Press moulding method for forming an optical element

摘要

In forming a plano-convex lens from a column-like lens blank by heating the blank to a temperature higher than the transition temperature thereof and by pressurizing an upper die with a closed space formed between the blank and the upper die, there are alternately repeated operations of pressurizing the upper die and stopping the application of pressure thereto. Through the control of the amount of displacement of the upper die, the maximum pressure of gas in the closed space at each pressurizing step is so controlled: as to be low according to the surface viscosity of the blank to the extent that no local concave deformation in the surface of the blank is produced; and as to be high to the extent that gas caught in the closed space is discharged at each step of stopping the application of pressure.