| 摘要 |
PURPOSE:To mold a disk base excellent in optical anisotropy by providing a gate insert pushing means allowing a gate insert member to retreat to a retreat position, based on the resin pressure in the cavity of a product, when resin material is injected. CONSTITUTION:A sprue bush 50 guiding resin material into a cavity 14 is provided, and a cylindrical gate insert member 52 is slidably fitted onto the outer peripheral surface of this sprue bush. In injection operation, the gate insert member 52 is gradually retreated from its advanced position against the energizing force of a compression coil spring 78 by the resin pressure of the resin material injected in the cavity 14 of a product, and the resin pressure in the cavity 14 is effectively absorbed with this retreating operation. Accordingly, the internal stress generated at the inner peripheral part of a disk base does not become large, and the optical anisotropy made in the base also becomes small. |
