JPH0778911B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium capable of recording and reproducing by a light beam, and particularly to a recording layer having a high coercive force and a low Curie temperature at room temperature. And a magneto-optical recording medium having a magneto-optical recording layer having an exchange-coupled two-layer structure composed of a read layer having a low coercive force and a high Curie temperature at room temperature.

[Conventional technology]

Conventionally, various attempts have been made to improve the reading characteristics of a magneto-optical recording medium, and one of them has been an exchange-coupling bilayer film composed of a film having good recording characteristics and a film having good reading characteristics as a magneto-optical recording layer. It is known that the read characteristics are improved by using the same (for example, JP-A-57-78652). Conventionally,
In such an exchange-coupling bilayer film, Tb-Fe, Dy-
Fe or the like is used, and Gd-Fe, Gd-Fe-Co, or the like is used for the read layer.

However, the amorphous magnetic materials such as Tb-Fe, Dy-Fe, etc. have the drawback of poor corrosion resistance. That is, when it comes into contact with the atmosphere or water vapor, the magnetic properties are deteriorated, and finally it is completely oxidized and becomes transparent, and the magnetic properties are lost.

In order to eliminate such a defect, it is generally provided with a protective layer made of a transparent material such as SiO ₂ , SiO, Al ₂ O ₃ , Si ₃ N ₄ or ZnS above or below the magneto-optical recording layer. Has been done. Among these substances, ZnS is widely used as a protective layer of the above-mentioned magneto-optical recording medium because of its excellent corrosion resistance. However, since ZnS lacks adhesion to a substrate having a hygroscopic property such as plastic, when such a substrate is used, a magneto-optical recording layer may be cracked or peeled between layers. In particular, under the environmental conditions adopted as a method for evaluating the durability of a magneto-optical recording medium, for example, at a high temperature and high humidity such as a temperature of 45 ° C and a relative humidity of 95%, the above-mentioned problems of cracks and peeling are avoided. I couldn't do it.

Excellent adhesion to the substrate to eliminate such problems
Attempts have also been made to improve durability by forming an undercoat layer made of SiO on a substrate and then further providing a protective layer made of ZnS on the undercoat layer.

However, even in this case, under the more severe environmental conditions, for example, the temperature of 60 ° C. and the relative humidity of 90%, the above-mentioned problems of cracks and peeling occur.

[Problems to be solved by the invention]

The present invention has been made in view of the above points, and an object of the present invention is to improve the environment resistance of a conventional magneto-optical recording medium having an exchange coupling bilayer film.

[Means for solving problems]

The above object of the present invention is achieved by the following present invention.

A magneto-optical recording layer having a double-layer structure exchange-coupled with a recording layer having high coercive force and low Curie temperature at room temperature and a read layer having low coercive force and high Curie temperature at room temperature was provided on a plastic substrate. In the magneto-optical recording medium, an undercoat layer made of SiO _{1 + X} (where 0 <X <1) is in contact with the substrate between the substrate and the magneto-optical recording layer; A magneto-optical recording medium, characterized in that a protective layer made of ZnS is provided by laminating.

[Action]

The magneto-optical recording medium of the present invention comprises an undercoat layer made of SiO _{1 + x} (where 0 <x <1, preferably 0.4 <x <0.9) in contact with a substrate, and laminated on this undercoat layer. It has a protective layer made of ZnS and can be used not only under the environmental conditions described above, such as temperature of 45 ° C and relative humidity of 95%, but also under severer conditions of 60 ° C and relative humidity of 90%. It does not cause the above-mentioned problems such as cracks and peeling and has extremely excellent environment resistance.

That is, as described above, when an undercoat layer made of SiO is provided on the substrate and then a protective layer made of ZnS is further provided thereon, SiO in the undercoat layer has a dangling bond forming a plastic substrate. Adhesion is excellent because it is covalently bonded to the atoms (oxygen atoms and carbon atoms in the case of a polycarbonate substrate). However, since oxygen atoms are deficient, the structure is not dense and water easily permeates. When the permeated water reaches the boundary with ZnS, the adhesion between ZnS and SiO deteriorates, and ZnS causes film peeling.

On the other hand, when the undercoat layer is made of SiO ₂ , Si does not covalently bond with the atoms constituting the plastic substrate because Si has no dangling bonds, and the adhesion to the substrate is poor. However, it is structurally dense and water does not permeate to the boundary with ZnS. Therefore, ZnS does not cause film peeling.

As described above, there are merits and demerits regardless of whether the undercoat layer is composed of SiO or SiO ₂ , and it is hard to say that it has excellent environment resistance.

On the other hand, the undercoat layer of the present invention is SiO _{1 + X} (where 0 <X
Since it consists of <1), there is a dangling bond in Si, and the dangling bond of Si is covalently bonded to the atoms constituting the plastic substrate, resulting in excellent adhesion. In addition, since oxygen is present in a larger amount than SiO 2, it is structurally dense and has an excellent effect of preventing moisture permeation to the protective layer made of ZnS. As described above, SiO _{1 + X} (where 0 <X <1) has both excellent characteristics of SiO and SiO ₂ , and since defects are suppressed, it is very excellent in environmental resistance. Of.

The undercoat layer having the composition of SiO _{1 + x} (where 0 <x <1) is formed, for example, by using SiO as a starting material and performing vacuum deposition in an O ₂ atmosphere, or by using SiO and SiO ₂ as the starting materials. As the above, it is preferable that these are vapor-deposited or sputtered at the same time.

FIG. 1 shows an example of the magneto-optical recording medium of the present invention having such an undercoat layer and a ZnS protective layer in contact therewith. In this magneto-optical recording medium, an undercoat layer 2 made of SiO _{1 + x} (where 0 <x <1) is provided in contact with a writing substrate 1a, and a protective layer 3 made of ZnS and a room temperature are further provided on the undercoat layer 2. Readout layer 4 with low coercivity and high Curie temperature at room temperature
a, a recording layer 4b having a high coercive force and a low Curie temperature at room temperature, a protective layer 5 and an adhesive layer 6 are sequentially laminated, and then a protective substrate 1b is adhesively formed.

Various magnetic materials used in this type of technology can be used as the material forming the exchange-coupled read layer and recording layer. For example, Gd-Fe and Gd described above as suitable read layers can be used. -Fe-Co and the like are suitable as the recording layer and include Tb-Fe and Dy-Fe. The protective layer 5 and the protective substrate 1b are provided for the purpose of further improving the environmental resistance, and may be provided as needed.

〔Example〕

In order to describe the present invention more specifically, examples of the present invention will be shown below.

Example 1 The magneto-optical memory medium illustrated in FIG. 1 was prepared as follows.

A 1.2 mm-thick plastic plate made of polycarbonate was used as the substrate 1a, and an undercoat layer 2 made of SiO _{1 + x} (where 0 <x <1) having a thickness of about 1300Å was formed on the substrate 1a by vacuum deposition. .

The undercoat layer 2 is formed by inserting the substrate 1a into a vacuum chamber of a well-known film forming apparatus capable of performing both vapor deposition and sputtering, and then evacuating the vacuum chamber to 5 × 10 ⁻⁶ Torr or less. Then, O ₂ gas was introduced and the SiO 2 as a starting material was evaporated at a pressure of 1 × 10 ⁻⁴ Torr. At this time, when the film formation was performed by controlling the vapor deposition rate so that the undercoat layer 2 had a refractive index of 1.55 ± 0.02,
An undercoat layer 2 having a composition of SiO _{1 + x} (however, x = 0.8) was obtained on 1a.

Next, while maintaining the vacuum of the vacuum chamber, a protective layer 3 made of ZnS having a thickness of about 900 Å was formed on the undercoat layer 2 by sputtering.

Next, as in the above case, without breaking the vacuum in the vacuum chamber, the film thickness of GdFeCo of about 400 was formed by high frequency sputtering.
After the Å read-out layer 4a is formed on the protection layer 3, the read-out layer 4a is subsequently formed with a film thickness of about 400 Å made of TbFe.
By forming the recording layer 4b of 1., a magneto-optical recording layer having a two-layer structure formed by exchange coupling was constructed.

Then, a protective layer 5 made of ZnS having a film thickness of 900 liters was formed on the recording layer 4b by the same sputtering as described above without breaking the vacuum.

Finally, the substrate 1a on which each of the above layers was formed was taken out from the vacuum chamber, and a hot-melt adhesive was used as the adhesive layer 6 to bond it to the protective plastic substrate 1b to complete the magneto-optical recording medium.

The magneto-optical recording medium thus obtained was heated at a temperature of 60 ° C and a relative humidity.
After carrying out an environment resistance test for 1000 hours while holding it in a 90% constant temperature and humidity chamber, this magneto-optical recording medium showed no particular change in appearance even after 1000 hours, and showed no cracks or film peeling. It was found that it did not occur and that it has excellent environmental resistance that has never been achieved.

Example 2 In the same manner as in Example 1 except that O ₂ when forming the undercoat layer 2 was 5 × 10 ⁻⁵ Torr and 8 × 10 ⁻⁵ Torr, respectively, the undercoat layer 2 was formed of SiO _{1 + x} (however, , X = 0.45) and SiO _{1 + x} (however, x = 0.7) were obtained.

When these magneto-optical recording media were subjected to the same environment resistance test as in Example 1, no cracks or film peeling were observed after 1000 hours in any case, and excellent environment resistance was obtained. It had a nature.

Comparative Example A magneto-optical recording medium having a conventional structure in which SiO ₂ and SiO ₂ were used as starting materials and SiO ₂ and SiO ₂ were used as the undercoat layer 2 in FIG. 1 except that oxygen was not introduced was used. Obtained.

An environment resistance test was conducted on these magneto-optical recording media in the same manner as in Example 1. After 300 hours had elapsed for the one having the undercoat layer 2 made of SiO, 400 hours for the one having the undercoat layer 2 made of SiO _2. After the lapse of time, film peeling and cracking occurred.

〔The invention's effect〕

As described above, according to the present invention, the environment resistance of the magneto-optical recording medium having the exchange-coupling bilayer film can be significantly improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of the magneto-optical recording medium of the present invention. 1a, 1b ... Substrate, 2 ... Undercoat layer 3, 5 ... Protective layer 4a ... Read-out layer, 4b ... Recording layer 6 ... Adhesive layer

Claims (1)

[Claims] 1. A plastic magneto-optical recording layer having an exchange-coupled two-layer structure comprising a recording layer having a high coercive force and a low Curie temperature at room temperature and a read layer having a low coercive force and a high Curie temperature at room temperature. In a magneto-optical recording medium provided on a substrate, SiO _{1 + X} (where 0 <X is provided between the substrate and the magneto-optical recording layer in contact with the substrate.
An undercoat layer consisting of <1) and Zn laminated on this undercoat layer
A magneto-optical recording medium comprising a protective layer made of S.