JPH08129748A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium capable of easily ensuring superior wear resistance while effectively suppressing spacing loss. CONSTITUTION: A protective layer 4 excellent in wear resistance and having magnetism is formed on a metallic magnetic thin film (vapor deposited film) 2 by simultaneously sputtering carbon excellent in wear resistance and a ferromagnetic substance such as cobalt to obtain the objective magnetic recording medium with a carbon-cobalt protective layer, e.g. a magnetic tape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium in which at least a magnetic recording layer is formed on the surface of a non-magnetic support, and the non-magnetic support is formed by a vacuum thin film forming technique such as vacuum deposition or sputtering. The present invention relates to a so-called ferromagnetic metal thin film type magnetic recording medium (for example, magnetic tape, magnetic disk) in which a metal magnetic thin film (ferromagnetic metal thin film) is formed as a magnetic recording layer on a support.

[0002]

2. Prior Art Conventionally than magnetic recording medium, containing γ-Fe ₂ O _3, Co on a nonmagnetic support gamma-Fe ₂ O
_{3, Fe 3 O 4, Fe} 3 O 4 containing Co, γ-Fe
Bertride compound of ₂ O ₃ and Fe ₃ O ₄ , Bertride compound containing Co, oxide ferromagnetic powder such as CrO ₂ or alloy magnetic powder containing Fe, Co, Ni or the like as a main component A coating type magnetic recording medium is widely used, which is prepared by coating and drying a magnetic paint in which a magnetic material is dispersed in an organic binder such as a vinyl chloride-vinyl acetate copolymer, polyester resin or polyurethane resin. There is.

On the other hand, in the field of video tapes, for example, there is a strong demand for high density magnetic recording in order to achieve high image quality. Corresponding to this, Fe system and C
A ferromagnetic metal material such as an o-Ni alloy is directly deposited on a non-magnetic support such as a polyester film or a polyimide film by plating or a vacuum thin film forming technique (vacuum deposition method, sputtering method, ion plating method, etc.). There is proposed a so-called ferromagnetic metal thin film type magnetic recording medium in which a magnetic layer is formed.

This ferromagnetic metal thin film type magnetic recording medium is
Not only excellent in coercive force (coercive force) and squareness ratio but also excellent in electromagnetic conversion characteristics at short wavelengths, it is possible to thin the magnetic layer, so recording demagnetization and thickness loss during reproduction are extremely small. In addition, since it is not necessary to mix an organic binder that is a non-magnetic material in the magnetic layer, there are various advantages such as the packing density of the magnetic material can be increased.

Among them, the vapor deposition tape having the magnetic layer formed by the vacuum vapor deposition method is already commercialized as a high band 8 mm (Hi8) tape and a digital microtape (NT tape) because of its high production efficiency and stable characteristics. Has been converted.

The magnetic layer of the vapor deposition tape is formed by heating a magnetic material with an electron beam or the like in a vacuum to evaporate it and depositing it on a non-magnetic support.

The vapor-deposited tape is suitable for high density recording because of its high reproduction output. In this case, the shorter the recording wavelength, the greater the effect of spacing loss, so the surface of the medium (that is, the magnetic layer) is designed to be smoother. However, when the surface is smoothed, friction becomes high and wear resistance becomes a problem.

In order to solve such a problem, the surface property is controlled by applying a lubricant or forming fine projections on the surface, but it is not so easy to control the surface property. Moreover, the process required for it is troublesome.

On the other hand, there has been developed a method of providing a protective layer by sputtering carbon on the surface to improve wear resistance.

However, when the carbon layer is provided on the surface of the medium in this manner, since the carbon is non-magnetic, a spacing loss corresponding to the thickness of the carbon layer is likely to occur, which easily causes deterioration of electromagnetic conversion characteristics.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium which can easily obtain excellent abrasion resistance while effectively suppressing spacing loss.

[0012]

In order to solve the above-mentioned problems, the present inventor has conducted earnest research and, as a result, formed a protective layer having a certain degree of magnetism to suppress a spacing loss and to prevent abrasion. The present invention succeeded in producing a magnetic recording medium having excellent properties and reached the present invention.

That is, the present invention relates to a magnetic recording medium in which a protective layer having magnetism is formed on the magnetic recording layer.

According to the magnetic recording medium of the present invention, since the protective layer having magnetism is formed on the magnetic recording layer (magnetic layer), the magnetic recording layer is used for the original magnetic recording, and at the same time, is protected. Since the layer itself also has magnetism, it does not hinder magnetic recording, but rather plays a part in magnetic recording.

As a result, the spacing loss due to the protective layer can be effectively suppressed and the electromagnetic conversion characteristics can be improved. Moreover, the wear resistance of the medium can be easily improved by the constituent material (especially carbon and a magnetic material such as Co) as the protective layer.

Specifically, the magnetic recording medium of the present invention comprises, as a protective layer having excellent wear resistance and magnetism, carbon having excellent wear resistance and ferromagnetic material such as cobalt at the same time. A protective layer in which carbon and cobalt are mixed is formed by sputtering.

In this case, it is desirable that the protective layer contains 60 to 40 atomic% of carbon and 40 to 60 atomic% of magnetic metal such as cobalt.

Further, it is preferable that the magnetic recording layer is composed of a metal magnetic thin film, and that the magnetic recording layer and the protective layer are respectively formed on the non-magnetic support as continuous films of the constituent materials.

As a method for forming the magnetic recording layer and the protective layer, there are a film forming method by a PVD method such as a vacuum deposition method and a sputtering method, a film forming method by a CVD method, and the like. The layers are formed as a continuous film.

As the above-mentioned non-magnetic support, a polymer support formed of a polymer material typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates and the like. Is mentioned. This shape begins with a tape,
It may be disc-shaped or the like.

The above magnetic metal thin film is formed as a continuous film by a PVD method such as plating, sputtering or vacuum deposition, and is made of a metal such as Fe, Co or Ni, or Co--.
Ni-based alloy, Co-Ni-Pt-based alloy, Fe-Co-N
In-plane magnetization recording metal magnetic film made of i-based alloy, Fe-Ni-B-based alloy, Fe-Co-B-based alloy, Fe-Co-Ni-B-based alloy, etc., Co-Cr-based alloy thin film, Co- A perpendicular magnetization recording metal magnetic thin film such as an O-based thin film is exemplified. These magnetic metals and magnetic alloys can also be used in the protective layer.

The thickness of such a metal magnetic thin film is usually 0.1.
Is about 3 μm.

Particularly, in the case of in-plane magnetization recording metal magnetic thin film,
Bi, Sb, Pb, Sn, Ga, on the non-magnetic support in advance
A base film of a low-melting point non-magnetic material such as In, Si, or Ti is formed in advance, a metal magnetic material is vapor-deposited or sputtered from the vertical direction, and the low-melting point non-magnetic material is diffused in the metal magnetic thin film to achieve orientation. The in-plane isotropy may be secured by improving the coercive force and the coercive force may be improved.

The protective layer is preferably formed to a thickness of 5 to 100 nm (further 5 to 30 nm). If this thickness is too large, the output tends to decrease, and if it is too small, the effect as a protective layer becomes poor.

In order to improve the durability of the back surface of the medium, a back coat layer may be formed on the back surface of the non-magnetic support (the surface opposite to the magnetic recording layer). In that case, examples of the material of the back coat layer include C and Al ₂ O.
₃ , Ti-N, Mo-C, Cr-C, SiO, Si
Examples thereof include O ₂ and Si—N, but are not limited to these.

The back coat layer is prepared by mixing and dispersing the above-mentioned materials in a binder, and usable binders are modified or non-modified vinyl chloride resins,
Polyurethane resin or polyester resin can be used, and further, fibrin resin, phenoxy resin or thermoplastic resin having a specific use method, thermosetting resin, reactive resin, electron beam irradiation curable resin, etc. You may use together.

To form the back coat layer, for example, the constituents of the back coat layer are dispersed in a binder, and ethers, esters, ketones, aromatic hydrocarbons, and aliphatic hydrocarbons are used depending on the kind of the binder. A coating material for a back coat layer is prepared by kneading with an organic solvent selected from hydrocarbons, chlorinated hydrocarbons and the like, the coating material is applied to the back surface of the non-magnetic support, dried and calendered. For the binder,
In order to further improve durability, it is preferable to add a curing agent such as a polyfunctional isocyanate in an amount of 5 to 30% by weight.

FIG. 1 shows a magnetic recording medium according to the present invention, for example, a vapor deposition tape.

According to this vapor deposition tape, the metal magnetic thin film 2 is formed on the base film 1 according to the present invention,
On the metal magnetic thin film 2, a magnetic continuous film made of carbon and a magnetic material is formed as a protective layer 4. Then, a back coat layer 3 may be formed on the surface of the base film 1 on the side opposite to the metal magnetic thin film 2, as indicated by an imaginary line.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described below in detail with reference to the drawings.

The chamber 100 of the continuous winding type vapor deposition apparatus shown in FIG.
After evacuating to 10 ^-9 atm, the cobalt alloy placed in the crucible 107 was evacuated in the chamber 100 by the electron beam 109 by the electron gun 106.
Was melted by heating and was vapor-deposited on a PET (polyethylene terephthalate) base film 1 having a thickness of 10 μm to form a metal magnetic thin film 2.

In this case, the incident angle of vapor deposition is 90 to 45 degrees from the normal direction of the base film 1, the feed rate of the base film 1 is 25 m / min, and the thickness of the vapor deposition film 2 is 200 m / min.
It was vapor-deposited to have a thickness of nm. The base film 1 was vapor-deposited while being fed from the unwinding roll 104 to the winding roll 108 along the cooling can 105.

In this vapor deposition, particularly when the metal magnetic thin film 2 is vapor-deposited, Ar gas is introduced from the Ar gas introduction pipe 103 to adjust the degree of vacuum. It is possible to control the coercive force and saturation magnetization of the magnetic thin film 2 by oxidizing and depositing a part of the magnetic particles while blowing oxygen gas from an oxygen gas supply pipe (not shown).

Next, in the continuous winding type sputtering apparatus shown in FIG. 3, a target in which cobalt 111 and carbon 112 are mixed as shown in FIG.
Using 127, the vapor-deposited film 1 produced by the above method is unwound from an unwinding roll 124 (corresponding to 108 above), wound up on a winding roll 128, and guided by a cooling can 125 while a base film is being guided. Protective layer 4 in which carbon and cobalt are mixed on the surface of the magnetic thin film 2 of 1.
Was formed by sputtering. At this time, target 127
Each sample film was prepared by changing the weight ratio of carbon and cobalt and sputtering to make the composition of the protective layer different.

The sputtering apparatus is constructed as a magnetron sputtering apparatus, and as shown in FIG.
After decompressing the inside of the chamber 120 to 10 ^-4 Pa in 1 and reducing the angle of the valve 122 that exhausts to the vacuum pump 121 side from the fully open state to 10 degrees, the exhaust speed is reduced, and the Ar gas introduction pipe 123 to Gas was introduced to make the vacuum degree 0.8 Pa.

A roll of Co alloy deposited is set on the unwinding roll 124, and a voltage of 600 V 129 is applied to the electrode 126 and the target 127 while cooling to -20 ° C. with a cooling can 125.
Then, a sputter layer (protective layer) 4 made of carbon and cobalt was formed to a thickness of 10 nm while maintaining a current of 10 A flowing. The sputtering method was a DC sputtering method, the distance d between the target 127 and the can 125 was 80 mm, and the feeding speed of the film 1 was 6 m / min.

After that, a polymer backcoat layer 3 having a thickness of 0.5 μm and containing carbon as a main component and a vinyl chloride binder as a curing agent was formed to prepare a raw material for a magnetic recording medium.

Next, a 0.1 wt% solution of naphthalene diol as an organic anticorrosive was applied on the metal magnetic thin film 2 by a coating machine using a gravure roll, and dried with a dryer at 100 ° C. Then, a 0.5 wt% solution mainly composed of an organic substance composed of a perfluoropolyether derivative was similarly coated by a gravure roll and then dried to form a top coat layer.

Then, this raw material of the magnetic recording medium was cut into a width of 8 mm to obtain the vapor deposition tape shown in FIG. FIG. 5 shows a flowchart of sample preparation.

Next, the composition ratio of the protective layer 4, the electromagnetic conversion characteristics and the still durability of the vapor deposition tape prepared by the above-mentioned manufacturing method were measured.

Table 1 below shows the measurement results of the composition ratio of carbon and cobalt of the target 127 used and the composition ratio of the formed protective layer. However, the composition ratio of the protective layer was measured by Auger electron spectroscopy, and the relative atomic number ratio was defined as the composition ratio. It can be seen that the composition ratio of the protective layer changes according to the composition ratio of the target.

[0042]

Further, Table 2 below shows the measurement results of electromagnetic conversion characteristics and still durability of each sample. The measurement is a Sony high band 8 mm VCR EV-S900.
I went with a modified version. The relative speed was 3.8 m / sec and the recording frequency was 7 MHz. The still durability was measured as the time until the output deteriorated by 3 dB with respect to the initial level.

[0044]

From these results, it is possible to improve electromagnetic conversion characteristics (reduce spacing loss) and wear resistance by providing a magnetic protective layer made of carbon and a magnetic material on the magnetic layer according to the present invention. Can also be good.

Based on the results in Table 2, the relationship between the composition ratio of the sputtering target (that is, the composition ratio of the protective layer) and the electromagnetic conversion characteristics and still durability is shown in FIG. From FIG. 6, when the cobalt atom ratio of the protective layer is less than 40%, the electromagnetic conversion characteristics tend to be extremely low, and the cobalt atom ratio is 60%.
%, The still durability is apt to be extremely deteriorated, so it is understood that the cobalt content of the protective layer is best in the range of 40% to 60%.

In this example, the vapor deposition layer (magnetic thin film)
Although Co was used as the material, it is not possible to improve the electromagnetic conversion characteristics and running durability by providing a magnetic protective layer on the surface of C.
In addition to o, metals such as Fe and Ni, Co-Ni alloys, C
o-Ni-Pt alloy, Fe-Co-Ni alloy, Fe
-Ni-B system alloy, Fe-Co-B system alloy, Fe-Co
This is also effective in the case of a perpendicular magnetization recording metal magnetic thin film such as an in-plane magnetization recording metal magnetic film made of a —Ni—B type alloy or a Co—Cr type alloy thin film or a Co—O type thin film. Such a magnetic material may be appropriately selected and used also in the protective layer.

Further, in this embodiment, as a sputter target for forming protective layers having different composition ratios, as shown in FIG.
Although the shape as described above was used, it is not particularly limited to this shape as long as the same effect can be obtained. Also, non-magnetic materials other than carbon may be used for similar purposes.

In addition, the above example can be variously modified based on the technical idea of the present invention.

[0050]

In the magnetic recording medium of the present invention, since the magnetic protective layer is formed on the magnetic recording layer, the magnetic recording layer is used for the original magnetic recording and at the same time the protective layer itself is formed. Since it has magnetism, it does not hinder magnetic recording, but rather plays a part in magnetic recording.

As a result, the spacing loss due to the protective layer can be effectively suppressed and the electromagnetic conversion characteristics can be improved. Moreover, the wear resistance of the medium can be easily improved by the constituent material (especially carbon and a magnetic material such as Co) as the protective layer.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic cross-sectional view of a vapor deposition device used for manufacturing the magnetic recording medium.

FIG. 3 is a schematic cross-sectional view of a sputtering apparatus used for manufacturing the magnetic recording medium.

FIG. 4 is a side view and a plan view of a target used in the sputtering apparatus.

FIG. 5 is a flowchart of a manufacturing process of the magnetic recording medium.

FIG. 6 is a graph showing the relationship between the composition ratio of the protective layer and the electromagnetic conversion characteristics and still durability of the magnetic recording medium.

[Explanation of symbols]

 1 ... Non-magnetic support (base film) 2 ... Metal magnetic thin film 3 ... Back coat layer 4 ... Protective layer 100, 120 ... Chamber 101, 121 ... Vacuum pump 102, 122・ ・ ・ Exhaust valve 103 ・ ・ ・ Ar gas introduction pipes 104, 124 ・ ・ ・ Unwind rolls 105, 125 ・ ・ ・ Cooling can 106 ・ ・ ・ Electron gun 107 ・ ・ ・ Crucible 108, 128 ・ ・ ・ Winding rolls 109 ・ ・ ・ Electron beam 111 ・ ・ ・ Cobalt 112 ・ ・ ・ Carbon 126 ・ ・ ・ Electrode 127 ・ ・ ・ Target

Front page continuation (72) Inventor Kazunobu Chiba 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (5)

[Claims] 1. A magnetic recording medium in which a protective layer having magnetism is formed on the magnetic recording layer. 2. The magnetic recording medium according to claim 1, wherein the protective layer contains carbon and a magnetic material, respectively. 3. A protective layer comprising carbon of 60 to 40 atomic% and 40 to 40
The magnetic recording medium according to claim 2, which contains 60 atomic% of a magnetic metal. 4. The magnetic recording medium according to claim 1, wherein the magnetic recording layer comprises a metal magnetic thin film. 5. The magnetic recording medium according to claim 1, wherein the magnetic recording layer and the protective layer are each formed as a continuous film of constituent materials.