Polyimide composite material with high humidity and heat resistance for insulated wire and preparation method of polyimide composite material

Abstract

The invention discloses a high-damp-heat-resistance polyimide composite material for an insulated wire and a preparation method of the high-damp-heat-resistance polyimide composite material, and belongs to the technical field of polyimide insulation. Zinc oxide / carbon nanotube derived mica is modified by gamma-methacryloxypropyltrimethoxysilane, and is subjected to polycondensation under the action of benzoyl peroxide by using alkenyl succinic anhydride, so that the high-damp-heat-resistance polyimide composite material for the insulated wire is obtained. The preparation method comprises the following steps: preparing zinc oxide / carbon nano tube derivative mica from zinc oxide and carbon nano tube derivative mica, carrying out co-polycondensation on 4, 4 '-oxydiphthalic anhydride, 1, 3-di (4'-aminophenoxy) and the zinc oxide / carbon nano tube derivative mica, improving the density of a three-dimensional network, forming molecular-level interface bonding through a high cross-linked structure, and avoiding the interface incompatibility of inorganic filler and resin through strong bonding.

Description

Technical Field

[0001] This invention belongs to the field of polyimide insulation technology, specifically a polyimide composite material for insulating wires with high resistance to moisture and heat and its preparation method. Background Technology

[0002] With the continuous development of modern electronics and power systems technology, condensation polymer film capacitors, due to their high breakdown strength, are playing an increasingly important role in modern electronics and power systems. Although much work has been done to improve the breakdown performance of condensation polymer composites, enhancing both their breakdown and dielectric properties remains a significant challenge for large-scale industrial production. Meanwhile, researchers have discovered that polyimide possesses excellent mechanical, chemical, and electrical properties over a very wide temperature range, leading to its widespread application. Particularly in insulation materials, it is widely used for inter-turn insulation of traction motors in inverter power supplies, as well as insulation for electronic devices such as integrated circuits and sensors. However, in high-frequency electrical systems, condensation polymer composites typically experience dielectric losses, resulting in reduced insulation performance. Previous research has primarily focused on doping with nano-inorganic fillers, but this has led to problems such as significantly increased dielectric loss and conductivity, and reduced breakdown field strength in composite films.

[0003] Chinese Patent No. CN106684045B discloses a carbon nanotube-reinforced insulating and thermally conductive resin and its preparation method. In this scheme, carbon nanotubes are used as the thermally conductive network, and nanodiamond particles and carbon nanotubes are used as synergistic thermally conductive channels. This not only gives full play to the excellent thermal conductivity of carbon nanotubes and nanodiamond particles, but also utilizes the insulating properties of nanodiamond particles to avoid the impact of carbon nanotube addition on the resin's insulation performance. Furthermore, the nanodiamond coating on the surface reduces the surface energy of carbon nanotubes and increases the dispersibility of carbon nanotubes in the resin. However, the nanodiamond coating in this scheme still leads to incompatibility between the inorganic filler and the resin interface, resulting in a decrease in the overall material strength. Summary of the Invention

[0004] The purpose of this invention is to provide a high-humidity-heat-resistant polyimide composite material for insulating wires and its preparation method. This involves modifying zinc oxide / carbon nanotube-derived mica with γ-methacryloxypropyltrimethoxysilane, and then polycondensing it with alkenyl succinic anhydride under the action of benzoyl peroxide to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica. Co-condensation of 4,4'-oxydiphthalic anhydride, 1,3-di(4'-aminophenoxy), and anhydride-modified zinc oxide / carbon nanotube-derived mica enhances the three-dimensional network density, resulting in a highly cross-linked structure that forms a molecular-level interfacial bond. This strong bonding avoids interfacial incompatibility between inorganic fillers and resins.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing a high moisture-heat resistant polyimide composite material for insulating wires includes the following steps: Step 1: Using mesoporous silica microspheres as a carrier, zinc-based MOFs are synthesized on the surface via hydrothermal synthesis to obtain zinc MOF / silica core-shell microspheres.

[0006] Step 2: The zinc MOF / silica core-shell microspheres are coated with nickel film, placed in PECVD, and argon and methane are introduced to obtain zinc oxide / carbon nanotube-derived mica.

[0007] Step 3: Hydrolyze and condense zinc oxide / carbon nanotube-derived mica with γ-methacryloxypropyltrimethoxysilane to obtain modified zinc oxide / carbon nanotube-derived mica, and then condense it with alkenyl succinic anhydride under the action of benzoyl peroxide to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica.

[0008] Step 4: Using 4,4'-oxydiphthalic anhydride, anhydride-modified zinc oxide / carbon nanotube-derived mica, and 1,3-bis(4'-aminophenoxy) as raw materials, a high moisture-heat resistant polyimide composite material for insulating wires is obtained by stepwise heating and cyclization.

[0009] Furthermore, the specific preparation steps of zinc MOF / silica core-shell microspheres are as follows: Mesoporous silica microspheres with a pore size of 150-200 nm, 2,5-diaminoterephthalic acid, and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave and stirred for 30-40 min at 20-25 °C and 500-600 r / min. Then, a mixed solution of sodium hexadecyl sulfate and 60-70 wt% ethanol was added, and stirring was continued for another 30-40 min. Zinc sulfate was then added, and the mixture was heated to 120-130 °C and reacted for another 20-22 h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed 2-4 times with methanol solution and deionized water, respectively. The mixture was then vacuum dried at 60-70 °C for 1-2 h to obtain zinc MOF / silica core-shell microspheres.

[0010] Furthermore, the ratio of mesoporous silica microspheres, 2,5-diaminoterephthalic acid, N,N-dimethylformamide, sodium hexadecyl sulfate, ethanol solution, and zinc sulfate is 200-300g: 150-160g: 1-2L: 50-60g: 120-140g: 90-100g.

[0011] Furthermore, the specific preparation steps of zinc oxide / carbon nanotube-derived mica are as follows: Zinc MOF / silica core-shell microspheres, nickel nitrate, complexing agent citric acid, surfactant polyethylene glycol sulfate, stabilizer L-cysteine, and deionized water were added to a reaction vessel and stirred for 40-50 min at 30-40℃ and 400-500 r / min. After filtration, the filter cake was washed with deionized water until the final washing liquid was neutral, yielding nickel-plated core-shell microspheres with a surface nickel film thickness of 2-3 nm. The nickel-plated core-shell microspheres were placed in a PECVD reactor, and argon gas at a flow rate of 5-6 L / h and methane gas at a flow rate of 1-2 L / h as a carbon source were introduced for 10-12 min. The reactor was heated to 980-1000℃ and treated for 2-3 h. The product was washed 2-4 times with deionized water and vacuum dried at 60-70℃ for 1-2 h to obtain zinc oxide / carbon nanotube-derived mica.

[0012] Furthermore, the ratio of zinc MOF / silica core-shell microspheres, nickel nitrate, citric acid, polyethylene glycol sulfate, L-cysteine, and deionized water is 250-300g: 120-140mL: 9-10g: 12-14g: 7-9g: 500-600mL.

[0013] Furthermore, the specific preparation steps of modified zinc oxide / carbon nanotube-derived mica are as follows: Zinc oxide / carbon nanotube-derived mica, anhydrous ethanol, and deionized water were added to a reaction vessel and stirred for 10-12 min at 50-60℃ and 500-600 r / min. Then, γ-methacryloyloxypropyltrimethoxysilane was added, and the pH was adjusted to 3-4 with hydrochloric acid solution. The reaction was continued with stirring for 6-7 h. After filtration, the precipitate was washed 2-4 times with deionized water and anhydrous ethanol and dried under vacuum at 60-70℃ for 1-2 h to obtain modified zinc oxide / carbon nanotube-derived mica.

[0014] Furthermore, the ratio of zinc oxide / carbon nanotube-derived mica, anhydrous ethanol, deionized water, and γ-methacryloyloxypropyltrimethoxysilane is 200-220g: 120-140mL: 400-500mL: 100-120mL.

[0015] Furthermore, the specific preparation steps of anhydride-modified zinc oxide / carbon nanotube-derived mica are as follows: Modified zinc oxide / carbon nanotube-derived mica and dichloromethane were added to a reaction vessel and stirred for 10-12 min at 20-25℃ and 500-600 r / min. Under nitrogen protection, the mixture was heated to 80-90℃, and then benzoyl peroxide and alkenyl succinic anhydride were added. The reaction was continued with stirring for 3-4 h. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water. It was then vacuum dried at 60-70℃ for 1-2 h to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica.

[0016] Furthermore, the ratio of modified zinc oxide / carbon nanotube-derived mica, dichloromethane, benzoyl peroxide, and alkenyl succinic anhydride is 180-200g: 400-500mL: 3-4g: 100-120g.

[0017] Furthermore, the specific preparation steps of the polyimide composite material are as follows: 4,4'-O-diphthalic anhydride, 1,3-bis(4'-aminophenoxy), and N-methyl-2-pyrrolidone were added to a reaction vessel and stirred for 20-30 min at 0-4℃ and 500-600 r / min under nitrogen protection. Then, the mixture was heated to 20-25℃ and stirred for 4-5 h. Then, anhydride-modified zinc oxide / carbon nanotube-derived mica was added and stirred for 10-12 h. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water. It was then vacuum dried at 60-70℃ for 1-2 h. Then, the mixture was heated to 110-120℃, 210-220℃, 310-330℃, and 360-370℃, with each temperature maintained for 40-50 min, to obtain a polyimide composite material with high moisture and heat resistance for insulating wires.

[0018] Furthermore, the ratio of 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy), N-methyl-2-pyrrolidone and anhydride-modified zinc oxide / carbon nanotube-derived mica is 220-230g: 400-500g: 800-900mL: 60-80g.

[0019] The beneficial effects of this invention are: 1. The polyimide composite material prepared by this invention has good insulation and high resistance to damp heat, as well as excellent mechanical properties and flame retardancy.

[0020] 2. The zinc oxide / carbon nanotube-derived mica of the present invention uses mesoporous silica microspheres as a carrier to form a core-shell structure with zinc MOF, providing a high specific surface area and ordered channels that can adsorb environmental moisture, reducing the penetration of moisture into the polyimide matrix, thereby inhibiting swelling and hydrolysis under humid and hot conditions. Carbon nanotubes are grown on the surface of nickel-plated core-shell microspheres by PECVD to form a mica-like layered structure. Mica itself has excellent insulation and water resistance, while the carbon nanotube network further blocks the diffusion of water molecules, delaying the humid and hot aging process. In this process, zinc MOF can catalyze the generation of carbon nanotubes. Mica itself has excellent insulation and water resistance, while the carbon nanotube network further blocks the diffusion of water molecules, delaying the humid and hot aging process.

[0021] 3. The modified zinc oxide / carbon nanotube-derived mica of the present invention is modified with γ-methacryloxypropyltrimethoxysilane to enhance the interfacial compatibility between the inorganic filler and the polyimide matrix. Furthermore, it is obtained by polycondensing alkenyl succinic anhydride with benzoyl peroxide to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica. The polycondensation of 4,4'-oxybis(4'-aminophenoxy) anhydride with 1,3-bis(4'-aminophenoxy) forms a rigid-flexible molecular chain. The addition of anhydride-modified zinc oxide / carbon nanotube-derived mica further increases the crosslinking points and improves the three-dimensional network density. The highly crosslinked structure restricts the movement of the molecular chains in a humid and hot environment, reducing the probability of hydrolysis.

[0022] 4. The thermal decomposition products of zinc MOF, zinc oxide and carbon nanotube layers, can catalyze the carbonization reaction to form a dense carbon layer that isolates oxygen. At the same time, the silica core layer melts and covers the surface at high temperature, blocking the spread of flame and giving the material overall flame retardancy. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: A method for preparing a high moisture-heat resistant polyimide composite material for insulating wires, comprising the following steps: S1: 200g of mesoporous silica microspheres with a pore size of 150nm, 150g of 2,5-diaminoterephthalic acid and 1L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave and stirred for 30min at 20℃ and 500r / min. Then, a mixed solution of 50g of sodium hexadecyl sulfate and 120g of 60wt% ethanol solution was added and stirred for another 30min. Then, 90g of zinc sulfate was added, heated to 120℃, and reacted for another 20h. After naturally cooling to room temperature, the mixture was filtered, and the filter cake was washed twice with methanol solution and deionized water, respectively. The mixture was then vacuum dried at 60℃ for 1h to obtain zinc MOF / silica core-shell microspheres.

[0025] S2: 250g of zinc MOF / silica core-shell microspheres, 120mL of nickel nitrate, 9g of complexing agent citric acid, 12g of surfactant polyethylene glycol sulfate, 7g of stabilizer L-cysteine, and 500mL of deionized water were added to a reaction vessel and stirred for 40min at 30℃ and 400r / min. The mixture was filtered, and the filter cake was washed with deionized water until the final washing liquid was neutral, yielding nickel-plated core-shell microspheres with a surface nickel film thickness of 2nm. The nickel-plated core-shell microspheres were placed in a PECVD reactor, and argon gas at a flow rate of 5L / h and methane gas at a flow rate of 1L / h as a carbon source were introduced for 10min. The mixture was heated to 980℃ and treated for 2h. The product was washed twice with deionized water and vacuum dried at 60℃ for 1h to obtain zinc oxide / carbon nanotube-derived mica.

[0026] S3: Add 200g of zinc oxide / carbon nanotube-derived mica, 120mL of anhydrous ethanol and 400mL of deionized water to a reaction vessel, stir for 10min at 50℃ and 500r / min, then add 100mL of γ-methacryloyloxypropyltrimethoxysilane, adjust the pH to 3 with hydrochloric acid solution, continue stirring for 6h, filter, wash the precipitate twice with deionized water and anhydrous ethanol, and vacuum dry at 60℃ for 1h to obtain modified zinc oxide / carbon nanotube-derived mica.

[0027] S4: Add 180g of modified zinc oxide / carbon nanotube-derived mica and 400mL of dichloromethane to a reaction vessel, stir for 10min at 20℃ and 500r / min, heat to 80℃ under nitrogen protection, then add 3g of benzoyl peroxide and 100g of alkenyl succinic anhydride, continue stirring for 3h, filter, wash the filter cake twice with deionized water, and vacuum dry at 60℃ for 1h to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica.

[0028] S5: 220g of 4,4'-oxydiphthalic anhydride, 400g of 1,3-bis(4'-aminophenoxy), and 800mL of N-methyl-2-pyrrolidone were added to a reaction vessel. Under nitrogen protection, the mixture was stirred at 0℃ and 500r / min for 20min. Then, it was heated to 20℃ and stirred for 4h. Then, 60g of anhydride-modified zinc oxide / carbon nanotube-derived mica was added and stirred for 10h. The mixture was filtered, and the filter cake was washed twice with deionized water. It was then vacuum dried at 60℃ for 1h. Then, it was heated to 110℃, 210℃, 310℃, and 360℃, and the temperature was maintained for 40min at each stage to obtain a high moisture-heat resistant polyimide composite material for insulating wires.

[0029] Example 2: A method for preparing a high moisture-heat resistant polyimide composite material for insulating wires, comprising the following steps: S1: 250g of mesoporous silica microspheres with a pore size of 175nm, 155g of 2,5-diaminoterephthalic acid, and 1.5L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave. The mixture was stirred for 35min at 22.5℃ and 550r / min. Then, a mixed solution of 55g of sodium hexadecyl sulfate and 130g of 65wt% ethanol was added, and the mixture was stirred for another 35min. Then, 95g of zinc sulfate was added, and the mixture was heated to 125℃ and reacted for another 21h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed three times each with methanol solution and deionized water. The mixture was then dried under vacuum at 65℃ for 1.5h to obtain zinc MOF / silica core-shell microspheres.

[0030] S2: 275g of zinc MOF / silica core-shell microspheres, 130mL of nickel nitrate, 9.5g of complexing agent citric acid, 13g of surfactant polyethylene glycol sulfate, 8g of stabilizer L-cysteine, and 550mL of deionized water were added to a reaction vessel and stirred at 35℃ and 450r / min for 45min. After filtration, the filter cake was washed with deionized water until the final washing liquid was neutral, yielding nickel-plated core-shell microspheres with a surface nickel film thickness of 2.5nm. The nickel-plated core-shell microspheres were placed in a PECVD reactor, and argon gas at a flow rate of 5.5L / h and methane gas at a flow rate of 1.5L / h as a carbon source were introduced for 11min. The mixture was heated to 990℃ and treated for 2.5h. The product was washed three times with deionized water and dried under vacuum at 65℃ for 1.5h to obtain zinc oxide / carbon nanotube-derived mica.

[0031] S3: Add 210g of zinc oxide / carbon nanotube-derived mica, 130mL of anhydrous ethanol and 450mL of deionized water to a reaction vessel, stir for 11min at 55℃ and 550r / min, then add 110mL of γ-methacryloyloxypropyltrimethoxysilane, adjust the pH to 3.5 with hydrochloric acid solution, continue stirring for 6.5h, filter, wash the precipitate three times with deionized water and anhydrous ethanol, and vacuum dry at 65℃ for 1.5h to obtain modified zinc oxide / carbon nanotube-derived mica.

[0032] S4: Add 190g of modified zinc oxide / carbon nanotube-derived mica and 450mL of dichloromethane to a reaction vessel, stir for 11min at 22.5℃ and 550r / min, heat to 85℃ under nitrogen protection, then add 3.5g of benzoyl peroxide and 110g of alkenyl succinic anhydride, continue stirring for 3.5h, filter, wash the filter cake three times with deionized water, and vacuum dry at 65℃ for 1.5h to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica.

[0033] S5: 225g of 4,4'-oxydiphthalic anhydride, 450g of 1,3-bis(4'-aminophenoxy), and 850mL of N-methyl-2-pyrrolidone were added to a reaction vessel. Under nitrogen protection, the mixture was stirred at 2℃ and 550r / min for 25min. Then, it was heated to 22.5℃ and stirred for 4.5h. Then, 70g of anhydride-modified zinc oxide / carbon nanotube-derived mica was added and stirred for 11h. The mixture was filtered, and the filter cake was washed three times with deionized water. It was then vacuum dried at 65℃ for 1.5h. Then, it was heated to 115℃, 215℃, 320℃, and 365℃, and the temperature was maintained for 45min at each stage to obtain a high moisture-heat resistant polyimide composite material for insulating wires.

[0034] Example 3: A method for preparing a high moisture-heat resistant polyimide composite material for insulating wires, comprising the following steps: S1: 300g of mesoporous silica microspheres with a pore size of 200nm, 160g of 2,5-diaminoterephthalic acid and 2LN,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave and stirred for 40min at 25℃ and 600r / min. Then, a mixed solution of 60g of sodium hexadecyl sulfate and 140g of 70wt% ethanol solution was added and stirred for another 40min. Then, 100g of zinc sulfate was added, and the mixture was heated to 130℃ and reacted for another 22h. After naturally cooling to room temperature, the mixture was filtered, and the filter cake was washed four times with methanol solution and deionized water, respectively. The mixture was then vacuum dried at 70℃ for 2h to obtain zinc MOF / silica core-shell microspheres.

[0035] S2: 300g of zinc MOF / silica core-shell microspheres, 140mL of nickel nitrate, 10g of complexing agent citric acid, 14g of surfactant polyethylene glycol sulfate, 9g of stabilizer L-cysteine, and 600mL of deionized water were added to a reaction vessel and stirred for 50min at 40℃ and 500r / min. The mixture was filtered, and the filter cake was washed with deionized water until the final washing liquid was neutral, yielding nickel-plated core-shell microspheres with a surface nickel film thickness of 3nm. The nickel-plated core-shell microspheres were placed in a PECVD reactor, and argon gas at a flow rate of 6L / h and methane gas at a flow rate of 2L / h as a carbon source were introduced for 12min. The mixture was heated to 1000℃ and treated for 3h. The product was washed 4 times with deionized water and vacuum dried at 70℃ for 2h to obtain zinc oxide / carbon nanotube-derived mica.

[0036] S3: Add 220g of zinc oxide / carbon nanotube-derived mica, 140mL of anhydrous ethanol and 500mL of deionized water to a reaction vessel, stir for 12min at 60℃ and 600r / min, then add 120mL of γ-methacryloyloxypropyltrimethoxysilane, adjust the pH to 4 with hydrochloric acid solution, continue stirring for 7h, filter, wash the precipitate 4 times with deionized water and anhydrous ethanol, and vacuum dry at 70℃ for 2h to obtain modified zinc oxide / carbon nanotube-derived mica.

[0037] S4: Add 200g of modified zinc oxide / carbon nanotube-derived mica and 500mL of dichloromethane to a reaction vessel, stir for 12min at 25℃ and 600r / min, heat to 90℃ under nitrogen protection, then add 4g of benzoyl peroxide and 120g of alkenyl succinic anhydride, continue stirring for 4h, filter, wash the filter cake 4 times with deionized water, and vacuum dry at 70℃ for 2h to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica.

[0038] S5: 230g of 4,4'-oxydiphthalic anhydride, 500g of 1,3-bis(4'-aminophenoxy), and 900mL of N-methyl-2-pyrrolidone were added to a reaction vessel. Under nitrogen protection, the mixture was stirred at 4℃ and 600r / min for 30min. Then, it was heated to 25℃ and stirred for 5h. Then, 80g of anhydride-modified zinc oxide / carbon nanotube-derived mica was added and stirred for 12h. The mixture was filtered, and the filter cake was washed four times with deionized water. It was then vacuum dried at 70℃ for 2h. Then, it was heated to 120℃, 220℃, 330℃, and 370℃, and the temperature was maintained for 50min at each stage to obtain a high moisture-heat resistant polyimide composite material for insulating wires.

[0039] Comparative Example 1: Based on Example 3, the zinc MOF / silica core-shell microspheres in step S2 were replaced with the mesoporous silica microspheres in step S1.

[0040] Comparative Example 2: Based on Example 3, the nickel-plated core-shell microspheres in step S2 were replaced with zinc MOF / silica core-shell microspheres.

[0041] Comparative Example 3: Based on Example 3, the modified zinc oxide / carbon nanotube-derived mica in step S4 was replaced with the zinc oxide / carbon nanotube-derived mica prepared in step S3.

[0042] The performance of the polyimide composite materials obtained in Examples 1-3 and Comparative Examples 1-3 was tested. The polyimide composite material was sprayed three times onto a copper wire with a circular cross-sectional area (d=1mm) and baked at 350℃ for 30min to obtain an insulating layer with a thickness of 15μm. The results are shown in Table 1. 1. Tensile strength and elongation at break: The tensile strength and elongation at break are tested in accordance with GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Cables - Part 11: General Test Methods for Thickness and Dimensional Measurement and Mechanical Properties".

[0043] 2. Limiting oxygen index test: The limiting oxygen index was tested in accordance with GB / T 2406.2-2009 "Determination of flammability of plastics by oxygen index method - Part 2: Room temperature test".

[0044] 3. Dielectric constant

[0093] Test equipment: Agilent E5063A network analyzer, test frequency: 1GHz 4. Place the polyimide composite material at 50°C and 100% relative humidity for 30 days before testing.

[0045] Table 1

[0046] As can be seen from Table 1, the polyimide composite materials obtained in Examples 1-3 have significantly better elongation at break, tensile strength, and limiting oxygen index than the comparative examples, and significantly lower dielectric constant than the comparative examples. This indicates that the composite materials prepared in this invention have good insulation and high resistance to damp heat, as well as excellent mechanical properties and flame retardancy.

[0047] In Comparative Example 1, the zinc MOF / silica core-shell microspheres in step S2 were replaced with the mesoporous silica microspheres in step S1. The lack of MOF pore adsorption capacity and the absence of zinc MOF microporous structure in the mesoporous silica resulted in a reduced specific surface area and weakened water adsorption capacity. This made it easier for water molecules to penetrate the matrix in a humid and hot environment. The lack of zinc oxide derived from zinc MOF also prevented the formation of a dense carbon layer at high temperatures, leading to decreased flame retardancy. Furthermore, the increased polarization caused by water penetration resulted in an increased dielectric constant.

[0048] Comparative Example 2 replaced the nickel-plated core-shell microspheres in step S2 with zinc MOF / silica core-shell microspheres. Without the carbon nanotube layered network, the moisture diffusion path was shortened, accelerating the hygrothermal aging rate. While carbon nanotubes can improve the matrix stress dispersion ability, their absence reduced the tensile strength retention rate. Furthermore, the uncarbonized nickel-plated microspheres had weak interfacial bonding with polyimide, making them prone to debonding and forming microcracks under hygrothermal conditions. In Comparative Example 3, the modified zinc oxide / carbon nanotube-derived mica in step S4 was replaced with the zinc oxide / carbon nanotube-derived mica prepared in step S3. Without silane coupling treatment, the inorganic filler and polyimide interface have hydroxyl hydrophilic groups, which become water penetration channels. The lack of acid anhydride modification led to a 30% reduction in matrix crosslinking points, an increase in the degree of freedom of molecular chain movement, and an increase in the probability of hydrolysis. The unmodified microspheres agglomerated in the matrix, and the local stress accelerated aging and fractured.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a polyimide composite material with high resistance to moisture and heat for insulating wires, characterized in that, Includes the following steps: Step 1: Using mesoporous silica microspheres as a carrier, zinc-based MOFs are synthesized on the surface via hydrothermal synthesis to obtain zinc MOF / silica core-shell microspheres; Step 2: The zinc MOF / silica core-shell microspheres are coated with nickel film, placed in PECVD, and argon and methane are introduced to obtain zinc oxide / carbon nanotube-derived mica; Step 3: Hydrolyze and condense zinc oxide / carbon nanotube-derived mica with γ-methacryloxypropyltrimethoxysilane to obtain modified zinc oxide / carbon nanotube-derived mica, and then condense it with alkenyl succinic anhydride under the action of benzoyl peroxide to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica. Step 4: Using 4,4'-oxydiphthalic anhydride, anhydride-modified zinc oxide / carbon nanotube-derived mica, and 1,3-bis(4'-aminophenoxy) as raw materials, a high moisture-heat resistant polyimide composite material for insulating wires is obtained by stepwise heating and cyclization.

2. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 1, characterized in that, The specific preparation steps of the zinc MOF / silica core-shell microspheres are as follows: Mesoporous silica microspheres with a pore size of 150-200 nm, 2,5-diaminoterephthalic acid, and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave and stirred for 30-40 min at 20-25 °C and 500-600 r / min. Then, a mixed solution of sodium hexadecyl sulfate and 60-70 wt% ethanol was added, and stirring was continued for another 30-40 min. Zinc sulfate was then added, and the mixture was heated to 120-130 °C and reacted for another 20-22 h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed 2-4 times with methanol solution and deionized water, respectively. The mixture was then vacuum dried at 60-70 °C for 1-2 h to obtain zinc MOF / silica core-shell microspheres.

3. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 2, characterized in that, The ratio of the mesoporous silica microspheres, 2,5-diaminoterephthalic acid, N,N-dimethylformamide, sodium hexadecyl sulfate, ethanol solution and zinc sulfate is 200-300g: 150-160g: 1-2L: 50-60g: 120-140g: 90-100g.

4. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 1, characterized in that, The specific preparation steps of the zinc oxide / carbon nanotube-derived mica are as follows: Zinc MOF / silica core-shell microspheres, nickel nitrate, complexing agent citric acid, surfactant polyethylene glycol sulfate, stabilizer L-cysteine, and deionized water were added to a reaction vessel and stirred at 30-40℃ and 400-500 r / min for 40-50 min. After filtration, the filter cake was washed with deionized water until the final washing liquid was neutral, yielding nickel-plated core-shell microspheres with a surface nickel film thickness of 2-3 nm. The nickel-plated core-shell microspheres were placed in a PECVD reactor, and argon gas at a flow rate of 5-6 L / h and methane gas at a flow rate of 1-2 L / h as a carbon source were introduced for 10-12 min. The reactor was heated to 980-1000℃ and treated for 2-3 h. After washing and vacuum drying, zinc oxide / carbon nanotube-derived mica was obtained.

5. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 4, characterized in that, The ratio of zinc MOF / silica core-shell microspheres, nickel nitrate, citric acid, polyethylene glycol sulfate, L-cysteine, and deionized water is 250-300g: 120-140mL: 9-10g: 12-14g: 7-9g: 500-600mL.

6. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 1, characterized in that, The specific preparation steps for the modified zinc oxide / carbon nanotube-derived mica are as follows: Zinc oxide / carbon nanotube-derived mica, anhydrous ethanol, and deionized water were added to a reaction vessel and stirred for 10-12 min at 50-60℃ and 500-600 r / min. Then, γ-methacryloyloxypropyltrimethoxysilane was added, and the pH was adjusted to 3-4 with hydrochloric acid solution. The reaction was continued to be stirred for 6-7 h. After filtration, washing, and vacuum drying, modified zinc oxide / carbon nanotube-derived mica was obtained. The ratio of zinc oxide / carbon nanotube-derived mica, anhydrous ethanol, deionized water, and γ-methacryloyloxypropyltrimethoxysilane is 200-220g: 120-140mL: 400-500mL: 100-120mL.

7. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 1, characterized in that, The specific preparation steps for the anhydride-modified zinc oxide / carbon nanotube-derived mica are as follows: Modified zinc oxide / carbon nanotube-derived mica and dichloromethane were added to a reaction vessel and stirred at 20-25℃ and 500-600 r / min for 10-12 min. Under nitrogen protection, the mixture was heated to 80-90℃, and then benzoyl peroxide and alkenyl succinic anhydride were added. The reaction was continued to be stirred for 3-4 h. The mixture was then filtered, washed, and vacuum dried to obtain anhydride-modified zinc oxide / carbon nanotube-derived mica. The ratio of the modified zinc oxide / carbon nanotube-derived mica, dichloromethane, benzoyl peroxide, and alkenyl succinic anhydride is 180-200g: 400-500mL: 3-4g: 100-120g.

8. The method for preparing a high moisture-heat resistant polyimide composite material for insulating wires according to claim 1, characterized in that, The specific preparation steps of the polyimide composite material are as follows: 4,4'-O-diphthalic anhydride, 1,3-bis(4'-aminophenoxy), and N-methyl-2-pyrrolidone were added to a reaction vessel and stirred at 0-4°C and 500-600 rpm for 20-30 min under nitrogen protection. Then, the mixture was heated to 20-25°C and stirred for 4-5 h. Then, anhydride-modified zinc oxide / carbon nanotube-derived mica was added and stirred for 10-12 h. The mixture was filtered, washed, and vacuum dried. Then, it was heated to 110-120°C, 210-220°C, 310-330°C, and 360-370°C, with each temperature maintained for 40-50 min, to obtain a polyimide composite material with high moisture and heat resistance for insulating wires.

9. The method for preparing a high moisture-heat resistant polyimide composite material for insulated wires according to claim 8, characterized in that, The ratio of the amounts of 4,4'-oxophthalic anhydride, 1,3-bis(4'-aminophenoxy), N-methyl-2-pyrrolidone, and anhydride-modified zinc oxide / carbon nanotube-derived mica is 220-230g: 400-500g: 800-900mL: 60-80g.

10. A polyimide composite material for insulating wires with high resistance to moisture and heat, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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