Patent ID: 6746631
Filing Date: 2004-06-08
Classification: B29C,B29D,B29K,B29L

Abstract:
A method for forming a plastic lens convex on one side and concave on the other side and having its maximum thickness in the central region of the lens and diminishing gradually in thickness radially towards the periphery of the lens, the method comprising the steps:providing a lens blank of substantially uniform thickness comprising at least one layer of a thermoplastic material; placing said lens blank between opposed concave and convex platens for forming, respectively, convex and concave surfaces on said lens blank, said concave platen holding a volume of a polymerizable composition comprising a monomer or an oligomer on a forming surface thereof, and wherein the radius of curvature (r2) of said convex platen and the radius of curvature (r1) of said concave platen correspond, respectively, to the relationship r1+r2=t&af;(n-1n)â€ƒwherein t is the thickness of the lens blank and n is the index of refraction of the lens blank; heating and pressing said platens together with said lens blank therebetween, said heating and pressing being sufficient to deform said lens blank and to cause polymerization of said polymerizable composition to take place to provide a layer of non-uniform thickness on the convex surface on said deformed lens blank, said layer of non-uniform thickness having maximum thickness in its central region and diminishing gradually in thickness radially towards the periphery of said layer, whereby there is formed a shaped lens, concave on one side and convex on the other, said lens having its maximum thickness in the central region thereof and diminishing gradually in thickness radially towards the periphery of said lens; and removing said shaped lens from between said platens.