Stress-relieved molded acrylic opthalmic lenses, and injection-coining mold processes for molding stress-relieved plus and minus to high-minus diopter ophthalmic lenses of optically superior
acrylic resin, able to pass standardized
impact drop tests for use as
eyeglass lenses, are described. The injection-coining processes use two-plate and three-plate mold assemblies. The cavity of a two plate runnerless mold is partially filled under partial
tonnage, and the movable half of the mold controlled to
coin and densify the
acrylic resin under secondary or full
tonnage, when a velocity-pressure
changeover point is reached. In a process which employs a three-plate mold
assembly, the lens mold cavities are partially filled under less than total clamp
tonnage, with a cavity plate held by
hydraulic pressure against a movable half of the mold. The mold
assembly is then closed under full tonnage when a velocity-pressure
changeover point is reached, collapsing the cavity plate a stationary platen, bringing the mold
assembly to a total stack height. The processes produce
impact resistant acrylic ophthalmic lenses which are stress-relieved and without weld lines, even in the high minus diopter range, with center thickness' as low as one
millimeter, and edge thickness' up to ten millimeters.