Analysis of Causes of Color Difference in Electrolytic Coloring of Aluminum Profiles

[China Aluminum Industry Network] The electrolytic coloring of aluminum profiles has good decorative properties, so it has been widely used at home and abroad, especially in the surface treatment production of architectural aluminum profiles. Our current main process is the electrolytic coloring of tin-nickel mixed salts. The color of the products produced is mainly champagne. Compared to the single nickel salt coloration, tin-nickel mixed salt electrolytic coloring products are bright and full of color and are deeply affected by color. The majority of customers love it; the main problem is that there is a color difference in the product, and the extrusion process in the production of aluminum profiles and the irrational oxidation coloring process can cause the product to show color differences.
The effect of the extrusion process on the coloration of the oxidation is mainly the influence of the die design, extrusion temperature, extrusion speed, and cooling method on the surface state and the homogeneity of the extruded profile. Mold design should be able to fully feed the kneading, otherwise it is easy to appear light (dark) with defects, the same profile may appear on the color separation; the same time, the state of the mold and profile extrusion lines and other factors also affect the oxidation of color. Extrusion temperature, speed, cooling method and cooling time are different, so that the profile of the material is not uniform, and color differences can also occur.
Anodizing has a very important influence on the color difference of electrolytic coloring, especially in the production process of vertical oxidation line, two colors are easy to appear. The vertical oxidation tank is 7.5m deep, and the temperature difference between upper and lower baths is easy to generate. The temperature is important for anodizing. The effect is that the temperature is high, the dissolution of the oxidation bath solution to the oxide film is intensified, and the pore size of the porous anodized film surface is increased, whereas the pore size of the porous anodized film surface is small. In addition, the temperature of the anodic oxide film is high and the temperature is relatively low. The electrolytic coloring mainly causes the metal ions of the coloring liquid to undergo an electrochemical reduction reaction on the surface of the barrier layer in the micropores of the oxide film, so that the metal ions in the coloring solution are deposited on the bottom of the anodic oxidation film hole to scatter the incident light. With the appearance of different colors, the more material that is deposited in the micropores, the darker the color. When the same amount of electricity is used, an equal amount of metal or metal compound is deposited on the high and low temperature parts. For the parts with high porosity and large surface pore size, the average number of deposits per hole is small, so the color is relatively Lighter, but darker, resulting in two colors of the coloring material. In the anodizing process, the conductivity has an effect on the oxide film and can also cause a color difference in the coloring material. This problem is mainly caused by the proneness of the horizontal production line, mainly due to the fact that the oxidized material is not in the upper row before the oxidation. Tight, resulting in poor conductivity of individual materials, making it relatively different oxide film, and then by coloring, it will produce color.
The electrolytic coloring process can directly reflect the color difference problem. The current distribution ability of the electrolytic coloring liquid has a decisive influence on the uniform coloring of the coloring material. Once the current is unevenly distributed, a significant color difference will be caused. The current distribution ability of the bath is mainly related to the conductivity and the degree of polarization of the bath. The coloring solution contains a certain amount of conductive salt, mainly to improve the conductivity of the coloring solution. When the conductive salt is not added in a timely manner, the conductivity is reduced, and the current distribution capability is reduced, causing color aberration. In addition, the additives in the coloring liquid will produce characteristic adsorption, thereby increasing the degree of polarization. If the material is consumed too much, the polarization degree of the electrolyte will be reduced, the current distribution capability will be reduced, and color aberration will also be caused. In actual production, it is necessary not only to increase the conductivity of the bath, but also to ensure that the conductive rod and the copper seat have a good electrical conductivity. The poor electrical conduction will cause uneven distribution of the power lines, resulting in color differences.
The above mainly describes several reasons that affect the color difference of the same tank material. The changes in the process parameters of anodization and electrolytic coloring can cause color differences between different tank materials. Therefore, it is necessary to control the stability of oxidation and coloring processes during production. To ensure the consistency of the parameters, thereby reducing the color problem of oxidation coloring material appears.