We manufacture aluminum sign frames, which are used for interpretive trail exhibits, as well as aluminum brochure holders, etc. Our products are powder coated by an outside vendor. One of our newest customers is in Hawaii, and their concern is how well powder coat will stand up to their hot sun and salt sprays. They have requested a medium gloss clear coat over their colored coat. Is this necessary? We are using TGIC polyesters for our coatings. R.R.
Your customer has to look no farther than any beach resort in Hawaii where most all the outdoor furniture is powder coated using TGIC polyester over aluminum. This stuff often sees direct saltwater and sunlight exposure much worse than any sign frame or brochure holder. A clear TGIC powder coating over the base TGIC color coat will provide some additional abrasion resistance, but not much else. Otherwise a single coating of TGIC polyester or acrylic powder coating will provide your customer with excellent UV resistance and salt spray resistance provided that you pretreat the substrate properly using a chromate conversion coating or a non-chrome conversion coating first. Be aware that the acrylic powder coatings are more brittle than TGIC polyesters.