Many new friends who are involved in the field of oxidation will encounter the problem of poor oxidation effect. Today, the experts of PTJ will talk to you about the reasons that may lead to the unsatisfactory oxidation effect. Talk about the various factors that lead to the unsatisfactory oxidation effect.
The surface of the aluminum oxide film is composed of a porous layer, which has a large specific surface area and high chemical activity. With this feature, various coloring treatments can be performed on the surface of the anodized film, in addition to improving the decorativeness and corrosion resistance of the product, and also imparting various functions to the surface of the aluminum product.
There are generally three types of anodized film coloring methods.
The first category: chemical impregnation method, chemical impregnation method is generally used for industrial products, interior decoration and crafts;
The second category: electrolytic coloring method, electrolytic aluminum coloring is generally used for architectural aluminum doors and windows;
The third category is the overall coloring method. The overall coloring method was used in the early days, but due to the limited color species and the relatively high cost, this technology has not been basically used at home and abroad.
Taking anodizing coloring as an example, how to solve the problem of color difference caused by anodizing is introduced. We first understand the process.
Process: pre-treatment → anodizing → post-treatment
Degreasing → alkaline washing → pickling → polishing
The pretreatment includes degreasing, alkaline washing, polishing, etc., the purpose is to make its surface smooth and shiny, and to remove surface impurities, making it easier to oxidize and color.
Degreasing is the use of degreasing agents to infiltrate, separate, emulsify, saponify, etc. to remove grease from the surface of the metal shell. By degreasing, you can remove the oil on the surface of the parts for subsequent alkaline washing and oxidation.
Alkali washing is to remove excess oil through the saponification of NaOH, and remove the natural oxide film, burrs, and impurities of the metal shell. Reacts with aluminum parts to remove surface dirt and remove natural oxide film. The purpose is to activate the surface. It also has the effect of removing squeeze stripes and obtaining different reflective surfaces.
Pickling is to remove dirt and ash on the surface after alkali etching to obtain a relatively clean surface. At the same time, the role of chemical reaction between the residual alkaline solution and the surface of the aluminum part is neutralized.
There are two types of polishing, one is electrolytic polishing and the other is chemical polishing. Electrolytic polishing is the use of electric current to cause the aluminum alloy to undergo an electrochemical reaction, and the unevenness of the aluminum alloy surface to varying degrees of deep solution, so that the surface of the aluminum piece has a smooth mirror effect. The electrolytically polished aluminum parts still retain most of their gloss after subsequent anodizing. The higher the purity of the aluminum sheet, the higher the reflectance. Chemical polishing is the selective dissolution of uneven areas on the surface of the sample through the chemical ion reaction between aluminum and the chemical polishing solution to eliminate wear marks and etch and level.
Anodizing is the process of oxidizing the anode to form an oxide film under the action of an applied current.
Washing → coloring → sealing → drying
After washing with water, sulfuric acid solution remains in the pores of the oxide film after anodizing. Therefore, aluminum products must be thoroughly cleaned before dyeing. Avoid bringing impurity ions into the dyeing tank, especially phosphate ions, fluoride ions, etc., set up pure water cleaning before the dyeing tank, and monitor the water quality.
Coloring is by chemical impregnation, which is generally considered to include both physical adsorption and the complexation reaction between organic dye functional groups and alumina.
Sealing treatment is an indispensable part of anodizing. After oxidation dyeing, only the sealing treatment can ensure the original color of the dyed film. There are a variety of sealing processes. Steam sealing, hot water sealing, and medium temperature sealing are all good choices. Some dyes can also choose cold sealing. The surface of the oxide film is porous, and dyes and crystal water can be adsorbed in these pores. Because of its strong adsorption, if it is not treated in time, it may also adsorb impurities and be contaminated. Therefore, it is necessary to perform filling treatment in time to improve the porosity Membrane strength and other properties. There are many methods for sealing treatment, such as boiling water method, high pressure steam method, impregnation metal salt method and filling organic matter (oil, synthetic resin).