Gasket for molding plastic lenses

Abstract

A clear, cylindrical, flexible gasket having an annular shoulder located on the interior surface thereof, midway between the ends. The gasket is sized to accept two lens half molds, one on either side of said shoulder to form a lens casting cavity. Each side of the shoulder has first and second annular protrusions extending therefrom for contacting and providing an annular double seal along the edges of each of the half molds. The surface of the shoulder which forms the side of the lens casting cavity is curved in order to reduce stress to a minimum during the shrinkage of the lens casting resin during the cure period. In addition, the casting surface of the shoulder is formed such that the final molded lens will have an outer ridge thereon. One end of the cylindrical gasket has an enlarged edge for additional strength and is provided with index markings thereon which extend beyond the edge and down the outer side of the clear gasket. Two identical fill ports are provided on opposite sides of the gasket. A necked down portion is provided at the point where the filling passage connects with the lens casting surface of the shoulder so that as the plastic resin of the lens being molded cures and shrinks, the plastic in the fill passage is automatically severed from the plastic which forms the final plastic lens product.