JP2809705B2 - Coating method - Google Patents

Description

The present invention relates to a method for forming an organic film having heat resistance, and is particularly useful for electric parts and automobile parts that require electrical insulation or corrosion protection at high temperatures. It is.

[Prior art] Conventionally, as a coating material for electric insulation or anticorrosion use requiring heat resistance, a method of applying an organic solvent solution such as a silicone resin or a polyimide resin, or a powder coating of a fluorine resin has been generally attempted. Have been. However, in these coatings, it is difficult to cover complicated shapes and pores, and the reliability of the electrical insulation or corrosion prevention function is poor.

On the other hand, in the coating of messy shapes and pores, electrophoretic coating is widely used practically, but the formation of a film by the electrophoretic coating method having good heat resistance cannot be performed satisfactorily.
It has not been fully commercialized.

The formation of a film of a polyamic acid, which is a precursor of a polyimide resin, by an electrophoretic method has been attempted to solve the above problem, and is disclosed in Japanese Patent Publication No. 48-16331.

However, the electrophoretic coating of polyamic acid resin has the drawbacks that the smoothness of the coating is poor and that a thick defect-free coating is difficult to obtain, which makes it difficult to maintain dielectric strength and prevent pitting corrosion. Has not reached.

[Problems to be solved by the present invention]

The present invention has a feature that the film formation of the above-mentioned polyamic acid resin by the electrophoresis method has a heat resistance and a feature that can cope with a complicated shape, but the defect-free film formation that hinders practical application is achieved. It is an object of the present invention to provide a novel method for forming a film capable of remarkably remedying the difficulties and maintaining dielectric strength and preventing pitting.

[Means for solving the problem]

The present invention comprises (A) a polyamic acid resin which is a precursor of a polyimide resin and (B) an aromatic maleimide compound, and the weight ratio of (A) and (B) is in the range of 95: 5 to 50:50. A colloidal aqueous dispersion, which is deposited on a conductive substrate by electrophoresis and heated to imidize and crosslink.

 Hereinafter, the present invention will be described in detail.

The polyamide resin (A) described above has a general formula A resin having a repeating unit having the structure of Tetracarboxylic acid anhydrides having the general formula and H ₂ N-
A resin obtained by addition reaction of diamines having the general formula structure of Y-NH _2. In the above general formula, X represents a phenyl group, a biphenyl group, a phenyl group or a polyphenyl group in which a phenyl group or a biphenyl group is bonded by O, CO, S, CH ₂ , C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or the like. Y is a phenyl group, a biphenyl group, a phenyl group or a biphenyl group represented by O, CO, S, SO ₂ , CH ₂ , C (CH ₃ )
₂ , a group selected from one or more of a polyphenyl group, an alkylene group, a xylylene group and the like linked by C (CF ₃ ) ₂ or the like.

In particular, X is a phenyl group, a biphenyl group, a diphenyl ether group, and a diphenyl ketone group; Y is one or more of a biphenyl group, a diphenyl ether group, a diphenyl ketone group, a dibiphenyl ether group, a triphenyl ether group, and a diphenyl biphenyl ether group. That
It is preferable from the viewpoint of adhesion to a substrate and heat resistance. The polyamic acid resin (A) may be partially imidized beforehand.

The above general formula used in the present invention The polyamic acid resin having repeating units has a COOH group of -COO by addition of an amine or an alkali metal ion.
The ionic group is dissociated in the presence of water, and can be dissolved or stably dispersed in colloid in water, and is precipitated again on the base material serving as the anode by electrophoresis and insolubilized.

In the present invention, by heating this after electrophoresis, the general formula The repeating unit is converted into a polyimide group having a main structure.

The aromatic maleimide compound (B) is, for example, a maleimide obtained by a reaction of maleic acid such as an aromatic monoamine such as phenylmaleimide or naphthylmaleimide, and a structure of the general formula H ₂ N—Y—NH ₂ described above. Wherein Y is a phenyl group, a biphenyl group, a phenyl group or a biphenyl group is O, CO, S, SO ₂ , CH ₂ , C (C
Bismaleimides obtained by the reaction of so-called aromatic diamines linked with H ₃ ) ₂ , C (CF ₃ ) ₂ etc. with maleic acid, such as aromatic polyamines obtained by condensation of aniline with formaldehyde or dimethylolbenzene And polymaleimides obtained by the reaction of maleic acid with the compounds.

These (B) aromatic maleimide compounds are insoluble in water, but in the coexistence of the (A) polyamic acid resin, the (A) polyamic acid resin neutralized with an amine or an alkali metal ion is used. It becomes a protective colloid agent in the aqueous layer, so that a stable colloidal dispersion can be formed, and the above (A) and (B) can be simultaneously deposited on a substrate by electrophoresis.

In the electrophoresis of the aqueous colloidal dispersion comprising the above (A) and (B) in the present invention, a thicker film can be formed under the same electrophoretic conditions as compared with the aqueous solution or aqueous dispersion alone (A). It is possible, and it is possible to significantly reduce the occurrence of pinholes and the like that occur when the coating thickness is increased in (A) alone.

The preferred weight ratio of the above (A) and (B) is 95: 5 to
More preferably, the ratio is from 90:10 to 60:40. If the weight ratio of (B) is less than 5%, the effect of the present invention is not remarkable, and if it exceeds 50%, the stability of the aqueous colloidal dispersion decreases.

The general method for preparing the aqueous colloidal dispersion comprising the above (A) and (B) will be described below. First, (A)
And (B) are dissolved, and (A) and (B) are dissolved in an organic solvent that can be uniformly mixed with water. Examples of these solvents include dimethylformamide, dimethylacetamide, N-vinylpyrrolidone, diglyme, dimethylimidazole and the like, ketones such as acetone, methyl ethyl ketone, isophorone; methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol, butyl Glycol ethers such as carbitol; alcohols such as ethanol, isopropanol and diacetone alcohol can be used in combination. In addition, as long as the dissolution of (A) and (B) is not inhibited, various organic solvents that are incompatible with water may be used in combination.

Further, together with the above (A) and (B), for example, silica,
Inorganic fillers such as alumina, zirconia, titanium oxide, barium sulfate, talc, iron oxide, aluminum nitride, boron nitride, silicon carbide, silicon nitride; coloring pigments, coloring dyes, leveling aids, defoaming agents, etc. Agents and the like may be dispersed and mixed.

Next, amines or alkali metal hydroxides serving as neutralizing agents are added. Tertiary amines are preferably used, and for example, triethylamine, tributylamine, triethanolamine, dimethylethanolamine, dimethylisopropanolamine, dimethylbenzylamine and the like are preferably used.

The amount of the amines added is usually 0.5 to 1.2 times equivalent to the carboxyl group in the polyamic acid resin (A), but the amount of the amines depends on the resin structure of (A) and the usage ratio of (A) and (B). Accordingly, the particle size of the colloidal dispersion described later changes, so that it is desirable to select the amount of addition so as to control the particle size.

Next, water is added to the solution neutralized by amines or the like and stirred to obtain a stable aqueous colloidal dispersion. The concentration of the aqueous dispersion is preferably selected such that the solid content of (A) and (B) is usually 5 to 20% by weight.

The size of the colloidal particles in the above aqueous colloidal dispersion is usually preferably from 10. nm to 5 μm, and can be controlled by the addition amount of the above-mentioned amines and the like.

Next, a substrate having conductivity is immersed in the aqueous colloidal dispersion, and a DC voltage is applied in the presence of the counter electrode, using the substrate as an anode and the counter electrode as a cathode. Normal,
Applied voltage is 10 ~ 200Volt, current flowing between poles is 0.05 ~ 10A
/ dm ^2, a constant voltage electrophoresis keeping the voltage constant, or it can be either a constant current electrophoresis keeping the current constant.

The electrophoresis time is usually from 1 to 10,000 seconds, and a film of about 2 to 100 μm (after drying) can be formed on the substrate.

The substrate used in the present invention is not particularly limited as long as the substrate has conductivity. For example, metal,
Substrates such as carbon, carbon fiber, or a conductive film formed on an insulator such as glass and ceramics.A conductor surface of a metal or the like is subjected to a surface treatment such as an oxide treatment or a phosphate treatment. It does not matter.

Next, the substrate is pulled out of the electrophoresis bath, washed with water and heated. In this heating step, the resins (A) and (B) deposited and deposited in the form of particles on the base material are melted to form a uniform film, and at the same time, an imidization reaction and a polymerization reaction of the maleimide compound of (B) occur, resulting in heat resistance. A smooth, defect-free coating with excellent properties is formed on the substrate. The heating is
It is preferable that the final temperature is usually 150 to 250 ° C,
A hot air drying oven, an infrared drying oven, a far-infrared oven, a high-frequency heating oven, or a combination thereof can be used, but the temperature is gradually increased, and the imidization and crosslinking reaction can be completed at 200 to 250 ° C. in the latter stage. More desirable.

In the film forming method of the present invention as described above, a smooth and defect-free film is formed on a substrate such as a metal, and as a result, a heat-resistant film having excellent dielectric strength and no pitting corrosion is realized. It has a remarkable effect that it can be achieved.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to examples. In addition, the characteristic evaluation shown in an Example and a comparative example was performed according to the following methods.

a) Adhesiveness It was evaluated by a tape-like tape test according to JIS-Z-5400 6.1.

b) Withstand voltage According to JIS-C-2110, AC 1 KV was applied, and when a leakage current of 0.5 mA was generated, a failure was judged. Here, the normal state means a state after standing at room temperature for 24 hours or more after imidization crosslinking. After the heat resistance test, the condition after the treatment at 300 ° C. for 200 hours, and after the chemical resistance test, the condition after immersion in a 10% aqueous sodium hydroxide solution at room temperature for 1 hour, followed by washing and drying.

c) Salt spray resistance Judgment was made on the appearance after treatment for 24 hours in accordance with JIS-Z-2371.

Example 1 Reaction of 2,2-bis [4- (3-aminophenoxy) phenyl] propane with 3,3 ', 4,4'-benzophenonetetracarboxylic anhydride in N, N-dimethylacetamide A polyamic acid resin (resin A) was obtained. By reacting 2,2-bis [4- (3-aminophenoxy) phenyl] propane with maleic anhydride, an aromatic bismaleimide resin (B) was obtained. Resin A90g, Resin B10g as resin solid part
And 11.6 g of dimethylethanolamine (0.6 equivalent)
Was gradually added, and water was added with stirring to prepare an aqueous solution for electrophoresis. The resin content of this aqueous solution was 7% by weight. This aqueous solution was placed in a stainless steel tank, and electrophoresis was performed by applying a voltage of 100 V for 15 seconds using the cylinder as an anode and a tank as a cathode in aluminum having an inner diameter of 5 mm, an outer diameter of 6 mm, and a length of 100 mm to be coated. Was. Thereafter, the aluminum cylinder was taken out, washed with water, and then heat-treated at 140 ° C. for 1 hour and then at 250 ° C. for 1 hour to perform imidization crosslinking. The thickness of the coating was 30 μm on both the inner and outer walls of the cylinder. Adhesion is 100/10
0. Normal, withstand voltage after heat resistance test and after chemical resistance test, all passed. The appearance did not change after the salt spray test.

Example 2 1,3-bis (3-aminophenoxy) benzene and 3,3
3 ', 4,4'-benzophenonetetracarboxylic anhydride
The reaction was performed in N, N-dimethylacetamide to obtain a polyamic acid resin (resin C). 4,4'-bis (aminophenyl) methane was reacted with maleic anhydride to obtain an aromatic maleimide resin (resin D). Resin C6 as resin solid component
0 g, resin D40 g, dimethylethanolamine 14.6
g (1.0 equivalent) was gradually added, and an aqueous solution for electrophoresis was prepared in the same manner as in Example 1. Resin solid content of this aqueous solution is 15% by weight
Met. Example 1
Using the same aluminum cylinder as the anode and the lead plate as the cathode
A current of 0 mA / dm ² was supplied for 180 seconds to perform electrophoresis. Thereafter, the same treatment as in Example 1 was performed to perform imidization crosslinking. The thickness of the coating was 28 μm on both the inner and outer walls of the cylinder.
Adhesion is 100/100; normal, after withstand heat test and after withstand chemical test, all withstand voltage passed. The appearance did not change after the salt spray test. Example 3 3,3'-diaminobenzophenone and 3,3 ', 4,4'-benzophenonetetracarboxylic anhydride were reacted in N, N-dimethylacetamide to obtain a polyamic acid resin (resin E). . 70 g of resin E and 30 g of resin B were mixed as resin solid components, and 15.7 g (0.8 equivalent) of dimethylethanolamine was gradually added thereto, to prepare an aqueous solution for electrophoresis in the same manner as in Example 1. The resin solid content of this aqueous solution was 10% by weight. This aqueous solution was placed in a plastic tank, and a voltage of 60 V was applied for 30 seconds using the same aluminum cylinder as the anode and the lead plate as the cathode, and electrophoresis was performed. Thereafter, the same treatment as in Example 1 was carried out to perform imidization and crosslinking. The thickness of the coating was 18 μm on both the inner and outer walls of the cylinder. Adhesion: 100/100; Dielectric strength after normal condition, after heat test and after chemical test. The appearance did not change after the salt spray test.

Example 4 1,3-bis (3-aminophenoxy) benzene and trimellitic anhydride were reacted in N, N-dimethylacetamide to obtain a polyamic acid resin (resin F). As a resin solid, 60 g of resin F and 40 g of resin B were mixed, and 17.6 g (1.0 equivalent) of dimethylethanolamine was gradually added.
An aqueous solution for electrophoresis was prepared in the same manner as described above. The resin solid content of this aqueous solution was 5% by weight. This aqueous solution was placed in a plastic tank, and a current of 800 mA / dm ² was passed for 30 seconds using the same aluminum cylinder as the anode and the lead plate as the cathode to perform electrophoresis. Thereafter, the same treatment as in Example 1 was performed to perform imidization crosslinking. The thickness of the coating was 35 μm on both the inner and outer walls of the cylinder. Adhesion: 100/100; Dielectric strength after normal condition, after heat test and after chemical test. The appearance did not change after the salt spray test.

Example 5 As a resin solid component, 90 g of resin A and 10 g of resin D were mixed, and 23.1 g (1.2 equivalents) of dimethylethanolamine was gradually added.
An aqueous solution for electrophoresis was prepared in the same manner as in Example 1. The resin solid content of this aqueous solution was 19% by weight. This aqueous solution was placed in a plastic tank, and a voltage of 150 V was applied for 6 seconds using the same aluminum cylinder as the anode and the lead plate as the cathode as in Example 1,
Electrophoresis was performed. Thereafter, the same treatment as in Example 1 was carried out to perform imidization and crosslinking. The thickness of the coating was 32 μm on both the inner and outer walls of the cylinder. Adhesion: 100/100; Dielectric strength after normal condition, after heat test and after chemical test.
The appearance did not change after the salt spray test.

Comparative Example 1 12.9 g (0.6 equivalent) of dimethylethanolamine was gradually added to 100 g of the resin A solid obtained in Example 1 to prepare an 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, and electrophoresis was performed by applying a voltage of 100 V for 15 seconds using the same aluminum cylinder as the anode and the tank as the cathode as in Example 1. Thereafter, the same treatment as in Example 1 was carried out to perform imidization and crosslinking. The thickness of the coating was 25 μm on both the inner and outer walls of the cylinder. The adhesion was 100/100; the withstand voltage in the normal state was acceptable, but the withstand voltage after the heat resistance test and the chemical resistance test was rejected. Even after the salt spray test, spot rust was observed.

Comparative Example 2 97 g of the resin C and 3 g of the resin D obtained in Example 2 were mixed, and 18.9 g (0.8 equivalent) of dimethylethanolamine was gradually added to prepare an aqueous solution for electrophoresis in the same manner as in Example 2.
The resin solid content of this aqueous solution was 12% by weight. This aqueous solution was placed in a plastic vessel, an anode similar to the aluminum cylinder as in Example 1, a current of 150 mA / dm ² lead plate as the cathode 180
The electrophoresis was performed by supplying electricity for 2 seconds. Thereafter, the same treatment as in Example 1 was carried out to perform imidization and crosslinking. The thickness of the coating was 22 μm on both the inner and outer walls of the cylinder. Adhesiveness is 100/100;
In addition, the withstand voltage in the normal state, after the heat resistance test and after the chemical resistance test was rejected. Even after the salt spray test, spot rust was observed.

Comparative Example 3 20 g of resin A and 80 g of resin B obtained in Example 1 were mixed, 4.3 g (1.0 equivalent) of dimethylethanolamine was gradually added, and then an aqueous solution for electrophoresis was prepared in the same manner as in Example 1. The resin solid content of this aqueous solution was 8% by weight. When this aqueous solution was stored at room temperature, aggregation and separation occurred in 6 hours, and re-dispersion was not possible.

Claims (1)

(57) [Claims] 1. A composition comprising (A) a polyamic acid resin which is a precursor of a polyimide resin and (B) an aromatic maleimide compound, and wherein the weight ratio of (A) and (B) is 95: 5 to 50:50. A method for forming a coating film, comprising: depositing a colloidal aqueous dispersion within a range on a conductive substrate by electrophoresis, and heating to imidize and crosslink.