JPH0721885B2 - Magneto-optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. 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.

As the recording medium of the prior art magneto-optical memory, materials such as MnBi, MnAlGe, MnSb, MnCuBi, GdFe, TbFe, GdCo, PtCo, TbCo, TbFeCo, GdFeCo, TbFeO ₃ , GdIG, GdTbFe, GdTbFeCoBi, CoFe ₂ O ₄ are used. 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 vapor deposition method or a sputtering method. The characteristics common to these magneto-optical recording media are that the easy axis of magnetization is perpendicular to the film surface, and that the Kerr effect and the Faraday effect are large.

Utilizing this property, the following methods are available as magneto-optical recording methods.

First, the entire film is magnetized to "0", that is, uniformly magnetized (this is called erase). Next, a laser beam is applied to the portion where "1" is to be recorded. When the laser beam is irradiated, the temperature rises, and when it approaches the Curie point, and when it further exceeds the Curie point, the coercive force is increased.
Hc approaches 0. Then, if the laser beam is turned off and returned to room temperature, the magnetization is reversed by the energy of the demagnetizing field,
Furthermore, when a laser beam is applied, an external magnetic field is applied in the direction opposite to the initial direction to return to room temperature, and the magnetization is reversed,
The signal "1" is recorded.

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

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

The first requirement for such a medium is that the Curie point is about 100 to 200 ° C and the compensation point is near room temperature.

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

Thirdly, it is possible to obtain a magnetically and mechanically uniform film over a relatively large area without using a method such as high temperature film formation or long time film formation.

In response to such demands, in recent years, amorphous perpendicular magnetic thin films of rare earth-transition metals have attracted great attention among the above materials.

However, in such a magneto-optical recording medium composed of a rare earth-transition metal amorphous thin film, when the magnetic thin film layer is stored in contact with the atmosphere, the rare earth is selectively corroded or oxidized by oxygen or water in the atmosphere. As a result, it becomes impossible to record and reproduce information.

Therefore, in general, much research has been conducted on a magnetic thin film layer having a structure in which a protective layer is provided on the surface thereof.

Conventionally, as such a moisture-proof protective layer, an attempt has been made to provide an inorganic vacuum-deposited film such as silicon monoxide, silicon dioxide aluminum nitride, silicon nitride, etc. (JP-A-58-80142). Has been done.

Of these protective layers, for example, an inorganic protective layer such as SiO 2 is formed by a sputtering method, a vapor deposition method, or the like.

However, according to these methods, it is difficult to form a film that is evenly and uniformly covered, and a protective layer having sufficient moisture resistance cannot be obtained. Therefore, deterioration over time of the magnetic thin film layer of the magneto-optical recording medium is not improved.

In addition, even a coating film protective layer of a room temperature curable resin does not have sufficient moisture resistance, and it takes a long time to cure, and there is an influence of moisture and oxygen permeation during that time, which promotes deterioration.

II Object of the invention The object of the present invention is to prevent deterioration of the magnetic thin film layer even in a high humidity atmosphere, excellent moisture resistance, less deterioration of C / N, and high initial C / N magneto-optical recording medium. To provide.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, the present invention has an amorphous perpendicular magnetic thin film layer of a rare earth-transition metal on a substrate via an intermediate layer, and further has a protective layer as an outermost layer in contact with the atmosphere on the magnetic thin film layer. The protective layer contains a radiation-curable compound having a molecular weight of 200 to 3,000 and is a coating film containing no radiation-curable unsaturated double bond-free thermoplastic resin and cured by ultraviolet rays. The magneto-optical recording medium has a thickness of 0.1 to 30 μm, and the intermediate layer has a refractive index of 2 or more.

IV Specific Configuration of the Invention The magneto-optical recording medium of the present invention is, as shown in FIG. 1 as an example, provided with an intermediate layer 21 on a substrate 11 made of glass, plastic or the like, and further on the magneto-optical recording medium. Magnetic thin film layer 31 for
Have.

This magnetic thin film layer is for magnetically recording information by a modulated heat beam or a modulated magnetic field, and is for magnetically-optically converting recorded information for reproduction.
A so-called perpendicular magnetization film is used.

As such a magnetic thin film layer, an alloy of a rare earth metal and a transition metal is formed by sputtering, vapor deposition or the like to have an ordinary thickness as an amorphous film.

Although there are various rare earth metals and transition metals, Gd and Tb are particularly preferable as the former and Fe and Co are preferable as the latter.

And as a preferable example thereof, GdFe, TbFe, TbFeCo, GdFeC
o, GdTbFe, etc.

Furthermore, a protective layer 41 is formed on the magnetic thin film layer.

The present invention may be formed as shown in FIG. 1, or the magnetic thin film layers may be opposed to each other with the magnetic thin film layers facing inside, and the magnetic thin film layers may be bonded using an adhesive or the like to perform writing from the back surface side of the substrate. .

Further, the substrate is usually made of resin and made of olefin resin such as acrylic resin, polycarbonate resin, epoxy resin, polymethylpentene, or the like, but it may be glass or the like.

The refractive index nb of such a substrate is usually about 1.45 to 1.58.

Since recording is preferably performed through the substrate,
86 to 92% transmittance for writing or reading light
The degree.

The substrate is usually in the shape of a disk and has a thickness of about 1.2 to 1.5 mm, but it may be a tape, a drum, or the like.

The protective layer 41 of the present invention is formed by curing a coating film of a radiation curable compound with ultraviolet rays, and is provided on the magnetic recording layer 31.

The radiation-curable compound in this case is a compound having a molecular weight of 200 to 3,000.

Examples of the radiation-curable compound to be used include acrylic double bonds having unsaturated double bonds exhibiting radical polymerizability, acrylic double bonds such as ester compounds thereof, and allyl double bonds such as diallyl phthalate. , Maleic acid, maleic acid derivatives, etc., selected from compounds such as polymers, oligomers, monomers, etc. containing or introduced in the molecule of a thermoplastic resin a group that crosslinks or is polymerized and dried by irradiation of radiation such as unsaturated bonds. Can be used.

Other usable polymer components include acrylic acid, methacrylic acid, acrylamide, etc. as monomers, and these can be selected and used.

As the polymer having a double bond, various polyesters, polyols, polyurethanes and the like can be modified with a compound having an acrylic double bond. Further, if necessary, a polyhydric alcohol and a polycarboxylic acid may be mixed to obtain various molecular weights. Therefore, it can be selected from these and used.

The radiation-curable compound is a part of the above, and other compounds can be used as long as they have a molecular weight of 200 to 3,000. These may be used alone or in combination. When used as a mixture, they can be used in combination with a radiation-curable compound having a molecular weight outside the above range. However, a thermoplastic resin having no radiation-curable unsaturated double bond is not used. This is because the moisture resistance is reduced.

In any case, the radiation-curable compound having a molecular weight of 200 to 3,000 used in the present invention is (A) a compound having a molecular weight of 200 to 3,000 and having at least one unsaturated double bond curable by radiation. Therefore, the number of unsaturated double bonds in the compound (A) is 1 or more, preferably 3 or more per molecule.

Although (A) can be used alone or in the form of a mixture, the moisture resistance can be improved by using (A) in the present invention.

When used as a mixture of (A) and a compound other than this, as a compound that can be used in combination with (A), (B) a compound having two or more unsaturated double bonds curable by radiation and having a molecular weight of 5,000 to There are 100,000 plastic-like compounds. In the case of the mixture of (A) and (B), the combination may be such that (A) is used in a ratio of 1/7 to 2 parts by weight with respect to (B). The unsaturated double bond in the compound (B) is 2 or more, preferably 5 or more per molecule.

Examples of the compound (A) having a radiation-curable unsaturated double bond used in the present invention include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1,
6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, polyfunctional oligoester acrylate (Aronix M-7100, M-5400, 5500, 5700 etc., Toa Gosei) ), An acrylic modified urethane elastomer (Nipporan 4040), or those into which a functional group such as COOH is introduced.

The plastic-like compound (B) used in the present invention is such that a radical is generated by radiation and a crosslinked structure is generated.
It contains two or more unsaturated double bonds in the molecular chain,
It can also be obtained by radiation-sensitively modifying a thermoplastic resin.

Specific examples of the radiation curable resin include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having a radical polymerizable property, and an aryl double bond such as diallyl phthalate. It is a resin containing or introducing into a molecule of a thermoplastic resin a group capable of being crosslinked or polymerized by irradiation with radiation, such as a heavy bond, an unsaturated bond such as maleic acid or a maleic acid derivative. Other compounds having an unsaturated double bond which undergoes cross-linking polymerization upon irradiation with radiation and has a molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000 can be used.

Resins containing a group capable of being crosslinked or polymerized by irradiation with radiation in the molecule of the thermoplastic resin include the following unsaturated polyester resins.

A polyester compound having a radiation-curable unsaturated double bond in the molecular chain, for example, a saturated polyester resin (2) having a polybasic acid and an ester bond of a polyhydric alcohol, wherein a part of the polybasic acid is maleic acid. And the unsaturated polyester resin containing a radiation-curable unsaturated double bond. The radiation-curable unsaturated polyester resin is prepared by adding maleic acid, fumaric acid and the like to one or more polybasic acid components and one or more polyhydric alcohol components, and then in a conventional method, that is, in the presence of a catalyst, 180 to 200 ° C. In a nitrogen atmosphere, after dehydration or dealcoholization reaction, raise the temperature to 240-280 ° C and
It can be obtained by a condensation reaction under a reduced pressure of 5 to 1 mmHg.
The content of maleic acid, fumaric acid, etc. is 1-40 mol% in the acid component, preferably cross-linking during production, radiation curability, etc.
It is 10 to 30 mol%.

Examples of the thermoplastic resin that can be modified into a radiation curable resin include the following.

(1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, such as UCC V
ROH, VYNC, VYBGX, VERR, VYES, VMCA, VAGH, etc. are mentioned, and by the method described below, an acrylic double bond, a maleic acid double bond, an allyl double bond is introduced, Sensitive degeneration.

(2) Saturated polyester resin Saturated polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2 propylene glycol, 1 , 3
Obtained by ester linkage with polyhydric alcohols such as butanediol, dipropylene glycol, 1,4 butanediol, 1,6 hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol, 1,4 cyclohexanedimethanol Examples include saturated polyester resins or resins obtained by modifying these polyester resins with SO ₃ Na or the like (for example, Vylon 53S), and these are similarly subjected to radiation-sensitive modification.

(3) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin and copolymers of these components,
The hydroxyl groups contained in these resins are subjected to radiation-sensitive modification by the method described below.

(4) Epoxy resin, phenoxy resin Epoxy resin obtained by reaction of bisphenol A with epichlorohydrin, methyl epichlorohydrin, for example, Shell Chemical (Epicoat 152, 154, 828, 1001, 100
4, 1007), made by Dow Chemical (DEN431, DER732, DER51
1, DER331), made by Dainippon Ink (Epiclon 400, 80
0), a phenoxy resin (PKHA, PKHC, PKHH) manufactured by UCC, which is a resin with a high degree of polymerization of the above epoxy, a copolymer of brominated bisphenol A and epichlorohydrin, manufactured by Dainippon Ink and Chemicals (Epiclon 145, 152, 153, 1120, etc., and those containing a carboxylic acid group are also included. Radiation-sensitive modification is carried out using the epoxy groups contained in these resins.

(5) Fibrin derivatives Various kinds are used, but particularly effective ones are nitrification cotton, cellulose acetobutyrate, ethyl cellulose,
Butyl cellulose, acetyl cellulose and the like are preferable. Utilizing the hydroxyl groups in the resin, radiation sensitive modification is performed by the method described below.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, An acrylic resin containing at least one of a hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component is also effective.

A photopolymerization sensitizer is added to such a radiation-curable compound.

The photopolymerization sensitizer may be any conventionally known one, for example, benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, benzoin series such as α-chlordeoxybenzoin, benzophenone, acetophenone, bisdialkylaminobenzophenone, etc. Examples thereof include ketones, quinones such as acetoraquinone and phenanthraquinone, and sulfides such as benzyl disulfide and tetramethylthiuram monosulfide. The photopolymerization sensitizer is 0.1 to 10% by weight based on the resin solid content.
The range of is desirable.

The thickness of such a protective layer is 0.1 to 30 μm, more preferably 1 to 10 μm.

If the film thickness is less than 0.1 μm, a uniform film cannot be formed, the moisture-proof effect in a high humidity atmosphere is not sufficient, and the durability of the magnetic thin film layer 31 is not improved. On the other hand, when it exceeds 30 μm, the recording medium warps due to shrinkage accompanying curing of the resin film, which is not practical.

Such a coating film may be generally formed by various known methods such as spinner coating, gravure coating, and spray coating. The conditions for forming the coating film at this time may be appropriately determined in consideration of the viscosity of the polymer of the coating film composition, the state of the substrate surface, the target coating film thickness, and the like.

Further, the intermediate layer 21 is provided between the substrate 11 and the magnetic thin film layer 31 as described above.

This intermediate layer is made of AlN, Si ₃ N ₄ , ZnS or the like. And
The refractive index of this intermediate layer is 2 or more. Further, the upper limit value of this refractive index is necessarily determined by the substance that currently exists.

The setting range of the refractive index is a range suitable for obtaining a broadening effect by irradiating the reading light and causing multiple interference of the reading light in the intermediate layer when reading the signal in the magnetic thin film layer. .

Therefore, with the refractive index in this range, the initial C / N ratio can be further improved.

Further, when the refractive index of this intermediate layer is less than 2, the above-mentioned width-increasing effect cannot be expected, which is not practically suitable. Furthermore, this intermediate layer also has a moisture-proof effect from the substrate to the magnetic thin film layer, especially in the case of a resin substrate.

This intermediate layer is formed by a method such as a vapor deposition method or a sputtering method.

The film thickness d of the intermediate layer is set so that d = λ / 4n, where λ is the laser wavelength used and n is the refractive index.

V. Effect of the Invention The magneto-optical recording medium of the present invention has a magnetic thin film layer on a substrate via an intermediate layer having a refractive index of 2 or more, and further on this,
The outermost layer is a protective layer that is a radiation-curable compound with a thickness of 1 to 30 μm that is cured by ultraviolet light, so its moisture resistance is improved, and there is little deterioration with time such as C / N even when used at high temperature and high humidity for a long time . The initial C / N is also high.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention.

〔Example〕

An intermediate layer made of ZnS was formed on the substrate made of PMMA having a diameter of 20 cm by high frequency magnetron sputtering.

The refractive index of this intermediate layer was measured by ellipsometry and was found to be 2.35. The film thickness was 900Å.

On this intermediate layer, an alloy thin film made of TbFeCo was deposited by sputtering to have a thickness of 0.1 μm to form a magnetic thin film layer.

The target used was an Fe target on which Tb and Co chips were placed.

On this magnetic thin film layer, a coating composition comprising 100 parts by weight of a polyfunctional oligoester acrylate (Aronix M-8030, molecular weight 200 to 3,000) and 5 parts by weight of a photosensitizer (Vicure 55) was applied by spinner coating. Then, 120 W / cm of ultraviolet rays were irradiated for 15 seconds to crosslink and cure (protective layer 1). The film thickness at this time was 10 μm (Sample No. 1).

Then, samples having the same material and thickness of the substrate and the same material and thickness of the magnetic thin film layer and different materials of the intermediate layer and the protective layer were prepared (Sample Nos. 2 and 3).

The protective layer 2 is formed by applying a coating composition using a bifunctional oligoester acrylate (Aronix M-6500, molecular weight 200 to 3,000) and crosslinking and curing the same under the same conditions as the protective layer 1.

Further, as a comparative example, a protective layer was produced by vapor deposition of SiO ₂ (Sample No. 4).

In addition, as a comparative example, sample No. 5 was prepared using protective layer 3 having the same structure as protective layer 1 except that N-vinylpyrrolidone (Aronix M-150, molecular weight 111) was used in sample No. 1. Further, Sample No. 6 using the protective layer 4 having the same structure as the protective layer 1 except that urethane acrylate (Aronix M-1200, molecular weight 5,000) was used was prepared.

Further, as comparative examples, in sample No. 1, sample No. 7 having a protective layer thickness of 0.01 μm and sample No. 8 having a thickness of 35 μm were prepared.

In addition, as a comparative example, in Sample Nos. 1 and 2, vinyl chloride-vinyl acetate copolymer (vinyl chloride-vinyl acetate) was used as the polyfunctional oligoester acrylate as a thermoplastic resin having no radiation-curable unsaturated double bond. A sample was prepared by changing the amount of the protective layer used (50:50) (Sample N
o.9, 10). In addition, in the sample No. 9, the protective layer 5 used in combination as described above in the composition of the protective layer 1 is
In No. 0, the protective layer 6 is used in combination with the composition of the protective layer 2 as described above.

The C / N ratios of the above samples were measured at the initial stage and after storage at 60 ° C and 90% RH for 300 hours.

The results are shown in Table 1. Table 1 also shows the molecular weights of the radiation-curable compounds.

From the results shown in Table 1, the effect of the present invention is clear. In samples No. 9 and 10, vinyl chloride-
When a thermoplastic resin having no radiation-curable unsaturated double bond, such as polyvinyl butyral or phenoxy resin, was used instead of the vinyl acetate copolymer,
Similar to Nos. 9 and 10, the C / N ratio after storage deteriorated by 10 dB or more.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. Explanation of symbols 11 …… Substrate, 21 …… Intermediate layer, 31 …… Magnetic thin film layer, 41 …… Protective layer

Claims (1)

[Claims] 1. A rare earth-transition metal amorphous perpendicular magnetic thin film layer is provided on a substrate via an intermediate layer, and a protective layer is provided on the magnetic thin film layer as an outermost layer in contact with the atmosphere. The protective layer contains a radiation-curable compound having a molecular weight of 200 to 3,000, and a coating film containing no radiation-curable unsaturated double bond-free thermoplastic resin is cured by ultraviolet rays. Is 0.1 to 30 μm, and the refractive index of the intermediate layer is 2 or more.