5 factors that cause yellowing of electrophoretic aluminum profiles

The paint film of electrophoretic aluminum profile has good decorative properties, but in the production process, the yellowing phenomenon of the paint film sometimes occurs, which affects the aesthetics of use. Next, aluminum profile manufacturers will introduce the five factors that cause yellowing of electrophoretic aluminum profiles: 　　1, the yellowing phenomenon caused by the electrophoretic paint itself, the anode electrophoretic paint is mainly composed of acrylic resin and amine-based resin. Electrophoretic aluminum profile is baking During the process, the resin undergoes a cross-linking reaction, resulting in a smooth and transparent coating film. However, some electrophoretic paint manufacturers have a relatively narrow curing range due to the immature production process or the use of poor quality chemical raw materials to reduce costs. If the baking is slightly insufficient, the hardness of the paint film is not enough; if the baking is a little too over, the paint film will turn yellow. 2. Yellowing phenomenon caused by poor conduction during oxidation. The aluminum profile has poor contact with the conductive rod, and the resistance at the contact will greatly increase, the end of the aluminum profile will heat up, the oxide film is formed too fast and accompanied by burning, and even oxidation Powdering of the film. At this time, the oxide film is a bit turbid, and the color is yellow. If electrophoresis production is carried out, a very obvious yellowing phenomenon will occur. Generally, this kind of yellowing phenomenon is only a few in the next row, and basically it appears in The end of the profile. 3. Yellowing phenomenon caused by over-curing. Currently, electrophoretic paints used in the market are basically baked and cured under the conditions of 180℃X30min. Under normal conditions, the paint film will basically not yellow. However, some manufacturers cure The temperature of the furnace is very uneven, and the local temperature even differs by more than 30°C; some manufacturers have poor temperature control systems in the curing furnace, and the actual temperature is too different from the displayed temperature. The poor quality electrophoretic paint is very yellow under this condition. , Even as if it was colored. 4. Yellowing caused by incomplete washing before electrophoresis. The oxide film is honeycomb-shaped, and its porous structure determines that sulfuric acid will remain in the pores of the oxide film. As we all know, the profile used for electrophoresis is very good if the water is not washed thoroughly. Yellowing may occur. For this kind of yellowing, it is generally considered that the acid radicals in the oxide film holes react 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 radicals remaining in the oxide film holes, the oxide film will react with sulfate radicals under high temperature conditions, so that the clear and transparent oxide film becomes turbid. Transparency decreases; at the same time, coupled with the high transparency of the electrophoretic paint film and the high reflectivity of light, this defect is further magnified, and the so-called yellowing is formed. 5. The yellowing phenomenon caused by the pollution of nitric acid in the oxidation tank In order to achieve a better ash removal effect, it is understandable to add a certain proportion of nitric acid in the neutralization tank, but if the washing control after neutralization is not good, the nitric acid will be Brought to the oxidation tank, when the nitrate in the oxidation tank reaches a certain concentration, it will have a certain impact on the oxidation, and even cause the yellowing of the electrophoretic profile. During the oxidation process, the nitrate that enters the pores of the oxide film will corrode the oxide film, corrode the barrier layer of the oxide film, make the oxide film hole deeper, and then change the structure of the film hole. This corrosion has two effects on the oxide film. Various effects: 1. The barrier layer of the oxide film becomes thinner, and the tightness of the bonding with the aluminum substrate becomes poor, which in turn causes the adhesion of the oxide film to decrease. 2. Under normal washing conditions, it is difficult to remove the sulfate in the film pores The electrophoretic aluminum profiles produced under this condition will also have yellowing.
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