JPH11328657A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain adhesion and lubrication properties under any use condition and secure superior travel performance and durability by forming a magnetic layer on a non-magnetic supporting body and holding a lubricant containing a prescribed ester compound and a prescribed perfluorocarboxylate at an outermost layer. SOLUTION: A ferromagnetic metallic thin film is formed as a magnetic layer 2 on a non-magnetic supporting body 1. A protecting layer 3 is formed on the magnetic layer 2. The protecting layer 3 is preferably formed of carbon, and a front face of the protecting layer is top coated with a lubricant layer. The lubricant is preferably a mixture of an ester compound expressed by a formula I of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid with a perfluorocarboxylate expressed by a formula II with a weight ratio of 10:90-90:10. An application amount is preferably 0.05-100 mg/m<2> and particularly preferably 0.1-50 mg/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium having at least a magnetic layer formed on a non-magnetic support. Specifically, the lubricant held in the outermost layer is defined,
The present invention relates to a magnetic recording medium that ensures excellent running properties and durability.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media include ferromagnetic powders such as oxide magnetic powders and alloy magnetic powders and binders such as vinyl chloride-vinyl acetate copolymers, polyester resins, urethane resins and polyurethane resins. A so-called coating type magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint composed of an organic solvent on a non-magnetic support, is widely used.

On the other hand, as the demand for high-density recording and long-time recording has increased, Co, Co-Ni alloys, Co-
A ferromagnetic metal magnetic material such as a Cr alloy or Co-O is directly coated on a non-magnetic support such as a polyester film or a polyimide film by plating or a vacuum thin film forming technique (a vacuum deposition method, a sputtering method, an ion plating method, etc.). A magnetic recording medium of a so-called ferromagnetic metal thin film type, in which a magnetic layer is formed by being attached, has been used. And
Such a ferromagnetic metal thin film type magnetic recording medium is available in a consumer video format (8 mm Hi-8 format, DV format) or a professional video format (DV format).
CAM).

This ferromagnetic metal thin film type magnetic recording medium is
Compared to the coating type magnetic recording medium, it has excellent magnetic properties such as coercive force, squareness ratio, etc., and not only excellent electromagnetic conversion characteristics in the short wavelength region, but also enables extremely thin magnetic layer, Since the thickness loss at the time of recording demagnetization and reproduction is extremely small, and there is no need to mix a binder, which is a nonmagnetic material, in the magnetic layer, it is possible to increase the packing density of the magnetic material. Has advantages.

[0005] In general, a magnetic recording medium records and records magnetic signals.
During the reproduction process, the head must be moved under a high-speed relative motion with the magnetic head, and the running must be performed smoothly and stably. Also, it is better that the wear and damage due to contact with the magnetic head be as small as possible.

However, in the above-described ferromagnetic metal thin film type magnetic recording medium, the surface of the magnetic layer is extremely smooth, so that a substantial contact area is increased and an adhesion phenomenon (so-called chipping) occurs. There are many drawbacks in durability, running properties, etc., such as ease of use and increase in the coefficient of friction.

Therefore, for example, attempts have been made to improve durability and running properties by applying a lubricant to the surface of the magnetic layer of the magnetic recording medium, that is, the surface of the ferromagnetic metal thin film. It is known that an organic fluorine compound is effective as a lubricant used in such an application. In particular, JP-A-05-19
No. 4970 discloses a magnetic recording medium that exhibits an excellent lubricating effect under any use conditions by using an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid as a lubricant. I have.
Further, the same publication discloses a magnetic recording medium which exhibits an excellent lubricating effect under any use conditions by using an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol as a lubricant. Have been.

[0008]

By the way, in the magnetic recording medium of the ferromagnetic metal thin film type, a technique for forming a carbon protective film on the ferromagnetic metal thin film has been established in order to secure more excellent durability. Have been. The ferromagnetic metal thin film type magnetic recording medium used for the above-mentioned consumer video format DVC tape, or the professional video format DVCAM tape, and the tape streamer use AIT tape, etc. A technique for forming a carbon protective film on a ferromagnetic metal thin film has been put to practical use. Practical use of the carbon protective film has ensured sufficient durability, and it is considered that the presence of the carbon protective film will be indispensable in future ferromagnetic metal thin film type magnetic recording media.

However, as described above, when an attempt is made to use a lubricant in order to improve durability and running properties, the energy on the surface of the carbon protective film is smaller than that of a ferromagnetic metal thin film, and the lubricant and carbon Since the adsorptivity with the protective film is weak, it is necessary to design a lubricant in consideration of the presence of the carbon protective film. In particular, the above-mentioned ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid and an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol have a large molecular weight, and these lubricants alone are used. Therefore, it is difficult to make the lubricant exist uniformly on the carbon protective film.

Accordingly, the present invention has been proposed in view of the above-mentioned conventional circumstances, and is particularly suitable for a ferromagnetic metal thin film type magnetic recording medium having a carbon protective film formed thereon. Provide a lubricant that maintains the lubricity and lubricity and maintains the lubrication effect for a long time,
An object of the present invention is to provide a magnetic recording medium having excellent durability.

[0011]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have made intensive studies and have found that an ester of a perfluoropolyether having a hydroxyl group at a terminal having a relatively large molecular weight and a long-chain carboxylic acid. It has been found that a mixture of a compound and a perfluorocarboxylic acid ester having a relatively small molecular weight is a suitable lubricant for a ferromagnetic metal thin film type magnetic recording medium having a carbon protective film.

The present inventors have conducted intensive studies and found that an ester compound of a perfluoropolyether having a carboxyl group at a terminal having a relatively large molecular weight and a long-chain alcohol, and a perfluorocarboxylic acid having a relatively small molecular weight. It has been found that a mixture with an ester is a suitable lubricant for a ferromagnetic metal thin film type magnetic recording medium having a carbon protective film.

That is, the magnetic recording medium of the present invention comprises at least a magnetic layer formed on a non-magnetic support, and the outermost layer comprises a perfluoropolyether having a hydroxyl group at a terminal represented by the following formula (5). A lubricant containing an ester compound with a chain carboxylic acid and a perfluorocarboxylic acid ester represented by the following chemical formula 6 is retained.

[0014]

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[0015]

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In the magnetic recording medium of the present invention, the mixing ratio of the ester compound of the perfluoropolyether having a hydroxyl group at the terminal to the long-chain carboxylic acid and the perfluorocarboxylic acid ester is 10% by weight. : 9
It is preferably 0 to 90:10.

The magnetic recording medium of the present invention comprises at least a magnetic layer formed on a non-magnetic support, and the outermost layer comprises a perfluoropolyether having a terminal carboxyl group represented by the following formula (7): A lubricant comprising an ester compound with a long-chain alcohol and a perfluorocarboxylic acid ester represented by the following formula (8) is retained in the outermost layer.

[0018]

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[0019]

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In the magnetic recording medium of the present invention, the mixing ratio of the ester compound of the perfluoropolyether having a carboxyl group at a terminal to a long-chain alcohol and the perfluorocarboxylic acid ester is 10% by weight. : 90 to 90:10.

Further, in the magnetic recording medium of the present invention, it is preferable that the magnetic layer is made of a ferromagnetic metal thin film.

Further, in the magnetic recording medium of the present invention, it is preferable that a protective film is formed as an outermost layer on the magnetic layer, and the protective film is made of carbon.

The magnetic recording medium of the present invention comprises a non-magnetic support having at least a magnetic layer formed thereon.
An ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid and a lubricant containing a perfluorocarboxylic acid ester, or an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol A lubricant containing a perfluorocarboxylic acid ester is retained.In these lubricants, adhesion and lubricity are maintained under any use conditions, and the lubricating effect is maintained for a long time. Good running properties and durability of the magnetic recording medium are ensured.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

The magnetic recording medium according to the present invention is a magnetic recording medium in which at least a magnetic layer is formed on a non-magnetic support. However, here, as shown in FIG. 1, a ferromagnetic metal thin film is formed as a magnetic layer 2 on a nonmagnetic support 1, and a protective film 3 is formed as an outermost layer on the magnetic layer 2. The recording medium will be described.

The magnetic recording medium of this embodiment has a ferromagnetic metal thin film formed as a magnetic layer 2 on a non-magnetic support 1. Here, the material of the non-magnetic support 1 is polyethylene terephthalate, polyethylene Polyesters such as naphthalate, polyethylene, polyolefins such as polypropylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate, polyvinyl chloride,
Examples thereof include vinyl resins such as polyvinylidene chloride, plastics such as polycarbonate, polyimide, polyamide, and polyamideimide; light metals such as aluminum alloys and titanium alloys; and ceramics such as glass. The form of the nonmagnetic support 1 may be any of a film, a sheet, a disk, a card, a drum, and the like.

The non-magnetic support 1 may be one in which one or more types of protrusions such as mountain-like protrusions, wrinkle-like protrusions, and granular protrusions are formed on the surface to control the surface roughness.

The mountain-like projections are formed, for example, by adding inorganic fine particles having a particle size of about 50 to 300 (nm) at the time of forming a polymer film, and have a height from the polymer film surface of 10 to 100 (nm). nm), the density is approximately 1 × 10
^{It is set to 4} to 1 × 10 ⁵ (pieces / nm ² ). Calcium carbonate, silica, alumina, and the like are preferable as the inorganic fine particles used to form the mountain-like projections.

The wrinkle-like projections are projections formed by, for example, applying and drying a dilute solution of a resin using a specific mixed solvent, and have a height of 0.01 to 10 (μm).
m), preferably 0.03 to 0.5 (μm), and the shortest interval between the projections is 0.1 to 20 (μm).

Examples of the resin for forming the wrinkle-like projections include polyester such as polyethylene terephthalate and polyethylene naphthalate, polyamide, polystyrene, polycarbonate, polyacrylate, polysulfone, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, and polyphenylene. It is a simple substance, a mixture, or a copolymer of an oxide, a phenoxy resin, or the like, and those having a soluble solvent are suitable. And the resin concentration which dissolved these resins in the good solvent 1-1000 (ppm)
The solution of a poor solvent of the resin, a solvent having a boiling point higher than the good solvent is added 10 to 100 times the amount of the resin, by applying and drying the surface of the polymer film, A thin film having very fine wrinkle-like irregularities can be formed.

The granular projections are formed by adhering organic ultrafine particles such as acrylic resin or inorganic fine particles such as silica or metal powder in a spherical or hemispherical shape. The height of the granular projections is 5 to 50 (nm), and the density is 1 × 10 ^{6 to} 5 (nm).
It should be about × 10 ⁷ (pieces / mm ² ).

If at least one of these projections is formed, the surface properties of the ferromagnetic metal thin film as the magnetic layer can be controlled, but the effect is increased by combining two or more of them.
In particular, if the wrinkle-like protrusions and the granular protrusions are formed on the nonmagnetic support 1 provided with the mountain-like protrusions, the durability and running properties are extremely improved.

In this case, the overall height of the projection is 1
The density is preferably in the range of 0 to 200 (nm), and the density is preferably 1 × 10 ⁵ to 1 × 10 ⁷ (pieces / mm ² ).

The ferromagnetic metal thin film serving as the magnetic layer 2 may be made of a metal such as Fe, Co, Ni, etc.
i alloy, Co-Pt alloy, Co-Ni-Pt alloy, Fe
-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy,
Fe-Co-B alloy, Co-Ni-Fe-B alloy, Co
-Cr alloy or a ferromagnetic metal material containing a metal such as Cr, Al or the like. In particular, when a Co—Cr alloy is used, a perpendicular magnetization film is formed.

The ferromagnetic metal thin film as the magnetic layer 2 is formed as a continuous film by a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method, and a sputtering method.

The above vacuum deposition method is performed in a range of 1 × 10 ⁻² to 1 × 10 ^−6.
A ferromagnetic metal material is evaporated under a vacuum of (Pa) by resistance heating, high-frequency heating, electron beam heating, etc., and an evaporated metal (ferromagnetic metal material) is deposited on a non-magnetic support. In order to obtain a magnetic force, oblique evaporation in which the ferromagnetic metal material is obliquely evaporated on the non-magnetic support 1 is used. Further, the above-mentioned vapor deposition in an oxygen atmosphere to obtain a higher coercive force is also included.

The above-mentioned ion plating method is also a kind of the vacuum evaporation method, and causes DC glow discharge and RF glow discharge in an inert gas atmosphere of 1 × 10 ^-2 to 1 × 10 ^-1 (Pa). This is to evaporate the magnetic metal material during discharge.

The above sputtering method is performed in a range of 1 × 10 ⁻¹ to 1
Glow discharge is caused in an atmosphere containing argon gas as a main component at 10 × 10 Pa, and atoms of the target surface are knocked out by the generated argon gas ions. Method, a high-frequency sputtering method, a magnetron sputtering method using magnetron discharge, and the like. In the case of using this sputtering method, a base film such as Cr, W, and V may be formed.

In any of the above methods, Bi, Sb, Pb, Sn, Ga, In, C
By depositing a base metal layer of d, Ge, Si, Tl, etc. in advance and forming the film in a direction perpendicular to the surface of the nonmagnetic support 1, there is no orientation of magnetic anisotropy, A magnetic layer having excellent anisotropy can be formed, which is suitable for, for example, a magnetic disk.

The thickness of the ferromagnetic metal thin film formed by such a method is preferably 0.01 to 1 (μm).

The protective film 3 formed on the ferromagnetic metal thin film serving as the magnetic layer 2 is preferably made of carbon, particularly preferably of diamond-like carbon having relatively high hardness. Examples of the protective film 3 include those made of SiO ₂ , silicon nitride, carbon nitride, ZrO ₂ , TiC, Al ₂ O _{3 and the} like.

Then, in the magnetic recording medium of this embodiment,
In particular, the protective film 3 serving as the outermost layer contains an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid represented by the following formula 9 and a perfluorocarboxylic acid ester represented by the following formula 10 Lubricant is retained.

[0043]

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[0044]

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The ester compound of perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid represented by the above formula 9 can be easily synthesized by the following method. For example, it is obtained by reacting a perfluoropolyether having a hydroxyl group at a terminal with carboxylic acid chloride using a base as a catalyst.

Here, the perfluoropolyether having a hydroxyl group at the terminal is preferably one having a hydroxyl group at both terminals, and HOCH ₂ CF ₂ (OC ₂ F ₄ )
_p (OCF ₂ ) _q OCF ₂ CH ₂ OH and the like.
The above-mentioned perfluoropolyether having a hydroxyl group at the terminal is, of course, not limited to these. In the above perfluoropolyether chemical formula, p and q each represent an integer of 1 or more.

The molecular weight of the perfluoropolyether having a hydroxyl group at the terminal is not particularly limited, but practically preferably about 600 to 5000. If the molecular weight is too large, the effect of the terminal group as an adsorptive group is diminished, and at the same time, the perfluoropolyether chain becomes large, so that it becomes difficult to dissolve in existing hydrocarbon solvents. vice versa,
If the molecular weight is too small, the lubricating effect of the perfluoropolyether chain will be lost.

In the perfluoropolyether having a hydroxyl group at the terminal, the perfluoropolyether chain may be partially hydrogenated. That is, a part (50% or less) of the fluorine atoms of the perfluoropolyether chain may be replaced with a hydrogen atom. In this case, a partially hydrogenated perfluoropolyether may be used as the perfluoropolyether.

The carboxylic acid chloride base includes
Both commercially available products and synthetic products can be used.

On the other hand, as the long-chain carboxylic acid, those having an arbitrary structure are possible.
It can be selected irrespective of the isomer structure, alicyclic structure and the presence or absence of an unsaturated bond. Although the molecular weight is also arbitrary, it is preferable that the alkyl group has at least 10 or more carbon atoms since it becomes difficult to dissolve in a general hydrocarbon-based organic solvent as the molecular weight decreases.

Further, the compound represented by the above formula
Can be easily synthesized by reacting a perfluorocarboxylic acid with a corresponding alcohol. As the perfluorocarboxylic acid ester, those having 6 to 10 carbon atoms in the perfluorocarboxylic acid portion are preferable. If the number of carbon atoms is less than 6, the lubricating effect is insufficient. If the number of carbon atoms exceeds 10, solidification occurs in a low-temperature region. As a result, the lubricating effect under low-temperature conditions is reduced. The same applies to the carbon number of the alkyl group R ′ in the ester moiety,
It is preferable that the carbon number is 9 to 25. When the number of carbon atoms is less than 9, the lubricating effect is insufficient, and when the number of carbon atoms exceeds 25, the lubricating effect under low temperature conditions is reduced. What is important here is that the ester portion of the perfluorocarboxylic acid ester is selected from an alkyl group containing no unsaturated bond. The ester containing no unsaturated bond can maintain the initial lubricating properties even during long-term storage.

Further, in the lubricant used in the magnetic recording medium of the present embodiment, the mixing ratio of the ester compound of perfluoropolyether having a hydroxyl group at a terminal to a long-chain carboxylic acid and the perfluorocarboxylic acid ester is as follows: The weight ratio is preferably from 10:90 to 90:10. Exceeding the above range makes it difficult to obtain the effects of the present invention.

By the way, in the magnetic recording medium of this embodiment,
As a method of retaining the lubricant in the outermost layer, a method of top-coating the lubricant layer on the surface of the magnetic layer 2 or the surface of the protective film 3 (here, the surface of the protective film 3) can be mentioned. here,
The application amount is 0.05 (mg / m ² ) to 100 (mg
/ M ² ), preferably from 0.1 (mg / m ² )
More preferably, it is 50 (mg / m ² ). If the coating amount is too small, the friction coefficient decreases,
The effect of improving the durability is not exhibited, and if the coating amount is too large, a shearing phenomenon occurs between the sliding member and the sliding portion, and the running performance is rather deteriorated.

Further, in the magnetic recording medium of this embodiment, a rust preventive may be used in combination, if necessary. As the rust inhibitor, any one can be used as long as it is generally used as a rust inhibitor for this type of magnetic recording medium, for example, phenols,
Examples include naphthols, quinones, heterocyclic compounds containing a nitrogen atom, heterocyclic compounds containing an oxygen atom, and heterocyclic compounds containing a sulfur atom.

Further, in the magnetic recording medium of this embodiment,
A so-called backcoat layer may be formed on the surface of the nonmagnetic support 1 opposite to the surface on which the magnetic layer 2 is formed. The back coat layer is formed by applying a back coat paint in which a binder resin and a powder component are mixed and dispersed in an organic solvent to a non-magnetic support.

As the binder resin used in the backcoat paint, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid Ester-acrylonitrile copolymer, thermoplastic polyurethane elastomer, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative,
Polyester resin, phenolic resin, epoxy resin, polyurethane curable resin, melamine resin, alkyd resin, silicone resin, epoxy-polyamide resin, nitrocellulose-melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer Examples thereof include a mixture of a coalesced diisocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a urea formaldehyde resin, a mixture of a low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, a polyamine resin, and a mixture thereof.

Alternatively, a binder resin having a hydrophilic polar group may be used in order to improve the dispersibility of the powder component.

On the other hand, examples of the powder component include carbon-based fine powder for imparting conductivity and inorganic pigments added for controlling surface roughness and improving durability. Examples of the carbon-based fine particles include furnace carbon, channel carbon, acetylene carbon, thermal carbon, and lamp carbon. Examples of the inorganic pigment include α-FeOOH, α-Fe ₂ O ₃ , and Cr _2.
O ₃ , TiO ₂ , ZnO, SiO, SiO ₂ , SiO ₂
・ 2H ₂ O, Al ₂ O ₃ , CaCO ₃ , MgCO
₃ , Sb ₂ O _{3 and the} like.

Further, as the organic solvent for the back coat paint, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone;
Ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ether;
Glycol ether solvents such as glycol dimethyl ether, glycol monoethyl ether and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; aliphatic hydrocarbon solvents such as hexane and heptane; methylene chloride, ethylene chloride, carbon tetrachloride General-purpose solvents such as chlorinated hydrocarbon solvents such as chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

Further, a lubricant may be used in combination with the back coat layer. In this case, there is a method of internally adding a lubricant to the back coat layer, or a method of applying a lubricant on the back coat layer. In any case, conventionally known lubricants such as fatty acids, fatty acid esters, fatty acid amides, metal soaps, aliphatic alcohols, and silicone-based lubricants can be used as the lubricant.

The magnetic recording medium of this embodiment has a non-magnetic support 1 on which at least a magnetic layer 2 is formed, and a protective film 3, which is the outermost layer, comprises a perfluoropolyether having a hydroxyl group at a terminal and a long chain. A lubricant containing an ester compound with a carboxylic acid and a perfluorocarboxylic acid ester is retained. In these lubricants, adhesion and lubricity are maintained under any use conditions, and the lubricant is used for a long time. Since the lubrication effect is maintained, good running properties and durability of the magnetic recording medium are ensured.

Further, in the magnetic recording medium of this embodiment, since the magnetic layer 2 is formed of a ferromagnetic metal thin film, it can sufficiently cope with high-density recording and long-time recording, and can be used as the outermost protective film 3. Forming a material made of carbon ensures sufficient durability.

As a magnetic recording medium to which the present invention is applied,
The following are also examples. The magnetic recording medium of this example has substantially the same configuration as that of the magnetic recording medium of the above-described example, and differs only in the lubricant held in the outermost layer. Therefore, only the lubricant will be described.

That is, in the magnetic recording medium of this example, an ester compound of a perfluoropolyether having a terminal carboxyl group and a long-chain alcohol represented by the following formula 11 is formed on the protective film 3 as the outermost layer. Formula 12
The lubricant containing the perfluorocarboxylic acid ester represented by is held.

[0065]

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[0066]

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The ester compound of perfluoropolyether having a carboxyl group at the terminal and a long-chain alcohol represented by the above formula (11) can be easily synthesized by the following method. For example, it is obtained by reacting a perfluoropolyether having a carboxyl group at a terminal with a long-chain alcohol in anhydrous toluene using, for example, p-toluenesulfonic acid or concentrated sulfuric acid as a catalyst.

Here, the perfluoropolyether having a carboxyl group at the terminal is preferably a perfluoropolyether having a carboxyl group at both terminals, and HOOCCF ₂ (O
C ₂ F ₄ ) _m (OCF ₂ ) _j OCF ₂ COOH and the like. The above-mentioned perfluoropolyether having a terminal carboxyl group is, of course, not limited to these. In the above perfluoropolyether chemical formula, m and j each represent an integer of 1 or more.

The molecular weight of the perfluoropolyether having a carboxyl group at the terminal is not particularly limited, but is practically preferably about 600 to 5000. If the molecular weight is too large, the effect of the terminal group as an adsorptive group is diminished, and at the same time, the perfluoropolyether chain becomes large, so that it becomes difficult to dissolve in existing hydrocarbon solvents. Conversely, if the molecular weight is too small, the lubricating effect of the perfluoropolyether chain will be lost.

In the perfluoropolyether having a carboxyl group at the terminal, the perfluoropolyether chain may be partially hydrogenated. That is, a part of the fluorine atoms of the perfluoropolyether chain (50%
Below) may be replaced by a hydrogen atom. In this case, a partially hydrogenated perfluoropolyether may be used as the perfluoropolyether.

On the other hand, as the long-chain alcohol, either a commercial product or a synthetic product can be used. In addition, it is preferable that at least one of the alkyl groups has 6 or more carbon atoms because the molecular weight of the alkyl group becomes difficult to dissolve in an ordinary organic solvent as the molecular weight decreases.

Further, the above-mentioned chemical formula 12 contained in the above-mentioned lubricant is used.
Can be easily synthesized by reacting a perfluorocarboxylic acid with a corresponding alcohol. As the perfluorocarboxylic acid ester, those having 6 to 10 carbon atoms in the perfluorocarboxylic acid portion are preferable. If the number of carbon atoms is less than 6, the lubricating effect is insufficient. If the number of carbon atoms exceeds 10, solidification occurs in a low-temperature region. As a result, the lubricating effect under low-temperature conditions is reduced. The same applies to the carbon number of the alkyl group R ′ in the ester moiety,
It is preferable that the carbon number is 9 to 25. When the number of carbon atoms is less than 9, the lubricating effect is insufficient, and when the number of carbon atoms exceeds 25, the lubricating effect under low temperature conditions is reduced. What is important here is that the ester portion of the perfluorocarboxylic acid ester is selected from an alkyl group containing no unsaturated bond. The ester containing no unsaturated bond can maintain the initial lubricating properties even during long-term storage.

Further, in the lubricant used in the magnetic recording medium of the present example, the mixing ratio of the ester compound of perfluoropolyether having a carboxyl group at the terminal and the long-chain alcohol to the perfluorocarboxylic acid ester is as follows:
The weight ratio is preferably from 10:90 to 90:10.
Exceeding the above range makes it difficult to obtain the effects of the present invention.

By the way, in the magnetic recording medium of this embodiment,
As a method of retaining the lubricant in the outermost layer, a method of top-coating the lubricant layer on the surface of the magnetic layer 2 or the surface of the protective film 3 (here, the surface of the protective film 3) may be mentioned. Here, the coating amount is 0.05 (mg / m ² ) to 100
(Mg / m ² ), preferably 0.1 (mg / m ² ).
m ² ) to 50 (mg / m ² ).
If the coating amount is too small, the effect of lowering the coefficient of friction and improving wear resistance and durability will not be exhibited, and if the coating amount is too large, the distance between the sliding member and the ferromagnetic metal thin film will not increase. As a result, a cracking phenomenon occurs, and the running performance is rather deteriorated.

The magnetic recording medium of this embodiment also has at least a magnetic layer 2 formed on a non-magnetic support 1 like the magnetic recording medium of the above-described example, and a protective film 3 which is the outermost layer has
An ester compound of a perfluoropolyether having a carboxyl group at the end and a long-chain alcohol and a lubricant containing a perfluorocarboxylic acid ester are retained, and these lubricants adhere under any use conditions. Since the lubricity and lubricity are maintained and the lubricating effect is maintained for a long period of time, good running properties and durability of the magnetic recording medium are ensured.

Also, in the magnetic recording medium of this embodiment, since the magnetic layer 2 is made of a ferromagnetic metal thin film, as in the magnetic recording medium of the above-described embodiment, it can sufficiently cope with high-density recording and long-time recording. If a protective film 3 made of carbon is formed as the outermost layer, sufficient durability is ensured.

The magnetic recording medium to which the present invention is applied as described above is manufactured as follows. That is, after forming a ferromagnetic metal thin film to be a magnetic layer on a non-magnetic support by, for example, a vacuum evaporation method, a protective film is formed by, for example, a magnetron sputtering method, and a predetermined lubricant is top-coated on the protective film. The lubricant is held on the protective film. Further, a back coat layer or the like may be formed as necessary.

As a vacuum deposition apparatus for forming the magnetic layer, there is a continuous winding type vacuum deposition apparatus as shown in FIG.

This vacuum deposition apparatus is configured for so-called oblique deposition, and is cooled to, for example, about -20 (° C.) in a vacuum chamber 11 in which the inside is evacuated to, for example, about 10 × ^-3 (Pa). A cooling can 12 rotating counterclockwise as shown by an arrow A in the figure, and a vapor deposition source 13 for a ferromagnetic metal thin film are arranged to face the cooling can 12.

In this vacuum evaporation apparatus, a supply roll 14 rotating in a counterclockwise direction in the drawing and a winding roll 15 rotating in a counterclockwise direction in the drawing are also provided in the vacuum chamber 11. The non-magnetic support 16 is unreeled from the supply roll 14 in the direction indicated by the arrow B in the drawing, travels along the peripheral surface of the cooling can 12, and
5 is wound up.

Guide rollers 17 and 18 are arranged between the supply roll 14 and the cooling can 12 and between the cooling can 12 and the take-up roll 15, respectively. A predetermined tension is applied to the non-magnetic support 16 running from the cooling can 12 according to the take-up roll 15, and the non-magnetic support 16
Is designed to run smoothly.

The evaporation source 13 is a container such as a crucible in which a ferromagnetic metal material such as Co is contained. In this vacuum evaporation apparatus, the ferromagnetic metal material of the evaporation source 13 is heated and evaporated. Is also provided. In other words, the ferromagnetic metal material of the evaporation source 13 is acceleratedly irradiated with the electron beam 20 from the electron beam source 19, and the ferromagnetic metal material is heated and evaporated as shown by the arrow C in the figure. Then, the ferromagnetic metal material is deposited on the nonmagnetic support 16 running along the peripheral surface of the cooling can 12 facing the evaporation source 13, and a ferromagnetic metal thin film is formed on the nonmagnetic support 16. It will be.

In the above-described vacuum vapor deposition apparatus, a deposition-preventing plate 21 is provided between the vapor deposition source 13 and the cooling can 12, and a shutter 22 is provided on the deposition-preventing plate 21 so as to be adjustable in position.
Only the vapor-deposited particles incident on the non-magnetic support 16 at a predetermined angle are passed. Thus, the ferromagnetic metal thin film is formed by the oblique deposition method.

Further, during the deposition of such a ferromagnetic metal thin film, an oxygen gas is supplied to the vicinity of the surface of the nonmagnetic support 16 through an oxygen gas inlet (not shown), whereby the magnetic properties and It is preferable to improve durability and weather resistance. In addition, in order to heat the evaporation source, known means such as a resistance heating means, a high-frequency heating means, and a laser heating means can be used in addition to the above-described heating means using an electron beam.

In this embodiment, an example in which a ferromagnetic metal thin film made of Co is formed by an oblique vapor deposition method has been described. A known thin film forming method can be applied. As a material of the ferromagnetic metal thin film, N
i, Fe, and alloys thereof can be used. The thickness of the ferromagnetic metal thin film is about 0.01 to 0.4 (μm), preferably about 0.1 to 0.2 (μm).

FIG. 3 shows a magnetron sputtering apparatus for forming the above protective film.

In this magnetron sputtering apparatus, a cooling can 32 rotating counterclockwise as shown by an arrow D in the figure and a target 33 opposed to the cooling can 32 are provided in a chamber 31. It is.

A vacuum pump 34 for reducing the pressure in the chamber 31 is connected to the chamber 31 through a valve 35, and a gas introduction pipe 36 for introducing a gas into the chamber 31 is connected to a gas supply unit 37. It is arranged with.

Therefore, the chamber 31 is evacuated by, for example, reducing the pressure of the chamber 35 to about 10 ^-4 (Pa) by the vacuum pump 34 and then reducing the angle of the valve 35 evacuated to the vacuum pump 34 side from the fully open state to 10 degrees. By reducing the speed and introducing Ar gas from the gas introduction pipe 36, the degree of vacuum is reduced to about 0.1.
8 (Pa). The cooling can 32 is cooled to, for example, about −40 ° C.

The target 33 is a material for a carbon protective film, and is supported by a backing plate 38 constituting a cathode electrode. On the back side of the backing plate 38, a magnet 3 for forming a magnetic field is provided.
9 are arranged.

In the chamber 31, a supply roll 40 rotating in a counterclockwise direction in the figure and a winding roll 41 rotating in a counterclockwise direction in the figure are also provided. The body 32 is moved from the supply roll 40 by an arrow E in the figure.
And travels along the peripheral surface of the cooling can 32, and is then wound up by a winding roll 41.

When a carbon protective film is formed by this magnetron sputtering apparatus, Ar gas is introduced from the gas introduction pipe 36, and a voltage of 3000 V is applied by using the cooling can 32 as an anode and the backing plate 38 as a cathode. A state in which a current of 4 A flows is maintained.

[0093] By the application of this voltage, the Ar gas is turned into plasma, and the ionized ions collide with the target 33, whereby the atoms of the target 33 are repelled.
At this time, a magnet 39 is provided on the back side of the backing plate 38, and a magnetic field is formed near the target 33.
Will be concentrated near.

The atoms ejected from the target 33 adhere to the non-magnetic support 30 on which the ferromagnetic metal thin film running along the peripheral surface of the cooling can 32 arranged opposite to the target 33 is formed. Thus, a protective film made of, for example, carbon is formed.

This protective film has a thickness of about 3 to 15 (nm), particularly 5 to 10 (nm), so as to reduce the spacing loss and obtain the effect of preventing the wear of the ferromagnetic metal thin film.
(Nm).

In this embodiment, an example in which the protective film is formed by magnetron sputtering has been described. Other methods for forming the protective film include known thin films such as ion beam sputtering, ion beam plating, and CVD. A forming method can be used.

[0097]

EXAMPLE Next, in order to confirm the effects of the present invention, a magnetic recording medium was actually manufactured and its characteristics were evaluated.

Experimental Example 1 In this experimental example, the effect obtained when a lubricant containing an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid and a perfluorocarboxylic acid ester was used as a lubricant. Was confirmed.

(Preparation of Sample) First, an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid was synthesized.

First, a perfluoropolyether having a terminal hydroxyl group, HOCH ₂ CF ₂ (OC ₂ F ₄ ) _p (O
CF ₂ ) _q OCF ₂ CH ₂ OH (molecular weight: 2000, where p and q each represent an integer of 1 or more.)
The perfluoropolyether and triethylamine in a molar ratio twice as much as that of this perfluoropolyether were dissolved in an organic solvent, and stearic acid chloride in a molar ratio twice as much as that in the above solution was further added dropwise over 30 minutes.

After completion of the dropwise addition, the mixture was stirred for 1 hour, and then heated under reflux for 30 minutes. And after cooling, it wash | cleaned in order of distilled water and dilute hydrochloric acid aqueous solution, and wash | cleaned again with distilled water until the washing | cleaning liquid became neutral. Subsequently, the organic solvent was removed, and the obtained compound was purified using silica gel column chromatography to obtain an ester compound. For convenience,
It will be referred to as Compound 1.

Next, in the same manner as in the above-mentioned compound 1, four kinds of compounds 2 to 5 which are ester compounds of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid were synthesized. Rf ₁ and R ₁ in the following Chemical Formula 13 of the perfluoropolyether having a terminal hydroxyl group used in producing each compound are as shown in Table 1 below. In Table 1, Rf ₁ and R ₁ in the following Chemical Formula 13 of the perfluoropolyether having a hydroxyl group at a terminal used in the production of Compound ₁ are also shown. Table 1
P, q, and n each represent an integer of 1 or more.

[0103]

Embedded image

[0104]

[Table 1]

2. Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium. That is, first, Co is applied to a 7.0 (μm) -thick polyethylene terephthalate film, which is a nonmagnetic support, by an oblique evaporation method using the above-described vacuum evaporation apparatus, and a 180-nm-thick magnetic film is formed. A ferromagnetic metal thin film to be a layer was formed. Next, using the above-mentioned magnetron sputtering device, a protective film of about 8 (nm) is formed on the ferromagnetic metal magnetic thin film.
A carbon protective film having a thickness of 5 mm was formed.

Next, on the surface of the polyethylene terephthalate film opposite to the surface on which the ferromagnetic metal thin film was formed, a 0.5 (μ)
m) to form a back coat layer.

Next, as described above, the ferromagnetic metal thin film and the carbon protective film were formed on one main surface side, and the carbon protective film surface of the non-magnetic support having the back coat layer formed on the other main surface side, Each of the compounds shown in Table 2 below was dissolved in a hexane solvent, and each was applied so that the coating amount was 5 (mg / m ² ) to obtain 13 types of magnetic recording media. These one
Three types of magnetic recording media were cut to a width of 6.35 (mm), and 13 types of sample tapes of Examples 1 to 8 and Comparative Examples 1 to 5 were produced.

[0108]

[Table 2]

3. Evaluation of Characteristics Next, the characteristics of the 13 types of sample tapes of Examples 1 to 8 and Comparative Examples 1 to 5 were evaluated. Here, durability and running performance were evaluated, and specifically, the friction coefficient, still durability, and shuttle durability were evaluated. The environmental conditions at the time of these evaluations were determined to be the most severe conditions after the present inventors examined.

(1) Method of Measuring Friction Coefficient The coefficient of friction was measured by measuring the environmental conditions in a thermostat at a temperature of 40 ° C.
(° C.) and the humidity were controlled at 80 (% RH), and the measurement was carried out by running each sample tape for 100 passes in this thermostat.
In addition, the numerical value of the 100th pass of friction running was defined as the friction coefficient.

(2) Still Durability Measuring Method Still durability was evaluated in a constant temperature bath at -5 (° C.).
A commercially available digital video camcorder (manufactured by Sony Corporation, model name: DCR VX1000) was used to measure the time until the reproduction output of each sample tape dropped by 3 (dB).

(3) Method of Measuring Shuttle Durability Shuttle durability is determined by measuring the environmental conditions in a thermostat at a temperature of 40 ° C.
(° C.), humidity 20 (% RH), using a commercially available digital video camcorder (manufactured by Sony Corporation, model name: DCR.VX1000) in this constant temperature bath, run each sample tape for 100 pass shuttle, After running 100 passes, how much (dB) the reproduced output dropped from the initial output was measured and evaluated.

These evaluations were performed immediately after the application of the lubricant and at a temperature of 45 (° C.) and a humidity of 80
(% RH), after storage for one month. Table 3 shows the results of the initial durability and running properties immediately after the application of the lubricant, and Table 4 shows the results of the durability and running properties after storage after storage for one month.

[0114]

[Table 3]

[0115]

[Table 4]

From the results shown in Tables 3 and 4, Examples 1 to 8 using a lubricant in which an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid and a perfluorocarboxylic acid ester were used. In all cases, under various conditions of use such as high temperature and high humidity, high temperature and low humidity, and low temperature, the friction coefficient, still durability, and shuttle durability deteriorated very little, and it can be seen that very good results were obtained.

On the other hand, a lubricant containing only an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid, or an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid In Comparative Examples 1 to 5 using a lubricant in which a lubricant combined with a perfluorocarboxylic acid ester containing an unsaturated bond, the friction coefficient and still durability under various use conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature It can be seen that the performance and the shuttle durability were greatly deteriorated, and good results could not be obtained.

From these results, it was confirmed that the initial characteristics can be maintained even after long-term storage by using a perfluorocarboxylic acid ester.

That is, if the present invention is applied and the lubricant containing an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid and a perfluorocarboxylic acid ester is retained in the outermost layer, It is confirmed that the lubricant maintains good adhesion and lubricity under any use conditions and maintains the lubricating effect for a long period of time, so that good running properties and durability of the magnetic recording medium are ensured. Was done.

Experimental Example 2 In this experimental example, the effect when a lubricant containing an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol and a perfluorocarboxylic acid ester was used as a lubricant. Was confirmed.

(Preparation of Sample) Synthesis of Ester Compound First, an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol was synthesized.

First, perfluoropolyether HOOCCF ₂ (OC ₂ F ₄ ) having a carboxyl group at the terminal
_m (OCF ₂ ) _j OCF ₂ COOH (molecular weight: 200
0, wherein m and j each represent an integer of 1 or more. ), Stearyl alcohol having a molar ratio twice that of this perfluoropolyether was heated and refluxed in anhydrous toluene using a small amount of p-toluenesulfonic acid and concentrated sulfuric acid as catalysts. At this time, the purification was performed while removing water to be purified. After the completion of the reaction, toluene was removed, and the obtained compound was purified using silica gel column chromatography to obtain an ester compound. This will be referred to as compound 6 for convenience.

Next, in the same manner as in the above-mentioned compound 6, four types of compounds 7 to 10 of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol were synthesized.
Rf ₂ and R ₂ in the following Chemical Formula 14 of the perfluoropolyether having a carboxyl group at both terminals used in producing each compound are as shown in Table 5 below. Table 5 also shows Rf ₂ and R ₂ in the following Chemical Formula 14 of the perfluoropolyether having a carboxyl group at both ends used in producing Compound 6.
In Table 5, j, k, and m each represent an integer of 1 or more.

[0124]

Embedded image

[0125]

[Table 5]

2. Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium. That is, a ferromagnetic metal thin film serving as a magnetic layer and a carbon protective film serving as a protective film were formed on a nonmagnetic support in the same manner as in Experimental Example 1, and a back coat layer was also formed.

Next, in the same manner as in Experimental Example 1 described above, each of the compounds shown in Table 6 below was dissolved in a hexane solvent and the coating amount was 5 (mg / m ² ) on the surface of the carbon protective film. To obtain 13 types of magnetic recording media. These 13 types of magnetic recording media are 6.35 (mm)
Examples 9 to 16 and Comparative Examples 6 to 10 were cut into widths.
13 sample tapes were produced.

[0128]

[Table 6]

3. Evaluation of Characteristics Next, the characteristics of the 13 types of sample tapes of Examples 9 to 16 and Comparative Examples 6 to 10 were evaluated. Here, durability and running performance were evaluated. Specifically, the friction coefficient, still durability, and shuttle durability were evaluated in the same manner as in Experimental Example 1 described above.

[0130] These evaluations were performed immediately after the lubricant was applied in the same manner as in the above-mentioned Experimental Example 1, and each sample tape was stored for one month in an environment of a temperature of 45 (° C) and a humidity of 80 (% RH). I went after. Table 7 shows the results of the initial durability and running properties immediately after the application of the lubricant, and Table 8 shows the results of the durability and running properties after storage after storage for one month.

[0131]

[Table 7]

[0132]

[Table 8]

From the results of Tables 7 and 8, Examples 9 to 16 using a lubricant in which an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long-chain alcohol and a perfluorocarboxylic acid ester were used.
In all cases, under various conditions of use such as high temperature and high humidity, high temperature and low humidity, or low temperature, the friction coefficient, still durability, and shuttle durability deteriorated very little, and it was found that very good results were obtained.

On the other hand, a lubricant containing only an ester compound of a perfluoropolyether having a terminal carboxyl group and a long-chain alcohol, or an ester compound of a perfluoropolyether having a terminal carboxyl group and a long-chain alcohol In Comparative Examples 6 to 10 using a lubricant in combination with a perfluorocarboxylic acid ester containing an unsaturated bond, the friction coefficient and still durability under various use conditions such as high temperature and high humidity, high temperature and low humidity, and low temperature were all used. It can be seen that the shuttle durability was greatly deteriorated and good results could not be obtained.

From these results, it was confirmed that the initial characteristics can be maintained even after long-term storage by using a perfluorocarboxylic acid ester.

That is, when the present invention is applied and the lubricant containing the ester compound of perfluoropolyether having a carboxyl group at the terminal and a long-chain alcohol and the perfluorocarboxylic acid ester is held in the outermost layer, It is confirmed that the lubricant maintains good adhesion and lubricity under any use conditions and maintains the lubricating effect for a long period of time, so that good running properties and durability of the magnetic recording medium are ensured. Was done.

[0137]

As described above, in the magnetic recording medium according to the present invention, at least a magnetic layer is formed on a nonmagnetic support, and a perfluoropolyether having a hydroxyl group at a terminal is formed on the outermost layer. A lubricant containing an ester compound with a long-chain carboxylic acid and a perfluorocarboxylic acid ester, or a lubricant containing an ester compound of a perfluoropolyether having a carboxyl group at a terminal with a long-chain alcohol and a perfluorocarboxylic acid ester Is maintained in the outermost layer. In these lubricants, adhesion and lubricity are maintained under any use conditions, and the lubricating effect is maintained for a long period of time. Performance and durability are ensured.

In the magnetic recording medium of the present invention, if the magnetic layer is made of a ferromagnetic metal thin film, it is possible to sufficiently cope with high-density recording and long-time recording, and a protective film made of carbon can be formed as the outermost layer. In this case, sufficient durability is ensured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view of a main part showing a configuration of a continuous winding type vacuum evaporation apparatus.

FIG. 3 is a schematic sectional view of a main part showing a configuration of a magnetron sputtering apparatus.

[Explanation of symbols]

 1 non-magnetic support, 2 magnetic layer, 3 protective film

Claims (10)

[Claims] 1. A magnetic recording medium comprising at least a magnetic layer formed on a non-magnetic support, comprising an ester compound of a perfluoropolyether having a terminal hydroxyl group and a long-chain carboxylic acid represented by the following formula 1. And a lubricant containing a perfluorocarboxylic acid ester represented by the following formula (2) is retained in the outermost layer. Embedded image Embedded image 2. The mixing ratio of the ester compound of a perfluoropolyether having a hydroxyl group at a terminal to a long-chain carboxylic acid and the perfluorocarboxylic acid ester is 10:90 to 90:10 by weight. The magnetic recording medium according to claim 1, wherein: 3. The magnetic recording medium according to claim 1, wherein said magnetic layer is made of a ferromagnetic metal thin film. 4. The magnetic recording medium according to claim 1, wherein a protective film is formed as an outermost layer on said magnetic layer. 5. The magnetic recording medium according to claim 4, wherein said protective film is made of carbon. 6. A magnetic recording medium having at least a magnetic layer formed on a non-magnetic support, comprising an ester compound of a perfluoropolyether having a carboxyl group at a terminal represented by the following formula 3 and a long-chain alcohol: And a lubricant containing a perfluorocarboxylic acid ester represented by the following formula (4) is retained in the outermost layer. Embedded image Embedded image 7. The mixing ratio of the ester compound of the perfluoropolyether having a carboxyl group at a terminal to a long-chain alcohol and the perfluorocarboxylic acid ester is 10:90 to 90:10 by weight. 7. The magnetic recording medium according to claim 6, wherein: 8. The magnetic recording medium according to claim 6, wherein said magnetic layer is made of a ferromagnetic metal thin film. 9. The magnetic recording medium according to claim 6, wherein a protective film is formed as an outermost layer on the magnetic layer. 10. The magnetic recording medium according to claim 9, wherein said protective film is made of carbon.