JP2003036562A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which is not influenced by the formation of a protective coating film and which has the excellent properties. SOLUTION: In the optical recording medium in which a reflective layer 2, a dye recording layer 3, the protective coating film 4, and so forth are constituted on a substrate 1, a barrier layer 5 is formed between the dye recording layer 3 and the protective coating film 4. The barrier layer 5 prevents the diffusion of the dye at forming the protective coating film 4 or the infiltration of a coating liquid or an adhesive into the dye recording layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc-shaped optical recording medium, and more particularly to an optical recording medium for recording / reproducing a dye-containing recording layer through a protective film.

[0002]

2. Description of the Related Art Currently, various optical recording media such as CD-Rs, CD-RWs, and MOs can store a large amount of information and can be easily randomly accessed. It is widely recognized and becoming popular as a memory device. Further, it is desired to increase the recording density by increasing the amount of information to be handled.

[0003]

One means for increasing the recording density of an optical recording medium is to increase the numerical aperture of an objective lens to miniaturize the light spot focused on the information recording surface. . However, when the numerical aperture of the objective lens is increased, the aberration of the focused light spot becomes large due to the influence of the warp of the disc and the like, and there is a problem that a good recording / reproducing signal cannot be stably obtained.

Generally, an optical recording medium has a recording layer composed of an alloy thin film layer, an organic dye-containing thin film layer, etc. on a transparent disk substrate, and a reflective layer on the side opposite to the substrate via the recording layer. A laminated structure having a protective layer covering these recording layer and reflective layer is used for recording / reproducing with laser light through the substrate.

The aberration caused by the warp of the medium is
In order to solve the above problems, the thinner the transparent substrate through which the recording / reproducing laser light passes, the smaller it becomes.
It has been proposed to reduce the thickness of the substrate to about 0.1 mm.

An optical recording medium corresponding to this is shown in FIG.
As described above, the reflective layer 2, the recording layer 3 and the protective coating 4 are laminated in this order on the disc substrate 1, and laser light is incident on the recording layer 3 through the protective coating 4 to perform recording and reproduction. is there. This protective coating is formed by bonding film- or sheet-shaped ones with an adhesive or by applying a coating liquid for film formation.

[0007]

Among various optical recording media, an optical recording medium having a recording layer containing an organic dye (hereinafter sometimes referred to as a dye recording layer), such as CD-R and DVD-R, is It is particularly widely used because it is relatively inexpensive and compatible with read-only optical recording media.

When the recording layer containing an organic dye is used in the optical recording medium of FIG. 3, an adhesive agent is used when a film- or sheet-like protective coating is attached to the dye recording layer in the manufacturing process of this optical recording medium. May attack the dye recording layer, degrading the recording / reproducing characteristics. Further, even when a protective coating is formed on the dye recording layer by using a coating liquid, the coating liquid may attack the dye recording layer as well as the adhesive, so that the recording / reproducing characteristics may be deteriorated.

An object of the present invention is to provide an optical recording medium which is excellent in recording and reproducing characteristics without the dye recording layer being affected by the formation of the protective film.

[0010]

The optical recording medium of the present invention comprises an optical recording medium having a reflective layer, a recording layer containing a dye and a protective coating on a substrate, and recording and reproducing through the protective coating. A barrier layer for preventing mixing of the recording layer and the protective coating layer is provided between the recording layer and the protective coating.

In such an optical recording medium of the present invention, a barrier layer is provided between the dye recording layer and the protective film, and the barrier layer is a dye recording layer for an adhesive component or a coating liquid when the protective film is formed. It prevents the mixing phenomenon such as diffusion and permeation of the dye, and diffusion of the dye to the protective coating side. As a result, the protective coating formed does not affect the dye recording layer, and the recording / reproducing characteristics of the optical recording medium are improved.

The preferred constructions of the barrier layer, the substrate, the reflective layer, the recording layer and the protective coating will be described in detail later.

In the present invention, the arithmetic surface roughness Ra of the protective film side (recording / reproducing light incident side) interface of the barrier layer is 2
When the thickness is less than or equal to nm, the scattering of laser light is prevented and the recording / reproducing characteristics are improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing the layer structure of an optical recording medium according to an embodiment of the present invention. This optical recording medium has a substrate 1, a reflective layer 2, a dye recording layer 3, a barrier layer 5 and a protective coating 4 which are sequentially formed on the substrate 1.
Although not shown, an undercoat layer may be provided below the reflective layer 2, and a writing implement writable layer may be provided on the lower surface of the substrate 1 in the drawing.

FIG. 2 is a sectional view of a double-sided recording type optical recording medium in which the optical recording medium of FIG. 1 is bonded so that the substrates face each other. In FIG. 2, two recordings are bonded together, but the reflective layer 2, the recording layer 3, the barrier layer 5, and the protective coating 4 may be sequentially formed on both surfaces of one substrate.

Next, each layer and substrate of this optical recording medium will be individually described in detail. (1) Reflective layer In the optical recording medium of the present invention, the reflective layer is preferably made of a metal or an alloy, particularly an alloy having good corrosion resistance and inexpensive. Further, in particular, when the wavelength of the recording / reproducing light becomes shorter than 500 nm, the surface roughness of the reflective layer becomes important in order to obtain a good recording / reproducing signal.

In an optical recording medium having a conventional structure for recording / reproducing through a substrate such as CD-R and DVD-R, the surface roughness of the dye recording layer surface is important for obtaining good recording / reproducing signal characteristics. However, the surface roughness of the reflective film does not have a great influence, and thus was not so important.

In the structure of the optical recording medium of the present invention represented by FIG. 1, the recording / reproducing light is reflected at the interface between the reflective layer 2 and the dye recording layer 3, so that a good recording / reproducing signal can be obtained. The surface roughness of the layer side interface of the reflective film provided on the substrate which is the support is important, and specifically, the arithmetic surface roughness Ra is preferably 2 nm or less, and preferably 1 nm or less. Is more preferable.

Incidentally, if the silver reflecting film usually used in the organic dye-based optical recording medium is made thick enough to obtain a sufficient amount of reflected light, the surface roughness becomes large and a good recording / reproducing signal can be obtained. There are some fears that cannot be met.

The arithmetical surface roughness Ra when various metal or alloy materials are formed to a thickness of 100 nm so as to obtain a sufficient amount of reflected light is measured by an atomic force microscope (Digital I).
When measured with Nano Scope IIIa manufactured by Nstruments, the following results were obtained. Silver 3.4 nm Silver containing 3 atomic% zinc 0.6 nm Silver containing 0.2 atomic% titanium 2.1 nm Silver containing 0.9 wt% palladium and 1.0 wt% copper 1 0.0 nm Silver containing 0.9 atomic% copper and 1.0 atomic% gold 1.6 nm Silver containing 0.9 atomic% copper and 2.0 atomic% gold 0.7 nm 0.9 atom Silver containing 0.4% copper, 1.0 atom% gold and 0.7 atom% neodymium 0.4 nm

From these results, titanium is the main component, titanium,
It is preferable to contain 0.1 to 15 atom% of at least one element selected from the group consisting of zinc, copper, palladium, and gold. 2 out of titanium, zinc, copper, palladium and gold
When more than one kind is contained, each may be 0.1 to 15 atom%, but the total amount thereof is preferably 0.1 to 15 atom%.

An alloy containing silver as a main component and containing 0.1 to 15 atomic% of at least one rare earth element is also preferable. Of the rare earths, neodymium is preferred.

As the reflective layer, a layer made of only gold is preferable because it has excellent corrosion resistance. However, it is more expensive than silver alloy.

A more preferred alloy composition contains silver as a main component, contains 0.1 to 15 atomic% of at least one element selected from the group consisting of titanium, zinc, copper, palladium and gold, and at least one element. Rare earth element of 0.1 to 15
Atomic% content.

The thickness of the reflective layer is 20 to 400 nm, especially 40.
Approximately 200 nm is preferable. It is known that the surface roughness decreases as the film thickness decreases. Therefore, when titanium is added (Ra =
Even if it was 2.1 nm), it can be used by reducing the thickness of the reflective layer.

(2) Recording Layer In the optical recording medium of the present invention, the recording layer contains a dye. The dye is preferably an organic dye from the viewpoint of easy film formation, for example, a phthalocyanine dye, a naphthalocyanine dye, a cyanine dye, an azo dye,
Squarylium dyes, metal-containing azo dyes, metal-containing indoaniline dyes, triarylmethane dyes, merocyanine dyes, azurenium dyes, naphthoquinone dyes, anthraquinone dyes, indophenol dyes,
A xanthene dye, an oxazine dye, a pyrylium dye, etc. can be used. Among the organic dyes, metal-containing azo dyes are preferable because they have excellent recording sensitivity and light resistance.

As the film forming method of the recording layer, a vacuum vapor deposition method,
Examples of commonly used thin film forming methods include a doctor blade method, a casting method, a spin coating method, and a dipping method.
The spin coating method is preferable in terms of mass productivity and cost. Further, the vacuum deposition method is preferable to the coating method from the viewpoint that a recording layer having a uniform thickness can be obtained.

In the case of film formation by the spin coating method, the number of rotations is preferably 10 to 15000 rpm, and after spin coating, a treatment such as heating or exposure to solvent vapor may be performed.

The coating solvent for forming the recording layer by a coating method such as a doctor blade method, a casting method, a spin coating method or a dipping method is not particularly limited as long as it does not attack the substrate. For example, ketone alcohol solvents such as diacetone alcohol and 3-hydroxy-3-methyl-2-butanone; cellosolve solvents such as methyl cellosolve and ethyl cellosolve; chain hydrocarbon solvents such as n-hexane and n-octane. Cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, n-butylcyclohexane, tert-butylcyclohexane, cyclooctane; perfluoroalkyl alcohols such as tetrafluoropropanol, octafluoropentanol, hexafluorobutanol Examples of system solvents include hydroxycarboxylic acid ester solvents such as methyl lactate, ethyl lactate, and methyl 2-hydroxyisobutyrate.

In the case of the vacuum deposition method, for example, a dye and, if necessary, various recording layer components such as additives are put in a crucible installed in a vacuum container, and the inside of the vacuum container is vacuum pumped to 10
After evacuation to about ⁻² to 10 ⁻⁵ Pa, the crucible is heated to evaporate the components of the recording layer and vapor-deposited on the substrate placed facing the crucible to form the recording layer.

The recording layer has a transition metal chelate compound (eg, acetylacetonate chelate, bisphenyldithiol, salicylaldehyde oxime, bisdithio-) as a singlet oxygen quencher in order to improve stability and light resistance of the recording layer. [alpha] -diketone, etc.) and a recording sensitivity improver such as a metal compound for improving recording sensitivity. Here, the metal-based compound means that a metal such as a transition metal is contained in the compound in the form of an atom, an ion, a cluster, etc., for example, an ethylenediamine-based complex, an azomethine-based complex, a phenylhydroxyamine-based complex, a phenanthroline-based complex, Dihydroxyazobenzene-based complex,
Dioxime complex, nitrosoaminophenol complex,
Examples thereof include organometallic compounds such as pyridyltriazine-based complexes, acetylacetonate-based complexes, metallocene-based complexes, and porphyrin-based complexes. The metal atom is not particularly limited, but a transition metal is preferable.

Further, if necessary, a near-infrared laser having a wavelength of about 770 to 830 nm, which is usually used for CD-R, or a wavelength 620-6, which is used for DVD-R, is used.
Red laser of about 90 nm or wavelength of 410 nm
And a so-called blue laser having a wavelength of 515 nm, etc. are used together with dyes suitable for recording using a plurality of wavelengths, thereby forming an optical recording medium capable of recording with laser light in a plurality of wavelength ranges. You can also

Further, when forming the dye recording layer, a binder, a leveling agent, an antifoaming agent and the like can be used in combination, if necessary. Preferred binders include polyvinyl alcohol, polyvinylpyrrolidone, nitrocellulose, cellulose acetate, ketone resins, acrylic resins, polystyrene resins, urethane resins, polyvinyl butyral, polycarbonate, polyolefins and the like.

The film thickness of the recording layer is not particularly limited because the suitable film thickness varies depending on the recording method and the like, but is usually 10 nm to 5 μm, preferably 30 nm to 3 μm.

(3) Barrier Layer This barrier layer is used for the diffusion of the dye into the protective film during the formation of the protective film, the penetration of the coating liquid for forming the protective film into the dye recording layer, or the adhesion of the protective film. This is to prevent a mixing phenomenon such as diffusion and permeation of the adhesive component into the dye recording layer.

The material forming this barrier layer is silicon oxide, particularly silicon dioxide, oxides such as zinc oxide, cerium oxide and yttrium oxide; sulfides such as zinc sulfide and yttrium sulfide; nitrides such as silicon nitride; carbonization. Silicon; a mixture of oxide and sulfur; and the alloys described below and the like. Among them, silicon oxide, zinc sulfide, zinc oxide, silicon nitride,
It is preferable to use at least one selected from silicon carbide, cerium oxide, yttrium oxide, and a mixture of oxide and sulfur. Further, a mixture of silicon oxide and zinc sulfide in a weight ratio of about 30:70 to 90:10 is also suitable. Further, a mixture of sulfur and yttrium dioxide and zinc oxide (Y ₂ O ₂ S-ZnO) is also suitable.

As the alloy, an alloy containing silver as a main component and 0.1 to 15 atom% of at least one element selected from the group consisting of titanium, zinc, copper, palladium and gold is preferable. . Further, those containing silver as a main component and containing at least one kind of rare earth element in an amount of 0.1 to 15 atomic% are also preferable. As the rare earth, neodymium, praseodymium, cerium and the like are suitable.

The thickness of this barrier layer is 2 to 2000 nm, preferably 2 to 20 nm, and particularly preferably 2 to 10 nm. If the thickness of the barrier layer is excessively small, the prevention of the above-mentioned mixing phenomenon will be insufficient. Even if the barrier layer is excessively thick, it is not necessary to prevent the mixing, and it may reduce the light transmittance. Particularly, in the case of an alloy, it is preferable that the thickness is 2 to 20 nm, particularly 2 to 10 nm because the light transmittance is excessively reduced.

(4) Protective film The material of the protective film formed on the barrier layer is not particularly limited as long as it protects the reflective layer from external force. As the material of the organic substance, thermoplastic resin, thermosetting resin,
Examples thereof include electron beam curable resins and UV curable resins.

The thermoplastic resin, thermosetting resin and the like can be formed by dissolving in a suitable solvent, applying a coating solution and drying. The UV curable resin can be formed as it is or by dissolving it in a suitable solvent to prepare a coating solution, applying the coating solution, and irradiating it with UV light to cure it. As a UV curable resin,
For example, an acrylate resin such as urethane acrylate, epoxy acrylate, polyester acrylate can be used. These materials may be used alone or as a mixture, and may be used not only as one layer but also as a multilayer film.

As a method for forming the protective film by coating,
As with the recording layer, a coating method such as a spin coating method or a casting method is used, and among them, the spin coating method is preferable.

The protective coating may be provided by adhering a thin film or sheet-shaped coating made of the above resin with an adhesive. As the adhesive, various kinds such as a room temperature curable adhesive, a thermosetting adhesive, an electron beam curable adhesive, and a UV curable adhesive can be used.

The thickness of the protective film is 0.1 μm to 0.3 m
In particular, 0.1 μm to 200 μm is preferable.

(5) Substrate The material of the substrate in the optical recording medium of the present invention is not particularly limited as long as it has necessary strength and durability.

Conventionally used as a substrate material,
For example, acrylic resin, methacrylic resin, polycarbonate resin, polyolefin resin (particularly amorphous polyolefin), polyester resin, polystyrene resin,
Any of those made of a resin such as an epoxy resin, one made of glass, and one having a resin layer made of a radiation curable resin such as a photocurable resin on glass can be used.

Injection-molded polycarbonate is preferable from the viewpoints of high productivity, cost, resistance to moisture absorption and the like. From the viewpoint of chemical resistance, moisture absorption resistance and the like, amorphous polyolefin is preferable. A glass substrate is preferable from the viewpoint of high-speed response.

Since the substrate does not have to be transparent at the wavelengths of the recording light and the reproducing light, in order to prevent vibration during high speed rotation, a resin such as polycarbonate may be filled with a filler such as carbon fiber to increase the rigidity. .

A guide groove for recording / reproducing light or a pit may be provided on the plate surface of the substrate. Such guide grooves and pits are preferably provided at the time of molding the substrate, but can be provided by using an ultraviolet curable resin layer on the substrate. If the guide groove is spiral, the groove pitch is 0.1 to 1.6.
It is preferably about μm.

(6) Laser etc. The laser light used for the optical recording medium of the present invention includes N ₂ , He-Cd, Ar, He-Ne, ruby, semiconductor, dye laser, etc. A semiconductor laser is preferable because it is compact, compact, and easy to handle.

Recording on the optical recording medium of the present invention obtained as described above is performed by irradiating the recording layer provided on both sides or one side of the substrate with a laser beam focused to about 1 μm. In the portion irradiated with laser light, thermal deformation of the recording layer such as decomposition, heat generation, and dissolution occurs due to absorption of laser light energy, and optical characteristics change.

The recorded information is reproduced by reading the difference in reflectance between the portion where the change in the optical characteristics is caused and the portion where the change in the optical characteristics is not caused by the laser light.

[0053]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited as long as the gist thereof is not exceeded.
The present invention is not limited to the following examples.

Example 1 Thickness with a guide groove having a track pitch of 0.74 μm and a thickness of 0.
An 80 nm silver reflection layer was provided on a 6 mm supporting substrate, and a metal-containing azo dye recording layer for DVD-R was provided with a thickness showing an absorbance of 0.7 (absorbance measured at a wavelength of 598 nm with air as a reference) of 0.7, and a thickness of 5 nm was provided thereon. After providing a barrier layer made of a mixture of zinc sulfide and silicon dioxide (weight mixing ratio 1: 1), a protective film made of a polycarbonate sheet having a thickness of 90 μm was used as a UV curable resin (Dainippon Ink and Chemicals, Inc.). It was pasted together with SD-318 manufactured by SMC.

For this optical recording medium, a wavelength of 650n
When recording and reproducing were performed by a recording and reproducing evaluator having m and a numerical aperture of 0.65, the push-pull signal amplitude before recording was 0.23,
A good reproduction signal having a reflectance of 21% and a modulation of 63% was obtained.

Example 2 A disk was prepared in the same manner as in Example 1 except that the barrier layer had a thickness of 10 nm.

When this optical recording medium was similarly recorded and reproduced by a recording and reproducing evaluator, a good reproduced signal with a push-pull signal amplitude of 0.23 before recording, a reflectance of 21% and a modulation of 62% was obtained. Was obtained.

Example 3 An optical recording medium was prepared in the same manner as in Example 1 except that a silicon dioxide layer having a thickness of 5 nm was formed as a barrier layer.

When this optical recording medium was similarly recorded and reproduced by a recording and reproducing evaluator, a good reproduced signal with a push-pull signal amplitude before recording of 0.22, a reflectance of 21% and a modulation of 62% was obtained. Was obtained.

Example 4 An optical recording medium was prepared in the same manner as in Example 3 except that the barrier layer had a thickness of 10 nm.

When this optical recording medium was similarly recorded and reproduced by a recording and reproducing evaluator, a good reproduced signal with a push-pull signal amplitude before recording of 0.20, a reflectance of 21% and a modulation degree of 60% was obtained. Was obtained.

Example 5 An optical recording medium was manufactured in the same manner as in Example 1 except that a layer made of a silver alloy containing 3 atomic% of zinc having a thickness of 5 nm was provided as the barrier layer.

When this optical recording medium was similarly recorded and reproduced by a recording and reproducing evaluator, a good reproduced signal with a push-pull signal amplitude before recording of 0.10, a reflectance of 18% and a modulation of 61% was obtained. Was obtained.

The surface roughness of the silver alloy barrier layer containing zinc was measured by an atomic force microscope (Digital Instrument).
Ra = 0.4 nm when measured by Nano Scope IIIa manufactured by ents.

Example 6 An optical recording medium was prepared in the same manner as in Example 5 except that the barrier layer had a thickness of 10 nm.

When this optical recording medium was recorded / reproduced by a recording / reproducing evaluator in the same manner, a good reproduced signal having a push-pull signal amplitude before recording of 0.25, a reflectance of 28% and a modulation degree of 64% was obtained. Was obtained.

The surface roughness of this silver alloy barrier layer was measured by an atomic force microscope (Na manufactured by Digital Instruments).
No Scope IIIa), Ra = 0.
It was 5 nm.

Comparative Example 1 An optical recording medium was prepared in the same manner as in Example 1 except that the barrier layer was not provided. However, when the protective substrate was pasted with the UV curable adhesive, the dye was dissolved in the adhesive, and a good optical recording medium could not be produced.

[0069]

As described above, the present invention provides a high density optical recording medium having a dye recording layer. This dye recording layer is not affected by the formation of the protective film, and the recording characteristics of the optical recording medium are extremely good.

[Brief description of drawings]

FIG. 1 is a sectional view in a thickness direction showing a configuration of an optical recording medium according to an embodiment.

FIG. 2 is a sectional view in the thickness direction showing the configuration of an optical recording medium according to another embodiment.

FIG. 3 is a cross-sectional view in the thickness direction showing a configuration of an optical recording medium according to a conventional example.

[Explanation of symbols]

1 substrate 2 reflective layer 3 recording layers 4 protective film 5 Barrier layer

Continued front page    (72) Inventor Kenjiro Seino             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation F-term (reference) 5D029 JA04 LA12 LB07 LB11

Claims (8)

[Claims] 1. An optical recording medium having a reflective layer, a recording layer containing a dye, and a protective coating on a substrate, and recording and reproducing through the protective coating, wherein recording is performed between the recording layer and the protective coating. An optical recording medium comprising a barrier layer for preventing the layer and the protective coating from being mixed with each other. 2. The barrier layer according to claim 1, wherein the barrier layer is selected from silicon oxide; zinc sulfide; zinc oxide; silicon nitride; silicon carbide; cerium oxide; yttrium oxide; yttrium sulfide; and a mixture of oxide and sulfur. At least 1
An optical recording medium comprising a seed. 3. The optical recording medium according to claim 1, wherein the barrier layer is made of zinc sulfide and silicon oxide. 4. The barrier layer according to claim 1, wherein the barrier layer contains silver as a main component and 0.1 to 15 atoms of at least one element selected from the group consisting of titanium, zinc, copper, palladium, and gold. % Optical recording medium. 5. The barrier layer according to claim 1, wherein the barrier layer contains silver as a main component, and further contains at least one rare earth element.
An optical recording medium containing 1 to 15 atomic%. 6. The optical recording medium according to claim 1, wherein the barrier layer has a thickness of 2 to 2000 nm. 7. The optical recording medium according to claim 1, wherein an arithmetic surface roughness Ra of an interface of the barrier layer on the protective film side is 2 nm or less. 8. The optical recording medium according to claim 4, wherein the barrier layer has a thickness of 2 to 20 nm.