Melt-anisotropic aromatic polyester fiber and method for manufacturing same

Abstract

Provided is a melt-anisotropic aromatic polyester fiber that excels in creep characteristics. The orthorhombic crystallinity in a crystal component of the melt-anisotropic aromatic polyester fiber is 15.0% or greater. For example, the density of the melt-anisotropic aromatic polyester fiber, derived according to a density gradient tube, may be 1.4080 g / cm3 or greater. Additionally, the melt-anisotropic aromatic polyester fiber may contain a melt-anisotropic aromatic polyester having 50 mol% or more of structural units derived from 4-hydroxybenzoic acid.

Description

Melt-anisotropic aromatic polyester fiber and its manufacturing method Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2022-199790, filed on December 14, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a melt-anisotropic aromatic polyester fiber and a method for producing the same.

[0003] While general-purpose fibers such as general-purpose polyester fibers are often used for tension members, the miniaturization of electrical appliances requires thinner cables and cords, so superfibers that are strong enough even with a small diameter are attracting attention. Furthermore, for applications such as optical cables, even a slight stretch of optical fiber results in an accelerated decrease in communication speed, so liquid crystal polymer fibers (e.g., melt-anisotropic aromatic polyester fibers and aramid fibers) with high dimensional stability are used. Melt-anisotropic aromatic polyester fibers are known to have excellent dimensional stability because they can be spun to obtain raw spun yarns that are highly oriented in the fiber axis direction, and then heat-treated and solid-phase polymerized to increase the crystallinity.

[0004] For example, regarding the crystallinity of melt-anisotropic aromatic polyester fibers, Patent Document 1 (JP 2010-150694 A) discloses a liquid crystalline polyester fiber characterized in that, in wide-angle X-ray diffraction measurement using CuKα radiation as a radiation source, the half-width of a peak having a maximum at 18 to 22° relative to the equatorial line direction is 3.5° or more.

[0005] Furthermore, with regard to a method for producing a melt-anisotropic aromatic polyester fiber, Patent Document 2 (JP-A-3-227407) describes a method for extruding and spinning a melt-anisotropic aromatic polyester using a vented extruder, in which the pressure at the vent is reduced to 100 to 760 mmHg and the pressure at the tip of the extruder is set to 5 to 30 kg / cm. ２ Then, adjust the pressure to 40 to 200 kg / cm using a gear pump with a volumetric efficiency of 50 to 90%. ２ and passing the mixture through a filter to spin the resulting mixture into fibers.

[0006] JP-A-2010-150694 JP-A-3-227407

[0007] However, in order to extend the life of various applications such as electrical products, further improvement in dimensional stability compared to conventional melt-anisotropic aromatic polyester fibers is required, and creep properties need to be improved. However, Patent Documents 1 and 2 do not describe any improvement in creep properties.

[0008] Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a melt-anisotropic aromatic polyester fiber having excellent creep properties.

[0009]

[0005] As a result of extensive research to achieve the above-mentioned object, the inventors of the present invention have found that changing the kneading conditions during melt spinning leads to differences in the creep properties of melt-anisotropic aromatic polyester fibers obtained by subsequent heat treatment of the spun raw yarn. Focusing on the crystalline structure of melt-anisotropic aromatic polyester fibers in relation to creep properties, they have found that melt-anisotropic aromatic polyester fibers with better creep properties have a higher degree of orthorhombic crystallization. Further research has led to the discovery that, possibly because low-temperature kneading of molten anisotropic aromatic polyester in a twin-screw extruder during melt spinning allows shear to be applied in a high-viscosity state, enabling the production of a spun raw yarn with a more uniform microcrystalline structure, heat treatment of such a spun raw yarn results in dense packing of molecular chains during solid-state polymerization, thereby increasing the proportion of orthorhombic crystals, which have a denser crystalline structure, and has led to the completion of the present invention.

[0010] That is, the present invention can be configured in the following aspects. [Aspect 1] A melt-anisotropic aromatic polyester fiber having a degree of orthorhombic crystallinity in the crystalline component of 15.0% or more (preferably 16.0% or more, more preferably 17.0% or more, even more preferably 18.0% or more, and 25.0% or less, preferably 24.0% or less, more preferably 23.0% or less). [Aspect 2] A melt-anisotropic aromatic polyester fiber according to Aspect 1, having a density of 1.4080 g / cm as determined by a density gradient tube. ３A melt-anisotropic aromatic polyester fiber having 50 mol % or more (preferably 53 mol % or more, more preferably 60 mol % or more, even more preferably 65 mol % or more, and even more preferably 70 mol % or more) of structural units derived from 4-hydroxybenzoic acid. [Aspect 4] A melt-anisotropic aromatic polyester fiber according to any one of Aspects 1 to 3, having a melting point of 260 to 380°C (preferably 270 to 360°C, more preferably 275 to 340°C, and even more preferably 275 to 330°C) measured by a differential scanning calorimeter in a nitrogen atmosphere at a heating rate of 10°C / min. [Aspect 5] A fiber structure at least partially comprising the melt-anisotropic aromatic polyester fiber according to any one of Aspects 1 to 4. [Embodiment 6] The melting point Mp of the melt-dispersible anisotropic aromatic polyester measured by a differential scanning calorimeter in a nitrogen atmosphere at a temperature increase rate of 10°C / min. ０ When a twin-screw extruder is used, the barrel temperature from the resin feed section to the kneading section outlet is set to the melting point Mp ０ Less than (preferably Mp ０ -5°C or lower, more preferably Mp ０ -10°C or less, more preferably Mp ０ A method for producing a melt-anisotropic aromatic polyester fiber, comprising at least the steps of: melt-kneading a melt-anisotropic aromatic polyester at a temperature (temperature) of −15° C. or lower; spinning the melt-kneaded mixture to obtain a raw spun yarn; and heat-treating the obtained raw spun yarn. [Aspect 7] A method for producing a melt-anisotropic aromatic polyester fiber according to Aspect 6, wherein the melt-kneading is carried out under conditions such 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).

[0011] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly dictates otherwise. As used herein, the terms "and / or," "at least one," and "one or more" include any and all combinations of the associated listed items.

[0012] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification and / or the drawings is included in the present invention, and in particular any combination of two or more of the claims set forth in the claims is included in the present invention.

[0013] The melt-anisotropic aromatic polyester fiber of the present invention has excellent creep properties. Furthermore, the production method of the present invention can produce melt-anisotropic aromatic polyester fiber with a high degree of orthorhombic crystallization.

[0014] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation and should not be used to define the scope of the present invention. The scope of the present invention is defined by the appended claims. The drawings are not necessarily drawn to scale and are exaggerated to illustrate the principles of the present invention.

[0023] Figure 1 is a schematic diagram for explaining a method for producing a melt-anisotropic aromatic polyester fiber according to one embodiment of the present invention.

[0015] [Melt-Anisotropic Aromatic Polyester Fiber] The melt-anisotropic aromatic polyester fiber of the present invention comprises a melt-anisotropic aromatic polyester. The melt-anisotropic aromatic polyester may be composed of structural units derived from, for example, an aromatic diol, an aromatic dicarboxylic acid, an aromatic hydroxycarboxylic acid, or the like. The structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in chemical composition, as long as the effects of the present invention are not impaired. Furthermore, the melt-anisotropic aromatic polyester may contain structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids, as long as the effects of the present invention are not impaired. For example, preferred structural units are shown in Table 1.

[0016]

[0017] In the structural units in Table 1, m is an integer of 0 to 2, and Y in the formula, in the range of 1 to the maximum number of possible substitutions, each independently represents a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (for example, a methoxy group, an ethoxy group, an isopropoxy group, a n-butoxy group, etc.), an aryl group (for example, a phenyl group, a naphthyl group, etc.), an aralkyl group (for example, a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (for example, a phenoxy group), an aralkyloxy group (for example, a benzyloxy group), etc.

[0018] More preferred structural units include the structural units described in Examples (1) to (18) shown in the following Tables 2, 3, and 4. When the structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

[0019]

[0020]

[0021]

[0022] In the structural units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n=1 and n=2 may exist alone or in combination; Y １ and Y ２ may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc. Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0023] Examples of Z include substituents represented by the following formulas.

[0024]

[0025] The melt-anisotropic aromatic polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferred to include both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) may be represented by the following formula (A), and the structural unit (B) may be represented by the following formula (B). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural unit (B) may preferably be in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and even more preferably 5 / 1 to 1 / 1.

[0026]

[0027]

[0028] The total of the structural units (A) and the structural units (B) may be, for example, 65 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more, based on the total structural units. In particular, melt-anisotropic aromatic polyesters in which the structural units (B) account for 4 to 45 mol % of the polymer are preferred.

[0029] The melt-type anisotropic aromatic polyester may contain structural units derived from 4-hydroxybenzoic acid, preferably at least 50 mol%, more preferably at least 53 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, and particularly preferably at least 70 mol%. The upper limit of the content of structural units derived from 4-hydroxybenzoic acid in the melt-type anisotropic aromatic polyester is not particularly limited, but may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0030] The melting point (hereinafter referred to as Mp) of the melt anisotropic aromatic polyester used in the present invention ０ The melting point (sometimes referred to as "melting point") is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, even more preferably 260 to 360°C, and even more preferably 260 to 330°C. In this specification, the melting point is the main absorption peak temperature observed when measured with a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of a sample is placed in an aluminum pan and sealed in a DSC apparatus, and nitrogen is flowed as a carrier gas at a flow rate of 200 mL / min. The endothermic peak is measured when the temperature is increased from room temperature (e.g., 25°C) at a rate of 10°C / min. If a clear peak does not appear in the first run of DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50°C / min to a temperature 50°C higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50°C at a rate of 80°C / min, and then the endothermic peak should be measured at a heating rate of 10°C / min.

[0031] The melt-dispersible aromatic polyester fiber may contain, within the scope of the present invention, a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, fluororesin, etc. Furthermore, the melt-dispersible aromatic polyester fiber may contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, barium oxide, etc., colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

[0032] 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, even more preferably 95% by weight or more, and still more preferably 99.9% by weight or more.

[0033] The melt-anisotropic aromatic polyester fiber of the present invention has a degree of orthorhombic crystallinity in the crystalline component of 15.0% or more. Melt-anisotropic aromatic polyesters have crystalline components such as orthorhombic and hexagonal crystallinity. Orthorhombic crystallinity has a crystalline structure in which molecular chains are more densely packed. Therefore, melt-anisotropic aromatic polyester fibers having a high proportion of orthorhombic crystallinity in the crystalline component not only have a high degree of crystallinity and orientation, but also have excellent creep properties due to their dense crystalline structure. The degree of orthorhombic crystallinity may be preferably 16.0% or more, more preferably 17.0% or more, and even more preferably 18.0% or more. The degree of orthorhombic crystallinity may be, for example, 25.0% or less, preferably 24.0% or less, and more preferably 23.0% or less. In this specification, the degree of orthorhombic crystallinity of the melt-anisotropic aromatic polyester fiber is calculated from diffraction peaks derived from orthorhombic crystals and hexagonal crystals in an X-ray diffraction profile obtained by wide-angle X-ray diffraction measurement (for example, diffraction peaks appearing near a diffraction angle 2θ of 19 to 21°, etc.), and is a value measured by the method described in the Examples below.

[0034] The melt anisotropic aromatic polyester fiber of the present invention has a high density due to a high proportion of orthorhombic crystals in which molecular chains are densely packed. For example, the density determined by a density gradient tube is 1.4080 g / cm ３The upper limit of the density is not particularly limited, and although it depends on the composition of the melt-dispersed anisotropic aromatic polyester, it may be, for example, 1.4200 g / cm ３ In this specification, the density of the melt-anisotropic aromatic polyester fiber is a value measured by the method described in the examples below.

[0035] The melt-anisotropic aromatic polyester fiber of the present invention may have a melting point of 260 to 380°C, preferably 270 to 360°C, more preferably 275 to 340°C, and even more preferably 275 to 330°C. The melting point of the melt-anisotropic aromatic polyester fiber is elevated from the melting point (Mp) of the raw spinning yarn by solid-state polymerization. The melting point of the melt-anisotropic aromatic polyester fiber is a value measured by the method described in the examples below.

[0036] The melt-anisotropic aromatic polyester fiber of the present invention may have a tensile strength of 20 cN / dtex or more, preferably 24 cN / dtex or more, and more preferably 25 cN / dtex or more. 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 melt-anisotropic aromatic polyester fiber is a value measured by the method described in the Examples below.

[0037] The melt-anisotropic aromatic polyester fiber of the present invention may have a time until the fiber breaks in a creep test by the method described in the Examples below of 30 hours or more, preferably 60 hours or more, and more preferably 68 hours or more.

[0038] The single fiber fineness of the melt-anisotropic aromatic polyester fiber of the present invention can be appropriately selected depending on the application, etc. For example, the single fiber fineness may be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. However, from the viewpoint of responding to the miniaturization of electrical appliances, etc., a small fineness is preferred, and for example, it may be 7 dtex or less. In addition, the lower limit of the single fiber fineness is not particularly limited, but may be, for example, about 0.01 dtex. The single fiber fineness is a value measured by the method described in the Examples below.

[0039] The melt-anisotropic aromatic 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 depending on the application, etc. For example, the number of filaments may be 2 to 5,000, preferably 3 to 4,000, and more preferably 5 to 3,000.

[0040] The total fineness of the melt-anisotropic aromatic polyester fiber of the present invention can be appropriately selected depending on the application, etc., and may be, for example, 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 2,000 dtex or less, and even more preferably 1,000 dtex or less. The lower limit of the total fineness is not particularly limited, but may be, for example, about 1 dtex.

[0041] [Method for producing melt anisotropic aromatic polyester fiber] The method for producing the melt anisotropic aromatic polyester fiber of the present invention is to measure the melting point Mp of the melt anisotropic aromatic polyester measured by a differential scanning calorimeter in a nitrogen atmosphere at a temperature rising rate of 10°C / min. ０ When a twin-screw extruder is used, the barrel temperature from the resin feed section to the kneading section outlet is set to the melting point Mp ０ The method comprises at least a step of melt-kneading a melt-anisotropic aromatic polyester at a temperature of less than 100°C, a step of spinning the melt-kneaded mixture to obtain a raw spun yarn, and a step of heat-treating the obtained raw spun yarn.

[0042] In the present invention, the kneading property of the molten anisotropic aromatic polyester is improved using a twin-screw extruder, and the molten anisotropic aromatic polyester is kneaded at a high viscosity by setting the kneading temperature in the kneading section of the twin-screw extruder to a low temperature below the melting point. It should be noted that this is the opposite temperature condition to the melting point of the resin, whereas it is common to promote melting by heating above the melting point of the resin. Furthermore, by spinning the molten kneaded product kneaded at such a low temperature and applying shear, it is possible to obtain a spun raw yarn with a more uniform microcrystalline structure. This spun raw yarn has densely packed molecular chains during solid-state polymerization by heat treatment, increasing the proportion of orthorhombic crystals, which have a denser crystalline structure. Furthermore, applying shear by kneading at a low temperature can provide more mechanical energy than the thermal energy required when heated above the melting point of the resin, thereby promoting melting more than conventional melt-kneading conditions. As a result, in addition to the formation of a crystalline structure, it is also possible to reduce the amount of unmelted material remaining, which makes it less likely for filters installed to remove foreign matter to become clogged and suppresses the occurrence of thread breakage during spinning. It is also commonly known to use a single-screw extruder in the melt spinning method, but if the extruder temperature is set below the melting point as described above in a single-screw extruder, poor resin biting, pressure fluctuations, and increased torque occur, making stable spinning impossible. This is thought to be due to the fact that, while a twin-screw extruder is designed to melt the resin by heat generation due to high shear, in a single-screw extruder, heat transfer from the extruder barrel during melting contributes significantly. Therefore, the same effect cannot be obtained using a single-screw extruder in the present invention.

[0043] A method for producing a melt-anisotropic aromatic polyester fiber will be described below with reference to FIG. 1 . FIG. 1 is a schematic diagram showing the internal configuration of a twin-screw extruder 100 used in producing a melt-anisotropic aromatic polyester fiber according to one embodiment of the present invention, viewed from the side. As shown in FIG. 1 , the twin-screw extruder 100 includes a hopper 11 for introducing a molten anisotropic aromatic polyester, a barrel 12, a screw 13 that rotates within the barrel 12, and a vent 14. The barrel 12 includes a resin feed section 21, a kneading section 22, and a transport section 23 arranged from upstream to downstream. The resin feed section 21, the kneading section 22, and the transport section 23 each include screw elements 13a, 13b, and 13c of the screw 13. The screw 13 (screw elements 13a, 13b, and 13c) represents one of the screws in the twin-screw extruder 100. FIG. 1 shows a simplified structure for explaining the method for producing a melt-anisotropic aromatic polyester fiber of the present invention, but a plurality of various types of equipment may be provided as needed, and in addition to the equipment shown in the figure, equipment generally used in twin-screw extruders may also be provided.

[0044] In Fig. 1, the solid molten anisotropic aromatic polyester introduced from a hopper 11 is transported in the X direction, which is the direction of advance, within a barrel 12 by the rotation of a screw 13, and is heated by a known heating means such as a heater installed in the barrel 12. In addition to heat transfer from the heating means, the solid molten anisotropic aromatic polyester melts as it advances in the X direction by applying shear between the inner wall of the barrel 12 and the screw 13 and between the screws 13. Note that a resin composition containing the molten anisotropic aromatic polyester, the thermoplastic polymer described above, various additives, etc. may also be introduced into the twin-screw extruder 100.

[0045] In the resin feed section 21, the solid molten anisotropic aromatic polyester supplied from the hopper 11 moves in the X direction while being compressed in a solid state by the rotation of the screw 13, and can be gradually melted by heat transfer from the heating means of the barrel 12 and shearing caused by the rotation of the screw 13. As the screw element 13a used in the resin feed section 21, for example, a full-flight screw is used.

[0046] In the kneading section 22, kneading is performed using shear-imparting screw elements such as kneading disks as the screw elements 13b, thereby promoting melting of the molten anisotropic aromatic polyester containing solids transported from the resin feed section 21. Although one kneading section 22 is provided in Fig. 1, kneading sections may be provided in multiple locations.

[0047] In the transport section 23, the viscosity of the molten kneaded material obtained in the kneading section 22 can be adjusted when it is transported to the spinning head. As the screw element 13c used in the transport section 23, for example, a full-flight screw is used.

[0048] In the present invention, the temperatures of the resin feed section 21 and the kneading section 22 in the barrel 12 are controlled to be equal to or lower than the melting point Mp of the molten anisotropic aromatic polyester fed into the twin-screw extruder 100. ０ By setting the temperature to a low temperature below Mp, it is possible to efficiently apply shear to the molten anisotropic aromatic polyester in a high viscosity state. ０ -5°C or lower, more preferably Mp ０ -10°C or less, more preferably Mp ０ From the viewpoint of promoting melting by heating, Mp ０ It may be -100°C or higher, and preferably Mp ０ -90°C or higher, more preferably Mp ０ In the production method of the present invention, the barrel temperature from the resin feed section to the outlet of the kneading section refers to the barrel temperature from the resin feed section to the outlet of the kneading section that is most downstream and adjacent to the transport section, when there are multiple kneading sections.

[0049] The heating means installed in the barrel 12 may be controlled to different temperatures in each region in the direction of travel from the upstream side to the downstream side, and it is preferable that the temperature of the barrel 12 from the resin feed section 21 to the outlet of the kneading section 22 is adjusted so that it gradually increases within the above temperature range.

[0050] In the present invention, the temperatures of the resin feed section 21 and the kneading section 22 in the barrel 12 may be adjusted within the above temperature range, and the temperature of the barrel 12 in the subsequent transport section 23 may be adjusted to Mp ０ or more, preferably Mp ０ +10°C or higher, more preferably Mp ０ The temperature may be +20° C. or higher. From the viewpoint of suppressing decomposition of the melt-type anisotropic aromatic polyester, the temperature may be 400° C. or lower, preferably 370° C. or lower, and more preferably 350° C. or lower.

[0051] The residence time in the kneading section 22 may be 10 seconds or more, preferably 15 seconds or more, and more preferably 20 seconds or more, from the viewpoint of efficiently applying shear to the molten anisotropic aromatic polyester and improving spinnability. Furthermore, from the viewpoint of suppressing deterioration of the molten anisotropic aromatic polyester, it may be 300 seconds or less, preferably 180 seconds or less, and more preferably 130 seconds or less. The residence time in the kneading section can be calculated from the volume of the kneading section and the discharge rate using the following formula: (internal space [cm ３ ]) = (volume in the kneading barrel [cm ３ ]) - (kneading section screw volume [cm ３ ]) (Kneading section residence time [s]) = (Barrel space [cm ３ ]) / (volume discharge amount [cm ３ / s])

[0052] Depending on the type of melt-anisotropic aromatic polyester, spinning conditions, etc., the capacity, distribution, and arrangement of the resin feed section, kneading section, and transport section, as well as the shape of the screws and the gaps between the screws, may be designed as appropriate, and in addition to screw elements such as full-flight screws and kneading disks, screw elements that return in the opposite direction to the traveling direction from upstream to downstream, such as back-kneading disks, may also be provided. Furthermore, a seal ring may be used in the element at the outlet of the kneading section for the purpose of efficiently retaining the resin in the kneading section and for the purpose of improving the sealing performance upstream of the vent.

[0053] Since air bubbles may be trapped in the twin-screw extruder 100 during melt-kneading due to air entrapment or the like, it is preferable to degas the twin-screw extruder 100 by, for example, providing a vent 14 in the twin-screw extruder 100 and connecting a vacuum pump or the like to reduce the pressure inside the twin-screw extruder 100. For example, the degree of vacuum may be 100 kPa or less, preferably 80 kPa or less, and more preferably 60 kPa or less, in absolute pressure.

[0054] The molten mixture obtained by melt-kneading in the twin-screw extruder 100 is then metered by a gear pump (not shown) from the transport section 23 and transported to the spinning head. In order to prevent the molten mixture from being contaminated with foreign matter such as unmelted material, a filter may be provided before or after the gear pump after it has been transported from the twin-screw extruder 100. In the present invention, the amount of unmelted material remaining can be reduced by melt-kneading in the twin-screw extruder, making the filter less likely to clog and enabling stable spinning.

[0055] After being transported to the spinning head, the molten mixture is extruded through a nozzle at a predetermined spinning temperature, and the resulting yarn is wound up by a godet roller or the like to produce a raw spun yarn of melt-anisotropic aromatic polyester fiber. The spinning temperature (spinneret temperature) can be set, for example, at a temperature equal to or higher than the melting point Mp of the melt-anisotropic aromatic polyester. ０ In contrast, Mp ０ -30 to Mp ０ +60°C, preferably Mp ０ -25℃~Mp ０ +50°C, more preferably Mp ０ -20℃ to MPa ０ +45°C. The spinning temperature may be from the barrel temperature of the kneading section +10°C to the barrel temperature of the kneading section +120°C, preferably from the barrel temperature of the kneading section +15°C to the barrel temperature of the kneading section +100°C, more preferably from the barrel temperature of the kneading section +20°C to the barrel temperature of the kneading section +90°C, and even more preferably from the barrel temperature of the kneading section +30°C to the barrel temperature of the kneading section +80°C. When the spinning temperature (spinneret temperature) is equal to or lower than the above upper limit, resin deterioration near the spinneret can be suppressed, and poor processability due to yarn breakage and yellowing of the product are less likely to occur.

[0056] Perhaps because a more uniform microcrystalline structure is formed in the raw spun yarn, by subjecting the raw spun yarn to heat treatment, solid-state polymerization of the melt-anisotropic aromatic polyester proceeds, the melting point rises from the melting point (Mp) of the raw spun yarn, and the degree of orthorhombic crystallinity in the fiber after heat treatment can be increased. In the heat treatment step, the heat treatment method is not particularly limited, and may be, for example, a batch-type heat treatment or a continuous heat treatment by conveying. The melting point (Mp) of the raw spun yarn can be measured by the same method as the melting point of the melt-anisotropic aromatic polyester fiber.

[0057] For example, in a batchwise heat treatment, the material may be wound around a bobbin in a packaged state, or in a skein or tow state, and the heat treatment is preferably performed in a packaged state in terms of simplifying the equipment and improving productivity. The bobbin must be able to withstand the temperature of solid-state polymerization, and is preferably made of a metal such as aluminum, brass, iron, or stainless steel.

[0058] In the case of continuous heat treatment by conveyance, the conveyance method may be either contact conveyance (for example, a conveyor system, a support roll system, or a heat treatment system using heated rollers) or non-contact conveyance (a roll-to-roll system). The treatment path does not have to be straight, and heat treatment may be performed by appropriately changing the length, angle, curvature, etc. of the treatment path by arranging return rollers or guides within the device.

[0059] The heat treatment step can be carried out by a known method, such as atmospheric heating or contact heating. The atmosphere is preferably air, an inert gas (e.g., nitrogen, argon), or a combination thereof. The heat treatment may also be carried out under reduced pressure.

[0060] In the heat treatment step, the heat treatment temperature may be 250 to 350°C, preferably 255 to 320°C, more preferably 260 to 315°C, and more preferably 280 to 310°C. Furthermore, the heat treatment temperature may be lower than the melting point (Mp) of the raw spun yarn to be subjected to the heat treatment step in order to prevent melting. For example, within the range of 250 to 350°C, the heat treatment temperature may be Mp-50°C or higher and lower than Mp°C, preferably Mp-40°C or higher and lower than Mp°C, and more preferably Mp-30°C or higher and lower than Mp°C. In the heat treatment step, the melting point of the molten anisotropic aromatic polyester fiber increases as the solid-state polymerization proceeds. Therefore, the initial heat treatment temperature in the heat treatment step may be set lower than the melting point (Mp) of the raw spun yarn. From the viewpoint of efficient strength improvement, the heat treatment temperature may be increased stepwise in accordance with the progress of the solid-state polymerization, and the heat treatment may be performed at a temperature higher than the melting point (melting point of the raw spun yarn) at the time of subjecting the fiber to the heat treatment step.

[0061] The heat treatment time of the heat treatment step can be appropriately set depending on the heat treatment method and heat treatment temperature, and can be set, for example, within a range of 15 minutes to 30 hours, preferably 2 to 24 hours, and more preferably 3 to 20 hours. The heat treatment time here refers to the holding time at a predetermined heat treatment temperature (for example, the maximum temperature).

[0062] In the method for producing the melt-anisotropic aromatic polyester fiber of the present invention, for example, a known oil agent or anti-fusing agent may be applied before the heat treatment step in order to improve the bundling ability of the fiber or to prevent fusing during the heat treatment.

[0063] [Fiber Structure] The melt-anisotropic aromatic polyester fiber of the present invention can be used in various applications as a fiber structure containing at least a portion thereof. 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, short-cut fiber, filament yarn, spun yarn, string-like material, or rope. The melt-anisotropic aromatic polyester fiber can also be used as various fabrics, such as nonwoven fabrics, woven fabrics, and knitted fabrics. Such fibers and fabrics can be produced using the melt-anisotropic aromatic polyester fiber by known methods.

[0064] The fiber structure of the present invention may be formed by combining the melt-anisotropic aromatic polyester fiber with other fibers, as long as the effects of the present invention are not impaired. For example, a composite fiber using the melt-anisotropic aromatic polyester fiber and other fibers (e.g., a mixed yarn in which the melt-anisotropic aromatic polyester fiber is mixed with other fibers) can be used. Also, composite fabrics using the melt-anisotropic aromatic polyester fiber and other fibers (e.g., mixed fabrics in which the melt-anisotropic aromatic polyester fiber is mixed with other fibers, or laminates of fabrics made of the melt-anisotropic aromatic polyester fiber and fabrics made of other fibers) can be used.

[0065] The melt anisotropic aromatic polyester fiber of the present invention can be used in the form of various fiber structures for various applications, such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products. For example, it can be used in advanced processed products such as tension members (electric wires, optical fibers, umbilical cables, heater wire cores, earphone cords, and other electrical cords), sailcloth, ropes (marine, mountain climbing, crane, yacht, tag, and other), ropes, land nets, slings, lifelines, fishing lines, sewing threads, screen cords, fishing nets, longlines, geogrids, protective gloves, ripstop protective clothing and outdoor clothing, rider suits, sports rackets, guts, reinforcing materials for medical catheters, sutures, screen gauze, filters, base fabrics for printed circuit boards, mesh conveyor belts, papermaking belts, dryer canvas, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses and pipes, and reinforcing materials for rubber and plastic materials, such as tires and conveyor belts. In particular, the melt-dispersed anisotropic aromatic polyester fiber of the present invention has excellent creep properties and can therefore be suitably used as a tension member.

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by these examples. In the following examples and comparative examples, various physical properties were measured by the following methods.

[0067] (Melting Point of Resin Chips (Granular Molded Body) and Fibers) Measurement was performed using a differential scanning calorimeter (DSC; "DSC60A Plus" manufactured by Shimadzu Corporation) in accordance with JIS K 7121, and the observed main absorption peak temperature was taken as the melting point. Specifically, 4 to 6 mg of a sample was placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen was flowed as a carrier gas at a flow rate of 200 mL / min, and the endothermic peak derived from the molten anisotropic aromatic polyester was measured when the temperature was raised from 25°C at a rate of 10°C / min.

[0068] (Amount of pressure increase) 50 kg of molten anisotropic aromatic polyester melt-kneaded under each condition in a twin-screw extruder was transported to a container equipped with a metal nonwoven fabric filter having a diameter of 76 mm and a mesh size of 30 μm, and the pressure was monitored using a resin pressure meter GC75 manufactured by Nagano Keiki Co., Ltd. installed in the container, and the amount of pressure increase before and after passing through was recorded.

[0069] (Spinnability) A molten anisotropic aromatic polyester was extruded, and a spinning test was carried out for 3 days after winding was started. The number of times that yarn breakage occurred was counted and evaluated according to the following criteria: ⊚: Number of yarn breakages was 0 / day; ◯: Number of yarn breakages was more than 0 / day and less than 0.7 / day; △: Number of yarn breakages was 0.7 / day or more and less than 2.0 / day; ×: Number of yarn breakages was 2.0 / day or more.

[0070] (Degree of Orthorhombic Crystallization) A melt anisotropic aromatic polyester fiber was mounted on a fiber-specific holder, and wide-angle X-ray diffraction (WAXD) measurement was performed by irradiating X-rays perpendicular to the fiber axis using a transmission method under the following measurement conditions: Measurement device: Bruker "D8 Discover IμS" Detector: 2D PSPC VANTEC-500 X-ray source: Cu Current: 1 mA Voltage: 50 kV Exposure time: 10 minutes Collimator diameter: 0.5 mm Camera length: 17 cm Detector position (2θ): 20° Sample position (ω): 10° Inclination angle (Ψ): 90° Measurement temperature: Room temperature (approximately 25°C)

[0071] An X-ray diffraction profile was obtained under the following conditions, with the horizontal axis representing the diffraction angle (2θ) and the vertical axis representing the intensity: Integration range: 2θ = 5 to 35°, γ (azimuth angle) = 250 to 290°, Step width: 0.05° (diffraction angle).

[0072] In the obtained X-ray diffraction profile, a baseline was set by connecting the values ​​at 2θ = 5° and 35° with a straight line. Based on this newly set baseline, the difference in intensity on the vertical axis from the actual measurement data to the baseline was converted into profile data with a new intensity.

[0073] The baseline-corrected profile data was fitted with a pseudo-Voigt function (a ratio of the Lorentzian function: α = 0) to fit the amorphous peak, with the peak height, peak top position, σ, and asymmetry parameter as variables. 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 amorphous amount (D).

[0074] For Peak A (peak top position near 19°), Peak B (peak top position near 20.5°), and Peak C (peak top position near 27°) of the baseline-corrected profile data, the crystal peaks were fitted using the following functions, with the peak height, peak top position, and σ as variables. All crystal peaks were assumed to be symmetric. Peak A: Pseudo Voigt function (α=1) Peak B: Pseudo Voigt function (α=0) Peak C: Pseudo Voigt function (α=0.5)

[0075] Then, fitting was performed by the least squares method so that the difference between the sum of all fitting functions, including the fitting function for the amorphous peak obtained above, and the profile data after baseline correction was minimized. The peak areas of these fitting functions were calculated as the amounts of crystallinity (A), (B), and (C), respectively.

[0076] The degree of orthorhombic crystallinity was calculated from the following formula using the crystal amount (A) of peak A derived from hexagonal crystals and the crystal amount (B) of peak B derived from orthorhombic crystals: degree of orthorhombic crystallinity (%) = (B) / {(A) + (B)} × 100

[0077] (Fiber Density) Density was measured with reference to the density gradient tube method (JIS L 1013:2010 8.17.2). In order to compare slight density differences due to differences in fiber packing caused by orthorhombic crystallization, each sample was measured five times, and the average value was rounded to four decimal places to calculate the density.

[0078] (Total fineness, single fiber fineness) Based on JIS L 1013:2010 8.3.1 A method, a 10 m reel of melt-anisotropic aromatic polyester fiber was taken using a measuring instrument "Wrap Reel by Motor Driven" manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd., and its weight (g) was multiplied by 1000 to perform measurements three times per level, and the average value of the three measurements was taken as the total fineness (dtex) of the obtained melt-anisotropic aromatic polyester fiber. In addition, the quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

[0079] (Tensile strength) With reference to JIS L 1013:2010 8.5.1, a tensile test was carried out five times for each sample using a strength and elongation tester "TENSORAPID5" manufactured by USTER Technologies under the conditions of a test length of 30 cm, a tensile speed of 15 cm / min, and an initial load of 0.33 g / dtex, and the average tensile strength (cN) of the five times was divided by the total fineness (dtex) measured by the above-mentioned method to calculate the tensile strength (cN / dtex).

[0080] (Creep properties) Using a creep tester "525-R CREAP TESTER" manufactured by Mize Testing Instruments Co., Ltd., measurement was started at a measurement temperature of 20° C. when a load of 0.18 N / dtex was applied to a fiber having a test length of 300 mm, and the time until the fiber broke was measured. Measurement was performed three times per sample, and the average value was calculated.

[0081] Example 1 A melt-polymerized anisotropic aromatic polyester (Mp ０ The chips (granular molded body) were dried with hot air at 120°C for 4 hours or more. Thereafter, the void volume in the barrel of the kneading section was reduced to 14.7 cm ３The mixture was fed into a twin-screw extruder, and melt-kneaded at a barrel temperature of 260°C from the resin feed section to the kneading section outlet and 325°C in the transport section downstream of the kneading section outlet. The residence time in the kneading section was adjusted to 21 seconds. A vacuum pump was connected to a vent section midway through the twin-screw extruder via a metal pipe, and the polymer-unfilled space in the twin-screw extruder was decompressed to 30 kPa. The molten mixture was then fed from the twin-screw extruder to a spinning head while being metered using a gear pump. The spinning head was equipped with a spinneret with a hole diameter of 0.10 mmφ and 100 holes, the spinneret temperature was set to 320°C, and the volumetric output was 42.0 cm ３ The molten mixture was extruded at a rate of 1 / min to obtain a raw spinning yarn of 560 dtex / 100 f. The obtained raw spinning yarn was then heat-treated at 275°C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of melt-anisotropic aromatic polyester fiber. The analysis results of the obtained melt-anisotropic aromatic polyester fiber are shown in Table 5.

[0082] [Example 2] The volume of the void in the barrel of the kneading section was 44.1 cm ３ The barrel temperature from the resin feed section to the kneading section outlet was 240°C, and the volumetric discharge rate was 126.1 cm ３ / min and the number of holes in the spinneret was 300, the same procedure as in Example 1 was repeated to obtain melt-anisotropic aromatic polyester fibers.

[0083] Example 3 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 220°C.

[0084] Example 4 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 200°C.

[0085] [Example 5] The void volume in the barrel of the kneading section was set to 29.4 cm ３ The barrel temperature from the resin feed section to the kneading section outlet was 230°C, and the volumetric discharge rate was 30.2 cm ３ A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the flow rate was changed to 1 / min and the residence time in the kneading zone was changed to 58.5 seconds.

[0086] [Example 6] The barrel temperature from the resin feed section to the kneading section outlet was set to 250°C, and the volumetric discharge rate was set to 7.0 cm ３ The same procedure as in Example 1 was carried out except that the flow rate was changed to 1 / min, the residence time in the kneading zone was changed to 126 seconds, and the number of holes in the spinneret was changed to 10, to obtain melt-anisotropic aromatic polyester fibers.

[0087] [Example 7] The barrel temperature from the resin feed section to the kneading section outlet was 230°C, and the volumetric discharge rate was 58.8 cm ３ A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the flow rate was changed to 1 / min and the residence time in the kneading zone was changed to 15 seconds.

[0088] Example 8: Volumetric discharge rate: 96.9 cm ３ A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the flow rate was changed to 1 / min and the residence time in the kneading zone was changed to 9.1 seconds.

[0089] Example 9 A melt-polymerized anisotropic aromatic polyester (Mp ０ The chips (granular molded body) were dried with hot air at 120°C for 4 hours or more. Thereafter, the void volume in the barrel of the kneading section was reduced to 14.7 cm ３ The mixture was fed into a twin-screw extruder, and melt-kneaded at a barrel temperature of 270°C from the resin feed section to the kneading section outlet and 340°C in the transport section downstream of the kneading section outlet. The residence time in the kneading section was adjusted to 21 seconds. A vacuum pump was connected to a vent section midway through the twin-screw extruder via a metal pipe, and the polymer-unfilled space in the twin-screw extruder was decompressed to 30 kPa. The molten mixture was then fed from the twin-screw extruder to a spinning head while being metered using a gear pump. The spinning head was equipped with a spinneret with a hole diameter of 0.10 mmφ and 100 holes, the spinneret temperature was set to 340°C, and the volumetric output was 42.0 cm ３ The molten mixture was extruded at a rate of 1 / min to obtain a raw spinning yarn of 560 dtex / 100 f. The raw spinning yarn was then heat-treated at 280°C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of melt-anisotropic aromatic polyester fiber.

[0090] Comparative Example 1 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that a φ50 mm single-screw extruder without a vent was used and the barrel temperature excluding the resin feed section was set to 320°C.

[0091] Comparative Example 2 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 300°C.

[0092] Comparative Example 3 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 285°C.

[0093] Comparative Example 4 A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 9, except that a φ50 mm single-screw extruder without a vent was used and the barrel temperature excluding the resin feed section was set to 350°C.

[0094]

[0095] As shown in Table 5, in Examples 1 to 9, melt-kneading was performed under specific low barrel temperatures from the resin feed section to the kneading section outlet of the twin-screw extruder, so that melt-anisotropic aromatic polyester fibers with a high degree of orthorhombic crystallization could be obtained. Therefore, the melt-anisotropic aromatic polyester fibers of Examples 1 to 9 have excellent creep properties.

[0096] On the other hand, in Comparative Examples 1 and 4, a single-screw extruder was used, and the barrel temperature from the resin feed section to the kneading section outlet was high, so the degree of orthorhombic crystallization could not be increased. Also, in Comparative Examples 2 and 3, a twin-screw extruder was used, but the barrel temperature from the resin feed section to the kneading section outlet was high, so the degree of orthorhombic crystallization could not be increased. Therefore, the melt-anisotropic aromatic polyester fibers of Comparative Examples 1 to 4 were inferior in creep properties to those of Examples 1 to 9.

[0097] The melt-dispersible aromatic 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 various textile products, and can be used, for example, as a tension member.

[0098] As described above, a preferred embodiment of the present invention has been described with reference to the drawings, but various additions, modifications, or deletions can be made without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention.

[0099] 100: Twin-screw extruder 11: Hopper 12: Barrel 13: Screw 13a, 13b, 13c: Screw element 14: Vent 21: Resin feed section 22: Kneading section 23: Transport section X: Flow direction

Claims

1. A melt-anisotropic aromatic polyester fiber having an orthorhombic crystallinity of 15.0% or more in the crystalline component.

2. The melt-anisotropic aromatic polyester fiber according to claim 1, having a density of 1.4080 g / cm3 as determined by a density gradient tube. ３ The above melt-melted anisotropic aromatic polyester fiber.

3. A 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, which has a melting point of 260 to 380°C as measured by a differential scanning calorimeter in a nitrogen atmosphere at a heating rate of 10°C / min.

5. A fiber structure comprising at least a portion of the melt-dispersed anisotropic aromatic polyester fiber according to claim 1 or 2.

6. The melting point Mp of the melt-dispersed anisotropic aromatic polyester measured by a differential scanning calorimeter in a nitrogen atmosphere at a heating rate of 10°C / min. ０ When a twin-screw extruder is used, the barrel temperature from the resin feed section to the kneading section outlet is set to the melting point Mp ０ a step of melt-kneading a melt-anisotropic aromatic polyester at a temperature of less than 1000°C; a step of spinning the melt-kneaded mixture to obtain a raw spun yarn; and a step of heat-treating the obtained raw spun yarn.

7. A method for producing melt-kneaded anisotropic aromatic polyester fibers according to claim 6, wherein the melt-kneading is carried out under conditions where the residence time in the kneading section of the twin-screw extruder is 10 seconds or more.