Ask the Expert Question-and-Answer Archive

by Ron Joseph

December, 2002

Painting CARC on Polypropylene

Q. I am working on a Military project in which we have purchased COTS equipment. One item in particular, a battery, has a 2-piece case made of a generic polypropylene; the top surface of which is yellow. For obvious camouflage reasons and other material degradation issues, we would like to paint this surface with a standard Military CARC paint. Is there a primer process to make this type of paint bond properly to the polypropylene surface? Would you believe the primer / paint combination to be effective across temperature extremes (-51:C to 71:C) without cracking or flaking?

A. I have not tested CARC on polypropylene, but expect that you might well run into adhesion difficulties especially if the coating system is stressed due to sudden temperature fluctuations. No matter what process you select, I strongly suggest that you conduct extensive performance tests before you go ahead and paint polypropylene on a production basis.

PPG Industries has a process that they recommend and you can find it at http://www.propolyamerica.com/products/documentation/process.pdf. Since PPG sells coatings to the automotive plastics market I assume that the company has already performed extensive tests on this topic. Nevertheless, you should not assume good adhesion until you have performed your own tests.

If the PPG system does not work for your application, you might need to look into processes that change the surface chemistry of the polypropylene, such as plasma, heat treatment, etc.

If you require assistance in this regard please do not hesitate to contact me and I can work further with you on this.