JPS60209940A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the percentage modulation of recording sensitivity and recording signal by constituting a recording medium in such a way that the light absorptive layer thereof exists between the conventional reflecting layer and a noval layer having increased reflectivity. CONSTITUTION:A recording medium 1 has a substrate 2 made of glass having 0.2mm. thickness and 1.5 refractive index. The 1st reflecting layer 3 consisting of a ZnS film deposited by evaporation to have 860Angstrom thickness and 2.3 refractive index is provided as a coating layer having increased reflectivity on one surface of the substrate 2. A light absorptive layer 4 as a recording layer is provided on the exposed surface of the layer 3. The layer 4 is formed by mixing a spiropyrane compd. exhibiting a high absorption characteristic at a >=700nm wavelength region, i.e., 5'-methoxy-1'-n-hexyl-3',3'-dimethyl-6-nitro-8-methoxy spiropyrane and a vinyl chloride/vinylidene chloride copolymer at 1:2 by weight, dissolving the mixture in a solvent and forming the layer by spinner coating. The 2nd reflecting layer 5 consisting of an Ag layer deposited by evaporation to have 1,000Angstrom reflectivity and 0.85-15.35 refractive index is provided as a light reflecting layer on the exposed surface of the layer 4.

Description

[Detailed description of the invention] Industrial applications The present invention relates to optical recording media.

BACKGROUND ART AND PROBLEMS There is a method of utilizing interference effects to improve the recording sensitivity and the degree of modulation of recording signals in an optical recording medium consisting of a transparent substrate, a light absorption layer, and a light reflection layer. , where the light absorption layer is a metal thin film such as Te, or which has been well studied in magneto-optical recording media (for example, A, E, Be
l1, F, W, Spong, IEEE, J.

Quantum Filectronics 14. p
, 497).

When the light-absorbing layer is formed using a light-absorbing organic material or a polymeric binder in which a light-absorbing substance is dispersed, the light-absorbing layer generally has a refractive index close to 1.5 and a relatively low absorbance. Since it is small, it is necessary to increase the thickness of the layer to the same extent as the wavelength of the laser beam in order to improve recording sensitivity. In this case, in an optical recording medium configured such that the light absorption layer faces the air, the thickness of the light absorption layer may be adjusted so that the phases of the light reflected from the two interfaces of the light absorption layer cancel each other out. , the absorbance in this layer increases, the reflectance decreases, and the recording sensitivity improves (for example, K, Y, Law; Appl
.

Phys, Let t, 3(i Ql p, 994
; D, G, Howe and J, Wrobe
l.

J, Vac, 8ci, Technol, 18(1)p,
92). However, when a storage layer is provided to preserve the light absorption layer (recording surface), or when recording and reproduction are performed through a substrate, a light absorption layer with a refractive index close to 1.5 will still have a refractive index of 1.5. To face the substrate or protective layer of 5 degrees,
Almost no reflection occurs at the interface, and no interference effect is obtained. Note that if a metal coating layer is provided at the interface of the light absorption layer in contact with the substrate or the protective layer, a strong G1 interference effect can be obtained, but this is not preferable because the metal itself has a large light absorption.

OBJECTS OF THE INVENTION In view of the above points, the present invention provides an optical recording medium that provides a strong interference effect and has improved recording sensitivity and modulation degree of recorded signals.

Summary of the Invention The optical recording medium of the present invention is formed by laminating a transparent substrate, a first reflective layer, a light absorption layer, and a second reflective layer, and the light absorption layer includes a first reflective layer and a second reflective layer. The first reflective layer is located between the transparent substrate and the light absorption layer, and is made of a material having a refractive index larger than the refractive index of the transparent substrate and the light absorption layer, and has a thickness of about 1.5 m (1+2 m). Here, λ is the wavelength of the laser beam, n is the refractive index of the first reflective layer, and m is 0 or a positive integer).

In the optical recording medium of the present invention configured in this way, the light reflectance at the interface between the first reflective layer and the light absorption layer increases and a strong interference effect is obtained, which improves the recording sensitivity and the modulation of the recording signal. The degree is thicker (improved).

EXAMPLES Hereinafter, examples of the optical recording medium of the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a recording medium 1 according to this embodiment. The recording medium 1 has a substrate 2 made of glass with a thickness of 0.2 rom and a refractive index of 1.5.

On one side of the substrate 2, a first reflective layer 3 of a ZnS vapor-deposited film having a thickness s 60 X% and a refractive index of 2.3 is provided as a reflectance-enhancing coating layer. A light absorption layer 4 as a recording layer is provided on the exposed surface of the first reflective layer 3. This light absorption layer 4 is made of a spiropyran compound of the following formula, which exhibits high absorption characteristics in a wavelength range of 7000 m or more, that is, 5'-methoxy-1
'-n-hexyl-3', 3'-redimethyl-6-
Nitro-8-methoxyspiro (2H-1-benzothiobilane-2,2'-indoline) and vinyl chloride-vinylidene chloride copolymer (Denkabinyl $10, manufactured by Denki Kagaku Kogyo Co., Ltd.)
00W) at a weight ratio of 1:2, dissolved in a solvent (tetrahydrofuran: cyclohexanone = 1:1), and formed by spinner coating, with a thickness of 0.7 μm.
and a refractive index of 1.5. The light absorption layer 4 develops a color when irradiated with ultraviolet rays, performs recording by absorbing semiconductor laser light with a wavelength of 780 to 8000 m, and is decolored by irradiation with visible light or heating.

A 10mm thick layer is formed on the exposed surface of the light absorption layer 4 as a light reflection layer.
A second reflective layer 5 is provided, which is an Ag vapor deposited layer with oX and a refractive index of 0.085 to i5.35.

In order to measure the characteristics of the recording medium 1 constructed as described above, ultraviolet rays were irradiated from the substrate 2 side to cause the light absorption layer 4 to develop color. For this purpose, a SOOW ultra-high-pressure mercury lamp (manufactured by Ushio Electric Co., Ltd.) was used to selectively irradiate ultraviolet rays in the vicinity of Toshiba's fu. The illumination intensity is about 15 mW/c〆. Next, this colored light absorption layer 4 was irradiated with semiconductor laser light from the substrate 2 side.

As a comparative example, a recording medium 6 (FIG. 2) having the same structure as the recording medium 1 of FIG. 1 except that the first reflective layer 3 is not provided is also used. was irradiated with ultraviolet light and semiconductor laser light.

The following results were obtained regarding the characteristics of each recording medium.

1. Change in reflectance of semiconductor laser light with respect to ultraviolet irradiation time (Figs. 3 and 4) The spirovir color development in the light absorption layer 4 was observed by changing the ultraviolet irradiation time to 0.5 and 15.60 seconds. Changes in reflectance at each wavelength of the accompanying laser light were measured, and in FIG. 3, the results for the recording medium 11 of this example are shown by a solid line, and the results for the recording medium 6 of the comparative example are shown by a dotted line.

As is clear from FIG. 3, compared to recording medium 6, recording medium 1 requires less ultraviolet irradiation and has a wavelength of 780 to 800 nm.
It can be seen that the reflectance in the vicinity has decreased and the cow conductor laser beam is more easily absorbed.

On the other hand, the placement medium 1 exhibits little decrease in reflectance in the vicinity of 600-yoonm, making it difficult for light in this wavelength range to be absorbed.

The change in reflectance at a wavelength of 7801 m in Figure 3 is plotted against the ultraviolet irradiation time and shown in Figure 4. It is also clear from FIG. 4 that the reflectance of the recording medium 1 of this example is significantly reduced by a smaller amount of ultraviolet irradiation than the recording medium 6 of the comparative example.

2. Recording sensitivity (Figure 5) Each sample of recording media 1 and 6 was exposed to the same ultraviolet rays as above.
The light absorption layer 4 is colored by irradiation, and then the semiconductor laser light is irradiated, and this irradiation (
Recording) Changes in reflectance before and after were measured.

Recording conditions 2 Laser light wavelength = 780 nm Laser power =
9mW (on sample) Laser beam diameter = 1.2μm (value @, pulse width =
0.1 to 7 μs The results obtained are shown in FIG.

As is clear from FIG. 5, compared to the recording medium 6 of the comparative example, the recording medium 1 of this example can obtain a large change in reflectance with a small amount of energy; for example, the energy density required to obtain a change in reflectance of 20% is As shown in Table 1, it is about 1/2 of that of the comparative example. In addition.

These results are a comparison of the best case measurements of each sample under various coloring conditions of the light absorption layer 4. Table 1 shows the amount of ultraviolet irradiation and the reflectance before recording. It is.

The recording sensitivity of the recording medium 1 of this embodiment is improved by increasing the reflectance at the interface between the first reflection layer N3 and the light absorption layer 4. This is thought to be because strong interference occurs with the light, and the incident laser light is further concentrated on the light absorption layer 4, reducing the amount of reflected light.

In this example, optical disks having various configurations of the recording media 1 and 6 except that the thickness of the substrate 2 was changed were fabricated as follows, and the recording and reproducing characteristics of the carriers were measured.

Shape of optical disc: diameter 8 cm + glass substrate thickness = 1.3 mm
;No pregroup.

Recording conditions = (ultraviolet # (360 nm) irradiation amount: 1.QJ
/cm) Laser light irradiation from the substrate side; wavelength of laser light =
78Qnm; Laser power = 53mW (on sample); Lens NA = 0.5; Carrier frequency 1fvl)iz; Use of square wave with duty ratio of 50%; Recording linear velocity = 2.6m/
S; recording wavelength = 2.6 μm; track pitch = approximately 5 μm
0 The envelope of the playback signal (for one round of the disk) obtained from each party's disk recorded in this way by a playback device using a home compact disk player is shown in Figure 6 (
Optical disc of Example; Curve-L L l -ys2!
'l j+ L V16th) ETA/II M
all M m r nosk; shown by curves C and d). In these figures, a unit of 0.5V on the vertical axis corresponds to 20% in reflectance. It can be seen that the envelope of the optical disc having the configuration of this example has a signal amplitude approximately twice that of the envelope of the optical disc of the comparative example, and the carrier level has improved by 6 dB.

It is more effective for the first reflective layer to have a refractive index higher than that of ordinary glass, interlayer resin, etc., and is preferably transparent.
) In addition, a multilayer structure in which high refractive index layers and low refractive index layers with a film thickness of -5 (1+2 m') are alternately stacked on λ such as TiO2, Zr (J2, Y2O3, etc.) may also be used. The value of m is not particularly limited, but is preferably an integer between θ and 3 for practical purposes.

The second reflective layer is a highly effective material with a refractive index close to 1.5, and uses a material obtained by dispersing various pigments, metal particles, etc. in a polymeric binder in addition to spiropyran compounds. can do.

The substrate may face either the first reflective layer or the second reflective layer.

Effects of the Invention In an optical recording medium, by configuring the light absorption layer to be a combination of the conventional reflection layer and the novel reflectance-enhancing layer of the present invention, an optical recording medium with improved recording sensitivity in the light absorption layer can be obtained. A type recording medium can be obtained. Additionally, if the light absorption layer is made of a spiropyran-based photochromic compound, the amount of ultraviolet rays required for color development prior to recording can be reduced, extending the lifespan of the light absorption layer and reducing the number of rewrites. Increased optical recording media can be obtained. Furthermore, the reflectance can be greatly changed not only by changing the absorbance of the recording medium but also by changing the refractive index or by changing the volume of the recording/reproducing method. Further, since the absorbance of the light absorption layer is low for light having a wavelength other than the wavelength of laser light, the storage stability of recording can be improved in a recording medium based on photochemical change.

[Brief Description of the Drawings] Figure 1 shows the configuration of an optical recording medium according to an embodiment of the present invention, Figure 2 shows the configuration of an optical recording medium according to a comparative example, and Figures 3 to 5 show the configuration of an optical recording medium according to an example of the present invention. FIG. 6 shows the envelope of the reproduced signal from the optical disc according to the embodiment of the present invention, and FIG. 7 shows the envelope of the reproduced signal from the optical disc according to the comparative example. In addition, in the symbols used in the drawings: 1... Recording medium 2... Substrate 3...・First reflective layer 4...
......Light absorption layer 5......Second reflective layer 6...
...It is a recording medium. Agent: Masaru Saturn Yoshio Tsunekami

Claims (1)

[Claims] A transparent substrate, a first reflective layer, a light absorbing layer, and a second reflective layer are laminated, and the light absorbing layer is provided between the first reflective layer and the second reflective layer. 4. The first reflective layer is on the light incident side and is made of a material having a refractive index larger than the refractive index of the transparent substrate and the light absorbing layer. (1+2m) (where λ is the wavelength of the laser beam, n is the refractive index of the first reflective layer, and m is not 0 or more or a positive integer). Optical recording medium.