JPH09212930A - Magneto-optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical disk which makes it possible to prevent the adherence of a magnetic head to the disk when a CSS system is applied and to obtain excellent CSS characteristics. SOLUTION: An ultraviolet curable resin protective layer 3 internally added with surfactant is formed on a recording magnetic layer 2, and a fluorine lubricant layer 4 is further formed on the protective layer. As the surfactant added to the protective layer, silicon surfactant having methyl fluoride group and modified with polyether is preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk, and more particularly to improvement of a protective layer and a lubricant layer.

[0002]

2. Description of the Related Art In a magneto-optical recording system, the temperature of a magnetic thin film is partially raised above a Curie point or a temperature compensation point, and the coercive force in this portion is eliminated to magnetize the magnetic thin film in the direction of an externally applied recording magnetic field. It is based on the principle of reversing the direction of an image, and is being put to practical use in an optical file system, an external storage device of a computer, a recording device for audio and video information, and the like.

As a magneto-optical disk used in this magneto-optical recording system, a recording magnetic layer having a large magneto-optical effect and having an easy axis of magnetization in the direction perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like. Layer (for example, a rare earth-transition metal alloy amorphous thin film), a reflective layer, and a dielectric layer are laminated to form a recording portion, and in order to prevent corrosion of the recording portion, an ultraviolet curable resin is formed on the recording portion. There is known one formed so as to cover a protective layer made of, for example.

In order to perform recording on such a magneto-optical disk, for example, laser light is irradiated from the substrate side and an external magnetic field is applied from the protective layer side to locally increase the coercive force of the recording magnetic layer. Reduce and magnetize this region in the direction of the external magnetic field. The portion magnetized in the direction of this external magnetic field becomes a recording pit. Further, such recording pits are detected by utilizing the fact that the polarization plane of the laser light rotates due to the magneto-optical effect of the recording magnetic layer.

In recent years, such a magneto-optical disk is required to have an increased recording capacity as the data handled by a computer is increased in capacity. Further, along with the digitization of video information, the demand for higher transfer rate and higher access has increased along with the increase in recording capacity.

Increasing the capacity of the magneto-optical disk has been steadily improved by shortening the wavelength of the laser light.

On the other hand, in order to increase the transfer rate and increase the access, particularly in the case of magnetic field modulation recording capable of direct overwriting, in the method of using a sliding magnetic head that slides directly on the disk surface, the rotation of the disk is Sliding becomes unstable as the speed increases, and the load applied to the head must be increased in order to stabilize the sliding. In that case, the friction between the head and the disk increases, which causes a problem that a motor for rotating the disk is loaded.

For this reason, a flying type magnetic head that levitates against the disk surface by utilizing an air flow is used. By levitating the flying magnetic head as close as possible without contacting the disk surface, it is possible to rotate the disk at a high speed while applying a magnetic field of a sufficient magnitude to the disk.

When such a floating magnetic head is used, it is advantageous in reducing power consumption, and therefore, the rotation start control of the disk is performed by the contact start stop method (CSS method) which is widely used in hard disk drives. Is done.

That is, in this CSS system, the rotation of the disk is stopped (sleep mode) except during recording and reproduction, and the magnetic head is in contact with the disk. And
The disk is rotated at a high speed at the time of start-up, and the air flow generated thereby causes the magnetic head to float above the disk surface, and recording / reproduction is performed in this state. Then, the rotation of the disk is further reduced at the time of stopping, and the magnetic head comes into contact with the disk again. This CS
In the S method, the rotation of the disk is stopped except during recording and reproduction, and the disk is driven to rotate only when necessary, so that power consumption can be suppressed. Therefore, it is a very preferable method to be applied to, for example, a book type computer that requires low power consumption.

[0011]

By the way, when the CSS method is applied to the magneto-optical disk, the sticking of the magnetic head to the protective layer serving as the air bearing surface of the head becomes a problem.

In the case of a hard disk, a groove (texturing) is mechanically provided on the surface of the disk to reduce the contact area with the head, or a fluorine-based lubricant is applied to the surface of the disk to improve the magnetic head performance. It is designed to prevent sticking.

However, in the case of a magneto-optical disk, the protective layer serving as the air bearing surface of the head is usually formed by spin coating an acrylic ultraviolet curing resin. FIG.
On the surface of the recording magnetic layer 22 formed on the substrate 21,
UV curable resin protective layer 23 formed by spin coating
However, as described above, the protective layer 23 of the ultraviolet curable resin tends to be thicker toward the outer peripheral side, and the film thickness becomes uneven, so that the texturing forming process is difficult.

It has been attempted to reduce the contact area between the protective layer and the head by making the bottom surface of the head spherical (r = 1500 mm) in the expectation of the same effect as texturing. However, since the protective layer made of an ultraviolet curable resin is relatively soft, when a head having such a shape is used, the head sticks to the protective layer when the disk rotation is stopped, and good CSS characteristics cannot be obtained.

On the other hand, various kinds of lubricants such as ester type, silicon type and fluorine type are known, but in order to prevent the sticking of the disk and the head, the main sticking agent is used. It is preferable to use a fluorine-based lubricant that causes the least water absorption of the causative water.

However, the fluorine-based lubricants used in hard disks and the like have very poor compatibility with acrylic resins. For this reason, when it is attempted to apply it to the surface of the protective layer 23 made of an acrylic ultraviolet curable resin, the applied fluorine-based lubricant 24 becomes spherical and is repelled to form a uniform layer, as shown in FIG. Have difficulty. As a countermeasure against this, a method of substituting a part of the group of the fluorine-based lubricant with a group having a good compatibility with the acrylic resin is conceivable, but the synthesis is very difficult and it cannot be said to be practical.

Therefore, the present invention has been proposed in view of such a conventional situation, and when the CSS method is applied, sticking between the magnetic head and the disk is prevented, and good CSS characteristics are obtained. It is an object to provide a magneto-optical disk.

[0018]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies and, as a result, found that when a surfactant is internally added to the UV-curable resin protective layer, the protective layer and the fluorine-based resin are added. It has been found that the compatibility of the lubricant is improved and the fluorine-based lubricant can be applied uniformly.

The magneto-optical disk of the present invention has been completed on the basis of such findings, and at least a recording magnetic layer is formed on a transparent substrate, and a surfactant is formed on the recording magnetic layer. The ultraviolet-curable resin protective layer and the fluorine-based lubricant layer internally added are formed.

In such a magneto-optical disk, the protective layer is modified by the action of the internally added surfactant, so that the fluorine-based lubricant is uniformly applied. Therefore,
When the CSS method is applied, sticking to the magnetic head is effectively prevented by this fluorine-based lubricant, and good CSS characteristics are obtained.

As the surface-active agent added internally to the protective layer, a silicon-based surface active agent having a fluoromethyl group as shown in Chemical formula 3 and further modified with a polyether is preferable.

[0022]

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As the lubricant, it is desirable to use a perfluoropolyether type lubricant represented by Chemical Formula 4.

[0024]

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[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a magneto-optical disk according to the present invention will be described below.

The magneto-optical disk of this embodiment is shown in FIG.
As shown in FIG. 3, a recording portion 2 is formed on a transparent substrate 1, and a protective layer 3 made of an ultraviolet curable resin and a fluorine-based lubricant layer 4 are formed on the recording portion 2. In this magneto-optical disc, as shown in FIG. 2, an optical pickup device 6 is arranged on the substrate side of the disc with the magneto-optical disc 5 interposed therebetween, and a flying magnetic head 7 is arranged on the protective layer 3 side. Information signals are recorded according to the method.

In such a magneto-optical disk, the substrate 1 is a disk-shaped transparent substrate having a thickness of about several mm, and the material thereof is plastic such as acrylic resin, polycarbonate resin, polyolefin resin, epoxy resin or the like. Besides the material, glass or the like is also used.

On the surface of the substrate 1 where the recording section 2 is provided, a guide groove or an address code having a depth of about ¼ of the wavelength of the laser beam used during reproduction is usually provided. Pits and the like (none of them are shown) are provided.

The recording section 2 is composed of at least a recording magnetic layer. A dielectric layer and a reflective layer may be used together for the purpose of increasing the Kerr effect due to multiple reflection and protecting the recording magnetic layer. In this case, the recording section is configured by laminating four layers of a first dielectric layer, a recording magnetic layer, a second dielectric layer, and a reflective layer in this order.

Of these, oxides and nitrides can be used for the first dielectric layer and the second dielectric layer, but oxygen in the dielectric layer adversely affects the recording magnetic layer. Nitride is more preferable because it is feared, and silicon nitride, aluminum nitride, or the like is preferable as a substance that does not allow oxygen and moisture to pass therethrough and allows the used laser beam to pass therethrough sufficiently.

Further, the recording magnetic layer is an amorphous magnetic thin film having an easy magnetization direction in a direction perpendicular to the film surface,
It is desirable to have a large coercive force at room temperature and a Curie point near 200 ° C., as well as excellent magneto-optical characteristics. As a recording material satisfying such conditions,
Examples thereof include rare earth-transition metal alloy amorphous thin films, and among them, TbFeCo based amorphous thin films are preferable. An additive element such as Cr may be added to the recording magnetic layer for the purpose of improving corrosion resistance.

The reflective layer is preferably composed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric layer 6, and a vapor-deposited film of a nonmagnetic metal is suitable. Further, it is desirable that this reflective layer is a thermally good conductor, and in consideration of availability, film formation, and the like,
Aluminum is suitable.

Each of these layers is formed by a so-called vapor phase plating technique such as vapor deposition or sputtering. At this time, the film thickness of each layer can be arbitrarily set, but usually several hundred to
It is set to about several thousand angstroms. It is preferable that these film thicknesses are determined in consideration of not only the optical properties of the individual layers but also the effects of the combination. This is because, for example, when the film thickness of the recording magnetic layer is thinner than the wavelength of the laser light, the laser light causes multiple interference with the light that has passed through the recording magnetic layer and is reflected at the boundary between the layers, and the combination of the film thickness results in the recording magnetic property. This is because the effective optical and magneto-optical characteristics of the layer fluctuate greatly.

A protective layer 3 made of an ultraviolet curable resin is formed on such a recording portion 2, and a fluorine-based lubricant layer 4 is further formed on the protective layer 3.

The protective layer 3 is provided to protect the recording section 2 from external impacts and to isolate it from water and oxygen in the atmosphere. Further, in the magneto-optical disk of this embodiment, a surfactant is internally added especially to the protective layer 3. This surfactant improves the compatibility between the protective layer 3 and the fluorine-based lubricant applied on the protective layer 3, and in order to form the fluorine-based lubricant layer 4 uniformly on the surface of the protective layer 3. Used.

As the surface active agent, a surface active agent represented by Chemical formula 5, that is, a silicon type surface active agent having a fluorinated methyl group and modified with a polyether is preferable.

[0037]

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Since such a silicone-based surfactant has a methyl fluoride group, it exhibits a good compatibility with a fluorine-based lubricant, and since it has a polyether group R, it is an ultraviolet curable resin. A good compatibility with is obtained.

In the chemical formula 5, the composition ratio n of the monomer component into which the methyl fluoride group is introduced is not particularly limited, but it is preferably 1 to 20 for practical use.

The polyether group R introduced is m
Is preferably 10 to 30.

On the other hand, as the UV curable resin, any of those used as a protective layer for a magneto-optical disk can be used, and an acrylic UV curable resin is preferable because it is excellent in waterproofness.

The amount of the surfactant added to the ultraviolet curable resin is preferably 0.05 to 0.5% by weight based on the ultraviolet curable resin. When the amount of the surfactant added is less than 0.05% by weight, the compatibility between the protective layer and the fluorine-based lubricant coated on the protective layer cannot be sufficiently improved. Further, when the amount of the surfactant added exceeds 0.5% by weight, the surfactant hinders the curing of the ultraviolet curable resin, and the hardness of the protective layer becomes low.

A lubricant layer 4 is formed on the protective layer 3 by applying a fluorine-based lubricant. The lubricant layer 4 is provided to prevent the magnetic head, which floats at a minute distance from the surface of the protective layer, from sticking to the disk. As the fluorine-based lubricant, a perfluoropolyether-based lubricant represented by Chemical formula 6 is preferable.

[0044]

[Chemical 6]

The coating thickness of this fluorine-based lubricant is 2 to 20 n
m is desirable. Fluorine-based lubricant coating thickness is 2n
If it is less than m, the effect of the lubricant is insufficient, and sticking of the magnetic head cannot be sufficiently prevented. Further, when the coating thickness of the fluorine-based lubricant exceeds 20 nm, sticking is rather induced by the lubricant, and dust adheres to the disk surface.

[0046]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results.

Experimental Example 1 First, a first Si ₃ N ₄ dielectric film, a TbFeCo recording magnetic layer, a second Si ₃ N ₄ dielectric film, and an Al reflective layer were sequentially formed on a polycarbonate substrate by sputtering. Then, a recording portion having a four-layer structure was formed.

Then, a protective layer was formed on the recording portion by spin-coating an ultraviolet-curable resin containing 0.1% by weight of the silicon-based surfactant shown in Chemical formula 7 on the surface.

[0049]

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Subsequently, a fluorine-based lubricant shown in Chemical formula 8 was spin-coated on this protective layer to form a lubricant layer having a thickness of 10 nm, and a magneto-optical disk was prepared.

[0051]

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Experimental Example 2 A magneto-optical disk was prepared in the same manner as in Experimental Example 1 except that no silicon-based surfactant was added to the protective layer and no lubricant layer was formed on the protective layer.

Experimental Example 3 A magneto-optical disk was prepared in the same manner as in Experimental Example 1 except that a silicon-based surfactant was not added to the protective layer and a silicon-based lubricant was used in the lubricant layer.

Experimental Example 4 A magneto-optical disk was prepared in the same manner as in Experimental Example 1 except that no silicon-based surfactant was added to the protective layer.

Experimental Example 5 The same as Experimental Example 1 except that a silicon-based surfactant having no methyl fluoride group was used as the surfactant added to the protective layer and a silicon-based lubricant was used in the lubricant layer. Then, a magneto-optical disk was created.

Experimental Example 6 A magneto-optical disk was prepared in the same manner as in Experimental Example 1, except that a silicon-based surfactant having no methyl fluoride group was used as the surfactant added to the protective layer.

Experimental Example 7 A magneto-optical disk was prepared in the same manner as in Experimental Example 1 except that a silicon-based lubricant was used for the lubricant layer.

With respect to the magneto-optical disk manufactured as described above, the coating property of the lubricant and the CSS characteristics were evaluated. The CSS characteristics are as follows:
Stable CS measured in a hot and humid environment with a relative humidity of 80%
The case where the S operation was performed 100,000 times or more was evaluated as good. Table 1 shows the results.

[0059]

[Table 1]

As shown in Table 1, in the disk of Experimental Example 2 in which the surfactant was not added to the protective layer and the lubricant layer was not formed, when the CSS operation was performed, the magnetic head contacted the disk, It will be damaged. From this, it is understood that in order to apply the magneto-optical disk to the CSS system, some kind of surface treatment is necessary to prevent the disk and the head from sticking to each other.

However, when the lubricant was directly applied to the protective layer made of only the ultraviolet curable resin (Experimental Example 3 and Experimental Example 4), the lubricant was repelled into a spherical shape on the surface of the protective layer, and the CSS I can't get it to work.

When a silicon-based surfactant was added to the protective layer and a silicon-based lubricant was applied to the protective layer (Experimental Examples 5 and 7), the methyl fluoride group in the surfactant was The lubricant can be uniformly applied to the surface of the protective layer regardless of the presence or absence, and the CSS operation can be performed at room temperature. However, when the CSS operation is performed in a high temperature and high humidity environment, sticking of the head occurs. This is considered to be due to the high water absorption of the silicon-based lubricant, and in addition to this, even if the coating thickness of the silicon-based lubricant was variously changed, the sticking could not be prevented.

On the other hand, when a surfactant having no methyl fluoride group was added to the protective layer and a fluorine-based lubricant was applied to this protective layer (Experimental Example 6), the time after application of the lubricant was measured. At the same time, the lubricant collects in a liquid state, so that a uniform lubricant layer cannot be formed.

On the other hand, in the magneto-optical disk of Experimental Example 1 in which a surfactant having a methyl fluoride group was added to the protective layer and a fluorine-based lubricant was applied on the protective layer, the surface of the protective layer was lubricated. The agent can be applied uniformly, and good CSS characteristics can be obtained not only at room temperature but also under high temperature and high humidity.

From this, it is effective to apply a fluorine-based lubricant to the surface of the protective layer, which is the air bearing surface of the head, in order to prevent sticking of the disk and the head. It was found that it was necessary to add a surfactant to the protective layer in order to uniformly coat.
As such a surfactant, a silicone-based surfactant having a methyl fluoride group and modified with a polyether is particularly preferable.

[0066]

As is apparent from the above description, in the magneto-optical disk of the present invention, an ultraviolet-curable resin protective layer containing a surfactant is internally formed on the recording portion, and the protective layer is formed on this protective layer. Since the fluorine-based lubricant layer is formed, when the information signal is recorded by the CSS method using the floating magnetic head, sticking of the magnetic head to the disk surface is prevented and good CSS characteristics are obtained. It is possible.

Therefore, according to the present invention, the CSS system can be applied to the magneto-optical disk, which greatly contributes to the high transfer rate, high access, and low power consumption of the magneto-optical disk.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one configuration example of a magneto-optical disk to which the present invention is applied.

FIG. 2 is a perspective view showing a state where recording is performed on the magneto-optical disk by a CSS method.

FIG. 3 is a sectional view showing a conventional magneto-optical disk.

FIG. 4 is a cross-sectional view showing how a lubricant is spherically repelled on the surface of a protective layer in a conventional magneto-optical disk.

[Explanation of symbols]

 1 transparent substrate 2 recording part 3 protective layer 4 lubricant layer 6 optical pickup device 7 floating magnetic head

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C07F 7/12 C07F 7/12 X C09D 133/00 PGC C09D 133/00 PGC 171/02 PLQ 171 / 02 PLQ 183/08 PMU 183/08 PMU

Claims (5)

[Claims] 1. A transparent magnetic substrate, on which at least a recording magnetic layer is formed, and an ultraviolet-curable resin protective layer containing a surfactant and a fluorine-based lubricant layer are formed on the recording magnetic layer. A magneto-optical disk characterized by being present. 2. The magneto-optical disk according to claim 1, wherein the surfactant internally added to the ultraviolet-curable resin protective layer is a silicon-based surfactant represented by Chemical formula 1. Embedded image 3. The magneto-optical disk according to claim 1, wherein the ultraviolet curable resin is an acrylic ultraviolet curable resin. 4. The magneto-optical disk according to claim 1, wherein the fluorinated lubricant layer is formed by applying the fluorinated lubricant represented by Chemical Formula 2 to the surface of the protective layer. Embedded image 5. The magneto-optical disk according to claim 1, wherein the information signal is recorded by a magnetic field modulation method.