Electrodeposition of polymers is an extension of coating technology in the field of electroplating. Like electroplating, it is a dip coating process. Metal plating technology uses metal ions, usually Ni2+ or Cu2+, to release well-attached deposits of metallic nickel, copper, etc. on the cathode. The chemistry of deposition can be described as 1/2 Me2+ + 1F (or 96,500 Coulombs) of electrons to produce 1/2 Me0. In the case of electrodeposition of ionizable polymers, the deposition reaction is described as R3NH + OH– + 1F → R3N + H2O, or the conversion of water-dispersed ammonium ions into ammonia-insoluble polymers, referred to as cathodic deposition. Alternatively, a large number of devices use the anodic deposition process RCOO– + H+ less 1F → RCOOH. It should be mentioned that "R" stands for any of the widely used polymers (acrylics, epoxies, alkyds, etc.).
The electrodeposition process is defined as utilizing "synthetic, water-dispersible, electrodepositable macroions".
Advantage
Metal ions, typically 1/2 Ni2+, exhibit an electrical equivalent weight of 1/2 Ni2+, approximately equal to 29.5 g, while polymer ions, commonly used for electrodeposition, exhibit a gram equivalent weight (GEW) of approximately 1600. Thus, 1F plates have 30 grams of nickel and 1600 grams of macroscopic deposits. The advantage is even greater if we consider the thickness of the deposit, since nickel has a specific gravity of 9, while colored organic coatings have a specific gravity of about 1.4.
Another advantage, and probably the reason for the rapid and still continuing industrial growth of polymer electrodeposition processes, is the formation of uniformly thick coatings on all surfaces of shaped workpieces, including extreme grooves like the inside of a car door. This ability to extend the coating into the groove is called throwing power.
Another advantage is the minimal vapor emissions of volatile organic compounds (VOCs), ranking electrodeposition with powder coating and radiation curing as the least polluting coating processes.
Finally, electrocoat tanks are less expensive to operate than any other painting method.
