JPS59199291A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium generating a high reproduction output with high sensitivity in a wavelength range of semiconductor laser, by a method wherein recording layer in an optical recording medium is constitued of at least two layers of a thin organic film comprising a naphthoquinone dye as a main constituent and a metallic reflective film. CONSTITUTION:In the optical recording medium of the type in which a recording layer is provided on one side of a base and information is recorded and read by a laser beam, the recording layer is constituted of at least two layers of the thin organic film comprising a naphthoquinone dye of the formula (wherein each of R and R' is an auxochrome) as a main constituent and the metallic reflective film. Since the optical recording medium is provided with a multilayer construction by introducing the metallic layer having a high reflectance, when an organic dye is used for a hole-forming layer, a large optical gradation quantity can be obtained by such a construction that the reflectance is enhanced after forming holes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording medium on which information can be recorded and reproduced using a laser beam, and more particularly to an optical recording medium having an organic dye as a recording layer.

Conventionally, many organic pigments have been used in the recording layer of this glaze, but they can be roughly divided into pigments that absorb visible light and pigments that absorb into the near-infrared region. The former is an application of dyes that have been used for dyeing to optical recording layers. In this case, a gas laser that oscillates with visible light is used as a recording/reproducing laser.

Gas lasers are unsuitable for modern optical recording devices due to their large size and high power consumption.
It has become desirable to use semiconductor lasers that solve these problems. The oscillation wavelength of existing semiconductor lasers is approximately 8
Since the wavelength is in the near-infrared light region of 00 nm, the recording layer cannot be made of a primary absorption dye, and the recording layer must be made of a dye that exhibits absorption in the near-infrared light region.

Until now, various metal phthalocyanines and squarylium have been used as near-infrared light-absorbing dye recording layers.

Cyanine dyes have been developed. Although metal phthalocyanine has excellent light hardening properties, it has the problem that its crystalline state changes when heated. That is, a thin film formed by vapor deposition is in an amorphous state, but when this film is heated to several hundred degrees Celsius, it becomes crystallized. Along with this crystallization, the optical properties also change, and the reflectance usually increases. Therefore, when writing is performed with a laser beam, changes in reflectance due to changes in the crystal state and changes in reflectance due to hole formation overlap, resulting in complex writing characteristics, which is a practical problem.

By changing the size of the molecular resonance structure of cyanine dyes, the absorption peak can be varied over a wide range from visible to near-infrared. When this dye is used as a recording layer, there is a problem that the characteristics deteriorate due to oxidation reaction caused by light absorption. Squarylium is a desirable dye because it has a relatively low optical hardness and its absorption is close to that of semiconductor laser light, but it has the drawback of low recording sensitivity.

As described above, hitherto known organic dye recording media have some drawbacks, and there are problems in putting them into practical use. As a result of intensive research to solve these problems with organic dye recording media, the inventors of the present invention discovered that naphthoquinone dyes represented by the following general formula are excellent as optical recording media.

0 11 R' 0 R and R' in the above general formula represent an auxochrome. This dye is
It exhibits excellent properties such as excellent light hardness and high recording sensitivity.

In addition to high recording sensitivity, an optical recording medium must have a high reproduction S/N ratio. In general, organic dye media are softer and have lower reflectance than metals. Therefore, the reflectance change before and after hole formation, 12+1, ie, the amount of light modulation, is smaller in the organic dye medium than in the metal medium. For this reason, the recording signal of the organic dye medium is small, and in order to increase the reproduction S/N, it is necessary to increase the change in reflectance before and after recording.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art and to provide an optical recording medium that has cylinder sensitivity and a large reproduction output in the wavelength region of a semiconductor laser.

That is, the present invention provides an optical recording medium in which a recording layer is provided on one or both sides of a substrate, and information is recorded and read by a laser beam. It is characterized by forming at least two layers: an organic thin film containing naphthoquinone dye represented by () as a main component, and a metal reflective film.

The naphthoquinone dye represented by the above general formula is 2.3
-Generally known as dicyano-1,4-naphthoquinone, 5,8
The absorption peak wavelength changes from the visible light region to the near-infrared light region depending on the type of auxochrome.

As an auxochrome that has an absorption peak wavelength in the near-infrared region,
R in the above general formula is an amine group (NH2).

R' is preferably a substituted phenylamino group (NH-(EjX, where X represents a substituent).

As the substituent X of the substituted phenylamino group, an alkyl group, an allyl group, an amino group, a substituted amino group or an alkoxyl group is used. Such dyes are collectively called 2,3-dicyano-5-amino-8-allylamino-1,4-naphthoquinone and are represented by the following structural formula.

The medium reflectance is determined by the complex refractive index (n-ik) of the medium. To obtain a large reflectance, n or k must be large, or the medium must be sufficiently small compared to 1. When a thin film of an organic dye given by the above structural formula is formed on a glass or acrylic resin substrate by vapor deposition and used as a medium, the medium reflectance depends on the film thickness. For example, in the case of a dye in which an ethoxyl group is coordinated at the cuboid position (hereinafter abbreviated as ethoxy dye), the maximum reflectance is obtained when the film thickness is 80 nm, but the value is 30 cm, and even larger reflectances are obtained. cannot be obtained. Therefore, the amount of light modulation before and after hole formation is at most 30 inches.

An effective means of increasing the amount of light modulation is to introduce a metal layer with high reflectance to form a multilayer structure. It has been found that when the above organic dye is used as the pore-forming layer, a large amount of light modulation can be obtained with a structure in which the reflectance increases after the pores are formed.

The present invention will be explained in more detail below with reference to the drawings. 1st
The figure shows a medium 40 consisting of an AL film 20 and an ethoxy dye film 30 formed on an acrylic disk 10 with a thickness of 1.2m7B.
It shows. From the direction indicated by arrow 50, wavelength 830
A nanometer AAGaAs semiconductor laser beam is focused by an optical system (not shown) and irradiated onto the medium 40 to form holes 60 in the ethoxy dye film 30. When determining the dependence of the reflectance R0 on the thickness of the ethoxy dye film 30 from the part where no holes are formed, the second
The results shown in the figure are obtained. In this figure, the reflective film AL
The thickness of the film 20 is 1100 nm, and the reflectance at a wavelength of 830 nm is shown. In the figure, the solid line indicates R8 at each film thickness.

The reflectance from the portion where the holes are formed is the reflectance when the ethoxy dye film thickness is zero, so in this case it is about 86 cm. As a result, since the jetoxy dye film thickness is 60 nm and the R8 is 15%, the reflectance changes from 15 to 86 before and after hole formation, resulting in a larger modulation amount than the single layer medium. I know that it will happen.

FIG. 3 shows a highly preferred embodiment. An At film 200 is formed on the acrylic substrate 100. A transparent film 300 and an ethoxy dye film 400 are laminated in this order.

A transparent film 30 is placed between the At film 200 and the ethoxy dye film 400.
By inserting 0, the recording sensitivity is improved compared to the medium of the embodiment shown in FIG. This is 5i02. used as a transparent film. Dielectric materials such as Si, N, etc. and PMMA
Since the thermal conductivity of resin such as (acrylic polymer) is low, the heat absorbed by the ethoxy dye film 400 is less likely to diffuse into the AL film 200, which has a high thermal conductivity. FIG. 4 shows the reflectance when the thickness of the ethoxy dye film 400 is changed when a 5in2 film is used as the transparent film 300, and the 5i02 film thickness is 20 nm and 60 nm. Note that the thickness of the AA film 200 is 1100 mm.
It was set as n. From this, when the St,2 film thickness is 20 nm,
For example, if the ethoxy dye film thickness is 4Qnm, the reflectance before pore formation is 17% and the reflectance after pore formation is 85%.
A light modulation amount of 68% can be obtained. Similarly, 5
When the i02 thickness is 60 nm, the ethoxy dye film thickness is 20 nm.
If it is nm, the amount of optical modulation will be 67%. By selecting the thicknesses of the transparent film 300 and the ethoxy dye film 400 in this way, it is possible to obtain an amount of light modulation that is more than twice as large as that of a single-layer ethoxy dye film medium.

As is clear from the above embodiments, an optical recording medium with a large amount of light modulation can be obtained by the present invention. In addition, in the example, an example was shown in which an organic dye having an ethoxyl group as a substituent was used, but almost the same effectiveness as in the example was obtained even when the above-mentioned organic dye and similar derivatives were used. In the example, the case where an AA film is used as the reflective layer is shown, but Ag
Membrane r Au membrane.

A metal film with high reflectivity such as a Cu film and a dielectric multilayer interference film can also be used. Furthermore, a retention film of dielectric, organic material, high melting point metal, etc. may be applied to the uppermost layer of the medium by a known method.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an optical recording medium according to the present invention, in which 10 is a substrate, 20 is a reflective film, 30 is an organic dye film, and 60
2 shows a hole, and FIG. 2 is a graph showing the reflectance of the optical recording medium shown in FIG. 1 as a function of dye film thickness. Section 3 1 is a sectional view of another optical recording medium according to the present invention. In the figure, 100 is a substrate, 200 is a reflective film, 300 is a transparent film, and 400 is an organic dye film. 4 is a graph showing the dependence of the reflectance of the optical recording medium of FIG. 3 on the organic dye film thickness. Figure 1 Figure 2 θ 200 40θ OtsuDO8001000 Normal thickness (A
) Figure 3 Figure 4 0 200 400 600 800 10θO
Atsushi (A)

Claims (1)

[Claims] An optical recording device in which a recording layer is provided on one or both sides of a substrate, and information is recorded and read by a laser beam,
Optical recording characterized in that the recording layer is composed of at least two layers: an organic thin film mainly composed of a naphthoquinone dye represented by the general formula (wherein R and R' represent an auxochrome) and a metal reflective film. Medium.