High-temperature corona-resistant polyimide-based composite dielectric and preparation method thereof

Abstract

The invention discloses a high-temperature corona-resistant polyimide-based composite dielectric and a preparation method thereof, and belongs to the technical field of preparation of high-temperature insulating dielectric materials. The problems that an existing thin film capacitor is poor in insulation performance and low in controllability in a high-temperature environment are solved. According to the invention, rigid sulfuryl is introduced between diamine and dianhydride by adopting an in-situ polymerization method, and sulfuryl-containing polyimide is cross-linked on the basis, so that compared with conventional polyimide cross-linking, films with seven structures are prepared. The breakdown field strength of the polyimide cross-linked film containing the sulfone groups on the two sides can reach 654.2 kV / mm and 463.1 kV / mm at the normal temperature and the high temperature (150 DEG C), and the corona resistance time is 640 s. Furthermore, the insulating property is excellent in a high-temperature environment. The polyimide provided by the invention has the characteristics of high heat resistance, good solution processability, good thermal stability and the like, is simple in preparation process flow and relatively low in cost, and can be popularized and implemented.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of electric insulation materials, and in particular relates to a high-temperature corona-resistant polyimide-based composite dielectric and a preparation method thereof. Background Art

[0002] Due to the extremely uneven distribution of green energy bases and load centers in my country, and with the demand for wind power grid connection and urban intensive construction, it is of great significance to develop UHV technology and build a high-quality AC and DC transmission network. However, with the continuous increase in voltage levels, the short-term failure of insulation in high-voltage equipment has become more frequent. The pulse oscillation method was used to conduct a field test of inter-turn overvoltage on dry-type air-core reactors. By detecting the change in the oscillation frequency of the test voltage waveform, it was found that the failure rate was as high as 7.4%. The State Grid Corporation of China found that the β-phase reactor of the 35kV capacitor was overheated during the infrared temperature measurement of the 220kV substation of Liaocheng Power Supply Bureau. The inspection results showed that an inter-turn short-circuit fault occurred in the insulation winding of the reactor. In addition, during the offline maintenance of the stator winding of the 1750MW main generator of Taishan Nuclear Power Plant, it was found that when a DC voltage of 81kV was applied, discharge occurred in the weak area of ​​the insulation. It can be seen that the breakdown damage of the insulating medium has also become a key issue restricting the development of high-voltage transmission technology.

[0003] Polyimide (PI), known as the "golden film", has been widely used in winding insulation of UHV reactors, wind turbine winding insulation, and inter-turn insulation of DC motors due to its high electrical strength (300kV / mm), operating temperature (350℃), and dimensional stability. However, as electrical equipment and power electronic devices develop towards high power, miniaturization, and thinness, traditional PI films can no longer meet the special needs of modern electrical equipment. In particular, slot insulation, winding insulation, and dielectric buffer layers used in motors require polyimide to have excellent electrical insulation properties. Therefore, the development of polyimide thin flexible insulating media with high insulation properties and its process methods has become one of the important research directions of the power equipment manufacturing industry.

[0004] In the prior art, inorganic phase doping modification and other methods are used to prepare composite dielectric materials with high temperature insulation. However, the introduction of high volume fraction inorganic fillers and poor compatibility lead to the generation of carrier traps inside the material, which reduces the breakdown field strength of the material.

[0005] Therefore, in current technology, the optimization of high-temperature insulation performance of polyimide from the perspective of molecular structure design has become an important research hotspot. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problem that the intrinsic insulation properties of existing polyimide dielectric materials are poor, and to provide a high-temperature corona-resistant polyimide-based composite dielectric and a preparation method thereof, as well as an application in electrical insulation, especially in polyimide intrinsic modification technology. The polyimide film prepared by the present invention has the characteristics of good solution processability and good insulation performance, and a modified polyimide flexible dielectric with excellent insulation properties is obtained, which can be widely used in the fields of microelectronics and communications.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The present invention provides a high-temperature corona-resistant polyimide-based composite dielectric and a preparation method thereof, comprising the following preparation steps:

[0009] (1) adding a sulfone-containing diamine monomer to an organic solvent and stirring to completely dissolve it; adding a sulfone-containing dianhydride monomer and subjecting it to polycondensation under vacuum conditions to obtain a modified polyamic acid glue solution (PAA);

[0010] (2) pouring the modified polyamic acid glue onto the surface of a clean glass substrate, coating the glass substrate with a coating machine, irradiating the glass substrate with an infrared lamp, and then thermal imidizing the glass substrate, and then cooling the glass substrate to room temperature to obtain a modified polyimide film;

[0011] On the one hand, in step (1), the diamine monomer is one of diaminodiphenyl ether and diaminodiphenyl sulfone, and the molar ratio thereof is 1:5 to 40, preferably 1:10 to 30; the dianhydride monomer is pyromellitic anhydride and 3,3'4,4'-diphenylsulfonetetracarboxylic dianhydride, and the molar ratio thereof is 1:5 to 50, preferably 1:10 to 30; and the organic solvent is selected from at least one of N,N-dimethylformamide and N,N-dimethylacetamide.

[0012] As a preferred embodiment, in step (1), the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.02-1.04;

[0013] As a preferred embodiment, in step (1), the polycondensation reaction temperature is -10 to 30°C, preferably -5 to 5°C;

[0014] As a preferred embodiment, in step (1), the polycondensation reaction time is 2 to 36 hours, preferably 8 to 24 hours.

[0015] As a preferred implementation, in step (2), the infrared lamp is selected to be 2000W and the irradiation time is 3 to 5s.

[0016] As a preferred embodiment, in step (2), the thermal imidization adopts gradient heating; in the technical solution of the present invention, the gradient heating can ensure that the modified polyimide is completely imidized while the solvent is completely volatilized, and the molecular chains are tightly stacked and free of defects;

[0017] Preferably, the heating rate of the gradient heating is 2-4°C / min;

[0018] Preferably, each temperature gradient of the gradient heating is 40-60°C;

[0019] Preferably, each constant temperature time of the gradient temperature increase is 60 to 240 minutes.

[0020] In some specific embodiments, the specific process of step (2) is: pouring the modified polyamic acid (PAA) glue obtained in step (1) onto the surface of a clean glass substrate, using a coating machine to evenly coat the glass substrate, then irradiating it with an infrared lamp for 3 to 5 seconds, and thermal imidization for 8 to 36 hours to convert the modified PAA film into a polyimide PI film;

[0021] Preferably, the coating speed of the scraping is 10 to 25 cm / min, more preferably 15 to 20 cm / min; the scraping time is 10 to 60 s, more preferably 20 to 40 s; preferably, the thickness of the modified polyimide film is 10 to 20 μm.

[0022] In another aspect, the present invention provides a modified polyimide flexible insulating medium obtained by the above preparation method.

[0023] The present invention adopts an in-situ polymerization method, introduces a sulfone group (-SO2) with strong electronegativity into the polyimide molecular chain, and then cross-links it through triaminopyrimidine to prepare a polyimide film material with high breakdown field strength. The DC breakdown field strength of the polyimide dielectric material at room temperature is 654.2MV / m, which is 119.1MV / m higher than that of the traditional cross-linked polyimide dielectric material prepared by using pyromellitic anhydride and diaminodiphenyl ether in the same proportion. The DC breakdown field strength at 150°C is also more than 400MV / m. Compared with the prior art, it also has the following beneficial effects:

[0024] (1) The present invention starts from the molecular structure design of polyimide and introduces a polar group -SO2 into the polyimide molecular chain. -SO2 has a strong electronegativity. Adding an appropriate amount of polar groups to the polyimide film can increase the electron beam density. At the same time, the -SO2 group has a large volume. Introducing it into the molecular chain of polyimide can destroy the arrangement of the chain and increase the free volume, thereby greatly reducing the breakdown voltage of the polyimide and significantly improving the insulation properties of the polyimide material.

[0025] (2) The present invention takes into account the structure of the polyimide molecular chain and cross-links the molecular chain, which can inhibit the internal relaxation loss of the polyimide dielectric material, reduce the generation of Joule heat, and thus avoid thermal breakdown, thereby improving the insulation performance under high temperature environment. In addition, the preparation process and the required equipment of the present invention are simple, safe and reliable, and low in cost, which is more conducive to its wide application in electrical insulation devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Example 1;

[0027] Figure 2 A cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Example 2;

[0028] Figure 3 This is a cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Example 3;

[0029] Figure 4 A cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Example 4;

[0030] Figure 5 This is a cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Comparative Example 1;

[0031] Figure 6 This is a cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Comparative Example 2;

[0032] Figure 7 This is a cross-sectional scanning electron microscope image of the polyimide insulating dielectric material prepared in Comparative Example 3;

[0033] Figure 8 The infrared spectrum curves of the polyimide insulating medium prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3;

[0034] Fig. 9 The DC breakdown Weibull distribution spectrum of the polyimide insulating medium prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 at room temperature;

[0035] Fig.10 The DC breakdown Weibull distribution spectrum of the polyimide insulating medium prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 at 150° C.

[0036] Fig.11 The corona resistance life time of the polyimide insulating medium prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3; DETAILED DESCRIPTION

[0037] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0038] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0039] Embodiment 1:

[0040] Step 1: In a 250 ml round-bottom flask, 1.877 g of diaminodiphenyl ether and 0.155 g of diaminodiphenyl sulfone are respectively dissolved in 25.0 ml of N, N-dimethylacetamide, 0.137 g of 3, 3'4, 4'-diphenyl sulfone tetracarboxylic dianhydride is dissolved in N, N-dimethylacetamide under water bath conditions, and then 2.097 g of pyromellitic anhydride is added to the solution in batches at a uniform interval, and the solution is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0041] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours for degassing, and then coat it on a glass substrate by a scraping process at a scraping speed of 25 cm / min for 30 seconds, and then undergo a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps: 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C, with a heating rate of 2°C / min. The insulation time of each insulation process is 60 to 120 minutes, and finally a polyimide film with a thickness of 10 μm is prepared, which is recorded as SPI.

[0042] Figure 1 is a cross-sectional SEM photograph of the polyimide insulating medium prepared in Example 1; Figure 1 It can be seen that the thickness of the modified polyimide insulating medium is 10 μm. The thickness of the insulating medium material prepared by this preparation method is relatively uniform. Figure 1 It can be seen that the prepared film has a smooth cross-section, basically free of defects such as holes, and has good density.

[0043] Embodiment 2:

[0044] Step 1: In a 250 ml round-bottom flask, 1.787 g of diaminodiphenyl ether, 0.147 g of diaminodiphenyl sulfone and 0.039 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N, N-dimethylacetamide, 0.137 g of 3, 3'4, 4'-diphenyl sulfone tetracarboxylic dianhydride is dissolved in N, N-dimethylacetamide under water bath conditions, and 2.097 g of pyromellitic anhydride is added to the solution in batches at a uniform interval, and the solution is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0045] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours for degassing, and then coat it on a glass substrate by a scraping process at a scraping speed of 25 cm / min for 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps: 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C. The heating rate is 2°C / min, and the insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 10 μm is prepared, which is recorded as 3ANSPI-30.

[0046] Figure 2 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 2; Figure 2 It can be seen that the thickness of the modified polyimide insulating medium is 10 μm. The insulating medium material prepared by the preparation method has a uniform and controllable thickness and has good compactness.

[0047] Embodiment 3:

[0048] Step 1: In a 250 ml round-bottom flask, 1.799 g of diaminodiphenyl ether, 0.17 g of diaminodiphenyl sulfone and 0.034 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N, N-dimethylacetamide, 0.137 g of 3, 3'4, 4'-diphenyl sulfone tetracarboxylic dianhydride is dissolved in N, N-dimethylacetamide under water bath conditions, and 2.097 g of pyromellitic anhydride is added to the solution in batches at a uniform interval, and the solution is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0049] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours for degassing, and then coat it on a glass substrate by a scraping process at a scraping speed of 25 cm / min for 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps: 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C. The heating rate is 2°C / min, and the insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 10 μm is prepared, which is recorded as 3ANSPI-35.

[0050] Figure 3 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 3; Figure 3 It can be seen that the thickness of the modified polyimide insulating medium is 10 μm. The thickness of the insulating medium material prepared by the preparation method is uniform and controllable. Figure 3 It can be seen that the prepared film has a smooth cross-section, basically free of defects such as holes and cracks, and has good density.

[0051] Embodiment 4:

[0052] Step 1: In a 250 ml round-bottom flask, 1.809 g of diaminodiphenyl ether, 0.148 g of diaminodiphenyl sulfone and 0.03 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N, N-dimethylacetamide, 0.137 g of 3, 3'4, 4'-diphenyl sulfone tetracarboxylic dianhydride is dissolved in N, N-dimethylacetamide under water bath conditions, and 2.097 g of pyromellitic anhydride is added to the solution in batches at a uniform interval, and the solution is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0053] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours for degassing, and then coat it on a glass substrate by a scraping process at a scraping speed of 25 cm / min for 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps: 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C. The heating rate is 2°C / min, and the insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 11 μm is prepared, which is recorded as 3ANSPI-40.

[0054] Figure 4 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 4; Figure 4 It can be seen that the thickness of the modified polyimide insulating medium is 11 μm. The insulating medium material prepared by the preparation method has a uniform and controllable thickness and has good compactness.

[0055] Comparative Example 1:

[0056] The specific process of preparing the polyimide insulating medium in this comparative example is as follows:

[0057] Step 1: In a 250 ml round-bottom flask, 1.937 g of diaminodiphenyl ether and 0.036 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N,N-dimethylacetamide, and then 2.22 g of pyromellitic anhydride is added to the solution in batches at a uniform interval under water bath conditions, and the mixture is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0058] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours, degassing it, and then coat it on a glass substrate by a scraping process. The scraping speed is 25 cm / min and the scraping time is 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps, 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C, and the heating rate is 2°C / min. The insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 10 μm is prepared, which is recorded as 3ANPI-30.

[0059] Figure 5 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 5; Figure 5 It can be seen that the thickness of the polyimide insulating medium is 10 μm. The insulating medium material prepared by the preparation method has a uniform and controllable thickness and has good compactness.

[0060] Comparative Example 2:

[0061] The specific process of preparing the polyimide insulating medium in this comparative example is as follows:

[0062] Step 1: In a 250 ml round-bottom flask, 1.946 g of diaminodiphenyl ether and 0.034 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N,N-dimethylacetamide, and then 2.22 g of pyromellitic anhydride is added to the solution in batches at a uniform interval under water bath conditions, and the mixture is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0063] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours, degassing it, and then coat it on a glass substrate by a scraping process. The scraping speed is 25 cm / min and the scraping time is 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps, 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C, and the heating rate is 2°C / min. The insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 10 μm is prepared, which is recorded as 3ANPI-35.

[0064] Figure 6 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 6; Figure 6 It can be seen that the thickness of the polyimide insulating medium is 10 μm. The insulating medium material prepared by the preparation method has a uniform and controllable thickness and has good compactness.

[0065] Comparative Example 3:

[0066] Step 1: In a 250 ml round-bottom flask, 1.953 g of diaminodiphenyl ether and 0.030 g of 2-4-6-triaminopyrimidine are dissolved in 25.0 ml of N,N-dimethylacetamide, and then 2.22 g of pyromellitic anhydride is added to the solution in batches at a uniform interval under water bath conditions, and the mixture is stirred under gradient vacuum at a vacuum rate of 160 n / min. After stirring for 12 hours, a modified polyamic acid glue solution with a solid content of about 15% is obtained;

[0067] Step 2: Place the polyamic acid glue solution in a vacuum oven for 8 hours, degassing it, and then coat it on a glass substrate by a scraping process. The scraping speed is 25 cm / min and the scraping time is 30 seconds. Then, it is subjected to a gradient heating thermal imidization treatment. The gradient heating is carried out in seven steps, 80°C → 120°C → 170°C → 210°C → 250°C → 300°C → 350°C, and the heating rate is 2°C / min. The insulation time of each insulation process is 60 to 120 minutes. Finally, a polyimide film with a thickness of 10 μm is prepared, which is recorded as 3ANPI-40.

[0068] Figure 7 is a cross-sectional SEM photograph of the modified polyimide insulating medium prepared in Example 7; Figure 7 It can be seen that the thickness of the polyimide insulating medium is 10 μm. The insulating medium material prepared by the preparation method has a uniform and controllable thickness and has good compactness.

[0069] Figure 8 The infrared spectra of the four polyimide insulating media provided in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 are compared; Figure 8 It can be seen that at 1728cm -1and 1781cm -1 The asymmetric and symmetric stretching vibration peaks of the carbonyl group (C=O) in the imide ring appear at 1374 cm -1 and 1566m -1 The stretching vibration peaks of the CN bond in the imide ring appear on the left and right sides. Both are at 1650cm -1 The asymmetric stretching vibration peaks of the carboxyl groups on the left and right disappeared. The formation of the imide structure and the disappearance of the carboxyl group indicated that the thermal imidization was successful and the copolymerized polyimide was obtained. The FTIR test results proved that a series of polyimide films with different structures were successfully prepared by the two-step method after thermal imidization treatment.

[0070] Fig. 9 and Fig.10 Weibull distribution diagram of DC breakdown field strength of polyimide insulating medium provided in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 at room temperature and 150° C.; Fig. 9 It can be seen that the breakdown field strength of 3ANSPI-35 prepared in Example 3 is significantly higher than that of other polyimide insulating media, with a maximum breakdown field strength of 654.2 kV / mm. The DC breakdown field strength of Example 3 at 150°C can also reach 463.1 kV / mm, which is better than the insulation performance of the cross-linked polyimide (3ANPI-30, 3ANPI-35, 3ANPI-40) prepared by traditional pyromellitic anhydride and diaminodiphenyl ether. This is because the -SO2 macromolecular group is introduced into the molecular chain of PI, resulting in an increase in the chain spacing and a decrease in the molecular chain packing density, which increases the free volume of the system. On the other hand, the cross-linked structure can inhibit the internal relaxation loss of the polyimide dielectric material, reduce the generation of Joule heat, and thus avoid breakdown.

[0071] Fig.11 The average aging life bar graph of the polyimide insulating medium provided for Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 shows that the life of the sample (3ANSPI-35) with the introduction of sulfone crosslinking is longer than that of the conventional PMDA-ODA crosslinking (3ANPI-35) film, indicating that the sulfone crosslinking is more conducive to improving the corona resistance. This may be partly attributed to the ether bond introduced in the diamine separating the large rigid planar conjugated structure of PMDA, thereby weakening the charge transfer along the chain under the action of the electric field, weakening the interchain CTC effect, and extending the corona resistance time.

Claims

1. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof, characterized in that The preparation method of polyamic acid glue solution is as follows: The monomers containing sulfone diamine and triamine are added into an organic solvent and stirred to completely dissolve; the monomer containing sulfone dianhydride is added and polycondensed under vacuum conditions to obtain a modified polyamic acid glue solution.

2. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof, characterized in that The polyimide film preparation method is as follows: The polyamic acid glue solution after being stirred completely is poured onto the surface of a clean glass substrate, and a coating machine is used to apply a film, and after being irradiated with an infrared lamp, thermal imidization is performed, and the modified polyimide film is obtained after the temperature is naturally lowered to room temperature.

3. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof according to claim 1, characterized in that: The diamine monomers are diaminodiphenyl ether and diaminodiphenyl sulfone, and the molar ratio thereof is 1:5 to 40, preferably 1:10 to 30; The organic solvent is selected from one of N,N-dimethylformamide and N,N-dimethylacetamide; The dianhydride monomers are pyromellitic anhydride and 3,3'4,4'-diphenylsulfone tetracarboxylic anhydride, and the molar ratio thereof is 1:5-50, preferably 1:10-30. The triamine monomer is 2-4-6 triaminopyrimidine, wherein the molar ratio of triamine to diamine is 1:20-50, preferably 1:30-40.

4. The high temperature corona resistant polyimide based composite dielectric and the preparation method thereof according to claim 1, characterized in that: The molar ratio of the diamine monomer to the dianhydride monomer is 1:1.02 to 1.08, preferably 1:1.02 to 1.

04.

5. The high temperature corona resistant polyimide based composite dielectric and the preparation method thereof according to claim 1, characterized in that: The polycondensation reaction temperature is -10 to 30°C, preferably -5 to 5°C; Preferably, the polycondensation reaction time is 2 to 36 hours. Preferably, the polycondensation reaction time is 8 to 24 hours.

6. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof according to claim 2, characterized in that: The infrared lamp is selected to be 2000W and the irradiation time is 3 to 5s.

7. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof according to claim 2, characterized in that: The thickness of the polyimide flexible insulating medium is 5 to 50 μm, preferably 10 to 20 μm.

8. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof according to claim 2, characterized in that: The thermal imidization in claim 2 adopts a gradient heating method; The heating rate of the gradient heating is 1 to 10°C / min, preferably 2 to 4°C / min; The temperature gradient of each section of the gradient heating is 20 to 80°C, preferably 40 to 60°C; The constant temperature time of each stage of the gradient heating is 30 to 360 minutes, and more preferably 60 to 240 minutes.

9. A high temperature corona resistant polyimide based composite dielectric and a preparation method thereof according to claim 2, characterized in that: The film after thermal imidization in claim 2 is kept cool and then soaked in 10-70°C for 5-20 minutes, preferably in 20-50°C for 10-15 minutes.

10. A high temperature corona resistant polyimide based composite dielectric prepared by the method according to any one of claims 1 to 9 and a preparation method thereof, characterized in that: The modified polyimide flexible insulating dielectric film is used in the fields of smart grid, aerospace, new energy vehicles, etc.

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