Preparation method and application of electric breakdown-resistant corona-resistant polyimide film
By introducing ethyl and nitrogen heterocyclic structures into the polyimide molecular chain, a polyimide film resistant to electrical breakdown and corona was prepared, solving the problem of insufficient insulation performance of traditional polyimide films and achieving a significant improvement in insulation performance. This film is suitable for applications such as high-voltage flexible DC transmission, electromagnetic equipment, and new energy vehicles.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2026-04-14
- Publication Date
- 2026-05-12
AI Technical Summary
Traditional polyimide films have insufficient dielectric insulation properties in fields such as high-voltage flexible DC power transmission, electromagnetic equipment, and new energy vehicles, and cannot meet the high insulation performance requirements of modern electrical equipment.
By introducing ethyl monomers with low rotational barriers and dianhydride monomers with nitrogen-containing heterocyclic structures into the polyimide molecular chain, breakdown-resistant and corona-resistant polyimide films can be prepared through modification, thereby increasing the band gap and reducing the free volume and optimizing the insulation performance.
The DC breakdown field strength, AC breakdown field strength, and high-frequency corona resistance life of polyimide films have been improved, enhancing insulation performance and meeting the application requirements of harsh working conditions with high temperature and high field.
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Figure CN122011458A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrical insulation material preparation technology, and relates to a method for preparing and applying a polyimide film resistant to electrical breakdown and corona. Background Technology
[0002] Metallized film capacitors are widely used in new energy vehicles, high-voltage flexible DC transmission, electromagnetic energy equipment, and de-icing devices due to their advantages such as high energy density and fast charge / discharge rates. However, research on the energy storage and insulation properties of dielectric materials in film capacitors still faces many bottlenecks, especially in harsh operating conditions such as high-temperature and high-field conditions in high-voltage flexible DC transmission converter valves, electric vehicle inverters, electromagnetic equipment pulse power systems, and wind turbine de-icing systems.
[0003] Polyimide (PI), as a high-performance insulating dielectric film, is widely used in important applications such as insulation of enameled wires for drive motor windings, winding insulation of high-voltage reactors, and dielectric insulation materials for capacitors. However, as electrical equipment and power electronic devices develop towards higher power, miniaturization, and lighter weight, traditional PI films can no longer meet the special requirements of modern electrical equipment, especially the dielectric films for capacitors, which require PI films with superior electrical insulation properties. Therefore, the development of polyimide thin insulating films with high insulation performance and their processing methods has become one of the important research directions in the power equipment manufacturing industry. Summary of the Invention
[0004] This invention addresses the technical problem of poor insulation performance of dielectric insulating films in film capacitors by providing a method for preparing and applying a breakdown- and corona-resistant polyimide film, particularly its application in intrinsic polyimide modification technology. The breakdown- and corona-resistant polyimide film prepared by this invention innovatively introduces ethyl structures with low rotational barriers into the main chain. This not only disrupts the rigid conjugated structure of the benzene ring but also fills the gaps between chain segments through rotation, reducing microscopic porosity defects. It possesses good solution processability, excellent breakdown resistance, and a long corona resistance lifetime, resulting in a polyimide dielectric material with excellent insulation properties.
[0005] The technical solution of the present invention: A method for preparing an electrical breakdown and corona resistant polyimide film includes the following steps: Step 1: Prepare polyamic acid adhesive solution: 4,4-Diaminodiphenyl ether was added to N'N-dimethylacetamide and stirred under ice-water bath conditions until completely dissolved; then ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride were added, and polycondensation reaction was carried out under vacuum conditions to obtain the modified polyamic acid liquid EPAA. The modified polyamic acid liquid EDPAA was obtained by replacing 4,4-diaminodiphenyl ether with a mixture of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether. In the system of obtaining modified polyamic acid liquid EDPAA, ethylenediaminetetraacetic acid dianhydride was removed to obtain modified polyamic acid liquid DPAA. Step 2: Preparation of electrical breakdown and corona resistant polyimide film: Modified polyamic acid liquids EPAA, EDPAA, and DPAA were poured onto a clean glass substrate surface and coated onto the glass substrate using an automatic coating machine. After a gradient heating process, the films were naturally cooled to room temperature and then demolded to obtain three types of electrical breakdown and corona resistant polyimide films.
[0006] In step (1), the total mass of 4,4-diaminodiphenyl ether, ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride, the total mass of 2-methylthiopyrimidine-4,6-diamine, 4,4-diaminodiphenyl ether, ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride, and the volume ratio of the total mass of 2-methylthiopyrimidine-4,6-diamine, 4,4-diaminodiphenyl ether and pyromellitic dianhydride to the volume of N'N-dimethylacetamide are all 3 g:(17~27) mL.
[0007] In step (1), the molar ratio of 4,4-diaminodiphenyl ether to the total molar ratio of ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride is 1:(1.02~1.04). The ratio of the total molar amount of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether to the total molar amount of ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride is 1:(1.02~1.04). The ratio of the total molar amount of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether to the molar amount of pyromellitic dianhydride is 1:(1.02~1.04).
[0008] In step (1), the mass ratios of ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride in the modified polyamic acid adhesive EPAA are 1:10, 1:15 and 1:20, respectively.
[0009] In step (1), the mass ratio of 2-methylthiopyrimidine-4,6-diamine to 4,4-diaminodiphenyl ether in the modified polyamic acid adhesive EDPAA is 1:15.
[0010] In step (1), the mass ratios of ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride in the modified polyamic acid adhesive EDPAA are 1:10, 1:15 and 1:20, respectively.
[0011] In step (1), the total mass ratio of 2-methylthiopyrimidine-4,6-diamine to 4,4-diaminodiphenyl ether in the modified polyamic acid adhesive DPAA is 1:10, 1:15 and 1:20, respectively.
[0012] In step (1), the stirring time is 30~60min, and the temperature of the ice water bath is -5~15℃.
[0013] In step (1), the vacuum condition is 0~0.02MPa, and the polycondensation reaction time is 12~14h.
[0014] In step (2), the coating speed is 0.2~0.6cm / s, the coating time is 10~30s, and the coating length is 200~250mm.
[0015] In step (2), the gradient heating process is as follows: 80℃ for 2 hours, 120℃ for 1 hour, 160℃ for 1 hour, 240℃ for 1 hour, 300℃ for 1 hour and 350℃ for 2 hours, with a heating rate of 2~4℃ / min.
[0016] In step (2), the demolding environment is a deionized water immersion environment, the demolding temperature is 10~35℃, and the demolding time is 15~30min.
[0017] All electrical breakdown and corona resistant polyimide films have a thickness of 20~30μm.
[0018] Application of a breakdown-resistant and corona-resistant polyimide film in the preparation of film capacitors.
[0019] Film capacitors are used in high-voltage flexible DC transmission converter valves, inverters for new energy vehicles and electric vehicles, pulse power systems for electromagnetic equipment, and de-icing systems for wind turbines, etc.
[0020] This invention employs an in-situ polymerization method to prepare a polyimide film with excellent insulation properties, resistant to electrical breakdown and corona discharge, by introducing a certain proportion of pyrimidine-containing diamine monomers and nitrogen-containing heterocyclic dianhydride monomers into the polyimide molecular chain. The DC breakdown field strength of this polyimide film at room temperature is 431.33 kV / mm (compared to 276.54 kV / mm for conventional polyimide), and the AC breakdown field strength at room temperature reaches 308.54 kV / mm (compared to 184.32 kV / mm for conventional polyimide). These figures represent improvements of 56% and 67% respectively compared to polyimide films prepared using the same proportions of pyromellitic dianhydride and diaminodiphenyl ether. Furthermore, the corona discharge lifetime at high frequencies reaches 1305 s (compared to 845 s for conventional polyimide), representing a 54% improvement in corona discharge lifetime.
[0021] The beneficial effects of this invention are: (1) This invention introduces a nitrogen-containing heterocyclic dianhydride monomer, ethylenediaminetetraacetic acid dianhydride, into the polyimide molecular chain. By increasing the band gap of the modified polyimide, electrons are more difficult to be excited from the valence band to the conduction band, reducing the intrinsic carrier concentration and decreasing the conductivity, thereby optimizing the insulation performance. The final embodiment results show that the DC breakdown strength of the breakdown-resistant and corona-resistant polyimide film prepared by this invention can reach 431.33 kV / mm at room temperature, and the AC breakdown field strength at room temperature can reach 308.54 kV / mm. At the same time, this invention prepares a breakdown-resistant and corona-resistant polyimide film by introducing a pyrimidine-containing diamine monomer, 2-methylthiopyrimidine-4,6-diamine, into the molecular chain. Its DC breakdown strength at room temperature can reach 395.24 kV / mm (compared to 276.54 kV / mm for pure PI), which has excellent insulation performance.
[0022] (2) This invention introduces ethylenediaminetetraacetic acid dianhydride monomer into the polyimide molecular chain. By introducing an aliphatic ethylenediamine structure, the percentage of free volume in the polyimide system is reduced. According to the free volume breakdown theory, a smaller free volume means a smaller free length between molecular chains, a smaller maximum mean free path for carriers to accelerate under an electric field, less energy gained by carriers, and thus less impact damage to the molecular chains, thereby optimizing insulation performance. The final embodiment results show that the breakdown-resistant and corona-resistant polyimide film prepared by this invention can achieve a corona resistance lifetime of 1305s at high frequencies.
[0023] (3) This invention, based on intrinsic modification to regulate the insulation performance of polyimide insulating dielectric materials, introduces ethylenediaminetetraacetic dianhydride monomer. On the one hand, this increases the band gap and reduces the carrier concentration by lowering the LUMO energy level of polyimide; on the other hand, it reduces the free volume in the polyimide system and decreases the mean free path of carrier acceleration through the aliphatic ethylenediamine structure in the ethylenediaminetetraacetic dianhydride monomer. This solves the problems of poor breakdown performance and short corona resistance lifetime of existing polyimide insulating dielectrics at high frequencies.
[0024] (4) The process of this invention is simple, the large-scale preparation technology is mature, and existing industrial equipment can meet the production technology requirements. Moreover, it can maintain the inherent mechanical properties and electrostrictive properties of polymer-based materials, which will provide guidance for the research and development of insulating dielectric materials for large-scale preparation of thin-film capacitors under high frequency and high field conditions. Attached Figure Description
[0025] Figure 1 The diagram shows the electronic density of states and energy level orbitals of four modified polyimides, where (a) is PI of Comparative Example 1, (b) is DPI-15 of Example 8, (c) is EPI-15 of Example 2, and (d) is DEPI-15-15 of Example 5. Figure 2The electrostatic potential distribution and bar charts of four modified polyimides are shown, where (a) is PI of Comparative Example 1, (b) is DPI-15 of Example 8, (c) is EPI-15 of Example 2, and (d) is DEPI-15-15 of Example 5. Figure 3 The free volume distribution diagrams are shown for four modified polyimides, where (a) is PI of Comparative Example 1, (b) is DPI-15 of Example 8, (c) is EPI-15 of Example 2, and (d) is DEPI-15-15 of Example 5. Figure 4 Comparison of infrared spectra of modified polyimide films obtained in different embodiments; Figure 5 The following are Weibull distribution diagrams of the breakdown strength of modified polyimide films obtained in different examples at room temperature: (a) is PI of Comparative Example 1, EPI-10 of Example 1, EPI-15 of Example 2 and EPI-20 of Example 3; (b) is PI of Comparative Example 1, DPI-10 of Example 7, DPI-15 of Example 8 and DPI-20 of Example 9; (c) is PI of Comparative Example 1, DEPI-15-10 of Example 4, DEPI-15-15 of Example 5 and DEPI-15-20 of Example 6; and (d) is a comparison diagram of the breakdown strength of PI of Comparative Example 1 and the electrical breakdown and corona resistance polyimide films of Examples 1-9. Figure 6 This is a comparison chart of the high-frequency corona resistance lifetime of the modified polyimide films obtained in Examples 2, 5, 8 and Comparative Example 1. Detailed Implementation
[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.
[0027] Example 1 Step 1: Prepare polyamic acid adhesive solution; In a three-necked flask, 4.0048 g of 4,4-diaminodiphenyl ether was dissolved in 49 ml of N'N-dimethylacetamide. Under ice-water bath conditions, 0.4751 g of ethylenediaminetetraacetic acid dianhydride was dissolved in N'N-dimethylacetamide. Then, 4.0045 g of pyromellitic dianhydride was added to the solution in multiple portions at uniform intervals. The mixture was stirred under vacuum at a stirring rate of 150 r / min for 12 h to obtain a polyamic acid solution with a solid content of 15%. Step 2: Prepare polyimide film; The polyamic acid adhesive solution was placed in a vacuum oven for 4 hours to remove bubbles. Then, an automatic coating machine was used to coat the glass substrate at a speed of 0.4 cm / s for 20 seconds. A gradient heating imidization treatment was then performed: 80℃ for 2 hours, 120℃ for 1 hour, 160℃ for 1 hour, 240℃ for 1 hour, 300℃ for 1 hour, and 350℃ for 2 hours, with a heating rate of 2℃ / min. The glass substrate was then immersed in deionized water for 30 minutes for demolding. Finally, the demolded polyimide film was placed in a high-temperature oven and allowed to stand at 60℃ for 4 hours. The resulting polyimide film, resistant to electrical breakdown and corona discharge, with a thickness of 20-30 μm, was designated EPI-10.
[0028] Example 2 The difference between this embodiment and Example 1 is that in step one, the amount of ethylenediaminetetraacetic acid dianhydride is 0.3267g and the amount of pyromellitic dianhydride is 4.1714g. The remaining operation process and parameter settings are the same as in Example 1, and a polyimide film with a thickness of 20~30μm that is resistant to electrical breakdown and corona is obtained, which is denoted as EPI-15.
[0029] Example 3 The difference between this embodiment and Example 1 is that in step one, the amount of ethylenediaminetetraacetic acid dianhydride is 0.2489g and the amount of pyromellitic dianhydride is 4.2378g. The remaining operation process and parameter settings are the same as in Example 1, and a polyimide film with a thickness of 20~30μm that is resistant to electrical breakdown and corona is obtained, which is denoted as EPI-20.
[0030] Example 4 The difference between this embodiment and Example 1 is that in step one, 3.7545g of 4,4-diaminodiphenyl ether, 0.1952g of 2-methylthiopyrimidine-4,6-diamine, 0.4750g of ethylenediaminetetraacetic acid dianhydride, and 4.0439g of pyromellitic dianhydride are used. The remaining operation process and parameter settings are the same as in Example 1, resulting in a 20-30μm thick polyimide film resistant to electrical breakdown and corona discharge, denoted as DEPI-15-10.
[0031] Example 5 The difference between this embodiment and Example 4 is that in step one, the amount of ethylenediaminetetraacetic acid dianhydride is 0.3267g and the amount of pyromellitic dianhydride is 4.1715g. The remaining operation process and parameter settings are the same as in Example 1, and a polyimide film with a thickness of 20~30μm that is resistant to electrical breakdown and corona is obtained, which is denoted as DEPI-15-15.
[0032] Example 6 The difference between this embodiment and Example 4 is that in step one, the amount of ethylenediaminetetraacetic acid dianhydride is 0.2488g and the amount of pyromellitic dianhydride is 4.2377g. The remaining operation process and parameter settings are the same as in Example 1, and a polyimide film with a thickness of about 20~30μm that is resistant to electrical breakdown and corona is obtained, which is denoted as DEPI-15-20.
[0033] Example 7 The difference between this embodiment and Example 1 is that in step one, 3.641 g of 4,4-diaminodiphenyl ether, 0.2840 g of 2-methylthiopyrimidine-4,6-diamine, and 4.4496 g of pyromellitic dianhydride are used, and ethylenediaminetetraacetic dianhydride is not added. The remaining operation process and parameter settings are the same as in Example 1, resulting in a 20-30 μm thick polyimide film resistant to electrical breakdown and corona discharge, denoted as DPI-10.
[0034] Example 8 The difference between this embodiment and Example 7 is that in step one, 3.7545 g of 4,4-diaminodiphenyl ether and 0.1952 g of 2-methylthiopyrimidine-4,6-diamine are used. The remaining operation process and parameter settings are the same as in Example 1, resulting in a 20-30 μm thick polyimide film resistant to electrical breakdown and corona discharge, denoted as DPI-15.
[0035] Example 9 The difference between this embodiment and Example 7 is that in step one, 3.8140 g of 4,4-diaminodiphenyl ether and 0.1487 g of 2-methylthiopyrimidine-4,6-diamine are used. The remaining operations and parameter settings are the same as in Example 1. A polyimide film with a thickness of 20-30 μm that is resistant to electrical breakdown and corona discharge is obtained, denoted as DPI-20.
[0036] Comparative Example 1 Step 1: Prepare polyamic acid adhesive solution; In a three-necked flask, 4.008 g of 4,4-diaminodiphenyl ether was dissolved in 48 ml of N'N-dimethylacetamide (molar ratio 1:15). Under ice-water bath conditions, 4.4496 g of pyromellitic dianhydride was added to the solution in multiple portions at uniform intervals. The mixture was stirred under vacuum at a stirring rate of 150 r / min for 12 h to obtain a polyamic acid solution with a solid content of 15%. Step two is the same as in Example 1, and the final modified polyimide film with a thickness of 20~30μm is prepared, denoted as PI.
[0037] Effect Analysis The structure and properties of the electrical breakdown and corona resistant polyimide films obtained in Examples 1-9 and the modified polyimide film obtained in Comparative Example 1 were characterized, and the results are as follows: Figure 1The electronic density of states and energy level orbitals of electrically breakdown-resistant and corona-resistant polyimide films and modified polyimide films are compared. Figure 1 It can be seen that the band gap of PI is 2.77 eV, that of DPI is 2.84 eV, and that of EPI is 2.82 eV. DPI and EPI exhibit higher band gaps than PI, which can effectively reduce the probability of electrons being excited from the valence band to the conduction band to form free electrons, reduce the intrinsic carrier concentration, and improve the insulation properties of the modified polyimide film.
[0038] Figure 2 To obtain the electrostatic potential distribution and histogram of the electrically breakdown-resistant and corona-resistant polyimide film and the modified polyimide film, from Figure 2 It is known that because nitrogen atoms are more electronegative than carbon atoms, they attract electrons near the ethyl group, causing the ethyl group to exhibit electron-withdrawing properties. Therefore, the ethyl group bonded to the nitrogen atom in EPI displays a positive electrostatic potential, thereby enhancing the electrophilic properties of EPI. A comparison table of the positive electrostatic potential area ratios of the four polyimides shows that EPI has the highest positive electrostatic potential ratio, significantly higher than PI. This indicates that the addition of ethylenediaminetetraacetic dianhydride may introduce more deep traps into the molecular chain, thereby enhancing the ability of EPI to capture charge carriers and helping to counteract the effects of an applied electric field.
[0039] Figure 3 The free volume distribution diagrams are shown for electrically breakdown-resistant and corona-resistant polyimide films and modified polyimide films. Figure 3 It is known that, due to the low rotational barrier of the ethylenediamine aliphatic chains in EPI, they exhibit flexibility and can fill the gaps between chain segments through rotation. Therefore, compared to pure PI and other modified polyimides, EPI has the smallest free volume, at 10.78%. A smaller free volume means a shorter free length between molecular chains, a smaller maximum mean free path for carrier acceleration under an electric field, less energy gained by carriers, reduced impact on the molecular chains, and improved insulation performance.
[0040] Figure 4 The images show a comparison of the infrared spectra of the electrically breakdown-resistant and corona-resistant polyimide films and the modified polyimide films obtained in different embodiments. Figure 4 It can be seen that the infrared spectra of the films prepared in Examples 1-9 and the film prepared in Comparative Example 1 are all around 3083 cm⁻¹. -1 An absorption peak for NH bonds is present at 1784 cm⁻¹. -1 ~1726 cm -1 The presence of carbonyl absorption peaks at these sites indicates successful imidization. Furthermore, the electrically resistant and corona-resistant polyimide films prepared in Examples 4-6 also exhibit a unique 1552 cm⁻¹ peak. -1The absorption peak at the C=N bond indicates the presence of a pyrimidine structure in the molecular chain, demonstrating the successful introduction of 2-methylthiopyrimidine-4,6-diamine into the polyimide film. The breakdown-resistant and corona-resistant polyimide films prepared in Examples 1-3 exhibit a unique 2874 cm⁻¹ absorption peak. -1 The absorption peak at this location corresponds to the aliphatic CN bond between the ethyl backbone (-CH2-CH2-) and the imide ring in ethylenediaminetetraacetic dianhydride, indicating that the ethylenediaminetetraacetic dianhydride monomer was successfully introduced into the polyimide film. These findings demonstrate that new monomers, ethylenediaminetetraacetic dianhydride and 2-methylthiopyrimidine-4,6-diamine, were introduced into the polyimide film without disrupting the polyimide structure.
[0041] Figure 5 This is a comparison chart of the breakdown strength of the electrical breakdown and corona-resistant polyimide films obtained in different embodiments and the modified polyimide film obtained in Comparative Example 1. Figure 5 It can be seen that as the proportion of ethylenediaminetetraacetic dianhydride increases, the breakdown strength of the films prepared in Examples 1-3 first increases and then decreases. The film prepared in Example 2 has the highest breakdown field strength at room temperature, which is 431.33 kV / mm, an improvement of 56% compared to the film prepared in Comparative Example 1 (276.54 kV / mm). This indicates that the flexible ethylenediamine aliphatic chains in EPI disrupt the conjugated structure of 4,4-diaminodiphenyl ether and pyromellitic dianhydride in traditional PI, reducing the parallel and close packing degree of molecular chains, inhibiting the migration of charge carriers along the molecular chains under the applied electric field. At the same time, the addition of ethylenediaminetetraacetic dianhydride reduces the gaps between molecular chains, weakening the impact of accelerated charge carriers on the molecular chains, thus improving the breakdown strength. As the proportion of 2-methylthiopyrimidine-4,6-diamine increases, the breakdown strength of the films in Examples 7-9 first increases and then decreases. The breakdown strength of the film prepared in Example 8 is 395.24 kV / mm at room temperature, which is 42.9% higher than that of the film prepared in Comparative Example 1 (276.54 kV / mm).
[0042] Figure 6The graph shows a comparison of the high-frequency corona resistance lifetimes of the breakdown-resistant and corona-resistant polyimide films obtained in Examples 2, 5, 8, and Comparative Example 1. The three films with the best breakdown performance from different examples were selected for high-frequency corona resistance lifetime testing. As can be seen from the graph, the film prepared in Example 2 has the longest corona resistance lifetime, at 21.76 min, which is 54.43% higher than the modified polyimide film prepared in Comparative Example 1 (14.09 min). This is because the EPI molecular chain rotation angle is relatively large, which can suppress the regular arrangement of molecular chains and form a highly uniform, grain-bound, and phase-separated dense glassy state, resulting in fewer defects in the corona discharge region. Simultaneously, the presence of ethylenediaminetetraacetic acid dianhydride can introduce trap states into the EPI, capturing charge carriers during the corona discharge process and weakening the bombardment of high-energy particles on the EPI backbone, ultimately improving its corona resistance lifetime.
[0043] In summary, the breakdown-resistant and corona-resistant polyimide film prepared by this invention has high breakdown strength and long corona resistance life.
[0044] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.
[0045] Table 1. Comparison of the area ratio of positive electrostatic potential for four types of polyimide
[0046] Table 2 Comparison of Free Volume Fractions of Four Polyimides
Claims
1. A method for preparing an electrically breakdown-resistant and corona-resistant polyimide film, characterized in that, Includes the following steps: Step 1: Prepare polyamic acid adhesive solution: 4,4-Diaminodiphenyl ether was added to N'N-dimethylacetamide and stirred under ice-water bath conditions until completely dissolved; then ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride were added, and polycondensation reaction was carried out under vacuum conditions to obtain the modified polyamic acid liquid EPAA. The modified polyamic acid liquid EDPAA was obtained by replacing 4,4-diaminodiphenyl ether with a mixture of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether. In the system of obtaining modified polyamic acid liquid EDPAA, ethylenediaminetetraacetic acid dianhydride was removed to obtain modified polyamic acid liquid DPAA. Step 2: Preparation of electrical breakdown and corona resistant polyimide film: Modified polyamic acid liquids EPAA, EDPAA, and DPAA were poured onto a clean glass substrate surface and coated onto the glass substrate using an automatic coating machine. After a gradient heating process, the films were naturally cooled to room temperature and then demolded to obtain three types of electrical breakdown and corona resistant polyimide films.
2. The method for preparing the electrical breakdown and corona-resistant polyimide film according to claim 1, characterized in that, In step (1), the total mass of 4,4-diaminodiphenyl ether, ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride, the total mass of 2-methylthiopyrimidine-4,6-diamine, 4,4-diaminodiphenyl ether, ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride, and the volume ratio of the total mass of 2-methylthiopyrimidine-4,6-diamine, 4,4-diaminodiphenyl ether and pyromellitic dianhydride to the volume of N'N-dimethylacetamide are all 3 g:(17~27) mL.
3. The method for preparing the electrical breakdown and corona-resistant polyimide film according to claim 2, characterized in that, In step (1), the molar ratio of 4,4-diaminodiphenyl ether to the total molar ratio of ethylenediaminetetraacetic dianhydride and pyromellitic dianhydride is 1:(1.02~1.04); the mass ratios of ethylenediaminetetraacetic dianhydride to pyromellitic dianhydride are 1:10, 1:15 and 1:20, respectively. The total molar ratio of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether to the total molar ratio of ethylenediaminetetraacetic acid dianhydride and pyromellitic dianhydride is 1:(1.02~1.04); wherein, in the synthesized modified polyamic acid adhesive EDPAA, the mass ratio of 2-methylthiopyrimidine-4,6-diamine to 4,4-diaminodiphenyl ether is 1:15; and the mass ratios of ethylenediaminetetraacetic acid dianhydride to pyromellitic dianhydride are 1:10, 1:15 and 1:20, respectively; The ratio of the total molar amount of 2-methylthiopyrimidine-4,6-diamine and 4,4-diaminodiphenyl ether to the molar amount of pyromellitic dianhydride is 1:(1.02~1.04); wherein, in the modified polyamic acid adhesive DPAA, the total mass ratio of 2-methylthiopyrimidine-4,6-diamine to 4,4-diaminodiphenyl ether is 1:10, 1:15 and 1:20, respectively.
4. The method for preparing the electrical breakdown and corona-resistant polyimide film according to claim 3, characterized in that, In step (1), the stirring time is 30~60 min, and the temperature of the ice water bath is -5~15℃; The vacuum conditions are 0~0.02MPa, and the polycondensation reaction time is 12~14h.
5. The method for preparing the electrical breakdown and corona-resistant polyimide film according to claim 4, characterized in that, In step (2), the coating speed is 0.2~0.6cm / s, the coating time is 10~30s, and the coating length is 200~250mm; The gradient heating process is as follows: 80℃ for 2 hours, 120℃ for 1 hour, 160℃ for 1 hour, 240℃ for 1 hour, 300℃ for 1 hour and 350℃ for 2 hours, with a heating rate of 2~4℃ / min. The demolding environment is a deionized water immersion environment, the demolding temperature is 10~35℃, and the demolding time is 15~30min.
6. The breakdown-resistant and corona-resistant polyimide film obtained by the preparation method of any one of claims 1-5 has a thickness of 20~30μm.
7. The application of the electrical breakdown and corona resistant polyimide film according to claim 6 in the preparation of film capacitors.
8. The application of the electrical breakdown and corona-resistant polyimide film according to claim 7 in the preparation of film capacitors, characterized in that, Film capacitors are used in high-voltage flexible DC transmission converter valves, new energy vehicle electric vehicle inverters, electromagnetic equipment pulse power systems, or wind turbine de-icing systems.