JPH11180043A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the heat resistivity of a disc by the use of at least a kind of compounds including a specific structure as an electronic receptive developer being a component of a thermochromic material forming a mask layer. SOLUTION: The optical recording medium is formed such that it has a mask layer having a light permeation rate changed by a variation of temperature through light irradiation on a light permeation substrate formed with minute bit rows or concentric guide grooves and making the effective spot diameter of a reproductive laser beam small by utilizing the alteration of a light permeation rate. The mask layer has only two components of an electronic donator coloring compound and an electronic receptor developer and consists mainly of a thermochromic material having a light permeation rate changed reversibly, wherein a kind of compounds indicated by the formula is contained as an electronic receptor developer. Besides, in the formula, R1 and R2 each shows an alkyl group or alkenyl group having 1-4C atoms, and (m) and (n) each indicates an integer of 0-2, provided that it is (m)+(n)>1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-density recording and / or
Or for the optical recording medium to be reproduced, in particular, using a light transmittance variable medium whose light transmittance changes due to temperature change,
The present invention relates to an optical recording medium capable of recording and / or reproducing information at a high density by reducing an effective spot diameter of an irradiation laser beam.

[0002]

2. Description of the Related Art In recent years, demands for increasing the capacity of optical discs have been increasing, and various proposals have been made for this. An optical disc can form a recording mark smaller than the light spot diameter by controlling the laser beam power at the time of recording, and there is no limit in principle to the improvement in recording density. However, there is a limit value that the light spot diameter when the laser beam is narrowed down by the lens cannot be reduced below a certain value. Therefore, increasing the density of an optical disc depends on how to reduce the diameter of the reproducing laser spot. The repetition wavelength (recording wavelength) of the recording mask at the reproduction limit is given by λ / 2NA. Where λ
Is the wavelength of light, and NA is the numerical aperture of the lens.

That is, in order to identify and reproduce a recording mark with a shorter recording wavelength, it is sufficient to reproduce with a light having a shorter wavelength λ or to use a lens having a larger numerical aperture NA. However, in general, it is technically difficult to shorten the wavelength of a semiconductor laser used for reproduction. On the other hand, it is not easy to incorporate a lens having a large numerical aperture NA into an optical disk device. Therefore, due to the temperature rise at the time of light irradiation, when the temperature increases, the absorbance decreases and the light transmittance increases, and when the laser beam is cooled after passing, the absorbance increases again and the light transmittance decreases. A method called disk super-resolution in which information is recorded on an optical disk at high density or information recorded at high density is reproduced by providing a material having properties (hereinafter referred to as a variable light transmittance medium) in a layer in the optical disk. Has been proposed.

[0004] The light intensity distribution of a laser beam used for information recording / reproduction usually shows a Gaussian distribution as shown in FIG.
The temperature distribution also becomes a distribution close to this. When such a laser beam is irradiated on the light transmittance variable medium, the light transmittance of each area corresponding to FIG. 3 becomes as shown in FIG. 4, and the central portion A in FIG. Only the light becomes transparent, and the other portion B in the light spot is masked, that is, a so-called disc super-resolution effect occurs. At this time, the effective spot diameter of the laser light transmitted through the central portion A becomes smaller than the actual irradiation spot diameter of the irradiation laser light. That is, as shown in FIG.
1 is a masking portion, and the actual laser spot 22
The smaller opening 23 becomes an effective laser spot.
Thus, by providing a light transmittance variable medium having a disk super-resolution effect in a layered manner on an optical disk (hereinafter, this light transmittance variable medium layer is referred to as a mask layer), the light in the spot of the laser light to be irradiated is provided. Since only light having a high transmittance is transmitted and light having a low light transmittance in the irradiation spot is masked, crosstalk between adjacent tracks and intersymbol interference between adjacent pits are prevented. Can be.

[0005] The above-mentioned mask layer is required to rapidly change and restore the light transmittance with respect to the irradiation of laser light for optical recording and reproduction. That is, the light transmittance increases during the passage of the irradiation laser light to the rotating optical disk,
It is necessary that the light transmittance be restored before the irradiation laser light passes again. As a light transmittance variable medium satisfying such conditions, for example, as proposed in JP-A-7-182693 and JP-A-8-306074,
There is a thermochromic material composed of two components, an electron donating color compound and an electron accepting developer.

The above two-component thermochromic material comprises:
It has the property of developing, erasing and discoloring by the exchange of electrons between the electron donating color compound and the electron accepting developer. By variously selecting the structures of the electron-donating color-forming compound and the electron-accepting color developer, it is possible to arbitrarily set the light absorption wavelength of the light transmittance variable medium and the color development, decoloration, and color change temperatures. It is. Above all, an optical recording medium having a mask layer in which a fluoran compound or a phthalide compound as an electron-donating color compound and a bisphenol-based developer as an electron-accepting developer is excellent in disc super-resolution Has been confirmed.

[0007]

By the way, an optical disk used for the purpose of storing recorded information for a long period of time, such as an optical disk, has not only good characteristics at the beginning but also heat and heat for a long period of time. Excellent resistance to light is also required. However, the organic material used for the above-described mask layer is generally inferior in heat and light resistance as compared with the inorganic material, and the combination of the fluoran compound or the phthalide compound and the bisphenol-based developer described above. There is also a problem that the long-term reliability of the obtained mask layer is not sufficient particularly in terms of heat resistance.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have repeatedly studied various components of the thermochromic material forming the mask layer, in particular, an electron-accepting color developer. As a result, it has been found that when at least one of the bisphenol compounds having a specific structure is used as the electron-accepting color developer, the heat resistance of the mask layer is improved and the deterioration due to heat is very small. Was.
That is, the optical recording medium of the present invention has a light transmittance that changes due to a temperature change due to light irradiation on a light-transmissive substrate on which a light-readable micro pit row or a concentric or spiral guide groove is formed. An optical recording medium having a mask layer to reduce the effective spot diameter of the reproduction laser beam by utilizing the change in light transmittance of the mask layer.
The mask layer is mainly composed of a thermochromic material whose light transmittance reversibly changes with only two components of an electron-donating color developing compound and an electron-accepting color developing agent. It contains at least one of the compounds represented by the formula (1).

[0009]

Embedded image (In the formula, R ₁ and R _{2 each} represent an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, m and n each represent an integer of 0 to 2, provided that m + n> 1. )

Among the compounds of the above general formula (1), (4-hydroxyphenyl) sulfone, 2,4'-
Dihydroxydiphenylsulfone, 3,4-dihydroxy-4′-methyldiphenylsulfone, or bis (3
(-Allyl-4-hydroxyphenyl) sulfone is preferable. Further, in each of the above structures, it is preferable that at least one phthalide compound represented by the general formula (2) is contained.

[0011]

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(Wherein A represents the following structural formulas (Ι) to (ΙΙ)
Represents a substituent represented by iota), R _3, R ₄ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, tetrahydrofurfuryl group, or a substituted or unsubstituted phenyl group, and the R ₃ R ₄ may combine to form a heterocycle with the nitrogen atom to which it is attached. R ₅ represents a hydrogen atom, an alkyl group, an alkoxy group or an alkyl mercapto group, and X and Y each represent CH or N. )

[0013]

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[0014]

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[0015]

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(Wherein R ₆ , R ₇ , R ₉ , R ₁₁ , R ₁₃ are
Each independently a hydrogen atom, an alkyl group, a cycloalkyl group,
It represents a tetrahydrofurfuryl group or a substituted or unsubstituted phenyl group, and R ₆ and R ₇ may combine to form a heterocyclic ring together with the nitrogen atom to which they are attached. R ₈ ,
R ₁₀ , R ₁₂ and R ₁₄ represent a hydrogen atom, an alkyl group, an alkoxy group, an alkyl mercapto group or a substituted or unsubstituted phenyl group. )

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The electron-accepting developer, which is a component of the mask layer of the optical recording medium of the present invention, is at least one of the compounds represented by the general formula (1), Two or more of these compounds may be used in combination. Specific examples of the electron-accepting color developer represented by the general formula (1) include the following compounds.

Bis (4-hydroxy-3-methylphenyl) sulfone bis (3-allyl-4-hydroxyphenyl) sulfone 3,4 ', 5-trihydroxydiphenylsulfone bis (4-hydroxyphenyl) sulfone 2,4' -Dihydroxydiphenylsulfone 3,4-dihydroxy-4'-methyldiphenylsulfone bis (4-hydroxy-3,5-dimethylphenyl) sulfone 2,5-dihydroxy-4'-methyldiphenylsulfone 2,4-dihydroxy-2 ' , 4'-Dimethyldiphenyl sulfone

Further, the above-mentioned electron-accepting developer is represented by (4-
Hydroxyphenyl) sulfone, 2,4′-dihydroxydiphenyl sulfone, 3,4-dihydroxy-4′-
Methyldiphenylsulfone or bis (3-allyl-
When 4-hydroxyphenyl) sulfone is used, the heat resistance of the mask layer is further improved. On the other hand, the electron donating color compound used in combination with the electron accepting developer is not particularly limited, and a known compound can be used. In particular, the general formula ( The phthalide compound represented by 2) is preferred.

Specific examples of the compound of the general formula (2) include the following. 3,3-bis (4-diethylaminophenyl) phthalide 3,3-bis (4-di-n-butylaminophenyl) phthalide 3- (4-diethylamino) -3- [4- (N-tetrahydrofurfuryl-N -Ethylamino) phenyl] phthalide 3,3-bis (4-diethylaminophenyl) -4-azaphthalide 3,3-bis (4-di-n-propylaminophenyl)
-4-azaphthalide 3,3-bis (4-di-n-butylaminophenyl)-
4-azaphthalide 3,3-bis (4-pyrrolidinophenyl) -4-azaphthalide 3- [4- (N-cyclohexyl-N-methylamino)
Phenyl] -3- (4-diethylaminophenyl) -4
-Azaphthalide 3- (4-diethylaminophenyl) -3- [4- (N
-Methyl-p-toluidino) phenyl] -4-azaphthalide 3,3-bis (4-diethylamino-2-ethoxyphenyl) phthalide

3,3-bis (4-di-n-butylamino-2-ethoxyphenyl) phthalide 3,3-bis [4- (N-ethylanilino) -2-ethoxyphenyl] phthalide 3,3-bis ( 4-Diethylamino-2-methoxyphenyl) -4-azaphthalide 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide 3,3-bis (4-diethylamino-2-ethoxyphenyl) -7- Azaphthalide 3,3-bis (4-diethylamino-2-n-pentoxyphenyl) -4-azaphthalide 3,3-bis (4-diethylamino-2-phenoxyphenyl) -4-azaphthalide 3,3-bis (4- Di-n-propylamino-2-n-
Propoxyphenyl) -4-azaphthalide 3,3-bis (4-di-n-butylamino-2-ethoxyphenyl) -4-azaphthalide 3,3-bis (4-pyrrolidino-2-methoxyphenyl) -4-azaphthalide

3- (4-di-n-butylamino-2-ethoxyphenyl) -3- (4-diethylaminophenyl) -4-azaphthalide 3,3-bis [4- (N-ethylanilino) -2-ethoxy Phenyl] -4-azaphthalide 3- (4-di-n-butylaminophenyl-2-ethoxyphenyl) -3- [4- (N-ethyl-N-tetrahydrofurfurylamino) phenyl] -4-azaphthalide 3- [4- (N-cyclohexyl-N-methylamino)
Phenyl] -3- (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide 3- [4- (N-ethylanilino) -2-ethoxyphenyl] -3- (4-diethylamino-2-ethoxyphenyl) -4 -Azaphthalide 3,3-bis (4-diethylamino-2-methylphenyl) phthalide 3,3-bis (4-di-n-butylamino-2-methylphenyl) phthalide 3- (4-diethylamino-2-methylphenyl) ) -3
-(4-Di-n-butyl-2-ethoxyphenyl) phthalide 3,3-bis (4-diethylamino-2-methylphenyl) -4-azaphthalide 3,3-bis (4-di-n-butylamino- 2-methylphenyl) -4-azaphthalide

3,3-bis (4-di-n-propylamino-2-ethylphenyl) -4-azaphthalide 3,3-bis (4-piperazino-2-methylphenyl)
-4-azaphthalide 3- (4-diethylamino-2-methylphenyl) -3
-[4- (N-tetrahydrofurfuryl-N-ethylamino) phenyl] -4-azaphthalide 3- (4-diethylamino-2-methylphenyl) -3
-(4-di-n-butyl-2-ethoxyphenyl) -4
-Azaphthalide 3,3-bis (4-diethylamino-2-ethylthiophenyl) phthalide 3- (4-diethylaminophenyl) -3- (4-diethylamino-2-ethylthiophenyl) phthalide 3,3-bis (4- Diethylamino-2-ethylthiophenyl) -4-azaphthalide 3,3-bis (4-di-n-butylamino-2-methylthiophenyl) -4-azaphthalide 3- (4-diethylaminophenyl) -3- (4- Diethylamino-2-ethylthiophenyl) -4-azaphthalide 3- (4-diethylamino-2-ethylthiophenyl)
-3- (4-Di-n-butylamino-2-ethoxyphenyl) -4-azaphthalide

3,3-bis (4-diethylaminophenyl) -4,7-diazaphthalide 3,3-bis (4-di-n-butylaminophenyl)-
4,7-diazaphthalide 3,3-bis (4-pyrrolidinophenyl) -4,7-diazaphthalide 3- [4 (N-cyclohexyl-N-methylamino) phenyl] -3- (4-dimethylaminophenyl)- 4,
7-diazaphthalide 3- (4-di-n-propylaminophenyl) -3-
[4- (N-tetrahydrofurfuryl-N-ethylamino) phenyl] -4,7-diazaphthalide 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4,7-diazaphthalide 3,3-bis ( 4-di-n-butylamino-2-ethoxyphenyl) -4,7-diazaphthalide 3- [4- (N-cyclohexyl-N-methylamino)
Phenyl] -3- (4-diethylamino-2-ethoxyphenyl) -4,7-diazaphthalide 3- [4- (N-ethylanilino) -2-ethoxyphenyl] -3- (4-di-n-butylamino- 2-ethoxyphenyl) -4,7-diazaphthalide 3- (4-diethylamino-2-ethoxyphenyl)-
3- [N-ethyl-p-toluidino] -4,7-diazaphthalide

3- [4- (N-cyclohexyl-N-methylamino) -2-methylphenyl] -3- (4-diethylamino-2-ethoxyphenyl) -4,7-diazaphthalide 3,3-bis (4 -Dimethylamino-2-methylphenyl) -4,7-diazaphthalide 3,3-bis (4-diethylamino-2-methylphenyl) -4,7-diazaphthalide 3,3-bis (4-di-n-butylamino -2-methylphenyl) -4,7-diazaphthalide 3,3-bis (4-pyrrolidino-2-methylphenyl)
-4,7-diazaphthalide 3,3-bis (4-diethylamino-2-ethylthiophenyl) -4,7-diazaphthalide 3- [4- (N-ethylanilino) phenyl] -3-
(4-di-n-propyl-2-methylthiophenyl)-
4,7-diazaphthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylaminophenyl) phthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylaminophenyl) -4-azaphthalide 3- (1-n-butyl-2-methylindol-3-yl) -3- (4-diethylaminophenyl) -4-azaphthalide

3- (4-di-n-butylaminophenyl) -3- (1-ethyl-2-methylindole-3-
Yl) -4,7-diazaphthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylamino-2-ethoxyphenyl)
Phthalide 3- [4- (N-ethylanilino) -2-ethoxyphenyl] -3- (1,2-dimethylindol-3-yl) phthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylamino-2-ethoxyphenyl)
-4-azaphthalide 3- (4-diethylamino-2-ethoxyphenyl)-
3- (1-n-octyl-2-methylindole-3-
Yl) -4-azaphthalide 3- (4-di-n-propylamino-n-propoxyphenyl) -3- (1-n-pentyl-2-methylidol-3-yl) -4-azaphthalide 3- [ 4- (N-ethylanilino) -2-ethoxyphenyl] -3- (1,2-dimethylindol-3-yl) -4-azaphthalide 3- (1-ethyl-3-methylindol-3-yl)
-3- (4-Diethylamino-2-methylphenyl) phthalide 3- (4-pyrrolidino-2-ethylphenyl) -3-
(1-ethyl-2-methylindol-3-yl) phthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylamino-2-methylphenyl)-
4-azaphthalide

3- (4-diethylamino-2-methylphenyl) -3- (1,2-dimethylindol-3-yl) -4-azaphthalide 3- (4-pyrrolidino-2-ethylphenyl) -3-
(1-ethyl-2-methylindol-3-yl) -4
-Azaphthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Diethylaminophenyl) -4,7-diazaphthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- (4-Di-n-butylamino-2-ethoxyphenyl) -4,7-diazaphthalide 3- (1,2-dimethylindol-3-yl) -3-
[4- (N-ethylanilino-2-ethoxyphenyl)]
-4,7-diazaphthalide 3- (1-ethyl-2-methylindol-3-yl)
-3- [4- (N-Tetrahydrofurfuryl-N-ethylamino) -2-ethylphenyl] -4,7-diazaphthalide 3- (1-n-butyl-2-methylindol-3-yl) -3 -(4-Diethylamino-2-ethylthiophenyl) -4,7-diazaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- ( 4-diethylaminophenyl) phthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-di-
n-butylaminophenyl) phthalide 3- [1,1-bis (1-n-butyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-
Pyrrolidinophenyl) phthalide

3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3
-[4- (N-cyclohexyl-N-methylamino) phenyl] phthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- [4 − (N
-Ethylanilino) phenyl] phthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-diethylamino-2-ethoxyphenyl) phthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-diethylamino-2-methylphenyl) -4-azaphthalide 3- [1,1- Bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-di-
n-propylaminophenyl) -4-azaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-di-
n-butylaminophenyl) -4-azaphthalide 3- [1,1-bis (1-n-butyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-
Pyrrolidinophenyl) -4-azaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- [4- (N
-Cyclohexyl-N-methylamino) phenyl] -4
-Azaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- [4- (N
-Ethylanilino) phenyl] -4-azaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide

3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3
-(4-Dimethylaminophenyl) -4,7-diazaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4-di-
n-butylaminophenyl) -4,7-diazaphthalide 3- [1,1-bis (1-ethyl-2-methylindol-3-yl) ethylene-2-yl] -3- [4- (N
-Methyl-p-toluidinophenyl] -4,7-diazaphthalide 3- [1,1-bis (1-n-butyl-2-methylindol-3-yl) ethylene-2-yl] -3- ( 4-
Di-n-propylamino-2-n-propoxyphenyl) -4,7-diazaphthalide 3- [1,1-bis (1-n-octyl-2-methylindol-3-yl) ethylene-2-yl] -3- (4
-Diethylamino-2-ethylphenyl) -4,7-diazaphthalide

Next, the optical recording medium of the present invention having a mask layer made of a thermochromic material composed mainly of the above-described electron-accepting developer and the electron-donating coloring compound will be described. That is, the shape of the optical recording medium of the present invention is not particularly limited. For example, various forms such as a disk, a card, and a tape are used, and its function is also a read-only type, a write-once type, Alternatively, any type such as a rewritable type may be used.

As an example, FIGS. 1 and 2 show the structure of an optical disk widely used as an optical recording medium. FIG.
2 shows a read-only optical disk 1, and FIG. 2 shows a recordable optical disk 11. In FIG. 1, a read-only optical disc 1 has a light-transmissive substrate 2 on which pits 2A that can be read out are formed, and an effective spot diameter of a laser beam irradiated from below the substrate 2 by the mask effect described above. In this case, a mask layer 3, a reflective layer 4 made of, for example, aluminum, and a protective film layer 5 made of a UV curable resin are laminated in this order.

On the other hand, in FIG. 2, the recordable optical disk 11 has a guide groove 12 which is concentric or spiral.
A light-transmitting substrate 12 on which A is formed, a mask layer 3 similar to the above, a recording layer 6 made of an optically recordable / reproducible substance,
The same reflective layer 4 and protective film layer 5 as described above are laminated in this order. Each of the optical disks 1 and 11 shown in FIG. 1 is a partial sectional view in the radial direction of a reflective optical disk. Further, a light transmission type that does not include the reflection layer 4 may be used, and further, a heat insulation layer, an enhancement layer,
Alternatively, a dielectric layer may be provided.

The light-transmitting substrate 2 is made of glass, a thermoplastic resin such as polycarbonate or polymethyl methacrylate, a thermosetting resin such as an epoxy resin, or a light-transmitting polymer material such as a light-curing resin. Can be used. The mask layer 3 is made of the above-described thermochromic material containing the electron-donating color compound and the electron-accepting color developer as components. The mixing ratio (weight ratio) of the thermochromic material is, for example, an electron donating color compound:
The electron-accepting developer is preferably in the range of 1: 0.5 to 1:50, more preferably 1: 1 to 1: 5. The thickness of the mask layer 3 is 50 to 5000 nm.
And more preferably 20
0 to 2000 nm. The mask layer 3 can be formed on a substrate by using a spin coating method, a dipping method, a spray method, a vacuum evaporation method, or the like. Above all, considering the formation of the mask layer 3 having a uniform thickness on an optical disk substrate having irregularities, the formation method is particularly
A vacuum deposition method excellent in film thickness controllability is preferred. Reflective layer 4
Can be formed by forming a metal such as aluminum, silver, gold, chromium, and nickel by a vacuum evaporation method, a sputtering method, or the like.

<Examples> The present invention will be specifically described with reference to the following examples. An electron-donating color developing compound and an electron-accepting color developing agent are used in combination as shown in Table 1 on a polycarbonate substrate on which a 4-fold dense EFM signal of a compact disc (CD) is recorded by a series of minute pits. In a vacuum chamber (10 ^-5 mbar, resistance heating)
Thus, a mask layer was formed with a thickness of 800 nm. Further, an aluminum reflective layer was formed thereon with a thickness of 70 nm by sputtering, and an ultraviolet-curable resin was formed as a protective layer on the reflective layer to complete a read-only optical disk.

(Electron-donating color compound) As the electron-donating color compound represented by the general formula (2), those represented by the following structural formulas (3) and (4) were used. Structural formula (3) 3- (4-Diethylamino-2-methylphenyl) -3- (1-methyl-2-phenylindol-3-yl) -4,7-diazaphthalide (trade name GN6
06, manufactured by Yamamoto Kasei Co., Ltd.) Structural formula (4): 3- [1,1-bis (1-ethyl-2-)
Methylindol-3-yl) ethylene-2-yl]-
3- (4-diethylaminophenyl) phthalide (trade name: GN169, manufactured by Yamamoto Kasei Co., Ltd.)

[0036]

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[0037]

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(Electron-accepting developer) Among the electron-accepting developers represented by the general formula (1), the compounds represented by the following structural formulas (5) to (8) as Examples 1 to 7 were used. , Comparative Example 1
Compounds represented by the following structural formulas (9) to (13) were used in combination with the above-described electron donating color compounds as shown in Table 1, respectively. Table 1 also shows the weight ratio of the coloring compound to the developer.

[0039]

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[0040]

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[0041]

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[0042]

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[0043]

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[0044]

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[0045]

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[0046]

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[0047]

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[0048]

[Table 1]

Each of the optical disks of Examples 1 to 7 and Comparative Examples 1 to 8 thus obtained was subjected to a heat resistance test under the following conditions.

(Heat resistance test conditions) Test time 720 hours Temperature 60 ° C Humidity 60% Wavelength 690n before and after test of mask layer of each disk
m, the absorbance at heat resistance,
(Absorbance after test / absorbance before test) × 100 was calculated, and the results are shown in Table 1. As is clear from the results in Table 1, the discs of Examples 1 to 7 showed almost no deterioration in heat resistance even after a long period of time, and the heat resistance was much higher than the discs of Comparative Examples 1 to 8. It was confirmed that it was good.

[0051]

As described above in detail, according to the present invention, at least one compound having a specific structure is used as an electron-accepting developer as one component of the thermochromic material constituting the mask layer. By using, the heat resistance of the disk can be improved.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view in the radial direction showing the structure of a read-only optical disc according to an embodiment of the present invention.

FIG. 2 is a partial longitudinal sectional view in the radial direction showing a structure of a recordable optical disc in one embodiment of the present invention.

FIG. 3 is a diagram comparing light intensity distributions of an irradiation spot diameter and an effective spot diameter of a mask layer.

FIG. 4 is a diagram showing light transmittance corresponding to each region in FIG. 3;

FIG. 5 is a diagram showing a mask effect of a mask layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Optical disk (optical recording medium) 2, 12 Light-transmitting substrate 2A Pit 3 Mask layer 4 Reflective layer 5 Protective film layer 6 Recording layer 12A Guide groove

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Hashimoto 1-43, Yuge-cho Minami, Yao-shi, Osaka Yamamoto Kasei Co., Ltd. (72) Inventor Mikiya Kuroda 3-12 Moriyacho, Kanagawa-ku, Yokohama, Kanagawa Japan Victor Co., Ltd. (72) Inventor Koji Tsujita 3-12-12 Moriyacho, Kanagawa-ku, Yokohama-shi, Kanagawa Japan Victory Co., Ltd.

Claims (3)

[Claims] 1. A mask layer on which light transmittance changes due to a temperature change due to light irradiation is provided on a light-transmitting substrate on which a light-readable micro pit row or a concentric or spiral guide groove is formed. In the optical recording medium wherein the effective spot diameter of the reproduction laser beam is reduced by utilizing the change in the light transmittance of the mask layer, the mask layer comprises an electron donating color compound and an electron accepting developer. A thermochromic material whose light transmittance is reversibly changed by only two components, and at least one compound represented by the following general formula (1) as the electron-accepting developer. An optical recording medium, comprising: Embedded image (In the formula, R ₁ and R _{2 each} represent an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, m and n each represent an integer of 0 to 2, provided that m + n> 1. ) 2. The method according to claim 1, wherein the electron accepting developer is (4-hydroxyphenyl) sulfone, 2,4′-dihydroxydiphenyl sulfone, 3,4-dihydroxy-4′-methyldiphenyl sulfone, or bis (3- The optical recording medium according to claim 1, which is (allyl-4-hydroxyphenyl) sulfone. 3. The phthalide compound represented by the following general formula (2):
The optical recording medium according to claim 1, comprising a seed. Embedded image (Wherein, A represents a substituent represented by the following structural formulas (Ι) to (ΙΙΙ), and R ₃ and R ₄ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a tetrahydrofurfuryl group or Represents a substituted or unsubstituted phenyl group;
₃ and R ₄ may be linked together to form a heterocycle with the nitrogen atom to which they are attached. R ₅ represents a hydrogen atom, an alkyl group, an alkoxy group or an alkyl mercapto group;
H or N is indicated. ) Embedded image Embedded image (Wherein, R ₆ , R ₇ , R ₉ , R ₁₁ and R ₁₃ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a tetrahydrofurfuryl group or a substituted or unsubstituted phenyl group; R ₆ and R ₇ may be linked together to form a heterocyclic ring together with the nitrogen atom to which they are bonded, R ₈ , R ₁₀ , R ₁₂ , R ₁₄
Represents a hydrogen atom, an alkyl group, an alkoxy group, an alkylmercapto group, or a substituted or unsubstituted phenyl group. )