Patent ID: 6785222
Filing Date: 2004-08-31
Classification: B29C,B29L,G11B

Abstract:
A read-only optical recording medium simulated ta read/write recording medium, the read/write recording medium having a disc shape with a diameter of 65 mm or less and a thickness between and including 0.45 mm and 0.7 mm, a recording area on the disc extending outwardly from a radial position 12.5 mm or less from a center of the disc, the recording area having a storage capacity of at least 2 Gigabytes and a ratio between the recording area and a non-recording area of the disc being 3.4 or more, the read-only optical recording medium comprising:a substrate formed to a disc shape having a thickness between and including 0.4 mm and 0.6 mm by injecting a resin into a mold having formed thereon a pit pattern on a recording track in which a smallest pit length and a recording track pitch are about 1.4 times larger than a pit length and a track pitch on the read/write recording medium; a first information recording layer formed on the pit pattern on the substrate; a light-transparent sheet between and including 0.05 mm and 0.1 mm in thickness and having on one side thereof a pit pattern formed by thermally stamping a pit-pattern stamper; a second information recording layer formed on the pit-pattern side of the light-transparent sheet, wherein the pit pattern on the substrate and the pit pattern on the light-transparent sheet join each other with a transparent resin between then, the transparent resin between the substrate and light-transparent sheet having a thickness between and including 20 &mgr;m and 35 &mgr;m; a center hole formed through the center of the substrate; an annular table-abutment integrally formed as part of the disc around and adjacent the center hole and being convex to one side of the substrate, the annular table-abutment having a recessed portion having a surface that faces away from the one side of the substrate and that is recessed toward the one side of the substrate; and a magnetic-clamping hub 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 one side of the substrate and a depressed portion depressed from the flange portion into the center hole toward the one side of the substrate, a height of the hub from a lower surface of the depressed portion to an upper portion of the flange portion being smaller than a thickness of the table-abutment.