Q. I am a design engineer at my plant where we finish products made from a ductile plastic. The product is manufactured from a nylon-based material, but it could also be polycarbonate- or polyurethane-based (ductile grades). We have found that when paint is applied to ductile plastics it reduces the impact strength of these engineering-grade materials quite significantly. Can you suggest a) a paint that is ductile-plastic-friendly, b) a surface treatment that may later be painted or c) another flexible, abrasion-resistant coating for this purpose that won’t weaken the plastic? B.U.
A. Although structural plastics are a little removed from my area of expertise, my guess is that the organic solvent in the paint is attacking the plastic surface. The reduction in impact strength probably results from the change in the surface. Change in the surface caused by traditional prepaint surface treatments for plastics could possibly also produce some harmful effect. I suggest you try a waterborne paint instead of solvent-containing paint or use a a plastic that already has the desired color, eliminating the need for painting.