JP2647423B2 - Metal coating method - Google Patents

Description

The present invention relates to an electric or electronic device which requires metal corrosion or electrical insulation, and a metal coating which does not deteriorate its performance in a heat-resistant environment. The present invention relates to a novel metal coating method which can be effectively used in the fields of automobile parts, aircraft parts, plant members and the like.

Conventional technology and its problems The method of performing metal corrosion and electrical insulation by forming a coating or coating of an organic resin is widely performed, but a coating of an organic resin has a low heat resistance and a temperature of, for example, 300 ° C. At a temperature exceeding this, deterioration occurs, and corrosion resistance and electrical insulation deteriorate. In recent years, these problems have been solved with the advent of heat-resistant resins such as silicone resin and polyimide resin.However, there is still a problem with the adhesion to metal, and silicon resin and polyimide resin have been added to intricately shaped metal products. However, it is difficult to uniformly coat such a heat-resistant resin. Conventionally, the coating of metal products having such complicated and complicated shapes is carried out by an electrophoretic coating method (electrocoating method) as disclosed in, for example, Japanese Patent Publication No. 48-16331.
However, it has been difficult to form a film having heat resistance and excellent adhesion to metal as it is.

An object of the present invention is to make it possible to form a coating having excellent heat resistance and excellent metal adhesion, which is a drawback of the above-mentioned prior art, even for a metal body such as a metal product having a complicated shape.

Specific contents of the invention The present invention has been made in view of such points,
The gist is the general formula (Here, 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 bridge member. A tetravalent group selected from the group consisting of non-fused polycyclic aromatic groups,
₂ has a bond at a meta position selected from the following group:
Represents a valent aromatic group. ) Consisting of a repeating unit represented by the formula, the logarithmic viscosity is 0.05 to
The carboxyl group of the polyamic acid of 0.6 dl / g is neutralized with a base and diluted with water to form a film forming electrophoresis bath, a metal body to be formed a film is immersed in the bath, and the metal body is used as an anode. The present invention provides a method for coating a metal, comprising performing electrophoresis to precipitate the polyamic acid on the surface of the metal body to form a film, and then performing a heat treatment to imidize the film.

 Hereinafter, the present invention will be described in detail.

The present invention uses the above general formula A polyamic acid having a repeating unit represented by the following formula: Although the production method is not particularly limited, it can be usually produced by polymerizing corresponding various diamines with tetracarboxylic dianhydride in an organic solvent.

Examples of the diamine used in the present invention include 3,3'-diaminobenzophenone, 1,3-bis (3-aminophenoxy) benzene, and 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-hexa Diamines such as fluoropropane, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] ketone, and bis [4- (3-aminophenoxy) phenyl] sulfone; These may be used alone or as a mixture of two or more.

As the tetracarboxylic dianhydride to be reacted with the diamine in the present invention, the following formula (Wherein R ₁ is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group,
Represents a tetravalent group selected from the group consisting of a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which the aromatic groups are connected to each other directly or by a bridge member. ), For example, ethylene tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, pyrrolimellitic dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride, 2 2,2 ', 3,3'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride Anhydride, 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) sulfodianhydride, 1,1-bi Bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 2,3,6 , 7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4 -Benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrene Tetracarboxylic dianhydride is preferred. Of these, particularly preferred tetracarboxylic dianhydrides are pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyl Tetracarboxylic dianhydride and bis (3,4-dicarboxyphenyl) ether dianhydride.

The above-described reaction for producing a polyamic acid from the diamine and the tetracarboxylic dianhydride 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-imidazolidinone, N, N-
Dimethylacetamide, N, N-dimethylmethoxyacetamide, 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 about 200 ° C. or lower, −20 ° C. or higher, preferably 50 ° C. or lower, −10 ° C. or higher, and more preferably about 0 ° C. or higher, about room temperature. 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,
Although it may vary depending on the reaction temperature and the diamine or acid dianhydride used, it is usually from 2 to 40 hours, preferably from 4 to 24 hours, for the reaction to proceed for a time sufficient to complete the formation of the polyamic acid.
About an hour is enough.

The polyamic acid solution of the present invention thus obtained is a solution containing 5 to 40% by weight, particularly preferably 10 to 30% by weight, of polyamic acid, and has a logarithmic viscosity of 0.05 to 0.6 dl / g (35 ° C.,
(A concentration measured with 0.5 g / ml N, N-dimethylacetamide). When the logarithmic viscosity is less than 0.05 dl / g, the strength of the heat-imidized electrodeposited film is insufficient, and the heat resistance is reduced. The logarithmic viscosity is 0.6dl / g
If the above is satisfied, the resin flow property at the time of thermal imidization is reduced, and the electrical insulating property is reduced due to a coating defect such as a pinhole.

In the present invention, the above-mentioned polyamic acid can be diluted with water by adding a base to a solid resin obtained as it is or as a solution thereof or by precipitating the solution from the solution to neutralize the carboxyl group.

As the base used for neutralization, ammonia; for example, secondary amines such as dialkylamine, diethanolamine, and morpholine; for example, triethylamine, tributylamine, triethanolamine, triisopropanolamine, dimethylethanolamine, dimethylisopropanolamine, diethylethanol Tertiary amines such as amine and dimethylbenzylamine; inorganic bases such as caustic soda and caustic potash are used, but tertiary amines are particularly preferable in view of stability after dilution with water and properties of a film obtained.

The amount of base required for imparting water dilutability is 30 to 110 mol% based on the carboxyl equivalent of the polyamic acid to be neutralized.
In general, and particularly preferably 40 to 100 mol%. By performing the neutralization in this manner, the polyamic acid becomes completely water-soluble or partially solubilized to become a suspended state and becomes water-dilutable. In any case, by neutralizing the polyamic acid and diluting it with water so as to have a resin concentration of the following degree, an electrophoretic bath for forming a film made of a polyamic acid aqueous solution that can be subjected to an electrophoretic treatment. You can do it.

The organic solvent used for producing the polyamic acid may be present in the polyamic acid aqueous solution thus obtained,
Although it may be added separately, the amount of addition is preferably 0.1 to 15 times by weight of the polyamic acid used. A metal body whose film is to be formed is immersed in an electrophoresis bath (hereinafter simply referred to as a bath) made of a water-soluble polyamic acid, and electrophoresis is performed using the metal body as an anode.

At this time, a filler or a coloring agent such as titanium oxide, iron oxide, alumina, barium sulfate or the like may be added to the bath. The resin concentration of the bath is usually 2 to 30% by weight, more preferably 3 to 20% by weight. As described above, the electrophoresis treatment usually involves immersing a metal to be coated in a bath, using the metal body as an anode, and using a bathtub wall or a counter electrode of an inert metal as a cathode.
This is performed by applying a voltage of ~ 300 volts. Electrophoresis may be performed at a constant current as needed. In this case, the current density is usually 5 to 200 mA / dm ² . The film-forming component of the neutralized polyamic acid salt dispersed in water is usually negatively charged, moves to the metal body serving as the anode, loses charge on the surface of the metal body, and becomes insoluble in water. Is deposited to form a polyamic acid resin film on the surface of the metal body, thereby covering the surface of the metal body.

In the present invention, the metal body for forming the coating is iron,
Any molded body of aluminum, copper, zinc, and other various alloys may be used. Further, the shape of the metal body is not limited at all, and for example, it is possible to form and cover a film even if it is cylindrical or bag-shaped. Thus, according to the present invention, a coating having an extremely uniform coating which cannot be achieved by a normal spraying method, an immersion method or the like is formed even on a material having a hanging shape.

In the present invention, the film-forming metal body thus pulled out of the bath is usually washed with water (the polyamic acid is not desorbed from the metal surface by washing with water since the film has already been insolubilized). About 380 ° C, preferably 180
~ 350 ° C, time required, usually 10 minutes ~ 15 hours,
By imidizing the polyamic acid forming the coating by performing a heat treatment for preferably about 15 minutes to 10 hours, more preferably about 30 minutes to 8 hours, a very tough polyimide resin coating is formed on the metal surface. Because In the heat treatment, it is not preferable to raise the temperature rapidly because it involves firing, and it is preferable to increase the temperature gradually or stepwise. As a device for performing the heat treatment, a normal dryer can be used. For example, a hot-air dryer, a far-infrared dryer, or the like can be suitably used at normal pressure or reduced pressure.

The thickness of the imide film formed on the surface of the metal body is usually 2 to 2.
It is about 50 μ, preferably about 5 to 40 μ.

In the present invention, the coating obtained by such a method has excellent adhesion to metal and does not change even when exposed to a temperature of 300 ° C. or more for a long time, and also has corrosion resistance, adhesion,
The insulation is also very good.

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

Examples In the following examples, the logarithmic viscosity is 35 ° C., 0.5 g / 100 ml
It is a value measured with N, N-dimethylacetamide. The property evaluation shown in the examples and comparative examples was performed according to the following methods.

(A) Adhesion Measured according to JIS-K-5400 6.15.

(B) Withstand voltage It was sequentially determined whether or not the voltage was 2 KV according to JIS-C-2110.

Example 1 In a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube,
53.0 g (0.25 mol) of 3,3′-diaminobenzophenone was added to N,
It was dissolved in 240 ml of N-dimethylacetamide. In this solution
3,3'4,4'-benzophenonetetracarboxylic dianhydride
77.6 g (0.241 mol) of powder was added and stirred at 10 ° C. for 24 hours to obtain a polyamic acid solution. The logarithmic viscosity of the obtained polyamic acid was 0.5 dl / g. 38.6 g of dimethylethanolamine (90 mol% based on carboxyl equivalent) was gradually added to the polyamic acid solution, and the mixture was stirred at room temperature for 20 minutes.
6.8 g was gradually added at room temperature with stirring and diluted with water to prepare a polyamic acid aqueous solution (resin concentration: 10% by weight). Put this aqueous solution into a plastic tank and use it as an electrophoresis bath for forming a coating.Immerse an aluminum plate to be coated as an anode, immerse a lead plate as a cathode, and apply a voltage of 100 V for 10 minutes to perform electrophoresis. went. Thereafter, the aluminum plate was taken out, washed with water, and subjected to dry imidization by heat treatment at 150 ° C. for 2 hours and 280 ° C. for 2 hours. The thickness of the polyimide acid resin film after the heat treatment was 20 μm. The result of the adhesion test was 100/100, and the withstand voltage was also a pass. Further, the test plate was exposed to high temperature at 300 ° C. for 240 hours, and the same test was performed. It was confirmed that the same result was obtained.

Example 2 A container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube was charged with 2,2.
2'-bis [4- (3-aminophenoxy) phenyl]
41.0 g (0.1 mol) of propane and 200 ml of N, N-dimethylacetamide were charged, cooled to about 0 ° C., and a powder of 20.93 g (0.096 mol) of pyromellitic dianhydride was added under a nitrogen atmosphere. The mixture was stirred at around 0 ° C. for 2 hours. Next, the solution was returned to room temperature and stirred under a nitrogen atmosphere for about 20 hours. The logarithmic viscosity of the polyamic acid solution thus obtained is
It was 0.4 dl / g. To this polyamic acid solution, 17.7 g of triethylamine (100 mol% based on carboxyl equivalent) was gradually added, and the mixture was stirred at room temperature for 1 hour. Then, 960 g of water was gradually added with stirring to dilute the polyamic acid aqueous solution ( Resin concentration 5% by weight). The aqueous solution is put into a stainless steel bath to form an electrophoresis bath for film formation, and a cylindrical galvanized steel sheet to be coated is immersed as an anode, and the bath is used as a cathode for 75 minutes.
Electrophoresis was performed by applying a voltage of V for 5 minutes. After that, take out the galvanized steel sheet, wash it with water, 120 ° C for 1 hour, 180 ° C2
Imidation was performed by heat treatment at 280 ° C. for 2 hours. The thickness of the polyimide resin film after the heat treatment was 22 μm for both the cylindrical inner wall and the outer wall. The result of the adhesion test under normal conditions was 100/100, and the withstand voltage was a pass. Further, the test plate was exposed to high temperature at 300 ° C. for 240 hours, and the same test was performed. It was confirmed that the same result was obtained.

Example 3 In a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube,
2,2-bis [4- (3-aminophenoxy) phenyl]
Add 41.0 g (0.1 mol) of propane and 219.6 g of N, N-dimethylacetamide, and add 3,3 ′, 4,
4'-benzophenonetetracarboxylic dianhydride 29.28
(0.091 mol) as a dry solid while adding the solution temperature carefully, while reacting at room temperature for 23 hours. The logarithmic viscosity of the polyamic acid thus obtained was 0.07 dl / g. Triethanolamine 8.
1 g (relative to carboxyl equivalent 50 mol%) was gradually added, and the mixture was stirred at 40 ° C. for 2 hours, and 170.6 g of water was gradually added and diluted to prepare a polyamic acid aqueous solution (resin concentration: 15% by weight). This aqueous solution was immersed in an aluminum plate as an anode and electrophoresed at 125 V for 5 minutes in the same manner as in Example 1. The polyamic acid aqueous solution adhering to the surface of the plate taken out of the bath was removed with dry air, and then 150 ° C. for 1 hour, then 260 ° C.
Dry imidization was performed by heat treatment at 2 ° C. for 2 hours. The thickness of the polyimide resin film after the heat treatment was 25 μm. The result of the adhesion test under normal conditions was 100/100, and the withstand voltage was also a pass. Further, the test plate was exposed to a high temperature of 300 ° C. for 240 hours, and the same test was performed. The same result was obtained.

Example 4 In the same manner as in Example 1, 73.0 g (0.25 mol) of 1,3-bis (3-aminophenoxy) benzene was dissolved in 240 ml of N, N-dimethylacetamide, and 3,3 ′, 4,4 74.1 g (0.230 mol) of 4'-benzophenonetetracarboxylic dianhydride
Was added and stirred at 10 ° C. for 24 hours to obtain a polyamic acid solution. The logarithmic viscosity of the obtained polyamic acid is 0.1 dl / g
Met. 32.8 g of dimethylethanolamine (80 mol% based on carboxyl equivalent) was gradually added to the polyamic acid solution, and the mixture was stirred at room temperature for 20 minutes. Then, 1419 g of water was gradually added at room temperature while stirring to prepare a polyamic acid aqueous solution ( Resin concentration 8% by weight). Put this aqueous solution into a plastic tank,
Using an aluminum plate to be coated as an anode and a lead plate as a cathode, voltage migration was performed up to a voltage upper limit of 150 V at a current density of 70 mA / d. Thereafter, the aluminum plate was taken out, washed with water, and subjected to dry imidization by heat treatment at 150 ° C. for 2 hours and 280 ° C. for 2 hours. The thickness of the polyimide resin film after the heat treatment was 20 μm. The results of the adhesion test
100/100, withstand voltage was also pass. Add this test plate to 300
Exposure to a high temperature of 240 ° C. and the same test gave the same results.

Example 5 In the same manner as in Example 1, 4,4'-bis (3-aminophenoxy) biphenyl 92 (0.25 mol) was dissolved in 240 ml of N, N-dimethylacetamide, and 54.4 g (0.240 mol) of pyrrolimetic anhydride was added to this solution. Mol), and stirred at 10 ° C. for 24 hours to obtain a polyamic acid solution. The logarithm of the obtained polyamic acid was 0.25 dl / g in viscosity. 21.4 g of dimethylethanolamine (relative to carboxyl equivalent 50 mol%) was gradually added to the polyamic acid solution, and the mixture was stirred at room temperature for 20 minutes.
1056 g of water was gradually added at room temperature with stirring to prepare a polyamic acid aqueous solution (resin concentration: 10% by weight). In the same manner as in Example 1 using this aqueous solution, an aluminum plate was
Electrode migration was performed by applying a voltage of V for 10 minutes. After that, take out the aluminum plate, wash it with water and 280 ℃ at 150 ℃ for 2 hours.
For 2 hours to carry out dry imidization. The thickness of the polyimide resin film after the heat treatment was 20 μm. The result of the adhesion test was 100/100, and the withstand voltage was also a pass. Furthermore, this test plate was exposed to high temperature of 300 ° C for 240 hours,
The same test yielded the same results.

Comparative Example-1 As in Example 1-1, 53.0 g (0.25 mol) of 3,3'-diaminobenzophenone and 78.9 g (0.254 mol) of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride were obtained. The reaction was performed to obtain a polyamic acid having a logarithmic viscosity of 0.8 dl / g. Example-
Neutralization, water-solubilization, electrodeposition, washing with water and dry imidization were carried out in the same manner as in Example 1 to obtain a polyimide-coated aluminum plate. The thickness of the polyimide resin film was 23μ. Although the result of the adhesion test was 100/100, which was good, insulation failure occurred due to the withstand voltage in a normal state. Further, the same test plate was subjected to high-temperature exposure at 300 ° C. for 240 hours, and the same test was performed. As a result, the adhesion test was 100/100, and the withstand voltage was poor insulation.

Comparative Example-2 53.0 g (0.25 mol) of 3,3'-diaminobenzophenone and 71.2 g (0.221 mol) of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride in the same manner as in Example 1-1. Was reacted to obtain a polyamic acid having a logarithmic viscosity of 0.03 dl / g. Example-
Neutralization, water-solubilization, electrodeposition, washing with water, and dry imidization were performed in the same manner as in Example 1, but no continuous film was formed.

Claims (1)

(57) [Claims] (1) General formula (Here, 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 bridge member. A tetravalent group selected from the group consisting of non-fused polycyclic aromatic groups,
₂ represents a divalent aromatic group selected from the following groups. ) Consisting of a repeating unit represented by the formula, the logarithmic viscosity is 0.05 to
The carboxyl group of the polyamic acid of 0.6 dl / g is neutralized with a base and diluted with water to form a film forming electrophoresis bath, a metal body to be formed a film is immersed in the bath, and the metal body is used as an anode. A method for coating a metal, comprising performing electrophoresis to precipitate the polyamic acid on the surface of the metal body to form a film, and then performing a heat treatment to imidize the film.