JP2001084550A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a high-density recording system constructible by applying magnetic layer made of magnetic paint to a helical scan magnetic recording system which uses a magnetoresistance effect reproducing head by specifying the product of the residual magnetism quantity and film thickness of the magnetic layer within a certain range and forming the magnetic layer on one-main- surface sides of nonmagnetic base where the number of rough projections whose each height is not less than a specific value is not more than a specific number. SOLUTION: The magnetic recording medium is optimized conforming to the characteristics of the magneto-resistance effect (MR) reproducing head. In concrete, the product Mr×δ of the residual magnetism quantity Mr and film thickness δ of the magnetic layer is 0.8 to 6.5 memu/cm2. Consequently, the magnetic recording medium does not saturate the MR reproducing head and high output can be obtained in a distortion-free state. On one main surface of a nonmagnetic base where the magnetic layer is formed, large-sized projections of >=0.273 μm in height are regulated to <=60 pieces/100 cm2. Consequently, the magnetic layer has a surface where frictional heat is hardly generated when the MR reproducing head and magnetic layer are in sliding motion.

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 magnetic layer coated with a magnetic paint, and is particularly suitable for use in a helical scan magnetic recording system using a magnetoresistive read head. The present invention relates to a simple magnetic recording medium.

[0002]

2. Description of the Related Art Recording media used in audio devices, video devices, computer devices, etc. include magnetic powders,
Applying a magnetic paint prepared by kneading and dispersing a binder and various additives in an organic solvent on a non-magnetic support,
A so-called coating type magnetic recording medium in which a magnetic layer is formed by drying the magnetic paint thereafter is known. This coating type magnetic recording medium is predominant as the above-mentioned recording medium because of its excellent productivity and versatility.

A magnetic recording medium is recorded / reproduced by a recording / reproducing apparatus having a magnetic head such as an inductive head. In recent years, this recording / reproducing apparatus has been reduced in size and weight, improved in image quality, and extended in time. Accordingly, high-density recording is also strongly required in the above-mentioned coating type magnetic recording medium.

In a coating type magnetic recording medium, in order to achieve high-density recording in a recording / reproducing system using an inductive head, a magnetic powder having a large saturation magnetic flux density and fine particles is used. As such magnetic powders, metal magnetic powders mainly composed of iron have been used instead of iron oxide-based magnetic powders conventionally used.

[0005] Metal magnetic powder has a higher saturation magnetic flux density than iron oxide-based magnetic powder and can be said to be suitable for high-density recording. Further, specifically, as a composition, a magnetic powder is used which is mainly composed of iron and to which cobalt is added. As a result, the magnetic powder exhibits a higher saturation magnetic flux density. Therefore, by using such a magnetic powder, the magnetic recording medium also has a high saturation magnetic flux density, and is adapted to a high-density recording in a recording / reproducing system using an inductive head.

In recent years, as a magnetic reproducing head suitable for high-density recording, a magnetoresistive effect reproducing head (hereinafter, referred to as a magnetoresistive reproducing head)
This is called an MR reproducing head. ) Is widespread. This MR
The reproducing head includes a magnetoresistive element (hereinafter, referred to as an MR element), which is a magnetic substance exhibiting a magnetoresistive effect, and electrodes for applying a current to the MR element. The MR reproducing head detects a magnetic flux generated from the magnetic recording medium as a change in resistance of the MR element, that is, a change in inter-terminal voltage. Then, the detected change in voltage between the terminals of the MR element is
It is output as a reproduction signal. This change in the voltage between the terminals of the MR element can be represented as a magnetoresistive response curve shown in FIG. When the change in the voltage between the terminals of the MR element is within a pseudo-linear region near the inflection point in the magnetoresistive response curve, it is possible to maintain a linearity and obtain a reproduction output without distortion.

[0007]

However, in a coating type magnetic recording medium, even if a high saturation magnetic flux density is achieved corresponding to a recording / reproducing system using an inductive head, reproduction by an MR reproducing head having high sensitivity is achieved. When considered, the amount of generated magnetic flux is too large. In this case, M
A change in the voltage between the terminals of the R element occurs in a region outside the pseudo-linear region in the magnetoresistive response curve, that is, in a region outside the region maintaining linearity.

For this reason, even if a coating-type magnetic recording medium achieves a high saturation magnetic flux density corresponding to a recording / reproducing system using an inductive head, the magnetic recording medium has a distortion when reproduced using an MR reproducing head. No output characteristics could be shown.

In the MR reproducing head, the frictional heat generated by the sliding motion with the magnetic recording medium causes noise. This is because the temperature of the MR element rises due to frictional heat generated on the surface of the MR reproducing head, and the resistance of the MR element changes. That is, the coating type magnetic recording medium is MR
As a result of generating frictional heat between the reproducing head and the reproducing head, there is a problem that the MR reproducing head cannot be operated stably and noise is generated.

Therefore, the present invention has been proposed in view of such circumstances, and the thickness of the magnetic layer, the amount of residual magnetization, and the surface properties are optimized in accordance with the MR reproducing head.
By applying the present invention to a helical scan magnetic recording system using an R reproducing head, an object is to construct an unprecedented high-density recording system and to provide a magnetic recording medium having extremely excellent electromagnetic conversion characteristics.

[0011]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention comprises a magnetic recording medium having a non-magnetic support and a magnetic layer coated with a magnetic paint. The product of the residual magnetization Mr of the layer and the film thickness δ
The value of δ is 0.8 to 6.5 memu / cm ² , and the magnetic layer has 60 coarse protrusions having a height of 0.273 μm or more.
It is characterized in that it is formed on one main surface side of a non-magnetic support having a size of 100 cm ² or less.

In the magnetic recording medium according to the present invention configured as described above, the product M of the residual magnetization Mr of the magnetic layer and the film thickness δ is obtained.
Since the value of r · δ is in the range of 0.8 to 6.5 memu / cm ² , for example, the reproduction of the recording signal by the MR reproducing head is performed within a region where the linearity of the magnetoresistive response curve is maintained. .

Further, at least one principal surface of the nonmagnetic support has coarse projections having a height of not less than 0.273 μm and not more than 60/100 cm ² . The magnetic layer has 60 coarse protrusions having a height of 0.273 μm or more / 100c.
It is formed on one main surface side of a nonmagnetic support having a size of m ² or less. Thus, the magnetic layer is less likely to generate frictional heat during a sliding motion with, for example, the MR reproducing head.

[0014]

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

A magnetic recording medium to which the present invention is applied has a nonmagnetic support and a magnetic layer formed by applying a magnetic paint.

The magnetic layer is formed by applying a magnetic paint prepared by kneading and dispersing a magnetic powder together with a binder or the like in an organic solvent, for example, on a non-magnetic support. In addition, the magnetic layer controls the type of the magnetic powder used, the mixing ratio of the magnetic powder and the binder, and the type and the mixing ratio of the other additives used to prevent the MR reproducing head from being saturated. , And is regulated so that a high output can be obtained without distortion. Specifically, the value of the product Mr · δ of the residual magnetization amount Mr of the magnetic layer and the film thickness δ is 0.8 to 6.5.
memu / cm ² .

The value of the product Mr · δ is 0.8 to 6.5 memu
/ Cm ² , the film thickness δ and the residual magnetization Mr can be arbitrarily set.
If r is too small, the value of the product Mr · δ will be 0.8me
It is difficult to secure mu / cm ² or more. Conversely, the film thickness δ
If the residual magnetization Mr is too large, distortion becomes a problem.

Here, as the magnetic powder used for the magnetic layer, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , FeOx (x = 1.33)
To 1.5), CrO ₂ , Co-containing γ-Fe ₂ O ₃ , Co-containing FeOx (x = 1.33 to 1.5), ferromagnetic metal powder, and plate-like hexagonal ferrite powder. Further, it is preferable to use a plate-like hexagonal ferrite powder as the magnetic powder, and it is more preferable to use a ferromagnetic metal powder.

The ferromagnetic metal powder used for the magnetic layer must contain at least Fe. Specifically, F
e, Fe-Co, Fe-Ni, Fe-Zn-Ni and F
It is a simple metal or an alloy mainly composed of e-Ni-Co or the like. The specific surface area of the particles of the ferromagnetic metal powder is 30 to 70 m
It is preferably ² / g. The crystallite size determined by the X-ray diffraction method is preferably 50 to 300 °. If the specific surface area of the particles of the ferromagnetic metal powder is too small, it may not be possible to sufficiently cope with high-density recording. On the other hand, if the specific surface area of the particles of the ferromagnetic metal powder is too large, the dispersibility in the magnetic coating material is deteriorated, so that it is difficult to form a magnetic layer having a smooth surface, and high density recording is required. It may not be possible to respond.

The magnetic properties of these ferromagnetic metal powders are such that the saturation magnetization (saturation magnetic flux density) (δ
s) is preferably at least 110 emu / g, and
More preferably, it is 0 emu / g. Further, the coercive force (Hc) is preferably from 1900 to 2600 Oe, more preferably from 2000 to 2400 Oe. Further, the squareness ratio (δr / δs) is preferably 0.78 or more, more preferably 0.78 to 0.95, and particularly preferably 0.80 to 0.95. Here, δs represents the saturation magnetic flux density, and δr represents the residual magnetic flux density. If the squareness ratio is less than 0.78,
There is a possibility that a sufficient reproduction output cannot be obtained.

The major axis length of the ferromagnetic metal powder, that is, the average particle diameter is preferably 0.5 μm or less,
More preferably, it is 0.01 to 0.3 μm. The needle ratio of the ferromagnetic metal powder is preferably from 5 to 20, and more preferably from 5 to 15.

Further, a non-metal such as B, C, Al, Si, P or the like, or a salt or oxide thereof may be added to the ferromagnetic metal powder in order to further improve the magnetic properties.

The water content of the magnetic powder is 0.01 to 2
% By weight, and it is preferable to optimize the water content depending on the type of the binder. Also, the p of the magnetic powder
H is preferably 4 to 12, more preferably 5 to 10. If necessary, add A to the magnetic powder.
The surface treatment may be performed with l, Si, P or an oxide thereof. The amount of Al, Si, P or their oxides used in the surface treatment is 0.1 to 1 with respect to the magnetic powder.
It is preferably 0% by weight. By performing the surface treatment, adsorption of a lubricant such as a fatty acid can be suppressed to 100 mg / m ² or less. Soluble Na,
In some cases, inorganic ions such as Ca, Fe, Ni, and Sr are included, but if the content is 500 ppm or less, the magnetic properties of the magnetic layer are not affected.

As the binder used in the magnetic layer, for example, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof and the like can be used. Specific thermoplastic resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylate, styrene, butadiene, ethylene, vinyl butyral, and vinyl. A polymer or a copolymer containing acetal and vinyl ether as constituent units can be given. Here, specific copolymers include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate -Vinylidene chloride copolymer, acrylate-styrene copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-acrylonitrile copolymer, methacrylate-styrene copolymer, vinylidene chloride- Examples thereof include an acrylonitrile copolymer, a butadiene-acrylonitrile copolymer, a styrene-butadiene copolymer, and a chlorovinyl ether-acrylate copolymer.

Examples of the thermoplastic resin include polyamide resins, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), polyvinyl fluoride, polyester resins, polyurethane resins, It is also possible to use a rubber-based resin or the like.

Specific examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acryl-based reactive resin, a formaldehyde resin, a silicone resin, Examples thereof include an epoxy-polyamide resin, a mixture of a polyester resin and a polyisocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate.

Here, examples of the polyisocyanate include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-isocyanate.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate; products of these isocyanates and polyalcohols; and polyisocyanates formed by condensation of isocyanates. Can be.

The binder for the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer and A combination of at least one resin of nitrocellulose and a polyurethane resin, or a combination of these resins and a polyisocyanate is preferable. Specific examples of the polyurethane resin include conventionally known polyurethane resins having a structure such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane.

The content of the binder in the magnetic layer is preferably 5 to 50 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder contained in the magnetic layer. In particular, when a combination of a vinyl chloride resin, a polyurethane resin and a polyisocyanate is used as a binder, the proportion of these in the total binder is 5 to 70% by weight for the vinyl chloride resin, and It is preferable that the content of the polyisocyanate is 2 to 50% by weight and the content of the polyisocyanate is 2 to 50% by weight.

In order to improve the dispersibility of the pigment, it is preferable to introduce at least one or more polar functional groups into the binder by copolymerization or addition reaction. Specific polar functional _{group, -SO 3 M, -OSO 3 M} ,
-COOM, -P = O (OM) ₂ , -OP = O (O
_{M) 2, -OH, -NR 2} , -N + R 3, an epoxy group, -
SH, -CN and the like. In the formula, M represents a hydrogen atom or an alkali metal base. In the formula, R represents a hydrocarbon group. The introduction amount of these polar functional groups is 10 ^-1 to 10
It is preferably ^-8 mol / g, more preferably 10 ^-2 to 10 ^-6 mol / g.

The magnetic layer may be composed of a single layer or a plurality of layers.

The nonmagnetic support is obtained by preparing an unstretched film from a resin which is a conventionally known material, and biaxially stretching the film by a sequential or simultaneous stretching method or the like.

As a material used for the non-magnetic support, conventionally known materials can be used.
Examples include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, polyaramid, aromatic polyamide and polybenzoxazole. In particular, it is preferable to use a high-strength material such as polyethylene naphthalate, polyamide, and polyimide.

Further, as a material used for the non-magnetic support,
It is also possible to use an aluminum or glass substrate or the like. If necessary, the surface roughness of the surface of the nonmagnetic support on which the magnetic layer is to be formed and the surface of the magnetic layer can be changed by using a laminated nonmagnetic support as disclosed in JP-A-3-224127. It is also possible to use a support.
Further, these non-magnetic supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust reduction treatment, or the like in advance. The surface of the non-magnetic support on which the magnetic layer is not formed is preferably rougher than the surface on which the magnetic layer is formed.

It is preferable to add inert particles to the non-magnetic support in order to improve the running durability of the magnetic recording medium. Specific inert particles include SiO ₂ , Ti
Inorganic particles such as O ₂ , Al ₂ O ₃ , CaSO ₄ , BaSO ₄ , CaCO ₃ , carbon black, zeolite, and other fine metal powders, silicon particles, polyimide particles, cross-linked copolymer particles, cross-linked polyester particles, and Teflon particles And the like. In particular, from the viewpoint of heat resistance, it is preferable to use inorganic particles, and it is particularly preferable to use SiO ₂ .

As a method of adding these inert particles to the nonmagnetic support, a method in which the inert particles are slurried with a solvent and then used as a polymerization solvent or a diluting solvent,
A method of adding directly after adjusting the film forming stock solution, and the like.

At least one main surface side of the nonmagnetic support is
A magnetic layer is formed. For this reason, it can be said that the surface properties of the magnetic layer are affected by the surface condition on one main surface side of the nonmagnetic support on which the magnetic layer is formed. Therefore, the surface state of at least one main surface of the nonmagnetic support is controlled so that the magnetic layer becomes suitable for reproduction by the MR reproducing head.

Specifically, on at least one principal surface side of the nonmagnetic support, the number of coarse projections having a height of 0.273 μm or more is 60/100 cm ² or less. In particular, it is preferable that the number of coarse projections having a height of 0.273 μm or more be 20/100 cm ² or less on one main surface side of the nonmagnetic support.

Here, the coarse projection in the present invention means an interference fringe generated when two non-magnetic supports in the form of a film are superposed and irradiated with a monochromatic sodium lamp having a wavelength of 0.546 μm. A protrusion having a single ring or more.

The number of the coarse protrusions can be controlled by appropriately selecting the particle size of the inert particles and the like added to the non-magnetic support, the amount of the particles added, the material, and the like. Further, when the nonmagnetic support has a composite structure of two or more layers, the number of coarse projections can also be controlled by adjusting the thickness of the layer on which the magnetic layer is formed. .

The non-magnetic support has a width in the width direction such that when the recording signal of the magnetic recording medium is reproduced by the MR reproducing head, the spacing between the magnetic layer and the MR reproducing head is optimized. It is preferable that the Young's modulus is 1000 kg / mm ² or more.

The Young's modulus in the width direction is 1000 kg / mm ²
If it is smaller, the magnetic recording medium floats from the MR read head, and a spacing loss occurs between the magnetic layer and the MR read head. For this reason, the reproduction output of the magnetic recording medium may decrease, and the error rate may deteriorate.

The Young's modulus can be adjusted by adjusting the stretching ratio in the length, direction, and width directions of stretching the nonmagnetic support. The Young's modulus in the width direction is 1000 kg / mm
^In order to obtain a nonmagnetic support having ² or more, it is preferable to use polyamide, polyethylene naphthalate, or polyimide.

The magnetic recording medium to which the present invention is applied is not limited to the above-described structure. For example, a non-magnetic paint and a magnetic paint are coated on a non-magnetic support, and then the non-magnetic paint and the magnetic paint are applied. May be dried, and a nonmagnetic layer and a magnetic layer may be laminated on the nonmagnetic support in this order.

The non-magnetic layer is formed by applying a non-magnetic paint prepared by kneading and dispersing at least a non-magnetic powder and a binder in an organic solvent on a non-magnetic support. The non-magnetic layer must be substantially non-magnetic so as not to affect the electromagnetic conversion characteristics of the magnetic layer. It may contain powder.

The non-magnetic powder used in the non-magnetic layer includes α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide , Titanium oxide,
Examples include silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, and barium sulfate.
These nonmagnetic powders can be used alone or in combination. In particular, titanium oxide,
It is preferable to use α-alumina, α-iron oxide or chromium oxide.

These non-magnetic powders have an average particle diameter of 0.0
It is preferably from 1 to 1.0 nm, and from 0.01 to 0.
5 nm, more preferably 0.02 to 0.1 n
m is particularly preferred.

The non-magnetic powder is preferably relatively hard. Specifically, the Mohs hardness is preferably 5 or more, and more preferably 6 or more. Further, it is preferable to use 3 to 25% by weight (preferably 3 to 20% by weight) of nonmagnetic powder having a Mohs hardness of 5 or more (preferably 6 or more) that can function as an abrasive.

As the binder used for the nonmagnetic layer, conventionally known binders can be used. Specific examples of the binder used for the non-magnetic layer include the same binders as the binders used for the magnetic layer described above.

As in the case of the binder used in the magnetic layer, a polar group may be introduced into the binder used in the non-magnetic layer in order to improve the dispersibility of the pigment. A polyisocyanate that crosslinks and cures the polymer.

The content of the binder in the nonmagnetic layer is 5 to 100 parts by weight of the nonmagnetic powder contained in the nonmagnetic layer.
It is preferably 50 parts by weight, more preferably 10 to 30 parts by weight. In particular, when a combination of a vinyl chloride resin, a polyurethane resin, and a polyisocyanate is used as the binder, the proportion of these in the total binder is 5 to 70% by weight for the vinyl chloride resin, 2-50% by weight of resin
For polyisocyanate, the content is preferably 2 to 50% by weight.

The binder used for the non-magnetic layer is preferably a binder having the same composition as the binder used for the magnetic layer. Thereby, the uniformity of the coating film of the non-magnetic coating material and the magnetic coating material can be improved, and a magnetic recording medium with few coating film defects can be obtained.

The non-magnetic layer may contain carbon black as an antistatic agent. As the carbon black, those obtained by various production methods can be used, and specific examples thereof include furnace black, thermal black, acetylene black, channel black, and lamp black.

As specific examples of carbon black products, BLACKPEARLS 2000, 1300, 1
000,900,800,700, VULCAN XC
-72 (above, manufactured by Cabot Corporation), $ 35, $ 50, $
55, $ 60 and $ 80 (above, Asahi Carbon Co., Ltd.)
3950B, 3750B, 3250B,
2400B, $ 2300B, $ 1000, $ 900, $
40, $ 30 and $ 10B (Mitsubishi Chemical Industries, Ltd.)
Manufactured) CONDUCTEXSC, RAVEN, 150, 5
0, 40, 15 (all manufactured by Konlon Via Carbon),
Ketchen Black EC, Ketchen Black ECDJ
-500 and Ketjen Black ECDJ-600 (all manufactured by Lion Aguso Co., Ltd.).

The average particle size of the carbon black is 35 n
m, more preferably 10 to 35 nm. The specific surface area of the carbon black is preferably 5 to 500 m ² / g, and 50 to 500 m ² / g.
More preferably, it is 300 m2 / g. DBP lubrication amount of carbon black is 10-100ml / 100g
And more preferably 50 to 300 ml / 100 g. Also, carbon black p
It is preferable that H is 2 to 10, the water content is 0.1 to 10%, and the tap density is 0.1 to 1 g / cc.

The DBP lubrication amount is a value generally used for evaluating the surface characteristics of carbon black.
Dibutyl phthalate is added little by little to carbon black, the state of carbon black is observed while kneading, and the amount of dibutyl phthalate added when finding a point forming one lump from the dispersed state is meant.

The amount of carbon black added to the nonmagnetic layer is preferably 3 to 20 parts by weight, more preferably 4 to 18 parts by weight, and more preferably 5 to 15 parts by weight, per 100 parts by weight of the nonmagnetic powder. It is particularly preferred that the amount is by weight.

Further, an organic powder can be added to the non-magnetic layer as needed. Specific examples of the organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment. Also, polyolefin resin powder,
It is also possible to add polyester resin powder, polyamide resin powder, polyimide resin powder, polyfluoroethylene resin, or the like.

The non-magnetic layer may contain a lubricant. Examples of the lubricant contained in the non-magnetic layer include fatty acids, fatty acid esters, and the like.

Specific fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachinic acid, oleic acid, linoleic acid and linolenic acid. And aliphatic carboxylic acids such as elaidic acid and palmitoleic acid, and mixtures of these fatty acids.

Further, specific fatty acid esters include:
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 ester compounds may be used alone or in combination.

The amount of these lubricants is 0.2 to 2 parts by weight based on 100 parts by weight of the nonmagnetic powder contained in the nonmagnetic layer.
It is preferably in the range of 00 parts by weight.

The magnetic recording medium to which the present invention is applied
A back coat layer may be formed on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed.
This back coat layer has a binder, carbon black, inorganic powder and the like.

As the binder used in the back coat layer, the same binders as those used in the above-described magnetic layer and non-magnetic layer can be used. The binder contained in the backcoat layer is preferably 5 to 100 parts by weight, more preferably 10 to 80 parts by weight, based on 100 parts by weight of the nonmagnetic powder contained in the backcoat layer.

As the carbon black used in the back coat layer, it is preferable to use two types of carbon black having different average particle sizes. Specifically, it is preferable to use fine-particle carbon black having an average particle size of 10 to 20 nm and coarse-particle carbon black having an average particle size of 230 to 300 nm.

The particulate carbon black can lower the surface electric resistance of the back coat layer, increase the holding power of the lubricant, and reduce the coefficient of friction. Further, the particulate carbon black can lower the light transmittance of the magnetic recording medium. In a recording / reproducing apparatus for a magnetic recording medium, for example, in the case of a magnetic tape, there is an apparatus that uses the light transmittance of the magnetic tape as a signal for a recording / reproducing operation. For this reason, it is effective to add particulate carbon black to the back coat layer in order to control the light transmittance of the magnetic tape. On the other hand, the coarse-grained carbon black has a function as a solid lubricant, and forms small projections on the surface of the back coat layer to reduce the contact area and reduce the friction coefficient.

A specific product name of the particulate carbon black used for the back coat layer is RAVEN20.
00B (18 nm), RAVEN 1500B (17n
m) (above, manufactured by Columbia Carbon Co., Ltd.), BP800
(17 nm) (Cabot), PRINTEX90
(14 nm), PRINTEX95 (15 nm), PR
INTEX85 (16 nm), PRINTEX75 (1
7nm) (above, manufactured by Degussa), # 3950 (16n
m) (manufactured by Mitsubishi Chemical Industries, Ltd.). Also,
Specific product names of coarse-grained carbon black include:
Thermal black (270 nm) (manufactured by Kahn Carb), RAVEN MTP (275 nm) (manufactured by Columbia Carbon) and the like.

As described above, when carbon blacks having different average particle sizes are used for the back coat layer, the weight ratio between the fine carbon black and the coarse carbon black is as follows. The ratio is preferably from 98: 2 to 75:25, and more preferably from 95: 5 to 85:15.
Further, the content of carbon black in the back coat layer is preferably 30 to 80 parts by weight, more preferably 45 to 65 parts by weight, based on 100 parts by weight of the binder.

Examples of the inorganic powder used for the back coat layer include calcium carbonate and inorganic powder having a Mohs hardness of 5 to 9.

The inorganic powder having a Mohs hardness of 5 to 9 includes α-iron oxide, α-alumina and chromium oxide (Cr ₂
O ₃ ) and the like. These inorganic powders having a Mohs hardness of 5 to 9 may be used alone or in combination. In particular, α-iron oxide or α-alumina,
It is preferably used as an inorganic powder having a Mohs hardness of 5 to 9.

These inorganic powders preferably have an average particle size of 80 to 250 nm, especially 100 to 250 nm.
Preferably it is 210 nm. Further, the content of the inorganic powder having a Mohs hardness of 5 to 9 is as follows.
3 to 30 parts by weight, preferably 3 to 2 parts by weight, per 0 parts by weight.
More preferably, it is 0.

By adding an inorganic powder having a Mohs' hardness of 5 to 9 to the back coat layer, the magnetic recording medium has improved running durability. Moreover, Mohs' hardness is 5-9.
By adding the inorganic powder of the above to the back coat layer,
The back coat layer has an appropriate polishing force. Thereby, for example, in the case of a tape-shaped magnetic recording medium, adhesion to a tape guide pole or the like in the magnetic recording medium recording / reproducing apparatus is reduced.

In the back coat layer, the same lubricant as that used in the above-described magnetic layer and non-magnetic layer is used.
It can be appropriately selected and used. The amount of the lubricant contained in the back coat layer is preferably 1 to 5 parts by weight based on 100 parts by weight of the binder contained in the back coat layer.

The back coat layer has a Mohs hardness of 5
-9, two types of carbon black having different average particle sizes, and calcium carbonate in combination. Thereby, the back coat layer becomes M
Deterioration is small with repeated sliding by the R reproducing head, the durability is excellent, and the friction coefficient is stable.

Further, various additives such as a dispersant, a plasticizer, an antistatic agent other than carbon black, an antifungal agent and the like are added to the above-mentioned magnetic layer, nonmagnetic layer and back coat layer as required. It is possible.

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)
A metal soap comprising the alkali metal or alkaline earth metal of the fatty acid,
Fluorine-containing compounds of the above fatty acid esters, amides of the above fatty acids, polyalkylene oxide alkyl phosphates, lecithin, trialkylpolyolefinoxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms)
And olefins such as ethylene and propylene), sulfates and copper phthalocyanine. These may be used alone or in combination. These dispersants are preferably added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin in any of the magnetic layer, the non-magnetic layer and the back coat layer.

In preparing a magnetic paint and a non-magnetic paint, a kneading step of dispersing a magnetic powder and a non-magnetic powder having a relatively high solid content at a high shear in a mixture containing a binder;
And dispersing the magnetic powder and the non-magnetic powder having a relatively low solid content in the mixture containing the binder by the impact force of beads or the like. If necessary, a mixing step may be provided before or after these steps. Further, each of these steps may be divided into two or more stages.

Components constituting the magnetic paint and the non-magnetic paint,
For example, all components such as a magnetic powder, a non-magnetic powder, a binder, carbon black, an abrasive, an antistatic agent, and a lubricant may be added at any step, or may be added at the beginning or during the step. . Further, individual components may be added in two or more steps. For example, polyurethane may be added separately in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

As the kneader used in the kneading step and the disperser used in the dispersing step, conventionally known kneaders and dispersers can be used.

The kneading machine includes an open kneader, a continuous kneader, a pressure kneader, and a continuous twin-screw kneader (extruder).
And the like, which has a strong kneading power. When a kneader is used, the magnetic powder or the non-magnetic powder and the binder are all or a part thereof (however, preferably 30% or more of the total binder) and 15 to 500 parts by weight with respect to 100 parts by weight of the magnetic powder.
It is kneaded in the range of parts by weight. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-79274.

Examples of the dispersing machine include a vertical sand mill, a horizontal sand mill, a spike mill, a pearl mill, a double cylinder pearl mill and the like. In the disperser, various pigments contained in the magnetic paint and the non-magnetic paint are dispersed by the glass beads. As this glass bead,
It is preferable to use zirconia beads, titania beads, steel beads, and the like.

The magnetic paint and the non-magnetic paint thus prepared are applied on a non-magnetic support. As a method for forming the non-magnetic layer and the magnetic layer on the non-magnetic support, a method of applying and drying one layer at a time (so-called wet-on-dry coating method) may be applied, A method of applying a magnetic paint on the non-magnetic layer in a state (a so-called wet-on-wet coating method) may be applied. However, in consideration of the uniformity of the coating film, the adhesiveness of the interface, and the productivity, it is preferable to apply the wet-on-wet coating method. At this time, for example, a die coater is used as the coating device.

Thereafter, the coating film is dried, and if necessary, a surface smoothing treatment such as a calendar treatment is performed. Here, in the calendar processing, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide, or a metal roll is used as the calendar processing roll. The calendering temperature is preferably 50 ° C. or more,
It is more preferable that the temperature is 0 ° C. or higher. The linear pressure is 200
kg / cm or more, preferably 300 kg / c
m is more preferable.

After the above-described steps and processing, a magnetic recording medium is manufactured by slitting or punching into a desired shape. For example, the magnetic recording medium is slit into a magnetic tape.

The magnetic recording medium manufactured in this manner is
It is optimized according to the characteristics of the R reproducing head. Specifically, the product Mr · of the residual magnetization amount Mr of the magnetic layer and the film thickness δ
The value of δ is 0.8 to 6.5 memu / cm ² . As a result, the magnetic recording medium can obtain a high output without saturating the MR reproducing head and without distortion.

Further, at least one main surface side of the non-magnetic support on which the magnetic layer is formed is provided with 60/100 cm ² or less coarse projections having a height of 0.273 μm or more. It has a surface that does not easily generate frictional heat during the sliding movement between the MR reproducing head and the magnetic layer. Accordingly, the magnetic recording medium has an improved error rate because noise due to frictional heat is reduced, and exhibits stable output characteristics.

Further, since the non-magnetic support has a Young's modulus in the width direction of 1000 kg / mm ² or more, the magnetic layer and the MR reproducing head can be used when the recording signal of the magnetic recording medium is reproduced by the MR reproducing head. Will be optimal. Therefore, the magnetic recording medium has an improved error rate.

This magnetic recording medium has excellent electromagnetic conversion characteristics without distortion and can be reliably reproduced by the MR reproducing head. Therefore, this magnetic recording medium achieves high-density recording corresponding to a helical scan magnetic recording system using an MR reproducing head, has reduced noise, and has realized high resolution.

By the way, the above-mentioned magnetic recording medium is MR
It is suitable as a magnetic tape for a helical scan magnetic recording system using a reproducing head. In this case, as the MR reproducing head, a shield type MR reproducing head in which an MR element is interposed between shields is used, and this is mounted on a rotating drum to constitute a magnetic recording / reproducing apparatus.

By combining the helical scan magnetic recording system using the MR reproducing head and the magnetic recording medium of the present invention, an unprecedented high-density recording system can be constructed.

FIGS. 1 and 2 show an example of the configuration of a rotary drum device mounted on this magnetic recording / reproducing apparatus. FIG.
FIG. 2 is a perspective view schematically showing the rotary drum device 1, and FIG. 2 is a plan view schematically showing a magnetic tape feed mechanism 10 including the rotary drum device 1.

As shown in FIG. 1, the rotary drum device 1
A cylindrical fixed drum 2, a cylindrical rotary drum 3, a motor 4 for rotating the rotary drum 3, and a pair of inductive magnetic heads 5a, 5 mounted on the rotary drum 3;
b, and a pair of MR reproducing heads 6 a and 6 b mounted on the rotating drum 3.

The fixed drum 2 is a drum that is held without rotating. On the side of this fixed drum 2,
A lead guide portion 8 is formed along the running direction of the magnetic tape 7. As will be described later, the magnetic tape 7 runs along the read guide portion 8 during recording and reproduction. The rotating drum 3 is arranged so that the center axis of the fixed drum 2 coincides with that of the fixed drum 2.

The rotary drum 3 is a drum that is driven to rotate at a predetermined rotation speed by the motor 4 during recording and reproduction on the magnetic tape 7. The rotating drum 3 is formed in a cylindrical shape having substantially the same diameter as the fixed drum 2.
And the central axes are aligned. A pair of inductive magnetic heads 5a, 5b and a pair of MRs are provided on the side of the rotary drum 3 facing the fixed drum 2.
The reproducing heads 6a and 6b are mounted.

Inductive magnetic heads 5a, 5b
Is a recording magnetic head in which a pair of magnetic cores are joined via a magnetic gap and a coil is wound around the magnetic core, and is used when recording a signal on the magnetic tape 7. These inductive magnetic heads 5a and 5b are mounted on the rotating drum 3 so that the angle formed between them with respect to the center of the rotating drum 3 is 180 °, and their magnetic gaps protrude from the outer periphery of the rotating drum 3. Have been. The inductive magnetic heads 5a and 5b are set so that the azimuth angles are opposite to each other so that azimuth recording is performed on the magnetic tape 7.

On the other hand, the MR reproducing heads 6a and 6b are reproducing magnetic heads provided with MR elements as magnetic sensing elements for detecting signals from the magnetic tape 7, and are used when reproducing signals from the magnetic tape 7. You. These MR reproducing heads 6a and 6b are mounted on the rotating drum 3 so that the angle formed between them with respect to the center of the rotating drum 3 is 180 °, and the magnetic gap portion protrudes from the outer periphery of the rotating drum. Incidentally, these MR reproducing heads 6a, 6
b is set such that the azimuth angles are opposite to each other so that signals recorded in azimuth on the magnetic tape 7 can be reproduced.

The magnetic recording / reproducing apparatus records a signal on the magnetic tape 7 and reproduces a signal from the magnetic tape 7 by sliding the magnetic tape 7 on the rotating drum device 1.

That is, at the time of recording and reproduction, the magnetic tape 7
As shown in FIG.
After passing through 2 and 13, the recording medium is sent to be wound around the rotary drum device 1, and recording and reproduction are performed by the rotary drum device 1. The magnetic tape 7 recorded and reproduced by the rotary drum device 1 is guided by guide rollers 14 and 15, a capstan 16,
After passing through a guide roller 17, it is sent to a take-up roll 18. That is, the magnetic tape 7 is fed at a predetermined tension and speed by the capstan 16 rotated and driven by the capstan motor 19, and is wound on the winding roll 18 via the guide roller 17.

At this time, the rotary drum 3 is driven to rotate by the motor 4 as shown by an arrow A in FIG. On the other hand, the magnetic tape 7 is attached to the lead guide 8 of the fixed drum 2.
Along the fixed drum 2 and the rotating drum 3 so as to slide obliquely. That is, the magnetic tape 7
1 is fed along the tape running direction from the tape inlet side along the lead guide portion 8 so as to slidably contact the fixed drum 2 and the rotating drum 3 as shown by the arrow B in FIG. The tape is sent to the tape exit side as shown in FIG.

Next, the internal structure of the rotary drum device 1 will be described with reference to FIG.

As shown in FIG. 3, a rotary shaft 21 is inserted through the center of the fixed drum 2 and the rotary drum 3. Note that the fixed drum 2, the rotating drum 3, and the rotating shaft 21 are made of a conductive material, are electrically conductive, and the fixed drum 2 is grounded.

[0102] Two bearings 22 and 23 are provided inside the sleeve of the fixed drum 2, whereby the rotating shaft 21 is rotatably supported with respect to the fixed drum 2. That is, the rotating shaft 21 is
By 23, it is rotatably supported by the fixed drum 2. On the other hand, the rotary drum 3 has a flange 24 formed on the inner peripheral portion thereof.
1 is fixed to the upper end. Thereby, the rotating drum 3 is configured to rotate with the rotation of the rotating shaft 21.

In order to transmit signals between the fixed drum 2 and the rotating drum 3, a rotary transformer 2, which is a non-contact type signal transmission device, is provided inside the rotating drum device 1.
5 are arranged. The rotary transformer 25 has a stator core 26 attached to the fixed drum 2 and a rotor core 27 attached to the rotating drum 3.

The stator core 26 and the rotor core 27
A magnetic material such as ferrite is formed in an annular shape around the rotation shaft 21. Also, the stator core 26
Includes a pair of signal transmission rings 26a and 26b corresponding to a pair of inductive magnetic heads 5a and 5b, a signal transmission ring 26c corresponding to a pair of MR reproduction heads 6a and 6b, and a pair of MR reproduction heads 6a. Transmission ring 26d for supplying the electric power necessary for driving the .6b
Are concentrically arranged. Similarly, the rotor core 27 has a pair of inductive magnetic heads 5a, 5a.
b, a pair of signal transmission rings 27a and 27b corresponding to b
A signal transmission ring 27c corresponding to the pair of MR reproducing heads 6a and 6b, and a pair of MR reproducing heads 6a and 6b.
And a power transmission ring 27d for supplying electric power required for driving the power supply are arranged concentrically.

The rings 26a, 26b, 26c,
26d, 27a, 27b, 27c, and 27d are rotating shafts 2
1 and each of the rings 26 a, 26 b, 26 c, 2 of the stator core 26.
6d and each ring 27a, 27b, 2 of the rotor core 27.
7c and 27d are arranged to face each other. The rotary transformer 25 includes the rings 26a, 26b, 26c, 26d of the stator core 26,
Each ring 27a, 27b, 27c, 2 of the rotor core 27
Signals and electric power are transmitted in a non-contact manner with 7d.

A motor 4 for driving the rotary drum 3 to rotate is attached to the rotary drum device 1. This motor 4 has a rotor 28 as a rotating part and a stator 29 as a fixed part. The rotor 28 is attached to the lower end of the rotating shaft 21 and includes a driving magnet 30. On the other hand, the stator 29 is attached to the lower end of the fixed drum 2 and
1 is provided. Then, by supplying a current to the drive coil 31, the rotor 28 is rotationally driven. Accordingly, the rotating shaft 21 attached to the rotor 28 rotates, and accordingly, the rotating drum 3 fixed to the rotating shaft 21 is driven to rotate.

Next, recording and reproduction by the above-described rotary drum device 1 will be described with reference to FIG. 4 which shows a schematic circuit configuration of the rotary drum device 1 and its peripheral circuits.

When recording a signal on the magnetic tape 7 using the rotary drum device 1, first, a current is supplied to the drive coil 31 of the motor 4, whereby the rotary drum 3 is driven to rotate. Then, while the rotary drum 3 is rotating, a recording signal from the external circuit 40 is supplied to the recording amplifier 41 as shown in FIG.

The recording amplifier 41 amplifies a recording signal from the external circuit 40 and, when the signal is recorded by one of the inductive magnetic heads 5a, the stator core 2 corresponding to the inductive magnetic head 5a.
6 to supply the recording signal to the signal transmission ring 26a, and to the signal transmission ring 26b of the stator core 26 corresponding to the inductive magnetic head 5b at the timing of recording the signal by the other inductive magnetic head 5b. Supply the recording signal.

Here, since the pair of inductive magnetic heads 5a and 5b are arranged so that the angle formed between them with respect to the center of the rotating drum 3 is 180 °, as described above, these inductive magnetic heads 5a and 5b are formed. Magnetic head 5
a and 5b are recorded alternately with a phase difference of 180 °. That is, the recording amplifier 41 alternates the timing of supplying a recording signal to one inductive magnetic head 5a and the timing of supplying a recording signal to the other inductive magnetic head 5b with a phase difference of 180 °. Switch to.

The recording signal supplied to the signal transmission ring 26a of the stator core 26 corresponding to the one inductive magnetic head 5a is transmitted to the signal transmission ring 27a of the rotor core 27 in a non-contact manner. And
The recording signal transmitted to the signal transmission ring 27a of the rotor core 27 is supplied to the inductive magnetic head 5a, and a signal is recorded on the magnetic tape 7 by the inductive magnetic head 5a.

Similarly, the recording signal supplied to the signal transmission ring 26b of the stator core 26 corresponding to the other inductive magnetic head 5b is transmitted to the signal transmission ring 27b of the rotor core 27 in a non-contact manner. And
The recording signal transmitted to the signal transmission ring 27b of the rotor core 27 is supplied to the inductive magnetic head 5b, and a signal is recorded on the magnetic tape 7 by the inductive magnetic head 5b.

When reproducing a signal from the magnetic tape 7 using the rotary drum device 1, first, a current is supplied to the drive coil 31 of the motor 4, whereby the rotary drum 3 is driven to rotate. You. Then, while the rotating drum 3 is rotating, as shown in FIG.
2 to the power drive 43.

The high-frequency current from the oscillator 42 is converted into a predetermined alternating current by the power drive 43 and then supplied to the power transmission ring 26d of the stator core 26. Then, the alternating current supplied to the power transmission ring 26d of the stator core 26 is transmitted to the power transmission ring 27d of the rotor core 27 in a non-contact manner. Then, the AC current transmitted to the power transmission ring 27d of the rotor core 27 is rectified by the rectifier 44 to become a DC current, which is supplied to the regulator 45, and the DC current is set to a predetermined voltage by the regulator 45.

The current set to a predetermined voltage by the regulator 45 is applied to the pair of MR reproducing heads 6a,
6b is supplied as a sense current. Note that a pair of MRs
The reproducing heads 6a, 6b include the MR reproducing heads 6a,
A reproduction amplifier 46 for detecting a signal from 6b is connected, and a current from the regulator 45 is also supplied to the reproduction amplifier 46.

Here, each of the MR reproducing heads 6a and 6b has an MR element whose resistance value changes according to the magnitude of an external magnetic field. In the MR reproducing heads 6a and 6b, the resistance value of the MR element changes due to the signal magnetic field from the magnetic tape 7, whereby a voltage change appears in the sense current.

The reproducing amplifier 46 detects this voltage change and outputs a signal corresponding to the voltage change as a reproduced signal. It is to be noted that the reproducing amplifier 46 operates at the time of reproducing a signal by the one MR reproducing head 6a.
The reproduction signal detected by the MR reproduction head 6a is output, and the reproduction signal detected by the MR reproduction head 6b is output at the timing of reproducing the signal by the other MR reproduction head 6b.

Here, a pair of MR reproducing heads 6a and 6b
Are arranged so that the angle between them with respect to the center of the rotating drum 3 is 180 °, as described above.
These MR reproducing heads 6a and 6b perform reproduction alternately with a phase difference of 180 °. That is, the reproducing amplifier 46 outputs the reproduction signal from one of the MR reproducing heads 6a to the other MR reproducing head 6a.
The timing at which the reproduced signal from b is output is 180 °
Alternately with a phase difference of

The reproduction signal from the reproduction amplifier 46 is supplied to the signal transmission ring 27c of the rotor core 27, and the reproduction signal is transmitted to the signal transmission ring 26c of the stator core 26 without contact. Stator core 26
The reproduction signal transmitted to the signal transmission ring 26c of FIG.
Supplied to Then, the reproduction signal is subjected to predetermined correction processing by the correction circuit 48, and then output to the external circuit 40.

In the case of the circuit configuration shown in FIG. 4, a pair of inductive magnetic heads 5a, 5b,
The pair of MR reproducing heads 6a and 6b, the rectifier 44, the regulator 45, and the reproducing amplifier 46 are mounted on the rotating drum 3 and rotate together with the rotating drum 3. On the other hand, the recording amplifier 41, the oscillator 42, the power drive 43, the reproducing amplifier 47, and the correction circuit 48 may be disposed on a fixed portion of the rotary drum device 1, or may be provided separately from the rotary drum device 1. Circuit.

Next, the M mounted on the rotary drum 3
The R reproducing heads 6a and 6b will be described in detail with reference to FIG. The MR reproducing head 6a and the MR reproducing head 6b have the same configuration except that the azimuth angles are set to be opposite to each other. Therefore, in the following description, these MR reproducing heads 6a and 6b are collectively referred to as the MR reproducing head 6.

The MR read head 6 is a read-only magnetic head mounted on the rotating drum 3 and detecting a signal from the magnetic tape 7 by a helical scan method using a giant magnetoresistance effect. In general, an MR reproducing head has higher sensitivity and a higher reproducing output than an inductive magnetic head that performs recording and reproduction using electromagnetic induction, and is therefore suitable for high-density recording. Therefore, by using the MR reproducing head 6 as the reproducing magnetic head, higher density recording can be achieved.

As shown in FIG. 5, the MR reproducing head 6 has a pair of magnetic shields 51 and 52 made of a soft magnetic material such as Ni—Zn polycrystal ferrite and a pair of magnetic shields 51 with an insulator 53 interposed therebetween. And a substantially rectangular MR element portion 54 sandwiched between the magnetic shields 51 and 52. In addition, a pair of terminals are led out from both ends of the MR element unit 54, and a sense current can be supplied to the MR element unit 54 through these terminals.

The MR element section 54 is formed by stacking an MR element having a giant magnetoresistance effect, a SAL (Soft Adjacent Layer) film, and an insulator film disposed between the MR element and the SAL film. The MR element is made of a soft magnetic material such as Ni-Fe or the like whose resistance changes according to the magnitude of an external magnetic field due to the anisotropic giant magnetoresistance effect (AMR). S
The AL film is for applying a bias magnetic field to the MR element by a so-called SAL bias method, and is made of a magnetic material having a low coercive force and a high magnetic permeability such as permalloy. The insulator film insulates between the MR element and the SAL film,
This is for preventing electric shunt loss, and is made of an insulating material such as Ta.

The MR element portion 54 is formed in a substantially rectangular shape, and a pair of magnetic shields 51 and 52 is used to expose the insulator 5 so that one side surface is exposed to the magnetic tape sliding surface 55.
3. More specifically, the MR element 54 has a pair of magnetic shields such that the short axis direction is substantially perpendicular to the magnetic tape sliding surface 55 and the long axis direction is substantially perpendicular to the magnetic tape sliding direction. 51 and 52 sandwich the insulator 53 therebetween.

The magnetic tape sliding surface 55 of the MR reproducing head 6 is cylindrically polished along the sliding direction of the magnetic tape 7 so that one side of the MR element 54 is exposed on the magnetic tape sliding surface 55. And is cylindrically polished along a direction perpendicular to the sliding direction of the magnetic tape 7. Thus, in the MR reproducing head 6, the MR element portion 54 or a portion in the vicinity thereof protrudes most. In this way, by making the MR element portion 54 or the vicinity thereof most protrude, the MR element portion 54 is formed.
Of the magnetic tape 7 can be improved.

When reproducing a signal from the magnetic tape 7 using the MR reproducing head 6 as described above, the magnetic tape 7 is slid on the MR element 54 as shown in FIG. The arrows in FIG. 6 schematically show how the magnetic tape 7 is magnetized.

Then, with the magnetic tape 7 slid in the MR element section 54, the MR element section 5 is connected via the terminals 54a and 54b connected to both ends of the MR element section 54.
4 is supplied with a sense current, and a voltage change of the sense current is detected. Specifically, a predetermined voltage Vc is applied from a terminal 54a connected to one end of the MR element 54, and a terminal 54b connected to the other end of the MR element 54 is
It is connected to the rotating drum 3. Here, the rotating drum 3 is electrically connected to the fixed drum 2 via the rotating shaft 21, and the fixed drum 2 is grounded. Therefore, one terminal 54b connected to the MR element 54 is
The rotating drum 3, the rotating shaft 21 and the fixed drum 2 are grounded.

Then, when a sense current is supplied to the MR element section 54 while the magnetic tape 7 is slid, the M formed on the MR element section 54 in response to the magnetic field from the magnetic tape 7.
The resistance value of the R element changes, and as a result, a voltage change occurs in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic tape 7 is detected, and the signal recorded on the magnetic tape 7 is reproduced.

In the MR reproducing head 6 used,
The MR element formed in the MR element section 54 may be any element exhibiting a giant magnetoresistance effect. For example, a so-called giant magnetoresistance effect in which a larger giant magnetoresistance effect can be obtained by laminating a plurality of thin films. Magnetoresistance effect element (GM
R element) can also be used. The method of applying a bias magnetic field to the MR element may not be the SAL bias method, for example, a permanent magnet bias method, a shunt current bias method, a self-bias method, an exchange bias method, a barber pole method, a split element method, Various methods such as a servo bias method can be applied. The giant magnetoresistance effect and various bias methods are described in detail in, for example, "Magnetoresistance Head-Basic and Application Translation by Kazuhiko Hayashi" issued by Maruzen Co., Ltd.

[0131]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described in detail based on experimental results.

Example 1 In Example 1, first, a needle-shaped metal magnetic powder having the following magnetic properties was prepared. However, the magnetic characteristics are values measured using a sample vibration magnetometer (manufactured by Towa Kogyo Co., Ltd.).

Magnetic properties Coercive force (Hc) = 2410 [Oe] Saturated magnetization (σs) = 150 [emu / g] Next, each composition is weighed, kneaded and dispersed according to the following composition. To prepare a magnetic paint and a non-magnetic paint.

<Magnetic paint composition> Metal magnetic powder 100 parts by weight Binder: polyvinyl chloride resin (MR-110, manufactured by Zeon Corporation) 20 parts by weight Abrasive: Al ₂ O ₃ 3 parts by weight Antistatic agent: carbon powder (0.025 μm) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

<Nonmagnetic paint composition> Nonmagnetic powder: iron oxide powder 100 parts by weight Binder: polyvinyl chloride resin (MR-110, manufactured by Zeon Corporation) 15 parts by weight Polyester polyurethane resin (manufactured by Toyobo) 5 parts by weight Lubricant: stearic acid 1 part by weight heptyl stearate 1 part by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Next, a polyethylene terephthalate film having a thickness of 6 μm was prepared as a nonmagnetic support.
Here, the one main surface of the polyethylene terephthalate film had 60 large protrusions having a height of 0.273 μm or more / 100 cm ² .

Next, a magnetic paint and a non-magnetic paint were applied on one main surface side of the polyethylene terephthalate film in the order of non-magnetic paint and magnetic paint. Next, after subjecting to an orientation treatment and drying the coating film, it was cut into a width of 8 mm to prepare a sample tape.

Here, the thickness of the magnetic layer was 0.1 μm. Thereby, the value of the product Mr · δ of the magnetic layer with the residual magnetization amount Mr and the film thickness δ was 3.0 memu / cm ² .

Examples 2 to 6 and Comparative Examples 1 to 9 In Examples 2 to 6 and Comparative Examples 1 to 9, the product of the residual magnetization amount Mr of the magnetic layer and the film pressure δ was calculated. The value of Mr · δ is
The results are shown in Table 1. Further, the same procedure as in Example 1 was carried out except that the number of coarse projections having a height of 0.273 μm or more on one main surface side of the non-magnetic support was polyethylene terephthalate as shown in Table 1. Thus, a magnetic recording medium was manufactured.

The electromagnetic conversion characteristics of the sample tapes of Examples 1 to 6 and Comparative Examples 1 to 9 thus produced were evaluated. Specifically, 8mmVT
After recording an information signal on a sample tape at a recording wavelength of 0.5 μm using a modified version of R, the shielded MR
The reproduction output (recording wavelength: 0.5 μm), noise level (value at a frequency lower by 1 MHz from the carrier signal), and error rate (symbol error rate) were measured by the reproduction head.

The element of the MR reproducing head used for reproduction is F
It is an eNi-AMR (anisotropic magnetoresistive element), the saturation magnetization is 800 emu / cc, the film thickness is 40 nm, the shield material is NiZn, and the distance between shields is 0.17 μm. The track width is 18 μm and the azimuth angle is 25 °
It is.

Table 1 shows the results.

[0143]

[Table 1]

As is clear from Table 1, Example 1
6, the residual magnetization amount Mr of the magnetic layer
The value of the product Mr · δ of the thickness and the film thickness δ is 0.8 to 6.5 memu.
/ Cm ² and the height of the magnetic layer is 0.273 μm.
The protrusions are formed on one main surface side of a nonmagnetic support having coarse protrusions of m or more and 60 protrusions / 100 cm ² or less. As a result, it was found that high output was obtained, noise was reduced, and the error rate was improved.

On the other hand, as shown in Comparative Examples 4, 5, and 6, when the value of Mr · δ was less than 0.8 memu / cm ² , it was found that a sufficient reproduction output could not be obtained. On the other hand, as shown in Comparative Examples 7, 8, and 9, the value of Mr · δ is 6.
When it exceeds 5 memu / cm ² , it was found that the MR element was saturated, the reproduced waveform was distorted, and the error rate was deteriorated.

Further, as shown in Comparative Examples 1, 2, and 3, when the number of coarse protrusions on the surface of the nonmagnetic support exceeds 60/100 cm ² , the error rate was deteriorated. .

Embodiments 7 to 13 In Embodiments 7 to 13, the value of Mr · δ is set to 3.0 me.
mu / cm ² , and as shown in Table 2, a magnetic tape was prepared in the same manner as in Example 1 except that a nonmagnetic support having a different number of coarse projections, a Young's modulus in the width direction and a different material was used. Produced. However, Young's modulus is 25 ° C, 65% RH
Below, values measured using a Tensilon type tensile tester.

In order to evaluate the electromagnetic conversion characteristics of these Examples 7 to 13, in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 9, the reproduction output (recording wavelength 0 .5 μm), noise level (1 MHZ from carrier signal)
The value at the frequency of z decrease) and the error rate (symbol error rate) were measured. Table 2 shows the results.

[0149]

[Table 2]

As is clear from Table 2, when a non-magnetic support having a Young's modulus in the width direction of 1000 kg / mm ² or more is used, the magnetic tape exhibits higher reproduction output and further reduces noise. It was found that the error rate was significantly improved.

[0151]

As is clear from the above description, in the magnetic recording medium according to the present invention, the value of the product Mr · δ of the residual magnetization amount Mr of the magnetic layer and the film thickness δ is 0.8 to 6. 5 memu /
cm ² and is optimized according to the characteristics of the MR reproducing head. Thus, when the recording signal is reproduced using the MR reproducing head,
The output of the R element is prevented, and high output and low noise are realized.

The magnetic layer is formed on one main surface side of the non-magnetic support having a height of not less than 0.273 μm and coarse protrusions of not more than 60/100 cm ^2. During sliding movement with the layer, frictional heat is less likely to be generated. Accordingly, the magnetic recording medium has a reduced error due to frictional heat, thereby improving the error rate and exhibiting stable recording and reproducing characteristics.

That is, this magnetic recording medium is, for example, MR
By using it for a helical scan magnetic recording system using a reproducing head, it is possible to construct an unprecedented high-density recording system.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration example of a rotary drum device mounted on a magnetic recording / reproducing device of a helical scan magnetic recording system.

FIG. 2 is a plan view schematically showing a configuration example of a magnetic tape feeding mechanism including the rotary drum device.

FIG. 3 is a sectional view showing an internal structure of the rotary drum device.

FIG. 4 is a diagram schematically showing a circuit configuration of the rotary drum device and its peripheral circuits.

FIG. 5 is a perspective view showing an example of an MR reproducing head mounted on the rotary drum, with a part cut away.

FIG. 6 is a diagram schematically showing how a signal from a magnetic tape is reproduced using an MR reproducing head.

FIG. 7 is a graph showing a magnetoresistive response curve showing a change in voltage between terminals of the MR element with respect to an external magnetic field.

[Explanation of symbols]

1 rotating drum device, 2 fixed drum, 3 rotating drum, 4 motor, 5a, 5b inductive magnetic head, 6 (6a, 6b) MR reproducing head, 7
Magnetic tape

Claims (3)

[Claims] 1. A magnetic recording medium having a nonmagnetic support and a magnetic layer coated with a magnetic paint, wherein the product Mr · δ of the residual magnetization amount Mr and the film thickness δ of the magnetic layer is 0. 0.8 to 6.5 memu / cm ² , and the magnetic layer is formed on one main surface side of a non-magnetic support member having 60/100 cm ² or less coarse projections having a height of 0.273 μm or more. A magnetic recording medium characterized in that: 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is used in a helical scan magnetic recording system using a magnetoresistive read head. 3. The magnetic recording medium according to claim 1, wherein the non-magnetic support has a Young's modulus in a width direction of 1000 kg / mm ² or more.