Mold material with additives

A mold half useful in the production of a contact lens by the polymerization of a polymerizable composition in a mold assembly comprised of said mold half and a second mold half, said mold half comprising an integral article having a central curved section defining a concave surface, a convex surface and a circumferential edge, at least the central portion of at least one of said concave surface and said convex surface having the dimensions of the back curve of the desired swelled or unswelled contact lens to be produced in said mold assembly and being sufficiently smooth and contoured so that the surface of said contact lens formed by polymerization of said polymerizable composition in contact with said surface is optically acceptable, said article having an annular flange integral width and surrounding said circular circumferential edge and extending therefrom in a plane normal to the axis of said concave surface, said article also having a generally triangular tab situated in a plane normal to said axis and extending from said flange, said article having a thinness and rigidity effective to transmit heat therethrough and to withstand prying forces applied to separate said mold half from said mold assembly, and said article being comprised of a composition comprising a thermoplastic polymer and an internal additive which is impregnated into said thermoplastic material by compounding. said internal additive and said thermoplastic polymer, said internal additive is present in amounts ranging from about 0.1% to about 20% by weight, said thermoplastic material being polystyrene or polypropylene and said additive being a polyethylene or polypropylene wax having a molecular weight ranging from about 5,000 to about 200,000, stearate salt, a glycerol ester having a molecular weight of about 200-2,000, an amide wax of the formula R.sub.1 CONH.sub.2, wherein R.sub.1 is a hydrocarbyl group, and the amide wax has a molecular weight of about 200-2,000, silicone having a molecular weight ranging from about 2,000 to about 100,000, Montan wax, oxidized wax, fatty acid having a molecular weight of about 200 to about 2,000, a complex ester or a combination thereof.

A mold assembly used in the production of a contact lens by the polymerization of a polymerizable composition in said mold assembly, said mold assembly comprising a front mold half and a back mold half in contact therewith thereby defining and enclosing a cavity therebetween, and a polymerizable composition in said cavity in contact with both mold halves, wherein

• said front mold half comprises a first article of thermoplastic polymer transparent to ultraviolet light, said article having a central curved section with a concave surface, a convex surface and a circular circumferential edge, wherein the portion of said concave surface in contact with said polymerizable composition has the curvature of the front curve of a contact lens to be produced in said mold assembly, and is sufficiently smooth so that the surface of a contact lens formed by polymerization of said polymerizable composition in contact with said surface is optically acceptable;
• said first article having an annular flange integral with and surrounding said circular circumferential edge and extending therefrom in a plane normal to the axis of said concave surface, and generally triangular tab situated in a plane normal to said axis and extending from said flange;
• said back mold comprised of an integral article having a central curved section with a concave surface, a convex surface and a circular circumferential edge, wherein the portion of said convex surface in contact with said polymerizable composition has the curvature of the back curve of a contact lens to be produced in said mold assembly and is sufficiently smooth that the surface of a contact lens formed by polymerization of said polymerization composition in contact with said surface is optically acceptable;
• said second article having an annular flange integral with and surrounding said circular circumferential edge with and surrounding said circular circumferential edge and extending therefrom in a plane normal to the axis of said convex surface, and a generally triangular tab situated in a plane normal to said axis and extending from said flange wherein the convex surface of said back mold half contacts the circumferential edge of said front mold half;
• said back mold being comprised of a composition comprising a thermoplastic polymer and an internal additive which is impregnated into said thermoplastic material by compounding said internal additive and said thermoplastic polymer, said internal additive is present in amounts ranging from about 0.1% to about 20% by weight, said thermoplastic material being polystyrene or polypropylene, and said additive being a polyethylene or polypropylene wax having a molecular weight ranging from about 5,000 to about 200,000, stearate salt, a glycerol ester having a molecular weight of about 200-2,000, an amide wax of the formula R.sub.1 CONH.sub.2, wherein R.sub.1 is a hydrocarbyl group, and the amide wax has a molecular weight of about 200-2,000, silicone having a molecular weight ranging from about 2,000 to about 100,000, Montan wax, oxidized wax, fatty acid having a molecular weight of about 200 to about 2,000, a complex ester or a combination thereof.

In an improved process for forming a contact lens from a mold assembly comprising a front mold half and a back mold half in contact therewith thereby defining and enclosing a cavity therebetween, and containing in said cavity a polymerizable composition in contact with said mold halves;

• said front mold half comprising a first article of thermoplastic polymer transparent to ultraviolet light, said article having a central curved section with a concave surface, a convex surface and a circular circumferential edge, wherein the portion of said concave surface in contact with said polymerizable composition has the curvature of the front curve of a contact lens to be produced in said mold assembly and is sufficiently smooth so that the surface of a contact lens formed by polymerization of said polymerizable composition in contact with said surface is optically acceptable;
• said back mold half comprising a second article of thermoplastic polymer transparent to ultraviolet light, said article having a central curved section with a concave surface, a convex surface and a circular circumferential edge, wherein the portion of said convex surface in contact with said polymerizable composition has the curvature of the back curve of a contact lens to be produced in said mold assembly and is sufficiently smooth so that the surface of a contact lens is formed by polymerization of said polymerizable composition in contact with said surface is optically acceptable, wherein the convex surface of said back mold contacts the circumferential edge of said front mold half;
• and the front mold half is clamped against the back mold half;
• and the polymerizable composition undergoes polymerization under precuring and curing conditions with ultraviolet light and the back curve is separated from the front curve and the contact lens during a demolding process and the front curve is subsequently separated from the contact lens, the improvement comprising utilizing a back curve mold that is comprised of a composition comprising a thermoplastic polymer and an internal additive which is impregnated into said thermoplastic material by compounding said internal additive and said thermoplastic polymer, said internal additive is present in amounts ranging from about 0.1% to about 20% by weight, said thermoplastic material being polystyrene or polypropylene, and said additive being a polyethylene or polypropylene wax having a molecular weight ranging from about 5,000 to about 200,000, stearate salt, a glycerol ester having a molecular weight of about 200-2,000, an amide wax of the formula R.sub.1 CONH.sub.2, wherein R.sub.1 is a hydrocarbyl group, and the amide wax has a molecular weight of about 200-2,000, silicone having a molecular weight ranging from about 2,000 to about 100,000, Montan wax, oxidized wax, fatty acid having a molecular weight of about 200 to about 2,000, a complex ester or a combination thereof.