Preparation method of high-performance polyimide film

Abstract

The invention discloses a preparation method of a high-performance polyimide film, and belongs to the technical field of polyimide films, the preparation method comprises the following steps: preparing a polyamide acid solution, preparing silicon dioxide with isocyanate groups on the surface, preparing silicon dioxide with hydroxyl on the surface, and mixing to prepare the film. The step of mixed membrane preparation comprises the following steps: mixing silicon dioxide with isocyanate groups on the surface, silicon dioxide with hydroxyl on the surface and N, N-dimethylacetamide, uniformly stirring, then mixing with a catalyst, a dehydrating agent and a polyamide acid solution, uniformly stirring, filtering and defoaming to obtain a membrane casting solution, forming a membrane from the membrane casting solution, standing at 100-105 DEG C, and drying to obtain the membrane. Performing longitudinal drafting and transverse drafting at the same time, raising the temperature to 300-310 DEG C, standing, raising the temperature to 450-460 DEG C, and standing; the polyimide film prepared by the invention has excellent optical performance, heat-resistant stability, mechanical performance and electric breakdown resistance.

Description

Technical Field

[0001] This invention relates to the field of polyimide film technology, and more specifically to a method for preparing a high-performance polyimide film. Background Technology

[0002] In recent years, with the rapid development of flexible optoelectronic technologies such as flexible displays and flexible solar cells, the demand for polymer optical films that combine excellent optical transparency and good thermal stability has been increasing. Traditional polymer optical films, including polyolefin films and polyester films, while possessing excellent optical properties, often suffer from poor thermal stability, making it difficult to meet the application requirements of advanced optoelectronic device manufacturing. Meanwhile, traditional high-temperature resistant polymer films, such as polyimide, polyetheretherketone, and polytetrafluoroethylene films, exhibit an opaque appearance due to highly conjugated molecular chain structures or high crystallinity, which also significantly limits their application in advanced optoelectronic devices. Therefore, research on high-temperature resistant transparent polymer optical films has received widespread attention from the materials science community both domestically and internationally.

[0003] Polyimides are generally polymerized from diamine and dianhydride monomers. Based on whether the main chain structure contains a benzene ring, polyimides can be divided into aromatic polyimides and non-aromatic polyimides. Aromatic polyimides have a large conjugated system in their molecular chains, which can form charge-transfer complexes. Therefore, the molecular chain is rigid and the intermolecular forces are strong. As a result, aromatic polyimide films made from aromatic polyimides have excellent thermal stability, mechanical properties, and electrical breakdown resistance. However, the poor light transmittance of aromatic polyimides limits their application in the fields of microelectronics and optoelectronics.

[0004] To improve the light transmittance of aromatic polyimide films, common methods include chemical modification and physical modification. Chemical modification typically involves introducing non-conjugated structures, flexible ether bonds, and large side groups into the aromatic polyimide molecule. However, this can lead to a decrease in the thermal stability, mechanical properties, and electrical breakdown resistance of the prepared aromatic polyimide film. Physical modification typically involves adding inorganic fillers such as silica, alumina, and titanium dioxide to the aromatic polyimide. However, inorganic fillers are prone to agglomeration and have poor compatibility with aromatic polyimide molecules, leading to phase separation problems in the prepared aromatic polyimide film. This, in turn, reduces the thermal stability, mechanical properties, and electrical breakdown resistance of the prepared aromatic polyimide film.

[0005] To address the aforementioned issues, current research primarily focuses on silane modification of inorganic fillers to introduce organic groups onto their surfaces and the use of colloidal silica as fillers. However, research has found that the additional coupling agent remaining in the hybrid material may affect important thermal / mechanical / optical properties (see Jia Yanjiang. Preparation and properties of colloidal silica-modified semi-alicylic colorless polyimide films. China University of Geosciences. May 2022). Colloidal silica still exhibits agglomeration problems in aromatic polyimide films, and the compatibility between colloidal silica and aromatic polyimide molecules is greatly affected by the number of hydroxyl groups on the surface of colloidal silica. The fewer the number of hydroxyl groups on the surface of colloidal silica, the more easily colloidal silica agglomerates in aromatic polyimide films (see Jia Yanjiang. Preparation and properties of colloidal silica-modified semi-alicylic colorless polyimide films. China University of Geosciences. May 2022), which in turn makes it difficult to achieve optimal optical properties, thermal stability, mechanical properties, and electrical breakdown resistance of the prepared aromatic polyimide films.

[0006] Existing technologies disclose that the introduction of isocyanate groups can improve the thermal stability of polyimides (see Zhou Chengfei. Research progress in the preparation of polyimides by isocyanate method. Synthesis Technology and Application. September 2015). Therefore, the applicant attempted to prepare polyimide films using a two-step method. First, polyamic acid with a high molecular weight was synthesized, and then polyimide was formed by dehydration through imidization. After modifying silica with a silane coupling agent containing isocyanate groups, silica with isocyanate groups on its surface was obtained. Then, silica with isocyanate groups on its surface was added to polyamic acid and imidized again. The reaction between the isocyanate groups and anhydride groups on the silica surface was used to achieve chemical interfacial bonding between silica and the polyimide matrix, thereby obtaining a high-performance polyimide film with excellent optical properties, thermal stability, mechanical properties, and electrical breakdown resistance. However, the applicant discovered during the preparation process that, due to the high reactivity of isocyanate groups, they are quite sensitive to water (see Tao Yao. Polyimide / silica hybrid materials based on sol-gel method: preparation and performance study. Shanghai Jiao Tong University. January 2017). This leads to two problems: First, the prepared silica with isocyanate groups on its surface easily absorbs moisture from the air during storage, affecting the effect of isocyanate groups on improving the performance of polyimide films; second, the water generated during the imidization of polyamic acid during dehydration reacts with isocyanate groups, also affecting the effect of isocyanate groups on improving the performance of polyimide films. Consequently, the optical properties, thermal stability, mechanical properties, and electrical breakdown resistance of the prepared aromatic polyimide films are still difficult to optimize. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing high-performance polyimide films. The prepared polyimide films possess excellent optical properties, thermal stability, mechanical properties, and electrical breakdown resistance.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a high-performance polyimide film comprises the following steps: preparing a polyamic acid solution, preparing silica with isocyanate groups on the surface, preparing silica with hydroxyl groups on the surface, and mixing them to form a film; The preparation of the polyamic acid solution involves mixing diamine, dianhydride, and N,N-dimethylacetamide under a nitrogen atmosphere and stirring at 5-10°C to obtain the polyamic acid solution. In the preparation of the polyamic acid solution, the mass ratio of diamine, dianhydride, and N,N-dimethylacetamide is 20-22:21.8-24:200-260. Preferably, the diamine is 4,4'-diaminodiphenyl ether; Preferably, the dianhydride is pyromellitic dianhydride; Preferably, the stirring time at 5-10℃ is 24-26 hours; To prepare silica with isocyanate groups on its surface, in a nitrogen atmosphere, a silane coupling agent with isocyanate groups, silica, and a first portion of toluene are mixed, stirred at 60-70°C, centrifuged, and the precipitate is collected, washed with toluene, and vacuum dried at 60-70°C to obtain silane-modified silica; the silane-modified silica is then mixed with Tween-80 and a second portion of toluene, stirred at room temperature, centrifuged, and the precipitate is collected and vacuum dried to obtain silica with isocyanate groups on its surface. In the preparation of silica with isocyanate groups on the surface, the mass ratio of the isocyanate-containing silane coupling agent, silica, the first part of toluene, Tween-80, and the second part of toluene is 20-25:20-25:200-300:10-12:200-300. The average particle size of the silica is 100 nm. Preferably, the silane coupling agent with isocyanate groups is 3-isocyanate-propyltrimethoxysilane; Preferably, the stirring time at 60-70℃ is 12-13 hours; Preferably, the stirring time at room temperature is 2-3 hours; The preparation of silica with hydroxyl groups on the surface involves mixing silica, glycerol, and water, ball milling, and vacuum drying to obtain silica with hydroxyl groups on the surface. In the preparation of silica with hydroxyl groups on the surface, the mass ratio of silica, glycerol, and water is 100-120:5-6:50-55; The average particle size of the silica is 40 nm; Preferably, the ball milling speed is 300-350 r / min, the ball-to-material ratio is 3-4:1, and the ball milling time is 30-40 min. The film-forming process involves mixing silica with isocyanate groups on its surface, silica with hydroxyl groups on its surface, and N,N-dimethylacetamide, stirring the mixture evenly at room temperature to obtain a mixed solution. This mixed solution is then mixed with a catalyst, a dehydrating agent, and a polyamic acid solution, stirred evenly at room temperature, filtered, and degassed to obtain a casting solution. The casting solution is then used to form a film, which is allowed to stand at 100-105°C while undergoing both longitudinal and transverse stretching. The temperature is then raised to 300-310°C and allowed to stand at 300-310°C. The temperature is then raised to 450-460°C and allowed to stand at 450-460°C to obtain a high-performance polyimide film. In the mixed film preparation process, the mass ratio of silica with isocyanate groups on its surface, silica with hydroxyl groups on its surface, N,N-dimethylacetamide, catalyst, dehydrating agent, and polyamic acid solution is 8-8.5:1.8-2:40-50:31-33:41-45:240-300. Preferably, the catalyst is pyridine; Preferably, the dehydrating agent is acetic anhydride; Preferably, the film thickness during film formation is 700-750 μm; Preferably, the standing time when standing at 100-105℃ is 5-6 minutes; Preferably, the drawing temperature during simultaneous longitudinal and transverse drawing is 50-60℃, the drawing speed for both longitudinal and transverse drawing is 25-30 mm / min, and the ratio of longitudinal and transverse drawing is 1.3-1.4 times. Preferably, the heating rate when the temperature rises to 300-310℃ is 2-3℃ / min; Preferably, the standing time when standing at 300-310℃ is 20-30 minutes; Preferably, the heating rate when the temperature rises to 450-460℃ is 1-1.5℃ / min; Preferably, the standing time when standing at 450-460℃ is 5-6 minutes.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a method for preparing high-performance polyimide films, resulting in polyimide films that simultaneously possess excellent optical properties, thermal stability, mechanical properties, and electrical breakdown resistance. The polyimide films prepared by this invention have a glass transition temperature of 371-378℃, a tensile strength of 228-247 MPa, an elastic modulus of 4.5-4.8 GPa, a coefficient of thermal expansion of 19-21 ppm / K, an electrical breakdown strength of 251-272 kV / mm, and a transmittance of 86.6-87.8% at a wavelength of 450 nm. Detailed Implementation

[0010] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0011] Example 1 A method for preparing a high-performance polyimide film specifically includes the following steps: 1. Preparation of polyamic acid solution: Under a nitrogen atmosphere, 20g of 4,4'-diaminodiphenyl ether (4,4'-ODA), 21.8g of pyromellitic dianhydride (PMDA) and 200g of N,N-dimethylacetamide were mixed and stirred at 50r / min for 24h at 5℃ to obtain a polyamic acid solution; 2. Preparation of silica with isocyanate groups on the surface: Under a nitrogen atmosphere, 20 g of 3-isocyanatopropyltrimethoxysilane, 20 g of silica, and 200 g of toluene were mixed and stirred at 50 r / min for 12 h at 60 °C. After centrifugation, the precipitate was collected, washed with toluene, and dried under vacuum at 60 °C to obtain silane-modified silica. All the obtained silane-modified silica was mixed with 10 g of Tween-80 and 200 g of toluene and stirred at 50 r / min for 2 h at room temperature. After centrifugation, the precipitate was collected and dried under vacuum at 60 °C to obtain silica with isocyanate groups on the surface. The average particle size of the silica is 100 nm. 3. Preparation of silica with hydroxyl groups on the surface: Mix 100g silica, 5g glycerol and 50g water, and ball mill at 300r / min for 30min. The ball-to-material ratio in the ball mill is 3:1. Dry under vacuum at 60℃ to obtain silica with hydroxyl groups on the surface. The average particle size of the silica is 40 nm; 4. Film Formation by Mixing: 8g of silica with isocyanate groups on the surface, 1.8g of silica with hydroxyl groups on the surface, and 40g of... N,N-dimethylacetamide was mixed and stirred at 200 r / min for 30 min at room temperature to obtain a mixture. The entire mixture was then mixed with 31 g pyridine, 41 g acetic anhydride, and 240 g polyamic acid solution and stirred at 200 r / min for 30 min at room temperature. The mixture was filtered and degassed to obtain a casting solution. The casting solution was coated onto a clean glass plate to form a film with a thickness of 700 μm. The film was allowed to stand at 100 °C for 5 min and then added to a biaxial stretching machine for simultaneous longitudinal and transverse stretching. The stretching temperature was 50 °C, and the stretching speed for both longitudinal and transverse stretching was 25 mm / min. The stretching ratio for both longitudinal and transverse stretching was 1.3 times. The temperature was increased to 300 °C at a rate of 2 °C / min and allowed to stand at 300 °C for 20 min. The temperature was then increased to 450 °C at a rate of 1 °C / min and allowed to stand at 450 °C for 5 min to obtain a high-performance polyimide film.

[0012] Example 2 A method for preparing a high-performance polyimide film specifically includes the following steps: 1. Preparation of polyamic acid solution: Under a nitrogen atmosphere, 21g of 4,4'-diaminodiphenyl ether, 23g of pyromellitic dianhydride and 220g of N,N-dimethylacetamide were mixed and stirred at 100r / min for 24.5h at 5℃ to obtain a polyamic acid solution; 2. Preparation of silica with isocyanate groups on the surface: Under a nitrogen atmosphere, 21 g of 3-isocyanatopropyltrimethoxysilane, 21 g of silica, and 220 g of toluene were mixed and stirred at 100 r / min for 12.5 h at 65 °C. After centrifugation, the precipitate was collected, washed with toluene, and dried under vacuum at 65 °C to obtain silane-modified silica. All the obtained silane-modified silica was mixed with 10.5 g of Tween-80 and 220 g of toluene and stirred at 100 r / min for 2.5 h at room temperature. After centrifugation, the precipitate was collected and dried under vacuum at 65 °C to obtain silica with isocyanate groups on the surface. The average particle size of the silica is 100 nm. 3. Preparation of silica with hydroxyl groups on the surface: 105g silica, 5.2g glycerol and 52g water were mixed and ball-milled at 300r / min for 30min. The ball-to-material ratio in the ball mill was 3:1. The mixture was then vacuum-dried at 60℃ to obtain silica with hydroxyl groups on the surface. The average particle size of the silica is 40 nm; 4. Film Formation by Mixing: 8.2g of silica with isocyanate groups on the surface, 1.8g of silica with hydroxyl groups on the surface, and 42g of... N,N-dimethylacetamide was mixed and stirred at 300 rpm for 35 min at room temperature to obtain a mixture. The entire mixture was then mixed with 31 g pyridine, 42 g acetic anhydride, and 260 g polyamic acid solution and stirred at 300 rpm for 30 min at room temperature. The mixture was filtered and degassed to obtain a casting solution. The casting solution was coated onto a clean glass plate to form a film with a thickness of 700 μm. The film was allowed to stand at 100 °C for 5 min and then added to a biaxial stretching machine for simultaneous longitudinal and transverse stretching. The stretching temperature was 50 °C, and the stretching speed for both longitudinal and transverse stretching was 25 mm / min. The stretching ratio for both longitudinal and transverse stretching was 1.3 times. The temperature was increased to 300 °C at a rate of 2 °C / min and allowed to stand at 300 °C for 25 min. The temperature was then increased to 450 °C at a rate of 1 °C / min and allowed to stand at 450 °C for 5 min to obtain a high-performance polyimide film.

[0013] Example 3 A method for preparing a high-performance polyimide film specifically includes the following steps: 1. Preparation of polyamic acid solution: Under a nitrogen atmosphere, 21.5 g of 4,4'-diaminodiphenyl ether, 23.5 g of pyromellitic dianhydride and 250 g of N,N-dimethylacetamide were mixed and stirred at 150 r / min for 25.5 h at 5 °C to obtain a polyamic acid solution; 2. Preparation of silica with isocyanate groups on the surface: Under a nitrogen atmosphere, 20 g of 3-isocyanatopropyltrimethoxysilane, 24 g of silica, and 280 g of toluene were mixed and stirred at 150 r / min for 12.5 h at 65 °C. After centrifugation, the precipitate was collected, washed with toluene, and dried under vacuum at 65 °C to obtain silane-modified silica. All the obtained silane-modified silica was mixed with 11.5 g of Tween-80 and 250 g of toluene and stirred at 150 r / min for 2.5 h at room temperature. After centrifugation, the precipitate was collected and dried under vacuum at 65 °C to obtain silica with isocyanate groups on the surface. The average particle size of the silica is 100 nm. 3. Preparation of silica with hydroxyl groups on the surface: 115g silica, 5.5g glycerol and 54g water were mixed and ball-milled at 350r / min for 35min. The ball-to-material ratio in the ball mill was 4:1. The mixture was then vacuum-dried at 65℃ to obtain silica with hydroxyl groups on the surface. The average particle size of the silica is 40 nm; 4. Film Formation by Mixing: 8.4 g of silica with isocyanate groups on its surface, 1.9 g of silica with hydroxyl groups on its surface, and 45 g of N,N-dimethylacetamide were mixed and stirred at 300 r / min for 40 min at room temperature to obtain a mixture. The entire mixture was then mixed with 32.5 g of pyridine, 44 g of acetic anhydride, and 290 g of polyamic acid solution and stirred at 300 r / min for 40 min at room temperature. The mixture was filtered and degassed to obtain a casting solution. The casting solution was coated onto a clean glass plate to form a film with a thickness of 700 μm, which was then allowed to stand at 102 °C for 5.5 min. The material is added to a biaxial stretching machine for simultaneous longitudinal and transverse stretching. The stretching temperature is 55℃, and the stretching speed for both longitudinal and transverse stretching is 28mm / min. The stretching ratio for both longitudinal and transverse stretching is 1.3 times. The temperature is increased to 305℃ at a rate of 2.5℃ / min, and then held at 305℃ for 25min. The temperature is then increased to 455℃ at a rate of 1.2℃ / min, and then held at 455℃ for 5.5min to obtain a high-performance polyimide film.

[0014] Example 4 A method for preparing a high-performance polyimide film specifically includes the following steps: 1. Preparation of polyamic acid solution: Under a nitrogen atmosphere, 22g of 4,4'-diaminodiphenyl ether, 24g of pyromellitic dianhydride and 260g of N,N-dimethylacetamide were mixed and stirred at 200r / min for 26h at 10℃ to obtain a polyamic acid solution; 2. Preparation of silica with isocyanate groups on the surface: Under a nitrogen atmosphere, 25g of 3-isocyanatopropyltrimethoxysilane, 25g of silica, and 300g of toluene were mixed and stirred at 200r / min for 13h at 70℃. After centrifugation, the precipitate was collected, washed with toluene, and dried under vacuum at 70℃ to obtain silane-modified silica. All the obtained silane-modified silica was mixed with 12g of Tween-80 and 300g of toluene and stirred at 200r / min for 3h at room temperature. After centrifugation, the precipitate was collected and dried under vacuum at 70℃ to obtain silica with isocyanate groups on the surface. The average particle size of the silica is 100 nm. 3. Preparation of silica with hydroxyl groups on the surface: 120g silica, 6g glycerol and 55g water were mixed and ball-milled at 350r / min for 40min. The ball-to-material ratio in the ball mill was 4:1. The mixture was then vacuum-dried at 70℃ to obtain silica with hydroxyl groups on the surface. The average particle size of the silica is 40 nm; 4. Film Formation by Mixing: 8.5g of silica with isocyanate groups on the surface, 2g of silica with hydroxyl groups on the surface, and 50g of... N,N-dimethylacetamide was mixed and stirred at 400 rpm for 50 min at room temperature to obtain a mixture. The entire mixture was then mixed with 33 g pyridine, 45 g acetic anhydride, and 300 g polyamic acid solution and stirred at 400 rpm for 50 min at room temperature. The mixture was filtered and degassed to obtain a casting solution. The casting solution was coated onto a clean glass plate to form a film with a thickness of 700 μm. The film was allowed to stand at 105 °C for 6 min and then added to a biaxial stretching machine for simultaneous longitudinal and transverse stretching. The stretching temperature was 60 °C, and the stretching speed for both longitudinal and transverse stretching was 30 mm / min. The stretching ratio for both longitudinal and transverse stretching was 1.3 times. The temperature was increased to 310 °C at a rate of 3 °C / min and allowed to stand at 310 °C for 30 min. The temperature was then increased to 460 °C at a rate of 1.5 °C / min and allowed to stand at 460 °C for 6 min to obtain a high-performance polyimide film.

[0015] Comparative Example 1 The preparation method of the high-performance polyimide film is basically the same as that in Example 1, except that in the second step of preparing silicon dioxide with isocyanate groups on the surface, the addition of Tween-80 is omitted, that is, the second step of preparing silicon dioxide with isocyanate groups on the surface is changed to: In a nitrogen atmosphere, 20g of 3-isocyanate-propyltrimethoxysilane, 20g of silica, and 200g of toluene were mixed and stirred at 50r / min for 12h at 60℃. After centrifugation, the precipitate was collected, washed with toluene, and dried under vacuum at 60℃ to obtain silica with isocyanate groups on its surface. The average particle size of the silica is 100 nm.

[0016] Comparative Example 2 The preparation method of the high-performance polyimide film is basically the same as that in Example 1, except that step 3, preparing silica with hydroxyl groups on the surface, is omitted, and the silica with hydroxyl groups on the surface added in step 4, mixing and film-forming step, is replaced by silica with isocyanate groups on the surface. Specifically, step 4, mixing and film-forming step, is changed to: 9.8g of silica with isocyanate groups on its surface, 40g N,N-dimethylacetamide was mixed and stirred at 200 r / min for 30 min at room temperature to obtain a mixture. The entire mixture was then mixed with 31 g pyridine, 41 g acetic anhydride, and 240 g polyamic acid solution and stirred at 200 r / min for 30 min at room temperature. The mixture was filtered and degassed to obtain a casting solution. The casting solution was coated onto a clean glass plate to form a film with a thickness of 700 μm. The film was allowed to stand at 100 °C for 5 min and then added to a biaxial stretching machine for simultaneous longitudinal and transverse stretching. The stretching temperature was 50 °C, and the stretching speed for both longitudinal and transverse stretching was 25 mm / min. The stretching ratio for both longitudinal and transverse stretching was 1.3 times. The temperature was increased to 300 °C at a rate of 2 °C / min and allowed to stand at 300 °C for 20 min. The temperature was then increased to 450 °C at a rate of 1 °C / min and allowed to stand at 450 °C for 5 min to obtain a high-performance polyimide film.

[0017] Comparative Example 3 The preparation method of the high-performance polyimide film is basically the same as that in Example 1, except that the average particle size of the silica used in step 3, which is prepared with hydroxyl groups on the surface, is changed from 40 nm to 100 nm.

[0018] Performance Test Example 1 High-performance polyimide films were prepared according to the methods of Examples 1-4 and Comparative Examples 1-3, respectively. In the preparation process, after the second step of preparing silica with isocyanate groups on the surface, the silica was immediately used in the fourth step of film mixing. The glass transition temperature (Tg), tensile strength, elastic modulus, coefficient of thermal expansion (CTE), electrical breakdown strength, and transmittance at 450 nm wavelength of the prepared high-performance polyimide films were measured. 450 (To be tested)

[0019] When testing the glass transition temperature (Tg), the dynamic mechanical analysis method (DMA) was used; when testing the tensile strength and elastic modulus, the standard GB / T 1040.3-2006 was followed.

[0020] The test results are shown in Table 1: Table 1

[0021] The results in Table 1 show that the glass transition temperature (Tg), tensile strength, elastic modulus, coefficient of thermal expansion (CTE), electrical breakdown strength, and transmittance at 450 nm wavelength of Comparative Examples 1-3 are significantly different. 450The results were inferior to those of Examples 1-4, indicating that the use of Tween-80, glycerol, and particle size selection have a significant impact on the performance of polyimide films during their preparation.

[0022] Performance Test Example 2 High-performance polyimide films were prepared according to the methods of Examples 1-4 and Comparative Examples 1-3. In each case, after the second step of preparing silica with isocyanate groups on the surface, the films were left to stand for 5 days at 25°C and 60% relative humidity before being used in the fourth step of film preparation. The glass transition temperature (Tg), tensile strength, elastic modulus, coefficient of thermal expansion (CTE), electrical breakdown strength, and transmittance at 450 nm wavelength of the prepared high-performance polyimide films were measured. 450 (To be tested)

[0023] When testing the glass transition temperature (Tg), the dynamic mechanical analysis method (DMA) was used; when testing the tensile strength and elastic modulus, the standard GB / T 1040.3-2006 was followed.

[0024] The test results are shown in Table 2: Table 2

[0025] The results in Tables 1 and 2 show that, compared with directly applying the prepared silica with isocyanate groups to the preparation of polyimide films, the glass transition temperature (Tg), tensile strength, elastic modulus, coefficient of thermal expansion (CTE), electrical breakdown strength, and transmittance at 450 nm wavelength (T0.05) of Comparative Example 1 are significantly improved when the silica with isocyanate groups on its surface is left in air for a period of time before being applied to the preparation of polyimide films. 450 The decrease in Tween-80 was greater than that in Examples 1-4, indicating that the use of Tween-80 in the preparation of polyimide films can avoid the influence of the external environment on silicon dioxide with isocyanate groups on the surface.

[0026] Analysis shows that the role of Tween-80 in this invention is to improve the hydrophobicity of silica with isocyanate groups by utilizing the interaction between hydroxyl groups and isocyanate groups (see Luo Shanguo et al. Interaction in polyurethane reaction system. Journal of Beijing Institute of Technology. August 1997). First, silica is modified with 3-isocyanate-propyltrimethoxysilane, and then isocyanate groups are grafted onto its surface. Then, a layer of Tween-80 is further coated on it. Tween-80, as a surfactant, has hydrophobic groups, which can improve the hydrophobicity of silica and reduce the influence of moisture in the external environment on isocyanate groups (see Gao Yun et al. Mechanism of corrosion inhibition of steel in Cl3CCOOH. Surface Technology. February 2025). Furthermore, since Tween-80 contains hydroxyl groups, during the imidization process, pyridine can catalyze the reaction between the hydroxyl groups in Tween-80 and some isocyanate groups (see Li Dezhong. Preparation of Isocyanate-Modified Sorbitol Composite Nucleating Agent and Its Influence on Polypropylene Properties. Hubei University of Technology. May 2019), thereby fixing the hydrophobic groups in the polyimide film.

[0027] In this invention, glycerol acts as a coating on the surface of silica, increasing the hydroxyl content. This allows it to promote the uniform dispersion of silica with isocyanate groups after being added to the polyamic acid solution, through the interactions between hydroxyl groups and isocyanate groups, and between hydroxyl groups and the polyamic acid solution (see Wang Wei. Influence of Inorganic Nanoparticles on the Performance of Polyimide Hybrid Films. Harbin University of Science and Technology. March 2006). Furthermore, the presence of hydrogen bonds also improves the performance of the prepared polyimide film. In addition, the glycerol on the silica surface has a hydration effect with the water generated during imidization (see Chen Meiqiong et al. Influence of Polyols on the Electrochemical Performance of Fumed Silica Electrolytes. Storage Battery. April 2010), thus preventing the water removed by the polyamic acid from affecting the isocyanate groups.

[0028] In this invention, the particle size of silica in silica with hydroxyl groups on the surface is controlled, thereby utilizing the particle size difference between silica with isocyanate groups on the surface and silica with hydroxyl groups on the surface to achieve the stacking of the two, which is more conducive to the uniform dispersion of the two.

Claims

1. A method for preparing a high-performance polyimide film, characterized in that, It is prepared from the following steps: preparing a polyamide acid solution, preparing silica with isocyanate groups on the surface, preparing silica with hydroxyl groups on the surface, mixing and film forming; The preparation of silica with isocyanate groups on the surface, in a nitrogen atmosphere, mixing isocyanate group-containing silane coupling agent, silica, the first portion of toluene, stirring at 60-70℃, centrifugation, taking the precipitate, washing, vacuum drying, to obtain silane modified silica; mixing silane modified silica with Tween-80, the second portion of toluene, stirring at room temperature, centrifugation, taking the precipitate, vacuum drying, to obtain silica with isocyanate groups on the surface; The preparation of silica with hydroxyl groups on the surface, mixing silica, glycerol, water, ball milling, vacuum drying, to obtain silica with hydroxyl groups on the surface.

2. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, The preparation of polyamide acid solution, mixing diamine, dianhydride, N,N-dimethylacetamide in a nitrogen atmosphere, stirring at 5-10℃, to obtain polyamide acid solution.

3. The method for preparing the high-performance polyimide film according to claim 2, characterized in that, In the preparation of polyamide acid solution, the mass ratio of diamine, dianhydride, N,N-dimethylacetamide is 20-22:21.8-24:200-260; The diamine is 4,4'-diamino diphenyl ether; The dianhydride is pyromellitic dianhydride; The stirring time when stirring at 5-10℃ is 24-26h.

4. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, In the preparation of silica with isocyanate groups on the surface, the mass ratio of isocyanate group-containing silane coupling agent, silica, the first portion of toluene, Tween-80, the second portion of toluene is 20-25:20-25:200-300:10-12:200-300; The average particle size of the silica is 100nm; The isocyanate group-containing silane coupling agent is 3-isocyanate propyl trimethoxysilane.

5. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, In the preparation of silica with isocyanate groups on the surface, the stirring time when stirring at 60-70℃ is 12-13h; The stirring time when stirring at room temperature is 2-3h.

6. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, In the preparation of silica with hydroxyl groups on the surface, the mass ratio of silica, glycerol, water is 100-120:5-6:50-55.

7. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, In the preparation of silica with hydroxyl groups on the surface, the average particle size of the silica is 40nm; The ball milling speed when ball milling is 300-350r / min, the ball to material ratio is 3-4:1, and the ball milling time is 30-40min.

8. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, In the mixing and film forming, the mass ratio of silica with isocyanate groups on the surface, silica with hydroxyl groups on the surface, N,N-dimethylacetamide, catalyst, dehydrating agent, polyamide acid solution is 8-8.5:1.8-2:40-50:31-33:41-45:240-300; The catalyst is pyridine; The dehydrating agent is acetic anhydride.

9. The method for preparing the high-performance polyimide film according to claim 1, characterized in that, The mixed film is prepared by mixing the silicon dioxide with isocyanate groups on the surface, the silicon dioxide with hydroxyl groups on the surface and N,N-dimethylacetamide, stirring uniformly at room temperature to obtain a mixed solution; mixing the mixed solution with a catalyst, a dehydrating agent and a polyamide acid solution, stirring uniformly at room temperature, filtering, defoaming to obtain a casting solution, and casting the casting solution to form a film, standing at 100-105 ℃, simultaneously performing longitudinal stretching and transverse stretching, increasing the temperature to 300-310 ℃, standing at 300-310 ℃, increasing the temperature to 450-460 ℃, and standing at 450-460 ℃ to obtain a high-performance polyimide film.

10. The method for preparing the high-performance polyimide film according to claim 9, characterized in that, In the mixed film forming, the film thickness during film forming is 700-750 μm; The standing time at 100-105 ℃ is 5-6 min; The stretching temperature during simultaneous longitudinal stretching and transverse stretching is 50-60 ℃, the stretching speed of longitudinal stretching and transverse stretching is 25-30 mm / min, and the stretching multiple of longitudinal stretching and transverse stretching is 1.3-1.4 times; The temperature increasing speed during increasing the temperature to 300-310 ℃ is 2-3 ℃ / min; The standing time at 300-310 ℃ is 20-30 min; The temperature increasing speed during increasing the temperature to 450-460 ℃ is 1-1.5 ℃ / min; The standing time at 450-460 ℃ is 5-6 min.

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