Fabrication of thermoplastic optical components by injection/compression molding

A method for molding a lens in a molding cavity defined by a pair of axially spaced molds slidably mounted within a sleeve, which comprises the steps of spacing the molds to define a cavity having a volume in excess of that required to form the finished lens, filling the cavity with a polymeric molding material at a temperature of the same order as the molds defining the molding cavity by extrusion through an inlet passage in said sleeve, at least the molds having been heated to a temperature above, but relatively close to, the glass transition temperature of the molding material, moving one or both molds to reduce the volume of the cavity to the desired size of the lens plus any allowance for thermal shrinkage thereby compressing the molding material within the cavity and causing any excess molding material to be extruded out of the mold cavity, applying pressure to the molten material through one or both of the molds to form the lens under conditions where shrinkage is accommodated while gradually cooling the molds, the sleeve and the lens through the glass transition temperature, and removing the molds and the lens from the sleeve.

An apparatus for molding finished ophthalmic lenses, comprising a plurality of molding assemblies, each molding assembly including a sleeve member having a bore extending therein, a pair of mold dies having contoured molding surfaces adapted to form complementary front and back surfaces of a lens, said dies further including outer peripheral surfaces dimensioned to be received in said bore with minimal clearance for sliding translation therein, said mold dies being received in said bore in spaced apart relationship to define therebetween a mold cavity;

• means for processing said plurality of molding assemblies individually and consecutively, including means for injecting a thermoplastic molding material in a molten state into said mold cavity, means for moving said mold dies together to compress said molding material and to squeeze excess molding material from said molding cavity.

An apparatus for molding finished ophthalmic lenses, comprising;

• a plurality of molding assemblies, each molding assembly including a sleeve member having a bore extending therein, a pair of mold dies having contoured molding surfaces adapted to form complementary front and back surfaces of a lens, said dies further including outer peripheral surfaces dimensioned to be received in said bore with minimal clearance for sliding translation therein, said mold dies being received in said bore in spaced apart relationship to define therebetween a mold cavity;
• means for processing each of said plurality of molding assemblies in successive fashion, including means for releasably engaging one of said plurality of molding assemblies, means for injecting a molten thermoplastic molding material having a glass transition temperature into said mold cavity, and means for moving said mold dies together to compress said molding material;
• means for thermally cycling said plurality of molding assemblies, including means for heating each of said molding assemblies to a temperature above the glass transition temperature of said molding material prior to being engaged by said means for engagement, and means for cooling each of said molding assemblies after being released by said means for engagement to cool the molding material below the glass forming temperature thereof.