Stock material or miscellaneous articles – Circular sheet or circular blank
Patent
1996-04-24
1997-09-02
Ryan, Patrick
Stock material or miscellaneous articles
Circular sheet or circular blank
428 642, 428 643, 428 644, 428332, 428336, 428 647, 425810, 430321, 430531, 3692752, 3692754, 264 11, 26432816, B32B 900
Patent
active
056629796
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a substrate for an optical disc on which an information signal is recorded, and more particularly to a disc substrate on which preliminary formed pits (hereinafter referred to as "prepit(s)") or grooves are provided to generate a tracking error signal.
BACKGROUND ART
Hitherto, an optical disc has been widely used as a recording medium for recording and/or reproducing an information signal by radiating a light beam on an information-recording surface thereof.
Such an optical disc known in the art includes an optical disc of a ROM (read only memory) type used only for reproducing an audio signal or an image signal already recorded thereon or reading out an information signal such as data signals, an optical disc of a DRAW (direct read after write) type on which an information signal is recordable in an unerasable manner only one time, a magneto-optical disc of a type capable of repeatedly recording and erasing an information signal thereon, or the like.
The optical disc of the ROM (read only memory) type includes a substrate made of a transparent material such as a synthetic resin or glass. Formed on a primary surface of the substrate as a signal-recording surface, are pits which are fine irregularities corresponding to the audio signal or other data signals recorded. The signal-recording surface of the substrate is covered with a reflecting film layer made of aluminum or the like.
Further, the magneto-optical disc capable of repeatedly recording the information signals also includes a substrate made of a transparent material such as a synthetic resin and glass, on a primary surface of which a vertically magnetized thin film layer having magneto-optical properties such as a Kerr effect or a Farady effect is formed. The vertically magnetized thin film layer is also covered with a reflecting film layer made of aluminum or the like. The vertically magnetized thin film layer of the magneto-optical disc, which serves as a signal recording layer, has been made of an amorphous alloy of a rare-earth element and a transition metal such as a Tb--Fe--Co alloy and the like.
Furthermore, the optical disc of a DRAW (direct read after write) type has a substrate made of a transparent material such as a synthetic resin and glass. Formed on a primary surface of the substrate is a signal-recording film layer composed of a low-melting metal thin film layer, a phase-changing film layer, an organic dye-containing film layer, or the like. In such an optical disc of the DRAW (direct read after write) type, the signal-recording film layer is also covered with a reflecting film layer made of aluminum, or the like.
Meanwhile, a huge number of optical discs have been used as a recording medium for an information signal-recording and/or reproducing apparatus. Therefore, it is desirable that the optical discs are produced with a high mass productivity and a low manufacturing cost. In order to meet such requirements, the substrate for the optical disc is obtained and widely used in the form of an injection-molded article made of a synthetic resin such as a polycarbonate resin.
The substrate used for the optical disc of the ROM type is formed with data pits which are fine irregularities corresponding to the audio signal or the image signal recorded. The recording tracks are formed on the substrate in a concentric or spiral relation to a center of the substrate of the optical disc. In the recording tracks, there are formed prepits which generate tracking error signals for controlling a scanning position of the light beam to be radiated to the surface of the optical disc, when detected.
Further, in the magneto-optical disc capable of repeatedly recording the information signals or the optical disc of the DRAW (direct read after write) type, the substrate is formed thereon with prepits which are in the form of fine irregularities arranged along virtual recording tracks disposed concentrically or spirally relative to the center of the substrate of the optical disc.
In the optical disc of the ROM (
REFERENCES:
patent: 5470627 (1995-11-01), Lee et al.
patent: 5521901 (1996-05-01), Dkada et al.
patent: 5541910 (1996-07-01), Tanaka et al.
Bahta Abraham
Ryan Patrick
Sony Corporation
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