JP2004348880A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-sided two layered recording and reproducing type optical recording medium wherein satisfactory recording signal characteristics are obtained also from a second recording layer. <P>SOLUTION: In the optical recording medium wherein a first substrate formed by successively forming a first recording layer consisting essentially of organic dye and a first reflection layer on the surface thereof and having a guide groove, and a second substrate formed by successively forming a second reflection layer, a second recording layer consisting essentially of organic dye and an inorganic protective layer on the surface thereof and having a guide groove, are stuck to each other via an organic transparent intermediate layer so that the surfaces of the substrates face outside and recording and reproduction of signal information formed in the first and the second recording layers are performed from the side of the surface of the first substrate, the guide groove of the second substrate has 200 to 600 Å depth, the light absorption spectrum of the second recording layer has 580 to 620 nm maximum absorption wavelength and absorbance at the maximum absorption wavelength is 1.5 to 2.0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

上記光記録媒体に対し、ＤＶＤ用評価装置（パルステック社製ＤＤＵ１０００、波長：６５７ｎｍ、ＮＡ：０．６５）を用いて、線速度８．５ｍ／ｓの条件でＤＶＤ（８−１６）信号を記録し、３．４９ｍ／ｓの線速度で再生評価を行ったところ、ＤＶＤ−ＲＯＭ規格を満足する結果が得られた（表１参照）。
なお、記録ストラテジは（ｎ−２）Ｔのマルチパルス方式とし、マルチパルス幅を１０／１６とした。
【表１】

【００２２】
＜実施例２＞
色素を、下記〔化２〕で表される構造式のスクアリリウム色素化合物に変えた点以外は、実施例１と同様にして本発明の光記録媒体を作成し、実施例１と同様な評価を行ったところ、実施例１と同様に良好な結果が得られた（表２参照）。
この光記録媒体の記録層の光吸収スペクトルは図７に示す通りであり、最大吸収波長は６００ｎｍであった。
【化２】

【表２】

【００２３】
＜実施例３＞
第２の記録層の吸光度（Ａｂｓ）が、１．４〜２．１となるように膜厚を変更した点以外は、実施例１と同様にして本発明の光記録媒体を作成し、実施例１と同様にして第２の記録層の変調度を評価したところ、図８に示すように、１．５以上の吸光度において６０％以上の良好な変調度が得られた。
【００２４】
＜実施例４＞
第２の基板の溝深さを６００Åとした点以外は、実施例１と同様にして本発明の光記録媒体を作成し、実施例１と同様にして第２の記録層の反射率を評価したところ、１８％であった。
【００２５】
＜実施例５＞
第２の基板の溝深さを２００Åとした点以外は、実施例１と同様にして本発明の光記録媒体を作成し、実施例１と同様にして第２の記録層のジッターを評価したところ、８％であった。
【００２６】
＜比較例１＞
色素を、上記〔化２〕で表される構造式のスクアリリウム色素化合物に変え、第２の基板の溝深さを８００Åとした点以外は実施例１と同様にして光記録媒体を作成し、実施例１と同様にして第２の記録層の反射率を評価したところ、１５％であった。
【００２７】
【発明の効果】
本発明１によれば、片面側から第１、第２の記録層の記録再生が可能な光記録媒体を提供できる。
本発明２〜４によれば、第１の記録層と第２の記録層を同様の記録ストラテジパターンで記録することが可能な光記録媒体を提供できる。
【図面の簡単な説明】
【図１】色素記録層の光吸収スペクトルを示す図。
【図２】２層の記録層を有する読み出し専用ＤＶＤの構造を示す断面図。
【図３】本発明の光記録媒体の構成例を示す図。
【図４】案内溝を形成した第１の基板上での層構成を示す図。
【図５】案内溝を形成した第２の基板上での層構成を示す図。
【図６】実施例１の記録層の光吸収スペクトルを示す図。
【図７】実施例２の記録層の光吸収スペクトルを示す図。
【図８】実施例３の第２の記録層の変調度を示す図。
【符号の説明】
１ 第１の基板
２ 第２の基板
３ 第１の記録層
４ 第２の記録層
５ 有機透明中間層
５′ 透明中間層
６ 第１の反射層
７ 第２の反射層
８ 無機保護層
９ 記録マーク
１０ 基板の溝部
１１ 基板の溝間部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical recording medium of a single-sided, dual-layer recording / reproducing type.
[0002]
[Prior art]
In addition to optical recording media such as read-only DVDs (digital versatile discs), recordable DVDs (DVD + RW, DVD + R, DVD-R, DVD-RW, DVD-RAM, etc.) have been put to practical use. The DVD + R, DVD + RW, and the like are located on an extension of the conventional recordable CD-R and CD-RW (recordable compact disc) technology, and have a recording function to ensure reproduction compatibility with a read-only DVD. The density (track pitch, signal mark length) and the thickness of the substrate are designed so as to meet the requirements of CD to DVD. For example, in the case of DVD + R, as in the case of CD-R, an optical recording layer is provided by spin coating a dye on a substrate, and an information recording substrate having a metal reflection layer provided behind the substrate is bonded to a substrate having the same shape via a bonding material. A configuration of bonding to a substrate is employed. In this case, a dye-based material is used for the optical recording layer. One of the features of the CD-R is that it has a high reflectance (65%) that satisfies the standard of the CD. This is because it is necessary to satisfy a specific complex refractive index, and the light absorption characteristics of the dye are suitable. This is the same for DVDs.
[0003]
By the way, a read-only DVD having two recording layers has been proposed in order to increase the recording capacity. FIG. 2 is a sectional view showing a layer structure of a DVD having such two recording layers. The first substrate 1 and the second substrate 2 are bonded together by sandwiching a transparent intermediate layer 5 'formed of an ultraviolet curable resin. The first recording layer 3 is formed on the inner surface of the first substrate, and the second recording layer 4 is formed on the inner surface of the second substrate. The first recording layer is formed as a translucent film using a dielectric film. The second recording layer is made of a metal film or the like and is formed as a reflection film. An irregular recording mark is formed on the first recording layer, and a recording signal is read by the effect of reflecting and interfering with a reproduction laser beam. Since signals are read from the two recording layers, a storage capacity of about 8.5 GB can be obtained at the maximum. The thickness of each of the first and second substrates is about 0.6 mm, and the thickness of the transparent intermediate layer is about 50 μm. The translucent film serving as the first recording layer is formed so that its reflectivity is about 30%, and the laser beam irradiated to reproduce the second recording layer is applied to the first recording layer. After about 30% of the total light amount is reflected and attenuated, the light is reflected by the reflection film of the second recording layer, further attenuated by the first recording layer, and then exits the disk. If the laser beam, which is the reproduction light, is focused so as to be focused on the first recording layer or the second recording layer, and the reflected light is detected, the signal of each recording layer can be reproduced. The wavelength of the laser beam used for recording and reproduction in the case of DVD is about 650 nm.
[0004]
However, in the above-mentioned recordable DVD, DVD + R, DVD-R, DVD + RW, etc., only one recording layer can be read from one side, and in order to obtain a larger storage capacity with these optical recording media, reproduction from both sides is required. It was necessary to make the structure to be. The reason is that an optical recording medium of a single-sided, dual-layer recording / reproducing type has two recording layers, so that when recording a signal by irradiating a writing laser beam from an optical pickup so as to focus on a deeper recording layer. This is because the first recording layer attenuates the laser beam, so that there is a problem that light absorption and light reflection required for recording of the second recording layer cannot be compatible.
Also, Patent Document 1 aims to write data from two surfaces of an optical recording medium to one recording medium on one side of an optical recording medium during recording and read data from one surface of the optical recording medium to two recording layers during reproduction. Have been proposed. However, the present invention is limited to a conventional configuration in which two types of substrates, a substrate surface incident recording configuration and a recording film surface incident configuration, are adhered to each other, and data actually recorded and reproduced on two recording layers is shown. Not. According to the study by the present inventors, even if the above configuration is adopted, practical recording / reproduction cannot be performed, and the above-mentioned problem relating to light absorption / reflection of the second recording layer cannot be solved.
[0005]
[Patent Document 1]
JP-A-11-66622
[Problems to be solved by the invention]
An object of the present invention is to provide an optical recording medium of a single-sided, dual-layer recording / reproducing type which solves the above-mentioned problems and can obtain good recording signal characteristics even from the second recording layer.
[0007]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 4).
1) A first substrate having a guide groove on which a first recording layer mainly composed of an organic dye and a first reflective layer are sequentially formed on the surface, a second reflective layer on the surface and a mainly composed of the organic dye A second recording layer to be formed and a second substrate having a guide groove in which an inorganic protective layer is sequentially formed are bonded together with an organic transparent intermediate layer with the substrate surface outside, and from the first substrate surface side, An optical recording medium for recording and reproducing signal information formed in a first and a second recording layer, wherein a depth of a guide groove of a second substrate is 200 to 600 °, and a light absorption of the second recording layer. An optical recording medium having a maximum absorption wavelength of a spectrum of 580 to 620 nm and an absorbance (Absorption) at the maximum absorption wavelength of 1.5 to 2.0.
2) The optical recording medium according to 1), wherein the thickness of the second recording layer is 1.5 to 2.5 times the thickness of the first recording layer.
3) The optical recording medium according to 1) or 2), wherein the thickness of the second reflective layer is at least five times the thickness of the first reflective layer.
4) The optical recording medium according to 1) or 2), wherein the thermal conductivity of the second reflective layer is higher than the thermal conductivity of the first reflective layer.
[0008]
Hereinafter, the present invention will be described in detail.
According to the present invention, the recording is performed such that the maximum absorption wavelength of the light absorption spectrum of the second recording layer falls within the range of 580 to 620 nm so that recording and reproduction can be performed at least at the laser beam wavelength for DVD (about 650 nm). The material is selected, and the thickness of the second recording layer is controlled so that the absorbance at the maximum absorption wavelength is 1.5 to 2.0, and the second recording layer is made of an inorganic material that is not easily deformed. By arranging the recording marks between the layers (the second reflective layer and the inorganic protective layer) to adjust the shape of the recording mark and setting the depth of the guide groove of the second substrate to 200 to 600 °, single-sided dual-layer recording / reproducing can be performed. The feature is that it is made possible. If the absorbance is less than 1.5, a good degree of modulation cannot be obtained, and if it exceeds 2.0, there is a problem in that the jitter deteriorates.
FIG. 3 shows a configuration example of the optical recording medium of the present invention.
In FIG. 3, 1 is a first substrate, 2 is a second substrate, 3 is a first recording layer, 4 is a second recording layer, 5 is an organic transparent intermediate layer, 6 is a first reflective layer, 7 Is a second reflective layer, 8 is an inorganic protective layer, and recording and reproduction are performed by light from the first substrate surface side.
For convenience of explanation, the structure combining the first substrate, the first recording layer, and the first reflection layer is referred to as a first information substrate, a second substrate, a second recording layer, and a second reflection layer. The configuration including the inorganic protective layer is referred to as a second information substrate.
Further, the above-mentioned layer configuration is an example, and an undercoat layer, an anti-sulfuration layer of an Ag reflection layer, a smoothing layer, an anti-oxidation layer, and the like may be provided as necessary.
[0009]
<Operation>
In the present invention, as for the first information substrate having the first recording layer, a conventional single unit in which the first recording layer and the first reflective layer formed on the first substrate are bonded to the second substrate is used. By adopting a configuration similar to that of a single recording layer medium (such as DVD + R), the reflectance and the recording signal modulation (contrast) can be obtained by the multiple interference effect at both interfaces of the first recording layer and the deformation of the substrate during mark formation.
Further, with respect to the second information substrate having the second recording layer, the reflectance and the recording signal modulation (contrast) are obtained and the second recording is performed by the substrate groove shape and the light absorption characteristics of the second recording layer. By arranging the layer between a layer made of an inorganic material that is difficult to deform (the second reflective layer and the inorganic protective layer), the shape of the recording mark is adjusted.
In order to obtain such an effect, it is preferable that the thickness of the second recording layer be 1.5 to 2.5 times the thickness of the first recording layer. If the thickness difference of the recording layers is out of this range, it is not easy to record on the two recording layers with the same recording strategy (emission pulse pattern of the recording laser) because the spread of the recording marks is different.
In general, the recording layer is formed by spin-coating a dye dissolved in a coating solvent. When the recording layer is formed on a substrate on which a guide groove is formed, the dye film thickness is formed between the groove and the groove. There is a difference. The dye film thickness in the present invention refers to the dye film thickness in the groove portion and the inter-groove portion in total. The value can be easily converted from the absorbance (Absorption) and the extinction coefficient.
[0010]
FIG. 4 shows a layer configuration on the first substrate in which the guide grooves are formed. The recording mark 9 formed on the first recording layer is formed in the groove 10 of the first substrate.
On the other hand, FIG. 5 shows a layer configuration on the second substrate on which the guide groove is formed. The recording mark 9 formed on the second recording layer is formed in the inter-groove portion 11 of the second substrate.
More preferably, in order to increase the reflection intensity of the second reflection layer, the thickness of the second reflection layer is set to be five times or more the thickness of the first reflection layer. If the dye film thickness is large, the heat conduction becomes poor, and the recording mark becomes difficult to spread. For example, as described above, when the film thickness of the second recording layer is 1.5 to 2.5 times the film thickness of the first recording layer, the second recording layer has a larger thickness than the first recording layer. Recording marks are difficult to spread. Therefore, by making the thickness of the second reflective layer in contact with the second recording layer larger than the thickness of the first reflective layer, the spread of the marks on the first and second recording layers can be made uniform. . The upper limit of the magnification is not particularly limited. However, if the thickness exceeds a certain level, the reflection intensity becomes saturated. Therefore, an appropriate magnification which is 5 times or more and does not cause waste in production may be selected.
Further, the thermal conductivity of the second reflective layer is made higher than the thermal conductivity of the first reflective layer, that is, a material having a higher thermal conductivity than the material of the first reflective layer as the material of the second reflective layer. The same effect can be obtained by using.
[0011]
As a recording method on the optical recording medium of the present invention, the same mark length modulation recording as that of the conventional DVD + R and DVD-R can be adopted. However, the recording strategy for forming the mark, that is, the light emission pulse of the recording laser is It is preferable to change between the second recording layer and the first recording layer. This is because the spread of the mark differs in each recording layer as described above. Specifically, it is preferable that the recording laser emission pulse times for forming signal marks of the same length have the following relationship.
Ws2> Ws1
Ws2: Recording laser emission pulse time for forming a shortest mark length signal on the second recording layer Ws1: Recording laser emission pulse time for forming a shortest mark length signal on the first recording layer
Further, DVD + R employs a so-called multi-pulse recording strategy in which one signal mark is irradiated with a recording laser with a plurality of emission pulses for a particularly long signal mark such as 14T, and this method is also preferably used in the present invention. When performing multi-pulse recording, it is preferable that the multi-pulse width when recording on the second recording layer is shorter than the multi-pulse width when recording on the first recording layer.
Also, by recording information on these recording conditions in the guide grooves in advance, it becomes easy to set recording conditions in the drive. That is, when the drive records information on the medium, the recording condition information is read out and the recording condition is set, thereby enabling error-free recording due to the deviation of the recording condition.
[0013]
Note that, as shown in FIGS. 4 and 5, the shapes of the grooves formed in the first and second substrates are not the same. In the case of a 4.7 GB, 0.74 μm pitch DVD + R or DVD-R, the first substrate groove shape preferably has a groove depth of 1000 to 2000 ° and a groove width (bottom width) of 0.2 to 0.3 μm. As shown in FIG. 4, in the case of spin coating film formation, the grooves tend to be filled with the dye, so that the interface shape between the dye recording layer and the reflective layer is determined by this filling amount and the substrate groove shape. This is because the above range is suitable for utilizing interfacial reflection.
On the other hand, the second substrate groove shape needs to have a groove depth of 200 to 600 °, and the groove width is preferably 0.2 to 0.4 μm. As shown in FIG. 5, the interface shape between the dye recording layer and the reflective layer is determined by the groove shape of the substrate, and the above range is suitable for utilizing the interface reflection.
In any of the first and second substrates, if the groove depth is deeper than the groove shape range, the reflectivity tends to decrease, and the groove depth is shallower than the groove shape range or the groove width is smaller than the above. If the groove shape is out of the range, it becomes difficult to form the recording marks to be formed, and jitter tends to increase.
The preferred dye film thickness is 400 to 1000 ° for the first recording layer (groove) and 600 to 2500 ° for the second recording layer (inter-groove). If the dye film thickness is thinner than this range, it is difficult to obtain a signal modulation degree (contrast), and if the dye film thickness is thicker, it is difficult to make the mark shapes uniform and jitter tends to increase.
[0014]
<Structure>
Hereinafter, the materials used for the optical recording medium of the present invention will be specifically described.
The optical recording medium of the present invention is configured to obtain a high reflectance by the multiple interference effect at both interfaces of the recording layer as in the case of DVD + R and CD-R, and the recording layer has a large refractive index n at the recording / reproducing wavelength. , An optical characteristic having a relatively small absorption coefficient k is required. Preferred ranges are n> 2, 0.03 <k <0.2. Such optical characteristics can be obtained by utilizing the characteristics of the long wavelength end of the light absorption band of the dye film.
FIG. 1 shows a light absorption spectrum of the dye recording layer.
Examples of materials that can be used for the first and second recording layers include cyanine dyes, phthalocyanine dyes, pyrylium / thiopyrylium dyes, azurenium dyes, squarylium dyes, azo dyes, and formazan chelate dyes , Ni, Cr and other metal complex salt dyes, naphthoquinone / anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aminium / diimmonium dyes and nitroso compounds Can be mentioned.
Above all, a dye compound having a maximum absorption wavelength of a light absorption spectrum of a film at 580 to 620 nm and easily obtaining desired optical characteristics at a DVD laser light wavelength (about 650 nm) includes film-forming properties by solvent coating and optical characteristics. From the viewpoint of easy adjustment, at least one selected from a tetraazaporphyrazine dye, a cyanine dye, an azo dye, and a squarylium dye is preferable.
It should be noted that, when the organic dye is used as a main component, it means that a sufficient amount of the dye is used to secure good recording / reproducing characteristics, but usually, an additive such as a binder or a stabilizer is added as needed. , Except that the recording layer is composed of only a dye.
[0015]
The material of the substrate used in the present invention can be arbitrarily selected from various materials used for the substrate of the conventional optical recording medium.
Examples of materials include acrylic resins such as polymethyl methacrylate, vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymer, epoxy resins, polycarbonate resins, amorphous polyolefin resins, polyester resins, and glass such as soda-lime glass. And ceramics. Among them, from the viewpoints of dimensional stability, transparency and flatness, polymethyl methacrylate resin, polycarbonate resin, epoxy resin, amorphous polyolefin resin, polyester resin, glass and the like are preferable. preferable.
[0016]
As the first and second reflective layer materials of the present invention, a substance having a high reflectance with respect to the wavelength of laser light is used, and examples thereof include Mg, Se, Y, Ti, Zr, Hf, V, Nb, and Ta. , Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ca, In, Si, Ge, Te, Pb , Po, Sn, Si, SiC, and other metals and metalloids. Among them, Au, Ag, and Al having high reflectivity are preferable. These may be used alone, in combination of two or more, or as an alloy.
The first reflective layer preferably has a thickness of 50 to 1000 °, and the second reflective layer preferably has a thickness of 1000 to 5000 °. When the first and second reflective layer materials are the same, it is preferable to make the film thickness difference as described above. Further, when a reflective layer is formed on the first recording layer, it is necessary to adjust the film thickness so that the light transmittance becomes 40% or more.
A protective layer may be provided for chemical and physical protection of the reflective layer. As a material for the protective layer, an ultraviolet curable resin or the like can be used.
[0017]
An inorganic protective layer is provided between the second recording layer and the organic transparent intermediate layer for the purpose of chemically and physically protecting the second recording layer.
Examples of the material used for the inorganic protective layer include inorganic substances having high light transmittance, such as SiO, SiO ₂ , MgF ₂ , SnO ₂ , ZnS, and ZnS—SiO ₂ . Particularly preferred is ZnS—SiO ₂ having a low crystallinity and a high refractive index.
The thickness of the protective layer is preferably in the range of 100 to 2000 μm. The organic transparent intermediate layer preferably also functions as an adhesive layer, and an existing acrylate, epoxy, urethane-based UV-curable or thermosetting adhesive can be used. . Further, a method of bonding with a transparent sheet may be used.
[0018]
Next, a method for manufacturing the optical recording medium of the present invention will be described.
Forming a first recording layer on a first substrate having grooves and / or pits formed on a surface thereof by a coating film forming means, and further providing a reflective layer thereon by a vacuum film forming means; To manufacture. Next, a reflective layer is formed on the second substrate having grooves and / or pits formed on the surface by a vacuum film forming means, and a second recording layer is further formed thereon by a coating film forming means. The second information substrate is manufactured by forming the inorganic protective layer by vacuum film forming means. Then, the first and second information substrates can be easily manufactured by bonding them together via an organic transparent intermediate layer made of an adhesive.
That is, the production method includes the following steps (a) to (f).
<Manufacture of first information board>
(A) A step of providing a first recording layer containing a dye as a main component on a first substrate having grooves and / or pits formed on a surface by a coating film forming means.
(B) A step of providing a reflective layer on the first recording layer by means of a vacuum film forming means.
<Manufacture of second information board>
(C) a step of providing a reflective layer by vacuum film forming means on the second substrate having grooves and / or pits formed on the surface.
(D) a step of providing a second recording layer containing a dye as a main component on the reflective layer by a coating film forming means;
(E) a step of providing an inorganic protective layer on the second recording layer by vacuum film forming means.
<Lamination process>
(F) A step of bonding the first information substrate and the second information substrate via an adhesive layer.
[0019]
<Recording layer forming step>
In the present invention, a recording layer containing a dye compound as a main component is usually provided by a coating film forming means. That is, a recording layer is formed by coating a coating solution obtained by dissolving the above-described organic dye compound in a solvent on a substrate. As a solvent for preparing the coating liquid, a known organic solvent (for example, alcohol, cellosolve, halogenated carbon, ketone, ether, etc.) can be used. As a coating method, a spin coating method is preferable because the film thickness can be controlled by adjusting the concentration, viscosity, and drying temperature of the solvent of the light absorbing layer.
<Reflective layer forming step>
In the present invention, the reflective layer is usually provided by vacuum film forming means. That is, the reflection layer is formed by, for example, vapor deposition, sputtering, or ion plating of the above-described light reflective substance.
<Inorganic protective layer forming step>
In the present invention, usually, an inorganic protective layer is provided on the second recording layer by a vacuum film forming means. That is, the inorganic protective layer material is formed, for example, by vapor deposition, sputtering, or ion plating to form the inorganic protective layer.
<Lamination process>
In the present invention, the first and second information substrates are bonded via an adhesive layer. That is, an adhesive is dropped on the surface of the above-mentioned inorganic protective layer, the first information substrate is covered from above and the adhesive is spread uniformly, and then cured by irradiation with ultraviolet rays.
[0020]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0021]
<Example 1>
On a polycarbonate substrate (first substrate) having a depth of about 1500 mm, a groove width of about 0.25 μm, a guide groove with a track pitch of 0.74 μm and a guide groove uneven pattern of 120 mm in diameter and 0.58 mm in thickness, A first recording layer having a film thickness of about 600 ° was provided by spin-coating a coating solution in which a squarylium dye compound having the structural formula shown in 2,2,3,3-tetrafluoropropanol was dissolved.
The light absorption spectrum of this first recording layer was as shown in FIG. 6, the maximum absorption wavelength was 609 nm, and the absorbance (Abs) at the maximum absorption wavelength was 0.9.
Next, on the first recording layer, Ag was provided to a thickness of about 200 ° by sputtering using Ar as a sputtering gas to form a first reflective layer, thereby obtaining a first information substrate.
On the other hand, Ar was sputtered onto a polycarbonate substrate (second substrate) having a depth of about 200 mm, a groove width of about 0.25 μm, a guide groove with a track pitch of 0.74 μm, a guide groove with a concave and convex pattern of 120 mm in diameter and 0.58 mm in thickness. Then, Ag was provided to a thickness of about 1200 ° by a sputtering method to form a second reflective layer.
Next, a squarylium dye compound having a structural formula represented by the following chemical formula 1 is spin-coated on the reflective layer while adjusting the film thickness so that the absorbance is 1.6 (the maximum absorption wavelength is 609 nm), as further sputtering gas Ar thereon, provided ZnS-SiO ₂ to a thickness of about 1500Å to form the inorganic protective layer by a sputtering method to obtain a second information substrate.
Next, the first information substrate and the second information substrate were bonded together with an ultraviolet curable adhesive (KARAYAD DVD003 manufactured by Nippon Kayaku) to obtain an optical recording medium having a layer configuration shown in FIG.
Embedded image

A DVD (8-16) signal was applied to the optical recording medium at a linear velocity of 8.5 m / s using a DVD evaluation device (DDU1000 manufactured by Pulstec, wavelength: 657 nm, NA: 0.65). Recording and reproduction evaluation at a linear velocity of 3.49 m / s yielded results satisfying the DVD-ROM standard (see Table 1).
The recording strategy was a (n-2) T multi-pulse system, and the multi-pulse width was 10/16.
[Table 1]

[0022]
<Example 2>
An optical recording medium of the present invention was prepared in the same manner as in Example 1 except that the dye was changed to a squarylium dye compound having a structural formula represented by the following chemical formula 2, and evaluated in the same manner as in Example 1. As a result, good results were obtained as in Example 1 (see Table 2).
The light absorption spectrum of the recording layer of this optical recording medium was as shown in FIG. 7, and the maximum absorption wavelength was 600 nm.
Embedded image

[Table 2]

[0023]
<Example 3>
An optical recording medium of the present invention was prepared and implemented in the same manner as in Example 1, except that the film thickness was changed so that the absorbance (Abs) of the second recording layer was 1.4 to 2.1. When the modulation degree of the second recording layer was evaluated in the same manner as in Example 1, as shown in FIG. 8, a good modulation degree of 60% or more was obtained at an absorbance of 1.5 or more.
[0024]
<Example 4>
An optical recording medium of the present invention was prepared in the same manner as in Example 1 except that the groove depth of the second substrate was set to 600 °, and the reflectance of the second recording layer was evaluated in the same manner as in Example 1. As a result, it was 18%.
[0025]
<Example 5>
An optical recording medium of the present invention was prepared in the same manner as in Example 1 except that the groove depth of the second substrate was set to 200 °, and the jitter of the second recording layer was evaluated in the same manner as in Example 1. However, it was 8%.
[0026]
<Comparative Example 1>
An optical recording medium was prepared in the same manner as in Example 1, except that the dye was changed to a squarylium dye compound having the structural formula represented by the above chemical formula 2, and the groove depth of the second substrate was set to 800 °. When the reflectance of the second recording layer was evaluated in the same manner as in Example 1, it was 15%.
[0027]
【The invention's effect】
According to the first aspect, it is possible to provide an optical recording medium capable of recording and reproducing the first and second recording layers from one side.
According to the second to fourth aspects of the invention, it is possible to provide an optical recording medium capable of recording the first recording layer and the second recording layer with the same recording strategy pattern.
[Brief description of the drawings]
FIG. 1 is a diagram showing a light absorption spectrum of a dye recording layer.
FIG. 2 is a sectional view showing the structure of a read-only DVD having two recording layers.
FIG. 3 is a diagram showing a configuration example of an optical recording medium of the present invention.
FIG. 4 is a diagram showing a layer configuration on a first substrate on which a guide groove is formed.
FIG. 5 is a diagram showing a layer configuration on a second substrate on which a guide groove is formed.
FIG. 6 is a view showing a light absorption spectrum of a recording layer of Example 1.
FIG. 7 is a view showing a light absorption spectrum of a recording layer of Example 2.
FIG. 8 is a diagram illustrating a modulation degree of a second recording layer according to the third embodiment.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 first substrate 2 second substrate 3 first recording layer 4 second recording layer 5 organic transparent intermediate layer 5 ′ transparent intermediate layer 6 first reflective layer 7 second reflective layer 8 inorganic protective layer 9 recording Mark 10 Substrate groove 11 Substrate groove

Claims (4)

A first recording layer having an organic dye as a main component on its surface, a first substrate having a guide groove in which a first reflective layer is sequentially formed; a second reflective layer on its surface, a first substrate having an organic dye as a main component; No. 2 recording layer and a second substrate having a guide groove in which an inorganic protective layer is sequentially formed are bonded together with an organic transparent intermediate layer, with the substrate surface facing outside. An optical recording medium for recording and reproducing signal information formed in the second recording layer, wherein the depth of the guide groove of the second substrate is 200 to 600 ° and the optical absorption spectrum of the second recording layer is An optical recording medium having a maximum absorption wavelength of 580 to 620 nm and an absorbance at the maximum absorption wavelength (Absorption) of 1.5 to 2.0. 2. The optical recording medium according to claim 1, wherein the thickness of the second recording layer is 1.5 to 2.5 times the thickness of the first recording layer. 3. The optical recording medium according to claim 1, wherein the thickness of the second reflective layer is at least five times the thickness of the first reflective layer. 3. The optical recording medium according to claim 1, wherein the thermal conductivity of the second reflective layer is higher than the thermal conductivity of the first reflective layer.

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