JPH07121865A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance durability by using a hard carbon film as a protective layer and incorporating a compd. represented by a specified chemical formula into an overcoat layer. CONSTITUTION:A magnetic layer b-2, a protective layer b-5 and an overcoat layer b-4 are successively formed. on a nonmagnetic substrate b-1. A hard carbon film is used as the protective layer b-5 and a compd. represented by a chemical formula RF-0-R-PO(OH) is incorporated into the overcoat layer b-4. In the formula, RF is 3-12C perfluoroalkenyl and R is a hydrocarbon chain such as arylene or alkylene. Since it is not necessary to increase the thickness of the hard carbon film, durability can be enhanced without deteriorating electromagnetic transducing characteristics. The thickness of the hard carbon film is preferably 10-200Angstrom .

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 such as a magnetic disk, a magnetic tape or a magnetic sheet, and more particularly to a magnetic recording medium having a ferromagnetic metal thin film provided on a support.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, γ-Fe ₂ O ₃ , Co-containing or adhered γ-Fe ₂ O ₃ or CrO ₂ on a support has been used.
Powdered magnetic materials such as metal oxide ferromagnetic powders such as, or metal ferromagnetic powders containing Fe, Co, Ni, etc. as the main components, and organic materials such as vinyl chloride-vinyl acetate copolymers, polyester resins, polyurethane resins, etc. A coating type magnetic recording medium prepared by coating and drying a magnetic coating material dispersed in a binder is widely used.

On the other hand, vacuum deposition, sputtering, ion
Ferromagnetic metal formed by a method such as plating
Thin films have also been investigated as magnetic layers for magnetic recording media for high-density recording.
Part has been put to practical use. However, such ferromagnetic metal thin film
Type magnetic layer contains moisture, oxygen, SO ₂， NO₂Said corrosive gas
Are susceptible to corrosion such as oxidation due to
Has the drawback that the magnetic layer is more likely to deteriorate than
It was

So far, in order to improve the corrosion resistance of such a metal thin film type magnetic recording medium, a higher fatty acid, a metal salt thereof, an alkylamine, a silane coupling agent, a phosphoric acid ester and a titanium coupling are formed on the surface of the magnetic layer. A technique of incorporating a compound such as an agent, a perfluoroalkylcarboxylic acid, the same metal salt, a naphthol, and a triazole into the overcoat layer as a rust preventive is known.

Further, in JP-A-5-12656, corrosion resistance is improved by using a compound having a perfluoroalkenyl group on one side and a phosphorus polar end group (phosphonic acid group) on the other side as a rust preventive agent. Techniques for significant improvements are shown.

This is because the phosphonic acid group is chemically stable adsorbed to the magnetic layer, while the fluorine-based terminal, which is excellent in water and oil repellency, lowers the surface energy of the medium and prevents the corrosion-causing moisture. We believe that suppressing diffusion to the surface of the magnetic layer produces an effective rust prevention effect.

However, in this rust preventive method, when foreign matter such as dust is placed on the surface of the magnetic layer, corrosion occurs from the foreign matter-attached portion and progresses to the surrounding area, so that the overall corrosion resistance is improved. Still not enough.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a magnetic recording medium having more excellent corrosion resistance, particularly a ferromagnetic metal thin film type magnetic recording medium.

[0009]

The above object of the present invention can be achieved by the following constitution.

1. On the non-magnetic support, magnetic layer, protective layer,
In a magnetic recording medium in which an overcoat layer is provided in this order, a hard carbon film is used for the protective layer, and a compound represented by the following chemical formula (1) is contained in the overcoat layer.

The chemical formula (1) RF-OR-P0 (OH) ₂ RF-includes the structure shown in the chemical formula (2) below. Chemical formula (2) (RF2) (RF1) C = C (RF3) -RF1 , RF2 and RF3 represent a fluorine atom or a perfluoroalkyl group.

Examples of -R- include a structure represented by the following chemical formula (3).

Chemical formula (3) —C ₆ H ₄ —C _n H _2n —, —C _n H _2n — In the formula, n represents an integer of 1 to 20.

2. The thickness of the hard carbon film described above is 10 to 20.
The magnetic recording medium as described in 1 above, wherein the magnetic recording medium is 0Å.

The anticorrosive effect of the magnetic layer depends on the degree of insulation between the magnetic layer and the corrosion source. Therefore, forming a dense and durable anticorrosive film on the surface of the magnetic layer improves the corrosion resistance.

On the other hand, since a magnetic recording medium is required to have high electromagnetic conversion characteristics, it is necessary to minimize the spacing loss between the magnetic layer and the recording / reproducing magnetic head. Therefore, it is desirable that the rust preventive film on the magnetic layer be as thin as possible.

Therefore, in order to improve the corrosion resistance of the magnetic recording medium, it is important to have a high rust preventive effect without deteriorating the electromagnetic conversion characteristics.

The hard carbon film used in the present invention is a laminated film containing carbon as a main component, but since it has many film defects, it has a weak resistance to the diffusion of corrosive gas and moisture and has a considerably large film thickness. If it does not, it will not show sufficient rust prevention effect. Therefore, obtaining the rust-preventing effect by the hard carbon film leads to a large deterioration of the electromagnetic conversion characteristics due to spacing loss, and thus defeats the purpose of improving the corrosion resistance of the magnetic recording medium described above.

However, even if the hard carbon film is not so thick and does not show a great rust-preventing effect, by incorporating the compound represented by the chemical formula (1) into the overcoat layer, high protection can be obtained. It turned out to produce a rust effect.

The rust prevention by the above method exhibits a higher rust prevention effect than the rust prevention using only the compound of the chemical formula (1), and in particular, the progress of corrosion when foreign matter adheres to the magnetic layer. It is excellent in terms of suppressing.

Regarding this reason, it is not clear that there are many unclear points, but it is considered as follows.

On the metal surface to which the foreign matter is attached, a difference in redox potential occurs between a portion where the foreign matter is placed and a portion where the foreign matter is not present, a local battery is formed, and corrosion occurs and progresses.

In the present invention, the presence of the hard carbon film between the magnetic layer and the foreign substance provides a physical shielding effect, and in addition, the overcoat layer permeates the defects of the hard carbon film, and the chemical formula (1 It is considered that the compound (1) adsorbs on the surface of the magnetic layer in the defective portion to give a chemical shielding effect, and the synergistic effect of these suppresses the progress of corrosion.

In the compound of the chemical formula (1) of the present invention,
The carbon number of RF- is more preferably 6 to 12, and in the chemical formula (3), the carbon number n of -R- is preferably 1 to 10.

Specific compounds of the present invention are listed below, but the present invention is not limited thereto.

Chemical formula 1-1 C ₃ F ₅ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ chemical compound 1-2 C ₆ F ₁₁ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ chemical compound 1- _{3 C 9 F 17 -OC 6 H} 4 -CH 2 -PO (OH) 2 of _{1-4 C 12 F 23 -OC 6 H} 4 -CH 2 -PO (OH) 2 of 1-5 C ₉ F ₁₇ - OC ₆ H ₄ -C ₄ H ₈ -PO (OH) ₂ compound 1-6 C ₉ F ₁₇ -OC ₆ H ₄ -C ₈ H ₁₆ -PO (OH) ₂ compound 1-7 C ₉ F ₁₇ -OC ₂ H ₄ -PO (OH) ₂ compound 1-8 C ₉ F ₁₇ -OC ₄ H ₈ -PO (OH) ₂ compound 1-9 C ₉ F ₁₇ -OC ₈ H ₁₆ -PO (OH) ₂ present invention, Since it is not necessary to increase the thickness of the hard carbon film so much, it is possible to provide a magnetic recording medium in which the deterioration of the electromagnetic conversion characteristics is not so large, and this is an object of the present invention to improve the corrosion resistance of the magnetic recording medium. It is in agreement with.

As shown in FIG. 1, the magnetic recording medium according to the present invention has a magnetic layer b-2 provided on a support b-1, a protective layer b-5 provided thereon, and an overcoat layer. b-
4 is provided. The magnetic layer b-2 may have a single layer structure or a multilayer structure of two or more layers.

In addition to the above layers, a back coat layer b-3 may be provided, and an undercoat layer (not shown) may be provided between the support and the magnetic layer.

Examples of the support include films of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, aromatic polyamides, cellulose derivatives, vinyl resins and the like.

Worm-shaped projections and / or granular projections can be formed on the support to control the surface roughness or shape of the ferromagnetic metal thin film surface described later. The worm-shaped projections are formed, for example, by coating a support with a polymer substance, drying it, and then stretching it.

On the other hand, the granular protrusions contain or disperse inorganic fine particles having a particle size of about 50 to 3000 Å in the polymer film at the time of forming the polymer film, or organic fine particles or silica, metal and metal oxides in the binder. It is formed by dispersing the fine particles of the above and coating or adhering it as an undercoat layer of the support. The height of this granular protrusion is 50 to 1000Å
Is preferred, and more preferably 100-500Å. The density is preferably 10 ³ to 10 ¹⁰ pieces / mm ² . By forming these protrusions, it is possible to further improve durability and running performance.

The magnetic layer is made of a ferromagnetic metal material such as Fe, Co, Ni, Co-Ni alloy, Co-Cr alloy or Fe-Co alloy on the support.
A ferromagnetic thin film is continuously formed by a vacuum thin film forming technique such as a vacuum deposition method, a sputtering method, or an ion plating method.

The above vacuum vapor deposition method is a method of evaporating a ferromagnetic metal material by electron beam heating or the like under a vacuum of 10 ^-4 to 10 ^-8 Torr and depositing it on a support, in order to further increase the coercive force. The ferromagnetic metal material may be obliquely deposited on the support, or the ferromagnetic metal thin film may be partially oxidized by vapor deposition in an oxygen atmosphere to form a multilayer structure having two or more layers.

Among the materials mentioned above, the ferromagnetic metal materials used for forming such a ferromagnetic thin film are Co--N.
It is preferable that the Ni content of the i alloy is 30 wt% or less from the viewpoint of performance. The thickness of the magnetic layer is preferably 500 to 10,000 Å, more preferably 800 to 3,000 Å in both the single layer structure and the multi layer structure.

When a backcoat layer is formed on the surface of the support opposite to the surface on which the ferromagnetic metal thin film is provided, the backcoat layer is vinyl chloride, vinyl chloride-vinyl acetate copolymer, phenol resin, polyurethane. One or more binder resins such as resins are used, and one type of conductive carbon black or a plurality of types of carbon black having different particle size or chemical properties are dispersed together or separately, and a coating liquid is dispersed on a support. Apply and form. As the organic solvent used during this dispersion, cyclohexanone,
Toluene, methyl ethyl ketone, benzene and the like can be mentioned. Further, an inorganic pigment may be dispersed together with carbon black in order to improve surface properties or durability.

A hard carbon film is provided on the protective layer,
The hard carbon film of the present invention can be formed by sputtering a carbon target or decomposing hydrocarbon gas such as methane, ethane, propane, butane, and benzene with a plasma CVD apparatus.

The hard carbon film is a film in which the electron orbital states of carbon atoms are SP2 and SP3 and which is in an amorphous state containing a diamond bond.
It can be judged from EM selected area diffraction and measurement of binding energy by ESCA. Furthermore, the Vickers hardness is as high as Hv = 2000-3000 (MHA-400 manufactured by NEC.
It has excellent wear resistance.

The thickness of the hard carbon film is preferably in the range of 10 to 200Å, more preferably 3 to 3 in terms of corrosion resistance and suppressing spacing loss of electromagnetic conversion characteristics.
0 to 100Å.

The overcoat layer may be added with a lubricant or an additive in addition to the compound represented by the chemical formula (1) to improve the running property and durability.

Lubricants and additives to be incorporated in the overcoat layer include perfluoropolyether, terminal-modified perfluoropolyether, higher fatty acid or its metal salt, fatty acid amide, fatty acid ester, perfluoroalkylcarboxylic acid or its Metal salt, perfluoroalkylcarboxylic acid ester, perfluoroalkylsulfonic acid, dimethylpolysiloxane, terminal or side chain modified dimethylpolysiloxane (modifying group: -OH, alkoxy, -NH ₂ R (R: alkyl, aryl group, etc.) , -COOH, epoxy group, vinylmercapto group, etc.), acidic phosphoric acid ester, phosphoric acid ester, phosphorous acid ester, phosphonic acid, and the like.

The overcoat layer is formed by dissolving or emulsion in a solvent (for example, CFC-113, HCFC-123, FC-72, FC-77, acetone, methanol), and coating or spraying this liquid on the magnetic layer. Alternatively, the magnetic layer is dipped in this solution and dried. Alternatively, the overcoat compound may be directly deposited by a method such as vapor deposition.

[0042]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

Examples 1 to 11 and Comparative Examples 15 to 22 Co-Ni alloys were deposited on the polyethylene terephthalate film having a thickness of 7 μm by the oblique vapor deposition method while introducing oxygen to form a ferromagnetic metal thin film having a thickness of 2000 Å. . Next, a hard carbon film was formed as a protective film on the surface of the ferromagnetic metal thin film by plasma CVD under the following conditions. The film forming conditions were as follows: benzene / argon 1: 1 (molar ratio) mixed gas was used as the source gas, a gas pressure of 10 Pa, a bias voltage of -2 kV was applied to the substrate, and the RF output of plasma generation was 0.5 Kw. A film is formed, and an overcoat layer is coated thereon at 0.3 mg / m ² as shown below, and a backcoat layer in which carbon black is dispersed in a vinyl chloride-polyurethane resin binder is provided on the back surface of the support. Then, this was cut into a width of 8 mm to prepare a sample tape.

Examples 12 to 14 and Comparative Example 23 A Co-Ni alloy was deposited on a 7 μm-thick polyethylene terephthalate film by oblique vapor deposition while introducing oxygen to form a ferromagnetic metal thin film having a thickness of 2000 Å.

Next, a hard carbon film was formed as a protective film on the surface of this ferromagnetic metal thin film by sputtering under the following conditions. First, the surface of the magnetic layer was bombarded with argon ions as a pretreatment. The film was formed under the gas pressure condition of 5x10 ^-4 Torr, argon gas was used as the discharge gas, and glassy carbon was used as the target, and the sputtering output was 1 k.
I went as W. On top of that, an overcoat layer was applied in an amount of 0.3 mg / m ² as shown below, and a backcoat layer in which carbon black was dispersed in a vinyl chloride-polyurethane resin binder was provided on the back surface of the support. A sample tape was produced by cutting into a width.

Comparative Examples 24 and 25 Co-Ni alloy was deposited on the polyethylene terephthalate film having a thickness of 7 μm by the oblique vapor deposition method while introducing oxygen to form a ferromagnetic metal thin film having a thickness of 2000 Å. Furthermore, a back coat layer in which carbon black was dispersed in a vinyl chloride-polyurethane resin binder was provided on the back surface of the support, and this was cut into a width of 8 mm to prepare a sample tape.

A list of compounds used in Examples and Comparative Examples is shown below.

Chemical formula 1-1 C ₃ F ₅ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ chemical compound 1-2 C ₆ F ₁₁ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ chemical compound 1- _{3 C 9 F 17 -OC 6 H} 4 -CH 2 -PO (OH) 2 of _{1-4 C 12 F 23 -OC 6 H} 4 -CH 2 -PO (OH) 2 of 1-5 C ₉ F ₁₇ - OC ₆ H ₄ -C ₄ H ₈ -PO (OH) ₂ compound 1-6 C ₉ F ₁₇ -OC ₆ H ₄ -C ₈ H ₁₆ -PO (OH) ₂ compound 1-7 C ₉ F ₁₇ -OC ₂ H ₄ -PO (OH) ₂ compound 1-8 C ₉ F ₁₇ -OC ₄ H ₈ -PO (OH) ₂ compound 1-9 C ₉ F ₁₇ -OC ₈ H ₁₆ -PO (OH) ₂ compound 1-10 C ₂ F ₃ -OC ₄ H ₈ -PO (OH) ₂ compound 1-11 C ₂ F ₃ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ compound 1-12 C ₁₅ F ₂₉ -OC ₄ H ₈ -PO (OH) ₂ compound 1-13 C ₁₅ F ₂₉ -OC ₆ H ₄ -CH ₂ -PO (OH) ₂ compound 1-14 CH _3- (CH ₂ ) ₁₆ -COOH compound 1-15 CH _3- ( CH ₂ ) ₁₇ -NH ₂ The composition of each sample is shown below.

Sample number Protective film Protective film thickness (Å) Overcoat layer Example 1 Plasma CVD film 80 Chemical 1-1 Example 2 ↑ 80 Chemical 1-2 Example 3 ↑ 80 Chemical 1-3 Example 4 ↑ 80 Formula 1-4 Example 5 ↑ 80 Formula 1-5 Example 6 ↑ 80 Formula 1-6 Example 7 ↑ 80 Formula 1-7 Example 8 ↑ 80 Formula 1-8 Example 9 ↑ 80 Formula 1-9 Implementation Example 10 ↑ 20 Chemical formula 1-3 Example 11 ↑ 150 Chemical formula 1-3 Example 12 Sputtered carbon film 20 Chemical formula 1-3 Example 13 ↑ 80 Chemical formula 1-3 Example 14 ↑ 150 Chemical formula 1-3 Comparative example 15 Plasma CVD film 80 Chem 1-10 Comparative Example 16 ↑ 80 Chem 1-11 Comparative Example 17 ↑ 80 Chem 1-12 Comparative Example 18 ↑ 80 Chem 1-13 Comparative Example 19 ↑ 80 Chem 1-14 Comparative Example 20 ↑ 80 Chem 1 -15 Comparative Example 21 ↑ 250 Chemical 1-3 Comparative Example 22 ↑ 200 None Comparative Example 23 Sputtered carbon film 200 None Comparative Example 24 Plasma CVD film 5 Chemical 1-3 Comparative Example 25 Sputtered carbon film 5 Chemical 1-3 Comparative Example 26 None 0 to 1-3 comparison Example 27 None 0 None Each sample tape was tested for corrosion resistance and measurement of electromagnetic conversion characteristics. Corrosion resistance test is conducted by applying about 30 dust particles per cm ^{2 to the} surface of the magnetic layer in advance at 60 ° C.
The amount of change in the saturation magnetization density after standing for 1 week under the condition of 90% RH was measured. In addition, the electromagnetic conversion characteristics can be measured using commercially available Hi
-8 VTR deck V-900 (manufactured by Sony) was used for measurement at a recording frequency of 7 MHz, and the output obtained with a sample tape (Comparative Example 23) having no protective layer or overcoat layer was set to 0 dB of the reference value. did.

The results are shown below. Sample number Corrosion resistance test result Electromagnetic conversion characteristic measurement value (dB) Example 1-8-1.6 Example 2-7-1.6 Example 3-7-1.6 Example 4-7-1.6 Example 5-7-1.6 Example Example 6-7-1.6 Example 7-7-1.6 Example 8-7-1.6 Example 9-7-1.6 Example 10-9-0.6 Example 11-7-3.0 Example 12-9-0.6 Example 13-7-1.6 Example 14-7-3.0 Comparative Example 15-14-1.6 Comparative Example 16-14-1.6 Comparative Example 17-13-1.8 Comparative Example 18-13-1.8 Comparative Example 19-14-1.6 Comparative Example 20 −14 −1.6 Comparative Example 21 −7 −5.0 Comparative Example 22 −15 −4.0 Comparative Example 23 −15 −4.0 Comparative Example 24 −15 −0.6 Comparative Example 25 −15 −0.6 Comparative Example 26 −15 −0.6 Comparative Example 27 − 20 0.0 As can be seen from the above results, the sample of the present invention in which the hard carbon film is used as the protective layer and the compound of the chemical formula (1) is used in the overcoat layer has a high rust prevention effect and a low electromagnetic conversion characteristic. It provides the result of satisfying the corrosion resistance required for the magnetic recording medium with a small amount of bottom.

[0051]

The magnetic recording medium according to the present invention has more excellent corrosion resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a magnetic recording medium of the present invention.

[Explanation of symbols]

 b-1 support b-2 magnetic layer b-3 backcoat layer b-4 overcoat layer b-5 protective layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Ito 1st Sakura-cho, Hino City, Tokyo Konica Stock Company In-house

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer comprising a ferromagnetic metal thin film, a protective layer and an overcoat layer provided in this order on a non-magnetic support, wherein a hard carbon film is used as the protective layer, and A magnetic recording medium comprising a compound represented by the following chemical formula (1) in an overcoat layer. Chemical formula (1) RF-O-R-P0 (OH) ₂ (In chemical formula (1), RF represents a perfluoroalkenyl group having 3 to 12 carbon atoms, and R is a hydrocarbon chain such as an arylene group or an alkylene group. Represents.) 2. The hard carbon film as described above has a thickness of 10 to 200.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is Å.