1. Principle of self-coating
Self-coating paint is composed of polymer emulsion, carbon black light pigment, HF acidic substance and H 2 0 2 oxidant.
When steel parts are immersed in acidic self-coating, the iron surface is dissolved and activated to generate Fe 3+ coagulants:
Another function of the oxidizing agent is to reduce air bubbles on the metal surface:
With the enrichment of Fe3+ in the bath near the metal interface, the resin emulsion will be coagulated and deposited on the activated metal surface to form a coating film with sufficient strength to be washed with water.
2. Characteristics of self-coating
Compared with electrophoretic coating, self-coating has the following characteristics.
(1) Energy saving. Because self-coating uses a chemical process, it does not consume electricity, and the energy consumption is 50% less than that of electrophoretic coating.
(2) High protection performance. In the autophoretic deposition process, the surface treatment (activation) of the metal is carried out simultaneously with the deposition of the coating film, and the adhesion of the coating film is very strong. compared to.
(3) The process is short. Self-coating does not require phosphating treatment, the number of processes is reduced, equipment investment can be reduced by 30% to 60%, and the floor space can be reduced by 20% to 50%.
(4) The production efficiency of self-coating is high. The self-swimming time is generally 1~2min, which is suitable for assembly line production. The content of the self-swimming bath solution is 5%~10%. After the paint piece is taken out of the bath solution, the surface adhered to the bath solution still has good permeability and reactivity, and can be deposited by chemical action within 30s. Therefore, The loss taken away by water washing is very small, the paint utilization rate is better than that of electrophoretic paint and no ultrafiltration system is required.
(5) No swimming penetration problem. As long as any part of the surface of the workpiece is in contact with the bath, a covering layer with a very uniform thickness can be obtained, and the thickness error is within ±1.3µm, which has better decorative and protective properties.
(6) Hangers do not need to be cleaned. After the coating film is cured, it is resistant to acid and alkali, so it is not necessary to remove the coating film on the hanger, which greatly reduces the labor workload in this area.
(7) The paint liquid does not contain any organic solvents. Fundamentally eliminate the problem of air pollution caused by organic volatiles
(8) Water-soluble substances such as surfactants. It will not deposit a large amount with film-forming substances, which fundamentally solves the problem of poor water resistance of general latex paints.
However, Bi Jing, a self-coating paint, is a water-based paint, and there are also problems with the stability of the bath, especially the continuous accumulation of metal particles in the bath, which is detrimental to the stability of the bath, but as long as the number of updates of the bath is 15 times Above, there is practical economy.
The self-foaming coating equipment is the same as the dipping equipment, consisting of a tank body and a circulation system. Since there is no thermal effect in the self-coating process and the latex paint has good stability at room temperature, no heat exchange device is provided. The process of self-coating is as follows: pre-degreasing→degreasing→water washing→pickling activation→water washing→autophoretic deposition→water washing→rinsing with chromic acid solution (or other sealing agent)→drying. Since many pores remain in the self-coating film, it will rust and turn yellow when baked, so it needs to be sealed. The new process has been sealed with a non-chromium passivating agent, which makes this coating method more valuable for popularization and application.
