JP2899008B2 - Information recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an information recording medium having a recording layer containing a dye capable of writing and / or reading information by using a high energy density laser beam and a metal reflective layer. It is about.

[Technical Background of the Invention] In recent years, information recording media using a beam of high energy density such as laser light have been developed and put into practical use. This information recording medium is called an optical disk,
It is used as a disk, an audio disk, a large-capacity still image file, and a disk memory for a large-capacity computer.

The optical disc has a disk-shaped substrate made of glass, synthetic resin, and the like, and Bi, Sn,
A recording layer made of a metal or semimetal such as In or Te; or a dye such as cyanine, metal complex, or quinone.
In general, an intermediate layer made of a polymer substance is provided on the surface of the substrate on which the recording layer is provided, from the viewpoint of improving the flatness of the substrate, improving the adhesive force with the recording layer, or improving the sensitivity of the optical disc. Is often done.

Further, for the purpose of improving the durability of the information recording medium, a protective layer is provided on the recording layer, or as a disk structure, a recording layer is provided on at least one of the two disc-shaped substrates. There has been proposed an air sandwich structure in which the two substrates are joined via a ring-shaped inner spacer and a ring-shaped outer spacer so that the recording layer is located inside and a space is formed. In an optical disk provided with such a protective layer or an optical disk having an air sandwich structure, the recording layer does not come into direct contact with the outside air, and information is recorded and reproduced by laser light transmitted through the substrate. This has the advantage that it does not suffer physical or chemical damage, or dust adheres to its surface and does not hinder the recording and reproduction of information.

Writing and reading of information to and from the optical disk are usually performed by the following method.

Writing of information is performed by irradiating the optical disk with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally raises the temperature, causing a physical or chemical change (for example, generation of pits). Information is recorded by changing its optical properties. Reading of information is also performed by irradiating the optical disk with a laser beam, and information is reproduced by detecting reflected light or transmitted light corresponding to a change in the optical characteristics of the recording layer.

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 advantages in characteristics of the recording medium itself, such as higher sensitivity than a recording material such as a metal, and also has a manufacturing advantage that a recording layer can be easily formed by a coating method. Has great advantages. However, the recording layer made of a dye generally has a low reflectance,
Alternatively, there is a disadvantage that it is difficult to obtain a high C / N.

There has been proposed an information recording medium in which a light-absorbing and reflective dye film having a film thickness set so that the reflectance is maximized is provided on a substrate (Japanese Patent Application Laid-Open No. 60-239947). However, the reflectance of this information recording medium is not sufficiently satisfied.

Therefore, it is desired to propose an information recording medium which is a recording layer using a dye advantageous in productivity, has a high reflectance, a small variation in the reflectance, and a C / N having a high recording signal.

[Object of the Invention] The present invention has a dye recording layer and a reflective layer on a substrate,
An object of the present invention is to provide an information recording medium having a high reflectivity, a small change in the reflectivity, and a high modulation degree and C / N value of a recording signal.

[Summary of the Invention] The present invention includes a dye recording layer and a metal, on which information can be written by irradiating a laser beam to form a pit on a disc-shaped substrate provided with a pre-groove for tracking. An information recording medium in which a reflective layer is provided in this order, wherein the layer thickness of the recording layer corresponds to one of the maximum values of the reflectance of the information recording medium from the maximum to the fourth value. The information recording medium is adjusted so as to have a thickness corresponding to the optical path length within the range of ± 10%.

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

1) The information recording medium as described above, wherein the dye is at least one dye selected from a cyanine dye, an azulenium dye, and a squarylium dye.

2) The information recording medium, wherein the dye recording layer contains 0.001 to 0.1 mol part of a metal complex dye based on 1 mol part of the dye.

3) an optical path having a thickness of the dye recording layer within an optical path length ± 10% corresponding to one of the maximum to fourth of the maximum values of the reflectance of the information recording medium; The information recording medium as described above, which has a long thickness.

4) The information recording medium, wherein the material of the plastic substrate is polycarbonate, polyolefin, or cell cast polymethyl methacrylate.

5) The information recording medium, wherein the metal is at least one metal or alloy selected from the group consisting of Au, Ag, Cu, Pt, Cr, Ti, Al, and stainless steel.

6) The information recording medium as described above, wherein the thickness of the reflective layer is in the range of 100 to 3000 °.

7) The information recording medium as described above, wherein the recording layer is a layer formed by a coating method.

8) The information recording medium, wherein the reflectance of the information recording medium is 40% or more.

[Detailed Description of the Invention] The information recording medium of the present invention has a basic configuration in which a dye recording layer and a metal reflective layer are provided in this order on a disk-shaped substrate.

The disk-shaped substrate in the present invention can be arbitrarily selected from various resin materials used as substrates of conventional information recording media. In view of the optical characteristics, flatness, workability, handleability, stability over time, and manufacturing cost of the substrate, examples of the substrate material include acrylic resins such as cell cast polymethyl methacrylate and injection-molded polymethyl methacrylate; Examples thereof include vinyl chloride resins such as vinyl chloride and vinyl chloride copolymer; epoxy resins; polycarbonate resins, amorphous polyolefins and polyesters. Preferably, polycarbonate, polyolefin and cell cast polymethyl methacrylate can be mentioned.

An undercoat layer may be provided on the surface of the substrate on which the recording layer is provided, for the purpose of improving flatness, improving adhesion, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. Examples of the material of the undercoat layer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer, polyvinyl alcohol, N-methylolacrylamide, styrene / sulfonic acid copolymer, and styrene / vinyl. Toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, etc. Molecular substances; organic substances such as silane coupling agents; and inorganic oxides (SiO ₂ , Al ₂ O _3, etc.);
Inorganic substances such as inorganic fluoride (MgF ₂ ) can be exemplified.

The undercoat layer is prepared, for example, by dissolving or dispersing the above substance in an appropriate solvent to prepare a coating solution, and then applying this coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. Can be formed. The thickness of the undercoat layer is generally 0.005 to 20 μm
And preferably in the range of 0.01 to 10 μm.

Further, a pre-groove layer and / or a pre-pit layer may be provided on the substrate (or the undercoat layer) for the purpose of forming irregularities representing information such as tracking grooves or address signals. As a material for the pregroove layer and the like, 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 pregroove layer is generally in the range of 0.05 to 100 μm, preferably in the range of 0.1 to 50 μm. When the substrate material is plastic as in the present invention, the substrate may be directly provided with pregrooves and / or prepits by injection molding or extrusion molding.

On a substrate (or a pre-groove layer or the like), a recording layer containing a dye capable of writing and / or reading information with a laser beam is provided. The dye used in the present invention is not particularly limited, and any dye may be used. For example, cyanine dyes, phthalocyanine dyes,
Pyrylium / thiopyrylium dyes, azulhenium dyes, squarylium dyes, metal complex dyes such as Ni and Cr, naphthoquinone / anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallyl Examples include methane dyes, aminium / diimmonium dyes, and nitroso compounds. Preferably, a cyanine dye, an azulenium dye, and a squarylium dye can be exemplified.

Among these, a dye having a high absorptivity to light in the near infrared region of 700 to 900 nm is preferable because a semiconductor laser that oscillates near infrared light is practically used as a recording / reproducing laser.

These dyes may be used alone or as a mixture of two or more. When a cyanine dye is used, the metal complex salt dye or the aminium / diimmonium dye is preferably used together as a quencher. In this case, it is preferable that a metal complex salt dye or the like is contained as a quencher in an amount of 0.001 to 0.1 mol part based on 1 mol part of the whole dye.

The recording layer can be formed by dissolving the dye and, if desired, a binder in a solvent to prepare a coating solution, then applying the coating solution to the substrate surface to form a coating film, and then drying the coating solution. it can.

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-cycloethane and chloroform; ethers such as tetrahydrofuran, ethyl ether and dioxane; ethanol; 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. In addition, these non-hydrocarbon organic solvents, aliphatic hydrocarbon solvent, alicyclic hydrocarbon solvent, as long as it is within 50% by volume,
It may contain a hydrocarbon solvent such as 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. In order to form a favorable alignment state of the dye, it is preferable to use a spin coating method.

When a binder is used as a material for the recording layer, the ratio of the dye to the binder is generally in the range of 0.01 to 99% (weight ratio), preferably in the range of 1.0 to 95% (weight ratio).

In the information recording medium of the present invention, a reflective layer made of metal is further provided on the dye recording layer. By providing the reflective layer, the effect of improving the reflectance, the S / N at the time of reproducing information, and the effect of improving the sensitivity at the time of recording can also be obtained.

Materials for the reflective layer include Mg, Se, Y, Ti, Zr, Hf,
V, Nb, Ta, Cr, MoW, Mn, Re, Fe, Co, Ni, Ru, Rh, P
d, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, G
Metals and metalloids such as e, Te, Pb, Po, Sn, Bi and the like can be mentioned. Further, an alloy such as stainless steel may be used. In the present invention, it is preferable to provide a reflective layer having a high thermal conductivity at a temperature of 400 K and made of a metal of at least 10 w / m ゜ k or more. Thereby, heat generated when the dye recording layer is irradiated with the laser beam can be rapidly transmitted to the reflection layer. Among these, Au, Ag, Cu, Pt, Al, C
r, Ni and stainless steel are particularly preferred. These substances may be used alone or in combination of two or more kinds or as an alloy.

The reflection layer can be formed on the recording layer by, for example, vapor deposition, sputtering, or ion plating of the above-mentioned light reflective substance. The thickness of the reflective layer is generally in the range of 100 to 3000 °, preferably in the range of 500 to 2000 °.

The information recording medium of the present invention is characterized in that the thickness of the recording layer is such that the optical path length is within ± 10% of the optical path length corresponding to the maximum value of the reflectance of the information recording medium. Having.

FIG. 1 is a diagram showing an example of the relationship between the reflectance of an information recording medium and the optical path length of a recording layer. In FIG. 1, the reflectance indicates the reflectance of the information recording medium of Example 1 at the measurement wavelength of 780 nm, and the optical path length is the product of the light transmission distance of the recording layer and the absolute refractive index. As shown in FIG. 1, as the optical path length changes, the reflectance changes and shows a plurality of maximum values. That is, the optical path length P1, P2, P3, respectively reflectance maximum in _{··· R max 1, R max 2} , R max 3, showing a .... Reflectance maxima direction from R _max 1 to R _max 3 thus gradually decreases.

In the present invention, the thickness of the recording layer is determined by the
The value should be within ± 10% of any of 1, P2, P3, ... By setting the thickness of the recording layer as described above, the reflectance of the information recording medium can be increased and the degree of modulation can be increased. Further, since the optical path length is set near the maximum value of the reflectance, the change in the reflectance caused by the change in the optical path length of the recording layer can be reduced, and the reflection due to the variation in the thickness of the recording layer of the information recording medium can be reduced. Variation in rate can be reduced.

The optical path length of the recording layer corresponding to the maximum value of the reflectance, and the relationship between the optical path length and the film thickness of the recording layer, the substrate of the information recording medium, the recording layer, the type of material forming the reflective layer, other layers, The film thickness of the recording layer cannot be unambiguously determined because it depends on the formation conditions of the recording layer and / or the reflective layer, the wavelength of the laser beam used for writing and / or reading information, and the like. The optimum thickness of the recording layer can be determined in consideration of the above.

As the optical path length for determining the thickness of the recording layer, when the optical path length P1 corresponding to the maximum value of the reflectance maximum R _max 1 is selected, an information recording medium having the maximum reflectance is obtained. Can be. When the optical path length P2 corresponding to R _max 2 having the second largest reflectance maximum is selected as the optical path length, the reflectance is slightly lower than when the optical path length P1 is selected. Increases, so that the degree of modulation increases and the variation in reflectance decreases. When other optical path lengths are selected, there is a similar tendency as described above. Therefore, in the information recording medium of the present invention, an optical path length at a point where an arbitrary reflectance is maximized is selected so that an optimal information recording medium can be obtained according to a desired performance of the information recording medium, and the optical path length of the optical path length is selected. A recording layer having a film thickness with an optical path length within a range of ± 10% is provided. In the present invention, the recording layer has a film thickness having an optical path length within a range of ± 10% of the optical path length corresponding to any one of the maximum values of the reflectance from the maximum value to the fourth value. Is preferable in terms of balance of reflectance, modulation degree, and the like. The reflectance of the information recording medium is preferably 40% or more.

The information recording medium of the present invention may further include a protective layer on the reflective layer for the purpose of physically and chemically protecting the recording layer and the entire information recording medium. Further, this protective layer may be provided on the side of the substrate where the recording layer is not provided in order to enhance the scratch resistance and the moisture resistance.

Examples of the material used for the protective layer include inorganic substances such as SiO, SiO ₂ , SiN 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 the present invention, a remarkable effect can be obtained when the above substance is provided by coating. This is particularly effective when the organic substance is provided by coating.

That is, it can also be formed by dissolving a thermoplastic resin, a thermosetting resin, or the like in an appropriate solvent to prepare a coating solution, applying the coating solution, and drying.
In the case of a UV curable resin, a coating solution is prepared as it is or dissolved in an appropriate solvent, and then this coating solution is applied.
It can also be formed by curing by irradiating UV light. 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) acrylate, and a photopolymerization initiator. And the like can be used. Various additives such as an antistatic agent, an antioxidant and a UV absorber may be added to these coating solutions according to the purpose. In the present invention, it is preferable to use a UV curable resin.

 The thickness of the protective layer is generally in the range from 0.1 to 100 μm.

In addition to the above, the protective layer can be formed, for example, by laminating a film obtained by extrusion of a plastic onto the dye recording layer via an adhesive layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating.

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

Example 1 Dye (A) having the following structural formula: And a dye (B) having the following structural formula per mole of the dye: The solution added at a rate of 0.01 mol was dissolved in 2,2,3,3-tetrafluoropropanol to prepare a dye recording layer coating solution.

On a disc-shaped polycarbonate substrate (outer diameter: 130 mm, inner diameter: 15 mm, thickness: 1.2 mm, track pitch: 1.6 μm, groove depth: 800 mm) provided with a tracking guide,
The coating solution was applied at a rotation speed of 500 rpm by a spin coating method, and then dried at a rotation speed of 2000 rpm for 1 minute to form a recording layer.

Au was deposited on the recording layer formed as described above to form a reflective layer having a thickness of 1300 °.

On the reflective layer, a UV-curable resin (trade name: UV3070, manufactured by Three Bond Co.) was applied as a protective layer at a rotation speed of 1500 rpm by a spin coating method, and then cured by irradiating ultraviolet rays with a high-pressure mercury lamp, A protective layer having a thickness of 1 μm was formed.

In the above method, the dye (A) in the dye recording layer coating solution
By changing the concentration of, an information recording medium comprising a substrate having recording layers of various thicknesses, a dye recording layer, a reflective layer and a protective layer was manufactured. About many obtained information recording media,
The reflectance (measuring wavelength: 780 nm) and the optical path length were measured and plotted to obtain the graph shown in FIG.

From FIG. 1, an optical path length P1 (3400 °) corresponding to the maximum value of the maximum reflectance R _max1 is obtained, and an information recording medium (sample 1) having a recording layer having a film thickness (1300 °) corresponding to the optical path length P1 is obtained. )
Was prepared by adjusting the concentration of the dye (A) in the coating solution for the dye recording layer in the above method to 2.75% by weight.

The C / N and reflectance (R
When f) was measured, the C / N was 55 dB and the reflectivity was 78%.

Comparative Example 1 Recording of a film thickness (900 °) was performed in the same manner as in Example 1 except that the concentration of the dye (A) in the coating solution for the dye recording layer was changed to 2.00% by weight. An information recording medium (Comparative Sample 1) having a layer (having an optical path length of 2354 Å) was manufactured.

When the C / N and the reflectance (Rf) of the comparative sample 1 were measured, the C / N was 52 dB and the reflectance was 71%.

[Evaluation of information recording medium] (1) Sensitivity test The information recording medium was rotated at a linear velocity of 5 m / sec and the frequency was 2.5
Information was written by forming bubbles (pits) using a semiconductor laser at MHz (pulse width: 200 nsec). Next, using a spectrum analyzer (TR4172: Takeda Riken Co., Ltd.), the laser output at which the carrier-to-noise output level ratio (C / N ratio) is maximized and the C / N ratio at that time
The ratio was measured (RBW = 30 KHz).

(2) Optical property test The specular reflectance was measured using a transmittance / reflectance measuring device manufactured by Mizojiri Optical Co., Ltd. The light source was a halogen lamp, the wavelength used was 780 nm, and the spot diameter was 1 mm.

[Effect of the Invention] The information recording medium of the present invention has a recording layer containing a dye having the specified thickness as described above, and a reflective layer made of metal thereon. Therefore, a remarkably excellent effect is obtained in that the reflectance is high, the modulation factor and the C / N value are large, and the variation in the reflectance due to the variation in the thickness of the recording layer during manufacturing is small.

[Brief description of the drawings]

FIG. 1 is a diagram in which the reflectance and the optical path length measured for various information recording media obtained in Example 1 are plotted. R _max : maximum reflectance, P: optical path length corresponding to maximum reflectance.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/24 B41M 5/26

Claims (3)

(57) [Claims] 1. A dye recording layer on which a laser beam is irradiated to form pits on a disc-shaped substrate provided with a tracking pre-groove, and a reflective layer made of a metal, comprising: An information recording medium provided in this order, wherein the layer thickness of the recording layer is ± 10% of the optical path length corresponding to any of the maximum values of the reflectance of the information recording medium from the maximum to the fourth. An information recording medium characterized in that the thickness is adjusted so as to have a thickness corresponding to the optical path length within the range of (1). 2. The information recording medium according to claim 1, wherein said recording layer is a layer formed by a coating method. 3. The information recording medium according to claim 1, wherein a protective layer made of a UV curable resin is provided on the reflective layer.