JPH103643A - Disk-shaped magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve electromagnetic conversion characteristics and more particularly high- density recording characteristics by providing the surface of a nomnagnetic base layer with a soft magnetic layer and a ferromagnetic layer formed by dispersing fine ferromagnetic hexagonal ferrite powder having a specific thickness into a binder. SOLUTION: This disk-shaped magnetic recording medium is formed of a double layered structure composed of the soft magnetic layer and the ferromagnetic layer and is provided with the soft magnetic layer and the ferromagnetic layer formed by dispersing fine ferromagnetmc hexagonal ferrite powder into the binder on the nonmagnetic base layer. The ferromagnetic layer is magnetically oriented in a perpendicular direction and the thickness thereof is specified to <=0.5μm. In addition, glossiness is measured in an arbitrary place and the dependence on the measurement direction which is the difference in the glossiness between the max. value and the min. value is specified in a range of 0 to 5% of an index. On the other hand, the soft magnetic layer is specified in coercive force Hc to <=200Oem, more preferably, 0.1 to 100Oe. If Hc is larger than this range, recording magnetization remains. Further, the saturation magnetic flux density Bs is specified to >=1500G, more preferably >=2000 to <=500G. If the density is smaller than this range, the magnetic flux passing the ground surface layer decrease. As a result, the electromagnetic conversion characteristics and more particularly the high-density characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk-shaped magnetic recording medium for high-density recording, which has a ferromagnetic layer and a soft magnetic layer, and contains a hexagonal ferrite fine powder in the uppermost layer.

[0002]

2. Description of the Related Art In the field of magnetic disks, 2 MB MF-2HD floppy disks using Co-modified iron oxide have been standardly mounted on personal computers. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of floppy disks.

Conventionally, a magnetic recording medium has a magnetic layer obtained by dispersing iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder in a binder on a non-magnetic support. Is widely used. Among them, ferromagnetic metal fine powder and hexagonal ferrite fine powder are known to have excellent high density recording characteristics. As a large-capacity disk using a ferromagnetic metal fine powder having excellent high-density recording characteristics, 10
4 MB as a large capacity disk using MB MF-2TD, 21 MB MF-2SD or hexagonal ferrite
MF-2ED, 21 MB floptical, etc., but were not sufficient in capacity and performance. Under such circumstances, many attempts have been made to improve the high-density recording characteristics.

As magnetic materials having excellent high-density recording characteristics, JP-A-61-217936 and JP-A-61-273735.
The bulletin proposes a hexagonal ferrite magnetic material. Hexagonal ferrite magnetic material is promising as a magnetic material used for magnetic recording media for high-density recording due to its small particle size, flat shape and easy axis of magnetization perpendicular to the plate surface. Have been watched.

Further, it has been disclosed in Japanese Patent Application Laid-Open Nos. 4-12312 and 62-2 that the self-demagnetization can be further reduced by orienting the hexagonal ferrite magnetic substance in the in-plane vertical direction.
JP-A No. 08415, JP-A-60-212817, JP-A-1-251427, and JP-A-1-251424 disclose examples in which two or more magnetic layers are further provided and a hexagonal ferrite vertically oriented in the upper layer is used. Bulletin, JP-A 1-2514
No. 26, JP-A-59-129935, JP-A-64
No. 79930, JP-A-64-55732 and JP-A-59-77628. However, sufficient characteristics have not yet been obtained.

In order to solve such a problem, an attempt has been made to form a soft magnetic metal thin film or particle coating film having a low coercive force and a high magnetic permeability as an underlayer, and to provide a coating layer containing hexagonal ferrite thereon. No. 56-98718, Japanese Unexamined Patent Publication No.
9-94231, JP-A-59-167843,
It is disclosed in JP-A-62-180522. However, these characteristics are no longer sufficient for the high-density recording required today.

On the other hand, a disk-shaped magnetic recording medium comprising a thin magnetic layer and a functional non-magnetic layer has recently been developed.
0MB class floppy disks have appeared. Japanese Patent Application Laid-Open No. 5-109061 shows these features.
Japanese Patent Application Laid-Open No. Hei 5-290354 discloses that a magnetic layer having a Hc of 1400 Oe or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing conductive particles are provided. Has been proposed in which the variation in thickness is within ± 15% and the surface electric resistance is regulated.

However, with the rapid increase in the density of disk-shaped magnetic recording media, it has become difficult to obtain satisfactory characteristics even with such a technique. In recent years, as a perpendicular magnetic recording medium that has been proposed, a soft magnetic layer (a magnetic layer using a magnetic material most suitable for a magnetic head having an extremely low Hc) is provided as a lower layer, and a perpendicular magnetization film is provided thereon, so that the flow of magnetic field lines is reduced. 2. Description of the Related Art A magnetic recording medium for high-density recording with an optimized path is known.

[0009] At present, the perpendicular magnetic recording medium has been mainly developed in the form of a tape medium, and no magnetic disk is heavily weighted. In a disk-shaped magnetic recording medium having a multilayer structure of a soft magnetic layer and a ferromagnetic layer, there is a problem that it is difficult to measure the degree of magnetic orientation. That is, in order to improve the density of a disk-shaped magnetic recording medium, the degree of magnetic orientation can be measured by a simple means, and a means for controlling the degree of orientation which contributes to the density increase has been desired.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a disk-shaped magnetic recording medium in which the electromagnetic conversion characteristics, especially the high-density recording characteristics, are significantly improved.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain a disk-shaped magnetic recording medium having good electromagnetic conversion characteristics, and as a result, the object of the present invention is as follows. The inventors have found that excellent high-density recording characteristics can be obtained, and have accomplished the present invention. That is, in a disk-shaped magnetic recording medium in which a soft magnetic layer and a ferromagnetic layer formed by dispersing a ferromagnetic hexagonal ferrite fine powder in a binder on a non-magnetic support in this order, the thickness of the ferromagnetic layer is reduced. 0.5
This is achieved by a disk-shaped magnetic recording medium characterized in that the measurement direction dependence of the glossiness at any position of the ferromagnetic layer is within 5%.

The object of the present invention can be more effectively achieved when the ferromagnetic layer is magnetically oriented in the vertical direction. The soft magnetic layer in the magnetic recording medium of the present invention has a Hc (coercive force) of 200 Oe or less, preferably 0.1 to 100 Oe, and a Bs (saturation magnetic flux density) of 1500 G.
The above is preferably 2000 G or more and 5000 G or less. If Hc is larger than the above value, the recording magnetization remains in the underlayer, and a phase shift of the magnetization occurs in the magnetic layer, which is not preferable. B
If s is smaller than the above value, the magnetic flux passing through the underlayer decreases, which is not preferable. Here, Hc uses the higher value in the longitudinal and vertical directions.

In the present invention, the measurement direction dependence of glossiness (hereinafter also referred to as “glossiness difference”) is within 5% at an arbitrary position of the ferromagnetic layer, but the glossiness difference is a digital glossiness. Using a meter (GK-45D manufactured by Suga Test Instruments Co., Ltd.), measurement was performed at eight locations at equal intervals on the circumference of a half of the disk radius, and the measurement direction was changed every 45 degrees from eight directions. Using the following equation obtained from the difference between the maximum value and the minimum value as an index, if this value is within 5%, the difference in glossiness between any two points in the ferromagnetic layer will be within 5%. You can think about it.

Gloss difference (%) = maximum value−minimum value The gloss difference in the present invention is preferably in the range of 0 to 5%. [Relationship between constituent features and effects] The reason why the present invention brings about such effects is not clear, but is considered as follows.

In short wavelength recording, the signal recording depth becomes shallow. By providing the soft magnetic layer as an underlayer of the ferromagnetic layer, a magnetic pole generated below the ferromagnetic layer when there is no underlayer can be short-circuited, and the demagnetizing field can be reduced. In order to exhibit such an effect of the underlayer, it is necessary to reduce the thickness of the upper layer according to the recording wavelength. Also, when the recording depth is short in short wavelength recording, separation loss due to surface roughness has a large effect, and when the surface roughness is large, the distance between the head and the medium increases and the effect of the underlayer is also lost. Seem.

On the other hand, in the case of a disk-shaped magnetic recording medium, it is necessary to obtain a constant output over the entire circumference of the disk, and this can be achieved by setting the orientation ratio to 0.85 or more, as disclosed in Japanese Patent Application Laid-Open No. Hei 5-109061. Is shown in However, in recent high-density recording, a constant output may not be obtained even when the orientation ratio is 0.85 or more. Although the cause is not clear, it is considered that the surface roughness is not uniform in the circumferential direction. In particular, in the case of the present invention, the surface roughness affects the effect of the soft magnetic layer.

Although the glossiness is originally an index of the surface roughness, it is presumed that the glossiness is affected by the orientation direction and agglomeration of the magnetic particles because the amount of reflected light is measured. By making the gloss constant at any location regardless of the measurement direction, not only the surface roughness becomes uniform, but also the orientation and aggregation of the magnetic material particles become uniform, and the magnetic characteristics become uniform, so that one round of the disk It is considered that a constant output can be obtained over the range.

Since the hexagonal ferrite is plate-like, when the thickness of the ferromagnetic layer is small, the easy axis tends to be oriented in the in-plane vertical direction regardless of the orientation. The object of the present invention can be achieved regardless of the orientation direction of the ferromagnetic layer, that is, the longitudinal direction, the non-oriented state, and the random direction. In order to obtain the magnetic recording medium of the present invention, in particular, the dependence of the glossiness in the measurement direction must be 5
%, There are various methods, but the following method is particularly effective.

For example, a coating method such as a simultaneous multi-layer coating method described below, which can obtain a smooth coating surface even when the ferromagnetic layer is a thin film, is employed. In producing a magnetic coating solution, a high-load dispersion method is employed. That, using a counter-magnetism counter-magnetism of 3000G or more, the magnetic orientation of the magnetic layer is oriented in the vertical direction of the magnetic layer and the coating speed during coating and drying,
Adjust the drying air temperature and drying air volume to dry the coating film in the magnet zone, and adjust the shape and size of the ferromagnetic hexagonal ferrite fine powder and the powder used for the soft magnetic layer that are optimal for the above. And selecting a binder used for the ferromagnetic layer and the soft magnetic layer, and using a dispersant to enhance the dispersibility of ferromagnetic hexagonal ferrite.

The above method is described in detail below. [Description of Hexagonal Ferrite Fine Powder] Examples of the hexagonal ferrite fine powder contained in the ferromagnetic layer of the present invention include various substitution products of barium ferrite, strontium ferrite, lead ferrite, and calcium ferrite, and Co substitution products. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. , Other than predetermined atoms, Al, Si,
S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, P
d, Ag, Sn, Sb, Te, Ba, Ta, W, Re,
Au, Hg, Pb, Bi, La, Ce, Pr, Nd,
It may contain atoms such as P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Ti,
Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
n, Nb-Zn-Co, Sb-Zn-Co, Nb-Zn
And the like can be used. material·
Some production methods contain specific impurities.

The particle size is 10 to 200 nm in hexagonal plate diameter,
Preferably it is 20 to 100 nm. When reproducing with a magnetoresistive head, it is necessary to reduce noise, and the plate diameter is 40
nm or less is preferable, but if it is 10 nm or less, stable magnetization cannot be expected due to thermal fluctuation. Above 200nm the noise is high,
Neither is suitable for high-density magnetic recording. Plate ratio (plate diameter /
1 to 15 is desirable. Preferably it is 2-7. When the plate ratio is small, the filling property in the ferromagnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area of this particle size range by the BET method is 10 to 2
00 m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. Crystallite size is 50-45
0 °, preferably 100-350 °. Particle plate diameter
Generally, the narrower the thickness distribution, the better. Although it is difficult to make a numerical value, it can be compared by randomly measuring 500 particles from a particle TEM photograph. Although the distribution is often not a normal distribution, when calculated and expressed as a standard deviation with respect to the average size, σ /
Average size = 0.1-2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. The coercive force Hc measured on the magnetic material can be made up to about 500 Oe to 5000 Oe.

A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Usually about 800 Oe to 4000 Oe, preferably 1500 Oe or more,
It is 3500 Oe or less. When the saturation magnetization of the head exceeds 1.4 Tesla, it is preferable to set it to 2000 Oe or more. Hc can be controlled by particle size (plate diameter / plate thickness), kind and amount of contained element, substitution site of element, particle generation reaction condition and the like. The saturation magnetization as is 40 emu / g to 80 emu / g. The higher the value of σs, the better, but the smaller the fine particles, the lower the tendency. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic substance, the surface of the magnetic substance particles is treated with a substance suitable for the dispersion medium and the binder. As the surface treatment agent, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides of Si, Al, P, etc., various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% by weight based on the magnetic material. The PH of the magnetic material is also important for dispersion. Usually 4-12
There is an optimum value depending on the dispersion medium and the polymer depending on the degree, but about 6 to 10 is selected from the chemical stability and storage stability of the medium.
Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the binder, but usually 0.01 to 2.0% by weight is selected. As a method for producing hexagonal ferrite, there are a glass crystallization method, a coprecipitation method, a hydrothermal reaction method and the like, but the present invention does not select a production method.

[Description of Soft Magnetic Layer] As the soft magnetic powder used in the soft magnetic layer of the present invention, Fe powder, Ni powder, C
o powder, magnetite powder, permalloy powder, sendust powder,
Mn-Zn ferrite powder, Ni-Zn ferrite powder, C
u-Zn ferrite powder and the like. These powders may be acicular, granular, or plate-shaped, but are preferably granular in order to reduce Hc. These soft magnetic powders include Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, B, Ge, and Nb.

When the specific surface area of these soft magnetic powders is represented by S _BET , it is 10 to 100 m ² / g, preferably 40 to 100 m ² / g.
70 m ² / g. 10 m ² / g or less and 100 m
If it is ² / g or more, it is difficult to obtain good surface properties, which is not preferable. The average particle diameter is 0.01 μm or more and 1 μm or less, the bulk density is 0.4 or more and 1.5 or less, and the adsorbed moisture is 0.1% or more and 2 or more.
%, Oil absorption using DBP is 5-100ml / 100g, p
H is preferably 3 or more and 10 or less. The surfaces of these powders are Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Sn
It is preferable to perform a surface treatment with O ₂ , Sb ₂ O ₃ , or ZnO. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ ,
TiO ₂ and ZrO ₂ , more preferably Al
₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination.

By mixing carbon black in the soft magnetic layer, it is possible to lower the surface electric resistance Rs and the light transmittance, which are known effects, and to obtain a desired micro-Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. Examples of carbon black include furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like.

Further, an organic powder can be added to the soft magnetic layer according to the purpose. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. As the production method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

A binder resin, a lubricant, a dispersant,
Additives, solvents, dispersion methods and the like can be applied to those of the ferromagnetic layer described below. In particular, with respect to the amount and type of the binder resin, the amount of the additive and the type of the dispersant, and the type of the dispersant, a known technique regarding the ferromagnetic layer can be applied. [Description of Binder] The binder, lubricant, dispersant, additive, solvent, dispersing method and the like of the ferromagnetic layer can be applied to the soft magnetic layer of the present invention. In particular, with respect to the amount and type of the binder, the amount of the additive and the type of the dispersant, and the type of the dispersant, a known technique regarding the ferromagnetic layer can be applied.

As the binder used in the ferromagnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., the number average molecular weight is 1,000 to 200,000, preferably 10,000 to
100,000 and a degree of polymerization of about 50 to 1,000.

Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin,
Epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, polyester polyol
And mixtures of polyurethane and polyisocyanate, and mixtures of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resins,
A combination of at least one selected from vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer and a polyurethane resin, or polyisocyanate to these. The combination is given.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, COO is required to obtain better dispersibility and durability.
M, SO ₃ M, OSO ₃ M, P = O (OM) ₂ , OP
ＯO (OM) ₂ , where M is a hydrogen atom or an alkali metal base, OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, SH, CN, etc. It is preferable to use one obtained by introducing one or more polar groups by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, ZEON Corporation MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9,7209, Toyobo Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Daiferamine 4020, 5020, 5 manufactured by Dainichi Seika
100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Co., Ltd., MX5004, Samprene S manufactured by Sanyo Kasei Co., Ltd.
P-150 and Saran F310, F210 manufactured by Asahi Kasei Corporation.

The binder used for the soft magnetic layer and the ferromagnetic layer of the present invention is in the range of 5 to 50% by weight, preferably 10 to 30% by weight, based on the soft magnetic powder or the fine hexagonal ferrite powder. Used. 5 to 30% by weight when using a vinyl chloride resin, 2 when using a polyurethane resin.
-20% by weight and polyisocyanate in a range of 2-20% by weight are preferably used in combination.
For example, when head corrosion occurs due to a small amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate. In the present invention, when polyurethane is used, the glass transition temperature is -5.
0 to 150 ° C, preferably 0 to 100 ° C, elongation at break of 100 to 2000%, and breaking stress of 0.05 to 10 kg /
cm ² and the yield point are preferably 0.05 to 10 kg / cm ² .

The magnetic recording medium of the present invention comprises two or more layers. Therefore, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate, or the other resin in the binder, the molecular weight of each resin forming the ferromagnetic layer, the amount of the polar group, or the amount described above. Of course, it is possible to change the physical properties of the resin between the soft magnetic layer and the ferromagnetic layer as necessary, and rather it should be optimized for each layer,
Known techniques for the multilayer magnetic layer can be applied. For example, when the amount of the binder is changed in each layer, it is effective to increase the amount of the binder in the ferromagnetic layer in order to reduce the abrasion on the surface of the ferromagnetic layer. The flexibility can be increased by increasing the amount of the binder in the soft magnetic layer.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate;
Products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL,
CORONATE 2030, CORONATE 2031, Millionet
MR, Millionet MTL, Takeda Pharmaceutical, Takene
D-102, Takenet D-110N, Takenet D
-200, Takenet D-202, manufactured by Sumitomo Bayer,
Desmodur L, Desmodur IL, Desmodur
N, Desmodur HL, etc. These can be used alone or in combination of two or more by utilizing the difference in curing reactivity.

[Description of Carbon Black and Abrasive] Carbon black used in the soft magnetic layer and the ferromagnetic layer of the present invention is a furnace black for rubber, a thermal black for rubber, and a color black.
Black, acetylene black, and the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle diameter is 5 nm to 300
nm, pH 2-10, water content 0.1-10%, tap density 0.1-1 g / cc. Specific examples of carbon black used in the present invention include BLACKPEARLS 2000, 130 manufactured by Cabot Corporation.
0, 1000, 900, 905, 800, 700, VU
LCANXC-72, manufactured by Asahi Carbon, # 80, # 6
0, # 55, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo Co., Ltd., # 2
400B, # 2300, # 900, # 1000, # 3
0, # 40, # 10B, manufactured by Columbian Carbon, C
ONDUCTEX SC, RAVEN 150, 50,
40, 15, RAVEN-MT-P, manufactured by EC Japan, Ketjen Black EC, and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, the amount of each magnetic layer relative to the magnetic material is 0.1 to 3%.
Preferably, it is used at 0% by weight. Carbon black has functions such as antistatic properties of the layer, reduction of the coefficient of friction, provision of light-shielding properties, and enhancement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination between the ferromagnetic layer and the soft magnetic layer, and exhibit the above-mentioned properties such as particle size, oil absorption, conductivity and pH. It is, of course, possible to use them properly depending on the purpose, and rather, they should be optimized in each layer. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

As the abrasive used in the ferromagnetic layer of the present invention, α-alumina, β-alumina having an α conversion of 90% or more,
Silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Known materials mainly having a Mohs hardness of 6 or more such as corundum, artificial diamond, silicon nitride, silicon carbide titanium, carbide, titanium oxide, silicon dioxide, boron nitride, etc. are used alone or in combination. In addition, a composite of these abrasives (abrasives surface-treated with other abrasives)
May be used. These abrasives may contain compounds or elements other than the main component, but the main component is 90%.
If it is above, the effect is not changed. The particle size of these abrasives is preferably 0.01 to 2 μm, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow.
Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as needed, or to achieve the same effect by widening the particle size distribution even with a single abrasive. Tap density 0.3-2g / cc, water content 0.1-5
%, The pH is preferably ^{2 to} 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specifically, AKP-12, AKP-15, AKP-20 manufactured by Sumitomo Chemical Co., Ltd.
AKP-30, AKP-50, HIT20, HIT-3
0, HIT-55, HIT60, HIT70, HIT8
0, HIT100, manufactured by Reynolds, ERC-DBM,
HP-DBM, HPS-DBM, Fujimi Abrasives, W
A10000, Uemura Kogyo Co., Ltd., UB20, Nippon Kagaku Kogyo Co., Ltd., G-5, Chromex U2, Chromex U1,
Toda Kogyo, TF100, TF140, Ibiden, Beta Random Ultra Fine, Showa Mining,
B-3 and the like. These abrasives can be added to the soft magnetic layer as needed. By adding to the soft magnetic layer, the surface shape can be controlled, and the state of protrusion of the abrasive can be controlled. The particle size and amount of the abrasive added to the ferromagnetic layer and the soft magnetic layer should, of course, be set to optimal values.

[Description of Additives] As the additives used in the ferromagnetic layer and the soft magnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone having polar groups, fatty acid modified silicone,
Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenyl ether, phenylphosphonic acid, aminoquinones , Various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof,
A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and metal salts thereof (such as Li, Na, K, and Cu) or 12 to 24 carbon atoms; 22 monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols (which may contain an unsaturated bond or may be branched), alkoxyalkoxy having 12 to 22 carbon atoms , Monobasic fatty acids having 10 to 24 carbon atoms (which may contain unsaturated bonds or may be branched) and monovalent, divalent, trivalent, tetravalent, pentavalent having 2 to 12 carbon atoms Mono- or di-fatty acid esters or tri-fatty acid esters, or monoalkyl ethers of alkylene oxide polymers comprising any one of hexahydric alcohols (which may contain an unsaturated bond or may be branched). Ter fatty acid esters, carbon 8-22 fatty acid amides, 8 carbon atoms
~ 22 aliphatic amines, and the like.

Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and isostearic acid. No. Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. Examples include 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, and alcohols such as oleyl alcohol, stearyl alcohol, and lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums Or a cationic surfactant such as a sulfonium, a carboxylic acid, a sulfonic acid, a phosphoric acid, a sulfate group, a phosphate group,
Anionic surfactants containing acidic groups such as amino acids,
Aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohol, alkylbedine-type amphoteric surfactants, and the like can also be used. For these surfactants,
It is described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposed products, oxides, and the like in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

Each of these lubricants and surfactants used in the present invention has a different physical action.
The type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose.
Controlling bleeding to the surface using fatty acids with different melting points in the soft magnetic layer and ferromagnetic layer, controlling bleeding to the surface using esters with different boiling points, melting points and polarities, adjusting the amount of surfactant Thus, it is considered that the stability of the coating is improved, and the amount of the lubricant added is increased in the intermediate layer to improve the lubrication effect, and it is a matter of course that the present invention is not limited to the examples shown here. Generally, the total amount of the lubricant is selected in the range of 0.1% by weight to 50% by weight, preferably 2% by weight to 25% by weight based on the magnetic substance or the soft magnetic powder.

All or a part of the additives used in the present invention may be added at any step in the production of magnetic and non-magnetic paints. There are a case where it is added in a kneading step using a body, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the ferromagnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the ferromagnetic layer after calendaring or after slitting.

[Description of Solvent] The organic solvent used in the present invention may be any desired ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol, and the like. Propanol,
Alcohols such as butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol; esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate and glycol acetate; and glycols Glycol ethers such as dimethyl ether, glycol monoethyl ether, dioxane, etc., aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin And chlorinated hydrocarbons such as dichlorobenzene, N, N-dimethylformamide, hexane and the like. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less. The type of the organic solvent used in the present invention may be the same for the ferromagnetic layer and the soft magnetic layer, but it is preferable to use a solvent having a high surface tension (such as cyclohexanone or dioxane) for the soft magnetic layer to improve the coating stability. Specifically, it is important that the arithmetic average value of the surface tension of the upper solvent composition does not fall below the arithmetic average value of the lower solvent composition. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong.
It is preferable that a solvent having a dielectric constant of 15 or more be contained in an amount of 50% by weight or more. Further, the dissolution parameters are preferably from 8 to 11.

[Description of Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the nonmagnetic support has a thickness of 2 to 100 μm, preferably 10 to 80 μm. An undercoat layer for improving adhesion may be provided between the nonmagnetic flexible support and the soft magnetic layer or the ferromagnetic layer. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. Although the present application is a double-sided magnetic layer disk-shaped medium in which a soft magnetic layer and a ferromagnetic layer are usually provided on both sides of a support, it may be provided on only one side. In this case, a back coat layer may be provided on the side opposite to the soft magnetic layer and the ferromagnetic layer in order to obtain effects such as antistatic and curl correction. This thickness is 0.1 to 4 μm, preferably 0.3 to 2.0 μm. These undercoat layers,
A known backcoat layer can be used.

The thickness of the ferromagnetic layer of the medium of the present invention is optimized depending on the saturation magnetization of the head to be used, the head gap length, and the band of the recording signal.
m or more and 0.5 μm or less, preferably 0.05 μm
0.4 μm or less, more preferably 0.1 μm or more
0.3 μm. The ferromagnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the soft magnetic layer as the underlayer of the medium according to the present invention is 0.2 μm or more and 5.0 μm or less, preferably 0.5 μm or more and 3.0 μm or less, and more preferably 1.
It is 0 μm or more and 2.5 μm or less. [Description of Support] Non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, and the like. Polyamide-imide, polysulfone,
Known films such as polyaramid, aromatic polyamide and polybenzoxazole can be used. It is preferable to use a high-strength support such as polyethylene naphthalate or polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. In addition, an aluminum or glass substrate can be used as the support of the present invention.

In order to achieve the object of the present invention, as a nonmagnetic support, the center plane average surface roughness measured by the Mirau method of TOPO-3D manufactured by WYKO Co. is 20 nm or less for SRa,
It is necessary to use one having a thickness of preferably 10 nm or less, more preferably 5 nm or less. These nonmagnetic supports not only have a small center plane average surface roughness, but also
It is preferable that there is no such coarse protrusion. The surface roughness can be freely controlled by the size and amount of the filler added to the support as required. Examples of these fillers include Ca, Si, and Ti.
In addition to oxides and carbonates such as, for example, acryl-based organic fine powders.

The maximum height SRmax of the support is 1 μm or less,
Ten point average roughness SRz is 0.5 μm or less, center plane peak height SRp is 0.5 μm or less, center plane valley depth SRv is 0.5
μm or less, the center plane area ratio SSr is preferably 10% or more and 90% or less, and the average wavelength Sλa is preferably 5 μm or more and 300 μm or less. In order to obtain the desired electromagnetic conversion characteristics and durability, the surface projection distribution of these supports can be arbitrarily controlled by a filler. Each of the supports having a size of 0.01 μm to 1 μm has a size of 0 to 2000 per 0.1 mm 2. Can be controlled in a range of

F-5 of non-magnetic support used in the present invention
The value is preferably 5 to 50 kg / mm ^TwoAnd also of the support
The heat shrinkage at 100 ° C. for 30 minutes is preferably 3% or less.
More preferably 1.5% or less, heat shrinkage at 80 ° C. for 30 minutes
The rate is preferably 1% or less, more preferably 0.5% or less.
Below. Breaking strength is 5-100Kg / mm^Two, Elastic modulus
Is 100 to 2000 kg / mm^TwoIs preferred. Thermal expansion
Tensile coefficient is 10^-Four-10 ^-8/ ° C, preferably 10^-Five
-10^-6/ ° C. Humidity expansion coefficient is 10^-Four/ RH% or less
Yes, preferably 10^-Five/ RH% or less. These hot features
Properties, dimensional characteristics, and mechanical strength characteristics depend on the in-plane direction of the support.
However, it is preferable that the difference is approximately equal to the difference within 10%.

[Description of Production Method] The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step,
It comprises a dispersion step and a mixing step provided before and after these steps as required. Each step may be divided into two or more steps. Magnetic material, soft magnetic powder, binder, carbon black, abrasive used in the present invention,
All raw materials such as an antistatic agent, a lubricant, and a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. When a kneader is used, the magnetic material or soft magnetic powder and all or a part of the binder (however, preferably 30% by weight or more of the total binder) and 15 to 500 parts per 100 parts of the magnetic material are used. It is kneaded. The details of these kneading treatments are described in Japanese Patent Application Nos. 62-264722 and 62-236872. Glass beads can be used to disperse the ferromagnetic layer liquid and the soft magnetic layer liquid, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When coating a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. First, a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the application of a magnetic paint, are used to apply a base layer first. JP-A-60-2
38179, a method of applying an upper layer by a support pressure type extrusion coating apparatus disclosed in JP-A-2-265672. Second, upper and lower layers are coated almost simultaneously by one coating head having two built-in coating liquid passage slits as disclosed in JP-A-63-88080 and JP-A-2-17971. Method. A third method is to apply the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of magnetic particles, Japanese Patent Application Laid-Open Nos. 62-95174 and 1-2369.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in No. 68. further,
The viscosity of the coating solution must satisfy the numerical range disclosed in Japanese Patent Application No. 1-312659. In order to realize the configuration of the present invention, it is of course possible to use a sequential multi-layer coating in which a ferromagnetic layer is provided thereon after coating and drying a base layer, and the effect of the present invention is not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

A sufficient isotropic orientation may be obtained even without orientation without using an orientation device. However, a known random orientation device such as alternately arranging cobalt magnets diagonally or applying an alternating magnetic field with a solenoid. It is preferable to use In the case of hexagonal ferrite, isotropic orientation generally tends to be three-dimensional random in the in-plane and vertical directions, but it can also be in-plane two-dimensional random. In addition, isotropic magnetic characteristics can be imparted in the circumferential direction by using a known method such as a different polarity opposed magnet and making the magnets vertically oriented. In particular, when performing high-density recording, vertical alignment is preferable. It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air.
0 m / min to 1000 m / min, the temperature of the drying air is preferably 60 ° C. or more, and a suitable preliminary drying can be carried out before entering the magnet zone.

A calendering roll is treated with a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll.
In particular, in the case of forming a double-sided magnetic layer, it is preferable to perform the treatment with metal rolls. The processing temperature is preferably 50 ° C. or higher,
More preferably, the temperature is 100 ° C. or higher. The linear pressure is preferably 200 kg / cm or more, more preferably 300 kg / cm.
g / cm or more.

[Description of Physical Properties] The saturation magnetic flux density Bs of the ferromagnetic layer of the magnetic recording medium according to the present invention is 800 G or more and 3000 G or less when hexagonal ferrite is used. Coercive force Hc and Hr are 1000 Oe or more and 500
0 Oe or less, preferably from 1500 Oe to 3
000 Oe or less. The distribution of coercive force is preferably narrow, and SFD and SFDr are preferably 0.6 or less. The squareness ratio is 0.55 or more and 0.67 or less in the case of two-dimensional random, and preferably 0.58 or more and 0.64 or less in the case of three-dimensional random. It is preferably 45 or more and 0.55 or less. In the case of vertical alignment, it is 0.6 or more, preferably 0.7 or more in the vertical direction, and when demagnetizing field correction is performed, it is 0.7 or more, preferably 0.8 or more. The orientation ratio is preferably 0.8 or more for both two-dimensional random and three-dimensional random. In the case of two-dimensional randomness, the squareness ratio in the vertical direction, Br, Hc and Hr
Is preferably within 0.1 to 0.5 times the in-plane direction.

The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is -10 ° C. to 40 ° C. and humidity is 0% to 95%.
Is 0.5 or less, preferably 0.3 or less, and the surface resistivity is preferably a magnetic surface of 104 to 1012 ohms.
/ sq, and the charge potential is preferably within the range of -500V to + 500V. The elastic modulus at 0.5% elongation of the ferromagnetic layer is preferably 100 to 2,000 kg / mm @ 2 in each direction within the plane, breaking strength is preferably 1 to 30 kg / cm ^2, modulus of elasticity of the magnetic recording medium plane directions And preferably 100 to 1500 kg / m
m ² , residual elongation is preferably 0.5% or less, heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less,
More preferably, it is 0.5% or less, most preferably 0.1% or less. Glass transition temperature of ferromagnetic layer (11
(Maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 0 Hz)
Is preferably 50 ° C. or more and 120 ° C. or less, and that of the lower soft magnetic layer is preferably 0 ° C. to 100 ° C. Loss modulus is 1 × 1
It is preferably in the range of 08 to 8 × 109 dyne / m ² , and the loss tangent is preferably 0.2 or less.
If the loss tangent is too large, adhesion failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium. The residual solvent contained in the ferromagnetic layer is preferably at most 100 mg / m ² , more preferably at most 10 mg / m ² . The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the soft magnetic lower layer and the ferromagnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a disk medium in which repeated use is emphasized, a larger porosity is often preferable in running durability. TO of ferromagnetic layer
Center plane surface roughness R measured by the Mirau method of PO-3D
a is 10 nm or less, preferably 5 nm or less, and more preferably 3 nm or less.
The surface roughness RRMS is preferably in the range of 2 nm to 15 nm. The maximum height SRmax of the ferromagnetic layer is 0.5 μm or less,
The ten-point average roughness SRz is 0.3 μm or less,
Rp is 0.3 μm or less, and valley depth SRv is 0.3 μm.
m, the center plane area ratio SSr is preferably 20% or more and 80% or less, and the average wavelength Sλa is preferably 5 μm or more and 300 μm or less. Surface protrusion of ferromagnetic layer is 0.01 μm to 1 μm
It is preferable to arbitrarily set the size in the range of 0 to 2000 to optimize the coefficient of friction. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder to be added to the ferromagnetic layer, and the roll surface shape of the calendar treatment.

The curl is preferably within ± 3 mm. When the magnetic recording medium of the present invention has a soft magnetic layer and a ferromagnetic layer, it is easily presumed that the physical properties of the soft magnetic layer and the ferromagnetic layer can be changed according to the purpose. For example, the elastic modulus of the ferromagnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the soft magnetic layer is made lower than that of the ferromagnetic layer to improve the contact of the magnetic recording medium with the head.

[0055]

【Example】

[Example 1] <Preparation of paint> Magnetic paint Y Barium ferrite magnetic powder 100 parts: Ba molar ratio composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 2500 Oe, specific surface area 50 m2 / g, σs 58 emu / g 30 nm, plate ratio 3.5 vinyl chloride copolymer (-SO ₃ K content) 12 parts MR 110 (made by Nippon Zeon Co., Ltd.) polyurethane (-SO ₃ Na content): UR8200 (manufactured by Toyobo Co., Ltd.) 3 parts phenylphosphonic acid 3 Part α-alumina (average particle size 0.2 μm): HIT55 (manufactured by Sumitomo Chemical) 10 parts # 50 (manufactured by Asahi Carbon Co.) 5 parts butyl stearate 10 parts butoxyethyl stearate 5 parts isohexadecyl stearate 3 parts 2 parts of stearic acid Methyl ethyl ketone 125 parts cyclohexanone 125 parts soft paint Z granular magnetite powder γ-Fe ₃ O ₄ 0 parts average primary particle diameter of 0.035 .mu.m, specific surface area 40m ² / g Hc55Oe by BET method, pH 7, TiO ₂ content of 90 wt% or more, DBP oil absorption of 27~38ml / 100g, Surface treatment agent Al ₂ O ₃ 8 Weight% Conductex SC-U (manufactured by Columbian Carbon Co.) 20 parts MR110 12 parts UR8200 5 parts Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / Cyclohexanone (8/2 mixed solvent) 250 parts For each of the above two paints, each component was kneaded with a kneader, and then dispersed using a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating liquid for the soft magnetic layer, 10 parts to the coating liquid for the ferromagnetic layer, and 40 parts of butyl acetate was added to each, to have an average pore diameter of 1 μm. The solution was filtered using a filter to prepare a coating solution for forming a soft magnetic layer and a coating solution for forming a ferromagnetic layer.

The obtained soft magnetic layer coating solution is coated so that the thickness after drying is 1.5 μm, and immediately thereafter, the thickness of the ferromagnetic layer is 0.2 μm thereon. 62 μm
In the above, a simultaneous multilayer coating is performed on a polyethylene terephthalate support having a center line surface roughness of 0.01 μm, and while both layers are still in a wet state, they are passed through a gap of a 6000G different-magnet opposed magnet. The film was passed through a drying zone at 40 ° C., 80 ° C., and 100 ° C. to perform a vertical alignment treatment. After drying, the product is treated at a temperature of 90 ° C. and a linear pressure of 300 Kg / cm with a seven-stage calender, punched into a 3.7-inch surface and polished, and then a 3.7-inch cartridge (US
The cartridge was placed in a Zip-disk cartridge manufactured by Iomega, and predetermined mechanical components were added thereto to obtain a 3.7-inch floppy disk.

The Hc of the Ba ferrite ferromagnetic layer of the obtained sample was 2650 Oe and Bs was 1300 G.
Hc and Bs of the soft magnetic layer were 45 Oe and 2000 G, respectively. Example 2 The thickness of the Ba ferrite ferromagnetic layer in Example 1 was set to 0.5 μm. [Embodiment 3] In the embodiment 1, as the opposite pole opposite magnet, 3
A floppy disk was obtained under the same conditions as in Example 1 except that 000 G was used. Example 4 In Example 1, a granular magnetite powder having an Hc of 210 Oe was used instead of the granular magnetite of the soft magnetic paint. [Example 5] In Example 1, MR110 of soft magnetic paint was used.
16 parts, UR8200 7 parts, and polyisocyanate 13 parts. Comparative Example 1 The thickness of the Ba ferrite ferromagnetic layer in Example 1 was set to 0.7 μm. [Comparative Example 2] A floppy disk was obtained under the same conditions as in Example 1 except that a different magnet of 2000 G and a magnet of 3000 G were used. Comparative Example 3 In Example 1, a granular magnetite powder having Hc of 270 Oe was used in place of the granular magnetite of the soft magnetic paint. Comparative Example 4 The soft magnetic paint MR110 in Example 1 was used.
18 parts, UR8200 8 parts and polyisocyanate 15 parts. Comparative Example 5 In Example 1, a nonmagnetic powder of titanium oxide (average particle size: 0.35 μm) was used in place of the granular magnetite powder, which was the soft magnetic powder of the soft magnetic layer.

[Comparison between Example and Comparative Example] Table 1 shows the evaluation results of each sample.

[0059]

[Table 1]

It can be seen that the disk-shaped medium of the present invention is much more excellent in high-density recording characteristics than the conventional disk-shaped medium. [Description of Measurement Method] Each sample of the floppy disk was measured by the following evaluation method. Measurement of playback output: Measurement of playback output was performed using a disk tester manufactured by Kokusai Denshi Kogyo (former Tokyo Engineering) and S
Using a K606B type evaluation device, a metal in-gap head having a gap length of 0.3 μm, and recording at a recording wavelength of 60 KFCI at a position of a radius of 24.6 mm, the reproduction output of the head amplifier was measured by an oscilloscope 76 manufactured by Tektronix.
It was measured with Model 33. The reproduction output was 10 times the output of Example-1.
It was shown as a relative value as 0.

Modulation: The maximum value V in one round of the reproduced waveform using the same conditions and under the same conditions as the measurement of the reproduced output.
_MAX , the minimum value V _MIN is ｛(V _MAX −V _MIN ) / (V _MAX
+ V _MIN )｝ × 100 (%). Magnetic properties (Hc, Br / Bm, SFD, Hr (90
゜): Using a vibration sample magnetometer (manufactured by Toei Kogyo Co., Ltd.)
It was measured at 10 KOe.

Thickness of ferromagnetic layer: A section sample of the layer cross section was prepared, and a scanning electron microscope (S-700, manufactured by Hitachi, Ltd.) was used.
(Type) was obtained from a cross-sectional photograph taken. Gloss difference: Digital gloss meter (Suga Test Instruments GK-4)
As described above, the measurement direction was changed every 45 degrees, and the measurement was performed from eight directions, and the difference between the maximum value and the minimum value was obtained.

Claims (3)

[Claims] 1. A disk-shaped magnetic recording medium comprising a soft magnetic layer and a ferromagnetic layer obtained by dispersing a ferromagnetic hexagonal ferrite fine powder in a binder on a non-magnetic support in this order. A magnetic recording medium having a thickness of 0.5 μm or less and a measurement direction dependency of glossiness at an arbitrary position of the ferromagnetic layer within 5%. 2. The disk-shaped magnetic recording medium according to claim 1, wherein said ferromagnetic layer is magnetically oriented in a vertical direction. 3. The soft magnetic layer has an Hc (coercive force) of 200O.
3. The disk-shaped magnetic recording medium according to claim 1, wherein Bs (saturation magnetic flux density) is 1500 G or more.