THE USE OF REACTABLE LIGHT STABILIZERS TO PREVENT MIGRATION AND TO IMPROVE DURABILITY OF COATINGS ON PLASTIC SUBSTRATES

摘要

One of the challenges of coating plastic substrates for exterior automotive applications involves the tendency for light stabilizers, which inhibit UV degradation of the coating, to migrate out of the topcoat and into the underlying plastic substrate. The consequent depletion of the stabilizer from the topcoat accounts for significantly poorer durability of coatings applied on plastic than on a nonpermeable substrate such as steel. This study investigates the migration of both nonreactable and reactable UV absorbers (UVAs) and Hindered Amine Light Stabilizers (HALS) in a fully formulated 2K urethane coating system applied on thermoplastic olefin (TPO) and steel substrates. Extensive migration of the nonreactable stabilizers occurs during exposure of the cured coating, and this migration correlates with poorer performance on TPO. Functionalization of the stabilizer with a group which covalently reacts into the coating prevents much of this migration, and the improved degree of retention of the reactable light stabilizers in the topcoat correlates with improved performance on TPO substrates. In addition, stabilizer variables such as the type and extent of functionalization as well as their chemical structure have an effect on both migration and performance of the stabilizers.