A benzoxazole-based polymer fiber and its preparation method

Abstract

This application provides a benzoxazole-based polymer fiber and its preparation method. The preparation method of the benzoxazole-based polymer fiber provided in this application includes the following steps: mixing 4,6-diaminoresorcinol monomer, terephthalic acid monomer and / or terephthalic acid derivative monomer, and 2-(4-aminophenyl)-5-aminobenzimidazole monomer in an acidic solvent, and performing a polymerization reaction to obtain a polyhydroxyamide precursor spinning solution; spinning the polyhydroxyamide precursor spinning solution to obtain polyhydroxyamide precursor fiber; and thermally cyclizing the polyhydroxyamide precursor fiber to obtain benzoxazole-based polymer fiber. The benzoxazole-based polymer fiber prepared by this application has excellent comprehensive properties, effectively improving the compression resistance and UV resistance of conventional polybenzoxazole fibers, and enhancing the interfacial bonding force between the fiber and resin, thus representing a novel benzoxazole-based polymer fiber.

Description

Technical Field

[0001] This invention relates to the field of organic fiber technology, and in particular to a benzoxazole-based polymer fiber and its preparation method. Background Technology

[0002] Benzooxazole-based polymer fibers, such as poly(p-phenylenebenzodioxazole) (PBO), possess characteristics such as high thermal decomposition temperature, high tensile strength, high modulus, high specific modulus, and high specific strength. They are novel polymer compounds developed in the 1970s by the Whright Laboratory in the United States to address practical needs. PBO fibers mainly include two types: AS-spun ordinary yarn and HM high-modulus fiber. HM high-modulus PBO fibers, produced through appropriate drawing and short-time heat treatment, are beneficial for improving fiber orientation along the crystal axis, achieving high modulus properties without sacrificing strength.

[0003] The preparation methods of PBO fibers can be divided into one-step and two-step methods depending on the spinning solution and reaction mechanism. Among them, the one-step method often uses deHCl polycondensation method, complex salt method, etc., to obtain PBO polymer spinning solution in one step, and then obtain PBO fibers after spinning. However, the obtained PBO polymer spinning solution has the characteristics of high intrinsic viscosity, high transport viscosity and difficulty in degassing the polymer. Therefore, the requirements for stirring and conveying equipment become more and more stringent in the later stage of the reaction. The stirring and conveying equipment is required to have high torque, high shear force and long continuous operation. However, after long-term continuous operation, the equipment is often damaged, resulting in long maintenance cycles and high maintenance costs. Two-step methods, such as Chinese patent CN110306254A, involve reacting 4,6-diaminoresorcinol and terephthaloyl chloride in a nonpolar solvent to generate a polyhydroxyamide precursor, which is then spun into polyhydroxyamide precursor fibers. After thermal cyclization, PBO fibers are obtained. This method solves problems such as excessively high viscosity of the solution to be spun and high equipment maintenance costs to a certain extent. However, it still has problems such as low rigidity of the solvent system, inability of the solution to form liquid crystals, and incomplete cyclization of the prepared fibers. These problems will lead to lower mechanical properties of the final fibers.

[0004] In order to effectively control the degree of cyclization, form a liquid crystal spinning solution, and improve the overall performance of benzoxazole-based polymer fibers, this application provides a benzoxazole-based polymer fiber and its preparation method. Summary of the Invention

[0005] In view of the defects and shortcomings of the benzoxazole-based polymer fibers prepared in the prior art, this application provides a benzoxazole-based polymer fiber and its preparation method. The benzoxazole-based polymer fiber prepared in this application has good comprehensive properties, can effectively improve the compression resistance and UV resistance of conventional PBO fibers, and improve the interfacial bonding force between the fiber and the resin. It is a novel benzoxazole-based polymer fiber.

[0006] One embodiment of this application provides a benzoxazole-based polymer fiber, which is represented by the following chemical formula:

[0007]

[0008] Wherein, X is selected from hydroxyl (-OH), chlorine (-Cl), or hydrogen (-H).

[0009] The benzoxazole-based polymer fiber provided in this embodiment has good comprehensive properties, which can effectively improve the compression resistance and UV resistance of conventional PBO fibers and enhance the interfacial bonding force between the fiber and the resin. It is a new type of benzoxazole-based fiber.

[0010] Another embodiment of this application provides a method for preparing benzoxazole-based polymer fibers, comprising the following steps:

[0011] 4,6-Diaminoresorcinol monomer (DAR), terephthalic acid monomer and / or terephthalic acid derivative monomer, and 2-(4-aminophenyl)-5-aminobenzimidazole monomer (BIA) are mixed in an acidic solvent, and antioxidants and absorbents are added. After polymerization, a polyhydroxyamide precursor spinning solution is obtained.

[0012] The polyhydroxyamide precursor spinning solution is spun to obtain polyhydroxyamide precursor fibers.

[0013] The polyhydroxyamide precursor fiber was thermally cyclized to obtain benzoxazole polymer fiber.

[0014] This embodiment introduces benzimidazole with a Lewis base structure into a relatively low-viscosity polyhydroxyamide. Due to the protonation of the imidazole ring, an electron branch density redistribution occurs, giving the single bonds of the carbon atoms connected to the benzene ring a double-bond-like capability. This restricts the rotational mobility of local molecules within the fiber, which is beneficial for fiber orientation. In addition to participating in the formation of the polymer structure, benzimidazole also has the effect of in-situ catalytic thermal cyclization of polyhydroxyamide fibers. Furthermore, the use of terephthalic acid monomers and / or terephthalic acid derivative monomers allows for flexible control of the introduction of active groups, which is beneficial for constructing a molecular hydrogen bond network. The formation of the hydrogen bond network can not only form intra-chain hydrogen bonds due to the connection between the strongly electronegative N and O atoms and the H atoms on the benzene ring, but also form inter-chain hydrogen bonds due to the connection between the active groups on both sides of the benzene ring and the N and H atoms of the imidazole ring on other molecular chains. These intra-chain and inter-chain forces can effectively improve the compression resistance and UV resistance of conventional PBO, and enhance the interfacial bonding between the fiber and the resin. It can overcome the shortcomings of existing two-step spinning methods, such as poor rigidity of the spinning solution and low ring-forming rate of the resulting fibers.

[0015] In one embodiment, the terephthalic acid derivative monomer is selected from one or more of 2,5-dihydroxyterephthalic acid and 2,5-dichloroterephthalic acid.

[0016] In this embodiment, when the terephthalic acid derivative monomer is selected from a mixture of 2,5-dihydroxyterephthalic acid and 2,5-dichloroterephthalic acid, the 2,5-dihydroxyterephthalic acid and 2,5-dichloroterephthalic acid can be mixed in any ratio. This embodiment flexibly controls the introduction of active groups (-OH and / or -Cl) by adjusting the type and amount of terephthalic acid and its derivatives. By introducing active groups (-OH and / or -Cl), the polymer molecules acquire the ability to construct a molecular hydrogen bond network. Through numerous intramolecular and intermolecular interconnecting hydrogen bonds, the compression resistance and UV resistance of conventional PBO fibers are effectively improved, and the interfacial bonding between the fiber and the resin is enhanced.

[0017] In one implementation method, before the polymerization reaction, a portion of the terephthalic acid monomer and / or terephthalic acid derivative monomer is added. After the polymerization reaction has proceeded for a period of time, the remaining terephthalic acid monomer and / or terephthalic acid derivative monomer is added.

[0018] In one implementation, the molar ratio of the first portion of terephthalic acid monomers and / or terephthalic acid derivative monomers added to the remaining terephthalic acid monomers and / or terephthalic acid derivative monomers added later is 1:1.

[0019] In one embodiment, the antioxidant is stannous chloride and the absorbent is phosphorus pentoxide.

[0020] The role of the antioxidant in this embodiment is to prevent or slow down the oxidative degradation of monomers.

[0021] In one embodiment, the acidic solvent is polyphosphoric acid.

[0022] Existing technologies typically use aprotic polar solvents such as dimethylacetamide (DMAC) and N-methylpyrrolidone (NMP) as reaction solvents in the preparation of PBO fibers. These solvents suffer from problems such as low rigidity of polyhydroxyamides in DMAC and NMP, inability to form liquid crystals, and incomplete fiber cyclization. This embodiment uses an acidic solvent, specifically polyphosphoric acid, and introduces benzimidazole with a Lewis base structure. During the thermal cyclization of the obtained polyhydroxyamide precursor fibers, the benzimidazole with the Lewis base structure can catalyze the thermal cyclization of the polyhydroxyamide fibers in situ, causing partial ring closure and forming a liquid crystal phase. The resulting novel benzoxazole-based polymer fibers exhibit high cyclization and cyclization rates and good overall performance.

[0023] In one embodiment, the mass of the 4,6-diaminoresorcinol monomer accounts for 5 wt% to 26 wt% of the mass of the polyhydroxyamide precursor spinning solution;

[0024] The mass of the 2-(4-aminophenyl)-5-aminobenzimidazole monomer accounts for 5 wt% to 12 wt% of the mass of the polyhydroxyamide precursor spinning solution;

[0025] The molar ratio of the terephthalic acid monomer and / or terephthalic acid derivative monomer to the 4,6-diaminoresorcinol monomer is 1:1.

[0026] The antioxidant accounts for 0.1 wt% to 2 wt% of the mass of the polyhydroxyamide precursor spinning solution;

[0027] The water-absorbing agent accounts for 0.5 wt% to 2.5 wt% of the mass of the polyhydroxyamide precursor spinning solution.

[0028] In one embodiment, the polymerization reaction is carried out at a temperature of 10°C to 40°C for a duration of 24 to 48 hours.

[0029] In one embodiment, the spinning is a dry-jet wet spinning process;

[0030] The dry-jet wet spinning process specifically involves: first, filtering and degassing the polyhydroxyamide precursor spinning solution sequentially; second, feeding it into a twin-screw extruder, where it is extruded under the shearing action of the twin-screw extruder; then, extruding it through the spinneret holes of the spinneret via a metering pump, and stretching it in the air gap; finally, sequentially performing coagulation bath molding, washing, drying, oiling, and winding to obtain polyhydroxyamide precursor fibers.

[0031] In this embodiment, the polyhydroxyamide precursor spinning solution undergoes 10%–20% ring closure during its entry into the twin-screw extruder through comprehensive temperature and time control. This increases the rigidity of the chain segments, and under the strong shearing action of the twin-screw extruder, an anisotropic liquid crystal spinning solution is formed, which is beneficial for subsequent spinning. Unlike the one-step synthesis of PBO in existing technologies, the polyhydroxyamide precursor spinning solution in this embodiment does not form a perfectly ordered three-dimensional crystalline structure during the spinning stage. Instead, during subsequent traction and thermal ring-forming treatments, the macromolecules can undergo further configurational adjustments along the highest orientation direction to a greater extent, forming a structure close to one-dimensional axial order, exhibiting greater tensile load bearing capacity.

[0032] In one embodiment, during the dry-jet wet spinning process, the temperature inside the twin-screw extruder is 40℃~180℃, the residence time of the polyhydroxyamide precursor spinning solution in the twin-screw extruder is 10min~20min, and the polyhydroxyamide precursor spinning solution forms an anisotropic liquid crystal spinning solution after being extruded from the twin-screw extruder.

[0033] The spinneret has more than 150 holes, the diameter of the spinneret holes is 0.1mm to 0.3mm, and the air gap is 5mm to 20mm.

[0034] The coagulation bath is one or more of water, phosphoric acid, and ethanol, and the temperature of the coagulation bath is 5℃~50℃; the winding is carried out by a winding machine at a winding speed of 2m / min~500m / min; the draw ratio is 5~30.

[0035] In one implementation, the thermal ring forming specifically involves: sequentially undergoing unwinding, five-roll traction, and thermal ring forming.

[0036] In one implementation method, during the thermal circulatory process, under an inert atmosphere, the temperature for thermal circulatory formation is 400℃~800℃, and the time for thermal circulatory formation is 5s~25s.

[0037] After thermal circulatory treatment, oiling and winding are carried out. The oiling rate is 1% to 3%, and the winding speed is 1m / min to 400m / min.

[0038] Excessive temperature or prolonged time during thermal cyclization can cause thermal degradation of fibers, resulting in a decrease in fiber strength and modulus.

[0039] As described above, the benzoxazole-based polymer fiber and its preparation method of this application have the following beneficial effects:

[0040] The benzoxazole-based polymer fiber prepared in this application is obtained by using benzimidazole with a Lewis base structure through polymerization and spinning to obtain polyhydroxyamide precursor fiber. During thermal cyclization, benzimidazole with a Lewis base structure can catalyze the thermal cyclization of polyhydroxyamide in situ, causing it to partially close the ring and form a liquid crystal phase. This improves the ring closure rate and endows it with good comprehensive properties. At the same time, the prepared benzoxazole-based polymer fiber can flexibly control the introduction of active groups and has the conditions to construct a molecular hydrogen bond network. It can effectively improve the compression resistance and UV resistance of conventional PBO fibers and enhance the interfacial bonding force between the fiber and the resin. Detailed Implementation

[0041] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0042] Unless otherwise specified, the raw materials, solvents, reagents and equipment used in the embodiments of this application were all purchased commercially.

[0043] Given the need for effective control of cyclization degree, formation of liquid crystal spinning solution, and improvement of fiber strength, modulus, and high-temperature resistance in existing technologies, this application introduces the structures of benzimidazole, terephthalic acid, and / or terephthalic acid derivatives into the main chain of p-phenylenebenzodioxazole, and prepares novel benzoxazole-based polymer fibers through a two-step method. This improves the cyclization rate of the polymer, giving it excellent comprehensive properties. Simultaneously, the introduction of active groups can be flexibly controlled, providing conditions for constructing molecular hydrogen bond networks, effectively improving the compression resistance and UV resistance of conventional PBO fibers, and enhancing the interfacial bonding between the fiber and resin.

[0044] The principle of preparing benzoxazole-based polymer fibers in this application is shown in the following equation:

[0045]

[0046] Wherein, X is selected from hydroxyl (-OH), chlorine (-Cl), or hydrogen (-H);

[0047] Formula (Ⅰ) is selected from one or more of 2,5-dihydroxyterephthalic acid (DHTA), terephthalic acid and 2,5-dichloroterephthalic acid (TA-Cl);

[0048] Formula (II) is a polyhydroxyamide precursor fiber;

[0049] Formula (Ⅲ) is a benzoxazole-based polymer fiber.

[0050] Example 1

[0051] Add 2L of polyphosphoric acid (PPA) and 61.50g of 4,6-diaminoresorcinol monomer to a nitrogen-purified polymerization reactor, stir for 20 min, then add 1.23g of stannous chloride, 6.15g of phosphorus pentoxide, 33.92g of 2,5-dichloroterephthalic acid and 61.50g of 2-(4-aminophenyl)-5-aminobenzimidazole monomer, stir for 30 min, then add the remaining 33.92g of 2,5-dichloroterephthalic acid, and stir the reaction at 10℃ for 24 h to obtain a polyhydroxyamide precursor spinning solution.

[0052] The polyhydroxyamide precursor spinning solution was filtered and degassed sequentially before entering a twin-screw extruder at a temperature of 40°C. After a 10-minute residence time, the solution was conveyed to a metering pump under the shearing action of the twin-screw extruder. After precise weighing by the metering pump, the solution was extruded through the spinneret orifices. After stretching in the air gap, the solution entered a water coagulation bath, followed by washing, drying, oiling, and winding to obtain polyhydroxyamide precursor fibers. The spinneret had 150 orifices with a diameter of 0.3 mm and an air gap of 5 mm. The coagulation bath temperature was 5°C. The winding was performed using a winding machine at a winding speed of 2 m / min, with a fiber draw ratio of 5.

[0053] The wound polyhydroxyamide precursor fiber was unwound, pulled with five rollers, and then thermally cyclized at high temperature in a nitrogen atmosphere. The thermal cyclization temperature was 400℃ and the thermal cyclization time was 5s to obtain a novel benzoxazole polymer fiber. Then, it was oiled and wound, with an oiling rate of 1% and a winding speed of 1m / min.

[0054] Example 2

[0055] In a nitrogen-purged polymerization reactor, 20 L of polyphosphoric acid (PPA) and 2.1 kg of 4,6-diaminoresorcinol monomer were added and stirred for 50 min. Then, 175.00 g of stannous chloride, 175.00 g of phosphorus pentoxide, 488.20 g of 2,5-dihydroxyterephthalic acid, 579.10 g of 2,5-dichloroterephthalic acid, and 1.4 kg of 2-(4-aminophenyl)-5-aminobenzimidazole monomer were added and stirred for 30 min. Then, the remaining 488.20 g of 2,5-dihydroxyterephthalic acid and 579.10 g of 2,5-dichloroterephthalic acid were added. The mixture was stirred and reacted at 20 °C for 36 h to obtain a polyhydroxyamide precursor spinning solution.

[0056] The polyhydroxyamide precursor spinning solution was filtered and degassed sequentially before entering a twin-screw extruder at a temperature of 110°C. After a 15-minute residence time, the solution was conveyed to a metering pump under shearing action. After precise weighing by the metering pump, the solution was extruded through the spinneret orifices. After stretching in the air gap, the solution entered a coagulation bath containing 5% ethanol aqueous solution. Following washing, drying, oiling, and winding, polyhydroxyamide precursor fibers were obtained. The spinneret had 200 orifices with a diameter of 0.2 mm and an air gap of 8 mm. The coagulation bath temperature was 30°C. Winding was performed using a winding machine at a speed of 230 m / min, with a fiber draw ratio of 12.

[0057] The wound polyhydroxyamide precursor fiber was unwound, pulled with five rollers, and then thermally cyclized at high temperature in a nitrogen atmosphere. The thermal cyclization temperature was 600℃ and the thermal cyclization time was 10s to obtain a novel benzoxazole polymer fiber. Then, it was oiled and wound, with an oiling rate of 2% and a winding speed of 200m / min.

[0058] Example 3

[0059] 200L of polyphosphoric acid (PPA) and 109.72kg of 4,6-diaminoresorcinol monomer were added to a nitrogen-purified polymerization reactor and stirred for 80min. Then, 8.48kg of stannous chloride, 10.55kg of phosphorus pentoxide, 51.02kg of 2,5-dihydroxyterephthalic acid and 50.64kg of 2-(4-aminophenyl)-5-aminobenzimidazole monomer were added and stirred for 30min. Then, the remaining 51.02kg of 2,5-dihydroxyterephthalic acid was added and the reaction was carried out at 40℃ for 48h to obtain a polyhydroxyamide precursor spinning solution.

[0060] The polyhydroxyamide precursor spinning solution was filtered and degassed sequentially before entering a twin-screw extruder at a temperature of 180°C. After a 20-minute residence time, the solution was conveyed to a metering pump under shearing action. After precise weighing by the metering pump, the solution was extruded through the spinneret orifices. After stretching in the air gap, the solution entered a coagulation bath containing a 15% phosphoric acid aqueous solution. Following washing, drying, oiling, and winding, polyhydroxyamide precursor fibers were obtained. The spinneret had 300 orifices with a diameter of 0.1 mm and an air gap of 20 mm. The coagulation bath temperature was 50°C. Winding was performed using a winding machine at a speed of 500 m / min, with a fiber draw ratio of 30.

[0061] The wound polyhydroxyamide precursor fiber was unwound, pulled with five rollers, and then thermally cyclized at high temperature in a nitrogen atmosphere. The thermal cyclization temperature was 800℃ and the thermal cyclization time was 25s to obtain a novel benzoxazole polymer fiber. Then, it was oiled and wound, with an oiling rate of 3% and a winding speed of 400m / min.

[0062] Comparative Example

[0063] The one-step preparation of conventional PBO fibers includes the following steps:

[0064] Add 20L of polyphosphoric acid (PPA) and 2.1kg of 4,6-diaminoresorcinol to a nitrogen-purified polymerization reactor, stir for 120min, add 1.56kg of terephthalic acid, stir for 60min, add 92.88g of stannous chloride and 284.3g of phosphorus pentoxide, and then add 929.48g of terephthalic acid. Perform staged heating: stir at 50℃ for 3h, stir at 70℃ for 3h, stir at 80℃ for 5h, stir at 100℃ for 5h, and stir at 120℃ for 5h. During the heating and polymerization process, add 172.67g of phosphorus pentoxide twice to obtain a prepolymer solution.

[0065] The prepolymer solution is first passed through a twin-screw extruder (160°C), and then through a spinning assembly for wet and dry spinning. After the spinning solution is stretched in an air layer (15mm), it enters a coagulation bath (water) to initially form fibers. After alkali washing, water washing, drying and winding, conventional PBO fibers are obtained.

[0066] The benzoxazole-based polymer fibers prepared in Examples 1 to 3, and the conventional PBO fibers prepared in the comparative example were irradiated under a 340 nm ultraviolet lamp for 288 hours. The changes in fiber strength are shown in Table 1.

[0067] Table 1 Test Results

[0068]

[0069]

[0070] As can be seen from Table 1, the benzoxazole-based polymer fibers prepared in Examples 1 to 3 exhibited high strength retention rates after irradiation under ultraviolet light; while the conventional PBO fibers prepared in the comparative examples showed low strength retention rates after irradiation under ultraviolet light.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing benzoxazole-based polymer fibers, characterized in that, Includes the following steps: 4,6-Diaminoresorcinol monomer, terephthalic acid derivative monomer, and 2-(4-aminophenyl)-5-aminobenzimidazole monomer were mixed in an acidic solvent, and antioxidants and absorbents were added. After polymerization, a polyhydroxyamide precursor spinning solution was obtained. The polyhydroxyamide precursor spinning solution is spun to obtain polyhydroxyamide precursor fibers. The polyhydroxyamide precursor fiber was thermally cyclized to obtain benzoxazole-based polymer fiber; the benzoxazole-based polymer fiber is represented by the following chemical formula: The terephthalic acid derivative monomer is selected from 2,5-dihydroxyterephthalic acid and 2,5-dichloroterephthalic acid; The antioxidant is stannous chloride, and the absorbent is phosphorus pentoxide; The spinning process is a dry-jet wet spinning method. The dry-jet wet spinning process specifically involves: first, filtering and degassing the polyhydroxyamide precursor spinning solution sequentially; second, feeding it into a twin-screw extruder, where it is extruded under the shearing action of the twin-screw extruder; then, extruding it through the spinneret holes of the spinneret via a metering pump, and stretching it in the air gap; finally, sequentially performing coagulation bath molding, washing, drying, oiling, and winding to obtain polyhydroxyamide precursor fibers. In the chemical formula of the benzoxazole polymer fiber, X is selected from hydroxyl and chlorine.

2. The preparation method according to claim 1, characterized in that, The acidic solvent is polyphosphoric acid.

3. The preparation method according to claim 1, characterized in that, The 4,6-diaminoresorcinol monomer accounts for 5 wt% to 26 wt% of the mass of the polyhydroxyamide precursor spinning solution. The 2-(4-aminophenyl)-5-aminobenzimidazole monomer accounts for 5 wt% to 12 wt% of the mass of the polyhydroxyamide precursor spinning solution. The molar ratio of the terephthalic acid derivative monomer to the 4,6-diaminoresorcinol monomer is 1:

1. The antioxidant accounts for 0.1 wt% to 2 wt% of the mass of the polyhydroxyamide precursor spinning solution. The mass of the absorbent is 0.5 wt% to 2.5 wt% of the mass of the polyhydroxyamide precursor spinning solution.

4. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 10℃ to 40℃ for a duration of 24h to 48h.

5. The preparation method according to claim 1, characterized in that, During the dry-jet wet spinning process, the temperature inside the twin-screw extruder is 40℃~180℃, the residence time of the polyhydroxyamide precursor spinning solution in the twin-screw extruder is 10min~20min, and the polyhydroxyamide precursor spinning solution forms an anisotropic liquid crystal spinning solution after being extruded from the twin-screw extruder. The spinneret has more than 150 holes, the diameter of the spinneret holes is 0.1mm to 0.3mm, and the air gap is 5mm to 20mm. The coagulation bath is one or more of water, phosphoric acid, and ethanol, and the temperature of the coagulation bath is 5℃~50℃; the winding is carried out by a winding machine at a winding speed of 2m / min~500m / min; the draw ratio is 5~30.

6. The preparation method according to claim 1, characterized in that, The thermal ring forming process specifically involves: unwinding, five-roll traction, and thermal ring forming in sequence.

7. The preparation method according to claim 1, characterized in that, During the thermal cyclization process, under an inert atmosphere, the temperature for thermal cyclization is 400℃~800℃, and the time for thermal cyclization is 5s~25s. After thermal circulatory treatment, oiling and winding are carried out. The oiling rate is 1% to 3%, and the winding speed is 1m / min to 400m / min.

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