GB1317006A - Double replication process for producing ophthalmic lenses - Google Patents

Abstract

1317006 Casting ophthalmic lenses and moulds therefor J O BEATTIE LABORATORIES INC 6 July 1970 [15 July 1969] 32735/70 Heading B5A Ophthalmic lenses are produced by (i) casting a first resin against a glass negative; (ii) casting a second resin against the positive produced from (i); and (iii) casting an optically clear thermosetting plastic e.g. poly(diethylene glycol bis-allyl carbonate) against the negative from (ii). The first resin may be a copolymer of 70% acrylonitrile and 30% methyl methacrylate, preferably crosslinked with 5-30% glycol dimethacrylate. The second resin may be a copolymer of (a) 96-50% methyl methacrylate with 4-50% of glycol dimethacrylate, divinylbenzene or acrylonitrile, (b) 96-50% styrene with 4-50% glycol dimethacrylate or divinylbenzene or (c) 10-90% styrene with 90-10% acrylonitrile crosslinked with 5-50% glycol dimethacrylate or divinylbenzene. A flexible membrane is preferably used in stages (i) and (ii) to accommodate shrinkage of the resin, the casting in these stages preferably being effected at a pressure of 50 lb/in<SP>2</SP>. The lens may have a raised focal segment portion.