Polyimide precursor, method for preparing the same, polyimide film, and use thereof

Abstract

In order to improve the AMOLED display quality, the application solves the residual image problem by using a polyimide material. The application discloses a polyimide precursor prepared from diamine monomers and dianhydride monomers. The application introduces 0.1-6 mol% fluorine-containing diamine monomers into the diamine monomers and 0-4 mol% fluorine-containing dianhydride monomers into the dianhydride monomers to reduce the dielectric constant of the polyimide precursor after curing. Meanwhile, the application discloses a preparation method of the polyimide precursor. The method controls the water content of the reaction system to perform high-temperature hydrolysis reaction, so as to control the proportion of the amine group as the end and the carboxyl group as the end, thereby achieving the effect of adjusting the viscosity of the polyimide precursor slurry. In the case of combining the fluorine-containing reaction raw materials and the high-temperature hydrolysis reaction, the viscosity of the polyimide precursor slurry is more controllable, the dielectric constant of the polyimide film is lower, and the expansion coefficient is smaller, thereby achieving a better effect of improving the residual image.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology. More specifically, this invention relates to a polyimide precursor and its preparation method, a polyimide film and its applications. Background Technology

[0002] Besides its excellent heat resistance, polyimide also surpasses other special engineering plastics in optical, mechanical, and electrical properties. It is widely used in aerospace and electronic / electrical heat-resistant insulation materials. In recent years, in the field of flexible displays, polyimide, with its lightweight and highly flexible characteristics, can serve as a substitute for glass substrates, meeting the demand for curved and foldable display devices. Furthermore, with the further improvement of display quality, the preparation of polyimide with special structures by adjusting the reaction process of polyimide monomers diamine and dianhydride to improve the image retention of LTPS-TFT devices has become a future trend in display panel development.

[0003] Image retention in AMOLED displays generally refers to recoverable residual images. Currently, the main research directions for addressing image retention are: 1) The hysteresis characteristics of the pixel circuit TFTs. For example, p-type LTPS-TFTs exhibit worse image retention compared to n-type LTPS-TFTs. This can be mitigated by adjusting the threshold voltage through voltage and current compensation methods; 2) OLED displays on polyimide substrates are more prone to image retention than those on glass substrates. Current solutions often involve increasing the thickness of the barrier layer to reduce water and hydrogen penetration, and adding a metal shielding layer to the buffer region to eliminate charge accumulation in the polyimide and inorganic layers. However, these solutions increase the weight and thickness of the barrier layer, and adding a metal shielding layer increases the number of masking and annealing processes by 4-5. Therefore, using polyimide materials to address image retention is crucial for improving the quality of future AMOLED displays. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0005] Another objective of this invention is to provide a polyimide precursor by introducing fluorinated diamine monomers and fluorinated dianhydride monomers into the diamine monomer and dianhydride monomer, thereby reducing the polarizability of the entire molecular chain and thus lowering the dielectric constant. By controlling the water content of the reaction system and carrying out a high-temperature hydrolysis reaction, the viscosity of the polyimide precursor slurry can be adjusted. With the combination of fluorinated reactants and a high-temperature hydrolysis reaction, the viscosity of the polyimide precursor slurry becomes more controllable, the dielectric constant of the polyimide film is lower, and the coefficient of thermal expansion is smaller, which can achieve a better effect in improving image retention.

[0006] To achieve these and other advantages of the invention, a first aspect of the invention provides a polyimide precursor prepared from a diamine monomer and a dianhydride monomer, further comprising a fluorinated diamine monomer and a fluorinated dianhydride monomer.

[0007] The fluorinated diamine monomer accounts for 0.1 to 6 mol% of 100 mol% of the diamine monomer;

[0008] The fluorinated dianhydride monomer accounts for 0 to 4 mol% of 100 mol% of the dianhydride monomer;

[0009] The total proportion of the fluorinated diamine monomer and the fluorinated dianhydride monomer is 0.1–8 mol%.

[0010] Preferably, the fluorinated diamine monomer has at least one biphenyl ring structure, and the fluorinated dianhydride monomer has at least one perfluoroalkyl group.

[0011] Preferably, the proportion of the end structure shown in formula (1) is 0-40%, and the proportion of the end structure shown in formula (2) is 60-100%.

[0012]

[0013] Where X represents a dianhydride residue with 4 to 40 carbon atoms, Y represents a diamine residue with an aromatic ring and 6 to 40 carbon atoms, and * indicates the position of the bond;

[0014] The end structure shown in equation (2) is obtained through a hydrolysis reaction;

[0015] The hydrolysis reaction is carried out by adding pure water after the diamine monomer and dianhydride monomer added before hydrolysis have reacted completely.

[0016] The reaction system for the hydrolysis reaction has a water content of 0.1–0.3 wt% and a reaction temperature of 80–120 °C.

[0017] When the diamine monomer is in excess, 100 mol% of the diamine monomer and 90-98 mol% of the dianhydride monomer are added before hydrolysis.

[0018] When the dianhydride monomer is in excess, 90-98 mol% of diamine monomer and 100 mol% of dianhydride monomer are added before hydrolysis.

[0019] Preferably, the additive is at least one selected from citric acid, lactic acid, tartaric acid, and malic acid, and the additive accounts for 0.01 to 0.1 mol% of the amount of the diamine monomer.

[0020] A second aspect of the present invention provides a method for preparing a polyimide precursor, comprising the following steps:

[0021] S1. Dissolve the first molar proportion of the diamine monomer in a good solvent to obtain a diamine solution;

[0022] S2. Add the second molar proportion of dianhydride monomer to the diamine solution and react to obtain a mixed solution;

[0023] S3. Add pure water to the mixed solution to react and obtain an acidified solution. The water content of the reaction system is 0.1-0.3 wt%, and the reaction temperature is 80-120℃.

[0024] S4. Cool the acidified solution, add the remaining molar proportion of diamine monomer or dianhydride monomer to continue the reaction, cool to room temperature, filter and degas to obtain polyimide precursor;

[0025] The molar amounts of the diamine monomer and the dianhydride monomer are not equal, with the first molar ratio being 90–100 mol% and the second molar ratio being 90–100 mol%.

[0026] Specifically, when the diamine monomer is in excess, the first molar ratio is 100 mol%, and the second molar ratio is 90-98 mol%.

[0027] When the diamine monomer is in excess, the dianhydride monomer is added in steps S2 in portions, with an interval of 30 to 60 minutes between the portions.

[0028] When the dianhydride monomer is in excess, the first molar ratio is 90–98 mol%, and the second molar ratio is 100 mol%.

[0029] Specifically, in step S2, the reaction temperature is 35–45°C, and the reaction time is 6–12 hours.

[0030] In step S3, the reaction time is 6-8 hours;

[0031] In step S4, the temperature is lowered to 35-45°C, and the reaction continues for 7-10 hours.

[0032] A third aspect of the present invention provides a polyimide film prepared from a polyimide precursor or a polyimide precursor obtained by the preparation method of the polyimide precursor.

[0033] Preferably, the dielectric constant of the polyimide film is 2.5 to 3.0, and the coefficient of thermal expansion of the polyimide film is 8 to 15 ppm / K.

[0034] The fourth aspect of this invention provides the application of a polyimide precursor in photosensitive materials for display panels.

[0035] The present invention has at least the following beneficial effects:

[0036] 1. By introducing fluorinated diamine monomers into diamine monomers and fluorinated dianhydride monomers into dianhydride monomers, the polarizability of the entire molecular chain can be reduced, the dielectric constant can be reduced, and the charge storage capacity of polyimide materials can be reduced, thereby improving the image retention effect.

[0037] 2. By controlling the water content of the reaction system to carry out high-temperature hydrolysis reaction, the content of the structures in formula (1) and formula (2) can be controlled, thereby adjusting the viscosity of polyimide;

[0038] 3. Adding dianhydride in batches can reduce the occurrence of equimolar ratios in localized areas during the reaction process, and can effectively control the polymerization rate and degree of polymerization;

[0039] 4. When the reaction raw materials include fluorinated diamine monomer and fluorinated dianhydride monomer, after the diamine monomer and dianhydride monomer react for a period of time, a high-temperature hydrolysis reaction is carried out by controlling the water content of the reaction system to reduce the proportion of end groups and increase the chain length. This can further reduce the dielectric constant of the polyimide precursor after curing and reduce the thermal expansion coefficient of the polyimide film, thereby achieving a better effect in improving the residual image.

[0040] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0041] Before the detailed description of this disclosure that follows, it should be understood that the terminology used herein is for the purpose of describing particular embodiments only. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0042] Furthermore, the terms or words used in this specification and claims are intended to be understood based on the principle that the inventors may appropriately define the concepts of the terms in order to best describe the invention, and are not limited to the conventional meanings.

[0043] The barrier layer mentioned in this invention is a barrier layer. In order to prevent the polyimide substrate layer from directly contacting the silicon contact surface and reduce the contact resistance between them, a layer of conductive material is added between the substrate layer and the silicon to form the barrier layer.

[0044] The buffer region mentioned in this invention is a buffer zone located on the barrier layer, between the barrier layer and silicon, which buffers the stress caused by direct contact between the two.

[0045] The first aspect of this invention provides a polyimide precursor prepared from a diamine monomer and a dianhydride monomer. The polyimide precursor prepared by this invention reduces the polarizability of the entire molecular chain by introducing a fluorinated diamine monomer into the diamine monomer and a fluorinated dianhydride monomer into the dianhydride monomer, thereby reducing the dielectric constant after curing and achieving the effect of improving image retention.

[0046] In some embodiments of the present invention, the fluorinated diamine monomer includes one or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2'-bis(trifluoromethyl)-5,5'-dihydroxybenzidine, and 2,2-bis(4-aminophenyl)hexafluoropropane;

[0047] The fluorinated diamine monomer may also be selected from the following structures:

[0048]

[0049] Preferably, the fluorinated diamine monomer has at least one biphenyl ring structure.

[0050] Relative to 100 mol% of the diamine monomer, the fluorinated diamine monomer is in the range of 0.1 to 6 mol%, for example, it can be 0.1 mol%, 0.2 mol%, 0.5 mol%, 0.8 mol%, 1.0 mol%, 1.5 mol%, 2.0 mol%, 2.5 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol%, 4.5 mol%, 5.0 mol%, 5.5 mol%, or 6.0 mol%.

[0051] In some embodiments of the present invention, the fluorinated dianhydride monomer includes one or more of the following: 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxybenzoyloxy)phenyl)hexafluoropropane dianhydride, 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride;

[0052] Alternatively, fluorinated dianhydride monomers with the following structures can be selected:

[0053]

[0054] Preferably, the fluorinated dianhydride monomer has at least one perfluoroalkyl group.

[0055] Relative to 100 mol% of the dianhydride monomer, the fluorinated dianhydride monomer is in the range of 0 to 4 mol%, for example, it can be 0.1 mol%, 0.2 mol%, 0.5 mol%, 0.8 mol%, 1.0 mol%, 1.5 mol%, 2.0 mol%, 2.5 mol%, 3.0 mol%, 3.5 mol%, or 4.0 mol%.

[0056] Preferably, the total percentage of the fluorinated diamine monomer and the fluorinated dianhydride monomer is 0.1-8 mol%. In the presence of the above-mentioned amounts of fluorinated dianhydride monomer and / or fluorinated diamine monomer, the viscosity of the polyimide precursor is 1000-10000 CP.

[0057] In order to achieve the desired solution viscosity of the polyimide precursor, some embodiments of the present invention provide a polymeric structure of a polyimide precursor including the polyamic acid structure shown in formula (3) and the polyimide structure shown in formula (4). The end structures of the present invention are shown in formula (1) and formula (2).

[0058]

[0059] In this context, X represents a dianhydride residue with 4 to 40 carbon atoms, and Y represents a diamine residue with an aromatic ring and 6 to 40 carbon atoms. Specifically, X is a residue obtained by removing four COOH groups from a tetracarboxylic acid (i.e., a residue obtained by removing two carboxylic anhydride (CO)₂O) groups from a tetracarboxylic dianhydride), and Y is a residue obtained by removing two -NH₂ groups from a diamine.

[0060] The proportions of the end structures shown in Formula (1) and Formula (2) can adjust the solution viscosity of the polyimide precursor. The proportion of the end structure shown in Formula (1) is 0-40%, and the proportion of the end structure shown in Formula (2) is 60-100%. Preferably, the proportion of the structure shown in Formula (1) is 0-30%, and the proportion of the end structure shown in Formula (2) is 70-100%. More preferably, the proportion of the structure shown in Formula (1) is 0-20%, and the proportion of the end structure shown in Formula (2) is 80-100%.

[0061] The end structure shown in formula (2) is obtained by hydrolysis reaction. The hydrolysis reaction is carried out by adding pure water after the diamine monomer and dianhydride monomer added before hydrolysis have reacted completely. If pure water is added in the early stage of the reaction between the dianhydride monomer and the diamine monomer, the weight-average molecular weight of the polyimide precursor will be reduced, which will affect the viscosity and other properties of the polyimide precursor. Only when the polyimide chains of the dianhydride monomer and the diamine monomer are basically formed can adding pure water achieve the effect of adjusting viscosity, changing dielectric constant and coefficient of thermal expansion.

[0062] The reaction system for the hydrolysis reaction has a water content of 0.1–0.3 wt% and a reaction temperature of 80–120 °C.

[0063] When the diamine monomer is in excess, 100 mol% of the diamine monomer and 90-98 mol% of the dianhydride monomer are added before hydrolysis. After the hydrolysis reaction is completed, the mixture is cooled to the reaction temperature, and then the remaining dianhydride monomer is added to carry out the reaction. The dianhydride monomer is added in portions before the hydrolysis reaction.

[0064] When the dianhydride monomer is in excess, 90-98 mol% of diamine monomer and 100 mol% of dianhydride monomer are added before hydrolysis. After the hydrolysis reaction is completed, the mixture is cooled to the reaction temperature, and then the remaining diamine monomer is added to carry out the reaction.

[0065] The diamine residue Y mentioned in formulas (1), (2), (3), and (4) above can be selected from residues of the diamine monomers shown below, wherein the diamine monomers can be selected from m-phenylenediamine, 1,5-naphthyldiamine, 2,6-naphthyldiamine, bis(3-amino-4-hydroxyphenyl) sulfone, bis(3-amino-4-hydroxyphenyl)propane, bis(3-amino-4-hydroxyphenyl)methane, bis(3-amino-4-hydroxyphenyl) ether, bis(3-amino-4-hydroxy)biphenyl, bis(3-amino-4-hydroxyphenyl)fluorene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-diethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diethyl-4,4'-diaminobiphenyl, 2,2',3,3'-tetramethyl -4,4'-diaminobiphenyl, 3,3',4,4'-tetramethyl-4,4'-diaminobiphenyl, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 1,4-bis(4-aminophenoxy)benzene, bis(4-aminophenoxyphenyl)sulfone, bis(3-aminophenoxyphenyl)sulfone, bis(4-aminophenoxy)biphenyl, bis{4-(4-aminophenoxy)phenyl} ether, 3,5-diaminobenzoic acid, 3-carboxy-4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, or one or more combinations thereof.

[0066] Preferably, the diamine monomer contains at least one ether bond, specifically one or more combinations of bis(3-amino-4-hydroxyphenyl) ether, 3,4'-diaminodiphenyl ether, bis{4-(4-aminophenoxy)phenyl} ether, 3-carboxy-4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenyl ether.

[0067] The dianhydride residue X mentioned in formulas (1), (2), (3), and (4) above can be selected from residues of the dianhydride monomers shown below, wherein the dianhydride monomers can be selected from 1,2,4,5-pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'- Benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- Dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3'-oxophthalic acid dianhydride, 4,4'-oxophthalic acid dianhydride, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid-1,4-phenylene ester, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2-dioxophenyl ... One or more combinations of the following: 3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 1,2,5,6-naphthalenetetracarboxylic anhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, 2,3,5,6-pyridinetetracarboxylic anhydride, 3,4,9,10-perylenetetracarboxylic anhydride, 3,3,4,4-diphenyl ketonetetracarboxylic anhydride, 1,2,4,5-pyromellitictetracarboxylic anhydride, and 4,4-oxobisphthalic anhydride.

[0068] Preferably, the dianhydride monomer having a biphenyl structure is one or more of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, and 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride.

[0069] The polyimide precursor mentioned in some specific embodiments of the present invention has a weight-average molecular weight of 50,000 to 200,000, a dielectric constant of 2.5 to 3.0 after curing, and a solution viscosity of 3,000 to 7,000 CP. In some embodiments of the present invention, by controlling the content of structures of formula (1) and formula (2), the solution viscosity range of the polyimide precursor can be narrowed; if not controlled, the viscosity range will be wider.

[0070] The polyimide precursor of the present invention further includes an additive, which is at least one selected from citric acid, lactic acid, tartaric acid, and malic acid, and the additive accounts for 0.01 to 0.1 mol% of the amount of the diamine monomer. Adding the additive can slow down the viscosity change of the polyimide precursor, improve the storage stability of the polyimide solution, and further reduce the dielectric constant of the polyimide film.

[0071] A second aspect of this invention provides a method for preparing polyimide, comprising the following steps:

[0072] S1. Dissolve the first molar proportion of the diamine monomer in a good solvent to obtain a diamine solution;

[0073] S2. Add the second molar proportion of dianhydride monomer to the diamine solution and react to obtain a mixed solution;

[0074] S3. Add pure water to the mixed solution to react and obtain an acidified solution. The water content of the reaction system is 0.1-0.3 wt%, and the reaction temperature is 80-120℃.

[0075] S4. Cool the acidified solution, add the remaining molar proportion of diamine monomer or dianhydride monomer to continue the reaction, cool to room temperature, filter and degas to obtain polyimide precursor;

[0076] The molar amounts of the diamine monomer and the dianhydride monomer are not equal, with the first molar ratio being 90–100 mol% and the second molar ratio being 90–100 mol%.

[0077] In step S2, the reaction temperature is 35–45°C, and the reaction time is 6–12 hours.

[0078] In step S3, the reaction time is 6-8 hours;

[0079] In step S4, the cooling temperature is 35-45°C, and the continued reaction time is 7-10 hours.

[0080] When the diamine monomer is in excess, the preferred molar ratio of the diamine monomer to the dianhydride monomer is (1.05-1.15):1, where the first molar ratio is 100 mol% and the second molar ratio is 90-98 mol%. Preferably, the dianhydride monomer is added in steps S2 in portions, with a time interval of 30-60 minutes between each addition. The amount added in each portion is half of the remainder after the previous addition, and is added in four portions.

[0081] The method for preparing polyimide precursors described in this invention involves first dissolving the diamine in an organic solvent, then adding most of the dianhydride in portions. After reacting for a period of time, pure water is added to control the water content of the reaction system, allowing solution A to undergo hydrolysis at high temperatures. The hydrolysis process does not cause any adverse effects; only a small amount of dianhydride needs to be added subsequently to ensure that the final anhydride / diamine molar ratio is close to the range disclosed for both the diamine monomer and the dianhydride monomer. This results in a high-performance polyimide precursor. Simultaneously, the small amount of residual water in the polyimide precursor slurry reduces its water absorption rate and improves its storage stability. Compared to traditional one-time addition, this method, by adding the dianhydride in portions, controls the polymerization rate, resulting in minimal temperature changes during the reaction and reducing the likelihood of localized gelation. Adding most of the dianhydride first to allow it to react fully with the diamine for a period before adding the remaining dianhydride allows the system to homogenize at a lower viscosity before slow chain growth, making it easier to obtain a polyimide precursor with controllable viscosity.

[0082] When the dianhydride monomer is in excess, the preferred molar ratio of the diamine monomer to the dianhydride monomer is 1:

[0083] When the molar ratio is (1.05–1.15), the first molar ratio is 90–98 mol%, and the second molar ratio is 100 mol%.

[0084] The method for preparing polyimide precursors in this invention involves first dissolving most of the diamine in an organic solvent, then adding the dianhydride monomer all at once. After reacting for a period of time, pure water is added to control the water content of the reaction system, allowing solution C to undergo hydrolysis at high temperatures. Finally, the remaining diamine is added all at once. The addition of free diamine to the system does not affect the final viscosity. While ensuring that the dianhydride / diamine ratio is close to the ranges disclosed for diamine and dianhydride monomers, during high-temperature film formation, the dianhydride-terminated polyimide segments dehydrate to generate anhydride-terminated polyimide segments. These segments then recombine with the free diamine in the system, undergoing further cyclization and dehydration to form a high-performance polyimide film.

[0085] In some embodiments of the present invention, when the diamine monomer used to prepare the polyimide precursor includes a fluorinated diamine monomer, the fluorinated diamine monomer and the diamine monomer are used in combination. It should be noted that the fluorinated diamine monomer is in the range of 0.1 to 6 mol% relative to 100 mol% of the diamine monomer.

[0086] In some embodiments of the present invention, during the preparation of the polyimide precursor, when the dianhydride monomer used to prepare the polyimide precursor includes a fluorinated dianhydride monomer, the fluorinated dianhydride monomer and the fluorinated unsubstituted dianhydride monomer are used in combination. It should be noted that the fluorinated dianhydride monomer is in the range of 0 to 4 mol% relative to 100 mol% of the dianhydride monomer.

[0087] In some embodiments of the present invention, when additives are required during the preparation of polyimide precursors, the additives are added after all diamine monomers and dianhydride monomers have reacted completely, and then stirred and mixed.

[0088] The good solvent mentioned in the preparation method of the present invention is a solvent that easily dissolves diamine monomers and dianhydride monomers. Preferably, the good solvent is an amide solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; a cyclic ester solvent such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; a carbonate solvent such as ethylene carbonate and propylene carbonate; a diol solvent such as triethylene glycol; a phenolic solvent such as m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone; 1,3-dimethyl-2-imidazolinone; sulfolane; and dimethyl sulfoxide. In addition, other common organic solvents can also be used, namely phenol, o-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine, mineral oil, naphtha, etc. Furthermore, these solvents can be used in combination. The above-mentioned good solvents have low water content, all below 0.01%.

[0089] A third aspect of the present invention provides a polyimide film, wherein the above-mentioned polyimide precursor slurry is degassed and then coated onto a substrate, and the substrate coated with the polyimide precursor is heated to obtain a polyimide wet film; the polyimide wet film is placed under a protective atmosphere to cure into a film, thereby obtaining a polyimide film.

[0090] The dielectric constant of the polyimide film is 2.5 to 3.0, and the coefficient of thermal expansion of the polyimide film is 8 to 15 ppm / K.

[0091] In some embodiments of the present invention, the prepared polyimide precursor slurry can be filtered in a clean and dry filter, and the filtered polyimide precursor slurry can be degassed by means of a degassing machine, depressurization, ultrasonic degassing, etc., or an unstable degassing agent can be added to the polyimide precursor slurry, stirred evenly, and then degassed. The thermally unstable degassing agent refers to a degassing agent that decomposes during heating. In subsequent heating processes, the degassing agent will be thermally decomposed and will no longer remain in the polyimide film.

[0092] Alternatively, the degassed polyimide precursor slurry can be coated onto a substrate, and the substrate coated with the polyimide precursor slurry can be placed on a heating plate to remove most of the solvent, thereby obtaining a polyimide wet film. Subsequently, the wet film is placed in a muffle furnace filled with high-purity nitrogen and cured into a film by staged heating to obtain a polyimide thin film.

[0093] In some embodiments of the present invention, the filter may be a gravity filter, a vacuum filter, a pressure filter, etc., with a pressure filter being the most preferred.

[0094] In some embodiments of the present invention, the coating method may be selected from spin coating, slot coating, spray coating, doctor blade coating, roller coating, etc.

[0095] In some embodiments of the present invention, the substrate refers to a substance on which a polyimide precursor slurry can be coated to form a film. It is any substance that has a dense structure that is substantially impermeable to liquids and gases, and there are no particular limitations on its shape or material.

[0096] In some embodiments of the present invention, the wet film is subjected to a single treatment by vacuum drying (HVCD), with the pressure controlled at 10-100 Pa and the temperature at 60-80 °C. The film prepared under these conditions is a polyamic acid film with a solvent content of 10-40%.

[0097] The aforementioned film is placed in a high-temperature oven for secondary treatment. The oxygen level in the oven is controlled at 0–1000 ppm, the maximum temperature of the oven is preferably 450–475°C, and the heating time is preferably 180–240 min. The temperature is raised from room temperature to 250°C at a rate of 1–10°C / min. The solvent evaporation rate is relatively slow, and the voids created after solvent evaporation can be filled by the polyimide precursor slurry within this timeframe. If the heating rate is too fast, the solvent evaporates too quickly, and the voids cannot be filled, resulting in film defects. In the temperature range of 250°C–450°C, the heating rate is controlled at 3–15°C / min. If the heating rate is too slow, the overall economic efficiency of the process will decrease; if it is too fast, it will lead to the deterioration of the polyimide condensed-state structure, potentially causing a decrease in the glass transition temperature.

[0098] The polyimide film thickness is 5–20 μm. More preferably, it is 5–18 μm, even more preferably 5–15 μm, and particularly preferably 5–10 μm, although its thickness may vary depending on its application.

[0099] The application of polyimide precursors in photosensitive materials for display panels in some embodiments of the present invention.

[0100] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0101] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0102] ODA: 4,4'-Diaminodiphenyl ether

[0103] TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl

[0104] MTB: 2,2'-dimethyl-4,4'-diaminobiphenyl

[0105] BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride

[0106] 6FDA: 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride

[0107] NMP: N-methyl-2-pyrrolidone

[0108] CA: Citric acid

[0109] <Example 1>

[0110] Under nitrogen atmosphere protection, 350g of NMP was added to a three-necked flask at room temperature, followed by 98mol% ODA (41.75g, 0.2254mol) and 2mol% TFMB (1.48g, 0.0046mol). The mixture was stirred until the powders were completely dissolved. Then, 98mol% BPDA (57.67g, 0.196mol) was added in four portions, each time half the remaining amount, until the fourth portion was completely added. Each addition was spaced 30 minutes apart. After each addition, 30g of [a specific chemical solution] was used. The mixture was rinsed with NMP, and after the addition was complete, the temperature was controlled at 35℃ for 8 hours. 1g of pure water was added to the system (the amount of water added to the system was 0.174wt%), the temperature was raised to 90℃, and high-temperature hydrolysis was carried out for 6 hours. After cooling to 45℃, the remaining 2mol% of BPDA (1.18g, 0.004mol) was added, and the mixture was rinsed with 4g of NMP. After continuing the reaction for 7 hours, the mixture was cooled to room temperature, filtered through a 1μm pore size PFA filter, and degassed for 24 hours to obtain a light yellow polyimide precursor slurry.

[0111] <Example 2>

[0112] Under nitrogen atmosphere protection, 350g of NMP was added to a three-necked flask at room temperature, followed by 96mol% ODA (38.05g, 0.2054mol) and 4mol% TFMB (2.74g, 0.0086mol). The mixture was stirred until the powders were completely dissolved. Then, 98mol% BPDA (57.67g, 0.196mol) was added in four portions, with each addition being half the remaining amount, until the fourth addition was complete. Each addition was spaced 30 minutes apart. After each addition, 30g of NMP was used as a buffer. After rinsing with MP, the mixture was reacted at 45°C for 10 hours. Then, 1 g of pure water was added to the system (the total amount of water added to the system was 0.175 wt%). The temperature was raised to 110°C and hydrolyzed at high temperature for 8 hours. The mixture was then cooled to 35°C, and the remaining 2 mol% BPDA (1.18 g, 0.004 mol) was added. The mixture was then rinsed with 4 g of NMP and reacted for another 10 hours. The mixture was then cooled to room temperature and filtered through a 1 μm pore size PFA filter. After degassing for 24 hours, a light yellow polyimide precursor slurry was obtained.

[0113] <Example 3>

[0114] Under nitrogen protection, 350g of NMP was added to a three-necked flask at room temperature, followed by 97mol% ODA (38.45g, 0.2076mol) and 3mol% TFMB (2.06g, 0.0064mol). The mixture was stirred until the powders were completely dissolved. Then, BPDA (57.67g, 0.196mol) and 6FDA (1.78g, 0.004mol) were mixed to obtain a mixed dianhydride. The 98mol% mixed dianhydride was added in four portions, each time half the remaining amount, until the fourth portion was completely added. Each addition was spaced 30 minutes apart. After each addition, the mixture was rinsed with 30g of NMP. The reaction was carried out at 40℃ for 8 hours. Then, 1g of water (0.175wt%) was added to the system, and the temperature was raised to 100℃ for high-temperature hydrolysis for 7 hours. After cooling to 40℃, the remaining 2mol% mixed dianhydride was added, and 4g of NMP was used to further dissolve it. The mixture was rinsed with NMP and reacted for another 8 hours. After cooling to room temperature, it was filtered through a 1μm pore size PFA filter and degassed for 24 hours to obtain a pale yellow polyimide precursor slurry.

[0115] <Example 4>

[0116] Same as Example 3, except that maleic acid (0.19g, 0.001mol) was added before degassing to obtain a pale yellow polyimide precursor slurry.

[0117] <Example 5>

[0118] ODA (36.31 g, 0.196 mol) and TFMB (1.28 g, 0.004 mol) were mixed to obtain a mixed diamine. Under nitrogen protection, 350 g of NMP and 97 mol% of the mixed diamine were added to a three-necked flask at room temperature. The mixture was stirred for 1 h until the powder was completely dissolved. Then, BPDA (62.96 g, 0.214 mol) was added all at once. After the addition was complete, the mixture was rinsed with 30 g of NMP. The reaction was carried out at 35 °C for 8 h. 1 g of pure water was added to the system (the total amount of water added to the system was 0.208 wt%), and the temperature was raised to 80 °C. The mixture was hydrolyzed at high temperature for 6 h. After cooling to 45 °C, the remaining 3 mol% of the mixed diamine was added, and the mixture was rinsed with 4 g of NMP. The reaction was continued for 7 h. After cooling to room temperature, the mixture was filtered and degassed to obtain a pale yellow polyimide precursor slurry.

[0119] <Example 6>

[0120] ODA (35.56 g, 0.192 mol) and TFMB (2.56 g, 0.008 mol) were mixed to obtain a mixed diamine. Under nitrogen protection, 350 g of NMP and 97 mol% of the mixed diamine were added to a three-necked flask at room temperature. The mixture was stirred for 1 h until the powder was completely dissolved. Then, BPDA (62.96 g, 0.214 mol) was added all at once. After the addition was complete, the mixture was rinsed with 30 g of NMP. The reaction was carried out at 45 °C for 10 h. 1 g of pure water was added to the system (the total amount of water added to the system was 0.207 wt%), and the temperature was raised to 110 °C. The mixture was hydrolyzed at high temperature for 8 h. The temperature was cooled to 35 °C, and the remaining 3 mol% of the mixed diamine was added. The mixture was rinsed with 4 g of NMP and the reaction was continued for 10 h. The mixture was then cooled to room temperature and filtered to obtain a pale yellow polyimide precursor slurry.

[0121] <Example 7>

[0122] ODA (35.93 g, 0.194 mol) and TFMB (1.92 g, 0.006 mol) were mixed to obtain a mixed diamine. Under nitrogen protection, 350 g of NMP and 97 mol% of the mixed diamine were added to a three-necked flask at room temperature. The mixture was stirred for 1 h until the powder was completely dissolved. Then, BPDA (66.32 g, 0.2254 mol) and 6FDA (2.04 g, 0.0046 mol) were added at once. After the addition was complete, the mixture was washed with 30 g of NMP. The reaction was carried out at 40 °C for 8 h. 1 g of pure water was added to the system (the total amount of water added to the system was 0.205 wt%), and the temperature was raised to 100 °C for high-temperature hydrolysis for 7 h. The mixture was cooled to 40 °C, and the remaining 3 mol% of the mixed diamine was added. The mixture was washed with 4 g of NMP and the reaction was continued for 8 h. The mixture was then cooled to room temperature and filtered to obtain a light yellow polyimide precursor slurry.

[0123] <Example 8>

[0124] Same as Example 7, except that citric acid (0.19g, 0.001mol) was added before degassing to obtain a pale yellow polyimide precursor slurry.

[0125] <Comparative Example 1>

[0126] The preparation process of Comparative Example 1 is the same as that of Example 1, except that the diamine raw materials are 98 mol% ODA (41.75 g, 0.2254 mol) and 2 mol% MTB (0.98 g, 0.0046 mol).

[0127] <Comparative Example 2>

[0128] The preparation process of Comparative Example 2 is the same as that of Example 3, except that the dianhydride raw materials are 94 mol% BPDA (55.31 g, 0.188 mol) and 6 mol% 6FDA (5.33 g, 0.012 mol).

[0129] <Comparative Example 3>

[0130] The preparation process of Comparative Example 3 is the same as that of Example 2, except that the diamine raw materials are 93 mol% ODA (36.86 g, 0.199 mol) and 7 mol% TFMB (4.8 g, 0.015 mol).

[0131] <Comparative Example 4>

[0132] The preparation process of Comparative Example 4 is the same as that of Example 2, except that it does not include the steps of adding 1g of pure water and heating to 110°C for 8h of high-temperature hydrolysis.

[0133] <Comparative Example 5>

[0134] The preparation process of Comparative Example 5 is the same as that of Example 2, except that 2g of pure water is added.

[0135] <Comparative Example 6>

[0136] The preparation process of Comparative Example 6 is the same as that of Example 2, except that pure water is not added and the temperature is directly raised to 110°C for 8 hours.

[0137] <Comparative Example 7>

[0138] The preparation process of Comparative Example 7 is the same as that of Example 5, except that the mixed diamine raw materials are 98 mol% ODA (36.31 g, 0.196 mol) and 2 mol% MTB (0.85 g, 0.004 mol).

[0139] <Comparative Example 8>

[0140] The preparation process of Comparative Example 8 is the same as that of Example 7, except that the dianhydride raw materials are 94 mol% BPDA (63.61 g, 0.2162 mol) and 6 mol% 6FDA (6.13 g, 0.0138 mol).

[0141] <Comparative Example 9>

[0142] The preparation process of Comparative Example 9 is the same as that of Example 6, except that the diamine raw materials are 93 mol% ODA (34.45 g, 0.186 mol) and 7 mol% TFMB (4.48 g, 0.014 mol).

[0143] <Comparative Example 10>

[0144] The preparation process of Comparative Example 10 is the same as that of Example 6, except that it does not include the steps of adding 1g of pure water and heating to 110°C for high-temperature hydrolysis for 8h.

[0145] <Comparative Example 11>

[0146] The preparation process of Comparative Example 11 is the same as that of Example 6, except that 2g of pure water is added.

[0147] <Comparative Example 12>

[0148] The preparation process of Comparative Example 12 is the same as that of Example 6, except that pure water is not added and the temperature is directly raised to 110°C for 8 hours.

[0149] The types and molar amounts of dianhydride monomers and diamine monomers in the polyimide solutions obtained in Examples 1-8 and Comparative Examples 1-12 are shown in Table 1.

[0150] Table 1

[0151] ODA (mol) TFMB (mol) MTB(mol) BPDA (mol) 6 FDA (mol) CA(mol) Example 1 0.2254 0.0046 / 0.2 / / Example 2 0.2054 0.0086 / 0.2 / / Example 3 0.2076 0.0064 / 0.196 0.004 / Example 4 0.2076 0.0064 / 0.196 0.004 0.001 Example 5 0.196 0.004 / 0.214 / / Example 6 0.192 0.008 / 0.214 / / Example 7 0.194 0.006 / 0.2254 0.0046 / Example 8 0.194 0.006 / 0.2254 0.0046 0.001 Comparative Example 1 0.2054 / 0.0086 0.2 / / Comparative Example 2 0.2076 0.0064 / 0.188 0.012 / Comparative Example 3 0.199 0.015 / 0.2 / / Comparative Example 4 0.2054 0.0086 / 0.2 / / Comparative Example 5 0.2054 0.0086 / 0.2 / / Comparative Example 6 0.2054 0.0086 / 0.2 / / Comparative Example 7 0.192 / 0.008 0.214 / / Comparative Example 8 0.194 0.006 / 0.2162 0.0138 / Comparative Example 9 0.186 0.014 / 0.214 / / Comparative Example 10 0.192 0.008 / 0.214 / / Comparative Example 11 0.192 0.008 / 0.214 / / Comparative Example 12 0.192 0.008 / 0.214 / /

[0152] <Testing Methods>

[0153] 1. Determination of weight-average molecular weight

[0154] Gel chromatography system (GPC): Waters Corporation, USA; Pump: Waters 1515 Isocratic HPLC pump; Column: Support particles with a pore size of 10 μm. 2 nm and 10 3 nm tandem, gel: 5μm rigid divinyl styrene particles, detector: water2414 Refractive Index Detector, mobile phase: DMF, column temperature: 35℃, flow rate: 1ml / min, injection volume: 100μL, injection concentration: 2mg / mL.

[0155] 2. Determination of solution viscosity

[0156] The polyimide precursor slurry sample was measured using a TA company DHR-1 at 25°C with a rotation speed of 0.314 rad / s.

[0157] 3. Measurement of transparency

[0158] The polyimide precursor slurry was measured using a PerkinElmer Lambda 35 UV spectrophotometer at a wavelength of 400 nm and a 1 cm optical path.

[0159] 4. Methods for determining dielectric constant

[0160] The dielectric constant of the polyimide films prepared from the polyimide precursor slurry prepared in the Examples and Comparative Examples was measured at 1 GHz using a Keysight SPDR measuring instrument.

[0161] 5. Linear expansion coefficient CTE test

[0162] The linear expansion coefficient CTE was measured using a TA-Q400, with nitrogen as the test atmosphere and a heating rate of 10℃ / min.

[0163] The properties of the polyimide precursor slurries obtained in Examples 1-8 and Comparative Examples 1-12 were tested according to the test methods described above, and the test results are shown in Table 2.

[0164] Table 2

[0165]

[0166]

[0167] According to Table 2, a comparison between Comparative Example 1 and Example 1 shows that without the addition of fluorinated diamine monomer and fluorinated dianhydride monomer, the transparency of the polyimide precursor slurry decreases and the dielectric constant after curing increases. A comparison between Comparative Example 2 and Example 3 shows that with an excess of fluorinated dianhydride monomer, the transparency of the polyimide precursor slurry increases, the dielectric constant after curing increases, and the coefficient of thermal expansion increases significantly. A comparison between Comparative Example 3 and Example 2 shows that with an excess of fluorinated diamine monomer, the dielectric constant of the cured polyimide precursor slurry increases, and the coefficient of thermal expansion increases. The viscosity of the polyimide precursor increases significantly when the high-temperature hydrolysis reaction step is not performed, as shown in Comparative Example 4 and Example 2. Comparative Example 5 and Example 2 show that when excess water is added, the viscosity of the polyimide precursor slurry decreases significantly, the dielectric constant increases after curing, and the coefficient of thermal expansion increases significantly. Comparative Example 6 and Example 2 show that when no water is added, the viscosity of the polyimide precursor slurry increases, the dielectric constant increases after curing, and the coefficient of thermal expansion increases. Examples 3 and 4 show that the addition of additives reduces the dielectric constant and coefficient of thermal expansion of the polyimide film.

[0168] According to Table 2, a comparison between Comparative Example 7 and Example 5 shows that without the addition of fluorinated diamine monomer and fluorinated dianhydride monomer, the transparency of the polyimide precursor slurry decreases and the dielectric constant after curing increases. A comparison between Comparative Example 8 and Example 7 shows that with an excess of fluorinated dianhydride monomer, the transparency of the polyimide precursor slurry increases, the dielectric constant after curing increases, and the coefficient of thermal expansion increases significantly. A comparison between Comparative Example 9 and Example 6 shows that with an excess of fluorinated diamine monomer, the dielectric constant of the cured polyimide precursor slurry increases, and the coefficient of thermal expansion increases significantly. A comparison between Comparative Example 1 and Example 6 shows that with an excess of fluorinated diamine monomer, the dielectric constant of the cured polyimide precursor slurry increases, and the coefficient of thermal expansion increases significantly. Comparing Example 0 and Example 6, it can be seen that without the high-temperature hydrolysis reaction step, the weight-average molecular weight of the polyimide precursor increases, the viscosity increases significantly, the dielectric constant after curing increases, and the coefficient of thermal expansion increases. Comparing Comparative Example 11 and Example 6, it can be seen that with excessive water addition, the viscosity of the polyimide precursor slurry decreases significantly, the dielectric constant after curing increases, and the coefficient of thermal expansion increases significantly. Comparing Comparative Example 12 and Example 6, it can be seen that without adding water, the viscosity of the polyimide precursor slurry increases, the dielectric constant after curing increases, and the coefficient of thermal expansion increases. Examples 7 and 8 show that after adding additives, the dielectric constant and coefficient of thermal expansion of the polyimide film decrease.

[0169] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A polyimide precursor prepared from a diamine monomer and a dianhydride monomer, characterized in that, The fluorine-containing diamine monomer and the fluorine-containing dianhydride monomer are included in the polyimide precursor. The fluorine-containing diamine monomer accounts for 0.1-6 mol% relative to 100 mol% of the diamine monomer. The fluorine-containing dianhydride monomer accounts for 0-4 mol% relative to 100 mol% of the dianhydride monomer. The total content of the fluorine-containing diamine monomer and the fluorine-containing dianhydride monomer accounts for 0.1-8 mol%. The polyimide precursor has an end structure represented by the following formula (1) in an amount of 0-40%, and has an end structure represented by the following formula (2) in an amount of 60-100%, the end structure represented by the formula (2) being obtained through a hydrolysis reaction, a water content of a reaction system of the hydrolysis reaction being 0.1-0.3 wt%, the hydrolysis reaction being controlled by controlling the water content of the reaction system, and the contents of the formula (1) and the formula (2) being controlled. In the formula, X represents a dianhydride residue with a carbon atom number of 4-40, Y represents a diamine residue with an aromatic ring and a carbon atom number of 6-40, and * represents a bonding position. The hydrolysis reaction is performed by adding pure water after the diamine monomer and the dianhydride monomer are completely reacted. The polyimide precursor further includes an additive, the additive being at least one of citric acid and maleic amide acid, and the additive accounting for 0.01-0.1 mol% of the diamine monomer. The solution viscosity of the polyimide precursor is 3000-7000 CP, the dielectric constant of a polyimide film prepared from the polyimide precursor is 2.5-3.0, and the thermal expansion coefficient of the polyimide film is 8-15 ppm / K.

2. The polyimide precursor of claim 1, wherein The fluorine-containing diamine monomer has at least one biphenyl ring structure, and the fluorine-containing dianhydride monomer has at least one perfluoroalkyl structure.

3. The polyimide precursor of claim 1, wherein The reaction temperature of the hydrolysis reaction is 80-120 °C. When the diamine monomer is excessive, 100 mol% of the diamine monomer and 90-98 mol% of the dianhydride monomer are added before hydrolysis. When the dianhydride monomer is excessive, 90-98 mol% of the diamine monomer and 100 mol% of the dianhydride monomer are added before hydrolysis.

4. The method for producing a polyimide precursor according to any one of claims 1 to 3, characterized by, The method includes the following steps: S1. Dissolving a first molar ratio of diamine monomers in a good solvent to obtain a diamine solution; S2. Adding a second molar ratio of dianhydride monomers to the diamine solution to obtain a mixed solution; S3. After the diamine monomers and the dianhydride monomers are completely reacted, adding pure water to the mixed solution to obtain an acidified solution, a water content of a reaction system of the hydrolysis reaction being 0.1-0.3 wt%, and a reaction temperature being 80-120 °C; S4. Cooling the acidified solution, adding a remaining molar ratio of diamine monomers or dianhydride monomers to continue the reaction, cooling to room temperature, filtering and degassing to obtain a polyimide precursor. The molar amounts of the diamine monomers and the dianhydride monomers are not equal, the first molar ratio is 90-100 mol%, and the second molar ratio is 90-100 mol%. The solution viscosity of the polyimide precursor is 3000-7000 CP, the dielectric constant of the polyimide film prepared from the polyimide precursor is 2.5-3.0, and the thermal expansion coefficient of the polyimide film prepared from the polyimide precursor is 8-15 ppm / K.

5. The method for preparing the polyimide precursor as described in claim 4, characterized in that, When the diamine monomer is in excess, the first molar ratio is 100 mol%, and the second molar ratio is 90-98 mol%; When the diamine monomer is in excess, the diamine monomer is added in steps in step S2, and the time interval for the stepwise addition is 30-60 min; When the dianhydride monomer is in excess, the first molar ratio is 90-98 mol%, and the second molar ratio is 100 mol%.

6. The method for preparing the polyimide precursor according to claim 4, characterized in that, In step S2, the reaction temperature is 35-45℃, and the reaction time is 6-12 h; In step S3, the reaction time is 6-8 h; In step S4, the temperature is lowered to 35-45℃, and the continued reaction time is 7-10 h.

7. A polyimide film characterized by comprising: The polyimide precursor prepared from the polyimide precursor of any one of claims 1-3 or the preparation method of the polyimide precursor of any one of claims 4-6.

8. Use of the polyimide precursor prepared from the polyimide precursor of any one of claims 1-3 or the preparation method of the polyimide precursor of any one of claims 4-6 in a display panel photosensitive material.

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