A polyimide film with excellent mechanical properties and unidirectional more excellent bending resistance and a preparation method thereof

Abstract

The application discloses a polyimide film with excellent mechanical properties and unidirectional more excellent bending resistance and a preparation method thereof, and belongs to the technical field of polymer film preparation. The preparation method provided by the application comprises the following steps: performing a polymerization reaction on raw materials in an organic solvent to obtain a precursor solution; performing film forming treatment on the precursor solution, performing uniaxial stretching treatment in a vertical direction after treatment at 100-200 DEG C for 30-300 s, performing heat treatment while the tension is maintained, and obtaining the polyimide film with excellent mechanical properties and unidirectional more excellent bending resistance after cooling; the raw materials are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers. The preparation process can endow the prepared film with excellent mechanical properties and bending resistance in the vertical direction, does not introduce exogenous substances and does not change the chemical structure of the polyimide, is suitable for large-scale production, and has a wide application prospect in the field of flexible display.

Description

Technical Field

[0001] This application belongs to the field of polymer film preparation technology, and particularly relates to a polyimide film with both excellent mechanical properties and superior unidirectional bending resistance, and a method for preparing the same. Background Technology

[0002] Polyimide (PI) film, with its unique electrical properties, high-temperature stability, chemical corrosion resistance, and high strength and toughness, has become a key material for flexible display devices, flexible solar cells, flexible printed circuit boards, and flexible touch panels. When used as a substrate material for flexible displays, polyimide film must withstand hundreds of thousands of folds. However, currently developed polyimide films develop irreversible creases on their surface and inside after only tens of thousands of folds. This permanent deformation leads to cracking and delamination between different layers of the flexible display, directly affecting the lifespan of the device. Therefore, there is an urgent need to improve the overall performance of polyimide film to expand its application scenarios.

[0003] Currently, there are two main methods to improve the intrinsic bending resistance of materials: (1) improving the entropy elasticity of materials. When an external force is applied, the deformation is mainly achieved by the extension of the long molecular chains that were originally in a coiled state along the stress direction; when the external force is removed, the spontaneous process of entropy increase will cause the molecular chains to return to the coiled state, producing elastic recovery. This elastic deformation caused mainly by entropy change is called entropy elasticity. For example, entropy elasticity gives rubber high elasticity and recoverability. (2) improving the energy elasticity of materials, that is, the elasticity caused by the change of internal energy (change of bond length and bond angle) when an object is deformed. It has the characteristics of linear elasticity and conforms to Hooke's law. For example, the introduction of point-to-surface multi-coordination structures, hydrogen bond-coordination cross-linking networks, composite ionic liquids and nanoparticles can prevent the plastic slippage of macromolecular chains under cyclic bending, thereby avoiding the early formation of creases, or giving the film self-healing properties after bending damage. For example, the prior art with application publication number CN 113667304 A discloses a preparation process for a light-colored, transparent, bend-resistant semi-aromatic polyimide film, which introduces nano-SiO2 and crown ether into the semi-aromatic polyimide to improve the bend resistance of the film.

[0004] However, existing polyimide films have the following problems: First, while the introduction of exogenous substances improves the bending resistance of the film, it also causes a decrease in the mechanical properties of the film; second, the preparation process is complicated and not conducive to large-scale production. Summary of the Invention

[0005] This application discloses a polyimide film with both excellent mechanical properties and superior unidirectional bending resistance, and its preparation method, aiming to solve the technical problems of poor mechanical properties and poor bending resistance of existing polyimide films.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a method for preparing a polyimide film that possesses both excellent mechanical properties and superior unidirectional bending resistance, the method comprising:

[0008] The raw materials are polymerized in an organic solvent to obtain a precursor solution;

[0009] The precursor solution is subjected to film formation treatment, and after treatment at 100-200℃ for 30-300s, it is subjected to uniaxial stretching treatment in a fixed vertical direction. While maintaining the tension, heat treatment is performed and then cooled to obtain a polyimide film with both excellent mechanical properties and superior uniaxial bending resistance.

[0010] The raw materials for preparation are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers.

[0011] Preferably, in conjunction with the first aspect, the film-forming treatment includes the following steps: coating the precursor solution to form a film;

[0012] When performing uniaxial stretching, the stretching ratio is 1.03-1.5;

[0013] The heat treatment process includes: treating at 210-230℃ for 0.5-1.5h, and annealing at 300-450℃ for 0.5-2h.

[0014] Preferably, in conjunction with the first aspect, the film-forming treatment includes the following steps:

[0015] The precursor solution was reacted with a catalyst and a dehydrating agent to obtain a colloidal solution, which was then separated and collected to obtain solid PI.

[0016] The PI solid was dissolved in an organic solvent and then coated into a film.

[0017] When performing uniaxial stretching, the stretching ratio is 1.03-1.5;

[0018] The heat treatment process includes annealing at 200-300℃ for 0.5-2 hours.

[0019] Preferably, in conjunction with the first aspect, the diamine monomer is one or more of the chemical structures shown in formulas (1)-(22);

[0020]

[0021] Preferably, in conjunction with the first aspect, the dianhydride monomer is one or more of the chemical structures shown in formulas (23)-(33);

[0022]

[0023] Preferably, in conjunction with the first aspect, the acyl chloride monomer is one or more of the chemical structures shown in formulas (34)-(36);

[0024]

[0025] Preferably, in conjunction with the first aspect, the organic solvent is one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone.

[0026] Preferably, in conjunction with the first aspect, the catalyst is one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine;

[0027] The water-absorbing agent is one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, and anhydrous calcium acetate.

[0028] Preferably, in conjunction with the first aspect, the ratio of carboxyl groups, catalyst, and dehydrating agent in the precursor solution is 1:1:3-10.

[0029] The second aspect of this application provides a polyimide film prepared by the method described in the first aspect, which has both excellent mechanical properties and superior unidirectional bending resistance.

[0030] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0031] The preparation method provided in this application involves forming a film by preparing a precursor solution of diamine monomer and dianhydride monomer, or diamine monomer, dianhydride monomer and acyl chloride monomer, followed by uniaxial stretching in a fixed vertical direction and heat treatment. On the one hand, this significantly improves the orientation of the molecular chains in the stretching direction, endowing the film with excellent mechanical properties (tensile strength increased by 30-60%, elastic modulus increased by 10-40%). On the other hand, the molecular chains with higher orientation in the stretching direction can hinder the transmission of stress along the vertical direction during bending. Combined with the stronger entropy elasticity of the molecular chains with lower orientation in the vertical direction, this greatly improves the bending resistance of the molecular chains in the vertical direction (static bending angle increased by 2-30%, dynamic bending resistance increased by 10-100%). Furthermore, the bending resistance and mechanical properties of the film can be effectively controlled by adjusting the stretching ratio and temperature. At the same time, the preparation method of this application is simple and easy to implement, does not introduce exogenous substances and does not change the chemical structure of polyimide, making it suitable for large-scale production and thus having broad application prospects in the field of flexible displays. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 A schematic diagram of the unidirectional bending resistance of a polyimide film prepared for an embodiment of this application, which possesses both excellent mechanical properties and superior unidirectional bending resistance.

[0034] Figure 2 A schematic diagram of the static bending resistance test of the polyimide film prepared for the embodiments of this application, which has both excellent mechanical properties and superior unidirectional bending resistance.

[0035] Figure 3 A schematic diagram of the dynamic bending resistance test of the polyimide film prepared for the embodiments of this application, which has both excellent mechanical properties and superior unidirectional bending resistance. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0037] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0038] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0039] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0040] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0041] It should be noted that all raw materials and reagents in the embodiments of this application were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0042] In a first aspect, embodiments of this application provide a method for preparing a polyimide film that possesses both excellent mechanical properties and superior unidirectional bending resistance, the method comprising:

[0043] The raw materials are polymerized in an organic solvent to obtain a precursor solution;

[0044] The precursor solution is subjected to film formation treatment, and after treatment at 100-200℃ for 30-300s, it is subjected to uniaxial stretching treatment in a fixed vertical direction. While maintaining the tension, heat treatment is performed. After cooling, a polyimide film with excellent mechanical properties and even better uniaxial bending resistance is obtained.

[0045] The raw materials for preparation are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers.

[0046] On the one hand, it can significantly improve the orientation of molecular chains in the stretching direction of the film, endowing the film with excellent mechanical properties (tensile strength increased by 30-60%, elastic modulus increased by 10-40%). On the other hand, the molecular chains with higher orientation in the stretching direction can hinder the transmission of stress along the molecular chains in the perpendicular direction during bending. Combined with the stronger entropy elasticity of the molecular chains in the perpendicular direction with lower orientation, this greatly improves the bending resistance of the molecular chains in the perpendicular direction (static bending angle increased by 2-30%, dynamic bending resistance increased by 10-100%). Furthermore, the bending resistance and mechanical properties of the film can be effectively controlled by adjusting the stretching ratio and temperature. At the same time, the preparation method of this application is simple and easy to implement, does not introduce exogenous substances and does not change the chemical structure of polyimide, and is suitable for large-scale production, thus having broad application prospects in the field of flexible displays.

[0047] It should be noted that the raw materials used in this application are preferably diamine monomers and dianhydride monomers, or preferably diamine monomers, dianhydride monomers, and acyl chloride monomers. Specifically, dianhydride monomers with weak electron-withdrawing groups and diamine monomers with weak electron-donating groups are selected to reduce the stacking of PI molecular chains and increase the free volume between chains, thereby reducing the charge transfer between molecular chains and preparing polyimide (PI) films. The polyimide material prepared after the reaction of diamine monomers, dianhydride monomers, and acyl chloride monomers has a network structure. The chain segment stacking of network polyimide is more dense than that of linear polyimide, increasing the free volume within the molecule, thus preparing polyimide (PI) films. These acyl chloride monomers can introduce amide bonds into the polyimide molecule, providing multiple hydrogen bonding sites. Polymers containing this structural unit can form a large number of hydrogen bonds intramolecularly or intermolecularly, improving the mechanical properties of the film.

[0048] In this embodiment, the film-forming process includes the following steps: coating the precursor solution to form a film; the stretching ratio is 1.03-1.5; the heat treatment process includes: treating at 210-230℃ for 0.5-1.5 hours and annealing at 300-450℃ for 0.5-2 hours. Specifically, coating the precursor solution to form a film produces a yellow polyimide (YPI) film. Fixing the vertical direction and performing heat treatment during stretching can significantly improve the bending resistance in the vertical direction. By controlling the stretching ratio and temperature, the bending resistance and mechanical properties of the film can be controlled.

[0049] In this embodiment, the film-forming process includes the following steps: adding a catalyst and a desiccant to the precursor solution to react and obtain a colloidal solution, which is then separated and collected to obtain PI solid; dissolving the PI solid in an organic solvent and coating it to form a film; the stretching ratio is 1.03-1.5; the heat treatment process includes annealing at 200-300℃ for 0.5-2 hours. Specifically, after adding a catalyst and a desiccant to the precursor solution to promote the imidization reaction, a colloidal solution is obtained, which is then poured into a poor solvent to precipitate, separate, dry, and collect to obtain PI solid; the PI solid is then dissolved in an organic solvent and coated to form a film, generating a colorless and transparent polyimide (CPI) film.

[0050] In this embodiment, the organic solvent is preferably one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). These organic solvents can effectively dissolve the raw materials, forming a uniform polymer solution, and then evaporate during the coating process, thereby improving the quality of the resulting film.

[0051] In this embodiment, the catalyst is preferably one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine; the desiccant is one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, or anhydrous calcium acetate. These catalysts can significantly improve the rate and selectivity of the imidization reaction. These desiccantes can remove water generated during the reaction, thereby promoting the imidization reaction and achieving a higher conversion rate.

[0052] In this embodiment, when the precursor solution is added to the catalyst and desiccant for reaction, the preferred ratio of carboxyl groups, catalyst, and desiccant in the precursor solution is 1:1:3-10. By controlling the proportion of each substance added during the reaction, colorless and transparent polyimide can be generated.

[0053] It should be noted that, inspired by traditional Chinese summer mats, although the bending resistance of PI film decreases in the stretching direction, in the process of fabricating devices in practical applications, the bending direction of the substrate or cover plate can be designed by selecting the vertical direction with better bending resistance of PI film, thereby significantly improving the overall bending resistance of the device.

[0054] It should be noted that the polyimide film prepared in this application has the general molecular formula structure shown in formula (37):

[0055]

[0056] Wherein, A1 is a dianhydride monomer, R is a diamine monomer, A2 is an acyl chloride monomer, m ranges from 1 to 1000, and n ranges from 0 to 1000.

[0057] Secondly, embodiments of this application also provide a polyimide film prepared by the method described in the first aspect, which possesses both excellent mechanical properties and superior unidirectional bending resistance. Based on the excellent mechanical properties and superior unidirectional bending resistance in the vertical direction of the prepared polyimide film, it has broad application prospects in the field of flexible displays.

[0058] The technical solution of this application will be further described below with reference to specific embodiments.

[0059] Example 1

[0060] This embodiment provides a method for preparing Al-polyimide film (Al-YPI), specifically including:

[0061] S101: Under a nitrogen atmosphere, 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was dissolved in NMP. After complete dissolution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA gel with a solid content of 15 wt%).

[0062] S102: After vacuum degassing and filtration, the PAA adhesive is evenly coated onto a clean glass plate using a coating machine. After treatment at 60℃ for 2 hours, the PAA adhesive is in a gel film state on the glass plate, which is convenient for uniaxial stretching. After peeling off the PAA gel film, it is placed in a biaxial stretching machine and kept at 150℃ for 30 seconds. The vertical direction of the gel film is fixed, and uniaxial stretching is performed. The ratio of the gel film in the stretching direction is 1.03, and the stretching rate is 0.7 mm / s. Then, heat treatment is performed while maintaining tension, that is, treatment at 150℃ for 1 hour, treatment at 220℃ for 1 hour, and then annealing at 400℃ for 0.5 hours. After cooling, Al-polyimide film (Al-YPI) is obtained.

[0063] according to Figure 1 As shown, the prepared polyimide film has a molecular chain structure similar to that of a cooling mat.

[0064] Example 2

[0065] This embodiment provides a method for preparing A2-polyimide film (A2-YPI). The component ratio, preparation operation and process parameters are basically the same as those in Example 1. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.06 to obtain A2-polyimide film (A2-YPI).

[0066] Example 3

[0067] This embodiment provides a method for preparing A3-polyimide film (A3-YPI). The component ratio, preparation operation and process parameters are basically the same as those in Example 1. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.09 to obtain A3-polyimide film (A3-YPI).

[0068] Example 4

[0069] This embodiment provides a method for preparing A4-polyimide film (A4-YPI). The component ratio, preparation operation and process parameters are basically the same as those in Example 1. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.12 to obtain A4-polyimide film (A4-YPI).

[0070] Example 5

[0071] This embodiment provides a method for preparing A5-polyimide film (A5-YPI), specifically including:

[0072] S501: Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4,4'-ODA) was dissolved in N,N-dimethylacetamide (DMAc). After complete dissolution, pyromellitic dianhydride (PMDA) and isophthaloyl chloride (IPC) were added. The molar ratio of PMDA to IPC was 1:1. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 18 wt%).

[0073] S502: After vacuum degassing and filtration, the PAA adhesive is evenly coated onto a clean glass plate using a coating machine. After treatment at 60℃ for 2 hours, the PAA adhesive is in a gel film state on the glass plate, which is convenient for uniaxial stretching. After peeling off the PAA gel film, it is placed in a biaxial stretching machine and kept at 150℃ for 30 seconds. The vertical direction of the gel film is fixed, and uniaxial stretching is performed. The ratio of the gel film in the stretching direction is 1.1, and the stretching rate is 0.7 mm / s. Then, heat treatment is performed while maintaining tension, that is, treatment at 150℃ for 1 hour, treatment at 220℃ for 1 hour, and then annealing at 350℃ for 0.5 hours. After cooling, A5-polyimide film (A5-YPI) is obtained.

[0074] Example 6

[0075] The preparation method, component ratio, preparation operation, and process parameters of A6-polyimide film (A6-YPI) provided in this embodiment are basically the same as those in Example 5. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.2 to obtain A6-polyimide film (A6-YPI).

[0076] Example 7

[0077] The preparation method, component ratio, preparation operation, and process parameters of A7-polyimide film (A7-YPI) provided in this embodiment are basically the same as those in Example 5. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.3 to obtain A7-polyimide film (A7-YPI).

[0078] Example 8

[0079] This embodiment provides a method for preparing A8-polyimide film (A8-CPI), specifically including:

[0080] S801: Under a nitrogen atmosphere, 3,4'-diaminodiphenyl ether (3,4'-ODA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were dissolved in N,N-dimethylacetamide (DMAc), with a molar ratio of 3,4'-ODA to TFMB of 1:1. After complete dissolution, 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) was added. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 18wt%).

[0081] S802: Pyridine and acetic anhydride are added to the PAA solution, with the ratio of carboxyl groups, pyridine, and acetic anhydride in PAA being 1:1:5. After stirring at room temperature for 6 hours, a chemically imidized CPI solution is obtained. The CPI solution is poured into deionized water to precipitate, and after being washed repeatedly with deionized water at least 3 times, it is vacuum dried to obtain a white PI solid.

[0082] S803: PI solid was dissolved in DMAc at 25℃ to obtain a CPI solution with a solid content of 20wt%. After vacuum degassing and filtration, the solution was uniformly coated onto a clean glass plate using a coating machine. After treatment at 60℃ for 2 hours, a CPI gel film was obtained. The film was peeled off from the glass plate and placed in a biaxial stretching machine. After being kept at 180℃ for 300 seconds, the vertical direction of the CPI gel film was fixed, and uniaxial stretching was performed. The ratio of the gel film to the stretching direction was 1.1, and the stretching rate was 0.7 mm / s. Then, heat treatment was performed while maintaining tension, i.e., annealing at 280℃ for 1 hour. After cooling, an A8-polyimide film (A8-CPI) was obtained.

[0083] Example 9

[0084] The preparation method, component ratio, preparation operation, and process parameters of the A9-polyimide film (A9-CPI) provided in this embodiment are basically the same as those in Example 8. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.3 to obtain the A9-polyimide film (A9-CPI).

[0085] Example 10

[0086] The preparation method, component ratio, preparation operation, and process parameters of A10-polyimide film (A10-CPI) provided in this embodiment are basically the same as those in Example 8. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.5 to obtain A10-polyimide film (A10-CPI).

[0087] Example 11

[0088] This embodiment provides a method for preparing A11-polyimide film (A11-CPI), specifically including:

[0089] S1101: Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) was dissolved in N,N-dimethylacetamide (DMAc). After complete dissolution, 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) and terephthaloyl chloride (TPC) were added. The molar ratio of 6FDA to TPC was 1:4. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 10 wt%).

[0090] S1102: Pyridine and acetic anhydride were added to the PAA solution, with the ratio of carboxyl groups, pyridine, and acetic anhydride in PAA being 1:1:5. After stirring at room temperature for 6 hours, a chemically imidized CPI solution was obtained. The CPI solution was poured into deionized water to precipitate the precipitate, and the solution was washed repeatedly with deionized water at least 3 times before being vacuum dried to obtain a white PI solid.

[0091] S1103: PI solid was dissolved in DMAc at 25℃ to obtain a CPI solution with a solid content of 10wt%. After vacuum degassing and filtration, the solution was uniformly coated onto a clean glass plate using a coating machine. After treatment at 60℃ for 2 hours, a CPI gel film was obtained. The film was peeled off from the glass plate and placed in a biaxial stretching machine. After being kept at 180℃ for 300 seconds, the vertical direction of the CPI gel film was fixed, and uniaxial stretching was performed. The ratio of the gel film to the stretching direction was 1.1, and the stretching rate was 0.7 mm / s. Then, heat treatment was performed while maintaining tension, i.e., annealing at 280℃ for 1 hour. After cooling, an A11-polyimide film (A11-CPI) was obtained.

[0092] Example 12

[0093] The preparation method, component ratio, preparation operation, and process parameters of A12-polyimide film (A12-CPI) provided in this embodiment are basically the same as those in Example 11. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.2 to obtain A12-polyimide film (A12-CPI).

[0094] Example 13

[0095] The preparation method, component ratio, preparation operation, and process parameters of A13-polyimide film (A13-CPI) provided in this embodiment are basically the same as those in Example 11. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.3 to obtain A13-polyimide film (A13-CPI).

[0096] Example 14

[0097] The preparation method, component ratio, preparation operation, and process parameters of A14-polyimide film (A14-CPI) provided in this embodiment are basically the same as those in Example 11. The difference is that uniaxial stretching is performed in this embodiment, and the proportion of gel film in the stretching direction is 1.4 to obtain A14-polyimide film (A14-CPI).

[0098] Meanwhile, to verify the comprehensive performance of the polyimide films prepared in the above embodiments, this application provides the following comparative examples for detailed illustration.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing B1-polyimide films (B1-YPI), specifically including:

[0101] S1501: Under a nitrogen atmosphere, 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was dissolved in NMP solvent. After complete dissolution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 15 wt%).

[0102] S1502: After vacuum degassing and filtration, PAA adhesive is uniformly coated onto a cleaned glass plate using a coating machine. After treatment at 80℃ for 1 hour, it is then treated at 150℃ for 1 hour and 220℃ for 1 hour. Finally, it is annealed at 400℃ for 0.5 hours and cooled to obtain B1-polyimide film (B1-YPI).

[0103] Comparative Example 2

[0104] This comparative example provides a method for preparing B2-polyimide films (B2-YPI), specifically including:

[0105] S1601: Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether (4,4'-ODA) was dissolved in solvent NMP. After complete dissolution, pyromellitic dianhydride (PMDA) and isophthaloyl chloride (IPC) were added, with a molar ratio of PMDA to IPC of 1:1. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 18 wt%).

[0106] S1602: After vacuum degassing and filtration, PAA adhesive is uniformly coated onto a cleaned glass plate using a coating machine. After treatment at 80℃ for 1 hour, it is then treated at 150℃ for 1 hour and 220℃ for 1 hour. Finally, it is annealed at 400℃ for 0.5 hours and cooled to obtain B2-polyimide film (B2-YPI).

[0107] Comparative Example 3

[0108] This embodiment provides a method for preparing B3-polyimide film (B3-CPI), specifically including:

[0109] S1701: Under a nitrogen atmosphere, 3,4'-diaminodiphenyl ether (3,4'-ODA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were dissolved in N,N-dimethylacetamide (DMAc), with a molar ratio of 3,4'-ODA to TFMB of 1:1. After complete dissolution, 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) was added. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 18wt%).

[0110] S1702: Pyridine and acetic anhydride were added to the PAA solution, with the ratio of carboxyl groups, pyridine, and acetic anhydride in PAA being 1:1:5. After stirring at room temperature for 6 hours, a chemically imidized CPI solution was obtained. The CPI solution was poured into deionized water to precipitate the precipitate, and the solution was washed repeatedly with deionized water at least 3 times before being vacuum dried to obtain a white PI solid.

[0111] S1703: PI solid was dissolved in DMAc at 25°C by stirring. After vacuum degassing and filtration, it was uniformly coated onto a clean glass plate using a coating machine. It was then treated at 60°C for 2 hours, annealed at 280°C for 1 hour, and cooled to obtain B3-polyimide film (B3-CPI).

[0112] Comparative Example 4

[0113] This embodiment provides a method for preparing B4-polyimide film (B4-CPI), specifically including:

[0114] S1801: Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) was dissolved in N,N-dimethylacetamide (DMAc). After complete dissolution, 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) and terephthaloyl chloride (TPC) were added. The molar ratio of 6FDA to TPC was 1:4. The reaction was stopped after stirring at room temperature for 10 hours to obtain a precursor solution (PAA adhesive with a solid content of 10 wt%).

[0115] S1802: Pyridine and acetic anhydride were added to the PAA solution, with the ratio of carboxyl groups, pyridine, and acetic anhydride in PAA being 1:1:5. After stirring at room temperature for 6 hours, a chemically imidized CPI solution was obtained. The CPI solution was poured into deionized water to precipitate the precipitate, and the solution was washed repeatedly with deionized water at least 3 times before being vacuum dried to obtain a white PI solid.

[0116] S1803: PI solid is dissolved in DMAc at 25°C by stirring. After vacuum degassing and filtration, it is uniformly coated on a clean glass plate using a coating machine. It is then treated at 60°C for 2 hours, annealed at 280°C for 1 hour, and cooled to obtain B4-polyimide film (B4-CPI).

[0117] To verify the comprehensive performance of the polyimide films prepared in the embodiments of this application, dichroic ratio / birefringence index, mechanical properties, static bending angle, and dynamic bending resistance were tested on the polyimide films prepared in the embodiments and comparative examples of this application.

[0118] (1) Orientation degree - dichroism ratio (R)

[0119] Because aromatic polymers contain numerous rigid ring structures in their backbone, the in-plane orientation of the thin film can be quantitatively and statistically analyzed by studying the variation of absorption peak intensity of functional groups with polarized infrared spectroscopy. The infrared spectra of the tested films were measured at polarization angles of 0-180°, with the 1170 cm⁻¹ peak value being [not specified]. -1 The peak at 1170 cm⁻¹ belongs to the benzene ring, and the vibrations of the benzene ring are coplanar with the PI backbone. Therefore, the peak at 1170 cm⁻¹ can be statistically analyzed. -1 The peak intensity at a certain point varies with the polarization angle. The dichroic ratio (R) is calculated using the following formula to characterize the in-plane orientation of the thin film:

[0120]

[0121] Where I 1170 (180), I 1170 (0) and I 1170 (90) represents the absorption intensity of the benzene ring peak on the PI chain when the polarization angle is 180°, 0° and 90°, respectively.

[0122] (2) Orientation degree - birefringence index (Δn)

[0123] The orientation differences of CPI thin films were analyzed and characterized using a prism coupler. Refractive index parameters included the in-plane refractive index (n) measured at a wavelength of 637.2 nm. TE ), out-of-plane refractive index (n TM The optical birefringence (Δn) of the polymer thin film is a function of its refractive index n. TE and n TM The difference between the values ​​is an important parameter reflecting the anisotropy of the refractive index, and is generally used to estimate the degree of orientation of polymer chains on the thin film plane.

[0124] Because this instrument works by calculating the refractive index by testing the reflectance and transmittance of a material, the low transmittance of YPI prevents it from measuring the refractive index. Therefore, the orientation of YPI is represented by the dichroic ratio. The orientation of CPI is represented by the birefringence index.

[0125] (3) Mechanical properties

[0126] The mechanical properties of the film were tested using an Instron 5967 universal testing machine, referring to GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics" Part 3: Test Conditions for Films and Sheets. The sample size was 1×6cm, the gauge length was 2cm, and the testing speed was 5mm / min.

[0127] (4) Bending resistance

[0128] according to Figure 2 As is known, in static flexural strength tests, a polyimide film is folded 180° between two 1mm planes (fold radius = 0.5mm) and heat-treated at 80°C for 2 hours to accelerate the accumulation of plastic deformation. After 2 hours of bending, the film is removed and cooled, and the unfolding angle (θ) of the PI film after the bending stress is relieved is measured to study its static flexural strength. Since the unfolding angle (θ) of the PI film is a supplementary angle to the bending angle and is a result of plastic deformation, and the unfolding angle of an undone PI film is 180°, a larger unfolding angle means that the PI film has better static flexural strength.

[0129] according to Figure 3 As is known, dynamic bending resistance is evaluated using a U-shaped dynamic bending test. By fixing the folding radius, the film is repeatedly folded and stretched, and the number of dynamic folds in which creases appear is observed. The more dynamic folds in which creases appear, the better the film's dynamic bending resistance.

[0130] The test results are shown in Tables 1 and 2.

[0131] Table 1. Comprehensive performance test results of the polyimide films prepared in the examples and comparative examples.

[0132]

[0133] The difference between Comparative Example 1 and Example 1 is that no stretching treatment was performed. The polyimide film prepared in Comparative Example 1 is isotropic. As shown in Table 1, the mechanical properties in the stretching direction are significantly improved, but the bending resistance decreases. However, the mechanical properties in the perpendicular direction remain basically unchanged, but the dynamic bending resistance is significantly increased. Therefore, the preparation process of this application can significantly improve both the unidirectional bending resistance and mechanical properties of anisotropic PI films, which has significant application value.

[0134] Table 2 shows the comprehensive performance test results of the polyimide films prepared in the examples and comparative examples.

[0135]

[0136]

[0137] The difference between Comparative Example 4 and Example 11 is that no stretching treatment was performed; the polyimide film prepared in Comparative Example 4 is isotropic. According to the test results in Table 2, the mechanical properties in the stretching direction are significantly improved, while the bending resistance remains unchanged. However, the mechanical properties in the perpendicular direction are essentially unchanged, but the dynamic bending resistance is significantly increased. Therefore, the preparation process of this application can simultaneously and significantly improve both the superior unidirectional bending resistance and mechanical properties of anisotropic PI films, demonstrating significant application value.

[0138] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0139] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a polyimide film possessing both excellent mechanical properties and superior unidirectional bending resistance, characterized in that, The preparation method includes: The raw materials are polymerized in an organic solvent to obtain a precursor solution; The precursor solution is subjected to film formation treatment, and after treatment at 100-200℃ for 30-300s, it is subjected to uniaxial stretching treatment in a fixed vertical direction. While maintaining the tension, heat treatment is performed. After cooling, a polyimide film with excellent mechanical properties and even better uniaxial bending resistance is obtained. The raw materials for preparation are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers; The film-forming process includes: coating the precursor solution to form a film; When performing uniaxial stretching, the stretching ratio is 1.03-1.5; The heat treatment process includes: treating at 210-230℃ for 0.5-1.5h, and annealing at 300-450℃ for 0.5-2h; The film-forming process includes: adding the precursor solution to a catalyst and a dehydrating agent to react, obtaining a colloidal solution, separating and collecting it to obtain PI solid; The PI solid was dissolved in an organic solvent and then coated into a film. When performing uniaxial stretching, the stretching ratio is 1.03-1.5; The heat treatment process includes annealing at 200-300℃ for 0.5-2 hours; The diamine monomer is one or more of the chemical structures shown in formulas (1)-(22); The dianhydride monomer is one or more of the chemical structures shown in formulas (23)-(33); 。 2. The preparation method according to claim 1, characterized in that, The acyl chloride monomer is one or more of the chemical structures shown in formulas (34)-(36); 。 3. The preparation method according to claim 1, characterized in that, The organic solvent is one or more of N,N'-dimethylethanolamine, N,N-dimethylformamide, and N-methyl-2-pyrrolidone.

4. The preparation method according to claim 1, characterized in that, The catalyst is one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine; The water-absorbing agent is one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, and anhydrous calcium acetate.

5. The preparation method according to claim 1, characterized in that, The ratio of carboxyl groups, catalyst, and dehydrating agent in the precursor solution is 1:1:3-10.

6. A polyimide film prepared by any one of claims 1-5, possessing both excellent mechanical properties and superior unidirectional bending resistance.

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