JPH11185234A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium with which a further larger capacity may be embodied by reducing the thickness of a nonmagnetic base, wear resistance and durability are improved by suppressing the curling of the magnetic recording medium as far as possible and electromagnetic conversion characteristics and traveling property are eventually improved. SOLUTION: The magnetic recording medium 1 is constituted by forming a ferromagnetic metallic thin film 3 on the nonmagnetic base 2. The nonmagnetic base 2 consists of an arom. polyamide film formed with 100<2> to 100<4> pieces/mm<2> of microprojections of 10 to 40 nm in average height on the surface formed with the ferromagnetic metallic thin film 3. A back-coating layer 4 is formed on the surface of the nonmagnetic base 2 on the side opposite to the surface formed with the ferromagnetic metallic thin film 3. This back- coating layer 4 consists of a material contg. a compd. polymerizable by electron rays and is formed by polymerizing this compd. by irradiation with the electron rays.

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 using a ferromagnetic metal thin film, and more particularly to a magnetic recording medium suitable for a long-time recording video tape or a large-capacity tape streamer.

[0002]

2. Description of the Related Art Conventionally, a polyethylene terephthalate film has been mainly used as a non-magnetic support for a metal thin film type magnetic recording medium. Specifically, as a non-magnetic support of a home video cassette tape, for example, an 8 mm tape, a polyethylene terephthalate film having a thickness of about 7 to 10 μm is used. A polyethylene terephthalate film having a thickness of about 5 to 7 μm is used as a non-magnetic support of a tape streamer for data backup of a computer.

[0003] By the way, as for a magnetic recording medium for a video cassette, further downsizing and long-time recording have been desired as the video cassette is downsized. Also, with the recent increase in the amount of information, it has been desired to increase the capacity of magnetic recording media for tape streamers. Therefore, in order to meet these demands, studies have been made to reduce the thickness of the magnetic recording medium.

In order to reduce the thickness of a magnetic recording medium,
It is easy to reduce the thickness of the nonmagnetic support. However, when a polyethylene terephthalate film is used as the non-magnetic support, if the thickness is reduced, the strength in the length direction or the width direction decreases.
When the strength of the magnetic recording medium in the longitudinal direction decreases, the magnetic recording medium is likely to be deformed when running on a video tape recorder or a drive. Further, the magnetic recording medium has a problem that when the strength in the width direction is reduced, wrinkles and breaks are likely to occur, and furthermore, poor contact with the head is likely to occur.

Therefore, the use of a polyamide film as a non-magnetic support for a metal thin-film magnetic recording medium has been studied and put into practical use.

[0006] Polyamide films have higher strength than polyethylene terephthalate films. Therefore,
Magnetic recording media using this polyamide film as a non-magnetic support can be made thinner, and are attracting attention as magnetic recording media suitable for long-term recording of video cassette tapes and large capacity of tape streamers. Have been.

[0007]

Generally, in order to achieve high-density recording, it is necessary to smooth the surface of a magnetic recording medium to some extent to reduce spacing loss as much as possible. On the other hand, if the surface of the magnetic recording medium is made too flat, it will interfere with head touch and running properties. Therefore, it is necessary to secure appropriate surface properties by controlling the fine shape of the surface.

Further, in the metal thin film type magnetic recording medium, the magnetic layer is made of a ferromagnetic metal thin film and the thickness of the magnetic layer is thin, so that the magnetic layer is easily affected by the surface properties of the nonmagnetic support. The surface shape of the nonmagnetic support is directly reflected on the surface shape of the magnetic layer.

Therefore, in the metal thin film type magnetic recording medium, it is necessary to control the surface shape of the non-magnetic support so that the fine shape of the surface of the magnetic layer is in an appropriate state.

Accordingly, the present inventors have filed a patent application
Japanese Patent Application Laid-Open No. 100511 discloses a magnetic recording medium in which the surface shape of a non-magnetic support made of a polyamide film is controlled so that the fine shape of the surface of the magnetic layer is optimized, and the electromagnetic conversion characteristics and running properties are improved. I have.

By the way, even for a metal thin film type magnetic recording medium using such a polyamide film as a nonmagnetic support, further thinning of the magnetic recording medium is strongly required in order to cope with a further increase in capacity. Requested. For example, in a magnetic recording medium for a tape streamer, since the recording capacity is doubled every two to three years, there is a strong demand for a thinner magnetic recording medium.

However, even in a metal thin-film type magnetic recording medium using the above polyamide film as a non-magnetic support, if the non-magnetic support is further thinned in order to further reduce the thickness of the magnetic recording medium, the magnetic recording medium can be used. Curved in the width direction,
So-called curling occurs. As a result, in this metal thin-film type magnetic recording medium, it is difficult to stably contact the magnetic head, and the electromagnetic conversion characteristics are greatly reduced, and the contact pressure with the magnetic head is increased, so that this magnetic recording There has been a problem that the edge portion of the medium is liable to be worn, which causes dropout and output reduction.

In view of the above, the present invention has been proposed in view of the conventional circumstances, and the thickness of the non-magnetic support has been reduced to achieve a further increase in capacity. Curling is suppressed as much as possible to improve wear resistance and durability,
As a result, it is an object of the present invention to provide a magnetic recording medium having improved electromagnetic conversion characteristics and running characteristics.

[0014]

A magnetic recording medium according to the present invention is a magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic support, wherein the non-magnetic support is formed of the ferromagnetic metal thin film. Has an average height of 10 to 40 nm on the surface where
Microprojection consists 10 ² to 10 ^40,000 / mm ² forming aromatic polyamide film. Moreover, in the magnetic recording medium according to the present invention, a back coat layer is formed on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed, and the back coat layer is formed by an electron beam. It is made of a material containing a polymerizable compound, and is formed by polymerizing the compound by electron beam irradiation.

[0015] The thickness of the nonmagnetic support is 1.0 to 4.0.
Preferably it is 5 μm. Further, the thickness of the back coat layer is preferably from 0.1 to 0.6 μm.

In the magnetic recording medium according to the present invention having the above-described structure, the surface shape of the nonmagnetic support made of the aromatic polyamino film is controlled so that the fine shape of the surface of the ferromagnetic metal thin film is optimal. Done. Therefore, the magnetic recording medium according to the present invention has both good electromagnetic conversion characteristics and good running properties.

In addition, the magnetic recording medium to which the present invention is applied has a high hardness backing formed by irradiation with an electron beam on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. A coat layer is formed. For this reason, the magnetic recording medium according to the present invention secures necessary and sufficient strength even if the thickness of the magnetic recording medium is thin, curl of the magnetic recording medium is suppressed as much as possible, and wear resistance and durability are improved. . Furthermore, in the magnetic recording medium according to the present invention, since the back coat layer is formed, curling of the magnetic recording medium is suppressed as much as possible, so that the magnetic recording medium can sufficiently contact the magnetic head. It has both good electromagnetic conversion characteristics and good recording / reproducing properties.

Further, in the magnetic recording medium according to the present invention, the non-magnetic support made of an aromatic polyamino film is reduced in thickness to 1.0 to 4.5 μm, so that a large capacity can be achieved. .

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view showing a magnetic recording medium to which the present invention is applied.

In the magnetic recording medium 1 according to the present invention, the ferromagnetic metal thin film 3 is formed on one main surface 2a of the nonmagnetic support 2 and the ferromagnetic metal thin film 3 of the nonmagnetic support 2 is formed. A back coat layer 4 is formed on one main surface 2b opposite to the surface to be formed.

The non-magnetic support 2 is made of an aromatic polyamide film. Preferably, the nonmagnetic support 2 is made of an aromatic polyamide film formed using an aromatic polyamide resin comprising the following chemical formula (I) or (II) or a copolymer thereof.

[0022]

Embedded image

The aromatic polyamide has about 20%
Polymers other than the above components may be copolymerized or blended in the following amounts.

When an aromatic polyamide film is prepared from these polymers, a solvent for film formation may be, for example,
Dimethylacetamide, dimethylformamide, n-methylpyrrolidone, hexamethylphosphoramide, γ-butyrolactone, tetramethylurea, dioxane, etc., or a mixed solvent thereof, or lithium chloride or calcium chloride as a neutralization product of the polymerization stock solution The above-mentioned solvent to which an inorganic salt such as lithium carbonate, lithium nitrate or the like is added is used.

Using such a film-forming solvent, an aromatic polyamide resin is produced by polymerization of an aromatic diamine and an aromatic dicarboxylic acid, and the aromatic polyamide resin is formed by a technique such as solution molding. Produce an aromatic polyamide film.

Here, the aromatic diamines include:
For example, p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 2-nitro-p-phenylenediamine, 2-chloro-p-phenylenediamine, 4,4′-diaminobiphenyl, 3,3′-chlorobenzidine And the like. The aromatic dicarboxylic acids include, for example, terephthalic acid chloride,
-Chloroterephthalic acid chloride, terephthalic acid hydrazide, p-aminobenzoic acid hydrazide, p-aminobenzoic acid chloride and the like.

The aromatic polyamide film obtained as described above is stretched in the length direction and the width direction, and has a thickness of 1.
The nonmagnetic support 2 has a thickness of 0 to 4.5 μm. By setting the thickness of the non-magnetic support 2 to this level, necessary strength can be ensured, and as a result, the thickness of the magnetic recording medium 1 can be reduced. Therefore, the magnetic recording medium 1 using the non-magnetic support 2 can realize higher density recording.

On the surface 2a of the non-magnetic support 2 on which the ferromagnetic metal thin film 3 is formed, fine protrusions having a height of 10 to ⁴⁰ nm are formed at a density of 10 ² to 10 40,000 / mm ^2. To do.

As a method of forming the fine projections, for example, a method of adding inert fine particles to the above-mentioned aromatic polyamide film or a method of providing a polymer coating containing fine particles on the nonmagnetic support 2 Or a combination thereof.

Examples of the inert fine particles serving as nuclei of the fine projections include inorganic fine particles such as silica, calcium carbonate, titanium dioxide, alumina, kaolin, talc, graphite, feldspar, molybdenum dioxide, carbon black, and barium nitrate. , Polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, cross-linked methyl methacrylate copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, organic fine particles such as benzoguanamine resin, etc., among others, It is preferable to use particles made of colloidal silica or a crosslinked polymer, from which spherical particles can be easily obtained.

As a method of adding these inert fine particles to the above-mentioned aromatic polyamide film, the inert fine particles may be added to the above-mentioned solvent before the above-mentioned polymerization, or may be added to all of the solvents used for the polymerization. The inert fine particles may be dispersed, or may be added during the preparation step of the polymer solution.

As another method for adding the inert fine particles to the aromatic polyamide film, an organic inorganic material which is the same as the aromatic polyamide resin and is insoluble in the solvent during the solution molding described above. A method using active fine particles is also included.

In this method, the organic inert fine particles described above are added to the aromatic polyamide resin which is a raw material of the non-magnetic support 2 at the time of solution molding and heated to a high temperature of 300 ° C. or more. Then, organic substances that do not decompose appear as protrusions. Here, by adjusting the amount of organic matter to be added, formed by the density of the projections 10 ² to 10 ^40,000 / mm
^{To be 2} .

A method of forming a polymer film containing inert fine particles on the non-magnetic support 2 to form fine projections includes, for example, a composition mainly composed of a water-soluble polymer containing inert fine particles. Is coated on the main surface 2a on which the ferromagnetic metal thin film 3 is formed on the nonmagnetic support 2 made of the aromatic polyamide film described above. As a result, fine projections are formed on the main surface 2a of the nonmagnetic support 2 on which the metal magnetic film 3 is formed. At this time, as the water-soluble polymer, for example, polyvinyl alcohol, tragacanth gum, casein, gelatin, methylcellulose,
Hydroxyethyl cellulose, carboxymethyl cellulose, polyester and the like are applied.

The method for forming the fine projections is as follows.
Even without relying on the method using inert fine particles,
The method is not limited to the above method, as long as the surface shape of the nonmagnetic support 2 or the polymer film has the same shape as that of the surface to which the fine particles are added.

The back coat layer 4 is made of a material containing a compound polymerizable by an electron beam, and is a layer formed by polymerizing the compound by electron beam irradiation.

The compound capable of being polymerized by an electron beam is a compound having an unsaturated bond capable of being polymerized by an electron beam, and preferably a compound having a plurality of carbon-carbon double bonds such as vinyl or vinylidene. For example,
Compounds containing an acryloyl group, acrylamide group, allyl group, vinyl ether group, vinyl thioether group and the like, and compounds such as unsaturated polyester.

Particularly preferably, as the compound having an unsaturated bond, a compound having an acryloyl group and a methacryloyl group at both ends of a straight chain and having a skeleton of polyester, polyurethane, epoxy resin, polyether or polycarbonate Is mentioned. The molecular weight is about 500-20,
000 is preferred.

Further, a monomer having an unsaturated carbon-carbon unsaturated bond in the molecule may be added to these compounds. Such monomers include, for example, acrylic acid, methacrylic acid, itaconic acid, methyl acrylate and its homologous alkyl acrylate,
Methyl methacrylate and its homologue alkyl methacrylate, styrene and its homologue α-
Examples include methylstyrene, β-chlorostyrene, and the like, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, vinyl propionate, and the like.

Further, such a monomer may have two or more unsaturated bonds in the molecule. In particular, unsaturated esters of polyols, such as ethylene diacrylate, diethylene glycol diacrylate, glycerol trimethacrylate, ethylene dimethacrylate, pentaerythritol tetramethacrylate, and glycidyl methacrylate having an epoxy ring, are preferred. Further, a compound having one unsaturated bond in a molecule and a compound having two or more unsaturated bonds may be used as a mixture.

When a monomer is added, the ratio to the polymer is preferably polymer / monomer = 2/8 or more. Outside this range, a large amount of energy is required for curing.

The back coat layer 4 is formed by polymerizing a material containing the above compound by irradiating the material with an electron beam using an electron beam accelerator described below.
As such an electron beam accelerator, a so-called Van de Graff type scanning method, double scanning method or curtain beam method can be adopted. Among them, a curtain beam method which is relatively inexpensive and can obtain a large output is particularly preferable.

As the electron beam characteristics, the acceleration voltage of the electron beam is 100 to 1000 kV, preferably 150 to 300 kV.
And the absorbed dose is 0.5 to 20 Mrad, preferably 2 to 10 Mrad. Here, when the acceleration voltage of the electron beam is less than 100 kV, the amount of transmitted energy is insufficient, and when it exceeds 1000 kV, the energy efficiency used for polymerization is lowered, which is not economical. If the absorbed dose is less than 0.5 megarad, the curing reaction is insufficient and the coating film strength cannot be obtained. If the absorbed dose exceeds 20 megarad, the energy efficiency used for curing decreases or the irradiated object generates heat. In particular, the nonmagnetic support 2 is undesirably deformed.

The back coat layer 4 may be added with an ordinary binder alone or as a mixture. Here, as the binder, for example, vinyl chloride-vinyl acetate copolymer,
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylic acid Ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, polycarbonate resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, Urea-formaldehyde resin and the like.

In addition, an inorganic pigment powder can be added to the back coat layer 4 as needed. As the inorganic pigment powder, for example, carbon black, graphite,
Zinc oxide, titanium oxide, barium sulfate, talc, kaolin, chromium oxide, cadmium sulfide, goethite, silica aerosil, fine powder of anhydrous alumina, calcium carbonate, molybdenum disulfide, fluorocarbon and the like are used. In addition, an antistatic agent, if necessary,
It is also possible to include a lubricant or the like.

The thickness of the back coat layer is set to 0.1.
It is preferably from 1 to 0.6 μm.

Examples of the material of the ferromagnetic metal thin film 3 include ferromagnetic metals such as Co, Fe, and Ni, and alloys thereof. The thickness of the ferromagnetic metal thin film 3 is
About 0.01 μm to 0.2 μm, preferably 0.1 μm
m to 0.2 μm is good.

In the magnetic recording medium 1 to which the present invention is applied, the surface shape of the ferromagnetic metal thin film 3 is controlled by controlling the surface shape of the non-magnetic support 2 made of an aromatic polyamide film. Optimal conditions are achieved. Therefore, the magnetic recording medium 1 to which the present invention is applied has both good electromagnetic conversion characteristics and good running properties.

Further, the magnetic recording medium 1 to which the present invention is applied
A high-hardness back coat layer 4 formed by polymerization by electron beam irradiation is formed on the surface of the nonmagnetic support 2 opposite to the surface on which the ferromagnetic metal thin film 3 is formed. For this reason, the magnetic recording medium 1 to which the present invention is applied ensures a necessary and sufficient strength even if the thickness of the magnetic recording medium 1 is small, curl of the magnetic recording medium 1 is suppressed as much as possible, and wear resistance and durability are improved. Is improved. Further, in the magnetic recording medium 1 to which the present invention is applied, since the back coat layer 4 is formed, curling of the magnetic recording medium 1 is suppressed as much as possible. As a result, it is possible to have both better electromagnetic conversion characteristics and better recording / reproducing properties.

The magnetic recording medium 1 to which the present invention is applied
By increasing the thickness of the nonmagnetic support 2 to 1.0 to 4.5 μm, the capacity can be increased.

In the magnetic recording medium 1, various kinds of rust inhibitors, antistatic agents, antifungal agents and the like may be added as necessary to the surface of the magnetic recording medium 1 and the materials for forming various layers.

Further, wear of the ferromagnetic metal thin film 3 is prevented,
In order to reduce spacing loss, it is preferable to form a carbon protective film on the ferromagnetic metal thin film 3. At this time, the carbon protective film has a thickness of about 3 to 15 nm, preferably about 5 to 10 nm. It is desirable that a lubricant be present on the surface of the carbon protective film.
Thereby, the magnetic recording medium 1 can further improve the effect of improving the running property based on the shape of the fine projection.

Next, the magnetic recording medium 1 to which the present invention is applied
A method of manufacturing the device will be described.

First, an aromatic polyamide film is prepared by solution molding or the like using the aromatic polyamide resin obtained by polymerization, and the above-mentioned water-soluble polymer containing the above inert fine particles is mainly formed on the aromatic polyamide film. The non-magnetic support 2 is obtained by coating the composition. At this time,
On the surface of the nonmagnetic support 2, fine projections whose height and ratio are controlled as described above are formed.

Next, a ferromagnetic metal thin film 3 is formed on one main surface 2a of the non-magnetic support 2 using a continuous winding type vacuum evaporation apparatus as shown in FIG.

The vacuum vapor deposition apparatus 10 is used for oblique vapor deposition, and has a cooling chamber which is cooled to, for example, about -20 ° C. and rotates in the direction of arrow A in FIG. An evaporation source 13 for a metal thin film is arranged so as to be opposed to 12.

The evaporation source 13 is one in which a ferromagnetic metal material is contained in a container such as a crucible. The ferromagnetic metal material in the evaporation source 13 is irradiated with an electron beam 15 accelerated and emitted from an electron beam generation source 14 to heat and evaporate the ferromagnetic metal material. Then, the heated and evaporated ferromagnetic metal material is fed out by the supply roll 16 in the direction of arrow B in the figure and is deposited on the non-magnetic support 2 running along the peripheral surface of the cooling can 12. A ferromagnetic metal thin film 3 is formed. Then, the non-magnetic support 2 on which the ferromagnetic metal thin film 3 is formed is taken up by a take-up roll 17.

At this time, a deposition-preventing plate 18 is provided between the vapor deposition source 13 and the cooling can 12, and a shutter 19 is provided on the deposition-preventing plate 18 so as to be adjustable in position. Only vapor particles incident at an angle of. The ferromagnetic metal thin film 3 is formed by such an oblique deposition method. Guide rollers 20 and 21 are arranged between the supply roll 16 and the cooling can 12 and between the cooling can 12 and the take-up roll 179, respectively, and apply predetermined tension to the running non-magnetic support 2. The non-magnetic support 2 runs smoothly.

In the above, an example in which the ferromagnetic metal thin film 3 is formed by the oblique deposition method has been described. However, as a method of forming the ferromagnetic metal thin film, other than this example, a known method such as a vertical evaporation method or a sputtering method may be used. Can be applied. In order to improve the adhesion strength to the nonmagnetic support 2 or to improve the corrosion resistance and wear resistance of the ferromagnetic metal thin film 3 itself,
It is desirable to form a ferromagnetic metal thin film containing oxygen by setting the atmosphere at the time of vapor deposition to an atmosphere in which oxygen gas is dominant.

Next, in order to prevent abrasion of the ferromagnetic metal thin film 3, it is desirable to form a carbon protective film on the ferromagnetic metal thin film 3 by using a magnetron sputtering apparatus 20 or the like as shown in FIG. .

In the magnetron sputtering apparatus 30, after the pressure in the chamber 31 is reduced by the vacuum pump 32, the angle of the valve 33 disposed to the vacuum pump 32 is narrowed to introduce Ar gas from the gas introduction pipe 34. Thus, the degree of vacuum is about 0.8 Pa. In the magnetron sputtering apparatus 30, a cooling can 35 that is cooled to, for example, −40 ° C. and rotates in the direction of arrow C in the drawing, and a target 36 that is arranged to face the cooling can 35 are provided in the chamber 31. I have. The target 36 is supported by a backing plate 37 constituting a cathode electrode. On the back side of the backing plate 37, a magnet 38 for forming a magnetic field is provided.

When a carbon protective film is formed by the magnetron sputtering apparatus 30, A
r gas was introduced, and the cooling can 35 was used as an anode and the backing plate 37 was used as a cathode.
A voltage of V is applied.

When the voltage is applied, the Ar gas is turned into plasma, and the ionized ions collide with the target 36, whereby the atoms of the target 36 are repelled. Then, the atoms ejected from the target 36 are fed out in the direction of arrow D in FIG.
The carbon protective film is formed on the ferromagnetic metal thin film 3 running along the peripheral surface of the metal film 5. Finally, the non-magnetic support 2 having the carbon protective film formed thereon is
It is wound by one.

As a method of forming the carbon protective film, a known thin film forming method such as an ion beam sputtering method, an ion beam plating method, or a CVD method can be used in addition to the above-described method.

Next, the nonmagnetic support 2 on which the ferromagnetic metal thin film 3 and the carbon protective film are formed can be polymerized with an electron beam on the surface 2b on the side where the ferromagnetic metal thin film 3 is not formed. A material containing an appropriate compound is applied. A curtain beam type electron beam accelerator (not shown) is set to a desired acceleration voltage and absorption dose, and the material is polymerized by accelerated irradiation of the material with the electron beam using the electron beam accelerator. Thus, the back coat layer 4 is formed.

Through the above steps, a magnetic recording medium to which the present invention is applied can be obtained.

[0067]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

The effect of the magnetic recording medium on the height and number of surface projections on the surface of the non-magnetic support on which the ferromagnetic metal thin film is formed, and on the presence of the backcoat layer formed by polymerization by electron beam irradiation In order to examine the magnetic tape, a magnetic tape was prepared by the following method.

First, to the dehydrated n-methylpyrrolidone,
2-Chloro-p-phenylenediamine corresponding to 0.9 mol ratio and 4,4'-diaminodiphenylsulfone corresponding to 0.1 mol ratio are stirred and dissolved, cooled, and correspond to 0.7 mol ratio therein. Terephthalic acid chloride was added and stirred for about 2 hours. Thereafter, sufficiently purified calcium hydroxide was added and stirred to obtain an aromatic polyamide solution.

Next, this aromatic polyamide solution was uniformly cast at 30 ° C. on a metal drum whose surface was polished,
For about 10 minutes to form an aromatic polyamide film.

Then, the aromatic polyamide film was peeled off from the drum, and stretched 1.1 times in the length direction while continuously immersed in a water bath at 30 ° C. for about 30 minutes. Further, this aromatic polyamide film was introduced into a tenter and stretched 1.3 times in the length direction at 320 ° C. to obtain a nonmagnetic support having a thickness of about 4 μm.

Next, a particle diameter of 1
SiO _{2 of} about 5 nm Was applied and dried to form a polymer film.

Here, a plurality of non-magnetic supports on which such a polymer film is formed are prepared in the same manner, and each non-magnetic support is subjected to the following steps to obtain a plurality of magnetic recording media. Was prepared. However, the surface properties of the polymer coating differ depending on the nonmagnetic support.

Next, the continuous winding type vapor deposition apparatus as shown in FIG. 2 was evacuated so that the inside thereof became a vacuum state of about 10 ⁻³ Pa, and the non-magnetic support on which the polymer film was formed was removed. This was set in this vapor deposition apparatus. Then, a ferromagnetic metal thin film made of Co was formed on the surface of the nonmagnetic support in the presence of a small amount of oxygen by a continuous vacuum oblique deposition method. At this time, the incidence angle of vapor deposition is 90 to 45 degrees in the normal direction of the nonmagnetic support, the traveling speed of the nonmagnetic support is 50 m / min, and the thickness of the ferromagnetic metal thin film is 0.18.
It was manufactured by adjusting the intensity of the electron beam so as to be μm.

Next, the pressure of the magnetron sputtering apparatus as shown in FIG. 3 was reduced to about 10 ⁻⁴ Pa, and then Ar gas was introduced to about ^0.8 Pa. Then, the non-magnetic support on which the ferromagnetic metal thin film is formed is set in the magnetron sputtering apparatus, and is run on a cooling can cooled to -40 ° C. at a speed of 5 m / min to protect the carbon on the ferromagnetic metal thin film. A film was formed.

Next, the following coating material for a back coat layer was applied to the surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film was formed.

<Coating for Back Coat Layer> Reinforcing agent: carbon black 100 parts by weight Binder: polyurethane resin 50 parts by weight Compound polymerizable by electron beam: ester acrylate oligomer 20 parts by weight diethylene glycol diacrylate 20 parts by weight butoxyethyl 20 parts by weight of acrylate Solvent: 300 parts by weight of methyl ethyl ketone / toluene = 4/1 300 parts by weight of the coating material for the back coat layer formed on the nonmagnetic support was adjusted to an electron acceleration voltage of 20 by an electron accelerator.
An electron beam was irradiated at 0 kV and a beam current of 15 mA to form a backcoat layer having a thickness of 0.5 μm.
At this time, the absorbed dose is 5 megarads.

Next, a lubricant composed of perfluoropolyether was applied on the carbon protective film to form a top coat layer, thereby producing a magnetic recording medium.

Finally, the magnetic recording medium was cut into a width of 8 mm to form a magnetic tape, and the magnetic tape was stored in a cassette body to obtain a cassette tape. The above steps were repeated to produce a plurality of magnetic tapes, and these magnetic tapes were designated as Examples 1 to 5 and Comparative Examples 1 and 2.

On the other hand, as a material for the back coat layer, a magnetic recording medium having a back coat layer formed of a conventional carbon black and polyurethane resin without containing a compound polymerizable by an electron beam was similarly cut. Then, a magnetic tape was produced, and Comparative Example 3 was obtained.

Then, the following physical property evaluation was performed on the non-magnetic support manufactured as described above and the magnetic tape manufactured using the non-magnetic support.

First, the following measurements were performed to evaluate the physical properties of the nonmagnetic support. This measurement was performed on all of the plurality of nonmagnetic supports on which the polymer coating was formed,
This was performed at the time when the non-magnetic support was produced during the manufacturing process of the magnetic tape.

Measurement of Surface Protrusion Height Using an atomic force microscope (AFM) manufactured by Digital Instrument, NanoScope III (trade name), the surface of the non-magnetic support on which the ferromagnetic metal thin film was formed was 5 μm × 5 μm of AFM. The height of each of the ten protrusions was measured within the measurement range, and the average value of these ten protrusions was calculated.

Measurement of the number of surface protrusions The number of fine protrusions having a height of 10 to 40 nm was measured using a scanning electron microscope (SEM), an ultra-high resolution cold F manufactured by JEOL Ltd.
Using an E-SEM “S-900” (trade name), counting at an acceleration voltage of 20 kV and a magnification of 30,000 or more, 1 mm
^It was converted to the number per ² pieces.

Table 1 shows the results of the above evaluation of the physical properties.

[0086]

[Table 1]

Next, the following measurements were performed on a plurality of magnetic tapes manufactured as described above.

Evaluation of Tape Properties The method of evaluating the properties of the magnetic tape includes Sony Corporation's A
The test was performed using a modified version of the IT drive SDX-S300C (trade name). The recording was at a relative speed of 10.04m /
Second, the shortest recording wavelength was 0.35 μm.

As a running durability, a 170 m length was run for 100 passes, and a block error rate after running one pass and a block error rate after running 100 passes were measured.

Further, a squealing state, that is, a slip state of the tape in the rotary head cylinder portion after running 100 passes was measured.

Evaluation of Storage Characteristics As a method for evaluating the storage characteristics of the magnetic tape, a magnetic tape recorded 170 m long at normal temperature and normal humidity of about 25 ° C. was stored at 45 ° C. and 80% humidity for 3 days. Thereafter, reproduction was performed again under normal temperature and normal humidity, and the increase in the error rate was measured.

Evaluation of Contact Characteristics with Head The minimum value / maximum value (%) of the output signal at the time of reproducing the magnetic tape, that is, the output signal when the collision waveform was viewed for one track was measured.

Evaluation of the degree of curl of the magnetic tape The width w of the magnetic tape and the maximum height h of the magnetic tape from the surface of the flat plate on which the magnetic tape was arranged were measured, and the ratio h /
The degree of curl was determined by the value of w.

Table 2 shows the results of the above physical property evaluation.

[0095]

[Table 2]

From the results shown in Tables 1 and 2, the magnetic recording medium, as in Examples 1 to 5, had the height of the surface protrusions on the surface of the nonmagnetic support on which the ferromagnetic metal thin film was formed. Is 10
1 to 100 million fine protrusions of ４０40 nm /
It was found that the tape characteristics, head contact characteristics, and storage characteristics can be improved by forming mm ² . On the other hand, in Comparative Example 1 in which the height of the surface projections was smaller than 10 nm and in Comparative Example 2 in which the height of the surface projections was larger than 40 nm, it was found that the tape characteristics and the storage characteristics were particularly deteriorated.

Further, in Examples 1 to 5 in which the surface shape of the non-magnetic support is appropriately controlled, no squeal of the magnetic tape occurs, and the running property is improved. all right.

Further, in Examples 1 to 5 having a back coat layer polymerized by irradiation with an electron beam, the curl degree was remarkably suppressed as compared with Comparative Example 3 in which a normal back coat layer was formed. Also, the tape characteristics, head contact characteristics, and storage characteristics have been significantly improved.

From the above results, in the magnetic recording medium 1 to which the present invention is applied, the surface shape of the nonmagnetic support 2 made of an aromatic polyamino film is controlled, and the fine shape of the surface of the ferromagnetic metal thin film 3 is optimized. State is made. Therefore, it has been found that the magnetic recording medium 1 to which the present invention is applied can realize good electromagnetic conversion characteristics and running properties.

Further, the magnetic recording medium 1 to which the present invention is applied
Has a high hardness back coat layer 4 formed by polymerization by electron beam irradiation on the surface of the nonmagnetic support 2 opposite to the surface on which the ferromagnetic metal thin film 3 is formed. Therefore, the magnetic recording medium 1 to which the present invention is applied has a necessary and sufficient strength even if the thickness of the magnetic recording medium 1 is small, curling of the magnetic recording medium 1 can be suppressed as much as possible, and wear resistance and durability can be improved. It has been found that the performance is improved.

Further, the magnetic recording medium 1 to which the present invention is applied
Since the back coat layer 4 is formed, the curl of the magnetic recording medium 1 is suppressed as much as possible, so that the magnetic recording medium 1 can sufficiently contact with the magnetic head, and the electromagnetic conversion characteristics and the recording / reproducing property can be improved. Improvement can be achieved.

The magnetic recording medium 1 to which the present invention is applied
Is a nonmagnetic support 2 made of an aromatic polyamino film.
By reducing the thickness to 1.0 to 4.5 μm, the capacity can be increased.

[0103]

As described above in detail, in the magnetic recording medium according to the present invention, the surface shape of the nonmagnetic support made of the aromatic polyamino film is controlled so that the fine shape of the surface of the ferromagnetic metal thin film is optimized. State is made. Therefore, the magnetic recording medium according to the present invention can realize good electromagnetic conversion characteristics and running properties.

In addition, the magnetic recording medium to which the present invention is applied has a high hardness backing formed by polymerization by electron beam irradiation on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. A coat layer is formed. For this reason, the magnetic recording medium according to the present invention secures necessary and sufficient strength even if the thickness of the magnetic recording medium is thin, curl of the magnetic recording medium can be suppressed as much as possible, and wear resistance and durability are improved. Therefore, high reliability can be obtained.

Further, in the magnetic recording medium according to the present invention,
The curl of the magnetic recording medium is suppressed as much as possible by the formation of the above-mentioned back coat layer, so that it is possible to sufficiently contact the magnetic head and to improve the electromagnetic conversion characteristics and the recording / reproducing properties. Can be.

In the magnetic recording medium according to the present invention, a large capacity can be achieved by reducing the thickness of the nonmagnetic support made of an aromatic polyamino film to 1.0 to 4.5 μm. .

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram illustrating an example of a vacuum evaporation apparatus for forming a ferromagnetic metal thin film.

FIG. 3 is a configuration diagram showing an example of a magnetron sputtering apparatus for forming a carbon protective film.

[Explanation of symbols]

1 magnetic recording medium, 2 nonmagnetic support, 3 ferromagnetic metal thin film, 4 back coat layer

Claims (3)

[Claims] 1. A magnetic recording medium having a ferromagnetic metal thin film formed on a non-magnetic support, wherein the non-magnetic support has an average height of 10 to 40 nm on a surface on which the ferromagnetic metal thin film is formed. 10 ^2-
10 ^40,000 / mm ² consists forming aromatic polyamide film, and the surface on which the ferromagnetic metal thin film is formed of the non-magnetic support member on the opposite surface, the back coat layer is formed, the A magnetic recording medium, wherein the back coat layer is made of a material containing a compound polymerizable by an electron beam, and is formed by polymerizing the compound by electron beam irradiation. 2. The thickness of the non-magnetic support is from 1.0 to 4.
2. The magnetic recording medium according to claim 1, wherein the thickness is 5 μm. 3. The thickness of the back coat layer is from 0.1 to 3.
2. The magnetic recording medium according to claim 1, wherein the thickness is 0.6 μm.