JPH076353A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a thin film type magnetic recording medium having excellent corrosion resistance, still durability and electromagnetic transducing characteristics. CONSTITUTION:A Co-based ferromagnetic thin film 2 is formed on a non- magnetic substrate 3 and a diamondlike carbon layer 1 is formed on the thin film 2 with hydrocarbon as starting material. The max. concn. of oxygen in the surface part of the ferromagnetic thin film corresponding to <=1/3 of the thickness is 10 to <30 atomic% and the thickness of the diamondlike carbon layer is 20 to <100Angstrom .

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 comprising a Co type ferromagnetic thin film layer, such as a magnetic tape.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, γ-Fe ₂ O ₃ , Cr containing γ-Fe ₂ O ₃ , Co on a non-magnetic support.
Dispersion of oxide magnetic powder such as O ₂ or powder magnetic material such as alloy magnetic powder mainly composed of Fe, Co, Ni, etc. in organic binder such as vinyl chloride copolymer, polyester resin or polyurethane resin. A coating type magnetic recording medium prepared by coating and drying a magnetic coating is widely used.

On the other hand, a ferromagnetic thin film formed by a method such as vacuum deposition, sputtering and ion plating has been studied as a magnetic recording medium for high density recording. Not only are these ferromagnetic thin films excellent in coercive force and squareness ratio, but also the residual magnetic flux density is high because the magnetic layer does not contain an organic binder, which is essential in the coating type medium. Furthermore, since the thickness of the magnetic layer can be made extremely thin, there is little thickness loss during reproduction.

On the other hand, although these ferromagnetic thin films have excellent electromagnetic conversion characteristics, they are more likely to be corroded and have poor still durability as compared with the coating type medium because they are made of a metal material.

In order to improve these performances, a protective layer of amorphous carbon by sputtering or diamond-like carbon by plasma CVD has recently been studied. Although these hard carbon films have the effect of improving the above performance, the spacing loss associated with the film thickness reduces the output particularly due to the short wavelength output.

In recent years, the MP tape has improved its short-wavelength output due to improvements in thinning, finer particles, surface smoothing, etc., and is approaching that of ME tape. Therefore, the greatest advantage of ME tape, the reduction due to spacing loss of short wavelength output, must be minimized.
It was necessary to form a hard carbon film of Å or more, so the short wavelength output was reduced by 2 dB or more.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a thin film type magnetic recording medium having excellent corrosion resistance, still durability and electromagnetic conversion characteristics. .

[0008]

The above object is to form a ferromagnetic thin film layer containing Co as a main component on a non-magnetic support, and to form a diamond-like carbon layer containing hydrocarbon as a raw material on the ferromagnetic thin film layer. In the magnetic recording medium formed with, the maximum oxygen concentration in the surface side 1/3 in the thickness direction of the ferromagnetic thin film layer is 10 at% or more and less than 30 at%, and the diamond-like carbon layer has a film thickness of 20 Å or more and less than 100 Å It is achieved by a magnetic recording medium characterized by

[0009]

The present invention has been obtained as a result of earnest research to achieve the above-mentioned object. The maximum oxygen concentration in the magnetic layer surface side 1/3, which is normally accompanied by introduction of oxygen during vapor deposition, is 10 at% to 30 at. % Or less, the spacing loss due to the non-magnetic oxide layer is reduced, and the diamond-like carbon layer is formed from 20Å to 100Å on the surface of the magnetic layer, increasing the spacing loss due to the diamond-like carbon layer. It is characterized by improving corrosion resistance and still durability while minimizing

The present invention will be described in detail below.

In the magnetic recording medium of the present invention, as shown in FIG. 1, a ferromagnetic thin film 2 is formed on a non-magnetic support 3 by vapor deposition, and a diamond-like carbon layer 1 is further formed thereon. There is. The magnetic recording medium will be described in detail below.

(A) Non-magnetic support The material for the non-magnetic support used in the present invention is as follows:
Polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamides, aromatic polyamides, polyimides, polyphenylene sulfides, polyether ether ketones, polycarbonates, etc. Plastics are used.

The roughness or shape of the ferromagnetic metal thin film layer can be controlled by forming worm-like protrusions or granular protrusions on the non-magnetic support.

The worm-shaped projections can be formed, for example, by coating a non-magnetic substrate with a polymer substance, drying it, and then stretching it. The above-mentioned granular projections disperse inorganic fine particles having a particle size of 50 Å to 3000 Å at the time of film formation of a polymer film and hold them inside, or disperse organic fine particles or silica or metal fine particles in a binder to provide non-magnetic support. It can be formed by applying or attaching as an undercoat layer of the body. The height of this granular protrusion is 50
Å ~ 1000 Å, more preferably 100 Å ~ 500 Å. The density is preferably 10 ³ to 10 ⁷ pieces / mm ² . By forming these protrusions, durability and running performance are improved.

The form of the non-magnetic support may be a tape, a sheet, a card, a disc or the like, and each material is selected according to the final form as a magnetic recording medium.

The thickness of these non-magnetic supports is tape,
In the case of a sheet, it is about 3 to 100 μm, preferably 4 to 50
μm, and in the case of a disk or a card, those in the range of 30 μm to 10 mm can be used.

(B) Ferromagnetic thin film layer A ferromagnetic thin film layer is provided on the non-magnetic support.

As the magnetic material used in the present invention, a known magnetic material which has been conventionally used can be used as long as it is Co or an alloy magnetic material containing Co as a main component. Specific examples of the magnetic material used in the method of the present invention include Fe-Co, Fe-Co-Ni, Co-Ni, Co-Cu, Co-A.
u, Co-Y, Co-La, Co-Pr, Co-Gd, Co-Sm, Co
-Si, Co-Pt, Co-Cr, Fe-Co-Cr, Co-V, Co-
W, Co-Mn, Co-Ti, Co-Ni-Cr, Fe-Co-Ni-Cr
Etc. can be mentioned.

The ferromagnetic thin film layer in the magnetic recording medium of the present invention preferably contains Co in an amount of 70% by weight or more based on the weight of all metal atoms. When the content of Co is out of the above range, the coercive force and the residual magnetic flux density are lowered, and the electromagnetic conversion characteristics may be deteriorated.

Further, oxygen is contained in the ferromagnetic thin film layer.

In general, an oxide gas having a high oxygen concentration is formed in the vicinity of the surface of the ferromagnetic thin film layer by introducing an oxidizing gas into the low incident air flow side during vapor deposition. The maximum concentration of oxygen in the oxide layer and the film thickness of the oxide layer change depending on the amount of the oxidizing gas introduced.

If the amount of the oxidizing gas introduced is too small, the maximum oxygen concentration and the film thickness of the oxide layer are reduced, resulting in deterioration of running durability, corrosion resistance and still durability, and further the oxygen concentration inside the magnetic layer is also increased. Since it is low, coercive force, output, and S / N are also low.

On the other hand, if the amount of the oxidizing gas introduced is too large, the coercive force increases, but the film thickness of the surface oxide layer increases and the output decreases. From the above, a predetermined amount of oxidizing gas to be introduced is determined that has good balance of characteristics such as durability, corrosion resistance, and electromagnetic conversion characteristics.

At this time, the maximum oxygen concentration of the surface oxide layer is
It becomes 30 to 50 at%, and the film thickness of the oxide layer becomes about 50 to 300 Å.

When a diamond-like carbon layer is formed on the ferromagnetic thin film layer by a plasma CVD apparatus, oxygen near the surface of the ferromagnetic thin film layer reacts with hydrogen or carbon by applying a negative bias voltage, and H ₂ O, It becomes CO _{2 and} escapes as gas. As a result, the oxygen concentration in the vicinity of the surface after diamond-like carbon film formation is reduced as compared with that before film formation, spacing loss is reduced, and electromagnetic conversion characteristics are improved. However, if the negative bias voltage is too high, abnormal discharge occurs and it becomes difficult to deposit a film. Negative bias voltage is -100V
It is preferably within the range of to -3 KV.

In the present invention, the maximum oxygen concentration in the surface side 1/3 of the ferromagnetic thin film layer after the diamond-like carbon layer is formed is 10 to 30 at%, preferably 10 to 25 at%.
If the maximum oxygen concentration in the surface side 1/3 is less than 10 at%, the coercive force is low and the electromagnetic conversion characteristics are insufficient. If it exceeds 30 at%, the output is reduced due to spacing loss due to the surface oxide layer.

The ferromagnetic thin film layer has a layer thickness of 5000 Å or less,
It is preferably in the range of 800 to 3500Å.

The ferromagnetic thin film layer may be composed of a plurality of layers. In this case, the ferromagnetic thin film layer 1/3 on the surface side of the uppermost layer.
The maximum oxygen concentration is 10 to 30 at%.

To form the ferromagnetic thin film layer, the ferromagnetic material is deposited on the non-magnetic support.

As the vapor deposition method, a vacuum vapor deposition method, an ion plating method or the like can be used. For heating, an electron beam heating method, a resistance heating method, a laser beam heating method, an induction heating method, or the like can be used.

The oxidizing gas used during the vapor deposition may be any gas containing at least one selected from oxygen, oxygen allotrope and oxygen active species. Other gases that can be used in combination with these gases include nitrogen (N ₂ ) gas, helium gas (He), xenon gas (Xe), radon gas (Rn), argon (Ar), neon (Ne) and the like. Active gas, carbon monoxide (CO), carbon dioxide (C
O ₂ ), hydrogen (H ₂ ) and water vapor (H ₂ O) can be used alone or in combination of two or more.

(C) Diamond-Like Carbon Layer A diamond-like carbon layer is provided on the ferromagnetic thin film layer.

The diamond-like carbon layer in the present invention can be produced by decomposing a hydrocarbon gas such as methane, ethane, propane, butane and benzene using a plasma CVD apparatus.

The diamond-like carbon layer is a film having an electronic structure of SP2 and SP3 and having an amorphous state including a diamond bond, which is judged from Raman analysis, TEM selected area diffraction and measurement of binding energy by ESCA. can do.

Further, the Vickers hardness is Hv = 2000-300
It is as high as 0 (kg / mm ² ) (measured with NEC MHA-400) and has excellent wear resistance.

The diamond-like carbon layer has a thickness of 20 to 100Å, preferably 20 to 50Å. 2
If it is less than 0Å, it has little effect on corrosion resistance and still durability,
On the other hand, if it exceeds 100Å, the spacing loss increases and the output decreases.

(D) Other Layers The magnetic recording medium of the present invention has a non-magnetic support on the above-mentioned non-magnetic support for the purpose of improving slipperiness of the magnetic recording medium, preventing electrification, preventing transfer, improving corrosion resistance, and improving abrasion resistance. Further, an overcoat layer or a backcoat layer may be provided after and / or before the formation of the magnetic thin film layer by a known coating method or vapor deposition method, for example. These coating methods and vapor deposition methods are described, for example, in JP-A-54
-123922, JP-A-54-123923, JP-A-56-71284, JP-A-56-71286, JP-A-56-71287, JP-A-56-11626
And Japanese Patent Laid-Open No. 57-135442.

The back coat layer is vinyl chloride, vinyl chloride
-One or more binder resins such as vinyl acetate, phenol resin, polyurethane resin, etc., one conductive carbon black or two or more carbon blacks with different particle size or chemical properties are dispersed together or separately. The coating liquid dispersed in the above is applied to the surface of the non-magnetic support opposite to the surface where the ferromagnetic thin film is provided. As the organic solvent used at the time of dispersion, cyclohexanone, toluene, methyl ethyl ketone, benzene, etc. are often used. Further, an inorganic pigment may be dispersed together with carbon black in order to improve surface properties or durability.

The overcoat layer as a lubricant is perfluoropolyether, per-terminal modified perfluoropolyether, both-end modified perfluoropolyether, fatty acid or its metal salt, fatty acid amide, fatty acid ester, acidic phosphoric acid ester, acidic. Amine phosphate, hydrogen phosphite, perfluoroalkyl carboxylic acid or its metal salt, perfluoroalkyl carboxylic acid ester, perfluoroalkyl sulfonic acid, or its ammonium salt can be used, as well as a rust preventive (for example, alkylphenol, Hydroquinone, cresol, naphthols, triazoles) and extreme pressure agents (eg, phosphoric acid extreme pressure agents such as trioleyl phosphate, sulfur extreme pressure agents such as dimethyl sulfide, and complex type poles such as thiophosphates). Pressure agent) It may be.

[0040]

EXAMPLES The present invention will be described in more detail below by showing Examples of the present invention. Needless to say, the present invention is not limited to the following examples and can be appropriately modified within the scope of the gist of the present invention.

(Example 1) Using a winding type vacuum vapor deposition machine,
Magnetic layer consisting of Co-Ni = 80-20 alloy on a polyethylene terephthalate film with a thickness of 10.0 μm θmax 90 degrees, θmi
The film was formed under the conditions of n40 degrees and a film thickness of 2000Å. The film was formed while introducing 400 SCCM of oxygen from the lowest incident angle side.

A diamond-like carbon layer was formed on this sample using a plasma CVD apparatus. The film forming conditions were as follows: benzene / argon 1: 1 (molar ratio) mixed gas was used as a raw material gas, the gas pressure was 10 Pa, the RF output of plasma generation was 0.5 KW, and the negative bias voltage was -2 KV. The diamond-like carbon layer thickness is set to 20Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 20.2 at%.

The still magnetic durability, corrosion resistance, and electromagnetic conversion characteristics of the manufactured magnetic recording medium were measured.

Still durability: After cutting the prepared sample into a width of 8 mm, it is put in a cassette for 8 mm VTR and a commercially available Hi8 VTR deck is used to first record the color bar signal and then perform still reproduction, and the reproduction output is the initial value. It was evaluated by the time until it was further reduced by -2 dB.

Corrosion resistance: After the tape pieces were stored at 60 ° C. and 90% relative humidity for 1 week, the reduction rate of saturation magnetization was measured.

Electromagnetic conversion characteristics: An output of 7 MHz was measured using a commercially available Hi8 VTR deck. However, here, the output of the sample in which the diamond-like carbon layer of Comparative Example 1 was not formed was set to 0 dB.

The results obtained are shown in Table 1.

(Example 2) A magnetic recording medium was prepared in the same manner as in Example 1 except that the diamond-like carbon layer had a thickness of 30 Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 20.8 at%.

(Example 3) A magnetic recording medium was prepared in the same manner as in Example 1 except that the diamond-like carbon layer had a thickness of 50 Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 19.4 at%.

(Example 4) A magnetic recording medium was prepared in the same manner as in Example 1 except that the diamond-like carbon layer had a thickness of 100 Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 19.6 at%.

Example 5 A magnetic recording medium was prepared in the same manner as in Example 1 except that 200 SCCM of oxygen was introduced from the lowest incident angle side and the thickness of the diamond-like carbon layer was 100 Å. did. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 13.2 at%.

Example 6 A magnetic recording medium was prepared in the same manner as in Example 1 except that 600 SCCM of oxygen was introduced from the lowest incident angle side and the thickness of the diamond-like carbon layer was set to 20 Å. did. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 27.3 at%.

Comparative Example 1 A magnetic recording medium was formed under the same conditions as in Example 1 except that the diamond-like carbon layer was not formed in Example 1. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 40.2 at%.

(Comparative Example 2) A magnetic recording medium was prepared in the same manner as in Example 1 except that the diamond-like carbon layer had a thickness of 10 Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 31.9 at%.

(Example 3) A magnetic recording medium was prepared in the same manner as in Example 1 except that the thickness of the diamond-like carbon layer was changed to 200Å. The maximum oxygen concentration in the magnetic layer surface side 1/3 by the Auger depth profile was 17.1 at%.

[0056]

[Table 1]

(Evaluation) As is clear from the above results,
The maximum oxygen concentration in the surface side 1/3 in the thickness direction of the ferromagnetic thin film layer is 10 at% or more and less than 30 at%, and the thickness of the diamond-like carbon layer is 20 Å or more and less than 100 Å. It is also high, and the decrease rate of saturation magnetization Φs after thermo storage is also low. Furthermore, the still durability is also good.

[0058]

EFFECTS OF THE INVENTION When a diamond-like carbon layer is formed on a ferromagnetic thin film layer, oxygen on the surface of the ferromagnetic thin film layer reacts with hydrogen and carbon by applying an appropriate negative bias voltage. Since it escapes as gas, spacing loss decreases. Furthermore, the diamond-like carbon layer of 20 to 100Å improves still durability and corrosion resistance.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part of a magnetic recording medium of the present invention.

[Explanation of symbols]

 1 diamond-like carbon layer 2 magnetic layer 3 non-magnetic support (substrate)

Claims (1)

[Claims] 1. A magnetic recording medium in which a ferromagnetic thin film layer containing Co as a main component is formed on a non-magnetic support, and a diamond-like carbon layer containing hydrocarbon as a raw material is formed on the ferromagnetic thin film layer. The maximum oxygen concentration in the surface side 1/3 in the thickness direction of the ferromagnetic thin film layer is 10 at% or more and less than 30 at%, and the film thickness of the diamond-like carbon layer is
A magnetic recording medium characterized by being 20 Å or more and less than 100 Å.