Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Patent
1988-03-04
1989-10-31
Robinson, Ellis P.
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
428 65, 428212, 428412, 428900, 428913, 430945, 369280, 369282, 369289, 369290, 346 76L, 3461351, B32B 302
Patent
active
048776670
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc.
FIG. 1 is a perspective view of an optical disc 4 according to the prior art. In the drawing, reference numeral 1 denotes a disc-shaped substrate which is formed of polycarbonate or the like and has a centering hole 1a (whose diameter is 15 mm, for example) in the center. 2 denotes an information recording layer which is formed concentrically at a specified radial area on the disc substrate 1 and which is used for recording and reproducing information by an input-output device, not shown. 3 denotes a disc of magnetic material whose outer diameter is smaller than the inner diameter of the information recording layer. The optical disc 4 is formed by bonding one disc 3 to the upper face of the disc substrate 1 with an adhesive, and further by bonding another disc 3 to the lower face thereof so that the substrate is sandwiched between a pair of discs 3.
FIG. 2 is a sectional view of the optical disc 4 mounted on an optical disc driver, in which the disks 3 are attracted by a magnet 5a mounted on a disc turntable 5. The optical disc 4 is rotated by turning the disc turntable 5. Under such condition, information is written in the information recording layer 2 or read out therefrom by irradiating the layer with a laser beam.
According to the aforementioned prior optical disc, there is a difference between the thermal expansion coeffcient (7.times.10.sup.-5 mm/.degree.C.) of the disc substrate 1 and that (1.times.10.sup.-5 mm/.degree.C.) of the discs 3 of magnetic material, and therefore a problem exists in that distortion occurs in the disc substrate 1 whose thermal expansion coefficient is larger due to temperature change in the internal section of the optical driver. The distortion increases variations in the birefringence of the laser beam in the disc substrate irradiated when reading out information, thereby increasing noise when reproducing the information.
SUMMARY OF INVENTION
The present invention was made to solve the above-discussed problem, and has an object of providing an optical disk whose distortion due to temperature change is inhibited.
The optical disc according to the invention comprises a disc substrate having an information recording layer in a specified radial area thereof and a disc of a specified diameter mounted at the center of the disc substrate. A bonding section of the disc to the disc substrate is formed of a material whose thermal expansion coefficient is almost equivalent to the thermal expansion coefficient of the disc substrate.
Since the bonding section of the disc to the disc substrate is of a material having a thermal expansion coefficient almost equivalent to that of the disc substrate according to the invention, the disc substrate is prevented from being affected by the thermal expansion of any portion of the disc other than the bonding section. As a result, distortion in the optical disc due to temperature change can be inhibited.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view showing an optical disc according to the prior art;
FIG. 2 is a sectional view of the optical disc according to the prior art;
FIGS. 3(a) and 3(b) show an optical disc according to an embodiment of the present invention, wherein FIG. 3(a) is a perspective view and FIG. 3(b) is a sectional view;
FIGS. 4(a) and 4(b) show an optical disc according to another embodiment of the invention, wherein FIG. 4(a) is a perspective view and FIG. 4(b) is a sectional view;
FIG. 5 is a perspective view showing an optical disc according to a further embodiment of the invention; and
FIG. 6 is a perspective view showing an optical disc according to a yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 3(a) and 3(b) show an optical disc according to an embodiment of the invention, wherein reference numerals 1, 2 and 3 denote the same parts as the foregoing prior art. Reference numeral 7 denotes a disc which is interposed between the disc substrate 1 and the disc 3. The disc 7 is f
REFERENCES:
patent: 1875086 (1932-08-01), McMann
patent: 3416154 (1968-12-01), Heller et al.
patent: 4616278 (1986-10-01), Yamaguchi et al.
patent: 4634617 (1987-01-01), Ohta et al.
patent: 4658393 (1987-04-01), Ohta et al.
patent: 4698715 (1987-10-01), Oishi
Fujisawa Hidemitsu
Hattori Michinobu
Kusaura Akio
Mitsubishi Denki & Kabushiki Kaisha
Robinson Ellis P.
Ryan P. J.
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