A method for preparing polyimide biaxially stretched film by catalysis of a thermally induced base generator

Abstract

The present invention relates to a method for preparing a polyimide biaxially stretched film using a thermally induced base generator catalyzed by a thermally induced base generator, comprising synthesizing a thermally induced base generator; synthesizing a polyamic acid resin using an aromatic diamine and an aromatic dianhydride; adding the thermally induced base generator and acetic anhydride for chemical cyclization to obtain a gel film; and then biaxially stretching the film to obtain the polyimide biaxially stretched film. The thermally induced base generator used in the present invention does not produce a catalytic effect at room temperature, and can improve the storage stability of the casting solution and expand its processing window. The film after biaxial stretching and heat setting has excellent mechanical properties, heat resistance, and dimensional stability. The polyimide biaxially stretched film prepared by the present invention can be widely used in industries such as electronics, electrical appliances, automobiles, machinery, aviation, aerospace, and chemicals.

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 catalyzing a thermal base generating agent. Background Art

[0002] Commercially available electronic-grade polyimide films, such as DuPont's Kapton, Ube Industries' Upilex, and Kaneka Chemical's Apical series, exhibit excellent mechanical properties, heat resistance, dimensional stability, and dielectric properties, and have been widely used in applications such as high-temperature insulation and flexible electronics. Chemical cyclization followed by biaxial stretching is currently the mainstream industrial process for preparing electronic-grade polyimide films. Compared to thermal cyclization, it offers advantages such as high production rates and high stretch ratios. U.S. Patent No. 5,460,890A describes a process for preparing gel films using chemical cyclization followed by biaxial stretching, significantly improving the film's mechanical properties and dimensional stability. However, the high reactivity of the chemical imide reaction and the relatively low temperatures required (0–100°C) in the chemical process cause the polyamic acid solution to rapidly transform into a gel state at room temperature (30 s–30 min), resulting in a loss of fluidity and thus complicating processing. Lowering the temperature to reduce the chemical cyclization reaction rate can effectively broaden the processing window; however, the increased viscosity of the polymer solution caused by low temperatures hinders degassing and tape casting. Moreover, the requirements for production equipment during low-temperature processing are complex, which increases production costs.

[0003] In epoxy resin research, the emergence of latent curing agents renders the blended epoxy resin components inert at room temperature. When certain triggering conditions (such as temperature, humidity, and light) are met, the epoxy resin system undergoes a rapid curing and crosslinking reaction, addressing issues such as epoxy resin's short shelf life, narrow processing window, and complex manufacturing processes. Patent CN118184960A describes a latent curing agent containing an amine compound and a dicyandiamide composition containing an epoxy group. This agent ensures the storage stability of epoxy resins at room temperature while offering advantages such as a low curing temperature, excellent solubility, and low agglomeration. Similarly, in polyimide research, there are also reports on the introduction of latent catalysts. To achieve low-temperature curing of polyimide resins and avoid degradation of the resin by alkaline catalysts before curing, latent curing catalysts are often added to the precursor solution to achieve excellent properties after low-temperature curing and maintain long-term 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 processability, high chemical resistance, high elasticity, high elongation properties and high adhesion to metals (especially copper).

[0004] Latent catalysts are generally organic base derivatives, such as 2,6-dimethylpiperidine and imidazole. These compounds readily decompose thermally, releasing carbon cations to produce substances such as olefins and organic bases. Their decomposition temperature is influenced by steric hindrance and electronic effects, making it adjustable within a range of 40–200°C. Therefore, by designing the structure of latent catalysts to regulate their decomposition temperature and rate, and thus enabling precise control of the chemical cyclization reaction, this approach is expected to address the challenges of traditional chemical cyclization methods for preparing biaxially stretched polyimide films, such as high equipment requirements, a narrow processing window, and difficulty in controlling the gel film. 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, widen 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 using a thermal base generator, comprising the following steps:

[0007] (1) Maleic anhydride is esterified with fatty alcohol under acidic catalysis to form maleic acid diester, and then an organic base is added to generate a thermal base generator through Michael addition reaction;

[0008] (2) A polyamic acid solution is synthesized in a non-protonic polar organic solvent using aromatic anhydride and aromatic diamine as monomers, and then the above-mentioned thermal base generator and acetic anhydride are mixed in. After scraping, the film is heated in a microwave oven to obtain a gel film;

[0009] (3) The gel film is stretched in a biaxial stretching device and then heat-set to obtain a polyimide biaxially stretched film.

[0010] 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:

[0011] .

[0012] 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:

[0013] .

[0014] Preferably, the reaction solvent in step (1) is a fatty alcohol, and the reaction is carried out under reflux for 6 to 20 hours.

[0015] The reaction equation of the thermal base generating agent is as follows:

[0016] .

[0017] 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.

[0018] Preferably, the molar ratio of the aromatic anhydride to the aromatic diamine in step (2) is 1:(0.97-1.03).

[0019] 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.

[0020] Preferably, the solid content of the polyamic acid solution in step (2) is 5-30 wt%, preferably 12-20 wt%.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Preferably, the heat setting process parameters in step (3) are: a heating rate of 0.5-10 °C / min, preferably 1-3 °C / min, a maximum temperature of 300-550 °C, and a residence time of 10-60 min.

[0025] Beneficial effects

[0026] The thermally induced 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 biaxial stretching and heat setting has excellent mechanical properties, heat resistance and dimensional stability; the polyimide biaxially stretched film prepared by the present invention can be widely used in industries such as electronics, electrical appliances, automobiles, machinery, aviation, aerospace and chemicals. DETAILED DESCRIPTION

[0027] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, 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 equally within the scope limited by the appended claims of the application.

[0028] Example 1

[0029] (1) Under acidic conditions, 0.6 mol of maleic anhydride, 1.2 mol of isopropanol, and 0.6 mol of imidazole were added to a 500 mL three-necked flask. The mixture was heated under reflux at 100 °C for 5 h, then cooled to room temperature to obtain a thermal base generator. The flask was sealed and retained.

[0030] (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%.

[0031] (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. An 800 µm thick 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 partially imidized polyamic acid-imide gel film.

[0032] (4) The gel film was 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 program of synchronous longitudinal and transverse stretching of 1.6 times. Subsequently, it was 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 to obtain a polyimide biaxially stretched film.

[0033] Example 2

[0034] A polyimide biaxially oriented 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, and then cooled to room temperature to obtain a thermal base generator, which was sealed and retained.

[0035] Example 3

[0036] A polyimide biaxially oriented 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 base generator, which was sealed and retained.

[0037] Example 4

[0038] A polyimide biaxially oriented 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, and the mixture was heated under reflux at 100 °C for 5 h, then cooled to room temperature to obtain a thermal base generator, which was sealed and retained.

[0039] Example 5

[0040] A polyimide biaxially oriented 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 base generator, which was sealed and retained.

[0041] Example 6

[0042] A polyimide biaxially oriented 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 cyclopentaneimine 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 base generator, which was sealed and retained.

[0043] Example 7

[0044] 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.

[0045] Example 8

[0046] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching was performed at a speed of 50 mm / min, a stretching temperature of 50 °C, and a procedure of synchronous stretching of 1.6 times in the longitudinal and transverse directions.

[0047] Example 9

[0048] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching was performed at a speed of 30 mm / min, a stretching temperature of 50 °C, and a procedure of synchronous stretching of 1.4 times in the longitudinal and transverse directions.

[0049] Example 10

[0050] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching was performed at a speed of 30 mm / min, a stretching temperature of 50 °C, and a procedure of synchronous stretching of 1.8 times in the longitudinal and transverse directions.

[0051] Example 11

[0052] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching was performed at a speed of 30 mm / min, a stretching temperature of 80 °C, and a procedure of synchronous stretching of 1.6 times in the longitudinal and transverse directions.

[0053] Example 12

[0054] A polyimide biaxially stretched film was prepared according to the method of Example 1, except that in step (4), the biaxial stretching was performed at a speed of 30 mm / min, a stretching temperature of 30 °C, and a procedure of synchronous stretching of 1.6 times in the longitudinal and transverse directions.

[0055] Comparative Example 1

[0056] A chemical cyclization polyimide film was prepared according to the method of Example 1, except that the biaxial stretching step was not performed in step (4), and the heat treatment was performed only according to the temperature control program of 200 °C for 1 h, 300 °C for 1 h, and 400 °C for 1 h.

[0057] Comparative Example 2

[0058] (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%.

[0059] (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. An 800 µm liquid film was scraped on a clean glass cup and then placed in an oven at 50 °C for 20 minutes to obtain a partially imidized polyamic acid-imide gel film. The film was then heat treated at 200 °C for 1 hour, 300 °C for 1 hour, and 400 °C for 1 hour to obtain a chemically imidized polyimide film.

[0060] Comparative Example 3

[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) 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. An 800 µm thick liquid film was scraped onto a clean glass cup and then placed in an oven at 50 °C for 20 min to obtain a partially imidized polyamic acid-imide gel film.

[0063] (3) The gel film was 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 synchronous stretching ratio of 1.6 in the longitudinal and transverse directions. Subsequently, the film was 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.

[0064] Comparative Example 4

[0065] (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%.

[0066] (2) After the polyamic acid solution was centrifuged and degassed, an 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 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.

[0067] Table 1. Comparison of mechanical properties of films in various examples and comparative examples

[0068]

[0069] As can be seen from the above table, Comparative Example 1 is a sample that was not biaxially stretched after chemical cyclization. Compared with the samples of Examples 1 to 12 that were chemically cyclized and biaxially stretched, it can be seen that the mechanical properties of the film after chemical cyclization were greatly improved after biaxial stretching and high-temperature heat treatment. The tensile strength, elongation at break, and elastic modulus of Example 1 were increased by 50%, 27%, and 43%, respectively, compared to the film of Comparative Example 1. Comparative Example 2 is a non-stretched film using a traditional chemical cyclization method, that is, by adding non-latent catalysts pyridine and acetic anhydride, and then heating it in an oven. Comparison with Comparative Example 1 shows that the performance of the film prepared by the introduction in this study is comparable to that prepared by the traditional chemical cyclization method, meaning that the thermal base generator developed by this study has a comparable catalytic effect to the traditional non-latent catalyst. Comparative Example 3 is a biaxially drawn film produced using a conventional chemical cyclization method. The heat treatment conditions for drawing are similar to those in Example 1. Comparison reveals that the mechanical properties of the polyimide films obtained in Comparative Example 3 and Example 1 are essentially equivalent. This demonstrates the practical application of the chemically cyclized biaxially drawn polyimide film developed in this study using a thermally induced base generator. This method avoids low-temperature processing (e.g., -10°C), requires minimal equipment, and offers high operability. Furthermore, the performance of the polyimide film produced is comparable to that of conventional non-latent catalytically cyclized biaxially drawn films, demonstrating its practical application. Comparative Example 4 is a polyimide film produced using a thermal cyclization method. However, due to the inability to obtain a well-supported gel film, subsequent drawing is impossible. A comparison of the mechanical properties of this polyimide film with those of Comparative Example 1 reveals that the tensile strength, elongation at break, and elastic modulus of the chemically imidized polyimide film are 50%, 100%, and 40%, respectively, higher than those of the thermally imidized film. This demonstrates that the chemical cyclization method is more advantageous for producing 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 catalysis 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; wherein, The organic base is at least one of pyrrole, imidazole, piperidine, 2,6-dimethylpiperidine, and cyclopentylimine; (2) using aromatic anhydride and aromatic diamine as monomers, synthesizing a polyamic acid solution in an aprotic polar organic solvent, then mixing the above-mentioned thermal base generator 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, wherein: The fatty alcohol in step (1) is at least one of fatty alcohols having 3 to 8 carbon atoms.

3. The method according to claim 1, wherein: 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.

4. The method according to claim 1, wherein: 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.

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

6. The method according to claim 1, wherein: 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, wherein: The heating process parameters in the microwave oven in step (2) are: microwave frequency of 0.1 to 5 kW, and heating time of 1 to 30 min.

8. The method according to claim 1, wherein: 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, wherein: 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 10-60min.

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