A high-temperature resistant colorless polyimide film and its preparation method

Abstract

The present invention relates to a high-temperature resistant colorless polyimide film and a preparation method thereof, belonging to the technical field of polymer films. The preparation method specifically comprises the following steps: selecting a diamine monomer and a dianhydride monomer and adding them to a high-boiling point solvent in proportion to react and generate a polyamic acid precursor solution; using a sol-gel method to deposit a SiO2 layer on a cellulose derivative to prepare modified cellulose; wherein the cellulose derivative is cellulose acetate; adding the modified cellulose to the polyamic acid precursor solution, mixing evenly, and then coating it on the surface of a carrier, cooling and peeling after staged heat treatment, thereby obtaining a high-temperature resistant colorless polyimide film. Two reinforcement methods, molecular design reinforcement and modified cellulose reinforcement, are adopted to significantly improve the comprehensive performance of the film. At the same time, through a staged annealing process, the internal stress of the PI can be eliminated while optimizing the interface bonding between SiO2 and AC, ultimately achieving a high-strength, high-heat-resistant, low-stress composite film.

Description

Technical Field

[0001] The present application relates to the technical field of polymer films, and more specifically, to a high-temperature resistant colorless polyimide film and a preparation method thereof. Background Art

[0002] Polyimide (PI) film, a high-performance polymer material with an imide ring as its core structure, is widely used in cutting-edge fields such as aerospace, microelectronics, and flexible displays due to its exceptional high-temperature resistance, excellent mechanical strength, and good chemical stability. Traditional PI film's molecular chains contain strongly conjugated aromatic structures and imide rings, forming a dense stack through charge transfer complexation (CTC). This imparts high thermal stability and mechanical properties, but also results in strong visible light absorption, resulting in a brownish-yellow color, which severely limits its application in flexible displays, optical packaging, and other fields.

[0003] In recent years, researchers have optimized the optical properties of PI films through molecular design, such as introducing fluorinated groups or alicyclic structures to inhibit CTC formation. However, such approaches are often accompanied by decreased mechanical properties or thermal stability. Furthermore, traditional preparation processes suffer from poor thickness uniformity and molecular chain relaxation caused by high-temperature imidization, further impacting the film's overall performance.

[0004] In summary, the present application provides a high-temperature resistant colorless polyimide film and a preparation method thereof. Summary of the Invention

[0005] In order to prepare a PI film with high light transmittance, excellent thermal stability and mechanical properties, the present application provides a high-temperature resistant colorless polyimide film and a preparation method thereof.

[0006] The present application provides a high-temperature resistant colorless polyimide film and a preparation method thereof, which adopts the following technical solutions:

[0007] A method for preparing a high-temperature resistant colorless polyimide film comprises the following steps:

[0008] S1, selecting a diamine monomer and a dianhydride monomer and adding them to a high boiling point solvent in proportion to react to generate a polyamic acid precursor solution;

[0009] S2. Depositing a SiO2 layer on a cellulose derivative using a sol-gel method to prepare modified cellulose; wherein the cellulose derivative is cellulose acetate;

[0010] S3. Adding modified cellulose to the polyamic acid precursor solution, mixing evenly and coating the mixture on the surface of the carrier, cooling and peeling the mixture after staged heat treatment to obtain a high-temperature resistant colorless polyimide film.

[0011] Furthermore, in step S1, the diamine monomer is obtained by mixing a fluorine-containing diamine monomer and a benzimidazole-containing diamine monomer.

[0012] Furthermore, the fluorine-containing diamine monomer is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 3,5-diaminotoluene trifluoride (3,5-DATFT), and 2,2',3,3'-tetrafluoro-4,4'-diaminobiphenyl (4,4'-F2BAPB).

[0013] Furthermore, the diamine monomer containing benzimidazole is at least one of 2-(4-aminophenyl)-5-aminobenzimidazole (APABI), 2,2'-bis(4-aminophenyl)benzimidazole (BABZ), 2-(4-aminophenyl)-5-(4-aminophenoxy)benzimidazole (AAPBI), and 2-(3,5-diaminophenyl)-benzimidazole (BBIA).

[0014] In the above scheme, by introducing fluorine, trifluoromethyl weak electron-withdrawing groups and benzimidazole large substituent groups into the molecular structure of the polyimide film, the charge transfer complex effect between the molecular chains is destroyed, the stacking density of the molecular chains is reduced, thereby reducing visible light absorption and improving transmittance.

[0015] Preferably, the fluorine-containing diamine monomer is TFMB, and the benzimidazole-containing diamine monomer is BBIA.

[0016] Furthermore, the dianhydride monomer is a monomer containing fluorine or an alicyclic structure.

[0017] Furthermore, the dianhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) and / or cyclobutanetetracarboxylic dianhydride (CBDA).

[0018] Furthermore, the high boiling point solvent is at least one of dimethylacetamide (DMAc), methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), sulfolane, hexamethylphosphoramide (HMPA), γ-butyrolactone (GBL), triethyl phosphate (TEP), diethylene glycol dimethyl ether (Diglyme), sodium thiocyanate solution (NaSCN), and ionic liquids (ILs).

[0019] Furthermore, in step S1, the polyamic acid precursor solution is specifically prepared by the following steps:

[0020] The diamine monomer and the high boiling point solvent are stirred at room temperature and an inert atmosphere at a rate of 30-90 rpm for 10-20 minutes, and then the dianhydride monomer is added, and the stirring reaction is continued at 0-4° C. for 20-24 hours to obtain a polyamic acid precursor solution.

[0021] Furthermore, the mass volume ratio of the diamine monomer to the high boiling point solvent is 1 g:(8-10) mL.

[0022] Furthermore, the molar ratio of the diamine monomer to the dianhydride monomer is 1:(1-1.2).

[0023] Furthermore, the modified cellulose is specifically prepared by the following steps:

[0024] A1. Add the precursor to the solvent, add deionized water dropwise and stir for 20-30 minutes, then adjust the pH value of the system to 2-4, and continue stirring at room temperature for 10-20 hours to obtain Si sol;

[0025] A2. Add the cellulose derivative, dispersant and coupling modifier to the Si sol, ultrasonically treat for 20-30 minutes at room temperature, then let it stand for 1-2 hours, and then centrifuge the system for 5-10 minutes. Wash the precipitate and dry it to constant weight to obtain modified cellulose.

[0026] Further preferably, in step S2, the modified cellulose is prepared by the following steps:

[0027] A1. Add the precursor to a solvent at a concentration of 0.1-1 mol / L, add deionized water dropwise to the system and stir at 30-90 rpm for 20-30 min. Then adjust the pH of the system to 2-4 with 1 mol / L HCl solution and continue stirring at room temperature for 10-20 h to obtain Si sol.

[0028] A2. A cellulose derivative, a dispersant, and a coupling modifier are added to a Si sol, and ultrasonically treated at a frequency of 20-30 kHz at room temperature for 20-30 minutes. The mixture is then allowed to stand for 1-2 hours. The system is then centrifuged at a rate of 3000-5000 rpm for 5-10 minutes. The precipitate is washed three times with a 70 wt% ethanol solution and dried at 40-60°C to a constant weight to obtain modified cellulose; wherein the cellulose derivative is cellulose acetate.

[0029] Furthermore, in step A1, the precursor is tetraethyl orthosilicate (TEOS) and / or methyl orthosilicate (TMOS).

[0030] Furthermore, in step A1, the solvent is at least one of ethanol, isopropanol or acetone.

[0031] Furthermore, in step A1, the molar ratio of the precursor to deionized water is 1:(5-7).

[0032] Furthermore, in step A2, the dispersant is polyvinyl pyrrolidone (PVP) and / or sodium dodecyl sulfate (SDS).

[0033] Furthermore, in step A2, the coupling modifier is 3-aminopropyltrimethoxysilane (APTES).

[0034] Furthermore, in step A2, the mass ratio of the cellulose derivative, the dispersant, the coupling modifier and the Si sol is 1:(0.05-0.1):(0.05-0.2):(15-20).

[0035] Furthermore, in step S3, the mass ratio of the modified cellulose to the polyamic acid precursor solution is (3-6):100.

[0036] Preferably, in step S3, the coating speed is set to 0.1 m / min and the coating pressure is set to 0.2-0.5 MPa.

[0037] Furthermore, in step S3, the specific operation of the heat treatment is as follows:

[0038] Under an inert atmosphere, heat the coated carrier to 80-100°C at a rate of 5-10°C / min and maintain for 0.5-1h, heat it to 150-200°C at a rate of 1-3°C / min, keep it for 1.5-2h, and then heat it to 350-400°C at a rate of 1-3°C / min and maintain it for 0.5-1h.

[0039] During the heat treatment process at the above stage, by treating at a low temperature of 80-100 ° C for 0.5-1 hour and slowly heating to a heat treatment stage of 150-200 ° C, residual solvents such as high boiling point solvents and water are removed step by step. While avoiding solvent residues that cause blistering or cracking of the film, the solvent is slowly evaporated to gradually relax the molecular chains in the system to reduce internal stress accumulation and the risk of agglomeration between modified cellulose. Subsequently, by treating at 350-400 ° C to undergo an imidization reaction to form a rigid ring structure, it promotes the transformation of polyamic acid (PAA) to polyimide (PI) while promoting the densification of cellulose and Si networks in the modified cellulose.

[0040] In summary, this application has the following beneficial effects:

[0041] The present application uses a weak electron-withdrawing group of fluorine and trifluoromethyl and a large substituent group of benzimidazole to destroy the charge transfer complex effect between the molecular chains, reduce the molecular chain packing density, thereby reducing visible light absorption and improving light transmittance. At the same time, a cellulose acetate (CA) material coated with SiO2 is also used to enhance the polyimide film. The cellulose chains of cellulose acetate replace some hydroxyl groups with acetyl groups to form a parallel arrangement similar to a quartz chain structure. This structure is topologically similar to the local arrangement of the silicon-oxygen tetrahedron of SiO2 (chain Si-O-Si bond). In terms of mechanical properties, the chain structure of cellulose acetate forms a synergistic enhancement effect with the silicon-oxygen skeleton of SiO2, with strong interfacial bonding and high stress transfer efficiency. The flexible chain segment of acetyl can relieve the stress concentration of SiO2 nanoparticles, realize energy dissipation during stress transfer, and improve the elongation at break and toughness of the film. In terms of high-temperature resistance, the introduction of acetyl groups reduces the polarity of the cellulose material, minimizing interactions with polyimide molecular chains and avoiding localized thermal stress concentration caused by filler agglomeration. Regarding transparency, the chain structure of cellulose ether is similar to the silicon-oxygen skeleton arrangement of SiO2, resulting in uniform dispersion and reduced light scattering. Acetyl groups reduce polarity and minimize phase separation with PI. Simultaneously, the low-polarity surface containing acetyl groups reduces the tendency for phase separation with polyimide, facilitating the formation of a uniformly dispersed nanocomposite material and avoiding haze caused by optical path length differences.

[0042] The molecular design reinforcement and the modified cellulose reinforcement, the two reinforcement methods can significantly improve the overall performance of the film through synergistic effects. Specifically, the SiO2 nanoparticles in the modified cellulose form a physical barrier by dispersing in the PI matrix, hindering crack propagation and improving the tensile strength and modulus of the film. The five-membered ring structure of benzimidazole has high rigidity, and the tight stacking of its molecular chains can further enhance the mechanical properties of PI. The combination of the two significantly improves the mechanical properties of the film, such as the fracture strength. Groups such as trifluoromethyl inhibit the rotation of the PI molecular chain through steric hindrance, reducing thermal motion ability. The thermal stability of SiO2 can further delay the thermal decomposition of the PI molecular chain and improve the temperature resistance of the film.

[0043] This application utilizes a staged annealing process to eliminate internal stress in the PI while optimizing the interface bonding between SiO2 and AC, ultimately achieving a high-strength, high-heat-resistant, low-stress composite film. Specifically, through a staged heat treatment process design, the stress-relieving temperature treatment is concentrated before 400°C, achieving the same stress-relieving purpose while avoiding the traditional high-temperature annealing stage at 400-450°C. This prevents prolonged treatment at this temperature, which can lead to phase separation in the modified cellulose and consequent film cracking. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] All reagents involved in the specific embodiments of this application are chemically pure. In addition, the cellulose acetate used has a CAS number of 9004-35-7, 39.8 wt% acetyl group, and is sourced from leaves; and the microcrystalline cellulose has a CAS number of 9004-34-6, a particle size of 50 μm, and is sourced from leaves.

[0046] Example 1

[0047] A method for preparing a high-temperature resistant colorless polyimide film comprises the following steps:

[0048] S1. Stirring the diamine monomer and the high-boiling-point solvent at room temperature and a nitrogen atmosphere at a rate of 90 rpm for 15 min, then adding the dianhydride monomer, and continuing the stirring reaction at 0° C. for 24 h to obtain a polyamic acid precursor solution;

[0049] The mass volume ratio of the diamine monomer to the high boiling point solvent is 1 g:8 mL, and the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.1;

[0050] The diamine monomer is obtained by mixing TFMB and BBIA in a molar ratio of 1:1, the dianhydride monomer is CBDA, and the high boiling point solvent is DMAc.

[0051] S2. Using a sol-gel method to deposit a SiO2 layer on a cellulose derivative to prepare modified cellulose, the specific operation is as follows:

[0052] A1. Add the precursor to a solvent at a concentration of 0.5 mol / L. Add deionized water dropwise to the system and stir at 90 rpm for 20 min. Then adjust the pH value of the system to 2 with 1 mol / L HCl solution. Continue stirring at room temperature for 10 h to obtain Si sol.

[0053] The precursor is TEOS, the solvent is ethanol, and the molar ratio of the precursor to deionized water is 1:5.

[0054] A2. Add a cellulose derivative, a dispersant, and a coupling modifier to a Si sol, ultrasonically treat the sol at room temperature at a frequency of 20 kHz for 20 min, then allow the sol to stand for 1.5 h. Centrifuge the sol at a rate of 3000 rpm for 10 min, wash the precipitate three times with a 70 wt% ethanol solution, and dry the precipitate at 40° C. to a constant weight to obtain modified cellulose.

[0055] The mass ratio of the cellulose derivative, the dispersant, the coupling modifier and the Si sol is 1:0.05:0.05:15; the cellulose derivative is cellulose acetate; the cellulose derivative is CA, the dispersant is PVP, and the coupling modifier is APTES.

[0056] S3, adding modified cellulose to a polyamic acid precursor solution, mixing well, and coating the mixture on a carrier surface, cooling the mixture after staged heat treatment, and peeling the mixture off to obtain a high-temperature resistant colorless polyimide film;

[0057] The mass ratio of the modified cellulose to the polyamic acid precursor solution is 4:100, and the coating speed is 0.1 m / min. The specific operation of the stage heat treatment is as follows:

[0058] Under a nitrogen atmosphere, the coated carrier was heated to 80°C at a rate of 5°C / min and maintained for 0.5h, then heated to 150°C at a rate of 2°C / min, maintained for 1.5h, and then heated to 350°C at a rate of 2°C / min and maintained for 0.5h.

[0059] Example 2

[0060] A method for preparing a high-temperature resistant colorless polyimide film comprises the following steps:

[0061] S1. Stirring the diamine monomer and the high-boiling-point solvent at room temperature and a nitrogen atmosphere at a rate of 90 rpm for 15 min, then adding the dianhydride monomer, and continuing the stirring reaction at 0° C. for 24 h to obtain a polyamic acid precursor solution;

[0062] The mass volume ratio of the diamine monomer to the high boiling point solvent is 1 g:9 mL, and the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.1;

[0063] The diamine monomer is obtained by mixing TFMB and BBIA in a molar ratio of 1:1, the dianhydride monomer is CBDA, and the high boiling point solvent is DMAc.

[0064] S2. Using a sol-gel method to deposit a SiO2 layer on a cellulose derivative to prepare modified cellulose, the specific operation is as follows:

[0065] A1. Add the precursor to a solvent at a concentration of 0.6 mol / L. Add deionized water dropwise to the system and stir at 90 rpm for 20 min. Then adjust the pH value of the system to 3 with 1 mol / L HCl solution. Continue stirring at room temperature for 15 h to obtain Si sol.

[0066] The precursor is TEOS, the solvent is ethanol, and the molar ratio of the precursor to deionized water is 1:6.

[0067] A2. Add a cellulose derivative, a dispersant, and a coupling modifier to a Si sol, ultrasonically treat the sol at room temperature at a frequency of 22 kHz for 30 minutes, then allow the sol to stand for 1.5 hours, and then centrifuge the sol at a rate of 4000 rpm for 10 minutes. Wash the precipitate three times with a 70 wt% ethanol solution, and dry the precipitate at 50°C to a constant weight to obtain modified cellulose.

[0068] The mass ratio of the cellulose derivative, the dispersant, the coupling modifier and the Si sol is 1:0.08:0.1:18; the cellulose derivative is cellulose acetate; the cellulose derivative is CA, the dispersant is PVP, and the coupling modifier is APTES.

[0069] S3, adding modified cellulose to a polyamic acid precursor solution, mixing well, and coating the mixture on a carrier surface, cooling the mixture after staged heat treatment, and peeling the mixture off to obtain a high-temperature resistant colorless polyimide film;

[0070] The mass ratio of the modified cellulose to the polyamic acid precursor solution is 5:100, and the coating speed is 0.1 m / min. The specific operation of the stage heat treatment is as follows:

[0071] Under nitrogen atmosphere, the coated carrier was heated to 90°C at a rate of 8°C / min and maintained for 45 min, then heated to 180°C at a rate of 2°C / min and maintained for 105 min, and then heated to 380°C at a rate of 2°C / min and maintained for 45 min.

[0072] Example 3

[0073] A method for preparing a high-temperature resistant colorless polyimide film comprises the following steps:

[0074] S1. Stirring the diamine monomer and the high-boiling-point solvent at room temperature and a nitrogen atmosphere at a rate of 90 rpm for 15 min, then adding the dianhydride monomer, and continuing the stirring reaction at 0° C. for 24 h to obtain a polyamic acid precursor solution;

[0075] The mass volume ratio of the diamine monomer to the high boiling point solvent is 1 g:10 mL, and the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.1;

[0076] The diamine monomer is obtained by mixing TFMB and TFMB in a molar ratio of 1:1, the dianhydride monomer is CBDA, and the high boiling point solvent is NMP.

[0077] S2. Using a sol-gel method to deposit a SiO2 layer on a cellulose derivative to prepare modified cellulose, the specific operation is as follows:

[0078] A1. Add the precursor to a solvent at a concentration of 0.8 mol / L. Add deionized water dropwise to the system and stir at 90 rpm for 20 min. Then adjust the pH value of the system to 4 with 1 mol / L HCl solution. Continue stirring at room temperature for 20 h to obtain a Si sol.

[0079] The precursor is TMOS, the solvent is isopropyl alcohol, and the molar ratio of the precursor to deionized water is 1:7.

[0080] A2. Add a cellulose derivative, a dispersant, and a coupling modifier to a Si sol, ultrasonically treat the sol at room temperature at a frequency of 28 kHz for 30 minutes, then allow the sol to stand for 1.5 hours, and then centrifuge the sol at a rate of 5000 rpm for 10 minutes. Wash the precipitate three times with a 70 wt% ethanol solution, and dry it at 60°C to a constant weight to obtain modified cellulose.

[0081] The mass ratio of the cellulose derivative, the dispersant, the coupling modifier and the Si sol is 1:0.1:0.2:20; the cellulose derivative is cellulose acetate; the cellulose derivative is CA, the dispersant is SDS, and the coupling modifier is APTES.

[0082] S3, adding modified cellulose to a polyamic acid precursor solution, mixing well, and coating the mixture on a carrier surface, cooling the mixture after staged heat treatment, and peeling the mixture off to obtain a high-temperature resistant colorless polyimide film;

[0083] The mass ratio of the modified cellulose to the polyamic acid precursor solution is 6:100, and the coating speed is 0.1 m / min. The specific operation of the stage heat treatment is as follows:

[0084] Under nitrogen atmosphere, the coated carrier was heated to 100°C at a rate of 10°C / min and maintained for 1 hour, then heated to 200°C at a rate of 3°C / min and maintained for 2 hours, and then heated to 400°C at a rate of 3°C / min and maintained for 1 hour.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 1 is that microcrystalline cellulose is used instead of CA.

[0087] Comparative Example 2

[0088] The difference between this comparative example and Example 1 is that the concentration of the Si sol is increased. Specifically, in step A1 of this comparative example, after the precursor is added with the solvent, its concentration is set to 1.5 mol / L.

[0089] Comparative Example 3

[0090] The difference between this comparative example and Example 1 is that in step S3 of this comparative example, the specific operation of the stage heat treatment is:

[0091] Under a nitrogen atmosphere, the coated support was heated to 80° C. at a rate of 5° C. / min and maintained for 0.5 h, and then heated to 350° C. at a rate of 5° C. / min and maintained for 2 h.

[0092] Performance Testing

[0093] The polyimide films prepared in Examples 1-3 and Comparative Examples 1-3 of the present application were prepared into samples with a size of 10 mm × 5 mm and a thickness of 30 μm. The high temperature resistance, transparency, and mechanical properties of the samples in different groups were tested. The specific test contents are as follows:

[0094] High-temperature performance test: The glass transition temperature (Tg) and thermal decomposition temperature (Td) of the sample were measured to determine the high-temperature performance of the sample. The Tg of the sample was measured using differential scanning calorimetry under a nitrogen atmosphere, with a heating rate set at 10°C / min and a temperature range of 50-500°C. The Td of the sample was measured using thermogravimetric analysis under a nitrogen atmosphere, with a heating rate set at 10°C / min, and the temperature at which the mass loss was 5% was recorded.

[0095] Transparency test: The transmittance and haze (500 nm) of the film were tested using a UV-visible spectrophotometer with a wavelength range of 200-800 nm. The transparency of the sample was determined by the transmittance and haze values.

[0096] Mechanical properties test: The tensile strength and elongation at break of samples in different groups were measured using a universal material testing machine with a tensile rate set at 5 mm / min.

[0097] The specific performance test results are shown in Table 1:

[0098] Table 1

[0099]

[0100] From the results shown in Table 1 above, it can be seen that the polyimide film products prepared in Examples 1-3 of the present application have better performance. Based on the results in the comparative examples, the Tg and Td values in Comparative Example 1 are both reduced, proving that the acetyl group of CA reduces polarity and has a better interface bonding effect with PI. However, microcrystalline cellulose contains a large number of crystalline regions and has strong polarity. At the same usage amount, its compatibility with the matrix is not as good as CA, which can easily lead to interface debonding, increase light scattering, and cause an increase in haze value and a decrease in thermal stability. In Comparative Example 2, by increasing the Si sol concentration and increasing the SiO2 content on the CA surface, the high temperature resistance was not further improved compared to Comparative Example 1, and SiO2 agglomeration caused interface defects, weakening the reinforcement effect on the PI molecular chain, resulting in a slight decrease in Tg and Td. At the same time, agglomeration also caused a decrease in mechanical properties and an increase in haze. In Comparative Example 3, there was no step annealing stage, the PI molecular chain was not sufficiently relaxed, and residual internal stress caused defects, resulting in a decrease in various properties.

[0101] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0102] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant colorless polyimide film, characterized in that: The method comprises the following preparation steps: S1, selecting a diamine monomer and a dianhydride monomer and adding them to a high boiling point solvent in proportion to react to generate a polyamic acid precursor solution; the diamine monomer is obtained by mixing a fluorine-containing diamine monomer and a benzimidazole-containing diamine monomer; S2. Using a sol-gel method to deposit a SiO2 layer on a cellulose derivative to prepare modified cellulose, the specific operation is as follows: A1. Add the precursor to the solvent to set its concentration to 0.1-1 mol / L, add deionized water dropwise and stir for 20-30 min, then adjust the pH value of the system to 2-4, and continue stirring at room temperature for 10-20 h to obtain Si sol; A2. Adding a cellulose derivative, a dispersant, and a coupling modifier to a Si sol, ultrasonically treating the sol at room temperature for 20-30 minutes, then allowing the sol to stand for 1-2 hours, and then centrifuging the sol for 5-10 minutes. Washing the precipitate and drying it to a constant weight to obtain modified cellulose; wherein the cellulose derivative is cellulose acetate; S3. Adding modified cellulose to the polyamic acid precursor solution, mixing evenly and coating it on the surface of the carrier, cooling and peeling after staged heat treatment, thus obtaining a high-temperature resistant colorless polyimide film.

2. The method for preparing a high-temperature resistant colorless polyimide film according to claim 1, characterized in that: The fluorine-containing diamine monomer is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,5-diaminobenzotrifluoride, and 2,2',3,3'-tetrafluoro-4,4'-diaminobiphenyl.

3. The method for preparing a high temperature resistant colorless polyimide film according to claim 1, characterized in that: The diamine monomer containing benzimidazole is at least one of 2-(4-aminophenyl)-5-aminobenzimidazole, 2,2'-bis(4-aminophenyl)benzimidazole, 2-(4-aminophenyl)-5-(4-aminophenoxy)benzimidazole and 2-(3,5-diaminophenyl)-benzimidazole.

4. The method for preparing a high-temperature resistant colorless polyimide film according to claim 1, characterized in that: In step S1, the mass volume ratio of the diamine monomer to the high boiling point solvent is 1 g:8-10 mL.

5. The method for preparing a high temperature resistant colorless polyimide film according to claim 1, characterized in that: In step A2, the mass ratio of the cellulose derivative, the dispersant, the coupling modifier and the Si sol is 1:0.05-0.1:0.05-0.2:15-20.

6. The method for preparing a high-temperature resistant colorless polyimide film according to claim 1, characterized in that: In step S3, the mass ratio of the modified cellulose to the polyamic acid precursor solution is 3-6:

100.

7. The method for preparing a high temperature resistant colorless polyimide film according to claim 1, characterized in that: In step S3, the specific operation of the heat treatment is as follows: Under a nitrogen atmosphere, heat the coated carrier to 80-100°C at a rate of 5-10°C / min and maintain for 0.5-1h, heat it to 150-200°C at a rate of 1-3°C / min, keep it for 1.5-2h, and then heat it to 350-400°C at a rate of 1-3°C / min and maintain it for 0.5-1h.

8. A polyimide film obtained by the method for preparing a high-temperature resistant colorless polyimide film according to any one of claims 1 to 7.

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