| 摘要 |
PROBLEM TO BE SOLVED: To form a watermark by providing parts not overlapping with light reducing layers, by partially forming the light reducing layers so as to lie upon a metallic thin film layer of a thickness capable of transmitting light. SOLUTION: An aluminum thin film layer 2 having a thickness of 0.01 to 0.04μm capable of transmitting light, is formed by vacuum evaporation on one surface of a film base 1 having a thickness of 10 to 100μm composed of polyester, polypropylene and the like, and light reducing layers 3 having a thickness of 0.01 to 0.1μm which constitutes a watermark forming layer together with the aluminum thin film layer 2 are partially formed by vacuum evaporation so as to lie upon one surface of this aluminum thin film layer 2. In this event, light transmissivity of non-overlapping parts of the light reducing layers 3 of the watermark forming layer is higher than light transmissivity of overlapping parts of the light reducing layers 3, and therefore a watermark is constituted by these parts having higher light transmissivity, that is, the non-overlapping parts of the light reducing layers 3.
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