Injection molding of contact lenses

Claim 1

A method of making a first quality stress-free "hard" contact lens blank comprising: (a) injecting a viscous plastic material into a mold having: (i) a cavity plate and defining at least one cylindrical cavity bore for reception of a cavity pin; (ii) cavity pin means disposed in said cavity bore, said cavity pin having one end defining a prescribed configuration at a first surface of the lens; (iii) an injection section adapted to engage said cavity plate along a part-line, said ejection section defining a bore axially aligned with said cavity bore; (iv) insert means in said cavity bore, said insert means defining a cylindrical opening adapted to receive at least the said end of said cavity pin means; (v) ejection pin means extending in said insert means and having an end defining a prescribed configuration at a second surface of the lens, said cavity pin means, ejection pin means and said insert defining a mold cavity which is of fixed configuration during molding; (b) controlling injection time, holding time, pressure, nozzle and mold temperatures approximately within the following prescribed limits while maintaining a fixed relationship in said mold cavity: Injection Time--1 to 10 seconds Hold Time--10 to 90 seconds Injection Pressure (PSI)--2,500 to 15,000 Nozzle Temperature--400° to 530° F. Material Temperature at Nozzle--370° to 530°0 F.; (c) separating the cavity plate and injection section and ejecting the molded lens from the mold; and (d) finishing the lens blank to a lens by an appropriate finishing step to impart the required optical characteristics with little or no finishing operations being required at the said first surface.

Claim 2

A method of making a first quality stress-free "hard" contact lens blank comprising: (a) injecting a viscous plastic material into a mold having: (i) a cavity plate and defining at least one cylindrical cavity bore for reception of a cavity pin; (ii) cavity pin means disposed in said cavity bore, said cavity pin having one end defining a prescribed configuration at a first surface of the lens; (iii) an injection section adapted to engage said cavity plate along a part-line, said ejection section defining a bore axially aligned with said cavity bore; (iv) insert means in said cavity bore, said insert means defining a cylindrical opening adapted to receive at least the said end of said cavity pin means; (v) ejection pin means extending in said insert means and having an end defining a prescribed configuration at a second surface of the lens, said cavity pin means, ejection pin means and said insert defining a mold cavity which is of fixed configuration during molding; (b) controlling injection time, holding time, pressure, nozzle and mold temperatures approximately within the following prescribed limits while maintaining a fixed relationship in said mold cavity: Injection Time--1 to 10 seconds Hold Time--10 to 90 seconds Injection Pressure (PSI)--2,500 to 15,000 Nozzle Temperature--400° to 530° F. Material Temperature at Nozzle--370° to 530°0 F.; (c) separating the cavity plate and injection section and ejecting the molded lens from the mold; and (d) finishing the lens blank to a lens by an appropriate finishing step to impart the required optical characteristics with little or no finishing operations being required at the said first surface.