JPH01213849A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enhance corrosion resistance and to improve stability with age by providing a 1st protective layer for which a metal oxide is used and the 2nd protective layer for which org. matter is used to a reflecting layer consisting of Al or Al alloy essentially consisting of the Al. CONSTITUTION:The plural protective layers consisting of the 1st protective layer for which the metal oxide is used and the 2nd protective layer for which the org. matter is used are successively provided on the reflecting layer which consists of the Al or the alloy essentially consisting of the Al and is provided in contact with a magneto-optical recording layer. The 1st protective layer for which the metal oxide is used prevents the oxidation of the reflecting layer. The corrosion resistance of the medium is improved by the org. matter which is used for the 2nd protective layer, is low in internal stress, prevents cracking and warping of the medium, is low in moisture permeability and is capable of highly suppressing corrosion by moisture.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording medium used for optical recording.

(Conventional technology and its issues) Among optical memory devices, magneto-optical recording is at the closest stage to practical use for erasable memory, which allows additional recording and erasing. At present, thin films of rare earth metals and transition metals are most often used as the recording layer of magneto-optical recording media in terms of overall characteristics.

This magneto-optical recording medium can be used for recording and recording during laser beam irradiation.
In order to improve reproduction efficiency, a method has also been proposed in which a reflective layer is provided on the magneto-optical recording layer on the substrate. This method is excellent in that a high C/N ratio can be obtained by using both the Kerr effect and the Faraday effect.

The reflective layer provided on the recording layer is generally made of a material with high reflectance, but Au, Ag, and PL are expensive and expensive.
Since Cu tends to corrode, thin films of Al or Al alloys are often used.

However, when Al or Al alloy is used, there is a problem in terms of corrosion resistance. That is, Al and Al alloys exhibit strong characteristics against general corrosion because they form a natural oxide film on their surfaces, but once pinholes are formed, corrosion current is concentrated, resulting in enlargement of the pinholes.

This reaction is particularly noticeable in the presence of moisture.

(Means for Solving the Problems) The present inventors have devised a highly corrosion resistant and high C/
As a result of intensive research to provide a magneto-optical recording medium with a high N ratio, we discovered that by configuring multiple protective layers with a specific material, a magneto-optical recording medium with a high carrier level and excellent stability over time can be obtained. Ta.

[Structure of the invention]

The gist of the present invention is to provide an interference layer made of a metal oxide on a substrate,
A magneto-optical recording layer made of an alloy of a rare earth metal and a transition metal, a reflective layer made of Al or an alloy mainly composed of Al provided in contact with the recording layer, a first protective layer made of a metal oxide, and a second protective layer made of an organic substance. The invention resides in a magneto-optical recording medium in which protective layers are sequentially provided.

The present invention will be explained in detail below.

First, examples of the substrate used in the present invention include glass, plastics such as acrylic resin and polycarbonate resin, and substrates in which grooved resin is formed on glass.

The thickness of the substrate is generally about 1 to 2 mm thick.

As the magneto-optical recording layer, for example, TbFe, TbFe
Amorphous magnetic alloys of rare earths and transition metals such as Co, TbCo, DyFeCo, and Mn 81% MnCuB
A polycrystalline perpendicular magnetization film such as i is used.

It is particularly effective for use in rare earth alloy magnetic films. A single layer may be used as the magneto-optical recording layer, and G d
Two or more recording layers may be stacked as shown in T b Fe / T b Fe 27). The thickness of the magneto-optical recording layer is 250 to 500. In the present invention, an interference layer is provided between the substrate and the magneto-optical recording layer. This layer uses the light interference effect of a transparent film with a high refractive index to reduce reflectance, thereby reducing noise and improving the C/N ratio. The interference layer may be a single layer film or a multilayer film.

Metal oxides are used as the interference layer. Metal oxides include Alz 03, Ta! Os, S ioz, 5i
Examples include metal oxides such as OSTiO alone, mixtures thereof, and composite oxides of Al-Ta-0. Furthermore, other elements such as Ti, ZrSWS
Mo, Yb, etc. may be used alone in the form of an oxide, or may be combined with Al or Ta to form an oxide. These metal oxides are dense and prevent moisture and oxygen from entering from the outside, have high corrosion resistance, and have low reactivity with the magneto-optical recording layer.Also, when using a resin substrate as a substrate, it is difficult to interact with the resin. Excellent adhesion.

The optimum thickness of this interference layer varies depending on the refractive index, but
Usually about 400 to 1500 people, especially 500 to 100 people
0 people is appropriate.

Tantalum oxide is particularly suitable for use as the interference layer.

An interference layer made of tantalum oxide has lower internal stress than an interference layer made of nitride, and the probability of cracking is much smaller.

The composition of tantalum oxide is a stoichiometric composition ratio (Ta.

A composition close to 0, ) is preferred; excess oxygen will lead to oxidation of the recording layer and will lower the refractive index, weakening the interference effect. Furthermore, when oxygen is insufficient, corrosion concentrates on unoxidized portions, making pinholes more likely to occur, and light absorption of the film increases, resulting in a drop in carrier level. The preferred refractive index in the oxidized state is in the range of 2.0≦n≦2°2 and IK+<0.15, where n''=niK is the complex refractive index measured at a wavelength of 630 nm.

In the present invention, a reflective layer and a protective layer are provided on the magneto-optical recording layer. The reflective layer is generally made of a material with high reflectance, but since Au, Ag, and PL are expensive and Cu is prone to corrosion, the present invention uses a thin film of Al or an alloy of Al.

Especially for Al, Ta, TiXZr, Mo, Pt, V, Cr,
Alloys containing a small amount of Pd (approximately 15 atomic % of Pd) have high reflectance, low thermal conductivity, and provide good characteristics in terms of high C/N ratio and sensitivity.

The thickness of the reflective layer is usually 250 Å or less, preferably 150 Å or less.
~250 people. If it is too thick, the sensitivity will decrease, and if it is too thin, the reflectance will decrease and the C/N ratio will also decrease.

A metal oxide is used as the first protective layer, and the purpose of this protective layer is to prevent oxidation of the reflective layer, so that the thickness of the reflective layer can be reduced. As a metal oxide, Alz 03,
Metal oxides such as Tax Os, Sing, 5iO1TiO alone or a mixture thereof, or Al-Ta,
-0 complex oxide, etc. are mentioned.

Furthermore, other elements such as Ti, Zr, W, M
o, Yb, etc. alone in the form of oxide or At.

It may be combined with Ta to form an oxide.

The film thickness of the second AI protection layer is usually preferably about 50 to 500 layers.

A second protective layer made of an organic material is further provided on the first protective layer. The organic material used for this second protective layer has low internal stress and does not cause cranking or warping of the medium. In addition, it is preferable that the material has low moisture permeability and can strongly suppress corrosion due to moisture, and has a 100% tensile stress of 50 Kgf/cm" or less as specified by JIS K2SO3 and a moisture permeability of 20 g/cm in 24 hours as specified by JIS Z 020B. It is preferable that the organic material has a 100% tensile stress of 30 Kgf/cm'' or less as specified above, and a water vapor permeability of 10 g/m'' or less in 24 hours as specified above.

As such an organic substance, polyurethane using a hydrocarbon polyol is preferably employed.

This polyurethane is mainly composed of hydrocarbon polyol with low hygroscopicity, and isocyanate compound is NC0.
10H=0.8-1.3 Preferably NC010H=0.
9-1. It is preferable to mix them at a distribution ratio of 1 and cure them.

Such a hydrocarbon polyol can be produced by a known method such as hydrogenating a butadiene polymer described in JP-A-50-90694, and polyurethane using this can be produced by a known method, for example, by hydrogenating a butadiene polymer as described in JP-A-50-90694. It is easily produced by a method such as reacting the above polyol with a polyisocyanate as described in No. 142695.

By providing this second protective layer, the corrosion resistance of the medium is further improved, and even when used as a veneer, it becomes resistant to damage such as scratching.

The thickness of the second protective layer is 0.1 to 100 μm, preferably 1 to 100 μm.
It is about 50um.

When this medium is further bonded to another substrate, the second protective layer also serves as an adhesive layer.

In this case, the thickness of the second protective layer (adhesive layer) is 1 μm to 200 μm.
μm is preferably about 3 μm to 100 μm.

Physical vapor deposition methods such as sputtering (P
chemical vapor deposition (CVD) such as VD), plasma CVD
etc. apply.

To form a magneto-optical recording layer, a reflective layer, and a protective layer using the PVD method, the usual method is to deposit each layer on a substrate by electron beam evaporation or sputtering using a target with a predetermined composition. It is.

Furthermore, a method using ion blating is also considered.

If the film deposition rate is too fast, it will increase the film stress, and if it is too slow, it will affect productivity, so it is usually 0.1 person/sec~
It is said to be around 100 people/sec.

In the case of the interference layer and the first protective layer, RF sputtering using Ta, OS target, etc., A using Ta target, etc.
DC or RF reactive sputtering using r and 02 gases, electron beam evaporation, and the like are preferred. Among these, the DC reactive sputtering method using Ar and 02 gas using a Ta target etc. is preferable because it is possible to control the amount of oxygen, the film formation rate is fast, and the rise in substrate temperature is small. . In this case, the refractive index of the interference layer can be easily controlled by changing the pressure.

The second protective layer can be easily formed by a spin code method or other conventional coating methods.

〔Example〕

The present invention will be explained in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Examples and Comparative Examples A polycarbonate substrate with a diameter of 130 mm was introduced into a sputtering apparatus, the exhaust was first evacuated to below 8X10-'torr, and a Ta target was reactively sputtered using a mixed gas of Ar and O2. A human interference layer was formed by two-dimensional simultaneous sputtering with Ar gas using a Tb target and a FeCo target.
b tt (F e 90COto) 300 of va
A human record layer was set up. Furthermore, sputtering was performed in Ar gas using an Al target equipped with Ta chips. ? T
A 300-layer reflective layer consisting of a 3 alloy was formed. Furthermore, a first protective layer 300 made of tantalum oxide is formed by sputtering a Ta target in a mixed gas of Ar and 0□.
I set up a person. Finally, a second protective layer was applied using polyurethane to a thickness of 108 m.

Polyurethane was obtained as follows.

"Production of component A""PolytailHA'" (Product name) (manufactured by Mitsubishi Chemical Corporation, number average molecular weight: approximately 2000, hydroxyl group equivalent: 0)
．． 907 meq/g polyolefin polyol)1
00g.

゛'ADEKAQUODOL゛゛ (Product name) (manufactured by Asahi Denka Co., Ltd., tetrafunctional polyol, hydroxyl group equivalent 13.1 meq/
g) 19.8g.

゛Paraffinic process oil゛° (Kyodo Oil stock%)
Formula % °゛Tin-based urethane catalyst” (manufactured by MD Kasei Co., Ltd.,
UL-22) 138 mg.

These were mixed uniformly at 50°C to obtain component A. The viscosity was 1800 cps at 25°C.

"Production of component B" 100 g of "Polytail HA" and 116 g of "paraffinic process oil P-200" are mixed uniformly at room temperature in a separable flask. Then, 2.4-) lylene diisocyanate 14.2
g and reacted at 80°C for 6 hours to obtain component B, which had a viscosity of 3800 cps at 25°C.

The A liquid and the B liquid thus prepared were mixed at a weight ratio of 5:1, vacuum defoamed, and then applied to a disk.

A pressed sheet was made using the liquid prepared in the same way and the physical properties were measured. It was 100% according to JIS K6301.
Tensile stress is 3kgf/cm" Tensile strength is 7kgf/
cm", and the moisture permeability specified by JIS Z0208 is 5 in 24 hours for a film with a thickness of 200 μm.
g/cm".

The disk created in this way was heated at 70°C185%R.
An accelerated test was conducted for 2000 hours under H conditions, and an increase in error rate was observed over time. Even after 2000 hours had passed, the error rate could be suppressed to 1.2 times. The results are shown in Figure 1.

As a comparative example, the structure up to the reflective layer was the same as that of the example, and the first
and one in which the second protective layer was not provided, and one in which the structure up to the first protective layer was the same as in the example and the second protective layer was not provided,
A second protective layer was directly provided in place of the first protective layer.

These disks were heated at 70°C 185%R as in the example.
An accelerated test was conducted at 200C for a time of 200°C, and an increase in error rate was observed over time. The error rate after 2000 hours was much higher than in the example.

The results are shown in Figure 1.

〔Effect of the invention〕

The magneto-optical recording medium of the present invention has excellent weather resistance.

[Brief explanation of the drawing]

FIG. 1 shows the results of measuring the increase in error rate over time in accelerated tests of Examples and Comparative Examples. In the figure, A is an example, the mouth is without the first protective layer, C is without the second protective layer, and 2 is a! This is the case without a layer. (Spontaneous) 1 Indication of the case Patent Application No. 39289 of 1988 2 Name of the invention Magneto-optical recording medium 3 Relationship to the person making the amendment case Applicant (596) Mitsubishi Chemical Industries, Ltd. 4 Agent Address: Mitsubishi Chemical Industries, Ltd., 2-5-2 Marunouchi, Chiyoda-ku, Tokyo 100 (1) In the specification, page 4, line 12, ``TiO'' should be corrected to read ``rTio.'' (2) On page 12, lines 8 to 9, “Weight ratio 5:1
" is corrected to "weight ratio 1:5". that's all

Claims (1)

[Claims] (1) An interference layer made of a metal oxide on a substrate, a magneto-optical recording layer made of an alloy of a rare earth metal and a transition metal, a reflective layer made of Al or an alloy mainly composed of Al provided in contact with the recording layer, and a metal A magneto-optical recording medium comprising a first protective layer made of an oxide and a second protective layer made of an organic substance.