| 摘要 |
PURPOSE:To obtain highly accurate plastic optical parts by forming the cross section of a lense molding into a shape inversely proportional to the variation in thickness in the optical axis direction along the radial direction of a lense having a longitudinally sectional form. CONSTITUTION:The cross sectional shape of a gate 8 is set up such that inversely proportional relation for variation in thickness along the radial direction of cross sectional shape including the axes of cavities 4 and 5 is formed. A molten resin is cast through a sprue 6, a runner 7, and a gate 8 into cavities 4 and 5 where the difference in the flow rates of the molten resin is counterbalanced by faster flows of resin passing through the gate 8 on both sides than the central part. The molten resin can thus be uniformely cast into the cavities 4 and 5 to supperss the occurrence of strain and thereby of residual stress. Since the welding of resins of difference temperatures due to nonuniform flow of the resin in the cavities can be prevented, teh occurrence of optical defects such as double refraction, etc., can be avoided, and high-quality lens can be obtained. |
