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Urethane Adhesion to E-coat

We are E-coating (PPG) products made of heavy steel and thin sheet metal (CABS FOR CONSTRUCTION EQUIPMENT). Our product is in the oven 78 minutes @ 196.
Doing this we are achieving a hardness of above 8H. Our problem is that we are having adhesion issues with our top coat. Top coat is urethane.

Is the E-coat too hard and is there a way of checking hardness besides the pencil test?

Bryan Cannon
- Greeneville, Tennessee, USA
2003

8H pencil hardness is very high. It looks like you are over-curing the E-coat. The best way to check for cure is with MEK / methyl ethyl ketone rubs with some cheese cloth. You do not want to get over a hundred rubs.

I worked with E-coat in the past on a coil line and also had some involvement with an automotive assembly plant. On the coil line the E-coat was first applied and then topcoat applied and the whole system cured together. E-coat has a very low moisture content after application so it does not have to be completely cured before the topcoat is applied.

Ronald Zeeman
- Brampton, ON, Canada
2003

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