U.S. patent number RE39,412 [Application Number 10/712,916] was granted by the patent office on 2006-11-28 for optical information medium, and method and apparatus for fabricating the same.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kiyoshi Inoue, Hisaki Miyamoto, Michiyoshi Nagashima, Sakae Noda.
United States Patent |
RE39,412 |
Miyamoto , et al. |
November 28, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Optical information medium, and method and apparatus for
fabricating the same
Abstract
The disk-shaped optical information medium of this invention
includes: a first substrate having a center hole; a second
substrate having a center hole; and a radiation curable resin
interposed between the first and second substrates for bonding
together the first and second substrates, wherein the optical
information medium further includes a stopper for preventing the
radiation curable resin from protruding into the center holes of
the substrates, and a space between the first and second substrates
of at least half of a clamp region for clamping the optical
information medium is filled with the resin.
Inventors: |
Miyamoto; Hisaki (Osaka,
JP), Nagashima; Michiyoshi (Nara-ken, JP),
Inoue; Kiyoshi (Osaka, JP), Noda; Sakae (Osaka,
JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
27458616 |
Appl.
No.: |
10/712,916 |
Filed: |
November 13, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
08861943 |
May 22, 1997 |
5972250 |
|
|
|
08599181 |
Feb 9, 1996 |
5681634 |
|
|
Reissue of: |
09366935 |
Aug 4, 1999 |
06263939 |
Jul 24, 2001 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Feb 15, 1995 [JP] |
|
|
7-27086 |
Mar 17, 1995 [JP] |
|
|
7-58933 |
Mar 17, 1995 [JP] |
|
|
7-58934 |
|
Current U.S.
Class: |
428/64.4;
369/275.4; 428/64.2; 428/156; 156/74; 156/295; 156/379.8; 156/539;
156/285; 156/275.7 |
Current CPC
Class: |
B29C
65/1448 (20130101); B29C 65/521 (20130101); B29C
66/322 (20130101); B29C 66/452 (20130101); B32B
37/1284 (20130101); G11B 7/26 (20130101); B29C
65/1435 (20130101); B29C 65/4845 (20130101); B29C
66/81267 (20130101); B29C 66/1122 (20130101); B29C
66/72321 (20130101); B29C 65/1406 (20130101); B29C
65/544 (20130101); B29C 66/65 (20130101); B29C
67/0044 (20130101); B29L 2017/005 (20130101); B32B
2310/0831 (20130101); B32B 2429/02 (20130101); B29C
65/524 (20130101); B29C 65/526 (20130101); B29C
65/528 (20130101); B29C 65/4815 (20130101); Y10T
428/24479 (20150115); Y10T 156/1702 (20150115); B29C
66/8322 (20130101); B29K 2995/0027 (20130101); B29C
66/71 (20130101); B29C 66/71 (20130101); B29K
2069/00 (20130101) |
Current International
Class: |
B32B
3/02 (20060101); B29C 65/14 (20060101); B29C
65/78 (20060101); B32B 3/10 (20060101); B32B
37/18 (20060101) |
Field of
Search: |
;428/64.6,64.1,64.2,64.4,156,282,323,409,414,448
;369/272,275.1,275.4 ;156/272.2,275.5,275.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
38 40 391 |
|
Jun 1989 |
|
DE |
|
40 41 199 |
|
Jul 1992 |
|
DE |
|
42 35 178 |
|
Nov 1999 |
|
DE |
|
0 408 763 |
|
Jan 1991 |
|
EP |
|
0 443 522 |
|
Aug 1991 |
|
EP |
|
0 528 106 |
|
Feb 1993 |
|
EP |
|
0 706 178 |
|
Apr 1996 |
|
EP |
|
2 004 404 |
|
Mar 1979 |
|
GB |
|
2 017 379 |
|
Oct 1979 |
|
GB |
|
57-133532 |
|
Aug 1982 |
|
JP |
|
62-195738 |
|
Aug 1987 |
|
JP |
|
62-213436 |
|
Oct 1987 |
|
JP |
|
63-9046 |
|
Jan 1988 |
|
JP |
|
63-50929 |
|
Mar 1988 |
|
JP |
|
63-63146 |
|
Mar 1988 |
|
JP |
|
63119040 |
|
May 1988 |
|
JP |
|
63-239628 |
|
May 1988 |
|
JP |
|
63-275052 |
|
Nov 1988 |
|
JP |
|
1-133227 |
|
Sep 1989 |
|
JP |
|
2-21438 |
|
Jan 1990 |
|
JP |
|
2-94040 |
|
Apr 1990 |
|
JP |
|
2-249150 |
|
Oct 1990 |
|
JP |
|
3209640 |
|
Sep 1991 |
|
JP |
|
351782 |
|
Nov 1991 |
|
JP |
|
3-209642 |
|
Dec 1991 |
|
JP |
|
4-10242 |
|
Jan 1992 |
|
JP |
|
4-271031 |
|
Sep 1992 |
|
JP |
|
5-20714 |
|
Jan 1993 |
|
JP |
|
6-131704 |
|
May 1994 |
|
JP |
|
6274940 |
|
Sep 1994 |
|
JP |
|
6-327577 |
|
Nov 1994 |
|
JP |
|
750035 |
|
Feb 1995 |
|
JP |
|
706178 |
|
Apr 1996 |
|
JP |
|
94-8469 |
|
Apr 1994 |
|
KR |
|
Other References
Office Action dated Feb. 14, 2000 issued by Chinese Patent Office
relative to Chinese Patent Application No. 96102425.9. cited by
other .
Office Action dated Aug. 22, 2002 issued by Japanese Patent Office
relative to Japanese Patent Application No. H08-027098. cited by
other .
Korean Patent Application No. 94-8469 and English translation
thereof. cited by other .
Korean Office Action dated Apr. 27, 1999, isssed in Korean Patent
Application No. 96-3660, and English translation thereof. cited by
other .
Korean Patent office Action in corresponding Korean Application No.
96-3660, dated Oct. 28, 1998 (4 pp.). cited by examiner.
|
Primary Examiner: Corcoran; Gladys J P
Attorney, Agent or Firm: Renner, Otto, Boisselle &
Sklar, LLP
Parent Case Text
.Iadd.NOTICE: More than one reissue application has been filed for
the reissue of U.S. Pat. No. 6,263,999. The reissue applications
are application Ser. No. 10/712,916 (the present application) and
Ser. No. 10/288,204(now abandoned), all of which are reissues of
U.S. Pat. No. 6,263,939..Iaddend.
This is a division of application Ser. No. 08/861,943, filed May
22, 1997, now U.S. Pat. No. 5,972,250, which is a division of
application Ser. No. 08/599,181, filed Feb. 9, 1996, now U.S. Pat.
No. 5,681,634.
Claims
What is claimed is:
.[.1. An apparatus for fabricating an optical information medium by
bonding together a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween, comprising: a table for integrally
rotating the first and second substrates, with the radiation
curable resin interposed therebetween, before the radiation curable
resin is cured; and centrally disposed means for absorbing through
the center holes of the first and second substrates the radiation
curable resin interposed between the first and second
substrates..].
.[.2. An apparatus according to claim 1, wherein an outer diameter
of the table is less than an outer diameter of each of the first
and second substrates..].
.[.3. An apparatus according to claim 2, wherein the outer diameter
of the table is about 70% or more than the outer diameter of each
of the first and second substrates..].
.[.4. An apparatus according to claim 1, wherein the means for
absorbing the radiation curable resin is at least one suction
port..].
.[.5. An apparatus according to claim 1, wherein the means for
absorbing the radiation curable resin is a plurality of suction
ports..].
.[.6. An apparatus according to claim 1, wherein the means for
absorbing the radiation curable resin comprises a suction
pump..].
.[.7. An apparatus according to claim 1, wherein the means for
absorbing the radiation curable resin comprises at least one
suction port in a boss..].
.[.8. An apparatus according to claim 1, wherein the means for
absorbing the radiation curable resin is a sponge..].
.[.9. An apparatus according to claim 1, wherein the resin which is
absorbed is excess resin..].
.Iadd.10. A disk-shaped optical information medium comprising: a
first substrate having a center hole; a second substrate having a
center hole; a radiation curable resin interposed between the first
and second substrates for bonding together the first and second
substrates, wherein the optical information medium further
comprises a stopper for preventing the radiation curable resin
formed at a portion closer to an outer circumference of the optical
information medium with respect to the stopper from spreading
toward a portion closer to an inner circumference of the optical
information medium, and the stopper is formed at a position closer
to the center holes of the substrates with respect to the center of
a clamp region for clamping the optical information medium, and a
space between the first and second substrates of at least a half of
the clamp region is filled with the radiation curable resin by
spreading the radiation curable resin to the position of the
stopper..Iaddend.
.Iadd.11. A disk-shaped optical information medium comprising: a
first substrate having a center hole; a second substrate having a
center hole; and a radiation curable resin interposed between the
first and second substrates for bonding together the first and
second substrates, wherein the optical information medium further
comprises a ring-shaped groove substantially concentric with the
center holes of the substrates, formed on at least one of the first
and second substrates, and the ring-shaped groove prevents the
radiation curable resin formed at a portion closer to an outer
circumference of the optical information medium with respect to the
ring-shaped groove from spreading toward a portion closer to an
inner circumference of the optical information medium with respect
to the ring-shaped groove, and the ring-shaped groove is formed at
a position closer to the center holes with respect to the center of
a clamp region for clamping the optical information medium, and a
space between the first and second substrates of at least a half of
the clamp region is filled with the radiation curable resin by
spreading the radiation curable resin to the position of the
ring-shaped groove..Iaddend.
.Iadd.12. A method for fabricating an optical information medium,
comprising the steps of: placing one of a first substrate having a
center hole and a second substrate having a center hole on the
other substrate with a radiation curable resin interposed
therebetween; curing the radiation curable resin by irradiating the
radiation curable resin with radioactive rays capable of passing
through at least one of the first and second substrates so as to
bond the first and second substrates together; and forming a
stopper for preventing the radiation curable resin formed at a
portion closer to an outer circumference of the optical information
medium with respect to the stopper from spreading toward a portion
closer to an inner circumference of the optical information medium,
at a position closer to the center holes of the substrates with
respect to the center of a clamp region for clamping the optical
information medium, wherein the step of placing one of the first
and second substrates on the other substrate includes the step of
filling a space between the first and second substrates of at least
a half of the clamp region with the radiation curable resin by
spreading the radiation curable resin to the position of the
stopper..Iaddend.
.Iadd.13. A method for fabricating an optical information medium,
comprising the steps of: placing one of a first substrate having a
center hole and a second substrate having a center hole on the
other substrate with a radiation curable resin interposed
therebetween; curing the radiation curable resin by irradiating the
radiation curable resin with radioactive rays capable of passing
through at least one of the first and second substrates so as to
bond the first and second substrates together; and forming a
ring-shaped groove substantially concentric with the center holes
of the substrates on at least one of the first and second
substrates, wherein the ring-shaped groove prevents the radiation
curable resin formed at a portion closer to an outer circumference
of the optical information medium with respect to the ring-shaped
groove from spreading toward a portion closer to an inner
circumference of the optical information medium with respect to the
ring-shaped groove, and the ring-shaped groove is formed at a
position closer to the center holes with respect to the center of a
clamp region for clamping the optical information medium, wherein
the step of placing one of the first and second substrates on the
other substrate includes the step of filling a space between the
first and second substrates of at least a half of the clamp region
with the radiation curable resin by spreading the radiation curable
resin to the position of the ring-shaped groove..Iaddend.
.Iadd.14. A disk-shaped optical information medium comprising: a
first substrate having a center hole and a thickness of 0.6 mm; a
second substrate having a center hole and a thickness of 0.6 mm;
and a radiation curable resin interposed between the first and
second substrates for bonding together the first and second
substrates, wherein the optical information medium further
comprises a stopper for preventing the radiation curable resin from
protruding into the center holes of the substrates, and a space
between the first and second substrates of at least a half of a
clamp region for clamping the optical information medium is filled
with the resin..Iaddend.
.Iadd.15. A disk-shaped optical information medium comprising: a
first substrate having a center hole and a thickness of 0.6 mm; a
second substrate having a center hole and a thickness of 0.6 mm;
and a radiation curable resin interposed between the first and
second substrates for bonding together the first and second
substrates, wherein the optical information medium further
comprises a ring-shaped groove substantially concentric with the
center holes of the substrates, formed on at least one of the first
and second substrates at a position closer to the center holes with
respect to the center of a clamp region for clamping the optical
information medium, and a space between the first and second
substrates of at least a half of a clamp region is filled with the
radiation curable resin..Iaddend.
.Iadd.16. A method for fabricating an optical information medium,
comprising the steps of: forming a pair of substrates each having a
center hole and a thickness of 0.6 mm; placing one of the pair of
substrates on the other substrate with a radiation curable resin
interposed therebetween; and curing the radiation curable resin by
irradiating the resin with radioactive rays capable of passing
through at least one of the pair of substrates so as to bond the
pair of substrates together, wherein the step of forming a pair of
substrates includes the step of forming a stopper for preventing
the radiation curable from protruding into the center holes on at
least one of the pair of substrates, and the step of placing one of
the pair of substrates on the other substrate includes the step of
filling at least a half of a clamp region of the optical
information medium with the radiation curable resin..Iaddend.
.Iadd.17. An apparatus for fabricating an optical information
medium by bonding together a first substrate having a center hole
and a second substrate having a center hole with a radiation
curable resin interposed therebetween, comprising: a table for
integrally rotating the first and second substrates, with the
radiation curable resin interposed therebetween, before the
radiation curable resin is cured; and centrally disposed means for
absorbing through the center holes of the first and second
substrates the radiation curable resin interposed between the first
and second substrates..Iaddend.
.Iadd.18. An apparatus according to claim 17, wherein an outer
diameter of the table is less than an outer diameter of each of the
first and second substrates..Iaddend.
.Iadd.19. An apparatus according to claim 18, wherein the outer
diameter of the table is about 70% or more than the outer diameter
of each of the first and second substrates..Iaddend.
.Iadd.20. An apparatus according to claim 17, wherein the means for
absorbing the radiation curable resin is at least one suction
port..Iaddend.
.Iadd.21. An apparatus according to claim 17, wherein the means for
absorbing the radiation curable resin is a plurality of suction
ports..Iaddend.
.Iadd.22. An apparatus according to claim 17, wherein the means for
absorbing the radiation curable resin comprises a suction
pump..Iaddend.
.Iadd.23. An apparatus according to claim 17, wherein the means for
absorbing the radiation curable resin comprises at least one
suction port in a boss..Iaddend.
.Iadd.24. An apparatus according to claim 17, wherein the means for
absorbing the radiation curable resin is a sponge..Iaddend.
.Iadd.25. An apparatus according to claim 17, wherein the resin
which is absorbed is excess resin..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information medium
where two optical information substrates are bonded together, and a
method and an apparatus for fabricating the same.
2. Description of the Related Art
In order to enhance the density of an optical disk, reducing the
wavelength of a reproduced laser beam and increasing the numerical
aperture (NA) of an objective lens are required. However,
increasing the NA of an objective lens makes the allowable tilt of
a disk very small. For example, for a substrate with a thickness of
1.2 mm which is the thickness of CDs, the tilt of the substrate
allowable for an objective lens with an NA of 0.6 is about
0.25.degree.. This is equal to the error occurring at the mounting
of an optical head to a player, meaning that no allowance is left
for the tilt of an optical disk due to a shape change of the disk.
Such an optical disk is not practical.
The allowable range for the tilt of a disk can be widened by
reducing the thickness of a substrate. Thus, a practical optical
disk with high density used for an objective lens with high NA can
be realized. For example, by reducing the thickness of the
substrate to 0.6 mm which is a half of the thickness of CDs, the
tilt allowable for an objective lens with an NA of 0.6 is as high
as about 0.75.degree.. In this case, even if an error of
0.25.degree. arises at the mounting of an optical head to a player,
a tilt of the disk of 0.5.degree. due to a shape change of the disk
is allowed.
An optical disk composed of a single thin substrate tends to bend
down by its own weight. To avoid this problem, it is recommended to
bond two substrates together. This serves, not only to increase the
mechanical strength, but also to double the capacity of the disk by
using two sides for information recording.
FIG. 1 is a sectional view of a typical optical disk having two
substrates bonded together with a radiation curable resin.
Referring to FIG. 1, a first substrate 1 has a first information
signal surface 2, on which a first reflection film 3 made of metal
and the like including aluminum as a main component is formed. A
second substrate 4 has a second information signal surface 5, on
which a second reflection film 6 made of the same material as the
first reflection film 3 is formed. A layer of a radiation curable
resin 7 is formed between the first and second reflection films 3
and 6, which are facing each other, so as to bond the first and
second substrates 1 and 4 together.
Referring to FIGS. 2A to 2D, a conventional method for fabricating
such an optical disk will be described (Japanese Laid-Open Patent
Publication No. 6-238846). The first substrate 1 having the first
information signal surface 2 is formed with a transparent resin
such as polycarbonate by injection molding and the like. The first
reflection film 3 is then formed on the first information signal
surface 2 of the first substrate 1 by sputtering, vapor deposition,
and the like. Also, the second substrate 4 having the second
information signal surface 5 is formed by injection molding and the
like, and the second reflection film 6 is formed on the second
information signal surface 5 of the second substrate 4 by
sputtering and vapor deposition. The first and second reflection
films 3 and 6 are made of metal including aluminum as a main
component. Then, while the first substrate 1 being rotated at low
speed, the radiation curable resin 7 is applied to the surface of
the first substrate 1 on which the first reflection film 3 is
formed, forming a donut-shaped resin layer (FIG. 2A). The second
substrate 4 is then placed on the radiation curable resin 7 so that
the second reflection film 6 on the second information signal
surface 5 of the second substrate 4 faces the radiation curable
resin (FIG. 2B). The first and second substrates 1 and 4 are then
rotated together at high speed to allow the radiation curable resin
to spread in the space between the first and second substrates 1
and 4 (FIG. 2C). The radiation curable resin is irradiated with
radioactive rays (UV rays in FIG. 2D) through the second substrate
4 and the second reflection film 6 formed thereon, to cure the
radiation curable resin and thus to bond the two substrates
integrally (FIG. 2D).
In this conventional example, each of the two bonded substrates has
an information signal surface, and the reflection film is formed on
each information signal surface. The reflection film allows a
slight amount of radioactive rays to pass therethrough and thus
causing the radiation curable resin to be cured. For example, when
the reflection film is made of aluminum and irradiated with UV
rays, the UV transmittance of the aluminum film is 1% or less,
which is large enough to cure the resin sufficiently.
The disk with bonded thin substrates has such a large capacity that
the capacity of only one side of the disk is enough for most
software. Accordingly, one of the bonded substrates can be a
transparent dummy substrate. In this case, the radiation curable
resin can be rapidly and easily cured with radioactive rays passing
through the transparent substrate (Japanese Laid-Open Patent
Publication Nos. 5-63668 and 5-195011).
Alternatively, a semi-transparent film can be formed on one of the
two substrates, and the two information signal surfaces can be
accessed from one side of the disk. In this case, the radiation
curable resin can be rapidly and easily cured with radioactive rays
through the semi-transparent film.
As described above, in the above conventional method for
fabricating a disk with two substrates bonded together, a radiation
curable resin is applied to one of the substrates to form a
donut-shaped resin layer while the substrate is being rotated at
low speed, and the radiation curable resin is allowed to spread in
a space between the two substrates while the two substrates are
being rotated at high speed. In this case, when the high-speed
rotation of the two substrates starts before the radiation curable
resin spreads toward the inner circumferences of the substrates,
the inner circumference portion of the disk is not supplied with a
sufficient amount of resin. The resultant disk is inferior in
strength. On the contrary, when the high-speed rotation of the two
substrates starts only after the resin has sufficiently spread in
the space between the two substrates, the resin tends to protrude
to center holes of the substrates. This causes troubles such as
decentering when the resultant disk is mounted on a turntable of a
player.
SUMMARY OF THE INVENTION
The disk-shaped optical information medium of this invention
includes: a first substrate having a center hole; a second
substrate having a center hole; and a radiation curable resin
interposed between the first and second substrates for bonding
together the first and second substrates, wherein the optical
information medium further includes a stopper for preventing the
radiation curable resin from protruding into the center holes of
the substrates, and a space between the first and second substrates
of at least a half of a clamp region for clamping the optical
information medium is filled with the resin.
In one embodiment of the invention, the stopper includes at least
one concave portion formed on at least one of the first and second
substrates.
In another embodiment of the invention, the concave portion is a
ring-shaped groove which is substantially concentric with the
center holes of the substrates.
In still another embodiment of the invention, the stopper includes
at least one concave portion formed on one of the first and second
substrates and at least one convex portion formed on the other
substrate.
In still another embodiment of the invention, the concave portion
is disposed to face the convex portion.
In still another embodiment of the invention, the stopper is formed
at a portion closer to the center holes of the substrates with
respect to the center of the clamp region, and the radiation
curable resin spreads to the position of the stopper.
In still another embodiment of the invention, the stopper is formed
at a position farther from the center holes of the substrates with
respect to the center of the clamp region, and another resin layer
is formed on a portion of the substrates closer to the center holes
with respect to the stopper.
In still another embodiment of the invention, the another resin
layer includes a radiation curable resin having a viscosity higher
than the radiation curable resin for bonding the first and second
substrates together.
In still another embodiment of the invention, the stopper includes
a sealant layer.
In still another embodiment of the invention, the sealant layer is
formed by printing a radiation curable resin.
In still another embodiment of the invention, the sealant layer is
made of a hot melt adhesive.
Alternatively, the disk-shaped optical information medium of this
invention includes: a first substrate having a center hole; a
second substrate having a center hole; and a radiation curable
resin interposed between the first and second substrates for
bonding together the first and second substrates, wherein the
optical information medium further includes a ring-shaped groove
substantially concentric with the center holes of the substrates,
formed on at least one of the first and second substrates at a
position closer to the center holes with respect to the center of a
clamp region for clamping the optical information medium, and a
space between the first and second substrates of at least a half of
the clamp region is filled with the radiation curable resin.
In one embodiment of the invention, an information signal surface
is formed on a portion of the at least one substrate closer to an
outer circumference of the substrate with respect to an outer rim
of the groove on the substrate, and a reflection film is formed on
the groove and the information signal surface.
Alternatively, the optical information medium of this invention
includes a first substrate having a center hole, a second substrate
having a center hole, and a radiation curable resin interposed
between the first and second substrates to integrate the first and
second substrates, wherein the radiation curable resin does not
exist in a region adjacent to the center holes of the first and
second substrates.
Alternatively, the disk-shaped optical information medium of this
invention includes: a first substrate having a center hole; a
second substrate having a center hole; and a radiation curable
resin interposed between the first and second substrates for
bonding together the first and second substrates, wherein an outer
circumference of at least one of the first and second substrates is
tapered.
Alternatively, the disk-shaped optical information medium of this
invention includes: a first substrate having a center hole; a
second substrate having a center hole; and a radiation curable
resin interposed between the first and second substrates for
bonding together the first and second substrates, wherein the
radiation curable resin has a weather-resistance pigment mixed
therein.
Alternatively, the disk-shaped optical information medium of this
invention includes: a first substrate having a center hole; a
second substrate having a center hole; and a radiation curable
resin interposed between the first and second substrates for
bonding together the first and second substrates, wherein the
radiation curable resin includes a resin of which color density
varies with the level of the curing of the resin.
According to another aspect of this invention, a method for
fabricating an optical information medium is provided. The method
includes the steps of: forming a pair of substrates each having a
center hole; placing one of the pair of substrates on the other
substrate with a radiation curable resin interposed therebetween;
and curing the radiation curable resin by irradiating the resin
with radioactive rays capable of passing through at least one of
the pair of substrates so as to bond the pair of substrates
together, wherein the step of forming a pair of substrates includes
the step of forming a stopper for preventing the radiation curable
resin from protruding into the center holes on at least one of the
pair of substrates, and the step of placing one of the pair of
substrates on the other substrate includes the step of filling at
least a half of a clamp region of the optical information medium
with the radiation curable resin.
In one embodiment of the invention, the step of placing one of the
pair of substrates on the other substrate includes the steps of:
applying the radiation curable resin to a portion of the substrate
on which the stopper is formed closer to an outer circumference of
the substrate with respect to the stopper to form a donut-shaped
resin layer while the substrate is being rotated, placing the other
substrate on the substrate with the stopper, and rotating both
substrates integrally; and curing the radiation curable resin by
irradiating the radiation curable resin with radioactive rays
passing through at least one of the substrates.
In another embodiment of the invention, the step of placing one of
the pair of substrates on the other substrate includes the step of:
mounting the pair of substrates on a rotational table having an
outer diameter smaller than an outer diameter of at least one of
the pair of substrates so as to rotate the pair of substrates.
In still another embodiment of the invention, the step of placing
one of the pair of substrates on the other substrate includes the
step of: mounting the pair of substrates on a rotational table
having an outer diameter smaller than an outer diameter of at least
one of the pair of substrates so as to rotate the pair of
substrates, and absorbing the radiation curable resin through the
center holes of the pair of substrates while the pair of substrates
are being rotated.
In still another embodiment of the invention, in the step of curing
the radiation curable resin, a transparent plate having an outer
diameter smaller than an outer diameter of at least one of the pair
of substrates is placed on the bonded pair of substrates and the
radiation curable resin is irradiated with the radioactive rays
passing through the transparent plate.
Alternatively, the method for fabricating an optical information
medium of this invention includes the steps of: forming a pair of
substrates each having a center hole; placing one of the pair of
substrates on the other substrate with a radiation curable resin
interposed therebetween; and curing the radiation curable resin
with radioactive rays capable of passing through at least one of
the pair of substrates so as to bond the pair of substrates
together, wherein the step of placing one of the pair of substrates
on the other substrate includes the step of disposing the radiation
curable resin so that the resin is away from the center holes of
the substrates.
In one embodiment of the invention, the step of forming a pair of
substrates includes the step of forming a stopper for preventing
the radiation curable resin from protruding into the center holes
on at least one of the pair of substrates.
In another embodiment of the invention, the step of placing one of
the pair of substrates on the other substrate includes the steps
of: applying the radiation curable resin to a portion of the
substrate on which the stopper is formed closer to an outer
circumference of the substrate with respect to the stopper to form
a donut-shaped resin layer while the substrate is being rotated,
forming a layer of another radiation curable resin on a portion of
the substrate closer to an inner circumference with respect to the
stopper, placing the other substrate on the substrate with the
stopper, and rotating the both substrates integrally; and curing
the radiation curable resin by irradiating the radiation curable
resin with radioactive rays passing through at least one of the
pair of substrates.
In still another embodiment of the invention, in the step of curing
the radiation curable resin, a transparent plate is placed on the
bonded pair of substrates and the radiation curable resin is
irradiated with the radioactive rays passing through the
transparent plate.
In still another embodiment of the invention, the another radiation
curable resin is applied by use of a roller.
Alternatively, the method for fabricating an optical information
medium of this invention includes the steps of: forming a pair of
substrates each having a center hole; placing one of the pair of
substrates on the other substrate with a radiation curable resin
interposed therebetween; and curing the radiation curable resin
with radioactive rays capable of passing through at least one of
the pair of substrates so as to bond the pair of substrates,
wherein, in the step of forming a pair of substrates, an outer
circumference of at least one of the pair of substrates is
tapered.
In one embodiment, the step of placing one of the pair of
substrates on the other substrate includes the step of: shaping the
radiation curable resin at outer circumferences of the pair of
substrates by use of a transfer roller having a shape corresponding
to a shape of a recess formed by the tapered outer circumference of
the pair of substrates.
In another embodiment of the invention, the step of placing one of
the pair of substrates on the other substrate includes the step of:
mounting the pair of substrates on a rotational table having an
outer diameter smaller than an outer diameter of at least one of
the pair of substrates so as to rotate the pair of substrates.
In still another embodiment of the invention, the step of placing
one of the pair of substrates on the other substrate includes the
step of: mounting the pair of substrates on a rotational table
having an outer diameter smaller than an outer diameter of at least
one of the pair of substrates so as to rotate the pair of
substrates, and absorbing the radiation curable resin through the
center holes of the pair of substrates while the pair of substrates
are being rotated.
In still another embodiment of the invention, the step of curing
the radiation curable resin includes the step of placing on the
bonded pair of substrates a transparent plate having another
diameter smaller than an outer diameter of at least one of the pair
of substrates and irradiating the radiation curable resin with the
radioactive rays passing through the transparent plate.
Alternatively, the method for fabricating an optical information
medium of this invention includes the step of bonding a first
substrate having a center hole and a second substrate having a
center hole with a radiation curable resin interposed therebetween,
wherein a sealant layer is formed of another radiation curable
resin on a portion of one of the substrates closer to an inner
circumference of the substrate, the viscosity of the another
radiation curable resin when it is not cured being higher than that
of the radiation curable resin for bonding formed on a portion of
the substrate closer to an outer circumference of the substrate,
and the radiation curable resins are cured by radioactive rays
passing through the first or second substrate to bond the first and
second substrates.
Alternatively, the method for fabricating an optical information
medium of this invention includes the step of bonding a first
substrate having a center hole and a second substrate having a
center hole with a radiation curable resin interposed therebetween,
wherein a sealant layer is formed by printing a radiation curable
resin on a portion of one of the substrates closer to an inner
circumference of the substrate, and the radiation curable resins
are cured by radioactive rays passing through the first or second
substrate to bond the first and second substrates.
Alternatively, the method for fabricating an optical information
medium of this invention includes the step of bonding a first
substrate having a center hole and a second substrate having a
center hole with a radiation curable resin interposed therebetween,
wherein a sealant layer is formed of a hot melt adhesive on a
portion of one of the substrates closer to an inner circumference
of the substrate, the first and second substrates are pressed with
the radiation curable resin and the sealant layer being interposed
therebetween, and the radiation curable resin is cured by
radioactive rays passing through the first or second substrate to
bond the first and second substrates.
Alternatively, the method for fabricating an optical information
medium of this invention includes the step of bonding a first
substrate having a center hole and a second substrate having a
center hole with a radiation curable resin interposed therebetween,
wherein a portion of the radiation curable resin protruding into
the center holes is removed before the radiation curable resin is
cured.
In one embodiment of the invention, the portion of the radiation
curable resin protruding to the center holes is removed by use of a
jig.
In another embodiment of the invention, the portion of the
radiation curable resin protruding to the center holes is removed
by absorbing through a suction port disposed on a boss of a spindle
for rotating the substrates.
In still another embodiment of the invention, the portion of the
radiation curable resin protruding to the center holes is removed
by absorbing by a sponge disposed on a boss of a spindle for
rotating the substrates.
Alternatively, the method for fabricating an optical information
medium of this invention includes the steps of: placing one of a
pair of substrates, each having a center hole, on the other
substrate with a radiation curable resin interposed therebetween;
and curing the radiation curable resin with radioactive rays
capable of passing through at least one of the pair of substrates
so as to bond together the pair of substrates, wherein a resin of
which color density varies with the degree of the curing of the
resin is used as the radiation curable resin, the color density of
the resin is measured when the resin is irradiated with radioactive
rays, and the curing of the resin is terminated when the resin
obtains a predetermined color density.
Alternatively, the method for fabricating an optical information
medium of this invention includes the step of bonding a first
substrate and a second substrate with radiation curable resin
interposed therebetween, wherein radioactive rays passing through
the first substrate and radioactive rays passing through the second
substrate radiate the radiation curable resin so as to cure the
radiation curable resin.
In one embodiment of the invention, at least one of radiation
intensity and duration of the radioactive rays is adjusted
according to a radioactive ray transmittance of the substrate
through which the radioactive rays pass.
According to still another aspect of the invention, an apparatus
for fabricating an optical information medium is provided. The
apparatus includes: means for applying a radiation curable resin,
while a first substrate having a stopper for preventing the
radiation curable resin from protruding into a center hole is being
rotated, to a portion of the first substrate closer to an outer
circumference of the first substrate with respect to the stopper,
to form a donut-shaped resin layer; means for placing a second
substrate on the first substrate; means for rotating the first and
second substrates integrally; and means for irradiating the
radiation curable resin with radioactive rays passing through at
least one of the first and second substrates.
In one embodiment of the invention, the apparatus further includes
means for placing a transparent plate on the bonded substrates.
In another embodiment of the invention, the apparatus further
includes means for applying another radiation curable resin to a
portion of the substrate closer to an inner circumference of the
substrate with respect to the stopper.
In still another embodiment of the invention, the means for
applying another radiation curable resin includes any of brush
means, roller means, and clean printing means.
Alternatively, the apparatus for fabricating an optical information
medium by bonding a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween of this invention includes: means for
applying a first radiation curable resin on a portion of the first
substrate closer to an inner circumference of the first substrate
and applying a second radiation curable resin having a viscosity
lower than the first radiation curable resin to a portion of the
first substrate closer to an outer circumference of the first
substrate while the first substrate is being rotated; means for
placing the second substrate on the first substrate; means for
rotating the first and second substrates integrally; and means for
irradiating the radiation curable resins with radioactive rays
passing through at least one of the first and second
substrates.
Alternatively, the apparatus for fabricating an optical information
medium by bonding a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween of this invention includes: means for
applying a portion of the radiation curable resin on a portion of
the first or second substrate closer to an inner circumference of
the first or second substrate; means for applying the remainder of
the radiation curable resin on a portion of the first substrate
closer to an outer circumference of the first substrate while the
first substrate is being rotated; means for placing the second
substrate on the first substrate; means for rotating the first and
second substrates integrally; and means for irradiating the
radiation curable resin with radioactive rays passing through at
least one of the first and second substrates.
Alternatively, the apparatus for fabricating an optical information
medium by bonding a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween of this invention includes: means for
applying a hot melt adhesive to a portion of the first or second
substrate closer to an inner circumference of the first or second
substrate; means for applying the radiation curable resin to a
portion of the first substrate closer to an outer circumference of
the first substrate while the first substrate is being rotated;
means for placing the second substrate on the first substrate;
means for rotating the first and second substrates integrally; and
means for irradiating the radiation curable resin with radioactive
rays passing through at least one of the first and second
substrates.
Alternatively, the apparatus for fabricating an optical information
medium by bonding a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween of this invention includes: a table
for integrally rotating the first and second substrates with the
radiation curable resin before being cured interposed therebetween;
and means for absorbing the radiation curable resin interposed
between the first and second substrates through the center holes of
the first and second substrates.
Alternatively, the apparatus for fabricating an optical information
medium by bonding a first substrate having a center hole and a
second substrate having a center hole with a radiation curable
resin interposed therebetween of this invention includes: means for
irradiating the radiation curable resin with radioactive rays
passing through at least one of the first and second substrates;
and means for measuring a color density of the radiation curable
resin.
In one embodiment of the invention, in the step of curing the
radiation curable resin, the radioactive rays are reflected near
the outer circumferences of the substrates placed on each other to
irradiate the outer circumferences of the substrates.
In another embodiment of the invention, the radioactive rays are
reflected by a mirror of a truncated cone shape disposed to
surround the outer circumferences of the substrates.
In still another embodiment of the invention, the apparatus further
includes means for irradiating the outer circumferences of the
substrate placed on each other with the radioactive rays.
Thus, the invention described herein makes possible the advantages
of (1) providing a thin optical information medium with good
appearance and high mechanical strength without protrusion of a
radiation curable resin to a center hole of the medium, (2)
providing a method for fabricating such an optical information
medium, and (3) providing an apparatus for fabricating such an
optical information medium.
These and other advantages of the present invention will become
apparent to those skilled in the art upon reading and understanding
the following detailed description with reference to the
accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a conventional optical disk.
FIGS. 2A to 2D are perspective views showing a conventional
fabrication process of the optical disk of FIG. 1.
FIG. 3 is a partial perspective sectional view of an optical disk
of Example 1 according to the present invention.
FIG. 4 is a partial sectional view of an injection molding
apparatus used for fabricating substrates for the optical disk of
Example 1 according to the present invention.
FIGS. 5A to 5D are perspective views showing a fabrication process
of the optical disk of Example 1 according to the present
invention.
FIG. 6 is a partial sectional view of an apparatus used for
fabricating the optical disk of Example 1 according to the present
invention.
FIG. 7 is a sectional view showing a step for fabricating the
optical disk of Example 1 according to the present invention.
FIG. 8 is a perspective view showing a step for fabricating an
optical disk of Example 2 according to the present invention.
FIG. 9 is a partial perspective sectional view of the optical disk
of Example 2 according to the present invention.
FIG. 10 is a partial perspective sectional view of an optical disk
of Example 3 according to the present invention.
FIG. 11 is another injection molding apparatus used for fabricating
a substrate of the optical disk of Example 3 according to the
present invention.
FIG. 12 is yet another injection molding apparatus used for
fabricating a substrate of the optical disk of Example 3 according
to the present invention.
FIGS. 13A to 13D are perspective views showing a fabrication
process of the optical disk of Example 3 according to the present
invention.
FIG. 14 is partial perspective sectional view showing a step for
fabricating an optical disk of Example 4 according to the present
invention.
FIG. 15 is a sectional view showing a step for fabricating an
optical disk of Example 5 according to the present invention.
FIG. 16 is a partial perspective sectional view of an optical disk
of Example 6 according to the present invention.
FIGS. 17A to 17D are perspective views showing a fabrication
process of the optical disk of Example 6 according to the present
invention.
FIG. 18 is a perspective view showing a step for fabricating an
optical disk of Example 8 according to the present invention.
FIG. 19 is a perspective view showing a step for fabricating an
optical disk of Example 9 according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An optical information medium (optical disk) of the present
invention is formed by bonding together a pair of substrates, each
having a center hole, by use of a radiation curable resin. The
optical disk of the present invention further includes a stopper
for preventing the radiation curable resin from protruding into the
center hole. The resin spreads in a space between the substrates
covering at least a half of a clamp region for securing the optical
disk to a turntable. The stopper is preferably a concave or convex
portion formed on each of the substrates.
When a groove which is substantially concentric with the center
hole is formed as the stopper on each substrate at a position
closer to the inner circumference (closer to the center hole) with
respect to the clamp region, the substrates are bonded together in
the following manner. While one of the substrates is being rotated
at low speed, a radiation curable resin is applied to a portion of
the substrate closer to the outer circumference with respect to the
groove, forming a donut-shaped resin layer. The other substrate is
placed on the substrate with the resin therebetween. The two
substrates are then rotated together at high speed, to allow the
radiation curable resin to spread substantially uniformly in the
space between the two substrates from the grooves to the outer
circumferences of the substrates. Then, the radioactive rays are
radiated to cure the radiation curable resin and thus to bond the
two substrates integrally.
When a groove is formed at a position closer to the outer
circumference with respect to the clamp region, the substrates are
bonded together in the following manner. While one of the
substrates is being rotated at low speed, a radiation curable resin
is applied to a portion of the substrate closer to the outer
circumference with respect to the groove, forming a donut-shaped
resin layer. At the same time, the radiation curable resin is also
applied to a portion of the substrate closer to the inner
circumference with respect to the groove but away from the center
hole. The other substrate is placed on the substrate with the resin
therebetween. The two substrates are then rotated together at high
speed, to allow the radiation curable resin to spread substantially
uniformly in the space between the two substrates covering the
portion closer to the outer circumferences with respect to the
grooves and the portion closer to the inner circumferences with
respect to the grooves but away from the center hole. Then, the
radioactive rays are radiated to cure the radiation curable resin
and thus to bond the two substrates integrally.
In the former case where the groove is formed at a position closer
to the inner circumference with respect to the clamp region, the
groove serves as a reservoir for excessive resin produced when the
resin spreads in the space between the two substrates. This
prevents the resin from spreading beyond the groove to the portion
closer to the inner circumference and thus the resin from
protruding into the center hole. Since the resin spreads in the
entire clamp region, the resultant disk has high strength.
In the latter case where the groove is formed at a position closer
to the outer circumference with respect to the clamp region, a thin
radiation curable resin layer is formed on a portion closer to the
inner circumference with respect to the groove, besides the resin
layer on a portion closer to the outer circumference with respect
to the groove, before the two substrates are bonded together. Thus,
the clamp region is supplied with a sufficient amount of resin.
Since the resin layer on the inner circumference portion is formed
thin and away from the center hole, the resin is prevented from
protruding into the center hole.
(Example 1)
A first example of the optical information medium according to the
present invention will be described.
FIG. 3 shows an optical disk of Example 1. The optical disk
includes disk-shaped first and second substrates 1 and 4
(thickness: 0.6 mm each) bonded together integrally with a
radiation curable resin 7. The first surface 1 has a first
information signal surface 2, on which a first reflection film 3
(thickness: 0.03 .mu.m to 0.2 .mu.m) made of aluminum as a main
component is formed. The second substrate 4 has a second
information signal surface 5, on which a second reflection film 6
is formed. The first and second substrates 1 and 4 are bonded
together with the information signal surfaces 2 and 5 facing each
other with the radiation curable resin 7 interposing.
Grooves and pits are formed on the information signal surfaces 2
and 5 of the substrates 1 and 4. When the disk is of a rewritable
type, a recording film (not shown) is formed on the information
signal surface 2 or 5 of at least one of the substrates 1 and
4.
In general, an optical disk has a clamp region (indicated by the
arrow in FIG. 3) for securing the optical disk to a turntable of a
recording/reproduction apparatus. The clamp region, which is of a
donut shape, occupies the region of the disk ranging from 11 mm to
16.5 mm from the center of the disk, in the case of DVDs. In other
words, the clamp region is a ring-shaped region with an inner
diameter of 22 mm and an outer diameter of 33 mm.
In Example 1, grooves 8 and 9 which are substantially concentric
with the center hole are formed on the first and second substrates
1 and 4, respectively. The function of the grooves 8 and 9 will be
described later in detail. In Example 1, the grooves 8 and 9 have a
depth of 0.3 mm or less and a width of 3 mm or less, and are formed
at a position closer to the inner circumference (closer to the disk
center) with respect to the outer rim of the clamp region. The
depth of the grooves is preferably equal to or less than a half the
thickness of each substrate.
If the grooves 8 and 9 are formed at a position closer to the outer
circumference with respect to the outer rim of the clamp region,
the clamp region is not supplied with a sufficient amount of resin.
In Example 1 where the radiation curable resin is used for bonding
the substrates together, the gap between the substrates is about 50
.mu.m, five times as large as that when a hot melt adhesive is used
(about 10 .mu.m). The Inventors have found from experiments that,
with the large gap between the substrates, if the clamp region is
not supplied with a sufficient amount of resin, the clamp region
fails in stably securing the optical disk to a turntable.
The Inventors have further found that, in order to obtain stable
clamping, it is necessary to supply the radiation curable resin to
at least a half of the clamp region. Specifically, in the case of
DVDs, the grooves 8 and 9 need to be positioned so that the
distance between the groove center and the disk center is 13.75 mm
(=11/2+16.5/2) or less. When the grooves 8 and 9 with a width of 3
mm are formed so that the groove center is positioned at a distance
of 12.5 mm or less from the disk center, substantially the entire
clamp region will be supplied with the radiation curable resin.
Accordingly, the grooves 8 and 9 are preferably formed so that the
groove center is positioned at a distance of 12.5 mm or less from
the disk center.
The insides of the grooves 8 and 9 are not necessarily filled with
the radiation curable resin 7. Accordingly, the inner end of the
radiation curable resin 7 is positioned at the outer rims of the
grooves 8 and 9 or at the inner rims of the grooves including the
inside of the grooves. FIG. 3 shows the latter case as an
example.
The grooves 8 and 9 can be formed by use of a jig for a stamper
having a pattern of information signals when the substrates 1 and 4
are formed by injection molding using the stamper. The size and
shape of the grooves 8 and 9 can be controlled by adjusting the
size and shape of the jig. The shape of the grooves 8 and 9 is not
limited to that shown in FIG. 3. Only one groove, instead of the
grooves 8 and 9, can be formed on either one of the substrates 1
and 4. Alternatively, a plurality of grooves can be formed close to
one another on one substrate.
FIG. 4 shows the injection molding of the substrate. A donut-shaped
stamper 12 having a center hole is attached to one surface of a
cylindrical movable mold 11 with a jig 13. A ring-shaped convex
portion 13a is formed on an end of the jig 13 and presses the
stamper 12 against the movable mold 11. The substrate 1 or 4 is
formed by injecting resin into a cavity 15 formed between the
movable mold 11 and a fixed mold 14 from right as seen from the
figure and then cooling the resin. At this formation of the
substrate, the groove 8 or 9 is formed on the substrate 1 or 4 due
to the convex portion 13a of the jig 13 for the stamper 12. Thus,
the size and shape of the grooves 8 and 9 can be controlled by
adjusting the size and shape of the convex portion 13a of the jig
13.
Next, referring to FIGS. 5A to 5D, a method for fabricating the
optical disk according to the present invention will be
described.
First, the first substrate 1 with the first information signal
surface 2 is formed by injection molding and the like. The first
reflection film 3 is formed on the first information signal surface
2 by sputtering and vapor deposition. The second substrate 4 with
the second information signal surface 5 is formed by injection
molding and the like. The second reflection film 6 is formed on the
second information signal surface 5 by sputtering and vapor
deposition. The reflection films 3 and 6 are made of metal
including aluminum as a main component.
While the first substrate 1 is rotated at low speed (20 to 120
rpm), the radiation curable resin 7 is applied to a portion of the
substrate 1 closer to the outer circumference with respect to the
groove 8 to form a donut-shaped resin layer (FIG. 5A). The second
substrate 4 is placed on the first substrate 1 so that the second
reflection layer 6 faces the radiation curable resin 7 (FIG. 5B).
The radiation curable resin 7 spreads in the space between the
substrates 1 and 4. At this time, the grooves 8 and 9 serve as
reservoirs for excessive resin, preventing the resin from spreading
beyond the grooves toward the inner circumference and thus the
resin from protruding into the center hole. In place of the
continuous ring-shaped grooves, a plurality of concave portions can
be arranged at positions close to one another and apart from the
disk center by an equal distance.
The substrates 1 and 4 are rotated together at high speed (300 to
5000 rpm), to allow the radiation curable resin to spread
substantially uniformly in the space between the two substrates
covering the portion from the grooves to the outer circumferences
(FIG. 5C). In Example 1, this step is performed using an apparatus
shown in FIG. 6. The apparatus includes a table 111 for rotating an
optical disk, a boss 112 having suction ports 113, and a suction
pump 114 connected to the suction ports 113. Since the radiation
curable resin has fluidity before being cured, the resin can be
absorbed by the suction pump 114 via the suction ports 113 formed
on the boss 112 on the table 111. In this way, the radiation
curable resin can spread uniformly in the space between the
substrates. In this example, the number of the suction ports 113 is
2 or more, each having an inner diameter of 1 mm or more. The
suction force can be experimentally optimized in accordance with
the viscosity of the resin, the rotation speed and duration of the
table 111 and the like.
The outer diameter of the table 111 is preferably smaller than that
of the first and second substrates 1 and 4, so as to prevent pat of
the radiation curable resin protruding from the outer
circumferences of the rotating substrates from attaching to the
table 111. In Example 1, a radius Rt of the table 111 is set at 59
mm or less, which is smaller than a radius Rs of the substrates (60
mm) by 1 mm or more. If the radius Rt of the table 111 is too
small, the table 111 fails to support the optical disk stably.
Thus, the radius Rt of the table 111 is preferably 70% or more of
the radius Rs of the optical disk.
As described above, a centripetal force is provided by absorbing
the radiation curable resin at the rotation of the substrates. This
prevents a large amount of resin from moving to the outer
circumference of the optical disk. Further, any resin which may
protrude from the outer circumference of the optical disk can be
prevented from attaching to the table and polluting the disk by
making the size of the table smaller than that of the optical
disk.
By absorbing the resin through the center hole of the optical disk,
it is ensured that the resin remains in the clamp region during the
high-speed rotation, and the resin can spread uniformly. Further,
since excessive resin protruding into the center hole of the
optical disk is pumped via the suction ports 113 and removed, the
resultant optical disk has good appearance.
Sponges can be disposed on the boss 112 in place of the suction
ports 113 for absorbing the radiation curable resin 7. In this
case, similarly, excessive resin protruding into the center hole of
the optical disk can be removed.
Thereafter, radioactive rays are radiated to the radiation curable
resin through the second substrate 4 and the second reflection film
6 to cure the resin, so as to bond the substrates 1 and 4
integrally (FIG. 5D).
Ultraviolet (UV) rays can be used as the radioactive rays, and a UV
curable resin as the radiation curable resin. The reflection film
made of metal including aluminum as a main component allows a small
amount of UV rays to transmit therethrough (transmittance: 1% or
less) which is large enough to cure the UV curable resin if the
thickness of the reflection film is 0.1 .mu.m or less.
Alternatively, a protection film made of the radiation curable
resin can be formed on the reflection film on the first or second
substrate, before the above process including the application of
the radiation curable resin for bonding, the placement of the other
substrate on the resin, and the radiation of radioactive rays.
Heat is generally generated at the curing of the radiation curable
resin by radioactive ray radiation. The substrates may sometimes be
warped a little by this heat. To prevent this trouble, a
transparent plate can be placed on the second substrate during
irradiation. The resin is then cured with radioactive rays passing
through the transparent plate, the second substrate, and the second
reflection film. As a result, the substrates are prevented from
warping, and a disk with a negligibly small tilt can be fabricated.
FIG. 7 shows this alternative step, where a transparent plate 10
presses the integrated first and second substrates 1 and 4. The
transparent plate can be made of glass.
In Example 1, the substrates both having information signals
recorded thereon were bonded together. Alternatively, one of the
substrates can be a dummy substrate where information signals have
not been recorded.
Also, in the case of a double-layer disk where a semi-transparent
film is formed on the information signal surface of the substrate
4, the radiation curable resin can be irradiated with radioactive
rays through the semi-transparent substrate 4. Thus, the substrates
can be easily bonded together.
The grooves 8 and 9 on the substrates prevent excessive resin from
spreading beyond the grooves to the inner circumference portions.
However, the resin is not necessarily accumulated in the grooves
uniformly. If the resin in the grooves 8 and 9 is not uniform and
air portions and resin portions are formed in a mixed condition in
the grooves, the appearance of the resultant disk will be poor.
This is why the reflection films are also formed on the grooves 8
and 9 as shown in FIG. 3. By forming the reflection films, the
grooves 8 and 9 become invisible from outside and the good
appearance can be maintained.
(Example 2)
In example 2, an optical disk where a groove is formed on each
substrate at a position closer to the outer circumference with
respect to the clamp region will be described with reference to
FIGS. 8 and 9.
As described above, in order to prevent the resin from protruding
to the center hole of the substrates, the resin should be applied
to a portion of a substrate closer to the outer circumference with
respect to the outer rim of the groove. This means, however, that
no resin is applied to the clamp region and therefore the resultant
disk is not secured to a turntable. In Example 2, in order to
prevent this trouble, the radiation curable resin is also applied
to a portion of the substrate closer to the inner circumference
with respect to the groove to form a resin layer 16, separately,
before the application of the radiation curable resin to a portion
closer to the outer circumference of the groove 8. The resin layer
16 can be formed by use of a roller 17 with a width of about 5 to
10 mm as shown in FIG. 8. As in Example 1, the resin layer 16 is
preferably positioned away from the center hole so as to prevent
the resin from protruding into the center hole of the
substrate.
FIG. 9 shows the optical disk of Example 2. The same components are
denoted by the same reference numerals as those in FIG. 3. The
grooves of the substrates are formed at a position closer to the
outer circumference with respect to the outer rim of the clamp
region (indicated by the arrow in FIG. 9). The resin layer 16 is
formed on a portion of the substrate closer to the inner
circumference with respect to the grooves, separately from the
application of the radiation curable resin 7 to a portion of the
substrate closer to the outer circumference with respect to the
grooves. As a result, though the resin may not be so uniform, a
sufficient amount of resin can be supplied in the clamp region and
cured.
Both the optical disks of Examples 1 and 2 are of a double-sided
reproduction type. In the case of an optical disk of a single-sided
reproduction type, the substrate 4 can be a transparent dummy plate
having neither an information signal surface nor a reflection film.
In this case, the radiation curable resin is irradiated with
radioactive rays through the transparent dummy plate. This makes it
possible to cure the resin in a shorter time than the case of the
optical disk of the double-sided reproduction type and thus shorten
the production time.
Also, in the case of a double-layer disk where a semi-transparent
film is formed on the information signal surface of the substrate
4, the radiation curable resin can be irradiated with radioactive
rays through the semi-transparent substrate 4. Thus, the substrates
can be easily bonded together.
(Example 3)
A third example of the optical information medium according to the
present invention will be described with reference to FIGS. 10, 11,
12 and 13A to 13D.
As shown in FIG. 10, a first substrate 1 has a first information
signal surface 2, on which a first reflection film 3 made of metal
and the like including aluminum as a main component is formed. A
second substrate 4 has a second information signal surface 5, on
which a second reflection film 6 is formed. The substrates 1 and 4
have a protrusion 40 (height: 0.01 to 0.2 mm, width: 0.1 to 2 mm)
and a groove 50 (depth: 0.05 to 0.3 mm, width: 0.3 to 3 mm),
respectively. A radiation curable resin 7 spreads in the space
between the substrates 1 and 4 from the outer rims of the
protrusion 40 and the groove 50 to the outer circumferences of the
substrates or from the inner rims of the protrusion 40 and the
groove 50 to the outer circumferences of the substrates including
the protrusion 40 and the groove 50. FIG. 10 shows the latter case
as an example.
The region indicated by the arrow in FIG. 10 is the clamp region
for securing the optical disk to a turntable of a reproduction
apparatus. In the clamp region, the radiation curable resin needs
to be cured sufficiently, and to attain this, the protrusion 40 and
the groove 50 need to be located closer to the center hole with
respect to the center of the clamp region. Further, the two
substrates need to be aligned with respect to the center of the
center hole to avoid decentering and cured sufficiently.
The protrusion 40 and the groove 50 of Example 3 serve as the
stopper, as the grooves 8 and 9 shown in FIG. 3, for preventing the
radiation curable resin from protruding into the center hole. The
groove 50 on the substrate 4 may be omitted. In this case, only the
protrusion 40 serves as the stopper for the radiation curable
resin. Alternatively, another protrusion can be formed on the
substrate 4 in place of the groove 50. In this case, the protrusion
on the substrate 4 needs to be located so as not to collide with
the protrusion 40 of the substrate 1. The protrusion 40 and the
groove 50 of Example 3 are of a continuous ring shape surrounding
the center holes of the substrates. However, the protrusion 40 and
the groove 50 do not necessarily have to be continuous. For
example, a plurality of protrusions can be arranged at positions
apart from the disk center by an equal distance. Alternatively, a
plurality of protrusions can be arranged on both of the substrates
so that the protrusions on one substrate can engage with the
protrusions on the other substrate when the two substrates are
bonded together.
Next, a method for fabricating the optical disk shown in FIG. 10
will be described with reference to FIGS. 11, 12, and 13A to
13D.
The first substrate 1 having the first information signal surface 2
is formed with a transparent resin such as polycarbonate by
injection molding and the like. The first reflection film 3 is
formed on the first information signal surface 2 by sputtering and
vapor deposition. The second substrate 4 having the second
information signal surface 5 is formed by injection molding and the
like, and the second reflection film 6 is formed on the second
information signal surface 5 by sputtering and vapor deposition.
The first and second reflection films 3 and 6 are made of metal
including aluminum as a main component.
The protrusion 40 which is substantially concentric with the center
hole is formed on the first substrate 1, while the groove 50 is
formed on the second substrate 4 so as to face the protrusion 40 of
the first substrate 1 when the substrates 1 and 4 are bonded
together. The protrusion 40 and the groove 50 can be formed by use
of a jig for a stamper having a pattern of information signals when
the substrates 1 and 4 are formed by injection molding using the
stamper. FIGS. 11 and 12 show the injection molding of the
substrate. A stamper 12 is attached to one surface of a movable
mold 11. The substrate is formed by injecting a resin into a cavity
15 formed between the movable mold 11 and a fixed mold 14 and then
cooling the resin. At this formation of the substrate, the groove
50 is formed on the substrate 4 by forming a convex portion 13 a on
a jig 13 as shown in FIG. 11, or the protrusion 40 is formed on the
substrate 1 by forming a concave portion 13b on the jig 13 as shown
in FIG. 12.
As shown in FIG. 13A, while the substrate 1 is being rotated at low
speed, the radiation curable resin 7 is applied to a portion of the
substrate 1 closer to the outer circumference with respect to the
protrusion 40 to form a donut- or spiral-shaped resin layer. Then,
as shown in FIG. 13B, the second substrate 4 is placed on the first
substrate 1 so that the second reflection film 6 faces the
radiation curable resin 7.
As shown in
FIG. 13C, the radiation curable resin 7 spreads in the space
between the substrates 1 and 4, while the substrates are being
rotated at high speed. At this time, the spread of the resin is
blocked by the protrusion 40, preventing the resin from spreading
beyond the protrusion 40 toward the center hole. Thus, the
radiation curable resin 7 spreads substantially uniformly in the
space between the substrates 1 and 4 from the protrusion 40 to the
outer circumferences of the substrates.
Thereafter, as shown in FIG. 13D, radioactive rays are radiated to
the radiation curable resin via the second substrate 4 and the
second reflection film 6 to cure the resin, so as to bond the
substrates 1 and 4 integrally.
UV rays can be used as the radioactive rays, and a UV curable resin
as the radiation curable resin. The reflection film made of metal
including aluminum as a main component allows a small amount of UV
rays to transmit therethrough (transmittance: 1% or less) so as to
cure the UV curable resin if the thickness of the reflection film
is 0.1 .mu.m or less.
Alternatively, a protection film made of the radiation curable
resin can be formed on the reflection film on the first or second
substrate, before the process shown in FIGS. 3A to 3D including the
application of the radiation curable resin for bonding, the
placement of the other substrate on the resin, and the radiation of
radioactive rays.
(Example 4)
In Example 4, a method for shaping the outer end of the radiation
curable resin at the outer circumferences of the substrates will be
described with reference to FIG. 14.
An optical disk having two substrates bonded together needs to have
mechanical strength large enough to be durable against drop, shock,
and the like. Conventionally, however, the following problem
arises: The radiation curable resin used for bonding the two
substrates tends to spread only to the signal recording portions,
not reaching the outer circumferences of the substrates. Even if
the resin reaches the outer circumferences, it is difficult to
obtain uniform spread of the resin. If the resin with non-uniform
spread is cured by being irradiated with radioactive rays, the
substrates tend to easily separate from each other at the end rims
thereof due to drop and shock, lowering the mechanical strength of
the resultant disk. In order to solve this problem, an outer
diameter .phi.a of the bonding surface of each of the first and
second substrates 1 and 4 is made slightly smaller than an outer
diameter .phi.b of the other surface opposite to the bonding
surface, forming a tapered end at the outer circumference of each
of the substrates 1 and 4 and thus forming tilt faces 18 and 19,
respectively. As a result, a recess is formed around the outer
circumference of the resultant optical disk. The recess is filled
with the radiation curable resin. The tapered end (tilt face) can
be formed only on one of the substrates 1 and 4. The tapered ends
can be of any shape as far as the relationship .phi.a.ltoreq..phi.b
is satisfied.
On the tilt faces of the substrates is accumulated only excessive
resin swept off from the space between the substrates 1 and 4 by
high-speed rotation of the substrates via a rotational table (not
shown) disposed below the substrates. The resin accumulated on the
tilt faces is therefore not uniform. In this example, a rotational
transfer roller 20 having a shape and size equal to those of the
recess formed by bonding the first and second substrates 1 and 4 is
used. The size of the roller 20 can be slightly smaller than that
of the recess. The roller 20 is driven in the directions shown in
FIG. 14 so as to abut against the substrates. When the roller 20 is
moved toward the substrates, the rotational table is switched to
low speed to allow the roller 20 to abut against the substrates and
rotate in a direction reverse to the rotational direction of the
rotational table. Alternatively, the roller can be fixed. The
radiation curable resin is extracted from an extraction nozzle 21
at an appropriate time so that the roller 20 can always transfer
the resin to the substrates. Thus, the shaping of the outer
circumferences of the substrates can be maintained. By curing the
resin by the radiation of radioactive rays under this stable, an
optical disk with high mechanical strength can be fabricated.
(Example 5)
In Example 5, a method for curing resin will be described with
reference to FIG. 15. Since radioactive rays are linear, the
radiation curable resin at the circumference of the substrates may
not be irradiated sufficiently enough to be cured completely within
a predetermined irradiation time. In order to solve this problem, a
reflector 24 is disposed at a position to enable the circumferences
of the substrates to be irradiated while a rotational table 22 is
rotated at low speed. With this structure, the radiation curable
resin 7 in the space between the substrates as well as at the
circumferences of the substrates can be uniformly and stably
cured.
Alternatively, a mirror of a truncated cone shape can be disposed
to surround the circumferences of the substrates. In this case, it
is not necessary to rotate the table.
(Example 6)
An optical information medium of Example 6 will be described with
reference to FIG. 16. First and second substrates 1 and 4 have
first and second information signal surfaces 2 and 5, on which
first and second reflection films 3 and 6 are formed, respectively.
A radiation curable resins 70 and 90 are interposed between the
first and second substrates 1 and 4. The resin 90 serves as a
sealant preventing the resin from protruding into the center hole
of the substrates.
Referring to FIGS. 17A to 17D, a method for fabricating such an
optical disk for double-sided reproduction according to the present
invention will be described.
The first substrate 1 having the first information signal surface 2
and the second substrate 4 having the second information signal
surface 5 are formed with a transparent resin such as polycarbonate
by injection molding and the like. The first and second reflection
films 3 and 6 are formed on the information signal surfaces 2 and
5, respectively, by sputtering and vapor deposition. The reflection
films 3 and 6 are made of metal including aluminum as a main
component, for example.
While the first substrate 1 is being rotated at low speed, the
radiation curable resin 70 which serves as a major adhesive for the
bonding of the substrates is applied to a portion of the first
substrate 1 closer to the outer circumference to form a
donut-shaped resin layer. At the same time, the radiation curable
resin 90 which has a viscosity higher than the radiation curable
resin 70 is applied to a portion of the first substrate 1 closer to
the inner circumference to form a donut-shaped resin layer (FIG.
17A). The second substrate 4 is then placed on the first substrate
1 with the second information signal surface 5 facing the radiation
curable resins 70 and 90 (FIG. 17B).
If the radiation curable resin 90 is not formed as described above,
the radiation curable resin 70 will spread in the space between the
substrates 1 and 4 when the substrate 4 is placed on the substrate
1, protruding into the center hole of the substrates 1 and 4. When
the resin is cured before it spreads to the inner circumferences of
the substrates, a sufficient amount of resin is not supplied to the
inner circumference portion, resulting in obtaining a disk with low
strength.
The radiation curable resin 90 which has high viscosity does not
spread so widely and thus does not protrude into the center hole of
the substrates 1 and 4. Though the radiation curable resin 70
spreads, it is prevented from protruding into the center hole by
being blocked by the radiation curable resin 90.
Thereafter, the substrates 1 and 4 are rotated together at high
speed so as to allow the radiation curable resin to spread
substantially uniformly in the space between the substrates 1 and 4
(FIG. 17C). Radioactive rays are radiated to the radiation curable
resins via the second substrate 4 and the second reflection film 6,
bonding the two substrates integrally (FIG. 17D).
In general, UV rays are used as the radioactive rays, and a UV
curable resin as the radiation curable resin. The metal reflection
film including aluminum as a main component allows a small amount
of UV rays to transmit therethrough so as to cure the UV curable
resin if the thickness of the reflection film is 0.1 .mu.m or
less.
A protection film made of the radiation curable resin can be formed
on the reflection film on the first or second substrate, before the
process shown in FIGS. 17A to 17D including the application of the
radiation curable resin for bonding, the placement of the other
substrate on the resin, and the radiation of radioactive rays.
Forming the protection film requires an additional step. However,
by protecting the reflection film with the protection film, the
selection of the radiation curable resin for bonding becomes less
restrictive, and the weather resistance of the reflection film can
be enhanced.
In Example 6, the radiation curable resin 90 as the sealant layer
was formed by spin coating. Instead, the sealant layer 90 can be
formed by printing. Printing is easier than spin coating for the
application of a radiation curable resin with a viscosity higher
than a certain level.
A hot melt adhesive having a viscosity higher than the radiation
curable resin 70 can also be used as the sealant layer 90. The hot
melt adhesive can be applied by use of a roll coater, for
example.
In Example 6, the substrates each having the information signal
surface were bonded. Instead, one of the substrates can be a dummy
substrate having no information signals recorded thereon.
Also, in the case of a double-layer disk where a semi-transparent
film is formed on the information signal surface of the substrate
4, the radiation curable resin can be irradiated with radioactive
rays through the semi-transparent substrate 4. Thus, the substrates
can be easily bonded together.
Thus, the optical disk of Example 6 has a sealant layer formed on a
portion of the substrate closer to the inner circumference.
Accordingly, when the radiation curable resin applied to the
substrate spreads toward the inner circumference, it will not
protrude to the center hole by being blocked by the sealant layer.
As a result, troubles such as decentering do not occur when the
disk is mounted on a turntable of a player. Further, since a
sufficient amount of resin is supplied to the inner circumference
of the disk, the bonding strength can be increased.
(Example 7)
An optical information medium of Example 7 will be described.
A radiation curable resin layer formed between substrates of the
optical disk of Example 7 contains a weather-resistance pigment.
Herein, UV rays are used as the radioactive rays and a UV curable
resin is used as the radiation curable resin.
In conventional optical disks, UV curable resin becomes decolorized
with time, consequently deteriorating the appearance of the bonded
substrates.
By mixing a weather-resistance pigment in the UV curable resin, the
decoloration of the UV curable resin becomes less eminent,
preventing the appearance of the bonded substrates from being
deteriorated with time.
The optical disk of Example 7 using the radiation curable resin
having a weather-resistance pigment mixed therein is fabricated as
follows.
A UV curable resin in which a weather-resistance pigment is mixed
uniformly is prepared. Using this resin as the radiation curable
resin 7, the conventional process shown in FIGS. 2A to 2D is
followed.
In Example 7, the substrates each having the information signal
surface were bonded. Instead, one of the substrates can be a dummy
substrate having no information signals recorded thereon.
The fabrication method of this example can also be applied to the
fabrication of optical disks of other examples according to the
present invention.
(Example 8)
An optical information medium of Example 8 will be described with
reference to FIG. 18.
In the optical disk of Example 8, a radiation curable resin of
which color density varies with the level of the curing thereof is
used as the resin for bonding substrates. Herein, a UV curable
resin is used as the radiation curable resin and UV rays are
radiated to the resin.
Conventionally, there is no way to determine the degree of the
curing of the UV curable resin, except for breaking the bonded
substrates and conduct a destructive test, directly measuring the
hardness of the UV curable resin. Thus, 100% inspection is not
possible, and it is difficult to obtain a uniform degree of curing
for all disks fabricated.
According to the optical disk of Example 8 having a radiation
curable resin of which color density varies with the degree of
curing, the degree of the curing of the radiation curable resin can
be determined by the color density of the resin in a
non-destructive manner. Thus, a uniform degree of curing for all
disks fabricated can be obtained by terminating the curing of the
resin when the resin obtains a predetermined color density.
As the UV curable resin with a color density varying with the
degree of curing, SD-1700 manufactured by Dainippon In &
Chemicals, Inc., for example, can be used.
A method for fabricating the optical disk of Example 8 will be
described.
A UV curable resin having a color density varying with the degree
of curing is prepared. Using this resin as the radiation curable
resin 7, a process similar to the conventional process shown in
FIGS. 2A to 2D is followed. That is, the UV curable resin is
applied to the first substrate 1. The second substrate 4 is placed
on the first substrate 1 with the second reflection film 6 facing
the UV curable resin. The substrates 1 and 4 are rotated together
with high speed so as to allow the UV curable resin to spread in
the space between the substrates 1 and 4.
In Example 8, an apparatus including a UV source 35 and a sensor 36
for detecting the color density of the UV curable resin as shown in
FIG. 18 is used at the curing of the UV curable resin, instead of
the conventional step shown in FIG. 2D.
When the UV curable resin is irradiated with UV rays from the UV
source 35 through the substrate 4, the color density of the UV
curable resin is detected with the sensor 36. The radiation of UV
rays is discontinued immediately after the color density of the UV
curable resin reaches a predetermined color density corresponding
to the complete curing of the UV curable resin which has been
previously determined. Thus, it is ensured that the UV curable
resin has been completely cured. A color-difference meter, for
example, can be used as the sensor 36.
Thus, this example makes it possible to confirm the complete curing
of the UV curable resin without conducting a destructive test,
conduct 100% inspection of products, and obtain a uniform degree of
curing for all disks fabricated.
In Example 8, the substrates each having the information signal
surface were bonded. Instead, one of the bonded substrates can be a
dummy substrate having no information signals recorded thereon.
(Example 9)
A method for fabricating an optical information medium of Example 9
will be described with reference to FIG. 19. Herein, a UV curable
resin is used as the radiation curable resin and UV rays are used
to irradiate the resin.
Curing of the UV curable resin starts from the portion closest to a
light source. Accordingly, the outer circumferences of bonded
substrates tend to warp toward a light source.
In the method of Example 9, a process similar to the conventional
process shown in FIGS. 2A to 2D is followed. That is, the UV
curable resin is applied to the first substrate 1. The second
substrate 4 is placed on the first substrate 1 with the second
reflection film 6 facing the UV curable resin. The substrates 1 and
4 are rotated together with high speed so as to allow the UV
curable resin to spread in the space between the substrates 1 and
4.
In Example 9, an apparatus including two UV sources 35 and 37 as
shown in FIG. 19 is used at the curing of the UV curable resin,
instead of the conventional step shown in FIG. 2D. The UV source 35
emits UV rays to irradiate the UV curable resin 7 through the
substrate 4 and cure the resin from the side of the substrate 4,
while the UV source 37 emits UV rays to irradiate the UV curable
resin 7 through the substrate 1 and cure the resin from the side of
the substrate 1.
At the curing of the UV curable resin 7, the UV curable sources 35
and 37 are operated alternately each for a predetermined time
period or simultaneously. Thus, the UV curable resin 7 is
substantially uniformly cured and contracted from both sides of the
substrates 1 and 4, preventing the substrates 1 and 4 from warping
due to non-uniform curing and contraction of the UV curable resin
7.
As a result, an optical disk having the first and second substrates
1 and 4 bonded integrally with reduced warping can be obtained.
In the case where the substrates 1 and 4 have different UV
transmittances, the intensity or duration of the UV radiation by
the UV sources 35 and 37 can be adjusted to supply different
amounts of light to the UV curable resin 7 between from the side of
the substrate 1 and from the side of the substrate 4 and thus to
obtain the same effect as that described above.
The same effect can also be obtained by using only the UV source 35
and turning over the substrates 1 and 4 with the UV curable resin 7
therebetween or moving the UV source 35 to the opposite position
where the UV source 37 is otherwise located.
A dummy substrate having neither an information signal surface nor
a reflection film can be used in place of the substrate 1 or 4 to
obtain the same effect as described above.
Thus, according to the present invention, an optical disk having
thin substrates bonded together where no protrusion of resin into
the center holes of the substrates is observed and good appearance
is maintained is provided. A method and an apparatus for
fabricating such an optical disk can also be provided.
According to an optical disk of the present invention, a stopper is
provided for preventing a radiation curable resin from protruding
into the center holes of the substrates. Also, at least a half of
the clamp region of the optical disk is supplied with the resin.
Thus, the resin is prevented from protruding into the center holes
of the substrates, and the clamp region has high strength,
providing stable clamping of the disk.
According to another optical disk of the present invention, a
sealant layer is formed near the inner circumference of the
substrate. Thus, the radiation curable resin spreading toward the
center hole is prevented from protruding into the center hole. As a
result, troubles such as decentering at mounting the optical disk
on a turntable of a player can be avoided.
The radiation curable resin before curing can be absorbed through
suction ports disposed at the center hole of the substrates, so as
to suppress the movement of the resin to the outer circumferences
of the substrates and remove resin protruding into the center hole.
Any resin protruding from the outer circumferences of the
substrates is prevented from attaching to a rotational table for
rotating the substrates by making the outer diameter of the
rotational table smaller than that of the substrates. Protruding
resin may be removed by a jig and the like before being cured.
Thus, an optical disk with reduced decentering is obtained.
A weather-resistance pigment can be mixed in the radiation curable
resin. This makes decoloration of the radiation curable resin less
visible and prevents the good appearance of the bonded substrates
from deteriorating with time.
A radiation curable resin of which color density varies with the
degree of the curing thereof can be used. This makes it possible to
measure the degree of the curing of the radiation curable resin
interposed between the bonded substrates in a non-destructive
manner. Thus, the degree of curing can be made uniform for all
optical disks by discontinuing the curing of the resin when a
predetermined color density is obtained.
In order to irradiate and cure the radiation curable resin from
both sides, the first and second substrates are simultaneously or
alternately for at least one time each, irradiated from both sides
with radioactive rays. This prevents the bonded substrates from
warping due to the contraction of the radiation curable resin.
Various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the scope
and spirit of this invention. Accordingly, it is not intended that
the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
* * * * *