JP2003059032A - Hexagonal ferrite powder and magnetic recording medium containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hexagonal ferrite powder easily subjected to dispersion treatment and which is satisfactory in dispersibility and to provide a coating type magnetic recording medium containing the same and satisfactory in running durability and electromagnetic transducing characteristics. SOLUTION: The hexagonal ferrite powder has 3-7 μmol/m<2> stearic acid adsorption and 1-4 μmol/m<2> stearyl amine adsorption. The magnetic recording medium having a magnetic layer on a substrate is characterized in that the magnetic layer contains the hexagonal ferrite powder.

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 tape and a magnetic disk, and more particularly, to a coating type in which a magnetic coating material containing mainly a ferromagnetic powder and a binder is coated on a support to form a magnetic layer. The present invention relates to a magnetic recording medium having excellent noise, output, C / N, and storage stability in the short wavelength region. Further, the present invention relates to a magnetic recording medium for high density recording including a magnetic layer, which is particularly suitable for use in a system using an MR head that utilizes a magnetoresistive effect for reproduction.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is polyethylene.
A non-magnetic support such as terephthalate and a strong support
Magnetic coating in which magnetic powder is uniformly dispersed in resin binder solution
And a magnetic layer formed by applying a material. Above magnetism
Γ-Fe has traditionally been used as powder ₂O₃Needle-like ferromagnetic powder
Has been used, but in recent years aiming to improve recording density
The one using ultrafine magnetic powder of hexagonal ferrite was opened.
It has been issued and partly put into practical use.

Generally, as factors that control the dispersion behavior of magnetic powder in a resin binder solution, progress of aggregation due to magnetostatic interaction between magnetic powder particles and the like, and magnetic powder surface and binder solution The progress of dispersion due to the interfacial chemical interaction with

The interfacial chemical interaction between the binder liquid and the surface of the powder is considered to occur in proportion to the surface area of the powder. In particular, it has become more and more difficult to disperse the ferromagnetic powder due to miniaturization of the ferromagnetic powder due to the recent increase in density.

By the way, when hexagonal ferrite fine particles are used for magnetic powder, the magnetic interaction is large because the shape of the fine particles is plate-like, and each magnetic powder is single crystal and polycrystal. It has been pointed out that it is difficult to disperse due to the fact that it is difficult to form a fine structure such as irregularities on the powder surface as compared with the conventional acicular particles formed of the above-mentioned aggregate, and lack of dispersion stability. For this reason, the surface of the medium obtained by coating is often not finished with a surface precision suitable for high density recording.

[0006] In response to such a point, conventionally, surface treatment with an organic coating has been proposed, but a sufficient effect has not been found. Even if the kneading process and the sand mill dispersion are combined, there is a limit in improving the dispersibility, improving the coating film strength and smoothing the coating film.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a hexagonal ferrite powder which is easy to disperse and has a good dispersity, and a coated magnetic material containing the same, which has good running durability and electromagnetic conversion characteristics. To provide a recording medium.

[0008]

An object of the present invention is that the adsorption amount of stearic acid is 3 to 7 μmol / m ² and the adsorption amount of stearylamine is 1 to 4 μmol / m ^2. In a magnetic recording medium having a ferrite powder and a magnetic layer on a support, the magnetic layer can be achieved by a magnetic recording medium containing the above hexagonal ferrite powder. Preferred embodiments of the present invention are as follows. (1) The above hexagonal ferrite powder having an average plate diameter of 10 to 35 nm. (2) Specific surface area (S _BET ) by BET method is 40 to 12
The above hexagonal ferrite powder having an amount of 0 m ² / g. (3) Al, Si, Ti, Zr, Sn, Sb, Ba, M
The above hexagonal ferrite powder having one or more hydroxides or oxides of rare earth elements including g, Sr, Zn and Y present on the surface.

[0009]

First, the hexagonal ferrite powder of the present invention will be described. The hexagonal ferrite powder of the present invention has a stearic acid adsorption amount of 3 to 7 μmol / m ² ,
It is preferably 3.5 to 6.5 μmol / m ² , and the stearylamine adsorption amount is 1 to 4 μmol / m ² , preferably 1.5 to 3.5 μmol / m ² . The hexagonal ferrite powder of the present invention can be manufactured by selecting the composition and crystal structure of the hexagonal ferrite powder and subjecting it to a surface treatment. The hexagonal ferrite powder applied to the present invention, depending on its composition, barium ferrite, strontium ferrite, lead ferrite,
Calcium ferrite and various substitution products of these,
There are Co substitution products and the like. Further, the crystal structure or basic composition represented by BaFe ₁₂ O _{19 in} which iron or an iron-substituted metal has an average valence of 3 has a M-type magnetoplumbite hexagonal ferrite; a divalent metal (hereinafter referred to as M). Existing in BaM ₂ Fe ₁₆ O ₂₇ having a crystal structure or basic composition of W-type magnetoplumbite hexagonal ferrite; BaMFe ₆ O ₁₁ having a crystal structure or basic composition of Y-type magnetoplumbite hexagonal crystal Series ferrite; crystal structure represented by Ba ₃ M ₂ Fe ₂₄ O ₄₁ or basic composition is Z-type magnetoplumbite hexagonal ferrite; and spinel ferrite is epitaxially compounded on the surface of these hexagonal ferrites. The so-called composite type hexagonal ferrite has the crystal structure or basic composition of the hexagonal ferrite of the present invention. It applies to bets powder. Of these, M-type magnetoplumbite is preferable. Here, M in the composition formula of hexagonal ferrite and the divalent metal constituting the spinel ferrite include
Examples are Co, Fe, Ni, Mn, Mg, Cu and Zn.

Among the hexagonal ferrite powders of the present invention,
Barium ferrite is preferable, and Fe / Ba is
It is preferably 11.1 to 12.9 (atomic ratio), and Co / Fe is preferably 0.5 to 1.5 atomic%, Zn.
/ Fe, preferably 1 to 4 atom% and Nb / Fe,
It is preferably 0.5 to 2 atomic%. In addition to the above, the hexagonal ferrite powder of the present invention contains Al, S
i, Mn, S, Sn, Ti, V, Cr, Cu, Y, M
o, Rh, Pd, Ag, Sn, Sb, Te, W, Re,
Au, Bi, La, Ce, Pr, Nd, P, Ni, B,
Atoms such as Ge can be included as composition atoms. Depending on the raw material and manufacturing method, unique and unknown impurities are also allowed.
The total amount of these is 0.5 to 15.0 atomic% with respect to Fe.
Is preferred.

The surface of the particles of the hexagonal ferrite powder of the present invention has Al, Si, Ti, Zr, Sn, Sb, Ba and M.
It is preferred that one or more hydroxides or oxides of rare earth elements including g, Sr, Zn, and Y be present. Here, the rare earth element containing Y is Y, Ce, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
Means m, Yb, Lu and La. The thickness of the layer existing on the particle surface is appropriately selected, but is preferably 1 to 40 Å, more preferably 2 to 20 Å. The form of the layer may be a continuous body whose surface is completely covered, a continuous body having holes or an island shape, but at least 30% of the surface thereof
The above is preferably coated. As a method for allowing the hydroxide or oxide to be present on the particle surface, a conventionally known method is used, for example, a hydroxide of the above element is deposited on the surface of a hexagonal ferrite powder, and then filtered and washed with water. Examples include a method of sequentially performing drying, heat treatment, and the like.

Although the detailed reason for the hexagonal ferrite powder of the present invention is not clear, the surface characteristics are modified and the average plate diameter is 10 because the stearic acid adsorption amount and the stearylamine adsorption amount are controlled within a specific range. Even in the range of up to 35 nm, the dispersibility of particles in the magnetic layer of the magnetic recording medium is ensured, and the amount of lubricant such as fatty acid adsorbed can be controlled appropriately, so that the output and S / N are excellent and the storage stability and running durability The sex can be improved.

The hexagonal ferrite powder used in the present invention preferably has an average plate diameter of 10 to 35 nm. In addition, the range of the average plate diameter is the same for the surface-treated one and the non-surface-treated one. If the average plate diameter is less than 10 nm, the amount of magnetization is remarkably reduced, and therefore it is not suitable for a recording medium.
If it exceeds, the noise component becomes large and it is not suitable for high density recording. The variation coefficient of the average plate diameter is preferably 30% or less. S _BET of the hexagonal ferrite powder used in the present invention is 40
-120 m < ² > / g is preferable and 45-110 m < ² > / g is more preferable. The range of S _BET is the same for the surface-treated and non-surface-treated areas. The S _BET
Is less than 40 m ² / g, noise deteriorates, and 120 m ² / g
If it exceeds, dispersibility tends to decrease.

On the other hand, the average plate ratio, which is the arithmetic average of the plate ratio expressed by the ratio of the plate diameter to the thickness of the hexagonal ferrite powder, is preferably 2-5. If the ratio is less than 2, it is difficult to produce the hexagonal ferrite powder, and if it exceeds 5, the magnetic cohesive force becomes more dominant than the dispersive force, which makes the dispersion difficult. The variation coefficient of the plate ratio is also preferably 30% or less. The variation coefficient of the plate diameter is calculated from 100 × σ / average plate diameter, and the variation coefficient of the plate ratio is calculated from 100 × σ / average plate ratio. σ indicates the standard deviation of the plate diameter or plate ratio.

In the present specification, the sizes of various powders such as hexagonal ferrite powder and carbon black (hereinafter referred to as "powder size") are measured by a high resolution transmission electron microscope photograph and an image analyzer. Desired. The size of the powder can be determined by tracing the contour of the powder in the high resolution transmission electron micrograph with an image analyzer. That is, the powder size is such that the powder is needle-shaped, spindle-shaped, or column-shaped (however,
If the height is larger than the maximum major axis of the bottom surface, etc., it is represented by the length of the major axis that constitutes the powder, that is, the major axis length, and the shape of the powder is plate-like or column-like (however, thickness or height). Is smaller than the maximum major axis of the plate surface or the bottom surface), it is represented by the maximum major axis of the plate surface or the bottom surface, that is, the plate diameter, and the powder has a spherical shape, a polyhedral shape, an unspecified shape, and the like. When the major axis that constitutes the powder cannot be specified from the shape, it is represented by the equivalent circle diameter.

The average powder size of the powder is the arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for about 500 powders. Further, the average acicular ratio of the powder is obtained by measuring the length of the short axis of the powder in the above measurement, that is, the short axis length, and determining (minor axis length / minor axis length) of each powder.
Refers to the arithmetic mean of the values of. Here, the short axis length, in the case of the definition of the powder size, refers to the length of the short axis constituting the powder, in the same case, refers to the thickness to height, respectively, in the case of Since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience. When the shape of the powder is specific, for example, in the case of the above definition of the powder size, the average powder size is called the average major axis length, and in the case of the same definition, the average powder size is called the average plate diameter. , (Plate diameter / thickness to height) is called the average plate ratio. In the case of the same definition, the average powder size is called the average particle size.

The hexagonal ferrite powder may be produced by any method such as a glass crystallization method, a hydrothermal synthesis method, a coprecipitation method and a flux method. In any of the methods, it is important to find the condition that the predetermined elemental composition, shape distribution and particle size distribution are sharp, in order to achieve high density. Of these, the hydrothermal synthesis method is preferable. The hexagonal ferrite powder has a saturation magnetization s of 40 to 80 A · m ² / k
g, preferably 45 to 70 A · m ² / kg, coercive force Hc
Is 160 to 400 kA / m, preferably 170 to 350
The kA / m and the pH of the magnetic powder are preferably optimized depending on the combination with the binder to be used, but usually pH 4 to
12, preferably 5.5 to 10.

A magnetic recording medium using the above hexagonal ferrite powder will be described below for each element. [Magnetic Layer] In the magnetic recording medium of the present invention, a magnetic layer containing hexagonal ferrite powder may be provided on one side or both sides of the support. The magnetic layer provided on one side thereof may be a single layer or multiple layers having different compositions. In addition, a non-magnetic layer (also referred to as a lower layer) may be provided between the support and the magnetic layer. The present invention preferably has a structure in which a magnetic layer is provided on the lower layer. The magnetic layer in this case is also referred to as an upper layer or an upper magnetic layer. The upper layer can be formed by applying the lower layer at the same time or sequentially and by wet-on-wet (W / W) in which the lower layer is wet, or in wet-on-dry (W / D) after the lower layer is dried. . W / W from the point of production yield
Is preferred. In W / W, since the upper layer / lower layer can be formed simultaneously, the surface treatment process such as the calendering process can be effectively utilized, and the surface roughness of the upper magnetic layer can be improved even in the thin layer.

[Lower Layer] Next, the detailed contents of the lower layer will be described. The lower layer is preferably composed mainly of non-magnetic inorganic powder and a binder. The non-magnetic inorganic powder used in the lower layer can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and silicon nitride having an α conversion rate of 90% or more. , Titanium carbide,
Titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred is titanium dioxide, because of its small particle size distribution and many means for imparting functions.
Zinc oxide, iron oxide and barium sulfate are more preferable, and titanium dioxide and α-iron oxide are more preferable. The average particle size of these non-magnetic inorganic powders is preferably 0.005 to 2 μm,
If necessary, non-magnetic inorganic powders having different average particle diameters may be combined, or a single non-magnetic inorganic powder may be used to broaden the particle size distribution to obtain the same effect. Especially preferred is that the average particle size of the non-magnetic inorganic powder is 0.01 μm
It is 0.2 μm. In particular, when the non-magnetic inorganic powder is a granular metal oxide, the average particle diameter is preferably 0.08 μm or less, and when it is a needle-shaped metal oxide, the average major axis length is 0.
It is preferably 3 μm or less, more preferably 0.2 μm or less. The tap density is usually 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content of the non-magnetic inorganic powder is usually 0.1 to 5% by mass, preferably 0.2 to
3% by mass, more preferably 0.3 to 1.5% by mass. The pH of the non-magnetic inorganic powder is usually 2 to 11,
The pH is particularly preferably between 5.5 and 10. S _BET of the non-magnetic inorganic powder is usually 1 to 100 m ² / g, preferably 5 to
80 m ² / g, more preferably from 10 to 70 m ² / g. The crystallite size of the non-magnetic inorganic powder is 0.004 μm ~
1 μm is preferable, and 0.04 μm to 0.1 μm is more preferable. The oil absorption using DBP (dibutyl phthalate) is usually 5 to 100 ml / 100 g, preferably 10 to
80 ml / 100 g, more preferably 20-60 ml /
It is 100 g. Specific gravity is usually 1 to 12, preferably 3
~ 6. The shape may be needle-like, spherical, polyhedral or plate-like. The Mohs hardness is preferably 4 or more and 10 or less. The amount of SA (stearic acid) adsorbed on the non-magnetic inorganic powder is 1 to 20 μmol / m ² , preferably ² to 15 μmo.
1 / m ² , more preferably 3 to 8 μmol / m ² . The pH is preferably between 3 and 6. The surface of these non-magnetic inorganic powders is treated with Al ₂ O ₃ , S
iO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , Zn
O and Y ₂ O ₃ are preferably present. Particularly preferred for dispersibility are _{Al 2 O 3, SiO 2,} TiO 2, ZrO 2, further preferred are _{Al 2 O 3, SiO 2,} ZrO 2. These may be used in combination, or may be used alone. Depending on the purpose, a co-precipitated surface-treated layer may be used, or a method in which alumina is first allowed to exist and then silica is present in the surface layer thereof, or the opposite method can be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that it is homogeneous and dense. As specific examples and manufacturing methods of the non-magnetic inorganic powder used in the lower layer of the present invention, WO98 / 3
5345 is exemplified.

By mixing carbon black in the lower layer, surface electric resistance Rs, which is a known effect, can be lowered, light transmittance can be reduced, and desired micro Vickers hardness can be obtained. It is also possible to bring about the effect of lubricant storage by including carbon black in the lower layer. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the kind of carbon black. The carbon black of the lower layer should have the following characteristics optimized depending on the desired effect, and the effect may be obtained more by using together.

The S _BET of the lower carbon black is usually
100 to 500 m ² / g, preferably 150 to 400 m ²
/ G, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 400 ml / 100 g. The average particle size of carbon black is usually 5 nm to 80 nm, preferably 10 to 50 nm, more preferably 10 to 40 n.
m. A small amount of carbon black having an average particle size larger than 80 nm may be included. The carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of carbon black used in the lower layer include those described in WO98 / 35345. These carbon blacks are 50% by mass with respect to the above non-magnetic inorganic powder (not including carbon black).
It can be used in a range not exceeding 40% and a range not exceeding 40% of the total mass of the non-magnetic layer. These carbon blacks can be used alone or in combination. 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).

In the lower layer, organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigment, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, polyfluorinated ethylene resin also Can be used. The manufacturing method is JP-A-62.
-18564 and those described in JP-A-60-255827 can be used.

For the binder resin, lubricant, dispersant, additive, solvent, dispersion method, etc. of the lower layer or the back layer described below, those of the magnetic layer described below can be applied. In particular, with respect to the amount and type of binder resin, the amount and type of additives and dispersants added, known techniques for the magnetic layer can be applied.

[Binder] As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,000 to 200,000, preferably 10.0.
The degree of polymerization is about 100 to 100,000 and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin And a mixture of an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. For these examples and the manufacturing method thereof, see JP-A-62-256219.
Are described in detail in. The above resins can be used alone or in combination, but are preferably selected from vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer, At least 1
Examples include a combination of a seed and a polyurethane resin, or a combination of these and a polyisocyanate.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. In order to obtain better dispersibility and durability, it is necessary to add -COO for all the binders shown here.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2, -
O-P = O (OM) 2, (M is a hydrogen atom or an alkali metal _{salt,), - NR 2, -N} + R 3 (R is a hydrocarbon group), epoxy group, -SH, -CN, It is preferable to use at least one polar group selected from the group introduced 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. In addition to these polar groups, it is preferable to have at least one OH group at the end of the polyurethane molecule, for a total of two or more OH groups. Since the OH group cross-links with the polyisocyanate as the curing agent to form a three-dimensional network structure, it is preferable that the OH group be contained in a large number in the molecule.
In particular, it is preferable that the OH group is at the terminal of the molecule because the reactivity with the curing agent is high. Polyurethane has 3 OH groups at the end of the molecule.
It is preferable to have at least four, and particularly preferable to have at least four. In the present invention, when polyurethane is used, the glass transition temperature is usually -50 to 150 ° C, preferably 0 ° C to 100 ° C, particularly preferably 30 to 100 ° C,
The elongation at break is 100 to 2000%, and the breaking stress is usually 0.
05-10 Kg / mm ² (≈0.49-98 MPa),
The yield point is 0.05-10 Kg / mm ² (≈0.49-9
8 MPa) is preferred. By having such physical properties, a coating film having good mechanical properties can be obtained.

Specific examples of these binders used in the present invention include vinyl chloride copolymers such as VAGH, VYHH, VMCH and VAG manufactured by Union Carbite Corporation.
F, VAGD, VROH, VYES, VYNC, VMC
C, XYHL, XYSG, PKHH, PKHJ, PKH
C, PKFE, Nisshin Chemical Industry Co., Ltd., MPR-TA, MP
R-TA5, MPR-TAL, MPR-TSN, MPR
-TMF, MPR-TS, MPR-TM, MPR-TA
O, 1000W made by Denki Kagaku, DX80, DX81, D
X82, DX83, 100FD, Nippon Zeon's MR-
104, MR-105, MR110, MR100, MR
555, 400X-110A, Nippon Polyurethane Co. Nipporan N2301, N230 as polyurethane resin
2, N2304, Dainippon Ink and Company Pandex T-5
105, T-R3080, T-5201, Barnock D
-400, D-210-80, Crisbon 6109,7
209, Toyobo Co., Ltd. Byron UR8200, UR830
0, UR-8700, RV530, RV280, polycarbonate carbonate polyurethane manufactured by Dainichiseika, diferamine 4020, 5020, 5100, 5300, 9020,
9022, 7020, Mitsubishi Kasei polyurethane, MX
5004, Sanyo Kasei Polyurethane, Sampren SP
-150, Asahi Kasei Polyurethane, Saran F310,
F210 etc. are mentioned.

The binder used in the nonmagnetic layer is in the range of 5 to 50% by mass, preferably 10 to 30% by mass, based on the nonmagnetic inorganic powder and the binder used in the magnetic layer is based on the hexagonal ferrite powder. Used in the range of%. When using a vinyl chloride resin, it is preferable to use a combination of 5 to 30% by mass, a polyurethane resin to use 2 to 20% by mass, and a polyisocyanate in a range of 2 to 20% by mass, but for example, a trace amount It is also possible to use only polyurethane or only polyurethane and isocyanate when head corrosion occurs due to dechlorination of the above.

When the magnetic recording medium of the present invention is composed of two or more layers, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, and the magnetic layer are used. It is of course possible to change the molecular weight of each resin to be formed, the amount of polar groups, or the physical properties of the above-mentioned resin with each layer if necessary, and rather, it should be optimized in each layer, Technology can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer, and in order to improve the head touch to the head, the non-magnetic layer The amount of binder can be increased to give flexibility.

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate,
Examples include products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates. Commercially available trade names of these isocyanates are Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Yakuhin, Takenate D-10.
2, Takenate D-110N, Takenate D-200,
Takenate D-202, Sumitomo Bayer Co., Desmodur L, Desmodul IL, Desmodul N, Desmodul HL, etc. are available either alone or in combination of two or more by utilizing the difference in curing reactivity. It can be used with each layer.

[Carbon Black, Abrasive] The magnet of the present invention
The carbon black used for the elastic layer is a rubber furnace.
Rubber, thermal for rubber, black for color, acetylene
A rack or the like can be used. S _BETIs 5 to 500
m²/ G, DBP oil absorption is 10 to 400 ml / 100
g, average particle size 5 nm to 300 nm, pH 2-1
0, water content 0.1 to 10%, tap density 0.1 to 1
g / cc is preferred. Specifically, WO98 / 353
And those described in 45.

Carbon black has the functions of preventing static charge of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving the film strength, etc. These differ depending on the carbon black used. Therefore, when the present invention has a multilayer structure, the type of each layer,
Change the amount and combination, particle size, oil absorption, conductivity, pH
It is, of course, possible to use them properly according to the purpose based on the above-mentioned various characteristics, etc., and rather it should be optimized in each layer.

In the present invention, an abrasive can be used in the magnetic layer and the like. As the abrasive, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide having an α conversion rate of 90% or more. , Known materials having a Mohs hardness of 6 or more are used alone or in combination. Further, a composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but if the main component is 90% or more, the effect remains the same. The average particle size of these abrasives is preferably 0.01 to 2 μm, and in order to improve the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. To improve durability, if necessary, combine abrasives with different particle sizes,
It is also possible to broaden the particle size distribution and obtain the same effect with a single abrasive. Tap density is 0.3-2g / m
1, water content is 0.1 to 5%, pH is 2 to 11, and S _BET is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but those having a corner in part of the shape are preferable because of high abradability. Specific examples thereof include those described in WO98 / 35345. Among them, the use of diamond as described above is effective in improving running durability and electromagnetic conversion characteristics. The particle size and amount of the abrasive added to the magnetic layer and the non-magnetic layer should be set to the optimum values.

[Additives] Additives used in the magnetic layer and non-magnetic layer of the present invention have additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. Performance can be improved. As a material exhibiting a lubricating effect, a lubricant is used which exerts a remarkable effect on the adhesion that occurs when the surfaces of substances are rubbed against each other. There are two types of lubricants. It is not possible to judge whether the lubricant used in the magnetic recording medium is completely fluid lubrication or boundary lubrication, but if classified according to the general concept, higher fatty acid ester, liquid paraffin, silicon derivative, etc. which show fluid lubrication and boundary It is classified into long-chain fatty acids that show lubrication, fluorine-based surfactants, and fluorine-containing polymers. In the coating type medium, the lubricant is present in the state of being dissolved in the binder or partially adsorbed on the surface of the hexagonal ferrite powder.The lubricant migrates to the surface of the magnetic layer. Is determined by the compatibility of the binder and the lubricant.
When the compatibility between the binder and the lubricant is high, the migration rate is low, and when the compatibility is low, the rate is high. One way to think about the compatibility is to compare both dissolution parameters. A non-polar lubricant is effective for fluid lubrication, and a polar lubricant is effective for boundary lubrication.

In the present invention, it is preferable to combine a higher fatty acid ester showing fluid lubrication having different characteristics with a long chain fatty acid showing boundary lubrication, and it is more preferable to combine at least three kinds. A solid lubricant may be used in combination with these. As the solid lubricant, for example, molybdenum disulfide, tungsten disulfide graphite, boron nitride, graphite fluoride or the like is used.
The long-chain fatty acid exhibiting boundary lubrication has 10 to 24 carbon atoms.
Monobasic fatty acid (which may contain an unsaturated bond or may be branched), and a metal salt thereof (L
i, Na, K, Cu, etc.). Fluorine-containing surfactants and fluorine-containing polymers are fluorine-containing silicones.
And fluorine-containing alcohols, fluorine-containing esters, fluorine-containing alkyl sulfates and their alkali metal salts. As the higher fatty acid ester exhibiting fluid lubrication, a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms, Mono-fatty acid ester, di-fatty acid ester or tri-fatty acid ester, alkylene, which is composed of any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohol (whether it contains an unsaturated bond or branched) Examples thereof include fatty acid esters of monoalkyl ethers of oxide polymers. Liquid paraffin, and silicon derivatives such as dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms). 5, alkoxy is C1-4, phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl is 1-5 carbon), silicone oil, polar group-containing silicone, fatty acid-modified silicone. , And fluorine-containing silicone.

As other lubricants, monohydric, dihydric, trihydric, tetrahydric, pentahydric and hexahydric alcohols having 12 to 22 carbon atoms (which may contain unsaturated bonds or may be branched),
Alkoxy alcohol having 12 to 22 carbon atoms (it may be unsaturated or branched), alcohol such as fluorine-containing alcohol, polyolefin such as polyethylene wax and polypropylene, polyolefin such as ethylene glycol and polyethylene oxide wax. Examples thereof include glycols, alkyl phosphates and their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyl ethers, fatty acid amides having 8 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms.

Phenylphosphonic acid, such as "PPA" produced by Nissan Kagaku Co., Ltd., such as α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzene, for showing antistatic effect, dispersing effect, plasticizing effect and the like. Phosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and their alkali metal salts, and the like can be used.

The lubricant used in the present invention is preferably fatty acid and fatty acid ester, and specifically, WO98.
/ 35345. In addition to these, different lubricants and additives can be used in combination.

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums or sulfoniums. Anionic surfactants containing acidic groups such as cationic surfactants such as carboxylic acids, carboxylic acids, sulfonic acids, phosphoric acid, sulfuric acid ester groups, phosphoric acid ester groups, amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols And amphoteric surfactants such as alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 1
Not 100% pure, isomers other than the main component, unreacted substances,
Impurities such as by-products, decomposition products and oxides may be contained. The content of these impurities is preferably 30% or less, more preferably 10% or less. In the present invention, it is also preferable to use a monoester and a diester in combination as the fatty acid ester as described in WO98 / 35345.

C of the surface of the magnetic layer of the magnetic recording medium of the present invention, particularly the disk-shaped magnetic recording medium, measured by Auger electron spectroscopy.
The / Fe peak ratio is preferably 5 to 100, particularly preferably 5 to 80. The measurement conditions of Auger electron spectroscopy are as follows. Apparatus: PHI-660 type manufactured by Φ Measuring conditions: Primary electron beam accelerating voltage 3KV Sample current 130nA Magnification 250 times Inclination angle 30 ° Under the above conditions, kinetic energy- (KineticEner)
gy) The range of 130 to 730 eV is integrated three times, and the intensities of the KLL peak of carbon and the LMM peak of iron are obtained in the differential form and the ratio of C / Fe is obtained.

On the other hand, the amount of lubricant contained in each of the upper and lower layers of the magnetic recording medium of the present invention is 5 to 100 parts by mass of hexagonal ferrite powder or non-magnetic inorganic powder.
30 parts by mass is preferred.

These lubricants and surfactants used in the present invention have different physical actions,
The type, the amount, and the combination ratio of the lubricant that produces the synergistic effect should be optimally determined according to the purpose.
To control the exudation to the surface using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control the exudation to the surface using esters with different boiling points, melting points and polarities, to adjust the amount of surfactant It is conceivable that the coating stability will be improved and that the amount of the lubricant added will be increased in the intermediate layer to improve the lubrication effect. Of course, 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 mass to 50% by mass, preferably 2 to 25% by mass, based on the hexagonal ferrite powder or the non-magnetic powder.

Further, all or a part of the additives used in the present invention may be added at any step in the production of the magnetic paint and the non-magnetic paint, for example, in the case of mixing with the magnetic substance before the kneading step, It may be added in a kneading step using a magnetic material, a binder and a solvent, in a dispersing step, after a dispersing step, or just before coating.
In some cases, the purpose may be achieved by applying a part or all of the additives simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendaring or after slitting.

[Layer Constitution] In the thickness constitution of the magnetic recording medium of the present invention, the support is usually 2 to 100 μm, preferably 2 to 8 μm.
It is 0 μm. The computer tape support is 3.
Those having a thickness in the range of 0 to 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0 to 5.5 μm) are used. An undercoat layer may be provided between the support, preferably a non-magnetic flexible support, and the non-magnetic layer or the magnetic layer to improve adhesion. The thickness of this undercoat layer is 0.01
˜0.5 μm, preferably 0.02 to 0.5 μm. A back layer may be provided on the support on the side opposite to the side on which the magnetic layer is provided in order to provide effects such as antistatic and curl correction. This thickness is usually 0.1-4 μm,
It is preferably 0.3 to 2.0 μm. Known undercoat layers and back layers can be used.

The thicknesses of the lower and upper magnetic layers of the present invention are optimized depending on the saturation magnetization amount of the head used, the head gap length, and the recording signal band, but generally 0.05 to 0.5 μm. And preferably 0.05 to
It is 0.30 μm. The thickness of the lower layer is usually 0.2 to 5.
It is 0 μm, preferably 0.3 to 3.0 μm, and more preferably 1.0 to 2.5 μm. The lower layer exhibits its effect as long as it is substantially non-magnetic. For example, even if a small amount of magnetic powder is intentionally or intentionally included, the effect of the present invention is exhibited. It goes without saying that they can be regarded as the same configuration. The residual magnetic flux density of the lower layer is substantially 10 m.
T or less or coercive force is 100 oersted (≈8 kA /
m) or less, preferably having no residual magnetic flux density and coercive force. When the lower layer contains magnetic powder, it is preferably contained in less than 1/2 of the total inorganic powder in the lower layer. Further, as the lower layer, a soft magnetic layer containing soft magnetic powder and a binder may be formed instead of the nonmagnetic layer. The soft magnetic layer has the same thickness as the lower layer.

In the case of a magnetic recording medium having two magnetic layers, a nonmagnetic layer or a soft magnetic layer may or may not be provided. For example, the magnetic layer on the side far from the support is 0.2 to 2 μm.
m, preferably 0.2 to 1.5 μm, and the magnetic layer on the side closer to the support can be 0.8 to 3 μm. When the magnetic layer is provided alone, it is usually 0.2 to 5 μm.
m, preferably 0.5 to 3 μm, more preferably 0.
5 to 1.5 μm.

[Back Layer] The magnetic recording medium of the present invention may be provided with a back layer. Although a back layer can be provided on a magnetic disk as well, in general, a magnetic tape for recording computer data is strongly required to have repetitive running property as compared with a video tape and an audio tape. In order to maintain such high running durability, the back layer preferably contains carbon black and inorganic powder.

It is preferable to use two kinds of carbon black having different average particle diameters in combination.
In this case, it is preferable to use fine particle carbon black having an average particle diameter of 10 to 20 nm and coarse particle carbon black having an average particle diameter of 230 to 300 nm in combination. Generally, the surface electrical resistance of the back layer can be set to be low and the light transmittance can be set to be low by adding the above-mentioned particulate carbon black. Since many magnetic recording devices use the light transmittance of the tape for the operation signal, in such a case, the addition of finely particulate carbon black is particularly effective. In addition, finely divided carbon black is generally excellent in holding power of a liquid lubricant, and contributes to reduction of friction coefficient when used in combination with a lubricant. On the other hand, the coarse-grained carbon black having an average particle diameter of 230 to 300 nm has a function as a solid lubricant, and also forms fine protrusions on the surface of the back layer to reduce the contact area and reduce the friction coefficient. Contribute to the reduction of

When a commercially available product is used as the fine particle carbon black and the coarse particle carbon black used in the present invention, specific products include WO98 / 35.
345 can be mentioned. In the back layer, when using two kinds of particles having different average particle diameters, 10 to 20 nm of fine particulate carbon black and 23
The content ratio (mass ratio) of the coarse particulate carbon black having a particle size of 0 to 300 nm is preferably in the range of former: latter = 98: 2 to 75:25, and more preferably 95: 5.
The range is 85:15. The content of carbon black (the total amount of two types when two types are used) in the back layer is usually 30 to 80 with respect to 100 parts by mass of the binder.
It is in the range of parts by mass, preferably in the range of 45 to 65 parts by mass.

As the inorganic powder, it is preferable to use two kinds of inorganic powders having different hardness together. Specifically, Mohs hardness 3 to
It is preferable to use a soft inorganic powder having a hardness of 4.5 and a hard inorganic powder having a Mohs hardness of 5 to 9. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, it is possible to stabilize the friction coefficient by repeated running. Moreover, with the hardness in this range, the sliding guide pole is not scraped. The average particle size of this inorganic powder is 30 to 50 nm.
It is preferably in the range of. Mohs hardness is 3 to 4.5
Examples of the soft inorganic powder include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more. The content of the soft inorganic powder in the back layer is 1 with respect to 100 parts by mass of carbon black.
The amount is preferably in the range of 0 to 140 parts by mass, more preferably 35 to 100 parts by mass.

By adding a hard inorganic powder having a Mohs hardness of 5 to 9, the strength of the back layer is enhanced and the running durability is improved. When these inorganic powders are used together with carbon black and the above-mentioned soft inorganic powders, a strong back layer is obtained with little deterioration even after repeated sliding. In addition, the addition of this inorganic powder imparts an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole or the like. Particularly when used in combination with a soft inorganic powder, the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back layer can be stabilized. The average particle size of the hard inorganic powder is 80 to
250 nm is preferable, and 100 to 210 nm is more preferable. Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina,
And chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Among these, α-iron oxide or α
-Alumina is preferred. The content of the hard inorganic powder is usually 3 to 30 parts by mass, preferably 3 to 20 parts by mass with respect to 100 parts by mass of carbon black.

When the soft inorganic powder and the hard inorganic powder are used together in the back layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, especially 3). As described above, it is preferable to select and use the soft inorganic powder and the hard inorganic powder. In the back layer,
It is preferable to contain two kinds of inorganic powders each having a specific average particle diameter and different Mohs hardness, and two kinds of carbon black different in the average particle diameter.

The back layer may contain a lubricant. The lubricant can be appropriately selected and used from the above-mentioned lubricants that can be used for the non-magnetic layer or the magnetic layer. In the back layer, the lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder.

[Support] The support used in the present invention is
It is preferably a non-magnetic flexible support, and has a heat shrinkage ratio of 0.5 at 100 ° C. for 30 minutes in each in-plane direction of the support.
% Or less, and the heat shrinkage ratio at 80 ° C. for 30 minutes is 0.5% or less, more preferably 0.2% or less. Further, it is preferable that the heat shrinkage ratio of the support at 100 ° C. for 30 minutes and the heat shrinkage ratio at 80 ° C. for 30 minutes are equal to each other within 10% in each in-plane direction of the support. The support is preferably non-magnetic. These supports include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, aromatic or aliphatic polyamides, polyimides, polyamideimides, polysulfones, polyaramids, polybenzoxazoles and the like. Known films can be used. Polyethylene naphthalate,
It is preferable to use a high strength support such as polyamide. Further, if necessary, in order to change the surface roughness of the magnetic surface and the base surface, a laminated type support as shown in JP-A-3-224127 can be used. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

To achieve the object of the present invention, the center surface average surface roughness Ra measured by a surface roughness meter TOPO-3D manufactured by WYKO as a support is 4.0 nm or less, preferably 2.0 nm or less. You need to use one. It is preferable that these supports not only have a small central surface average surface roughness but also that they have no coarse protrusions of 0.5 μm or more.
Further, the surface roughness shape can be freely controlled by the size and amount of the filler added to the support, if necessary. An example of these fillers is C
In addition to oxides and carbonates such as a, Si and Ti, organic powders such as acrylics can be used. Maximum height of support Rma
x is 1 μm or less, ten-point average roughness Rz is 0.5 μm or less,
Center face peak height Rp is 0.5 μm or less, center face valley depth Rv
Is 0.5 μm or less, the central surface area ratio Sr is 10% or more, 9
0% or less and the average wavelength λa is preferably 5 μm or more and 300 μm or less. To obtain the desired electromagnetic conversion characteristics and durability,
The distribution of surface protrusions of these supports can be arbitrarily controlled by a filler, and each of those having a size of 0.01 to 1 μm can be controlled within a range of 0 to 2000 per 0.1 mm ² .

The F-5 value of the support used in the present invention is preferably 5 to 50 Kg / mm ² (≈49 to 490 MP).
a), and the heat shrinkage of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, 8
The heat shrinkage ratio at 0 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5-100
Kg / mm ² (≈49 to 980 MPa), elastic modulus is 10
0 to 2000 Kg / mm ² (≈ 0.98 to 19.6 GP
a) is preferred. The coefficient of thermal expansion is 10 ^-4 to 10 ^-8 / ° C, preferably 10 ^-5 to 10 ^-6 / ° C. The coefficient of humidity expansion is 10 ⁻⁴ / RH% or less, preferably 10 ⁻⁵ /
RH% or less. These thermal characteristics, dimensional characteristics, and mechanical strength characteristics are preferably substantially equal to each other within 10% in each in-plane direction of the support.

[Manufacturing Method] The step of manufacturing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each process may be divided into two or more stages. All raw materials such as magnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. In addition, individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, conventionally known manufacturing techniques can be used as a part of the steps. In the kneading step, it is preferable to use an open kneader, a continuous kneader, a pressure kneader, an extruder having a strong kneading power. When a kneader is used, the magnetic powder or non-magnetic powder and all or part of the binder (however, 30% of the total binder)
% Or more) and 15 to 100 parts of magnetic powder
Kneading is performed in the range of up to 500 parts. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-106338.
79274. Further, glass beads can be used to disperse the magnetic layer liquid and the non-magnetic layer liquid, and zirconia beads, titania beads, and steel beads, which are dispersion media having high specific gravity, are suitable. The particle size and packing rate of these dispersion media are optimized for use. A 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 lower layer is first coated by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for coating a magnetic paint, and when the lower layer is in a wet state, Japanese Patent Publication No. 1-46186 or 60-238
179, a method of coating an upper layer by a support pressure type extrusion coating apparatus disclosed in JP-A-2-265672. Secondly, JP-A-63-88080 and JP-A-2-
17971, a method of coating the upper and lower layers almost simultaneously by one coating head having two slits for passing the coating liquid therein, as disclosed in JP-A-2-265672. A third method is a method of coating the upper and lower layers substantially at the same time by using an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of magnetic particles, JP-A-62-95174 and JP-A-1-236968 are used.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in US Pat. Further, the viscosity of the coating liquid needs to satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the constitution of the present invention, it is of course possible to apply a lower layer and then dry it, and then to form a magnetic layer on the lower layer. In this case, 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-mentioned simultaneous multilayer coating.

In the case of a disk, a sufficiently isotropic orientation may be obtained without using an orientation device without orientation, but cobalt magnets are alternately arranged diagonally, an AC magnetic field is applied by a solenoid, etc. It is preferable to use a known random orientation device. Generally, hexagonal ferrite tends to be in-plane and vertical three-dimensional random, but in-plane two-dimensional random is also possible. In addition, it is also possible to impart isotropic magnetic characteristics in the circumferential direction by using a known method such as a magnet with opposite poles and by using a vertical orientation. Vertical alignment is particularly preferable for high-density recording. Alternatively, spin coating may be used for circumferential orientation.

In the case of a magnetic tape, it is oriented in the longitudinal direction using a cobalt magnet or a solenoid. It is preferable to control the drying position of the coating film by controlling the temperature of the drying air, the air volume, and the coating speed. The coating speed is 20 m / min.
1000 m / min, the temperature of the drying air is preferably 60 ° C. or higher, and an appropriate preliminary drying can be carried out before entering the magnet zone. As a calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide, or a metal roll is used, but it is preferable that both metal rolls are used in the case of forming a double-sided magnetic layer. The treatment temperature is preferably 50 ° C. or higher, more preferably 100 ° C. or higher. The linear pressure is preferably 200 kg / cm (≈196 kN / m) or more,
More preferably, 300 kg / cm (≈294 kN /
m) or more.

[Physical Properties] The magnetic layer thickness of the magnetic recording medium according to the present invention is preferably 0.01 to 0.5 μm, and the residual magnetic flux density × magnetic layer thickness is preferably 5 to 200 mT · μm. The coercive force Hc is preferably 1800 to 5000 oersted (≈144 to 400 kA / m), and 1800 to
3000 oersted (≈144 to 240 kA / m) is more preferable. The coercive force distribution is preferably narrow, and SF
D (switching field distribution) and SFDr are preferably 0.6 or less.

In the case of a magnetic disk, the squareness ratio (SQ) is 2
In the case of dimensional random, it is usually 0.55 to 0.67, preferably 0.58 to 0.64, in the case of three-dimensional random, 0.45 to 0.55 is preferable, and in the case of vertical alignment, Usually, it is 0.6 or more, preferably 0.7 or more, and when diamagnetic field correction is performed, it is usually 0.7 or more, preferably 0.8 or more. The orientation ratio of both two-dimensional random and three-dimensional random is preferably 0.8 or more. In the case of two-dimensional random, the squareness ratio in the vertical direction, Br in the vertical direction, and Hc in the vertical direction are preferably within 0.1 to 0.5 times the in-plane direction. In the case of magnetic tape, the squareness ratio (SQ) is 0.
It is 7 or more, preferably 0.8 or more.

The magnetic recording medium of the present invention is worn against the head.
The friction coefficient is in the range of temperature -10 to 40 ° C and humidity 0 to 95%.
In general, 0.5 or less, preferably 0.3 or less, surface solid
Resistive is preferably magnetic surface 10^Four-10¹²Ohm / s
q, and the charge position is preferably -500V to + 500V. Magnetism
The elastic modulus at 0.5% elongation of the layer is preferably in each direction in the plane.
100-2000Kg / mm²(≈ 980-19600
N / mm²), The breaking strength is preferably 10 to 70 kg /
mm²(≒ 98 to 686 N / mm²), Bullets on magnetic recording media
The sex ratio is preferably 100 to 1500 Kg / in each in-plane direction.
mm²(≈980 to 14700 N / mm²), The residual
Any temperature below 0.5%, preferably below 100 ° C
The heat shrinkage ratio is preferably 1% or less, more preferably
0.5% or less, most preferably 0.1% or less
It Glass transition temperature of magnetic layer (movement measured at 110 Hz
Maximum of loss modulus of dynamic viscoelasticity measurement) is 50 ° C or higher 12
0 ° C or lower is preferable, and that in the lower layer is preferably 0 ° C to 100 ° C.
Good Loss elastic modulus is 1 × 10 ³~ 1 x 10^FourN / cm²
Is preferable, and the loss tangent is 0.2 or less.
Preferably there is. Adhesive failure if the loss tangent is too large
Is likely to occur. These thermal and mechanical properties are
It is preferable that it is substantially equal within 10% in each direction. Porcelain
The residual solvent contained in the organic layer is preferably 100 mg / m
²Or less, more preferably 10 mg / m²It is the following. Paint
The porosity of the cloth layer is preferably 30 volume for both the lower layer and the upper layer.
The amount is not more than%, more preferably not more than 20% by volume. Sky
The porosity is preferably small in order to achieve high output,
Depending on the purpose, it may be better to secure a certain value.
For example, it is empty on disk media where repeated use is important.
In many cases, the larger the porosity, the better the running durability.

The center surface average surface roughness Ra of the surface of the magnetic layer measured by a surface roughness meter TOPO-3D manufactured by WYKO is preferably 5.0 nm or less, more preferably 4.0 nm or less, and particularly preferably 3. It is 5 nm or less. The maximum height Rmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, and the center plane peak height Rp is 0.3 μm or less.
Center plane valley depth Rv is 0.3 μm or less, center plane area ratio Sr
Is preferably 20% or more and 80% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. It is possible to arbitrarily set the surface protrusions of the magnetic layer having a size of 0.01 to 1 μm in the range of 0 to 2000, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient by this. These can be easily controlled by controlling the surface property by the filler of the support, the particle size and amount of the powder added to the magnetic layer, the roll surface shape of the calender treatment, and the like. The curl is preferably within ± 3 mm. It is easily estimated that the physical properties of the lower layer and the upper layer of the magnetic recording medium of the present invention can be changed depending on the purpose. For example, the elastic modulus of the upper layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the upper layer to improve the contact of the magnetic recording medium with the head.

[0065]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In addition, "part" means "part by mass" unless otherwise specified. <Production of Hexagonal Ferrite Magnetic Powder> Example A1 As a raw material for producing hexagonal ferrite, various compounds were weighed from the following basic formulation in terms of oxide (described in A1 of Table 1).

B ₂ O ₃ 4.7 mol BaCO ₃ 10.0 mol Fe ₂ O ₃ X mol CoCO ₃ 0.05 × X mol ZnO Y mol Nb ₂ O ₅ Z mol

The composition except B ₂ O ₃ was dissolved in citric acid at 120 ° C., and the temperature was kept at about 200 ° C. to uniformly mix the raw materials,
It was hydrolyzed at 450 ° C. Further, it was calcined in air at 600 ° C. to remove free carbon. After adding B ₂ O ₃ and thoroughly mixing with a powder mixer, the mixture was put into a Pt-Rh crucible attached to a stirrer, melted at 1300 to 1350 ° C. for 2 hours, and spouted between rotating stainless steel cooling twin rolls. An amorphous body was obtained by crushing. Then, the amorphous body was spread in a ceramic container to a thickness of 2 cm, transferred to an electric furnace maintained at 650 ° C. for 2 hours, immediately transferred to an electric furnace maintained at 850 ° C., and maintained for 3 hours. Then, the treated product was put into a metal hopper at room temperature and cooled to obtain a crystal powder. The crystal powder was pulverized with a planetary mill, immersed in a 2 mol / l acetic acid aqueous solution, kept at 80 ° C. for 5 hours to remove glass components, and filtered to collect fine crystals. The recovered fine crystals were washed with a large amount of ion exchanged water to obtain a ferromagnetic powder. Then, 300 g of the ferromagnetic powder thus obtained is added to 30 g.
It was well dispersed in 00 ml of water to obtain a slurry. Further, a chloride containing Al was mixed with 100 parts by weight of the untreated magnetic powder in an amount of 4 atomic% of Al / Fe and added to the slurry. After the slurry was sufficiently stirred, twice the equivalent amount of aqueous ammonia was added to the above chloride to deposit Al hydroxide on the surface of the magnetic powder. The obtained precipitate was filtered, washed with water, and dried at 120 ° C to obtain magnetic powder A1.

Example A2 Table 1 shows X, Y and Z in the above basic formulation.
A ferromagnetic powder was obtained in the same manner as in Example A1 except that the changes were made as described in (A2). Next, 300 g of the magnetic powder thus obtained was well dispersed in 3000 ml of water to obtain a slurry. Al / Fe is atomic%
Was mixed and added to the above slurry. After thoroughly stirring the slurry, 2 equivalents of N 2 with respect to the above chloride were added.
The aOH aqueous solution was added to deposit the hydroxide of AL on the surface of the magnetic powder. The resulting precipitate was filtered, washed with water, and dried to obtain magnetic powder A2.

Example A3 An aqueous suspension of hexagonal ferrite powder obtained in the same manner as in Example 1 and having Al hydroxide deposited on the surface of the magnetic powder (hexagonal ferrite concentration 100 g / L ) Under stirring at 60 ° C., an aqueous solution of sodium silicate (0.6% by weight of fine particle hexagonal ferrite powder as SiO ₂ ) and a zinc sulfate aqueous solution (fine particle hexagonal ferrite powder as ZnO 1 .8% by weight). Then, the pH of this suspension was adjusted to 7.5 with an aqueous sodium hydroxide solution, and aged for 30 minutes. Such a suspension is cooled to room temperature, filtered, washed with water, and then in air at 120 ° C.
Heat dried for 5 hours. The obtained dried product was placed in air for 6
After firing at 50 ° C for 60 minutes, pulverize with a jet mill,
On the surface of hexagonal ferrite particles, zinc silicate (Zn ₂ S
A hexagonal ferrite powder A3 having a coating layer composed of 5% by weight of zinc silicate based on the hexagonal ferrite powder in terms of i0 ₄ ) was obtained.

Comparative Example H1 Table 1 shows X, Y and Z in the above basic formulation.
The changes were made as described in (described in A2). The composition except B ₂ O ₃ is dissolved in citric acid at 120 ° C.
The starting materials were uniformly mixed and hydrolyzed at 450 ° C. Further, it was calcined in air at 600 ° C. to remove free carbon. After adding B ₂ O ₃ and thoroughly mixing with a powder mixer,
Put it in a Pt-Rh crucible with an agitator and add 1100
It was melted at 1200 ° C. for 2 hours, jetted between rotating stainless steel cooling twin rolls to obtain an amorphous body, and pulverized. Next, the amorphous body was spread in a ceramic container to a thickness of 2 cm, transferred into an electric furnace maintained at 650 ° C., held for 2 hours, immediately transferred into an electric furnace maintained at 800 ° C., and held for 2.5 hours. Then, the treated product was put into a metal hopper at room temperature and cooled to obtain a crystal powder. The crystal powder was pulverized with a planetary mill, immersed in a 2 mol / l acetic acid aqueous solution, kept at 80 ° C. for 5 hours to remove glass components, and filtered to collect fine crystals. The collected fine crystals were washed with a large amount of ion-exchanged water, dehydrated and dried at 100 ° C. to obtain a ferromagnetic powder. 300 g of the obtained magnetic powder was well dispersed in 3000 ml of water to form a slurry. Further CaCl
₂ against 100 parts by weight of untreated magnetic powder, Ca / Fe
Was added to the above-mentioned slurry. After sufficiently stirring the slurry, a 2-fold equivalent of an aqueous solution of NaOH was added to the chloride to add C on the surface of the magnetic powder.
The hydroxide of a was deposited. The precipitate obtained is filtered off,
After washing with water and drying, magnetic powder H1 was obtained.

Comparative Example H2 A ferromagnetic powder H2 was obtained in the same manner as Comparative Example H1 except that the treatment for depositing Ca hydroxide was not performed.

When each of the magnetic powders obtained above was analyzed by the X-ray diffraction method, it showed a magnetoplumbite structure. The ferromagnetic powder was observed with a transmission electron microscope to measure the average powder size. The mixture was degassed in nitrogen at 250 ° C. for 30 minutes, and the specific surface area was measured by the BET method. The magnetic characteristics were measured using a VSM with an applied magnetic field of 800 kA / m. The amount of stearic acid adsorbed was measured by the following. Hexagonal ferrite powder 5
g, stearic acid 0.02 mol / l, 0.05 m
Add to each flask containing a methyl ethyl ketone solution containing ol / l, 0.1 mol / l concentration. The flask was sealed and stirred with a magnetic stirrer for 20 hours.
Then, solid-liquid separation is performed with a centrifuge, and the stearic acid concentration in the supernatant is titrated with a 0.03 mol / l KOH / ethanol solution to determine the stearic acid concentration not adsorbed on the magnetic substance. Similarly, the concentration of non-adsorbed stearic acid is determined for each of the above magnetic substances having stearic acid concentrations. Then, the saturated adsorption amount of stearic acid per 1 g of hexagonal ferrite powder is determined and divided by the specific surface area (S _BET ) to determine the saturated adsorption amount of stearic acid per m ² , which is the stearic acid adsorption amount in the present invention. . The amount of stearylamine adsorbed was measured as follows. Hexagonal ferrite powder 5g
With stearylamine 0.02 mol / l, 0.05
Add to each flask containing a tetrahydrofuran solution containing mol / l, 0.1 mol / l concentration. The flask was sealed and stirred with a magnetic stirrer for 20 hours. Then, solid-liquid separation is performed with a centrifuge, and the stearylamine concentration in the supernatant is titrated with a 0.03 mol / l hydrochloric acid / ethanol solution to determine the concentration of stearylamine not adsorbed on the magnetic substance. Similarly, the concentration of unadsorbed stearylamine is determined for each of the above-mentioned magnetic substances having stearylamine concentrations. Next, the saturated adsorption amount of stearylamine per 1 g of hexagonal ferrite powder is determined and divided by the specific surface area (S _BET ) to determine the saturated adsorption amount of stearylamine per m ² , which is taken as the adsorption amount of stearylamine in the present invention. . Further, the adsorption amount of stearic acid and the like can be obtained by using gas chromatography. The characteristics of the obtained barium ferrite are shown in Table 1.

[0073]

[Table 1]

Preparation of Magnetic Recording Medium Using the barium ferrite obtained above, a magnetic tape was prepared as follows. Examples 1 and 2 and Comparative Examples 1 and 2 <Preparation of paint> In the examples, the indication "part" means "part by weight". Magnetic liquid formulation Barium ferrite (described in Table 2) 100 parts Binder resin Vinyl chloride copolymer 12 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization: 300) Polyester polyurethane resin 4 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 , -SO 3 Na group: 1 × 10 ^-4 eq / g containing) phenyl phosphonic acid 3 parts α- alumina (average particle size: 0.15 μm) 5 parts Carbon black (average particle size: 7 nm) 5 parts Butyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Nonmagnetic liquid prescription acicular hematite 80 parts (S _BET : 55 m ² / g, average major axis length: 0.10 μm, average acicular ratio: 7, pH: 8.8, aluminum treatment: Al ₂ O ₃ 20% (average particle size: 17 nm, DBP oil absorption: 80 ml / 100 g, S _BET : 240 m ² / g, pH 7.5) Binder resin Vinyl chloride copolymer 12 parts (-SO ₃ 1 × 10 ⁻⁴ eq / g of K group, degree of polymerization: 300) Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, —SO ₃ Na group: 1 × 10 ^-4 eq / g) Phenylphosphonic acid 3 parts Butyl stearate 3 parts Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 280 parts

For each of the above magnetic liquid formulation and non-magnetic liquid formulation, after kneading the pigment, polyvinyl chloride, phenylphosphonic acid and 50% by mass of each solvent with a kneader, the polyurethane resin and the remaining components were kneaded. Was added and dispersed with a sand grinder. To the obtained dispersion liquid, 15 parts of isocyanate was added to the non-magnetic liquid, 14 parts to the magnetic liquid, and 30 parts of cyclohexanone was added to each,
Filtering with a filter having an average pore size of 1 μm,
Coating solutions for forming the non-magnetic layer and for forming the magnetic layer were prepared.

The obtained coating liquid 1 for the lower non-magnetic layer was coated on a polyethylene terephthalate support having a thickness of 7 μm so that the thickness after drying was 1.5 μm, and immediately thereafter, for the lower non-magnetic layer. While the coating layer is still wet,
Wet simultaneous multilayer coating was carried out by controlling the coating amount of the magnetic liquid formulation so that a predetermined magnetic layer thickness was obtained, and while both layers were still in a wet state, they were passed through an aligning device for longitudinal alignment. The orienting magnet at this time passes through a rare earth magnet (surface magnetic flux 500 mT) and then a solenoid magnet (magnetic flux density 500 mT).
After passing through the inside, the magnetic layer was dried to such an extent that the orientation was not returned in the solenoid, and the magnetic layer was dried and wound. After that, the roll temperature was adjusted to 9 with a 7-step calendar composed of metal rolls
A web-shaped magnetic recording medium was obtained by carrying out calendering treatment at 0 ° C. and slitted into a width of 8 mm to prepare a sample of 8 mm video tape. The magnetic properties of the samples were measured using a vibrating sample magnetometer. Further, the surface roughness and electromagnetic conversion characteristics were measured. In addition, a sample of DDS cartridge tape was prepared by slitting to a width of 3.8 mm.

<Evaluation of tape> Electromagnetic conversion characteristics (output, C
/ N) was measured by the following method. 8 for data recording
MIG head on the millimeter deck (head gap 0.2μ
m, track width 17 μm, saturation magnetic flux density 1.5 T, azimuth angle 20 °, and reproducing MR head (SAL bias,
The MR element has Fe-Ni, a track width of 6 μm, a gap length of 0.2 μm, and an azimuth angle of 20 °). Relative speed between tape and head is 10.2m using MIG head
/ Sec, the optimum recording current is determined from the input / output characteristics of 1/2 Tb (λ = 0.5 μm), and a signal is recorded with this current, and the MR
Played on the head. C / N was set from the peak of the reproduced carrier to degaussing noise, and the resolution bandwidth of the spectrum analyzer was set to 100 kHz. The characteristics of the tape of Comparative Example 1 are shown.

The surface roughness was measured by using a light interference three-dimensional roughness meter "TOPO-3D" manufactured by WYKO (Arizona, USA) to measure a sample area of 250 μm square. In calculating the measurement value, corrections such as inclination correction, spherical correction, and cylindrical correction were performed according to JIS-B601, and the center surface average surface roughness Ra was used as the surface roughness value. Friction coefficient at room temperature (μ value): Friction coefficient of the first pass (RT μ1) of the magnetic layer surface and friction coefficient of the 100th pass (RT μ100) An 8 mm tape was passed at an angle of 180 degrees to a SUS420J of 4 mmφ, and a load of 10 g, Slide at a speed of 18 mm per second,
The friction coefficient was calculated based on Euler's formula. μ = (1 /
π) ln (T2 / 10) T2 is a sliding resistance value (g). The measurement was repeated up to 100 passes to determine the friction coefficient μ1 of the first pass and the friction coefficient μ100 of the 100th pass. 60
The friction coefficient (60 ° C. 90% μ1) in the first pass on the magnetic layer surface after storage at 90 ° C. RH for 1 week was also determined in the same manner as above.
Regarding the dirt on the guide pole, the dirt on the guide pole touching the magnetic layer surface after running the cartridge 5 times with a DDS drive was evaluated. The dirt of the guide pole was visually observed, wiped with a tissue, and the dirt was sensory evaluated. The evaluation was made into 5 grades, 1 being a small amount of stains, a large number being a large amount of stains, and 5 being the largest amount of stains.

[0080]

[Table 2]

[0081]

As described above, since the hexagonal ferrite powder particles according to the present invention have an appropriate fatty acid adsorption amount, the hexagonal ferrite powder particles according to the present invention are dispersed in a binder on a support. The magnetic recording medium of the present invention provided with the magnetic layer has a stable friction coefficient even after storage at high temperature and high humidity, and has less dirt and the like due to fatty acid metal salts and the like, less dirt on the guide pole, and storability. Excellent in. Further, the hexagonal ferrite powder of the present invention has a good affinity with a binder having a polar group, and the surface smoothness, output, S /
N is also excellent. In addition, in the electromagnetic conversion characteristics, it can be expected that DO (dropout) and MP (missing pulse) due to adhesion of dirt are reduced.

Claims (2)

[Claims] 1. A stearic acid adsorption amount of 3 to 7 μmol /
m ² and the adsorbed amount of stearylamine is 1 to 4 μmol
/ M ² Hexagonal ferrite powder. 2. A magnetic recording medium having a magnetic layer on a support, wherein the magnetic layer contains the hexagonal ferrite powder according to claim 1.