Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article
Reexamination Certificate
1997-09-24
2001-04-03
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Light polarizing article or holographic article
C264S001380, C264S001600, C264S001900, C264S002100, C264S107000, C425S810000
Reexamination Certificate
active
06210609
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to a method of manufacturing an optical recording medium and particularly to a method of manufacturing an optical recording medium having at least two minute concave and convex surfaces or more.
2. Background of the Invention
An optical recording medium used for recording and/or reproducing information by irradiating rays of light includes a read-only memory (ROM) type, a write-once type, and a rewritable type. In the ROM type optical recording medium such as a compact disk, for example, a minute concave and convex surface such as a phase pit where a data information, a tracking servo signal and so on are recorded, a pregroove or the like is formed in its information recording layer. In the write-once type or rewritable optical recording medium such as a magneto-optical recording medium, a phase-change recording medium, a minute concave and convex surface such as a pregroove or the like is formed.
FIG. 1
is a schematic, cross-sectional view of an optical disk, e.g., a compact disk (CD).
When this optical recording medium is formed, a transparent substrate
1
made of polycarbonate or the like and having a thickness of 1.2 mm is formed by injection molding, and at the same time a minute concave and convex surface
2
such as a pregroove is formed. A reflective film
4
formed of an AL evaporated film or the like is formed on the minute concave and convex surface
2
so as to have a thickness of several tens of nm, thereby an information recording layer
5
formed of the minute concave and convex potion
2
and the reflective film
4
being formed. Further, a protective film
6
made of an ultraviolet curing resin, for example, and having a thickness of several &mgr;m is laminated on the information recording layer
5
. Thus, the optical recording medium is formed.
An optical recording medium having a plurality of laminated information recording layers has been proposed in order to increase a recording information amount.
FIG. 2
is a schematic, cross-sectional view of an optical recording medium having a dilayer structure.
This optical recording medium is arranged such that first and second information recording layers
11
,
12
are laminated on a transparent substrate
10
with a transparent intermediate film
33
being disposed therebetween.
The first information recording layer
11
consists of a first minute concave and convex surface
21
formed at the same time when the substrate
10
is formed by injection molding of resin such as polycarbonate or the like, and a semitransparent film
13
made of, for example, SiN and deposited thereon. The second information recording layer
12
is formed of a second minute concave and convex surface
22
laminated on the first information recording layer
11
by photopolymerization (2P) method, and a reflective film
14
formed of an Al evaporated film or the like and deposited thereon. A protective film
16
made of an ultraviolet curing resin, for example, is formed on the second information recording layer
12
.
As shown in
FIGS. 1 and 2
, reading light L is irradiated on the optical recording medium from its substrate side thereof, thereby information being read out from the information recording layers thereof. In this case, as shown in
FIG. 2
, when information is read out from the optical recording medium having the first and second information recording layers
11
,
12
, respective rays of light L focused on the first and second information recording layers
11
,
12
are irradiated on the first and second information recording layers
11
,
12
from the same side, thereby the information being read out from the first and second information recording layers
11
,
12
.
However, each of the optical recording medium having a single information recording layer shown in FIG.
1
and the optical recording medium having two information recording layers shown in
FIG. 2
has an asymmetrical structure in its thickness direction in view of its material. Therefore, immediately after the optical recording medium is manufactured, shrinkage of the ultraviolet curing resin forming the protective film
16
tends to warp the substrates
1
and
10
and to keep them in their warped states. Secular changes thereof mainly brings their deformation such as warps resulting from absorption or removal of vapor in the air. Therefore, it leads to an unsatisfactory operation of reading a signal by an optical pickup.
When the optical recording medium having a dilayer structure shown in
FIG. 2
is formed, the first and second minute concave and convex surfaces
21
,
22
forming the first and second information recording layers
11
,
12
must be independently and respectively formed by injection molding or the 2P method. Therefore, it leads to low productivity.
SUMMARY OF THE INVENTION
In view of such aspects, it is an object of the present invention to provide a method of manufacturing an optical recording medium which has a structure symmetrical with respect to a thickness direction of the optical recording medium and which can easily be manufactured.
According to a first aspect of the present invention, when an optical recording medium having at least first and second minute concave and convex surfaces formed therein is manufactured, the first and second minute concave and convex surfaces are simultaneously molded on both surfaces of a substrate of the optical recording medium. Therefore, it is possible to manufacture a multilayer optical recording medium having an excellent symmetrical structure with respect to a vertical cross section direction of the substrate, i.e., in the thickness direction of the optical recording medium. Moreover, it is possible to effectively suppress the deformation thereof resulting from curing or shrinkage of an light curing resin or the like, absorption or removal of vapor in the air into or from a substrate, a transparent intermediate film or the like, and so on.
Since the first and second minute concave and convex surfaces are simultaneously formed on both of the surfaces of the substrate of the optical recording medium, it is possible to manufacture, with high productivity, the multilayer-structure optical recording medium which is very effectively used for increasing a capacity of recording information.
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patent: 4447381 (1984-05-01), Matey
patent: 4535434 (1985-08-01), Kishi
patent: 4956214 (1990-09-01), Imataki et al.
patent: 5078947 (1992-01-01), Nishizawa et al.
patent: 5189531 (1993-02-01), Palmer et al.
patent: 5728324 (1998-03-01), Welch et al.
patent: 368 442 A2 (1990-05-01), None
Arakawa Nobuyuki
Kashiwagi Toshiyuki
Takeda Minoru
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
Vargot Mathieu D.
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