Anodizing, how to control the chromatic aberration? The secret is here
The surface of the oxide film of aluminum is made up of a porous layer, which has a large surface area and has a high chemical activity. With this characteristic, various coloring treatments can be done on the surface of anodic oxide film, in addition to improving the decoration and corrosion resistance of the products, and giving various functions to the surface of aluminum products.
There are three types of coloring methods in anodic oxide film.
First class: chemical impregnation
Chemical impregnation is generally used in interior decoration and handicraft
The second category: electrolytic coloring
Electrolytic coloring is usually used in building aluminum doors and windows
The third category: holistic coloring
The whole coloring method has been used in the early stage, but because the color is limited and the cost is relatively high, this technology has not been adopted at home and abroad.
Taking anodic oxidation of aluminum as an example, this paper introduces how to solve the problem of chromatic aberration in anodic oxidation. First of all, the first understanding of the process.
Oil removal, alkali washing, acid washing and polishing
Pretreatment includes oil removal, alkali washing, polishing and so on. The purpose is to make the surface smooth and glossy and remove the surface impurities to make it easier to oxidize and color.
Oil removal is the use of oil removal, separation, emulsification, saponification and other functions to remove the oil from the surface of the metal shell. By removing oil, oil can be removed from the surface of the product in order to wash, oxidize, and so on.
Alkali washing by caustic soda (NaOH) of the saponification off excess oil and remove the natural oxide film, burr, mobile phone shell metal impurities. In order to remove the surface dirt and remove the natural oxide film, the purpose is to activate the surface and remove the stripes and get different reflective surfaces.
Pickling is a stain on the surface after removal of alkali to get a more clean surface. At the same time, the effect of the residual alkaline solution on the surface chemical reaction of aluminum parts is also discussed.
There are two kinds of polishing, one is electropolishing and one is chemical polishing. Electrolytic polishing is based on the action of electric current, which causes the electrochemical reaction of aluminum alloy. It causes deep solutions to various parts of the surface of aluminum alloy, resulting in smooth mirror effect on the surface of aluminum parts. The electrolytic polishing aluminum, after subsequent anodic oxidation, can still maintain most luster. The higher the purity of the aluminum wafer, the higher the reflectivity. Chemical polishing is to eliminate the abrasion and leveling through the selective dissolution of the uneven surface of the sample through the chemical ion reaction between aluminum and chemical polishing liquid.
Anodizing is the process of oxidizing on the anode and forming a layer of oxide film under the action of an applied current.
3. Post treatment
Washing, coloring, sealing and drying
After the water washing is anodized, there is a sulphuric acid solution in the membrane hole of the oxide film. Therefore, the aluminum products must be cleaned thoroughly before dyeing. To avoid staining the tank with human impurity ions, especially phosphate, fluoride and so on, we should set up pure water before the dyeing tank, and monitor the water quality.
Coloring is made by chemical impregnation, which is usually considered as both physical adsorption and complex reaction of organic dye functional groups and alumina.
The seal hole treatment is an indispensable part of anodic oxidation. After the oxidation dyeing, only by sealing the hole to ensure the original color of the dye film. There are many kinds of sealing technology. Steam sealing, hot water sealing and middle temperature sealing are all good choices. Some dyes can also choose cold sealing process. The surface of the oxide film is porous, in these pores can absorb dye, can also absorb water of crystallization. Due to strong adsorption, if not promptly treated, may also adsorb impurities being contaminated, so to timely filling, so as to improve the strength of porous membrane. Many closed method processing, such as boiling water, high pressure steam, impregnated metal salts and filling method of organic matter (oil, synthetic resin, etc.).