JPH0766581B2 - 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.

Prior art and its problems As recording media for magneto-optical memory, MnBi, MnAlGe, MnSb, MnCuBi, GdFe, TbFe, GdCo, PtCo, TbCo, TbFeCo, GdFeCo, TbFeO ₃ , GdIG, GdTdFe, GdTdFeCoBi, CoFe ₂ O ₄ Materials such as 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.

The requirements for such a medium are firstly 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 large. Third, it is possible to obtain a magnetically and mechanically uniform film over a relatively large area.

In response to such demands, recently, rare earth-transition metal amorphous perpendicular magnetic thin films have attracted great attention among the above materials.

However, in such a magneto-optical recording medium comprising 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 done on the surface of the magnetic thin film layer having a structure provided on the protective surface.

Conventionally, as such a moisture-proof protective layer, an attempt has been made to provide an inorganic vacuum-deposited film or resin film of silicon monoxide, silicon dioxide, aluminum nitride, silicon nitride or the like (JP-A-58-58).
80142) are disclosed.

In an optical recording medium, it is advantageous to perform recording / reproduction from the substrate side, and a transparent substrate is used.

As a substrate for an optical disk, a resin substrate is preferable in view of ease of manufacturing, handling, and the like. Among these, acrylic resin, polycarbonate, etc. are particularly preferable in terms of transparency, productivity, economy, and the like. Bonate resins are preferred.

An intermediate layer made of an inorganic material is usually formed on such a resin substrate, and a magnetic thin film layer is formed via this intermediate layer.

This intermediate layer has a function as an interference layer, has a function of improving the C / N ratio, and a function of imparting corrosion resistance to prevent deterioration of the magnetic thin film layer.

As a material of such an intermediate layer, for example, SiO, silicon oxide such as SiO ₂ , AlN, Si ₃ N ₄ , ZnS, Si, Ge, etc. have been proposed, among which silicon oxide, zinc sulfide is C /
The points of improving N ratio and corrosion resistance are preferable.

By the way, when comparing the acrylic resin and the polycarbonate resin among the above substrate materials, the acrylic resin is superior in optical uniformity, and therefore the acrylic resin is more advantageous in terms of the C / N ratio. . However, the aryl resin is inferior to the polycarbonate resin in durability.

Therefore, by forming an intermediate layer of silicon oxide or zinc sulfide on the acrylic resin, the corrosion resistance is improved and the C / N ratio is also improved. In this case, zinc sulfide is advantageous in terms of C / N ratio,
Silicon oxide is advantageous in terms of corrosion resistance. However, neither is satisfactory.

On the other hand, the polycarbonate resin is inferior to the acrylic resin in the C / N ratio, but is advantageous in durability and has a great advantage that it is excellent in dimensional accuracy stability against warping and the like.

In the case of a polycarbonate resin substrate, the silicon oxide intermediate layer is superior to the zinc sulfide intermediate layer in terms of C / N ratio and corrosion resistance.

However, even in the case of the silicon oxide intermediate layer, the conventionally used film structure has insufficient C / N ratio, corrosion resistance, durability and the like, and further improvement is required.

II Object of the invention The object of the present invention is excellent in recording / reproducing characteristics, moreover, deterioration of the magnetic thin film layer is prevented, corrosion resistance and durability are excellent, and
An object of the present invention is to provide a magneto-optical recording medium excellent in stability of dimensional accuracy against warpage and the like.

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

That is, the present invention is a magneto-optical recording medium having a silicon oxide intermediate layer on a resin substrate and a rare earth-transition metal magnetic thin film layer on the intermediate layer, wherein the substrate is a polycarbonate resin, and the oxidation is The oxygen content on the substrate side of the silicon intermediate layer is larger than that on the magnetic thin film layer side, and the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 from the substrate side of the silicon oxide intermediate layer is 1.4 to 2.5 of the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 from the layer side
It is a magneto-optical recording medium characterized by being doubled.

IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

An embodiment of the magneto-optical recording medium of the present invention is shown in FIG.

Referring to FIG. 1, a magneto-optical recording medium 1 of the present invention comprises a substrate 2
It has an intermediate layer 3 on top.

The intermediate layer 3 of the present invention is made of a silicon oxide (SiOx) material.

The O / Si atomic ratio (x) of the silicon oxide (SiOx) intermediate layer 3 is preferably 0.7 to 1.2, more preferably 0.7 to 1.0 as the average of the entire layer.

When x is less than 0.7, the amount of reflected light is reduced and the characteristics are adversely affected.

Further, if it exceeds 1.2, the apparent Kerr rotation angle decreases, and the same characteristics are adversely affected.

In the thickness direction of the intermediate layer 3, there is a predetermined oxygen concentration distribution so that the oxygen content on the substrate side in the intermediate layer 3 is larger than that on the magnetic thin film layer 4 side described later. .

Such an oxygen concentration distribution in the silicon oxide intermediate layer 3 is, for example, the O / Si atomic ratio in the silicon oxide intermediate layer at positions 1/4 from the substrate 2 side of the silicon oxide intermediate layer 3 is the magnetic thin film layer. Four
It is preferably 1.4 to 2.5 times, especially 1.5 to 2.5 times, and more preferably 1.6 to 2.0 times the O / Si atomic ratio in the silicon oxide intermediate layer at the position 1/4 from the side.

If this value is less than 1.4 times, the C / N ratio, corrosion resistance, and durability will deteriorate. On the other hand, if it exceeds 2.5 times, the electrical characteristics will mainly deteriorate. Therefore, when this value becomes 1.6 to 2.0 times the above-mentioned preferable range, the C / N ratio and durability are significantly improved.

The oxygen concentration distribution as described above is provided in the silicon oxide intermediate layer 3 for the following reason.

That is, first, by setting the refractive index of the polycarbonate resin substrate 2 (about 1.57 at 830 nm) and the oxygen concentration (value of x) of the silicon oxide intermediate layer 3, the polycarbonate resin substrate 2 and the silicon oxide intermediate layer 3 are This is because it is possible to effectively prevent reflection at the interface and obtain good recording / reproducing characteristics.

Secondly, by lowering the oxygen concentration of the silicon oxide intermediate layer 3 on the magnetic thin film layer 4 side, deterioration of the magnetic thin film layer 4 containing Fe and Co as essential components described later can be effectively prevented. Is.

The oxygen concentration distribution may be continuous or discontinuous.

O / which exists in the thickness direction of the silicon oxide intermediate layer 3
The atomic ratio distribution of Si is measured, for example, by the method described below.

That is, first, elemental analysis is performed by SIMS (secondary ion mass spectrometry), AES, ESCA, etc. while ion-etching the silicon oxide intermediate layer 3 from the magnetic thin film layer 4 side at a constant etching rate. Then, the time required to reach the polycarbonate resin substrate 2 and detect the carbon C is measured.

By doing so, the time required to etch the film thickness of the silicon oxide intermediate layer 3 can be measured.

The average atomic ratio of O / Si at a predetermined location in the layer is calculated from the elemental analysis results in the layer from the beginning of this required time to 1/4 hour and from the time of reaching 3/4 hour to the substrate.

Needless to say, the average O / Si atomic ratio of the entire layer can also be calculated.

In order to form the silicon oxide intermediate layer 3 having an oxygen concentration distribution in the film thickness direction as described above, usually, a multi-source sputtering method or an oxygen reactive sputtering method using a target having two or more different compositions is used. Good. The target may be so-called SiO ₂ , SiO, Si or the like.

Moreover, it is also possible to appropriately use other vapor deposition methods.

The thickness of the silicon oxide intermediate layer 3 thus formed is 50
It is 0 to 1500Å, more preferably 700 to 1000Å.

Further, Ar or the like existing in the film forming atmosphere may be included.

In addition, a small amount of elements such as Al, Cr and Ba may be added depending on the case.

The material of the substrate 2 on which the above-mentioned silicon oxide intermediate layer 3 is provided is polycarbonate resin.

The polymerbonate resin used in the present invention may be any of an aliphatic polycarbonate, an aromatic-aliphatic polycarbonate, and an aromatic polycarbonate, but an aromatic polycarbonate resin is particularly preferable. Of these, a polycarbonate resin made of bisphenol is preferable in terms of melting point, crystallization point, handling and the like. Among them, the bisphenol A type polycarbonate resin is most preferably used.

The number average molecular weight of the polycarbonate resin is 10,000.
It is preferably about 15,000.

The refractive index at 830 nm of such a substrate 2 is usually about 1.55 to 1.59.

Since recording is performed through the substrate 2, the transmittance for writing light or reading light is 86% or more.

The substrate 2 is usually disk-shaped and has a thickness of about 1.2 to 1.5 mm.

A tracking groove may be formed on the surface of the disk-shaped substrate on which the magnetic thin film layer is formed.

The depth of the groove is about λ / 8n, especially λ / 6n to λ / 12n (here,
n is the refractive index of the substrate). The width of the groove is
It is about the track width.

Then, it is usually preferable to irradiate the writing light and the reading light from the back surface side of the substrate with the magnetic thin film layer located in the concave portion of the groove as a recording track portion.

With this configuration, the write sensitivity and the read C / N ratio are improved, and the tracking control signal is increased.

Further, the other substrate shape may be a tape, a drum, or the like.

The magnetic thin film layer 4 is formed on the silicon oxide intermediate layer 3 described above.

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

As the material of such a magnetic thin film layer 4, an alloy of a rare earth metal such as Gd and Tb and a transition metal such as Fe and Co is formed as an amorphous film by a sputtering or vapor deposition method. And Co are essential components.

In this case, the total content of Fe and Co is preferably 65 to 85 at%.

And the balance is substantially rare earth metals, especially Gd and / or Tb.

And, as a preferable example thereof, TbFeCo, GdFeCo, GdTdFe
There are Co etc.

In these magnetic thin film layers, Cr in the range of 10 at% or less,
Al, Ti, Pt, Si, Mo, Mn, V, Ni, Cu, Zn, Ge, Au, etc. may be contained.

In addition, as a rare earth element, Sc, Y, L in the range of 10 at% or less
a, Ce, Pr, Nd, Pm, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu
Etc. may be contained.

Further, it is preferable to provide one or more kinds of various protective layers on the side of the magnetic thin film layer 4 opposite to the substrate 2.

In FIG. 1, a first protective layer 5 and a second protective layer 6 are provided.

In this case, the material of the first protective layer 5 is not particularly limited as long as it has a function as a protective layer.
It is preferably an oxide or nitride thin film.

As the oxide, silicon oxide such as silicon monoxide and silicon dioxide, aluminum oxide, titanium oxide, zinc oxide and the like are preferable.

Further, as the nitride, silicon nitride, aluminum nitride, titanium nitride, boron nitride and the like are preferable.

Among these, silicon oxide of SiOx (x = 0.6 to 1.5) is particularly preferable.

The thickness of such a thin film is about 0.1 to 10 μm.

The thin first protective layer 5 may be formed by vacuum vapor deposition, sputtering, or the like.

On the other hand, for the second protective layer 6, various known inorganic or organic substances may be used.

More preferably, a radiation-curable compound cured with radiation such as electron beam or ultraviolet ray is used.

The radiation-curable compound used is an acrylic double bond having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, an acrylic double bond such as methacrylic acid, or an ester compound thereof, or a diallyl phthalate. Examples include monomers, oligomers and polymers having or introduced in the molecule a group that is crosslinked by irradiation with radiation such as allyl double bond, unsaturated double bond such as maleic acid or maleic acid derivative, or polymerized and dried. it can.

A compound having a molecular weight of less than 2000 is used as the radiation-curable monomer, and a compound having a molecular weight of 2000 to 10000 is used as the oigomer.

These include styrene, ethylene acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, and the like. Preferred are pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropondiacrylate (methacrylate), polyfunctional oligoester acrylate (Aronix M-7100, M -5400, M-55
00, M-5700, M-6250, M-6500, M-8030, M-80
60, M-8100, etc., Toa Gosei), acrylic modified urethane elastomer (Nipporan 4040), or those into which functional groups such as COOH have been introduced, phenol ethylene oxide adduct acrylate (methacrylate), the following general A compound having an acrylic group (methacrylic group) or ε-caprolactone-acrylic group on the pentaerythritol fused ring represented by the formula, _{1) (CH 2 = CHCOOCH 2} ) 3 -CCH 2 OH ( special acrylate _{A) 2) (CH 2 =} CHCOOCH 2) 3 -CCH 2 OH 3 ( special acrylate B) 3) [CH ₂ = CHCO (OC ₃ H ₆ ) n-OCH ₂ ] _3- CCH ₂ CH
₃ (Special acrylate C) In the formula, a compound of m = 1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), a compound of m = 1, a = 3, b = 3 (hereinafter referred to as a special pentaerythritol condensate B) , M = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate D) , And special acrylates represented by the following general formula.

_{8) CH 2 = CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) _{12) AM-N n -M-} A A: acrylate, M: 2 dihydric alcohol N: 2 dibasic acid (special Arurireto L) As the radiation-curable oligomer, a polyfunctional oligoester acrylate represented by the following general formula And acrylic modified urethane elastomers, or those into which a functional group such as COOH is introduced.

Further, a radiation-curable compound obtained by subjecting a thermoplastic resin to radiation-sensitive modification may be used.

Specific examples of such a radiation curable resin include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having radical polymerizability, such as diallyl phthalate. It is a resin in which a group such as an allyl double bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation is contained or introduced in 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, and fibrin derivatives.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymer), polyamide resins, polyamide resins, phenol 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.

The film thickness of the second protective layer 6 of such a radiation curable compound 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 an atmosphere with high humidity is not sufficient, and the durability of the magnetic thin film layer 4 is not improved. If it exceeds 30 μm, warpage of the recording medium or cracks in the protective film may occur due to shrinkage during curing of the resin film, which is not practical.

Such a coating film may be usually formed by combining various known methods such as spinner coating, gravure coating, spray coating and dipping. The layer forming conditions of the coating film at this time may be appropriately determined in consideration of the viscosity of the mixture of the coating film composition, the target coating film thickness, and the like.

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

When using an electron beam, the radiation characteristics are as follows: acceleration voltage 10
It is expedient to use a radiation accelerator of 0 to 750 KV, preferably 150 to 300 KV, and to irradiate it with an absorbed dose of 0.5 to 20 megarads.

On the other hand, when ultraviolet rays are used, a photopolymerization sensitizer is usually added to the above-mentioned radiation-curable compounds.

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 preferably in the range of 0.1 to 10% by weight based on the resin solid content.

Then, in order to cure the coating film containing such a photopolymerization sensitizer and the radiation-curable compound by ultraviolet rays, various known methods may be used.

For example, a UV bulb such as a xenon discharge tube or a hydrogen discharge tube may be used.

On such a protective layer 6, a protective plate 8 is usually provided via an adhesive layer 7.

That is, the protective plate 8 is used only in the case of so-called single-sided recording in which recording / reproduction is performed only from the back surface (surface on the side where the magnetic thin film layer 4 is not provided) of the substrate 2.

The resin material of the protective plate 8 is not particularly required to have transparency, and various resins such as polyethylene, polyvinyl chloride, polystyrene, polypropylene,
Polyvinyl alcohol, methacrylic resin, polyamide,
Various types of thermoplastic resin such as polyvinylidene chloride, polycarbonate, polyacetal, fluororesin, phenol resin, urea resin, unsaturated polyester resin, polyurethane, alkyd resin, melamine resin, epoxy resin, silicon resin, etc. are used. It is possible.

In addition, various inorganic materials such as glass and ceramic are used as the protective plate 8.
You may use as.

The shape, dimensions, etc. of this product are substantially the same as those of the substrate 2 described above.

Such a protective plate 8 is bonded via the adhesive layer 7 as described above. The adhesive layer is usually an adhesive such as a hot melt resin and has a film thickness of about 1 to 100 μm.

On the other hand, instead of using the protective plate 8 described above, one more set of substrates having the magnetic thin film layer 4, the protective layers 5 and 6 and the like is used, and both magnetic thin film layers are made to face each other to face each other to form an adhesive layer. 7
It is also possible to use a so-called double-sided recording type in which writing is performed from the back surface side of both substrates by bonding using.

Further, it is preferable to provide a hard coat layer as various protective films on the back surface of the substrate 2 or the protective plate 8 (the surface on the side where the magnetic thin film layer 4 is not provided).

The material of the hard coat layer may be the same as the material of the second protective layer 6 described above.

V. Effect of the Invention The magneto-optical recording medium of the present invention has a silicon oxide intermediate layer having a predetermined oxygen concentration distribution between the substrate and the magnetic thin film layer. Therefore, the recording and reproducing characteristics are excellent, and the deterioration of the magnetic thin film layer with time is small.

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 1 A silicon oxide intermediate layer was sputter-deposited to a thickness of 800 L on a substrate made of a bisphenol A-based polycarbonate resin (molecular weight 15000) having a diameter of 13 cm and a thickness of 1.2 mm.

During sputtering, the target was Si and Si in order to provide a predetermined concentration distribution in the silicon oxide intermediate layer.
A binary target using two kinds of O ₂ was used and their use was temporally controlled. As a result of elemental analysis in the film after layering, the O / Si ratio (x1) from the substrate side to the position 1/4 of the film thickness
Was 1.2, and the O / Si ratio (x4) from the magnetic thin film layer side to the 1/4 position was 0.6. Also, the average O / Si ratio of the entire film (x)
Was 0.9.

21at% Tb, 68at% Fe, 7a on top of this silicon oxide intermediate layer
A t% Co, 4at% Cr alloy thin film was sputtered to a thickness of 800Å to form a magnetic thin film layer.

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

A first protective layer of SiOx (x = 1.0) is formed on this magnetic thin film layer by sputtering to a film thickness of 1000Å, and a coating composition containing the following radiation-curable compound is applied on the first protective layer. A second protective layer was formed by spinner coating.

(Coating composition) Polyfunctional oligoester acrylate 100 parts by weight Photosensitizer 5 parts by weight After applying such a coating composition, it was irradiated with ultraviolet rays for 15 seconds to be crosslinked and cured to obtain a cured film.

The film thickness at this time was 5 μm.

The same process as above was performed on the back surface of the substrate. Further, a polycarbonate resin protective plate having a diameter of 13 cm was adhered onto the second protective layer with an adhesive to obtain a sample of the present invention (Sample No. 1). Sample N according to this
Various samples were prepared in the same manner as in No. 1 except that the silicon oxide intermediate layer was replaced with the SiOx intermediate layer shown in Table 1 below.

Samples No. 9 and No. 10 used injection-molded acrylic resin as the substrate material.

For the above samples, the following characteristic values were measured.

(1) C / N ratio (storage deterioration) C / N ratio at the initial stage and C / N after storage at 60 ° C, 90% RH for 1000 hours
The amount of change in the ratio was measured under the following conditions.

Rotation speed 4m / sec Carrier frequency 500KHz Resolution 30KHz Recording power (830nm) 3 to 4mW Reproduction power (830nm) 1mW (2) Bit error rate Bit of EFM signal after initial storage at 1000C and 90% RH for 1000 hours The error rate was measured.

The results are shown in Table 1.

From the results shown in Table 1, the effect of the present invention is clear.

That is, the present invention shown in No. 1 to No. 4 is C / N
Both the ratio and the bit error rate show good results.
In particular, No. 1 and No. 2 have extremely excellent results because the values of x and x ₄ / x ₁ are within the optimum range. If x ₄ / x ₁ is 1.4 or more, storage deterioration is prevented. It turns out that the effect is extremely large.

Those using an acrylic substrate (No. 7 and No. 8) are not preferable in practical use because they have a large storability, especially warpage and deformation of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magneto-optical recording medium, 2 ... Substrate 3 ... SiOx intermediate layer, 4 ... Magnetic thin film layer, 5 ... First protective layer, 6 ... Second protective layer, 7 ... Adhesive layer, 8 ... Protection plate

Claims (2)

[Claims] 1. A magneto-optical recording medium having a silicon oxide intermediate layer on a resin substrate, and a rare earth-transition metal magnetic thin film layer on the intermediate layer, wherein the substrate is a polycarbonate resin, and the oxidation is The oxygen content on the substrate side of the silicon intermediate layer is larger than that on the magnetic thin film layer side, and the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 from the substrate side of the silicon oxide intermediate layer is 1.4 to 2.5 of the O / Si atomic ratio in the silicon oxide intermediate layer at the position of 1/4 from the layer side
A magneto-optical recording medium characterized by being doubled. 2. The magneto-optical recording medium according to claim 1, wherein the average O / Si atomic ratio of the entire silicon oxide intermediate layer is 0.7 to 1.2.