WO2023155030A1

WO2023155030A1 - Polyimide membrane, preparation method therefor and use thereof

Info

Publication number: WO2023155030A1
Application number: PCT/CN2022/000071
Authority: WO
Inventors: 沈奕; 吕岳敏; 詹前贤; 高嘉桐; 欧建平
Original assignee: 汕头超声显示器技术有限公司; 汕头超声显示器（二厂）有限公司; 汕头超声显示器有限公司
Priority date: 2022-02-21
Filing date: 2022-04-22
Publication date: 2023-08-24
Also published as: CN114213658B; CN114213658A

Abstract

The present invention relates to a polyimide membrane, a preparation method therefor and use thereof. Both sides of the polyimide membrane are formed with different hydrophilic properties by means of different degrees of polymerization. One side is hydrophilic and the other side is non-hydrophilic, so that when the polyimide membrane is used as the substrate of a flexible electronic device, the electrical circuit on the membrane has good adhesion, and the polyimide membrane can also be easily peeled from the mother glass.

Description

A kind of polyimide membrane and its manufacture method and application

technical field

The invention relates to the technical field of polyimide film preparation, in particular to a polyimide film with hydrophilicity on one side and non-hydrophilicity on the other side, a manufacturing method and application thereof.

Background technique

Polyimide films generally have good heat resistance and can be used as substrates for flexible electronic devices (such as touch screens, displays, etc.). Usually, the polyimide film is first polymerized on the glass substrate, and then the circuit is formed on the polyimide film through coating, photolithography and other processes, and finally the polyimide film is peeled off from the glass substrate. The aforementioned flexible electronic device is obtained.

However, there is a contradiction between the hydrophilic property of the polyimide film and the adhesion performance of the circuit on the film: if the polyimide film has good hydrophilicity, although the circuit formed on the polyimide film has a good Adhesion, but when the polyimide film is peeled off the glass substrate, it is difficult to peel off the polyimide film from the glass substrate; on the contrary, if the polyimide film has good hydrophobicity, The imide film is very easy to peel off from the glass substrate, but the adhesion of the circuit formed on the polyimide film is poor.

Contents of the invention

The problem to be solved by this invention is to provide a kind of polyimide film and its manufacture method, this polyimide film has hydrophilicity on one side, the other side has non-hydrophilicity, makes this polyimide film as When the substrate of flexible electronic devices is used, the circuit on the film has good adhesion, and it is also easy to peel off the polyimide film from the glass substrate. The technical scheme adopted is as follows:

A polyimide film is characterized in that the polyimide film is a fully aromatic copolymerized polyimide polymer prepared by alternating copolymerization of diamine compounds and dianhydride compounds, and its chemical structure is simple. The formula is:

Among them, X is a reactive residue of a hydrophobic diamine compound, Y is a reactive residue of a hydrophobic dianhydride compound; m and n represent the degree of polymerization, m and n are both integers greater than 0, and the aromatic type The copolymerized polyimide polymer forms the polyimide film by coating or casting, and an electric field is applied before polymerization so that one side of the polyimide film has m>n, and the other side has n>m .

Through different degrees of polymerization, different hydrophilic properties are formed on both sides of the polyimide film: when m<n, the hydrophilic property of this surface is stronger, and it is suitable for forming circuits on this surface by processes such as coating and photolithography ; And when m>n, the hydrophilic property of the surface is weak, and it is easy to peel off from the glass substrate.

As a preferred version of the present invention, the diamine compound includes a hydrophilic diamine compound and a hydrophobic diamine compound, wherein the hydrophilic diamine compound is 9,9-bis(2-methoxyethoxy) The molar ratio of methyl-2,7-diaminofluorene to 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene is 1-60%. By adjusting the ratio of hydrophilic diamine compound and hydrophobic diamine compound on different sides of the film, membrane surfaces with different hydrophilic properties can be obtained, because 9,9-bis(2-methoxyethoxy)methyl -2,7-diaminofluorene has a group with relatively high electronegative property, which will drift under the action of a strong electric field before polymerization and gather to the high potential side.

As a further preferred solution of the present invention, the hydrophobic diamine compound includes at least one of the following compounds: p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,3'- Diaminodiphenyl ether, diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3 , 3'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2'-bistrifluoromethyl-4, 4'-diphenyl ether diamine, 2,2'-bistrifluoromethyl-4,4'-diphenylsulfide diamine, 2,2'-bistrifluoromethyl-4,4'-diphenyl Sulfonediamine, 4,4'-diaminodiphenylmethane.

As a further preferred solution of the present invention, the hydrophobic dianhydride compound includes 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1-50%.

As a further preferred solution of the present invention, the dianhydride compound also includes at least one of 3,3',4,4'-biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride.

As a preferred solution of the present invention, the molar ratio of the diamine compound to the dianhydride compound is 1:0.98˜1:1.02.

In addition, the present invention also provides the preparation method of described polyimide film, it is characterized in that comprising the following steps:

Step 1: Completely dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene in a strong polar aprotic solvent in a polymerization bottle, then add 2,2' -bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, and 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene with 2,2'-bis (3,4-dicarboxylic acid) hexafluoropropane dianhydride is in an equimolar ratio, and the stirring reaction is carried out for 5 to 10 hours under a reaction environment of 20 to 60 ° C and normal pressure to obtain the first polyamic acid solution;

Step 2: Dissolve the second diamine compound completely in a strong polar aprotic solvent in the polymerization bottle, and the second diamine compound is a hydrophobic diamine compound; then add the second dianhydride compound, Stirring and reacting for 5-10 hours under a reaction environment of 20-60°C and normal pressure to obtain the second polyamic acid solution;

Step 3: Evenly mix the first polyamic acid solution with the second polyamic acid solution and apply it on the glass substrate to form a coating, apply an electric field perpendicular to the glass substrate on the coating, and the glass substrate in the electric field The potential on the outside is higher than the potential inside the glass substrate, and then heat-baked at 60-80°C under the condition of maintaining the electric field to remove part of the organic solvent;

Step 4: Gradually raise the temperature of the glass substrate from room temperature to 250-350°C, the heating time is 1-5 hours, and the heating rate is 1-10°C/min, then naturally cool to 25-80°C, and remove the film to obtain the polyimide Amine film.

The potential on the outside of the glass substrate is higher and the film is formed as a coated polyimide solution, which has higher hydrophilicity, while the potential inside the glass substrate is lower and has lower hydrophilicity, thus forming double-sided hydrophilicity Different polyimide films.

As a preferred version of the present invention, the second dianhydride compound is 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, or 2,2'-bis(3,4-di Carboxylic acid) an equal proportion mixture of hexafluoropropane dianhydride and at least one of 3,3',4,4'-biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride. Wherein, the molar ratio of the second diamine compound to the second dianhydride compound is 1:0.98˜1:1.02. Hydrophobic diamine compounds include at least one of the following compounds: p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, diaminodiphenyl ether, Phenylsulfone, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethane base) biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2'-bistrifluoromethyl-4,4'-diphenyl ether diamine, 2,2'-bistrifluoromethyl-4,4'-diphenylsulfidediamine, 2,2'-bistrifluoromethyl-4,4'-diphenylsulfonediamine, 4,4'- Diaminodiphenylmethane.

As a further preferred solution of the present invention, the strong polar aprotic solvent includes N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone A mixture of one or more than two solvents.

In addition, the polyimide film of the present invention is applied to a flexible touch substrate.

Compared with the prior art, the present invention has the following advantages: the polyimide film of the present invention and the manufacturing method thereof form different hydrophilic properties on both sides of the polyimide film through different degrees of polymerization, and one side has a hydrophilic property. The other side has non-hydrophilicity, so that when this polyimide film is used as the substrate of flexible electronic devices, the circuit on the film has good adhesion, and it is also easy to remove the polyimide film from the glass peeled off the substrate.

Description of drawings

Fig. 1 is the schematic diagram of step 3 in each embodiment of the present invention; Wherein, each mark is: 1- glass substrate, 2- two kinds of polyamic acid solution mixed coatings, 3- upper electrode, 4- lower electrode, 5- coating Glue scraper (for glass substrate coating), 6-infrared lamp for drying, 7-roller (for conveying glass substrate).

Detailed ways

Embodiment one

This embodiment discloses a kind of preparation method of polyimide membrane, comprises the following steps:

Step 1: Completely dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene in N,N-dimethylformamide in a polymerization bottle, then add etc. 2,2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride in molar ratio, stirred and reacted for 8 hours under a reaction environment of 50° C. and normal pressure, to obtain polyamic acid solution A;

Step 2: Dissolve p-phenylenediamine completely in N, N-dimethylformamide in the polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropanedianhydride, in Stirring reaction was carried out for 8 hours under a reaction environment of 50° C. and normal pressure to obtain polyamic acid solution B;

Step 3: As shown in Figure 1, the polyamic acid solution A and the polyamic acid solution B are evenly mixed and coated on the glass substrate 1 to form a coating 2, and an electric field perpendicular to the glass substrate 1 is applied on the coating 2, And the potential on the outside of the glass substrate 1 (corresponding to the upper electrode 3 in FIG. 1 ) is higher than the potential inside the glass substrate 1 (corresponding to the lower electrode 4 in FIG. 1 ). Remove part of the organic solvent;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 320° C. for 4 hours at a rate of 8° C./min, then naturally cool to 40° C. and remove the film to obtain a polyimide film.

Embodiment two

Step 1: Completely dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene in N,N-dimethylformamide in a polymerization bottle, then add etc. 2,2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride in molar ratio, stirred and reacted for 6 hours under a reaction environment of 50° C. and normal pressure to obtain polyamic acid solution A;

Step 2: Dissolve m-phenylenediamine completely in N, N-dimethylformamide in the polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, in Stirring and reacting for 10 hours under a reaction environment of 50° C. and normal pressure to obtain a polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 350° C. for 3 hours at a rate of 2° C./min, then naturally cool to 60° C. and remove the film to obtain a polyimide film.

Embodiment three

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in dimethyl sulfoxide in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 8 hours at 60° C. and normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Completely dissolve 4,4'-diaminodiphenyl ether in dimethyl sulfoxide in a polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride , carrying out a stirring reaction for 6 hours under a reaction environment of 50° C. and normal pressure to obtain a polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 300° C. for 2 hours at a rate of 4° C./min, then naturally cool to 40° C. and remove the film to obtain a polyimide film.

Embodiment four

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in N-methylpyrrolidone in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 6 hours at 30° C. and normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Dissolve diaminodiphenylsulfone completely in N-methylpyrrolidone in a polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride and 3,3' , 4,4'-biphenyl-type tetracarboxylic dianhydride mixed solvent in equal proportions, stirred and reacted for 6 hours under a reaction environment of 60° C. and normal pressure, to obtain polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 270° C. for 2 hours at a rate of 1° C./min, then naturally cool to 25° C. and remove the film to obtain a polyimide film.

Embodiment five

Step 1: Completely dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene in N,N-dimethylformamide in a polymerization bottle, then add etc. 2,2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride in molar ratio, stirred and reacted for 10 hours under a reaction environment of 50° C. and normal pressure to obtain polyamic acid solution A;

Step 2: Completely dissolve 4,4'-diaminobiphenyl in N,N-dimethylformamide in a polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid)hexafluoro A mixed solvent of propane dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride in equal proportions was stirred and reacted for 5 hours under a reaction environment of 60°C and normal pressure to obtain a polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 250° C. for 1 hour at a rate of 5° C./min, then naturally cool to 70° C. and remove the film to obtain a polyimide film.

Embodiment six

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in dimethyl sulfoxide in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 5 hours at 40° C. and normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Completely dissolve 4,4'-diamino-3,3'-dimethylbiphenyl in dimethyl sulfoxide in a polymerization bottle, then add 2,2'-bis(3,4-bis Carboxylic acid) an equal proportion mixed solvent of hexafluoropropane dianhydride and 3,3',4,4'-biphenyl type tetracarboxylic dianhydride, carried out a stirring reaction for 8 hours under a reaction environment of 30° C. and normal pressure, Obtain polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 350° C. for 4 hours at a rate of 4° C./min, then naturally cool to 40° C. and remove the film to obtain a polyimide film.

Embodiment seven

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in N-methylpyrrolidone in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 7 hours at 20° C. and normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Completely dissolve 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl in N-methylpyrrolidone in a polymerization bottle, then add 2,2'-bis(3 , 4-dicarboxylic acid) an equal proportion mixed solvent of hexafluoropropane dianhydride and pyromellitic dianhydride was stirred and reacted for 10 hours at 30° C. and under normal pressure reaction environment to obtain polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 320° C. for 5 hours at a rate of 3° C./min, then naturally cool to 80° C. and remove the film to obtain a polyimide film.

Embodiment eight

Step 2: Completely dissolve 2,2'-bistrifluoromethyl-4,4'-diphenylsulfide diamine in N,N-dimethylformamide in a polymerization bottle, then add 2,2' - A mixed solvent of bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride and pyromellitic dianhydride in equal proportions, stirred and reacted for 9 hours under a reaction environment of 40°C and normal pressure to obtain polyamic acid Solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 280° C. for 4 hours at a rate of 6° C./min, then naturally cool to 30° C. and remove the film to obtain a polyimide film.

Embodiment nine

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in dimethyl sulfoxide in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 8 hours at 30° C. and normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Completely dissolve 2,2'-bistrifluoromethyl-4,4'-diphenylsulfonediamine in dimethyl sulfoxide in a polymerization bottle, then add 2,2'-bis(3, 4-dicarboxylic acid) a mixed solvent of hexafluoropropane dianhydride and pyromellitic dianhydride in equal proportions was stirred and reacted for 9 hours under a reaction environment of 40° C. and normal pressure to obtain a polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 320° C. for 3 hours at a rate of 8° C./min, then naturally cool to 50° C. and remove the film to obtain a polyimide film.

Embodiment ten

Step 1: Dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene completely in N-methylpyrrolidone in a polymerization bottle, and then add an equimolar ratio of 2 , 2′-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, stirred and reacted for 10 hours at 60° C. under a normal pressure reaction environment to obtain polyamic acid solution A;

Step 2: Completely dissolve 4,4'-diaminodiphenylmethane in N-methylpyrrolidone in a polymerization bottle, then add 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride , 3,3 ', 4,4'-biphenyl type tetracarboxylic dianhydride and pyromellitic dianhydride mixed solvent in equal proportions, carried out stirring reaction for 10 hours at 20°C and normal pressure reaction environment, to obtain Polyamic acid solution B;

Step 4: Gradually raise the temperature of the glass substrate 1 from room temperature to 350° C. for 3 hours at a rate of 10° C./min, then naturally cool to 30° C. and remove the film to obtain a polyimide film.

In the above-mentioned Examples 1 to 10, the polyamic acid solution A uses a hydrophilic diamine compound, and the polyamic acid solution B uses a hydrophobic diamine compound. At the same time, electric fields with different potentials are applied on both sides of the glass substrate. The potential of the upper electrode 3 is higher than that of the lower electrode 4, therefore, the polyimide membranes prepared in Examples 1 to 10 all have hydrophilicity on one side and non-hydrophilicity on the other side.

Simultaneously, adopt contact angle meter to measure the water droplet contact angle of two faces of the sample of embodiment one to embodiment ten, measurement result is as follows:

the	外侧面接触角(°)Outer surface contact angle (°)	内侧面接触角(°)Medial surface contact angle (°)	内外侧面接触角差(°)Contact angle difference between inner and outer surfaces (°)
实施例1Example 1	4040	8989	4949
实施例2Example 2	5656	9494	3838
实施例3Example 3	3737	7676	3939
实施例4Example 4	4242	9898	5656
实施例5Example 5	3838	9595	5757
实施例6Example 6	6464	102102	3838
实施例7Example 7	5656	8989	3333
实施例8Example 8	3434	9393	5959
实施例9Example 9	3636	9696	6060
实施例10Example 10	5050	104104	5454

The relationship between the above water drop contact angle and hydrophilicity and hydrophobicity is: when the water drop contact angle is obviously less than 90°, it is hydrophilic; when the water drop contact angle is close to or exceeds 90°, it is hydrophobic. A small water droplet contact angle indicates that the surface has high hydrophilicity, and a large water droplet contact angle indicates that the surface has high hydrophobicity. According to the test shown in the table above, the inner and outer surfaces of the samples from Examples 1 to 10 show hydrophobicity and hydrophilicity respectively, so that when the samples from Examples 1 to 10 are used as substrates for flexible electronic devices, The circuit on the film has good adhesion, and it is also easy to peel the polyimide film from the glass substrate.

In addition, in each embodiment, the molar ratio of the second diamine compound to the second dianhydride compound can be adjusted according to actual production needs, as long as the molar ratio of the corresponding diamine compound to the dianhydride compound is within 1 :0.98～1:1.02 is enough.

In addition, it should be noted that, in the specific embodiments described in this specification, the names of various parts may be different, and all equivalent or simple changes made according to the structure, features and principles described in the patent concept of the present invention include Within the protection scope of the patent of the present invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims. All should belong to the protection scope of the present invention.

Claims

A polyimide film is characterized in that the polyimide film is a fully aromatic copolymerized polyimide polymer prepared by alternating copolymerization of diamine compounds and dianhydride compounds, and its chemical structure is simple. The formula is:

Among them, X is a reactive residue of a hydrophobic diamine compound, Y is a reactive residue of a hydrophobic dianhydride compound; m and n represent the degree of polymerization, m and n are both integers greater than 0, and the aromatic type The copolymerized polyimide polymer forms the polyimide film by coating or casting, and an electric field is applied before polymerization so that one side of the polyimide film has m>n, and the other side has n>m .
The polyimide film according to claim 1, wherein the diamine compound comprises a hydrophilic diamine compound and a hydrophobic diamine compound, wherein the hydrophilic diamine compound is 9,9-diamine compound (2-methoxyethoxy) methyl-2,7-diaminofluorene, the molar ratio of 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene is 1 to 60%.
The polyimide film according to claim 2, wherein the hydrophobic diamine compound comprises at least one of the following compounds: p-phenylenediamine, m-phenylenediamine, 4,4'-diamino Diphenyl ether, 3,3'-diaminodiphenyl ether, diaminodiphenylsulfone, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2' -Bistrifluoromethyl-4,4'-diphenyl ether diamine, 2,2'-bistrifluoromethyl-4,4'-diphenylsulfide diamine, 2,2'-bistrifluoromethyl Base-4,4'-diphenylsulfonediamine, 4,4'-diaminodiphenylmethane.
The polyimide film according to claim 1, characterized in that: the molar ratio of the diamine compound to the dianhydride compound is 1:0.98˜1:1.02.
A kind of preparation method of polyimide membrane described in claim 1 is characterized in that comprising the following steps:

Step 1: Completely dissolve 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene in a strong polar aprotic solvent in a polymerization bottle, then add 2,2' -bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, and 9,9-bis(2-methoxyethoxy)methyl-2,7-diaminofluorene with 2,2'-bis (3,4-dicarboxylic acid) hexafluoropropane dianhydride is in an equimolar ratio, and the stirring reaction is carried out for 5 to 10 hours under a reaction environment of 20 to 60 ° C and normal pressure to obtain the first polyamic acid solution;

Step 2: Dissolve the second diamine compound completely in a strong polar aprotic solvent in the polymerization bottle, and the second diamine compound is a hydrophobic diamine compound; then add the second dianhydride compound, Stirring and reacting for 5-10 hours under a reaction environment of 20-60°C and normal pressure to obtain the second polyamic acid solution;

Step 3: Evenly mix the first polyamic acid solution with the second polyamic acid solution and apply it on the glass substrate to form a coating, apply an electric field perpendicular to the glass substrate on the coating, and the glass substrate in the electric field The potential on the outside is higher than the potential inside the glass substrate, and then bake at 60-80°C under the condition of maintaining the electric field to remove part of the organic solvent;

Step 4: Gradually raise the temperature of the glass substrate from room temperature to 250-350°C, the heating time is 1-5 hours, the heating rate is 1-10°C/min, then naturally cool to 25-80°C, and remove the film to obtain the polyimide Amine film.
The preparation method according to claim 5, characterized in that: in the step 2, the second dianhydride compound is 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, Or at least one of 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride A mixture of equal proportions.
The preparation method according to claim 5 or 6, characterized in that: the strong polar aprotic solvent comprises N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide Or a mixed solvent of one or more than two kinds of N-methylpyrrolidone.
An application of the polyimide film according to claim 1, characterized in that: the polyimide film is applied to a flexible touch base.