Polyimide film with excellent mechanical property and more excellent one-way bending resistance and preparation method thereof

Abstract

The invention discloses a polyimide film with excellent mechanical properties and more excellent one-way bending resistance and a preparation method of the polyimide film, and belongs to the technical field of polymer film preparation. The preparation method provided by the invention comprises the following steps: carrying out polymerization reaction on preparation raw materials in an organic solvent to obtain a precursor solution; and carrying out film forming treatment on the precursor solution at 100-200 DEG C for 30-300 seconds, carrying out uniaxial stretching treatment in a fixed vertical direction, carrying out heat treatment while keeping tension, and cooling to obtain the polyimide film with excellent mechanical properties and more excellent one-way bending resistance. The preparation raw materials are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers. According to the preparation process, the prepared film can be endowed with excellent mechanical properties and bending resistance in the vertical direction, allogenic materials are not introduced, the chemical structure of polyimide is not changed, and the preparation process is suitable for large-scale production and has a wide application prospect in the field of flexible display.

Description

Technical Field

[0001] The present application belongs to the technical field of polymer film preparation, and in particular relates to a polyimide film having both excellent mechanical properties and unidirectional better bending resistance and a preparation method thereof. Background Art

[0002] Polyimide (PI) film has become one of the key materials for flexible display devices, flexible solar cells, flexible printed circuit boards, and flexible touch panels due to its unique electrical properties, high temperature stability, chemical corrosion resistance, and high toughness. When used as a flexible display substrate material, polyimide film needs to withstand hundreds of thousands of foldings. However, the polyimide film currently developed will form irreversible creases on the surface and inside of the film after tens of thousands of foldings. This permanent deformation will cause cracking and debonding of different interlayer structures of flexible display screens, directly affecting the service life of the equipment. Therefore, it is urgent to improve the comprehensive performance of polyimide film to expand its application scenarios.

[0003] At present, 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, deformation is mainly achieved by the long molecular chains that were originally in a curled state stretching 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 curled state, resulting in elastic recovery. This elastic deformation caused mainly by entropy changes 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 changes in internal energy (changes in bond length and bond angle) when an object is deformed, which has the characteristics of linear elasticity and conforms to Hooke's law. For example, introducing point-to-surface multi-coordination structures, hydrogen bond-coordination cross-linked networks, composite ionic liquids and nanoparticles, etc., can prevent the plastic slip 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 process for preparing a light-colored, transparent, and fold-resistant semi-aromatic polyimide film, in which nano-SiO2 and crown ether are introduced into the semi-aromatic polyimide to improve the fold-resistant performance of the film.

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

[0005] The present application discloses a polyimide film having both excellent mechanical properties and unidirectional better bending resistance and a preparation method thereof, aiming to solve the technical problems of poor mechanical properties and poor bending resistance of existing polyimide films.

[0006] In order to achieve the above purpose, the technical solution of this application is:

[0007] The first aspect of the present application provides a method for preparing a polyimide film having both excellent mechanical properties and unidirectional better bending resistance, the preparation method comprising:

[0008] The prepared raw materials are subjected to polymerization reaction in an organic solvent to obtain a precursor solution;

[0009] The precursor solution is subjected to film-forming treatment, treated at 100-200° C. for 30-300 seconds, and then uniaxially stretched in a fixed vertical direction, heat treated while maintaining the tension, and cooled to obtain a polyimide film having both excellent mechanical properties and unidirectional better bending resistance;

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

[0011] In combination with the first aspect, preferably, the film forming process comprises the following steps: coating the precursor solution to form a film;

[0012] and, when subjected to uniaxial stretching treatment, the stretching ratio is 1.03-1.5;

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

[0014] In combination with the first aspect, preferably, the film forming process comprises the following steps:

[0015] Adding a catalyst and a water absorbent to the precursor solution for reaction to obtain a colloidal solution, and separating and collecting to obtain a PI solid;

[0016] Dissolving the PI solid in an organic solvent and coating it to form a film;

[0017] and, when subjected to uniaxial stretching treatment, the stretching ratio is 1.03-1.5;

[0018] And, the heat treatment process includes: annealing at 200-300° C. for 0.5-2 h.

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

[0020]

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

[0022]

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

[0024]

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

[0026] In combination with the first aspect, preferably, 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] In combination with the first aspect, preferably, the ratio of carboxyl group, catalyst and water absorbent in the precursor solution is 1:1:3-10.

[0029] The second aspect of the present application provides a polyimide film having excellent mechanical properties and unidirectional better bending resistance, which is prepared by the preparation method described in the first aspect.

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

[0031] The preparation method provided by the present application is to prepare a precursor solution of diamine monomer and dianhydride monomer or diamine monomer, dianhydride monomer and acyl chloride monomer for film forming treatment, and perform uniaxial stretching in a fixed vertical direction while performing heat treatment; on the one hand, the orientation degree of the molecular chain of the film in the stretching direction can be significantly improved, giving the film excellent mechanical properties (tensile strength increased by 30-60%, elastic modulus increased by 10-40%); on the other hand, the molecular chain in the stretching direction with a higher degree of orientation can hinder the stress transmission along the molecular chain in the vertical direction during the bending process, combined with the strong entropy elasticity of the molecular chain in the vertical direction with a lower degree of orientation, thereby greatly improving the bending resistance of the molecular chain in the vertical direction (static bending angle increased by 2-30%, dynamic bending resistance increased by 10-100%); and the bending resistance and mechanical properties of the film can be effectively regulated by regulating the stretching ratio and temperature; at the same time, the preparation method of the present application is simple and easy, does not introduce exogenous substances and does not change the chemical structure of polyimide, is suitable for large-scale production, and thus has broad application prospects in the field of flexible displays. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 A schematic diagram of the unidirectional bending resistance of a polyimide film having both excellent mechanical properties and unidirectionally better bending resistance prepared in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of a static bending resistance test of a polyimide film having excellent mechanical properties and unidirectionally better bending resistance prepared in an embodiment of the present application;

[0035] Figure 3 Schematic diagram of dynamic bending resistance test of the polyimide film with excellent mechanical properties and unidirectional better bending resistance prepared in an embodiment of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work 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 of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

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

[0039] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and 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 the present application.

[0040] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

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

[0042] In a first aspect, the present application provides a method for preparing a polyimide film having both excellent mechanical properties and unidirectional better bending resistance, the preparation method comprising:

[0043] The prepared raw materials are subjected to polymerization reaction in an organic solvent to obtain a precursor solution;

[0044] The precursor solution is subjected to film-forming treatment, treated at 100-200° C. for 30-300 seconds, and then uniaxially stretched in a fixed vertical direction, and heat treated while maintaining the tension, and after cooling, a polyimide film having both excellent mechanical properties and unidirectional better bending resistance is obtained;

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

[0046] Among them, on the one hand, the orientation degree of the molecular chains in the stretching direction of the film can be significantly improved, giving the film excellent mechanical properties (tensile strength increased by 30-60%, elastic modulus increased by 10-40%); on the other hand, the molecular chains in the stretching direction with a higher degree of orientation can hinder the stress transmission along the vertical molecular chains during the bending process, combined with the strong entropy elasticity of the vertical molecular chains with a lower degree of orientation, thereby greatly improving the bending resistance of the vertical molecular chains (static bending angle increased by 2-30%, dynamic bending resistance increased by 10-100%); and the bending resistance and mechanical properties of the film can be effectively regulated by regulating the stretching ratio and temperature; at the same time, the preparation method of the present application is simple and easy, does not introduce exogenous substances and does not change the chemical structure of polyimide, is suitable for large-scale production, and thus has broad application prospects in the field of flexible displays.

[0047] It should be noted that the raw materials used in the present application are preferably diamine monomers and dianhydride monomers, or preferably diamine monomers, dianhydride monomers and acyl chloride monomers. Among them, dianhydride monomers with weak electron-withdrawing groups and diamine monomers with weak electron-donating groups are selected to reduce the accumulation of PI molecular chains, increase the interchain free volume, and reduce the charge transfer effect between molecular chains, thereby preparing a polyimide (PI) film; the polyimide material prepared after the reaction of diamine monomers, dianhydride monomers and acyl chloride monomers has a reticular structure, and the chain segment stacking of the reticular polyimide is denser than that of linear polyimide, and the free volume inside the molecule is increased, thereby preparing a polyimide (PI) film. These acyl chloride monomers can introduce amide bonds in polyimide molecules, provide multiple hydrogen bonding sites, and the polymer containing this structural unit can form a large number of hydrogen bonds within or between molecules, thereby improving the mechanical properties of the film.

[0048] In an embodiment of the present application, the film forming process includes the following steps: applying the precursor solution to form a film; the stretching ratio is 1.03-1.5; the heat treatment process includes: treating at 210-230°C for 0.5-1.5h, and annealing at 300-450°C for 0.5-2h. Among them, the precursor solution is applied to form a film to form a yellow polyimide (YPI) film. Fixing the vertical direction and performing heat treatment during the stretching process can greatly 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 adjusted.

[0049] In the embodiment of the present application, the film forming process includes the following steps: adding a catalyst and a water absorbent to the precursor solution to react, obtaining a colloidal solution, separating and collecting, and obtaining a PI solid; dissolving the PI solid in an organic solvent, coating to form a film; the stretching ratio is 1.03-1.5; the heat treatment process includes: annealing at 200-300°C for 0.5-2h. Among them, after adding a catalyst and a water absorbent to the precursor solution to promote the imidization reaction, a colloidal solution is obtained, which is poured into a poor solvent for precipitation, separation, drying and collection to obtain a PI solid; after dissolving the PI solid in an organic solvent, coating to form a film to generate a colorless and transparent polyimide (CPI) film.

[0050] In the embodiment of the present application, 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 for preparation to form a uniform polymer solution, and evaporate during the film formation process, thereby improving the quality of the generated film.

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

[0052] In the embodiment of the present application, when the precursor solution is added with a catalyst and a water absorbent for reaction, the ratio of carboxyl group, catalyst and water absorbent in the precursor solution is preferably 1:1:3-10. By controlling the addition ratio of each substance during the reaction, a colorless and transparent polyimide can be generated.

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

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

[0055]

[0056] Wherein, A1 is a dianhydride monomer, R is a diamine monomer, A2 is an acyl chloride monomer, the value range of m is 1-1000, and the value range of n is 0-1000.

[0057] In the second aspect, the embodiment of the present application also provides a polyimide film having excellent mechanical properties and unidirectional better bending resistance, which is prepared by the preparation method described in the first aspect. The prepared polyimide film has excellent mechanical properties and unidirectional better bending resistance in the vertical direction, and has broad application prospects in the field of flexible displays.

[0058] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0059] Example 1

[0060] This embodiment provides a method for preparing an A1-polyimide film (A1-YPI), which specifically includes:

[0061] S101: Under a nitrogen atmosphere, 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was dissolved in NMP, and after it was completely dissolved, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added, and the reaction was stirred at room temperature for 10 hours and then stopped to obtain a precursor solution (PAA glue with a solid content of 15wt%);

[0062] S102: After vacuum degassing and filtration, the PAA glue solution is evenly coated on a clean glass plate with a coating machine. After being treated at 60°C for 2 hours, the PAA glue solution is in a gel film state on the glass plate for uniaxial stretching. The PAA gel film is peeled off and taken out and placed in a biaxial stretching machine. After being kept at a constant temperature of 150°C 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°C for 1 hour, treatment at 220°C for 1 hour, and then annealing at 400°C for 0.5 hour. After cooling, an A1-polyimide film (A1-YPI) is obtained.

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

[0064] Example 2

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

[0066] Example 3

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

[0068] Example 4

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

[0070] Example 5

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

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

[0073] S502: After vacuum degassing and filtration, the PAA glue solution is evenly coated on a clean glass plate with a coating machine. After being treated at 60°C for 2 hours, the PAA glue solution is in a gel film state on the glass plate for uniaxial stretching. The PAA gel film is peeled off and placed in a biaxial stretching machine. After being kept at a constant temperature of 150°C 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°C for 1 hour, treatment at 220°C for 1 hour, and then annealing at 350°C for 0.5 hour. After cooling, A5-polyimide film (A5-YPI) is obtained.

[0074] Example 6

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

[0076] Example 7

[0077] This embodiment provides a preparation method for A7-polyimide film (A7-YPI), and the component ratio, preparation operation and process parameters are basically the same as those in Example 5. The difference is that in this embodiment, uniaxial stretching is performed, and the ratio of the 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 an A8-polyimide film (A8-CPI), which specifically includes:

[0080] S801: Under 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'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) was added, and the reaction was stirred at room temperature for 10 h before stopping the reaction to obtain a precursor solution (PAA glue with a solid content of 18 wt%).

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

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

[0083] Example 9

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

[0085] Example 10

[0086] This embodiment provides a method for preparing an A10-polyimide film (A10-CPI), and the component ratio, preparation operation, and process parameters are basically the same as those in Example 8, except that in this embodiment, uniaxial stretching is performed, and the ratio of the gel film in the stretching direction is 1.5 to obtain an A10-polyimide film (A10-CPI).

[0087] Embodiment 11

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

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

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

[0091] S1103: PI solid is stirred and dissolved with DMAc at 25°C to obtain a CPI solution with a solid content of 10wt%. After vacuum degassing and filtration, it is evenly coated on a clean glass plate with a coating machine, and treated at 60°C for 2h to obtain a CPI gel film. After being peeled off from the glass plate, it is placed in a biaxial stretching machine. After maintaining a constant temperature at 180°C for 300s, the vertical direction of the CPI 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 0.7mm / s. Then, heat treatment is performed while maintaining tension, that is, annealing at 280°C for 1h. After cooling, A11-polyimide film (A11-CPI) is obtained.

[0092] Example 12

[0093] This embodiment provides a method for preparing an A12-polyimide film (A12-CPI), and the component ratios, preparation operations, and process parameters are basically the same as those in Example 11, with the difference being that in this embodiment, uniaxial stretching is performed, and the ratio of the gel film in the stretching direction is 1.2 to obtain an A12-polyimide film (A12-CPI).

[0094] Embodiment 13

[0095] This embodiment provides a method for preparing an A13-polyimide film (A13-CPI), and the component ratios, preparation operations, and process parameters are basically the same as those in Example 11, with the difference being that in this embodiment, uniaxial stretching is performed, and the ratio of the gel film in the stretching direction is 1.3 to obtain an A13-polyimide film (A13-CPI).

[0096] Embodiment 14

[0097] This embodiment provides a method for preparing an A14-polyimide film (A14-CPI), and the component ratios, preparation operations, and process parameters are basically the same as those in Example 11, except that in this embodiment, uniaxial stretching is performed, and the ratio of the gel film in the stretching direction is 1.4 to obtain an A14-polyimide film (A14-CPI).

[0098] At the same time, in order to verify the comprehensive performance of the polyimide film prepared in the above examples, the present application provides the following comparative examples for detailed description.

[0099] Comparative Example 1

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

[0101] S1501: Under a nitrogen atmosphere, 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was dissolved in a solvent NMP. After the PABZ was completely dissolved, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The reaction was stirred at room temperature for 10 h and then stopped to obtain a precursor solution (PAA glue having a solid content of 15 wt%).

[0102] S1502: After vacuum degassing and filtration, the PAA glue solution is evenly coated on a clean glass plate with a coating machine, treated at 80°C for 1 hour, 150°C for 1 hour, 220°C for 1 hour, and then annealed at 400°C for 0.5 hour. After cooling, a B1-polyimide film (B1-YPI) is obtained.

[0103] Comparative Example 2

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

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

[0106] S1602: After vacuum degassing and filtration, the PAA glue solution is evenly coated on a clean glass plate with a coating machine, treated at 80°C for 1 hour, 150°C for 1 hour, 220°C for 1 hour, and then annealed at 400°C for 0.5 hour. After cooling, a B2-polyimide film (B2-YPI) is obtained.

[0107] Comparative Example 3

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

[0109] S1701: Under 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'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) was added, and the reaction was stirred at room temperature for 10 h before stopping the reaction to obtain a precursor solution (PAA glue with a solid content of 18 wt%).

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

[0111] S1703: The PI solid was dissolved by stirring with DMAc at 25°C. After vacuum degassing and filtration, it was evenly coated on a clean glass plate with a coating machine, treated at 60°C for 2h, annealed at 280°C for 1h, and cooled to obtain a B3-polyimide film (B3-CPI).

[0112] Comparative Example 4

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

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

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

[0116] S1803: The PI solid was dissolved by stirring with DMAc at 25°C. After vacuum degassing and filtration, it was evenly coated on a clean glass plate with a coating machine, treated at 60°C for 2h, annealed at 280°C for 1h, and cooled to obtain a B4-polyimide film (B4-CPI).

[0117] In order to verify the comprehensive performance of the polyimide film prepared in the embodiment of the present application, the polyimide film prepared in the embodiment of the present application and the comparative example was tested for dichroic ratio / birefringence index, mechanical properties, static bending angle and dynamic bending resistance:

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

[0119] Since there are a large number of rigid ring structures on the main chain of aromatic polymers, the polarized infrared spectroscopy can be used to study the changes in the absorption peak intensity of the functional groups on the chain with the polarization angle to quantitatively calculate the degree of orientation in the film plane. -1 The peak at 1170cm is attributed to the benzene ring, and the vibration of the benzene ring is coplanar with the PI main chain. -1 The peak intensity at changes with the polarization angle, and the dichroic ratio (R) is calculated according to the following formula to characterize the in-plane orientation of the film:

[0120]

[0121] Among them I 1170 (180) I 1170 (0) and I 1170 (90) are the absorption intensities of the benzene ring peak on the PI chain when the polarization angles are 180°, 0°, and 90°, respectively.

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

[0123] The orientation difference of CPI film was characterized by prism coupling analysis. The refractive index parameters included the in-plane refractive index (n TE ), out-of-plane refractive index (n TM ) and birefringence (Δn). The optical birefringence (Δn) of the polymer film is the refractive index n TE and n TM The difference between them is an important parameter reflecting the refractive index anisotropy and is generally used to estimate the degree of orientation of polymer chains on the film plane.

[0124] Since the working principle of this instrument is to calculate the refractive index by the reflectivity and transmittance of the test material, the low transmittance of YPI makes it impossible to test the refractive index. Therefore, the orientation degree of YPI is represented by the dichroic ratio. The orientation degree 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 in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics" Part 3: Test conditions for films and sheets. The sample size was 1×6 cm, the fixture gauge length was 2 cm, and the test rate was 5 mm / min.

[0127] (4) Bending resistance

[0128] according to Figure 2 As we know, in the static bending resistance test, the polyimide film is folded 180° between two 1mm planes (folding radius = 0.5mm) and heat treated at 80°C for 2h to accelerate the accumulation of plastic deformation. After bending for 2h, the film is taken out and cooled, and the unfolding angle (θ) of the PI film after the bending stress is removed is measured to study the static bending resistance. Since the unfolding angle (θ) of the PI film is the supplementary angle of the bending angle and is the result of plastic deformation, and the unfolding angle of the PI film without folding is 180°, a larger unfolding angle means that the PI film has better static bending resistance.

[0129] according to Figure 3 As we know, the dynamic bending resistance is evaluated by the U-shaped dynamic bending test. By fixing the folding radius, the film is repeatedly folded and stretched, and the number of dynamic folding times when the crease appears is observed. The more dynamic bending times the film has, the better the dynamic bending resistance of the film.

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

[0131] Table 1 Comprehensive performance test results of polyimide films prepared in Examples and Comparative Examples

[0132]

[0133] The difference between Comparative Example 1 of the present application and Example 1 is that no stretching treatment is performed, and the polyimide film prepared in Comparative Example 1 is isotropic. According to Table 1, the mechanical properties in the stretching direction are greatly improved, but the bending resistance is reduced. However, the mechanical properties in the vertical direction are basically unchanged, but the dynamic bending resistance times are greatly improved. Therefore, through the preparation process of the present application, the unidirectional and more excellent bending resistance and mechanical properties of the anisotropic PI film can be significantly improved at the same time, which has significant application value.

[0134] Table 2 Comprehensive performance test results of polyimide films prepared in Examples and Comparative Examples

[0135]

[0136]

[0137] The difference between Comparative Example 4 and Example 11 of the present application is that no stretching treatment is performed, and 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 greatly improved but the bending resistance does not change. However, the mechanical properties in the vertical direction are basically unchanged, but the dynamic bending resistance times are greatly improved. Therefore, through the preparation process of the present application, the unidirectional and more excellent bending resistance and mechanical properties of the anisotropic PI film can be significantly improved at the same time, which has significant application value.

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

[0139] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions recorded in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing a polyimide film having both excellent mechanical properties and unidirectional better bending resistance, characterized in that: The preparation method comprises: The prepared raw materials are subjected to polymerization reaction in an organic solvent to obtain a precursor solution; The precursor solution is subjected to film-forming treatment, treated at 100-200° C. for 30-300 seconds, and then uniaxially stretched in a fixed vertical direction, and heat treated while maintaining the tension, and after cooling, a polyimide film having both excellent mechanical properties and unidirectional better bending resistance is obtained; The preparation raw materials are diamine monomers and dianhydride monomers, or diamine monomers, dianhydride monomers and acyl chloride monomers.

2. The preparation method according to claim 1, characterized in that: The film forming process comprises: coating the precursor solution to form a film; and, when subjected to uniaxial stretching treatment, the stretching ratio is 1.03-1.5; And, the heat treatment process includes: treating at 210-230° C. for 0.5-1.5 h, and annealing at 300-450° C. for 0.5-2 h.

3. The preparation method according to claim 1, characterized in that: The film forming process comprises: adding a catalyst and a water absorbent to the precursor solution for reaction to obtain a colloidal solution, and separating and collecting to obtain a PI solid; Dissolving the PI solid in an organic solvent and coating it to form a film; and, when subjected to uniaxial stretching treatment, the stretching ratio is 1.03-1.5; And, the heat treatment process includes: annealing at 200-300° C. for 0.5-2 h.

4. The preparation method according to claim 1, characterized in that: The diamine monomer is one or more of the chemical structures shown in formulas (1) to (22); 5. The preparation method according to claim 1, characterized in that: The dianhydride monomer is one or more of the chemical structures shown in formulas (23)-(33); 6. 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); 7. 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.

8. The preparation method according to claim 3, 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.

9. The preparation method according to claim 3, characterized in that: The ratio of carboxyl group, catalyst and water absorbent in the precursor solution is 1:1:3-10.

10. A polyimide film having excellent mechanical properties and unidirectional better bending resistance, prepared by the preparation method according to any one of claims 1 to 9.

Images