Summary for carc paint testing with acetone Discussion
CARC paint testing with acetone is discussed as a practical field check, but Ted Mooney cautions that results depend on cure and comparison to a known-good panel. Andrea Barnes, a QA manager, reported that a customer was rubbing the covers with acetone on paper towels for 10 seconds and seeing green residue, raising doubts about whether the coating was truly CARC. Ted suggests the parts may be undercured, especially if they are heavier gauge or hung differently and therefore cure differently. He says the acetone rub test is acceptable even with paper towels, but the key is to compare the suspect part against a verified good panel. In his view, properly cured CARC paint should not be affected by acetone, though uncured curing agents or surface contaminants may transfer to the cloth.
CARC = chemical agent resistant coating
Q. I am the QA Manager for a power supply company that designs and manufactures power supplies for military use. We have been building a particular power supply that requires CARC paint. For the past 4 years there has been no paint issues. Until now. I was contacted by the customers QA telling me the covers of the units were not CARC paint. They are testing the paint with acetone
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and paper towels. They apply the acetone to the paper towels and rub hard for 10 seconds. They repeated this test a number of times. The paper towels still showing paint residue. Is there a documented method of testing the paint to make sure it is CARC? I know the paint is chemical resistant, but is using the paper towels too abrasive? I used the acetone method but with non-abrasive wipes. The first wipes did show green, but it eventually faded and the paint on the cover didn’t seem affected.
Andrea Barnes
Electronics Manufacturing – San Jose, California, USA
2004
A. Just a thought… Are these covers hung lower than the rest of the unit or are they heavier gauge material? My thought is that the last property that develops in a cure cycle is the full cross link responsible for chemical resistance. If these parts are not quite as fully cured as they should be it could cause this problem. The acetone rub test is good even with paper towels, but you should have on-hand a known-good panel for comparison. CARC Paints should not be affected by the acetone, but curing agents or other surface contaminants may show up on the rubbing cloth.
I hope that’s helpful,
Jeff Watson
– Pearland, Texas
A. Just a quick clarification to Jeff’s excellent answer. The way to know whether what has rubbed off is paint or just “curing agents or other surface contaminants” is by simply doing the procedure twice. The first rubbing removes any contaminants; so the second rubbing should take off nothing. Acetone will remove alkyd paints but not CARC. See TB-43-0242.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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