Thin film capacitor dielectric resin film

Abstract

This invention discloses a dielectric resin film for thin-film capacitors, relating to the field of thin-film capacitor technology. The dielectric resin film of this invention comprises at least: a polyetherimide heat-resistant layer; and a modified polyvinylidene fluoride dielectric layer disposed between two polyetherimide heat-resistant layers; the polyetherimide heat-resistant layer is a blend film of polyetherimide, benzoxazine, and calcium silicate nanoparticles; and the modified polyvinylidene fluoride dielectric layer is a blend film of polyvinylidene fluoride and polymethyl methacrylate. The modified dielectric resin film for thin-film capacitors prepared by this invention combines high heat resistance, high breakdown strength, high dielectric constant, and low loss, meeting the stringent requirements of various fields such as automotive electronics, aerospace, and industrial equipment.

Description

Technical Field

[0001] This invention relates to the field of thin-film capacitor technology, and more specifically to dielectric resin films for thin-film capacitors. Background Technology

[0002] Film capacitors are electronic components used to store and release electrical energy. They are primarily made by stacking and winding polymer films together, using polymer films as the dielectric layer and metal foil as the electrodes. Due to their advantages such as fast charging speed and high power density, they are indispensable electronic components in many fields, including smart grids, green new energy technologies, and advanced weaponry. With the increasing demands for miniaturization, lightweighting, and applications in extreme environments, higher requirements are being placed on the energy storage capacity and reliability of polymer dielectrics at high temperatures. Under a constant applied electric field, when the external temperature approaches the glass transition temperature of the polymer, the leakage current inside the dielectric increases exponentially. This leakage current is converted into Joule heat, generating large conductivity losses. This not only leads to a significant reduction in charging and discharging efficiency but also a significant reduction in breakdown field strength, ultimately causing the failure or damage of electrical equipment. Therefore, polymer dielectrics used in high-temperature environments need to possess excellent dielectric properties such as high dielectric constant and low dielectric loss, as well as low conductivity loss and high breakdown field strength to ensure high charging and discharging efficiency and high discharge energy density.

[0003] Currently, high-temperature polymer dielectrics for film capacitors are mainly thermoplastic engineering plastics with high glass transition temperatures (Tg), such as polyetherimide (PEI), polyphenylene sulfide (PPS), polyester (PET), and polyetheretherketone (PEEK). Although these engineering plastics have high Tg, meeting mechanical temperature resistance requirements, their high-temperature dielectric energy storage performance is still unsatisfactory. For example, at 150°C, conductivity loss still increases significantly, leading to a significant decrease in breakdown field strength, charge / discharge efficiency, and energy storage density. Therefore, developing a novel dielectric film that simultaneously achieves high heat resistance, high breakdown strength, high dielectric constant, and low loss has become an urgent technical challenge in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a dielectric resin film for thin-film capacitors, thereby solving the following technical problems: Existing thin-film capacitors using dielectric resin films suffer from poor breakdown resistance at high temperatures, high dielectric loss, and low charge / discharge efficiency.

[0005] The objective of this invention can be achieved through the following technical solutions: The dielectric resin film of a film capacitor includes at least: Polyetherimide heat-resistant layer; A modified polyvinylidene fluoride dielectric layer is disposed between the two polyetherimide heat-resistant layers; The polyetherimide heat-resistant layer is a blend film of polyetherimide, benzoxazine and calcium silicate nanoparticles; The modified polyvinylidene fluoride dielectric layer is a blend film of polyvinylidene fluoride and polymethyl methacrylate.

[0006] As a further aspect of the present invention: the thickness of the polyetherimide heat-resistant layer is 5-15 μm, and the thickness of the modified polyvinylidene fluoride dielectric layer is 5-25 μm.

[0007] As a further aspect of the present invention, the method for preparing the modified polyvinylidene fluoride dielectric layer includes the following steps: Polyvinylidene fluoride and polymethyl methacrylate were added to N,N-dimethylformamide to obtain a blend solution; The blended solution is coated onto a glass substrate, dried, and then subjected to a first annealing and quenching to obtain a modified polyvinylidene fluoride dielectric layer.

[0008] As a further aspect of the present invention, the mass ratio of the polyvinylidene fluoride and the polymethyl methacrylate is 3-5:1-2.

[0009] As a further aspect of the present invention: the first annealing temperature is 190-220℃ and the time is 5-15min, and the quenching temperature is -5-5℃ and the time is 1-10s.

[0010] As a further aspect of the present invention, the preparation method includes the following steps: Calcium chloride dihydrate and triethylamine were added to anhydrous ethanol, followed by a mixture of hydrochloric acid solution and tetraethyl orthosilicate solution. After stirring, the mixture was centrifuged, washed, and dispersed in N,N-dimethylformamide to obtain a calcium silicate nanoparticle dispersion. Polyetherimide and benzoxazine were added to the calcium silicate nanoparticle dispersion, coated onto a glass substrate, dried, pre-cured, and then subjected to a second annealing to obtain a polyetherimide heat-resistant layer.

[0011] As a further aspect of the present invention: the mass ratio of the polyetherimide, the benzoxazine and the calcium silicate nanoparticles is 10:0.1-1:0.1-0.5.

[0012] As a further aspect of the present invention: the pre-curing program is set to 1-3 hours at 90-110℃, 1-3 hours at 140-160℃, and 1-3 hours at 190-200℃, and the second annealing temperature is 180-220℃ and the time is 10-14 hours.

[0013] The beneficial effects of this invention are: The dielectric resin film for thin-film capacitors prepared by this invention has a sandwich structure. A three-layer symmetrical structure is formed by hot-pressing a polyetherimide heat-resistant layer, a modified polyvinylidene fluoride dielectric layer, and another polyetherimide heat-resistant layer. This hot-pressing composite forms an integrated film with strong interlayer bonding, avoiding problems such as interlayer separation and warping caused by differences in thermal expansion coefficients, thus ensuring the long-term reliability of the capacitor under thermal cycling conditions. The outer polyetherimide heat-resistant layer is a blend of polyetherimide, benzoxazine, and calcium silicate nanoparticles, giving the film extremely high mechanical strength, rigidity, and thermal stability, serving as a robust support and protective layer. The middle layer is a blend of modified polyvinylidene fluoride and polymethyl methacrylate. Polyvinylidene fluoride provides a high dielectric constant, and it greatly improves the flexibility and breakdown strength of this middle layer. The dielectric resin film for thin-film capacitors prepared by this invention simultaneously achieves high heat resistance, high breakdown strength, high dielectric constant, and low loss, meeting the stringent requirements of various fields such as automotive electronics, aerospace, and industrial equipment.

[0014] In this invention, polymethyl methacrylate (PMMA) is introduced into polyvinylidene fluoride (PVDF) via a casting process. Amorphous PMMA acts as a "soft interface," filling the intergranular gaps of PVDF, resulting in a more uniform interface in the inner layer. It also improves the interaction between polymer chains. The dipole shielding network formed by the carbonyl groups in the PMMA molecular chain and the fluorine atoms in PVDF reduces the interface defect density, thereby reducing conductive loss and increasing dielectric breakdown strength. Furthermore, the introduction of PMMA significantly alters the crystallization behavior of PVDF. The addition of PMMA effectively disrupts the regularity of the PVDF molecular chains, inhibiting the formation of the high-loss ferroelectric β-phase, while promoting the formation of the non-polar γ-phase. After specific vacuum annealing and quenching processes, a microstructure dominated by the γ-phase is formed, allowing the intermediate layer to retain a high dielectric constant while significantly reducing polarization and conductivity losses. The high insulation properties of polymethyl methacrylate effectively suppress leakage loss and charge migration. At the same time, the dense layered structure constructed by the hot pressing process effectively blocks the cross-interface migration path of charge carriers, significantly optimizing the overall energy storage performance at high temperatures.

[0015] The polyetherimide itself in the heat-resistant layer prepared in this invention has a high glass transition temperature, providing a robust thermodynamic framework for the film. Further introduction of a benzoxazine crosslinking network and calcium silicate nanoparticles provides extremely high thermal stability, ensuring dimensional stability of the film during long-term high-temperature operation without softening or deformation. After curing, the benzoxazine forms a dense aromatic heterocyclic network that entangles with the polyetherimide segments, effectively limiting the migration path of charge carriers at high temperatures, thereby suppressing conductive losses. Simultaneously, the formed crosslinking network enhances mechanical strength and breakdown strength, which is beneficial for improving the high-temperature energy storage density of the dielectric material. This invention also uses triethylamine as a capping agent to surface-modify the calcium carbonate nanoparticles, enabling the positively charged calcium silicate inorganic particles to achieve sedimentation-free blending in the polymer solution and uniformly dispersed within the polyetherimide matrix, forming a synergistic heat-resistant network and improving the heat resistance of the outer layer. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: The preparation method of the polyetherimide heat-resistant layer includes the following steps: 0.312 g of tetraethyl orthosilicate was added to 40 mL of anhydrous ethanol and mixed thoroughly. Then, 2 mL of deionized water and 1 mL of hydrochloric acid were added to form a hydrochloric acid solution. The mixture was stirred until homogeneous, forming a mixed solution of hydrochloric acid solution and tetraethyl orthosilicate solution. 0.221 g of calcium chloride dihydrate was added to 60 mL of anhydrous ethanol and stirred for 20 min until completely dissolved. 4.2 mL of triethylamine was added and stirred to mix thoroughly. Then, the mixture was poured into the solution and stirred for 3 h. The solution was then centrifuged at 8000 r / min for solid-liquid separation. The solution was washed and purified with anhydrous ethanol to obtain calcium silicate nanoparticles. Finally, a calcium silicate nanoparticle dispersion with a concentration of 20 g / L was prepared using N,N-dimethylformamide as a solvent. 10g of polyetherimide powder and 0.5g of benzoxazine powder were added to the above 10mL calcium silicate nanoparticle dispersion, stirred thoroughly, coated onto a smooth and level glass substrate, and dried in an 80℃ drying oven for 12 hours. The oven temperature was then programmed to be increased to 100℃ for 2 hours, 150℃ for 2 hours, and 200℃ for 2 hours for pre-curing. Then, a second annealing was performed under vacuum at 200℃ for 12 hours to obtain a polyetherimide heat-resistant layer.

[0018] Example 2: The preparation method of the polyetherimide heat-resistant layer includes the following steps: 0.312 g of tetraethyl orthosilicate was added to 40 mL of anhydrous ethanol and mixed thoroughly. Then, 2 mL of deionized water and 1 mL of hydrochloric acid were added to form a hydrochloric acid solution. The mixture was stirred until homogeneous, forming a mixed solution of hydrochloric acid solution and tetraethyl orthosilicate solution. 0.221 g of calcium chloride dihydrate was added to 60 mL of anhydrous ethanol and stirred for 20 min until completely dissolved. 4.2 mL of triethylamine was added and stirred to mix thoroughly. Then, the mixture was poured into the solution and stirred for 3 h. The solution was then centrifuged at 8000 r / min for solid-liquid separation. The solution was washed and purified with anhydrous ethanol to obtain calcium silicate nanoparticles. Finally, a calcium silicate nanoparticle dispersion with a concentration of 20 g / L was prepared using N,N-dimethylformamide as a solvent. 10g of polyetherimide powder and 0.7g of benzoxazine powder were added to the above 20mL calcium silicate nanoparticle dispersion, stirred thoroughly, coated onto a smooth and level glass substrate, and dried in an 80℃ drying oven for 12 hours. The oven temperature was programmed to be increased to 100℃ for 2.5 hours, 150℃ for 2.5 hours, and 200℃ for 2 hours for pre-curing. Then, a second annealing was performed under vacuum at 200℃ for 12 hours to obtain a polyetherimide heat-resistant layer.

[0019] Example 3: The preparation method of the modified polyvinylidene fluoride dielectric layer includes the following steps: 10g of polyvinylidene fluoride and 3g of polymethyl methacrylate powder were dissolved in N,N-dimethylformamide and continuously magnetically stirred for 12 hours under a constant temperature water bath at 60℃ until a uniform and stable blend solution was formed. The solution was coated onto a plasma-treated glass substrate, and the wet film thickness was controlled by a precision doctor blade. The substrate was then pre-dried in a 75℃ drying oven for 2 hours, followed by a first annealing treatment in a 200℃ high-temperature oven for 10 minutes. The substrate was then rapidly immersed in a 0℃ ice-water bath for 5 seconds to achieve rapid quenching and obtain a modified polyvinylidene fluoride dielectric layer.

[0020] Example 4: The preparation method of the modified polyvinylidene fluoride dielectric layer includes the following steps: 10g of polyvinylidene fluoride and 4g of polymethyl methacrylate powder were dissolved in N,N-dimethylformamide and continuously magnetically stirred for 12 hours under a constant temperature water bath at 60℃ until a uniform and stable blend solution was formed. The solution was coated onto a plasma-treated glass substrate, and the wet film thickness was controlled by a precision doctor blade. The solution was then pre-dried in a 75℃ drying oven for 2 hours, followed by a first annealing treatment in a 200℃ high-temperature oven for 12 minutes. Subsequently, the solution was rapidly immersed in a 0℃ ice-water bath for 5 seconds to achieve rapid quenching and obtain a modified polyvinylidene fluoride dielectric layer.

[0021] Example 5: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride dielectric layer prepared in Example 3 was sandwiched between two layers of polyetherimide heat-resistant layer prepared in Example 1. The mixture was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick thin-film capacitor dielectric resin film.

[0022] Example 6: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride dielectric layer prepared in Example 3 was sandwiched between two layers of polyetherimide heat-resistant layer prepared in Example 2. The mixture was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick thin-film capacitor dielectric resin film.

[0023] Example 7: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride dielectric layer prepared in Example 4 was sandwiched between two layers of polyetherimide heat-resistant layer prepared in Example 1. The mixture was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick thin-film capacitor dielectric resin film.

[0024] Example 8: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride dielectric layer prepared in Example 4 was sandwiched between two layers of polyetherimide heat-resistant layer prepared in Example 2. The mixture was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick thin-film capacitor dielectric resin film.

[0025] Comparative Example 1: The preparation method of the polyetherimide film includes the following steps: 10.5g of polyetherimide powder was added to the solvent N,N-dimethylformamide and stirred thoroughly. The mixture was then coated onto a smooth, level glass substrate and dried in an 80°C oven for 12 hours. The oven temperature was then programmed to rise to 100°C for 2 hours, 150°C for 2 hours, and 200°C for 2 hours for pre-curing. A second annealing was then performed under vacuum at 200°C for 12 hours to obtain a polyetherimide film with a thickness of 10μm.

[0026] Comparative Example 2: The preparation method of polyvinylidene fluoride film includes the following steps: 13g of polyvinylidene fluoride powder was dissolved in N,N-dimethylformamide and continuously magnetically stirred for 12h under a constant temperature water bath at 60℃ until a uniform and stable blend solution was formed. The solution was then coated onto a plasma-treated glass substrate, and the wet film thickness was controlled by a precision doctor blade. The sample was then pre-dried in a 75℃ drying oven for 2h, and then transferred to a 200℃ high-temperature oven for a first annealing treatment of 10min. Subsequently, it was rapidly immersed in a 0℃ ice-water bath for 5s to achieve rapid quenching, resulting in a polyvinylidene fluoride film with a thickness of 15μm.

[0027] Comparative Example 3: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride film prepared in Comparative Example 2 was sandwiched between two layers of polyetherimide heat-resistant layer prepared in Example 1. The film was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick film capacitor dielectric resin film.

[0028] Comparative Example 4: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride dielectric layer prepared in Example 3 was sandwiched between two polyetherimide films prepared in Comparative Example 1. The film was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick thin-film capacitor dielectric resin film.

[0029] Comparative Example 5: The method for preparing the dielectric resin film of a thin-film capacitor includes the following steps: The modified polyvinylidene fluoride film prepared in Comparative Example 2 was sandwiched between two layers of polyetherimide film prepared in Comparative Example 1. The film was then placed in a hot press preheated to 180°C with a pressure of 1 MPa for 30 minutes to obtain a 30 μm thick film capacitor dielectric resin film.

[0030] Performance testing Dielectric property testing: The dielectric constant and dielectric loss parameters of the prepared dielectric resin film were tested using a broadband dielectric spectrometer and an impedance spectrometer (Novocontrol Concept 80). The testing environment for the dielectric resin film material was set to a high temperature of 150℃ and a frequency of 1000Hz. Before the experiment, the dielectric resin film to be tested needed to be processed. The processing included: first, cutting the dielectric resin film to be tested to a suitable size, and then depositing gold electrodes on both sides of the film using a magnetron sputtering instrument. Then, the film thickness was measured, and the area of ​​the deposited electrodes was calculated. After that, the dielectric properties of the composite dielectric material were tested using the equipment. The test results are shown in Table 1. Leakage current density test: Leakage current density is the leakage current per unit area, which is usually used to describe the insulation ability of a material. A leakage current test platform constructed using a high-voltage DC power supply (Keithley, 2290-10) and a current source meter (Keithley, 2635B) was used to test the leakage current data of the material at 150°C. Before the test, gold electrodes need to be plated on both sides of the dielectric resin film to be tested, and the electrode area needs to be calculated to facilitate the subsequent calculation of leakage current density; the test results are shown in Table 1. DC Breakdown Performance Test: The breakdown performance of dielectrics is one of the important indicators for measuring their insulation performance. A high-voltage power supply manufactured by Bohr High Voltage Engineering Co., Ltd. was used to conduct the DC breakdown performance test of the dielectric thin film. First, a layer of gold electrodes needs to be deposited on both sides of the dielectric resin film to be tested using a magnetron sputtering instrument. To ensure the reliability and accuracy of the test, at least 12 dielectric resin films were prepared for each group to be tested. Before the test, the specific thickness of the dielectric resin film to be tested was measured and recorded using high-precision equipment. The breakdown test was then conducted on the dielectric resin film by increasing the voltage at 150°C until the film broke down, and the data was recorded. At least 12 sets of effective breakdown strength data were required for each group of dielectric resin films. The test results are shown in Table 1. Charge-discharge cycle testing: Cyclic reliability is crucial for the application range of capacitors and is one of the important indicators of capacitor stability. The cycle life of dielectric resin films was tested using the PolyK Technologies PK-HVP20 ferroelectric testing module under conditions of 150℃ and 200MV / m electric field strength. Gold electrodes were deposited on both sides of the dielectric film under test before testing. The test results are shown in Table 1. Table 1: Statistical Table of Performance Test Data of Dielectric Resin Films in Examples 5-8 and Comparative Examples 3-5

[0031] As shown in Table 1, the dielectric resin film of the thin-film capacitor prepared by this invention exhibits excellent performance with low dielectric loss, high breakdown strength, and ultra-long cycle life at a high temperature of 150℃. In Comparative Example 3, the middle layer is a pure polyvinylidene fluoride film, resulting in a dielectric resin film with high dielectric loss. At high temperatures, polarization loss and conductivity loss are significantly superimposed. In Comparative Example 4, the outer layer is a pure polyetherimide film, resulting in a dielectric resin film with reduced dielectric loss. However, at high temperatures, the outer layer is prone to softening, leading to a decrease in interlayer bonding and an accelerated performance degradation rate. In Comparative Example 5, the dielectric resin film is a stack formed by pure polyvinylidene fluoride film and pure polyetherimide film, resulting in high dielectric loss, low breakdown strength, and short cycle life at high temperatures.

[0032] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A thin-film capacitor dielectric resin film, characterized in that, At least including: Polyetherimide heat-resistant layer; A modified polyvinylidene fluoride dielectric layer is disposed between the two polyetherimide heat-resistant layers; The polyetherimide heat-resistant layer is a blend film of polyetherimide, benzoxazine and calcium silicate nanoparticles; The modified polyvinylidene fluoride dielectric layer is a blend film of polyvinylidene fluoride and polymethyl methacrylate.

2. The dielectric resin film of the thin-film capacitor according to claim 1, characterized in that, The thickness of the polyetherimide heat-resistant layer is 5-15 μm, and the thickness of the modified polyvinylidene fluoride dielectric layer is 5-25 μm.

3. The dielectric resin film of the thin-film capacitor according to claim 1, characterized in that, The preparation method of the modified polyvinylidene fluoride dielectric layer includes the following steps: Polyvinylidene fluoride and polymethyl methacrylate were added to N,N-dimethylformamide to obtain a blend solution; The blended solution is coated onto a glass substrate, dried, and then subjected to a first annealing and quenching to obtain a modified polyvinylidene fluoride dielectric layer.

4. The dielectric resin film for a thin-film capacitor according to claim 3, characterized in that, The mass ratio of the polyvinylidene fluoride to the polymethyl methacrylate is 3-5:1-2.

5. The dielectric resin film for a thin-film capacitor according to claim 3, characterized in that, The first annealing temperature is 190-220℃ and the time is 5-15 min, and the quenching temperature is -5-5℃ and the time is 1-10 s.

6. The dielectric resin film of the thin-film capacitor according to claim 1, characterized in that, The preparation method includes the following steps: Calcium chloride dihydrate and triethylamine were added to anhydrous ethanol, followed by a mixture of hydrochloric acid solution and tetraethyl orthosilicate solution. After stirring, the mixture was centrifuged, washed, and dispersed in N,N-dimethylformamide to obtain a calcium silicate nanoparticle dispersion. Polyetherimide and benzoxazine were added to the calcium silicate nanoparticle dispersion, coated onto a glass substrate, dried, pre-cured, and then subjected to a second annealing to obtain a polyetherimide heat-resistant layer.

7. The dielectric resin film for a thin-film capacitor according to claim 6, characterized in that, The mass ratio of the polyetherimide, the benzoxazine, and the calcium silicate nanoparticles is 10:0.1-1:0.1-0.

5.

8. The dielectric resin film for a thin-film capacitor according to claim 6, characterized in that, The pre-curing process is set at 90-110℃ for 1-3 hours, 140-160℃ for 1-3 hours, and 190-200℃ for 1-3 hours. The second annealing temperature is 180-220℃ and the time is 10-14 hours.

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