JPH04265541A - Optical recording medium - Google Patents

Abstract

PURPOSE:To offer such an optical recording medium having higher reflectance in a nonrecorded area, especially suitable as a DRAW type optical disk. CONSTITUTION:The optical recording medium has a structure consisting of a base substrate and a recording layer and a reflecting layer successively formed on the substrate. Between the substrate and the recording layer, there is provided a metal half-transparent layer comprising gold, silver, copper, aluminum, platinum, etc., or alloy of these. By providing the metal half-transparent layer between the substrate and the recording layer, reflectance in a nonrecorded area can be increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical recording media, and particularly to write-once optical discs (CD-WO) which are compatible with read-only optical discs (CDs).

0002

[Background Art] As for optical information recording media, read-only discs such as compact discs (CDs) have become widely used, and research into write-once optical discs and rewritable optical discs, which are expected to have great demand in the future, will follow. is being actively carried out. Among these, cyanine dyes, phthalocyanine dyes,
Write-once optical disks that use organic dyes such as naphthalocyanine dyes are attracting attention because they can be formed by spin coating and are expected to be cheaper than optical disks that use inorganic materials such as tellurium. There is. In recent years, a write-once optical disc (CD-WO), which is compatible with a read-only optical disc, i.e., a compact disc (CD) and can record once, has been proposed. Research and development of optical discs is actively being conducted. In particular, to increase the reflectance of the unrecorded area to the reproduction laser beam (for example, increase the reflectance to 70%).
% or more), various disk structures are being considered.

For example, Japanese Patent Laid-Open No. 2-87339 discloses that a recording layer having a specific optical constant and a metal reflective layer made of gold, silver, copper, aluminum, etc. are placed on a substrate in order to increase the reflectance. A structure in which layers are laminated to a certain thickness has been proposed. According to this structure, the reflectance for laser light is 70
% or more is also possible. Several other disk structures have been proposed for increasing the reflectance in unrecorded areas, but the most common structure is one in which a recording layer and a metal reflective layer are sequentially formed on the above-mentioned substrate.

[0004] The disk having the above-mentioned structure utilizes interference between the amplitude reflected wave at the interface between the substrate and the recording layer and the amplitude reflected wave at the interface between the recording layer and the reflective layer. The constant has a significantly small extinction coefficient,
It needs to have a large refractive index, and its optical film thickness needs to be set to a predetermined thickness. Therefore, the range of optical constants of dyes that satisfy these conditions becomes extremely narrow, and the dyes that can actually be used are limited. However, dyes with excellent light resistance to natural light or reproduction laser light generally have a large extinction coefficient, and therefore cannot be used for the above purpose. Such pigments include phthalocyanine pigments,
There are naphthalocyanine dyes, etc.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its first object is to provide an optical recording medium having a novel structure to increase reflectance. The second purpose is to widen the range of optical constants of dyes that can be used in the recording layer, so that dyes with excellent light resistance can be used in the recording layer.

[0006]

[Means for Solving the Problems] The optical recording medium of the present invention has a structure in which a recording layer and a reflective layer are sequentially laminated on a substrate, and a metal semi-transparent layer is provided between the substrate and the recording layer. That's what happens.

The substrate may be made of thermoplastic resins such as vinyl chloride, acrylic resins, polyolefin resins, polycarbonate resins, and polyvinyl acetal resins, thermosetting resins such as epoxy resins, unsaturated polyester resins, and vinyl ester resins, glass, etc. There are materials that can be used, and the shape is preferably a plate.

[0008] The recording layer is made of an organic dye thin film having absorption at the recording laser wavelength. Examples of organic dyes that can be used include cyanine dyes, phthalocyanine dyes, naphthalocyanine dyes, merocyanine dyes, etc.
Particularly desirable are phthalocyanine and naphthalocyanine dyes. These dyes can be formed into a film by dissolving them in an organic solvent and spin coating, or if they can be vapor deposited, by vacuum vapor deposition.

[0009] The metal of the metal semi-transparent layer of the present invention includes gold, silver, copper, aluminum, platinum, etc., which have a high reflectance.
Alloys of these are desirable. These metal films can be formed by vacuum evaporation, sputtering, or the like. The thickness of the metal semi-transparent layer varies depending on the metal used, but it is preferably adjusted so that the light transmittance is 20% or more when only the metal semi-transparent layer is laminated on the substrate.
In particular, it is preferable that the transmittance is about 50%. The specific film thickness is preferably about 3 nm to 20 nm. If the film thickness is too small, it will be difficult to form a complete film,
If the film thickness is too large, the amount of light reaching the recording layer will be too small.

The reflective layer is preferably made of gold, copper, aluminum, platinum, or an alloy thereof. Those with high reflectance are preferred. These metal films can be formed by vacuum evaporation, sputtering, or the like. The thickness of the reflective layer is preferably 50 nm or more.

In the optical recording medium of the present invention, a protective layer may be further provided on the reflective layer. As the protective layer, various resin materials such as ultraviolet curing resin and thermosetting resin can be used. Further, as the protective layer, a film of silicon dioxide or the like may be formed by sputtering, vacuum evaporation, or the like.

The optical recording medium of the present invention utilizes amplitude reflected waves at the interface between the metal semi-transparent layer and the recording layer in order to increase the reflectance. Further, it is preferable that this reflected wave is amplified by interfering with the amplitude reflected wave from the interface between the recording layer and the reflective layer, and for this purpose, it is preferable that these amplitude reflected waves have phases such that they amplify each other. It is preferable to adjust the optical thickness of the metal semi-transparent layer and the recording layer.

Writing and reproduction on the optical recording medium of the present invention are performed, for example, by irradiating a laser beam from the substrate side to melt, vaporize, or decompose the recording layer and deform it to form a recording section. This can be done by irradiating the same laser beam with a power lower than that used for writing and detecting the change in reflectance between the recorded and unrecorded areas.

[0014]

[Examples] Examples of the present invention are shown below.

Example 1 Polycarbonate substrate (outer diameter 120 mm and inner diameter 15 m)
A metal semi-transparent layer made of gold was formed in a donut shape (track pitch 1.6 μm) to a thickness of 10 nm by vacuum evaporation. Then, a recording layer made of copper phthalocyanine was formed to a thickness of 100 nm by vacuum evaporation. A gold film with a thickness of 60 nm was formed thereon as a reflective layer by vacuum evaporation. Further, an ultraviolet curing resin [SD-17, trade name of Dainippon Ink and Chemicals Co., Ltd.] was spin-coated on the outermost layer, and the resin was cured by irradiation with ultraviolet rays to form a protective layer. The obtained optical recording medium (
The reflectance of the optical disc) at 780 nm was 71%.

[0016] The optical disc obtained above was heated from the substrate side with a semiconductor laser of 780 nm wavelength at a linear velocity of 1.25 m.
A signal was recorded at 8 mW at 500 kHz and a duty ratio of 50/50. The recorded signal was reproduced using a 780 nm semiconductor laser of 0.5 mW. As a result, the reflectance at the recording section was reduced, and the C/N was 40 dB.

Example 2 An optical disk was produced in the same manner as in Example 1 except that copper was formed to a thickness of 10 nm by sputtering instead of gold as the metal semi-transparent layer in Example 1 above. The reflectance of the obtained optical disc at 780 nm was 72%. Further, recording and reproduction were performed under the same conditions as in Example 1. As a result, the reflectance at the recording section was reduced, and the C/N was 40 dB.

Comparative Example 1 An optical disc was produced in the same manner as in Example 1 except that the metal semi-transparent layer was not formed. The reflectance of the obtained optical disc at 780 nm was 50%.

[0019]

Effects of the Invention The optical recording medium according to claim 1 can increase the reflectance by providing a metal semi-transparent layer between the substrate and the recording layer, and also uses a dye with a high extinction coefficient in the recording layer. However, it shows sufficiently high reflectance.

Claims (1)

[Claims] 1. An optical recording medium having a structure in which a recording layer and a reflective layer are sequentially laminated on a substrate, and a metal semi-transparent layer is provided between the substrate and the recording layer.