Paint Adhering to Powder

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

Posted on: 2/1/2004

Question: I use powder coating as a primer for my stock products.

Question:

I use powder coating as a primer for my stock products. We prepare them for paint with a scotch brite pad, as you would with a normal liquid primer. Is there a chemical that can be sprayed onto the powder coating so the paint adheres better without scuffing the surface with the scotch brite pad? B. W.

Answer:

Due to the inherent chemical resistance properties of most all powder coatings, using chemicals to prepare a powder coated primed surface for liquid topcoat is impractical. This is especially true for epoxies, which have the best chemical resistance and are normally selected as powder primers. Polyester powder coatings have less chemical resistance than epoxy powder coatings. But even polyesters have good chemical resistance and are certainly more chemical resistant than liquid primers. Sometimes the liquid topcoat solvent can soften the powder primer for a good bond, but don’t count on it, especially with epoxy powder primers. Scuff sanding the powder primer is the best way to ensure a good bond between topcoat and primer.

Some people under cure the powder primer to allow the topcoat solvent a chance to soften the powder primer for a good bond. This can work if the liquid topcoat is force cured using heat that will complete the cure of the primer as well.

Finally, verify with your powder coating formulator that the powder primer you are using does not have any additives that can be an impediment for the bonding of the topcoat liquid coating. Problem additives that come to mind are slip agents and gloss duller agents, although there are others as well.

I am afraid that you will have to continue to scuff sand the powder primer as you are currently doing to ensure a good bond with the liquid topcoat. There are no shortcuts for doing a good job and I am sure your customers appreciate your efforts to provide them a “top notch” paint job.

 



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