Chrome and Resist Lacquer

Question:

We are a third tier automotive OEM supplier of resist chrome plating or stop chrome plating on ABS and ABS / PC plastic parts like car grills, hub caps, etc. for two area chrome plating companies. We spray resist lacquers to stop the chrome plating process in areas chrome is not desired.

Our paint supplier says that the paint is designed to perform this process at 1/2 to 1 dft mil. We paint to 1 1/2 dft mil with a very smooth finish. We get parts returned to us that are over plated onto our paint area. The chrome will be loose and have no adhesion to our painted area. What other possibilities are there for this problem besides just light paint? Our customers tell me it is our fault, period, and back charges us for the part. We can pull the chrome back to the line where the paint stops and raw plastic starts. The paint is nice, smooth and dark. I don’t know a whole lot about the chrome process and I can’t get any help from our customers. I have, in the past during troubled times, repeatedly painted a part to 20 dft mils and marked it special and have seen it over plate as well. There has to be more variables than just poor painting or thin film coverage. R. H.

Answer:

I don’t know a whole lot about the chrome process either. I leave that to the wizards, the guys who wear the pointed hats embroidered with the moon and stars. This question was sent to me and Arthur Kushner. Although he is better qualified to answer the plating parts of the question, I couldn’t resist (no pun intended) answering the coatings parts. I just finished answering a question from C. M. about excessive film thickness in which I said, “Paints are engineering materials. They are designed to provide specific performance characteristics at a specific film thickness.” The supplier of your resist lacquer said, “The paint is designed to perform this process at 1/2 to 1 dft mil.” Although you get a nice looking film at 11/2 mils, it is about twice the recommended film thickness. Apparently, you don’t get a good-looking film at the recommended film thickness. If this is the case, you must modify your application technique. For example, if you are getting dry spray, hold the spray gun closer to the part and slow down the gun movement. In the old days, we used to say, “Add more solvent.” Today, the air quality folks don’t want to hear that. In any event, I suggest you reduce the film thickness to that recommended by the paint supplier.