| 摘要 |
PURPOSE:To easily manufacture large-size Fresnel lens having good flatness by a press molding using molds consisting of a convex mold to form the mother mold size of Fresnel lens having a high releasing resistance and a concave mold facing the convex mold. CONSTITUTION:A wholly convex Fresnel lens mother mold is carved in a mold 8 to form the lens face of Fresnel lens, and concave face is carved in the counter mold 9 in such a way as to match the said mold 8. To these molds 8 and 9, a pressure is applied in the direction of arrow 10 at a proper temperature in order to press a transparent resin sheet, e.g., of vinyl chloride or acrylate, between them. Thus, in releasing the molded Fresnel lens from the molds, warping caused by differences in its releasing resistance can be prevented within such a range that no trouble arises when being used. |
