JPS62754B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating a coating surface of aluminum (including aluminum alloys).

Conventional methods for treating aluminum as a base for painting include mechanically or electrochemically treating the aluminum surface to form a countless uneven surface and using this surface as an anchor to improve the adhesion of the paint. The paint does not adhere well and pinholes easily appear, and the corrosion resistance after painting is insufficient.
There is also a method of anodizing in sulfuric acid or oxalic acid solution to form an anodized film and using this as a base for painting, but some paints improve adhesion and others do not.For example, silicone resin paint , Fluorine resin paints do not have good adhesion.

This invention provides an aluminum coating surface treatment method that improves the adhesion to all paints, including those with poor adhesiveness such as silicone resin paints and fluororesin paints. An aluminum coating characterized by roughening the surface by chemical or electrochemical treatment and then anodizing the surface in an electrolytic solution containing phosphoric acid as a main component to form an anodic oxide film. It depends on the surface treatment method.

The degree of surface roughening varies depending on the use of the final coated board, but for example, it is 0.2 to 1.0 μHa when precision is required, such as a printing board, and 0.1 to 0.5 μHa when used as an exterior or interior material. For items that undergo post-processing, such as can stock, the roughened surface is anodized in an electrolyte containing phosphoric acid as a main component to form an anodized film on the roughened surface. .

The combination of surface roughening treatment and phosphoric acid anodic oxidation treatment is a feature of the invention, and by performing these treatments in series, a coating base with excellent adhesion to all paints is formed. The thickness of the anodic oxide film to be formed is desirably 0.5 to 3 μm for printing plates, 3 to 9 μm for decorative purposes such as interior and exterior materials, and 0.5 μm or less for processing of can stock and the like.

Anodizing treatment is carried out, for example, in a bath containing 3% phosphoric acid or a small amount of sulfuric acid.
It is carried out at a current density of 3 A/dm ² .

Example After degreasing a JIS1100 aluminum plate according to a conventional method, AC electrolytic etching was performed for 30 seconds at a current density of 40 A/dm ² in a solution containing 1% HNO ₃ and 0.1% HCl to obtain a surface roughness of 0.3 μHa. A uniform rough surface was obtained. In an aqueous solution consisting of 3% phosphoric acid and 2% chromic acid.
After removing etching residue by soaking at 50°C for about 1 minute, it was soaked in a 3% phosphoric acid solution.
Anodic oxidation treatment was performed for 10 minutes at a current density of 0.7 A/dm ² to form an anodic oxide film with a thickness of 1 μm. Next, a silicone resin paint was applied to the surface of the aluminum plate, which had been subjected to the coating primer treatment as described above, and was baked and dried.

In order to examine the adhesion of the paint film, a cross cut was made with a razor and a peeling test (hereinafter referred to as the "primary test") was performed in accordance with JISH8602-1977, and no peeling of the paint film was observed. In addition, this painted board was left in a constant temperature and humidity room at a temperature of 40℃ and a humidity of 90% for 10 days, and then a similar test (hereinafter referred to as a secondary test) was carried out.
However, there was no peeling of the coating, and good coating adhesion was observed.

Comparative Example (1) A JIS 1100 aluminum plate was subjected to electrolytic surface roughening to remove etching residue in the same manner as in the example, and a silicone resin paint was applied thereto and baked and dried. When a secondary test was conducted on this coated board, peeling of the paint film occurred about 2 mm wide from the cross cut portion.

(2) After degreasing a JIS1100 aluminum plate in accordance with a conventional method, a phosphoric acid anodic oxide film similar to that in the example was formed. When a silicone resin paint was applied to this surface, baked and dried, and a primary test was conducted, peeling occurred almost all over the surface.

(3) A JIS1100 aluminum plate was electrolytically etched in the same manner as in the example, and then subjected to a known sulfuric acid anodic oxidation treatment to form an anodic oxide film with a thickness of 1 μm. A silicone resin paint was applied to this surface and baked to dry. When a secondary test was conducted to examine the adhesion of the paint film, some peeling of the paint film occurred.

Claims (1)

[Claims] 1 The feature is that aluminum is treated chemically or electrochemically to roughen the surface, and then the surface is anodized in an electrolyte containing phosphoric acid as the main component to form an anodized film. How to prepare a base for painting aluminum.