Injection moulding plastic lenses - in a cavity of reducible size having an overflow pocket

摘要

The appts. includes a pair of cavity defining dies movable towards each other after injection and an overflow pocket adapted to receive the excess material forced from the cavity. During injection a relatively wide cavity can be maintained to enable easy flow of the material, obviating defects such as knit lines. Redn. of the cavity size enables thin lenses, both concave and convex to be formed. A lens can be formed which required no finishing operation, such as grinding.