Cracks in Lacquer After Powder Coating

Ask an Expert From: Products Finishing, , from Powder Coating Consultants, Div. of Ninan, Inc.

Posted on: 4/1/2005

Question: I’m a sales manager for a powder coating company in Dunfermline, Scotland.

Question:

I’m a sales manager for a powder coating company in Dunfermline, Scotland. The problem we have is that when we lacquer alloy wheels that have been powder coated, the lacquer cracks after a day or so. We have tried all sorts of methods, for example curing for a short and long time, one pass with the spray gun/couple of passes, hot, cold and luke-warm. We are at our wits end to know what to do. Can you help? S. G.

Answer:

How interesting, a question with an international flavor. First of all we may be having a language problem. Many of my European friends refer to liquid paint as lacquer. In the States, we refer to a specific type (formulation) of liquid paint as lacquer. I wonder which one you mean? Well I guess it doesn’t much matter since it won’t affect my answer anyways.

Most lacquers and some other liquid paints are remarkably harder and less flexible than most common powder coatings. As such, powder coatings can handle much higher mechanical forces without cracking. If this is the case you can be cracking the liquid paint or lacquer without affecting the powder coating, under certain mechanical (and sometimes thermal) conditions. If this is your problem, simply select another type of liquid paint (or lacquer) with better mechanical properties, and the problem will go away.

Another possibility that comes to mind is the solvent in your liquid coating (or lacquer) is incompatible with the powder coating. This condition can cause the powder coating to “check” or crack (sometimes called crazing), also causing cracks in the liquid topcoat. In this case, check with the powder coating formulator and have them recommend a different powder formula that will be compatible with the liquid paint or vice versa.

 



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