Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1995-09-26
2001-06-19
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S286000, C369S288000, C428S064400
Reexamination Certificate
active
06249509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an optical disc. The optical disc includes optical recording discs such as, for example, magneto-optical discs, phase change type optical recording discs, and write-once optical recording discs as well as read-only optical discs.
2. Background Art
In general, optical discs have information-carrying means in the form of a recording layer or a row of pits on one surface of a substrate. For writing and reading purposes, a light beam, typically a laser beam is directed to the information-carrying means from the rear surface of the substrate. The substrate is generally made of a transparent material for this reason. In the prior art, resin substrates are generally used in order to reduce the disc weight and facilitate formation of grooves and pits for tracking and other purposes.
Over the recent past, active research has been made on optical discs that carry moving picture digital information. To this end, it is essential to increase the capacity and data transfer rate of optical discs and hence, the diameter and revolution of optical discs.
However, resin substrates are difficult to manufacture to uniform quality. Especially when the resin substrates have a large diameter, they tend to be non-uniform, allowing birefringence and other factors to adversely affect writing and reading performance. Additionally, the resin substrates are less resistant to heat and moisture and undergo deformation and deterioration in a hot humid atmosphere. Also since resin substrates with a large diameter are less stiff, high-speed revolution at 1,800 rpm or higher, especially 3,000 rpm or higher causes axial runouts, resulting in a significant increase of focusing and tracking errors.
Under these circumstances, attention is paid to glass substrates having high mechanical strength. The glass substrates, however, are likely to fail, especially near their corner, upon receipt of impact as by accidental dropping or hitting. Although substrates of chemically strengthened glass having higher mechanical strength are known, they can be crushed into scattering chips. Some optical discs are received in cartridges, but still can be broken as a result of vibration of the disc within the cartridge.
Japanese Patent Application Kokai (JP-A) No. 203409/1994 discloses a disc-shaped recording medium comprising a disc-shaped glass substrate and a disc-shaped resin substrate joined thereto wherein the resin substrate has a larger diameter than the glass substrate. The periphery of this recording medium has a cross section as shown in
FIG. 5. A
resin substrate
4
having a larger diameter is joined to a glass substrate
2
with an adhesive layer
5
while a recording layer
3
on the glass substrate
2
is disposed inside. However, this structure cannot fully prevents a failure of the corner of the glass substrate when impact is applied thereto from an oblique direction.
Japanese Utility Model Application Kokai No. 38340/1982 discloses an optical information recording disc having a glass substrate received in a plastic holder frame. This optical information recording disc is shown in
FIG. 6
as comprising a glass substrate
2
, a metallization
31
coated on the glass substrate
2
and selectively etched by laser processing in accordance with external signals for recording information, a plastic holder frame
7
having a concave for receiving the metallized glass substrate
2
, and a protective plate
10
removably fitted in the plastic holder frame
7
above the concave for covering the glass substrate
2
. The protective plate
10
is rigidly secured to the frame
7
by a stop ring
8
. This optical information recording disc requires to remove the protective plate
10
upon writing and attach the protective plate
10
again upon reading. This structure intends to prevent direct contact of the recording surface with the ambient atmosphere and reduce the weight, but not to prevent a failure of the glass substrate near its corner. In fact, this optical information recording disc is less effective for preventing a failure of the glass substrate
2
near its periphery since the periphery of the glass substrate
2
is in close fit with the plastic holder frame
7
.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an optical disc having a glass substrate which is designed to prevent a failure of the glass substrate near its corner upon receipt of physical shocks.
In a first aspect, the present invention provides an optical disc comprising a disc-shaped glass substrate and a protective resin member. The substrate defines a pair of major surfaces and an outer side and has information carrying means on one major surface. The protective member includes a disc-shaped covering portion and an annular rim extending from the periphery of the covering portion. The glass substrate is integrally joined to the protective member. The information-carrying means of the glass substrate faces the covering portion of the protective member. The outer side of the glass substrate is surrounded by the protective member rim to leave a space between the outer side of the glass substrate and the inner surface of the protective member rim. Preferably, another space is left between the one major surface of the glass substrate near the periphery thereof and the covering portion of the protective member.
In a second aspect, the present invention provides an optical disc comprising a pair of disc-shaped glass substrates each defining a pair of major surfaces and an outer side and having information-carrying means on one major surface. A protective resin member includes a disc-shaped partition portion and an annular rim extending from the periphery of the partition portion in opposite directions. The pair of glass substrates are integrally joined to the protective member such that the partition portion of the protective member intervenes between the glass substrates with each information-carrying means disposed inside. The outer side of each the glass substrate is surrounded by the protective member rim to leave a space between the outer side of the glass substrate and the inner surface of the protective member rim.
In preferred embodiments according to the first and second aspects of the invention, the distance from the covering portion to the free end of the protective member rim is greater than the distance from the covering portion of the protective member to the other major surface of the glass substrate; the protective member further includes an annular lug extending inwardly from the free end of the annular rim, the lug covering the other major surface of the glass substrate near the periphery thereof; an adhesive sheet is used to integrally join the glass substrate to the protective member; and the space between the outer side of the glass substrate and the inner surface of the protective member rim is filled with a resin.
In the optical disc of the present invention, the protective resinous member has a peripheral annular rim which radially surrounds the outer side of the glass substrate along its circumference with a shock absorbing space left therebetween. This structure is effective for preventing a failure of the glass substrate near its outer corner by external shocks from any direction.
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Hirata Hideki
Kuribayashi Isamu
Tanabe Hiroshi
Utsunomiya Hajime
Larson & Taylor
Lasker R. J.
Neyzari Ali
TDK Corporation
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