JP3073720B2 - Information recording and playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium having a recording layer containing a dye capable of writing (recording) and reading (reproducing) information using a laser beam having a high energy density and a metal reflective layer. The present invention relates to an information recording / reproducing method to be used.

[0002]

2. Description of the Related Art In recent years, information recording media using high energy density beams such as laser beams have been developed and put into practical use. This information recording medium is called an optical disk, and is used as a video disk, an audio disk, a large-capacity still image file, a large-capacity computer disk memory, and the like.

[0003] The optical disk has the following basic structure: a disk-shaped substrate made of glass, synthetic resin, or the like, and a metal or semimetal such as Bi, Sn, In, Te, or a cyanine-based or metal A recording layer made of a dye based on a 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.

[0004] 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 laser light, 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 laser light, and information is reproduced by detecting reflected light or transmitted light corresponding to a change in optical characteristics of the recording layer.

As described above, metals and dyes are known as recording materials for forming the recording layer of such information recording media. 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, a recording layer made of a dye has a drawback that it is generally difficult to obtain a low reflectance or a high C / N.

[0006]

An information recording medium in which a light-absorbing / reflecting dye film having a film thickness set so that the reflectance is maximized on a substrate has already been proposed (Japanese Patent Application Laid-Open (JP-A) No. Sho. No. 60-23997). However, the reflectance of this information recording medium cannot be sufficiently satisfied. Therefore, there is a need for a proposal of 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.

According to the present invention, there is provided an information recording medium using an information recording medium having a dye recording layer and a reflective layer on a substrate, having a high reflectivity, a small change in reflectivity, and a high degree of modulation of a recording signal and a high C / N value. An object of the present invention is to provide a recording and reproducing method.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an information recording medium in which a dye recording layer and a reflective layer made of metal are provided in this order on a disk-shaped substrate while rotating the information recording medium on the dye recording layer is provided. Information is recorded by irradiating a laser beam for use to form pits, and then irradiating the information recording medium on which the information is recorded with a laser beam for information reproduction to form a pit in the pit formation region in the dye recording layer. In the information recording / reproducing method of reproducing recorded information by detecting a difference in reflectivity to the information reproducing laser light in an area where the information recording medium is not provided, the film thickness of the recording layer is set as an information recording medium. A thickness of an optical path length within a range of ± 10% of an optical path length corresponding to one of the maximum values to the fourth maximum value of the reflectivity of the information reproducing laser beam with respect to the information recording medium; In the information recording and reproducing method characterized by using the information recording medium is adjusted to so that.

An information recording medium particularly preferably used in the information recording / reproducing method of the present invention is as follows. 1) An information recording medium in which the dye in the recording layer is at least one dye selected from cyanine dyes, azulenium dyes, and squarylium dyes. 2) An information recording medium in which the dye recording layer contains 0.001 to 0.1 mol parts of the metal complex dye based on 1 mol part of the dye. 3) An information recording medium in which the material of the plastic substrate is polycarbonate, polyolefin, or cell cast polymethyl methacrylate.

4) The metal of the reflection layer is made of Au, Ag, Cu,
An information recording medium comprising at least one metal or alloy selected from the group consisting of Pt, Cr, Ti, Al and stainless steel. 5) An information recording medium in which the thickness of the reflective layer is in the range of 100 to 3000 Å. 6) An information recording medium in which the recording layer is a layer formed by a coating method. 7) An information recording medium in which the reflectance of the information recording medium is 40% or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An information recording medium used in the information recording / reproducing method of the present invention has a basic structure in which a dye recording layer and a metal reflection layer are provided in this order on a disk-shaped substrate. The disk-shaped substrate can be arbitrarily selected from various resin materials used as a substrate of a conventional information recording medium. From the viewpoints of the optical characteristics of the substrate, flatness, workability, handleability, stability over time, and manufacturing cost, examples of the substrate material include acrylic resins such as cell cast polymethyl methacrylate and injection-molded polymethyl methacrylate, and polystyrene. Examples thereof include vinyl chloride resins such as vinyl chloride and vinyl chloride copolymer, epoxy resin, polycarbonate resin, amorphous polyolefin, and polyester. Preferred are polycarbonate, polyolefin and cell cast polymethyl methacrylate.

An undercoat layer is provided on the surface of the substrate on which the recording layer is provided, for the purpose of improving flatness, improving adhesive strength, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. Is also good. As a material of the undercoat layer, for example, polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer, polyvinyl alcohol,
N-methylol acrylamide, styrene / sulfonic acid copolymer, styrene / vinyl toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, Polymer substances such as ethylene / vinyl acetate copolymer, polyethylene, polypropylene, and polycarbonate; organic substances such as silane coupling agents; and inorganic oxides (SiO ₂ , Al ₂ O
₃ ) and inorganic substances such as inorganic fluorides (MgF ₂ ).

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 0.1.
005 to 20 μm, preferably 0.01 to
It is in the range of 10 μm.

Further, a pre-groove layer and / or a pre-pit layer may be provided on the substrate (or undercoat layer) for the purpose of forming irregularities representing information such as tracking grooves or address signals. Examples of the material for the pre-groove layer include acrylic acid monoesters, diesters,
A mixture of at least one monomer (or oligomer) of a triester and a tetraester and a photopolymerization initiator can be used.

In forming the pre-groove layer, for example, first, a mixed solution comprising the above-mentioned acrylate ester and the polymerization initiator is applied to a precisely formed master (stamper). After the substrate is placed, the liquid layer is cured by irradiating ultraviolet rays through the substrate or the matrix to fix the substrate to the liquid layer. 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 to 1
It is in the range of 00 μm, preferably in the range of 0.1 to 50 μm. When the substrate material is plastic, pre-grooves and / or pre-pits may be provided directly on the substrate 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 reading information with a laser beam is provided. The dye used in the present invention is not particularly limited. For example, cyanine dyes, phthalocyanine dyes, pyrylium and thiopyrylium dyes, azulenium dyes, squarylium dyes, metal complex salt dyes such as Ni and Cr, naphthoquinone and anthraquinone dyes, indophenol dyes, and indoaniline dyes Dyes, triphenylmethane dyes, triallylmethane dyes, aminium / diimmonium dyes, and nitroso compounds can be exemplified. Preferred are cyanine dyes, azurenium dyes, and squarylium dyes. 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 emits 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, the quencher preferably contains a metal complex salt dye or the like in an amount of 0.001 to 0.1 mol based on 1 mol of all dyes.

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

Solvents for preparing a dye coating solution include esters such as ethyl acetate, butyl acetate, and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; dichloromethane;
Halogenated hydrocarbons such as dichloroethane and chloroform; ethers such as tetrahydrofuran, ethyl ether and dioxane; alcohols such as ethanol, n-propanol, isopropanol and n-butanol; amides such as dimethylformamide; Fluorinated solvents such as tetrafluoropropanol can be exemplified. In addition, these non-hydrocarbon organic solvents,
As long as the content is within 50% by volume, it may contain a hydrocarbon solvent such as an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or an aromatic hydrocarbon solvent. Various additives such as an antioxidant, a UV absorber, a plasticizer, and a lubricant may be further added to the coating solution according to the purpose.

When a binder is used, examples of the binder include cellulose derivatives such as gelatin, nitrocellulose and cellulose acetate, dextran, rosin, and the like.
Natural organic high molecular substances such as rubber, and polyethylene,
Hydrocarbon resins such as polypropylene, polystyrene, and polyisobutylene; vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and vinyl chloride-vinyl acetate copolymer; acrylic resins such as polymethyl acrylate and polymethyl methacrylate; polyvinyl Synthetic organic polymer substances such as alcohols, chlorinated polyolefins, epoxy resins, butyral resins, rubber derivatives, and initial condensates of thermosetting resins such as phenol / formaldehyde resins.

Examples of the coating method include a spray method, a spin coating method, a dip method, a roll coating method, a blade coating method, a doctor call 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 in combination as a material for the recording layer, the ratio of the dye to the binder is generally from 0.01 to 99.
% (Weight ratio), preferably 1.0 to 95%
(Weight ratio).

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

As the material of the reflection layer, Mg, Se, Y,
Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W,
Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, I
r, Pt, Cu, Ag, Au, Zn, Cd, Al, G
a, In, Si, Ge, Te, Pb, Po, Sn, Bi
And the like (including semimetals). 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 may be used as an alloy.

The reflection layer is formed, for example, by depositing a light-reflective substance,
It can be formed on the recording layer by sputtering or ion plating. The thickness of the reflective layer is generally in the range of 100 to 3000 Å,
In particular, it is preferably in the range of 500 to 2000 angstroms.

In the information recording medium used in the information recording / reproducing method of the present invention, the thickness of the recording layer is ± 10% of the optical path length corresponding to the maximum value of the reflectance of the information recording medium with respect to the information reproducing laser beam. The thickness is such that the optical path length is within the range.

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 a 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 local maxima. That is, the optical path lengths P1, P2, P3,.
.. at each of the reflectance maximum values R _max 1 and R _max
2, R _max 3 _,. The maximum value of the reflectance is R _max
Gradually decreases toward 1 to R _max 3.

In the information recording medium used in the information recording / reproducing method of the present invention, the thickness of the recording layer is determined by adjusting the optical path length to P1, P2,
A value within a range of ± 10% of one of P3 and P4 (the optical path length corresponding to the reflectance maximum up to the fourth). 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 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 caused by the variation in the film thickness of the recording layer of the information recording medium. 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 of the recording layer and the film thickness are determined based on the substrate of the information recording medium, the recording layer, the reflective layer, and / or other layers. The thickness of the recording layer cannot be uniquely determined because it varies depending on the type of material to be formed, the conditions for forming the recording layer and / or the reflective layer, the wavelength of laser light used for writing and / or reading information, and the like. However, the optimum thickness of the recording layer can be determined in consideration of the above points.

When an optical path length P1 corresponding to R _max 1 where the maximum value of the reflectance is maximum is selected as the optical path length for determining the film thickness of the recording layer, the information recording with the maximum reflectance is performed. Medium can be obtained. In addition, when the optical path length P2 corresponding to the second largest R _max2 of the reflectance is selected as the optical path length, the reflectance is slightly lower than when the optical path length P1 is selected. Since the film thickness increases, the degree of modulation increases, and the change 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, a point at which an arbitrary reflectance is maximized so that an optimum information recording medium can be obtained according to the desired performance of the information recording medium (range from the maximum to the fourth).
Is selected, and a recording layer having a film thickness that provides an optical path length within a range of ± 10% of the optical path length is provided. That is, the recording layer having a film thickness having an optical path length within the 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. It is preferable from the viewpoint of the balance between the rate and the modulation degree. The reflectance of the information recording medium is preferably 40% or more.

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

Examples of the material used for forming the protective layer include inorganic substances such as SiO, SiO ₂ , SiN ₄ and MN.
gF _2, SnO _2, etc. can be mentioned. 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. The above-mentioned substances can exhibit remarkable curing when 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, it can also be formed by applying a coating solution as it is or after dissolving it in an appropriate solvent, applying the coating solution, and irradiating with UV light to cure. UV curable resins include (meth) such as urethane (meth) acrylate, epoxy (meth) acrylate, and polyester (meth) acrylate.
Oligomers of acrylates, monomers such as (meth) acrylic acid esters, and the like, and ordinary UV-curable resin components such as a photopolymerization initiator 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 0.1 to 100 μm.
m. The protective layer can be formed, for example, by laminating a film obtained by extrusion of a plastic on the dye recording layer via an adhesive layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating.

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

Example 1 Dye (A) having the following structural formula:

[0037]

Embedded image

A dye (B) having the following structural formula is added to 1 mol of the dye:

[0039]

Embedded image

The solution containing 0.01 mol was added to 2,2,2
It was dissolved in 3,3-tetrafluoropropanol to prepare a dye recording coating solution. Disc-shaped polycarbonate substrate provided with a separately prepared tracking guide (outer diameter: 13
0 mm, inner diameter: 15 mm, thickness: 1.2 mm, tracking pitch: 1.6 μm, groove depth: 800 angstrom), and applying the coating solution at a rotation speed of 500 rpm by a spin coating method. Number 20
The recording layer was formed by drying at 00 rpm for 1 minute. Then, Au is vapor-deposited on the recording layer to have a thickness of 130 μm.
A reflection layer of 0 Å was formed.

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

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

From FIG. 1, it can be seen that the maximum reflectance maximum value, R,
_The optical path length P1 (3400 angstroms) corresponding to _max 1 is obtained, and an information recording medium (sample 1) having a recording layer having a film thickness (1300 angstroms) corresponding to the optical path length P1 is placed on the dye (A) of the dye recording layer coating film. ) Of 2.7
It was made to 5% by weight and produced by the above method.

When the C / N and the reflectance (Rf) of the sample 1 were measured by the evaluation method described later, C / N = 55 dB,
The reflectance was 78%.

Comparative Example 1 A film was prepared in the same manner as in Example 1 (Sample 1) except that the concentration of the dye (A) in the dye recording layer coating solution was changed to 2.00% by weight. Thick (90
An information recording medium (Comparative Sample 1) having a recording layer with a thickness of 0 Å and an optical path length of 2354 Å was manufactured. When the C / N and the reflectance (Rf) of 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 bubbles (pits) were formed using a semiconductor laser at a frequency of 2.5 MHz (pulse width 200 ns). Then, information was written (recorded). Next, a spectrum analyzer (T
R4172: Takeda Riken Co., Ltd.) was used to measure the laser output at which the carrier-to-noise output level ratio (C / N ratio) was maximized and the C / N ratio at that time (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.

[0047]

According to the information recording / reproducing method of the present invention, an information recording medium having a recording layer containing a dye having a specified film thickness and a reflective layer made of metal thereon is used. Therefore, the reflectance is high in the recording information reproducing step, the modulation factor and the C / N value are large, and the variation of the reflectance due to the variation in the thickness of the recording layer at the time of manufacturing the information recording medium is remarkable. It has excellent effects.

[Brief description of the drawings]

FIG. 1 is a plot of reflectance and optical path length measured for various information recording media obtained in Example 1.

[Explanation of symbols]

R _max reflectance maximum value P Optical path length corresponding to reflectance maximum value

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/24 G11B 7/004

Claims (1)

(57) [Claims] A pit is formed by irradiating a laser beam for information recording onto a dye recording layer while rotating an information recording medium in which a dye recording layer and a reflective layer made of metal are provided in this order on a disk-shaped substrate. The information recording is performed by forming the information recording medium, and thereafter, the information recording medium on which the information is recorded is irradiated with a laser beam for information reproduction, and the pit formation region and the pit-free region in the dye recording layer are formed. In an information recording / reproducing method comprising reproducing recorded information by detecting a difference in reflectance with respect to the information reproducing laser light, the information recording medium has a recording layer whose film thickness is equal to that of the information reproducing laser light. The information is adjusted so as to have an optical path length within a range of ± 10% of the optical path length corresponding to any of the maximum values of the reflectance from the maximum to the fourth to the information recording medium. Information recording and reproducing method which comprises using a recording medium.