Aluminum is a light and soft non-ferrous metal, which is very easy to oxidize in the air, so people have come up with a solution, that is, the aluminum oxidation process, which grows a protective film on its outer layer to make it durable, and can be dyed into colorful colors, which is pleasing to the eye.
The principle of aluminium anode treatment is a process of making decorative and protective films on objects made of aluminum and its alloys. The alumina film formed on aluminum is made by direct current through a suitable sulfuric acid electrolyte under sufficient voltage, in which the object aluminum is the anode, and another material (lead or special graphite plate) is used as the cathode, and the industrial aluminum profile is energized for a certain period of time to gradually grow the oxide film of the required thickness.
After the film is produced, in addition to some aluminum natural colors do not need to be treated, the next step is to carry out coloring treatment, generally speaking, the coloring of aluminum is mainly divided into the following types:
1. Organic dyeing
2. Inorganic staining
3. Electrolytic coloring
4. Plating and coloring
Below we mainly discuss the principles, advantages and disadvantages of commonly used organic dyeing and electrolytic coloring, as well as the product occasions used:
1. The electrolytic coloring film is based on the transparent anodized film of sulfuric acid primary electrolysis, and the oxide film (also called the secondary electrolytic film) is electrolytically colored with AC in a solution containing metal salts, and the weather resistance, light fastness and service life of the electrolytic coloring film are much better than that of the dyed film, and its energy consumption and coloring cost are much lower than that of the overall coloring film. At present, it is widely used for building aluminum profile coloring, but the electrolytic coloring tone is monotonous, usually only bronze, black, golden yellow, jujube red and so on. And the operation is not easy to control.
2. Organic dyeing, organic dyeing is based on the adsorption theory of substances, adsorption is divided into physical adsorption and chemical adsorption, and the physical adsorption of industrial aluminum profiles is the adsorption of molecules or ions in the form of electrostatic force; Chemiadsorption, adsorption by chemical force, which combines the two to produce organic staining, is usually carried out at a certain temperature. Due to the high porosity of the anodized film, strong adsorption capacity and easy organic dyeing, this method is fast coloring, bright color, easy to operate, after dyeing, the dye can be firmly attached to the membrane pores, which improves the anti-corrosion ability and anti-fouling ability of the film layer until it can maintain a beautiful color, and is suitable for a large number of aluminum daily necessities that do not need to be used outdoors, indoor aluminum industrial products and decorations, etc., with colorful appearance. To meet the modern society's people's interest in censorship and pursuit of beauty, and improve the competitiveness of the product market. Organic dyeing has some characteristics and requirements for oxide films:
1. The oxide film layer should have sufficient porosity
2. The inner wall of the membrane pore should maintain a certain activity
3. The anodized film obtained by aluminum in sulfuric acid solution is colorless and porous, so it is the most suitable for dyeing.
4. The oxide film layer must have a certain thickness, and the thinner film layer can only be dyed with a very light color
5. The hard anodized film is a conventional oxide film layer with chromic acid, which is not suitable for organic dyeing
6. The oxide film layer should be complete and uniform, and there should be no defects such as scratches, sand holes, and pitting corrosion.
7. The film itself has a suitable color, and there is no difference in metallographic structure, such as different grain sizes or serious segregation, etc., so there are certain requirements for aluminum alloy materials, and when the content of silicon, magnesium, manganese, iron, copper, chromium and other alloys is too high, it often causes the oxide film to be dull, and the hue changes occur during dyeing.
