| 摘要 |
PURPOSE:To improve the rigidity of a disc by providing an annular information medium layer to one side of a substrate and making the thickness of the substrate at the inner peripheral part of the medium layer thicker than the thickness of the substrate where the information medium layer is provided. CONSTITUTION:A substrate 12, an information medium layer 13, a protection coating film 14 and a center hole are provided and the thickness of the substrate 12 of the inner peripheral 12-1 of the information medium layer 13 is made thick. Since it is possible for the relation of Ds/D=0.35-0.5 conventionally (D is a diameter of the substrate 2 and Ds is a diameter of the center hole), the rigidity is improved by 1.5-1.8 times in comparison with a conventional structure and the amplitude is reduced to 1/4-1/2. |
