JPH06243520A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium adaptable to high density recording and having high C/N and high reliability. CONSTITUTION:At least a dielectric layer, a magneto-optical recording layer, an Ag-based reflecting layer and a protective layer of a UV-curing resin contg. a triazinethiol compd. are successively formed on a substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium for recording / reproducing information by light using thermo-magnetic recording and magneto-optical effect.
The present invention relates to a magneto-optical recording medium.

[0002]

2. Description of the Related Art In recent years, along with a dramatic increase in the amount of information, there is an increasing demand for improving the recording density of information recording media. The optical disc has a high recording density and is excellent in random accessibility and portability. In particular, a magneto-optical disk can be repeatedly recorded and has excellent reliability, so that it has already been commercialized as a recording medium for external storage devices for computers and recording devices.

The recording density of the magneto-optical disk currently commercialized is 300 per one side of a disk having a diameter of 5.25 inches.
It is about megabyte (MByte). In order to increase this to about 1 gigabyte (GByte), the track pitch is shortened, the recording bit interval is shortened,
It has been proposed to change the modulation method of the recording signal.

However, when the same recording medium as the current medium is used and the bit interval is actually shortened and recorded, the carrier-to-noise ratio (hereinafter abbreviated as C / N) indicating the reproduced signal quality.
Was found to decrease. Since the C / N being low means that the error rate at the time of signal reproduction becomes high, it is necessary to improve the C / N as compared with the existing medium in order to shorten the recording bit interval and increase the recording density. is there.

The C / N of the magneto-optical disk is governed by the reflectance and the magnetic Kerr rotation angle, and more specifically, it is represented by the product of the square root of the reflectance and the magnetic Kerr rotation angle. This is called a figure of merit. Therefore, in order to reduce the recording bit interval and increase the recording density, it is essential to increase the reflectance of the magneto-optical recording medium or the magnetic Kerr rotation angle.

[0006]

A magneto-optical disk is generally constructed by providing a plurality of layers such as a magneto-optical recording layer, a light interference layer, a light reflecting layer and a protective layer on a transparent substrate. . The figure of merit governing C / N must be considered collectively for all these layers. An object of the present invention is to provide a magneto-optical recording medium exhibiting an excellent figure of merit and having high reliability by optimizing the materials constituting all layers, the layer thickness, and the layer constitution.

[0007]

The present invention provides a protective layer comprising at least a dielectric layer, a magneto-optical recording layer, a reflective layer containing Ag as a main component, and a UV-curable resin containing a triazine thiol compound on a substrate. It is a magneto-optical recording medium characterized by sequentially having. The present invention will be described in detail below.

Examples of the substrate for the magneto-optical recording medium used in the present invention include glass, plastic such as polycarbonate, or a substrate having a grooved resin for guiding an optical head formed on glass. The thickness of the substrate is 1-2 m
m is common. The dielectric layer is a layer that interferes with light, is provided between the substrate and the magneto-optical recording layer, multiple-reflects light between the substrate and the magneto-optical recording layer, and increases the apparent magnetic Kerr rotation angle. Plays a role of causing an interference effect.

Further, the dielectric layer serves to enhance the adhesion between the substrate and the magneto-optical recording layer, to insulate the magneto-optical recording layer and the substrate, and to protect the magneto-optical recording layer from moisture penetrating through the plastic substrate. Also has roles. The dielectric layer can be further provided between the magneto-optical recording layer and the reflective layer.
This makes it possible to further enhance the light interference effect and increase the magnetic Kerr rotation angle. The dielectric layer provided between the magneto-optical recording layer and the reflecting film plays a role of insulating light between the magneto-optical recording layer and the reflecting layer in addition to the role of interfering light.

As a material used for the dielectric layer, an amorphous thin film made of silicon nitride, tantalum oxide, silicon oxide, aluminum oxide, titanium oxide, zinc sulfide or the like or a mixture thereof is generally used. The thickness of the dielectric layer is usually about 500 to 1000Å. The magneto-optical recording layer is a layer for condensing and heating laser light to perform thermomagnetic recording. Since the magnetization must be perpendicular to the film surface for recording, it is desirable that the magneto-optical recording layer has a large perpendicular magnetic anisotropy.

As the magneto-optical recording layer, a rare earth-transition metal amorphous alloy such as TbFeCo is generally used, and the magneto-optical recording layer preferably has a film thickness of about 10 nm to 40 nm. The reflective layer plays a role of reflecting the light transmitted through the magneto-optical recording layer and returning it to the magneto-optical recording layer again. As a result, the efficiency of light utilization is increased, the reflectance and the magnetic Kerr rotation angle are increased, and the coefficient of performance is increased.

The reflective film also affects the thermal conductivity of the magneto-optical recording medium. While aluminum or aluminum alloy is used as the reflective layer of the magneto-optical disk currently commercialized, the present invention is characterized in that a reflective layer mainly containing Ag is used. By using a reflective layer mainly containing Ag instead of conventional aluminum or aluminum alloy, a good performance coefficient can be obtained. Since a simple substance of Ag is easily corroded by sulfide gas, an element having a corrosion prevention effect, for example, A
u, Pt, Pd, etc. may be added to Ag to form a reflective layer.

The added amount of the added element is usually 0.
It is set to about 5 to 15 atom%. It is possible to obtain a good performance coefficient by using Au or Au alloy, Cu or Cu alloy other than Ag as the reflective layer. However, since Au and Au alloys are expensive, there is a problem in terms of the cost of the medium, and Cu and Cu alloys are very susceptible to corrosion, so there is a problem in terms of reliability.

Since Ag and Ag alloy are relatively corroded as compared with Al, Al alloy, Au, etc., which are conventional materials for the reflective layer, the protective layer must have the effect of suppressing the corrosion of Ag alloy, etc. I won't. By coating an ultraviolet curing agent containing a triazine thiol-based compound on the outside of the reflective layer mainly composed of Ag, and by effectively irradiating ultraviolet rays to form a protective layer, corrosion of the reflective layer is significantly suppressed,
The reliability as a recording medium is enhanced.

Preferred examples of the triazine thiol compound include compounds represented by the following general formula [1].

[0016]

[Chemical 1]

-R in the general formula [1] is -SR ¹ , -N.
It represents R ² R ^3, but R ^1, R ^2, R ³ is a hydrogen atom or a hydrocarbon group, the hydrocarbon group, an alkyl group, an alkenyl group, an aryl group are preferably exemplified. As the UV curable resin, it is preferable to use an acrylic UV effect resin, and the triazine thiol compound is used as 0.00
It is melted in a proportion of 1 to 0.05% by weight, preferably 0.01 to 0.03% by weight, and applied on the reflective layer by spin coating or the like. The thickness of the protective layer can be set arbitrarily, but is preferably about 2 to 20 μm.

[0018]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Example 1 A 1.2 mm thick glass substrate was used as the substrate. A tantalum oxide thin film was formed as a dielectric layer on the substrate by the reactive sputtering method. After that, the surface was etched with high frequency plasma for 5 minutes to smooth the surface.

The initial film thickness was set so that the thickness of the tantalum oxide layer after etching was about 65 nm. Next, a Tb ₂₀ Fe ₇₂ Co ₈ (atomic%) amorphous alloy with a thickness of about 20 nm was formed on this tantalum oxide layer by a DC magnetron sputtering method to form a magneto-optical recording layer. Ag was formed thereon to a thickness of about 50 nm by a DC magnetron sputtering method to form a reflective layer.

On the reflective layer, 0.02% by weight of the triazine thiol compound represented by the following structural formula [2] against the solvent.
What was melt | dissolved in the ultraviolet curing agent SD-318 (made by Dainippon Ink and Chemicals, Inc.) in the ratio of this was spin-coated, and it ultraviolet-irradiated and hardened, and it was set as the protective layer of about 3 micrometers in thickness.

[0021]

[Chemical 2]

The magneto-optical recording / reproducing characteristics at a wavelength of 800 nm were examined for the magneto-optical recording medium manufactured as described above. The recording characteristic and the reproducing characteristic were confirmed by measuring the magnetic Kerr hysteresis curve and the reflectance. That is,
It can be seen that if the squareness ratio of the hysteresis curve is 1 and the coercive force is large, good recording characteristics are exhibited, and if the product of the square root of reflectance and the magnetic Kerr rotation angle is large at the wavelength used, good reproduction characteristics are obtained. You can see that.

The reflectance was measured through the substrate at the mirror surface portion of the disk. First, the relative reflectance with respect to the aluminum film was measured with a spectrophotometer at an incident angle of 2 degrees, and the absolute reflectance of the aluminum film measured in advance was used for calibration. In an actual drive, the light reflected on the substrate surface does not contribute to the signal. Therefore, the light reflected on the substrate surface was calculated from the optical constants of the glass substrate, and the reflectance was subtracted from the measured value.
The measurement of the magnetic Kerr hysteresis curve was carried out by the polarization plane modulation method through the substrate at the mirror surface portion of the disk as in the case of the reflectance.

The magnetic Kerr rotation angle was determined by comparing the hysteresis curve with the output change when the Glan-Thompson prism analyzer was rotated by a unit angle. However, in this case as well, since the light reflected by the surface of the substrate and having no rotation of the plane of polarization is included, a rotation angle smaller than the actual rotation angle can be obtained. Therefore, the actual rotation angle of the magnetic Kerr is determined by correcting the obtained rotation angle in consideration of the light reflected on the substrate surface.

From the shape of the hysteresis curve, it was found that the squareness ratio was 1 and the coercive force was about 800 kA / m. This is at a level equivalent to that of magneto-optical disks currently commercialized, and no difference was observed, so it can be said that the recording characteristics are good. Also, the reflectance is 20.4%,
The magnetic Kerr rotation angle is 1.30 degrees, and the performance coefficient given by the product of the square root of reflectance and the magnetic Kerr rotation angle is 5.
A value of 9 was obtained.

By the way, when the performance at 800 nm of a magneto-optical disk having a reflective layer of an Al alloy currently commercialized was measured, the reflectance was 23.1%, the magnetic Kerr rotation angle was 1.00, and the coefficient of performance was: It was about 4.8. It can be said that it has much better reproduction characteristics than the magneto-optical disks currently commercialized. To check the reliability,
The medium was subjected to a high temperature and high humidity deterioration accelerated test for 500 hours under the conditions of 85 ° C. and 85% RH, and it was observed whether corrosion occurred. Corrosion did not occur in the accelerated test, and no significant difference was observed in the reflectance, so it can be said that the reliability is excellent.

Example 2 A disk was prepared in the same manner as in Example 1 except that the triazine thiol compound used for the surface treatment of the reflective layer was a compound represented by the following structural formula [3].

[0028]

[Chemical 3]

The recording characteristics, the reproducing characteristics and the reliability were evaluated by the same method as in Example 1, but no significant difference was found in the evaluation results from Example 1, showing good characteristics. Comparative Example 1 A disk was prepared in the same manner as in Example 1 except that the surface of the reflective layer was not treated with the triazine thiol compound.

Recording characteristics, reproduction characteristics, and reliability were evaluated in the same manner as in Example 1. Regarding the evaluation results of the recording characteristics and the reproducing characteristics, no significant difference from Example 1 was observed, and good characteristics were shown. However, when a deterioration acceleration test was performed in the same manner as in Example 1, corrosion occurred in the reflective layer,
It turned out to be a reliability issue.

[0031]

As described above in detail, according to the present invention, there is provided a magneto-optical recording medium having a high C / N and a high reliability, which corresponds to high density recording.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Kuriwada 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd.

Claims (1)

[Claims] 1. A substrate having at least a dielectric layer, a magneto-optical recording layer, a reflective layer containing Ag as a main component, and a protective layer made of an ultraviolet curable resin containing a triazine thiol-based compound. Magneto-optical recording medium.