A semi-aromatic polyimide dielectric thin film and its preparation method

Abstract

This application relates to the field of dielectric material preparation technology, and more particularly to a semi-aromatic polyimide dielectric film and its preparation method. The preparation method of the semi-aromatic polyimide dielectric film includes the following steps: mixing an aliphatic dianhydride monomer, a rigid diamine monomer containing side ethyl groups, and a solvent to perform a copolymerization reaction to obtain a precursor solution; after forming the precursor solution into a film, performing an imidization reaction to obtain the semi-aromatic polyimide dielectric film; wherein the imidization reaction includes a first heat preservation stage, a second heat preservation stage, and a third heat preservation stage. This application improves the crosslinking density by introducing ethyl side chains into the semi-aromatic polyimide structure, and simultaneously controls the short-range ordered structure using a specific imidization process, thereby controlling the structure of the resulting dielectric film at the molecular level and significantly improving the high-temperature energy storage performance of the dielectric film.

Description

Technical Field

[0001] This application relates to the field of dielectric material preparation technology, and in particular to a semi-aromatic polyimide dielectric film and its preparation method. Background Technology

[0002] Polymer-based dielectric capacitors are crucial in industries such as aerospace, oil exploration, hybrid electric vehicles, and wind power. However, the limited heat resistance of dielectric polymers significantly restricts their use in high-temperature environments, posing a major obstacle to the development of polymer capacitors. Currently, commercially available biaxially oriented polypropylene (BOP) typically operates at temperatures not exceeding 80°C. To ensure proper use in hybrid electric vehicles, the solution lies in maintaining its excellent insulation properties through the combined operation of refrigeration equipment. Besides BOP, other commercial polymers such as polyphenylene ether (PPE), polyurethane, and polycarbonate also exhibit good dielectric properties in certain applications, but their application in high-temperature environments is limited. PPE possesses excellent electrical insulation and heat resistance, but its heat distortion temperature is generally lower than that of polyimide, limiting its long-term stability at high temperatures. While polyurethane excels in flexibility and mechanical strength, its heat resistance and dielectric constant are unsatisfactory at high temperatures, making it prone to aging and performance degradation. Furthermore, polycarbonate has lower heat resistance and a limited operating temperature range; although it performs well in some low-temperature applications, its high-temperature stability is insufficient. Therefore, these materials still face challenges in high-end applications. In contrast, polyimide, with its excellent thermal stability, chemical resistance, and outstanding dielectric properties, is an ideal material for improving the performance of polymer capacitors used in high-temperature applications.

[0003] Polyimide (PI) possesses excellent thermal stability and is considered one of the most promising materials among next-generation high-temperature, high-performance dielectric materials. Even so, PI still faces significant challenges: under high temperatures and electric fields, PI tends to form charge-transfer complexes (CTCs), which compromise its electrical insulation properties and limit its application under extreme conditions. This fundamental limitation casts doubt on the reliability and performance consistency of PI-based capacitors, especially in applications requiring stability under harsh conditions. Current methods to mitigate CTC formation, such as molecular structure modification and the introduction of large bandgap inorganic fillers, have provided some direction. However, the high-temperature energy storage performance of dielectrics obtained through these methods remains unsatisfactory. Summary of the Invention

[0004] The purpose of this application is to address the deficiencies and shortcomings of the prior art by providing a semi-aromatic polyimide dielectric film and its preparation method, wherein the semi-aromatic polyimide dielectric obtained by the preparation method has excellent high-temperature energy storage performance.

[0005] To achieve the above objectives, this application provides a method for preparing a semi-aromatic polyimide dielectric film, comprising the following steps:

[0006] An aliphatic dianhydride monomer, a rigid diamine monomer containing a side ethyl group, and a solvent are mixed and copolymerized to obtain a precursor solution.

[0007] After the precursor solution is formed into a film, an imidization reaction is carried out to obtain a semi-aromatic polyimide dielectric film. The imidization reaction includes a first heat preservation stage, a second heat preservation stage, and a third heat preservation stage. The first heat preservation stage is held at 65-75℃ for 1.8-2.2h, the second heat preservation stage is held at 185-195℃ for 1.8-4.2h, and the third heat preservation stage is held at 250-270℃ for 0.8-1.2h.

[0008] Optionally, the aliphatic dianhydride monomer includes at least one of cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and bicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride.

[0009] Optionally, the rigid diamine monomer containing a side ethyl group includes at least one of 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-methyl-6-ethylaniline), and 4,4'-diamino-3,3'-diethylbiphenylmethane.

[0010] Optionally, the molar ratio of the aliphatic dianhydride monomer and the rigid diamine monomer containing a side ethyl group is 1:0.9-1.1.

[0011] Optionally, the first heat preservation stage is to keep warm at 70℃ for 2 hours, the second heat preservation stage is to keep warm at 190℃ for 2 hours, and the third heat preservation stage is to keep warm at 250-260℃ for 1 hour.

[0012] Optionally, the heating rate during the imidization reaction is 4-6 °C / min.

[0013] Optionally, the thickness of the precursor solution liquid film obtained by film formation is 275-325 μm.

[0014] Optionally, the copolymerization reaction is carried out at room temperature for 11-13 hours.

[0015] Optionally, after the imidization reaction, the preparation method further includes a post-treatment, which includes the following steps:

[0016] The film obtained from the imidization reaction is peeled off from the substrate.

[0017] This application also provides a semi-aromatic polyimide dielectric film obtained by the preparation method described in the above technical solution.

[0018] This application provides a method for preparing a semi-aromatic polyimide dielectric film, comprising the following steps: mixing an aliphatic dianhydride monomer, a rigid diamine monomer containing a side ethyl group, and a solvent to perform a copolymerization reaction to obtain a precursor solution; after forming the precursor solution into a film, performing an imidization reaction to obtain a semi-aromatic polyimide dielectric film; wherein the imidization reaction includes a first holding stage, a second holding stage, and a third holding stage; the first holding stage is held at 65-75℃ for 1.8-2.2 h; the second holding stage is held at 185-195℃ for 1.8-4.2 h; and the third holding stage is held at 250-270℃ for 0.8-1.2 h. This application improves the crosslinking density by introducing ethyl side chains into the semi-aromatic polyimide structure, and simultaneously controls the short-range ordered structure using a specific imidization process. The specific temperature of the ethyl group and the imidization reaction are synergistically controlled to achieve appropriate crosslinking, thereby controlling the structure of the obtained dielectric film at the molecular level and significantly improving the high-temperature energy storage performance of the dielectric film. As can be seen from the embodiments of this application, the semi-aromatic polyimide dielectric obtained by the preparation method provided in this application achieves a maximum discharge energy density of 7.48 J / cm² at 200°C and an electric field strength of 610 MV / m. 3 With an energy efficiency of over 85%, and a semi-aromatic polyimide dielectric with an energy efficiency of 90%, its discharge energy density can reach 6.50 J / cm². 3 . Attached Figure Description

[0019] The above and other objects, features, and advantages of this application will be apparent from the following description of the preferred embodiments and drawings illustrating the gist of this application and its use, in which:

[0020] Figure 1 This is a schematic diagram illustrating the synthesis of dielectric thin films for Example 1 and Comparative Example 1.

[0021] Figure 2 This is a schematic diagram of the structure of the semi-aromatic polyimide dielectric film obtained in Example 1.

[0022] Figure 3 The diagram shows the area fitting results of the short-range ordered structure and amorphous region of the dielectric thin film obtained in Example 1 and Comparative Examples 2-3.

[0023] Figure 4 The graph shows the inter-chain spacing test results of the dielectric films obtained in Example 1 and Comparative Examples 1-5.

[0024] Figure 5 The graphs show the DSC test results of the dielectric thin films obtained in Example 1 and Comparative Examples 1-5.

[0025] Figure 6 The thermogravimetric analysis results of the dielectric thin films obtained in Example 1 and Comparative Examples 1-5 are shown in the figure.

[0026] Figure 7 The infrared spectra of the dielectric films obtained in Example 1 and Comparative Examples 2-3 are shown.

[0027] Figure 8 The graph shows the dielectric properties of the dielectric films obtained in Example 1 and Comparative Example 1 at different temperatures.

[0028] Figure 9 The graph shows the energy storage performance test results of the dielectric films obtained in Example 1 and Comparative Examples 1-5 at a high temperature of 200°C.

[0029] Figure 10 The graph shows the pulse discharge performance test results of the dielectric film and the biaxially oriented polypropylene film obtained in Example 1.

[0030] Figure 11 The graph shows the cycling test results of the dielectric thin film obtained in Example 1 under conditions of 200°C and 200 MV / m.

[0031] Figure 12 The graph shows the energy storage performance test results of the dielectric thin film obtained in Example 2 at a high temperature of 200°C.

[0032] Figure 13 The graph shows the energy storage performance test results of the dielectric thin film obtained in Example 3 at a high temperature of 200°C. Detailed Implementation

[0033] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0034] This invention provides a method for preparing a semi-aromatic polyimide dielectric film, comprising the following steps:

[0035] An aliphatic dianhydride monomer, a rigid diamine monomer containing a side ethyl group, and a solvent are mixed and copolymerized to obtain a precursor solution.

[0036] After the precursor solution is formed into a film, an imidization reaction is carried out to obtain a semi-aromatic polyimide dielectric film. The imidization reaction includes a first heat preservation stage, a second heat preservation stage, and a third heat preservation stage. The first heat preservation stage is held at 65-75℃ for 1.8-2.2h, the second heat preservation stage is held at 185-195℃ for 1.8-4.2h, and the third heat preservation stage is held at 250-270℃ for 0.8-1.2h.

[0037] This application first mixes an aliphatic dianhydride monomer, a rigid diamine monomer containing a side ethyl group, and a solvent to carry out a copolymerization reaction to obtain a precursor solution.

[0038] In some embodiments of this application, the aliphatic dianhydride monomer comprises at least one of cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and bicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride. The preferred species are cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, or bicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, more preferably bicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride.

[0039] In some embodiments of this application, the rigid diamine monomer containing a side ethyl group comprises at least one of 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-methyl-6-ethylaniline), and 4,4'-diamino-3,3'-diethylbiphenylmethane, preferably 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-methyl-6-ethylaniline), or 4,4'-diamino-3,3'-diethylbiphenylmethane, more preferably 4,4'-diamino-3,3'-diethylbiphenylmethane. In this application, the introduction of the side ethyl group increases the steric hindrance of the polyimide imidization ring-closing reaction, thereby increasing the possibility of intermolecular imidization and improving the final crosslinking density of the semi-aromatic polyimide dielectric, thus improving the high-temperature energy storage performance.

[0040] In some embodiments of this application, the molar ratio of the aliphatic dianhydride monomer to the rigid diamine monomer containing a side ethyl group is 1:0.9-1.1, preferably 1:1.

[0041] This application does not specifically limit the type of solvent, as long as it can dissolve the aliphatic dianhydride monomer and the rigid diamine monomer containing a side ethyl group, and allow the two to undergo a copolymerization reaction. In some embodiments of this application, the solvent includes at least one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, resorcinol, and dimethyl sulfoxide, preferably N,N-dimethylacetamide, N,N-dimethylformamide, resorcinol, or dimethyl sulfoxide, more preferably N,N-dimethylformamide, resorcinol, or dimethyl sulfoxide, and most preferably N-methylpyrrolidone or N,N-dimethylformamide. In some embodiments of this application, the ratio of the aliphatic dianhydride monomer to the solvent is 1 mmol: 4-6 mL, preferably 1 mmol: 5 mL.

[0042] In some embodiments of this application, the copolymerization reaction is carried out at room temperature for 11-13 hours, preferably 11.5-12.5 hours, and more preferably 12 hours. In some embodiments of this application, the copolymerization reaction is carried out under stirring conditions. This application does not specifically limit the atmosphere of the copolymerization reaction; the copolymerization reaction can be carried out under any atmosphere. In the embodiments of this application, the copolymerization reaction is carried out in a nitrogen atmosphere. In this application, unless otherwise specified, room temperature refers to ambient temperature, typically 15-35°C, preferably 15-30°C.

[0043] In some embodiments of this application, the aliphatic dianhydride monomer, the rigid diamine monomer containing a side ethyl group, and the solvent are mixed as follows: the rigid diamine monomer containing the side ethyl group is dissolved in a portion of the solvent, and then the aliphatic dianhydride monomer and the remaining solvent are added sequentially; the portion of the solvent is preferably half of the total solvent volume. In the polyimide reaction, dissolving the diamine first helps ensure the uniformity of the reaction, allowing the diamine and dianhydride to come into sufficient contact, thereby ensuring the smooth progress of the reaction. Furthermore, dissolving the diamine allows for better control of the reaction rate, avoiding excessively rapid reactions or the formation of byproducts. For diamines with poor solubility, dissolving them first can improve reaction efficiency and reduce side reactions between the diamine and moisture or oxygen in the air.

[0044] In this application, the aliphatic dianhydride monomer and the rigid diamine monomer containing a side ethyl group are copolymerized through a copolymerization reaction to obtain a precursor in a reaction solution. In this application, after the copolymerization reaction is completed, the resulting reaction solution (i.e., the precursor solution) does not require further treatment and can be directly used in subsequent steps.

[0045] After obtaining the prepolymer solution, this application forms a film from the prepolymer solution and then performs an imidization reaction to obtain a semi-aromatic polyimide dielectric film.

[0046] In some embodiments of this application, the method further includes degassing the precursor solution before film formation. This application does not specifically limit the degassing method, as long as it removes gas from the precursor solution. In some embodiments of this application, the degassing method is vacuum degassing; those skilled in the art can determine the specific conditions of the vacuum degassing using conventional techniques; in some embodiments of this application, the vacuum degassing pressure is 0.1 kg / cm². 2 The vacuum degassing time is 2 minutes.

[0047] This application does not impose any particular limitation on the thickness of the precursor solution liquid film obtained by film formation; those skilled in the art can adjust it according to the desired thickness of the dielectric film. In some embodiments of this application, the thickness of the precursor solution liquid film obtained by film formation is 275-325 μm, preferably 300 μm, and the thickness of the resulting semi-aromatic polyimide dielectric film is about 10 μm.

[0048] This application does not specifically limit the film-forming method; any liquid film of the desired thickness can be obtained. In the embodiments of this application, after the precursor solution is poured onto the substrate, it is coated with a doctor blade to form a film.

[0049] This application does not have any special restrictions on the material of the substrate. In the embodiments of this application, the substrate is a glass substrate.

[0050] In this application, the imidization reaction includes a first holding stage, a second holding stage, and a third holding stage. The first holding stage is held at 65-75°C for 1.8-2.2 hours, the second holding stage is held at 185-195°C for 1.8-4.2 hours, and the third holding stage is held at 250-270°C for 0.8-1.2 hours. In some embodiments of the present invention, the first holding stage is held at 70°C for 2 hours, the second holding stage is held at 190°C for 2 hours, and the third holding stage is held at 250-260°C for 1 hour. During the imidization reaction in this application, most of the solvent in the precursor solution film can be removed during the first holding stage; during the second and third holding stages, the imidization reaction and crosslinking reaction occur, while the solvent is removed, forming a short-range ordered structure. The specific programmed temperature rise process described above ensures that the obtained semi-aromatic polyimide dielectric film has a high degree of short-range ordered structure.

[0051] In the embodiments of this application, the heating rate during the imidization reaction is 4-6 °C / min, preferably 5 °C / min. In some embodiments of this application, a slower heating rate is selected. This heating rate facilitates the orderly rearrangement of molecular chains, reduces residual stress, thereby improving the thermal stability and mechanical properties of the material. It also ensures the complete imidization reaction, improving insulation and chemical resistance. Furthermore, the above heating rate can promote the elimination of byproducts, avoid internal defects, and form a uniform and dense microstructure. Heating rates higher than this may lead to stress accumulation, incomplete imidization, structural defects, and other problems, affecting the final quality of the material.

[0052] In some embodiments of this application, the preparation method further includes post-processing, which includes the following steps:

[0053] The film obtained from the imidization reaction is peeled off from the substrate.

[0054] This application does not specifically limit the peeling method, as long as the film can be peeled off completely. In an embodiment of this application, the peeling method involves immersing the substrate with the film on it in water after it has been naturally cooled to room temperature, preferably at a water temperature of 80°C. After peeling using this method, the resulting film is preferably dried. This application does not specifically limit the drying method, as long as it removes moisture. In an embodiment of this invention, the drying temperature is 100°C and the time is 24 hours.

[0055] This application also provides a semi-aromatic polyimide dielectric film obtained by the preparation method described in the above technical solution.

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Example 1

[0058] Under a nitrogen atmosphere, 0.1 mmol of 4,4'-diamino-3,3'-diethylbiphenylmethane and 0.5 mL of N-methylpyrrolidone were mixed and stirred at room temperature (25 °C) to dissolve. Then, 0.1 mmol of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride and 0.5 mL of N-methylpyrrolidone were added sequentially to obtain a mixture. The mixture was stirred and reacted at room temperature (15 °C-30 °C) for 12 h to obtain a semi-aromatic polyamic acid (PAA) prepolymer solution.

[0059] The semi-aromatic polyamic acid (PAA) precursor solution was prepared at 0.1 kg / cm². 2After degassing under vacuum pressure for 2 minutes, the solution is poured onto a glass substrate and coated with a 200 μm doctor blade. The glass substrate coated with the precursor solution film is then placed in a forced-air oven and heated to 70°C at a rate of 5°C / min and held for 2 hours. The temperature is then increased to 190°C at a rate of 5°C / min and held for 2 hours. Finally, the temperature is increased to 260°C at a rate of 5°C / min and held for 1 hour. The substrate is then allowed to cool naturally to room temperature. The substrate with the film is then immersed in water at 80°C to peel off the resulting semi-aromatic polyimide film. The film is then dried at 100°C for 24 hours to obtain a semi-aromatic polyimide dielectric film.

[0060] Example 2

[0061] The dielectric film was prepared according to the method of Example 1, except that 4,4'-diamino-3,3'-diethylbiphenylmethane was replaced with 4,4'-methylenebis(2,6-diethylaniline), and the 260°C in the imidization reaction was replaced with 250°C.

[0062] Example 3

[0063] The dielectric film was prepared according to the method of Example 1, except that 4,4'-diamino-3,3'-diethylbiphenylmethane was replaced with 4,4'-methylenebis(2-methyl-6-ethylaniline), and the 260°C in the imidization reaction was replaced with 250°C.

[0064] Comparative Example 1

[0065] The dielectric film was prepared according to the method of Example 1, except that 4,4'-diamino-3,3'-diethylbiphenylmethane was replaced with 4,4-diaminodiphenylmethane.

[0066] Comparative Example 2

[0067] The dielectric film was prepared according to the method of Example 1, except that the 260°C in the imidization reaction was replaced with 230°C.

[0068] Comparative Example 3

[0069] The dielectric thin film was prepared according to the method of Example 1, except that the 260°C in the imidization reaction was replaced with 290°C.

[0070] Comparative Example 4

[0071] The dielectric film was prepared according to the method of Example 2, except that the 260°C in the imidization reaction was replaced with 230°C.

[0072] Comparative Example 5

[0073] The dielectric film was prepared according to the method of Example 2, except that the 260°C in the imidization reaction was replaced with 290°C.

[0074] Figure 1 This diagram illustrates the synthesis of the dielectric thin film for Example 1 and Comparative Example 1. When R is ethyl, this diagram corresponds to the reaction process of Example 1; when R is hydrogen, this diagram corresponds to the reaction process of Comparative Example 1. Figure 1 It can be seen that during the second heat treatment stage at 190℃, intramolecular imidization occurs in the precursors, and during the third heat treatment stage at 260℃, imidization and ring-closing reactions occur simultaneously between the precursors (i.e., the reaction that occurred at 190℃). Figure 1 (not shown at 260°C) and crosslinking reactions (such as...) Figure 1 (The intermolecular imine reaction shown at 260℃) forms a short-range ordered structure.

[0075] Figure 2 This is a schematic diagram of the structure of the semi-aromatic polyimide dielectric film obtained in Example 1. Figure 2 As shown, in this dielectric film structure, the aggregated structure includes amorphous regions and short-range ordered structures (π-packing and ch-packing). In the amorphous regions, donor and acceptor interactions exist both intermolecularly and intramolecularly, i.e., electron complexation transfer products are present. The specific imidization reaction process in Example 1 can precisely control the ratio of amorphous regions and short-range ordered structures. The presence of ethyl groups increases the steric hindrance of the polyimide imidization ring-closing reaction, thereby increasing the possibility of intermolecular imidization and significantly increasing the crosslinking density. The short-range ordered structure and the crosslinked structure effectively synergistically optimize the high-temperature capacitance performance of the dielectric film. The short-range ordered structure can reduce electron complexation transfer products, while the crosslinked structure can maintain the stability of the polymer chain at high temperatures. The presence of the short-range ordered structure reduces intermolecular and intramolecular donor and acceptor interactions, reducing electron charge transfer through intermolecular and intramolecular connections. The crosslinked structure, through the generation of the crosslinked network, restricts the movement of the polymer chain at high temperatures, giving the polymer better heat resistance.

[0076] The dielectric thin films obtained in Example 1 and Comparative Examples 2-3 were characterized by X-ray diffraction (XRD), and the areas of short-range ordered structures (π-packing and ch-packing) and amorphous regions were fitted. The results are as follows: Figure 3 As shown. By Figure 3It can be seen that as the temperature of the third insulation stage increases, the area ratio of ch-packing and π-packing gradually decreases. This means that the temperature of the third insulation stage of the imidization reaction will cause a significant change in the aggregated state structure of the semi-aromatic polyimide. When the temperature of the third insulation stage of the imidization reaction is 290℃, the area ratio of the amorphous region increases to more than 85%, which means that the electron complex transfer product is significantly increased, which is not conducive to improving the high-temperature energy storage performance.

[0077] The inter-chain spacing of the dielectric films obtained in Example 1 and Comparative Examples 1-5 was tested by XRD, and the results are as follows: Figure 4 As shown. Figure 4 The results show that as the temperature of the third insulation stage increases, the interchain spacing gradually decreases, indicating that the interaction between chains gradually strengthens, and cross-linking may have occurred. In addition, the interchain spacing of polyimide containing side ethyl groups is smaller than that of polyimide without side ethyl groups prepared at the same temperature of the third insulation stage, indicating that the presence of side ethyl groups increases the degree of cross-linking.

[0078] The glass transition temperature and specific heat capacity of the dielectric thin films obtained in Example 1 and Comparative Examples 1-5 were tested using differential scanning calorimetry (DSC), and the results are as follows: Figure 5 As shown, comparative examples 3 and 5 do not have a glass transition region, and therefore are not shown. Figure 5 It can be seen that as the temperature of the third heat treatment stage increases, the glass transition temperature increases and the specific heat capacity decreases, indicating that the degree of crosslinking gradually increases. The polyimide containing side ethyl groups has a higher glass transition temperature than the polyimide without side ethyl groups prepared at the same temperature of the third heat treatment stage, that is, a greater degree of crosslinking. This shows that the presence of ethyl groups can improve the degree of crosslinking. The glass transition temperature of Example 1 increased by 37°C compared to Comparative Example 1, while the glass transition temperature of Comparative Example 2 increased by only 15°C compared to Comparative Example 4. When the temperature of the third heat treatment stage reaches 290°C, there is no glass transition region for either the product of Comparative Example 3 (containing side ethyl groups) or the product of Comparative Example 5 (without side ethyl groups), which also means a further enhancement of the degree of crosslinking.

[0079] Thermogravimetric analysis (TGA) was performed on the dielectric thin films obtained in Example 1 and Comparative Examples 1-5, and the results are as follows: Figure 6 As shown in the figure, the thermal decomposition temperature decreases with increasing temperature in the third holding stage, indicating a structural change and the formation of less stable intermolecular imine bonds. The decreasing temperature also indicates a deepening of cross-linking. Furthermore, the mass loss decreases with increasing temperature in the third holding stage, indicating that a cross-linking reaction has occurred. In addition, the mass loss of the dielectric film obtained in Example 1 is smaller than that in Comparative Example 1, indicating a relatively higher cross-linking density.

[0080] The infrared (FI-IR) spectra of the dielectric films obtained in Example 1 and Comparative Examples 2-3 were tested, and the results are as follows: Figure 7 As shown. At 1602cm -1 The peak at that location corresponds to the C=O stretching vibration peak of tertiary or secondary amides, and it becomes increasingly obvious with the temperature change of the third heat preservation stage, indicating the existence of cross-linking reaction.

[0081] The dielectric properties of the dielectric films obtained in Example 1 and Comparative Example 1 were tested at different temperatures, and the results are as follows: Figure 8 As shown. By Figure 8 It can be seen that from a frequency of 10 2 Hz to 10 6 The dielectric constant of the dielectric film obtained in Example 1 changed by 0.09, 0.13, and 0.22 at operating temperatures of 150°C, 200°C, and 250°C, respectively, and the dielectric loss changed by 0.04, 0.011, and 0.020 at the same operating temperatures. In Comparative Example 1, the dielectric constant of the dielectric film changed by 0.11 at 150°C, 200°C, and 250°C, and the dielectric loss changed by 0.011, 0.0040, and 0.015 at the same operating temperatures. This indicates that both dielectric films exhibit good dielectric stability with small changes, mainly due to the cross-linking reaction of the polymers, which gives both polymers good heat resistance. At a frequency of 10 Hz... 2 At a frequency of 10 Hz, the dielectric constants of the dielectric film obtained in Example 1 at 150°C, 200°C, and 250°C are 3.52, 3.58, and 3.62, respectively, while the dielectric constants of the dielectric film obtained in Comparative Example 1 at 150°C, 200°C, and 250°C are 3.34, 3.34, and 3.30, respectively; at a frequency of 10 Hz, the dielectric constants of the dielectric film obtained in Example 1 at 150°C, 200°C, and 250°C are 3.34, 3.34, and 3.30, respectively. 6 At Hz, the dielectric constants of the dielectric film obtained in Example 1 at 150°C, 200°C, and 250°C are 3.43, 3.45, and 3.40, respectively, while the dielectric constants of the dielectric film obtained in Comparative Example 1 at 150°C, 200°C, and 250°C are 3.23, 3.23, and 3.19, respectively. Therefore, at the same frequency and temperature, the dielectric constants of the dielectric film obtained in Example 1 are higher than those in Comparative Example 1. This is attributed to the superior degree of crosslinking of the dielectric film obtained in Example 1 compared to that obtained in Comparative Example 1.

[0082] The energy storage performance of the dielectric films obtained in Example 1 and Comparative Examples 1-5 at a high temperature of 200°C was tested, and the results are as follows: Figure 9 As shown. The dielectric films obtained in Comparative Example 1 and Example 1 both exhibit high energy densities of 5.72 J / cm². 3(Electric field strength is 620 MV / m, energy efficiency is 71.97%) and 7.48 J / cm 3 (Electric field strength is 680 MV / m, energy efficiency is 87.18%). Due to the presence of ethyl groups, the dielectric film obtained in Example 1 achieves an energy efficiency of 90% while maintaining a relatively high energy density of 6.50 J / cm². 3 This is because the presence of ethyl groups results in a higher crosslinking density while maintaining a certain proportion of ordered structure. This indicates that the synergistic effect of short-range ordered structure and crosslinked structure is beneficial for energy storage applications in terms of loss suppression and heat resistance. The difference in crosslinking density and microstructure leads to a significant performance gap, proving that the method of this application can effectively improve the high-temperature energy storage performance of dielectric films.

[0083] The pulse discharge performance of the dielectric film and the biaxially oriented polypropylene (BOPP) film (same thickness as in Example 1) obtained in Example 1 were tested, and the results are as follows: Figure 10 As shown. By Figure 10 It can be seen that, under pulsed discharge at 200℃ and 200MV / m, the power density of the dielectric thin film obtained in Example 1 is 0.46MW / cm². 3 The discharge time was 1.44 μs. Under pulsed discharge at 120℃ (the maximum operating temperature of BOPP) and 200 MV / m, the power density of the BOPP film was 0.12 MW / cm². 3 The discharge time was 3.01 μs. It can be seen that the power density of the dielectric film obtained in Example 1 is nearly four times that of BOPP, while the discharge time is only half that of BOPP, proving that the dielectric film obtained in Example 1 has excellent high-temperature energy storage performance.

[0084] The dielectric film obtained in Example 1 was subjected to cyclic pulse discharge at 200°C and 200 MV / m to test its cycling performance. The results are as follows: Figure 11 As shown. By Figure 11 It can be seen that the dielectric film can cycle up to 100,000 times while maintaining 90% energy efficiency, indicating that it has excellent cycle stability.

[0085] The energy storage performance of the dielectric thin films obtained in Examples 2-3 at a high temperature of 200°C was tested, and the results are as follows: Figure 12-13 As shown. By Figure 12 and 13 It can be seen that the dielectric films obtained in Examples 2-3 can all maintain a breakdown electric field of 680 MV / m, and the energy density can reach 7.24 J / cm², respectively. 3 and 7.01 J / cm 3 This demonstrates that the dielectric films obtained in Examples 2-3 also possess excellent high-temperature energy storage performance.

[0086] Although preferred embodiments of this application have been shown and described, it is conceivable that those skilled in the art can devise various modifications to this application within the spirit and scope of the appended claims.

Claims

1. A method for preparing a semi-aromatic polyimide dielectric film, comprising the following steps: An aliphatic dianhydride monomer, a rigid diamine monomer containing a side ethyl group, and a solvent are mixed and copolymerized to obtain a precursor solution. After the precursor solution is formed into a film, an imidization reaction is carried out to obtain a semi-aromatic polyimide dielectric film. The imidization reaction includes a first heat preservation stage, a second heat preservation stage, and a third heat preservation stage. The first heat preservation stage is held at 65-75℃ for 1.8-2.2h, the second heat preservation stage is held at 185-195℃ for 1.8-4.2h, and the third heat preservation stage is held at 250-270℃ for 0.8-1.2h. The aliphatic dianhydride monomers include at least one of cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and bicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride; The heating rate during the imidization reaction is 4-6 °C / min; The copolymerization reaction is carried out at room temperature for 11-13 hours.

2. The preparation method according to claim 1, characterized in that, The rigid diamine monomer containing a side ethyl group includes at least one of 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-methyl-6-ethylaniline), and 4,4'-diamino-3,3'-diethylbiphenylmethane.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the aliphatic dianhydride monomer and the rigid diamine monomer containing a side ethyl group is 1:0.9-1.

1.

4. The preparation method according to claim 1, characterized in that, The first heat preservation stage is to keep warm at 70℃ for 2 hours, the second heat preservation stage is to keep warm at 190℃ for 2 hours, and the third heat preservation stage is to keep warm at 250-260℃ for 1 hour.

5. The preparation method according to claim 1, characterized in that, The thickness of the precursor solution liquid film obtained by film formation is 275-325 μm.

6. The preparation method according to claim 1, characterized in that, After the imidization reaction, the preparation method further includes a post-processing step, which includes the following step: peeling the film obtained by the imidization reaction from the substrate.

7. The semi-aromatic polyimide dielectric film obtained by the preparation method according to any one of claims 1-6.

Images