Sequentially arranged polyimide copolymer for capacitor and preparation method and application thereof

Abstract

The invention discloses a sequentially arranged polyimide copolymer for a capacitor as well as a preparation method and application of the sequentially arranged polyimide copolymer. The preparation method of the polyimide copolymer comprises the following steps: under a stirring condition, dropwise adding a 4, 4 '-diphenyl ether dianhydride solution into a diamine monomer (one of 2, 2-bis (4-aminophenyl) propane, p-phenylenediamine and 4, 4'-(1, 4-phenylene diisopropylidene) diphenylamine) solution, and stirring to react; the molar ratio of the 4, 4 '-diphenyl ether dianhydride to the diamine monomer is 1: 2; adding hexafluorodianhydride into the obtained solution, and stirring for reaction; and drying the obtained solution, evaporating the solvent, performing high-temperature treatment, and cooling to obtain the sequentially arranged polyimide copolymer for the capacitor. The polyimide copolymer has high glass transition temperature, high breakdown strength and high energy storage density, still has high charge-discharge efficiency and low leakage current density at high temperature, and effectively improves the high-temperature performance of a capacitor.

Description

Technical Field

[0001] The invention relates to the technical field of high energy storage density organic dielectric film materials and capacitors, and in particular to a sequentially arranged polyimide copolymer for capacitors, a preparation method and application thereof. Background Art

[0002] Dielectric film capacitors have been widely used in power electronic systems such as electric vehicles, grid-connected photovoltaic power generation and oil exploration due to their advantages such as fast charge and discharge rates and high power density. Compared with inorganic ceramic materials, polymer dielectrics have become the preferred material for film capacitors due to their low cost, easy processing and high reliability. In recent years, with the increasing maturity of third-generation semiconductor technology, power electronic equipment is developing towards high power and high integration. However, the high temperature conditions brought about by high integration and high power density put forward higher requirements on the heat resistance of film capacitors. At present, the safe operating temperature of commercial biaxially oriented polypropylene film (BOPP) is limited to 105 ℃, and when the temperature gradually rises to 120 ℃ or above, the conductivity loss and accumulated heat of BOPP show an exponential upward trend, resulting in a sharp drop in charge and discharge efficiency, significantly increasing the failure probability of film capacitors, and thus seriously threatening the stability and safety of the entire power electronic system. To this end, researchers are actively exploring and developing film materials for film capacitors suitable for high temperature environments to solve the problem of poor performance of commercial BOPP dielectrics under high temperature conditions. Pure polymer materials can avoid the problems of filler dispersion and interfacial bonding, and show great potential in the large-scale production of high-performance polymer dielectrics. In order to improve the heat resistance of pure polymer film materials, researchers have adopted the strategy of designing highly conjugated structures. However, the insulation properties and thermal stability of materials are often mutually exclusive. To resolve this contradiction, a series of cycloolefin polymers with non-conjugated structures and non-planar structures have been reported. However, in the face of extreme temperatures (>200 °C), cycloolefin polymer film materials obtain high discharge energy density at the expense of charge and discharge efficiency, which means that they cannot meet the energy storage density requirements of film capacitors under extreme working conditions. Therefore, the development of pure polymer-based dielectric materials that have both heat resistance and high energy storage performance remains a key research direction in this field.

[0003] In summary, the development of a new high-temperature resistant, high energy storage density pure polymer dielectric material is of great significance for improving the performance of polymer film capacitors and meeting the requirements of practical engineering applications. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a sequentially arranged polyimide copolymer for capacitors and a preparation method and application thereof.

[0005] The technical solution adopted by the present invention is as follows.

[0006] A polyimide copolymer arranged in sequence for capacitors, having the following structural formula:

[0007] Among them, X is selected from , , One of them. Corresponding to polymer co-PI ABAC 、co-PI A’BA’C and co-PI A”BA”C .

[0008] The invention is based on the design principle of balancing the thermal stability and electrical insulation of the material. The capacitor uses a polyimide copolymer arranged in sequence, which is obtained by reacting diamine monomers (one of 2,2-bis(4-aminophenyl)propane (referred to as diamine A), p-phenylenediamine (referred to as diamine A'), 4,4'-(1,4-phenylenediisopropyl)diphenylamine (referred to as diamine A"), 4,4'-biphenyl ether dianhydride (referred to as dianhydride B) and hexafluorodianhydride (referred to as dianhydride C).

[0009] The method for preparing the above-mentioned sequentially arranged polyimide copolymer for capacitor comprises the following steps: (1) under stirring conditions, adding a 4,4'-biphenyl ether dianhydride solution dropwise to a diamine monomer solution and stirring for reaction; the diamine monomer is one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine (referred to as diamine A'), and 4,4'-(1,4-phenylene diisopropylidene) diphenylamine, and the molar ratio of 4,4'-biphenyl ether dianhydride to the diamine monomer is 1:2; (2) adding hexafluorodianhydride to the solution obtained in step (1) and stirring to react; (3) The solution obtained in step (2) is dried to evaporate the solvent, subjected to high temperature treatment, and cooled to obtain a sequentially arranged polyimide copolymer for capacitors.

[0010] The preparation method of the sequentially arranged polyimide copolymer for capacitors of the present invention comprises prepolymerizing diamine and different dianhydrides in sequence, followed by imidization reaction and high-temperature treatment, placing in cold water to remove the film and drying the moisture, thus obtaining the corresponding sequentially arranged polyimide copolymer for capacitors.

[0011] Preferably, the solvent of the 4,4'-biphenyl ether dianhydride solution in step (1) is N-methylpyrrolidone (NMP) with a concentration of 0.025-0.25 M; Preferably, the solvent of the diamine monomer solution in step (1) is N-methylpyrrolidone, and the concentration is 0.05-0.5M.

[0012] Preferably, the stirring reaction in step (1) is carried out at room temperature (25-28° C.) and for 1-3 h.

[0013] Preferably, in step (2), the molar ratio of hexafluorodianhydride to diamine monomer is (0.5-1.5):2.

[0014] More preferably, the molar ratio of hexafluorodianhydride to diamine monomer is 1:2.

[0015] Preferably, the stirring reaction in step (2) is carried out at room temperature (25-28° C.) and for 1-3 h.

[0016] Preferably, the hexafluorodianhydride in step (2) is added in 2-3 portions; Preferably, the drying temperature in step (3) is 80-90° C. and the drying time is 12-16 h.

[0017] Preferably, the high temperature treatment in step (3) is: 150-160°C for 1-2h, 200-210°C for 1-2h, and 250-260°C for 1-2h.

[0018] Preferably, the solution is poured onto a glass plate before drying in step (3); Preferably, in step (3), after cooling, the mixture is immersed in cold water to release the polyimide copolymer, and then dried.

[0019] More preferably, the drying temperature is 80-90° C. and the drying time is 12-16 h.

[0020] The above-mentioned capacitor sequentially arranged polyimide copolymer is used in the preparation of high temperature capacitors.

[0021] The sequentially arranged polyimide copolymer for capacitors of the present invention is mainly obtained by imidization reaction of diamine monomers (one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, and 4,4'-(1,4-phenylenediisopropyl)diphenylamine), 4,4'-biphenyl ether dianhydride, and hexafluorodianhydride. The sequential arrangement effect of polymer units is achieved by controlling the molar ratio of two different dianhydride monomers and the order of reaction. On the one hand, the ether bond in the dianhydride monomer 4,4'-biphenyl ether dianhydride can improve the polymer E g , thereby ensuring the electrical insulation performance of the material. At the same time, in order to balance the sacrifice brought by the flexible ether bond T gThe cost of introducing the trifluoromethyl-containing dianhydride monomer hexafluorodianhydride is reduced. By arranging the two different polymer units in sequence, the contradiction between the heat resistance and electrical insulation properties of the material is alleviated. The sequentially arranged polyimide copolymer for the capacitor of the present invention has both excellent heat resistance and excellent high energy storage density, providing strategies and directions for the design of polymer film capacitor materials for extreme working conditions. At the same time, the preparation process has extremely high operability, the raw materials are easily available, and it is suitable for industrial application. The material of the present invention can be used as a dielectric material for film capacitors for normal temperature and high temperature.

[0022] Compared with the prior art, the advantages and beneficial effects of the present invention are: (1) The present invention utilizes commercially available diamine and dianhydride monomers to undergo imidization reaction to obtain a polyimide copolymer, which can adapt to high temperature environments of 200°C and above and work stably, meeting the requirements of practical engineering applications for film capacitors.

[0023] (2) The sequentially arranged polyimide copolymer for capacitors of the present invention optimizes the heat resistance and electrical insulation properties of the material by sequentially arranging two different polyimide derivative units, thus breaking through the contradiction between the two properties being mutually exclusive during material design, and obtaining a high glass transition temperature, high breakdown strength and high energy storage density. The process operability is strong, the raw materials are readily available, and the material is suitable for large-scale process applications.

[0024] (3) The present invention optimizes the selection of monomers and uses a specific controllable polymerization technology to achieve the addition of target units one by one in a predetermined order, thereby formulating a polyimide copolymer (ABAC type) with a clear sequence structure. The sequential arrangement of two different units can avoid the long-distance conjugated structure formed by the introduction of flexible ether bonds, inhibit the formation of long-distance charge transfer complexes, hinder the migration of carriers, and enable the material to maintain a low leakage current density at high temperature and strong field.

[0025] (4) The polyimide copolymer arranged sequentially for capacitors of the present invention has a maximum charge-discharge density of up to 5.53 J cm at 200 °C with a charge-discharge efficiency of >90%. -3 , breakdown strength up to 563 MV m -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the preparation process of the sequentially arranged polyimide copolymer dielectric film material for the capacitor according to Example 1 of the present invention.

[0027] Figure 2 The figure shows the thermal properties test results of 8 different PI-based polymer dielectric film materials.

[0028] Figure 3The figure shows the dielectric properties test results of 8 different PI-based polymer dielectric film materials at 200 ℃.

[0029] Figure 4 The figure shows the energy storage performance test results of 8 different PI-based polymer dielectric film materials at 200 ℃.

[0030] Figure 5 The figure shows the breakdown test results of 8 different PI-based polymer dielectric film materials at 200 ℃.

[0031] Figure 6 The figure shows the leakage current test results of 8 different PI-based polymer dielectric film materials at 200 ℃. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further explained below in conjunction with specific embodiments and drawings.

[0033] Example 1 A sequentially arranged polyimide copolymer dielectric film material for capacitors, denoted as co-PI ABAC , and its preparation method comprises the following steps (preparation process as shown in Figure 1 shown): (1) Dissolve 0.1129 g of diamine A (2,2-bis(4-aminophenyl)propane, 0.50 mmol) in 5 mL of NMP solution and stir at room temperature; (2) While stirring the solution prepared in step 1, add dropwise 5 mL of NMP solution containing 0.0774 g of dianhydride B (4,4'-biphenyl ether dianhydride, 0.25 mmol), and continue stirring at room temperature for 3 h. (3) Add 0.1098 g of dianhydride C (hexafluorodianhydride, 0.25 mmol) powder to the above solution in 2-3 portions and continue stirring at room temperature for 2 h; (4) The mixed solution was poured onto a 50 mm × 50 mm glass plate and placed at 80 °C for 12 h to evaporate the NMP solvent. (5) Transferring the glass plate to a heating box for high temperature treatment. The high temperature conditions are: 150 °C for 1 h, 200 °C for 1 h, and 250 °C for 1 h. (6) Cooling the glass plate after the reaction is completed to room temperature and immersing it in cold water to separate the copolymer dielectric film from the glass plate; (7) Place the film separated from the glass plate in a heating oven at 80 °C for 12 h to dry out excess moisture.

[0034] The sequentially arranged copolymer dielectric film material prepared above has a thickness of 8-10 μm, and a length and width of 50 mm.

[0035] Example 2 A sequentially arranged polyimide copolymer dielectric film material for a capacitor, the preparation method of which comprises the following steps: Dissolve 0.0671 g of p-phenylenediamine (referred to as diamine A') in 5 mL of NMP solution. After the powder is completely dissolved, add 0.0963 g of 4,4'-biphenyl ether dianhydride (the molar ratio of diamine to dianhydride is 2:1) dissolved in 5 mL of NMP solution. Stir at room temperature for 3 h, then add 0.1366 g of hexafluorodianhydride (0.31 mmol) powder to the above solution in 2-3 portions, and continue stirring for 2 h. The subsequent steps are consistent with steps (4) to (7) of Example 1, and are referred to as co-PI A‘BA’C .

[0036] Example 3 A sequentially arranged polyimide copolymer dielectric film material for a capacitor, the preparation method of which comprises the following steps: 0.1436 g of 4,4'-(1,4-phenylenediisopropyl)diphenylamine (referred to as diamine A") was dissolved in 5 mL of NMP solution. After the powder was completely dissolved, 5 mL of NMP solution containing 0.0646 g of 4,4'-biphenyl ether dianhydride (the molar ratio of diamine to dianhydride was 2:1) was added to the solution. After stirring at room temperature for 3 h, 0.0918 g of hexafluorodianhydride (0.21 mmol) powder was added to the above solution in 2-3 portions, and stirring was continued for 2 h. The subsequent steps were consistent with steps (4) to (7) of Example 1, and were referred to as co-PI A”BA”C .

[0037] Comparative Example 1 A conventional PI-based polymer dielectric film material, the preparation method of which comprises the following steps: 0.1436 g of 4,4'-diaminodiphenyl ether was dissolved in 10 mL of NMP solution. After the powder was completely dissolved, 0.1564 g of pyromellitic anhydride (the molar ratio of the two was 1:1) was added to the solution and stirred at room temperature for 4 h. The subsequent steps were consistent with steps (4) to (7) of Example 1 and were recorded as regular PI.

[0038] Comparative Example 2 A PI-based polymer dielectric film material, the preparation method of which comprises the following steps: Dissolve 0.1265 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1735 g of 4,4'-biphenyl ether dianhydride (the molar ratio of the two is 1:1) to the solution and stir at room temperature for 4 h. The subsequent steps are consistent with steps (4) to (7) of Example 1, and are recorded as PI AB .

[0039] Comparative Example 3 A PI-based polymer dielectric film material, the preparation method of which comprises the following steps: Dissolve 0.1019 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1981 g of hexafluorodianhydride (molar ratio of 1:1) to the solution and stir at room temperature for 4 h. The subsequent steps are consistent with steps (4) to (7) of Example 1, denoted as PI AC .

[0040] Comparative Example 4 A PI-based polymer dielectric film material, the preparation method of which comprises the following steps: Dissolve 0.1507 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1493 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (the molar ratio of the two is 1:1) to the solution and stir at room temperature for 4 h. The subsequent steps are consistent with steps (4) to (7) of Example 1, and are denoted as PI AD .

[0041] Comparative Example 5 A random copolymerization PI-based polymer dielectric film material, the preparation method of which comprises the following steps: Dissolve 0.1129 g of 2,2-bis(4-aminophenyl)propane in 5 mL of NMP solvent. Dissolve 0.0774 g of 4,4'-biphenyl ether dianhydride and 0.1098 g of hexafluorodianhydride in 5 mL of NMP solvent. After both are completely dissolved, add the dianhydride NMP solution to the diamine solution and stir at room temperature for 4 h. The subsequent steps are consistent with steps (4) to (7) of Example 1, recorded as r-co-PI.

[0042] Performance Testing (1) The differential scanning calorimetry (DSC) results of the film samples prepared in Examples 1-3 and Comparative Examples 1-5 are as follows: Figure 2 As shown, it reflects the thermal properties of the sample. Figure 2 It can be seen that co-PI ABACThe ether-containing unit B (4,4'-biphenyl ether dianhydride) was introduced to ensure the thermal properties of the sample. At the same time, the two trifluoromethyl groups in unit C (hexafluorodianhydride) reduced the free volume of atomic movement between units, restricted the free movement of molecules, and thus increased the glass transition temperature of the material. T g Among them, co-PI ABAC The samples are better than other comparison ratios such as regular PI, and the ordered polymer T g (363 ℃) also has a relatively disordered polymer r-co-PI T g (335℃) high.

[0043] (2) The energy storage performance of the film sample is related to its dielectric constant and dielectric loss. The dielectric properties of the film samples prepared in Examples 1-3 and Comparative Examples 1-5 at 200°C are as follows: Figure 3 As shown. Since polar groups are introduced into units A, B, and C, co-PI ABAC The dielectric constant of the 200°C and 10°C 2 ~10 6 The frequency range is basically maintained at 10 -3 In addition, co-PI A’BA’C and co-PI A”BA”C Different types of polar groups are introduced, so the dielectric constant is significantly improved compared with non-copolymers. However, due to the small or large number of polar groups on the benzene rings of units A' and A", the dipole loss of the polymer increases. A’BA’C and co-PI A”BA”C Dielectric loss is higher than co-PI ABAC The level is high.

[0044] (3) The energy storage performance of the film sample at 200 °C is as follows: Figure 4 As shown. Among them, co-PI ABAC 、co-PI A’BA’C and co-PI A”BA”C At high temperature of 200 ℃, the maximum discharge energy density with charge and discharge efficiency ≥ 90% U d90 5.53, 4.9 and 4.5 J•cm respectively -3 , which is more consistent with the non-copolymer and disordered copolymer U d90 There is a significant improvement, indicating that the sequence combination and order of polymer units have an impact on the energy storage performance of the material. The results show that ABAC is the best sequence combination, followed by A'BA'C and A"BA"C.

[0045] (4) Weibull breakdown of the film sample at 200 °C is as follows: Figure 5 As shown in Figure 2, Weibull breakdown strength is an important indicator for measuring the electrical insulation performance of samples. The order of the copolymer effectively improves the Weibull breakdown strength of the material. ABAC The Weibull breakdown strength of the steel was improved most significantly, reaching 563 MV m -1 ,co-PI A’BA’C and co-PI A”BA”C Next is the Weibull breakdown strength of 548 MV m -1 and 539 MV m -1 .

[0046] (5) The leakage current test results of the film sample at 200°C are as follows: Figure 6 As shown, it reflects the insulation performance and electrical stability of the material. At 200 °C, due to the synergistic effect of the ether bond and the polar group trifluoromethyl in the unit fragment, the structural stability of the material at high temperature is guaranteed, while the electron migration excited by thermal and electric field coupling is suppressed. Therefore, the corresponding co-PI ABAC The leakage current level is the lowest, for example 250 MV m -1 , 200 ℃, co-PI ABAC The current density is 10 -4 Order of magnitude.

[0047] At the same time, the electron jumping distance in the material is calculated by fitting the jumping conduction model. d The smaller the jump distance, the deeper the trap depth, which means the better the effect of suppressing charge transfer. ABAC The jump distance calculated by fitting is the shortest (d=0.73 nm), and co-PI A’BA’C and co-PI A”BA”C It is also shorter than the jumping distances obtained by fitting non-copolymers and disordered copolymers, which are 1.19 and 1.20 nm, respectively.

Claims

1. A polyimide copolymer arranged in sequence for capacitors, characterized in that: The structural formula is as follows: Among them, X is selected from , , One of them.

2. The method for preparing the sequentially arranged polyimide copolymer for capacitors according to claim 1, characterized in that: The following steps are involved: (1) under stirring conditions, adding a 4,4'-biphenyl ether dianhydride solution dropwise to a diamine monomer solution and stirring for reaction; the diamine monomer is one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, and 4,4'-(1,4-phenylene diisopropylidene) diphenylamine, and the molar ratio of 4,4'-biphenyl ether dianhydride to the diamine monomer is 1:2; (2) adding hexafluorodianhydride to the solution obtained in step (1) and stirring to react; (3) The solution obtained in step (2) is dried to evaporate the solvent, treated at high temperature, and cooled to obtain a sequentially arranged polyimide copolymer for capacitors.

3. The preparation method according to claim 2, characterized in that: In step (1), the solvent of the 4,4'-biphenyl ether dianhydride solution is N-methylpyrrolidone, and the concentration is 0.025-0.25M; The solvent of the diamine monomer solution in step (1) is N-methylpyrrolidone, and the concentration is 0.05-0.5M.

4. The preparation method according to claim 2, characterized in that: The stirring reaction temperature in step (1) is room temperature and the time is 1-3 hours.

5. The preparation method according to claim 2, characterized in that: In step (2), the molar ratio of hexafluorodianhydride to diamine monomer is (0.5-1.5):

2.

6. The preparation method according to claim 2, characterized in that: The stirring reaction in step (2) is carried out at room temperature for 1-3 hours.

7. The preparation method according to claim 2, characterized in that: The hexafluorodianhydride in step (2) is added in 2-3 portions; The drying temperature in step (3) is 80-90°C and the drying time is 12-16 h.

8. The preparation method according to claim 2, characterized in that: In step (3), the high temperature treatment is as follows: 150-160°C for 1-2h, 200-210°C for 1-2h, and 250-260°C for 1-2h.

9. The preparation method according to claim 2, characterized in that: In step (3), the solution is poured onto a glass plate before drying; After cooling in step (3), the polyimide copolymer is separated by immersion in cold water, and then dried.

10. Use of the sequentially arranged polyimide copolymer for capacitors according to claim 1 in the preparation of high temperature capacitors.

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