Colorless transparent polyimide resin and film and preparation method thereof

Abstract

The invention belongs to the technical field of polyimide films, and particularly relates to colorless transparent polyimide resin, a film and a preparation method thereof. The colorless transparent polyimide resin is formed by polymerizing dianhydride and diamine which are equal in mole in a strong-polarity aprotic organic solvent, the dianhydride comprises 9, 9-bis (3, 4-dicarboxyphenyl) fluorene dianhydride, and the use amount of the dianhydride is (4.5-99.5)% of the total mole number of the dianhydride; the diamine comprises 2, 2-bis [4-(2-trifluoromethyl-4-aminophenoxy) phenyl] hexafluoropropane, and the use amount of the diamine is (4.5-100)% of the total mole number of the diamine. The polyimide film prepared from the polyimide film has excellent comprehensive performance, can be applied to high-tech fields such as space telescopes, flexible solar cells, transparent glass protective films, OLED (Organic Light Emitting Diode) display screens and liquid crystal alignment films, and has good potential market and application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of polyimide films, and in particular relates to a colorless and transparent polyimide resin and film and a preparation method thereof. Background Art

[0002] Polyimide film is a type of polymer material with extremely excellent comprehensive properties. With its outstanding heat resistance, low temperature resistance, flame retardancy, electrical properties and mechanical properties, it is widely used in many high-tech fields such as electronic microelectronics, printed circuit boards, wires and cables, motor main insulation, shipbuilding, aerospace, laser, optoelectronics, etc.

[0003] However, the molecular structure of traditional polyimide films is of the pyromellitic anhydride type, and their main monomer raw materials are pyromellitic anhydride and 4,4'-diaminodiphenyl ether. Due to the obvious CTC effect in the molecular structure of polyimide prepared from these monomers, the obtained polyimide film has a darker color and a lower visible light transmittance.

[0004] Chinese patent CN117964895A discloses a high temperature resistant transparent polyimide, a polyimide film and a preparation method thereof. By starting from multiple aspects such as molecular structure design, polymerization process regulation, and film preparation process optimization, a comprehensive balance of multiple properties such as heat resistance and optical transparency is achieved, so that the polyimide film simultaneously achieves high heat resistance, low expansion and high transparency. However, when the film thickness of the film is only 10±2μm, its visible light transmittance data still fails to exceed 92%, indicating that the transparency of the film is still insufficient and needs to be further improved. In addition, the maximum temperature required to reach the film during the preparation process is as high as 410°C, which also brings relatively large energy consumption problems.

[0005] Chinese patent CN114685786A discloses a polyimide film and its preparation method and application. The molecular main chain of the polyimide contains an end group protection group, which realizes the effective protection of the active end group in the molecular chain, and makes the aggregated structure of the film more stable, effectively improving the optical stability of the polyimide film under high temperature environment, and has important applications in the fields of electronics, microelectronics, optical display, optical communication, etc. However, the introduction of phthalic anhydride as an end-capping agent in the molecular structure not only increases the number of reactants, but also hinders the growth of molecular weight in the subsequent curing process, resulting in the failure to give full play to the mechanical properties of the film. In addition, the visible light transmittance data of the polyimide film is below 92%, which needs to be improved. In addition, during the film preparation process, the required maximum temperature reaches 400 ° C, resulting in large energy consumption. Therefore, it is urgent to develop a method for preparing a polyimide film that can improve visible light transmittance, optimize mechanical properties, and reduce energy consumption to meet the stringent requirements of the growing high-tech field for material performance. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a colorless and transparent polyimide resin. The polyimide film prepared by using the same has excellent comprehensive performance and can be applied to high-tech fields such as space telescopes, flexible solar cells, transparent glass protective films, OLED displays, liquid crystal orientation films, etc., and has good potential market and application prospects.

[0007] Another object of the present invention is to provide a polyimide film and a method for preparing the same.

[0008] The technical solution adopted by the present invention is as follows: The colorless and transparent polyimide resin is polymerized by equimolar amounts of dianhydride and diamine in a highly polar aprotic organic solvent, wherein the dianhydride includes 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and its usage is (4.5-99.5)% of the total molar number of the dianhydride; and the diamine includes 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, and its usage is (4.5-100)% of the total molar number of the diamine.

[0009] The dianhydride also includes 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phthalic dianhydride , 1,3-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 1,2-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride or 4,4'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride.

[0010] The diamines also include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodicyclohexylmethane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 1,3-phenylenediamine, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, Aminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,2-bis(3-aminophenoxy)benzene, 1,2-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl ether, 4,4'-bis(3-aminophenoxy)diphenyl ether, 4,4'-bis(4-aminophenoxy)diphenyl sulfide, 4,4'-bis(3-aminophenoxy)diphenyl sulfide, 4,4'-bis(4-aminophenoxy)diphenylmethane, 4,4'-bis(3-aminophenoxy)diphenylmethane, 4,4'-bis(4-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)benzophenone, 1,3-bis(2-trifluoromethyl-3-aminophenoxy)benzene, 1,3-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 1,2-bis(2-trifluoromethyl-3-aminophenoxy)benzene, 1,2-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 1,4-bis(2-trifluoromethyl-3-aminophenoxy)benzene, 1,4-bis(2-trifluoromethyl-4 -aminophenoxy)benzene, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy)diphenyl sulfone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenyl sulfone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenyl ether, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy)diphenyl ether, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenyl sulfide, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy)diphenyl sulfide, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenylmethane, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy)diphenylmethane, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)benzophenone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)benzophenone, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy)benzophenone ...4'-Bis(2-trifluoromethyl-3-aminophenoxy)benzophenone, 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, One or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-trifluoromethyl-3-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]propane, 3,5-bis(4-aminophenoxy)benzoic acid, 3,5-bis(2-trifluoromethyl-4-aminophenoxy)benzoic acid or 3,5-diaminobenzoic acid.

[0011] The highly polar aprotic organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and dimethyl sulfoxide.

[0012] The polyimide film is prepared by using the colorless and transparent polyimide resin.

[0013] The method for preparing the polyimide film comprises the following steps: Put a strongly polar aprotic organic solvent into a reaction kettle, add dianhydride and diamine under a nitrogen atmosphere, stir and react until the homogeneous phase is transparent, then add a dehydrating agent and a catalyst for subsequent reaction, after the subsequent reaction is completed, precipitate, filter, and vacuum dry to obtain a solid, and dissolve the solid in a strongly polar aprotic organic solvent to obtain a colorless and transparent polyimide resin; then carry out coating, solvent removal, curing, and demolding in sequence to obtain a polyimide film.

[0014] The dehydrating agent is one or more of acetic anhydride, propionic anhydride, trifluoroacetic anhydride or dicyclohexylcarbodiimide.

[0015] The catalyst is one or more of pyridine, picoline, dimethylpyridine, triethylamine, tripropylamine, tributylamine or tertiary amine.

[0016] The precipitating agent used in the precipitation is one or more of water, methanol, ethanol, isopropanol, propanol, butanol or isobutanol.

[0017] The temperature for removing the solvent and solidifying is below 250°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The polyimide film prepared by the present invention has excellent mechanical properties, a visible light transmittance of more than 93%, low water absorption, and a low dielectric constant. It can be applied to high-tech fields such as space telescopes, flexible solar cells, transparent glass protective films, OLED displays, and liquid crystal alignment films, and has good potential markets and application prospects; (2) The preparation process of the present invention is simple, has low energy consumption, is easy to operate, and the source of reaction raw materials is convenient. The preparation process can be completed in general equipment, which is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the FTIR graph of the polyimide film prepared in Example 1. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the embodiments, but they do not limit the implementation of the present invention.

[0021] The raw materials used in the examples and comparative examples are conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are conventional methods in the art unless otherwise specified.

[0022] Example 1 The preparation method of the polyimide film comprises the following steps: 37.5 g of N-methyl-2-pyrrolidone was added to the reactor, and the system temperature was adjusted to 2.5 ± 2.5 °C. Under nitrogen atmosphere, 8.5 g (0.013 mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane was added and stirred until completely dissolved. Then, 3.4 g (0.011 mol) of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride was added twice, half each time, with an interval of 30 min. After the addition was completed, 0.92 g (0.0 0.02mol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, stir and react for 12h until homogeneous and transparent, then add 0.31g of pyridine and 1.2g of acetic anhydride, continue stirring and reacting at 55±25℃ for 8h to obtain a homogeneous viscous solution, add the obtained solution into a pure water precipitant to form a white solid, filter, put it into a vacuum oven at 80℃ and dry it to obtain a solid, dissolve the solid in N-methyl-2-pyrrolidone, and prepare a colorless and transparent polyimide resin with a solid content of 25%, recorded as CPI-S1; CPI-S1 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min under a pressure of -0.095±0.005MPa and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C for film removal to obtain a polyimide film, recorded as CPI-1, with a viscosity of 1926.7mPa·s at 55°C.

[0023] CPI-1 was tested using a Fourier transform infrared spectrometer. The FTIR graph is shown below: Figure 1 As shown by Figure 1 It can be seen that 1250cm -1 The characteristic absorption peak of aromatic ether bond is 1380cm -1 The CN stretching vibration peak is at 1500-1600cm -1 The peak at 1750cm is the vibration peak of the benzene ring skeleton. -1 and 1780cm -1 The corresponding peaks are C=O symmetric stretching vibration peak and C=O asymmetric stretching vibration peak, respectively, which verifies the successful synthesis of polyimide film.

[0024] Example 2 The preparation method of the polyimide film comprises the following steps: 37.5 g of N,N-dimethylacetamide was added to the reactor, and the system temperature was adjusted to 2.5±2.5°C. Under nitrogen atmosphere, 8.5 g (0.013 mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane was added and stirred until completely dissolved. Then, 3.1 g (0.01 mol) of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride was added twice, half each time, with an interval of 30 minutes. After the addition was completed, 1.4 g (0.003 mol) of 9,9-bis(3,4-dicarboxyphenyl) The mixture was added with 2.5 g of dimethylpyridine and 10.5 g of trifluoroacetic anhydride, and stirred for 12 h until the homogeneous phase became transparent. Then, 2.5 g of lutidine and 10.5 g of trifluoroacetic anhydride were added, and the mixture was stirred for 8 h at 55±25°C to obtain a homogeneous viscous solution. The obtained solution was added to a mixed precipitant of pure water and methanol in a volume ratio of 1:1 to form a white solid. After filtering, the solid was placed in a vacuum oven at 80°C for drying to obtain a solid. The solid was dissolved in N,N-dimethylacetamide to prepare a colorless and transparent polyimide resin with a solid content of 25%, which was recorded as CPI-S2. The viscosity of the polyimide resin at 55°C was 2243.3 mPa·s. CPI-S2 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min at a pressure of -0.095±0.005MPa, and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min, and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C to remove the film, thereby obtaining a polyimide film, recorded as CPI-2.

[0025] Example 3 The preparation method of the polyimide film comprises the following steps: 20g of N-methyl-2-pyrrolidone and 27.5g of N,N-dimethylformamide were added to the reactor, and the system temperature was adjusted to 2.5±2.5℃. Under nitrogen atmosphere, 7.8g (0.012mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane and 0.3g (0.0006mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane were added, and stirred until completely dissolved. 0.27g (0.0006mol) of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added to the reactor. After an interval of 30min, 5.5g (0.012mol) of 9, 9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, half of it was added each time, with an interval of 30 minutes between two times, and the reaction was stirred for 14 hours until the homogeneous phase was transparent, and then 1.32g of pyridine, 1g of triethylamine, 2g of trifluoroacetic anhydride and 1.2g of acetic anhydride were added, and the reaction was continued for 6 hours under the condition of 55±25℃ to obtain a homogeneous viscous solution, and the obtained solution was added to a mixed precipitant of pure water and ethanol with a volume ratio of 3:1 to form a white solid, which was filtered and placed in a vacuum oven at 80℃ for drying to obtain a solid, which was dissolved in N-methyl-2-pyrrolidone to prepare a colorless and transparent polyimide resin with a solid content of 25%, recorded as CPI-S3, and its viscosity at 55℃ was 1163.3mPa·s; CPI-S3 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min at a pressure of -0.095±0.005MPa, and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min, and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C to remove the film, thereby obtaining a polyimide film, recorded as CPI-3.

[0026] Example 4 The preparation method of the polyimide film comprises the following steps: 680g of N-methyl-2-pyrrolidone was added to the reactor, and the system temperature was adjusted to 2.5±2.5℃. Under nitrogen atmosphere, 6.54g (0.01mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane and 40g (0.2mol) of 3,3'-diaminodiphenyl ether were added, and stirred until completely dissolved. 4.6g (0.01mol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride was added to the reactor. After an interval of 30min, 62g (0.2mol) of 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride was added to the reactor twice, half of which was added each time, with an interval of 30min. After the addition was completed, The mixture was stirred and reacted for 18 hours until the homogeneous phase became transparent, and then 12.5 g of picoline, 25 g of triethylamine, 50.5 g of acetic anhydride and 12.5 g of trifluoroacetic anhydride were added, and the mixture was stirred and reacted for 12 hours at 55±25°C to obtain a homogeneous viscous solution. The obtained solution was added to a mixed precipitant of pure water and methanol in a volume ratio of 5:1 to form a white solid. After filtering, the mixture was placed in a vacuum oven at 80°C and dried to obtain a solid. The solid was redissolved in a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone in a volume ratio of 1:5 to prepare a colorless and transparent polyimide resin with a solid content of 25%, which was recorded as CPI-S4 and had a viscosity of 3833.3 mPa·s at 55°C. CPI-S4 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min at a pressure of -0.095±0.005MPa, and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min, and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C for film removal to obtain a polyimide film, which was recorded as CPI-4.

[0027] Comparative Example 1 The preparation method of the polyimide film comprises the following steps: 37.5 g of N-methyl-2-pyrrolidone was added to the reaction kettle, and the system temperature was adjusted to 2.5 ± 2.5 °C. Under nitrogen atmosphere, 8.5 g (0.013 mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane was added and stirred until completely dissolved. Then, 4 g (0.013 mol) of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride was added three times, with an equal amount added each time, and each time was separated by 30 minutes. After the addition was completed, the reaction was stirred for 12 minutes. h until the homogeneous phase is transparent, then 0.39 g of pyridine and 1.41 g of acetic anhydride are added, and the reaction is continued under stirring at 55±25°C for 8 h to obtain a homogeneous viscous solution, and the obtained solution is added to a pure water precipitant to form a white solid, which is filtered and placed in a vacuum oven at 80°C for drying to obtain a solid, which is then dissolved in N-methyl-2-pyrrolidone to prepare a polyimide resin with a solid content of 25%, recorded as RPI-S1, and its viscosity at 55°C is 1070.0 mPa·s; RPI-S1 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min at a pressure of -0.095±0.005MPa, and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min, and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C to remove the film, thereby obtaining a polyimide film, recorded as RPI-1.

[0028] Comparative Example 2 The preparation method of the polyimide film comprises the following steps: 37.5 g of N-methyl-2-pyrrolidone was added to the reaction kettle, and the system temperature was adjusted to 2.5 ± 2.5 °C. Under nitrogen atmosphere, 7.2 g (0.011 mol) of 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane was added and stirred until completely dissolved. Then, 5.1 g (0.011 mol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene anhydride was added three times, with an equal amount added each time, and each time was separated by 30 minutes. After the addition was completed, the reaction was stirred and reacted. 12h until homogeneous and transparent, then add 0.31g of pyridine and 1.2g of acetic anhydride, continue stirring and reacting at 55±25℃ for 8h to obtain a homogeneous viscous solution, add the obtained solution into a pure water precipitant to form a white solid, filter, put it into a vacuum oven at 80℃ and dry it to obtain a solid, dissolve the solid in N-methyl-2-pyrrolidone, and prepare a polyimide resin with a solid content of 25%, recorded as RPI-S2, and its viscosity at 55℃ is 3925.0mPa·s; RPI-S2 was allowed to stand for 48 hours. After the bubbles were completely eliminated, it was coated on a clean and smooth glass plate with a 250µm scraper to obtain a film with a thickness of 20μm. It was then baked at 80°C for 1 hour in nitrogen to remove the solvent. The temperature was then raised to 150°C at a rate of 5°C / min at a pressure of -0.095±0.005MPa, and kept warm for 1 hour. The temperature was then raised to 250°C at a rate of 5°C / min, and kept warm for 1 hour. After natural cooling, the glass plate was immersed in hot water at 90±10°C to remove the film, thereby obtaining a polyimide film, recorded as RPI-2.

[0029] The polyimide films prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests, and the test methods were as follows: Young's modulus (MPa): Tested in accordance with GB / T 1040.3-2006; Elongation at break (%): Tested in accordance with GB / T 1040.3-2006; Tensile strength (MPa): Tested in accordance with GB / T 1040.3-2006; Tensile yield stress (MPa): Tested in accordance with GB / T 1040.3-2006; Maximum visible light transmittance (%): Tested in accordance with GB / T 2410-2008; Water absorption (%): Tested in accordance with GB / T 1034-2008; Relative dielectric constant: Tested in accordance with GB / T 1409-2006; The test results are shown in Table 1: Table 1 Polyimide film performance test results

[0030] From the data in Table 1, it can be seen that the polyimide films prepared in Examples 1-4 have very excellent comprehensive properties, not only having high visible light transmittance, low water absorption and low relative dielectric constant, but also having excellent mechanical properties. The tensile strength of the polyimide films prepared in Comparative Examples 1-2 is relatively low.

Claims

1. A colorless and transparent polyimide resin, characterized in that: The invention is prepared by polymerizing equimolar dianhydrides and diamines in a highly polar aprotic organic solvent, wherein the dianhydride comprises 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and its usage is (4.5-99.5)% of the total molar number of the dianhydride; and the diamine comprises 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, and its usage is (4.5-100)% of the total molar number of the diamine.

2. The colorless and transparent polyimide resin according to claim 1, characterized in that: The dianhydride also includes one or more of 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phthalic anhydride, and 1,3-bis(3,4-dicarboxyphenoxy)phthalic anhydride.

3. The colorless and transparent polyimide resin according to claim 1, characterized in that: The diamines also include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodicyclohexylmethane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl ether, 4,4'-bis(3-aminophenoxy)diphenyl ether, 4,4'-bis(4-aminophenoxy)diphenyl sulfide, 1,3-bis(2-trifluoromethyl-3-aminophenoxy)benzene, 1,3-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 1,4-bis(2-trifluoromethyl-3-aminophenoxy)benzene, 1,4-bis(2-trifluoromethyl-4- 4,4'-bis(2-trifluoromethyl-3-aminophenoxy) diphenyl sulfone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy) diphenyl sulfone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy) diphenyl ether, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy) diphenyl ether, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy) diphenyl sulfide, 4,4'-bis(2-trifluoromethyl-3-aminophenoxy) diphenyl sulfide, 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane At least one of [4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-trifluoromethyl-3-aminophenoxy)phenyl]propane and 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]propane.

4. The colorless and transparent polyimide resin according to claim 1, characterized in that: The highly polar aprotic organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and dimethyl sulfoxide.

5. A polyimide film, characterized in that: The colorless and transparent polyimide resin is prepared by using the colorless and transparent polyimide resin described in any one of claims 1 to 4.

6. A method for preparing a polyimide film according to claim 5, characterized in that: The following steps are involved: Put a strongly polar aprotic organic solvent into a reaction kettle, add dianhydride and diamine under a nitrogen atmosphere, stir and react until the homogeneous phase is transparent, then add a dehydrating agent and a catalyst for subsequent reaction, after the subsequent reaction is completed, precipitate, filter, and vacuum dry to obtain a solid, and dissolve the solid in a strongly polar aprotic organic solvent to obtain a colorless and transparent polyimide resin; then carry out coating, solvent removal, curing, and demolding in sequence to obtain a polyimide film.

7. The method for preparing a polyimide film according to claim 6, characterized in that: The dehydrating agent is one or more of acetic anhydride, propionic anhydride, trifluoroacetic anhydride or dicyclohexylcarbodiimide.

8. The method for preparing a polyimide film according to claim 6, characterized in that: The catalyst is one or more of pyridine, picoline, dimethylpyridine, triethylamine, tripropylamine, tributylamine or tertiary amine.

9. The method for preparing a polyimide film according to claim 6, characterized in that: The precipitating agent used in the precipitation is one or more of water, methanol, ethanol, isopropanol, propanol, butanol or isobutanol.

10. The method for preparing a polyimide film according to claim 6, characterized in that: The temperature for removing the solvent and solidifying is below 250°C.

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