Polyamide acid solution, polyimide, polyimide film, and preparation method and application thereof

Abstract

This invention provides a polyamic acid solution, polyimide, a polyimide film, its preparation method, and its applications. The polyimide film is obtained by blending a low-crosslinking, high-molecular-weight polyamic acid solution with a high-rigidity, low-molecular-weight, crosslinkable polyamic acid solution, followed by solution molding and imidization. This invention utilizes a crosslinked sacrificial network structure to dissipate energy during material stretching, while avoiding material uniformity problems caused by introducing other incompatible systems. The performance advantages of the constructed interpenetrating network structure effectively improve the overall mechanical properties of the polyimide film. The resulting polyimide film exhibits excellent mechanical properties and can be used as a flexible display substrate, etc.

Description

Technical Field

[0001] This invention relates to the field of polyimide, and more specifically, to a polyamic acid solution, polyimide, polyimide film, preparation method thereon, and application. Background Technology

[0002] New flexible display technologies are showing a trend towards being lightweight, ultra-thin, and flexible. Polyimide film, as the only polymer material that can meet the requirements for flexible display substrates, has received widespread attention and application in recent years.

[0003] Flexible substrate polyimides place high demands on their heat resistance, thermal dimensional stability, and mechanical properties. While conventional rigid polyimide materials can meet the requirements for heat resistance and thermal dimensional stability, their mechanical properties often exhibit brittleness. For example, PI prepared from pyromellitic anhydride and p-phenylenediamine cannot form films due to its excessive brittleness. In applications, copolymerization or blending is often used to improve the performance of membrane materials. Considering the influence of intermolecular entanglement on material properties, this invention proposes a method for preparing and applying high-strength, high-elongation-at-break polyimide films. This involves blending micro-crosslinked and crosslinkable polyamic acid solutions, followed by molding and processing. Subsequent thermal imidization and thermal crosslinking form an interpenetrating network system, which can improve the mechanical and heat resistance properties of the membrane material. The development and application of this type of material provides new ideas and methods for achieving high-performance modification of polyimide film materials. Summary of the Invention

[0004] This invention primarily addresses the challenge of simultaneously increasing the strength and flexibility of polyimide films. To this end, it proposes a method for preparing and applying polyamic acid solutions, polyimide, and high-strength, high-elongation-at-break polyimide films. The technical approach involves constructing a polyimide interpenetrating network with a specific structure. The main polyimide network is formed by micro-crosslinked high-molecular-weight polyimide composed of polyamines, primarily consisting of rigid or semi-rigid monomers. The interpenetrating network is formed by low-molecular-weight, heat-covalently crosslinked low-molecular-weight polyimide, which is predominantly rigid. The resulting two polyamic acid solutions are blended and modified, followed by molding and post-reaction treatment to obtain a membrane material with excellent mechanical properties.

[0005] One objective of this invention is to provide a polyamic acid solution comprising polyamic acid solution A and polyamic acid solution B, and / or a mixture thereof; wherein the polyamic acid in polyamic acid solution A contains rigid dianhydride structural units, diamine structural units and polyamine structural units, and the polyamic acid in polyamic acid solution B contains rigid dianhydride, diamine structural units and monomer structural units containing double or triple bonds.

[0006] The polyamic acid in the polyamic acid solution A has a molecular weight of 1.0 × 10⁻⁶. 5 ~2.0×10 5 The preferred value is 1.2 × 10⁻⁶. 5 ~1.8×10 5 .

[0007] The polyamic acid in the polyamic acid solution B has a molecular weight of 0.2 × 10⁻⁶. 4 ~2×10 4 The preferred value is 0.3×10 4 ~1.2×10 4 .

[0008] The mass ratio of polyamic acid solution A to polyamic acid solution B is (98:2) to (85:15), preferably (95:5) to (90:10).

[0009] In polyamic acid solution A, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the polyamine structural unit is derived from the polyamine.

[0010] In polyamic acid solution A, the rigid dianhydride is a non-bridged dianhydride monomer, preferably at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride.

[0011] In polyamic acid solution A, the diamine is a diamine with 1 or fewer bridging atoms, preferably at least one selected from 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodibenzophenone, 2-(diaminophenyl)benzimidazole-5-amine, 2-(4-aminophenyl)-1H-benzoxazole-5-amine, and trans-1,4-cyclohexanediamine.

[0012] In polyamic acid solution A, the polyamine is a symmetrical polyamine, preferably at least one selected from tris(4-aminophenyl)amine, tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5,7-tetraaminoadamantane, and octaaminophenyl cubic siloxane.

[0013] In polyamic acid solution B, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the monomer structural unit containing double or triple bonds is derived from the monomer containing double or triple bonds.

[0014] In polyamic acid solution B, the rigid dianhydride is a non-bridged dianhydride monomer, preferably at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-anthracitetetracarboxylic dianhydride.

[0015] In polyamic acid solution B, the diamine is a non-bridged diamine monomer, preferably at least one of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0016] In polyamic acid solution B, the monomer containing a double or triple bond structure is an acid anhydride containing a crosslinkable alkenyl double bond or alkynyl triple bond structure, preferably at least one of maleic anhydride, 4-ethynyl phthalic anhydride, 4-phenylethynyl phthalic anhydride, norbornene anhydride, and 4,4'-(ethynyl-1,2-diyl)phthalic anhydride.

[0017] The second objective of this invention is to provide a method for preparing the polyamic acid solution, comprising the steps of preparing a high molecular weight polyamic acid solution A, preparing a low molecular weight polyamic acid solution B, and blending polyamic acid solution A and polyamic acid solution B.

[0018] The preferred method for preparing the polyamic acid solution includes the following steps:

[0019] (1) Polyamic acid solution A is obtained by copolymerizing rigid dianhydride, diamine and polyamine in an aprotic polar solvent;

[0020] (2) Polyamic acid solution B is obtained by copolymerizing rigid dianhydride, diamine and monomers containing double or triple bonds in an aprotic polar solvent;

[0021] (3) Mix polyamic acid solution A and polyamic acid solution B together.

[0022] In step (1) of the method for preparing the polyamic acid solution:

[0023] First, a rigid dianhydride and a diamine are reacted in an inert atmosphere in an aprotic polar solvent. Then, a polyamine is added to continue the reaction to prepare a polyamic acid solution A. Preferably,

[0024] The molar ratio of rigid dianhydride to diamine is (1.03–1.08):1, preferably (1.04–1.06):1;

[0025] The reaction temperature of rigid dianhydride with diamine is 0–60°C, preferably 20–40°C; the reaction time is 2–12 h, preferably 4–8 h.

[0026] According to the ratio of primary amines, the ratio of polyamines to diamines is 0.005 to 0.05, preferably 0.01 to 0.04;

[0027] The reaction time after adding the polyamine is 1 to 8 hours, preferably 2 to 4 hours;

[0028] The solid content of the polyamic acid solution A is 10-20 wt%, preferably 12-16 wt%.

[0029] In step (2) of the method for preparing the polyamic acid solution:

[0030] First, a rigid dianhydride and a diamine are reacted in an inert, aprotic, polar solvent. Then, a monomer containing a double or triple bond structure is added to continue the reaction to prepare a polyamic acid solution B. Preferably,

[0031] The molar ratio of rigid dianhydride to diamine is (0.9–0.96):1, preferably (0.92–0.94):1;

[0032] The reaction temperature of rigid dianhydride with diamine is 0–60°C, preferably 20–40°C, and the reaction time is 2–12 h, preferably 4–8 h.

[0033] The molar ratio of the anhydride of the monomer containing a double or triple bond structure to the amino group of the diamine is 0.08 to 0.2, preferably 0.12 to 0.16;

[0034] The reaction time after adding monomers containing double or triple bonds is 1 to 4 hours, preferably 2 to 3 hours.

[0035] The solid content of the polyamic acid solution B is 10-20 wt%, preferably 12-16 wt%.

[0036] In step (3) of the method for preparing the polyamic acid solution:

[0037] The mass ratio of polyamic acid solution A to polyamic acid solution B is (98:2) to (85:15), preferably (95:5) to (90:10).

[0038] A third objective of this invention is to provide a polyimide comprising polyimide A and polyimide B, and / or mixtures thereof; wherein polyimide A contains rigid dianhydride structural units, diamine structural units and polyamine structural units, and polyimide B contains rigid dianhydride, diamine structural units and monomer structural units containing double or triple bonds.

[0039] In polyimide A, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the polyamine structural unit is derived from the polyamine.

[0040] In polyimide A, the rigid dianhydride is a non-bridged dianhydride monomer, preferably at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride.

[0041] In polyimide A, the diamine is a diamine with 1 or fewer bridging atoms, preferably at least one selected from 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodibenzophenone, 2-(diaminophenyl)benzimidazole-5-amine, 2-(4-aminophenyl)-1H-benzoxazole-5-amine, and trans-1,4-cyclohexanediamine.

[0042] In polyimide A, the polyamine is a symmetrical polyamine, preferably at least one selected from tris(4-aminophenyl)amine, tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5,7-tetraaminoadamantane, and octaaminophenyl cubic siloxane.

[0043] In polyimide B, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the monomer structural unit containing double or triple bonds is derived from the monomer containing double or triple bonds.

[0044] In polyimide B, the rigid dianhydride is a non-bridged dianhydride monomer, preferably at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-anthracitetetracarboxylic dianhydride.

[0045] In polyimide B, the diamine is a non-bridged diamine monomer, preferably at least one of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0046] In polyimide B, the monomer containing a double or triple bond structure is an acid anhydride containing a crosslinkable alkenyl double bond or alkynyl triple bond structure, preferably at least one of maleic anhydride, 4-ethynyl phthalic anhydride, 4-phenylethynyl phthalic anhydride, norbornene anhydride, and 4,4'-(ethynyl-1,2-diyl)phthalic anhydride.

[0047] The polyimide is obtained by imidization of the polyamic acid solution described above or the polyamic acid solution obtained by the preparation method described above.

[0048] The fourth objective of this invention is to provide a polyimide film comprising the polyimide.

[0049] The fifth objective of this invention is to provide a method for preparing a polyimide film, wherein the polyamic acid solution or the polyamic acid solution obtained by the preparation method is formed into a film and then subjected to imidization treatment.

[0050] The molding process employs a coating method to form a film, preferably at least one of casting coating, spin coating, and spray coating; the thickness of the coated polyamic acid liquid film is 50–500 μm, preferably 100–300 μm.

[0051] The imidization treatment is preferably a thermal imidization treatment. More preferably, the thermal imidization treatment includes low-temperature pre-baking of the liquid film, medium-temperature cross-linking reaction, and high-temperature complete imidization. The temperature of the low-temperature pre-baking stage is 80-150°C, and the residence time is 0.5-2h. Then, the temperature is increased to the temperature of the medium-temperature cross-linking reaction (220-350°C) at a heating rate of 0.5-5°C / min, and the residence time is 0.5-2h. Finally, the temperature is increased to the temperature of high-temperature complete imidization (350-480°C), and the residence time is 0.25-2h.

[0052] The preferred method for preparing the polyimide film of the present invention includes the following steps:

[0053] (1) Polyamic acid solution A is obtained by copolymerizing rigid dianhydride, diamine and polyamine in an aprotic polar solvent;

[0054] (2) Polyamic acid solution B is obtained by copolymerizing rigid dianhydride, diamine and monomers containing double or triple bonds in an aprotic polar solvent;

[0055] (3) Mix polyamic acid solution A and polyamic acid solution B together;

[0056] (4) The blended solution obtained in step (3) is molded into a film and then subjected to imidization treatment.

[0057] In step (1) of the method for preparing the polyimide film of the present invention, the rigid dianhydride refers to a non-bridged dianhydride monomer, preferably one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride, wherein more preferably are pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 3,3',4,4'-biphenyl dianhydride with a certain degree of symmetry.

[0058] In step (1) of the method for preparing the polyimide film of the present invention, the diamine monomer refers to a diamine monomer with bridging atoms less than or equal to 1, preferably 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4, One or more of 4-diaminobenzophenone, 2-(diaminophenyl)benzimidazole-5-amine, 2-(4-aminophenyl)-1H-benzoxazole-5-amine, and trans-1,4-cyclohexanediamine, with more preferably 1,4-p-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl having a certain symmetrical structure.

[0059] In step (1) of the method for preparing the polyimide film of the present invention, the polyamine refers to a polyamine with a symmetrical structure selected for the crosslinking reaction, preferably one or more of tris(4-aminophenyl)amine, tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5,7-tetraaminoadamantane, and octaaminophenyl cubic siloxane.

[0060] In step (1) of the method for preparing the polyimide film of the present invention, a rigid dianhydride and a diamine are first reacted in an inert atmosphere in an aprotic polar solvent, and then a polyamine is added to continue the reaction to prepare a polyamic acid solution A.

[0061] In step (1) of the method for preparing the polyimide film of the present invention, the molar ratio of rigid dianhydride to diamine is (1.03-1.08):1, preferably (1.04-1.06):1.

[0062] In step (1) of the method for preparing the polyimide film of the present invention, the ratio of polyamine to diamine is 0.005 to 0.05, preferably 0.01 to 0.04, according to the ratio of primary amines.

[0063] In step (1) of the method for preparing the polyimide film of the present invention, the solid content of the polyamic acid solution A is 10-20 wt%, preferably 12-16 wt%.

[0064] In step (1) of the method for preparing the polyimide film of the present invention, the polyamic acid in the polyamic acid solution A has a molecular weight of 1.0 × 10⁻⁶. 5 ~2.0×10 5 The preferred value is 1.2 × 10⁻⁶. 5 ~1.8×10 5 .

[0065] In step (1) of the method for preparing the polyimide film of the present invention, the reaction temperature of the rigid dianhydride and the diamine is 0-60°C, preferably 20-40°C; the reaction time is 2-12h, preferably 4-8h.

[0066] In step (1) of the method for preparing the polyimide film of the present invention, the reaction time after adding the polyamine is 1 to 8 hours, preferably 2 to 4 hours.

[0067] In step (2) of the method for preparing the polyimide film of the present invention, the rigid dianhydride refers to a non-bridged dianhydride monomer, preferably one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-anthracitetetracarboxylic dianhydride, more preferably highly symmetrical pyromellitic dianhydride and 2,3,6,7-naphthalenetetracarboxylic dianhydride.

[0068] In step (2) of the method for preparing the polyimide film of the present invention, the diamine refers to a non-bridged diamine monomer, preferably one or more of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, more preferably a highly symmetrical non-substituted diamine, such as 1,4-p-phenylenediamine or 4,4'-diaminobiphenyl.

[0069] In step (2) of the method for preparing the polyimide film of the present invention, the monomer containing a double or triple bond structure is an acid anhydride containing a crosslinkable alkenyl double bond or alkynyl triple bond structure, preferably maleic anhydride, 4-ethynyl phthalic anhydride, 4-phenylethynyl phthalic anhydride, norbornene anhydride, 4,4'-(ethynyl-1,2-diyl)phthalic anhydride, and more preferably a monofunctional monomer, such as maleic anhydride, norbornene anhydride, 4-ethynyl phthalic anhydride, 4-phenylethynyl phthalic anhydride.

[0070] In step (2) of the method for preparing the polyimide film of the present invention, rigid dianhydride and diamine are first reacted in an inert atmosphere in an aprotic polar solvent, and then a monomer containing a double or triple bond structure is added to continue the reaction to prepare polyamic acid solution B.

[0071] In step (2) of the method for preparing the polyimide film of the present invention, the molar ratio of rigid dianhydride to diamine is (0.9-0.96):1, preferably (0.92-0.94):1.

[0072] In step (2) of the method for preparing the polyimide film of the present invention, the molar ratio of the anhydride of the monomer containing a double bond or a triple bond structure to the amino group of the diamine is 0.08 to 0.2, preferably 0.12 to 0.16.

[0073] In step (2) of the method for preparing the polyimide film of the present invention, the solid content of the polyamic acid solution B is 10-20 wt%, preferably 12-16 wt%.

[0074] In step (2) of the method for preparing the polyimide film of the present invention, the polyamic acid in the polyamic acid solution B has a molecular weight of 0.2 × 10⁻⁶. 4 ~2×10 4 The preferred value is 0.3×10 4 ~1.2×10 4 .

[0075] In step (2) of the method for preparing the polyimide film of the present invention, the reaction temperature of the rigid dianhydride and the diamine is 0-60°C, preferably 20-40°C, and the reaction time is 2-12h, preferably 4-8h.

[0076] In step (2) of the method for preparing the polyimide film of the present invention, the reaction time after adding the monomer containing double or triple bond structure is 1 to 4 hours, preferably 2 to 3 hours.

[0077] In step (3) of the method for preparing the polyimide film of the present invention, the mass ratio of polyamic acid solution A to polyamic acid solution B is (98:2) to (85:15), preferably (95:5) to (90:10).

[0078] In step (4) of the method for preparing the polyimide film of the present invention, the forming process adopts a coating method to form the film, and the coating method is preferably at least one of casting coating, spin coating, and spraying.

[0079] In step (4) of the method for preparing the polyimide film of the present invention, the thickness of the coated polyamic acid liquid film is 50-500 μm, preferably 100-300 μm.

[0080] In step (4) of the method for preparing the polyimide film of the present invention, the imidization treatment is preferably a thermal imidization treatment, which includes low-temperature pre-baking of the liquid film, medium-temperature crosslinking reaction, and high-temperature complete imidization. The temperature of the low-temperature pre-baking stage is 80-150°C, and the residence time is 0.5-2h. Then, the temperature is increased to the temperature of the medium-temperature crosslinking reaction, 220-350°C, at a heating rate of 0.5-5°C / min, and the residence time is 0.5-2h. Finally, the temperature is increased to the temperature of the high-temperature complete imidization, 350-480°C, and the residence time is 0.25-2h.

[0081] The sixth objective of this invention is to provide a polyimide film obtained by the preparation method or the application of the polyimide film in flexible display substrate materials.

[0082] The present invention provides a high-strength, high-elongation-at-break polyimide film system in which interpenetrating networks are formed between molecular chains. The resulting film has good strength properties and a certain degree of flexibility. At the same time, the selected rigid system gives the film excellent heat resistance and thermal dimensional stability, making it suitable for use as a flexible display substrate material.

[0083] The technical solution of this invention effectively solves the problem of improving the strength and modulus of polyimide films while also ensuring a certain degree of flexibility in the film material. The cross-linked sacrificial network form is used to dissipate energy during the stretching process of the material. The interpenetrating cross-linked polyimide system also avoids the defects of insufficient compatibility and surface smoothness caused by conventional organic-inorganic hybridization processes. By utilizing the performance advantages brought by the constructed interpenetrating network structure, the comprehensive mechanical properties of polyimide films can be effectively improved.

[0084] The present invention will be further illustrated below through embodiments. Detailed Implementation

[0085] To enable those skilled in the art to better understand the present invention and to better demonstrate its beneficial effects, the present invention will be further elaborated with reference to specific examples. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0086] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0087] According to a preferred embodiment of the present invention, the method for preparing the high-strength, high-elongation-at-break polyimide film includes the following steps:

[0088] (1) Preparation of low-crosslinking, high-molecular-weight polyamic acid solution A;

[0089] (2) Preparation of high-rigidity, low-molecular-weight, crosslinkable polyamic acid solution B;

[0090] (3) Polyamic acid solution A and polyamic acid solution B are mixed;

[0091] (4) Solution molding and thermal imidization treatment.

[0092] In step (1), a low-crosslinking, high-molecular-weight polyamic acid solution is prepared, wherein the low-crosslinking, high-molecular-weight polyamic acid solution is obtained by copolymerization of rigid dianhydride, diamine monomer and symmetrical polyamine in an aprotic polar solvent.

[0093] The copolymerization reaction first involves stirring dianhydride and diamine in an inert, aprotic polar solvent. The process for preparing anhydride-terminated polyamic acid solution by reacting dianhydride and diamine is shown below:

[0094]

[0095] The dianhydride and diamine are fed in a molar ratio of (1.03–1.08):1, with a preferred ratio of (1.04–1.06):1; the solid content is 10–20 wt%, preferably 12–16 wt%; the inert atmosphere refers to the reaction under an atmosphere such as nitrogen or argon; the aprotic polar solvent refers to commonly used amide solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.; the stirring reaction is carried out at a temperature of 0–60°C, preferably 20–40°C, and for a reaction time of 2–12 h, preferably 4–8 h.

[0096] The copolymerization reaction refers to the addition of a small amount of polyamine after the reaction of dianhydride and diamine, followed by stirring to form a cross-linked structure. The ratio of the polyamine to the added diamine is 0.005 to 0.05 based on the primary amine quantity, preferably 0.01 to 0.04, for example, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, etc. The stirring reaction time is 1 to 8 hours, preferably 2 to 4 hours.

[0097] The high molecular weight polyamic acid solution has a molecular weight of 1.0 × 10⁻⁶. 5 ~2.0×10 5 The preferred molecular weight is 1.2 × 10⁻⁶. 5 ~1.8×10 5 .

[0098] The crosslinking reaction of the polyamic acid A solution is shown below:

[0099]

[0100] In step (2), a high-rigidity, low-molecular-weight, crosslinkable polyamic acid solution B is prepared. The polyamic acid solution is obtained by copolymerization of rigid dianhydride and diamine monomers and monomers containing double or triple bonds in an aprotic polar solvent.

[0101] The copolymerization reaction first involves stirring dianhydride and diamine in an inert atmosphere using an aprotic polar solvent. The dianhydride and diamine are added in a molar ratio of (0.9–0.96):1, preferably (0.92–0.94):1; the solid content is 10–20 wt%, preferably 12–16 wt%. The inert atmosphere refers to the reaction under nitrogen or argon atmosphere; the aprotic polar solvent refers to commonly used amide solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; the stirring reaction is carried out at a temperature of 0–60°C, preferably 20–40°C, for a reaction time of 2–12 h, preferably 4–8 h.

[0102] The copolymerization of monomers containing double or triple bonds refers to the addition of monomers containing double or triple bonds for further reaction. The ratio of the added crosslinkable anhydride to the amino functional groups in the diamine is 0.08–0.2, preferably 0.12–0.16, for example, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, etc. The stirring reaction time is 1–4 hours, preferably 2–3 hours.

[0103] The low molecular weight polyamic acid solution has a molecular weight of 0.2 × 10⁻⁶. 4 ~2×10 4 The preferred molecular weight is 0.3 × 10⁻⁶. 4 ~1.2×10 4 .

[0104] The reaction of the polyamic acid B solution is shown below:

[0105]

[0106] In step (3), the polyamic acid solution blending refers to blending polyamic acid solutions A and B, where solution A is the main solution for film formation and solution B is a small amount of additive solution. The mass ratio of the two is 98:2 to 85:15, preferably 95:5 to 90:10. For example, it can be 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, 89:11, 88:12, 87:13, 86:14, 85:15, etc.

[0107] In step (4), the solution forming process and thermal imidization treatment refer to the process of obtaining a polyamic acid liquid film of a certain thickness on a glass plate by coating, and then placing the sample in an atmosphere heating oven for thermal imidization treatment.

[0108] The coating method is a conventional liquid film coating method such as casting coating, spin coating, or spraying; the liquid film thickness is controlled between 50 and 500 μm, preferably between 100 and 300 μm; the thermal imidization treatment refers to placing the sample in an atmosphere heating oven for programmed temperature rise, and the atmosphere oven refers to an oven protected by nitrogen or an inert gas, such as argon.

[0109] The programmed temperature rise includes a low-temperature pre-baking stage for the liquid film, a medium-temperature cross-linking reaction, and a high-temperature complete imidization stage. The low-temperature pre-baking stage is set at 80–150°C with a residence time of 0.5–2 hours. Subsequently, the temperature is increased at a certain rate to the medium-temperature cross-linking reaction temperature, controlled at 0.5–5°C / min, preferably 1–3°C / min, and then increased to 220–350°C, preferably 250–320°C. During this process, imidization of solutions A and B, and cross-linking of solution B, occur in the liquid film. After reaching the set temperature, the residence time is 0.5–2 hours. The temperature is then further increased to the high-temperature complete imidization stage, set at 350–480°C, preferably 380–450°C, to achieve complete imidization of the liquid film. After reaching the set temperature, the residence time is 0.25–2 hours.

[0110] The high-strength, high-elongation-at-break polyimide film system forms an interpenetrating network between its molecular chains, as shown below:

[0111]

[0112] The testing equipment and testing conditions used in this invention are as follows:

[0113] Mechanical property characterization of blended materials: The mechanical properties of blended materials were characterized using a universal tensile tester.

[0114] Thermal property characterization of blended materials: Thermogravimetric analysis was used to characterize the stability of the materials, and thermomechanical analysis was used to calculate the glass transition temperature and coefficient of thermal expansion of the materials.

[0115] Example 1

[0116] (1) Preparation of polyamic acid A solution: 4.331 g (40 mmol) of 1,4-p-phenylenediamine was dissolved in 85 g of N-methylpyrrolidone and stirred under a nitrogen atmosphere. Then, 4.542 g of pyromellitic dianhydride (20.8 mmol) and 6.127 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (20.8 mmol) were added. After stirring at 25 °C for 4 h, 0.075 g of tris(4-aminophenyl)amine (0.26 mmol) was added and the reaction was continued for 2 h to obtain polyamic acid A solution. The molecular weight was determined to be 1.7 × 10⁻⁶ by GPC. 5 Da.

[0117] (2) Preparation of polyamic acid B solution: 5.253 g (48.6 mmol) of 1,4-p-phenylenediamine was dissolved in 85 g of N-methylpyrrolidone and stirred under a nitrogen atmosphere. 9.7473 g (44.7 mmol) of pyromellitic dianhydride was added to the solution, and the mixture was stirred at 25 °C for 4 h. Subsequently, 0.765 g (7.8 mmol) of maleic anhydride was added, and the mixture was stirred for 2 h to obtain polyamic acid B solution. The molecular weight was determined to be 0.3 × 10⁻⁶ by GPC. 4 Da.

[0118] (3) Mix polyamic acid solution A and solution B at a mass ratio of 95:5 and stir for 2 hours until uniformly dissolved to obtain a casting solution for coating.

[0119] (4) The casting solution was coated onto a glass plate using a casting method, with the gap between the doctor blade and the glass plate set to 300 μm. The liquid film was placed in a hot oven under a nitrogen atmosphere, and the temperature was programmed to rise as follows: from room temperature to 140℃ at a rate of 3℃ / min, held at 140℃ for 2 hours, then increased to 300℃ at a rate of 3℃ / min, held at that temperature for 1 hour, then increased to 450℃ at a rate of 3℃ / min, held at that temperature for 1 hour. Finally, heating was stopped and the film was allowed to cool naturally to obtain a polyimide film.

[0120] Examples 2-12

[0121] The monomers, polymerization reactions, molding processes, and thermal imidization conditions in Examples 2-12 were the same as in Example 1. The parameters in the preparation methods and the properties of the resulting films are shown in Table 1 below.

[0122] Example 13

[0123] (1) Preparation of polyamic acid A solution: 1.763 g (16.3 mmol) of 1,4-p-phenylenediamine and 3.263 g of polyamic acid A solution were mixed.

[0124] (16.3 mmol) diaminodiphenyl ether was dissolved in 85 g of N-methylpyrrolidone and stirred under a nitrogen atmosphere. Then, 9.974 g (33.8 mmol) of 3,3,4,4-biphenyltetracarboxylic dianhydride was added, and the mixture was stirred at 25 °C for 4 h. After that, 0.063 g of tris(4-aminophenyl)amine (0.22 mmol) was added, and the reaction was continued for 2 h to obtain polyamic acid solution A. The molecular weight was determined to be 1.8 × 10⁻⁶ by GPC. 5 Da.

[0125] (2) Preparation of polyamic acid B solution: 5.253 g (48.6 mmol) of 1,4-p-phenylenediamine was dissolved in 85 g of N-methylpyrrolidone and stirred under a nitrogen atmosphere. 9.7473 g (44.7 mmol) of pyromellitic dianhydride was added to the solution, and the mixture was stirred at 25 °C for 4 h. Subsequently, 0.765 g (7.8 mmol) of maleic anhydride was added, and the mixture was stirred for 2 h to obtain polyamic acid B solution. The molecular weight was determined to be 0.3 × 10⁻⁶ by GPC. 4 Da.

[0126] (3) Mix polyamic acid solution A and solution B at a mass ratio of 95:5 and stir for 2 hours until uniformly dissolved to obtain a casting solution for coating.

[0127] (4) The casting solution was coated onto a glass plate using a casting method, with the gap between the doctor blade and the glass plate set to 300 μm. The liquid film was placed in a hot oven under a nitrogen atmosphere, and the temperature was programmed to rise as follows: from room temperature to 140℃ at a rate of 3℃ / min, held at 140℃ for 2 hours, then increased to 300℃ at a rate of 3℃ / min, held at that temperature for 1 hour, then increased to 450℃ at a rate of 3℃ / min, held at that temperature for 1 hour. Finally, heating was stopped and the film was allowed to cool naturally to obtain a polyimide film.

[0128] The mechanical properties of the resulting polyimide film increased from tensile strength (183 MPa), modulus (4.6 GPa), and elongation at break (18.7%) of the film obtained from polymer A solution to 275 MPa, 7.4 GPa, and 21.7%, respectively.

[0129] Comparative Example 1 - Comparative Example 2

[0130] The polymerization reaction, molding process, and thermal imidization conditions of Comparative Examples 1 and 2 were the same as those of Example 1, but polyamic acid solution A and polyamic acid solution B were directly molded into films. The parameters in the preparation method and the properties of the obtained films are shown in Table 1 below.

[0131] Table 1. Performance of the polyimide films obtained in the examples and comparative examples.

[0132]

Claims

1. A polyamic acid solution comprising polyamic acid solution A and polyamic acid solution B, and / or a mixture thereof; wherein, The polyamic acid in polyamic acid solution A contains rigid dianhydride structural units, diamine structural units, and polyamine structural units; the polyamic acid in polyamic acid solution B contains rigid dianhydride structural units, diamine structural units, and monomer structural units containing double or triple bonds; the molecular weight of the polyamic acid in polyamic acid solution A is 1.0 × 10⁻⁶. 5 ~2.0×10 5 The polyamic acid in the polyamic acid solution B has a molecular weight of 0.2 × 10⁻⁶. 4 ~2×10 4 The mass ratio of polyamic acid solution A to polyamic acid solution B is (98:2) to (85:15).

2. The polyamic acid solution according to claim 1, characterized in that: The polyamic acid in the polyamic acid solution A has a molecular weight of 1.2 × 10⁻⁶. 5 ~1.8×10 5 ; The polyamic acid in the polyamic acid solution B has a molecular weight of 0.3 × 10⁻⁶. 4 ~1.2×10 4 ; The mass ratio of polyamic acid solution A to polyamic acid solution B is (95:5) to (90:10).

3. The polyamic acid solution according to claim 1, characterized in that: In polyamic acid solution A, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the polyamine structural unit is derived from the polyamine. In polyamic acid solution B, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the monomer structural unit containing double or triple bonds is derived from the monomer containing double or triple bonds.

4. The polyamic acid solution according to claim 3, characterized in that... In polyamic acid solution A: The rigid dianhydride is a non-bridged dianhydride monomer; and / or, The diamine is a diamine with 1 or fewer bridging atoms; and / or, The polyamine is a symmetrical polyamine.

5. The polyamic acid solution according to claim 4, characterized in that: The rigid dianhydride is selected from at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride; and / or, The diamine is selected from at least one of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodibenzophenone, 2-(diaminophenyl)benzimidazole-5-amine, 2-(4-aminophenyl)-1H-benzoxazole-5-amine, and trans-1,4-cyclohexanediamine; and / or, The polyamine is selected from at least one of tris(4-aminophenyl)amine, tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5,7-tetraaminoadamantane, and octaaminophenyl cubic siloxane.

6. The polyamic acid solution according to claim 3, characterized in that... In polyamic acid solution B: The rigid dianhydride is a non-bridged dianhydride monomer; and / or, The diamine is a non-bridged diamine monomer; and / or, The monomer containing double or triple bonds is an acid anhydride containing crosslinkable alkenyl double bonds or alkynyl triple bonds.

7. The polyamic acid solution according to claim 6, characterized in that: The rigid dianhydride is selected from at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyl dianhydride, 2,3,3',4-biphenyl dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-anthracitetetracarboxylic dianhydride; and / or, The diamine is selected from at least one of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl; and / or The monomer containing a double or triple bond structure is selected from at least one of maleic anhydride, 4-ethynylphthalic anhydride, 4-phenylethynylphthalic anhydride, norbornene anhydride, and 4,4'-(ethynyl-1,2-diyl)phthalic anhydride.

8. A method for preparing a polyamic acid solution according to any one of claims 1 to 7, comprising the steps of preparing a high molecular weight polyamic acid solution A, preparing a low molecular weight polyamic acid solution B, and blending polyamic acid solution A and polyamic acid solution B.

9. The method for preparing the polyamic acid solution according to claim 8, characterized in that... Includes the following steps: (1) Polyamic acid solution A is obtained by copolymerizing rigid dianhydride, diamine and polyamine in an aprotic polar solvent; (2) Polyamic acid solution B is obtained by copolymerizing rigid dianhydride, diamine and monomers containing double or triple bonds in an aprotic polar solvent; (3) Mix polyamic acid solution A and polyamic acid solution B together.

10. The method for preparing the polyamic acid solution according to claim 9, characterized in that... In step (1): First, a rigid dianhydride and a diamine are reacted in an inert atmosphere in an aprotic polar solvent. Then, a polyamine is added to continue the reaction to prepare a polyamic acid solution A.

11. The method for preparing the polyamic acid solution according to claim 10, characterized in that: The molar ratio of rigid dianhydride to diamine is (1.03–1.08):1; The reaction temperature of rigid dianhydrides with diamines is 0–60℃; the reaction time is 2–12 h. Based on the ratio of primary amines, the ratio of polyamines to diamines is 0.005 to 0.05; The reaction time after adding polyamine is 1–8 hours; The solid content of the polyamic acid solution A is 10-20 wt%.

12. The method for preparing the polyamic acid solution according to claim 11, characterized in that: The molar ratio of rigid dianhydride to diamine is (1.04–1.06):1; The reaction temperature of rigid dianhydrides with diamines is 20–40 °C; the reaction time is 4–8 h. Based on the ratio of primary amines, the ratio of polyamines to diamines is 0.01 to 0.04; The reaction time after adding polyamine is 2-4 hours; The solid content of the polyamic acid solution A is 12-16 wt%.

13. The method for preparing the polyamic acid solution according to claim 9, characterized in that... In step (2): First, rigid dianhydride and diamine are reacted in an inert atmosphere in an aprotic polar solvent. Then, monomers containing double or triple bonds are added to continue the reaction to prepare polyamic acid solution B.

14. The method for preparing the polyamic acid solution according to claim 13, characterized in that: The molar ratio of rigid dianhydride to diamine is (0.9–0.96):1; The reaction temperature of rigid dianhydrides with diamines is 0–60℃, and the reaction time is 2–12 h. The molar ratio of anhydride to amino group of diamine in monomers containing double or triple bonds is 0.08–0.

2. The reaction time after adding monomers containing double or triple bonds is 1–4 hours; The solid content of the polyamic acid solution B is 10-20 wt%.

15. The method for preparing the polyamic acid solution according to claim 14, characterized in that: The molar ratio of rigid dianhydride to diamine is (0.92–0.94):1; The reaction temperature of rigid dianhydrides with diamines is 20–40 °C, and the reaction time is 4–8 h. The molar ratio of anhydride to amino group of diamine in monomers containing double or triple bonds is 0.12–0.

16. The reaction time after adding monomers containing double or triple bonds is 2–3 hours; The solid content of the polyamic acid solution B is 12-16 wt%.

16. A polyimide comprising polyimide A and polyimide B, and / or mixtures thereof; wherein, Polyimide A contains rigid dianhydride structural units, diamine structural units, and polyamine structural units, while polyimide B contains rigid dianhydride, diamine structural units, and monomer structural units containing double or triple bonds. The polyimide is obtained by imidization of a polyamic acid solution according to any one of claims 1 to 7 or a polyamic acid solution obtained by any one of claims 8 to 15.

17. The polyimide according to claim 16, characterized in that: In polyimide A, the rigid dianhydride structural unit is derived from rigid dianhydride, the diamine structural unit is derived from diamine, and the polyamine structural unit is derived from polyamine; In polyimide B, the rigid dianhydride structural unit is derived from the rigid dianhydride, the diamine structural unit is derived from the diamine, and the monomer structural unit containing double or triple bonds is derived from the monomer containing double or triple bonds.

18. A polyimide film comprising the polyimide according to any one of claims 16 to 17.

19. A method for preparing a polyimide film according to claim 18, comprising molding a polyamic acid solution according to any one of claims 1 to 7 or a polyamic acid solution obtained by the preparation method according to any one of claims 8 to 15 into a film, and then performing an imidization treatment.

20. The method for preparing the polyimide film according to claim 19, characterized in that: The molding process employs a coating method to form a film; and / or, The imidization treatment is a thermal imidization treatment.

21. The method for preparing the polyimide film according to claim 20, characterized in that: The coating method is at least one of casting coating, spin coating, and spray coating; the thickness of the coated polyamic acid liquid film is 50–500 μm; and / or, The thermal imidization treatment includes low-temperature pre-drying of the liquid film, medium-temperature cross-linking reaction, and high-temperature complete imidization. The low-temperature pre-drying stage is carried out at a temperature of 80–150°C for 0.5–2 h. Subsequently, the temperature is increased to the medium-temperature cross-linking reaction temperature of 220–350°C at a heating rate of 0.5–5°C / min for 0.5–2 h. Finally, the temperature is increased to the high-temperature complete imidization temperature of 350–480°C for 0.25–2 h.

22. The method for preparing the polyimide film according to claim 21, characterized in that: The thickness of the coated polyamic acid liquid film is 100–300 μm.

23. The use of the polyimide film of claim 18 or the polyimide film obtained by any one of claims 19 to 22 in flexible display substrate materials.

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