JPH08221737A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve electromagnetic transducing characteristics and running durability by specifying the ratio of the center line average roughness of the surface of a magnetic layer on a nonmagnetic substrate in the transverse direction to that in the longitudinal direction measured with a contact needle type surface roughness gauge. CONSTITUTION: In the magnetic recording medium obtd. by forming at least one magnetic layer on a nonmagnetic substrate, the ratio (Ra2/Ra1) of the center line average surface roughness Ra2 of the surface of the magnetic layer in the transverse direction to that Ra1 in the longitudinal direction measured by 0.08mm cutoff with a contact needle type surface roughness gauge is regulated to 1.2-2.0. A means of regulating the ratio is not especially limited and the ratio is regulated, e.g. by selecting the shape of ferromagnetic powder and controlling the squareness ratio, selecting the shape of inorg. powder when a nonmagnetic layer based on the inorg. powder is formed, controlling the surface of the nonmagnetic substrate or selecting a coating method. When acicular ferromagnetic powder is used, the acicularity ratio is preferably reduced. When platy ferromagnetic powder is used, the orienting property is preferably made high because the surface roughness of the magnetic layer in the transverse direction is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having at least one magnetic layer or at least one magnetic layer and a non-magnetic layer and having excellent electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art Conventionally, as magnetic recording media such as video tapes, audio tapes, computer tapes, etc., ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO ₂ , ferromagnetic alloy powder, hexagonal ferrite, etc. are used. A non-magnetic support coated with a magnetic layer dispersed in a binder is widely used.
In recent years, ferromagnetic alloy powders and hexagonal ferrite have been used as magnetic materials having excellent electromagnetic conversion characteristics suitable for high density recording. For metal thin films, oblique vapor deposition and sputtered films are drawing attention. Also, there is a method of increasing the output in a wide frequency band by using a multilayer structure of magnetic layers having different magnetic characteristics, or a method of providing a non-magnetic layer in the lower layer and thinning the upper layer to increase the output particularly in a short wavelength. It has already been put to practical use. On the other hand, in order to achieve excellent electromagnetic conversion characteristics, it is necessary to improve the magnetic characteristics of the magnetic layer and at the same time enhance the surface smoothness. However, simply increasing the surface smoothness raises the coefficient of friction and lowers the running property and durability. Various proposals have been made to control the surface property for such problems. For example, JP-A-61-168124
In the publication, the center line average surface roughness Ra and the maximum height R _max of the magnetic layer are described, in JP-A-4-125810, the center line average surface roughness and center line depth, and in JP-A-5-73884, the surface. Each is focused on the number of protrusions. In addition, many examples can be given, such as focusing on the surface spatial frequency and the surface waviness component. In addition, many attempts have been made to reduce the coefficient of friction with a lubricant. On the other hand, as the capacity of a magnetic recording medium (hereinafter, “magnetic recording medium” may be simply referred to as “medium”) increases, the thinning of the medium progresses, and the medium strength decreases. In particular, when smoothing the magnetic layer in order to achieve the high electromagnetic conversion characteristics required in recent years in such a thin medium, it is very difficult to secure running property and durability with these techniques. Is coming.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium for high density recording which has good electromagnetic conversion characteristics and excellent running durability.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied a method for improving the running property and durability by lowering the friction coefficient of a magnetic recording medium which is smooth and has good electromagnetic conversion characteristics. As a result, they have found that there is a solution to the directionality of the surface roughness of the magnetic layer, which has never been noticed. That is, the present invention has the following configurations. In a magnetic recording medium in which at least one magnetic layer is provided on a non-magnetic support, the center line average surface roughness in the longitudinal direction of the magnetic layer surface measured with a stylus type surface roughness meter at a cutoff of 0.08 mm. The magnetic recording medium is characterized in that the ratio (Ra2 / Ra1) of the width Ra1 to the centerline average surface roughness Ra2 of the magnetic layer surface in the width direction is 1.2 to 2.0. In a magnetic recording medium in which a nonmagnetic layer and a magnetic layer are formed in this order on a nonmagnetic support, the longitudinal direction of the surface of the magnetic layer measured with a stylus type surface roughness meter at a cutoff of 0.08 mm. Of the center line average surface roughness Ra1 of the magnetic layer and the center line average surface roughness Ra2 of the magnetic layer surface in the width direction (Ra2 / R
a1) is 1.2 to 2.0. In a magnetic recording medium in which a non-magnetic layer and a magnetic layer are formed in this order on a non-magnetic support, the thickness of the magnetic layer is 0.05 to 1 μm, and a stylus surface roughness meter is used. The ratio (Ra2 / Ra1) of the centerline average surface roughness Ra1 in the longitudinal direction of the magnetic layer surface and the centerline average surface roughness Ra2 in the width direction of the magnetic layer surface measured with a cutoff of 0.08 mm is 1. 2 to 2.0 and the total thickness of the magnetic recording medium is 3 to
A magnetic recording medium having a thickness of 10 μm.

The reason why the magnetic recording medium of the present invention exhibits excellent electromagnetic conversion characteristics, reduced friction coefficient, and excellent running durability is not clear, but it is considered as follows. A magnetic head for recording / reproducing runs substantially in the longitudinal direction of the medium and traces the surface of the magnetic layer. Therefore, if Ra in the longitudinal direction of the stylus surface roughness meter is small, vertical movement of the head in the traveling direction is reduced, stable recording / reproduction is possible, high output is obtained, and modulation noise is also reduced. It is considered possible. If Ra in the longitudinal direction is large, the spacing between the magnetic layer and the head tends to be large, and the traveling becomes unstable, so that the modulation noise becomes high. On the other hand, when Ra in the width direction is large, the friction coefficient in the width direction of the tape becomes small, and it is considered that displacement of the tape in the width direction in the deck running system, that is, vertical movement can be prevented. On the contrary, if Ra in the width direction of the tape is small, the friction coefficient in the width direction becomes high, and once the tape is displaced to one side and travels, it will be difficult to return to the original center traveling position. Rubbing occurs between the regulation portion of the cylinder and the edge of the tape, resulting in severe damage to the tape. That is, a completely new point of view of the present invention is that electromagnetic conversion characteristics reduce the surface roughness Ra1 in the tape longitudinal direction, running durability increases the surface roughness Ra2 in the tape width direction, and (Ra2 /
The inventors have found that the ratio of Ra1) can be independently improved by defining the ratio in a specific range.

The present invention sets the value of (Ra2 / Ra1) to 1.2.
It is controlled to ˜2.0, preferably 1.5 to 1.8. When (Ra2 / Ra1) is less than 1.2, running durability is deteriorated, and when (Ra2 / Ra1) is more than 2.0, electromagnetic conversion characteristics start to deteriorate, which is not preferable. Ra1 is usually 1 to 40 nm, preferably 1 to 2
It is 0 nm, more preferably 3 to 15 nm. Ra1
Is less than 1 nm, the friction coefficient in the longitudinal direction becomes high and the running durability begins to deteriorate, which is not preferable. Ra1 is 2
If it exceeds 0 nm, the electromagnetic conversion characteristics are deteriorated, which is not preferable.

In the present invention, the thickness of the magnetic layer is
When the magnetic layer is provided as a single layer on the non-magnetic support, the thickness is usually 0.5 to 10 μm, preferably 1 to 4 μm,
When it is provided on the non-magnetic layer provided on the non-magnetic support, it is 0.01 to 1 μm, preferably 0.05 to 0.8.
μm, more preferably 0.1 to 0.5 μm, and the total thickness of the magnetic recording medium is 3 to 30 μm, preferably 3 to 10 μm.
μm, and more preferably 5 to 8 μm. Here, the nonmagnetic layer is also referred to as a lower layer or a lower nonmagnetic layer, and the magnetic layer provided on the lower layer is also referred to as an upper layer or an upper magnetic layer. Also,
In the present invention, in addition to the upper magnetic layer, one or more magnetic layers may be provided instead of the non-magnetic layer or below or above the non-magnetic layer. Therefore, (R
The value of a2 / Ra1) is the value of the uppermost layer.

Ra1 or Ra2 in the present invention is a stylus type surface roughness meter manufactured by Kosaka Laboratory, cut off 0.08 mm, needle diameter 2 μR, needle pressure 70 mg, speed 0.
1 mm / s, measurement length (in the case of Ra1, in the longitudinal direction, R
In the case of a2, it is a value obtained by measuring 20 times at 0.5 mm in the width direction and averaging them. Here, the measurement conditions and procedures in the measurement in the longitudinal direction and the measurement in the width direction are the same except for the directionality thereof. It should be added that, in the past, simply referring to the center line average surface roughness Ra was a concept indicating Ra1 in the present invention. That is, in the present invention,
For the first time, the concept of centerline average surface roughness Ra2 in the width direction was introduced. In other words, the present invention was found for the first time to be effective in achieving this object by adjusting the surface roughness by dividing Ra in the longitudinal direction and the width direction.

It goes without saying that the present invention can obtain the same effect not only in the coating type magnetic recording medium but also in the metal thin film medium. As the metal thin film, generally, a known thin film containing Fe or Co as a main component by oblique vapor deposition or a sputtering method and optionally containing Ni or Cr can be used. The coating type magnetic recording medium in the present invention will be described in detail below.

In the present invention, the means for adjusting the ratio of the width direction Ra2 to the length direction Ra1 to 1.2 to 2 is not particularly limited, but the following method is preferably exemplified. Selecting the shape of the ferromagnetic powder and controlling the squareness ratio. As for the ferromagnetic powder, for example, when acicular ferromagnetic powder is used, it is preferable to reduce the acicular ratio, specifically, the acicular ratio is 3 to 10, and particularly preferably 5 to 8,
It is considered that this is because the shape of the ferromagnetic powder gives directionality to the shape of the magnetic layer surface. On the contrary, in the case of hexagonal ferrite, it is preferable to increase the plate ratio, specifically, 2-1.
0, especially 3 to 7, is preferable. It was also found that the degree of orientation of the ferromagnetic powder also affects the directionality of roughness, and for needle-shaped ferromagnetic powder, it is better to reduce the orientation within the range that does not affect the electromagnetic conversion characteristics. Is preferable, and specifically, the SQ in the longitudinal direction is 0.75 to 0.9.
0, particularly 0.75 to 0.85 is preferable.

On the contrary, in the plate-like ferromagnetic powder, the larger the orientation, the larger the surface roughness in the width direction, which is preferable. Specifically, it is 0.70 to 0.95, particularly 0.80 to 0.95. . When providing a non-magnetic layer, select the shape of the inorganic non-magnetic powder that is the main component of the non-magnetic layer. It is extremely effective to provide a non-magnetic layer between the non-magnetic support and change the shape of the inorganic non-magnetic powder therein. Specifically, the acicular inorganic non-magnetic powder preferably has a small acicular ratio,
Spherical particles or spherical particles are preferable to acicular particles. In the case of acicular particles, the acicular ratio is preferably in the range of 2-10. It is considered that this is because the surface shape of the lower layer is influenced by the shape of the inorganic non-magnetic powder, which affects the shape of the magnetic layer surface. Controlling the surface of the non-magnetic support on the side where the magnetic layer or the non-magnetic layer is provided.

It is also possible to change the ratio of Ra1 and Ra2 by controlling the surface of the non-magnetic support. Specifically, when the non-magnetic support containing the filler is strongly stretched in the width direction, a difference in direction occurs in the shape of the periphery of the filler, and the surface roughness in the width direction can be increased in the longitudinal direction. Specifically, it is possible to select the F5 values in the longitudinal direction and the width direction of the non-magnetic support. Here, the F5 value means the elongation (Strai-Strain curve) of the non-magnetic powder on the S-S curve (Stress-Strain curve).
n) is the stress corresponding to 5%. Longitudinal F5 value is usually, 5~30Kg / mm ^2, preferably in the range from 10~18Kg / mm ^2, the width direction F5
The value is usually 5 to 30 Kg / mm ² , preferably 12 to 2
It is in the range of 0 kg / mm ² . Also, (longitudinal direction F5
The value / F5 value in the width direction) is preferably controlled to 1.1 to 2.0, particularly 1.2 to 1.6.

Select a coating method. It is also possible to control the directionality of the surface roughness by selecting the coating method. Specifically, the surface roughness in the width direction is increased by adding minute periodic fluctuations to the width distribution of the slit clearance by extrusion coating, and the surface roughness in the longitudinal direction is increased by increasing the accuracy of the liquid supply amount. Can be made smaller. Specifically, the slit clearance in the width direction is usually within ± 0.5% to ± 5, preferably ± 1%.
The value of (Ra2 / Ra1) can be controlled by making a minute periodic fluctuation within ± 3%.

In the present invention, a magnetic recording medium having a predetermined (Ra2 / Ra1) can be produced by using these methods alone, preferably by using some of them in combination. Note that the method of controlling the value of (Ra2 / Ra1) is not limited to the above-mentioned items 1 to 4, and known methods can be applied.

Next, as the ferromagnetic powder used in the magnetic layer of the present invention, γ-FeOx (x = 1.33 to 1.5), C
Known ferromagnetic metal powders such as o-modified γ-FeOx (x = 1.33 to 1.5), ferromagnetic alloy fine powder containing Fe or Ni or Co as a main component (75% or more) can be used. The ferromagnetic strong alloy powder has a Co content of 20 to 40 with respect to Fe.
%, Ni content is preferably 0 to 5% in proportion to the purpose. A needle ratio of 2 to 20 can be used, but a needle ratio of 4 to 8 is preferable. These ferromagnetic powders include
For the purpose of controlling the anisotropy and coercive force, controlling the amount of magnetization, controlling the distribution, and improving the stability against corrosion, in addition to the specified atoms, Al, Si, S, Sc, Ti, V, Cr, Cu,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hg, Pb, Bi, La,
Ce, Pr, Nd, P, Co, Mn, Zn, Ni, S
Atoms such as r, B, Ge, Nb can be contained.

These ferromagnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513, JP-B-46-28466, and JP-B-46-387.
No. 55, Japanese Patent Publication No. 47-4286, No. 47-1
2422 report, Japanese Patent Publication No. 47-17284, Japanese Patent Publication No. 4
7-18509, Japanese Patent Publication No. 47-18573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-39639, U.S. Pat. Nos. 3,026,215, 3,031,341, 3100194, 3242005. , No. 3,389,014.

Among the above-mentioned ferromagnetic powder, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of a ferromagnetic alloy fine powder can be used, and the following method can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, a metal carbonyl compound Pyrolysis method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, evaporation of the metal in a low pressure inert gas to produce a fine powder. How to get it. The ferromagnetic alloy powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it. Any of the method of forming the oxide film on the surface by adjusting the partial pressure of oxygen gas and the inert gas without using an organic solvent can be used. The ferromagnetic alloy powder preferably uses an oxide such as Y, Al, Si, or Nd as a sintering inhibitor, and particularly preferably an oxide of Y and Al, the amount of which is 1 to 20% in atomic ratio with respect to Fe, It is preferably 3 to 12%. These sintering inhibitors are generally used in combination, and their ratio is optimally set according to the purpose.
If the ferromagnetic powder particles are expressed by the BET specific surface area, it is 25
˜80 m ² / g, preferably 40 to 70 m ² / g. Below 25m ² / g, the noise becomes high, 80m ² / g
The above is not preferable because the surface property is difficult to obtain. Σ _{s of} iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu
/ G or more, and 100e in the case of ferromagnetic metal fine powder
It is preferably mu / g or more, more preferably 110 emu / g.
It is g to 170 emu / g. The coercive force is preferably 500 to 3000 Oe, more preferably 800 to 2500 Oe or less.

The tap density of γ-iron oxide is preferably 0.5 g / cc or more, more preferably 0.8 g / cc or more.
In the case of alloy powder, 0.2 to 0.8 g / cc is preferable and 0.
If it is used at 8 g / cc or more, oxidation easily proceeds in the consolidation process of the ferromagnetic powder, and it becomes difficult to obtain a sufficient σ _S.
If it is 0.2 g / cc or less, the dispersion tends to be insufficient. γ
When iron oxide is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%.
%. Also, the amount of cobalt atom to iron atom is 0 to
It is 15%, preferably 2-8%.

Hexagonal plate-shaped hexagonal ferrite can be used for the magnetic layer of the present invention. As the hexagonal ferrite, barium ferrite, strontium ferrite, lead ferrite, calcium ferrite substitutes, Co substitutes, and hexagonal Co powder can be used. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, and magnetoplumbite-type barium ferrite and strontium ferrite that partially contain a spinel phase.In addition, anisotropy control and magnetization control , For controlling distribution, controlling temperature characteristics, etc.
Al, Si, S, Sc, T in addition to predetermined atoms depending on the purpose
i, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, Pr, Nd, P, Co, M
Atoms such as n, Zn, Ni, Sr, B, Ge and Nb can be added. Generally, Co-Ti, Co-Ti-
Zr, Co-Ti-Zn, Ni-Ti-Zn, Ir-Z
It is possible to use those to which an element such as n is added, but particularly preferable are Co or Ti substitution products of barium ferrite and strontium ferrite. When the SFD in the longitudinal direction of the magnetic layer is 0.3 or less, the distribution of coercive force becomes small, which is preferable. To control the coercive force,
Methods such as controlling the particle diameter and particle thickness, making the thickness of the spinel phase of hexagonal ferrite constant, making the amount of substitution elements of the spinel phase constant, making the place of the substitution site of the spinel phase constant, etc. is there.

The particle size of the hexagonal ferrite used in the present invention means the plate width of hexagonal plate-like particles and is measured by using an electron microscope. In the present invention, the particle diameter (plate diameter) is 0.
01-0.2 μm, particularly preferably 0.03-0.1 μm
It is specified in the range of m. Further, the average thickness (plate thickness) of the fine particles is 0.001 to 0.2 μm, and particularly preferably 0.003 to 0.05 μm. Furthermore, the plate ratio (particle size / plate thickness) is 1 to 15, preferably 3 to 7. The specific surface area (S _BET ) of these hexagonal ferrite magnetic materials by the BET method is usually 25 to 100 m ² /
g, preferably 40 to 70 m ² / g. 25m ² /
If it is less than g, noise becomes high, and if it is more than 100 m ² / g, it is difficult to obtain surface properties, which is not preferable. The coercive force of the hexagonal ferrite magnetic material is preferably 1000 to 4000 Oe,
More preferably, it is 1200 to 3000 Oe. 10
When it is less than 00 Oe, the short wavelength output is lowered, and when it is 4000 Oe or more, recording by a head is difficult and it is not preferable. σ _S
Is 50 emu or more, preferably 60 emu / g or more. The tap density is preferably 0.5 g / cc or more, and 0.
It is more preferably 8 g / cc or more.

The other preferable ranges of the ferromagnetic powder contained in the magnetic layer of the present invention are as follows. Crystallite size is 50-450Å, preferably 100-35
It is 0Å. R1500 of the ferromagnetic powder is preferably 1.5 or less. More preferably r1500 is 1.0
It is the following. r1500 indicates the percentage of the amount of magnetization remaining without being reversed when a magnetic field of 1500 Oe is applied in the opposite direction after the magnetic recording medium is saturated. The water content of the ferromagnetic powder is preferably 0.01 to 2%.
The water content of the ferromagnetic powder is preferably optimized depending on the type of binder. The pH of the ferromagnetic powder is preferably optimized by combining with the binder used. Its range is from 4 to 12, preferably from 6 to 10. The ferromagnetic powder may be surface-treated with Al, Si, P, or an oxide thereof, if necessary. Surface treatment with Al ₂ O ₃ or SiO ₂ is preferable, and it is preferable to change the amount and ratio depending on the binder used.
The amount is 0.1-10% with respect to the ferromagnetic powder, and when surface-treated, adsorption of lubricants such as fatty acids is 100 mg / m
^It is preferably ² or less, which is preferable. Soluble Na in ferromagnetic powder,
Inorganic ions such as Ca, Fe, Ni, and Sr may be contained, but if it is 500 ppm or less, the characteristics are not particularly affected. The ferromagnetic powder used in the present invention preferably has few voids, and the value is 20% by volume or less, more preferably 5% by volume or less.

The Br of the magnetic layer of the present invention is usually from 1000 to 1,000.
4000G, preferably 1500-4000G,
The SFD is preferably 0.6 or less. Next, the lower non-magnetic layer will be described. The inorganic non-magnetic powder used in the lower non-magnetic layer of the present invention can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like. . Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide having an α conversion rate of 90% or more. Silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide,
Boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred is titanium dioxide,
Zinc oxide, iron oxide and barium sulfate are preferable, and titanium dioxide is more preferable. The particle size of these non-magnetic powders is preferably 0.005 to 2 μ, but if necessary, non-magnetic powders having different particle sizes may be combined, or a single non-magnetic powder may have a wide particle size distribution to achieve the same effect. You can also Especially preferred is 0.01 μ to 0.2
is μ. The crystallite size of the inorganic non-magnetic powder is 10 to 1
000Å is preferable. Tap density is 0.05-2g / c
c, preferably 0.2 to 1.5 g / cc. The water content is 0.1 to 5%, preferably 0.2 to 3%. pH 2
However, the range of 6 to 9 is particularly preferable. The specific surface area is 1 to 100 m ² / g, preferably 5 to 50 m ² / g, more preferably 7 to 40 m ² / g. Crystallite size is 0.01μ
˜2 μ is preferable. The oil absorption using DBP is 5-100 ml /
100g, preferably 10-80ml / 100g, more preferably 2
It is 0 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be needle-like, spherical, polyhedral or plate-like. The ignition loss is preferably 20% or less. The inorganic non-magnetic powder model used in the present invention
A hardness of 4 to 10 is preferable. The roughness factor of these powder surfaces is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. The amount of stearic acid (SA) adsorbed is 1 to 20 μmol / m ² , and more preferably ² to 15 μmol / m ² . Lower non-magnetic inorganic powder 2
Wet heat to water at 5 ℃ is 200erg / cm ^{2 to} 600erg / cm 2
It is preferably in the range of ² . In addition, a solvent having a heat of wetting in this range can be used. 100-400
A suitable amount of water molecules on the surface at 1 ° C is 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 6. The surface of these powders is Al ₂ O ₃ , SiO ₂ , T
Surface treatment with iO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO is preferred. Especially preferred for dispersibility is Al
₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ are preferable, but Al ₂ O ₃ , SiO ₂ , and ZrO ₂ are more preferable. These may be used in combination, or may be used alone. Depending on the purpose, a co-precipitated surface treatment layer may be used, or a structure in which the surface layer is first treated with alumina and then the surface layer is treated with silica, or the reverse structure may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that it is homogeneous and dense.

Specific examples of the inorganic non-magnetic powder used in the present invention include UA5600 and UA56 manufactured by Showa Denko.
05, Nanotite, Sumitomo Chemical AKP-20, AKP-
30, AKP-50, HIT-55, HIT-100,
ZA-G1, manufactured by Nippon Kagaku Kogyo G5, G7, S-1,
Toda Kogyo TF-100, TF-120, TF-1
40, R516, DPN250, DPN250BX, TTO-51B, TTO-55A, TTO-5 manufactured by Ishihara Sangyo.
5B, TTO-55C, TTO-55S, TTO-55
D, FT-1000, FT-2000, FTL-10
0, FTL-200, M-1, S-1, SN-100,
R-820, R-830, R-930, R-550, C
R-50, CR-80, R-680, TY-50, Titanium Industry ECT-52, STT-4D, STT-30
D, STT-30, STT-65C, Mitsubishi Materials T-1, Nippon Shokubai NS-O, NS-3Y, NS-8Y,
MT-100S, MT-100T, MT-15 manufactured by Teika
0W, MT-500B, MT-600B, MT-100
F, Sakai Chemical FINEX-25, BF-1, BF-1
0, BF-20, BF-1L, BF-10P, Dowa Mining DEFIC-Y, DEFIC-R, Titanium Industry Y-
LOP and the thing which baked it.

Since titanium dioxide is a particularly preferred inorganic non-magnetic powder, the production method will be described in detail by taking titanium dioxide as an example. The methods for producing these titanium oxides are mainly the sulfuric acid method and the chlorine method. In the sulfuric acid method, the source ore of illuminite is cooked with sulfuric acid,
Extract Ti, Fe, etc. as sulfates. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration.
Thermal hydrolysis is performed to precipitate the hydrous titanium oxide.
After this is filtered and washed, impurities are washed and removed, and a particle size adjusting agent and the like are added, and then calcined at 80 to 1000 ° C. to obtain crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the nucleating agent added at the time of hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. In the chlorine method, natural or synthetic rutile is used as the raw ore. Ore is chlorinated in the reduced state at high temperature, Ti is TiC
Fe becomes FeCl _{2 in} l ₄ , and the iron oxide which is solidified by cooling is separated from liquid TiCl ₄ . The crude T obtained
iCl ₄ was purified by rectification and then added with a nucleating agent to give 1
Instantly react with oxygen at a temperature of 000 ° C. or higher to obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method. For the surface treatment, after coarsely pulverizing the titanium oxide material, water and a dispersant are added, wet pulverization and centrifugation are performed to perform coarse particle classification. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al, Si, Ti, Zr, Sb, S
An aqueous solution of salts such as n and Zn is added to neutralize the acid,
Alternatively, alkali is added to cover the surface of the titanium oxide particles with the hydrous oxide produced. By-produced water-soluble salts are removed by decantation, filtration and washing, and finally the slurry pH is adjusted and filtered, followed by washing with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product. Further, not only the water system but also the titanium oxide powder can be subjected to AlCl ₃ and SiCl ₄ vapors, and then steam can be introduced to perform the Al and Si surface treatment. For other pigment manufacturing methods, see "Characte
Rization of Powder Surface
s "Academic Press can be referred to.

Spherical titanium dioxide can be obtained by the above method.

Further, carbon black can be mixed in the lower layer to reduce Rs, which is a known effect. For this purpose, a furnace for rubber, a thermal for rubber, a black for color, acetylene black, etc. can be used. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400 m ² / g, DBP oil absorption is 20-400 ml /
The amount is 100 g, preferably 30 to 200 ml / 100 g. The particle size is 5 to 80 mμ, preferably 10 to 50 mμ, and more preferably 10 to 40 mμ. pH is 2-1
0, water content is 0.1-10%, tap density is 0.1-1
g / cc is preferred. A specific example of the carbon black used in the present invention is BLACK manufactured by Cabot Corporation.
PEARLS 2000, 1300, 1000, 90
0, 800, 880, 700, VULCAN XC-7
2, Mitsubishi Kasei Kogyo Co., Ltd., # 3050B, 3150B, 3
250B, # 3750B, # 3950B, # 950, #
650B, # 970B, # 850B, MA-600, Columbia Carbon Co., CONDUCTEX SC, R
AVEN 8800,8000,7000,5750,
5250, 3500, 2100, 2000, 1800,
1500, 1255, 1250, Ketjen Black EC manufactured by Akzo and the like. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the paint.
5% of these carbon blacks are added to the above inorganic powder.
It can be used within a range not exceeding 0% by weight and not exceeding 40% by weight of the total weight of the non-magnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

The organic inorganic powder used in the present invention is acrylic styrene resin powder, benzoguanamine resin powder,
Examples include melamine-based resin powder and phthalocyanine-based pigment, polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder,
Polyfluorinated ethylene resin is used. As the manufacturing method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

It is to be noted that an undercoat layer is provided in a general magnetic recording medium, but this is provided in order to improve the adhesive force between the support and the magnetic layer, and the thickness is 0. It is less than 0.5 μm, which is different from the lower layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesiveness between the underlayer and the support. Binder, lubricant, dispersant, additive, solvent for the lower non-magnetic layer,
For the dispersion method and the like, that of the magnetic layer can be applied. In particular, with regard to the amount and kind of binder, the amount and kind of additive and dispersant added, known techniques for the magnetic layer can be applied. The thickness of such a lower non-magnetic layer is 0.2 to 5 μ, preferably 1 to
3μ.

The non-magnetic layer in the present invention is mainly composed of the inorganic non-magnetic powder as described above, and even if a small amount of magnetic material is contained within the range in which the effect of the present invention is exhibited. It belongs to the category of the non-magnetic layer of the invention. A small amount of magnetic material is 20 for inorganic non-magnetic powder.
% By weight or less. If it exceeds 20% by weight, the effect of the present invention is lost.

As the binder used in the upper and lower layers of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,000 to 200,000, preferably 100.
The degree of polymerization is about 100 to 100,000 and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid,
Acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

Further, as the thermosetting resin or the reaction type resin, a phenol resin, an epoxy resin, a polyurethane curing type resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. For these examples and the manufacturing method thereof, see JP-A-62-256219.
Are described in detail in.

The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol.
Resin, vinyl chloride / vinyl acetate / maleic anhydride copolymer, a combination of at least one selected from the group and a polyurethane resin, or a combination of these with polyisocyanate.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate carbonate polyurethane, polyester polycarbonate carbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, in order to obtain better dispersibility and durability, -COO is added as necessary.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2, -
From O—P═O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), an epoxy group, SH, CN, etc. It is preferable to use one having at least one selected polar group introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbite Corporation.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, ZEON Corporation MR-105, MR110, MR1
00, 400X-110A, Nippon Polyurethane Co., Ltd. Nipporan N2301, N2302, N2304, Dainippon Ink and Chemicals Pandex T-5105, T-R3080,
T-5201, Barnock D-400, D-210-8
0, Crisbon 6109, 7209, Toyobo Co., Ltd. Byron UR8200, UR8300, UR-8600, UR
-5500, UR-4300, RV530, RV28
0, manufactured by Dainichiseika, Daiferamine 4020, 502
0,5100,5300,9020,9022,702
0, Mitsubishi Kasei Co., MX5004, Sanyo Kasei Co., Ltd. Sampren SP-150, TIM-3003, TIM-300
5, Asahi Kasei Corp. Saran F310, F210 and the like.

The binder used in the magnetic layer of the present invention is a ferromagnetic powder, and when a lower layer is provided, the binder used in the lower non-magnetic layer is an inorganic non-magnetic powder.
It is used in the range of 5 to 50% by weight, preferably 10 to 30% by weight. 5 when using vinyl chloride resin
-30% by weight, 2-2 when polyurethane resin is used
It is preferable to use 0% by weight and polyisocyanate in the range of 2 to 20% by weight in combination. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 100 ° C., the elongation at break is 100 to 2000% by weight, the stress at break is 0.05 to 10 Kg / cm ² , and the yield point is 0.05 to 10 Kg / cm. ² is preferred.

When the magnetic recording medium of the present invention comprises two or more layers, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, and the amount of each resin. It is of course possible to change the molecular weight, the amount of polar group, or the physical properties of the resin described above, for example, by using the lower non-magnetic layer or the upper magnetic layer, and known techniques relating to multilayer media can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the upper magnetic layer in order to reduce scratches on the surface of the upper magnetic layer, and to improve the head touch to the head, lower layer This is achieved by increasing the amount of binder in the non-magnetic layer to give flexibility.

Polyisocyanate used in the constituent layer of the present invention
As tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o- Isocyanates such as toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate; products of these isocyanates with polyalcohol; and isocyanates. Polyisocyanate produced by condensation can be used. Commercially available product names of these isocyanates include:
Nippon Polyurethane Co., Coronate L, Coronate H
L, Coronet 2030, Coronet 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Takenet D-102, Takenet D-110N, Takenet
D-200, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodul L, Desmodule IL, Desmodule N, Desmodule HL, etc., and these may be used alone or with different curing reactivity. It can be used for each layer in two or more combinations.

The carbon black used in the magnetic layer of the present invention may be a furnace for rubber, thermal for rubber, black for color, acetylene black or the like. Specific surface area is 5-500 m ² / g, DBP oil absorption is 1
0-400ml / 100g, particle size 5mμ-300m
It is preferable that μ, pH is 2 to 10, water content is 0.1 to 10%, and tap density is 0.1 to 1 g / CC. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 1300 manufactured by Cabot Corporation.
1000, 900, 800, 700, VULCAN X
C-72, Asahi Carbon Co., Ltd., # 80, # 60, # 55,
# 50, # 35, Mitsubishi Kasei Co., Ltd., # 2400B, #
2300, # 900, # 1000, # 30, # 40, #
10B, Columbia Carbon Co., CONDUCTEX
SC, RAVEN 150, 50, 40, 15 and the like. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the amount of the ferromagnetic powder. Carbon black has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving the film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have an upper magnetic layer,
It is of course possible to change the type, amount and combination of the lower non-magnetic layer, and to use the lower non-magnetic layer properly according to the purpose based on the above-mentioned various characteristics such as particle size, oil absorption, electric conductivity and pH. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Society.

Specifically, the abrasive used in the present invention includes α-alumina, β-alumina having an α conversion rate of 90% or more,
Silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Corundum, artificial diamond, silicon nitride, silicon carbide,
Known materials having a Mohs hardness of 6 or more, such as titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. A composite of these abrasives (abrasive surface-treated with other abrasives)
May be used. These abrasives may contain compounds or elements other than the main component, but the main component is 90%.
If it is above, there is no change in the effect. The particle size of these abrasives is preferably 0.01 to 2 μm, and particularly preferably 0.1 to 0.3 μm. If necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution to obtain the same effect. Tap density is 0.3-2 g / cc, water content is 0.1-5
%, PH 2 to 11, and specific surface area 1 to 30 m ² / g are preferable. The abrasive used in the present invention may have any of a needle shape, a granular shape, a spherical shape, and a dice shape, but those having a corner in a part of the shape have high abradability and are preferable. Specific examples of the polishing agent used in the present invention include those manufactured by Sumitomo Chemical Co., Ltd .:
AKP-20, AKP-30, AKP-50, HIT-
50, HIT100, manufactured by Nippon Kagaku Kogyo Co., Ltd .: G5, G7,
S-1, Toda Kogyo KK: TF-100, TF-140 and the like. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.
The number of abrasives present on the magnetic layer surface and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5 pieces / 100 μm ² or more.

Other additives used in the magnetic layer or non-magnetic layer of the present invention include a lubricating effect, an antistatic effect,
Those having a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide, graphite,
Boron nitride, fluorinated graphite, silicone oil, polar group silicone, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate ester and its alkali metal salt, alkyl sulfate ester and Its alkali metal salt, polyphenyl ether,
Fluorine-containing alkyl sulfate and its alkali metal salt, monobasic fatty acid having 10 to 24 carbon atoms (it may contain an unsaturated bond or may be branched), and these metal salts (Li, Na, K, Cu, etc.), or a monovalent, divalent, trivalent, tetravalent, pentavalent or hexavalent alcohol having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched), carbon Alkoxy alcohol having 12 to 22 carbon atoms, monobasic fatty acid having 10 to 24 carbon atoms (may contain an unsaturated bond or may be branched)
And a monovalent, divalent, trivalent, tetravalent, pentavalent, or hexavalent alcohol having 2 to 12 carbon atoms (including an unsaturated bond,
Also, it may be branched) and a monofatty acid ester or a difatty acid ester or a trifatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, a fatty acid amide having 8 to 22 carbon atoms,
Aliphatic amines having 8 to 22 carbon atoms can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, myristin. Examples thereof include octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol and lauryl alcohol.

Further, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfonium, anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group, amino acid, aminosulfonic acid, sulfuric acid of aminoalcohol, or the like. Amphoteric surfactants such as phosphoric acid esters and alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

The types and amounts of these lubricants and surfactants used in the present invention can be properly selected in the non-magnetic layer and the magnetic layer. For example, to control bleeding to the surface using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface using esters with different boiling points and polarities, and to adjust the amount of surfactant. It is conceivable that the coating stability will be improved, the amount of the lubricant added will be increased in the non-magnetic layer to improve the lubrication effect, and the invention is not limited to the examples shown here.

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

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

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

The non-magnetic support (also simply referred to as "support") used in the present invention is polyethylene terephthalate,
Known films such as polyesters such as polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide, polybenzoxazole, etc. Can be used,
Especially when using a thin support having a thickness of 10 μm or less,
It is preferable to use a high strength support such as polyethylene naphthalate or polyamide. Further, in order to change the surface roughness of the magnetic surface and the base surface, if necessary, it is possible to use the method described in JP-A-3-2241.
It is also possible to use a laminated type support as shown in 27. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance.

An undercoat layer may be provided between the non-magnetic support and the lower layer to improve the adhesion. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm
m. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1
˜2 μm, preferably 0.3 to 1.0 μm. Known layers can be used as the undercoat layer and the backcoat layer.

The non-magnetic support used in the present invention preferably has no coarse protrusions of 1 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the support, if necessary. As an example of these fillers, Ca,
In addition to oxides and carbonates such as Si and Ti, organic fine powders such as acrylics can be used. Maximum height Rma of the support
x is 1 μm or less, ten-point average roughness Rz is 0.5 μm or less,
The center plane peak height Rp is 0.5 μm or less, the center line valley depth R
v is preferably 0.5 μm or less. The surface protrusions of these supports can be controlled by a filler in the range of 0.01 to 1 μm and 0 to 2000 per 0.1 mm ² .

The heat shrinkage ratio of the support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat at 80 ° C. for 30 minutes. The shrinkage ratio is preferably 1% or less, more preferably 0.
It is 5% or less. Breaking strength is 5-100 kg in both directions
/ Mm ² , and the elastic modulus is preferably 100 to 2000 Kg / mm ² .

The step of producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each step may be divided into two or more steps. All raw materials such as ferromagnetic powder, inorganic non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent, etc. used in the present invention may be added at the beginning or in the middle of any step. Absent. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong force such as a continuous kneader or a pressure kneader is used. It is preferable to use one having kneading power. When a continuous kneader or a pressure kneader is used, the ferromagnetic powder or the inorganic non-magnetic powder and all or part of the binder (however, 30% by weight or more of the total binder is preferable) and 100 parts by weight of the ferromagnetic powder are used. Kneading is performed in the range of 15 to 500 parts by weight. Details of these kneading treatments are described in JP-A-1-166338 and JP-A-64-79274.
It is described in. Further, when adjusting the non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are suitable.

The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. First, the lower layer is coated by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for coating a magnetic coating, and when the lower layer is in a wet state, Japanese Examined Patent Publication No. 60-238
179, the upper layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-A-2-265672.

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

In order to prevent the deterioration of the electromagnetic conversion characteristics and the like of the magnetic recording medium due to the aggregation of the ferromagnetic powder, Japanese Patent Laid-Open No. Sho 62-62
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in Japanese Patent Application Laid-Open No. 95174/1992 or Japanese Patent Laid-Open No. 1-236968. Further, the viscosity of the coating liquid needs to satisfy the numerical range disclosed in JP-A-3-8471.

The orienting device used in the production of the present invention may be a known one, but generally 100
A cobalt magnet or solenoid of 0 to 10000G is used. Specifically, a homopolar facing cobalt magnet, a solenoid magnet, and a superconducting magnet are preferable. Further, it is preferable to perform appropriate preliminary drying so that the coating film is dried near the exit of the oriented magnet zone. The coating speed is 20 to 1000 m /
The temperature of minute and dry air is preferably 60 ° C. or higher.

Examples of the calendering roll used in the production of the present invention include heat-resistant plastic rolls or metal rolls such as epoxy, polyimide, polyamide and polyimideamide. Comrades,
Metal rolls, or a combination of plastic and metal rolls are used. The treatment temperature is preferably 70 ° C or higher, more preferably 80 ° C or higher. The linear pressure is preferably 200 Kg / cm to 500 Kg / cm, more preferably 300 Kg / cm to 500 Kg / cm.

The elastic modulus of the magnetic layer of the present invention at 0.5% elongation is preferably 100 to 2000K in both the running direction and the width direction.
g / mm ² , breaking strength is preferably 1 to 30 Kg / c
m ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1500 Kg / mm ^{2 in} both the running direction and the width direction, the residual spread is preferably 0.5% or less, and the heat shrinkage rate at any temperature of 100 ° C. or less is preferably It is 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. Glass transition temperature of magnetic layer (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is 50 ° C. or higher 12
0 ° C or lower is preferable, and that of the lower nonmagnetic layer is 0 ° C to 10 ° C.
0 ° C is preferred. Loss elastic modulus is 1 × 10 ⁸ to 8 × 10 ⁹ dy
It is preferably in the range of ne / cm ² and the loss tangent is 0.2
The following is preferred. If the loss tangent is too large, adhesive failure will occur easily. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
/ M ² or less. It is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer. The porosity is preferably 30% by volume or less for both the lower non-magnetic layer and the magnetic layer.
More preferably, it is 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, the running durability is often preferable when the porosity is large.

The maximum height Rmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, the center line peak height Rp is 0.3 μm or less, and the center line valley depth Rv is 0.3 μm.
Hereinafter, the surface protrusions of the magnetic layer having a size of 0.01 μm to 1 μm can be changed as needed in the range of 0 to 2000 per 1 mm ₂ . These can be easily controlled by a surface control by a filler of the support or a roll surface shape of calendar treatment.

The magnetic recording medium of the present invention preferably has a lower non-magnetic layer and an upper magnetic layer, but it is easily presumed that the physical properties of the lower layer and the upper layer can be changed according to the purpose. is there. For example, the elastic modulus of the upper layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the upper layer to improve the contact of the magnetic recording medium with the head.

[0059]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. Lower non-magnetic coating material X: Inorganic non-magnetic powder: TiO ₂ crystalline rutile 80 parts Average primary particle diameter 0.020 μm, specific surface area by BET method 60 m ² / g pH 7 TiO ₂ content 90% or more, surface treatment agent Al ₂ O ₃ 8% by weight carbon black 20 parts Average primary particle size 16 nm DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer 12 parts -SO ₃ Na content: 1 × 10 ^-4 eq / g Polymerization degree 300 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Magnetic paint Y: Ferromagnetic metal Powder 100 parts Composition Fe / Co = 80/20 Hc 2100Oe, a specific surface area of 61m ² / g Crystallite size 195Å by the BET method, sintering inhibitor Y ₂ O ₃ 8 wt%, Al ₂ O ₃ 6 wt%, SiO ₂ 0. 2% by weight Particle size (major axis length) 0.08 μm, acicular ratio 4, σ _S 140 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na content: 1 × 10 ⁻⁴ eq / g, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (particle size 0.15 [mu] m) 5 parts Carbon black (particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts Magnetic paint Z: Hexagonal Balimum ferrite 100 parts Hc 2100 Oe, by BET method a specific surface area of 40 m ² / g average particle size (plate diameter) 0.05 .mu.m, the average thickness 0.01μm σ _S 60emu / g, surface treated Al ₂ O ₃ 5 wt%, SiO ₂ 2 wt% vinyl chloride copolymer 12 parts -SO ₃ Na ^{content: 1 × 10 -4 eq / g} , polymerization degree 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (particle size 0.3 [mu] m) 5 parts mosquitoes - carbon black (particle size 0.015 .mu.m) 5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts For each of the above three paints, each component was continuously dipped.
After kneading with a dough, it was dispersed using a sand mill. Polyisocyanate was added to the obtained dispersion liquid as the lower non-magnetic coating material X.
5 parts to the coating solution of No. 4 and 4 parts to each of the magnetic paint Y and the magnetic paint Z, 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone were further added, and the mixture was filtered using a filter having an average pore size of 1 μm, Non-magnetic paint X and magnetic layer forming paints Y and Z were prepared.

Examples 1 to 3 The thickness of the lower non-magnetic coating material X after drying was 2.0 μm, and the thickness of the magnetic layer after drying the magnetic coating material Y was 0.
The simultaneous multilayer coating by the extrusion method was applied to a polyethylene naphthalate support having a thickness of 5 μm and a center line surface roughness of 0.005 μm so that the thickness was 2 μm.
In minutes (this coating method is A). This non-magnetic support contains 0.2 μm spherical silica as a filler,
Having been subjected strongly stretched in the transverse direction during film, F5 value in the longitudinal direction 14 kg / mm ^2, and a width direction 16 Kg / mm ^2. Subsequently, it was longitudinally oriented with a homopolar facing cobalt magnet having a magnetic force of 2000 G and then dried. After that, the temperature of 90
Processing was carried out at ℃, slitting to a width of 8mm, 8mm video tape was manufactured. The obtained sample was designated as A-1 (described in Table 1). Next, samples obtained in the same manner as in Example 1 except that the ferromagnetic metal fine powder of the magnetic coating material Y of Example 1 had an acicular ratio of 6 and 8 were designated as A-2 and A-3.

Comparative Example 1 A sample obtained in the same manner as in Example 1 except that the ferromagnetic metal fine powder had an acicular ratio of 10 was designated as B-1. Examples 4 and 5 Samples obtained in the same manner as in Example 1 except that the strength of the oriented magnet was 4000 G and 1000 G in Example 1 were A.
-4 and A-5.

Examples 6 and 7 Spherical α-iron oxide (average primary particle diameter 0.04 μm, BE as the inorganic non-magnetic powder of the lower non-magnetic coating material X in Example 1)
Example 1 except that a specific surface area according to the T method of 40 m ² / g, pH 7, surface treatment agent Al ₂ O ₃ 2% by weight) was used.
Sample obtained in the same manner as in A-6, needle-shaped α iron oxide (long axis length 0.15 μm, short axis length 0.03 μm, B
Example 1 except that a specific surface area by the ET method of 50 m ² / g, pH 7, and a surface treatment agent Al ₂ O ₃ 4% by weight) were used.
A sample obtained in the same manner as above was designated as A-7.

[0063] The support was further strengthened F5 value stretching in the width direction in Examples 8 and 9 Example 1 longitudinal 13 kg / mm ^2, and the width direction 17Kg / mm ^2, a longitudinal direction 12 Kg / mm ^2, the width direction 18Kg / Mm
Samples obtained in the same manner as in Example 1 except that the support No. ² was used were designated as A-8 and A-9.

[0064] Comparative Examples 2 and 3 Example 1 in the longitudinal direction and the width direction longitudinal 15 Kg / mm ² equally performs F5 value stretching, widthwise 15 Kg / mm ²
And the support, the longitudinal 17Kg / mm ² the F5 value strengthened longitudinal stretching, the sample obtained except for using a support which is in the width direction 13 kg / mm ² in the same manner as in Example 1 B- 2 and B-3.

Examples 10 and 11 In Example 1, the magnetic coating material Y was coated on the support without using the coating material X so that the dry film thickness was 2.5 μm (this coating method is referred to as B). A-10 was used as the sample obtained in the same manner as in Example 1 except that the coating was directly applied using, and the slit clearance of the upper layer of the extrusion coating head of Comparative Example 1 was allowed to have a periodic minute fluctuation within ± 5. A sample obtained in the same manner as in Comparative Example 1 except for the above was designated as A-11 (this coating method is designated as C).

Example 12 A-12 was prepared as in Example 1 except that the magnetic paint Z was used instead of the magnetic paint Y of Example 1.
And Comparative Example 4 A sample obtained in the same manner as in Example 10 except that the magnetic coating material Z in place of the magnetic coating material Y in Example 10 was used was B-
It was set to 4.

Example 13 In Example 1, the thickness of the non-magnetic support was 2.5 μm.
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that the thickness of the lower layer was 1.0 μm. The obtained sample was A-13. The samples obtained above were evaluated by the following, and the results are shown in Table 1.

[0068]

[Table 1] [Evaluation Method] (Center Line Average Surface Roughness) Using a stylus-type three-dimensional surface roughness meter (manufactured by Kosaka Laboratory), cutoff 0.08 mm, needle diameter 2 μm, needle pressure 70 mg, speed 0.1 mm / S, a measurement length (in the case of Ra1, measured in the longitudinal direction, in the case of Ra2, measured in the width direction) was measured 20 times at 0.5 mm, and the average value was obtained. (Electromagnetic conversion characteristics) Sony 8mm VCR EV
Using S900, the output of the 7.6 MHz carrier signal and the noise 1 MHz away from the carrier were measured, and the output and C /
I asked for N. As a standard, 8 mm tape SAGP6-120 manufactured by Fuji Photo Film Co., Ltd. was used. (Running property) 8mm video deck EVS90 made by Sony
Using 0, the tape was run for the entire length, the tape was observed every 20 passes, and the number of runs at which significant damage to the tape end portion was observed was determined.

It can be seen from Table 1 that the magnetic recording medium of the present invention exhibits excellent electromagnetic conversion characteristics and also has very good running properties.

[0070]

According to the present invention, the ratio (Ra2 / Ra1) of the centerline average surface roughness Ra1 in the longitudinal direction of the magnetic layer surface to the centerline average surface roughness Ra2 in the width direction of the magnetic layer surface is 1.2. ~
By setting 2.0, the medium layer thickness is particularly 3 to 10 μm.
Even if it is extremely thin, it is possible to secure the electromagnetic conversion characteristics and the running property, so that it is possible to record a high-density recording medium used in a consumer digital VTR system for a long time.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and at least one magnetic layer provided on the surface of the magnetic layer, measured with a stylus surface roughness meter at a cutoff of 0.08 mm. The ratio of the center line average surface roughness Ra1 to the center line average surface roughness Ra2 in the width direction of the magnetic layer surface (Ra2 /
Ra1) is 1.2 to 2.0. 2. A magnetic recording medium in which a nonmagnetic layer and a magnetic layer are formed in this order on a nonmagnetic support, and the magnetic property measured at a cutoff of 0.08 mm using a stylus type surface roughness meter. The ratio (Ra2 / Ra1) of the centerline average surface roughness Ra1 in the longitudinal direction of the layer surface and the centerline average surface roughness Ra2 in the width direction of the magnetic layer surface is 1.2 to 2.0. Magnetic recording medium. 3. A magnetic recording medium in which a non-magnetic layer and a magnetic layer are formed in this order on a non-magnetic support, wherein the magnetic layer has a thickness of 0.05 to 1 μm and a stylus type. Ratio of the centerline average surface roughness Ra1 in the longitudinal direction of the magnetic layer surface and the centerline average surface roughness Ra2 in the width direction of the magnetic layer surface measured at a cutoff of 0.08 mm using a surface roughness meter (Ra2 /
Ra1) is 1.2 to 2.0, and the total thickness of the magnetic recording medium is 3 to 10 μm.