JP2740814B2 - Magneto-optical recording medium - Google Patents

Description

The present invention relates to a rewritable magneto-optical recording medium,
In particular, the present invention relates to a magneto-optical recording medium that effectively prevents mechanical deformation and corrosion deterioration due to moisture.

[Related Art] In recent years, as a rewritable optical recording medium, a magneto-optical recording medium utilizing a magneto-optical effect has been vigorously researched and developed.
Some have been put to practical use. This magneto-optical recording medium has advantages such as large-capacity, high-density recording, non-contact recording / reproducing, and easy access, and is also capable of overwriting (document information files, video / still image files, and computers). It is expected to be used for memories and the like.

The magneto-optical recording medium has a perpendicular magnetization film, that is, a magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface as a recording layer, and records, reproduces, and erases information by irradiating a laser beam and applying a magnetic field. It is supposed to do. The recording layer includes an alloy of a heavy rare earth / light rare earth metal having an amorphous structure and a transition metal, for example, Tb-Fe-Co, Gd-Tb-
The use of materials such as Fe-Co, Dy-Fe-Co, Dy-Tb-Fe-Co, Gd-Dy-Fe-Co has been proposed. These materials are susceptible to corrosion due to oxidation, and have the disadvantage that magnetic properties such as coercive force and perpendicular magnetic anisotropy of the recording layer deteriorate with time. For this reason, in many cases, the recording medium has a three-layer structure in which the recording layer is covered with a protective film in a sandwich manner.

On the other hand, as a substrate for a magneto-optical recording medium, a glass substrate with a pregroove, a polycarbonate (PC) substrate, or the like is used. In particular, a polycarbonate substrate is practically advantageous because it is inexpensive.

However, this polycarbonate substrate has high moisture permeability and oxygen permeability, and is likely to be warped or deformed due to temperature and humidity during use. In particular, when the outside air changes from a dry state to a humid state, the frequency of occurrence of the warp increases. Further, the recording layer is damaged through the pinholes of the protective film due to the permeation of oxygen.

The mechanical deformation and corrosion deterioration described above are not sufficient even if the recording layer is covered with the protective layer in a sandwich manner.

On the other hand, Japanese Patent Application Laid-Open No. 63-20745 discloses that the resin substrate portion in contact with the outside world is covered with a water-repellent resin or a low moisture-permeable resin so that the C / N and the bit error rate can be changed over time. Techniques for reducing are disclosed.

[Problems to be solved by the invention]

However, the material used as the cover layer in the technology disclosed in the above-mentioned publication is organic, and its protective effect is not sufficient even if it is said to be water repellent or low moisture permeable. It has been desired to improve.

The present invention solves such problems of the prior art, and provides a magneto-optical recording medium that can prevent warpage and deformation even in an environment where the temperature and humidity are largely changed, and that can stably maintain reproduction characteristics for a long period of time. The purpose is to:

[Means for solving the problem]

To achieve the above object, according to the present invention, a light-transmitting resin substrate, a recording layer formed of an amorphous magnetic alloy film formed on the substrate, and a protective film covering both surfaces of the recording layer are provided. In the magneto-optical recording medium provided, a cover layer made of a composite of an oxide and a nitride of an inorganic material is provided on the substrate surface opposite to the recording surface of the recording medium and on the inner and outer peripheral edges of the recording medium. Is provided, and a magneto-optical recording medium is provided.

 Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a configuration example of a magneto-optical recording medium according to the present invention. This magneto-optical recording medium is a transparent resin substrate 1
A first protective layer (undercoat) 2, a magneto-optical recording layer 3, and a second protective layer (top coat) 4 are sequentially laminated thereon, and further, a surface opposite to a recording surface of the medium and A cover layer 5 is formed on inner and outer ends (inner and outer peripheral side portions) of the medium.

For the translucent resin substrate 1, a resin such as polycarbonate (PC), polymethyl methacrylate (PMMA), or epoxy is used.

The magneto-optical recording layer 3 is made of an amorphous magnetic alloy in which at least one or more rare earth metals such as Tb, Gd, Dy and Nd are combined with at least one or more transition metals Fe and Co. You. Examples of such alloys include TbFeCo, GdTbFeCo,
NdDyFeCo, TbDyFeCo and the like are exemplified. The magneto-optical recording layer 3 is formed to a thickness of 400 to 1000 ° by a sputtering method, a vapor deposition method or the like.

The first and second protective layers 2 and 4 use SiN, SiAlON, or the like,
It is formed to a thickness of 400 to 1000 mm by a vapor deposition method or a sputtering method. Since the first protective layer 2 also serves as an enhancement film, the first protective layer 2 is set to have a film thickness corresponding to the refractive index so that the apparent magneto-optical effect is maximized by multiple reflection. In addition, the first protective layer 2 and the second protective layer 4 may be formed of the same material, or may be formed of different materials in consideration of their functions.

The cover layer 5 is formed to a thickness of 100 to 3000 ° by a vapor deposition method or a sputtering method using a composite of an oxide and a nitride of an inorganic material. Specific materials used for forming the cover layer 5 include SiAlON and the like. This cover layer 5
Is to improve the moisture permeability and oxygen permeability of the recording medium, sufficiently prevent warping and deformation even in an environment where the temperature and humidity are largely changed, and make it possible to stably maintain the reproduction characteristics of the recording medium for a long period of time.

〔Example〕

Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.

(Example 1) A polycarbonate substrate (about 130 mm in diameter and 1.2 mm in thickness) was set in a sputtering apparatus, and an SiN protective film (undercoat) was formed to a thickness of 800 mm on the substrate by sputtering. A Tb ₁₂ Dy ₁₂ Fe ₆₈ Co ₈ magneto-optical recording layer is formed to a thickness of 800 mm, and a SiAlON protective film (top coat) is
The film was formed to a thickness of 0 °. The disk thus obtained was set on a sputtering apparatus so that a cover layer could be formed on the side opposite to the recording surface of the disk. Then, vacuum evacuation was performed until the degree of vacuum in the chamber of the sputtering apparatus reached 1 × 10 ⁻⁷ torr, and moisture and occluded air in the polycarbonate substrate were dehydrated and degassed. Next, the mixed gas of Ar + O ₂
The chamber was introduced at a ratio of r: O ₂ = 5: 1 so that the inside of the chamber became 3 × 10 ⁻³ torr. Thereafter, a DC voltage was applied to the SiAlON target, discharge was performed at a power of about 1 kW, and the discharge was continued until the film thickness became 1000 mm, a cover layer was formed, and a single-plate recording medium was obtained.

On the other hand, a recording medium of a comparative example was obtained in the same manner as described above except that the cover layer was not formed.

With respect to the recording media (single-plate disks) of Example 1 and Comparative Example produced as described above, first, the amount of warpage was measured. The result is shown in FIG. The recording medium of the comparative example without the cover layer had a warp of 100 μm or more, and the warp reached 600 μm for a large recording medium. However, according to the recording medium of Example 1, the warpage is reduced due to the provision of the cover layer.
It was reduced to about 10 μm. This is probably because the formation of the cover layer balanced the stress on both sides of the substrate.

Next, with respect to both recording media, the amount of warpage and the surface state when continuously changing from a dry state of 70 ° C. and 20% RH to a high humidity of 70 ° C. and 80% RH were examined. As a result, the amount of warpage increased about twice in the recording medium of the comparative example, and did not change in the recording medium of Example 1. In the case of the recording medium of the comparative example, no crack was observed because of the large amount of warpage.

As described above, the cover layer of Example 1 showed a sufficient effect on the warpage of the medium.

Furthermore, the effect of the two recording media on the change with time under high temperature and high humidity of 80 ° C. and 85% RH was examined. FIG. 3 shows the change over time in the amount of warpage. In the recording medium of the comparative example, the amount of warpage slightly increased after elapse of 500 hours, and then slightly decreased thereafter, but the amount of warpage was also about 100 μm. On the other hand, in the recording medium of Example 1, the amount of warpage was unchanged, and the size was about 10 μm.

As described above, in Example 1, a remarkable improvement in the long-term stability of mechanical properties was remarkably observed.

Next, with respect to both recording media, the change with time of the error rate under high temperature and high humidity of 80 ° C. and 85% RH was examined. The result is shown in FIG. Note that the error rate is normalized by an initial value in the figure. The recording medium of Example 1 did not change even after lapse of 2000 hours. However, in the recording medium of the comparative example, the error rate deteriorated 10 times after 500 hours,
In addition, it has deteriorated to such a degree that measurement cannot be performed thereafter due to cracks or the like.

As described above, in the recording medium of Example 1, a remarkable improvement was also observed in the long-term stability of the error rate (reproduction characteristics).

〔The invention's effect〕

As described in detail above, according to the present invention, a cover layer made of a composite of an oxide and a nitride of an inorganic material is provided on the substrate surface opposite to the recording surface and on the inner and outer peripheral edges of the recording medium. Therefore, it is possible to sufficiently prevent the recording medium from warping and deformation even in an environment in which the temperature and the humidity are largely changed, and to stably maintain the reproduction characteristics for a long period of time. Therefore,
A highly reliable and high quality magneto-optical recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the configuration of a magneto-optical recording medium according to the present invention, FIG. 2 is a view showing the results of measurement of the amount of warpage in the recording media of Examples and Comparative Examples of the present invention, and FIG. FIG. 4 is a graph showing the change over time in the amount of warpage under high temperature and high humidity in the recording media of Examples and Comparative Examples. FIG. 4 shows the error rates of the recording media of Examples and Comparative Examples under high temperature and high humidity. It is a figure showing a temporal change. DESCRIPTION OF SYMBOLS 1 ... Translucent resin substrate 2 ... 1st protective layer (undercoat) 3 ... Magneto-optical recording layer 4 ... 2nd protective layer (top coat) 5 ... Cover layer

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-115037 (JP, A) JP-A-62-1197939 (JP, A) JP-A-63-122037 (JP, A) JP-A-62-1979 20156 (JP, A) JP-A-63-124244 (JP, A) JP-A-61-139961 (JP, A) JP-A-2-18729 (JP, A) JP-A-1-217745 (JP, A) JP-A-63-253549 (JP, A)

Claims (1)

(57) [Claims] 1. A magneto-optical device comprising a light-transmitting resin substrate, a recording layer made of an amorphous magnetic alloy film formed on the substrate, and protective films covering both surfaces of the recording layer. In a recording medium, a cover layer made of a composite of an oxide and a nitride of an inorganic material is provided on a substrate surface opposite to a recording surface of the recording medium and on inner and outer peripheral ends of the recording medium. Magneto-optical recording medium.