Off-Gassing During Curing

Q. I’m trying to educate my customer on a current defect: painted plastic substrate gas-out during the curing process. I seem to remember a great article and don’t know how to search for it. Can you point me in the right direction? We are low baking 2k painting over molded PC and PCABS. We also mold a lot of the parts that we paint, so we are very aware of molding stresses causing this issue.—P.P.

A. Without knowing the type of coating you are applying, it is difficult to give you a definitive answer. You mentioned that you use a low-bake 2k process; is it waterborne or solvent? How controlled is your finish environment in regards to air movement or humidity? Many things can contribute to the out-gassing you are referring to. You mentioned a defect. What type of defect are you referring to? Is it pinholing, hot spots or some other defect?

At the lab I work in, we evaluate the aspect or appearance of the coating on both our batches and even product from the field to make sure our products are meeting the designed performance standards. Depending on the coating requirements, we do this evaluation over various substrates, such as glass, metal and plastics, to make sure our formula does not contribute to these issues. If we notice deviations in the coating performances, we make or recommend adjustments to help the product perform as designed.

ABS (Acrylonitrile Butadiene Styrene) and PC (Polycarbonate), are hydrocarbon or petroleum-based byproducts. During the molding process, plastics heat up and typically fume or gas out things like acrylonitrile. How much time is there between the molding and painting process? Are the parts still warm? Sometimes when painting is done close to the molding process, the part is still off-gassing, which may be manifesting itself into your coating process. You may want to contact your current coating supplier to see if modifications can be made to your paint to help eliminate the issues. 

Originally published in the July 2015 issue.