Optical disc having a protective layer which is thicker at its o

Details Optical disc having a protective layer which is thicker at its o Optical disc having a protective layer which is thicker at its o

1998-01-14

2000-01-18

Letscher, George J.

Dynamic information storage or retrieval

Storage medium structure

Layered

G11B 584

Patent

active

060163038

ABSTRACT:
An optical disc having a functional film, formed by a thin metal plate, and a protective film, formed on a transparent substrate, is disclosed. The protective film satisfies a condition d.gtoreq.2d.sub.0, where d is a maximum film thickness at an outer periphery of the protective film and d.sub.0 is a mean film thickness at a flat portion on a data area. A magneto-optical disc having a functional film which is a metal thin film having magneto-optical effects is also disclosed, wherein the protective film satisfies a condition that a difference L.sub.1 between a maximum film thickness d at the outer periphery of the protective film and a mean film thickness d.sub.0 at a flat portion of the data area is 40 .mu.m or less and the protective film has a curved surface having a radius of curvature R.sub.1 .gtoreq.12.48 mm at the outer periphery of the protective film. The present invention provides an optical disc having superior recording properties and a sufficient corrosion resistance even when the disc is provided with a highly corrosive thin metal film, such as a rare earth-transition metal amorphous thin film.

REFERENCES:
patent: 4584259 (1986-04-01), Mayer et al.
patent: 4788095 (1988-11-01), Machida et al.
patent: 4957824 (1990-09-01), Ohkawa
patent: 4980875 (1990-12-01), Ishiwata et al.
patent: 5202863 (1993-04-01), Miyatake et al.
patent: 5210673 (1993-05-01), Ito et al.

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