Preparation method and application of tensile mica tape based on dielectric reinforcement of polyimide film

Abstract

The invention discloses a preparation method and application of a tensile mica tape based on polyimide film dielectric reinforcement, and relates to the technical field of mica tape preparation. The invention aims to solve the problem of low dielectric strength of the traditional main insulation mica tape of the offshore high-voltage wind driven generator. The method comprises the following steps: bonding the mica paper and the polyimide film, or bonding the mica paper, the polyimide film and the glass wool cloth, and then carrying out hot pressing and curing to obtain the polyimide film dielectric reinforcement-based tensile mica tape. The tensile mica tape based on polyimide film dielectric reinforcement is applied to a main insulating material of a stator bar of an offshore high-voltage wind driven generator. The invention can obtain the preparation method and application of the tensile mica tape based on dielectric reinforcement of the polyimide film.

Description

Technical Field

[0001] This invention relates to the field of mica tape preparation technology, specifically to a method for preparing tensile-resistant mica tape based on dielectric reinforcement of polyimide film and its application. Background Technology

[0002] With the deepening development and utilization of renewable energy sources such as wind power, offshore wind turbines are gradually developing towards higher voltage levels, larger capacities, and higher power densities. The main insulation of the generator stator bars is generally composed of mica tape wrapped in multiple layers and then impregnated with epoxy resin. The overall performance of the mica tape has a significant impact on the overall performance and operational stability of the generator. Due to the low dielectric strength of mica tape, higher voltage levels require sufficient insulation thickness to ensure electrical safety, significantly increasing the number of mica tape wrapping layers. This increased insulation thickness severely affects heat dissipation within the stator bars, and heat accumulation can easily lead to aging of the internal insulation, seriously affecting the safe operation of the generator.

[0003] In addition, the wrapping process of mica tape requires it to have sufficient tensile strength. Therefore, designing a high dielectric strength tensile mica tape is of great practical significance for achieving stable operation of offshore high-voltage wind turbines and adapting to their development trend of high voltage, large capacity and high power. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of low dielectric strength of traditional offshore high-voltage wind turbine main insulation mica tape, and to provide a method for preparing tensile-resistant mica tape based on dielectric reinforcement of polyimide film and its application.

[0005] A method for preparing a tensile-resistant mica tape based on dielectric reinforcement of polyimide film, comprising the following steps:

[0006] Mica paper is bonded to a polyimide film, or mica paper is bonded to a polyimide film and a glass fiber cloth, and then hot-pressed and cured to obtain a tensile-resistant mica tape based on the dielectric reinforcement of the polyimide film; the tensile-resistant mica tape based on the dielectric reinforcement of the polyimide film is a polyimide-mica paper-glass fiber cloth mica tape, a polyimide-mica paper-polyimide mica tape, a polyimide-glass fiber cloth-mica paper-glass fiber cloth mica tape, or a polyimide-glass fiber cloth-mica paper-glass fiber cloth-polyimide mica tape.

[0007] An application of a tensile-resistant mica tape based on polyimide film dielectric reinforcement, wherein the tensile-resistant mica tape based on polyimide film dielectric reinforcement is used in the main insulation material of the stator bar of an offshore high-voltage wind turbine.

[0008] The beneficial effects of this invention are:

[0009] (1) This invention discloses a method for preparing a tensile-resistant mica tape based on dielectric reinforcement of a polyimide film. A high-dielectric-strength polyimide film is used as the dielectric reinforcement layer to dielectrically reinforce a conventional mica paper-epoxy resin-glass cloth mica tape system. Compared to conventional mica tape, this mica tape utilizes a high-dielectric-strength polyimide film to regulate the electric field distribution within the mica tape, concentrating the electric field more in the high-dielectric-strength polyimide film layer and reducing the electric field strength in the low-dielectric-strength mica paper-epoxy resin layer and glass cloth-epoxy resin layer. Under the reinforcement of the polyimide film, the electrons in the low-dielectric-strength mica paper-epoxy resin layer and glass cloth-epoxy resin layer experience less electric field force and are less likely to be accelerated and ionized by collisions, thus improving the dielectric strength of the mica tape. In addition, the polyimide film also plays a role in suppressing the development of breakdown paths. Electrons within the polyimide film layer, mica paper-epoxy resin layer, and glass fiber cloth-epoxy resin layer undergo collisional ionization under the influence of an electric field, forming electron avalanches. When these avalanches reach the interface between the polyimide film layer and the glass fiber cloth-epoxy resin layer, the moving electrons are braked, and the breakdown stops. The dual effect of the polyimide film in modulating the electric field strength and suppressing the breakdown path significantly improves the dielectric strength of the polyimide-reinforced mica tape.

[0010] (2) The tensile-resistant mica tape based on polyimide film dielectric reinforcement prepared by the present invention, compared with ordinary mica tape, not only has a significantly improved dielectric strength, but also maintains its tensile strength well, ensuring the necessary tensile performance when wrapping the mica tape. The present invention is expected to be applied to the main insulation of the stator bars of high-voltage offshore wind turbines, which is of great significance for realizing the development of offshore wind turbines towards higher voltage levels, larger capacity, and higher power density.

[0011] This invention provides a method for preparing tensile-resistant mica tape based on dielectric reinforcement of polyimide film and its application. Attached Figure Description

[0012] Figure 1 Scanning electron microscope image showing the mica tape reinforced by the polyimide film of the present invention;

[0013] Figure 2 Weibull breakdown failure probability diagram for mica tape at different reinforcement positions of polyimide films;

[0014] Figure 3 Dielectric spectrum of mica tape at different reinforcement positions of polyimide films;

[0015] Figure 4 Tensile stress-strain diagrams of mica tapes at different reinforcement locations of polyimide films;

[0016] Figure 5 A graph showing the variation in tensile strength of mica tape at different reinforcement locations of polyimide films;

[0017] Figure 6 A graph showing the variation in thermal conductivity of mica tape at different reinforcement locations of polyimide films;

[0018] Figure 7 Weibull breakdown failure probability diagram for mica tapes reinforced with different polyimide film thicknesses;

[0019] Figure 8 Dielectric spectrum diagram of mica tape reinforced with different polyimide film thicknesses;

[0020] Figure 9 The tensile stress-strain of mica tapes reinforced with different polyimide film thicknesses is represented.

[0021] Figure 10 A graph showing the variation in tensile strength of mica tape reinforced with different polyimide film thicknesses;

[0022] Figure 11 A graph showing the variation in thermal conductivity of mica tapes reinforced with different polyimide film thicknesses;

[0023] Figure 12 This diagram shows the electric field intensity distribution inside the mica tape reinforced by polyimide film.

[0024] Figure 13 A graph showing the variation of electric field intensity inside the glass fiber cloth / epoxy resin layer with the thickness of the PI film.

[0025] Figure 14 The graph shows how the electric field intensity inside the mica paper / epoxy resin layer changes with the thickness of the PI film. Detailed Implementation

[0026] Specific Implementation Method 1: This implementation method describes a method for preparing a tensile-resistant mica tape based on dielectric reinforcement of polyimide film, which is carried out according to the following steps:

[0027] Mica paper is bonded to a polyimide film, or mica paper is bonded to a polyimide film and a glass fiber cloth, and then hot-pressed and cured to obtain a tensile-resistant mica tape based on the dielectric reinforcement of the polyimide film; the tensile-resistant mica tape based on the dielectric reinforcement of the polyimide film is a polyimide-mica paper-glass fiber cloth mica tape, a polyimide-mica paper-polyimide mica tape, a polyimide-glass fiber cloth-mica paper-glass fiber cloth mica tape, or a polyimide-glass fiber cloth-mica paper-glass fiber cloth-polyimide mica tape.

[0028] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the polyimide-mica paper-glass fiber cloth mica tape is prepared according to the following steps:

[0029] Epoxy resin is evenly coated on both sides of the mica paper and one side of the polyimide film. One side of the glass fiber cloth is fully soaked in epoxy resin. Then, one side of the mica paper is bonded to the side of the glass fiber cloth soaked in epoxy resin and fully impregnated. Then, the other side of the mica paper is bonded to the side of the polyimide film coated with epoxy resin. Finally, hot pressing and curing are performed to obtain polyimide-mica paper-glass fiber cloth mica tape.

[0030] The other steps are the same as in Specific Implementation Method 1.

[0031] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the polyimide-mica paper-polyimide mica tape is prepared according to the following steps:

[0032] Epoxy resin is evenly coated on both sides of mica paper, and epoxy resin is evenly coated on one side of two layers of polyimide film. Then, the mica paper is placed between the epoxy resin coated sides of the two layers of polyimide film, and finally, hot pressing and curing are performed to obtain polyimide-mica paper-polyimide mica tape.

[0033] The other steps are the same as in Specific Implementation Method 1 or 2.

[0034] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the polyimide-glass fiber cloth-mica paper-glass fiber cloth-mica tape is prepared according to the following steps:

[0035] Epoxy resin is evenly coated on both sides of the mica paper and one side of the polyimide film. One side of each of the two glass fiber cloths is fully soaked in epoxy resin. The mica paper is then placed between the epoxy resin-soaked sides of the two glass fiber cloths and fully impregnated. The epoxy resin-coated side of the polyimide film is then bonded to the outer surface of one of the glass fiber cloths. Finally, hot pressing and curing are performed to obtain polyimide-glass fiber cloth-mica paper-glass fiber cloth mica tape.

[0036] The other steps are the same as those in Specific Implementation Methods One to Three.

[0037] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the polyimide-glass fiber cloth-mica paper-glass fiber cloth-polyimide mica tape is prepared according to the following steps:

[0038] Epoxy resin is evenly coated on both sides of mica paper and one side of two polyimide films. One side of each of the two glass fiber cloths is fully soaked in epoxy resin. The mica paper is then placed between the epoxy resin-soaked sides of the two glass fiber cloths and fully impregnated. The epoxy resin-coated side of one polyimide film is then bonded to the outer surface of one glass fiber cloth, and the epoxy resin-coated side of the other polyimide film is bonded to the outer surface of the other glass fiber cloth. Finally, hot pressing and curing are performed to obtain polyimide-glass fiber cloth-mica paper-glass fiber cloth-polyimide mica tape.

[0039] The other steps are the same as those in Specific Implementation Methods One through Four.

[0040] Specific Embodiment Six: The difference between this embodiment and Specific Embodiments One to Five is that the polyimide film is prepared according to the following steps: polyimide powder is added to an N-methylpyrrolidone solution, and stirred at 300-400 r / min for 10-12 h at a temperature of 80-100℃ to obtain a polyimide solution; the polyimide solution is coated into a film, and then dried at 80-90℃ for 10-12 h to obtain a polyimide film with a thickness of 7 µm, 13 µm, 25 µm, 36 µm or 44 µm; the mass ratio of the polyimide powder to the volume of the N-methylpyrrolidone solution is 1 g: (5-5.5) mL.

[0041] The other steps are the same as those in Specific Implementation Methods 1 to 5.

[0042] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the mica paper is prepared according to the following steps: adding mica powder to deionized water and stirring for 5 to 10 minutes at an ultrasonic frequency of 40 to 50 kHz and a vacuum pressure of -3 kPa to -10 kPa to obtain mica slurry; then filtering with an iron mesh with a pore size of 0.18 to 0.22 mm, and then drying at 100 to 105°C for 10 to 15 minutes to obtain mica paper; the ratio of the mass of mica powder to the volume of deionized water is (4.1 to 4.15) g: (450 to 500) mL.

[0043] The other steps are the same as those in Specific Implementation Methods 1 to 6.

[0044] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the epoxy resin adhesive is prepared in the following steps: epoxy resin and methylhexahydrophthalic anhydride are mixed and stirred at 300-350 r / min for 10-12 h at a temperature of 75-80°C to obtain a suspension; then 2,4,6-tris(dimethylaminomethyl)phenol is added and stirred for another 10-15 min to obtain the epoxy resin adhesive; the mass ratio of epoxy resin, methylhexahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol is 100:85:(0.5-1).

[0045] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0046] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that the hot pressing temperature is 75~80℃ and the pressure is 3~4 MPa; the curing is first cured at 100~105℃ for 2~2.5 h, and then cured at 120~125℃ for 4~4.5 h.

[0047] The other steps are the same as those in Specific Implementation Methods 1 to 8.

[0048] Specific Implementation Method 10: Application of a tensile mica tape based on polyimide film dielectric reinforcement in the main insulation material of the stator bar of an offshore high-voltage wind turbine.

[0049] The beneficial effects of the present invention are verified using the following embodiments:

[0050] Example 1: Preparation method of polyimide-mica paper-glass fiber cloth mica tape, which is carried out according to the following steps:

[0051] Step S1: Prepare a polyimide film;

[0052] 1 g of polyimide powder was added to 5 mL of N-methylpyrrolidone solution and stirred at 400 r / min for 12 h at 80 °C to obtain a polyimide solution. The polyimide solution was coated into a thin film using a coater and then placed in a forced-air drying oven at 80 °C for 12 h. The solvent was dried and the film was annealed to eliminate internal stress, resulting in a polyimide film with a thickness of 25 µm.

[0053] Step S2: Prepare mica paper;

[0054] 4.1 g of mica powder was added to 500 mL of deionized water and stirred for 5 min at an ultrasonic frequency of 40 kHz and a vacuum pressure of -5 kPa to obtain mica slurry; then filtered using an iron mesh with a pore size of 0.20 mm and dried at 100℃ for 10 min to obtain mica paper.

[0055] Step S3: Prepare epoxy resin solution;

[0056] 10g of E51 epoxy resin was mixed with 8.5g of hexahydrophthalic anhydride and stirred at 300 r / min for 12 h at 75℃ to obtain a suspension; then 0.1g of 2,4,6-tris(dimethylaminomethyl)phenol was added and stirred for another 10 min to obtain an epoxy resin solution.

[0057] Step S4: Prepare polyimide-mica paper-glass fiber cloth mica tape;

[0058] Epoxy resin was uniformly coated on both sides of the mica paper and one side of the polyimide film. One side of the glass fiber cloth was fully soaked in epoxy resin. Then, one side of the mica paper was bonded to the side of the glass fiber cloth soaked in epoxy resin and fully impregnated. The other side of the mica paper was then bonded to the side of the polyimide film coated with epoxy resin. The mixture was then hot-pressed at 75°C and 3 MPa to ensure close contact between the layers. The mixture was then placed in a vacuum drying oven and cured at 100°C for 2 hours. Finally, it was cured at 120°C for another 4 hours to obtain a polyimide-mica paper-glass fiber cloth mica tape, named PI-Mg (PI represents polyimide film, M represents mica paper, and g represents glass fiber cloth).

[0059] Example 2:

[0060] Epoxy resin was uniformly coated on both sides of mica paper, and simultaneously, epoxy resin was uniformly coated on one side of two layers of polyimide film. The mica paper was then placed between the epoxy resin-coated sides of the two polyimide films, and finally, hot-pressed and cured to obtain a polyimide-mica paper-polyimide mica tape, named PI-M-PI. In this example, glass fiber cloth was not added, and all other experimental conditions were the same as in Example 1.

[0061] Example 3:

[0062] Epoxy resin was uniformly coated on both sides of the mica paper and one side of the polyimide film. One side of each of the two glass fiber cloths was thoroughly soaked in epoxy resin. The mica paper was then placed between the epoxy resin-soaked sides of the two glass fiber cloths and fully impregnated. The epoxy resin-coated side of the polyimide film was then bonded to the outer surface of one of the glass fiber cloths. Finally, hot pressing and curing were performed to obtain a polyimide-glass fiber cloth-mica paper-glass fiber cloth mica tape, named PI-gMg. All other experimental conditions were the same as in Example 1.

[0063] Example 4:

[0064] Epoxy resin was uniformly coated on both sides of mica paper and one side of two polyimide films. One side of each of the two glass fiber cloths was thoroughly soaked in epoxy resin. The mica paper was then placed between the epoxy resin-soaked sides of the two glass fiber cloths and fully impregnated. One polyimide film coated with epoxy resin was then bonded to the outer surface of one glass fiber cloth, and the other polyimide film coated with epoxy resin was bonded to the outer surface of another glass fiber cloth. Finally, hot pressing and curing were performed to obtain a polyimide-glass fiber cloth-mica paper-glass fiber cloth-polyimide mica tape, named PI-gMg-PI. All other experimental conditions were the same as in Example 1.

[0065] Example 5:

[0066] PI-gMg was also prepared in this example. The difference was that the polyimide film thickness was 7 µm, while all other experimental conditions were the same as in Example 3.

[0067] Example 6:

[0068] PI-gMg was also prepared in this example. The difference was that the polyimide film thickness was 13 µm, while all other experimental conditions were the same as in Example 3.

[0069] Example 7:

[0070] PI-gMg was also prepared in this example. The difference was that the polyimide film thickness was 36 µm, while all other experimental conditions were the same as in Example 3.

[0071] Example 8:

[0072] PI-gMg was also prepared in this example. The difference was that the polyimide film thickness was 44 µm, while all other experimental conditions were the same as in Example 3.

[0073] Comparative Example 1:

[0074] Step 1: Weigh 4.1 g of mica powder into a beaker, add 500 mL of deionized water, and stir in an ultrasonic environment for 5 min to obtain mica slurry; obtain mica paper by vacuum-assisted filtration and heating to dry the moisture; the drying conditions are 100℃ for 10 min.

[0075] Step 2: Mix 10 g of E51 epoxy resin with 8.5 g of methylhexahydrophthalic anhydride thoroughly, stir to obtain a suspension, then add 0.1 g of 2,4,6-tris(dimethylaminomethyl)phenol as a catalyst, and continue stirring for 10 min to obtain epoxy resin solution.

[0076] Step 3: Evenly coat both sides of the mica paper prepared in Step 1 with the epoxy resin solution prepared in Step 2. Thoroughly soak two layers of glass fiber cloth with the epoxy resin solution, and place the mica paper between the glass fiber cloths for complete impregnation. Hot-press the mica tape at 75℃ and 3 MPa, ensuring close contact between the layers. Then place the mica tape in a vacuum drying oven and perform step curing at 100℃ for 2 h and 120℃ for 4 h to obtain a smooth and flat mica tape. Name this structure gMg. The breakdown field strength, tensile strength, and thermal conductivity of the mica tape obtained under these comparative conditions were measured to be 41.70 kV / mm, 118.58 MPa, and 0.251 W / (m·K), respectively.

[0077] Figure 1 Scanning electron microscope (SEM) image of the mica tape reinforced by the polyimide film of the present invention; as shown. Figure 1 As shown, the polyimide reinforcing film layer, the glass fiber cloth-epoxy resin layer, and the mica paper-epoxy resin layer are dense and uniform inside, and the media between each layer are tightly bonded together without obvious defects.

[0078] Figure 2 Weibull breakdown failure probability diagram showing mica strips at different reinforcement locations of polyimide films; such as Figure 2 As shown in the figure, the breakdown field strengths of the polyimide film-reinforced mica tapes with four structures, namely PI-Mg, PI-M-PI, PI-gMg, and PI-gMg-PI, are 53.94 kV / mm, 68.40 kV / mm, 60.93 kV / mm, and 60.76 kV / mm, respectively, which are significantly higher than the 41.70 kV / mm of the gMg mica tape.

[0079] Figure 3 Dielectric spectrum diagrams of mica tapes at different reinforcement locations in polyimide films; such as Figure 3As shown, the introduction of polyimide film increases the relative permittivity of mica tape to varying degrees. The relative permittivity of the five types of mica tape is between 4 and 5.5, and the loss factor tanδ remains below 0.04 over a wide frequency range.

[0080] Figure 4 Tensile stress-strain diagrams of mica tapes at different reinforcement locations of polyimide films. Figure 5 This graph shows the variation in tensile strength of mica tape at different reinforcement locations on polyimide films; for example... Figure 4-5 As shown, the tensile strength of mica tape decreased to varying degrees, but the tensile strength of PI-gMg and PI-gMg-PI mica tapes was well maintained due to the double-layer glass fiber cloth reinforcement structure, reaching 103.24 MPa and 101.7 MPa, respectively.

[0081] Figure 6 A graph showing the variation in thermal conductivity of mica tape at different reinforcement locations of polyimide films; such as Figure 6 As shown, since the polyimide film itself has low thermal conductivity, the polyimide film will affect the thermal conductivity of the mica tape, thus causing the thermal conductivity of the mica tape to decrease.

[0082] Figure 7 Weibull breakdown failure probability diagram for mica tapes reinforced with different polyimide film thicknesses. Figure 8 The dielectric spectrum of mica tapes reinforced with different polyimide film thicknesses is shown. Figure 9 This represents the tensile stress-strain of mica tapes reinforced with different polyimide film thicknesses. Figure 10 This graph shows the variation in tensile strength of mica tape reinforced with different polyimide film thicknesses. Figure 11 This graph shows the variation in thermal conductivity of mica tapes reinforced with different polyimide film thicknesses. (Example:) Figure 7-11 As shown, the thickness of the polyimide reinforcing film was further adjusted, and its breakdown, tensile and thermal conductivity properties were tested. It was found that the breakdown field strength of the mica tape first increased and then decreased with the increase of the film thickness. The maximum breakdown field strength of the mica tape occurred when the polyimide film thickness was 25µm, and its tensile strength and thermal conductivity were at a high level.

[0083] Taking into account the dielectric strength, tensile strength, and thermal conductivity of mica tape, it was found that PI-gMg mica tape with a polyimide film thickness of 25 μm has excellent comprehensive performance due to the dielectric reinforcement effect of its single-layer polyimide film and the tensile reinforcement effect of its double-layer glass fiber cloth. While ensuring that the tensile strength and thermal conductivity are reduced by only 12.9% and 6.4% respectively, the dielectric strength of the mica tape is increased by 46.1%.

[0084] Figure 12This diagram shows the electric field distribution inside the mica tape reinforced by the polyimide film. Figure 13 The graph shows the variation of the electric field intensity inside the glass fiber cloth / epoxy resin layer with the thickness of the PI film. Figure 14 The graph shows the variation of the electric field intensity inside the mica paper / epoxy resin layer with the thickness of the PI film. Further simulation analysis was performed on the electric field intensity distribution inside the polyimide film-reinforced mica tape, as shown below. Figure 12 As shown, the average electric field strength inside the mica tape is taken as 60.93 kV / mm. The actual voltage applied to both ends of the mica tape is calculated based on the thickness of each mica tape (mica paper-epoxy resin layer thickness 150 µm, glass fiber cloth-epoxy resin layer thickness 38 µm). Figure 12 (a) shows the distribution of the internal electric field intensity of the mica tape at different polyimide film reinforcement positions. The change from blue to red in the color chart represents the change of electric field intensity from low to high. The electric field strength within each layer of the gMg mica tape is similar and at a moderate level. The electric field strength within the PI-Mg, PI-M-PI, PI-gMg, and PI-gMg-PI mica tapes is concentrated within the polyimide film, while the electric field strength within the glass fiber cloth-epoxy resin layer and the mica paper-epoxy resin layer decreases significantly. This demonstrates that the introduction of the polyimide film can regulate the electric field distribution within the mica tape, allowing the electric field to be more concentrated within the polyimide layer with higher dielectric strength. Conversely, it reduces the electric field strength within the glass fiber cloth-epoxy resin layer and the mica paper-epoxy resin layer, where electrons experience less electric force and are less likely to be accelerated and ionized by collisions, leading to breakdown of the mica tape and thus significantly improving its dielectric strength. Figure 12 (b) shows the internal electric field distribution of mica tapes with different polyimide-reinforced film thicknesses. It can be seen that as the polyimide film thickness increases, the electric field intensity within the glass fiber cloth-epoxy resin layer and the mica paper-epoxy resin layer gradually decreases, demonstrating that the reinforcing effect of the polyimide film on the dielectric strength of the mica tape gradually increases. The specific changes in the corresponding electric field intensity are shown in the figure. Figure 13-14 As shown. However, with the increase of polyimide film thickness, the probability of defects appearing inside the film increases, the film quality decreases, and breakdown is more easily initiated inside the film. This results in a decrease in the dielectric strength of the mica tape when the film thickness is greater than 25 µm.

[0085] like Figure 13-14As shown, when the 25 µm thick polyimide film reinforces the mica tape to reach its breakdown field strength (60.93 kV / mm), the electric field strengths within the glass fiber cloth-epoxy resin layer and the mica paper-epoxy resin layer are 58.68 kV / mm and 56.48 kV / mm, respectively, which are much higher than the 41.70 kV / mm breakdown field strength of the gMg mica tape. This indicates that in addition to suppressing breakdown caused by charged particles inherent in the medium by regulating the electric field strength of each layer of the mica tape, the polyimide film also inhibits the development of breakdown paths within the mica tape. Whether inside the polyimide film layer or the glass fiber cloth-epoxy resin layer and the mica paper-epoxy resin layer, electrons are accelerated under the applied electric field, constantly undergoing collisional ionization to form electron avalanches. When the electron avalanches reach the interface between the polyimide film layer and the glass fiber cloth-epoxy resin layer, the avalanches are blocked by the interface, the moving electrons are braked, and the breakdown stops. Therefore, based on the dual effect of polyimide film in regulating the electric field strength and suppressing the breakdown path inside the mica tape, the dielectric strength of polyimide-reinforced mica tape has been qualitatively improved.

Claims

1. A method for manufacturing a tensile-resistant mica tape based on dielectric reinforcement of a polyimide film, characterized in that, The preparation method is carried out according to the following steps: The mica paper is bonded with the polyimide film or the mica paper is bonded with the polyimide film and the glass cloth, and then hot-pressed and cured to obtain the tensile-resistant mica tape based on polyimide film dielectric reinforcement; the tensile-resistant mica tape based on polyimide film dielectric reinforcement is polyimide-mica paper-glass cloth mica tape, polyimide-mica paper-polyimide mica tape, polyimide-glass cloth-mica paper-glass cloth mica tape or polyimide-glass cloth-mica paper-glass cloth-polyimide mica tape.

2. The method of claim 1, wherein the polyimide film is prepared by the steps of: (a) dissolving a polyimide precursor in a solvent to prepare a polyimide solution; (b) coating the polyimide solution on a release film; (c) drying the polyimide solution to form a polyimide film; and (d) peeling the polyimide film from the release film. The polyimide-mica paper-glass cloth mica tape is prepared according to the following steps: Both sides of the mica paper and one side of the polyimide film are uniformly coated with epoxy resin glue solution, and one side of the glass cloth is fully dipped in the epoxy resin glue solution; then one side of the mica paper is bonded with the side of the glass cloth dipped in the epoxy resin glue solution and fully immersed; and then the other side of the mica paper is bonded with the side of the polyimide film coated with the epoxy resin glue solution, and finally hot-pressed and cured to obtain the polyimide-mica paper-glass cloth mica tape.

3. The method for preparing a tensile-resistant mica tape based on dielectric reinforcement of polyimide film according to claim 1, characterized in that, The polyimide-mica paper-polyimide mica tape is prepared according to the following steps: Both sides of the mica paper and one side of the polyimide film are uniformly coated with epoxy resin glue solution, and one side of the glass cloth is fully dipped in the epoxy resin glue solution; then one side of the mica paper is bonded with the side of the glass cloth dipped in the epoxy resin glue solution and fully immersed; and then the other side of the mica paper is bonded with the side of the polyimide film coated with the epoxy resin glue solution, and finally hot-pressed and cured to obtain the polyimide-mica paper-glass cloth mica tape.

4. The method for preparing a tensile-resistant mica tape based on dielectric reinforcement of polyimide film according to claim 1, characterized in that, The polyimide-mica paper-polyimide mica tape is prepared according to the following steps: Both sides of the mica paper and one side of the polyimide film are uniformly coated with epoxy resin glue solution, and one side of the glass cloth is fully dipped in the epoxy resin glue solution; then one side of the mica paper is bonded with the side of the glass cloth dipped in the epoxy resin glue solution and fully immersed; and then the other side of the mica paper is bonded with the side of the polyimide film coated with the epoxy resin glue solution, and finally hot-pressed and cured to obtain the polyimide-mica paper-glass cloth mica tape.

5. The method for preparing a tensile-resistant mica tape based on dielectric reinforcement of polyimide film according to claim 1, characterized in that, The polyimide-mica paper-polyimide mica tape is prepared according to the following steps: Both sides of the mica paper and one side of the polyimide film are uniformly coated with epoxy resin glue solution, and one side of the glass cloth is fully dipped in the epoxy resin glue solution; then one side of the mica paper is bonded with the side of the glass cloth dipped in the epoxy resin glue solution and fully immersed; and then the other side of the mica paper is bonded with the side of the polyimide film coated with the epoxy resin glue solution, and finally hot-pressed and cured to obtain the polyimide-mica paper-glass cloth mica tape.

6. The method of claim 1, 2, 3, 4 or 5, wherein the polyimide film is prepared by the steps of: (a) dissolving a polyimide in a solvent to form a solution; (b) coating the solution on a substrate to form a film; (c) drying the film; and (d) removing the film from the substrate. The polyimide-mica paper-polyimide mica tape is prepared according to the following steps: Both sides of the mica paper and one side of the polyimide film are uniformly coated with epoxy resin glue solution, and one side of the glass cloth is fully dipped in the epoxy resin glue solution; then one side of the mica paper is bonded with the side of the glass cloth dipped in the epoxy resin glue solution and fully immersed; and then the other side of the mica paper is bonded with the side of the polyimide film coated with the epoxy resin glue solution, and finally hot-pressed and cured to obtain the polyimide-mica paper-glass cloth mica tape. The polyimide film is prepared according to the following steps: polyimide powder is added to an N-methyl pyrrolidone solution, stirred at a speed of 300-400 r / min for 10-12 h at a temperature of 80-100 ℃ to obtain a polyimide solution; The polyimide solution is coated into a film shape, and then dried at 80-90℃ for 10-12 h to obtain a polyimide film with a thickness of 7 µm, 13 µm, 25 µm, 36 µm or 44 µm; the ratio of the mass of the polyimide powder to the volume of the N-methylpyrrolidone solution is 1 g:(5-5.5) mL.

7. The method of claim 1, 2, 3, 4 or 5, wherein the polyimide film is a polyimide film having a dielectric constant of 3.5 or less, a dielectric loss of 0.005 or less, a tensile strength of 100 MPa or more, and a modulus of 3 GPa or more. The mica paper is prepared by the following steps: adding mica powder into deionized water, stirring at an ultrasonic frequency of 40-50 KHz and a vacuum pressure of-3 kPa to-10 kPa for 5-10 min to obtain a mica slurry; then filtering with an iron mesh with a pore size of 0.18-0.22 mm, and drying at 100-105℃ for 10-15 min to obtain the mica paper; the ratio of the mass of the mica powder to the volume of the deionized water is (4.1-4.15) g:(450-500) mL.

8. The method of claim 1, 2, 3, 4 or 5, wherein the polyimide film is a polyimide film having a dielectric constant of 3.5 or less, a dielectric loss of 0.005 or less, a tensile strength of 100 MPa or more, and a modulus of 3 GPa or more. The epoxy resin glue solution is prepared by the following steps: mixing epoxy resin and methylhexahydrophthalic anhydride, stirring at a speed of 300-350 r / min at a temperature of 75-80℃ for 10-12 h to obtain a suspension; then adding 2,4,6-tris(dimethylaminomethyl)phenol, and continuing to stir for 10-15 min to obtain the epoxy resin glue solution; the mass ratio of the epoxy resin, methylhexahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol is 100:85:(0.5-1).

9. The method of claim 1, 2, 3, 4 or 5, wherein the polyimide film is stretched in the longitudinal direction by 5 to 50% at a temperature of 100 to 200°C. The hot-pressing temperature is 75-80℃, and the pressure is 3-4 Mpa; the curing is first carried out at 100-105℃ for 2-2.5 h, and then at 120-125℃ for 4-4.5 h.

10. The use of a tensile-resistant mica tape based on polyimide film dielectric reinforcement prepared according to the method of any one of claims 1 to 9, characterized in that, The application of the tensile-resistant mica tape based on polyimide film dielectric reinforcement in the main insulation material of a stator bar of a high-voltage wind turbine generator at sea.

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