JP3187408B2 - Information recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a disc-shaped information recording medium (optical disc) on which information can be recorded by a laser.

[Technical background of the invention] DRAW (Direct Read After Writ
The e) type information recording medium has, as a basic structure, a disc-shaped transparent substrate made of plastic, glass, etc., and a metal or semi-metal such as Bi, Sn, In, Te, or a pigment provided thereon. A recording layer. Writing information on an optical disc is performed, for example, by irradiating the optical disc with a laser beam. The irradiated portion of the recording layer absorbs the light and locally rises in temperature, resulting in a physical change or phase change such as pit formation. Information is recorded by causing a chemical change, such as a change, to change its optical properties. Reading of information from the optical disk is also performed by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected light or transmitted light corresponding to a change in the optical characteristics of the recording layer. Irradiation of a laser beam for writing and reading information on the optical disk is usually performed at a predetermined position on the disk surface. For this reason, the laser beam is guided and accurately follows the irradiation target position (generally called tracking).
For this purpose, for example, an inverted trapezoidal type pre-groove (tracking guide) is provided on the disk surface. Furthermore, preformat information such as address information necessary for data recording is generally formed as prepits on the inner side of the disk.

As described above, the DRAW type information recording medium has a basic configuration in which a recording layer and the like are provided on the substrate on which the pregroove and, if desired, the prepit are formed.

As the recording material for forming the recording layer of such an information recording medium, metals and dyes are known as described above. An information recording medium using a dye has a great advantage in manufacturing that a recording layer can be easily formed by a coating method. However, those which are generally considered to be highly sensitive among the recording materials of optical disks have a reflectivity of 30 to 40% for both metals and dyes. Therefore, the recording layer made of a dye also has a drawback that the reflectance is generally low.

An information recording medium in which a metal reflective layer is provided on a dye recording layer in order to improve the reflectance is disclosed in JP-A-2-87340. Here, the reflective layer is used to obtain high reflectance.
It is provided with a relatively thick layer thickness of about 50 nm. Such an optical disc has a high reflectance with respect to light from the substrate side.
The tangent gradient at the oscillation wavelength of the reproduction laser is 0.6
(% / Nm). For this reason, there is a tendency that the magnitude of the reflectance is extremely changed at a wavelength slightly shifted from the oscillation wavelength of the reproduction laser, that is, at a wavelength slightly lower or higher than the oscillation wavelength. For example, an optical disk that exhibits a 70% reflectance at a reproduction laser oscillation wavelength of 790 nm is 66 nm at 785 nm.
%. In general, the oscillation wavelength of a semiconductor laser used in an optical disk drive varies slightly depending on the product, and the wavelength also changes depending on the use environment such as temperature. For this reason, when recording or reproduction is performed using the optical disk having the high reflectance, a tracking error,
There is a problem that a malfunction such as a read error easily occurs. Therefore, an optical disk having a small change in reflectance in a wavelength region near the oscillation wavelength of a reproduction laser is desired.

[Object of the Invention] An object of the present invention is to provide a novel information recording medium which has a recording layer made of a dye and has a small variation in reflectance in a wavelength region near an oscillation wavelength of a reproducing laser. Aim.

Another object of the present invention is to provide a disc-shaped information recording medium (optical disc) having a high reflectance in a wide wavelength range.

[Summary of the Invention] In the present invention, a recording layer composed of a cyanine dye or a metal complex dye capable of recording and reproducing information by a laser beam, a reflective layer composed of a metal, and a protective layer are provided in this order on a disk-shaped substrate. In the information recording medium, the reflective layer is a thin layer having a thickness of 0.3 to 30 nm so that the laser light transmittance of a predetermined reproducing laser to be used is 10% or more, and the protective layer has a thickness of 50 to 5000 nm. And the reflectance characteristic of the information recording medium is represented by a reflectance curve in which the vertical axis represents the reflectance (%) and the horizontal axis represents the wavelength (nm), at the oscillation wavelength of the reproducing laser used. An information recording medium (optical disc) characterized in that a tangent gradient (% / nm) of the information recording medium is in the range of +0.6 to -0.6.
It is in.

Preferred embodiments of the information recording medium of the present invention are as follows.

1) The information recording medium, wherein the thickness of the protective layer is in the range of 50 to 10,000 nm.

2) The information recording medium, wherein the gradient (% / nm) of the tangent is a curve in the range of +0.5 to -0.5.

3) The information recording medium has a reflectance in the range of 80 to 120% of the reflectance at the oscillation wavelength in a wavelength range of ± 20 nm of the oscillation wavelength of the recording or reproducing laser. Information recording medium.

4) The information recording medium as described above, wherein an enhance layer having a layer thickness in the range of 30 to 300 nm is provided between the recording layer and the reflective layer.

5) The metal of the reflective layer is Ti, Zr, Ta, Cr, Mo, W, N
i, Rh, Pd, Pt, Cu, Ag, Au, Zn, Al, In, Si, Ge, T
The information recording medium as described above, which is at least one selected from the group consisting of e, Sn, Bi, Sb, Tl, Pt, and C.

6) The metal of the reflective layer is Ni, Cu, Au, Zn, Al, In, Pt.
And C is at least one selected from the group consisting of:

7) The information recording medium, wherein the reflective layer has a transmittance of 15% or more.

8) The information recording medium, wherein the thickness of the reflective layer is in the range of 1.0 to 20 nm.

9) The information recording medium, wherein the protective layer is made of a cured product of an ultraviolet curable resin.

10) The information recording medium as described above, wherein the thickness of the protective layer is in the range of 500 to 5000 nm.

11) The information recording medium, wherein the dye of the recording layer is a cyanine dye.

The transmittance of the reflective layer was measured by forming a reflective layer on a glass plate and then irradiating the glass plate side with light having a reproduction wavelength.

[Effect of the Invention] As described above, by forming the information recording medium of the present invention into a very thin layer so that the transmittance of the reflective layer is 10% or more, the laser light transmitted through the reflective layer is protected. The light is reflected at the interface between the layer and the air and returns to the acquisition side. The thickness of the protective layer is set so that the reflected light at the interface between the protective layer and the air interferes with the laser light reflected at the interface between the reflective layer and the recording layer. Even if the wavelength is in the vicinity, the reflectance at the oscillation wavelength does not greatly change. This makes it possible to obtain an information recording medium having a small change in reflectance in a wavelength region near the oscillation wavelength of the reproduction laser.

Therefore, even if the oscillation wavelength of the semiconductor laser used in the optical disk drive is slightly shifted or the oscillation wavelength changes due to the use environment such as the temperature, the focusing at the time of reproduction can be performed by using the information recording medium of the present invention. Malfunctions such as errors and tracking errors hardly occur.

[Detailed Description of the Invention] The present inventors provide an optical disk having a basic structure of a recording layer, a reflective layer, and a protective layer made of a dye which can be formed by coating, and have a wavelength near an oscillation wavelength of a reproduction laser. The inventors of the present invention have conducted intensive studies to obtain a recording medium having a small variation in reflectance in a region, and have reached the present invention.

An example of the information recording medium of the present invention will be described with reference to the attached FIG.

FIG. 1 is a cross-sectional view of an optical disk having a basic configuration in which a recording layer 12 made of a dye, a reflective layer 13 made of a metal, and a protective layer 14 are provided on a substrate 11 in this order.

The above-mentioned optical disc has a dye recording layer 12 formed by applying a coating liquid for forming a dye layer on a transparent substrate 11 made of plastic or the like by a spin coating method or the like, and a reflection layer is formed thereon to improve the reflectance. The layer 13 is formed by sputtering metal or the like, and a protective layer 14 is further formed to protect them.

The reflective layer is conventionally provided with a relatively large layer thickness in order to improve the reflectance, and almost no light transmitted through the reflective layer of the irradiated laser beam. In the present invention, the reflection layer is formed so that the laser beam transmitted without reflection can be reflected at the interface between the protective layer and the air while reflecting the incident laser light by the reflection layer and securing a certain degree of reflectance, as in the related art. Is relatively thin, and its transmittance is 10% or more. The reflected light at the interface between the protective layer and the air mainly interferes with the laser light reflected at the interface between the reflective layer and the recording layer. The thickness of the protective layer is set as described later so as not to largely change from the reflectivity of the protective layer.

As described above, by providing the protective layer having the layer thickness set as described above on the thin reflective layer, the reflectivity characteristics of the information recording medium are represented by the vertical axis with the reflectance (%) and the horizontal axis with the horizontal axis. When represented as a reflectance curve on coordinates where is the wavelength (nm),
The tangent gradient (% / nm) of the information recording medium at the oscillation wavelength of the reproducing laser to be used is in the range of +0.6 to -0.6 (preferably in the range of +0.5 to -0.5). be able to. Further, it is preferable that the information recording medium has a reflectance in the range of 80 to 120% of the reflectance at the oscillation wavelength in a wavelength range of ± 20 nm of the oscillation wavelength of the reproduction laser, so that the reproduction can be performed in a wider range of conditions. This is preferable because it becomes possible.

The information recording medium used in the optical information recording method of the present invention can be manufactured using, for example, the materials described below.

The substrate used in the present invention can be arbitrarily selected from various materials used as a substrate of a conventional information recording medium. Examples of substrate materials include acrylic resins such as glass and polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymer; epoxy resins; polycarbonate resins; amorphous polyolefins and polyesters. Preferably, polycarbonate, amorphous polyolefin and polymethyl methacrylate can be used in view of the optical properties, flatness, workability, handleability, stability over time and production cost of the substrate.

Further, on the substrate, a pre-groove or a pre-groove and a pre-pit are provided for the purpose of forming irregularities representing information such as tracking grooves or address signals. The prepit is generally formed on the inner peripheral side without the pregroove. When the substrate material is plastic, it is preferable that pregrooves and prepits are provided directly on the substrate by injection molding or extrusion molding.

The pre-groove and the pre-pit may be provided by forming a pre-groove layer or the like. As the material, a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester and tetraester and a photopolymerization initiator can be used. The pre-groove layer is formed by first applying a mixed solution composed of the above-mentioned acrylate and a polymerization initiator on a precisely formed master (stamper), and then placing a substrate on the coating solution layer. The liquid layer is cured by irradiating ultraviolet rays through the substrate or the matrix to fix the substrate and the liquid phase. Next, the substrate provided with the pre-groove layer is obtained by peeling the substrate from the matrix. The thickness of the pre-groove layer is generally 0.05-100 μm
And preferably in the range of 0.1 to 50 μm.

The shape of the pre-groove has a half width generally of 0.2 to 1.0.
in the range of μm, preferably in the range of 0.3 to 0.8 μm, particularly preferably in the range of 0.4 to 0.7 μm, and the depth is generally in the range of 400 to 4000 °, preferably in the range of 600 to 3000 °,
It is particularly preferably in the range of 600 to 2000 °.

 A recording layer is provided on the substrate.

As the dye used in the recording layer, a cyanine dye such as an indolenine dye or an all-generic complex salt dye is used.

The following are specific examples of the dye.

i) Cyanine dye: [1] (CH ₃ ) ₂ N- (CH = CH) ₅ -CH = ⁺ N (CH ₃ ) ₂ ClO ₄
− [4] Φ ⁺ −L = Ψ (X ^m− ) _{1 / m} (where Φ and Ψ are each an indolenine ring residue, a thiazole ring residue, or an oxazole ring residue which may be condensed with an aromatic ring. , A selenazole ring residue, an imidazole ring residue, a pyridine ring residue, a thiazolopyrimidine ring residue or an imidazoquinoxaline ring residue, and L forms monocarbocyanine, dicarbocyanine, tricarbocyanine or tetracarbocyanine. X ^m- is a m-valent anion, m is 1 or 2, and X ^m- is further substituted on Φ, L or Ψ to form an inner salt. And Φ and L or L and Ψ may be further linked to form a ring) Examples of specific compounds represented by the above general formula include the following a) to k) Can be

ii) Metal complex salt dyes: (Where R ^{1 to} R ⁴ are an alkyl group or an aryl group, respectively, and M is a divalent transition metal atom) (Where R ¹ and R ² are an alkyl group or a halogen atom, respectively, and M is a divalent transition metal atom) (However, R ¹ and R ² are a substituted or unsubstituted alkyl group or aryl group, respectively, and R ³ is an alkyl group, a halogen atom or an R ⁴ —N—R ⁵ group (where R ⁴ and R ⁵ are A substituted or unsubstituted alkyl group or aryl group, respectively)
M is a transition metal atom, and n is an integer of 0 to 3) (Where [Cat] is a cation necessary to neutralize the complex salt, M is Ni, Cu, Co, Pd or Pt, and n is 1 or 2) (Where [Cat] is a cation necessary to neutralize the complex salt, M is Ni, Cu, Co, Pd or Pt, and n is 1 or 2) (Where X is a hydrogen atom, a chlorine atom, a bromine atom or a methyl group, n is an integer of 1 to 4, and A is a quaternary ammonium group) (Where X ¹ and X ² are each a nitro group and / or a halogen atom, n ₁ and n ₂ are each an integer of 1 to 3, R ¹ and R ² are an amino group, a monoalkylamino group, X ¹ and X ² , n ₁ and n _2, and R ¹ and R ² may be the same or different even if they are the same as dialkylamino, acetylamino, and benzoylamino (including substituted benzoylamino). M is Cr or
Is a Co atom, and Y is hydrogen, sodium, potassium, ammonium, aliphatic ammonium (including substituted aliphatic ammonium) or alicyclic ammonium.) The dye layer is formed by combining the dye and, if desired, a binder. It can be carried out by dissolving in a solvent to prepare a coating solution, coating the coating solution on the substrate surface to form a coating film, and then drying.

Ethyl acetate, as a solvent for the dye coating solution preparation,
Esters such as butyl acetate and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane and chloroform; ethers such as tetrahydrofuran, ethyl ether and dioxane; ethanol; n- Examples thereof include alcohols such as propanol, isopropanol and n-butanol, amides such as dimethylformamide, and fluorine-based solvents such as 2,2,3,3-tetrafluoropropanol. These non-hydrocarbon organic solvents account for 50% by volume.
As long as it is within, it may contain a hydrocarbon-based solvent such as an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or an aromatic hydrocarbon solvent.

Antioxidants, UV absorbers, plasticizers,
Various additives such as a lubricant may be added according to the purpose.

When a binder is used, examples of the binder include cellulose derivatives such as gelatin, nitrocellulose, and cellulose acetate; natural organic polymer substances such as dextran, rosin, and rubber; and carbonized materials such as polyethylene, polypropylene, polystyrene, and polyisobutylene. Hydrogen resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride
Thermal curing of vinyl resins such as polyvinyl acetate copolymers, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyolefins, epoxy resins, butyral resins, rubber derivatives, phenol / formaldehyde resins, etc. And synthetic organic polymer substances such as a precondensate of a hydrophilic resin.

Examples of the application method include a spray method, a spin coating method, a dip method, a roll coating method, a blade coating method, a doctor roll method, and a screen printing method.

The ratio of dye to binder is generally in the range of 0.01-99% (weight ratio), preferably in the range of 1.0-95% (weight ratio).

The thickness of the recording layer is generally in the range of 10 to 1000 nm, preferably in the range of 30 to 800 nm, and more preferably in the range of 50 to 500 nm.

An enhancement layer may be provided on the recording layer to improve the reflectance.

Materials for the enhancement layer include SiO ₂ , AlN, ZnS and
Inorganic materials such as Si ₃ N _4; polybutadiene, ethylene-based polymer, mention may be made of a polymer such as a fluorine-based resin.

The light-reflective substance that is the material of the reflection layer is a substance having a high reflectance to laser light, and examples thereof include Be, B,
C, Sc, Rb, Sr, As, Os, Tl, At, Fr, Ra, Mg, Se,
Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, F
e, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, C
d, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi, Sb, and the like. Of these, preferably Ti, Z
r, Ta, Cr, Mo, W, Ni, Rh, Pd, Pt, Cu, Ag, Au, Z
n, Al, In, Si, Ge, Te, Sn, Bi, Sb, Tl, Pt and C
And particularly preferably, Ni, Cu, Au, Zn, Al, In, and Pt.
And C. These substances may be used alone or in combination of two or more kinds or as an alloy.

In the present invention, not all the laser light incident on the reflective layer is reflected but transmitted by 10% or more (preferably 12% or more, more preferably 15% or more), and the interface between the protective layer and air is transmitted. So that it can be reflected. Therefore, the thickness of the reflective layer is generally in the range of 0.3 to 30 nm, preferably in the range of 1 to 30 nm, particularly preferably 5 to 20 nm
It is. In particular, when Au is used as the material of the reflective layer, the above range of the layer thickness is preferable.

The reflection layer can be formed on the substrate by, for example, vapor deposition, sputtering, or ion plating of the light-reflective substance.

 A protective layer is provided on the reflective layer.

Examples of the material used for the protective layer include inorganic substances such as SiO, SiO ₂ , Si ₃ N ₄ , MgF ₂ , and SnO ₂ . Further, examples of the organic substance include a thermoplastic resin, a thermosetting resin, a UV-curable resin, and the like, and a UV-curable resin is preferable. In order to obtain the effect of the present invention, it is preferable to provide an organic substance by coating.

The protective layer can be formed, for example, by laminating a film obtained by extrusion of a plastic on a protective layer made of a resin soluble in a saturated hydrocarbon solvent via an adhesive layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating. Also,
In the case of a thermoplastic resin or a thermosetting resin, they can also be formed by dissolving these in an appropriate solvent to prepare a coating solution, applying the coating solution, and drying. In the case of a UV curable resin, it can also be formed by preparing a coating solution as it is or by dissolving it in an appropriate solvent, applying the coating solution, and irradiating with UV light to cure. UV curable resins include oligomers of (meth) acrylates such as urethane (meth) acrylate, epoxy (meth) acrylate, and polyester (meth) acrylate, and monomers such as (meth) acrylic acid ester, and a photopolymerization initiator. And the like can be used. Various additives such as an antistatic agent, an antioxidant, and an LV absorber may be added to these coating solutions according to the purpose.

The thickness of the above protective layer is generally in the range of 50 to 5000 nm, preferably in the range of 100 to 5000 nm, more preferably 5 to 5000 nm.
It is in the range of 00-5000 nm. The protective layer may be colored.

In the present invention, the layer of the reflective layer is formed such that the laser light that is transmitted without being reflected can be reflected at the interface between the protective layer and air while ensuring that the incident laser light is reflected by the reflective layer and a certain degree of reflectance is maintained. The thickness is relatively thin, and the transmittance is a thin layer in the range of 10% or more. The reflected light at the interface between the protective layer and the air interferes with the laser light reflected at the interface between the reflective layer and the recording layer. The rate does not fluctuate significantly.

That is, the “shift” between the phase of the laser beam reflected at the interface between the reflective layer and the recording layer and the phase of the laser beam reflected at the interface between the protective layer and the air is adjusted so that the optical thickness satisfies the following equation By calculating and setting the thickness of the protective layer, it is considered that the reflectance near the oscillation wavelength of the laser light can be reduced.

nd = jλ (n: refractive index of protective layer, d: layer thickness of protective layer, j: integer, λ: wavelength of laser) However, there is “jumping” of phase at the interface between the dye layer and another layer. From this, it was found that it was difficult to define the above calculated value by the thickness of the protective layer.

For this reason, it is preferable that the layer thickness of the protective layer is set as follows while referring to the optical layer thickness.

1) If the reflectance curve of the information recording medium before the protective layer is provided with respect to the light wavelength is lower at the oscillation wavelength of the laser used than at the longer wavelength side, the information after the protective layer is formed. The reflectance of the recording medium is 10 to
The thickness of the protective layer is set so as to have a maximum on the short wavelength side of about 200 nm.

2) If the reflectance curve of the information recording medium before the protective layer is provided with respect to the light wavelength is higher at the longer wavelength side at the oscillation wavelength of the laser used, the information recording after the protective layer is formed. The reflectance of the medium is 10 to 200 n
The thickness of the protective layer is set so as to have a maximum on the long wavelength side of about m.

As described above, by providing the protective layer having the layer thickness set as described above on the thin reflective layer, the fluctuation of the reflectance in the wavelength region near the oscillation wavelength of the reproducing laser used is reduced. be able to.

In the present invention, the optical information recording medium may be a single plate having the above-described configuration, or two substrates having the above-described configuration are arranged such that the reflection layer faces inside, and an adhesive or the like is used. By bonding together, a recording medium of a lamination type can also be manufactured. Further, the recording layer of the present invention can be used in place of a reflective layer such as aluminum of a read-only optical disk such as a CD.

Recording on the optical information recording medium is performed, for example, as follows.

First, the optical information recording medium is moved at a constant linear velocity or constant angular velocity (CD
In the case of a format signal, the recording light such as a semiconductor laser light is irradiated from the substrate side to the groove of the pre-groove while rotating at 1.2 to 1.4 m / sec.
A signal such as a CD format EFM signal is recorded by forming pits in the recording layer of the groove. Generally, a semiconductor laser beam having an oscillation wavelength in the range of 750 to 850 nm is used as the recording light. Generally 1 to 15mW
It is recorded with the laser power.

The formation of the pits in the recording layer includes forming a cavity in the recording layer, forming a buildup on the surface of the recording layer on the side of the substrate, forming both the cavity and the buildup, or a phase change such as association / non-association or orientation / non-orientation. It is performed by

At the time of recording, tracking control is performed by the push-pull method or the like using the tracking pre-groove. Recording of information is performed on the pre-groove grooves or lands between the grooves.

Reproduction of information, for example, by irradiating the semiconductor laser light from the substrate side while rotating the recording medium at the same constant linear velocity or constant angular velocity as described above, and detecting the reflected light,
Information can be reproduced while performing tracking control by a three-beam method or the like.

Hereinafter, Examples and Comparative Examples of the present invention will be described. However, these examples do not limit the present invention.

Example 1 The following dyes: 4.8 g was dissolved in 100 ml of 2,2,3,3-tetrafluoropropanol while applying ultrasonic waves for 1 hour to prepare a dye coating solution.

Disc-shaped polycarbonate substrate with a pre-groove (outer diameter: 120 mm, inner diameter: 15 mm, thickness: 1.2 mm, track pitch: 1.6 μm, groove width: 0.45 μm, groove depth: 900 mm, groove area: diameter The above dye coating solution is applied by spin coating at a speed of 750 rpm for 5 seconds on the substrate surface on the side where the pregroove (44 mm to 117 mm range) is provided, and the rotation speed is increased by 50 rpm every second for 16 seconds. Thereafter, the final rotation speed was kept at 1000 rpm for 30 seconds and dried to form a dye recording layer having a layer thickness of 400 nm.

Au on the dye recording layer, using a DC sputtering device,
Sputtering was performed for 5 seconds under the conditions of an Ar pressure of 2 Pa, a power of 480 W, and a deposition rate of 2 nm (layer thickness) / second to form a reflective layer having a layer thickness of 10 nm.

Further, on the reflective layer, the above-mentioned ultraviolet curable resin (trade name: 307)
0, manufactured by Three Bond Co., Ltd.)
The coating was performed at a speed of 500 rpm. After drying, the coating layer was irradiated with ultraviolet rays ( ²⁰⁰ w / cm ² mercury lamp for 10 seconds) to form a protective layer having a thickness of 2.5 μm.

Thus, an information recording medium (see FIG. 1) in which the dye recording layer, the reflective layer, and the protective layer were provided on the substrate was manufactured.

A reflective layer was formed on a glass plate in the same manner as above, and the transmittance was measured using a spectrophotometer (Hitachi, Ltd.). As a result, it was 40% at a wavelength of 790 nm.

Example 2 An information recording medium was manufactured in the same manner as in Example 1, except that the thickness of the reflective layer was changed from 10 nm to 20 nm as described below.

Au on the dye recording layer, using a DC sputtering device,
Ar pressure is 2 Pa, electric power is 480 W, and deposition rate is 2 nm (layer thickness) / second.
A reflective layer of nm was formed.

A reflective layer was formed on a glass plate in the same manner as described above, and the transmittance was measured using a spectrophotometer (Hitachi, Ltd.). The result was 17% at a wavelength of 790 nm.

Comparative Example 1 An information recording medium was manufactured in the same manner as in Example 1, except that the thickness of the reflective layer was changed from 10 nm to 50 nm as described below.

Au on the dye recording layer, using a DC sputtering device,
Sputtering under conditions of Ar pressure of 2 Pa, power of 480 W, deposition rate of 2 nm (layer thickness) / second for 25 seconds, and a layer thickness of 50
A reflective layer of nm was formed.

A reflective layer was formed on a glass plate in the same manner as described above, and the transmittance was measured using a spectrophotometer (Hitachi, Ltd.). The result was 1% at a wavelength of 790 nm.

Comparative Example 2 An information recording medium was manufactured in the same manner as in Example 1, except that the thickness of the reflective layer was changed from 10 nm to 200 nm as described below.

Au on the dye recording layer, using a DC sputtering device,
Ar pressure is 2Pa, electric power is 480W, and deposition rate is 2nm (layer thickness) / second.
A reflective layer having a thickness of 00 nm was formed.

A reflective layer was formed on a glass plate in the same manner as described above, and the transmittance was measured using a spectrophotometer (Hitachi, Ltd.). The result was 0% at a wavelength of 790 nm.

[Evaluation of Information Recording Medium] 1) Reflectivity The obtained information recording medium was irradiated with light having a wavelength in the range of 770 to 850 nm from the substrate side using a spectrophotometer (Hitachi, Ltd.) to determine the unrecorded portion. The reflectance was measured.

2) Using a C / N drive device (DDU-1000, manufactured by Pulstec Co., Ltd.), modulation was performed at a laser power (recording power) of 7 mW and a linear velocity of 1.3 m / sec when recording with a laser with an oscillation wavelength of 790 nm. A signal with a frequency of 720 kHz (duty: 33%) was recorded. Then, when the recorded signal is reproduced with a reproduction power of 0.5 mW, C
/ N was measured using a spectrum analyzer (TR4135, manufactured by Advantest).

3) Dependence on wavelength of focus error (tracking focusing error) The information recording medium on which the signal is recorded in the above 2) is reproduced,
The ratio of the focus error amplitude when tracking focusing is deviated to the error amplitude of the compact disc (CD) {EFλ (λ is the laser wavelength)} is λnm, λ
The wavelength was measured at +5 nm and λ-5 nm, and the wavelength dependence (α (%)) of the focus error was determined from the following equation.

The measurement results are shown in FIG. 2 and FIG.

FIG. 1 shows 1) Example 1 measured in reflectance.
2 shows the reflectance curves of the reflectance at 770 to 850 nm of Comparative Example 1 and Comparative Example 1. In Examples 1 and 2, it can be seen that there is no extreme increase or decrease in reflectivity around 790 nm, which is the laser oscillation wavelength.

The gradient of the reflectance curve at a wavelength of 790 nm was determined by using the reflectance curve of FIG. 2 and drawing a tangent to the curve at a wavelength of 790 nm.

As is clear from Table 1, the optical disc of the present invention (Examples 1 and 2) has a laser oscillation wavelength of 79 nm.
The gradient of the reflectance is small at 0 nm, and the change of the reflectance is small at around 790 nm. Also, C / N has not decreased. In addition, since the reflectance gradient is set to be small at 790 nm, which is the laser oscillation wavelength, according to the present invention, the focus error wavelength dependency is, of course, small for a laser having a wavelength of 790 nm, although it is naturally small. , 780 nm and 800 nm. Therefore, focusing stability is good for each laser.

On the other hand, in the optical disks of Comparative Examples 1 and 2 provided with the conventional reflective layer, the gradient of the reflectance is large at 790 nm, and the reflectance changes largely around 790 nm. In addition, the focus error wavelength dependency is large for lasers with wavelengths of 780 nm and 790 nm (generally, when α exceeds 10, focusing decreases and a focusing error is likely to occur). Only small. Therefore, it cannot be said that focusing stability is good for various lasers.

[Brief description of the drawings]

FIG. 1 is a plan view showing a basic configuration of the information recording medium of the present invention. FIG. 2 is a graph (reflectance curve) showing the reflectance at 770 to 850 nm of the optical disks obtained in Examples 1 and 2 and Comparative Example 1. Substrate: 11 Recording layer: 12 Reflective layer: 13 Protective layer: 14

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-3452 (JP, A) JP-A-1-110986 (JP, A) JP-A-1-242288 (JP, A) JP-A-2- 54440 (JP, A) JP-A-2-164586 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26 G11B 7/24 516

Claims (3)

(57) [Claims] 1. An information recording medium comprising a disc-shaped substrate on which a recording layer made of a cyanine dye or a metal complex dye capable of recording and reproducing information by a laser beam, a reflective layer made of a metal, and a protective layer are provided in this order. Wherein the reflective layer is a thin layer having a thickness of 0.3 to 30 nm so that the laser light transmittance of a predetermined reproducing laser to be used is 10% or more, the protective layer has a thickness of 50 to 5000 nm, and When the reflectance characteristic of the information recording medium is represented by a reflectance curve in which the vertical axis represents the reflectance (%) and the horizontal axis represents the wavelength (nm), the information recording medium at the oscillation wavelength of the reproducing laser used. An information recording medium characterized in that the gradient (% / nm) of the tangent line is in the range of +0.6 to -0.6. 2. The information recording medium according to claim 1, wherein the dye in the recording layer is a cyanine dye. 3. In a wavelength range of ± 20 nm of an oscillation wavelength of a predetermined reproduction laser to be used, a reflectance of 80 to 80 at the oscillation wavelength is used.
3. The information recording medium according to claim 1, wherein a reflectance in a range of 120% is secured.