JP2011122079A - Method of making thick film by applying solution of polyimide soluble into polar organic solvent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making a thick film by using a heat-resistant polyimide copolymer being soluble in an organic polar solvent and having a glass transition temperature of 300°C or higher. <P>SOLUTION: A method for making a thick film is provided which comprises coating a substrate with a polar organic solvent-soluble heat-resistant polyimide synthesized by (1) reacting 2 mol eq. of PMDA with 1 mol eq. of HOABSO<SB>2</SB>to form a low-molecular weight imide compound composed of PMDA and HOABSO<SB>2</SB>bonded to both amino groups thereof, (2) reacting 2 mol eq. of BCD with 4 mol eq. of mDADE to form a low-molecular weight imide compound and mDADE bonded to both ends thereof, and (3) reacting 2 mol eq. of BPDA with 1 mol eq. of mTPE and subjecting them to polycondensation, hot-drying the wet film to evaporate the solvent therefrom to a tack-free state, further coating the substrate a plurality times, and drying the resultant film to remove the solvent therefrom. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  Conventional polyimides include DuPont's “KAPTON” produced from pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (DADE), and biphenyltetracarboxylic dianhydride (BPDA) and paraphenylene. “Upilex” from Ube Industries, Ltd. manufactured from diamine (PPD) is known. These polyimides do not dissolve in the solvent, and it is necessary to perform dehydration imidization and solvent removal in parallel after casting on the support at the precursor polyamic acid stage. At this time, since water is detached, it is difficult to foam during film formation. In particular, it is not easy to remove this water and solvent to form a thick film.

The super heat resistant resins “KAPTON” and “Upilex” have a glass transition temperature (Tg) of 420 ° C. and a thermal decomposition start temperature (Td) of 500 ° C. or more. As a polymer with excellent electrical insulation, mechanical strength, and chemical resistance, it is widely used as aerospace, vehicle materials, electronic / electrical parts, semiconductor materials, etc.
(D. Wilson, HD Steinberger, RM Morgenrother; Blackie, “polyimides” New York (1990)).

A technique for manufacturing a thick film polyimide sheet by applying a polyamic acid varnish before imidization to a support is known. In JP-A-2005-139337, a polyamic acid varnish before imidization is applied to a support, and the amount of residual solvent in the varnish is 5 or less in terms of the number of solvent molecules per polyamic acid repeating unit. Thereafter, a method for producing a thick film polyimide sheet having a thickness of 80 to 1000 μm, which is dried and imidized, is described. According to the method, it is desirable to repeatedly apply and dry the polyamic acid varnish twice or more. However, the disadvantages of performing dehydration imidization and solvent removal in parallel after casting on a support at the stage of polyamic acid, which is a polyimide precursor, are as described above.
One of the present inventors has newly developed a method for producing polyimide that overcomes the disadvantages of insoluble organic solvents (International Publication 2008/120398).

International Publication 2008/120398 JP 2005-139337 A

  By using a polyimide copolymer that is soluble in an organic polar solvent, that is, an organic solvent solution of polyimide that has been imidized, water does not desorb during high-temperature treatment, so only solvent removal is possible. The problem was how to form a film with care. That is, a problem is how to form a film more easily than in the past.

According to the present invention, a polyimide that is soluble in an organic polar solvent and having a glass transition temperature of 300 ° C. or more is coated on a support, the solvent is heated and dried to a semi-dry state, and a plurality of times After the coating, a method of drying to remove the solvent and forming a thick film is provided. The semi-dry state as referred to in the present invention refers to a state in which the solvent concentration remaining in the polyimide solution after coating is 10% by weight to 50% by weight.

As polyimide used here, pyromellitic dianhydride (PMDA), bis (3-amino-4-hydroxyphenyl) sulfone (HOAB.SO ₂ ), bicyclo (2,2,2) oct-7 -Ene-2,3,5,6-tetracarboxylic dianhydride (BCD, commonly referred to as bicyclooctene tetracarboxylic dianhydride), 3,4'-diaminodiphenyl ether (mDADE) or 4,4'- It consists of diaminodiphenyl ether (4,4′-DADE), biphenyltetracarboxylic dianhydride (BPDA) or benzophenonetetracarboxylic dianhydride (BTDA), 1,3-bis (4-aminophenoxy) benzene (mTPE). A thing was used.
HOAB · SO ₂ has the following chemical formula.

ＢＣＤは、下記の化学式を有する。

BCD has the following chemical formula:

ｍＴＰＥは、下記の化学式を有する。

mTPE has the following chemical formula:

本発明で使用するポリイミドは、下記の製造方法により製造され、下記に示した繰り返し単位を有する。

The polyimide used by this invention is manufactured with the following manufacturing method, and has the repeating unit shown below.

Method for producing Solpit-A (trademark) which is a polyimide copolymer soluble in a polar organic solvent used in the present invention
(1) Use PMDA, HOAB · SO ₂ , BCD, mDADE, BPDA and mTPE (a) 2 molar equivalents of pyromellitic dianhydride (PMDA) and bis (3-amino-4-hydroxyphenyl) sulfone ( HOAB · SO ₂ ) is reacted with 1 molar equivalent in an organic polar solvent at 160 to 200 ° C. in the presence of a catalyst to produce a low molecular weight imide compound in which PMDA is bonded to both amino groups of HOAB · SO _2. ,the first stage,
(B) The low molecular weight imide compound produced in the first step is reacted with 2 molar equivalents of bicyclooctenetetracarboxylic dianhydride (BCD) and 4 molar equivalents of 3,4′-diaminodiphenyl ether (mDADE). A low molecular weight imide compound in which mDADE is bonded to the terminal is formed in the second stage, and (c) 2 molar equivalents of biphenyltetracarboxylic dianhydride (BPDA) and 1 in the low molecular weight imide compound formed in the second stage. , 3-bis (4-aminophenoxy) benzene (mTPE) 1 molar equivalent is added and reacted, followed by a third step of synthesizing a polyimide copolymer soluble in an organic polar solvent by polycondensation.
Formula (I) below:
_{[(MDADE-BCD-mDADE)} - (PMDA-HOAB · SO 2 -PMDA) - (mDADE-BCD-mDADE) - (BPDA-mTPE-BPDA)] n
(Here, the bond between the compounds is an imide bond.)
The heat-resistant polyimide soluble in the organic solvent which has the repeating unit represented by this was manufactured.

(2) Use PMDA, HOAB · SO ₂ , BCD, 4,4′-DADE, BPDA and mTPE (a) 2 molar equivalents of pyromellitic dianhydride (PMDA) and bis (3-amino-4-hydroxyphene) a sulfonyl) sulfone (HOAB · _SO 2) 1 mole equivalent of an organic polar solvent and reacted at 160 to 200 ° C. in the presence of a catalyst, low molecular weight PMDA is attached to both an amino group HOAB · SO ₂ Producing an imide compound, the first stage,
(B) 2 mol equivalent of bicyclooctene tetracarboxylic dianhydride (BCD) and 4 mol equivalent of 4,4′-diaminodiphenyl ether (4,4′-DADE) to the low molecular weight imide compound produced in the first step To a low molecular weight imide compound in which 4,4′-DADE is bonded to both ends, and (c) the low molecular weight imide compound produced in the second step is converted to a biphenyltetracarboxylic acid diester. 2 mol equivalent of anhydride (BPDA) and 1 mol equivalent of 1,3-bis (4-aminophenoxy) benzene (mTPE) were added and reacted, and a polyimide copolymer soluble in an organic polar solvent was obtained by polycondensation. It consists of a third stage of synthesis.
Formula (II) below:
[(4,4′-DADE-BCD-4,4′-DADE)-(PMDA-HOAB · SO ₂ -PMDA)-(4,4′-DADE-BCD-4,4′-DADE)-(BPDA -MTPE-BPDA)] _n
(Here, the bond between the compounds is an imide bond.)
A heat-resistant polyimide soluble in a polar organic solvent having a repeating unit represented by

(3) Use PMDA, HOAB · SO ₂ , BCD, mDADE, BTDA and mTPE (i) 2 molar equivalents of pyromellitic dianhydride (PMDA) and bis (3-amino-4-hydroxyphenyl) sulfone ( HOAB · SO ₂ ) is reacted with 1 molar equivalent in an organic polar solvent at 160 to 200 ° C. in the presence of a catalyst to produce a low molecular weight imide compound in which PMDA is bonded to both amino groups of HOAB · SO _2. ,the first stage,
(B) The low molecular weight imide compound produced in the first step is reacted with 2 molar equivalents of bicyclooctenetetracarboxylic dianhydride (BCD) and 4 molar equivalents of 3,4′-diaminodiphenyl ether (mDADE). The low molecular weight imide compound having mdADE bonded to the terminal is converted into the second stage, and (c) the low molecular weight imide compound formed in the second stage is added with 2 molar equivalents of benzophenone tetracarboxylic dianhydride (BTDA) and 1 , 3-bis (4-aminophenoxy) benzene (mTPE) 1 molar equivalent is added and reacted, followed by polycondensation to synthesize a polyimide copolymer soluble in a polar organic solvent.
Formula (III) below:
_{[(MDADE-BCD-mDADE)} - (PMDA-HOAB · SO 2 -PMDA) - (mDADE-BCD-mDADE) - (BTDA-mTPE-BTDA)] n
(Here, the bond between the compounds is an imide bond.)
The heat-resistant polyimide soluble in the organic solvent which has the repeating unit represented by this was manufactured.

(4) Use PMDA, HOAB · SO ₂ , BCD, 4,4′-DADE, BTDA and mTPE (a) 2 molar equivalents of pyromellitic dianhydride (PMDA) and bis (3-amino-4-hydroxyphene) a sulfonyl) sulfone (HOAB · _SO 2) 1 mole equivalent of an organic polar solvent and reacted at 160 to 200 ° C. in the presence of a catalyst, low molecular weight PMDA is attached to both an amino group HOAB · SO ₂ Producing an imide compound, the first stage,
(B) 2 mol equivalent of bicyclooctene tetracarboxylic dianhydride (BCD) and 4 mol equivalent of 4,4′-diaminodiphenyl ether (4,4′-DADE) to the low molecular weight imide compound produced in the first step To a low molecular weight imide compound in which 4,4′-DADE is bonded to both ends, and (c) the low molecular weight imide compound produced in the second step is mixed with benzophenone tetracarboxylic acid diester. 2 mol equivalent of anhydride (BTDA) and 1 mol equivalent of 1,3-bis (4-aminophenoxy) benzene (mTPE) were added and reacted, and a polyimide copolymer soluble in an organic polar solvent was obtained by polycondensation. It consists of a third stage of synthesis.
Formula (IV) below:
[(4,4′-DADE-BCD-4,4′-DADE)-(PMDA-HOAB · SO ₂ -PMDA)-(4,4′-DADE-BCD-4,4′-DADE)-(BTDA -MTPE-BTDA)] _n
(Here, the bond between the compounds is an imide bond.)

The heat-resistant polyimide soluble in the organic solvent which has the repeating unit represented by this was manufactured. In the present invention, 4,4′-DADE can be used instead of mDADE. Further, BTDA can be used instead of BPDA.

The polyimide used in the present invention has a functionality containing bicyclooctene tetracarboxylic dianhydride (referred to as BCD) together with PMDA, DADE and BPDA, and is soluble in a polar organic solvent. By adding BCD, the polyimide was further imparted with a feature that was superior in solubility in an organic solvent as compared with PMDA and exhibited high adhesion characteristics. The polyimide used in the present invention coexists with bis (3-amino-4-hydroxyphenyl) sulfone (referred to as HOAB · SO ₂ ) and BCD as an aromatic diamine that binds to PMDA and exhibits functionality and becomes soluble in a solvent. Thus, 1,3-bis (4-aminophenoxy) benzene (mTPE), which strengthens the adhesiveness, is employed.

The polyimide used in the present invention is produced by a three-step reaction using PMDA, HOAB · SO ₂ , BCD, mDADE or 4,4′-DADE, BPDA or BTDA, mTPE. That is, in the first stage, an oligomer having both ends of PMDA is produced, in the second stage, an oligomer having both ends of mdADE or 4,4′-DADE is produced, and in the third stage, polycondensation is carried out. Manufactures polyimide copolymers soluble in polar organic solvents.

The polyimide used in the present invention can be used as a polyimide having functions such as electrodeposition, photosensitivity, and adhesiveness.

As the polar organic solvent for dissolving the polyimide, for example, N-methylpyrrolidone, N, N-dimethylacetamide, sulfolane, N, N-dimethylformamide and the like can be preferably used. Is not limited.

  By using a polyimide copolymer that is soluble in an organic polar solvent, a solution in which imidization has been completed is used, so water is not desorbed during high-temperature treatment, so care must be taken only to remove the solvent. It can be formed into a film. That is, film formation can be performed more easily than before.

The molecular weight of the polyimide can be 20,000 to 200,000, preferably 50,000 to 150,000.
Although there is no restriction | limiting in the density | concentration of the polyimide component in an organic solvent, Usually, what is applyable should just be used, for example, a thing of about 20 to 5% can be used. A concentration of less than 5% can be used, but if the concentration is low, the number of coatings increases. If the concentration exceeds 20%, the fluidity of the polymer is poor and coating becomes difficult.

  The coating is uniformly cast on a support such as a glass plate, stainless steel plate, or copper plate, and the solvent is evaporated. The temperature at that time is preferably 50 to 200 ° C., more preferably 80 to 150 ° C. Below these temperatures, it takes a long time to evaporate. At higher temperatures, the surface is not uniform during evaporation, causing problems such as foaming.

The drying time is a trade-off with temperature, and takes a short time when it is high and a long time when it is low. Usually, it is about 1 hour at 100 ℃. Here, it is important to sufficiently adjust the degree of drying, and the residual amount of the solvent is 10 to 50% by weight, more preferably 15 to 40% by weight. If it is too dry when applying in multiple stages, it will peel off without being compatible with the original film during the next application. Also, if the drying is insufficient and the solvent is too much, it becomes sticky and difficult to process.
After removing part of the solvent, peel off the support while maintaining the film shape, attach the film to a metal frame, etc., and dry it at a high temperature to completely remove the solvent and remove the film with the desired film thickness. Obtainable. For example, 250 ° C, 1 hour, 350 ° C, 3 hours, etc. can be applied as usual.

According to the present invention, the film thickness of the final product is not particularly limited, but it is difficult to completely remove the solvent inside the film that is too thick. Usually, a film having a thickness of 50 to 300 μm is preferable. Actually, it is possible up to about 300 μm, preferably up to about 200 μm.
When a conventional amic acid solution is used, it is necessary to perform desorption of water and removal of the solvent in parallel, which causes many problems in maintaining flatness of the flat surface and generating holes by foaming. In the present invention, since a solution in which imidization is completed is used, water does not desorb during high-temperature treatment, and film formation can be performed by paying attention only to removal of the solvent.

  The plurality of times of application may be the same in the direction of application of the upper and lower films, but may be different.

Examples are shown below, but the present invention is not limited thereto.
[Production Example 1]
Product name: (2 PMDA + HOAB·SO ₂ ) (2BCD + 4mDADE) (2BPDA + mTPE) Product Name: Solpit A Manufacture of a 500 ml glass three-necked glass flask equipped with a stainless steel vertical stirrer A serpentine cooler with a separation trap was attached. While passing nitrogen gas, the flask was placed in a silicon bath and heated and stirred. A small amount of toluene added to the reaction solution is refluxed, and the generated water is retained in the moisture separation trap.

(1) In a glass 500 ml three-necked flask, 4.36 g (20 mmol) of pyromellitic dianhydride (hereinafter referred to as PMDA), bis (3-amino-4-hydroxyphenyl) sulfone (hereinafter referred to as HOAB. 2.80 g (10 mmol) of SO _{2 in} a solution of 1.2 g (12 mmol) of γ-valerolactone, 2.0 g (14 mmol) of pyridine, 80 g of N-methylpyrrolidone (hereinafter referred to as NMP), and 25 g of toluene. Added to. The reactor was placed in a silicon bath, and heated and stirred at an oil bath temperature of 180 ° C. and a rotational speed / minute (hereinafter abbreviated as r.pm) 180 for 50 minutes while passing nitrogen. The reactor was removed from the silicon bath and air cooled for 30 minutes.

  (2) 65 g of NMP was added to 8.00 g (40 mmol) of 3,4'-diaminodiphenyl ether (mDADE) and stirred for 10 minutes. Then, 4.96 g (20 mmol) of bicyclooctenetetracarboxylic dianhydride (BCD) was added together with 65 g of NMP, stirred for 10 minutes, and the reactor was again placed in a silicon bath at 180 ° C. and 180 rpm for 30 minutes. The reaction was followed by air cooling at room temperature for 30 minutes.

  (3) 5.88 g (20 mmol) of BPDA was added, followed by 2.92 g (10 mmol) of mTPE along with 80 g of NMP. After stirring at room temperature for 20 minutes, the reactor was placed in a silicon bath and heated and stirred at 180 ° C. and 180 r.p.m. to initiate the polymerization reaction. Thereafter, sampling was performed every hour, and the reaction was carried out for 6 and a half hours. A 10% strength polyimide solution was obtained. A part after the reaction is diluted with NMP, and after high speed liquid chromatograph (GPC: HL8 320, manufactured by Tosoh Corporation), 1 hour, 2 hours, 3 hours, 4 hours, 5 hours after the start of the polymerization reaction, The molecular weight and molecular distribution after 6 hours and 6 and a half hours were measured. The results are shown in the table.

（註）Ｍｎ：数平均分子量；Ｍｗ：重量平均分子量；Ｍｚ：Ｚ平均分子量

(Ii) Mn: Number average molecular weight; Mw: Weight average molecular weight; Mz: Z average molecular weight

  The polyimide solution was applied on a glass plate and stirred at 150 ° C. for 30 minutes, and then the polyimide film was peeled off from the glass plate, fixed to a metal frame, heated and stirred at 280 ° C. for 1 hour to prepare a sample.

Thermal analysis was performed using a TG-GTA apparatus manufactured by McScience. The primary weight loss temperatures were 405 ° C, Tm 545 ° C, and Tg 330 ° C. According to Production Example 1, a polyimide having a repeating unit [(mDADE-BCD-mDADE) (PMDA-HOAB · SO ₂ -PMDA) (mDADE-BCD-mDADE) (BPDA-mTPE-BPDA)] _n (trade name: Solpit A ) Was generated.
Example 1
The polymer solution of Solpit A manufactured according to Preparation Example 1 was applied to a thickness of 750 μm on a glass plate using an applicator. This was transferred to a drier and heated at 100 ° C. for 1 hour, then at 130 ° C. for 0.5 hour. The residual amount of the solvent by TGA analysis was 15% by weight.
On this semi-dried film, it was further applied to a thickness of 750 μm and heated at 100 ° C. for 1 hour. Subsequently, this was dried at 130 ° C. for 0.5 hour. The film was peeled off from the glass plate, and the film was attached to a metal frame and further heated at 250 ° C. for 1 hour and 350 ° C. for 2 hours.
The thickness of the obtained film was 102 μm. From the TGA measurement, no solvent remained, and the SEM photo observation showed no interface and was a uniform film.
(Example 2)
On the glass plate, the polymer solution of Solpit A produced in Production Example 1 was applied to a thickness of 750 μm. Heat in a dryer at 70 ° C for 2 hours. The residual amount of the solvent by TGA analysis was 34% by weight. Similarly, it was applied to a thickness of 750 μm for the second time and heated at 100 ° C. for 1 hour, 200 ° C., 1 hour, and 350 ° C. for 2 hours. A uniform film of 98 μm was obtained.
(Example 3)
The treatment was carried out in the same manner as in Example 1 in which application was performed twice, and the third application of the Solpit A polymer solution produced in Production Example 1 was performed. Subsequently, it heated at 100 degreeC for 1 hour, and also dried at 130 degreeC for 0.5 hour. The film was peeled off from the glass plate, and the film was attached to a metal frame and further heated at 250 ° C. for 1 hour and 350 ° C. for 3 hours. The thickness of the obtained film was 165 μm. From the TGA measurement, no solvent remained.
(Reference Example 1)
The polymer solution of Solpit A produced in Production Example 1 was applied on a glass plate to a thickness of 750 μm. It was heated at 100 ° C for 1 hour in a dryer and dried at 130 ° C for 0.5 hour. Furthermore, it heated at 250 degreeC for 1 hour. The residual amount of the solvent by TGA analysis was 4% by weight. On this film, it was further applied to a thickness of 750 μm. Heat at 100 ° C for 1 hour. It dried at 130 degreeC for 0.5 hour. The film was peeled off from the glass plate, and the film was attached to a metal frame and further heated at 250 ° C. for 1 hour and 350 ° C. for 2 hours. In SEM photo observation, an interface was observed between the two layers.

Claims (6)

(1) Existence of catalyst in 2 mole equivalents of pyromellitic dianhydride (PMDA) and 1 mole equivalent of bis (3-amino-4-hydroxyphenyl) sulfone (HOAB.SO ₂ ) in an organic polar solvent First, the reaction is performed at 160 to 200 ° C. to produce a low molecular weight imide compound in which PMDA is bonded to both amino groups of HOAB · SO ₂ .
(2) To the low molecular weight imide compound produced in the first step, 2 molar equivalents of bicyclooctenetetracarboxylic dianhydride (BCD), 3,4′-diaminodiphenyl ether (mDADE) or 4,4′-diaminodiphenyl ether (4) 4M equivalents are reacted to form a low molecular weight imide compound having mDADE or 4,4′-DADE bonded to both ends, and (3) produced in the second step. 2 mol equivalent of biphenyltetracarboxylic dianhydride (BPDA) and 1 mol equivalent of 1,3-bis (4-aminophenoxy) benzene (mTPE) were added to the low molecular weight imide compound thus reacted, and polycondensation was performed. A third step of synthesizing a polyimide copolymer soluble in an organic polar solvent,
Formula (I) below:
_{[(MDADE-BCD-mDADE)} - (PMDA-HOAB · SO 2 -PMDA) - (mDADE-BCD-mDADE) - (BPDA-mTPE-BPDA)] n or,
Formula (II) below:
[(4,4′-DADE-BCD-4,4′-DADE)-(PMDA-HOAB · SO ₂ -PMDA)-(4,4′-DADE-BCD-4,4′-DADE)-(BPDA -MTPE-BPDA)] _n
(Here, the bond between the compounds is an imide bond.)

An organic polar solvent solution of a heat-resistant polyimide soluble in an organic solvent, having a repeating unit represented by the formula (1) and having a glass transition temperature of 300 ° C. or higher is applied onto a support, and the solvent is heated and dried. A method of creating a thick film by making it semi-dried, applying it several times, and drying to remove the solvent. (1) Existence of catalyst in 2 mole equivalents of pyromellitic dianhydride (PMDA) and 1 mole equivalent of bis (3-amino-4-hydroxyphenyl) sulfone (HOAB.SO ₂ ) in an organic polar solvent First, the reaction is performed at 160 to 200 ° C. to produce a low molecular weight imide compound in which PMDA is bonded to both amino groups of HOAB · SO ₂ .
(2) To the low molecular weight imide compound produced in the first step, 2 molar equivalents of bicyclooctenetetracarboxylic dianhydride (BCD), 3,4′-diaminodiphenyl ether (mDADE) or 4,4′-diaminodiphenyl ether (4) 4M equivalents are reacted to form a low molecular weight imide compound having mDADE or 4,4′-DADE bonded to both ends, and (3) produced in the second step. 2 mol equivalent of benzophenone tetracarboxylic dianhydride (BTDA) and 1 mol equivalent of 1,3-bis (4-aminophenoxy) benzene (mTPE) were added to the low molecular weight imide compound thus reacted, and polycondensation was performed. A third step of synthesizing a polyimide copolymer soluble in an organic polar solvent,
Formula (III) below:
_{[(MDADE-BCD-mDADE)} - (PMDA-HOAB · SO 2 -PMDA) - (mDADE-BCD-mDADE) - (BTDA-mTPE-BTDA)] n or,
Formula (IV) below:
[(4,4′-DADE-BCD-4,4′-DADE)-(PMDA-HOAB · SO ₂ -PMDA)-(4,4′-DADE-BCD-4,4′-DADE)-(BTDA -MTPE-BTDA)] _n
(Here, the bond between the compounds is an imide bond.)
An organic polar solvent solution of a heat-resistant polyimide soluble in an organic solvent, having a repeating unit represented by the formula (1) and having a glass transition temperature of 300 ° C. or higher is applied onto a support, and the solvent is heated and dried. A method of creating a thick film by making it semi-dried, applying it several times, and drying to remove the solvent. The method according to claim 1, wherein a film having a thickness of 50 to 300 μm is produced. The method according to any one of claims 1 to 3, wherein the solvent residual amount is 10 to 50% by weight by drying after coating. The method according to any one of claims 1 to 4, which is produced by completely removing the solvent by drying. 6. The method according to any one of claims 1 to 5, wherein the plurality of times of application are the same or different in the direction of application of the overlapping films.