JPH05182177A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having good electromagnetic conversion characteristics, particularly excellent dispersibility in a lower nonmagnetic layer and excellent smoothness of the surface. CONSTITUTION:A lower nonmagnetic layer containing an inorg. powder dispersed in A binder is formed on a nonmagnetic supporting body, and an upper magnetic layer containing a ferromagnetic powder dispersed in a binder is formed thereon while the lower nonmagnetic layer is in a wet state. In this process, it is specified that the upper magnetic layer has <=1.0mum dry thickness and that the lower nonmagnetic layer contains a nonmagnetic inorg. powder each particle of which has a surface layer covered with an inorg. oxide.

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 high density coating type magnetic recording medium.

[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 higher in density year by year and the recording wavelength is becoming shorter, and recording methods from analog to digital are being studied. To meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer have been proposed.However, from the viewpoint of productivity and practical reliability such as corrosion, the ferromagnetic powder is dispersed in the binder. 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. As the coating type magnetic recording medium, ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, Cr
A material in which a nonmagnetic support is coated with a magnetic layer in which O ₂ , a ferromagnetic alloy powder or the like is dispersed in a binder is widely used.

[0003] Various methods have been proposed for improving the electromagnetic conversion characteristics of the coating type magnetic recording medium, such as improving the magnetic characteristics of the 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 problem 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, is becoming more serious. ..

Therefore, the magnetic layer has been thinned. However, if the magnetic layer is thinned to about 2 μm or less, the influence of the non-magnetic support is likely to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics and DO Deterioration is seen. Therefore, JP-A-5
As in JP-A 7-198536, if the nonmagnetic thick undercoat layer is provided on the surface of the support and then the magnetic layer is provided as the upper layer, the influence of the surface roughness of the support can be eliminated. However, there was a problem that the head wear and durability were not improved. This is because a thermosetting resin is conventionally used as a binder in the non-magnetic lower layer, so that the lower layer is cured,
It is thought that this is due to the fact that friction between the magnetic layer and the head and contact with other members are performed without buffering, and the magnetic recording medium having such a lower layer is somewhat inflexible. Be done. In order to solve this, it is possible to use a non-curable resin as a binder in the lower layer, but in the conventional method, when the lower layer is coated and dried and then the magnetic layer is coated as the upper layer, the lower layer is a coating solution of the upper layer. It swells with an organic solvent and causes turbulence in the coating liquid of the upper layer to deteriorate the surface properties of the magnetic layer, resulting in problems such as deterioration of electromagnetic conversion characteristics. In order to make the magnetic layer thinner, it is conceivable to reduce the coating amount, or to add a large amount of solvent to the magnetic coating liquid to reduce the concentration. If you take the former,
If the coating amount is reduced, sufficient leveling time does not occur after coating, and drying starts, which causes a problem of coating defects such as streaks and marking patterns, resulting in very poor yield. When the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids,
There are various adverse effects such as insufficient filling of the magnetic material and insufficient strength of the coating film due to the large number of voids. In the invention of Japanese Patent Laid-Open No. 62-154225, such a poor yield was a big problem.

The present applicant has proposed, as one means for solving these problems, Japanese Patent Laid-Open Nos. 63-191315 and 63-131315.
A method of providing a non-magnetic layer as a lower layer by 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,
We proposed a magnetic recording medium that can improve running durability.

However, even if such a method is applied, the following problems cannot be solved.
In recent years, a magnetic recording medium is required to have a very smooth surface property in order to reduce a spacing loss with a head for higher density and higher output. For this reason, the lower non-magnetic layer which is not directly exposed on the surface has good dispersibility as much as possible, and there is an increasing need for the surface property to be smooth when simultaneous multilayer coating is performed. In the above-mentioned simultaneous multi-layer coating technique, it is not possible to improve the surface property of the magnetic layer by ensuring the surface property of the lower non-magnetic layer by atomizing the powder used for the lower layer in order to smooth the magnetic surface. It is thought that. However, when such fine particles are used, the fine particles tend to agglomerate, which rather deteriorates the surface property of the lower layer and thus deteriorates the surface property of the magnetic layer. The problem is that even if the magnetic layer is made thinner to improve the electromagnetic conversion characteristics, it is difficult to control the interface between the magnetic layer and the lower layer due to the poor dispersibility of the powder in the lower layer, and the interface is disturbed. There is also a problem that a uniform magnetic layer cannot be obtained. That is, when the magnetic layer is made thinner, the dispersibility of the lower non-magnetic layer further contributes to the surface property in the case of simultaneous multi-layering, but conventional techniques cannot find suitable solutions to these problems. There's a problem.

That is, there is a problem in that it is necessary to further improve the dispersibility of the non-magnetic powder, but no suitable means has been found.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a magnetic recording medium having good electromagnetic conversion characteristics, and more specifically, a magnetic recording medium having excellent dispersibility of the lower non-magnetic layer and excellent surface smoothness. The task is to do.

[0009]

According to the present invention, a lower non-magnetic layer in which an inorganic powder is dispersed in a binder is provided on a non-magnetic support, and the lower non-magnetic layer is ferromagnetic in a wet state. In a magnetic recording medium provided with an upper magnetic layer in which a powder is dispersed in a binder, a dry thickness of the upper magnetic layer is 1.0 μm or less, and the lower non-magnetic layer is a surface layer coated with an inorganic oxide. The magnetic recording medium is characterized by containing the non-magnetic inorganic powder having the above, whereby the above-mentioned problems can be solved.

The present invention improves the dispersibility of the inorganic powder in the lower non-magnetic layer to facilitate the control of the interface between the lower non-magnetic layer and the upper magnetic layer to ensure the surface properties of the upper magnetic layer and to perform electromagnetic conversion. It has improved characteristics. And the present invention is
Lower layer coating in order to provide an upper magnetic layer (hereinafter, simply referred to as a magnetic layer or an upper layer) having a dry film thickness of 1 μm or less on a lower non-magnetic layer (hereinafter, simply referred to as a non-magnetic layer or a lower layer) without coating defects. The liquid is characterized in that a non-magnetic inorganic powder having a surface layer coated with an inorganic oxide is used, and the upper layer is first coated on the non-magnetic support while the lower layer is wet. That is, the present invention is an extremely thin magnetic layer excellent in mass productivity, which suppresses coating defects such as pinholes and stripes,
The present invention provides a magnetic recording medium having performance comparable to that of a ferromagnetic metal thin film.

In the present invention, the details of the effect of improving the dispersibility of the powder by coating the surface of the inorganic powder with an inorganic oxide are unknown, but the water (hydroxyl group) present on the surface of the inorganic powder is It is considered that they interact with each other and affect the dispersibility of the powder. The present inventor has found that controlling the water content improves the dispersibility of the powder. That is, in the present invention, the water content is controlled by treating the water present on the surface of the inorganic powder with an inorganic compound to cause a reaction, and a surface-treated layer comprising an inorganic oxide layer is formed on the surface. To be done.

The water content of the non-magnetic inorganic powder used in the present invention is controlled to be preferably 0.05 to 10% by weight, particularly preferably 0.1 to 8% by weight when the coating solution is prepared. Preferably. In the present invention, the structure of the inorganic oxide or the layer thereof is arbitrary as long as it is an oxide, whether it is a single species or one composed of two or more elements,
Usually, it has a structure polymerized through H ₂ O. However, the existence state of each differs depending on the manufacturing method. For example, Al ₂ O
₃ exists on the TiO ₂ surface relatively uniformly, but Si
O ₂ is present in the form of particles that are solidified.

Depending on the purpose, a co-precipitated surface-treated layer may be used, or a structure in which the surface layer is first treated with alumina and then the surface layer is treated with silica, or the reverse structure may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense. Other inorganic oxides include ZrO ₂ and Sn.
_{O 2, Sb 2 O 3,} ZnO , and the like.

In the present invention, the non-magnetic inorganic powder is an inorganic oxide such as Al ₂ O based on the total weight of the non-magnetic inorganic powder.
₃ to 1 to 21% by weight, preferably 2 to 18% by weight, Si
0.02 to 20% by weight of O ₂ , preferably 0.1 to 18
Wt%, a ZrO ₂ 0.05 to 15 wt%, preferably covers 0.5 to 10 wt%. The proportion of Al ₂ O ₃ in the above inorganic oxide is preferably 50% by weight or more.

As the inorganic powder to be surface-treated, titanium dioxide, barium sulfate, zinc oxide, α-iron oxide and goethite are preferable. As the non-magnetic inorganic powder, rutile type titanium dioxide is mainly used, and the inorganic oxide is preferably 5 to 30% by weight, particularly preferably 7%.
It is desirable that the content is up to 20% by weight.

For example, in order to form a surface-treated layer of non-magnetic inorganic powder, coarse particles are classified by dry pulverizing a non-magnetic inorganic powder material, adding water and a dispersant, wet pulverizing and centrifuging. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of an aqueous salt solution of Al, Si, Ti, Zr, Sb, Sn, Zn or the like is added, and an acid or an alkali for neutralizing the same is added, and the surface of the inorganic powder particles is coated with the produced hydrous oxide. To do. Water-soluble salts produced as by-products are decanted, filtered,
It is removed by washing, and finally the pH of the slurry is adjusted, filtered, and washed with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product.
Further, not only the water system but also the vapors of AlCl ₃ and SiCl ₄ are passed through the non-magnetic inorganic powder, and then the vapor is introduced so that A
It is also possible to perform a surface treatment of Si.

For other surface treatment methods, see "Charac
terization of Powder Surfaces ", Academic Press can be referred to. In the present invention, the lower non-magnetic layer may include untreated inorganic powder that is not the above-mentioned non-magnetic inorganic powder, but the non-magnetic inorganic powder is 51 to 99.8% by weight of the inorganic powder, preferably 60 to It is desirable to set it in the range of 95% by weight.

Next, in the present invention, the solvent used for the coating liquid of the lower non-magnetic layer and the upper magnetic layer is a compound having a solubility parameter of 8 to 11 and a dielectric constant at 20 ° C. of 15 or more. It is preferable to contain 15% by weight or more.
That is, in the multi-layer coating of the present invention, the affinity between the upper magnetic layer and the lower non-magnetic layer is important. Usually, a solvent having relatively strong polarity such as cyclohexanone or methyl ethyl ketone is used as a main component in the magnetic layer. After being applied in multiple layers, the solvent permeates between the upper and lower layers before drying. As a result, if the solvent composition of the upper and lower layers is extremely different, severe surface roughening occurs.

In the present invention, the solvent includes a single compound or a mixture of a plurality of compounds, and means the total of organic solvent compounds in the coating solution composition. Therefore, in the present invention, the solubility parameter of the solvent is 8 to 11
When a plurality of types of compounds are used for the above purpose, the types of the compounds may be different in the upper layer and the lower layer, but the same kind of compound composition is practically used in order to obtain the solubility parameters 8 to 11. It is extremely preferable to

When the compound is selected, it is preferable that the compound having a dielectric constant at 20 ° C. of 15 or more is 15% by weight or more. For example, examples of the compound exhibiting this value include methyl ethyl ketone. An example of the solvent composition in the present invention by weight ratio is as follows: methyl ethyl ketone: cyclohexanone: toluene: butyl acetate = 10: 5: 5: 4 (solubility parameter; 9.2) in the upper layer,
In the lower layer, methyl ethyl ketone: cyclohexanone: toluene: butyl acetate = 9: 5: 6: 4 (solubility parameter;
9.2) etc. are illustrated. Further, in the present invention, it is preferable to specify the solvent of the upper layer and the solvent of the lower layer in the same kind,
It is preferable that the binder, which is necessarily the dispersoid, has the same kind of compound in the upper layer and the lower layer.

The binder composition may be composed of a known binder, and preferably, a mixed system of vinyl chloride resin, urethane resin, and polyisocyanate is exemplified, but the details will be described later. The _{binder, -COOM, -OSO 3 M, -SO} 3 M, -PO (OM 1) (OM 2), - OPO (OM 1) (O
M ₂ ), —NR ₄ X (where M, M ₁ and M ₂ are Li,
Na, K, H, —NR ₄ or NHR ₃ is shown, R is an alkyl group or H, and X is a halogen atom. )
The inclusion of at least one polar group selected from the above is preferable in order to improve the dispersibility of the inorganic powder.

The volume ratio of the binder in the lower layer is in the range of 2.0 to 0.3 times the volume of the inorganic powder, and the volume ratio of the binder in the upper layer is 1.8 to 0.5 times. It is desirable to ensure the dispersibility of the inorganic powder and the ferromagnetic powder and the surface property of each layer. 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, and the present invention includes factors that can contribute as a means therefor. It is preferable to select other control factors.

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 paint of the magnetic layer and the respective dispersions of the lower non-magnetic layer so as to approximate each other, and the second means is to control the thixotropic properties of the lower non-magnetic layer and the magnetic layer. This is to control the size and shape of the powder to be mechanically controlled so as not to mechanically generate a mixed region in the upper and lower layers.

As a concrete method of the first means, each coating solution has a shearing stress A10 ⁴ at a shearing 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 needle-shaped nonmagnetic powder or scale-shaped nonmagnetic powder for the lower nonmagnetic layer in order to prevent a mixed region from occurring at the interface between the lower nonmagnetic layer and the upper magnetic layer. Be done. Compared with conventional granular non-magnetic powder, when needle-shaped non-magnetic powder is present in an array, it forms a strong coating film even in the undried state, and even if the ferromagnetic powder in the upper magnetic layer rotates, it will form an interface at the interface. It can be controlled so that no mixing occurs. Another means for preventing the mixed region from occurring is to use scale-like non-magnetic powder in the lower non-magnetic layer and spread it in a so-called tile shape. It is possible to prevent mixing at the interface even when the ferromagnetic powder rotates.

The factors relating to these adjustments include the factors in the present invention. For example, regarding the dispersed inorganic powder or magnetic powder, (1) particle size (specific surface area, average particle size, etc.), (2) ) Structure (oil absorption, particle morphology, etc.), (3) powder surface properties (pH, loss on heating, etc.),
(4) For the binding agent such as the particle attractive force (σ _S etc.),
With respect to the solvent such as (1) molecular weight, (2) type of functional group, etc., (1) type (polarity etc.), (2) binder solubility, (3) solvent prescription amount, water content and the like can be mentioned.

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 preferably 0.6 μm, and preferably σ is 0.2 μm or less. That is, when 3σ is 0.6 μm or less, it means that 97% of the segments have a thickness of 0.6 μm or less. Further, it is preferable that 3σ ≦ 6d / 10.

These d, Δd and σ are obtained as follows. A magnetic recording medium is cut out in a thickness of about 0.1 μm with a diamond cutter in the longitudinal direction and observed with a transmission electron microscope at a magnification of 10,000 to 100,000 times, preferably 20,000 to 50,000 times, and a photograph thereof is taken (printing of a photograph). The size is A4 to A5). After that, the interface is visually judged by paying attention to the shape difference between the ferromagnetic powder and the inorganic powder in the upper magnetic layer and the lower non-magnetic layer, and the edges of the magnetic layer are also blacked. First, Δ
The method of obtaining d will be described. The distance between the ridge or valley at the interface between the upper magnetic layer and the lower non-magnetic layer, which have been framed as described above, is Δd. The standard deviation σ is determined by edging as described above, and then measuring the length of the line between the edging by the image processing device IBAS2 manufactured by Zeiss. The measurement of the thickness of the magnetic layer was performed by segmenting a space having a length of 21 cm into 100 to 300 segments, and the number was calculated to obtain d.

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

[0029]

[Equation 1]

The above-mentioned Δd focuses only on the variation at the interface, but the standard deviation σ of the average thickness d includes the element of the surface roughness of the upper magnetic layer and the variation in the upper layer including the variation at the interface. It refers to the variation in layer thickness. It is preferable that the variation of the interface has 3σ of 0.6 μm or less. Thereby, the uniformity of the magnetic layer thickness is ensured and the surface roughness Ra is set to Ra.
≦ λ / 50, that is, λ / Ra of 50 or more, preferably 75
As described above, it is possible to regulate 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 playback output fluctuations and amplitude modulation noise, resulting in high playback output and high C /
N can be realized.

In the present invention, the shortest recording wavelength λ varies depending on the type of 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 the scanning tunneling microscope (STM) is 30 ≦ d / R _rms between the mean value d of the dry thickness of the magnetic layer.
It is preferable that If the thickness of the magnetic layer is thin, self-demagnetization loss should be reduced and output should be improved, but the reduction in the thickness of the magnetic layer will reduce the pressing margin, resulting in poor calender formability and surface roughness. growing. In order to improve output by reducing self-demagnetization loss, surface roughness by STM that satisfies the above equation is preferable.

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. Achieving such surface properties can be achieved, for example, by satisfying at least one of the following three conditions within the conditions of the present invention. (1) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more, and the ferromagnetic powder contained in the upper magnetic layer is a needle-like ferromagnetic powder, and the average particle diameter of the inorganic powder is 1/2 to 4 of crystallite size of needle-like ferromagnetic powder
Be double. (2) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more, and the ferromagnetic powder contained in the upper magnetic layer is a needle-like ferromagnetic powder, and the average particle size of the inorganic powder is Is 1/3 or less of the major axis length of the acicular 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,
Further, the non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the average particle size thereof is equal to or smaller than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer.

In (1) to (3), the size and shape of the ferromagnetic powder of the upper magnetic layer and the inorganic powder of the lower non-magnetic layer are limited to secure the surface property of the lower non-magnetic layer and the inorganic powder is strong. The size is such that the magnetic powder is aligned mechanically and stably. The volume filling rate of the lower layer of the inorganic powder is preferably 20 to 60%, more preferably 2%.
It is preferably in the range of 5 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. Further, since it is possible to expect a known effect (for example, to reduce the surface electric resistance) by adding carbon black, it is preferable to use it in combination with the above inorganic powder, but carbon black has very poor dispersibility. However, carbon black cannot ensure sufficient electromagnetic conversion characteristics. In order to obtain good dispersibility, 60% by weight or more must be selected from metal oxides, metals and alkaline earth metal salts. If the inorganic powder is less than 60% by weight of the non-magnetic powder and the carbon black is 40% or more of the non-magnetic powder, the dispersibility becomes insufficient and desired electromagnetic conversion characteristics cannot be obtained.

When the thickness of the magnetic layer is 5 times or less of the major axis length, the filling degree by the calendar is remarkably improved, and a magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained. Less than,
General items that can be selected by the present invention will be described. Examples of the inorganic powder that can be used in the present invention include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Specifically, TiO
₂ (rutile, anatase), TiO _x , cerium oxide,
Tin oxide, tungsten oxide, ZnO, ZrO ₂ , Si
O ₂ , Cr ₂ O ₃ , α-alumina with α conversion of 90% or more, β
Alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgC
O ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO
₄ , silicon carbide, titanium carbide and the like are used alone or in combination. The shape, size, etc. of these inorganic powders are arbitrary, and different inorganic powders may be combined as necessary, or a single inorganic powder may have a selected particle size distribution and the like.

The following are preferable inorganic powders. The tap density is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. Water content is 0.1-5%, preferably 0.2-3%. The pH is preferably 2 to 11, particularly preferably 4 to 10. The specific surface area is 1 to 100 m ² / g, preferably 5 to 70 m ² / g, and more preferably 7 to 50 m ² / g.
Is. The crystallite size is preferably 0.01 μm to 2 μm. Regarding the particle size, the average particle size is 0.1 μm or less, preferably 0.08 or less in the granular form, and the major axis length is 0.05 to 1.0 μm, preferably 0.06 in the acicular form. ˜0.5 μm, acicular ratio 3˜30, preferably 5
Is selected from the range of .about.15. Oil absorption using DBP is 5-100ml / 100g, preferably 10-80ml
/ 100g, more preferably 20-60ml / 100g
Is. SA (stearic acid) adsorption amount is 1 to 20 μmo
1 / m ² , and more preferably ² to 15 μmol / m ² . The roughness factor of the powder surface is preferably 0.8 to 1.5, more preferably ² to 15 μmol / m ² . The heat of wetting in water at 25 ° C is 200 erg / cm ² ~
600 erg / cm ² is preferred. Further, a solvent having a heat of wetting in the range can be used. 100-40
The amount of water molecules on the surface at 0 ° C is appropriately 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. The specific gravity is 1 to 12, preferably 3 to 6. The loss on ignition 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 ECT-52, STT
-4D, STT-30D, STT-30, STT-65
C, T-1 manufactured by Mitsubishi Materials, NS- manufactured by Nippon Shokubai Co., Ltd.
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.

As the non-magnetic inorganic powder used in the present invention, titanium oxide (particularly titanium dioxide) is particularly preferable. Hereinafter, the production method of this titanium oxide will be described in detail. Titanium oxide is mainly produced by the sulfuric acid method and the chlorine method. In the sulfuric acid method, a raw illuminite ore is distilled with sulfuric acid to extract Ti, Fe and the like as sulfates. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration and then subjected to thermal hydrolysis to precipitate hydrous titanium oxide. After filtering and washing this,
After removing contaminants by washing and adding a particle size regulator etc.,
If it is fired at 80 to 1000 ° C., it becomes crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the core material added at the time of hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. For the chlorine method, natural ore natural rutile and synthetic rutile are used. Ore is chlorinated under high temperature reduction conditions, Ti for TiCl ₄ and Fe for FeCl ₂
And iron oxide that became solid by cooling is liquid TiC
Separated from l ₄ . The obtained crude TiCl ₄ is purified by rectification, then a nucleating agent is added, and it is instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher to obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

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 is 0.1-10%, tap density is 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's # 3050, # 3150, # 3250,
# 3750, # 3950, # 2400B, # 2300,
# 1000, # 970, # 950, # 900, # 8
50, # 650, # 40, MA40, MA-600, manufactured by Columbia Carbon Co., CONDUCTEX SC, 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, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the non-magnetic coating material. These carbon blacks can be used alone or in combination.

The carbon black usable 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.
Used in the range of 1. In general magnetic recording media, an undercoat layer is provided, but this is provided in order to improve the adhesive force between the support and the magnetic layer and has a thickness of 0.5 μm. The following is different from the lower non-magnetic layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesion between the underlayer and the support.

As the ferromagnetic powder used in the magnetic layer of the present invention, 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 contain 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. 4, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-2206
No. 2, JP-B-47-22513, JP-B-46-284
No. 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
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. Nos. 3,026,215 and 303.
No. 1341, No. 3100194, No. 3242005
No. 3,389,014 and the like.

Among the above-mentioned 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 metal in a low pressure inert gas to form 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, and immersing it in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying it. It is possible to use any of the above method and the method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent.

BET was used as the ferromagnetic powder for the upper magnetic layer of the present invention.
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. The 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 more preferably 110 emu / g to 170 e.
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 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 preferably 0.5 g / cc or more, more preferably 0.8 g / cc or more. 0.2 to 0.8 for alloy powder
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 it becomes difficult to obtain a sufficient saturation magnetization (σ _S ). 0.2 cc / g
Below, dispersion tends to be insufficient.

When FeOx is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, 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, the adsorption of the lubricant such as fatty acid becomes 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 few voids, and the value thereof is 20% by volume or less, more preferably 5% by volume or less. The shape is selected from needle-like, granular, rice-like, plate-like, etc. 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 the like. Barium ferrite, strontium ferrite, lead ferrite, calcium ferrite Each substitution product, Co substitution product, etc. can be used. Specific examples include magnetobranbite type barium ferrite and strontium ferrite, and further magnetobranbite type barium ferrite and strontium ferrite containing a part of a spinel phase, and barium ferrite and strontium ferrite are particularly preferable. It is a substitution product. In order to control the coercive force, Co-Ti, Co-Ti-Zr,
A material to which an element such as Co-Ti-Zn, Ni-Ti-Zn, or Ir-Zn is added can be used.

When barium ferrite is used, the plate diameter means the plate width of hexagonal plate-like particles and is measured by 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 non-magnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The glass transition temperature of the thermoplastic resin is −
100-150 ° C, number average molecular weight 1000-2000
00, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether, etc. as a constituent unit, polyurethane resins, and 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 can 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 at least one polar group selected from H, CN, etc. introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include those manufactured by Union Carbide Co .: VAGH and V.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry Co., Ltd .: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku: 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, manufactured by 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 Dainichiseika Co., Ltd .: Daifuelamine 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 the range 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 nonmagnetic layer of the present invention is in the range of 5 to 50% by weight based on the total amount of the nonmagnetic powder.
It is preferably used in the range of 10 to 35% by weight. Further, when using a vinyl chloride resin, 3 to 30% by weight, when using a polyurethane resin, 3 to 30% by weight,
The polyisocyanate is preferably used in combination within the range of 0 to 20% by weight.

In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the elongation at break is 100 to 2000%, and the stress at break 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. As a structure of three or more layers, the upper magnetic layer is composed of a plurality 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 idea of using ferromagnetic powder having a small average major axis length and a small crystallite size can be applied. Further, the lower non-magnetic layer may be formed of a plurality of non-magnetic layers. However, it is roughly classified into an upper magnetic layer and a lower non-magnetic layer.

Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or 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. The polyisocyanate used in the present invention includes tolylene diisocyanate and 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 are: Nippon Polyurethane Co .: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Yakuhin: Takenate D-102, Takenate D-. 110N, Takenate D-200, Takenate D-202, Sumitomo Bayer Co .: Death Module L, Death Module IL, Death Module N, Death Module HL, etc. One or more combinations can be used for both the lower non-magnetic layer and the upper magnetic layer.

As the carbon black used in the upper magnetic layer of the present invention, there may be used rubber furnaceeness, rubber thermal, color black, 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 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 Kasei Kogyo: # 2400
B, # 2300, # 900, # 1000, # 30, # 4
0, # 10B, manufactured by Conlon Via Carbon Co .: CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5, etc. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the 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 according to the purpose based on various characteristics 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).

As the abrasive used in the upper magnetic layer of the present invention, 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 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. Further, 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, it is possible to combine abrasives having different particle sizes, or to use a single abrasive to broaden the particle size distribution and 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 needle-like, spherical, or dice-like, but those having a corner in part of the shape are preferable because of high abradability.

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 in different types, amounts and combinations for the lower layer and the upper layer, and to use them properly according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Ester and its alkali metal salt, alkyl sulfate ester and its alkali metal salt,
Polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (which may contain unsaturated bonds or may be branched), and these metal salts ( Li, N
a, K, Cu, etc.) or a monovalent one having 12 to 22 carbon atoms,
Dihydric, trihydric, tetrahydric, pentahydric, hexahydric alcohol (may contain unsaturated bonds or may be branched), alkoxy alcohol having 12 to 22 carbon atoms, 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms,
Any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohol (may contain unsaturated bonds or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a mono-alkyl ether fatty acid ester of an alkylene oxide polymer, and a carbon number of 8 to
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid,
Linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, 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, phosphoric acid ester group, amino acid, aminosulfonic acid, sulfuric acid of amino alcohol 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. The content of these impurities is preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in the lower non-magnetic layer and the upper magnetic layer in different types and amounts according to need. For example, fatty acids with different melting points are used to control bleeding to the surface in the lower non-magnetic layer and upper magnetic layer, bleeding to the surface is controlled using esters with different boiling points and polarities, and the amount of surfactant is adjusted. By doing so, it is conceivable that the stability of coating is improved, the amount of lubricant added is increased in the lower non-magnetic layer, and the lubricating effect is improved, and of course, the present invention is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. There is a case where it is added in a kneading step using a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, a case where it is added immediately before coating and the like. 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-cured 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, Anone BF, Anone 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 .: NJ Erb LO, N Jorb 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, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, glycol ethers such as benzene, benzene, Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine 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. The content of these impurities is preferably 30% by weight or less, more preferably 10% by weight or less. It is important that a solvent having a high surface tension (cyclohexanone, dioxane, etc.) is used for the lower layer to improve the stability of coating, and specifically, the arithmetic average value of the upper layer solvent composition does not fall below the arithmetic average value of the lower layer solvent composition.

The thickness of the magnetic recording medium of the present invention is 1-100 μm, preferably 4-80 μm for the non-magnetic support, 0.5-10 μm for the lower layer, preferably 1-5 μm, and 0.05 μm or more for the upper layer. 0 μm or less, preferably 0.05
μm or more and 0.6 μm or less, more preferably 0.05 μm
It is m or more and 0.3 μm or less. The total thickness of the upper layer and the lower layer is 1/100 to 2 times the thickness of the non-magnetic support. Further, an undercoat layer may be provided between the non-magnetic support and the lower layer to improve the adhesion. The thickness of these is 0.01 to 2 μm, preferably 0.05 to 0.5 μm.
m. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1
˜2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used.

The non-magnetic support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone, aramid and aromatic polyamide. The film can be used. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. To achieve the object of the present invention, the non-magnetic support has a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less, and more preferably 0.01 μm.
You need to use: Further, it is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no large protrusions of 1 μ or more. Also,
The roughness shape of the surface is freely controlled by the size and amount of the filler added to the support, if necessary. An example of these fillers is C
In addition to oxides and carbonates such as a, Si, and Ti, organic fine powders such as acrylics can be used.

In addition, the F of the non-magnetic support in the tape running direction is
The -5 value is preferably 5 to 50 Kg / mm ² , the F-5 value in the tape width direction is preferably 3 to 30 Kg / mm ² , and the F-5 value in the tape longitudinal direction is the F-5 value in the tape width direction.
Generally, the value is higher than 5 values, but it is not limited to this value especially when the strength in the width direction needs to be increased. Also, 100 ° C. in the tape running direction and width direction of the non-magnetic support 3
The heat shrinkage percentage at 0 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage percentage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less.
The breaking strength in both directions 5 to 100 kg / mm ^2, the elastic modulus is preferably from 100 to 2,000 kg / mm ^2.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each process may be divided into two or more steps. All raw materials such as 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. In addition, the individual raw materials may be divided and added in two or more steps. 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. When a continuous kneader or a pressure kneader is used, 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. 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 simultaneous multi-layer coating method as disclosed in JP-A No. 62-212933 can be used for more efficient production. 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 paint, and when the lower layer is in a wet state, JP-B-1-46186 and JP-A-60-46186. -23
The upper layer is coated by the 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. 2,265,672, the upper layer and the lower layer are coated almost simultaneously by a single coating head having two slits for passing the coating liquid therein. 3. The upper layer and the lower layer are coated almost simultaneously by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic powder, JP-A-62-95174 is used.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in Japanese Patent Laid-Open No. 1-236968. Further, it is preferable that the viscosity of the coating liquid satisfies the numerical range disclosed in Japanese Patent Application No. 1-312659.

In the present invention, the above-mentioned lower layer coating solution is applied on the non-magnetic support by a so-called wet-on-wet coating method in which the coating solution is superposed in a wet state. The wet-on-wet coating method used to provide the lower layer and the upper layer in the present invention is a so-called sequential coating method in which the first layer is first coated and then the next layer is coated thereon as quickly as possible in a wet state, and a multilayer coating method. At the same time, it refers to a method of applying the extrusion coating method and the like.

As the wet-on-wet coating method, the 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 it is further preferable to perform an appropriate drying step in advance before orientation so that the orientation after drying becomes the highest. Further, when the present invention is applied to the disk medium, an orientation method that randomizes the orientation is rather required.

Further, a heat-resistant plastic roll of epoxy, polyimide, polyamide, polyimide amide, etc. is used as the calendering roll. Further, it is 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 2 or more at a temperature of 80 ° C. or more.

The friction coefficient of the upper layer and the opposite surface of the magnetic recording medium of the present invention to SUS420J is preferably 0.5 or less, further 0.3 or less, the surface resistivity of the magnetic layer is 10 ⁴ to 10 ¹¹ ohm / sq, the lower layer Is preferably 10 ⁴ to 10 ⁸ ohm / sq, and the surface electric resistance of the back layer is preferably 10 ³ to 10 ⁹ ohm.

The elastic modulus at 0.5% elongation of the upper layer 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.

Both the upper layer and the lower layer have a porosity of 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, 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 characteristic of the magnetic recording medium of the present invention is a magnetic field of 5
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 non-magnetic 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 700-4000 Kg / mm ² , yield stress 3-20 Kg / mm ² , preferably 3-15 Kg / mm ² .
² , yield elongation is 0.2-8%, preferably 0.4-5%
Is desirable.

This influences the durability because the ferromagnetic powder, the binder, the carbon black, the inorganic powder and the 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 μm, preferably 20 to 90 mg or the total thickness is 9.5 μm
When 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. Further, 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 spectroscope 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. Further, 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. and storage elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / cm.
² , and the loss elastic modulus E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 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 the binder, carbon black, and solvent, and associated with durability.

The 180 ° adhesion strength of the 8 mm width tape at 23 ° C. and 70% RH between the non-magnetic support and the magnetic layer is preferably 10 g or more. Further, the abrasion of the steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.7 × 10 ^{−7 to} 5 × 10 ⁻⁷ m ³ . This is a measure of the durability that is directly related to the wear of the surface of the magnetic layer and is mainly related to the ferromagnetic powder.

Further, five magnetic recording media of the present invention were photographed with an 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.
The above is desirable. The abrasive 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 the 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.

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

[0091]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. Example 1 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations.

Example 1-1 Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% by weight Inorganic powder surface treatment layer Al ₂ O ₃ (10% by weight) ) Specific surface area according to BET method 40 m ² / g DBP oil absorption amount 27 to 38 g / 100 g pH 7 carbon black 20 parts Average particle size 16 mμ DBP oil absorption amount 80 ml / 100 g pH 8.0 Specific surface area according to BET method 250 m ² / g volatile matter 1 .5% vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group 1 × 1 ^-4 eq / g containing butyl stearate 1 part coating solution ferromagnetic metal for stearate 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts the upper magnetic layer powder composition Fe / Zn / Ni = 92/ 4/4 100 parts Hc 1600 Oe BET specific surface area 60 m ² / g Crystallite size 195 Å Average major axis length 0.20 μm, acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Surface treatment agent: Al ₂ O ₃ , SiO ₂ vinyl chloride system copolymer 12 parts of -SO ₃ Na group containing 1 × 10 ^-4 eq / g, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (average particle size 0.3 [mu] m) 2 parts carbon black (average particle 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 50 parts Toluene 60 parts For each of the above two paints, after kneading each component with a continuous kneader, disperse using a sand mill. It was To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid for the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate was further added to each to have an average pore diameter of 1 μm. Filtration was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 2 μm, and immediately after that the thickness of the upper magnetic layer was 0.5 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. Then, after drying, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 1-1.

Similarly, the factors shown in Tables 1 and 2 were changed, and samples, Examples 1-2 to 1-12, and Comparative examples 1-1 to 1 were used.
-3 was prepared, the performance was evaluated in the same manner as described above, and the results are shown in Tables 1-2. Centerline average surface roughness (Ra): A three-dimensional surface roughness meter (manufactured by Kosaka Laboratory) was used, and the cutoff was 0.
It was measured at 25 mm.

Electromagnetic conversion characteristics 1.7 MHz output: FUJIX8 manufactured by Fuji Photo Film Co., Ltd.
A 7 MHz signal was recorded using an 8 mm video deck, and the 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The control is 8 mm tape SAG P6-120 manufactured by Fuji Photo Film Co., Ltd. 2. C / N: FUJIX8 8m manufactured by Fuji Photo Film Co., Ltd.
A 7 MHz signal was recorded using an m video deck, noise generated at 6 MHz when this signal was reproduced was measured with a spectrum analyzer, and the ratio of the reproduced signal to this noise was measured.

[0096]

[Table 1]

[0097]

[Table 2]

As is clear from the above table, the example samples are
Since the surface of the inorganic powder contains a surface-treated layer of Al ₂ O ₃ , SiO ₂ , ZrO _2, etc. as shown in the above table, the dispersibility is improved, the Ra is low, and the electromagnetic conversion characteristics are good. Comparative Example 1
In the case of -1, since the inorganic powder does not include the surface treatment layer, the dispersibility is poor, Ra and σ are high, and the electromagnetic conversion characteristics are poor. In Comparative Example 6-2, the electromagnetic conversion characteristics are poor because the magnetic layer is thick. In Comparative Example 3, a sample could not be prepared due to the successive layers.

Example 2 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Example 2-1 Lower non-magnetic layer coating liquid; same as in Example 2-1 Upper magnetic layer coating liquid Co-substituted barium ferrite 100 parts Specific surface area by BET method 35 m ² / g Average particle size 0.06, plate-like The ratio 5 vinyl chloride copolymer 9 parts -SO ₃ Na group 1 × 10 ^-5 eq / g containing, polymerization degree 300 particulate abrasive (Cr ₂ O, an average particle diameter of 0.3 [mu] m) 7 parts toluene 30 parts Methyl ethyl ketone 30 Parts After kneading the above composition with a kneader for about 1 hour, the following composition was further added and dispersed with the kneader for about 2 hours.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content average molecular weight 35000 methyl ethyl ketone 200 parts cyclohexanone 100 parts toluene 100 parts Next, the following carbon black and a coarse particle abrasive were added, and a dispersion treatment was carried out for 2000 hours with a sand grinder for 2000 hours.

Carbon black (average particle size 20 to 30 mμ) 5 parts Ketjen Black EC coarse particle abrasive made by Lion Akzo 2 parts α-alumina (AKP-12 made by Sumitomo Chemical Co., average particle size 0.5 μm) The composition was added, and the mixture was dispersed again in a sand grinder to obtain a coating liquid for the upper magnetic layer.

Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts Tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer obtained as described above were applied to polyethylene terephthalate having a thickness of 75 μm. First, the lower non-magnetic layer coating liquid was applied first, and then the upper magnetic layer coating liquid was applied in a wet state, and the back surface was treated in the same manner. The dry thickness of the lower non-magnetic layer is 2
μm, and the thickness of the magnetic layer was 0.5 μm. Then, calendar processing was performed to obtain a magnetic recording medium. After that, this magnetic recording medium was punched out into 3.5 inches,
The liner was put in a 3.5-inch cartridge having been installed inside, and predetermined mechanical parts were added to obtain a 3.5-inch floppy disk of Example 2-1. Further, similarly, the factors described in Table 3 were changed, and samples, Examples 2-2 to 2-7, and Comparative example 2 were used.
-1 was prepared, the performance was evaluated, and the results are shown in Table 3.

Initial 2F output: The sample of Example 2-1 was set as 100 and calculated as a relative value. Drive used is P
It is D211 (made by Toshiba Corporation).

[0104]

[Table 3]

From the above table, in the same manner as in Example 1, the sample floppy disk of Example had Al ₂ O ₃ and S on the surface of the inorganic powder.
Since the treatment layers such as iO ₂ and ZrO ₂ are included as shown in the above table, the dispersibility is improved, the Ra is low, and the electromagnetic conversion characteristics are good. In Comparative Example 2-1, the treatment layer is not included in the inorganic powder, so the dispersibility is poor, Ra and σ are high, and the electromagnetic conversion characteristics are poor.

Example 3 Polyethylene terephthalate (thickness 1
0 μm, F5 value: MD direction 20 Kg / mm ² , TD direction 14 Kg / mm ² , Young's modulus: MD direction 750 Kg
/ Mm ² , TD direction 470 Kg / mm ² ) or polyethylene terenaphthalate (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
750 Kg / mm ² ) and the following formulation was stirred with a Dispa stirrer for 12 hours to prepare an undercoat liquid.

Polyester resin (containing —SO ₃ Na group) 100 parts Tg 65 ° C. Na content 4600 ppm Cyclohexanone 9900 parts Using the obtained undercoat liquid, it was applied on the above non-magnetic support by dry coating at a thickness of 0.1 μm. did.

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. Formulation of coating liquid for upper magnetic layer Ferromagnetic powder: Fe alloy powder (Fe-Co-Ni) 100 parts Composition; Fe: Co: No: Ni = 92: 6: 2 Al ₂ O ₃ is used as a sintering inhibitor 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) 12000 weight average molecular weight (Mw) 38,000 polyurethane resin 5 parts -SO ₃ Na 8 x 10 ^-5 eq / g content -OH 8 x 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 menu After 6 hours mixed and dispersed in a sand mill ethyl ketone 150 parts The above composition,
Polyisocyanate (Coronate L) and oleic acid
5 parts, 7 parts of stearic acid and 15 parts of butyl stearate were added to obtain a coating liquid for the upper magnetic layer.

Coating liquid formulation for lower non-magnetic layer TiO ₂ 85 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment layer Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 4. 1 pH 6.5-8.0 Carbon black 5 parts Average particle size 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) 38,000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g containing -OH 8 × 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 cyclohexane 100 parts Methyl ethyl ketone 100 parts the above composition in a sand mill After 4 hours mixed and dispersed,
5 parts of polyisocyanate (Coronate L), 5 parts of oleic acid, 5 parts of stearic acid and 15 parts of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

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

Next, a coating solution was prepared according to the following formulation. BC layer formulation Carbon black 100 parts S _BET 220m ² / g Average particle size 17mμ DBP oil absorption 75ml / 100g Volatile content 1.5% pH 8.0 Bulk density 15 lbs / ft ³ Nitrocellulose RS1 / 2 100 parts Polyester polyurethane 30 Parts Nipolan (manufactured by Nippon Polyurethane Co.) Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation) 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 non-magnetic support provided with the magnetic layer to a dry thickness of 0.5 μm. The raw fabric thus obtained was cut into a width of 8 mm to prepare 8 mm video tapes of Sample 1 (PET support) and Sample 2 (PEN support).

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, 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 with an IBASII image processing device, and the average value d and the standard deviation σ were determined.

The average thickness d 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 thickness variation of the magnetic layer was 0.008 μm or less. Practically, σ is 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,
Then, it was washed with THF three times. 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 particle 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 practice, the acicular ratio is 2 to 20.
Has been found to be necessary, and is 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
Using 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 the thickness is practically required to be 10 nm or less, 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. In practice, Ra was found to be 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 practice
It was found that the thickness is preferably not more 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
Was found. Hr (90 °) is practically 100
0 to 2800 Oe is required, preferably 1200 to 25
It was found to be 00 Oe. It has been found that Br / Bm needs to be 0.75 or more for practical use, and is preferably 0.8 or more. It has been 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.

Apply the magnetic tape directly to the 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 0Å. Practically preferably 400Å
It was found to be below, and particularly preferably 100 to 300Å. (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 was 1200 Kg / mm ² at 0.5% elongation elastic modulus, the yield stress was 6 to 7 Kg / mm ² , and the yield elongation was 0.8%.
Practically preferably, Young's modulus is 400 to 2000 Kg / mm ^{2 at} 0.5% elongation elastic modulus of the tape, and particularly preferably 500 to 1500 Kg / mm ² at 0.5% elongation elastic modulus of the tape.
I found out. It has been found that the yield stress is practically preferably 3 to 20 Kg / mm ² , and particularly preferably 4 to 15. The yield elongation is practically preferably 0.2 to
It was found to be 8%, particularly preferably 0.4 to 5%. (7) Bending rigidity, circular stiffness Using a loop stiffener tester, width 8 mm, length 5
A 0 mm sample is used as a ring, and the force required to give a displacement of 5 mm at a displacement rate of about 3.5 mm / sec 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, 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) Stretch failure The crack elongation was measured at 23 ° C. and 70% RH.

Both ends of a 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 400 times to measure the elongation at which 5 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.

The sample was stored in a constant temperature bath 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 ratio. As a result, the heat shrinkage rate was 0.2%. Practically preferably 0.4% or less, particularly preferably 0.1 to
It was found to be 0.3%. (10) ESCA Cl / Fe spectrum α and N / Fe spectrum β were measured.

An X-ray photoelectron spectroscope (manufactured by PERKIN-FLMER) was used for the measurement of α and β. 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. Five minutes after the sample was evacuated to vacuum, 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 obtained by calculation and designated as α.

The N-1S spectrum and Fe-2P (3
/ 2) The integral intensity ratio with the spectrum was calculated and set as β. As a result, α was 0.45 and β was 0.07. Practically, it has been found that α is 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 (Rheovibron manufactured by Toyo Baldwin Co., Ltd.). 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 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 having a width of 8 mm was attached to a 3M adhesive tape, and 180 peel strength was measured at 23 ° C. and 70% RH. The result obtained was 50 g. It was found that the adhesion strength is preferably 10 g or more, and particularly preferably 20 g or more in practical use. (13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured.

The sample was fixed on the prepared glass by sticking both ends thereof with adhesive tape, and was slid by applying a load of 50 g to a 6.25 mmφ steel ball. At that time, after traveling once for a distance of 20 mm at a speed of 20 mm / sec, the steel ball was moved to a new magnetic surface and the same operation was repeated 20 times. Then, 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 are 0.7 × 10 ^{-5 to} 1.1.
It was × 10 ^-5 m ³ . Practically preferably 0.1-10
^{-5 to} 5 x 10 ^-5 m ³ , particularly preferably 0.4 x 1
It was 0 ^{−5 to} 2 × 10 ⁻⁵ m 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 polishing agent on the surface. 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, 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 10% or less, and particularly preferably 10% or less.

An 8 mm video tape having the above-described method and characteristics was compared with a tape currently on the market, and the results are shown in Table 4.

[0132]

[Table 4]

The evaluation method was the above-mentioned 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 and 90% for 2 weeks without rust on the surface.

× It should be stored at 60 ° C and 90% for 2 weeks and have rust on the surface. Running durability: 120 minutes of reproduction was repeated 100 times by incorporating in an 8 mm cassette. ○ No clogging that lasts for 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.

[0136]

According to the present invention, the dispersibility of the inorganic powder in the lower non-magnetic layer of the coating type magnetic recording medium having an extremely thin magnetic layer thickness of 1 μm or less is improved, so that the surface property of the magnetic layer can be improved and the lower layer and Disclosed is a magnetic recording medium that suppresses the disturbance of the interface of the upper layer to ensure a uniform magnetic layer and that can exhibit electromagnetic conversion characteristics comparable to those of a metal thin film type magnetic recording medium.

Claims (5)

[Claims] 1. An upper layer in which a lower layer non-magnetic layer having inorganic powder dispersed in a binder is provided on a non-magnetic support, and a ferromagnetic powder is dispersed in the binder while the lower non-magnetic layer is in a wet state. In a magnetic recording medium provided with a magnetic layer, the dry thickness of the upper magnetic layer is 1.0 μm or less, and the lower nonmagnetic layer contains a nonmagnetic inorganic powder having a surface layer coated with an inorganic oxide. A magnetic recording medium characterized by: 2. The inorganic oxide coating the surface of the non-magnetic inorganic powder contained in the lower non-magnetic layer is Al ₂ O ₃ or Si.
At least one selected from O ₂ and ZrO ₂ , and Al ₂ O ₃ is 1 to 1 with respect to the total weight of the nonmagnetic inorganic powder.
21% by weight, SiO ₂ 0.04 to 20% by weight, ZrO
_2. The magnetic recording medium according to claim 1, wherein ₂ covers 0.05 to 15% by weight. 3. The non-magnetic inorganic powder is 51 to 99.8 wt% of the whole inorganic powder contained in the lower non-magnetic layer, and the non-magnetic inorganic powder is mainly composed of rutile titanium dioxide. 5 to 30% by weight of the inorganic oxide
The magnetic recording medium according to claim 1, comprising: 4. The solvent used in the coating liquid for the lower non-magnetic layer and the upper magnetic layer both has a solubility parameter of 8 to 10.
11. The magnetic recording medium according to claim 1, wherein the compound having a dielectric constant of 11 and a dielectric constant at 20 ° C. of 15 or more is contained in an amount of 15% by weight or more. 5. The binder contained in the lower non-magnetic layer is-
_{COOM, -OSO 3 M, -SO 3} M, -PO (OM 1) (O
M ₂ ), —OPO (OM ₁ ) (OM ₂ ), —NR ₄ X (where M, M ₁ and M ₂ represent Li, Na, K, H, —NR ₄ or NHR ₃ and R represents Represents an alkyl group or H, X
Represents a halogen atom. 2. The magnetic recording medium according to claim 1, further comprising at least one polar group selected from