Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-17
2001-11-06
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S273700, C156S275500, C156S275700, C156S286000, C369S286000
Reexamination Certificate
active
06312547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing an optical disk with multiple layers of recording surfaces.
2. Description of Related Art
As shown in
FIG. 1
, a conventional optical disk
50
for a type of recording with multiple layers has a first disk
1
having a first and second information recording surface and a second disk
2
having a third and fourth information recording surface with both disks adhered to each other by using an adhesive
8
or the like. The first disk
1
has a configuration in which a first semi-transparent reflective film
4
, an intermediate layer
5
having the second information recording surface, a second reflective film
6
, and a protection film
7
are laminated in sequence on a first information recording surface of a first optically transparent substrate
3
.
First pits
9
for carrying first information signals and second pits
10
for carrying second information signals are formed on the first information recording surface of the first optically transparent substrate
3
and the second information recording surface of the intermediate layer
5
, respectively. These first and second pits
9
and
10
have such a shape as to be able to perform reading by means of a reproducing beam that is emitted from the side of the first optically transparent substrate
3
(in the direction shown by the arrow in the figure). The second disk
2
has the same configuration as that of the first disk
1
and an explanation is omitted.
The aforementioned optical disk
50
is manufactured in the processes as shown in FIG.
2
A through FIG.
2
E.
First, as shown in
FIG. 2A
, the first optically transparent substrate
3
is prepared on which the first semi-transparent reflective film
4
is formed on the first information recording surface on which the first pits
9
for carrying the first information signals are formed.
Subsequently, as shown in
FIG. 2B
, with the first reflective layer
4
directed upward, the aforementioned first optically transparent substrate
3
is placed on a spin table
20
. The spin table
20
is formed of a disk having a high degree of optical transparency and is provided with a shaft
21
, on the center thereof, for attaching the substrate. Since there is provided a center hole
3
a
at the center of the first optically transparent substrate
3
, the first optically transparent substrate
3
is fixedly absorbed to the spin table
20
by inserting the center hole
3
a
of the first optically transparent substrate
3
onto the shaft
21
of the spin table
20
.
Subsequently, a resin P that hardens under an ultraviolet light and which becomes the intermediate layer
5
, in a process to be described later, is deposited on the first reflective layer
4
by means of a dispenser (not shown) in the shape of a donut around the center hole
3
a
of the first optically transparent substrate
3
. Thereafter, a stamper
22
, on which the second pits
10
for carrying the second information signals are formed, is placed over the first reflective film
4
with the surface where the second pits
10
are formed directed downwardly. Since there is formed a center hole
22
a
at the center of the stamper
22
in the same way as the center hole
3
a
of the aforementioned first optically transparent substrate
3
, the stamper
22
is placed on the same shaft as the first optically transparent substrate
3
by inserting the center hole
22
a
of the stamper
22
onto the shaft
21
of the spin table
20
.
Subsequently, as shown in
FIG. 2C
, high-speed rotation of the spin table
20
causes the resin P to spread into the spacing between the stamper
22
and the first reflective film
4
, and causes the excessive amount of resin P to be thrown off to form a film of the resin P, uniform in thickness. Subsequently, in the process shown in
FIG. 2D
, the intermediate layer
5
is formed by irradiating the bottom side of the spin table
20
(in the direction shown by the arrow in the figure) with ultraviolet light so as to harden the resin P.
Subsequently, as shown in
FIG. 2E
, the stamper
22
is removed to reveal the second pits
10
for carrying the second information signals transferred on the intermediate layer
5
. The second reflective layer
6
having a reflectance higher than that of the first reflective film
4
is formed on the second information recording surface to which the second pits of the intermediate layer
5
are transferred. Thereafter, the protection film
7
is formed on the second reflective film
6
to complete the first disk
1
.
Then, the second disk
2
with third and fourth information recording surfaces formed by the same processes as those described above and the first disk
1
manufactured in the aforementioned processes are adhered to each other by means of the adhesive
8
with the respective protection films
7
facing each other to complete the optical disk
50
.
The optical disk
50
manufactured as described above is designed, for example, so as to read information signals provided by the first pits
9
with the light derived from the semi-transparent reflective film and reflected from the first reflective film
4
, the semi-transparent reflective film allows a laser beam incident via the first optically transparent substrate
3
to transmit partially and reflect partially. The optical disk
50
is also designed so as to read information signals provided by the second pits
10
with the light which is transmitted through the first reflective film
4
and the intermediate layer
5
, and then reflected on the second reflective film
6
. Therefore, it is very important in providing improved reliability in reading information signals to make the intermediate layer
5
uniform in thickness.
It is difficult to make the thickness of the intermediate layer uniform since the aforementioned optical disk
50
employs the liquid-state ultraviolet light hardening resin P in the intermediate layer
5
due to the easy formation of air bubbles therein.
Accordingly, in the case of carrying out the rotational processing by means of the spin table
20
, the processing is carried out in a chamber (not shown) in a reduced-pressure state to remove air bubbles contained in the intermediate layer
5
. In addition, the intermediate layer
5
is made uniform in thickness by varying the amount of drops of the resin P, and the speed and time of the spin table
20
. However, it was very difficult to make the intermediate layer
5
uniform in thickness by controlling the amount of drops of the resin P, and the speed and time of the spin table
20
. Because of this problem, air bubbles were not able to be completely removed in the chamber having a reduced pressure.
OBJECT AND SUMMARY OF THE INVENTION
The present invention was developed in view of such circumstances. Its object is to provide an optical disk with an intermediate layer more uniform in thickness than before and with high reliability.
A method for manufacturing an optical disk according to a first aspect of the present invention is characterized by comprising the steps of: forming a first semi-transparent reflective film for reflecting part of the incident light and partly transmitting the incident light onto a first information recording surface of an optically transparent substrate with the first recording surface on one side thereof; laminating an optically transparent sheet on the first reflective film, preparing a stamper with a second information recording surface; applying a liquid-state resin to one of the optically transparent sheets and the stamper, superimposing the optically transparent substrate on the stamper in a space of reduced pressure with the optically transparent sheet and the liquid-state resin interposed therebetween, and pressing the optically transparent substrate and stamper against each other with a predetermined pressure; forming, on the optically transparent sheet, a ultraviolet hardened resin layer to which the second information recording surface is transferred, by irradiating via the optic
Fujimori Jiro
Maruyama Haruhisa
Motokawa Masaaki
Ball Michael W.
Haran John T.
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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