JPH08306032A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having satisfactory electromagnetic transducing characteristics, running performance and preservation stability. CONSTITUTION: A lower layer contg. inorg. powder dispersed in a binder is formed on a substrate and a magnetic layer as an upper layer contg. ferromagnetic powder dispersed in a binder is formed on the lower layer to obtain the objective magnetic recording medium. The dry thickness of the magnetic layer is <=1.0μm, the inorg. powder in the lower layer has a Mohs hardness of >=3 and the lower layer contains a P-contg. org. compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having a very thin magnetic layer of 1.0 μm or less. More specifically, it relates to a coating type magnetic recording medium for high density recording.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks and the like. Magnetic recording media are becoming denser year by year and the recording wavelength is becoming shorter, and the recording method is being studied from analog method to digital method. In order to meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer have been proposed. Thus, a so-called coating type magnetic recording medium coated on a support is excellent. However, since the coating type medium has a low filling degree of the magnetic substance with respect to the metal thin film, the electromagnetic conversion characteristics are inferior. Coated magnetic recording media include ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, Cr
A magnetic layer in which O ₂ , a ferromagnetic alloy powder or the like is dispersed in a binder, and which is coated on a non-magnetic support is widely used.

Various methods have been proposed for improving the electromagnetic conversion characteristics of a coating type magnetic recording medium, such as improving the magnetic characteristics of a ferromagnetic powder and smoothing the surface. Is not enough. Further, in recent years, the recording wavelength has tended to become shorter as the recording density becomes higher, and the problems of self-demagnetization loss during recording and thickness loss during reproduction, in which the output decreases when the thickness of the magnetic layer is large, are becoming more serious. .

For this reason, the magnetic layer is made thinner. However, if the magnetic layer is thinned to about 2 μm or less, the influence of the nonmagnetic support tends to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics and dropout Tend to worsen. For this reason, as described in JP-A-57-198536, if the nonmagnetic thick undercoat layer is provided on the support surface and then the magnetic layer is provided as the upper layer, the influence of the surface roughness of the support is reduced. However, there is a problem that the wear and durability of the head are not improved. Conventionally, since a thermosetting resin is used as a binder as the non-magnetic lower layer, the lower layer is cured, and friction between the magnetic layer and the head and contact with other members are performed in an unbuffered state. This is considered to be due to the fact that the magnetic recording medium having such a lower layer has a little poor flexibility. 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, when the lower layer is applied and dried and then the magnetic layer is applied as the upper layer, the lower layer is coated with the upper layer coating solution. It swells with an organic solvent and causes an effect such as causing a turbulent flow in the upper layer coating solution, thereby deteriorating the surface properties of the magnetic layer and deteriorating electromagnetic conversion characteristics. Further, in order to make the magnetic layer thinner, it is conceivable to reduce the coating amount or to reduce the concentration by adding a large amount of solvent to the magnetic coating liquid. In the former case, if the amount of application is reduced, there is not enough time for leveling after application, and drying starts, so that application defects, for example, a problem such as streaks or engraved patterns remain, and the yield is extremely poor. . When the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids, and sufficient filling properties of the magnetic substance cannot be obtained. Causes various adverse effects, such as insufficient strength. JP-A-62-154
In the invention of Japanese Patent No. 225, such a poor yield was a major problem.

[0005] The present applicant has disclosed one of the means for solving these problems as disclosed in JP-A-63-191315 and JP-A-63-191315.
A method of providing a non-magnetic layer as a lower layer using the simultaneous multilayer coating method as described in each publication of 187418, and providing an upper magnetic layer containing a ferromagnetic powder while the lower layer is in a wet state is adopted. By doing so, there are no coating defects, excellent productivity, and reproduction output, electromagnetic conversion characteristics such as C / N,
A magnetic recording medium that can improve running durability was proposed.

However, even if such a method is applied, the following problems cannot be solved.
In the above-mentioned simultaneous multi-layer coating technique, it is considered that the powder used in the lower layer in order to smooth the magnetic surface can be made into fine particles to secure the surface property of the lower layer and improve the surface property of the magnetic layer. .. However, when such fine particles are used, there is a problem that the fine particles are easily aggregated, and the surface properties of the lower layer are rather deteriorated and the surface properties of the magnetic layer are deteriorated. The problem is that even if the magnetic layer is further thinned to improve the electromagnetic conversion characteristics, it is difficult to control the interface between the magnetic layer and the lower layer due to poor dispersibility of the powder in the lower layer. There is also a problem that a uniform magnetic layer cannot be obtained. Further, since the surface area of the fine particles is large, the lubricant contained in the magnetic layer or the non-magnetic layer is adsorbed or absorbed, and the amount of the lubricant on the surface of the magnetic layer is significantly reduced. Accordingly, there is a problem that jitter and still life decrease due to an increase in the friction coefficient of the magnetic recording medium become apparent.

In order to improve the dispersibility of the non-magnetic powder, the surface of the non-magnetic powder is treated with a conventionally known treatment agent such as TiO 2.
₂ , for non-magnetic powders such as silica, pentaerythritol,
Known methods include treatment with polyols such as trimethylolpropane, organic acids such as fatty acids, alkanolamines such as triethanolamine and trimethylolamine, silicon resins, and silicon-based materials such as alkylchlorosilanes. The agent has a problem that the dispersibility is improved but the running property is not improved. Further, if a large amount of a lubricant is used to improve the running property, there is a problem that the coating film strength is reduced.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having good electromagnetic conversion characteristics and to provide a magnetic recording medium having good running properties and good storage stability. I do.

[0009]

The above objects of the present invention are as follows.
(1) A lower layer in which an inorganic powder is dispersed in a binder on a support
An upper magnetic layer, which is provided with ferromagnetic powder dispersed in a binder.
In a magnetic recording medium provided with a layer, the upper magnetic layer is dried.
The dry thickness is 1.0 μm or less, and
The mechanical powder has a Mohs hardness of 3 or more, and the lower layer is made of phosphorus.
Magnetic recording containing an organic compound containing (P)
It can be achieved by recording media. Preferred embodiments of the present invention are as follows.
It is as follows. (2) The organic compound containing phosphorus (P) is α-naphthyl
Acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethyl
Benzenephosphonic acid, phenylphosphonic acid, phenylphos
Characterized by at least one selected from sphinic acid
The magnetic recording medium according to (1) above. (3) A binder having an S-containing polar group as the binder
According to (1) above, which contains at least one kind.
Magnetic recording medium. (4) The binder having the S-containing polar group is -OSO.₃ M
Or -SO₃ M (for the above, M is a hydrogen atom or
Lucari metal) described in (1) above.
Magnetic recording medium. (5) The inorganic powder is TiO₂ (Rutile, Anata
ZE), TiO_X(1 ≦ x <2), cerium oxide, sulfur oxide
, Tungsten oxide, ZnO, ZrO₂ , SiO ₂ ,
Cr₂ O₃ , Α-alumina with α conversion rate of 90% or more, β-Al
Mina, γ-alumina, α-iron oxide, goethite, colander
Aluminum, silicon nitride, titanium carbide, magnesium oxide,
Boron nitride, molybdenum disulfide, copper oxide, MgCO₃ , C
aCO₃ , BaCO₃ , SrCO₃ , BaSO_Four , Carbonization
At least one selected from silicon and titanium carbide
The magnetic recording medium according to (1) above. (6) The ferromagnetic powder used in the magnetic layer is Fe or
Or a ferromagnetic alloy powder containing Ni or Co as a main component,
Choice from spherium ferrite and strontium ferrite
(1) characterized in that it is at least one
The magnetic recording medium described. (7) The ferromagnetic powder used in the magnetic layer is a predetermined source.
Other than child, Al, Si, S, Sc, Ti, V, Cr, C
u, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te,
Ba, Ta, W, Re, Au, Hg, Pb, Bi, L
a, Ce, Pr, Nd, P, Co, Mn, Zn, Ni,
Contain at least one atom selected from Sr and B
(6) The magnetic recording medium as described in (6) above. (8) The magnetic recording medium has a 0.5% elongation elastic modulus of 400.
~ 2000Kg / mm²The above characterized in that
The magnetic recording medium according to (1). (9) The elastic modulus of the support is 1 in both the running direction and the width direction.
00-2000Kg / mm² Before being characterized by
The magnetic recording medium according to item (1).

According to the present invention, the lower layer contains an organic compound containing phosphorus (P) (hereinafter, also referred to as "P-containing organic compound") to improve the dispersibility of the inorganic powder in the lower layer and improve the magnetic properties of the lower and upper layers. The amount of free fatty acids in the lower and upper magnetic layers can be reduced by easily controlling the interface with the layer and securing the surface properties of the upper magnetic layer and controlling the interaction between the inorganic powder and the fatty acids contained in the lower layer. By controlling this, the running durability of the upper magnetic layer is improved, and the electromagnetic conversion characteristics particularly in short-wavelength recording are improved. The present invention relates to a method in which an inorganic powder is contained in a lower coating liquid in order to provide an upper magnetic layer having a dry film thickness of 1 μm or less (hereinafter, also simply referred to as a magnetic layer or an upper layer) in a lower layer without coating defects. When used, the upper layer can be first coated on the support while the lower layer is wet. That is, the present invention provides a pinhole,
An object of the present invention is to provide a magnetic recording medium having an extremely thin magnetic layer which suppresses coating defects such as streaks and which is excellent in mass productivity, and which has performance comparable to a ferromagnetic metal thin film and excellent in running durability.

The P-containing organic compound used in the present invention comprises:
Those capable of adsorbing or reacting with the inorganic powder are preferred. That is, the present invention is intended to relatively reduce the ratio or probability of the adsorption state of the inorganic powder and the fatty acid by including the P-containing organic compound in the lower layer.
In other words, as a result, the ratio of fatty acids contained in the lower layer in the free state not adsorbed to the inorganic powder increases, and the fatty acids gradually seep out to the surface of the upper magnetic layer to improve the running property. To fulfill. Further, since the free fatty acid amount is larger than before, the absolute amount of the fatty acid contained in the magnetic recording medium can be reduced as compared with the related art,
As a result, it also has the effect of preventing adverse effects due to plasticization of the magnetic recording medium. Further, the inorganic powder supporting the P-containing organic compound has an effect of improving the dispersibility of the lower layer.

As the inorganic powder, metal oxides are particularly preferable, and TiO ₂ (rutile), α-Fe ₂ O ₃ ,
ZnO, CeO _{2 and the} like are preferable. As the fatty acid, a fatty acid conventionally used as a lubricant is used, and examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linoleic acid, and elaidic acid. The P-containing organic compound is not particularly limited as long as the above function is satisfied.
Preferably, an organic compound having a functional group capable of being firmly supported on the inorganic powder by forming a chemical bond by reacting with a functional group of the inorganic powder, for example, an OH group or the like, and more specifically, having a pKa of 3 or less Organic acid, an epoxy group-containing compound having a molecular weight of 3000 or less, a silane coupling agent, a surface treatment agent such as a titanate coupling agent, and the like, and these can be used alone or in combination.

The method of causing these P-containing organic compounds to adsorb or react with the lower inorganic powder is not particularly limited, and any means can be adopted. For example, before preparing the coating liquid, the organic compound and the inorganic powder are mixed in advance to adsorb or react the organic compound on the surface of the inorganic powder, and when the coating liquid is prepared, the inorganic powder and the binder are kneaded and dispersed. In that case, a method of adding an organic compound at an appropriate time and adsorbing and reacting with an inorganic powder can be mentioned.

The P-containing organic compound is preferably added before or simultaneously with the mixing and dispersion of the binder and the inorganic powder, and the fatty acid is added after the inorganic powder, the P-containing organic compound and the binder are mixed and dispersed. Is preferred. That is, when preparing a lower layer coating solution, the P-containing organic compound,
When a fatty acid is added after the inorganic powder and the binder are dispersed, the inorganic powder is adsorbed with the P-containing organic compound, and is dispersed in the resin, so that the adsorption of the fatty acid and the inorganic powder is inhibited. . As a result, the amount of free fatty acids not adsorbed or reacted with the inorganic powder (hereinafter, free fatty acids are referred to as free fatty acids) increases. In the present invention, the effect is particularly remarkable when a compound having a structure whose structure is particularly sterically complicated as compared with fatty acid is selected as the P-containing organic compound.

The amount of the free fatty acids is 100 × (the amount of free fatty acids in the upper and lower layers / the total amount of fatty acids in the upper and lower layers)
And calculated from values measured by the following quantitative methods (used in Examples described later). (1) Method for measuring the total amount of fatty acids in the upper and lower layers (measurement of charged amount) A coating film composed of the upper and lower layers of a magnetic recording medium is scraped off with a cutter blade or the like, and the weight of the coating film is measured. A powder such as an inorganic powder is treated with 12N hydrochloric acid. Next, 200 cc of n-hexane is used per 1 g of coating weight, the oil layer is separated by a separating funnel, and the fatty acid in the oil layer is quantified by gas chromatography. (2) Method for measuring amount of free fatty acid in upper layer and lower layer The upper layer and lower layer of the magnetic recording medium are scraped off with a cutter blade or the like, the coating film weight is measured, and 20 per 1 g of coating film weight is measured.
After extraction with 0 cc of n-hexane, fatty acids are quantified by gas chromatography.

Gas chromatography conditions: use of solvent cut, column temperature 150-280 ° C., heating rate 8 ° C./min As defined above, free fatty acids can be easily extracted with n-hexane, but inorganic powders that are not free fatty acids. This is based on the property that almost no fatty acids are adsorbed on the water. In the present invention, the fatty acid is usually 2.0% by weight or less, preferably 1.5% by weight, based on the total weight of the lower layer and the upper layer.
The magnetic recording medium is preferably contained in an amount of not more than 50% by weight, and the free fatty acid content is preferably 50% by weight or more, preferably 60% by weight or more. When the amount of the free fatty acid is less than 50% by weight or the absolute amount is more than 2.0% by weight, the plasticization of the coating film composed of the upper layer and the lower layer is promoted or the dispersibility is deteriorated, so that the surface property and the coating property are reduced. It is not preferable because the film strength is lowered and the supply of fatty acid to the upper layer surface is reduced to deteriorate the running property.

The P-containing organic compound used in the present invention will be described in more detail. Examples of the organic acid having a pKa of 3 or more include α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphonic acid and phenylphosphinic acid.

Examples of the epoxy group-containing compounds include those having the following general structures. However,
R ₁ , R ₂ and R ₃ are aliphatic and aromatic groups, and X is
In ~ 7, -OPO (OM) ₂ or -PO (OM)
_2, the reduction _{8, -SO 3 M, -OSO 3} M, -OPO
(OM) ₂ , -PO (OM) ₂ , -COOM (where
M is selected from a hydrogen atom or an alkali metal),
At least one of the two Xs represents -OPO (OM) ₂ or -PO (OM) ₂ .

[0019]

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[0020]

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[0021]

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[0022]

[Chemical 4]

[0023]

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[0024]

[Chemical 6]

[0025]

[Chemical 7]

[0026]

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The following are specific examples of titanate coupling agents. Tetraoctyl bis (ditridecyl phosphite) titanate, tetra (2,2
-Diallyloxymethyltributyl) bis (tridecyl) phosphite titanate, bis (dioctylbylophosphate) oxyanate titanate, bis (dioctylbylophosphate) ethylene titanate, isopropyl tri (dioctylphosphate) titanate,
Examples include tetraisopropyl bis (dioctyl phosphite) titanate.

The added amount of these P-containing organic compounds is 0. 0 relative to the specific surface area of the inorganic powder by the BET method.
3 to 30 μmol / m ² is desired, and more preferably 1 to 30 μmol / m ^2.
〜１０10 μmol / m ² . In the present invention, it is desirable that the interface between the upper layer and the lower layer is flat and the thickness of the upper magnetic layer is as uniform as possible. It is preferable to select other regulators.

The following two are exemplified as specific means for controlling the fluctuation or disorder of the interface. The first means is to control the thixotropic properties of the magnetic coating material of the magnetic layer and the respective dispersions of the lower layer so as to approximate each other. The purpose is to control the shape so that a mixed region is not formed in the upper layer and the lower layer mechanically by defining the shape.

As a specific method of the first means, each coating solution is subjected to a shear stress A10 ⁴ at a shear rate of 10 ⁴ sec ^−1.
And the ratio of A10 ⁴ / A10 to the shear stress A10 at a shear rate of 10 sec ⁻¹ is adjusted to 100 ≧ A10 ⁴ / A10 ≧ 3. A second means is to use a needle-like nonmagnetic powder or flake-like nonmagnetic powder for the lower layer in order to prevent a mixed region from being formed at the interface between the lower layer and the upper magnetic layer. Compared to conventional granular non-magnetic powder, if the needle-shaped non-magnetic powder is aligned and present, it forms a strong coating even in the undried state, and even if the ferromagnetic powder in the upper magnetic layer rotates, the It can be controlled so as not to cause mixing. Another means for preventing the mixed region from occurring is to use a scale-like non-magnetic powder for the lower layer and spread it in a tile-like manner. It is possible to prevent mixing at the interface even when the is rotated.

Factors involved in these adjustments are, for example, (1) particle size (specific surface area, average primary particle diameter, etc.) and (2) structure (oil absorption, For the binder, (1) molecular weight, (3) powder surface properties (pH, loss on heating, etc.), (4) particle suction force (σ _S, etc.), etc.
(2) For the solvent such as the type of the functional group, (1) the type (polarity, etc.), (2) the solubility of the binder, (3) the formulation amount of the solvent, the water content, and the like.

Further, in the magnetic recording medium of the present invention, the average value Δd of the variation in thickness at the interface (that is, the variation width in the thickness direction of the interface) is ½ of the average value d of the dry thickness of the magnetic layer.
The standard deviation 3σ of the thickness of the magnetic layer is 0.6 μm, preferably σ is 0.2 μm or less. That is, 3σ of 0.6 μm or less means that 97% of each segment should be within 0.6 μm or less. Further, it is preferable that 3σ ≦ 6d / 10.

These d, Δd, and σ are obtained as follows (see FIG. 1). A magnetic recording medium is cut out in a thickness of about 0.1 μm with a diamond cutter in the longitudinal direction, and the magnification is 10,000 to 100,000 with a transmission electron microscope.
The photograph is taken at a magnification of, preferably, 20,000 to 50,000 times and photographed (the print size of the photograph is A4 to A5).
Is). Thereafter, the interface is visually determined by paying attention to the shape difference between the upper magnetic layer and the lower ferromagnetic powder or the inorganic powder, and the black border and the magnetic layer surface are similarly bordered black. First, how to obtain Δd will be described. The distance between the ridge or valley at the interface between the bordered upper magnetic layer and the lower layer is defined as Δd. Further, the standard deviation σ is determined by trimming as described above.
Then, the length of the interval between the bordered lines is measured by an image processing device IBAS2 manufactured by Zeiss. The measurement of the thickness of the magnetic layer was performed by dividing the interval of 21 cm into 100 to 300 segments, and d was determined.

The standard deviation σ is the thickness of each segment x
_{If i} , it is expressed by the following equation 1.

[0035]

[Equation 1]

Δd is Δd = (Δd ₁ + Δd ₂ + ... +
Δd _m ) / m (m = 10 to 20). While Δd focuses only on the variation at the interface, the standard deviation σ of the average thickness d is the thickness of the upper magnetic layer including both the surface roughness factor of the upper magnetic layer and the variation at the interface. Means fluctuation. The variation of this interface is 3σ is 0.6
It is preferably μm or less. Thereby, the uniformity of the magnetic layer thickness is ensured and the surface roughness Ra is Ra ≦ λ /
50, that is, λ / Ra of 50 or more, preferably 75 or more,
More preferably, it can be regulated to 100 or more. Here, Ra represents a value obtained by measuring the center line average roughness measured using an optical interference roughness meter.

Further, λ / 4 ≦ d with respect to the shortest recording wavelength λ.
≦ 3λ, preferably λ / 4 ≦ d ≦ 2λ (ie 0.2
5 ≦ d / λ ≦ 2) and the surface roughness Ra of the magnetic layer is Ra ≦ λ
The relationship of / 50 is preferable. This prevents fluctuations in reproduction output and amplitude modulation noise, and achieves high reproduction output and high C /
N can be realized.

In the present invention, the shortest recording wavelength λ varies depending on the type of the magnetic recording medium.
5 μm and 0.67 μm for digital audio. The thickness of the magnetic layer can be obtained by actual measurement as described above. For the element uniquely contained in the magnetic layer by fluorescent X-ray, a magnetic layer sample having a known thickness is measured, a calibration curve is prepared, and then unknown. The thickness of the sample material can also be determined from the intensity of the fluorescent X-ray.

Further, according to the present invention, the root mean square roughness R _rms of the surface of the magnetic layer measured by a scanning tunneling microscope (STM) is 30 ≦ d / R _rms between the magnetic layer and the dry thickness average value d. It is preferable that the relationship When the magnetic layer becomes thin,
Although the self-demagnetization loss should be reduced and the output should be improved, the calender moldability is deteriorated and the surface roughness is increased because the pressing margin is reduced by reducing the thickness of the magnetic layer. In order to improve the output by reducing the self-demagnetization loss, it is preferable to use the surface roughness by STM which satisfies the above equation.

R _rms by AFM is preferably 10 nm or less. Optical interference surface roughness R measured by 3d-MIRAU
It is preferable that a is 1 to 4 nm, R _rms is 1.3 to 6 nm, and the P-V value (Peak-Valley) value is 80 nm or less. The glossiness of the surface of the magnetic layer is preferably 250 to 400% after calendering. Such surface properties can be achieved, for example, by satisfying at least one of the following four conditions within the conditions of the present invention. (1) The non-magnetic powder contained in the lower 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, and the average particle diameter of the inorganic powder is acicular. １ ／ to 4 times the crystallite size of the ferromagnetic powder of the above. (2) The non-magnetic powder contained in the lower 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, and the inorganic powder has a needle-shaped average particle diameter. Is not more than 1/3 of the major axis length of the ferromagnetic powder. (3) The ferromagnetic powder contained in the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate,
In addition, the non-magnetic powder contained in the lower layer contains an inorganic powder, and the average particle size is equal to or less than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer. (4) The inorganic powder contained in the lower layer contains an inorganic non-magnetic powder having a surface layer coated with an inorganic oxide.

(1) to (3) are to limit the size and shape of the ferromagnetic powder of the upper magnetic layer and the inorganic powder of the lower layer to secure the surface properties of the lower layer, and to make the inorganic powder mechanically reduce the ferromagnetic powder. It is a size that allows stable alignment. The volume filling rate of the lower layer of the inorganic powder is preferably 20 to 60%, more preferably 25 to 55%.

The inorganic powder preferably contains at least 60% by weight of the non-magnetic powder, and the inorganic powder is preferably a metal oxide, an alkaline earth metal salt or the like. In addition, since a known effect (for example, reduction of surface electric resistance) can be expected by adding carbon black, it is preferable to use in combination with the above-mentioned inorganic powder, but since carbon has very poor dispersibility, Carbon alone cannot secure sufficient electromagnetic conversion characteristics. In order to obtain good dispersibility, it is necessary to select 60% by weight or more from metal oxides, metals and alkaline earth metal salts. The inorganic powder is less than 60% by weight of the nonmagnetic powder, and the carbon black is 4% of the nonmagnetic powder.
If it is 0% or more, the dispersibility becomes insufficient and desired electromagnetic conversion characteristics cannot be obtained. In the present invention, the inorganic powder does not include carbon black.

When the thickness of the magnetic layer is 5 times or less the major axis, the degree of filling by the calendar is remarkably improved, and a magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained. Next, (4) will be described. The inorganic oxide coated on the surface of the inorganic powder contained in the lower layer is preferably A
l ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ ,
Sb ₂ O ₃ , ZnO and the like are preferable, and A is more preferable.
L ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a co-precipitated surface treatment tank may be used according to the purpose, or a structure in which the surface layer is treated with silica and then the surface layer is treated with silica or vice versa 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.

Hereinafter, general items which can be selected by the present invention will be described.
I will describe. The inorganic powder that can be used in the present invention is, for example,
Metal, metal oxide, metal carbonate, metal sulfate, metal
Non-magnetic inorganic powder such as nitride, metal carbide, metal sulfide
Is mentioned. Specifically, TiO₂ (Rutile, Anata
ZE), TiO_X(1 ≦ x <2), cerium oxide, sulfur oxide
, Tungsten oxide, ZnO, ZrO₂ , SiO₂ ,
Cr₂ O₃ , Α-alumina with α conversion rate of 90% or more, β-Al
Mina, γ-alumina, α-iron oxide, goethite, colander
Aluminum, silicon nitride, titanium carbide, magnesium oxide,
Boron nitride, molybdenum disulfide, copper oxide, MgCO₃ , C
aCO₃ , BaCO ₃ , SrCO₃ , BaSO_Four , Carbonization
Silicon, titanium carbide, etc. may be used alone or in combination.
Be done. The shape, size, etc. of these inorganic powders are arbitrary.
These combine different inorganic powders as needed.
Or the particle size distribution etc. can be selected even for a single non-magnetic powder.
Can also be.

The following are preferred as the inorganic powder. The tap density is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. Moisture content is 0.1-5
%, Preferably 0.2-3%. pH 2-11, especially 4
-10 is preferable. The specific surface area is 1 to 100 m ² / g,
Preferably 5 to 70 m ² / g, more preferably 7 to 50
m ² / g. Crystallite size is 0.01 μm to 2 μm
Is preferred. As for the particle size, the average particle diameter is 0.1 μm or less, preferably 0.08 μm or less in the case of particles, and the major axis length is 0.05 to 1.0 μm, preferably 0.05 in the case of needles. ˜0.5 μm, acicular ratio 5-20, preferably 5-15. The oil absorption using DBP is 5-100 ml / 100 g, preferably 10-
80 ml / 100 g, more preferably 20-60 ml /
100 g. SA (stearic acid) adsorption amount is 1-2
0 μmol / m ² , more preferably ^{2 to} 15 μmol / m ²
m ² . Roughness factor of powder surface is 0.8 ~
1.5 is preferable, and more preferably 2 to 15 μmol /
m ² . Heat of wetting in water at 25 ° C is 200 erg /
cm ^{2 to} 600 erg / cm ² are preferred. In addition, a solvent having a heat of wetting in this range can be used. 10
The amount of water molecules on the surface at 0 to 400 ° C is 1 to 10/10
0Å is suitable. The pH of the isoelectric point in water is preferably between 3 and 9. Specific gravity is 1 to 12, preferably 3
~ 6.

The above-mentioned inorganic powder is not necessarily required to be 100% pure, and the surface is treated with another compound, for example, each compound such as Al, Si, Ti, Zr, Sn, Sb, Zn, etc., according to the purpose. And their oxides may be formed on the surface. At that time, if the purity is 70% or more, the effect is not reduced. The ignition loss is preferably 20% or less.

Specific examples of the inorganic powder used in the present invention include UA5600 and UA560 manufactured by Showa Denko KK
5, Sumitomo Chemical Co., Ltd. AKP-20, AKP-30, AKP
-50, HIT-55, HIT-100, ZA-G1,
Nippon Kagaku Kogyo G5, G7, S-1, Toda Kogyo T
F-100, TF-120, TF-140, R516,
Ishihara Sangyo Co., Ltd. TTO-51B, TTO-55A, TTO
-55B, TTO-55C, TTO-55S, TTO-
55S, TTO-55D, FT-1000, FT-20
00, FTL-100, FTL-200, M-1, S-
1, SN-100, R-820, R-830, R-93
0, R-550, CR-50, CR-80, R-68
0, TY-50, Titanium Industry Co., Ltd. ECT-52, STT
-4D, STT-30D, STT-30, STT-65
C, Mitsubishi Materials T-1 and Nippon Shokubai NS-
O, NS-3Y, NS-8Y, MT-100 manufactured by Teika
S, MT-100T, MT-150W, MT-500
B, MT-600B, MT-100E, FI made by Sakai Chemical Co., Ltd.
NEX-25, BF-1, BF-10, BF-20, B
F-1L, BF-10P, Dowa Kogyo DEFIC-
Y, DEFIC-R, Y-LOP manufactured by Titanium Industry Co., Ltd. and a product obtained by firing the same.

The non-magnetic inorganic powder used in the present invention
In particular, titanium oxide (particularly titanium dioxide) is preferred.
Yes. Hereinafter, the method for producing this titanium oxide will be described in detail. Oxidation
There are mainly two methods for producing tongue: the sulfuric acid method and the chlorine method. The sulfuric acid method
Luminite raw ore is distilled with sulfuric acid to remove Ti, Fe, etc.
Extract as sulfate. Iron sulfate was separated by crystallization and removed, leaving
After filtration and purification of the titanyl sulfate solution, thermal hydrolysis was performed.
To precipitate the hydrous titanium oxide. After filtering and washing this,
After removing contaminants by washing and adding a particle size regulator etc.,
If it is fired at 800 to 1000 ° C., it becomes coarse titanium oxide.
Rutile type and anatase type are nuclei added during hydrolysis.
It is divided according to the type of material. This crude titanium oxide is crushed,
It is created by subjecting it to sizing and surface treatment. Chlorine method is raw ore
Natural rutile and synthetic rutile are used. Ore is reduced at high temperature
Chlorinated in the state, Ti _Four Fe is FeCl
₂ The iron oxide that has become solid by cooling becomes liquid Ti
Cl _Four And separated. Obtained crude TiCl_Four Is due to rectification
After purification, add a nucleating agent and
And react instantaneously with oxygen to obtain crude titanium oxide. This
The pigmentary properties of the crude titanium oxide produced in the oxidative decomposition process
The finishing method for giving is the same as the sulfuric acid method.

In the present invention, carbon black can be used for the lower layer, and R _S (surface electric resistance), which is a known effect, can be lowered. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the carbon black. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400, DBP oil absorption is 20-400 ml / 10
It is 0 g, preferably 30 to 200 ml / 100 g.
The average particle size is 5 m-80 m, preferably 10-50 m
μ, and more preferably 10 to 40 mμ. pH is 2
10, water content 0.1 ~ 10%, tap density 0.1 ~
1 g / cc is preferred.

Specific examples of the carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72, Mitsubishi Kasei Kogyo # 3050, # 3150, # 3250,
# 3750, # 3950, # 2400B, # 2300,
# 1000, # 970, # 950, # 900, # 8
50, # 650, # 40, MA40, MA-600, manufactured by Columbian Carbon Co., CONDUCTEXSC, R
AVEN 8800, 8000, 7000, 575
0, 5250, 3500, 2100, 2000, 180
0, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo and the like. The carbon black may be surface-treated with a dispersant or the like, or may be grafted with a resin for use, or a part of the surface thereof may be graphitized. Further, the carbon black may be previously dispersed with a binder before being added to the non-magnetic coating material. These carbon blacks can be used alone or in combination in the range of 0.1 to 30% based on the inorganic powder.

The carbon black that can be used in the present invention is
For example, (“Carbon Black Handbook”, edited by Carbon Black Association) can be referred to. The non-magnetic organic powder used in the present invention is an acrylic styrene resin powder,
Examples thereof include benzoguanamine resin powder, melamine-based resin powder, and phthalocyanine-based pigment, and polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluorinated ethylene resin powder are used. The manufacturing method is disclosed in JP-A-62-18564.
Nos. 60-255827 and 60-255827 can be used.

These non-magnetic powders are usually used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.1 to the binder.
Used in the range of 1. In general magnetic recording media, an undercoat layer is provided. This is provided to improve the adhesive strength between the support and the magnetic layer, and has a thickness of 0.5 μm. The following 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.

The ferromagnetic powder used in the magnetic layer of the present invention includes magnetic iron oxide FeOx (x = 1.33 to 1.5), C
Known ferromagnetic powders such as o-modified FeOx (x = 1.33 to 1.5), ferromagnetic alloy powder containing Fe or Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used. Further, ferromagnetic alloy powder is more preferable. . These ferromagnetic powders include Al, Si, S, Sc, Ti, V, Cr, C in addition to the specified atoms.
u, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te,
Ba, Ta, W, Re, Au, Hg, Pb, Bi, L
a, Ce, Pr, Nd, P, Co, Mn, Zn, Ni,
It may contain atoms such as Sr and B. These ferromagnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before dispersion. Specifically, Japanese Patent Publication No. 44-14090
No., JP-B-45-18372, JP-B-47-2206
2, JP-B-47-22513, JP-B-46-284
66, Japanese Patent Publication No. 46-38755, Japanese Patent Publication No. 47-42
No. 86, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-17
No. 284, Japanese Patent Publication No. 47-18509, Japanese Patent Publication No. 47-1
No. 8573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-
39639, U.S. Pat.
No. 1341, No. 3100194, No. 3242005
No. 3,389,014 and the like.

Of the above ferromagnetic powders, the ferromagnetic alloy powder may contain a small amount of hydroxide or oxide.
What was obtained by the well-known manufacturing method of a ferromagnetic alloy 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 powder of the upper magnetic layer of the present invention was BET
The specific surface area according to the method is 25 to 80 m ² / g,
It is preferably 40 to 70 m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, surface properties are difficult to obtain, which is not preferable. The crystallite size of the ferromagnetic powder of the upper magnetic layer of the present invention is 450 to 100Å, preferably 350 to 100Å. Σ _{S of the} iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu / g or more, and in the case of the ferromagnetic metal powder, 100 emu / g or more is preferable, and 110 emu / g to 170 e is more preferable.
mu / g. Coercive force is 1100 Oe or more, 2500
It is preferably Oe or less, and more preferably 1400 Oe or more and 2000 Oe or less. The acicular ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.

The r1500 of the ferromagnetic powder is preferably 1.5 or less. More preferably r1500 is 1.
It is 0 or less. The 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 saturation magnetization of the magnetic recording medium. The water content of the ferromagnetic powder is preferably 0.01 to 2%.
It is preferable to optimize the water content of the ferromagnetic powder depending on the type of binder. The tap density of γ-iron oxide is 0.5g / cc
The above is preferable, and 0.8 g / cc or more is more preferable. In the case of alloy powder, 0.2 to 0.8 g / cc is preferable, and if it is used at 0.8 g / cc or more, oxidation easily proceeds in the consolidation process of the ferromagnetic powder, and sufficient saturation magnetization (σ _S ) can be obtained. Becomes difficult. If it is 0.2 cc / g or less, the dispersion tends to be insufficient.

When γ iron oxide is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, and more preferably 5 to 10%. The amount of cobalt atom to iron atom is 0 to 15%, preferably 2 to 8%.
The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4-12,
It is preferably 6 to 10. Ferromagnetic powder, if necessary,
The surface treatment may be performed with Al, Si, P or an oxide thereof. The amount is 0.1 with respect to the ferromagnetic powder.
It is preferably 10%, and when the surface treatment is performed, adsorption of a lubricant such as fatty acid is 100 mg / m ² or less, which is preferable. The ferromagnetic powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 500 ppm or less, the characteristics are not particularly affected.

The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape is selected from needle-like, granular, rice-like, plate-like or the like so as to satisfy the above-mentioned conditions. SFD of ferromagnetic powder 0.6
In order to achieve the following, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For that purpose, there are methods such as improving the particle size distribution of goethite, preventing the sintering of γ-hematite, and slowing the deposition rate of cobalt for cobalt-modified iron oxide as compared with the conventional method.

In the present invention, a hexagonal plate-like ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate is exemplified by plate-like hexagonal ferrite, and barium ferrite, strontium ferrite, lead ferrite, calcium ferrite Hexagonal Co powder such as each substitution product and Co substitution product can be used. Specific examples include magnetobranbite-type barium ferrite and strontium ferrite, and magnetobranvite-type barium ferrite and strontium ferrite containing a part of a spinel phase.
Particularly preferred are barium ferrite and strontium ferrite substitutes. In addition, in order to control the coercive force, Co--Ti, C is added to the hexagonal ferrite.
o-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
A material to which an element such as n or Ir-Zn is added can be used.

When barium ferrite is used, the plate diameter means the width of the plate of hexagonal plate-like particles, and is measured using an electron microscope. In the present invention, the plate diameter is 0.001 to 1 μm.
In m, the plate thickness may be ½ to 1/20 of the diameter. The specific surface area (S _BET ) is preferably 1 to 60 m ² / g, and the specific gravity is preferably 4 to 6. As the binder used in the lower and upper magnetic 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 1
50 ° C., number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and degree of polymerization of about 50 to 1
It is about 000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid,
Acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, a polymer or copolymer containing as a structural unit, a polyurethane resin,
There are various rubber resins. Further, as thermosetting resin or reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin And a mixture of an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like.

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 the lower layer or the upper layer. These examples and the manufacturing method thereof are described in detail in JP-A-62-256219.

The above resins may be used alone or in combination, but are preferably selected from the group of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. Examples thereof include a combination of at least one of the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate 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 1)
(OM ₂ ), -OP = O (OM ₁ ) (OM ₂ ), -NR
₄ X (where M, M ₁ and M ₂ are H, Li, Na,
K, -NR _4, shows a -NHR _3, R represents an alkyl group or H, X is a halogen atom. ), OH, N
R ₂ , N ⁺ R ₃ , (R is a hydrocarbon group), epoxy group, S
It is preferable to use one obtained by introducing at least one or more polar groups selected from H, CN and the like 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.

The vinyl chloride-based copolymer is preferably an epoxy group-containing vinyl chloride-based copolymer,
Vinyl chloride repeating unit, a repeating unit having an epoxy group, optionally _{-SO 3 M, -OSO 3 M,} -COO
M and -PO (OM) ₂ (wherein M is a hydrogen atom,
Or a vinyl chloride copolymer containing a repeating unit having a polar group such as an alkali metal). When used in combination with a repeating unit having an epoxy group, an epoxy group-containing vinyl chloride copolymer containing a repeating unit having —SO ₃ Na is preferable.

The content of the repeating unit having a polar group in the copolymer is usually in the range of 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 in the range of 1.0 to 30 mol% (preferably 1 to 20 mol%). And the vinyl chloride polymer is
Usually from 0.01 to 1 mol of vinyl chloride repeating unit
It contains a repeating unit having an epoxy group of 0.5 mol (preferably 0.01 to 0.3 mol).

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 is 0.
If it is less than 01 mol, it may not be possible to effectively prevent the release of hydrochloric acid gas from the vinyl chloride-based copolymer, while on the other hand, it is higher than 30 mol% or has an epoxy group per 1 mol of vinyl chloride repeating units. When the amount of the repeating unit is more than 0.5 mol, the hardness of the vinyl chloride-based copolymer may decrease, and when this is used, the running durability of the magnetic layer may decrease.

When the content of the repeating unit having a specific polar group is less than 0.01 mol%, 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 in the range of 15,000 to 60,000.

Such a vinyl chloride copolymer having an epoxy group and a specific polar group can be produced, for example, as follows. For example, in the case of producing a vinyl chloride copolymer into which an epoxy group and -SO ₃ N are introduced as a polar group, 2-vinyl having a reactive double bond and -SO ₃ Na as a polar group is used. Sodium (meth) acrylamide-2-methylpropanesulfonate (a monomer having a reactive double bond and a polar group) and diglycidyl acrylate are mixed at a low temperature, and this is mixed with vinyl chloride at 100 ° C. under pressure. It can be produced by polymerizing at the following temperature.

Examples of the monomer having a reactive double bond and a polar group used for introducing a polar group by the above method include the above-mentioned sodium 2- (meth) acrylamido-2-methylpropanesulfonate. And 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonic acid and its sodium or potassium salt, (anhydride) maleic acid and Examples thereof include (meth) acrylic acid and (meth) acrylic acid-2-phosphate.

In introducing an epoxy group, glycidyl (meth) acrylate is generally used as a monomer having a reactive double bond and an epoxy group. In addition to the above-mentioned production method, for example, a vinyl chloride-based copolymer having a polyfunctional -OH is produced by a polymerization reaction of vinyl chloride and vinyl alcohol, and the copolymer and the polarities described below. A method of reacting a compound containing a group and a chlorine atom (dehydrochlorination reaction) to introduce a polar group into the copolymer can be used.

ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ C
H ₂ OSO ₃ M, ClCH ₂ COOM, ClCH ₂ PO
(OM) _{2 In} addition, epichlorohydrin is usually used to introduce an epoxy group using this dehydrochlorination reaction.

The vinyl chloride copolymer may contain other monomers. Examples of other monomers include vinyl ether (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether), α
-Mono-olefins (eg ethylene, propylene), acrylates (eg (meth) acrylates containing functional groups such as (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitriles (eg , (Meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), vinyl ester (eg, vinyl acetate, vinyl propionate, etc.).

Specific examples of these binders used in the present invention include those manufactured by Union Carbide: VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku: 100
0W, DX80, DX81, DX82, DX83, 10
0FD, manufactured by Zeon Corporation: MR105, MR110, M
R100, 400X110A, made by Nippon Polyurethane Company:
Nipporan N2301, N2302, N2304, Dainippon Ink and Chemicals: Pandex T-5105, T-R30
80, T-5201, Burnock D-400, D-21
0-80, Crisbon 6109, 7209, Toyobo Co., Ltd .: Byron UR8200, UR8300, UR860
0, UR5500, UR4300, RV530, RV2
80, manufactured by Dainichi Seika Co., Ltd .: Daifelamin 4020, 502
0, 5100, 5300, 9020, 9022, 702
0, Mitsubishi Kasei: MX5004, Sanyo Kasei: Sampren SP-150, Asahi Kasei: Saran F310, F
210 and the like.

The binder used in the upper magnetic layer of the present invention is used in an amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the ferromagnetic powder. When a vinyl chloride resin is used, it is preferably used in a range of 5 to 30% by weight, a polyurethane resin is used in a range of 2 to 20% by weight, and a polyisocyanate is used in a range of 2 to 20% by weight.

The binder used in the lower layer of the present invention is used in a total amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the nonmagnetic powder. Further, when a vinyl chloride resin is used, 3 to 30% by weight, when a polyurethane resin is used, 3 to 30% by weight, and polyisocyanate is preferably used in a range of 0 to 20% by weight.

When an epoxy group-containing resin having a molecular weight of 30,000 or more is used in the present invention in an amount of 3 to 30% by weight based on the nonmagnetic powder, a resin other than the epoxy group-containing resin is added in an amount of 3 to 30% by weight based on the nonmagnetic powder. %, When a polyurethane resin is used, 3 to 30% by weight and 0 to 20% by weight of polyisocyanate can be used, but the epoxy group is 4 × 10 ^{−5 with respect} to the total weight of the binder (including the curing agent). ~ 16x1
It is preferably contained in the range of 0 ⁻⁴ eq / g.

In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 kg.
/ Cm ² , and the yield point is preferably 0.05 to 10 Kg / cm ² . 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. In this case, the general concept of a plurality of magnetic layers can be applied to the relationship between the uppermost magnetic layer and the lower magnetic layer. For example, the uppermost magnetic layer has a higher coercive force than the lower magnetic layer,
The concept of using a ferromagnetic powder having a small average major axis length and a small crystallite size can be applied. Further, the lower layer may be formed of a plurality of nonmagnetic layers. However, broadly speaking,
It has a configuration of an upper magnetic layer and a lower layer.

Therefore, the amount of the binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or Of course, it is possible to change the physical properties of the resin described above between the lower magnetic layer and the upper magnetic layer as required. As the polyisocyanate used in the present invention, tolylene diisocyanate, 4,4 '
-Isocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine isocyanate, isophorone diisocyanate, triphenylmethane triisocyanate,
Further, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd .: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd .: Takenate D-102, Takenate D- 110N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer: Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These are used alone or by utilizing the difference in curing reactivity. One or more combinations can be used for both the lower and upper magnetic layers.

As the carbon black used in the upper magnetic layer of the present invention, there may be used furnace for rubber, thermal for rubber, black for color, acetylene black and the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, and particle diameter is 5 mμ to 300.
It is preferable that mμ, 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, 130 manufactured by Cabot Corporation.
0, 1000, 900, 800, 700, VULCAN
XC-72, Asahi Carbon Co., Ltd .: # 80, # 60, # 5
5, # 50, # 35, manufactured by Mitsubishi Chemical Industries: # 2400
B, # 2300, # 900, # 1000, # 30, # 4
0, $ 10B, manufactured by Columbian Carbon: CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5 and so on. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be graphitized on a part of the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the ferromagnetic powder. Carbon black has the functions of preventing electrification of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the lower layer and the upper layer, and can be used in accordance with the purpose based on the various characteristics shown above such as particle size, oil absorption, electric conductivity, and pH. Of course, it is possible to use them properly. The carbon black that can be used in the upper layer of the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

The abrasive used in the upper magnetic layer of the present invention includes α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond having an α conversion of 90% or more. Known materials mainly having a Mohs hardness of 6 or more such as silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 9
If it is 0% or more, the effect is the same. The particle size of these abrasives is preferably 0.01 to 2 μm, but 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 to 2 g / cc, water content is 0.1 to 5%, pH is 2 to 11, specific surface area is 1 to 30 m.
² / g is preferred. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness.

Specific examples of the polishing agent used in the present invention include: AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd .: G
5, G7, S-1, manufactured by Toda Kogyo: TF-100, TF
Examples include −140, 100ED, 140ED and the like.
It is of course possible to use the abrasives used in the present invention by changing the type, amount and combination of the lower layer and the upper layer, and selectively using them according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

As the additives used in the upper layer and / or the lower layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Esters and their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds, May be branched), and their metal salts (Li, Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent having 12 to 22 carbon atoms. Alcohol (can contain unsaturated bonds or be branched , Alkoxy alcohols having 12 to 22 carbon atoms, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and carbon atoms 2
A monofatty acid ester consisting of 1 to 12 monohydric, dihydric, trihydric, tetrahydric, pentahydric, or hexahydric alcohol (which may contain an unsaturated bond or may be branched) or Di-fatty acid ester or tri-fatty acid ester, fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid amide having 8 to 22 carbon atoms, 8 to carbon number
22, aliphatic amines, and the like. Specific examples of these include lauric acid, myristic acid, palmitic acid,
Stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate,
Anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, 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, and phosphoric acid ester group, amino acids, aminosulfonic acids, 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 for the lower layer and the upper magnetic layer. For example, by using fatty acids with different melting points in the lower and upper magnetic layers to control bleeding to the surface, using esters with different boiling points and polarities to control bleeding to the surface, and adjusting the amount of surfactant It is conceivable that the stability of the coating is improved, the amount of the lubricant added is increased in the lower layer to improve the lubrication effect, and it is needless to say that the examples are not limited to those shown here.

All or a part of the additives used in the present invention may be added at any step of the production of the magnetic paint. For example, when mixing with the ferromagnetic powder before the kneading step, the In a kneading step using a solvent and a binder and a solvent, there is a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. Examples of commercial products of these lubricants used in the present invention are: NAA-102, NAA-415, NAA-31 manufactured by NOF CORPORATION.
2, NAA-160, NAA-180, NAA-17
4, NAA-175, NAA-222, NAA-34,
NAA-35, NAA-171, NAA-122, NA
A-142, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, Nymeen L-201, Nymeen L-202, Nymeen S-202. , Nonion E-208, Nonion P-20
8, 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 O
P-80R, Nonion OP-85R, Nonion LT-2
21, nonion ST-221, nonion OT-221,
Monogly MB, Nonion DS-60, Anon BF, Anon LG, Butyl stearate, Butyl laurate, Erucic acid, Kanto Chemical Co., Ltd .: Oleic acid, Takemoto Yushi Co., Ltd .: FA
L-205, FAL-123, manufactured by Shin Nippon Rika Co., Ltd .: Engerb LO, Engerb IPM, Sanso Sizer E4
030, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, KF-96, KF-
96L, KF-96H, KF410, KF420, KF
965, KF54, KF50, KF56, KF-90
7, KF-851, X-22-819, X-22-82
2, KF-905, KF-700, KF-393, KF
-857, KF-860, KF-865, X-22-9
80, KF-101, KF-102, KF-103, X
-22-3710, X-22-3715, KF-91
0, KF-3935, Lion Armor Co., Ltd .: Armide P, Armide C, Armoslip CP, Lion Yushi Co., Ltd .: Duomin TDO, Nisshin Oil Co., Ltd .: BA-41
G, Sanyo Chemical Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, Ionette MO
-200, IONET DL-200, IONET DS-
300, Ionet DS-1000, Ionet DO-
For example, 200 is given.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol. Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene; Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, 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% by weight or less, more preferably 10% by weight or less. If necessary, the organic solvent used in the present invention is preferably of 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 the solvents used for the coating liquids of the lower non-magnetic layer and the upper magnetic layer both have a solubility parameter of 8 to 11 and a dielectric constant at 20 ° C. It is preferable that 15% or more of the solvent is contained in 15% or more.

The thickness of the magnetic recording medium of the present invention is 1-100 μm, preferably 4-80 μm for the support, 0.5-10 μm for the lower layer, preferably 1-5 μm, and 0.
05 μm or more and 1.0 μm or less, preferably 0.05 μm
Not less than 0.6 μm and more preferably not less than 0.05 μm and not more than 0.3 μm. The total thickness of the upper layer and the lower layer is used in the range of 1/100 to 2 times the thickness of the support. Further, an undercoat layer for improving adhesion may be provided between the support and the lower layer. These thicknesses are from 0.01 to
It is 2 μm, preferably 0.05 to 0.5 μm. A back coat layer may be provided on the side of the support opposite to the magnetic layer side. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used.

The support used in the present invention is preferably non-magnetic, and polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, Known films such as aromatic polyamide can be used. Corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment,
Dust removal processing may be performed. In order to achieve the object of the present invention, the support has a center line average surface roughness of 0.0
It is necessary to use one having a size of 3 μm or less, preferably 0.02 μm or less, and more preferably 0.01 μm or less.
Further, it is preferable that these supports have not only a small center line average surface roughness but also no large protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti,
Organic fine powders such as acryl-based powders can be used.

In addition, the F-5 value in the tape running direction of the support is
Is preferably 5 to 50 kg / mm ² , Tape width direction
F-5 value is preferably 3 to 30 Kg / mm² And
The F-5 value in the tape longitudinal direction is the F-5 value in the tape width direction.
It is generally higher, but especially the strength in the width direction is increased.
This is not the case when it is necessary to do so. Also, of the support
Heat absorption in the tape running direction and width direction at 100 ° C for 30 minutes
Reduction ratio is preferably 3% or less, more preferably 1.5%
The heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less.
Lower, more preferably 0.5% or less. Breaking strength
5-100 kg / mm in both directions² , Elasticity is how to run
100 to 2000 kg / mm in both direction and width² Is preferred
New

The step of producing the magnetic paint of 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 as necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but a strong kneading force such as a continuous kneader or a pressure kneader is used in the kneading step. The high Br of the magnetic recording medium of the present invention can be obtained by using the material having the same. In the case of using a continuous kneader or a pressure kneader, all or part of the ferromagnetic powder and the binder (however, 30% by weight or more of the total binder is preferable) and the ferromagnetic powder 100.
Kneading is performed in the range of 15 to 500 parts per part. For details of these kneading treatments, see JP-A-1-106338.
And JP-A-64-79274. Further, when preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads and metal beads are suitable.

In the present invention, the production can be performed more efficiently by using the simultaneous multilayer coating method as disclosed in JP-A-62-212933. 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. The lower layer is first coated by a gravure coating, a roll coating, a blade coating, an 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. 1-46186 or JP-A-60-46186. -23
The upper layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-A-8179 and JP-A-2-265672. 2. JP-A-63-88080, JP-A-2-17921
No. 2, JP-A-2-265672, the upper layer and the lower layer are coated almost simultaneously by one coating head having two slits for passing the coating liquid therein. 3. The upper layer and the lower layer are coated almost at the same time by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to aggregation of the ferromagnetic powder, JP-A-62-95174 and JP-A-1-23
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in No. 6968. Further, regarding the viscosity of the coating liquid, Japanese Patent Application No. 1-312659
It is preferable to satisfy the numerical range disclosed in the publication.

In the present invention, the lower layer coating solution is preferably provided on the support by a so-called wet-on-wet coating method in which the lower layer coating solution is applied in a wet state.
In the present invention, wet-on
The wet coating method refers to a so-called sequential coating method in which the first layer is first coated and then the next layer is coated thereon in a wet state as quickly as possible, and a method in which multiple layers are simultaneously coated in the extrusion coating method.

As a wet-on-wet coating method, a magnetic recording medium coating method disclosed in JP-A-61-139929 can be used. In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000G (Gauss)
It is preferable to use the above solenoid and a cobalt magnet of 2000 G or more in combination, and further it is preferable to previously provide an appropriate drying step before orientation so that the orientation property after drying becomes the highest. Further, when the present invention is applied to the disk medium, an alignment method that randomizes the alignment is required.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, it is also possible to perform processing by using metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 Kg / cm, more preferably 300 Kg / cm or more, and the speed is 20 m / min.
The range is 700 m / min. The effect of the present invention can be further enhanced by a linear pressure of 300 Kg / cm or more at a temperature of 80 ° C. or more. The friction coefficient of the upper layer of the magnetic recording medium of the present invention and the opposite surface to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, the surface resistivity of the magnetic layer is 10 ⁴ to 10 ¹¹ ohm / sq, and the lower layer is used alone. Surface resistivity when applied is 10 ⁴ -10 ⁸ ohm / s
q, the surface electric resistance of the back layer is preferably 10 ³ to 10 ⁹ ohm.

The elastic modulus of the upper layer at an elongation of 0.5% is preferably 300 to 2000 kg / mm in both the running direction and the width direction.
² , the breaking strength is preferably ^{2 to} 30 kg / cm ² , and the elastic modulus of the magnetic recording medium is preferably 1 in both the running direction and the width direction.
0 to 1500 Kg / mm ² , the residual spread is preferably 0.5% or less, and the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less, most preferably 0.1% or less. It is 1% or less.

The porosity of the upper and lower layers is preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, the running durability is often preferable when the porosity is large. It is easy to set these values in an appropriate range according to the purpose.

The magnetic characteristics of the magnetic recording medium of the present invention are as follows.
When measured with KOe, the squareness ratio in the tape running direction is 0.
It is 70 or more, preferably 0.80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less.

The magnetic recording medium of the present invention has a lower layer and an upper 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. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. The magnetic recording medium of the present invention preferably has the following physical property values.

The Young's modulus of the magnetic recording medium of the present invention measured by a tensile tester is 400 to 5000 kg / mm ² ,
Preferably, it is 700 to 4000 Kg / mm ² , and the Young's modulus of the magnetic layer is 400 to 5000 Kg / mm ² .
Preferably 700 to 4000 Kg / mm ² , yield stress 3 to 20 Kg / mm ² , preferably 3 to 15 Kg / mm
^2. It is desirable that the yield elongation is 0.2 to 8% and 0.4 to 5%.

This affects the durability because the ferromagnetic powder, binder, carbon black, inorganic powder and support are involved. The bending rigidity (annular stiffness) of the magnetic recording medium of the present invention is preferably 40 to 300 mg when the total thickness is more than 11.5 μm, and the total thickness is 10.5 ± 1.
In the case of μm, preferably 20 to 90 mg and the total thickness is 9.5 μm
When it is thinner, it is preferably 10 to 70 mg.

This is mainly related to the support and is important for ensuring durability. The cracking elongation of the magnetic recording medium of the present invention measured at 23 ° C. and 70% RH is preferably 20% or less. The Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium of the present invention measured with an X-ray photoelectron spectrometer is preferably 0.
3 to 0.6, N / Fe spectrum β is preferably 0.0
It is 3 to 0.12.

This is related to the ferromagnetic powder, the inorganic powder and the binder, and is important in obtaining durability. The glass transition temperature Tg of the magnetic layer of the magnetic recording medium of the present invention measured using a dynamic viscoelasticity measuring device (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 40 to. 120 ° C., elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / cm ² , and loss elastic modulus E ″ (50 ° C.) is preferably 0.5.
× 10 ¹¹ to 8 × is desirably 10 ¹¹ dyne / cm ^2. The loss tangent is preferably 0.2 or less. If the loss tangent is too large, sticking failure tends to occur. These are important properties associated with durability, associated with binders, carbon black, and solvents.

Further, the support 23 and the magnetic layer 23
The 180 ° adhesion strength of the 8 mm wide tape at 70 ° C and 70% RH is preferably 10 g or more. Also,
The wear of the steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ . This is a measure of the durability that is directly related to the wear of the magnetic layer and is mainly associated with the ferromagnetic powder.

Further, five pieces of the magnetic recording medium of the present invention were photographed with a SEM (electron microscope) at a magnification of 50,000 times, and the number of the abrasives on the surface of the magnetic layer was preferably 0.1 / μm ² visually.
The above is desirable. Further, the number of abrasives present on the end face of the upper magnetic layer of the magnetic recording medium of the present invention is 5/100 μm.
² or more is preferable. These are scales that are affected by the abrasive and binder in the magnetic layer and exert an effect on durability.

The residual solvent of the magnetic recording medium of the present invention measured by gas chromatography is preferably 50 mg / m ² or less. The residual solvent contained in the upper layer is preferably 50 m.
g / m ² or less, more preferably 10 mg / m ² or less, and it is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer.

The sol fraction, which is the ratio of the soluble solid content extracted from the magnetic recording medium of the present invention with THF to the weight of the magnetic layer, is preferably 15% or less. This is influenced by the ferromagnetic powder and the binder,
It is a measure of durability.

[0108]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. “Part”
Means parts by weight. Basic recipe Lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area by BET method 40 m ² / g DBP oil absorption 27-38 ml / 100 g pH 7 carbon black 20 Part Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer (MR-110) 12 parts —SO ₃ Na group 5 × 10 ^-6 eq / g containing epoxy group (3.5% by weight in monomer unit) Degree of polymerization 350 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 20 0 part Upper magnetic layer: Common to the following examples Ferromagnetic alloy powder Composition (%) Fe: Ni: Co = 93: 3: 3 100 parts Hc 1600 Oe Specific surface area 58 m ² / g Crystallite size 170Å Particle size (long axis) Length) 0.18 μm, needle ratio 8 Saturation magnetization (σ _s ): 125 emu / g Vinyl chloride copolymer (MR-110) 12 parts —SO ₃ Na group 5 × 10 ⁻⁶ eq / g containing epoxy group ( (3.5% by weight in monomer units) Degree of polymerization 350 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α -Alumina (average particle size 0.3 μm) 5 parts Carbon black (average particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone For each of the 00 parts of the two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The obtained lower non-magnetic layer coating solution was dried to a thickness of 2 μm, and immediately thereafter, a thickness of the upper magnetic layer was adjusted to 0.2 μm so that the thickness was 7 μm. Simultaneous multilayer coating was performed on a polyethylene terephthalate support having a center average surface roughness of 0.01 μm, and while both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used for orientation. After drying and drying, the film was treated with a seven-stage calender consisting of metal rolls at a temperature of 90 ° C. and slit into a width of 8 mm to produce a video tape.

Example 1 To a basic formulation, 2.4 parts of phenylphosphonic acid as a surface treating agent for an inorganic powder were added simultaneously with the inorganic powder and a binder. This is 3 μm with respect to the specific surface area of the powder used.
ol / m ² . Example 2 The inorganic powder of the lower layer of the basic formulation was changed to the following αFe ₂ O ₃ αFe ₂ O ₃ 80 parts Average particle size 0.03 μm Specific surface area by BET method 35 m ² / g Further, phenylphosphonic acid was 2.1 parts. Was added. This is 3 μmol / m ^{2 based} on the specific surface area of the powder used.

Example 3 The inorganic powder of the lower layer of the basic formulation was changed to the following BaSO ₄ BaSO ₄ 80 parts Average particle size 0.04 μm Specific surface area by BET method 50 m ² / g Further, 3.0 parts of phenylphosphonic acid was added. did. This is 3 μmol / m ^{2 based} on the specific surface area of the powder used.

Example 4 The inorganic powder in the lower layer of the basic formulation was changed to the following TiO ₂ TiO ₂ 80 parts Average particle size 0.08 μm Specific surface area by BET method 16 m ² / g Also, 5.5 parts of phenylphosphonic acid was added. did. This is 3 μmol / m ^{2 based} on the specific surface area of the powder used.

Example 5 Phenylphosphonic acid (2.4 parts) was added according to the present invention to the basic formulation as a surface treating agent for inorganic powder. This is an amount corresponding to 3 μmol / m ^{2 based} on the specific surface area of the powder used. Further, the thickness of the upper magnetic layer was 0.8 μm. Example 6 0.4 parts of phenylphosphonic acid was added to the basic formulation as a surface treating agent for inorganic powder. This is an amount corresponding to 3 μmol / m ^{2 based} on the specific surface area of the powder used.

Example 7 20 parts of phenylphosphonic acid was added to the basic formulation as a surface treating agent for inorganic powder. This is an amount corresponding to 25 μmol / m ² with respect to the specific surface area of the powder used. Comparative Example 1 The following formulation was used without using the lower layer TiO ₂ .

Carbon black 50 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer (MR-110) 18 parts − 5 × 10 ⁻⁶ eq / g SO ₃ Na group Epoxy group (6.5% by weight in monomer unit) Degree of polymerization 350 Polyester polyurethane resin 7 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 200 parts Comparative Example 2 The basic formula is as follows.

Comparative Example 3 TiO ₂ in the basic formulation, which had been previously surface-treated with the polyol trimethylolpropane, was used. The prescription itself has not changed. Comparative Example 4 2.4 parts of lauric acid was added as a lower layer inorganic powder dispersant to the basic formulation. This is 3 μmol / m ^{2 based} on the specific surface area of the powder used.

Comparative Example 5 To the basic formulation, 2.4 parts of phenylphosphonic acid was added as a lower layer inorganic powder dispersant. This is 3 μmol / m ^{2 based} on the specific surface area of the powder used. Further, the thickness of the magnetic layer was set to 1.5 μm.

The obtained samples were evaluated as follows, and the results are shown in Tables 1 and 2. Evaluation method Fatty acid amount (prepared amount, free fatty acid amount): The above method was used. In addition, about the charge amount, it showed by weight part with respect to 100 weight part of inorganic powders. However, Comparative Example 1 is shown in parts by weight relative to 100 parts by weight of carbon black. Central average surface roughness: Three-dimensional surface roughness meter (made by Kosaka Laboratory)
Was measured at a cutoff of 0.25 mm. C / N: A FUJIX8 8 mm video tape manufactured by Fuji Photo Film Co., Ltd. was used to record a 7 MHz signal, and when this signal was reproduced, the noise generated at 6 MHz was measured with a spectroanalyzer (made by HP). The signal ratio was measured.

Jitter: The jitter value of each sample was measured with a jitter meter. μ value: 23 ° C., RH 70%, sample and stainless steel pole (SUS420J: pole surface roughness Ra 0.0
6 to 0.08 μm; contact roughness meter, cutoff 0.25
(measured by μ) and contact (winding angle: 180 °) with a tension (T ₁ ) of 20 g to hold the sample horizontally through a guide member in a load cell.
/ Ts necessary for running horizontally at a speed of (T
₂ ) was measured. Based on this measured value, the friction coefficient μ value was determined by the following calculation formula.

Μ = (1 / π) ln (T ₂ / T ₁ ).

[0121]

[Table 1]

[0122]

[Table 2]

The above examples are summarized as follows from the above table. Examples 1 to 3: The surface smoothness was improved by improving the dispersibility of the lower inorganic powder by the surface treatment agent, and the electromagnetic conversion characteristics such as C / N were also improved. In addition, since the lower layer inorganic powder strongly adsorbs the organic compound which is a surface treating agent, the fatty acid which is a lubricant, that is, stearic acid is prevented from adsorbing to the inorganic powder, and the fatty acid is effectively used, and jitter and running property are improved. .

Example 4: The average particle diameter of the inorganic powder is larger than that of Example 1, but when it is about 0.08, the surface roughness and the electromagnetic conversion characteristics are not significantly reduced. Example 5: Although the magnetic layer is thicker than in Example 1, the electromagnetic conversion characteristics are not significantly reduced at about 0.8.

Example 6: Since the amount of the surface treating agent was smaller than that of Example 1, the surface roughness and the like were reduced due to the decrease in dispersibility, but the effect was sufficient. Example 7: Although the amount of the surface treatment agent was larger than that of Example 1, the electromagnetic conversion characteristics were slightly reduced due to the degree of filling, but the effect was sufficient. Comparative Example 1: Since the lower layer did not contain inorganic powder, the electromagnetic conversion characteristics were degraded due to the lowering of the decoy head due to flexibility and the lowering of the surface property of the lower layer at the time of coating.

Comparative Example 2: Since the lower inorganic powder was not treated with the P-containing organic compound, the lower inorganic powder was apt to agglomerate. As a result, the surface properties were reduced and the electromagnetic conversion characteristics were reduced. As a result, the lubricating effect was not sufficient, and jitter and the like were reduced.

Comparative Examples 3 and 4: The polyols and lauric acids as surface treatment agents were exchange-adsorbed by stearic acid used as a lubricant, and the dispersibility and running properties were also reduced.

Comparative Example 5: Since the magnetic layer was thick, the electromagnetic conversion characteristics deteriorated due to thick loss. Example 8 Polyethylene terephthalate (thickness 10 μm as a support
m, F5 value: MD direction 20 Kg / mm ² , TD direction 1
4 Kg / mm ² , Young's modulus: MD direction 750 Kg / m
m ² , TD direction 470 Kg / mm ² ) or polyethylene terephthalate (thickness 7 μm, F5 value: MD direction 22 Kg / mm ² , TD direction 18 Kg / mm ² , Young's modulus: MD direction 750 Kg / mm ² , TD direction 7
50 kg / mm ² ), and the mixture was stirred with a disperser stirrer for 12 hours according to the following formulation to prepare an undercoat liquid.

Polyester resin (containing —SO ₃ Na group) 100 parts Tg 65 ° C. Na content 4600 ppm Cyclohexanone 9900 parts The obtained undercoat liquid was applied to the support at a dry thickness of 0.1 μm by bar coating using a bar coater.

On the other hand, a coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. The upper magnetic layer coating liquid formulation ferromagnetic powder: Fe alloy powder (Fe-Co-Ni) 100 parts Composition; Fe: Co: Ni = 92 : 6: a for Al ₂ O ₃ 2 sintered inhibitor used Hc 1600 Oe, σ _S 119 emu / g major axis length 0.13 μm, acicular ratio 7 crystallite size 172 Å, water content 0.6 wt% vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g, —OH , Epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38,000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g included —OH 8 × 10 ⁻⁵ eq / g containing Tg 38 ℃, Mw 50000 α-alumina (average particle diameter 0.15 [mu] m) 12 parts ^{_{S BET 8.7m 2 / g, pH}} 8.2, water content 0.06 wt% cyclohexanone 150 parts methyl ethyl After 6 hours mixed and dispersed in a sand mill ketone 150 parts The above composition,
Polyisocyanate (Coronate L) and oleic acid
1 part, 1 part of stearic acid and 1 part of butyl stearate were added to obtain a coating liquid for the upper magnetic layer.

Formulation of Coating Solution for Lower Nonmagnetic Layer 85 parts of TiO ₂ Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 1 pH 6.5 to 8.0 Carbon black 5 parts Average particle diameter 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 S _BET 250 m ² / g Coloring power 143% Vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ^-5 eq / g, -OH, epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ^-5 eq / g containing -OH 8 × 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 P-containing organic compound (phenylphosphonic acid) 2.4 parts of cyclohexane 100 parts methylate After 4 hours mixed and dispersed in a sand mill ethyl ketone 100 parts The composition,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid and 1 part of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

After the above coating solution was applied in a wet state using two doctors having different gaps, the permanent magnet 3
Alignment treatment was performed with 500 gauss and then with a solenoid 1600 gauss, followed by drying. Then, a metal roll and a super calender treatment with the metal roll were performed at a temperature of 80 ° C. Coating thickness is magnetic layer 0.3μm, non-magnetic layer 3.0μm
Met.

Next, a coating solution was prepared according to the following formulation. BC layer formulation Carbon black 100 parts S _BET 220 m ² / g Average particle size 17 mμ DBP oil absorption 75 ml / 100 g Volatile content 1.5% pH 8.0 Bulk density 15 lbs / ft ³ Nitrocellulose RS1 / 2 100 parts Polyester polyurethane 30 Part Nipolan (manufactured by Nippon Polyurethane Co.) Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (sedimentability) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts The above composition was pre-kneaded and kneaded with a roll mill. Next, with respect to 100 parts by weight of the above dispersion, 100 parts by weight of carbon black S _BET 200 m ² / g average particle size 200 mμ DBP oil absorption 36 ml / 100 g pH 8.5 α-Al ₂ O ₃ (average particle size 0.2 μm) Disperse with a sand grinder with a composition added with 0.1 part,
After filtration, the following composition was added to 100 parts by weight of the above dispersion to prepare a coating liquid.

Methyl ethyl ketone 120 parts Polyisocyanate 5 parts The obtained coating liquid was applied on the opposite side of the support provided with the magnetic layer to a dry thickness of 0.5 μm. The raw material thus obtained was cut into a width of 8 mm, and sample 1 (PET support) and sample 2 (PEN support)
8 mm video tape was prepared.

The following measurement was performed on the obtained 8 mm video tape, and the measurement results were obtained. (1) TEM (Transmission Electron Microscope) An ultrathin section of the magnetic layer was observed. The medium was cut to a thickness of about 0.1 μm with a diamond cutter, which was observed with a transmission electron microscope and photographed. The interface between the upper and lower layers of the photographed image and the surface of the magnetic layer were removed, the thickness of the magnetic layer was measured by an IBASII image processing device, and the average value d and the standard deviation σ were obtained.

The average value d of the thickness of the magnetic layer was 0.45 μm. Practically 1 μm or less, particularly preferably 0.6 μm
It turned out to be: The standard deviation σ of the magnetic layer thickness variation was 0.008 μm or less. In practice, σ is equal to 0.
It was found that the thickness was 02 μm or less, particularly preferably 0.01 μm or less. The magnetic tape was stretched so that the magnetic layer floated from the support, and the magnetic layer was peeled off by squeezing with a cutter blade. 500 mg of the peeled magnetic layer was added to 1N-N
reflux for 2 hours in 100 ml of aOH / methanol solution,
The binder was hydrolyzed. Since the ferromagnetic powder has a large specific gravity and sinks to the bottom, the supernatant liquid was removed.

Next, decantation was carried out to wash with water three times,
Thereafter, it was washed three times with THF. The ferromagnetic powder obtained is 5
It was dried in a vacuum dryer at 0 ° C. Next, the obtained ferromagnetic powder was dispersed in collodion and observed with a TEM at a magnification of 60,000. As a result, the major axis length of the ferromagnetic powder was 0.13 μm.
And the acicular ratio was 10. It has been found that the particle major axis length needs to be 0.4 μm or less for practical use, and is preferably 0.3 μm or less. Also, in practical use, the acicular ratio is 2 to 20.
Was required, and it was found that it was preferably 2 to 15. (2) AFM (Atomic Force Micro)
Scope) The surface roughness R _rms was measured. The surface of the magnetic layer is Digita
l Instrument Nanoscope II
With a tunnel current of 10 nA and a bias voltage of 400 m
The V was scanned over a range of 6 μm × 6 μm. For the surface roughness, R _rms in this range was obtained.

As a result, R _rms was 6 nm. It was found that 10 nm or less is necessary for practical use, and preferably 8 nm or less. (3) Surface roughness meter The surface roughness was measured using 3d-MIRAU. WYK
Approximately 250 × by MIRAU method using TOPO3D manufactured by O company
Ra, R _rms , Peak-Vall of 250 mm area
The ey value was measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by optical interference. Ra was 2.7 nm. For practical use, it was found that Ra is preferably 1 to 4 nm, more preferably 2 to 3.5 nm. R _rms was 3.5 nm. It was found that 1.3 to 6 nm is preferable for practical use, and more preferably 1.5 to 5 nm. The PV value was 20 to 30 nm. 80 in practical use
It was found that the thickness is preferably equal to or less than nm, more preferably 10 to 60 nm. (4) VSM (Vibration Sample Type Magnetometer) The magnetic characteristics of the magnetic layer of the magnetic tape obtained by using VSM were measured. It was measured at Hm 5 kOe using a vibrating sample type magnetometer manufactured by Toei Industry Co., Ltd.

As a result, Hc is 1620 Oe and Hr (9
0 °) is 1800 Oe, Br / Bm is 0.82, SFD
Was 0.583. Practically Hc is 1500-25
00 Oe is required, preferably 1600 to 2000 Oe
It turned out to be. Hr (90 °) is practically 100
From 0 to 2800 Oe, preferably from 1200 to 25
It was found to be 00 Oe. It has been found that Br / Bm is practically 0.75 or more, preferably 0.8 or more. It was found that the SFD is practically required to be 0.7 or less, and preferably 0.6 or less. (5) X-ray Diffraction X-ray diffraction was performed using the ferromagnetic powder taken out from the magnetic layer in (1) above.

The magnetic tape is directly applied to an X-ray diffractometer,
It was obtained from the spread of the full width at half maximum of the diffraction lines of the (4,4,0) plane and the (2,2,0) plane. As a result, the crystallite size was 18
It turned out to be 0 °. Practically preferably 400 °
It has been found that the temperature is particularly preferably 100 to 300 °. (6) Tensile test Young's modulus, yield stress, and yield elongation of the magnetic tape obtained by the tensile tester were measured. Tensile tester (Universal tensile tester STM-T-50B manufactured by Toyo Baldwin Co., Ltd.
P) was used in an atmosphere of 23 ° C. and 70% RH at a pulling rate of 10% / min.

As a result, the Young's modulus of the magnetic tape is
0.5% elongation elastic modulus 1200 kg / mm² , Yield stress
 6-7 Kg / mm² The yield elongation was 0.8%.
Practically preferably Young's modulus is 0.5% elongation elastic modulus of the tape
400 to 2000 kg / mm² Especially preferred
0.5% elongation elastic modulus 500-1500 Kg / mm ² 
I found out. Yield stress is practically preferable
3-20Kg / mm²And particularly preferably 4 to 15.
I understand. The yield elongation is practically preferably 0.2 to
8%, particularly preferably 0.4 to 5%.
all right. (7) Bending rigidity, annular stiffness Using a loop stiffener tester, width 8 mm, length 5
A sample of 0 mm is formed into a ring, and the displacement speed is about 3.5 mm / sec.
The force required to give a displacement of 5 mm is expressed in mg.

As a result, the 8 mm p6-120 tape had a thickness of 10.5 μm and a stiffness of 40 to 40.
It was 60 mm. It was found that when the thickness is practically 10.5 ± 1 μm, the stiffness is preferably 20 to 90 mg, particularly preferably 30 to 70 mg. When the thickness is 11.5 μm or more, it is practically preferably 40 to
It was found to be 200 mg. It was found that when the thickness is 9.5 μm or less, it is practically preferably 10 to 70 mg. (8) Stretching fracture Crack generation elongation was measured at 23 ° C. and 70% RH.

The both ends of the test piece having a tape length of 10 cm were set to 0.
It is pulled at a pulling speed of 1 mm / sec, and the surface of the magnetic layer is observed under a microscope at a magnification of 400 times to measure the elongation at which five or more obvious cracks are generated on the surface of the magnetic layer. As a result, the elongation at occurrence was 4%. It was found that it is practically preferably 20% or less, and particularly preferably 10% or less. (9) Heat Shrinkage The heat shrinkage of the magnetic tape after storage at 70 ° C. for 48 hours was measured.

It was stored in a thermostat at 70 ° C. for 48 hours, and the change in length before and after that was divided by the length before storage to obtain the heat shrinkage. As a result, the heat shrinkage rate was 0.2%. Practically, it is preferably 0.4% or less, and particularly preferably 0.1 to 0.1%.
It was found to be 0.3%. (10) ESCA Cl / Fe spectrum α and N / Fe spectrum β were measured.

For the measurement of α and β, an X-ray photoelectron spectrometer (PERKIN-FLMER) was used. The Mg anode was used as the X-ray source, and the measurement was performed at 300 W. First, the lubricant of the video tape was washed off with n-hexane and then set on the X-ray photoelectron spectrometer. The distance between the X-ray source and the sample was 1 cm. The sample was evacuated to vacuum, and after 5 minutes, Cl-2P spectrum, N-1S spectrum and Fe-
The 2P (3/2) spectrum was integrated for 10 minutes and measured.
The bath energy was constant at 100 eV. The integrated intensity ratio between the measured Cl-2P spectrum and the Fe-2P (3/2) spectrum was calculated and set as α.

The N-1S spectrum and Fe-2P (3
/ 2) The integral intensity ratio with respect to the spectrum was calculated and set to β. As a result, α was 0.45 and β was 0.07. In practice, α was found to be preferably 0.3 to 0.6, and particularly preferably 0.4 to 0.5. In practice, β was found to be preferably 0.03 to 0.12, and particularly preferably 0.04 to 0.1. (11) Rheovibron The dynamic viscoelasticity at 110 Hz was measured.

The viscoelasticity of the tape was measured at a frequency of 110 Hz using a dynamic viscoelasticity measuring device (Leo Vibron manufactured by Toyo Baldwin). Tg is the peak temperature of E ″. This method applies vibration from one end of the tape and measures the vibration propagating to the other end. As a result, Tg was 73 ° C and E '
(50 ° C.) is 4 × 10 ¹⁰ dyne / cm ² , E ″ (5
(0 ° C.) was 1 × 10 ¹¹ . It has been found that the Tg is preferably 40 to 120 ° C, and particularly preferably 50 to 110 ° C for practical use. Practically E '(50 ℃) is 0.8 × 10
It was found that it was ^{11 to} 11 × 10 ¹¹ dyne / cm ² , and particularly preferably 1 × 10 ^{11 to} 9 × 10 ¹¹ dyne / cm ² . Practically, E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² ,
Particularly preferably 0.7 × 10 ^{11 to} 5 × 10 ¹¹ dyne /
It was found to be cm ² . (12) Adhesion Strength The adhesion strength between the support and the magnetic layer was measured by the 180 ° peeling method.

A tape slit to a width of 8 mm was attached to a 3M adhesive tape, and the 180 peel strength was measured at 23 ° C. and 70% RH. The result obtained was 50 g. It has been found that the practically preferable adhesion strength is 10 g or more, and particularly preferably 20 g or more. (13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured.

A sample was fixed on a prepared glass by attaching both ends of the sample with an adhesive tape, and a steel ball of 6.25 mmφ was slid by applying a load of 50 g. At that time, after traveling once at a speed of 20 mm / sec for a distance of 20 mm, the steel ball was moved to a new magnetic surface and the same operation was repeated 20 times. After that, observe the sliding surface of the steel ball with a microscope of 40 times,
The diameter was calculated assuming that the surface was a circle, and the amount of wear was calculated from the diameter.

The obtained results were 0.7 × 10 ^{−5 to} 1.1.
It was × 10 ^-5 mm ³ . 0.1 × 1 for practical use
0 ^{−5 to} 5 × 10 ⁻⁵ mm ³ , particularly preferably 0.4
× 10 ^{-5 to} 2 × 10 ^-5 mm ³ . (14) SEM (Scanning Electron)
The surface state of the magnetic layer was observed by ic Microscope SEM.

Magnification 50 with Hitachi electron microscope S-900
Five pieces were photographed at 00 times to measure the surface abrasive. As a result, the number of abrasives was 0.2 / μm ² . In practice,
It was found that the number of abrasives was 0.1 / μm ² or more, and particularly preferably 0.12 / μm ^{2 to} 0.5 / μm ² . (15) GC (Gas Chromatography) The residual solvent of the magnetic tape was measured by GC.

Gas chromatography GC manufactured by Shimadzu Corporation
Using -14A, a 20 cm ² sample was heated to 120 ° C. and the residual solvent in the medium was measured. As a result, the residual solvent was 8 mg / m ² . Practically, preferably 50
mg / m ² or less, particularly preferably 20 mg / m ²
It turned out to be: (16) Sol Fraction The ratio of the soluble solids extracted with THF from the magnetic layer of the magnetic tape to the weight of the magnetic layer was determined. As a result, the sol fraction was 7%. Practically, the sol fraction is preferably 15
It has been found that the content is not more than%, particularly preferably not more than 10%.

An 8 mm video tape having the above characteristics was compared with a tape currently on the market, and the results are shown in Table 3.

[0154]

[Table 3]

The evaluation method was based on the above method or a general method. The criteria for judgment are as follows. Jitter: ○ Less than 0.2 μsec × 0.2 μsec or more Storage stability: ○ Storage at 60 ° C., 90% for 2 weeks, no rust on the surface.

X: Stored at 60 ° C, 90% for 2 weeks, with rust on the surface. Running durability: The assembly was assembled in an 8 mm cassette and the reproduction for 120 minutes was repeated 100 times. ○ No clogging lasting 5 minutes or more. × Clogging occurs after repeated 100 passes. Scratch: Run in still mode for 10 minutes.

○ No scratch is visually observed. × A scratch is visually observed. BER measurement method (Bit error rate): Random signals were converted to 24-25 by a computer. The scrambled interleaved NRZ-I signal is used, and the data obtained by PR4 demodulating the data obtained by recording / reproducing this test signal is compared with the test signal to detect an error,
The ratio of the error is BER.

[0158]

INDUSTRIAL APPLICABILITY The present invention can suitably control the amount of lubricant in an extremely thin coating type magnetic recording medium having a magnetic layer thickness of 1.0 μm or less, and further improves the dispersibility of the inorganic powder in the lower non-magnetic layer. Therefore, the surface property of the magnetic layer can be improved, the disorder of the interface between the lower layer and the upper layer can be suppressed, and the magnetic layer can be uniformly ensured. Furthermore, the maximum amount of the fatty acid as a lubricant can be used for the maximum effect. (EN) A magnetic recording medium capable of ensuring running property with suppressed jitter, improving durability and storability of a coating film, and exhibiting electromagnetic conversion characteristics comparable to those of a metal thin film type magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of measuring σ and Δd of an upper magnetic layer.

Claims (9)

[Claims] 1. A magnetic recording medium in which a lower layer in which an inorganic powder is dispersed in a binder is provided on a support, and an upper magnetic layer in which a ferromagnetic powder is dispersed in the binder is provided on the support, and the upper magnetic layer is dried. A magnetic recording medium having a thickness of 1.0 μm or less, the inorganic powder of the lower layer having a mohs hardness of 3 or more, and containing an organic compound containing phosphorus (P) in the lower layer. 2. The phosphorus (P) -containing organic compound is α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, p
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least one selected from -ethylbenzenephosphonic acid, phenylphosphonic acid, and phenylphosphinic acid. 3. A magnetic recording medium comprising at least one binder having an S-containing polar group as the binder. 4. The binder having an S-containing polar group is —O.
SO ₃ M or -SO ₃ M (M per above hydrogen atom,
Or an alkali metal).
The magnetic recording medium described. 5. The inorganic powder is TiO₂ (Rutile, a
Natase), TiO _X(1 ≦ x <2), cerium oxide,
Tin oxide, tungsten oxide, ZnO, ZrO₂ , Si
O₂ , Cr₂ O₃ , Α-alumina with an α conversion rate of 90% or more,
β-alumina, γ-alumina, α-iron oxide, goethite, Kora
And dam, silicon nitride, titanium carbide, magnesium oxide
Aluminum, boron nitride, molybdenum disulfide, copper oxide, MgCO
₃ , CaCO₃ , BaCO₃ , SrCO₃ , BaSO
_Four , At least one selected from silicon carbide and titanium carbide
The magnetic recording medium according to claim 1, wherein 6. The ferromagnetic powder used in the magnetic layer is at least one selected from a ferromagnetic alloy powder containing Fe, Ni, or Co as a main component, barium ferrite, and strontium ferrite. The magnetic recording medium according to claim 1. 7. The ferromagnetic powder used in the magnetic layer comprises Al, Si, S, Sc, Ti, V, C in addition to predetermined atoms.
r, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb,
Te, Ba, Ta, W, Re, Au, Hg, Pb, B
i, La, Ce, Pr, Nd, P, Co, Mn, Zn,
7. The magnetic recording medium according to claim 6, containing at least one atom selected from Ni, Sr, and B. 8. The magnetic recording medium according to claim 1, wherein the 0.5% elongation elastic modulus of the magnetic recording medium is 400 to 2000 kg / mm ² . 9. The magnetic recording medium according to claim 1, wherein the support has an elastic modulus of 100 to 2000 kg / mm ² in both the running direction and the width direction.