JPH0935349A - Magneto-optical disk and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magneto-optical disk having high reliability in magnetic field modulation recording by forming the resin protective film on the side facing a magnetic head or coming into contact or sliding therewith of a resin film formed with projecting parts by irradiation with a laser. SOLUTION: The surface of the magneto-optical disk formed with the curable resin protective film on the side facing the magnetic head is irradiated with the laser like pulses while moving its focal, by which the many projections are formed on the protective film. The height of the projections is preferably 0.01 to 5.0μm as an example. A layer which generates heat by absorption of the laser is formed on the surface of the protective film on the magnetooptical disk. This layer is composed, as an example, of org. matter of colored plastics, etc., thin films of inorg. matter and metals formed by sputtering, org. and inorg. coating materials, pigments, carbon black, etc. The coefft of friction between the floating magnetic head and the surface of an optical disk is drastically lowered and the magneto-optical disk having high reliability in magnetic field modulated recordihg is obtd by such projecting parts.

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 a method for manufacturing the same, and more particularly to a magneto-optical recording medium suitable for use in a magnetic field modulation method using a flying magnetic head.

[0002]

2. Description of the Related Art A conventional magneto-optical disk is widely used in which a protective film made of resin is formed directly or through another layer on a recording layer made of TbFeCo or the like provided on a plastic substrate. ing. The requirements for the protective film are that it has excellent weather resistance, protects the recording layer, and does not contain a substance that causes deterioration of the recording layer or other layers, and that the material is not expensive and the productivity is good. It is highly safe and a thermosetting or ultraviolet curable resin is generally used.

It has been pointed out that the magneto-optical recording is excellent in recording density and cost per bit, but is slow in writing speed, as compared with magnetic recording only. This is because conventional magneto-optical recording uses a permanent magnet and employs an optical modulation method in which recording is performed by turning on / off a laser light for recording, and therefore it is difficult to overwrite information, and when rewriting information. The reason is that there is a two-step process of erasing all information and then recording new information.

[0004]

In recent years, as a means for solving this problem, a magnetic field modulation method capable of directly overwriting information on previously recorded information, that is, laser light is continuously or continuously applied to the recording layer. Attention has been paid to a method of irradiating in a pulsed manner, and recording at least a portion irradiated with laser light by modulating the direction of a magnetic field by a recording magnetic head.

By the way, the magnetic field modulation method uses a flying head as a recording magnetic head (ISOM'87).
Proceedings, P149 ~), or a method using a magnetic head in which a coil is wound around a core is proposed. In the method using the flying head, the flying head is levitated by several μm from the magneto-optical disk, and the magnetic head is arranged at a position about 0.1 mm away from the magneto-optical disk to generate a high magnetic field (for example, several hundred oersteds) at a high frequency ( Magneto-optical recording is performed by modulating at, for example, several MHz.

However, in these systems, the recording magnetic head and the magneto-optical disk are separated from each other by only a small distance of several μm to 0.1 mm. There is a problem that the surface of the magneto-optical disk is scratched by coming into contact with the disk and the scratch is also exerted on the recording layer to destroy the information. In particular, in the method using the flying head, the head is only a few μm away from the magneto-optical disk even when flying, and when flying the head by the CSS (contact start stop) method, the flying head starts and the flying head moves when landing. It slides directly on the magneto-optical disk.

Further, recently, a system for recording, reading, and rewriting information while the magnetic head is continuously slid on the magneto-optical disk has been developed. When a conventional magneto-optical disk with a resin protective film on the outermost surface is used for recording with the magnetic field modulation method as described above, the outermost surface of the magneto-optical disk facing the recording magnetic disk has insufficient strength or is smooth. When the floating head is used, the head and the resin protective film are attracted to each other to make it difficult to fly the head, or the protective film is scratched due to contact or sliding with the floating head. In some cases, the sliding may cause damage to the recording layer, or moisture or chemicals may invade from the scratch to deteriorate the recording layer and destroy the recording.

In order to solve these problems, the resin used for the resin protective film is made of SiO ₂ , Al ₂ O ₃ or the like in order to improve the abrasion resistance of the surface of the magneto-optical disk and provide the surface roughness. A means for dispersing the filler and a means for forming irregularities on the surface of the resin film by using a mechanical means such as a burnisher (JP-A-4-195749, etc.) have been proposed.

However, since an ultraviolet curable acrylic resin is generally used as the resin, the curing is not sufficiently performed due to the dispersion of the filler, noise is increased due to the mixing of the filler, and the hardness of the filler is high. There was a problem that the flying head was scratched due to excessive flow. In addition, when the unevenness is mechanically formed, a part of the protective film scraped off during the unevenness formation or the uncut residue on the protective film side remains on the protective film and adheres to the flying head, which makes the flying of the head unstable. Further, there arises a problem that a weak spot is partially formed on the protective film and the protective film is broken from there.

A method has also been proposed in which a lubricant is added to the base protective film resin to obtain both roughness and lubricity (Japanese Patent Laid-Open No. 40149/1990), but since the lubricant is dissolved in the resin, If the part of the upper part of the filler that actually slides with the magnetic head is not covered with resin, lubricity may not be obtained, or even if the upper part of the filler could be covered with resin, the film thickness is too thin. However, there was a problem that the resin film was immediately damaged.

A method has also been proposed in which a lubricant is applied on the resin protective film after curing to prevent the resin protective film and the flying head from being attracted to each other. There are many examples in which the adsorption of is enhanced. There is also a problem that the lubricant is scraped off by the floating head, and the effect is not exerted due to sliding a large number of times.

Due to the above problems, it is difficult to obtain a magneto-optical disk suitable for the magnetic field modulation method. Recently, it has been found that a material equivalent to the protective film resin and having a concavo-convex pattern on the protective film has good CSS characteristics, and a protective film in which an organic filler is dispersed or an ultraviolet curable resin is screen-printed. There has been proposed a protective film or the like which is formed into an uneven shape by a method such as spraying.

However, from the standpoint of stably producing a large number of products having the same performance, all of them were uneasy.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a magneto-optical disk suitable for magnetic field modulation recording.

[0014]

The gist of the present invention is a magneto-optical disk used for recording by a magnetic field modulation method, wherein a resin protective film on the side facing, contacting or sliding with the magnetic head is The present invention resides in a magneto-optical disk, which is a resin film having a protrusion formed by laser irradiation.

When a laser such as a YAG laser, an argon laser, or a semiconductor laser is irradiated so as to focus on the surface of the magneto-optical disk having the curable resin protective film facing the magnetic head, the resin is generated by the heat generated by absorption. To melt. When cooling-solidification occurs from the peripheral portion of the melting spot, the peripheral edge portion of the spot rises due to surface tension, and a crater-like projection having a depressed central portion is formed.

By adjusting conditions such as laser output and irradiation time, it is possible to make the peripheral edge portion and the central portion of the spot swell and form a recess in the middle. By moving the focus while irradiating the laser, it is possible to form protrusions of various shapes. It is also possible to form a pattern in which circular or elliptical protrusions are regularly arranged by applying a pattern formed by curved continuous protrusions or pulse-like modulation.

According to the method of irradiating the laser in a pulsed manner while fixing the laser and moving the disk, it is possible to form a large number of the above-mentioned projections on the protective film at a constant interval with a simple optical system. . As a method of moving the disk, a method of rotating the disk with a turntable, a method of moving the disk horizontally and vertically using an XY stage, and the like can be used.

The protrusions thus formed are smooth,
Since it has both protrusions and depressions, the contact area becomes small when it comes into contact with the flying magnetic head, and the frictional force can be reduced. Further, since it is made of the same resin as that of the resin protective film, there is no fear that the protrusions will be peeled off from the protective film due to frictional force.

Further, if the material of the resin protective film has the excellent points (hardness, weather resistance, lubricity, etc.), it can be directly provided on the protrusion. In addition, since the laser output, irradiation time, pulse interval, etc. can be controlled accurately,
The projections having the most effective size and height can be repeatedly formed at desired intervals with good reproducibility.

The height of the protrusions does not hinder the flying of the head.
About 0.01 to 5.0 μm is preferable. The shape of the protrusions is preferably rounded so that the head is not caught or scraped. When forming the protrusions, if a layer that generates heat due to laser absorption is formed on the outermost surface of the magneto-optical disk that faces, contacts, or slides with the recording magnetic head, only the protective film resin will protect the laser. It is desirable that a larger amount of heat is generated than that generated by absorption, the protrusion formation can be performed more efficiently, and thermal damage to the recording layer can be more effectively prevented. As such a layer, organic materials such as colored plastics, thin films of inorganic materials and metals formed by sputtering or the like, organic and inorganic paints and pigments, carbon black and the like can be considered.

If a photosensitive dye having an absorption maximum in the vicinity of the wavelength of the laser used for forming protrusions is applied as a substance that absorbs heat from the laser and heat is generated by the light absorption of the dye, it is further effective. It is desirable that the protrusion can be formed physically. Also, since most of the irradiated laser light is absorbed by the dye layer, even if the laser power for forming protrusions becomes larger than the optimum one, it is transmitted to the reflective layer and recording layer below the resin protective film. It is also possible to prevent the laser light from reaching and damaging.

Of course, if the dye is soluble in the protective film resin, the one in which the film of the protective film resin in which the dye is dissolved or dispersed is formed on the surface of the disk facing the magnetic head can similarly obtain the desired effect. You can The dye used in the present invention is preferably a dye which is easily available, has excellent safety, and has low reactivity with the resin protective film after curing.

Further, it is required that the coating solvent is inexpensive and easily available, has high safety, and has good solubility in the coating solvent and the protective film resin. As specific examples, cyanine dyes, carbocyanine dyes, styryl dyes, and oxanol dyes are preferably used. If the product name is used, for example, cyanine dyes NK-3212 and NK-1046 from Japan Photosensitive Dye Research Institute Co., Ltd. , Carbocyanine dye NK-1045, Styryl dye NK-557, N
Examples thereof include K-92, NK-342, oxanol dye NK-1447, and merocyanine dye NK-2045.

The preferred range of use of these dyes is as follows:
There is some difference due to the difference in solubility depending on the dye, but 0.01 to 5 wt% when mixed with the protective film resin before curing, 0.5 to 10 w when dissolved in a solvent and applied on the resin protective film.
About t% is preferable. As the coating solvent, methanol, ethanol, triethylamine, water or the like that does not adversely affect the recording film of the magneto-optical disk, the substrate resin, and the resin protective film can be used depending on the type of dye.

[0025]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The following devices / methods were used for measurement of physical properties and the like in the present specification and examples. In the CSS test, a magneto-optical disk was attached to the spindle motor, the ABS (air bearing slider) size was 5mm x 5mm, and the levitation magnetic head with two rails with a rail width of 1.9mm was used in the disk recordable range. After arranging on the innermost circumference side (radial position r of the core = 25 mm), the disk is rotated at a maximum rotational speed of 3600 rpm and stopped repeatedly 10,000 times to observe the extent to which the disk surface is damaged.

The time was 1 second for increasing the rotation speed, 3600 rpm for 3 seconds, 1 second for decreasing the rotation speed, and 1 second for stopping, for a total of 6 seconds. At the same time, when the floating magnetic head changes from the landing state to the floating state, the force that pulls the head in the rotating direction of the magneto-optical disk is applied to the load cell (UT-100 manufactured by Minebea Co., Ltd.).
The friction coefficient was calculated from the displayed numerical value.
This was used as the friction coefficient between the flying magnetic head and the magneto-optical disk, and measurement and recording were performed for each rotation.

[0027]

Example 1 As a curable resin, an ultraviolet curable composition having the composition shown in Table 1 was prepared. 100 nm silicon nitride and Tb ₂₁ Fe ₇₂ Co ₇ are sputtered onto a polycarbonate resin substrate.
The UV curable resin composition shown in Table 1 was applied as a curable resin onto a magneto-optical disk having a diameter of 90 mm, in which 40 nm, 30 nm of silicon nitride and 50 nm of aluminum were formed in this order by a spin coater. The shake-off speed was 2000 rpm, and shaken off for 10 seconds.

Subsequently, ultraviolet rays were irradiated to cure the surface. The disk having this resin protective film was attached to a rotary head with the protective film surface facing upward, and while being rotated at 100 rpm, a laser was applied in a pulsed manner to form protrusions. The laser used was a 488 nm Ar laser. The distance between the laser and the board surface was about 15 μm, and irradiation was performed in a pulsed manner with a power of 160 mW. The pulse irradiation condition was a duty of 10%, and the frequency was gradually changed so that both the track interval and the pit center interval were 50 μm. (For example, 30nm from the center
At 6.28 Hz, irradiation time 1.59 × 10 ⁻⁵ se
c) As a result, recesses with a raised peripheral portion having a diameter of about 25 μm were uniformly formed.

When measured with a laser interference microscope, the depth from the highest point of swelling of the peripheral portion to the deepest portion of the recess was about 50 nm. CSS on this disc as described above
I did a test. After the completion of 10,000 times, the surface of the magneto-optical disk protective film was closely observed, but no scratches were observed.

The coefficient of friction when the head is flying is 0 throughout.
It was stable at 1 to 0.3, and no scratches or the like were found on the observation of the magnetic head surface after the CSS test.

[0031]

[Table 1]

[0032]

[Comparative Example 1] The conditions for forming a protective film with an ultraviolet curable resin were the same as those in Example 1 without forming protrusions by a laser on a magneto-optical disk prepared in the same manner as in Example. A CSS test was conducted. The surface of the resin protective film observed before the CSS test was smooth by visual observation, microscopic observation and electron microscopic observation.

As a result, although the head floated about the first 10 times, the friction coefficient fluctuated significantly when the head floated, and all of them showed a large value of 1 or more. After that, abnormal noise was generated and the friction coefficient was sharply reduced. When the disk surface was observed, the head sliding portion was scratched and the protective film was destroyed.

[0034]

According to the present invention, the resin protective film, which is the outermost surface of the magneto-optical disk facing the recording magnetic head, or which contacts or slides, is provided with projections by laser irradiation. By using a protective film, even when the floating magnetic head and the magneto-optical disk surface make contact or slide, the contact area is reduced to prevent adsorption, and the friction coefficient between them is greatly reduced to reduce the number of times the head slides. It is possible to provide a magneto-optical disk which can withstand motion, and which is particularly reliable in magnetic field modulation recording.

According to the method of the present invention, the optimum protrusion height,
The diameter, density, and dispersion pattern can be arbitrarily selected, and accurate and precise control can be performed. Further, while the above effects are obtained, the film thickness of the resin protective film can be suppressed to the conventional level, and the material can be supplied at a relatively low cost. Further, in the present invention, in forming the protrusion, a layer which generates heat due to absorption of laser is formed on the outermost surface of the magneto-optical disk facing the recording magnetic head, or in contact with or sliding against the recording magnetic head. A larger amount of heat is generated than that generated when only the film resin absorbs the laser, the projections can be formed more efficiently, and the thermal damage to the recording layer can be prevented more effectively.

Further, as a substance that absorbs laser light and generates heat, a photosensitive dye having an absorption maximum around the wavelength of the laser used for forming protrusions is coated on the protective film or dissolved in the protective film resin. Alternatively, by dispersing, the heat generated by the light absorption of the dye is added, and the protrusions can be formed more effectively. Also, since most of the irradiated laser light is absorbed by the dye layer, even if the laser power for forming protrusions becomes larger than the optimum one, it is transmitted to the reflective layer and recording layer below the resin protective film. It is possible to prevent the laser light from reaching and damaging the laser light.

Claims (5)

[Claims] 1. A magneto-optical disk used for recording by a magnetic field modulation method, wherein a resin protective film on the side facing, contacting or sliding with the magnetic head has a protrusion formed by laser irradiation. A magneto-optical disk characterized by being a resin film. 2. The magneto-optical disk according to claim 1, wherein the formed protrusion has a substantially circular or elliptical shape with a raised peripheral edge. 3. The magneto-optical disk according to claim 1, wherein a layer that absorbs laser light and generates heat is formed on the side facing, contacting or sliding with the magnetic head. A magneto-optical disk. 4. The magneto-optical disk according to claim 1, wherein a dye film is formed on the resin protective film. 5. The magneto-optical disk according to claim 1, wherein the resin protective film is formed of a resin in which a dye is dissolved or dispersed in the resin.