JP3173624B2 - Magneto-optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin protective layer of a magneto-optical disk of a magnetic field modulation recording system.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 4-64936 discloses a method of adding a filler to a resin protective layer of a magneto-optical disk to roughen the surface of the protective layer.
It is known from U.S. Pat. The purpose of adding the filler is to prevent the magnetic head from being attracted and the head from crashing.

The inventor has found that the flying height when using a flying magnetic head can be changed by changing the surface roughness of the protective layer. Generally, if the surface is rough, the flying height of the head is small, and if the surface roughness is small, the flying height is large. Further, the flying height varies depending on the relative speed between the disk and the head. When the disk is used at a constant rotation speed (CAV), the speed is higher on the outer periphery and the flying height is increased.
As the flying height increases, the magnetic field from the magnetic head weakens, and when the magnetic field at the inner periphery is set to an optimum value, the C / N ratio at the outer periphery decreases. If the flying height differs between the inner and outer circumferences, the intensity of the magnetic field applied to the magneto-optical recording layer changes, and uniform recording cannot be performed.

[0004]

It is an object of the present invention to (1) make the flying height of a magnetic head uniform at both the inner and outer peripheral portions of the head, thereby enabling uniform recording, and (2) flying height at the outer peripheral portion. It is an object of the present invention to prevent an increase in the recording and to enable recording with a small recording magnetic field.

[0005]

According to the present invention, there is provided a magneto-optical disk in which at least a magneto-optical recording layer and a resin protective layer containing a filler are sequentially laminated on one main surface of a transparent substrate. The disk is characterized in that it is smaller on the outer peripheral part than on the inner peripheral part and its surface roughness is rougher on the outer peripheral part than on the inner peripheral part of the disk.

[0006]

The flying height of the magnetic head is determined by the relative speed between the head and the magneto-optical disk and the surface roughness of the resin protective layer. Here, if the surface roughness of the resin protective layer is made larger at the outer periphery and made smaller at the inner periphery, the influence of the surface roughness acts so that the flying height becomes smaller at the outer periphery. By balancing this with the increase in the flying height at the outer periphery due to the increase in the relative speed, the inner circumference /
A uniform flying height can be obtained regardless of the outer circumference. As a result, there is no need to change the rotation speed of the disk between the inner circumference and the outer circumference, and uniform recording characteristics can be obtained even when the rotation speed is constant.

[0007]

FIG. 1 shows a magneto-optical disk 1 according to an embodiment.
In the figure, reference numeral 2 denotes a transparent synthetic resin substrate such as polycarbonate or acrylic, and here a polycarbonate substrate is used. Note that a glass substrate may be used instead of the synthetic resin substrate.
Reference numeral 3 denotes a magneto-optical recording layer, and any layer can be used within the range of known techniques. In the embodiment, the magneto-optical recording layer 3 is made of a first dielectric layer of silicon nitride (about 100 nm thick), a Gd-Dy-Fe-based magneto-optical recording layer (about 20 nm thick), and a second dielectric layer of silicon nitride. (About 30 nm thick) and an Al reflective layer (about 40 nm
Thickness) were sequentially laminated. Reference numeral 4 denotes a resin protective layer formed by spin-coating a urethane acrylate-based UV-curable resin in which 1 wt% of a SiO2 filler having an average particle size of 4 μm is dispersed and spin-cured. Here, the conditions of the spin coating are appropriately selected, and an air flow is formed from the inner circumference to the outer circumference on the resin protection layer forming surface during the spin coating, and the air flow is increased toward the outer circumference, so that the thickness of the resin protection layer 4 is reduced. The inner periphery was greatly reduced at the outer periphery, and the surface roughness was increased at the outer periphery and decreased at the inner periphery. The material of the ultraviolet curable resin to be used can be arbitrarily, for example, acrylic or urethane, and the type and amount of the filler are also arbitrary. The thickness of the resin protective layer 4 is about 5 μm in the average thickness of the entire disk, about 5.5 μm in the inner circumference of the magneto-optical recording layer 3 (24 mm from the center of the 3.5-inch disk), and the outer circumference. (40 mm from the center of the disk) and was about 4.5 μm. This magneto-optical disk is referred to as a first embodiment.

Returning to FIG. 1, the magneto-optical disk 1 is clamped and rotated by the clamp 01, and the optical pickup 02 is rotated.
The recording is performed by applying a magnetic field with the floating magnetic head 03.

By using a resin protective layer 4 containing no filler and pressing a mold having a surface roughness changed at the inner and outer peripheries to the protective resin while the resin protective coating layer 4 is in a semi-cured state, the resin is transferred. A magneto-optical disk was manufactured in which the surface roughness of the protective layer 4 was different between the inner and outer circumferences. The other points were the same as in Example 1. This magneto-optical disk is referred to as Comparative Example A.

A magneto-optical disk having the same structure as that of the first embodiment and having the resin protective layer 4 having a constant thickness on the inner and outer circumferences was manufactured. This magneto-optical disk is referred to as Comparative Example 1. In Comparative Example 1, the surface roughness is equal on the inner circumference and the outer circumference.

The above three types of magneto-optical disks are rotated at a rotational speed of 24.
Rotation was performed at 00 rpm (constant number of rotations), and recording was performed using the floating magnetic head 03. The recording conditions were as follows: rotation speed 2400 rpm, recording laser power 8 mW, current applied to the magnetic head 500 mA, recording frequency r = 24 mm, 3.87 MHz, r = 32 mm, 5.16 MHz, r = 40 mm, 6.44 MHz, and the recording frequency. The recording bit length is the same by changing the inner, middle, and outer circumferences. Note that r indicates a radial position from the center of the disk 1. The surface roughness of the resin protective layer 4 was defined as the average surface roughness at each radial position.

As shown in FIG. 2, in Comparative Example 1, the flying height of the magnetic head increases toward the outer periphery, and the flying height is 5 to 9 μm.
It changes within a range of about m. On the other hand, in the first embodiment,
The difference between the inner and outer flying heights is small, and the flying height is in the range of 5 ± 1 μm. According to experiments, in the case of a 3.5-inch magneto-optical disk, the outer peripheral portion (radial position r) of the magneto-optical recording layer
Is 40 mm) and the ratio of the surface roughness of the inner peripheral portion (radius position r is 24 mm) to 2: 1 to 3: 1, the magnetic head 03
Was maintained in the range of 5 μm ± 1 μm.
When this ratio is larger than this, the flying height of the magnetic head at the outer peripheral portion decreases, and when it is smaller than this, the flying height of the magnetic head at the outer peripheral portion increases. In each of the magneto-optical disks, since the resin protective layer 4 had a sufficient surface roughness, no head suction or head crash occurred.

FIG. 3 shows the results regarding the C / N ratio between the example and the comparative example. Under the above recording conditions, in Example 1, almost the same C / N is obtained from the inner circumference to the outer circumference. On the other hand, in Comparative Example 1, since the magnetic field applied to the magneto-optical recording layer 3 decreases toward the outer periphery, the C / N decreases at the outer periphery,
Uniform characteristics cannot be obtained. Therefore, it is necessary to change the rotation speed between the inner circumference and the outer circumference, or to change the recording magnetic field from the head 03 between the inner circumference and the outer circumference.

[0014]

According to the present invention, (1) uniform recording can be performed by keeping the flying height of the magnetic head constant, and (2)
By preventing the magnetic head from floating more than necessary at the outer periphery, the distance between the magnetic head and the magneto-optical disk can be reduced, and recording can be performed with a small recording magnetic field.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a use state of a magneto-optical disk according to an embodiment.

FIG. 2 shows the surface roughness (R) of the magneto-optical disk of the embodiment.
FIG. 6A is a characteristic diagram showing a relationship between the flying height of the magnetic head and a).

FIG. 3 is a characteristic diagram showing the C / N ratio of the magneto-optical disk of the example when recording was performed at a rotation speed of 2400 rpm, a recording laser power of 8 mW, and a magnetic head applied current of 500 mA.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-optical disk 2 Substrate 3 Magneto-optical recording layer 4 Resin protective layer 01 Clamp 02 Optical pickup 03 Flying magnetic head

Claims (1)

(57) [Claims] 1. A magneto-optical disk in which at least a magneto-optical recording layer and a resin protective layer containing a filler are sequentially laminated on one main surface of a transparent substrate, the thickness of the resin protective layer is set to the inner peripheral portion of the disk. A magneto-optical disk characterized in that the surface roughness is smaller at the outer periphery than at the outer periphery and the surface roughness is greater at the outer periphery than at the inner periphery of the disk.