Patent ID: 6918267

Claim:
A press molding apparatus for simultaneously press molding a plurality of materials into a plurality of optical elements, comprising: at least one upper mother mold and at least one lower mother mold, each having a shape extending in a direction; a plurality of upper molding surfaces and a plurality of lower molding surfaces aligned on the at least one upper mother mold and the at least one lower mother mold, respectively, in said direction; a heater for heating the upper and/or the lower mother molds; upper and lower supporting members each for supporting the at least one upper mother mold and the at least one lower mother molds so that the upper molding surfaces and the lower molding surfaces are faced to each other; and a drive shaft coupled to the upper supporting member or the lower supporting member so that the upper mother mold or the lower mother mold move towards and away from each other for press molding; wherein each of the upper and the lower mother molds satisfies the relationship given by: L×α×ΔT/t <0.0008, (1) where L represents the length (mm) of the mother mold in said direction, t, the thickness (mm) of the mother mold, α, the thermal expansion coefficient (/° C.) of the mother mold, and ΔT, the temperature difference (° C.) produced between both ends in the thickness direction of the mother mold during the press molding.