JPH083920B2 - Magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording medium used for optical recording.

(Prior art and its problems) Among optical memory elements, an erasable type memory capable of additionally recording and erasing is at the stage where the magneto-optical recording method is most practically used. As a recording layer of a magneto-optical recording medium, a rare earth / transition metal thin film is currently widely used in view of its comprehensive characteristics.

In the past, two such magneto-optical recording media were often attached via an adhesive layer. However, recently there is a strong demand for using the medium as a single plate due to the simplification of the medium and the magnetic field modulation method.

When the medium is used as a single plate, it is necessary to provide a protective layer on the medium in order to improve scratch resistance. Conventionally, a material having a high hardness, such as a silicone-based hard coating material, has been used as the protective layer.

However, such a high hardness protective layer generally has a very high stress and is apt to cause cracks and stress corrosion in the medium.

In addition, since the moisture vapor transmission rate is not sufficiently small, the corrosion of the medium due to water is often not negligible.

The present inventors have conducted diligent studies to overcome the above-mentioned drawbacks and found that a magneto-optical recording medium having both scratch resistance and corrosion resistance can be obtained by forming a protective layer with a film having two different properties. I found it.

(Structure of the invention) The gist of the present invention is at least a substrate, in a magneto-optical recording medium having a magneto-optical recording layer, 100% tensile stress specified by JIS K 6301 on the recording layer is 50 kgf / cm ² or less, and JIS Z
[0208] An intermediate protective layer having a moisture permeability of 20 g / m ² or less in 24 hours specified by 0208, and a surface protective layer having a hardness of H or more in a pencil hardness test according to JIS K 5400, which are sequentially laminated. It exists on a magnetic disk.

 Hereinafter, the present invention will be described in detail.

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

 The substrate generally has a thickness of about 1 to 2 mm.

Examples of the magneto-optical recording layer include TbFe, TbFeCo, and Tb.
Amorphous magnetic alloys of rare earths and transition metals such as Co and DyFeCo,
A polycrystalline perpendicular magnetization film such as MnBi or MnCuBi is used.
A single layer may be used as the magneto-optical recording layer, or GdTd
Two or more recording layers such as Fe / TbFe may be stacked.

In the present invention, the intermediate protective layer provided with the intermediate protective layer and the surface protective layer on the magneto-optical recording layer, the 100% tensile stress specified in JIS K 6301 is 50 kgf / cm ² or less, and JIS Z
A material having a moisture permeability specified by 0208 of 20 g / m ² or less for 24 hours is used. Preferably 100% tensile stress 30kgf specified above
/ cm ² or less, and moisture permeability of the provisions is 10 g / m ² or less of organic matter 24 hours gives good results.

As such an organic material, polyurethane using a hydrocarbon polyol is preferably adopted.

As the polyurethane, a hydrocarbon-based polyol having low hygroscopicity is used as a main component, and an isocyanate compound is NCO /
OH = 0.8 to 1.3, preferably NCO / OH = 0.9 to 1.1, preferably mixed and distributed in a distribution ratio so as to be cured.

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

By providing this intermediate protection method, the corrosion resistance of the medium is greatly improved. That is, since the internal stress is low, cracks and warpage of the medium do not occur, and the moisture permeability is low, so corrosion due to moisture can be strongly suppressed.

The film thickness of the intermediate protection method is 1 μm to 200 μm, preferably 3 μm
It is about m to 100 μm.

However, since such an intermediate protective layer is soft and easily scratched, and does not have the property as a surface protective layer, it is necessary to provide a surface protective layer on the intermediate layer.

As the surface protective layer, a compound having a hardness of H or more in a pencil hardness test according to JIS K 5400 is effective from the viewpoint of preventing scratches, and any compound can be used as long as this condition is satisfied, but spin coating is used because of the simplicity of the process. What can be applied by a coating method such as a coating method is preferable. Examples of the material for forming the surface protective layer that can be formed by a spin coating method or other ordinary coating methods include thermosetting resins such as silicone-based, acrylic-based, melamine-based, and epoxy-based resins, alkyltrialkoxysilane, and tetraalkoxysilane. Partial co-hydrolysate,
There are silicone-based hard coating agents in which colloidal silica is blended therein, and photopolymerizable photopolymers such as acrylates, photocrosslinkable photopolymers, and azide-based photopolymers.

The thickness of these surface protective layers is from 1 μm to 200 μm, preferably from 2 μm to 100 μm.

An interference layer may be provided between the substrate and the magneto-optical recording layer. This layer is used to reduce the noise and improve the C / N ratio by lowering the reflectance by using the light interference effect of the transparent film having a high refractive index. The interference layer may be a single layer film or a multilayer film. A metal oxide or a metal nitride is used as the interference layer. As the metal oxide, Al ₂ O ₃ , Ta ₂ O ₅ , SiO ₂ ,
Metal oxides such as SiO and TiO alone or a mixture thereof,
Alternatively, an Al-Ta-O composite oxide or the like may be used. Further, other elements such as Ti, Zr, W, Mo, and Yb may be used alone or in combination with Al and Ta to form an oxide. These metal oxides are dense and prevent invasion of moisture and oxygen from the outside, have high corrosion resistance and low reactivity with the reflective layer, and have excellent adhesion to the resin when a resin substrate is used as the substrate.

Examples of the metal nitride include silicon nitride and aluminum nitride. These metal nitrides are dense and prevent moisture and oxygen from entering from the outside, and silicon nitride is particularly preferable.

If the ratio of Si and N in silicon nitride is too large, the refractive index of the film will be lowered and the denseness will be poor. On the other hand, if N is too small, absorption is caused in the film and the carrier level is lowered.
Therefore, the ratio of Si to N is preferably a stoichiometric composition ratio (Si ₃ N ₄ ) or a state in which Si is slightly larger than that. Specifically, the atomic ratio of Si and N is preferably 0.75 to 1.0 in Si / N.
The refractive index of silicon nitride is 2.0 ≦ n ≦ 2.5 and 0 <K <0.2, where n ^* = n−iK (i represents an imaginary number) is the complex refractive index (n ^* ) measured at a wavelength of 633 nm. The range is good.

Tantalum oxide is particularly preferable as the interference layer.

The tantalum oxide interference layer has a smaller internal stress than a nitride interference layer, and the probability of cracking is much smaller.

The composition of tantalum oxide is preferably a composition close to the stoichiometric composition ratio (Ta ₂ O ₅ ). Excess oxygen will lead to oxidation of the recording layer. Further, when oxygen is insufficient, corrosion concentrates on the unoxidized portion and pinholes are easily generated.

The refractive index in the preferred oxidation state is 2.0 ≦ n ≦ when the complex refractive index measured at a wavelength of 633 nm is n ^* = n−iK.
2.2 and | K | <0.15.

The optimum film thickness of the interference layer varies depending on the refractive index, but is usually about 400Å to 1500Å, particularly about 500 to 1000Å.

In the case of a reflective type magneto-optical recording medium, a reflective layer is provided on the recording layer, that is, between the recording layer and the outermost organic protective layer. The reflective layer is generally considered to be a substance with high reflectance.
A thin film of u, Ag, Pt, Cu, Al or an alloy of Al is used.

In particular, Al or an alloy of Al is preferable, and Ta,
0.1 to 1 of at least one of Ti, Zr, Mo, Pt, V, Cr and Pb
The alloy added with about 5 atom%, preferably about 1-10 atom%, has a high reflectance, a low thermal conductivity and a high C / N ratio and good sensitivity.

When the reflective layer is provided, its thickness is usually 100 to 1000Å, preferably about 200 to 600Å. 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 protective layer made of a metal oxide or a metal nitride may be further provided on the reflective layer. As the metal oxide and the metal nitride, those used as the above-mentioned interference layer are used as they are.

In addition, when a metal oxide is used as the protective layer, the reflective layer may be oxidized, but the reflective layer of Al or Al alloy forms a strong oxide film on the surface and has a depth of tens of Å.
The above oxidation does not occur.

The thicker the protective layer is, the higher the protective ability is. However, the thicker the protective layer is, the larger the decrease in sensitivity is. Therefore, usually about 50Å to 500Å is suitable.

A physical vapor deposition method such as sputtering (PV method) is used for forming each layer such as an interference layer, a recording layer, a reflective layer, and a protective layer on a substrate.
D), chemical vapor deposition (CVD) such as plasma CVD, etc. are applied.

In order to form an interference layer, a magneto-optical recording layer, a reflection layer, a protective layer, etc. by PVD method, each layer is deposited on a substrate by electron beam evaporation or sputtering using a target having a predetermined composition. Is the usual method.

A method using ion plating is also conceivable.

If the deposition rate of the film is too fast, the film stress will increase, and if it is too slow, it will affect the productivity, so it is usually set at about 0.1Å / sec to 100Å / sec.

When tantalum oxide is used as the protective layer, an RF sputtering method using a Ta ₂ O ₅ target or the like, a DC or RF reactive sputtering method using Ar and O ₂ gas using a Ta target or the like, an electron beam evaporation method, or the like is preferable. Of these, the Ar target using a Ta target etc. can be controlled because the amount of oxygen can be controlled, the film formation rate is high, and the rise in the substrate temperature is small.
The DC reactive sputtering method using O ₂ and O ₂ gas is preferable.

The outermost organic protective layer is formed by spin coating,
It is possible to easily form a film by another ordinary coating method.

(Examples) Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Examples and Comparative Examples A polycarbonate substrate having a diameter of 130 mm was introduced into a sputtering apparatus, and first, the gas was evacuated to a pressure of 8 × 10 ^-7 torr and Ar at 20 sc.
cm, O ₂ was introduced at 5 sccm, and the pressure was adjusted to 0.8 Pa. In this state, a 4 inch φ Ta target was DC-sputtered at a power of 500 W, and an interference layer of tantalum oxide was formed at a rate of 4 ° / sec.

The refractive index of this film measured at 633 nm was n ^* = 2.1−0.03i.

After exhausting the chamber once, Ar gas 30sccm 0.3Pa
Introduced so that the pressure performs simultaneous sputtering of Tb target and Fe ₉₀ Co ₁₀ target _{Tb 22 (Fe 90 Co 10)} 78
Was formed on the interference layer by 300 mm. Furthermore, using an Al target with a Ta chip, sputter in Ar gas
_A 300 Å reflective layer made of an alloy of ₉₇ Ta ₃ was formed.

An intermediate protective layer made of polyurethane obtained as described below was provided on the reflective layer.

"Manufacture of ingredient A""PolytailHA" (trade name) (manufactured by Mitsubishi Kasei Co., Ltd.,
Number-average molecular weight: about 2000, hydroxyl group equivalent: 0.907 meq / g polyolefin polyol) 100 g, "Adeka Quadol" (trade name) (Asahi Denka Co., Ltd., 4-functional polyol, hydroxyl group equivalent 13.7 meq / g) 19.8 g, "paraffin-based process oil" (Kyodo Oil Co., Ltd., P-200) 110 g, "tin-based urethane catalyst" (MD Kasei Co., Ltd., UL-
22) 138 mg, which were uniformly mixed at 50 ° C. to obtain Component A. The viscosity was 1800 cps at 25 ° C.

"Production of Component B" 100 g of "Polyterre HA", 116 g of "paraffin-based process oil P-200", and these are uniformly mixed at room temperature in a separable flask. Then, 14.2 g of 2,4-tolylene diisocyanate was added and reacted at 80 ° C. for 6 hours to obtain a component B. Viscosity is 25 ℃
It was 3800 cps.

The liquid A and the liquid B thus prepared were mixed at a weight ratio of 1: 5, vacuum defoamed, and then applied to a disc, and the temperature was kept at 80 ° C. and 60 ° C.
It was cured for a minute to form a protective layer.

A press sheet was made using the liquid prepared in the same way and the physical properties were measured, and the 100% tensile stress in JIS K 6301 was 3 kg.
The f / cm ² tensile strength was 7 kgf / cm ² . In addition, JIS Z 0208
The water vapor transmission rate as defined in (4) was 5 g / m ² for 24 hours with a film having a thickness of 200 μm.

SEIKA BEAM VDAL 250 (manufactured by Dainichiseika Kogyo Co., Ltd., UV curable resin) is spin coated on this intermediate layer,
A surface protective layer was obtained by irradiating UV rays for 1 minute at 15 cm under a W / cm N type high pressure mercury lamp to cure it. The film thickness was 50 μm.

When the hardness of this surface protective layer was measured by the pencil hardness test specified in JIS K 5400, it was 3H.

When the disk thus prepared was subjected to an accelerated test for 2000 hours at 70 ° C. and 85% RH, no cracks or pinholes were generated.

Comparative Example 1 The structure up to the reflective layer was the same as that of the example, and the same surface protective layer as that of the example was directly provided on the reflective layer without using the intermediate protective layer.

When the disk thus prepared was subjected to an accelerated test for 2000 hours at 70 ° C. and 85% RH, cracks were generated on the entire surface.

(Comparative Example 2) After forming the reflective layer in the same manner as in the example, "Loctite 350" (manufactured by Nippon Loctite Co., Ltd., UV curable resin) was spin-coated, and 80 W / cmN type high pressure mercury lamp F was used.
It was irradiated with ultraviolet rays at a position of 15 cm for 1 minute to cure it to form an intermediate protective layer. The film thickness was 50 μm.

When a sheet was made with "Loctite 350" and subjected to a tensile test, it was a hard resin that did not stretch to 100%.

The same surface protective layer as in Example 1 was formed on this intermediate layer.

When the disk thus produced was subjected to an accelerated test for 2000 hours under the conditions of 70 ° C. and 85% RH, cracks were generated on the entire surface.

(Effects of the Invention) As described above, a medium excellent in weather resistance and scratch resistance is obtained by stacking a low stress, low moisture permeability intermediate layer and a high hardness surface protective layer as a protective layer of a magneto-optical recording medium. Can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-85646 (JP, A) JP-A-62-245548 (JP, A) JP-A-63-20745 (JP, A) JP-A-1- 287848 (JP, A) JP-A-1-273247 (JP, A)

Claims (1)

[Claims] 1. In a magneto-optical recording medium having at least a substrate and a magneto-optical recording layer, the 100% tensile stress defined by JIS K 6301 on the recording layer is 50 kgf / cm ² or less and JIS Z 0208.
The magneto-optical property is characterized in that an intermediate protective layer having a water vapor transmission rate of 20 g / m ² or less in 24 hours specified in 4 and a surface protective layer having a hardness of H or more in a pencil hardness test according to JIS K 5400 are sequentially laminated. recoding media.