Preparation method of glass-like polyimide insulating dielectric film for winding insulation and application of glass-like polyimide insulating dielectric film in preparation of electrical insulating device

Abstract

The invention discloses a preparation method of a glass-like polyimide insulating medium film for winding insulation and application of the glass-like polyimide insulating medium film in preparation of an electrical insulating device, and belongs to the technical field of preparation of electrical insulating materials. The invention aims to solve the problem that the existing polyimide dielectric medium is poor in high-temperature insulation characteristic and electrical insulation stability. The preparation method comprises the following steps: reacting dianhydride with diamine to generate polyamic acid, prepolymerizing the polyamic acid by using a cyclizing agent and a catalyst, adding a cross-linking agent containing reversible dynamic bonds, and reacting amide groups in polyimide with amino groups in the cross-linking agent to realize mutual cross-linking. And then forming the glass-like polyimide dielectric film through a thermal imidization process. The glass-like polyimide insulating medium film for winding insulation is applied to preparation of an electrical insulating device. Electrical insulation devices include but are not limited to the fields of smart power grids, new energy automobiles, AC / DC power transmission networks and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of electrical insulating materials, and in particular relates to a method for preparing a glass-like polyimide insulating dielectric film for winding insulation and an application of the film in preparing electrical insulating devices. Background Art

[0002] Polyimide has excellent electrical strength (300kV / mm), temperature resistance (T g ≥350℃) and dimensional stability, and is widely used in wind turbine winding insulation, DC motor interturn insulation, and traction motor winding insulation. However, during the continuous operation of the motor, the current in the winding continues to flow and rotate, and long-term power-on and friction will cause a large amount of heat accumulation. Under high temperature conditions, the insulation performance of polyimide deteriorates significantly, and the overall electrical insulation reliability is poor, resulting in premature breakdown, which seriously shortens the service life of the motor. Therefore, the development of a polyimide dielectric that inherently possesses excellent high-temperature insulation properties and electrical insulation stability has become an important challenge facing current technology. Summary of the invention

[0003] The purpose of the present invention is to solve the problem of poor high temperature insulation properties and electrical insulation stability of existing polyimide dielectrics, and to provide a method for preparing a glass-like polyimide insulating dielectric film for winding insulation and its application in the preparation of electrical insulation devices.

[0004] The present invention firstly uses dianhydride and diamine to react to generate polyamic acid, uses a cyclizing agent and a catalyst to prepolymerize the polyamic acid, then adds a cross-linking agent containing a reversible dynamic bond, uses the amide group in the polyimide and the amino group in the cross-linking agent to react to achieve mutual cross-linking, and then forms a glass-like polyimide dielectric film through a thermal imidization process.

[0005] A method for preparing a glass-like polyimide insulating dielectric film for winding insulation is specifically completed by the following steps:

[0006] 1. Under vacuum conditions, a diamine monomer and a dianhydride monomer are used to carry out a polymerization reaction in an organic solvent to obtain a polyamic acid glue solution;

[0007] 2. Under vacuum conditions, a cyclizing agent and a catalyst are added to the polyamic acid glue solution for prepolymerization to obtain a mixed solution of polyimide and polyamic acid;

[0008] 3. adding a cross-linking agent containing a reversible dynamic bond to the mixed solution of polyimide and polyamic acid, and stirring under vacuum conditions to obtain a mixed solution of modified polyimide and polyamic acid;

[0009] The cross-linking agent containing a reversible dynamic bond in step 3 is one or a mixture of 4,4'-dithiodiphenylamine, carbohydrazide, 1,3-bis(3-aminopropyl)tetramethyldisiloxane;

[0010] Fourth, the mixed solution of modified polyimide and polyamic acid is degassed and then coated to form a wet film, which is then assisted by thermal imidization to obtain a glass-like polyimide insulating dielectric film for winding insulation.

[0011] Glass-like polyimide insulating dielectric films used for winding insulation are used in the preparation of electrical insulating devices.

[0012] Principles and beneficial effects of the present invention:

[0013] The invention firstly uses dianhydride monomer and diamine monomer to react to generate polyamic acid, adds a cyclizing agent and a catalyst to perform a prepolymerization reaction to generate a mixed solution of polyimide and polyamic acid, then adds a cross-linking agent containing a reversible dynamic bond, utilizes the amino group in the cross-linking agent to react with the amide group in the polyimide to achieve mutual cross-linking, and then obtains a glass-like polyimide dielectric film after thermal imidization; compared with the prior art,

[0014] The glass-like polyimide insulating dielectric film prepared by the present invention has the following advantages:

[0015] First, the breakdown field strength of polyimide under high temperature and high field is usually low, and its electrical insulation stability is poor; however, the glass-like polyimide dielectric prepared by the present invention has a cross-linked network structure constructed by reversible dynamic bonds, which makes the polyimide molecular chains more compact and reduces the free volume between the polyimide chains, shortens the mean free path of electron transmission, and inhibits electron transition under high temperature and high field, so that the high-temperature breakdown performance is greatly improved, solving the problem that the insulation performance of traditional polyimide dielectrics decreases sharply due to high-temperature intrinsic electron excitation; and the reversible dynamic bonds can rearrange the cross-linked network of polyimide under high temperature and high field, thereby improving the high-temperature electrical insulation stability of polyimide;

[0016] 2. The process of the present invention is simple and has mature large-scale preparation technology. Existing industrial equipment can meet production needs. It can also maintain the flexibility and uniformity of polymer materials, effectively solving the problems of agglomeration and degradation of mechanical properties caused by doping modification, and various challenges faced by industrialization such as mismatch of polymer matrix molding technology. It will provide guidance for the large-scale preparation of all-organic dielectric films for high-temperature and high-field applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the chemical structural formula of the cross-linking agent 4,4'-dithiodiphenylamine;

[0018] Figure 2 is the chemical structural formula of the cross-linking agent hydrazine carbonate;

[0019] Figure 3 The chemical structural formula of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 1, 2 and 3;

[0020] Figure 4 The chemical structural formula of the glass-like polyimide insulating dielectric film for winding insulation prepared in Example 4;

[0021] Figure 5 is the chemical structural formula of the copolymerized polyimide insulating dielectric film prepared in Comparative Example 2;

[0022] Figure 6 A free volume comparison diagram of the glass-like polyimide insulating dielectric film for winding insulation prepared in Example 2 and the polyimide insulating dielectric film prepared in Comparative Example 1 obtained through DFT simulation analysis;

[0023] Figure 7 This is a comparison diagram of infrared spectra of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1;

[0024] Figure 8 A comparison chart showing the changing trends of dielectric constant and dielectric loss with frequency of the glass-like polyimide insulating dielectric films for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1;

[0025] Fig. 9 A comparison diagram of the breakdown field strength of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1 at 150° C.;

[0026] Fig.10 A comparison diagram of the breakdown field strengths of the glassy polyimide insulating dielectric film for winding insulation prepared in Example 2, the polyimide insulating dielectric film prepared in Comparative Example 1, and the copolymeric glassy polyimide film prepared in Comparative Example 2 at 150° C.;

[0027] Fig.11 This is a test chart of the high temperature insulation stability of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 at 150°C. DETAILED DESCRIPTION

[0028] Specific implementation method 1: This implementation method is a method for preparing a glass-like polyimide insulating dielectric film for winding insulation, which is specifically completed in the following steps:

[0029] 1. Under vacuum conditions, a diamine monomer and a dianhydride monomer are used to carry out a polymerization reaction in an organic solvent to obtain a polyamic acid glue solution;

[0030] 2. Under vacuum conditions, a cyclizing agent and a catalyst are added to the polyamic acid glue solution for prepolymerization for a period of time to obtain a mixed solution of polyimide and polyamic acid;

[0031] 3. Adding a cross-linking agent containing a reversible dynamic bond to the mixed solution of polyimide and polyamic acid, stirring and reacting for a period of time under vacuum conditions to obtain a mixed solution of modified polyimide and polyamic acid;

[0032] The cross-linking agent containing a reversible dynamic bond in step 3 is one or a mixture of 4,4'-dithiodiphenylamine, carbohydrazide, 1,3-bis(3-aminopropyl)tetramethyldisiloxane;

[0033] Fourth, the mixed solution of modified polyimide and polyamic acid is degassed and then coated to form a wet film, which is then assisted by thermal imidization to obtain a glass-like polyimide insulating dielectric film for winding insulation.

[0034] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the diamine monomer described in step 1 is one or a mixture of 2,2'-bis(trifluoromethyl)diaminobiphenyl, diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene and 4,4'-diaminodicyclohexylmethane. The other steps are the same as those in specific embodiment 1.

[0035] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the dianhydride monomer described in step 1 is a mixture of one or more of 4,4'-(hexafluoroisopropyl) diphthalic anhydride, pyromellitic anhydride, 3,3',4,4'-benzophenonetetracarboxylic anhydride and 1,2,3,4-cyclobutanetetracarboxylic anhydride. The other steps are the same as those of specific embodiment 1 or 2.

[0036] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: the organic solvent described in step 1 is one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; the polymerization reaction temperature described in step 1 is 0°C to 25°C, and the polymerization reaction time is 6h to 24h;

[0037] Furthermore, the temperature of the polymerization reaction in step 1 is 0° C. to 10° C. The other steps are the same as those in specific embodiments 1 to 3.

[0038] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the molar ratio of the diamine monomer and the dianhydride monomer described in step 1 is (1 to 1.08): (1.02 to 1.2); the mass of the diamine monomer described in step 1 accounts for 12% to 35% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent; the mass of the dianhydride monomer described in step 1 accounts for 12% to 35% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent;

[0039] Furthermore, the mass of the diamine monomer described in step 1 accounts for 15% to 20% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent; the mass of the dianhydride monomer described in step 1 accounts for 15% to 20% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent;

[0040] Furthermore, the molar ratio of the diamine monomer to the dianhydride monomer in step 1 is (1-1.02):(1-1.02). The other steps are the same as those in specific embodiments 1 to 4.

[0041] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: the cyclizing agent in step 2 is a mixture of one or two of acetic anhydride and propionic anhydride; the catalyst in step 2 is a mixture of one or more of pyridine, isoquinoline and triethylamine; the molar ratio of the cyclizing agent in step 2 to the diamine monomer in step 1 is (0.6-1):1; the molar ratio of the catalyst in step 2 to the diamine monomer in step 1 is (0.6-1):1; the prepolymerization temperature in step 2 is 0°C to 30°C, and the prepolymerization time is 6h to 24h. The other steps are the same as those in specific embodiments 1 to 5.

[0042] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: the mass of the cross-linking agent containing reversible dynamic bonds described in step 3 accounts for 0.1% to 10% of the total mass of the mixed solution of polyimide and polyamic acid and the cross-linking agent containing reversible dynamic bonds; the stirring reaction time under vacuum conditions in step 3 is 12h to 24h, the stirring reaction temperature is 0℃ to 30℃, and the stirring reaction rate is 100r / min to 240r / min. The other steps are the same as specific embodiments 1 to 6.

[0043] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the thermal imidization process described in step 4 is to use a gradient temperature increase and be carried out in six steps:

[0044] Step 1: Raise the temperature from room temperature to 60°C and keep at 60°C for 10 to 720 minutes;

[0045] Step 2: Raise the temperature from 60°C to 80°C~100°C, and keep it at 80°C~100°C for 10min~720min;

[0046] Step 3: Raise the temperature from 80℃~100℃ to 100℃~150℃, and keep it at 100℃~150℃ for 10min~720min;

[0047] Step 4: Raise the temperature from 100°C to 150°C to 150°C to 200°C, and keep the temperature at 150°C to 200°C for 10min to 720min;

[0048] Step 5: Raise the temperature from 150°C to 200°C to 250°C, and keep at 200°C to 250°C for 10min to 720min;

[0049] Step 6: Raise the temperature from 200℃~250℃ to 250℃~300℃, and keep at 250℃~300℃ for 10min~720min;

[0050] The heating rate is 1°C / min to 15°C / min.

[0051] Furthermore, the heating rate is 3°C / min to 15°C / min. The other steps are the same as those in the first to seventh embodiments.

[0052] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: the degassing treatment described in step 4 is: placing the mixed solution of modified polyimide and polyamic acid in a vacuum oven and letting it stand for 12h to 24h; the coating method described in step 4 is to prepare the mixed solution of modified polyimide and polyamic acid into a wet film by scraping, spin coating or drip coating; the thickness of the glass-like polyimide insulating dielectric film for winding insulation described in step 4 is 3μm to 20μm;

[0053] Furthermore, the coating speed of the scraping is 10 cm / min to 25 cm / min, and the time is 10 s to 60 s. The other steps are the same as those of the first to eighth embodiments.

[0054] Specific implementation method ten: This implementation method is to use a glass-like polyimide insulating dielectric film for winding insulation in the preparation of an electrical insulating device.

[0055] Furthermore, electrical insulation devices include but are not limited to smart grids, new energy vehicles, AC and DC power transmission networks and other fields.

[0056] The invention can obtain a glass-like polyimide insulating dielectric film used for winding insulation.

[0057] The following examples are used to verify the beneficial effects of the present invention:

[0058] Embodiment 1: A method for preparing a glass-like polyimide insulating dielectric film for winding insulation is specifically completed by the following steps:

[0059] 1. In a 150 mL conical flask, 2.1135 g of diamine monomer was dissolved in 25.0 mL of organic solvent. Under vacuum conditions, 2.9926 g of dianhydride monomer was added to the solution in batches at a uniform interval. The mixture was stirred and reacted for 12 h at a temperature of 0 ° C and under vacuum conditions to obtain a polyamic acid glue solution with a solid content of about 15%;

[0060] The diamine monomer described in step 1 is 2,2'-bis(trifluoromethyl)diaminobiphenyl;

[0061] The dianhydride monomer described in step 1 is 4,4'-(hexafluoroisopropyl) diphthalic anhydride;

[0062] The organic solvent described in step 1 is N,N-dimethylacetamide;

[0063] 2. Under vacuum conditions, 0.6738 g of a cyclizing agent and 0.522 g of a catalyst were uniformly added dropwise to the polyamic acid glue solution, and the mixture was stirred at a temperature of 30° C. and a vacuum condition for 12 h at a stirring rate of 200 r / min to obtain a mixed solution of polyimide and polyamic acid;

[0064] The cyclizing agent described in step 2 is acetic anhydride;

[0065] The catalyst described in step 2 is pyridine;

[0066] 3. Add 0.0051 g of a cross-linking agent containing a reversible dynamic bond to the mixed solution of polyimide and polyamic acid, and stir for 12 h at a temperature of 30° C. and a vacuum condition at a rate of 200 r / min to obtain a mixed solution of modified polyimide and polyamic acid having a solid content of about 15%;

[0067] The cross-linking agent containing a reversible dynamic bond described in step 3 is 4,4'-dithiodiphenylamine;

[0068] Fourth, the mixed solution of modified polyimide and polyamic acid is subjected to degassing treatment and then prepared into a wet film by a coating method, and then assisted by thermal imidization treatment to obtain a glass-like polyimide insulating dielectric film for winding insulation with a thickness of 12 μm (denoted as F-PI / 0.1 (SS));

[0069] The degassing treatment described in step 4 is as follows: placing the mixed solution of the modified polyimide and the polyamic acid in a vacuum oven and leaving it to stand for 12 hours;

[0070] The coating method described in step 4 is to prepare a wet film from the mixed solution of modified polyimide and polyamic acid by scraping, the scraping speed is 25 cm / min, and the scraping time is 30 s;

[0071] The thermal imidization process described in step 4 is: using a gradient temperature increase, divided into six steps:

[0072] Step 1: Raise the temperature from room temperature to 60°C and keep at 60°C for 30 minutes;

[0073] Step 2: Raise the temperature from 60°C to 80°C and keep at 80°C for 30 minutes;

[0074] Step 3: Raise the temperature from 80°C to 150°C and keep at 150°C for 30 minutes;

[0075] Step 4: Raise the temperature from 150°C to 200°C, and keep at 200°C for 30 minutes;

[0076] Step 5: Raise the temperature from 200°C to 250°C, and keep at 250°C for 30 minutes;

[0077] Step 6: Raise the temperature from 250°C to 300°C, and keep at 300°C for 30 minutes;

[0078] The heating rate is 1°C / min.

[0079] Example 2: The difference between this example and Example 1 is that in step 3, 0.0153 g of a cross-linking agent containing a reversible dynamic bond is added to the mixed solution of polyimide and polyamic acid. In step 4, a glass-like polyimide insulating dielectric film (denoted as F-PI / 0.3 (SS)) with a thickness of 12 μm for winding insulation is obtained. The other steps and parameters are the same as those in Example 1.

[0080] Example 3: The difference between this example and Example 1 is that in step 3, 0.0255 g of a cross-linking agent containing a reversible dynamic bond is added to the mixed solution of polyimide and polyamic acid; in step 4, a glass-like polyimide insulating dielectric film (denoted as F-PI / 0.5 (SS)) with a thickness of 12 μm for winding insulation is obtained. The other steps and parameters are the same as those in Example 1.

[0081] Example 4: The difference between this example and Example 1 is that: in step 3, 0.0153 g of a cross-linking agent containing a reversible dynamic bond is added to the mixed solution of polyimide and polyamic acid; the cross-linking agent containing a reversible dynamic bond described in step 3 is carbohydrazide; in step 4, a glass-like polyimide insulating dielectric film (denoted as F-PI / 0.3 (NN)) with a thickness of 12 μm for winding insulation is obtained. The other steps and parameters are the same as those in Example 1.

[0082] Comparative Example 1: A method for preparing a polyimide insulating dielectric film is specifically completed by the following steps:

[0083] 1. In a 150 mL conical flask, 2.1135 g of diamine monomer was dissolved in 25.0 mL of organic solvent. Under vacuum conditions, 2.9926 g of dianhydride monomer was added to the solution in batches at a uniform interval. The mixture was stirred and reacted for 12 h at a temperature of 0 ° C and under vacuum conditions to obtain a polyamic acid glue solution with a solid content of about 15%;

[0084] The diamine monomer described in step 1 is 2,2'-bis(trifluoromethyl)diaminobiphenyl;

[0085] The dianhydride monomer described in step 1 is 4,4'-(hexafluoroisopropyl) diphthalic anhydride;

[0086] The organic solvent described in step 1 is N,N-dimethylacetamide;

[0087] 2. Degassing the polyamic acid glue solution and then preparing it into a wet film by a coating method, and then assisting with thermal imidization treatment to obtain a polyimide insulating dielectric film (denoted as F-PI) with a thickness of 12 μm;

[0088] The degassing treatment described in step 2 is as follows: placing the mixed solution of the modified polyimide and the polyamic acid in a vacuum oven and leaving it to stand for 12 hours;

[0089] The coating method described in step 2 is to prepare the polyamic acid glue solution into a wet film by scraping, the scraping speed is 25 cm / min, and the scraping time is 30 s;

[0090] The thermal imidization process described in step 2 is: using a gradient temperature increase, divided into six steps:

[0091] Step 1: Raise the temperature from room temperature to 60°C and keep at 60°C for 30 minutes;

[0092] Step 2: Raise the temperature from 60°C to 80°C and keep at 80°C for 30 minutes;

[0093] Step 3: Raise the temperature from 80°C to 150°C and keep at 150°C for 30 minutes;

[0094] Step 4: Raise the temperature from 150°C to 200°C, and keep at 200°C for 30 minutes;

[0095] Step 5: Raise the temperature from 200°C to 250°C, and keep at 250°C for 30 minutes;

[0096] Step 6: Raise the temperature from 250°C to 300°C, and keep at 300°C for 30 minutes;

[0097] The heating rate is 1°C / min.

[0098] Comparative Example 2: A method for preparing a copolymerized glassy polyimide film is specifically completed by the following steps:

[0099] 1. In a 150 mL conical flask, 2.1135 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl and 0.0153 g of 4,4'-dithiodiphenylamine were dissolved in 25.0 mL of N,N-dimethylacetamide. Under vacuum, 2.9926 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl was added to the solution in batches at a uniform speed. The mixture was stirred at 0°C and vacuum for 12 h to obtain a modified polyamic acid glue solution with a solid content of about 15%.

[0100] 2. Under vacuum, 0.6738 g of acetic anhydride and 0.522 g of pyridine were added to the modified polyamic acid glue solution by uniform titration, and stirred for 12 h at a temperature of 30° C. under vacuum conditions to perform a prepolymerization reaction to obtain a modified polyamic acid and polyimide mixed solution;

[0101] 3. Degassing the modified polyamic acid and polyimide mixture and then preparing it into a wet film by a coating method, and then assisting with thermal imidization treatment to obtain a copolymer glassy polyimide film with a thickness of 12 μm (denoted as F-PI-0.3SS);

[0102] The degassing treatment described in step 3 is as follows: placing the mixed solution of the modified polyimide and the polyamic acid in a vacuum oven and letting it stand for 12 hours;

[0103] The coating method described in step 2 is to prepare a wet film from the mixed solution of modified polyimide and polyamic acid by scraping, the scraping speed is 25 cm / min, and the scraping time is 30 s;

[0104] The thermal imidization process described in step 2 is: using a gradient temperature increase, divided into six steps:

[0105] Step 1: Raise the temperature from room temperature to 60°C and keep at 60°C for 30 minutes;

[0106] Step 2: Raise the temperature from 60°C to 80°C and keep at 80°C for 30 minutes;

[0107] Step 3: Raise the temperature from 80°C to 150°C and keep at 150°C for 30 minutes;

[0108] Step 4: Raise the temperature from 150°C to 200°C, and keep at 200°C for 30 minutes;

[0109] Step 5: Raise the temperature from 200°C to 250°C, and keep at 250°C for 30 minutes;

[0110] Step 6: Raise the temperature from 250°C to 300°C, and keep at 300°C for 30 minutes;

[0111] The heating rate is 1°C / min.

[0112] The dielectric films obtained in Examples 1-4 and Comparative Examples 1-2 were characterized in terms of structure and performance, and the results are as follows:

[0113] Figure 6 A free volume comparison diagram of the glass-like polyimide insulating dielectric film for winding insulation prepared in Example 2 and the polyimide insulating dielectric film prepared in Comparative Example 1 obtained through DFT simulation analysis;

[0114] Depend on Figure 6 It can be seen that the free volume of the glass-like polyimide dielectric obtained by introducing dynamic reversible bonds is significantly reduced, which shows that the introduction of dynamic bonds can enhance the molecular forces between polyimide chains, promote the close stacking of polyimide molecular chains, reduce the free volume between molecular chains, thereby shortening the free path of electron migration and inhibiting electron transition.

[0115] Figure 7 This is a comparison diagram of infrared spectra of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1;

[0116] Depend on Figure 7 It can be seen that the glassy polyimide insulating medium used for winding insulation has a -1 The characteristic peak near 1726 cm -1 Symmetrical stretching vibrations of the two carbonyl groups on the imide ring occur at 1377 cm -1 The characteristic peaks at correspond to the stretching vibration of CN of the imine ring of fluorinated polyimide. These three characteristic peaks correspond to the characteristic peaks of polyimide, proving that in the process of preparing glassy polyimide, the N atom of the amino group in 2,2'-bis(trifluoromethyl)diaminobiphenyl replaces the position of the O atom in -COC- in 4,4'-(hexafluoroisopropyl)diphthalic anhydride, indicating that 4,4'-(hexafluoroisopropyl)diphthalic anhydride successfully reacts with 2,2'-bis(trifluoromethyl)diaminobiphenyl. At the same time, the F-PI / 0.3(SS) glassy polyimide insulating medium prepared in Example 2 has a wavelength of 500-600cm -1 The absorption peak of SS bond appears, which indicates that the dynamic disulfide bond is successfully introduced into the polyimide. The F-PI / 0.3 (NN) type glassy polyimide dielectric prepared in Example 4 has an absorption peak of 1660-1680 cm -1The absorption peak of -C=O bond appeared, which indicated that the reversible urea bond was successfully introduced into the polyimide.

[0117] Figure 8 A comparison chart showing the changing trends of dielectric constant and dielectric loss with frequency of the glass-like polyimide insulating dielectric films for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1;

[0118] Depend on Figure 8 It can be seen that at room temperature, the dielectric constant of the glassy polyimide insulating medium is significantly reduced compared to the polyimide prepared in Comparative Example 1. This is because the introduction of reversible dynamic bonds makes the polarization reaction of polyimide at high frequencies more rapid, thereby improving the dielectric constant of polyimide. In addition, the dielectric constant and dielectric loss of the glassy polyimide insulating medium have high frequency stability and basically do not change with changes in frequency.

[0119] Fig. 9 A comparison diagram of the breakdown field strength of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 and the polyimide insulating dielectric film prepared in Comparative Example 1 at 150° C.;

[0120] Depend on Fig. 9 It can be seen that compared with polyimide, the glass-like polyimide dielectric containing a reversible dynamic bond crosslinker exhibits a higher breakdown field strength at high temperature, and the breakdown field strengths of the glass-like polyimide insulating dielectrics prepared in Examples 2 and 4 at 150°C are 822MV / m and 803MV / m, respectively. This shows that the glass-like polyimide insulating dielectric obtained by introducing a reversible dynamic bond can withstand a higher electric field at high temperature without breakdown failure, and has excellent high-temperature insulation properties.

[0121] Fig.10 A comparison diagram of the breakdown field strengths of the glassy polyimide insulating dielectric film for winding insulation prepared in Example 2, the polyimide insulating dielectric film prepared in Comparative Example 1, and the copolymeric glassy polyimide film prepared in Comparative Example 2 at 150° C.;

[0122] Depend on Fig.10It can be seen that compared with polyimide, the insulation performance of the F-PI-0.3SS copolymer glassy polyimide film obtained by introducing amine monomers containing dynamic reversible bonds into polyimide by copolymerization is significantly reduced at high temperatures. However, by introducing amine monomers containing dynamic reversible bonds into polyimide as cross-linking agents, the high-temperature insulation performance of the F-PI / 0.3 (SS) glassy polyimide insulating dielectric film used for winding insulation is significantly improved. This shows that by controlling the addition order, the glassy polyimide dielectric obtained by using amine monomers containing reversible dynamic bonds as cross-linking agents can withstand higher electric fields at high temperatures without breakdown failure, and has excellent high-temperature insulation properties.

[0123] Fig.11 This is a test diagram of high temperature insulation stability of the glass-like polyimide insulating dielectric film for winding insulation prepared in Examples 2 and 4 at 150°C;

[0124] It can be seen from Figure 11 that the glass-like polyimide insulating dielectric film for winding insulation obtained by introducing a reversible dynamic bond cross-linking agent can withstand 50,000 cycles of high electric field impact at 150°C and 500MV / m without insulation breakdown. This shows that the introduction of reversible dynamic bonds enhances the structural stability of polyimide and has good high-temperature insulation stability.

Claims

1. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation, characterized in that The preparation method is specifically completed according to the following steps:

1. Under vacuum conditions, a diamine monomer and a dianhydride monomer are used to carry out a polymerization reaction in an organic solvent to obtain a polyamic acid glue solution; 2. Under vacuum conditions, a cyclizing agent and a catalyst are added to the polyamic acid glue solution for prepolymerization for a period of time to obtain a mixed solution of polyimide and polyamic acid; 3. Adding a cross-linking agent containing a reversible dynamic bond to the mixed solution of polyimide and polyamic acid, stirring and reacting for a period of time under vacuum conditions to obtain a mixed solution of modified polyimide and polyamic acid; The cross-linking agent containing a reversible dynamic bond in step 3 is one or a mixture of 4,4'-dithiodiphenylamine, carbohydrazide, 1,3-bis(3-aminopropyl)tetramethyldisiloxane; Fourth, the mixed solution of modified polyimide and polyamic acid is degassed and then coated to form a wet film, which is then assisted by thermal imidization to obtain a glass-like polyimide insulating dielectric film for winding insulation.

2. The method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, characterized in that The diamine monomer described in step 1 is one or a mixture of 2,2'-bis(trifluoromethyl)diaminobiphenyl, diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene and 4,4'-diaminodicyclohexylmethane.

3. The method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, characterized in that The dianhydride monomer described in step 1 is one or a mixture of 4,4'-(hexafluoroisopropyl) diphthalic anhydride, pyromellitic anhydride, 3,3',4,4'-benzophenonetetracarboxylic anhydride and 1,2,3,4-cyclobutanetetracarboxylic anhydride.

4. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The organic solvent described in step 1 is one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; the polymerization reaction temperature described in step 1 is 0°C to 25°C, and the polymerization reaction time is 6h to 24h.

5. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The molar ratio of the diamine monomer and the dianhydride monomer described in step one is (1-1.08):(1.02-1.2); the mass of the diamine monomer described in step one accounts for 12%-35% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent; the mass of the dianhydride monomer described in step one accounts for 12%-35% of the total mass of the diamine monomer, the dianhydride monomer and the organic solvent.

6. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The cyclizing agent described in step 2 is a mixture of one or two of acetic anhydride and propionic anhydride; the catalyst described in step 2 is a mixture of one or more of pyridine, isoquinoline and triethylamine; the molar ratio of the cyclizing agent described in step 2 to the diamine monomer described in step 1 is (0.6-1):1; the molar ratio of the catalyst described in step 2 to the diamine monomer described in step 1 is (0.6-1):1; the prepolymerization temperature described in step 2 is 0°C-30°C, and the prepolymerization time is 6h-24h.

7. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The mass of the cross-linking agent containing reversible dynamic bonds described in step three accounts for 0.1% to 10% of the total mass of the mixed solution of polyimide and polyamic acid and the cross-linking agent containing reversible dynamic bonds; the stirring reaction time under vacuum conditions in step three is 12h to 24h, the stirring reaction temperature is 0℃ to 30℃, and the stirring reaction rate is 100r / min to 240r / min.

8. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The thermal imidization process described in step 4 is: using a gradient temperature increase, divided into six steps: Step 1: Raise the temperature from room temperature to 60°C and keep at 60°C for 10 to 720 minutes; Step 2: Raise the temperature from 60°C to 80°C~100°C, and keep it at 80°C~100°C for 10min~720min; Step 3: Raise the temperature from 80℃~100℃ to 100℃~150℃, and keep it at 100℃~150℃ for 10min~720min; Step 4: Raise the temperature from 100°C to 150°C to 150°C to 200°C, and keep the temperature at 150°C to 200°C for 10min to 720min; Step 5: Raise the temperature from 150°C to 200°C to 250°C, and keep at 200°C to 250°C for 10min to 720min; Step 6: Raise the temperature from 200℃~250℃ to 250℃~300℃, and keep at 250℃~300℃ for 10min~720min; The heating rate is 1°C / min to 15°C / min.

9. A method for preparing a glass-like polyimide insulating dielectric film for winding insulation according to claim 1, 2 or 3, characterized in that The degassing treatment described in step 4 is: placing the mixed solution of modified polyimide and polyamic acid in a vacuum oven and letting it stand for 12 hours to 24 hours; the coating method described in step 4 is to prepare the mixed solution of modified polyimide and polyamic acid into a wet film by scraping, spin coating or drip coating; the thickness of the glass-like polyimide insulating dielectric film for winding insulation described in step 4 is 3μm to 20μm.

10. Application of the glass-like polyimide insulating dielectric film for winding insulation prepared by the preparation method according to claim 1, characterized in that Glass-like polyimide insulating dielectric films used for winding insulation are used in the preparation of electrical insulating devices.

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