Liquid crystal polyester fiber and its manufacturing method

Abstract

The objective of this invention is to obtain a liquid crystal polyester fiber that improves weather resistance even without incorporating ultraviolet absorbers into the fiber or attaching weather-resistant ultraviolet absorbers after spinning. The liquid crystal polyester fiber of this invention is essentially composed solely of liquid crystal polyester, uses less than 5% by mass of ultraviolet absorbers, and exhibits a strength retention rate of over 60% in the JIS L 0891 xenon arc lamp weathering fastness test.

Description

Technical Field

[0001] This invention relates to a liquid crystal polyester fiber and its manufacturing method. Prior Technology

[0002] As a high-strength polyester fiber, liquid crystal polyester fibers composed of aromatic dicarboxylic acids, aromatic diphenols and / or aromatic hydroxycarboxylic acids, and their derivatives are commonly used. For example, liquid crystal polyester fibers can be obtained by melt spinning and fiberizing a liquid crystal polyester polymer containing p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, followed by heat treatment for solid-state polymerization.

[0003] It is known that this type of liquid crystal polyester fiber has poor weather resistance compared to ordinary polyester fiber and is not suitable for use in outdoor or other light-exposed environments. Therefore, when used outdoors, it is usually designed to avoid exposure to ultraviolet rays by covering the fibers with highly weather-resistant fibers or by using weather-resistant agents to cover the outer side of the fibers.

[0004] For example, Patent Document 1 discloses a method in which a resin composition liquid containing carbon black and ultraviolet absorber is applied to molten anisotropic polyester fiber by dip-Nip method, and then a resin that is substantially free of additives is coated and applied. Patent document 2 discloses a melt anisotropic aromatic polyester fiber containing 0.5 to 10 wt% of ultraviolet absorber in the fiber. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-287680 [Patent Document 2] Japanese Patent Application Publication No. 2015-175075 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] However, in Patent Document 1, although the weather resistance is improved, the UV absorber is attached in subsequent steps, which makes it easy for the absorber to fall off due to repeated use, thus making it impossible to predict the durability. In Patent Document 2, the fiber is mixed with an ultraviolet absorber, which results in a decrease in fiber strength.

[0008] Therefore, the purpose of this invention is to solve the problems mentioned above and obtain a liquid crystal polyester fiber that can improve weather resistance even without mixing a large amount of ultraviolet absorber into the fiber or attaching a weather-resistant ultraviolet absorber after the fiber is spun. [Technical means to solve the problem]

[0009] To achieve the above objectives, the inventors studied the resin composition and the fiber manufacturing method, thereby completing this invention. This invention relates to a liquid crystal polyester fiber, which is a fiber composed of liquid crystal polyester, wherein the amount of ultraviolet absorber used is less than 5% by mass, and the strength retention rate in the xenon arc lamp weathering fastness test of JIS L 0891 is more than 60%.

[0010] The inter-fiber interweaving degree of the aforementioned liquid crystal polyester fiber is preferably below 10. The total fineness of the aforementioned liquid crystal polyester fiber is preferably below 600 dtex. The preferred fineness of the monofilament of the aforementioned liquid crystal polyester fiber is below 25 dtex. The liquid crystal polyester fiber mentioned above is preferably obtained by solid-phase polymerization of liquid crystal polyester fiber that does not melt on the surface after being exposed to 250°C for 1 hour.

[0011] The aforementioned liquid crystal polyester is preferably a copolyester composed of 6-hydroxy-2-naphthoic acid, terephthalic acid, hydroquinone and 2,6-naphthoic acid.

[0012] The present invention is also a method for manufacturing liquid crystal polyester fiber as described above, characterized by comprising: step (1), wherein liquid crystal polyester resin is melt-spun at a shearing speed of 1×10 4~1×10 6 sec -1 and a spinning draft of 5~50; and step (2), wherein the fiber obtained by step (1) is heat-treated at the melting point of the liquid crystal polyester resin of -60℃~10℃ to solid-state polymerization.

[0013] The above step (1) is preferably to wind the spun fibers obtained by spinning onto the first spool and wind the wound spun fibers onto the second spool for step (2). [Effects of the Invention]

[0014] According to the present invention, a liquid crystal polyester fiber with high strength and long-term weather resistance can be obtained. Simple Explanation of the Diagram

[0015] none Implementation

[0016] The present invention will now be described in detail. The liquid crystal polyester fiber of this invention has the following characteristics: the content of ultraviolet absorber is less than 5% by mass, and the strength retention rate in the xenon arc lamp weathering fastness test according to JIS L 0891 is more than 60%. That is, it has the following characteristics: even with reduced use of ultraviolet absorber to improve weather resistance or with no ultraviolet absorber used at all, it still exhibits excellent weather resistance. Therefore, liquid crystal polyester fibers with stable properties over a long period can be produced without the various problems that arise from the use of large amounts of ultraviolet absorber.

[0017] To achieve this objective, the selection of the liquid crystal polyester resin used and the manufacturing conditions of the fiber are appropriately adjusted.

[0018] <Liquid Crystal Polyester Resin> The liquid crystal polyester fiber of the present invention is composed of aromatic dicarboxylic acids, aromatic diphenols and / or aromatic hydroxycarboxylic acids, and their derivatives, and may also contain copolymers of these with alicyclic dicarboxylic acids, alicyclic diols, aliphatic diols, and their derivatives, depending on the circumstances. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, 4,4'-dicarboxybiphenyl, 2,6-naphthalenedicarboxylic acid, 1,2-bis(4-carboxyphenoxy)ethane, and others, obtained by substituting the hydrogen in the aromatic ring of these compounds with alkyl, aryl, alkoxy, or halogen groups. Examples of aromatic diphenols include hydroquinone, resorcinol, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxybenzophenone, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylethane, 2,2-bis(4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl sulfide, 2,6-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, and others, obtained by substituting the hydrogen in their aromatic rings with alkyl, aryl, alkoxy, or halogen groups. Examples of aromatic hydroxycarboxylic acids include p-hydroxybenzoic acid, m-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 1-hydroxynaphthalene-5-carboxylic acid, and others, obtained by substituting the hydrogen in their aromatic rings with alkyl, aryl, alkoxy, or halogen groups. Examples of alicyclic dicarboxylic acids include trans-1,4-dicarboxycyclohexane, cis-1,4-dicarboxycyclohexane, and those obtained by substituting the hydrogen atoms in their aromatic rings with alkyl, aryl, alkoxy, or halogen groups. Examples of alicyclic and aliphatic diols include trans-1,4-dihydroxycyclohexane, cis-1,4-dihydroxycyclohexane, ethylene glycol, 1,4-butanediol, and benzenediethanol.

[0019] Among the combinations thereof, the preferred aromatic polyesters in this invention include, for example, copolyesters composed of 6-hydroxy-2-naphthoic acid, terephthalic acid, hydroquinone, and 2,6-naphthoic acid. The preferred composition is a copolyester consisting of 50-70 mol% 6-hydroxy-2-naphthoic acid, 5-7 mol% terephthalic acid, 10-30 mol% hydroquinone, and 15-25 mol% 2,6-naphthoic acid.

[0020] In the liquid crystal polyester fiber of the present invention, the amount of ultraviolet absorber used is 5% by mass or less relative to the fiber mass. That is, even with a small amount of ultraviolet absorber used, sufficient weather resistance is achieved. Therefore, the amount of ultraviolet absorber used can also be 0% by mass. More preferably, the amount of ultraviolet absorber used is 3% by mass or less, and even more preferably 2% by mass or less.

[0021] The aforementioned ultraviolet absorbers refer to those commonly used in the fiber industry, such as benzophenone-based, benzotriazole-based, or titanium dioxide and cerium oxide-based ultraviolet absorbers.

[0022] The content of the aforementioned ultraviolet absorbers can be determined using known methods, depending on the type of ultraviolet absorber. For example, in the case of inorganic ultraviolet absorbers such as titanium dioxide and cerium oxide, it can be determined by ICP.

[0023] When the liquid crystal polyester fiber of the present invention contains an ultraviolet absorber, the ultraviolet absorber can be mixed into the fiber or attached to the surface of the liquid crystal polyester fiber.

[0024] The liquid crystal polyester fiber of the present invention is preferably composed of substantially only the aforementioned liquid crystal polyester resin. Specifically, "substantially composed of substantially only liquid crystal polyester resin" means that the content of liquid crystal polyester resin relative to the total fiber mass is 95% or more, and that no other resins or additives are actively added. Furthermore, regarding the oils and other agents used in the fiber manufacturing process, since they are not actively added, the liquid crystal polyester fiber to which these are attached is included in the category of "substantially composed of substantially only liquid crystal polyester resin".

[0025] The liquid crystal polyester fiber of this invention is a liquid crystal polyester fiber that retains more than 60% of its strength in the xenon arc lamp weathering fastness test according to JIS L 0891. Furthermore, in the tests described in this specification, the weathering fastness test results according to JIS L 0891 were obtained under the conditions described in the examples. That is, because it is a fiber with weather resistance that meets the above standards, it can be better used in applications such as heater line tension components, ropes, and fishing lines, where durability is especially required in harsh operating environments.

[0026] The strength retention rate of the liquid crystal polyester fiber of the present invention is preferably 70% or more.

[0027] The inter-fiber interweaving degree of the liquid crystal polyester fiber of the present invention is preferably below 10. The method for determining the inter-fiber interlacing degree is as follows: According to JIS L 1013 interlacing degree determination method, a 100 g load is suspended below the fiber, allowing the fiber to hang vertically. A hook with a 10 g load is inserted above the fiber. The interlacing degree between the fibers is calculated using the following formula, based on the distance (mm) the hook descends before stopping due to the interlacing of the fibers. Fifty measurements are performed, and the average value is taken as the inter-fiber interlacing degree. Interweaving degree between single fibers = 1000 / hook descent distance (mm)

[0028] The interweaving between individual fibers occurs because the heat during solid-state polymerization softens the fiber surface, causing the fibers to fuse together. The resulting interweaving not only reduces softness and knot strength, but also leads to fibrillation when the fibers are rewound from the point of fusion after solid-state polymerization in a spool, further degrading quality. Therefore, the interweaving between individual fibers is preferably set at the lower value described above.

[0029] The liquid crystal polyester fiber of the present invention preferably exhibits a strength of 20 cN / dtex or higher under constant elongation conditions as shown in the JIS L 1013 (2010) 8.5.1 standard test. More preferably, it is 24 cN / dtex or higher, and most preferably 28 cN / dtex or higher. As mentioned above, the strength of liquid crystal polyester fibers containing ultraviolet absorbers may sometimes decrease. However, an important characteristic of liquid crystal polyester fibers is their excellent strength; therefore, it is preferable that the strength does not decrease. The liquid crystal polyester fiber of the present invention preferably does not use ultraviolet absorbers, or even when ultraviolet absorbers are used, the blending amount is set to meet the above-mentioned strength range.

[0030] Liquid crystal polyester fibers are generally used in applications requiring high strength, and therefore, it is desirable for them to possess the aforementioned strength. Furthermore, the liquid crystal polyester fiber of this invention also exhibits excellent performance in terms of weather resistance, minimal interfilament fusion, and strength.

[0031] The elongation of the liquid crystal polyester fiber of the present invention, measured under constant elongation conditions as shown in JIS L 1013(2010) 8.5.1 standard test, is preferably 2~5%.

[0032] The liquid crystal polyester fiber of this invention can be a monofilament or a multifilament, but is more preferably a multifilament. Its fiber composition is not particularly limited, but the total fineness is preferably 600 dtex or less. Furthermore, the monofilament fineness is preferably 25 tex or less. By setting it within the above range, it can be better used in various industrial materials, and therefore is better.

[0033] The total fineness is preferably 400 dtex or less, and more preferably 300 dtex or less. The monofilament fineness is preferably 10 dtex or less, and more preferably 5 dtex or less.

[0034] The lower limit of the total fineness is not particularly limited, but is preferably 4 dtex. More preferably, the lower limit of the total fineness is 10 dtex.

[0035] The aforementioned monofilament fineness is preferably below 4 dtex, and more preferably below 2 dtex.

[0036] The liquid crystal polyester fiber of the present invention is preferably manufactured to have the total fineness and monofilament fineness as described above, so that it can be better used in various industrial materials.

[0037] The weight-average molecular weight (Mw) of the liquid crystal polyester resin used in this invention, converted from polystyrene, is preferably 30,000 or more, and more preferably 50,000 or more. By setting Mw to 30,000 or more, an appropriate viscosity is achieved at the spinning temperature, which improves fiber-forming properties. The higher the Mw, the higher the strength, elongation, and modulus of elasticity of the obtained fiber. Furthermore, from the viewpoint of achieving excellent flowability, Mw is preferably less than 250,000, and more preferably less than 150,000. Moreover, the Mw mentioned in this invention refers to the value obtained by the method described in the embodiments.

[0038] Regarding ease of melt spinning and heat resistance, the melting point of the liquid crystal polyester of the present invention is preferably in the range of 200~380°C, more preferably 250~350°C, and even more preferably 290~340°C. Furthermore, regarding the melting point, in differential calorimetry measurements using a differential scanning calorimeter (DSC manufactured by PerkinElmer), the temperature was increased from 50°C at a rate of 20°C / min. After observing the endothermic peak temperature (Tm1), the temperature was maintained at approximately Tm1+20°C for 5 minutes, and then cooled to 50°C at a rate of 20°C / min. The temperature was then increased again at a rate of 20°C / min, and the observed endothermic peak temperature (Tm2) was taken as the melting point.

[0039] The manufacturing method of the liquid crystal polyester fiber of the present invention is not particularly limited, as long as the liquid crystal polyester fiber with the above-mentioned properties can be obtained. Fibers that meet the above parameters can be produced by adjusting the composition of the resin used and the manufacturing method. Specifically, it can be manufactured, for example, by the following manufacturing method. The manufacturing method detailed below is also part of this invention.

[0040] The method for manufacturing liquid crystal polyester fiber of the present invention is characterized by having: Step (1) involves melt spinning liquid crystal polyester resin at a shearing speed of 1×10⁴~1×10⁶ sec⁻¹ and a spinning draw ratio of 5~50; and Step (2) involves heat-treating the fibers obtained in step (1) at a melting point of -60°C to -10°C to achieve solid-state polymerization.

[0041] That is, the feature is that: melt spinning with the specific shear rate and spinning draw ratio as described above is carried out, and heating is performed within a specific temperature range during solid-state polymerization using heat treatment.

[0042] The above step (1) can be performed according to the general method for manufacturing liquid crystal polyester fibers. The following is a detailed description of an example of the manufacturing method of this type of liquid crystal polyester fiber. When extruding resin, an extruder-type extruder is preferred. The extruded polymer is metered using a metering device and, if necessary, passed through one or more foreign matter removal filters before being guided to the spinning nozzle. The foreign matter removal filters are preferably metal nonwoven filters. Furthermore, the filters used are preferably a combination of filters with mesh sizes of 1 to 100 μm. Moreover, it is preferable to use a filter with a finer mesh on the downstream side. The mesh size of the downstream filter is preferably less than half that of the upstream filter, and more preferably less than one-fifth.

[0043] At this point, the temperature from the polymer piping to the spinning nozzle (spinning temperature) is preferably set above the melting point of the liquid crystal polyester and below its thermal decomposition temperature, more preferably above the melting point of the liquid crystal polyester +10°C and below 400°C, and even more preferably above the melting point of the liquid crystal polyester +20°C and below 370°C. Furthermore, the temperature from the polymer piping to the spinning nozzle can also be adjusted independently. In this case, by setting the temperature of the part near the spinning nozzle higher than the temperature upstream of it, the ejection is stabilized.

[0044] In step (1) above, the shear rate is preferably in the range of 1×10⁴ to 1×10⁶ sec⁻¹. Within this range, uneven alignment of molecular chains is less likely to occur, resulting in stable fiber strength, which is preferable. More preferably, it is 5×10⁴ to 4×10⁵ sec⁻¹. Furthermore, in this specification, the shear rate (sec⁻¹) is calculated using the following formula. Shear rate = 4Q / πr 3 (Where, r is the radius of the nozzle orifice (cm), and Q is the polymer ejection rate per orifice (cm³ / sec)) If it falls within the above range, there is a tendency for the fibers to be sufficiently oriented, making it easy to obtain fine fibers and to achieve the desired physical properties.

[0045] In step (1) above, the spinning draw ratio is between 5 and 50. If the spinning draw ratio is less than 5, uneven fiber diameter is likely to occur. If the spinning draw ratio exceeds 50, the fiber cannot withstand the draw ratio and is prone to breakage, which is therefore less desirable. Furthermore, the aforementioned spinning draw ratio is defined as the quotient obtained by dividing the winding speed by the ejection linear speed.

[0046] In this invention, the liquid crystal polyester fiber before solid-state polymerization preferably does not melt on the surface after being treated at 250°C for 1 hour. "Does not melt on the surface after being treated at 250°C for 1 hour" means that after treating the liquid crystal polyester fiber before solid-state polymerization at 250°C for 1 hour in a nitrogen atmosphere, when the fiber bundle is divided into two parts, fibrillation caused by the fusion of monofilaments does not occur. Therefore, there is very little fusion between monofilaments after solid-state polymerization. To produce liquid crystal polyester fibers that meet these parameters, it is preferable to slowly apply shear stress during the spinning and melting process until it is extruded from the spinning nozzle.

[0047] In step (1) of the method for manufacturing liquid crystal polyester fiber of the present invention, it is preferable to apply the shearing speed slowly. In fiber spinning, pressure is applied to flowing resin, forcing it out of the spinning nozzle to form a fiber shape. In this invention, it is preferable to gradually increase the shear rate rather than rapidly apply it. That is, it is preferable to gradually increase the shear rate by adjusting the shape and diameter of the piping, the number of filters, and the fineness of their mesh, rather than drastically increasing the shear rate. This allows the resin to maintain sufficient orientation even in the molten state, and melt spinning is performed in this state. Therefore, the resulting fibers also have relatively high orientation before solid-state polymerization. Consequently, due to the higher orientation, the fiber properties are also better.

[0048] Furthermore, even when subsequent solid-state polymerization is carried out at relatively low temperatures (e.g., the melting point of the liquid crystal polyester resin used as a raw material is below -10°C, more preferably below -15°C, and even more preferably below -20°C), liquid crystal polyester fibers with sufficient strength can be obtained. The liquid crystal polyester fibers obtained by this method have excellent fiber strength and weather resistance, and are less prone to interfiber fusion.

[0049] The diameter of the spinneret orifice is preferably between 0.05 mm and 0.2 mm. As described above, in order to enable solid-state polymerization at low temperatures and to gradually increase the shear rate, this type of spinneret orifice diameter is preferred. The lower limit is more preferably 0.1 mm, and more preferably 0.07 mm. The upper limit is more preferably 0.15 mm, and more preferably 0.1 mm.

[0050] Furthermore, in order to improve the productivity of multifilament spinning, the number of holes in one spinning nozzle is preferably more than 2 holes and less than 1,000 holes, more preferably more than 5 holes and less than 500 holes, and even more preferably more than 10 holes and less than 200 holes.

[0051] The polymer ejected from the self-spinning nozzle is cured by passing through an insulated zone and a cooling zone, and then wound up using a roller (guide roller) rotating at a certain speed. Since the yarn-forming properties deteriorate if the insulated zone is too long, it is preferably set to 400 mm from the surface of the self-spinning nozzle, more preferably to 300 mm, and even more preferably to 200 mm. The insulated zone can also be heated to increase the ambient temperature, preferably within a range of 100°C to 500°C, more preferably 200°C to 400°C. Cooling can be achieved using inert gases, air, water vapor, etc.; to reduce environmental impact, parallel or annular airflow is preferred.

[0052] To improve productivity, the take-up speed is preferably 50 m / min or higher, more preferably 300 m / min or higher, and even more preferably 500 m / min or higher. Since the liquid crystal polyester used in this invention has excellent spinnability at spinning temperatures, the take-up speed can be set to a high speed. There is no particular upper limit; regarding the liquid crystal polyester used in this invention, in terms of spinnability, it is approximately 3,000 m / min.

[0053] In this invention, from the viewpoint of improving spinning performance and productivity, in order to obtain the aforementioned spinning draw ratio, it is preferable to set the polymer ejection rate to 10-2,000 g / min, more preferably 30-1,000 g / min, and even more preferably 50-500 g / min. By setting it to 10-2,000 g / min, liquid crystal polyester with good spinning performance can be obtained.

[0054] Take-up can be achieved using a known take-up machine to form packages in shapes such as cheese, pirn, and cone, preferably in the form of cheese packages with a higher take-up weight. During take-up, to reduce frictional resistance with the guide plate and rollers, various oils can be applied using oiling rollers and oiling nozzles.

[0055] To further improve strength and modulus of elasticity, the liquid crystal polyester fibers obtained in this manner are preferably subjected to solid-state polymerization in step (2). Solid-state polymerization can be carried out in roll form, spool form, tow form (e.g., placed on a metal mesh), or continuously in the form of filaments between rollers. From the viewpoint of simplifying equipment and improving productivity, it is preferred to carry out the process in roll form.

[0056] The manufacturing method of the liquid crystal polyester fiber of the present invention is more preferably to take the first spool of the spun fiber obtained by spinning in step (1) and wind the spun fiber onto the second spool for step (2). In this way, by rewinding the first spool after spinning to the second spool, the winding density can be reduced, making the solid-phase polymerization reaction easier to carry out, thus achieving better results.

[0057] Solid-phase polymerization can be carried out in inert gas environments such as nitrogen, oxygen-containing reactive gas environments such as air, or under reduced pressure. However, to simplify equipment and prevent oxidation of fibers or adhering substances, it is preferable to carry out the polymerization in a nitrogen environment. In this case, the environment for solid-phase polymerization is preferably a low-humidity gas with a dew point below -40°C.

[0058] The optimal solid-state polymerization temperature is above -60°C of the melting point of the liquid crystal polyester resin used as raw material. By setting a high temperature near this melting point, solid-state polymerization can be carried out rapidly. The solid-state polymerization temperature can be increased to around -15°C or -10°C of the melting point of the liquid crystal polyester fiber supplied for solid-state polymerization. If this range is exceeded, the monofilament fibers will fuse together during the heating process, resulting in fiber adhesion. Furthermore, gradually or continuously increasing the solid-state polymerization temperature over time can prevent fusion and improve the time efficiency of solid-state polymerization, which is preferable. In this case, solid-state polymerization can proceed from several minutes to tens of hours depending on the target properties. To obtain fibers with excellent strength and elastic modulus, it is preferable to proceed at the maximum limiting temperature (solid-state polymerization temperature) for more than 5 hours, and more preferably for more than 10 hours. Also, since the solid-state polymerization reaction will saturate over time, approximately 100 hours is sufficient.

[0059] The packaged product after solid-state polymerization can be supplied directly as a finished product. However, to improve the efficiency of product transportation, it is preferable to rewind the packaged product after solid-state polymerization to increase the winding density. During the rewinding of the packaged product after solid-state polymerization, in order to prevent deformation of the packaged product caused by unwinding and to suppress fibrillation during slight fusion peeling, it is preferable to rotate the packaged product and simultaneously unwind the filaments in a direction perpendicular to the axis of rotation (the direction around the fiber), i.e., lateral unwinding. Furthermore, the rotation of the packaged product is preferably achieved by active drive rather than free rotation.

[0060] Furthermore, the liquid crystal polyester fiber in this invention can be applied to various finishing oils for a visible purpose.

[0061] The liquid crystal polyester multifilament of this invention can be used not only as a multifilament, but also, for example, by splitting it into monofilaments, and is also preferably used as a short fiber, cut fiber, etc. Furthermore, it can also be used as a fiber structure such as woven fabrics, knitted fabrics, non-woven fabrics, and braided tapes.

[0062] Regarding the liquid crystal polyester fiber of this invention, as a specific application of the liquid crystal polyester multifilament of this invention, it can be widely used in general industrial materials, civil and building materials, sports applications, protective clothing, rubber reinforcement materials, electrical materials (especially as tension members), audio materials, and general clothing. As effective applications, it can be used in mesh, filters, ropes, nets, fishing nets, computer ribbons, printing substrate base fabrics, papermaking canvas, airbags, airships, tent base fabrics, riding clothing, fishing lines, various lines (sailboat, paraglider, balloon, kite lines), curtain cords, screen support ropes, various ropes in automobiles or airplanes, and power transmission ropes for electrical products or robots. In particular, it is especially suitable for applications such as heater wire tension members, ropes, and fishing lines. [Example]

[0063] The present invention will now be described in detail with reference to specific embodiments. However, the present invention is not limited to the embodiments described below. The evaluation of the physical properties in the embodiments is carried out in the following manner.

[0064] 1) Tensile test (strength, elongation, modulus of elasticity) According to JIS L 1013 (2010), using an Orientec RTA-100 tensile testing machine, 10 tests were performed with a specimen length of 200 mm and a tensile speed of 200 mm / min, and the average value was expressed.

[0065] 2) Weather resistance evaluation According to JIS L 0891, a xenon weathering tester (model: XEL-1WN) manufactured by Suga Test Instruments Co., Ltd. was used to irradiate the heat-treated filament for 60 hours under the conditions of irradiation density of 150 W / m² (300~400 nm), black panel temperature of 63°C, and humidity of 50%RH in the test chamber to conduct a lightfastness test. The strength retention rate was calculated based on the strength before and after irradiation. Furthermore, the strength here is measured using the method described in the tensile test above. Regarding the strength retention rate, 60% or more is marked as ○, 30% or more but less than 60% is marked as △, and less than 30% is marked as ×. Intensity retention rate = (Intensity after irradiation / Intensity before irradiation) × 100

[0066] 3) Inter-fiber cross-linking According to the JIS L 1013 method for determining interlacing degree, a 100 g load is suspended below the fiber, allowing the filament to hang vertically. A hook with a 10 g load is inserted above the filament. The interlacing degree between individual fibers is calculated using the following formula, based on the distance (mm) the hook descends before stopping due to the interlacing of the filaments. Fifty measurements are performed, and the average value is taken as the interlacing degree. Inter-fiber interlacing degree = 1000 / hook descent distance

[0067] [Example 1] As an aromatic polyester, an aromatic polyester is used, which is polymerized by polymerizing 55 moles of 6-hydroxy-2-naphthoic acid, 5.5 moles of terephthalic acid, 22.5 moles of hydroquinone, and 17 moles of 2,6-naphthoic acid. The resin has a melting point of 320°C. The resin was dried in a vacuum dryer at 140°C for 24 hours to achieve a moisture content of 10 ppm. Then, it was melt-extruded using a 25 mm diameter single-screw extruder, and metered using a gear pump to supply the resin to the spinning unit. The spinning temperature from the extruder outlet to the spinning unit was set to 360°C. Two types of nonwoven metal filters with different pore sizes were configured in the spinning unit: the upstream pore size was set to 50 μm, and the downstream pore size was set to 10 μm. Resin was ejected from a spinning nozzle with 48 pores of 0.09 mm diameter and 0.27 mm land length at a rate of 15 g / min (0.3125 cc / min per pore). The ejected resin was allowed to cool and solidify slowly, followed by the application of an oiling agent, and then the 48 filaments were wound together at 700 m / min. The shear rate was set to 72,500 sec⁻¹, and the spinning draw ratio was set to 17. No yarn breakage occurred during the approximately 120-minute winding process, indicating good yarn production. Subsequently, the yarn was rewound from the spinning spool to the heat-treated spool at a rate of 300 m / min. During the 100,000 m rewinding process, no monofilament breakage or fraying occurred, and rewinding was easily implemented with good operability. Treating the fiber at 300°C in nitrogen for 10 hours yielded a fiber with a total fineness of 220.3 dtex, a monofilament fineness of 4.6 dtex, a strength of 28.5 cN / dtex, an elongation of 4.0%, and an elastic modulus of 550 cN / dtex.

[0068] [Example 2] Instead of winding 48 filaments together, the fibers were wound in units of 6 filaments in eight sections. Otherwise, the spinning and heat treatment were carried out in the same manner as in Example 1 to obtain fibers with a total fineness of 27.8 dtex, a single filament fineness of 4.6 dtex, a strength of 29.5 cN / dtex, an elongation of 3.8%, and an elastic modulus of 550 cN / dtex.

[0069] [Example 3] The winding speed was set to 1,400 m / min for winding. Otherwise, the spinning and heat treatment were carried out in the same manner as in Example 1 to obtain fibers with a total fineness of 110.3 dtex, a single filament fineness of 2.3 dtex, a strength of 27.6 cN / dtex, an elongation of 3.8%, and an elastic modulus of 560 cN / dtex.

[0070] [Example 4] The spinning unit used a metal nonwoven filter with an upstream pore size of 30 μm and a downstream pore size of 10 μm. Otherwise, spinning and heat treatment were performed in the same manner as in Example 1 to obtain fibers. The physical properties of the obtained fibers are shown in Table 1.

[0071] [Comparative Example 1] As an aromatic polyester, an aromatic polyester (melting point 290°C) polymerized by polymerizing 73 moles of p-hydroxybenzoic acid and 27 moles of 6-hydroxy-2-naphthoic acid was used, and the heat treatment temperature was set to 280°C. Otherwise, in the same manner as in Example 1, fibers with a total fineness of 220.5 dtex, a single filament fineness of 4.6 dtex, a strength of 23.8 cN / dtex, an elongation of 3.3%, and an elastic modulus of 635 cN / dtex were obtained.

[0072] [Comparative Example 2] As an aromatic polyester, an aromatic polyester (melting point 310°C) polymerized by polymerizing 60 moles of p-hydroxybenzoic acid, 20 moles of biphenyl phenol, 5 moles of isophthalic acid, and 15 moles of terephthalic acid was used. Otherwise, in the same manner as in Example 1, fibers with a total fineness of 220.8 dtex, a single filament fineness of 4.6 dtex, a strength of 23.7 cN / dtex, an elongation of 2.5%, and an elastic modulus of 1,028 cN / dtex were obtained.

[0073] [Comparative Example 3] The spinning unit used a metal nonwoven filter with a pore size of 10 μm. Otherwise, spinning and heat treatment were performed in the same manner as in Example 1 to obtain fibers. The physical properties of the obtained fibers are shown in Table 1.

[0074] [Comparative Example 4] The fiber was spun in the same manner as in Example 1, and then treated at 320°C in nitrogen for 10 hours to obtain the fiber. The physical properties of the obtained fiber are shown in Table 1.

[0075] [Comparative Example 5] The filter pore size on the upstream and downstream sides of the spinning assembly was set to 10 μm. Otherwise, spinning and heat treatment were performed in the same manner as in Example 1 to obtain fibers. The physical properties of the obtained fibers are shown in Table 1. [Comparative Example 6] Add 3% by mass of an ultraviolet absorber to the aromatic polyester resin of Comparative Example 1 and spin it. Otherwise, obtain fibers in the same manner as in Comparative Example 1. The physical properties of the obtained fibers are shown in Table 1. [Example 5] Add 3% by mass of an ultraviolet absorber to the aromatic polyester resin of Example 1 and spin it. Otherwise, obtain fibers in the same manner as in Comparative Example 1. The physical properties of the obtained fibers are shown in Table 1. Furthermore, regarding "whether there is melting after 250°C for 1 hour", those that "do not melt on the surface after 1 hour at 250°C" are marked as "○", and others are marked as "×".

[0076] [Comparative Example 7] The fiber was spun in the same manner as in Example 1, and then treated at 320°C in nitrogen for 10 hours to obtain the fiber. The physical properties of the obtained fiber are shown in Table 1.

[0077] [Table 1] Spinneret internal filter (μm) UV absorber addition amount (quality%) spinning fineness (dtex) filament quantity Monofilament fineness (dtex) 250℃× Has it melted after 1 hour? Heat treatment temperature (°C) Fiber properties after heat treatment Interfiber cross-linking Weather resistance evaluation upstream side Downstream side Total fineness (dtex) strength (cN / dt) elongation (%) Elastic modulus (cN) / dex) Intensity after irradiation (cN / dtex ) Strength retention rate (%) evaluate Example 1 50 10 0 220 48 4.6 ○ 300 220.3 28.5 4.0 550 2.1 21.5 75.4 ○ Example 2 50 10 0 28 6 4.6 ○ 300 27.8 29.5 3.8 550 1.5 20.7 70.2 ○ Example 3 50 10 0 110 48 2.3 ○ 300 110.3 27.6 3.8 560 3.5 18.0 65.2 ○ Example 4 30 10 0 220 48 4.6 ○ 300 220.1 29.1 4.0 550 2.3 21.4 73.5 ○ Comparative Example 1 50 10 0 220 48 4.6 ○ 280 220.5 23.8 3.3 635 1.6 10.1 42.4 △ Comparative Example 2 50 10 0 220 48 4.6 ○ 300 220.8 23.7 2.5 1028 4.8 1.9 8.0 × Comparative Example 3 - 10 0 220 48 4.6 × 300 220.4 28.3 3.9 540 18.2 15.2 53.7 △ Comparative Example 4 50 10 0 220 48 4.6 ○ 320 221.1 30.5 4.2 560 25.3 14.8 48.5 △ Comparative Example 5 10 10 0 220 48 4.6 × 300 220.3 27.5 3.8 530 15.9 15.2 55.3 △ Comparative Example 6 50 10 3 220 48 4.6 ○ 280 220.1 17.5 2.9 547 1.6 8.3 47.4 △ Actual example 5 50 10 3 220 48 4.6 ○ 300 220.0 21.8 3.7 520 4.5 17.4 79.8 ○ Comparative Example 7 - 10 0 220 48 4.6 × 320 221.1 29.6 4.2 560 29.5 13.5 45.6 △

[0078] As shown in Table 1 above, the fibers of the examples exhibit excellent strength properties, demonstrating a high strength retention rate even in the weathering fastness test using a xenon weathering tester. Furthermore, excellent weathering fastness is achieved even without extensive mixing with ultraviolet absorbers or the application of weather-resistant ultraviolet absorbers after fiber spinning. Additionally, the fibers of the examples exhibit excellent interfiber bonding properties, resulting in high-quality fibers where the monofilaments do not fuse together, even after heat treatment using solid-state polymerization. The fibers of Comparative Examples 1, 3-7 showed poor strength retention in the weather fastness test, and the fiber of Comparative Example 2 showed significantly poor weather resistance. Furthermore, the fibers of Comparative Examples 4 and 5 had a higher degree of interweaving between individual fibers, and the fiber of Comparative Example 7 showed visible fusion between individual fibers. [Industrial Applicability]

[0079] The liquid crystal polyester fiber of the present invention is particularly well suited for applications requiring weather resistance, specifically, for example, for applications such as heater line tension members, ropes, fishing lines, etc.

[0080] none

Claims

1. A liquid crystal polyester fiber, which is a fiber composed of liquid crystal polyester, wherein the amount of ultraviolet absorber used is less than 5% by mass, and the strength retention rate in the xenon arc lamp weathering fastness test of JIS L 0891 is more than 60%.

2. The inter-fiber interweaving degree of the liquid crystal polyester fiber as requested in item 1 is less than 10.

3. The liquid crystal polyester fiber of request item 1 or 2 has a total fineness of 600 dtex or less.

4. The liquid crystal polyester fiber of request item 1 or 2 has a single filament fineness of 25 dtex or less.

5. The liquid crystal polyester fiber as claimed in item 1 or 2 is obtained by solid-phase polymerization of liquid crystal polyester fiber whose surface does not melt after passing through 250°C for 1 hour.

6. Liquid crystal polyester fiber as requested in item 1 or 2, wherein, The liquid crystal polyester is a copolyester composed of 6-hydroxy-2-naphthoic acid, terephthalic acid, hydroquinone, and 2,6-naphthoic acid.

7. A method for manufacturing liquid crystal polyester fiber according to any one of claims 1 to 6, characterized in that it comprises: step (1), wherein liquid crystal polyester resin is melt-spun at a shear rate of 1×10⁴ to 1×10⁶ sec⁻¹ and a spinning draft of 5 to 50; and step (2), wherein the fiber obtained by step (1) is heat-treated at a melting point of the liquid crystal polyester resin of -60°C to -10°C to achieve solid-state polymerization.

8. The method for manufacturing liquid crystal polyester fiber as described in claim 7, wherein, Step (1) The spun fibers obtained by spinning are wound onto the first spool and the wound spun fibers are wound onto the second spool for step (2).