JP2009026379A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which has sufficient reliability. <P>SOLUTION: The film surface incidence type optical recording medium 20 comprising a reflective layer 23, a recording layer 22 primarily consisting of pigment, and a cover layer 24 sequentially laminated on a substrate 21 on which a guide groove is formed, and has sufficient storage stability by setting storage elastic modulus of the cover layer 24 within a preset range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium and the like, and more particularly to an optical recording medium having a recording layer containing a dye.

  In recent years, blue lasers capable of ultra-high density recording have been rapidly developed, and write-once type optical recording media corresponding thereto have been developed. In particular, development of a dye-coated write-once medium that enables efficient production at a relatively low cost is strongly desired.

The present inventors have proposed an extremely high-density dye-coated write-once optical recording medium having good recording and reproducing characteristics using a substrate having a relatively shallow groove depth that can be stably molded (Patent Document). 1). That is, a substrate having guide grooves formed thereon, a layer having at least a light reflection function on the substrate, a recording layer containing as a main component a dye having a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded state, And a cover layer on which the recording / reproducing light is incident on the recording layer in this order, and a recording groove on the side far from the surface on which the recording / reproducing light beam obtained by focusing the recording / reproducing light is incident is recorded. When the groove portion is used, the optical recording medium is configured such that the reflected light intensity of the recording pit portion formed in the recording groove portion is larger than the reflected light intensity when not recorded in the recording groove portion mainly due to a phase change.
JP 2007-026541 A

However, even such an optical recording medium has the following problems regarding reliability. Usually, in the case of such an optical recording medium, an environmental test in which the optical recording medium is left for 100 hours in an environment of a temperature of 80 ° C. and a relative humidity of 80% RH is performed as a reliability evaluation index. The characteristics of the optical recording medium are evaluated before and after the environmental test, and the lifetime (reliability) of the optical recording medium is estimated based on whether the degree of deterioration is within a predetermined range. There are two types of optical recording medium lifetimes: an Archival lifetime and a shelf lifetime. That is, a recording medium is required that a recorded signal can be reproduced with a predetermined quality even after the environmental test (Achival life) and can be recorded and reproduced with a predetermined quality after the environmental test (Shelf life).
However, in the optical recording medium described in Patent Document 1, it has been found that the shelf characteristics may be insufficient but the shelf characteristics may be insufficient in this environmental test.

The present invention has been made to solve such problems.
That is, the optical recording medium described in Patent Document 1 is to provide an optical recording medium having sufficient reliability.

Accordingly, the inventors of the present invention have reached the present invention as a result of intensive studies on the relationship between the reliability and the elastic modulus of the cover layer in the optical recording medium described in Patent Document 1.
That is, according to the present invention, the main component is a substrate on which guide grooves are formed, a layer having at least a light reflection function on the substrate, and a dye having a light absorption function with respect to a recording / reproducing light wavelength in an unrecorded state. And a cover layer on which recording / reproducing light is incident on the recording layer in this order, and a recording / reproducing light beam obtained by focusing the recording / reproducing light from a surface on which the recording / reproducing light enters the cover layer When the far-side guide groove portion is used as a recording groove portion, in an optical recording medium in which the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity when not recorded in the recording groove portion, When performing an environmental test that is allowed to stand for 100 hours in an 80% RH environment, both the storage elastic modulus E5b ′ at 5 ° C. and the storage elastic modulus E55b ′ at 55 ° C. before the environmental test of the cover layer are both 100. And the ratio (E5b ′ / E55b ′) is 10 or less, and both the storage elastic modulus E5a ′ at 5 ° C. and the storage elastic modulus E55a ′ at 55 ° C. after the end of the environmental test are both There is provided an optical recording medium characterized by being 100 MPa or less and a ratio (E5a ′ / E55a ′) of 10 or less.
Here, when the cover layer has a structure of two or more layers having different compositions, at least the cover layer disposed on the side closest to the recording layer has the above-described characteristics.

  Thus, according to the present invention, an optical recording medium having good reliability can be obtained.

  Hereinafter, the best mode for carrying out the present invention (hereinafter, an embodiment of the present invention) will be described. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention.

  FIG. 1 is a diagram for explaining a write-once medium having a film surface incident configuration having a recording layer mainly composed of a dye to which the present embodiment is applied. In the present embodiment, the substrate 21 in which the groove is formed has at least a layer having a reflection function (reflection layer 23) and a dye that absorbs recording / reproducing light in an unrecorded (before recording) state as main components. A recording layer 22 having a light absorption function and a cover layer 24 are sequentially laminated, and recording / reproduction light beam 27 collected through an objective lens is incident from the cover layer 24 side for recording / reproduction. Do it. That is, a “film surface incidence configuration” (also referred to as a reverse stack) is adopted. In the following, a layer having a reflection function is simply referred to as a “reflection layer”, and a recording layer having a light absorption function mainly composed of a dye is simply referred to as a “recording layer”. When the recording / reproducing light beam 27 is incident on the cover layer 24 side of the film surface incident configuration, a high NA (numerical aperture) of about NA (numerical aperture) = 0.6 to 0.9 is usually used for high-density recording. Objective lens 28 is used. As the recording / reproducing light wavelength λ, a red to blue-violet wavelength (about 350 nm to 600 nm) is often used. Furthermore, for high-density recording, it is preferable to use a wavelength range of 350 nm to 450 nm, but the present invention is not necessarily limited thereto.

  In the present embodiment, in FIG. 1, the guide groove portion (the recording / reproducing light beam is incident) on the side far from the incident surface (the surface on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24. (Guide groove portion on the side far from the surface) is a recording groove portion, and recording is such that the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity of the recording groove portion when not recorded (hereinafter referred to as LtoH recording) I do. The main mechanism is that the increase in reflected light intensity is due to the phase change of reflected light at the recording pit portion. That is, a change is used before and after recording of the reciprocating optical path length of the reflected light in the recording groove.

Here, the film surface incident type optical recording medium 20 covers a guide groove portion (coincident with the groove portion of the substrate) far from the incident surface (the surface on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24. The inter-groove portion 25 (in-groove) and the guide inter-groove portion (matching the inter-groove portion of the substrate) close to the surface on which the recording / reproducing light beam is incident are referred to as a cover layer groove portion 26 (on-groove).
Here, by controlling the optical characteristics such as the groove shape and the refractive index of each layer, LtoH recording is realized with the cover layer groove portion (in-groove) as a recording track (hereinafter referred to as in-groove recording). It becomes possible.

Here, by using a material having a predetermined elastic modulus for the cover layer 24, the optical recording medium 20 having excellent reliability can be obtained. Specifically, when an environmental test is performed for 100 hours in an 80 ° C./80% RH environment, the cover layer 24 has a storage elastic modulus E5b ′ at 5 ° C. before the environmental test and a storage elasticity at 55 ° C. The ratio E55b ′ is 100 MPa or less, the ratio (E5b ′ / E55b ′) is 10 or less, and the storage elastic modulus E5a ′ at 5 ° C. after the end of the environmental test and the storage elasticity at 55 ° C. By setting the ratios E55a ′ to 100 MPa or less and the ratio (E5a ′ / E55a ′) to 10 or less, the optical recording medium 20 having excellent reliability can be obtained.
Further, when the cover layer 24 is composed of two or more layers having different compositions, excellent reliability can be obtained by providing a cover layer having the above storage elastic modulus characteristics at least on the side closest to the recording layer 22. The optical recording medium 20 can be obtained.

Here, the storage elastic modulus of the cover layer can be measured by the following method.
(A) Storage elastic modulus (E ′) measuring device and measuring conditions / measuring device of cover layer material: Viscoelastic spectrometer EXSTAR6000 / DMS6100 (manufactured by SII Nanotechnology Co., Ltd.)
・ Frequency setting: 10Hz
Set temperature range: -100 ° C to 150 ° C
-Temperature rising rate: 2 ° C./min.
(B) Measurement sample preparation method and storage elastic modulus measurement method (1) A coating solution of a cover layer material is spin-coated on a PET film so as to have a thickness of about 150 to 200 μm, and irradiated with ultraviolet rays using a high-pressure mercury lamp. It hardens | cures by (about 1000 mJ / cm < ² >), and a cover layer material laminated | multilayer film is produced.
(2) Cut the cover layer material laminated film obtained in (1) with a width of 10 mm and a length of about 3 cm, peel off only the cover layer material film from the PET film, and the thickness of the cover layer material film actually obtained. Is measured with a micrometer.
(3) The cover layer material film obtained in (2) is mounted on the measuring apparatus (chuck-clamp distance 5 mm), and E ′ is measured in a predetermined temperature range under a nitrogen flow.
The above measurement method shows the measurement method when the composition of the coating liquid of the cover layer material is known in advance, but in the case of a cover layer already formed as an optical recording medium, if possible, (B) Similar to (2), the measurement may be performed with a part of the cover layer peeled off from the optical recording medium.

(Concerning preferred embodiments of specific layer structure and materials)
In the following, regarding the specific materials and aspects of the layer configuration shown in FIG. 1, considering the situation where the development of the blue wavelength laser is advanced, the case where the wavelength λ of the recording / reproducing light beam 27 is around 405 nm is assumed. I will explain.

(Substrate 21)
The substrate 21 may be made of plastic, metal, glass or the like having an appropriate workability and rigidity in a film surface incident configuration. Unlike conventional substrate surface incidence configurations, there are no restrictions on transparency or birefringence. The guide groove is formed on the surface. However, in the case of metal or glass, it is necessary to provide a light or thermosetting thin resin layer on the surface and to form the groove there. In this respect, it is preferable in terms of manufacturing to use a plastic material and to form the shape of the substrate 21, particularly the disk shape, and the surface guide groove all at once by injection molding.

  As the plastic material that can be injection-molded, polycarbonate resin, polyolefin resin, acrylic resin, epoxy resin, and the like conventionally used in CDs and DVDs can be used. The thickness of the substrate is preferably about 0.5 mm to 1.2 mm. The total thickness of the substrate and the cover layer is preferably 1.2 mm, which is the same as that of a conventional CD or DVD. This is because the cases used in conventional CDs and DVDs can be used as they are. In the Blu-ray disc, the substrate thickness is 1.1 mm and the cover layer thickness is 0.1 mm.

  A tracking guide groove is formed in the substrate 21. In the present embodiment, the track pitch at which the cover layer groove portion 25 becomes the recording groove portion is 0.1 μm to 0.6 μm in order to achieve higher density than CD-R and DVD-R. Preferably, it is more preferable to set it as 0.2 micrometer-0.4 micrometer. The groove depth is preferably in the range of approximately 30 nm to 70 nm. The groove depth is appropriately optimized within the above range in consideration of the recording groove portion reflectance in an unrecorded state, the signal characteristics of the recording signal, the push-pull signal characteristics, the optical characteristics of the recording layer, and the like.

  In the present embodiment, since the interference due to the phase difference of the reflected light in the recording groove portion and the recording groove portion is used, it is necessary that both exist in the focused light spot. For this reason, the recording groove width (width between cover layer grooves) is preferably smaller than the spot diameter (diameter in the groove transverse direction) on the recording layer surface of the recording / reproducing light beam 27. In an optical system having a recording / reproducing light wavelength λ = 405 nm and NA (numerical aperture) = 0.85, when the track pitch is 0.32 μm, it is preferably in the range of 0.1 μm to 0.2 μm. Outside these ranges, it is often difficult to form grooves or inter-groove portions.

  The shape of the guide groove is usually rectangular. In particular, when the recording layer 22 is formed by coating, which will be described later, it is desirable that the dye is selectively accumulated on the substrate groove in several tens of seconds until the solvent of the solution containing the dye is almost evaporated. For this reason, it is also preferable that the shoulder between the substrate grooves of the rectangular groove is rounded so that the dye solution easily falls and accumulates in the substrate groove portion. Such a groove shape having a round shoulder can be obtained by etching the surface of a plastic substrate or stamper by exposing it to plasma or UV ozone for several seconds to several minutes. Etching with plasma is suitable for obtaining the shape of the shoulder of the rounded groove portion because the sharp portion such as the shoulder of the groove portion of the substrate (edge of the groove portion) is selectively cut away.

  The guide groove is usually added by groove modulation, groove modulation such as groove meandering, groove depth modulation, or irregular pits due to intermittent or intermittent recording grooves, in order to give additional information such as addresses and synchronization signals. Have a signal. For example, in a Blu-ray disc, a wobble address method using two modulation methods, MSK (minimum-shift-keying) and STW (saw-tooth-wobbles), is used.

(Layer with light reflection function)
The layer having the light reflection function (reflective layer 23) preferably has a high reflectance with respect to the recording / reproducing light wavelength and a reflectance of 70% or more with respect to the recording / reproducing light wavelength. Examples of visible light used as a recording / reproducing wavelength, particularly those exhibiting high reflectivity in the blue wavelength region, include Au, Ag, Al, and alloys containing these as main components. More preferably, it is an alloy mainly composed of Ag having a high reflectance at λ = 405 nm and a small absorption. Mainly composed of Ag, Au, Cu, rare earth elements (particularly Nd), Nb, Ta, V, Mo, Mn, Mg, Cr, Bi, Al, Si, Ge, etc. 0.01 atomic% to 10 atomic% By adding, the corrosion resistance against moisture, oxygen, sulfur and the like can be increased, which is preferable. In addition, a dielectric mirror in which a plurality of dielectric layers are stacked can be used.

  The film thickness of the reflective layer 23 is preferably 70 nm or less, and more preferably 65 nm or less in order to maintain the groove step on the surface of the substrate 21. Except for the case where a two-layer medium described later is formed, the lower limit of the reflective layer thickness is preferably 30 nm or more, more preferably 40 nm or more. The surface roughness Ra of the reflective layer 23 is preferably 5 nm or less, and more preferably 1 nm or less. Ag has a property that flatness is increased by the addition of an additive. In this sense, the content of the additive element is preferably 0.1 atomic% or more, more preferably 0.5 atomic% or more. The reflective layer 23 can be formed by sputtering, ion plating, electron beam evaporation, or the like.

(Recording layer mainly composed of dye)
The dye used in this embodiment refers to an organic compound having a remarkable absorption band due to its structure in the visible light (and vicinity) wavelength region of 300 nm to 800 nm. In an unrecorded state (before recording) in which such a dye is formed as the recording layer 22, it has absorption at the wavelength λ of the recording / reproducing light beam, changes in quality due to recording, and changes in reflected light intensity of the reproducing light on the recording layer 22. A dye that causes an optical change that can be detected as is called a “principal dye”. The main component dye may exhibit the above function as a mixture of a plurality of dyes.

  The main component dye content is preferably 50% or more, more preferably 80% or more, and still more preferably 90% or more in terms of weight%. As the main component dye, a single dye absorbs with respect to the wavelength λ of the recording / reproducing light beam and is preferably altered by recording to cause the above optical change. However, it has absorption with respect to the wavelength λ of the recording / reproducing light beam 27. However, the function may be shared so that the other dye is indirectly altered to cause an optical change by generating heat. In addition to this, a dye as a so-called quencher for improving the temporal stability (temperature, humidity, light stability) of a dye having a light absorption function may be mixed with the main component dye. Examples of the inclusion other than the main component dye include a binder (binder) made of a low-polymer material and a dielectric.

  The main component dye is not particularly limited by the structure. In the present embodiment, recording causes a change in the refractive index to decrease in the recording layer 22, and in principle, as long as the absorption coefficient in an unrecorded (before recording) state is a value larger than 0, optical There are no strong constraints on the physical characteristics. It is only necessary that the main component dye has absorption with respect to the wavelength λ of the recording / reproducing light beam, changes its property due to its own light absorption and heat generation, and lowers the refractive index. Here, the alteration refers specifically to phenomena such as expansion, decomposition, sublimation, and melting due to absorption and heat generation of the main component dye. The coloring matter itself as the main component may be altered, accompanied by some structural change, and the refractive index may be lowered. The decrease in the refractive index may be a cavity formed in the recording layer and / or the interface, or may be a decrease in the refractive index due to thermal expansion of the recording layer.

  The temperature showing such alteration is preferably in the range of 100 ° C to 500 ° C, and more preferably in the range of 100 ° C to 350 ° C. From the viewpoint of storage stability and reproduction light resistance, it is more preferably 150 ° C. or higher. Moreover, if the decomposition temperature is 300 ° C. or lower, the jitter characteristics particularly at a high linear velocity of 10 m / s or higher tend to be good, which is preferable. It is preferable that the decomposition temperature is 280 ° C. or lower because there is a possibility that the characteristics in high-speed recording are further improved. Usually, the above-described alteration behavior is measured as the thermal characteristics of the main component dye, and the rough behavior can be measured as the weight reduction onset temperature by the thermogravimetric analysis-differential thermal analysis (TG-DTA) method.

Examples of the dye having the above-described properties include methine-based, (metal-containing) azo-based, pyrone-based, porphyrin-based compounds, and the like, and mixtures thereof. More specifically, metal-containing azo dyes (JP-A-9-277703, JP-A-10-026692 etc.) and pyrone dyes (JP-A 2003-266954) are inherently excellent in light resistance. And the weight reduction start temperature _Td in TG-DTA is 150 to 400 degreeC, and it is preferable at the point which has a sharp weight loss characteristic (The volatility of a decomposition product is high and it is easy to form a cavity.). Particularly preferred are metal-containing azo dyes.

  More specifically, the azo dye includes a compound having a coupler component having a 6-hydroxy-2-pyridone structure and any one diazo component selected from isoxazole triazole and pyrazole, and the organic compound. Examples thereof include metal complex compounds composed of metal ions coordinated with a dye compound. In particular, metal-containing pyridone azo compounds having the following general formulas [I] to [III] are preferable.

(In the formula, R _{1 to} R ₁₀ are each independently a hydrogen atom or a monovalent functional group.)
Further, a metal-containing cyclic β-diketone azo compound comprising a cyclic β-diketone azo compound represented by the following general formula [IV] or [V] and a metal ion is preferable.

(In the formula, ring A is a nitrogen-containing heteroaromatic ring formed together with a carbon atom and a nitrogen atom, and X, X ′, Y, Y ′, and Z are each independently a substituent other than a hydrogen atom (including spiro). ) Which may have a carbon atom, an oxygen atom, a sulfur atom, a nitrogen atom represented by N—R ₁₁ , C═O, C═S, C═NR ₁₂ , and a β-diketone structure Forms a 5- or 6-membered ring structure: R ₁ represents a hydrogen atom, a linear or branched alkyl group, a cyclic alkyl group, an aralkyl group, an aryl group, a heterocyclic group, an acyl group represented by —COR ₁₃ , —NR ₁₄ represents any of the amino groups representing R ₁₅ , R ₁₂ represents a hydrogen atom, a linear or branched alkyl group, or an aryl group, R ₁₃ represents a hydrocarbon group or a heterocyclic group, R ₁₄ , R ₁₅ represents a hydrogen atom, a hydrocarbon group or a heterocyclic group. Moreover is substituted they optionally And may be. The X, X ', Y, Y ', there at Z if the nitrogen atom represented by the carbon atom or N-R _11, adjacent the binding of both even double bond a single bond Further, when X, X ′, Y, Y ′, and Z are a carbon atom, a nitrogen atom represented by N—R ₁₁ , and C═NR ₁₂ , adjacent ones are condensed with each other and saturated. Or an unsaturated hydrocarbon ring or a heterocyclic ring may be formed.)
A metal-containing azo compound comprising a compound represented by the following general formula [VI] and a metal is also preferred.

Wherein A and A ′ represent a residue that forms a heteroaromatic ring together with the carbon atom and nitrogen atom to which they are bonded, X represents a group having an active hydrogen, and R ₁₆ and R ₁₇ are each independently Represents hydrogen or any substituent.)
Furthermore, the metal-containing group azo compound represented by the following general formula [VII] is also mentioned.

(In Formula [VII], Ring A is a nitrogen-containing heteroaromatic ring formed together with a carbon atom and a nitrogen atom, and XL is capable of coordinating a metal when X becomes an anion when L is eliminated. R ₁₈ and R ₁₉ each independently represents a hydrogen atom, a linear or branched alkyl group, a cyclic alkyl group, an aralkyl group or an alkenyl group, which are each condensed with adjacent substituents or with each other. A ring may be formed, and R ₂₀ , R ₂₁ and R ₂₂ each independently represents hydrogen or an arbitrary substituent.)

These azo dyes have a main absorption band from a shorter wavelength than the azo dyes conventionally used in CD-R and DVD-R, and the absorption coefficient k _d near 400 nm is 0. It is preferable because it is a large value of about 3 to 1. Examples of metal ions include divalent metal ions such as Ni, Co, Cu, Zn, Fe, and Mn. Particularly, when Ni and Co are contained, they are excellent in light resistance, high temperature and high humidity environment resistance. It is preferable. In addition, the metal-containing azo dye represented by the formula [VIII] can be used as the compound Y described later after having a longer wavelength.
More specifically, the pyrone dye is preferably a compound having the following general formula [VII] or [IX].

(In the formula [VIII], R _{23 to} R ₂₆ represent a hydrogen atom or an arbitrary substituent, or R ₂₃ and R ₂₄ , R ₂₅ and R ₂₆ are condensed to form a hydrocarbon ring or a heterocyclic structure. The hydrocarbon ring and the heterocyclic ring may have a substituent, X ₁ represents an electron-withdrawing group, X ₂ represents a hydrogen atom or -QY (Q is a direct bond, carbon number 1 Or an alkylene group, an arylene group, or a heteroarylene group represented by 2, and Y represents an electron-withdrawing group, and the alkylene group, the arylene group, and the heteroarylene group may have any substituent other than Y. Z is —O—, —S—, —SO ₂ —, —NR ₂₇ — (R ₂₇ is a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group, a cyano group, or a hydroxy group. _{, -NR 28 R 29 (R 28} , R 29 are each independently hydrogen atom, an optionally substituted hydrocarbon Or an optionally substituted heterocyclic group, -COR ₃₀ - (R ₃₀ represents a optionally substituted hydrocarbon group or an optionally substituted heterocyclic _{group.), - COR 31 (R} 31 is substituted Represents a hydrocarbon group which may be substituted or a heterocyclic group which may be substituted.

(In the formula [IX], R _{32 to} R ₃₅ represent a hydrogen atom or an arbitrary substituent, or R ₃₂ and R ₃₃ , R ₃₄ and R ₃₅ are condensed to form a hydrocarbon ring or a heterocyclic structure. The hydrocarbon ring and the heterocyclic ring may have a substituent, and ring A represents a carbocyclic ketone ring or a heterocyclic ketone ring which may have a substituent together with C═O. , Z represents —O—, —S—, —SO ₂ —, —NR ₃₆ — (R ₃₆ represents a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group, a cyano group, or a hydroxy group. , —NR ₃₇ R ₃₈ (R ₃₇ and R ₃₈ are each independently a hydrogen atom, an optionally substituted hydrocarbon group or an optionally substituted heterocyclic group, —COR ₃₉ — (R ₃₉ is optionally substituted) Represents a good hydrocarbon group or an optionally substituted heterocyclic group.), —COR ₄₀ (R ₄₀ represents an optionally substituted hydrocarbon group or a substituent). Represents a heterocyclic group which may be substituted; represents)) represents)) represents)

In the optical recording medium 20 to which this embodiment is applied, a dye X refractive index n _d is greater than about 2 in a recording and reproducing light wavelength λ when unrecorded recording layer 22, n _d <n _c ( n _c is reduced the average n _d of mixed refractive index) comprising dyes or other organic matter in the recording and reproducing light wavelength of the cover layer lambda, the inorganic material (mixture Y), the recording layer 22, and n _c It is also possible to make it equal or less. In this case, a dye _satisfying n _d > n _c mainly realizes a light absorption function using a dye having a large k _{d, and} a dye satisfying n _d <n _c is mainly mixed with a material that causes deformation by decomposition. It is preferable to do. In this case, the material may be a pigment.
The dye X is n _d > n _c , particularly n _d > 2, and the main absorption band is a long wavelength side of the recording / reproducing light wavelength and has a high refractive index. Such a dye preferably has a main absorption band peak in the range of 300 nm to 400 nm and a refractive index n _d in the range of 2 to 3.

  Specific examples of the dye X include porphyrin, stilbene, (carbo) styryl, coumarin, pyrone, chalcone, triazole, methine (cyanine, oxonol), sulfonylimine, azlactone compounds, and the like. A mixture is mentioned. In particular, coumarin dyes (JP 2000-043423 A), carbostyril dyes (JP 2001-287466 A), the above-mentioned pyrone dyes (JP 2003-266554 A), etc. are appropriately decomposed or sublimated. Since it has temperature, it is preferable. Moreover, although it is not a main absorption band, the phthalocyanine which has the strong absorption band according to it in the vicinity of 350 nm-400 nm, a naphthalocyanine compound, its derivative (s), and these mixtures are also preferable.

Examples of the mixture Y include metal-containing azo dyes having a main absorption band in the wavelength band of 600 nm to 800 nm. A dye suitable for use in CD-R and DVD-R, and preferably has an absorption coefficient k _d of 0.2 or less, more preferably 0.1 or less near 405 nm. Although the refractive index n _d is very high at 2.5 or more at the long wavelength end λ _L , it is conveniently about 1.5 because it is sufficiently away from the absorption peak at the short wavelength end.
More specifically, a metal-containing azo compound represented by the general formula [X] disclosed in JP-A-6-65514 is exemplified.

(In the formula [X], R ₄₁ and R ₄₂ are a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, a nitro group, a cyano group, COOR ₄₅ , COR ₄₆ , OR ₄₇ and SR ₄₈ (R _{45 to} R ₄₈ represent an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group or a cyclic alkyl group), and X represents a hydrogen atom or an alkyl having 1 to 3 carbon atoms. Group, a branched alkyl group, OR ₄₉ , SR ₅₀ (R ₄₉ , R ₅₀ represents an alkyl group having 1 to 3 carbon atoms), R ₄₃ and R ₄₄ are a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, It represents a branched alkyl group or a cyclic alkyl group, and may be bonded to an adjacent benzene ring, or a nitrogen atom, R ₄₃ and R ₄₄ may form a ring.)
Alternatively, a metal-containing azo compound represented by the general formula [XI] disclosed in JP 2002-114922 A is also preferable.

(In the formula [XI], R ₅₁ and R ₅₂ are a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, a nitro group, a cyano group, COOR ₅₅ , COR ₅₆ , OR ₅₇ and SR ₅₈ (R _{55 to} R ₅₈ represent an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group or a cyclic alkyl group), and X represents a hydrogen atom or an alkyl having 1 to 3 carbon atoms. group, branched alkyl _{group, OR 59, SR 60 (R} 59, R 60 represents an alkyl group having 1 to 3 carbon atoms) represents, R _53, R ₅₄ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms ).

  In the present embodiment, the recording layer 22 is formed by a coating method, a vacuum vapor deposition method, or the like, but is particularly preferably formed by a coating method. In other words, the recording layer 22 coating solution is prepared by dissolving the above dye as a main component together with a binder, a quencher and the like in a suitable solvent, and coating on the reflection layer 23 described above. The concentration of the main component pigment in the solution is usually in the range of 0.01 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, more preferably 0.2 wt% to 2% by weight. Thereby, the recording layer 22 is usually formed to a thickness of about 1 nm to 100 nm. In order to make the thickness less than 50 nm, the dye concentration is preferably less than 1% by weight, and more preferably less than 0.8% by weight. It is also preferable to further adjust the number of rotations of application.

  Solvents for dissolving the main dye material and the like include alcohols such as ethanol, n-propanol, isopropanol and n-butanol diacetone alcohol; fluorinated hydrocarbons such as tetrafluoropropanol (TFP) and octafluoropentanol (OFP) Solvents; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether; esters such as butyl acetate, ethyl lactate and cellosolve acetate; chlorinated hydrocarbons such as dichloromethane and chloroform; dimethylcyclohexane Hydrocarbons; ethers such as tetrahydrofuran, ethyl ether, dioxane; ketones such as methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone It can be. These solvents are appropriately selected in consideration of the solubility of the main component dye material or the like to be dissolved, and two or more kinds can be mixed and used.

  As the binder, organic polymers such as cellulose derivatives, natural polymer substances, hydrocarbon resins, vinyl resins, acrylic resins, polyvinyl alcohol, and epoxy resins can be used. Further, the recording layer 22 can contain various dyes or anti-fading agents other than the dyes in order to improve light resistance. As the antifading agent, a singlet oxygen quencher is generally used. The amount of the anti-fading agent such as a singlet quencher is usually 0.1% to 50% by weight, preferably 1 to 30% by weight, more preferably based on the recording layer material. 5% to 25% by weight.

  Examples of the coating method include a spray method, a spin coating method, a dip method, and a roll coating method. In particular, in a recording medium on a disk, the spin coating method ensures the uniformity of the film thickness and the defect density. Is preferable.

(Cover layer 24)
The cover layer 24 is made of a material that is transparent to the recording / reproducing light beam 27 and has little birefringence. Usually, a plastic plate (referred to as a sheet) is bonded with an adhesive, or after application, light, radiation, or It is formed by curing with heat or the like. The cover layer 27 preferably has a transmittance of 70% or more with respect to the wavelength λ of the recording / reproducing light beam, and more preferably 80% or more.

  The plastic used as the sheet material is polycarbonate, polyolefin, acrylic, cellulose triacetate, polyethylene terephthalate, or the like. For adhesion, light, radiation curing, thermosetting resin, or pressure sensitive adhesive is used. As the pressure-sensitive adhesive, pressure sensitive adhesives made of acrylic, methacrylate, rubber, silicon, and urethane polymers can be used.

  For example, after preparing a coating solution by dissolving a photocurable resin constituting the adhesive layer in an appropriate solvent, this coating solution is applied onto the recording layer 22 or an interface layer described later to form a coating film, and coating Overlay the polycarbonate sheet on the membrane. Thereafter, the coating liquid is further stretched and developed by rotating the medium in a superposed state as necessary, and then cured by irradiating ultraviolet rays with a UV lamp. Alternatively, a pressure sensitive adhesive is applied to the sheet in advance, the sheet is overlaid on the recording layer 22 or the interface layer, and then pressed and pressed with an appropriate pressure.

  The pressure-sensitive adhesive is preferably an acrylic or methacrylate polymer pressure-sensitive adhesive from the viewpoint of transparency and durability. More specifically, 2-ethylhexyl acrylate, n-butyl acrylate, iso-octyl acrylate and the like are used as main component monomers, and these main component monomers are used as acrylic acid, methacrylic acid, acrylamide derivatives, maleic acid, hydroxyl ethyl acrylate, A polar monomer such as glycidyl acrylate is copolymerized. Glass transition temperature Tg, tack performance (adhesive force immediately formed when contacted at low pressure), peel strength by adjusting the molecular weight of the main monomer, mixing its short chain components, and adjusting the crosslink point density with acrylic acid The physical properties such as shear holding force can be controlled. As the solvent for the acrylic polymer, ethyl acetate, butyl acetate, toluene, methyl ethyl ketone, cyclohexane and the like are used. The pressure-sensitive adhesive preferably further contains a polyisocyanate-based crosslinking agent.

The pressure-sensitive adhesive is made of the above-mentioned material. A predetermined amount is uniformly applied to the surface of the cover layer sheet material in contact with the recording layer side, and the solvent is dried. If it has, it is cured by applying pressure to the surface) with a laminating roller or the like. When the cover layer sheet material coated with the pressure-sensitive adhesive is bonded to the surface of the recording medium on which the recording layer is formed, it is preferably bonded in a vacuum so as not to entrain air and form bubbles.
Also, after applying the above-mentioned pressure-sensitive adhesive on the release film and drying the solvent, the cover layer sheet is bonded, and the release film is further peeled off to integrate the cover layer sheet and the pressure-sensitive adhesive layer, and then the recording medium You may paste together.

  When the cover layer 24 is formed by a coating method, a spin coating method, a dip method, or the like is used. In particular, the spin coating method is often used for a medium on a disk. Similarly, as the cover layer material by coating, urethane, epoxy, acrylic resin, or the like is used, and after coating, it is irradiated with ultraviolet rays, electron beams, or radiation to accelerate radical polymerization or cationic polymerization and cure.

  The cover layer material is preferably a composition comprising an acrylic or methacrylate oligomer and / or monomer from the viewpoint of transparency and durability. More specifically, (meth) acrylate oligomers such as polyether (meth) acrylate, polyester (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, iso- One or more monofunctional (meth) acrylate monomers such as octyl acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, and phenoxyethyl (meth) acrylate A uniformly mixed composition is preferred. Control of physical properties such as glass transition temperature Tg, tack performance (adhesive force immediately formed when contacted at low pressure), peel strength, shear holding force, etc. by adjusting the molecular weight of the oligomer and the type and amount of the monomer can do.

  The recording mechanism of the optical recording medium in the present invention utilizes bulging deformation of the recording layer toward the cover layer. Therefore, it is preferable that the cover layer has an appropriate softness, that is, a storage elastic modulus of a certain level or less. This is because if the storage elastic modulus is too high, the bulging deformation of the recording layer is suppressed, making it difficult to form a recording mark. In addition, before and after the environmental test, if the storage elastic modulus of the cover layer changes greatly in the operating temperature range (the operating temperature range of the optical recording medium is usually 5 ° C. to 55 ° C.), the recording / reproducing characteristics are increased. It will change. For this reason, in order to keep the shelf life long, it is preferable that the change in the storage elastic modulus is small before and after the environmental test. Therefore, the cover layer material is required to have a modulus of elasticity in the operating temperature range that is equal to or less than a predetermined value and a small change in temperature of the storage modulus before and after the environmental test.

  Specifically, the value of the storage elastic modulus before the environmental test needs to be 100 MPa or less in both cases of 5 ° C. (E5b ′) and 55 ° C. (E55b ′). The pressure is preferably 50 MPa or less, more preferably 30 MPa or less, and particularly preferably 10 MPa or less.

  Similarly, the value of the storage elastic modulus after the environmental test must be 100 MPa or less in both cases of 5 ° C. (E5a ′) and 55 ° C. (E55a ′). The pressure is preferably 50 MPa or less, more preferably 30 MPa or less, and particularly preferably 10 MPa or less.

  Further, before and after the environmental test, the ratio of the storage elastic modulus (E5b ′ / E55b ′, E5a ′ / E55a ′) at 5 ° C. and 55 ° C. needs to be 10 or less. Preferably it is 5 or less, More preferably, it is 3 or less, Most preferably, it is 2 or less.

  Since the amount of deformation of the bulge of the recording layer (the bulge height toward the cover layer) is usually 200 nm or less, if the thickness of the cover layer material arranged on the side closest to the recording layer is about 5 μm or more, the bulge The amount of deformation is sufficiently absorbed by the cover layer closest to the recording layer, and the bulge deformation during recording is not affected by the elastic modulus characteristics of the cover layer material disposed thereon. Therefore, when the cover layer has a structure of two or more layers having different compositions, if the cover layer disposed on the side closest to the recording layer has the above characteristics, the storage elastic modulus of the other cover layers is You may remove | deviate from the said range.

  As a material having a small change in elastic modulus even after an environmental test (high temperature and high humidity), a cured material obtained from the above composition is preferably a material excellent in wet heat resistance. Specifically, a cured product obtained by sufficiently irradiating the composition with radiation to such an extent that unreacted (meth) acrylate does not remain, and an additive such as a photopolymerization initiator that can be volatilized during an environmental test. Those having a small amount of addition and those having a low water absorption are preferred.

  The material having a low elastic modulus and little change in the operating temperature range is, for example, a resin material containing a molecular chain having a large molecular weight and a crosslinked structure having a low crosslinking density, and the glass transition temperature ( Tg) is not present in the operating temperature range. Specifically, it is a mixed composition of a (meth) acrylate polymer and / or oligomer having a high molecular weight molecular chain and a low molecular weight (meth) acrylate, and if necessary, a photopolymerization initiator is added and cured with radiation. There are cured products obtained.

  The cover layer 24 may further be provided with a layer having a thickness of about 0.1 μm to 50 μm on the surface in order to impart functions such as scratch resistance and fingerprint resistance to the incident light side surface. The thickness of the cover layer depends on the wavelength λ of the recording / reproducing light beam and the NA (numerical aperture) of the objective lens 28, but is preferably in the range of 0.01 mm to 0.3 mm, more preferably in the range of 0.05 mm to 0.15 mm. More preferred. It is preferable that the entire thickness including the thickness of the adhesive layer, the hard coat layer, and the like be in an optically acceptable thickness range. For example, in a so-called Blu-ray disc, it is preferable to control to about 100 μm ± 3 μm or less.

(Other configurations)
In the present embodiment, in particular, by providing an interface layer between the recording layer 22 and the cover layer 24, the swelling of the recording layer 22 toward the cover layer 24 can be used effectively. It is desirable that the reflection at the interface layer be as small as possible. This is because the phase change of the reflected light from the reflection layer 23 which is the main reflection surface is selectively used. It is not preferable in the present embodiment that the interface layer has a main reflection surface. For this reason, it is desirable that the difference in refractive index between the interface layer and the recording layer 22 or between the interface layer and the cover layer 24 is small. The difference is preferably 1 or less, more preferably 0.7 or less, and still more preferably 0.5 or less.

  Note that the effect of preventing the elution of the recording layer 22 by the solvent when the cover layer 24 is applied using the interface layer is known, and such an effect is also used in the present embodiment. Is possible as appropriate. The material used for the interface layer is preferably a material that is transparent to the recording / reproducing light wavelength and is chemically, mechanically, and thermally stable. Here, “transparent” means that the transmittance with respect to the recording / reproducing light beam 27 is 80% or more, and more preferably 90% or more. The upper limit of the transmittance is 100%.

The interface layer is preferably a dielectric compound such as a metal, an oxide such as a semiconductor, a nitride, a carbide, a sulfide, a fluoride such as magnesium (Mg), calcium (Ca), or a mixture thereof. As described above, the refractive index of the interface layer preferably has a difference from the refractive index of the recording layer or the cover layer of 1 or less, and the value is preferably in the range of 1 to 2.5. Depending on the hardness and thickness of the interface layer, the deformation of the recording layer 22, particularly the bulge deformation toward the cover layer 24, can be promoted or suppressed. In order to effectively utilize the bulging deformation, a dielectric material having a relatively low hardness is preferable, and in particular, ZnO, In ₂ O ₃ , Ga ₂ O ₃ , ZnS, sulfides of rare earth metals, other metals, A material in which a semiconductor oxide, nitride, or carbide is mixed is preferable. A sputtered plastic film or a plasma polymerized film of hydrocarbon molecules can also be used.

  In the present embodiment, in addition to the interface layer between the recording layer 22 and the cover layer 24 described above, mutual contact / diffusion prevention of the layers is provided on each interface of the substrate 21, the reflective layer 23, and the recording layer 22. Alternatively, an interface layer can be inserted for adjusting the phase difference and the reflectance.

(Other embodiments)
(Translucent recording medium for multilayer recording)
In the optical recording medium to which the present embodiment is applied, when the thickness of the reflective layer is reduced so that approximately 50% or more of the recording / reproducing light is transmitted through the reflective layer, a so-called multilayer recording medium is possible. Become. That is, a recording medium in which a plurality of recording layers and a reflective layer (hereinafter collectively referred to as an information layer) are provided on a substrate.

  FIG. 2 is a diagram for explaining an optical recording medium provided with two information layers. The information layer on which the recording / reproducing light beam 107 is incident is called the L1 layer, and the information layer on the far side is called the L0 layer. The L1 layer preferably has a transmittance of 50% or more. If the translucent reflective layer 113 of the L1 layer is, for example, an Ag alloy, the thickness of the Ag alloy is preferably 1 nm to 50 nm, more preferably 5 nm to 30 nm, still more preferably 5 nm to 20 nm. . Such a highly transmissive reflective layer is called a translucent reflective layer. A transparent intermediate layer 114 is provided between the L0 layer and the L1 layer in order to prevent signal interference. In addition, the same material as the above-mentioned reflection layer 23 (FIG. 1) can be used for the reflection layer 103 in the L0 layer in FIG.

For example, in the optical system with the recording / reproducing light beam 107 wavelength λ = 405 nm and NA (numerical aperture) = 0.85, the thickness of the intermediate layer 114 is about 25 μm and the thickness of the cover layer 111 is about 75 μm. Similarly, the thickness distribution of the intermediate layer 114 is preferably about ± 2 μm or less.
For each of the L0 layer and the L1 layer, different layer configurations may be used within the range of the layer configuration in the optical recording medium 100 to which the present embodiment is applied, or the same layer configuration may be used. The composition and materials of the recording layer mainly composed of the dye used for each information layer may be different or the same.

In the present embodiment, since the phase change is mainly used, it is expected that the amount of light transmitted through the L1 layer hardly changes before and after recording. This means that the amount of light transmitted to the L0 layer and the amount of light reflected from the L0 layer hardly change regardless of whether the L1 layer is recorded or not recorded. This is preferable because the layer can be recorded and reproduced.
Even in the multilayer recording medium as described above, the effect of the present invention can be achieved because the cover layer 111 has predetermined characteristics.

(About optical recording apparatus used in the present invention)
The basic structure of the recording apparatus used in the present invention can be the same as that of a conventional optical recording apparatus. For example, conventionally known methods can be applied to the focus servo method and tracking servo method. It suffices that the spot at the focal position of the focused beam is applied to the cover layer groove portion and follows the cover layer groove portion by the tracking servo. Usually, a push-pull signal is used.

  When recording is performed between the cover layer grooves, the focused recording / reproducing light beam raises the temperature of the recording layer main component dye and generates heat to cause alteration (expansion, decomposition, sublimation, melting, etc.). When performing mark length modulation recording, the power of the recording / reproducing light beam (recording power) is modulated in accordance with the mark length. The mark length modulation method is not particularly limited, and EFM modulation (CD), EFM + modulation (DVD), 1-7PP modulation (Blu-ray), etc., which are commonly used Run-Length-Limited codes, can be applied.

  However, in a recording / reproducing system based on the HtoL polarity signal, the polarity of the recording data signal may be reversed in advance so that the recording signal polarity at the mark and space is reversed during LtoH recording. In this way, the recorded signal can be apparently equivalent to a signal of HtoL polarity.

  Normally, the recording power is set to the high level Pw at the mark portion, and the low level Ps between the marks (spaces). Ps / Pw is usually 0.5 or less. Ps is a power that does not cause the above alteration in the recording layer by a single irradiation, and is used to preheat the recording layer prior to Pw. Known recording pulse strategies are also used as appropriate in the recording method and recording apparatus of the present invention. For example, the recording power Pw irradiation time corresponding to the recording mark portion is further irradiated intermittently in a short time, modulated to a plurality of power levels, or after a certain time Ps from Pw irradiation until shifting to Ps. A recording strategy such as irradiation with a lower power level Pb can be used.

Hereinafter, the present embodiment will be described in more detail based on examples. Note that this embodiment is not limited to the examples.
On a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm and a groove depth of about 45 nm is formed, an Ag _98.1 Nd _1.0 Cu _0.9 alloy target (composition is atomic%) is sputtered. A reflective layer having a thickness of about 70 nm was formed. A metal layer having a thickness of about 2 nm was formed by sputtering Nb on the reflective layer. Furthermore, a mixed solution obtained by diluting a metal-containing azo dye A composed of a ligand A represented by the following structural formula and divalent Ni to 1.2% by weight with octafluoropentanol (OFP) is prepared. A film was formed by spin coating.

  The conditions of the spin coating method are as follows. That is, 1.5 g of the dye solution was applied in the form of a ring around the center of the disk, the disk was rotated at 1200 rpm for 7 seconds, the dye was stretched, and then rotated at 9200 rpm for 3 seconds to coat the dye. After coating, the disk was kept in an environment of 80 ° C. for 1 hour to evaporate and remove OFP as a solvent.

Thereafter, an ITO (In ₂ O ₃ —SnO ₂ ) target was sputtered to form an interface layer having a thickness of about 16 nm. On top of that, a UV curable resin 1 composed of the components shown in Table 1 was spin-coated, and preliminarily cured by irradiating ultraviolet rays of about 60 mJ / cm ² with a high-pressure mercury lamp to form a layer of about 15 μm. . A UV curable resin 2 composed of the components shown in Table 1 is spin-coated thereon, and UV light is irradiated at about 890 mJ / cm ² with the high-pressure mercury lamp. By curing, a transparent cover layer having a total thickness of 100 μm was formed. Here, the storage elastic modulus at 5 ° C. of the UV curable resin 2 was 1690 MPa, and the storage elastic modulus at 55 ° C. was 47 MPa (the measuring method of the storage elastic modulus is as described later).

  Evaluation of recording / reproduction of a disk is performed using a pulse having an optical system having a recording / reproduction light wavelength λ = 406 nm, NA (numerical aperture) = 0.85, and a focused beam spot diameter of about 0.42 μm (a point where the intensity becomes 1 / e ^ 2). The measurement was performed using an ODU1000 tester manufactured by Tech. The disk was rotated at a linear velocity of 4.9 m / s, and recording was performed by changing the recording power. For reproduction, the linear velocity was 4.9 m / s and the reproduction power was 0.30 mW. A mark modulation signal (1-7PP) was used for recording. The reference clock period T was 15.15 ns (channel clock frequency 66 MHz). Jitter measurement is performed by equalizing the waveform of the recorded signal with a limit equalizer and binarizing it. The time difference distribution σ between the rising edge and falling edge of the binarized signal and the rising edge of the channel clock signal is calculated. Measurement was performed with a time interval analyzer, and channel clock period was set to T, and measurement was performed with σ / T (data to clock jitter Data to Clock Jitter). These measurement conditions generally conform to the measurement conditions for Blu-ray Disc.

  The method for measuring the storage elastic modulus (E ′) of the material forming the cover layer and the method for preparing the sample to be measured are as follows.

(A) Measuring method and measuring device for storage elastic modulus (E ′) of cover layer material: Viscoelastic spectrometer EXSTAR6000 / DMS6100 (manufactured by SII Nanotechnology)
・ Frequency setting: 10Hz
Set temperature range: -100 ° C to 150 ° C
-Temperature rising rate: 2 ° C./min.

(B) Measurement sample preparation method (1) A cover layer material coating solution is spin-coated on a PET film so as to have a thickness of about 150 to 200 μm, and is irradiated with ultraviolet rays with a high-pressure mercury lamp (about 1000 mJ / cm ² ). To obtain a cover layer material laminated film.
(2) Cut the cover layer material laminated film obtained in (1) with a width of 10 mm and a length of about 3 cm, peel off only the cover layer material film from the PET film, and the thickness of the cover layer material film actually obtained. Was measured with a micrometer.
(3) The cover layer material film obtained in (2) was mounted on the measuring device (chuck-clamp distance 5 mm), and E ′ was measured in a predetermined temperature range under a nitrogen flow.

The environmental test was carried out by storing the optical disc and the elastic modulus measurement film sample for 100 hours in an environment with a temperature of 80 ° C. and a relative humidity of 80%, and measuring the jitter value and storage elastic modulus before and after the test.
Table 2 shows the measurement results of the storage elastic modulus of the UV curable resin 1 before and after the environmental test.

  Jitter values were measured by performing recording and reproduction before and after the environmental test. The results were 6.4% and 7.4%, respectively. Before and after the environmental test, since the change in jitter was sufficiently small, it was confirmed that the reliability (Shelf life) of this optical disk was sufficiently high.

It is a figure explaining the structure of the optical recording medium based on this invention. It is a figure explaining the structure of the optical recording medium based on this invention which provided the two information layers.

Explanation of symbols

20, 100 Optical recording medium 21, 101 Substrate 22, 102, 112 Recording layer 23, 103 Reflective layer 24, 111 Cover layer 25 Cover layer groove part 26 Cover layer groove part 27, 107 Recording / reproducing light beam 28, 108 Objective lens 29 Surface on which recording / reproducing light beam is incident 113 Translucent reflective layer 114 Intermediate layer

Claims (1)

A substrate on which guide grooves are formed;
A layer having at least a light reflecting function on the substrate;
A recording layer containing as a main component a dye having a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded state;
A cover layer on which recording / reproducing light enters the recording layer in this order,
When the recording / reproducing light beam obtained by converging the recording / reproducing light is a recording groove that is a guide groove on the side far from the surface on which the cover layer is incident,
In the optical recording medium in which the reflected light intensity of the recording pit part formed in the recording groove part is larger than the reflected light intensity in the recording groove part when not recorded, the cover layer has a single layer structure having the same composition or two layers having different compositions. Before performing the environmental test of the cover layer having the above-described configuration and being placed on the side closest to the recording layer among the cover layers when performing an environmental test that is left in an 80 ° C./80% RH environment for 100 hours. The storage elastic modulus E5b ′ at 5 ° C. and the storage elastic modulus E55b ′ at 55 ° C. are both 100 MPa or less, and the ratio (E5b ′ / E55b ′) is 10 or less, and
The storage elastic modulus E5a ′ at 5 ° C. after the end of the environmental test and the storage elastic modulus E55a ′ at 55 ° C. are both 100 MPa or less, and the ratio (E5a ′ / E55a ′) is 10 or less. An optical recording medium.

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