JPH0589539A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the magneto-optical disk which is improved in the corrosion resistance of the magneto-optical disk and can maintain characteristics even when the disk is used with a disk cartridge type or is preserved under high- temp. and high-humidity conditions. CONSTITUTION:A corrosion preventive film 3 is provided between the reflection layer 8 and UV curing resin layer 4 of the magneto-optical disk constituted by forming a 1st dielectric layer 6, a recording magnetic layer 5, a 2nd dielectric layer 7, the reflection layer 8 and the UV curing resin layer 4 on a transparent substrate 1. The corrosion preventive film 3 is formed of a Cr film or chemically converted Cr film.

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 a magneto-optical recording medium suitable for use in a disc cartridge format.

[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. ..

Such a magneto-optical recording medium generally has a recording magnetic layer or a reflective layer having a large magneto-optical effect and a curl having an easy axis of magnetization on one side of a transparent substrate made of polycarbonate or the like in a direction perpendicular to the film surface. It is known that a recording portion is provided by laminating dielectric layers for increasing the rotation angle and improving the corrosion resistance. For the recording magnetic layer, a rare earth-transition metal alloy amorphous thin film such as a TbFeCo amorphous thin film is generally used.

As the magneto-optical recording medium, specifically, a Si ₃ N ₄ dielectric layer, a TbFeCo recording magnetic layer, a Si ₃ N ₄ dielectric layer, and an Al reflection film are sequentially formed on a transparent substrate. The recording portion is formed by, and a protective film made of an ultraviolet curable resin or the like is further provided on the recording portion,
The one that reads the signal by irradiating the laser beam from the transparent substrate side, or the transparent substrate with the above-mentioned recording part is pasted through the protective film with the reflective layers back to back, and read from both sides. A double-sided magneto-optical recording medium has been proposed.

The above-mentioned double-sided specification magneto-optical recording medium is 5.2.
It has been put into practical use as a 5-inch size magneto-optical disk. On the other hand, a single-sided magneto-optical recording medium having a recording portion on only one surface of a substrate is a disk that is housed in a cartridge as a 3.5-inch magneto-optical disk. It is being considered for use in a cartridge format. In particular, the latter magneto-optical disc used in the disc cartridge format is less likely to be damaged, and is excellent in storability and portability, so that it is expected to be used in many fields.

[0006]

However, the magneto-optical disk housed in the cartridge is more corrosive to the metal than the magneto-optical disk left outside because the inside of the cartridge is likely to be hot and humid. It will be saved in a high environment. A rare earth-transition metal alloy used as a recording magnetic layer of a magneto-optical disk is very easily oxidized and has a property of easily combining with oxygen in the air to form an oxide. For this reason, when the magneto-optical disk is stored under such highly corrosive metal conditions, oxidation gradually progresses, leading to corrosion or pitting and signal loss, and particularly rare earth metals are selected. Oxidation causes a problem that the S / N ratio is deteriorated as the coercive force and the residual magnetic Kerr rotation angle are reduced.

Therefore, the present invention has been proposed in view of such conventional circumstances, and provides a magneto-optical recording medium which is excellent in corrosion resistance and can maintain good recording / reproducing characteristics even when used in a disk cartridge format. The purpose is to provide.

[0008]

In order to achieve the above-mentioned object, the magneto-optical recording medium of the present invention is an optical recording medium in which at least a recording magnetic layer, a reflective layer and a protective layer are laminated in this order on a transparent substrate. In the magnetic recording medium, a corrosion prevention film is provided between the reflection layer and the protection layer.

In the magneto-optical disk of the present invention, for example, as shown in FIG. 1, a recording portion 2 is laminated on one main surface of a substrate 1, and ultraviolet rays to be a corrosion preventing film 3 and a protective layer are formed on the surface of the recording portion. The cured resin layer 4 is covered.

The substrate 1 is a disk-shaped transparent substrate having a thickness of about several millimeters, and as the material thereof, a plastic material such as an acrylic resin, a polycarbonate resin, a polyolefin resin, an epoxy resin or the like, or a 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 section 2 includes a recording magnetic layer 5, a dielectric layer 6, and
7 has a four-layer structure including a reflective layer 8 and a first dielectric layer 6, a recording magnetic layer 5, a second dielectric layer 7,
The reflective layers 8 are stacked in this order.

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

Further, the recording magnetic layer 5 is an amorphous magnetic thin film having an easy magnetization direction in a direction perpendicular to the film surface, and is of course excellent in magneto-optical characteristics and has a large coercive force at room temperature. It is desirable to have a Curie point around 200 ° C. As a recording material satisfying such conditions, a rare earth-transition metal alloy amorphous thin film and the like can be mentioned, and among them, a TbFeCo based amorphous thin film is 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 8 is preferably formed 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 preferable. .. Further, the reflective layer 8 is preferably a thermally good conductor, and aluminum is suitable in consideration of availability, film formation, and the like.

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 set arbitrarily, but usually several hundred to
It is set to about several thousand Å. These film thicknesses are preferably determined not only by considering the optical properties of each layer alone, but also by considering the effect of combination. This is, for example, the recording magnetic layer 5
This is because the multiple optical interference with the light transmitted through the layer and reflected at the boundary of each layer causes the effective optical and magneto-optical characteristics of the recording magnetic layer 5 to vary greatly depending on the combination of the film thicknesses.

The ultraviolet curable resin layer 4 is provided for the purpose of protecting the recording portion 2. The thickness of the ultraviolet curable resin layer 4 is about 3 to 5 μm, and an acrylic ultraviolet curable resin or the like is usually used.

The above is the basic structure of the magneto-optical disk. In the magneto-optical disk of the present invention, a corrosion prevention film is provided between the reflection layer and the ultraviolet curable resin layer, and the magneto-optical disk is housed in a cartridge or exposed to high temperature. Even when stored under humid conditions,
Corrosion and pitting corrosion do not occur in the recording magnetic layer and reflective layer.

As the material of the corrosion prevention film, Cr, T
A metal such as i that is easily passivated by H ₂ O is preferable. A corrosion prevention film is formed by a method of depositing Cr, Ti or the like on the Al reflection film by a method such as sputtering. By providing such a corrosion inhibiting film between the reflective layer and the ultraviolet curing resin layer, even if H ₂ O intrudes from the ultraviolet curing resin layer, H ₂ O is passivated corrosion preventing film, whereby H
_Since the progress of ₂ O is blocked, corrosion and pitting of the reflective film and the recording magnetic layer are prevented.

The thickness of the corrosion prevention film is 100 to 100.
0Å is desirable, more preferably 300Å ~
It is 500Å. If the thickness of the anticorrosion film is too thin, a sufficient anticorrosion effect cannot be expected, and if it is too thick, the heat sink function of the reflective film may be adversely affected. Further, the corrosion prevention film may be a Cr chemical conversion film formed by performing a surface treatment with a Cr chemical conversion liquid.
The Cr conversion coating is a very thin oxide coating, and it contains Cr ₂ O ₃
・ It is composed of xH ₂ O. The method for producing this coating is so-called chromate treatment, and it is easily formed by immersing it in a treatment liquid containing Cr ^{6 +} (Cr chemical conversion liquid).
Even though the corrosion prevention film formed by this treatment is very thin, it is possible to obtain the same effect as that of the above metal film.

[0020]

[Function] The first Si ₃ N ₄ dielectric layer, Tb, is formed on the transparent substrate.
FeCo recording magnetic layer, second Si ₃ N ₄ dielectric layer, Al
When a magneto-optical disk having a reflective layer and an ultraviolet curable resin layer laminated in this order is stored under high temperature and high humidity conditions, the reflective layer and the recording magnetic layer are gradually oxidized from the ultraviolet curable resin layer side to cause corrosion, Leads to pitting corrosion.

It is considered that this is because H ₂ O penetrating through the ultraviolet effect resin layer penetrates into the reflective layer and the recording magnetic layer, and causes oxidation of the reflective layer and the recording magnetic layer. In the magneto-optical recording medium having such a structure, if a corrosion prevention film such as a Cr film is provided between the reflection layer and the protection layer, the corrosion prevention film prevents the progress of H ₂ O that has entered from the UV curable resin layer side. In rare cases, corrosion and pitting of the reflective layer and recording magnetic layer are prevented.

[0022]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Experimental Example 1 This experimental example is an example in which a magneto-optical disk was manufactured without providing a corrosion prevention film and the progress of corrosion was observed.

First, a first Si ₃ N ₄ dielectric film, a TbFeCo recording magnetic layer, and a first Si ₃ N ₄ dielectric film were formed on a substrate made of polycarbonate.
A second Si ₃ N ₄ dielectric film and an Al reflection film were sequentially formed by sputtering to form a recording portion. Then, an ultraviolet curable resin layer was formed on this recording portion to manufacture a magneto-optical disk. The film thickness of each layer and the ultraviolet curable resin layer constituting the recording portion are as follows.

Recording part First Si ₃ N ₄ dielectric film: 1000Å TbFeCo recording magnetic layer: 230Å Second Si ₃ N ₄ dielectric film: 600Å Al reflective film: 700Å UV curable resin layer: 5 μm

The magneto-optical disk thus produced was left to stand for 2000 hours under the conditions of a temperature of 80 ° C. and a relative humidity of 85% to cause corrosion, and the progress of the corrosion was examined. First, when the corroded portion is observed with an epi-illumination optical microscope, the corroded portion is observed as a double circle. Further, when this corroded portion is analyzed using EPMA, FT-IR, and TEM, the outer circle of the double circle is the portion where the Al reflection film is corroded, and the inner circle is corroded by the TbFeCo magnetic film. It was found that this corrosion is progressing from the UV curable resin layer side.

Therefore, it was found from the above that it is sufficient to prevent the progress of the corrosion factor penetrating from the ultraviolet effect resin layer side in order to prevent the corrosion.

Experimental Example 2 In this experimental example, a Cr film was provided between the reflective film and the ultraviolet curable resin layer to fabricate a magneto-optical disk, and the corrosion resistance was evaluated.

In the same manner as in Experimental Example 1, the recording portion was formed on the transparent substrate. Then, a Cr film serving as a corrosion prevention film is formed on the recording portion by sputtering so as to have a film thickness shown in Table 1, and an ultraviolet curable resin layer is further formed on the corrosion prevention film to form a film thickness of the corrosion prevention film. Various magneto-optical discs (Sample Disc 1 to Sample Disc 6) of different types were produced.

Each of the magneto-optical discs manufactured in this manner was stored under the conditions of a temperature of 80 ° C. and a relative humidity of 85%.
It was left to stand for 00 hours, and the state of occurrence of corrosion after standing was observed.
Table 1 shows the number of corroded portions of each magneto-optical disk. The number of corroded portions was measured for 6 magneto-optical disks of each constitution.

For comparison, a magneto-optical disk (comparative disk) not provided with a corrosion prevention film was also left under the same conditions and the state of corrosion was observed. The results are also shown in "Table 1".

[0032]

[Table 1]

As can be seen from Table 1, the sample discs 1 to 6 provided with the Cr film all had a smaller number of corroded portions than the comparative discs, and the sample discs 1 to 6 were between the reflective layer and the ultraviolet effect resin layer. It can be seen that the corrosion resistance is improved by providing the corrosion prevention film on the. Also, C
The effect of the r film is not sufficiently exhibited when the film thickness of the Cr film is too thin, and the film thickness of the Cr film is 100 Å or more, further 3
It can be seen that it becomes more prominent when it is set to 00Å or more. However, when the Cr film is too thick, Al
This may adversely affect the heat sink function of the reflective film. Therefore, in order to obtain the corrosion prevention effect while maintaining the performance of the magneto-optical disk, the thickness of the corrosion prevention film should be 100
It has been found that it may be set to ˜1000Å, more preferably 300 to 500Å.

Experimental Example 3 This experimental example is an example in which a Cr conversion film was provided between the reflection film and the ultraviolet curable resin layer to fabricate a magneto-optical disk, and the corrosion resistance was evaluated.

In the same manner as in Experiment 1, the recording portion was formed on the transparent substrate. Then Na ₂ CO ₃ (sodium carbonate)
30Kg and NaCrO ₄ (sodium chromate) 15K
g, NaSiO ₃ (sodium silicate) 1 kg 1 m ³
It was dipped in a Cr chemical conversion solution dissolved in pure water to form a Cr chemical conversion coating as a corrosion protection film. At this time, the temperature of the Cr chemical conversion liquid is kept constant (50 ° C.), the immersion time is changed to form Cr chemical conversion coatings having different film qualities, and an ultraviolet curable resin layer is formed on the Cr chemical conversion coatings for various optical discs ( Sample disks 7 to 11) were produced.

Each optical disk manufactured in this manner was subjected to 2000 at a temperature of 80 ° C. and a relative humidity of 50%.
It was left for a period of time, and the state of occurrence of corrosion after standing was observed. Table 2
Shows the number of corroded parts on each magneto-optical disk. In addition,
The evaluation was performed with 20 samples for one type of optical disk, and the total number and the number of occurrences per disk are shown in "Table 2".

For comparison, a magneto-optical disk (comparative disk) having no corrosion prevention film was left under the same conditions, and the state of corrosion was observed. The results are also shown in "Table 2". The data is the total number of generated portions of 20 sheets and the number of generated sheets per sheet.

[0038]

[Table 2]

As can be seen from Table 2, the sample disks 8 to 11 have a smaller number of corroded portions than the comparative disks, and by providing the Cr chemical conversion coating between the reflective layer and the ultraviolet curable resin, It can be seen that the corrosion resistance is improved. Further, if the immersion time is short, a sufficient effect cannot be obtained. From the results shown in Table 2, it was found that immersion at 50 ° C. for 10 minutes or more was sufficient.

Next, the immersion time in the Cr chemical solution is kept constant (1
0 minutes), the temperature of the Cr chemical conversion liquid is changed to form a Cr chemical conversion film having a different film quality, and an ultraviolet curable resin layer is formed on the Cr chemical conversion film to form various optical disks (sample disks 12 to sample desks 16). Was produced.

Each optical disk manufactured in this manner was subjected to 2000 at a temperature of 80 ° C. and a relative humidity of 50%.
It was left for a period of time, and the state of occurrence of corrosion after standing was observed. Table 3
Shows the number of corroded parts on each magneto-optical disk. In addition,
The evaluation was performed with 20 samples for one type of optical disk, and the total number and the number of occurrences per disk are shown in "Table 3".

[0042]

[Table 3]

As can be seen from Table 3, the results of sample disks 14 to 16 were good.
Therefore, when the immersion time is 10 minutes, the temperature of the Cr chemical solution is 50 ° C.
It was found that sufficient eating habits can be obtained by the above.

From the results shown in Tables 2 and 3, it was found that sufficient corrosion resistance can be obtained when the immersion time is 10 minutes or longer and the temperature of the Cr chemical conversion liquid is 50 ° C. or higher.

[0045]

As is clear from the above description, in the present invention, since the anticorrosion film is provided between the reflective layer and the protective layer of the magneto-optical recording medium, the reflective film which advances from the ultraviolet effect resin layer side. The corrosion of the recording magnetic layer can be prevented. Therefore, according to the present invention, the corrosion resistance of the magneto-optical disk is remarkably improved, so that even when used as a disk cartridge, corrosion and pitting corrosion hardly occur, and a magneto-optical disk having sufficient storage stability is obtained. It is possible.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing a configuration example of a magneto-optical disk of the present invention.

[Explanation of symbols]

 1 ... Transparent substrate 2 ... Recording part 3 ... Corrosion prevention film 4 ... UV curable resin layer 5 ... Recording magnetic layer 6, 7 ... Dielectric layer 8 ... Reflection layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 18, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

It is considered that this is because H ₂ O, which has penetrated through the ultraviolet curable resin layer and penetrated, advances to the reflective layer and the recording magnetic layer and causes the oxidation of the reflective layer and the recording magnetic layer. In the magneto-optical recording medium having such a structure, when a corrosion prevention film such as a Cr film is provided between the reflection layer and the protection layer, the corrosion prevention film prevents the progress of H ₂ O that has entered from the UV curable resin layer side. In rare cases, corrosion and pitting of the reflective layer and recording magnetic layer are prevented.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

Therefore, it was found from the above that it is sufficient to prevent the progress of the corrosion factor penetrating from the ultraviolet curable resin layer side in order to prevent the corrosion.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0033

[Correction method] Change

[Correction content]

As can be seen from Table 1, in all of Sample disks 1 to 6 provided with the Cr film, the number of corroded portions was smaller than that of the comparative disk, and the area between the reflective layer and the ultraviolet curable resin layer was small. It can be seen that the corrosion resistance is improved by providing the corrosion prevention film on the. Also,
It can be seen that the effect of the Cr film is not sufficiently exhibited when the film thickness of the Cr film is too thin, and becomes more remarkable when the film thickness of the Cr film is 100 Å or more, further 300 Å or more. However, if the Cr film is too thick, A
1 There is a possibility that the heat sink effect of the reflective film may be adversely affected. Therefore, in order to obtain the corrosion prevention effect while maintaining the performance of the magneto-optical disk, the thickness of the corrosion prevention film should be 100
It was found that the amount should be set to 1000 Å, more preferably 300 to 500 Å.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

In the same manner as in Experiment 1, the recording portion was formed on the transparent substrate. Then, 30 kg of Na ₂ CO ₃ (sodium carbonate) and Na ₂ CrO ₄ (sodium chromate)
15 kg, Na ₂ SiO ₃ (sodium silicate) 1 kg
Was immersed in a Cr chemical conversion solution dissolved in 1 m ³ of pure water to form a Cr chemical conversion coating serving as a corrosion prevention film. At this time, the temperature of the Cr chemical solution is constant (50 ° C.), the immersion time is changed,
Various optical discs (Sample Disc 7 to Sample Disc 11) were produced by forming Cr chemical conversion coatings having different film qualities and forming an ultraviolet curable resin layer on the Cr chemical conversion coating.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

As can be seen from Table 3, the results of sample disks 14 to 16 were good. Therefore, when the immersion time is 10 minutes, the temperature of the Cr chemical liquid is 5
It was found that sufficient corrosion resistance can be obtained at 0 ° C or higher. In the same manner as in Experiment 1, the recording portion was formed on the transparent substrate.

[Procedure Amendment 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

[0045]

As is apparent from the above description, in the present invention, since the corrosion prevention film is provided between the reflective layer and the protective layer of the magneto-optical recording medium, the reflective film that advances from the ultraviolet curable resin layer side. The corrosion of the recording magnetic layer can be prevented. Therefore, according to the present invention, the corrosion resistance of the magneto-optical disk is remarkably improved, so that even when used as a disk cartridge, corrosion and pitting corrosion hardly occur, and a magneto-optical disk having sufficient storage stability is obtained. It is possible.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Nakajima 6-5-6 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Magne Products Co., Ltd.

Claims (3)

[Claims] 1. A magneto-optical recording medium in which at least a recording magnetic layer, a reflective layer, and a protective layer are laminated in this order on a transparent substrate, and a corrosion prevention film is provided between the reflective layer and the protective layer. A magneto-optical recording medium characterized by the above. 2. The magneto-optical recording medium according to claim 1, wherein the corrosion prevention film is a Cr film. 3. The magneto-optical recording medium according to claim 1, wherein the corrosion prevention film is a Cr conversion film.