JPH06111365A - Optical recording medium - Google Patents

Abstract

PURPOSE:To produce the optical recording medium which has a high reflectivity and decreased crosstalks by successively laminating an interference layer having a small attenuation factor for optical path adjustment, a recording layer consisting of org. dyestuff, a reflection layer and further a protective layer on a substrate. CONSTITUTION:This optical recording medium consists of the structure formed with the interference layer having the small attenuation factor for adjusting the optical path length, the recording layer and the reflection layer on the substrate. The disk exhibiting the high reflectivity is produced by unifying the phases of the amplitude reflection waves by the boundaries of the substrate/ the interference layer and the recording layer/the reflection layer. Since the unnecessary deformation of the substrate is suppressed, the crosstalks are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write-once optical disc, and more particularly to an optical recording medium suitable for a write-once optical disc compatible with a read-only type optical disc.

[0002]

2. Description of the Related Art As an optical information recording medium, a read-only type disc typified by a compact disc has been widely spread, and subsequently, a write-once type optical disc, which is expected to have great demand,
Also, research on rewritable optical discs has been actively conducted.
Among them, the write-once type optical disc using an organic dye such as a cyanine dye, a phthalocyanine dye, or a naphthalocyanine dye has a lower cost than an optical disc using an inorganic material such as tellurium because the film can be formed by spin coating. Since it can be expected to become more popular, it is attracting new attention. In recent years, a write-once optical disc compatible with a read-only optical disc, that is, a compact disc and capable of recording once has been proposed. The compact disc standard (CD standard)
Research and development of write-once optical discs conforming to the above are actively carried out. In particular, various disc structures have been studied in order to make the reflectance of the unrecorded portion 70% or more with respect to the reproduction laser beam.

Currently proposed disks (Japanese Patent Laid-Open Nos. 2-87339, 2-87340, and 2-792).
In 35), in order to make the reflectance 70% or more, a recording layer having a specific optical constant on the substrate, further Au, Ag, Cu,
A metal reflective layer such as Al is laminated to a predetermined thickness to satisfy the CD standard. A disk having a structure in which an optical interference layer is provided between a recording layer and a reflection layer (Japanese Patent Laid-Open No. 2-18086) has also been proposed, but these have a structure of a substrate, a recording layer, a dye layer that does not absorb light, and a reflection layer. .

[0004]

There have been proposed several disk structures for increasing the reflectance of the unrecorded area to 70% or more, but the above-mentioned structures of the substrate, the dye layer and the reflective layer are generally used. Target. However, in the case of this disc structure, the substrate /
Since the interference of the amplitude reflection wave due to the dye layer and the dye layer / reflection layer and the interface within the dye film thickness is utilized, a dye having an extremely small extinction coefficient of optical constant and a large refractive index is used. It is necessary to set the optical film thickness at a predetermined place. Therefore, the range of the optical constant of the dye satisfying the conditions is very narrow, and the selection of the recording material that can be actually used is limited. Further, a metal reflection film such as gold, copper, aluminum, platinum, or an alloy thereof is laminated on the reflection layer to a predetermined thickness.

Further, in these discs, there is a problem that crosstalk occurs in which information of recorded tracks is read out when reproducing adjacent tracks.
The present invention provides an optical recording medium having high reflectance and little crosstalk.

[0006]

According to the present invention, even if a dye having a larger extinction coefficient is taken into consideration, the reflectance is set to 70 by inserting an interference layer between the substrate and the recording layer in consideration of the film thickness of the dye layer.
% Or more, while finding a recording medium with less crosstalk. An optical recording medium of the present invention is characterized by a structure in which an interference layer having a small extinction coefficient for adjusting an optical path length, a recording layer made of an organic dye, a reflective layer, and a protective layer are sequentially laminated on a substrate. It is a medium.

At this time, each film is formed so that the phases of the amplitude reflected waves at the interface between the substrate / interference layer and the interference layer / dye layer are aligned, and the reflectivity of the disk is 70% or more. Further, by disposing the recording layer adjacent to the interference layer and separated from the substrate, deformation of the substrate due to melting and decomposition of the recording layer at the time of recording can be suppressed and crosstalk can be reduced.

Examples of the substrate include thermoplastic resins such as vinyl chloride resin, acrylic resin, polyolefin resin, polycarbonate resin and polyvinyl acetal resin, thermosetting resins such as epoxy resin, unsaturated polyester resin and vinyl ester resin, and glass. Some are made of material,
The shape is preferably a plate shape.

Organic dyes used in the recording layer include naphthalocyanine dyes, phthalocyanine dyes, merocyanine dyes,
There are polymethine dyes, anthraquinone dyes, porphyrin dyes, and the like. The film-forming of these dyes can be dissolved in an organic solvent and spin-coated, or those that can be vapor-deposited can be formed by vacuum vapor deposition.

Of these dyes, naphthalocyanine dyes are known to have excellent light resistance and environmental resistance. Therefore, even with a dye having a large extinction coefficient, such as a naphthalocyanine dye, the thickness of the dye layer is reduced to reduce the absolute amount of light absorption, and an interference layer having an optimum optical film thickness is provided between the dye layer and the reflective layer. A high reflectance was obtained by inserting and aligning the phases of the amplitude reflected waves at the interface between the substrate / dye layer and the interference layer / reflection layer. In the structure in which such an interference layer is inserted,
The permissible range of the dye used in the recording layer can be expanded.

It is desirable that the optical interference layer has a small extinction coefficient and can be formed into a predetermined film with good quality, and an azo dye, a cyanine dye, an anthraquinone dye or the like can be used. These dyes can be dissolved in an organic solvent to form a film by spin coating or vacuum evaporation. The reflective layer is preferably gold, copper, aluminum, platinum, or alloys thereof, which have high reflectivity. These metal films can be formed by vacuum vapor deposition, sputtering or the like.

[0012]

With the structure of the interference layer, the recording layer and the reflective layer having a small extinction coefficient for adjusting the optical path length on the substrate,
By aligning the phases of the amplitude reflected waves at the substrate / interference layer and the recording layer / reflective layer interfaces, a disk exhibiting high reflectance can be manufactured. Moreover, since unnecessary deformation of the substrate is suppressed, crosstalk can be reduced.

[0013]

【Example】

Example Polycarbonate substrate (outer diameter: 120 mm, inner diameter: 15
mm, track pitch: 1.6 μm, manufactured by Idemitsu Petrochemical Co., Ltd.) as an interference layer, a cyanine dye NK-529.
100 mg (manufactured by Japan Photosensitive Dye Research Institute) was dissolved in 4.5 ml of a coating solvent tetrafluoropropanol, and a film was formed at 120 nm by a spin coating method. As a recording layer thereon, 30 mg of a naphthalocyanine dye (Nc-S-4-Ch) was dissolved in 4.5 ml of cyclohexane, and a film having a thickness of 60 nm was formed by spin coating. A 60 nm-thick gold film was formed thereon as a reflective layer by a vacuum evaporation method. Further, an ultraviolet curable resin was spin-coated on the outermost layer and then irradiated with ultraviolet rays to be cured. On the optical disk obtained as described above, a semiconductor laser having a wavelength of 780 nm was used from the substrate side to obtain a linear velocity of 1.25 m.
7T (309KH) corresponding to the EFM signal in 1 / sec
z), (duty ratio 50/50) simple signal 8mW
Recorded in. When the recorded signal was reproduced with a semiconductor laser of 0.5 mW of 780 nm, the reflectance decreased in the recording portion, the C / N at that time was 43 dB, and the crosstalk was 5 dB.

Comparative Example Polycarbonate substrate (outer diameter: 120 mm, inner diameter: 15
mm, track pitch: 1.6 μm, manufactured by Idemitsu Petrochemical Co., Ltd.) Naphthalocyanine dye (Nc-S) as a recording layer
-4-Ch) (30 mg) was dissolved in 4.5 ml of cyclohexane, and a film was formed at 60 nm by a spin coating method. As an interference layer thereon, 100 mg of cyanine dye NK-529 (manufactured by Japan Photosensitive Dye Research Institute) was dissolved in 4.5 ml of tetrafluoropropanol, and a film having a thickness of 120 nm was formed by a spin coating method. A 60 nm-thick gold film was formed thereon as a reflective layer by a vacuum evaporation method. Furthermore, after UV-curing resin was spin-coated on the outermost layer, it was irradiated with UV rays to be cured. The optical disk obtained as described above was subjected to EF at a linear velocity of 1.25 m / sec with a semiconductor laser having a wavelength of 780 nm from the substrate side.
A simple signal of 7T (309 KHz) and (duty ratio 50/50) corresponding to the M signal was recorded at 8 mW. When the recorded signal was reproduced with a semiconductor laser of 0.5 mW of 780 nm, the reflectance decreased in the recording part and the C / N at that time was decreased.
Was 45 dB and crosstalk was 10 dB.

[0015]

According to the present invention, by optimizing each film thickness in the structure of substrate / interference layer / recording layer / reflection layer, an optical recording medium having high reflectance and little crosstalk can be manufactured.

Claims (2)

[Claims] 1. An interference layer having a small extinction coefficient for adjusting an optical path length, a recording layer made of an organic dye, and a reflective layer, which are arranged in this order on a substrate.
An optical recording medium in which a protective layer is further laminated. 2. The optical recording medium according to claim 1, wherein the organic dye is a naphthalocyanine dye.