U.S. patent application number 10/857169 was filed with the patent office on 2005-12-01 for optical recording medium.
This patent application is currently assigned to TDK Corporation. Invention is credited to Komaki, Tsuyoshi, Ushida, Tomoki, Yamada, Takashi.
Application Number | 20050266201 10/857169 |
Document ID | / |
Family ID | 35344848 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050266201 |
Kind Code |
A1 |
Yamada, Takashi ; et
al. |
December 1, 2005 |
OPTICAL RECORDING MEDIUM
Abstract
An optical recording medium includes a support substrate, a
first resin layer and a second resin layer formed on opposite
surface sides of the support substrate, an information recording
layer formed between the first resin layer and the support
substrate and containing a recording film, and a moisture-proof
layer formed between the second resin layer and the support
substrate and the moisture-proof layer contains at least one
element among elements contained in the recording film. According
to the present invention, since the first resin layer is formed on
the moisture-proof layer containing at least one element among
elements contained in the recording film, on the information
recording layer and the second resin layer is formed on the
moisture-proof layer, it is possible to form the first resin layer
and the second resin layer having substantially the same physical
properties on the opposite sides of the support substrate and it is
therefore possible to suppress the warpage of the optical recording
medium due to heat and moisture to the minimum.
Inventors: |
Yamada, Takashi; (Tokyo,
JP) ; Komaki, Tsuyoshi; (Tokyo, JP) ; Ushida,
Tomoki; (Tokyo, JP) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE
SUITE 6300
SEATTLE
WA
98104-7092
US
|
Assignee: |
TDK Corporation
Tokyo
JP
|
Family ID: |
35344848 |
Appl. No.: |
10/857169 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
428/64.4 ;
G9B/7.142; G9B/7.19 |
Current CPC
Class: |
G11B 2007/24316
20130101; G11B 2007/24314 20130101; Y10T 428/21 20150115; G11B
7/252 20130101; G11B 7/254 20130101; G11B 7/24067 20130101; G11B
7/258 20130101; G11B 7/243 20130101; G11B 7/2403 20130101 |
Class at
Publication: |
428/064.4 |
International
Class: |
B32B 003/02 |
Claims
1. An optical recording medium comprising a support substrate, a
first resin layer and a second resin layer formed on opposite
surface sides of the support substrate, an information recording
layer formed between the first resin layer and the support
substrate and containing a recording film, and a moisture-proof
layer formed between the second resin layer and the support
substrate, the moisture-proof layer containing at least one element
among elements contained in the recording film.
2. An optical recording medium in accordance with claim 1, wherein
the recording film contains Sb and Te and the moisture-proof layer
contains at least one of Sb and Te.
3. An optical recording medium in accordance with claim 1, wherein
the moisture-proof layer contains as a primary component the same
element as that contained in the recording film as a primary
component.
4. An optical recording medium in accordance with claim 3, wherein
the recording film contains a phase change material as a primary
component and the moisture-proof layer contains as a primary
component the same phase change material as that contained in the
recording film as a primary component.
5. An optical recording medium in accordance with claim 1, wherein
the moisture-proof layer is formed so as to have a thickness of 20
to 300 nm.
6. An optical recording medium in accordance with claim 2, wherein
the moisture-proof layer is formed so as to have a thickness of 20
to 300 nm.
7. An optical recording medium in accordance with claim 3, wherein
the moisture-proof layer is formed so as to have a thickness of 20
to 300 nm.
8. An optical recording medium in accordance with claim 4, wherein
the moisture-proof layer is formed so as to have a thickness of 20
to 300 nm.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an optical recording medium
and, particularly, to an optical recording medium which can be
prevented from warping as desired.
DESCRIPTION OF THE PRIOR ART
[0002] Optical recording media such as the CD, DVD and the like
have been widely used as recording media for recording digital
data. These optical recording media can be roughly classified into
write-once type optical recording media such as the CD-R and DVD-R
that enable writing but not rewriting of data, and data rewritable
type optical recording media such as the CD-RW and DVD-RW that
enable rewriting of data.
[0003] When data are to be reproduced from an optical recording
medium, a laser beam whose power is set to a reproducing power is
first projected onto the optical recording medium. Since a region
where a recording mark is formed in the optical recording medium
has different reflectivity with respect to the laser beam from
those of other regions, the amount of the laser beam reflected from
the optical recording medium varies dependent upon the presence or
absence of a recording mark. Therefore, it is possible to generate
a reproduced signal and reproduce data by detecting the amount of
the laser beam reflected from the optical recording medium and
converting it to an electrical signal using a light detector.
[0004] Accordingly, it is necessary for reading data recorded in an
optical recording medium in a desired manner to reliably make a
laser beam reflected from an optical recording medium enter a light
receiving surface of a light detector.
[0005] However, in the case where an optical recording medium is
greatly warped due to heat or moisture applied thereto during use,
since the incident angle of the laser beam entering the optical
recording medium greatly varies, it is difficult to reliably make
the laser beam reflected from the optical recording medium enter
the light detector.
[0006] Therefore, in order to reproduce data recorded in the
optical recording medium in a desired manner it is required to
reduce the warpage of the optical recording medium, and Japanese
Patent Application Laid Open No. 4-195745 discloses an optical
recording medium in which the warpage thereof is suppressed by
forming a layer for preventing the warpage thereof on the reverse
surface thereof.
[0007] The optical recording medium disclosed in Japanese Patent
Application Laid Open No. 4-195745 includes a first dielectric
layer formed on an obverse surface of a substrate and a second
dielectric layer formed on a reverse surface of the substrate and
having substantially the same thermal expansion coefficient as that
of the first dielectric layer. In the thus constituted optical
recording medium, stress and bending moment generated in the first
dielectric layer due to heat or moisture applied to the optical
recording medium during use are canceled by stress and bending
moment generated in the second dielectric layer, thereby preventing
the optical recording medium from warping.
[0008] On the other hand, a next-generation type optical recording
medium that offers improved recording density and has an extremely
high data transfer rate has been recently proposed. In such a
next-generation type optical recording medium, recording density is
to be increased by increasing the numerical aperture NA of an
objective lens for condensing the laser beam and shortening the
wavelength .lambda. of the laser beam.
[0009] However, if the numerical aperture NA of the objective lens
for condensing the laser beam is increased, then, as shown by
Equation (1), the permitted tilt error of the optical axis of the
laser beam to the optical recording medium, namely, the tilt margin
T, has to be greatly decreased. 1 T d NA 3 ( 1 )
[0010] In Equation (1), d is the distance from a light incidence
plane to the surface of an information recording layer in which
data are to be recorded, namely, the thickness of a layer(s)
through which a laser beam passes until it reaches the information
recording layer. As apparent from Equation (1), the tilt margin T
decreases as the numerical aperture NA of the objective lens
increases and increases as the thickness d of the layer(s) through
which the laser beam passes decreases.
[0011] Therefore, in a next-generation type optical recording
medium, the tilt margin T is to be increased by forming a thin
resin layer having a thickness of about 100 .mu.m on an information
recording layer and projecting a laser beam from the side of the
resin layer onto the optical recording medium, thereby recording
data therein and reproducing data therefrom.
[0012] Accordingly, the next-generation type optical recording
medium is constituted by sequentially laminating an information
recording layer and a resin layer on a support substrate having a
thickness of about 1.1 mm and has an asymmetrical structure unlike
a DVD type optical recording medium constituted by laminating
disk-like substrates each having a thickness of about 0.6 mm via an
information recording layer and having a symmetrical structure.
[0013] Therefore, since the thicknesses of the support substrate
and the resin layer are different from each other in the
next-generation type optical recording medium, the optical
recording medium tends to warp due to heat or moisture applied
thereto and, particularly in the case where the support substrate
and the resin layer are formed of different materials, since
rigidity, linear thermal expansion coefficients, Young's modulus,
internal stresses or the like are different between the material
forming the support substrate and the material for forming the
resin layer, the optical recording medium much more tends to
warp.
[0014] Thus, since the next-generation type optical recording
medium particularly tends to warp, it has also been tried in the
next-generation type optical recording medium to suppress the
warpage thereof by forming on a reverse surface side of a support
substrate a resin layer having substantially the same physical
properties as that of a resin layer formed on an obverse surface
side of the support substrate and canceling out stresses to be
applied to the obverse surface and the reverse surface of the
support substrate.
[0015] Therefore, even in the case where resin layers are formed on
both the obverse and reverse surface sides of the support substrate
of the same material, it is actually impossible to form the resin
layers having the same physical properties and it is difficult to
suppress the warpage of the optical recording medium in a desired
manner.
[0016] Further, although it is required to develop a
next-generation type optical recording medium for business use, as
well as that for private use, since a smaller amount of warpage is
allowed in and severe conditions are imposed on the optical
recording medium for business use in comparison with those in the
optical recording medium for private use, it is necessary to much
reduce the warpage of the optical recording medium.
SUMMARY OF THE INVENTION
[0017] It is therefore an object of the present invention to
provide an optical recording medium which can be prevented from
warping as desired.
[0018] The inventors of the present invention vigorously pursued a
study for accomplishing the above object and, as a result, reached
the conclusion that even in the case where resin layers are formed
on obverse and reverse surface sides of a support substrate of
ultraviolet ray curable resins having substantially the same
physical properties, the resin layer formed on the obverse surface
side of the support substrate and the resin layer formed on the
reverse side surface of the support substrate do not have the same
physical properties and this is because the ultraviolet ray curable
resins are influenced by layers serving a base during the curing
process of the ultraviolet ray curable resins and some change in
property of the ultraviolet ray curable resins occurs.
[0019] Therefore, through much and various trial and error, the
inventors of the present invention made the discovery that in the
case of forming a moisture-proof layer containing at least one
element among elements contained in a recording film included in an
information recording layer on a reverse surface side of a support
substrate, forming one resin layer on the information recording
layer and forming another resin layer on the moisture-proof layer,
it was possible to form the resin layers to have substantially the
same physical properties.
[0020] The present invention is based on these finings and the
above object of the present invention can be accomplished by an
optical recording medium including a support substrate, a first
resin layer and a second resin layer formed on opposite surface
sides of the support substrate, an information recording layer
formed between the first resin layer and the support substrate and
containing a recording film, and a moisture-proof layer formed
between the second resin layer and the support substrate, the
moisture-proof layer containing at least one element among elements
contained in the recording film.
[0021] According to the present invention, since it is possible to
prevent physical properties of the first resin layer as a resin
layer formed on the obverse surface side of the support substrate
and those of the second resin layer as a resin layer formed on the
reverse surface side of the support substrate from differing
greatly, stresses applied to the obverse and reverse surfaces of
the support substrate can be canceled. Therefore, it is possible to
prevent the optical recording medium from warping due to heat or
moisture applied thereto in a desired manner.
[0022] In the present invention, the recording film preferably
contains Sb and Te and the moisture-proof layer preferably contains
at least one of Sb and Te.
[0023] In the present invention, the moisture-proof layer
preferably contains as a primary component the same element as that
contained in the recording film as a primary component.
[0024] In the present invention, it is more preferable for the
recording film to contain a phase change material as a primary
component and for the moisture-proof layer to contain as a primary
component the same phase change material as that contained in the
recording film as a primary component.
[0025] In the present invention, a moisture-proof layer is
preferably formed so as to have a thickness of 20 to 300 nm and
more preferably formed so as to have a thickness of 30 to 200 nm.
In the case where a moisture-proof layer is thinner than 20 nm, it
is difficult to obtain a moisture-proof layer having a sufficient
moisture-proof characteristic and, on the other hand, in the case
where a moisture-proof layer is thicker than 300 nm, it takes a
longer time for forming the moisture-proof layer, thereby lowering
the productivity of the optical recording medium.
[0026] The above and other objects and features of the present
invention will become apparent from the following description made
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic perspective view showing an optical
recording medium that is a preferred embodiment of the present
invention.
[0028] FIG. 2 is an enlarged schematic cross-sectional view of the
part of the optical recording medium indicated by A in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] FIG. 1 is a schematic perspective view showing an optical
recording medium that is a preferred embodiment of the present
invention and FIG. 2 is a schematic enlarged cross-sectional view
indicated by A in FIG. 1.
[0030] As shown in FIG. 1, an optical recording medium 1 according
to this embodiment is formed disk-like and is formed with a center
hole at the center portion thereof for setting the optical
recording medium 1 to a data recording and reproducing
apparatus.
[0031] The optical recording medium 1 shown in FIGS. 1 and 2 is so
constituted that a laser beam having a wavelength .lambda. of 380
nm to 450 nm is projected via an objective lens (not shown) having
a numerical aperture NA which satisfies that .lambda./NA is equal
to or smaller than 640 nm in a direction indicated by an arrow in
FIG. 2, whereby data are recorded therein or data are reproduced
therefrom.
[0032] As shown in FIG. 2, the optical recording medium 1 includes
a support substrate 2, an information recording layer 3 formed on
one surface of the support substrate 2, a first resin layer 4
formed on the information recording layer 3, a first hard coat
layer 5 formed on the first resin layer 4, a moisture-proof layer 6
formed on the other surface of the support substrate 2, a second
resin layer 7 formed on the moisture-proof layer 6, and a second
hard coat layer 8 formed on the second resin layer 7.
[0033] The support substrate 2 serves as a support of the optical
recording medium 1.
[0034] The material used to form the support substrate 2 is not
particularly limited insofar as the support substrate 2 can serve
as the support of the optical recording medium 1 and the support
substrate 2 can be formed of polycarbonate resin or polyolefin
resin, for example. The thickness of the support substrate 2 is not
particularly limited and the support substrate 2 preferably has a
thickness of about 1.1 mm.
[0035] Grooves 2a and lands 2b for guiding the laser beam are
spirally formed on one surface of the support substrate 2 from a
portion in the vicinity of the center thereof toward an outer
periphery thereof or from an outer periphery thereof toward a
portion in the vicinity of the center thereof. Although not
particularly limited, the depth of the groove 2a is preferably set
to 10 nm to 40 nm and the pitch of the grooves 2a is preferably set
to 0.2 .mu.m to 0.4 .mu.m.
[0036] As shown in shown in FIG. 2, the information recording layer
3 includes a reflective film 31 formed on the support substrate 2,
a second dielectric film 32 formed on the reflective film 31, a
recording film 33 formed on the second dielectric film 32, a first
dielectric film 34 formed on the recording film 33, and a heat
radiation film 35 formed on the first dielectric film 34.
[0037] The reflective film 31 serves to reflect the laser beam
entering through the first resin layer 4 so as to emit it through
the first resin layer 4 and serves to increase a C/N ratio of a
reproduced signal by a multiple interference effect.
[0038] The material for forming the reflective film 31 is not
particularly limited insofar as it can reflect the laser beam and
the reflective film 31 can be formed of Mg, Al, Ti, Cr, Fe, Co, Ni,
Cu, Zn, Ge, Ag, Pt, Au, Nd, In, Sn or the like. Among these
materials, it is preferable to form the reflective layer 31 of a
metal material having a high reflectivity, such as Al, Au, Ag, Cu
or alloy containing at least one of these metals, such as alloy of
Ag and Cu.
[0039] The thickness of the reflective film 31 is not particularly
limited and the reflective film 31 is preferably formed so as to
have a thickness of 10 nm to 300 nm and more preferably formed so
as to have a thickness of 20 nm to 200 nm.
[0040] The first dielectric film 34 and the second dielectric film
33 serve to physically and chemically protect the recording film 33
and to adjust optical characteristics of the optical recording
medium 1 so that the difference in the reflectivity between a
portion where a recording mark described later is formed and other
portions of the recording film 33 is increased by a multiple
interference effect when data recorded in the recording film 33 are
reproduced, whereby a reproduced signal having a high C/N ratio can
be obtained.
[0041] The material for forming the first dielectric layer 34 and
the second dielectric layer 32 is not particularly limited and it
is preferable to form the first dielectric layer 34 and the second
dielectric layer 32 of oxide, nitride, sulfide or fluoride
containing at least one metal selected from a group consisting of
Si, Zn, Al, Ta, Ti, Co, Zr, Pb, Ag, Sn, Ca, Ce, V, Cu, Fe, and Mg,
or a combination thereof.
[0042] The first dielectric layer 34 preferably has a thickness of
10 nm to 50 nm and more preferably has a thickness of 20 nm to 30
nm. In the case where the first dielectric layer 34 is thinner than
10 nm, it is difficult for the first dielectric layer 34 to serve
to protect the recording film 33 and improve optical
characteristics of the optical recording medium 1. On the other
hand, in the case where the first dielectric layer 34 is thicker
than 50 nm, it take a longer time for forming the first dielectric
layer 34, thereby lowering the productivity of the optical
recording medium 1.
[0043] Further, the second dielectric layer 32 preferably has a
thickness of 5 nm to 20 nm and more preferably has a thickness of
10 nm to 15 nm. In the case where the second dielectric layer 32 is
thinner than 5 nm, it is difficult for the second dielectric layer
32 to serve to protect the recording film 33 and on the other hand,
in the case where the second dielectric layer 32 is thicker than 20
nm, it take a longer time for forming the second dielectric layer
32, thereby lowering the productivity of the optical recording
medium 1.
[0044] The recording film 33 is a layer in which data are to be
recorded. In this embodiment, the recording film 33 is formed of a
phase change material and data are recorded in the recording film
33 and data are reproduced from the recording film 33 utilizing the
difference in reflectivity between when the phase change material
is in a crystalline phase and when it is in an amorphous phase.
[0045] When data are to be recorded in the recording film 33, a
laser beam whose power is modulated between a recording power Pw
and a bottom power Pb is projected onto the recording film 33 and a
region of the recording film 33 irradiated with the laser beam is
heated to a temperature equal to or higher than the melting point
of the phase change material. The power of the laser beam is then
set to the bottom power Pb, thereby quickly cooling the region of
the recording film 33 irradiated with the laser beam and the phase
change material is changed to an amorphous state, thereby forming a
recording mark.
[0046] On the other hand, when data recorded in the recording film
33 is to be erased, a laser beam whose power is modulated between
the recording power Pw, the bottom power Pb and an erasing power Pe
is projected onto the recording film 33, thereby heating a region
of the recording film 33 irradiated with the laser beam to
temperature equal to or higher than the crystallization temperature
of the phase change material and the phase change material is
crystallized, thereby erasing a recording mark. Since the phase
change reactions of the phase change material contained in the
recording film 33 from an amorphous phase to a crystalline phase
and from the crystalline phase to the amorphous phase are
reversible, data recorded in the recording film 33 can be
repeatedly rewritten.
[0047] The phase change material for forming the recording film 33
is not particularly limited but a material capable of changing from
an amorphous phase to a crystal phase in a short time is preferable
in order to rewrite data recorded in the recording film 33 at a
high velocity. Illustrative examples of materials having such a
characteristic include a SbTe system material. As the SbTe system
material, SbTe may be used alone or a SbTe system material to which
additives are added in order to shorten time required for
crystallization and improve the long-term storage reliability of
the optical recording medium 10 may be used.
[0048] Concretely, it is preferable to form the recording film 33
of a SbTe system material represented by the compositional formula:
(Sb.sub.xTe.sub.x).sub.yM.sub.y, where x is equal to or larger than
0.55 and equal to or smaller than 0.9 and y is equal to or larger
than 0 and equal to or smaller than 0.25, and it is more preferable
to form the recording film 33 of a SbTe system material represented
by the above mentioned compositional formula wherein x is equal to
or larger than 0.65 and equal to or smaller than 0.85 and y is
equal to or larger than 0 and equal to or smaller than 0.25.
[0049] M is an element other than Sb and Te and while M is not
particularly limited, it is preferable for the element M to be one
or more elements selected from the group consisting of In, Ag, Au,
Bi, Se, Al, P, Ge, H, Si, C, V, W, Ta, Zn, Mn, Ti, Sn, Pd, Pb, N, O
and rare earth elements in order to shorten time required for
crystallization and improve the storage reliability of the optical
recording medium 1.
[0050] It is preferable to form the recording film 33 so as to have
a thickness of 2 nm to 40 nm, is more preferable to form it so as
to have a thickness of 4 nm to 30 nm and is further preferable to
form it so as to have a thickness of 5 nm to 20 nm. In the case
where the recording film 33 is thinner than 2 nm, the difference in
optical characteristics between before and after recording data
becomes small and a signal having a high C/N ratio cannot be
obtained when data are reproduced. On the other hand, in the case
where the recording film 33 is thicker than 40 nm, the amount of
heat required for forming a recording mark becomes great and there
is risk of recording sensitivity declining.
[0051] The heat radiation film 35 serves to quickly radiate heat
generated in the recording film 33 toward a light incidence
plane.
[0052] The material for forming the heat radiation film 35 is not
particularly limited insofar as it can quickly radiate heat
generated in the recording film 33 but it is preferable to use a
material having a thermal conductivity higher than that of the
first dielectric film 34 for forming the heat radiation film 35.
Illustrative examples of materials having such a characteristic
include oxide, nitride, sulfide or fluoride containing at least one
metal selected from a group consisting of Al, Si, Ce, Ti, Zn, Ta,
or a combination thereof.
[0053] It is preferable for the heat radiation film 35 to have a
thickness of 15 nm to 40 nm. In the case where the heat radiation
film 35 is thinner than 15 nm, sufficient heat radiation
characteristics cannot be obtained and, on the other hand, in the
case where the heat radiation film 35 is thicker than 40 nm, it
takes much time to form the heat radiation film 35, thereby
lowering the productivity of the optical recording medium 1.
[0054] The first resin layer 4 serves to transmit the laser beam
and serves as a protecting layer for the surface of the information
recording layer 3.
[0055] It is required for the first resin layer 4 to be optically
transparent and have small absorption, reflection and birefringence
with respect to light within the same wavelength region as that of
the laser beam having a wavelength of 390 to 420 nm, and the first
resin layer 4 is formed of ultraviolet ray curable resin, for
example.
[0056] The ultraviolet ray curable resin used for forming the first
resin layer 4 contains a photo-polymerizable monomer, a
photo-polymerizable oligomer, a photoinitiator and other additives
as occasion demands. As a photo-polymerizable monomer, one of a
molecular weight of less than 2,000 is preferable, and illustrative
examples of such monomers include a monofunctional acrylate
(methacrylate) and a multifunctional acrylate (methacrylate).
Illustrative examples of photo-polymerizable oligomers include an
oligomer containing or introduced with, in a molecule, a functional
group such as an acrylic double bond, an allylic double bond, an
unsaturated double bond or the like, each of which is bridgeable or
polymerizable by irradiation with an ultraviolet ray. As a
photoinitiator, conventional photoinitiators can be employed and
for example, a molecular cleavage type photo-polymerization
initiator may be employed.
[0057] It is preferable for the first resin layer 4 to have a
thickness of 30 .mu.m and 200 .mu.m.
[0058] The first hard coat layer 5 serves to physically protect the
first resin layer 4 and to prevent the first resin layer 4 from
being damaged.
[0059] The material for forming the first hard coat layer 5 is not
particularly limited but it is preferable to form the first hard
coat layer 5 of a material having high transparency and abrasion
resistance. Concretely, it is preferable to form the first hard
coat layer 5 of a hard coat composition prepared by adding
inorganic fine particles having an average diameter equal to or
smaller than 100 nm to ultraviolet ray curable resin.
[0060] It is preferable to form the first resin layer 4 so as to
have a thickness of 1 .mu.m to 10 .mu.m and is more preferable to
form it so as to have a thickness of 1 .mu.m to 5 .mu.m. In the
case where the first resin layer 4 is thinner than 1 .mu.m, it is
difficult to form the first resin layer 4 having necessary hardness
and abrasion resistance, and on the other hand, in the case where
the first resin layer 4 is thicker than 10 .mu.m, there arises a
risk of generating cracks in the first resin layer 4 due to
internal stress.
[0061] As shown in FIG. 2, the moisture-proof layer 6, the second
resin layer 7 and the second hard coat layer 8 are formed on the
other surface of the support substrate 2.
[0062] The moisture-proof layer 6 serves to prevent water from
entering the support substrate 2 through the second resin layer
7.
[0063] In this embodiment, the moisture-proof layer 6 contains at
least one element among elements contained in the recording film
33.
[0064] It is preferable for the moisture-proof layer 6 to contain
one of the elements among Sb and Te contained in the recording film
33 and is more preferable for it to contain as a primary component
the same phase change material as that contained in the recording
film 33 as a primary component.
[0065] It is preferable to form the moisture-proof layer 6 so as to
have a thickness of 20 nm to 300 nm and is more preferable to form
it so as to have a thickness of 30 nm to 200 nm. In the case where
the moisture-proof layer 6 is thinner than 20 nm, it is difficult
to form a moisture-proof layer 6 having sufficient moisture-proof
characteristics and on the other hand, in the case where the
moisture-proof layer 6 is thicker than 300 nm, it takes much time
to form the moisture-proof layer 6, thereby lowering the
productivity of the optical recording medium 1.
[0066] The second resin layer 7 serves to cancel stress and bending
moment generated in the first resin layer 4 with stress and bending
moment generated therein, thereby preventing the optical recording
medium 1 from warping.
[0067] It is preferable for the second resin layer 7 to have the
same physical properties such as rigidity, linear thermal expansion
coefficient, Young's modulus, internal stress and the like as those
of the first resin layer 4 and it is therefore preferable to form
the second resin layer 7 of the same ultraviolet ray curable resin
as that used for forming the first resin layer 7. However, it is
sufficient for the ultraviolet ray curable resin used for forming
the second resin layer 7 to have substantially the same physical
properties after curing but it is not absolutely necessary to form
the second resin layer 7 of the same ultraviolet ray curable resin
as that used for forming the first resin layer 7.
[0068] In this specification, ultraviolet ray curable resin having
substantially the same physical properties after curing as those of
the first resin layer 4 means ultraviolet ray curable resin in
which among the physical properties such as rigidity, linear
thermal expansion coefficient, Young's modulus, internal stress and
the like, at least Young's modulus and the linear thermal expansion
coefficient differ from those of the first resin layer by 5% or
less.
[0069] Similarly to the first resin layer 4, it is preferable for
the second resin layer 7 to have a thickness of 30 .mu.m to 200
.mu.m. However, it is not absolutely necessary for the second resin
layer 7 to have the same thickness as that of the first resin layer
4 and the second resin layer 7 may have a different thickness from
the first resin layer 4 insofar as the physical properties of the
second resin layer 7 are not greatly different from those of the
first resin layer 4.
[0070] The second hard coat layer 8 serves to cancel stress
generated in the first hard coat layer 5 with that generated
therein.
[0071] It is preferable for the second hard coat layer 8 to have
the same physical properties as those of the first hard coat layer
5 and it is therefore preferable to form the second hard coat layer
8 of the same hard coat composition as that used for the first hard
coat layer 5.
[0072] Similarly to the first hard coat layer 5, it is preferable
to form the second hard coat layer 8 so as to have a thickness of 1
.mu.m to 10 .mu.m and is more preferable to form it so as to have a
thickness of 1 .mu.m to 5 .mu.m.
[0073] The optical recording medium 1 having the above-described
configuration can be fabricated in the following manner.
[0074] The support substrate 2 having the groove 2a and the land 2b
on one surface thereof is first fabricated by injection molding
using a stamper.
[0075] Then, the reflective film 31, the second dielectric film 32,
the recording film 33, the first dielectric film 34 and the heat
radiation film 35 are sequentially formed by a gas phase growth
process such as sputtering process on the substantially entire
surface of the support substrate 2 on which the groove 2a and the
lands 2b are formed, whereby the information recording layer 3 is
formed.
[0076] Further, ultraviolet ray curable resin is applied by a spin
coating method onto the information recording layer 3 to form a
coating layer and an ultraviolet ray is projected onto the coating
layer, whereby the ultraviolet ray curable resin is cured and the
first resin layer 4 is formed.
[0077] Then, a hard coat composition containing ultraviolet ray
curable resin and inorganic fine particles is applied by a spin
coating method onto the first resin layer 4 to form a coating layer
and an ultraviolet ray is projected onto the coating layer, whereby
the ultraviolet ray curable resin is cured and the first hard coat
layer 5 is formed.
[0078] Further, the support substrate 2 is set in a sputtering
apparatus in such a manner that the surface thereof on which no
grooves 2a and lands 2b are formed is directed upward and the
moisture-proof layer 6 is formed on the surface of the support
substrate 2 by a gas phase growth process such as sputtering
process using a target containing at least one element among
elements contained in the recording film 33.
[0079] Then, ultraviolet ray curable resin whose physical
properties after curing are the same as those of the first resin
layer 4 is applied by a spin coating method onto the moisture-proof
layer 6 to form a coating layer and an ultraviolet ray is projected
onto the coating layer, whereby the ultraviolet ray curable resin
is cured and the second resin layer 7 is formed.
[0080] In a study done by the inventors of the present invention,
it was found that in the case where a moisture-proof layer 6
serving as a base layer when a second resin layer 7 was formed
contained at least one element among elements contained in a
recording film 33, when a first resin layer 4 was formed on the
information recording layer 3 and a second resin layer 7 was formed
on the moisture-proof layer 6, it was possible to prevent the
physical properties of the first resin layer 4 and those of the
second resin layer 7 from differing greatly. Therefore, it is
possible to form the first resin layer 4 and the second resin layer
7 having substantially the same physical properties on the opposite
surfaces of the support substrate 2.
[0081] Finally, a hard coat composition whose physical properties
after curing are the same as those of the first hard coat layer 5
is applied by a spin coating method onto the second resin layer 7
to form a coating layer and an ultraviolet ray is projected onto
the coating layer, whereby the ultraviolet ray curable resin is
cured and the second hard coat layer 8 is formed.
[0082] Thus, the optical recording medium 1 is completed.
[0083] According to this embodiment, since it is possible to form
the first resin layer 4 and the second resin layer 7 to have
substantially the same physical properties on the opposite surfaces
of the support substrate 2, it is possible to suppress the warpage
of the optical recording medium 1 to the minimum.
[0084] Hereinafter, working examples will be set out in order to
further clarify the advantages of the present invention.
WORKING EXAMPLES AND COMPARATIVE EXAMPLES
[0085] A sample # 1 was fabricated in the following manner.
[0086] A disk-like polycarbonate substrate having a thickness of
1.1 mm and a diameter of 120 mm was first fabricated by an
injection molding process.
[0087] Then, a reflective film containing Ag as a primary component
and having a thickness of 100 nm, a second dielectric film
containing a mixture of ZnS and SiO.sub.2 and having a thickness of
10 nm, a recording film containing an alloy Sb--Te--Ge as a primary
component and having a thickness of 10 nm, a first dielectric film
containing a mixture of ZnS and SiO.sub.2 and having a thickness of
20 nm and a heat radiation film containing AlN as a primary
component and having a thickness of 30 nm were sequentially formed
on one surface of the polycarbonate substrate using the sputtering
process, thereby forming an information recording layer.
[0088] Further, the polycarbonate substrate formed with the
information recording layer was set on a spin coating apparatus and
the information recording layer was coated using the spin coating
method with ultraviolet ray curable resin having the composition
identified below to form a coating layer. Then, an ultraviolet ray
was projected onto the coating layer so that a total amount thereof
was 3000 mJ/cm.sup.2, whereby the ultraviolet ray curable resin was
cured and a first resin layer having a thickness of 100 .mu.m was
formed.
1 Urethane acrylate (Negami Chemical 50 weight % Industrial Co.,
Ltd; Product Name "ART RESIN UN-5200") Trimethylolpropane
triacrylate 33 weight % (NIPPON KAYAKU CO., LTD.; Product Name
"KAYARAD TMPTA") Phenoxyhydroxypropyl acrylate 14 weight % (NIPPON
KAYAKU CO., LTD.; Product Name "KAYARAD R-128") 1-hydroxycyclohexyl
phenyl 3 weight % ketone (CIBA-GUIGY CO., LTD.; Product Name
"IRG184")
[0089] Then, the polycarbonate substrate formed with the first
resin layer was reversed and a moisture-proof layer containing an
alloy Sb--Te--Ge and as a primary component and having a thickness
of 100 nm was formed on the other surface of the polycarbonate
substrate by the sputtering process.
[0090] Finally, the same ultraviolet ray curable resin as that used
for forming the first resin layer was applied by the spin coating
method onto the moisture-proof layer to form a coating layer. Then,
an ultraviolet ray was projected onto the coating layer so that a
total amount thereof was 3000 mJ/cm.sup.2, whereby the ultraviolet
ray curable resin was cured and a second resin layer having a
thickness of 100 .mu.m was formed. Thus, the sample #1 was
fabricated.
[0091] Further, a sample #2 was fabricated in the manner of
fabricating the sample #1 except that a moisture-proof layer
containing Ag as a primary component was formed.
[0092] Then, each of the sample #1 and the sample #2 was held at a
temperature of 25.degree. C. and relative humidity of 95% until the
water content therein was saturated and the temperature thereof
became 25.degree. C. Thereafter, each of them was set in a
high-accuracy laser warpage angle measuring machine manufactured
and sold by KEYENCE CORPORATION "LA-2000" (Product Name) and the
warpage angle .beta..sub.1 at a position spaced by 58 mm from the
center thereof was measured.
[0093] Further, each of the sample #1 and the sample #2 was set in
the above mentioned high-accuracy laser warpage angle measuring
machine at a temperature of 25.degree. C. and relative humidity of
10% and the warpage angle .beta..sub.2 at a position spaced by 58
mm from the center thereof was measured. When the warpage angle
.beta..sub.2 of each sample was determined, warpage angles were
successively measured at a temperature of 25.degree. C. and
relative humidity of 10% until the warpage angle did not vary and
the maximum value thereof was determined as the warpage angle
.beta..sub.2 thereof. Here, each of the warpage angles .beta..sub.1
and .beta..sub.2 was defined to be plus when each sample warped
toward the first resin layer and minus when it warped toward the
second resin layer.
[0094] Then, the difference (.beta..sub.1-.beta..sub.2) between the
warpage angles .beta..sub.1 and .beta..sub.2 for each sample was
caculated and the degree of warpage of each sample was rated. The
degree of warpage was rated to be "GOOD" when the difference
(.beta..sub.1-.beta..sub.2) in the warpage angles was equal to or
smaller than 0.35 degrees and "BAD" when it was larger than 0.35
degrees. The results of the measurement are shown in Table 1.
2 TABLE 1 warpage warpage difference angle .beta..sub.1 angle
.beta..sub.2 in warpage (deg) (deg) angles (deg) rating sample #1
0.05 -0.25 0.30 GOOD sample #2 0.02 -0.73 0.75 BAD
[0095] As shown in Table 1, it was found that in the sample #1, the
difference in the warpage angles thereof was 0.30 degrees and
smaller than 0.35 degrees and that the warpage of the optical
recording medium could be prevented. To the contrary, in the sample
#2, the difference in the warpage angles thereof was 0.75 degrees
and could not suppressed to be equal to or smaller than 0.35
degrees.
[0096] The present invention has thus been shown and described with
reference to a specific embodiment and working example. However, it
should be noted that the present invention is in no way limited to
the details of the described arrangements but changes and
modifications may be made without departing from the scope of the
appended claims.
[0097] For example, in the optical recording medium 1 shown in
FIGS. 1 and 2, although the first hard coat layer 5 is formed on
one side of the support substrate 2 and the second hard coat layer
8 is formed on the other side of the support substrate 2, it is not
absolutely necessary to form two hard coat layers and one or both
of the first hard coat layer 5 and the second hard coat layer 8 may
be omitted.
[0098] Further, in the above described embodiment, although the
first dielectric film 34 and the second dielectric film 32 are
formed on the opposite sides of the recording film 33, it is not
absolutely necessary to form the first dielectric film 34 and the
second dielectric film 32 on the opposite sides of the recording
film 33 and the first dielectric film 34 may be omitted in the case
where the difference in reflectivity between a region of the
recording film 33 where a recording mark is formed and regions
where no recording mark is formed is large.
[0099] Furthermore, in the above described embodiment, although the
heat radiation film 35 is provided, it is not absolutely necessary
to provide the heat radiation film 35 and the heat radiation film
35 may be omitted in the case where heat generated in the recording
film 33 can be quickly radiated by a dielectric film formed in the
vicinity of the recording film 3 or the recording film 33
itself.
[0100] Moreover, in the above described embodiment, although the
reflective film 31 is provided, it is not absolutely necessary to
provide the reflective film 31 and the reflective film 31 may be
omitted in the case where the difference in reflectivity between a
region of the recording film 33 where a recording mark is formed
and regions where no recording mark is formed is large.
[0101] According to the present invention, it is possible to
provide an optical recording medium which can be prevented from
warping in a desired manner.
* * * * *