Electrophoretic coating adopts electrodeposition process and has the following characteristics:
The use of water-soluble paint and water as the dispersion medium saves a lot of organic solvents, greatly reduces air pollution and environmental hazards, and avoids the risk of fire;
The efficiency of electrophoretic coating is high, the loss of paint is small, and the utilization rate of paint can reach more than 95%;
The thickness of the coating film is uniform, and the edge coverage is good, which can meet the requirements of complex shape workpiece coating;
The mechanical properties of the coating film are excellent, and it also has good adhesion and impact resistance;
The equipment is complicated, the investment cost of the automated assembly line is high, the power consumption is large, the management of the coating is complicated, the construction control is strict, and wastewater treatment is required;
The volume of the electrophoresis tank is large, and it is troublesome to change the color.
crafting process
The surface of the workpiece should be pretreated before painting. The current commonly used electrophoretic coating process is as follows: workpiece-pre-degreasing-degreasing-water washing-hot water washing-surface adjustment-phosphating-water washing-deionized water washing-hot air drying- Electrophoretic deposition-ultrafiltration cycle washing-baking film formation-cooling-coating topcoat.
In order to ensure the quality of the coating, strict scientific management of the electrophoretic fluid is required, and the solid content, pigment-base ratio , pH, conductivity, and electrophoretic coating thickness of the electrophoretic fluid should be measured regularly, and adjusted on the basis of the measured data. Various parameters of electrophoretic coating.
1. Electrophoresis voltage
The voltage has a great influence on the paint film, the higher the voltage, the thicker the paint film. Increasing the voltage can improve the coating ability and shorten the construction time for difficult-to-coat parts. However, if the electrophoretic voltage exceeds the breakdown voltage of the coating, the coating will be broken down and cause coating defects. Therefore, it is necessary to determine a good electrophoretic coating. Voltage. Electrophoretic coating adopts the constant voltage method, and the selection of voltage is generally determined by the type of coating and the requirements of construction.
2. Electrophoresis time
The thickness of the paint film increases with the prolongation of the electrophoresis time, but when the paint film reaches a certain thickness, the thickness cannot be increased by continuing to extend the time, but the side reaction will increase; on the contrary, the electrophoresis time is too short and the coating film is too thin. The electrophoresis time should be determined according to the voltage used. Under the premise of ensuring the quality of the coating, the shorter the time, the better. Generally, the electrophoresis time is 1~3min under voltage, and 3~4min for large workpieces. If the shape of the object to be coated is complex, the voltage can be appropriately increased to extend the electrophoresis time.
3. Electrophoresis temperature
As the temperature of the electrophoretic fluid increases, the rate of electrophoretic deposition is accelerated, and the rate of film formation is fast. However, if the temperature is too high, it will lead to rough coating, orange peel, and easy to cause deterioration of the coating. Therefore, it is necessary to control the electrophoresis temperature, which is generally controlled at 15~30°C.
4. Paint solids
The electrophoretic fluid with low solid content is used, the loss of the electrophoretic fluid brought out by the workpiece is small, the electroosmosis is good, the water consumption is small during washing, and the wastewater treatment is easy. If the solid content is too low and the coating is too thin, the appearance of the coating will deteriorate, pinholes are likely to occur, and the electrophoretic fluid is difficult to maintain; if the solid content is too high, the coating is prone to roughness and orange peel. Generally, the solid content of the anolyte electrophoresis liquid is controlled at 10%~15%, and the solid content of the cathodic electrophoretic liquid is controlled at 18%~20%.
In addition, the parameters affecting the electrophoretic coating include the pH of the coating, the resistance of the coating, the distance between electrodes, etc., and the appropriate process parameters should be selected according to the specific coating requirements.
