Electrocoating is an efficient means of applying a corrosion protective coating on metallic parts with complex shapes and/or recessed areas. Cationic electrocoating offers improvement in corrosion protection over the earlier anodic electrocoat products due at least in part to the fact that electrochemical oxidation of the metal occurs at the anode and not at the cathode.
The first commercially successful cationic electrocoating products were based on amine functional epoxy polymers, generally crosslinked with urethane type crosslinkers. These products have had wide success in primer applications, and have provided excellent protection against corrosion of ferrous substrates. The major limitation of the cationic epoxy electrocoat technology has been the poor performance in exterior applications where the coating is subject to degradation by ultraviolet light.
To overcome the poor UV resistance of the cationic epoxy products, coating manufacturers have turned to cationic acrylic electrocoat technologies. These products are generally an improvement in terms of resistance to ultraviolet light, but have not demonstrated the corrosion protection that is available in the epoxy electrocoat products.
Over the past several years, research into cationic acrylic electrocoatings has identified two important considerations that significantly affects the corrosion resistance:
- 1.
The use of heavy metal containing inhibiting pigments, especially leaded pigments.
- 2.
The use of epoxy modifiers to improve the corrosion resistance of the coating.
This paper will present data to show the extent to which the use of leaded pigments and epoxy modifiers can impact corrosion resistance and UV degradation. In addition, some general guidelines will be presented which should be helpful in selecting an electrocoat product for a desired application.