Corona-resistant polyimide composite film, preparation method and application

Abstract

The invention discloses a corona-resistant polyimide composite film, a preparation method and application, and belongs to the field of corona-resistant insulating materials. The preparation method comprises the following steps: mixing layered silicate in an aprotic polar solvent, then adding a surface modifier, and dispersing to obtain an inorganic dispersion liquid; dissolving diamine in an aprotic polar solvent, adding the inorganic dispersion liquid, and adding dianhydride in batches for multiple times; after polyamic acid becomes sticky, coating with a scraper, and after longitudinal and transverse stretching, carrying out gradient thermal imidization to obtain a polyimide film containing silicate; the preparation method comprises the following steps: putting a silicate-containing polyimide membrane into a potassium hydroxide aqueous solution for hydrolysis treatment, and soaking the membrane into a titanium tetrachloride aqueous solution for ion exchange when the membrane is washed by distilled water until the pH value of the aqueous solution is neutral; and carrying out gradient thermal imidization treatment on the polyimide film to obtain the corona-resistant polyimide composite film of which the surface layer is coated with titanium dioxide and the interior is filled with lamellar silicate, so that the corona resistance of the polyimide film can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of corona-resistant insulating materials, and particularly relates to a corona-resistant polyimide composite film, a preparation method and an application thereof. Background Art

[0002] As power technology evolves toward high voltage and high frequency, pulse-width modulation (PWM) variable-frequency motors are widely used. However, long-term, repetitive overvoltages, caused by electrical and thermal factors, can easily lead to aging and breakdown of insulation materials, resulting in motor failure. Consequently, there is an urgent need to improve the insulation and corona resistance of insulation materials to meet the demands of high-voltage technology development.

[0003] At present, people take advantage of the high insulation properties of polyimide and the corona resistance of inorganic fillers to combine polyimide with inorganic materials to prepare composite insulating materials. For example, DuPont's Kapton-100CRC film is composed of aluminum oxide-rich particle layers on both sides and a polyimide base layer in the middle. The relevant corona resistance mechanism shows that inorganic nanoparticles can provide shallow traps for the film, which is conducive to homogenizing space charge and improving the electrical aging threshold. The layered silicate material makes the corona-resistant interface overlap together, which is conducive to the lateral development of local discharge, slowing the breakdown speed and thus improving the corona resistance. Currently, there are related patents that mix inorganic nanoparticles with layered silicates and add them to polyamic acid to prepare corona-resistant films. In CN 109749082 A, the synergistic interaction between nanoparticles and nanosheets forms a multi-layer structure with good dispersion, improving the corona resistance and breakdown strength of the composite material. CN114989466A uses surface modifiers and ultrasonic dispersion to disperse nano-inorganic materials and layered inorganic materials, improving the dispersibility of the inorganic filler, resulting in a corona-resistant film with a corona resistance of up to 130 minutes. While these patents utilize the synergistic effects of inorganic nanoparticles and layered particles, the corona-resistant layer lacks a clear internal structure; instead, the inorganic materials are randomly stacked, failing to fully utilize the corona resistance of the inorganic filler. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a corona-resistant polyimide composite film, a preparation method and an application thereof, thereby solving the problems in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a corona-resistant polyimide composite film comprises the following steps:

[0007] The layered silicate is placed in an aprotic polar solvent and mixed, and then a surface modifier is added and dispersed to obtain an inorganic dispersion;

[0008] Dissolving a diamine in an aprotic polar solvent, adding the inorganic dispersion, and then adding dianhydride in batches multiple times to obtain a polyamic acid; coating the polyamic acid with a doctor blade after it becomes sticky to obtain a gel film, and then stretching it longitudinally and transversely, and then performing gradient thermal imidization to obtain a polyimide film containing silicate;

[0009] placing the silicate-containing polyimide membrane in a potassium hydroxide aqueous solution for hydrolysis treatment, washing with distilled water until the pH of the aqueous solution is neutral, and then immersing the polyimide membrane in a titanium tetrachloride aqueous solution for ion exchange;

[0010] The polyimide film is then subjected to gradient thermal imidization treatment to obtain the product.

[0011] Furthermore, the layered silicate is one of montmorillonite, hydrotalcite, kaolinite and mica, the added amount of the layered silicate accounts for 10%-30% of the total mass of the diamine and dianhydride, and the particle size of the layered silicate is 0.7 μm.

[0012] Furthermore, the surface modifier is one of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, 3-aminopropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and the mass of the surface modifier accounts for 0.1-0.3% of the mass of the layered silicate.

[0013] Further, the diamine is one or two of p-phenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]sulfone and 4,4′-diaminodiphenyl sulfone;

[0014] The dianhydride is one or two of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphthalic dianhydride.

[0015] Furthermore, the aprotic polar solvent is one of: N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone

[0016] Furthermore, the viscosity of the polyamic acid after tackification is 80,000-100,000 cP.

[0017] Furthermore, the concentration of the potassium hydroxide aqueous solution is 2 mol / L, and the concentration of the titanium tetrachloride aqueous solution is 0.4 mol / L.

[0018] Furthermore, the process parameters of the hydrolysis treatment are: constant temperature water bath 25° C., hydrolysis time 30-120 min; and ion exchange time 2-6 h.

[0019] A corona-resistant polyimide composite film is prepared using the above-mentioned preparation method.

[0020] Application of the above-mentioned corona-resistant polyimide composite film in the preparation of insulating materials.

[0021] Beneficial effects of the present invention:

[0022] The present invention utilizes an ion exchange method to construct a corona-resistant polyimide film with regular layers, the surface of which is coated with inorganic particles and the interior is filled with lamellar silicate. The titanium dioxide particles on the surface act as shallow traps, which can homogenize the electric field and avoid charge accumulation and damage. Even if there are a small number of deep traps on the surface of the film, the lamellar silicate inside can cause local discharge to develop laterally, increase the breakdown path, and reduce the breakdown speed. The titanium dioxide particles on the surface and the silicate inside can work synergistically to significantly improve the corona resistance of the polyimide film. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] A method for preparing a corona-resistant polyimide composite film comprises the following steps:

[0025] S1, placing the layered silicate in an aprotic polar solvent and mixing it, then adding a surface modifier, using mechanical shearing to disperse it, and stirring at a speed of 2000 rpm to obtain an inorganic dispersion;

[0026] S2, dissolving a diamine in an aprotic polar solvent, adding the above-mentioned inorganic dispersion, and then continuously adding dianhydride in batches to obtain a polyamic acid; after the polyamic acid becomes sticky, coating it with a doctor blade to obtain a gel film, and after longitudinal and transverse stretching, performing gradient thermal imidization to obtain a silicate-containing polyimide film;

[0027] S3, placing the above-mentioned silicate-containing polyimide membrane in 1000 mL of 2 mol / L potassium hydroxide aqueous solution for hydrolysis treatment, and after washing with distilled water until the pH of the aqueous solution is neutral, immersing the polyimide membrane in 0.4 mol / L titanium tetrachloride aqueous solution for ion exchange;

[0028] S4, subjecting the polyimide film to a gradient thermal imidization treatment to form a corona-resistant polyimide composite film with a surface layer coated with titanium dioxide particles and an interior filled with lamellar silicate.

[0029] The layered silicate in S1 is one of montmorillonite, hydrotalcite, kaolinite and mica, the added amount of the layered silicate accounts for 10%-30% of the total mass of the diamine and dianhydride, and the particle size of the layered silicate is 0.7 μm.

[0030] In S1, the surface modifier is one of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, 3-aminopropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and the mass of the surface modifier accounts for 0.1-0.3% of the mass of the layered silicate.

[0031] In S2, the diamine is one or two of p-phenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]sulfone and 4,4′-diaminodiphenyl sulfone.

[0032] In S2, the dianhydride is one or two of pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydiphthalic dianhydride.

[0033] The aprotic polar solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0034] In S2, the viscosity of the polyamic acid after tackification is 80,000-100,000 cP.

[0035] In S2, the gel film is first subjected to longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1:1.1 and the transverse stretching ratio being 1:1.1-1.3; the process parameters of the gradient thermal imidization (the gradient thermal imidization parameters of S2 and S4 are the same) are: 150°C / 5min, 200°C / 5min, 250°C / 5min, and 350°C / 5min, respectively.

[0036] In S3, the hydrolysis treatment process parameters are: constant temperature water bath 25°C, hydrolysis time 30-120 min.

[0037] In S3, the ion exchange time is 2-6 hours.

[0038] The technical solution of the present invention is described below through the following examples and comparative examples;

[0039] Example 1

[0040] Step 1: 10 g of montmorillonite powder was placed in 90 g of N,N-dimethylacetamide (DMAc), and then 0.2% of vinyltriethoxysilane was added based on the mass fraction of the montmorillonite powder. The mixture was mechanically sheared and dispersed at 2000 rpm to obtain a uniformly dispersed inorganic dispersion.

[0041] Step 2: 1.62 g of p-phenylenediamine (PDA), 7 g of 4,4′-diphenyl ether diamine (ODA), and 78.08 g of DMAc were added to a 250 mL three-necked flask equipped with a temperature-controlled water bath and a stirring device. After mechanical stirring at 50°C until the solid was completely dissolved, 39.04 g of the above-mentioned inorganic dispersion was added, and 10.9 g of pyromellitic dianhydride (PMDA) was added to the reactor in batches. After the resin viscosity test reached 80,000-100,000 cP, a corona-resistant polyimide film containing montmorillonite was obtained by defoaming, coating, stretching, and gradient imidization treatment;

[0042] Step 3: The polyimide membrane was placed in 1000 mL of a 2 mol / L potassium hydroxide aqueous solution for hydrolysis for 30 min. After washing with distilled water until the pH of the aqueous solution was neutral, the membrane was immersed in a 0.4 mol / L titanium tetrachloride aqueous solution for ion exchange for 4 h.

[0043] Step 4: The film is then subjected to gradient imidization to obtain a corona-resistant polyimide film with a surface coated with titanium dioxide particles. The thickness of the corona-resistant polyimide film is 25 μm.

[0044] Example 2

[0045] The only difference between this embodiment and embodiment 1 is that the hydrolysis treatment time in step 3 is 60 minutes.

[0046] Example 3

[0047] The only difference between this embodiment and embodiment 1 is that the hydrolysis treatment time in step 3 is 90 minutes.

[0048] Example 4

[0049] The only difference between this embodiment and embodiment 1 is that the hydrolysis treatment time in step 3 is 120 minutes.

[0050] Comparative Example 1

[0051] 10 g of montmorillonite powder was placed in 90 g of DMAc, and then 0.2% of vinyltriethoxysilane was added, and mechanical shearing and dispersion were performed at a speed of 2000 rpm to obtain a uniformly dispersed inorganic dispersion.

[0052] 1.62 g PDA, 7 g ODA, and 78.08 g DMAc were added to a 250 mL three-necked flask equipped with a temperature-controlled water bath and a stirring device. After mechanical stirring at 50° C. until the solid was completely dissolved, 39.04 g of the above-mentioned inorganic dispersion was added, and 10.9 g PMDA was added to the reactor in batches. After the resin viscosity test reached 80,000-100,000 cP, a corona-resistant polyimide film containing montmorillonite was obtained by defoaming, coating, stretching, and gradient imidization treatment. The thickness of the corona-resistant polyimide film was 25 μm.

[0053] Comparative Example 2

[0054] 1.62 g PDA, 7 g ODA, and 78.08 g DMAc were added to a 250 mL three-necked flask equipped with a temperature-controlled water bath and a stirring device. After mechanical stirring at 50°C until the solids were completely dissolved, 10.9 g PMDA was added to the reactor in batches. After the resin viscosity test reached 80,000-100,000 cP, defoaming, coating, and gradient imidization were performed to obtain a polyimide film.

[0055] The polyimide membrane was placed in 1000 mL of a 2 mol / L potassium hydroxide aqueous solution for hydrolysis for 60 min. After washing with distilled water until the pH of the aqueous solution was neutral, the membrane was immersed in a 0.4 mol / L titanium tetrachloride aqueous solution for ion exchange for 4 h.

[0056] The film was then subjected to gradient imidization to obtain a corona-resistant polyimide film with a surface coated with titanium dioxide particles. The thickness of the corona-resistant polyimide film was 25 μm.

[0057] Experimental testing

[0058] The corona-resistant polyimide composite films prepared in Examples 1-4 and the corona-resistant polyimide films of Comparative Examples 1-2 were subjected to performance tests. The test methods are as follows:

[0059] 1) Mechanical properties: The mechanical properties of the film were tested using an AGS-J electronic universal testing machine from Shimadzu Corporation of Japan. The effective size of the sample was 100 mm × 15 mm, and the tensile rate was 50 mm / min.

[0060] 2) Breakdown strength: Utilizing the HT-5 / 20 breakdown field strength tester manufactured by Guilin Electrical Science Research Institute, a cylindrical electrode with a diameter of 6 mm, air atmosphere, and a voltage rise rate of 0.5 kV / s.

[0061] 3) Corona resistance: The test was conducted using an HP-3kV high-frequency pulse voltage tester manufactured by Guilin Electrical Science Research Institute. The pulse waveform was square wave, the pulse frequency was 20 kHz, and the pulse interval was 25 μs.

[0062] The test results are shown in Table 1 below:

[0063] Table 1 Performance test results of membrane

[0064]

[0065] The test results in Table 1 show that the mechanical properties, breakdown strength, and corona resistance of the corona-resistant composite film initially increase and then significantly decrease with increasing hydrolysis time. This is likely due to the prolonged hydrolysis time, which results in an uneven surface with numerous defects that cannot be completely eliminated even after subsequent imidization treatment. When the hydrolysis time is 60 minutes, the corona-resistant polyimide composite film, coated with titanium dioxide particles on the surface and filled with lamellar silicate, exhibits comparable mechanical properties to the corona-resistant polyimide films in Comparative Examples 1 and 2, but exhibits significantly improved breakdown strength and corona resistance, with a corona resistance time of 180 minutes.

[0066] In summary, the present invention uses the ion exchange method to construct a corona-resistant polyimide film with regular layers, which is coated with inorganic particles on the surface and filled with lamellar silicate inside. The surface titanium dioxide particles and the silicate filled inside can play a synergistic role, greatly improving the corona resistance of the polyimide film, and can be used in the field of motor insulation materials.

[0067] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0068] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing a corona-resistant polyimide composite film, characterized in that: The following steps are involved: The layered silicate is placed in an aprotic polar solvent and mixed, and then a surface modifier is added and dispersed to obtain an inorganic dispersion; Dissolving a diamine in an aprotic polar solvent, adding the inorganic dispersion, and then adding dianhydride in batches multiple times to obtain a polyamic acid; coating the polyamic acid with a doctor blade after it becomes sticky to obtain a gel film, and then stretching it longitudinally and transversely, and then performing gradient thermal imidization to obtain a polyimide film containing silicate; placing the silicate-containing polyimide membrane in a potassium hydroxide aqueous solution for hydrolysis treatment, washing with distilled water until the pH of the aqueous solution is neutral, and then immersing the polyimide membrane in a titanium tetrachloride aqueous solution for ion exchange; The polyimide film is then subjected to gradient thermal imidization treatment to obtain the product.

2. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The layered silicate is one of montmorillonite, hydrotalcite, kaolinite and mica. The added amount of the layered silicate accounts for 10%-30% of the total mass of the diamine and dianhydride. The particle size of the layered silicate is 0.7 μm.

3. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The surface modifier is one of gamma-aminopropyltriethoxysilane, vinyltriethoxysilane, 3-aminopropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and the mass of the surface modifier accounts for 0.1-0.3% of the mass of the layered silicate.

4. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The diamine is one or two of p-phenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]sulfone and 4,4′-diaminodiphenyl sulfone; The dianhydride is one or two of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphthalic dianhydride.

5. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The aprotic polar solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

6. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The viscosity of the polyamic acid after tackification is 80,000-100,000 cP.

7. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The concentration of the potassium hydroxide aqueous solution is 2 mol / L, and the concentration of the titanium tetrachloride aqueous solution is 0.4 mol / L.

8. The method for preparing a corona-resistant polyimide composite film according to claim 1, wherein: The process parameters of the hydrolysis treatment are: a constant temperature water bath at 25° C., a hydrolysis time of 30-120 min; and an ion exchange time of 2-6 h.

9. A corona-resistant polyimide composite film, characterized in that: It is prepared using the preparation method according to any one of claims 1 to 8.

10. Use of the corona-resistant polyimide composite film according to claim 9 in the preparation of insulating materials.

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