Cathodic electrophoresis water-soluble resin is a cationic compound, which is neutralized with organic acid and dissolved in water. It exists in the DC electric field in the equilibrium state of molecules and ions. The potential difference between the two poles occurs, the ions move in a directional direction, the cations move to the cathode, and electrons are deposited on the cathode surface, while the anions move to the anode, Electrons are released on the anode and oxidized to acid. This is the basic principle of electrophoretic coating. It is a very complex electrochemical reaction, including four simultaneous processes: electrolysis, electrophoresis, electrodeposition and electroosmosis.

1. Electrolysis when the current passes through the electrolytic electric aqueous solution, the water will have an electrolytic reaction, releasing hydrogen at the anode and oxygen at the cathode. Therefore, during the coating process, the voltage should be reduced as much as possible and other impurity ions should be prevented from mixing in the paint solution, because excessive gas will be released during the electrolytic reaction, which will affect the quality of the paint film.

2. Electrophoresis is called electrophoresis when the charged colloidal particles dispersed in the medium move in the opposite direction of the electrode with its charge under the action of DC voltage. In the electrophoretic paint solution, in addition to the negatively charged resin particles, the non charged pigment and physical pigment particles adsorbed on the charged colloidal resin particles also move with the electrophoresis.

3. Electrodeposition under the action of electric field, the charged resin particles electrophoretically reach the cathode, release electrons and deposit on the cathode surface to form a water-insoluble paint film, which is called electrodeposition. It is the main reaction in the process of electrophoretic coating. Electrodeposition is first carried out at the parts with particularly high power line density, such as the edge corners and top of the coated workpiece. Once deposition occurs, the coated workpiece (cathode) has a certain degree of insulation, and the electric field moves backward with the coated surface until a completely uniform coating is obtained.

4. Electroosmosis is the reverse process of electrophoresis. When the colloidal particles of the paint solution are affected by the electric field, move to the cathode and deposit, the medium (water) adsorbed on the cathode passes through the deposited paint film from the cathode into the paint solution under the action of internal osmotic force, which is called electroosmosis. The function of electroosmosis is to dehydrate the electrodeposited paint film. Generally, the water content of the newly deposited paint film is 5 ~ 15%, which can be directly dried at high temperature without foaming or sagging.