JP2001291226A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance durability and reliability by effectively restraining a magnetic disk and a magnetic head from wearing so much by high-speed sliding while keeping high-density recording and high transferring rate of a magnetic recording medium of multi-layer coating type, particularly a magnetic disk. SOLUTION: The upper layer (magnetic layer) 20 of the multi-layer coating type magnetic disk 3 contains nomnagnetic powder having 8 or higher Mohs' hardness and 0.2-0.6 μm average primary particle size. The centerline surface average roughness Ra of the surface of the layer 20 is 4 nm or smaller. Projections based on the nonmagnetic powder are formed on the surface of the layer 20 so that the projections having 10-50 nm height exist by 50-400 pieces/400 μm2 and those having higher than 50 nm height exist by 1-20 pieces/400 μm2.

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, such as a magnetic (recording) disk, manufactured by multi-layer coating.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media (media) such as floppy (registered trademark) disks have been widely used as external storage media such as word processors and personal computers. In recent years, along with the remarkable improvement in performance of personal computers and the like, the performance of magnetic disks has also been required to be improved. For example, for a removable flexible magnetic disk represented by a 3.5-inch floppy disk, not only the recording density but also the data density have been improved. There is a demand for an improved transfer rate. In response to such a request,
Already 100MB (Mbps) such as Zip and LS-120
i) Magnetic recording disks having a class recording capacity have appeared. However, with today's rapid increase in the processing capability of personal computers and the like, the emergence of magnetic disks having higher recording capacities has been anticipated.
A magnetic disk having a surface recording density exceeding 00 MB has also been demanded.

In order to simultaneously achieve a high recording density and a high data transfer rate, high-speed rotation of a magnetic disk is indispensable. At such a high line speed, the amount of spacing between the magnetic head and the magnetic disk must be kept low. Recording reproduction spacing, the deterioration of the electromagnetic conversion characteristics (increase or isolated reproduction wave of the pulse width PW ₅₀ outputs I
The deterioration of the overwrite characteristic due to the decrease in the STAA) and the decrease in the magnetic field strength cause the high-density recording to be difficult.

In order to make the sliding with the magnetic head smooth, measures for smoothing the surface of the magnetic disk have been studied. For that purpose, it is necessary to make the ferromagnetic powder finer and to disperse it in an organic solvent to a high degree.
It has been known that a binder plays an important role in improving dispersibility, and a binder in which a polar functional group having strong interaction with a magnetic powder is introduced into a molecular skeleton is mainly used. In addition, additives such as silane coupling agents and titanate coupling agents other than the binder are also effective,
It has been reported (Japanese Patent Application Laid-Open Nos. 10-40534 and 9-128736). The application of mechanical energy is indispensable in order to break up the aggregates of particles and enhance dispersibility in the dispersion treatment process, but progress has been made steadily in this field, and various types of high-performance dispersion Machine has appeared. In addition, calendar processing is also effective for improving dispersibility, and various improvements have been attempted.

On the other hand, when a conventional magnetic head slider is used for recording / reproducing a magnetic disk at a high linear velocity,
Increase in spacing is inevitable due to the levitation force acting on the slider. This phenomenon is considered to be caused by the lubrication effect of the air film, since the portion of the outer edge of the slider chamfered by a smooth curved surface called blend R functions just like the taper of the floating hard disk slider. .

Therefore, in order to avoid such a problem,
Various magnetic recording apparatuses have been developed which employ a so-called floating magnetic head slider which generates a positive pressure having a taper flat structure similar to that used in a hard disk, or further includes a negative pressure mechanism. by this,
It is possible to perform high-speed recording and reproduction while maintaining a stable low spacing amount of 40 to 100 nm without almost bringing the magnetic head into contact with the magnetic disk. The disk rotation speed is 3000 rpm, the relative speed is 13.2 m / s, and the recording density is high. A performance of around 100-200 MB has been obtained.

However, as described at the beginning, the demand for the recording density has now exceeded 200 MB, and it has been necessary to suppress the spacing amount to less than 40 nm.

[0008]

In order to respond to such a demand, the present applicant has previously proposed a contact type head slider having a contact pad in which a magnetic head is embedded (Japanese Patent Application No. 11-251).
No. 815). Hereinafter, the outline of the invention of the prior application will be described.

In the head slider for a flexible magnetic disk of the prior application, a pad in which a magnetic head is embedded is provided on a surface facing the flexible magnetic disk, and the relative speed between the pad and the magnetic head is 1. 3m /
In the state where the magnetic head is in contact with the flexible magnetic disk at a speed of s to 25.0 m / s, the magnetic head records or reproduces signals on the flexible magnetic disk. According to the prior application, there is no floating mechanism having a taper flat or a negative pressure mechanism like a conventional head slider for a hard disk, and recording / reproducing by a magnetic head is performed from a low speed in a state of being in contact with the surface of a flexible magnetic disk. The operation can be performed stably over a wide range up to a high speed for a long time, the density of the flexible magnetic disk can be increased, the transfer rate can be increased, and the power consumption can be reduced.

FIG. 3 shows an HGA (head slider suspension) 2 having a head slider 1 according to an embodiment attached to a tip thereof. The HGA 2 is a rectangular plate elongated in the radial direction of the flexible magnetic disk 3. A magnetic head slider 1 is supported by the tip of the suspension beam 5, comprising a base plate 4 in a shape of a circle and a suspension beam 5 stuck on the lower surface of the tip of the base plate 4 in an overlapping manner. Note that two head sliders 1 and two HGAs 2 are arranged so as to face up and down.
As shown in FIG. 1, the flexible magnetic disk 3 is sandwiched from both sides.

The base plate 4 is formed at its base end with a constricted narrow portion on both left and right sides. The base end portion of the constricted portion is held by a carriage of a linear motor (not shown). A cantilever arm 7 protruding laterally is integrally formed on one of the side portions.

Although not shown in the drawings, when the cantilever arm 7 is relatively lifted by the lifter due to the movement of the linear motor in the front-rear direction, the base plate 4 tends to bend mainly at the narrow portion, and the one side of the base plate 4 is bent. Despite the edge being lifted, the tip is pushed upwards while remaining substantially horizontal without twisting.

[0013] Incidentally, a front-rear direction of "D ₁ direction" is a linear motor shown in FIG., A seek direction for recording or reproducing by the magnetic head. The “D ₂ direction” indicates the traveling direction (rotation direction) of the flexible magnetic disk 3.
Running direction (D ₃ ) of the flexible magnetic disk 3
May be reversed. A linear motor (not shown) moves parallel to the radial direction of the flexible magnetic disk 3, and the base plate 4 moves in the radial direction of the flexible magnetic disk 3 by driving the linear motor. .

The suspension beam 5 includes an adhered portion 8 adhered to the lower surface of the distal end portion of the base plate 4 via a pivot spring, a suspension portion 9 which becomes narrower toward the distal end, and a distal end portion of the suspension portion 9. A slider supporting portion 10 for supporting the head slider 1. The suspension part 9 has several holes 11, 11,
.. Are formed so that appropriate elasticity is imparted. In particular, a U-shaped link portion 12 having an opening at the tip is formed at the tip of the suspension portion 9, and a substantially rectangular slider support portion 10 is formed between the tips of the link portion 12.

The material of the suspension beam 5 is as follows.
Spring constant 20 consisting of three layers such as SUS / adhesive / SUS
It is made of a very soft laminate material of about 0 mgf / mm, and the link portion 12 at the tip end has a roll rigidity of 0.2 μN · m / degree and a pitch rigidity of 0.04 μm.
The flexibility of N · m / degree is secured.
Although the details are omitted, the suspension beam 5 is
It is mechanically connected to the back surface of the head slider 1 and is also electrically connected to a lead terminal extending from a magnetic head embedded in the center of a magnetic pole pad, which will be described later, and also functions as a signal line.

The magnetic head slider 1 has a vertically long trapezoidal shape when viewed from a plane. A contact pad (magnetic pole pad) 14 having a magnetic head 13 buried in a tip portion thereof, and a corner portion on the opposite side. Contact pads 15, 15 are each supported. The magnetic head slider 1 is formed of a sputtered alumina body or the like by a thin film process.
Since it is extremely thin, 50 μm or less, the rigidity is about eight digits softer than a picos slider having a thickness of about 300 μm used for a hard disk, and its own weight is as light as 500 μg or less. As a result, it is possible to smoothly follow the surface of the flexible magnetic disk 9 and, since it is extremely lightweight, a force generated with respect to an externally applied acceleration is very weak. Excellent impact resistance.

The contact pads 14, 15, 15 are made of diamond-like carbon (hereinafter abbreviated as DLC) or the like, and the magnetic pole pad 14 has a magnetic head 13 having a magnetic gap for recording / reproducing embedded therein. The periphery of the magnetic core is surrounded by DLC or the like on the sliding surface. FIG.
Shows the positional relationship between the magnetic pole pad 14 and the flexible magnetic disk 3 when recording / reproducing.

The hardness of the contact pads 14, 15, and 15 is required to be 700 or more in terms of abrasion resistance.
The material is not limited to DLC as long as it gives such characteristics. Contact pad 1
The angles α of the corners of the sides 4, 15, and 15 that come into contact with the flexible magnetic disk 8 need to be obtuse angles of 90 degrees or more in order to suppress the abrasion of the medium. Preferably, it is 115 degrees or more. The sliding surface shape of the magnetic pole pad 14 is elliptical, and the contact pad 1
Although the sliding surfaces 5 and 15 are formed in a perfect circle, the shape is not limited to this, and may be any of a rectangle, a square, and a triangle. The magnetic head 13 employs a so-called planar type thin-film inductive head whose windings are parallel to the surface of the magnetic head slider 1 so that the structure can be accommodated inside such a thin head slider 1, but is not limited thereto. is not. The magnetic head slider 1 is attached to the lower surface of the slider support 10 at the tip of the suspension beam 5.

The pivot spring 16 has a base portion having a length substantially half the length thereof, and link pieces 18 extending from the left and right ends of the distal end edge of the base portion 17 toward the distal ends and approaching each other. 18 and the link piece 1
A pressing piece 19 erected between the tips of 8, 8 is integrally formed.

The link piece 18 of the pivot spring 16
Numeral 18 is bent between the base 17 and the tip, and is biased downward toward the tip, and bias 19 is bent between the link pieces 18 and 18 and biased downward toward the tip. . A triangular pressing portion 19a is provided at the center of the tip side edge of the pressing piece 19 of the pivot spring 16.
The tip of the pressing portion 19a is formed at a position corresponding to the slider supporting portion 10 of the suspension beam 5. And the pivot spring 16
The base 17 of the suspension beam 5 is sandwiched between the front end of the base plate 4 and the base end of the suspension beam 5. As a result, the slider support 10 is pressed by the pressing portion 19 a of the pivot spring 16 so that the suspension beam 5 can move downward. The flexible magnetic disk 9 is bent and an appropriate load is applied to the flexible magnetic disk 9. The pivot spring 16 is formed of an ultra-thin stainless steel having a spring constant of about 250 mgf / mm. Therefore, even if a load as low as 200 mgf is applied to the position of the center of gravity of the head slider 1 and run-out fluctuation of the flexible magnetic disk 3 occurs, The width of the load variation is as narrow as 100 to 800 mgf, and uniform contact pressure is applied to each of the contact pads 14, 15, 15. As a result, steady and unsteady run-out fluctuations of the flexible magnetic disk 3 are tracked very well, and stable recording / reproduction is realized.

The contact-type magnetic head slider of the invention of the prior application described above slides at a relatively high speed relative to a magnetic disk rotating at a high speed of, for example, 3000 rpm or more, so that the load load becomes extremely small from the viewpoint of durability. It is designed and can flexibly follow the surface shape of the magnetic disk.

[0022]

However, as compared with the above-mentioned floating magnetic head slider, the wear of the magnetic head and the magnetic disk is inevitable because the magnetic head and the magnetic disk are always in contact with each other. May lead to a decrease in gender.

The present invention has been made in order to improve the situation described above, and has an object to be suitable for use in combination with the contact type magnetic head slider, while maintaining a high recording density and a high transfer rate. Another object of the present invention is to provide a magnetic recording medium, such as a magnetic disk, which has improved durability and high reliability by minimizing wear of the magnetic head itself and wear of the magnetic head during high-speed sliding. .

[0024]

That is, the magnetic recording medium of the present invention has a multi-layer coating type in which a second layer is formed on a first layer by multi-layer coating, and at least the second layer is formed as a magnetic layer. In the magnetic recording medium, the center line average roughness Ra of the surface of the magnetic layer is 4 nm or less, and the magnetic layer has a Mohs hardness of 8 or more and an average primary particle size of 0.2 to 0.6 μm.
m of non-magnetic powder, and the protrusions on the surface of the magnetic layer based on the non-magnetic powder have a height of 10 to 50.
50 to 400 nm protrusions / 400 μm ² , height 5
The number of protrusions larger than 0 nm is 1 to 20/400 μm ² .

In the present invention, the center line average roughness Ra of the surface of the magnetic layer needs to be 4 nm or less, preferably 3.5 nm or less. Ra of this magnetic layer is 4 nm.
If it exceeds, the surface becomes too rough and the number of effective protrusions described below decreases, so that not only the effect of the invention is not sufficiently exhibited, but also the amount of spacing increases, and the electromagnetic conversion characteristics deteriorate.

In the present invention, the nonmagnetic powder to be contained in the magnetic layer has a Mohs hardness of 8 or more and an average primary particle size of 0.3.
It is required to have a thickness of 2 to 0.6 μm, preferably 0.2 to 0.4 μm. The Mohs hardness is specified to be 8 or more because, for example, a high hardness material such as DLC is being used as a component of the pad of the magnetic head slider from the viewpoint of durability. However, unless the hardness is increased, wear on the magnetic recording medium side such as a magnetic disk cannot be suppressed.

When the average primary particle diameter of the non-magnetic powder is less than 0.2 μm or more than 0.6 μm, the height of the projections described later is properly maintained without deteriorating the electromagnetic conversion characteristics. It becomes difficult.

In the present invention, the projections mainly based on the non-magnetic powder contained in the magnetic layer must exist on the surface of the magnetic layer under appropriate conditions.

That is, 50 to 400 protrusions having a height of 10 to 50 nm / 400 μm ² , preferably 50 to 20
There must be 0 protrusions / 400 μm ² and 1-20 protrusions / 400 μm ^{2 with} a height greater than 50 nm. If the height of the projections is lower than the above range or if the density is small, the magnetic head slider comes into direct contact with the ferromagnetic powder of the magnetic recording medium, and the magnetic recording medium is easily damaged. When the height of the protrusions is higher than the above range or when the density of the protrusions is high, the polishing force of the magnetic recording medium increases, and the wear rate of the magnetic head increases, leading to a decrease in reliability. In addition, the amount of spacing is increased and electromagnetic conversion characteristics are deteriorated, which is not preferable.

According to the present invention, in the multilayer coating type magnetic recording medium, as described above, the center line average roughness R
a, the Mohs hardness and average primary particle size of the non-magnetic powder contained in the magnetic layer, and the height and density of the protrusions based on the non-magnetic powder are properly specified, so that high recording density and high transfer To provide a magnetic recording medium such as a magnetic disk having high durability and high reliability, which can effectively suppress the wear of the magnetic recording medium and the magnetic head due to high-speed sliding while maintaining the rate. Is possible.

The magnetic recording medium of the present invention having such features, particularly the magnetic disk, is a contact-type magnetic recording disk system, in particular, a next-generation magnetic recording system using the contact-type head slider of the above-mentioned prior application. When it is applied to the system, its features are fully exhibited, and it greatly contributes to improving the performance of the system.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically based on embodiments.

In the magnetic recording medium of the present invention, the first layer can be a magnetic layer, but it is usually preferable to form it as a non-magnetic layer. If the first layer is a non-magnetic layer as described above, the second layer laminated thereon can be effectively smoothed or made thin. The first layer and the second layer described above may each be composed of a plurality of layers, or between the nonmagnetic support and the first layer and between the first layer and the second layer as described later. Another layer such as an undercoat layer may be interposed therebetween.

The thickness of the second layer formed as a magnetic layer in the magnetic recording medium of the present invention is 0.1 μm or more,
It is preferably 0.5 μm or less. When the thickness is within the range, the height and the number of the protrusions described above can be adjusted.

In the present invention, the amount of the non-magnetic powder to be contained in the magnetic layer is 2 parts by weight or more and less than 20 parts by weight, preferably 5 to 15 parts by weight based on 100 parts by weight of the magnetic powder. Good. When the amount is less than 2 parts by weight, the magnetic recording medium is easily damaged, and when the amount is more than 20 parts by weight, the output decreases.

Specific examples of the non-magnetic powder (Mohs hardness of 8 or more) contained in the magnetic layer in the present invention include aluminum oxide, chromium oxide (Cr ₂ O ₃ ), silicon carbide, diamond, silicon nitride, titanium nitride, titanium Carbide, titanium carbide and the like can be mentioned, and many of these are known as abrasives.

In the present invention, the number and height of the projections formed on the surface of the magnetic layer may be adjusted by including a suitable amount of the above-mentioned non-magnetic powder having an appropriate size as long as the thickness of the magnetic layer is within the above-mentioned appropriate range. Can be done by The height and the number of the protrusions can be adjusted by a conventionally known means, for example, a calendering process, a burnishing process, etc., and are not limited to the above-mentioned methods. However, regarding the size of the non-magnetic powder, even if the average primary particle diameter is less than 0.2 μm, or more than 0.6 μm, the height of the projections is kept within an appropriate range without deteriorating the electromagnetic conversion characteristics. It becomes difficult to control.

In the present invention, the shape of the nonmagnetic powder to be contained in the magnetic layer is not particularly limited, and may be, for example, any of a needle shape, a spherical shape, and a die shape. Specific examples of the non-magnetic powder include AKP-30, AKP-50, HI
T-50, HIT-55, and HIT-60 (manufactured by Sumitomo Chemical Co., Ltd.) can be mentioned. When forming the magnetic layer, these non-magnetic powders may be mixed and dispersed with the ferromagnetic powder, or may be dispersed in a binder in advance to form a coating, and then the coating is mainly mixed with the ferromagnetic powder. It may be added later to the magnetic paint composed of a binder.

The number and height of the protrusions formed on the surface of the magnetic layer can be measured by AFM (atomic force microscope). Here, measurement was carried out for four arbitrary points in an area of 10 μm square, and the projection height and the number of projections were defined by the projection amount and the number from the center line of each particle.

In the present invention, the thickness of the magnetic layer is set to 0.5
Since the thickness is set to μm or less, recording demagnetization can be reduced, and output at a short wavelength and electromagnetic conversion characteristics such as overwriting are improved. The thickness d of the magnetic layer is preferably λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ of the system.

As the binder used in the present invention, a thermoplastic resin, a thermosetting resin, a reactive resin and the like which are conventionally known for magnetic recording media can be used.
000 to 100,000 are preferred.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and acrylate-acrylonitrile copolymer. Acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer Methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-allylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like.

Examples of the thermosetting resin or the reactive resin include a phenol resin, a polyamine resin, and a urea-formaldehyde resin (refer to the revised edition of “Plastic Handbook” (Asakura Shoten)).

The polar functional group contained in the binder is -S
_{O 3 M, -OSO 3 M,} -COOM, P = O (OM) 2.
(Where M is a hydrogen atom or an alkali metal such as lithium, potassium, sodium, etc.), -N
R ₁ R ₂ , -NR ₁ R ₂ R ₃ ⁺ X ⁻ side chain type having a terminal group, and> NR ₁ R ₂ ⁺ X ⁻ main chain type (here, in the formula, R ₁ , R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group, and X ⁻ is a halogen element ion such as fluorine, chlorine, bromine or iodine or an inorganic or organic ion.). Further, a polar functional group such as —OH, —SH, —CN, or an epoxy group may be contained in the binder. The amount of these polar functional groups is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g. If the number of the functional groups is too small, the effect on the dispersion of the magnetic powder will not be exhibited. These binders can be used alone or in combination of two or more. The amount of the binder in the coating film is 1 to 200 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic powder or nonmagnetic powder.

Specific examples of the binder that can be used in the present invention include VAGH, VYHH, VMCH, and VA.
GF, VAGD, VROH, VYES, VYNC, VM
CC, XYHL, XYSG, PKHH, PKHJ, PK
HC, PKFE (Union Carbide), MR
110, MR100, MR112, MR555 and MR
104 (manufactured by Zeon Corporation), Nipporan N230
1, N2302 and N2304 (manufactured by Nippon Polyurethane Industry Co., Ltd.), Byron UR8200, UR8300,
RV530 and RV280 (manufactured by Toyobo Co., Ltd.), Diferamine 4020, 9020, 9022, and 702
0 (manufactured by Dainichi Seika Co., Ltd.), Saran F310 and F21
0 (manufactured by Asahi Kasei Corporation).

The ferromagnetic powder used for the magnetic layer in the present invention includes metals such as Fe, Co and Ni, Fe—Co, Fe
-Ni, Fe-Al, Fe-Ni-Al, Fe-Al-
P, Fe-Ni-Si-Al, Fe-Ni-Si-Al
-Mn, Fe-Mn-Zn, Fe-Ni-Zn, Co-
Ni, Co-P, Fe-Co-Ni, Fe-Co-Ni
-Cr, Fe-Co-Ni-P, Fe-Co-B, Fe
-Co-Cr-B, Mn-Bi, Mn-Al, Fe-C
alloys such as oV. Of course, for the purpose of preventing sintering or maintaining the shape during reduction, Al, Si, P,
Even if a metal element such as B or Y is added, as long as it is an appropriate amount, the effect of the present invention is not hindered.

Known ferromagnetic metal powders can be used, and the following methods can be used for producing them. (1) a method of reducing with a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen; and (2) a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles. (3) a method of thermally decomposing a metal carbonyl compound, (4) a method of adding a reducing agent such as sodium borohydride, hypophosphite, or hydrazine to an aqueous solution of a ferromagnetic metal, and (5) There is a method of evaporating metal in a low-pressure inert gas to obtain fine powder.

The ferromagnetic metal powder thus obtained can be used as it is, but usually, in order to make it chemically stable, an oxide film is formed on the particle surface by a known slow oxidation treatment. It is better to form As a method of the slow oxidation treatment, a method of immersing in an organic solvent and then sending an oxygen-containing gas to form an oxide film on the surface and then drying,
Alternatively, a method of forming an oxide film on the surface by adjusting the partial pressure of an oxygen gas and an inert gas without using an organic solvent is often used.

Further, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe
Belt compound of ₂ O ₃ and Fe ₃ O, Co-containing Fe ₃
Belt compound of γ-Fe ₂ O ₃ and Fe ₃ O ₄ containing O ₄ and Co, oxidation of CrO ₂ containing one or more metal elements such as Te, Sb, Fe, B, etc. Things can be used.

Further, hexagonal plate-like ferrites can also be used, and M-type, W-type, Y-type, and Z-type barium ferrites, strontium ferrites, calcium ferrites, lead ferrites, and those for controlling coercive force. Co-Ti, Co-Ti-Zn, Co-Ti-N
b, Co-Ti-Zn-Nb, Cu-Zr, Ni-Ti
The addition of such as can also be used. The coercive force of the ferromagnetic powder can be used in any range, but is preferably 1500 for a magnetic recording disk suitable for high-density recording.
3,000 Oe. Therefore, in the present invention, it is preferable to use ferromagnetic metal powder or hexagonal plate-like ferrite.

The specific surface area of the ferromagnetic powder used in the present invention is 20 to 80 m ² / g, preferably 30 to 70 m ² / g.
m ² / g is desirable. When the specific surface area is within this range, the ferromagnetic powder is finely divided, high-density recording is possible, and a magnetic recording medium having excellent noise characteristics can be obtained.

Further, the ferromagnetic powder used in the present invention has a major axis length of 0.05 to 0.30 μm and an axial ratio of 4 to 1.
It is preferably 5. When the major axis length is less than 0.05 μm, dispersion in the magnetic paint becomes difficult, and the major axis length is less than 0.1 μm.
If it exceeds 30 μm, the noise characteristics may deteriorate, which is not preferable. If the axial ratio is less than 5, the orientation of the ferromagnetic powder decreases and the output decreases. If the axial ratio exceeds 15, the short-wavelength signal output may decrease, which is not preferable. In the case of plate-like ferrite, the plate diameter is preferably about 0.01 to 0.5 μm and the plate thickness is about 0.001 to 0.2 μm. As the major axis length, the axial ratio, the plate diameter, and the plate thickness, an average value of 100 or more samples randomly selected from a transmission electron micrograph is adopted. The ferromagnetic powder preferably has a water content of 0.1 to 3%.

In the present invention, non-magnetic powders indispensable for the constitution of the non-magnetic layer include, for example, α-F
Non-magnetic iron oxide such as e ₂ O ₃ , goethite, rutile type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, BN, α-alumina , Β-alumina, γ-alumina, calcium sulfate, barium sulfate,
There are molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate, and the like, and these powders can be used alone or in combination.

These non-magnetic powders can be doped with an appropriate amount of impurities according to the purpose. Al, S, and S are used for the purpose of improving dispersibility, imparting conductivity, and improving color tone.
Surface treatment with compounds such as i, Ti, Sn, Sb, and Zr is also possible.

The shape of these non-magnetic powders is acicular, spherical,
Any shape such as a dice shape may be used. The specific surface area of the nonmagnetic powder is 10 to 80 m ² / g, preferably 20 to 70 m ² / g.
m ² and the size is preferably 0.5 μm or less.

Specific examples of the non-magnetic powder used for the non-magnetic layer include HIT-100, HIT-82 (manufactured by Sumitomo Chemical), DPN-250, DPN-250BX, and DPN.
-270BX, DPN-500BX, (made by Toda Kogyo),
TTO-51B, TTO-55A, TTO-55B, T
TO-55C, TTO-55S, TTO-55D, SN
-100, E270, E271, E300, E303
(Made by Ishihara Sangyo).

The nonmagnetic layer may contain carbon black such as rubber furnace, pyrolytic carbon, color black, and acetylene black, if necessary (for example, for antistatic purposes). Specific surface area is 10-1000m
² / g, DBP oil absorption 20-1000ml / 100
g, and the particle diameter is preferably 0.05 μm or less. The above-mentioned DPB oil absorption refers to the amount of dibutyl phthalate obtained by adding dibutyl phthalate to carbon black little by little, observing the state of carbon black while kneading, and finding a point forming one lump from the dispersed state. It means the amount added (ml).

Specific examples of the carbon black used in the present invention include BLACKPEARLS1000,
900, 800, 700, VULCANXC-72 (manufactured by Cabot), # 60, # 70 and # 80 (manufactured by Asahi Carbon Co., Ltd.), MA-600, # 3950B, # 375
0B, # 3250B, # 2400B, # 2300B, #
1000, # 900, # 40, and # 30 (manufactured by Mitsubishi Kasei Kogyo Co., Ltd.), CONDUCEX, SC, RAVEN7
000, 5750, 5250, 3500, 2000, 1
000, 850 (manufactured by Konlon Via Carbon), Ketjen Black ECDJ-600 (Lion Aguso Co., Ltd.)
Manufacture), Printex 90, 80, 75, 55, 45
(Made by Degussa).

When the specific surface area and the particle size of the nonmagnetic powder and carbon black are in the above ranges, the nonmagnetic layer is smoothed with the finer shape, and as a result, the magnetic disk can be smoothed. It is possible to obtain a magnetic recording medium which has excellent modulation noise characteristics and is less affected by spacing loss.

The non-magnetic powder has no magnetic cohesion and is easier to disperse than the ferromagnetic powder (except for carbon black). Difficulty dispersing the body. If the specific surface area is too small, surface smoothness that can withstand high-density recording cannot be secured.

In the present invention, it is possible to use a polyisocyanate in combination for crosslinking and curing the binder. Examples of the polyisocyanate include tolylene diisocyanate, alkylene diisocyanate, 4,4'-diphenylmethane diimocyanate, and adducts thereof. Specific examples of these isocyanates include Coronate L, Coronate HL, Coronate 2030, and Coronate 2031 (Nippon Polyurethane Industry Co., Ltd.)
Manufactured), Takenate D-102, Takenate D-110
N, Takenate D-200 and Takenate D-202 (manufactured by Takeda Pharmaceutical Co., Ltd.).

The amount of the polyisocyanate to be added to the binder is 5 to 80 parts by weight, preferably 10 to 60 parts by weight, based on 100 parts by weight of the binder. These polyisocyanates can be used in both the magnetic layer and the non-magnetic layer, or can be used in only one layer. When used in both layers, the compounding amount can be contained in each layer in an equal amount, or can be changed at an arbitrary ratio.

In the present invention, the lubricant is added to the magnetic layer and / or
Alternatively, it can be contained in a nonmagnetic layer. Examples of the lubricant include fine powders such as graphite, molybdenum disulfide, and tungsten disulfide; fatty acids having 10 to 22 carbon atoms; fatty acid esters of alcohols having 2 to 26 carbon atoms; fluorocarbons; Examples include silicone oils such as siloxane and fluoroalkylpolysiloxane, primary to tertiary amines having at least one alkyl chain having 10 to 22 carbon atoms, amino alcohols and derivatives thereof.

Of these, fatty acid esters are generally preferably and frequently used in coating type displays. Specific examples of this fatty acid ester include butyl stearate,
Isopropyl stearate, butyl oleate, 2-ethylhexyl stearate, 2-hexyldecyl stearate, heptyl stearate, butyl palmitate,
2-ethylhexyl myristate, a mixture of butyl stearate and butyl palmitate, oleyl oleate,
Various ester compounds such as butoxyethyl stearate, 2-butoxy-1-propyl stearate, diethylene glycol dioleate and glycerin oleate can be mentioned.

The amount of the lubricant to be added is preferably 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic or nonmagnetic powder. Further, in order to optimize the amount of the lubricant present on the surface of the magnetic recording medium, the lubricant may be applied after the calendering process. In this case, the lubricant is applied after being dissolved in an organic solvent, and the organic solvent is selected so as not to dissolve the binder.

When a lubricant is used for the purpose of reducing hydrolysis which is likely to occur when the magnetic disk is used under high humidity and preventing transfer to another layer during the storage period, when a lubricant is used, the fatty acid or fatty acid used as a raw material is not used. It is preferable to appropriately select an isomer structure and a branch position such as alcohol branch / straight chain and cis / trans.

In the present invention, a dispersing agent can be added in order to satisfactorily disperse the raw material powder in the magnetic layer and / or the non-magnetic layer. Specific examples of dispersants include nonionic surfactants such as polyoxyalkylene alkyl ethers and polyoxyalkylene phenol ethers; anionic surfactants such as polyoxyalkylene phosphates, sulfonic acids, and various fatty acids; There are cationic surfactants such as quaternary ammonium salts, and amphoteric surfactants. Various coupling agents such as a silane coupling agent, a titanium coupling agent, and an aluminum coupling agent can also be used as the dispersant.

These dispersants and coupling agents can be selectively used for each layer depending on the purpose, and may be used for only one of the layers.

Examples of the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyamides and polyimides. , A film, a sheet, a substrate, etc. composed of a polymer material represented by polycarbonates.

In the present invention, when forming the nonmagnetic layer and the magnetic layer, an undercoat layer may be provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer in order to improve the adhesion.
This thickness is preferably from 0.01 to 1 μm, and more preferably from 0.03 to 0.5 μm. In forming the undercoat layer, known ones conventionally used in magnetic tapes and magnetic recording disks can be used. The surface roughness of the non-magnetic support is 8 nm or less, preferably 5 nm or less in Ra measured by Maxim 3D5700 manufactured by ZYGO. Further, it is preferable that these supports have no coarse protrusions of 0.4 μm or more.
If there are coarse protrusions exceeding 0.4 μm on the non-magnetic support, even if a magnetic layer or a non-magnetic layer is applied, the shape of the magnetic layer or the non-magnetic layer extends to the surface, which causes deterioration of running durability and dropout. The surface roughness shape is controlled by the size and amount of the filler added to the support. Examples of these fillers include oxides and carbonates such as Ca, Si and Ti, and organic fine powders such as acryl.

In order to form a coating film on the non-magnetic support, both layers may be formed into a coating material, which may be coated and dried.
Solvents used in the preparation of this paint, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanone, alcohol solvents such as methanol, ethanol, propanol, butanol, isobutyl alcohol, methyl acetate, ethyl acetate, butyl acetate,
Ester solvents such as propyl acetate, ethyl lactate and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; methylene chloride; ethylene Halogenated hydrocarbon solvents such as chloride, carbon tetrachloride, chloroform and chlorobenzene are used. These organic solvents need not necessarily be of high purity, and may contain a small amount of impure components. To be specific, if the content is 20% or less, impure components such as isomers, unreacted substances, decomposed products, oxides, and moisture may be contained.

The coating is prepared by a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Raw materials such as ferromagnetic powder, non-magnetic powder, carbon black, binder, lubricant, and solvent used in the present invention may be added at the beginning or during any of the steps. Further, individual raw materials may be added in two or more steps in a divided manner.

For dispersion and kneading, conventionally known devices such as a roll mill, a ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, and an ultrasonic disperser are used.

The coating material thus produced is applied to a non-magnetic support by various known methods such as gravure coating, roll coating, blade coating, and die coating. In the production of a magnetic recording disk having a multilayer structure, a dynamic multilayer coating method using a die coater is preferred. The lip configuration of the die coater is 2
A lip method, a three lip method, a four lip method, or the like is used.

FIG. 1 is a longitudinal sectional view showing an example of the magnetic disk of the present invention. This magnetic disk 3 can be formed, for example, by the multilayer coating apparatus shown in FIG. First, the film-shaped nonmagnetic support 22 unwound from the supply roll
Is sent to the extrusion-type extrusion coater 30 while being sent in the direction of arrow A. Here, the respective paints for the lower layer 21 and the upper layer 20 are simultaneously applied on the non-magnetic support 22 in multiple layers. Extrusion coater 30 has liquid pools 25 and 26
Is provided, and each paint is supplied through the slits 31 and 32, and the nonmagnetic support 22 is wet-on-wet.
Overlap at the same time.

In the simultaneous multi-layer coating method using the wet-on-wet method, the magnetic paint of the upper layer 20 is applied on the lower layer 21 in a wet state, so that the lower layer 2
The surface of the first layer (that is, the boundary surface with the upper layer 20) is smoothed, the surface properties of the upper layer 20 are improved, and the adhesion between the two layers is also improved. As a result, the performance required for a magnetic recording medium that requires high output and low noise, particularly for high-density recording, is satisfied, film peeling is eliminated, and film strength is improved. In addition, dropout can be reduced, and reliability is improved. Note that this multi-layer coating may be sequentially performed by multi-layer coating.

On the other hand, for example, Japanese Unexamined Patent Publication No.
In the case of the wet-on-dry method disclosed in No. 3, it is necessary to select a lower layer paint having sufficient solvent resistance to the upper layer paint.

The upper and lower layers formed by the wet-on-wet multi-layer coating method have a case where a clear boundary substantially exists, and a case where the components of both layers are mixed with a certain thickness. There may be a boundary region, but the upper or lower layer excluding such a boundary region may be a magnetic layer or a non-magnetic layer. Either case is included in the scope of the present invention.

After the coating step, a non-alignment treatment is performed while the magnetic layer is not dried. This is done by passing through an AC magnetic field generator, where the frequency of the AC magnetic field is 10
It is preferable that the magnetic field strength is 50 to 500 Oe. Further, if necessary, it may be passed through a magnetic field applied in the longitudinal direction before the non-alignment treatment. This makes the surface of the magnetic disk smoother. The orientation ratio (the ratio of the squareness ratio in the longitudinal direction to the squareness ratio in the direction perpendicular thereto) of the ferromagnetic powder by the non-orientation treatment is preferably 0.9 or more, and more preferably 0.95 or more. preferable.

After the formation of the coating film, a calendar process is performed. A well-known method conventionally used for a magnetic recording medium is applied to the calendar processing. That is,
It is carried out by passing the support after coating film formation between heated rolls while applying pressure. Rolls are usually epoxy,
A heat-resistant plastic roll such as polyimide, polyamide, or polyimide amide is used, and a metal roll can also be used. Processing temperature is 70 ° C to 120 ° C
(Preferably 80 ° C to 110 ° C). The linear pressure is usually between 200 and 450 kg / cm. The calendering machine has a processing speed of 30 m / min to 500 m / min and a speed of 5 to 1 m.
The one provided with a zero-stage roll is preferable.

[0081]

EXAMPLES Hereinafter, specific examples and comparative examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 Based on the following composition, ferromagnetic powder or non-magnetic powder, an abrasive, an additive and an organic solvent were first mixed, kneaded with an extruder, and the remaining raw materials were added. Dispersion treatment was performed with a sand mill to obtain magnetic and non-magnetic paints.

<Magnetic Coating Composition> Fe-based metal ferromagnetic powder (coercive force = 170 kA / m, saturation magnetization = 150 Am ² / kg, major axis length = 0.1 μm) 100 parts by weight polyvinyl chloride resin (functional group) [-OSO ₃ K] = 6 × 10 ⁻⁵ mol / g) 15 parts by weight α-Al ₂ O ₃ (average particle size = 0.3 μm, Mohs hardness 9) 5 parts by weight Myristic acid 1 part by weight Isocetyl stearate 5 parts by weight Butyl stearate 2 parts by weight Methyl ethyl ketone 150 parts by weight Cyclohexanone 150 parts by weight

<Non-magnetic coating composition> Acicular α-Fe ₂ O ₃ (specific surface area = 53 m ² / g, major axis length = 0.15 μm, acicular ratio = 11) 100 parts by weight carbon black (manufactured by Lion Agzo, Inc.) Ketjen Black EC) 15 parts by weight Polyvinyl chloride resin (functional group [-OSO ₃ K] = 6 × 10 ⁻⁵ mol / g) 25 parts by weight Myristic acid 1 part by weight Isocetyl stearate 5 parts by weight Butyl stearate 2 Parts by weight methyl ethyl ketone 150 parts by weight cyclohexanone 150 parts by weight

Next, 3 parts by weight and 5 parts by weight of a polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) were added to the magnetic paint and the non-magnetic paint, respectively.
62 μm thick PET using a die coater shown in
(Polyethylene terephthalate) Coating was performed on a film so that the thickness was 0.2 μm and 1.5 μm, respectively.
Then, while the coating film was not dried, non-orientation treatment was performed under the conditions of an alternating magnetic field of 150 Oe and a frequency of 60 Hz. After drying, 5
A smoothing treatment was performed at 90 ° C. and 200 kg / cm using a calender in a stage, and a 3.5-inch diameter disk was punched out. This was annealed at 60 ° C. for 48 hours, and the obtained floppy disk was stored in a cartridge.

Examples 2 to 10 Except that the conditions of the nonmagnetic powder were changed as shown in Table 1,
A 3.5-inch floppy disk was obtained by the same composition and method as in Example 1.

Example 11 The same polyvinyl chloride resin as in Example 1 was used as a binder.
0 parts by weight and a polyurethane resin (functional group [—SO ₃ N
a) = 15 × 10 ⁻⁵ mol / g) except that 5 parts by weight were used.
A 5 inch floppy disk was obtained.

Comparative Examples 1 to 8 3.5 inch floppy disks were obtained by the same composition and method as in Example 1 except that the conditions for the nonmagnetic powder were changed as shown in Table 1.

Examples 12 to 16 3.5 inch floppy disks were obtained by the same composition and method as in Example 1 except that the conditions for the nonmagnetic powder were changed as shown in Table 2.

Comparative Examples 9 and 10 3.5 inch floppy disks were obtained by the same composition and method as in Example 1 except that the conditions for the nonmagnetic powder were changed as shown in Table 3.

[0091]

[Table 1]

[Table 2]

Next, with respect to the floppy disks manufactured in the above Examples and Comparative Examples, the electromagnetic conversion characteristics and the head wear rate were measured, and the still mode sliding test was performed.

First, in order to measure the electromagnetic conversion characteristics, a spin stand comprising a motor whose rotation speed can be controlled, a jig for mounting the magnetic head at a desired location, and a circuit for detecting signal input / output. A type of measuring machine was used. The number of rotations of the motor was 4800 rpm, and the measurement position was 20 mm from the center of the disk. As the magnetic head, a thin film head having a track width of 6 μm is used.
It is covered with the DLC pad formed by the method. The slider on which the pad is mounted is brought into contact with the magnetic recording disk, and the baseline (= G
ND) to peak amplitude, ISTAA and ISTA
Pulse width at half the level of A, it was measured PW _50. Generally, ISTAA is used as an indicator of S / N and PW ₅₀
Is very sensitive to the distance between the magnetic head and the medium, so-called magnetic spacing, and is therefore used as an indicator of the state of contact. ISTAA and PW ₅₀ are the values of Example 1 each being 0
It was expressed as a relative value as dB, 100%.

For each tape, a non-contact type surface roughness meter (Maxim3D5700, Zy
The center line average roughness Ra was measured by a Go company.

The reliability was evaluated as follows using the same spin stand type measuring device and magnetic head slider as described above. That is, a sliding test was performed for a predetermined time in a so-called seek mode in which the slider reciprocated within a predetermined range on the rotating magnetic disk, and the head wear rate at this time was examined. The moving range of the slider was 10 to 20 mm from the center, and the range was reciprocated at 5 Hz. The disk rotation speed was 3600 rpm, the test environment was normal temperature and normal humidity, and the sliding time was 48 hours. Also,
A sliding test is performed in a so-called still mode in which the slider is continuously slid while fixing the position of the slider, and the change with time of ISTAA is examined. The test was terminated.
The surface condition of the magnetic disk at the end of the test was visually observed. The rotation speed of the magnetic disk is 3600 rpm
m, the test environment was normal temperature and normal humidity. Tables 3 and 4 show the test results.

[Table 3] ○: no scratch, △: intermittent scratch, ×: continuous circumferential scratch

[Table 4]

[0096] Table 3 and Table 4, the floppy disk in the embodiments of the present invention has a high reproducing output at all surface smoothness, PW ₅₀ is low. Also, the head wear rate is low and the durability of the still mode is excellent. The floppy disks of Comparative Examples 1 and 2 in which the average particle size of the non-magnetic powder is smaller than 0.2 μm have no protrusions having a height of 50 nm or more and exhibit high electromagnetic conversion characteristics, but have poor durability in a still mode. The average particle size of the non-magnetic powder is 0.6
The floppy disks of Comparative Examples 3 and 4 larger than μm have a high wear rate of the magnetic head and are inferior in reliability. Moreover, deterioration of the PW ₅₀ because the surface is roughened is observed. The floppy disk of Comparative Example 5 is an example in which the two types of projections do not satisfy the conditions of the present invention, and have poor still durability. The floppy disk of Comparative Example 6 contained a large amount of nonmagnetic powder, had a Ra of more than 4 nm, and had a high frequency of protrusions.
The durability has deteriorated. In addition, ISTAA, PW ₅₀ also both bad. Since the floppy disks of Comparative Examples 7 and 8 containing a nonmagnetic powder having a Mohs' hardness of 8 or less have a low relative strength to DLC, media damage in the still mode occurs early. In the floppy disk of Comparative Example 9, since the number of surface projections having a height of 10 to 50 nm exceeds 400 and Ra exceeds 4 nm, the wear of the magnetic head becomes remarkable and the durability is deteriorated. Comparative Example 1
0 floppy disk has an average primary particle diameter of 0.2 μm
Since there is no smaller protrusion having a height of 50 nm or more, the durability is deteriorated.

[0097]

As is apparent from the above, according to the present invention, in the multilayer coating type magnetic recording medium, the center line average roughness Ra of the surface of the magnetic layer and the Mohs hardness of the non-magnetic powder contained in the same layer. Since the average primary particle size, the height and the density of the protrusions on the surface of the magnetic layer based on the nonmagnetic powder are specified to appropriate values, the magnetic recording medium can be maintained while maintaining a high recording density and a high transfer rate. Wear due to high-speed sliding and wear of the head can be effectively reduced, and durability and reliability can be improved. When applied to the next-generation contact magnetic recording disk system proposed by the present inventor, the magnetic recording medium having such characteristics, particularly the magnetic disk, can fully exhibit the characteristics and improve the performance of the system. Can make a great contribution to

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magnetic disk according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a multilayer coating apparatus used for manufacturing a magnetic disk.

FIG. 3 is a perspective view of a flexible magnetic disk head slider attached to the tip of the HGA.

FIG. 4 is a cross-sectional view showing a contact state between a magnetic head attached to a slider and a flexible magnetic disk.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic head slider, 3 ... Flexible magnetic disk, 5 ... Suspension beam, 13 ... Magnetic head,
14 magnetic pad, 20 upper layer, 21 lower layer, 22 non-magnetic support

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Hatsue Koishikawa 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kazuo Goto 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F term (reference) 5D006 BA10 BA19 DA02 FA00 FA02

Claims (5)

[Claims] 1. A multilayer coating type magnetic recording medium in which a second layer is formed on a first layer by a multilayer coating and at least the second layer is formed as a magnetic layer, wherein a center line of a surface of the magnetic layer is provided. The magnetic layer has an average roughness Ra of 4 nm or less, a Mohs hardness of 8 or more, and an average primary particle size of 0.2 to 0.1.
6 μm of nonmagnetic powder, and the height of the protrusions on the surface of the magnetic layer based on the nonmagnetic powder is 10 to 10 μm.
50nm projections 50 to 400 pieces / 400 [mu] m ^2, 50nm larger protrusion height is 1-20 / 400 [mu] m ²
A magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the first layer is formed as a non-magnetic layer. 3. The method according to claim 1, wherein the magnetic layer has a thickness of 0.1 μm or more and 0.5 μm or more.
The magnetic recording medium according to claim 1, having a thickness of not more than m. 4. The magnetic recording medium according to claim 1, wherein the compounding amount of the nonmagnetic powder contained in the magnetic layer is at least 2 parts by weight and less than 20 parts by weight based on 100 parts by weight of the magnetic powder. . 5. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is configured on a magnetic disk.