| 摘要 |
PURPOSE:To produce a lens having good appearance in low cost by passing the resin injected into a cavity through the narrowest space in the cavity and subsequently reducing the vol. of the cavity to the vol. corresponding to a desired lens to solidify the resin. CONSTITUTION:When a molten thermoplastic resin is injected into a cavity 4, the temp. of a mold 30 (or the cavity 4) is set to temp. higher than the flow starting temp. of the resin. The injection of the molten resin is started in such a state that the vol. of the cavity 4 is made wider than the vol. (space) corresponding to a desired lens. At the time of this injection, the injected resin is passed through the narrowest space in the cavity 4 and, thereafter, the vol. of the cavity 4 is reduced to the vol. corresponding to the desired lens and the cavity is perfectly filled with the resin to solidify the resin. As a result, the resin advances from the almost center part of the cavity toward the periphery of the cavity so as to expand a concentric circle and the generation of the appearance deficiency of a lens such as a weld line or voids is suppressed. |
