Transparent abrasion-resistant flexible polymeric coating

Abstract

A process for preparing an adhesive, transparent, corrosion and abrasion resistant polymeric coating on a substrate, such as a glass, plastic or metal such as aluminum or steel. The substrate is coated with a mixture of up to about 15% by weight of an expanding polycyclic monomer such as a spiroorthocarbonate or spiroorthoester, a diepoxy oligomer such as a diglycidyl ether, and a lactone in a concentration of from about 1:2.5 to 1:4.5 by weight of the oligomer. To this mixture is added a catalytic quantity of a boron trihalide-amine complex and a catalytic quantity of an aromatic photocatalyst which releases a carbonium ion upon ultraviolet irradiation. The coated substrate is exposed to broad wavelength UV light for from about 2 to 20 seconds to initiate polymerization. Polymerization of the coating is completed by heating the coated substrate at a temperature of from about 50.degree. to 120.degree. C. for a sufficient period to complete polymerization to a flexible, tough, abrasive and corrosion resistant transparent coating. If the substrate is very thin, the heating may be omitted, as determined by the artisan. Instead of heating to complete polymerization, a di- or tri- functional acrylate may be added to the initial mixture. Preferably, the expanding monomer is a spiroorthoester formed in situ by the reaction of a lactone such as .gamma.-butyrolactone with an epoxide, as known in the art.