JP2571350C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001]     [Industrial applications]   The present invention relates to a high density coated magnetic recording medium. [0002]     [Prior art]   Magnetic recording media include recording tapes, video tapes, computer tapes,
Widely used as discs. The recording density of magnetic recording media has been increasing year by year, Recording formats are being studied from analog to digital.
ing. To meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer
However, in terms of practical reliability such as productivity and corrosion, ferromagnetic powder
A so-called coating type magnetic recording medium which is dispersed on a substrate and coated on a support is excellent. Only
However, the coating type medium has a low magnetic substance filling degree with respect to the metal thin film,
Exchange characteristics are inferior. Coated magnetic recording media include ferromagnetic iron oxide and Co-modified ferromagnetic acid.
Iron fossil, CrO_TwoA magnetic layer in which a ferromagnetic alloy powder or the like is dispersed in a binder is used as a non-magnetic support.
What is applied to is widely used. [0003]   To improve the electromagnetic conversion characteristics of a coating type magnetic recording medium, it is necessary to improve the magnetic characteristics of the ferromagnetic powder.
, Surface smoothing, etc., and various methods have been proposed.
Is not enough.   Also, in recent years, the recording wavelength tends to be shortened with the increase in density, and the thickness of the magnetic layer is reduced.
If the thickness is too large, the output will decrease, and the problem of self-demagnetization loss during recording and thick loss during reproduction will increase.
Has become. [0004]   For this reason, the thickness of the magnetic layer is reduced, but the thickness of the magnetic layer is reduced to about 2 μm or less.
When it is thin, the effect of the non-magnetic support tends to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics
And DO tend to deteriorate. For this reason, as disclosed in JP-A-57-198536,
First, a non-magnetic thick undercoat layer is provided on the support surface, and then the magnetic layer is provided as an upper layer.
By doing so, the influence of the surface roughness of the support can be eliminated,
There was a problem that wear and durability were not improved. This is conventionally a non-magnetic underlayer.
Since the thermosetting resin is used as a binder, the lower layer is cured and the magnetic layer and the head
Friction and contact with other members is performed without buffering.
It is thought to be due to the fact that the magnetic recording medium
. In order to solve this, it is conceivable to use an uncured resin as a binder for the lower layer.
However, in the conventional method, the lower layer is coated and dried, and then the magnetic layer is coated as the upper layer.
The lower layer is swollen by the organic solvent of the upper layer coating solution, causing turbulence in the upper layer coating solution.
Problems such as degrading the surface properties of the magnetic layer and degrading the electromagnetic conversion characteristics Is generated. To reduce the thickness of the magnetic layer, it is necessary to reduce the amount of coating.
Alternatively, it is conceivable to reduce the concentration by adding a large amount of a solvent to the magnetic coating solution. The former
When removing, if the amount of application is reduced, there is not enough time for leveling after application and drying starts.
This can cause problems such as coating defects, for example, streaks and engraved patterns.
And yield is very poor. If the latter method is used, the concentration of the magnetic coating solution
If the film is too thin, there will be many voids in the resulting coating film, and sufficient magnetic substance filling properties will not be obtained.
And the strength of the coating film is insufficient due to many voids.
Cause harm. In the invention of Japanese Patent Application Laid-Open No. 62-154225, the yield is
Bad was a big problem. [0005]   When the coercive force is low, the magnetic layer has a large self-demagnetization loss, and is not suitable for short-wavelength recording.
Therefore, it is necessary to have a considerable Hc. Means that can be used for such purposes
An undercoat layer having a binder of only 0.5 to 5.0 μm is provided between the nonmagnetic support and the magnetic layer.
It has been proposed that the Hc of the magnetic layer be 1000 Oe (Japanese Patent Laid-Open No.
198536). [0006]   Further, in order to further improve the electromagnetic conversion characteristics, the self-demagnetization loss due to the high Hc is required.
At the same time, the recording demagnetization must be reduced. To achieve this goal,
Along with Hc, it is necessary to reduce the demagnetization loss due to the perpendicular magnetization component received during short wavelength recording.
It is necessary. For this reason, the ferromagnetic powder with high Hc is strongly oriented in the in-plane direction,
It was found that the residual coercive force in the layer normal direction should be increased. [0007]   However, conventionally known techniques have the following problems to achieve this purpose.
is there.   According to the technique disclosed in the above-mentioned JP-A-57-198536, the upper
And a method of applying the lower layer, but the upper layer and the lower layer are simultaneously coated.
When performing the above, mixing of the upper layer and the lower layer occurs, and not only the surface property is deteriorated, but also the orientation is disturbed.
. As a technique for improving the orientation in simultaneous multi-layer coating, JP-A-3-4903
Japanese Patent Publication No. 2 (1995) discloses a multi-stage alignment using a layer in which carbon black is dispersed as a lower layer. Although disclosed, fillers with low true specific gravity, such as carbon black,
The upper and lower layers during simultaneous multilayer coating due to the rotating Brownian motion of the ferromagnetic powder during
Although the interface of the magnetic layer is disturbed and the squareness ratio measured in the in-plane direction is high, the residual
There is a problem that the improvement of the magnetic force is insufficient. [0008]   Further, the magnetic recording medium having the structure of the lower non-magnetic layer and the upper magnetic layer as described above may be used.
In order to improve the electromagnetic conversion characteristics, it is necessary to reduce the self-demagnetization loss by increasing the Hc.
Sometimes it is also necessary to reduce recording demagnetization. In order to achieve this object, the above-mentioned high Hc
In both cases, it is necessary to reduce the demagnetization loss during short wavelength recording. This demagnetization loss is
It becomes larger when the coercive force in the longitudinal direction and the coercive force in the width direction of the upper magnetic layer are low. Especially,
If the coercive force in the width direction is low, the crosstalk (demagnetization due to the magnetic field of the adjacent track) will be large.
And the RF output decreases and the BER (block error rate) increases
There's a problem. [0009]   The lower non-magnetic layer described above as a known technique for such a multilayer coating type magnetic recording medium is used.
Using only the binder or the binder and carbon black as the conductive layer, the upper magnetic layer
Japanese Patent Application Laid-Open No. 57-198536 discloses a method of successively superposing layers using short needle ferromagnetic powder.
And JP-A-62-1115. However, these are simultaneous layers
In this case, the nonmagnetic lower layer and the upper magnetic layer
Mixing or turbulence may cause turbulence at the interface between the two layers. Such a mixture between two layers
In this case, the disturbance extremely lowers the orientation of the ferromagnetic powder in the magnetic layer. [0010]   Furthermore, short acicular ferromagnetic powder, that is, a ferromagnetic powder having a short major axis length and a small acicular ratio
Is difficult to flow orient, so the orientation of the ferromagnetic powder is further reduced and sufficient electromagnetic conversion
There is a problem that characteristics cannot be obtained. [0011]     [Problems to be solved by the invention]   The present invention provides superior power with high RF output, reduced dropout and BER.
The purpose is to provide a magnetic recording medium having magnetic conversion characteristics and excellent productivity. Is what you do. [0012]     [Means for Solving the Problems]   That is, the object of the present invention is to disperse an inorganic powder in a binder on a non-magnetic support.
A lower non-magnetic layer is provided, and an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder is provided thereon. The thickness of the lower nonmagnetic layer is 0.5 μm or more,The upper magnetic layer has a major axis length of 0.The inorganic powder contained in the nonmagnetic layer is an inorganic powder having a true specific gravity of 3 or more.
This can be achieved by a magnetic recording medium. [0013]   The present invention suppresses fluctuation or disturbance at the interface between the upper magnetic layer and the lower nonmagnetic layer. Coercive force in the longitudinal and width directions of the magnetic layer of a magnetic recording medium having a thin magnetic layer of
Is set to a specific value or more, so that the electromagnetic conversion characteristics especially in short wavelength recording can be improved. Layer (hereinafter, also simply referred to as a magnetic layer or upper layer) as a lower non-magnetic layer (hereinafter, simply referred to as non-magnetic layer).
Also referred to as the active layer or lower layer. Inorganic coating in the lower layer coating solution
First, the lower layer is placed on a non-magnetic support while the lower layer is wet.
It is obtained by applying the upper layer. That is, the present invention relates to coating of pinholes, streaks, etc.
Ultra-thin magnetic layer with excellent mass productivity that suppresses fabric defects Comparable to ferromagnetic metal thin film
It is an object of the present invention to provide a magnetic recording medium having the following performance. [0014]   In the present invention, in the longitudinal direction of the magnetic layer (the longitudinal direction is the in-plane
Hc for the magnetic recording medium sample in the VSM.
After applying a magnetic field of 10 kOe in the in-plane direction of the magnetic layer, the residual magnetic field of the sample is reduced.
The external magnetic field applied in the longitudinal direction parallel to the upper magnetic layer surface necessary to cancel means. Similarly, in the width direction (width direction is parallel to the plane and perpendicular to the coating orientation direction.
Hc in the upper magnetic layer surface of the magnetic recording medium sample by VSM.
After applying a magnetic field of 10 kOe in parallel and in the width direction, the residual magnetic field of the sample is reduced to
An external magnetic field applied in the width direction parallel to the upper magnetic layer surface necessary to cancel
To taste. [0015] This improves the electromagnetic conversion characteristics, especially the reproduction output, and suppresses crosstalk.
And BER can be reduced. And high output can be secured. This is because both Hc are the longitudinal direction and width of the ferromagnetic powder.
This is considered to correspond to the directional magnetization component.
In the present invention, both Hc are set to be large since the contribution of the coercive force increases.
Accordingly, it is considered that the recording demagnetization in the longitudinal direction and the width direction is suppressed. [0016]   In addition, in order to secure the performance of the magnetic layer, the productivity which has been a problem in the prior art was reduced.
The means for securing was solved by using inorganic powder for the lower layer,
The embodiment is not particularly limited, but in the present invention, the inorganic powder contained in the lower layer and
And its lower layer(0.5 μm or more)Is preferably defined.   In the present invention, in order to secure both Hc, the major axis length is preferably 0.25 μm or less.
Or less than 0.2 μm and an acicular ratio of 12 or less, preferably 7 to 11.
In this case, a conductive alloy powder is used. The term “major axis length” used here is based on technical common sense.
It refers to the average major axis length. [0017]Alloy of Fe and Co having an amount of 2% or more, or an alloy containing the alloy as a main component (75% or more) ), And for the purpose of improving the characteristics, other than predetermined atoms, Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta
, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It can include atoms such as n, Zn, Ni, Sr, and B. Of the Fe and Co
The alloy preferably contains 5% or more of Co, and preferably contains up to about 20%.
No.   In the present invention, ferromagnetic powders other than those described above, for example, magnetic acid
Iron oxide FeOx (x = 1.33-1.5), Co-modified FeOx (x = 1.33-1)
. 5) can be used in combination with the above ferromagnetic alloy powder. [0018]   The inorganic powder used for the lower layer is preferably a true specific gravity of 3 or more, especially
It is preferably 4 to 8, and the average particle size is 0.2 μm or less, preferably 0.005 to 0.5.
08 μm granular particles or a major axis length of 0.05 to 1.0 μm, preferably 0.1 μm.
Examples are needle-like particles having a needle-like ratio of 0.5 to 0.5 μm and a needle-like ratio of 5 to 20, preferably 5 to 15.
It is. Specific inorganic powders can be selected from the following inorganic powders. Also
, True specific gravity is synonymous with true density and means only the substance except pores of inorganic powder, voids between powders, etc.
Means the density of [0019]   Examples of the inorganic powder include, for example, metals (Cu, Cr, Ag, Al, Ti,
W, etc.), metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metals
Sulfide and the like. Specifically, TiO_Two(Rutile, anatase), TiO_x,
Cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO_Two, SiO_Two, Cr
_TwoO_Three, 90% or more α-alumina, β-alumina, γ-alumina, α-iron oxide,
-Tight, corundum, silicon nitride, titanium carbide, magnesium oxide, nitride
Boron, molybdenum disulfide, copper oxide, MgCO_Three, CaCO_Three, BaCO_Three, SrC
O_Three, BaSO_Four, Silicon carbide, titanium carbide, etc. are used alone or in combination
You. The shape, size, etc. of these inorganic powders are arbitrary, and they may be different if necessary.
Combine different inorganic powders, or select particle size distribution etc. even with a single non-magnetic powder
You can also. [0020]   As the inorganic powder that can be used, those having the following properties are preferable. Tap dense
The degree is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. The moisture content is 0.
1-5%, preferably 0.2-3%. pH 2-11. Oil absorption using DBP
5-100ml / 100g, preferably 10-80ml / 100g, more preferably
Or 20 to 60 ml / 100 g. The above non-magnetic powder is not necessarily 100% pure
It is not necessary to be smart, and the surface may be coated with another compound such as Al, Si, T depending on the purpose.
Treated with compounds such as i, Zr, Sn, Sb, Zn, etc. to form their oxides on the surface
May be implemented. At that time, if the purity is 70% or more, the effect will not be reduced.
No. The ignition loss is preferably 20% or less. [0021]   Specific examples of the inorganic powder used in the present invention include UA56 manufactured by Showa Denko KK
00, UA5605, AKP-20, AKP-30, AKP-50 manufactured by Sumitomo Chemical Co., Ltd.
, HIT-55, HIT-100, ZA-G1, N5, G7,
S-1, Toda Kogyo TF-100, TF-120, TF-140, R516,
Ishihara Sangyo TTO-51B, TTO-55A, TTO-55B, TTO-55
C, TTO-55S, TTO-55S, TTO-55D, FT-1000, FT
-2000, FTL-100, FTL-200, M-1, S-1, SN-100
, R-820, R-830, R-930, R-550, CR-50, CR-80
, R-680, TY-50, ECT-52, STT-4D, ST manufactured by Titanium Industry Co., Ltd.
T-30D, STT-30, STT-65C, T-1 manufactured by Mitsubishi Materials Corporation, Japan
NS-O, NS-3Y, NS-8Y made by Catalyst Co., Ltd., MT-100S, MT made by Teika Co., Ltd.
-100T, MT-150W, MT-500B, MT-600B, MT-100
E, FINEX-25, BF-1, BF-10, BF-20, BF- manufactured by Sakai Chemical Co.
1L, BF-10P, Dowa Kogyo DEFIC-Y, DEFIC-R, Titanium
It is Y-LOP manufactured by Kogyo Co., Ltd. and a product obtained by sintering it. [0022]   As the nonmagnetic inorganic powder used in the present invention, titanium oxide (particularly, dioxide
Titanium) is preferred. Hereinafter, the method for producing the titanium oxide will be described in detail. Of titanium oxide The manufacturing methods mainly include a sulfuric acid method and a chlorine method. In the sulfuric acid method, raw ore of illuminite is steamed with sulfuric acid.
And extract Ti, Fe, etc. as sulfate. The iron sulfate is removed by crystallization separation, and the remaining
After filtering and refining the titanyl sulfate solution, it was subjected to thermal hydrolysis to precipitate hydrous titanium oxide.
In the hall. After filtration and washing, contaminants are removed by washing, and a particle size adjusting agent is added.
After that, firing at 80 to 1000 ° C. results in crude titanium oxide. Rutile and anater
The zeotype is determined by the type of nucleus material added at the time of hydrolysis. This crude oxide titanium
Crushed, sized, surface treated, etc. Chlorine method uses raw ore natural rutile and
Synthetic rutile is used. The ore is chlorinated in high-temperature reduced state, and Ti is TiCl_Four
Fe is FeCl_TwoAnd the iron oxide solidified by cooling becomes liquid TiCl_FourWhen
Separated. The obtained crude TiCl_FourIs purified by rectification and then a nucleating agent is added.
At a temperature of 1000 ° C. or higher to obtain crude titanium oxide. this
The finishing method to give pigmentary properties to the crude titanium oxide produced in the oxidative decomposition process is
Same as the sulfuric acid method. [0023]   In the present invention, carbon black may be used in the lower layer in addition to the inorganic powder.
And the known effect R_s(Surface electrical resistance) and the like can also be reduced. this
Carbon black includes furnace for rubber, thermal for rubber, and black for color.
And acetylene black. Specific surface area is 100-500
m^Two/ G, DBP oil absorption 20-400 ml / 100 g, particle size 5 mμ-30
mμ, pH 2-10 Water content 0.1-10%, Tap density 0.1-1 g / c
c is preferred. [0024]   Specific examples of carbon black used in the present invention, manufactured by Cabot Corporation,
BLACKPEARLS 2000, 1300, 1000, 900, 800, 8
80, 700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050, # 3
150, # 3250, # 3750, # 3950, # 2400B, # 2300, #
1000, # 970, # 950, # 900, # 850, # 650, # 40,
MA40, MA-600, manufactured by Columbia Carbon, CONDUCTEX SC
8800, 8000, 7000, 5750, 5250, 350 manufactured by RAVEN 0, 2100, 2000, 1800, 1500, 1255, 1250, Akzo
Ketjen Black EC manufactured by the company. Carbon black as a dispersant
Even if the surface is treated with or grafted with resin, part of the surface is graphite
You may use what was made into. Before adding carbon black to paint
May be dispersed in advance with a binder. These carbon blacks are used alone
, Or in combination. [0025]   Examples of the carbon black that can be used in the present invention include (“Carbon Black Handbook”,
Carbon Black Association).   In the present invention, a nonmagnetic organic powder may be used in the lower layer, if desired, in addition to the inorganic powder.
For example, acrylic styrene resin powder, benzoguanamine
Fat powder, melamine resin powder, and phthalocyanine pigment.
Fin resin powder, polyester resin powder, polyamide resin powder, polyimide
Resin resin powder, polyfluoroethylene resin powder, and the like. The manufacturing method is
As described in JP-A-62-18564 and JP-A-60-255827.
Can be used. [0026]   Non-magnetic powders such as these inorganic powders are usually added in a weight ratio of 2 to the binder.
It is used in a range of 0 to 0.1 and a volume ratio of 10 to 0.1.   In general magnetic recording media, an undercoat layer is provided.
This is provided to improve the adhesion between the support and the magnetic layer, etc.,
The thickness is also 0.5 μm or less, which is different from the lower non-magnetic layer of the present invention. In the present invention
However, it is preferable to provide an undercoat layer in order to improve the adhesion between the underlayer and the support.
New [0027]   As the multi-step orientation method of the upper magnetic layer in the present invention, a conventionally known method can be used.
Specifically, while the coating layers (upper and lower layers) are still wet, 3000 Gauss
Soleno with a magnetic force of 1500 gauss after being oriented with a cobalt magnet having a magnetic force
There is a method in which orientation is performed by using an id. [0028]   The dry thickness of the lower layer is 0.5 μm or more, preferably 0.5 to 5.0 μm.
desirable. When the thickness is less than 0.5 μm, productivity is reduced and calender moldability is reduced.
Deteriorated and sufficient electromagnetic conversion characteristics were obtained.Disappears.   The present invention suppresses the disorder of the orientation of the ferromagnetic powder at the interface between the upper magnetic layer and the lower nonmagnetic layer.
And has the function of simultaneously suppressing disturbance or vertical fluctuation of the interface itself.
However, in the present invention, various factors relating to control of these interfaces are appropriately selected.
You can do it.   Such factors include the viscosity of the magnetic paint in the magnetic layer and the viscosity of each dispersion in the lower non-magnetic layer.
Adjusting the properties, for example, checking the coating solution for the upper magnetic layer and the coating solution for the lower non-magnetic layer.
Controlling so that the xotropy is close to each other may be mentioned. [0029]   As a specific method, each coating solution has a shear rate of 10^Foursec^-1Shear stress A1
0^FourAnd shearing speed 10 sec^-1Stress A10 ratio to A10 A10^Four/ A10 to 10
0 ≧ A10^Four/ A10 ≧ 3.   Factors involved in this adjustment include, for example, dispersed inorganic powder or magnetic powder.
Regarding the powdery material, (1) particle size (specific surface area, average primary particle size, etc.), (2)
Structure (oil absorption, particle morphology, etc.), (3) Properties of powder surface (pH, loss on heating, etc.), (
4) Attraction force of particles (σ_s(1) molecular weight, (2) functional
Regarding the solvent such as the type of group, (1) type (polarity, etc.), (2) binder solubility, (3
) Solvent formulation, water content and the like. [0030]   Further, the magnetic recording medium of the present invention has a thickness variation at the interface (that is, the thickness of the interface).
The average value Δd of the fluctuation width in the direction is less than or equal to １ ／ of the average dry thickness d of the magnetic layer.
Preferably, the standard deviation 3σ of the thickness of the magnetic layer is 0.6 μm.
In other words, σ is 0.2 μm or less. That is, if 3σ is 0.6 μm or less, each segment
It means that it is only necessary that 97% of the particles be 0.6 μm or less.   Further, it is preferable that 3σ ≦ 6d / 10. [0031]   These d, Δd, and σ are obtained as follows.   The magnetic recording medium is about 0.1μm thick with a diamond cutter over the longitudinal direction.
Cut out to taste, with a transmission electron microscope, magnification 10000 to 100000 times, preferably
Observe at 20000 to 50,000 times and take a photograph (Photo print
The size is A4 to A5). Then, the ferromagnetic powder of the upper magnetic layer and the lower non-magnetic layer
The interface is visually judged by paying attention to the difference in shape of the inorganic powder, and the black border and the magnetic layer surface
The surface is similarly blackened. First, a method of obtaining Δd will be described. Aforementioned border
The distance between the peak or the valley at the interface between the upper magnetic layer and the lower non-magnetic layer is Δd. or,
The standard deviation σ is obtained by edging as described above, and then using a Zeiss image processing device.
Measure the length of the interval between the lines bordered by IBAS2. Measurement of magnetic layer thickness is length
The interval of 21 cm is segmented into 100 to 300, and the number of segments is calculated to obtain d.
Was.   The standard deviation σ is the thickness of each segment x_iThen, it is expressed by the following equation 1. [0032]     (Equation 1)[0033]   The aforementioned Δd focuses only on the fluctuation at the interface, but the standard deviation of the average thickness d is
The difference σ is the difference between the surface roughness of the upper magnetic layer and the fluctuation at the interface.
It means a change in thickness. This interface variation is preferably such that 3σ is 0.6 μm or less.
Good.   Thereby, the uniformity of the thickness of the magnetic layer is ensured and the surface roughness Ra is set to Ra ≦ λ /
50, that is, λ / Ra is 50 or more, preferably 75 or more, more preferably 100 or more.
Can be regulated above. Here, Ra was measured using an optical interference roughness meter. It refers to the value obtained by measuring the core wire average roughness. [0034]   Further, λ / 4 ≦ d ≦ 3λ, preferably λ / 4 ≦ d ≦, with respect to the shortest recording wavelength λ.
2λ (that is, 0.25 ≦ d / λ ≦ 2) and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 5
It is preferable that they have a relationship of 0.   This prevents fluctuations in reproduction output and amplitude modulation noise, and achieves high reproduction output and high C / N.
Can be realized. [0035]   In the present invention, the shortest recording wavelength λ varies depending on the type of the magnetic recording medium.
For example, 0.7 μm for 8 mm metal video, 0.5 μm for digital video
m and 0.67 μm for digital audio.   The thickness of the magnetic layer is determined by actual measurement as described above,
Measure a magnetic layer sample with a known thickness for the elements included and create a calibration curve
Then, the thickness of the sample of the unknown material can be determined from the intensity of the fluorescent X-ray.
You. [0036]   Further, the present invention provides a method for measuring the square of the surface of a magnetic layer by a scanning tunneling microscope (STM).
Average roughness R_rmsIs 30 ≦ d / R between the dry thickness average value d of the magnetic layer and_rmsconnection of
It is preferred that there is.   If the thickness of the magnetic layer becomes thinner, the self-demagnetization loss should be reduced and the output should be improved.
However, the reduction in thickness due to the reduction in the thickness of the magnetic layer reduces the pressing margin, resulting in poor calendar moldability.
It becomes worse and the surface roughness increases. To improve output by reducing self-demagnetization loss
Is preferably a surface roughness by STM which satisfies the above equation. [0037]   R by AFM_rmsIs preferably 10 nm or less. Measured with 3d-MIRAU
Light interference surface roughness Ra is 1 to 4 nm, R_rmsIs 1.3 to 6 nm, and the PV value (Pe
(ak-Valley) value is preferably 80 nm or less.   The glossiness of the magnetic layer surface is preferably from 250 to 400% after the calendering treatment.   To achieve such surface properties, for example, the following four conditions are further required within the conditions of the present invention. Can be achieved by also satisfying the condition (1). (1) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more.
The ferromagnetic powder contained in the upper magnetic layer is a needle-shaped ferromagnetic powder,
The average particle size of the powder is 1/2 to 4 times the crystallite size of the acicular ferromagnetic powder. (2) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more.
The ferromagnetic powder contained in the upper magnetic layer is a needle-shaped ferromagnetic powder,
The average particle size of the powder is not more than 1/3 of the major axis length of the acicular ferromagnetic powder. (3) The ferromagnetic powder contained in the upper magnetic layer has an easy axis of magnetization in a direction perpendicular to the flat plate.
Hexagonal plate-shaped ferromagnetic powder, and the non-magnetic powder contained in the lower non-magnetic layer is inorganic
Powder, the average particle diameter of which is equal to or less than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer.
There is. (4) The surface layer in which the inorganic powder contained in the lower non-magnetic layer is covered with the inorganic oxide
Containing inorganic non-magnetic powder.   (1) to (3) are the ferromagnetic powder of the upper magnetic layer and the inorganic powder of the lower nonmagnetic layer.
Size and shape to ensure the surface properties of the lower non-magnetic layer and inorganic powder
Is a size that allows the ferromagnetic powder to be mechanically and stably aligned. [0038]   Further, the volume filling ratio in the lower layer of the inorganic powder is preferably 20 to 60%,
More preferably, it is desirable to be in the range of 25 to 55%.   The inorganic powder preferably contains at least 60% by weight of the nonmagnetic powder.
Preferably, the inorganic powder is a metal oxide, an alkaline earth metal salt, or the like.
Good. In addition, known effects (for example,
Can be used in combination with the above inorganic powders.
However, since carbon black has very poor dispersibility,
Black alone cannot secure sufficient electromagnetic conversion characteristics. Good dispersibility
Metal oxides, metals, alkaline earth metal salts at least 60% by weight
You need to choose from. When the inorganic powder is less than 60% by weight of the non-magnetic powder,
If the carbon black is more than 40% of the nonmagnetic powder, the dispersibility becomes insufficient and
Electromagnetic conversion characteristics cannot be obtained. [0039]   When the thickness of the magnetic layer is 5 times or less the major axis length, the degree of filling by the calendar is improved.
A remarkable magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained.   Next, (4) will be described.   As the inorganic oxide coated on the surface of the inorganic powder contained in the lower non-magnetic layer,
, Preferably Al_TwoO_Three, SiO_Two, TiO_Two, ZrO_Two, SnO_Two, Sb_TwoO_Three, Zn
O and the like are preferable, and more preferable is Al_TwoO_Three, SiO_Two, ZrO_TwoIt is. these
May be used in combination or alone. Also, depending on the purpose
Alternatively, a surface treatment tank co-precipitated may be used.
A structure in which the surface layer is treated with silica, and the reverse structure may be adopted. In addition, surface treatment
The physical layer may be a porous layer according to the purpose.
Is preferred. [0040]   Hereinafter, general items that can be selected in the present invention will be described.   The ferromagnetic powder used in the magnetic layer of the present invention includes a dispersant, a lubricant,
The treatment may be performed in advance with an activator, an antistatic agent or the like before dispersion. Concrete
Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-47
22062, JP-B-47-22513, JP-B-46-28466, and JP-B
46-38755, JP-B-47-4286, JP-B-47-12422,
JP-B-47-17284, JP-B-47-18509, JP-B-47-18573
No. JP-B-39-10307, JP-B-48-39639, U.S. Pat. No. 302
No. 6215, No. 3031341, No. 3100194, No. 3242005,
No. 3,389,014. [0041]   Among the above ferromagnetic powders, a small amount of hydroxide or oxide
Things may be included. Using a ferromagnetic alloy powder obtained by a known manufacturing method
And the following methods can be given. Complex organic acid salts (mainly
(Oxygenate) and reducing gas such as hydrogen, reducing iron oxide with reducing gas such as hydrogen
To obtain Fe or Fe-Co particles by reduction with Thermal decomposition of materials, sodium borohydride,
Reduction by adding a reducing agent such as acid salt or hydrazine;
For example, a method of evaporating in an active gas to obtain a fine powder. Obtained in this way
The ferromagnetic alloy powder is subjected to a known slow oxidation treatment, that is, immersion in an organic solvent, followed by drying.
Immersion in an organic solvent and then sending an oxygen-containing gas to form an oxide film on the surface
After drying, adjust the partial pressure of oxygen gas and inert gas without using organic solvent
Any of the methods of forming an oxide film on the surface can be used
You. [0042]   When the ferromagnetic powder of the upper magnetic layer of the present invention is represented by the specific surface area by the BET method, it is 25 to 8
0m^Two/ G, preferably 40 to 70 m^Two/ G. 25m^Two/ G or less
Noise rises, 80m^Two/ G or more is not preferable because it is difficult to obtain surface properties.   R1500 of the ferromagnetic powder is preferably 1.5 or less. More preferred
R1500 is 1.0 or less. r1500 is the saturation magnetization of the magnetic recording medium
Later, when a magnetic field of 1500 Oe is applied in the opposite direction, the amount of magnetization remaining without inversion
%. [0043]   The water content of the ferromagnetic powder is preferably 0.01 to 2%. Depending on the type of binder
Therefore, it is preferable to optimize the water content of the ferromagnetic powder. 0.2 for alloy powder
0.8 g / cc is preferable.
Oxidation easily progresses in the dense process, and sufficient saturation magnetization (σ_s) Is difficult to obtain.
At 0.2 cc / g or less, dispersion tends to be insufficient. [0044] You.   It is preferable to optimize the pH of the ferromagnetic powder depending on the combination with the binder used.
. Its range is from 4 to 12, preferably from 6 to 10. Ferromagnetic powder required
May be subjected to a surface treatment with Al, Si, P or an oxide thereof.
Absent. The amount is 0.1 to 10% with respect to the ferromagnetic powder. Adsorption of lubricants such as 100mg / m^TwoThe following is preferred. Yes for ferromagnetic powder
It may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr.
If it is not more than 00 ppm, there is no particular effect on the characteristics. [0045]   Further, the ferromagnetic powder used in the present invention preferably has a smaller number of vacancies, and the value is preferably
It is 20% by volume or less, more preferably 5% by volume or less.   As the binder used in the lower non-magnetic layer and the upper magnetic layer of the present invention, a conventionally known binder may be used.
Plastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. Thermoplastic
As the system resin, the glass transition temperature is -100 to 150C, and the number average molecular weight is 100.
0 to 200,000, preferably 10,000 to 100,000, and a polymerization degree of about 50 to 1
It is about 000. Examples include vinyl chloride, vinyl acetate, vinyl
Nyl alcohol, maleic acid, acrylic acid, acrylate, vinylidene chloride
, Acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, pig
Diene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc.
Or copolymers containing as a structural unit, polyurethane resin, various rubber-based resins
There is fat. In addition, phenolic resins and epoxy resins are used as thermosetting resins or reactive resins.
Xy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin,
Acrylic-based reaction resin, formaldehyde resin, silicone resin, epoxy-poly
Mixture of amide resin, polyester resin and isocyanate prepolymer, polyether
Mixture of steal polyol and polyisocyanate, polyurethane and polyisocyanate
And the like. [0046]   For details on these resins, see "Plastic Handbook" published by Asakura Shoten.
It is described in.   It is also possible to use a known electron beam-curable resin for the lower layer or the upper layer.
You. These examples and the production method thereof are described in detail in JP-A-62-256219.
Are listed. [0047]   Although the above resins can be used alone or in combination, vinyl chloride is preferred. Resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol
Fat, vinyl chloride vinyl acetate maleic anhydride copolymer at least selected from the group of
Combination of one type and polyurethane resin, or combination of these with polyisocyanate
Items. [0048]   Polyurethane resin structure is polyester polyurethane, polyetherpolyuree
Tan, polyether polyester polyurethane, polycarbonate polyurethane
, Polyester polycarbonate polyurethane, polycaprolactone polyurethane
A known material such as a resin can be used.   For better dispersibility and durability for all binders shown here
As required, -COOM, -SO_ThreeM, -OSO_ThreeM, -P = O (OM₁) (
OM_Two), -OP = O (OM₁) (OM_Two), -NR_FourX (where M, M₁, M_TwoIs
, H, Li, Na, K, -NR_Four, -NHR_ThreeR is an alkyl group or H
And X represents a halogen atom. ), OH, NR^Two, N⁺R^Three, (R is hydrocarbon
Group), epoxy group, SH, CN, etc.
It is preferable to use those introduced by copolymerization or addition reaction. Such polarity
The amount of groups is 10^-1-10^-8Mol / g, preferably 10^-2-10^-6In mol / g
is there. [0049]   The vinyl chloride copolymer is preferably an epoxy group-containing vinyl chloride copolymer.
Polymers include a vinyl chloride repeating unit, and a repeating unit having an epoxy group.
, Optionally -SO_ThreeM, -OSO_ThreeM, -COOM and -PO (OM)_Two(After
M is a repeating unit having a polar group such as a hydrogen atom or an alkali metal)
And vinyl chloride-based copolymers containing With a repeating unit having an epoxy group
-SO in combination_ThreeEpoxy group-containing vinyl chloride system containing a repeating unit having Na
Copolymers are preferred. [0050]   The content of the repeating unit having a polar group in the copolymer is usually 0.01 to 5%.
. 0 mol% (preferably, 0.5 to 3.0 mol%).   The content of the repeating unit having an epoxy group in the copolymer is usually 1.0 to
It is in the range of 30 mol% (preferably 1 to 20 mol%). And vinyl chloride
The polymer is usually used in an amount of 0.01 to 0.5 mol per 1 mol of the vinyl chloride repeating unit (
(Preferably 0.01 to 0.3 mol) containing a repeating unit having an epoxy group.
Things. [0051]   When the content of the repeating unit having an epoxy group is less than 1 mol%, or
The amount of the repeating unit having an epoxy group per mole of the vinyl repeating unit is 0.01.
If the amount is less than the mole, release of hydrochloric acid gas from the vinyl chloride copolymer is effectively prevented.
On the other hand, it may be higher than 30 mol% or
The amount of the repeating unit having an epoxy group per 1 mol of the repeating unit is from 0.5 mol.
If the amount is too high, the hardness of the vinyl chloride copolymer may be low.
May decrease the running durability of the magnetic layer. [0052]   Further, the content of the repeating unit having a specific polar group is less than 0.01 mol%.
And the dispersibility of the ferromagnetic powder may be insufficient.
The coalescing may become hygroscopic and the weather resistance may decrease.   Usually, the number average molecular weight of such a vinyl chloride copolymer is from 15,000 to 60,000.
In range. [0053]   Such a vinyl chloride copolymer having an epoxy group and a specific polar group is, for example,
For example, it can be manufactured as follows.   For example, an epoxy group and -SO as a polar group_ThreeVinyl chloride in which Na is introduced
When a copolymer of the type is produced, a reactive double bond and -SO_ThreeN
a 2- (meth) acrylamide-2-methylpropanesulfonic acid nato having a
Lithium (a monomer having a reactive double bond and a polar group) and diglycidylacrylic acid
The rate is mixed at a low temperature, and this is mixed with vinyl chloride at a temperature of 100 ° C. or less under pressure.
It can be produced by polymerizing. [0054]   Having a reactive double bond and a polar group used for the introduction of a polar group by the above method
Examples of the monomer include 2- (meth) acrylamido-2-methylpropane described above.
2- (meth) acrylamido-2-methylpropa
Sulfonic acid, vinyl sulfonic acid and its sodium or potassium salt, (
Ethyl (meth) acrylate-2-sulfonate and sodium or potassium salts
, (Anhydride) maleic acid and (meth) acrylic acid, (meth) acrylic acid-2-li
Acid esters. [0055]   In addition, the introduction of an epoxy group requires a monomer having a reactive double bond and an epoxy group.
In general, glycidyl (meth) acrylate is used.   In addition, in addition to the above-described production method, for example, a method in which vinyl chloride and vinyl alcohol are used.
A vinyl chloride copolymer having a polyfunctional -OH is produced by a polymerization reaction.
Reaction of the union with a compound containing a polar group and a chlorine atom described below (desalting
(Acid reaction) to introduce a polar group into the copolymer. [0056]         ClCH_TwoCH_TwoSO_ThreeM,         ClCH_TwoCH_Two OSO_ThreeM,         ClCH_TwoCOOM,         ClCH_TwoPO (OM)_Two   In addition, the introduction of an epoxy group using this dehydrochlorination reaction is usually carried out using epichlorohydrin.
Use phosphorus. [0057]   The vinyl chloride copolymer may contain another monomer. other
Examples of the monomer include vinyl ether (eg, methyl vinyl ether,
Vinyl ether, lauryl vinyl ether), α-monoolefin (eg, ethyl
, Propylene), acrylates (eg, methyl (meth) acrylate,
(Meth) acrylic acid containing functional groups such as droxyethyl (meth) acrylate
Stele), unsaturated nitrile (eg, (meth) acrylonitrile), aromatic vinyl (
Examples: styrene, α-methylstyrene), vinyl esters (eg, vinyl acetate, And vinyl lopionate. [0058]   Specific examples of these binders used in the present invention include Union Carbide
Company: VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYE
S, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC
, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, MPR-
TAO, manufactured by Denki Kagaku: 1000 W, DX80, DX81, DX82, DX83
, 100FD, manufactured by Zeon Corporation: MR105, MR110, MR100, 400
X110A, manufactured by Nippon Polyurethane Industries: Nipporan N2301, N2302, N2
304, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105, T-R3080, T-
5201, Burnock D-400, D-210-80, Crisbon 6109, 7
209, manufactured by Toyobo: Byron UR8200, UR8300, UR8600, U
R5500, UR4300, RV530, RV280, manufactured by Dainichi Seika: Daifue
Lamin 4020, 5020, 5100, 5300, 9020, 9022, 702
0, manufactured by Mitsubishi Kasei: MX5004, manufactured by Sanyo Kasei: Samprene SP-150, Asahi
Karan Corporation: Saran F310, F210 and the like. [0059]   The binder used in the upper magnetic layer of the present invention is 5 to 50% by weight based on the ferromagnetic powder.
, Preferably in the range of 10 to 35% by weight. Vinyl chloride resin
5 to 30% by weight when using, 2 to 20% by weight when using polyurethane resin
% And polyisocyanate in the range of 2 to 20% by weight.
preferable. [0060]   The binder used in the lower non-magnetic layer of the present invention, based on the non-magnetic powder, is 5 to 5 in total.
It is used in a range of 50% by weight, preferably in a range of 10 to 35% by weight. Also salt
When a vinyl chloride resin is used, 3 to 30% by weight of polyurethane resin is used.
In the range of 3 to 30% by weight and polyisocyanate in the range of 0 to 20% by weight.
It is preferable to use them together. [0061]   In the present invention, an epoxy group-containing resin having a molecular weight of 30,000 or more is used for the nonmagnetic powder.
When 3 to 30% by weight is used, the resin other than the epoxy group-containing resin is
3 to 30% by weight, and 3 to 30 weight% when using a polyurethane resin.
%, Polyisocyanate can be used in an amount of 0 to 20% by weight, but the epoxy group is
4 × 10 based on the total weight (including the curing agent)^-Five~ 16 × 10^-Foureq / g
It is preferable to be included. [0062]   In the present invention, when a polyurethane resin is used, the glass transition temperature is -50 to
100 ° C, elongation at break 100-2000%, stress at break 0.05-10 kg / c
m^Two, Yield point is 0.05 to 10 kg / cm^TwoIs preferred.   The magnetic recording medium of the present invention basically has two layers, but may have three or more layers.
. The configuration of three or more layers is that the upper magnetic layer is composed of two or more magnetic layers.
You. In this case, the relationship between the uppermost magnetic layer and the lower magnetic layer is based on the consideration of ordinary magnetic layers.
The method can be applied. For example, the uppermost magnetic layer has a higher coercive force than the lower magnetic layer.
The idea of using ferromagnetic powder with high average long axis length and small crystallite size is appropriate.
Can be used. Further, the lower non-magnetic layer may be formed of a plurality of non-magnetic layers. However
Broadly speaking, the structure is composed of an upper magnetic layer and a lower nonmagnetic layer. [0063]   Therefore, the amount of binder, vinyl chloride resin in the binder, polyurethane resin,
The amount of polyisocyanate or other resin, the amount of each resin forming the magnetic layer
The molecular weight, polar group content, or the physical properties of the resin described above
Of course, it is possible to change between the upper magnetic layer.   As the polyisocyanate used in the present invention, tolylene diisocyanate, 4
-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate
, Xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-
Toluidine isocyanate, isophorone diisocyanate, triphenylmethane
Isocyanates such as triisocyanate, and these isocyanates
Products with polyalcohols and polyisocyanates Liisocyanate and the like can be used. Commercialization of these isocyanates
Trade names include those manufactured by Nippon Polyurethane Corporation: Coronate L, Coronate
HL, Coronate 2030, Coronate 2031, Millionate MR, Millione
MTL, manufactured by Takeda Pharmaceutical Co., Ltd .: Takenate D-102, Takenate D-110N,
Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer: Desmodu
L, death module IL, death module N, death module HL, etc.
, These alone or in combination of two or more utilizing the difference in curing reactivity
Thus, both the lower non-magnetic layer and the upper magnetic layer can be used. [0064]   The carbon black used in the upper magnetic layer of the present invention is a furnace black for rubber,
Thermal, black for color, acetylene black, etc. can be used
. Specific surface area is 5-500m^Two/ G, DBP oil absorption is 10-400ml / 100g
, Particle size is 5 μm to 300 μm, pH is 2 to 10, water content is 0.1 to 10%,
The tip density is preferably 0.1 to 1 g / cc. The carbon black used in the present invention
As a specific example of the product, BLACKPEARLS 2000, manufactured by Cabot Corporation,
1300, 1000, 900, 800, 700, VULCAN XC-72, Asahi
Carbon: 80, 60, 55, 50, 35, Mitsubishi Kasei:
$ 2400B, $ 2300, $ 900, $ 1000, $ 30, $ 40, $ 10B
, Manufactured by Konlon Via Carbon: CONDUCTEX SC, RAVEN 150
, 50, 40, 15 and the like. Surface treatment of carbon black with dispersant
Even if used or grafted with resin, part of the surface is graphitized
You can use something. Before adding carbon black to magnetic paint
May be dispersed in advance with a binder. These carbon blacks are used alone
, Or in combination. Strong when using carbon black
It is preferable to use 0.1 to 30% of the amount based on the magnetic powder. Carbon black
The magnetic layer has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light shielding properties, and improving film strength.
These differ depending on the carbon black used. Therefore used in the present invention
The type, amount and combination of these carbon blacks in the lower and upper
Size, oil absorption, conductivity, pH, etc. Of course it is possible to divide. Carbon black that can be used in the upper layer of the present invention
For example, refer to “Carbon Black Handbook” (edited by Carbon Black Association).
Can be. [0065]   As the abrasive used in the upper magnetic layer of the present invention, α-Al
Mina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Random, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide
Well-known materials with a Mohs hardness of 6 or more, such as tan, silicon dioxide, boron nitride, etc.
Used alone or in combination. In addition, a composite of these abrasives (abrasives)
Which has been surface-treated with another abrasive). Most of these abrasives
Compound or element other than the main component may be contained, but if the main component is 90% or more,
No change in effect. The particle size of these abrasives is preferably from 0.01 to 2 μm.
However, if necessary, it is possible to combine abrasives with different particle sizes,
The same effect can be obtained by widening the diameter distribution. Tap density is 0.3-2
g / cc, water content 0.1-5%, pH 2-11, specific surface area 1-30m^Two/
g is preferred. The shape of the abrasive used in the present invention is needle-like, spherical, dice-like,
Although any of these may be used, those having a corner in a part of the shape are preferable because of high abrasiveness. [0066]   Specific examples of the abrasive used in the present invention include AKP-2 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-30, AKP-50, HIT-50, manufactured by Nippon Chemical Industry: G5, G
7, S-1, manufactured by Toda Kogyo: TF-100, TF-140, 100ED, 140
ED and the like. The abrasive used in the present invention is of a type, amount and quantity in the lower layer and the upper layer.
Of course, it is possible to change the combination and use them according to the purpose. these
The abrasive may be added to the magnetic paint after it has been dispersed with a binder in advance.
No. [0067]   The additives used in the present invention include a lubricating effect, an antistatic effect, a dispersing effect,
Those having a plastic effect and the like are used. Molybdenum disulfide, tungsten disulfide
, Graphite, boron nitride, graphite fluoride, silicone oil, polar group Silicone, fatty acid modified silicone, fluorine-containing silicone, fluorine-containing alcohol
, Fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate
Ter and its alkali metal salts, alkyl sulfates and their alkali metals
Salts, polyphenyl ethers, fluorine-containing alkyl sulfates and their alka
Metal salts, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds,
And metal salts thereof (Li, Na, K, Cu, etc.).
Or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms
(Which may contain an unsaturated bond or may be branched), and has 12 to 2 carbon atoms.
2 alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (unsaturated
And may be branched), and C2-12 monovalent, divalent, trivalent
Any one of polyhydric, tetrahydric, pentahydric and hexahydric alcohols (including unsaturated bonds,
A mono-fatty acid ester or di-fatty acid ester consisting of
Teralkylates of tri- or tri-fatty acid esters and alkylene oxide polymers
Ter fatty acid ester, C8-C22 fatty acid amide, C8-C22 fat
Group amines and the like can be used. Specific examples of these are lauric acid, myristin
Acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid
, Linoleic acid, linolenic acid, elaidic acid, octyl stearate, stearin
Amyl acid, isooctyl stearate, octyl myristate, butyl stearate
Toxiethyl, anhydrosorbitan monostearate, anhydrosorbitan
Distearate, anhydrosorbitan tristearate, oleyl alcohol
, Lauryl alcohol. [0068]   In addition, alkylene oxide, glycerin, glycidol, alkyl
Nonionic surfactants such as enol ethylene oxide adducts, cyclic amines,
Steroids, quaternary ammonium salts, hydantoin derivatives, heterocycles, phos
Cationic surfactants such as phonium or sulfoniums, carboxylic acids, sulfonium
Anions containing acidic groups such as fonic acid, phosphoric acid, sulfate groups, phosphate groups, etc.
Surfactants, amino acids, aminosulfonic acids,
Can also be used amphoteric surfactants such as phosphates and alkylbedynes. About these surfactants, "Handbook of Surfactants" (published by Sangyo Tosho Co., Ltd.)
In more detail. These lubricants and antistatic agents are not necessarily 100% pure
It is not pure, but isomers, unreacted materials, by-products, decomposition products, oxides, etc.
Impurities may be included. Preferably, these impurities are 30% or less.
Is preferably 10% or less. [0069]   These lubricants and surfactants used in the present invention are a lower non-magnetic layer and an upper magnetic layer.
The type and amount can be properly used as needed. For example, a lower non-magnetic layer,
The upper magnetic layer uses fatty acids with different melting points to control bleeding to the surface,
Use surfactants with different polarities to control bleeding to the surface
The amount of lubricant added can be increased in the lower non-magnetic layer to improve coating stability by adjusting
To improve the lubrication effect. Of course, it is limited to only the examples shown here.
Not something. [0070]   All or some of the additives used in the present invention may be used in the production of magnetic paints.
May be added in the step of, for example, mixing with ferromagnetic powder before the kneading step.
When adding in the kneading process using ferromagnetic powder, binder and solvent,
In some cases, it is added after dispersion, or it is added just before coating. The present invention
Examples of commercial products of these lubricants used in Nippon Yushi: NAA-102,
NAA-415, NAA-312, NAA-180, NAA-174, NAA-
175, NAA-222, NAA-34, NAA-35, NAA-171, NA
A-122, NAA-142, NAA-160, NAA-173K, Castor hardening
Fatty acids, NAA-42, NAA-44, Cation SA, Cation MA, Cation
AB, Cation BB, Nymeen L-201, Nymeen L-202, Nymy
N-202, Nonion E-208, Nonion P-208, Nonion S-207
, Nonion K-204, Nonion NS-202, Nonion NS-210, Nonio
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-85R, Nonion LT-221, Nonion On ST-221, Nonion OT-221, Monogly MB, Nonion DS-60
, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid
, Manufactured by Kanto Chemical Co., Ltd .: oleic acid, manufactured by Takemoto Yushi Co., Ltd .: FAL-205, FAL-123
, Manufactured by Shin Nippon Rika Co., Ltd .: NGJELB LO, NGJOLUB IPM, Sansocizer E
4030, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, KF-96, KF-96L, KF-96H
, KF410, KF420, KF965, KF54, KF50, KF56, KF
-907, KF-851, X-22-819, X-22-822, KF-905
, KF-700, KF-393, KF-857, KF-860, KF-865,
X-22-980, KF-101, KF-102, KF-103, X-22-3
710, X-22-3715, KF-910, KF-3935, Lion Armor
-Armide P, Armide C, Armoslip CP, Lion Yushi
: Duomin TDO, manufactured by Nisshin Oil Co., Ltd .: BA-41G, manufactured by Sanyo Chemical Co., Ltd .: Profuan
2012E, Newpole PE61, Ionet MS-400, Ionet MO
-200, IONET DL-200, IONET DS-300, IONET DS
-1000 and Ionette DO-200. [0071]   The organic solvent used in the present invention is acetone in any ratio, methyl ethyl ketone,
Methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone
, Tetrahydrofuran, and other ketones, methanol, ethanol, propanol
, Butanol, isobutyl alcohol, isopropyl alcohol, methylcyclo
Alcohols such as hexanol, methyl acetate, butyl acetate, isobutyl acetate
, Isopropyl acetate, ethyl lactate, glycols such as glycol acetate, glycols
Glyco such as dimethyl ether, glycol monoethyl ether, dioxane, etc.
Ether, benzene, toluene, xylene, cresol, chlorobenzene
, Such as aromatic hydrocarbons, methylene chloride, ethylene chloride, tetrachloride
Chlorination of carbon, chloroform, ethylene chlorohydrin, dichlorobenzene, etc.
Hydrocarbons, N, N-dimethylformamide, hexane and the like can be used.
These organic solvents are not necessarily 100% pure.
Impurities such as substances, by-products, decomposition products, oxides, and moisture may be included. This Their impurity content is preferably 30% by weight or less, more preferably 10% by weight or less.
is there. The type of the organic solvent used in the present invention is the same in the upper layer and the lower layer if necessary.
Is preferred. The amount added may be changed. High surface tension solvent in lower layer
(Cyclohexanone, dioxane, etc.) to increase coating stability.
It is important to note that the arithmetic mean of the upper solvent composition does not fall below the arithmetic mean of the lower solvent composition.
It is important. In order to improve dispersibility, it is preferable that the polarity is somewhat strong.
The solvent used for the coating solution for the non-magnetic layer and the upper magnetic layer has a solubility parameter of 8 to
11, and preferably contains 15% or more of a solvent having a dielectric constant of 15 or more at 20 ° C.
Good. [0072]   In the thickness configuration of the magnetic recording medium of the present invention, the nonmagnetic support is preferably 1 to 100 μm,
Is 4 to 80 μm, the lower layer is 0.5 to 10 μm, preferably 1 to 5 μm, and the upper layer is 0.1 μm. is there. The total thickness of the upper and lower layers is in the range of 1/100 to 2 times the thickness of the nonmagnetic support.
Used in box. Also, an undercoat layer for improving adhesion between the nonmagnetic support and the lower layer
May be provided. Their thickness is 0.01 to 2 μm, preferably 0.05
０．５0.5 μm. Also, a back coat layer is formed on the non-magnetic support on the side opposite to the magnetic layer side.
May be provided. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0
μm. Known undercoating layers and backcoat layers can be used. [0073]   The non-magnetic support used in the present invention is polyethylene terephthalate or polyethylene.
Polyesters such as nannaphthalate, polyolefins, cellulose triacetate
Tate, polycarbonate, polyamide, polyimide, polyamideimide, poly
Known films such as sulfon, aramid, and aromatic polyamide can be used.
These supports are treated in advance with corona discharge treatment, plasma treatment, easy adhesion treatment, and heat treatment.
Processing, dust removal processing, and the like may be performed. To achieve the object of the present invention, a non-magnetic
The support has a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less.
m or less, more preferably 0.01 μm or less. Also
These non-magnetic supports have not only low center line average surface roughness but also 1 μm. It is preferable that there are no such coarse protrusions. Also, if necessary, the surface roughness
Freely controlled by the size and amount of filler added to the support
It is. Examples of these fillers include oxides such as Ca, Si, and Ti.
And organic fine powders such as acrylics in addition to carbonates and carbonates. [0074]   The F-5 value of the non-magnetic support in the tape running direction is preferably 5 to 50 kg.
/ Mm^TwoAnd the F-5 value in the tape width direction is preferably 3 to 30 kg / mm.^TwoAnd
Generally, the F-5 value in the tape longitudinal direction is higher than the F-5 value in the tape width direction.
However, this is not always the case when it is necessary to increase the strength in the width direction.   In addition, heat collection at 100 ° C. for 30 minutes in the tape running direction and the width direction of the nonmagnetic support was performed.
The shrinkage ratio is preferably 3% or less, more preferably 1.5% or less, at 80 ° C. for 30 minutes.
The heat shrinkage is preferably 1% or less, more preferably 0.5% or less. Breaking strength
The degree is 5 to 100 kg / mm in both directions.^Two, Elastic modulus is 100-2000Kg / mm^Two
Is preferred. [0075]   The step of producing the magnetic paint of the magnetic recording medium of the present invention includes at least a kneading step,
It consists of a dispersing step and a mixing step optionally provided before and after these steps. Individual
Each process may be divided into two or more steps. Used in the present invention
Ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent
Any of the raw materials may be added at the beginning or during any of the steps. Also, individual
Each raw material may be divided and added in two or more steps. For example, Polyure
Divided into the kneading step, dispersion step, and mixing step for adjusting viscosity after dispersion
May be. [0076]   In order to achieve the object of the present invention, a conventionally known manufacturing technique is used as a part of the steps.
Of course, it can be used, but in the kneading process, a continuous kneader or a pressure kneader is used.
By using a material having a strong kneading force such as a
Br can be obtained. Ferromagnetic when using a continuous or pressure kneader
All or part of the powder and binder (but preferably at least 30% by weight of the total binder) And kneading treatment in the range of 15 to 500 parts per 100 parts of ferromagnetic powder.
. The details of these kneading processes are described in JP-A-1-106338 and JP-A-64-106.
No. 79274. When preparing the lower non-magnetic layer liquid,
It is preferable to use a heavy dispersion medium, and zirconia beads and metal beads are preferable.
Suitable. [0077]   In the present invention, a simultaneous multilayer coating method as disclosed in JP-A-62-212933 is used.
By using, it is possible to produce more efficiently. Multilayer as in the present invention
The following configuration is proposed as an example of an apparatus and method for applying a magnetic recording medium having the following configuration.
Wear. 1. Gravure coating, roll coating, and blade commonly used for applying magnetic paint
First, the lower layer is applied by a coating or extrusion coating device, and the lower layer is wetted.
The Japanese Patent Publication No. Hei 1-46186, Japanese Patent Application Laid-Open No. 60-238179,
Pressurized support type extrusion coating apparatus disclosed in Japanese Patent Application Laid-Open No. 2-265672.
To coat the upper layer. 2. JP-A-63-88080, JP-A-2-17921, JP-A-2-2656
No. 72, which has two slits for applying the coating solution,
The upper layer and the lower layer are applied almost simultaneously by a pad. 3. Extract with backup roll disclosed in JP-A-2-174965
The upper layer and the lower layer are applied almost simultaneously by a trusion coating device. In addition, it is possible to prevent a decrease in electromagnetic conversion characteristics and the like of the magnetic recording medium due to aggregation of the ferromagnetic powder.
Therefore, it is disclosed in JP-A-62-95174 and JP-A-1-236968.
It is desirable to apply shear to the coating liquid inside the coating head by such a method. Sa
Further, the viscosity of the coating solution is determined by the number disclosed in Japanese Patent Application No. 1-312659.
It is preferable to satisfy the value range. [0078]   In the present invention, the so-called wet-coating liquid for the lower layer is applied in a wet state.
It is provided on a non-magnetic support by a to-on-wet coating method.   What is the wet-on-wet coating method used to provide the lower layer and the upper layer in the present invention , First coat the next layer on the first layer in wet condition as soon as possible
So-called sequential coating method, and method of applying multiple layers simultaneously by extrusion coating method
Etc. [0079]   As a wet-on-wet coating method, Japanese Patent Application Laid-Open No. 61-139929
The magnetic recording medium coating method shown in the report can be used.   In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000G (gau
S) It is preferable to use a combination of the above solenoid and a cobalt magnet of 2000G or more.
In addition, an appropriate drying step is required before orientation so that the orientation after drying is the highest.
Is preferably provided. When the present invention is applied as a disk medium,
Rather, an orientation method that randomizes the orientation is required. [0080]   Epoxy, polyimide, polyamide, poly
Use a heat-resistant plastic roll such as imidoamide. Also, metal low
They can be processed by each other. The processing temperature is preferably 70 ° C. or more, more preferably
Preferably, it is 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably
Or 300 kg / cm or more, and the speed is in the range of 20 m / min to 700 m / min.
You. The effect of the present invention is further enhanced at a linear pressure of 300 kg / cm or more at a temperature of 80 ° C. or more.
The effect can be improved. [0081]   Friction of upper layer of magnetic recording medium of the present invention and its opposite surface against SUS420J
The coefficient is preferably 0.5 or less, more preferably 0.3 or less, and the magnetic layer surface resistivity is 10 or less.^Four
-10¹¹Ohm / sq, surface resistivity when the lower layer is applied alone is 10^Four~ 1
0⁸Ohm / sq, surface electric resistance of the back layer is 10^Three-10⁹Ohm / sq is good
Good. [0082]   The elastic modulus of the upper layer at 0.5% elongation is preferably 300 to 2 in both the running direction and the width direction.
000Kg / mm^Two, Breaking strength is preferably 2 to 30 kg / cm^Two, Magnetic recording media
Is preferably 100 to 1500 kg / mm in both the running direction and the width direction.^Two, Residual growth is preferably 0.5% or less, heat shrinkage at any temperature below 100 ° C
Is preferably 1% or less, more preferably 0.5% or less, and most preferably 0% or less.
. 1% or less. [0083]   The porosity of both the upper layer and the lower layer is preferably 30% by volume or less, more preferably.
Or less than 20% by volume. The smaller the porosity is, the higher the output is.
However, depending on the purpose, it may be better to secure a certain value. For example, repeat
In magnetic recording media for data recording, where the use is important, the higher the porosity, the longer the running durability
Properties are often preferred. Set these values in appropriate ranges according to the purpose.
Can be easily implemented. [0084]   The magnetic properties of the magnetic recording medium of the present invention were measured at a magnetic field of 5 KOe.
The squareness ratio in the direction is 0.70 or more, preferably 0.80 or more, more preferably
0.90 or more. The squareness ratio of the two directions perpendicular to the tape running direction is
It is preferable that it is 80% or less of the squareness ratio. The SFD of the magnetic layer is 0.6 or less
Is preferred. [0085]   The magnetic recording medium of the present invention has a lower layer and an upper layer.
It is easily estimated that these physical properties can be changed. For example
, Increase the elastic modulus of the magnetic layer to improve running durability and at the same time increase the elastic modulus of the non-magnetic layer.
For example, the magnetic recording medium may be lower than the magnetic layer to improve the contact with the head of the magnetic recording medium.   The magnetic recording medium of the present invention preferably has the following physical property ranges. [0086]   The Young's modulus of the magnetic recording medium of the present invention measured by a tensile tester is 400 to 50.
00Kg / mm^Two, Preferably 700 to 4000 kg / mm^TwoAnd said magnetic
The layer has a Young's modulus of 400 to 5000 kg / mm.^Two, Preferably 700-4000K
g / mm^Two, Yield stress is 3-20Kg / mm^Two, Preferably 3 to 15 kg / mm^Two
, And the yield elongation is desirably 0.2 to 8% and 0.4 to 5%. [0087]   This involves ferromagnetic powder, binder, carbon black, inorganic powder, and support.
It affects the durability.   The flexural rigidity (annular stiffness) of the magnetic recording medium of the present invention is 11.1 in the total thickness.
When it is thicker than 5 μm, preferably 40 to 300 mg when the total thickness is 10.5 ± 1 μm
Preferably 20 to 90 mg, and preferably 10 to 10 when the total thickness is less than 9.5 μm.
70 mg. [0088]   This is mainly related to the support and is important for ensuring durability.   In addition, crack generation elongation of the magnetic recording medium of the present invention measured at 23 ° C. and 70% RH.
But preferably 20% or less.   The magnetic layer of the magnetic recording medium of the present invention measured using an X-ray photoelectron spectrometer.
Surface Cl / Fe spectrum α is preferably 0.3 to 0.6, N / Fe spectrum
Is preferably 0.03 to 0.12. [0089]   This is related to ferromagnetic powder, inorganic powder and binder, and is important for durability.
It is.   Further, the magnetic layer of the magnetic recording medium of the present invention measured using a dynamic viscoelasticity measuring device.
The glass transition temperature Tg of the sample (the pole of the loss elastic modulus in the dynamic viscoelasticity measurement measured at 110 Hz)
Is preferably from 40 to 120 ° C., and the storage modulus E ′ (50 ° C.) is preferred.
0.8 × 10¹¹~ 11 × 10¹¹dyne / cm^TwoAnd the loss modulus E ″
(50 ° C.) is preferably 0.5 × 10¹¹~ 8 × 10¹¹dyne / cm^TwoIs
Is desirable. Further, the loss tangent is preferably 0.2 or less. Loss tangent is
If it is too large, adhesion failure is likely to occur. These are binder, carbon black,
It is an important property related to durability and related to solvents and solvents. [0090]   In addition, an 8 mm width tape at 23 ° C. and 70% RH between the nonmagnetic support and the magnetic layer.
The 180 ° adhesion strength of the loop is preferably 10 g or more.   The wear of a steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.7 ×
10^-7~ 5 × 10^-7m^ThreeIt is desirable that This directly affects the surface of the magnetic layer. It is a measure of durability mainly related to ferromagnetic powder, which is a measure of wear. [0091]   Further, five images of the magnetic recording medium of the present invention were taken with a SEM (electron microscope) at a magnification of 50,000 times.
The number of the abrasives on the surface of the shaded magnetic layer is preferably 0.1 / μm.^Twothat's all
It is desirable that Further, the magnetic recording medium of the present invention exists on the end face of the upper magnetic layer.
Abrasives 5 / 100μm^TwoThe above is preferred. These are combined with the abrasive of the magnetic layer
It is a measure that is affected by the agent and exerts an effect on durability. [0092]   In addition, the magnetic recording medium of the present invention, the magnetic recording medium was measured using a gas chromatography.
The residual solvent of the gas recording medium is preferably 50 mg / m^TwoIt is desirable that:   The residual solvent contained in the upper layer is preferably 50 mg / m^TwoLess preferred
Or 10mg / m^TwoBelow, the residual solvent contained in the upper layer
It is preferable that the amount is smaller than the distillation solvent.   The magnetic properties of the soluble solids extracted from the magnetic recording medium of the present invention with THF
It is desirable that the sol fraction, which is the ratio to the layer weight, is 15% or less. this is
, Which is affected by the ferromagnetic powder and the binder, and is a measure of durability. [0093]     【Example】   Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.
There is no. In the examples, “parts” means “parts by weight” unless otherwise specified.   Thickness of magnetic layer: For elements specifically contained in the magnetic layer by fluorescent X-rays,
Measure the magnetic layer sample and create a calibration curve. Next, the thickness of the unknown sample is fluoresced.
It was determined from X-ray intensity. [0094]   Example 1   A magnetic coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulation.
. Magnetic coating solution for upper magnetic layer   100 parts of ferromagnetic powder     Fe alloy powder (Co added 5%)     Hc 1600 Oe, saturation magnetization (σ_S) 130 emu / g     Long axis length 0.18μm, needle ratio 8   Vinyl chloride copolymer 10 parts     -SO_ThreeContains Na and epoxy group   5 parts of polyurethane resin     -SO_ThreeNa content, molecular weight 45000   α-alumina (average particle size 0.2μm) 5 parts   Cyclohexanone 100 parts   200 parts of methyl ethyl ketone   After mixing and dispersing in the above composition sand mill for 6 hours,
Nate L), 5 parts of stearic acid, and 10 parts of butyl stearate.
A magnetic coating solution for a magnetic layer was obtained. [0095] Coating solution for lower non-magnetic layer   Granular TiO_Two(Average particle size 0.04 μm) 100 parts   5 parts of carbon black (average particle size 20mμ)   8 parts of vinyl chloride copolymer     -SO_ThreeContains Na and epoxy group   5 parts of polyurethane resin     -SO_ThreeContains Na group, molecular weight 45,000   α-alumina (average particle size 0.2μm) 5 parts   Cyclohexanone 150 parts   Methyl ethyl ketone 50 parts   After mixing and dispersing the above composition in a sand mill for 4 hours, 5 parts of stearic acid,
Add 10 parts of butyl acrylate and 5 parts of polyisocyanate (Coronate L) to add lower layer
A coating solution for a non-magnetic layer was obtained. [0096]   Apply the above coating solution in a wet state using two doctors with different caps. Then, after orientation treatment with a permanent magnet, it was dried. The support is 5.5 μm polyoxyethylene.
Use a polyethylene naphthalate film, and apply carbon black on the surface of the support opposite to the magnetic layer.
A backing layer containing a layer was provided. Thereafter, a super calendar process was performed. Paint
The thickness of the cloth was 0.5 μm for the magnetic layer and 2.5 μm for the lower non-magnetic layer. Gain in this way
The raw material was cut to 3.81 mm width and digital audio tape (DAT) was cut.
Created. [0097] The tapes were prepared by changing the factors shown in Nos. These tapes are used in the same way as above.
And the results are shown in Tables 1 and 2.   Hc: Measured with Hm10KOe using a vibrating sample magnetometer manufactured by Toei Kogyo.   C / N: The noise spectrum is measured when the reproduction output is measured, and the reproduction output and the central recording
Calculate C / N from the ratio of noise level 0.1MHz away from wave number (4.7MHz)
I did.   The spectrum analyzer used was HP-3585A, and the single magnetic layer of Comparative Example 1 was used.
The tape No. was set to 0 dB as a control. [0098]   BER (Block Error Rate): BER is an error in 10,000 tracks
The number of flags is expressed by the following formula.   BER = error flag / 10000 × 128 blocks   The DAT signal configuration encodes an analog signal, one code is 8 bits, and one block.
Is 32 symbols × 8 bits = 256 bits, so that one track has 128 blocks.
It consists of a lock. Two tracks, that is, 128 × 2 block signals are stored in memory
, Shuffle, and detect errors. Use Sony DAT deck
Hewlett-Packard HP5328A is used as a counter,
The measurement was performed by connecting to a personal computer.   Dropout: 4.7MHz single frequency signal input, threshold
Measured at a level (-10 dB) with a 0.5 microsecond dropout counter
. [0099]     [Table 1] [0100]     [Table 2] [0101]   As is clear from the above table, the embodiment of the present invention has a high Rf output,
And excellent electromagnetic conversion characteristics with reduced BER. Comparative Example 1 shows that the lower layer This is an example of creating a magnetic recording medium by the method, and BER and dropout are poor.
. Comparative Example 3 is an example in which carbon black was used instead of the inorganic powder.
R, reproduction output cannot be satisfied. Comparative Example 4 is a ferromagnetic alloy powder having a predetermined size or more.
, The Hc in the width direction and the longitudinal direction is lower than that of the present invention, so that the reproduction is high.
No output is obtained and the BER is high. Comparative Example 5 uses ferromagnetic powder having a large acicular ratio.
This is an example in which Hc in the width direction is lower than that of the present invention, so that a high reproduction output can be obtained.
Nor does BER improve. [0102]     【The invention's effect】   The present invention relates to a magnetic layer of a magnetic recording medium having a thin magnetic layer having a dry thickness of 1 μm or less.
By setting each holding force in the longitudinal direction and width direction of the
Improvement of reproduction output in wavelength recording, reduction and improvement of dropout and BER
A magnetic recording medium having improved electromagnetic conversion characteristics can be obtained. Also, the present invention
A magnetic layer having a uniform thickness and 1 μm or less is provided on the lower non-magnetic layer without coating defects,
Extremely thin, ferromagnetic gold with a magnetic layer that suppresses holes and streaks and has excellent mass productivity
An object of the present invention is to provide a magnetic recording medium having performance comparable to a metal thin film.

Claims (1)

Claims: 1. A lower nonmagnetic layer in which an inorganic powder is dispersed in a binder is provided on a nonmagnetic support, and an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder is provided thereon. Magnetic recording The thickness of the layer is 0.5 μm or more, and the upper magnetic layer has a major axis length of 0.25 μm. The upper magnetic layer has a coercive force (Hc) of 1500 Oe in the longitudinal direction. A magnetic recording medium, wherein the inorganic powder contained is an inorganic powder having a true specific gravity of 3 or more. 2. An inorganic powder contained in the lower nonmagnetic layer has an average particle size of 0.2.
μm or less, or the major axis length is 0.05 to 1.0 μm and the acicular ratio is 20. Including the above, and further Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh
, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb,
Selected from Bi, La, Ce, Pr, Nd, P, Mn, Zn, Ni, Sr, B . , Anatase), TiO _x , cerium oxide, tin oxide, tungsten oxide, Zn
O, ZrO ₂ , Cr ₂ O ₃ , alumina having an α conversion of 90% or more, β alumina, γ alumina, α iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, molybdenum disulfide, copper oxide, BaCO ₃ , SrCO ₃ , BaSO ₄ ,
Characterized by containing at least one selected from silicon carbide and titanium carbide The magnetic recording medium according to claim 1. Prepare a lower non-magnetic layer coating solution and an upper magnetic layer coating solution containing a ferromagnetic powder and a binder, and apply the lower non-magnetic layer coating solution and the upper magnetic layer coating solution on a non-magnetic support. Wherein the ferromagnetic powder has a coercive force. The dry thickness of the coating solution for the lower non-magnetic layer on the non-magnetic support is 0.5 μm or more.
So that the lower non-magnetic layer obtained is wet while the lower non-magnetic layer is wet. The upper magnetic layer coating solution is applied so that the upper magnetic layer . Granular particles having a diameter of 0.2 μm or less, or needles having a major axis length of 0.05 to 1.0 μm Manufacturing method.