Paint on Plastics

Question:

I need information on the pretreatment and coating of plastic parts. I have been out of the automotive coating industry for three years (after eight years of electrocoat experience) and am trying to re-enter it. I need to brush up on plastic coating technology information. I would appreciate any help. S. T.

Answer:

Not much has changed in pretreating and painting plastics in the past three years. The rules for painting plastic substrates are still the same as painting other substrates. The substrate must be clean, free from oily soils, release agents and particulates. Certain plastic substrates must be pretreated to promote adhesion. The applied coating must be compatible with the substrate.

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To remove oily soils, plastics are cleaned using alkaline cleaners, detergent cleaners, emulsion cleaners and solvents. Release agents are best removed using recommendations from their suppliers. If necessary, plastic substrates are pretreated using abrasives, chemical etching, corona discharge, combustion spray, plasma spray and lasers. Some plastic substrates must be primed to promote adhesion or to prevent attack by the solvents in a topcoat.

Compatibility of the coating with the substrate means its solvents should not attack, dissolve or otherwise destroy the substrate, although, it is possible that the solvent attack can promote adhesion.