JP2002353016A - Ferromagnetic metal powder and magnetic recording medium containing the ferromagnetic metal powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ferromagnetic metal powder which has iron as a main component and has superior electromagnetic conversion characteristic and superior traveling durability, and to provide a recording medium containing the ferromagnetic metal powder. SOLUTION: This ferromagnetic metal powder has iron powder having oxide films on the surfaces of its particles as a main component. The oxide films contain oxide crystals, and thicknesses ratios of the oxide films for the sizes of the crystals are 0.5-1.1. Further, this magnetic recording medium contains the ferromagnetic metal powder in its magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferromagnetic fine metal powder and a magnetic recording medium having a magnetic layer containing the ferromagnetic metal powder provided on a support. The present invention relates to a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art At present, magnetic recording media are tapes for recording,
Widely used, such as video tapes and computer disks. The configuration of the magnetic recording medium is such that a magnetic layer is laminated on a support, and in a tape-shaped medium, a back coat layer is laminated on the surface opposite to the magnetic layer as necessary. In a disk-shaped medium, a configuration is adopted in which magnetic layers are laminated on both surfaces of a nonmagnetic layer support.

[0003] Generally, in a coating type magnetic recording medium, a ferromagnetic powder is dispersed in a binder, and a lubricant,
An abrasive and, if necessary, carbon black are added and laminated on a support. In the case of a deposition type magnetic recording medium, a magnetic film is formed on a support by a vacuum deposition method. The magnetic substance used in the vacuum deposition method is a metal or alloy mainly composed of cobalt deposited in an oxygen atmosphere, and a protective film or a lubricant film is formed on the deposited magnetic film as needed.

[0004] With respect to the magnetic recording medium thus obtained,
In recent years, needs for media having higher performance have been increasing. For example, audio tapes for recording and reproducing music are required to have higher original sound reproduction capabilities. In addition, video tapes are required to have excellent original image reproduction capability. Further, computer backup tapes / disks are required to have high durability and no data loss. In addition, it is required that the electromagnetic conversion characteristics have little change over time and there is no deterioration in running durability.

[0005] In order to have such excellent electromagnetic conversion characteristics and ensure running durability, development of a magnetic material having high Hc, high orientation, high weather resistance, and stable binders and lubricants has been developed. In addition, thinning and smoothing of the magnetic layer are performed. For example, there has been proposed a coating type magnetic recording medium having a configuration in which a magnetic layer is thinned in order to realize a high output of the magnetic layer and an intermediate layer is laminated between the support and the magnetic layer.

[0006]

The above magnetic recording medium is
In reducing the thickness of the magnetic layer, attempts have been made to increase the degree of filling by miniaturizing the ferromagnetic powder particles, increase the recording density, and smooth the surface of the magnetic layer to increase the recording / reproducing efficiency. However, when the magnetic layer is smoothed, the friction coefficient increases, so that problems such as poor running are likely to occur. Therefore, in order to reduce the friction coefficient without impairing the smoothness, carbon black and a lubricant have been conventionally added to the magnetic layer.

However, when a large amount of carbon black is used, the maximum magnetic flux density (Bm) and the residual magnetization (Bm) of the magnetic layer are increased.
r) also decreases, so that the electromagnetic conversion characteristics cannot be improved. In addition, when a large amount of a lubricant such as a fatty acid or a fatty acid ester is used, the magnetic layer is plasticized, so that there is a problem that durability is reduced. On the other hand, in order to enable high-speed transfer, it is necessary to increase the relative speed between the head for recording and reproducing signals and the magnetic tape. But,
When the relative speed is increased, the head and the magnetic tape slide at high speed, so that the surface of the magnetic tape is liable to be damaged such as being scraped. Further, the shavings formed on the surface of the head adhere to the surface of the head and cause head burn-in stain, which causes a reduction in output due to spacing loss. Particularly in an environment of low humidity, the coefficient of friction between the head and the medium is reduced, and the cleaning power of the head is reduced. Therefore, in order to enable high-speed transfer, it is necessary to develop a magnetic tape having higher durability.

As a method of increasing the surface strength of the magnetic tape to increase the durability, there is a method of adding an abrasive to the magnetic layer. According to this method, there is an advantage that not only the surface strength of the magnetic tape is increased, but also the cleaning action of removing the adhered matter on the head surface by sliding with the head is enhanced. However, it is necessary to use a large amount of abrasive in order to obtain a strength sufficient to withstand high-speed sliding. If a large amount of abrasive is used, the maximum magnetic flux density (B
Not only does m) decrease and the electromagnetic conversion characteristics decrease, but also there is a problem that the head is excessively worn and the life of the head is shortened. In order to cope with this problem, researches for optimizing the amount, size, hardness, shape, and the like of the abrasive to be used have been conducted, but no satisfactory results have yet been obtained.

The present invention has been made in order to solve the problems of the prior art, and an object of the present invention is to provide a ferromagnetic metal powder having excellent abrasion resistance and having a cleaning action. It is in. Another object of the present invention is to provide a magnetic tape using the ferromagnetic metal powder having a cleaning action, which can be used in a magnetic recording / reproducing system having a high recording density and a high transfer speed. . That is, an object of the present invention is to provide a new magnetic tape having sufficient electromagnetic conversion characteristics, durability, and head wear resistance under a high recording density and a high transfer speed.

[0010]

In order to develop a ferromagnetic metal powder having abrasion resistance and a magnetic recording medium having a high density recording / high output and a high storage stability, the present inventors have developed a fine magnetic recording medium. A detailed examination of the granularity of the magnetic metal powder and the structure of the metal crystal part and the oxide film showed that the crystallite size of the oxide film crystal was related to the cleaning performance of the head, and a ferromagnetic metal powder with a specific crystallite size was used. The present inventors have found that the magnetic recording medium has excellent electromagnetic conversion characteristics and excellent running durability, and have completed the present invention.

That is, the invention according to claim 1 is a ferromagnetic metal powder containing iron as a main component and having an oxide film on its surface, wherein the oxide film contains an oxide crystal, and the crystal of the oxide crystal The ratio of the thickness of the oxide film to the element size is 0.5
To 1.1, which relates to a ferromagnetic metal powder.

A second aspect of the present invention provides a magnetic layer containing a ferromagnetic metal powder and a binder or a nonmagnetic layer containing a nonmagnetic powder and a binder, a ferromagnetic metal powder and a binder on a nonmagnetic support. And a magnetic layer comprising, in this order, the ferromagnetic metal powder is the ferromagnetic metal powder according to claim 1.

Further, preferred embodiments of the magnetic recording medium of the present invention include the following. (1) The coercive force (Hc) of the ferromagnetic metal powder is 159.
2-238.8 kA / m (2000-3000 O
e), the saturation magnetization (σs) is 125 to 180 A · m ² / k
g, SFD (switching field distribution) 0.4
A magnetic recording medium that is: (2) A magnetic recording medium wherein the thickness of the magnetic layer is 0.05 to 1.0 μm and the thickness of the nonmagnetic layer is 0.5 to 2.0 μm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the ferromagnetic metal powder of the present invention and a magnetic recording medium containing the same will be described in more detail.

[Ferromagnetic Metal Powder] The ferromagnetic metal powder of the present invention is a ferromagnetic metal powder containing iron as a main component and having an oxide film on its surface, wherein the oxide film contains oxide crystals. The ratio of the thickness of the oxide film to the crystallite size of the oxide crystal is 0.5 to 1.1.

The ferromagnetic metal powder of the present invention has an oxide film containing oxide crystals on the surface of a metal mainly composed of iron. Hereinafter, a metal mainly composed of iron and an oxide film on the surface of the metal will be described in this order.

[0017] 1. Metal mainly composed of iron The metal mainly composed of iron in the present invention contains at least 50% by mass or more of iron. Such ferromagnetic metals include:
For example, Fe, Fe-Co, Fe-Ni, Co-Ni-
Fe or an Fe alloy such as Fe can be used. Further, the metal mainly composed of iron in the present invention is the above-mentioned Fe
Alternatively, a metal other than the Fe alloy can be contained within a range of 20% by mass or less. Examples of metals other than Fe or an Fe alloy include aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, Examples include tantalum, tungsten, rhenium, silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, bismuth and the like. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. Further, the shape of the metal containing iron as a main component is not particularly limited, as long as it is acicular particles or spindle-shaped particles,
It is preferable because a high coercive force (Hc) can be obtained.

[0018] 2. The oxide film on the metal surface includes an oxide crystal, and a ratio of a thickness of the oxide film to a crystallite size of the oxide crystal is 0.5 to 1.1. When the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal is small, it means that the number of crystals present in the oxide film per unit volume is close to one. Conversely, when the ratio of the thickness of the oxide film to the crystallite size of the oxide film is large, it means that a plurality of crystals are contained in the oxide film per unit volume. Therefore, when the two are compared, it can be said that the number of crystals per unit volume which is closer to one is greater in abrasion resistance and superior in head cleaning performance than that in which a plurality is included. Note that the relationship between the thickness of the oxide film measured from the direction perpendicular to the particle surface of the ferromagnetic metal powder and the crystallite size in the film indicates that the oxide film is thicker and thinner than the crystallite size. There are things. The fact that the crystallite size of the oxide crystal is larger than the thickness of the oxide film means that
Although seemingly contradictory, the (311) direction of the oxide crystal whose crystallite size is measured can be considered to have an angle that does not coincide with the vertical direction of the particle surface. It is not at all inconsistent that the thickness is larger than the thickness of the oxide film.

The ratio of the thickness of the oxide film to the crystallite size of the oxide crystal is 0.5 to 1.1.
It is preferably 1.0, and more preferably 0.5 to 0.9. The present inventor has conducted various studies using Rietveld analysis described below. As a result, the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal in the range of 0.5 to 1.1 is the above-mentioned metal. It has been found that a ferromagnetic metal powder having the oxide crystal on its surface has a particularly suitable hardness and has an excellent cleaning effect on head contamination. When the crystallite size of the oxide crystal is large, the core metal can be densely covered with the oxide crystal,
It has also been found that an oxide film with good stability can be obtained.

The crystallite size of the oxide crystal is determined by the Hall equation from the spread of the peak half width of X-ray diffraction.

Β cos θ / λ = 1 / ε + 2η sin θ / λ (where, θ: diffraction angle, λ: X-ray wavelength, β: spread of diffraction peak, ε: crystallite size, η: crystal lattice spacing in lattice strain This is the integral width of the size distribution of.), And can be obtained as the reciprocal of the value at which the straight line of the plot of sin θ / λ vs βcos / λ cuts off the vertical axis.
(Hall, WH; Proc. Phys. Soc., A62., 741 (1949)).

For the peak width of the X-ray diffraction, the {311} plane and the {622} plane of magnetite or iron spinel crystal obtained by Rietveld analysis are used. The X-ray diffraction pattern to which the Rietveld analysis is applied is obtained by packing a ferromagnetic metal powder in a powder sample plate and using a Rigaku X-ray diffractometer RIN.
Using T2500H (copper negative electrode, with graphite monochromator), voltage-current: 50 kV-200 mA,
Slit system: 1 ° -1 ° -0.3mm, measurement range (2
θ): 25 to 105 °, measurement mode: step scan, step interval (2θ): 0.05 °, and integration time in each step: 8 seconds.

The thickness of the oxide film can be measured by the following method. First, particles ultrasonically dispersed in water were placed on a mesh, and a transmission electron microscope H-90 manufactured by Hitachi, Ltd. was used.
The particles are photographed using a 00 type, and a photograph with a total magnification of 3,000,000 times is obtained. In the particles in the photograph, the metal part in the center is black, and the surrounding coating part is observed to be whiter than the center. Next, the boundary line between the metal part and the coating part and the line on the coating part surface were taken in with a scanner, and the distance between the lines was set to Kontron.
The average thickness of the oxide film is determined by automatic measurement with the image analyzer KS-400.

As for the composition of the oxide film, the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal is 0.5 to 0.5%.
There is no particular limitation as long as it is within the range of 1.1,
Iron ions (Fe ²⁺ , Fe ³⁺ ), oxygen (O ²⁻ ), and aluminum (Al ³⁻ ) can be contained at any ratio. In order to easily adjust the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal in the range of 0.5 to 1.1, various additives are added to the ferromagnetic metal powder of the present invention. can do. The amount of the various additives was Co to Fe
Is 10 to 45 at%, Al is 5 to 15 at%, and Y is 5 to 12 at%, preferably Co is 15 to 30 at%, Al is 7 to 10 at%, and Y is 8 to 12 at%.
It is.

[0024] 3. Metallic crystal part and oxidation of ferromagnetic metal powder
Structural Analysis of Product Crystal Part The Rietveld analysis method in X-ray diffraction measurement is applied to the structural analysis of the metal crystal part and the oxide crystal of the ferromagnetic metal powder of the present invention. X of ferromagnetic metal powder containing Fe as a main component
In the line diffraction, a small broad peak exists in addition to the main peak from the α-Fe crystal. It has been confirmed that this small diffraction peak originates in the oxide film on the surface of the ferromagnetic metal powder, and its strongest peak angle is close to the magnetite crystal. However, other characteristics are not necessarily disclosed. The present inventor applied the X-ray diffraction Rietveld analysis method to the X-ray diffraction pattern analysis of the metal magnetic material including the small diffraction peak, and determined the crystal structure of α-Fe and the oxide of the surface coating and its crystallinity. And succeeded in making the present invention based on this success.

That is, the present inventor conducted a detailed analysis of the structure analysis of the metal crystal part and the oxide crystal of the ferromagnetic metal powder by applying Rietveld analysis in X-ray diffraction measurement. It has been found that when a ferromagnetic metal powder having a large crystallite size of the product crystal is used, the cleaning properties of the head during running of the magnetic tape are excellent. In particular, a magnetic recording medium using a ferromagnetic metal powder in which the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal of the oxide film is 0.5 to 1.1 has excellent electromagnetic conversion characteristics and excellent running properties. It has been found that it exhibits durability.

The X-ray diffraction Rietveld analysis method is described, for example, in "5th X-ray Analysis Seminar-Powder X-Ray Rietveld Analysis p21" (Japan Society for Analytical Chemistry, X-ray analysis research conference). As described above, based on the measured X-ray diffraction pattern, the parameters derived from the X-ray diffraction device and the parameters related to the crystal are precisely calculated, and the calculated X
The crystal structure analysis is performed while approximating the X-ray diffraction pattern to the X-ray diffraction pattern. In the crystal analysis of the ferromagnetic metal powder in the X-ray diffraction Rietveld analysis method, for example, a Rigaku X-ray diffractometer RINT2500H is used.
You can use the "Riet belt analysis" software attached to.

[0027] 4. Characteristics of Ferromagnetic Metal Powder The crystallite size of the ferromagnetic metal powder of the present invention is, for example, 80
Å250 °, preferably 100-200 °. The average major axis length is usually 0.00
It is 5 to 0.2 μm, and preferably 0.03 to 0.15 μm. Average major axis length / average minor axis length is 3 to 20
And preferably 4 to 10. In addition, when the ferromagnetic metal powder of the present invention is represented by a specific surface area by the BET method, 25
８０80 m ² / g, preferably 30-70 m ² / g. When the specific surface area is 25 to 80 m ² / g, noise can be suppressed low and a suitable smooth surface can be obtained.

Coercive force (Hc) of the ferromagnetic metal powder of the present invention
Is, for example, 159.2 to 238.8 kA / m (200
0 to 3000 Oe), and the saturation magnetization (σs) is 125 to 1
It is preferable that 80 A · m ² / kg and SFD are 0.4 or less. Coercive force (Hc) 159.2 to 238.8k
With A / m, stable recording is possible even at a small recording wavelength. Further, the saturation magnetization (σs) is 125 to 1
If it is 80 A · m ² / kg, excellent recording signal intensity can be obtained. In addition, SFD (switching field distributi
When on) is 0.4 or less, the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. The change over time of the demagnetization in the saturation magnetization s is preferably small, and the demagnetization after storage at 60 ° C. and 90% RH for one week is preferably 15% or less, more preferably 10% or less. Demagnetization over time is 15
%, The storage stability is good, and a magnetic recording medium having excellent electromagnetic conversion characteristics can be provided.

Each value of the size, average major axis length, average minor axis length and average needle ratio of the ferromagnetic metal powder of the present invention can be determined by the following measuring methods. The average major axis length of the ferromagnetic metal powder is
The particles ultrasonically dispersed in water are placed on a mesh, and the particles are photographed using a transmission electron microscope Model H-9000 manufactured by Hitachi, Ltd. to obtain a photograph with a total magnification of 200,000. This particle photograph was placed on a digitizer of an image analyzer KS-400 manufactured by Kontron, and the contour of the powder was traced to determine the particle size, major axis length, minor axis length, and needle ratio, and an average value of 500 particles was obtained. I do.

[0030] 5. Production of Ferromagnetic Metal Powder of the Present Invention Preferred methods for producing the ferromagnetic metal powder of the present invention include the following methods. A starting material having a long axis length and an acicular ratio that are well aligned and having a uniform particle size is subjected to a sintering prevention treatment, and a metal oxide (eg,
FeO _x : 1 ≦ x ≦ 1.5, for example, Fe ₂ O ₃ , Fe
The acicular ratio of a metal (eg, Fe) can be controlled from ₃ O ₄ ). Examples of the starting material include monodisperse goethite or monodisperse hematite.

The average major axis length of the starting material is 0.03 to
The needle ratio is preferably from 3 to 15 at 0.25 μm. It is important that the shape of the starting material, the major axis length, the minor axis length, and the needle ratio are well matched. The average major axis length of the starting material is 0.0
When the thickness is 3 to 0.25 μm, the coercive force (Hc) and the saturation magnetization (σs) can be set in target ranges. When the ferromagnetic metal powder of the present invention is used for a magnetic recording medium, a desired surface can be obtained. Roughness is obtained, and excellent S / N with small noise can be obtained. Further, when the needle ratio of the starting material is 3 to 15, a desired coercive force Hc can be obtained when the ferromagnetic metal powder is used, and it can be used as a medium for high density recording. Further, since Bm of the magnetic recording medium is large, the overwrite characteristics are also excellent.

In order to form an oxide film on the surface of the starting material, aluminum oxide (Al ₂ O ₃ ) is deposited on the surface of the starting material. A known method can be used as a method of depositing Al ₂ O ₃ . In addition, the oxide film can be formed around the source metal by a known oxidation method, for example, a gradual oxidation treatment.
If carbon dioxide gas is contained in the gas used at the time of slow oxidation, it will be adsorbed at basic points on the surface of the ferromagnetic metal powder,
Such carbon dioxide gas may be contained. Further, a predetermined additive (Y or the like) can be added at the time of forming the oxide film. In the case of an oxide film in which the ratio of the thickness of the oxide film to the crystallite size of the oxide crystal is in the range of 0.5 to 1.1, the oxygen concentration in the ventilation gas at the time of forming the oxide film, the processing temperature and the processing time are appropriately adjusted. It can be formed by adjusting.

As means for adjusting various values of the ferromagnetic metal powder of the present invention, the following methods (1) and (2) can be exemplified. (1) To mainly specify the element composition inside the ferromagnetic metal powder. Particularly in the case of a ferromagnetic metal powder mainly composed of Fe,
Identify trace elements that interact with Fe. As the trace element, Ca, Mg, Co, Ni, Cr and the like are preferable.
It is preferable to add this trace element at the time of preparation of goethite or hematite and / or after the preparation by surface treatment. (2) Pretreatment before reduction in a method of converting an oxide of a ferromagnetic metal element into a ferromagnetic metal powder by reduction, for example, dehydration conditions such as goethite, annealing conditions, and the like;
For example, temperature, reducing gas, reduction processing time, etc. are selected. In particular, in order to make the shape of the metal part, the size of the major axis and the minor axis uniform, and the form and the acicular ratio as large and uniform as 3 to 12, the reduction treatment conditions are selected and the metal part is selected. It is very important to adjust the shape, the crystallinity, the thickness of the oxide layer, and the crystallinity of the oxide layer.

Specifically, the conditions for treating the trace element-containing goethite obtained in the above (1) are as follows. The dehydration conditions are usually 250 to 400 ° C., preferably 300 to 40 ° C. in a rotary electric furnace under a nitrogen atmosphere.
It is carried out at 0 ° C. for 0.5 to 2 hours, preferably for 0.5 to 1 hour. The annealing conditions are usually 500 to 800 ° C., preferably 550 to 700 ° C. for 1 to 5 hours, preferably 2 to 3 hours in a stationary reduction furnace under a nitrogen atmosphere.
Time. After the dehydration treatment, a step of washing the hematite obtained by the dehydration treatment with water before the annealing treatment to remove the soluble alkali metal may be provided.

The reduction conditions are usually 350 to 600 ° C., preferably 425 to 600 ° C. in a rotary reducing furnace under a hydrogen atmosphere.
After a reduction treatment at a temperature of 530 ° C. for a period of usually 0.25 to 1 hour, preferably 0.25 to 0.5 hour, and then replacing the atmosphere with nitrogen, the temperature is usually 450 to 650 ° C., preferably 5 to 500 ° C.
Heating at a temperature of 00 to 600 ° C. for usually 0.5 to 3 hours, preferably 1 to 2 hours, then switching to pure hydrogen and performing a reduction treatment at the above temperature for 3 to 5 hours.

The monodisperse goethite or monodisperse hematite is finally reduced to pure metal with pure hydrogen. Annealing with αFe ₂ O ₃ at an intermediate stage is useful for increasing the crystal ratio. When reducing from αFe ₂ O ₃ to Fe ₃ O ₄ or FeO, various reducing gases can be used instead of pure hydrogen. Since water is known to be involved in sintering during reduction, the water generated by reduction must be removed from the system in a short time in order to adjust the generation of generated nuclei to one as much as possible and to increase the crystallinity. It is preferable to remove water or adjust the amount of water generated by reduction. Such adjustment of water can be performed by adjusting the partial pressure of the reducing gas or the amount of the reducing gas.

[0037] [magnetic recording medium] 1. Magnetic Layer The ferromagnetic metal powder is used for the magnetic layer in the magnetic recording medium of the present invention. When a magnetic layer is formed using the ferromagnetic metal powder of the present invention, the ferromagnetic metal powder of the present invention, a binder, a curing agent, and the like are usually used in the preparation of a magnetic paint, methyl ethyl ketone, dioxane, It is kneaded and dispersed together with a solvent such as cyclohexanone, ethyl acetate or the like to obtain a coating material for forming a magnetic layer. The kneading and dispersion can be performed according to a usual method.

As the binder used for the magnetic layer of the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used. Preferred binders are vinyl chloride resins, vinyl chloride-vinyl acetate resins,
Cellulosic resins such as nitrocellulose, phenoxy resins,
It is a polyurethane resin. Among them, it is more preferable to use a vinyl chloride resin, a vinyl chloride-vinyl acetate resin, or a polyurethane resin because the hardness of the back coat layer described later is close to the hardness of the magnetic layer and the back reflection can be reduced. Furthermore, a part of the binder includes a polyurethane resin containing a cyclic structure and an ether group,
It is preferable from the viewpoint of improving dispersibility.

A binder such as a polyurethane resin is contained in a molecule.
-SO_ThreeM, -OSO_ThreeM, -COOM, -PO_ThreeM
M ', -OPO_ThreeMM ', -NRR', -N⁺RR'R "
(Where M and M ′ each independently represent a hydrogen atom,
Li metal, alkaline earth metal or ammonium salt,
R, R 'and R "are each independently an alkyl having 1 to 12 carbons.
At least one polar group selected from
And particularly preferably -SO_ThreeM, -O
SO_ThreeM. The amount of these polar groups is preferably 1
× 10^-Five~ 2 × 10^-Foureq / g, particularly preferably
5 × 10^-Five~ 1 × 10 ^-Foureq / g. The amount of polar groups
1 × 10^-Five~ 2 × 10^-Foureq / g, binding
Agent is sufficiently adsorbed on powder, and binder is sufficiently dissolved in solvent
Therefore, the dispersibility is also improved.

Specific examples of these binders used in the magnetic layer include, for example, VAG manufactured by Union Carbide.
H, VYHH, VMCH, VAGF, VAGD, VRO
H, VYES, VYNC, VMCC, XYHL, XYS
G, PKHH, PKHJ, PKHC, PKFE, Nissin Chemical Industries' MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, Electrochemical 1000
W, DX80, DX81, DX82, DX83, 100
FD, ZEON MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N23 made by Nippon Polyurethane
02, N2304, Dainippon Ink Pandex T-5
105, T-R3080, T-5201, Barnock D
-400, D-210-80, Crisbon 6109, 7
209, Toyobo Byron UR8200, UR830
0, UR-8700, RV530, RV280, Daiferamine 4020, 5020, 5100, 5100 manufactured by Dainichi Seika
300, 9020, 9022, 7020, Mitsubishi Chemical M
X5004, Sanyo Kasei sampler SP-150, Asahi Kasei Saran F310, F210, and the like.

The binder used in the magnetic layer is used in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, based on the magnetic powder. 5 to 30% by weight when using a vinyl chloride resin, 2 when using a polyurethane resin.
-20% by weight, and polyisocyanate is preferably used in combination of 2-20% by weight,
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 magnetic recording medium of the present invention, when polyurethane is used, the glass transition temperature is -50 to 150C, preferably 0 to 100C,
Breaking elongation is 100-2000%, breaking stress is 0.49-
98 MPa (0.05 to 10 kg / mm ² ), yield point 0.49 to 98 MPa (0.05 to 10 kg / mm ² )
Is preferred.

Number average molecular weight (Mn) of polyurethane resin
Is preferably from 5,000 to 100,000, more preferably from 10,000 to 50,000, particularly preferably from 20,000 to 40,000. When the number average molecular weight is in the range of 5,000 to 100,000, the strength and durability of the coating film are sufficient, and the solubility and dispersibility in a solvent are also good.

In a polyurethane resin containing a cyclic structure and an ether group, the cyclic structure affects rigidity, and the ether group contributes to flexibility. This polyurethane resin has high solubility, a large radius of inertia (expansion of molecules), and good dispersibility of powder. In addition, the polyurethane resin has two characteristics of hardness (high Tg, high Young's modulus) and toughness (elongation) of the polyurethane resin itself.

The coating material for forming a magnetic layer contains α
-Includes commonly used additives or fillers such as abrasives such as Al ₂ O ₃ and Cr ₂ O ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, silicone oils, and dispersants. You may go out. In the magnetic layer of the magnetic recording medium of the present invention, Tg is preferably 30 to 150 ° C. from the viewpoint of improving running durability.
Further, the thickness of the magnetic layer of the magnetic recording medium of the present invention is preferably from 0.03 to 0.5 μm from the viewpoint of sharpness of magnetization reversal for improving digital recording performance.
It is more preferred that the thickness be from 0.05 to 0.3 μm. Also,
The magnetic recording medium of the present invention preferably has a squareness ratio of 0.82 or more and an SFD of 0.4 or less from the viewpoint of high output and high erasing characteristics.

[0045] 2. Non-magnetic support The non-magnetic support used in the magnetic recording medium of the present invention is preferably a flexible support. For example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN)
Such as polyesters, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfon, aramid,
A known film such as an aromatic polyamide can be used.
These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment and the like in advance. In order to achieve the object of the present invention, the nonmagnetic support has a center line average surface roughness of usually 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less.
It is preferable to use one having a size of μm or less. Further, it is preferable that these supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The shape of the surface roughness can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and organic fine powders such as acrylic.

The magnetic recording medium of the present invention widely includes those having a magnetic layer on one surface of the nonmagnetic support. The magnetic recording medium of the present invention includes those having a layer other than the magnetic layer. For example, a backcoat layer provided on the surface opposite to the magnetic layer, a nonmagnetic layer containing nonmagnetic powder, a soft magnetic layer containing soft magnetic powder, a second magnetic layer, a cushion layer, an overcoat layer, an adhesive layer, and a protective layer You may have. These layers can be provided at appropriate positions so that the function can be effectively exhibited. The magnetic recording medium of the present invention is preferably a magnetic recording medium having a nonmagnetic layer containing a nonmagnetic inorganic powder and a binder on a nonmagnetic support and the magnetic layer in this order.

[0047] 3. Non-magnetic layer The non-magnetic layer is not particularly limited in its configuration as long as it is substantially non-magnetic, but is usually made of at least a resin, and preferably contains a powder, for example, an inorganic powder or an organic powder in the resin. And those dispersed in This inorganic powder is usually a non-magnetic powder, but a magnetic powder can be used as long as the lower layer is substantially non-magnetic. Here, that the lower layer is substantially a non-magnetic layer means that the lower layer is allowed to have magnetism as long as the electromagnetic conversion characteristics of the upper layer are not substantially reduced.

The nonmagnetic powder can be appropriately selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and nonmagnetic metals. Examples of the inorganic compound include titanium oxide (TiO ₂ , TiO), α-alumina, β-alumina, γ-alumina, α-iron oxide, chromium oxide, zinc oxide, tin oxide, and α-alumina having an α conversion of 90 to 100%. Tungsten, vanadium oxide, silicon carbide, cerium oxide, corundum, silicon nitride, titanium carbide, silicon dioxide, magnesium oxide, zirconium oxide, boron nitride, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, goethite, hydroxide Aluminum or the like can be used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred are titanium dioxide and iron oxide. Examples of the non-magnetic metal include Cu, Ti, Zn, and Al.

The average particle diameter of the non-magnetic powder is 0.00
It is preferably from 5 to 2 μm, but if necessary, non-magnetic powders having different average particle diameters may be combined, or even a single non-magnetic powder may have the same effect by broadening the particle size distribution. Among them, preferred are those having an average particle diameter of 0.0
It is a non-magnetic powder of 1 to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle size is 0.08 μm.
m or less, and in the case of a needle-shaped metal oxide, the average major axis length is preferably 0.3 μm or less.
It is more preferably 2 μm or less. Tap density is typically 0,1.
3-1. 5 g / ml, preferably 0.4 to 1.3 g /
ml. The water content of the nonmagnetic powder is usually 0.2 to 5% by weight, preferably 0.3 to 3% by weight, and more preferably 0.3 to 1.5% by weight. The pH value of the non-magnetic powder is 6
Particularly preferred is from 9 to 9. The specific surface area of the non-magnetic powder is 1 to 100 m ² / g, preferably 5 to 50 m ² / g, more preferably 7 to 40 m ² / g. The nonmagnetic powder preferably has a crystallite size of 0.01 to 2 μm. D
The oil absorption using BP is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 2 to 100 ml / 100 g.
It is 0 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spindle shape, a spherical shape, a polyhedral shape, and a plate shape.

Specific examples of the non-magnetic powder used for the non-magnetic layer include Nanotite manufactured by Showa Denko and HI manufactured by Sumitomo Chemical.
T-100, Hit-82, α-iron oxide DP manufactured by Toda Kogyo
N-250BX, DPN-245, DPN-270B
X, DPN-550BX, DPN-550RX, DBN
-650RX, DAN-850RX, titanium oxide TTO-51B, TTO-55A, TTO-55 manufactured by Ishihara Sangyo
B, TTO-55C, TTO-55S, TTO-55
D, SN-100, titanium industry STT-4
D, STT-30D, STT-30, STT-65C,
α-iron oxide α-40, Teica titanium oxide MT-100
S, MT-100T, MT-150W, MT-500
B, MT-600B, MT-100F, MT-500H
D, Sakai Chemical FINEX-25, BF-1, BF-1
0, BF-20, ST-M, Dowa Mining Iron Oxide DEFI
CY, DEFIC-R, Nippon Aerosil AS2B
M, TiO ₂ P25, Ube Industries 100A, 500A,
And baked products thereof.

As for the binder, lubricant, dispersant, additive, solvent, dispersing method, etc. of the non-magnetic layer, those described above for the magnetic layer can be applied. 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 like, the known technology for the magnetic layer can be applied.

[0052] 4. Back coat layer When the magnetic recording medium of the present invention has a back coat layer,
It is preferable to use a particulate oxide for the back coat layer. As the particulate oxide, it is preferable to use any of titanium oxide, α-iron oxide and a mixture thereof. Conventionally used titanium oxide and α-iron oxide can be used. The shape of the particles is not particularly limited. In the case of a spherical shape, one having a particle size of 0.01 to 0.1 μm is suitable, and in the case of a needle shape, one having a needle ratio of 2 to 20 is suitable, and the long axis length is 0.05. It is preferably about 0.3 μm. At least a part of the surface of the particulate oxide is
Modified to another compound or another compound, for example, Al
_It may be coated with ₂ O ₃ , SiO ₂ or ZrO ₂ .

It is preferable to use carbon black in the back coat layer for preventing static charge. As the carbon black used for the back coat layer, those commonly used for magnetic recording tapes can be widely used. For example, furnace black for rubber, thermal black for rubber, carbon black for color, acetylene black and the like can be used. In order to prevent the unevenness of the back coat layer from being reflected on the magnetic layer, the particle size of the carbon black is preferably set to 0.3 μm or less. A particularly preferred particle size is 0.01 to 0.1 μm. The amount of carbon black used in the back coat layer is preferably in a range where the optical transmission density (transmission value of TR-927 manufactured by Macbeth) is 2.0 or less.

In order to improve running durability, it is advantageous to use two types of carbon black having different average particle sizes. In this case, the average particle size is 0.01 to
A first carbon black in the range of 0.04 μm;
The combination with the second carbon black having an average particle size in the range of 0.05 to 0.3 μm is preferred. Second
The content of carbon black is 0.1% with the total amount of the particulate oxide and the first carbon black being 100 parts by mass.
1 to 10 parts by weight is suitable, and 0.3 to 3 parts by weight is preferred.

The mass ratio of the particulate oxide to carbon black is from 60/40 to 90/10, more preferably 70/40.
30 to 80/20. As described above, by including the particulate oxide in a larger amount than the carbon black,
A back coat layer having good powder dispersibility and a smooth surface can be formed. The paint for forming a back coat layer having such a composition has higher thixotropy than a conventional paint for forming a back coat mainly composed of carbon black. For this reason, it is possible to perform the application by the extrusion method or the gravure method at a high concentration. By applying such a high-concentration paint, it is possible to form a back coat layer having high adhesive strength to a support and high mechanical strength despite its thin film thickness.

The amount of the binder used is selected from the range of 10 to 40 parts by mass, more preferably 20 to 32 parts by mass, based on the total mass of the particulate oxide and carbon black as 100 parts by mass. The film strength of the back coat layer thus formed is high, and the surface electric resistance is low. As the binder for the back coat layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used.

The back coat layer can be prepared by applying a coating material for forming a back coat layer in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent, on the surface opposite to the magnetic layer. it can. As in the above preferred embodiment, if the amount of the particulate oxide used is larger than the carbon black, sufficient dispersibility can be ensured, so that the back coat layer is formed without performing the roll kneading conventionally required. Paint can be prepared. Further, if the content ratio of carbon black is low, the amount of residual cyclohexanone after drying can be reduced even when cyclohexanone is used as a solvent.

[0058] 5. The layered magnetic layer may be composed of a single layer or two or more layers. The thickness of the magnetic layer is, for example, 0.03-1.
μm, preferably 0.05 to 0.5 μm, more preferably 0.05 to 0.3 μm. Also,
A magnetic recording medium having two magnetic layers is also preferable. In this case, for example, the upper layer is 0.2 to 2 μm, preferably 0.2 to 2 μm.
It can be 1.5 μm and the lower layer can be 0.8-3 μm. In the case where the magnetic layer is solely used, it is usually 0.1
To 5 μm, preferably 0.1 to 3 μm, more preferably 0.1 to 1.5 μm. When a soft magnetic layer is provided between the nonmagnetic support and the magnetic layer, for example, the magnetic layer is set to 0.03 to 1 μm, preferably 0.05 to 0.5 μm, and the soft magnetic layer is set to 0.8 to 3 μm. Can be On the other hand, the thickness of the non-magnetic layer can be 0.1 to 3 μm, preferably 0.5 to 3 μm, and more preferably 0.8 to 3 μm. The thickness of the non-magnetic layer is preferably larger than the thickness of the magnetic layer.

The thickness of the back coat layer formed on the magnetic recording medium of the present invention is preferably set in the range of 0.05 to 0.5 μm. Among them, it is preferable to set within the range of 0.05 to 0.4 μm, and 0.05 to 0.3 μm
Is more preferably set within the range. The dry thickness of the back coat layer is generally about 0.2 to 1 μm, and more preferably 0.2 to 0.6 μm. In the magnetic recording medium of the present invention, the back coat layer is hardly reflected on the magnetic layer even when wound up and stored at a high tension.
８8 μm is possible.

[0060] 6. Manufacture of magnetic recording medium The magnetic recording medium of the present invention is manufactured , for example, by applying a paint to the surface of a running non-magnetic support so that the layer thickness after drying is within the above-mentioned predetermined range. can do. A plurality of magnetic paints or non-magnetic paints may be sequentially or simultaneously layer-applied. Applicators for applying magnetic paint include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat,
Squeeze coat, impregnation coat, reverse roll coat,
Transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat and the like can be used. These are described in, for example, “Latest Coating Technology” (Showa 58) published by Sogo Gijutsu Center.
May 31).

When manufacturing a magnetic recording tape having two or more layers on one side, for example, the following method can be used. (1) Gravure generally applied in the application of magnetic paint,
First, the lower layer is applied by a coating device such as a roll, a blade, an extrusion, etc., and before the lower layer is dried, it is disclosed in JP-B 1-446186, JP-A-60-238179, JP-A-2-265672 and the like. Using a disclosed support pressurized extrusion coating device, etc.
A method of applying the upper layer. (2) JP-A-63-88080, JP-A-2-17
No. 971, JP-A-2-265672, and a method for applying upper and lower layers almost simultaneously using a single coating head having two paint passage slits. (3) A method in which the upper and lower layers are coated almost simultaneously using an extrusion coating device with a backup roll disclosed in JP-A-2-174965.

The applied magnetic layer is dried after subjecting the ferromagnetic powder contained in the magnetic layer to a magnetic field orientation treatment. The magnetic field alignment treatment can be appropriately performed by a method known to those skilled in the art. After drying, the magnetic layer is subjected to a surface smoothing treatment using a super calender roll or the like. By performing the surface smoothing treatment, pores generated by removing the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved. Therefore, a magnetic recording tape having high electromagnetic conversion characteristics can be obtained.

Epoxy, calendering rolls
Use a heat-resistant plastic roll such as polyimide, polyamide, or polyamide-imide. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention preferably has a surface with good smoothness. In order to improve the smoothness, it is effective to subject the magnetic layer formed by selecting a specific binder as described above to the above-described calendering treatment. In the calendering treatment, the temperature of the calender roll is set to 60 to 100 ° C, preferably 70 to 100 ° C, particularly preferably 80 to 100 ° C, and the pressure is set to 980 to 4900N.
/ M (100-500 kg / cm), preferably 196
0 to 4410 N / m (200 to 450 kg / cm), particularly preferably 2940 to 3920 N / m (300 to 40 N / m).
0 kg / cm). The magnetic recording medium that has been subjected to the calendering process is generally subjected to a heat treatment.

The obtained magnetic recording medium can be used after being cut into a desired size by using a cutting machine or the like.
The cutting of the magnetic recording medium is preferably performed by using the slit method. By using this method, it is possible to easily control the range of the protrusion amount of the back coat layer with respect to the vertex of the support at the end face of the cross section of the magnetic tape and the protrusion amount of the magnetic layer at the other end face. Further, the magnetic recording medium of the present invention has a center plane surface roughness Ra of the magnetic layer measured by an optical interference type surface roughness meter of 5.0 nm or less, preferably 4.5 nm or less when the measurement range is 121 μm × 92 μm. And 8.5n in the range of 1.2mm x 0.9mm
It is preferably not less than m and not more than 21.5 nm. By having such irregularities, there is an advantage that a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability can be obtained.

[0066]

The present invention will be described in more detail with reference to the following examples. Note that the present invention is not limited to the following examples unless departing from the scope of the present invention. [Preparation of Ferromagnetic Metal Powder] In Examples A1 to A4 and Comparative Examples B1 to B2, the following ferromagnetic metal powder mainly containing Fe was prepared by reducing and oxidizing iron oxide containing Co, Al and Y. Prepared.

(Example A1) An average major axis length of 0.12 μm containing 30 atomic% of Co with respect to Fe, and an average needle ratio of 8
Of α-FeOOH was prepared. This α-FeOO
The needle-like particles of H are 1.6 equivalents of N with respect to the aqueous ferric salt solution.
adding an aqueous aOH solution to form a precipitate of ferric hydroxide;
The suspension containing the precipitate was aged for 13 hours while maintaining at 45 ° C. At that time, Co was added by adding a cobaltous salt during aging.

On the other hand, 9.6 g of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) was dissolved in 5 liters of pure water, and 1
A solution whose pH was adjusted to 12.5 using an aqueous 0% NaOH solution was prepared. 50 g of the above-mentioned spindle-type α-FeOOH powder containing Co is suspended in this aqueous solution and stirred sufficiently. Carbon dioxide gas is blown into the slurry to neutralize the slurry to a pH of 9 or less, and the surface of the α-FeOOH particles contains water. After depositing aluminum oxide (Al ₂ O ₃ .nH ₂ O),
The water-containing and aluminum oxide-coated particles are filtered, washed with water, and then heated at 400 ° C. for 3 hours to remove the Al ₂ O ₃ -coated C.
o-containing iron oxide.

This was converted to yttrium nitrate (Y ₂ (NO ₃ ) ₃ )
Is suspended in 1 liter of an aqueous solution of 4.5 g of
After stirring sufficiently, the slurry was put into a drier and
After evaporating the water at ℃, the suspension was suspended in 5 liters of pure water, filtered, heated, washed with pure water at 60 ° C, and dried. The thus obtained iron oxide particles containing Al, Y and Co were introduced into a rotary furnace at 500 ° C. for 1 hour by introducing a stream of H _2.
Heated and reduced for hours. After the reduction was completed, N ₂ gas was introduced and cooled to 60 ° C., and N ₂ gas containing 500 ppm of O ₂ was introduced to perform slow oxidation treatment for 8 hours to obtain a ferromagnetic metal powder. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

[0070]

[Table 1]

(Example A2) The temperature of the slow oxidation treatment was set to 50.
A ferromagnetic metal powder was obtained in the same manner as in Example A1 except that the temperature, the O ₂ concentration was 800 ppm, and the time for slow oxidation was 10 hours. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

(Example A3) The temperature of the slow oxidation treatment was set to 65.
A ferromagnetic metal powder was obtained in the same manner as in Example A1, except that the temperature, the O ₂ concentration was 300 ppm, and the slow oxidation time was 12 hours. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

(Example A4) The temperature of the slow oxidation treatment was set to 45.
A ferromagnetic metal powder was obtained in the same manner as in Example A1, except that the temperature, the O ₂ concentration was 1000 ppm, and the slow oxidation time was 15 hours. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

(Comparative Example B1) The temperature of the slow oxidation treatment was set to 50
A ferromagnetic metal powder was obtained in the same manner as in Example A1, except that the temperature, the O ₂ concentration was 2000 ppm, and the time for slow oxidation was 3 hours. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

(Comparative Example B2) The temperature of the slow oxidation treatment was set to 40
A ferromagnetic metal powder was obtained in the same manner as in Example A1, except that the temperature, the O ₂ concentration was 3000 ppm, and the slow oxidation time was 10 hours. Table 1 shows powder properties and magnetic properties of the obtained ferromagnetic metal powder.

The various sizes of the ferromagnetic metal powder obtained as described above were measured by the above-described methods. The magnetic properties were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo) with an external magnetic field of 10 kOe (7.96 × 10 ⁵ A /
m).

[Manufacture of magnetic recording medium] A magnetic recording medium using each of the ferromagnetic metal powders prepared as described above was manufactured.
Measurements were made for each characteristic. In addition, "part" in the examples
Means "parts by weight" unless otherwise specified. (Example 1) Magnetic layer coating liquid ferromagnetic metal powder (use the same as in Example 1) 100 parts Vinyl chloride copolymer (MR-110 manufactured by Zeon Corporation) 10 parts Polyurethane resin (UR8200 manufactured by Toyobo) 6 parts α-Al ₂ O ₃ (average particle diameter: 0.15 μm) 5 parts Carbon black (average particle diameter: 0.08 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts Non-magnetic layer coating liquid Non-magnetic powder αFe ₂ O ₃ hematite 80 parts Average major axis length: 0.15 μm Specific surface area ( _BET ) by BET method: 52 m ² / g pH: 8 Tap density: 0.8 g / ml DBP Oil absorption: 27-38 ml / 100 g, surface coating compound: Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle diameter: 16 nm DBP Oil absorption: 80 ml / 100 g pH: 8.0 Specific surface area by BET method (S _BET ): 250 m ² / g Volatile content: 1.5% Vinyl chloride-based copolymer (MR-110 manufactured by Zeon Corporation) 12 parts Polyester polyurethane Resin (UR5500A manufactured by Toyobo) 5 parts α-Al ₂ O ₃ (average particle size: 0.3 μm) 1 part Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts

Each of the above-mentioned paints was kneaded with an open kneader, and then dispersed using a sand mill. To the obtained dispersion, 5 parts of a polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was added to each, and the mixture was filtered using a filter having an average pore diameter of 1 μm. A coating solution was prepared.

Coating solution for back coat layer (formulation of back coat layer) Carbon black 100 parts Specific surface area (S _BET ) by BET method 220 m ² / g Average particle diameter 17 mμ DBP oil absorption 75 ml / 100 g Volatile matter 1.5% pH 8 0.0 Bulk density 15 lbs / ft ³ Nitrocellulose resin 100 parts Polyester polyurethane 30 parts (Nipporan (manufactured by Nippon Polyurethane)) Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation) 5 parts Methyl ethyl ketone 500 parts Toluene 500 copies

The above composition was preliminarily kneaded and kneaded with a roll mill. Next, based on 100 parts by mass of the dispersion, 100 parts by mass of carbon black Specific surface area (S _BET ) by BET method 200 m ² / g Average particle size 200 μm DBP oil absorption 36 ml / 100 g pH 8.5 α-Al ₂ O ₃ (Average particle size 0.2 μm) Disperse with a sand grinder with a composition to which 0.1 part tyl ethyl ketone 120 parts polyisocyanate 5 parts was added,
The following composition was added to 100 parts by mass of the dispersion after filtration to prepare a coating solution.

The obtained coating solution for a non-magnetic layer is coated with a non-magnetic layer so that the thickness after drying becomes 1.2 μm, and immediately thereafter, the thickness of the magnetic layer becomes 0.26 μm thereon. Simultaneous multilayer coating is performed on a magnetic support, and while both layers are still wet, a cobalt magnet having a magnetic force of 500 mT and 400
After being oriented and dried by a solenoid having a magnetic force of mT, a 7-stage calender composed of a metal roll and an epoxy resin roll is treated at a temperature of 100 ° C. at a speed of 200 m / min and then the other surface of the support. A coating solution for a back coat layer was applied to a thickness of 0.5 μm. afterwards,
Using a cutting device, a slit was cut to a width of 6.35 mm under the condition of a slit speed of 300 m / min and a meshing depth of the upper blade and the lower blade of 0.5 mm to prepare a 123 minute DVCPRO tape.

(Examples 2 to 4) and (Comparative Examples 1 and 2) Examples 2 to 4 and Comparative Examples 1 and 2 were performed in the same manner as in Example 1 except that the ferromagnetic metal powders shown in Table 1 were used. A tape was produced in the same manner as in Example 1. In Comparative Example 3, a tape was produced in the same manner as in Example 2 except that the amount of α-Al ₂ O _{3 in the} coating solution for the magnetic layer was changed from 5 parts to 10 parts.

[Evaluation as Magnetic Recording Medium] The tapes manufactured in the above Examples and Comparative Examples were evaluated as follows.
The results are shown in Table 2. <C / N> Professional digital VTR (DVCPRO) A
FUJIF using J-D750 (Matsushita Electric Industrial)
Using the ILM DVCPRO tape as a reference, 2
C / N was determined from the ratio of the carrier output at 0.9 MHz to the noise at 18.7 MHz. Also, at 60 ° C. 90% RH,
The C / N after storage for one week was similarly determined and the change was examined. Table 2 shows the results.

<Initial head wear> Commercial VTR
(DVCPRO) AJ-D750 (Matsushita Electric Industrial)
Was used to measure the amount of wear of the head after running eight consecutive recording, rewinding, and reproducing operations at 23 ° C. and 50% RH. Those having a thickness of 0.4 μm or less were evaluated as good (○), and those exceeding 0.4 μm were evaluated as poor (x). Table 2 shows the results.

<VTR running at 23 ° C. 10% environment> Using an AJ-D750 (manufactured by Matsushita Electric Industrial Co., Ltd.) digital VTR (DVCPRO) for business use, playback is performed at 23 ° C. 10% RH environment.
The rewinding was repeated 100 times, and the occurrence of dirt such as burn-in to the head during running and the decrease in output were observed. Table 2 shows the results
Shown in

[0086]

[Table 2]

From the results shown in Table 2 above, Examples 1 to 4 based on the present invention are superior to Comparative Examples 1 to 3 in terms of electromagnetic conversion characteristics, less head wear, smaller output reduction, and running durability. It turns out that it is excellent.

[0088]

According to the ferromagnetic metal powder of the present invention, a ferromagnetic metal powder having high abrasion resistance and excellent head cleaning properties can be provided. Further, according to the magnetic recording medium using the ferromagnetic metal powder of the present invention, a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent running durability can be provided. That is, with the magnetic recording medium of the present invention, it is possible to provide a magnetic recording medium capable of coping with magnetic recording and reproduction having a high recording density and a high transfer speed.

Claims (2)

[Claims] An iron-based ferromagnetic metal powder having an oxide film on a surface, wherein the oxide film contains an oxide crystal, and the film of the oxide film with respect to a crystallite size of the oxide crystal. A ferromagnetic metal powder having a thickness ratio of 0.5 to 1.1. 2. A magnetic layer containing a ferromagnetic metal powder and a binder or a non-magnetic layer containing a non-magnetic powder and a binder and a magnetic layer containing a ferromagnetic metal powder and a binder on a non-magnetic support in this order. A magnetic recording medium comprising: the ferromagnetic metal powder according to claim 1, wherein the ferromagnetic metal powder is the ferromagnetic metal powder according to claim 1.