JP2007242166A - Optical recording medium - Google Patents

Abstract

Provided is a single-sided dual-layer recording / reproducing type optical recording medium capable of obtaining good recording signal characteristics from two information recording layers.
(1) An optical recording medium capable of recording and / or reproducing optically readable information, wherein at least a first recording layer made of an organic dye and a semi-transmissive first reflective layer are laminated. A first substrate and at least a second substrate on which a second recording layer composed of a second reflective layer and an organic dye is laminated so that both substrates are located outside via a transparent intermediate layer, An optical recording medium in which a difference in recording sensitivity in the plane of the second recording layer is suppressed by an in-plane difference in film thickness of the first reflective layer.
(2) fr / [(fmin + fmax) / 2] where the thickness of the first reflective layer is f, fr is the thickness at the radius r, fmax is the maximum thickness in the plane, and fmin is the minimum thickness in the plane. Is in the range of 0.97 to 1.03.
[Selection] Figure 16

Description

In addition to optical recording media such as read-only DVD-ROMs, recordable DVDs (DVD + RW, DVD + R, DVD-R, DVD-RW, DVD-RAM, etc.) have been put into practical use. These DVD + R, DVD + RW, etc. are positioned on the extension of conventional recordable CD-R, CD-RW (recordable compact disc) technology, and are recorded to ensure playback compatibility with playback-only DVDs. The density (track pitch, signal mark length) and substrate thickness are designed to meet the DVD conditions from the CD conditions.
For example, in the case of DVD + R, an information recording substrate having an optical recording layer provided by spin coating a dye on a substrate and a metal reflective layer behind it is formed in the same shape via a bonding material as in CD-R. A configuration in which the substrate is bonded is adopted. In this case, a dye material is used for the optical recording layer. CD-R is characterized by having a high reflectivity (65%) that satisfies the CD standard. In order to obtain a high reflectivity in the above configuration, the light absorption layer has a recording / reproducing light wavelength. This is because a specific complex refractive index needs to be satisfied, and the light absorption characteristics of the dye are suitable. The same applies to DVDs.

By the way, a read-only DVD has been proposed that has two information recording layers in order to increase the recording capacity. FIG. 1 is a sectional view showing the structure of a DVD having such an information recording layer. The board | substrate 1 and the board | substrate 2 are bonded together by pinching | interposing the transparent intermediate | middle layer 5 formed with the ultraviolet curing resin. A translucent layer 3 that is a first information recording layer on which an uneven recording mark is formed is formed on the inner surface of the substrate 1, and a second information recording layer is formed on the inner surface of the substrate 2. A reflective layer 4 is formed. The semi-transmissive layer 3 is formed using a dielectric film or a thin metal film, and the reflective layer 4 is formed from a metal film or the like.
Information recorded in each information recording layer is read by the effect of reflecting / interfering the reproduction laser beam. Since signals are read from the two information recording layers, a maximum storage capacity of about 8.5 GB can be obtained. Moreover, the thickness of the board | substrate 1 and the board | substrate 2 is 0.6 mm, respectively, and the thickness of the transparent intermediate | middle layer 5 is about 40 micrometers. The transflective layer 3 is formed so that the reflectance thereof is about 30%, and the laser light irradiated for reproducing the information of the second information recording layer is the total amount of light in the first information recording layer. After about 30% is reflected and attenuated, it is reflected by the reflective layer 4 which is the second information recording layer, further attenuated by the semi-transmissive layer 3, and then leaves the disc. The signal of each information recording layer can be reproduced by narrowing the laser light, which is the reproduction light, so that the focal point comes on the first or second information recording layer and detecting the reflected light. In the case of DVD, the laser beam wavelength used for recording / reproduction is about 650 nm.

However, the above recordable DVDs, that is, DVD + R, DVD-R, DVD-RW, DVD + RW, and the like have only one information recording layer that can be read from one side, and in order to obtain a larger storage capacity with these optical information media. It was necessary to be able to reproduce from both sides. On the other hand, since a single-sided dual-layer recording / reproducing type optical recording medium has two information recording layers, when a signal is recorded by irradiating a writing laser beam focused on the information recording layer at the back from the optical pickup, Since one information recording layer attenuates laser light, there is a problem that light absorption and light reflection necessary for recording of the second information recording layer cannot be achieved at the same time.
As a known technique corresponding to this problem, Patent Document 1 discloses that a semi-transmissive layer is mainly composed of any one of Au, Ag, and Cu, and Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, An optical recording medium made of an alloy containing at least one selected from Mg, Pd, Zr, Pt, Ta, W, Si, Zn, and In and using a dye recording layer is disclosed in Patent Document 2 as a plurality of It is a writable optical recording medium having an information recording layer, and since the material of the reflective film is AgC, high light transmittance, thermal conductivity and storage reliability can be ensured while suppressing an increase in material cost. A featured optical recording medium is disclosed.
However, in the case of having two or multiple information recording layers, in addition to the information recording layer, a protective layer, a semi-transmissive layer, and the like are stacked, so that the recording characteristics are in-plane due to variations in the film thickness distribution in the plane of each layer Will cause variations. In particular, if the recording sensitivity varies greatly within the plane, depending on the drive actually used, there is a possibility of deviating from the optimum recording power, and recording characteristics such as errors occur during reproduction. In particular, in the second information recording layer, when the uniformity of the thickness of the semi-transmissive layer is deteriorated, the variation in the amount of light irradiated in the surface becomes large, and there is a concern that the recording sensitivity is deteriorated in the surface.
For this problem, Patent Documents 1 and 2 have no description about the problem and its solution.

JP-A-2005-054097 Japanese Patent Laid-Open No. 2004-039146

  An object of the present invention is to provide a single-sided dual-layer recording / reproducing type optical recording medium that solves the above-mentioned problems and that can obtain good recording signal characteristics from two information recording layers.

The above problems are solved by the following inventions 1) to 11).
1) An optical recording medium capable of recording and / or reproducing optically readable information, and at least a first substrate on which a first recording layer made of an organic dye and a semi-transmissive first reflective layer are laminated At least the second reflective layer and the second substrate on which the second recording layer made of an organic dye is laminated are provided so that both substrates are outside through the transparent intermediate layer. An optical recording medium characterized in that a difference in recording sensitivity in a plane of the second recording layer is suppressed by an in-plane difference in film thickness.
2) The optical recording medium according to 1), wherein a second reflective layer, a first protective layer, a second recording layer, and a second protective layer are laminated on the second substrate.
3) The optical recording medium according to 1), wherein a second reflective layer, a second recording layer, and a second protective layer are laminated on the second substrate.
4) fr / [(fmin + fmax) / 2] where f is the film thickness at the radius r, fmax is the maximum film thickness in the plane, and fmin is the minimum film thickness in the plane. The optical recording medium according to any one of 1) to 3), wherein the optical recording medium is in a range of 0.97 to 1.03.
5) The second recording layer thickness is d, the second protective layer thickness is e, dr and er are the thicknesses at the radius r, dmax and emax are the maximum in-plane thicknesses, and dmin and emin are the in-plane thicknesses. Any one of 1) to 4), wherein dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] is in the range of 0.96 to 1.04 as the minimum film thickness. An optical recording medium according to 1.
6) The thickness of the second recording layer is d, the thickness of the second protective layer is e, the thickness of the first reflective layer is f, dr, er, and fr are the thicknesses at the radius r, and dmax, emax, and fmax are surfaces. {Dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2]} × {fr / [(fmin + fmax) / 2]} is in the range of 0.975 to 1.025. The optical recording medium according to any one of 1) to 5).
7) The optical recording medium according to any one of 1) to 6), wherein the thickness of the first reflective layer is 7 to 10 nm.
8) The optical recording medium according to any one of 1) to 7), wherein the light transmittance of the first reflective layer is 30 to 60% and the light reflectance is 15 to 35%.
9) The optical recording medium according to 8), wherein an auxiliary layer is provided adjacent to the first reflective layer, and the auxiliary layer is made of a metal or semimetal oxide or nitride.
10) The optical recording medium according to 8), wherein the first reflective layer is composed of a mixture of at least two selected from the group consisting of a metal or a semimetal, an oxide, and a nitride.
11) It has an auxiliary layer adjacent to the first reflective layer, the first reflective layer is made of a single metal or metalloid, and the auxiliary layer is made of a metal or metalloid oxide or nitride. 8) The optical recording medium as described in 8).

Hereinafter, the present invention will be described in detail.
Examples of the layer structure of the optical recording medium of the present invention are shown in FIGS.
FIG. 2: A first substrate 21 having a first information layer in which a first recording layer 23 made of an organic dye and a semi-transmissive first reflective layer 24 are sequentially laminated on a surface having a light guide groove, and a light guide groove A second information layer in which a second reflective layer 29, a first protective layer (inorganic protective layer) 28, a second recording layer 27 made of an organic dye, and a second protective layer (inorganic protective layer) 26 are sequentially laminated on the surface thereof. The first substrate and the second substrate 22 are bonded to each other with the recording layer facing inward so that the laminated films face each other through the transparent intermediate layer 25, and irradiated with laser light from the first substrate side. An optical recording medium for recording / reproducing signal information on / from a recording layer.
FIG. 3: A first substrate 21 having a first information layer in which a first recording layer 23 made of an organic dye and a semi-transmissive first reflective layer 24 are sequentially laminated on a surface having a light guide groove, and a light guide groove A transparent intermediate layer comprising a second reflective layer 29, a second recording layer 27 made of an organic dye, and a second substrate 22 having a second information layer in which a second protective layer (inorganic protective layer) 26 is sequentially laminated on the surface of the transparent intermediate layer. 25, the recording layer is bonded so that the laminated films face each other, and laser light is irradiated from the first substrate side, whereby signal information is recorded on and reproduced from the first and second recording layers. Optical recording medium to perform.

In the above configuration, the semi-transmissive first reflective layer is formed of an alloy, formed of a mixture of an alloy and a metal or metalloid oxide and / or nitride, or a metal or metalloid simple substance or oxide. By forming with a mixture of at least two selected from nitrides, an optical recording medium with few defects and high reliability can be obtained.
In the normal case, the semi-transmissive first reflective layer preferably has a light transmittance of 30 to 60% and a light reflectance of 15 to 35% with respect to the recording / reproducing laser beam. If the light transmittance is less than 30%, the light transmittance may be too low to make recording and reproduction of the second recording layer difficult. If the light reflectance is less than 15%, the light reflectance is too low and the first recording is difficult. Since recording / reproducing of a layer may be difficult, good single-sided / bi-layer recording / reproducing may be difficult. In addition, the light transmittance, the light reflectance, and the light absorptance are 100% in total, but the light transmittance and the light reflectance are contradictory, and the light reflectance decreases as the light transmittance increases. Since the light transmittance decreases as the light reflectance increases, the upper limit of the light transmittance is preferably 60% and the upper limit of the light reflectance is preferably 35%. In order to make the above numerical range, the film thickness may be selected in accordance with a material appropriately selected from the materials described later.
The film thickness of the first reflective layer is usually 5 to 30 nm. If it is thinner than 5 nm, it is not preferable because the transmittance increases and it becomes difficult to prevent deterioration of the characteristics of the first recording layer, and if it exceeds 30 nm, it is difficult to satisfy the above-mentioned light transmittance. A preferable range is 7 to 10 nm, and more preferably 8 to 9 nm.

Here, in the single-sided dual-layer recording / reproducing type optical recording medium having the layer structure shown in FIG. 2, the recording power, asymmetry, and jitter of the second recording layer when the thickness of the first reflective layer is changed (changed). The relationship is shown in FIGS. This is a result of reproducing evaluation at a linear velocity of 3.83 m / s after recording a DVD (8-16) signal at a wavelength of 657 nm, NA: 0.65, and a linear velocity of 30.64 m / s. The specific layer configuration of each layer is the same as that of Example 1 described later, except for the first reflective layer thickness.
4 and 5, when the thickness of the first reflective layer is varied in the range of 9.1 to 9.7 nm, the asymmetry at a fixed recording power is about 10%, and Po (recording power at which jitter is optimized) is about. It can be seen that the change is 2 mW.
On the other hand, FIG. 6 and FIG. 7 show the relationship between the recording power, asymmetry, and jitter when recording / reproduction of the first recording layer is performed as in the case of the second recording layer.
From FIG. 6 and FIG. 7, regarding the first recording layer, the sensitivity difference hardly changes compared to the second recording layer even when the thickness of the first reflective layer is varied in the range of 9.1 to 9.7 nm (fixed). It can be seen that the asymmetry difference in recording power is about 2-3%.
From the above results, it was confirmed that the sensitivity of only the second recording layer can be changed by changing the thickness of the first reflective layer. By applying this knowledge, the sensitivity of only the second recording layer can be controlled by changing the light transmittance by changing the film thickness of the first reflective layer.
However, fr / [(fmin + fmax) / 2] is obtained, where f is the film thickness at the radius r, fmax is the maximum film thickness in the plane, and fmin is the minimum film thickness in the plane. Therefore, it is necessary to control the film thickness of the first reflective layer so that it falls within the range of 0.97 to 1.03 (1 ± 0.03). Outside this range, the variation in the thickness of the first reflective layer becomes large and a difference in recording sensitivity of the first recording layer occurs in the surface, which adversely affects recording quality.

Next, in-plane recording power in the optical recording medium (the material and film thickness of each layer are the same as those in FIG. 2) that is not affected by the first recording layer and the first reflective layer shown in FIG. The relationship between asymmetry and jitter is shown in FIGS. The inner circumference, the middle circumference, and the outer circumference in the figure are positions with radii of 25 mm, 40 mm, and 57 mm, respectively.
From FIG. 9, it can be seen that a maximum difference of about 10% (medium asymmetry-inner circumference asymmetry) occurs in the plane for asymmetry at a fixed recording power.
In addition, asymmetry at a fixed recording power decreases as the thickness of the second recording layer and the second protective layer increases. This is because the recording power required for pit formation increases as the recording layer thickness or the protective layer thickness increases. Therefore, the second recording layer thickness is d, the second protective layer thickness is e, dr and er are the thicknesses at the radius r, dmax and emax are the maximum in-plane thicknesses, and dmin and emin are the in-plane thicknesses. The relationship between dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] and the asymmetry of the second recording layer when the minimum film thickness was obtained was examined. The results are shown in FIG.
From FIG. 11, if dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] is in the range of 0.96 to 1.04 (1 ± 0.04), as described above, It can be seen that the asymmetry difference between the inside and outside of the second recording layer can be eliminated and the sensitivity difference can be eliminated by the thickness of one reflective layer.
Furthermore, as shown in FIG. 12, {dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2]} × {fr / [(fmin + fmax) / 2]} is 0.975-1. If it is in the range of 025 (1 ± 0.025), the asymmetry difference is within 10%, and there is no problem in reproduction after recording with an actually used drive, and sufficient characteristics can be obtained. Furthermore, if it is in the range of 0.985 to 1.015 (1 ± 0.015), the asymmetry difference is preferably within 5%.

<About the substrates (first and second substrates)>
The substrate must be transparent to the laser used when performing recording / reproduction from the substrate side, but need not be transparent when performing recording / reproduction from the recording layer side. As the substrate material, for example, a polyester resin, an acrylic resin, a polyamide resin, a polycarbonate resin, a polyolefin resin, a phenol resin, an epoxy resin, a polyimide resin such as a polyimide resin, glass, ceramic, metal, or the like can be used. A tracking guide groove or guide pit and a preformat such as an address signal may be formed on the surface of the substrate.
Further, the groove shapes formed in the first substrate and the second substrate are not the same. In the case of 4.7 GB, 0.74 μm pitch DVD + R, and DVD-R, the groove shape of the first substrate is preferably groove depth: 1000 to 2000 mm and groove width (bottom width): 0.2 to 0.3 μm. In the case of spin coating, since the groove tends to be filled with a dye, the interface shape between the first recording layer and the first reflective layer is determined by this filling amount and the substrate groove shape, so that the interface reflection is reduced. The above range is suitable for use.
On the other hand, the groove shape of the second substrate is preferably groove depth: 200 to 600 mm and groove width: 0.2 to 0.4 μm. Since the interface shape between the second recording layer and the second reflective layer is determined by the substrate groove shape, the above range is suitable for utilizing the interface reflection.
If the groove depth is deeper than the groove shape range in both the first substrate and the second substrate, the reflectivity is likely to decrease. Further, if the groove depth is shallower than the groove shape range or the groove width is shifted, the shape of the formed recording mark becomes difficult to be uniform, and jitter tends to increase.

<About the recording layers (first and second recording layers)>
The recording layer causes an optical change due to the irradiation of the laser beam and records information by the change, and a material containing an organic dye as a main component is used as the material. Here, the main component means that it contains a sufficient amount of an organic dye necessary for recording and reproduction, but usually only an organic dye is used except for a small amount of additives that are appropriately added as necessary.
Examples of organic dyes include azo, formazan, dipyrromethene, (poly) methine, naphthalocyanine, phthalocyanine, tetraazaporphyrin, squarylium, croconium, pyrylium, naphthoquinone, anthraquinone (in) (Dansylene), xanthene, triphenylmethane, azulene, tetrahydrocholine, phenanthrene, triphenothiazine dyes, or metal complexes thereof. Among these, azo (metal chelate) dye, formazan (metal chelate) dye, squarylium (metal chelate) dye, dipyrromethene (metal chelate) dye, trimethine cyanine dye, and tetraazaporphyrin dye are preferable.
The above dyes preferably have a decomposition start temperature of 100 to 360 ° C., particularly 100 to 350 ° C. as thermal decomposition characteristics. If the decomposition start temperature exceeds 360 ° C., pit formation at the time of recording is not performed well, and jitter characteristics deteriorate. Further, if the temperature is lower than 100 ° C., the storage stability of the disk deteriorates.

For the purpose of improving optical characteristics, recording sensitivity, signal characteristics, etc., the above dyes may be mixed with other organic dyes, metals, metal compounds, or a layer composed of a dye layer and other organic dyes, metals, metal compounds. May be laminated.
Examples of such metals and metal compounds include In, Te, Bi, Se, Sb, Ge, Sn, Al, Be, TeO ₂ , SnO, As, Cd, and the like. It can be used by laminating.
Furthermore, various materials such as ionomer resin, polyamide resin, vinyl resin, natural polymer, silicone, liquid rubber, or a silane coupling agent may be dispersed and mixed in the dye, For the purpose of improving characteristics, 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 can be mixed.

The recording layer can be formed by ordinary means such as vapor deposition, sputtering, CVD, and solvent coating. When the coating method is used, the above-described dye or the like can be dissolved in an organic solvent, and the coating can be performed by a conventional coating method such as spraying, roller coating, dipping, or spin coating. Organic solvents generally used include alcohols such as methanol, ethanol and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide Ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane Aromatics such as benzene, xylene, monochlorobenzene and dichlorobenzene; cellosolves such as methoxyethanol and ethoxyethanol; hexane and penta , Cyclohexane, and hydrocarbons such as methylcyclohexane.
A preferable dye film thickness is 40 to 1000 mm in the first recording layer (groove), and 600 to 3000 mm in the second recording layer (inter-groove). This is because if the dye film thickness is thinner than this range, it is difficult to obtain the degree of signal modulation (contrast). On the contrary, if the dye film thickness is thick, the mark shapes are difficult to align and jitter is likely to increase.

<Reflection layers (first and second reflection layers)>
As the first reflective layer material, a substance having a high reflectance with respect to the wavelength of the laser beam is preferable. Examples thereof include Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, and Pt. , Ta, W, Si, Zn, In, at least one kind of metal and metalloid can be mentioned. Among them, one of Au, Ag, and Cu is the main component, and Au, Ag, Cu, An alloy in which 0.1 to 10% by weight of at least one selected from Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, Pt, Ta, W, Si, Zn, and In is added is preferable. In particular, In is preferable (since it is an alloy, naturally, combinations of Au and Au, Ag and Ag, and Cu and Cu are excluded). By adding 0.1% by weight or more, the crystal grains become fine and a thin film having excellent corrosion resistance is obtained. However, adding more than 10% by weight is not preferable because the reflectance decreases.
The base material is most preferably Ag having a high sputter rate, and the additive is particularly preferably Au, Cu, Mg, or In having a small refractive index n and a large absorption coefficient k.
Ag has the smallest n among all elements and has the highest light utilization efficiency. Therefore, it is particularly preferable that the total amount of additives is 5% by weight or less in order not to impair the characteristics.

Examples of the metal or metalloid oxide used in the first reflective layer include aluminum oxide, titanium oxide, chromium oxide, magnesium oxide, zirconium oxide, tantalum oxide, silicon oxide, calcium oxide, tin oxide, indium oxide, and indium tin oxide. Etc. Similarly, examples of the metal or metalloid nitride include aluminum nitride, titanium nitride, silicon nitride, and zirconium nitride.
In the case where an alloy mainly composed of Au, Ag, or Cu is used as the material of the first reflective layer, Au, Ag, Cu, Al, Ti, V, Using a target added with 1 to 10% by weight of at least one selected from Cr, Ni, Nd, Mg, Pd, Zr, Pt, Ta, W, Si, Zn, and In, a pressure of 0.01 Pa to several Pa An alloy reflective layer can be formed by sputtering at a power of 1 to ²⁰ W / cm ^{2 in} an Ar atmosphere.
In addition, as the material for the first reflective layer, a mixture of the above alloy and a metal or metalloid oxide and / or nitride is used, or a metal or metalloid simple substance, oxide or nitride is selected. In the case of using at least two kinds of the mixture, it can be formed by sputtering using a target in which each material is mixed in a predetermined ratio. Moreover, a mixture thin film can also be formed by simultaneously discharging and sputtering a plurality of targets on which each material of the mixture is set.

The first reflective layer may have a laminated structure by providing an auxiliary layer. As the auxiliary layer material, a metal or metalloid oxide or nitride can be used.
When laminating the first reflective layer made of metal or metalloid and the auxiliary layer made of metal or metalloid oxide or nitride, first, Au, Ag, Cu, Al, Ti, Cr, Mg, Ta, A film made of any of W, Si, Zr, etc. is formed by sputtering, followed by aluminum oxide, titanium oxide, chromium oxide, magnesium oxide, zirconium oxide, tantalum oxide, silicon oxide, calcium oxide, tin oxide, indium oxide, etc. A laminated film may be formed by sputtering using a target consisting of at least one of the above, and Al, Ti, Cr, Mg, Zr, Ta, Si, Ca, Oxidized by reactive sputtering using Ar, O ₂ mixed gas, targeting at least one of Sn, In, ITO, etc. A film may be formed.
Similarly, a nitride film can be laminated on the sputtered film made of the above metal or metalloid with at least one of aluminum nitride, titanium nitride, silicon nitride, zirconium nitride and the like as targets, and Al, Ti, A nitride film can also be formed by reactive sputtering using Ar and N ₂ mixed gas with at least one of Si, Zr and the like as a target.

Further, when an auxiliary layer similar to the above is laminated on the first reflective layer made of an alloy mainly composed of any one of Au, Ag, and Cu, the reflective layer made of the alloy is first formed by sputtering. Subsequently, an auxiliary layer may be laminated in the same manner as described above.
The same material as described above is basically used for the second reflective layer, but an alloy is preferable in order to obtain an optical recording medium with few defects and high reliability.
The preferable first reflective layer thickness is 7 to 10 nm as described above. Moreover, the preferable 2nd reflection layer film thickness is 50-5000cm, More preferably, it is 100-3000cm. If the thickness is less than 50 mm, sufficient wobble characteristics are difficult to obtain. If the thickness is more than 5000 mm, the jitter characteristics deteriorate.

<Inorganic protective layer (first and second protective layers)>
The first protective layer is provided mainly for the purpose of forming guide grooves, guide pits, and preformats, and a mixture of SnO ₂ , In ₂ O ₃ , SiO ₂ or the like is preferable as a material.
Further, the second protective layer is provided for the purpose of chemically and physically protecting the second recording layer made of the dye with respect to the material of the transparent intermediate layer, and the material is SiO, SiO ₂ , MgF ₂ , SnO _2. , ZnS, ZnS—SiO _{2 and} other inorganic materials having high light transmittance are preferable.
The thickness of the protective layer is preferably in the range of 100 to 2000 mm for both the first and second protective layers. If it is thinner than this range, it is difficult to obtain sufficient wobble characteristics, and if it is thicker than this range, the jitter characteristics deteriorate.

<About transparent intermediate layer>
The transparent intermediate layer is preferably used as an adhesive layer, and as the material thereof, an existing acrylate-based, epoxy-based, urethane-based ultraviolet curable adhesive or thermosetting adhesive can be used. Furthermore, the method of bonding with a transparent sheet may be used.
The film thickness is preferably in the range of 45 to 70 μm. Outside this range, it becomes difficult to reproduce the signal of each information recording layer by narrowing the laser beam, which is the reproduction light, so that the focal point comes on the first or second information recording layer and detecting the reflected light. .

  It was possible to provide a single-sided dual-layer recording / reproducing type optical recording medium in which a good difference in in-plane sensitivity was obtained from two information recording layers and good recording signal characteristics were obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited by these Examples. In the examples, “parts” represents parts by weight.

<Examples 1-2 and Comparative Examples 1-3>
On the surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.60 mm, a second substrate having a guide groove uneven pattern having a groove depth of about 34 nm, a groove width of about 0.255 μm, and a track pitch of 0.74 μm is prepared. As the sputtering gas, Ag was provided to a thickness of about 120 nm by sputtering to form a second reflective layer. Sputtering was performed using a sputtering machine Big Sprinter manufactured by Unaxis, with an Ar flow rate of 20 sccm and a sputtering power of 3.5 kW, and the sputtering rate was 30 nm / s.
Next, a mixture of SnO ₂ , In ₂ O ₃ , and SiO ₂ [composition ratio, 69.9: 16: 14.1 (wt%)] is formed as a first protective layer on the second reflective layer by 15 nm, 2 As a recording layer, a squarylium dye compound of the following [Chemical Formula 1] was spin-coated so that the absorbance was 1.04.
Furthermore, ZnS—SiO ₂ was provided to a thickness of about 140 nm by sputtering using Ar as a sputtering gas to form a second protective layer.
FIG. 13 shows dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] as the second recording layer thickness d and the second protective layer thickness e at this time.

On the other hand, a first substrate having a guide groove uneven pattern having a groove depth of about 167 nm, a groove width of about 0.245 μm, and a track pitch of 0.74 μm is prepared on the surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.58 mm. The squarylium dye of the following [Chemical Formula 1] and the formazan chelate dye of the following [Chemical Formula 2] were mixed at a ratio of 7: 3, and a coating solution dissolved in 2,2,3,3-tetrafluoropropanol was spin-coated. A first recording layer was provided. This recording layer had a maximum absorption wavelength of 609 nm and an absorbance (Abs) at the maximum absorption wavelength of 0.65. At this time, the thickness of the recording layer in the groove portion was 60 nm.
Further, a first reflective layer was formed on the first recording layer by sputtering using Ar as a sputtering gas and using a sputtering target of AgIn alloy (Ag 99.97, In 0.03% by weight).
Next, the first substrate and the second substrate having been formed into a film were bonded with an ultraviolet curable adhesive (manufactured by Nippon Kayaku Co., Ltd .: KARAYAD DVD003) to obtain an optical recording medium having a layer structure shown in FIG.
The in-plane distribution of the first reflective layer thickness f at this time = fr / [(fmin + fmax) / 2] is shown in FIG. 14, and the second recording layer thickness d, the second protective layer thickness e, and the first reflection. FIG. 15 shows {dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2]} × {fr / [(fmin + fmax) / 2]} as the layer thickness f.

The optical recording media of Examples 1-2 and Comparative Examples 1-3 were evaluated.
Each of the radial positions (23, 25, 40, 45, and 50) shown in FIG. 16 was obtained using a DVD evaluation apparatus (DDU1000 manufactured by Pulstec Corporation, wavelength: 657 nm, NA: 0.65) at a linear velocity of 22.98 m / s. 55, 58 mm), a DVD (8-16) signal is recorded, reproduced and evaluated at a linear velocity of 3.83 m / s, and an asymmetry difference (Δ asymmetry) = asymmetry (Pw = 36 mW) max) -Asymmetry (min).
The results are shown in FIG. 16 and Table 1. In Examples 1 and 2, Δ asymmetry is 0.04 or less, and it can be seen that it is remarkably superior to Comparative Examples 1 to 3 of 0.13 or more.

Sectional drawing which shows the structure of DVD which has a two-layer information recording layer. The figure which shows the layer structural example of the optical recording medium of this invention. The figure which shows the other layer structural example of the optical recording medium of this invention. The figure which shows the relationship between the recording power of the 2nd recording layer when the thickness of the 1st reflection layer is shaken, and asymmetry. The figure which shows the relationship between the recording power of a 2nd recording layer when a 1st reflective layer film thickness is shaken, and jitter. The figure which shows the relationship between the recording power and asymmetry of the 1st recording layer when the 1st reflection layer film thickness is shaken. The figure which shows the relationship between the recording power of a 1st recording layer when a 1st reflection layer film thickness is shaken, and a jitter. The figure which shows the optical recording medium of a structure which is not influenced by the 1st recording layer and the 1st reflective layer. FIG. 9 is a diagram showing a relationship between in-plane recording power and asymmetry in the optical recording medium having the layer configuration shown in FIG. 8. FIG. 9 is a diagram showing a relationship between in-plane recording power and jitter in the optical recording medium having the layer configuration shown in FIG. 8. FIG. 9 is a diagram showing the relationship between dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] and asymmetry of the second recording layer in the optical recording medium having the layer configuration shown in FIG. In the optical recording medium having the layer structure shown in FIG. 8, {dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2]} × {fr / [(fmin + fmax) / 2]} The figure which shows the relationship of the asymmetry of a layer. The figure which shows dr / [(dmin + dmax) / 2] * er / [(emin + emax) / 2] of the optical recording medium of an Example and a comparative example. The figure which shows fr / [(fmin + fmax) / 2] of the optical recording medium of an Example and a comparative example. The figure which shows {dr / [(dmin + dmax) / 2] * er / [(emin + emax) / 2]} * {fr / [(fmin + fmax) / 2]} of the optical recording medium of an Example and a comparative example. The figure which shows the asymmetry for every radial position of the optical recording medium of an Example and a comparative example.

Claims (11)

  An optical recording medium capable of recording and / or reproducing optically readable information, comprising at least a first substrate on which a first recording layer made of an organic dye and a semi-transmissive first reflective layer are laminated, and at least The second reflective layer and the second substrate on which the second recording layer made of an organic dye is laminated are provided so that both substrates are located outside via the transparent intermediate layer, and the thickness of the first reflective layer An optical recording medium characterized in that a difference in recording sensitivity in the plane of the second recording layer is suppressed by the difference in plane.   2. The optical recording medium according to claim 1, wherein a second reflective layer, a first protective layer, a second recording layer, and a second protective layer are laminated on the second substrate.   2. The optical recording medium according to claim 1, wherein a second reflective layer, a second recording layer, and a second protective layer are laminated on the second substrate.   Fr / [(fmin + fmax) / 2] is 0, where f is the thickness at the radius r, fmax is the maximum thickness in the plane, and fmin is the minimum thickness in the plane. The optical recording medium according to any one of claims 1 to 3, wherein the optical recording medium is in a range of .97 to 1.03.   The film thickness of the second recording layer is d, the film thickness of the second protective layer is e, dr and er are the film thickness at the radius r, dmax and emax are the maximum film thickness in the plane, and dmin and emin are the minimum film in the plane. 5. The thickness of dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2] is in the range of 0.96 to 1.04, according to claim 1. Optical recording media.   The film thickness of the second recording layer is d, the film thickness of the second protective layer is e, the film thickness of the first reflective layer is f, dr, er, and fr are the film thicknesses at the radius r, and dmax, emax, and fmax are in-plane. {Dr / [(dmin + dmax) / 2] × er / [(emin + emax) / 2]} × {fr / [(fmin + fmax) / 2] Is in the range of 0.975 to 1.025. 6. The optical recording medium according to claim 1, wherein:   The optical recording medium according to claim 1, wherein the first reflective layer has a thickness of 7 to 10 nm.   8. The optical recording medium according to claim 1, wherein the first reflective layer has a light transmittance of 30 to 60% and a light reflectance of 15 to 35%.   9. The optical recording medium according to claim 8, further comprising an auxiliary layer adjacent to the first reflective layer, wherein the auxiliary layer is made of an oxide or nitride of a metal or a metalloid.   9. The optical recording medium according to claim 8, wherein the first reflective layer is made of a mixture of at least two selected from a simple substance of metal or metalloid, an oxide, and a nitride. An auxiliary layer is provided adjacent to the first reflective layer, wherein the first reflective layer is made of a single metal or metalloid, and the auxiliary layer is made of a metal or metalloid oxide or nitride. Item 9. The optical recording medium according to Item 8.