JP2007179703A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium improved in reliability of a second recording layer. <P>SOLUTION: In the optical recording medium, a first recording layer 20, a spacer layer 40 and the second recording layer 50 are laminated in this order from a light incident side, wherein the second recording layer 50 includes an organic dye, a surface in contact with at least the second recording layer 50 in the spacer layer 40 is formed by using a cured product formed by curing a UV curing resin containing trimethylolpropane triacrylate and a surface in contact with the second recording layer 50 has ≥5.9 mN/μm<SP>2</SP>Young's modulus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical recording medium capable of recording information and reading information by light irradiation.

  An optical recording medium having a recording layer containing a dye such as CD-R or DVD-R can record a large amount of information and can be randomly accessed. Therefore, it is widely recognized and widely used as an external recording device in an information processing apparatus such as a computer.

  In recent years, it has been required to further increase the recording capacity of an optical recording medium due to an increase in the amount of information handled. Therefore, it is possible to provide two recording layers containing a dye on the substrate, record information on the two recording layers from one side, and read information recorded on the two recording layers from one side. Possible so-called single-sided two-layer optical storage media have been proposed (see, for example, Patent Documents 1 to 7).

  A so-called 2P method is known as a method for manufacturing such an optical recording medium. In the 2P method, for example, first, a first recording layer and a translucent reflective layer are formed on a groove of a transparent cured substrate of a thermoplastic resin on the light incident side. Subsequently, a stamper having a concavo-convex surface corresponding to the groove for the second recording layer is opposed to the semitransparent reflective layer, a photocurable resin is filled between the stamper and the semitransparent reflective layer, and ultraviolet irradiation is performed. The photo-curable resin is cured by, for example, to form a spacer layer, the stamper is peeled off, and a second recording layer, a reflective layer, and the like are formed on the groove of the spacer layer.

In this specification, each recording layer is referred to as a first recording layer and a second recording layer in order from the light incident side.
JP-A-2-78033 Japanese Patent Laid-Open No. 2-78034 Japanese Patent Laid-Open No. 2-118930 JP-A-4-321947 JP 2000-159841 A JP 2000-345073 A JP 2001-288206 A

  In such an optical recording medium, since the first recording layer is formed on a thermoplastic resin, the reliability as a recording medium is relatively high. However, the second recording layer is formed on a cured product of a photocurable resin. Therefore, the reliability of the second recording layer may be lowered particularly when the second recording layer contains an organic dye or a metal complex dye.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a recording medium capable of improving the reliability of the second recording layer.

  The inventors of the present invention have made extensive studies to achieve the above-described object. As a result, the surface of the spacer layer that is in contact with the second recording layer is a cured product of a photo-curing resin containing trimethylolpropane triacrylate (TMPTA). The present inventors have found that the reliability of the second recording layer can be sufficiently improved as compared with the conventional recording layer when the Young's modulus of this surface is not less than a predetermined value.

In the optical recording medium according to the present invention, the first recording layer, the spacer layer, and the second recording layer are laminated in this order from the light incident side. The second recording layer contains an organic dye and / or a metal complex dye, and at least a surface in contact with the second recording layer of the spacer layer is formed by a cured product obtained by curing a photocurable resin containing trimethylolpropane triacrylate. The Young's modulus of the surface in contact with the second recording layer in the spacer layer is 5.9 mN / μm ² or more.

According to the present invention, the reliability of the second recording layer is sufficiently improved as compared with the related art. The reason why such an effect is obtained is not clear, but, for example, by having a cured product obtained by curing a photocurable resin containing trimethylolpropane triacrylate, the surface of the spacer layer becomes more hydrophobic, and high temperature and high humidity. It becomes difficult to be affected by moisture in the test, and because the Young's modulus is 5.9 mN / μm ² or more, elastic deformation of the resin surface due to thermal influences in a high temperature and high humidity environment is suppressed. This is thought to be because the physical alteration and deformation of the recording pits are less likely to occur.

When the optical recording medium according to the present invention is defined from another viewpoint, the first recording layer, the spacer layer, and the second recording layer are laminated in this order from the light incident side, and the second recording layer is an organic dye. And / or the surface of the spacer layer in contact with at least the second recording layer is a cured product of a photocurable resin containing at least 20 wt% of trimethylolpropane triacrylate in all monomers. Such a cured resin can easily have a Young's modulus of 5.9 mN / μm ² or more.

  Here, the second recording layer preferably contains an organic dye, and examples of the organic dye include a cyanine dye.

  According to the present invention, it is possible to provide an optical recording medium in which the reliability of the second recording layer is sufficiently high.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

First, the structure of the optical recording medium according to the present embodiment will be described with reference to FIG. FIG. 1 is a partial cross-sectional view showing a preferred embodiment of an optical recording medium 100 of the present invention. The optical recording medium 100 shown in FIG. 1 includes a first recording layer 20, a semitransparent reflective layer 30, a spacer layer 40, a second recording layer 50, a reflective layer 60, an adhesive layer 70, and a dummy substrate 80 on a substrate 10. It has a laminated structure provided in close contact in this order. The optical recording medium 100 is a write-once type optical recording disk, and recording / reading with light having a short wavelength of 630 to 685 nm is possible. Further, the recording and reading light is applied to the optical recording medium 100 from the substrate 10 side, that is, from the bottom of FIG.

(Substrate 10)
The substrate 10 is, for example, a disk having a diameter of about 64 to 200 mm and a thickness of about 0.6 mm. Recording on the first recording layer 20 and the second recording layer 50 and reading of data from these recording layers are performed by light incident from the substrate 10. Therefore, it is preferable that at least the substrate 10 is substantially transparent to recording light and reading light, and more specifically, the transmittance of the substrate 10 with respect to recording light and reading light is preferably 88% or more. . As the material of the substrate 10, a resin or glass that satisfies the above-described conditions regarding transmittance is preferable, and among these, a cured product of a thermoplastic resin such as polycarbonate resin, acrylic resin, amorphous polyethylene, TPX, and polystyrene resin is particularly preferable.

  A tracking groove 12 is formed as a recess on the surface of the substrate 10 where the first recording layer 20 is formed, that is, on the inner surface side. The groove 12 is preferably a spiral continuous groove having a depth of 0.1 to 0.25 μm, a width of 0.20 to 0.50 μm, and a groove pitch of 0.6 to 1.0 μm. It is preferable. By configuring the groove in this way, a good tracking signal can be obtained without reducing the reflection level of the groove. The groove 12 can be formed at the same time when the substrate 10 is molded by injection molding or the like using the resin.

(First recording layer 20)
The first recording layer 20 is an optical recording layer containing an organic dye and / or a metal complex dye. Metal complex dyes may be mixed, organic dyes may be mixed, and metal complex dyes and organic dyes may be mixed.

(Metal complex dye)
First, the metal complex dye will be described. As metal complex dyes, azo metal complex dyes, indoaniline metal complex dyes, ethylenediamine metal complex dyes, azomethine metal complex dyes, phenylhydroxyamine metal complex dyes, phenanthroline metal complex dyes, nitrosoaminophenol metal complex dyes, pyridyltriazine metal complexes Various metal complex dyes such as a dye, an acetylacetonate metal complex dye, a metallocene metal complex dye, and a porphyrin metal complex dye can be employed. In particular, as the metal complex dye, among these, an azo metal complex dye, that is, a complex compound of an azo compound and a metal is preferable. A mixture of a plurality of metal complex dyes may be employed.

式（１）中、Ｑ^１は窒素原子及び該窒素原子に結合する炭素原子のそれぞれに結合して複素環又は該複素環を含む縮合環を形成する２価の残基を示す。Ｑ^２は互いに結合する２つの炭素原子のそれぞれに結合して縮合環を形成する２価の残基を示す。 The azo metal complex dye is not particularly limited as long as it is a complex compound of an azo compound having a functional group (azo group) represented by -N = N- and a metal. For example, examples of the azo metal complex dye include a complex compound of an azo compound and a metal each having an aromatic ring bonded to two nitrogen atoms of the azo group, and more specifically, in the following general formula (1): The complex compound of the azo compound and metal represented can be illustrated.

In formula (1), Q ¹ represents a divalent residue which forms a heterocyclic ring or a condensed ring containing the heterocyclic ring by bonding to a nitrogen atom and a carbon atom bonded to the nitrogen atom. Q ² represents a divalent residue which is bonded to each of two carbon atoms bonded to each other to form a condensed ring.

X ¹ is a functional group having one or more active hydrogens. For example, a hydroxyl group (—OH), a thiol group (—SH), an amino group (—NH ₂ ), a carboxy group (—COOH), an amide group ( -CONH _2), a sulfonamide group _(-SO 2 _NH 2), a sulfo group _(-SO 3 H), - such as _NSO 2 CF ₃ and the like.

ここで、式（４）中、Ｒ^７及びＲ^８は互いに同一であっても異なっていてもよく、それぞれ独立に炭素数１〜４のアルキル基を示し、Ｒ^９及びＲ^１０は互いに同一であっても異なっていてもよく、それぞれ独立にニトリル基又はカルボン酸エステル基を示し、Ｘ^１は上述のものと同義である。なお、上記カルボン酸エステル基としては、−ＣＯＯＣＨ_３、−ＣＯＯＣ_２Ｈ_５又は−ＣＯＯＣ_３Ｈ_５が好ましい。

ここで、式（５）中、Ｒ^１１は、水素原子又は炭素数１〜３のアルコキシ基を示し、Ｒ^１２、Ｒ^７及びＲ^８は互いに同一であっても異なっていてもよく、それぞれ独立に炭素数１〜４のアルキル基を示し、Ｘ^１は上述のものと同義である。

ここで、式（６）中のＲ^１１、Ｒ^１２、Ｒ^７、Ｒ^８及びＸ^１はそれぞれ、式（５）中のＲ^１１、Ｒ^１２、Ｒ^７、Ｒ^８及びＸ^１と同義である。

ここで、式（７）中のＲ^１１、Ｒ^１２、Ｒ^７、Ｒ^８及びＸ^１はそれぞれ、式（５）中のＲ^１１、Ｒ^１２、Ｒ^７、Ｒ^８及びＸ^１と同義である。 Examples of such azo compounds include compounds represented by the following general formulas (4) to (7).

Here, in formula (4), R ⁷ and R ⁸ may be the same or different from each other, each independently represents an alkyl group having 1 to 4 carbon atoms, and R ⁹ and R ¹⁰ are the same as each other. It may be present or different, and each independently represents a nitrile group or a carboxylate group, and X ¹ has the same meaning as described above. As the above-mentioned carboxylic acid ester _group, -COOCH 3, preferably -COOC ₂ H ₅ or -COOC ₃ H _5.

Here, in formula (5), R ¹¹ represents a hydrogen atom or an alkoxy group having 1 to 3 carbon atoms, and R ¹² , R ⁷ and R ⁸ may be the same or different from each other, and each independently. Represents an alkyl group having 1 to 4 carbon atoms, and X ¹ has the same meaning as described above.

Wherein each ^{R 11, R 12, R 7} , R 8 and ^{X 1} in the formula (6) has the same meaning as ^{R 11, R 12, R 7} , R 8 and ^{X 1} in formula (5) .

Wherein each ^{R 11, R 12, R 7} , R 8 and ^{X 1} in the formula (7) has the same meaning as ^{R 11, R 12, R 7} , R 8 and ^{X 1} in formula (5) .

Further, as the metal (center metal) constituting the above complex compound, titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) , Copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In) , Tin (Sn), antimony (Sb), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and the like. Alternatively, as the metal, V, Mo, and W, which is the oxide ions ^{respectively, VO 2+, VO 3+, MoO} 2+, MoO 3+, may have as ^{WO 3+} like.

一般式（８）、（９）、（１０）中、ＭはＮｉ^２＋、Ｃｏ^２＋、又はＣｕ^２＋を示し、ｍはＭの価数を示す。

これらのなかでは、Ａ１３〜Ａ３１で表される錯化合物が好ましい。また、化合物Ａ４９で表される分子からニトロ基及びジエチルアミノ基を除いた構造を有するものであってもよい。 Examples of the complex compound of the azo compound of the general formula (1) and the metal include complex compounds represented by the following general formulas (8), (9), and (10), and complexes represented by the following Tables 1 to 6. Compound (No. A1-A49) etc. are mentioned. These complex compounds are used alone or in combination. In addition, No. In the complex compounds represented by A1 to A49, two azo compounds are coordinated to one central metal element. It should be noted that two types of azo compound and central metal each indicate that they are contained at a molar ratio of 1: 1, and one where the central metal is indicated by “V═O” indicates that the azo compound is acetylacetone vanadium. Shows the coordinated position.

In general formulas (8), (9), and (10), M represents Ni ²⁺ , Co ²⁺ , or Cu ²⁺ , and m represents the valence of M.

Among these, complex compounds represented by A13 to A31 are preferable. Moreover, you may have a structure remove | excluding the nitro group and the diethylamino group from the molecule | numerator represented by compound A49.

Depending on the type of X ^1, the complex compound may be formed in a state of active hydrogen that X ¹ has is dissociated.

かかる錯化合物は、公知の方法に準じて合成することができる（例えば、古川、Ａｎａｌ． Ｃｈｅｍ． Ａｃｔａ．， １４０， ２８９（１９８２）を参照。）。 The above complex compound may contain a counter anion (counter cation) when the complex compound is present as an anion, or a counter anion (counter anion) when the complex compound is present as a cation. As the counter cation, alkali metal ions such as Na ⁺ , Li ⁺ and K ⁺ , ammonium ions, and the like are preferably used. Further, salt formation may be performed using a cyanine dye described later as a counter cation. As the counter anion, PF ₆ ⁻ , I ⁻ , BF ₄ ⁻ , an anion represented by the following formula (11), and the like are preferably used.

Such a complex compound can be synthesized according to a known method (see, for example, Furukawa, Anal. Chem. Acta., 140, 289 (1982)).

(Organic dye)
The organic dye is not particularly limited as long as it is a known one or can be synthesized by a known method or according to a known method. Examples of such organic dyes include cyanine dyes, squalium dyes, croconium dyes, azurenium dyes, xanthene dyes, merocyanine dyes, triarylamine dyes, anthraquinone dyes, azomethine dyes, oxonol dyes, and intermolecular CT dyes. Is mentioned.

ここで、式（２）及び（３）中、Ｑ^３は置換基を有していてもよいベンゼン環又は置換基を有していてもよいナフタレン環を構成する原子群を示し、Ｒ^１及びＲ^２はそれぞれ独立にアルキル基、シクロアルキル基、フェニル基若しくは置換基を有していてもよいベンジル基、又は互いに連結して３〜６員環を形成する基を示し、Ｒ^３はアルキル基、シクロアルキル基、アルコキシ基、フェニル基又は置換基を有していてもよいベンジル基を示し、前記Ｒ^１、Ｒ^２及びＲ^３が示す基は置換基を有していてもよい。 Among these, a cyanine dye is preferable, and a cyanine dye having a group represented by the following general formula (2) or (3) is more preferable.

Here, in the formulas (2) and (3), Q ³ represents an atomic group constituting a benzene ring which may have a substituent or a naphthalene ring which may have a substituent, and R ¹ and R ² independently represents an alkyl group, a cycloalkyl group, a phenyl group or a benzyl group which may have a substituent, or a group which is linked to each other to form a 3- to 6-membered ring, and R ³ represents an alkyl group , A cycloalkyl group, an alkoxy group, a phenyl group or a benzyl group which may have a substituent, the groups represented by R ¹ , R ² and R ³ may have a substituent.

ここで、式中、Ｌは下記一般式（１３ａ）で表される２価の連結基を示し、Ｒ^２１及びＲ^２２はそれぞれ独立に炭素数１〜４のアルキル基若しくは置換基を有していてもよいベンジル基、又は互いに連結して３〜６員環を形成する基を示し、Ｒ^２３及びＲ^２４はそれぞれ独立に炭素数１〜４のアルキル基若しくは置換基を有していてもよいベンジル基、又は互いに連結して３〜６員環を形成する基を示し、Ｒ^２５及びＲ^２６はそれぞれ独立に炭素数１〜４のアルキル基又はアリール基を示し、Ｑ^１１及びＱ^１２はそれぞれ独立に置換基を有していてもよいベンゼン環又は置換基を有していてもよいナフタレン環を構成する原子群を示す。ただし、Ｒ^２１、Ｒ^２２、Ｒ^２３及びＲ^２４のうち少なくとも１個はメチル基でない基を示し、下記一般式（１３ａ）で表される２価の連結基は置換基を有していてもよい。

シアニン色素として、より具体的には、例えば下記表７〜１２に表される化合物（Ｎｏ．Ｔ１〜Ｔ６７）などが挙げられる。

Examples of the cyanine dye include cyanine dyes represented by the following general formula (12).

Here, in the formula, L represents a divalent linking group represented by the following general formula (13a), and R ²¹ and R ²² each independently have an alkyl group having 1 to 4 carbon atoms or a substituent. An benzyl group which may be bonded to each other, or a group which is linked to each other to form a 3- to 6-membered ring, R ²³ and R ²⁴ may each independently have an alkyl group having 1 to 4 carbon atoms or a substituent; A benzyl group or a group linked to each other to form a 3- to 6-membered ring; R ²⁵ and R ²⁶ each independently represents an alkyl group or an aryl group having 1 to 4 carbon atoms; and Q ¹¹ and Q ¹² are each An atomic group constituting a benzene ring which may have a substituent independently or a naphthalene ring which may have a substituent is shown. However, at least one of R ²¹ , R ²² , R ²³ and R ²⁴ represents a group that is not a methyl group, and the divalent linking group represented by the following general formula (13a) may have a substituent. Good.

More specifically, examples of the cyanine dye include compounds (No. T1 to T67) shown in Tables 7 to 12 below.

Oxonol dyes can also be used suitably. Examples of the oxonol dye include oxonol dye No. 1 described in Table 13. 1, no. 2 etc. can be illustrated.

(Method for manufacturing the first recording layer)
As a method for forming such a first recording layer, an organic dye and / or a metal complex dye is dissolved or dispersed in a solvent such as an organic solvent to obtain a mixed solution, and this mixed solution is applied onto the substrate 10 and applied. It can be formed by removing the solvent from the film. As the solvent of the mixed solution, alcohol solvents (including alkoxy alcohol systems such as keto alcohol systems and ethylene glycol monoalkyl ether systems), aliphatic hydrocarbon solvents, ketone solvents, ester solvents, ether solvents, Aromatic solvents, alkyl halide solvents and the like can be mentioned. Among them, alcohol solvents and aliphatic hydrocarbon solvents are preferable.

  As the alcohol solvent, an alkoxy alcohol system, a keto alcohol system, or the like is preferable. In the alkoxy alcohol solvent, the alkoxy moiety preferably has 1 to 4 carbon atoms, the alcohol moiety preferably has 1 to 5 carbon atoms, more preferably 2 to 5 carbon atoms, and the total number of carbon atoms. It is preferable that it is 3-7. Specifically, ethylene glycol monoalkyl ether (cellosolve) such as ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (also called ethyl cellosolve, ethoxyethanol), butyl cellosolve, 2-isopropoxy-1-ethanol, etc. And 1-methoxy-2-propanol, 1-methoxy-2-butanol, 3-methoxy-1-butanol, 4-methoxy-1-butanol, 1-ethoxy-2-propanol and the like. Examples of keto alcohols include diacetone alcohol. Furthermore, fluorinated alcohols such as 2,2,3,3-tetrafluoropropanol can also be suitably used.

  As the aliphatic hydrocarbon solvent, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, cyclooctane, dimethylcyclohexane, n-octane, iso-propylcyclohexane, t-butylcyclohexane and the like are preferable. Cyclohexane and the like are preferable.

  Examples of the ketone solvent include cyclohexanone.

  In the present embodiment, a fluorinated alcohol such as 2,2,3,3-tetrafluoropropanol is particularly preferable. Further, alkoxy alcohols such as ethylene glycol monoalkyl ether are preferable, and ethylene glycol monoethyl ether, 1-methoxy-2-propanol, 1-methoxy-2-butanol and the like are particularly preferable. A solvent may be used individually by 1 type, or 2 or more types of mixed solvents may be sufficient as it. For example, a mixed solvent of ethylene glycol monoethyl ether and 1-methoxy-2-butanol is preferably used.

  The mixed solution may contain a binder, a dispersant, a stabilizer and the like as appropriate in addition to the above components.

  Examples of the application method of the mixed solution include a spin coating method, a gravure application method, a spray coating method, and a dip coating method, and among these, the spin coating method is preferable.

  The thickness of the first recording layer 20 thus formed is preferably 50 to 300 nm. Outside this range, the reflectivity decreases and it becomes difficult to perform reproduction in accordance with the DVD standard. Further, when the film thickness of the first recording layer 20 positioned above the groove 12 is 100 nm or more, particularly 130 to 300 nm or more, the degree of modulation becomes extremely large.

  The extinction coefficient (imaginary part k of the complex refractive index) of the first recording layer 20 with respect to recording light and reproduction light is preferably 0 to 0.20. When the extinction coefficient exceeds 0.20, sufficient reflectance tends not to be obtained. The refractive index of the first recording layer 20 (the real part n of the complex refractive index) is preferably 1.8 or more. When the refractive index is less than 1.8, the degree of signal modulation tends to be small. The upper limit of the refractive index is not particularly limited, but is usually about 2.6 for the convenience of organic dye synthesis.

  The extinction coefficient and refractive index of the first recording layer 20 can be obtained according to the following procedure. First, a measurement sample is prepared by providing a recording layer on a predetermined transparent substrate at about 40 to 100 nm, and then the reflectance of the measurement sample through the substrate or the reflectance from the recording layer side is measured. Desired. In this case, the reflectance is measured by specular reflection (about 5 °) using the wavelength of the recording / reproducing light. Further, the transmittance of the sample is measured. From these measured values, the extinction coefficient and the refractive index can be calculated according to the method described in, for example, Kyoritsu Zensho “Optics”, Kozo Ishiguro, pages 168 to 178.

(Translucent reflective layer 30)
The translucent reflective layer 30 is a layer having a light transmittance of 40% or more and an appropriate light reflectance. Further, it is desirable that the translucent reflective layer 30 has low light absorption and has a certain degree of corrosion resistance. Further, it is desirable that the translucent reflective layer 30 has a blocking property so that the first recording layer 20 is not affected by the seepage of the spacer layer 40.

  Specifically, as the translucent reflective layer 30, for example, a metal or alloy thin film having high reflectivity can be employed.

As a material of the translucent reflective layer 30, a material having a moderately high reflectance at the wavelength of the reproduction light, for example,
Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Pd, Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Zn, Cd, Metals and metalloids such as Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi, and rare earth metals can be used alone or as an alloy. Among these, Au, Al, and Ag have high reflectivity and are suitable as materials for the translucent reflective layer 30. In addition to these as main components, other components may be included.

  Among them, an alloy containing 50% or more of Ag, for example, an Ag—Bi alloy is preferable. The concentration of Ag is preferably about 98 to 99.5 atomic%.

  In order to ensure high transmittance, the thickness of the translucent reflective layer 30 is usually preferably 50 nm or less. More preferably, it is 30 nm or less. More preferably, it is 20 nm or less. However, since the first recording layer 20 is not affected by the spacer layer 40, a certain amount of thickness is required, which is usually 3 nm or more. More preferably, it is 5 nm or more.

  It is also possible to form a multilayer film by alternately stacking a low refractive index thin film and a high refractive index thin film using a material other than metal, and use it as a reflective layer.

  Examples of the method for forming the translucent reflective layer 30 include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition. Further, it is known for improving the reflectivity, improving the recording characteristics, improving the adhesion, etc. between the translucent reflective layer 30 and the first recording layer 20 or between the translucent reflective layer 30 and the spacer layer 40. An inorganic or organic intermediate layer or adhesive layer can also be provided.

(Spacer layer 40)
The spacer layer 40 is a transparent layer that separates the translucent reflective layer 30 and the second recording layer 50. The spacer layer 40 is a cured product formed by curing a photocurable resin such as an ultraviolet curable resin (including delayed curing type) containing trimethylolpropane triacrylate (TMPTA) as a monomer. Further, the Young's modulus of the surface of the spacer layer 40 that contacts the second recording layer 50 is 5.9 mN / μm ² or more.

The Young's modulus in this specification is an indentation hardness test (25 ° C., maximum load 100 mgf (about 0.98 mN)) using a diamond triangular pyramid indenter (ridge spacing 115 degrees) as an indenter, and maintaining load-unloading. The load-displacement curve is obtained by time 2 s, number of divisions 100 times, step interval 100 msec), and the intersection of the tangent line on the unloading curve side at the maximum displacement point of this load-displacement curve and the X axis on the X coordinate It is a value calculated from the following equation by obtaining (a) and the intersection (b) on the X coordinate between the perpendicular drawn from the maximum displacement point in the X axis direction and the X axis.
E = 1.775 × 10 ⁻³ × (F / a) × b where F is the maximum load (mN) and E is the Young's modulus (mN / μm ² ).
By this measuring method, the Young's modulus of a portion having a thickness of about 0.5 μm in the vicinity of the surface of the spacer layer can be measured.

  Although the photocurable resin used in this embodiment is not specifically limited, Other monomers can be included as a monomer other than trimethylolpropane triacrylate. For example, other monomers such as methyl, ethyl, propyl, butyl, amyl, 2-ethylhexyl, octyl, nonyl, dodecyl, hexadecyl, octadecyl, cyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonyl Phenoxyethyl, tetrahydrofurfuryl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-chloro-2-hydroxypropyl, dimethylaminoethyl, diethylaminoethyl, nonylphenoxyethyl tetrahydrofurfuryl, caprolactone-modified tetrahydrofurfuryl, isobornyl, Monofunctional (meth) acrylates such as (meth) acrylates having groups such as dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, etc. And the like. 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,8-octane Diacrylate such as diol, 1,9-nonanediol, tricyclodecane dimethanol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, dis of tris (2-hydroxyethyl) isocyanurate Di (meth) acrylate of diol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of (meth) acrylate, neopentyl glycol, 2 mol of ethylene oxide per 1 mol of bisphenol A Di (meth) acrylate of diol obtained by adding propylene oxide or propylene oxide, diol or tri (meth) acrylate of triol obtained by adding 3 mol or more of ethylene oxide or propylene oxide to 1 mol of trimethylolpropane, bisphenol Di (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, pentaerythritol tri (meth) acrylate, didiol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of A1 Poly (meth) acrylate of pentaerythritol, caprolactone-modified tris [(meth) acryloxyethyl] isocyanurate, poly (meth) acrylate of alkyl-modified dipentaerythritol, capro Ton modified dipentaerythritol poly (meth) acrylate, hydroxypivalic acid neopentyl glycol diacrylate, caprolactone modified hydroxypivalic acid neopentyl glycol diacrylate, ethylene oxide modified phosphoric acid (meth) acrylate, ethylene oxide modified alkylated phosphoric acid ( And (meth) acrylate. Also, N-vinyl-2-pyrrolidone, acryloylmorpholine, vinylimidazole, N-vinylcaprolactam, N-vinylformamide, vinyl acetate, (meth) acrylic acid, (meth) acrylamide, N-hydroxymethylacrylamide or N-hydroxyethyl Examples include acrylamide and alkyl ether compounds thereof. In addition, this photocurable resin may contain only trimethylol propane triacrylate as a monomer.

  The Young's modulus of the cured product of trimethylolpropane triacrylate is relatively high compared to the cured product of other monomers as described above, so the Young's modulus of the cured product depends on the weight ratio of trimethylolpropane triacrylate in all monomers. Can often be adjusted. For example, the Young's modulus of the cured product can usually be increased by increasing the weight ratio of trimethylolpropane triacrylate in all monomers. When the weight ratio of trimethylolpropane triacrylate in all monomers is 20 wt% or more, the above-mentioned Young's modulus can be easily achieved.

  In addition, the photocurable resin preferably contains a photopolymerization initiator in order to improve curability by irradiation with light such as ultraviolet rays. As the photopolymerization initiator, those generally used as photopolymerization initiators can be appropriately selected and used in consideration of their reactivity and the like. Specific examples of the photopolymerization initiator include benzoin alkyl ether, benzophenone, dialkoxyacetophenone, benzoylphosphine oxide, benzoin oxime ketone, benzyl dialkyl ketal, 1-hydroxy-cyclohexyl-phenyl ketone (Irgacure 184), 2-methyl-1 [4- (Methylthio) phenyl] -2-morpholinopropan-1-one (Irgacure 907), bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (Irgacure 819), 2-hydroxy-2- Methyl-1-phenyl-propan-1-one (Darocur 1173), [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959), 2 − Ndyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (Irgacure 369), and mixtures thereof, such as Irgacure 184 and benzophenone (Irgacure 500), Darocur 1173 and Irgacure 184 (Irgacure 1000). The above-mentioned “Irgacure” and “Darocur” are registered trademarks.

  The photocurable resin as described above can be used as the spacer layer 40 by coating the coating solution as it is or by dissolving it in an appropriate solvent, and applying the coating solution and curing it by irradiating light such as ultraviolet light. A cured product can be formed.

  As a method for applying the coating solution, a method such as a spin coating method or a casting method is used, and among these, the spin coating method is preferable. Further, a resin having a high viscosity can be applied and formed by screen printing or the like. It is preferable to use a photocurable resin that is liquid at 20 to 40 ° C. without using a solvent. The viscosity is preferably adjusted to 20 to 1000 mPa · s.

  The thickness of the spacer layer 40 is usually preferably 5 μm or more. In order to separately apply focus servo to the first recording layer 20 and the second recording layer 50, a certain distance is required between the two recording layers. Although it depends on the focus servo mechanism, a distance of usually 5 μm or more, preferably 10 μm or more is required.

  However, if the spacer layer 40 is too thick, it takes time to adjust the focus servo to the two recording layers, the moving distance of the objective lens also becomes long, and further, the time is required for curing and the productivity is lowered. In general, the thickness is preferably 100 μm or less.

  On the spacer layer 40, a groove 42 for the second recording layer 50 is formed in the same manner as the substrate 10. The groove 42 is manufactured by a 2P method described later, that is, by transferring and curing a resin stamper having projections and depressions to a photocurable resin.

The spacer layer 40 may be one layer as shown in FIG. 1, but may be two layers including the upper layer 40a and the lower layer 40b as shown in FIG. 2, and may be three or more layers. In any case, the upper layer 40a in contact with the second recording layer 50 is formed of a cured product obtained by curing an ultraviolet curable resin containing trimethylolpropane triacrylate, and the Young's modulus of the surface of the upper layer 40a is 5.9 mN / μm ² or more. It is. In particular, it is preferable that the Young's modulus of the lower layer 40b is lower than the Young's modulus of the upper layer 40a because warpage of the optical disk can be reduced.

  In addition, the material of layers other than the upper layer 40a will not be specifically limited if it is transparent, The hardened | cured material of various photocurable resins, the hardened | cured material of a thermoplastic resin, etc. can be utilized.

(Second recording layer 50)
The second recording layer 50 is formed using an optical recording material containing an organic dye and / or a metal complex dye.

  The illustration of the dye, the formation method of the second recording layer, and the like are the same as those of the first recording layer 20, and thus description thereof is omitted here. Note that the dye in the second recording layer 50 may be the same as or different from the dye in the first recording layer 20.

(Reflection layer 60)
The reflective layer 60 is a layer that reflects light. For example, a thin film of a metal or alloy having a light reflectance can be employed. Examples of the metal and alloy include gold (Au), copper (Cu), aluminum (Al), silver (Ag), and AgCu. The thickness of the reflective layer 60 is preferably 10 to 300 nm. Such a reflective layer 60 can be easily formed by vapor deposition, sputtering, or the like.

(Adhesive layer 70)
The adhesive layer 70 is a layer that bonds the dummy substrate 80 and the reflective layer 60 together. The adhesive layer 70 does not need to be transparent, but it is preferable that the adhesive strength is high and the shrinkage rate at the time of curing and adhesion is low, the shape stability of the optical recording medium is high.

  In addition, a known inorganic or organic protective layer may be provided between the adhesive layer 70 and the reflective layer 60 in order to suppress adverse effects on the reflective layer 60.

  The film thickness of the adhesive layer 70 is usually preferably 2 μm or more and more preferably 5 μm or more so as to obtain sufficient productivity while obtaining sufficient adhesive force. However, in order to make the optical recording medium as thin as possible and to improve the productivity by reducing the curing time, it is usually preferably 100 μm or less.

The material of the adhesive layer 70 is a hot melt adhesive, an ultraviolet curable adhesive, a heat curable adhesive,
Adhesive adhesives, pressure-sensitive double-sided tapes and the like are used, and methods suitable for them, for example, roll coater method, screen printing method, spin coating method and the like can be mentioned. In the case of DVD ± R, a screen printing method or a spin coating method is used by using an ultraviolet curable adhesive comprehensively determined from workability, productivity, and disk characteristics.

(Dummy substrate 80)
The dummy substrate 80 is a substrate similar to the substrate 10. Note that the dummy substrate does not need to be transparent.

  In the optical recording medium 100, any other layer may be sandwiched as necessary as long as it is not between the spacer layer 40 and the second recording layer 50. Alternatively, any other layer may be provided on the outermost surface of the medium.

  When recording or appending to the optical recording medium 100 having the above configuration, recording light having a predetermined wavelength is applied to the surface of the substrate 10 of the optical recording medium 100, that is, the lower surface of the optical recording medium 100 as shown in FIG. Irradiate in pulses. That is, in this optical recording medium, the outer surface of the substrate 10 becomes the light incident surface 10a. At this time, by performing appropriate focusing, a desired portion of the first recording layer 20 or the second recording layer 50 selectively absorbs light energy and changes the light reflectance of the recording layer in that portion. Let

  When reading is performed, reading light weaker than that at the time of recording may be similarly focused on a desired portion of the first recording layer 20 or the second recording layer 50, and the difference in reflectance may be measured.

In the optical recording medium 100 according to the present embodiment, the surface of the spacer layer 40 that contacts the second recording layer, that is, the spacer layer 40 or the upper layer 40a is cured by curing a photocurable resin containing trimethylolpropane triacrylate. The Young's modulus of this surface is 5.9 mN / μm ² or more. Thereby, the reliability of the 2nd recording layer 50 shows a favorable value compared with the past.

Here, even if the surface of the spacer layer 40 in contact with the second recording layer is a cured product obtained by curing a photocurable resin containing trimethylolpropane triacrylate, the Young's modulus of less than 5.9 mN / μm ² is sufficient. Even if the reliability is not obtained and the Young's modulus of the surface of the spacer layer 40 in contact with the second recording layer is 5.9 mN / μm ² or more, the cured product contains trimethylolpropane triacrylate. Even when the cured resin is not a cured product, sufficient reliability cannot be obtained.

  In the above embodiment, an optical recording disk having two recording layers as a recording layer has been described. However, three or more recording layers may be provided. Even in this case, if the above-mentioned recording layer is formed on the above-mentioned spacer, good reliability can be obtained.

(Method for producing optical recording medium)
Next, a method for manufacturing this optical recording medium will be described with reference to FIGS. First, the case where the spacer layer 40 is a single layer will be described with reference to FIGS. 3A and 4B.

  First, as shown in FIG. 3A, the first recording layer 20 is formed by applying the first recording layer coating liquid to the substrate 10 having the pregroove 12 on one side and drying it. . Next, the translucent reflective layer 30 is formed on the first recording layer 20.

  Subsequently, a stamper S having projections 42a corresponding to the grooves of the second recording layer is prepared, and the projections 42a of the stamper S are arranged to face the semitransparent reflection layer 30, and the stamper S and the semitransparent reflection layer are arranged. The spacer photo-curing resin is sandwiched between 30 and the stamper and the substrate are rotated at a high speed to remove excess photo-curing resin, and then the photo-curing resin is cured by irradiating ultraviolet rays through the stamper ( (See (a) of FIG. 4). Then, as shown in FIG. 4A, the stamper S is peeled off to form the spacer layer 40 having the groove 42 as the tracking groove on the semitransparent reflective layer 30. Thereafter, the second recording layer 50, the reflective layer 60, the dummy substrate 80, and the adhesive layer 70 are formed on the spacer layer 40 as described above, and the optical recording medium 100 as shown in FIG. 1 is obtained.

  Next, a case where the spacer layer 40 is two layers will be described. Here, as shown in FIG. 3 (b), the above-mentioned spacer photo-curing resin is applied onto the stamper S in advance, and then cured by irradiation with ultraviolet rays to form an upper layer 40a made of a cured product on the stamper S. Form.

  Subsequently, the stamper S is disposed so as to face the translucent reflective layer 30, and another lower layer 40b is filled between the stamper S and the translucent reflective layer 30, for example, by being filled with another photocurable resin or the like and cured. Then, the stamper S is peeled off as shown in FIG. 4B to complete the optical recording medium as shown in FIG.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

(Examples 1-4)
In each of the examples, an optical recording medium for Young's modulus measurement, in which a part without a groove was provided, and an optical recording medium for a reliability test, in which a groove was provided as usual, were prepared.

(UV curable resin for spacers)
Polypropylene glycol (# 700) diacrylate (NK ester APG-700, manufactured by Shin-Nakamura Chemical Co., Ltd.) as a bifunctional monomer, trimethylolpropane triacrylate (NK ester A-TMPT, Shin-Nakamura Chemical Co., Ltd.) as a trifunctional monomer Co., Ltd. was mixed in the ratio of Examples 1 to 4 in FIG. 5, and 2 wt% of a polymerization initiator (IRGACURE 184, Ciba Specialty Chemicals Co., Ltd.) was added to the total amount of monomers. It was.

(Optical recording medium for reliability measurement)
A polycarbonate substrate having a diameter of 120 mm and a thickness of 0.58 mm having a spiral pregroove on one side was prepared. Next, 0.8 wt% of azo metal complex dye A16 and cyanine dye T53 is added to 2,2,3,3-tetrafluoropropanol so as to be a weight ratio of 60:40, and coating for the first recording layer is performed. A liquid was prepared. The obtained coating solution for the first recording layer was applied on the surface of the polycarbonate resin substrate on which the pregroove was formed by a spin coating method at 2000 rpm and dried at 80 ° C. for 1 hour to form the first recording layer (thickness 110 nm). ) Was formed. Next, a translucent reflective layer (thickness: 12 nm) was formed on the first recording layer by an Ag—Bi alloy by sputtering.

  Subsequently, a polyolefin stamper having protrusions corresponding to the spiral groove of the second recording layer is prepared, and the protrusions of the polyolefin stamper are arranged to face the translucent reflective layer, and the stamper and the translucent reflective layer After sandwiching the UV curable resin for spacers of Examples 1 to 4 above, the stamper and the substrate are rotated at a high speed to remove excess UV curable resin, and then the UV curable resin is cured by irradiating ultraviolet rays through the polyolefin stamper. I let you. Then, the polyolefin stamper was peeled to form a spacer (thickness 55 μm) having a groove as a tracking groove on the translucent reflective layer.

  Next, 1.0 wt% of azo metal complex dye A3 and cyanine dye T49 is added to 2,2,3,3-tetrafluoropropanol so as to have a weight ratio of 35:65, and coating for the second recording layer is performed. A liquid was prepared. The obtained coating solution for the second recording layer was applied on the spacer layer by a spin coating method at 2000 rpm and dried at 80 ° C. for 1 hour to form a second recording layer (thickness 130 nm). Next, a reflective layer (thickness 120 nm) was formed by Ag on the second recording layer by sputtering.

  In addition, a polycarbonate substrate with a diameter of 120 mm and a thickness of 0.58 mm is prepared, placed opposite to the reflective layer, an ultraviolet curable resin is sandwiched between the reflective layer and the polycarbonate substrate, and the lower substrate and the upper substrate are fastened. The excess ultraviolet curable resin was removed by rotating, and the ultraviolet curable resin was irradiated with ultraviolet rays through the upper transparent substrate to cure the ultraviolet curable resin to form an adhesive layer, thereby completing the optical recording medium.

  Then, the recording power of the second recording layer of the optical recording medium obtained in this way is used as an optical disk evaluation apparatus (0DU-1000) manufactured by Pulstec Industrial Co., Ltd. equipped with a laser with a wavelength of 650 nm and an optical head with NA = 0.65. It measured using. Here, the recording power was obtained as a value at which a linear velocity was 7.68 m / s and an eye pattern in which the center of the eye was located at the center of the 14T waveform was obtained. Subsequently, the degree of modulation (14T signal amplitude divided by the maximum reflectance of the 14T signal) and PI (Inner-code-Parity) error (number of errors per ECC block) were measured with this recording power. After recording, an acceleration test was performed at 80 ° C. and 80% RH (relative humidity) for 200 hours to further measure the degree of modulation and PI error.

(Optical recording medium for Young's modulus measurement)
A polycarbonate stamper with a diameter of 120 mm and a thickness of 0.58 mm and a polyolefin stamper having protrusions corresponding to the spiral groove of the second recording layer are prepared, and the protrusions of the polyolefin stamper are arranged opposite to the polycarbonate substrate. Then, the UV curable resin for spacers of Examples 1 to 4 described above is sandwiched between the stamper and the polycarbonate substrate, and the excess UV curable resin is removed by rotating the stamper and the polycarbonate substrate at a high speed, and then passed through the polyolefin stamper. The ultraviolet curable resin was cured by irradiating with ultraviolet rays. Thereafter, the polyolefin stamper was peeled off to form a spacer (thickness 55 μm) having a groove as a tracking groove on the polycarbonate substrate. Here, a mirror portion not provided with a groove is previously provided in a portion having a radius of 24 mm or less of the stamper, and a portion having a radius of 24 mm of the spacer has a mirror-like surface without a groove. Then, Young's modulus was measured at the mirror portion of the spacer. Specifically, the measurement is performed using an ultra-indentation hardness tester ENT1100 manufactured by Elionix Co., Ltd., 25 ° C., load 100 mgf, holding time between load and unloading is 2 seconds, and the indenter is a diamond triangular pyramid indenter. (Edge spacing 115 degrees) was used. Specifically, a load-displacement curve is obtained under the conditions of a maximum load of 100 mgf (about 0.98 mN) at 25 ° C., a load-unload holding time of 2 s, a division number of 100, and a step interval of 100 msec. On the X coordinate between the intersection of the tangent line on the unloading curve side at the maximum displacement point of the curve and the X axis on the X coordinate, and the perpendicular drawn from the maximum displacement point in the X axis direction and the X axis The intersection (b) was obtained, and the Young's modulus was calculated by the following formula.
E = 1.775 × 10 ⁻³ × (F / a) × b where F is the maximum load (mN) and E is the Young's modulus (mN / μm ² ).

  After that, in order to confirm whether the Young's modulus of the surface of the second recording layer side of the spacer layer is maintained as desired after the production as an optical recording medium, the optical recording medium produced as described above was destroyed and the Young The rate was remeasured. The blade of a cutter knife was pressed against the end face of the disk, and the two polycarbonate substrates bonded together were destroyed while destroying the adhesive layer. As a result, peeling occurred at the interface between the second recording layer and the reflective layer. The dye used in the second recording layer was washed away using 2,2,3,3-tetrafluoropropanol to expose the spacer layer surface, and the Young's modulus of the spacer surface was determined in the same manner as described above.

(Example 5)
In Example 5, an oxonol dye NO. 1: Oxonol dye NO. A mixture containing 2 = 70: 30 by weight is used, and the oxonol dye NO. 1: Oxonol dye NO. The same procedure as in Example 2 was performed except that a mixture containing 2 = 60: 40 by weight was used.

(Example 6)
In advance, the ultraviolet curable resin of Example 2 was applied onto a polyolefin stamper by spin coating at 8000 rpm, and cured by irradiating with ultraviolet rays to form a 5 μm spacer upper layer. Between the spacer upper layer and the translucent reflective layer, ultraviolet rays were formed. A cured resin SD6200 (Tg = 49 ° C., manufactured by Dainippon Ink & Chemicals, Inc.) was sandwiched and cured to form a two-layer spacer (total film thickness 55 μm).

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the spacer UV curable resin was changed to that of Comparative Example 1 in FIG.

(Comparative Examples 2 to 5)
In the ultraviolet curable resin for spacers, the same procedure as in Examples 1 to 4 was performed except that ethoxylated isocyanuric acid triacrylate was used instead of trimethylolpropane triacrylate.

(Comparative Example 6)
The UV curable resin for spacers was the same as Example 1 except that it did not contain trimethylolpropane triacrylate.

  The Young's modulus results are shown in FIG. 5, and the reliability results are shown in FIG. Note that, between the second recording layers, after the initial test and after the acceleration test, the degree of modulation needs to exceed 60%, and the PI error is desirably less than 280. In the figure, “not measurable” means that the degree of modulation was too low to measure.

  First, the Young's modulus of the spacer surface hardly changed before and after the second recording layer was laminated.

Further, as in Examples 1 to 6, the upper layer of the spacer in contact with the second recording layer is obtained by curing a photocurable resin containing trimethylolpropane triacrylate, and the surface Young's modulus is 5 When it was 9.9 mN / μm ² or more, both the initial stage and after the acceleration test showed a sufficiently high degree of modulation and a sufficiently small PI error.

On the other hand, Young's modulus of trimethylolpropane triacrylate containing Young's modulus is less than 5.9 mN / μm ² (about 600 mgf / μm ² ), or Young's modulus of 5.9 mN / min without containing trimethylolpropane triacrylate. In Comparative Examples 2 to 4, which are μm ² or more, and Comparative Example 6, the reliability particularly after the acceleration test was not sufficient.

FIG. 1 is a schematic sectional view of an optical recording medium according to the present invention. FIG. 2 is a schematic sectional view of another optical recording medium according to the present invention. FIG. 3 is a schematic cross-sectional view showing a method for manufacturing an optical recording medium. FIG. 4 is a schematic cross-sectional view subsequent to FIG. 3 showing the method for manufacturing the optical recording medium. FIG. 5 is a table showing the configuration of the spacer resin according to Examples 1 to 6 and Comparative Examples 1 to 6, the configuration of the second recording layer, and the Young's modulus before and after the second recording layer lamination on the spacer surface. FIG. 6 is a table showing the modulation degree and PI error of the optical recording media according to Examples 1 to 6 and Comparative Examples 1 to 6 after the initial stage and after the acceleration test.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Board | substrate, 20 ... 1st recording layer, 30 ... Semi-transparent reflective layer, 40 ... Spacer layer, 50 ... 2nd recording layer, 60 ... Reflective layer, 70 ... Adhesive layer, 80 ... Dummy board | substrate, 12, 42 ... Groove 100: Optical recording medium.

Claims (5)

In order from the light incident side, the first recording layer, the spacer layer, and the second recording layer are laminated in this order,
The second recording layer includes an organic dye and / or a metal complex dye,
Of the spacer layer, at least the surface in contact with the second recording layer is formed of a cured product of a photocurable resin containing trimethylolpropane triacrylate,
An optical recording medium in which a Young's modulus of a surface of the spacer layer in contact with the second recording layer is 5.9 mN / μm ² or more. In order from the light incident side, the first recording layer, the spacer layer, and the second recording layer are laminated in this order,
The second recording layer includes an organic dye and / or a metal complex dye,
An optical recording medium in which at least a surface of the spacer layer in contact with the second recording layer is formed by a cured product of a photocurable resin containing 20 wt% or more of trimethylolpropane triacrylate in all monomers.   The optical recording medium according to claim 1, wherein the second recording layer contains an organic dye.   The optical recording medium according to claim 3, wherein the organic dye is a cyanine dye. The optical recording medium according to claim 4, wherein the cyanine dye has a group represented by the following general formula (2) or (3).

In the formulas (2) and (3), Q ³ represents an atomic group constituting a benzene ring which may have a substituent or a naphthalene ring which may have a substituent, and R ¹ and R ² are Each independently represents an alkyl group, a cycloalkyl group, a phenyl group or a benzyl group which may have a substituent, or a group which is linked to each other to form a 3- to 6-membered ring, and R ³ represents an alkyl group, a cycloalkyl group A group, an alkoxy group, a phenyl group or a benzyl group which may have a substituent, and the groups represented by R ¹ , R ² and R ³ may have a substituent.

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