JP2007080389A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium of a single-sided recording and reproducing type having two sets of recording structural bodies and capable of obtaining satisfactory recording signal characteristics also from a second information recording layer. <P>SOLUTION: In the optical recording medium, a first recording structural body formed on a first substrate and a second recording structural body formed on a second substrate are layered via an intermediate layer and recording/reproduction is performed respectively in the first and the second recording structural bodies by irradiation with a laser beam from the first recording structural body side. The surface of the second substrate has a wobbled projecting part, the second recording structural body has at least a reflection layer, an upper protective layer, a second dye recording layer and a lower protective layer in this order and the upper protective layer comprises any one of an oxide, a nitride, a sulfide and a carbide or the mixture thereof of an element which is not identical with an element of metal or semi-metal which constitutes the reflection layer and has 1 to 70 nm film thickness. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an optical recording medium capable of recording and reproducing information and recording information by causing optical changes such as transmittance and reflectance in a recording layer by irradiating a light beam.
In particular, it is applied to a dual-layer DVD (Digital Video Disc or Digital Versatile Disc) having two write-once information recording layers.

Patent Document 1 discloses an invention in which two information recording layers made of organic dyes can be written from one side of an optical information medium during recording, and two information recording layers are read from one side of the optical information medium during reproduction. Has been proposed. However, the present invention is limited to a configuration in which two types of substrates, a conventional substrate surface incidence recording configuration and a recording film surface incidence configuration, are attached, and the problem relating to light absorption and reflection of the second information recording layer described later cannot be solved.
Further, Patent Document 2 describes a laminated structure of a metal reflective layer, a dye-containing recording layer, and a protective layer, and there is a description that SiO and SiO ₂ can be used as an inorganic protective layer, but this is specifically implemented. There is no description about the manufacturing conditions and optically necessary characteristics for the purpose.
Japanese Patent Application No. 2004-133993, which is the prior application of the present applicant, discloses an optical recording medium having a second recording layer, a metal reflective layer, a metal oxide layer constituting the reflective layer, a dye recording layer, and a protective layer. However, the purpose is to improve the wettability of the pigment and to improve the coating unevenness.
Further, Patent Document 3 discloses an optical recording medium having a structure in which a second barrier layer is provided between an intermediate layer (adhesive layer) and a second light absorption layer, and Au is used as a material for the second barrier layer. Only the examples used are described. However, when the metal is used in this way, the absorption coefficient k of the complex refractive index n-ik is increased, so that the object of the present invention can be achieved as can be seen from a comparative example of the present invention described later. I can't. Further, in this document, as described in [0039], “the material of the second barrier layer is preferably that k is 0.1 or more”, the absorption coefficient k as in the present invention is set to 0.00. The technical idea of keeping it below 05 is not disclosed.

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, DVD + R, like CD-R, spin-coats cyanine and azo metal chelate dyes on a substrate to provide an optical recording layer, and an information recording substrate provided with a metal reflective layer behind it. The structure of bonding with the board | substrate of the same shape through is employ | adopted. In this case, a dye material is used for the optical recording layer. One feature of CD-R is that it has a high reflectivity (65%) that satisfies the CD standard, but in order to obtain a high reflectivity by 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 which 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 two information recording layers. The first substrate 11 and the second substrate 12 are bonded together by sandwiching a transparent intermediate layer 15 formed of an ultraviolet curable resin. A translucent layer 13 as a first information recording layer is formed on the inner surface of the first substrate 11, and a reflective layer as a second information recording layer is formed on the inner surface of the second substrate 12. 14 is formed. The translucent layer 13 is made of a dielectric film or a thin metal film, and the reflective layer 14 is made of a metal film or the like. An uneven recording mark is formed on the semi-transparent layer 13, and the recording signal 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 1st board | substrate 11 and the 2nd board | substrate 12 is each 0.6 mm, and the thickness of the transparent intermediate | middle layer 15 is about 50 micrometers. The first information recording layer is formed so that the reflectance thereof is about 30%, and the laser light irradiated to reproduce the second information recording layer is the total amount of light in the first information recording layer. After about 30% of the light is reflected and attenuated, it is reflected by the second information recording layer, further attenuated by the first information recording layer, and then leaves the disc. The signal of each information recording layer is reproduced by detecting the reflected light by narrowing the laser light, which is the reproduction light, so that the focal point is located on the first information recording layer or the second information recording layer, respectively. be able to. In the case of DVD, the laser beam wavelength used for recording / reproduction is about 650 nm.

Japanese Patent Laid-Open No. 11-066662 Japanese Patent Laid-Open No. 10-340483 JP 2000-31384 A

The recordable DVDs described above, ie, DVD + R, DVD-R, DVD-RW, DVD + RW, etc. 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. Therefore, it was necessary to have a configuration for reproducing from both sides. The reason for this is that when a single-sided dual-layer recording / reproducing type optical information medium records a signal by irradiating a writing laser beam while focusing on the information recording layer (second information recording layer) in the back from the optical pickup. This is because, since the first information recording layer attenuates the laser beam, there is a problem that light absorption and light reflection necessary for recording of the second information recording layer cannot be achieved.
A more detailed problem is that, in an optical recording medium having a recording layer made of a dye produced by an ordinary spin coating method, the dye film thickness of the concave portion of the substrate is thicker than the convex portion, and recording is performed in the concave portion that is a recording track. In some cases, the heat insulating effect of the convex portion suppresses the spread of the pits to the adjacent track, but it has a convex portion wobbled on the second substrate surface as in the present invention (and has address information as necessary). ), The second recording structure formed on the second substrate has at least a reflective layer, an upper protective layer, a second dye recording layer, and a lower protective layer in this order, and the convex portion of the second substrate is used as a recording track. When recording information, in order to obtain sufficient signal amplitude and reflectivity, it is necessary to increase the average film thickness as compared with the case of recording in a normal recess. Further, the dye recording layer thickness formed on the convex portion is almost the same as or slightly thinner than the dye recording layer thickness formed on the concave portion between the tracks. Heat generation during heating and dye decomposition spreads to adjacent tracks, and a phenomenon is observed in which jitter increases and wobble signal quality deteriorates.
An object of the present invention is to provide a single-sided recording / reproducing type optical recording medium which can solve these problems and obtain good recording signal characteristics from a second information recording layer.

The above problems are solved by the following inventions 1) to 9).
1) The first recording structure formed on the first substrate and the second recording structure formed on the second substrate are laminated via an intermediate layer, and the laser from the first recording structure side In an optical recording medium in which recording and reproduction are respectively performed on the first and second recording structures by light irradiation, the second recording structure has at least a reflective layer having a wobbled convex portion on the second substrate surface. , An upper protective layer, a second dye recording layer, and a lower protective layer in this order, and the upper protective layer is an oxide, nitride, sulfide of an element that is not the same as the metal or metalloid element forming the reflective layer, An optical recording medium comprising any one of carbides or a mixture thereof and having a thickness of 1 to 70 nm.
2) The optical recording medium according to 1), wherein the upper protective layer is thinner than the dye recording layer.
3) The optical recording medium according to 1) or 2), wherein the refractive index of the upper protective layer is 1.5 to 3.
4) The optical recording medium according to any one of 1) to 3), wherein the upper protective layer contains a transparent conductive oxide.
5) The transparent conductive oxide is at least one of indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, and InGaO ₃ (ZnO) m (m is a natural number) 4) The optical recording medium described.
6) The optical recording medium according to any one of 1) to 5), wherein the lower protective layer contains zinc sulfide.
7) The optical recording medium according to 6), wherein the lower protective layer contains a transparent conductive oxide.
8) The transparent conductive oxide is at least one of indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, and InGaO ₃ (ZnO) m (m is a natural number) 7) The optical recording medium described.
9) The optical recording medium according to any one of 1) to 8), wherein the reflective layer is made of Ag or an Ag alloy and has a thickness of 80 to 200 nm.

Hereinafter, the present invention will be described in detail.
In the optical recording medium having the first and second sets of recording structures, the present invention provides an upper protective layer between the reflective layer and the dye recording layer of the second recording structure on the back side as viewed from the light incident side. And the recording property is improved by reducing the crosstalk between adjacent tracks by making the dye recording layer thinner.
In the case of the first recording layer on the near side of a normal DVD ± R and a two-layer recording medium, a dye recording layer having a thickness of 60 to 100 nm is provided on the surface having a groove having a depth of 100 to 200 nm by a coating means. As a result, the dye film thickness of the groove portion where information is recorded by light irradiation is relatively thick, and the dye film thickness of the land portion where information is not recorded is relatively thin, so that thermal interference between adjacent grooves is reduced. ing. The larger the laser power used for recording, the greater the influence of thermal interference, which causes a deterioration in signal quality, that is, jitter. Therefore, it has been found that the higher the recording speed, the higher the power required and the greater the influence of thermal interference.

  In the configuration of the present invention, in order to form the second dye recording layer located on the back side when viewed from the light incident side of the optical recording medium, the reflective layer is formed on the substrate in the reverse order of normal CD-R and DVD ± R. Is sputtered, a dye recording layer is applied, and a protective layer is sputtered. Accordingly, among the lands and grooves alternately arranged on the substrate surface, recording is performed on the land portion in front of the recording / reproducing pickup, that is, the convex portion of the substrate. Since the groove portion is relatively thick as in the case of, the influence of thermal diffusion on the adjacent lands becomes larger, and the jitter indicating the recording quality tends to increase. Therefore, an upper protective layer is provided on the reflective layer as in the present invention, the optical path length of the recording laser is controlled, the film thickness of the dye recording layer is reduced, and the heat radiation from the dye recording layer to the metal reflective layer is controlled. Therefore, it is possible to manufacture an optical recording medium suitable for high-speed recording.

The material of the upper protective layer includes silicon oxide, indium oxide, tin oxide, zinc oxide, gallium oxide, niobium oxide, aluminum oxide, magnesium oxide, tantalum oxide, etc .; carbides such as silicon carbide, titanium carbide, tantalum carbide, etc. Sulfides such as zinc sulfide, cadmium sulfide, and antimony sulfide; heat-resistant compounds having a high melting point or decomposition point such as nitrides such as silicon nitride and aluminum nitride, and mixtures thereof are preferably highly transparent materials.
In order to avoid the same as Japanese Patent Application No. 2004-133993 which is the prior application of the applicant, the oxide or nitride of an element which is not the same as the metal or metalloid element forming the reflective layer in the present invention 1 , Only when using sulfides and carbides.
In order to increase the optical path length of the recording laser and make the recording layer thin, those having a refractive index of 1.5 or more are preferable, and materials having a high refractive index are preferably 3 or less because they tend to absorb much. Examples of inorganic materials having a refractive index of less than 1.5 include fluorides such as LiF, CaF, AlF, MgF ₂ , and HfF ₂ , but they are chemically unstable and sputtering with good productivity is difficult. . Note that these oxides, sulfides, nitrides, and carbides do not necessarily have a stoichiometric composition, and the compositions can be controlled or mixed for controlling the refractive index and the like.

In particular, when a transparent conductive oxide such as indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, InGaO ₃ (ZnO) m (m is a natural number) is added, conductivity can be imparted to the target. Since DC sputtering becomes possible, it contributes to a reduction in production tact due to an increase in sputtering rate and a reduction in production equipment costs. In order to enable DC sputtering, the specific resistance of the target must be 1 Ωcm or less, but if it is 0.1 Ωcm or less, problems such as arc do not occur even when high sputtering power is applied, and productivity is increased. This is preferable. More preferably, if it is 0.01 Ωcm or less, the arc cutting device or the pulse superimposing device is not required for the sputtering power source, so that the cost of the production device can be further reduced.
The addition amount of the transparent conductive oxide is required to be 5 mol% or more to make the specific resistance of the target 1 Ωcm or less, and 8 mol% or more to make it 0.1 Ωcm or less.

The thickness of the upper protective layer is in the range of 1 to 70 nm. Preferably it is 4-40 nm. When there is no upper protective layer, the dye recording layer is in direct contact with the metal reflection layer having high thermal conductivity, so heat due to laser light irradiation used for recording and heat due to heat generation during dye decomposition are extremely easy to escape to the metal reflection layer, Jitter increases and wobble signal quality deteriorates.
If the thickness of the upper protective layer is less than 1 nm, the difference is only an optically negligible difference, and no significant difference appears in the recording characteristics. Ag and Ag alloys have high thermal conductivity, and general Ag alloys used for optical disks have a thermal conductivity of 100 W / m · K or more at room temperature (calculated from specific resistance measured by a four-probe method). ), But the bulk thermal conductivity of the metal or metalloid oxide, nitride, sulfide, and carbide used in the present invention determined by the laser flash method is 20 W / m · K or less. 1/10 or less. The thin film is expected to have a lower thermal conductivity.

  By providing the upper protective layer with a thickness of 1 nm or more, the optically unrecorded and post-recording reflectivity can be increased, and the modulation factor (I14 / I14H when used for DVD) can be increased. In addition, the heat-insulating effect of the upper protective layer can moderately suppress heat dissipation to the metal reflective layer and suppress the spread of the recording mark in the planar direction. When the film thickness d of the upper protective layer is increased, nd / λ (n is the refractive index at the reproduction light wavelength λ of the upper protective layer) increases, and the reflectivity and the degree of modulation once increase and reach the maximum respectively. When d is further increased, the reflectivity and the degree of modulation decrease, and the jitter increases accordingly. Therefore, the upper protective layer has a thickness of more than 70 nm when the refractive index is 1.5 to 1.6, and the upper protective layer has a thickness of more than 40 nm when the refractive index is 2.7 to 3. The degree of modulation becomes small, and the heat generated in the recording layer by the recording laser beam cannot escape to the reflection layer, so that the recording mark spreads too much and the jitter deteriorates. Further, it becomes difficult to set the reflectance of the recording structure on the back side to 15% or more, and it is difficult to apply to the DVD playback player.

Further, in order to control heat storage and heat dissipation during recording, it is preferable to make the thickness of the upper protective layer thinner than the thickness of the dye recording layer, and sufficiently ensure the optical reflectance and the degree of modulation (for example, DVD + R). In order to satisfy the DL standard, a reflectance of 16 to 30% and a modulation degree of 0.6 or more are required.) In order to satisfy the DL standard, the thickness of the upper protective layer is in the range of 1 to 70% of the thickness of the dye recording layer. More preferably, it is within.
In addition, when the upper protective layer that is harder than metal is used to suppress the deformation of the reflective layer and grooves during recording and to ensure a recording power margin, the thickness of the upper protective layer is that of the dye recording layer. More preferably, it is in the range of 4 to 40% of the film thickness.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view showing an example of the layer structure of the optical recording medium of the present invention: first substrate 1 / first dye recording layer 2 / translucent reflective layer 3 / intermediate layer 4 / lower protective layer 5 / Second dye recording layer 6 / upper protective layer 7 / reflective layer 8 / second substrate 9.
The first recording structure 100 includes the first dye recording layer 2 and the translucent reflective layer 3, and the second recording structure 200 includes the lower protective layer 5, the second dye recording layer 6, the upper protective layer 7, It consists of a reflective layer 8. For the first recording structure, a conventional single recording layer medium (DVD + R, DVD-R, etc.) in which a first substrate on which a first dye recording layer and a translucent reflective layer are formed is bonded to a single second substrate. ), The reflectivity and the recording signal modulation degree (contrast) can be obtained by the multiple interference effect at both interfaces of the first dye recording layer and the deformation of the first substrate at the time of mark formation. obtain. In addition, for the second recording structure, a light-transmitting protective layer made of a material that is difficult to deform while obtaining the required reflectance and recording signal modulation degree (contrast) by the substrate groove shape and the light absorption characteristics of the dye. Is disposed between the second dye recording layer and the transparent intermediate layer 4 made of an organic resin or the like, thereby preventing the dye from being eluted by the organic resin or the like and adjusting the mark shape.

As materials for the first and second substrates, polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin And transparent glass. Polycarbonate resins and acrylic resins that are excellent in terms of optical properties and cost are preferred.
The first and second substrates are usually provided with grooves having a pitch of 0.8 μm or less for guiding the recording / reproducing light. However, the grooves are not necessarily geometrically rectangular or trapezoidal grooves. Optical grooves may be formed by forming waveguides having different refractive indexes by injection or the like.
The thicknesses of the first and second substrates are changed in order to take chromatic aberration in accordance with the NA of the evaluation pickup. Usually, when NA is about 0.6 to 0.65, 0.6 mm is preferable.

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 or 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, the groove tends to be filled with the dye, and the interface shape between the dye recording layer and the reflective layer is determined by the dye filling amount and the substrate groove shape. The above range is suitable. 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. As shown in FIG. 2, since the interface shape between the dye recording layer and the 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, tracking during recording becomes unstable, and the shape of the formed recording mark is difficult to be obtained, and jitter tends to increase.

The optical recording medium of the present invention is configured to obtain a high reflectance by the multiple interference effect at both interfaces of a recording layer containing a dye (dye recording layer) as in the case of DVD + R and CD-R. Requires an optical characteristic that the refractive index n of the complex refractive index n-ik is large and the absorption coefficient k is relatively small at the recording / reproducing wavelength λ. The ranges of n and k are n> 2, 0.02 <k <0.2, and preferably n is 2.2 to 2.8 and k is 0.03 to 0.07. When k is less than 0.02, the sensitivity of the recording laser light is small, so the sensitivity is deteriorated. When it exceeds 0.2, the reflectivity is lowered, and when two recording layers are provided, the depth is viewed from the light incident direction. This is because it becomes difficult to sufficiently increase the reflectance of the recording layer on the side.
Such optical characteristics can be obtained by utilizing the characteristics of the long wavelength end of the light absorption band of the dye film. The optical recording medium of the present invention corresponds to a red laser beam of 600 to 800 nm, and a preferable recording / reproducing wavelength λ is 650 to 670 nm. In designing the medium, the wavelength of the laser beam used for recording / reproduction is first determined from the above wavelength range, and then the material and film thickness of each layer may be selected so as to satisfy the conditions of the present invention.

Dye materials that can be used for the first and second dye recording layers include cyanine dyes, phthalocyanine dyes, tetraazaporphyrazine dyes, pyrylium / thiopyrylium dyes, azurenium dyes, squarylium dyes, and azo dyes. Dyes, formazan chelate dyes, metal complex dyes such as Ni and Cr, naphthoquinone dyes / anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aminium dyes / diimonium System dyes and nitroso compounds. Among them, the maximum absorption wavelength of the light absorption spectrum of the film is in the range of 580 to 620 nm, and as a dye compound that easily obtains desired optical characteristics at the DVD laser light wavelength (about 650 nm), the film-forming properties and optical characteristics of solvent coating are Considering the ease of adjustment, tetraazaporphyrazine dyes, cyanine dyes, azo dyes, and squarylium dyes are preferable. Inclusion of these dyes facilitates the formation of smaller marks and is compatible with high-density recording.
In addition, the dye recording layer of the present invention may be prepared using only a dye, but may contain other third component such as a binder and a stabilizer as required.

The film thickness of the first and second dye recording layers is usually 30 to 150 nm. If it is less than 30 nm, it is difficult to obtain sufficient contrast, and the modulation tends to be small. On the other hand, if it exceeds 150 nm, it is difficult to write a small recording mark.
In high-density recording where the shortest mark length is 0.5 μm or less, the film thickness is preferably 50 to 100 nm. If it is less than 50 nm, the reflectance is too low, and the film thickness tends to be nonuniform, which is not preferable. On the other hand, if it is thicker than 100 nm, the heat capacity becomes large and the recording sensitivity is deteriorated, and the edge tends to be disturbed due to the non-uniform thermal conductivity and the jitter tends to increase.
The film thickness of the second dye recording layer is preferably about 1.0 to 2.0 times the film thickness of the first dye recording layer. If the film thickness difference of the recording layer deviates from this range, it becomes difficult to record with the same recording strategy (light emitting pulse pattern of the recording laser) on both layers due to the difference in the spread of the recording mark. There is.
The first and second dye recording layers are usually formed by spin coating. Although the dye recording layer after spin coating is in a substantially uniform state, the recording causes deformation, perforation, and substrate deformation of the dye recording layer, and the recording mark can be determined from the reflectance change of that portion. Usually, the difference in reflectance before and after recording is greater than 5%. In addition, when it forms into a film on the board | substrate in which the guide groove was formed, a difference arises in a pigment | dye film thickness by a groove part and an inter-groove part.

As the reflective layer and the translucent reflective layer material, those having a high reflectance with respect to the laser light wavelength are preferable. For example, Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, Pt, Mention may be made of metals and metalloids such as Ta, W, Si, Zn. Among them, Au, Ag, Cu, or Al is the main component and is different from these four elements. Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, Pt, Ta An alloy to which at least one selected from W, Si, Zn, and In is added in an amount of 0.1 to 10% by weight is preferable. In particular, Ag having a high thermal conductivity and high reflectivity is a main component, and at least selected from Au, Pd, Pt, Cu, Al, Nd, Bi, Mg, Zr, Ta, Si, Zn, and In. An alloy added with 0.1 to 10% by weight of one kind is preferable.
By adding 0.1% by weight or more, the crystal grains become fine and a thin film having excellent corrosion resistance is obtained. However, addition of more than 10% by weight is not preferable because the reflectance decreases.

The thickness of the reflective layer is preferably 80 to 200 nm, and more preferably 100 nm or more in order to obtain a sufficiently high reflectance. In order to improve the heat dissipation of the second recording structure, it is preferable that the thickness is larger. However, if the thickness exceeds 200 nm, the film formation takes time and the material cost increases, which is not preferable from the viewpoint of manufacturing cost. Visual flatness will also deteriorate.
The translucent reflective layer has a transmittance of about 30 to 60% and a reflectance of about 15 to 30% so that sufficient light reaches the second dye recording layer. The film thickness is preferably in the range of 5 to 30 nm.
When the first dye recording layer and the transparent intermediate layer made of acrylic resin or the like are in contact with each other through an extremely thin semi-transparent reflective layer having a film thickness of 30 nm or less, the dye and acrylic resin pass through the semi-transparent reflective layer. It is necessary not to melt. In the case of a translucent reflective layer made of a material having large crystal grains such as a pure metal thin film, care must be taken because the thin film tends to be island-like and the resin easily penetrates from the grain boundary.

It is necessary to provide a lower protective layer between the second dye recording layer and the intermediate layer for the purpose of chemically and physically protecting the dye recording layer.
Materials for the lower protective layer include silicon oxide, indium oxide, tin oxide, zinc oxide, gallium oxide, niobium oxide, aluminum oxide, magnesium oxide, tantalum oxide, etc .; silicon, germanium, silicon carbide, titanium carbide, graphite Semimetals or semiconductors such as; fluorides such as magnesium fluoride, aluminum fluoride, lanthanum fluoride, and selenium fluoride; sulfides such as zinc sulfide, cadmium sulfide, and antimony sulfide; nitrides such as silicon nitride and aluminum nitride; Examples thereof include chalcogenide compounds such as ZnSe, GaSe, and ZnTe, and mixtures of these substances.
In particular, a material containing a large amount of zinc sulfide, cadmium sulfide, antimony sulfide, and silicon oxide having a low internal stress is preferable. Further, a mixture of these materials may be used to optimize the refractive index n and the absorption coefficient k. These materials have a high melting point, and n and k are substantially equal to the weighted average of the mixing ratio when the materials mixed at the time of target sintering do not react with each other.

Above all, when zinc sulfide, which is relatively toxic and has a high sputtering rate and is inexpensive, is mainly used, the productivity can be increased and the production cost can be reduced. The blending ratio of zinc sulfide is preferably 60 to 95 mol%, and if it exceeds 95 mol%, a thin film is not deposited well on the second dye recording layer. In order to adjust the refractive index n, the blending ratio of zinc sulfide should be 95 mol% or less and mixed with materials having different refractive indexes n.
When preparing a thin film of a mixture, it is possible to simultaneously sputter a plurality of targets, but this is not preferable because the apparatus cost increases and the control of the ratio is difficult. Therefore, it is advantageous in production to produce a mixture target of zinc sulfide and an additive material and perform sputtering.
Zinc sulfide has a refractive index n of about 2.35, and is used in CD-RW, DVD-RW, and DVD + RW that are currently commercially available when a mixture with silicon oxide is used to make the refractive index lower than 2.35. Since the target used can be used, it can be produced with stable quality.
Further, the refractive index n can be increased by adding 5 mol% or more of silicon, silicon carbide, titanium oxide, or germanium. In the case of less than 5 mol%, the refractive index improving effect is negligibly small.

In particular, when a transparent conductive oxide such as indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, InGaO ₃ (ZnO) m (m is a natural number) is added, conductivity can be imparted to the target. Since DC sputtering becomes possible, it contributes to a reduction in production tact due to an increase in sputtering rate and a reduction in production equipment costs. In order to enable DC sputtering, the specific resistance of the target must be 1 Ωcm or less, but if it is 0.1 Ωcm or less, problems such as arc do not occur even when high sputtering power is applied, and productivity is increased. This is preferable. More preferably, if it is 0.01 Ωcm or less, the arc cutting device or the pulse superimposing device is not required for the sputtering power source, so that the cost of the production device can be further reduced. However, as the amount added increases, the stress of the film increases and peeling occurs from the interface between the dye recording layer and the lower protective layer, so the upper limit of the amount added is 30 mol%.

The thickness of the lower protective layer is preferably in the range of 10 to 300 nm. If it is less than 10 nm, the intermediate layer material penetrates into the second recording layer from the defect of the protective layer, and the dye changes. On the other hand, if the thickness exceeds 300 nm, the increase in the substrate temperature during sputtering increases the film stress, so that the substrate is easily deformed and the protective layer is peeled off. Further, when the absorption coefficient k is not zero, the reflectivity from the dye recording layer is reduced by absorption.
The thickness of the lower protective layer is preferably 40 to 180 nm, more preferably when the wavelength of the recording laser beam is 600 to 700 nm and the refractive index of the protective layer material is in the range of 1.9 to 2.4. 100-160 nm.
Basically, the product of the refractive index n and the film thickness d may be equal. That is, when the refractive index is reduced, it is necessary to increase the film thickness. This is because the reflectance needs to be equal, and the optical path length difference (2 × n × d) is a phase difference, so that it is difficult to obtain a phase difference, that is, modulation at a very thin film thickness.

  According to the present invention, in an optical recording medium having two sets of recording structures, an upper protective layer is provided between the reflective layer and the dye recording layer of the second recording structure on the back side when viewed from the light incident side, By thinning the recording layer, it is possible to provide an optical recording medium in which crosstalk between adjacent tracks is reduced and recording characteristics are improved.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples. For example, although the recording / reproducing conditions were evaluated as 8X (linear speed 30.6 m / sec) of DVD, the speed can be increased if a higher speed design is performed.

この光記録媒体の第２の色素記録層に対して、パルステック工業社製のＯＤＵ１０００（波長６５７ｎｍ、ＮＡ：０．６５）を用いて、線速度３０．６４ｍ／ｓ（８倍速記録）の条件でＤＶＤ（８−１６）信号を記録した後、３．８３ｍ／ｓで再生評価を行ったところ、表２の結果が得られた。パワーマージンは、ジッタ値が９％以下となるパワー下限値Ｐ１と上限値Ｐ１について（Ｐ２−Ｐ１）×２／（Ｐ２＋Ｐ１）を計算した値である。
また、表２中の「記録後反射率（％）」は、記録後波形を示す図３中の「Ｉ_１４Ｈ」に相当し、「Ｉ１４／Ｉ１４Ｈ」は次式で示される変調度である。
Ｉ１４／Ｉ１４Ｈ＝（Ｉ_１４Ｈ−Ｉ_１４Ｌ）／Ｉ_１４Ｈ
表２から分るように、実施例１〜２６の光記録媒体は、何れも優れた記録特性を示し、反射率も１６％以上であったが、上部保護層を設けない比較例１、及び上部保護層の膜厚が７０ｎｍを超える比較例２では、ジッタが低くならず、パワーマージンも非常に小さかった。 Examples 1-26, Comparative Examples 1-2
On a polycarbonate substrate having a plate thickness of 0.57 mm on which concave grooves having a groove depth of 160 nm, a groove width of 0.35 μm, and a track pitch of 0.74 μm were formed, A coating solution dissolved in 3-tetrafluoropropanol was spin-coated to provide a first dye recording layer having a thickness of about 40 nm.
Further thereon, an Ag alloy containing 0.5 atomic% of In was sputtered to form a translucent reflective layer having a thickness of 9 nm, thereby obtaining a first information substrate on which a first recording structure was formed.
Next, on a polycarbonate substrate having a plate thickness of 0.6 mm on which convex grooves having a groove depth of 34 nm, a groove width of 0.3 μm, and a track pitch of 0.74 μm are formed, an Ag reflection layer having a film thickness described in Table 1; An upper protective layer having the material and thickness shown in Table 1 is formed, and a coating solution in which the squarylium dye compound of the following [Chemical Formula 1] is dissolved in 2,2,3,3-tetrafluoropropanol is spin-coated thereon. Thus, a second dye recording layer having a thickness of about 70 nm was provided.
Further thereon, a lower protective layer having the materials and thicknesses shown in Table 1 was formed to obtain a second information substrate on which a second recording structure was formed.
Next, the first and second information substrates were bonded together using an ultraviolet curable adhesive (KARAYAD DVD576M manufactured by Nippon Kayaku Co., Ltd.) so that the intermediate layer thickness was 50 μm to obtain an optical recording medium. .

For the second dye recording layer of this optical recording medium, a linear velocity of 30.64 m / s (8 × speed recording) using ODU1000 (wavelength 657 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. After recording a DVD (8-16) signal, reproduction evaluation was performed at 3.83 m / s. The results shown in Table 2 were obtained. The power margin is a value obtained by calculating (P2−P1) × 2 / (P2 + P1) for the power lower limit value P1 and the upper limit value P1 at which the jitter value is 9% or less.
Further, “reflectance after recording (%)” in Table 2 corresponds to “I _14H ” in FIG. 3 showing the waveform after recording, and “I14 / I14H” is a modulation degree represented by the following equation.
_{I14 / I14H = (I 14H -I} 14L) / I 14H
As can be seen from Table 2, the optical recording media of Examples 1 to 26 all showed excellent recording characteristics and the reflectance was 16% or more, but Comparative Example 1 in which no upper protective layer was provided, and In Comparative Example 2 in which the thickness of the upper protective layer exceeded 70 nm, the jitter was not lowered and the power margin was very small.

Sectional drawing which shows the structure of DVD which has two information recording layers. 1 is a schematic cross-sectional view showing an example of a layer configuration of an optical recording medium of the present invention. The figure which shows the waveform after recording.

Explanation of symbols

Maximum reflectivity of I _14H 14T mark Minimum reflectivity of I _14L 14T mark Maximum reflectivity of I _3H 3T mark Minimum reflectivity of I _3L 3T mark

Claims (9)

  The first recording structure formed on the first substrate and the second recording structure formed on the second substrate are laminated via an intermediate layer, and laser light irradiation from the first recording structure side Thus, in the optical recording medium in which recording and reproduction are performed respectively on the first and second recording structures, the second recording structure has at least a reflective layer and an upper part. A protective layer, a second dye recording layer, and a lower protective layer are provided in this order, and the upper protective layer is made of an oxide, nitride, sulfide, or carbide of an element that is not the same as the metal or metalloid element forming the reflective layer. An optical recording medium comprising any one or a mixture thereof and a film thickness of 1 to 70 nm.   2. The optical recording medium according to claim 1, wherein the thickness of the upper protective layer is thinner than the thickness of the dye recording layer.   The optical recording medium according to claim 1 or 2, wherein the refractive index of the upper protective layer is 1.5 to 3.   The optical recording medium according to claim 1, wherein the upper protective layer contains a transparent conductive oxide. 5. The transparent conductive oxide is at least one of indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, and InGaO ₃ (ZnO) m (m is a natural number). Optical recording media.   The optical recording medium according to claim 1, wherein the lower protective layer contains zinc sulfide.   The optical recording medium according to claim 6, wherein the lower protective layer contains a transparent conductive oxide. 8. The transparent conductive oxide is at least one of indium oxide, zinc oxide, gallium oxide, tin oxide, niobium oxide, and InGaO ₃ (ZnO) m (m is a natural number). Optical recording media. The optical recording medium according to claim 1, wherein the reflective layer is made of Ag or an Ag alloy and has a thickness of 80 to 200 nm.

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