Stripping Coatings

Q. I own a custom painting shop that serves plants that outsource their finishing operations. We also do refinishing, which involves stripping of existing coatings. Because of our layout, we use chemical strippers. I have a good background on the chemistry of solvent-containing and waterborne materials, but I will have to do some additional work on better chemical strippers for powder coatings because we find them more difficult to strip. My guess is that in addition to being thicker, possibly denser and less porous, there are some chemical differences as well. Can you steer me toward some sources of this type of information? G. C.

A. Depending on their chemical composition, stripping powder coatings can be a real problem. I don’t think it’s a matter of porosity, because powder coatings tend to be naturally more porous than liquid coatings. I agree with your assessment that the differences are in the chemistry of the coatings themselves; the molecular weight of the base resins and the degree of cross-linking. There is also the feeling that residual solvent present in a cured liquid coating film permits attack more easily by chemical strippers.

As you know, one thing all successful strippers have in common is that they contain cresol or some other phenolic in addition to a solvent such as methylene chloride. I don’t know of any sources of written information other than my chapter “Choosing a Method to Strip Organic Coatings” in the PRODUCTS FINISHING 2007 DIRECTORY AND TECHNOLOGY GUIDE (www.pfonline.com/articles/pfdizzo01.html) and of course supplier literature. Unfortunately, the chapter does not provide the information you need, though. I suggest you contact powder coating suppliers for their help in recommending strippers. Powder coating suppliers are listed on page 361 of the aforementioned Directory. On the Internet, this information can be found at www.pfonline.com/suppliers.html.