JP2000242918A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure superior traveling durability and high reliability to the recording and readout of data as well as to attain a large recording capacity. SOLUTION: The magnetic recording medium has a nonmagnetic substrate 1 and a ferromagnetic metallic thin film 2 formed on one principal face of the nonmagnetic substrate 1. The nonmagnetic substrate 1 has a 1st aromatic polyamide film 3 constituting the other principal face and a 2nd aromatic polyamide film 4 formed on the 1st aromatic polyamide film 3. Inert particles contained in the 1st aromatic polyamide film 3 are coarser than inert particles contained in the 2nd aromatic polyamide film 4. The thickness of the nonmagnetic substrate 1 except the 1st aromatic polyamide film 3 is >=2.0 μm. A back coat layer 5 containing at least a binder and an acicular nonmagnetic pigment is formed on the other face of the nonmagnetic substrate 1 opposite to the face on which the ferromagnetic metallic thin film 2 is formed.

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 ferromagnetic metal thin 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 to practical use, an increase in the recording capacity is particularly required in order to achieve a large-capacity recording and a miniaturization in combination with the downsizing of the computer and the increase in the information processing capability. In addition, the use environment of magnetic tapes is widespread, so it can be used under a wide range of environmental conditions (especially in the circumstance where temperature and humidity fluctuates rapidly). Reliability and the like for the performance of recording, reading and the like are also required more than before.

In general, a magnetic tape has a configuration in which a magnetic layer is provided on a nonmagnetic support made of a flexible material such as a synthetic resin. In order to achieve the above-mentioned large capacity (volume recording capacity), the magnetic layer is formed by a method such as reducing the particle size of the magnetic powder, improving its dispersibility, or further reducing the thickness of the magnetic layer. It is said that an effective method is to increase the recording density of the magnetic tape itself and to reduce the total thickness of the magnetic tape.

Conventionally, polyester, mainly polyethylene terephthalate film, has been used as a nonmagnetic support for magnetic recording media. In particular, a polyethylene terephthalate film of about 7 to 10 μm is used as a support for a home video cassette tape, for example, an 8 mm tape, and a polyethylene film of about 5 to 7 μm is used as a tape streamer for data backup of a computer. I have.

[0005] For example, as disclosed in JP-A-6-215350, a non-magnetic support is mainly composed of polyester, specifically, a polyethylene naphthalate film to be used as a video tape. The recording time of the magnetic recording medium is extended.

On the other hand, the use of a polyamide film as a nonmagnetic support instead of the above-mentioned polyethylene terephthalate film or polyethylene naphthalate film has been studied and put to practical use. Polyamide film has a higher strength than polyethylene terephthalate film, and a magnetic recording medium using this polyamide film as a support can be reduced in thickness.
Attention has been paid to a magnetic recording medium corresponding to a large capacity of a tape streamer. In particular, in tape streamers, the capacity has doubled in two to three years, and in order to cope with the increase in capacity, it is desired to further reduce the thickness of the magnetic recording medium.

[0007]

However, the rigidity of the non-magnetic support is expressed by E × t ³ when the Young's modulus of the non-magnetic support is E and the thickness is t, and therefore, for example, the rigidity of the non-magnetic support is the same. In order to reduce the thickness of the non-magnetic support by half while maintaining the rigidity, the Young's modulus of the material of the support must be increased by eight times. Therefore, simply reducing the thickness of the nonmagnetic support is insufficient in mechanical strength.

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

Further, the relative speed between the magnetic head and the magnetic recording medium has been increasing, and a highly durable magnetic recording medium with less wear of the magnetic layer has been required. It is essential to control the fine shape of the surface.

On the other hand, when the magnetic layer is made of a ferromagnetic metal thin film, the thickness of the magnetic layer is small, so that the magnetic layer is easily affected by the surface properties of the non-magnetic support. The surface state, that is, the irregularities on the surface of the non-magnetic support are directly expressed as irregularities on the surface of the magnetic layer.

Therefore, in a magnetic recording medium having a ferromagnetic metal thin film, it is necessary to control the surface shape of the nonmagnetic support so that the fine shape of the surface of the magnetic layer is in an appropriate state. In such a situation, it is necessary to smooth the surface of the nonmagnetic support in order to reduce spacing loss. However, in the case of the non-magnetic support, there is a problem that if the surface on which the ferromagnetic metal thin film is formed is smoothed, handling in the manufacturing process becomes difficult.

The present invention has been proposed in view of the above-described conventional circumstances, and has a large recording capacity, excellent running durability, and high reliability in data recording and reading. An object of the present invention is to provide a magnetic recording medium for a large-capacity tape streamer.

[0013]

A magnetic recording medium according to the present invention is a magnetic recording medium having a nonmagnetic support and a ferromagnetic metal thin film formed on one main surface of the nonmagnetic 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, The inert particles contained in the first aromatic polyamide film are larger than the inert particles contained in the second aromatic polyamide film, and the non-magnetic support is The thickness excluding the first aromatic polyamide film is 2.
0 μm or more, and a back coat layer containing at least a binder and an acicular non-magnetic pigment is formed on a surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. It is characterized by having been done.

In the magnetic recording medium according to the present invention as described above, the surface of the main surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film is formed is contained in the first aromatic polyamide film. Of the inert particles. For this reason, in this magnetic recording medium, this 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 ferromagnetic metal thin film. For this reason, the influence of relatively large inert particles contained in the first aromatic polyamide film is small on the surface of the main surface on which the ferromagnetic metal thin film is formed. Therefore, in this magnetic recording medium, the surface of the ferromagnetic metal thin film has a desired excellent surface property. Further, in this magnetic recording medium, a back coat layer containing at least a binder and a needle-like non-magnetic pigment is provided on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. Since the back coat layer to be formed is formed, the rigidity of the magnetic recording medium is increased, deformation during running is suppressed as much as possible, and durability is improved.

The magnetic recording medium of the present invention is a magnetic recording medium having a non-magnetic support and a ferromagnetic metal thin film formed on one main surface of the non-magnetic support. The 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, and 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 is 2.0 μm or more, and a metal thin film is formed on a surface of the nonmagnetic support opposite to a surface on which the ferromagnetic metal thin film is formed. Specially To.

In the magnetic recording medium according to the present invention as described above, the surface of the main surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film is formed is contained in the first aromatic polyamide film. Of the inert particles. For this reason, in this magnetic recording medium, this 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 ferromagnetic metal thin film. For this reason, the influence of relatively large inert particles contained in the first aromatic polyamide film is small on the surface of the main surface on which the ferromagnetic metal thin film is formed. Therefore, in this magnetic recording medium, the surface of the ferromagnetic metal thin film has a desired excellent surface property. Further, in this magnetic recording medium, since the metal thin film is formed on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed, the rigidity of the magnetic recording medium increases, The deformation during running is suppressed as much as possible, and the durability is improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment An embodiment of the present invention will be described below in detail.

The magnetic recording medium shown in this embodiment is:
As shown in FIG. 1, a non-magnetic support 1 and a ferromagnetic metal thin film 2 formed on one main surface 1a of the non-magnetic support 1 are provided. In this magnetic recording medium,
The non-magnetic support 1 has at least a relatively large inert particle, a first aromatic polyamide film 3 constituting the other main surface 1b, and a relatively small inert particle.
And the second aromatic polyamide film 4 formed on the aromatic polyamide film 3. Further, in this magnetic recording medium, the thickness of the non-magnetic support 1 excluding the first aromatic polyamide film 3 is 2.0.
μm or more. In this magnetic recording medium, a back coat layer 5 containing at least a binder and a needle-shaped non-magnetic pigment is formed on the other main surface 1b of the non-magnetic support.

Hereinafter, a non-magnetic support 1, a ferromagnetic metal thin film 2
The back coat layer 5 and the binder and additives used for each of 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 3 and the second aromatic polyamide film 4, 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 3 and the second aromatic polyamide film 4 are preferably made of, for example, an aromatic polyamide represented by the following formula (I) and / or (II) in an amount of 50 mol% or more, preferably: Is at least 70 mol%. Thus, the following formulas (I) and / or (II)
By containing 50% or more of the aromatic polyamide represented by the formula (1), the nonmagnetic support 1 has excellent dimensional stability even when heat history is added, and has a high Young's modulus. It will be.

[0022]

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.

Further, the first aromatic polyamide film 3
And, from the viewpoint of increasing the rigidity, the second polyamide film 4 may be a polymer in which the aromatic ring is bonded at the para-position occupies 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 3 and the second aromatic polyamide film 4, a stock solution corresponding to the first aromatic polyamide film 3 and a second aromatic polyamide film 3 Two kinds of stock solutions corresponding to No. 4 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 3 have an average primary particle size of the inert particles contained in the second aromatic polyamide film 4. It is large compared to.

Specifically, the average particle size of the inert particles contained in the first aromatic polyamide film 3 is 0.03 to 0.03.
It is preferably 1.5 μm. And the addition amount of the inert particles contained in the first aromatic polyamide film 3 is preferably 0.05 to 2.0 wt%,
Further, the content is more preferably 0.1 to 1.0 wt%.

As described above, by defining the average particle size and the content of the inert particles contained in the first aromatic polyamide film 3, the surface on which the back coat layer 5 is formed can have a desired surface. It can be roughness. Accordingly, the magnetic recording medium has excellent handling characteristics, and can run well for a long period of time.

Also, the second aromatic polyamide film 4
In order to improve the smoothness and lubricity of the surface of the ferromagnetic metal thin film 2, the inert particles contained in
0.15 μm, the amount of addition is 0.01 wt% to 1 wt%
It is preferred that

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. When the average particle size of the inert particles is larger than 0.15 μm, the smoothness of the ferromagnetic metal thin film may be deteriorated. Furthermore, the second
If the amount of inert particles added to the aromatic polyamide film is less than 0.01% by weight, there may be a disadvantage that a sufficient number of protrusions for improving lubricity cannot be secured, and If the content is more than 1 wt%, the number of protrusions becomes excessive, which may adversely affect the surface properties of the ferromagnetic metal thin film.

On the other hand, in the non-magnetic support 1, the total thickness excluding the first aromatic polyamide film 3 is 2.0 μm or more. 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 3 and the second aromatic polyamide film 4, 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 5 is formed.

As described above, by defining the total thickness excluding the first aromatic polyamide film 3 to be 2.0 μm or more, the relatively large inert particles contained in the first aromatic polyamide film 3 can be reduced. The effect on the second aromatic polyamide film 4 can be minimized. In other words, the first aromatic polyamide film 3
When the total thickness excluding the thickness is defined as 2.0 μm or more, the surface properties (undulation, etc.) of the second aromatic polyamide film 4
Deterioration, formation of voids in the second aromatic polyamide film 4, or formation of coarse protrusions on the surface of the second aromatic polyamide film 4 can be prevented. Therefore, the ferromagnetic metal thin film 2 formed on the second aromatic polyamide film 4 has a desired surface property and is excellent in electromagnetic conversion characteristics, and the occurrence of dropout is reduced and reliability is improved. It will be excellent.

Further, in the non-magnetic support 1, 0.12 mm of the surface of the main surface 1 a on which the ferromagnetic metal thin film 2 is formed
Preferably μm or more coarse protrusions is 250 pieces / 100 cm ² or less, more, more preferably 200 / cm ² or less. The coarse protrusion can be measured on the main surface 1b of the nonmagnetic support 1 by the 3D-MIRAU method.

As described above, by setting the number of coarse protrusions of 0.12 μm or more on the surface of the main surface 1a on which the ferromagnetic metal thin film 2 is formed to 250/100 cm ² or less, the surface of the ferromagnetic metal thin film 2 Deterioration of surface properties and the like due to the coarse projections are less likely to occur. For this reason, in this magnetic recording medium, it is possible to reduce projections and the like that cause dropout.

Further, in this nonmagnetic support, the surface roughness (SRa) of the main surface 1a on which the ferromagnetic metal thin film 2 is formed is preferably 1.5 nm to 5.0 nm, more preferably 2.0 nm. More preferably, it is 3.5 nm. The surface roughness is adjusted by the size and amount of the inert particles added to the second aromatic polyamide film 4 or the layer structure of the nonmagnetic support 1. As described above, by setting the surface roughness of the main surface 1a on which the ferromagnetic metal thin film 2 is formed to 1.5 nm to 5.0 nm, it is possible to ensure good electromagnetic conversion characteristics and running durability of the magnetic recording medium. it can.

Further, in this non-magnetic support, the surface undulation of the main surface 1a on which the ferromagnetic metal thin film 2 is formed is preferably 2.5 nm or less, more preferably 2.0 nm.
m is more preferable. This surface undulation is
The surface roughness can be measured by performing fast Fourier transform (FFT) analysis on data obtained when measuring the surface roughness. That is, the surface roughness (S
The data obtained at the time of measuring Ra) is subjected to FFT analysis, and the amplitude of a wavelength of 20 μm or less is obtained, whereby the surface undulation of the main surface 1a of the nonmagnetic support 1 is measured. Thus, by setting the surface waviness of the main surface 1a on which the ferromagnetic metal thin film 2 is formed to 2.5 nm or less, 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 5 is formed is provided.
Is controlled by the size and amount of inert particles added to the first aromatic polyamide film 3, and is preferably as large as possible from the viewpoint of handleability in the production process. However, this surface roughness (SR
If a) is too large, after the ferromagnetic metal thin film 2 is formed,
4 nm to 15 nm, preferably 5 nm to 10 n, because the influence of set-off when the film is wound up into a roll becomes large.
m.

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.

[0044] Furthermore, the non-magnetic support 1, the ferromagnetic metal thin film 2 ³ 10 on one main surface side of the surface which is formed to 1
It is preferable that 0 ⁵ / mm ² in density projection is formed.

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

The ferromagnetic metal thin film 2 ferromagnetic metal thin film 2, the non-magnetic substrate 1, is formed on the main surface 1a of the second aromatic polyamide film 4 side. The ferromagnetic metal thin film 2 is formed using a continuous winding type vacuum evaporation apparatus as shown in FIG.

[0047] The vacuum deposition apparatus 10 is used for the oblique evaporation, internal, for example, about 10 ^- to ³ Pa about in the vacuum chamber 11 which is in a vacuum state, for example, cooled to about -20 ° C. Figure 2 The cooling can 12 includes a cooling can 12 that rotates in the direction of the middle arrow A, and a metal thin film deposition source 13 disposed at a position facing the cooling can 12. The evaporation source 13 is a container in which a ferromagnetic metal material is accommodated in a container such as a crucible.

As shown in FIG. 2, the vacuum evaporation apparatus 10 has a non-magnetic support roll 16 mounted on a rotatable supply shaft 22 and a rotatable rotation driven by a drive source (not shown). The magnetic tape roll 17 is mounted on the take-up shaft 23, and the non-magnetic support 2 is caused to run continuously via the cooling can 12.

When the ferromagnetic metal thin film 2 is formed by using the vacuum evaporation apparatus 10 having such a configuration, first, the ferromagnetic metal material in the evaporation source 13 is accelerated from the electron beam generation source 14. The emitted electron beam 15 is irradiated to heat and evaporate the ferromagnetic metal material.

Then, the heated and evaporated ferromagnetic metal material is applied to the non-magnetic support roll 16 mounted on the supply shaft 22.
The ferromagnetic metal thin film 2 is formed on the non-magnetic support 2 which is fed out in the direction of arrow B in FIG. 2 and runs along the peripheral surface of the cooling can 12. Finally,
The nonmagnetic support 2 on which the ferromagnetic metal thin film 2 is formed is wound around a magnetic tape roll 17 mounted on a winding shaft 23.

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 position-adjustable. Only vapor particles incident at an angle of. The ferromagnetic metal thin film 2 is formed by such an oblique deposition method.

Further, the ferromagnetic metal thin film 2
It is preferable that oxygen gas be introduced into the vicinity of the surface of the non-magnetic support 2 via an oxygen gas inlet (not shown). By introducing oxygen gas, the magnetic properties, durability and weather resistance of the metal magnetic thin film 2 can be improved.

Guide rollers 20 and 21 are disposed between the non-magnetic support roll 16 and the cooling can 12 and between the cooling can 12 and the magnetic tape roll 17, respectively. Is applied with a predetermined tension so that the non-magnetic support 2 runs smoothly.

In order to heat the evaporation source 13, in addition to the heating means using the electron beam as described above, for example,
Known means such as resistance heating means, high-frequency heating means, and laser heating means may be used.

In the above, an example in which the ferromagnetic metal thin film 2 is formed by the oblique deposition method has been described.
In addition to this example, a known thin film forming method such as a vertical vapor deposition method or a sputtering method can be applied as a method for forming a thin film. Further, as the ferromagnetic metal material, in addition to Co, Ni, F
e, or an alloy thereof can be used. However, for the purpose of improving the adhesion strength to the nonmagnetic support 1, or improving the resistance and abrasion resistance of the ferromagnetic metal thin film itself, it is obtained when the atmosphere at the time of vapor deposition is an atmosphere in which oxygen gas is dominant. It is desirable to use a metal magnetic film containing oxygen. The thickness of the ferromagnetic metal thin film 2 is 0.0
The thickness is preferably about 1 μm to 0.2 μm, and more preferably 0.1 μm to 0.2 μm.

Backcoat layer 5 The backcoat layer 5 is formed on the main surface 1b of the nonmagnetic support 1 opposite to the main surface 1a on which the ferromagnetic metal thin film 2 is formed. This back coat layer 5 is mainly composed of acicular non-magnetic pigment, carbon black and a binder.

As the acicular non-magnetic pigment, it is preferable to use an acicular non-magnetic pigment having a ratio of a major axis to a minor axis, that is, an aspect ratio of 10 or more. By using an acicular nonmagnetic pigment having an aspect ratio of 10 or more, not only the thickness direction of the magnetic recording medium but also mechanical strength such as tensile strength and bending strength in a plane direction such as a longitudinal direction and a width direction can be improved. It can be improved. The material of the acicular nonmagnetic pigment is not particularly limited, and for example, hematite, goethite, titanium oxide, aluminum oxide, or the like can be used.

In the back coat layer 5, it is preferable to use two types of carbon black having different average particle sizes. In this case, the average particle size is 10
It is preferable to use fine-grained carbon black having a particle size of ２０20 μm and coarse-grained carbon black having an average particle size of 230 to 300 μm.

In general, the surface electric resistance of the back coat layer 5 can be set low and the light transmittance can be set low by adding the above-mentioned fine particle carbon black.
Some magnetic recording devices use the light transmittance of the tape and use it as an operation signal. In such a case, the addition of fine carbon black is particularly effective.

In addition, since fine carbon black particles generally have excellent holding power to a lubricant, a lubricant can be used in combination, and as a result, the coefficient of friction can be reduced.

On the other hand, coarse-grained carbon black having a particle size of 230 to 300 μm has a function as a solid lubricant, and forms fine projections on the surface. It is possible to reduce the coefficient of friction. However, coarse carbon black
In a severe running system, the tape may slide off from the back coat layer 5 easily, which may lead to an increase in the error ratio.

Specifically, examples of the fine carbon black include the following. RAVEN2
000B (18mμ), RAVEN 1500B (17m
μ) (above, manufactured by Columbia Carbon Co., Ltd.), BP800
(17mμ) (Cabot), PRINTENT9
0 (14mμ), PRINTEX95 (15mμ), P
RINTEX85 (16mμ), PRINTEX75
(17 mμ) (all manufactured by Degussa), # 3950 (16
mμ) (Mitsubishi Chemical Industries, Ltd.). As the coarse carbon black, thermal black (270 mμ)
(Karncarb), RAVEN MTP (275m
μ) (manufactured by Columbia Carbon Co., Ltd.).

In the case of using two types of back coat layers 5 having different average particle sizes, the
μ fine particle carbon black and 230-300 μm coarse particle carbon black content ratio by weight ratio,
Fine particle carbon black: coarse particle carbon black = 98: 2 to 75:25 is preferable, and more preferably 95: 5 to 85:15. Further, the content of carbon black (in the case of adding fine particles and coarse particles, the total amount thereof) in the back coat layer 5 is usually in the range of 30 to 80 parts by weight with respect to 100 parts by weight of a binder described later. And preferably in the range of 45 to 65 parts by weight.

Further, assuming that the amount of the binder contained in the back coat layer 5 is B and the amount of the acicular nonmagnetic pigment is P,
The ratio P / B between these binders and the needle-shaped non-magnetic pigment is 0.1.
It is preferably from 5 to 5.0. When the P / B ratio is 0.
If it is less than 5, the effect of reinforcing the mechanical strength in the plane direction of the magnetic recording medium cannot be obtained because the content of the acicular nonmagnetic pigment is small. On the other hand, if the P / B ratio is larger than 5, the content of the binder is small, so that the strength of the back coat layer 5 itself is weak, and a powder drop phenomenon occurs, or the durability of the back coat layer 5 itself deteriorates.

The binder used for the back coat layer 5 includes, for example, a thermoplastic resin, a thermosetting resin, a reactive resin, and a mixture thereof.

Examples of the thermoplastic resin include vinyl chloride,
Polymer containing vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, and vinyl ether as constituent units Or a copolymer. Examples of the copolymer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, and acrylate-vinylidene chloride copolymer. Polymer, acrylate-styrene copolymer, methacrylate-acrylonitrile copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-styrene copolymer, vinylidene chloride-acrylonitrile copolymer , Butadiene-
An acrylonitrile copolymer, a styrene-butadiene copolymer, and a chlorovinyl ether-acrylate copolymer can be exemplified. In addition to the above, polyamide resins, cellulose resins (cellulose acetate butyrate,
Cellulose diacetate, cellulose propionate, nitrocellulose, etc.), polyvinyl fluoride, polyester resin, polyurethane resin, various rubber resins and the like can also be exemplified.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, and epoxy resin. -Polyamide resins, mixtures of polyester resins and polyisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, mixtures of polyurethane and polyisocyanates.

[0068] Further, the binding agent as described above, in order to further improve the excellent dispersibility and durability, if _{necessary, -COOM, -SO 3 M, -OSO} 3 M, -P = O
(OM) ₂ , -OP = O (OM) ₂ (M represents a hydrogen atom or an alkali metal base), -OH, -N
It is preferable to introduce at least one polar group selected from R ₂ , -N ⁺ R ₃ (R represents a hydrocarbon group), an epoxy group, -SH, -CN, etc. by copolymerization or addition reaction. Such a polar group is 10 ^-1 to 10 ^-8 mol / g.
(More preferably, 10 ⁻² to 10 ⁻⁶ mol / g).

The polyisocyanate contained in the binder includes, for example, tolylene diisocyanate,
Isocyanates such as 4-4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate; these isocyanates and polyalcohols; And polyisocyanates formed by condensation of isocyanates.

Further, the thickness of the back coat layer 5 is preferably from 0.1 μm to 0.6 μm.
If the thickness of the back coat layer 5 is too small, the effect of reinforcing the mechanical strength of the magnetic recording medium will not be exhibited, and
If the thickness of the magnetic recording medium is too large, cracks are likely to occur in the magnetic recording medium.

The back coat layer 5 may contain a lubricant. Examples of the lubricant include a fatty acid and a fatty acid ester. As fatty acids, for example, acetic acid, propionic acid,
Aliphatic carboxylic acids such as octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachinic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid or these And mixtures thereof.

The fatty acid esters include, for example,
Butyl stearate, sec-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyldecyl stearate, butyl palmitate, 2-ethylhexylmilli State, a mixture of butyl stearate and butyl palmitate, oleyl oleate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether acylated with stearic acid, diethylene glycol dipalmitate, Hexamethylenediol is acylated with myristic acid to form a diol, and various ester compounds such as oleate of glycerin. These can be used alone or in combination.

In the back coat layer 5, the lubricant is preferably added in an amount of usually 1 to 5 parts by weight based on 100 parts by weight of the binder resin.

Further, various additives can be added to the back coat layer 5. Examples of the additive include a dispersant added to the coating solution for forming the back coat layer 5 in order to disperse the magnetic powder or the non-magnetic powder or the like in the binder. Examples of the additive include a plasticizer, conductive particles other than carbon black (antistatic agent), and a fungicide, which are added as necessary.

Examples of the dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Stearic acid, behenic acid, oleic acid, elaidic acid,
1 carbon atom such as linoleic acid, linolenic acid, stearic acid
2 to 18 fatty acids (RCOOH, R represents 11 to 1 carbon atoms)
7 alkyl groups or alkenyl groups), metal soaps of the above fatty acids comprising alkali metals or alkaline earth metals, amides of the above fatty acids, polyalkylene oxide alkyl phosphates, lecithin, trialkyl polyolefinoxy quaternary ammonium salts (Alkyl has 1 to 5 carbon atoms, olefins include ethylene and propylene, etc.), sulfate, copper phthalocyanine, and the like. These may be used alone or in combination. In particular, it is preferable to use a combination of copper oleate, copper phthalocyanine, and barium sulfate for the back coat layer 5. The dispersant is added in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the binder resin.

As described above, in the magnetic recording medium according to the present embodiment, the ferromagnetic metal thin film 2
Since the back coat layer 5 is formed on the surface 1b opposite to the surface 1a on which is formed, mechanical strength is sufficiently ensured and durability is improved. As a result, in the magnetic recording medium to which the present invention is applied, the deformation of the shape is suppressed, the contact with the magnetic head can be sufficiently obtained, and better electromagnetic conversion characteristics, recording / reproducing characteristics, and running properties are realized. Is done.

In this magnetic recording medium, a protective film 6 may be formed on the ferromagnetic metal thin film 2 as shown in FIG. By forming the protective film 6 on the ferromagnetic metal thin film 2, abrasion of the ferromagnetic metal thin film 2 can be prevented. To form the protective film 6, carbon is deposited on the ferromagnetic metal thin film 2 using a magnetron sputtering device 30 as shown in FIG.

In this magnetron sputtering apparatus 30, the inside of the chamber 31 is, for example, about 10 ⁻⁴ Pa by the vacuum pump 32.
After the pressure has been reduced to the extent, the angle of the valve 33 for exhausting to the vacuum pump 32 side is reduced, thereby reducing the exhaust speed and introducing Ar gas from the gas introduction pipe 34 to reduce the degree of vacuum to about 0.8 Pa, for example. It is said. Further, the magnetron sputtering apparatus 30 includes, for example,-
A cooling can 35 that is cooled to 40 ° C. and rotates in the direction of arrow C in FIG. 4 and a target 36 that is arranged to face the cooling can 35 are provided. Target 36
Is a material of the protective film 6, and carbon is used. Further, 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.

The magnetron sputtering apparatus 30
The magnetic tape roll 17 on which the ferromagnetic metal thin film 2 is formed is mounted on a rotatable supply shaft 39, and a magnetic tape roll 17 is rotatably driven by a driving source (not shown). The non-magnetic support 2 on which the ferromagnetic metal thin film 2 is formed is mounted on the cooling can 35.
The vehicle is continuously driven in the direction D in FIG.

When the protective film 6 is formed by this magnetron sputtering device 30, first, the gas introduction pipe 34
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 0 V is applied so that a current of about 1.4 A flows.

Then, by applying this voltage, Ar gas is turned into plasma and the ionized ions collide with the target 36, whereby 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, so that the ionized ions are concentrated near the target 26. The atoms ejected from the target 36 are fed out from the magnetic tape roll 17 in the direction of arrow D in FIG. 4 and run on the outer peripheral surface of the cooling can 35 on the ferromagnetic metal thin film 2 of the nonmagnetic support 2. To form a protective film 6.
Finally, the nonmagnetic support 2 on which the protective film 6 is formed is wound by a magnetic tape roll 42 mounted on a winding shaft 41.

At this time, the protective film 6 should have a thickness of about 3 nm to 15 nm so as to minimize the spacing loss and to obtain the effect of preventing the abrasion of the ferromagnetic metal thin film 2. More preferably, the film thickness is 5
nm to about 10 nm.

In the above, the method using magnetron sputtering has been described as a method for forming the protective film 6. In addition to this method, a known thin film forming method such as ion beam sputtering, ion beam plating, and CVD is used. Can be used.

Incidentally, in this magnetic recording medium, it is preferable that a lubricant is present on the surface of the protective film 6. The presence of the lubricant can further enhance the running performance improving effect based on the shape of the fine projections on the surface of the non-magnetic support 2.

Further, this magnetic recording medium has a surface,
The back surface, the protective film 6, the gap between the ferromagnetic metal thin films 2, the interface between the protective film 6 and the ferromagnetic metal thin film 2, the interface between the ferromagnetic metal thin film 2 and the nonmagnetic support 2, the inside of the nonmagnetic support 2, and the like. If necessary, various additives such as a rust inhibitor, an antistatic agent, and a fungicide can be added by known means.

<Second Embodiment> Next, a second embodiment of the present invention will be described. As shown in FIG. 5, the magnetic recording medium according to the present embodiment has a non-magnetic support 51
And a ferromagnetic metal thin film 52 formed on one main surface 51 a of the nonmagnetic support 51. In this magnetic recording medium, the non-magnetic support 51 has at least relatively large inert particles, and the first aromatic polyamide film 53 constituting the other main surface 51b and the relatively small inert particles. And a second aromatic polyamide film 54 formed on the first aromatic polyamide film 53. Further, in this magnetic recording medium, the thickness of the non-magnetic support 51 excluding the first aromatic polyamide film 53 is 2.0 μm or more.

Here, the nonmagnetic support 51 and the ferromagnetic metal thin film 52 have the same configuration as the nonmagnetic support 1 and the ferromagnetic metal thin film 2 described in the first embodiment. Here, description of the nonmagnetic support 51 and the ferromagnetic metal thin film 52 will be omitted.

The magnetic recording medium according to the present embodiment has a structure in which the nonmagnetic support 51 has a metal surface 51b opposite to the main surface 51a on which the ferromagnetic metal thin film 52 is formed. A thin film 55 and a back coat layer 56 are formed. Hereinafter, the metal thin film 55 and the back coat layer 56 will be described.

As the metal used for the metal thin film 55,
For example, Cu, Al, Ni, Cr, or an alloy thereof may be used. The thickness of the metal thin film 55 is preferably 0.1 μm to 0.5 μm. Here, when the thickness of the metal thin film 55 is thinner than 0.1 μm,
The effect of reinforcing the mechanical strength of the magnetic recording medium does not appear.
When the thickness of the metal thin film 55 is larger than 0.5 μm,
Cracks in the magnetic recording medium are likely to occur. By setting the thickness of the metal thin film 55 to 0.1 μm to 0.5 μm, the mechanical strength of the magnetic recording medium can be reinforced without causing cracks.

The metal thin film 55 is formed on the surface 51 a of the nonmagnetic support 51 on which the ferromagnetic metal thin film 52 is formed by a continuous winding vacuum evaporation apparatus as shown in FIG.
It is formed by evaporating the above-mentioned metal material on the surface 51b on the opposite side to the above.

The metal thin film 55 may be formed by a vertical evaporation method, a sputtering method, or the like in addition to the above-described oblique evaporation method.
It can be formed by a known thin film forming method such as CVD.

[0092] The back coat layer 56 is formed on the metal thin film as necessary. This back coat layer 56
Is mainly composed of carbon black, an inorganic powder and a binder. Here, the carbon black and the binder constituting the back coat layer 56 include the above-described first material.
Almost the same one used for the back coat layer 6 of the magnetic recording medium according to the embodiment is used.

On the other hand, inorganic powders having a Mohs hardness of 5
To 9 are preferably used. Mohs hardness is 5
By using the inorganic powder of No. 9, the magnetic recording medium can be repeatedly provided with running durability, and the back coat layer 56 can be strengthened. When these inorganic powders are used together with the above-described carbon black and calcium carbonate, the back coat layer 56 becomes a strong back coat layer with little deterioration even by repeated sliding due to its filler effect.

When the inorganic powder used in the back coat layer 56 has a relatively high Mohs hardness of 5 to 9, a moderate polishing force is generated on the surface of the back coat layer 56,
Adhesion to guide poles and the like is reduced. As a magnetic recording medium, in particular, when calcium carbonate and an inorganic powder are used in combination for the back coat layer, the sliding characteristics against a rough guide pole or the like are improved, and the friction coefficient of the back coat layer 56 is also stabilized. Can be planned. The inorganic powder preferably has an average particle size in the range of 80 to 250 μm, and more preferably 100 to 210 μm.
mμ range.

Examples of the inorganic powder include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ CO ₃ ). These inorganic powders may be used alone or in combination of two or more. Among these, α-iron oxide or α-alumina is preferred. The content of the inorganic powder having a Mohs' hardness of 5 to 9 is usually 3 to 30 parts by weight, preferably 3 to 20 parts by weight, based on 100 parts by weight of carbon black. In particular, it is preferable that the back coat layer 56 contains two types of carbon black having different average particle sizes, calcium carbonate having the above size, and the inorganic powder having the above-mentioned Mohs hardness of 5 to 9.

The magnetic recording medium according to the present embodiment has a surface 51 on which the ferromagnetic metal thin film 52 of the nonmagnetic support 51 is formed.
Since the metal thin film 55 is formed on the surface 51b opposite to the surface a, the mechanical strength is sufficiently ensured, and the durability is improved. As a result, in the magnetic recording medium to which the present invention is applied, the deformation of the shape is suppressed, the contact with the magnetic head can be sufficiently obtained, and better electromagnetic conversion characteristics, recording / reproducing characteristics, and running properties are realized. Is done.

In this magnetic recording medium, a protective film may be formed on the ferromagnetic metal thin film 51. By forming the protective film on the ferromagnetic metal thin film 51, the wear of the ferromagnetic metal thin film 51 can be prevented.

[0098]

EXAMPLES [First Experimental Example] In this experimental example, a nonmagnetic support was provided on the surface opposite to the surface on which the ferromagnetic metal thin film was formed.
The effect when the back coat layer containing the acicular nonmagnetic pigment was formed was confirmed as follows.

1. Preparation of Sample Tape First, a sample tape was prepared as follows.

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 vessel, and 2-chloroparaphenylenediamine corresponding to 80 mol% as an aromatic diamine component and 4,4′-diamino equivalent corresponding to 20 mol% were added thereto. 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 the side on which the ferromagnetic metal thin film was formed, that is, a polymer solution for the second aromatic polyamide film (hereinafter, referred to as solution A). The content of the particles was 0.1 wt% with respect to the aromatic polyamide.

Further, silica particles having an average particle size of 1.5 μm were added in a similar manner to the aromatic polyamide by 0.05 wt%.
A layer on the back coat layer forming surface side,
A polymer solution (hereinafter referred to as solution B) for a polyamide film was prepared.

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

Then, the stock solutions of Solution A and Solution B were passed through a filter having a cut of 5 μm, then laminated in 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 remaining 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.

First, the continuous winding type vapor deposition apparatus as shown in FIG. 2 was evacuated so that the inside thereof was evacuated to a vacuum of about 10 ⁻³ Pa. The magnetic support was set on this vapor deposition device. And
By a continuous oblique evaporation method, a ferromagnetic metal thin film made of Co was formed on the surface of the second aromatic polyamide film of the nonmagnetic support in the presence of a small amount of oxygen. At this time, the incident angle of the vapor deposition is such that the normal direction of the nonmagnetic support is 90 to 45 degrees, and the traveling speed of the nonmagnetic support is 50 m
And the intensity of the electron beam was adjusted such that the thickness of the ferromagnetic metal thin film was 0.18 μm at a rate of 1 / min.

Next, the pressure of the magnetron sputtering apparatus as shown in FIG. 4 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 at a speed of 5 m / min on a cooling can cooled to about −40 ° C., so that carbon is deposited on the ferromagnetic metal thin film. Was formed.

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

Back coating composition Goethite (major axis length 0.2 μm, aspect ratio 30) 100 parts by weight Carbon black (# 50, manufactured by Asahi Corporation) 50 parts by weight Polyester polyurethane 100 parts by weight (N-2304, manufactured by Nippon Polyurethane Co., Ltd.) Solvent: 500 parts by weight of methyl ethyl ketone 500 parts by weight of toluene Then, the prepared back coating is applied to the surface of the nonmagnetic support opposite to the side on which the ferromagnetic metal thin film is formed, and dried to obtain a dry thickness of 0. A 4 μm back coat layer was formed. Next, a lubricant composed of perfluoropolyether was applied on the protective film to produce a magnetic recording medium. Finally,
This magnetic recording medium was cut into a tape having a width of 8 mm to form a magnetic tape, and the magnetic tape was stored in a cassette body to obtain a sample tape.

<Embodiment 2> The extrusion amount of the solution A was increased,
Example 1 was repeated except that the amount of extrusion of the solution B was reduced by that amount to produce a non-magnetic support so that the total thickness was 4 μm.
A sample tape was produced in the same manner as described above.

As a result, in Example 2, the thickness of the second aromatic polyamide film was 2.2 μm.

<Embodiment 3> The extrusion amount of the solution A was increased,
Example 1 was repeated except that the amount of extrusion of the solution B was reduced by that amount to produce a non-magnetic support so that the total thickness was 4 μm.
A sample tape was produced in the same manner as described above.

As a result, in Example 3, the thickness of the second aromatic polyamide film was 3.0 μm.

Example 4 Example 1 was repeated 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 addition amount was adjusted to 0.1 wt%. A sample tape was produced in the same manner.

<Example 5> As the silica particles to be added to the solution B, those having an average particle diameter of 0.5 μm were used, the addition amount was adjusted to be 0.1 wt%, and the extrusion amount of the solution A was further adjusted. , And reduce the pushing amount of B solution by that amount,
A sample tape was produced in the same manner as in Example 1 except that the nonmagnetic support was produced so that the total thickness was 4 μm.

As a result, in Example 5, the thickness of the second aromatic polyamide film was 2.5 μm.

<Example 6> As the silica particles to be added to the solution B, those having an average particle size of 0.5 μm were used, the addition amount was adjusted to be 0.1 wt%, and the extrusion amount of the solution A was further adjusted. , And reduce the pushing amount of B solution by that amount,
A sample tape was produced in the same manner as in Example 1 except that the nonmagnetic support was produced so that the total thickness was 4 μm.

As a result, in Example 6, the thickness of the second aromatic polyamide film was 3.1 μm.

<Comparative Example 1> A sample tape was prepared in the same manner as in Example 1 except that the back layer paint having the following composition was used.

Back coating composition carbon black (# 50, manufactured by Asahi Corporation) 100 parts by weight Polyester polyurethane 100 parts by weight (trade name: N-2304 manufactured by Nippon Polyurethane Co.) Solvent: 500 parts by weight methyl ethyl ketone 500 parts by weight toluene <Comparative Example 2> A sample tape was prepared in the same manner as in Example 2, except that the composition described in Comparative Example 1 was used as the back layer paint.

Comparative Example 3 A sample tape was prepared in the same manner as in Example 3 except that the composition described in Comparative Example 1 was used as the back layer paint.

Comparative Example 4 A sample tape was prepared in the same manner as in Example 4, except that the composition described in Comparative Example 1 was used as the back layer paint.

Comparative Example 5 A sample tape was prepared in the same manner as in Example 5, except that the composition described in Comparative Example 1 was used as the back layer paint.

Comparative Example 6 A sample tape was prepared in the same manner as in Example 6, except that the composition described in Comparative Example 1 was used as the back layer paint.

2. Evaluation of Characteristics Next, the above Examples 1 to 6 and Comparative Examples 1 to 6
Various physical property values and characteristic characteristics of the 12 sample tapes were measured and evaluated by the following methods.

Measurement of Film Thickness Measurement of the film thickness was performed by cutting out a section of the film by a microtome method, photographing the film at 10 places at a magnification of 5,000 times using a transmission electron microscope (TEM), and obtaining an average value at 10 places. It was thick.

Measurement of Surface Roughness Surface roughness (SRa) is defined by the following equation.

[0129]

(Equation 1)

When measuring the surface roughness of the surface on which the back coat layer is to be formed, a surface roughness meter “ET” manufactured by Kosaka Laboratories was used.
-30HK ", stylus diameter 2μmR, stylus pressure 10m
g, cutoff value 0.25mm, X direction measurement length 0.8m
The measurement was performed under the conditions of the measurement length of 0.12 μm in the m and Y directions.

When measuring the surface roughness of the surface on which the ferromagnetic metal thin film is to be formed, a non-contact method using a surface roughness measuring device “ET-30HK” manufactured by Kosaka Laboratories is used. Cutoff value 0.08mm, X direction measurement length 0.1m
The measurement was performed under the conditions of a measurement length of 0.02 μm in the m and Y directions. In addition, this non-contact measurement is generally used when measuring the surface roughness of a highly flat 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 a polyamide film was determined by a high-scanning electron microscope (SE
With M), and counted at a magnification of 5,000 times or more, 1 mm ²
It was converted to the number per hit.

[0133] Characterization of the magnetic recording medium in tape characteristics Examples and Comparative Examples,
Sony Corporation AIT Drive SDX-S300C
(Product name) was modified. Recording was performed at a relative speed of 10.04 m / sec and a minimum recording wavelength of 0.35 μm.
m.

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

-Running durability As for the running durability, the vehicle was run for 1000 passes over a length of 170 m.
The error rate after running one pass, the error rate after running 100 passes, and the error rate after running 1000 passes were measured.

Contact Characteristics with Head The contact characteristics with the head are as follows: 170 m length is 1000
The minimum value / maximum value (%) of the output signal when the output signal (hitting waveform) at the time of tape reproduction was viewed for one track was measured after the first pass and the 10,000 pass.

Examples 1 to 6 and Comparative Examples 1 to 6
Table 1 shows the results of measurement of the tape thickness, surface roughness, and number of surface projections for the sample tape of Table 1, and Table 2 shows the results of characteristic evaluation.

[0138]

[Table 1]

[0139]

[Table 2]

Table 2 shows that the sample tapes of Comparative Examples 1 to 6 in which the acicular nonmagnetic pigment was not contained in the back coat layer had a large error rate and dropout. Further, in the sample tapes of Comparative Examples 1 to 6, the tape contact was significantly reduced after running 10,000 passes, indicating that sufficient durability was not obtained.

On the other hand, in Examples 1 to 6 in which the backcoat layer contained the acicular nonmagnetic pigment, the error rate and the dropout were small. Further, Examples 1 to
In the sample tape of Example 6, the tape contact hardly decreased after running 10,000 passes, indicating that sufficient durability was obtained.

Therefore, the thickness of the magnetic recording medium can be reduced by forming a back coat layer containing an acicular non-magnetic pigment on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. Even if it is thin, necessary and sufficient strength is secured,
It has been found that the long-term storage property of the magnetic recording medium, that is, the durability can be improved.

[Second Experimental Example] In this experimental example, the effect when a metal thin film is formed on the surface of a nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film is formed is as follows. Confirmed.

1. Preparation of Sample Tape Example 7 First, a nonmagnetic support was prepared, a ferromagnetic metal thin film was formed on the nonmagnetic support, and a protective film was formed on the ferromagnetic metal thin film. Here, the nonmagnetic support, the ferromagnetic metal thin film, and the protective film were formed in the same manner as in Example 1 described above.

Next, the raw material on which the ferromagnetic metal thin film and the protective film were formed was set in a continuous winding type vacuum evaporation apparatus as shown in FIG. 2, and the inside thereof was set to about 10 ⁻² Pa. The air was evacuated so as to be in a vacuum state, and on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film was formed, that is, on the main surface of the first aromatic polyamide film, a reinforcing material made of Al was used. A metal thin film was formed. The film forming conditions at this time are as follows:
The incident angle of vapor deposition was set to 0 to 25 degrees, and the feed rate of the nonmagnetic support was set to 60 m / min. In addition, the thickness of the metal thin film is set to 0.
It was manufactured by adjusting the intensity of the electron beam to 2 μm.

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

Back coating composition carbon black (Asahi Co., # 50) 100 parts by weight Polyester polyurethane 100 parts by weight (trade name N-2304 manufactured by Nippon Polyurethane Co.) Solvent: methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight The back coating was applied on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film was formed, and dried to form a back coat layer having a dry thickness of 0.4 μm. Next, a lubricant composed of perfluoropolyether was applied on the protective film to produce a magnetic recording medium. Finally, the magnetic recording medium was cut into a tape having a width of 8 mm to form a magnetic tape, and the magnetic tape was stored in a cassette body to obtain a sample tape.

<Embodiment 8> The extrusion amount of the solution A was increased,
Example 7 was repeated except that the extrusion amount of the solution B was reduced by that amount to produce a non-magnetic support so that the total thickness became 4 μm.
A sample tape was produced in the same manner as described above.

As a result, in Example 8, the thickness of the second aromatic polyamide film was 2.2 μm.

<Embodiment 9> The extrusion amount of the solution A was increased,
Example 7 was repeated except that the extrusion amount of the solution B was reduced by that amount to produce a non-magnetic support so that the total thickness became 4 μm.
A sample tape was produced in the same manner as described above.

As a result, in Example 9, the thickness of the second aromatic polyamide film was 3.0 μm.

Example 10 The procedure of Example 7 was repeated except that silica particles having an average particle size of 0.5 μm were used as the silica particles to be added to the solution B, and the addition amount was adjusted to 0.1 wt%. A sample tape was produced in the same manner.

<Example 11> As the silica particles to be added to the solution B, those having an average particle size of 0.5 μm were used, the addition amount was adjusted to be 0.1 wt%, and the extrusion amount of the solution A was further adjusted. Was increased in the same manner as in Example 7, except that the extrusion amount of the solution B was reduced and the non-magnetic support was manufactured so that the total thickness became 4 μm.

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

<Example 12> As the silica particles to be added to the solution B, those having an average particle size of 0.5 μm were used, the addition amount was adjusted to be 0.1 wt%, and the extrusion amount of the solution A was further adjusted. And a non-magnetic support was prepared in the same manner as in Example 7 except that the non-magnetic support was prepared so that the total thickness was 4 μm by reducing the amount of extrusion of the solution B by that amount.

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

Comparative Example 7 A sample tape was prepared in the same manner as in Example 7, except that a metal thin film for reinforcement was not formed.

Comparative Example 8 A sample tape was produced in the same manner as in Example 8, except that no reinforcing metal thin film was formed.

Comparative Example 9 A sample tape was produced in the same manner as in Example 9 except that no reinforcing metal thin film was formed.

Comparative Example 10 A sample tape was produced in the same manner as in Example 10 except that no reinforcing metal thin film was formed.

<Comparative Example 11> A sample tape was prepared in the same manner as in Example 11, except that no reinforcing metal thin film was formed.

<Comparative Example 12> A sample tape was produced in the same manner as in Example 12, except that no reinforcing metal thin film was formed.

2. Evaluation of Characteristics Table 1 shows the results of measuring the tape thickness, surface roughness, and the number of surface protrusions on the sample tapes of Examples 7 to 12 and Comparative Examples 7 to 12 by the same method as in Experimental Example 1 described above. And the results of the characteristic evaluation are shown in Table 2.

[0164]

[Table 3]

[0165]

[Table 4]

Table 4 shows that the sample tapes of Comparative Examples 7 to 12 in which the reinforcing metal thin film was not formed had many error rates and dropouts. Also,
In the sample tapes of Comparative Examples 7 to 12, 1000
It can be seen that the tape contact is significantly reduced after the 0-pass running, and that sufficient durability has not been obtained.

On the other hand, in Examples 7 to 12 in which the reinforcing metal thin film was formed, it can be seen that the error rate and the dropout were small. In addition, in the sample tapes of Examples 7 to 12, the tape contact hardly decreased after running 10,000 passes, indicating that sufficient durability was obtained.

Therefore, by forming a reinforcing metal thin film on the surface of the non-magnetic support opposite to the surface on which the ferromagnetic metal thin film is formed, even if the thickness of the magnetic recording medium is small. It was found that the necessary and sufficient strength was secured, and the long-term storage property of the magnetic recording medium, that is, the durability, could be improved.

[0169]

According to the present invention, a backcoat layer containing a needle-shaped nonmagnetic pigment or a reinforcing metal thin film is provided on the surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. By forming the magnetic recording medium, necessary and sufficient strength is secured even if the thickness of the magnetic recording medium is thin, and a magnetic recording medium with excellent durability can be realized. As a result, the magnetic recording medium of the present invention can stably run for a long time even on a drive, and can cope with long-time recording and large capacity.

In the magnetic recording medium according to the present invention, one main surface of the non-magnetic support on which the lower non-magnetic layer and the upper magnetic layer are formed exhibits a desired excellent surface property, and the other main surface also has a desired surface property. It can be in a desired state. 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 cross-sectional view illustrating a configuration example of a magnetic recording medium according to the present invention.

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

FIG. 3 is a cross-sectional view showing another configuration example of the magnetic recording medium according to the present invention.

FIG. 4 is a schematic configuration diagram illustrating an example of a magnetron sputtering apparatus for forming a protective film.

FIG. 5 is a sectional view showing another configuration example of the magnetic recording medium according to the present invention.

[Explanation of symbols]

1,51 non-magnetic support, 2,52 ferromagnetic metal thin film, 3,53 first aromatic polyamide film,
4,54 First aromatic polyamide film, 5,5
6 Back coat layer, 55 metal thin film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G11B 5/73 G11B 5/704 // C08L 77:00 F term (reference) 4F006 AA38 AB73 BA06 CA02 DA01 4J038 EA011 KA08 KA18 PB11 PC08 5D006 BB01 CB03 CB06 CB08 CC01 CC02 CC04

Claims (3)

[Claims] 1. A magnetic recording medium having a non-magnetic support and a ferromagnetic metal thin film formed on one main surface of the non-magnetic support, wherein the non-magnetic support has at least another main surface. A first aromatic polyamide film, a second aromatic polyamide film formed on the first aromatic polyamide film, and a first aromatic polyamide film formed on the first aromatic polyamide film. The active particles are larger than the inert particles contained in the second aromatic polyamide film, and the non-magnetic support has a thickness of 2 excluding the first aromatic polyamide film. A backcoat layer containing at least a binder and an acicular nonmagnetic pigment is formed on a surface of the nonmagnetic support opposite to the surface on which the ferromagnetic metal thin film is formed. A magnetic recording medium, comprising: 2. A magnetic recording medium having a nonmagnetic support and a ferromagnetic metal thin film formed on one main surface of the nonmagnetic support, wherein the nonmagnetic support has at least another main surface. A first aromatic polyamide film, a second aromatic polyamide film formed on the first aromatic polyamide film, and a first aromatic polyamide film formed on the first aromatic polyamide film. The active particles are larger than the inert particles contained in the second aromatic polyamide film, and the non-magnetic support has a thickness of 2 excluding the first aromatic polyamide film. A magnetic recording medium having a thickness of at least 0.0 μm and a metal thin film formed on a surface of the nonmagnetic support opposite to a surface on which the ferromagnetic metal thin film is formed. 3. The metal thin film is made of Cu, Al, Ni, C
3. The magnetic recording medium according to claim 2, wherein the magnetic recording medium contains at least one of r and an alloy thereof.