1, Electrophoresis paint itself caused by the yellow appearance
Anodic electrophoretic paint is mainly composed of acrylic resin and amine resin. Electrophoresis profiles in the baking process, the resin attack cross-linking reaction to generate a flat, bright coating. However, some electrophoretic paint manufacturers because of the immature production process, perhaps to reduce the cost of using poor quality chemical raw materials, and then lead to its curing a relatively narrow scale. Slightly lacking in baking, the film hardness not; baking a little too far, the film will be attacked yellowing, production management to bring some difficulties.
2, Oxidation caused by poor conductive yellow appearance
If the profile and the conductive rod touch poorly, the resistance at the contact point will greatly increase, the end of the profile will be heated, the oxide film will be generated too fast and accompanied with the appearance of burning, and even the powdering of the oxide film will appear. At this time the oxide film is somewhat dirty, the color appears yellowing, if it is then electrophoretic production will show a very significant yellowing appearance. This yellowing appearance usually only a few rows in a row, and are basically present in the end of the profile. Therefore, we must adopt a way to ensure that the profile and the conductive rod touch outstanding.
3, electrophoresis before washing caused by incomplete yellowing appearance
Oxide film is honeycomb, the porous layout of the oxide film will determine the hole will remain sulfuric acid. Typically, the profiles used for electrophoresis, if the water is not completely washed, it is able to show yellow appearance. About this phenomenon of yellowing, usually think that the oxide film holes in the acid root reaction with electrophoretic paint and then make the electrophoretic film yellowing, about this know, can not agree, because this yellowing is not a film attack Yellowing, but the yellowing of the oxide film. Normal oxide film is crystal clear, clear, if the oxide film hole left more sulfate, high temperature case, the oxide film will react with sulfate attack, and then make the crystal clear, bright oxide film becomes dirty, clear Together with the high transparency of the electrophoretic paint film, the high reflectivity of the light, and then to make this shortcoming further expanded to form the said yellowing. Therefore, several washing before electrophoresis is crucial, not just to ensure water quality, but also to ensure that the washing temperature and washing time.
4, Oxidation bath caused by nitric acid pollution caused by the appearance of yellowing
In order to achieve a better ash removal effect, adding a certain amount of nitric acid to the neutralization tank is understandable. However, if the neutralization is not good after the washing operation, nitric acid is taken to the oxidation tank where the nitrate reaches a certain concentration When it will form a certain impact on the oxidation, and even lead to electrophoretic profiles yellowing. Oxidation process, the nitrate into the pores of the oxide film will have an etching effect on the oxide film, corrosion oxide film barrier layer, the oxide film hole becomes deeper, thereby changing the layout of the film hole. This corrosion attack on the oxide film two kinds of impact: 1, the oxide film of the thinning of the barrier layer, the tight adhesion of the aluminum substrate deterioration, and thus the formation of the adhesion of the oxide film decreased. 2, under normal washing conditions, it is difficult to remove sulfate in the membrane hole. Under the conditions produced by electrophoresis profiles the same will have yellowing appearance. How to avoid the appearance of such yellowing? Add a neutralizing agent in the pure water tank before scald tank, adjust the pH value of 8 to 9.5, washed with water for 2 to 3 minutes, neutralize the sulfate in the pores of the oxide membrane with the amine radical, Then electrophoresis production, it will not show yellow appearance.
