Pretreatment for Painting

A high-quality conversion coating is essential for the durability of painted metal goods. The process of applying an inorganic conversion coating to a metallic surface involves removing any surface contaminants, then chemically converting the clean surface into a non-conductive, inorganic conversion coating. Conversion coatings increase the overall surface area and promote adhesion of the subsequently applied organic film. In addition, conversion coatings change the chemical nature of the surface, which increases corrosion resistance. It is these two functions, increasing surface area and changing the surface chemistry, that serve as a base for preparing the substrate material for paint finishes.

There are a number of driving forces in the pretreatment industry today with quality, cost and the environment being the most predominant. While these aren’t new issues, the pretreatment industry has responded to the needs of finishers by creating technology to address each of these requirements. In understanding the complete manufacturing process, including paint formulations, application equipment and regulatory impacts, it’s possible to address each driver simultaneously.

The conversion coating chemistries predominately used today are either zinc or iron phosphate. There is movement to replace these technologies with new types of phosphate-free or very-low-phosphate metal pretreatments. The new-generation technologies have been commercialized by many vendors over the past several years and are rapidly becoming industry standards. Regardless of the chemistry, conversion coatings are used to promote adhesion and improve corrosion resistance. Depending on the conversion coating and the desired performance, the conversion coating can be applied at a number of points in the process.

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