Synthetic plastic correction lenses

摘要

Polarising correction lenses are mfd. by placing polarising element in a mould, injecting a synthetic monomer on each side of the element, polymerising the monomer and extracting the composite lens from the mould. The polarising element is pref. formed from a transparent sheet of polyvinyl alcohol contg. a proportion of oriented molecules of dehydrated alcohol, opt. polyvinyl butyral or mixts. are used. The outer elements are moulded from methyl methacrylate or cellulose derivs., pref. cellulose acetobutyrate. A polyvinyl alcohol adhesive is used to cement the layers. Thermosetting monomers such as diethylene glycol bis-allyl carbonate are used for the outer layers. The faces of the lenses are concave and convex respectively and are ground and polished to an exact configuration. Plastic lenses are mass produced by moulding and used as such without finishing, or correction by grinding and polishing.