JP2002056517A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance running durability of a magnetic recording medium. SOLUTION: In a so called thin type magnetic recording medium 10 having a magnetic layer 3 formed on a non-magnetic substrate 1 by applying magnetic paint and having 0.01-0.3 [μm] thickness, the electric resistance value of the magnetic layer 3 is numerically specified to be 1.0×105-1.0×109 [Ω/sq].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art In recent years, in magnetic recording media used in audio devices, video devices, computer devices, etc., the amount of information has increased due to digital recording and the like, and higher density recording and shorter wavelength recording have been promoted. There is an increasing demand for improved characteristics of recording media.

[0003] Under such circumstances, in a magnetic recording medium, various raw materials for forming a magnetic layer have been studied for the purpose of high-density recording and high-speed recording.
Studies have been made on fine-particle magnetic powders having high dispersibility and binders having excellent dispersibility.

In addition, the frequency of recording and reproduction has been shortened, and accordingly, there has been an increasing demand for thinning the magnetic layer to, for example, 0.3 μm or less. Furthermore, magnetic recording devices that require high-density recording must simultaneously increase the speed of recording and reproduction, and therefore, there is a demand for improvements in the durability and reliability of magnetic recording media.

[0005] In response to the above-mentioned requirements, in the magnetic recording medium 100 having the conventional structure shown in FIG. 8, a non-magnetic support 101 is provided on a non-magnetic support 101 with a coating material containing non-magnetic particles and a binder resin as main components. The base layer 102 is formed by adding a function for improving the durability to the base layer 102,
Various other functions are provided to improve the running performance and reliability (Japanese Patent Application Laid-Open No. 8-329449).

[0006] In particular, in order to improve the running properties of the magnetic recording medium, it is necessary to reduce the electric resistance of the magnetic recording medium.
A small amount of aggregated carbon is applied to the magnetic layer 103 and the underlayer 1.
02 was added.

[0007]

However, in the magnetic recording medium 100 having the structure shown in FIG. 8, since the magnetic layer 103 and the underlayer 102 are formed in layers,
It is necessary to consider that chemical or physical interaction may occur between the components in these layers, and the production conditions and coating conditions are restricted, which causes the process to be complicated. Was.

Further, as described above, when carbon is contained in the magnetic layer 103 in order to reduce electric resistance, the specific gravity of carbon is relatively small, so that carbon tends to collect near the surface layer of the magnetic layer 103. The magnetic recording medium 10 may degrade the static magnetic characteristics and the electromagnetic conversion characteristics, increase the viscosity of the magnetic paint, or adversely affect the surface roughness of the magnetic recording medium. In the case of forming a thin layer of 3 μm or less, such inconvenience became remarkable.

Further, if carbon is contained in the underlayer 102 in order to reduce the electric resistance, the stability and physical properties of the underlayer-forming paint are affected, so that manufacturing conditions and application conditions are restricted. Cause the process to be complicated,
In the same manner as described above, problems such as adversely affecting the surface roughness of the magnetic recording medium occurred.

In view of the above-mentioned circumstances, the present inventor has considered that the running property and durability of a thin-layer type magnetic recording medium having a magnetic layer thickness of 0.01 to 0.3 [μm] are considered. In order to improve the properties, the physical properties of the magnetic recording medium and the additives were examined.

[0011]

The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer formed by applying a magnetic paint on one main surface of a non-magnetic support. Is formed directly on a nonmagnetic support or via a thin material layer having a thickness of about 0.5 [μm] or less. The thickness of this magnetic layer is 0.01 to
0.3 assumed to be thin magnetic recording medium is a [μm], the electrical resistance of the magnetic layer, and to define particular numerically, which, 1.0 × 10 ⁵ ~1.0 × 10
⁹ [Ω / sq].

According to the present invention, 0.0
In a magnetic recording medium on which a thin magnetic layer having a thickness of 1 to 0.3 [μm] is formed, durability under various environments is improved, and stable running properties are secured.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer formed by applying a magnetic paint on one main surface of a non-magnetic support. Directly on a non-magnetic support, or 0.5 [μ
m] formed with a thin material layer of the following order. The thickness of this magnetic layer is 0.01 to 0.3 [μ
m], a thin magnetic recording medium, an antistatic agent is added to the magnetic layer, the surface of the magnetic component and other additives is coated with a conductive material, and a quaternary ammonium is used as a binder. By including a salt, the electric resistance of the magnetic layer is controlled, and the electric resistance of the magnetic layer is particularly specified numerically. This is defined as 1.0 × 10 ^{5 to} 1.0 × 10 ⁹ [Ω /
sq].

Hereinafter, the magnetic recording medium 10 of the present invention will be described with reference to FIG. 1 showing an example of a schematic structure thereof, but the magnetic recording medium of the present invention is not limited to the following examples.

The magnetic recording medium 10 shown in FIG. 1 has a thickness of 0.01 to 0.2 mm on the nonmagnetic support 1 without an intervening underlayer.
This is a so-called thin-layer type magnetic recording medium having a configuration in which a magnetic layer 2 having a thickness of 3 [μm] is formed. The backcoat layer 2 is formed on the main surface of the nonmagnetic support 1 opposite to the surface on which the magnetic layer 2 is formed.

The material constituting the non-magnetic support 1 is as follows.
For example, a polyethylene terephthalate film can be applied, but various known materials can be applied to the magnetic recording medium 10 of the present invention. That is, polyesters such as polyethylene naphthalate, polyethylene,
Polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamide imide, other plastics, paper, aluminum, The same can be applied to metals such as copper, aluminum alloys, light alloys such as titanium alloys, ceramics, single crystal silicon, and the like.

The nonmagnetic support 1 may be subjected to various surface treatments and various decorations. For example, a fine uneven shape may be appropriately formed, or the surface may be subjected to a pretreatment such as a corona discharge treatment or an electron beam irradiation treatment. By arranging an inorganic filler such as kaolin or an organic filler on the surface of the non-magnetic support, the surface roughness can be controlled.

Next, the magnetic layer 2 formed on the non-magnetic support 1 will be described. In the magnetic recording medium of the present invention, the magnetic layer 2 is formed to have a thickness of, particularly, 0.3 μm or less in order to increase the recording density and cope with shorter wavelength recording. A magnetic layer 2 for recording and reproducing information;
Is formed to a thickness of 0.01 μm or more in order to exhibit the function of In the coating type magnetic recording medium, the magnetic layer 2 is formed by using a magnetic powder, a binder (binder), an antistatic agent, a curing agent, a lubricant, a dispersant, an abrasive, a rust inhibitor, an organic solvent, and the like. These are adjusted by a conventionally known method to produce a magnetic paint, and the magnetic paint is applied to the nonmagnetic support 1 to a predetermined thickness to form a magnetic paint. The raw materials for these magnetic paints are added in a predetermined step so that the raw materials do not cause a chemical reaction. In addition, the individual raw materials can be added in plural times.

The magnetic powder forming the magnetic layer 3 of the magnetic recording medium 10 of the present invention is made of ferromagnetic iron oxide particles (γ-Fe
₂ O ₃ , Fe ₃ O ₄ ), ferromagnetic iron oxide powder containing Co and Ni, ferromagnetic chromium oxide powder, ferromagnetic metal powder, iron carbide powder, barium ferrite and the like can be used. Depending on the application, the magnetic powder may contain Al, Si, P,
S, Ca, Sc, Ti, V, Cr, Mn, Cu, Zn,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Pd and the like can be contained. Further, by depositing carbon (carbon or graphite) on the magnetic powder in the magnetic paint, the electric resistance of the magnetic layer can be reduced. When the magnetic powder is coated with carbon, vapor deposition by chemical vapor deposition (CVD), physical vapor deposition (PVD), reduction of organic compounds,
It can be carried out by various methods such as thermal decomposition of hydrocarbons and the like and incomplete combustion. As described above, by depositing carbon on the magnetic powder in the magnetic paint, the electric resistance of the magnetic layer 3 is adjusted to be 1.0 × 10 ^{5 to} 1.0 × 10 ⁹ [Ω / sq]. adjust.

The binder in the magnetic paint is a vinyl copolymer having a quaternary ammonium salt as a functional group and a number average molecular weight (Mn) of 10,000 or less, or a polyester polyurethane resin. Having a quaternary ammonium salt as a functional group, and having a number average molecular weight (M
It is desirable that n) include those having 10,000 or less. By using these resins, the electric resistance of the magnetic layer can be reduced. When the number average molecular weight of the binder resin exceeds 10,000, the magnetic powder dispersing ability essential for high-density recording tends to decrease. Therefore, the number average molecular weight of the binder resin is selected to be 10,000 or less.

[0021] In addition, as a binder,
Any known polymer resin can be applied
You. For example, vinyl polymers such as vinyl chloride and vinyl acetate
And copolymers of these and acrylic acid esters
Body, urethane resin such as polyester polyurethane, nitrite
Cellulose derivatives such as rocellulose, epoxy resins,
Examples include a cetal resin and a phenoxy resin. The above conclusion
The mixture resin has a known functional group in the molecular structure.
There may be. For example, -SO_FourM, -SO_ThreeM, -S
O_TwoM, -COOM, -NH_Two, -NR _Two, -NR_Three,
-OH, -OPO_ThreeM_Two, -OPO_ThreeR_TwoEpoxy group,
(In this case, M is a hydrogen atom or an alka
R represents an alkyl group, an alkenyl group, an alcohol
Xyl group etc.). As the binder, the above functional groups
That has at least one type of functional group
Is desirable, and in particular, the effect of reducing the electric resistance of the magnetic layer.
Are preferred. These sensuality
The group is 1.0 × 10 per 1 g of resin.^-6~ 1.0 × 1
0^-2It is preferable that it is contained in an equivalent amount.

The molecular weight of the binder is desirably about 10,000 or less in terms of number average molecular weight in order to disperse the magnetic coating material well. In particular, when a vinyl copolymer and a polyester polyurethane resin are used, good dispersibility can be secured by setting the molecular weight to about 10,000 or less.

Further, by adding a polyisocyanate-based curing agent to the binder, crosslinking is promoted and durability of the magnetic layer can be improved. Examples of the curing agent, tolylene diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, 4,4 ^'- diphenylmethane diisocyanate,
Isocyanates such as naphthylene-1,5-diisocyanate, reaction products of these with polyhydric alcohols, condensates of isocyanates (polyisocyanates), and the like can be used.

Specific trade names of the binder include Coronate-L, Coronate-HL and Coronate-2030.
(The above are the product names of Nippon Polyurethane Co., Ltd.), Takenate D
-200 and Takenate D-202 (these trade names are manufactured by Takeda Pharmaceutical Co., Ltd.), and these can be used alone or in combination of two or more.

In the magnetic recording medium 10 of the present invention, the electric resistance of the magnetic layer 3 is set to 1.0 × 10 ^{5 to} 1.0 × 10 ⁹ [Ω /
sq], but in the magnetic paint, a conductive fine powder such as carbon, and other inorganic salts,
By adding an antistatic agent such as an ester, a monohydric or polyhydric alcohol, an amine, a silicone compound, and various surfactants, the electric resistance of the magnetic layer can be reduced. As the kind of the antistatic agent, conventionally known ones can be widely applied.

The type and amount of the antistatic agent can be adjusted according to the respective properties and other components in the magnetic coating material, and one or more of them can be used in combination.

When a surfactant is used as an example of the antistatic agent, examples of the cationic surfactant include fatty acid amine salts, primary amine salts, tertiary amines, quaternary ammonium compounds, and pyridine derivatives. Can be used.

Examples of the anionic surfactant include sulfated oil, sulfated ester oil, sulfated amide oil, sulfated salts of olefins, sulfated aliphatic alcohols, alkylsulfates, fatty acid ethylsulfonates, and alkylsulfones. Acid salts, alkyl naphthalene sulfonates, alkyl benzene sulfonates, mixtures of naphthalene sulfonic acids and formalin, succinate sulfonates, phosphate esters, soaps and the like can be applied.

Examples of the nonionic surfactant include a partial fatty acid ester of a polyhydric alcohol, an ethylene oxide adduct of an aliphatic alcohol, an ethylene oxide adduct of a fatty acid, an ethylene oxide adduct of an aliphatic amino or fatty acid amide, and an alkylphenol. Ethylene oxide adducts of alkyl naphthol, ethylene oxide adducts of partial fatty acid esters of polyhydric alcohols, polyethylene glycol and the like.

As the amphoteric surfactant, a carboxylic acid derivative-based surfactant, an imidazoline derivative-based surfactant and the like can be used.

As the lubricant, any conventionally known lubricants such as fatty acids, fatty acid esters, fatty acid salts, higher alcohols, polyhydric alcohols, polyhydric alcohol esters, amides, silicone oils, and fluorine-containing organic compounds can be used. it can. Further, a solid lubricant such as graphite and molybdenum disulfide may be added to the lubricant.

As the dispersant, fatty acids (C 10 -C 2)
0) and its metal salts, esters and metal soaps, phosphoric acid esters, amides, silane coupling agents, titanate coupling agents, aluminate coupling agents, and the like.

As the abrasive, any conventionally known ones such as inorganic fillers such as metal oxides, metal sulfides, sulfates, carbonates, nitrides, carbides, corundum and artificial diamond can be used. . Further, by applying carbon (carbon or graphite) or a conductive substance to the abrasive in the magnetic paint, the electric resistance of the magnetic layer can be reduced. When the abrasive is coated with carbon, various methods such as vapor phase growth by chemical vapor deposition (CVD), physical vapor deposition (PVD), reduction of organic compounds, thermal decomposition of hydrocarbons, and incomplete combustion are used. It can be carried out. By depositing carbon on the abrasive in this way, the electric resistance of the magnetic layer 3 can be increased to 1.0 × 10 ⁵ to 1.0.
Adjust so as to be 0 × 10 ⁹ [Ω / sq].

In addition, rust inhibitors, antibacterial (antifungal) agents,
As the organic solvent and the like, and particularly the magnetic dispersion used in the coating type magnetic recording medium, the solvent for preparing the magnetic dispersion, and the like, any conventionally known materials can be applied.

As the solvent for preparing the magnetic paint,
For example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ester; glycol ethers such as glycol monoethyl ether and dioxane Known solvents such as solvents, aromatic hydrocarbon solvents such as benzene, toluene and xylene can be used.

The preparation of the magnetic paint prepared by using the above-mentioned magnetic powder and a binder can be carried out by a known method. For example, a roll mill, a ball mill, a sand mill, a tron mill, a high-speed stone mill, a basket mill,
Disperser, homomixer, kneader, continuous kneader,
Kneading and adjustment are performed using an extruder, a homogenizer, an ultrasonic disperser, or the like.

On the non-magnetic support 1, a magnetic paint is applied,
Methods for forming the magnetic layer 2 include air doctor coating, blade coating, rod coating, extrusion coating,
Conventionally known methods such as an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a transfer roll coat, and a cast coat can be applied.

In the magnetic recording medium 10 of the present invention, in addition to the above, between the magnetic layer 3 and the non-magnetic support 1, a thickness of 0.1 mm is provided.
A configuration in which a material layer of less than 5 [μm] made of a predetermined material may be formed. By forming the magnetic layer 3 on the non-magnetic support 1 via the material layer, the mechanical strength of the magnetic recording medium 1 can be improved, and various other functions can be provided. For example, by applying a paint prepared by dispersing an inorganic additive such as a filler in a resin to form a material layer, the surface properties of the upper magnetic layer 3 can be improved. Further, by forming the material layer in a thin layer of less than 0.5 [μm], the magnetic recording medium 10 can be formed as a thin layer as a whole, the recording capacity per volume can be increased, and It can be a magnetic recording medium.

After the application of the magnetic paint, the back coat layer 2 is formed on the main surface opposite to the magnetic layer formation surface side using a conventionally known material for forming the back coat layer 2. Thereafter, a magnetic powder orientation treatment is performed by a known method by applying a magnetic field or using a permanent magnet to improve the magnetic properties of the magnetic layer. Then, the magnetic recording medium 10 is obtained by performing a calendering process, performing a surface treatment on the magnetic tape, and cutting the magnetic tape into a predetermined width.

Next, a magnetic head suitable for the magnetic recording medium 10 of the present invention and a magnetic recording system provided with the magnetic head will be described.

The magnetic recording medium 10 of the present invention is a so-called thin magnetic recording medium in which the magnetic layer 3 is formed as a thin layer of 0.01 to 0.3 [μm]. It is suitable for a recording system. In this case, as a high-sensitivity magnetic head, a magnetoresistive type M
An R head, a GMR head and the like can be mentioned. However, the present invention is not limited thereto, and a reproducing head such as a thin-film inductive head is also effective as long as it has high sensitivity and a sufficient S / N can be obtained. Particularly, it is suitable for a magnetic recording system corresponding to high-density recording.

As the MR reproducing head, there are a shield type MR head having an MR element sandwiched between shields, a yoke type MR head having an MR element sandwiched between high permeability materials, and the like. These heads may be used in a fixed linear recording system, or may be applied to a helical scan recording system mounted on a rotating drum such as a video system.

Hereinafter, a helical scan magnetic recording system using an MR reproducing head will be described as an example.

In this case, the MR reproducing head is an MR reproducing head.
It is assumed that a recording / reproducing apparatus is configured by using a shield type MR head in which an element is sandwiched between shields and mounting the MR head on a rotating drum.

The magnetic recording / reproducing apparatus of the helical scan magnetic recording system is a helical scan type magnetic recording / reproducing apparatus that performs recording / reproducing by using a rotating drum, and an MR head is used as a reproducing magnetic head mounted on the rotating drum. Use

An example of a rotary drum device mounted on the magnetic recording / reproducing apparatus will be described with reference to the drawings. FIG.
Shows a schematic perspective view of the rotary drum device 11, and FIG.
FIG. 2 is a schematic plan view of a magnetic recording medium feeding mechanism 30 including the rotating drum device 11.

As shown in FIG. 2, the rotating drum device 11
Are cylindrical fixed drum 12 and cylindrical rotary drum 1
3, a motor 14 for driving the rotary drum 13 to rotate, a pair of inductive magnetic heads 15a and 15b mounted on the rotary drum 13, and a pair of MR heads 16a and 16b mounted on the rotary drum 13. ing.

The fixed drum 12 is a drum that is held without rotating. On the side surface of the fixed drum 12, a lead guide portion 18 is formed along the running direction of the tape-shaped magnetic recording medium 10. As described below,
At the time of recording / reproduction, the magnetic recording medium 10 runs along the read guide portion 18. The rotating drum 13 is arranged so that the center axis of the fixed drum 12 coincides with that of the fixed drum 12.

The rotating drum 13 is a drum that is driven to rotate at a predetermined rotation speed by a motor 14 during recording and reproduction on the magnetic recording medium 10. This rotating drum 13
Is formed in a cylindrical shape having substantially the same diameter as the fixed drum 12, and is arranged such that the center axis of the fixed drum 12 coincides with that of the fixed drum 12. The fixed drum 12 of the rotary drum 13
A pair of inductive magnetic heads 15a and 15b and a pair of MR heads 16a and 16b
Is installed.

Inductive magnetic heads 15a, 15
b denotes 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 recording medium 10. You. These inductive magnetic heads 15a and 15b are mounted on the rotating drum 13 such that the angle formed between them with respect to the center of the rotating drum 13 is 180 °, and their magnetic gaps protrude from the outer periphery of the rotating drum 13. Have been. Note that these inductive magnetic heads 15a and 15b are set so that the azimuth angles are opposite to each other so that azimuth recording is performed on the magnetic recording medium 10.

On the other hand, the MR heads 16a and 16b serve as magneto-sensitive elements for detecting signals from the magnetic recording medium
A reproducing magnetic head having a magnetic recording medium 1
Used when reproducing a signal from zero. The MR heads 16a and 16b are mounted on the rotating drum 13 so that the angle formed between them by 180 degrees with respect to the center of the rotating drum 13 and the magnetic gap portion protrudes from the outer periphery of the rotating drum. Note that these MR heads 16a and 16b are set so that the azimuth angles are opposite to each other so that signals recorded in azimuth on the magnetic recording medium 10 can be reproduced.

Then, the magnetic recording / reproducing apparatus slides the magnetic recording medium 10 on such a rotating drum device 11,
A signal is recorded on the magnetic recording medium 10 and a signal is reproduced from the magnetic recording medium 10.

That is, at the time of recording / reproduction, the magnetic recording medium 10
As shown in FIG. 3, the recording medium is sent from the supply reel 21 via guide rollers 22 and 23 so as to be wound around the rotary drum device 11, and recording and reproduction are performed by the rotary drum device 11. The magnetic recording medium 10 recorded and reproduced by the rotating drum device 11 is sent to a take-up roll 28 via guide rollers 24 and 25, a capstan 26, and a guide roller 27. That is, the magnetic recording medium 10
The paper is fed at a predetermined tension and speed by a capstan 26 rotated and driven by a capstan motor 29, and is wound on a winding roll 28 via a guide roller 27.

At this time, the rotary drum 13 is driven to rotate by a motor 14 as shown by an arrow A in FIG. On the other hand, the magnetic recording medium 10 is sent along the reel guide portion 18 of the fixed drum 12 so as to slide obliquely with respect to the fixed drum 12 and the rotating drum 13. That is, the magnetic recording medium 10 is moved along the running direction from the tape entrance side to the fixed drum 1 as shown by the arrow B in FIG.
2 and is fed along the lead guide portion 18 so as to be in sliding contact with the rotating drum 13, and then sent to the tape exit side as shown by the arrow C in FIG.

Next, the internal structure of the rotary drum device 11 will be described with reference to FIG. As shown in FIG. 4, at the center of the fixed drum 12 and the rotating drum 13,
The rotation shaft 31 is inserted. In addition, the fixed drum 12,
The rotating drum 13 and the rotating shaft 31 are made of a conductive material, are electrically conductive, and the fixed drum 12 is grounded.

Further, two bearings 32 and 33 are provided inside the sleeve of the fixed drum 12, whereby the rotating shaft 31 is rotatably supported with respect to the fixed drum 12. That is, the rotating shaft 31 is
2, 33, it is supported rotatably with respect to the fixed drum 12. On the other hand, the rotating drum 13 has a flange 34 formed on the inner peripheral portion thereof, and the flange 34 is fixed to the upper end of the rotating shaft 31. Thus, the rotating drum 13 rotates with the rotation of the rotating shaft 31.

In order to transmit signals between the inside 12 of the rotary drum device 11 and the rotary drum 13, a rotary transformer 35 which is a non-contact type signal transmission device is provided. The rotary transformer 35 is connected to the fixed drum 12
The stator core 36 attached to the
And a rotor core 37 attached to the

The stator core 36 and the rotor core 37 are
A magnetic material such as ferrite is formed in an annular shape around the rotation axis 31. The stator core 36 includes a pair of inductive magnetic heads 15a and 15b.
A pair of signal transmission rings 36a, 36b corresponding to
A signal transmission ring 36c corresponding to the pair of MR heads 16a and 16b and a power transmission ring 36d for supplying power required for driving the pair of MR heads 16a and 16b.
Are concentrically arranged. Similarly, the rotor core 37 has a pair of inductive magnetic heads 15a,
15b corresponding to a pair of signal transmission rings 37a, 37
b, a signal transmission ring 37c corresponding to the pair of MR heads 16a, 16b, and a pair of MR heads 16a, 16b.
A power transmission ring 37d for supplying power required for driving b is concentrically arranged.

These rings 36a, 36b, 36c,
36d, 37a, 37b, 37c, and 37d are rotating shafts 3
1, each of the rings 36a, 36b, 36c, 3 of the stator core 36.
6d and each ring 37a, 37b, 37 of the rotor core 37
c and 37d are arranged to face each other.
The rotor transformer 35 is connected to a stator core 36
Signals and electric power are transmitted in a non-contact manner between each of the rings 36a, 36b, 36c, 36d and each of the rings 37a, 37b, 37c, 37d of the rotor core 37.

The rotary drum device 11 is provided with a motor 14 for rotating and rotating the rotary drum 13. The motor 14 includes a rotor 38 as a rotating part,
And a stator 39 which is a fixed portion. Rotor 3
8 is attached to the lower end of the rotating shaft 31 and includes a driving magnet 40. On the other hand, the stator 39
Is attached to the lower end of the fixed drum 12 and has a driving coil. By supplying a current to the driving coil 41, the rotating shaft 31 attached to the rotor 38 rotates, and accordingly, the rotating shaft 31
Is driven to rotate.

Next, the rotary drum device 11 as described above
FIG. 5 schematically shows the circuit configuration of the rotary drum device 11 and its peripheral circuits for recording and reproduction by
This will be described with reference to FIG.

When a signal is recorded on the magnetic recording medium 10 using the rotary drum device 11, first, a current is supplied to the drive coil 41 of the motor 14, whereby the rotary drum 13 is driven to rotate. Then, while the rotating drum 13 is rotating, as shown in FIG.
Is supplied to the recording amplifier 51.

The recording amplifier 51 amplifies the recording signal from the external circuit 50, and transmits the signal of the stator core 36 corresponding to the inductive magnetic head 15a at the timing when the signal is recorded by one of the inductive magnetic heads 15a. Supply the recording signal to the use ring 36a,
At the time of recording a signal by the other inductive magnetic head 15b, a recording signal is supplied to the signal transmission ring 36b of the stator core 36 corresponding to the inductive magnetic head 15b.

Here, as described above, the pair of inductive magnetic heads 15a and 15b
Are arranged so that the angle between them becomes 180 ° with respect to the center of the magnetic head, and these inductive magnetic heads 15b and 15b alternately record with a phase difference of 180 °. That is, the recording amplifier 51
The timing at which the recording signal is supplied to one inductive magnetic head 15a and the timing at which the recording signal is supplied to the other inductive magnetic head 15b are 18
Switching is performed alternately with a phase difference of 0 °.

The recording signal supplied to the signal transmission ring 36a of the stator core 36 corresponding to the one inductive magnetic head 15a is transmitted to the signal transmission ring 37a of the rotor core 37 in a non-contact manner. Then, the recording signal transmitted to the signal transmission ring 37a of the rotor core 37 is supplied to the inductive magnetic head 15a, and the signal is recorded on the magnetic recording medium 10 by the inductive magnetic head 15a.

Similarly, the recording signal supplied to the signal transmission ring 36b to the stator core 36 corresponding to the other inductive magnetic head 15b is transmitted to the signal transmission ring 37b of the rotor core 37 without contact. Then, the recording signal transmitted to the signal transmission ring 37b of the rotor core 37 is supplied to the inductive magnetic head 15b, and the signal is recorded on the magnetic recording medium 10 by the inductive magnetic head 15b.

Further, using the rotary drum device 11,
When reproducing a signal from the magnetic recording medium 10, first, a current is supplied to a driving coil of a motor 14, whereby the rotating drum 13 is driven to rotate. Then, while the rotating drum 13 is rotating, as shown in FIG.
High frequency current is supplied from the oscillator 52 to the power drive 53.
Supplied to

The high-frequency current from the oscillator 52 is converted into a predetermined alternating current by the power drive 53 and then supplied to the power transmission ring 36 d of the stator core 36. The alternating current supplied to the power transmission ring 36d of the stator core 36 is transmitted to the power transmission ring 37d of the rotor core 37 in a non-contact manner. The AC current transmitted to the power transmission ring 37d of the rotor core 37 is rectified by the rectifier 54 to become a DC current, which is supplied to the regulator 55. The DC current is set to a predetermined voltage by the regulator 55.

The current set to a predetermined voltage by the regulator 55 is applied to the pair of MR heads 16a, 1
6b is supplied as a sense current. Note that a pair of MRs
The heads 16a, 16b include the MR heads 16a, 1
A reproduction amplifier 56 for detecting a signal from 6b is connected, and a current from the regulator 55 is also supplied to the reproduction amplifier 56.

Here, each of the MR heads 16a and 16b has an MR element whose resistance value changes according to the magnitude of an external magnetic field. In the MR heads 16a and 16b, the resistance value of the MR element changes due to the signal magnetic field from the magnetic recording medium 10, whereby a voltage change appears in the sense current.

The reproducing amplifier 56 detects this voltage change and outputs a signal corresponding to the voltage change as a reproduced signal. The reproducing amplifier 56 outputs the signal detected by the MR head 16a at the time of reproducing the signal by one MR head 16a, and outputs the signal at the timing of reproducing the signal by the other MR head 16b. The reproduced signal detected by the MR head 16b is output.

Here, a pair of MR heads 16a, 16b
As described above, the MR heads 16a and 16b are alternately reproduced with a phase difference of 180 ° since they are arranged so that the angle between them with respect to the center of the rotating drum 13 is 180 °. It will be. That is,
The reproduction amplifier 56 outputs a reproduction signal from one of the MR heads 16a and the other MR head 16b.
And the timing at which the reproduced signal is output are alternately switched with a phase difference of 180 °.

The reproduction signal is supplied from the reproduction amplifier 56 to the signal transmission lead 37c of the rotor core 37, and the reproduction signal is transmitted to the signal transmission ring 36c of the stator core 36 without contact. Stator core 36
The reproduction signal transmitted to the signal transmission ring 36c is amplified by the reproduction amplifier 57 and then corrected by the correction circuit 58.
Supplied to Then, the reproduction signal is subjected to predetermined correction processing by the correction circuit 58, and then output to the external circuit 50.

When the circuit configuration is as shown in FIG. 5, a pair of inductive magnetic heads 15a and 15
b, a pair of MR heads 16a and 16b, a rectifier 54, a regulator 55, and a reproducing amplifier 56
3 and rotates together with the rotating drum 13. on the other hand,
Recording amplifier 51, oscillator 52, power drive 5
3. The reproduction amplifier 57 and the correction circuit 58 are disposed on a fixed portion of the rotary drum device 11 or are external circuits configured separately from the rotary drum device 11.

Next, the MR heads 16a and 16b mounted on the rotary drum 13 will be described in detail with reference to FIG. The MR heads 16a and 16b
Have the same configuration except that the azimuth angles are set to be opposite to each other. Therefore, in the following description, these MR heads 16a and 16b are collectively referred to as MR heads 16a and 16b.
Called head 16.

The MR head 16 is mounted on the rotating drum 13 and is provided with a helical scan system.
This is a read-only magnetic head that detects a signal from the magnetic head using the magnetoresistance effect. Generally, the MR head has higher sensitivity and higher reproduction output than an inductive magnetic head that performs recording and reproduction using electromagnetic induction, and thus is suitable for high-density recording. Therefore, M as a reproducing magnetic head
By using the R head 16, higher density recording can be achieved.

As shown in FIG. 6, the MR head 16 includes a pair of magnetic shields 61 and 62 made of a soft magnetic material such as Ni—Zn polycrystalline ferrite and the like.
And a substantially rectangular MR element portion 64 sandwiched between a pair of magnetic shields 61 and 62 via the third magnetic shield 61. In addition, a pair of terminals is led out from both ends of the MR element unit 64, and the MR element unit 6 is connected through these terminals.
4 can be supplied with a sense current.

The MR element section 64 includes an MR element having a magnetoresistance effect, a SAL (Soft Adjacent Layer) film,
An insulator film provided between the element and the SAL film is laminated. The MR element is made of Ni whose resistance changes according to the magnitude of an external magnetic field due to the anisotropic magnetoresistance effect (AMR).
-Made of a soft magnetic material such as Fe. The SAL 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 is used to insulate the MR element and the SAL film from each other and to prevent electronic shunt loss, and is made of an insulating material such as Ta.

The MR element portion 64 is formed in a substantially rectangular shape, and is supported by a pair of magnetic shields 61 and 62 via an insulator 63 so that one side surface is exposed to the magnetic recording medium sliding surface 65. Have been. More specifically, the MR element section 64 has a pair of short axis directions substantially perpendicular to the magnetic recording medium sliding surface 65 and a long axis direction substantially perpendicular to the magnetic recording medium sliding direction. Magnetic shields 61, 62
Is sandwiched via an insulator 63.

The sliding surface 65 of the magnetic recording medium of the MR head 16 is placed on the sliding surface 65 of the magnetic recording medium.
The cylindrical surface is polished along the sliding direction of the magnetic recording medium 10 so that one side surface is exposed, and the cylindrical surface is polished along the direction perpendicular to the sliding direction of the magnetic recording medium 10. As a result, the MR head 16
The element portion 64 or a portion in the vicinity thereof is made to protrude most, so that the contact characteristics of the MR element portion 64 with the magnetic recording medium 10 can be improved.

When a signal from the magnetic recording medium 10 is reproduced using the MR head 16 as described above,
As shown in FIG. 7, the magnetic recording medium 10 is
To slide. Note that the arrows shown in FIG. 7 schematically show how the magnetic recording medium 10 is magnetized.

Then, the magnetic recording medium 10 is
While sliding on the R element section 64, a sense current is supplied to the MR element section 64 via terminals 64a and 64b connected to both ends of the MR element section 64, and a voltage change of the sense current is detected. . Specifically, a predetermined voltage Vc is applied from a terminal 64a connected to one end of the MR element section 64, and a terminal 64b connected to the other end of the MR element section 64.
Is connected to the rotating drum 13. Here, the rotating drum 13 is electrically connected to the fixed drum 12 via the rotating shaft 31, and the fixed drum 12 is grounded. Therefore, one terminal 64 b connected to the MR element section 64 is grounded via the rotating drum 13, the rotating shaft 31 and the fixed drum 12.

When a sense current is supplied to the MR element section 64 with the magnetic recording medium 10 slid, the MR element formed on the MR element section 64 responds to a magnetic field from the magnetic recording medium 10. The resistance value changes, resulting in a voltage change in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic recording medium 10 is detected, and the signal recorded on the magnetic recording medium 10 is reproduced.

In the MR head 16 used, M
The MR element formed in the R element section 64 may be any element that exhibits a magnetoresistance effect. For example, a so-called giant magnetic element in which a plurality of thin films are stacked to obtain a greater magnetoresistance effect. A resistance effect element (GMR element) can also be used.

The method of applying a bias magnetic field to the MR element need not be the SAL bias method, but may be, 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, or the like. Various methods such as a method and a servo bias method can be applied. The giant magnetoresistance effect and various bias methods are described in detail in, for example, "Magnetoresistance Head Basics and Applications Translated by Kazuhiko Hayashi" by Maruzen Co., Ltd.

Hereinafter, the magnetic recording medium 10 of the present invention will be specifically described with reference to magnetic recording media of Examples and Comparative Examples. However, the present invention is not limited to this.

Example 1 First, the composition of the magnetic layer dispersion prepared from the magnetic dispersion composition used to form the magnetic layer 2 constituting the magnetic recording medium 10 is shown below. [Dispersion composition for magnetic layer] Ferromagnetic powder: Fe-Co (30 atomic% of Co): 100 [parts by weight] Binder: vinyl chloride vinyl acetate copolymer A: 17 [parts by weight] Inorganic powder (polishing agent): α-alumina: 2 parts by weight Solvent: cyclohexanone: 100 parts by weight Methyl ethyl ketone: 100 parts by weight Toluene: 100 parts by weight Lubricant: butyl stearate: 2 parts by weight Stearic acid: 1 part by weight Parts) Antistatic agent: (shown below): 0.3 [parts by weight]

The above-mentioned materials were kneaded with a kneader, sand-milled and dispersed to obtain a magnetic layer dispersion. Then, 3 [parts by weight] of a curing agent “Coronate L” made by Nippon Polyurethane were added, and the mixture was stirred and uniformed to obtain a magnetic paint.

The magnetic powder has a specific surface area of about 45 [m ² /
g], major axis diameter 0.1 [μm], σ _s 145 [emu /
g] and Hc2300 [Oe]. The vinyl chloride-vinyl acetate copolymer A has a number average molecular weight (Mn)
9000, a glass transition point of 70 ° C. and a functional group containing 0.1 [mmol / g] of a sulfonate were used. α-Alumina having a particle size of 0.3 [μm] was used.

In Example 1, oleyl alcohol sulfate sodium salt of the following Chemical Formula 1 was applied as an antistatic agent in the magnetic paint.

Embedded image CH ₃ (CH ₂ ) ₇ CH ＝ CH (CH ₂ ) ₇ C
H ₂ SO ₃ Na

After applying the magnetic paint, a back coat layer was formed, and thereafter, a magnetic field orientation treatment was performed, followed by drying and winding. Further, the magnetic layer 3 was subjected to a calendering treatment and a curing treatment to form a magnetic layer 3 having a thickness of 0.3 [μm].

The molecular weight was measured by the GPC method (high performance liquid chromatography [Water: Model 1500 / detector: Sh
odex RI SE-61], column [Shodex KF804 + KF803 +
KF802 + KF801]. The glass transition point is measured by a vibron method (heating rate 2 [° C./min], 10 [H
z]). The specific surface area is measured using a surface area measuring device (BET).
Method).

The wide tape prepared as described above and slit to an arbitrary width was used as a sample magnetic tape.

[Example 2] Sorbitan monolaurate shown in the following [Chemical Formula 2] was applied as an antistatic agent in [Dispersion Composition for Magnetic Layer] of [Example 1].

Embedded image Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

[Example 3] The magnetic powder in the [dispersion composition for magnetic layer] of the above [Example 1] was coated with 3% by weight of carbon by carbon dioxide adsorption drying. Was. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

[Example 4] A number average molecular weight (Mn) of 8000 and a glass transition were used in place of the vinyl chloride-vinyl acetate copolymer A as a binder in [Dispersion composition for magnetic layer] in [Example 1]. A vinyl chloride-vinyl acetate copolymer B containing a quaternary ammonium salt of 0.1 [mmol / g] as a functional group at a point of 70 [° C] was used. The other conditions were the same as in the above [Example 1] to produce a sample magnetic tape.

Example 5 A number average molecular weight (Mn) of 9000 and a glass transition were used in place of the vinyl chloride-vinyl acetate copolymer A as a binder in [Dispersion Composition for Magnetic Layer] of [Example 1]. A polyester polyurethane resin containing a quaternary ammonium salt as a functional group at a point of 65 ° C. and 0.08 [mmol / g] was used. The other conditions were the same as in the above [Example 1] to produce a sample magnetic tape.

Example 6 The above-mentioned [Dispersion composition for magnetic layer]
Α-Fe having a particle size of 0.3 [μm] coated with particulate carbon instead of α-alumina as an inorganic powder (abrasive)
₂ O ₃ was used. The other conditions were the same as in the above [Example 1] to produce a sample magnetic tape.

[Example 7] [Dispersion composition for magnetic layer]
The magnetic powder in which 3% by weight of carbon was applied by carbon dioxide adsorption drying was used. As a binder, number average molecular weight (Mn) 8000, glass transition point 70
[° C.], quaternary ammonium salt as a functional group
[Mmol / g] -containing vinyl chloride-vinyl acetate copolymer B was used. In place of α-alumina as an inorganic powder (polishing agent) in [magnetic layer dispersion composition], α-Fe ₂ O ₃ having a particle diameter of 0.3 [μm] coated with particulate carbon was used. Was. Other conditions were the same as in the above [Example 1].
A sample magnetic tape was made.

[Comparative Example 1] The above [Dispersion Composition for Magnetic Layer]
Instead of the antistatic agent therein, 3 [parts by weight] of carbon black having a particle size of 30 [nm] was added. The other conditions were the same as in the above [Example 1] to produce a sample magnetic tape.

Comparative Example 2 [Dispersion Composition for Magnetic Layer]
Instead of the antistatic agent, 10 [parts by weight] of carbon black having a particle size of 30 [nm] was added. The other conditions were the same as in the above [Example 1] to produce a sample magnetic tape.

[Embodiment 1] to [Embodiment 7]
The magnetic properties (square ratio and coercive force), the electric resistance of the magnetic layer, and the running durability were measured for the magnetic tapes of the respective samples prepared in Comparative Examples 1 and 2. The magnetic characteristics are measured using a magnetic property measuring device (VS
M).

The electrical resistance of the magnetic layer is determined by the mechanical characteristics of the magnetic tape [Part 4 of JIS magnetic tape recording / reproducing system, JIS C 5565-1989 (IEC 94-1994)].
4-1986)]], 5.7 “Electrical Resistance of Magnetic Layer and Backcoat Layer (if Any)”. At this time, at room temperature of 22 ° C. and humidity of 60% RH,
It was left for at least 4 hours and then measured under the same environment.

In the test for running durability, a magnetic tape was cut into a width of 8 [mm] and examined using an 8 mm video deck. The VCR has a Sony WV-
A long-time (one hour) still test was performed using TW1. In the running durability test, the circuit for protecting the tape was released. The recording frequency is 5 [MHz]. The level reduction of the magnetic tape of each sample after running for one hour was quantified, and the level reduction width of Comparative Example 1 was set to 100.
As [%], comparative evaluation was performed based on this.

The evaluation results are shown in the following [Table 1]. In addition,
In Table 1, those with a level down width of 90% or less were evaluated as ○, those with a level of 90 to 105 [%] as Δ, and those with a level of 105% or more as x.

[0106]

[Table 1]

As shown in [Table 1], the thickness was 0.0
A magnetic recording medium having a thin magnetic layer of 1 to 0.3 [μm], wherein the electric resistance of the magnetic layer is 1.0 × 10 ⁵
１．０1.0 × 10 ⁹ Ω / sq [Example 1]
It has been found that the magnetic tapes of Examples 7 to 7 have very little level reduction and good magnetostatic characteristics even when they are run continuously many times (for a long time).

On the other hand, the magnetic layer did not contain an antistatic agent and carbon black was added, and the electric resistance of the magnetic layer exceeded 1.0 × 10 ⁹ [Ω / sq] (Comparative Example 1).
In the case of, the level reduction was large when the magnetic tape was run many times as compared with the magnetic tapes of [Example 1] to [Example 7].

Further, as shown in [Comparative Example 2], when carbon black is added to the magnetic layer to lower the electric resistance, the electric resistance of the magnetic layer becomes 1.0 × 10 ⁵ to 1.0.
If the amount is to be within the range of 0 × 10 ⁹ [Ω / sq], about 10 parts by weight of carbon black is required, and the amount of carbon black is excessive. , The strength of the magnetic layer deteriorates, the magnetic layer is peeled off during running, the level is greatly reduced, and it becomes difficult to maintain the function as the magnetic layer.

The magnetic recording medium of the present invention is not limited to the above example. For example, in addition to the case where the antistatic agent is contained in the magnetic layer 3, the non-magnetic support 1
It can be contained in the inside or in the back coat layer 2. Further, an antistatic agent can be appropriately applied on the magnetic layer 3 as a top coat layer.

In the magnetic recording medium of the present invention, in a so-called thin magnetic recording medium 10 having a thickness of 0.01 to 0.3 [μm] or less, the electric resistance of the magnetic layer 3 is set to 1 0.0 × 10 ^{5 to} 1.0 × 10 ⁹ [Ω / sq]
As a result, running durability could be improved.

[0112]

According to the magnetic recording medium of the present invention, in a so-called thin magnetic recording medium 10 having a thickness of 0.01 to 0.3 [μm] or less, the electric resistance of the magnetic layer 3 is reduced. From 1.0 × 10 ^{5 to} 1.0 × 10 ⁹ [Ω / s
q], it was possible to improve the running durability by making the number within the numerical value.

In the present invention, the thickness of the magnetic layer is set to 0.3
By setting the thickness to μm or less, the thickness loss at the time of reproducing the short wavelength component and the self-demagnetization loss at the time of recording are reduced, and a high-density recording magnetic recording medium having excellent magnetic characteristics can be obtained. did it.

In the present invention, even when a predetermined material layer is formed between the magnetic layer and the non-magnetic support 1, the thickness of the material layer is preferably set to less than 0.5 μm. By making the finally obtained magnetic recording medium a thin-layer type, the recording capacity per unit volume could be increased, and a magnetic recording medium of high density recording could be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic perspective view of a configuration example of a rotary drum device mounted on a magnetic recording / reproducing device of a helical scan magnetic recording system.

FIG. 3 shows a schematic configuration diagram of an example of a magnetic recording medium feeding mechanism including a rotary drum device.

FIG. 4 is a schematic sectional view of the internal structure of the rotary drum device.

FIG. 5 shows a rotary drum device and its peripheral circuits.
1 shows a schematic diagram of a circuit configuration.

FIG. 6 is a schematic perspective view, partially cut away, of an example of an MR head mounted on a rotating drum.

FIG. 7 is a schematic diagram showing how a signal from a magnetic recording medium is reproduced using an MR head.

FIG. 8 is a schematic sectional view of a magnetic recording medium having a conventional structure.

[Explanation of symbols]

1,101 non-magnetic support, 2 back coat layer 3,
103 magnetic layer, 10, 100 magnetic recording medium, 11
Rotary drum device, 12 fixed drum, 13 rotary drum, 14 motor, 15a inductive magnetic head, 15b inductive magnetic head, 16 MR
Head, 16a MR head, 16b MR head, 1
8 Lead guide part, 21 supply reel, 22 to 25,
27 guide roller, 26 capstan, 28 take-up roll, 29 capstan motor, 30 magnetic recording medium feed mechanism, 31 rotating shaft, 32, 33 bearing,
34 flange, 35 rotary transformer, 36 stator core, 37 rotor core, 38 rotor, 39 stator, 40 magnet, 41 driving coil, 50
External circuit, 51 Recording amplifier, 52 oscillator, 5
3 power drive, 54 rectifier, 55 regulator, 56 playback amplifier, 57 playback amplifier, 58
Correction circuit, 61 magnetic shield, 62 magnetic shield,
63 insulator, 64 MR element portion, 65 sliding surface of magnetic recording medium, 102 underlayer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) G11B 5/702 G11B 5/702 5/708 5/708 5/712 5/712 5/738 5/738 / / C08L 67:00 C08L 67:00 F term (reference) 4F006 AA35 AB12 AB18 AB23 AB37 AB72 AB73 AB74 BA06 BA07 CA02 DA04 4J038 BA081 CD021 CF021 CG141 DA011 DB001 DF061 DG111 DG262 GA03 GA06 GA07 GA08 GA09 GA11 GA08 BA09 BA08 P09 BA10 BA11 BA15 BA19 CA05 FA02 FA05

Claims (14)

[Claims] 1. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint on a nonmagnetic support, wherein the magnetic layer is formed directly on the nonmagnetic support. The thickness of the magnetic layer is 0.01 to 0.3 [μm], and the electric resistance of the magnetic layer is 1.0 × 10 ^{5 to} 1.0 × 1.
0 ⁹ [Ω / sq]. 2. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint on a nonmagnetic support, wherein the magnetic layer has a thickness of 0.5 [m] on the nonmagnetic support. μ
m], the thickness of the magnetic layer is 0.01 to 0.3 [μm], and the electric resistance of the magnetic layer is 1.0 × 10 ⁵ to 1.0 × 1
0 ⁹ [Ω / sq]. 3. The magnetic recording medium according to claim 1, wherein the magnetic layer contains an antistatic agent. 4. The magnetic recording medium according to claim 2, wherein the magnetic layer contains an antistatic agent. 5. The magnetic recording medium according to claim 1, wherein carbon is applied to the surface of the magnetic powder in the magnetic paint. 6. The magnetic recording medium according to claim 2, wherein carbon is adhered to the surface of the magnetic powder in the magnetic paint. 7. A binder in the magnetic paint, wherein the binder contains a vinyl copolymer, the vinyl copolymer having a quaternary ammonium salt as a functional group, and a number average molecular weight ( Mn) is 10,000
2. The magnetic recording medium according to claim 1, wherein: 8. The binder in the magnetic coating material contains a vinyl copolymer, the vinyl copolymer having a quaternary ammonium salt as a functional group, and a number average molecular weight ( Mn) is 10,000
3. The magnetic recording medium according to claim 2, wherein: 9. The binder in the magnetic coating material contains a polyester polyurethane resin, the polyester polyurethane resin having a quaternary ammonium salt as a functional group, and a number average molecular weight (Mn).
2. The magnetic recording medium according to claim 1, wherein is less than or equal to 10,000. 10. The binder in the magnetic coating material contains a polyester polyurethane resin, which has a quaternary ammonium salt as a functional group and a number average molecular weight (Mn).
3. The magnetic recording medium according to claim 2, wherein is less than or equal to 10,000. 11. The magnetic recording medium according to claim 1, wherein an abrasive is contained in the magnetic layer, and the abrasive is a solid whose surface is coated with a conductive substance. . 12. The magnetic recording medium according to claim 2, wherein an abrasive is contained in the magnetic layer, and the abrasive is a solid whose surface is coated with a conductive material. . 13. The magnetic recording medium according to claim 1, wherein at least one of recording and reproduction is performed by a magnetic recording system including a magnetoresistive effect type magnetic head. 14. The magnetic recording medium according to claim 2, wherein at least one of recording and reproduction is performed by a magnetic recording system including a magnetoresistive magnetic head.