JPH07282477A - Optical recording medium and its production - Google Patents

Abstract

PURPOSE:To improve perpendicular magnetic anisotropy, to increase the Faraday rotating angle and to improve recording and reproducing characteristics by impressing a magnetic field perpendicularly to a film plane and orienting magnetic particulates in a magnetic field direction. CONSTITUTION:This optical recording medium is constituted by forming a magnetic recording thin film 2 on a transparent substrate 1 and providing the surface thereof with a reflection layer 3 consisting of gold, etc. In such a case, the magnetic recording thin film 2 is formed by dispersing the magnetic particulates having a magneto-optical effect into a nonmagnetic binder. The external magnetic field is impressed perpendicularly to the film plane to disperse the magnetic particulates into the nomnagnetic binder at the time of forming such magnetic particulates as a coating film. The external magnetic field is impressed perpendicularly to the film plane to orient the magnetic particulates in the direction perpendicular to the film plane at the time of forming such particulates as the coating film, by which the perpendicular magnetic anisotropy is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for recording / reproducing information signals by utilizing magneto-optical characteristics such as magnetic Kerr effect and Faraday effect, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, Mn has been used as a magneto-optical recording medium.
Bi, MnCuBi, and other polycrystalline thin films, GdCo, Gd
Fe, TbFe, DyFe, GdTbFe, TbDyF
Amorphous thin films such as e and single crystal thin films such as GIG are known. Among these thin films, film-forming properties for forming large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, reading efficiency for reading written signals with a good S / N ratio, etc. Considering the above, recently, the amorphous thin film is considered to be excellent as a magneto-optical recording medium.

The above-mentioned magneto-optical recording medium is prepared by laminating a recording thin film and an inorganic protective film on a substrate. However, since the magneto-optical recording medium is prepared by a process such as vacuum deposition and sputtering, it is necessary to enlarge the manufacturing apparatus. However, there is a problem that productivity is deteriorated due to a large number of laminated films. Therefore, conventionally, a coating type magneto-optical recording medium in which magnetic particles are dispersed in a non-magnetic binder and a dispersion liquid is applied to form a magnetic recording layer has been studied.

On the other hand, the use of a short wavelength laser as a means for increasing the density of magneto-optical recording has been studied. However, since the Kerr rotation angle of the heavy rare earth-3d transition metal amorphous alloy thin film becomes smaller as the wavelength becomes shorter, the reproduction output decreases when reproduced by a short wavelength laser. Therefore, it is necessary to use a new magneto-optical recording material for short wavelength.

[0005]

However, the coating type magneto-optical recording medium using the magnetic recording layer in which the magnetic fine particles are dispersed in the non-magnetic binder is optically uniform (reduction of noise) and Characteristics such as being a magnetized film, having a large Faraday rotation angle and being capable of magneto-optical recording are required.

The present invention has been completed as a result of research for improving such a coating type magneto-optical recording medium and satisfying the required characteristics, and improving the perpendicular magnetic anisotropy. It is another object of the present invention to provide an optical recording medium having improved recording / reproducing characteristics by increasing the Faraday rotation angle.

The present invention also improves the perpendicular magnetic anisotropy,
By increasing the Faraday rotation angle, it is an object to manufacture an optical recording medium having improved recording / reproducing characteristics with high productivity.

[0008]

That is, according to the present invention, in an optical recording medium having a recording magnetic thin film in which magnetic fine particles having a magneto-optical effect are dispersed in a non-magnetic binder, a magnetic field is applied perpendicularly to the film surface. Then, the optical recording medium is characterized in that the magnetic fine particles are oriented in the magnetic field direction.

Further, the present invention is a method of manufacturing an optical recording medium in which magnetic fine particles having a magneto-optical effect are dispersed in a non-magnetic binder to form a recording magnetic thin film. Is applied to orient the magnetic fine particles in the magnetic field direction, which is a method for manufacturing an optical recording medium.

The present invention will be described in detail below. FIG. 1 is an explanatory diagram showing an example of the optical recording medium of the present invention. In the figure, the optical recording medium of the present invention comprises a transparent magnetic film 2 formed on a transparent substrate 1 and a reflective layer 3 made of gold or the like on the transparent magnetic film 2. The magnetic recording thin film 2 has a magneto-optical effect. Magnetic fine particles are dispersed in a non-magnetic binder, and an external magnetic field is applied perpendicularly to the film surface to form a coating film. It is made by improving the sex.

Examples of magnetic fine particles used in the present invention include Co, Ba ferrite, and Bi-substituted garnet. The average particle size is 500 Å or less, preferably 50 to 500 Å, particularly preferably 20 Å to 20
It is 0Å. The amount of the magnetic fine particles mixed with the non-magnetic binder is 10 to 40%, preferably 15 to 40% by volume.
A range of 30% is desirable.

The non-magnetic binder used in the present invention includes polymethacrylate, polycarbonate,
Examples thereof include polymer materials such as polystyrene, and anisotropic melt polymer materials such as liquid crystal polymers obtained by polymerizing a phenyl group on the side chain of polyethylene terephthalate. These polymeric materials are dissolved in an organic solvent such as toluene, isopropanol, and methyl cellosolve to disperse the above magnetic fine particles,
A recording magnetic thin film is formed by coating the substrate with a spinner or the like, drying and thinning it.

The thin film is controlled by the coating conditions such as the spinner rotation speed and rotation time. The thickness of the recording magnetic thin film is
0.01 μm to 5 μm, preferably 0.5 μm to 2 μm
Is desirable. In the drying process, an external magnetic field is applied in the direction perpendicular to the film surface to orient the magnetic fine particles in the magnetic field direction.
The external magnetic field is preferably in the range of 1 kOe to 10 kOe, particularly preferably 3 kOe to 7 kOe.

In some cases, in order to improve the dispersibility of the magnetic fine particles in the non-magnetic binder, the surface of the particles may be subjected to a coupling treatment, a microencapsulation treatment, and a dispersant may be added.

In a recording magnetic thin film in which magnetic fine particles are dispersed in a non-magnetic binder, the magnetic characteristics of the magnetic fine particles having a random distance distribution are as follows. The dipole interaction (magnetic interaction) of is determined.

In particular, when a polymer is used as the non-magnetic binder, the magnetic interaction between the magnetic fine particles in the polymer cannot be ignored. By changing the dispersion state of the magnetic fine particles in the polymer, it is possible to reduce the interaction between the magnetic fine particles, and in this case, the reversal magnetic field can be reduced. Here, in order to change the dispersion state of the magnetic fine particles in the polymer, a means of applying an external magnetic field in the C-axis direction (perpendicular to the recording magnetic thin film surface) of the magnetic fine particles to orient it is adopted. As a result, the agglomeration state of the particles changes, abnormal dispersion occurs, the perpendicular magnetic anisotropy improves, and the magneto-optical effect (Faraday effect) also increases.

In this case, the polymer material used has a molecular weight of 200,000 to 500,000 and a molecular weight distribution of 1.0 to 2.0.
If it is sharp in the range, the C-axis orientation of the magnetic fine particles is further improved.

When an anisotropic molten polymer material, that is, for example, a liquid crystal polymer having a large fluidity in the stress direction, is used as the non-magnetic binder, C of the magnetic fine particles is further improved.
Axial orientation is improved.

Further, the Faraday rotation angle of the magnetic thin film decreases but the coercive force increases as the amount of the magnetic fine particles mixed in the non-magnetic binder increases. Therefore, the compounding amount of the magnetic fine particles in the non-magnetic binder is 15% by volume.
The range of up to 30% is preferred. Further, the size of the magnetic fine particles used here is preferably in the range of 50 to 500 Å from the viewpoint that medium noise is not generated during reproduction.

The surface roughness of the magnetic thin film is 1 because the loss due to the scattering of the laser light during recording and reproduction is small.
The range of 00 to 500Å is preferable.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 Polymethacrylate (PMM) was used as a non-magnetic binder.
Cobalt carbonyl fine particles [C
o ₂ (CO) ₈ ] was mixed at a volume fraction of 18%, and dispersed at 120 ° C. for 8 hours while stirring. After applying this cobalt fine particle dispersion solution on a polyolefin substrate, it is dried at room temperature while applying an external magnetic field Hd = 4 kOe perpendicularly to the film surface to form a magnetic recording thin film. An optical recording medium was prepared by attaching it to a thickness of 40 nm.

In addition, with the material constitution shown in Table 1 below, in the same manner as in Example 1, Examples 2 to 6 and Comparative Examples 1 to 7
The optical recording medium of Table 1 below shows the material configurations of the optical recording media produced in the examples and comparative examples.

[0024]

[Table 1]

(Note) (1) Cobalt carbonyl fine particles: [Co ₂ (CO)
₈ ] (2) Co-substituted Ba ferrite fine particles: composition BaFe
_10.2 Co _0.9 Ti _0.9 O ₁₉ and aspect ratio 3.5 (3) PMMA is polymethacrylate and PS is polystyrene. (4) Liquid crystal polymer: Zydar, manufactured by Unitika Ltd. (5) Surface roughness is measured with Talysurf: surface roughness meter.

The magnetization curves of the optical recording media prepared in Examples and Comparative Examples were measured by applying a magnetic field perpendicular to the film surface.
Then, each squareness ratio and coercive force were obtained. The measurement was carried out at room temperature (23 ° C.) using a VSM: vibrating sample magnetometer.

In the comparative example, the squareness ratio was as small as 0.2 or less, and the coercive force was also as small as 0.25 kOe or less.
On the other hand, in the example, the squareness ratio was 0.85 or more, and the coercive force was 0.8 to 1.0 kOe. From this, it is understood that the example has a larger perpendicular magnetic anisotropy. The measurement is a vibrating sample magnetometer (VS
M).

Next, the Faraday rotation angle (θ _F ) deg / of the optical recording media prepared in Examples 1-6 and Comparative Examples 1-7.
μm was measured in the wavelength range of 830 nm. The results are shown in Table 2. From the result, in the embodiment, θ _F is 0.28 to 0.
29, compared with θ _F = 0.18 to 0.19 of the comparative example, 5
An increase in θ _F of about 0% was observed.

[0029]

[Table 2]

(Note) (1) The Faraday rotation angle (θ _F ) was measured using a magnetic rotation spectrometer (MOE-7: manufactured by JASCO Corporation).

Next, using the optical recording media prepared in Examples 1 to 6 and Comparative Examples 1 to 7, a semiconductor laser of 830 nm was used.
(Wavelength), recording laser power 10 mW, linear velocity 3 m / s
When a recording test was performed with ec and an applied magnetic field of 500 Oe, stable recording bits with a mark length of 3.8 μm could be obtained. In addition, using the optical recording media of Examples and Comparative Examples, the reproduction signal of the mark recorded under the above conditions was measured and evaluated with a reproduction power of 2.0 mW and a C / N ratio. The results are shown in Table 3.

The recording / reproducing characteristics were evaluated using a magneto-optical recording / reproducing evaluation device (LM52A: manufactured by Shibasoku Co., Ltd.). From the results of Table 3, the optical recording medium of each example has a larger C / N ratio than the optical recording medium of the comparative example.
It can be seen that it has excellent characteristics.

[0033]

[Table 3]

[0034]

As described above, the optical recording medium of the present invention has a large perpendicular magnetic anisotropy and excellent magnetic characteristics as compared with the conventional coating type recording medium, and has a large magneto-optical effect. It has the effect of excellent characteristics. Further, the method for producing an optical recording medium of the present invention can produce a coating type recording medium having excellent productivity and the above-mentioned characteristics as compared with the conventional optical recording medium.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an optical recording medium of the present invention.

[Explanation of symbols]

 1 transparent substrate 2 magnetic recording thin film 3 reflective layer

Claims (8)

[Claims] 1. In an optical recording medium having a recording magnetic thin film in which magnetic fine particles having a magneto-optical effect are dispersed in a non-magnetic binder, a magnetic field is applied perpendicularly to the film surface to orient the magnetic fine particles in the magnetic field direction. An optical recording medium characterized by the following. 2. The non-magnetic binder has a molecular weight of 2
The optical recording medium according to claim 1, wherein a high molecular material having a molecular weight distribution of from 1.0 to 500,000 and a molecular weight distribution of from 1.0 to 2.0 is used. 3. The optical recording medium according to claim 1, wherein an anisotropic molten polymer material is used as the non-magnetic binder. 4. The optical recording medium according to claim 3, wherein the anisotropic molten polymer is a liquid crystal polymer. 5. The magnetic fine particles have an average particle size of 50 to 50.
The optical recording medium according to claim 1, wherein the optical recording medium has a range of 0Å. 6. The volume fraction of the magnetic fine particles in the non-magnetic binder is in the range of 15 to 30%.
The optical recording medium described. 7. The average surface roughness of the recording magnetic thin film layer is 1
The optical recording medium according to claim 1, wherein the optical recording medium has a thickness of 00 to 500Å. 8. A method for producing an optical recording medium in which a magnetic fine particle having a magneto-optical effect is dispersed in a non-magnetic binder to form a recording magnetic thin film, and a magnetic field is applied perpendicularly to the film surface. A method for manufacturing an optical recording medium, which comprises orienting magnetic fine particles in a magnetic field direction.