JPH0535236B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a coating method for obtaining a colored electrodeposition coating film with excellent adhesion, corrosion resistance, and weather resistance on the surface of aluminum or aluminum alloy (hereinafter simply referred to as aluminum). [Technical background of the invention and its problems] In order to form a coating film with good adhesion on the surface of aluminum, a surface treatment is performed in advance to form appropriate irregularities on the surface of the aluminum material to be coated. In this case, the means for forming the unevenness include (a) mechanical methods such as sandblasting and liquid honing, and (b) chemical methods such as immersion in a single bath of hydrochloric acid, nitric acid, hydrofluoric acid, or sulfuric acid or a mixed bath of these. method,
(c) Electrochemical methods include direct current or alternating current electrolysis in an aqueous solution containing chlorine, nitric acid, or a mixed aqueous solution of other acids, and then a chemical film such as a boehmite film or a chromic acid film is formed on the aluminum surface, or The method used is to apply an anodized film using sulfuric acid, oxalic acid, or phosphoric acid as an electrolyte and then paint. However, if the surface of aluminum is painted with moderate irregularities, there will be no problems with the adhesion of the paint film, but the paint film will have difficulty adhering to the raised parts of the base, resulting in poor corrosion resistance, making it difficult to use outdoors. In this case, a lot of corrosion occurs, and in terms of weather resistance, it is easy to cause corrosion, so the gloss of the coating film is significantly reduced, and it cannot be used as an exterior material. [Purpose of the Invention] This invention was developed in order to solve the above problem, and when applying colored coating to the surface of aluminum, it is necessary to apply a unique base treatment to the surface of the material to be coated in advance. The purpose is to establish a new coating method that can obtain a colored electrodeposition coating film with excellent adhesion, corrosion resistance, and weather resistance by applying two layers of electrodeposition coating under specific conditions. It is something. [Summary of the Invention] In order to achieve the above object, the colored electrodeposition coating method for aluminum according to the present invention involves applying a milky white or satin finish treatment to the surface of a material to be coated by a conventional method, and then
Acid value 10-150, glass transition temperature 0-40℃, degree of neutralization
Colored electrodeposition coating is performed using an anionic synthetic resin vehicle with acrylic properties of 50 to 120, and then further coated without drying with an acid value of 10 to 150, a glass transition temperature of 0 to 40°C, and a degree of neutralization of 70 to 120. This method is characterized by applying a clear electrodeposition coating using a transparent anionic synthetic resin having acrylic properties as a vehicle, and then baking and drying the coating film. Hereinafter, the colored electrodeposition coating method for aluminum according to the present invention will be explained in more detail in the order of steps. In the case of the present invention, in the first step, the surface of the aluminum is subjected to a milky white or matte finish treatment, but prior to this, degreasing is performed. , Perform pretreatment using conventional methods such as washing to remove oily substances adhering to the surface of the material to be coated. Suitable methods for milky white or matte finish in this process include a chemical method of immersion in an acidic etching agent such as sulfuric acid, nitric acid, or hydrochloric acid, and an electrochemical method of anodizing using hydrochloric acid, sodium chloride, or ammonium chloride. However, in any case, the treatment in this step is to at least coat the surface of the aluminum in order to form a coating film with good adhesion during electrodeposition coating in the subsequent process.
A milky white or satin finish treatment with a surface roughness of 0.5 μmRa or more is required; if the surface roughness is less than 0.5 μmRa, a coating film with good adhesion cannot be formed, probably because the anchoring effect is small. In the case of the former chemical method, when using sulfuric acid or nitric acid as the etching agent, aluminum is preferably immersed in an acidic aqueous solution with a concentration of 5% or more (upper limit is 30%) and a bath temperature of 40 to 80°C for 20 minutes or more.
When soaking for 30 to 80 minutes and using hydrochloric acid as an etching agent, the concentration is 5% or more (upper limit is 20%),
Aluminum is added in an acidic aqueous solution with a bath temperature of 20 to 40℃.
It is sufficient to carry out the immersion treatment for at least 1 minute, preferably 10 to 30 minutes, and it is also possible to use a mixed acid of these. On the other hand, in the case of the latter electrochemical method,
Using hydrochloric acid, sodium chloride, or ammonium chloride as an electrolyte, aluminum is anodized at a chlorine concentration of 1 to 2%, a bath temperature of 30 to 80° C., and 0.01 to 0.1 A/cm ² and 6 to 30 chrome/cm ² . In addition to the above-mentioned method, mechanical methods such as sandblasting and liquid honing can also be used to produce a milky white or matte finish with a surface roughness of 0.5 μmRa. Next, a boehmite film, a chromic acid-based chemical film, or an anodized film using an electrolyte such as sulfuric acid, oxalic acid, or phosphoric acid is applied to the surface of the material to be coated. These treatments are carried out for the purpose of stabilizing the shape of the unevenness obtained in the previous milky-white or matte finish treatment step and imparting corrosion resistance to the aluminum base material. At that time, the boehmite film is formed by immersing it in boiling water or an alkaline bath containing an amine compound such as triethanolamine in the boiling water for 3 to 30 minutes. The immersion is carried out in an aqueous solution containing dichromic acid as a main component at a bath temperature of 20 to 40°C and a immersion time of 1 to 5 minutes. The anodic oxide film may be a general sulfuric acid alumite, for example, aluminum is immersed in an aqueous solution with a sulfuric acid concentration of 15% at a bath temperature of 20°C and a current density of 1A/dm ^{2 .}
An anodic oxide film with a thickness of 6 μm or more is formed under the following electrolytic conditions, and then washed with hot water at 60 to 80°C for 2 to 10 minutes. Note that even without applying these chemical coatings or anodic oxidation coatings, the adhesion is sufficiently improved due to the anchoring effect due to the unevenness obtained in the milky white or satin finish treatment in the previous step. In the method of the present invention, aluminum that has undergone the above-mentioned surface treatment is sequentially subjected to colored electrodeposition using enamel electrodeposition and clear electrodeposition using transparent resin paint, and finally, the coating film is baked and dried. (This two-coat electrodeposition coating method was first developed by the present applicant for the purpose of improving the weather resistance of colored coatings, and has already been published in Japanese Patent Application No. 59-279532 (Patent Publication No. 4-34637).
However, for the first coat of colored electrodeposition coating, acid value is 10 to 150, glass transition temperature is 0 to 40℃,
Use an enamel electrodeposition paint bath of the desired color using an anionic synthetic resin with acrylic properties with a neutralization degree of 50 to 120 as a vehicle, and adjust the bath temperature to an appropriate level depending on the type of material to be coated, coating thickness, etc. Electrodeposition coating is performed by selecting the solid content, DC applied voltage, and processing time, and for the second coat of clear electrodeposition coating, an acid value of 10 to 150,
We use a clear electrodeposition paint bath whose vehicle is a transparent anionic synthetic resin with acrylic properties with a glass transition temperature of 0 to 40°C and a degree of neutralization of 70 to 120.The type of material to be coated, coating thickness, etc. Electrodeposition coating is performed by selecting the bath temperature, solid content, DC applied voltage, and treatment time according to the conditions, and then the coating film is baked and dried. In this case, after the first coat of enamel film is formed, baking drying is not performed, and the second coat of clear coat is applied with a voltage higher than the voltage used to form the first coat of wet film. Do this. When a two-layered coating film is formed on the surface of the material to be coated using the method described above, the first coat of colored enamel coating is mixed with the anodized coating on the base material surface, which has been appropriately roughened by the surface treatment. It has perfect adhesion and excellent corrosion resistance, and this is further protected by the second clear coating, which not only gives the coating an extremely high gloss and a vivid color tone, but also allows for colored coatings. Since yoking, which is a defect of the film, is completely prevented, the weather resistance of the entire coating film is significantly improved, and a colored electrodeposition coating film that is completely ideal in terms of both performance and aesthetics can be obtained. [Examples of the Invention] Hereinafter, three typical examples and two comparative examples of the present invention will be listed, and the embodiments thereof will be specifically explained, but the present invention is not limited to these examples only. It's not a thing. Example 1 150×70×1.8t aluminum extrusion shape (JIS
A6063S-T ₅ ) was used as a test piece, and after degreasing in a conventional manner, it was placed in a 10% sulfuric acid aqueous solution at a bath temperature of 80°C.
It was immersed for 60 minutes at ℃ to obtain a satin appearance with a surface roughness of 0.7 μm Ra. Next, sulfuric acid concentration 15%, bath temperature 20℃
Anodization treatment was carried out for 30 minutes in an electrolytic solution at a current density of 1.0 A/dm ² . This test piece was used as a beige-colored enamel electrodeposition paint (manufactured by Shinto Paint Co., Ltd.) with a solid content of 12% and using an anionic synthetic resin vehicle with an acid value of 55, glass transition temperature of 28°C, and medium acrylic properties of 70%. Bath temperature 22℃ in the bath
A DC voltage of 150V was applied and electrodeposition was performed for 2 minutes. Next, after washing this with water, the solid content is prepared using an anionic synthetic resin as a vehicle, which has acrylic properties with an acid value of 31, a glass transition temperature of 26°C, and a degree of neutralization of 70%.
Apply a DC voltage of 250V in a 10% clear electrodeposition paint (manufactured by Shinto Paint Co., Ltd.) bath at a bath temperature of 22℃, perform electrodeposition for 2 minutes, and after washing with water, apply it for 30 minutes at a temperature of 180℃. After baking and drying, a test piece with a film thickness of 22 μm and a good beige appearance was obtained. Table 1 shows the results of the coating film adhesion, impact test, and due cycle test for this test piece. Example 2 150×70×1.8t aluminum extrusion shape (JIS
A6063S-T ₅ ) was used as a test piece, and after degreasing using a conventional method, it was placed in a 10% nitric acid aqueous solution at a bath temperature of 80°C.
It was immersed at ℃ for 50 minutes to obtain a matte appearance with a surface roughness of 0.8 μm Ra. Next, sulfuric acid concentration 15%, bath temperature 20℃
Anodization treatment was carried out for 30 minutes in an electrolytic solution at a current density of 1.0 A/dm ² . This test piece was used as a beige-colored enamel electrodeposition paint (manufactured by Shinto Paint Co., Ltd.) with a solid content of 12% and using an anionic synthetic resin vehicle with an acid value of 55, glass transition temperature of 28°C, and medium acrylic properties of 70%. Bath temperature 22℃ in the bath
A DC voltage of 150V was applied and electrodeposition was performed for 2 minutes. Next, after washing this with water, the solid content is prepared using an anionic synthetic resin as a vehicle, which has acrylic properties with an acid value of 31, a glass transition temperature of 26°C, and a degree of neutralization of 70%.
Apply a DC voltage of 250V in a 10% clear electrodeposition paint (manufactured by Shinto Paint Co., Ltd.) bath at a bath temperature of 22℃, perform electrodeposition for 2 minutes, and after washing with water, apply it for 30 minutes at a temperature of 180℃. After baking and drying, a test piece with a film thickness of 22 μm and a good beige appearance was obtained. Table 1 shows the results of the coating film adhesion, impact test, and due cycle test for this test piece. Example 3 150×70×1.8t aluminum extrusion shape (JIS
A6063S-T ₅ ) was used as a test piece, and after degreasing using a conventional method, the bath temperature was 40°C in a sodium chloride aqueous solution with a chlorine concentration of 1.5%, and a current of 0.07 A/dm ² was applied using carbon as the counter electrode. Anodizing was performed at a density of 21 coulombs to obtain a matte appearance with a surface roughness of 0.7 μm Ra. Next, sulfuric acid concentration 15%, bath temperature 20℃
Anodization treatment was carried out for 30 minutes in an electrolytic solution at a current density of 1.0 A/dm ² . This test piece was coated with a beige-colored enamel electrodeposition paint (manufactured by Shinto Paint Co., Ltd.) with a solid content of 12% using an anionic synthetic resin vehicle with an acid value of 55, a glass transition temperature of 28°C, and a degree of neutralization of 70%. ) Bath temperature 22 in the bath
Electrodeposition was carried out for 2 minutes by applying a DC voltage of 150 V at ℃. Next, after washing this with water, the acid value was 31,
250 V at a bath temperature of 22°C in a 10% solids clear electrodeposition paint (manufactured by Shinto Toyo Co., Ltd.) using an anionic synthetic resin vehicle with acrylic characteristics with a glass transition temperature of 26°C and a degree of neutralization of 70%. Electrodeposition was applied for 2 minutes by applying a DC voltage of
After baking and drying for 1 minute, the film thickness was 22 μm.
A test piece with a good beige appearance was obtained. Table 1 shows the results of the coating film adhesion, impact test, and due cycle test for this test piece. Comparative example 1 150 x 70 x 1.8t aluminum extruded shape (JIS
A6063S-T ₅ ) was used as a test piece, and after degreasing using a conventional method, 70g/of caustic soda was added at a bath temperature of 50°C.
It was immersed in a bath at 10°C for 10 minutes to obtain a matte appearance with a surface roughness of 0.3 μmRa. Next, the test piece after the etching treatment was subjected to the same anodizing treatment, enamel coating, and clear coating as in Example 1, and then baked and dried. A test piece exhibiting an external appearance was obtained. Table 1 shows the results of the coating film adhesion, impact test, and due cycle test for this test piece. Comparative example 2 150 x 70 x 1.8t aluminum extruded shape (JIS
A6063S-T ₅ ) was used as a test piece, and after being subjected to the same degreasing treatment, satin finish treatment, and anodization treatment as in Example 2, the acrylic properties of acid value 55, glass transition temperature 28℃, and neutralization degree 70% were evaluated. Beige colored enamel electrodeposition paint with a solid content of 12% using an anionic synthetic resin as a vehicle (manufactured by Shinto Toyo Co., Ltd.) in a bath at 150V at a bath temperature of 22℃.
A DC voltage of 200 mL was applied to perform electrodeposition coating for 2 minutes. Next, this was washed with water and subjected to baking drying treatment at a temperature of 180° C. for 30 minutes, and a test piece with a film thickness of 15 μm and a good beige color appearance was obtained. Table 1 shows the results of the coating film adhesion, impact test, and due cycle test for this test piece.

〔Effect of the invention〕

As described above, if the method of the present invention is used for colored electrodeposition coating of aluminum, colored electrodeposition with excellent adhesion and weather resistance and a beautiful gloss that could not be obtained using conventional techniques can be achieved. Since a coated film can be obtained, it is possible to provide an aluminum material that is optimal for interior and exterior materials of buildings and various kitchen appliances.

Claims (1)

[Claims] 1 After applying a milky white or matte finish treatment to the surface of the material to be painted using a conventional method, an anionic synthetic resin having acrylic properties with an acid value of 10 to 150, a glass transition temperature of 0 to 40°C, and a degree of neutralization of 50 to 120 is applied. Colored electrodeposition coating is applied as a vehicle, and then further acid value 10 is applied without drying.
~150, glass transition temperature 0~40℃, neutralization degree 70~120
1. A method for colored electrodeposition coating of aluminum or aluminum alloy, which comprises applying a clear electrodeposition coating using a transparent anionic synthetic resin having acrylic properties as a vehicle, and then baking and drying the coating film.