JPH0633262A - Surface coating method of aluminum or aluminum alloy base body - Google Patents

Abstract

PURPOSE:To form a multilayer film excellent in insulating property by applying electrodeposition coating on a ceramic coating film formed by an anodic spark discharge method on the surface of an aluminum metal base body. CONSTITUTION:A ceramic coating film is formed by an anodic spark discharging on the surface of an Al or alloy base body. Further, an electrodeposition coating film is formed on the ceramic film. By this method, excellent insulating property can be imparted to an Al die-cast or cast product. As for anodic spark discharging method, such a method is preferable that the Al base body is dipped in the electrolytic bath of an aq. soln. containing water-soluble or colloidal silicate and/or oxoacid, or suspension of ceramic fine particles in the soln. As for the electrodeposition coating, it is preferable that the ceramic film is sufficiently washed with deionized water or the like, hydro-extracted and dried, and then dipped in a cation electrodeposition coating material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the surface coating of aluminum and aluminum alloy substrates using the anodic spark discharge method and the electrodeposition coating method, which forms a multi-layer coating having excellent insulating properties on the surface of aluminum and aluminum alloy substrates. It is about the method.

[0002]

2. Description of the Related Art Various methods are known as methods for forming surface coatings having different characteristics on an aluminum material such as an aluminum or aluminum alloy substrate. For example, a method of forming a ceramic film by an anode spark discharge method to impart corrosion resistance is known (Japanese Patent Publication No. 58-17278, Japanese Patent Publication No. 59-45722, Japanese Patent Publication No. 60-12438). It has been shown that the formation of a ceramic film by this method improves the corrosion resistance as a whole. On the other hand, the electrodeposition coating method is also known as a method for forming a surface coating. On aluminum material such as aluminum or aluminum alloy substrate,
When the electrodeposition coating method is applied, the aluminum material is first subjected to a phosphoric acid conversion film treatment, a chromate film treatment, an anodization and the like as a base treatment. When a ceramic film is formed on an aluminum material such as an aluminum or aluminum alloy substrate, the insulating property is improved, but there is no known method capable of further improving the insulating property.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method capable of improving the insulating property of a material having a ceramic film formed on the surface of an aluminum or aluminum alloy material.

[0004]

The present invention has been made based on the finding that the above object can be efficiently achieved by forming an electrodeposition coating film on a ceramic film formed on the surface of an aluminum or aluminum alloy material. Of.
That is, the present invention provides a surface coating method for an aluminum or aluminum alloy substrate, which comprises subjecting a ceramic film formed on the surface of an aluminum or aluminum alloy substrate by an anode spark discharge method to electrodeposition coating. Examples of the aluminum substrate used in the present invention include aluminum and aluminum alloys. A film can be evenly formed on complicated shaped products such as aluminum die castings and castings. In the present invention, first, a ceramic film is formed on an aluminum substrate by the anodic spark discharge method. As a method and composition for forming a ceramic film by the anode spark discharge method, those described in JP-B-58-17298 and JP-A-3-94077 can be used. More specifically, as an anode spark discharge method for forming a ceramic film, an aqueous solution containing a water-soluble or colloidal silicate and / or oxyacid salt or an electrolytic bath in which ceramic fine particles are suspended is used. A method in which an aluminum-based material is dipped in to perform anode spark discharge is preferable.

Here, as the silicate, general M ₂ O.
nSiO ₂ (M is an alkali metal, n is 0.5 to 100)
Various types of water-soluble substances such as sodium silicate, potassium silicate, and lithium silicate, and water-dispersible substances include colloidal silica and the like. Examples of the oxyacid salt include tungstic acid, stannate, molybdic acid, borate, aluminate, phosphate and the like, or a mixture of two or more thereof. In the present invention, the silicate or oxygenate can be used alone, as a mixture of two or more kinds, or as a mixture of both. Furthermore, addition of a soluble inorganic fluorine compound to an aqueous solution is effective in promoting formation of a spark discharge film. As the soluble inorganic fluorine compound used here, HF, NaF, KF, HBF ₄ , NaBF ₄ , KBF ₄ , H ₂ SiF ₈ ,
Na ₂ SiF ₅ , K ₂ SiF _8, etc. can be increased. Further, various insoluble and dispersible ceramic fine particles may be suspended in the electrolytic bath. For example, Al ₂ O ₃ , Al (OH) ₃ , SiO ₂ ,
_{3Al 2 O 3 · 2SiO 2,} TiO 2, ZrO 2, partially stabilized zirconia, stabilized zirconia, oxide ceramics or SiC, such as _{Cr 2 O 3, TiC, TiN} , TiB, ZrB, BN, WC, WS
Non-oxide ceramics such as i ₂ and MoSi ₂ can be cited. These may be used alone or as a mixture of two or more kinds (Japanese Patent Application Nos. 1-228639 and 2-54827). Among these, in particular, as the bath type, it is preferable to use a bath containing silicate, a suspension of ceramic fine particles, or a suspension of ceramic fine particles in an oxyacid salt.

Water-soluble in an aqueous solution used for the electrolytic bath or
Colloidal silicate and / or oxygenate concentration is 5 g /
Liter or more is preferable, and 25 to 200 g / liter is preferable.
It is suitable. Especially for oxygenates, if the concentration is close to saturation,
The film formation speed increases the most, but forms with increasing concentration
The phenomenon that the formed film becomes non-uniform is likely to occur.
The above concentration is preferable. The pH of the aqueous solution is arbitrary
However, it is good to set it to 3 to 13.5. Usually these metal substrates
No special pretreatment is required when forming a spark discharge film on the
It may be fine, but degreasing, etching, pickling, etc.
It is desirable to clean it. Also, boehmite treatment etc.
No preparation is required. For the cathode, iron, stainless steel,
An insoluble electrode such as nickel is used. Bath for spark discharge
The temperature is preferably 5 to 90 ° C, preferably 15 to 60 ° C.
More preferable. Formation rate of film by spark discharge at low temperature
On the other hand, the formed film is non-uniform at high temperatures
It is easy to become. Electrolysis is performed by the constant current method,
Flow density is 0.2 to 20 A / dm²Good to do in
1-5 A / dm ²Is. Sparks are uniformly emitted over the entire surface of the sample.
Electrolyze for 1 to 30 minutes after birth. Preferably 2-10
It's a minute. Also, the voltage at the end of electrolysis reaches 150 V or higher.
Must be done, especially above 300V and below 500V
The bottom is desirable. The output of the rectifier may be a direct current of any wave size.
, Pulse waveform (rectangular waveform), sawtooth waveform or DC
Half-wave waveforms are preferred. More pulse waveforms and sawtooth waveforms
preferable. The thickness of the spark discharge coating can be arbitrary
However, it should be 1 to 30 μ, preferably 3 to 10 μ.
Yes.

In the present invention, electrodeposition coating can be carried out by a conventional method. For example, in the "Painting Dictionary" published by Asakura Shoten, pages 154 to 161 and the section "5.9 Electrodeposition coating" and "Painting Technology Handbook", published by Nikkan Kogyo Shimbun, page 196 to page 161. See pages 205 and 293-307. In the present invention, the ceramic film formed by anodic spark discharge should be thoroughly washed with deionized water or the like, preferably drained and dried, and then immersed in an electrodeposition coating solution for electrodeposition. The types of electrodeposition coatings are roughly classified into cation type and anion type, but cation type electrodeposition coatings are preferable. The cationic electrodeposition paint used here may be of any type, and examples thereof include epoxy type and acrylic type. Epoxy resins are preferred for use for the purpose of corrosion resistance. On the other hand, examples of the anionic electrodeposition coating material include coating materials using a polycarboxylic acid resin having a main skeleton of a drying oil, polybutadiene, epoxy ester, polyacrylic acid ester, acryl melamine type and the like. The liquid temperature, the stirring of the paint, the anode, etc. should be in accordance with the properties of the paint used, and generally in the epoxy cationic electrodeposition paint,
The liquid temperature is 25 to 30 ° C., and the anode is a diaphragm anode using an Anion exchange diaphragm. The energization method is basically a constant voltage method, and there are a so-called Dokan method in which a predetermined voltage is applied from the start of energization and a slow start method in which the voltage is gradually increased from the start, but the slow start method is more preferable. .
The voltage is determined by the properties of the paint and the required film thickness, but is 10 to 50 V from the optimum voltage by general pretreatment.
It is better to raise it. It is 190 to 350 V for the epoxy-based cationic electrodeposition coating. The thickness of the cationic electrodeposition coating film may be arbitrary, but it is 3 to 50 μm, preferably 10 μm.
It is preferable to set it to -30 μ. After the electrodeposition process, it is preferable to perform the baking process in a baking furnace. Although the conditions vary depending on the type of paint, it is usually good to carry out at 130 to 230 ° C. for 10 to 60 minutes.

[0008]

According to the present invention, excellent insulating properties can be imparted to aluminum parts, particularly die castings and casting parts, which are increasingly used due to the demand for recycling and weight reduction. Therefore, the aluminum and aluminum alloy materials on which the multilayer film is formed by the method of the present invention are expected to be widely used due to their properties such as weight reduction and general properties such as corrosion resistance and excellent insulating properties. There is. Further, by forming this multilayer film on an aluminum wire or an electric wire having aluminum as the outermost layer, for example, an aluminum clad electric wire, an excellent insulated covered electric wire can be obtained. Next, the present invention will be described with reference to examples.

[0009]

【Example】

Example 1 An aluminum die casting part (JIS ADC-12 material) was degreased, activated and cleaned, and then immersed in a K ₂ O-nSiO ₂ solution (200 g / liter) to form a ceramic film of 5 μm by a spark discharge method. . Washing was sufficiently performed with city water and ion-exchanged water, and drained and dried at 130 ° C. for 10 minutes. After cooling, an epoxy-cationic electrodeposition coating composition (Dipsol Co., Ltd., trade name ED-63) consisting of an epoxy-polyamide resin and a pigment (titanium white, carbon, etc.), a solvent and a neutralizer
0), liquid temperature 28 ℃, voltage 220V, electrodeposition, 1
It was baked at 80 ° C. for 20 minutes. As a result, a beautiful cationic electrodeposition coating film of 15 μm without cissing, dents, pinholes, bumps, etc. was formed. Example 2 An aluminum die-cast component similar to that of Example 1 was cleaned in the same manner and then K ₂ O—nSiO ₂ , 200 g / liter, NaF 4,
It was dipped in a g / l liquid and a 5 μm ceramics film was formed by a spark discharge method. Then, after washing and drying in the same manner as in Example 1, cationic electrodeposition coating was performed under the same conditions. As a result, a beautiful 15 μm cationic electrodeposition coating film was formed.

Example 3 An aluminum die-cast component similar to that of Example 1 was cleaned in the same manner, and then Cr ₂ O ₂ fine particles (Nihon Denko Co., Ltd.) were added to an aqueous solution of Na ₄ P ₂ O ₁₇ · 10H ₂ O of 80 g / liter. ), Product name, ND-8
02, average particle diameter 0.7 μm) In a solution in which 50 g / liter was suspended, a ceramic film of 3 μm was formed by a spark discharge method. Then, after washing and drying in the same manner as in Example 1, the same cationic electrodeposition coating material was electrodeposited at a liquid temperature of 280 ° C. and a voltage of 240 V, and baked at 180 ° C. for 20 minutes.
As a result, a beautiful cationic electrodeposition coating film of 11 μm without cissing, dents, pinholes, bumps or the like was formed.

Example 4 A ceramic film was formed on the same substrate as in Example 1 by the same operation as in Example 1, and the same washing and drying were performed. After left to cool, polybutadiene resin and pigment (white titanium,
Carbon, etc.), an anionic electrodeposition paint (Kansai Paint Co., Ltd., trade name # 7200) consisting of a solvent and a neutralizing agent, and is electrodeposited at a liquid temperature of 28 ° C. and a voltage of 110 V to 180 ° C.
Baked for 20 minutes. As a result, a beautiful 15 μm anion electrodeposition coating film without cissing, dents, pinholes or bumps was formed. Comparative Example 1 The same aluminum die casting component as in Example 1 was blasted, degreased, etched, activated and cleaned, and then chromated (Dipsol Co., Ltd., AL-710).
A, 20 ml / liter, AL-710B, 3 g / liter), followed by cation electrodeposition coating under the same conditions as in Example 1, except that the chromate film treatment was followed by water washing and drying. Comparative Example 2 A ceramic film was formed on the same parts as in Example 1 by the same operation by the spark discharge method, and washing and drying were performed in the same manner. However, electrodeposition coating was not performed.

The dielectric breakdown voltage of the aluminum substrate having the multilayer coating on the surface obtained in the above Examples and Comparative Examples was measured as follows. Dielectric breakdown voltage Measured with a breakdown voltage meter B-5110AF type (manufactured by Faith Co., Ltd.) by a method according to the varnish coating film test method of the insulation strength test method of JIS C2110 solid electrical insulating material. The results are shown below.

[Table 1] Table-1

Claims (1)

[Claims] 1. A method of coating a surface of an aluminum or aluminum alloy substrate, which comprises performing electrodeposition coating on a ceramic film formed on the surface of an aluminum or aluminum alloy substrate by an anode spark discharge method.