Anodic Oxidation Dyeing Technology

January 16, 2019

[China Aluminum Network] With the improvement of people's living standards, the demand for home decoration is also increasing, not only requires good performance, but also have bright colors. Powder spraying is in the ascendant, with both good performance and colors that satisfy people. However, the thick powder concealed the metallic luster and regretted it. Anodized dyes just make up for this regret, not only maintain the metallic luster, but also have extremely bright colors, not only can be used in household appliances, automobiles, nameplate logo, etc., but also a good choice for home decoration. This article mainly focuses on anodizing and dyeing of sulfuric acid. It is the author's accumulated experience in the work and is discussed together with everyone.

1 Principle of Oxidation Dyeing It is well known that the anodic oxide film is composed of a large number of hexagonal cells perpendicular to the metal surface. Each unit cell has a film hole in the center and has a strong adsorption force. When the oxidized aluminum product is immersed in the dye In the solution, the dye molecules enter into the pores of the oxide film through diffusion, and simultaneously form covalent bonds and ionic bonds that are difficult to separate from the oxide film. This bond is reversible and desorption occurs under certain conditions. Therefore, after the dyeing process, the pores must be sealed and the dye should be fixed in the film pores to increase the corrosion resistance and wear resistance of the oxide film.

2 Effect of Anodizing Process on Dyeing In the entire process of oxidative dyeing, poor dyeing due to oxidation process is common. The film thickness and the uniform pore size of the oxide film are the premise and basis for obtaining a uniform color when dyeing. In order to obtain a uniform and uniform oxide film, it is important to ensure sufficient circulation quantity, cooling capacity, and good electrical conductivity. In addition, oxidation is important. The stability of the process.

Sulfuric acid concentration is controlled at 180-200 g/l. Slightly higher concentration of sulfuric acid can accelerate the dissolution reaction of the oxide film, facilitate the expansion of the pores, and make it easier to dye;

Aluminum ion concentration, controlled at 5-15g/l. Aluminum ions less than 5g/l, the resulting oxide film has reduced adsorption capacity, affecting the speed of color, aluminum ions greater than 15

At g/l, the uniformity of the oxide film is affected, and irregular film layers tend to occur.

Oxidation temperature is controlled at about 20°C. The effect of oxidation bath temperature on the dyeing is very significant. Too low temperature causes dense film holes in the oxide film, and the dyeing speed is significantly slowed down. The temperature is too high, the oxide film is loose, and the powder is easily pulverized. , is not conducive to the control of dyeing, oxidation tank temperature difference should be within 2 °C is appropriate.

The current density is controlled at 120-180a/m2. If the current density is too large, the electrolysis time of the aluminum product in the bath must be shortened accordingly in the case of a certain film thickness, so that the dissolution of the oxide film in the solution is reduced, the film pores are dense, and the dyeing time is prolonged. At the same time, the film is easily pulverized.

Film thickness, dyeing requirements Oxide film thickness is generally 10µm above the solution. If the film thickness is too low, the dyeing tends to occur unevenly. At the same time, when a dark color (for example, black) is required, the film thickness is insufficient, resulting in a limited amount of dye deposition and the desired color depth cannot be achieved.

In summary, anodization is the pre-process of dyeing and is the basis of dyeing. The problem of anodization is difficult to see or even impossible to see before dyeing. Once dyed, we can clearly see phenomena such as uneven color. At this time, production workers often attribute the cause of the problem to abnormal dyeing and ignore the reason for finding the oxidation process. I often make these mistakes when I am exposed to oxidative staining.

3 Dyeing 3.1 Washing before dyeing

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