JPH08279137A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve the traveling durability of a high-output medium by specifying the thickness, saturation magnetic flux density and coercive force of a magnetic layer, the powder compsn. in the magnetic layer, the average major axis length of the powder and further, the change rate of the saturation magnetic flux density and coercive force of the magnetic layer decreasing during preservation under a specific environment. CONSTITUTION: This magnetic recording medium is so constituted that the thickness of the magnetic layer is 0.01 to 0.8μm, the saturation magnetic flux density is 3800 to 6000 gauss, the coercive force is 2000 to 30000e, the powder compsn. in the magnetic layer is mainly composed of Fe and Co and Co/Fe is 15 to 45atm.%. The powder is composed of bobbin-like particles having the average major axis length of 0.05 to 0.13μm. Further, the rate of the degradation in the saturation magnetic flux density of the magnetic layer after preservation for seven days in the environment of 60 deg.C and 90% RH is specified to <=5%, the saturation magnetic flux density itself to >=3700 gauss and the change rate of the coercive force within ±3% of the coercive force before the preservation. As a result, the traveling durability and high-temp. preservable property of the high-output medium are improved.

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, and more particularly to a coating type magnetic recording medium for recording / reproducing digital signals at high density.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks and the like. Magnetic recording media have become denser year by year and the recording wavelength has become shorter, and the recording method is being studied from analog to digital.

In order to meet the demand for higher density, magnetic recording media using a metal thin film for the magnetic layer have been studied, but ferromagnetic powder is used as a binder in view of practical reliability such as productivity and corrosiveness. A so-called coating type magnetic recording medium dispersed in a support and coated on a support is excellent. However, since the coating type medium has a low filling degree of the magnetic substance with respect to the metal thin film, the electromagnetic conversion characteristics are poor.

As the coating type magnetic recording medium, a magnetic layer in which ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO ₂ , ferromagnetic alloy powder, etc. are dispersed in a binder is coated on a non-magnetic support. Is widely used. Various methods have been proposed to improve the electromagnetic conversion characteristics of the coating type magnetic recording medium, such as improvement of the magnetic characteristics of the ferromagnetic powder and smoothing of the surface. Not a thing. In addition, in recent years, the recording wavelength tends to become shorter with higher density, and the problem of self-demagnetization loss at the time of recording and output loss when the thickness of the magnetic layer is thick and the thickness loss at the time of reproduction are increasing. A coating type magnetic recording medium having an extremely thin layer has also been proposed.

In recent years, Hi-8 and consumer digital VC
In R, a tape formed by depositing a metal thin film, a so-called ME (metal
evaporated) tape has been put to practical use, and alloy powder tape, so-called MP (metal particulate) tape and ME.
Systems in which both tape and tape are used have been put to practical use. In particular, in DVC, whose format is specified in 1994, ME having higher performance than Hi-8ME is set as a sub-reference.

In order to coexist with ME tape in a DVC system, MP, like ME, must also have a thin magnetic layer to achieve high output. Various MP tapes comparable to ME tapes have been proposed from the viewpoint of the composition of ferromagnetic metal powder.
For example, Japanese Patent Laid-Open No. 6-215360 discloses a magnetic recording medium using a ferromagnetic metal powder containing Fe atoms, Al atoms and atoms of rare earth elements, and prevents surface roughness of a magnetic layer. , A digital recording medium having good electromagnetic conversion characteristics and running durability.

Further, Japanese Patent Laid-Open No. 6-139553 discloses a ferromagnetic metal powder mainly composed of α-Fe having a coercive force of 1620 Oe to 2100 Oe and a saturation magnetization of 12.
0 to 160 emu / g, specific surface area by N ₂ gas adsorption of 48 to 65 m ² / g, major axis length of 0.08 to 0.21 μm,
Disclosed is a magnetic recording medium using a ferromagnetic metal powder having a minor axis length of 10 to 20 nm, an acicular ratio of 7 to 11 and a crystallite size of 110 to 170Å, and having excellent electromagnetic conversion characteristics, particularly a recording wavelength of 1 μm. It is said that the following magnetic recording medium having a high short wavelength output is provided.

Further, Japanese Patent Application Laid-Open No. 6-36265 discloses that
It is mainly composed of iron and contains Al and / or Si and a rare earth element, and Al and / or Si is 0.
5 to 5.0% by weight, the rare earth element is 1 to 10 relative to Fe
Disclosed is a magnetic recording medium using a ferromagnetic metal powder of which weight percentage is excellent, and is made excellent in switching field distribution (SFD),
As a result, it intends to provide a magnetic recording medium having excellent electromagnetic conversion characteristics.

Further, in Japanese Patent Laid-Open No. 6-236539, a ferromagnetic metal powder containing Fe, Al and at least one rare earth element selected from the group consisting of Sm, Nd, Y and Pr is used as a crystallite. Is 120Å and the film thickness is 0.5 μm
Disclosed is a magnetic recording medium provided with a magnetic layer formed below and a non-magnetic layer below, and a magnetic recording medium having good electromagnetic conversion characteristics in a high frequency band and no noise and having a good configuration as a digital recording medium. It is supposed to be provided.

On the other hand, the invention described in Japanese Unexamined Patent Publication (Kokai) No. 4-330623 and the like is mentioned as an invention for achieving the above object by specifying the shape of the ferromagnetic metal powder and the magnetic characteristics of the magnetic layer. This publication discloses that in a magnetic recording medium having a multilayered magnetic layer, the coercive force of the outermost magnetic layer is 1700 to 2200 Oe and the saturation magnetic flux density is 3000 to 4
The ferromagnetic metal powder of 500 Gauss has an average major axis length of 0.25 μm or less and a crystallite size of 200 Å or less, and the magnetic powder contained in the magnetic layer other than the outermost layer is 350 Å. The following magnetic recording medium made of iron oxide is disclosed, and it is stated that the magnetic recording medium has high electromagnetic conversion characteristics, few dropouts, and excellent running durability.

By the way, it is well known that an MP tape satisfying the electromagnetic conversion characteristics comparable to that of the ME tape can be obtained, and that the MP tape is superior to the ME tape in preservability under high temperature and high humidity environment. However, when placed in a high temperature and high humidity environment for a long period of time, there has been a problem that the magnetic characteristics, especially the fluctuation of the coercive force and the decrease of the saturation magnetic flux density are remarkable. In particular, it has not been possible to find a means for obtaining a magnetic recording medium satisfying the above-mentioned storability while ensuring good electromagnetic conversion characteristics and running durability.

[0012]

The present invention has a high output comparable to that of a ferromagnetic metal thin film type magnetic recording medium, and is excellent in running durability and long-term storage stability at high temperature and high humidity. The purpose is to provide.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-magnetic layer mainly composed of an inorganic non-magnetic powder and a binder resin and a magnetic material mainly composed of a ferromagnetic metal powder and a binder resin on a non-magnetic support. In the magnetic recording medium in which the layers are formed in this order, the thickness of the magnetic layer is 0.01 to 0.8 μm, the ferromagnetic metal powder in the magnetic layer is mainly Fe and Co, and Co / Fe is Spindle-shaped particles having an average major axis length of 0.05 to 0.13 μm and a coercive force (Hc) of 2000 to 3000 O.
and the saturation magnetic flux density (Bm) of the magnetic layer is 3800
˜6000 gauss, the magnetic layer is 60 ° C., 90% R
After storage in an H environment for 7 days, the Hc of the magnetic layer was within ± 3% of the Hc before storage, and the Bm of the magnetic layer was
Can be achieved by a magnetic recording medium characterized by being 5% or less and 3700 gauss or more.

The present invention is directed to the composition and shape of the ferromagnetic metal powder contained in the magnetic layer provided on the non-magnetic layer, the magnetic properties of the magnetic layer, and the Hc and Hc after storage under a specific forced high temperature and high humidity environment. The feature is that the change in Bm is specified. The ferromagnetic metal powder used in the magnetic layer of the present invention is
Mainly composed of Fe and Co, and Co / F
e is 15 to 45 atom%, preferably 18 to 40 atom%,
More preferably, it is 20 to 35 atomic%. Co is Fe
Is less than 15 atom%, the required Hc and σ are
_{If S} is not obtained, and if it is more than 45 atomic%, spindle-shaped particles having a uniform shape cannot be obtained, which is not preferable.

In the magnetic recording medium of the present invention, after the magnetic layer is stored in an environment of 60 ° C. and 90% RH for 7 days, the Hc of the magnetic layer is within ± 3% of the Hc before storage, preferably ±. It is within 2 and more preferably within ± 1, and the decrease of Bm of the magnetic layer is 5% or less, preferably 3%.
Or less, more preferably 2% or less, and 3700
Gauss or higher, preferably 3800 to 5800 gauss.

In the present invention, the ferromagnetic metal powder is the above-mentioned F
Components other than e and Co can be contained, and the above-mentioned storability can be controlled by appropriately selecting these components. Other components include Al, rare earth elements, and other arbitrary elements such as Na, Ca, Ni, and S.
i, S, Ti, V, Cr, Cu, Mo, Rh, Pd, A
g, Sn, Sb, Te, Ba, Ta, W, Re, Au,
Examples thereof include Hg, Pb, Bi, P, Mn, Zn, Sr and B.

The rare earth elements are Sc, Y, La, Ce and P.
r, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
Each element of o, Er, Tm, Yb, and Lu. In the present invention, the ferromagnetic metal powder used in the magnetic layer preferably has the following embodiments. Al is 20 atomic% or less with respect to Fe, preferably 15
It is contained in the ferromagnetic metal powder in an amount of not more than atomic%, more preferably not more than 10 atomic%. Alternatively, Al may not be contained in the ferromagnetic metal powder at all.

The sum of at least one or more rare earth elements, preferably at least one or more of Y, La, Ce, Nd and Sm, is 1 to 15 atom%, preferably 2 to 12 atom%, more preferably Fe. Is contained in the ferromagnetic metal powder at 3 to 10 atomic%. The total sum of the rare earth elements is 40 atomic% or more with respect to Al, preferably 40 to 200 atomic%, more preferably
50 to 150 atomic% is contained. If the Al content is 0,
The total sum of rare earth elements is 1 atom% or more, preferably 2 to 12 atom% with respect to Fe.

In the present invention, a ferromagnetic metal powder satisfying all of the above items 1 to 3 is particularly preferable. The shape of the ferromagnetic metal powder in the magnetic layer of the present invention is spindle-shaped particles, and the average major axis length thereof is 0.05 to 0.13 μm, preferably 0.06 to 0.110 μm, and more preferably 0.06
5 to 0.090 μm (Note that the evaluation of the ferromagnetic metal powder contained in the magnetic layer in the present invention is described to that effect, but if there is no such description, the evaluation to the ferromagnetic metal powder is to the magnetic layer. Before being applied in). Hc becomes low when the average major axis length is 0.06 μm or less, 0.05
If it is smaller than μm, it becomes extremely low, which is not suitable for the present invention.

The crystallite size is 120 to 220.
Å, preferably 130 to 200 Å, more preferably 1
It is 35 to 190Å. In the present invention, the fusiform shape of the fusiform particles means that at least a figure when projected onto a particle surface perpendicular to the plane placed parallel to the plane including the major axis of the particle is as shown in FIG. The center part is thicker than both ends. The general characteristic of the spindle-shaped particles is a shape in which the central part of the shaft is thick in the direction perpendicular to the major axis 1 and gradually decreases toward the end to close at the end. The major axis length can be represented by r1 and the minor axis length can be represented by r2 in FIG. The axial ratio (r1 / r2) is usually 3.0 to 8.0, preferably 3.5 to 7.0.

In the present invention, the spindle-shaped ferromagnetic metal powder is used, and as a result, it is possible to use a very uniform powder even if the average major axis length is extremely small, and the coating property and orientation are improved. It is presumed that it contributes to the preservation improvement. The method for producing such spindle-shaped particles is not particularly limited, and a conventionally known method can be applied. For example, the following method can be mentioned.

A ferrous salt (eg FeCl ₂ ) and cobalt salt (eg CoCl ₂ ) aqueous solution (preferably pH 5 to 5)
8) and an aqueous solution of alkali carbonate (preferably NaOH, N
a ₂ CO ₃ aqueous solution) to oxidize the suspension containing FeCO ₃ obtained by reacting it with air, and further oxidize at a temperature higher than room temperature, preferably at 30 to 120 ° C. to form spindle-shaped goethite. Then, in this suspension, a Co-containing compound (eg, cobalt sulfate, cobalt chloride, etc.), a rare earth element-containing compound (eg, chloride, nitrate, etc.), an Al-containing compound (eg, sodium aluminate, sodium metaaluminate, etc.), etc. Is added and mixed to prepare a spindle-shaped goethite suspension containing these. The Co-containing compound is preferably before addition of the rare earth element-containing compound and the Al-containing compound.

The addition of the Co-containing compound, the Al-containing compound, the rare earth element-containing compound, etc. to the spindle-shaped goethite-containing suspension is carried out after the suspension is filtered to remove NaCl, NaOH, etc. , You may go. Then, the suspension is vacuum filtered with an Oliver filter or the like, granulated, dried, and reduced. The reduction may be a stationary reduction furnace or a fluidized bed reduction furnace. The reduction temperature is 30
It is preferable to perform the steam flow controlled to about 0 to 800 ° C.

After that, it is preferable to perform gradual oxidation in order to form an oxide film on the powder. This is a method of immersing in an organic solvent and then drying, or immersing in an organic solvent and then feeding an oxygen-containing gas to the surface. It is possible to use either a method of forming an oxide film and then drying it, or a method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent. The phase reaction is preferable because a uniform oxide film can be formed.

Further, in order to prepare the spindle-shaped ferromagnetic metal powder of the present invention, Japanese Patent Application No. 5-2 previously filed by the applicant of the present application.
The method for producing monodisperse hematite particles and the method for producing ferromagnetic metal powder described in Japanese Patent No. 74750 can be appropriately applied. That is, the hematite particles or, if necessary, the goethite particles are treated with the Co-containing compound, the rare earth element-containing compound, the Al-containing compound, etc., and then reduced.

Σ _{S of the} ferromagnetic metal powder used in the present invention
Is usually 135 to 170 emu / g, preferably 13
8 to 165 emu / g, more preferably 140 to 16
It is 0 emu / g. Hc of ferromagnetic metal powder is usually
1950-3000 Oe, preferably 2000-280
It is 0 Oe. When σ _S is smaller than 135 emu / g, the output is reduced, and when it is larger than 170 emu / g, demagnetization becomes remarkable and the dispersion cannot be sufficiently performed, so that the surface property of the magnetic layer is difficult to be obtained.

The Bm of the magnetic layer of the magnetic recording medium of the present invention is 3
800-6000 gauss, preferably 4000-580
It is 0 gauss, and more preferably 4200 to 5500 gauss. Further, the Hc of the magnetic layer is 2000 to 3000 O.
e, preferably 2050 to 2800 Oe, and more preferably 2100 to 2600 Oe. Hc is 2000O
When it is smaller than e, the compatibility of the input / output characteristics with the metal thin film cannot be obtained and the output becomes insufficient. There is no particular restriction on the higher Hc, but there is no merit to make it higher than necessary.

The squareness ratio (Br / Bm) of the magnetic layer is 0.7.
It is 5 or more, preferably 0.78 to 0.94, and more preferably 0.80 to 0.90. If it is smaller than 0.75, the output becomes insufficient, and if it is larger than 0.90 and particularly larger than 0.94, the surface property deteriorates. B of magnetic layer
When m and Hc are smaller than the lower limit values, the output is reduced, and when m and Hc are larger than the upper limit values, demagnetization is large.

In the ferromagnetic metal powder used in the present invention, it is preferable that the surface layer of the particle has a higher content ratio of each of Al, rare earth elements and O to Fe than in the entire particle. By selecting the elemental composition of the surface layer of the ferromagnetic metal powder in this way, the magnetic properties of the ferromagnetic metal powder can be obtained, and in spite of the fine particles, functions such as weather resistance, durability, and reduction of polishing power are obtained. Therefore, the magnetic layer has effects such as demagnetization of the magnetic layer, running durability, and reduction of head wear.

In the present invention, a spindle-shaped ferromagnetic metal powder is used, the kneading is strengthened and the calender is strengthened, so that the surface properties of the magnetic layer are excellent and the surface roughness is usually 0.5 to 3.
nm, preferably 0.8 to 2.8 nm, more preferably 1.0 to 2.5 nm. This surface roughness is WY
Optical interference three-dimensional roughness meter "T" manufactured by KO (US Arizona)
OPO3D ”is used to measure Ra of the surface of the magnetic layer by the MIRAU method in an area of about 250 nm × 250 nm. The measurement wavelength is about 650 nm, and spherical correction and cylindrical correction are added.

In the present invention, the thickness of the magnetic layer is 0.
01-0.8 μm, preferably 0.05-0.5 μm,
More preferably, it is 0.08 to 0.3 μm. 0.0
If the thickness is less than 1 μm, a uniform coating film cannot be obtained and the output in the low frequency range becomes insufficient. On the other hand, if it is larger than 0.8 μm, the output in the high frequency range tends to decrease and the overwrite characteristic is deteriorated, which is not preferable.

Increasing the packing degree of the magnetic layer in the present invention is to improve the output and C /
It is an essential item for obtaining N. In the present invention, it is important to enhance the kneading by using the spindle-shaped particles, sufficiently disperse them, and sufficiently disperse them into the primary particles. Since it is a spindle-shaped particle, it is more effective than the conventional long needle-shaped particle that the particle is less likely to be broken even if a high share is applied during kneading. Next, in order to increase the filling degree of the magnetic layer, it is necessary to strengthen the calender conditions. After forming the coating film, press firmly with the metal rolls before hardening of the magnetic layer progresses, and form a proper slip between the metal roll and the plastic roll to control the surface properties and form the magnetic layer surface. Is important for increasing the filling degree and maintaining the surface property. Next, detailed contents of the non-magnetic layer (also referred to as a lower layer) will be described.

The inorganic non-magnetic powder used in the non-magnetic layer of the present invention is selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides. be able to. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, goethite, corundum, silicon nitride, and titanium carbide having an α conversion rate of 90% or more. Bite, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulphate, barium sulphate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred are easy availability, cost, small particle size distribution,
Titanium dioxide, zinc oxide, iron oxide, and barium sulfate are preferable, and titanium dioxide and α-iron oxide are more preferable because they have many means for imparting functions. The particle size of these inorganic non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, the inorganic non-magnetic powders having different particle sizes may be combined, or a single inorganic non-magnetic powder may have a wide particle size distribution. You can also have the effect of. Especially preferred is a particle size of the inorganic non-magnetic powder of 0.01μ.
It is m-0.2 micrometer. Tap density is 0.05-2g /
ml, preferably 0.2-1.5 g / ml. The inorganic non-magnetic powder has a water content of 0.1 to 5% by weight, preferably 0.2 to 3% by weight, and more preferably 0.3 to 1.5% by weight. The pH of the inorganic non-magnetic powder is 2 to 11, but the pH is preferably 5 to 10. The specific surface area of the inorganic non-magnetic powder is 1 to 100 m ² / g, preferably 5 to
70m ² / g, more preferably from 10~65m ² / g. The crystallite size of the inorganic non-magnetic powder is 0.004 μm
˜1 μm is preferable, and 0.04 μm to 0.1 μm is more preferable. The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. Specific gravity is 1 to 1
2, preferably 3-6. The shape may be needle-like, spherical, polyhedral or plate-like.

The loss on ignition is preferably 20% by weight or less, and it is considered most preferable not to have it. The inorganic nonmagnetic powder used in the present invention preferably has a Mohs hardness of 4 or more and 10 or less. The roughness factor of the surface of these inorganic nonmagnetic powders is preferably 0.8 to 1.5, and more preferably 0.9 to 1.5.
1.2. The amount of SA (stearic acid) adsorbed on the inorganic non-magnetic powder is 1 to 20 μmol / m ² , and more preferably 2 to
It is 15 μmol / m ² . The heat of wetting of the inorganic non-magnetic powder in water at 25 ° C. is preferably in the range of 200 erg / cm ^{2 to} 600 erg / cm ² . In addition, a solvent having a heat of wetting in this range can be used. The amount of water molecules on the surface at 100 to 400 ° C is appropriately 1 to 10 / 100A. The pH of the isoelectric point in water is preferably between 3 and 6.

Al ₂ O is formed on the surface of these inorganic non-magnetic powders.
Surface treatment with ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, Y ₂ O ₃ is preferable. Especially preferred for dispersibility is Al
₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ are preferable, but Al ₂ is more preferable.
O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination, or may be used alone. Alternatively, a co-precipitated surface-treated layer may be used depending on the purpose, or a method of treating the surface layer with silica after first treating with alumina,
Alternatively, the reverse method can be adopted. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that it is homogeneous and dense.

Specific examples of the inorganic non-magnetic powder used in the non-magnetic layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α-hematite manufactured by Toda Kogyo Co., DPN-2.
50, DPN-250BX, DPN-245, DPN-270BX, Titanium Oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-5
5D, SN-100, α Hematite E270, E271, E300, S made by Titanium Industry
TT-4D, STT-30D, STT-30, STT-65C, TAYCA's MT-100S, M
T-100T, MT-150W, MT-500B, MT-600B, MT-100F, MT-500HD,
Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining D
EFIC-Y, DEFIC-R, AS2BM, TiO2P25 made by Nippon Aerosil, 100A, 500A made by Ube Industries, Y-LOP made by Titanium Industry, and fired products thereof can be mentioned.

Particularly preferred inorganic non-magnetic powders are titanium dioxide and α-iron oxide (α-Fe ₂ O ₃ ). α-iron oxide (hematite) is implemented under the following conditions. The α-Fe ₂ O ₃ particle powder is a suspension containing ferrous hydroxide colloid obtained by adding an equal amount or more of an aqueous alkali hydroxide solution to a normal ferrous iron solution at a pH of 11 or more.
Method for producing acicular goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of ℃ or less, a suspension containing FeCO ₃ obtained by reacting a ferrous salt aqueous solution and an alkali carbonate aqueous solution A method for producing goethite particles in the shape of spindles by aerating an oxygen-containing gas to carry out an oxidation reaction, which is obtained by adding less than an equal amount of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to an aqueous ferrous salt solution. Oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid to carry out an oxidation reaction to generate acicular goethite core particles, and then ferrous salt containing the acicular goethite core particles. In the aqueous solution, the F in the aqueous solution of the ferrous salt is added.
A method of growing the acicular goethite core particles by adding an oxygen-containing aqueous solution in an amount equal to or more than that of e ²⁺ and then aerating an oxygen-containing gas, and an alkali hydroxide in an amount less than that of the ferrous aqueous solution or A needle-shaped goethite nucleus particle is produced by carrying out an oxidation reaction by passing an oxygen-containing gas through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an alkaline carbonate aqueous solution, and then producing acidic to medium The acicular goethite particles obtained by the method of growing the acicular goethite nucleus particles in the crystalline region are used as precursor particles.

It should be noted that Ni and Z, which are usually added during the reaction for producing goethite particles, for improving the characteristics of the particle powder.
There is no problem even if a different element such as n, P or Si is added. Needle-shaped goethite particles, which are precursor particles, are added to 200 to 5
Dehydration in the temperature range of 00 ° C, or if necessary, further 3
Annealing is performed by heat treatment in the temperature range of 50 to 800 ° C. to obtain acicular α-Fe ₂ O ₃ particles.

There is no problem if the needle-shaped goethite particles to be dehydrated or annealed have a sintering inhibitor such as P, Si, B, Zr or Sb attached to the surface. Annealing by heat treatment in the temperature range of 350 to 800 ° C. is performed by annealing pores generated on the particle surface of the needle-shaped α-Fe ₂ O ₃ particles obtained by dehydration, thereby making the polar surface of the particle This is because it is preferable that the pores are melted and the pores are covered to form a smooth surface form.

Α-Fe ₂ O ₃ used in the present invention
The particle powder is a suspension obtained by dispersing the acicular α-Fe ₂ O ₃ particles obtained by dehydration or annealing in an aqueous solution,
The Al compound is added to adjust the pH, and the α-Fe ₂ O ₃ is added.
After coating the particle surface of the particles with the additive compound, filtration,
It can be obtained by washing with water, drying, pulverizing, and if necessary, further performing deaeration / dense treatment. As the Al compound used, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate and alkali aluminate salts such as sodium aluminate can be used. In this case, the amount of the Al compound added is 0.01 to 50% by weight in terms of Al based on the α-Fe ₂ O ₃ particle powder. 0.0
When it is less than 1% by weight, the dispersion in the binder resin is insufficient, and when it exceeds 50% by weight, Al compounds floating on the particle surface interact with each other, which is not preferable. In the inorganic non-magnetic powder of the lower layer in the present invention, starting with the Si compound as well as the Al compound,
It is also possible to coat with one or more compounds selected from P, Ti, Mn, Ni, Zn, Zr, Sn and Sb. The amount of each of these compounds used together with the Al compound is in the range of 0.01 to 50% by weight based on the α-Fe ₂ O ₃ particle powder. If it is less than 0.01% by weight, the effect of improving the dispersibility by addition is scarce, and if it exceeds 50% by weight, compounds floating other than on the particle surface interact with each other, which is not preferable.

The production method of titanium dioxide is as follows. The methods for producing these titanium oxides are mainly the sulfuric acid method and the chlorine method. In the sulfuric acid method, a raw illuminite ore is digested with sulfuric acid, and Ti, Fe, etc. are extracted as a sulfate. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration and then subjected to thermal hydrolysis to precipitate hydrous titanium oxide. After this is filtered and washed, impurities are washed and removed, and a particle size adjusting agent and the like are added, and then calcined at 80 to 1000 ° C. to obtain crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the nucleating agent added at the time of hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. In the chlorine method, natural or synthetic rutile is used as the raw ore. Ore is chlorinated in a high temperature reduced state and Ti is T
Fe becomes FeCl _{2 in} iCl ₄ , and iron oxide which becomes solid by cooling is separated from liquid TiCl ₄ . The obtained crude TiCl ₄ is purified by rectification, then a nucleating agent is added, and it is instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher,
Crude titanium oxide is obtained. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

For the surface treatment, coarse particles are classified by dry pulverizing the titanium oxide material, adding water and a dispersant, wet pulverizing and centrifuging. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al, Si, Ti, Zr, Sb, S
An aqueous solution of salts such as n and Zn is added to neutralize the acid,
Alternatively, alkali is added to cover the surface of the titanium oxide particles with the hydrous oxide produced. By-produced water-soluble salts are removed by decantation, filtration and washing, and finally the slurry pH is adjusted and filtered, followed by washing with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product. Further, not only the water system but also the titanium oxide powder can be subjected to AlCl ₃ and SiCl ₄ vapor, and then steam can be introduced to perform the Al and Si surface treatment. For other pigment manufacturing methods, see GD Parfitt and KSW Sing ”Cha
racterization of Powder Surfaces ”Academic Press, 1
You can refer to 976.

In the present invention, the surface electric resistance Rs, which is a known effect, is obtained by mixing carbon black in the non-magnetic layer.
Can be lowered, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. The micro-Vickers hardness of the non-magnetic layer is usually 25-
60 kg / mm ^2, preferably in order to adjust the head contact, a 30 to 50 kg / mm ^2, NEC made thin hardness meter H
Using MA-400, ridge angle 80 degrees, tip radius 0.1μ
The measurement is performed by using a diamond triangular pyramid needle of m at the tip of the indenter. It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example 0.8% or less for VHS. For this purpose, a furnace for rubber, a thermal for rubber, a black for color, acetylene black, etc. can be used.

The specific surface area of carbon black is 100 to 5
00 m ² / g, preferably 150 to 400 m ² / g, DB
P oil absorption is 20-400 ml / 100g, preferably 30-2
It is 00 ml / 100 g. Carbon black particle size is 5m
μ to 80 mμ, preferably 10 to 50 mμ, and more preferably 10 to 40 mμ. Carbon black 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 is preferred. A specific example of carbon black used in the present invention is BL manufactured by Cabot Corporation.
ACKPEARLS 2000, 1300, 1000,
900, 800, 880, 700, VULCAN XC
-72, Mitsubishi Kasei Kogyo Co., Ltd., # 3050B, 3150
B, 3250B, # 3750B, # 3950B, # 95
0, # 650B, # 970B, # 850B, MA-60
0, MA-230, # 4000, # 4010, Columbia Carbon Co., CONDUCTEX SC, RAVE
N8800,8000,7000,5750,5250,3500,2100,2000,1800,150
0,1255,1250, Ketjen Black EC manufactured by Akzo, etc. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the paint. These carbon blacks are 50% by weight based on the above inorganic non-magnetic powder.
It can be used within the range of not exceeding 40% of the total weight 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 addition, an organic powder can be added to the non-magnetic layer according to the purpose. For example, acrylic styrene resin powder, benzoguanamine resin powder,
Examples include melamine-based resin powder and phthalocyanine-based pigment, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluorinated ethylene resin can also be used. As the manufacturing method, those described in JP-A-62-18564 and JP-A-60-255827 can be used. The undercoat layer is provided in a general magnetic recording medium, but it is provided in order to improve the adhesive force between the support and the magnetic layer, and the thickness is generally 0.5 μm or less. Target.

Binder, lubricant, dispersant for the non-magnetic layer,
As for the additive, solvent, dispersion method and the like, those of the magnetic layer (also referred to as upper layer) can be applied. In particular, the amount of binder, type,
As for the amounts and types of additives and dispersants to be added, known techniques for magnetic layers can be applied. Next, the magnetic layer will be described in detail. The ferromagnetic metal powder used in the present invention is mainly the above-mentioned spindle-shaped ferromagnetic metal powder,
A usual ferromagnetic metal powder other than the spindle-shaped ferromagnetic metal powder can be used together. The composition is selected according to the above-mentioned spindle-shaped ferromagnetic metal powder or a known ferromagnetic metal powder composition. The ferromagnetic metal powder which can be used together is 0.1 to 60% by weight, preferably 0.5 to 5% by weight of the total ferromagnetic metal powder.
0% by weight. These ferromagnetic metal powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion. Specifically, Japanese Patent Publication Nos. 44-14090, 45-18372, and 47-2
2062, Japanese Examined Sho 47-22513, Japanese Examined Sho 46-28466, Japanese Examined Sho
46-38755, JP-B 47-4286, JP-B 47-12422, JP-B 47-17284, JP-B 47-18509, JP-B 47-18573
No. 3, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-39639, US Patent 30
No. 26215, No. 3031341, No. 3100194, No. 3242005, No.
It is described in No. 3389014.

The ferromagnetic metal powder which can be used in combination may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder that can be used in combination, those obtained by a known manufacturing method can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, a metal carbonyl compound Pyrolysis method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, evaporation of the metal in a low pressure inert gas to produce a fine powder. How to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. How to make
Any of the methods of adjusting the partial pressures of oxygen gas and inert gas to form an oxide film on the surface without using an organic solvent can be used.

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 1,0.
00-200,000, preferably 10,000-10
The degree of polymerization is about 50,000 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 acetate
There are polymers or copolymers containing polyurethane, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

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, Examples thereof include an epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Further, a known electron beam-curable resin can be used for the non-magnetic layer or the magnetic layer.

These examples and the method for producing them are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin,
Examples include a combination of at least one selected from vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer and a polyurethane resin, or a combination of these with polyisocyanate. The structure of polyurethane resin is polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane,
Known materials such as polyester polycarbonate polyurethane, polycaprolactone polyurethane, and polyolefin polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3
M, -P = O (OM) ₂ , -OP-O (OM) ₂ ,
(Wherein M represents a hydrogen atom or an alkali metal _{salt,), - OH, -NR 2} , -N + R 3 (R is a hydrocarbon group), epoxy group, -SH, -CN, sulfobetaine,
It is preferable to use one having at least one polar group selected from phosphobetaine and carboxybetaine introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 1
It is 0 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbite Corporation.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku Co., Ltd. 1000
W, DX80, DX81, DX82, DX83, 100
FD, MR-104, MR-105 manufactured by Nippon Zeon Co., Ltd.
MR110, MR100, 400X-110A, Nippon Polyurethane Nipporan N2301, N2302, N
2304, Pandex T-510 manufactured by Dainippon Ink and Chemicals, Inc.
5, T-R3080, T-5201, Barnock D-4
00, D-210-80, Crisbon 6109, 720
9. Byron UR8200, UR8300, manufactured by Toyobo Co., Ltd.
UR-8600, UR-5500, UR-4300, R
V530, RV280, FB-84, FB-79, manufactured by Dainichiseika, Daiferamine 4020, 5020, 510
0, 5300, 9020, 9022, 7020, Mitsubishi Kasei Corp., MX5004, Sanyo Kasei Samprene SP-
150, TIM-3003, TIM-3005, Saran F310, F210 and the like manufactured by Asahi Kasei Corporation. Among them, MR-104, MR110, MPR-TA, UR-
8200, UR8300, UR-8600, UR-55
00, UR-4300 and TIM-3005 are preferred.

The binder used in the magnetic layer of the present invention is in the range of 5 to 25% by weight, preferably 8 to 8% by weight based on the ferromagnetic powder.
Used in the range of 22% by weight. When using a vinyl chloride resin, 5 to 30% by weight, when using a polyurethane resin, 2 to 20% by weight, and polyisocyanate is 2 to 20% by weight.
It is preferable to use these in combination within the range of weight%. In particular, it is desirable that the magnetic layer does not contain polyisocyanate and the non-magnetic layer contains polyisocyanate.

In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100 ° C and the elongation at break is 1
0 to 2,000%, breaking stress 0.05 to 10 kg /
The cm ² and the yield point are preferably 0.05 to 10 kg / cm ² . The magnetic recording medium of the present invention comprises two or more layers. Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or the amount described above. It is of course possible to change the physical properties of the resin between the non-magnetic layer and the magnetic layer as necessary, and known techniques relating to the multilayer magnetic layer 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. This is achieved by increasing the amount of binder in the layer to give flexibility.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and naphthylene-1. ，
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate, and the like, products of these isocyanates with polyalcohols, and polyisocyanates formed by condensation of isocyanates. -, Etc. can be used. Commercially available trade names of these isocyanates are Nippon Polyurethane Co., Ltd., Coronate L, Coronet HL, Coronet 2030, Coronet 2031, Millionate M.
R, Millionate MTL, Takeda Yakuhin, Takenet D
-102, Takenet D-110N, Takenet D-2
00, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodule L, Desmodule IL, Desmodule N
Desmodule HL, Dainippon Ink's Burnock D50
There are two or the like, and these can be used as a non-magnetic layer or a magnetic layer in combination of two or more by utilizing the difference in curing reactivity.

Carbon black used in the present invention is a rubber furnace, a rubber thermal, a color black,
Acetylene black, etc. can be used. Specific surface area is 5-500 m ² / g, DBP oil absorption is 10-400
ml / 100 g, particle size 5 mμ to 300 mμ, pH 2 to 10, water content 0.1 to 10%, tap density 0.
1 to 1 g / CC is preferable. A specific example of the carbon black used in the present invention is BLA manufactured by Cabot Corporation.
CKPEARLS 2000, 1300, 1000, 9
00, 800, 700, VULCAN XC-72, Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3.
5, Mitsubishi Kasei Co., Ltd., # 2400B, # 2300, #
5, # 900, # 950, # 970, # 1000, # 3
0, # 40, # 10B, Columbia Carbon Co., CO
NDUCTEX SC, RAVEN 150, 50, 4
0, 15 and so on. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the ferromagnetic powder. Carbon black has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving film strength, etc.
These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different characteristics, such as particle size, oil absorption, electric conductivity, pH, etc., in the magnetic layer and the non-magnetic layer by changing the types, amounts and combinations thereof. Of course, it is possible to use properly according to the purpose. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Society.

As the abrasive used in the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized with an α-conversion rate of 90% or more. Silicon Titanium Car
Known materials such as bite, titanium oxide, silicon dioxide, boron nitride, etc., mainly having a moth of 6 or more are used alone or in combination. 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 the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is 0.0
It is preferably 1 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may have a wide particle size distribution to obtain the same effect. Tap density is 0.3-2 g / cc, water content is 0.1-5%,
The PH is preferably ^{2 to} 11, and the specific surface area is preferably 1 to 30 m ² / g.

The shape of the abrasive used in the present invention is needle-like,
It may have a spherical shape or a dice shape, but one having a corner in a part thereof is preferable because of high abrasivity. Specific examples of the abrasive used in the present invention include A manufactured by Sumitomo Chemical Co., Ltd.
KP-20, AKP-30, AKP-50, HIT-5
0, HIT-60, HiT-60A, HIT-70A,
HIT-80, HIT-80G, HIT-100, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo KK, T
Examples include F-100 and TF-140. The abrasives used in the present invention can be of different types, amounts and combinations in the non-magnetic layer and the magnetic layer and can be used properly according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. The number of abrasives present on the magnetic layer surface and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5 pieces / 100 μm ² or more.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, graphite fluoride, silicon
Oil, polar group-containing silicone, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing ester, polyolefin, polyglycol
, Alkyl phosphates and their alkali metal salts,
Alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt, monobasic fatty acid having 10 to 24 carbon atoms (may contain unsaturated bond, or may be branched) ) And their metal salts (Li, Na,
K, Cu, etc., or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (may contain an unsaturated bond or may be branched. ), An alkoxy alcohol having 12 to 22 carbon atoms, and 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms,
Any one of trivalent, tetravalent, pentavalent, and hexavalent alcohol (may contain an unsaturated bond or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a mono-alkyl ether fatty acid ester of an alkylene oxide polymer, and 8 to 8 carbon atoms
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used.

Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, Isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate,
Examples thereof include oleyl alcohol and lauryl alcohol. Further, nonionic surfactants such as alkylene oxide-based, glycerin-based, glycidyl-based, and alkylphenol-ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium. Or a cationic surfactant such as sulfonium, carboxylic acid, sulfonic acid,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, phosphoric acid ester groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkylbedine type, etc. Etc. can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants and antistatic agents are not always 100%
Impurities such as isomers, unreacted products, by-products, decomposed products, and oxides may be included in addition to the main component. These impurities are preferably 30% or less, more preferably 10% or less.

The types and amounts of these lubricants and surfactants used in the present invention can be appropriately selected in each layer. For example, fatty acids having different melting points in the non-magnetic layer and magnetic layer are used to control bleeding to the surface, esters having different boiling points and polarities are used to control bleeding to the surface, and the amount of surfactant is adjusted. Therefore, it is considered that the stability of coating is improved, the amount of the lubricant added is increased in the non-magnetic layer, and the lubrication effect is improved. Of course, the present invention is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. In some cases, it may be added in a kneading step using 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.

Examples of commercial products of these lubricants used in the present invention are NAA-102 and NAA-4 manufactured by NOF CORPORATION.
15, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, cation SA, cation MA, cation A
B, cation BB, nymine L-201, nymine L-202, nymine S-202, nonion E-20
8, nonion P-208, nonion S-207, nonion K-204, nonion NS-202, nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monoguri MB, Nonion DS-6
0, anon BF, anon LG, butyl stearate, butyl laurate, erucic acid, Kanto Chemical Co., oleic acid, Takemoto Yushi Co., FAL-205, FAL-123,
Made by Shin Nippon Rika Co., Ngerb LO, Njorbu IP
M, Sansosizer-E4030, Shin-Etsu Chemical Co., TA
-3, KF-96, KF-96L, KF96H, KF4
10, KF420, KF965, KF54, KF50,
KF56, KF907, KF851, X-22-81
9, X-22-822, KF905, KF700, KF
393, KF-857, KF-860, KF-865
X-22-980, KF-101, KF-102, KF
-103, X-22-3710, X-22-3715,
KF-910, KF-3935, Lion Armor Co., Amid P, Amid C, Amoslip C
P, Lion Oil & Fat Co., Duomin TDO, Nisshin Oil Co., BA-41G, Sanyo Chemical Co., Ltd., Profan 2012
E, Newpole PE61, Ionette MS-400,
Ionet MO-200 Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionet DO-200 and the like.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., and methanol.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc., methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycoacetate -Esters such as glycol, dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same type in the magnetic layer and the non-magnetic layer. The addition amount may be changed. Solvents with high surface tension in the non-magnetic layer (cyclohexanone, dioxane, etc.)
It is important that the stability of coating is increased by using, specifically, the arithmetic average value of the solvent composition of the magnetic layer does not fall below the arithmetic average value of the solvent composition of the non-magnetic layer. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and it is preferable that the solvent composition contains 50% by weight or more of a solvent having a dielectric constant of 15 or more and 20 or less. The dissolution parameter is preferably 8-11.

The thickness of the magnetic recording medium of the present invention is such that the non-magnetic support has a thickness of 1 to 100 μm, and is particularly effective when a thin non-magnetic support having a thickness of 1 to 8 μm is used. The total thickness of the magnetic layer and the non-magnetic layer is 1/1 of the thickness of the non-magnetic support.
It is used in the range of 0 to 2 times. Further, an adhesive layer for improving adhesion is provided between the non-magnetic support and the non-magnetic layer coating layer.

The thickness of the adhesive layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3
Is about 1.0 μm. Known adhesive layers and back coat layers can be used. The non-magnetic support used in the present invention has a micro Vickers hardness of 75 kg / mm ² or more, and is biaxially stretched polyethylene naphthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenzoxidazole. A known film such as the above can be used. In particular, a nonmagnetic support using aramid resin or polyethylene naphthalate is preferable.

Corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, etc. may be performed on these non-magnetic supports in advance. To achieve the object of the present invention, the center line average surface roughness of the surface of the non-magnetic support on which the magnetic layer is applied is 10 nm or less and 0.1 nm or more, preferably 6 nm or less and 0.2 nm or more, and more preferably 4 nm or less. It is necessary to use one having a thickness of 0.5 nm or more. Also,
It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no large protrusions of 1 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the non-magnetic support, if necessary. Examples of these fillers include oxides and carbonates of Al, Ca, Si, Ti and the like, which may be crystalline or amorphous, and organic fine powders of acrylic or melamine type. Further, in order to achieve compatibility with running durability, it is preferable that the surface on which the back layer is applied be rougher than the surface on which the magnetic layer is applied.
The center line surface roughness of the back layer coated surface is preferably 1 nm or more, more preferably 4 nm or more. When changing the roughness between the magnetic layer-coated surface and the back layer-coated surface, a dual-structured support may be used, or a coating layer may be provided.

The F-5 value of the non-magnetic support used in the present invention in the tape running direction is preferably 10 to 50 kg / mm.
² , F-5 value in the tape width direction is preferably 10 to 30K
g / mm ² and the tape F-5 value in the longitudinal direction of the tape is
It is generally higher than the F-5 value in the width direction, but this is not the case when it is necessary to particularly increase the strength in the width direction. The heat shrinkage ratio of the non-magnetic support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less at 80 ° C. for 30 minutes. The shrinkage rate is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5-100 in both directions
Kg / mm ^2, an elastic modulus 100~2,000Kg / mm ²
Is preferred. The light transmittance at 900 nm in the present invention is preferably 30% or less, more preferably 3% or less.

The step of producing 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 step may be divided into two or more steps. All the raw materials such as the ferromagnetic 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. Further, individual raw materials may be added in two or more steps in a divided manner. 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, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong force such as a continuous kneader or a pressure kneader is used. It is preferable to use one having kneading power. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferable) and 15 to 500 parts per 100 parts of the ferromagnetic powder. The kneading is performed within the range. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-64-79274. Further, when the non-magnetic layer liquid is prepared, it can be prepared according to the above magnetic paint, but it is preferable to use a dispersion medium having a high specific gravity, and zirconia beads are preferable.

The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. First, the non-magnetic layer coating layer is coated by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for coating a magnetic coating material, and the non-magnetic layer coating layer is kept in a wet state. The magnetic layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-B-1-46186, JP-A-60-238179, and JP-A-2-265672.

2, JP-A-63-88080, JP-A-2-17971,
The upper and lower layers are coated almost simultaneously by one coating head having two slits for passing the coating liquid therein as disclosed in JP-A-2-265672. 3. The upper and lower layers are coated almost simultaneously by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In order to prevent the deterioration of the electromagnetic conversion characteristics and the like of the magnetic recording medium due to the agglomeration of magnetic particles, it is disclosed in JP-A-62-951.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in JP-A-74-36968. Furthermore, regarding the viscosity of the coating liquid, see
It is necessary to satisfy the numerical range disclosed in No. 8471.

In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1,000 G or more and a cobalt magnet of 2,000 G or more together with the same poles facing each other, and further to provide an appropriate drying step before orientation so that the orientation after drying becomes the highest. preferable. Needle-shaped, plate-shaped,
It is known that it is effective to tilt the easy axis of magnetization in the vertical direction regardless of the spindle shape, and it is also effective to combine it with this.

In addition, a known method for enhancing the adhesiveness by combining an adhesive layer containing a polymer as a main component before the simultaneous multi-layer coating of the non-magnetic layer and the magnetic layer, and corona discharge, UV irradiation, and EB irradiation is combined. It is preferable.

Further, as the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide, or a metal roll is used. Further, it is preferable that the treatment is carried out by a metal roll and a combination of a metal roll and a plastic roll. The treatment temperature is preferably 70 to 120 ° C., more preferably 8
It is 0 to 100 ° C or higher. The linear pressure is preferably 200-
350 kg / cm, more preferably 250-300K
g / cm or more. The processing speed is usually 50 to 400
m / min, preferably 120 to 250 m / min.

The coefficient of friction of the magnetic layer surface of the magnetic recording medium of the present invention and the surface opposite thereto to SUS420J is preferably 0.1 to 0.5, more preferably 0.2 to 0.3. The surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq, the elastic modulus at 0.5% elongation of the magnetic layer is the running direction,
Preferably in the width direction 100 to 2,000 Kg / m
m ² , the breaking strength is preferably 1 to 30 Kg / cm ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1,500 Kg / mm ^{2 in} the running direction and the long direction, and the residual elongation is preferably 0.5% or less. The heat shrinkage at any temperature of 100 ° C. or lower is preferably 1% or less, more preferably 0.5%
Below, most preferably, it is 0.1% or less, and 0% is ideal. The glass transition temperature of the magnetic layer (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is 50 ° C or higher and 120
The temperature of the nonmagnetic layer is preferably 0 ° C to 100 ° C. Loss elastic modulus is 1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ²
Is preferable, and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesive failure will occur easily. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
It is preferable that the residual solvent contained in the magnetic layer is less than the residual solvent contained in the non-magnetic layer. The porosity of the magnetic layer in both the non-magnetic layer and the magnetic layer is preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, the running durability is often preferable when the porosity is large.

The squareness ratio in two directions perpendicular to the tape running direction of the magnetic recording medium of the present invention is 80% of the squareness ratio in the running direction.
The following is preferable. The SFD of the magnetic layer is preferably 0.6 or less, more preferably 0.5 or less,
Ideally it is zero. Longitudinal remanence coercive force Hr
Also, it is preferably 1800 Oe or more and 3000 Oe or less. Hc and Hr in the vertical direction are preferably 1000 Oe or more and 5000 Oe or less.

RMS obtained by AFM evaluation of magnetic layer
The surface roughness RRMS is preferably in the range of 1 nm to 15 nm.

Although the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. Further, it is effective in the present invention to improve the head contact by changing the method of tensing the support, and the support which is tensified in a direction perpendicular to the tape longitudinal direction has better head contact. It often becomes.

[0079]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. In the examples, the indication "part" means "part by weight".

Preparation of ferromagnetic metal powder Preparation of ferromagnetic metal powder A In a 150 l tank equipped with a stirrer, 35 mol of 1.7 mol / l ammonium carbonate and 2.0 mol / l ammonia water 15
Citric acid 0.5 mol / l aqueous solution 0.4
While bubbling with nitrogen added with 1 and bubbling nitrogen in another tank, dissolved ferrous sulfate and cobalt sulfate (Fe ^{2 +} concentration: 1.35 mol / l, Co concentration: 0.3 mol / l ) 40 l of aqueous solution was added and mixed. 10
After stirring for a minute, the temperature of the suspension was brought to 40 ° C. and a precipitate containing ferrous iron was formed. Air was introduced instead of nitrogen, and the precipitate was oxidized to produce goethite liquid crystal. When the Fe ^{2 +} concentration in the suspension became 0.25 mol / l, the air oxidation was stopped, the temperature was changed to nitrogen, the temperature of the suspension was heated to 50 ° C., and the temperature was maintained for 2 hours. Was cooled to 40 ° C., and 1 l of a 1.1 mol / l aqueous solution of sodium aluminate was added. After that, nitrogen was changed to air and the oxidation reaction was promoted to produce spindle-shaped goethite. The obtained particles were filtered and washed with water. A part of it was dried and a transmission electron micrograph was taken to determine the average particle size. The average major axis length was 0.15.
The average acicular ratio was 10 μm. Also in nitrogen 120
After heating and dehydration for 30 minutes at ℃, the specific surface area was measured to be 120 m ²
/ G.

The obtained goethite was made into a 2% slurry in water, and an aqueous cobalt sulfate solution was added with stirring (iron 100
Co equivalent to 18 atomic parts with respect to atomic parts), followed by stirring for 10 minutes, and then added yttrium chloride aqueous solution (corresponding to 12 atomic parts of Y with respect to 100 atomic parts of iron), and continued with stirring for 10 minutes. An aqueous solution of sodium aluminate was added (corresponding to 8 atom parts of Al with respect to 100 atom parts of iron). After adding sodium aluminate, diluted sulfuric acid was added to neutralize the slurry. After washing with filtered water, 5%
After making a slurry and adjusting pH to 10 with NaOH, 120 ° C
Heated for 2 hours. After that, the cake was filtered and washed with water, passed through a molding machine, and then dried to obtain a spindle-shaped goethite that was subjected to a sintering prevention treatment.

The spindle-shaped goethite thus obtained was placed in a static reduction furnace, heated in nitrogen at 350 ° C. for 20 minutes to be dehydrated, and then heated at 600 ° C. for 2 hours to make hematite crystallize. Raised. The temperature was set to 470 ° C., the gas was changed from nitrogen to hydrogen, and reduction was performed for 6 hours. After switching to nitrogen and cooling to room temperature, change the mixing ratio of air and nitrogen to an oxygen concentration of 0.5%, monitor the temperature of the metal powder, gradually oxidize, and set the oxygen concentration to 1% when the heat generation subsides. , Gradually oxidized. In this way, the oxygen concentration was increased and finally air was gradually oxidized. After that, the ferromagnetic metal powder A was prepared by vaporizing distilled water so that the water content was 1% with respect to the metal powder, transporting it with air, adjusting the humidity and stabilizing it.

Preparation of Ferromagnetic Metal Powders B to R In the preparation of the ferromagnetic metal powder A, the size and acicular ratio (axial ratio) of the spindle-shaped goethite, the amount of Co, the kind and addition amount of the rare earth element, and the addition of Al. B to P were prepared by changing the amount and further reducing conditions. Q was created by further weakening the gradual oxidation treatment. R is long needle-shaped goethite (average major axis length 0.20 μm, average needle-shaped ratio 15, specific surface area 150
m ² / g) was used and processed in the same manner as the ferromagnetic metal powder A.

Table 1 shows the overall composition of the obtained ferromagnetic metal powders A to R, and Table 2 shows the magnetic properties thereof. The compositional components in Table 1 are atomic% with respect to Fe. 2 to 4 show micro Auger data of ferromagnetic metal powders A to C. Figure 2
4, the sputtering time of 10 minutes is approximately 80 to 200 Å in depth from the grain surface.

[0085]

[Table 1]

[0086]

[Table 2]

Examples 1 to 17, Comparative Examples 1 to 7 Nonmagnetic layer formulation a Inorganic nonmagnetic powder αFe ₂ O ₃ hematite 80 parts Long axis length 0.15 μm Specific surface area by BET method 52 m ² / g pH 6 Tap density 0 2.8 DBP oil absorption 27-38 ml / 100 g, surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g volatile matter 1.5% vinyl chloride copolymer 12 parts Nippon Zeon MR-110 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group 1 × 10 ^{- 4} eq / g containing α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 1 part butyl stearate 1 part stearic acid 1 part Methyl ethyl ketone 100 parts cyclohexanone 50 parts torr In emissions 50 parts nonmagnetic layer formulation b nonmagnetic layer formulations a, the exception that the inorganic nonmagnetic powder from hematite titanium oxide is the same as the non-magnetic layer formulation a.

Inorganic non-magnetic powder TiO ₂ 80 parts Specific surface area by BET method 45 m ² / g pH 6.8 Tap density 0.6 Moisture 1.5% Aqueous solution Na 20 ppm Aqueous solution Ca 5 ppm Magnetic layer formulation a Ferromagnetic metal fine powder ( D) 100 parts Composition (Table 1) Shape, size, magnetic properties: Table 2 Polyester polyurethane resin (binder resin) 12 parts Neopentyl glycol / cyclohexanedimethanol / hydroxypivalic acid / phthalic acid / MDI = 3.2 / 0 .7 / 0.8 / 4.4 / 1.0 -SO 3 Na group containing 1 × 10 ^-4 eq / g α-Al ₂ O ₃ (average particle diameter 0.13 [mu] m) 5 parts mosquitoes - carbon black (average Particle size 0.08 μm) 0.5 part Isoamyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts Magnetic layer formulation b Strong magnetic Metallic powder (A-P) 100 parts Composition (Table 1) shape, size, magnetic properties: Table 2 binder resin of vinyl chloride copolymer 12 parts (SO ₃ Na group containing 1 × 10 ^-4 eq / g, and Polymerization degree 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 content) α-alumina (average particle size) Diameter 0.13 μm) 5.0 parts Carbon black (average particle size 40 nm) 1.0 part Butyl stearate 1 part Stearic acid 5 parts Mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 200 parts For each of the above paints, Open ingredients
After kneading with a dough, it was dispersed using a sand mill. However, the magnetic layer was prepared by adding ferromagnetic metal powder, binder resin, and carbon black, 40 parts of methyl ethyl ketone and cyclohexanone (1: 1), and thoroughly kneading with an open kneader, and then diluting with the remaining organic solvent. After going, α
-Alumina was added and dispersed by a sand mill. Immediately before the end of dispersion, the remaining additives were added. 5 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the resulting coating solutions of the non-magnetic layer formulations a to b, and the magnetic layer formulations a to b.
Add 6 parts to the coating solution of b, and further add 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone,
Filtration was carried out using a filter having an average pore size of μm to prepare coating solutions of non-magnetic layer formulations a to b and magnetic layer formulations a to b, respectively.

The coating solution of the non-magnetic formulation a or b thus obtained was dried so that the thicknesses shown in Tables 3 to 4 were obtained, and immediately after that, the thickness of the magnetic layer was changed to Table 3 below. The coating solution of the magnetic layer formulation a or b is applied to the polyethylene naphthalate support having a thickness of 5.5 μm and a center line surface roughness of 0.002 μm so as to obtain the values described in Table 1 to 4. While the layer was still wet, a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 3000 G were used to orient and dry the layer. 200-280
Treatment is performed at a speed of 200 m / min. At a speed of 200 g / cm. Then, a three-stage calender consisting of a metal roll and a plastic roll is used at 90 ° C. for 200 m / min at a linear pressure of 200 to 28.
The treatment was performed at 0 Kg / cm. After that, the thickness is 0.5 μm
Of the back layer. Slit to a width of 8 mm, Table 3 ~
Various 8 mm video tapes shown in FIG. 4 were manufactured. However, Comparative Example 7 was a single layer having only the magnetic layer without providing the non-magnetic layer in the above.

The obtained samples were evaluated as follows, and the results are shown in Tables 3-4. The analysis method of the composition of the ferromagnetic metal powder in Table 1 and the evaluation method of the magnetic characteristics shown in Table 2 are also shown.

[0091]

[Table 3]

[0092]

[Table 4]

Evaluation Method <Analysis Method of Ferromagnetic Metal Powder Composition> 0.1 g of ferromagnetic metal powder (when determining the composition of the ferromagnetic metal powder in the magnetic layer, a magnetic layer equivalent to 0.1 g of the ferromagnetic metal powder) To)
After adding N hydrochloric acid to dissolve it to 25 ml, dilute it to 1 N, dilute it with a 1 N hydrochloric acid solution so that the concentration matches the standard solution, and adjust the concentration to obtain a test solution. This test solution is used as an ICP emission spectrometer (SPS1200) manufactured by Seiko Denshi Kogyo.
It is measured in A), the content of each element is determined, and the ratio to Fe is expressed in atomic%. As the standard solution, a commercially available reagent for atomic absorption analysis (metal standard solution) was used. <Analytical Method for Composition of Ferromagnetic Metal Powder Surface Layer> Micro Auger μ-AES (PH1-66, manufactured by ULVAC-PHI, Inc.)
0) using argon ion etching (accelerating voltage:
3.5kV, ion current 0.2μA, 2mm × 2
mm raster scan)
The ept Profile was measured.

Device body: Acc. Volt. 15kV
Tilt 60 °, Sample Current 40
nA <Magnetic characteristics> Ferromagnetic metal powder (Table 2: Before application to magnetic layer) Using a vibrating sample type magnetometer VSM-5 (manufactured by Toei Industry Co., Ltd.), time constant 0.03 seconds, sweep speed 5 minutes / 10
The measurement was performed with kOe and a measurement magnetic field Hm = 10 kOe.

Magnetic layer Using a vibrating sample type magnetometer VSM-5 (manufactured by Toei Industry Co., Ltd.), time constant 0.1 sec, sweep speed 3 min / 10 k
Oe was measured with a measurement magnetic field Hm = 10 kOe. Storability After the tape was stored in an environment of 60 ° C. and 90% RH for 7 days, the tape was measured by the above-mentioned magnetic layer measurement method and calculated by the following formula.

Hc fluctuation after storage (%) = 100 × (Hc before storage−Hc after storage) / (Hc before storage) Bm decrease after storage (%) = 100 × (Bm before storage−Bm after storage) / (storage Before Bm) <Average particle size of ferromagnetic metal powder> Before application to magnetic layer Take a 100,000 times photograph with a transmission electron microscope photograph of 300 kV, and use an image analyzer (IBASS manufactured by Carl Zeiss).
In -1), the electron micrograph was traced to read the minor axis length and the major axis length (n = 500), and the average particle size was obtained. The axial ratio is represented by average major axis length / average minor axis length.

After application to the magnetic layer, pretreatment was carried out in the order of peeling the magnetic layer → hydrolysis of the binder resin → washing → drying. Magnetic layer peeling: The magnetic tape was stretched to make the magnetic layer float from the non-magnetic support, and the magnetic layer was peeled by squeezing with a cutter blade. Hydrolysis of binder resin: 500 mg of peeled magnetic layer
Reflux for 2 hours in 100 ml of N NaOH / methanol solution.

Washing: Washing with decantation 3 times and then with THF 3 times. Drying: It was dried in a vacuum dryer at 50 ° C. The average particle diameter of the obtained ferromagnetic metal powder was determined in the same manner as in the measuring method before application to the magnetic layer. <Crystallite size of ferromagnetic metal powder> Powder X-ray diffraction method (5
0kV-150mA: CuK β ray used) α-Fe
It was determined from the spread of the half-value widths of the diffraction lines of the (110) plane and the (220) plane of. <Specific surface area by BET method> Auto-soap (USA: manufactured by Canterchrome Co., Ltd .: handled by Yuasa Ionics Co., Ltd.) was used to degas in a nitrogen atmosphere at 250 ° C. for 30 minutes by a BET single point method (partial pressure 0.30) It was measured. <Thickness of magnetic layer> Single layer After measuring the total thickness of the tape, remove the magnetic layer at the measurement point with a solvent (wipe it with a solvent-impregnated paper cloth) and measure the thickness of the tape. Thickness. Thickness is MIN
Measure with ICON (manufactured by Tokyo Seimitsu Co., Ltd.) (measure each 6 points and give the average value). When the magnetic layer is extremely thin (about 1 μm
The following) may be measured by the same method as in the case of multiple layers.

In the case of multiple layers: A magnetic recording medium was cut out with a diamond cutter to a thickness of about 0.1 μm in the longitudinal direction, observed with a transmission electron microscope at a magnification of 30,000, and photographed. The print size of the photograph is A4 size. After that, paying attention to the shape difference between the ferromagnetic powder and the non-magnetic powder in the magnetic layer and the non-magnetic layer, the interface is visually judged and the edge of the magnetic layer is blacked, and the surface of the magnetic layer is also blacked. Company IB
The distance between the bordered lines was measured by AS-2). The measurement point was measured over a range of 21 cm in the length of the sample photograph. The simple arithmetic mean of the measured values at that time was divided by the magnification to obtain the thickness of the magnetic layer. <Surface Roughness of Magnetic Layer> Ra of an area of about 250 nm × 250 nm was measured on the surface of the magnetic layer by the MIRAU method using an optical interference three-dimensional roughness meter “TOPO3D” manufactured by WYKO (Arizona, USA). The measurement wavelength is about 650 nm, and spherical correction and cylindrical correction are added. <Electromagnetic conversion characteristics><Reproductionoutput> A 7.6 MHz signal was recorded on a VTR (EV-S900) manufactured by Sony Corporation, and the reproduction output when this signal was reproduced was measured with a spectrum analyzer. The output of the reference tape was 0 dB. <C / N> 7.6MHz signal reproduction output and -1MHz distance when reproducing this signal (6.6MHz)
The noise generated at 1 is measured with a spectrum analyzer, and the ratio of the reproduction output to this noise is defined as C / N. The C / N of the reference tape was set to 0 dB. <Running Durability> The tape was run 100 times with 10 units of 8 mm video deck FUJIX8 manufactured by Fuji Photo Film Co., Ltd. in an atmosphere of 23 ° C. and 70% RH. During that time, the output decrease was measured, and the dirt on each part in the deck after running was evaluated. ◯: Output decrease was within 3 dB, and stains on various parts inside the deck were not visually observed. Δ: Output decrease was within 3 dB, but a lot of stains on each part in the deck were visually observed. Poor: The output was reduced by 3 dB or more, and there were many stains on various parts inside the deck. <Head Wear> A commercially available 8 mm video deck was remodeled to double speed and head wear of the virgin tape was evaluated. The tape uses 4 rolls of 180m and 4 at 5 ℃ and 80% RH.
After running for 0 hours, head height before and after running (head)
The height was measured and the amount of change (μm) was determined.

[0100]

INDUSTRIAL APPLICABILITY The present invention specifies the composition and shape of the ferromagnetic metal powder contained in the magnetic layer provided on the non-magnetic layer, and the magnetic characteristics of the magnetic layer, and under a specific forced high temperature and high humidity environment. By identifying the changes in Hc and Bm after storage, it is possible to sufficiently withstand the environment of high temperature and high humidity, and to obtain a high output, C that is comparable to a ferromagnetic metal thin film type magnetic recording medium.
It is possible to provide a coating type magnetic recording medium having / N and excellent in running durability.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the shape of a spindle-shaped ferromagnetic metal powder used in the present invention.

FIG. 2 shows data obtained by micro-Auger analysis of the surface layer composition of the ferromagnetic metal powder A, in which the horizontal axis represents the sputtering time and the vertical axis represents the atomic concentration (%). The atomic concentration is 1
00% is the total sum of each element.

FIG. 3 shows data obtained by micro-Auger analysis of the surface layer composition of the ferromagnetic metal powder B, in which the horizontal axis represents the sputtering time and the vertical axis represents the atomic concentration (%). The atomic concentration is 1
00% is the total sum of each element.

FIG. 4 shows data obtained by micro-Auger analysis of the surface layer composition of the ferromagnetic metal powder C, in which the horizontal axis represents the sputtering time (distribution in the depth direction) and the vertical axis represents the atomic concentration (%). The atomic concentration of 100% is the sum of each element.

Claims (4)

[Claims] 1. A magnetic layer in which an inorganic non-magnetic powder and a non-magnetic layer containing a binder resin as a main component and a ferromagnetic metal powder and a magnetic layer containing a binder resin as a main component are formed in this order on a non-magnetic support. In the recording medium, the magnetic layer has a thickness of 0.01 to 0.8 μm, the ferromagnetic metal powder in the magnetic layer is mainly Fe and Co, and Co / Fe is 15 to 4
5 atomic% and the average major axis length is 0.05 to 0.13
The magnetic layer has a coercive force (Hc) of 2000 to 3000 Oe, a saturation magnetic flux density (Bm) of 3800 to 6000 gauss, and the magnetic layer is 60 ° C., 90 ° C. After storage in an environment of% RH for 7 days, the Hc of the magnetic layer is within ± 3% of the Hc before storage, and the decrease in Bm of the magnetic layer is 5% or less and 3700 gauss or more. A magnetic recording medium characterized by the above. 2. The ferromagnetic metal powder has a saturation magnetization (σ _S )
Contains Al in an amount of 135 to 170 emu / g in an amount of 20 atomic% or less with respect to Fe, contains at least one or more kinds of rare earth elements in a total amount of 1 to 15 atomic% with respect to Fe, and has a ratio of 4 to Al.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium contains 0 atomic% or more. 3. In the ferromagnetic metal powder, the surface layer of the particle is composed of Al, the rare earth element, and Fe of each of O as compared with the entire particle.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a large content ratio with respect to. 4. The surface roughness of the magnetic layer is 0.5 to 3 nm.
The magnetic recording medium according to claim 1, wherein