Polyimide-ceramic fiber composite paper as well as preparation method and application thereof

Abstract

The invention relates to the technical field of papermaking, and discloses polyimide-ceramic fiber composite paper as well as a preparation method and application thereof. The polyimide-ceramic fiber composite paper is obtained by carrying out imidization on polyamic acid salt-ceramic fiber composite paper; the polyamic acid salt-ceramic fiber composite paper comprises polyamic acid salt chopped fibers and ceramic fibers which are wound with each other; the polyamide acid salt chopped fiber is obtained by processing a polyamide acid salt solution which is catalytically converted by polyamide acid. The polyimide-ceramic fiber composite paper prepared by the method has excellent heat resistance and mechanical strength, and is suitable for being used as a high-temperature insulating material in the industries of aerospace, new energy and the like.

Description

Technical Field

[0001] The present invention relates to the field of papermaking, and particularly to a polyimide-ceramic fiber composite paper, a preparation method thereof, and an application thereof. Background Art

[0002] High-temperature resistant insulating paper is one of the most widely used insulating materials in the electrical engineering field. As a special polymer with high heat resistance, polyimide has excellent insulating properties and chemical stability, and is an ideal material for electronic and electrical components. In recent years, with the development of electronic devices towards miniaturization, intelligence, and integration, the requirements for insulating materials have become increasingly strict. Polyimide paper prepared by the wet papermaking process has been favored by the electronic and electrical industries due to its excellent physical and chemical properties. However, limited by the temperature resistance of the polymer, the long-term use temperature of polyimide paper usually does not exceed 250°C, which to a certain extent limits its application space.

[0003] Currently, there are mainly two preparation processes for polyimide paper products: (1) Prepared by the wet papermaking and hot pressing forming process of polyamic acid short fibers (for example, CN 102839560 B). During the hot pressing forming process, polyamic acid undergoes imidization to transform into polyimide. However, polyamic acid is in a semi-stable state, and with the change of time or storage conditions, the polyamic acid short fibers are extremely prone to degradation, resulting in performance decline. Therefore, the tensile index of the polyimide paper obtained by this method is generally low. (2) Directly using polyimide short fibers for wet papermaking to prepare polyimide paper. However, due to the lack of reactive groups or charges on the surface of polyimide short fibers in this process, the intermolecular force between fibers is weak, and the tensile index of the prepared paper is also low.

[0004] As a new material, inorganic fibers show broad development prospects in the electrical engineering field due to their ultra-high heat resistance, excellent electrical insulation properties, and environmental friendliness. During the operation of electrical equipment, there is often a phenomenon of temperature rise, especially in high-power electrical equipment. Inorganic fibers can withstand relatively high environmental temperatures, and their heat resistance is generally above 800°C, and the thermal decomposition temperature of some fibers is higher than 1000°C, which can effectively prevent material aging and performance decline, and ensure the stable operation and service life of electrical equipment. In the insulating materials of high-voltage equipment, transformers, and cables, the dielectric properties of inorganic fibers can effectively inhibit current leakage and short-circuit phenomena, ensuring the safety and reliability of the equipment. Therefore, to improve the high-temperature resistance of polyimide paper, inorganic fibers can be introduced during the preparation process to develop a preparation method that can significantly improve the heat resistance and mechanical strength of polyimide paper, which has significant practical application value. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a polyimide-ceramic fiber composite paper, its preparation method and application. The polyimide-ceramic fiber composite paper prepared by the method of the present invention has both excellent heat resistance and mechanical strength, and is suitable as a high-temperature insulating material in industries such as aerospace and new energy.

[0006] The specific technical solution of the present invention is as follows: In the first aspect, the present invention provides a polyimide-ceramic fiber composite paper, which is obtained by imidization of a polyamic acid salt-ceramic fiber composite paper; the polyamic acid salt-ceramic fiber composite paper includes intertwined polyamic acid salt short fibers and ceramic fibers; the polyamic acid salt short fibers are obtained by processing a polyamic acid salt solution catalyzed and converted from polyamic acid.

[0007] In the second aspect, the present invention provides a preparation method of a polyimide-ceramic fiber composite paper, which includes the following steps: a) Prepare a polyamic acid solution.

[0008] b) Use a catalyst to convert polyamic acid into polyamic acid salt, and process the obtained polyamic acid salt solution into polyamic acid salt short fibers.

[0009] c) Disperse the polyamic acid salt short fibers and ceramic fibers in water to obtain a slurry, and perform wet papermaking to obtain a polyamic acid salt-ceramic fiber composite paper.

[0010] d) Perform imidization treatment on the polyamic acid salt-ceramic fiber composite paper to obtain a polyimide-ceramic fiber composite paper.

[0011] The polyimide-ceramic fiber composite paper prepared by the method of the present invention is composed of mutually entangled polyimide short fibers and ceramic fibers. First, due to the presence of ceramic fibers, the heat resistance and insulation of the paper can be significantly improved. Second, in the prior art, when using polyimide short fibers to make paper, since there are few reactive groups or charges on the surface of polyimide short fibers, the intermolecular force between the fibers is weak, resulting in a low tensile index of the prepared paper; if using polyamic acid short fibers to make paper, although polyamic acid has active groups, it is extremely easy to hydrolyze in water, resulting in a brittle paper. Therefore, the present invention ingeniously first converts polyamic acid into polyamic acid salt, and then makes it transform into polyimide through imidization treatment after wet papermaking. Compared with polyimide short fibers, polyamic acid salt short fibers have rich surface active groups, and chemical reactions can occur between the fibers to produce chemical entanglement, and the interaction between the fibers can also be increased during the imidization process, improving the tensile index of the polyimide paper (that is, the polyamic acid salt has rich surface active groups, which can enhance fiber interweaving, the interaction force is strong, and the paper is not easy to tear); compared with polyamic acid, polyamic acid salt has strong anti-hydrolysis ability, can remain stable in aqueous solution for a long time, and rapidly dehydrates to transform into polyimide above 200°C. In summary, the method of the present invention can not only maintain a high level of active groups in the fibers, but also inhibit their depolymerization in water, thereby significantly improving the mechanical properties and electrical properties of the paper. In addition, since the use of polyamic acid salt short fibers can increase the interfacial strength between the fibers, there is no need to use additional additives, avoiding the negative impact of additives on the product.

[0012] Preferably, in step a), the preparation process of the polyamic acid solution includes: polymerizing diamine, diamine containing sulfonic acid group and dianhydride in an organic solvent to obtain a polyamic acid solution.

[0013] First, the diamine containing sulfonic acid group can increase the hydrophilicity of polyimide acid salt and enhance the dispersion of fibers in water; second, the sulfonic acid group can generate an interaction force with the ceramic fibers pretreated with silane coupling agent, enhancing the interaction between the two.

[0014] More preferably, the diamine containing sulfonic acid group accounts for 10-30 mol% of the total diamine.

[0015] The present invention finds that the proportion of the diamine containing sulfonic acid group is crucial: too high a sulfonic acid group will lead to too strong water solubility of the fibers, and too low will lead to insufficient interaction force between the polyamic acid salt short fibers and the ceramic fibers.

[0016] Preferably, in step a), the diamine is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone and 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0017] Preferably, in step a), the diamine containing a sulfonic acid group is selected from one or more of 1,4-phenylenediamine-2-sulfonic acid, 3,5-diaminobenzenesulfonic acid, 2,2'-disulfonic acid benzidine, and 4,4'-diamino-3,3'-biphenyl disulfonic acid.

[0018] Preferably, in step a), the dianhydride is selected from one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, hydroquinone diether dianhydride, resorcinol diether dianhydride, and bisphenol A diether dianhydride.

[0019] Preferably, in step a), the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0020] Preferably, in step a), the molar ratio of the total diamine to the dianhydride is 1:(0.8 - 1.2).

[0021] Preferably, in step a), the temperature of the polymerization reaction is 0 - 15°C, and the time is 4 - 12 h.

[0022] Preferably, in step b), the average diameter of the polyamide acid salt short fibers is 5 - 10 μm, and the average length is 1 - 10 mm; in step c), the average diameter of the ceramic fibers is 1 - 5 μm, and the average length is 0.1 - 1 mm.

[0023] The present invention discovers that the average diameter and average length of the above two kinds of fibers have an important influence on the performance of the final paper: The polyamide acid salt short fibers with an average diameter of 5 - 10 μm have a high specific surface area, and the fibers are closely combined, which can improve the uniformity and mechanical strength of the paper, are more likely to form a dense structure, reduce the porosity, and are suitable for insulation or high-temperature applications. Too fine fibers are prone to agglomeration and difficult to disperse, and additional dispersants need to be added or the process needs to be optimized. Too thick fibers result in loose paper and a decrease in mechanical properties. The polyamide acid salt short fibers with an average length of 1 - 10 mm have good dispersion uniformity and are suitable for the wet forming process, reducing the risk of agglomeration; too short fibers lead to insufficient interweaving and rely on adhesives or hot pressing to enhance the binding force; too long fibers are difficult to disperse and require high-shear stirring or special dispersion. The ceramic fibers with an average diameter of 1 - 5 μm have a high specific surface area, can enhance the interfacial bonding between the fibers and the polyamide acid salt short fibers, are more likely to form a dense structure, reduce the porosity of the material, improve the mechanical properties, and enhance the high-temperature stability. Too fine fibers are difficult to disperse and prone to agglomeration; too thick fibers have insufficient interfacial bonding force. The ceramic fibers with an average length of 0.1 - 1 mm have good dispersibility and are suitable for forming complex shapes, suppressing crack propagation by a random distribution method, and enhancing the toughness of the product. Too long fibers will cause the rheology of the slurry to become weak and the fibers to settle easily.

[0024] Preferably, in step b), the catalyst is selected from one or more of triethylamine, pyridine, benzimidazole and 1-ethylpiperidine.

[0025] Preferably, in step b), the molar ratio of the catalyst to the total diamine is (0.5-2):1.

[0026] Preferably, in step b), the solid content of the polyamide acid salt solution is 10-25 wt%.

[0027] Preferably, in step b), the processing of the polyamide acid salt short fibers includes: subjecting the polyamide acid salt solution to vacuum degassing treatment, then extruding it through a porous spinneret into water, and performing defibration, cutting, fibrillation and drying by a disk refiner to obtain the polyamide acid salt short fibers.

[0028] Preferably, in step c), the mass ratio of the polyamide acid salt short fibers to the ceramic fibers is 100:(10-30).

[0029] The present invention finds that the proportion of the above-mentioned ceramic fibers has an important influence on the performance of the final paper: if the ceramic fibers are too few (<10%), the temperature resistance and tensile index of the paper are insufficient and cannot meet the requirements of high-temperature and high-load scenarios; but excessive ceramic fibers (>30%) will cause stress concentration due to fiber agglomeration, the interfacial bonding between the fibers and the polyamide acid salt short fibers becomes poor, cracks are easy to expand along the interface, the toughness decreases, and the tensile index and tear index of the paper are reduced.

[0030] Preferably, in step c), the ceramic fibers are pretreated with a silane coupling agent.

[0031] The polyamide acid salt short fibers have rich surface charges and can generate charge interaction forces with the ceramic fibers treated with the silane coupling agent, which helps the dispersion and composite of the ceramic fibers, and thus is beneficial to preparing a paper with high tensile strength and tear resistance.

[0032] Preferably, in step c), the solid content of the slurry is 0.5-2 wt%.

[0033] Preferably, in step c), the wet papermaking includes papermaking, pressing and drying treatments.

[0034] More preferably, in step c), the temperature of the drying treatment is 80-120°C and the time is 10-30 min.

[0035] Preferably, in step d), the imidization treatment includes: first maintaining the temperature at 150-250°C for 10-20 min, and then maintaining the temperature at 300-400°C for 5-10 min.

[0036] The principle and advantages of the above multi-stage imidization treatment of the present invention are as follows: Gradual heating can activate reaction sites step by step, enabling the molecular chains to rearrange orderly and ensuring the same degree of cyclization of the overall material. Solvent is preferentially removed at a low temperature stage (below 150°C), imidization is initiated at a medium temperature stage (around 200°C), and deep cyclization is completed at a high temperature stage (above 300°C). This segmented strategy can maximize the cyclization rate, approaching 100%, forming a rigid heteroaromatic ring structure, and endowing the material with a high glass transition temperature and excellent heat resistance.

[0037] In the third aspect, the present invention provides the application of the polyimide-ceramic fiber composite paper obtained by the above preparation method as a high-temperature resistant insulating material in industries such as aerospace and new energy.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The polyimide-ceramic fiber composite paper prepared by the method of the present invention is composed of mutually entangled polyimide short fibers and ceramic fibers. The presence of ceramic fibers can significantly improve the heat resistance and insulation of the paper.

[0039] (2) In the preparation method of the present invention, polyamic acid is first converted into polyamic acid salt, and then it is converted into polyimide through imidization treatment after wet papermaking. This method can not only maintain a high number of active groups of the fibers during wet papermaking but also inhibit their depolymerization in water, thus significantly improving the mechanical and electrical properties of the paper. In addition, the present invention does not require the use of additional additives, avoiding the negative impact of additives on the product. Specific Embodiments

[0040] The present invention will be further described below in conjunction with embodiments.

[0041] General Embodiment First, a polyimide-ceramic fiber composite paper, which is obtained by imidizing a polyamic acid salt-ceramic fiber composite paper; the polyamic acid salt-ceramic fiber composite paper includes mutually entangled polyamic acid salt short fibers and ceramic fibers; the polyamic acid salt short fibers are obtained by processing a polyamic acid salt solution catalyzed and converted from polyamic acid.

[0042] Secondly, a preparation method of a polyimide-ceramic fiber composite paper, which includes the following steps: a) Prepare a polyamic acid solution: Polymerize diamine, diamine containing sulfonic acid group, and dianhydride in an organic solvent to obtain a polyamic acid solution; wherein, the diamine containing sulfonic acid group accounts for 10-30 mol% of the total diamine.

[0043] Preferably, in step a), the diamine is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, and 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0044] Preferably, in step a), the sulfonic acid group-containing diamine is selected from one or more of 1,4-phenylenediamine-2-sulfonic acid, 3,5-diaminobenzenesulfonic acid, 2,2-disulfonic acid-based benzidine, and 4,4'-diamino-3,3'-biphenyldisulfonic acid.

[0045] Preferably, in step a), the dianhydride is selected from one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, hydroquinone diether dianhydride, resorcinol diether dianhydride, and bisphenol A diether dianhydride.

[0046] Preferably, in step a), the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0047] Preferably, in step a), the molar ratio of the total diamine to the dianhydride is 1:(0.8 - 1.2).

[0048] Preferably, in step a), the temperature of the polymerization reaction is 0 - 15 °C, and the time is 4 - 12 h.

[0049] b) Using a catalyst to convert the polyamic acid into a polyamic acid salt, and processing the obtained polyamic acid salt solution into short polyamic acid salt fibers.

[0050] Preferably, in step b), the processing of the short polyamic acid salt fibers includes: subjecting the polyamic acid salt solution to vacuum degassing treatment, then extruding it through a porous spinneret into water, and performing defibration, cutting, fibrillation, and drying by a disk refiner to obtain short polyamic acid salt fibers.

[0051] Preferably, in step b), the average diameter of the short polyamic acid salt fibers is 5 - 10 μm, and the average length is 1 - 10 mm; Preferably, in step b), the catalyst is selected from one or more of triethylamine, pyridine, benzimidazole, and 1-ethylpiperidine.

[0052] Preferably, in step b), the molar ratio of the catalyst to the total diamine is (0.5 - 2):1.

[0053] Preferably, in step b), the solid content of the polyamic acid salt solution is 10 - 25 wt%.

[0054] c) Short-cut polyamide acid fibers and ceramic fibers are dispersed in water to obtain a slurry, and wet papermaking is carried out to obtain a polyamide acid-ceramic fiber composite paper.

[0055] Preferably, in step c), the wet papermaking includes papermaking, pressing and drying treatments.

[0056] Preferably, in step c), the mass ratio of the short-cut polyamide acid fibers to the ceramic fibers is 100∶(10 - 30).

[0057] Preferably, in step c), the ceramic fibers are pretreated with KH550.

[0058] Preferably, in step c), the average diameter of the ceramic fibers is 1 - 5 μm, and the average length is 0.1 - 1 mm.

[0059] Preferably, in step c), the solid content of the slurry is 0.5 - 2 wt%.

[0060] More preferably, in step c), the temperature of the drying treatment is 80 - 120 °C, and the time is 10 - 30 min.

[0061] d) The polyamide acid-ceramic fiber composite paper is imidized to obtain a polyimide-ceramic fiber composite paper.

[0062] Preferably, in step d), the imidization treatment includes: first, heat preservation at 150 - 250 °C for 10 - 20 min, and then heat preservation at 300 - 400 °C for 5 - 10 min.

[0063] Finally, the present invention provides the application of the polyimide-ceramic fiber composite paper obtained by the above preparation method as a high-temperature resistant insulating material in industries such as aerospace and new energy.

[0064] Specific examples and comparative examples Example 1 Step a: In a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (CAS No.: 101 - 80 - 4) (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (CAS: 88 - 45 - 9) (1 mol, 0.19 kg) and pyromellitic dianhydride (CAS: 89 - 32 - 7) (5 mol, 1.09 kg) are dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted in a 5 °C environment for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After subjecting the polyamic acid salt solution to vacuum degassing treatment, it is extruded into water through a porous spinneret, and then subjected to defibration, cutting, fibrillation, and drying by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Ultrasonically clean the ceramic fibers in a 5 wt% NaOH solution for 10 min, and dry them at 60 °C for 1 h to remove surface impurities and activate them. Then, prepare a 1 wt% KH550 solution with a mixed solution of ethanol and water. Immerse the fibers and KH550 in the solution at a mass ratio of 50:1, treat them at 40 °C for 15 min, and dry them at 120 °C for 1 h. Sequentially add 1.0 kg of short polyamic acid salt fibers and 0.2 kg of KH550-treated ceramic fibers (fiber average length 0.5 mm, average diameter 1 μm) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, and perform papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to high-temperature treatment at 300 °C for 10 min for imidization to obtain a polyimide-ceramic fiber composite paper.

[0065] Example 2: The difference from Example 1 lies in using different types of reagents such as diamine and dianhydride Step a: Under a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl sulfone (CAS No.: 80-08-0) (4 mol, 0.99 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and biphenyl dianhydride (CAS No.: 2420-87-3) (5 mol, 1.47 kg) in N,N-dimethylacetamide (15.02 kg), and stir and react in an environment at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add pyridine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After subjecting the polyamic acid salt solution to vacuum degassing treatment, it is extruded into water through a porous spinneret, and then subjected to defibration, cutting, fibrillation, and drying by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially add 1.0 kg of short polyamic acid salt fibers and 0.2 kg of KH550-treated (same as Example 1) ceramic fibers (fiber average length 0.5 mm, average diameter 1 μm) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, and perform papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to high-temperature treatment at 300 °C for 10 min for imidization to obtain a polyimide-ceramic fiber composite paper.

[0066] Example 3: The difference from Example 1 is that different types of diamines, dianhydrides and other reagents are used. Step a: In a nitrogen atmosphere, 2,2′-bis[4-(4-aminophenoxyphenyl)]propane (CAS No.: 13080-86-9) (4 mol, 1.64 kg), 2,2-disulfonic acid benzidine (CAS No.: 117-61-3) (1 mol, 0.34 kg) and bisphenol A diether dianhydride (CAS: 38103-06-9) (5 mol, 2.60 kg) were dissolved in N,N-dimethylacetamide (25.95 kg), and stirred and reacted in a 5 °C environment for 6 h to obtain a polyamic acid solution. Step b: Benzimidazole (5 mol) was added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyamic acid salt solution with a solid content of 15% was obtained. The polyamic acid salt solution was subjected to vacuum defoaming treatment and then extruded into water through a porous spinneret, and was disintegrated, cut, fibrillated and dried by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm. Step c: 1.0 kg of short polyamic acid salt fibers and 0.2 kg of ceramic fibers treated with KH550 (the same as in Example 1) (fiber average length 0.5 mm, average diameter 1 μm) were successively added to an appropriate amount of water, stirred and mixed to obtain a slurry with a solid content of 2 wt%, and then paper was made, pressed, and dried at 120 °C for 20 min to obtain the base paper. Step d: The obtained base paper was subjected to imidization at a high temperature of 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0067] Example 4: The difference from Example 1 is only that step d of Example 4 uses a stepped imidization process, which is specifically as follows: Step a: In a nitrogen atmosphere, 4,4′-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg) and pyromellitic dianhydride (5 mol, 1.09 kg) were dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted in a 5 °C environment for 6 h to obtain a polyamic acid solution. Step b: Triethylamine (5 mol) was added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyamic acid salt solution with a solid content of 15% was obtained. The polyamic acid salt solution was subjected to vacuum defoaming treatment and then extruded into water through a porous spinneret, and was disintegrated, cut, fibrillated and dried by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm. Step c: Put 1.0 kg of chopped polyamide acid fibers and 0.2 kg of ceramic fibers treated with KH550 (same as Example 1) (average fiber length 0.5 mm, average diameter 1 μm) into an appropriate amount of water in sequence, stir and mix to obtain a slurry with a solid content of 2 wt%, perform papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; In step d), the imidization treatment includes: first maintaining the temperature at 250 °C for 10 min, and finally maintaining the temperature at 300 °C for 5 min.

[0068] Example 5: The difference from Example 1 is only that the sulfonic acid-containing diamine accounts for 10 mol% of the total diamine.

[0069] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4.5 mol, 0.90 kg), 1,4-phenylenediamine-2-sulfonic acid (0.5 mol, 0.09 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.79 kg), and stir and react in a 5 °C environment for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamide acid salt solution with a solid content of 15%, subject the polyamide acid salt solution to vacuum degassing treatment, then extrude it through a porous spinneret into water, and perform defibration, cutting, fibrillation, and drying with a disc refiner to obtain chopped polyamide acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Put 1.0 kg of chopped polyamide acid fibers and 0.2 kg of ceramic fibers treated with KH550 (same as Example 1) (average fiber length 0.5 mm, average diameter 1 μm) into an appropriate amount of water in sequence, stir and mix to obtain a slurry with a solid content of 2 wt%, perform papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to high-temperature treatment at 300 °C for 10 min for imidization to obtain a polyimide-ceramic fiber composite paper.

[0070] Example 6: The difference from Example 1 is only that the sulfonic acid-containing diamine accounts for 30 mol% of the total diamine.

[0071] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (3.5 mol, 0.70 kg), 1,4-phenylenediamine-2-sulfonic acid (1.5 mol, 0.28 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.73 kg), and stir and react in a 5 °C environment for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After subjecting the polyamic acid salt solution to vacuum degassing treatment, it is extruded into water through a porous spinneret, and then defibrated, cut, fibrillated, and dried by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially add 1.0 kg of short polyamic acid salt fibers and 0.2 kg of ceramic fibers (average fiber length 0.5 mm, average diameter 1 μm) treated with KH550 (same as Example 1) to an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, perform papermaking, pressing, and drying treatment at 120 °C for 20 min to obtain a base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0072] Example 7: The difference from Example 1 is only that: in Step c, the amount of ceramic fibers treated with KH550 is 0.1 kg.

[0073] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.79 kg), and stir and react in a 5 °C environment for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After subjecting the polyamic acid salt solution to vacuum degassing treatment, it is extruded into water through a porous spinneret, and then defibrated, cut, fibrillated, and dried by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially add 1.0 kg of short polyamic acid salt fibers and 0.1 kg of ceramic fibers (average fiber length 0.5 mm, average diameter 1 μm) treated with KH550 (same as Example 1) to an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, perform papermaking, pressing, and drying treatment at 120 °C for 20 min to obtain a base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0074] Example 8: The difference from Example 1 is only that: in Step c, the amount of ceramic fibers treated with KH550 is 0.3 kg.

[0075] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg) and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.79 kg), and stir and react at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After vacuum degassing the polyamic acid salt solution, extrude it through a porous spinneret into water, and then carry out defibration, cutting, fibrillation and drying by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially put 1.0 kg of short polyamic acid salt fibers and 0.3 kg of ceramic fibers (with an average fiber length of 0.5 mm and an average diameter of 1 μm) treated with KH550 (the same as in Example 1) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, and then carry out papermaking, pressing and drying at 120 °C for 20 min to obtain a base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0076] Comparative Example 1 (using short polyamic acid fibers) Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg) and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.79 kg), and stir and react at 5 °C for 6 h to obtain a polyamic acid solution; Step b: After vacuum degassing the polyamic acid solution, extrude it through a porous spinneret into water, and then carry out defibration, cutting, fibrillation and drying by a disk refiner to obtain short polyamic acid fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially put 1.0 kg of short polyamic acid fibers and 0.2 kg of ceramic fibers (with an average fiber length of 0.5 mm and an average diameter of 1 μm) treated with KH550 (the same as in Example 1) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, and then carry out papermaking, pressing and drying at 120 °C for 20 min to obtain a base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0077] Comparative Example 2 (using short polyimide fibers) Step a: In a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) were dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Triethylamine (5 mol) and acetic anhydride (10 mol) were added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyimide solution with a solid content of 15% was obtained. The polyimide solution was subjected to vacuum degassing treatment and then extruded through a porous spinneret into water, and then defibrated, cut, fibrillated, and dried by a disk refiner to obtain polyimide short fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: 1.0 kg of polyimide cut fibers and 0.2 kg of ceramic fibers treated with KH550 (same as in Example 1) (fiber average length 0.5 mm, average diameter 1 μm) were successively added to an appropriate amount of water, stirred and mixed to obtain a slurry with a solid content of 2 wt%, and then subjected to papermaking, pressing, and drying at 120 °C for 20 min to obtain a polyimide-ceramic fiber composite paper.

[0078] Comparative Example 3 (without ceramic fibers) Step a: In a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) were dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Triethylamine (5 mol) was added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyamic acid salt solution with a solid content of 15% was obtained. The polyamic acid salt solution was subjected to vacuum degassing treatment and then extruded through a porous spinneret into water, and then defibrated, cut, fibrillated, and dried by a disk refiner to obtain polyamic acid salt short fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: 1.0 kg of polyamic acid salt short fibers were added to an appropriate amount of water, stirred and mixed to obtain a slurry with a solid content of 2 wt%, and then subjected to papermaking, pressing, and drying at 120 °C for 20 min to obtain a base paper; Step d: The obtained base paper was subjected to imidization at 300 °C for 10 min to obtain a polyimide paper.

[0079] Comparative Example 4: The difference from Example 1 is only that: The diamine containing a sulfonic group accounts for 5 mol% of the total diamine.

[0080] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4.75 mol, 0.95 kg), 1,4-phenylenediamine-2-sulfonic acid (0.25 mol, 0.05 kg) and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.84 kg), and stir and react at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After vacuum degassing the polyamic acid salt solution, extrude it through a porous spinneret into water, and then carry out defibration, cutting, fibrillation, and drying by a disk refiner to obtain short cut polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially put 1.0 kg of short cut polyamic acid salt fibers and 0.2 kg of ceramic fibers (fiber average length 0.5 mm, average diameter 1 μm) treated with KH550 (same as Example 1) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, carry out papermaking, pressing, and drying at 120 °C for 20 min to obtain a base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0081] Comparative Example 5: The difference from Example 1 is only that: The diamine containing a sulfonic group accounts for 40 mol% of the total diamine.

[0082] Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (3 mol, 0.60 kg), 1,4-phenylenediamine-2-sulfonic acid (2 mol, 0.38 kg) and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.73 kg), and stir and react at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After vacuum degassing the polyamic acid salt solution, extrude it through a porous spinneret into water, and then carry out defibration, cutting, fibrillation, and drying by a disk refiner to obtain short cut polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially put 1.0 kg of short cut polyamic acid salt fibers and 0.2 kg of ceramic fibers (fiber average length 0.5 mm, average diameter 1 μm) treated with KH550 (same as Example 1) into an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, carry out papermaking, pressing, and drying at 120 °C for 20 min to obtain a base paper; Step d: The obtained base paper was subjected to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0083] Comparative Example 6: The difference from Example 1 is only that: in step c, the amount of KH550-treated ceramic fibers is 0.05 kg.

[0084] Step a: In a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) were dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Triethylamine (5 mol) was added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyamic acid salt solution with a solid content of 15% was obtained. The polyamic acid salt solution was subjected to vacuum defoaming treatment and then extruded into water through a porous spinneret, and was defibrated, cut, fibrillated, and dried by a disk refiner to obtain polyamic acid salt short fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: 1.0 kg of polyamic acid salt short fibers and 0.05 kg of KH550-treated (same as in Example 1) ceramic fibers (fiber average length 0.5 mm, average diameter 1 μm) were successively added to an appropriate amount of water, stirred and mixed to obtain a slurry with a solid content of 2 wt%, and then subjected to papermaking, pressing, and drying at 120 °C for 20 min to obtain a base paper; Step d: The obtained base paper was subjected to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0085] Comparative Example 7: The difference from Example 1 is only that: in step c, the amount of KH550-treated ceramic fibers is 0.4 kg.

[0086] Step a: In a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) were dissolved in N,N-dimethylacetamide (11.79 kg), and stirred and reacted at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Triethylamine (5 mol) was added to the polyamic acid solution, and after stirring and reacting at room temperature for 1 h, a polyamic acid salt solution with a solid content of 15% was obtained. The polyamic acid salt solution was subjected to vacuum defoaming treatment and then extruded into water through a porous spinneret, and was defibrated, cut, fibrillated, and dried by a disk refiner to obtain polyamic acid salt short fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Put 1.0 kg of chopped polyamide acid fibers and 0.4 kg of ceramic fibers treated with KH550 (the same as in Example 1) (fiber average length 0.5 mm, average diameter 1 μm) into an appropriate amount of water in sequence, stir and mix to obtain a slurry with a solid content of 2 wt%, carry out papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0087] Comparative Example 8: The only difference from Example 1 is that the specifications of the chopped polyamide acid fibers in Step c are different Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4-phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N'-dimethylacetamide (11.79 kg), and stir and react in an environment at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamide acid salt solution with a solid content of 15%, subject the polyamide acid salt solution to vacuum degassing treatment, then extrude it through a porous spinneret into water, carry out defibering, cutting, fibrillation, and drying with a disk refiner to obtain chopped polyamide acid fibers with an average length of 20 mm and an average diameter of 15 μm; Step c: Put 1.0 kg of chopped polyamide acid fibers and 0.2 kg of ceramic fibers treated with KH550 (the same as in Example 1) (fiber average length 0.5 mm, average diameter 1 μm) into an appropriate amount of water in sequence, stir and mix to obtain a slurry with a solid content of 2 wt%, carry out papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0088] Comparative Example 9: The only difference from Example 1 is that the specifications of the ceramic fibers in Step c are different Step a: In a nitrogen atmosphere, dissolve 4,4'-diaminodiphenyl ether (4 mol, 0.80 kg), 1,4--phenylenediamine-2-sulfonic acid (1 mol, 0.19 kg), and pyromellitic dianhydride (5 mol, 1.09 kg) in N,N-dimethylacetamide (11.79 kg), and stir and react in an environment at 5 °C for 6 h to obtain a polyamic acid solution; Step b: Add triethylamine (5 mol) to the polyamic acid solution, stir and react at room temperature for 1 h to obtain a polyamic acid salt solution with a solid content of 15%. After subjecting the polyamic acid salt solution to vacuum degassing treatment, it is extruded into water through a porous spinneret, defibered, cut, fibrillated, and dried by a disk refiner to obtain short polyamic acid salt fibers with an average length of 5 mm and an average diameter of 5 μm; Step c: Sequentially add 1.0 kg of short polyamic acid salt fibers and 0.2 kg of ceramic fibers (fiber average length 5 mm, average diameter 10 μm) treated with KH550 (same as in Example 1) to an appropriate amount of water, stir and mix to obtain a slurry with a solid content of 2 wt%, perform papermaking, pressing, and drying at 120 °C for 20 min to obtain the base paper; Step d: Subject the obtained base paper to imidization by high-temperature treatment at 300 °C for 10 min to obtain a polyimide-ceramic fiber composite paper.

[0089] Performance testing (I) Detection method The thickness of the test samples is 0.25 mm: (1) The determination method of the thickness index is carried out in accordance with the national standard GB / T451.3-2002; (2) The determination method of the tensile index is carried out in accordance with the national standard GB / T12914-2008; (3) The determination method of the tear index is carried out in accordance with the national standard GB / T455-2002; (4) The determination of the dielectric strength index is carried out in accordance with the standard ASTM D-149; (5) Heat resistance performance: Keep a propane flame at 600 °C 2 cm away from the sample and continuously burn, and record the time when the whole material is burned through.

[0090] (II) Test results (1) Performance of different preparation processes Table 1: Relevant performance test results of the papers prepared in Examples 1-3 and Comparative Examples 1-3 As can be seen from Table 1: The papers obtained in Examples 1-3 of the present invention all have excellent tensile, tear resistance, insulation performance and heat resistance. The papers prepared with short polyamic acid fibers in Comparative Example 1 have lower tensile and tear resistance. The papers prepared with short polyimide fibers in Comparative Example 2 have poor bonding strength and low tear resistance. The papers prepared without ceramic fibers in Comparative Example 3 have low heat resistance performance.

[0091] (2) Influence of different contents of sulfonic group-containing diamine Table 2: Relevant performance test results of the papers prepared in Examples 1 / 5 / 6 and Comparative Examples 4 / 5 As can be seen from Table 2, when the sulfonic acid group content is 20 mol% (Example 1), the fiber dispersibility and interfacial bonding are the best, and the performance is optimal. In Comparative Example 4, the content of the diamine containing sulfonic groups is too low (5 mol%), resulting in insufficient interaction between fibers and a decrease in performance; while in Comparative Example 5, the content of the diamine containing sulfonic groups is too high (40 mol%), which causes fiber swelling due to excessive hydrophilicity and a loose structure.

[0092] (3) Influence of different amounts of ceramic fibers Table 3: Test results of relevant properties of the papers prepared in Example 1 / 7 / 8 and Comparative Examples 6 / 7 As can be seen from Table 3, when the amount of ceramic fibers in Example 1 is 20%, the fiber reinforcement effect is the best. When the ceramic fibers are excessive (more than 30%) in Comparative Example 7, agglomeration occurs, the interfacial bonding becomes poor, and the performance decreases. While in Comparative Example 6, the content of ceramic fibers is too low to effectively improve the mechanical properties and heat resistance of the paper.

[0093] (4) Influence of different average fiber lengths Table 4: Test results of relevant properties of the papers prepared in Example 1 and Comparative Examples 8 / 9 As can be seen from Table 4, compared with Example 1, in Comparative Example 8 (the polyamide acid salt fibers are too long), dispersion is difficult and the paper is loose; in Comparative Example 9 (the ceramic fibers are too thick), the interfacial bonding is poor, both resulting in a significant decrease in performance.

[0094] (5) Influence of different imidization processes Table 5: Test results of relevant properties of the papers prepared in Example 1 and Example 4 As can be seen from Table 4, stepwise imidization (Example 4) promotes the orderly rearrangement of molecular chains through gradient heating, and the cyclization is more complete. The heat resistance and mechanical properties are further improved compared with Example 1.

[0095] The raw materials and equipment used in the present invention are, unless otherwise specified, common raw materials and equipment in the art; the methods used in the present invention are, unless otherwise specified, conventional methods in the art.

[0096] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A polyimide-ceramic fiber composite paper, characterized in that: It is obtained by imidization of a polyamic acid salt-ceramic fiber composite paper; The polyamic acid salt-ceramic fiber composite paper includes intertwined short polyamic acid salt fibers and ceramic fibers; The short polyamic acid salt fibers are obtained by processing a polyamic acid salt solution catalytically converted from polyamic acid.

2. A preparation method of a polyimide-ceramic fiber composite paper, characterized in that It includes: a) Preparing a polyamic acid solution; b) Using a catalyst to convert polyamic acid into polyamic acid salt, and processing the obtained polyamic acid salt solution into short polyamic acid salt fibers; c) Dispersing the short polyamic acid salt fibers and ceramic fibers in water to obtain a slurry, and performing wet papermaking to obtain a polyamic acid salt-ceramic fiber composite paper; d) Performing imidization treatment on the polyamic acid salt-ceramic fiber composite paper to obtain a polyimide-ceramic fiber composite paper.

3. The preparation method according to claim 2, characterized in that: In step a), the preparation process of the polyamic acid solution includes: polymerizing diamine, diamine containing sulfonic acid group and dianhydride in an organic solvent to obtain a polyamic acid solution; The diamine containing sulfonic acid group accounts for 10-30 mol% of the total diamine.

4. The preparation method according to claim 3, characterized in that: In step a), The diamine is selected from one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone and 2,2'-bis[4-(4-aminophenoxyphenyl)]propane; The diamine containing sulfonic acid group is selected from one or more of 1,4-phenylenediamine-2-sulfonic acid, 3,5-diaminobenzenesulfonic acid, 2,2-disulfonic acid group benzidine and 4,4'-diamino-3,3'-biphenyl disulfonic acid; The dianhydride is selected from one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, hydroquinone diether dianhydride, resorcinol diether dianhydride and bisphenol A diether dianhydride; The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; The molar ratio of the total diamine to the dianhydride is 1:(0.8-1.2); The temperature of the polymerization reaction is 0-15 °C, and the time is 4-12 h.

5. According to the preparation method described in claim 2, it is characterized in that: In step b), the average diameter of the short polyamic acid salt fibers is 5-10 µm, and the average length is 1-10 mm; In step c), the average diameter of the ceramic fibers is 1-5 µm, and the average length is 0.1-1 mm.

6. The preparation method according to claim 2, wherein: In step b), The catalyst is selected from one or more of triethylamine, pyridine, benzimidazole and 1-ethylpiperidine; The molar ratio of the catalyst to the total diamine is (0.5-2):1; The solid content of the polyamic acid salt solution is 10-25 wt%.

7. The preparation method according to claim 2 or 5 or 6, characterized in that: In step b), the processing of the short polyamic acid salt fibers includes: performing vacuum degassing treatment on the polyamic acid salt solution, extruding it into water through a porous spinneret, and performing defibration, cutting, fibrillation and drying by a disk refiner to obtain short polyamic acid salt fibers.

8. The preparation method according to claim 2, characterized in that: In step c), The mass ratio of the short polyamic acid salt fibers to the ceramic fibers is 100:(10-30); The ceramic fibers are pretreated with a silane coupling agent; The solid content of the slurry is 0.5-2 wt%.

9. The preparation method according to claim 2, characterized in that: In step d), the imidization treatment includes: first, heat preservation is carried out at 150 - 250 °C for 10 - 20 min, and finally, heat preservation is carried out at 300 - 400 °C for 5 - 10 min.

10. Application of the polyimide-ceramic fiber composite paper described in claim 1 or the polyimide-ceramic fiber composite paper obtained by the preparation method described in any one of claims 2 - 9 as a high-temperature resistant insulating material.

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