Q. I am a manufacturing engineer in a plant that produces small appliances. We are having trouble with a baking enamel. When a part is rejected because of a paint defect, we try to recoat it, but the second coat won’t adhere to the first, causing us problems. What is the best type of polymer for a baking enamel that allows it to be recoated with excellent adhesion? A.K.
A. Small appliances that are finished using enamels have excellent mar resistance, because slip agents are added to enamel formulations. However, when they are recoated, the slip agent can interfere with adhesion. The first thing to do is investigate this possibility as a root of your problem. Baking enamels that use most resin polymer types can be recoated with excellent intercoat adhesion if they don’t contain a slip agent. Enamels that offer the best adhesion, both substrate and intercoat, are formulated using epoxy resin polymers. However, when applied over enamels formulated using slip agents, even they will have poor intercoat adhesion. Another possible cause for intercoat adhesion failure is that the original enamel is under-cured.