JPH0594644A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the recording medium which has excellent corrosion resistance and has the reflectivity uniform over the entire surface of a film surface by forming a recording layer to the outer peripheral end of a transparent substrate and forming a UV curing resin layer on the peripheral surface covering the outer peripheral end face of this recording layer. CONSTITUTION:A recording part 2 is laminated on one main surface of the transparent substrate 1 and a protective layer 3 is provided on the upper front surface of this recording part 2. Further, the UV curing resin layer 4 is provided on the peripheral surface covering the outer peripheral end face of the recording part 2. A disk-shaped transparent acrylic resin or carbonate resin, etc., having several mm thickness are used for the substrate 1. Guide grooves or address code pits (not shown in Fig.) having a depth of about 1/4 the wavelength of the laser beam to be used at the time of reproducing are provided on the substrate 1 surface on the side to be provided with the recording part 2. The recording part 2 is constituted of a recording layer 5, dielectric layers 6, 7 and a reflection layer 4 up to the outer peripheral line part of the substrate 1 and is laminated with a 1st dielectric layer 6, the magnetic recording layer 5, a 2nd dielectric layer 7, and a reflection layer 8 in this order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to improvement of corrosion resistance.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a magnetic thin film is partially heated above a Curie point or a temperature compensation point to eliminate the coercive force of this portion and reverse the direction of a recording magnetic field applied from the outside. The basic principle is to perform recording by reading the recorded information by the magnetic Kerr effect or the magnetic Faraday effect, and it is being put to practical use in an external storage device of a computer or a recording device of audio and video information. ..

As a magneto-optical recording medium used in such a magneto-optical recording system, a recording layer, a reflective layer, a Kerr rotation angle and a corrosion resistance are improved on one side of a transparent substrate made of polycarbonate or the like. It is known that a recording portion is provided by laminating dielectric layers for this purpose. The recording layer is required to have an easy axis of magnetization in the direction perpendicular to the film surface and to have a large magneto-optical effect. Usually, a rare earth-transition metal alloy amorphous thin film such as a TbFeCo amorphous thin film is used. To be done.

[0004]

However, since the rare earth-transition metal alloy amorphous thin film that becomes the recording layer is very easily oxidized, if it is exposed to the atmosphere and left to stand in the atmosphere, H ₂ O in the atmosphere will be lost. Oxygen and oxygen gradually oxidize the recording layer, leading to corrosion and pitting corrosion, which induces signal dropout, and decreases the coercive force and the residual magnetic Kerr rotation angle. Therefore, conventionally, in such a magneto-optical recording medium,
In order to prevent corrosion of the recording layer, it is proposed that a protective layer made of an ultraviolet curable resin or the like is provided on the recording portion, and the protective layer suppresses contact between the recording layer and the atmosphere.

However, even in the magneto-optical recording medium having such a structure, the corrosion from the upper surface of the recording portion is prevented by the protective layer provided, but the outer peripheral end surface of the recording portion is still exposed to the atmosphere, so that recording Corrosion of the part proceeds from the outer peripheral end face side, and signal deterioration cannot be sufficiently suppressed.

Therefore, in order to cover the entire surface of the recording layer with the protective layer, the recording layer is formed with an outer diameter smaller than the outer diameter of the substrate, and the ultraviolet curable resin is applied onto the recording layer so as to cover it. A magneto-optical recording medium having a protective layer has been developed. However, when the recording portion is formed with an outer diameter smaller than that of the substrate, the film thickness of the recording portion varies in the vicinity of the outer peripheral edge due to the manufacturing principle.

That is, each layer forming the recording portion is usually formed by a vacuum thin film forming technique such as a vacuum vapor deposition method or a sputtering method. For example, when the sputtering method is adopted, a mask that regulates the outer diameter of the recording portion is provided along the outer circumference of the transparent substrate, discharge is performed by using the material corresponding to each layer as a target, and the substrate provided with the mask is discharged. The sputtered particles will be deposited.

However, in a vacuum thin film forming technique such as a sputtering method, when a film is formed on a substrate on which a mask is provided, it becomes more difficult for the adhered material to adhere to the portion where the mask is provided, and thus the formation becomes difficult. The thickness of each of the layers thus formed varies near the outer peripheral edge of each layer. For this reason, the formed recording portion has an unstable reflectance near the outermost periphery, and it is unavoidable that this portion is designed not to be used as a data area. Therefore, the amount of recorded information is reduced, and in particular,
This is a major obstacle when miniaturizing the magneto-optical recording medium as a mini disk or the like.

In addition, the protective layer formed by coating the recording portion with the ultraviolet curable resin has poor adhesion to the outer peripheral end surface of the recording portion, and completely prevents corrosion factors from entering the recording portion. I can't.

Therefore, the present invention has been proposed in view of such a conventional situation, and is a magneto-optical recording medium which is excellent in corrosion resistance and can obtain stable recording / reproducing characteristics over the entire surface of the recording portion film surface. The purpose is to provide.

[0011]

In order to achieve the above-mentioned object, the magneto-optical recording medium of the present invention is a magneto-optical recording medium in which at least a recording layer and a protective layer are formed on a transparent substrate. The recording layer is formed up to the outer peripheral edge of the transparent substrate, and an ultraviolet curable resin layer is formed on the peripheral surface of the recording layer so as to cover the outer peripheral end surface of the recording layer.

[0012]

In the magneto-optical recording medium of the present invention, since the recording layer is formed up to the outer peripheral edge of the transparent substrate, a mask for regulating the outer diameter of the recording layer is formed when forming the recording layer. It does not need to be provided on the substrate. Therefore, the film thickness of the recording layer does not vary near the outer peripheral edge, and a uniform reflectance is exhibited over the entire film surface.

A protective layer is provided on the upper surface of the recording layer, and an ultraviolet curable resin layer is formed on the peripheral surface of the recording layer so as to cover the outer peripheral end surface of the recording layer. The protective layer and the ultraviolet curable resin layer protect the water and oxygen in the atmosphere and improve the corrosion resistance.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

In the magneto-optical recording medium of this embodiment, as shown in FIG. 1, a recording portion 2 is laminated on one main surface of a transparent substrate 1, and a protective layer 3 is provided on the upper surface of the recording portion 2. An ultraviolet curable resin layer 4 is formed on the peripheral surface of the recording portion so as to cover the outer peripheral end surface.
It is equipped with.

The substrate 1 is a disk-shaped transparent substrate having a thickness of about several millimeters, and as its material, a plastic material such as an acrylic resin, a polycarbonate resin, a polyolefin resin, an epoxy resin or the like, or glass or the like is used. To be done. On the side of the surface of the substrate 1 on which the recording portion is provided, a guide groove, an address code pit, etc. having a depth of about ¼ of the wavelength of the laser beam used during reproduction are usually provided (all shown in the figure. Is omitted.) Is provided.

The recording portion 2 has a four-layer structure including a recording layer 5, dielectric layers 6 and 7 and a reflective layer 8 which are formed up to the outer peripheral edge of the transparent substrate, and has a first dielectric on the substrate 1. The layer 6, the recording magnetic layer 5, the second dielectric layer 7, and the reflective layer 8 are laminated in this order.

Of these, oxides and nitrides can be used as the first dielectric layer 6 and the second dielectric layer 7, but oxygen in the dielectric layers 6 and 7 is a recording layer. Nitride is more preferable because it may adversely affect 5 and it is preferable to use silicon nitride or aluminum nitride as a substance that is advantageous in preventing the permeation of oxygen and water molecules and can sufficiently transmit the laser light used. Is.

The recording layer 5 is an amorphous magnetic thin film having a direction of easy magnetization in a direction perpendicular to the film surface and, of course, has excellent magneto-optical characteristics and a large coercive force at room temperature.
Moreover, it is desirable to have a Curie point near 200 ° C.
Recording materials that meet such conditions include rare earth-transition metal alloy amorphous thin films and the like.
A Co-based amorphous thin film is suitable. In this recording magnetic layer,
An additive element such as Cr may be added for the purpose of improving the corrosion resistance.

The reflective layer 8 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 7, and a nonmagnetic metal vapor deposition film is preferred. .. Further, the reflective layer 8 is preferably a thermally good conductor, and aluminum is suitable in consideration of availability, film formation, and the like.

Further, the protective layer 3 and the ultraviolet curable resin layer 4
Are provided to prevent corrosion and pitting of the recording portion.
By providing the protective layer 3 on the upper surface of the recording unit 2 and further providing the ultraviolet curable resin layer 4 on the peripheral surface so as to cover the outer peripheral end face, the recording unit 2 is completely isolated from water and oxygen in the atmosphere,
Corrosion resistance is secured.

Here, as the material of the UV-curable resin layer 4, any conventionally known UV-curable resin such as acrylic UV-curable resin can be used, and if selected in consideration of characteristics such as waterproofness. Good. Further, as the material for the protective layer 3, any of those usually used as a protective layer material in this type of magneto-optical recording medium can be used. However, the ultraviolet curable resin used for the ultraviolet curable resin layer 4 is used. The material for the protective layer is advantageous in terms of cost reduction and simplification of manufacturing. The thickness of the protective layer 3 is about 3 to 5 μm from the viewpoint of corrosion prevention effect and practicability.

The above magneto-optical disc is manufactured as follows. First, the substrate 1 on which an uneven pattern is formed in advance
A recording portion 2 having the same outer diameter as the substrate 1 is formed on the top. Each of the layers 5, 6, 7, and 8 that form the recording unit 2 can be formed by a vacuum thin film forming technique such as sputtering, molecular beam epitaxy, or vacuum evaporation.

For example, when each layer is formed by sputtering, the target corresponding to the layer to be formed is placed in the chamber of the sputtering apparatus and the substrate 1 is placed on the substrate placing table in the chamber. Place. Then, by discharging the target, sputtered particles are generated from the surface of the target and deposited on the substrate.

At this time, in the magneto-optical recording medium, since the recording portion 2 may be formed up to the outer peripheral edge portion of the transparent substrate, it is not necessary to provide a mask for regulating the outer diameter of the recording portion on the substrate. Therefore, the film thickness of each layer does not vary in the vicinity of the outer peripheral edge, and the recording portion 2 having a uniform reflectance over the entire film surface is formed.

When the sputtered particles adhere to the side surface of the substrate 1 during sputtering, the ultraviolet curable resin layer 4 having good adhesion is formed in the subsequent step of forming the ultraviolet curable resin layer.
May not be formed, or the recording portion may not be completely isolated from the atmosphere by the ultraviolet curable resin layer 4. Therefore, in the present embodiment, the inconvenience is eliminated by using the substrate mounting table shown in FIG.

In other words, the substrate mounting table is mounted on the pallet 21 for mounting the substrate 1 and the center hole 23 of the substrate 1 so that the position of the substrate is regulated by inserting the pallet 21 into the center portion 24 and the pallet 21. And a fixing portion 25 for fixing the.

The pallet 21 is a plate-shaped body having a circular recess 26 having substantially the same diameter as the substrate 1,
The step 2 on which the outer peripheral edge of the substrate 1 is placed along the outer circumference.
7 is provided. Further, a cylindrical protrusion 28 having a diameter slightly larger than that of the center hole 23 of the substrate 1 is formed in the center of the recess 26, and the center 24 is provided on the protrusion. .. The center portion 24 is formed by integrally molding a cylindrical insertion portion 24a that is inserted into the center hole 23 of the substrate 1 and a truncated cone-shaped fitting portion 24b that is fitted to the fixed portion. Further, the fixing portion 25 is a truncated cone, and the bottom surface thereof has a recess 25a into which the fitting portion 24b of the center portion 24 is fitted.
have.

When the substrate 1 is placed on the substrate mounting table having such a structure and the sputtering is performed, the side surface of the substrate 1 is protected by the wall surface of the recess 26 of the pallet.
The sputtered particles do not adhere to the side surface of the substrate 1. Therefore, the ultraviolet curable resin layer 4 having a high adhesiveness and capable of completely protecting the recording portion from the corrosive factors in the atmosphere is formed in the subsequent step of forming the ultraviolet curable resin layer.

After the recording portion 2 is formed in this way, a protective layer 3 for protecting the recording portion 2 and an ultraviolet curable resin layer 4 are formed. In order to form the protective layer 3, the forming method is appropriately selected depending on the material used. For example, when an ultraviolet curable resin is used, the ultraviolet curable resin is applied by a coating method such as a spin coat method. After being applied to, the composition is irradiated with ultraviolet rays and cured.

On the other hand, in order to form the ultraviolet curable resin layer 4, for example, as shown in FIG. 3, the roll 31 is rotationally moved while the disc side surface 32 is closely attached to the roll 31 to which the ultraviolet curable resin is attached. UV curable resin 33
By coating (roll coating method) or by spraying an ultraviolet curable resin on the side surface of the disk to apply the resin (spray coating method).
After being applied to No. 2, it is irradiated with ultraviolet rays to be cured.

The protective layer 3 and the ultraviolet curable resin layer 4 are also provided.
When and are formed using the same UV curable resin,
As shown in FIG. 4, when the ultraviolet curable resin 33 is applied to the upper surface of the recording portion 2 by the spin coating method, a predetermined amount is applied to the disc along the outer peripheral side and the peripheral surface of the upper surface of the recording portion. If the cover 41 is provided with a gap, the ultraviolet curable resin 33 is applied from the upper surface to the outer peripheral end surface. Then, by curing this, the protective layer 3 and the ultraviolet curable resin layer 4 are simultaneously formed.

The protective layer 3 and the ultraviolet curable resin layer 4 thus formed have high adhesion to the recording portion 2 and can completely prevent the entry of corrosion factors into the recording portion 2.

Next, the above-mentioned magneto-optical disk (Example disk) was evaluated for corrosion resistance. In addition, the evaluation of the corrosion resistance is performed by using a magneto-optical disk at a temperature of 90 ° C. and a relative humidity of 85%.
It was carried out by leaving it for a predetermined time under the above condition, and counting the number of corroded portions of 40 μm or more after standing. The relationship between the standing time and the number of outer corrosions is shown in FIG.

As a comparison, the corrosion resistance of a magneto-optical disk (comparative disk) having no ultraviolet curable resin layer on the side surface of the recording portion was evaluated in the same manner. The results are also shown in FIG.

As can be seen from FIG. 5, the magneto-optical disk in which the ultraviolet curable resin layer is not formed on the side surface of the recording portion is apt to corrode, and after leaving for 1000 hours, nearly 80 corroded portions are generated. There is. On the other hand, in the case of the magneto-optical disk on which the ultraviolet curable resin layer is formed, 1500
Even after being left for a long time, no corroded portion was observed and good corrosion resistance was obtained.

Therefore, it was found from this fact that the provision of the ultraviolet curable resin layer on the side surface of the recording portion is extremely effective in improving the corrosion resistance of the magneto-optical disk.

[0038]

As is apparent from the above description, in the magneto-optical recording medium of the present invention, the recording layer is formed up to the outer peripheral edge of the transparent substrate, and the upper surface of the recording layer is formed. Since the protective layer is provided, and the ultraviolet curable resin layer is formed on the peripheral surface so as to cover the outer peripheral end surface, the magneto-optical recording medium is excellent in corrosion resistance and the recording layer exhibits a uniform reflectance over the entire film surface. Can be obtained. Therefore,
According to the present invention, the outer peripheral edge of the recording layer can be used as a signal area, which is advantageous in reducing the size of the magneto-optical recording medium.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a configuration of a magneto-optical recording medium of the present invention.

FIG. 2 is a schematic cross-sectional view showing a configuration of a substrate mounting table for mounting a substrate during sputtering.

FIG. 3 is a schematic cross-sectional view showing an example of a method for forming an ultraviolet curable resin layer.

FIG. 4 is a schematic cross-sectional view showing another example of the method for forming an ultraviolet curable resin layer.

FIG. 5 is a characteristic diagram showing the relationship between the standing time and the number of corrosion occurrences under high temperature and high humidity conditions for a magneto-optical recording medium.

[Explanation of symbols]

 1 ... Substrate 3 ... Protective layer 4 ... UV curable resin layer 5 ... Recording layer

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[Procedure amendment]

[Submission date] May 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Here, as the material of the UV-curable resin layer 4, any conventionally known UV-curable resin such as acrylic UV-curable resin can be used, and if selected in consideration of characteristics such as waterproofness. Good. Further, as the material for the protective layer 3, any of those usually used as a protective layer material in this type of magneto-optical recording medium can be used. However, the ultraviolet curable resin used for the ultraviolet curable resin layer 4 is used. The material for the protective layer is advantageous in terms of cost reduction and simplification of manufacturing. The thickness of the protective layer 3 is about 3 to 8 μm from the viewpoint of corrosion prevention effect and practicability.

Claims (1)

[Claims] 1. A magneto-optical recording medium in which at least a recording layer and a protective layer are formed on a transparent substrate, the recording layer being formed up to the outer peripheral edge of the transparent substrate, and the outer periphery of the recording layer. A magneto-optical recording medium, characterized in that an ultraviolet curable resin layer is formed on the peripheral surface so as to cover the end face.