Dynamic information storage or retrieval – Storage medium structure – Layered
Reexamination Certificate
1998-06-05
2001-11-06
Ometz, David L. (Department: 2652)
Dynamic information storage or retrieval
Storage medium structure
Layered
Reexamination Certificate
active
06314079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical disc obtained on laminating two optical discs, each having an information recording surface on a substrate, and a method for manufacturing the optical disc.
2. Related Art
In the field of information recording, researches into the optical information recording system are proceeding briskly. This optical information recording system has a number of advantages, such as non-contact recording/reproduction, recording density higher by not less than one digit than with the magnetic recording medium recording system, or compatibility to memory configurations of the read-only, write-once and overwrite type memories. Thus, the optical information recording system is finding a wide field of application in both the industrial and domestic usages as a
As an optical disc capable of recording/reproducing the information by optical means, there are a read-only optical disc, a phase-change type optical disc and a magneto-optical disc.
In keeping up with the demand for high recording density, a laminated optical disc of the sole surface readout type, that is an optical disc in which a laser light beam is adapted to fall on one disc side and the focal point position of the laser light beam is changed to selectively read and write the information from or on the two optical discs. This increases the volume of the information per optical disc. There is also no necessity of providing two pickups or a mechanism for moving the sole pickup to both sides. Therefore, the laminated disc is convenient in promptly having access to disc data or in reducing the size of the recording/reproducing apparatus.
For producing the sole surface readout type laminated disc, two manufacturing methods have been proposed. In the first one of the manufacturing methods, a substrate is molded by injection molding and a first information recording portion is formed on one substrate surface. On the first information recording portion is formed a reflective surface, for example, for forming an optical disc. On the surface of the information recording portion is applied a UV curable resin onto which a stamper carrying the embossed information is pressed in order to mold a second information recording portion. At this time, the thickness of the UV curable resin needs to be controlled precisely. Moreover, since the first and second information recording portions are formed by respective different methods, it is difficult to perform control so that the same signals can be recorded on the two recording surfaces.
In the second manufacturing method, a disc substrate is prepared by injection molding and an information recording portion is formed on one substrate surface for preparing an optical disc. This operation is repeated once to complete two optical discs. These two discs are laminated by bonding the surface of information recording portion of one of the discs to the surface of the other disc opposite to its information recording portion by a UV curable resin to complete a sole optical disc. In this case, the thickness of the UV curable resin is easier to control than with the first manufacturing method. Moreover, since the substrates and the information recording portions are prepared by the same method, the signals on the respective surfaces are of uniform quality.
However, the optical disc prepared by laminating two optical discs with the above-described second method has a drawback that focal point of the laser light of the reproducing apparatus is more susceptible to blurring than with the conventional single disc thus leading to unstable playback signals and deteriorated playback properties.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disc in which two optical discs are laminated together to realize high recording density and improved recording/reproducing characteristics, and a method for producing the optical disc.
For overcoming the above problem, the present inventors have conducted perseverant researches on the laminated disc of the single surface readout type and clarified the conditions responsible for occurrence of unstable recording and/or reproduction of information signals. This finding has led to completion of the present invention.
That is, in the laminated disc of the single surface readout system, that is in the optical disc having two laminated optical discs, obtained by the above-mentioned second manufacturing method, the two laminated optical discs are formed by the same molding method and the information recording portions are formed by the same method, the two optical discs thus formed tend to be warped in the same direction. With the laminated discs
30
,
40
of the single surface readout system, the optical discs
31
,
41
, warped in the same direction, are laminated together, as shown in
FIGS. 1 and 2
, warping is accentuated, as a result of which focal point blurring of the laser light beam in the reproducing apparatus is produced to distort playback signals to deteriorate the quality of the information signals.
In one aspect, the present invention provides an optical disc including a first disc having a first information recording portion on one surface of a first substrate, and a second disc warped in a direction opposite to the direction of warping of the first disc, in which the second disc has a second information recording portion on one surface of a second substrate, and in which the first disc is laminated to the second disc so that the surface of the first disc having the information recording portion will face the surface of the second substrate carrying the second information recording portion.
During reproduction of the information signals, a laser light beam is incident on the surface of the first substrate not carrying the first information recording portion. The first disc or the second disc is selectively reproduced by varying the focal point position of the laser light beam.
With the above-described optical disc according to the present invention, the disc is prepared by laminating two optical discs warped in the opposite directions, the warping of one of the optical discs is counterbalanced by the warping of the other optical disc thus suppressing the warping of the laminated disc.
In another aspect, the present invention provides a method for producing an optical disc wherein, when laminating a first disc having a first information recording portion on one surface of a first substrate to a second disc having a second information recording portion on one surface of a second substrate, the direction of warping of the first disc set so as to be opposite to the direction of warping of the second disc. The first disc is laminated to the second disc so that the surface of the first substrate having the first information recording surface will face the surface of the second substrate carrying the second information recording portion.
With the above-described manufacturing method for an optical disc according to the present invention, since the disc is prepared by laminating two optical discs warped in the opposite directions, the warping of one of the optical discs is counterbalanced by the warping of the other optical disc thus suppressing the warping of the laminated disc.
Since the optical disc suppressed in warping is used on a reproducing apparatus capable of selectively reproducing the first or second optical discs with variable focal point positions of the laser light beam, the information signals can be reproduced satisfactorily.
With the manufacturing method for an optical disc according to the present invention, since the warping of one of two discs warped in opposite directions can be counterbalanced by that of the other disc, a laminated optical disc is produced which is suppressed in warping and hence is stabilized in recording and/or reproducing characteristics.
REFERENCES:
patent: 5598398 (1997-01-01), Best et al.
patent: 5766717 (1998-06-01), Kaneko et al.
patent: 5831952 (1998-11-01), Yamada et al.
patent: 5846627 (1998-12
Nakayama Hiroshi
Nomura Hiroshi
Shimizu Jun
Castro Angel
Ometz David L.
Sonnenschein Nath & Rosenthal
Sony Corporation
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