JP2837178B2 - Coating method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for forming a heat-resistant film having no pinholes on a base material such as a metal, and more particularly to a field of electric insulation and heat resistance. It is useful in the field of anticorrosion applications requiring

[Conventional technology]

Conventionally, as a technique for forming a heat-resistant film on a substrate having a complicated shape, as disclosed in JP-B-48-16331 and JP-A-49-52252, a polyamic acid resin is electrophoretically treated. A method has been proposed in which a polyimide resin film is formed by precipitating on a substrate and imidizing by heating to form a polyimide resin film. However, in the electrophoretic coating of a polyamic acid resin, it is difficult to repair pinholes caused by gas generation due to electrolysis of water on the surface of the substrate serving as an electrode, and there are difficulties in reliability of insulation and corrosion resistance. And it has not yet been put to practical use.

As a method for solving these drawbacks, for example, Japanese Patent Laid-Open No.
Although an electrophoresis method in a non-aqueous solvent as described in -51436 has been proposed, it is not practical because of danger such as ignition. Further, as disclosed in JP-B-48-8457, a method of immersing in an organic solvent after fixing has been proposed. In this method, although pinholes are reduced, a coating film is formed with elution of polyamic acid. It is difficult to ensure reliable uniformity of the coating thickness.

[Problems to be solved by the invention]

As described above, to solve the problem of pinholes and sagging that hinders the practical use of electrophoretic coating of polyamic acid resin,
It is an object of the present invention to propose an improved coating formation method which can be widely applied in the fields of electrical insulation and corrosion protection.

[Means for solving the problem]

That is, the present invention provides a base material having a polyamic acid resin film deposited on the surface thereof by electrophoresis, which is formed of N-methyl-2-pyrrolidone, N, N
-Dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, N, N-diethylacetamide, dimethylsulfoxide and N, N
-A film forming method comprising: immersing in a mixed solution comprising an organic solvent selected from dimethylmethoxyacetamide and water and having a weight ratio of 20:80 to 60:40, followed by drying and heating. , Preferably a method in which the weight ratio of the organic solvent to water is from 20:80 to 95: 5.

The present invention provides a base material obtained by precipitating a polyamic acid resin on the surface by electrophoresis, wherein the weight ratio of an organic solvent having a boiling point of 100 ° C. or higher and water capable of dissolving the polyamic acid resin and uniformly mixing with water is 20:80. This is a method for forming a coating film, characterized by drying and heating after immersion in a mixed solution of about 95: 5.

The polyamic acid resin used in the present invention has a general formula (R ₂ and R ₂ are as described below). The production method is not particularly limited, but is usually produced by polymerizing various diamines with tetracarboxylic dianhydrides in an organic solvent. can do.

Diamines as a raw material of the polyamic acid resin, a divalent aromatic group having a bond at the meta position in the general formula, R ₂ in the above general formula, from the viewpoint of adhesion to the most common metal as a substrate, Ie It is preferably selected from the group having the structure of, for example, 3,3'-diaminobenzophenone, 1,3-bis (3-
Aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) biphenyl, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4
-(3-aminophenoxy) phenyl] -1,1,1,3,3,3
-Hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (3-
Aminophenoxy) phenyl] sulfone;
These may be used alone or as a mixture of two or more.

The tetracarboxylic dianhydride to be reacted with a diamine is represented by the following formula (In the formula, R ₁ is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, or an aromatic group directly or mutually linked by a crosslinking member. Represents a tetravalent group selected from the group consisting of non-fused polycyclic aromatic groups), for example, ethylenetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic acid Dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,3'-benzophenonetetracarboxylic dianhydride, 3,3 ', 4,4'- Biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis ( 3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3
-Dicarboxyphenyl) ethane dianhydride, bis (2,3
-Dicarboxyphenyl) methane dianhydride, bis (3,4
-Dicarboxyphenyl) methane dianhydride, 2,3,6,7-
Naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,2,3,4-benzenetetra Carboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrene tetra A carboxylic dianhydride or the like is used. Of these, particularly preferred tetracarboxylic dianhydrides are pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'- Biphenyltetracarboxylic dianhydride and bis (3,4-dicarboxyphenyl) ether dianhydride.

The polyamic acid forming reaction is usually performed in an organic solvent. Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, N, N
-Diethylacetamide, N, N-dimethyltoxacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylurea, N-methylcaprolactam, tetrahydrofuran,
m-dioxane, p-dioxane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis [2- (2-
Methoxyethoxy) ethyl] ether and the like.
These organic solvents may be used alone or in combination of two or more. The reaction temperature is usually 200 ° C or lower, preferably 50 ° C or lower. The reaction pressure is not particularly limited, and the reaction can be sufficiently performed at normal pressure. The reaction time depends on the type of solvent, the reaction temperature and the diamines and acid dianhydrides used,
Usually, the reaction is allowed to proceed for a time sufficient to complete the formation of the polyamic acid. Usually 4 to 24 hours are sufficient.

The above-mentioned polyamic acid is neutralized by adding a base to a solid resin obtained as it is or by precipitating it out of the solution to make it dilutable in water. As the base, ammonia, for example, secondary amines such as dialkylamine, diethanolamine, and morpholine; for example, triethylamine, tributylamine, triethanolamine, triisopropanolamine, dimethylethanolamine, dimethylisopropanolamine, diethylethanolamine, dimethylbenzylamine and the like Inorganic bases such as caustic soda and caustic potash are used, but tertiary amine acids are particularly preferred from the viewpoint of stability after water-solubilization and the properties of the resulting film.

The amount of the base necessary for imparting water dilutability is generally 30 to 110 mol%, particularly preferably 40 to 100 mol%, based on the carboxyl equivalent of the polyamic acid. By performing the neutralization, the polyamic acid becomes completely water-soluble or partially solubilized to be in a suspended state, so that the polyamic acid becomes water-dilutable. In either case, electrophoresis is possible. The organic solvent used for producing the polyamic acid may be present in the polyamic acid aqueous solution thus obtained, or may be separately added, but the amount added is 0.1 to 15% by weight of the polyamic acid used. Double is preferred.

At this time, a filler or a coloring agent such as titanium oxide, iron oxide, alumina and barium sulfate may be added to the bath. The resin concentration of the electrophoresis bath is usually 2 to 30% by weight, more preferably 3 to 20% by weight. Electrophoresis is usually performed by immersing a base material such as a metal to be coated in a bath, using the base material as an anode and a bathtub wall or a counter electrode of an inert metal as a negative electrode, usually 10 to 50.
This is performed by applying a voltage of 0 volt. Electrophoresis may be performed at a constant current as needed. In this case, the current density is usually 5 to 1000 mA / dm ² . The neutralized polyamic acid salt moves to the base material serving as the anode, loses electric charge on the surface of the base material, becomes insoluble in water, and covers the surface of the base material.

The film thickness of the polyamic acid resin on the substrate is usually 5 to 50 μm.
It is.

The substrate according to the present invention is not particularly limited as long as it is a conductive substance. For example, various metals, carbon, metal layers formed on an insulator such as plastic or ceramic, or these May be surface-treated.

The polyamic acid resin film on the substrate obtained as described above contains bubbles generated by the electrolysis reaction of water that occurs on the surface of the substrate during electrophoresis. Since the holes are present in the coating film, it causes insulation failure and hole contact. Therefore, it is important that the polyamic acid on the substrate is reflowed in the drying and heating step to repair defects caused by bubbles. However, the fact that the polyamic acid resin itself has a high softening point and is extremely difficult to reflow makes it difficult to repair the above-mentioned defects. Contacting the above-mentioned polyamic acid resin with an organic solvent capable of dissolving by a method such as immersion is a powerful method capable of repairing the pinhole portion by dissolving and reflowing the resin. A sagging phenomenon occurs in the vertical portion of the material surface, resulting in a non-uniform film thickness, or an extremely thin film at an edge portion, which significantly impairs the original purpose such as insulation and corrosion protection.

In the present invention, the polyamic acid resin obtained as described above is subjected to electrophoresis in a mixed solution obtained by dissolving the polyamic acid resin and mixing an organic solvent capable of being uniformly mixed with water at a predetermined ratio with water. The base material precipitated is immersed.

In the present invention, since the polyamic acid resin precipitated by electrophoresis is already insoluble in water, only the organic solvent migrates to the polyamic acid resin and swells, and the swollen polyamic acid resin is the mixed liquid Since it is insoluble in, the pinhole can be repaired in the drying and heating step without causing the above-mentioned phenomenon such as sagging.

The mixing ratio of the above organic solvent and water is preferably 20:80 to 95: 5 by weight. When the amount of the organic solvent is less than this ratio, the effect of repairing pinholes is insufficient, and when the amount of the organic solvent exceeds this range, sagging occurs during drying and heating. Particularly, the mixing ratio of the above organic solvent and water is particularly preferably from 40:60 to 80:20.

The immersion time in the above mixture is 1 to 300 seconds, preferably 2 to 200 seconds. When the immersion time is shorter than 1 second, the effect of repairing the pinhole is insufficient, and when the immersion time is longer than 300 seconds, dripping occurs during drying and heating. The above organic solvent preferably has a boiling point of 100 ° C. or higher, particularly preferably 120 ° C. or higher. Examples of the above organic solvents include N-methyl-2-pyrrolidone, N,
N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, N, N-diethylacetamide, dimethylsulfoxide, N, N-dimethylmethoxyacetamide, ethylene glycol monoethyl ether, Ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and the like are used. The polyamic acid resin is dissolved, can be uniformly mixed with water, and has a boiling point of 100 ° C.
If it is above, it is not limited to these exemplified organic solvents.

The polyamic acid resin-coated substrate treated as described above is dried and heated in a heating furnace, the imidization reaction proceeds with the evaporation of the solvent, and is converted into a polyimide resin film having excellent heat resistance. As the heating method, various known methods such as hot air drying, infrared drying, far infrared drying, and electromagnetic induction heating can be used alone or in combination. Needless to say, the required temperature and time vary depending on the heating method, but it is preferably 150 ° C. or more at which the imidization reaction sufficiently proceeds,
It is particularly preferred to choose the conditions under which the final temperature reaches ~ 300 ° C.

〔The invention's effect〕

As described above, in the film formation of the present invention, there is no defect such as pinholes or sagging, and as a result, a heat-resistant film excellent in insulation reliability and corrosion resistance can be provided.

〔Example〕

 Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 3,3'-Diaminobenzophenone and 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride were reacted in N, N-dimethylacetamide at 10 ° C to obtain a polyamic acid resin. 28.1 parts by weight (100 mol%) of dimethylethanolamine was added to 100 parts by weight of the solid content of the resin, and the mixture was stirred and mixed. Thereafter, water was added to prepare a polyamic acid aqueous solution A for electrophoresis. The resin solid content of this aqueous solution was 7% by weight. Put this aqueous solution in a stainless steel tank, immerse the aluminum plate, and use the aluminum plate as the cathode and the tank as the anode.
Electrophoresis was performed by applying a voltage of 100 v for 10 seconds to obtain a base material having a polyamic acid resin film deposited on the surface. Then N, N
The substrate was immersed in a mixed solution of 30 parts by weight of dimethylacetamide and 70 parts by weight of water for 10 seconds, and dried by heating at 140 ° C. for 1 hour and then at 250 ° C. for 1 hour. The coating thickness is 21μ
Met. The appearance of this substrate is smooth, normal and 250 ° C2
The withstand voltage after heat treatment at 00 ° C. for 1 hour was 1 kv or more.

Example 2 2,2-bis [4- (3-aminophenoxy) phenyl] propane and 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride were added to N, N-dimethylacetamide in 10%.
C. to obtain a polyamic acid resin. 15.0 parts by weight (70 mol%) of dimethylethanolamine was added to 100 parts by weight of the solid content of the resin, and the mixture was stirred and mixed. Thereafter, water was added to prepare an aqueous solution of polyamic acid B for electrophoresis. The resin solid content of this aqueous solution was 10% by weight. This aqueous solution was placed in a stainless steel tank, the aluminum plate was immersed, a voltage was applied to the aluminum plate as a cathode and the tank was used as an anode for 100 v for 20 seconds, electrophoresis was performed, and a polyamic acid resin film was deposited on the surface as a substrate. . Then, the base material was mixed with a mixture of 60 parts by weight of N, N-dimethylacetamide and 40 parts by weight of water.
The substrate was immersed for 2 seconds and dried by heating at 140 ° C. for 1 hour and then at 250 ° C. for 1 hour. The coating thickness was 35μ. The appearance of this substrate was smooth, and both the state and the withstand voltage after heat treatment at 250 ° C. for 200 hours were 1 kv or more.

Example 3 1,3-bis (3-aminophenoxy) benzene and 3,3
3 ′, 4,4′-Benzophenonetetracarboxylic dianhydride was reacted in N, N-dimethylacetamide at 10 ° C. to obtain a polyamic acid resin. 30.3 parts by weight (80 mol%) of triethanolamine was added to 100 parts by weight of the solid content of the present resin, followed by stirring and mixing. Thereafter, water was added to prepare a polyamic acid aqueous solution C for electrophoresis. The resin solid component of this aqueous solution is
It was 8% by weight. This aqueous solution was placed in a stainless steel bath, the aluminum plate was immersed, and the aluminum plate was
Electrophoresis was performed by applying a current of 200 mA / dm ² for 20 seconds using the bath as an anode to obtain a substrate having a polyamic acid resin film deposited on the surface. Thereafter, the substrate was immersed in a mixed solution of 20 parts by weight of N-methyl-2-pyrrolidone and 80 parts by weight of water for 200 seconds, and dried by heating at 140 ° C. for 1 hour and then at 250 ° C. for 1 hour. The coating thickness was 30μ. The appearance of this substrate is smooth, and the withstand voltage after heating at 250 ° C. for 200 hours under normal conditions is as follows:
Both were more than 1kv.

Example 4 1,3-bis (3-aminophenoxy) benzene and pyromellitic dianhydride were added to N, N-dimethylacetamide in 1
The reaction was carried out at 0 ° C. to obtain a polyamic acid resin. Dimethylethanolamine 14.0 based on 100 parts by weight of the solid content of the resin
Parts by weight (40 mol%) were added and mixed by stirring. Thereafter, water was added to prepare a polyamic acid aqueous solution D for electrophoresis. The resin solid content of this aqueous solution was 8% by weight. This aqueous solution was placed in a stainless steel tank, the aluminum plate was dipped, the aluminum plate cathode, a current of 200 mA / dm ² to the bath as the anode 2
The electrophoresis was performed by applying a current for 0 second to deposit a polyamic acid resin film on the surface. Thereafter, the base material was added to a mixed solution consisting of 50 parts by weight of N, N-dimethylformamide and 50 parts by weight of water.
The substrate was immersed for 2 seconds and dried by heating at 140 ° C. for 1 hour and then at 250 ° C. for 1 hour. The coating thickness was 30μ. The appearance of the substrate was smooth, and the withstand voltage after heating at 250 ° C. for 200 hours under normal conditions was 1 kv or more.

Comparative Example 1 Electrophoresis was performed on an aluminum plate using an aqueous solution for electrophoresis in exactly the same manner as in Example 1 to obtain a base material having a polyamic acid resin film deposited on its surface. Then 20 in water
It was immersed for 0 seconds, and dried by heating in the same manner as in Example 1. The coating thickness was 21μ. Although the appearance of this substrate was smooth, the withstand voltage after heating at 250 ° C. for 200 hours under normal conditions was only 1 kv or less.

Comparative Example 2 An electrophoresis was performed on an aluminum plate using an aqueous solution for electrophoresis in exactly the same manner as in Example 1 to obtain a substrate on which a polyamic acid resin was deposited on the surface. Thereafter, the substrate was immersed in a mixed solution of 95 parts by weight of N, N-dimethylacetamide and 5 parts by weight of water for 5 seconds, and heated and dried in the same manner as in Example 1. The coating thickness was 20μ. Although sagging occurred on the appearance of this substrate, the withstand voltage in normal state was 1 kv or more,
The withstand voltage after the heat treatment for 0 hours was as low as 1 kv or less.

Claims (1)

(57) [Claims] 1. A substrate on which a polyamic acid resin coating is deposited on the surface by electrophoresis, is coated with N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl -2-imidazolidinone, N, N
-Diethylacetamide, dimethyl sulfoxide and N, comprising an organic solvent selected from N-N-dimethylmethoxyacetamide and water, and immersed in a mixed solution having a weight ratio of 20:80 to 60:40, and then dried. And heating.