, in the batch-type heat treatment, for example, it can be heat-treated in a state of being wound around a bobbin in a package form or in a hank form or a tow form. From the viewpoint of simplifying equipment and improving productivity, it is preferably carried out in a package form. The bobbin needs to withstand the temperature of solid-phase polymerization and is preferably made of a metal such as aluminum, brass, iron, or stainless steel.

[0119] In the case of continuous heat treatment by conveyance, as the conveyance method, it can be carried out in any of the contact conveyance (for example, conveyor belt method, support roll method, heat treatment method in the form of a heated roll) and non-contact conveyance (roll-to-roll method). In addition, the treatment path may not be a straight line, and return rollers and guides may be arranged in the apparatus to appropriately change the length, angle, curvature, etc. of the treatment path for heat treatment.

[0120] The heat treatment step can use a known method. For example, gas atmosphere heating, contact heating, etc. can be cited. As the gas atmosphere, air, an inert gas (for example, nitrogen, argon), or a gas atmosphere formed by combining them can be suitably used. In addition, heat treatment can also be carried out under reduced pressure.

[0121] In the heat treatment step, the heat treatment temperature can be 250 to 350 °C, preferably 255 to 320 °C, more preferably 260 to 315 °C, and even more preferably 280 to 310 °C. In addition, in order to prevent melting, the heat treatment temperature can be lower than the melting point (Mp) of the spinning dope to be subjected to the heat treatment step. For example, in the range of 250 to 350 °C, it can be Mp - 50 °C or more and lower than Mp °C, preferably Mp - 40 °C or more and lower than Mp °C, and more preferably Mp - 30 °C or more and lower than Mp °C. In the heat treatment step, as the solid-phase polymerization proceeds, the melting point of the molten anisotropic aromatic polyester fiber rises. Therefore, as long as the initial heat treatment temperature in the heat treatment step is lower than the melting point (Mp) of the spinning dope, from the viewpoint of efficiently increasing the strength, the heat treatment temperature can be gradually increased corresponding to the progress state of the solid-phase polymerization and heat treatment can be carried out at a temperature exceeding the melting point (the melting point of the spinning dope) at the time of supplying to the heat treatment step.

[0122] The heat treatment time of the heat treatment process can be appropriately set according to the heat treatment method and heat treatment temperature. For example, it can be set in the range of 15 minutes to 30 hours, preferably 2 to 24 hours, more preferably 3 to 20 hours. The heat treatment time here represents the holding time at a given heat treatment temperature (e.g., the maximum temperature).

[0123] In the method for manufacturing the melt anisotropic aromatic polyester fiber of the present invention, for example, in order to improve the bundling property of the fiber and prevent thermal adhesion during heat treatment, a known sizing agent and anti-fusion adhesion agent can be applied before the heat treatment process.

[0124] [Fiber structure]

[0125] For the melt anisotropic aromatic polyester fiber of the present invention, it can be made into a fiber structure containing at least a part of it for various uses. The fiber structure containing the melt anisotropic aromatic polyester fiber of the present invention can be used in any fiber form such as staple fiber, chopped fiber, filament yarn, textile yarn, cord, rope, etc. In addition, it can also be used as various fabrics such as non-woven fabric, woven fabric, knitted fabric, etc. using the melt anisotropic aromatic polyester fiber. Such fibers and fabrics can be manufactured by using the melt anisotropic aromatic polyester fiber by a known method.

[0126] As long as the effects of the present invention are not impaired, the fiber structure of the present invention can combine the melt anisotropic aromatic polyester fiber with other fibers. For example, a composite fiber using the melt anisotropic aromatic polyester fiber and other fibers (e.g., a mixed fiber yarn formed by mixing the melt anisotropic aromatic polyester fiber and other fibers, etc.) can be used. In addition, a composite fabric using the melt anisotropic aromatic polyester fiber and other fibers (e.g., a mixed fiber fabric formed by mixing the melt anisotropic aromatic polyester fiber and other fibers, a laminate of a fabric formed by the melt anisotropic aromatic polyester fiber and a fabric formed by other fibers, etc.) can be used.

[0127] The melt anisotropic aromatic polyester fibers of the present invention can be used in various applications in the form of various fiber structures for general industrial materials, civil / construction materials, various reinforcing materials, electrical / electronic component materials, various fiber products, etc. For example, it can be used in tensile members (flexible cords of various electrical products such as electric wires, optical fibers, umbilical cables, heating wire cores, headphone cords, etc.), canvas, ropes (marine, mountaineering, crane, sailing, tags, etc.), climbing ropes, sports nets, slings, life-saving ropes, fishing lines, sewing threads, window screen threads, fishing nets, rope hooks, geogrids, protective gloves, tear-resistant fabrics for protective clothing / outdoor clothing, rider clothing, sports rackets, catgut, reinforcing materials for medical catheters, sutures, screen meshes, filters, base fabrics for printed circuit boards, mesh conveyor belts, belts for papermaking, dryer canvas, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses / pipes, highly processed products such as rubber / plastic reinforcing materials for tires / conveyor belts, etc. In particular, the creep characteristics of the melt anisotropic aromatic polyester fibers of the present invention are excellent, so they can be suitably used as tensile members.

[0128] Examples

[0129] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by any of them. It should be noted that in the following examples and comparative examples, various physical properties were measured by the following methods.

[0130] (Melting points of resin chips (granular molded bodies) and fibers)

[0131] According to JIS K 7121, measurement was carried out using a differential scanning calorimeter (DSC; "DSC60APlus" manufactured by Shimadzu Corporation), and the temperature of the observed main absorption peak was taken as the melting point. Specifically, in the above DSC apparatus, 4 to 6 mg of the sample was sealed in an aluminum pan, and nitrogen gas as the carrier gas was allowed to flow at a flow rate of 200 mL / min, and the endothermic peak from the melt anisotropic aromatic polyester was measured when heating from 25°C at a rate of 10°C / min.

[0132] (Pressure increase amount)

[0133] 50 kg of the melt anisotropic aromatic polyester that had been melt-kneaded under various conditions in a twin-screw extruder was transported to a container provided with a metal non-woven fabric filter having a size of Φ76 and a mesh of 30 μm and passed through it. The pressure was monitored by a resin pressure gauge GC75 manufactured by Nagano Keiki Co., Ltd. provided in the container, and the pressure increase amount before and after its passage was recorded.

[0134] (Spinnability)

[0135] After ejecting the molten anisotropic aromatic polyester and starting winding, a spinning test was conducted for 3 days, and the number of thread breaks occurring at this time was counted, and evaluation was carried out according to the following criteria.

[0136] ◎: The number of thread breaks is 0 times / day

[0137] ○: The number of thread breaks is more than 0 times / day and less than 0.7 times / day

[0138] △: The number of thread breaks is 0.7 times / day or more and less than 2.0 times / day

[0139] ×: The number of thread breaks is 2.0 times / day or more

[0140] (Orthorhombic crystallinity)

[0141] The molten anisotropic aromatic polyester fiber was installed on a fiber-specific support, and wide-angle X-ray diffraction (WAXD) measurement was carried out by making X-rays incident orthogonally to the fiber axis under the following measurement conditions using the transmission method.

[0142] Measurement device: "D8 Discover IμS" manufactured by Bruker

[0143] Detector: Two-dimensional PSPC·VANTEC-500

[0144] X-ray source: Cu

[0145] Current: 1 mA

[0146] Voltage: 50 kV

[0147] Exposure time: 10 minutes

[0148] Collimator diameter: 0.5 mm

[0149] Camera length: 17 cm

[0150] Detector position (2θ): 20°

[0151] Sample position (ω): 10°

[0152] Rotation angle (Ψ): 90°

[0153] Measurement temperature: Room temperature (about 25 °C)

[0154] Based on the following conditions, an X-ray diffraction pattern with the diffraction angle (2θ) on the horizontal axis and the intensity on the vertical axis was obtained.

[0155] Integration range: 2θ = 5~35°, γ (azimuth angle) = 250~290°

[0156] Step size: 0.05° (diffraction angle)

[0157] In the obtained X-ray diffraction pattern, a baseline was set by connecting the values of 2θ = 5° and 35° with a straight line. Based on this newly set baseline, the difference in the intensity of the vertical axis from the measured data to the baseline was converted into spectral data of new intensity.

[0158] For the spectral data after baseline correction, using the Pseudo-Voigt function (ratio of Lorentz function: α = 0), with the peak height, peak top position, σ, and asymmetry parameter as variables, the amorphous peak was fitted. At this time, the initial value of the peak top position of the fitting function was set near 20.6°. The peak area of this fitting function was calculated as the amorphous content (D).

[0159] For peak A (near the peak top position of 19°), peak B (near the peak top position of 20.5°), and peak C (near the peak top position of 27°) in the spectral data after baseline correction, using the following functions, with the peak height, peak top position, and σ as variables, the crystalline peaks were fitted. All the crystalline peaks were symmetric.

[0160] Peak A: Pseudo-Voigt function (α = 1)

[0161] Peak B: Pseudo-Voigt function (α = 0)

[0162] Peak C: Pseudo-Voigt function (α = 0.5)

[0163] Next, including the fitting function of the amorphous peak obtained previously, fitting was performed by the least squares method in such a way that the difference between the sum of all the fitting functions and the spectral data after baseline correction was minimized. The peak areas of these fitting functions were calculated as the crystalline contents (A), (B), and (C), respectively.

[0164] Using the crystalline content (A) of peak A from the hexagonal crystal and the crystalline content (B) of peak B from the orthorhombic crystal, the degree of orthorhombic crystallization was calculated according to the following formula.

[0165] Degree of orthorhombic crystallization (%) = (B) / {(A)+(B)}×100

[0166] (Fiber density)

[0167] Density measurement was carried out with reference to the density gradient tube method (JIS L 1013:2010 8.17.2). In order to compare the minute density differences caused by the packing differences of the fibers due to orthorhombic crystallization, the average value obtained by measuring each sample 5 times was rounded to the fourth decimal place for calculation.

[0168] (Total fineness, single fiber fineness)

[0169] Based on JIS L 1013:2010 8.3.1 Method A, using the measuring instrument "Wrap Reel by Motor Driven" manufactured by Daiei Kagaku Seiki Co., Ltd., melt anisotropic aromatic polyester fiber was formed into 10 m skeins. Multiply its weight (g) by 1000 times, and conduct 3 measurements for each level. Take the average value of the 3 measurement values as the total fineness (dtex) of the obtained melt anisotropic aromatic polyester fiber. In addition, take the quotient obtained by dividing this value by the number of filaments as the single fiber fineness (dtex).

[0170] (Tensile strength)

[0171] Referring to JIS L 1013:2010 8.5.1, use the tensile strength tester "TENSORAPID5" manufactured by USTER Technologies to conduct 5 tensile tests on each sample under the conditions of a test length of 30 cm, a tensile speed of 15 cm / minute, and an initial load of 0.33 g / dtex. Divide the average tensile strength (cN) of the 5 tests by the total fineness (dtex) measured by the above method to calculate the tensile strength (cN / dtex).

[0172] (Creep characteristics)

[0173] Use the creep testing machine "525-R CREAP TESTER" manufactured by MYS Tester to start testing from the moment when a load of 0.18 N / dtex is applied to a fiber with a test length of 300 mm at a measurement temperature of 20 °C, and measure the time until the fiber breaks. Conduct 3 tests on each sample and calculate its average value.

[0174] [Example 1]

[0175] Small pieces (granular molded bodies) of melt anisotropic aromatic polyester (Mp0: 278 °C) with a structural unit (A) from 4-hydroxybenzoic acid and a structural unit (B) from 6-hydroxy-2-naphthoic acid at 73 / 27 (mol%) were dried in hot air at 120 °C for more than 4 hours. Then, put it into a barrel with an internal void volume of 14.7 cm in the kneading section 3In a twin-screw extruder, the barrel temperature from the resin supply section to the outlet of the kneading section was set at 260 °C, and the barrel temperature of the conveying section closer to the downstream than the outlet of the kneading section was set at 325 °C, and melt-kneading was carried out. At this time, the residence time in the kneading section was adjusted to 21 seconds. At this time, a vacuum pump was connected via a metal pipe from the vent hole section in the middle of the twin-screw extruder, and the space in the twin-screw extruder where the polymer was not filled was depressurized to 30 kPa. Then, while metering with a gear pump, the melt-kneaded material was supplied from the twin-screw extruder to the spinneret. The spinneret had a spinning nozzle with a pore diameter of 0.10 mmΦ and 100 holes, and the temperature of the spinning nozzle was set at 320 °C, and the melt-kneaded material was ejected at a volume ejection rate of 42.0 cm 3 / min to obtain a spun raw yarn of 560 dtex / 100f. Then, the obtained spun raw yarn was heat-treated at 275 °C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of the melt anisotropic aromatic polyester fiber. The analysis results of the obtained melt anisotropic aromatic polyester fiber are shown in Table 5.

[0176] [Example 2]

[0177] The internal void volume of the barrel in the kneading section was set at 44.1 cm 3 , the barrel temperature from the resin supply section to the outlet of the kneading section was set at 240 °C, the volume ejection rate was set at 126.1 cm 3 / min, and the number of holes in the spinning nozzle was set at 300. Otherwise, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0178] [Example 3]

[0179] The barrel temperature from the resin supply section to the outlet of the kneading section was set at 220 °C. Otherwise, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0180] [Example 4]

[0181] The barrel temperature from the resin supply section to the outlet of the kneading section was set at 200 °C. Otherwise, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0182] [Example 5]

[0183] The internal void volume of the barrel in the kneading section was set at 29.4 cm 3 , the barrel temperature from the resin supply section to the outlet of the kneading section was set at 230 °C, the volume ejection rate was set at 30.2 cm 3 / min, and the residence time in the kneading section was set at 58.5 seconds. Otherwise, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0184] [Example 6]

[0185] The barrel temperature from the resin supply section to the outlet of the kneading section was set at 250 °C, the volume discharge rate was set at 7.0 cm 3 / min, the residence time in the kneading section was set at 126 seconds, the number of holes in the spinning nozzle was set at 10, and except for this, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0186] [Example 7]

[0187] The barrel temperature from the resin supply section to the outlet of the kneading section was set at 230 °C, the volume discharge rate was set at 58.8 cm 3 / min, the residence time in the kneading section was set at 15 seconds, and except for this, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0188] [Example 8]

[0189] The volume discharge rate was set at 96.9 cm 3 / min, the residence time in the kneading section was set at 9.1 seconds, and except for this, the melt anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0190] [Example 9]

[0191] Small pieces (granular molded bodies) of a melt anisotropic aromatic polyester (Mp0: 311 °C) with a structural unit (A) derived from 4-hydroxybenzoic acid and a structural unit (B) derived from 6-hydroxy-2-naphthoic acid of 78 / 22 (mol%) were hot air dried at 120 °C for 4 hours or more. Then, they were put into a twin-screw extruder with the internal void volume of the kneading section set at 14.7 cm 3 . The barrel temperature from the resin supply section to the outlet of the kneading section was set at 270 °C, and the barrel temperature of the conveying section closer to the downstream than the outlet of the kneading section was set at 340 °C, and melt kneading was carried out. At this time, the residence time in the kneading section was adjusted to 21 seconds. At this time, a vacuum pump was connected via a metal tube from the vent hole part in the middle of the twin-screw extruder, and the space in the twin-screw extruder where the polymer was not filled was depressurized to 30 kPa. Then, while metering with a gear pump, the melt kneaded material was supplied from the twin-screw extruder to the spinneret. The spinneret had a spinning nozzle with a pore diameter of 0.10 mmΦ and 100 holes, the temperature of the spinning nozzle was set at 340 °C, and the melt kneaded material was ejected at a volume discharge rate of 42.0 cm 3 / min to obtain a spun raw yarn of 560 dtex / 100f. Then, the obtained spun raw yarn was heat treated at 280 °C for 16 hours in a nitrogen atmosphere to obtain a heat treated yarn of the melt anisotropic aromatic polyester fiber.

[0192] [Comparative Example 1]

[0193] A Φ50 mm single-screw extruder without vent holes in the extruder was used, and the barrel temperature except for the resin supply part was set at 320 °C. Otherwise, the molten anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0194] [Comparative Example 2]

[0195] The barrel temperature from the resin supply part to the outlet of the kneading part was set at 300 °C. Otherwise, the molten anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0196] [Comparative Example 3]

[0197] The barrel temperature from the resin supply part to the outlet of the kneading part was set at 285 °C. Otherwise, the molten anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1.

[0198] [Comparative Example 4]

[0199] A Φ50 mm single-screw extruder without vent holes in the extruder was used, and the barrel temperature except for the resin supply part was set at 350 °C. Otherwise, the molten anisotropic aromatic polyester fiber was obtained in the same manner as in Example 9.

[0200]

[0201] As shown in Table 5, in Examples 1 to 9, since the barrel temperature from the resin supply part to the outlet of the twin-screw extruder was set at a specific low temperature condition for melt-kneading, a molten anisotropic aromatic polyester fiber with a high orthorhombic crystallinity could be obtained. Therefore, the creep characteristics of the molten anisotropic aromatic polyester fibers of Examples 1 to 9 were excellent.

[0202] On the other hand, in Comparative Examples 1 and 4, since a single-screw extruder was used and the barrel temperature from the resin supply part to the outlet of the kneading part was high, the orthorhombic crystallinity could not be increased. In addition, in Comparative Examples 2 and 3, although a twin-screw extruder was used, the barrel temperature from the resin supply part to the outlet of the kneading part was high, so the orthorhombic crystallinity could not be increased. Therefore, compared with Examples 1 to 9, the creep characteristics of the molten anisotropic aromatic polyester fibers of Comparative Examples 1 to 4 were poor.

[0203] Industrial Applicability

[0204] The molten anisotropic aromatic polyester fiber of the present invention can be used for various applications such as general industrial materials, civil / construction materials, various reinforcing materials, electrical / electronic component materials, and various fiber products. For example, it can be used as a tensile member.

[0205] As described above, while referring to the attached Figure 1 drawings, preferred embodiments of the present invention have been described. However, various additions, changes, or deletions can be made without departing from the gist of the present invention, and these embodiments are also included within the scope of the present invention.

Claims

1. A melt anisotropic aromatic polyester fiber, wherein the orthorhombic crystallinity of the crystalline component is 15.0% or more.

2. The melt anisotropic aromatic polyester fiber according to claim 1, having a density of 1.4080 g / cm 3 or more as determined by a density gradient tube.

3. The melt anisotropic aromatic polyester fiber according to claim 1 or 2, which comprises a melt anisotropic aromatic polyester having 50 mol% or more of structural units derived from 4-hydroxybenzoic acid.

4. The melt anisotropic aromatic polyester fiber according to claim 1 or 2, having a melting point of 260 to 380 °C as measured by a differential scanning calorimeter at a heating rate of 10 °C / min in a nitrogen atmosphere.

5. A fiber structure which is constituted by comprising the melt anisotropic aromatic polyester fiber according to claim 1 or 2 in at least a part thereof.

6. A method for producing a melt anisotropic aromatic polyester fiber, which method comprises at least: a step of melt-kneading a melt anisotropic aromatic polyester using a twin-screw extruder under the condition that the barrel temperature from the resin supply part to the outlet of the kneading part is lower than the melting point Mp0, where the melting point of the melt anisotropic aromatic polyester measured by a differential scanning calorimeter at a heating rate of 10 °C / min in a nitrogen atmosphere is Mp0; a step of spinning the melt-kneaded product to obtain a spun yarn; and a step of heat-treating the obtained spun yarn.

7. The method for producing a melt anisotropic aromatic polyester fiber according to claim 6, wherein the melt-kneading is carried out under the condition that the residence time in the kneading part of the twin-screw extruder is 10 seconds or more.

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