JPH11167745A - Optical information recording medium - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] An optical information recording medium and a recording / reproducing method which exhibit high reflectivity even at a short wavelength and obtain high recording / reproducing contrast. SOLUTION: The optical information recording medium is a substrate / (high refractive index layer /
(Low refractive index layer) m / recording layer / (low refractive index layer / high refractive index layer)
An optical information recording medium having a layer structure of p (where m and p are the number of laminations), recording information by changing the complex refractive index of a recording layer material by irradiating a laser beam, and satisfying the following requirements. (1) m is 1 or more, (2) high refractive index layer, the film thickness of the low refractive index layer is, in both reproduction _{wavelength, n i d i = λ 0} /4 (n i
The high refractive index layer or low refractive index layer material having a refractive index of, d _i is the thickness, lambda ₀ is reproduction wavelength), (3) the thickness of the recording layer is reproduced _{wavelength, n S d S = (λ} 0 / 2) t (n _S is the refractive index of the recording layer material, d _S is the film thickness of the recording layer material, λ ₀ is the reproduction wavelength, t
(4) The real part of the complex refractive index of the recording layer material is larger than the real part of the complex refractive index of the adjacent low refractive index layer material. (5) p is 0 or 1 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical information recording medium,
And its recording method.

[0002]

2. Description of the Related Art In recent years, CD-Rs have appeared on the market, and their usefulness is being recognized. CD-R is CD or CD-R
Compatible with OM, general CD player and CD-R
A disc that can be played back by the OM drive and can be recorded only once. CD-R achieves the same high reflectivity as CD and CD-ROM by applying a gold reflective film to enable reproduction by CD player and CD-ROM drive. A recording layer is applied, and then a gold reflective film is provided, on which a protective layer made of an ultraviolet curable resin is formed.

Further, a cyanine-based dye, a phthalocyanine-based dye, an azo metal complex or the like whose wavelength matching property is optimized to enable recording by a recording laser beam is used as a recording layer. The recording contrast is obtained by a change in the constant or deformation of the substrate. Currently C
With the shift from D-ROMs to DVD-ROMs, research on write-once optical information recording media has been advanced from CD-Rs to DVD-Rs. The recording / reproducing wavelength changes from around 780 (nm) to 635 to 650 (nm) due to the shift from the CD-based media to the DVD-based media, and the recording layer material is changed to cope with this. The CD-R and the DVD-R have the same physical layer configuration.

Patents corresponding to a blue laser include, for example, JP-A-7-304256 (optical recording medium comprising a porphyrin derivative and a polymer having a molecular structure having a coordinating ability in a side chain), and JP-A-7-304257 (porphyrin derivative). And an optical recording medium comprising a molecular compound having a coordination ability and a polymer.

[0005]

The reflectivity of a reflection type optical information recording medium can be set arbitrarily. However, in order to obtain a high contrast, it is preferable that the reflectivity before recording is high. . In the case of a read-only ROM-type optical information recording medium (CD or CD-ROM, etc.), a high reflectance of the optical information recording medium is required in order to reduce drive costs as much as possible. In order to take advantage of the characteristics of the organic material, it is best to increase the reflectance. Further, in the case of a write-once optical information recording medium or a rewritable optical information recording medium, compatibility with a ROM-type optical information recording medium is always important. High reflectivity is important.

However, conventional ROM-type optical information recording media,
And, the optical information recording medium compatible with the ROM type optical information recording medium has a recording layer and a reflective layer on a substrate as a main component, and since a metal is used as a material of the reflective layer,
For example, in the case of gold used in a CD-R or the like, the wavelength dispersibility becomes remarkable from about 600 nm or less, and a significant decrease in reflectance occurs (FIG. 1). For example, gold has a reflectance of about 80% at 550 nm. Therefore, when a gold reflective layer is used, in the configuration of substrate / recording layer / gold reflective layer,
At a wavelength of 550 nm or less, a reflectance of about 50% becomes difficult, and it cannot be said that the reflectance is high. By using aluminum or silver instead of gold, the reflectance can be improved even at a shorter wavelength than gold, but the tendency is the same, and lower reflectance at a shorter wavelength is unavoidable.

In the case where a metal is used, the corrosiveness of the metal and the stability of a chemical / physical reaction with the recording material are often problems. Therefore, even if a low reflectance and a low recording / reproduction contrast are allowed by the reproduction system circuit or the signal processing technology, no matter where the recording / reproduction wavelength is set, high reflection / high recording / reproduction is possible. Contrast is always required from the reproduction side. Further, since the increase in the density of the optical information recording medium is mainly achieved by shortening the wavelength of the laser light source, it is easily imagined that the demand for a high reflectance type optical information recording medium in a short wavelength region will increase.
Therefore, an object of the present invention is to provide an optical information recording medium which exhibits a high reflectance even at a short wavelength and can obtain a high recording / reproducing contrast, and a recording / reproducing method thereof.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on an optical information recording medium which can obtain a high reflectance at an arbitrary wavelength as well as a short wavelength and can perform recording, as an optical information recording medium. The present inventors have found that an optical information recording medium having a structure in which the recording layer is sandwiched by the high-reflection multilayer film structure as described above is very excellent in terms of high reflectivity and recording contrast and is easy to realize. Could be reached.

The major feature of the optical information recording medium of the present invention is that
(1) The use of a metal reflective layer, which was conventionally required for high reflectance, (2) The use of a narrow band filter structure as an application of the high reflectance technique using a dielectric laminate coating, 3) The recording layer was used instead of the one-part dielectric layer. According to the present invention, by adopting the above-described configuration, (1) high reflectance type optical information can be obtained even at an arbitrary wavelength where high reflectance cannot be obtained when a conventional metal reflective layer is used. A recording medium is provided, and (2) information of very high contrast can be recorded / reproduced by changing the optical constant of the recording layer by recording.

In the present invention, a dye is used as the most suitable recording layer. In this case, by using anomalous dispersion based on the absorption of the dye, the recording layer can be used as a high refractive index layer or a low refractive index layer. It can also be used as a layer. That is, the wavelength dependence of the complex refractive index of the dye is as shown in FIG. 2, and the real part of the complex refractive index changes largely near the absorption region, and has a high real part of the complex refractive index on the longer wavelength side than the absorption wavelength. On the other hand, on the shorter wavelength side than the absorption wavelength, it has a low complex refractive index real part. Moreover, since the absorption coefficient (imaginary part of the complex refractive index) is small in the wavelength region showing the real part of the high complex refractive index and the real part of the low complex refractive index, a laminate of the high-reflectance layer and the low-reflectance layer is small. In this case, the reflectance can be sufficiently increased. As can be seen from FIG. 2, the wavelength region where the real part of the complex refractive index is high and the wavelength region where the real part is low are very close to each other with the absorption band peak at the center. Therefore, if the absorption spectrum of the recording layer changes due to recording, the complex refractive index greatly changes accordingly, so that a large recording / reproducing contrast can be obtained.

Further, as is conventionally known, the effect of a multi-layer film is to improve the characteristics of a single-layer film by using a multi-layer film, or to wait for characteristics that do not exist in a single-layer film. It is. For example, a two-layer or three-layer antireflection film can reduce the reflectance over the entire visible region as compared with a single-layer film, or a multilayer reflection enhancement film can provide a reflectance exceeding 99% in a specific wavelength region. The effect of this multilayer can be easily analyzed by a characteristic matrix derived from the boundary conditions of the electromagnetic field. The analysis using the characteristic matrix is described in detail, for example, in "Applied Optics II, Masao Tsuruta, Baifukan," p142. For example, in a multilayer film having the configuration of air layer / (high refractive index layer / low refractive index layer) m / substrate, the material of the high refractive index layer is TiO ₂ (refractive index n _{1 at} 550 nm = n ₁ =
2.40), the material of the low refractive index layer was MgF ₂ (refractive index n _{2 at} 550 nm = 1.38), and the substrate was BSC7 (55
The refractive index at 0 nm n _s = 1.52) and the refractive index of air to n ₀
If = 1.0, the characteristic matrix is applied as follows. Here, N = 0, 1, 2, 3,....

(Equation 1) Therefore, the energy reflectance R _{m + 1} is

(Equation 2) Becomes When this is actually calculated, FIG. 3 (N = 4, center wavelength λ ₀ = 550 nm, wavelength dispersion of each material is not considered)
become that way. As can be seen from these results, high reflectivity can be obtained by appropriately selecting the film thickness at an arbitrary wavelength by using a multilayer film.

Usually, in the case of an optical information recording medium having a high reflectance and a high contrast, the allowable range of the complex refractive index required for the recording layer material is very narrow. In general, the imaginary part of the complex refractive index before recording must be small. This is a CD-R or DVD-
When the recording layer is a single layer such as R, it is an unavoidable problem. To achieve high reflectivity and thus high contrast, the real part of the complex refractive index of the recording layer material is large and the imaginary part of the complex refractive index is small. Condition is imposed. Thereby,
The range of choice of the recording layer material is extremely limited.

On the other hand, since the optical information recording medium of the present invention has a multilayer structure, it is possible to increase the reflectance even if the imaginary part of the complex refractive index of the recording layer material is large. Furthermore, because the recording layer optimized for film thickness is sandwiched by a high-reflection multilayer film, the reflectivity decreases sharply only in a very narrow wavelength range, and the high reflectivity in other wavelength ranges. Since the reflectance spectrum is maintained, even if the complex refractive index of the recording layer material is slightly changed, the reflectance spectrum in an unrecorded state shifts, and a very large recording contrast can be generated.

Hereinafter, the recording layer material that can be used in the optical information recording medium of the present invention will be described in detail. As the recording layer of the present invention, for example, a dye or a dye exhibiting photochromic properties,
Compounds exhibiting thermochromic properties are suitable. In the case of a dye exhibiting photochromic properties, for example, light causes a ring-opening and ring-closing reaction to cause a change between a colorless body and a colored body, so that a very large spectral change, that is, a very large change in an optical constant occurs. A large recording contrast can be obtained together with an increase in the reflectance when recording is not performed. Examples of the dye exhibiting photochromic properties include fulgides, diarylethenes, azobenzenes, spirobilanes, and stilbenes.

In the case of a compound exhibiting thermochromic properties, for example, a change in the state of molecular assembly or a change in structure due to heat causes a very large spectral change, that is, a very large change in the optical constant. Along with increasing the reflectance, a large recording contrast can be obtained. As the compound exhibiting thermochromism, for example, as a compound exhibiting thermochromism due to a change in molecular skeleton, bianthrone, polythiophene derivatives, spiropyran and merocyanine, spirooxazine having a 7-ring, quinone and b-hydroxy secondary amine And azamethine dyes, diazaanthracenophane and the like. Further, as those exhibiting thermochromism by tautomerization, those exhibiting keto-enol tautomerization of azomethines such as N-salicylidenebenzylamine, those exhibiting thermochromism by acid-base reaction, or complexes Cholesteric liquid crystals, polyacetylene, and the like can be given as those exhibiting thermochromism due to formation and those exhibiting thermochromism due to structural change in the state of molecular assembly. Also, cyanine (polymethine)
Dyes, tetraazaporphyrin dyes such as phthalocyanine and naphthalosinine, dyes such as porphyrin dyes,
Since it has a large absorption in the range of 300 to 900 nm, it is one of the most suitable materials for the present invention in terms of stability, productivity, and wavelength matching.

The real part n and the imaginary part k of the complex refractive index are connected in a Kramers-Kronig relation (for example, “3.
Light pencil “p243 New Technology Communications”.

(Equation 3)

That is, as is apparent from the above equation, n is large on the long wavelength side of the absorption peak wavelength, and conversely, n is small on the short wavelength side of the absorption peak wavelength. Also, from the Kramers-Kronig relationship, the sharper the absorption curve and the stronger the absorption, the larger the n on the long wavelength side near the absorption peak, the smaller the n on the short wavelength side, and the lower the dye as a high refractive index layer. It can also be used as a refractive index layer. On the other hand, when the absorption curve is relatively broad, the change in n near the absorption peak is relatively small, so that the dye does not have characteristics of both the high refractive index layer and the low refractive index layer. May not be desirable. However, when a high-refractive-index layer or a low-refractive-index layer is used, any dye having a relatively broad absorption curve can be used satisfactorily, so long as the difference in refractive index between adjacent layers is large. However, in the present invention, the recording layer is not limited to a dye compound or a dye compound exhibiting photochromic properties, or a compound exhibiting thermochromic properties, as long as the optical constant changes at the recording / reproducing wavelength. I don't care. Therefore, in the present invention, not only a change in the complex refractive index but also a material whose film thickness changes by recording may be used. Examples of such a material whose thickness changes include those mainly made of a general thermoplastic resin or thermosetting resin, or a shape memory resin such as polynorbornene, polyisoprene, styrene, butadiene copolymer, or polyurethane. can give.

In the present invention, the dye layer is preferably formed by vapor deposition. This is because the low refractive index layer and the high refractive index layer are formed by a dry process such as vapor deposition or sputtering. Is easy to control. That is, in the multilayer film structure utilizing the interference effect in the present invention, the thickness of each layer is very important, but in the conventionally used spin coating method, the type and solvent of the solvent that dissolves the recording layer material such as a dye are conventionally used. Film thickness, the film thickness varies greatly between the inner and outer circumferences of the disc structure, and the film thickness varies greatly depending on the combination of the solvent, the difference between the lots of the solvent, the number of rotations and the rotation pattern, the temperature and humidity of the working environment, etc. Therefore, it is not easy to control the film thickness. On the other hand, when a dye is formed by vapor deposition, the film thickness control becomes very simple. Dyes that can be formed by vapor deposition
For example, "Reversible lasermarki
ng process in anthraquino
ne dyfilms, A .; H. Sporer, AP
PLIED OPTICS / Vo1.26, No. 7 /
1April 1987 p1240 "and the like. However, in the present invention, the recording layer material such as a coloring matter cannot be deposited in all structures, and accordingly, a spin coating method can be used depending on the situation.

The high refractive index layer materials usable in the present invention include ZrO ₂ (2.1), TiO ₂ (2.40), ZnS
(2.32), PbCl ₂ or the like can be used. MgF ₂ (1.38), CeF
_{3 (1.63), A1 2 O} 3 (1.62), SiO 2 (1.
46), Na ₃ AlF ₆ (1.35) and the like can be used.

<< Recording Layer >> As the dye, in addition to the above examples,
For example, polymethine dyes, naphthalocyanine, phthalocyanine, squarylium, coroconium, pyrylium, naphthoquinone, anthraquinone (indanthrene), xanthene, triphenylmethane, azulene, tetrahydrocholine, phenanthrene, triamine Examples include phenothiazine dyes and metal complex compounds, and the above dyes may be used alone or in combination of two or more.

Metals and metal compounds such as In, Te, Bi, Al, Be, TeO ₂ , SnO,
As, Cd and the like can be used in the form of dispersion mixing or lamination. Further, various materials such as a polymer material, for example, an ionomer resin, a polyamide resin, a vinyl resin, a natural polymer, silicone, and a liquid rubber, or a silane coupling agent may be dispersed and used in the dye. It can be used together with a stabilizer (for example, a transition metal complex), a dispersant, a flame retardant, a lubricant, an antistatic agent, a surfactant, a plasticizer, and the like for the purpose of improving the properties.

When the coating method is used, the above-mentioned dyes and the like are dissolved in an organic solvent, and the coating is performed by a conventional coating method such as spraying, roller coating, dipping, and spin coating, or by a vapor deposition method. The vapor deposition method is most preferable due to its characteristics. Examples of the organic solvent generally include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylacetamide and N, N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. , Tetrahydrofuran, dioxane, diethyl ether, ethers such as ethylene glycol monomethyl ether, esters such as methyl acetate, ethyl acetate, chloroform, methylene chloride, dichloroethane, carbon tetrachloride, aliphatic halogenated carbons such as trichloroethane,
Or benzene, xylene, monochlorobenzene,
Aromatic substances such as dichlorobenzene, cellsolves such as methoxyethanol and ethoxyethanol, and hydrocarbons such as hexane, pentane, cyclohexane, and methylcyclohexane can be used. The film thickness of the recording layer, the recording-reproducing wavelength lambda _0, the real part of the complex refractive index of the recording-reproducing wavelength is n, substantially nd = (λ _0/2)
It is necessary to be near the film thickness satisfying xt (t is an integer of 1 or more).

<< Substrate >> As a necessary characteristic of the substrate, the substrate must be transparent to the laser beam used only when recording / reproducing is performed from the substrate side, and is transparent when recording / reproducing is performed from the recording layer side. No need. As the substrate material, for example,
Plastics such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, and polyimide, glass, ceramic, and metal can be used.
Note that a guide groove or guide pit for tracking and a preformat such as an address signal may be formed on the surface of the substrate.

<< Intermediate Layer >> Layers provided other than the substrate, the recording layer, and the protective layer, including the undercoat layer and the like, will be referred to herein as intermediate layers. This intermediate layer has (a) improved adhesion and (b)
Water or gas barrier, (c) improvement of storage stability of recording layer, (d) improvement of reflectance, (e) protection of substrate and recording layer from solvent, (f) guide groove, guide pit, It is used for the purpose of forming a preformat or the like. For the purpose of the above (a), various polymer materials such as polymer materials, for example, ionomer resin, polyamide resin, vinyl resin, natural resin, natural polymer, silicone, liquid rubber, and silane coupling For the purposes of (b) and (c), an inorganic compound other than the above-mentioned polymer material, for example, SiO ₂ , MgF ₂ , Si
O, TiO ₂ , ZnO, TiN, SiN and the like can be used. For the purpose (d), an organic thin film having a metallic luster such as a methine dye or a xanthene dye can be used. For the purposes (e) and (f), an ultraviolet curable resin or a thermosetting resin can be used. A resin, a thermoplastic resin, or the like can be used. The thickness of the undercoat layer, enter the recording-reproducing wavelength _0, when the real part of the complex refractive index of the recording-reproducing wavelength is n, it is necessary that a film thickness satisfying the nd = ON _0/4.

<< Protective Layer / Substrate Hard Coat Layer >> The protective layer or the substrate hard coat layer (a) protects the recording layer (reflection / absorption layer) from scratches, dust, dirt, etc.
(B) improvement in storage stability of the recording layer (reflection / absorption layer),
(C) Used for the purpose of improving the reflectance. For these purposes, the materials shown in the undercoat layer can be used. As inorganic materials, SiO, SiO ₂
And the like, and, as an organic material, polymethyl acrylate, polycarbonate, epoxy grease, polystyrene, polyester resin, vinyl resin, cellulose, aliphatic hydrocarbon resin, aromatic hydrocarbon resin,
Thermosoftening and heat melting resins such as natural rubber, styrene butadiene resin, chloroprene rubber, wax, alkyd resin, drying oil and rosin can also be used. Among the above materials, the most preferable substance for the protective layer or the hard coat layer on the substrate surface is an ultraviolet curable resin having excellent productivity.

The thickness of the protective layer or the hard coat layer on the substrate surface is 0.01 to 30 μm, preferably 0.05 to 1 μm.
0 μm is appropriate. In the present invention, the undercoat layer,
As in the case of the recording layer, the protective layer and the substrate surface hard coat layer may contain a stabilizer, a dispersant, a flame retardant, a lubricant, an antistatic agent, a surfactant, a plasticizer, and the like.

<< Adhesive Layer >> An adhesive layer may be required when two or more optical information recording media are adhered. Particularly preferred in the present invention are hot melt type (hot melt type) adhesives,
Alternatively, it is an ultraviolet curable adhesive. The ultraviolet curable adhesive is an adhesive which is cured by the initiation of radical polymerization by irradiation with ultraviolet light. The composition is generally composed of (1) an acrylic oligomer, (2) an acrylic monomer, (3) a photopolymerization initiator, and (4) a polymerization inhibitor. The oligomer is a polyester-based, polyurethane-based, or epoxy-based. Benzophenone, benzoin ether and the like can be used as a photopolymerization initiator such as an acrylate ester. The hot melt adhesive is one in which a liquid adhesive is hardened by solvent volatilization or reaction and develops an adhesive force, whereas an ordinary-temperature solid thermoplastic resin develops an adhesive force by a physical change of heat melting and cooling and solidification. Hot melt adhesives are EVA, polyester,
A polyamide type, a polyurethane type, or the like can be used.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the optical information recording medium of the present invention and the effects thereof will be described below.

Example 1 (1) Layer structure Substrate 1 / (high refractive index layer / low refractive index layer) m / recording layer / (low refractive index layer / high refractive index layer) p / substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 2, lamination number p: 2 Recording / reproduction is performed from the substrate 1 side at the recording / reproduction wavelength ₀ : 500 (nm) on the optical information recording medium having the above configuration.
FIG. 4 shows the results of calculating the reflectance when the complex refractive index of the unrecorded recording layer is n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

In the optical information recording medium constructed under the above conditions, the unrecorded recording layer has a complex refractive index of n ^* = 2.50.
FIG. 5 shows the calculation result of the reflectance when −i0.1 is assumed.
The complex refractive index of the unrecorded recording layer is given by n ^* = 2.50−
FIG. 6 shows the calculation results of the reflectance when i0.2 is assumed. FIG. 7 shows the results of FIGS. 4 to 6 shown on the same drawing.

From the above results, even if the imaginary part of the complex refractive index of the recording layer becomes very large (generally, a CD-R or DVD-
For the R dye material, the imaginary part of the complex refractive index is 0.03 to 0.5.
If the imaginary part of the complex refractive index becomes larger than about 05,
High reflectivity is obtained, and the reflectivity has a large wavelength range where the reflectivity decreases. Since the reflectivity decrease region is a relatively narrow wavelength range, the reflectivity shifts to a high level. It can be seen that the efficiency and the recording contrast can be increased at the same time. On the other hand, in the optical information recording medium of the present invention, since the recording contrast is basically caused by the shift of the reflectance spectrum, the reflectance spectrum must be changed by the change of the complex refractive index of the recording layer. In this regard, according to the present example, it is understood that the change of the imaginary part of the complex refractive index of the recording layer due to recording is not preferable in terms of recording contrast.

Example 2 (1) Layer Structure Substrate 1 / (high refractive index layer / low refractive index layer) m / recording layer / (low refractive index layer / high refractive index layer) p / substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 2, lamination number p: 2 Recording / reproduction is performed from the substrate 1 side at the recording / reproduction wavelength ₀ : 500 (nm) on the optical information recording medium having the above configuration.
FIG. 4 shows the results of calculating the reflectance when the complex refractive index of the unrecorded recording layer is n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

In the optical information recording medium constructed under the above conditions, only the real part of the complex refractive index of the recording layer at the time of recording changes, and the complex refractive index of the recording layer at that time is given by n ^* = 2.25-i.
FIG. 8 shows the calculation result of the reflectance at 0.01, and only the real part of the complex refractive index of the recording layer changes at the time of recording, and the complex refractive index of the recording layer at that time is n ^* = 2.00− FIG. 9 shows the calculation result of the reflectance at the time of i0.01, and only the real part of the complex refractive index of the recording layer changes during recording, and the complex refractive index of the recording layer at that time is n ^* = 1.75− FIG. 10 shows the calculation results of the reflectance when i0.01 was obtained.

FIG. 11 shows the result of FIG. 4 and FIGS. 8 to 9 shown on the same figure. From this result, if the real part of the complex refractive index of the recording layer changes even a little, the reflectance spectrum shifts, and a very large high recording contrast can be obtained. It can also be seen that high reflectance can be sufficiently achieved. For example, if the recording / reproducing wavelength is now around 480 nm, the reflectivity is 80% in the unrecorded state n ^* = 2.50-i0.01, but the real part of the complex refractive index of the recording layer changes by recording. However, when n ^* = 2.25-i0.01, the reflectance is reduced to approximately 20%.

Example 3 (1) Layer Structure Substrate 1 / (High refractive index layer / Low refractive index layer) m / Recording layer / (Low refractive index layer / High refractive index layer) p / Substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) complex refractive index of recording layer: n ^* = 2.50-i0.01 (4) Number of layers m: 2, number of layers p: 2 Recording / reproduction is performed from the substrate 1 side at a recording / reproduction wavelength of ₀ : 500 (nm).

The dependency of the reflectance at 500 nm on the recording layer thickness when the complex refractive index of the unrecorded recording layer is n ^* = 2.50-i0.01 under the above-mentioned layer configuration conditions was calculated. The result is shown in FIG. This result shows the fact that with the lowest point of the reflectance at the wavelength optical thickness of the recording layer is λ _0/2. The wavelength dependence of the reflectance when the thickness of the recording layer is 50 nm is the same as that in FIG. 4 (reflectance spectrum before recording). In the optical information recording medium configured under the above conditions, only the recording layer thickness changes during recording, and the calculation result of the reflectance when the recording layer thickness becomes 52 nm at that time is shown in FIG. Only the film thickness changes,
FIG. 14 shows a calculation result of the reflectance when the recording layer thickness is 54 nm at that time. FIG. 14 shows the reflectance when the recording layer thickness changes to 56 nm at the time of recording. FIG. 15 shows the calculation results, and FIG. 16 shows the calculation results of the reflectance when only the recording layer thickness changes during recording and the recording layer thickness at that time becomes 58 nm. FIG.
(Recording layer thickness 50 nm), FIG. 14 (Recording layer thickness 54 n)
m) and FIG. 16 (recording layer thickness 58 nm) on the same drawing are shown in FIG. From this result, if the recording layer thickness changes even slightly, the reflectance spectrum shifts,
It can be seen that a very large high recording contrast is obtained, and a high reflectivity is sufficiently achieved. For example, if the recording / reproducing wavelength is near 500 nm, the unrecorded state n
^* = 2.50-i0.01, the reflectance was 90% when the film thickness was 58 nm, but only the film thickness of the recording layer was changed by recording. When the film thickness was 50 nm, the reflectance was approximately 0%. To decline.

Example 4 (1) Layer Structure Substrate 1 / (high refractive index layer / low refractive index layer) m / recording layer / (low refractive index layer / high refractive index layer) p / substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 2, lamination number p: 1 Recording / reproduction is performed from the substrate 1 side at the recording / reproduction wavelength ₀ : 500 (nm) on the optical information recording medium having the above configuration.
FIG. 18 shows the results of calculating the reflectance when the complex refractive index of the unrecorded recording layer is n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

Compared to the case where the layer configuration is symmetrical as in the first to third embodiments (the number of layers m = P, FIG. 4), even if the layer configuration is asymmetric and the layer configuration is simplified (the number of layers m ≠) p) Although the wavelength region where the reflectance is significantly reduced becomes slightly broader and the minimum reflectance is slightly increased, it can be seen that the basic performance is sufficiently satisfactory.

Example 5 (1) Layer Structure Substrate 1 / (High refractive index layer / Low refractive index layer) m / Recording layer / (Low refractive index layer / High refractive index layer) p / Substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 1, lamination number p: 2 Recording / reproduction is performed on the optical information recording medium having the above-described configuration from the substrate 1 side at a recording / reproduction wavelength of ₀ : 500 (nm).
FIG. 19 shows the result of calculating the reflectance when the complex refractive index of the recording layer at the time of non-recording is set to n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

As compared with the case where the layer configuration is symmetrical (the number of layers m = P, FIG. 4), even if the layer configuration is asymmetric and the layer configuration is simplified (the number of layers m ≠ p), the reflectance is significantly reduced. Although the wavelength range is slightly broadened and the minimum reflectance is slightly increased, it can be seen that the basic performance is sufficiently satisfactory. As described above, the symmetric configuration (the number of stacked layers m = P = 2, FIG. 4) and the asymmetric configuration (m = 2, P = 1, FIG. 18) and (m = 1, P = 2,
FIG. 20 shows the result of FIG. 19) shown on the same figure.

Example 6 (1) Layer structure Substrate 1 / (high refractive index layer / low refractive index layer) m / recording layer / (low refractive index layer / high refractive index layer) p / substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 1, lamination number p: 2 Recording / reproduction is performed on the optical information recording medium having the above-described configuration from the substrate 1 side at a recording / reproduction wavelength of ₀ : 500 (nm).
FIG. 19 shows the result of calculating the reflectance when the complex refractive index of the recording layer at the time of non-recording is set to n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

In the optical information recording medium constructed under the above conditions, the unrecorded recording layer has a complex refractive index of n ^* = 2.50.
FIG. 21 shows the calculation result of the reflectance when −i0.1 is assumed.
The complex refractive index of the unrecorded recording layer is given by n ^* = 2.50−
FIG. 22 shows the calculation results of the reflectance when i0.2 is assumed. 19 and FIG. 21 to FIG.
2 is shown in FIG. 23. From this result, even if the imaginary part of the complex refractive index of the recording layer becomes very large (in general, the imaginary part of the complex refractive index of the dye material of CD-R or DVD-R is about 0.03 to 0.06). If the imaginary part of the complex refractive index is larger than this, the reflectance is greatly reduced.) A high reflectance is obtained, and a large wavelength region where the reflectance is reduced is relatively narrow. Therefore, it can be understood that a shift in the reflectance spectrum can simultaneously increase the reflectance and the recording contrast. On the other hand, in the optical information recording medium of the present invention, since the recording contrast is basically generated by the shift of the reflectance spectrum, the reflectance spectrum must be changed by the change of the complex refractive index of the recording layer. In this regard, according to the present embodiment,
It can be seen that the change of the imaginary part of the complex refractive index of the recording layer due to recording is not preferable in terms of recording contrast.

Example 7 (1) Layer Structure Substrate 1 / (High refractive index layer / Low refractive index layer) m / Recording layer / (Low refractive index layer / High refractive index layer) p / Substrate 2 (2) Substrate and Refractive index of each layer Substrate Refractive index: 1.52 Refractive index of low refractive index layer 1:38 (MgF ₂ ) Refractive index of high refractive index layer: 2.40 (TiO ₂ ) (however, low refractive index layer, high refractive index) (3) Thickness of each layer Thickness of low refractive index layer: d = λ ₀ /(4×1.38) Thickness of high refractive index layer: d = λ ₀ /(4×2.40) thickness of the recording layer: d = [λ ₀ / (4 × n)] × t, where t = 2, where n is the real part of the complex refractive index of the recording layer. : 1, lamination number p: 2 Recording / reproducing is performed on the optical information recording medium having the above configuration from the substrate 1 side at a recording / reproducing wavelength of 0: 500 (nm).
FIG. 19 shows the result of calculating the reflectance when the complex refractive index of the recording layer at the time of non-recording is set to n ^* = 2.50-i0.01 under the above-described layer configuration conditions.

In the optical information recording medium constructed under the above conditions, only the real part of the complex refractive index changes during recording, and the complex refractive index of the recording layer at that time becomes n ^* = 2.25-i0.01. FIG. 24 shows a calculation result of the reflectance in the case where only the real part of the complex refractive index changes during recording, and the reflection when the complex refractive index of the recording layer at that time becomes n ^* = 2.00-i0.01. FIG. 25 shows the calculation result of the refractive index. During recording, only the real part of the complex refractive index changes, and the complex refractive index of the recording layer at that time is n ^* = 1.
FIG. 26 shows the calculation result of the reflectance when 75-i0.01 was obtained. FIG. 19 and FIGS.
Are shown in FIG. 27 on the same figure. From this result, if the real part of the complex refractive index of the recording layer changes even a little, the reflectance spectrum shifts, and a very large high recording contrast can be obtained. It can also be seen that high reflectance can be sufficiently achieved. For example, if the recording / reproducing wavelength is 45
Assuming that it is near 0 nm, the unrecorded state n ^* = 2.50-i
Although the reflectivity was 80% at 0.01, the real part of the complex refractive index of the recording layer was changed by recording, and n ^* = 2.00
When −i0.01, the reflectance is reduced to about 20%.

In the present embodiment, the complex refractive index of the recording layer may be changed, for example, by changing the structure of the dye, changing the aggregate state, changing the association state, changing the crystal state, changing the phase,
Degradation and the like. Whether a material such as a dye moves to a short wavelength or a long wavelength by recording from the absorption spectrum of the unrecorded material depends on the structure of the material, the presence or absence of the substituent, the type of the substituent, the location of the substituent, the substituent It depends on the size of
This is because, for example, the absorption spectrum of an H-aggregate of a dye generally moves to a shorter wavelength, and the absorption spectrum of a J-aggregate moves to a longer wavelength, and these changes are determined by the type and position of the substituent. The effect of the substituents on the formation of the aggregates is completely different when the structure and the like are changed. "The Photographic Society of Japan, Vol. 58, No. 4, 1995 (Heisei 7), p361.

[0046]

According to the present invention, a metal reflective layer conventionally required for increasing the reflectance is unnecessary, and a high reflectance type optical information recording medium can be used even at an arbitrary wavelength at which a high reflectance cannot be obtained with the metal reflective layer. Is provided, and a novel optical information recording medium and a recording method for an optical information recording medium that can record and reproduce high-contrast information by slightly changing the optical constant of the recording layer by recording are provided. As a result, a high reflectance is achieved in a wavelength region that cannot be achieved by the metal reflection film, and a high-contrast recording can be performed. Further, the limited range of optical constants required for the recording layer material can be relaxed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the wavelength dependence of a gold reflection film.

FIG. 2 is a diagram showing the wavelength dependence of the complex refractive index of a dye.

FIG. 3 is a diagram showing an example of a reflectance spectrum of a multilayer structure.

FIG. 4 is a diagram showing a result of calculating a reflectance when the complex refractive index of the recording layer before recording is set to n * = 2.50-i0.01 under the layer configuration conditions of Examples 1 and 2.

FIG. 5 is a view showing a result of calculating a reflectance when a complex refractive index of a recording layer at the time of unrecording is set to n * = 2.50-i0.1 under a layer configuration condition of Example 1.

FIG. 6 is a diagram showing a result of calculating a reflectance when a complex refractive index of a recording layer at the time of unrecording is set to n * = 2.50-i0.2 under a layer configuration condition of Example 1.

FIG. 7 is a view showing a result of showing FIGS. 4 to 6 on the same figure.

FIG. 8 shows that, under the layer configuration conditions of Example 2, only the real part of the complex refractive index of the recording layer changes during recording, and the complex refractive index of the recording layer at that time becomes n * = 2.25-i0.01. The figure which shows the result of having calculated the reflectance in the case of having performed.

FIG. 9 shows that, under the layer configuration conditions of Example 2, only the real part of the complex refractive index of the recording layer changes during recording, and the complex refractive index of the recording layer at that time is n * = 2.00-i0.01. The figure which shows the result of having calculated the reflectance in the case.

FIG. 10 shows that, under the layer configuration conditions of Example 2, only the real part of the complex refractive index of the recording layer changes during recording, and the complex refractive index of the recording layer at that time is n * = 1.75-i0.01. The figure which shows the result of having calculated the reflectance in the case.

FIG. 11 is a view showing a result of showing FIGS. 4 and 8 to 9 on the same figure.

FIG. 12 shows the dependency of the reflectance at 500 nm on the thickness of the recording layer when the complex refractive index of the recording layer before recording is n * = 2.50-i0.01 under the layer configuration conditions of Example 3. The figure which shows the calculation result.

FIG. 13 is a diagram showing calculation results when only the recording layer thickness changes during recording and the recording layer thickness at that time becomes 52 nm under the layer configuration conditions of Example 3.

FIG. 14 is a diagram showing a calculation result of the reflectance when only the recording layer thickness changes during recording and the recording layer thickness at that time becomes 54 nm under the layer configuration conditions of Example 3.

FIG. 15 is a diagram showing calculation results when only the recording layer thickness changes during recording and the recording layer thickness at that time becomes 56 nm under the layer configuration conditions of Example 3.

FIG. 16 is a diagram showing calculation results when only the recording layer thickness changes during recording and the recording layer thickness at that time becomes 58 nm under the layer configuration conditions of Example 3.

17 (recording layer thickness 50 nm), FIG. 14 (recording layer thickness 54 nm), and FIG. 16 (recording layer thickness 58n)
m) A diagram showing the results shown on the same figure.

FIG. 18 is a diagram showing a result of calculating a reflectance when the complex refractive index of the recording layer when recording is not performed is set to n * = 2.50-i0.01 under the layer configuration conditions of Example 4.

FIG. 19 is a diagram illustrating a result of calculating a reflectance when the complex refractive index of the recording layer when recording is not performed is set to n * = 2.50-i0.01 under the layer configuration conditions of Examples 5 to 7.

FIG. 20 is a diagram showing the results of FIGS. 4, 18, and 19 shown on the same diagram.

FIG. 21 is a diagram showing a result of calculating a reflectance when a complex refractive index of a recording layer at the time of unrecording is set to n * = 2.50-i0.1 under a layer configuration condition of Example 6.

FIG. 22 is a view showing the result of calculating the reflectance when the complex refractive index of the recording layer is set to n * = 2.50-i0.2 under the layer configuration conditions in Example 6.

FIG. 23 is a diagram showing the results of FIG. 19 and FIGS. 21 to 22 shown on the same diagram.

FIG. 24 shows that, under the layer configuration conditions of Example 7, only the real part of the complex refractive index changes during recording, and n * = 2.2 of the recording layer at that time.
The figure which shows the result of having calculated the reflectance at the time of 5-i0.01.

FIG. 25 shows that the real part of the complex refractive index changes during recording under the layer configuration conditions of Example 7, and the recording layer at that time has n * = 2.0.
The figure which shows the result of having calculated the reflectance at the time of becoming 0-i0.01.

FIG. 26 shows that the real part of the complex refractive index changes during recording under the layer configuration conditions of Example 7, and the recording layer at that time has n * = 1.7.
The figure which shows the result of having calculated the reflectance at the time of 5-i0.01.

FIG. 27 is a view showing a result of showing FIGS. 19, 24 and 25 on the same figure.

Continuing on the front page (72) Inventor Yasunobu Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Yasuhiro Higashi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd.

Claims (14)

[Claims] 1. An optical information recording medium for recording and reproducing information by irradiating a laser beam, wherein the optical information recording medium has at least a substrate / (high refractive index layer / low refractive index layer) m / recording layer / (low It has a layer configuration of refractive index layer / high refractive index layer) p (where m and p are the number of laminations), records information by changing the complex refractive index of the recording layer material by irradiating laser light, and An optical information recording medium which satisfies the following requirements. (1) m is 1 or more, and (2) the thicknesses of the high refractive index layer and the low refractive index layer are at least n _i at least at the reproduction wavelength.
d _i = λ _0/4 (where n _i is the high refractive index layer or low refractive index layer refractive index of the material, d _i is the high refractive index layer or low refractive index layer thickness of the material,, lambda ₀ is reproduction wavelength ), (3) the thickness of the recording layer is at least reproducing _{wavelength, n S d S = (λ} 0/2) t
(Where n _S is the refractive index of the recording layer material, d _S is the film thickness of the recording layer material, λ ₀ is the reproduction wavelength, and t is an integer of 1 or more), and (4) the real part of the complex refractive index of the recording layer material is (5) p is 0 or 1 or more, which is larger than the real part of the complex refractive index of the adjacent low refractive index layer material. 2. An optical information recording medium for recording and reproducing information by irradiating a laser beam, wherein the optical information recording medium is at least a substrate / (high refractive index layer / low refractive index layer) m / high refractive index layer / It has a layer structure of recording layer / high refractive index layer / (low refractive index layer / high refractive index layer) p (where m and p are the number of repeated layers), and changes the complex refractive index of the recording layer material by laser light irradiation. An optical information recording medium, which records information by satisfying the following requirements. (1) m is 1 or more, and (2) the thicknesses of the high refractive index layer and the low refractive index layer are at least n _i at least at the reproduction wavelength.
d _i = λ _0/4 (where n _i is the high refractive index layer or low refractive index layer refractive index of the material, d _i is the high refractive index layer or low refractive index layer thickness of the material,, lambda ₀ is reproduction wavelength ), (3) the thickness of the recording layer is at least reproducing _{wavelength, n S d S = (λ} 0/2) t
(Where n _S is the refractive index of the recording layer material, d _S is the film thickness of the recording layer material, λ ₀ is the reproduction wavelength, and t is an integer of 1 or more), and (4) the real part of the complex refractive index of the recording layer material is (5) p is 0 or 1 or more, which is smaller than the real part of the complex refractive index of the adjacent high refractive index layer material. 3. An optical information recording medium for recording and reproducing information by irradiating a laser beam, wherein the optical information recording medium is at least a substrate / (high refractive index layer / low refractive index layer) m / recording layer / (low It has a layer structure of refractive index layer / high refractive index layer) p (where m and p are the number of repetitions of lamination). Information is recorded by changing the film thickness of the recording layer material by irradiating a laser beam. An optical information recording medium characterized by satisfying the following requirements. (1) m is 1 or more, and (2) the thicknesses of the high refractive index layer and the low refractive index layer are at least n _i at least at the reproduction wavelength.
d _i = λ _0/4 (where n _i is the high refractive index layer or low refractive index layer refractive index of the material, d _i is the high refractive index layer or low refractive index layer thickness of the material,, lambda ₀ is reproduction wavelength ), (3) the thickness of the recording layer is at least reproducing _{wavelength, n S d S = (λ} 0/2) t
(Where n _S is the refractive index of the recording layer material, d _S is the film thickness of the recording layer material, λ ₀ is the reproduction wavelength, and t is an integer of 1 or more), and (4) the real part of the complex refractive index of the recording layer material is (5) p is 0 or 1 or more, which is larger than the real part of the complex refractive index of the adjacent low refractive index layer material. 4. An optical information recording medium for recording and reproducing information by irradiating a laser beam, wherein the optical information recording medium is at least a substrate / (high refractive index layer / low refractive index layer) m / high refractive index layer / It has a layer structure of recording layer / high-refractive-index layer / (low-refractive-index layer / high-refractive-index layer) p (where m and p are the number of times of lamination), and changes the film thickness of the recording layer material by irradiating a laser beam. An optical information recording medium, which records information by satisfying the following requirements. (1) m is 1 or more, and (2) the thicknesses of the high refractive index layer and the low refractive index layer are at least n _i at least at the reproduction wavelength.
d _i = λ _0/4 (where n _i is the high refractive index layer or low refractive index layer refractive index of the material, d _i is the high refractive index layer or low refractive index layer thickness of the material,, lambda ₀ is reproduction wavelength ), (3) the thickness of the recording layer is at least reproducing _{wavelength, n S d S = (λ} 0/2) t
(Where n _S is the refractive index of the recording layer material, d _S is the film thickness of the recording layer material, λ ₀ is the reproduction wavelength, and t is an integer of 1 or more), and (4) the real part of the complex refractive index of the recording layer material is (5) p is 0 or 1 or more, which is smaller than the real part of the complex refractive index of the adjacent high refractive index layer material. 5. The optical information recording medium according to claim 1, wherein the main component of the recording layer is a dye compound. 6. The optical information recording medium according to claim 5, wherein the dye compound of the recording layer is a dye compound exhibiting photochromic properties. 7. The optical information recording medium according to claim 1, wherein the main component of the recording layer is a compound exhibiting thermochromism. 8. The optical information recording medium according to claim 5, wherein the main component of the recording layer is formed by a vapor deposition method. 9. The recording method according to claim 1, wherein the reflectance of the recording layer is lower than that of the unrecorded state by recording.
The optical information recording medium according to 5, 6, 7 or 8. 10. The optical information recording medium according to claim 1, wherein the information reproduction wavelength is 550 nm or less. 11. Recording of information by irradiating the optical information recording medium of claim 1, 2, 5, 6, 7, 8, 9 or 10 with a laser beam to change the complex refractive index of the recording layer material. Recording method for an optical information recording medium. 12. Recording of information by irradiating the optical information recording medium according to claim 3, 4, 5, 6, 7, 8, 9 or 10 with a laser beam and changing the film thickness of the recording layer material. Recording method for an optical information recording medium. 13. The recording method for an optical information recording medium according to claim 11, wherein the reflectance of the recording layer material at the time of recording is lower than the reflectance at the time of non-recording. 14. The recording method for an optical information recording medium according to claim 11, wherein information is recorded at a recording wavelength of 550 nm or less.