Patent ID: 7305689
Filing Date: 2007-12-04
Classification: B29C,B29L,G11B

Abstract:
1. A read-only optical recording medium comprising: a substrate having a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm; a first information recording layer having a pit pattern formed on first side of the substrate, the first information recording layer passing a predetermined amount of a light beam irradiated through the substrate, the pit pattern of the first information recording layer having a pit length of 0.14 to 0.31 μm/bit; a second information recording layer having a pit pattern; a light-transparent layer formed on the first information recording layer, for providing a space between the first and second information recording layers; a center hole formed at the center of the substrate; an annular table-abutment integrally formed as a part of the substrate around and adjacent the center hole and being convex to second side of the substrate that is opposite the first and second information recording layers, the annular table-abutment having a recessed portion having a surface that faces away from the second side of the substrate and that is recessed toward the second side of the substrate; and a magnetic-clamping hub fixed to the annular table-abutment, the hub being fixed to the surface of the recessed portion of the annular table-abutment, the hub having a flange portion fixed to the surface of the recessed portion of the table-abutment on the surface of the table-abutment that faces away from the second side of the substrate and a depressed portion depressed from the flange portion into the center hole toward the second side of the substrate, a height of the hub from a lower surface of the depressed portion to an upper surface of the flange portion being smaller than a thickness of the table-abutment; wherein the second information recording layer reflects a light beam which is focused thereon through the first information recording layer and the light-transparent layer.