Abstract: A stamper for injection-molding a plastic substrate for an optical disk characterized in that a rear surface of the stamper a surface roughness between 0.3 to 2.0 S.

Abstract: An improved electrolytic cleaning method for stamper which comprises suspending a stamper and an opposite electrode plate in an electrolytic stamper cleaning solution as opposed to each other by an electrode jig, the opposite electrode plate and the electrode jig each being made of substantially the same material as that of the stamper, and applying a DC voltage between the stamper and the opposite electrode so that the former serves as an anode and the later serves as a cathode to perform electrolytic cleaning under agitation of the cleaning solution.

Abstract: A stamper cleaning apparatus comprises an electrocleaning tank for performing electrodegreasing, a washing room adjacent to this cleaning tank, a shower, disposed in the upper section of the washing room, for water-washing a stamper by spraying washing water onto the stamper while the stamper is positioned inside the washing room and is wet with an electrocleaning solution, a water drain tank, disposed in the lower section of the washing room, for collecting water after the stamper is washed with water and for draining the water, and a small drying room disposed in the upper section of the washing room for operating to heat and dry the stamper after the shower has operated during the predetermined time the stamper is held in the washing room.

Abstract: A metal mold to be used for injection-molding of a flat plastic disc. The flat, annular mold cavity has a substantially continuously increasing axial thickness away from the injection gate. The gate can be in the center or on the outer periphery of the mold. A split mold type is disclosed wherein at least one of the inner opposed surfaces tapers away from an imaginary flat center plane. Alternatively, a stamper having a tapering thickness can be used in a mold having parallel opposed inner surfaces.

Abstract: Method and apparatus for producing a desired thickness distribution on a stamping plate in a rotary electroforming process. The stamping plate is used to produce a high density information recording carrier. A shielding plate is detachably mounted adjacent a fixed anode in an electrochemical bath. Another shielding plate is detachably mounted adjacent the rotary cathode. During electroforming either or both shielding plates are put into position or removed at appropriate times to produce the desired thickness distribution.