JPH0771867B2 - Optical information recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel high-sensitivity and high-density optical information recording medium capable of recording / reproducing information using laser light. More specifically, it is suitable for recording / reproducing information by utilizing the change in reflectance or transmittance caused by the deformation or removal of the portion irradiated with laser light, which is a high-density energy beam, due to melting, decomposition, etc. And a heat mode optical information recording medium.

[Conventional technology]

In optical recording using a laser beam, since the writing or reading heads are not in contact with each other, the recording material is characterized by not being worn and deteriorated. Therefore, various optical recording materials have been researched and developed. In particular, in the fields of optical discs, laser printers, facsimiles, etc., many optical information recording materials using laser light are known. As a typical example thereof, it is known to use a metal-based substance found in metals, alloys, or oxides such as Te, Bi, In, and Ge in the recording layer as a light absorbing substance. However, since the metal-based material has not only high thermal conductivity and melting point but also high surface reflectance,
There is a drawback in that the energy of laser light cannot be used effectively. In addition, these metal-based materials have a serious problem in terms of toxicity.

On the other hand, as an optical information recording material other than the above-mentioned metallic materials, it is also known to use an organic dye such as fluorescein, sudan black B, congoled, sudan blue, and rhodamine 6G in the recording layer as a light absorbing substance (for example, (Kaisho 56-55289 and Japanese Patent Publication No. 57-209191).

Generally, the thermal conductivity of organic substances is as small as 1/10 to 1/100 of that of metals, so not only the heat generated by photothermal conversion can be effectively used, but also the dissipation of heat in the horizontal direction is reduced, It becomes possible to record faithful signals, that is, high density recording. However, since these known organic substances mainly show absorption in the visible light region, the recording laser light source is limited to Ar ⁺ laser (488 nm) or He-Ne laser (633 nm), and the near infrared light region (~ It has an oscillation wavelength of 800nm) and is not suitable for recording by a semiconductor laser that can reduce the size and weight of the entire device.

Cyanine dyes and the like are known as organic compounds exhibiting absorption in the near infrared region, for example, in JP-A-58-114989.
However, since the cyanine dye has poor stability to moisture, oxygen, light, etc., it has a drawback that the recording state cannot be kept stable.

[Problems to be solved by the invention]

As described above, conventionally proposed organic optical recording materials do not have sufficient light absorption ability or light reflection ability, or have problems in durability, storage stability, etc. At present, there is nothing that satisfies the performance.

As a result of extensive research to improve the above-mentioned drawbacks of the prior art, the present inventors have found that a metal complex group of monoazo compounds has a large molecular absorption coefficient in the visible and near-infrared light regions. Found out. When the recording layer containing the metal complex was irradiated with laser light, it was found that the light-heat conversion occurred efficiently, and the portion irradiated with laser light had a large change in reflectance or transmittance. I went (Japanese Patent Application No. 60-297944).

The present invention has been made for the purpose of further improving the above invention.

[Means for solving problems]

The inventors of the present invention have added a so-called antioxidant to the recording material containing the metal complex group of the previous invention. As a result, the state of the recording layer changes very little even after being left for a long time, and the stability and long-term stability of the recording portion are improved. It was confirmed that an optical information recording medium with little deterioration in recording characteristics after being left for a period of time can be obtained.

That is, the optical information recording medium of the present invention basically comprises a support and a recording layer, and the recording layer contains a metal complex of a monoazo compound represented by the following general formula (1) and an antioxidant. It is characterized by that.

(In the formula, X is a residue which forms a heterocyclic ring which may be substituted with an electron-donating group or an electron-withdrawing group together with a nitrogen atom and a carbon atom to which it is bonded, and Y is , Is a residue which, together with the two carbon atoms to which it is attached, forms an aromatic ring which may be substituted with an electron-donating group, and Z is a hydroxy group or a carboxyl group. In the above formula, as the electron-donating group, monomethylamino,
Lower monoalkylamino groups having up to 4 carbon atoms such as monoethylamino, dimethylamino, diethylamino, di-n-
Examples include lower dialkylamino groups having up to 4 carbon atoms such as butylamino, lower alkoxy groups having up to 4 carbon atoms such as methoxy and ethoxy, lower alkyl groups having up to 4 carbon atoms such as methyl and ethyl, amino groups and hydroxyl groups. . The alkyl moiety may be sulfonated, for example. When Z is a hydroxyl group, preferable electron donating groups are dimethylamino group, diethylamino group, hydroxyl group, methoxy group,
Alternatively, it is a methyl group, and when Z is a carboxyl group, it is a dimethylamino group, a diethylamino group or a hydroxyl group.

On the other hand, examples of the electron-withdrawing group include a halogen atom such as chlorine and bromine, a nitro group, a cyano group, a trifluoromethyl group and a carboxyl group. Preferred electron withdrawing groups are chlorine, bromine or nitro groups.

These substituents may be one kind or two kinds.

Examples of the heterocycle include pyridyl, thiazolyl, benzothiazolyl, quinolyl, pyrimidyl, hydroxybenzothiazolyl, and other heterocycles. Preferred heterocycles are thiazolyl and benzothiazolyl. On the other hand, examples of the aromatic ring include phenyl and naphthyl. When a benzene ring is selected as the aromatic ring, it is preferably substituted with the electron donating group. The electron-donating group has an auxiliary color effect and an effect of increasing the stability of the complex.

Representative examples of the monoazo compound forming a complex in the present invention include the following when Z is a hydroxyl group.

1) Thiazolylazo compounds.

2) Hydroxybenzothiazolylazo compound.

3) Benzothiazolylazo compounds.

4) Pyridylazo compounds.

5) Quinolylazo compounds.

6) Pyrimidylazo compounds.

The following are typical examples when Z is a carboxyl group.

1) Thiazolylazo compounds.

2) Benzothiazolylazo compounds.

3) Pyridylazo compounds.

These compounds are described in, for example, Bunko Kagaku, Vol. 11, P621-P62.
8 (1962) and Nippon Chemistry Magazine, Vol. 83, No. 11, P1185-P1
It is synthesized according to the method described in 189 (1962).

In the present invention, the metal forming a complex with the monoazo compound is generally not particularly limited to a metal capable of forming a complex with the monoazo compound, but iron, cobalt, and an iron group element selected from nickel are particularly good, and copper Copper group elements selected from silver, gold, and gold are also used. Complexes composed of these metals generally have an absorption maximum wavelength on the longer wavelength side than the absorption maximum wavelength of the monoazo compound itself, and at the same time, its molecular absorption coefficient (ε) increases, so that it efficiently absorbs the recording laser light and It is preferably used because it causes conversion. Particularly, a complex in which divalent iron is selected as a metal has a maximum absorption wavelength in a long wavelength region and has a large molecular absorption coefficient in a semiconductor laser oscillation wavelength region, and is therefore practically effective. The attribution of this characteristic absorption band is not always clear, but it is considered to be due to iron-> ligand type charge transfer.

The ratio of the monoazo compound and the coordination metal used in the present invention is usually stoichiometrically set to 1/1, 2/1, etc., but the optical properties of the product may greatly affect the purpose. It is desirable to select an appropriate ratio according to

The metal complex of the monoazo compound used in the present invention is synthesized by any method. For example, it can be obtained by reacting one or more kinds of the monoazo compound represented by the formula (I) with one or more kinds of metal salts in water and / or an organic solvent.

Examples of the metal salt used in the synthesis of the metal complex include chloride, hydroxide, nitrate, sulfate, and phosphate of the target metal.
Examples thereof include ammonium sulfate, oxalate, perchlorate, acetate, formate, carbonate, stearate and borate.

The recording layer in the optical information recording medium of the present invention comprises a combination of a metal complex of the monoazo compound and an antioxidant, and is made of glass, aluminum, an inorganic material such as ceramics, or a synthetic resin material such as polymethylmethacrylate, polycarbonate or polyester. It is provided on a support made of. The support is transparent or opaque, and a support having optical characteristics suitable for each of the incident directions of the recording and reproducing laser light is used. In particular, when incident from the transparent support surface side, recording / reproduction can be performed without being affected by defects such as dust or scratches adhering to the surface, and therefore it is more preferably used. It is also possible to use a so-called air-sand Germany structure recording material in which two transparent supports on a disk provided with a recording layer are arranged so that the surfaces of the respective recording layers are located inside and are bonded so as to have voids. The shape of the support can be selected according to the purpose of use, and examples thereof include a disk shape, a tape shape, and a sheet shape. Particularly, in the case of a disk shape, a pregroup may be provided in order to smoothly perform tracking. good.

As the antioxidant used in the present invention, various ones can be used, but a phenol-based, aromatic amine-based or dithiocarbamate-based one is particularly preferable because of good compatibility with the metal complex. It is illustrated as an example. The examples are as follows.

(1) Monophenol type (2) Bisphenol (3) Aromatic amine type Mixture of diallyl-p-phenylenediamine (4) Dithiocarbamate system (5) Others Polymers of mercaptobenzimidazole and its derivatives 2,2,4-trimethyl-1,2-dihydroquinoline Among these compounds, the compound having two aromatic rings has the effect of improving the stability of the recording portion and the long-lasting effect. The effect of improving the recording characteristics after being left for a certain period becomes great. Particularly preferred compounds are bisphenol-based, dithiocarbamate-based or mercaptobenzimidazole-based compounds.

The greater the amount of the antioxidant used in the present invention,
The stabilizing effect is remarkable, but since it does not have a light-absorbing ability itself, the sensitivity decreases if the amount is too large. Usually, 0.01 to 2 moles, and preferably 0. 2 moles per mole of metal in the metal complex.
It is used in a range of 1 to 1.2 mol, particularly preferably 0.2 to 0.5 mol.

The metal complex used in the recording layer may optionally be composed of two or more kinds of monoazo compounds and / or metal elements, and by mixing these, the laser light absorption wavelength may be selected or adjusted. It is possible.

If necessary, these recording layers may be combined with other materials such as resins, dissolved in a suitable solvent, and formed by a simple coating method such as spin coating, dipping method, bar coating method or cast method. You can At this time, if necessary, other stabilizers, surfactants, dispersants, leveling agents and the like may be used in combination.

The thickness of the recording layer provided is preferably 10 to 500 nm, and at the same time, the transmittance for recording laser light is preferably 70% or less. When the transmittance is more than 70%, it does not have sufficient light absorption ability or light reflection ability.

The resin used in combination with the above is preferably a thermoplastic or self-oxidizing resin, polycarbonate, polymethyl methacrylate, polystyrene, polyethylene, polyethylene oxide, polyvinyl butyral, polyvinyl acetate, nitrocellulose, polyvinyl alcohol, It is possible to appropriately select from a wide range of resins such as methyl cellulose and polyamide. Nitrocellulose is particularly preferable because it has a strong oxidizing action. The weight ratio of the organometallic complex to the resin is generally 0.1% or more, preferably 10% or more, particularly preferably 30% or more. If the amount is too small, it may not be possible to obtain a sufficient light-absorbing ability or an optical density difference.

The optical information recording medium of the present invention basically comprises a support 10 and a recording layer 20 as shown in FIG. The recording or reproducing laser light is indicated by arrows 100 or 200. If necessary, an undercoat layer 30 may be provided on the support as shown in FIG. _{2, and} a protective layer 40 such as SiO ₂ on the recording layer may be provided as shown in FIGS. 3 and 4. Nitrocellulose is particularly preferable for the undercoat layer. Furthermore, as shown in FIGS. 5 and 6, Al, Ag,
Reflective layer 50 of metal such as Au or SiO ₂ , Si ₃ N as shown in FIG.
It is also possible to provide a transparent dielectric layer 60 such as ₄ . In general, when providing a metal reflection layer, not only further steps such as a vacuum vapor deposition method are required, but the optical characteristics of the optical information recording medium due to repeated reflection largely depend on the film thickness of the recording layer. It becomes necessary to strictly control the film thickness. The optical information recording medium of the present invention, without providing a metal reflection layer,
It has the feature that the reflectance or change in reflectance required for recording and reproduction can be obtained.

Information recording is performed by irradiating an optical recording material with a laser beam having a high energy density to cause a chemical change or a physical shape change in a part of the recording layer. That is, the portion irradiated with the laser beam is melted, decomposed or the like by the heat generated through the photothermal conversion, and is deformed or removed to perform recording. The pits formed by the laser light can be formed with low energy, and the beam diameter of the laser light is 1
When condensed to about μm, the pits are preferably formed within the range of power of 1 to 10 mW on the surface of the recording layer and irradiation time of 50 to 500 nsec.

On the other hand, in the reading of information, the output is attenuated to 1/5 to 1/10 of that at the time of recording, and the low-output laser light set so that the recording layer does not cause a chemical change or a physical shape change is used as continuous light. This is done by irradiating and detecting a change in the reflected light amount or the transmitted light amount depending on the presence or absence of a pit. Usually, it is preferable to detect by reflected light that can be recorded / reproduced by a single optical system.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

All parts in the examples represent parts by weight. The monoazo compounds used in the examples are represented by the abbreviations mentioned above.

Example 1 An iron complex was obtained by adding 1/2 equivalent of a ferrous ammonium sulfate aqueous solution to a 1,4-dioxane solution of TAM, adjusting the pH, and extracting with chloroform. The complex has λmax of 760 nm and ε of 2.7 × 10 ⁴ · mol ⁻¹ · cm ^{−1 in} chloroform.
Showed absorption of.

Meanwhile, nitrocellulose (viscosity 1/2 second, nitrogen content 12%)
DMF (dimethylformamide) solution of 3 was passed through a 3 μm membrane filter, and then spin-coated on PMMA (polymethylmethacrylate) disk to obtain a dry film thickness of 0.8.
An undercoat layer of μm was provided. Next, with respect to 1 mol of the iron complex,
A chloroform solution containing 4,4′-thiobis (6-tert-butyl-3-methylphenol) in a proportion of 0.4 mol was prepared, and after passing through a 0.2 μm membrane filter, spin-coated on the above disk and dried. A recording layer having a film thickness of 60 nm was provided.

FIG. 2 schematically shows the optical information recording medium manufactured in this way. The optical information recording medium in which the recording layer 20 was placed on the PMMA substrate 10 was rotated at a linear velocity of 11 m / sec, and a semiconductor laser beam with an oscillation wavelength of 780 nm was condensed to a beam diameter of 1.2 μm from above and irradiated in pulses. .

In this case, the irradiation power of the laser beam was 6 mW, the pulse width was 500 nsec, and the duty ratio was 50%. By this irradiation, a pit train 70 as shown in FIG. 7 was formed on the recording layer. In the figure, the pit bottom does not reach the PMMA substrate, but the substrate may be exposed if the irradiation energy is relatively large. As a result of observation with a scanning electron microscope, the rim 80 around the pit was also small, and the pit had a good shape. Next, on the recording pit row that rotates under the same conditions,
When a 1 mW semiconductor laser beam was irradiated as continuous light and the signal was reproduced by changing the reflected light intensity, a CNR of 52 dB was obtained. On the other hand, when recording / reproducing was performed from the recording film side to the similarly prepared material, a good reproduced signal was obtained.
In addition, this optical information recording medium is 100 ° C under the environment of 40 ° C and 95% RH.
When I played it back after leaving it for a while, the CNR was 51 dB,
It was stable with no substantial reduction observed.

A good reproduction signal was obtained even when a He—Ne laser beam with an oscillation wavelength of 633 nm was used under the same conditions in place of the semiconductor laser.

Examples 2 to 6 In Example 1, optical information recording media were produced by variously changing the type and addition amount of the antioxidant. The results are shown in Table 1 together with Example 1. From Table 1, it is recognized that the recording characteristics are stabilized by using the antioxidant together with the metal complex.

According to the observation of a reflection optical microscope, in the control example in which the antioxidant is not added, the crystallization of the recording layer occurs after standing for 100 hours, which causes the scattering of the laser beam during reproduction, resulting in an increase in the noise level. It seems to be. In the optical information recording medium having stable recording characteristics, no change in state due to crystallization of the recording layer was observed in the recorded portion and the unrecorded portion even after being left for 100 hours.

[Brief description of drawings]

1 to 6 are sectional views showing the structures of various embodiments of the optical information recording medium of the present invention. FIG. 7 is a sectional view showing the structure of an optical information recording medium according to an embodiment of the present invention in a recorded state. In the figure, 100 and 200 denote incident directions of recording or reproducing laser light. Further, 10 is a support, 20 is a recording layer, 30 is an undercoat layer, 40 is a protective layer, 50 is a reflective layer, and 60 is a transparent dielectric layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shiro Nagata Kuraray Co., Ltd., a stock company at 2045 Saezu Aoeyama, Kurashiki City, Okayama Prefecture (56) References JP 62-30090 (JP, A) JP 63 -9578 (JP, A) JP 63-9579 (JP, A) JP 59-11385 (JP, A)

Claims (24)

[Claims] 1. A recording medium comprising a support and a recording layer, the recording layer having the general formula: (In the formula, X is a residue which forms a heterocyclic ring together with the nitrogen atom and carbon atom to which it is bonded, and Y is
A residue that, together with the two carbon atoms to which it is attached, forms an aromatic ring. Z is a hydroxyl group or a carboxyl group. ) An optical information recording medium characterized by containing a complex of a monoazo compound represented by (4) and a metal and an antioxidant. 2. The heterocyclic ring is substituted with at least one electron-donating group or electron-withdrawing group, or the aromatic ring is substituted with at least one electron-donating group. The optical information recording medium as set forth in claim 1. 3. The optical information recording medium according to claim 1, wherein the heterocycle is a heterocycle selected from the group consisting of thiazolyl, benzothiazolyl, pyridyl, quinolyl, pyrimidyl and hydroxybenzothiazolyl. 4. The optical information recording medium according to claim 1, wherein the aromatic ring is phenyl or naphthyl. 5. The optical information recording medium according to claim 2, wherein the electron donating group is one or more groups selected from an alkyl group and an alkoxy group. 6. The optical information recording medium according to claim 2, wherein the electron-donating group is at least one group selected from the group consisting of an amino group, a substituted amino group and a hydroxyl group. 7. The optical information recording medium according to claim 2, wherein the electron-withdrawing group is one or more groups selected from the group consisting of a halogen atom, a nitro group, a cyano group and a trifluoromethyl group. . 8. The optical information recording medium according to claim 1, wherein the recording layer is composed only of a complex of a monoazo compound and a metal. 9. The optical information recording medium according to any one of claims 1 to 8, wherein the antioxidant is a phenol compound. 10. The optical information recording medium according to claim 8, wherein the antioxidant is a bisphenol compound. 11. The optical information recording medium according to any one of claims 1 to 8, wherein the antioxidant is an aromatic amine. 12. The optical information recording medium according to any one of claims 1 to 8, wherein the antioxidant is a dithiocarbamate. 13. The antioxidant according to claim 1, which is mercaptobenzimidazole or a derivative thereof.
The optical information recording medium according to any one of items. 14. The antioxidant is 4,4'-dioxydiphenyl, 2,2-alkylenebis (4-alkyl-6-tert-butylphenol), 4,4'-alkylenebis (6-tertiary).
Butyl-3-alkylphenol), 4,4'-thiobis (6-tert-butyl-2-alkylphenol), 4,4 '
11. The optical information according to claim 10, which is -thiobis (6-tert-butyl-3-alkylphenol), 2,2'-thiobis (4-alkyl-6-tert-butylphenol) or a derivative thereof. recoding media. 15. The optical information recording medium according to claim 11, wherein the antioxidant is N-alkyl-N'-phenyl-P-phenylenediamine or a derivative thereof. 16. The antioxidant is 0.01 per mol of the metal complex.
Claims 1 to 15 present in a proportion of 2 mol
The optical information recording medium according to any one of items. 17. The antioxidant is 0.2 per mol of the metal complex.
The optical information recording medium according to claim 16, wherein the optical information recording medium is present in a proportion of 0.5 mol. 18. The optical information recording medium according to any one of claims 1 to 17, wherein the recording layer further contains another resin. 19. The optical information recording medium according to claim 18, wherein the resin is polymethyl methacrylate, polystyrene, polyethylene, polyethylene oxide, polyamide or polyvinyl butyral. 20. The optical information recording medium according to claim 1, which is covered with a protective layer. 21. The optical information recording medium according to claim 1, further comprising a reflective layer provided between the substrate and the recording layer. 22. The optical information recording medium according to claim 1, wherein a reflective layer is provided on the recording layer. 23. The optical information recording medium according to claim 21, wherein a transparent dielectric layer is provided between the reflective layer and the recording layer. 24. The optical information recording medium according to claim 1, wherein an undercoat layer is provided between the substrate and the recording layer.