JPH0461638A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve availability of laser light energy, recording sensitivity, recording and reproducing stability, and reliability by allowing a recording material and self-convergent non-linear optical material to coexist in a recording layer. CONSTITUTION:A recording layer 1 containing a recording material and self- convergent nonlinear optical material is formed on a substrate. The self- convergent nonlinear optical material incorporated into the recording layer 1 with the recording material is such a material that shows nonlinear increase in the refractive index with increase in temp. and/or intensity of laser light 2. The laser light 2 for writing entering the recording layer 1 is absorbed by the layer 1 to give local temp. increase. The refractive index of the self- convergent nonlinear optical material in the layer 1 changes according to the temp. increase and/or light-induced polarization, and the refractive index in the center area of the convergent point 3 changes most. Therefore, the incident light is further converged to increase the light intensity and temp. of the center area of the convergent point 3. Thus, availability of laser light energy, recording sensitivity, recording and reproducing stability, and reliability of the medium can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical recording medium, and in particular, an optical recording medium that has excellent self-focusing properties of laser light, high sensitivity, and excellent recording and reproducing stability and reliability. Regarding optical recording media.

[Prior Art] Conventionally, as an optical recording medium, a recording layer with a low melting point is irradiated with laser light to cause the recording material in the recording layer to melt or decompose, thereby creating a permanent hole or a deformed spot, thereby creating a signal. There is a method for recording. On the other hand, there is also a method of recording signals on a recording film by utilizing reversible or irreversible phase changes such as crystal-amorphous transition. In this case as well, it is necessary to irradiate the recording layer with laser light to raise the temperature. Furthermore, as another method, GdTbC
There is a magneto-optical recording medium that irradiates a magnetic material with a laser beam in an external magnetic field to raise its temperature, reverses the direction of magnetization, and reads the resulting change in the rotation angle of the light as a signal. All of the above methods have in common that signals are recorded by increasing the temperature of the recording layer, and these are called thermal mode recording methods.

By the way, in the optical recording medium of the thermal mode recording method,
When writing signals using strong laser light, a highly sensitive recording material is required so that high-speed writing, that is, recording can be performed with low laser energy. On the other hand, during reproduction, a weak laser beam for reading is irradiated. In this case, the recording layer must be stable so that the recorded signal does not change or unrecorded areas are written.6 In normal cases, the intensity of the recording laser beam and reproduction laser beam is In order to satisfy the above conflicting conditions by changing the laser intensity, a recording material with a sufficiently large threshold value for the laser intensity is required.

In optical recording media in which signals are recorded by changes in reflectance, such as deformation such as melting or decomposition of the recording material, or phase change, the energy of the irradiated laser light may be effectively absorbed during recording, causing changes. Although this is necessary, a recording material with high reflectance has large heat transfer loss and reflection loss, and it is not easy to find a recording material that satisfies the above two contradictory conditions.

Japanese Patent Laid-Open No. 63-228439 discloses that a self-focusing material layer is provided in an optical recording medium in addition to a recording layer, and the effective rate of laser light is increased by converging incident light onto the recording layer by this self-focusing material layer. A method to increase this is proposed. This method is
This method uses a self-focusing material layer as a thermal lens to focus laser light onto a separately provided recording layer.

[ff problem to be solved by the invention] However, in this method, it is necessary to increase the polarization or temperature of the two layers, the self-focusing material layer and the recording layer, and the portion where the laser energy is not used for recording is occurs in Furthermore, since the focal length of the thermal lens moves as the refractive index of the self-focusing material layer changes, there is also a drawback that the spot diameter at the convergence point changes.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide an optical recording medium that has excellent utilization efficiency of laser light energy, high sensitivity, and excellent recording and reproducing stability and reliability.

[Means for Solving the Problems] The optical recording medium of the present invention is an optical recording medium in which recording is performed by increasing the temperature of a recording material in a recording layer with a laser beam to cause a phase change, magnetic change, or shape change. In the recording layer,
It is characterized by the coexistence of a recording material and a self-focusing nonlinear optical material.

The present invention will be explained in detail below.

The optical recording medium of the present invention has a recording layer containing a recording material and a self-focusing nonlinear optical material formed on a substrate. This recording layer may contain a recording material and a self-focusing nonlinear optical material in a uniform or dispersed state in a transparent polymer layer on a substrate. It may be something that is attached to.

In the present invention, the self-focusing nonlinear optical material includes:
As a self-focusing material, a low-molecular or high-molecular compound having nonlinear optical properties is used. As such a self-focusing nonlinear optical substance, an inorganic substance having nonlinear optical properties, such as chalcogenide fine particles, semiconductor fine particles, lithium niobate, potassium niobate fine particles, etc. can be used. In addition, examples of low-molecular or high-molecular organic compounds having nonlinear optical properties include para-nitroaniline, meta-nitroaniline, nuclear or substituted Nfm nitroaniline, 4-amino-4°nitrostilbene and its substituted products, merocyanine and benzylidene. Heteroderivatives such as aniline can also be used. Further, conjugated substances such as polydiacetylene, polyvinylenearylene, and polyvinylenethienylene and substituted substances thereof, compounds such as phthalocyanine, naphthalocyanine, and porphyrin, substituted substances thereof, and metal complexes thereof can also be used. Furthermore, the above-mentioned low-molecular or high-molecular organic compound is connected to a polymer side chain such as polymethacrylic acid ester, polyacrylic acid ester, polyvinyl alcohol ester, polyvinyl alcohol ether, cellulose ester, or cellulose ether through an appropriate atomic group or bond. Compounds can also be used.

On the other hand, in the present invention, as the recording material, thermally decomposable or meltable organic dyes, low melting point metal particles, phase change materials such as phase change alloy particles, magneto-optical recording material particles, etc. are used. Among these, quinocyanine dyes, merocyanine dyes, phthalocyanine dyes, and squarylium dyes are used as thermally decomposable or meltable recording organic dyes. The low melting point metal fine particles include In and Sn.

Fine particles of metals and alloys such as PB and SB are used. As the phase change type alloy fine particles, fine particles of metals and alloys such as Se and Te are used.

In the present invention, the absorption of laser light and thermal conversion can also be promoted by coexisting a light-absorbing dye in the recording layer. In this case, the light-absorbing dye is
It is desirable to use a material that has strong absorption at the writing laser wavelength and also effectively acts on the process of converting absorbed light energy into heat. Examples of light-absorbing dyes include metal complexes containing conjugated π electrons, such as nickel bis(dithiophenyl) derivatives, catechol, thiophenol, etc. having similar structures.
Amine phenol, phenylene diamine complex, etc. can be used.

In the present invention, the ratio of the recording material and the self-focusing nonlinear optical material in the recording layer is preferably 1:0.1 to 10 (weight ratio): recording material: self-focusing nonlinear optical material . That is, if the amount of the self-focusing nonlinear optical material is too small, the sufficient improvement effect of the laser beam convergence according to the present invention cannot be obtained, and if it is too large, the signal intensity and S/N ratio will decrease, so it is set within the above range. is preferable. In addition, when using a light-absorbing dye, the ratio of recording material: light-absorbing dye = 1:0.1 to 1 is determined depending on the reflection and absorption characteristics of both.
(weight ratio).

As a method for forming the recording layer of the optical recording medium of the present invention, the following methods (1) to (4) can be adopted.

(2) A recording material, a self-focusing nonlinear optical material, and, if necessary, a light-absorbing dye are made into ink, and the dope is applied to a substrate and cured.

■ A recording sheet containing a separately prepared recording material, a self-focusing nonlinear optical material, and, if necessary, a light-absorbing dye is attached to the substrate.

(2) A recording material, a self-focusing nonlinear optical material, and, if necessary, a light-absorbing dye are formed into a thin film on a substrate by a PVD method such as sputtering or vapor deposition.

Note that when forming the recording layer, it is necessary to create positioning signals such as guide groups and wobbles on the substrate in advance. Further, ROM signals, read control signals, sector numbers, etc. can be created in advance.

In the optical recording medium of the present invention, when a reflective layer is provided, gold, silver, copper, aluminum or an alloy thereof, etc.
A highly reflective metal is vapor-deposited or sputtered on the side of the substrate opposite to the surface on which the recording layer is formed, or a separately prepared reflective layer film is laminated thereon. Note that as a reflective layer for confining laser light energy, a layer of a substance having a lower refractive index than the recording layer can be formed between the substrate and the recording layer by vapor deposition or sputtering.

Such an optical recording medium of the present invention can be used in any form such as an optical disk, an optical card, or an optical tape.

[Function] The function of the self-focusing nonlinear optical material contained together with the recording material in the recording layer in the optical recording medium of the present invention will be explained with reference to the drawings.

A self-focusing nonlinear optical material is a material whose refractive index nonlinearly increases as laser intensity and/or temperature increases. As shown in FIG. 1, a writing laser beam 2 incident on a recording layer 1 in which a recording material and a self-focusing nonlinear optical material coexist is absorbed within the recording layer 1, causing a local temperature rise. The refractive index of the self-focusing nonlinear optical material in the recording layer 1 changes due to temperature rise and/or photo-induced polarization, but at this time, the laser beam 2 is highest at the center and at the periphery, as shown in FIG. Since it has a weak intensity distribution 4, the refractive index at the center of the convergence point 3 increases the most.

Therefore, the incident light is further restricted, and the light intensity and temperature at the center increase. And finally, Figure 2 and N4
As shown in the figure, the convergence point of 3° is further narrowed down and a peak of 4° of enhanced laser intensity is obtained. Therefore, only the recording material present at the center of the convergence point 3' undergoes melting, phase change, etc., and the change spreads toward the periphery with this as a core, resulting in good recording.

On the other hand, in a recording layer that does not contain a self-focusing nonlinear optical material, such a change in refractive index does not occur, so the states shown in Figures 1 and 3 remain, and the convergence of the laser beam is is small.

For this reason, in the optical recording medium of the present invention containing a self-focusing nonlinear optical material in the recording layer, high temperatures are more likely to occur than in the case where the self-focusing nonlinear optical material is not included, and the apparent sensitivity of the recording layer is has been improved. Moreover, since the self-focusing nonlinear optical material coexists with the recording material in the recording layer, the laser beam is effectively used to increase the temperature of the recording material.

In addition, in the case of reproduction, the reading laser light intensity is several tens of minutes lower than the recording laser light intensity, and the self-focusing effect of the self-focusing nonlinear optical material does not occur, so the recording changes. It can be stored and played stably without any problems.

[Example] The present invention will be described in more detail with reference to Examples below.

Example 1 Indium, polycarbonate pregroove substrate,
germanium, 4-methylnitroaniline in a weight ratio of 2
A recording layer was prepared by codeposition at a ratio of :1:1. Using a recording laser beam with an output of 8 mW, the obtained optical recording medium was subjected to a constant linear velocity of 1.3 m/s, 50 m/s.
Signals were written at 0 kHz. Then 0.5mW
As a result of repeated reproduction using a reproduction laser beam, it was confirmed that the recording was stably maintained.

Example 2 Indium-tin-silver alloy (composition, In20wt%, Sn
100 parts by weight of fine particles (20 wt %, balance silver) and diethylaminonitrostilbene were prepared in a weight ratio of 10=1. An ink prepared by kneading this ink into 50 parts by weight of a polyurethane binder was blade coated onto a polycarbonate substrate to prepare a recording layer, and recording and reproduction tests were conducted under the same conditions as in Example 1. As a result, it was confirmed that the records were maintained stably.

Example 3 100 parts by weight of a phthalocyanine silicon complex having an alkyl side chain and an indolenine cyanine dye were prepared in a weight ratio of 4:1. This was melt-kneaded with 400 parts by weight of polycarbonate and extruded to form a sheet. An optical disk was created by laminating this sheet onto a polycarbonate pregroove substrate and laminating a gold-deposited polycarbonate sheet behind it. Recording and reproduction tests were performed on this optical disc under the same conditions as in Example 1, and as a result, it was confirmed that recording was stably maintained.

Example 4 5e-Te alloy (composition, Se 20 wt%, balance Te) 9 to 100 parts by weight of polyvinyl alcohol with varanitrobiphenylanilino-N-alkyl ether added to the side chain
An optical disk was prepared by dispersing the particles in a proportion of 150 parts by weight and forming a sheet having a thickness of 25 μm and pasting it on a polycarbonate pregroove substrate. Regarding this optical disc, constant linear velocity 5.5 m/s, 6.3 MHz
Recording and reproduction tests were conducted in the same manner as in Example 1 except for the following. As a result, it was confirmed that the records were maintained stably.

Example 5 100 parts by weight of methacrylic acid ester with baratonitrobiphenyl ether ethoxy ester added to the side chain, and B
By kneading 30 parts by weight of fine particles of 1-Fe garnet,
A magneto-optical recording medium was prepared by laminating a 50 μm thick sheet to a polymethyl methacrylate pregroove substrate. When recording and reproducing tests were performed on this magneto-optical recording medium in the same manner as in Example 1, it was confirmed that recording was stably maintained.

[Effects of the Invention] As detailed above, the optical recording medium of the present invention has excellent convergence of laser light, and therefore has high sensitivity, stable recording and reproduction, and high reliability. provided.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams showing the convergence state of laser light on the recording layer of the optical recording medium of the present invention, with FIG. 1 showing the initial stage of laser light irradiation and FIG. 2 showing the final stage of laser light irradiation. . 3 and 4 are diagrams showing the laser intensity at the laser beam convergence point, where FIG. 3 shows the laser intensity in the state of FIG. 1, and FIG. 4 shows the laser intensity in the state of FIG. 2. show. 1... Recording layer, 2... Laser light, 33°.
...Convergence point. Patent Applicant Ube Industries Co., Ltd. Agent Patent Attorney Tsuyoshi Shigeno No. 3 Figure 2 Figure 4

Claims (1)

[Claims] (1) In an optical recording medium in which recording is performed by increasing the temperature of a recording material in a recording layer with a laser beam to cause a phase change, magnetic change, or shape change, the recording layer has a self-focusing nonlinear An optical recording medium characterized by coexisting with an optical substance.