Acids for Lowering pH

Q. When we purge our electrocoat system and make up the volume with DI water, the pH goes up to the point that we must add acid to the tank. We have been discussing what is the best economical acid to lower the pH in the bath? We have a black cathodic system that we use to coat steel-only parts. The line is a manual overhead hoist. —T.F.

A. The acid used to control pH in your system is specific to the chemistry and materials you use as resin and pigment paste. Your paint supplier is the only accredited party that knows what is the proper acid or acids to be used to control pH. The supplier knows the formula and the type of solubilizing acids employed. Acid selection is very critical to the proper operation and performance of your ecoat system.

The acids used must solubilize the resin as well as contribute to proper deposition and rinse ability of the electrocoat for acceptable general appearance of the final product. Although all acids will lower the pH of the bath, only the correct acid or acids must be used.

Early electrocoat systems from the late 1970s and early 1980s operated primarily with acetic acid. Over the years, with technological advances in electrocoat chemistries to improve environmental impacts, operating robustness and corrosion protection, other acids have been introduced.

Typical acids employed to control pH in today’s electrocoat world can be organic and inorganic. Besides acetic acid, some other known acids are lactic, sulfamic, citric, formic, and others.