Method for preparing polyimide bidirectionally-drawn film through catalysis of thermally-induced alkali production agent

Abstract

The invention relates to a method for preparing a polyimide bidirectionally-drawn film through catalysis of a thermally-induced alkali production agent. The method comprises the following steps: synthesizing the thermally-induced alkali production agent; aromatic diamine and aromatic dianhydride are used for synthesizing polyamide acid resin, a thermally induced base generator and acetic anhydride are added for chemical cyclization to obtain a gel film, and then the gel film is subjected to two-way drafting to prepare the polyimide two-way drafted film. The thermally induced alkali generator adopted by the invention cannot generate catalytic action at room temperature, and can improve the storage stability of the membrane casting solution and widen the processing window of the membrane casting solution; the film subjected to two-way drafting and heat setting has excellent mechanical properties, heat resistance and dimensional stability; the polyimide bidirectionally drawn film prepared by the invention can be widely applied to the fields of electronics, electric appliances, automobiles, machinery, aviation, spaceflight, chemical engineering and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of polyimide films, and particularly relates to a method for preparing a polyimide biaxially stretched film by catalysis of a thermal base generating agent. Background Art

[0002] Commercial products such as DuPont's Kapton, Ube Industries' Upilex and Kaneka Chemical's Apical series have good mechanical properties, heat resistance, dimensional stability and dielectric properties, and have been widely used in high-temperature insulation, flexible electronics and other fields. Bidirectional stretching by chemical cyclization is the mainstream process for preparing electronic-grade polyimide films in industry. Compared with the thermal cyclization method, it has the advantages of high production rate and high stretching ratio. US Patent US5460890A describes a process for preparing gel film by chemical cyclization and bidirectional stretching, which greatly improves the mechanical properties and dimensional stability of the film. However, the chemical imine reaction activity in the chemical method is high, the required temperature is low (0~100°C), and the polyamide acid solution quickly (30 s~30 min) turns into a gel state at room temperature and loses fluidity, which brings difficulties to processing. If the chemical cyclization reaction rate is reduced by lowering the temperature, the processing window can be effectively widened; but the viscosity of the polymer solution caused by low temperature increases, which is not conducive to the degassing and casting of the casting solution. Moreover, the requirements for production equipment during low-temperature processing are complex, which increases production costs.

[0003] In the study of epoxy resin, the emergence of latent curing agent makes the blended epoxy resin components inert at room temperature. When a certain triggering condition (temperature, humidity, light, etc.) is reached, the epoxy resin system can undergo a rapid curing and crosslinking reaction, solving the problems of short storage period, narrow processing window, and complex process of epoxy resin. Patent CN118184960A designs a latent curing agent containing an amine compound and a dicyandiamide composition containing an epoxy compound, which ensures the storage stability of epoxy resin at room temperature, and has the advantages of low curing temperature, good solubility, and not easy to agglomerate. Similarly, in the study of polyimide, there are also reports on the introduction of latent catalysts. In order to achieve low-temperature curing of polyimide resin and avoid the degradation of the resin by the alkaline catalyst before curing, a latent curing catalyst is often added to the precursor solution to obtain excellent performance after low-temperature curing and maintain long storage stability. For example, patent CN112368641A introduces a latent catalyst containing a guanidine derivative or a biguanide derivative, which is mixed into a photosensitive polyimide mixed resin to give it good pattern processing properties, high chemical resistance, high elasticity, high elongation properties and high adhesion to metals (especially copper).

[0004] The structure of latent catalysts is generally a derivative of organic bases, such as 2,6-dimethylpiperidine, imidazole, etc. These compounds are easy to thermally decompose, release carbon cations, and produce substances such as olefins and organic bases. Their decomposition temperature is affected by steric hindrance and electronic effects, thereby achieving an adjustable decomposition temperature within the range of 40-200 °C. Therefore, by designing the structure of latent catalysts to control their decomposition temperature and decomposition rate, and then achieving precise control of chemical cyclization reactions, it is expected to solve the problems of high equipment requirements, narrow processing window, and difficult gel film control in the preparation of polyimide biaxially stretched films by traditional chemical cyclization. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a polyimide biaxially stretched film by catalyzing a thermal base generator. The thermal base generator can improve the storage stability of the casting solution, broaden its processing window, and achieve precise control of the chemical cyclization process by regulating the types of its substituents, which is beneficial to improving the performance stability of the film.

[0006] The present invention provides a method for preparing a polyimide biaxially stretched film by catalysis of a thermal base generating agent, comprising the following steps: (1) Maleic anhydride is subjected to an esterification reaction with a fatty alcohol under acidic catalytic conditions to generate a maleic acid diester, and then an organic base is added to generate a thermal base generator through a Michael addition reaction; (2) using aromatic anhydride and aromatic diamine as monomers, synthesizing a polyamic acid solution in a non-protonic polar organic solvent, then mixing the above-mentioned thermal base generating agent and acetic anhydride, scraping the film and heating it in a microwave oven to obtain a gel film; (3) The gel film is stretched in a biaxial stretching device and then heat-set to obtain a polyimide biaxially stretched film.

[0007] Preferably, the fatty alcohol in step (1) is at least one of fatty alcohols having 3 to 8 carbon atoms, preferably one of the following structures:

[0008] .

[0009] Preferably, the organic base in step (1) is at least one of pyrrole, imidazole, piperidine, 2,6-dimethylpiperidine and cyclopentylimine, such as the following structure:

[0010] .

[0011] Preferably, the reaction solvent in step (1) is a fatty alcohol, and the reaction is carried out under reflux for 6 to 20 hours.

[0012] The reaction equation of the thermal base generator is as follows:

[0013] .

[0014] Preferably, the aromatic anhydride in step (2) is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ketone tetracarboxylic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, and 4,4'-biphenyl ether dianhydride; and the aromatic diamine is at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 2-(4-aminophenyl)-5-aminobenzimidazole.

[0015] Preferably, the molar ratio of the aromatic anhydride to the aromatic diamine in step (2) is 1:(0.97-1.03).

[0016] Preferably, the aprotic polar organic solvent in step (2) is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, m-cresol and p-chlorophenol.

[0017] Preferably, the solid content of the polyamic acid solution in step (2) is 5-30 wt %, preferably 12-20 wt %.

[0018] Preferably, the molar amount of acetic anhydride in step (2) is 1.0 to 10 times, preferably 2.5 to 4 times, of the aromatic diamine; the molar amount of the thermal base generator is 0.1 to 5 times, preferably 1 to 3 times, of the aromatic diamine.

[0019] Preferably, the heating process parameters in the microwave oven in step (2) are: microwave frequency of 0.1-5 kw, and heating time of 1-30 min.

[0020] Preferably, the stretching temperature in step (3) is 20-80°C, preferably 40-60°C; the longitudinal stretching ratio of the gel film is 1.0-2.5, preferably 1.1-1.6; the transverse stretching ratio is 1.0-2.5, preferably 1.0-1.4; and the stretching rate is 10-50 mm / min.

[0021] Preferably, the heat setting process parameters in step (3) are: heating rate of 0.5-10 °C / min, preferably 1-3 °C / min, maximum temperature of 300-550 °C, and residence time of 10-60 min.

[0022] Beneficial Effects

[0023] The thermal alkali generator used in the present invention does not produce catalytic effects at room temperature, and can improve the storage stability of the casting solution and widen its processing window; the film after bidirectional stretching and heat setting has excellent mechanical properties, heat resistance and dimensional stability; the polyimide bidirectional stretching film prepared by the present invention can be widely used in the fields of electronics, electrical appliances, automobiles, machinery, aviation, aerospace and chemical industries. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0025] Example 1 (1) Under acidic conditions, add 0.6 mol maleic anhydride, 1.2 mol isopropanol and 0.6 mol imidazole into a 500 mL three-necked flask, heat under reflux at 100 °C for 5 h, cool to room temperature to obtain a thermal base generator, and seal the flask for later use.

[0026] (2) Under nitrogen protection, 0.2 mol of 4,4'-diaminodiphenyl ether and 474.1413 g of N,N-dimethylacetamide were added to a 500 mL three-necked flask. After the solid was dissolved, 0.2 mol of pyromellitic anhydride was added under ice bath and the reaction was continued for 6 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0027] (3) At room temperature, 0.6 mol of a thermal base generator and 0.6 mol of acetic anhydride were added to the polyamic acid solution. After stirring and dispersing for 20 min, the solution was centrifuged for degassing. A 800 µm liquid film was scraped off on a clean glass plate and then reacted in a microwave oven at 3 kW for 5 min to obtain a partially imidized polyamic acid-imide gel film.

[0028] (4) The gel film is fixed in a biaxial stretching machine and subjected to synchronous biaxial stretching at a stretching speed of 30 mm / min, a stretching temperature of 50 °C, and a longitudinal and transverse synchronous stretching of 1.6 times. Subsequently, the gel film is heat treated at 200 °C for 1 h, 300 °C for 1 h, and 400 °C for 1 h to obtain a polyimide biaxially stretched film.

[0029] Example 2

[0030] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (1), 0.6 mol of maleic anhydride, 1.2 mol of tert-butyl alcohol and 0.6 mol of imidazole were added to a 500 mL three-necked flask under acidic conditions, heated under reflux at 100 °C for 5 h, cooled to room temperature to obtain a thermal alkali generator, and sealed for later use.

[0031] Example 3

[0032] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (1), 0.6 mol of maleic anhydride, 1.2 mol of n-hexanol and 0.6 mol of pyrrole were added to a 500 mL three-necked flask under acidic conditions, and the mixture was heated under reflux at 100 °C for 5 h, then cooled to room temperature to obtain a thermal alkali generator, which was sealed and retained.

[0033] Example 4

[0034] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (1), 0.6 mol of maleic anhydride, 1.2 mol of isopropanol and 0.6 mol of pyrrole were added to a 500 mL three-necked flask under acidic conditions, heated under reflux at 100 °C for 5 h, and then cooled to room temperature to obtain a thermal alkali generator, which was sealed and retained.

[0035] Example 5

[0036] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (1), 0.6 mol of maleic anhydride, 1.2 mol of isopropanol and 0.6 mol of piperidine were added to a 500 mL three-necked flask under acidic conditions, heated under reflux at 100 °C for 5 h, and then cooled to room temperature to obtain a thermal alkali generator, which was sealed and retained.

[0037] Example 6

[0038] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (1), 0.6 mol of maleic anhydride, 1.2 mol of isopropanol and 0.6 mol of cyclopentaneimide were added to a 500 mL three-necked flask under acidic conditions, and the mixture was heated to reflux at 100 °C for 5 h, then cooled to room temperature to obtain a thermal alkali generator, which was sealed and retained.

[0039] Example 7

[0040] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), asynchronous biaxial stretching was performed at a speed of 10 mm / min, a stretching temperature of 50 °C, and a procedure of first longitudinal stretching 1.6 times and then transverse stretching 1.6 times.

[0041] Example 8

[0042] The polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the stretching was carried out at a speed of 50 mm / min, a stretching temperature of 50 °C, and a synchronous biaxial stretching procedure with a 1.6-fold longitudinal and transverse stretching.

[0043] Example 9

[0044] The polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the stretching was carried out at a speed of 30 mm / min, a stretching temperature of 50 °C, and a synchronous biaxial stretching procedure with a 1.4-fold longitudinal and transverse stretching.

[0045] Example 10

[0046] The polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the stretching was carried out at a speed of 30 mm / min, a stretching temperature of 50 °C, and a synchronous biaxial stretching procedure with a 1.8-fold longitudinal and transverse stretching.

[0047] Example 11

[0048] The polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the stretching was carried out at a speed of 30 mm / min, a stretching temperature of 80 °C, and a synchronous biaxial stretching procedure with a 1.6-fold longitudinal and transverse stretching.

[0049] Example 12

[0050] The polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the stretching was carried out at a speed of 30 mm / min, a stretching temperature of 30 °C, and a synchronous biaxial stretching procedure with a 1.6-fold longitudinal and transverse stretching.

[0051] Comparative Example 1

[0052] The chemically cyclized polyimide film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching step was not performed, and only heat treatment was carried out according to the temperature control procedure of 1 h at 200 °C, 1 h at 300 °C, and 1 h at 400 °C.

[0053] Comparative Example 2

[0054] (1) Under nitrogen protection, 0.2 mol of 4,4'-diaminodiphenyl ether and 474.1413 g of N,N-dimethylacetamide were added to a 500 mL three-necked flask. After the solid was completely dissolved, 0.2 mol of pyromellitic dianhydride was added under an ice bath, and the reaction was continued for 6 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0055] (2) 0.6 mol of pyridine and 0.6 mol of acetic anhydride were added dropwise into a three-necked flask at -10 °C while stirring. After 30 minutes, the mixture was centrifuged for degassing. A 800 µm liquid film was scraped off on a clean glass cup and then placed in an oven at 50 °C for reaction for 20 minutes to obtain a partially imidized polyamic acid-imide gel film. The film was then heat treated at 200 °C for 1 h, 300 °C for 1 h, and 400 °C for 1 h to obtain a chemically imidized polyimide film.

[0056] Comparative Example 3

[0057] (1) Under nitrogen protection, 0.2 mol of 4,4'-diaminodiphenyl ether and 474.1413 g of N,N-dimethylacetamide were added to a 500 mL three-necked flask. After the solid was dissolved, 0.2 mol of pyromellitic anhydride was added under ice bath and the reaction was continued for 6 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0058] (2) 0.6 mol of pyridine and 0.6 mol of acetic anhydride were added dropwise into a three-necked flask at -10 °C while stirring. After 30 min, the mixture was centrifuged for degassing. A 800 µm liquid film was scraped off on a clean glass cup and then placed in an oven at 50 °C for reaction for 20 min to obtain a partially imidized polyamic acid-imide gel film.

[0059] (3) The gel film is fixed in a biaxial stretching machine, and is subjected to synchronous biaxial stretching at a stretching speed of 30 mm / min, a stretching temperature of 50 °C, and a longitudinal and transverse synchronous stretching of 1.6 times. Subsequently, it is heat treated according to a temperature control program of 200 °C for 1 h, 300 °C for 1 h, and 400 °C for 1 h, thereby obtaining a polyimide biaxially stretched film.

[0060] Comparative Example 4

[0061] (1) Under nitrogen protection, 0.2 mol of 4,4'-diaminodiphenyl ether and 474.1413 g of N,N-dimethylacetamide were added to a 500 mL three-necked flask. After the solid was dissolved, 0.2 mol of pyromellitic anhydride was added under ice bath and the reaction was continued for 6 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0062] (2) After the polyamic acid solution was centrifuged for degassing, a 800 µm liquid film was scraped onto a clean glass plate and then reacted in a microwave oven at 3 kW for 5 min to obtain a polyamic acid gel film. The polyamic acid gel film was then heat treated at 200°C for 1 h, 300°C for 1 h, and 400°C for 1 h to obtain a thermal imidization polyimide film.

[0063] Table 1. Comparison of the mechanical properties of the films in each example and comparative example

[0064] As can be seen from the above table, Comparative Example 1 is a sample that has not been biaxially drawn after chemical cyclization. Comparing it with the samples of Examples 1 to 12 that have been chemically cyclized and biaxially drawn, it can be seen that after the chemically cyclized film is biaxially drawn and heat-treated at high temperature, the mechanical properties of the film are greatly improved. The tensile strength, elongation at break, and elastic modulus of Example 1 are 50%, 27%, and 43% higher than those of the film in Comparative Example 1, respectively. Comparative Example 2 is a non-drawn film prepared by the traditional chemical cyclization method, that is, by adding a non-latent catalyst pyridine and acetic anhydride and then heat-treating in an oven. Comparing it with Comparative Example 1, it can be seen that the film properties prepared by this study are comparable to those prepared by the traditional chemical cyclization method, which means that the thermally generated base agent developed in this study has a comparable catalytic effect to the traditional non-latent catalyst. Comparative Example 3 is a biaxially drawn film prepared by the traditional chemical cyclization method, and its heat treatment conditions for drawing are similar to those of Example 1. After comparison, it is found that the mechanical properties of the polyimide film obtained in Comparative Example 3 are basically the same as those of Example 1, which proves that the chemically cyclized biaxially drawn polyimide film prepared by using the thermally generated base agent developed in this study, on the one hand, avoids low-temperature processing (such as -10 °C), has low equipment requirements, and strong operability; on the other hand, the properties of the polyimide film prepared by it are comparable to those of the traditional non-latent catalytic cyclization biaxially drawn film, and it has practical application value. Comparative Example 4 is a polyimide film prepared by the thermal cyclization method. Since it is impossible to obtain a gel film with good supportability, subsequent drawing cannot be carried out; comparing its mechanical property data with those of Comparative Example 1, it can be seen that the tensile strength, elongation at break, and elastic modulus of the polyimide film after chemical imidization are 50%, 100%, and 40% higher than those of the film after thermal imidization, respectively, which means that the chemical cyclization method is more conducive to preparing high-performance polyimide films.

Claims

1. A method for preparing a polyimide biaxially stretched film catalyzed by a thermal base generator, comprising the following steps: (1) Maleic anhydride is subjected to an esterification reaction with a fatty alcohol under acidic catalytic conditions to generate a maleic acid diester, and then an organic base is added to generate a thermal base generator through a Michael addition reaction; (2) using aromatic anhydride and aromatic diamine as monomers, synthesizing a polyamic acid solution in a non-protonic polar organic solvent, then mixing the above-mentioned thermal base generating agent and acetic anhydride, scraping the film and heating it in a microwave oven to obtain a gel film; (3) The gel film is stretched in a biaxial stretching device and then heat-set to obtain a polyimide biaxially stretched film.

2. The method according to claim 1, characterized in that: The fatty alcohol in step (1) is at least one of fatty alcohols having 3 to 8 carbon atoms; the organic base is at least one of pyrrole, imidazole, piperidine, 2,6-dimethylpiperidine, and cyclopentylimine.

3. The method according to claim 1, characterized in that: The aromatic anhydride in step (2) is at least one of pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-diphenyl ketone tetracarboxylic acid dianhydride, 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, and 4,4'-biphenyl ether dianhydride; the aromatic diamine is at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 2-(4-aminophenyl)-5-aminobenzimidazole.

4. The method according to claim 1, characterized in that: The non-protonic polar organic solvent in step (2) is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, m-cresol, and p-chlorophenol.

5. The method according to claim 1, characterized in that: The solid content of the polyamic acid solution in step (2) is 5-30 wt %.

6. The method according to claim 1, characterized in that: The molar amount of acetic anhydride in step (2) is 1.0 to 10 times that of the aromatic diamine; the molar amount of the thermal base generating agent is 0.1 to 5 times that of the aromatic diamine.

7. The method according to claim 1, characterized in that: The heating process parameters in the microwave oven in step (2) are: microwave frequency of 0.1-5 kw, and heating time of 1-30 min.

8. The method according to claim 1, characterized in that: The stretching temperature in step (3) is 20-120° C.; the longitudinal stretching ratio of the gel film is 1.0-2.5, and the transverse stretching ratio is 1.0-2.5; and the stretching rate is 5-50 mm / min.

9. The method according to claim 1, characterized in that: The heat setting process parameters in step (3) are: heating rate of 0.5-10 °C / min, maximum temperature of 300-550 °C, and residence time of 10-60 min.

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