In order to obtain the durability and corrosion resistance of the aforementioned automotive coatings, phosphating treatment is used as a pre-treatment for coating. Phosphating treatment (also known as phosphate chemical treatment) is a technology that uses the dissociation (equilibrium) reaction of phosphoric acid to precipitate insoluble phosphate metal salts (phosphating film) on the surface of cleaned (degreased) metal substrates . The function of the phosphating film is to improve the adhesion and corrosion resistance of the coating film .
With regard to the adhesion, because the obtained phosphating film crystals are slightly dissolved into the metal surface, the adhesion of the crystals is good. In addition, due to the surface irregularities of numerous crystals, the surface area increases and the adhesion of the coating film is improved. Then, with the improvement of coating adhesion
High, preventing the intrusion of corrosion-generating substances, and improving its corrosion resistance (especially inhibiting corrosion under the paint film).
The coating film will blister and rust in a short period of time without phosphating treatment. The water and air passing through the coating film reach the surface of the steel plate, forming red rust and swelling the paint film, and the water and air passing through the coating film reach the galvanized steel plate, forming white rust, and reacting with the coating film to form metal soap . Increased by 10 times, so the coating film is more strongly bulged. Phosphating film is an insoluble film formed on the metal surface by chemical reaction . Due to its good adhesion (physical) and chemical stability, it is treated as a substrate .
In order to obtain a good and stable phosphating film and ensure its adhesion and corrosion resistance, the management of pretreatment is very important. At the same time, it is necessary to have a good understanding of the basic reaction mechanism and elements of phosphating treatment.
