A high-strength PBO composite insulating paper and its preparation method

Abstract

This invention belongs to the field of new materials and specialty papers, and discloses a high-strength PBO composite insulating paper and its preparation method. The main steps are as follows: A modified PHA precursor solution is coated onto the surface of PBO base paper to form a modified PHA-PBO composite paper; the composite paper is dried and then hot-pressed to obtain the high-strength PBO composite insulating paper. Compared with untreated PBO paper or ordinary PHA-PBO composite paper, the composite paper prepared by the above method can significantly reduce the porosity of PBO paper, thereby significantly improving the uniformity of PBO paper, resulting in modified PBO paper with excellent mechanical properties, further improving the breakdown strength of PBO paper, and enhancing the insulation performance of PBO paper.

Description

Technical Field

[0001] This invention belongs to the field of new materials and specialty paper, and discloses a high-strength PBO composite insulating paper and its preparation method. Background Technology

[0002] PBO fiber (poly(p-phenylenebenzodioxazole) fiber, ZylonAS) is a linear polyaromatic heterocyclic liquid crystal polymer molecule. PBO fiber has superior properties such as higher specific strength, specific modulus and high temperature resistance than para-aramid, and is therefore regarded as a new generation of super fiber for advanced aerospace structural composite materials.

[0003] PBO chopped fibers and pulp are used to make PBO paper. Its unique chemical structure ensures excellent electrical properties even under high temperature and humidity conditions. It does not melt or burn at 300℃, exhibits stable chemical properties, and maintains good mechanical properties, making it a high-grade insulating paper (H-class and above). It can be used in H-class and above generators, motors, dry-type transformers, etc. PBO paper can be further coated, laminated, pressed, and shaped to prepare PBO honeycomb materials, used in aircraft radar radomes and secondary load-bearing structural components such as wings, fairings, floors, engine cowlings, and cargo doors.

[0004] However, with the continuous development and upgrading of electrical engineering, higher requirements are placed on the mechanical strength and insulation performance of high-performance paper-based materials in complex working environments to ensure the safe operation of high-power traction transformers, generators, and other related equipment. In the production of PBO paper, PBO chopped fibers and pulp undergo papermaking and hot pressing. The PBO chopped fibers are rod-shaped with a relatively smooth surface, providing a skeletal structure for the paper. The pulp fibers are relatively flexible with a large specific surface area, encapsulating the chopped fibers and forming PBO paper with a certain strength. The interwoven fiber network structure helps disperse the structural stress of the paper-based material and better maintains the paper's strength. However, due to the smooth surface of the PBO chopped fibers and the scarcity of chemically active groups, the adhesion and wettability are poor, resulting in weak interfacial bonding. The loosely bonded fibers create numerous pores, leading to a high internal porosity (40%-60%) in the prepared PBO paper, and the PBO pulp cannot melt. Furthermore, the smooth surface and strong inertness of PBO fibers result in a lack of bonding between fibers during papermaking, leading to poor mechanical properties of the paper.

[0005] Therefore, improving the strength and insulation properties of PBO paper has become one of the urgent problems to be solved in the field of electrical engineering. Summary of the Invention

[0006] This invention addresses the numerous shortcomings of existing technologies by providing a high-strength PBO composite insulating paper and its preparation method. The main steps are as follows: A modified PHA precursor solution is coated onto the surface of PBO base paper to form a modified PHA-PBO composite paper; the composite paper is dried and then hot-pressed to obtain the high-strength PBO composite insulating paper. Compared with untreated PBO paper or ordinary PHA-PBO composite paper, the composite paper prepared by the above method can significantly reduce the porosity of PBO paper, thereby significantly improving the uniformity of PBO paper, resulting in modified PBO paper with excellent mechanical properties, further enhancing the breakdown strength of PBO paper, and improving its insulation performance.

[0007] The specific technical solution of the present invention is as follows:

[0008] The inventors first provided a method for preparing high-strength PBO composite insulating paper, the specific steps of which are as follows:

[0009] (1) Preparation of PBO base paper

[0010] PBO chopped fibers, PBO pulp fibers, and PBO precipitated fibers are placed in a water-containing dispersant and dispersed at high speed. A dispersant is added to obtain uniformly dispersed PBO pulp. The pulp is then wired, pressed, and vacuum dried to obtain PBO base paper.

[0011] By weight, it contains 30-50 parts of PBO chopped fiber, 5-15 parts of PBO pulp fiber, and 30-80 parts of PBO precipitated fiber.

[0012] The PBO chopped fibers used have a length of 2-8 mm and a fineness of 2-5 dtex; the specific surface area of ​​the PBO pulp fibers is 12-21 m². 2 / g, average fiber length 0.5-1.4mm; PBO precipitated fiber specific surface area 20-32 m² 2 / g, with an average fiber length of 0.3-1.2mm.

[0013] The dispersant used is one or a mixture of any two or more of the following: hydroxyethyl cellulose, sodium lignosulfonate, maleic acid acrylic acid copolymer, polyoxyethylene ether and nonionic polyacrylamide; the amount of dispersant used is 0.2-2 wt% of the total mass of the three fibers; the dispersion time is 15-60 min, and the concentration of PBO pulp obtained is 0.2-5 wt%.

[0014] (2) Preparation of precursor PHA polymer solution

[0015] In a reaction vessel, an appropriate amount of aprotic polar solvent is added under a nitrogen atmosphere, followed by the addition of monomer 4,6-diaminoresorcinol hydrochloride (DAR hydrochloride), terephthaloyl chloride (TPC), and antioxidant stannous chloride. The mixture is stirred for 10-40 min. Then, methylpyridine is added as a catalyst, and the mixture is stirred at -10 to 40 °C for 10-25 h to obtain a PHA polymer solution.

[0016] The aprotic polar solvent is selected from one or more combinations of N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; the molar ratio of 4,6-diaminoresorcinol hydrochloride (DAR hydrochloride) to terephthaloyl chloride (TPC) is 1:1, and the amount of 4,6-diaminoresorcinol hydrochloride is 9-17 wt% of the total mass of the final PHA polymer solution; the amount of stannous chloride is 0.3-1.2 wt% of the mass of DAR hydrochloride; and the amount of methylpyridine is 0.5-2.5 wt% of the mass of DAR hydrochloride.

[0017] (3) Preparation of mica nanosheets and precursor PHA polymer blend solution

[0018] The PHA polymer solution was diluted with the same aprotic polar solvent as in step (2) to obtain a polymer solution with a solid content of 3-12 wt%. Mica nanosheets were ultrasonically dispersed in an appropriate amount of the same aprotic polar solvent as in step (2), and the concentration of the mica nanosheet dispersion was 1-8 wt%. Then, the ultrasonically dispersed mica nanosheet dispersion was added to the continuously stirred PHA polymer solution and stirred for 6-10 h.

[0019] The amount of mica nanosheets used is 0.2-3 wt% of the total mass of the three types of fibers, and the ultrasonic dispersion time is 3-20 h.

[0020] Unlike existing technologies, this invention does not involve adding mica nanosheets for mixing and dispersion during the PBO papermaking process. Instead, the mica nanosheets are ultrasonically dispersed and then slowly added to the PHA polymerization solution, followed by prolonged stirring to obtain a mixed solution. The PHA polymer solution has a low apparent viscosity after dilution, ensuring good dispersibility of the mica nanosheets in the PHA solution.

[0021] (4) Preparation of modified PBO composite paper

[0022] The PBO base paper is laid flat on a funnel, and the blending solution is filled into the paper gaps and covered the surface using a vacuum filtration process. After further drying, the other side of the composite paper is treated in the same way. Then, the residual solvent is removed by washing with water and dried. Finally, the modified PHA-PBO composite paper is hot-pressed and subjected to high-temperature thermal cyclization to obtain high-strength PBO composite insulating paper.

[0023] The paper is dried using a stepped heating method, maintaining 80℃ for 1 hour, 100℃ for 3 hours, and 120℃ for 5 hours. The conditions for hot pressing and high-temperature thermal circulation are: temperature 150-270℃, pressure 4-20MPa, time 10-60s, hot pressing 1-6 times; thermal circulation temperature 300-450℃, time 10-30min, and vacuum degree -0.05MPa to -0.095MPa.

[0024] The purpose of hot pressing is to reduce porosity and defects in paper, increase the physical and mechanical interlocking between fibers, help form a dense paper structure, and improve the overall performance of paper.

[0025] The high-strength PBO composite insulating paper prepared by the above method has a basis weight of 40-100 g / m³. 2 It has a thickness of 40-110μm, a tensile strength of 90-160MPa, and a breakdown strength of 30-100KV / mm. Compared with existing PBO base paper, aramid composite insulating paper, or PBO insulating paper, it has significantly improved mechanical and insulating properties.

[0026] The inventors further claim protection for the high-strength PBO composite insulating paper obtained by the above preparation method.

[0027] Compared with the prior art, the beneficial effects of this invention are:

[0028] (1) Compared with the conventional PBO paper preparation process, the PBO composite paper preparation process adopted in this invention produces PHA that is easily soluble in aprotic organic solvents and has low apparent viscosity. It can fully fill the voids inside the PBO paper. The PHA precursor can form PBO molecules by closing the ring at high temperature, which can avoid interfacial compatibility problems. Moreover, the PHA precursor preparation process is simple, safe to operate, and the solvent used can be reused and recycled, which is not harmful to the environment.

[0029] (2) The present invention employs a double-sided vacuum filtration method to allow the mica nanosheet / PHA polymer blend solution to fully penetrate into the pores of the PBO base paper. This allows the mica nanosheets, which have excellent insulation properties and high volume resistivity, to penetrate into the paper pores, further enhancing the insulation performance of the PBO paper. Simultaneously, the dense film formed on the paper surface completely encapsulates the chopped fibers, and the solvent partially swells the PBO chopped fibers. The addition of mica nanosheets and the solvent swelling effect both increase the interfacial bonding area between fibers, thereby improving stress transmission between interfaces and shortening the distance between fibers. Therefore, the strength of the PBO composite paper is significantly improved. Coating and filling the porous paper surface with the PHA / mica nanosheet blend solution effectively improves paper uniformity, further reducing the possibility of charge injection, resulting in smaller breakdown holes and no obvious fibers at the edges.

[0030] (3) PBO pulp fibers and precipitated fibers can enhance the interaction between PBO composite paper fibers, acting as a "bridging and bonding" agent between the fibers. This invention uses both PBO pulp fibers and precipitated fibers. The selected pulp fibers have many branches, high crystallinity, and certain strength, presenting a three-dimensional network structure in the PBO base paper. After softening by heat, they can effectively bond the chopped fibers and precipitated fibers together. The precipitated fibers are in the form of a thin film, with low crystallinity, good fragmentation, length uniformity, and surface activity. They have a fine filamentous structure, large specific surface area, better dispersion performance, and mechanical bonding force, effectively encapsulating the chopped fibers and pulp fibers. In addition, adding a certain proportion of precipitated fibers during the PBO papermaking process can better promote the interaction between the chopped fibers, improve paper uniformity, and ultimately increase the interlayer bonding strength and mechanical properties of the paper.

[0031] In summary, the high-strength PBO composite insulating paper and its preparation method provided by this invention have the advantages of simple operation, green and environmentally friendly operation, and controllable process. The content of mica nanosheet material and solid content of PHA solution can also be adjusted according to needs to obtain PBO paper with different strengths and insulation properties, which can meet the application needs of aerospace, national defense, electrical and transportation fields. Detailed Implementation

[0032] The following will provide a further detailed description of the above-described contents of the present invention. The following are merely preferred embodiments of the present invention, and should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described contents of the present invention fall within the scope of the present invention. Unless otherwise specified, the following embodiments are all implemented using conventional prior art.

[0033] Example 1: A method for preparing high-strength PBO composite insulating paper, comprising the following steps:

[0034] (1) Preparation of PBO base paper

[0035] PBO chopped fibers, PBO pulp fibers, and PBO precipitated fibers were gradually added to a water-containing dispersant in a weight ratio of 50:15:35 and dispersed at high speed. At the same time, 0.5% of hydroxyethyl cellulose (hydroxyethyl cellulose) was added as a dispersant and stirred at high speed for 20 minutes to obtain a uniformly dispersed PBO pulp with a concentration of 0.5 wt%. The pulp was then wired, pressed, and vacuum dried to obtain PBO base paper.

[0036] The chopped fiber length is 6 mm, the fineness is 5 dtex, the average pulp fiber length is 1.3 mm, and the specific surface area is 13 m². 2 / g, the average length of the precipitated fibers is 1.1mm, and the specific surface area is 24m².2 / g.

[0037] (2) Preparation of precursor PHA polymer solution

[0038] In a reaction vessel under a nitrogen atmosphere, 190 g of N,N-dimethylacetamide was added, followed by 0.25 g of antioxidant stannous chloride, 27.1 g of monomer 4,6-diaminoresorcinol hydrochloride, and 25.8 g of terephthaloyl chloride. The mixture was stirred for 18 min. Then, 0.47 g of methylpyridine was added, and the mixture was stirred at 6 °C for 25 h to obtain the PHA polymer solution.

[0039] (3) Preparation of mica nanosheets and precursor PHA polymer blend solution

[0040] The PHA polymer solution was diluted with N,N-dimethylacetamide to obtain a 5 wt% PHA solution. Mica nanosheets were ultrasonically dispersed in an appropriate amount of N,N-dimethylacetamide solvent for 5 hours to prepare a 5.5 wt% mica nanosheet dispersion, wherein the mica nanosheets accounted for 0.5 wt% of the total mass of the three types of fibers. The mica nanosheet dispersion was then gradually added to the continuously stirred 5 wt% PHA solution for 7 hours to obtain a mica nanosheet / PHA blend solution.

[0041] (4) Preparation of modified PBO composite paper

[0042] The PBO base paper is laid flat on a funnel, and the blend solution is filled into the paper gaps and covered the surface using a vacuum filtration process with a vacuum degree of -0.06MPa. After further drying, the other side of the composite paper is treated in the same way. Then, the paper is washed with water to remove residual solvent and dried.

[0043] The drying process involved maintaining the temperature at 80℃ for 1 hour, at 100℃ for 3 hours, and at 120℃ for 5 hours. The resulting modified PHA-PBO composite paper was then hot-pressed at 180℃ for 20 seconds and 8 MPa for 4 cycles. The hot-pressed composite paper was then subjected to high-temperature thermal circulatory treatment at a vacuum of -0.06 MPa, at 350℃, for 20 minutes to obtain the modified PBO composite paper.

[0044] Testing revealed that the tensile strength of the PBO base paper in this embodiment was 43.2 MPa, and the breakdown strength was 36.5 KV / mm. The basis weight of the modified PBO composite paper was 45 g / m³. 2 It has a thickness of 58.4 μm, a tensile strength of 109.2 MPa, and a breakdown strength of 54.8 KV / mm.

[0045] Example 2: A method for preparing high-strength PBO composite insulating paper, comprising the following steps:

[0046] Steps (1) and (2) are the same as in Example 1;

[0047] (3) Preparation of mica nanosheets and precursor PHA polymer blend solution

[0048] The PHA polymer solution was diluted with N,N-dimethylacetamide to obtain an 8 wt% PHA solution. Mica nanosheets were ultrasonically dispersed in an appropriate amount of N,N-dimethylacetamide solvent for 9 hours to prepare a 4 wt% mica nanosheet dispersion, wherein the mica nanosheets accounted for 1 wt% of the total mass of the three types of fibers. The mica nanosheet dispersion was then gradually added to the continuously stirred 8 wt% PHA solution for 7 hours to obtain a mica nanosheet / PHA blend solution.

[0049] (4) Preparation of modified PBO composite paper

[0050] PBO base paper was laid flat on a funnel, and the blending solution was filled into the paper's voids and covered the surface using a vacuum filtration process at a vacuum degree of -0.08 MPa. Further drying was then performed, and the other side of the composite paper was treated in the same way. After washing to remove residual solvent, it was dried. The drying process involved maintaining the temperature at 80℃ for 1 hour, at 100℃ for 3 hours, and at 120℃ for 5 hours. Finally, the obtained modified PHA-PBO composite paper was hot-pressed at 220℃ for 30 seconds and a pressure of 13 MPa, repeated three times. The hot-pressed composite paper was then subjected to high-temperature thermal circulatory treatment at a vacuum degree of -0.07 MPa, a temperature of 400℃, and a time of 20 minutes to obtain the modified PBO composite paper.

[0051] Testing revealed that the tensile strength of the PBO base paper in this embodiment was 43.2 MPa, and the breakdown strength was 36.5 KV / mm. The basis weight of the modified PBO composite paper was 53 g / m³. 2 It has a thickness of 62.3 μm, a tensile strength of 116.8 MPa, and a breakdown strength of 61.7 KV / mm.

[0052] Example 3: A method for preparing high-strength PBO composite insulating paper, comprising the following steps:

[0053] Steps (1) and (2) are the same as in Example 1;

[0054] (3) Preparation of mica nanosheets and precursor PHA polymer blend solution

[0055] The PHA polymer solution was diluted with N,N-dimethylacetamide to obtain a PHA solution with a mass fraction of 11 wt%. Mica nanosheets were ultrasonically dispersed in an appropriate amount of N,N-dimethylacetamide solvent for 9 hours to prepare a 3 wt% mica nanosheet dispersion, wherein the mass of mica nanosheets accounted for 1.5 wt% of the total mass of the three types of fibers. Then, the mica nanosheet dispersion was gradually added to the 11 wt% PHA solution under continuous stirring for 9 hours to obtain a mica nanosheet / PHA blend solution.

[0056] (4) Preparation of modified PBO composite paper

[0057] PBO base paper was laid flat on a funnel, and the blending solution was filled into the paper's voids and covered the surface using a vacuum filtration process at a vacuum degree of -0.09 MPa. Further drying was then performed, and the other side of the composite paper was treated in the same way. After washing away residual solvent with water, it was dried. The drying process involved maintaining the temperature at 80℃ for 1 hour, at 100℃ for 3 hours, and at 120℃ for 5 hours. Finally, the obtained modified PHA-PBO composite paper was hot-pressed twice at a temperature of 250℃ for 18 seconds and a pressure of 17 MPa. The hot-pressed composite paper was then subjected to high-temperature thermal circulatory treatment at a vacuum degree of -0.08 MPa, a temperature of 450℃, and a time of 30 minutes to obtain the modified PBO composite paper.

[0058] The tensile strength of the PBO base paper in this embodiment was tested to be 43.2 MPa, and the breakdown strength was 36.5 KV / mm. The basis weight of the modified PBO composite paper was 60 g / m³. 2 It has a thickness of 70.3 μm, a tensile strength of 130.4 MPa, and a breakdown strength of 74.1 KV / mm.

[0059] Example 4: A method for preparing high-strength PBO composite insulating paper, comprising the following steps:

[0060] (1) Preparation of PBO base paper

[0061] PBO chopped fibers, PBO pulp fibers, and PBO precipitated fibers were gradually added to a water-containing dispersant in a weight ratio of 35:20:45 and dispersed at high speed. Polyoxyethylene ether was added at 0.8% of the total mass of the three fibers as a dispersant and stirred at high speed for 30 minutes to obtain a uniformly dispersed PBO pulp with a concentration of 1.2 wt%. The pulp was then wired, pressed, and vacuum dried to obtain PBO base paper.

[0062] The chopped fiber length is 5mm, the fineness is 4dtex, the average pulp fiber length is 0.8mm, and the specific surface area is 16m². 2 / g, the average length of the precipitated fibers is 0.7mm, and the specific surface area is 27m². 2 / g.

[0063] (2) Preparation of precursor PHA polymer solution

[0064] In a reaction vessel under a nitrogen atmosphere, 175 g of N,N-dimethylacetamide was added, followed by 0.08 g of antioxidant stannous chloride, 21.48 g of monomer 4,6-diaminoresorcinol hydrochloride, and 20.47 g of terephthaloyl chloride. The mixture was stirred for 20 min. Then, 0.31 g of methylpyridine was added, and the mixture was stirred at 0 °C for 18 h to obtain the PHA polymer solution.

[0065] Steps (3) and (4) are the same as in Example 3;

[0066] The tensile strength of the PBO base paper in this embodiment was tested to be 48.5 MPa, and the breakdown strength was 40.1 KV / mm. The basis weight of the modified PBO composite paper was 67 g / m³. 2 It has a thickness of 63.6 μm, a tensile strength of 140.4 MPa, and a breakdown strength of 79.4 KV / mm.

[0067] Example 5: A method for preparing high-strength PBO composite insulating paper, comprising the following steps:

[0068] (1) Preparation of PBO base paper

[0069] PBO chopped fibers, PBO pulp fibers, and PBO precipitated fibers were gradually added to a water-containing dispersant in a weight ratio of 25:10:65 and dispersed at high speed. Polyoxyethylene ether, at a total mass of 1.2% of the three fibers, was added as a dispersant and stirred at high speed for 50 minutes to obtain a uniformly dispersed PBO pulp with a concentration of 1.0 wt%. The pulp was then wired, pressed, and vacuum dried to obtain PBO base paper.

[0070] The chopped fiber length is 3mm, the fineness is 2.5dtex, the average pulp fiber length is 0.6mm, and the specific surface area is 20m². 2 / g, the average length of the precipitated fibers is 0.4mm, and the specific surface area is 30m². 2 / g.

[0071] (2) Preparation of precursor PHA polymer solution

[0072] In a reaction vessel under a nitrogen atmosphere, 150 g of N,N-dimethylacetamide was added, followed by 0.15 g of antioxidant stannous chloride, 19.57 g of monomer 4,6-diaminoresorcinol hydrochloride, and 18.65 g of terephthaloyl chloride. The mixture was stirred for 30 min. Then, 0.39 g of methylpyridine was added, and the mixture was stirred at 6 °C for 20 h to obtain the PHA polymer solution.

[0073] Steps (3) and (4) are the same as in Example 3;

[0074] The tensile strength of the PBO base paper in this embodiment was tested to be 51.7 MPa, and the breakdown strength was 43.1 KV / mm. The basis weight of the modified PBO composite paper was 63 g / m³. 2 It has a thickness of 55.8 μm, a tensile strength of 148.2 MPa, and a breakdown strength of 88.4 KV / mm.

[0075] A comparative example is a method for preparing PBO composite paper, the steps of which are as follows:

[0076] (1) Preparation of PBO base paper

[0077] PBO chopped fibers and PBO pulp fibers were gradually added to a water-containing desolventizer at a weight ratio of 40:60 and dispersed at high speed. Hydroxyethyl cellulose (0.5% of the total mass of the two fibers) was added as a dispersant and stirred at high speed for 50 minutes to obtain a uniformly dispersed PBO pulp with a concentration of 1 wt%. The pulp was then wired, pressed, and vacuum dried to obtain PBO base paper.

[0078] The chopped fiber length is 5 mm, the fineness is 4 dtex, the average pulp fiber length is 0.6 mm, and the specific surface area is 24 m². 2 / g,

[0079] (2) Preparation of precursor PHA polymer solution

[0080] In a reaction vessel under a nitrogen atmosphere, 150 g of N,N-dimethylacetamide was added, followed by 0.15 g of antioxidant stannous chloride, 19.57 g of monomer 4,6-diaminoresorcinol hydrochloride, and 18.65 g of terephthaloyl chloride. The mixture was stirred for 30 min. Then, 0.39 g of methylpyridine was added, and the mixture was stirred at 6 °C for 20 h to obtain the PHA polymer solution.

[0081] (3) Preparation of PBO composite paper

[0082] The PHA polymer solution was diluted with N-methylpyrrolidone to obtain an 11 wt% PHA solution. PBO base paper was laid flat on a platform, and the 11 wt% PHA solution was evenly coated onto the paper surface using a scraper. The paper was then immersed in the aqueous solution for 1 hour and washed, followed by drying. The other side of the paper was treated in the same manner. The drying process involved maintaining the temperature at 80°C for 1 hour, at 100°C for 3 hours, and at 120°C for 5 hours. Finally, the resulting PHA-PBO composite paper was hot-pressed at 220°C for 6 minutes and a pressure of 15 MPa. The hot-pressed composite paper was then subjected to high-temperature thermal cyclization at a vacuum of -0.06 MPa, a temperature of 400°C, and a time of 23 minutes to obtain the PBO composite paper.

[0083] The tensile strength of the PBO base paper in this comparative example was 34.2 MPa, and the breakdown strength was 28.7 KV / mm. The tensile strength of the modified PBO composite paper was 61.3 MPa, and the breakdown strength was 47.2 KV / mm.

[0084] By comparing the above comparative examples and embodiments, it can be seen that the technical solution of the present invention uses mica nanosheets mixed with a polyhydroxyamide (PHA) precursor solution, and the process consistently uses a non-protic polar solvent, which has the advantages of energy saving, environmental protection, and resource reuse. Using PBO precipitated fibers as the paper matrix effectively improves the structure of PBO paper and enhances its overall performance. The high-temperature cyclization of the PHA precursor into PBO avoids the problem of poor interfacial compatibility and improves the uniformity of the paper. The introduction of mica nanosheets can significantly improve the mechanical properties and breakdown strength of PBO paper. Furthermore, the content of mica nanosheet material and the solid content of the PHA solution can be adjusted according to requirements to obtain PBO papers with different strengths and insulation properties, meeting the application needs of aerospace, defense, electrical, and transportation fields.

[0085] The above embodiments illustrate and describe the basic principles, product features, and advantages of the method of the present invention. The present invention is not limited to the above embodiments; various changes and modifications can be made without departing from the scope of the invention, and all such changes are claimed to be included within the scope of protection.

Claims

1. A method for preparing high-strength PBO composite insulating paper, characterized in that, The specific steps are as follows: (1) Preparation of PBO base paper PBO chopped fibers, PBO pulp fibers, and PBO precipitated fibers are placed in a water-containing dispersant and dispersed at high speed. A dispersant is added to obtain PBO pulp with a concentration of 0.2-5 wt%. The pulp is then wired, pressed, and vacuum dried to obtain PBO base paper. By weight, it contains 30-50 parts of PBO chopped fiber, 5-15 parts of PBO pulp fiber, and 30-80 parts of PBO precipitated fiber. (2) Preparation of precursor PHA polymer solution In a reaction vessel, an appropriate amount of aprotic polar solvent is added under a nitrogen atmosphere, followed by the sequential addition of monomer 4,6-diaminoresorcinol hydrochloride, terephthaloyl chloride, and antioxidant stannous chloride. The mixture is stirred for 10-40 min; then, methylpyridine is added as a catalyst, and the reaction is carried out at -10 to 40 °C for 10-25 h to obtain a PHA polymer solution. (3) Preparation of mica nanosheets and precursor PHA polymer blend solution The PHA polymer solution was diluted with the same aprotic polar solvent as in step (2) to obtain a polymer solution with a solid content of 3-12 wt%. Mica nanosheets were ultrasonically dispersed in an appropriate amount of the same aprotic polar solvent as in step (2), and the concentration of the mica nanosheet dispersion was 1-8 wt%. The ultrasonically dispersed mica nanosheet dispersion was then added to the continuously stirred PHA polymer solution and stirred for 6-10 h. The amount of mica nanosheets used was 0.2-3 wt% of the total mass of the three fibers, and the ultrasonic dispersion time was 3-20 h. (4) Preparation of modified PBO composite paper The PBO base paper is laid flat on a funnel, and the blending solution is filled into the paper gaps and covered the surface using a vacuum filtration process, followed by further drying. The other side of the composite paper is then treated in the same way, and then washed with water to remove residual solvent before drying. Finally, the modified PHA-PBO composite paper is hot-pressed and subjected to high-temperature thermal cyclization to obtain high-strength PBO composite insulating paper.

2. The method for preparing high-strength PBO composite insulating paper according to claim 1, characterized in that, The PBO chopped fibers used in step (1) have a length of 2-8 mm and a fineness of 2-5 dtex; the specific surface area of ​​the PBO pulp fibers is 12-21 m². 2 / g, average fiber length 0.5-1.4mm; PBO precipitated fiber specific surface area 20-32m² 2 / g, with an average fiber length of 0.3-1.2mm.

3. The method for preparing high-strength PBO composite insulating paper according to claim 1 or 2, characterized in that, The dispersant used in step (1) is one or a mixture of any two or more of the following: hydroxyethyl cellulose, sodium lignosulfonate, maleic acid acrylic acid copolymer, polyoxyethylene ether and nonionic polyacrylamide; the amount of dispersant used is 0.2-2 wt% of the total mass of the three fibers; the dispersion time is 15-60 min.

4. The method for preparing high-strength PBO composite insulating paper according to claim 1, characterized in that, In step (2), the aprotic polar solvent is selected from one or a combination of N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

5. The method for preparing high-strength PBO composite insulating paper according to claim 1 or 4, characterized in that, In step (2), the molar ratio of 4,6-diaminoresorcinol hydrochloride to terephthaloyl chloride is 1:1, the amount of 4,6-diaminoresorcinol hydrochloride is 9-17 wt% of the total mass of the final PHA polymer solution, the amount of stannous chloride is 0.3-1.2 wt% of the mass of 4,6-diaminoresorcinol hydrochloride, and the amount of methylpyridine is 0.5-2.5 wt% of the mass of 4,6-diaminoresorcinol hydrochloride.

6. The method for preparing high-strength PBO composite insulating paper according to claim 1, characterized in that, In step (4), the paper is dried by step heating: 80℃ for 1 hour, 100℃ for 3 hours, and 120℃ for 5 hours.

7. The method for preparing high-strength PBO composite insulating paper according to claim 1, characterized in that, The conditions for hot pressing in step (4) are: temperature 150-270℃, pressure 4-20MPa, time 10-60s, and hot pressing 1-6 times.

8. The method for preparing high-strength PBO composite insulating paper according to claim 1 or 7, characterized in that, The conditions for high-temperature thermal circulation in step (4) are: thermal circulation temperature 300-450℃, time 10-30min, and vacuum degree -0.05MPa to -0.095Mpa.

9. High-strength PBO composite insulating paper prepared by any one of claims 1-8.

10. The high-strength PBO composite insulating paper according to claim 9, characterized in that: The quantitative amount is 40-100g / m 2 Thickness 40-110μm, tensile strength 90-160MPa, breakdown strength 30-100KV / mm.