Mold for injection- molding or pressing of e.g. DVD blanks takes advantage of improved optical properties of polymethacrylate plastic and overcomes separation debris problem by designed, thin central section tearing

摘要

The injection gap between injector and blank, is less than 0.3 mm and the cutting gap between the edge of the impact cylinder (9) and the blank is less than 2 mm. Independent claims are included for the method of making the blank and the blank itself. The molten plastic is injected under high pressure through the sprue bush into the mold, where it sets. The sprue bush (5) is sheared off using the impact cylinder. The pin (10) ejects the sprue. The disc is removed following opening. Preferred features: The cavity for sprue section is immediately behind the injection gap. The spacing is at least 0.5 mm between its center (5) and the blank (11). In the method of manufacture, roughened edges due to extraction of the blank are found centrally at the edge of the disc hole.