JP2003123316A - Optical information medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize a warpage and to prevent a damage of the surface of a light-transmissive layer immediately after manufactured and after stored in an environment under a high temperature and high humidity in the optical information medium which has an information recording layer on the surface of a supporting base body and a light-transmissive layer on the information recording layer, and which information recording layer is irradiated with a laser beam for recording or reproducing through the light-transmissive layer. SOLUTION: The optical information medium has the information recording layer on the supporting base body, the light-transmissive layer on the information recording layer, and is used by making the laser beam for recording or reproducing incident on the information recording layer through the light- transmissive layer. The light-transmissive layer of the optical information medium is composed of a resin and the dynamic elastic modulus of the light- transmissive layer is 1.5 to 3.0 GPa at 25 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical information medium such as a read-only optical disc and an optical recording disc.

[0002]

2. Description of the Related Art In recent years, optical recording media such as read-only optical discs and optical recording discs record and store enormous amounts of information such as moving image information. Therefore, it is required to increase the recording density to increase the capacity of the medium. In order to meet the demand, research and development for higher recording density have been actively conducted.

One of them is, for example, a DVD (Di
As can be seen in gital Versatile Disk), the recording / reproducing wavelength is shortened, and the numerical aperture (NA) of the objective lens of the recording / reproducing optical system is increased to reduce the laser beam spot diameter during recording / reproducing. It is suggested to do so.
Comparing DVD and CD, the recording / reproducing wavelength is 780 nm
To 650 nm and NA from 0.45 to 0.6, the recording capacity of 6 to 8 times (4.7 GB /
Aspect) has been achieved.

Furthermore, recently, in order to record a high-quality moving image for a long time, the recording / reproducing wavelength is shortened to about 400 nm, and the numerical aperture of the objective lens is increased to about 0.85. More than 4 times, ie 20GB
Attempts have been made to achieve recording capacities of more than one side.

However, if the NA is increased in this way, the tilt margin becomes small. The tilt margin is
The tolerance of the tilt of the optical recording medium with respect to the optical system, which is NA
Determined by When the recording / reproducing wavelength is λ and the thickness of the transparent substrate on which the recording / reproducing light is incident is t, the tilt margin is proportional to λ / (t · NA ³ ). Further, when the optical recording medium tilts with respect to the laser beam, that is, when tilt occurs, wavefront aberration (coma aberration) occurs. Assuming that the refractive index of the substrate is n and the tilt angle is θ, the wavefront aberration coefficient is (1/2) · t · {n ² · sin θ · cos θ} · NA ³ / (n
² −sin ² θ) ^-5/2 . From these equations, it is understood that the thickness t of the base body should be reduced in order to increase the tilt margin and suppress the occurrence of coma. In fact, in DVD, the tilt margin is secured by making the thickness of the substrate approximately half (about 0.6 mm) of the thickness of the CD substrate (about 1.2 mm).

By the way, there has been proposed a structure in which the base can be made thinner in order to record a higher quality moving image for a long time. In this structure, a substrate having a normal thickness is used as a supporting substrate for maintaining rigidity, pits and recording layers are formed on the surface thereof, and a light transmitting layer having a thickness of about 100 μm is provided as a thin substrate thereon. Recording / reproducing light is made incident through this light transmitting layer. With this structure, the base can be made significantly thinner than in the conventional case, so that it is possible to achieve a high recording density by increasing the NA. A medium having such a structure is described in, for example, Japanese Patent Application Laid-Open No. 10-289489.
The medium described in the publication has a light transmission layer made of a photocurable resin.

However, when the light transmitting layer is made of a photocurable resin such as an ultraviolet curable resin, the medium warps due to the shrinkage that occurs during curing. Warping also occurs when the medium is stored in a high temperature and high humidity environment. If the medium warps, a read error is likely to occur, and if the amount of warp is large, the medium may not be readable.

Japanese Unexamined Patent Publication (Kokai) No. 8-19496 discloses an optical disk having a resin protective coat.
According to the publication, the tensile breaking elongation of the protective coat is set to 15% or more to prevent warpage of the optical disc when stored in a high temperature and high humidity environment. However, this publication does not mention that recording / reproducing light is incident through the protective coat.

However, according to the research conducted by the inventors of the present invention, when recording / reproducing light is incident through a light transmitting layer (protective coat) having a thickness of about 100 μm, the tensile breaking elongation of the light transmitting layer is only 15%. It has been found that good recording / reproducing characteristics cannot be obtained due to the warp of the medium only by the above. Moreover, it was found that the recording / reproducing characteristics were further deteriorated because the warp of the medium was increased by the storage under the conditions of high temperature and high humidity. In particular, there has been a problem when the beam spot diameter of the laser beam is reduced and recording / reproducing is performed at a high linear velocity. A particular problem was that the stability of the focus servo became insufficient.

In order to reduce the warp of the medium, it is sufficient to form the light transmitting layer from a resin which has a very small shrinkage upon curing and is soft, but in that case, the surface hardness of the light transmitting layer becomes insufficient. , The surface of the light transmitting layer is easily scratched. In the thin light transmitting layer described above, the diameter of the laser beam on the surface of the light transmitting layer is small because the distance between the surface of the light transmitting layer and the information recording layer is short. Therefore, scratches on the surface of the light transmitting layer have a bad influence on recording / reproducing characteristics.

[0011]

It is an object of the present invention to have an information recording layer on the surface of a supporting substrate and a light transmitting layer on the information recording layer, and a laser for recording or reproducing through the light transmitting layer. In an optical information medium in which a beam is irradiated on the information recording layer, it is to reduce warpage immediately after production and after storage under high temperature and high humidity conditions, and prevent scratches on the surface of the light transmitting layer.

[0012]

The above object is achieved by the present invention described in (1) to (16) below. (1) An information recording layer is provided on a supporting substrate, and a light transmission layer is provided on the information recording layer, and a laser beam for recording or reproduction is incident on the information recording layer through the light transmission layer. The optical information medium, wherein the light transmitting layer is made of resin, and the dynamic elastic modulus of the light transmitting layer at 25 ° C. is 1.5 to 3.0 GPa. (2) The dynamic elastic modulus of the light transmitting layer at 80 ° C. is 0.0
The optical information medium of (1) above, which is 5 to 1.0 GPa. (3) The tensile elastic modulus at 25 ° C. of the light transmitting layer is 0.6.
The optical information medium according to (1) or (2) above, which has a density of up to 1.5 GPa. (4) The optical information medium according to any one of (1) to (3), wherein the glass transition point of the light transmitting layer is 70 to 140 ° C. (5) The optical information medium according to any one of (1) to (4) above, wherein the transmittance of the light transmission layer at the wavelength of the laser beam for recording or reproduction is 80% or more. (6) The optical information medium according to any one of (1) to (5) above, wherein the light transmitting layer contains a cured product of the radiation curable composition. (7) The light information of the above (6), wherein the light transmission layer contains the reaction initiator contained in the radiation-curable composition, and the absorption coefficient of the reaction initiator at a wavelength of 405 nm is 500 or less. Medium. (8) The optical information medium according to any one of (1) to (7), wherein the thickness of the light transmission layer is 30 to 200 μm. (9) When the wavelength of the laser beam for recording or reproduction is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, then λ / NA ≦ 680 nm
Recording or reproduction is performed under the condition that (1) above is satisfied.
An optical information medium according to any one of (8) to (8). (10) An information recording layer is provided on a supporting substrate, a light transmitting layer is provided on the information recording layer, and a laser beam for recording or reproducing is incident on the information recording layer through the light transmitting layer. An optical information medium for recording or reproducing under the condition that λ / NA ≦ 680 nm is satisfied, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam. When the supporting substrate is a disk with a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is T-Skew, an environment of 80 ° C. and 80% RH 5 down
An optical information medium having | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg both before and after a high temperature / high humidity storage test in which it is stored for 0 hours. (11) An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproduction is incident on the information recording layer through the light transmitting layer. Λ / NA ≦ 6, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam.
An optical information medium for recording or reproducing under the condition that 80 nm is satisfied, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is When T-Skew is set, | R-Skew | ≦ 0.4deg and | T-Skew | ≦ 0.15deg both before and after the high temperature dry storage test in which it is stored in a dry environment at 80 ° C. for 50 hours. Optical information medium. (12) An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer, and a laser beam for recording or reproducing is incident on the information recording layer through the light transmitting layer. Λ / NA ≦ 6, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam.
An optical information medium for recording or reproducing under the condition that 80 nm is satisfied, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is When T-Skew is used, light with | R-Skew | ≦ 0.4deg and | T-Skew | ≦ 0.15deg both before and after the low temperature storage test in which it is stored at −25 ° C. for 50 hours. Information medium. (13) An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer, and a laser beam for recording or reproduction is incident on the information recording layer through the light transmitting layer. Λ / NA ≦ 6, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam.
An optical information medium for recording or reproducing under the condition that 80 nm is satisfied, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is When T-Skew is used, it should be stored at 20 ° C for 12 hours in a constant humidity environment of 50% RH and at room temperature.
A temperature cycle of performing high temperature storage for 12 hours at 0 ° C. is repeated 6 times, and a temperature rising rate at the time of transition from the room temperature storage to the high temperature storage and a temperature decrease at the time of transition from the high temperature storage to the room temperature storage. An optical information medium having | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg both before and after a temperature cycle test with a speed of 10 ° C./hour. (14) An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is incident on the information recording layer through the light transmitting layer. Λ / NA ≦ 6, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam.
An optical information medium for recording or reproducing under the condition that 80 nm is satisfied, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is When T-Skew is used, it should be stored under a constant temperature environment of 60 ° C for 12 hours at 20% RH and for 8 hours.
A humidity cycle of performing high humidity storage of 12% RH for 12 hours is repeated, and the rate of increase in humidity at the time of transition from the normal humidity storage to the high humidity storage and the high humidity storage to the normal humidity storage. Humidity decrease rate when shifting to 1
An optical information medium having | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg both before and after the humidity cycle test with 0% / hour. (15) An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproduction is incident on the information recording layer through the light transmitting layer. Λ / NA ≦ 6, where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens of the optical system that irradiates the laser beam.
An optical information medium for recording or reproducing under the condition that 80 nm is satisfied, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, the radial warp angle is R-Skew, and the circumferential warp angle is When T-Skew is used, a temperature cycle of 1 hour storage in a -20 ° C environment and 1 hour storage in a 70 ° C dry environment is repeated 50 times before and after a thermal shock test. An optical information medium having -Skew | ≤0.4 deg and | T-Skew | ≤0.15 deg. (16) The optical information medium according to any one of (1) to (9), which is the optical information medium according to any one of (10) to (15).

[0013]

In the present invention, in the optical information medium in which information is reproduced by irradiating the information recording layer with a laser beam through the light transmitting layer having a thickness of about 100 μm, the dynamic elasticity of the light transmitting layer at 25 ° C. The rate is a value within a predetermined range. This reduces the warp of the medium,
Moreover, the surface of the light transmitting layer is not easily scratched.

In a preferred embodiment of the present invention, 80 ° C.
The dynamic elastic modulus of the light transmitting layer at is a value within a predetermined range. As a result, even if the medium is stored under high temperature and high humidity conditions, the warp of the medium does not significantly increase.

Further, in a preferred embodiment of the present invention, the tensile elastic modulus at 25 ° C. of the light transmitting layer is set to a value within a predetermined range. This further reduces the warpage of the medium, and
The surface of the light transmission layer becomes more difficult to be damaged.

Further, in a preferred aspect of the present invention, the glass transition point of the light transmitting layer is set to a value within a predetermined range. As a result, the warp of the medium is further reduced, and the surface of the light transmission layer is further hard to be damaged.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A configuration example of an optical information medium of the present invention,
As shown in FIG. This optical information medium is a recording medium, and has a recording layer 4 as an information recording layer on a support base 20, and a light transmission layer 2 on this recording layer 4. A laser beam for recording or reproduction enters through the light transmitting layer 2.

The present invention can be applied regardless of the type of recording layer. That is, for example, even if it is a phase change recording medium,
It can be applied to both a pit formation type recording medium and a magneto-optical recording medium. Incidentally, a dielectric layer or a reflective layer is usually provided on at least one side of the recording layer for the purpose of protecting the recording layer and optical effects, but it is omitted in FIG. Further, the present invention is applicable not only to the recordable type shown in the drawing but also to the read-only type. In that case, a supporting substrate 20 having pits integrally formed thereon is used, and a reflecting layer made of a metal film, a semi-metal film, a dielectric multilayer film or the like is provided thereon, and the shape of the pits is transferred to this reflecting layer. . In this case, the reflective layer constitutes the information recording layer.

Next, the specific structure of each part of the medium of the present invention will be described.

The support substrate 20 is provided to maintain the rigidity of the medium. The thickness of the supporting substrate 20 is usually 0.2.
˜1.2 mm, preferably 0.4 to 1.2 mm, and it may be transparent or opaque. Support base 2
0 may be made of resin as in the ordinary optical recording medium, but may be made of glass. The groove (guide groove) 21 usually provided in the optical recording medium can be formed by transferring the groove provided in the supporting substrate 20 to each layer formed thereon, as shown in the figure. Groove 21
Is an area existing on the front side when viewed from the recording / reproducing light incident side, and an area existing between adjacent grooves is called a land.

The light transmitting layer 2 has a light transmitting property for transmitting a laser beam. The thickness of the light transmitting layer 2 in the present invention is preferably 30 to 200 μm, more preferably 5
More than 0 μm and 200 μm or less, more preferably 70 to 150
μm. If the light transmitting layer is too thin, the optical influence of dust adhering to the surface of the light transmitting layer becomes large. Also, due to the higher NA, the distance between the optical pickup and the medium becomes smaller, and the optical pickup easily contacts the medium surface.
If the light transmission layer is thin, a sufficient protection effect cannot be obtained against the contact of the optical pickup. On the other hand, if the light transmission layer is too thick, it becomes difficult to achieve a high recording density by increasing the NA. If the light transmission layer is thick, the shrinkage due to curing during formation of the light transmission layer becomes large, and as a result, the warp of the medium becomes large. However, since the light transmission layer in the present invention has a small dynamic elastic modulus, even if it is a relatively thick light transmission layer having a thickness of more than 50 μm, or even 70 μm or more, the warp that occurs during curing is small and the warp that occurs is small. Relaxed over time. As a result, it is possible to obtain a medium with less warpage than ever before.

The light transmission layer 2 has a dynamic elastic modulus at 25 ° C. of 1.5 to 3.0 GPa, preferably 1.8 to 2.8 GPa. If the dynamic elastic modulus at 25 ° C. is too small, the surface of the light transmitting layer is likely to be damaged. On the other hand, if the dynamic elastic modulus at 25 ° C. is too large, the warp of the medium becomes large.

The light transmission layer 2 has a dynamic elastic modulus at 80 ° C. of preferably 0.05 to 1.0 GPa, more preferably 0.1 to 0.9 GPa. If the dynamic elastic modulus at 80 ° C. is too small, the surface of the light transmission layer is likely to be damaged during storage under high temperature and high humidity conditions. On the other hand, if the dynamic elastic modulus at 80 ° C. is too large, the warp of the medium becomes large due to storage under high temperature and high humidity conditions.

The tensile modulus of the light transmitting layer 2 at 25 ° C. is preferably 0.6 to 1.5 GPa, more preferably 0.8 to 1.4 GPa. If the tensile elastic modulus at 25 ° C. is too low, the surface of the light transmitting layer is likely to be damaged.
On the other hand, if the tensile modulus at 25 ° C. is too large, the warp of the medium becomes large.

The light transmission layer 2 has a glass transition point of preferably 70 to 140 ° C, more preferably 80 to 130 ° C. When the light transmitting layer 2 is made of a radiation curable resin or a thermosetting resin, when the glass transition point is high, the shrinkage at the time of curing becomes large, and thus the warp of the medium becomes large. On the other hand, if the glass transition point of the light transmitting layer 2 is too low, the surface of the light transmitting layer is likely to be damaged. If the glass transition point is low, the medium tends to warp greatly when stored in a high temperature environment. The reason is as follows. Thin films such as a reflective layer, a recording layer, and a dielectric layer are formed on the medium by a sputtering method, and stress due to these thin films exists. Further, the medium also has a stress due to the light transmitting layer 2. Media warpage is determined by the balance of these stresses. On the other hand, when the glass transition point of the light transmitting layer 2 is low, the light transmitting layer 2 becomes soft when the medium is stored at high temperature. Therefore, even if the warp is small at room temperature, if the light transmission layer 2 is softened and the stress balance is lost, the warp of the medium is increased.

The tensile modulus in this specification is JI.
It is defined in S K7127-1989. At the time of measurement, the length of the test piece: 60 mm, the width of the test piece: 10 mm, the distance between the marked lines: 40 ± 1 mm, the distance between the grips: 44 ± 1 mm, the pulling speed: 30 mm / min, and other measurement conditions It suffices to comply with JIS K7127-1989. The reason why these conditions are different from JIS K7127-1989 is that the size of the medium (optical disk) (usually, about 12 cm) is taken into consideration so that the light transmission layer separated from the medium can be measured.

The dynamic elastic modulus in this specification is JIS K724.
It is the dynamic storage modulus specified in 4-4. In the measurement, the frequency was 3.5 Hz, the heating rate was 3 ° C / min, and the plane dimension of the test piece was 50 mm × 4 mm.
The rules of S K7244-4 should be followed. Further, the glass transition point can be measured at the same time when the dynamic elastic modulus is measured.

As described above, by setting the dynamic elastic modulus at room temperature and high temperature, the tensile elastic modulus at room temperature, and the glass transition point in the above ranges in the optical recording layer, the warpage of the medium immediately after production is reduced. In addition, it is possible to suppress an increase in warpage due to storage in a high temperature and high humidity environment.

When the wavelength of the laser beam for recording or reproduction is λ, and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, recording or recording is performed by an apparatus satisfying λ / NA ≦ 680 nm. The present invention is particularly effective when applied to a medium on which reproduction is performed. A small λ / NA means that recording / reproducing light of a relatively short wavelength is relatively high in NA.
It means that irradiation is performed by using the objective lens, and in that case, the beam spot diameter of the laser beam focused on the surface of the information recording layer becomes small. In that case, as described above, the tilt margin of the medium becomes small and the coma becomes large. As a result, the allowable amount of warp of the medium becomes small. Therefore, the present invention is particularly effective when λ / NA is small as described above. If good recording / reproducing characteristics can be realized in the range of 400 nm ≦ λ / NA,
Generally sufficient.

The present invention is characterized in that the physical properties of the light transmitting layer are within the above range, and thereby the above-mentioned various effects are realized. Therefore, the specific configuration of the resin forming the light transmitting layer and the method of forming the light transmitting layer are not particularly limited. For example, applying a resin or a composition that becomes a resin after curing,
Any method may be used, such as a method of curing as necessary, or a method of attaching a resin sheet prepared in advance with an ultraviolet-curable adhesive or pressure-sensitive adhesive. However, the dynamic elastic modulus,
In order to obtain a light-transmitting layer having a tensile elastic modulus and a glass transition point within the ranges defined by the present invention, a radiation-curable composition is applied by a spin coating method and then cured by radiation to form a light-transmitting layer. Is preferred. In this specification, radiation is a concept including electromagnetic waves such as ultraviolet rays and particle beams such as electron beams.

The radiation-curable composition usually contains at least one of monofunctional or polyfunctional monomers, oligomers and polymers, and further contains a photopolymerization initiator (reaction initiator) and a photopolymerization initiation auxiliary. , A polymerization inhibitor, etc. are contained. Such a composition is disclosed, for example, in the above-mentioned JP-A-8-
It can be selected from the constituent materials of the protective coating agent for high density optical discs described in Japanese Patent No. 194968.

The composition used in the present invention is preferably a composition containing at least a linear bifunctional oligomer having functional groups at both ends and a monofunctional monomer. If the content of the bifunctional oligomer is too large or the molecular weight of the bifunctional oligomer is too large, the dynamic elastic modulus and tensile elastic modulus after curing become small. In addition, the addition of the monofunctional monomer improves the adhesion between the light transmission layer and the surface on which it is formed. However, if the addition amount of the monofunctional monomer is too large, the dynamic elastic modulus and the tensile elastic modulus after curing become small.

A small amount of a trifunctional monomer may be added to increase the glass transition point, dynamic elastic modulus and tensile elastic modulus. Further, by adding a monomer and / or oligomer having a cyclic skeleton in the molecule, it is possible to improve the dynamic elastic modulus and the tensile elastic modulus without increasing the shrinkage rate during curing.

Therefore, depending on the physical properties of the light transmitting layer required in the present invention, the types of monomers and oligomers used for forming the light transmitting layer, their molecular weights, and their contents may be appropriately selected. The composition preferably used in the present invention can be selected from commercially available products.

Examples of the oligomer or monomer used in the radiation-curable composition include the followings.

Examples of the bifunctional oligomer include polyester acrylate, epoxy acrylate and urethane acrylate. As polyester acrylate, Aronix M-620 manufactured by Toagosei Chemical Industry Co., Ltd.
0, Aronix M-6400X, Aronix M-6410X,
Aronix M-6420X is mentioned. As epoxy acrylate, Showa High Polymer Co., Ltd. Lipoxy SP-15
06, Lipoxy SP-1509, Lipoxy SP-1519-1, Lipoxy SP-1563, Lipoxy VR-77, Lipoxy VR-60, Lipoxy VR-90; Viscoat 54 manufactured by Osaka Organic Chemical Industry Co., Ltd.
0: Kayarad R-167 manufactured by Nippon Kayaku Co., Ltd .; Epoxy ester 3002A, Epoxy ester 3 manufactured by Kyoeisha Yushi Co., Ltd.
002M, epoxy ester 80MFA; Nadecor DM-851, Nadecor DA-811 and Nadecol DM- manufactured by Nagase & Co., Ltd.
Examples include 811, Nadecor DA-721, and Nadecor DA-911. As a urethane acrylate, Negami Industry Co., Ltd.
Art range UN-1000PEP, Art range UN-9000P
EP, Art Range UN-9200A, Art Range UN-2500,
Art Range UN-5200, Art Range UN-llO2, Art Range UN-380G, Art Range UN-500, Art Range U
N-9832; Aronix M-1200 manufactured by Toagosei Co., Ltd .; Chemlink 9503, Chemlink 9504, Chemlink 9505 manufactured by Sartomer.

As the monofunctional monomer, benzyl acrylate, benzyl methacrylate, butoxyethyl acrylate, butoxyethyl methacrylate, butanediol monoacrylate, cyclohexyl acrylate,
Cyclohexyl methacrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, alicyclic modified neopentyl glycol acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentenyloxyethyl methacrylate, 2-ethoxyethyl Acrylate, 2-ethoxyethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
2-hydroxypropyl methacrylate, isobornyl acrylate, isobornyl methacrylate, isodecyl acrylate, isodecyl methacrylate, isooctyl acrylate, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-methoxyethyl acrylate, methoxydiethylene glycol methacrylate, methoxyethylene Glycol acrylate, morpholine acrylate, phenoxyhydroxypropyl acrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol acrylate, EO-modified phthalate acrylate, EO-modified phthalate methacrylate, stearyl acrylate, stearyl methacrylate, tetrahydrofurfuryl Acrylate, tetrahydrofurfuryl methacrylate, vinyl acetate, include N- vinylpyrrolidone.

The radiation-curable composition preferably used in the present invention has a relatively high viscosity, specifically, the viscosity at 25 ° C. is 2000 to 20000 mPa · s, preferably 3000 to 15000 mPa · s. On the other hand, in JP-A-8-19496, the composition of 25 ° C.
The preferred viscosity is 5 to 300 cP (5 to 300
The range of mPa · s) is disclosed.

The radiation-curable composition used in the present invention preferably has a shrinkage ratio at the time of curing of 7% or less, particularly 6% or less. If the cured product has a dynamic elastic modulus, a tensile elastic modulus and a glass transition point within the ranges defined by the present invention, it is possible to reduce the shrinkage ratio during curing in this way. However, it is not necessary to make the shrinkage ratio upon curing extremely small, and it is usually not necessary to make the shrinkage ratio less than 4%.

It should be noted that, in the above-mentioned JP-A-8-194968, it is possible to suppress warpage of the optical disk due to storage in a high temperature and high humidity environment by setting the protective coating of the optical disk to have a tensile breaking elongation of 15% or more. Is listed. However, as described above, since the composition for forming a protective coat described in the publication and the composition used in the present invention have different viscosities, the light transmission layer formed by curing the composition described in the publication is It is not considered to have the physical properties of the light transmitting layer in the invention. Moreover, the publication only mentions that a protective coat having a thickness of 1 to 50 μm is provided to prevent corrosion of the recording portion, and that the recording light and the reproducing light are incident through the protective coat. There is no. Therefore, the publication does not consider high-density recording by injecting a recording / reproducing beam having a short wavelength through a thin light transmitting layer having a thickness of about 100 μm. Also,
When a low-viscosity composition as described in the publication is used,
It is virtually impossible to form a light transmission layer having a thickness of more than 50 μm.

In the example of the publication, the composition was applied to a polycarbonate plate having a thickness of 0.5 mm so as to have a thickness of 50 μm and cured, and immediately after curing (25 ° C., 50% RH, after 1 hour) and The degree of warpage is evaluated after the durability test (85 ° C., 90% RH, after 3 days). However, in the example of the publication, only the magnitude of the warp is relatively evaluated, and the warp is not quantitatively evaluated.

The light transmitting layer in the present invention may be a laminate of two or more resin layers. As the laminated type, for example, a structure in which a surface layer having better scratch resistance than the inner layer is laminated on the inner layer having a relatively low dynamic elastic modulus, and the surface layer constitutes the surface of the light transmitting layer. Is mentioned. In this structure, even if the surface layer is considerably thinner than the inner layer, sufficient scratch resistance can be obtained, so that the surface layer can be thinned. Therefore, the requirements for the physical properties of the surface layer constituent material are not strict. Therefore, the surface layer constituent material is
It is possible to relatively freely select a resin having good scratch resistance from various resins.

The inner layer and surface layer in this structure are
It is preferably a cured product of the radiation curable composition described above. As for the composition used for forming the internal layer, as described above, the composition is selected so that the dynamic elastic modulus after curing becomes low. On the other hand, in the composition used for forming the surface layer, it is preferable that the ratio of the polyfunctional oligomer and / or the polyfunctional monomer is relatively high. Thereby, the hardness of the surface layer can be increased. Further, when the ratio of the monofunctional monomer is relatively high, the adhesiveness between the surface layer and the inner layer is improved.

When a two-layer structure including a surface layer and an inner layer is used,
The thickness of the surface layer is preferably 0.1 to 10 μm, more preferably 0.3 to 5 μm. If the surface layer is too thin,
Insufficient protection effect. On the other hand, if the surface layer is too thick,
It becomes difficult to set the physical properties of the entire light transmission layer within the range limited by the present invention.

The inner layer may have a multi-layer structure of two or more layers.

When the light transmission layer has a multi-layer structure made of a radiation curable resin, it is usually a composition for forming an upper layer after coating and curing a composition for forming a lower layer. Apply and cure. However, in order to improve the adhesiveness between the lower layer and the upper layer, a method of laminating the upper layer when the lower layer is in a semi-cured state and finally completely curing all layers is proposed. You may use it.

The light transmission layer preferably has a transmittance of a laser beam for recording or reproduction of 80% or more. If this transmittance is low, a large laser power is required for recording, which is not preferable. When the radiation curable composition used for forming the light transmitting layer contains a reaction initiator such as a photopolymerization initiator, the reaction initiator preferably has an extinction coefficient of 500 or less, particularly 100 or less at a wavelength of 405 nm. . As a result, the transmittance of the light transmission layer in the short wavelength region around 400 nm can be increased, which is suitable for a high density recording / reproducing system using a short wavelength laser.
Examples of the reaction initiator having an absorption coefficient of 500 or less at a wavelength of 405 nm include benzophenone, diethoxyacetophenone, 2-hydroxy-2-methyl-1.
-Phenylpropan-1-one, 1-hydroxycyclohexyl-phenyl ketone, methyl benzoyl formate.

In the disk-shaped medium having the light transmitting layer to which the present invention is applied, the warp is small before and after the storage test described below. The warp angle of the disk-shaped medium mainly depends on the constituent material of the medium, the diameter of the medium, and the thickness of the medium. In the medium having the structure shown in FIG. 1, when the supporting substrate 20 is made of a resin plate having a thickness of 0.4 to 1.2 mm and a diameter of 60 to 135 mm, the present invention is applied to warp before and after the following storage test. It is easy to keep the angle within the range of | R-Skew | ≤0.4deg, | T-Skew | ≤0.15deg, and | R-Skew | ≤0.35deg, | T-Skew | ≤0. It is also possible to fit within the range of 14 deg. The R-Skew is a warp angle in the radial direction, and the T-Skew is a warp angle in the circumferential direction. The warp angle after the storage test is measured by leaving each storage test for 24 hours in an environment of 25 ° C. and 50% RH, and within 48 hours after the completion of the storage test. The above-mentioned storage test is the following six types of tests.

(1) High-temperature / high-humidity storage test Stored in an environment of 80 ° C. and 80% RH for 50 hours.

(2) High temperature dry storage test Storage is carried out in a dry environment at 80 ° C. for 50 hours.

(3) Low-temperature storage test Storage at −25 ° C. for 50 hours.

(4) Temperature Cycle Test In a constant humidity environment of 50% RH, a temperature cycle of performing room temperature storage at 20 ° C. for 12 hours and high temperature storage at 60 ° C. for 12 hours was repeated 6 cycles, and The temperature rising rate at the time of shifting from the room temperature storage to the high temperature storage and the temperature falling rate at the time of shifting from the high temperature storage to the room temperature storage are 10 ° C./hour.

(5) Humidity Cycle Test In a constant temperature environment of 60 ° C., a humidity cycle of performing normal humidity storage of 20% RH for 12 hours and high humidity storage of 80% RH for 12 hours was repeated 6 cycles, And,
The humidity increasing rate at the time of shifting from the normal humidity storage to the high humidity storing and the humidity decreasing rate at the time of shifting from the high humidity storage to the normal humidity storage are 10% / hour.

(6) Thermal shock test [0054] Immediately after storing for 1 hour in an environment of -20 ° C, a temperature cycle of storing for 1 hour in a dry environment of 70 ° C is repeated 50 times.

[0055]

EXAMPLES The optical recording disk samples shown in Table 1 were prepared by the following procedure.

A disc-shaped support substrate having a groove (made of polycarbonate, diameter 120 mm, thickness 1.2 mm)
A reflecting layer made of Al ₉₈ Pd ₁ Cu ₁ (atomic ratio) was formed on the surface of by using a sputtering method. The groove depth is the wavelength λ
The optical path length at 405 nm was set to λ / 6. The recording track pitch in the land / groove recording method is
It was 0.3 μm.

Then, a second dielectric layer having a thickness of 20 nm was formed on the surface of the reflective layer by a sputtering method using an Al ₂ O ₃ target.

Next, a recording layer having a thickness of 12 nm was formed on the surface of the second dielectric layer by sputtering using an alloy target made of a phase change material. Recording layer composition (atomic ratio)
Was Sb ₇₄ Te ₁₈ (Ge ₇ In ₁ ).

Then, a 130-nm-thick first dielectric layer was formed on the surface of the recording layer by a sputtering method using a ZnS (80 mol%)-SiO ₂ (20 mol%) target.

Then, an ultraviolet curable resin was applied on the surface of the first dielectric layer by spin coating, and a light transmitting layer having a thickness of 100 μm was formed by irradiating with ultraviolet rays to obtain an optical recording disk sample. The ultraviolet curable resin used for each sample and its viscosity at 25 ° C. are shown in Table 1. All UV curable resins are Nippon Kayaku Co., Ltd.
It is made. In addition, for all UV curable resins, reaction initiators (1
-Hydroxycyclohexyl-phenyl ketone: Ciba
Specialty Chemicals Co., Ltd. Irgacure 18
4) was used.

Next, the recording layer of each sample was initialized (crystallized) by a bulk eraser.

With respect to each sample, the radial warp angle R-Skew and the circumferential warp angle T-Skew were measured using an optical disk mechanical property evaluation device DC-1010C manufactured by Cores Co., Ltd. Further, the same measurement was carried out immediately after the sample was stored in an environment of 80 ° C. and 80% RH for 50 hours and further left in the environment of 25 ° C. and 50% RH for 24 hours. The results are shown in Table 1.

Further, steel wool # 0000 was loaded 24.
While pressing at 5 kPa, 1 on the surface of the light transmission layer of each sample
After reciprocating 0 times, the abrasion resistance was evaluated by examining the degree of scratches on the surface of the light transmitting layer. The results are shown in Table 1. In Table 1, "best" means that almost no scratches were observed, "good" means that there were few scratches, "somewhat bad" means that there were many scratches, and "bad". Is when the wound is severe.

The wavelength of the light transmission layer of each sample is 405.
The transmittance at nm was measured by a spectrophotometer manufactured by Shimadzu Corporation. The results are shown in Table 1.

Table 1 shows the dynamic elastic modulus at 25 ° C. and 80 ° C., the tensile elastic modulus at 25 ° C. and the glass transition point Tg of the light transmitting layer of each sample.

The dynamic elastic modulus and the glass transition point Tg
At the time of measurement, a light transmission layer was cut from the sample into a rectangle having a plane size of 50 mm × 4 mm with a cutter knife to prepare a test piece, and this test piece was used to make a rheovibron dynamic viscoelasticity measuring instrument manufactured by Orientec Co., Ltd. (Dynamic Viscoela
stometer RHEOVIBRON) Model-01FP. This measurement was carried out under the conditions defined herein. In addition, when measuring the tensile modulus, the plane dimension is 60 mm x 1
Using a test piece cut into a 0 mm rectangle, JI
Based on S K7127-1989 and the measurement conditions defined in this specification, the measurement was performed using TRM-100 type Tensilon manufactured by Orientec Co., Ltd. In addition, when cutting out the test piece,
There were cases where a dielectric layer, a recording layer, a reflective layer, etc. were attached to the test piece, but the attachment of these layers did not affect the measured values of the dynamic elastic modulus and the tensile elastic modulus.

[0067]

[Table 1]

The effects of the present invention are clear from Table 1. That is, in the sample in which the dynamic elastic modulus of the light transmitting layer, the tensile elastic modulus and the glass transition point are all within the limits defined in the present invention, the warp angle is measured immediately after the production and after the high temperature and high humidity storage test. Small enough.

The comparative sample in which the tensile elastic modulus and the warp angle after storage are not described is subjected to light exposure when chucking the sample for measuring the tensile elastic modulus and during the high temperature and high humidity storage test. The light transmitting layer is cracked or the light transmitting layer is broken.

The samples shown in Table 1 were subjected to the above-mentioned high temperature dry storage test, low temperature storage test, temperature cycle test, humidity cycle test and thermal shock test. In any case, it was within the range of | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a configuration example of an optical information medium of the present invention.

[Explanation of symbols]

2 Light transmission layer 20 Support substrate 21 groove 4 recording layers

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 7/24 G11B 7/24 535G 7/004 7/004 Z (72) Inventor Tomoki Takita Chuo-ku, Tokyo Nihonbashi 1-chome 13-1 F-term in TDK Corporation (reference) 5D029 LA02 LB07 LC04 LC11 LC12 LC21 5D090 AA01 CC18 DD01 JJ01

Claims (16)

[Claims] 1. An information recording layer is provided on a supporting substrate, a light transmitting layer is provided on the information recording layer, and a laser beam for recording or reproducing is incident on the information recording layer through the light transmitting layer. The optical information medium used in 1., wherein the light transmitting layer is made of resin, and the dynamic elastic modulus of the light transmitting layer at 25 ° C. is 1.5 to 3.0 GPa. 2. The optical information medium according to claim 1, wherein the dynamic elastic modulus of the light transmitting layer at 80 ° C. is 0.05 to 1.0 GPa. 3. The optical information medium according to claim 1, wherein the tensile modulus of elasticity of the light transmitting layer at 25 ° C. is 0.6 to 1.5 GPa. 4. The glass transition point of the light transmitting layer is 70 to 140.
The optical information medium according to any one of claims 1 to 3, which has a temperature of ° C. 5. The optical information medium according to claim 1, wherein the transmittance of the light transmission layer at the wavelength of the laser beam for recording or reproduction is 80% or more. 6. The optical information medium according to claim 1, wherein the light transmitting layer contains a cured product of a radiation curable composition. 7. The light according to claim 6, wherein the light transmitting layer contains the reaction initiator contained in the radiation curable composition, and the absorption coefficient of the reaction initiator at a wavelength of 405 nm is 500 or less. Information medium. 8. The optical information medium according to claim 1, wherein the thickness of the light transmitting layer is 30 to 200 μm. 9. When the wavelength of the laser beam for recording or reproduction is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA ≦ 6.
The optical information medium according to any one of claims 1 to 8, wherein recording or reproduction is performed under the condition that 80 nm is satisfied. 10. An information recording layer is provided on a supporting substrate, a light transmitting layer is provided on the information recording layer, and a laser beam for recording or reproducing is incident on the information recording layer through the light transmitting layer. And a wavelength of the laser beam is λ and a numerical aperture of an objective lens of an optical system for irradiating the laser beam is NA, recording / reproducing is performed under the condition of λ / NA ≦ 680 nm. An information medium, wherein the supporting substrate is a disk having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is T-Sk.
Ew, high temperature to store for 50 hours in an environment of 80 ° C and 80% RH
An optical information medium having | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg both before and after the high humidity storage test. 11. An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is applied to the information recording layer through the light transmitting layer. When the wavelength of the laser beam used for incidence is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA
An optical information medium for recording or reproducing under the condition that ≦ 680 nm is established, wherein the supporting substrate is a disk shape having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is To T-Sk
ew, optical information that is | R-Skew | ≦ 0.4deg and | T-Skew | ≦ 0.15deg both before and after the high temperature dry storage test of storing in a dry environment at 80 ° C for 50 hours Medium. 12. An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is applied to the information recording layer through the light transmitting layer. When the wavelength of the laser beam used for incidence is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA
An optical information medium for recording or reproducing under the condition that ≦ 680 nm is established, wherein the supporting substrate is a disk shape having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is To T-Sk
ew, an optical information medium having | R-Skew | ≦ 0.4deg and | T-Skew | ≦ 0.15deg both before and after a low temperature storage test in which it is stored for 50 hours in an environment of −25 ° C. . 13. An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is applied to the information recording layer through the light transmitting layer. When the wavelength of the laser beam used for incidence is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA
An optical information medium for recording or reproducing under the condition that ≦ 680 nm is established, wherein the supporting substrate is a disk shape having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is To T-Sk
When ew, in a constant humidity environment of 50% RH, a temperature cycle of storing at room temperature at 20 ° C. for 12 hours and at room temperature at 60 ° C. for 12 hours is repeated 6 times, Before and after the temperature cycle test in which the temperature rising rate at the time of shifting to the high temperature storage and the temperature lowering rate at the time of shifting from the high temperature storage to the room temperature storage are 10 ° C./hour, | R-Skew | ≦ 0 An optical information medium having a value of 4 deg and | T-Skew | ≦ 0.15 deg. 14. An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is applied to the information recording layer through the light transmitting layer. When the wavelength of the laser beam used for incidence is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA
An optical information medium for recording or reproducing under the condition that ≦ 680 nm is established, wherein the supporting substrate is a disk shape having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is To T-Sk
When ew, in a constant temperature environment of 60 ° C., a humidity cycle of performing a normal humidity storage of 20% RH for 12 hours and a high humidity storage of 80% RH for 12 hours is repeated 6 cycles, and
Before or after a humidity cycle test in which the humidity increase rate at the time of transition from the normal humidity storage to the high humidity storage and the humidity decrease rate at the transition from the high humidity storage to the normal humidity storage are 10% / hour. Also, an optical information medium having | R-Skew | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg. 15. An information recording layer is provided on a disc-shaped supporting substrate, and a light transmitting layer is provided on the information recording layer. A laser beam for recording or reproducing is applied to the information recording layer through the light transmitting layer. When the wavelength of the laser beam used for incidence is λ and the numerical aperture of the objective lens of the optical system for irradiating the laser beam is NA, λ / NA
An optical information medium for recording or reproducing under the condition that ≦ 680 nm is established, wherein the supporting substrate is a disk shape having a diameter of 60 to 135 mm, a radial warp angle is R-Skew, and a circumferential warp angle is To T-Sk
ew, before and after a thermal shock test in which a temperature cycle in which a temperature cycle of storing for 1 hour in a dry environment of 70 ° C is repeated immediately after storage for 1 hour in an environment of -20 ° C | R-Skew An optical information medium with | ≦ 0.4 deg and | T-Skew | ≦ 0.15 deg. 16. The optical information medium according to claim 1, which is the optical information medium according to any one of claims 10 to 15.