JPS6256599A - Method for coating aluminum or aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain freely many kinds of paint films different from each other in surface luster by successively coating the surface of a material to be coated with one of clear and mat paints and with the remaining paint by electrodeposition and by properly setting the thicknesses of the resulting paint films. CONSTITUTION:The pretreated surface of Al or an Al alloy as a material to be coated is subjected to primary coating with one of clear and mat paints by electrodeposition. While the resulting paint film is in the uncured state, secondary coating with the remaining paint is carried out by electrodeposition. The resulting paint films are then dried and baked. The paint films are different from each other in thickness, the thicknesses of the paint films are properly set according to the desired luster, and the surface luster of the coated product is arbitrarily regulated by combining the different thicknesses. The thicknesses of the paint films are easily regulated by changing voltage applied.

Description

Detailed Description of the Invention [Technical Field of the Invention] This invention provides a method of applying two types of electrodeposition paints to the surface of aluminum or Aluminum 11 alloy (hereinafter collectively referred to simply as aluminum) to create a glossy surface. This invention relates to a coating method capable of obtaining a wide variety of different coating films.

[Technical background of the invention and its problems]

Conventionally, in order to form a glossy coating film on the surface of aluminum, anodic oxidation coating or chemical conversion coating treatment was applied in advance to impart corrosion resistance to aluminum 11, which is the material to be coated, and to improve the adhesion of the coating film. After performing electrolytic coloring and other appropriate coloring treatments as necessary, a clear paint such as water-soluble thermosetting acrylic resin paint is electrodeposited on the surface of the film, and the baking process is generally followed by drying. However, recently there has been a gradual increase in demand for products with matte coatings that have low specular gloss.

However, when trying to obtain a coating film with a desired gloss for these painted products, with ordinary electrodeposition paints,
Since the paint itself has its own gloss, no matter how much you try to change the thickness of the paint film, the gloss of the paint film hardly changes, and it is very difficult to freely obtain the desired gloss. In order to arbitrarily obtain various types of gloss, it was necessary to arrange a large number of weight paint tanks for each type of paint in the aluminum surface treatment line and use these selectively.

[Purpose of the invention]

This invention was developed to deal with the above problem, and it is possible to
The electrodeposition coating film made of clear paint and the electrodeposition coating film made of matte paint are applied first, and the thickness of each coating film is set appropriately. The object of the present invention is to provide a new method for coating aluminum that can freely obtain various types of coating films with different degrees of strength.

[Summary of the invention]

The coating method according to the present invention to achieve the above object includes:
In the aluminum painting process, on the surface of the material to be painted,
The first coating is performed using an electrodeposition coating method using either a clear paint or a matte paint, and then the second coating is applied using an electrodeposition coating method using the other paint while this coating remains uncured. After painting, baking of the paint film is characterized by performing a drying process.

The coating method according to the present invention will be explained in more detail below.
In the case of this invention, the surface of the aluminum material to be painted is subjected to the following surface treatment before painting in order to improve the adhesion of the paint film and to impart corrosion resistance to the aluminum itself. put.

The most common method for surface treatment is anodic oxide film treatment, in which aluminum is pretreated using conventional methods such as degreasing and cleaning to remove oils and fats adhering to the surface of the material to be coated. An anodic oxide film with a thickness of about 10 μm is formed by immersing aluminum in 15% aqueous sulfuric acid and electrolytically treating it at a bath temperature of 20°C and a current density of IA/dm. , 2 with boiling water of 60-80℃
Perform hot water washing for ~10 minutes.

In this case, the underlying anodic oxide film is not necessarily limited to the above-mentioned sulfuric acid film, but may also be an oxalic acid film, phosphoric acid film, other chemical conversion film, or boehmite film, and after the anodic oxide film is formed, the film may be electrolytically colored or Coloring treatment such as dyeing may also be applied.

In the coating method of the present invention, aluminum that has been subjected to the above-mentioned surface treatment is coated, and electrodeposition coating with a clear paint and electrodeposition coating with a matte paint are performed in two steps,
For the clear coating, a commonly used water-soluble thermosetting acrylic resin paint (for example, Clear Al-50YB for Aluminum manufactured by Shinto Paint Co., Ltd.) is used, and for the matte coating, a water-soluble thermosetting acrylic resin paint is used. Acrylic resin matte paint (
For example, Nirekron M 3400 manufactured by Kansai Paint Co., Ltd.)
use. The matting method for this paint is to finely disperse the acrylic resin component during the process of water solubilization. This prevents the surface of the paint film from becoming flat, and maintains the unevenness of the paint film during electrodeposition to obtain a matte appearance.

The order of painting is the case where the first coat is electrocoated with a clear paint as the primary coating, and the second coat is electrocoated with a matte paint as the secondary coating, and vice versa.
] There are cases where the first coat is electrocoated with a matte paint, and the second coat is electrocoated with a clear paint as a second coat. The thickness of each coating film is not constant, and an appropriate coating thickness is selected depending on the desired gloss, and the external surface gloss of the coated product can be arbitrarily adjusted by combining these thicknesses. Further, the coating film thickness can be easily adjusted by changing the applied voltage.

Furthermore, in the case of the present invention, after the first coating film is formed, the baking process is not performed without drying, and the second coating is applied while the coating film remains uncured. After performing electrodeposition coating by applying a high voltage equal to or higher than the voltage that formed the film on the first coating, in the final process, the surface coating film during the first and second coating is applied. Baking is done by drying.

When aluminum is subjected to the above series of treatments, a two-layer composite coating film is formed on the surface of the material to be coated, consisting of clear paint and matte paint, and both of these electrodeposited coatings are hidden from light. Since the paint film is formed with a low-strength paint, the upper layer paint film is affected by the lower layer paint film, and the overall gloss varies depending on the paint film thickness of the L lower layer.
By selecting the order of coating and the thickness of the coating, the overall gloss appearance of the coating can be adjusted freely.

Figures 1 and 2 are line graphs comparing these relationships using experimental values, with the surface gloss of the paint film set on the vertical axis, and the type of paint used in the secondary coating and the film thickness set on the horizontal axis. , which shows how the gloss of the entire coating film changes depending on the combination of primary coating and secondary coating.

According to this line graph, the first coat is clear paint, and the second coat is clear paint.
When a matte coating is applied to the first coat (Figure 1), the thickness of the lower layer clear coating has little effect on the upper layer matte coating, and the second coat of matte coating is thicker. As the color increases, the gloss gradually decreases, and the coating thickness reaches 6 μm.
Above this level, the gloss becomes constant, so it becomes possible to adjust the gloss in a range where the film thickness of the matte coating is 6 μm or less.

Coupled with the fact that the second coat of electrodeposition is generally more difficult to perform than the first coat of electrodeposition, it is suitable for adjustment in a high gloss range.

Also, contrary to the above case, the first coat is matte painting,
When clear painting is applied to the second coat (Fig. 2), 1
As the coating film of COATRO's matte coating becomes thinner, the gloss increases, and when the coating thickness becomes 6 pm or more, it becomes difficult to be affected by the coating thickness of the matte coating. On the other hand, the clear paint film of [2 Co. 1-1] gradually increases in gloss as it becomes thicker, and when the film thickness becomes 6 μm or more, the change in gloss decreases, so the clear paint film thickness increases. Gloss can be adjusted at 6 μm or less, making it suitable for adjustment in low gloss bands.

In addition to these coating film thicknesses, when the T base is colored alumite, the gloss may change depending on the shade of the color tone.

[Embodiments of the invention]

Hereinafter, typical examples of the present invention and comparative examples thereof will be listed below, and embodiments will be specifically described, but the present invention is not limited only to these examples.

Example 1 A 6063S aluminum plate was electrolyzed by the usual sulfur electrolysis method to form an anodic oxide film with a thickness of about 10 μm on the surface, and then washed in hot water at a temperature of 80° C. for 5 minutes.

The aluminum plate on which this anodized film was formed was electrocoated for 2 minutes by applying a DC voltage of 100 to 200 μ in a clear electrocoating paint (Al-50YB manufactured by Shinto Toyo Co., Ltd.) at a bath temperature of 22°C. I did this. Next, after washing with water, the bath temperature was 22°C in a matte paint (M 3400 manufactured by Kansai Paint Co., Ltd.).
After applying a DC voltage of 140 to 250 ν at ℃ and performing electrodeposition coating for 2 minutes, it was washed with water and heated at a temperature of 190 ℃ for 30 minutes.
After a minute baking and drying treatment, a good coating film with a 60° specular gloss of 15 to 65 was obtained. Table 1 shows the properties of the obtained coating film.

Comparative Example 1 6 which was subjected to the same anodic oxidation film and hot water washing treatment as in Example 1
053S aluminum plate was electrodeposited for 2 minutes in a clear electrodeposition paint (A 1-50YB manufactured by Shinto Toyo Co., Ltd.) at a bath temperature of 22°C and a DC voltage of 100 to 200V was applied. After that, I washed it with water, baked it for 30 minutes at a temperature of 190°C, and then dried it, resulting in a 60° specular gloss of 98.
~99 coatings were obtained. The properties of the obtained coating film are shown in Table 1-.

Table 1 Example 2 A 6063S aluminum plate was electrolyzed by the usual sulfuric acid electrolysis method to form an anodized film with a thickness of about 10 μm on the surface, and then washed in hot water at a temperature of 80° C. for 5 minutes.

The aluminum plate on which this anodized film was formed was placed in a matte electrodeposition paint (M, 3400 manufactured by Kansai Paint Co., Ltd.) at a bath temperature of 2.
Electrodeposition was performed for 2 minutes by applying a DC voltage of 100 to 150 cm at 2°C.Next, after washing with water, the bath temperature was 22°C in a clear fixed paint (Shinto Toyo Co., Ltd. m Al-50VB).
After applying a DC voltage of 140 to 250 V at ℃ and performing electrodeposition coating for 2 minutes, washing with water and applying a DC voltage of 140 to 250 V at a temperature of 190 ℃ for 30 minutes.
When a drying process was performed during minute baking, a good coating film with a 60° surface gloss of 25 to 98 was obtained. Table 2 shows the properties of the resulting coating film.

Comparative Example 2 6 with the same anodized film and hot water washing treatment as in Example 2
063S aluminum plate was coated with a matte electrodeposition coating (M3400 manufactured by Kansai Paint Co., Ltd.) at a bath temperature of 22°C.
After applying a DC voltage of ~150μ and performing electrodeposition coating for 2 minutes, washing with water and baking at a temperature of 190℃ for 30 minutes and drying, the gloss level at 60℃ was 10 to 30.
A coating film was obtained. Table 2 shows the properties of the resulting coating film.

Table 2 [Effects of the Invention] As described above, if the method of the present invention is applied to coating Aluminum 11, a large number of paint tanks can be coated by combining electrodeposition coating with clear paint and electrodeposition coating with matte paint. It is possible to freely obtain a wide variety of coating films with different surface gloss levels by applying at least two coats.

[Brief explanation of drawings]

Figures 1 and 2 are line graphs showing the relationship between the film thickness of clear coating and the coating thickness of matte coating and surface glossiness during painting.

Claims (1)

[Claims] In the coating process for aluminum or aluminum alloy, the surface of the material to be coated is coated with either clear paint or matte paint by electrodeposition coating, and then this coating film is coated with either clear paint or matte paint. A method for coating aluminum or an aluminum alloy, which comprises performing a second coating using an electrodeposition coating method using the other coating material while the other coating material remains uncured, and then subjecting the coating film to a baking drying treatment.