Yellowing of electrophoretic aluminium profiles: yellowing caused by incomplete washing before electrophoresis
The oxide film is honeycomb-like, and its porous structure determines the residual sulfuric acid in the oxide film pore. It is well known that if the profiles used for electrophoresis are not washed thoroughly, yellowing is likely to occur. For this yellowing phenomenon, it is generally believed that the acid radical in the pore of the oxide film reacts with the electrophoretic paint to cause the yellowing of the electrophoretic paint film. In fact, this yellowing is not the yellowing of the paint film, but the yellowing of the oxide film. The normal oxide film is clear and transparent. If there are more sulfate residues in the hole of the oxide film, the oxide film will react with sulfate at high temperature, which makes the clear and transparent oxide film turbid and transparent. At the same time, the high transparency of the electrophoretic paint film and the high reflectivity of the light make the defect further enlarged, and then the defect will be formed. That yellowing. Therefore, several washing before electrophoresis is very important, not only to ensure the water quality, but also to ensure the washing temperature and time.