JPH07121861A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance output in a high-frequency region, durability and corrosion resistance by forming two magnetic layers separately contg. different ferromagnetic metal powders and making the saturation magnetization of the ferromagnetic metal powder contained in the lower magnetic layer smaller than that in the upper magnetic layer. CONSTITUTION:A nonmagnetic substrate 1 drawn from a feed roll 32 is successively coated with a magnetic coating material for a 1st magnetic layer, a magnetic coating material for a 2nd magnetic layer and a coating material for an underlayer by means of extrusion coaters 10-12. This medium is then passed through a magnet for orientation or a magnet 33 for perpendicular orientation and it is introduced into a drier 34, where 1st and 2nd magnetic layers are formed. The 1st and 2nd magnetic layers separately contain different ferromagnetic metal powders satisfying deltas(A)<deltas(B) [where deltas(A) is the saturation magnetization of the ferromagnetic metal powder contained in the 1st magnetic layer and deltas(B) is that in the 2nd magnetic layer]. The objective medium excellent in output in a high-frequency region, running durability at high temp., still durability and corrosion resistance is obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic recording medium.
Examples of the application of the present invention include a magnetic recording tape for Hi8 and a magnetic recording medium for high definition, but the present invention is not limited to them.

[0002]

2. Description of the Related Art In Japanese Patent Application Laid-Open No. 57-143735, a magnetic layer is laminated and a lower layer is made of metal powder having a σs of 140 emu / g or more,
A technique for improving corrosion resistance and surface smoothness by using a metal powder having σs of 140 emu / g or less for the upper layer is disclosed. Further, in JP-A-60-223018, by providing a layer containing hexagonal ferrite powder in the upper layer and a layer containing ferromagnetic alloy powder in the lower layer, a high reproduction output from low frequency to high frequency and good reproduction output can be obtained. A technique for obtaining running durability is disclosed. However, the present inventor has found that these techniques have problems of deterioration of output in a high frequency range, deterioration of running durability at high temperature, and deterioration of still durability. Further, it was discovered that the corrosion resistance is not sufficient for Hi8 or high definition.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having excellent output in a high frequency range, running durability at high temperature, still durability and corrosion resistance.

[0004]

The above object of the present invention can be achieved by the following constitutions.

(1) At least one of three types of layers, a non-magnetic layer, a layer containing a high magnetic permeability material, or a layer containing ferromagnetic iron oxide, is provided on a support, and a strong layer is provided thereon. A second magnetic layer containing a magnetic metal powder is provided, and a first magnetic layer containing a ferromagnetic metal powder different from the ferromagnetic metal powder of the second magnetic layer is further provided thereon. When the saturation magnetization amount of the ferromagnetic metal powder contained in the metal magnetic layer is s (A) and the saturation magnetization amount of the ferromagnetic metal powder contained in the second magnetic layer is s (B), s (A) < A magnetic recording medium that is σs (B).

(2) At least one of three types of layers, a nonmagnetic layer, a layer containing a high magnetic permeability material, or a layer containing ferromagnetic iron oxide, is provided on a support, and a strong layer is provided thereon. A second magnetic layer containing magnetic powder is provided, and a first magnetic layer containing a ferromagnetic metal powder different from the ferromagnetic powder of the second magnetic layer is further provided on the second magnetic layer. When the weight% of Al in the magnetic metal powder to Fe is Al (A)%, and the weight% of Al in the ferromagnetic powder of the second magnetic layer to Fe is Al (B)%, Al (A)% A magnetic recording medium with> Al (B)%.

(3) At least one of three types of layers, a non-magnetic layer, a layer containing a high magnetic permeability material, or a layer containing ferromagnetic iron oxide, is provided on a support, and a strong layer is provided thereon. A magnetic recording medium, wherein a second magnetic layer containing magnetic iron oxide powder or ferromagnetic metal powder is provided, and a first magnetic layer containing hexagonal ferrite powder is further provided thereon.

(4) At least one of three types of layers, a non-magnetic layer, a layer containing a high magnetic permeability material, or a layer containing ferromagnetic iron oxide, is provided on a support, and a strong layer is provided thereon. A second magnetic layer containing magnetic powder is provided, and a first magnetic layer containing a ferromagnetic metal powder different from the ferromagnetic powder of the second magnetic layer is further provided on the second magnetic layer. When the average major axis length of the magnetic metal powder is l (A) nm and the average major axis length in the ferromagnetic powder of the second magnetic layer is l (B) nm, l (B) −
A magnetic recording medium in which l (A) ≧ 20 nm and l (A) ≦ 180 nm.

In the present application, the method for measuring the composition of the ferromagnetic powder was the method described below.

<Overall composition>: Regarding the abundance ratio of each element of Fe, Co, Ni, Nd, Si and Al in the overall composition of the ferromagnetic powder, a sample was obtained by using a wavelength dispersive X-ray fluorescence analyzer (WDX). After measuring the fluorescent X-ray intensities of the respective elements therein, the viewfinder parameter method (hereinafter referred to as FP method).
It was calculated and calculated according to.

The FP method will be described below.

For the measurement of fluorescent X-ray, W manufactured by Rigaku Denki Co., Ltd.
The DX system 3080 was used under the following conditions.

X-ray tube: Rhodium tube Output: 50KV, 50mA Spectroscopic crystal: LiF (for Fe, Co, Ni, Nd), PET (for Al), RX-4 (for Si) Absorber: 1/1 (Fe only 1/10) Slit: COARSE Filter: OUT PHA: 15-30 (for Al and Si), 10-30 (Fe, C
(For o, Ni, Nd) Counting time: peak = 40 seconds, background = 40 seconds
(Measurement of two points before and after the peak) The measurement of fluorescent X-rays is not limited to the above-mentioned device, and various devices can be used.

The following four kinds of metal compounds were used as standard samples.

The standard sample is an Analytical Reference Mater.
ials international alloy SRM1219 (0.15 wt% C, 0.42 wt% Mn, 0.03 wt% P, 0.55 wt% Si, 0.16 wt% Cu, 2.16 wt% Ni, 15.64 wt% Cr, Mo is contained in an amount of 0.16% by weight and V is contained in an amount of 0.06% by weight.).

The standard sample 2 is an Analytical Reference Mat.
erials international alloy SRM1250 (Ni 37.7
8 wt%, Cr 0.08 wt%, Mo 0.01 wt%, Co 16.10
% By weight and 0.09% by weight of Al. ).

The standard sample 3 is magnetic iron oxide powder (Mn 0.14
%, P 0.15% by weight, S 0.19% by weight, Si 0.36% by weight, Co 3.19% by weight, Zn 1.26% by weight, Ca 0.07% by weight, Na 0.02% by weight. ).

The standard sample 4 is a ferromagnetic metal powder (Nd 2.73
Contains by weight%. ).

The weight% of the elements in the standard samples 1 and 2 are the values on the data sheet provided by the manufacturer, and the weight% of the elements in the standard samples 3 and 4 are the values analyzed by the ICP emission spectrometer. This value was input as the elemental composition value of the standard sample in the calculation of the FP method below.

For the calculation of the FP method, the finder was used for finding parameter software, Version 2.1 made by Technos, under the following conditions.

Sample model: Bulk sample Balanced component sample: Fe Input component: Measured X-ray intensity (KCPS) Analysis unit: wt% The calculated abundance ratio of each element (wt%) is 100 Fe atoms.
It is a quantitative value by converting it as the weight% of other elements with respect to the weight%.

<Surface Composition> Fe, Co, Ni, Si, Al in the composition of the surface of the ferromagnetic metal powder (the surface here means the surface layer portion from the surface of the powder to a depth of 100 Å).
The abundance ratio of each element was determined by using an XPS surface analyzer.

The method will be described below.

First, the XPS surface analyzer is set under the following conditions.

X-ray anode: Mg resolution: 1.5 to 1.7 eV (resolution is 3d of clean Ag)
It is specified by the half-width of the 5/2 peak. ) In addition, so-called adhesive tape is not used for fixing the sample. The type of XPS surface analyzer is not particularly limited, and various devices can be used, but in the present application, ESCALAB-200R manufactured by VG was used.

Narrow scan was performed in the measurement range shown in Table 1 to measure the spectrum of each element. At this time, the data acquisition gap was set to 0.2 eV, and integration was performed until a count of at least the minimum count shown in Table 1 was obtained.

[0027]

[Table 1]

The energy position of the obtained spectrum is corrected so that the peak of C or higher is 284.6 eV.

Next, COMMON DATA P made by VAMAS-SCA-JAPAN
ROCESSING SYSTEM Ver. To perform data processing on 2.3 (hereinafter referred to as VAMAS software), use the software provided by each device manufacturer to obtain the VA using the above spectra.
Transfer to a computer that can use MAS software.

Then, after the transferred spectrum is converted into the VAMAS format by using the VAMAS software, the following data processing is performed.

Before starting the quantitative processing, Coun for each element
The t Scale is calibrated and 5 points smoothing is performed.

The quantitative processing is as follows.

With the peak position of each element as the center, the peak area intensity is determined within the above-mentioned quantitative range. Using the sensitivity coefficient shown in Table 1, the atomic% of each element was determined. Number of atoms%
Was converted into the number of atoms with respect to 100 Fe atoms and used as a quantitative value.

The above is the method for measuring the composition of the ferromagnetic powder in the present application.

Next, specific embodiments of the present invention will be shown below.

In the present invention, it is preferable that the non-magnetic layer contains acicular non-magnetic powder. Further, an overcoat layer may be provided on the first magnetic layer, if necessary.
In addition, the film thickness of a layer including two or more different magnetic layers is usually 0.
It is 1 to 1.2 μ, preferably 0.2 to 1.0 μ, and more preferably 0.3 to 0.8 μ. The coercive force of the first magnetic layer is preferably larger than that of the second magnetic layer. The coercive force of the first magnetic layer is preferably 1500 to 2200 Oe, preferably 1700 to 2000 Oe, more preferably 1750 to 1950 Oe.

In the invention of claim 1, σs (A) is 130 emu.
/ g or less and σs (B) is preferably 130 emu / g or more. Further, σs (A) is preferably lower than σs (B) by 5 emu / g or more, more preferably 10 emu / g or more.

In the invention of claim 2, Al (A)% is preferably 2% by weight or more, more preferably 4% by weight or more. The Al (B)% is preferably 4% by weight or less, more preferably 2% by weight or less. And, Al (A)% is preferably larger than Al (B)% by 1% by weight or more, more preferably 2% by weight or more.

In particular, when the ferromagnetic metal powder is used for the first magnetic layer, if the conventional two-layered structure is used, the fatty acid is easily adsorbed to the ferromagnetic metal powder and the fatty acid is not formed on the surface of the magnetic layer. Although it almost disappears and the tape characteristics are deteriorated, by adopting the constitution of the present invention, free fatty acids are sequentially supplied from the layers below the first magnetic layer, and such tape deterioration is prevented. Further, the following method is preferable to further promote this effect.

Use a ferromagnetic powder, a non-magnetic powder, or a high magnetic permeability material surface-treated with Si or Al. Use a binder containing a polar group. This allows the binder to be a ferromagnetic powder, a non-magnetic powder, or a high magnetic permeability. A tight coating on the surface of the material can prevent fatty acids from over-adsorbing to these powders.

The thickness of the first magnetic layer is 0.01 to 0.8 μm,
Preferably 0.05-0.5 μm, more preferably 0.1-
0.3 μm This makes it easy to supply fatty acids from the lower layer.

Fatty acids are added at the final stage of the preparation of the paint for each layer.

Next, the structure of the magnetic recording medium of the present invention will be sequentially described in detail.

(A) Non-magnetic support As the material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate and cellulose diacetate. Cellulose derivatives such as, and plastics such as polyamide, aramid resin, and polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape, film, sheet, card,
There are disc shape and drum shape.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 2-100.
μm, preferably 3 to 50 μm, about 30 μm to 10 mm in the case of a disc or card, and appropriately selected depending on the recorder etc. in the case of a drum.

The non-magnetic support may have a single-layer structure or a multi-layer structure. Further, this non-magnetic support may be subjected to surface treatment such as corona discharge treatment.

A back coat layer is provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided for the purpose of improving the running property of the magnetic recording medium, preventing charging, and preventing transfer. It is preferable that an undercoat layer be provided between the magnetic layer and the non-magnetic support.

(B) First Magnetic Layer and Second Magnetic Layer The thickness of the first magnetic layer is usually 0.01 to 0.8 μm,
It is preferably 0.05 to 0.5 μm, particularly preferably 0.1 to
0.3 μm. When the thickness is 0.01 μm or more, recording is sufficient and sufficient reproduction output is obtained, while when it is 0.8 μm or less, film thickness loss can be ignored and sufficient reproduction output is obtained. The thickness of the second magnetic layer is preferably 0.1 μm or more, more preferably 0.2 to 0.5 μm.

The content of the ferromagnetic powder is usually 60 to 95% by weight, preferably 70 to 90% by weight, particularly preferably 75 to 85% by weight, based on the total solid content in the layer.

(B-1) Magnetic Powder As the magnetic powder used in the present invention, ferromagnetic iron oxide powder, ferromagnetic metal powder, hexagonal plate-like powder and the like can be mentioned. Among these, as the magnetic powder used in the first magnetic layer, ferromagnetic metal powder and hexagonal ferrite powder can be preferably used.

As the ferromagnetic iron oxide powder, γ-Fe is used.
₂ O ₃ , Fe ₃ O ₄ or FeOx (1.33 <x
Examples thereof include compounds represented by <1.5) and cobalt-modified iron oxide to which Co is added, represented by Co-FeOx (1.33 <x <1.5).

Examples of the ferromagnetic metal powder include Fe, Co, Fe-Al system, Fe-Al-Ni system, Fe-Al-Zn system, Fe-Al-Co system, and F system.
e-Al-Ca system, Fe-Ni system, Fe-Ni-Al system, Fe-Ni-Co system, Fe-Ni-
Si-Al-Mn system, Fe-Ni-Si-Al-Zn system, Fe-Al-Si system, Fe-Ni-Zn
System, Fe-Ni-Mn system, Fe-Ni-Si system, Fe-Mn-Zn system, Fe-Co-Ni-P
Examples thereof include ferromagnetic metal powders such as those based on Ni-Co, Ni-Co, and Fe, Ni, Co, and the like. Among these, the Fe-based metal powder has excellent electrical characteristics. On the other hand, from the viewpoint of corrosion resistance and dispersibility, Fe-Al system, Fe-Al-Ca
System, Fe-Al-Ni system, Fe-Al-Zn system, Fe-Al-Co system, Fe-Ni-Si-A
Fe-Al type ferromagnetic metal powders such as l-Co type and Fe-Co-Al-Ca type are preferable.

Particularly preferred ferromagnetic metal powder for the purpose of the present invention is a magnetic metal powder containing iron as a main component, and Al or Al and Ca, in which Al is Al in a weight ratio of Fe: Al = 100: 0.5.
~ 100: 20, Ca: Fe: Ca = 100: 0.1 to 1 by weight
It is desirable to contain it in the range of 00:10. By setting the ratio of Fe: Al in such a range, the corrosion resistance is remarkably improved,
Also, by setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics can be improved and dropout can be reduced. Although the reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, it is considered that the coercive force is improved and the aggregates are reduced due to the improved dispersibility.

The ferromagnetic powder of the first magnetic layer used in the present invention has a crystallite size by X-ray diffraction of usually 17 nm or less, preferably 15 nm, more preferably 12 nm or less, and its average major axis length is less than 300 nm. It is preferably 40 to 200 nm, and more preferably 50 to 180 nm.
When the crystallite size of the ferromagnetic powder and the average major axis length thereof are within the above range, the surface properties of the magnetic recording medium can be improved and the electrical characteristics can be improved.
The above average major axis length is an average value of 500 major axis lengths of ferromagnetic metal powder measured by a transmission electron micrograph. The crystallite size of Fe (11
0) It was measured by the Scherrer method using Si powder as the standard, using the integral width of the diffraction line.

The coercive force (Hc) of the ferromagnetic powder used in the present invention is usually preferably in the range of 600 to 5,000 Oe.

The ferromagnetic powder preferably has a saturation magnetization amount (σ _s ) which is a magnetic characteristic, usually 70 emu / g or more. When the saturation magnetization is 70 emu / g or more, the electromagnetic conversion characteristics are good, and when the ferromagnetic powder is a ferromagnetic metal powder, the saturation magnetization is 120 emu / g.
The above is desirable.

As a preferable ferromagnetic metal powder, in the whole composition, Fe atoms and Al contained in the ferromagnetic powder are contained.
Fe: Al = 100: 0.5-100: 2 by weight in atomic content ratio
It is 0. A structure in which the content ratio of Fe atoms and Al atoms present in the surface region of 100 Å or less at the ESCA analysis depth of the ferromagnetic metal powder is Fe: Al = 30: 70 to 70:30 in terms of atomic number ratio. Those having are preferred. Or with Fe atom
Ni atoms, Al atoms and Si atoms are preferably contained in the ferromagnetic powder, further at least one of Co atoms and Ca atoms is contained in the ferromagnetic powder, the content of Fe atoms 100 parts by weight and When, the content of Ni atoms is 1 part by weight or more and less than 10 parts by weight, the content of Al atoms is 0.1 parts by weight or more and less than 5 parts by weight, the content of Si atoms is 0.1 parts by weight or more and 5 parts by weight. It is preferable that the content of Co atom and / or the content of Ca atom (however, the total amount when both Co atom and Ca atom are contained) is 0.1 part by weight or more and less than 13 parts by weight. . Further, the content ratio of Fe atoms, Ni atoms, Al atoms, Si atoms, Co atoms and / or Ca atoms present in the surface region of 100 Å or less at the analysis depth by ESCA of the ferromagnetic powder is Fe: Ni: Al: Si (Co and / or Ca) = 100: (4 or less):
It is preferable to have a structure of (40 to 250): (10 to 70): (5 to 80).

The ferromagnetic metal powder preferably contains Fe, Al, and one or more rare earth elements selected from the group consisting of Sm, Nd, Y, and Pr as its constituent elements.
In this case, the ferromagnetic metal powder, in its overall composition,
Al atom is 2 to 10 parts by weight with respect to 100 parts by weight of Fe atom, and one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr is 1 to 8 parts by weight. Preferably, ESCA analysis depth of the ferromagnetic powder is 100Å
The number of Fe atoms present in the following surface region is 100, the number of Al atoms is 70 to 200, and the number of atoms of one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr is , 0.5 to 30
Is preferred.

More preferably, the ferromagnetic metal powder further contains Na or Ca as a constituent element, and in the entire composition thereof, Al atom is 2 to 10 per 100 parts by weight of Fe atom.
1 to 8 parts by weight of one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr, Na atoms less than 0.1 parts by weight, and Ca atoms 0.1 to 2 parts by weight. It is preferable that the amount is 100 parts by weight, and the number of Fe atoms existing in the surface region of 100 Å or less as analyzed by ESCA of the ferromagnetic powder is 100.
On the other hand, the number of Al atoms is 70 to 200, and Sm, Nd, Y and Pr are
The number of one or more rare earth elements selected from the group consisting of and is 0.5 to 30, the number of Na atoms is 2 to 30, and the number of Ca atoms is 5 to 30.

More preferably, the ferromagnetic metal powder further contains Co, Ni and Si as its constituent elements, and the total composition thereof has 2 to 2 Co atoms per 100 parts by weight of Fe atoms.
0 parts by weight, Ni atoms are 2 to 20 parts by weight, Al atoms are 2 to 10 parts by weight, Si atoms are 0.3 to 5 parts by weight, and from the group consisting of Sm, Nd, Y and Pr. The atom of the selected one or more rare earth elements is 1 to 8 parts by weight, and the Na atom is 0.
It is preferably less than 1 part by weight, the Ca atom is 0.1 to 2 parts by weight, and the Co atom is 100 atom with respect to 100 Fe atom existing in the surface region of 100 Å or less in the analysis depth by ESCA of the ferromagnetic powder. The number is less than 0.1, the number of Ni atoms is less than 0.1, the number of Al atoms is 70 to 200, the number of Si atoms is 20 to 130, and is selected from the group consisting of Sm, Nd, Y and Pr. The one or more rare earth elements are 0.5 to 30, the number of Na atoms is less than 30, and the number of Ca atoms is 5 to 30.

Fe, Co, Ni, Al, S in the above total composition
The abundance ratio of one or more rare earth elements, Na and Ca selected from the group consisting of i, Sm, Nd, Y and Pr, and Fe, Co, Ni, Al, Si, Sm, Nd and Y on the surface are also The ferromagnetic metal powder in which the abundance ratio of one or more rare earth elements selected from the group consisting of and Pr, Na and Ca is within the above range is 1700 Oe.
It is preferable because it has the above high coercive force (Hc), the high saturation magnetization amount (σ _s ) of 120 emu / g or more, and the high dispersibility.

The content of this ferromagnetic metal powder is usually 60 to 95% by weight, preferably 70 to 90% by weight, particularly preferably 75, based on the total solid content in the layer.
~ 85% by weight.

The hexagonal plate-like powder may be, for example, hexagonal ferrite. Such a hexagonal ferrite is composed of barium ferrite, strontium ferrite, etc., and even if part of the iron element is replaced with another element (for example, Ti, Co, Zn, In, Mn, Ge, Hb). Good. Regarding this ferrite magnetic material, IEEE
It is described in detail in trans on MAG-18 16 (1982).

Of these, barium ferrite can be preferably used in the present invention.

As an example of the barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder, an average particle diameter in which a part of Fe is replaced by at least Co or Zn (length of diagonal line of plate surface of hexagonal ferrite) Is 400 to 900Å, and the plate ratio (value obtained by dividing the length of the diagonal of the plate surface of hexagonal ferrite by the plate thickness) is 2.0 to 10.0, preferably 2.0 to 6.0.
And Ba-ferrite having a coercive force (Hc) of 450 to 1500 Oe. Ba-Ferrite powder C Fe
The coercive force is controlled to an appropriate value by substituting a part with o, and by further substituting with Zn, a high saturation magnetization that cannot be obtained only by Co replacement is realized, and a high reproduction output is provided. A magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. In addition, Ba-ferrite used in the present invention further comprises a part of Fe containing Ti, In, and M.
It does not matter if it is substituted with a transition metal such as n, Cu, Ge, or Sn.

The Ba-ferrite used in the present invention is represented by the following general formula.

BaO · n ((Fe _1-m M _m ) ₂ O ₃ ) where m> 0.36 (where Co + Zn = 0.08 to 0.3, Co / Zn
= 0.5-10), n is 5.4-11.0, preferably
5.4 to 6.0, M represents a substituted metal, and magnetic particles that are a combination of two or more elements having an average valence of 3 are preferable.

In order to obtain a sufficient reproduction output when used as a magnetic recording medium, it is preferable that the average particle size of the Ba-ferrite is 300 Å or more, in order to improve the surface smoothness and lower the noise level. It is preferably 900 Å or less. Also, by setting the plate ratio to 2.0 or more, a vertical alignment ratio suitable for high density recording when used as a magnetic recording medium can be obtained, and the plate ratio can be improved to improve the surface smoothness and reduce the noise level. Is preferably 10.0 or less. Further, the coercive force is preferably 450 Oe or more for holding the recording signal, and 1,500 Oe or less is preferable for preventing the head from being saturated.

The barium ferrite magnetic powder used in the present invention generally has a saturation magnetization (σ _s ) which is a magnetic characteristic,
From the viewpoint of electromagnetic conversion characteristics, 50 emu / g or more is desirable.

Further, according to the present invention, as the recording density becomes higher, Ba having a specific surface area by the BET method of 30 m ² / g or more is obtained.
-It is desirable to use ferrite magnetic powder.

As a method for producing the hexagonal magnetic powder used in the present invention, for example, the oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite can be prepared, for example, from boric acid. Fusing with such a glass-forming substance, the resulting melt is rapidly cooled to form a glass, which is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass In addition to the glass crystallization method of removing the components by heat treatment, a coprecipitation-firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method and the like can be applied.

Even one kind of the above magnetic powder can be used in one magnetic layer,
Alternatively, two or more kinds may be used in combination.

(B-2) Binder As the binder contained in the first magnetic layer and the second magnetic layer,
For example, polyurethane, polyester, vinyl chloride resin such as vinyl chloride copolymer, etc. are typical ones,
These resins are -SO ₃ M, -OSO ₃ M, -COOM and -PO (O
M ¹ ) ₂ preferably contains a repeating unit having at least one polar group selected from sulfobetaine groups. However, in the above polar group, M is a hydrogen atom or Na, K, Li
Represents an alkali metal such as M ¹ is a hydrogen atom or Na, K, L
represents an alkali metal such as i or an alkyl group. The polar group has the effect of improving the dispersibility of the magnetic powder, the content of each resin is 0.1 ~ 8.0 mol%, preferably 0.2 ~ 6.0
Mol%. When this content is 0.1 mol% or more,
When the dispersibility of the magnetic powder is improved and when the content is 8.0 mol% or less, the magnetic coating becomes difficult to gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The content of the binder is usually 8 to 25 parts by weight, preferably 10 to 20 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

The binder is not limited to one kind alone, and two or more kinds may be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is a weight ratio, preferably 90:10. It is desirable to use a combination of ˜10: 90, particularly preferably 70:30 to 30:70.

(B-3) Other components In the present invention, in order to improve the quality of the first magnetic layer and the second magnetic layer, an abrasive, a lubricant, a durability improver,
Additives such as a dispersant, an antistatic agent and a conductive fine powder may be contained as other components.

As the polishing agent, known substances can be used. The average particle size of this abrasive is usually 0.05 to 0.6 μm, preferably 0.05 to 0.5 μm, and particularly preferably 0.05 to 0.3 μm. The content of the abrasive is usually 3 to 2 with respect to 100 parts by weight of the magnetic powder.
The amount is 0 parts by weight, preferably 5 to 15 parts by weight, and particularly preferably 5 to 10 parts by weight.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the addition amount of the fatty acid is preferably 0.2 to 10% by weight with respect to the magnetic powder from the viewpoint of running property, exudation of the fatty acid on the surface, and output.
Particularly preferably, it is 0.5 to 5% by weight. In addition, the amount of fatty acid ester added was 0.2% relative to the magnetic powder in terms of still durability, exudation of fatty acid ester on the surface, and output.
~ 10% by weight is preferred, particularly preferably 0.5-5% by weight
Is. When a fatty acid and a fatty acid ester are used together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10. The fatty acid may be a monobasic acid or a dibasic acid and has 6 to 6 carbon atoms.
30 is preferable, and the range of 12 to 22 is more preferable. Further, as the lubricant other than the above fatty acids and fatty acid esters, known substances can be used, and for example, silicone oil, fluorocarbon, fatty acid amide, α-olefin oxide and the like can be used.

Examples of the curing agent include polyisocyanates. Examples of the polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and hexamethylene diisocyanate ( There are aliphatic polyisocyanates such as adducts of HMDI) with active hydrogen compounds. The weight average molecular weight of the polyisocyanate is 100.
It is desirable to be in the range of ~ 3,000.

Examples of the dispersant include those described in paragraph No. 0093 of JP-A-4-214218. These dispersants are usually 0.5 to
Used in the range of 5% by weight.

Antistatic agents include cationic surfactants such as quaternary amines; anionic surfactants containing an acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid;
Examples thereof include amphoteric surfactants such as aminosulfonic acid; natural surfactants such as saponin. The above-mentioned antistatic agent is usually added in the range of 0.01 to 40% by weight with respect to the binder.

Further, in the present invention, conductive fine powder can be preferably used as the antistatic agent. Examples of the antistatic agent include carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, organic compounds of silver, metal particles such as copper powder, and metal oxides such as zinc oxide, barium sulfate and titanium oxide. Examples include pigments coated with a conductive material such as a tin oxide coating or an antimony solid solution tin oxide coating. The average particle diameter of the conductive fine powder is usually 5 to 700 nm, preferably 5 to 200 nm.
nm, more preferably 5 to 50 nm. The content of the conductive fine powder is 0.1 to 10 parts by weight, preferably 0.1 to 2 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the magnetic powder.

(C) Lower Layer The lower layer is formed with a single layer or a plurality of layers between the non-magnetic support and the second magnetic layer.

As the lower layer, for example, a magnetic layer (C-1) containing a ferromagnetic iron oxide powder, a non-magnetic layer (C-2) containing a non-magnetic powder, and a layer (C containing a high magnetic permeability material). −
3), or a layer composed of a combination of these layers. In the present invention, the non-magnetic layer (C-2) is preferable among them, and the non-magnetic layer containing needle-shaped non-magnetic powder is particularly preferable.

The total thickness of the lower layers is usually the total of the lower layers.
The thickness is 0.1 to 2.5 μm, preferably 0.2 to 2.0 μm, and particularly preferably 0.5 to 2.0 μm. When the thickness is 2.5 μm or less, the surface roughness of the upper layer surface after layering is small, so-called layer surface roughness is less likely to occur, and preferable electromagnetic conversion characteristics are obtained. On the other hand, when it is 0.1 μm or more,
The effect of the lower layer appears at the time of calendering, high smoothness is obtained, electromagnetic conversion characteristics are improved, and it is also preferable from the viewpoint of supplying free fatty acid to the upper layer.

(C-1) Magnetic Layer The lower magnetic layer contains magnetic powder. Also, it contains a binder and other components as necessary.

(C-1-1) Magnetic Powder As the magnetic powder contained in the lower magnetic layer, ferromagnetic iron oxide can be preferably used. These magnetic powders may be used alone or in combination of two or more.

Of these magnetic powders, Co is preferable.
-Contains iron oxide. When the lower magnetic layer contains Co-containing iron oxide, the reproduction output becomes good in the region where the recording wavelength is large, particularly in the region of 1 μm or more.

Further, the ferromagnetic iron oxide powder is preferably surface-treated with a Si compound and / or an Al compound. The total content of Si and Al is 10 wt% of both Si and Al with respect to the ferromagnetic iron oxide powder.
The following is preferable, more preferably 0.1 to 5% by weight, and Si / Al ≧ 3 is preferable. The surface treatment can be carried out by the method described in JP-A-2-83219.

The content of the magnetic powder is usually 70 to 90% by weight, preferably 75 to 85% by weight, based on the total solid content in the layer.

(C-1-2) Binder The binder contained in the lower magnetic layer is (B
-The compounds exemplified in 2) can be used,
The amount is usually 5 to 2 with respect to 100 parts by weight of the ferromagnetic powder.
It is 5 parts by weight, preferably 10 to 20 parts by weight.

(C-1-3) Other components As other components contained in the lower magnetic layer,
The compounds exemplified in (B-3) can be used. The amount is not particularly limited and can be appropriately selected as long as the object of the present invention is not impaired.

(C-2) Nonmagnetic Layer The nonmagnetic layer contains nonmagnetic powder. Also, it contains a binder and other components as necessary.

(C-2-1) Non-Magnetic Powder In the present invention, various known non-magnetic powders can be appropriately selected and used.

Examples of the non-magnetic powder include carbon black, graphite, TiO ₂ , barium sulfate, ZnS and MgC.
O ₃ , CaCO ₃ , ZnO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂
O ₃ , α-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide , Tungsten carbide, titanium carbide, tribolite, diatomaceous earth, dolomite and the like.

Of these, preferred are carbon black, CaCO ₃ , TiO ₂ , barium sulfate, α-Al ₂ O ₃ and α-Fe ₂ O.
Inorganic powder such as ₃ , α-FeOOH, Cr ₂ O _3, etc.
-Fe ₂ O ₃ and α-FeOOH are preferable, and α-Fe ₂ is particularly preferable.
O ₃ .

The shape of this non-magnetic powder is preferably the one described in columns 0126 to 0131 of Japanese Patent Application No. 5-142144.

Further, the non-magnetic powder is a Si compound and / or
Alternatively, it is preferably surface-treated with an Al compound. When the non-magnetic powder subjected to such surface treatment is used, the surface condition of the uppermost layer which is the magnetic layer can be improved. The content of Si and / or Al is 0.1 to 10% by weight of Si and 0.1 to 10% by weight of Al with respect to the non-magnetic powder.
It is preferable that Si is 0.1 to 5% by weight, Al is 0.1 to 5% by weight, and particularly, Si is 0.1 to 2% by weight and Al is 0.1 to 2% by weight. The weight ratio of Si and Al should be Si / Al ≧ 3. The surface treatment can be carried out by the method described in JP-A-2-83219.

The content of the non-magnetic powder in the non-magnetic layer is usually 50 to 99% by weight, preferably 60 to 95% by weight, based on the total of all components constituting the non-magnetic layer.
And particularly preferably 70 to 95% by weight. When the content of the nonmagnetic powder is within the above range, the surface condition of the magnetic layer and the nonmagnetic layer can be improved.

(C-2-2) Binder The binder contained in the lower nonmagnetic layer is as follows.
The compounds exemplified in (B-2) can be used, and the amount thereof is usually 5 to 150 parts by weight, preferably 10 to 120 parts by weight, relative to 100 parts by weight of the non-magnetic powder.

(C-2-3) Other Components As the other components contained in the lower non-magnetic layer, the compounds exemplified in (B-3) can be used. The amount is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected.

(C-3) Layer Containing High Magnetic Permeability Material The layer containing the high magnetic permeability material contains a high magnetic permeability material. Also, it contains a binder and other components as necessary.

(C-3-1) High magnetic permeability material As a high magnetic permeability material, its coercive force Hc is 0 <Hc ≦ 1.0 × 1.
0 ⁴ (A / m), preferably 0 <Hc ≦ 5.0 × 10 ³ (A / m). When the coercive force is within the above range, the effect of stabilizing the magnetized region of the uppermost layer is exhibited as the high magnetic permeability material.

In the present invention, it is preferable to appropriately select a material having a coercive force range as the high magnetic permeability material. Examples of such a high magnetic permeability material include a metal soft magnetic material and an oxide soft magnetic material.

As the metal soft magnetic material, Fe-Si alloy, Fe-Al alloy (Alperm, Alfenol, Alfer), permalloy (Ni-Fe based binary alloy, and Mo, Cu, Cr, etc. were added thereto. Multi-component alloy), Sendust (Fe-Si-Al {9.6 wt%
Of Si, 5.4% Al, and the balance being Fe}), Fe-Co alloys, and the like. Among them, sendust is preferable as a preferable metal soft magnetic material. The metal soft magnetic material as the high magnetic permeability material is not limited to those exemplified above, and other metal soft magnetic materials can be used. The high-permeability material can be used alone or in combination of two or more.

As the oxide soft magnetic material, spinel type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ , CoFe ₂ O ₄ and NiFe _{2 are used.}
O ₄ , MgFe ₂ O ₄ , Li _0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni
Examples thereof include -Zn type ferrite, Ni-Cu type ferrite, Cu-Zn type ferrite, Mg-Zn type ferrite, and Li-ZN type ferrite. Among these, Mn-Zn ferrite and Ni-Zn ferrite are preferable. These soft oxide magnetic materials can be used alone or in combination of two or more.

This high-permeability material is made into a fine powder using a ball mill or other crushing device, and its particle size is 1 to 1,000 m.
It is preferably μ, particularly 1 to 500 mμ. In order to obtain such a fine powder, in the metal soft magnetic material,
It can be obtained by spraying a molten alloy in a vacuum atmosphere. Further, the soft oxide magnetic material can be made into a fine powder by a glass crystallization method, a coprecipitation firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like.

Further, it is preferable that the high magnetic permeability material is surface-treated with a Si compound and / or an Al compound. When the non-magnetic powder subjected to such surface treatment is used, the surface condition of the uppermost layer which is the magnetic layer can be improved. The content of Si and / or Al is 0.1 to 10% by weight of Si and 0.1 to 10% by weight of Al with respect to the non-magnetic powder.
It is preferable that Si is 0.1 to 5% by weight, Al is 0.1 to 5% by weight, and particularly, Si is 0.1 to 2% by weight and Al is 0.1 to 2% by weight. The weight ratio of Si and Al should be Si / Al ≧ 3. The surface treatment can be carried out by the method described in JP-A-2-83219.

In the layer containing the high magnetic permeability material, the content of the high magnetic permeability material is 10 to 99% by weight, preferably 50 to 95% by weight, and more preferably 60 to 90% by weight.
When the content of the high magnetic permeability material is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained.

The layer containing the high magnetic permeability material may contain non-magnetic particles.

(C-3-2) Binder As the binder contained in the layer containing the high magnetic permeability material in the lower layer, the compounds exemplified in (B-2) can be mentioned, and the amount thereof is High permeability material 10
It is usually 5 to 30 parts by weight, preferably 1 to 0 parts by weight.
0 to 25 parts by weight.

(C-3-3) Other Components As the other components contained in the lower layer containing the high magnetic permeability material, the compounds exemplified in (B-3) can be mentioned. The amount is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected.

—Manufacture of Magnetic Recording Medium— In the magnetic recording medium of the present invention, it is preferable that the upper layer is laminated by a so-called wet-on-wet method performed when the lower layer is in a wet state. As this wet-on-wet method, a method used for manufacturing a known magnetic recording medium having a multilayer structure can be appropriately adopted.

For example, generally, magnetic powder, binder,
A high-concentration paint is prepared by kneading a dispersant, a lubricant, an abrasive, an antistatic agent, etc. and a solvent, and then the high-concentration paint is diluted to prepare a coating paint, and then this paint is non-magnetically supported. Apply to the surface of the body.

Examples of the solvent include, for example, JP-A-4-1422
For example, those described in Paragraph No. 0119 of No. 18 can be used.

In kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used.

Examples of this kneading disperser include those disclosed in
Examples thereof include those described in paragraph No. 0112 of 4-214218. Of the above kneading dispersers, 0.05-0.5KW
The kneading disperser capable of providing a power consumption load (per 1 kg of magnetic powder) is a pressure kneader, an open kneader,
Continuous kneader, two roll mill, three roll mill, etc.

In order to coat the first magnetic layer, the second magnetic layer and the lower layer on the non-magnetic support, specifically, as shown in FIG. 1, first, the non-magnetic support fed from the supply roll 32 is used. Body 1
In addition, by the extrusion type extrusion coaters 10, 11 and 12, the magnetic coating material for the first magnetic layer, the magnetic coating material for the second magnetic layer and the coating material for the lower layer are applied in multiple layers by the wet-on-wet method, and then for orientation. After passing through the magnet or the vertical orientation magnet 33, it is introduced into the dryer 34, and hot air is blown from the nozzles arranged above and below to dry it. Next, the dried non-magnetic support 1 with each coating layer is guided to a super calendar device 37 including a combination of calendar rolls 38, subjected to calendering here, and then wound on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce a magnetic recording tape for 8 mm video, for example.

In the above method, each paint may be supplied to the extrusion coaters 10, 11 and 12 through an in-line mixer (not shown). It should be noted that in the figure, the arrow indicates the conveying direction of the non-magnetic support. Extrusion coaters 10, 11 and 12 are provided with liquid pools 13 and 14, respectively, and the coating materials from the coaters are piled up in a wet-on-wet system. That is, the magnetic coating for the first magnetic layer and the magnetic coating for the second magnetic layer are applied in multiple layers immediately after the coating of the lower layer coating material (when not dried).

As the extrusion coater, in addition to the three extrusion coaters shown in FIG. 2A, the extrusion coaters of the types shown in FIGS. 2B and 2C can be used. Of these, the extrusion coater shown in (b) is preferred in the present invention. With this extrusion coater (b), the lower layer coating material, the magnetic coating material for the second magnetic layer, and the magnetic coating material for the first magnetic layer are applied simultaneously by extrusion.

As the solvent to be blended in the above paint or the diluent solvent for applying this paint, those described in paragraph No. 0119 of JP-A-4-214218 can be used. These various solvents may be used alone or in combination of two or more.

The magnetic field in the oriented magnet or the vertical orientation magnet is about 20 to 10,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 °.
It's about a minute.

In the wet-on-wet system,
A combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can also be used. Further, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater and the like can be combined.

In the multi-layer coating in this wet-on-wet system, the upper magnetic layer is coated while the lower layer is in a wet state, so that the surface of the lower layer (that is, the boundary surface with the uppermost layer) becomes smooth. At the same time, the surface properties of the upper layer are improved, and the adhesiveness between the upper and lower layers is also improved. As a result, especially for high density recording, high output and low noise are required, for example, the performance required as a magnetic tape is satisfied, and high durability performance is required. The peeling is eliminated, the film strength is improved, and the durability is sufficient. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Surface smoothing-In the present invention, it is also possible to carry out a surface smoothing process by calendering.

Thereafter, if necessary, burnishing treatment or blade treatment is carried out for slitting.

In the surface smoothing treatment, temperature, linear pressure, C / s (coating speed) and the like can be mentioned as calendar conditions.

In the present invention, the above temperature is usually 50
~ 140 ° C, the above linear pressure is 50 ~ 400kg / cm, the above C / S is 20 ~
It is preferable to keep it at 1,000 m / min. If these values are not satisfied, it may be difficult or impossible to keep the surface properties of the magnetic recording medium in good condition.

The thickness of the first magnetic layer obtained as a result of the above treatment is 0.01 to 0.8 μm, preferably 0.05 to 0.5 μm, and more preferably 0.1 to 0.3 μm.

[0131]

Embodiments of the present invention will be described below. However, the present invention is not limited to the following examples.

The components, ratios and operation sequences shown below can be variously modified without departing from the scope of the present invention. In the following examples, all "parts" are "parts by weight".

Each component of the following coating composition was kneaded and dispersed using a kneader and a sand mill to prepare a coating. However,
The average major axis diameter, crystallite size, and film thickness were appropriately changed as shown in Tables 1 to 3.

{Paint-a} Ferromagnetic metal powder (magnetic powder with numbers shown in the table) 100 parts Potassium sulfonate group-containing vinyl chloride resin 10 parts (Zeon Corporation MR-110) Sodium sulfonate group-containing Polyurethane resin 10 parts α-alumina (average particle size 0.15 μm) 8 parts Carbon black (average particle size 40 nm) 0.5 part Stearic acid 1 part Butyl stearate 1 part Cyclohexane 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts After kneading the above ingredients 5 parts of polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) were added.

{Paint A} α-Fe ₂ O ₃ 100 parts (Si, Al compound (Si content 0.9% by weight to nonmagnetic powder, Al content 0.2% by weight) surface treatment) Potassium sulfonate group-containing vinyl chloride Resin 12 parts (Nippon Zeon Co., Ltd., MR-110) Sodium sulfonate group-containing polyurethane resin 8 parts α-alumina (average particle size 0.2 μm) 5 parts Carbon black (average particle size 15 nm) 10 parts Stearic acid 1 Parts Butyl stearate 1 part Cyclohexane 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts After kneading the above components, 5 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added.

{Paint B} Paint B is α-F in Paint A.
It was obtained in the same manner as the paint A except that Co-γ-Fe ₂ O ₃ (Hc: 650 Oe) was used instead of e ₂ O ₃ .

(Average major axis length 0.14 μm, crystallite size 3
0 nm, Si content in magnetic powder 0.8% by weight, Al content 0.1% by weight) {Paint C} Paint C is replaced with α-Fe ₂ O ₃ in Paint A.
Fe-Si-Al Sendust alloy powder (Hc = 40 (A / m), μ; = 200
(H / m) average major axis length 80 nm, crystallite size 8 nm, Si content 1.2% by weight in powder, Al content 0.2% by weight)
same as.

{Paint-b} In the paint a, instead of the ferromagnetic metal powder, Co-substituted barium ferrite BsO · 6 ((Fe _0.5 Ti
_0.5 ) ₂ O ₃ ) (Hc: 1100 Oe, BET50m ² / g, σs; 64emu / g
Same as a except that plate ratio 4) was used.

{Ferromagnetic metal powder (1)} (spindle-like shape) Fe Co Ni Si Al Ca Nd Overall composition 100 6 3 2 4 0.5 3 (wt%) Surface composition 100 0 0 50 100 10 10 (Number of atoms %) (Average major axis length, crystallite size, and saturation magnetization amount are shown in Tables 2 to 4) {Ferromagnetic metal powder (2) to (4)} (spindle-like shape) Fe Co Ni Si Al Ca Nd Overall composition 100 7 3 2 2 0.5 3 (% by weight) Surface composition 100 0 0 50 80 10 10 (% by atom) (Average major axis length, crystallite size and saturation magnetization are shown in Tables 2-4) Examples 1 to 13 and Comparative Examples 1 to 6 Using the above-mentioned coating materials shown in Table 2, Table 3 and Table 4, a wet-on-wet method was applied on a polyethylene terephthalate film having a thickness of 10 μm, and then applied. While the film is still undried, magnetic field orientation treatment is performed, followed by drying, and then surface smoothing treatment with a calendar. To form a lower layer and a second magnetic layer and first magnetic layer has a thickness that is.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene terephthalate film on the side opposite to the magnetic layer, the coating film is dried, and calendered according to the above-mentioned calendering conditions. Thus, a back coat layer having a thickness of 0.8 μm was formed to obtain a wide original magnetic tape.

Carbon black (Raven 1035) 40 parts Barium sulfate (average particle diameter 300 nm) 10 parts Nitrocellulose 25 parts Polyurethane resin 25 parts (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) Polyisocyanate compound 10 parts (Nippon Polyurethane) (Coronate L, manufactured by Co., Ltd.) Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The magnetic tape of the original fabric thus obtained is slit into 8 parts.
A mm-width magnetic recording medium for video was created. The following evaluations were performed on this magnetic recording medium. The results are shown in Tables 2-4
It was shown to.

(Evaluation and measurement method) <Output characteristics> A single wave of 9 MHz was recorded, and the output level when the signal was reproduced was expressed by comparison with a reference sample (8 mm tape SG manufactured by Konica).

<Running durability at high temperature> Using a measuring VCR S-550 (manufactured by Sony Corporation) in an environment of 40 ° C and 80% humidity, the tape was run for the entire length, and the RF output decreased. The head was clogged when it continuously occurred for 2 dB or more and 1 second or more, and the number of times was counted.

<Tape demagnetization rate (%)> Temperature 60 ° C, humidity 90%
Demagnetization rate when the tape is left for 1 week in the environment
(%) Was measured. Saturation magnetic flux density B of tape before and after leaving
Based on the value of, the tape demagnetization rate (%) was calculated by the following formula.

{(B ₁ before leaving)-(B ₂ after leaving)} / (B ₁ before leaving) × 100 (%) <Still life> Color bar signal is output under the environment of 0 ° C. and RH 10%. It shows the time from the initial output in the still mode to the 2dB drop during recording and playback.

The evaluation results are shown below.

[0147]

[Table 2]

[0148]

[Table 3]

[0149]

[Table 4]

As shown in Comparative Examples 1, 3, and 6, the effect of the present invention cannot be obtained with the conventional two-layer structure. Further, as shown in Comparative Examples 2, 4, and 5, even if the medium has a three-layer structure, the saturation magnetization amount of the ferromagnetic metal powder in each layer and the weight of Al in the ferromagnetic powder with respect to Fe are as in the present invention. %, The average major axis length of the ferromagnetic metal powder or the ferromagnetic metal powder in the second magnetic layer and the hexagonal ferrite powder in the first magnetic layer, the output in the high frequency range, which is the effect of the present invention. And the improvement of running durability at high temperature, still durability and corrosion resistance cannot be achieved.

[0151]

The magnetic recording medium of the present invention is excellent in output in a high frequency range, running durability at high temperature, still durability and corrosion resistance.

[Brief description of drawings]

FIG. 1 is a diagram for explaining simultaneous multilayer coating for producing the magnetic recording medium of the present invention by wet-on-wet coating by an extrusion coating method.

FIG. 2 is a view of a coater head for applying the coating material of the present invention.

[Explanation of symbols]

 1 Support 10 Extrusion Coater 11 Extrusion Coater 12 Extrusion Coater 32 Supply Roll 33 Orientation Magnet 34 Dryer 37 Super Calendar Device 38 Calendar Roll 39 Winding Roll

Claims (4)

[Claims] 1. A non-magnetic layer, a layer containing a high-permeability material, or a layer containing ferromagnetic iron oxide is provided on the support, and at least one layer is provided on the support, and the ferromagnetic layer is formed thereon. A second magnetic layer containing a metal powder is provided, and a first magnetic layer containing a ferromagnetic metal powder different from the ferromagnetic metal powder of the second magnetic layer is further provided on the second magnetic layer. The saturation magnetization of the contained ferromagnetic metal powder is σs (A),
A magnetic recording medium in which σs (A) <σs (B), where the saturation magnetization σs (B) of the ferromagnetic metal powder contained in the magnetic layer is taken. 2. A non-magnetic layer, a layer containing a high-permeability material, or a layer containing ferromagnetic iron oxide is provided on the support, and at least one layer is provided on the support, and the ferromagnetic layer is formed on the support. The second magnetic layer containing the powder is provided, and the first magnetic layer containing a ferromagnetic metal powder different from the ferromagnetic powder of the second magnetic layer is further provided on the second magnetic layer. When the weight% of Al in the metal powder to Fe is Al (A)% and the weight% of Al in the ferromagnetic powder of the second magnetic layer to Fe is Al (B)%, Al (A)%> A magnetic recording medium that is Al (B)%. 3. A non-magnetic layer, a layer containing a high-permeability material, or a layer containing ferromagnetic iron oxide is provided on the support, and at least one layer is provided on the support, and the ferromagnetic material is formed on the layer. A magnetic recording medium, wherein a second magnetic layer containing iron oxide powder or ferromagnetic metal powder is provided, and a first magnetic layer containing hexagonal ferrite powder is further provided thereon. 4. A non-magnetic layer, a layer containing a high-permeability material, or a layer containing ferromagnetic iron oxide is provided on a support, and at least one layer is provided on the support, and the ferromagnetic layer is formed on the layer. A second magnetic layer containing a powder is provided, and a first magnetic layer containing a ferromagnetic powder different from the ferromagnetic powder of the second magnetic layer is further provided thereon, and the ferromagnetic powder of the first magnetic layer is provided. Is 1 (A) nm, and the average major axis length of the ferromagnetic powder of the second magnetic layer is 1 (B) nm, then 1 (B) −l (A) ≧ 20,
A magnetic recording medium with l (A) ≦ 180.