JPS6240651A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a magnetic film layer even in high- humidity atmosphere and to obtain a photomagnetic recording medium having excellent moistureproofness by providing a coating layer which thoroughly covers a this amorphous vertical magnetic film layer of a rare earth-transition metal formed via an intermediate layer on a substrate. CONSTITUTION:The magnetic alloy consisting of the rare earth-transition metal (for example, TbFeCo) is sputtered to form the thin amorphous vertical magnetic film layer 4 via the intermediate layer 3 consisting of Si3N4, etc. on the substrate 2 consisting of PMMA, etc. The coating layer 5 is provided to thoroughly cover the film layer 4. The material to be used for the layer 5 is not limited if the material has relatively low misture permeability, for which inorg. films of SiO, SiO2, etc. and various cured org. films are usable. Since the coating layer 5 exists not only on the top surface of the film layer 4 but also on the side faces thereof, the moistureproofness is improved and the photomagnetic recording medium 1 having the excellent moistureproofness even in the high- humidity atmosphere is obtd.

Description

Detailed Description of the Invention (1) Background Technical Field of the Invention The present invention relates to a magneto-optical recording medium that records and reproduces information using heat and light such as laser light.

prior art As a recording medium for magneto-optical memory, MnB i, MnA1Ge, MnS b.

MnCuB i, GdFe, TbFe.

GdCo, PtCo, TbCo.

TbFeCo, GdFeCo.

TbFeO3, GdIG, GdTbFe.

Materials such as GdTbFeCoBt and CoFe204 are known. These are formed as a thin film on a transparent substrate such as plastic or glass by a method such as a vacuum evaporation method or a sputtering method. These lights? The characteristics common to all IA recording media are:

The axis of easy magnetization is perpendicular to the film surface, and the Kerr effect and Faraday effect are large.

There is one method of magneto-optical recording that takes advantage of this property, for example, the following method.

First, the entire film is magnetized to 0'', that is, uniformly (this is called erasing), and then a laser beam is irradiated to the part where you want to record ``1''. The temperature of the area irradiated with the laser beam rises, and when it approaches the Curie point, and when it exceeds the Curie point, the coercive force He approaches O. Then, when the laser beam is turned off and the temperature is returned to room temperature, the reversal occurs. The magnetization is reversed by the energy of the magnetic field, and furthermore, when irradiated with a laser beam,
When an external magnetic field is applied in the opposite direction to the initial one and the temperature is returned to room temperature,
The magnetization is reversed and a signal '1' is recorded.

Furthermore, since the initial state of recording is "0", the portion that is not irradiated with the laser beam remains "on".

Reading of a recorded magneto-optical memory is similarly performed by using a laser beam and by rotating the plane of polarization of the reflected light depending on the direction of magnetization of the laser beam irradiation light, that is, by utilizing the magneto-optic effect.

The following requirements are required for such a medium: First, the temperature of one curie point is about 100 to 200°C, and the compensation point is around room temperature.

Second, defects such as grain boundaries that cause noise are relatively small.

Thirdly, a magnetically and mechanically uniform film can be obtained over a relatively large area without using methods such as high-temperature film formation or long-time film formation.

In response to these demands, among the above materials.

In recent years, amorphous perpendicular magnetic thin films of rare earth-transition metals have attracted much attention.

However, in magneto-optical recording media made of such rare earth-transition metal amorphous thin films, if the magnetic thin film layer is stored in contact with the atmosphere, the rare earths may be selectively corroded or oxidized by oxygen and water in the atmosphere. This makes it impossible to record or reproduce information.

Therefore, in general, many researches have been made on devices having a structure in which a protective layer is provided on the surface of the magnetic thin film layer.

Conventionally, as such a moisture-proof protective layer, attempts have been made to provide inorganic vacuum-deposited films or resin films of silicon oxide, silicon dioxide, aluminum nitride, silicon nitride, etc.
However, these protective layers do not have sufficient moisture resistance and do not significantly improve the aging deterioration of the magnetic thin film layer of the magneto-optical recording medium.

II. OBJECTS OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium with excellent moisture resistance, in which deterioration of the magnetic thin film layer is prevented even in a high humidity atmosphere.

■Disclosure of invention Such objects are achieved by the present invention as described below.

That is, the present invention provides a magneto-optical recording medium having an amorphous perpendicular magnetic thin film layer of a rare earth-transition metal on one surface of a substrate via an intermediate layer, in which a coating layer is provided to completely cover the magnetic thin film layer. This is a magneto-optical recording medium characterized by a layered structure.

(2) Specific Structure of the Invention A preferred embodiment of the magneto-optical recording medium of the present invention is shown in FIG.

In FIG. 1, a magnetic recording medium 1 of the present invention has an amorphous perpendicular magnetic thin film layer 4 of rare earth-transition metal on one surface of a substrate 2 with an intermediate layer 3 interposed therebetween. A covering layer 5 is provided on the top and side surfaces, and the magnetic thin film layer 4 is completely covered by the covering layer 5.

In the magnetic thin film layer 4 of the present invention, information is magnetically recorded using a modulated heat beam or a modulated magnetic field, and the recorded information is reproduced by magneto-optical conversion.

The magnetic thin film layer 4 is preferably an amorphous film formed to a normal thickness by sputtering, vapor deposition, or the like using an alloy of rare earth metals and transition metals.

There are various rare earth metals and transition metals, but the former include Gd and Tb, and the latter includes Fe.
, Go are preferred.

Suitable examples include GdFe, TbFe, T
Examples include bFeCo, GdFeCo, and GdTbFe.

The substrate 2 on which such a magnetic thin film layer 4 is formed via the intermediate layer 3 may be made of resin such as acrylic resin, polycarbonate resin, epoxy resin, or olefin resin such as polymethylpentene, or glass. preferable.

The refractive index nb of such a substrate 2 is usually 1.45 to 1.45.
It is about 58.

Note that since it is preferable to perform recording through the substrate 2, the transmittance for writing light or reading light is 86%.
The above shall apply.

In addition, the board is usually disk-shaped and has a length of 1.2 to 1.5 m.
The thickness should be about m.

Tracking grooves may be formed on the surface of such a disk-shaped substrate on which the magnetic thin N layer is formed.

The depth of the groove is approximately I/8n, especially I/7n to I/12n (where n is the refractive index of the substrate), and the width of the groove is approximately the track width. Ru.

It is preferable that writing light and reading light are irradiated from the back side of the substrate, using the magnetic thin film layer located in the recessed part of the groove as a recording track part.

With this configuration, the writing sensitivity and the reading S/N ratio are improved, and the tracking control signal is also increased.

We also use tape as another form of substrate.

It may also be a drum or the like.

A coating as shown in FIG. A layer 5 is provided.

Such a coating layer 5 is provided to provide moisture resistance from the top or side surfaces of the magnetic thin film layer 4.

If the coating layer 5 has a relatively low moisture permeability,
There is no particular restriction, and for example, - a non-molecular film formed by depositing silicon oxide, silicon dioxide, aluminum nitride, silicon nitride, etc. by various vacuum film-forming methods, or a coating film containing a radiation-curable compound can be coated with ultraviolet rays or electron beams. Various organic films such as those cured by wire or the like may be used.

Among these, it is preferable to use a cured film of a radiation-curable compound as the coating layer 5.

The radiation-curable compounds to be used include acrylic acid, methacrylic acid, and acrylic double bonds such as ester compounds thereof, which have unsaturated double bonds that are sensitive to ionization energy and exhibit radical polymerizability, and diallylphthalate. Seven polymers, oligomers, and polymers containing or introducing into the molecule groups that can be crosslinked or polymerized and dried by radiation irradiation, such as allylic double bonds, maleic acid, unsaturated double bonds such as maleic acid derivatives, etc. be able to.

As a radiation-curable monomer, a compound with a molecular weight of less than 2000 is used, and as an oligomer, a compound with a molecular weight of 12ooo-too
oo is used.

These include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1.8-hexane glycol diacrylate, 1.8-hexane glycol dimethacrylate, etc., but particularly preferred ones are as pentaerythritol tetraacrylate (
methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate (Aronix M-7100, M-5400, M-5500, M-5700
, M-6250, M-6500, M-8030, M-8
060, M-8100, etc. (Toagosei), urethane elastomers with acrylic modified products of Tuboran 4040), or those into which functional groups such as C0OH have been introduced, and phenol ethylene oxide adducts such as 7-acrylate (
methacrylate), an acrylic group (methacrylic group) or ε in the pentaerythritol condensed ring represented by the general formula below.
-Caprolactone-A compound with an acrylic group, 1) (CH2=CHC0OH2) 3-CCH2
0H (special acrylate A) 2) (CH2=CHC00H2)3-CCH2C
H3 (special acrylate B) 3) (CH2=CHOC(OC3Ha)n-CC
H2) 3-CCH2CH3 (special acrylate C) (special acrylate D) (special acrylate E) A compound where m = 1, a = 2, b = 4 (hereinafter referred to as special pentaerythritol condensate A), m = 1, a=3. Compound where b=3 (hereinafter referred to as special pentaerythritol condensate B), m=1, a=6, b=
o compound (hereinafter referred to as special pentaerythritol condensate C
), m = 2, a = = 6, b = o (hereinafter referred to as
Examples include special pentaerythritol condensates (referred to as special pentaerythritol condensates), and special acrylates represented by the general formula below.

8) CH2=CHCOO-(CH2CH20)4-
CCH2CH3 (special acrylate H) (special acrylate I) (special acrylate) J) A-(X-Y-)-X-A )
A+M-N-)-M-An A: acrino solid, M: dihydric alcohol N: dibasic acid (special acrylate L) In addition, as radiation-curable oligomers, polyfunctional oligoester acrylates represented by the following general formula and Examples include acrylic modified urethane elastomers, and those into which functional groups such as C0OH are introduced.

Wiping medium R1, R2: alkyl, n: regular ω In addition, a radiation-curable compound obtained by radiation-sensitizing a thermoplastic resin may be used.

Specific examples of such radiation-curable resins include acrylic acid, methacrylic acid, or acrylic double bonds such as ester compounds thereof, and diallylphthalate, which exhibits an unsaturated double bond that has radical polymerizability. It is a thermoplastic resin in which groups that can be crosslinked or polymerized by radiation irradiation, such as allylic double bonds and unsaturated bonds such as maleic acid and maleic acid derivatives, are contained or introduced into the molecule of the thermoplastic resin.

Examples of thermoplastic resins that can be modified into radiation-curable resins include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, m-fiber derivatives, and the like.

Other resins that can be used for radiation sensitivity modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins, and derivatives (PVP
Also effective are acrylic resins containing at least one of olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, hydroxyl group-containing acrylic esters, and methacrylic esters as polymerization components.

The thickness of the coating film 5 of such a radiation-curable compound is 0.
1 to 30 gm, more preferably 1 to 10 lm.

If the film thickness is less than 0.1 pm, a uniform thickness cannot be formed, the moisture-proofing effect in a humid atmosphere will not be sufficient, and the durability of the magnetic thin film layer 4 will not be improved. Also, 30p
If it exceeds m, the shrinkage that accompanies the curing of the resin film causes warping of the recording medium and cracks in the protective film, making it unsuitable for practical use.

Such a coating film can usually be deposited using a combination of various known methods such as spinner coating, gravure coating, spray coating, and dipping. It should be determined appropriately by considering the viscosity of the mixture, the condition of the substrate surface, the desired coating thickness, etc.1
,X.

In order to cure such a coating film to form the coating film 5, the coating film may be irradiated with radiation such as an electron beam or an ultraviolet ray.

When using an electron beam, it is convenient to use a radiation accelerator with an accelerated fi pressure of 100 to 750 KV, preferably 150 to 300 KV, and to irradiate at an absorbed dose of 0.5 to 20 Megaland. be.

On the other hand, when ultraviolet rays are used, a photopolymerizable sensitizer is usually added to the radiation-curable compound as described above.

The photopolymerization sensitizer may be a conventionally known one, such as benzoin-based ones such as benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, α-glordeoxybenzoin, benzophenone, acetophenone, bisdialkylaminobenzophenone, etc. Examples include ketones, quinones such as acedraquinone and phenanthraquinone, and sulfites such as benzyl disulfide and tetramethylthiuram monosulfite.

The photopolymerization sensitizer is 0.1 to 10 times ψ based on the resin solid content.
A range of % is desirable.

In order to cure a coating film containing such a photopolymerizable sensitizer and a radiation-curable compound using ultraviolet rays, various known methods may be used.

For example, an ultraviolet light bulb such as a xenon emitter tube or a wood emitter tube may be used.

The coating layer 5 of the present invention may be one of the above-mentioned inorganic film compositions instead of using the radiation-curable compound as described above.

Further, the covering layer 5 does not necessarily have to be one layer, and may be formed as a laminate of two layers (number of layers - L) of different compositions as necessary.

As shown in FIG. 1, such a covering layer 5 is provided so as to cover the side surfaces of the magnetic thin film layer 4 1- and the magnetic thin film layer 4 and the intermediate layer 3, and the covering layer 5 covers the substrate 2. It is coated on the outer periphery and the inner periphery.

As described above, there is an intermediate layer 3 between the substrate 2 and the magnetic thin film layer 4, and this intermediate layer 3 is usually formed of one layer as shown in FIG.

If necessary, it may be a laminate with two layers.

There are no particular restrictions on this kind of intermediate layer material.
S i02 , S No, AuN, Si3 N4 , Z
nS etc. are suitable.

Further, one or two various protective layers may be provided between the magnetic thin film layer 4 and the covering layer 5.

The present invention may be formed, for example, as shown in FIG. 1, or by placing two substrates facing each other with their respective magnetic thin film layers inside and bonding them together using an adhesive or the like, so that the back side of the substrate It may also be a so-called double-sided recording medium in which fortune-telling is performed from the side.

Note that the entire outer surface of the medium of the present invention on which the above-mentioned coating has been applied may be further coated with a new protective film so as to be completely sealed.

■ Effects of the Invention The magneto-optical recording medium of the present invention has a coating layer not only on the top surface of the magnetic thin film layer, but also on the top surface and side surfaces, as in the conventional case.
Since the magnetic thin film layer is protected, moisture resistance is improved, and there is little deterioration over time even when used for long periods in high temperature and high humidity environments.

(2) Specific Examples of the Invention The present invention will be described in more detail below with reference to Examples.

[Example 1] An intermediate layer made of Si3N4 was deposited to a thickness of 900 mm on a substrate made of PMMA with a diameter of 20 cm and a thickness of 1.2 mm by high-frequency magnetron sputtering.

On this intermediate layer, a thin alloy film made of TbFeCo was formed by sputtering to a thickness of 0.1 gm to form a magnetic thin film layer.

Note that the target used was an Fe target with Tb and Co chips on top.

100% polyfunctional oligoester acrylate (Aronix M-8030) so as to completely cover this magnetic thin film layer.
A coating composition consisting of a heavy coating and 5 parts by weight of a photosensitizer (PiCure 55) was applied by spinner coating and dipping, and then 80 W/cm ultraviolet rays were applied for 15 seconds.
It was irradiated with EC to crosslink and cure to form a coating layer.

The thickness of the coating layer at this time was 10] (sample N
o, 1).

[Comparative example 1] The coating layer provided in Example 1 was not provided.

The rest was the same as in Example 1 (sample N
o, 2).

[Comparative Example 2] The coating layer provided in Example 1 was provided only on the upper surface of the magnetic thin film layer, and was not provided on the side edges thereof.

The rest was the same as in Example 1 (sample N
o, 3).

Initial C/N ratio and 60℃, 9
After storing each sample in an atmosphere of 0% RH for 300 hours with only the substrate side exposed, the amount of change in the C/N ratio was measured under the following conditions.

Rotation speed 4 al / sec
Carrier frequency 500KHz resolution
30KHz recording power (830nm)
3-4mW reproduction power (830nm)
The 1 mW results are shown in Table 1.

Table 1 60℃, 90%RH No. Initial After storage for 300 hours 1
52.0 51.52 (comparison)
51.5 Due to the occurrence of many pinholes within 40 hours, recording and reproduction were not possible due to cracks occurring from the outer periphery within 60 hours. From the results shown in Table 1, it is clear that the present invention The effect.

It's obvious.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing one example of the present invention. Explanation of symbols 1... magneto-optical recording medium, 2... substrate, 3...
intermediate layer, 4... magnetic thin film layer, 5... covering layer,

Claims (1)

[Claims] (1) In a magneto-optical recording medium having an amorphous perpendicular magnetic thin film layer of a rare earth-transition metal, a coating layer is formed on one surface of the substrate via an intermediate layer so as to completely cover the magnetic thin film layer. A magneto-optical recording medium characterized by: