JPH0778915B2 - Method for manufacturing magneto-optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magneto-optical recording medium that records and reproduces information using heat and light such as laser light.

The prior art recording medium of the problems magneto-optical memory, MnBi, MnAlGe, MnSb, MnCuBi , GdFe, TbFe, GdCo, PtCo, TbCo, TbFeCo, GdFeCo, TbFeO 3, GdIG, GdTbFe, GdTbFeCoBi, 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 in the direction perpendicular to the film surface, and that the Kerr effect and the Faraday effect are large.

Utilizing this property, as a method of a magneto-optical recording medium,
For example, there is the following method.

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 emitted, the temperature rises, and when the Curie point is approached and when the Curie point is exceeded, the holding power is maintained.
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 irradiating with a laser beam, if an external magnetic field is applied in the direction opposite to the initial direction and the temperature is returned to room temperature, 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 a magneto-optical recording medium composed of such a rare earth-transition metal crystalline 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 and water in the atmosphere. It becomes impossible to record and reproduce the information.

Therefore, in general, many studies have been made on a structure having a protective layer between the magnetic thin film layer and the substrate.

Examples of these protective layers include inorganic vacuum-deposited films such as SiO and SiO ₂ or coating protective layers of room temperature curable resin.

However, with these protective layers, sufficient moisture resistance cannot be obtained, and there are problems such as storage deterioration.

Therefore, in order to deal with such a problem, the present inventors have proposed to form a plasma polymerized film on a substrate (patent application dated August 17, 1985).

Further, as the required characteristics of the medium, the above-mentioned characteristics and the improvement of durability, especially the improvement of the adhesive force between the substrate and the magnetic thin film are further demanded.

II Object of the Invention An object of the present invention is to provide a method for producing a magneto-optical recording medium which has excellent durability and storage stability in a high humidity atmosphere.

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

That is, the present invention provides a magneto-optical recording medium in which an inorganic gas is used as a processing gas, a plasma-polymerized film is provided on a plasma-treated substrate, and an amorphous perpendicular magnetic thin film layer of a rare earth-transition metal is provided on the plasma-polymerized film. It is a manufacturing method.

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

The substrate used in the magneto-optical recording medium of the present invention is usually made of resin, and is made of olefin resin such as acrylic resin, polycarbonate, epoxy resin, polythymerpentene, etc., but it may be glass or the like. Good.

Since recording is preferably performed through the substrate,
The transmittance for writing light or reading light must be 86% or more.

The substrate 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 / 7n to λ / 12n (where,
n is the refractive index of the substrate). The width of the groove is
It is about the track width.

Then, it is 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 S / 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 plasma polymerized film of the present invention is preferably a thin film containing C. In this case, C may be formed alone or may be formed by containing C and other elements. When C and other elements are contained to form the plasma polymerized film, it is preferable to contain one or more kinds of H, N and O as the other elements.

As a raw material gas, methane, ethane, propane, butane, pentane, which is a gas at ordinary temperature, is usually used because of its good operability.
One or more kinds of ethylene, propylene, butene, butadiene, acetylene, methylacetylene, and other saturated or unsaturated hydrocarbons are used, but if necessary, they may be formed by plasma polymerization using a liquid hydrocarbon at room temperature as a raw material. Good.

One or more of such hydrocarbons may include H ₂ , O ₂ , O ₃ , H ₂
It is also preferable to use, as a raw material gas, one or more kinds of NO _x such as O, N ₂ , NO, N ₂ O, and NO ₂ , NO ₃ , NH ₃ , CO, and CO ₂ added.

Further, if necessary, sources such as Si, B, P and S can be added to the raw material as trace components.

When the plasma polymerized film is formed of C alone, the carbon film can be generated by performing plasma polymerization on a mixed gas obtained by adding a large amount of hydrogen to a hydrocarbon gas.

In this carbon film, the carbon structure changes depending on conditions such as the mixed gas ratio, plasma power, and substrate temperature.

The film thickness of the plasma polymerized film formed by using such a raw material is generally about 10 to 1000Å.

Even if this film thickness is 1000 Å or more, there is no difference in the effect of the present invention, and it is not necessary to make it more than this value.

Further, if it is less than 10Å, the present invention is not effective.

An ellipsometer or the like may be used to measure the film thickness.

The film thickness can be controlled by controlling the reaction time at the time of forming the plasma polymerized film, the flow rate of the raw material gas, and the like.

The plasma polymerized film forms a polymerized film by bringing the above-mentioned discharge plasma of the source gas into contact with the substrate.

When the principle of plasma polymerization is outlined, when a gas is kept at a low pressure and an electric field is applied, free electrons, which are present in a small amount in the gas, have a very large intermolecular distance as compared with atmospheric pressure, and thus are subjected to electric field acceleration to generate 5 to 10 eV. Acquires the kinetic energy (electron temperature) of.

When the accelerated electrons collide with atoms or molecules, the orbits or molecular orbits are separated, and these are dissociated into electrons, ions, neutral radicals, and other normally unstable chemical species.

The dissociated electrons are again accelerated by the electric field to dissociate another atom or molecule, and the chain action immediately turns the gas into a highly ionized state. And this is called plasma gas.

Since gas molecules have few opportunities to collide with electrons, they do not absorb much energy and are kept at a temperature close to room temperature.

A system in which the kinetic energy of electrons (electron temperature) is separated from the thermal motion of molecules (gas temperature) is called low-temperature plasma. Here, the chemical species are subjected to addition such as polymerization while maintaining their original shape. The present invention aims to form a plasma polymerized film on a substrate by utilizing this situation. Since low temperature plasma is used, there is no thermal effect on the substrate.

An example of an apparatus for forming a plasma polymerized film on the surface of a substrate is shown in FIG. FIG. 1 shows a plasma processing apparatus using a variable frequency power source.

In FIG. 1, in the reaction vessel R, the raw material gas from the raw material gas source 511 or 512 is supplied to the mass flow controller 5 respectively.
Supplied via 21 and 522. When separate gases are supplied from the gas source 511 or 512, they are mixed and supplied in the mixer 53.

The raw material gas may have a flow rate range of 1 to 250 ml / min.

In the reaction container R, the substrate 111 to be processed is provided with one rotary electrode 5
Backed by 52.

Then, an electrode 551 facing the rotary electrode 552 is provided so as to sandwich the substrate 111 to be processed.

One electrode 551 is connected to, for example, a variable frequency power source 54, and the other rotary electrode 552 is grounded at 8.
Further, in the reaction vessel R, a vacuum system for exhausting the inside of the vessel is provided, and this includes an oil rotary pump 56, a liquid nitrogen trap 57, an oil conversion pump 58 and a vacuum controller 59. These vacuum systems have 0.01-10
Keep within Torr vacuum range.

In the operation, the inside of the reaction vessel R is first evacuated to 10 ^-5 Torr or less, and then the processing gas is supplied in a mixed state into the vessel at a predetermined flow rate.

At this time, the vacuum in the reaction vessel is controlled within the range of 0.01 to 10 Torr.

When the flow rate of the raw material gas becomes stable, the power is turned on. Thus, the plasma polymerized film is formed on the substrate on the substrate.

Note that Ar, N ₂ , He, H ₂ or the like may be used as the carrier gas.

Further, the applied current, the processing time, etc. may be set under normal conditions.

As the plasma generation source, in addition to high frequency discharge, microwave discharge, direct current discharge, alternating current discharge or the like can be used.

The plasma-polymerized film thus formed contains C or C and one or more of H, N, and O as described above, and C
Content in the plasma polymerized film is 30 to 100 at%, more preferably 30 to 90 at%.

When the content of C is less than 30 at%, the film strength of the plasma-polymerized film is lowered and it cannot be put to practical use.

The content of H, N, O, which is contained in one or more kinds in addition to C, is such that the atomic ratio of hydrogen and carbon (H / C ratio) is 1 or less, particularly 1/6.
〜1, atomic ratio of nitrogen to carbon (N / C ratio) is 3/10 or less, especially 1/20 to 3/10, atomic ratio of oxygen to carbon (O / C ratio) is 3/10
In the following, the range of 1/20 to 3/10 is particularly preferable. Thus, the scratch resistance is improved by containing at least one of H, N and O in addition to C.

The content of C, H, N, O and other elements in the plasma polymerized film may be analyzed according to SINS (secondary ion mass spectrometry) or the like.

When using SIMS, C, H, N, O on the plasma polymerized film surface
It may be calculated by counting and other elements.

Alternatively, while performing ion etching with Ar etc., C, H,
It may be calculated by measuring the profiles of N, O and other elements.

For the measurement of SIMS, see Surface Science Basic Course Vol. 3 (19
84) Basics and applications of surface analysis (p70) "SIMS and LAMMA"
You can follow the description.

Such a plasma polymerized film is formed on a plasma-treated substrate.

By plasma-treating the surface of the substrate, the adhesive force between the substrate and the plasma polymerized film is improved.

The principle, method, formation conditions, etc. of the plasma treatment method for the substrate surface are basically the same as those of the plasma polymerization method described above.

However, as a general rule, the plasma treatment uses an inorganic gas as a treatment gas, and on the other hand, as a general rule, an organic gas (which may be mixed with an inorganic gas) is used for forming the plasma-polymerized film by the above-mentioned plasma polymerization method. Used as raw material gas.

The plasma processing gas of the present invention is not particularly limited.

That is, H ₂ , Ar, He, O ₂ , N ₂ , air, NH ₃ , O ₃ , H ₂
Any one selected from NO _x such as O, NO, N ₂ O, and NO ₂ and these may be used alone or as a mixture.

Further, the frequency of the plasma processing power source is not particularly limited, and may be DC, AC, microwave, or the like.

The plasma-polymerized film as described above is formed on the substrate thus plasma-treated, and a magnetic thin film layer is further formed on the plasma-polymerized film directly or via an intermediate layer.

Information is magnetically recorded on the magnetic thin film layer by a modulated heat beam or a modulated magnetic field, and the recorded information is magnetic-optically converted and reproduced.

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 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.

In these cases, the rare earth metal is 15 to 35 at% and the transition metal is 65
Approximately 85 at%.

The thickness of the magnetic thin film layer is about 0.05 to 0.1 μm.

In addition, a magnetic thin film layer may be provided via the intermediate layer. In this case, the material of the intermediate layer is SiO ₂ , SiO, Al.
Examples include N, Si ₃ N ₄ , ZnS and the like formed by vacuum deposition, sputtering or the like.

Such an intermediate layer has a thickness of 0.05 to 0.2 μm.

Further, it is preferable to provide a top coat layer on the magnetic thin film layer in order to further improve moisture resistance.

As the top coat layer to be used, 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.

Examples of the radiation-curable compound used include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, such as diallyl phthalate. Examples thereof include monomers, oligomers and polymers having or introduced in the molecule a group capable of being crosslinked by irradiation with radiation such as unsaturated double bonds such as allyl double bonds, maleic acid and maleic acid derivatives, or introduced into the molecule. .

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 10,000 is used as the oligomer.

These include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, etc., but particularly preferred ones As, pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (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 condensed ring represented by the formula, _{1) (CH 2 = CHCOOH 2} ) 3 -CCH 2 OH ( special acrylate _{A) 2) (CH 2 =} CHCOOH 2) 3 -CCH 2 CH 3 ( special acrylate B) 3) [CH ₂ = CHOC (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: Acrylic acid M: Dihydric alcohol N: Dibasic acid (special acrylate L) Further, the radiation-curable oligomer 3 is 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 molecule that crosslinks or polymerizes by irradiation with radiation, such as an allyl double bond, an unsaturated bond such as maleic acid or a maleic acid derivative, or the like, is contained in or added to the molecule of the thermoplastic resin.

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

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

If the film pressure 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 31 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 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, in order to cure such a coating film with electron beams or ultraviolet rays, various known methods may be used.

When ultraviolet rays are used for curing, a photopolymerization sensitizer is added to the above-mentioned radiation-curable compound.

The photopolymerization sensitizer may be a conventional one, and examples thereof include benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, benzoin compounds of α-chlordeoxybenzoin, benzophenone, acetophenone, bisdialkylaminobenzophenone, and other ketones. And quinones such as acetoraquinone and phenanthraquinone, sulfides such as benzyl disulfide and tetramethylthiuram monosulfide, and the like. The photopolymerization sensitizer is preferably in the range of 0.1 to 10% by weight based on the resin solid content.

For ultraviolet irradiation, for example, an ultraviolet light bulb such as a xenon discharge tube or a hydrogen discharge tube may be used.

On the other hand, when an electron beam is used, the radiation characteristics are
It is convenient to use a radiation accelerator with an accelerating voltage of 100 to 750 KV, preferably 150 to 300 KV, and to irradiate it with an absorbed dose of 0.5 to 20 megarads.

In particular, as the irradiation source, the method of using an electron beam with a radiation heater and the method of using the above-mentioned ultraviolet rays are advantageous from the viewpoints of controlling absorbed dose, introducing into production high / low lines, shielding ionizing radiation, etc. .

In addition, a protective layer such as silicon oxide or silicon nitride may be used.

The present invention may be formed and configured as described above. In addition, a pair of substrates having a magnetic thin film layer is used, the magnetic thin film layer is faced to the inside, and the substrates are bonded together with an adhesive or the like,
It may be a so-called double-sided recording type in which writing is performed from the back surface side of the substrate.

Further, in the case of single-sided recording, a protective plate may be adhered to the medium as described above.

According to the present invention, a plasma-polymerized film containing C or C and at least one element selected from N, H, and O is provided on the plasma-treated substrate. On top of the,
A magneto-optical recording medium is manufactured by forming an amorphous perpendicular magnetic thin film layer of rare earth-transition metal directly or through an intermediate layer.

Therefore, the obtained medium has excellent durability and also has an excellent effect on storage stability in a high humidity atmosphere.

The magneto-optical recording medium according to the present invention is useful as various information recording media for various purposes.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

Example 1 A PMMA substrate having a diameter of 20 cm was placed in a vacuum chamber,
After drawing a vacuum of 10 _-5 Torr, Ar was used as a processing gas,
Flow rate: 13.56MHz while maintaining gas pressure 0.1 Torr at 50ml / min
Was applied to generate plasma, and the substrate surface was plasma-treated.

Then, a plasma polymerized film was further formed on the substrate under the following conditions.

The elemental analysis of these plasma-polymerized films was measured by SIMS, and the film thickness was measured by an ellipsometer.

The results are shown in Table 1.

An intermediate layer of Si ₃ N ₄ was formed on the thus formed plasma polymerized film by high frequency magnetron sputtering to a film thickness of 900 Å.

Further thereon, a magnetic thin film layer and a top coat layer shown below were formed.

(Formation of magnetic thin film layer) TbFeCo alloy thin film is sputtered to 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.

(Formation of Topcoat Layer) On this magnetic thin film, a coating composition comprising 100 parts by weight of a polyfunctional oligoester acrylate (Aronix M-8030) and 5 parts by weight of a photosensitizer (Vicure 55) was formed by spinner coating. Then, after that, 120 W / cm ultraviolet rays were irradiated for 15 seconds to crosslink and cure. The film thickness at this time was 10 μm.

In this way, various magneto-optical disks shown in Table 1 below were manufactured, and the characteristic values shown below were measured.

(1) Adhesive strength An adhesive tape was adhered to the magnetic thin film layer side of the manufactured magneto-optical disk at a constant pressure, and the adhesive tape was separated at a constant speed in the angular direction of 180 °, and the force required for peeling was measured. .

The evaluation is based on the adhesive strength of Sample No. 6 (Comparative Example), and the improvement rate of the adhesive strength of other samples is shown in (%).
(The number of measurement points was n = 5 for each sample, and the average value of 5 points was calculated.) (2) C / N ratio (dB) The initial C / N ratio and 60 ° C, 90% RH atmosphere C / N after storage for 300 hours by exposing only the substrate side of each sample
The amount of change in the ratio was measured under the following conditions.

Rotation speed: 4m / sec Carrier frequency: 500KHz Resolution: 30KHz Recording power: 3 to 4mW (830nm) Reproduction power: 1mW (830nm) (3) Bit error rate Initial, 60 ° C, 90% RH above Similarly, E after storage for 300 hours
The bit error rate of the FM signal was measured.

The results are shown in Table 1.

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

[Brief description of drawings]

 FIG. 1 is a schematic diagram of a plasma polymerization apparatus. Explanation of symbols 53 …… Mixer 54 …… DC, AC and variable frequency power supplies 56 …… Oil rotary pump 57 …… Liquid nitrogen trap 58 …… Oil diffusion pump 59 …… Vacuum controller 111 …… Substrate 511,512 …… Processing Gas source 521,522 …… Mass flow controller 551,552 …… Electrode

Claims (5)

[Claims] 1. A method for producing a magneto-optical recording medium, wherein a plasma-polymerized film is provided on a plasma-treated substrate using an inorganic gas as a processing gas, and an amorphous perpendicular magnetic thin film layer of a rare earth-transition metal is provided on the plasma-polymerized film. Method. 2. The plasma polymerized film is C, or C and H,
The method for manufacturing a magneto-optical recording medium according to claim 1, further comprising at least one of N and O. 3. The C content of the plasma polymerized film is 30 to 10
The method for manufacturing a magneto-optical recording medium according to claim 2, wherein the content is 0 at%. 4. A method of manufacturing a magneto-optical recording medium according to claim 1, wherein an intermediate layer is provided between the plasma polymerized film and the amorphous perpendicular magnetic thin film layer. . 5. The method for manufacturing a magneto-optical recording medium according to claim 1, wherein a protective layer is provided on the surface of the amorphous perpendicular magnetic thin film layer.