Preparation method of liquid crystal polyarylate fiber

Abstract

The invention discloses a preparation method of liquid crystal polyarylate fibers, and belongs to the technical field of preparation of high-performance fibers. The method comprises the following steps: treating high-molecular-weight liquid crystal polyarylate resin in a vacuum drying oven; putting the dried liquid crystal polyarylate resin into a double-screw extruder with protective gas, melting and mixing by the double-screw extruder, and extruding into a spinning box in a melt form; the melt is extruded by a spinneret plate of a spinning assembly, melt trickles extruded from spinneret orifices of the spinneret plate sequentially pass through a heat preservation area and a slow cooling area and then are oiled by an oiling roller, and after drafting, the melt trickles are wound by a winding roller to obtain nascent filaments; and carrying out heat treatment on the nascent filament in an inert gas protection atmosphere to obtain the liquid crystal polyarylate fiber. The preparation method has the advantages that the problem of low tensile strength of easily broken wires in the preparation process is avoided, so that the product is suitable for high-frequency and high-speed 5G cable materials, 5G high-speed communication cable materials and the like; the conditions such as tow adhesion and rapid fiber curing which are not beneficial to tow winding are improved, and the obtained fiber tows are uniform in fineness, high in strength and stable in quality.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance fiber preparation, and specifically relates to a method for preparing liquid crystal polyarylate fiber. Background Art

[0002] Liquid crystal polymer is abbreviated as LCP (full name: Liquid Crystal Polymer), which is an intermediate state between liquid and crystal. LCP can show unique characteristics at the temperature of its liquid crystal phase interval, such as low melt viscosity, significantly better fluidity than ordinary polymers, and excellent orientation order (i.e. high orientation), etc. Therefore, LCP materials have high strength, high modulus, outstanding heat resistance, extremely small linear expansion coefficient, excellent flame retardancy, electrical insulation, chemical corrosion resistance, weathering resistance, microwave permeability, and excellent molding and processing performance, etc., and have a growing and huge application demand in the fields of national defense, aerospace, 5G communications, and automotive electronics.

[0003] The aforementioned liquid crystal polymers are divided into thermotropic liquid crystal polymers and lyotropic liquid crystal polymers according to the conditions for the formation of liquid crystals. The former is usually defined as: the liquid crystal state is formed by temperature changes, and the polymer melts in a specific temperature range (between the melting point and the clearing point) to present an ordered liquid crystal phase; the latter is usually defined as: the liquid crystal state is formed by dissolving in an appropriate solvent and reaching a critical concentration (the formation of the liquid crystal phase depends on the interaction between the solvent and the polymer), such as para-aramid (Kevlar® of Dupont, USA, Twaron® of Teijin, Japan), PBO fiber (Zylon® of Toyobo, Japan, etc.). In general, the liquid crystal state of lyotropic liquid crystal polymers is formed in solution, and the liquid crystal state of thermotropic liquid crystal polymers is formed in the melt or above the glass transition temperature. Lyotropic liquid crystals can be used to produce fibers or films by solvent spinning, and thermotropic liquid crystals can be injection molded, extruded, etc. Since the advent of Kevlar, an LCP product of DuPont, USA in 1956, its superior performance has gradually attracted people's attention, and large-scale research has been gradually carried out in the 1970s and 1980s.

[0004] The technical information of the above-mentioned liquid crystal polyarylate fiber can be found in the public Chinese patent documents. For example, CN104389045A recommends "a method for preparing thermotropic liquid crystal polyarylate fiber", and its steps are shown in paragraphs 0006 to 0009 of its specification. It is said that the tensile strength of the polyarylate fiber finally obtained can reach 4-4.5GPa (paragraph 0010 of the specification); for example, CN115323502A provides "a spinning device and method for preparing liquid crystal polyarylate fiber", which is to add liquid crystal polyarylate resin into the feed section of the extruder through the feed port, melt extrude it through the extruder, and draw it through the spinning machine to cool and solidify to prepare the fiber material. As for the selection of the extruder, it adopts a model with three screws arranged in parallel or in a triangular arrangement, and reduces the melt viscosity of the liquid crystal polyarylate under the multiple high-frequency shearing action of the screw, increases its fluidity, thereby reducing the processing temperature of the polymer. Among them, the speed of the screw is 100-600 rpm, and the temperature of each functional zone of the extruder is: the temperature of the feeding section and the melting section is 280-320°C, the temperature of the viscosity reduction section is 290-330°C, the temperature of the melt pressurizing section is 300-325°C, the temperature of the exhaust section is 310-330°C, and the temperature of the melt homogenizing section is 300-340°C.

[0005] The above preparation methods of liquid crystal polymer fibers are all carried out using the traditional melt spinning method, that is, the spinning raw materials are melted, and the fiber bundles are ejected from the spinneret after metering, and then wound into rolls after cooling. On the one hand, due to the weak shear force of the single-screw extruder and the high temperature requirements for the molten polymer, it is necessary to operate under high-temperature melting conditions to ensure the spinnability of the polymer; in addition, the higher temperature will also cause the cross-linking carbonization of the melt (the polymer decomposes deeply under high temperature or oxygen-deficient conditions to generate carbonaceous residues such as graphite microcrystals or amorphous carbon), which increases energy consumption. On the other hand, even if multi-screw extrusion spinning is used, the melting performance requirements of the raw materials are very high, which limits the production conditions to a certain extent. And when the melt is in a molten form and passes through the spinneret through the extruder, its molecular chain orientation is arranged in the flow state, so that the primary fiber has a high degree of orientation, and it will quickly solidify within a distance of about 10 cm below the spinneret. After solidification, it is difficult to carry out traction treatment, and it needs to be treated complexly before it can be used again, which greatly increases the process difficulty.

[0006] As is known in the industry, the molecular chain of liquid crystal polyarylate contains a rigid aromatic ring structure. The molecular chain has a high degree of orientation in the molten or solution state, but poor fluidity, which makes it difficult to stretch evenly during spinning and easily forms stress concentration during the spinning process, thereby causing broken fibers. In addition, liquid crystal polyarylate fibers usually require high-temperature heat treatment to improve crystallinity and orientation. If the post-treatment temperature or tension is not properly controlled, the tensile strength will be low due to imperfect crystallization, and excessive stretching will increase the film properties of the fiber. In addition, due to the unique liquid crystal behavior, molecular structure rigidity and highly ordered orientation, the spinning process is relatively complex. For example, temperature, shear force, solvent, etc. must be controlled within an extremely narrow range to achieve stable spinning. The above-mentioned problems are precisely the factors that the industry is currently paying attention to and have become the factors that are committed to exploration and improvement. Summary of the invention

[0007] The task of the present invention is to provide a method for preparing liquid crystal polyarylate fibers with controllable process parameters and excellent fiber properties, which can solve the technical problems of easy fiber breakage, low tensile strength and harsh spinning conditions in the preparation process of liquid crystal polyarylate fibers.

[0008] The task of the present invention is accomplished by a method for preparing a liquid crystal polyarylate fiber, comprising the following steps: S1 drying treatment, the high molecular weight liquid crystal polyarylate resin is dried in a vacuum drying oven to remove free water molecules to obtain a dry liquid crystal polyarylate resin; S2. melt-mixing, feeding the dried liquid crystal polyarylate resin obtained in step S1 into a twin-screw extruder with protective gas, melt-mixing and extruding the resin into a spinning box in the form of a melt by the twin-screw extruder, controlling the temperature of the feeding section and the melting section, the melt compression section and the exhaust section of the twin-screw extruder, wherein the twin-screw extruder is provided with two symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt; S3. preparing spun yarn, wherein the melt extruded from step S2 to the spinning box is extruded by a spinneret in the structural system of the spinning assembly of the spinning box, and the melt stream extruded from the spinneret holes of the spinneret passes through a heat preservation zone and a slow cooling zone in sequence, and then is oiled by an oiling roller, and then is drawn by a drawing device, and finally is taken up by a winding roller, wherein the spinneret hole diameter, extrusion speed and number of spinneret holes of the spinneret are controlled, and the drawing ratio of the drawing is controlled to obtain spun yarn; S4. Prepare the finished product by heat treating the spun silk obtained in step S3 under an inert gas atmosphere and controlling the heat treatment temperature to be lower than the melting point of the polyarylate resin to obtain liquid crystal polyarylate fibers.

[0009] In a specific embodiment of the present invention, the liquid crystal polyarylate resin described in step S1 is prepared by mixing and polymerizing two or more of the following: p-hydroxybenzoic acid, biphenyl dicarboxylic acid, terephthalic acid, isophthalic acid, 6-hydroxy-2-naphthoic acid, 2,6-naphthalene diol, hydroquinone and resorcinol.

[0010] In another specific embodiment of the present invention, the high molecular weight standard of the high molecular weight liquid crystal polyarylate resin in step S1 is: Mn is greater than 2×10 4 g / mol; the vacuum degree of the vacuum drying oven is 5-100 Pa, the drying temperature is 110-180°C and the temperature is kept constant at 110-180°C for 3-8 hours; the drying refers to drying until the moisture content of the resin is less than 10ppm.

[0011] In another specific embodiment of the present invention, the protective gas described in step S2 is nitrogen; the temperature of the feed section and the melting section of the twin-screw extruder is controlled to be 260-350°C, the temperature of the melt compression section is controlled to be 280-320°C, and the temperature of the exhaust section is controlled to be 300-325°C, and the screw speed of the twin-screw extruder is 20-200rpm.

[0012] In another specific embodiment of the present invention, the insulation zone described in step S3 is provided with an insulation jacket intended to prolong the time that the melt is in a viscous flow state, the temperature of the insulation jacket is 300-320°C, and the length of the insulation jacket is 15-20cm; the temperature of the slow cooling zone is 260-285°C.

[0013] In another specific embodiment of the present invention, the temperature of the spinning assembly in step S3 is 280-340°C.

[0014] In a more specific embodiment of the present invention, the control of the spinneret hole diameter, extrusion speed and the number of spinneret holes in step S3 is to control the spinneret hole diameter of the spinneret to 0.07-0.2 mm, the extrusion speed to 12-100 m / min and the number of spinneret holes to 5-300 holes.

[0015] In a further specific embodiment of the present invention, the spinneret drawing ratio during drawing by the drawing device in step S3 is 8-160 times; and the winding speed of the winding roller is 800-2000rpm.

[0016] In yet another specific embodiment of the present invention, the temperature of the heat treatment in step S4 is 250-300° C., and the heat treatment time is 10-40 hours.

[0017] In yet another specific embodiment of the present invention, the liquid crystal polyarylate fiber in step S4 has a breaking strength greater than 25 g / d, a tensile modulus greater than 750 g / d, a dielectric constant less than 2.6, a dielectric loss less than 0.00115, and a water absorption rate less than 0.1%.

[0018] One of the technical effects of the technical solution provided by the present invention is that a twin-screw extruder equipped with a negative pressure degassing system is used to melt the liquid crystal polyarylate resin, and the high orientation of the liquid crystal polyarylate is fully utilized, the operation in the spinning process and the subsequent heat treatment process are optimized, and the liquid crystal polyarylate primary silk is heat-treated to obtain a liquid crystal polyarylate fiber with extremely high mechanical properties, a breaking strength greater than 25g / d, a tensile modulus greater than 750g / d, a dielectric constant less than 2.6, a dielectric loss less than 0.00115, and a low water absorption rate of only less than 0.1%, which can avoid The problem of low tensile strength of easily broken wires during the preparation process is eliminated, making the product suitable for high-frequency and high-speed 5G cable materials and 5G high-speed communication cable materials, etc.; secondly, through the treatment of the insulation zone of the spinning process, the situation that is not conducive to the winding of the yarn bundles and rapid fiber solidification caused by excessively high or low ambient temperature is greatly improved, and the production equipment is highly integrated, which provides convenience for the implementation of the heat treatment stage and solves the problems of complicated steps and harsh conditions in the spinning process. The final fiber bundles have uniform fineness, high strength and stable quality. There are no harsh bottleneck factors affecting the process in the preparation process, which is suitable for industrial continuous production. DETAILED DESCRIPTION Example 1

[0019] The steps of the preparation method of liquid crystal polyarylate fiber are as follows: S1. Drying treatment, Mn (number average molecular weight) greater than 2×10 4 g / mol and a high molecular weight liquid crystal polyarylate resin prepared by mixing and polymerizing the following p-hydroxybenzoic acid and terephthalic acid in the same weight ratio (or in the same weight fraction) is subjected to a drying treatment in a vacuum drying oven with a vacuum degree of 60 Pa to remove free water molecules, the drying temperature is controlled to be 110° C., and the temperature is kept constant at 110° C. for 8 hours, and the moisture content of the above resin is dried to be less than 10 ppm, and the moisture content is determined by a method such as a Karl Fischer coulometric method, a thermogravimetric analysis-mass spectrometry (TGA-MS) or a near infrared spectroscopy online monitoring method, etc., to obtain a dry liquid crystal polyarylate resin; S2. Melt-mixing, feeding the dried liquid crystal polyarylate resin obtained in step S1 into a twin-screw extruder with nitrogen as protective gas, melt-mixing by the twin-screw extruder and extruding the melt into a spinning box for spinning, controlling the screw speed of the twin-screw extruder to 200 rpm, controlling the temperatures of the feeding section and the melting section of the twin-screw extruder to 300° C. respectively, controlling the temperature of the melt compression section to 300° C., and controlling the temperature of the exhaust section to 300° C. In this step, two mutually symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt are provided on the aforementioned twin-screw extruder; S3. Prepare nascent silk. The spinneret in the structural system of the spinning assembly of the spinning box extrude the melt extruded into the spinning box in step S2. The melt stream extruded from the spinneret holes of the spinneret passes through the insulation zone and the slow cooling zone in turn and is oiled by the oiling roller. It is then stretched by the stretching device and finally taken up by the winding roller to obtain nascent silk. In this step, the insulation zone is provided with an insulation cover for prolonging the time that the melt is in a viscous flow state. The temperature of the insulation cover is 310°C and the length of the insulation cover is 20cm. The temperature of the slow cooling zone is 270°C and the temperature of the spinning assembly is 300°C. The diameter of the spinneret holes of the spinneret is 0.1mm. The speed at which the spinneret holes of the spinneret extrude the melt is 12m / min. The number of spinneret holes is 150. The stretching ratio of the stretching is 100 times and the winding speed of the winding roller is 800m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340°C, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10 cm below the spinneret, and if the ambient temperature is too high, the melt will be too "liquefied", which is prone to adhesion, which is not conducive to the traction of the filament bundle and may even cause filament breakage. Therefore, in this embodiment, the temperature of the spinning assembly is selected to be 300°C; S4. Prepare the finished product, and perform heat treatment on the spun yarn obtained in step S3 under an inert gas such as argon or nitrogen protective atmosphere to improve the tensile strength, dimensional stability, chemical resistance and other properties. The heat treatment device is a heat treatment furnace with a closed cavity with a gas inlet and outlet, and the heat treatment temperature is controlled to be lower than the melting point of the polyarylate resin. In this embodiment, the temperature is controlled to be 270°C, and the heat treatment time is 20 hours. Since the obtained liquid crystal polyarylate (LCP) fiber has a breaking strength of 26.3 g / d, a tensile modulus of 820 g / d, a dielectric constant of 2.23, a dielectric loss of 0.0013 and a water absorption rate of 0.023%, it is widely used in high-frequency and high-speed 5G circuit board materials, 5G communication cable materials, aerospace composite materials and high-temperature resistant filter materials, etc. Example 2

[0020] The steps of the preparation method of liquid crystal polyarylate fiber are as follows: S1. Drying treatment, Mn (number average molecular weight) greater than 2×10 4 g / mol and a high molecular weight liquid crystal polyarylate resin prepared by mixing and polymerizing the following biphenyl dicarboxylic acid, isophthalic acid and terephthalic acid in the same weight ratio (or in the same weight fraction) is subjected to a drying treatment in a vacuum drying oven with a vacuum degree of 5 Pa to remove free water molecules, the drying temperature is controlled to be 180° C., and the temperature is kept constant at 180° C. for 3 hours, and the resin is dried until the moisture content is less than 10 ppm, and the moisture content is determined by a Karl Fischer coulometric method, a thermogravimetric analysis-mass spectrometry (TGA-MS) method or a near infrared spectroscopy online monitoring method, etc., to obtain a dry liquid crystal polyarylate resin; S2. Melt-mixing, the dried liquid crystal polyarylate resin obtained in step S1 is put into a twin-screw extruder with nitrogen as a protective gas, melt-mixed by the twin-screw extruder and extruded into a spinning box in the form of a melt for spinning, the screw speed of the twin-screw extruder is controlled to 20 rpm, the temperature of the feeding section and the melting section of the twin-screw extruder is controlled to 260° C. respectively, the temperature of the melt compression section is controlled to 280° C. and the temperature of the exhaust section is controlled to 310° C. In this step, two mutually symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt are provided on the aforementioned twin-screw extruder; S3. Prepare nascent silk. The melt extruded into the spinning box in step S2 is extruded from the spinneret in the structural system of the spinning assembly of the spinning box. The melt stream extruded from the spinneret holes of the spinneret passes through the insulation zone and the slow cooling zone in turn and is oiled by the oiling roller. It is then stretched by the stretching device and finally taken up by the winding roller to obtain nascent silk. In this step, the insulation zone is provided with an insulation cover for prolonging the time that the melt is in a viscous flow state. The temperature of the insulation cover is 300°C and the length of the insulation cover is 18 cm. The temperature of the slow cooling zone is 260°C and the temperature of the spinning assembly is 280°C. The diameter of the spinneret holes of the spinneret is 0.07 mm. The speed at which the spinneret holes of the spinneret extrude the melt is 45 m / min. The number of spinneret holes is 5. The stretching ratio of the stretching is 160 times and the winding speed of the winding roller is 2000 m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340°C, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10 cm below the spinneret, and if the ambient temperature is too high, the melt will be too "liquefied", which is prone to adhesion, which is not conducive to the traction of the filament bundle and may even cause filament breakage. Therefore, in this embodiment, the temperature of the spinning assembly is selected to be 280°C; S4. Prepare the finished product, and perform heat treatment on the spun yarn obtained in step S3 under an inert gas such as argon or nitrogen protective atmosphere to improve the tensile strength, dimensional stability, chemical resistance and other properties. The heat treatment device is a heat treatment furnace with a closed cavity with a gas inlet and outlet, and the heat treatment temperature is controlled to be lower than the melting point of the polyarylate resin. In this embodiment, it is controlled to 260°C, and the heat treatment time is 30h. Since the obtained liquid crystal polyarylate (LCP) fiber has a breaking strength of 25.6g / d, a tensile modulus of 800g / d, a dielectric constant of 2.06, a dielectric loss of 0.0011 and a water absorption rate of 0.025%, it is widely used in high-frequency and high-speed 5G circuit board materials, 5G communication cable materials, aerospace composite materials and high-temperature resistant filter materials, etc. Example 3

[0021] The steps of the preparation method of liquid crystal polyarylate fiber are as follows: S1. Drying treatment, Mn (number average molecular weight) greater than 2×10 4 g / mol and a high molecular weight liquid crystal polyarylate resin prepared by mixing and polymerizing the following 6-hydroxy-2-naphthoic acid, 2,6-naphthalene diol, hydroquinone and resorcinol in the same weight ratio (or in the same weight fraction) is subjected to a drying treatment in a vacuum drying oven with a vacuum degree of 100 Pa to remove free water molecules, the drying temperature is controlled to be 140° C., and the temperature is kept constant at 140° C. for 5 hours, and the moisture content of the above resin is dried to be less than 10 ppm, and the moisture content is determined by a method such as Karl Fischer coulometric method, thermogravimetric analysis-mass spectrometry (TGA-MS) or near infrared spectroscopy online monitoring method, etc., to obtain a dry liquid crystal polyarylate resin; S2. Melt-kneading, feeding the dried liquid crystal polyarylate resin obtained in step S1 into a twin-screw extruder with nitrogen as protective gas, melt-kneading by the twin-screw extruder and extruding the melt into a spinning box for spinning, controlling the screw speed of the twin-screw extruder to 80 rpm, controlling the temperatures of the feeding section and the melting section of the twin-screw extruder to 350° C., controlling the temperature of the melt compression section to 320° C., and controlling the temperature of the exhaust section to 325° C. In this step, two mutually symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt are provided on the aforementioned twin-screw extruder; S3. Prepare nascent silk. The spinneret in the structural system of the spinning assembly of the spinning box extrude the melt extruded into the spinning box in step S2. The melt stream extruded from the spinneret holes of the spinneret passes through the insulation zone and the slow cooling zone in turn and is oiled by the oiling roller. It is then stretched by the stretching device and finally taken up by the winding roller to obtain nascent silk. In this step, the insulation zone is provided with an insulation cover for prolonging the time that the melt is in a viscous flow state. The temperature of the insulation cover is 320°C and the length of the insulation cover is 15 cm. The temperature of the slow cooling zone is 285°C and the temperature of the spinning assembly is 340°C. The diameter of the spinneret holes of the spinneret is 0.2 mm. The speed at which the spinneret holes of the spinneret extrude the melt is 100 m / min. The number of spinneret holes is 300. The stretching ratio of the stretching is 8 times and the winding speed of the winding roller is 1400 m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340°C, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10 cm below the spinneret, and if the ambient temperature is too high, the melt will be too "liquefied", which is prone to adhesion, which is not conducive to the traction of the filament bundle and may even cause filament breakage. Therefore, in this embodiment, the temperature of the spinning assembly is selected to be 340°C; S4. Prepare the finished product, and perform heat treatment on the spun yarn obtained in step S3 under an inert gas such as argon or nitrogen protective atmosphere to improve the tensile strength, dimensional stability, chemical resistance and other properties. The heat treatment device is a heat treatment furnace with a closed cavity with a gas inlet and outlet, and the heat treatment temperature is controlled to be lower than the melting point of the polyarylate resin. In this embodiment, it is controlled to 300°C and the heat treatment time is 10h. Since the obtained liquid crystal polyarylate (LCP) fiber has a breaking strength of 28.2g / d, a tensile modulus of 810g / d, a dielectric constant of 1.89, a dielectric loss of 0.0012 and a water absorption rate of 0.032%, it is widely used in high-frequency and high-speed 5G circuit board materials, 5G communication cable materials, aerospace composite materials and high-temperature resistant filter materials, etc. Example 4

[0022] The steps of the preparation method of liquid crystal polyarylate fiber are as follows: S1. Drying treatment, Mn (number average molecular weight) greater than 2×10 4g / mol and a high molecular weight liquid crystal polyarylate resin prepared by mixing and polymerizing the following p-hydroxybenzoic acid, biphenyl dicarboxylic acid, terephthalic acid and isophthalic acid in the same weight ratio (or in the same weight fraction) is subjected to a drying treatment in a vacuum drying oven with a vacuum degree of 80 Pa to remove free water molecules, the drying temperature is controlled to be 120° C., and the temperature is kept constant at 120° C. for 6 hours, and the moisture content of the above resin is dried to be less than 10 ppm, and the moisture content is determined by a method such as a Karl Fischer coulometric method, a thermogravimetric analysis-mass spectrometry (TGA-MS) or a near infrared spectroscopy online monitoring method, etc., to obtain a dry liquid crystal polyarylate resin; S2. Melt-kneading, feeding the dried liquid crystal polyarylate resin obtained in step S1 into a twin-screw extruder with nitrogen as protective gas, melt-kneading by the twin-screw extruder and extruding the melt into a spinning box for spinning, controlling the screw speed of the twin-screw extruder to 110 rpm, controlling the temperatures of the feeding section and the melting section of the twin-screw extruder to 310° C., controlling the temperature of the melt compression section to 290° C., and controlling the temperature of the exhaust section to 320° C. In this step, two mutually symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt are provided on the aforementioned twin-screw extruder; S3. Prepare nascent silk. The melt extruded into the spinning box in step S2 is extruded from the spinneret in the structural system of the spinning assembly of the spinning box. The melt stream extruded from the spinneret hole of the spinneret passes through the insulation zone and the slow cooling zone in turn and is oiled by the oiling roller. It is then stretched by the stretching device and finally taken up by the winding roller to obtain the nascent silk. In this step, the insulation zone is provided with an insulation cover for prolonging the time that the melt is in a viscous flow state. The temperature of the insulation cover is 315°C and the length of the insulation cover is 16 cm. The temperature of the slow cooling zone is 280°C and the temperature of the spinning assembly is 320°C. The diameter of the spinneret hole of the spinneret is 0.15 mm. The speed at which the spinneret hole of the spinneret extrude the melt is 70 m / min. The number of spinneret holes is 210. The stretching ratio of the stretching is 70 times and the winding speed of the winding roller is 1600 m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340°C, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10 cm below the spinneret, and if the ambient temperature is too high, the melt will be too "liquefied", which is prone to adhesion, which is not conducive to the traction of the filament bundle and may even cause filament breakage. Therefore, in this embodiment, the temperature of the spinning assembly is selected to be 320°C; S4. Prepare the finished product, and perform heat treatment on the spun yarn obtained in step S3 under an inert gas such as argon or nitrogen protective atmosphere to improve the tensile strength, dimensional stability, chemical resistance and other properties. The heat treatment device is a heat treatment furnace with a closed cavity with a gas inlet and outlet, and the heat treatment temperature is controlled to be lower than the melting point of the polyarylate resin. In this embodiment, it is controlled to 250°C and the heat treatment time is 40h. Since the obtained liquid crystal polyarylate (LCP) fiber has a breaking strength of 30.1g / d, a tensile modulus of 830g / d, a dielectric constant of 1.62, a dielectric loss of 0.0014 and a water absorption rate of 0.028%, it is widely used in high-frequency and high-speed 5G circuit board materials, 5G communication cable materials, aerospace composite materials and high-temperature resistant filter materials, etc.

[0023] This table is a summary table of relevant technical indicators of liquid crystal polyarylate fibers obtained in Examples 1 to 4 of the present invention: .

Claims

1. A method for preparing liquid crystal polyarylate fiber, characterized in that: The following steps are involved: S1 drying treatment, the high molecular weight liquid crystal polyarylate resin is dried in a vacuum drying oven to remove free water molecules to obtain a dry liquid crystal polyarylate resin; S2. melt-mixing, feeding the dried liquid crystal polyarylate resin obtained in step S1 into a twin-screw extruder with protective gas, melt-mixing and extruding the resin into a spinning box in the form of a melt by the twin-screw extruder, controlling the temperature of the feeding section and the melting section, the melt compression section and the exhaust section of the twin-screw extruder, wherein the twin-screw extruder is provided with two symmetrical air valves having a negative pressure degassing system for removing moisture that may exist in the liquid crystal polyarylate resin and a small amount of low-molecular substances that may be produced to ensure the purity of the melt; S3. preparing spun yarn, wherein the melt extruded from step S2 to the spinning box is extruded by a spinneret in the structural system of the spinning assembly of the spinning box, and the melt stream extruded from the spinneret holes of the spinneret passes through a heat preservation zone and a slow cooling zone in sequence, and then is oiled by an oiling roller, and then is drawn by a drawing device, and finally is taken up by a winding roller, wherein the spinneret hole diameter, extrusion speed and number of spinneret holes of the spinneret are controlled, and the drawing ratio of the drawing is controlled to obtain spun yarn; S4. Prepare the finished product by heat treating the spun silk obtained in step S3 under an inert gas atmosphere and controlling the heat treatment temperature to be lower than the melting point of the polyarylate resin to obtain liquid crystal polyarylate fibers.

2. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The liquid crystal polyarylate resin described in step S1 is prepared by mixing and polymerizing two or more of the following: p-hydroxybenzoic acid, biphenyl dicarboxylic acid, terephthalic acid, isophthalic acid, 6-hydroxy-2-naphthoic acid, 2,6-naphthalene diol, hydroquinone and resorcinol.

3. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The high molecular weight standard of the high molecular weight liquid crystal polyarylate resin in step S1 is: Mn is greater than 2×10 4 g / mol; the vacuum degree of the vacuum drying oven is 5-100 Pa, the drying temperature is 110-180°C and the temperature is kept constant at 110-180°C for 3-8 hours; the drying refers to drying until the moisture content of the resin is less than 10ppm.

4. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The protective gas described in step S2 is nitrogen; the temperature of the feed section and the melting section of the twin-screw extruder is controlled to be 260-350°C, the temperature of the melt compression section is controlled to be 280-320°C, and the temperature of the exhaust section is controlled to be 300-325°C, and the screw speed of the twin-screw extruder is 20-200rpm.

5. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The insulation zone described in step S3 is provided with an insulation jacket for extending the time the melt is in a viscous flow state, the temperature of the insulation jacket is 300-320°C, and the length of the insulation jacket is 15-20cm; the temperature of the slow cooling zone is 260-285°C.

6. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The temperature of the spinning assembly in step S3 is 280-340°C.

7. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The control of the spinneret hole diameter, extrusion speed and number of spinneret holes in step S3 is to control the spinneret hole diameter of the spinneret to 0.07-0.2 mm, the extrusion speed to 12-100 m / min and the number of spinneret holes to 5-300 holes.

8. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The spinneret drawing ratio during drawing by the drawing device in step S3 is 8-160 times; the winding speed of the winding roller is 800-2000rpm.

9. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The heat treatment temperature in step S4 is 250-300° C., and the heat treatment time is 10-40 hours.

10. The method for preparing liquid crystal polyarylate fiber according to claim 1, characterized in that: The liquid crystal polyarylate fiber in step S4 has a breaking strength greater than 25 g / d, a tensile modulus greater than 750 g / d, a dielectric constant less than 2.6, a dielectric loss less than 0.00115, and a water absorption rate less than 0.1%.