Powder Coating Q&A: Primer Options for Powder

Q. We make steel cabinets used to house electrical devices such as audio and video equipment or communication devices. We use a single coat of hybrid powder for most of our products. Some of our customers are asking for superior corrosion resistance for when the cabinet is installed in buildings that have limited control of heat and humidity in a shop environment. They have seen rust near edges and inside corners. What type of primer would be best to enhance the corrosion resistance of our cabinets?

A. Any primer or two-coat process should improve corrosion resistance. The “best” depends on how much additional protection you are trying to add. You could have the panels e-coated. E-coat is a high quality immersion primer that penetrates and provides overall coverage. A drawback is the cost and handling associated with sending parts to another coater. You could also use a powder primer. Powder primer is durable and can be enhanced with zinc content for the highest level of corrosion resistance.

Adding another layer of powder will complicate your process and increase your cost, but it can be done in-house. If you have a batch system, I would use an epoxy powder primer. After the part is clean, apply the primer coat and put the part in the oven for a partial cure. Consult with the supplier on the appropriate amount of cure cycle. Bring the part out, enable it to cool and apply your topcoat. Put the part back in the oven for a full cure cycle. I would not use zinc primer. The corrosion protection may be better, but you will have more difficulty handling and applying the zinc-rich material. Also, zinc primers are most effective on a blasted steel surface and you most likely do not blast your panels. It is more difficult if your system is conveyorized. If there is space, install another booth for the primer and small infrared oven to provide a short cure cycle.

Originally published in the November 2015 issue.