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Powder coating (epoxy polyester) on zinc trivalent passivated plating

Can we do epoxy polyester powder coating on zinc plating with trivalent passivation.
When we have done the trials we have faced the problem with adhesion. Kindly suggest.

Tanuj
- Delhi
2006

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I've been involved with the same issue, Tanuj, and it's tricky. In the rapid development cycle for RoHS-compatible trivalent chromates, corrosion resistance was the highest priority challenge, and it was addressed in several different proprietary ways such as with thick-film chromates and thin film chromates plus secondary topcoat. Conductivity and powder coat adhesion and other issues were secondary in this race, and some of these proprietary chromate systems offer good powder coating adhesion and others offer poor adhesion.

But you generally can't dictate to the plating shop what chromate they must use, and in some cases they are unwilling to even tell you in order to retain their competitive advantage. At this point, and in my opinion, the best resolution is to work with a process supplier who promises good adhesion with their process (which may be thick film or a thin film without topcoat), have sample parts done in their lab and tested, and have them introduce you to shops that use that process.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006