JPH036396A - Film formation method - Google Patents

Abstract

PURPOSE:To make a polyamic acid resin coating film free from pinholes and sag and to form a heat resistant coating film having superior corrosion preventiveness and reliability by immersing a base material with the polyamic acid resin coating film having heat resistance formed by electrophoresis in a mixture of a specified org. solvent capable of dissolving the polyamic acid resin with water. CONSTITUTION:An Al plate to be treated is put in a stainless steel vessel filled with an aq. polyamic acid soln. for electrophoresis and electric current is supplied between the Al plate as the cathode and the vessel as the anode to form a polyamic acid resin coating film having heat resistance on the surface of the Al plate by electrophoresis. This coating film is liable to undergo deterioration in characteristics owing to pinholes and sag. In order to prevent deterioration, the film is immersed in a liq. mixture prepd. by mixing an org. solvent having >=100 deg.C b.p., capable of readily dissolving the polyamic acid resin and miscible with water, e.g. N-methyl-2-pyrrolidone with water in 20:80-95:5 ratio and the film is dried and heated. A heat resistant coating film free from pinholes and sag as defects and having superior corrosion resistance is formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for forming a heat-resistant coating without pinholes etc. on a base material such as metal, and is particularly applicable to the field of electrical insulation and heat-resistant coating. It is useful for corrosion protection applications that require.

[Conventional technology]

Conventionally, as a technique for forming a heat-resistant film on a base material having a complicated shape, there has been developed
, as disclosed in JP-A-49-52252, a polyamic acid resin is deposited on a substrate by electrophoresis,
A method has been proposed in which a polyimide resin film is formed by imidization by heating. However, in the electrophoretic coating of polyamic acid resin, it is difficult to repair pinholes caused by gas generation due to water electrolysis on the surface of the base material that becomes the electrode, and it is difficult to double the insulation and corrosion resistance. However, the current situation is that it has not been put into practical use.

As a method to solve these drawbacks, for example, Japanese Patent Application Laid-open No. 52
Although an electrophoresis method in a nonaqueous solvent as described in No. 51436 has been proposed, it is not practical due to the risk of ignition. Furthermore, as disclosed in Japanese Patent Publication No. 48-8457, a method of immersing in an organic solvent after electrodeposition has been proposed.
In this method, although pinholes are reduced, phenomena such as sagging of the coating film occur due to elution of polyamic acid, making it difficult to ensure reliable uniformity of coating film thickness.

[Problem to be solved by the invention] As described above, the problems of pinholes and blurring that hinder the practical application of electrophoretic coating of polyamic acid resin are solved, and improvements that can be widely applied to the fields of electrical insulation and corrosion protection are achieved. It is an object of the present invention to propose a method for forming a film according to the present invention.

[Means to solve the problem]

In the present invention, a base material on which a polyamic acid resin film has been deposited on the surface by electrophoresis is immersed in a mixed solution of water and an organic solvent that dissolves the polyamic acid resin and is uniformly miscible with water.
A film forming method characterized by drying and heating, preferably using an organic solvent with a boiling point of 100°C or higher, and preferably using a combination of an organic solvent and water. Weight percentage is 20
: This method has a ratio of 80 to 95:5.

In the present invention, a base material on which a polyamic acid resin has been deposited on the surface by electrophoresis is prepared using an organic solvent having a boiling point of 100°C or higher that can dissolve the polyamic acid resin and can be uniformly mixed with water, and water in a weight ratio of 20: This film forming method is characterized by immersing the film in a mixed solution of 80 to 95:5, followed by drying and heating.

The polyamic acid resin used in the present invention has a repeating unit represented by the general formula 'R+, Rz are as described below), and its manufacturing method is not particularly limited, but usually various diamines are converted into tetracarboxylic dianhydride. It can be produced by polymerizing with other compounds in an organic solvent.

The diamines that are the raw materials for the above polyamic acid resin are selected from the viewpoint of adhesion to metals, which are the most common base materials, and R2 in the above general formula is a divalent aromatic group having a bond at the meta position, i.e. For example, 3,3'-diaminobenzophenone, 1,3bis(3-aminophenoxy)benzene, 4,
4bis(3-aminophenoxy)biphenyl, 2,2-
Bis(4-(3-aminophenoxy)phenyl)propane, 2.2-bis(4-(,3-aminophenoxy)phenyl)-1,LL3,3.3-hexafluoropropane, bis(4-( Examples include 3-aminophenoxy)phenyl sulfide, bis(4-(3-aminophenoxy)phenylkoketone, bis[4(3-aminophenoxy)phenyl]sulfone, etc.), which may be used alone or in combination with two
It is used by mixing more than one species.

The tetracarboxylic dianhydride to be reacted with diamines has the following formula: (represents a tetravalent group selected from the group consisting of non-fused polycyclic aromatic groups in which aromatic groups are interconnected directly or through a bridge member), for example, ethylenetetra Carboxylic dianhydride, cyclopenkune tetracarboxylic dianhydride, pyromellitic dianhydride, 3.3', 4.4" -benzophenone tetracarboxylic dianhydride, 2.2°, 3.3" -Henzophenonetetracarboxylic dianhydride, 3.3', 4.
4°-biphenyltetracarboxylic dianhydride, 2.2
', 3,3'-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4dicarboxyphenyl)propananhydride, 2I2-bis(213-dicarboxyphenyl)propananhydride, bis(3 ,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1.1-bis(2
,3dicarboxyphenyl)ethannihydride,bis(2
,3-dicarboxyphenyl)methane dianhydride, bis(
3,4-dicarboxyphenyl)methane dianhydride, 2,
3,6.7-naphthalenetetracarboxylic dianhydride, 1
', 4,5.8-naphthalenetetracarboxylic dianhydride, L2,5.6-naphthalenetetracarboxylic dianhydride, 1,2,3.4-benzenetetracarboxylic dianhydride, 3,4, 9.10-Perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, L2,7.8-phenanthrenetetracarboxylic dianhydride, etc. are used. Among these, particularly preferred tetracarboxylic dianhydrides are pyromellitic dianhydride, 3.3', 4.4''hensiphenonetetracarboxylic dianhydride, 3.3', 4.4' -biphenyltetracarboxylic dianhydride, and bis(3,4-dicarboxyphenyl)ether dianhydride.

The polyamic acid production reaction is usually carried out 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 -dimethyltoxyacetamide, 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,
Examples include bis[2-(2-methoxyethoxy)ethyl]ether. These organic solvents may be used alone or in combination
It is also possible to use a mixture of more than one species. The reaction temperature is usually 20
0"C or less, preferably 50C or less. The reaction pressure is not particularly limited, and normal pressure can be sufficient. The reaction time depends on the type of solvent, reaction temperature, and diamines and acid dianhydrides used. However, the reaction is usually carried out for a sufficient period of time to complete the production of polyamic acid, usually 4 to 24 hours being sufficient.

The above-mentioned polyamic acid can be diluted with water by adding a base to the solid resin obtained as it is as a solution or by precipitation from the solution. Bases include ammonia, secondary amines such as dialkylamine, jetanolamine, morpholine; for example tri, ethylamine, tributylamine, triethanolamine, triisopropanolamine, dimethylethanolamine, dimethylisopropanolamine, Tertiary amines such as diethylethanolamine and dimethylbenzylamine are often used; inorganic bases such as caustic soda and caustic potash are used; however, tertiary amines are particularly preferred from the viewpoint of stability after solubilization and the properties of the resulting film.

The amount of base necessary to impart water dilutability is generally 30 to 110 mol%, and particularly preferably 40 to 100 mol%, based on the carboxyl equivalent of the polyamic acid.

By performing neutralization, the polyamic acid becomes completely water-soluble or partially water-solubilized into a suspended state and has water-dilubility. Electrophoresis is possible in either case. The organic solvent used in the production of the polyamic acid may be present in the polyamic acid aqueous solution obtained in this way, or may be added separately, but the amount added is 0.1 to 0.1 of the polyamic acid used. 15 times by weight is preferred.

At this time, fillers and colorants such as titanium oxide, iron oxide, alumina, barium sulfate, etc. may be added to the bath. The resin concentration in the electrophoresis bath is usually 2 to 30% by weight, more preferably 3 to 20% by weight. In electrophoresis, a base material such as a metal to be coated is immersed in a bath, the base material is used as an anode, and the bath wall or an inert metal counter electrode is used as a bacterial species.
This is done by applying a voltage of ~500 volts. Furthermore, electrophoresis may be performed at a constant current if necessary. In this case, the current density is usually 5 to 10,100 O/dn.

The neutralized polyamic acid salt moves to the base material that is the anode, loses its charge on the surface of the base material, becomes insoluble in water, and covers the surface of the base material.

11- The coating thickness of polyamic acid resin on the base material is usually 5 to 50μ
It is.

In addition, the base material referred to in the present invention is not particularly limited as long as it is a conductive material, and includes, for example, various metals, carbon, a metal layer formed on an insulator such as plastic or ceramic, or a metal layer formed on an insulator such as various metals, carbon, plastic, or ceramic. The metal 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, and if it is dried as is, it often becomes difficult to form bubbles. Holes exist in the paint film, causing poor insulation and porosity.

Therefore, it is important that the polyamic acid on the base material reflows during the drying and heating process to repair defects caused by air bubbles. However, the polyamic acid resin itself has a high softening point and is extremely difficult to reflow.
This makes the above defects difficult to repair. Bringing the polyamic acid resin into contact with an organic solvent capable of dissolving it by immersion or other methods is an effective method for repairing pinholes by dissolving and reflowing the resin. In addition, sagging occurs on the vertical portions of the substrate surface, making the film thickness non-uniform, and the film thickness becomes extremely thin at edge portions, which significantly impairs the original purpose of insulation, corrosion protection, etc.

In the present invention, the polyamic acid resin obtained as described above is placed on the surface of the polyamic acid resin obtained by electrophoresis in a mixed liquid in which an organic solvent that dissolves the above polyamic acid resin and is uniformly miscible with water is mixed with water at a predetermined ratio. The substrate on which the deposit has been deposited is immersed in the solution.

In the present invention, since the polyamic acid resin precipitated by electrophoresis is already insoluble in water, only the organic solvent transfers to the polyamic acid resin and causes it to swell, and the swollen polyamic acid resin is mixed with the above mixture. Since it is insoluble, pinholes can be repaired during the drying and heating process without causing the above-mentioned phenomena such as sag.

The mixing ratio of the organic solvent and water is preferably 20:80 to 95:5 by weight. If the organic solvent is less than this ratio, the effect of repairing pinholes will be insufficient, and if the organic solvent is more than this range, sag will occur during drying and heating, which is inappropriate. In particular, the mixing ratio of the organic solvent and water is preferably 40:60 to 80:20.

The immersion time in the above mixing is 1 to 300 seconds, preferably 2 to 200 seconds. If the immersion time is less than 1 second, the effect of repairing pinholes will be insufficient, and if the immersion time is more than 300 seconds, sagging will occur during drying and heating, which is inappropriate. The above organic solvent has a boiling point of 1
A temperature of 00°C or higher is suitable, and a temperature of 120"C or higher is particularly preferable. Examples of the above-mentioned solvents include N-methyl-2
-pyrrolidone, N,N-dimethylacetamide, N,N
-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, N,N-diethylacetamide, dimethyl sulfoxide, N,N-dimethylmethoxyacetamide, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether , diethylene glycol motsubutyl ether, diethylene glycol dimethyl ether, etc. are used, but the organic solvents are limited to these exemplified organic solvents as long as they can dissolve the polyamic acid resin, can be uniformly mixed with water, and have a boiling point of 100°C or higher. isn't it.

The polyamic acid resin-coated substrate treated as described above is dried and heated in a heating furnace, and as the solvent evaporates, the imidization reaction proceeds and is converted into a polyimide resin coating 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. As a matter of course,
The required temperature and time will vary depending on the heating method, but it is preferably 150'C or higher so that the imidization reaction can sufficiently proceed.
It is particularly preferred to choose conditions such that a final temperature of 180-300°C is reached.

〔Effect of the invention〕

As described above, in the film formation of the present invention, there are no defects such as pinholes or sag, and as a result, a heat-resistant film with excellent insulation reliability and corrosion prevention reliability can be provided.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Implementation ■Sat 3.3'-diaminobenzophenone and 3.3', 4.4
'Benzophenonetetracarboxylic dianhydride N.

A polyamic acid resin was obtained by reacting in N-dimethylacetamide at 10°C. 28.1 parts by weight (10 parts by weight) of dimethylethanolamine per 100 parts by weight of solid content of this resin.
0 mol %) was added and mixed with stirring. The drained water was added to prepare an aqueous polyamic acid solution A for electrophoresis. The resin solid content of this aqueous solution was 7% by weight. This aqueous solution was placed in a stainless steel tank, an aluminum plate was immersed, and a voltage of 100 V was applied for 10 seconds using the aluminum plate as a cathode and the tank as an anode to conduct electrophoresis. A polyamic acid resin coating was deposited on the surface of the substrate. And so. Thereafter, the substrate was immersed for 10 seconds in a mixed solution consisting of 30 parts by weight of N,N-dimethylacetamide and 70 parts by weight of water, and then heated for 1 hour at 140°C for 25 hours.
Heat drying was performed at 0°C for 1 hour. Coating thickness is 21μ
Met. The appearance of this board is smooth, and the normal and 250
The withstand voltage after heat treatment at 200°C is lk.
It was more than v.

Actual difference 71 2.2-bis(4-(3-aminophenoxy)phenyl)propane and 3.3',4.4'-benzophenonetetracarboxylic dianhydride in N,N-dimethylacetamide at 10% The reaction was carried out at °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 this resin, and the mixture was stirred and mixed. The drained water was added to prepare polyamic acid aqueous solution 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, an aluminum plate was immersed, and a voltage of 100V was applied for 20 seconds using the aluminum plate as a cathode and the tank as an anode to perform electrophoresis, and a polyamic acid resin film was deposited on the surface of the base material. . Then 60 parts by weight of N,N-dimethylacetamide and 40 parts by weight of water.
The base material was immersed for 6 seconds in a mixed solution consisting of parts by weight at 140°.
The film was dried by heating at 250° 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 lkv or more.

Examples of implementation: 1. 3-bis(3-aminophenoxy)benzene and 3.
3', 4,4'-benzophenonetetracarboxylic dianhydride was reacted in N,N-dimethylacetamide at 10°C to obtain a polyamic acid resin. Solid content of this resin 1
30.3 parts by weight (80 mol %) of triethanolamine was added to 00 parts by weight and mixed with stirring. The drained water was added to prepare a polyamic acid aqueous solution C for electrophoresis. The resin solid content of this aqueous solution was 8% by weight. This aqueous solution was placed in a stainless steel tank, an aluminum plate was immersed in it, the aluminum plate was used as a cathode, and the tank was used as an anode at 200 mA/d.
Electrophoresis was performed by applying a current of rrY for 20 seconds to obtain a base material on which a polyamic acid resin coating was deposited. Thereafter, the base material was immersed for 200 seconds in a mixed solution consisting of 20 parts by weight of N-methyl-2-pyrrolidone and 80 parts by weight of water.
It was heated and dried at 250°C for 1 hour at 250°C. The coating thickness was 30μ. The appearance of this substrate was smooth, and the withstand voltage was lkv or higher both under normal conditions and after heat treatment at 250° C. for 200 hours.

1. 3-Bis(3-aminophenoxy)benzene and pyromellitic dianhydride were reacted in N,N-dimethylacetamide at 10°C to obtain a polyamic acid resin. 14.0 parts by weight (40 mol %) of dimethylethanolamine was added to 100 parts by weight of the solid content of this resin, and the mixture was stirred and mixed. The drained water was added to prepare a polyamic acid aqueous solution for electrophoresis. The resin solid content of this aqueous solution was 8% by weight. This aqueous solution was placed in a stainless steel tank, an aluminum plate was immersed, and the aluminum plate was used as a cathode and the tank was used as an anode for 20 minutes.
Electrophoresis was performed by applying a current of 0 m/dnf for 20 seconds to deposit a polyamic acid resin film on the surface.

Then 50 parts by weight of N,N-dimethylformamide and 5 parts by weight of water.
The base material is immersed in a mixed solution containing 0 parts by weight for 100 seconds,
Heat drying was performed at 140°C for 1 hour and then at 250°C for 1 hour. The coating thickness was 30μ. Book 9 The appearance of the substrate was smooth, and the withstand voltage was 11 (ν or more) both in the normal state and after heat treatment at 250° C. for 200 hours.

Electrophoresis was carried out in the same manner as in Example 2 using the electrophoresis aqueous solution B obtained in Example 2. Then ethylene glycol monoethyl ether 80ffi! 1 part and 20M water
The obtained base material was immersed in a mixed solution consisting of 50% of the total amount of water for 150 seconds, heated at 140"C for 1 hour, and then heated and dried at 250°C for 1 hour. The coating thickness was 34μ. This substrate The appearance was smooth, and the withstand voltage was 1.v or more both in the normal state and after heat treatment at 250° C. for 200 hours.

Disaster Preparedness I Electrophoresis was carried out in the same manner as in Example 1 using the electrophoresis aqueous solution B obtained in Example 1. Thereafter, the obtained base material was immersed for 180 seconds in a mixed solution consisting of 40 parts by weight of diethylene glycol dimethyl ether and 60 parts by weight of water.
Heat drying was performed at 0°C for 1 hour and then at 250°C for 1 hour. The film thickness was 19μ and 0. The appearance of this board is smooth, normal and 250°
The withstand voltages after heat treatment for C200 hours were both lkv or more.

Kitakari M1 Using an aqueous solution for electrophoresis in exactly the same manner as in Example 1,
Electrophoresis was performed on an aluminum plate to form a base material on which a polyamic acid resin coating was deposited. 200 for draining the water
The sample was immersed for a second, and then heated and dried in the same manner as in Example 1.

The coating thickness was 21μ. Although the appearance of this substrate was smooth, the withstand voltage in both the normal state and after heat treatment at 250''C for 200 hours was only ν or less.

General comparison■) Using an aqueous solution for electrophoresis in exactly the same manner as in Example 1,
Electrophoresis was performed on an aluminum plate to obtain a base material on which polyamic acid resin was deposited.

Then 95 parts by weight of N,N-dimethylacetamide and 5 parts by weight of water.
The base material was immersed for 5 seconds in the mixed solution in the same amount as in Example 1, and then heated and dried in the same manner as in Example 1. The coating thickness was 20μ.

The appearance of the zero base material is blurred, and the normal withstand voltage is lk.
However, the withstand voltage after heat treatment at 250"C for 200 hours was as low as 1.v or less.

This indigo ±1 Using an aqueous solution for electrophoresis in exactly the same manner as in Example 2,
Electrophoresis was performed on an aluminum plate to obtain a base material on which polyamic acid resin was deposited. Thereafter, the base material was immersed for 280 seconds in a mixed solution consisting of 15% by weight of diethylene glycol dimethyl ether and 85% by weight of water, and then heated and dried in the same manner as in Example 2. The coating thickness was 35μ. The appearance of this board was smooth, but it was
The withstand voltages after the 0-hour heat treatment were both as low as IKv or less.

Claims (1)

[Claims] 1) A base material on which a polyamic acid resin film has been deposited on the surface by electrophoresis is immersed in a mixed solution of water and an organic solvent that dissolves the polyamic acid resin and can be uniformly mixed with water. A film forming method characterized by drying and heating. 2) The method according to claim 1, wherein the organic solvent has a boiling point of 100°C or higher. 3) The weight ratio of organic solvent and water is 20:80 to 95:5
The method according to claim 1.