Electrophoretic coatings are not a simple electrochemical reaction process, but include more complex colloid chemistry, physical chemistry and electrochemical processes. At present, it is generally believed that electrophoretic coating includes several processes such as electrolysis, electrophoresis, electrodeposition, and electroosmosis.
1. Electrolysis
A direct current is passed through the electrolyte solution, and the oxidation reaction and reduction reaction are carried out on the two electrodes respectively, and the phenomenon of generating redox products on the electrodes is called electrolysis. The electrophoretic coating is dissolved or dispersed in water, which itself is a kind of electrolyte. At a relatively dilute concentration, a direct current is passed through to generate an electrolytic reaction to decompose the solution, and the electrophoretic coating is dissociated into anions and cations. At the same time, the water also decomposes, producing hydrogen and oxygen near the electrodes. The metal pole dissolves and produces metal ions.
The electrolytic process mechanism of cathodic electrophoretic coating is just opposite to that of anodic electrophoretic coating.
This electrolysis process often produces a negative effect. If the control is not good, it will seriously affect the quality , and pinholes, bubbles and other phenomena will occur.
2. Electrophoresis
In solution, under the action of a DC electric field, the phenomenon that charged resin particles move to the opposite electrode is called electrophoresis. During cathodic electrophoretic coating, positively charged resin particles move to the cathode; during anodic electrophoretic coating, negatively charged resin particles move to the anode, where the pigment and extender pigment particles are wrapped in charged resin particles Then electrophoresis.
3. Electrodeposition
After the charged particles reach the object to be coated on the opposite electrode, they are electro-deposited to form a coating film (recommended instrument: coating rod), which is called electrodeposition, which is the main reaction in the electrophoretic coating process and plays a role very important role.
4. Electroosmosis
The coating film just deposited on the surface of the object to be coated is a loose and porous semi-permeable membrane. In the case of continuing to energize, the moisture in the coating film will penetrate through the coating film and move to the electrophoretic liquid. This makes the coating The phenomenon of membrane dehydration is called electroosmosis. It is the reverse process of electrophoresis.
