Process for the preparation of liquid crystalline polyarylate fibers

Abstract

The application relates to a preparation method of liquid crystal polyarylate fibers and belongs to the technical field of high-performance fiber preparation. The steps are as follows: high-molecular-weight liquid crystal polyarylate resin is put into a vacuum drying box; the dried liquid crystal polyarylate resin is put into a double-screw extruder with a protective gas, is melt-mixed by the double-screw extruder and is extruded into a spinning box in the form of a melt; the melt is extruded from a spinning plate of a spinning assembly, the melt stream extruded from the spinning hole of the spinning plate is sequentially subjected to heat preservation and slow cooling and is then oiled by an oiling roller, and the obtained primary silk is wound by a winding roller after being drawn. The primary silk is subjected to heat treatment in an inert gas protective atmosphere to obtain liquid crystal polyarylate fibers. The method has the advantages that the problem of low tensile strength of the prepared fibers is avoided, the product is suitable for high-frequency high-speed 5G cable materials and 5G high-speed communication cable materials, the situation that the fiber tow is not conducive to winding, such as adhesion of the fiber tow and rapid fiber solidification, is improved, and the obtained fiber tows are uniform in fineness, high in strength and stable in quality.

Description

Technical Field

[0001] This invention belongs to the field of high-performance fiber preparation technology, and specifically relates to a method for preparing liquid crystal polyarylate fibers. Background Technology

[0002] Liquid crystal polymers, abbreviated as LCP (Liquid Crystal Polymer), are an intermediate state between liquid and crystal. LCPs exhibit unique properties at temperatures within their liquid crystal phase range, such as lower melt viscosity, significantly better flowability than ordinary polymers, and excellent orientational order (i.e., high orientation). Therefore, LCP materials possess properties such as high strength, high modulus, outstanding heat resistance, extremely low coefficient of linear expansion, excellent flame retardancy, electrical insulation, chemical corrosion resistance, weather resistance, microwave transmittance, and excellent molding and processing performance, leading to a rapidly growing and significant application demand in fields such as defense, aerospace, 5G communications, and automotive electronics.

[0003] Based on the conditions under which liquid crystals form, the aforementioned liquid crystal polymers are classified into thermotropic liquid crystal polymers and lyotropic liquid crystal polymers. The former is generally defined as forming a liquid crystal state through temperature changes; within a specific temperature range (between the melting point and the clearing point), the polymer melts and exhibits an ordered liquid crystal phase. The latter is generally defined as forming a liquid crystal state after dissolving in a suitable 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 fibers (DuPont Kevlar®, Teijin Twaron®) and PBO fibers (Toyobo Zylon®, etc.). In general, the liquid crystal state of lyotropic liquid crystal polymers forms in solution, while the liquid crystal state of thermotropic liquid crystal polymers forms in the melt or above the glass transition temperature. Lyotropic liquid crystals can be used for solvent spinning to produce fibers or films, while thermotropic liquid crystals can be used for injection molding, extrusion molding, etc. Since the introduction of Kevlar, an LCP product from DuPont in 1956, its superior performance has gradually gained attention, and large-scale research began in the 1970s and 1980s.

[0004] The technical information of the aforementioned liquid crystal polyarylate fibers can be found in published Chinese patent documents. For example, CN104389045A recommends "a method for preparing thermotropic liquid crystal polyarylate fibers," the steps of which are described in paragraphs 0006 to 0009 of its specification. It is claimed that the tensile strength of the final polyarylate fibers can reach 4-4.5 GPa (paragraph 0010 of the specification). Another example is CN115323502A, which provides "a spinning equipment and method for preparing liquid crystal polyarylate fibers." This method involves adding liquid crystal polyarylate resin into the feed section of an extruder through a feed inlet, melting and extruding it through the extruder, and then drawing, cooling, and solidifying it through a spinning machine to obtain the fiber material. As for the selection of the extruder, it adopts a model with three parallel or triangular screws. By reducing the melt viscosity of the liquid crystal polyarylate under the multiple high-frequency shearing action of the screw, its fluidity is increased, thereby reducing the processing temperature of the polymer. The screw speed is 100-600 rpm, and the temperatures of each functional zone of the extruder are as follows: 280-320℃ for the feeding and melting zones, 290-330℃ for the viscosity reducing zone, 300-325℃ for the melt pressurizing zone, 310-330℃ for the exhaust zone, and 300-340℃ for the melt homogenizing zone.

[0005] The above methods for preparing liquid crystal polymer fibers all utilize traditional melt spinning, where the raw material is melted, metered, and then extruded as fiber bundles through a spinneret. After cooling, the fibers are wound into rolls. However, single-screw extruders have relatively weak shear forces and require high temperatures for the molten polymer, necessitating operation under high-temperature melting conditions to ensure spinnability. Furthermore, the high temperatures can cause cross-linking and carbonization of the melt (deep decomposition of the polymer under high temperature or oxygen-deficient conditions, generating carbonaceous residues such as graphite microcrystals or amorphous carbon), further increasing energy consumption. Even with multi-screw extrusion spinning, the requirements for the melt properties of the raw material are very high, limiting production conditions to some extent. Moreover, when the melt passes through the spinneret in molten form, the molecular chains align in a flowing state, resulting in high orientation of the nascent fibers. These fibers rapidly solidify within approximately 10 cm below the spinneret, making further traction difficult and requiring complex processing before reuse, significantly increasing the process complexity.

[0006] As is known in the industry, liquid crystal polyarylates contain rigid aromatic ring structures in their molecular chains. While exhibiting high molecular chain orientation in the molten or solution state, their poor flowability makes uniform stretching during spinning difficult, easily leading to stress concentration and fiber breakage. Furthermore, liquid crystal polyarylate fibers typically require high-temperature heat treatment to improve crystallinity and orientation. Improper control of post-treatment temperature or tension can result in low tensile strength due to incomplete crystallization, while excessive stretching can increase fiber film properties. Additionally, the unique liquid crystal behavior, rigid molecular structure, and highly ordered orientation make the spinning process relatively complex. For example, temperature, shear force, and solvents must be controlled within extremely narrow ranges to achieve stable spinning. These aforementioned issues are precisely what the industry is currently focusing on and striving to improve. Summary of the Invention

[0007] The objective of this invention is to provide a method for preparing liquid crystal polyarylate fibers with controllable process parameters and excellent fiber properties. This method 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 objective of this invention is achieved by providing a method for preparing liquid crystal polyarylate fibers, 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, and dried liquid crystal polyarylate resin is obtained. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder with a protective gas, melt-mixed by the twin-screw extruder and extruded into the spinning box in the form of melt. The temperature of the feeding section, melting section, melt compression section and exhaust section of the twin-screw extruder is controlled. The twin-screw extruder is equipped with two mutually symmetrical air valves of a negative pressure degassing system for removing any moisture and any small amount of low molecular weight substances that may be present in the liquid crystal polyarylate resin, in order to ensure the purity of the melt. S3. Preparation of nascent filament: The melt extruded from step S2 into the spinning box is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret holes passes through the heat preservation zone and the slow cooling zone in sequence, and then is oiled by the oiling roller. It is then drawn by the drawing device and finally wound by the winding roller. The diameter of the spinneret holes, the extrusion speed and the number of spinneret holes are controlled, and the draw ratio of the drawing is controlled to obtain nascent filament. S4. To prepare the finished product, the nascent fiber obtained in step S3 is heat-treated under an inert gas protective atmosphere and the heat treatment temperature is controlled below the melting point temperature of the polyaryl ester resin to obtain liquid crystal polyaryl ester fiber.

[0009] In a specific embodiment of the present invention, the liquid crystal polyarylate resin mentioned in step S1 is formed by compounding and polymerizing two or more of the following: p-hydroxybenzoic acid, biphenyl phthalic acid, terephthalic acid, isophthalic acid, 6-hydroxy-2-naphthoic acid, 2,6-naphthodiol, 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 mentioned in step S1 is: Mn greater than 2 × 10⁻⁶. 4 g / mol; the vacuum degree of the vacuum drying oven is 5-100 Pa, the drying temperature is 110-180℃ and is kept constant at 110-180℃ for 3-8 hours; the drying refers to drying until the moisture content of the resin is less than 10 ppm.

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

[0012] In another specific embodiment of the present invention, the heat preservation zone in step S3 is provided with a heat preservation sleeve designed to prolong the time when the melt is in a viscous flow state. The temperature of the heat preservation sleeve is 300-320°C and the length of the heat preservation sleeve 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 orifice diameter, extrusion speed and number of spinneret orifices in step S3 is to control the spinneret orifice diameter to 0.07-0.2 mm, the extrusion speed to 12-100 m / min and the number of spinneret orifices to 5-300 orifices.

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

[0016] In yet another specific embodiment of the present invention, the heat treatment temperature 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 described 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 present invention is that, by employing a twin-screw extruder equipped with a negative pressure degassing system to melt-treat the liquid crystal polyarylate resin, and by fully utilizing the highly oriented characteristics of liquid crystal polyarylate, the spinning process and subsequent heat treatment processes have been optimized. After further heat treatment, the resulting liquid crystal polyarylate filament exhibits extremely high mechanical properties: 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 low water absorption rate of less than 0.1%, thus avoiding… The product avoids the problems of easily broken filaments and low tensile strength during the preparation process, making it suitable for high-frequency, high-speed 5G cable materials and 5G high-speed communication cable materials. Secondly, by treating the heat preservation zone during the spinning process, the product greatly improves the situation of filament adhesion and rapid fiber solidification caused by excessively high or low ambient temperatures, which are not conducive to filament winding. Moreover, the high integration of the production equipment facilitates the implementation of the heat treatment stage, solving the problems of cumbersome spinning process steps and harsh conditions. The final fiber filaments are uniform in fineness, high in strength, and stable in quality. There are no harsh bottleneck factors affecting the process during preparation, making it suitable for continuous industrial production. Detailed Implementation Example 1

[0019] The steps for preparing liquid crystal polyarylate fibers are as follows: S1. Drying treatment, to ensure that Mn (number average molecular weight) is greater than 2 × 10⁻⁶. 4 A high molecular weight liquid crystal polyarylate resin, prepared by mixing and polymerizing p-hydroxybenzoic acid and terephthalic acid in the same weight ratio (or in the same weight parts), was 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 was controlled at 110 °C and held at 110 °C for 8 hours until the water content of the resin was less than 10 ppm. The water content was determined by methods such as Karl Fischer coulometric method, thermogravimetric analysis-mass spectrometry (TGA-MS), or near-infrared spectroscopy online monitoring, etc., to obtain the dried liquid crystal polyarylate resin. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder equipped with nitrogen as a protective gas. The twin-screw extruder melts and mixes the resin and then extrudes it into the spinning box for spinning. The screw speed of the twin-screw extruder is controlled at 200 rpm. The temperatures of the feed section and the melting section of the twin-screw extruder are each controlled at 300°C. The temperatures of the melt compression section and the exhaust section are also controlled at 300°C. In this step, the twin-screw extruder is equipped with two symmetrical air valves of a negative pressure degassing system designed to remove any moisture and small amounts of low-molecular-weight substances that may be present in the liquid crystal polyarylate resin, thereby ensuring the purity of the melt. S3. Preparation of nascent filament: The melt extruded into the spinning box in step S2 is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret holes passes sequentially through the heat preservation zone and the slow cooling zone, then is oiled by the oiling roller, then drawn by the drawing device, and finally wound by the winding roller to obtain nascent filament. In this step, the heat preservation zone is equipped with a heat preservation sleeve designed to prolong the time the melt is in a viscous flow state. The temperature of the heat preservation sleeve is 310°C, and the length of the heat preservation sleeve is 20cm. The temperature of the slow cooling zone is 270°C, the temperature of the spinning assembly is 300°C, the diameter of the spinneret holes is 0.1mm, the speed at which the spinneret holes extrude the melt is 12m / min, the number of spinneret holes is 150, the draw ratio 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℃, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10cm below the spinneret. If the ambient temperature is too high, the melt will become too "liquefied", which will easily cause 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 as 300℃. S4. Preparation of the finished product: The nascent filaments obtained in step S3 are subjected to heat treatment under an inert gas atmosphere, such as argon or nitrogen, to improve tensile strength, dimensional stability, and chemical resistance. The heat treatment apparatus is a heat treatment furnace with a closed cavity and gas inlet and outlet. The heat treatment temperature is controlled below the melting point of the polyaryl ester resin. In this embodiment, it is controlled at 270°C, and the heat treatment time is 20 hours. Since the obtained liquid crystal polyaryl ester (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 filter materials, etc. Example 2

[0020] The steps for preparing liquid crystal polyarylate fibers are as follows: S1. Drying treatment, to ensure that Mn (number average molecular weight) is greater than 2 × 10⁻⁶. 4 A high molecular weight liquid crystal polyarylate resin, composed of biphenyl phthalic acid, isophthalic acid, and terephthalic acid in equal weight ratios (or equal parts by weight), was subjected to drying treatment in a vacuum drying oven with a vacuum degree of 5 Pa to remove free water molecules. The drying temperature was controlled at 180°C and held at 180°C for 3 hours until the water content of the resin was less than 10 ppm. The water content was determined by methods such as Karl Fischer coulometric method, thermogravimetric analysis-mass spectrometry (TGA-MS), or near-infrared spectroscopy online monitoring, etc., to obtain the dried liquid crystal polyarylate resin. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder equipped with nitrogen as a protective gas. The twin-screw extruder melts and mixes the resin and then extrudes it into the spinning box for spinning. The screw speed of the twin-screw extruder is controlled at 20 rpm. The temperatures of the feed section and the melting section of the twin-screw extruder are each controlled at 260°C. The temperature of the melt compression section is controlled at 280°C and the temperature of the exhaust section is controlled at 310°C. In this step, the aforementioned twin-screw extruder is equipped with two mutually symmetrical air valves of a negative pressure degassing system designed to remove any moisture and small amounts of low-molecular-weight substances that may be present in the liquid crystal polyarylate resin, thereby ensuring the purity of the melt. S3. Preparation of nascent filament: The melt extruded into the spinning box in step S2 is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret's spinneret holes passes sequentially through the heat preservation zone and the slow cooling zone, then is oiled by the oiling roller, then drawn by the drawing device, and finally wound by the winding roller to obtain nascent filament. In this step, the heat preservation zone is equipped with a heat preservation sleeve designed to prolong the time the melt is in a viscous flow state. The temperature of the heat preservation sleeve is 300°C, and the length of the heat preservation sleeve is 18cm. The temperature of the slow cooling zone is 260°C, the temperature of the spinning assembly is 280°C, the diameter of the spinneret's spinneret holes is 0.07mm, the speed at which the spinneret's spinneret holes extrudes the melt is 45m / min, the number of spinneret holes is 5, the draw ratio of the drawing is 160 times, and the winding speed of the winding roller is 2000m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340℃, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10cm below the spinneret. If the ambient temperature is too high, the melt will become too "liquefied", which will easily cause 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 as 280℃. S4. Preparation of the finished product: The nascent fiber obtained in step S3 is subjected to heat treatment in an inert gas atmosphere such as argon or nitrogen to improve tensile strength, enhance dimensional stability, and improve chemical resistance. The heat treatment device is a heat treatment furnace with a closed cavity and gas inlet and outlet. The heat treatment temperature is controlled below the melting point of the polyaryl ester resin. In this embodiment, it is controlled at 260°C and the heat treatment time is 30 hours. Since the obtained liquid crystal polyaryl ester (LCP) fiber has a breaking strength of 25.6 g / d, a tensile modulus of 800 g / 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 filter materials, etc. Example 3

[0021] The steps for preparing liquid crystal polyarylate fibers are as follows: S1. Drying treatment, to ensure that Mn (number average molecular weight) is greater than 2 × 10⁻⁶. 4 A high molecular weight liquid crystal polyarylate resin, composed of 6-hydroxy-2-naphthoic acid, 2,6-naphthodiol, hydroquinone, and resorcinol in equal weight ratios (or equal parts by weight), was subjected to drying treatment in a vacuum drying oven with a vacuum degree of 100 Pa to remove free water molecules. The drying temperature was controlled at 140°C and held at 140°C for 5 hours until the water content of the resin was less than 10 ppm. The water content was determined by methods such as Karl Fischer coulometric method, thermogravimetric analysis-mass spectrometry (TGA-MS), or near-infrared spectroscopy online monitoring, etc., to obtain the dried liquid crystal polyarylate resin. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder equipped with nitrogen as a protective gas. The twin-screw extruder melts and mixes the resin and then extrudes it into the spinning box for spinning. The screw speed of the twin-screw extruder is controlled at 80 rpm. The temperatures of the feed section and the melting section of the twin-screw extruder are each controlled at 350°C. The temperature of the melt compression section is controlled at 320°C and the temperature of the exhaust section is controlled at 325°C. In this step, the aforementioned twin-screw extruder is equipped with two mutually symmetrical air valves of a negative pressure degassing system designed to remove any moisture and small amounts of low-molecular-weight substances that may be present in the liquid crystal polyarylate resin, thereby ensuring the purity of the melt. S3. Preparation of nascent filament: The melt extruded into the spinning box in step S2 is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret's spinneret holes passes sequentially through the heat preservation zone and the slow cooling zone, then is oiled by the oiling roller, then drawn by the drawing device, and finally wound by the winding roller to obtain nascent filament. In this step, the heat preservation zone is equipped with a heat preservation sleeve designed to prolong the time the melt is in a viscous flow state. The temperature of the heat preservation sleeve is 320°C, and the length of the heat preservation sleeve is 15cm. The temperature of the slow cooling zone is 285°C, the temperature of the spinning assembly is 340°C, the diameter of the spinneret's spinneret holes is 0.2mm, the speed at which the spinneret's spinneret holes extrudes the melt is 100m / min, the number of spinneret holes is 300, the draw ratio of the drawing is 8 times, and the winding speed of the winding roller is 1400m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340℃, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10cm below the spinneret. If the ambient temperature is too high, the melt will become too "liquefied", which will easily cause 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 as 340℃. S4. Preparation of the finished product: The nascent filaments obtained in step S3 are subjected to heat treatment under an inert gas atmosphere, such as argon or nitrogen, to improve tensile strength, dimensional stability, and chemical resistance. The heat treatment apparatus is a heat treatment furnace with a closed cavity and gas inlet and outlet. The heat treatment temperature is controlled below the melting point of the polyaryl ester resin. In this embodiment, it is controlled at 300°C, and the heat treatment time is 10 hours. Since the obtained liquid crystal polyaryl ester (LCP) fiber has a breaking strength of 28.2 g / d, a tensile modulus of 810 g / 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 filter materials, etc. Example 4

[0022] The steps for preparing liquid crystal polyarylate fibers are as follows: S1. Drying treatment, to ensure that Mn (number average molecular weight) is greater than 2 × 10⁻⁶. 4A high molecular weight liquid crystal polyarylate resin, composed of p-hydroxybenzoic acid, biphenyl phthalic acid, terephthalic acid, and isophthalic acid in equal weight ratios (or equal parts by weight), was subjected to drying treatment in a vacuum drying oven with a vacuum degree of 80 Pa to remove free water molecules. The drying temperature was controlled at 120°C and held at 120°C for 6 hours until the water content of the resin was less than 10 ppm. The water content was determined by methods such as Karl Fischer coulometric method, thermogravimetric analysis-mass spectrometry (TGA-MS), or near-infrared spectroscopy online monitoring, etc., to obtain the dried liquid crystal polyarylate resin. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder equipped with nitrogen as a protective gas. The twin-screw extruder melts and mixes the resin and then extrudes it into the spinning box for spinning. The screw speed of the twin-screw extruder is controlled at 110 rpm. The temperatures of the feed section and the melting section of the twin-screw extruder are each controlled at 310°C. The temperature of the melt compression section is controlled at 290°C and the temperature of the exhaust section is controlled at 320°C. In this step, the aforementioned twin-screw extruder is equipped with two mutually symmetrical air valves of a negative pressure degassing system designed to remove any moisture and small amounts of low-molecular-weight substances that may be present in the liquid crystal polyarylate resin, thereby ensuring the purity of the melt. S3. Preparation of nascent filament: The melt extruded into the spinning box in step S2 is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret's spinneret holes passes sequentially through the heat preservation zone and the slow cooling zone, then is oiled by the oiling roller, then drawn by the drawing device, and finally wound by the winding roller to obtain nascent filament. In this step, the heat preservation zone is equipped with a heat preservation sleeve designed to prolong the time the melt is in a viscous flow state. The temperature of the heat preservation sleeve is 315°C, and the length of the heat preservation sleeve is 16cm. The temperature of the slow cooling zone is 280°C, the temperature of the spinning assembly is 320°C, the diameter of the spinneret's spinneret holes is 0.15mm, the speed at which the spinneret's spinneret holes extrudes the melt is 70m / min, the number of spinneret holes is 210, the draw ratio of the drawing is 70 times, and the winding speed of the winding roller is 1600m / min. Since the melting point of high-performance liquid crystal polyarylate is generally between 280-340℃, if the ambient temperature is too low, the melt will solidify rapidly at a distance of about 10cm below the spinneret. If the ambient temperature is too high, the melt will become too "liquefied", which will easily cause 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 as 320℃. S4. Preparation of the finished product: The nascent filaments obtained in step S3 are subjected to heat treatment under an inert gas atmosphere, such as argon or nitrogen, to improve tensile strength, dimensional stability, and chemical resistance. The heat treatment apparatus is a heat treatment furnace with a closed cavity and gas inlet and outlet. The heat treatment temperature is controlled below the melting point of the polyaryl ester resin. In this embodiment, it is controlled at 250°C, and the heat treatment time is 40 hours. Since the obtained liquid crystal polyaryl ester (LCP) fiber has a breaking strength of 30.1 g / d, a tensile modulus of 830 g / 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 filter materials, etc.

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

Claims

1. A method for preparing liquid crystal polyarylate fibers, characterized in that: Includes the following steps: S1. Drying treatment, the high molecular weight standard is: Mn greater than 2×10 4 The high molecular weight liquid crystal polyarylate resin (g / mol) is dried in a vacuum drying oven with a vacuum degree of 5-100 Pa to remove free water molecules, resulting in dried liquid crystal polyarylate resin. The liquid crystal polyarylate resin in this step is polymerized by mixing two or more of the following: p-hydroxybenzoic acid, biphenyl phthalic acid, terephthalic acid, isophthalic acid, 6-hydroxy-2-naphthoic acid, 2,6-naphthodiol, hydroquinone, and resorcinol. The drying temperature is 110-180℃ and is maintained at 110-180℃ for 3-8 hours until the water content of the resin is less than 10 ppm. S2. Melt mixing: The dried liquid crystal polyarylate resin obtained in step S1 is fed into a twin-screw extruder with nitrogen as the protective gas and a screw speed of 20-200 rpm. The twin-screw extruder melts and mixes the resin and extrudes it into the spinning box in the form of melt. The temperature of the feeding section and melting section of the twin-screw extruder is controlled at 260-350℃, the temperature of the melt compression section is controlled at 280-320℃, and the temperature of the exhaust section is controlled at 300-325℃. The twin-screw extruder is equipped with two mutually symmetrical air valves of a negative pressure degassing system for removing any moisture and small amounts of low molecular weight substances that may be present in the liquid crystal polyarylate resin, thereby ensuring the purity of the melt. S3. Preparation of nascent filament: The melt extruded from step S2 into the spinning box is extruded by the spinneret in the spinning assembly structure system of the spinning box. The fine stream of melt extruded from the spinneret's spinneret holes passes sequentially through a heat preservation zone and a slow cooling zone, then is oiled by an oiling roller, then drawn by a drawing device, and finally wound by a winding roller. The spinneret hole diameter, extrusion speed, and number of spinneret holes are controlled, as is the draw ratio, to obtain nascent filament. The heat preservation zone is equipped with a heat preservation sleeve designed to prolong the time the melt remains in a viscous flow state. The temperature of the heat preservation sleeve is 300-320℃. The insulation sleeve is 15-20cm long; the temperature of the slow cooling zone is 260-285℃; the temperature of the spinning assembly is 280-340℃; the control of the spinneret orifice diameter, extrusion speed, and number of spinneret orifices involves controlling the spinneret orifice diameter to 0.07-0.2mm, the extrusion speed to 12-100m / min, and the number of spinneret orifices to 5-300; the spinneret draft ratio during drafting by the drafting device is 8-160 times; and the winding speed of the winding roller is 800-2000rpm. S4. Preparation of finished product: The nascent fiber obtained in step S3 is heat-treated under an inert gas protective atmosphere, and the heat treatment temperature is controlled below the melting point of the polyaryl ester resin to obtain liquid crystal polyaryl ester fiber. The heat treatment temperature is 250-300℃, and the heat treatment time is 10-40h. The liquid crystal polyaryl ester fiber has 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 water absorption rate less than 0.1%.