JP2000048342A - Magnetic record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure oxidation and corrosion resistances by imparting intrasurface angle dependency to the coercive force of a magnetic recording layer and specifying a range of the ratio of the max. value of the coercive force to the min. value. SOLUTION: The ratio of the max. value of the coercive force to the min. value is adjusted to >1 to 3.5. The max. value of the coercive force is preferably >=100 kA/m for a high density record medium and the upper limit of the coercive force is limited in accordance with the characteristics of a magnetic recording head and an erasing head. A protective layer preferably comprises a carbon material from the viewpoint of wear resistance and the thickness is preferably 3-20 nm from the viewpoint of oxidation or corrosion resistance and the viewpoint of spacing loss. A magnetic material used in the magnetic record layer is, e.g. a simple ferromagnetic metal such as Co, Fe or Ni or an alloy such as Co-Ni, Co-Ni-Pt, Co-Cr, Co-Cr-Ta or Co-Cr-Pt.

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, and more particularly, to a magnetic recording medium having a magnetic recording layer and a protective layer formed by a vacuum thin film forming technique and having excellent corrosion resistance.

[0002]

2. Description of the Related Art In recent years, magnetic recording devices associated with audio devices, video devices, computer devices, and the like have been increasingly reduced in size and weight, improved in image quality, extended in time, or digitally recorded. There has been a strong demand for high-density recording for magnetic recording media used in devices. As a magnetic recording medium that meets this demand, a medium using a thin-film type magnetic recording layer has been put to practical use. This uses a thin magnetic recording layer in which a ferromagnetic metal thin film such as Co or a Co alloy is deposited on a non-magnetic support by a thin film forming technique such as sputtering, vapor deposition, ion plating or plating. . Above all, a method for producing a thin-film magnetic recording medium by oblique deposition in which magnetic particles are incident obliquely to a non-magnetic support (in the thickness direction) is industrially established.

[0003] Thin-film magnetic recording media are excellent in magnetic properties such as coercive force Hc, residual magnetic flux density Br and squareness ratio Rs. Since the magnetic recording layer does not contain a non-magnetic component such as a binder, the packing density of the magnetic material is high. Therefore, even if the thickness of the magnetic recording layer is extremely thin, for example, 1 μm or less, the residual magnetic flux Φr required for the magnetic recording medium can be secured. Due to these characteristics, the thickness loss at the time of recording demagnetization and reproduction is small, and it is suitable as a high-density magnetic recording medium.

[0004] However, the demand for higher density is further increased, and it is considered that a magnetic recording layer having a sub-quarter micron thickness is used. In such an ultra-thin magnetic recording layer, there is a high possibility that corrosion due to oxidation or rust of the magnetic metal is directly linked to a fatal error such as a loss of reproduced signal or an increase in dropout.

Conventionally, a technique of forming a protective layer and a top coat layer on the surface of a magnetic recording layer has been used to improve the corrosion resistance and durability of a metal thin film type magnetic recording medium. This top coat layer contains a lubricant, a rust inhibitor and the like. In addition, a DLC (Diamon
d-like Carbon) is often used.
By using this protective layer, the durability and corrosion resistance of the metal thin-film magnetic recording medium have been greatly improved.

[0006]

As a characteristic required for the protective layer, it is required that the magnetic recording layer be formed thinner in order to reduce spacing loss. On the other hand, in order to improve corrosion resistance, it is required to form a continuous film. These are conflicting requirements. In particular, if there are irregularities or discontinuities on the surface of the magnetic recording layer, discontinuities also occur in the protective layer formed in these portions, and the magnetic recording layer is oxidized from the missing portions of the protective layer, generating rust.

The thin magnetic recording layer strongly reflects the surface properties of the underlying nonmagnetic support. PET (Polyethlen
On the surface of a non-magnetic support such as e-terephthalate), there may be irregularities which are inevitably generated during the manufacturing process or minute convexes which are intentionally formed for improving the running property. When a magnetic recording layer is formed on such a non-magnetic support by an oblique deposition method, magnetic particles do not enter a portion that is a shadow of a convex portion or a concave portion, and thus a discontinuous portion is generated in the magnetic recording layer. . For this reason, a missing portion also occurs in the protective layer formed in the discontinuous portion, and oxidation of the magnetic recording layer proceeds.

The present invention has been made in view of the above-mentioned problems, and has been proposed to ensure the continuity of a thin magnetic recording layer and a protective layer even if the magnetic recording layer and the protective layer are thin. It is an object to provide a high magnetic recording medium.

[0009]

In order to solve the above-mentioned problems, the present inventor pays attention to the in-plane angle dependence of the coercive force of the magnetic recording layer, and sets the ratio between the maximum value and the minimum value to be within a specific range. Then, they found that oxidation resistance or corrosion resistance could be improved, and completed the present invention.

That is, the magnetic recording medium of the present invention is a magnetic recording medium having a magnetic recording layer and a protective layer on a non-magnetic support, wherein the coercive force of the magnetic recording layer has an in-plane angle dependency. When the ratio between the maximum value and the minimum value of the coercive force is 1
And 3.5 or less.

The ratio of the maximum value and the minimum value of the coercive force is more preferably more than 1 and not more than 2.5.

The maximum value of the coercive force is preferably 100 kA / m or more for the purpose of a high-density magnetic recording medium. The upper limit of the coercive force is limited by the characteristics of the magnetic recording head and the erasing head.

The protective layer is preferably made of a carbon-based material from the viewpoint of abrasion resistance. The thickness of the protective layer is preferably 3 nm or more and 20 nm or less from the viewpoints of oxidation resistance or corrosion resistance and spacing loss.

FIG. 1 shows an example of a magnetic recording medium formed by oblique vapor deposition, which is a typical method of manufacturing a thin film type magnetic recording medium.
The operation of the present invention will be described with reference to FIGS.

FIG. 3 is a diagram showing the principle of the oblique deposition method. That is, when the length direction of the long non-magnetic support 1 is the y-axis, the width direction is the x-axis, and the vertical (thickness) direction is the z-axis, the non-magnetic support traveling in the y-axis direction is: Incident angle i from z-axis direction
Then, the magnetic particle beam 5 is incident, and the magnetic recording layer 6 is formed. The incident angle i is an important angle that determines the magnetic characteristics of the magnetic recording layer 6, and is usually 40 to
A value around 50 ° is adopted.

In order to enhance the uniformity of the magnetic recording layer formed on the wide non-magnetic support 1, a molten magnetic metal in a wide Hearse is also used as a source of the magnetic particle beam 5. FIG. 1 shows the relationship between the angle of incidence θ of the magnetic particle beam incident from the width direction (x-axis direction) with respect to the center line of the nonmagnetic support 1 and the width of the hearth. conventionally,
As shown in FIG. 1A, the width of the molten magnetic metal 4 in the hearth 3 is selected to be approximately equal to the width of the nonmagnetic support 1 or the width of the magnetic recording layer 6. At this time, the incident angle θ of the magnetic particle beam 5 from the width direction with respect to the center line of the nonmagnetic support 1
In the prior art, a maximum of about 40 ° or less with respect to the center line of the nonmagnetic support 1 is employed.

As described above, by setting the incident angle θ of the magnetic particle beam 5 from the width direction of the nonmagnetic support 1 to be narrow, the orientation of the magnetic recording layer 6 in the y-axis direction is improved. Therefore, the in-plane angle dependence of the coercive force of the magnetic recording layer 6 is large, and the ratio of the in-plane maximum and minimum values of the coercive force is 4 or more. JP-A-9-92533 discloses that the electromagnetic conversion characteristics of a thin-film magnetic recording medium can be improved by setting the ratio to 4 to 6.

However, when the incident angle θ of the magnetic particle beam 5 from the width direction of the non-magnetic support 1 is set to be small, it exists on the surface of the non-magnetic support 1 as shown in FIG. The minute projections 2 cause a large shadow 2 s of the incident magnetic particle beam 5. No magnetic recording layer is formed in the shadow 2s portion. Therefore, the protective layer in this portion also becomes discontinuous, and oxidation and corrosion occur. FIG. 2 is a plan view showing the relationship between the micro-projections 2 and the magnetic particle beam 5 as viewed from the z-axis direction of the non-magnetic support 1.

In the present invention, the main point is to reduce or eliminate the shadow 2s of the incident magnetic particle beam 5 to prevent oxidation and corrosion. That is, FIG.
As shown in (2), by setting the incident angle θ of the magnetic particle beam 5 from the width direction of the non-magnetic support 1 to be wide, the shadow 2s
Is so large that the area does not substantially matter. For this purpose, as shown in FIG. 1 (b), the width of the hearth 3 and the width of the molten magnetic metal 4 in the hearth 3 are selected to be wider than in the prior art, so that the magnetic particle beam 5 from the width direction of the non-magnetic support 1 can be formed. The incident angle θ can be increased.

The incident angle θ of the magnetic particle beam 5 from the width direction at the center line position in the x-axis direction of the non-magnetic support 1 is 45 °.
It is desirable that the angle is set to not less than 80 ° and preferably not more than 50 ° and not more than 75 °. When the incident angle θ is selected as described above,
The in-plane angle dependence of the coercive force is smaller than in the prior art, and the ratio of the maximum value to the minimum value is more than 1 to 3.5 or less. When the value exceeds 3.5, the generation of the shadow 2s cannot be ignored, and a value of 1 means an in-plane isotropic magnetic recording medium.
This is not a realistic value as long as magnetic anisotropy is imparted by the oblique deposition method explained in principle in FIG. When the ratio between the maximum value and the minimum value of the in-plane coercive force is set to be more than 1 and not more than 2.5, the effect of oxidation and corrosion of the magnetic recording layer is further ensured.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail. First, a roll-to-roll type vacuum evaporation apparatus used for manufacturing the magnetic recording medium of the present invention will be described with reference to a schematic sectional view of FIG.

The chamber 11 of the vacuum evaporation apparatus is roughly divided into a transport system for transporting the non-magnetic support 1 and a film-forming system for forming a magnetic recording layer, both of which are separated by partition walls. It is evacuated by differential evacuation by a vacuum pump (not shown).

The long and wide non-magnetic support 1 wound around the supply roll 13 is sent out at a constant speed into the chamber 11 of the transfer system while being wound around the cooling can 14, and is returned to the take-up roll 15 again. It is wound. The cooling can 14 has a cooling medium circulated therein to cool the surface and prevent the nonmagnetic support 1 from being thermally deformed. Reference numeral 16 denotes a guide roll for applying a constant tension to the non-magnetic support 1. Each of the rolls has a width substantially equal to that of the nonmagnetic support 1. The feed speed and tension of the nonmagnetic support 1 are managed by a drive unit and a control unit (not shown).

In the chamber 11 of the film forming system, a wide hearth 3 is provided below the cooling can 14, and a molten magnetic metal 4 such as Co or a Co alloy is accommodated therein. The liquid surface of the molten magnetic metal 4 has an electron beam source 1
7 irradiates an electron beam 18 as a heat source to heat and evaporate the molten magnetic metal 4. Electron beam 1
Numeral 8 is deflected by an electromagnet (not shown), and scans substantially the entire length of the liquid surface of the molten magnetic metal 4 in the width direction. A constant amount of magnetic metal ingot or wire (both not shown) is continuously supplied to the hearth 3 to keep the liquid level of the molten magnetic metal 4 constant at all times.

The evaporated molten magnetic metal 4 becomes a magnetic particle beam 5 and is obliquely incident on the non-magnetic support 1 wound around the cooling can 14 to form a magnetic recording layer (not shown) on the surface thereof. The incident area and the incident angle i of the magnetic particle beam 5
Is restricted by the incident angle limiting mask 20, and the minimum value of i is selected in the range of about 40 to 50 °. In the present embodiment, the minimum value of i is 45 ° and the maximum value is 90 °,
The magnetic particle beam 5 was set to be tangent to the cooling can 14. The non-magnetic support 1 on which the magnetic particle beam 5 is incident
The opening end of the gas nozzle 19 is provided in the vicinity of, and a gas such as oxygen can be introduced to improve the magnetic characteristics, durability, weather resistance, and the like of the magnetic recording layer.

Now, the features of the vacuum deposition apparatus shown in FIG.
The width of the hearth 3 (depth in the direction of the paper in the figure). The width of the hearth 3 is wider than the width of the nonmagnetic support 1, and therefore, the width of the molten magnetic metal 4 contained in the hearth 3 is also wider than the width of the nonmagnetic support 1. The electron beam 18 can also scan over the entire width of the molten magnetic metal 4. For this purpose, an electromagnet (not shown) for deflecting the electron beam 18 may be changed, or a plurality of electron beam sources 17 may be provided in the width direction of the hearth 3 and divided and scanned.

The relationship between the width of the hearth 3 and the width of the nonmagnetic support 1 will be described in more detail with reference to FIG. FIG. 5 is a schematic perspective view showing a relative positional relationship between the hearth 3, the nonmagnetic support 1 wound around the cooling can 14, and the magnetic particle beam 5.

That is, the width of the hearth 3 and the molten magnetic metal 4 accommodated therein is wider than the width of the nonmagnetic support 1 wound around the cooling can 14. With this configuration, the incident angle θ of the magnetic particle beam 5 that enters from the width direction of the nonmagnetic support 1 is controlled to be 45 ° or more and 80 ° or less at the center line position of the nonmagnetic support 1. That is, the angle at which the magnetic particle beam 5 incident from the end of the molten magnetic metal 4 is incident from the width direction of the nonmagnetic support 1 is 45 ° or more.
It is set in the range of 0 °.

As described above, by injecting the magnetic particle beam 5 from a wide range in the width direction of the non-magnetic support, the magnetic particle beam 5 shown in FIG.
As described in (b), even if unevenness is present on the non-magnetic support 1, no shadow 2s is generated, or the shadow 2s
Is so small that it can be ignored. Therefore,
A magnetic recording medium having excellent oxidation resistance and corrosion resistance, with no discontinuous portions or missing portions in the magnetic recording layer 6 and no discontinuous or missing portions in the protective layer formed thereon. can do.

For the purpose of oblique deposition, the incident angle i with respect to the thickness (z-axis) direction of the non-magnetic support 1 whose principle is shown in FIG. 3 is about 40 to 50 ° in the present invention. In this embodiment, the angle is set to 45 °.

The embodiment of the magnetic recording medium of the present invention has been described above. In addition to the vapor deposition method using an electron beam as a heat source as a source of the magnetic particle beam 5, a vapor deposition method using high-frequency induction heating or resistance heating, The magnetic recording layer may be formed by an ion plating method, an electric field evaporation method, a sputtering method, a laser ablation method, or the like.

As the non-magnetic support used in the magnetic recording medium of the present invention, any of those used in ordinary magnetic recording media can be used, such as polyethylene terephthalate,
Polyesters such as polyethylene-2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; vinyl resins such as polyvinyl chloride; vinylidene resins such as polyvinylidene chloride; Organic polymers such as polyamide imide and polyimide are exemplified. A base material layer made of an organic binder may be provided on the surface of the nonmagnetic support to improve the adhesiveness.

Further, a filler such as SiO ₂ or latex may be contained in the base material layer or the nonmagnetic support to form minute surface projections. As an example, an undercoat layer having a surface density of about 10 ⁷ particles / mm ² is formed by applying an emulsion solution in which a water-soluble latex containing an acrylate ester as a main component is dispersed on a nonmagnetic support. I do. Alternatively, silica microparticles may be internally added to the non-magnetic support to form surface protrusions.

These minute projections control the surface properties of the metal magnetic thin film and contribute to improving the running properties of the magnetic recording tape. In the present invention, there is no possibility that the non-magnetic support having such minute projections may impair the oxidation resistance and corrosion resistance.

The magnetic material used for the magnetic recording layer is C
a simple ferromagnetic metal such as o, Fe or Ni, or Co-N
i-based alloy, Co-Ni-Pt-based alloy, Co-Cr alloy,
Co such as Co-Cr-Ta alloy and Co-Cr-Pt alloy
System alloy, Fe-Co-Ni alloy, Fe-Ni-B alloy,
F such as Fe-Co-B alloy and Fe-Co-Ni-B alloy
Examples thereof include an e-based alloy or the like, or an alloy having a structure in which an oxide, a nitride, a carbide, or the like is precipitated in these ferromagnetic materials or at grain boundaries. The magnetic recording layer is formed as a single layer or a multilayer. In the case of lamination, a non-magnetic layer may be interposed as an intermediate layer.

As a material of the protective layer formed on the magnetic recording layer, for example, carbon, graphite, DLC, Si
O ₂ , Si ₃ N ₄ , SiON, SiC, Al ₂ O ₃ , A
_{lN, TiO 2, Cr 2 O} 3, TiN, TiC, ZrO
₂ , BC, etc. are used alone or as a composite membrane. Further, an organic polymer to which a vacuum thin film forming technique can be applied, such as polyparaxylylene (trade name: parylene) or fluororesin, can also be used. These materials may be used in a single layer or a laminate. Among them, DLC is preferably employed because of its high protective effect. DLC is PVD (Physical Vapor Deposit) such as ion plating and sputtering.
ion) method, plasma CVD method, ECR (Electron Cyclo
tron Resonance) Plasma CVD method, arc jet C
It can be formed as a thin film by various CVD (Chemical Vapor Deposition) methods such as a VD method.

FIG. 6 is a schematic sectional view of a plasma CVD apparatus for forming a DLC as an example of a CVD apparatus for forming a protective layer. In the plasma CVD apparatus of FIG. 6, components having functions similar to those of the vacuum evaporation apparatus shown in FIG. 4 are denoted by the same reference numerals.

A non-magnetic support 1 having a magnetic recording layer formed on one surface and a back coat layer formed on the other surface
Is supplied from the supply roll 13 and the guide roll 1
6. Run through the cooling can 14 and the guide roll 16 and wind it up on the take-up roll 15. A reaction tube 21 having an opening at an upper portion thereof is provided over the entire length of the cooling can 14 in the axial direction. A gas nozzle 19 is connected to a lower portion of the reaction tube 21, and a reaction gas containing a hydrocarbon-based gas as a main component is introduced from the gas nozzle 19. DC is contained in the reaction tube 21.
A mesh-shaped electrode 22 to which a DC voltage of +500 to 2000 V from a power supply 23 is applied is housed, and a plasma of a hydrocarbon-based gas is generated between the mesh-shaped electrode 22 and the cooling can 14 at the ground potential, and the non-magnetic supporting member travels. A protective layer of DLC can be continuously formed on the surface of the magnetic recording layer of the body 1.
These components are housed in a vacuum chamber 11,
The inside of the chamber can be evacuated from an exhaust port 12 by a vacuum pump (not shown) and controlled to a desired degree of vacuum. As the reaction gas, one obtained by diluting an aromatic hydrocarbon such as toluene or an aliphatic hydrocarbon such as methane or acetylene with a carrier gas is used.

A top coat layer may be formed on the surface of the protective layer for the purpose of lubrication and rust prevention. The top coat layer is formed, for example, by applying a top coat solution in which a lubricant, a rust inhibitor and the like are dissolved in a solvent such as alcohol and toluene. Usable solvents include alcohol solvents such as methanol, ethanol, and isopropanol; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ester. Ester solvents such as glycol dimethyl ether, glycol monoethyl ether,
Ether solvents such as dioxane, benzene, toluene,
Aromatic hydrocarbon solvents such as xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Organic chlorinated compound solvents such as ethylene chlorohydrin and dichlorobenzene are exemplified. Further, a fluorine alcohol-based solvent can also be used.

Examples of the lubricant include ester compounds of higher fatty acids and higher alcohols, silicone compounds, and hydrocarbon compounds containing fluorine. A perfluoropolyether compound is a typical example that can be preferably used.

As the rust preventive, any of the rust preventives conventionally used in magnetic recording media can be used, for example, phenols such as dihydric phenol, alkylphenol and nitrophenol, naphthol. ,
Naphthols such as nitronaphthol, nitrosonaphthol, aminonaphthol, and halogen-substituted naphthol; quinones such as methylquinone, hydroxyquinone, aminoquinone and nitroquinone; benzophenone and its derivatives hydroxyarylbenzophenone; ,
Nitrogen-containing heterocyclic compounds such as kynurenic acid or riboflavin; oxygen-containing heterocyclic compounds such as tocopherol or guanosine; sulfur-containing heterocyclic compounds such as sulfolansulforenthione; compounds containing a mercapto group such as thiophenol, dithizone, and thiooxin; Examples thereof include thiocarboxylic acids such as acids and rubeanic acids and salts thereof, and thiazole compounds such as diazosulfide and benzothiazoline.

As a vaporizable rust inhibitor, amylamine,
Organic amines such as ethanolamine, naphthylamine, cyclohexylamine, dicyclohexylamine, and isopropylamine; organic esters of nitrite; organic esters of thionitrite; trimethylsulfonium nitrite; diisopropylammonium nitrite; dicyclohexylammonium nitrite; cyclohexylamine carbonate Etc. are exemplified. In addition, benzoic acid, nitrous acid, benzotriazole and derivatives thereof can also be used. Any of the above rust preventives can be used alone or as a mixture as a solute of the top coat solution of the present invention.

Further, in order to maintain the lubricating effect by coping with the use conditions in more severe environments, the extreme pressure agent is added to the lubricant or its composition in a mixing ratio of about 30/70 to 70/30 by weight. May be used in combination. An extreme pressure agent is a compound that, when partial metal contact occurs in the boundary lubrication area, reacts with the metal surface due to the frictional heat involved, and forms a reaction product film to obtain a friction / wear prevention effect. Any of conventionally known phosphorus-based extreme pressure agents, sulfur-based extreme pressure agents, halogen-based extreme pressure agents, organometallic extreme pressure agents and composite extreme pressure agents can be used.

In the magnetic recording medium of the present invention, the thickness of the top coat layer, that is, the formation density is not particularly limited, but is preferably 0.3 to 100 mg / m ² as an example.
More preferably, it is 0.5 to 20 mg / m ² .
If the formed density is less than 0.3 mg / m ² , sufficient durability and running stability cannot be obtained. If the formed density exceeds 100 mg / m ² , the durability also decreases, and a phenomenon of sticking to a magnetic drum or the like occurs. The method for forming the top coat layer is not particularly limited, but various application methods such as gravure coating and dip coating are applied.

On the other surface of the non-magnetic support, a coating type or thin film type back coat layer may be provided. The configuration of the back coat layer is not particularly limited. The coating back coat layer is formed by dispersing non-magnetic particles in an organic binder to control the surface roughness and conductivity. Examples of the material of the non-magnetic particles include hematite, boehmite, fused alumina, α, β Alumina, mica, kaolin, talc, clay, silica, magnesium oxide, titanium oxide (rutile and anatase), zinc oxide, zinc sulfide, calcium carbonate, magnesium carbonate, barium carbonate, barium sulfate, lead sulfate , Inorganic compounds such as tungsten sulfide, polyethylene, polyvinyl chloride, polyimide,
Examples thereof include polymer resins such as polytetrafluoroethylene, starch, nonmagnetic metals, carbon, and the like. The non-magnetic particles have a mean particle size of 0.05 to 1 μm, preferably 0.1 to 0.7 μm, and are usually added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the organic binder. Is done. Further, from the viewpoint of paint suitability and durability, it is preferable that the particles have an isotropic shape such as a substantially spherical shape and a substantially regular polyhedron.

The organic binder material used for the coating backcoat layer is not particularly limited, but any of conventionally used thermoplastic resins, thermosetting resins, and reactive resins can be used. It is desirable that the thermoplastic resin be used in combination with a thermosetting resin, a reactive resin, or the like. The resin preferably has an average molecular weight of 5,000 to 200,000, and 10,000.
To 100,000 are more preferred. As the thermoplastic resin, for example, vinyl chloride resin, vinyl acetate resin, vinyl fluoride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, Vinyl chloride-acrylonitrile copolymer, vinylidene chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-
Vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, polyurethane Resin, polyester polyurethane resin, polyester resin, polycarbonate polyurethane resin, polycarbonate resin, polyamide resin, polyvinyl butyral resin, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene Copolymers, polyester resins, amino resins, various synthetic rubbers and the like can be mentioned. Examples of thermosetting resins and reactive resins include phenolic resins, epoxy resins,
Polyurethane curing resin, urea formaldehyde resin,
Melamine resins, alkyd resins, silicone resins, polyamine resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, mixtures of low molecular weight glycols, high molecular weight diols and isocyanates, and mixtures of these resins Is exemplified. Among these resins, it is preferable to use a polyurethane resin, a polycarbonate resin, a polyester resin, an acrylonitrile-butadiene copolymer, which is considered to impart flexibility. These resins are
In order to improve the dispersibility of non-magnetic particles, -SO ₃ M, -O
SO ₃ M, —COOM, or —PO (OM ′) ₂
(Where M represents H or an alkali metal such as Li, Ka, or Na, and M ′ represents H or an alkali metal such as Li, Ka, or Na, or an alkyl group). Other polar functional groups include -NR ₁ R
₂ , -NR ₁ R ₂ R ₃ ⁺ X ⁻ side chain type having a terminal group, and> NR ₁ R ₂ ⁺ X ⁻ main chain type (here, R ₁ , R ₂ , R ₃ is a hydrogen atom or a hydrocarbon group, X ^- represents fluorine, chlorine, bromine, halogen ion or an inorganic iodine, the organic ions). In addition, a polar functional group such as —OH, —SH, —CN, or an epoxy group may be used. The content of these polar functional groups is 10 ^-1 to 1
0 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mo
1 / g. These organic binders can be used alone or in combination of two or more. The amount of these organic binders in the applied back coat layer is 1 to 200 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the nonmagnetic particles.

As a curing agent for crosslinking and curing the above-mentioned organic binder, for example, polyisocyanate or the like can be added. As the polyisocyanate, an adduct of trimethylolpropane and 2,4-tolylene diisocyanate (TDI) (for example, trade name Coronate L-5)
Although 0) is generally used, an adduct of an alkylene diisocyanate such as 4,4-diphenylmethane diisocyanate (MDI) or hexane diisocyanate (HDI) may be used. In addition, polyglycidylamine compounds such as tetraglycidyl metaxylenediamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, tetraglycidylaminodiphenylmethane, triglycidyl-p-aminophenol, and 2-dibutylamino-
Polythiol compounds such as 4,6-dimercapto-substituted triazines, epoxy compounds such as triglycidyl isocyanurate, mixtures of epoxy compounds and isocyanate compounds, mixtures of epoxy compounds and oxazoline compounds,
A mixture of an imidazole compound and an isocyanate compound,
Any conventionally known compounds such as methylnadic anhydride can be used. The mixing ratio of these curing agents to the organic binder is 5 to 80 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the organic binder.

A lower coating backcoat layer may be formed between the coating backcoat layer and the nonmagnetic support for the purpose of improving the adhesiveness of the coating backcoat layer. The lower coating backcoat layer is formed by dissolving an organic binder alone or a carbon powder and, if necessary, other nonmagnetic powder and an organic binder in a solvent to form a coating, coating this on a nonmagnetic support, and drying. Is done.

Solvents used in the paint for forming the back coat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as methanol, ethanol, propanol and butanol, methyl acetate, ethyl acetate, and the like. Esters such as propyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, ethers such as diethylene glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene, xylene, methylene chloride, ethylene Halogenated hydrocarbons such as chloride, carbon tetrachloride, chloroform and dichlorobenzene are used.

The coating method for forming the coating backcoat layer on the non-magnetic support is not particularly limited, and may be air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure Any of the conventional methods such as coat, kiss coat, cast coat, extrusion coat, and spin coat can be adopted. The coated back coat layer formed on the non-magnetic support is dried with heated air or the like to remove the organic solvent, and is subjected to a curing treatment if necessary.

As the material used for the thin film back coat layer, for example, carbon, graphite, diamond-like carbon, SiO ₂ , Si ₃ N ₄ , SiON, SiC,
Al ₂ O ₃ , AlN, TiO ₂ , Cr ₂ O ₃ , TiN,
TiC, ZrO ₂ , MgO, BN, CoO, a nonmagnetic metal or the like is used alone or as a composite film. Further, an organic polymer to which a vacuum thin film forming technique can be applied, such as polyparaxylylene (trade name: parylene) or fluororesin, can also be used. These materials may be used in a single layer or a laminate.

The method of forming the thin film back coat layer includes various sputtering methods such as a vacuum thin film forming method, ie, DC sputtering method, RF sputtering method, ion beam sputtering method, magnetron sputtering method, reactive sputtering method, vapor deposition method, and reactive sputtering method. An evaporation method, an ion plating method, or the like is employed. Plasma CVD or E
A CR plasma CVD method, a reduced pressure CVD method, or the like may be employed. In the case of an organic polymer thin film, it can be formed by an evaporation method or plasma polymerization of a raw material gas. In either method, it is desirable to form the non-magnetic support and the like while cooling the non-magnetic support and the like so as not to thermally deform the non-magnetic support and the coating backcoat layer provided thereon.

A top coat layer may be formed on these back coat layers. In the case of a coating type back coat layer,
A commonly used lubricant or rust inhibitor may be separately added.

[0054]

EXAMPLES Hereinafter, the magnetic recording medium of the present invention will be described in more detail with reference to Reference Examples and Comparative Examples. However, the present invention is not limited to the following examples.

[Embodiment 1] This embodiment is an example in which the present invention is applied to a magnetic recording medium for a digital video cassette.

A magnetic recording layer was formed on one main surface of a non-magnetic support made of 6 μm PET using a continuous winding type vacuum evaporation apparatus shown in FIG. In this embodiment,
Incident angle θ of magnetic particle beam from width direction of non-magnetic support
Was set to a maximum of 50 ° at the center line position of the non-magnetic support (see FIG. 1B). That is, the electron beam was scanned such that the incident angle θ of the magnetic particle beam from the width direction of the nonmagnetic support was 0 ° to 50 ° at the center line position of the nonmagnetic support. An example of the evaporation conditions is shown below. Magnetic metal: Co 100% Incident angle i 45 to 90 ° Traveling speed 25 m / min Oxygen introduction amount 0.6 slm Vacuum degree during vapor deposition 2 × 10 ^-2 Pa Film thickness 170 nm

Next, a back coat layer was formed on the other surface (back surface) of the non-magnetic support. The paint for the back coat layer is
The following composition was used as an example. 100 parts by weight of carbon particles (Carbon black # 60 manufactured by Asahi Carbon Co.) 100 parts by weight of organic binder (mainly composed of polyurethane) Solvent 250 parts by weight (methyl ethyl ketone / toluene / cyclohexanone =
2/1/1) This composition was mixed by a ball mill, and a curing agent (Coronate L) was added to the organic binder by 10 parts by weight just before coating. The coating was applied by a gravure coater at a running speed of 150 m / sec so that the dry coating thickness was 0.5 μm.

Next, a protective layer made of DLC was formed on the magnetic recording layer 6. This protective layer was formed by the plasma CVD apparatus shown in FIG. An example of the plasma CVD conditions is shown below. Introduced gas: toluene diluted with carrier gas Reaction pressure 10 Pa DC voltage 1.5 kV Protective layer thickness 10 nm

Thereafter, a top coat solution obtained by dissolving a perfluoropolyether compound in toluene was gravure coated on the protective layer 6 so that the dry weight was 3 mg / m ² in areal density. After drying, this was cut into a 6.35 mm width and stored in a cassette to complete the magnetic recording medium of Example 1.

Example 2 Example 1 was the same as Example 1 except that the angle of incidence θ of the magnetic particle beam from the width direction of the non-magnetic support was 60 ° at the center line position of the non-magnetic support. A magnetic recording layer was formed according to the method described in Example 1. That is, the electron beam was scanned so that the incident angle θ of the magnetic particle beam from the width direction of the nonmagnetic support was 0 ° to 60 ° at the center line position of the nonmagnetic support. Subsequently, a back coat layer, a protective layer and a top coat layer are formed;
The sheet was cut into a width of 35 mm and housed in a cassette to complete the magnetic recording medium of Example 2.

Example 3 Example 1 was the same as Example 1 except that the angle of incidence θ of the magnetic particle beam from the width direction of the non-magnetic support was 70 ° at the center line position of the non-magnetic support. A magnetic recording layer was formed according to the method described in Example 1. That is, the electron beam was scanned so that the incident angle θ of the magnetic particle beam from the width direction of the nonmagnetic support was 0 ° to 70 ° at the center line position of the nonmagnetic support. Subsequently, a back coat layer, a protective layer and a top coat layer are formed;
The sheet was cut into a width of 35 mm and housed in a cassette to complete the magnetic recording medium of Example 3.

Example 4 The incident angle θ of the magnetic particle beam from the width direction of the non-magnetic support was set to be a maximum of 70 ° at the center line position of the non-magnetic support, and the thickness of the protective layer was The magnetic recording layer was formed in the same manner as in Example 1 except that the thickness was changed to 4 nm. Subsequently, a back coat layer, a protective layer, and a top coat layer were formed, cut to a width of 6.35 mm, and stored in a cassette to complete the magnetic recording medium of Example 4.

Reference Example 1 The incident angle θ of the magnetic particle beam from the width direction of the non-magnetic support was set to be 70 ° at the center line position of the non-magnetic support, and the thickness of the protective layer was The magnetic recording layer was formed in the same manner as in Example 1 except that the thickness was changed to 2 μm. Subsequently, a back coat layer, a protective layer and a top coat layer were formed, cut to a width of 6.35 mm, and stored in a cassette to complete the magnetic recording medium of Reference Example 1.

Reference Example 2 An incident angle i (see FIG. 3) of the non-magnetic support from the z-axis direction was set to 25 °, that is, an incident angle closer to the vertical direction than in the example. Further, except that the incident angle θ of the magnetic particle beam from the width direction of the non-magnetic support was set to 70 ° at the center line position of the non-magnetic support, the magnetic recording layer was the same as in Example 1. It was created. Subsequently, a back coat layer, a protective layer and a top coat layer were formed, cut to a width of 6.35 mm, and stored in a cassette to complete the magnetic recording medium of Reference Example 2.

Comparative Example 1 Example 1 was repeated except that the incident angle θ of the magnetic particle beam from the width direction of the nonmagnetic support was 40 ° at the maximum at the center line position of the nonmagnetic support. A magnetic recording layer was formed according to the method described in Example 1. That is, the electron beam was scanned such that the incident angle θ of the magnetic particle beam from the width direction of the nonmagnetic support was 0 ° to 40 ° at the center line position of the nonmagnetic support. Subsequently, a back coat layer, a protective layer and a top coat layer are formed;
The sheet was cut into a width of 35 mm and stored in a cassette to complete the magnetic recording medium of Comparative Example 1.

Examples 1-4 and Reference Examples 1-2 prepared above
The magnetic characteristics, durability, and electromagnetic conversion characteristics of the magnetic recording medium of Comparative Example 1 were measured.

[Magnetic Characteristics] The coercive force Hc and the in-plane angle dependence of the coercive force were measured using a sample vibration type magnetometer (VS.
M), applied magnetic field 10 kOe, sweep speed 3 min /
It was measured under the condition of 10 kOe.

The in-plane angle dependence of the coercive force is 6.35.
A measurement sample was cut out from the magnetic recording medium sheet before cutting at a different mm to change the angle, and used for measurement. This measurement may be performed using a sample cut into a circular shape while changing the relative angle between the circular sample and the applied magnetic field. FIG. 7 shows the in-plane angle dependence of the coercive force of the magnetic recording medium of the first embodiment. The horizontal axis indicates the angle, the y-axis direction (longitudinal direction) of the magnetic recording medium is 0 °, x
The axial direction (width direction) is set to 90 °. From the graph of FIG. 7, the ratio (Hc _max / Hc _min ) of the maximum value and the minimum value of the in-plane coercive force of the magnetic recording medium of Example 1 was 3.5.

[Durability] As a measure of the durability of the magnetic recording medium against oxidation and corrosion, the magnetic recording medium was stored for 50 days in a high-temperature, high-humidity environment of 60 ° 90% RH, and the amount of decrease in the residual magnetization Φr was initially measured. The values are normalized by values. Further, from an accelerated test of the decrease in the residual magnetization Φr, an estimated life until the residual magnetization Φr was deteriorated by 15% in a standard environment was calculated.

[Electromagnetic Conversion Characteristics] A signal having a wavelength of 0.5 μm was recorded by a digital video recorder (a modified device manufactured by Sony), and the reproduced output was measured. The measured values were compared with each other by normalizing the reproduction output of a commercially available digital video cassette (the same recording wavelength of 0.5 μm) to 0 dB.

Examples 1 to 5 measured by the above measuring methods
4. Table 1 shows the measurement results of the magnetic recording media of Reference Examples 1 and 2 and Comparative Example 1.

[0072]

[Table 1]

Consider the measurement results in [Table 1]. Example 1
3 are obtained by changing the maximum value of the incident angle θ.
_The magnetic recording medium was manufactured by the same manufacturing method except that the value of _max / Hc _min was changed in the range of 3.5 to 2.4. In these series of examples, as the value of Hc _max / Hc _min decreases, the oxidation resistance and corrosion resistance, that is, the amount of residual magnetic flux deterioration decreases. In other words, the incident angle θ from the width direction of the non-magnetic support is widely dispersed, and the influence of the shadow due to the protrusions and recesses on the surface of the non-magnetic support and the area of the missing portion of the magnetic recording layer caused by this are reduced as much as possible. It is clear that the durability of the magnetic recording medium can be improved by reducing the size.

Example 4 is a magnetic recording medium manufactured by the same manufacturing method as in Example 3, except that only the protective layer thickness was reduced to 4 μm. This magnetic recording medium is Hc _max / Hc _min
Is 2.5, which is almost the same as that of the third embodiment, but the residual magnetic flux deterioration amount is slightly large at 34%, and the estimated life is 26 years. For a magnetic recording medium requiring high reliability, such as for a data streamer, the estimated life is required to be around 30 years. Therefore, the magnetic recording medium of the fourth embodiment satisfies the minimum requirement.

Reference Example 1 is a magnetic recording medium manufactured by the same manufacturing method as in Example 3, except that only the protective layer thickness is reduced to 2 μm. This magnetic recording medium is Hc _max / Hc _min
Is 2.4 which is the same as that of Example 3, but the residual magnetic flux deterioration amount is as large as 40%, and the estimated life is 22 years. Therefore, it is not suitable for a magnetic recording medium requiring high reliability, such as for a data streamer.

Reference Example 2 is based on the same manufacturing method as in Example 3 except that the minimum value of the incident angle i is 25 °.
The thickness of the protective layer is also the same as 10 μm. In this magnetic recording medium, when depositing the magnetic recording layer, an oblique deposition angle from the z-axis direction was small, that is, an incident angle i closer to the perpendicular was employed. Therefore, the influence of the shadow due to the projections on the surface of the nonmagnetic support and the area of the missing portion of the magnetic recording layer caused by the shadow are small, and the durability of the magnetic recording medium can be improved. However, the value of the coercive force itself is small, and the output of the electromagnetic conversion characteristics is reduced to -4.0 dB.

Comparative Example 1 is a magnetic recording medium manufactured by the same manufacturing method as in Examples 1 to 3, except that the maximum value of the incident angle θ is set to 40 °. That is, since the incident angle θ from the width direction of the non-magnetic support is set to be small, Hc _max / H
The value of c _min is 3.9, which is out of the predetermined range. Therefore, the influence of the shadow due to the convex portion on the surface of the non-magnetic support and the area of the missing portion of the magnetic recording layer caused by this are large, the residual magnetic flux deterioration amount is as large as 38%, and the estimated lifetime is 23.
Year. This value is a value when the thickness of the protective layer is 10 μm. When the thickness of the protective layer is reduced as in Example 4 or Reference Example 1, the durability is out of the standard.

The magnetic recording medium of the present invention has been described in detail by taking a digital video cassette tape as an example.
These are merely examples, and the present invention is not limited to these examples. That is, the present invention can be widely applied to those using a thin film type magnetic recording layer, such as an analog video cassette tape and a magnetic recording medium for data recording.

[0079]

As is apparent from the above description, according to the magnetic recording medium of the present invention, even if the magnetic recording layer has a reduced thickness, the number of missing or discontinuous portions is reduced, and the magnetic recording layer is formed on the magnetic recording layer. The loss or discontinuity of the protective layer can also be reduced. Therefore, the durability of the magnetic recording layer such as oxidation resistance and corrosion resistance is improved, and a highly reliable magnetic recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between an incident angle θ of a magnetic particle beam incident from a width direction (x-axis direction) of a nonmagnetic support and a width of a hearth.

FIG. 2 is a schematic plan view showing a state where a shadow of a magnetic particle beam is generated by minute projections on the surface of a nonmagnetic support.

FIG. 3 is a schematic perspective view showing the principle of the oblique vapor deposition method and showing the thickness (z-axis) direction of a non-magnetic support and an incident angle i formed by a magnetic particle beam.

FIG. 4 is a schematic sectional view of a roll-to-roll type vacuum deposition apparatus.

FIG. 5 is a perspective view showing the relationship between the width of a hearth and the width of a magnetic recording medium.

FIG. 6 is a schematic sectional view of an example of a plasma CVD apparatus for forming a protective layer.

FIG. 7 is a graph showing the in-plane angle dependence of the coercive force of the magnetic recording medium of Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support, 2 ... Micro convex part, 2s ... Shadow, 3 ... Hearth, 4 ... Molten magnetic metal, 5 ... Magnetic particle beam, 6 ... Magnetic recording layer 11 ... Chamber, 12 ... Exhaust port, 13 ... Supply Roll, 14: cooling can, 15: take-up roll, 1
6 Guide roll, 17 Electron beam source, 18 Electron beam, 19 Gas nozzle, 20 Incident angle limiting mask, 21 Reaction tube, 22 Electrode, 23 DC power supply

Claims (5)

[Claims] 1. A magnetic recording medium having a magnetic recording layer and a protective layer on a non-magnetic support, wherein a coercive force of the magnetic recording layer has an in-plane angle dependency, and a maximum value of the coercive force. 2. The ratio of the minimum values exceeds 1 and
5. A magnetic recording medium, wherein the number is 5 or less. 2. The method according to claim 1, wherein the ratio between the maximum value and the minimum value of the coercive force is 1
2. The magnetic recording medium according to claim 1, wherein the ratio is more than 2.5 and not more than 2.5. 3. The maximum value of the coercive force is 100 kA / m.
3. The magnetic recording medium according to claim 1, wherein: 4. The magnetic recording medium according to claim 1, wherein the protective layer is made of a carbon-based material. 5. The protective layer has a thickness of 3 nm or more and 20 n or more.
3. The magnetic recording medium according to claim 1, wherein m is equal to or less than m.