JP2001067651A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which exhibits a high C/N in magnetic recording of high density and a manufacturing method therefor. SOLUTION: In a magnetic recording medium in which a non-magnetic layer incorporating non-magnetic powder and a binder is provided on a non-megnetic flexible supporting body, and at least a magnetic layer incorporating ferromagnetic powder and the binder is provided on it, the average thickness (d) of the magnetic layer is 0.01 to 0.1 μm, the non-magnetic powder is acicular, and is distributed in the non-magnetic layer with its major axis being at an average angle of <=35 deg. to a plane of the non-magnetic flexible supporting body. A coating liquid for formation of the non-magnetic layer and a coating liquid for formation of the magnetic layer are simultaneously or successively applied on the non- magnetic flexible supporting body so as to form the magnetic layer on the non-magnetic layer, and then the non-magnetic plasticized supporting body is subjected to a treatment for smoothing and magnetic field orientation while the coated layer is still in the wetted state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magnetic recording medium exhibiting high output and a good C / N ratio in high-density recording, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, recording wavelengths have tended to be shorter with higher densities, and the problem of self-demagnetization loss during recording, in which the output is reduced when the magnetic layer is thicker, has become greater. For this reason, the thickness of the magnetic layer has been reduced. However, when a magnetic layer of 2 μm or less is directly applied to the support, the influence of the nonmagnetic support tends to appear on the surface of the magnetic layer. Tend to worsen. As one means for solving this problem, as described in JP-A-63-191315 and JP-A-63-187418, a non-magnetic layer is formed under the magnetic layer using a simultaneous multilayer coating method. There is a method in which a layer is provided and a high-concentration magnetic coating liquid is applied thinly. According to these inventions, the yield is dramatically improved, and good electromagnetic conversion characteristics can be obtained. It is also known to use acicular nonmagnetic powder for the nonmagnetic lower layer in order to smooth the surface of the magnetic layer to further increase the recording density. However, in order to meet recent demands for narrow tracks and low noise, it is necessary to further smooth the surface and improve the orientation of magnetic particles.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium exhibiting a high C / N ratio in high-density magnetic recording and a method of manufacturing the same.

[0004]

Means for Solving the Problems In order to provide a magnetic recording medium having a high C / N ratio in high-density magnetic recording, the inventors have intensively studied to improve the surface properties of the magnetic layer and the orientation of the magnetic material. . As a result, the following invention has been made. That is, the present invention provides a nonmagnetic layer containing a nonmagnetic powder and a binder (hereinafter, also referred to as a lower layer or a nonmagnetic lower layer) on a nonmagnetic flexible support, on which a ferromagnetic powder and a binder are provided. In a magnetic recording medium provided with at least a magnetic layer (hereinafter also referred to as a magnetic upper layer) containing:
01 to 0.1 μm, the non-magnetic powder is acicular, and its major axis is an average of 35 to the non-magnetic flexible support plane.
The present invention relates to a magnetic recording medium, wherein the magnetic recording medium is distributed in the nonmagnetic layer at an angle equal to or less than degree. Further, the present invention provides a coating solution for forming a non-magnetic layer containing a non-magnetic powder and a binder and a coating solution for forming a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic flexible support. The method is characterized in that a magnetic layer is formed on a non-magnetic flexible support so that a magnetic layer is formed on the layer, simultaneously or sequentially, and smooth coating and magnetic field orientation are performed while the coating layer is in a wet state. The present invention relates to a method for manufacturing the magnetic recording medium of the present invention.

[0005] In the above magnetic recording medium, the following aspects are preferred. (1) A magnetic recording medium comprising the needle-shaped nonmagnetic powder in which three or more particles form a bundle structure. (2) A magnetic recording medium wherein the thickness of the nonmagnetic layer is less than 0.5 μm. (3) The magnetic recording medium, wherein the nonmagnetic powder has an average major axis length of 0.2 μm or less and a needle ratio in a range of 2 to 20. (4) The magnetic recording medium wherein the nonmagnetic layer contains granular particles having an average primary particle size of 50 nm or less, and the content ratio of the granular particles to the acicular nonmagnetic powder is in the range of 5:95 to 40:60. . (5) the granular particles have an average primary particle size of 30 nm or less;
A magnetic recording medium that is a carbon black having an oil absorption of 200 ml / 100 g or less.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Magnetic Layer] In this specification, a magnetic layer is also called a magnetic upper layer. In the magnetic recording medium of the present invention, the thickness of the magnetic upper layer is in the range of 0.01 to 0.1 μm.
By setting the thickness of the magnetic upper layer within this range, the C / N ratio and resolution of digital recording can be improved. When a very thin magnetic layer is coated (especially wet on wet)
In this way, the lower layer greatly affects the orientation state of the magnetic material and the surface roughness of the magnetic surface. At this time, a needle-shaped non-magnetic powder is used for the lower layer of the non-magnetic layer, and the major axis of the needle-shaped non-magnetic powder is set at an average angle of 35 degrees or less with respect to the plane of the non-magnetic flexible support. It has been found that the distribution in the inside can improve the orientation and surface properties of the magnetic material. this is,
The orientation of the magnetic material in the upper layer is reduced by reducing the orientation of the long axis of the non-magnetic powder in the thickness direction and reducing the geometric unevenness,
This is because the smoothness of the interface between the upper and lower layers and the surface of the magnetic layer is improved. This effect becomes more remarkable as the magnetic upper layer is thinner.

Further, when the thickness of the lower layer is reduced, the direction of the long axis of the acicular particles in the lower layer tends to be parallel to the surface of the support, and the above-mentioned effect is further enhanced. However, when the thickness of the lower layer is reduced, the molding effect by the calendar tends to be reduced. In such a case, it is preferable that a granular powder having an average primary particle size of 50 nm or less is mixed with the acicular nonmagnetic powder at a specific ratio. In the lower layer before applying the calendar,
This is because the granular particles enter between the acicular particles to form appropriate voids, and the calenders crush the voids, thereby enhancing the molding effect. A desired effect can be obtained by using the above-mentioned granular particles and the mixing ratio. The granular particles have an average primary particle size of 30 nm or less and an oil absorption of 200
It is particularly preferable to use a carbon black of not more than ml / 100 g, since this kind of carbon black has appropriate softness. The mixing of fine particles of carbon black in the lower layer is disclosed in JP-A-6-236542. However, the carbon black described in this publication has an oil absorption of 300 ml / 100 g, which is larger than the preferable range in the present invention. In the present invention, a carbon black having a preferable oil absorption is preferable because dispersion is better and carbon black can easily enter between the acicular particles.

In the magnetic recording medium of the present invention, the average value d of the thickness of the magnetic layer is suitably 0.01 to 0.1 μm, preferably 0.02 to 0.09 μm, and more preferably 0.03 to 0.07 μm. The object of the present invention can be achieved by using a single magnetic layer or a plurality of magnetic layers. In the case of a plurality of magnetic layers, for example, the technology described in JP-A-6-139555 can be applied. In the magnetic recording medium of the present invention, since the thickness of the magnetic layer is relatively thin, a saturated recording state is obtained. Therefore, it is ideal that the thickness of the magnetic layer does not fluctuate. However, if the relationship between the standard deviation σ and d of the magnetic layer thickness is in the range of σ / d ≦ 0.5, the thickness fluctuation of the magnetic layer is practically allowable. further,
It is preferable that σ / d ≦ 0.3. As a specific means for reducing σ, for example, as described in Japanese Patent No. 2566096, (1) a lower layer non-magnetic coating solution is thixotropic, and (2) an acicular non-magnetic powder is used for the lower layer. , (3) wet on dry to apply the magnetic upper layer after coating and drying the non-magnetic lower layer
There are methods. The residual magnetization of the magnetic layer is 6.26 × 10 ^-7 to
Suitably, it is 6.26 × 10 ⁻⁶ T (0.0005 to 0.005 emu / cm ² ). The amount of residual magnetization can be appropriately optimized by a recording / reproducing method. There are various methods for setting the residual magnetization amount in the above range. For example, when this medium is reproduced at the inductive head, a larger value can be set within the range of the residual magnetization amount. When the O / W request to set the magnetic layer to set the thin (e.g. 0.1μm or less), [sigma] s is to use a large ^{140~160 A · m 2 / kg (} emu / g) alloy powder as magnetic powder preferable. On the other hand, when reproducing with the MR head, it is appropriate to increase the number of particles and at the same time, set the amount of residual magnetization to a smaller value within the above range. In this case, the magnetic powder should have a σs of 50 to 130 A · m ² / kg (emu / g).
It is appropriate to improve the packing density as much as possible by reducing the amount of binder in the lower layer.

In the magnetic layer of the present invention, as the magnetic powder, for example, an alloy powder having a s of 100 to 160 A · m ² / kg (emu / g), a s 50 to 80 A · m ² / kg (emu / g) ) Hexagonal ferrite, macenite, and Co-ferrite can be used. The coercive force Hc of the magnetic layer is 119 to 318 kA / m (1500 to 4000 Oe), preferably 143
~ 279 kA / m (1800 ~ 3500 Oe), more preferably 159 ~ 239
Since it is kA / m (2000 to 3000 Oe), the same magnetic powder is preferably used for Hc. The magnetic particle size is preferably small as far as the influence of the thermal fluctuation does not occur, and does not depend on the reproducing head.
Practically, in the case of acicular particles, the average major axis length is 0.05 to 0.2 μm
It is appropriate that the minor axis diameter is in the range of 0.01 to 0.025 μm. For hexagonal ferrite, the plate diameter is 0.01 to
It is appropriate that the thickness is in the range of 0.2 μm and the thickness is in the range of 0.001 to 0.1 μm. However, in the case where smaller particles are provided due to the progress of technology, the present invention is not limited to the above range.
Smaller particles can also be used.

The magnetic powder contains Al, S, and
i, S, Sc, Ti, V, Cr, Cu, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
It may contain atoms such as d, P, Co, Mn, Zn, Ni, Sr, and B. A to improve thermal stability
l, Si, Ta, Y, etc. can be adhered or solid-solved on the surface. In particular, in order to increase Hc, Co, Sm, Nd or the like can be added in an amount of 5 to 40% by weight based on Fe. These magnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion.

As the binder used for the magnetic upper layer, known binders, for example, those described in Japanese Patent Nos. 2566096 and 2571351 can be used. These binders include functional groups (SO ₃ M, PO
Preferably to contain ₃ M, etc.), is also preferable further comprising epoxy groups. The molecular weight is between 10,000 and 100,000, preferably between 20,000 and 60,000. The amount used is 5 to 25 parts, preferably 5 to 20 parts, more preferably 5 to 15 parts based on 100 parts by weight of the magnetic powder.

For the magnetic layer, known abrasives such as α-alumina and Cr ₂
O ₃ etc. can be included, but the average particle size is wet on wet
It is preferable that the thickness is 1/3 or more and 5 times or less the thickness of the magnetic layer in the application, and 1/3 or more and 2 times or less the thickness of the magnetic layer in the wet on dry application. If it is too large, it will cause a noisy traffic out. Particularly in the case of wet-on-dry coating, the abrasive is liable to become projections, so that fine particles are preferred. Known techniques can be used for the pH and surface treatment of the abrasive. In addition, a solid lubricant (carbonate having a particle size of 30 μm or more) or a liquid lubricant such as a fatty acid or the same ester can be added to the magnetic layer.

[Non-magnetic layer] In this specification, the non-magnetic layer may be referred to as a lower layer or a non-magnetic lower layer. The non-magnetic powder used as the main component in the non-magnetic lower layer is acicular, and the major axis length is
It is suitable that the thickness is 0.2 μm or less, preferably 0.15 μm or less, and more preferably 0.1 μm or less. The needle ratio of the nonmagnetic powder is 2 to 20, preferably 3 to 10. Specifically, a nonmagnetic powder particularly preferred in the present invention is a needle-shaped metal oxide having a pH of 5 or more. Since these have high adsorptivity to functional groups, they are well dispersed and have high mechanical strength of the coating film. Other preferred embodiments of the non-magnetic powder, the oil absorption using DBP is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g,
More preferably, the powder is 20 to 60 ml / 100 g.
The specific gravity is 1 to 12, preferably 3 to 6. The ignition loss is preferably 20% by weight or less. The non-magnetic powder used in the present invention preferably has a Mohs hardness of 4 or more. The roughness factor of the powder surface is preferably in the range of 0.8 to 1.5, and more preferably 0.9 to 1.2. Stearic acid (SA)
The adsorption amount is 1 to 20 μmol / m ² , more preferably 2 to 15 μmol / m ² .
μmol / m ² . The heat of wetting of the lower nonmagnetic powder in water at 25 ° C. is 2.0 × 10 ⁻⁵ J / cm ² (200 erg / cm ² ) to 6.0 × 10 ^−5.
It is preferably in the range of J / cm ² (600 erg / cm ² ). Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is 1 to 10
Individual / 100 Angstroms range but suitable. The pH of the isoelectric point in water is preferably between 5 and 10.

At least a part of the surface of these nonmagnetic powders is composed of Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO
It is preferable to perform a surface treatment so as to be coated with. Particularly preferred surface coating compounds for dispersibility are Al ₂ O ₃ , SiO ₂ , Ti
O ₂ and ZrO ₂ . These may be used in combination or may be used alone. Alternatively, a co-precipitated surface treatment layer may be used depending on the purpose, or a structure in which the surface is first treated so as to be covered with alumina and then the surface layer is treated so as to be covered with silica, and vice versa. Can also be taken. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense. These needle powders include TiO ₂ , hematite, α-alumina, β-alumina, γ-alumina, ZrO ₂ , CeO ₂ , Cr ₂ O ₃ , Si
Oxides such as O ₂ , non-magnetic metals and the like can be mentioned.

The acicular nonmagnetic powder contained in these lower layers is
It is appropriate that the major axis is distributed at an angle of 35 degrees or less on average with respect to the plane of the non-magnetic support, preferably 30 degrees or less on average. The angle of the needle-shaped nonmagnetic powder contained in the lower layer can be determined based on a photograph obtained by observing and photographing a sample section with a transmission electron microscope and further performing image processing, as described in detail in Examples. . In order to distribute the acicular nonmagnetic powder at a predetermined angle in the nonmagnetic layer, a method of repeatedly applying the lower layer thinly (for example, with a thickness within three times the minor axis length), and only the lower layer or the lower layer After applying the magnetic layer and the magnetic layer, a smoothing process using a smooth lot bar or the like and applying a shearing force along the plane of the support can be employed. However, the latter smoothing treatment is preferred because the needle-shaped nonmagnetic powder can be efficiently oriented.

Further, it is preferable that the acicular nonmagnetic powder is formed of a bundle-like aggregate in which three or more particles form a bundle-like structure. However, if there are more than 100 bundled aggregates, it may cause traffic out, so it is desirable that the powder does not contain more than 100 bundled aggregates. The bundle of three or more nonmagnetic powders is formed by the following method. That is, the needle-shaped non-magnetic powder is subjected to a dense treatment or kneaded with a kneader or the like to generate so-called activation, and ZrO
_It is obtained by appropriately destroying the aggregated structure with a high specific gravity, such as steel or steel, and removing 100 or more aggregated particles with a filter to prepare a coating solution.

Further, in the lower layer,
5: 95-40: 60, preferably 10: 90-30:
Mixed with granular powder with average primary particle size of 50 nm or less in the range of 70
Preferably. As these granular powders, for example,
TiO_Two, Hematite, alumina, ZrO _Two, CeO_Two, Cr_TwoO_Three, S
iO_TwoSuch as oxides, non-magnetic metals, organic resin fillers, and carbon
Black and the like. The above granular powder is particularly
Average primary particle size 30 nm or less, preferably 20 nm or less, oil absorption
Preferred is a carbon black of 200 ml / g or less, preferably 150 ml / g.
No.

The lower layer may be mixed with a magnetic material for the purpose of, for example, imparting thixotropic properties. At this time, when the magnetization contributes to the recording / reproduction, it becomes a substantially thick film,
The thin layer effect is impaired. From such a viewpoint, H
A magnetic material having a high c (80% or more of the upper layer Hc) and hardly magnetized can be added to the lower layer within 30% by volume of the lower layer or a soft magnetic material having almost no residual magnetization.

The binder used for the lower layer may be the same as that for the magnetic upper layer, but preferably contains a functional group (described above) for improving dispersibility, and has a molecular weight of 20,000 to 50,000, preferably 3,000 to 50,000. 50,000. If the molecular weight is too large, the calender molding effect will deteriorate. It is more effective to apply a surface treatment to the non-magnetic powder with alumina or an aromatic phosphorus compound which promotes dispersion. For details, reference can be made to the binders described in Japanese Patent Nos. 2566088 and 2634792.

[Common to magnetic layer and non-magnetic layer]
For the lower layer, the following polyisocyanates may be used as a binder. Tolylene diisocyanate, 4-4 '
Diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, Isocyanates such as phenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used.
Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L and Corone-L.
HL, CORONATE 2030, CORONATE 2031, Millionate MR, Millionate MTL, manufactured by Takeda Pharmaceutical Co., Ltd.
Takenet D-102, Takenet D-110N, Takenet D-200, Takenet D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc., and these can be used alone or in combination of two or more by using the difference in curing reactivity as the non-magnetic layer and the magnetic layer.

Examples of the carbon black used for the upper layer of the present invention include furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 1
0-400ml / 100g, particle size 5mμ-300m
It is preferable that μ, pH is 2 to 10, water content is 0.1 to 10% by weight, and tap density is 0.1 to 1 g / ml. 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, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 5
5, # 50, # 35, manufactured by Mitsubishi Chemical Corporation, # 2400
B, # 2300, # 900, # 1000 # 30, # 4
0, # 10B, manufactured by Konlon Via Carbon, CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5 and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the ferromagnetic powder. Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength. These functions differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts and combinations in the magnetic layer and the lower layer, and are based on the above-mentioned properties such as particle size, oil absorption, conductivity and pH. Of course, it is possible to use them properly according to the purpose. Carbon black that can be used in the magnetic layer of the present invention is, for example, "Carbon black".
Bon Black Handbook "Carbon Black Association Edition" can be referred to.

The abrasive used in the present invention includes α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, titanium nitride having an α conversion of 90% or more. -Bytes,
Known materials mainly having a Mohs hardness of 6 or more, such as titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used.
These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% by weight or more. Tap density is 0.3-2g / ml,
Preferably, the water content is 0.1 to 5% by weight, the pH is 2 to 11, and the specific surface area is 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specific examples of the abrasive used in the present invention include AKP-20, AKP-30, and AK manufactured by Sumitomo Chemical Co., Ltd.
P-50, HIT-50, HIT-55, HIT-60
A, HIT-70, HIT-100, manufactured by Nippon Chemical Industry Co., Ltd., G
5, G7, S-1, manufactured by Toda Kogyo Co., Ltd., TF-100, TF
-140 and the like. The abrasive used in the present invention can be of different types, amounts and combinations for the magnetic layer (upper and lower layers) and the non-magnetic layer, and can be of course used according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

In the present invention, additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like can be used. Molybdenum disulfide, tungsten graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar group, fatty acid modified silicone
, Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol,
Alkyl phosphates and their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds) And may be branched), and their metal salts (Li, Na, K, C
u) or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched), Carbon number 12 ~
22 alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and monovalent, divalent, trivalent, having 2 to 12 carbon atoms;
Mono- or di-fatty acid esters or tri-fatty acid esters, alkylene oxides comprising any one of tetravalent, pentavalent and hexavalent alcohols (which may contain unsaturated bonds or may be branched) Fatty acid esters of polymerized monoalkyl ethers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

Specific examples thereof 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 and lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums Or a cationic surfactant such as a sulfonium, a carboxylic acid, a sulfonic acid,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfate groups, phosphate groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, alkylbedine type, etc. Etc. can also be used.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
It is not 0% pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in the lower layer and the magnetic upper layer in different types and amounts as needed. For example, controlling the oozing to the surface using fatty acids having different melting points in the lower layer and the magnetic upper layer,
Controls bleeding to the surface using esters with different boiling points and polarities, improves coating stability by adjusting the amount of surfactant, and increases the amount of lubricant added to the non-magnetic layer for lubricating effect However, the present invention is not limited to the example shown here. Further, all or a part of the additives used in the present invention may be added at any step of the production of the magnetic paint, for example, when mixed with the ferromagnetic powder before the kneading step, the ferromagnetic powder and the binder , A kneading step with a solvent, a dispersing step, a dispersing step, a dispersing step, and a dissolving step immediately before coating. Also, after applying the magnetic layer according to the purpose,
The purpose may be achieved by applying a part or all of the additive by simultaneous or sequential application. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after the slit is completed.

Examples of commercial products of these lubricants used in the present invention include NAA-102 and NAA-4 manufactured by NOF Corporation.
15, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, Cation SA, Cation MA, Cation A
B, cation BB, Nimin L-201, Nimin L-202, Nimin S-202, Nonion E-20
8, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laureate, erucic acid, manufactured by Kanto Chemical Co., Inc., oleic acid, manufactured by Takemoto Yushi, FAL-205, FAL-123,
Engelbu LO, Engelbu IP manufactured by Shin Nippon Rika Co., Ltd.
M, Sansocizer-E4030, manufactured by Shin-Etsu Chemical Co., Ltd., TA-
3, KF-96, KF-96L, KF96H, KF41
0, KF420, KF965, KF54, KF50, K
F56, KF907, KF851, X-22-819,
X-22-822, KF905, KF700, KF39
3, KF-857, KF-860, KF-865, X-
22-980, KF-101, KF-102, KF-1
03, X-22-3710, X-22-3715, KF
-910, KF-3935, manufactured by Lion Armor Co., Ltd., Armide P, Aromide C, Amoslip CP, manufactured by Lion Yushi, Deuomin TDO, manufactured by Nisshin Oil Co., Ltd., BA
-41G, Sanyo Kasei Co., Ltd., Profan 2012E, Newport PE61, Ionet MS-400, Ionet MO-200 Ionet DL-200, Ionet D
S-300, Ionnet DS-1000 Ionnet DO
-200 and the like.

[Nonmagnetic Flexible Support] The thickness of the magnetic recording medium of the present invention is such that the nonmagnetic flexible support has a thickness of 1 to 100 μm.
m, preferably 3 to 80 μm.
The thickness of the magnetic upper layer is 0.01 to 0.1 μm, preferably 0.02 to 0.09
Suitably, it is μm. An undercoat layer for improving adhesion may be provided between the nonmagnetic flexible support and the lower layer. The undercoat layer thickness is suitably from 0.01 to 2 μm, preferably from 0.02 to 0.5 μm. Also,
A back coat layer may be provided on the non-magnetic support on the side opposite to the magnetic layer side. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and backcoat layers can be used.

The non-magnetic flexible support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulostriacetate, polycarbonate, polyamide, polyimide and polyamide. Imide, polysulfone, aramid,
A known film such as an aromatic polymer can be used. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance.

As the nonmagnetic flexible support, a surface having a surface roughness spectrum measured by AFM having a roughness intensity at a wavelength of 1 to 5 μm is 0.5 nm ² or less, preferably 0.4 nm ² or less, and more preferably 0.3 nm ² or less. The roughness intensity at a wavelength of 0.5 μm to 1 μm is 0.
It is preferable to use those having a thickness of 02 to 0.5 nm ² , preferably 0.04 to 0.3 nm ² . The surface roughness can be freely controlled by applying the size and amount of the filler added to the support or by dispersing the filler in a binder. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and organic fine powders such as acrylic. When the nonmagnetic support used in the present invention is a tape, the yank ratio in the MD direction is 3.9.
^{~14.7 GPa (400~1500 Kg / mm 2} ), preferably 4.9 to 12.7
GPa (500-1300kg / mm ² ), yanking rate in TD direction 4.9-19.6G
Pa (500-2000 kg / mm ² ), preferably 6.9-17.6 GPa (70
TD / MD ratio is 1/1 to 1/5, preferably 1/1 to 1/3 at 0 to 1800 kg / mm ² ).

The heat shrinkage of the support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, at 80 ° C. for 30 minutes. The heat shrinkage is preferably 1% or less, more preferably 0.5% or less. Breaking strength 0.049-0.9 in both directions
8 GPa (5 to 100 kg / mm ² ) is preferred.

[Method of Manufacturing Magnetic Recording Medium] The magnetic recording medium of the present invention can be manufactured by applying and drying a paint for forming each layer. The step of producing the paint comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting viscosity after dispersion.

The organic solvent used in the method for producing a magnetic recording medium of the present invention may be any desired ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol and the like. Alcohols such as alcohol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate;
Esters such as isopropyl acetate, ethyl lactate and glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether and dioxane, benzene, toluene, xylene, cresol,
Aromatic hydrocarbons such as chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, chlorinated hydrocarbons such as dichlorobenzene, N, N-dimethylformamide,
Hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The type of the organic solvent used in the present invention is preferably the same for the magnetic layer and the non-magnetic layer. The amount added may be changed. Use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the non-magnetic layer to improve coating stability. Specifically, it is important that the arithmetic average value of the upper solvent composition does not fall below the arithmetic average value of the lower solvent composition. is there. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that the solvent composition contains 50% or more of a solvent having a dielectric constant of 15 or more. Further, the dissolution parameters are preferably from 8 to 11.

In order to manufacture the magnetic recording medium of the present invention, it is needless to say that a known manufacturing technique can be used as a part of the process. By using a material having a strong kneading force such as a kneader, a magnetic recording medium having a high residual magnetic flux density (Br) can be obtained. When a continuous kneader or a pressure kneader is used, the ferromagnetic powder and the binder all or a part thereof (however, preferably 30% or more of the total binder) and 15 to 500 parts by weight based on 100 parts by weight of the ferromagnetic powder.
It is kneaded in the range of parts by weight. Details of these kneading processes are described in JP-A-1-106338 and JP-A-6-106338.
4-79274. When preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are preferable.

In the production of the magnetic recording medium of the present invention, the major axis of the acicular nonmagnetic powder is distributed in the nonmagnetic layer at an average angle of 35 degrees or less with respect to the plane of the nonmagnetic flexible support. further,
As described above, for the purpose of forming a non-magnetic powder composed of three or more bundles, the needle-shaped non-magnetic powder is thickly processed or kneaded with a kneader or the like to generate so-called activation, and further, After appropriately breaking the aggregated structure with high specific gravity such as ZrO ₂ or steel, 100 or more aggregated particles can be removed with a filter to prepare a coating solution. A coating solution for forming a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic flexible support and a coating solution for forming a magnetic layer containing a ferromagnetic powder and a binder are coated on the nonmagnetic layer with a magnetic material. Simultaneously or sequentially coated on a non-magnetic flexible support to form a layer,
While the coating layer is in a wet state, a method of performing smoothing treatment and magnetic field orientation can be used.

Examples of the apparatus and method for applying the magnetic recording medium having the above-mentioned multilayer structure include the following methods and apparatuses. 1, the lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the application of magnetic paint, and the lower layer is wet while the lower layer is in a wet state. The upper layer is applied by a support pressure type extrusion coating apparatus disclosed in Japanese Unexamined Patent Publication No. 60-238179 and Japanese Patent Application Laid-Open No. 2-265672. 2, JP-A-63-88080, JP-A-2-17971, JP-A-2-265672, the upper and lower layers by one coating head containing two coating liquid passage slits as disclosed in JP-A-2-265672 Are applied almost simultaneously. 3. The upper and lower layers are applied almost simultaneously by an extrusion coating apparatus with a back-up roll disclosed in Japanese Patent Application Laid-Open No. 2-174965.

Incidentally, in order to prevent a decrease in the electromagnetic conversion characteristics and the like of the magnetic recording medium due to agglomeration of the magnetic particles, Japanese Patent Laid-Open No. 62-951 discloses a method.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in Japanese Patent Application Laid-Open No. 74-136 or Japanese Patent Application Laid-Open No. 1-236968. Furthermore, regarding the viscosity of the coating liquid,
It is appropriate to satisfy the numerical range disclosed in JP-A-3-8471. Further, the smoothening treatment can be performed, for example, by applying a stainless steel plate to the surface of the coating layer on the wafer. In addition, a method using a solid smoother as described in JP-B-60-57387, static A method of scraping and measuring the coating liquid with a rod that is rotating or rotating in the direction opposite to the web running direction, a method of smoothing the surface of a coating liquid film by bringing a flexible sheet into surface contact, etc. Can also. In addition, 100
Solenoid with mT (1000G) or more and 200 mT (2000G)
It is preferable that the above-mentioned cobalt magnets are used together with the same polarity facing each other. When the present invention is applied to a disk medium, an orientation method for randomizing the orientation is required.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide can be used as the calendering roll. Further, the treatment can be carried out by metal rolls. The processing temperature is preferably 70 ° C. or higher, more preferably 8 ° C.
Suitably, it is 0 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / c.
Suitably, it is at least m. The friction coefficient of the magnetic layer surface of the magnetic recording medium of the present invention and the opposite surface thereof to SUS420J is preferably 0.5 or less, more preferably 0.3 or less.
The surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / s
q, the elastic modulus of the magnetic layer at 0.5% elongation is preferably 0.98 to 19.6 GPa (100 to 2000 k
g / mm ² ), and the breaking strength is preferably 9.8 × 10 ^{−5 to} 2.9 × 10 ^5
-3 GPa (1 to 30 kg / cm ² ), and the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa in both the running direction and the long direction.
(100-1500 kg / mm ² ), residual elongation is preferably 0.5% or less, and heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less.
Below, most preferably 0.1% or less is appropriate respectively. The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus in the dynamic viscoelasticity measurement measured at 110 Hz) is 50 ° C.
It is preferably at least 120 ° C. and at most 120 ° C.
0 ° C. is preferred. Loss modulus is 1 × 10 ³ -8 × 10 ⁴ N /
It is preferably in the range of cm ² (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
Suitably, it is less than m ² . The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the lower layer and the magnetic layer.
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 in which repetitive use is emphasized, a higher porosity is often preferable in running durability. The magnetic characteristics of the magnetic recording medium of the present invention
When measured at 398 KA / m (5 KOe), the squareness ratio in the tape running direction is at least 0.70, preferably at least 0.80, and more preferably at least 0.90. It is preferable that the squareness ratio in the two directions perpendicular to the tape running direction is 80% or less of the squareness ratio in the running direction. The SFD (Switching Field Distribution) of the magnetic layer is 0.
It is preferably 6 or less. The surface of the magnetic layer has a roughness component intensity of 0.2 nm at a wavelength of 1 to 5 μm in the roughness spectrum.
² or less, and the intensity of the roughness component at a wavelength of 0.5 to 1.0 μm is 0.02 to
It is suitably a 0.1 nm ^2. To improve the C / N ratio, the smaller the roughness intensity is, the better. However, to improve the running durability, the roughness intensity in the wavelength range of 0.5 to 1.0 μm is maintained at 0.02 to 0.1 nm ² . There is a need.

Although the magnetic recording medium of the present invention has a lower layer and an upper magnetic layer, it is easily presumed that the physical properties of the lower layer and the magnetic 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 lower layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. What kind of physical properties are to be provided to each of the two or more magnetic layers can be referred to a known technique regarding the magnetic layer. For example, making the Hc of the upper magnetic layer higher than the Hc of the lower layer is disclosed in JP-B-37-2218 and JP-A-58-1983.
There are many inventions such as Japanese Patent Application Laid-Open No. 56228/1993, but by increasing the thickness of the magnetic layer as in the present invention, higher H
Recording is also possible with the magnetic layer c.

[0041]

Next, the details of the present invention will be specifically described with reference to examples. In the examples, "parts" indicates "parts by weight".
Means Non-magnetic lower layer Non-magnetic powder α-Fe ₂ O ₃ 80 parts Average major axis length 0.1 μm Specific surface area by BET method 48 m ² / g pH 8, Fe ₂ O ₃ content 90% or more DBP oil absorption 27-38 ml / 100 g Surface coating compound Al ₂ O ₃ carbon black 20 parts Average primary particle diameter 16 μm DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer 10 parts Nippon Seon MR-110 polyester polyurethane resin 5 parts Molecular weight 35,000 Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts

Magnetic layer Ferromagnetic metal fine powder Composition Fe / Co = 80/20 100 parts Hc 183 kA / m (2300 Oe), specific surface area by BET method 54 m ² / g Crystallite size 165 Å, surface coating compound Al ₂ O ₃ , particle size (major axis diameter) 0.1 μm, needle ratio 8 σs: 150 Am ² / kg (emu / g) Vinyl chloride copolymer 5 parts MR-110 polyester polyurethane resin manufactured by Nippon Seon Co., Ltd. 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g containing α-alumina (particle size 0.1 μm) 5 parts Carbon black (Particle size 0.10 μm 0.5 parts Butyl stearate 1.5 parts Stearic acid 0.5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts

Each of the above two paints was kneaded with a continuous kneader, and then dispersed for 6 hours in a ball mill using a steel wheel. To the obtained dispersion, 3 parts of polyisocyanate was added to the lower layer coating solution and 1 part to the magnetic layer coating solution, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was added to each, and a filter having an average pore diameter of 1 μm was added. The solution was filtered using-to prepare a coating solution for forming a lower layer and a magnetic layer. The resulting lower layer coating solution is 5.5 μm thick and has a thickness of 5.5 μm so that the thickness of the magnetic layer becomes 0.1 μm immediately after drying so that the thickness after drying becomes 0.3 μm. 0.5μm, 1μm and 5 wavelengths in roughness spectrum
roughness component intensity respectively 0.05 nm ² of [mu] m, 0.09 nm ^2, and 0.
A 11 nm ^2, 600 yank Bu rate of MD and TD, respectively kg /
Simultaneous multi-layer coating on polyethylene naphthalate supports of mm ² and 900 kg / mm ² , and while both layers are still wet, a stainless steel plate with a surface roughness Ra of 1.5 nm 300 mT (3000G) after smoothing
After being oriented and dried by a rare earth magnet having a magnetic force of 150 mT (1500 G) and a solenoid having a magnetic force of 150 mT (1500 G), the material is treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls to a width of 8 mm. An 8 mm videotape was manufactured by slitting.

Evaluation method (1) The C / N ratio was measured using a drum tester. The head used was a MIG head having a Bs of 1.2T for recording and reproduction and a cap length of 0.22 μm. A head / medium relative speed at the time of recording / reproduction was 10.5 m / sec, a single frequency signal of 21 MHz was recorded, and the reproduction spectrum was observed with a Shiva Soku spectrum analyzer. The C / N ratio was a ratio between a carrier output of 21 MHz and a noise of 19 MHz. (2) Thickness measurement A sample tape was cut out to a thickness of about 0.1 μm in the longitudinal direction with a Tyrmont cutter, and the magnification was 1000 with a transmission electron microscope.
Observation and photography were performed at a magnification of 00, and a line was drawn on the surface of the magnetic layer and the interface between the magnetic layer and the lower layer, and the measurement was performed using an image processing apparatus IBAS2 manufactured by Zeiss. When the measurement length was 21 cm, the measurement was performed 85 to 300 times, and the average value d and the standard deviation σ were calculated. (3) Confirmation of Orientation Angle and Bundle Structure of Acicular Non-Magnetic Powder Read from a slice photograph in the same manner as in the thickness measurement described above. The orientation angle was determined by averaging 500 angles of the major axis of the primary particles of the acicular nonmagnetic powder with the nonmagnetic support and averaging them. (4) Ra Measurement The center line average roughness of the surface of the magnetic layer was determined using a light interference type surface roughness meter “TOPO-3D” manufactured by WYKO. (6) SQ VSM was measured with an external magnetic field of 796 kA / m (10 kOe).

[0045]

[Table 1]

[0046]

[Table 2]

Description of Examples / Comparative Examples The electromagnetic conversion characteristics were based on Comparative Example 1 (0 dB). The video tape of Comparative Example 1 was manufactured by the method disclosed in
It was produced in the same manner as in Example 1 of JP-A-6-236542. The effect was determined based on whether the C / N ratio (in general, an error rate of one digit affects the error rate at 2 dB) is improved by 2 dB or more.
In the table, “needle hematite” is needle hematite, “carbon” is carbon black, and “granular hematite” is granular hematite. Example 1 is an example that satisfies all the requirements described in claims 1 to 6. The C / N ratio was improved by 4.9 dB as compared with Comparative Example 1. Example 2 Like the example 1, the example satisfies all the requirements described in claims 1 to 6. The thickness of the lower layer is close to the upper limit of claim 3, and the major axis length of the nonmagnetic powder contained in the lower layer is
This is an example in which a value close to the upper limit is used. Although slightly inferior to Example 1, a C / N ratio of 4.7 dB, which is almost the same performance, was obtained. Example 3 This is an example in which the lower non-magnetic powder in which the number of particles constituting the bundle structure is out of the range of Claim 2 and the number of the lower non-magnetic powder is 2 is increased by extending the lower layer dispersion time from 6 minutes to 10 minutes. Compared with Examples 1 and 2, the orientation of the magnetic material was slightly reduced, and the C / N ratio was lowered to 4.34 dB. Example 4 is an example in which the thickness of the lower layer is close to the upper limit of Claim 3, and the carbon content of the lower layer is high (30:70). Since the orientation and surface properties were slightly deteriorated, the C / N ratio was lower than in Examples 1 and 2, namely, 4.1 dB. Example 5 is an example in which the thickness of the magnetic layer is as thin as 0.03 μm and the content of the lower layer carbon is low (5:95). Although the orientation is good, since the magnetic layer is thin, the amount of magnetization decreases and the output decreases.
However, the C / N ratio was as high as 4.6 dB. Example 6 is an example in which the lower layer is as thick as 0.7 μm and the orientation angle of the lower layer granular powder is as large as 29 degrees. Ra became 3.2 nm, and the surface property deteriorated, so that the C / N ratio was lowered to 2.9 dB. Example 7: Average primary particle size of 35 nm as granular powder for lower layer
This example is the same as Example 1 except that titanium oxide was used.
The C / N ratio was 3.3 dB, which was lower than in Example 1. Example 8: Average primary particle diameter of 20 nm as granular powder for lower layer
This example is the same as Example 1 except that granular hematite was used. The C / N ratio was 3.5 dB, which was slightly lower than in Example 1. In Examples 7 and 8, the calender molding effect was lower than when the granular powder added to the lower layer was the carbon described in Claim 5, so that the C / N ratio was slightly lower. Example 9: Example similar to Example 1 except that no granular powder was added to the lower layer. The lower layer was poor in the calender molding effect containing no granular powder, and the Ra tended to be 3.7 nm with poor surface properties, and the C / N ratio was rather low at 3.5 dB. Comparative Example 2 This is an example in which in Example 1, granular hematite was used for the lower layer instead of the acicular nonmagnetic powder. C / N ratio is -1
dB, and the smoothing and orientation improving effects caused by the acicular powder could not be obtained. Comparative Example 3: An example in which the lower layer is thicker than that of Example 1 and no smoothing is performed. The orientation angle of the lower layer powder is out of the range of Claim 1. The effect of smoothing and improving the orientation is impaired. The C / N ratio was as low as 0.7 dB, and the output was sufficient. Comparative Example 4: An example in which the lower layer was thick, the dispersion time was shortened, and the coating was performed without filtering the coating solution. In an example in which the number of needle-like particles constituting the bundle structure is large, the C / N ratio was as low as -0.9 dB.

Continuation of the front page (72) Inventor Yoshihiko Mori 2-12-1, Ogimachi, Odawara-shi, Kanagawa Prefecture Fuji Photo Film Co., Ltd. Odawara Factory F-term (reference) 5D006 BA19 CA04 CA05 EA05 FA09 5D112 AA03 AA05 AA22 BD08 CC03 CC17 CC19 DD04

Claims (7)

[Claims] A magnetic recording medium comprising: a nonmagnetic flexible support; a nonmagnetic layer containing a nonmagnetic powder and a binder; and a magnetic layer containing at least a ferromagnetic powder and a binder. In the above, the average thickness d of the magnetic layer is 0.01 to 0.1 μm, the nonmagnetic powder is acicular, and its major axis is at an average angle of 35 ° or less with respect to the nonmagnetic flexible support plane. A magnetic recording medium distributed in the non-magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the acicular nonmagnetic powder is formed by forming a bundle structure of three or more particles. 3. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic layer is less than 0.5 μm. 4. The non-magnetic powder has an average major axis length of 0.2 μm or less and an acicular ratio in a range of 2 to 20.
The magnetic recording medium according to any one of the above items. 5. The non-magnetic layer contains granular particles having an average primary particle size of 50 nm or less, and the content ratio of the granular particles to the acicular non-magnetic powder is in the range of 5:95 to 40:60. Item 6. A magnetic recording medium according to Item 4. 6. The magnetic recording medium according to claim 5, wherein the granular particles are carbon black having an average primary particle diameter of 30 nm or less and an oil absorption of 200 ml / 100 g or less. 7. A coating solution for forming a nonmagnetic layer containing a nonmagnetic powder and a binder and a coating solution for forming a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic flexible support, The method is characterized in that a magnetic layer is formed on a non-magnetic flexible support so that a magnetic layer is formed on the layer, simultaneously or sequentially, and smooth coating and magnetic field orientation are performed while the coating layer is in a wet state. A method for manufacturing a magnetic recording medium according to claim 1.