JP2001067650A - 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. SOLUTION: In a magnetic recording medium in which a non-magnetic layer incorporating non-magnetic powder and a binder is provided on a non-magnetic 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 0.3 μm, the non-magnetic powder is acicular, and the average major axis length (L) of the non-magnetic powder and the average thickness D of the non-magnetic layer satisfy the relation of 1/10<=L/D<=2.

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 showing high output and good C / N ratio in high density recording.

[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 having a high C / N ratio in high-density magnetic recording.

[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 0.3 μm, the non-magnetic powder is acicular, and the average long axis length L of the non-magnetic powder and the average thickness D of the non-magnetic layer
Satisfies the relationship of 1/10 ≦ L / D ≦ 2.

[0005] In the above magnetic recording medium, the following aspects are preferred. (1) A magnetic recording medium wherein the thickness of the nonmagnetic layer is less than 0.5 μm. (2) 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 the range of 2 to 20. (3) 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. . (4) 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. (5) The surface of the non-magnetic flexible support on which the non-magnetic layer and the magnetic layer are provided has a roughness intensity at a wavelength of 1 to 5 μm in a spectrum of surface roughness measured by an atomic force microscope (AFM). (PSD) is at 0.5 nm ² or less, the magnetic recording medium of the PSD is less than the wavelength 0.5 [mu] m 1 [mu] m is 0.02~0.5nm ^2.

[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 0.3 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 nonmagnetic powder is used for the nonmagnetic lower layer, and the major axis length is appropriate for the thickness of the lower layer, that is, the average major axis length L of the nonmagnetic powder.
And that the average thickness D of the nonmagnetic layer satisfies the relationship of 1/10 ≦ L / D ≦ 2, the orientation and surface properties of the magnetic material can be improved. This is because when the major axis length of the nonmagnetic powder is appropriate for the thickness of the lower layer, the degree of freedom in the thickness direction of the major axis is reduced and the nonmagnetic powders are arranged in a plane. This phenomenon becomes more remarkable as the thickness of the lower layer becomes thinner. The thickness of the lower layer and the major axis length of the acicular powder in the magnetic recording medium of the present invention are partially known as numerical values (for example, see JP-A-6-2365).
No. 42), it is not known that the above effects can be obtained when the relationship of 1/10 ≦ L / D ≦ 2 is satisfied.

[0007] When the thickness of the lower layer is further reduced, the above-mentioned effects become remarkable, but the voids between the acicular particles are reduced, and the molding effect in the calendar tends to be reduced. In such a case, the needle-shaped non-magnetic powder at a specific ratio has an average primary particle size.
It is preferable to mix a granular powder of 50 nm or less. This is because the granular particles enter between the acicular particles and form appropriate voids. A desired effect can be obtained by using the above-mentioned granular particles and the mixing ratio. As the granular particles, it is particularly preferable to use a carbon black having an average primary particle diameter of 30 nm or less and an oil absorption of 200 ml / 100 g or less, because 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, carbon black having a preferable oil absorption is preferable because of its better dispersion. When the magnetic layer is thin in the magnetic recording medium of the present invention,
The surface property of the non-magnetic support is important, and the above effect is further enhanced by controlling the roughness at a specific wavelength, as described later.

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 0.3 μm, preferably 0.01 to 0.2 μm, and more preferably 0.01 to 0.1 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. Furthermore, σ
It is preferred that /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. And (3) a wet-on-dry method in which a nonmagnetic lower layer is applied and dried, and then a magnetic upper layer is applied. The residual magnetization of the magnetic layer is 6.28 × 10 ^{-7 to} 6.
It is suitably 28 × 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 setting the magnetic layer to be thin (for example, 0.1 μm or less) from the demand of O / W, σs
It is preferable to use an alloy powder of 140 to 160 A · m ² / kg (emu / g) having a large value. 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 σs of the magnetic powder is 50
It is suitable to improve the packing density as much as possible, for example, by using a material having a thickness of up to 130 A · m ² / kg (emu / g) and reducing the amount of binder in the upper layer / 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 119,400 to 318,400 A / m (1500 to 4000 Oe), preferably 143,280 to 278,600 A / m (1800 to 3500 Oe), and more preferably 159,200 to 238,800 A / m (2000 to 3000 Oe). Therefore, the same Hc is preferable for the magnetic powder. 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 in the range of 0.05 to 0.2 μm, and the minor axis diameter is 0.01
Suitably, it is in the range of 0.00.025 μm. For hexagonal ferrite, the plate diameter is in the range of 0.01 to 0.2 μm, and the thickness is
Suitably, it is in the range of 0.001 to 0.1 μm. However,
If the technology advances to provide smaller particles, the present invention is not limited to the above range, and smaller particles can 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.

As the binder used in the magnetic layer, known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1000 to 2
00000, preferably 10,000 to 100,000, and the degree of polymerization is suitably about 50 to 1,000. Examples of such thermoplastic resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid, acrylate, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylate, styrene, butadiene, ethylene, Examples thereof include polymers or copolymers containing vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. As the thermosetting resin or the reactive resin, phenol resin,
Epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, polyester polyol and Examples thereof include a mixture of polyisocyanate and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Also, a known electron beam-curable resin can be used for the non-magnetic layer and the magnetic layer. These examples and the manufacturing method thereof are described in, for example,
It is described in detail in Japanese Patent No. 56219. The above resins can be used alone or in combination, but are preferably selected from vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, and vinyl chloride vinyl acetate maleic anhydride copolymer. Examples include a combination of at least one kind with a polyurethane resin, or a combination of these with a polyisocyanate.
The structure of the polyurethane resin is polyester polyurethane,
Known examples include polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane. For all of the binders shown here, COOM,
SO ₃ M, OSO ₃ M, P = O (OM) ₂ , OP = O
(OM) ₂ , (where M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group) epoxy group, SH, CN, etc. It is preferable to use those having polar groups 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 ^-2 mol / g.
10 ^-6 mol / g.

[0013] α-alumina and Cr ₂ which are known abrasives are used for the magnetic layer.
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 a lower layer or a non-magnetic lower layer. The non-magnetic powder used as a main component in the non-magnetic lower layer is acicular. Further, the major axis length L of the nonmagnetic powder is 1/1 to the lower layer thickness D.
0 ≦ L / D ≦ 2, preferably 1/8 ≦ L / D ≦ 1.5,
More preferably, it is appropriate that 1/5 ≦ L / D ≦ 1. The long axis length of the non-magnetic powder 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
It is 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 have an oil absorption using DBP of 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, more preferably 20 to 60 m.
l / 100g powder. 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. The stearic acid (SA) adsorption amount is 1 to 20 μmol /
m ² , more preferably ² to 15 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
Is preferably in the range of ^{~6.0 × 10 -5 J / cm 2} (200erg / cm 2 ~600erg / 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 in the range of 1 to 10/100 angstroms, but is suitable. PH of isoelectric point in water is 5
It is preferably between 10 and 10.

The surface of these nonmagnetic powders is composed of Al ₂ O ₃ , Si
It is preferable to perform a surface treatment with O ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO. Particularly preferable surface treatment for dispersibility is Al ₂ O ₃ , S
iO ₂ , TiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface treatment layer coprecipitated may be used according to the purpose, or a structure in which the surface layer is treated with alumina and then the surface layer is treated with silica, or the reverse structure may be adopted. 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-like powders include TiO ₂ , hematite, α-alumina, β-alumina, γ-alumina, Zr
Examples include oxides such as O ₂ , CeO ₂ , Cr ₂ O ₃ , and SiO ₂ , and non-magnetic metals.

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 more 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 in 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, etc. are used as additives. 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 a lower layer and a magnetic upper layer according to the type and amount as required. 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, manufactured by Sanyo Kasei Co., Ltd., Profan 2012E, Newport PE61, Ionet MS-400, Ionet MO-200, Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionnet D
O-200 and the like.

[Nonmagnetic Flexible Support] The thickness of the magnetic recording medium of the present invention is 1 to 100 μm.
m, preferably 3 to 80 μm.
The thickness of the magnetic upper layer is 0.01 to 0.3 μm, preferably 0.02 to 0.2
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, cellulose acetoacetate, 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.

In order to achieve the object of the present invention, a nonmagnetic flexible support having a surface roughness spectrum measured by AFM with a roughness intensity at a wavelength of 1 to 5 μm of 0.5 nm ² or less, preferably 0.4 nm ² or less. , More preferably 0.3 nm ² or less, wavelength 0.5
The roughness intensity of μm to ¹ μm is 0.02 to 0.5 nm ² , preferably 0.02 to 0.5 nm ² .
It is preferred to use one that is between ⁴ and 0.3 nm2. 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 to 14.7 GPa (400 to 1500 kg).
/ mm ² ), preferably 4.9-12.7 GPa (500-1300 kg / mm ² ), T
The yanking rate in the D direction is 4.9 to 19.6 GPa (500 to 2000 kg / mm ² ),
TD / M at 6.9 to 17.6 GPa (700 to 1800 kg / mm ² )
The D ratio is 1/1 to 1/5, preferably 1/1 to 1/3.

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, and 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, 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 the conventional 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.

The following configuration can be proposed as an example of an apparatus and method for applying a magnetic recording medium having a multilayer configuration as in the present invention. 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 the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of the magnetic particles, Japanese Patent Application Laid-Open No.
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 necessary to satisfy the numerical range disclosed in JP-A-3-8471. In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 100 mT (1000 G) or more and a cobalt magnet of 200 mT (2000 G) or more in the same polarity facing each other, and furthermore, a proper drying step before orientation so that the orientation after drying is the highest. Is preferably provided. 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 and 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 / cm
It is appropriate that the above is true. The friction coefficient of the magnetic layer surface of the magnetic recording medium of the present invention and the opposite surface to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq.
The elastic modulus of the magnetic layer at 0.5% elongation is preferably 0.98 to 19.6 GPa (100 to 2000 kg /
mm ² ), the breaking strength is preferably 9.8 × 10 ^{−5 to} 2.9 × 10 ⁻³ G
Pa (1 to 30 kg / cm ² ), the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (10
0-1500 kg / mm ² ), and the residual elongation is preferably 0.
The heat shrinkage at any temperature of 5% or less and 100 ° C or less is preferably 1% or less, more preferably 0.5% or less,
Most preferably, the content is 0.1% or less. 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. or higher and 1
The temperature is preferably 20 ° C. or lower, and that of the lower layer is preferably 0 ° C. to 100 ° C. The loss modulus is 1 × 10 ³ to 8 × 10 ⁴ N / cm ² (1
It is preferably in the range of × 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 preferably 0.6 or less. In the roughness spectrum, the surface of the magnetic layer has a roughness component intensity at a wavelength of 1 to 5 μm of 0.2 nm ² or less, and a roughness component intensity of a wavelength of 0.5 μm or more and less than 1.0 μm is 0.
It is suitably a 02~0.1nm ^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 these physical properties can be changed between the lower layer and the magnetic layer 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.

[0039]

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 treatment agent 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 183,080 A / 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 · m ² / kg (emu / g) Vinyl chloride copolymer 5 parts MR-110 polyester polyurethane resin 3 manufactured by Nippon Seon Co., Ltd. 3 Part 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 using a sand mill. 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. -
And a coating solution for forming a lower layer and a magnetic layer was prepared. The obtained lower layer coating solution is coated with a 5.5 μm-thick A layer so that the thickness after drying is 0.3 μm and immediately thereafter, the thickness of the magnetic layer is 0.1 μm thereon.
FM roughness Suhe ° vector at the wavelength 0.5 [mu] m, 1 [mu] m and 5μm roughness component intensity is 0.05 nm, respectively ^2, 0.09 nm ^2, and a 0.11 nm ^2,
The MD and TD yank rates are 5.88 GPa (600 kg / mm ² ), respectively.
And 8.82 GPa (900 kg / mm ² ) on a polyethylene naphthalate support at the same time, and while both layers are still wet, a rare earth magnet having a magnetic force of 300 mT (3000 G) and 150 mT ( After being oriented and dried by a solenoid having a magnetic force of 1500 G), it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, slit to a width of 8 mm, and produced an 8 mm video tape. .

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) AFM measurement Using Digital Instruments NanoScoff3, 70 ° ridge angle, SiN
The surface roughness of a 30 μm square square was measured using a quadrangular pyramid as a probe. A power spectrum is created by frequency analysis of the surface roughness. The PSD (Power Spectrum Density) is calculated by multiplying the sampling interval by the square of the height.
m represents the measured power with ² units. 0.05 μm,
PSD was calculated for the roughness components at each pitch of 1.0 μm and 5.0 μm. (4) Friction coefficient In an environment of 21 ° C and 50%, SU of 0.2 mm roughness and 2 mmφ
Wrap the tape 90 degrees around the rod of S303, load 10g,
Sliding at a speed of 18 mm / sec and a stroke of 10 mm for 100 lots, the largest coefficient of friction was measured. (5) 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).

[0043]

[Table 1]

[0044]

[Table 2]

Description of Examples and 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 (which generally affects the error rate by one digit at 2 dB) improves by 2 dB or more, or whether the friction coefficient does not significantly exceed 0.3. Example 1 is an example that satisfies all the requirements described in claims 1 to 6. The C / N ratio was improved by 5.2 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 2, and the major axis length of the non-magnetic powder contained in the lower layer is Claim 3.
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 4.8 dB, which is almost the same performance, was obtained. Example 3 This is an example in which the average thickness D of the lower layer is large, the L / D is close to the lower limit specified in claim 1, and the support has a PSD exceeding the range described in claim 6. Since the surface properties are worse than in Examples 1 and 2, C /
The N ratio was a low 2.4 dB. Example 4: The lower layer average thickness D is large, and L / D is claim 1.
Is an example in which the mixing ratio of the granular powder to the lower layer is close to the lower limit specified in the above. Similar to the third embodiment, compared to the first and second embodiments.
The C / N ratio became lower, 2.9 dB. Example 5: The long axis length of the lower layer powder is 0.35 μm which exceeds the range described in claim 3, the mixing ratio of the carbonate to the lower layer is the lower limit described in claim 4, and the L / D is close to the upper limit. It is an example. The calender moldability tends to decrease, and the C / N ratio becomes a low 3.1 dB. Example 6: 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. C
The / N ratio was 4.1 dB, which was slightly lower than in Example 1. Example 7: Example similar to Example 6, except that a nonmagnetic powder having a major axis length exceeding the range described in claim 3 was used. The C / N ratio was 2.5 dB lower than that of Example 6. 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 6 to 8, the C / N ratio was slightly lower because the calender molding effect was lower than in the case where the granular powder added to the lower layer was the carbon described in Claim 5. Example 9: Example similar to Example 1 except that a smooth support having a surface roughness outside the range described in claim 6 was used. The C / N ratio was as high as 5 dB, but the coefficient of friction was as high as 0.31. Example 10: An example in which the mixing ratio of carbon to the lower layer is the lower limit described in claim 4, and the oil absorption of the carbon is out of the range described in claim 5. Dispersion is poor due to large oil absorption, and as a result,
The surface properties tended to be degraded, and the C / N ratio was a low 2.6 dB. Example 11: Example 1 except that no granular powder was mixed in the lower layer
This is an example similar to. Since the calender molding effect was poor, the surface properties were poor, and the C / N ratio was a low 2.4 dB. Comparative Example 2: Example in Example 1 except that granular hematite was used for the lower layer instead of the acicular nonmagnetic powder. The C / N ratio was -1.3 dB, and the smoothing and orientation improving effects caused by the acicular powder could not be obtained. Comparative Example 3; L / D below the lower limit stated in claim 1
Example similar to Example 1 except having C / N ratio is 0.3d
B, and no smoothing and orientation improving effects were obtained. Comparative Example 4 Example 1 except that a non-magnetic powder having a long major axis exceeding the upper limit of L / D described in claim 1 was used.
Example similar to. The C / N ratio was -0.5 dB, and
The turbulence of the interface became larger than that of.

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 FA09

Claims (6)

[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 0.3 μm, the nonmagnetic powder is acicular, and the average major axis length L of the nonmagnetic powder and the average thickness D of the nonmagnetic layer are 1/10 ≦ L
A magnetic recording medium satisfying the relationship of / D ≦ 2. 2. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic layer is less than 0.5 μm. 3. The magnetic recording medium according to claim 1, 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 nonmagnetic layer contains granular particles having an average primary particle diameter of 50 nm or less, and the content ratio of the granular particles to the acicular nonmagnetic powder is in a range of 5:95 to 40:60. Item 4. A magnetic recording medium according to Item 3. 5. The magnetic recording medium according to claim 4, wherein the granular particles are carbon black having an average primary particle size of 30 nm or less and an oil absorption of 200 ml / 100 g or less. 6. The surface of the non-magnetic flexible support on which the non-magnetic layer and the magnetic layer are provided, the surface of which is provided with an atomic force microscope (AFM).
Wavelength of 1 to 5 μm in the spectrum of surface roughness measured in
Roughness strength (PSD) is at 0.5 nm ² or less, the magnetic recording medium according to any one of claims 1 to 5 PSD is less than the wavelength 0.5 [mu] m 1 [mu] m is 0.02~0.5nm ^2.