Why is there a pre-treatment process for electrophoretic processing?

Why is there a pre-treatment process for electrophoretic processing?

Electrophoretic coating, like other coating methods, requires surface treatment of the coated parts 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. Not only do different surface treatment processes and quality seriously affect the coating quality, but surface treatment costs also have a significant impact. Therefore, when designing technology, we must choose targeted, effective, and low-cost surface treatment processes and methods as much as possible based on the coating method, material, and surface state of the coated parts.

Why is there a pre-treatment process for electrophoretic processing?

In the pre-treatment process of electrophoretic processing, there are processes such as oil removal, rust removal, phosphating, and surface adjustment that are coordinated with each other. It can be said that pre-treatment is indispensable in electrophoretic coating, as it relates to the stability of the electrophoretic paint solution and the quality of the coating on the surface of the workpiece after electrophoresis.

Electrophoretic processing uses phosphating treatment as a pre-treatment for coating to obtain durability and corrosion resistance of electrophoretic workpiece coatings. 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 film) on the surface of cleaned (degreased) metal substrates. The function of phosphating film is to improve the adhesion and corrosion resistance of the coating film (electrophoretic coating film) applied on it.

Regarding adhesion, due to the micro dissolution of the phosphate film crystals into the metal surface, the adhesion of the crystals is good. Moreover, due to the numerous surface irregularities of the crystals, the surface area is increased, which improves the adhesion of the coating film. Then, as the adhesion of the coating film increases, it prevents the invasion of corrosive substances and improves its corrosion resistance (especially preventing corrosion expansion under the coating film).

The coating will bubble and rust in the short term without phosphating treatment. The water and air passing through the coating film reach the surface of the workpiece, forming red rust and bulging the coating film. 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. Its volume increases several times, thus more strongly bulging the coating film. Phosphating film is an insoluble film formed on metal surfaces through chemical reactions. Due to its good adhesion (physical) and chemical stability, it is used as a durable substrate for anti rust coatings.

To obtain excellent and stable phosphating film, ensuring its adhesion and corrosion resistance, pre-treatment management is crucial, and a good understanding of the basic reaction mechanism and elements of phosphating treatment is also necessary.