Patent ID: 7718097

Claim:
A process for producing a plastic lens which comprises, using a mold constituted with a pair of mold members facing each other and a plastic gasket which fixes the mold members to form a cavity and has an inlet for injecting a composition of a material monomer into the cavity, injecting the composition of a material monomer into the cavity through the inlet of the plastic gasket, sealing the inlet of the plastic gasket and, thereafter, conducting polymerization, wherein the inlet of the plastic gasket is sealed by ultrasonic welding and wherein the sealing of the inlet of the plastic gasket by ultrasonic welding is conducted under a condition such that a portion of the inlet of the gasket to be sealed by ultrasonic welding is closed under a pressure and a portion of the inlet of the gasket at a side of the cavity from the portion to be sealed by ultrasonic welding is tightly closed so as to avoid transmission of ultrasonic waves to the portion of the inlet of the gasket at a side of the cavity from the portion of the inlet of the gasket to be sealed by ultrasonic welding, wherein said portion of the inlet of the gasket at a side of the cavity from the portion to be sealed by ultrasonic welding is tightly closed so as to block any powder of gasket material formed at the portion of the inlet of the gasket to be sealed by ultrasonic welding from passing into the cavity, and wherein said portion of the inlet of the gasket at a side of the cavity from the portion to be sealed by ultrasonic welding, is not welded by ultrasonic waves for the ultrasonic welding.