The typical coating process of frame electrophoretic coating in the industry is "pretreatment+bottom integration cathodic electrophoretic" coating process or spraying powder coating process. The corrosion resistance and weathering resistance of the coating meet the technical requirements and meet the safety and environmental protection requirements. Due to its advantages of safety, environmental protection, high coating utilization rate and automatic production, the cathodic electrophoretic coating of the bottom surface has been adopted by most automobile manufacturers in the coating of frame, carriage and other parts.
There are many factors affecting the appearance roughness of the electrophoretic paint film. The common reasons are poor surface quality of the substrate, uneven and rough phosphating film, high ratio of color to base of the electrophoretic bath solution, high electrophoretic construction voltage, abnormal solvent content of the bath solution, and high pH of the bath solution. Through testing and confirming the process parameters of pre-treatment degreasing tank solution, surface conditioning tank solution, phosphating tank solution, electrophoresis tank solution, etc., it was found that the other parameters were within the range of process requirements, except for the abnormal rise of the pH of the electrophoresis tank solution. The coating process was checked, and the rough appearance of the electrophoretic coating film caused by electrophoretic coating, polar spacing, rotation speed of circulating pump, phosphating slag, water washing tank, and contamination of electrophoretic tank fluid was eliminated.
Poor crystallization of phosphating film
The function of the phosphating film is to improve the adhesion and corrosion resistance of the electrophoretic paint film coated on it. The crystallization of the phosphating film is required to be uniform and compact, and the size is less than 8 μ m. Further analyze whether phosphating has adverse effects on the surface roughness of electrophoretic paint film.
Disorder of face to base ratio
The ratio of pigment to base material (resin) in electrophoretic coating refers to the ratio of pigment to base material (resin) in electrophoretic paint, bath solution or paint film. The ratio of pigment to base material of electrophoretic bath solution and the newly prepared electrophoretic original bath solution should be the same. However, during the electrophoretic process, the pigment and resin may not be deposited on the coated object according to the original ratio, resulting in the phenomenon that the ratio of pigment to base of bath solution, paint film and original paint is different. The imbalance of the ratio of pigment to base of electrophoretic bath solution is easy to cause the defects of paint film such as shrinkage, roughness and loss of gloss, It affects the performance of the paint film, so it is necessary to regularly test the ratio of color to base of the tank liquid, and add lotion or color paste to adjust the ratio of color to base of the tank liquid according to the test results.
Low solvent content
The solvent in the electrophoresis tank solution plays a solubilizing role on the electrophoretic paint resin. The solubilizing process is divided into three processes: penetration, swelling and dissolution. The solubilizing effect is mainly determined by the structure and polarity of the solvent and the electrophoretic paint resin. Solvent can improve the stability of electrophoresis bath solution, and the addition of solvent can promote the leveling performance of electrophoresis paint film, thus improving the appearance quality of electrophoresis paint film. Solvents can also adjust the thickness of electrophoretic paint film. Different types of electrophoretic paint have their own suitable cosolvent, and the composition and proportion of cosolvent need to be within a certain range. Only in this way can the stable appearance quality of electrophoretic paint film be guaranteed.