Like other coating methods, electrophoretic coating requires surface treatment before coating. Surface treatment is an important task that needs to be carried out before coating. Different coating methods, materials, and surface states require different surface treatment processes and methods. Different surface treatment processes and treatment quality not only seriously affect coating quality, but also have a greater impact on surface treatment costs. In the process of technical design, we must choose surface treatment programs and methods with strong pertinence, good treatment effect, and low cost as much as possible based on the coating method, coating materials, and surface conditions.
In the pretreatment process of electrophoresis, the processes of oil removal, rust removal, phosphating, and surface adjustment are coordinated with each other. It can be said that pre-treatment is essential in electrophoretic coating, as it relates to the stability of the electrophoretic paint bath after electrophoresis and the quality of the coating on the surface of the workpiece.
Electrophoretic treatment uses phosphating treatment as a pre-treatment for the durability and corrosion resistance of coatings on electrophoretic workpieces. Phosphating treatment (also known as phosphate chemical treatment) is a technique that utilizes the dissociation (equilibrium) reaction of phosphoric acid to precipitate insoluble phosphate metal salts (phosphating films) on the surface of clean (degreased) metal substrates. The function of phosphating film is to improve the adhesion and corrosion resistance of its coating (electrophoretic coating).
Regarding adhesion, due to the fact that the prepared phosphate film crystals are slightly soluble on the metal surface, the crystal adhesion is good. In addition, due to the many surface irregularities and surface areas of the crystal, the adhesion of the coating is improved. Then, as the adhesion of the coating increases, it can prevent the invasion of corrosive substances, thereby improving its corrosion resistance (especially preventing expansion under the paint film).
Coatings without phosphating treatment will bubble and rust in a short period of time. The water and air passing through the film form red rust on the surface of the workpiece, causing the paint film to protrude. The air and water passing through the film reach the galvanized steel plate, forming white rust, which also reacts with the film to form metal soap. Its volume increases several times, making the film more effectively protrude. Phosphating film is an insoluble film formed on the surface of metals through chemical reactions. Due to its excellent adhesion (physical) and chemical stability, it is used as a substrate for durable anti rust coatings.
In order to obtain excellent and stable phosphating film, ensure its adhesion and corrosion resistance, pre-treatment management 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.
