Polyimide-based composite dielectric film material and preparation method thereof

Abstract

The invention relates to the field of dielectric energy storage materials, and discloses a polyimide-based composite dielectric film material and a preparation method thereof.The dielectric film is prepared from, by mass, 4-20 parts of modified barium strontium titanate and 100 parts of fluorinated polyamide acid solution, the modified barium strontium titanate is prepared from the following raw materials: hydroxylated barium strontium titanate, 3-glycidyl ether oxypropyl trimethoxy silane, perfluoropolyether alcohol and a catalyst, and the fluorinated polyamide acid solution is prepared from the following raw materials: a fluorine-containing diamine monomer and a fluorine-containing dianhydride monomer; according to the technical scheme, the polyimide film dielectric film is prepared from fluorinated polyamide and modified silane barium strontium titanate, the dispersity of barium strontium titanate in a polyimide matrix is remarkably improved, the compatibility of barium strontium titanate and fluorinated polyimide is remarkably improved, and the dielectric energy storage performance of the dielectric film is remarkably improved; the hydroxylated barium strontium titanate is modified through the 3-glycidyl ether oxypropyl trimethoxy silane and the perfluoropolyether alcohol, so that the dielectric loss of the dielectric film is remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of dielectric energy storage materials, and in particular to a polyimide-based composite dielectric thin film material and its preparation method. Background Technology

[0002] Film capacitors are an important basic electronic component. Compared to ceramic capacitors and aluminum / tantalum capacitors, film capacitors have superior characteristics such as high insulation resistance, high withstand voltage, low dielectric loss, excellent frequency characteristics, and self-healing properties. Currently, the most commonly used film dielectric in film capacitors is BOPP, which has a relative permittivity of only 2-3 and an energy density of less than 2 J / cm³. 3 Furthermore, its temperature resistance is around 105 ℃. Under high temperature and high electric field conditions, it has high conductivity loss, is prone to overheating, and is susceptible to thermal runaway. However, fields such as renewable energy grid connection, new energy vehicles, underground oil and gas extraction, and advanced electromagnetic energy equipment require film capacitors to operate stably under high temperature conditions of 150~250 ℃. Therefore, the development of high temperature resistant film capacitor materials is imperative.

[0003] Polyimide (PI) is an aromatic heterocyclic polymer compound with imide chain segments in its molecular structure. It has a high glass transition temperature (Tg>250℃) and excellent thermal stability, making it one of the most promising polymer dielectric materials for high-temperature capacitors. However, pure polyimide materials have a low relative dielectric constant and low energy storage density at high temperatures, which greatly limits their application in high-temperature dielectric energy storage. Therefore, to improve the dielectric energy storage performance of polyimide materials, existing technologies have proposed adding dielectric ceramics to polyimide films. For example, the preparation method of a thick film of barium strontium titanate / polyimide dielectric tunable composite material disclosed in publication CN100516140A involves adding barium strontium titanate to polyimide and then casting it into a dielectric film. This technique allows for the control of the dielectric properties of the dielectric film through film thickness.

[0004] This invention, through in-depth research on the aforementioned technical solution of adding barium strontium titanate to polyimide, reveals that the content of barium strontium titanate in polyimide has a significant impact on the performance of polyimide dielectric films. Excessive addition of barium strontium titanate nanoparticles leads to a significant reduction in the toughness and processability of the polyimide dielectric film, while insufficient addition results in only a minor improvement in the dielectric energy storage performance. Consequently, the barium strontium titanate / polyimide dielectric film cannot simultaneously possess both excellent processability and high dielectric energy storage performance. Therefore, providing a barium strontium titanate / polyimide dielectric film that combines excellent processability and high dielectric energy storage performance is of great significance. Summary of the Invention

[0005] The objective of this invention is to provide a polyimide thin-film dielectric film with low dielectric loss.

[0006] This invention prepares polyimide dielectric films by using fluorinated polyamide and modified barium strontium titanate silane, which significantly improves the dispersibility of barium strontium titanate in the polyimide matrix, significantly increases the compatibility of barium strontium titanate with fluorinated polyimide, and significantly improves the dielectric energy storage performance of the dielectric film.

[0007] This invention modifies hydroxylated barium strontium titanate with 3-glycidyl etheroxypropyltrimethoxysilane and perfluoropolyether alcohol, which significantly reduces the dielectric loss of the dielectric film.

[0008] The specific technical solution of this invention is as follows: A polyimide-based composite dielectric film material comprises, by mass ratio: a modified barium strontium titanate and a fluorinated polyamic acid solution in a ratio of 4 to 20:100. The modified barium strontium titanate comprises: hydroxylated barium strontium titanate, 3-glycidyl etheroxypropyltrimethoxysilane, perfluoropolyether alcohol, and a catalyst. The fluorinated polyamic acid solution comprises: a fluorinated diamine monomer and a fluorinated dianhydride monomer.

[0009] Preferably, the fluorinated diamine monomer is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB).

[0010] As a preferred option, the fluorinated dianhydride monomer is 4,4′-(hexafluoroisopropene) phthalic anhydride (6FDA).

[0011] Preferably, the catalyst is 4-dimethylaminopyridine.

[0012] Preferably, the particle size of hydroxylated barium strontium titanate is 30~200 nm.

[0013] A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) A fluorinated polyamic acid solution is prepared by reacting a fluorinated diamine monomer and a fluorinated dianhydride monomer; (2) 3-glycidyl etheroxypropyltrimethoxysilane and hydroxylated barium strontium titanate were reacted to prepare barium strontium titanate epoxide; (3) Modified barium strontium titanate is prepared by reacting perfluorinated polyether alcohol, catalyst and barium strontium titanate epoxide; (4) Add modified barium strontium titanate to a fluorinated polyamic acid solution, mix evenly, and cast into a film. The film is then subjected to imidization treatment to produce a polyimide-based composite dielectric film.

[0014] Preferably, the reaction conditions in step (1) include: temperature 60~80 ℃ and time 2~5 h.

[0015] Preferably, the reaction conditions in step (2) include: temperature 20~80 ℃ and time 8~24 h.

[0016] Preferably, the reaction conditions in step (3) include: temperature 90~110 ℃ and time 4~12 h.

[0017] Preferably, the conditions for casting film formation include: film thickness of 50~100 μm, drying temperature of 30~80 ℃, and drying time of 2~6 h.

[0018] Preferably, the imidization treatment conditions include: temperature 80~300 ℃, time 2~6 h. This invention provides a polyimide-based composite dielectric film material and its preparation method. The dielectric film of this technical solution uses fluorinated polyamide as the matrix. Fluorinated polyimide introduces strongly negatively charged fluorine atoms into the polyamide molecular chain. Compared with ordinary polyamide, it significantly reduces the polymer's dielectric loss, significantly reduces water absorption, significantly improves breakdown strength, significantly improves high-temperature resistance, and significantly improves energy storage performance under high-temperature conditions.

[0019] To improve the dielectric energy storage performance of dielectric films, this invention adds modified barium strontium titanate to the polymer matrix. The polymer matrix chosen in this invention is fluorinated polyamide. To enhance the compatibility and dispersibility of barium strontium titanate in fluorinated polyamide, fluorine-containing groups are introduced onto the surface of barium strontium titanate. Therefore, this invention uses a fluorinated silane coupling agent and hydroxylated barium strontium titanate to prepare modified barium strontium titanate. However, this invention found that the dielectric loss of the dielectric film made from the modified barium strontium titanate prepared with the fluorinated polyamide using the fluorinated silane coupling agent and hydroxylated barium strontium titanate is still relatively high. Therefore, this invention aims to significantly reduce the dielectric loss of the dielectric film based on the above technical solutions. This invention found that modifying hydroxylated barium strontium titanate with 3-glycidoxypropyltrimethoxysilane to form epoxide barium strontium titanate, and then reacting the epoxide barium strontium titanate with perfluoropolyether alcohol to prepare a dielectric film with modified barium strontium titanate, significantly reduces the dielectric loss.

[0020] Compared with the prior art, this application has the following technical effects: (1) Fluorinated polyamide was used as the substrate of the dielectric film, which significantly reduced the dielectric loss and water absorption of the dielectric film, significantly improved the breakdown strength of the dielectric film, and significantly improved the high-temperature energy storage performance of the dielectric film.

[0021] (2) Grafting fluorine-containing groups onto the surface of barium strontium titanate significantly improves the compatibility and dispersibility of barium strontium titanate in fluorinated polyamides, and significantly improves the dielectric constant and energy storage density of the material.

[0022] (3) Modified barium strontium titanate prepared by modifying hydroxylated barium strontium titanate with 3-glycidyl etheroxypropyltrimethoxysilane and then further modifying it with perfluoropolyether alcohol can significantly reduce the dielectric loss of the dielectric film. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments.

[0024] To better understand the content of this invention, further explanation is provided below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of this invention.

[0025] Example 1: A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare barium strontium titanate epoxide nanoparticles. (4) Strontium barium titanate nanoparticles, perfluoropolyether alcohol (SJK-1000) and catalyst (4-dimethylaminopyridine) were mixed in a solvent (toluene and butanone in a volume ratio of 1:1) at a mass ratio of 1:3:0.05. After ultrasonic mixing, the mixture was stirred under reflux at 100°C for 8 h. After the reaction was completed, the reaction product was separated, washed and dried to prepare modified strontium barium titanate. (5) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 4:100 and stir for 30 min, then sonicate at 2000 Hz for 15 min to prepare a mixture; (6) The mixture was dropped onto the glass substrate, and the doctor blade height was adjusted to 50 μm to form a thin film. The glass substrate with the film was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0026] Example 2: A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare barium strontium titanate epoxide nanoparticles. (4) Strontium barium titanate nanoparticles, perfluoropolyether alcohol (SJK-1000) and catalyst (4-dimethylaminopyridine) were mixed in a solvent (toluene and butanone in a volume ratio of 1:1) at a mass ratio of 1:3:0.05. After ultrasonic mixing, the mixture was stirred under reflux at 100°C for 8 h. After the reaction was completed, the reaction product was separated, washed and dried to prepare modified strontium barium titanate. (5) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 8:100 and stir for 30 min, then sonicate at 2000 Hz for 15 min to prepare a mixture; (6) The mixture was dropped onto the glass substrate, and the doctor blade height was adjusted to 50 μm to form a thin film. The glass substrate with the film was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0027] Example 3: A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare barium strontium titanate epoxide nanoparticles. (4) Strontium barium titanate nanoparticles, perfluoropolyether alcohol (SJK-1000) and catalyst (4-dimethylaminopyridine) were mixed in a solvent (toluene and butanone in a volume ratio of 1:1) at a mass ratio of 1:3:0.05. After ultrasonic mixing, the mixture was stirred under reflux at 100°C for 8 h. After the reaction was completed, the reaction product was separated, washed and dried to prepare modified strontium barium titanate. (5) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 12:100, stir for 30 min, and then sonicate at 2000 Hz for 15 min to prepare a mixture; (6) The mixture was dropped onto the glass substrate, and the doctor blade height was adjusted to 50 μm to form a thin film. The glass substrate with the film was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0028] Example 4: A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare barium strontium titanate epoxide nanoparticles. (4) Strontium barium titanate nanoparticles, perfluoropolyether alcohol (SJK-1000) and catalyst (4-dimethylaminopyridine) were mixed in a solvent (toluene and butanone in a volume ratio of 1:1) at a mass ratio of 1:3:0.05. After ultrasonic mixing, the mixture was stirred under reflux at 100°C for 8 h. After the reaction was completed, the reaction product was separated, washed and dried to prepare modified strontium barium titanate. (5) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 16:100, stir for 30 min, and then sonicate at 2000 Hz for 15 min to prepare a mixture; (6) The mixture was dropped onto the glass substrate, and the doctor blade height was adjusted to 50 μm to form a thin film. The glass substrate with the film was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0029] Example 5: A method for preparing a polyimide-based composite dielectric thin film material includes the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare barium strontium titanate epoxide nanoparticles. (4) Strontium barium titanate nanoparticles, perfluoropolyether alcohol (SJK-1000) and catalyst (4-dimethylaminopyridine) were mixed in a solvent (toluene and butanone in a volume ratio of 1:1) at a mass ratio of 1:3:0.05. After ultrasonic mixing, the mixture was stirred under reflux at 100°C for 8 h. After the reaction was completed, the reaction product was separated, washed and dried to prepare modified strontium barium titanate. (5) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 20:100, stir for 30 min, and then sonicate at 2000 Hz for 15 min to prepare a mixture; (6) The mixture was dropped onto the glass substrate, and the doctor blade height was adjusted to 50 μm to form a thin film. The glass substrate with the film was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0030] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that barium strontium titanate was not added, and the following steps were included: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Fluorinated polyamic acid solution was dropped onto a glass substrate, and the height of the squeegee was adjusted to 50 μm to form a thin film. The glass substrate with the film attached was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first, treatment at 80 °C for 2 h, then treatment at 150 °C for 1 h, then treatment at 200 °C for 1 h, then treatment at 250 °C for 1 h, and then treatment at 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0031] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the barium strontium titanate was not modified, and the following steps were included: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate to the fluorinated polyamic acid solution at a mass ratio of 4:100 and stir for 30 min, then sonicate at 2000 Hz for 15 min to prepare a mixture; (3) The mixture was dropped onto the glass substrate, and the height of the squeegee was adjusted to 50 μm to form a thin film. The glass substrate with the film attached was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first, 80 °C for 2 h, then 150 °C for 1 h, then 200 °C for 1 h, then 250 °C for 1 h, and then 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0032] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 did not use perfluoropolyether alcohol, and included the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, and then add 3-glycidyl etheroxypropyltrimethoxysilane (the mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1). After ultrasonic mixing, reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry to prepare modified barium strontium titanate. (4) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 4:100 and stir for 30 min, then sonicate at 2000 Hz for 15 min to prepare a mixture; (5) The mixture was dropped onto the glass substrate, and the height of the squeegee was adjusted to 50 μm to form a thin film. The glass substrate with the film attached was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first, treatment at 80 °C for 2 h, then treatment at 150 °C for 1 h, then treatment at 200 °C for 1 h, then treatment at 250 °C for 1 h, and then treatment at 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0033] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses a fluorinated silane coupling agent (trifluoropropyltrimethoxysilane) to modify barium strontium titanate, including the following steps: (1) Add 1.6 g of TFMB and 16 mL of DMAc to a 30 mL round-bottom flask and stir to dissolve under nitrogen protection. Then add 2.22 g of 6FDA in three portions. Place the round-bottom flask in an oil bath at 65 °C and heat and stir continuously for 3 h to prepare a fluorinated polyamic acid solution (mass concentration of 20%). (2) Add barium strontium titanate nanoparticles to hydrogen peroxide solution (mass fraction 30 wt%) at a mass-volume ratio of 1 g: 50 mL, disperse evenly by ultrasonication, and reflux at 100 °C for 3 h. After the reaction is completed, separate the reaction product, wash and dry to prepare hydroxylated barium strontium titanate nanoparticles. (3) Add hydroxylated barium strontium titanate nanoparticles to an ethanol aqueous solution (the volume ratio of water to ethanol is 1:9) at a mass-volume ratio of 1 g:50 mL, then add trifluoropropyltrimethoxysilane (the mass ratio of trifluoropropyltrimethoxysilane to hydroxylated barium strontium titanate is 1.5:1), mix evenly by ultrasonication, and then reflux and stir at 80 °C for 18 h. After the reaction is completed, separate the reaction product, wash and dry it to prepare modified barium strontium titanate. (4) Add modified barium strontium titanate to fluorinated polyamic acid solution at a mass ratio of 4:100 and stir for 30 min, then sonicate at 2000 Hz for 15 min to prepare a mixture; (5) The mixture was dropped onto the glass substrate, and the height of the squeegee was adjusted to 50 μm to form a thin film. The glass substrate with the film attached was placed in a vacuum oven at 60 °C and dried under vacuum for 4 h to remove the solvent. The glass substrate was then placed in a forced-air drying oven for imidization treatment. The imidization treatment conditions were: first, treatment at 80 °C for 2 h, then treatment at 150 °C for 1 h, then treatment at 200 °C for 1 h, then treatment at 250 °C for 1 h, and then treatment at 300 °C for 1 h. After the imidization treatment was completed, the glass substrate was removed and the film was peeled off in deionized water. The film was then placed in a 50 °C oven and dried under vacuum for 4 h to form a fluorinated polyimide composite dielectric film material.

[0034] Example of detection: The dielectric constant, dielectric loss and energy density of the dielectric films prepared in Examples 1-5 and Comparative Examples 1-4 were tested at a frequency of 10 kHz. The test results are shown in Table 1. Table 1 Test results of dielectric film performance As shown in Table 1, the dielectric constants of the dielectric films (Examples 1-5) prepared by this invention are 3.1-6.4, the dielectric losses are 0.0021-0.0052, and the energy storage densities are 3.08-2.04 J / cm². 3 Compared with the dielectric film without added barium strontium titanate (Comparative Example 1), the dielectric constant and energy storage density of the film were significantly increased. Furthermore, with increasing amounts of modified barium strontium titanate, the dielectric constant and dielectric loss of the dielectric film gradually increased, while the energy storage density initially increased and then decreased, reaching its highest value when the mass ratio of modified barium strontium titanate to fluorinated polyamic acid was 16:100.

[0035] Comparative Example 2 represents a technical solution without modification of barium strontium titanate; Comparative Example 3 represents a technical solution without the use of perfluoropolyether alcohol; and Comparative Example 4 represents a technical solution that directly modifies barium strontium titanate using a fluorinated silane coupling agent. Comparing the results of Example 1 and Comparative Examples 1-4, it was found that directly adding unmodified barium strontium titanate to the polymer significantly increases the dielectric constant of the dielectric film, thereby improving its energy storage performance. However, the increase in dielectric loss is also extremely significant. Using a silane coupling agent, on the other hand, significantly reduces the dielectric loss of the dielectric film. Further analysis revealed that both the content and volume of barium strontium titanate significantly affect the dielectric loss of the dielectric film. Increased volume and content of barium strontium titanate lead to a significant increase in dielectric loss. Modification of barium strontium titanate with a silane coupling agent can significantly improve its dispersibility in polymers and significantly inhibit its polymerization, thereby significantly reducing the dielectric loss of the dielectric film.

[0036] Furthermore, after modifying barium strontium titanate with only fluorinated silane coupling agents, the dielectric loss of the dielectric film did not change significantly compared with that of conventional silane coupling agents, and its dielectric constant was still significantly higher than that of the technical solution of this invention. After in-depth analysis, it was found that different silane coupling agents had different grafting amounts on the surface of barium strontium titanate. The more grafting, the more organic groups were formed on the surface of strontium titanate, thereby reducing the dielectric constant of barium strontium titanate. The 3-glycidoxypropyltrimethoxysilane used in this invention contains both epoxy and methoxysilyl groups. When it reacts with hydroxyl groups, it can undergo two reactions: epoxy ring-opening reaction and methoxysilyl hydrolysis reaction, which can graft COC bonds and Si-OC bonds. Conventional silane coupling agents can only graft Si-OC bonds. The more organic matter grafted onto barium strontium titanate, the more its dielectric constant will decrease significantly. This also explains the phenomenon that the dielectric constant of the dielectric film of Example 1 of this invention is significantly lower than that of Comparative Examples 2-4 under the same addition amount. Furthermore, at the same addition amount, although the dielectric loss of the dielectric film modified with barium strontium titanate using only silane coupling agents (Comparative Examples 2 and 3) decreased, the dielectric loss was still relatively high. In contrast, the dielectric film prepared by the present invention, which reacts the silane coupling agent with barium strontium titanate first, and then with perfluoropolyether alcohol, has a lower dielectric constant but also extremely low dielectric loss. Therefore, the present invention can increase the dielectric constant of the dielectric film by increasing the amount of modified barium strontium titanate without significantly increasing the dielectric loss. This results in a high-energy-storage-performance dielectric film with high dielectric constant and low dielectric loss. In contrast, conventional silane coupling agent-modified barium strontium titanate polyimide dielectric films, due to limitations in dielectric loss, exhibit limited improvement in dielectric energy storage performance despite an increase in dielectric constant.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A polyimide-based composite dielectric thin film material, characterized in that, The raw materials, by mass ratio, include: a modified barium strontium titanate and a fluorinated polyamic acid solution in a ratio of 4 to 20:

100. The raw materials for the modified barium strontium titanate include: hydroxylated barium strontium titanate, 3-glycidyl etheroxypropyltrimethoxysilane, perfluoropolyether alcohol, and a catalyst. The raw materials for the fluorinated polyamic acid solution include: a fluorinated diamine monomer and a fluorinated dianhydride monomer.

2. The polyimide-based composite dielectric film material according to claim 1, characterized in that, The fluorinated diamine monomer is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), the fluorinated dianhydride monomer is 4,4′-(hexafluoroisopropene) phthalic anhydride (6FDA), and the catalyst is 4-dimethylaminopyridine.

3. The polyimide-based composite dielectric film material according to claim 1, characterized in that, The particle size of hydroxylated barium strontium titanate is 30~200 nm.

4. A method for preparing a polyimide-based composite dielectric thin film material according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) A fluorinated polyamic acid solution is prepared by reacting a fluorinated diamine monomer and a fluorinated dianhydride monomer; (2) 3-glycidyl etheroxypropyltrimethoxysilane and hydroxylated barium strontium titanate were reacted to prepare barium strontium titanate epoxide; (3) Modified barium strontium titanate is prepared by reacting perfluorinated polyether alcohol, catalyst and barium strontium titanate epoxide; (4) Add modified barium strontium titanate to a fluorinated polyamic acid solution, mix evenly, and cast into a film. The film is then subjected to imidization treatment to produce a polyimide-based composite dielectric film.

5. The preparation method according to claim 4, characterized in that, The reaction conditions in step (1) include: temperature 60~80℃ and time 2~5 h.

6. The preparation method according to claim 4, characterized in that, The reaction conditions in step (2) include: temperature 20~80℃, time 8~24 h.

7. The preparation method according to claim 4, characterized in that, The reaction conditions in step (3) include: temperature 90~110℃, time 4~12 h.

8. The preparation method according to claim 4, characterized in that, The conditions for casting film formation include: film thickness of 50~100μm, drying temperature of 30~80℃, and drying time of 2~6h.

9. The preparation method according to claim 4, characterized in that, The conditions for imidization treatment include: temperature 80~300℃, time 2~6 h.

10. The preparation method according to claim 4 or 9, characterized in that, The imidization treatment conditions were as follows: first, treatment at 80 °C for 2 h, then at 150 °C for 1 h, then at 200 °C for 1 h, then at 250 °C for 1 h, and finally at 300 °C for 1 h.

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