Highly insulating polyimide film, method for preparing the same, and use thereof

Abstract

The application discloses a preparation method and application of high-insulation polyimide film, and belongs to the technical field of polyimide film. The preparation steps comprise the following steps: diamine and dianhydride are subjected to polycondensation reaction to obtain a PAA resin solution; during the synthesis process of the PAA resin solution, an amine group modified nano-SiO2 dispersion liquid is synchronously added and fully stirred and mixed uniformly; subsequently, the nano-composite PAA resin solution is coated on the surface of a substrate, gradient temperature imidization treatment is adopted, and a polyimide film is prepared; finally, the polyimide film is subjected to low-temperature plasma treatment with HMDSO as a reactive gas source, and a target product, the high-insulation polyimide film, is obtained. The high-insulation polyimide film prepared by the application can maintain the insulation strength at 400 V / μm or above for a long time, can withstand a voltage of 5 KV or above, and is not affected by environmental humidity changes. The obtained film has excellent insulation performance while maintaining excellent mechanical performance, can be widely applied in the fields of electronic and electrical appliances, new energy, flexible electronics and the like, and can accurately match the core requirements of insulation performance and stability of insulation materials in the above-mentioned fields.

Description

Technical Field

[0001] This invention belongs to the field of polyimide film technology, specifically relating to a high-insulation polyimide film, its preparation method, and its application. Background Technology

[0002] Polyimide (PI) film is widely hailed as the "golden film" in the electronics field due to its excellent electrical insulation properties. Its insulation strength is typically between 200-300 V / μm, and its withstand voltage is between 2-3KV, making it an indispensable core insulation material in high-end fields such as aerospace, electronics and electrical engineering, new energy, and flexible electronics. It is widely used in key scenarios such as flexible printed circuit boards (FPC), high-temperature motor slot insulation, high-voltage transformer wrapping materials, spacecraft electronic component packaging, and 5G communication equipment.

[0003] With the rapid development of modern industrial technology, especially in fields such as aerospace, new energy vehicles, and high-voltage power electronics, the demand for miniaturized, lightweight, high-power-density, and adaptable equipment to extreme operating conditions is constantly increasing, placing more stringent requirements on the insulation performance of PI films. For example, next-generation high-voltage power modules, aero-engine sensors, and new energy vehicle motor controllers need to operate stably for extended periods in complex environments with high temperature, high humidity, strong electromagnetic interference, and high voltage stress. This requires insulating materials to possess higher and more stable insulation strength, posing unprecedented challenges to the insulation performance of PI films.

[0004] Currently, the insulation performance of traditional PI films is easily degraded by various factors. In particular, the C=O and NH bonds of the imide ring in the PI molecular chain are highly polar and readily form hydrogen bonds with water molecules, becoming the main adsorption sites. Furthermore, the presence of micropores, free volume, and inter-chain gaps within the film provides diffusion pathways for water molecules. The absorption of moisture from the environment by the PI film significantly weakens its insulation performance, representing its weakest point in insulation failure. Its insulation performance has become a core bottleneck restricting the performance improvement and reliability assurance of high-end electrical and electronic equipment. Therefore, developing a simple, cost-effective technical solution that can significantly improve the insulation performance of PI films while maintaining their original excellent thermal stability and mechanical properties has significant engineering application value and industrial prospects, and has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-insulation polyimide film, its preparation method and application, thereby solving the problems in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a highly insulating polyimide film includes the following steps: Under nitrogen protection, aromatic diamine monomers are dissolved in an organic solvent to obtain a diamine solution; Under nitrogen protection, aromatic dianhydrides were added in batches to the diamine solution and stirred to carry out a polycondensation reaction, resulting in a PAA resin solution. Amine-modified nano-SiO2 particles were dispersed in an organic solvent and subjected to high-speed shear dispersion to obtain an amine-modified nano-SiO2 dispersion. Amine-modified nano-SiO2 dispersion was mixed with PAA resin solution to obtain nano-composite PAA resin solution; A nanocomposite PAA resin solution was coated onto a substrate and then subjected to gradient heating heat treatment to form a gel film. The gel membrane was subjected to imidization treatment to obtain a polyimide film containing amine-modified nano-SiO2; A high-insulation polyimide film was obtained by subjecting a low-temperature plasma treatment of an amino-modified nano-SiO2 polyimide film with a reactive gas source introduced during the treatment.

[0007] Furthermore, the aromatic diamine is at least one of p-phenylenediamine and 4,4'-diaminodiphenyl ether; The aromatic dianhydride is at least one of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0008] Furthermore, the reaction temperature of the polycondensation reaction is 10–30°C, and the reaction time is 6–24 h.

[0009] Furthermore, the solid content of the PAA resin solution is 15-20%, and the viscosity is 100,000-150,000 mPa·s.

[0010] Furthermore, the amine-modified nano-SiO2 particles are obtained by amine modification of nano-SiO2 particles with APTES, and the particle size of the nano-SiO2 particles is 5-20 nm. The high-speed shear dispersion is carried out at a rotation speed of 2000-3000 r / min and a shear dispersion time of 1-2 h.

[0011] Furthermore, the amine-modified nano-SiO2 dispersion was added to the PAA resin solution and stirred for 2-4 hours.

[0012] Furthermore, the gradient heating heat treatment process is as follows: the temperature is increased to 70-90°C at a heating rate of 2-10°C / min, and held for 10-20 minutes.

[0013] Further, the imidization process is as follows: heating at 2-10℃ / min to 150-200℃ and holding for 25 min, heating at 2-10℃ / min to 200-250℃ and holding for 30 min, then heating at 2-10℃ / min to 250-300℃ and holding for 30 min; finally heating at 2-10℃ / min to 300-340℃ and holding for 30 min.

[0014] Furthermore, during the low-temperature plasma treatment, a reactive gas source, hexamethyldisiloxane, is introduced, with a treatment power of 80-150W and a treatment time of 30-120s.

[0015] A highly insulating polyimide film was prepared using the method described above.

[0016] The above-mentioned high-insulation polyimide film is used in the packaging of electronic components.

[0017] The beneficial effects of this invention are: 1. In the existing process of preparing PI films, the free volume and inter-chain gaps between PI molecular chains lead to the formation of inherent microporous structures within the film. These micropores provide natural channels for the permeation and diffusion of water molecules, ultimately resulting in a significant decrease in the insulation performance of the PI film. To address this issue, this invention proposes to introduce amine-modified nano-SiO2 particles into polyamic acid (PAA) resin to construct a PAA / amine-modified nano-SiO2 composite system. On the one hand, the steric hindrance filling effect of nanoparticles effectively fills the free volume generated by the stacking of PI molecular chains, densifying the film's microstructure and significantly reducing the number and size of micropores. On the other hand, the amine (-NH2) groups on the surface of the nano-SiO2 particles can form strong hydrogen bonds with the carboxyl (-COOH) and amide (-CONH-) groups on the PAA molecular chains, strengthening the interfacial bonding between the filler and the matrix, significantly improving the compatibility between the two phases, thereby suppressing secondary porosity defects caused by filler agglomeration from the source. This invention eliminates the problem of moisture-induced insulation performance degradation of thin films at its root by regulating the microstructure and interfacial interactions of the thin film.

[0018] 2. In the existing technology, during the PI film casting stage, the rapid escape of solvent and dehydrated cyclized water molecules forms an interconnected microporous network on the film surface. Simultaneously, air or moisture may remain within these micropores. When the film is subjected to high voltage, these interconnected micropores become the "preferred path" for electrical breakdown. The local discharge induced by the concentrated electric field rapidly propagates along the microporous network, eventually penetrating the entire film thickness and forming a conductive channel, causing the film to completely lose its insulating ability. To address this issue, this invention proposes a low-temperature plasma post-treatment process based on hexamethyldisiloxane (HMDSO) as the reactive gas source. On one hand, after low-temperature plasma pretreatment, the CN and C=O bonds on the PI film surface break, generating active free radicals such as C・ and N・. These free radicals undergo free radical addition with the active siloxane groups generated by HMDSO cracking, completing the anchoring and cross-linking of hydrophobic groups. Adjacent siloxane free radicals further undergo Si-O-Si bonding reactions, constructing a three-dimensional network cross-linked structure. Unreacted methyl groups (-CH3) are uniformly distributed on the surface of the cross-linked network, forming a stable hydrophobic interface. On the other hand, the cross-linking reaction promotes a more compact arrangement of the film surface molecular chains, while the etching effect of the plasma can slightly "fuse" the edges of the micropores, achieving physical closure of the surface micropores. By combining "low power + short time," the plasma interaction depth is controlled within the film surface, ensuring that the matrix molecular chains are not affected, thereby improving the insulation performance of the PI film.

[0019] 3. The prepared high-insulation polyimide film has stable mechanical properties, and its insulation strength can be maintained above 400V / μm for a long time, with a withstand voltage of above 5KV, and is not affected by changes in environmental humidity. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0021] A method for preparing a highly insulating polyimide film includes the following steps: S1, Under nitrogen protection, the aromatic diamine monomer is added to the organic solvent and stirred until the aromatic diamine monomer is completely dissolved to obtain a homogeneous diamine solution; S2, under nitrogen protection, add aromatic dianhydride to the diamine solution in batches and stir continuously to carry out polycondensation reaction until the viscosity of the system stabilizes, and then obtain PAA resin solution. S3, add amino-modified nano-SiO2 particles into an organic solvent, and use a high-speed shear dispersion device to shear disperse the mixture to obtain a stable amino-modified nano-SiO2 dispersion; S4. Under continuous stirring, the amine-modified nano-SiO2 dispersion obtained in S3 is added to the PAA resin solution prepared in S2 and stirred thoroughly to ensure that the SiO2 nanoparticles are uniformly dispersed in the PAA system to form a stable nano-composite PAA resin solution. S5. The nano-composite PAA resin solution is coated onto the substrate using a doctor blade coater, and a gradient heating heat treatment is performed to form a stable gel film. S6. Fix the gel film onto the needle plate and place it in a high-temperature oven for imidization treatment to obtain an amino-modified nano-SiO2 polyimide film. S7. The amine-modified nano-SiO2 polyimide film is subjected to low-temperature plasma treatment. A reactive gas source is introduced during the low-temperature plasma treatment. After the low-temperature plasma modification treatment of the base film surface, a high-insulation polyimide film is obtained.

[0022] in: In S1, the aromatic diamine is at least one of p-phenylenediamine (PDA) and 4,4'-diaminodiphenyl ether (ODA); the organic solvent is at least one of N,N'-dimethylacetamide (DMAc) and N,N'-dimethylformamide (DMF).

[0023] In S2, the aromatic dianhydride is at least one of pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

[0024] In S2, the polycondensation reaction temperature is 10–30℃, the reaction time is 6–24 h, the solid content of the PAA resin solution is 15–20%, and the viscosity is 100,000–150,000 mPa·s. In S3, the amine-modified nano-SiO2 particles are obtained by amine modification of nano-SiO2 particles using APTES, and the particle size of the nano-SiO2 particles is 5-20 nm; the high shear speed is 2000-3000 r / min, and the shear dispersion time is 1-2 h.

[0025] In S4, an amino-modified nano-SiO2 dispersion is added to the PAA resin solution and stirred for 2-4 hours.

[0026] In S5, a nano-composite PAA resin solution is coated on the substrate with a coating thickness of 12.5–50 μm. The gradient heating heat treatment is as follows: the temperature is increased to 70–90 °C at a heating rate of 2–10 °C / min, and held for 10–20 min to form a gel film.

[0027] In step S6, the gel film is peeled off from the substrate, fixed on a needle plate, and placed in an oven for imidization treatment; after cooling to room temperature, a nanocomposite polyimide film is obtained.

[0028] The imidization process is as follows: heat to 150-200℃ at 2-10℃ / min and hold for 25 min, heat to 200-250℃ at 2-10℃ / min and hold for 30 min, then heat to 250-300℃ at 2-10℃ / min and hold for 30 min, and finally heat to 300-340℃ at 2-10℃ / min and hold for 30 min.

[0029] In S7, the low-temperature plasma reactive gas source is hexamethyldisiloxane (HMDSO), with a processing power of 80-150W and a processing time of 30-120s.

[0030] In this invention, amine-modified nano-SiO2 particles, on the one hand, utilize a filling effect to fill the free volume between PI molecular chains and reduce porosity; on the other hand, the -NH2 groups on the SiO2 surface form strong hydrogen bonds with the -COOH and -CONH- groups of the PAA molecular chains, improving compatibility with the polyimide matrix and preventing filler agglomeration that forms new pore defects. The PI film surface is then treated with reactive gas source hexamethyldisiloxane (HMDSO) low-temperature plasma surface treatment to achieve molecular chain crosslinking and micropore sealing on the PI film surface.

[0031] The technical solution of the present invention will be described below through the following embodiments and comparative examples; wherein, in the embodiments and comparative examples, the sources of the relevant raw materials are as follows: APTES-modified nano-SiO2 was prepared through the following steps: Step 1: Take an appropriate amount of nano SiO2 (purchased from Ningbo Jinlei Nanomaterials Technology Co., Ltd., model: JL-SiO2-N10), place it in a vacuum drying oven at 100℃ and dry for 4 h to remove surface adsorbed water and impurities; after cooling to room temperature, add anhydrous ethanol at a solid-liquid ratio of 1:50 (g:mL), and ultrasonically disperse for 30 min to obtain a uniform SiO2 ethanol suspension.

[0032] Step 2: In an Erlenmeyer flask, mix APTES: anhydrous ethanol: deionized water in a volume ratio of 1:10:2; slowly add glacial acetic acid to adjust the pH of the system to 5.0; stir magnetically for 30 min to allow APTES to be fully hydrolyzed to generate silanol groups.

[0033] Step 3: Transfer the pretreated SiO2 ethanol suspension to a three-necked flask, heat to 60°C, and maintain magnetic stirring (400 r / min). Using a dropping funnel, slowly add APTES hydrolysate to the suspension, with a SiO2 to APTES mass ratio of 1:0.2. After the addition is complete, continue the reaction at a constant temperature for 5 hours.

[0034] Step 4: After the reaction is complete, the precipitate is washed three times with anhydrous ethanol and then twice with deionized water. After each washing, the precipitate is centrifuged. Finally, the precipitate is dried in a vacuum drying oven at 60°C for 8 hours to obtain APTES amine-modified nano-SiO2 powder.

[0035] Comparative Example 1 A method for preparing a polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 213.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0036] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0037] S3: After vacuum degassing of the PAA resin solution, the PAA resin solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90°C at a rate of 4°C / min, and held at that temperature for 15 min to form a gel film.

[0038] S4: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0039] Comparative Example 2 A method for preparing a polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0040] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0041] S3: Weigh 0.234g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0042] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0043] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0044] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0045] Comparative Example 3 A method for preparing a polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 213.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0046] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0047] S3: After vacuum degassing of the PAA resin solution, the polyamic acid solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90°C at a rate of 4°C / min, and held at that temperature for 15 min to form a gel film.

[0048] S4: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0049] S5: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a processing power of 100W and a processing time of 60S.

[0050] Example 1 A method for preparing a highly insulating polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0051] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0052] S3: Weigh 0.234g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0053] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0054] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0055] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0056] S7: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a treatment power of 100W and a treatment time of 60S. This yields a highly insulating polyimide film.

[0057] Example 2 A method for preparing a highly insulating polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0058] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0059] S3: Weigh 0.468g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0060] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0061] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0062] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0063] S7: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a treatment power of 100W and a treatment time of 60S. This yields a highly insulating polyimide film.

[0064] Example 3 A method for preparing a highly insulating polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0065] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0066] S3: Weigh 0.05g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0067] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0068] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0069] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0070] S7: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a treatment power of 100W and a treatment time of 60S. This yields a highly insulating polyimide film.

[0071] Example 4 A method for preparing a highly insulating polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0072] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0073] S3: Weigh 0.234g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0074] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0075] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0076] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0077] S7: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a treatment power of 150W and a treatment time of 60S. This yields a highly insulating polyimide film.

[0078] Example 5 A method for preparing a highly insulating polyimide film includes the following steps: S1: Take 3.888 g of p-phenylenediamine (36 mmol) and 16.8 g of 4,4'-diaminodiphenyl ether (84 mmol) and place them in 193.4 g of N,N'-dimethylacetamide (DMAc). Stir mechanically at room temperature for 1 h to allow the diamine to dissolve completely.

[0079] S2: Under nitrogen protection, 26.16 g of pyromellitic dianhydride (120 mmol) was added in portions to the diamine solution and reacted at room temperature for 8 h to obtain a PAA resin solution with a solid content of 18% and a viscosity of 120000 mPa·s.

[0080] S3: Weigh 0.234g of APTES amine-modified nano-SiO2 and place it in 20g of DMAc solution for high-speed shear dispersion at 2500r / min for 1h to obtain SiO2 dispersion.

[0081] S4: Under nitrogen protection, the SiO2 dispersion was added to the PAA resin solution in S2 and mechanically stirred at room temperature for 2 hours to obtain an amine-modified nano-SiO2 / PAA composite system solution.

[0082] S5: After vacuum degassing, the amine-modified nano-SiO2 / PAA composite system solution is coated onto the glass substrate using a coating machine to a thickness of 25 μm. The glass substrate is then placed in an oven and heated to 90 °C at a rate of 4 °C / min, and held at that temperature for 15 min to form a gel film.

[0083] S6: Fix the gel film onto the needle plate, place it in an oven and heat it to 180℃ at 4℃ / min and hold for 25 min, then heat it to 250℃ at 4℃ / min and hold for 30 min, then heat it to 300℃ at 4℃ / min and hold for 30 min, and finally heat it to 340℃ at 4℃ / min and hold for 30 min to perform imidization treatment, thus preparing the polyimide film.

[0084] S7: The polyimide film is placed in a low-temperature plasma for surface treatment. HMDSO is used as the plasma reactive gas source, with a treatment power of 100W and a treatment time of 120S. This yields a highly insulating polyimide film.

[0085] Experimental Test The polyimide films prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests. The test items and test procedures are as follows: 1) Mechanical properties (tensile strength, elongation at break, modulus): tested according to the standard method of GB / T13542.2-2021.

[0086] 2) Water absorption rate: Tested according to the standard method of GB / T1034-2008.

[0087] 3) Insulation strength: Tested according to the standard method of GB / T13542.2-2021.

[0088] 4) Insulation strength after 24 hours of immersion in water: Immerse the sample in water for 24 hours, wipe the water off the film surface, and test it according to the standard method of GB / T13542.2-2021.

[0089] 5) Pressure resistance: Tested according to the standard method of GB / T1048.1-2016.

[0090] 6) Water immersion pressure resistance: Immerse the sample in water for 24 hours, wipe the water off the film surface, and test it according to the standard method of GB / T1048.1-20016.

[0091] The test results are shown in Table 1 below: Table 1. Performance test results of polyimide films The data in Table 1 is analyzed as follows: 1. Comparing Example 1 with Comparative Examples 1-3, it can be seen that after the PI film is internally composited with amine-modified nano-SiO2 and the film surface is treated with HMDSO low-temperature plasma, the insulation strength of the PI film reaches over 400V / μm, the withstand voltage reaches over 5KV, and the mechanical properties remain stable. After immersion in water for 24 hours, the insulation strength and withstand voltage tests showed no significant decrease, indicating that its insulation performance can be maintained for a long time without being affected by changes in environmental humidity.

[0092] 2. Comparing Example 1 and Examples 2-3, it can be seen that the amount of amine-modified nano-SiO2 added needs to be controlled within a suitable range. Excessive addition not only damages the mechanical properties of the substrate itself but also easily leads to agglomeration due to uneven powder dispersion, resulting in secondary porosity defects and failing to improve insulation performance. Insufficient addition cannot fully fill the free volume generated by the accumulation of PI molecular chains, thus having little effect on improving insulation performance.

[0093] 3. Comparing Examples 1 and 4-5, it can be seen that the processing power and processing time of low-temperature plasma need to be strictly controlled. If the processing power is too high or the processing time is too long, the plasma energy will penetrate into the interior of the thin film substrate. Excessive bombardment and energy accumulation of high-energy particles will cause damage to the PI molecular chains, resulting in irreversible damage to the mechanical properties of the thin film and failing to achieve the goal of improving insulation performance.

[0094] 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.

[0095] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a highly insulating polyimide film, characterized in that, Includes the following steps: Under nitrogen protection, aromatic diamine monomers are dissolved in an organic solvent to obtain a diamine solution; Under nitrogen protection, aromatic dianhydrides were added in batches to the diamine solution and stirred to carry out a polycondensation reaction, resulting in a PAA resin solution. Amine-modified nano-SiO2 particles were dispersed in an organic solvent and subjected to high-speed shear dispersion to obtain an amine-modified nano-SiO2 dispersion. Amine-modified nano-SiO2 dispersion was mixed with PAA resin solution to obtain nano-composite PAA resin solution; A nanocomposite PAA resin solution was coated onto a substrate and then subjected to gradient heating heat treatment to form a gel film. The gel membrane was subjected to imidization treatment to obtain a polyimide film containing amine-modified nano-SiO2; A high-insulation polyimide film was obtained by subjecting a low-temperature plasma treatment of an amino-modified nano-SiO2 polyimide film with a reactive gas source introduced during the treatment.

2. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The aromatic diamine is at least one of p-phenylenediamine and 4,4'-diaminodiphenyl ether; The aromatic dianhydride is at least one of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

3. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The reaction temperature of the polycondensation reaction is 10–30°C, and the reaction time is 6–24 h.

4. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The solid content of the PAA resin solution is 15-20%, and the viscosity is 100,000-150,000 mPa·s.

5. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The amine-modified nano-SiO2 particles are obtained by amine modification of nano-SiO2 particles with APTES, and the particle size of the nano-SiO2 particles is 5-20 nm. The high-speed shear dispersion is carried out at a rotation speed of 2000-3000 r / min and a shear dispersion time of 1-2 h.

6. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, Amine-modified nano-SiO2 dispersion was added to PAA resin solution and stirred for 2-4 hours.

7. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The gradient heating heat treatment process is as follows: the temperature is increased to 70-90℃ at a heating rate of 2-10℃ / min, and held for 10-20min.

8. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The imidization process is as follows: heat to 150-200℃ at 2-10℃ / min and hold for 25 min; heat to 200-250℃ at 2-10℃ / min and hold for 30 min; heat to 250-300℃ at 2-10℃ / min and hold for 30 min; and finally heat to 300-340℃ at 2-10℃ / min and hold for 30 min.

9. The method for preparing a highly insulating polyimide film according to claim 1, characterized in that, The low-temperature plasma treatment involves introducing a reactive gas source, hexamethyldisiloxane, with a treatment power of 80-150W and a treatment time of 30-120s.

10. A highly insulating polyimide film, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

11. The application of the high-insulation polyimide film of claim 10 in the encapsulation of electronic components.

Images