Spacer-rings for moulds of synthetic optical lenses - contg. polyisobutylene, sulpho-chlorinated polyethylene, ethylene-vinyl acetate copolymer and chalk

摘要

A spacer-ring for the 2 parts of a mould, esp. a glass mould, for making optical lenses from casting resin such as diethylene glycol bis-allyl carbonate, is formed from a compsn. contg. polyisobutylene, a sulpho-chlorinated polyethylene, an ethylene-vinyl acetate copolymer, and chalk as filler. The compsn. does not contain a plasticiser which cold diffuse into the lens matl. Exchange reactions do not occur between the compsn. of the ring and the casting resin. The elasticity of the ring is sufficient to prevent sepn. of the lens from the sections of the mould during moulding. The rings form a water-tight seal, so that polymsn. can be carried out in a water-bath. The lenses can easily be removed from the moulds. Spacer-rings of height 25 mm. and wall thickness only 2.5 mm. can be made by mass-prodn. methods. The rings are useful for the prodn. of lenses with a dioptric effect. After use, the spacer-ring cab be ground down, and the granulate can be cast again.