JPH1125517A - Optical recording medium and recording / reproducing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce and show a high degree of modulation even in a red laser wavelength region used for a general-purpose DVD-ROM drive, which can be recorded and reproduced by a red laser capable of recording at a high density and is inexpensive. DVD with large playback wavelength margin
A recording material for an R recording medium is provided. SOLUTION: In an optical recording medium in which a recording layer is provided on a first substrate and a reflective layer, a protective layer or a second substrate is provided thereon, the recording layer is formed by an optical device at a wavelength of 630 to 640 nm when not recorded. Constants are refractive index: n ≧ 2.0, extinction coefficient: k <
The first dye having a refractive index of 0.2 and a non-recording optical constant at a wavelength of 630 to 640 nm having a refractive index of n <2.0, an extinction coefficient of k <0.02, and a wavelength of 640 to 670 nm. The optical constant at the time of recording is n <2.0 at the time of recording, and the extinction coefficient is:
The second dye that satisfies k ≧ 0.15 is formed as a main component.

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, and more particularly, to irradiating a light beam to cause an optical change in the transmittance and reflectance of a recording material, thereby recording information. The present invention relates to an information recording medium that can be reproduced and can be additionally recorded.

[0002]

2. Description of the Related Art At present, as a next-generation large-capacity optical disk, D
VD-R is under development. Elemental technologies for improving recording capacity include recording material development for miniaturizing recording pits,
It is necessary to develop technology such as adoption of an image compression technology represented by MPEG2 and shortening of the wavelength of a semiconductor laser for reading recorded pits.

Hitherto, as a semiconductor laser in the red wavelength region, a 670 nm band A for a bar code reader and a measuring instrument has been used.
Although only the 1GaInP laser diode has been commercialized, the red laser is being used in the optical storage market in earnest as the density of optical disks increases.

In the case of a DVD drive, 635 is used as a light source.
It is standardized at two wavelengths, a laser diode in the nm band and a laser diode in the 650 nm band. For high-density recording, it is desirable that the wavelength be shorter, and for a write-once media drive, the wavelength is preferably 635 nm. On the other hand, a read-only DVD
-ROM drives are beginning to be commercialized at a wavelength of about 650 nm.

[0005] Under these circumstances, the most desirable DVD-R
Media is a medium that can record and reproduce at a wavelength of about 635 nm, and can reproduce at a wavelength of about 650 nm. Furthermore, the oscillation wavelength of a semiconductor laser has the characteristic that it changes with temperature and shifts to longer wavelengths at higher temperatures.
Therefore, in order to obtain a stable reproduction output at the above two laser wavelengths, it is necessary to have a high degree of modulation in the entire wavelength range of 630 to 670 nm.

[0006]

However, at present, the recording materials developed so far can be reproduced only in one of the wavelength ranges. Accordingly, an object of the present invention is to provide a red laser (635 ± 5) capable of recording at high density.
nm) which can be recorded and reproduced, and is inexpensive and used in a general reproduction DVD-ROM drive.
It is an object of the present invention to provide a recording material for a DVD-R recording medium having a large reproduction wavelength margin and exhibiting a high degree of modulation even in a wavelength region (40 to 670 nm) and capable of reproducing, and a recording and reproducing method using the same.

[0007]

As a result of various studies, the present inventors have mixed a second dye exhibiting a specific change with a first dye as a main component, and recorded 640 to 670 of a second dye during recording.
The present inventors have found that reproduction can be performed not only in the recording wavelength range but also in the above-mentioned wavelength range by increasing the absorption coefficient in the nm wavelength range.

That is, the optical recording medium according to the first aspect comprises a recording layer provided directly or via an undercoat layer on a first substrate, and a reflective layer, a protective layer or a second substrate provided thereon. In the optical recording medium, the recording layer has a wavelength of 630.
The optical constant before recording at 640 nm to 640 nm is the refractive index: n
≧ 2.0, extinction coefficient: k <0.2, the first dye having a non-recording optical constant at a wavelength of 630 to 640 nm has a refractive index: n <2.0, extinction coefficient: k < 0.02 and a second dye having an optical constant n <2.0 during recording at a wavelength of 640 to 670 nm and an extinction coefficient: k ≧ 0.15 as a main component. It is a feature.

The optical recording medium according to the second aspect is the first aspect.
Wherein the second dye is a dye whose optical constant during recording at a wavelength of 640 to 670 nm is generated by a chemical change due to light and / or heat of a recording laser.

[0010] The optical recording medium according to the third aspect is the first aspect.
Wherein the second dye is a dye whose optical constant during recording at a wavelength of 640 to 670 nm is generated by chromism caused by light and / or heat of a recording laser.

According to a fourth aspect of the present invention, there is provided a recording / reproducing method using the optical recording medium according to the first, second, or third aspect, wherein recording is performed by using a laser having a wavelength of 630 to 640 nm. Laser and wavelength 640-
It is characterized by reproducing with a 670 nm laser.

Here, the configuration of the optical recording medium according to claim 1 is a red laser (635 ± 5 nm) capable of high-density recording.
Recording and playback, and low-cost DV for general playback
The red laser (640-640) used in the D-ROM drive
670 nm). The limitations according to claim 2 are as follows:
The present invention defines specific physical properties of a recording material for realizing the optical recording medium of the first aspect. The limitation according to claim 3 defines another specific physical property of a recording material for realizing the optical recording medium according to claim 1.

[0013]

Next, an embodiment of the present invention will be described. First, in order to facilitate understanding of the configuration and operation of the optical recording medium according to the present invention, a brief description will be given of a conventional technique. A recordable CD (CD-R) compliant with the Compact Disc (CD) standard has been commercialized as an optical recording medium having a reflective layer on a substrate. This CD
In 1R, information is recorded / reproduced by irradiating the recording layer with laser light having a wavelength of 770 to 830 nm and detecting reflected light that causes a physical or chemical change in the recording layer. Recently, semiconductor lasers with shorter wavelengths have been developed.
A red semiconductor laser having a wavelength of 630 to 680 nm has been put to practical use. By shortening the wavelength of the recording / reproducing laser, the beam diameter can be further reduced, and a high-density optical recording medium can be realized.

The present invention relates to a high-density optical recording medium using a recording material capable of recording and reproducing at a wavelength of 630 to 680 nm. Further, recording and reproduction can be performed by a red laser (635 ± 5 nm) capable of recording at a high density, and high modulation can be performed even in the wavelength range of a red laser (640 to 670 nm) which is inexpensive and used in DVD-ROM drives for general reproduction. The present invention relates to a high-density optical recording medium having a high reproduction wavelength margin and a large reproduction wavelength margin. Hereinafter, the recording / reproducing principle will be described.

A DVD-R shows a high reflectance when not recorded, reduces the reflectance by recording, and reproduces the output difference. In order to realize this, the recording body configuration has an organic dye layer and a metal reflective layer laminated, and the dye has a high absorption coefficient such that the long wavelength end of the absorption spectrum of the film matches the recording wavelength region. Use materials. As a result, it is possible to achieve both a high refractive index and a small absorption coefficient in the recording wavelength range, and it is possible to obtain a high reflectance of an unrecorded portion due to multiple reflection and a high degree of modulation after recording (recording wavelength The reproduction is possible at the same wavelength as.

It is considered that the cause of the decrease in reflectivity due to recording is a change in the optical constant of the dye, which is mainly caused by decomposition of the dye due to heat and separation, and a deformation of the substrate and the metal reflection layer. Therefore, in the above configuration, the dye layer hardly absorbs in a wavelength region longer than the recording wavelength, and as a result, a high refractive index cannot be obtained. For this reason, a high reflectance at the time of non-recording can be obtained, but a change in the optical constant at the time of recording is small and a difference in reflectance cannot be obtained.

According to the present invention, a reflectance difference is obtained by mixing a dye whose absorption coefficient increases in this wavelength region due to heat and light during recording in a wavelength region longer than the recording wavelength. As described above, the recording medium having this configuration is obtained by multiple reflection between the organic dye layer / metal reflective layer interface and the organic dye layer / first substrate interface. The obtained reflectance greatly depends on the absorption coefficient of the organic dye layer. The absorption coefficient is highest when the absorption coefficient is 0, and as the absorption coefficient increases to a certain extent, the light absorption between the organic dyes increases, and the reflectance increases. The rate drops sharply. The present invention utilizes this phenomenon. By mixing a dye whose absorption coefficient increases in the wavelength range due to heat and light during recording in a wavelength range longer than the recording wavelength, a reflectance difference can be obtained. Naturally, it should not affect the recording / reproducing characteristics in the second dye recording wavelength region, and it is desirable that the optical characteristics thereof have no absorptivity in the recording wavelength region.

As described above, in the recording layer of the optical recording medium according to the present invention, the optical constant at the wavelength of 630 to 640 nm when not recorded has a refractive index: n ≧ 2.0 and an extinction coefficient: k <0.2. When a certain first dye and an optical constant at a wavelength of 630 to 640 nm when not recorded have a refractive index: n <2.0, an extinction coefficient: k <
0.02 and the optical constant during recording at a wavelength of 640 to 670 nm is n <2.0 during recording, and the extinction coefficient: k ≧ 0.
15 and a mixture with the second dye. In this case, it is necessary that the second dye has almost no absorption coefficient in a recording wavelength range (wavelength 630 to 640 nm), and the second dye undergoes a chemical change by light or heat due to light irradiation at the time of recording.
A material that increases the absorption in the 70 nm region is used.

The constitution of the recording medium that can be used in the present invention, the necessary material characteristics, and specific examples of the material will be described below. <Structure of Recording Medium> The basic structure of the recording medium of the present invention is a structure in which a first substrate and a second substrate are bonded together with an adhesive via a recording layer. The recording layer may be a single layer of an organic dye layer, or may be a laminate of an organic dye layer and a metal reflection layer to increase the reflectance. A layer between the recording layer and the substrate may be formed with an undercoat layer or a protective layer interposed therebetween, or a configuration in which they are laminated for improving the function may be used. The most commonly used structure is a first substrate / organic dye layer / metal reflective layer / protective layer / adhesive layer / second substrate structure.

<Substrate> The required characteristics of the substrate are that it must be transparent to the laser beam used only when recording / reproducing from the substrate side, and transparent when recording / reproducing from the recording layer side. No need. Therefore, in the present invention,
When only one layer of the substrate is used, the substrate need not be transparent, and when two substrates are used in a sandwich form, only the second substrate according to claim 1 may be transparent, The substrate may be transparent or opaque.

As the substrate material, for example, polyester,
Plastic such as acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, and polyimide, glass, ceramic, and metal can be used. In addition, 1
When only layers are used, or when two substrates are used in a sandwich shape, a guide groove and a guide pit for tracking and a preformat such as an address signal are formed on the surface of the first substrate described in the claims. There is a need.

<Intermediate Layer> Layers provided other than the substrate, the recording layer, the reflective layer, and the protective layer, including the undercoat layer and the like, are herein referred to as intermediate layers. This intermediate layer comprises (a) improved adhesion, (b) a barrier against water or gas, (c) improved storage stability of the recording layer, (d) improved reflectance, and (e) substrate from solvent. And protection of the recording layer, and (f) formation of project grooves, guide pits, preformats, and the like.

For the purpose of the above (a), a polymer material,
For example, various polymer substances such as an ionomer resin, a polyamide resin, a vinyl resin, a natural resin, a natural polymer, silicone, a liquid rubber, and a silane coupling agent can be used. For the purposes (b) and (c), an inorganic compound such as Si
O ₂ , MgF ₂ , SiO, TiO ₂ , ZnO, TiN,
Metals or metalloids, such as SiN, for example Zn, Cu, N
i, Cr, Ge, Se, Au, Ag, Al and the like can be used. For the purpose of (d), a metal such as Al or Ag or 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, a thermosetting resin, a thermoplastic resin, or the like can be used. The thickness of the thin film of the undercoat layer is suitably 0.01 to 30 μm, preferably 0.05 to 10 μm.

The substrate to be used must be transparent to the laser used only when recording / reproducing is performed from the substrate side. When recording / reproducing is performed from the recording layer side, the substrate does not need to be transparent. As a substrate material, for example, plastic such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, polyimide, glass, ceramic, or metal can be used. still,
Guide grooves and guide pits for tracking on the surface of the substrate
Further, a preformat such as an address signal may be formed.

<Recording Layer> The recording layer has a wavelength of 630 to 640.
The optical constant before recording in nm is a refractive index: n ≧ 2.
0, extinction coefficient: first dye with k <0.2, wavelength 63
The optical constant before recording at 0 to 640 nm is the refractive index:
n <2.0, extinction coefficient: k <0.02, and wavelength 64
The optical constant at the time of recording at 0 to 670 nm is n <
2.0, a mixture with the second dye satisfying an extinction coefficient: k ≧ 0.15.

As the first dye, a material having a high absorption coefficient such that the long wavelength end of the absorption spectrum of the film matches the recording wavelength (wavelength 630 to 640 nm) region is used.
As a result, it is possible to achieve both a high refractive index and a small absorption coefficient in the recording wavelength range, and it is possible to obtain a high degree of modulation in the recording wavelength range even after recording.

The second dye has a recording wavelength (wavelength 630 to 640).
nm) region should have almost no absorption coefficient,
And chemical change by light or heat by light irradiation at the time of recording,
A material that increases absorption in the wavelength range of 640 to 670 nm is used.

Examples of the primary dye which is the main component include polymethine dyes, naphthalocyanine dyes, phthalocyanine dyes, squarylium dyes, coroconium dyes, pyrylium dyes, naphthoquinone dyes, anthraquinone (indanthrene) dyes, xanthene dyes and triphenylmethane. And azulene-based, tetrahydrocholine-based, phenanthrene-based, and triphenothiazine-based dyes and metal complex compounds. 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, etc. 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.

The second dye has no absorption in the recording wavelength region when not recorded, and has a wavelength of 640 to 6 due to thermal decomposition, photolysis, thermochromism, photochromism, or the like during recording.
The above-described dyes and the like which increase the absorption coefficient at 70 nm can be used.

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. Is most preferred.

As the organic solvent, generally, alcohols such as methanol, echinol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N, N-dimethylacetamide and N, N-dimethylformamide, dimethyl sulfoxide and the like Sulfoxides, ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; and aliphatic halogenated carbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride, and trichloroethane. Or benzene, xylene,
Aromatic substances such as monochlorobenzene and 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 is 100 to 10 μm, preferably 200 to 2000 °.

<Metal reflective layer> The reflective layer can be made of a metal, a semi-metal, etc., which can provide a high reflectance by itself and are hardly corroded.
Examples of the material include Au, Ag, Cu, Cr, Ni, and Al, and Au and Al are preferable. These metals and metalloids may be used alone or as two or more alloys. Further, a dielectric multilayer film may be used. Examples of the film forming method include vapor deposition and sputtering, and the film thickness is 50 to 3000 °, preferably 100 to 1000 °.

<Protective layer / substrate surface hard coat layer> The protective layer or substrate surface hard coat layer (a) protects the recording layer (reflection / absorption layer) from scratches, dust, dirt, etc., (b)
It is used for the purpose of improving the storage stability of the recording layer (reflection / absorption layer) and (c) improving the reflectance.

For these purposes, the materials shown in the undercoat layer can be used. As the inorganic material, SiO, SiO ₂ or the like can also be used. As the organic material, polymethyl acrylate, polycarbonate, epoxy resin, polystyrene, polyester resin,
Vinyl resin, cellulose, aliphatic hydrocarbon resin, aromatic hydrocarbon resin, natural rubber, styrene-butadiene resin,
Thermosoftening and heat melting resins such as 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 30 μm.
10 to 10 μm is appropriate. In the present invention, the undercoat layer, the protective layer, and the substrate surface hard coat layer each include a stabilizer, a dispersant, a flame retardant, a lubricant, an antistatic agent, a surfactant, and a plasticizer, as in the case of the recording layer. Etc. can be contained.

[0036]

【Example】

[Embodiment: Simulation] The layer structure of the optical recording medium of the present invention and the simulation results by the recording / reproducing method are shown below. FIG. 1 shows the first dye film thickness of the first substrate / first dye layer (described below) / gold reflective layer / second substrate structure at the time of non-recording,
The relationship with the reflectance at a wavelength of 635 nm from the first substrate side is shown. The complex refractive index of the first dye layer at a wavelength of 635 nm is n
= 2.3-0.02i. Usually, the thickness of the organic dye layer is such that a second peak value of reflectance is obtained (about 1200).
It can be seen that a high reflectance is obtained when no recording is performed by selecting Å).

FIG. 2 similarly shows the relationship with the reflectance at a wavelength of 650 nm. The complex refractive index of the first dye layer at a wavelength of 650 nm is n = 2.0-0.007i. FIG. 3 similarly shows the relationship with the reflectance at a wavelength of 670 nm.
The complex refractive index of the first dye layer in nm is n = l. 7-0.
004i. In any case, it can be seen that a high reflectance can be similarly obtained at the same film thickness when recording is not performed. After recording, a large change in the optical constant is obtained at the wavelength of 635 nm, but a very large change cannot be expected at the wavelengths of 650 and 670 nm. As a result, reproduction is possible at the wavelength of 635 nm, but only a very small modulation degree is obtained at the wavelengths of 650 and 670 nm.

FIG. 4 shows the optical constants (n _{0) of} the first substrate / first dye layer + second dye / gold reflective layer / second dye of the second substrate structure.
= N + ki) and the relationship between the reflectance and the second peak value from the first substrate side at a wavelength of 670 nm when the thickness of the organic dye layer is changed. FIG. 4 shows the reflectance change when the optical constant before recording is changed by recording. The change indicates that a change in the absorption coefficient (extinction coefficient), that is, an increase in the absorption coefficient gives a larger change in reflectance than a change in the refractive index. When the absorption coefficient (extinction coefficient) is 0.02 or less when not recorded and 0.5 or more after recording, a sufficient degree of modulation can be obtained.

FIG. 5 shows the organic dye film thickness of the first substrate / first dye layer + second dye / gold reflective layer / second substrate structure after recording and the reflectance at a wavelength of 650 nm from the first substrate side. Shows the relationship. The complex refractive index of the first dye layer at a wavelength of 650 nm is n
= 1.6-0.2i. FIG. 6 also shows a wavelength 670
The relationship with the reflectance in nm is shown, and the complex refractive index of the first dye layer at a wavelength of 670 nm is n = 1.6-0.22i. In any case, the reflectance decreases after recording with the same film thickness, and it can be seen that a high reflectance can be obtained.

[Example: Media evaluation] Depth 1400
Å, on a 0.6 mm thick injection molded polycarbonate substrate (first substrate) having a guide groove with a half width of 0.35 μm and a track pitch of 1.0 μm, the structural formula is
Compound represented by the following formula (first dye / second dye = 2 /
1 (weight ratio) in a mixed solution of 1-methylcyclohexane and 2-methoxyethanol is applied by spinner coating so that the film thickness after drying becomes 1100 °, and reflection of 2000 ° of gold is performed by sputtering. A layer was provided to form a recording layer. Next, a smooth injection-molded polycarbonate substrate (second substrate) having a thickness of 0.6 mm was bonded using a hot melt adhesive to obtain a recording medium.

[0041]

Embedded image (First dye)

[0042]

Embedded image (second dye)

[Comparative Example] Here, a recording medium formed of only the first dye as the recording layer dye in the examples was used. This recording medium has an oscillation wavelength of 635 nm and a beam diameter of 1.0.
In this example, EF was used while tracking from the second substrate side in the embodiment and from the first substrate side in the comparative example using a semiconductor laser beam of μm.
M signal (linear velocity 3.0m / sec, shortest mark length 0.4μ
m) and record the same laser wavelength and wavelength 650,670
Reproduction was performed with continuous light of nm (reproduction power 0.7 mW), and the reproduction waveform was observed. The results are shown in [Table 1].

[0044]

[Table 1] However, modulation degree (%) = [(11T signal amplitude) / (unrecorded signal output)] × 100

[0045]

As is apparent from the above description, claim 1
According to the invention, recording is possible at 635 ± 5 nm,
It is possible to provide a recording material optical characteristic and a recording medium configuration of an optical information recording medium that can be reproduced in a wavelength range of 30 to 670 nm.

Further, according to the second and third aspects of the present invention, which are specific material structures for realizing the optical recording medium of the first aspect, it is possible to perform recording and reproduction with high quality signal characteristics.

Further, according to the invention of claim 4, it is possible to provide an effective recording / reproducing method using the optical recording medium of claims 1 to 3. As a result, with the optical information recording medium of the present invention, a red laser (635 ±
5 nm), an optical information recording medium capable of recording and reproducing, inexpensive, and capable of reproducing with a high degree of modulation even in a red laser (640 to 670 nm) wavelength region used in DVD-ROM drives for general reproduction. It became. Also,
INDUSTRIAL APPLICABILITY The optical recording medium and recording / reproducing method of the present invention can be effectively applied to a large-capacity write-once optical disc for data and a large-capacity write-once compact disc, and have a remarkable contribution to the technical fields such as a large-capacity optical card. There is.

[Brief description of the drawings]

FIG. 1 shows the relationship between the first dye film thickness and the reflectance from the first substrate side in the optical recording medium of the present invention having a first substrate / first dye layer / gold reflective layer / second substrate structure. It is a graph at the wavelength of 635 nm when not recording.

FIG. 2 is a graph similar to FIG. 1, showing a wavelength of 650 nm;
At the time of the last record.

FIG. 3 is a graph similar to FIG. 1, showing a wavelength of 670 nm;
At the time of the last record.

FIG. 4: First substrate / first dye layer + second dye / gold reflective layer /
In the optical recording medium of the present invention having the second substrate structure, the second peak value of the reflectance from the first substrate side when the optical constant (n, k) of the second dye and the thickness of the organic dye layer are changed. (Wavelength 670 nm).

FIG. 5: First substrate / first dye layer + second dye / gold reflective layer /
FIG. 9 is a graph showing the relationship between the organic dye film thickness and the reflectance from the first substrate side in the optical recording medium of the present invention having a second substrate structure, which is at a wavelength of 635 nm and is green.

FIG. 6 is a graph similar to FIG. 5, but showing a wavelength of 670 nm;
At the time of recording.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunobu Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo Stock inside Ricoh Company (72) Inventor Yasuhiro Higashi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside the company Ricoh

Claims (4)

[Claims] 1. An optical recording medium comprising a recording layer provided directly or via an undercoating layer on a first substrate, and a reflective layer, a protective layer or a second substrate provided thereon. A first dye having a refractive index: n ≧ 2.0 and an extinction coefficient: k <0.2 at 630 to 640 nm when unrecorded, and an unrecorded optical at a wavelength of 630 to 640 nm The constants are refractive index: n <2.0, extinction coefficient: k <0.02, and
An optical recording medium comprising, as main components, a second dye having an optical constant n <2.0 and an extinction coefficient: k≥0.15 at the time of recording at a wavelength of 640 to 670 nm. . 2. The method according to claim 1, wherein the second dye has a wavelength of 64.
An optical recording medium characterized in that an optical constant at the time of recording at 0 to 670 nm is a dye generated by a chemical change due to light and / or heat of a recording laser. 3. The method according to claim 1, wherein the second dye has a wavelength of 64.
An optical recording medium characterized in that the optical constant at the time of recording at 0 to 670 nm is a dye generated by chromism due to light and / or heat of a recording laser. 4. A recording / reproducing method using an optical recording medium according to claim 1, wherein recording is performed with a laser having a wavelength of 630 to 640 nm, and reproduction is performed with a laser having a wavelength of 630 to 640 nm and a laser having a wavelength of 640 to 670 nm. A recording / reproducing method characterized in that: