Preparation method and application of polyimide dielectric film

Abstract

The invention provides a preparation method and application of a polyimide dielectric film, and the method comprises the following steps: polymerizing a diamine monomer and an excessive dianhydride monomer in a polar solvent in a nitrogen atmosphere to obtain a polyamide acid solution; adding an end-capping reagent containing a phthalonitrile group and an amino group into the polyamide acid solution, and reacting to obtain a phthalonitrile group-terminated polyamide acid solution; adding a ring-closing agent into the phthalonitrile group-terminated polyamide acid solution to generate a phthalonitrile group-terminated polyimide solution, and settling, washing and drying the phthalonitrile group-terminated polyimide solution to obtain phthalonitrile group-terminated polyimide powder; polyimide powder is dissolved in a polar solvent, a wet film is prepared on a substrate in a coating mode, the wet film is heated, and the polyimide dielectric film is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric materials, and particularly to a preparation method and application of a polyimide dielectric film. Background Art

[0002] With the rapid development of modern technologies and industries, the energy demand is increasing day by day. As traditional fossil energy reserves are limited, it has become an inevitable choice to develop green and clean new energy. In recent years, the development and utilization of renewable energy such as solar energy and wind energy have attracted much attention, and there is an urgent need for efficient energy storage and conversion devices. As an electrical energy storage device, dielectric capacitors have high power density and fast discharge ability, and are widely used in fields such as medical defibrillators and hybrid electric vehicles. However, the energy density of dielectric capacitors is relatively low, which restricts the miniaturization and high integration of energy storage systems.

[0003] Under extreme conditions, such as in high-temperature environments, the application of dielectric capacitors faces challenges. For example, the temperature under the hood of a hybrid electric vehicle may exceed 140 °C, while the maximum operating temperature of the biaxially oriented polypropylene (BOPP) dielectric material in a commercial power inverter is only 105 °C, requiring an additional cooling system, which increases the volume and mass of the system. Similarly, electronic devices in aircraft and underground oil exploration also need to operate at high temperatures, and a cooling system is not practical. Therefore, the development of high-temperature-resistant and high-energy-storage-density dielectric materials is of great significance for the simplification, lightweight, and integration of power electronic devices.

[0004] Polyimide is considered an ideal substitute for high-temperature dielectric materials due to its high temperature resistance, easy processing, easy structure regulation, and relatively wide bandgap. However, existing intrinsic polyimide has problems such as low dielectric constant, low breakdown field strength, and low energy storage density. In current research, by introducing various functional organic fillers (such as polyvinylidene fluoride, polythiourea), ceramic fillers (such as BaTiO3, Al2O3), and conductive fillers (such as graphene) into the PI matrix, both its dielectric properties and breakdown field strength have been improved. However, the organic fillers decompose at high temperatures and form micropores inside the material, resulting in the generation of carrier traps inside the material, leading to an increase in energy loss, and reducing the breakdown field strength and service life of the material; for inorganic fillers, the introduction of high volume fractions of fillers will inevitably introduce phase separation problems, resulting in the loss of the basic properties of the material.

[0005] Therefore, it is necessary to design a preparation method and application of a polyimide dielectric film to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a polyimide dielectric film to provide a polyimide dielectric film with high dielectric constant, high breakdown field strength, and high energy storage density suitable for energy storage capacitors.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a polyimide dielectric film, comprising the following steps:

[0008] S1. Under a nitrogen atmosphere, a diamine monomer and an excessive dianhydride monomer are polymerized in a polar solvent to obtain a polyamic acid solution;

[0009] S2. Under a nitrogen atmosphere, a capping agent containing a phthalonitrile group and an amino group is added to the polyamic acid solution, and after reaction, a polyamic acid solution capped with a phthalonitrile group is obtained;

[0010] S3. Under a nitrogen atmosphere, a cyclization agent is added to the polyamic acid solution capped with a phthalonitrile group to generate a polyimide solution capped with a phthalonitrile group. After the polyimide solution capped with a phthalonitrile group is sedimented, washed, and dried, a polyimide powder capped with a phthalonitrile group is obtained;

[0011] S4. The polyimide powder is dissolved in a polar solvent, and a wet film is prepared on a substrate by a coating method, and the wet film is heat-treated to obtain a polyimide dielectric film.

[0012] As a further improved technical solution of the present invention, in step S1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1 - 1.4, the molecular weight of the polyamic acid is 1000 - 10000, the solid content of the polyamic acid solution is 10 - 30%, and the viscosity range is 100 - 30000 cPs.

[0013] As a further improved technical solution of the present invention, the diamine monomer is an aromatic diamine monomer, the dianhydride monomer is an aromatic dianhydride monomer or an alicyclic dianhydride monomer, and the polar solvent is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, m-cresol, chloroform, tetrahydrofuran, γ-butyrolactone, and 3-methyl-N,N-dimethylpropanamide.

[0014] As a further improved technical solution of the present invention, in step S2, the capping agent is selected from one or more of the following structures:

[0015]

[0016] Wherein, R1, R2, R3, and R4 are each independently selected from the following groups: H, F, Cl, Br, I, CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3, OCF3, OCH2CH3.

[0017] As a further improved technical solution of the present invention, in step S3, the cyclizing agent includes a dehydrating agent and a catalyst. The dehydrating agent is at least one of acetic anhydride, propionic anhydride, butyric anhydride, and sodium acetate, and the catalyst is at least one of triethylamine, isoquinoline, pyridine, and N-methylpyridine.

[0018] As a further improved technical solution of the present invention, the molar ratio of the end-capping agent to the diamine monomer is 0.1-0.3.

[0019] As a further improved technical solution of the present invention, the thickness of the polyimide dielectric film is 3-15 μm.

[0020] As a further improved technical solution of the present invention, in step S4, the heat treatment is carried out in a stepwise temperature-rising manner. The lowest treatment temperature is 50-100°C, the highest treatment temperature is 300-450°C, the treatment time for each temperature step is 0.5-3 h, and the total treatment time is 4-10 h.

[0021] As a further improved technical solution of the present invention, the stepwise temperature-rising operation is carried out in the following order: heating at 70-100°C for 1 h, heating at 180-250°C for 1 h, heating at 250-300°C for 1 h, and heating at 300-350°C for 2 h.

[0022] Another object of the present invention is to provide the application of the above polyimide dielectric film in an energy storage capacitor. The glass transition temperature Tg of the polyimide dielectric film is greater than 220°C, and the energy storage density at 25°C is greater than 5 J / cm 3 and the energy storage density at 150°C is greater than 3 J / cm 3 .

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1. Through the molecular structure design of the phthalonitrile group end-capping agent (S2), a strongly polar nitrile group is introduced at the end of the polyimide molecular chain, significantly enhancing the dipole polarization response ability of the molecular chain. Combining with the rigid imide ring structure formed by the cyclization reaction (S3), while maintaining a high dielectric constant, the dielectric loss is reduced by the orientation order of the molecular chain, and the energy storage density breaks through 8 J / cm 3 , realizing the synergistic improvement of high dielectric performance and energy storage density.

[0025] 2. The precise metering of the end-capping agent amine group (S2) enables molecular weight controllable polymerization, avoiding the local electric field concentration caused by end-group defects; the closed-loop treatment (S3) promotes the close packing of molecular chains, and together with the gradient heating film-forming process (S4), a dense structure without pinhole defects is formed. The thermal cross-linking property of the phthalonitrile group forms a three-dimensional network structure in the heat treatment stage (S4), making the breakdown field strength reach more than 750 MV / m.

[0026] 3. The whole-process nitrogen protection (S1-S3) effectively inhibits the oxidation side reaction and ensures the integrity of the molecular chain structure; the stepwise addition strategy of the closed-loop agent (S3) significantly improves the imidization degree and significantly reduces the residual stress; the solvent re-dissolution film-forming process (S4) breaks through the limitations of the traditional thermal imidization process and greatly reduces the surface roughness of the film.

[0027] The technical solution of the present invention solves the contradiction that it is difficult to have both a high dielectric constant and a high breakdown field strength through triple innovations of molecular design - process regulation - structure optimization. The prepared film can still maintain a high energy storage efficiency at a high temperature of 150 °C, and is particularly suitable for energy storage capacitor applications under extreme working conditions such as new energy vehicles and pulsed power systems. Detailed implementation manners

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be described in detail below with reference to specific embodiments.

[0029] Example 1:

[0030] S1. Under a nitrogen atmosphere, 4.95 g (24.75 mmol) of 4,4'-diaminodiphenyl ether was added to a reaction flask, and then added to 30 g of N,N-dimethylacetamide solution. After 4,4'-diaminodiphenyl ether was completely dissolved, 8.53 g (27.5 mmol) of 4,4'-biphenyl ether dianhydride was added, and 23.9 g of N,N-dimethylacetamide solution was added to make the solid content 20%. The temperature was raised to 35 °C and reacted for 5 h to obtain a polyamic acid solution.

[0031] S2. Under a nitrogen atmosphere, 1.175 g (5.0 mmol) of 4-(4-aminophenoxy)phthalonitrile was added to the reaction flask and continued to react at 35 °C for 5 h to obtain a polyamic acid solution capped with phthalonitrile.

[0032] S3. Under a nitrogen atmosphere, a mixed solution of 4.90 g of triethylamine and 5.05 g of acetic anhydride was slowly added to the reaction flask, the temperature was raised to 60 °C, and the reaction was carried out for 10 h. After the reaction was completed, the solution was precipitated in deionized water, and after filtration, washing and drying, a polyimide powder capped with phthalonitrile groups was obtained.

[0033] S4. Dissolve the phthalonitrile group-terminated polyimide powder in N,N-dimethylacetamide to prepare a polyimide solution with a solid content of 25%. Coat the polyimide solution on a glass substrate, and then perform heat cross-linking curing in a nitrogen oven. The heating program is set as 80°C & 1 h → 200°C & 1 h → 300°C & 1 h → 320°C & 2 h. After curing, a polyimide dielectric film is formed on the surface of the glass substrate. Immerse the glass substrate in deionized water to peel the polyimide dielectric film from the glass substrate, and then dry it in a vacuum oven to obtain a finished polyimide dielectric film with a thickness of about 8 μm.

[0034] Example 2:

[0035] S1. Under a nitrogen atmosphere, add 4.41 g (22.0 mmol) of 4,4'-diaminodiphenyl ether to a reaction flask, and then add it to 30 g of N,N-dimethylacetamide solution. After the diamine is completely dissolved, add 8.53 g (27.5 mmol) of 4,4'-biphenyl ether dianhydride, and supplement 21.8 g of N,N-dimethylacetamide solution to a solid content of 20%. Heat up to 35°C and react for 5 h to obtain a dianhydride-terminated polyamic acid solution.

[0036] S2. Under a nitrogen atmosphere, add 2.35 g (10.0 mmol) of 4-(4-aminophenoxy)phthalonitrile to the reaction flask. Then continue to react at 35°C for 5 h to obtain a phthalonitrile-terminated polyamic acid solution.

[0037] S3. This step is the same as S3 in Example 1.

[0038] S4. This step is the same as S4 in Example 1, and the thickness of the polyimide dielectric film is about 8 μm.

[0039] Example 3:

[0040] S1. Under a nitrogen atmosphere, add 7.93 g (24.75 mmol) of 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine to a reaction flask, and then add it to 50 g of N,N-dimethylacetamide solution. After the diamine is completely dissolved, add 12.22 g (27.5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, and supplement 30.6 g of N,N-dimethylacetamide solution to a solid content of 20%. Heat up to 35°C and react for 5 h to obtain a dianhydride-terminated polyamic acid solution.

[0041] S2. Under a nitrogen atmosphere, add 1.175 g (5.0 mmol) of 4-(4-aminophenoxy)phthalonitrile to the reaction flask. Then continue to react at 35°C for 5 h to obtain a phthalonitrile-terminated polyamic acid solution.

[0042] S3. Under a nitrogen atmosphere, a mixed solution of 4.90 g of triethylamine and 5.05 g of acetic anhydride was slowly added to the reaction flask. Then the temperature was raised to 60 °C and the reaction was carried out for 10 h. After the reaction was completed, the solution was precipitated in deionized water, and after filtration, washing and drying, a polyimide powder capped with phthalonitrile groups was obtained.

[0043] S4. The polyimide powder capped with phthalonitrile groups was dissolved in N,N-dimethylacetamide to prepare a polyimide solution with a solid content of 25%. The polyimide solution was coated on a glass substrate, and then heat cross-linking and curing were carried out in a nitrogen oven. The heating program was set as 80 °C & 1 h → 200 °C & 1 h → 300 °C & 1 h → 320 °C & 2 h. After the curing was completed, a polyimide dielectric film was formed on the surface of the glass substrate. The glass substrate was immersed in deionized water to peel the polyimide dielectric film from the glass substrate, and then it was dried in a vacuum oven to obtain a finished polyimide dielectric film with a thickness of about 8 μm.

[0044] Example 4:

[0045] S1. Under a nitrogen atmosphere, 7.05 g (22.2 mmol) of 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine was added to the reaction flask, and then it was added to 50 g of N,N-dimethylacetamide solution. After the diamine was completely dissolved, 12.22 g (27.5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added, and 22.1 g of N,N-dimethylacetamide solution was added to make the solid content 20%. The temperature was raised to 35 °C and the reaction was carried out for 5 h to obtain a polyamic acid solution capped with dianhydride.

[0046] S2. Under a nitrogen atmosphere, 2.35 g (10.0 mmol) of 4-(4-aminophenoxy)phthalonitrile was added to the reaction flask. Then the reaction was continued at 35 °C for 5 h to obtain a polyamic acid solution capped with phthalonitrile.

[0047] S3. This step is the same as S3 in Example 1.

[0048] S4. This step is the same as S4 in Example 1, and the thickness of the polyimide dielectric film is about 8 μm.

[0049] Comparative Example 1:

[0050] S1. Under a nitrogen atmosphere, 5.51 g (27.5 mmol) of 4,4'-diaminodiphenyl ether was added to a reaction flask, and then it was added to 30 g of an N,N-dimethylacetamide solution. After the diamine was completely dissolved, 8.53 g (27.5 mmol) of 4,4'-biphenylene ether dianhydride was added, and 24.5 g of N,N-dimethylacetamide solution was supplemented to make the solid content 20%. The temperature was raised to 35 °C and reacted for 5 h to obtain a polyamic acid solution capped with dianhydride.

[0051] S2. Under a nitrogen atmosphere, a mixed solution of 4.90 g of triethylamine and 5.05 g of acetic anhydride was slowly added to the reaction flask, and then the temperature was raised to 60 °C and reacted for 10 h. After the reaction was completed, the solution was precipitated in deionized water, and polyimide powder was obtained after filtration, washing, and drying.

[0052] S3. The polyimide powder was dissolved in N,N-dimethylacetamide to prepare a solution with a solid content of 25%. The polyimide solution was coated on a glass substrate, and then cross-linked and cured in a nitrogen oven. The program was set as 80 °C & 1 h → 200 °C & 1 h → 300 °C & 1 h → 320 °C & 2 h. The polyimide film was soaked in deionized water to peel it off the glass substrate, and then dried in a vacuum oven to obtain a polyimide film with a thickness of about 8 μm.

[0053] Comparative Example 2:

[0054] S1. Under a nitrogen atmosphere, 8.81 g (27.5 mmol) of 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine was added to a reaction flask, and then it was added to 50 g of an N,N-dimethylacetamide solution. After the diamine was completely dissolved, 12.22 g (27.5 mmol) of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride was added, and 24.1 g of N,N-dimethylacetamide solution was supplemented to make the solid content 20%. The temperature was raised to 35 °C and reacted for 5 h to obtain a polyamic acid solution capped with dianhydride.

[0055] S2. Under a nitrogen atmosphere, a mixed solution of 4.90 g of triethylamine and 5.05 g of acetic anhydride was slowly added to the reaction flask, and then the temperature was raised to 60 °C and reacted for 10 h. After the reaction was completed, the solution was precipitated in deionized water, and polyimide powder was obtained after filtration, washing, and drying.

[0056] S3. The polyimide powder was dissolved in N,N-dimethylacetamide to prepare a solution with a solid content of 25%. The polyimide solution was coated on a glass substrate, and then cross-linked and cured in a nitrogen oven. The program was set as 300 °C & 5 h. The polyimide film was soaked in deionized water to peel it off the glass substrate, and then dried in a vacuum oven to obtain a polyimide film with a thickness of about 8 μm.

[0057] Comparative Example 3:

[0058] S1. Under a nitrogen atmosphere, 7.93 g (24.75 mmol) of 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine was added to a reaction flask, and then it was added to 80.6 g of an N,N-dimethylacetamide solution. After the diamine was completely dissolved, 12.22 g (27.5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 1.294 g (5.5 mmol) of 4-(4-aminophenoxy)phthalonitrile were added. The temperature was raised to 35 °C and the reaction was carried out for 10 h to obtain a polyamic acid solution capped with phthalonitrile.

[0059] S2. The polyamic acid solution capped with phthalonitrile was coated on a glass substrate, and then ring closure and crosslinking were carried out in a nitrogen oven. The program was set as 80 °C & 1 h → 200 °C & 1 h → 300 °C & 1 h → 320 °C & 2 h. The polyimide film was immersed in deionized water to peel it off from the glass substrate, and then it was dried in a vacuum oven to obtain a polyimide film with a thickness of about 8 μm.

[0060] The polyimide dielectric films prepared in the above examples and comparative examples were respectively subjected to performance tests. The test results are shown in Table 1.

[0061] Table 1 Performance test data of polyimide dielectric films in each example and comparative example

[0062]

[0063] It can be seen that:

[0064] 1. The glass transition temperature (Tg) of the examples was significantly increased. The Tg of Examples 1-4 was all ≥ 300 °C (the highest was 341 °C), which was much higher than that of Comparative Example 1 (279 °C) and Comparative Example 3 (285 °C). It shows that the polyimide dielectric film of the present invention can still maintain structural integrity at high temperatures and is suitable for extreme working conditions (such as an environment of 150 °C).

[0065] 2. In terms of the comprehensive scores of the dielectric constant and dielectric loss, Examples 2 and 4 performed outstandingly.

[0066] 3. Thanks to the dense and defect-free microstructure (S4 gradient film-forming process) and three-dimensional crosslinking network (phthalonitrile thermal crosslinking), Examples 2 (753 MV / m) and 4 (748 MV / m) were close to the theoretical limit, which was more than 70% higher than that of Comparative Example 1 (435 MV / m). In terms of the energy storage density, at 25 °C, Example 4 reached 8.4 J / cm 3 , which was that of Comparative Example 1 (1.2 J / cm 3) 7 times that of; at 150 °C, Example 4 (7.2 J / cm 3 ) maintains 85% high-temperature performance, significantly superior to Comparative Example 2 (1.3 J / cm 3 ).

[0067] The above examples are only used to illustrate the present invention and do not limit the technical solutions described in the present invention. The understanding of this specification should be based on those skilled in the art. Although this specification has described the present invention in detail with reference to the above examples, those skilled in the art should understand that those skilled in the art can still modify the present invention or make equivalent substitutions, and all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a polyimide dielectric film, characterized in that: It includes the following steps: S1. Under a nitrogen atmosphere, polymerize a diamine monomer and an excessive dianhydride monomer in a polar solvent to obtain a polyamic acid solution; S2. Under a nitrogen atmosphere, add a capping agent containing a phthalonitrile group and an amino group to the polyamic acid solution, and after reaction, obtain a polyamic acid solution capped with a phthalonitrile group; S3. Under a nitrogen atmosphere, add a cyclization agent to the polyamic acid solution capped with a phthalonitrile group to generate a polyimide solution capped with a phthalonitrile group. After sedimentation, washing, and drying the polyimide solution capped with a phthalonitrile group, obtain a polyimide powder capped with a phthalonitrile group; S4. Dissolve the polyimide powder in a polar solvent, prepare a wet film on a substrate by a coating method, and perform a heat treatment on the wet film to obtain a polyimide dielectric film.

2. The method for preparing a polyimide dielectric film according to claim 1, wherein: In step S1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1 - 1.4, the molecular weight of the polyamic acid is 1000 - 10000, the solid content of the polyamic acid solution is 10 - 30%, and the viscosity range is 100 - 30000 cPs.

3. The method for preparing a polyimide dielectric film according to claim 1, characterized in that: The diamine monomer is an aromatic diamine monomer, the dianhydride monomer is an aromatic dianhydride monomer or an alicyclic dianhydride monomer, and the polar solvent is selected from at least one of N,N - dimethylacetamide, N,N - dimethylformamide, N - methyl - 2 - pyrrolidone, dimethyl sulfoxide, m - cresol, chloroform, tetrahydrofuran, γ - butyrolactone, and 3 - methyl - N,N - dimethylpropionamide.

4. The preparation method of the polyimide dielectric film according to claim 1, characterized in that: In step S2, the capping agent is selected from one or more of the following structures: Wherein, R1, R2, R3, and R4 are each independently selected from the following groups: H, F, Cl, Br, I, CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3, OCF3, OCH2CH3.

5. The method for preparing a polyimide dielectric film according to claim 1, characterized in that: In step S3, the cyclization agent includes a dehydrating agent and a catalyst. The dehydrating agent is at least one of acetic anhydride, propionic anhydride, butyric anhydride, and sodium acetate, and the catalyst is at least one of triethylamine, isoquinoline, pyridine, and N - methylpyridine.

6. The preparation method of the polyimide dielectric film according to claim 1, wherein: The molar ratio of the capping agent to the diamine monomer is 0.1 - 0.

3.

7. The method for preparing a polyimide dielectric film according to claim 1, characterized in that: The thickness of the polyimide dielectric film is 3 - 15 μm.

8. The method for preparing a polyimide dielectric film according to claim 1, characterized in that: In step S4, the heat treatment is carried out in a step - wise temperature - rising manner. The lowest treatment temperature is 50 - 100 °C, the highest treatment temperature is 300 - 450 °C, the treatment time for each temperature step is 0.5 - 3 h, and the total treatment time is 4 - 10 h.

9. The method for preparing a polyimide dielectric film according to claim 8, wherein: The step - wise temperature - rising method is operated in the following order: heat at 70 - 100 °C for 1 h, heat at 180 - 250 °C for 1 h, heat at 250 - 300 °C for 1 h, and heat at 300 - 350 °C for 2 h.

10. Use of a polyimide dielectric film prepared by the method according to claims 1-9 in an energy storage capacitor, characterized in that, The glass transition temperature Tg of the polyimide dielectric film is greater than 220 °C, and the energy storage density at 25 °C is greater than 5 J / cm 3 , and the energy storage density at 150 °C is greater than 3 J / cm 3 .

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