Method for producing polyimide film

Abstract

To provide a method for producing a polyimide film with a higher foreign matter removal rate than conventional methods, without increasing the adhesive strength of an adhesive roll, for removing foreign matters adhered to the surface of the polyimide film.SOLUTION: There is provided a method for producing a polyimide film, characterized by bringing an adhesive roll with an adhesive force of 40 to 200 hPa into contact with the polyimide film being conveyed by roll transportation at a wrap angle of 70° or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyimide film, and more particularly to a method for producing a polyimide film that efficiently removes foreign matter adhering to the surface of the polyimide film. [Background technology]

[0002] In the manufacturing process for obtaining a polyimide film from a gel film obtained by continuously extruding or coating a polyamic acid solution onto a film on a support, the film is typically stretched in the longitudinal direction, then the film edges are gripped and stretched in the width direction, followed by drying and heat treatment in succession (see, for example, Patent Documents 1 and 2). The pin clip method, in which the film edges are gripped, is commonly used. However, the pin clip method creates a hole in the film edge, which creates a problem in that film debris is generated at the pin hole and adheres to the film surface when the film is peeled from the pin.

[0003] The following methods are well known as methods for removing foreign matter such as scraps and dust adhering to the surface of a polyimide film. These methods include capturing foreign matter adhering to the film surface by pressing a nonwoven fabric or scraper against the polyimide film, removing foreign matter by spraying an air jet against the film, and blowing air at high speed to remove the dust from the polyimide film surface and then aspirating it (see, for example, Patent Documents 3 and 4). However, methods of removing foreign matter by pressing a nonwoven fabric or scraper against the polyimide film are prone to damaging the polyimide film. Furthermore, while blowing air against a polyimide film to remove foreign matter is effective for relatively large foreign matter, it is less effective for removing small dust particles or highly adhesive foreign matter.

[0004] On the other hand, the use of an adhesive roll has been proposed for removing small dust particles and strongly adhesive foreign matter from polyimide films (see Patent Document 5). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-163493 [Patent Document 2] Japanese Patent Application Publication No. 11-180606 [Patent Document 3] Japanese Patent Application Publication No. 2023-125670 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-36752 [Patent Document 5] Japanese Patent Application Laid-Open No. 2003-181945 Summary of the Invention [Problem to be solved by the invention]

[0006] The method of Patent Document 5 is preferable because it does not impact the polyimide film. Generally, using a highly adhesive adhesive roll can achieve high foreign matter removal capabilities. However, increasing the adhesive strength can lead to poor peeling between the adhesive roll and the polyimide film, and increasing the conveying tension can cause wrinkles in the polyimide film, worsening film conveyability. Therefore, it is difficult to achieve both foreign matter removal capabilities and film conveyability. When a thermoplastic polyimide with a low glass transition temperature and good processability is used for the surface layer, foreign matter adhering inside the oven becomes embedded in the polyimide film. Therefore, high adhesive strength is required for foreign matter removal, making it particularly difficult to achieve both the aforementioned foreign matter removal capabilities and film conveyability.

[0007] An object of the present invention is to provide a method for producing a polyimide film that has a higher rate of removing foreign matter adhering to the surface of the polyimide film than conventional methods without increasing the adhesive strength of an adhesive roll. [Means for solving the problem]

[0008] In order to solve the above problems, the present inventors have conducted extensive research, focusing on the wrap angle of the polyimide film that is brought into contact with an adhesive roll in the process of removing foreign matter adhering to the polyimide film.

[0009] The present invention provides a method for producing a polyimide film, characterized in that an adhesive roll having an adhesive strength of 40 to 200 hPa is brought into contact with a polyimide film being transported by rolls at a wrap angle of 70° or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a polyimide film that can remove foreign matter adhering to the surface of the polyimide film at a higher rate than conventional methods without increasing the adhesive strength of an adhesive roll.

[0011] According to the present invention, foreign matter can be removed with low adhesive strength, and therefore high foreign matter removal capability can be obtained while suppressing wrinkles in the polyimide film that occur during transport. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram for evaluating the foreign matter removal capability of an adhesive roll. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing a polyimide film of the present invention will be specifically described below.

[0014] <Polyimide film> The polyimide film referred to in the present invention is produced by imidizing a film using polyamic acid dissolved in an organic solvent, and the polyamic acid in the organic solvent solution may be partially imidized or may contain a small amount of an inorganic compound.

[0015] The polyamic acid, which is a precursor in the present invention, is preferably composed of an aromatic tetracarboxylic acid and an aromatic diamine, and is preferably composed of a repeating unit represented by the following chemical formula [I].

[0016] [ka]

[0017] In the above formula, R1 is a tetravalent organic group having at least one aromatic ring and having 25 or less carbon atoms, and R2 is a divalent organic group having at least one aromatic ring and having 25 or less carbon atoms.

[0018] In the present invention, the aromatic tetracarboxylic acids and aromatic diamines are polymerized in a ratio such that the mole numbers of each are approximately equal, but one may be polymerized in excess of the other within a range of 10 mol %, preferably 5 mol %.

[0019] Specific examples of the aromatic tetracarboxylic acids include pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3',3,4'-biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, pyridine-2,3,5,6-tetracarboxylic acid, or anhydrides thereof, or aromatic tetracarboxylic acids derived from ester compounds or halides of the acids thereof.

[0020] Specific examples of the aromatic diamines include paraphenylenediamine, metaphenylenediamine, benzidine, paraxylylenediamine, 4,4'-diaminodiphenylethanol, 3,4'-diaminophenylethanol, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,5-diaminodiphenylsulfone, 3,3'-dimethoxybenzidine, 1,4-bis(3-methyl-5-aminophenyl)benzene, and derivatives thereof.

[0021] Combinations of aromatic tetracarboxylic acid components and aromatic diamine components that are particularly suitable for the polyimide produced by the method of the present invention include pyromellitic dianhydride and 4,4'-diaminodiphenylethanol, and 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether. Copolymerization of these and / or copolymerization with paraphenylenediamine are also preferred. Multilayer structures can also be formed during film formation, provided that the present invention is not impaired. The intrinsic viscosity of the polyimide (measured in sulfuric acid at 25°C) is preferably 0.2 to 3.0, more preferably 0.8 to 2.0.

[0022] Specific examples of organic solvents used to form the polyamic acid solution in the present invention include organic polar amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. These organic solvents may be used alone or in combination with two or more, and may also be used in combination with a non-solvent such as benzene, toluene, or xylene. Furthermore, the residual solvent content can be measured by using an organic solvent that hydrolyzes to form an amine when used to form the polyamic acid solution in the present invention.

[0023] The organic solvent solution of amic acid used in the present invention preferably contains 5 to 40 wt %, more preferably 10 to 30 wt %, of solids, and its viscosity, as measured with a Brookfield viscometer, is 10 to 2000 Pa·s, preferably 100 to 1000 Pa·s, because this allows for stable liquid transfer. The polymerization reaction is carried out continuously in the organic solvent with stirring and / or mixing at a temperature range of 0 to 80°C for 10 minutes to 30 hours, although the polymerization reaction may be divided into sections or the temperature may be adjusted as necessary.

[0024] In this case, there is no particular restriction on the order of addition of the two reactants, but it is preferable to add the aromatic tetracarboxylic acid to the solution of the aromatic diamine.

[0025] Vacuum degassing during the polymerization reaction is an effective method for producing a high-quality organic solvent solution of polyimide acid. Furthermore, a small amount of an end-capping agent may be added to the aromatic diamine before the polymerization reaction to control the polymerization.

[0026] Specific examples of the ring-closing catalyst used in the present invention include aliphatic tertiary amines such as trimethylamine and triethylamine, and heterocyclic tertiary amines such as isoquinoline, pyridine, and beta-picoline. It is preferable to use at least one amine selected from heterocyclic tertiary amines.

[0027] Specific examples of the dehydrating agent used in the present invention include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and / or benzoic anhydride.

[0028] The content of the ring-closing catalyst relative to the polyimide acid is preferably in the range of 0.5 to 8.0 in terms of the ring-closing catalyst content (mol) / polyamic acid content (mol).

[0029] The content of the dehydrating agent relative to the polyamic acid is preferably in the range of dehydrating agent content (mol) / polyamic acid content (mol) of 0.1 to 4.0. In this case, a gelation retarder such as acetylacetone may be used in combination.

[0030] <Method of manufacturing polyimide film> The polyimide film of the present invention is preferably produced by continuously extruding or applying a polyamic acid solution in the form of a film onto a rotating support, peeling the resulting gel film from the support, stretching, drying, and heat treating it.

[0031] Typical methods for producing polyimide films from polyamic acid solutions include a thermal ring-closure method in which a polyamic acid solution that does not contain a ring-closure catalyst and a dehydrating agent is cast onto a support from a slitted die to form a film, which is then heated and dried on the support to form a self-supporting gel film, which is then peeled off from the support and further subjected to a dry heat treatment at high temperature to form an imidized film; and a chemical ring-closure method in which a polyamic acid solution that contains a ring-closure catalyst and a dehydrating agent is cast onto a support from a slitted die to form a film, which is then peeled off from the support, heated and dried / imidized, and then subjected to a heat treatment.

[0032] The present invention may employ any of the above ring-closure methods, but the chemical ring-closure method is preferable because it can produce a self-sustaining gel film in a short time, although it requires equipment for adding a ring-closure catalyst and a dehydrating agent to an organic solvent solution of polyamic acid.

[0033] In the present invention, the adhesive roll is placed in a step subsequent to the drying step after the support is peeled off, preferably immediately after the dryer or immediately before the winding of the final product, but is preferably placed immediately after the dryer in order to prevent the transfer of unevenness caused by winding the film with foreign matter still attached.

[0034] The glass transition temperature of the polyimide film obtained in the present invention is preferably 300° C. or lower, more preferably 270° C. or lower, and even more preferably 250° C. or lower, in order to improve processability.

[0035] The adhesive roll in the present invention is a rotatable elastic roll having an adhesive roll surface, and when this roll surface is brought into contact with a polyimide film, the adhesive force of the elastic roll surface causes dust adhering to the continuously running polyimide film to adhere to the roll surface and be removed, and specifically, the adhesive roll preferably has a hardness of 20° to 60°, more preferably 25° to 50°.

[0036] The polyimide film of the present invention has a low glass transition temperature of the surface layer, so when foreign matter adheres to the film inside the oven, the foreign matter adheres to the polyimide film surface so as to be buried in the film. Therefore, an adhesive roll with higher adhesive strength than that of ordinary polyimide films is required, and the adhesive strength must be 40 hPa to 200 hPa. If the adhesive strength is too high, peeling marks and wrinkles will occur when the polyimide film is peeled from the adhesive roll.

[0037] When the adhesive roll and polyimide film are brought into contact, the polyimide film must be conveyed at a wrap angle of 70° or more with the support. A large wrap angle causes foreign matter on the surface of the polyimide film to float up, resulting in a higher foreign matter removal capability than when the wrap angle is small, and foreign matter can be removed with lower adhesive force.

[0038] In this invention, adhesive strength refers to the adhesive strength between rubber and polyimide film or foreign matter, and is expressed as the force required to peel the rubber from the polyimide film or foreign matter. Therefore, if adhesive strength is high, a strong force is required to peel the polyimide film or foreign matter from the rubber. Generally, rubber with low hardness has high adhesive strength. Adhesion strength was measured in accordance with JIS-K6301, "Vulcanized Rubber Physical Experimental Method," for "a sample consisting of two parallel metal plates bonded with rubber," and the adhesive strength between the metal plate and rubber was calculated using the following formula: Adhesive strength = maximum peel load / adhesive area.

[0039] The adhesive roll material is not particularly specified, but examples include natural rubber, chloroprene, nitrile rubber, butyl rubber, ethylene-propylene rubber, hypalon, silicone rubber, fluororubber, and urethane rubber. The roll shape is not particularly restricted, but flat, radial crown, reverse crown, and tapered crown are used. A flat roll is preferred. [Example]

[0040] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods and evaluation criteria for each property described above and in the following examples are as follows:

[0041] (1) Foreign matter removal ability A film test piece with foreign matter adhering thereto was prepared, and an adhesive roll was pressed against the test piece. The foreign matter removal rate was calculated from the number of foreign matters that could be removed, and the foreign matter removal ability was evaluated according to the following criteria. The state in which the test piece was attached to a flat surface was taken as the wrap angle of 0°, and the wrap angle was adjusted by attaching the test piece to the support roll shown in Figure 1. ◎: Foreign matter removal rate 100% 〇: Foreign matter removal rate is 70% or more but less than 100% △: Foreign matter removal rate is 30% or more but less than 70% ×: Foreign matter removal rate less than 30%.

[0042] (2) Film transport status An adhesive roll was brought into contact with the film during roll transport, and the state of the film transport was judged based on whether or not wrinkles occurred. ◎: No wrinkles were generated in the film when peeled off. Good: Slight wrinkles occurred on the film when peeled off. ×: Wrinkles occurred on the film when peeled off.

[0043] Example 1 As shown in Figure 1, a test piece was attached to a support roll at a wrap angle of 70°, and an adhesive roll with an adhesive strength of 120 hPa and a hardness of 35° was pressed against the test piece, resulting in a foreign matter removal rate of 85%. No wrinkles were observed in the film during film transport. The test piece used was a film with a polyimide surface with a glass transition temperature of 230°C.

[0044] Example 2 As shown in Figure 1, a test piece was attached to a support roll at a wrap angle of 70°, and an adhesive roll with an adhesive strength of 90 hPa and a hardness of 25° was pressed against the test piece, resulting in a 100% foreign matter removal rate. Regarding the film transport condition, slight wrinkles occurred in the film. The test piece used was a film with a polyimide surface with a glass transition temperature of 230°C.

[0045] Example 3 As shown in Figure 1, a test piece was attached to a support roll at a wrap angle of 70°, and an adhesive roll with an adhesive strength of 90 hPa and a hardness of 25° was pressed against the test piece, resulting in a 100% foreign matter removal rate. Regarding the film transport condition, slight wrinkles occurred in the film. The test piece used was a film with a polyimide surface with a glass transition temperature of 350°C.

[0046] Comparative Example 1 As shown in Figure 1, a test specimen was attached to a support roll at a wrap angle of 70°, and an adhesive roll with an adhesive strength of 20 hPa and a hardness of 35° was pressed against the test specimen, resulting in a foreign matter removal rate of 0%. No wrinkles were observed in the film during film transport. The test specimen used was a film with a polyimide surface with a glass transition temperature of 230°C.

[0047] Comparative Example 2 A test specimen was attached to a flat surface so that the embrace angle was 0°, and an adhesive roll with an adhesive strength of 90 hPa and a hardness of 35° was pressed against the specimen, resulting in a foreign matter removal rate of 0%. Regarding the film transport condition, slight wrinkles occurred in the film. The test specimen used was a film with a polyimide surface with a glass transition temperature of 230°C.

[0048] Comparative Example 3 A test specimen was attached to a flat surface so that the embrace angle was 0°, and an adhesive roll with an adhesive strength of 400 hPa and a hardness of 40° was pressed against the specimen to evaluate the degree of foreign matter removal and peeling. The foreign matter removal rate was 50%, and wrinkles in the film were confirmed during film transport. The test specimen used was a film with a polyimide surface layer with a glass transition temperature of 230°C.

[0049] Comparative Example 4 As shown in Figure 1, a test piece was attached to a support roll at a wrap angle of 70°, and an adhesive roll with an adhesive strength of 220 hPa and a hardness of 8° was pressed against the test piece, resulting in a foreign matter removal rate of 50%. No wrinkles were observed in the film during film transport. The test piece used was a film with a polyimide surface with a glass transition temperature of 230°C. The above results are summarized in Table 1.

[0050] [Table 1] [Explanation of symbols]

[0051] 1: adhesive roll 2: Test piece 3: Support roll 4: Embracing angle

Claims

1. A method for producing a polyimide film, characterized in that an adhesive roll having an adhesive strength of 40 to 200 hPa is brought into contact with a polyimide film being transported by a roll at a wrap angle of 70° or more.

2. 2. The method for producing a polyimide film according to claim 1, wherein the adhesive roll has a hardness of 20 to 60 degrees.

Images