A Brief Analysis of the Causes of Color Difference in Electrolytic Coloring of Aluminum Profiles
The electrolytic coloring of aluminum profiles has good decorative properties, so it is widely used at home and abroad, especially in the surface treatment production of architectural aluminum profiles. The current main process of our company is to use tin-nickel mixed salt electrolytic coloring, and the color of the products produced is mainly champagne. Compared with single nickel salt coloring, tin-nickel mixed salt electrolytic coloring products are bright in color and full in tone. The majority of customers love it; the main problem is that the product has color difference, and the unreasonable extrusion process and oxidation coloring process in the production process of aluminum profiles will cause color difference in the product.
The influence of extrusion process on oxidation coloring is mainly the influence of mold design, extrusion temperature, extrusion speed, cooling method, etc. on the surface state and structure uniformity of extruded profiles. The mold design should be able to fully knead the incoming materials, otherwise bright (dark) band defects will easily appear, and color separation may occur on the same profile; at the same time, the state of the mold and the extrusion lines on the surface of the profile also affect the oxidation coloring. Extrusion temperature, speed, cooling method and cooling time are different, so that the structure of the profile is not uniform, and the color difference will also occur.
Anodic oxidation has a very important influence on the color difference of electrolytic coloring, especially in the production process of vertical oxidation line, it is easy to appear two-sided color. The depth of vertical oxidation tank is 7.5m, and the temperature difference between the upper and lower baths is easy to produce. Temperature has an important effect on anodic oxidation. The influence of temperature is high, the dissolution of the oxide film by the oxidation bath solution is intensified, and the pore size on the surface of the porous anodized film will increase. On the contrary, the pore size on the surface of the porous anodized film will be smaller. In addition, the higher the temperature, the higher the porosity of the anodized film, and vice versa. Electrolytic coloring is mainly to make the metal ions of the coloring liquid undergo 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 liquid are deposited on the bottom of the pores of the anodized film, and the incident light is scattered. And show different colors, the more substances deposited in the micropores, the darker the color. Under the condition of passing the same electricity, the same amount of metal or metal compound is deposited on the parts with high and low temperatures. For the part with high porosity and large surface pore size, the average deposit per hole is less, so its color is relatively It is lighter, and vice versa, the color is darker, resulting in two colors of the coloring material. In the process of anodizing, the conductivity will affect the oxide film, and it will also cause the color difference of the coloring material. This problem is easy to appear in the horizontal production line. Tight, resulting in poor electrical conductivity of individual materials, so that the oxide film is relatively different, and then after coloring, there will be color difference.
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 distribution is uneven, it will cause obvious color difference. The current distribution capability of the bath is mainly related to the conductivity and polarization of the bath. The coloring solution contains a certain amount of conductive salt, which is mainly to improve the conductivity of the coloring solution. When the conductive salt is not added in time, the conductivity and current distribution ability will decrease, which will cause color difference. In addition, the additives in the coloring solution will produce characteristic adsorption, thereby increasing the degree of polarization. Excessive consumption of this substance will reduce the degree of polarization of the electrolyte, reduce the ability of current distribution, and cause color difference. In actual production, it is necessary not only to improve the conductivity of the bath solution, but also to ensure that the conductive rod and copper seat have good electrical conductivity. Poor electrical conductivity will cause uneven distribution of power lines and chromatic aberration.
The above mainly introduces several reasons that affect the color difference of the same tank material. The change of each process parameter of anodic oxidation and electrolytic coloring will cause the color difference between different tank materials. Therefore, the stability of the oxidation and coloring process should be controlled in production , to ensure that all parameters are consistent, thereby reducing the occurrence of chromatic aberration of oxidized colorants.