Q. M.W.’s question in the September edition of Painting Clinic about "Hard, Abrasion-Resistant Coatings" doesn’t identify the plastic substrate that influences the type of coating selected. It also doesn’t state whether it was pigmented or clear.
For maximum hardness and abrasion resistance, I would select a molded-in color matched to the cool gray Pantone color, utilizing a polycarbonate substrate so that baking could be done if the technology selected required it. A clear coat could then be applied.
Three technologies come to mind:
1. UV-curable coatings such as those used on polycarbonate automotive headlight lenses would work. This would require infrared flash and UV lamps to cure. Other lower-temperature and lower-cost substrates besides polycarbonate could be used, too.
2. A polysiloxane coating such as those used on eyeglasses, ski goggles and safety shields would work, but would require curing temperatures of around 230°F, which would necessitate the use of a polycarbonate substrate.
3. A polyurethane coating could be either clear or pigmented. A pigmented coating would, of course, eliminate the need to color match the substrate, and a lower-heat-resistant substrate could also be used. Maximum cure, even with baking, is achieved after two weeks. Perhaps a basecoat and clearcoat combination could do the job with this type technology.
I would opt for a UV-curable coating based on a personal bias. —C.S.
A. Thank you for writing to Painting Clinic, C.S. The coatings you suggested are excellent choices. I like UV-curable coatings, too, probably for the same reasons you do, including their ability to be applied and cured on heat-sensitive substrates.