Chrome-free single-step in-situ phosphatizing coatings

The current process of organic coating on metals involves multiple steps and considerable energy, labor, and process control. It also generates toxic wastes such as chlorinated solvents, cyanide, cadmium, lead, and carcinogenic chromates. The green chemistry technology of in-situ phosphatizing coatings (ISPCs) developed in our laboratory is a one-step self-phosphating process in which the formation of a metal phosphate layer on the substrate surface and the curing of polymer paint film take place independently, but simultaneously. The generation of a metal phosphate layer in-situ essentially eliminates the metal surface pre-treatment step which employs a phosphating line/bath. The use of chemical bonds linked to the paint polymers to seal the pores of the metal phosphate layer in-situ enhances coating adhesion and suppresses metal corrosion without post-treatment final rinses containing chromium (Cr6+). The successful application of ISPCs in three types of low-VOC commercial paints on bare and pre-treated cold-rolled steel and 2024 T3 aluminum coupons are presented in this chapter. The protective performance of ISPCs is shown to be superior to that of the current multi-step coating practice.