Patent ID: 6270698
Filing Date: 2001-08-07
Classification: B29C,B29D,B29L,Y10S

Abstract:
A method of molding a negative diopter stress-relieved ophthalmic lens out of acrylic resin material by an injection-coining mold process, the method comprising the steps of:providing an injection molding machine having a mold clamp and a mold material injection screw, with a two plate fixed cavity mold having a movable half and a stationary half with at least one mold cavity defined between the movable half and stationary half, the mold cavity having varying thickness dimensions, with a center thickness less than a peripheral thickness, and an overflow area extending from the mold cavity, the movable mold half operatively controlled to exert variable clamping pressure against the stationary mold half,preparing the injection molding machine for operation with acrylic resin as a molding material by inputting predetermined molding process control parameters into a control system, the molding process control parameters being selected to avoid formation of stresses in the lens, the molding process control parameters including plastic temperature, plastic flow rate, plastic pressure, plastic cooling rate, clamp closing velocity, velocity-pressure changeover position and coining stroke,initiating the mold process by closing the mold halves together under a primary clamp pressure at a specified partial tonnage,advancing the injection screw to partially fill the mold and to reach a velocity-pressure change over position, at whicha secondary clamp pressure is applied to the mold at a specified tonnage greater than the partial tonnage to perform a coining operation on the acrylic resin material in the mold,holding the injection screw under time and pressure,advancing the injection screw under the packing time and pressure,retracting the injection screw back to a metering ready position,allowing the acrylic resin material to solidify within the mold during a specified cooling time,opening a movable half of the mold to a stop point, andejecting a stress-relieved acrylic lens out of the mold.