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Adhesion on Polycarbonate /ABS parts

I am painting a molded part that is made from Polycarbonate and ABS blend. We are using a 2 part polyurethane paint. The paint is applied by hand spray in a vented booth. The parts air dry on hangers.

My question. Our adhesion has been intermittent. The first lot passed the scratch type adhesion test. The next 2 lots did not. We have considered contamination of the molded part and are addressing that with the molding vendor. Any suggestions of possible causes. What other variables (from the painting process side) affect adhesion?

Greg Paul
- Ann Arbor, Michigan, USA
2002

Greg, it does not appear you are cleaning the plastic parts before painting them. If a mold release is used to prevent the parts sticking in the molds, this material could interfere with the paint adhesion. You may want to either specify that no mold release is used or add a cleaning procedure to your process.

Roy Nuss
Trevose, Pennsylvania, USA
2002

We invesitgated contamination by comparing "as molded" parts, cleaned parts, and some that were contaminated with known agents present at the molder (gloves and bags). We had poor adhesion to both control and the test groups. We are now testing primers.

Greg Paul
- Ann Arbor, Michigan
2002

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2002

Greg,

What Roy said sounds very logical. Preparation is always the key to good adhesion.

But there's something else. If the moulder happens, by mistake, to drop in some Polyoelfins such as Pe or PP into the Banbury of whatever mixer, hells bleedin' bells, these should go to the top surface and sure make adhesion DIFFICULT.

If I wanted to sabotage a PVC, ABs, etc. etc. moulded or extruded part, I'd add some Pe or PP to the mixer. And you mentioned that 'bags' etc had been in the mix. Oh dear, oh dear, oh DEAR !

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).