JP2000285438A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium excellent in electromagnetic conversion characteristics in which the occurrence of cupping is prevented even when a nonmagnetic support is made thin. SOLUTION: A nonmagnetic support 1 comprises a first aromatic polyamide film composing the other major surface, and a second aromatic polyamide film formed thereon wherein inert particles contained in the first aromatic polyamide film are larger than those contained in the second aromatic polyamide film. The nonmagnetic support 1 has thickness of 2.0 μm or above excluding the first aromatic polyamide film and a back coat layer 4 is formed on the other major surface thereof.

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 having a metal magnetic film formed on one main surface of a non-magnetic support, and more particularly to a magnetic recording medium suitable for use as a large-capacity tape streamer. .

[0002]

2. Description of the Related Art In recent years, with the spread of office computers such as minicomputers and personal computers, magnetic tapes (so-called tape streamers) for recording computer data as external storage media have been actively studied. . When a magnetic tape for such a purpose is put into practical use, an increase in the recording capacity is strongly required in order to achieve a large-capacity recording and a miniaturization, particularly in conjunction with the downsizing of the computer and the increase in the information processing capability.

On the other hand, as for a magnetic recording medium for a video cassette, further downsizing and long-time recording are desired with the downsizing of the video cassette.

In addition, the magnetic tape can be used under a wide range of environmental conditions (especially, in a highly fluctuating temperature and humidity condition) due to the spread of the usage environment, reliability in data storage, and in repeated running at high speed, can be used many times. There has also been a demand for reliability of performance such as stable recording and reading of data.

In general, a magnetic tape has a structure in which a magnetic layer is provided on a non-magnetic support made of a flexible material such as a synthetic resin. In order to achieve the above-mentioned large recording capacity (volume recording capacity), the recording density of the magnetic layer itself is increased by making the magnetic layer a ferromagnetic metal thin film, and the total thickness of the magnetic tape is reduced. It is said that this is an effective method. That is, as the magnetic tape, a so-called vapor deposition tape formed by forming a metal magnetic thin film on a non-magnetic support is effective.

In this vapor-deposited tape, a polyester, mainly a polyethylene terephthalate film, is used as a nonmagnetic support. In particular, a polyethylene terephthalate film of about 7 to 10 μm is used as a non-magnetic support used for a home video cassette tape, for example, an 8 mm tape, and a tape streamer for backing up data of a computer is 5 to 7 μm.
m polyethylene film is used.

As a method for extending the recording time of a magnetic recording medium used for a video tape, for example, as described in JP-A-6-215350, polyester is mainly used as a non-magnetic support. It is said that it is desirable to use polyethylene naphthalate as a component, more specifically. On the other hand, use of a polyamide film having a higher strength than the above-described polyethylene terephthalate or polyethylene naphthalate film has been studied. A magnetic recording medium using this polyamide film as a non-magnetic support has a high strength of the non-magnetic support, so the thickness of the non-magnetic support can be reduced, and the recording time of the video cassette tape can be reduced. Has attracted attention as a magnetic recording medium corresponding to a large-capacity tape streamer.

[0008]

By the way, particularly in the field of tape streamers, the capacity tends to be increased, and accordingly, further thinning of the magnetic tape is desired. However, considering that the stiffness of the magnetic tape is proportional to the cube of the total thickness when the thickness of the non-magnetic support is halved, to obtain the same stiffness, it is necessary to use Young's material for the non-magnetic support. The rate must be multiplied by eight. Therefore, simply reducing the thickness of the non-magnetic support will result in insufficient mechanical strength of the magnetic tape.

In magnetic tapes, when the thickness of the nonmagnetic support is reduced, so-called cupping tends to increase. As described above, when the magnetic tape is capped, it becomes difficult to contact the magnetic head, causing a significant reduction in the electromagnetic conversion characteristics, and the edges that easily come into contact with the magnetic head are liable to be worn, causing dropout. Or the output may decrease or the error rate may deteriorate.

As described above, the magnetic tape has disadvantages such as mechanical strength and cupping as the recording capacity is improved. That is, the conventional magnetic tape has a problem that when the recording capacity is improved by reducing the thickness, the mechanical strength is reduced, the output is reduced, and the error rate is deteriorated.

Accordingly, the present invention has been made based on such a technical background, and it is possible to prevent the occurrence of cupping or the like even when the thickness of the non-magnetic support is reduced, and to obtain an excellent electromagnetic conversion. An object of the present invention is to provide a magnetic recording medium having characteristics.

[0012]

According to the present invention, there is provided a magnetic recording medium comprising at least a metal magnetic film formed on one main surface of a non-magnetic support. The non-magnetic support has at least a first aromatic polyamide film constituting the other main surface and a second aromatic polyamide film formed on the first aromatic polyamide film. First
The inert particles contained in the aromatic polyamide film are larger than the inert particles contained in the second aromatic polyamide film, and the nonmagnetic support is A thickness excluding the aromatic polyamide film of 2.0 μm or more, and a backcoat layer formed on the other main surface of the nonmagnetic support.

In the magnetic recording medium according to the present invention having the above-described structure, the surface of the other main surface of the non-magnetic support opposite to the surface on which the metal magnetic film is formed has a first aromatic polyamide film. And is affected by the inert particles contained therein. Therefore, in this magnetic recording medium, the other main surface exhibits a desired surface roughness. Further, this magnetic recording medium has at least a second aromatic polyamide film between the first aromatic polyamide film and the metal magnetic film. For this reason, the influence of the relatively large inert particles contained in the first aromatic polyamide film is small on the surface of one main surface on which the metal magnetic film is formed. Therefore, in this magnetic recording medium, the surface of the metal magnetic film has a desired excellent surface property.

Further, in this magnetic recording medium, since the back coat layer is formed on the other main surface, cupping of the non-magnetic support can be prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a magnetic recording medium according to the present invention will be described below in detail with reference to the drawings.

The magnetic recording medium shown as the embodiment is
As shown in FIG. 1, a non-magnetic support 1, a metal magnetic film 2 formed on one main surface 1a of the non-magnetic support 1, and a non-magnetic support 1 formed on another main surface 1b of the non-magnetic support 1 And a back coat layer 4 provided. In this magnetic recording medium, the nonmagnetic support 1 has at least relatively large inert particles, and the first aromatic polyamide film 5 constituting the other main surface 1b and the relatively small inert particles. , And a second aromatic polyamide film 6 formed on the first aromatic polyamide film 5. Further, in this magnetic recording medium, the thickness of the nonmagnetic support 1 excluding the first aromatic polyamide film 5 is 2.0 μm or more.

Hereinafter, the non-magnetic support 1, the metal magnetic film 2, the back coat layer 4, and the binder and additives used for these layers will be described in detail.

Non-magnetic support 1 First, the non-magnetic support 1 is composed of the first aromatic polyamide film 5 and the second aromatic polyamide film 6, as described above. This non-magnetic support 1
By using an aromatic polyamide film, it is excellent in physical properties such as tensile strength, and has sufficient strength to withstand even a very thin overall thickness.

The first aromatic polyamide film 5 and the second aromatic polyamide film 6 are preferably, for example, an aromatic polyamide represented by the following formula (I) and / or (II) in an amount of 50% by mole or more, preferably Is at least 70 mol%.

[0020]

Embedded image

In the above formula, X and Y represent -O
_{-, - CH 2 -, -} CO -, - SO 2 -, - S -, - C
(CH ₃ ) ₂ — or the like, but is not limited thereto. Further, in the above formula, part of the hydrogen atoms on the aromatic ring may be a halogen group (particularly chlorine), a nitro group, an alkyl group having 1 to 3 carbon atoms (particularly, a methyl group), or an alkoxy group having 1 to 3 carbon atoms. It may be substituted by a substituent such as a group, or hydrogen in an amide bond constituting the polymer may be substituted by another substituent.

Also, the first aromatic polyamide film 5
And from the viewpoint of increasing the rigidity, the second polyamide film 6 may be a polymer in which the aromatic ring is bonded at the para position to account for 60% or more, more preferably 80% or more of the total aromatic ring. preferable. In addition, from the viewpoint of reducing the hygroscopicity, part of the hydrogen atoms on the aromatic ring is a halogen group (particularly,
(A chlorine atom), a nitro group, an alkyl group having 1 to 3 carbon atoms (especially a methyl group), an aromatic ring substituted with an alkoxy group having 1 to 3 carbon atoms, etc., is a polymer occupying 30% or more of the whole. Is preferred.

Further, the aromatic polyamide contains at least 50 mol% of the repeating unit represented by the above formula (I) and / or the above formula (II), and less than 50 mol% represents another repeating unit. For example, a polymer obtained by copolymerizing or blending an aromatic polyimide unit or another aromatic polyamide unit can be used, but it is preferable to use a wholly aromatic polyamide (aramid).

Further, in the non-magnetic support 1, the aromatic polyamide film has a composite structure composed of at least two layers, and each layer is mainly composed of the polymer represented by the above formula. As long as each layer has the same composition, it may be different. However,
From the viewpoint of productivity, it is advantageous that each layer has the same composition.

Further, in order to form the first aromatic polyamide film 5 and the second aromatic polyamide film 6, a stock solution corresponding to the first aromatic polyamide film 5 and a second aromatic polyamide film The two kinds of stock solutions corresponding to No. 6 were prepared by a known method, for example,
As described in Japanese Patent No. 2617, it can be formed by laminating with a merging pipe or by laminating in a die.

On the other hand, the inert particles added to the nonmagnetic support 1 include SiO ₂ , TiO ₂ , Al ₂ O ₃ , Ca
Inorganic particles such as SO ₄ , BaSO ₄ , CaCO ₃ , carbon black, zeolite, and other fine metal powders, and organic polymers such as silicon particles, polyimide particles, cross-linked copolymer particles, cross-linked polyester particles, and Teflon particles Etc. can be used. Among them, it is preferable to use the above-mentioned inorganic particles from the viewpoint of heat resistance.

As a method for adding the inert particles, a method in which the particles are sufficiently slurried in a solvent in advance and then used as a solvent for polymerization or a solvent for dilution, or a method of directly adding after preparing a stock solution for forming each layer. There are ways to do that.

In this magnetic recording medium, the inert particles contained in the first aromatic polyamide film 5 have an average primary particle size of the inert particles contained in the second aromatic polyamide film 6. It is large compared to.

Specifically, the average particle size of the inert particles contained in the first aromatic polyamide film 5 is 0.03 to 0.03.
It is preferably 1.5 μm. The amount of the inert particles contained in the first aromatic polyamide film 5 is:
It is preferably from 0.05 to 2.0 wt%, and more preferably from 0.1 μm to 1.0 μm.

As described above, by defining the average particle diameter and the content of the inert particles contained in the first aromatic polyamide film 5, the surface on which the back coat layer 4 is formed can have a desired surface. It can be roughness. Thereby, the magnetic recording medium has excellent handling characteristics. In addition, the magnetic recording medium using the non-magnetic support 1 has excellent running properties and can run well for a long period of time.

The second aromatic polyamide film 6
In order to improve the smoothness and lubricity of the surface of the metal magnetic film 2, the inert particles contained in
It is preferable that the addition amount is 0.15 μm and the addition amount is 0.01 wt% to 1 wt%.

When the average particle size of the inert particles contained in the second aromatic polyamide film is less than 0.03,
There is a possibility that an inconvenience such that a sufficient projection for improving the slipperiness is not formed. If the average particle size of the inert particles is larger than 0.15 μm, the smoothness of the metal magnetic film may be deteriorated. Further, when the amount of the inert particles added in the second aromatic polyamide film is less than 0.01 wt%, there is a possibility that a disadvantage that a sufficient number of protrusions for improving the slipperiness cannot be secured. If the content is more than 1 wt%, the number of protrusions may become excessive and adversely affect the surface properties of the metal magnetic film.

On the other hand, the non-magnetic support 1 has a total thickness of 2.0 μm or more excluding the first aromatic polyamide film 5. Preferably, 2.
It is 5 μm or more. Here, in the present embodiment,
Since the non-magnetic support 1 is composed of the first aromatic polyamide film 5 and the second aromatic polyamide film 6, the total thickness excluding the first aromatic polyamide film is the thickness of the second aromatic polyamide film. Is synonymous with

In the present invention, the non-magnetic support 1
Is not limited to such a configuration, and may be a configuration including three or more aromatic polyamide films.
In this case, the total thickness excluding the first aromatic polyamide film indicates the thickness of the nonmagnetic support 1 excluding the aromatic polyamide film constituting the surface on which the back coat layer 4 is formed.

As described above, by defining the total thickness excluding the first aromatic polyamide film 5 to be 2.0 μm or more, the relatively large inert particles contained in the first aromatic polyamide film 5 can be reduced. The influence on the surface of the second aromatic polyamide film 6 can be minimized. In other words, if the total thickness excluding the first aromatic polyamide film 5 is specified to be 2.0 μm or more, the deterioration of the surface properties (such as undulation) of the second aromatic polyamide film 6 and the second aromatic polyamide film 6 and the formation of coarse projections on the surface of the second aromatic polyamide film 6 can be prevented. Therefore, the metal magnetic film 2 formed above the second aromatic polyamide film 6 has a desired surface property and is excellent in electromagnetic conversion characteristics. It will be excellent.

In the non-magnetic support 1, it is preferable that the number of coarse projections of 0.12 μm or more on the main surface on which the metal magnetic film 2 is formed is 250/100 cm ² or less. More preferably, the number is 200 / cm ² or less. In addition, this coarse projection is formed on the non-magnetic support 1.
Can be measured by the 3D-MIRAU method.

As described above, coarse protrusions of 0.12 μm or more on the main surface of the metal magnetic film 2 are formed.
By setting the number of pieces per 100 cm ² or less, deterioration of the surface properties or the like due to the coarse projections hardly occurs on the surface of the metal magnetic film 2. For this reason, in this magnetic recording medium, it is possible to reduce projections and the like that cause dropout.

Further, in the non-magnetic support 1, the surface roughness (SRa) of one main surface on which the metal magnetic film 2 is formed is preferably 1.5 nm to 5.0 nm, and more preferably 2 nm to 5.0 nm. More preferably, it is 0.0 to 3.5 nm. The surface roughness (SRa) is adjusted by the size and amount of inert particles added to the second aromatic polyamide film 6 or the layer configuration of the nonmagnetic support 1. As described above, by setting the surface roughness (SRa) of one main surface on which the metal magnetic film 2 is formed to 1.5 nm to 5.0 nm, good electromagnetic conversion characteristics and running durability of the magnetic recording medium can be obtained. Can be secured.

Further, in the non-magnetic support 1, the surface undulation of one main surface on which the metal magnetic film 2 is formed is 2.5
nm or less, and more preferably 2.0 nm or less. This surface undulation is obtained by performing FFT on the data obtained when measuring the surface roughness (SRa).
(Fast Fourier transfer) It can measure by analyzing. That is, (S
Ra) FFT analysis of the data obtained at the time of measurement,
The surface undulation of one main surface of the non-magnetic support 1 is measured by obtaining an amplitude value of 0 μm or less. As described above, the surface waviness of one main surface on which the metal magnetic film 2 is formed is reduced by 2.5%.
By setting the thickness to be equal to or less than nm, it is possible to secure good electromagnetic conversion characteristics and running durability of the magnetic recording medium.

Further, in this non-magnetic support 1, the surface roughness (SRa) of the surface on the side where the back coat layer 4 is formed is provided.
Is adjusted by the size and amount of inert particles added to the first aromatic polyamide film 5, and it is desirable that the particle size be as large as possible from the viewpoint of handling properties in the production process. However, this surface roughness (SR
If a) is too large, the influence of set-off when the metal magnetic layer 2 is formed and then wound up into a roll becomes large, so that the thickness is 4 nm to 15 nm, preferably 5 nm to 10 nm.

Further, by setting the thickness of the non-magnetic support 1 to 2.5 μm to 5.0 μm, the required strength can be obtained, and the thickness of the magnetic recording medium can be reduced to cope with an increase in capacity. Can be done.

Further, in the non-magnetic support 1, projections are formed at a density of 10 ³ to 10 ⁵ pieces / mm ² on the surface on one main surface on which the metal magnetic film 2 is formed. preferable.

As described above, the surface on the one main surface side has a density of 10 ³ -1.
By forming projections at a density of 0 ⁵ / mm ² ,
The surface property of the metal magnetic film can be brought into a desired state.
In other words, 10 ³ to 10 ⁵ pieces / mm
^By forming the projections at a density of 2, the surface of the metal magnetic film 2 has a desired surface roughness. This makes the magnetic recording medium excellent in running durability and electromagnetic conversion characteristics.

Metal Magnetic Film 2 Next, the metal magnetic film 2 is formed on the second aromatic polyamide film on the non-magnetic support 1 described above.

At this time, the metal magnetic film 2 is formed, for example, as shown in FIG.
It is formed using a continuous winding type vacuum evaporation apparatus as shown in FIG.

The vacuum evaporation apparatus 11 is configured for so-called oblique evaporation, and is, for example, −20 ° C. in a vacuum chamber 12 in which the inside is in a vacuum state of about 10 ⁻³ (Pa).
Cooled to the extent, counterclockwise direction in the figure (arrow A direction)
An evaporation source 14 for the metal magnetic film 2 is arranged so as to face the rotating cooling can 13.

The evaporation source 14 is a container such as a crucible in which a ferromagnetic metal material such as Co is contained.
(Ferromagnetic metal material) is heated with an electron beam 16 accelerated from an electron beam source 15 to heat the ferromagnetic metal material.
This is evaporated from the supply roll 18 rotating in the counterclockwise direction in the figure and is fed in the direction of arrow B in the figure, and adheres to the non-magnetic support 1 running along the peripheral surface of the cooling can 13 (evaporation). ) To form the metal magnetic film 2. Then, the nonmagnetic support 1 on which the metal magnetic film 2 is formed
Is taken up by a take-up roll 19.

At this time, a deposition-preventing plate 20 is provided between the vapor deposition source 14 and the cooling can 13, and a shutter 21 is provided on the deposition-preventing plate 20 so as to be adjustable in position. Only vapor particles incident at an angle of. Thus, the metal magnetic film 2 is formed by the oblique deposition method.

Note that guide rollers 22 and 23 are disposed between the supply roll 18 and the cooling can 13 and between the cooling can 13 and the take-up roll 19, respectively. Cooling can 1
A predetermined tension is applied to the non-magnetic support 1 running from 3 to the take-up roll 19 so that the non-magnetic support 1 runs smoothly.

Further, during the deposition of the metal magnetic film 2, oxygen gas is supplied to the surface of the non-magnetic support 1 through an oxygen gas inlet (not shown). The improvement of the property and weather resistance is aimed at. In addition, in order to heat the evaporation source 14, in addition to the above-described heating means using an electron beam, known means such as a resistance heating means, a high-frequency heating means, and a laser heating means can be used.

In the above, an example in which a film is formed using a ferromagnetic metal material made of Co or the like by an oblique vapor deposition method has been described. Known thin film forming methods such as a vapor deposition method and a sputtering method can be applied, and as the ferromagnetic metal material,
In addition to Co, Ni, Fe, or an alloy thereof can be used. However, the adhesive strength with the non-magnetic support 1 is improved,
Alternatively, for the purpose of improving the resistance and abrasion resistance of the metal magnetic film itself, it is desirable to use the metal magnetic film 2 containing oxygen obtained when the atmosphere at the time of vapor deposition is an atmosphere in which oxygen gas is dominant. The thickness of the metal magnetic film 2 is 0.0
About 1 to 0.2 μm, preferably 0.1 to 0.2 μm
It is about.

Further, this magnetic recording medium has a metal magnetic film 2
It is desirable to form a carbon protective film on the metal magnetic film 2 using a magnetron sputtering device 30 as shown in FIG.

The outside of the magnetron sputtering apparatus 30 is covered with a chamber 31. After the pressure in the chamber 31 is reduced to about 10 ^-4 (Pa) by the vacuum pump 32, the exhaust speed is reduced by reducing the angle of the valve 33 to be discarded to the vacuum pump 32 side from the fully opened state to 10 degrees. Ar gas is introduced from the gas introduction pipe 34, and the degree of vacuum is set to about 0.8 Pa.

The magnetron sputtering apparatus 30 has a cooling can 35, which is cooled to, for example, about -40 ° C. and rotates in a counterclockwise direction (direction of arrow A) in FIG. A target 36 to be arranged is provided.

The target 36 is a material for the carbon protective film, and 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.
Are arranged. This magnetron sputtering apparatus 30
When the carbon protective film is formed by the gas introduction pipe 34,
From the cooling can 35 as an anode and the backing plate 37 as a cathode.
A voltage of 000 (V) is applied so that a current of 1.4 A flows.

By the application of this voltage, Ar gas is turned into plasma, and the ionized ions collide with the target 36, whereby the atoms of the target 36 are repelled.
At this time, a magnet 38 is provided on the back side of the backing plate 37, and a magnetic field is formed near the target 36.
Will be concentrated near.

The atoms ejected from the target 36 are fed in the direction of arrow B in the figure from the supply roll 39 rotating in the counterclockwise direction in the figure, and travel along the peripheral surface of the cooling can 35. 2 adheres on the non-magnetic support 1 on which the film is formed, and a carbon protective film is formed. Then, the nonmagnetic support 1 on which the carbon protective film is formed is taken up by a take-up roll 41.

This carbon protective film has a thickness of about 3 to 15 nm so that the spacing loss can be reduced and the effect of preventing the metal magnetic film 2 from being worn can be obtained.
In particular, the thickness is preferably about 5 to 10 nm.

In the above, an example in which a carbon protective film is formed by magnetron sputtering has been described. In addition to this example, methods for forming a carbon protective film include ion beam sputtering, ion beam plating, and CV.
A known thin film forming method such as a method D can be used.

Further, in this magnetic recording medium, it is desirable that a lubricant is present on the surface of the carbon protective film. Thereby, the magnetic recording medium can further improve the effect of improving the running property based on the shape of the fine projections.

Further, the magnetic recording medium has a surface,
Back surface or its vicinity or a carbon protective film, a gap in the metal magnetic film 2, an interface between the carbon protective film and the metal magnetic film 2, an interface between the metal magnetic film 2 and the non-magnetic support 1, a non-magnetic support 1 Inside, etc., if necessary by known means rust inhibitor,
Various additives such as an antistatic agent and a fungicide can be present.

Backcoat Layer 4 In this magnetic recording medium, the backcoat layer 4 is formed on the surface of the nonmagnetic support 1 opposite to the surface on which the metal magnetic film 2 is formed. This back coat layer 4 is made of an electron beam cured film containing an electron beam curable resin, or
It is preferable to comprise an organic plasma polymerized film containing an organic plasma polymerizable resin.

First, the case where the back coat layer 4 is formed of an electron beam cured film will be described.

The electron beam cured film is a layer obtained by irradiating a layer containing a compound polymerizable by an electron beam with an electron beam. Here, the compound that can be polymerized by an electron beam generally refers to a compound called “electron beam-curable resin”, and refers to a compound having a π bond that can be polymerized by irradiation with an electron beam. For example, examples of the electron beam-curable resin include carbon and vinyl-vinylidene.
A compound having a plurality of carbon double bonds is preferable, and examples thereof include a compound containing an acryloyl group, a methacryloyl group, an acrylamide group, an allyl group, a vinyl ether group, a vinyl thioether group, and the like, and a compound such as an unsaturated polyester.

Particularly preferred examples of the electron beam-curable resin include compounds 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. The molecular weight of the electron beam-curable resin is about 500.
~ 20,000 is preferred.

Further, a monomer having an unsaturated carbon-carbon bond in the molecule can be added to the electron beam-curable resin. Examples of the monomer include acrylic acid, methacrylic acid, itaconic acid, methyl acrylate and its homologous alkyl acrylate, methyl methacrylate and its homologous methacrylic acid alkyl ester, styrene and its homologues. Certain α-methylstyrene, β-chlorostyrene and the like, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, vinyl propionate and the like can be mentioned. This monomer may have two or more unsaturated bonds in the molecule. In particular, it is preferable to use unsaturated esters of polyols such as ethylene diacrylate, diethylene glycol diacrylate, glycerol trimethacrylate, ethylene dimethacrylate, pentaerythritol tetramethacrylate, and glycidyl methacrylate having an epoxy ring.

Further, as the electron beam-curable resin,
A compound having a single 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 with the polymer is preferably polymer / monomer = 2/8 or more. Outside this range, a large amount of energy is required for curing the ultraviolet curable resin.

The electron beam-curable resin is irradiated with an electron beam using an electron beam accelerator or the like. As the electron beam accelerator, a Van de Graff type scanning system, double scanning system or curtain beam system can be used, but a curtain beam system which is relatively inexpensive and can provide a large output is preferable. As the electron beam characteristics, the acceleration voltage 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. If the accelerating voltage is lower than 100 kV, the amount of transmitted energy is insufficient and a sufficient curing reaction does not proceed. If the accelerating voltage exceeds 1000 kV, the energy efficiency used for polymerization is lowered, which is not economical. When the absorbed dose is less than 0.5 Mrad, the curing reaction is insufficient, and the desired coating strength cannot be obtained. When the absorbed dose exceeds 20 Mrad, the energy efficiency used for curing decreases, Heat is generated, and the nonmagnetic support 1 may be deformed, which is not preferable.

Further, an ordinary binder may be added to the back coat layer 4 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, methacrylate-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 can be mentioned.

Further, an inorganic pigment powder can be added to the back coat layer 4 as needed. As the inorganic pigment powder, carbon black, graphite, zinc oxide, titanium oxide, barium sulfate, talc, kaolin, chromium oxide, cadmium sulfide, goethite, silica aerosil, anhydrous alumina fine powder, calcium carbonate, molybdenum disulfide and the like are used. . Similarly, an antistatic agent, a lubricant, and the like can be contained in the back coat layer as needed.

Further, the thickness of the back coat layer 4 is preferably 0.1 to 0.6 μm. If the thickness of the back coat layer 4 is less than 0.1 μm, cupping cannot be reduced, and the effect of preventing cupping may not be obtained. If the thickness of the back coat layer exceeds 1.0 μm, the cupping in the reverse direction may increase, and the thickness of the magnetic recording medium itself may increase, making it difficult to reduce the thickness of the magnetic recording medium. is there.

Next, the case where the back coat layer 4 is made of an organic plasma polymerized film will be described.

The organic plasma polymer film is a very thin and uniform film, is a three-dimensionally developed dense film, and has the feature of having a strong structure in close contact with the nonmagnetic support. Thereby, the occurrence of cupping can be suppressed by using the organic plasma polymer film as the back coat layer 4.

This organic plasma polymer film is formed by a so-called plasma polymerization method. What is plasma polymerization?
It is formed by mixing discharge plasma of a carrier gas such as Ar, He, H ₂ , and N ₂ with a monomer gas, and bringing the mixed gas into contact with the surface of the substrate to be processed.

The principle of the plasma polymerization method will be described below.

First, when an electric field is applied while maintaining the carrier gas at a low pressure, the free electrons present in the carrier gas in a small amount are subjected to an electric field acceleration because of a very large intermolecular distance as compared with the normal pressure. Speed energy (electron temperature). When the free electrons that have acquired this velocity energy collide with atoms and molecules in the gas mixture, the atoms and molecules are broken down into atomic orbitals and molecular orbitals, causing unstable chemical species such as electrons, ions, and neutral radicals. To dissociate. Further, the dissociated electrons are subjected to electric field acceleration again to cause a chain reaction such as dissociation of another atom or molecule. According to this chain action, the mixed gas is in a highly ionized state, which is called a plasma gas. However, when the collision frequency between the gas molecules and the electrons is low, the gas molecules do not absorb much energy and are kept at a temperature close to room temperature. A system in which electron velocity energy (electron temperature) and molecular thermal motion (gas temperature) are separated in this way is called low-temperature plasma. In this low-temperature plasma state, chemical species remain relatively intact and polymerization occurs. Can proceed with the additive chemical reaction. Then, by bringing the above-mentioned mixed gas into a low-temperature plasma state, an organic plasma polymer film can be formed on the other main surface of the nonmagnetic support 1. As described above, when low-temperature plasma is used, there is an advantage that the other main surface of the nonmagnetic support 1 has almost no thermal effect.

Here, as the monomer gas, a carbon-hydrogen system, a carbon-hydrogen-oxygen system,
Any organic compound can be used, including carbon-halogen, carbon-oxygen-halogen, carbon-hydrogen-halogen, and organic metals.Especially, ethylene, acetylene, styrene, acrylonitrile, methyl methacrylate, butadiene, and benzene can be used. Organic compounds having an unsaturated bond such as In addition, organic silicon compounds such as various silanes having a siloxane bond and various organic compounds containing sulfur or nitrogen may be used.

As the plasma generating source, any of microwave discharge, DC discharge, AC discharge and the like can be used in addition to high frequency discharge. The degree of vacuum during plasma polymerization is 1 to 1
It is preferably about 000 Pa.

Further, the thickness of the organic plasma polymer film is as follows:
It is preferably from 0.1 to 1.0 μm. If the thickness of the organic plasma polymer film is less than 0.1 μm, cupping may not be reduced. If the thickness of the organic plasma polymer film exceeds 1.0 μm, cupping in the reverse direction may increase, the thickness of the magnetic recording medium itself may increase, and it may be difficult to reduce the thickness of the magnetic recording medium.

[0080]

EXAMPLES Hereinafter, the present invention will be described more specifically by describing specific examples and comparative examples of the above-described magnetic recording medium. The various physical properties and characteristics in this example were measured by the following methods.

<Measurement of Film Thickness> For the measurement of the film thickness, a section of the film cross section was cut out by the microtome method, and photographed at 5,000 times magnification using a transmission electron microscope (TEM) at a magnification of 5,000 times, and the average value of the 10 positions was measured. Was used as the layer thickness.

<Measurement of Surface Roughness> SRa is defined by the following equation.

[0083]

(Equation 1)

When measuring the surface roughness (SRa) of the surface on which the back coat layer is to be formed, a stylus diameter of 2 μmR and stylus pressure were measured using a surface roughness measuring device “ET-30HK” manufactured by Kosaka Laboratory. 10 mg, the cutoff value was 0.25 mm, the measured length in the X direction was 0.8 mm, and the measured value was 0.12 μm in the Y direction.

When measuring the surface roughness (SRa) of the surface on which the metal magnetic film is to be formed, a non-contact method using a surface roughness measuring device “ET-30HK” manufactured by Kosaka Laboratory is used. The cut-off value was 0.08 μm, the measurement length in the X direction was 0.1 mm, and the measurement was 0.02 μm in the Y direction. In addition, this non-contact measurement is generally used when measuring the surface roughness of a highly flattened surface, and is measured by an optical design displacement sensor using a critical angle focus error detection method. That is.

<Number of surface protrusions> The number of protrusions formed by adding inert particles to the polyamide film was counted using a high-scanning electron microscope (SEM) at a magnification of 5,000 or more and 1 mm ^It was converted to the number per ² pieces.

<Tape Characteristics> The evaluation of the characteristics of the magnetic recording media in Examples and Comparative Examples was performed using AIT manufactured by Sony Corporation.
The test was performed using a modified drive SDX-S300C (trade name). The recording was performed at a relative speed of 10.04 m / sec.
c, recording was performed at the shortest recording wavelength of 0.35 μm.

Measurement of Dropout The dropout was measured by using a dropout counter for 1 minute in which the output attenuation was 6 dB and the duration was 1 μsec or more.

Running Durability The running durability was evaluated by measuring the error rate after running 1 pass and the error rate after running 100 passes after running the 170 m length for 100 passes.

<Contact Characteristics with Head> As the contact characteristics with the head, the magnetic tape 170m was run for 10,000 passes, and the output signal (collision waveform) during tape reproduction was 1 unit.
The minimum value / maximum value (%) of the output signal in terms of the number of tracks was measured after running one pass and after running 10,000 passes.

<Measurement of Cupping> Measurement of cupping was performed using a cupping measuring apparatus having an optical microscope 50 as shown in FIG. In this cupping measuring device, first, a magnetic tape 5 loaded with a predetermined tension is used.
1 is wound over a pair of rolls 52. Next, the optical microscope 5
0 (magnification: 100 ×) by the driving means 53
1 is positioned at the center or both ends in the width direction. In this cupping measurement device, the optical microscope 50 is driven in the vertical direction, so that the magnetic tape 51 is focused at the center or both ends in the width direction. At this time, in the cupping measuring device, the height difference between the center portion and both ends in the width direction of the magnetic tape 51 is measured by the micrometer 54 that is interlocked with the vertical movement of the optical microscope 50.

At this time, a state where the metal magnetic film is convex is defined as negative cupping, and a state where the metal magnetic film is concave is defined as positive cupping.

Example 1 First, a slurry was prepared by dispersing dry silica particles having an average particle diameter of 0.1 μm in N-methyl-2-pyrrolidone (NMP).

Next, NMP and the above slurry were charged into a polymerization tank, into which 2-chloroparaphenylenediamine corresponding to 80 mol% as an aromatic diamine component and 4,4′-diamino equivalent corresponding to 20 mol% were added. The diphenyl ether was dissolved, and 2-chloroterephthalic acid chloride corresponding to 100 mol% was added thereto, followed by stirring for 2 hours to complete the polymerization. This was neutralized with lithium hydroxide to obtain a layer on which a metal magnetic film was formed, that is, a polymer solution (hereinafter referred to as solution A) for a second aromatic polyamide film. The content of the particles was 0.1 wt% with respect to the aromatic polyamide.

In the same manner, the silica particles having an average particle size of 1.5 μm were added to the aromatic polyamide by 0.05 wt%.
The layer on the back coat forming surface side, that is, the polymer solution for the first polyamide film (referred to as solution B) was prepared.

The solution A and the solution B were also adjusted to a polymer concentration of 10% by weight and the solution viscosity at 30 ° C. was adjusted to 3000 poise to be a film forming stock solution.

Then, the undiluted solution of solution A and solution B was passed through a filter having a cut of 5 μm, and then laminated into two layers and cast on a metal belt to produce a film. The extruded amount was the same so that the thickness of the final film was 4 μm. The cast film is heated at 180 ° C. with hot air for 2 hours.
After heating for one minute to evaporate the solvent, the film having self-holding property was continuously peeled off from the belt.

Next, the film was introduced into a water tank having a concentration gradient of NMP, and the residual solvent and the inorganic salts generated by the neutralization were extracted with water, and the water was dried and heat-treated with a tenter. During this time, 1.1 times each in the longitudinal direction and width direction of the film.
After stretching by 1.5 times and 1.5 times, drying and heat treatment at 280 ° C. for 1.5 minutes, the resultant was gradually cooled at a rate of 20 ° C./sec to obtain a nonmagnetic support.

Next, using the non-magnetic support thus produced, an original magnetic tape was produced in the following manner.

That is, the continuous winding type vapor deposition apparatus as shown in FIG. 2 was evacuated so that the inside thereof was brought into a vacuum state of about 10 ⁻³ (Pa), and the non-magnetic The support was set in this vapor deposition apparatus. Then, a metal magnetic film made of Co was formed on the surface of the second aromatic polyamide film in the nonmagnetic support in the presence of a small amount of oxygen by a continuous vacuum oblique deposition method.
The incidence angle of the vapor deposition is 90 to 45 in the normal direction of the non-magnetic support.
The electron beam intensity was adjusted so that the running speed of the nonmagnetic support was 50 m / min and the thickness of the metal magnetic film was 0.18 μm.

Next, the pressure of the magnetron sputtering apparatus as shown in FIG. 3 was reduced to about 10 ⁻⁴ (Pa), and Ar gas was introduced thereinto.
a. Then, the non-magnetic support having the metal magnetic film formed thereon is set in this magnetron sputtering apparatus, and is run at a speed of 5 m / min on a cooling can cooled to −40 ° C. to form a carbon protective film on the metal magnetic film. Formed.

Next, a back coat paint was prepared according to the following composition.

<Back coating composition> Carbon black: 100 parts by weight Polyurethane resin: 50 parts by weight Ester acrylate oligomer: 20 parts by weight Diethylene glycol diacrylate: 20 parts by weight Butoxyethyl acrylate: 20 parts by weight Methyl ethyl ketone 80%, toluene 20%: 300 parts by weight Then, this back coat paint is applied to the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed, and irradiated with an electron beam so that the absorbed dose becomes 5 megarads. A back coat layer having a thickness of 0.4 μm was formed.

Next, perfluoropolyether was applied as a lubricant on the carbon protective film. The raw tape thus obtained was slit into a width of 8 mm and then housed in a cassette body to prepare a cassette tape.

Examples 2 and 3 In Examples 2 and 3, a non-magnetic support was manufactured by adjusting the amount of extrusion of the solution A and the amount of extrusion of the solution B so that the total thickness was 4 μm. Except for the above, a magnetic tape was produced in the same manner as in Example 1.

As a result, in Example 2, the thickness of the second aromatic polyamide film was 2.2 μm, and in Example 3, the thickness of the second aromatic polyamide film was 3.0 μm. I have.

Example 4 Example 4 was carried out in the same manner as in Example 1 except that silica particles having an average particle diameter of 0.5 μm were used as the silica particles added to the solution B, and the silica particles were adjusted to be 0.1 wt%. A magnetic tape was produced.

Examples 5 and 6 In Examples 5 and 6, a non-magnetic support was manufactured by adjusting the extrusion amount of the solution A and the extrusion amount of the solution B so that the total thickness was 4 μm. Except for the above, a magnetic tape was produced in the same manner as in Example 4.

As a result, in Example 5, the thickness of the second aromatic polyamide film was 2.5 μm, and in Example 3, the thickness of the second aromatic polyamide film was 3.1 μm. I have.

Example 7 In Example 7, a plasma polymerized film having a thickness of 0.3 μm was formed on the surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film was formed under the following conditions. A magnetic tape was produced in the same manner as in Example 1.

Monomer gas: ethylene Monomer gas flow rate: 30 ml / min Carrier gas: argon Carrier gas flow rate: 70 ml / min Vacuum degree: 70 Pa High frequency power supply: 13.56 MHz, 300 W

Examples 8 and 9 In Examples 8 and 9, a non-magnetic support was manufactured so that the total thickness was 4 μm by adjusting the extrusion amount of the solution A and the extrusion amount of the solution B. Except for the above, a magnetic tape was produced in the same manner as in Example 7.

As a result, in Example 8, the thickness of the second aromatic polyamide film was 2.2 μm, and in Example 9, the thickness of the second aromatic polyamide film was 3.0 μm. I have.

Example 10 Example 10 was carried out in the same manner as in Example 7 except that silica particles having an average particle diameter of 0.5 μm were used as the silica particles added to the solution B, and the silica particles were adjusted to be 0.1 wt%. A magnetic tape was produced.

Examples 11 and 12 In Examples 11 and 12, the amount of solution A extruded and B
A magnetic tape was produced in the same manner as in Example 10, except that the non-magnetic support was produced so as to have a total thickness of 4 μm by adjusting the extrusion amount of the liquid.

As a result, in Example 11, the thickness of the second aromatic polyamide film was 2.5 μm,
In Example 12, the thickness of the second aromatic polyamide film was 3.1 μm.

Comparative Example 1 In Comparative Example 1, a backcoat paint prepared according to the following composition was applied to the surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film was formed, and dried. Later thickness is 0.4μ
A magnetic tape was produced in the same manner as in Example 1 except that the back coat layer was formed so as to obtain m.

100 parts by weight of carbon black (manufactured by Asahi Corporation, # 50) 100 parts by weight of polyester polyurethane (manufactured by Nipporan Company, trade name: N-2304) Solvent: 500 parts by weight of methyl ethyl ketone Toluene 500 parts by weight

Comparative Examples 2 and 3 In Comparative Examples 2 and 3, a non-magnetic support was manufactured so that the total thickness was 4 μm by adjusting the extrusion amount of the solution A and the extrusion amount of the solution B. Except for the above, a magnetic tape was produced in the same manner as in Comparative Example 11.

As a result, in Comparative Example 2, the thickness of the second aromatic polyamide film was 2.2 μm, and in Comparative Example 3, the thickness of the second aromatic polyamide film was 3.0 μm. I have.

Comparative Example 4 Comparative Example 4 was carried out in the same manner as in Comparative Example 1 except that silica particles having an average particle size of 0.5 μm were used as the silica particles added to the solution B, and were adjusted to be 0.1 wt%. A magnetic tape was produced.

Comparative Examples 5 and 6 In Comparative Examples 5 and 6, a non-magnetic support was manufactured by adjusting the extrusion amount of Solution A and the extrusion amount of Solution B so that the total thickness was 4 μm. Except for the above, a magnetic tape was produced in the same manner as in Comparative Example 4.

As a result, in Comparative Example 5, the thickness of the second aromatic polyamide film was 2.5 μm, and in Comparative Example 6, the thickness of the second aromatic polyamide film was 3.1 μm. I have.

[0124] For characterization above Examples 1 to 12 fabricated as described above, the surface roughness of the surface for forming the magnetic metal films (SRa), the maximum amplitude value of less waviness wavelength 20μm and 0.12μm
The density of the above coarse protrusions was measured. Table 1 shows the results of these measurements.

[0125]

[Table 1]

From the results shown in Table 1, it was found that Examples 1 to 12 had excellent surface properties. For this reason, even if an electron beam cured film or an organic plasma polymer film is formed as a back coat layer on the other main surface of the nonmagnetic support, the surface roughness of the surface on which the metal magnetic film is formed (SR
It can be seen that a) is not affected.

Table 2 shows the results of evaluating the above-mentioned characteristics of Examples 1 to 12 and Comparative Examples 1 to 6.

[0128]

[Table 2]

From the results shown in Table 2, in all of Examples 1 to 12 and Comparative Examples 1 to 6, the inert particles in the first aromatic polyamide film were different from those in the second aromatic polyamide film. Large compared to the inert particles in the second, the thickness of the second aromatic polyamide film is 2.0μ
When it is at least m, it can be seen that it has sufficient running durability and excellent reliability.

In the case where the back coat layer has an electron beam curable film as in Examples 1 to 6 or an organic plasma polymer film as in Examples 7 to 12, Comparative Example 1 In addition, as compared with Comparative Example 6, it is understood that the error rate after running many times and the contact characteristics with the head are significantly superior. From this, it can be seen that in Examples 1 to 12, cupping did not occur even when a thin nonmagnetic support having a thickness of 4.0 μm was used. In Examples 1 to 12, since cupping does not occur, the contact with the magnetic head is good, and the electromagnetic conversion characteristics are excellent. Further, in Examples 1 to 12, since cupping does not occur, uneven wear at both ends in the width direction of the magnetic tape is prevented, thereby preventing the occurrence of dropout, the reduction of output and the deterioration of error rate. can do.

[0131]

As described in detail above, in the magnetic recording medium according to the present invention, a predetermined back coat layer is formed on the surface of the non-magnetic support opposite to the surface on which the metal magnetic film is formed. By forming, cupping can be prevented. Therefore, this magnetic recording medium has excellent running durability and electromagnetic conversion characteristics, and also has excellent handling characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic configuration diagram of a continuous winding type vacuum evaporation apparatus used for forming a metal magnetic film.

FIG. 3 is a schematic configuration diagram of a magnetron sputtering apparatus used when forming a carbon protective film.

FIG. 4 is a schematic configuration diagram of a cupping measurement device.

[Explanation of symbols]

1 non-magnetic support, 2 metal magnetic film, 4 back coat layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 3/00 C08K 3/00 5D006 C08L 77/10 C08L 77/10 C09D 5/23 C09D 5/23 177 / 10 177/10 C23C 14/12 C23C 14/12 // C08J 5/18 CFG C08J 5/18 CFG F term (reference) 4F071 AA56 AB03 AB18 AB21 AB24 AB26 AD06 AH14 BC01 BC10 BC14 BC16 4F100 AA20H AA37 AA37H AB01A AK01DAK17 AK25D AK47B AK47C AK51 AK54 AL05 BA04 BA05 BA07 BA10A BA10D BA13 CA21 CA23B CA23C CC00D DD06C DD07B DD07C DE01B DE01C DE01H EH66 EJ61D GB41 JB14D JG06 FAL1 JL00 JL04 JL05 YY00 YY00B YY00B YY00B YY00B YY00B YY01B FA191 FA241 FA251 FA261 FA271 FA281 NA22 PA17 PB11 PC08 4K029 AA11 AA21 AA25 BA01 BA06 B A34 BA43 BA62 BB02 BD11 CA01 CA02 CA05 CA12 CA15 DB21 DC39 5D006 BB01 CB03 CB06 CB07 CB08 CC01 EA03 FA05

Claims (11)

[Claims] 1. A magnetic recording medium in which at least a metal magnetic film is formed on one main surface of a non-magnetic support, wherein the non-magnetic support has at least a first aromatic material constituting another main surface. An aromatic polyamide film, and a second aromatic polyamide film formed on the first aromatic polyamide film, and the inert particles contained in the first aromatic polyamide film are the second aromatic polyamide film. The non-magnetic support has a thickness of 2.0 μm or more excluding the first aromatic polyamide film, which is larger than the inert particles contained in the aromatic polyamide film of A magnetic recording medium, wherein a back coat layer is formed on the other main surface of the non-magnetic support. 2. The magnetic recording medium according to claim 1, wherein the back coat layer contains an electron beam curable resin. 3. The magnetic recording medium according to claim 1, wherein the back coat layer contains an organic plasma polymerization type resin. 4. The method according to claim 1, wherein the nonmagnetic support has a density of protrusions of 0.12 μm or more on one main surface on which the metal magnetic film is formed.
^2. The magnetic recording medium according to claim 1, wherein the number is 50 pieces / 100 cm ² or less. 5. The nonmagnetic support has a surface roughness (SRa) of one principal surface on which the metal magnetic film is formed, of 1.5 to 5.
2. The magnetic recording medium according to claim 1, wherein the thickness is 0 nm. 6. The non-magnetic support according to claim 1, wherein a surface undulation of one main surface on which the metal magnetic film is formed has a maximum amplitude value of undulation having a wavelength of 20 μm or less of 2.5 nm or less. The magnetic recording medium according to claim 1. 7. The inert particles contained in the first aromatic polyamide film have an average particle size of 0.03 to 1.5.
2. The magnetic recording medium according to claim 1, wherein the diameter of the magnetic recording medium is μm. 8. The magnetic recording medium according to claim 1, wherein the inert particles of the first aromatic polyamide film are contained in an amount of 0.05 to 2.0 wt%. 9. The inert particles of the second aromatic polyamide film are smaller than the average particle size of the inert particles contained in the first aromatic polyamide film, and the average particle size thereof. Is 0.03 to 0.15 μm,
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is contained in an amount of 0.01 to 1.0 wt%. 10. The thickness of the non-magnetic support is 2.5 to 2.5.
2. The magnetic recording medium according to claim 1, wherein the thickness is 5.0 [mu] m. 11. The non-magnetic support according to claim 1, wherein the other main surface located on the side opposite to the one main surface on which the metal magnetic film is formed has a surface roughness (SRa) of 4 to 20 nm. The magnetic recording medium according to claim 1.