[China Aluminum Industry Network] The electrophoretic aluminum paint film has good decorative properties, but during the production process, yellowing of the paint film sometimes occurs, affecting the aesthetics of the use. Below, aluminum manufacturers introduce electrophoretic aluminum. 5 factors of profile yellowing: 1. Yellowing phenomenon caused by electrophoretic paint itself Anodic electrophoretic paint is mainly composed of acrylic resin and amine-based resin. During the baking process of electrophoresis profiles, the resin undergoes cross-linking reaction, resulting in a smooth, transparent coating film. However, some electrophoretic paint manufacturers are immature due to the production process, or Is to reduce the cost of the use of poor quality chemical raw materials, resulting in a narrow range of its curing. Bake a little lack, the film hardness is not enough; baking a little too much, the paint film will occur yellowing. 2. Yellowing caused by poor conductivity during oxidation Poor contact between the profile and the conductive rod, the resistance at the contact point will increase greatly, the tip of the profile will be heated, the oxide film will be generated too fast and accompanied by burning, and even the powder of the oxide film will appear. The oxide film is sometimes cloudy. The color appears yellow, and if it is electrophoretically produced, there will be a very obvious yellowing phenomenon. This yellowing phenomenon generally has only a few branches in the next row, and basically appears at the end of the profile. 3. Yellowing caused by excessive At present, the electrophoretic paints used in the market are basically baked and cured under the conditions of 180°CX30min. Under normal conditions, the paint film will not be yellowed. However, some manufacturers have very uneven temperature in the curing oven, and the local temperature is even A difference of more than 30 °C; some manufacturers curing furnace temperature control system is poor, the actual temperature and display temperature difference is too large, poor quality electrophoretic paint yellowing phenomenon in this condition is very obvious, and even like a colored like. 4. Yellowing caused by incomplete washing before electrophoresis Oxide film is honeycomb, its porous structure will determine the residual sulfuric acid in the oxide film hole. It is known that if the profile used for electrophoresis is not completely washed, it is very likely to appear yellowing phenomenon. For this yellowing phenomenon Generally speaking, it is thought that the acid radical in the oxide film reacts with the electrophoretic paint to make the electrophoretic film yellow. For this understanding, I can't agree with it. I think this yellowing is not the yellowing of the film. It is the yellowing of the oxide film. The normal oxide film is clear and transparent. If more sulfate is left in the oxide film, the oxide film will react with the sulfate at high temperature, resulting in clear and transparent oxidation. The film became turbid and its transparency decreased; at the same time, the high transparency of the electrophoretic paint film and high reflectivity of the light caused the defect to be further amplified to form the yellowing. 5. Yellowing caused by oxidation of the oxidation bath solution by nitric acid In order to achieve a better ash removal effect, it is understandable to add a certain percentage of nitric acid in the neutralization tank, but if the water washing control is not good after neutralization, nitric acid is brought to the oxidation tank and the nitrate in the oxidation tank reaches a certain concentration. When it does, it will cause some influence on the oxidation, and even cause yellowing of the electrophoretic profile. In the oxidation process, the nitrate that enters the hole of the oxide film will etch the oxide film and erode the barrier layer of the oxide film to make oxidation. The deeper film hole changes the structure of the film hole. This kind of corrosion has two effects on the oxide film: 1. The oxide film has a thinner barrier layer, and the adhesion to the aluminum matrix becomes poorer, which in turn causes the adhesion of the oxide film. Reduced .2. Under normal washing conditions, it is difficult to remove the sulfate in the membrane pores. The electrophoresis aluminum profiles produced under this condition will also have yellowing.
