PURPOSE: To obtain a mold providing an optical disc base with small internal strain and a few errors for recording and reproducing of information by providing a inclined face in such a way that a part projected in a cavity of an inner peripheral holder ring becomes higher to the outer peripheral side and specifying the height of the projected part.
CONSTITUTION: A mold for an optical disc base provides a fixed mirror face 1 and a movable mirror face 2 to form a cavity 3 wherein a molten resin is filled. A inner peripheral holder ring 8 has a projected part in the cavity 3 and when a resin is filled, the resin receives a shearing stress. Magnitude of the shearing stress is determined in accordance with the slope θ to a stamper 12 of the projected part and the height h determined by using the stamper 12 of the inner peripheral holder ring 8 as a standard. The taper angle θ and the height h are 0°<θ<90° and 0mm<h≤1.2mm. When this inner peripheral holder ring is used, the molten resin easily passes between the fixed mirror and the inner peripheral holder ring and shearing stress generated becomes thereby small. In addition, as the optical disc base is easily released from the movable mirror face after molding, no strain is produced in the base during releasing.
OGUSHI MASAYASU
YOSHIKAWA ATSUO
