JPH06139553A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having satisfactory electromagnetic transducing characteristics and high output especially at <=1mum short recording wavelength. CONSTITUTION:When a magnetic layer contg. a magnetic substance dispersed in a binder is formed on a nonmagnetic flexible substrate to obtain a magnetic recording medium, powders of a ferromagnetic alloy based on alpha-Fe are used as the magnetic substance. This powder has 1,620-2,100Oe coercive force Hc, 120-160emu/g saturation magnetization 6sigmas, 48-65m<2>/g specific surface area measured by adsorption of gaseous N2, 0.08-0.21mum major axis size, 10-20mum minor axis size, 7-11 acicularity ratio and 110-170Angstrom crystallite size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a high density coating type magnetic recording medium having a recording wavelength of 1 .mu.m or less.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks and the like. Magnetic recording media have become denser year by year and the recording wavelength has become shorter, and the recording method is being studied from analog to digital. A magnetic recording medium using a metal thin film for the magnetic layer has been proposed to meet this demand for higher density, but it is not sufficient in terms of productivity and practical reliability such as corrosion. A so-called coating type magnetic recording medium which is dispersed in and coated on a support is superior.
However, the coating type is inferior in electromagnetic conversion characteristics to the metal thin film because the filling degree of the magnetic material is low. As the coating type magnetic recording medium, ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, Cr
A magnetic layer in which O ₂ and a ferromagnetic alloy powder are dispersed in a binder is coated on a non-magnetic support is widely used.

In order to improve the performance of these high density coating type magnetic recording media, studies using a ferromagnetic alloy powder as a magnetic material have been earnestly conducted. Coercive force (Hc) of magnetic material
In the conventional 8 mm video, the optimum value was 1400 to 1600 Oe, but in recent years, the saturation magnetic flux density of the head is 1000.
Something that exceeds 0 gauss has been found,
Further, by thinning the magnetic layer by the method described in JP-A-63-187418, it is possible to use up to about 2100 Oe without any problem in erase and overwrite suitability. Therefore, a magnetic material having a higher Hc has been desired.

However, in order to increase Hc, it is effective to increase the major axis length in the case of an alloy needle-shaped magnetic material whose shape anisotropy is dominant. Larger size, more noise and lower short wavelength output. For this reason, it is necessary to increase the coercive force while maintaining the particle size of the magnetic material as fine particles. For this purpose, the minor axis length and the crystallite size must be reduced while keeping the major axis length short, and the acicular ratio must be a certain constant value. Hc
Therefore, optimum values exist for the needle-like ratio, the major axis length, the minor axis length, and the crystallite size. Further, if σs is not high to some extent, the magnetization of the magnetic recording medium is insufficient, and the higher it is to secure a short wavelength output, the better, but it has an optimum value in consideration of crystallite size and demagnetization. As described above, the higher the Hc and σs of the magnetic substance alone, the better, and the long axis length, the short axis length, and the crystallite size improve the short wavelength output,
The smaller the better for noise reduction, the better, but the Hc and the particle size have a contradictory relationship, and the BET specific surface area by N2 gas is also closely related to the particle size, but the Hc is further increased. In order to increase Hc, the specific surface area should be as small as possible with respect to the particle size in order to increase Hc.

In a digital recording medium which has been put into practical use in recent years, mutual interference occurs between adjacent magnetization reversals in continuous high density magnetization reversals, resulting in a decrease in output peak value with respect to an isolated reversal waveform. The deviation of the peak position causes a detection error (error), which hinders the improvement of the recording density. In order to solve this and improve the recording density, it is necessary to reduce the full width at half maximum of the isolated inverted waveform to reduce the interference between codes. For this purpose, it is known that reducing the magnetic layer thickness, reducing Br / Hc, and reducing the surface roughness are effective, but it is still unknown how to specifically achieve this. It wasn't done.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having a good electromagnetic conversion characteristic, and particularly to provide a magnetic recording medium having a recording wavelength of 1 μm or less and a high short wavelength output.

[0007]

Through the experiments for producing the above magnetic substance and its magnetic recording medium, Hc,
As a result of searching for a delicate balance of σs, major axis length, minor axis length, acicular ratio, crystallite size, and specific surface area, a magnetic layer in which a magnetic material is dispersed in a binder is formed on a non-magnetic flexible support. In the provided magnetic recording medium, the magnetic substance is a ferromagnetic alloy powder mainly composed of α-Fe, and the powder coercive force Hc thereof is 162.
0 or more and 2100 Oe (Oersted) or less, saturation magnetization σ
s is 120 to 150 emu / g, specific surface area by N ₂ gas adsorption is 48 to 60 m ² / g, major axis length is 0.08 to 0.21 μm,
It has been found that a crystallite size of 110 to 170 angstroms with a minor axis length of 10 to 20 mμ and an acicular ratio of 7 to 11 is good in terms of balance of characteristics of all magnetic recording media.

That is, the present invention exerts an extremely excellent effect due to the balance in the above-mentioned specific range. Specifically, when Hc exceeds 2100 Oe, the recording characteristics and erasing characteristics of the magnetic recording medium deteriorate and are satisfactory. Cannot obtain a short wavelength output. When Hc is less than 1620 Oe, the short wavelength output is reduced and a sufficient area recording density cannot be obtained. When the saturation magnetization σs is less than 120 emu / g, the saturation magnetization of the magnetic recording medium is insufficient, the output is reduced, and the saturation magnetization is 150 emu / g.
If it exceeds, demagnetization is remarkable, the minor axis length and the crystallite size are likely to be large, and the desired fine particles cannot be achieved. If the specific surface area is less than 48 m ² / g, the particle size becomes large, noise increases and the short wavelength output decreases, and if the specific surface area exceeds 60 m ² / g, it depends on the particle size, but it is extremely fine particles. Therefore, it becomes difficult to disperse, and the pores on the surface increase, so that the desired Hc cannot be obtained. Long axis length is 0.08μ
When it is less than m, the magnetic substance aggregates due to the fine particles and the dispersion becomes difficult. If the major axis length is less than 0.08 μm and the acicular ratio is less than 7, a desired Hc cannot be obtained with an alloy magnetic body due to shape anisotropy. Similarly, if the minor axis length is less than 10 mμ, superparamagnetism becomes dominant and desired Hc cannot be obtained, and the ratio of the thickness of the oxide film to the whole increases and σs decreases. Crystallite size is 1
If it is less than 10 angstroms, as in the case of the short axis length, it approaches the region where superparamagnetism is dominant, and the desired Hc cannot be obtained. If the major axis length exceeds 0.21 μm, the particle size becomes large and the noise characteristics and short wavelength output are reduced. If the minor axis length and the crystallite size are too large, the acicular ratio is lowered due to the relationship with the major axis length, and the desired Hc cannot be obtained. As described above, we experimentally found that a very narrow range is a preferable range in consideration of the balance of magnetic properties.

As the magnetic material used in the present invention, a ferromagnetic alloy fine powder containing Fe, Ni or Co as a main component (65% by weight or more) can be used. Preferably, αFe is the main component, Ni is 10 wt% or less, and Co is 30 wt% or less. These ferromagnetic powders include Ca, Al, Si, S, Sc, Ti, V,
Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, S
b, Te, Ba, Ta, W, Re, Au, Hg, Pb,
Bi, La, Ce, Pr, Nd, P, Co, Mn, Z
It may contain atoms such as n, Ni, Sr, B and Sm. For these ferromagnetic fine powders, the dispersant described later,
Treatment with a lubricant, surfactant, antistatic agent or the like may be performed in advance before dispersion. Specifically, Japanese Patent Publication Sho 44
-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062
Gazette, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466, Japanese Patent Publication No. 46-38755, Japanese Patent Publication No. 47-4286, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-17284. , Japanese Examined Sho 47
-18509, Japanese Patent Publication No. 47-18573, Japanese Patent Publication No. 39-10307
Japanese Patent Publication, Japanese Patent Publication No. 48-39639, U.S. Pat.No. 30,262,15, 3,303,141, 3,100,194, 3242.
No. 005, No. 3389014 and the like.

Among the above magnetic materials, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of a ferromagnetic alloy fine powder can be used, and the following method can be mentioned.
1, a method of reducing with a reducing gas such as complex organic acid salt (mainly oxalate) and hydrogen, 2, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, 3, a method of thermally decomposing a metal carbonyl compound, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, 4, a low pressure inert gas of a metal And the like to obtain a fine powder. The ferromagnetic alloy powder thus obtained is a known gradual oxidation treatment, that is, a method of immersing in an organic solvent and then drying, 5, particularly an alloy magnetic powder obtained by reducing spindle-type goethite is preferable,
This is a ferrous salt (eg FeC) at pH 5-8.
l ₂ ) is reacted with an aqueous solution of NaOH and Na ₂ CO ₃ to carry out oxidation at a temperature higher than room temperature while blowing air. Then, after removing NaCl and NaOH by a filter press or the like, a surface treatment agent such as Zn, Al, Ni, Si, Co or Nd, and a known coagulant or sintering inhibitor (silicate, aluminum salt, magnesium) Surface treatment in an alkaline state by adding a salt or a calcium salt). After that, vacuum filtration is performed with an Oliver filter or the like, granulation, drying, and reduction are performed. The reduction may be a stationary reduction furnace or a fluidized bed reduction furnace. The reduction temperature is controlled in a hydrogen stream controlled to about 300 to 500 ° C. After that, gradual oxidation is performed to form an oxide film on the alloy.This is a method of dipping in an organic solvent, feeding an oxygen-containing gas to form an oxide film on the surface, and then drying, an oxygen gas without using an organic solvent. Although any of the methods of forming an oxide film on the surface by adjusting the partial pressure of the inert gas can be used, the gas phase reaction is preferable because a uniform oxide film can be formed. Here, the spindle type refers to a shape similar to a weight (claw), that is, a shape in which both ends of a cylindrical shape are sharpened. That is, it means a shape in which a thread is wound thickly in the center and thinly wound on both ends on a cylindrical winding core. The spindle type is preferable because the filling degree is remarkably improved.

The BET method is applied to the magnetic particles of the magnetic layer of the present invention.
If expressed in terms of specific surface area of 48 to 65 m ²/ G and is preferred
52-59m²/ G. 48m²less than / g
The height is high, 66m²If it is larger than / g, the surface property is difficult to obtain.
Unfavorable. Crystallites of magnetic particles of the magnetic layer of the present invention
The size is 100-180 angstroms and is preferred
It is 120 to 170 angstrom. σs is 1
20 emu / g or more is preferable, and 12 is more preferable.
It is 0 emu / g to 160 emu / g. Coercive force is 1600 Oe or less
The upper limit is preferably 2100 Oe or less, more preferably 170
It is 0 Oe or more and 2000 Oe or less. The acicular ratio of the magnetic material is 5 or more
Upper 15 or less is preferable, more preferably 7 or more and 12 or less
Is. Squareness ratio of magnetic powder = σr / σs is 0.45
It is 0.55, preferably 0.47 to 0.52. Magnetism
The water content of the body is preferably 0.01 to 2% by weight.
The water content of the magnetic material should be optimized depending on the type of binder.
preferable. The bulk density is preferably 0.2 to 0.7 g / ml,
If it is more than 0.7 g / ml, oxidation will proceed in the compaction process of the magnetic substance.
It is easy, and the reducing gas does not pass sufficiently, so the desired H
It becomes difficult to obtain c and σs. Bulk density 0.2g / ml or less
Below, dispersion is likely to be insufficient.

The ignition point of the alloy magnetic material is preferably high in order to suppress the demagnetization of the magnetic material as much as possible, but there is an adverse effect of decreasing σs due to the thickness of the oxide film. The ignition point of the alloy magnetic body is about 9
It is sufficient if the temperature is 0 ° C or higher. It is preferable to optimize the pH of the magnetic substance depending on the combination with the binder used. The range is 4 to 12, but preferably 6 to 10.
The magnetic material may be surface-treated with Al, Si, P or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% by weight, particularly preferably 1 to 5% by weight of aluminum and 3% by weight or less of silicon. The surface treatment is preferable because the adsorption of the lubricant such as fatty acid becomes 110 mg / g of the magnetic substance or less. Particularly, the adsorption amount of stearic acid is preferably 80 to 110 mg / g of magnetic material. Soluble Na, Ca, Fe, Ni,
It may contain inorganic ions such as Sr, but 200ppm
If it is below, it does not particularly affect the characteristics. 200 ppm
If it exceeds the range, salt will be deposited on the surface of the magnetic layer when it is stored for a long period of time or in a high humidity state, which may cause clogging of the head or poor running.

The magnetic material used in the present invention preferably has few voids, and the value is 20% by volume or less, more preferably 5% by volume or less. Regarding the shape, if the characteristics of the particle size shown above are satisfied, needle-like shape,
It may be rod-shaped, spindle-shaped or rice-shaped, but spindle-shaped is particularly preferable. SFD (Switch) of this magnetic material
ing Field Distribution) 0.
In order to achieve 6 or less, it is necessary to reduce the Hc distribution and size distribution of the magnetic material.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 100.
0-200000, preferably 10,000-10000
0, the degree of polymerization is about 50 to 1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetate. Polymers, copolymers, polyurethane resins, and various rubber-based resins containing a vinyl group, vinyl ether, or the like as a constituent unit. Also,
Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, Examples thereof include a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the upper layer or the lower layer. For these examples and the manufacturing method thereof, see JP-A-62-256219.
Are described in detail in. The above resins can be used alone or in combination, but are preferably selected from vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. Examples thereof include a combination of at least one kind and a polyurethane resin, or a combination of these with polyisocyanate.

The structure of polyurethane resin is polyester
Polyurethane, Polyether Polyurethane, Polyether
Polyester Polyurethane, Polycarbonate Polyurethane
Tongue, polyester polycarbonate carbon polyurethane, polyethylene
You can use known ones such as lycaprolactone polyurethane
Wear. Better for all binders shown here
COO is necessary to obtain excellent dispersibility and durability.
M, SO₃M, OSO₃M, P = O (OM)₂, OP
= O (OM)₂, (M is hydrogen atom or
Lucari metal base), OH, NR₂, N⁺R₃(R is carbonized water
Elementary group) Epoxy group, SH, CN, etc.
At least one polar group is introduced by copolymerization or addition reaction.
It is preferable to use the added one. Such polarity
The amount of groups is 10 ^-1-10^-8Mol / g, preferably 10
^-2-10^-6Mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbite Corporation.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku Co., Ltd. 1000
W, DX80, DX81, DX82, DX83, 100
FD, MR-105, MR110, MR manufactured by Zeon Corporation
-121, MR100, 400X110A, Nippon Polyurethane Nipporan N2301, N2302, N23
04, Pandex T-5105 made by Dainippon Ink and T
-R3080, T-5201, Barnock D-400,
D-210-80, Crisbon 6109, 7209, Toyobo Co., Ltd. Byron UR8200, UR8300, UR-860
0, UR-5500, UR-4300, RV530, RV280, manufactured by Dainichiseika, Daiferamine 4020, 5020, 510
0,5300,9020,9022,7020, Mitsubishi Kasei, MX5004, Sanyo Kasei, Sampren SP
-150, Asahi Kasei Corp., Saran F310, F210 and the like.

The binder used in the magnetic layer of the present invention is in the range of 5 to 50 wt% with respect to the magnetic material, preferably 10 to 3
Used in the range of 0 wt%. When vinyl chloride resin is used, it is 5 to 40% by weight, when polyurethane resin is used, it is 2 to 20% by weight, and polyisocyanate is 2 to 20% by weight.
It is preferable to use these in combination within the range of wt%. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 100 ° C. and the elongation at break is 100 to 2
000%, the breaking stress is preferably 0.05 to 10 kg / cm ² , and the yield point is preferably 0.05 to 10 kg / cm ² . The magnetic recording medium of the present invention may have a structure of two or more layers.
Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or the amount described above. Of course, it is possible to change the physical properties of the resin between the lower non-magnetic layer and the upper magnetic layer as required.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and naphthylene-1. ，
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate, and the like, products of these isocyanates with polyalcohols, and polyisocyanates formed by condensation of isocyanates. -, Etc. can be used. Commercially available trade names of these isocyanates are Nippon Polyurethane Co., Ltd., Coronate L, Coronet HL, Coronet 2030, Coronet 2031, Millionate MR.
Millionate MTL, Takeda Pharmaceutical Co., Takenet D-1
02, Takenate D-110N, Takenate D-20
0, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodule L, Desmodule IL, Desmodule N Desmodule HL, etc., and these are used alone or by utilizing the difference in curing reactivity. The upper layer and the lower layer can be used in one or more combinations.

The carbon black used in the magnetic layer of the present invention may be a furnace for rubber, thermal for rubber, black for color or acetylene black. Specific surface area is 5-500 m ² / g, DBP oil absorption is 1
0-400ml / 100g, particle size 5mμ-300m
It is preferable that μ, pH is 2 to 10, water content is 0.1 to 10% by weight, and tap density is 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 13 manufactured by Cabot Corporation.
00, 1000, 900, 800, 700, VULCA
NXC-72, Asahi Carbon Co., Ltd., # 80, # 60, #
55, # 50, # 35, Mitsubishi Kasei Co., Ltd., # 2400
B, # 2300, # 900, # 1000 # 30, # 4
0, # 10B, CONDUCIA Carbon Co., CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5 and so on. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the amount of the magnetic material. Carbon black has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving the film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the upper layer and the lower layer, and have the objectives based on the characteristics shown above such as particle size, oil absorption, electric conductivity, and pH. Of course, it is possible to use them properly according to. For example, it is possible to prevent charging by using carbon black having a high conductivity in the lower layer and to reduce the friction coefficient by using carbon black having a large particle size in the magnetic layer. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

Examples of the organic powder used in the magnetic layer of the present invention include acrylic styrene resin powder, benzguanamine resin powder, melamine resin powder and phthalocyanine pigment. Polyolefin resin powder, polyester resin powder, polyamid resin Powder, polyimid resin powder, and polyfluorinated ethylene resin are used. As the manufacturing method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

As the abrasive used in the magnetic layer of the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, and nitriding having an α conversion of 90% or more. Silicon, titanium carbide carbide, titanium oxide, silicon dioxide, boron nitride,
Known materials having a Mohs hardness of 6 or more are mainly used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 90% by weight.
If it is above, there is no change in the effect. The particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution and obtain the same effect. . Tap density is 0.3 to 2 g / ml, water content is 0.1 to 5% by weight, pH is 2 to 11, specific surface area is 1 to 3.
0 m ² / g is preferred. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like,
Those having a corner in a part of the shape are preferable because of high polishing property.

Specific examples of the abrasive used in the present invention include AKP-20, AKP-30 manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, Hit-55, Hit-
80G, HIT-100, Nippon Kagaku Kogyo G5, G7, S
-1, Toda Kogyo KK, TF-100, TF-140 and the like. It is of course possible to use the abrasives used in the present invention by changing the type, amount and combination of the upper layer and the lower layer and selectively using them according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. The number of abrasives present on the magnetic layer surface and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5 pieces / 100 μm ² or more.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, graphite fluoride, silicon
Oil, polar group-containing silicone, 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 (unsaturated bonds May be included or may be branched), and these metal salts (Li,
Na, K, Cu, etc.), or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (including an unsaturated bond or branched). It doesn't matter),
Alkoxy alcohol having 12 to 22 carbon atoms, 10 carbon atoms
-24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and monovalent C2-12,
A mono-fatty acid ester or a di-fatty acid ester consisting of any one of divalent, trivalent, tetravalent, pentavalent, and hexavalent alcohols (which may contain an unsaturated bond or may be branched) or Tri-fatty acid ester, monoalkyl ether fatty acid ester of alkylene oxide polymer, fatty acid amide having 8 to 22 carbon atoms, aliphatic amine having 8 to 22 carbon atoms, and the like can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid,
Behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate,
Octyl myristate, butoxyethyl stearate,
Anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol
Le is given. Further, nonionic surfactants such as alkylene oxide-based, glycerin-based, glycidyl-based, and alkylphenol-ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium. Or a cationic surfactant such as sulfonium, carboxylic acid,
Amphoteric amphiphiles such as anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group, amino acid, aminosulfonic acid, sulfuric acid or phosphoric acid ester of amino alcohol, alkylbedine type, etc. Surfactants and the like can also be used.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 10
Impurities such as isomers, unreacted substances, by-products, decomposed substances, and oxides may be included in addition to the main component, instead of being 0% pure. The content of these impurities is preferably 30% or less, more preferably 10% or less. The types and amounts of these lubricants and surfactants used in the present invention can be properly selected for the intermediate layer and the magnetic layer. For example,
Applying by adjusting the amount of surfactant by controlling the bleeding to the surface using fatty acids whose melting points are different in the intermediate layer and magnetic layer, controlling the bleeding to the surface using esters with different boiling points and polarities. It is considered that the stability is improved, the amount of the lubricant added is increased in the intermediate layer to improve the lubrication effect, and of course the examples are not limited to those shown here.

Further, all or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a magnetic material before the kneading step, they are combined with the magnetic material. When added in the kneading step with the agent and the solvent, when added in the dispersion step, when added after dispersion,
It may be added just before coating. Examples of commercial products of these lubricants used in the present invention include NA manufactured by NOF CORPORATION
A-102, NAA-415, NAA-312, NAA
-160, NAA-180, NAA-174, NAA-
175, NAA-222, NAA-34, NAA-3
5, NAA-171, NAA-122, NAA-14
2, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, nymine L-201, nymine L-202, nymi- S-2
02, nonion E-208, nonion P-208, nonion S-207, nonion K-204, nonion NS-
202, Nonion NS-210, Nonion HS-20
6, 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-85R, Nonion LT-22
1, nonion ST-221, nonion OT-221, monogly MB, nonion DS-60, anon BF, anon LG, butyl stearate, butyl laurate, erucic acid, Kanto Chemical Co., oleic acid, Takemoto Yushi Co., Ltd., FAL
-205, FAL-123, manufactured by Shin Nippon Rika Co., Ltd., Engerb LO, Enjorb IPM, Sansosizer-E40
30, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-96, KF-
96L, KF96H, KF410, KF420, KF9
65, KF54, KF50, KF56, KF907, K
F851, X-22-819, X-22-822, KF
905, KF700, KF393, KF-857, KF
-860, KF-865, X-22-980, KF-1
01, KF-102, KF-103, X-22-371
0, X-22-3715, KF-910, KF-393
5, Lion Armor Co., Amid P, Armide C, Amoslip CP, Lion Oil & Fat Co., Deuomin TDO, Nisshin Oil Co., BA-41G, Sanyo Kasei Co., Profan 2012E , Newport PE61, Ionet MS-400, Ionet MO-200 Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionet DO-200, ICI Solspers 3000, 5000, 9000, 1334.
5,22000, others Phenylphosphonic acid, benzoic acid, etc. may be mentioned.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., and methanol.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc., methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycoacetate -Esters such as glycol, dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components.
The content of these impurities is preferably 30% or less, more preferably 10% or less. If necessary, the type and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the non-magnetic layer. A solvent with a high solubility parameter for the magnetic layer, which uses a solvent with a high volatility for the intermediate layer to improve the surface properties, a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the magnetic layer, and improves the stability of coating. Examples of such methods include increasing the filling degree by using, but it goes without saying that the present invention is not limited to these examples.

The thickness of the magnetic recording medium of the present invention has a non-magnetic flexible support of 1 to 100 μm, preferably 4 to 15 μm.
m, 0.5 μm to 10 μm, preferably 1 to 5 when a lower non-magnetic layer is provided between the flexible support and the magnetic layer.
.mu.m, the magnetic layer is 1 .mu.m or more and less than 10 .mu.m, and when a lower non-magnetic layer is provided between the flexible support and the magnetic layer, it is 0.
05 μm or more and 0.8 μm or less, preferably 0.08 μm
Or more and 0.5 μm or less, more preferably 0.1 μm or more and 0.3 μm or less. The total thickness of the magnetic layer and the intermediate layer is 1/100 to 2 times the thickness of the non-magnetic flexible support. In addition, an undercoat layer for improving the adhesiveness may be provided between the non-magnetic flexible support and the lower non-magnetic layer and the magnetic layer. The thickness of these is 0.01
˜2 μm, preferably 0.05 to 0.5 μm. In addition, a backcoat layer may be provided on the side opposite to the side of the nonmagnetic support magnetic layer. This thickness is 0.1-2 μm,
It is preferably 0.3 to 1.0 μm. Known non-magnetic layers and back coat layers can be used as the underlying layers.

The non-magnetic flexible support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, and cellulose.
Known films such as striacate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamid can be used. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. To achieve the object of the present invention, the non-magnetic flexible support has a center line average surface roughness (cutoff value of 0.25 mm) of 0.03 μm or less, preferably 0.0.
It is necessary to use those having a thickness of 2 μm or less, and more preferably 0.01 μm or less. Further, these non-magnetic supports have not only a small center line average surface roughness but also a thickness of 1 μm.
It is preferable that the above-mentioned coarse protrusions are not present. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the support, if necessary. Examples of these fillers include Ca, Si, and Ti.
In addition to oxides and carbonates such as, organic fine powders such as acrylics are listed. The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 5 to 50 kg / m.
m ² , the F-5 value in the tape width direction is preferably 3 to 30 k
It is g / mm ² , and the F-5 value in the tape longitudinal direction is generally higher than the F-5 value in the tape width direction, but especially when it is necessary to increase the strength in the width direction. Is not the case.

The heat shrinkage of the non-magnetic 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, 80 ° C. 30
The heat shrinkage per minute is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5-10 in both directions
0 kg / mm ² , elastic modulus is 100-2000 kg / m
m ² is preferred.

In the present invention, a lower nonmagnetic layer may be provided between the nonmagnetic flexible support and the magnetic layer. The lower non-magnetic layer preferably comprises a non-magnetic powder and a binder, and examples of the non-magnetic powder include metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. It can be selected by mixing the above inorganic compound and carbon black. As the inorganic compound, for example, α-alumina, β-alumina, γ-with an α conversion rate of 90% or more.
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, α-goethite, β-goethite, γ-goethite, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, sulphur oxide, magnesium oxide, stannic oxide tank, siliconium oxide, boron nitride, zinc oxide, carbonic acid Calcium, calcium sulfate, barium sulfate, molybdenum sulfide and the like are used alone or in combination. In particular, titanium oxide, rouge, barium sulfate, and aluminum oxide are preferable. The particle size of these non-magnetic powders is 0.01 to 2 μm.
However, if desired, non-magnetic powders having different particle sizes may be combined, or a single non-magnetic powder may be used to broaden the particle size distribution to obtain the same effect. When the non-magnetic powder is granular or spherical, the average particle size is 0.01 μm or more and 0.08 μm or less, and when the non-magnetic powder is acicular, the major axis length is 0.05 to
Those having a length of 0.3 μm and a short axis length of 5 μm to 30 μm are preferable. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content is 0.1 to 5% by weight, preferably 0.2 to 3% by weight. The pH is 2-11. The specific surface area is 1 to 100 m ² / g, preferably 5 to
70m ² / g, more preferably from 7~50m ² / g. The crystallite size is preferably 0.01 μm to 2 μm. Oil absorption using DBP is 5-100ml / 100g, preferably 10-80ml /
It is 100 g, more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 2 to 8. The shape may be needle-like, spherical, dice-like, or plate-like. The above non-magnetic powder does not necessarily have to be 100% pure, and the surface may be treated with other compounds depending on the purpose. At that time, if the purity is 70% or more, the effect is not reduced. For example, in the case of using titanium oxide, it is generally used to treat the surface with alumina, and in the case of valley, the surface is covered with silica and alumina in the range of 0.1 to 10 wt%, It is preferable to control the polarity.
The loss on ignition is preferably 20% by weight or less. The Mohs hardness of the inorganic powder used in the present invention is preferably 4 or more. The production method and application of titanium oxide are "titanium oxide-
Physical Properties and Applied Technology ”, written by Manabu Seino, Gihodo Publishing Co., Ltd. 199
The method described in 1 year can be referred to. Further, in the case of a valve stem, it is desirable to use a product obtained by surface-treating α-hematite obtained as an intermediate when producing magnetic iron oxide or a magnetic alloy.

Specific examples of the non-magnetic powder used in the present invention include Showa Denko UA5600, UA5605 and Sumitomo Chemical AK.
P-20, AKP-30, AKP-50, HIT-5
0, HiT-100, ZA-G1, Nippon Chemical Industry Co., G
5, G7, S-1, Toda Kogyo Co., Ltd., TF-100, TF
-120, TF-140, DNS-230, DNS-235, DNA-24
0, DPN-245, DPN-250BX, Ishihara Sangyo TTO-51B, TTO-55A, T
TO-55B, TTO-55C, TTO-55S, TTO-55D, TTO-55G, FT-1000, F
T-2000, FTL-100, FTL-200, M-1, S-1, SN-100, E-270,
E-271, E272, Titanium Industry ECT-52, STT-4D, STT-30D, S
TT-30, STT-65C, Mitsubishi Materials T-1, Nippon Shokubai NS-O, NS-3
Y, NS-8Y, TAYCA MT-100S, MT-100T, MT-150W, MT-500B, M
T-600B, MT-100F, Sakai Chemical FINEX-25, BF-1, BF-10, BF-20,
BF-1L, BF-10P, Dowa Mining DEFIC-Y, DEFIC-R, and Titanium Industry Y-LOP are included.

When carbon black is used, it is used for the rubber furnace, rubber thermal, color black,
Acetylene black, etc. can be used. Specific surface area is 100 to 500 m ² / g, preferably 150 to 40
0m ² / g, DBP oil absorption 20~400ml / 100
g, preferably 30 to 200 ml / 100 g. The particle size is 5 m-80 m, preferably 10-50 m, and more preferably 10-40 m. pH is 2 to 10, water content is 0.1 to 10% by weight, tap density is 0.1 to 1 g.
/ Ml is preferred. Specific examples of the carbon black used in the present invention include BLACKP manufactured by Cabot Corporation.
EARLS 2000, 1300, 1000, 900,
800, 880, 700, VULCAN XC-72,
# 3050B, 3150B, 325, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
0B, # 3750B, # 3950B, # 950, # 65
0B, # 970B, # 850B, MA-600, manufactured by Conlonvia Carbon Co., CONDUCTEX SC, RA
VEN 8800,8000,7000,5750,5250,3500,2100,2000,18
Examples include 00,1500,1255,1250 and Ketjenblack EC manufactured by Axor. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Also,
Carbon black may be dispersed with a binder in advance before being added to the paint. These carbon blacks can be used within a range not exceeding 50% by weight based on the above inorganic powder and not exceeding 40% by total weight of the non-magnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

Examples of the organic powder used in the present invention include acrylic styrene resin powder, benzguanamine resin powder, melamine resin powder and phthalocyanine pigment. Polyolefin resin powder, polyester resin powder, polyamid resin powder, polyimidite. Resin powder and polyfluorinated ethylene resin are used. As the manufacturing method, those described in JP-A-62-18564 and JP-A-60-255827 can be used. These non-magnetic powders are used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.1 with respect to the binder. Incidentally, an undercoat layer is provided in a general magnetic recording medium,
This is provided in order to improve the adhesive force between the support and the magnetic layer, non-magnetic layer, etc., and has a thickness of 0.5 μm or less, which is different from the lower layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesiveness between the underlayer and the support.

The step of producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each process may be divided into two or more stages. All the raw materials such as the magnetic material, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. In addition, individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong force such as a continuous kneader or a pressure kneader is used. High Br of the magnetic recording medium of the present invention could be obtained only by using a material having a kneading power. When a continuous kneader or a pressure kneader is used, all or part of the magnetic substance and the binder (however, 30% by weight or more of the total binder is preferable) and 15 to 500 parts by weight per 100 parts by weight of the magnetic substance. Kneading is performed within the range of parts. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274.

The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1, the lower layer is first coated by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for coating a magnetic coating, and when the lower layer is in a wet state, Japanese Patent Publication No. 1-46186 or The upper layer is coated by the support pressure type extrusion coating apparatus disclosed in JP-A-60-238179 and JP-A-2-265672. 2. Upper and lower layers by one coating head having two slits for passing the coating liquid as disclosed in JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672. Are applied almost simultaneously. 3, the upper and lower layers are coated almost simultaneously by the extrusion coating apparatus with back-up roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the agglomeration of magnetic particles, the inside of the coating head is coated by the method as disclosed in JP-A-62-95174 and JP-A-1-236968. It is desirable to apply shear to the coating solution of. Further, for the viscosity of the coating liquid, see JP-A-3-8471.
It is necessary to satisfy the numerical range disclosed in the publication.

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 1000 G (Gauss) or more and a cobalt magnet of 2000 G or more in combination, and it is preferable to further provide an appropriate drying step in advance before orientation so that the orientation after drying becomes the highest. Further, when the present invention is applied to a disk medium, an orientation method that randomizes the orientation is rather required. It is also preferable from the standpoint of improving electromagnetic conversion characteristics that a magnetic field in the vertical direction is applied if necessary so as to have a magnetization component oblique to the in-plane.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide or polyimide amide is used as the calendar treatment roll. Further, it is also possible to treat with metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the processing speed at that time is preferably 100 m / min to 500 m / min and a calender machine having 5 stages or more and 11 stages or less.

The coefficient of friction of the magnetic layer surface of the magnetic recording medium of the present invention and the surface opposite thereto to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ^-5 to 10 ^-12 o. M / sq, 0.5 of magnetic layer
The elastic modulus at% elongation is preferably 1 in both the running direction and the width direction.
00-2000 kg / mm ² , breaking strength is preferably 1
30 kg / cm ^2, modulus of elasticity of the magnetic recording medium in both the running direction and the long direction preferably 100 to 1,500 / m
m ² , the residual spread is preferably 0.5% or less, the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less,
It is more preferably 0.5% or less, and most preferably 0.1% or less. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less.
It is less than or equal to mg / m ² , and the residual solvent contained in the upper layer is preferably smaller than the residual solvent contained in the lower layer. The porosity of the magnetic layer is preferably 30% by volume or less, and more preferably 20% by volume or less in both the lower nonmagnetic layer and the magnetic layer. The porosity of the lower non-magnetic layer is preferably smaller than that of the magnetic layer, but it may be preferable to increase the porosity of the non-magnetic lower layer depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, the opposite is often preferable.

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 5
When measured in kOe, the squareness ratio in the tape running direction is 0.
It is 70 or more, preferably 0.80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. SFD (Switching) of magnetic layer
The field distribution is preferably 0.6 or less. Centerline surface roughness of magnetic layer (3
D MIURA method) Ra is preferably 1 nm to 10 nm, but its value should be appropriately set depending on the purpose. Ra is preferably as small as possible in order to improve electromagnetic conversion characteristics, but is preferably as large as it is in order to improve running durability. AFM (Atomic Force Mic)
It is preferable that the RMS surface roughness RRMS (root mean square roughness) obtained by evaluation by ro Scope) is in the range of 3 nm to 16 nm.

The magnetic recording medium of the present invention may have a multi-layer structure of two or more layers, but it is easily presumed that the physical properties of the upper layer and the lower layer can be changed according to the purpose. For example, the elastic modulus of the upper layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the upper layer to improve the contact of the magnetic recording medium with the head.

[0041]

EXAMPLES Next, the present invention will be described more specifically by way of examples. In the examples, the indication "part" means "part by weight".

Method for producing magnetic material Sodium carbonate (Na ₂ CO ₃ ) (10 kg) was dissolved in 120 kg of water, and then N ² gas was introduced into a bubble column type reaction tank while flowing, then ferrous chloride (FeCl ₂ ) 8 kg. 30 kg
After dissolving in water, the solution was placed in this reaction vessel to precipitate ferrous ions. While maintaining the slurry temperature at 35 ° C, add 2 kg of succinic acid and change the N2 gas to air to adjust the pH to 2
The reaction was carried out for about 2 hours while keeping it at -3. Then, the slurry is filtered with a filter press and washed until it becomes neutral, long axis length 0.2 μm, axial ratio 8, specific surface area 140 m ² / g
To obtain a spindle-shaped goethite. Next, 2 kg of this goethite was taken as a solid content, and sodium silicate, sodium aluminate, cobalt sulfate, and nickel sulfate were added to 40 liters of distilled water, and the mixture was sufficiently stirred to maintain the surface at 30 ° C. and subjected to surface treatment. Then, it was washed, filtered, granulated and dried to obtain a surface-treated goethite. Then, after substituting with nitrogen gas in a stationary reduction furnace, the temperature was raised in a hydrogen gas flow of 50 l / min and reduction was carried out at 350 ° C. While further lowering the temperature, the atmosphere was replaced with nitrogen, and oxygen gas was further introduced therein to carry out gradual oxidation to obtain a spindle-shaped metal magnetic powder. Hc of the obtained metal magnetic powder was 1750 Oe, specific surface area by BET method was 55 m ² / g, crystallite size was 150 Å,
The major axis length was 0.15 μm, the acicular ratio was 8, and σs was 125 emu / g. In order to change the coercive force, it was adjusted by changing the conditions of reduction temperature, time and hydrogen gas flow rate. The particle size was adjusted by changing the size of goethite. The size of goethite depends on the pH and Fe ^++.
It was carried out by changing the concentration and the reaction time. σs was adjusted by changing the amount of oxygen gas and the gradual oxidation temperature during gradual oxidation.

The characteristics of the magnetic material produced under the above conditions are shown in Table 1 below.

[0044]

[Table 1]

Examples 1 to 4 and Comparative Examples 1 to 6 (single magnetic layer) The magnetic layer was prepared as follows. Ferromagnetic fine metal powder 100 parts (composition; see table) Vinyl chloride copolymer 12 parts -SO ₃ Na Content: 1x10 ^-4 eq / g Polymerization degree 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-alumina (particle size 0.3 μm) 2 parts Carbon black (particle size 0.10 μm) 0.5 part Butyl Stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts

Each component of the above coating composition was kneaded with a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.) and then dispersed using a sand mill. To the obtained dispersion liquid, 3 parts of polyisocyanate was added, 40 parts of butyl acetate was further added, and the mixture was filtered through a filter having an average pore size of 1 μm to form a lower non-magnetic layer and an upper magnetic layer. Each of the coating solutions of was prepared. Coating was performed on a polyethylene terephthalate support having a thickness of 7 μm and a center line surface roughness of 0.01 μm so that the thickness of the obtained magnetic layer was 3 μm, and both layers were still in a wet state. Oriented with a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G, the film was oriented and dried, and then a back layer was provided.
At a speed of 250 m / min, and after curing, 8 mm
8 mm video tape was manufactured by slitting to the width of.

Examples 5 to 8 and Comparative Examples 7 to 12 Nonmagnetic lower layer Nonmagnetic powder α-Fe ₂ O ₃ α Hematite 80 parts Average major axis length 0.14 μm Minor axis length 24 mμ, specific surface area by BET method 50 m ² / G pH 7 Surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5 wt% Chloride Vinyl-vinyl acetate-vinyl alcohol copolymer 12 parts-Containing 5 x 10 ^-4 eq / g of polar group of -SO ₃ Na Composition ratio 86: 13: 1 Degree of polymerization 300 Polyester polyurethane resin 5 parts Neopentyl glycol / Caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 5 parts butyl stearate 1 part 1 part of stearic acid Me Ethyl ketone 200 parts

The magnetic layer is the magnetic layer prepared as described above.
For the non-magnetic layer, the above components were kneaded with a Labo Plastomill (manufactured by Toyo Seiki) and then dispersed using a sand mill. 1 part of polyisocyanate was added to the obtained dispersion, 40 parts of butyl acetate was further added, and the mixture was filtered through a filter having an average pore size of 1 μm to prepare a coating solution for the lower non-magnetic layer. The thickness of the obtained lower layer non-magnetic layer coating liquid was adjusted so that the thickness after drying was 2 μm and immediately thereafter the thickness of the upper magnetic layer was 0.15 μm. Center line surface roughness of 0.01 μm at 7 μm
Simultaneous multi-layer coating was performed on the polyethylene terephthalate support, and while both layers were still wet, 3000
After being oriented by a cobalt magnet having a magnetic force of G and a solenoid having a magnetic force of 1500 G and dried, a 7-stage calender consisting of only metal rolls was processed at a temperature of 90 ° C. and a calendering speed of 250 m / min for 8 mm. 8 mm video tape was manufactured by slitting to the width of.

The results when the magnetic layer is a single layer having a thickness of 3 μm are shown in Tables 2 and 3 below.

[0050]

[Table 2]

[0051]

[Table 3]

The results in the case of the multi-layer structure in which the thickness of the magnetic layer is 0.15 μm are shown in Tables 4 and 5 below.

[0053]

[Table 4]

[0054]

[Table 5]

Evaluation Method (Specific Surface Area by BET Method) A canter soap (manufactured by US Canterchrome) was used. After dehydration in a nitrogen atmosphere at 250 ° C. for 30 minutes, it was measured by the BET single point method (partial pressure 0.30).

(Hc, σr, squareness ratio, σs) A vibrating sample type magnetometer (manufactured by Toei Industry Co., Ltd.) was used.
The measurement was carried out at 0 kOe and, in the case of the tape sample, at 5 kOe.

(Center line average surface roughness) Using a three-dimensional surface roughness meter (TOPO3D manufactured by WYKO), Ra, Rrms, peak to val of 250 nm × 250 nm area by MIRAU method.
The ley value was measured. The measurement wavelength is about 650 nm, and spherical correction and cylindrical correction are added. This measurement method is an optical interference type surface roughness meter that measures without contact.

(AFM rms average surface roughness) STM
(Scanning Transparent Mic
ro Scope) is measured by Digital Instrument's Na
Using noscope2, tunnel current: 10nA, bias voltage: 40
A range of 6 μm × 6 μm was scanned under the condition of 0 mV. The surface roughness was compared by obtaining Rrms in this range.

(Major axis diameter and minor axis diameter of magnetic material) The average particle diameters of the major axis and the minor axis were determined by a transmission electron microscope photograph of 100,000 times.

(Crystallite size) By X-ray diffraction (4,
It was calculated from the spread of the full width at half maximum of the diffraction lines of the (4,0) plane and the (2,2,0) plane.

(Output and C / N measuring method) An external contact type drum tester was used. Tape head relative speed is 3.8m /
sec, the head used is a laminated sendust head having a gap length of 0.2 μm and a track width of 20 μm. The frequency used was 7.6 MHz (recording wavelength λ = 0.5 μm), and the C / N ratio was determined from the output when reproduced at the optimum recording current and the noise at 6.6 MHz. The reference is an 8-mm video tape superAG manufactured by Fuji Photo Film.

(Overwrite O / W Suitability Evaluation Method) Using the drum tester, sine wave recording of 1.9 MHz is first performed on the sample after erasing, and the output is measured using a spectrum analyzer. After that, 7.6MH
The 1.9 MHz output after the sine wave signal of z was superposed and recorded was measured again using a spectrum analyzer, and the difference was evaluated. The larger the difference, the more overwrite (O /
W) Good suitability. In a digital recording system having a recording wavelength of 1 μm or less, it is preferably −23.5 dB or less.

(Method of measuring d, σ) A magnetic recording medium was cut out in a thickness of about 0.1 μm with a diamond cutter over the longitudinal direction, and a transmission electron microscope was used to magnify 10,000 to 100,000 times, preferably 20,000 to 50 times. 00
Observation was performed at 0 times, and the photograph was taken. The print size of the photograph is A4 to A5. After that, attention was paid to the shape difference between the magnetic substance and the non-magnetic powder in the magnetic layer and the lower non-magnetic layer, and the interface was visually judged to be black, and the surface of the magnetic layer was also black. After that, Zeiss image processing device IB
At AS2, the length of the interval of one thousand pits was measured. When the length of the sample photograph is 21 cm, the measurement is performed 100 to 300 times. The average value of the measured values at that time was d, and the standard deviation of the measured values was σ.

[0064]

In a magnetic recording medium comprising a magnetic layer having a magnetic material dispersed in a binder on a non-magnetic flexible support, the magnetic material is a ferromagnetic alloy powder mainly composed of α-Fe. And its powder coercive force Hc is 1620 Oe or more 2100
Oe or less, saturation magnetization σs is 120 to 150 emu / g, specific surface area due to N ₂ gas adsorption is 48 to 60 m ² / g, and major axis length is 0.
08-0.21 μm, minor axis length 0.01-0.02 μm,
A crystallite size of 110 to 170 angstroms with a needle-like ratio of 7 to 11 is good in terms of balance of all medium characteristics, and specifically, tape Hc, tape Bm, tape squareness ratio, It was found that the characteristics of tape Ra, output, and over write (O / W) were all excellent.

Claims (7)

[Claims] 1. A magnetic recording medium comprising a magnetic layer having a magnetic material dispersed in a binder on a non-magnetic flexible support, wherein the magnetic material is a ferromagnetic alloy powder mainly composed of α-Fe. Yes, the coercive force Hc of the powder is 1620 Oe or more 210
0 Oe or less, saturation magnetization σs of 120 to 160 emu / g, N ₂
The specific surface area by gas adsorption is 48 to 65 m ² / g, the major axis length is 0.08 to 0.21 μm, the minor axis length is 10 to 20 mμ, the acicular ratio is 7 to 11, and the crystallite size is 110 to 170 angstrom. Characteristic magnetic recording medium. 2. The coercive force Hc of the ferromagnetic alloy powder mainly containing α-Fe is 1720 Oe or more and 2000 Oe or less, the saturation magnetization σs is 122 to 140 emu / g, and the squareness ratio is 0.48 to.
0.51, specific surface area due to N ₂ gas adsorption is 52 to 59 m ²
/ g, major axis length 0.1 to 0.18 μm, minor axis length 10 to 18 m
2. The magnetic recording medium according to claim 1, wherein the crystallite size is 120 to 160 angstroms at .mu. and an acicular ratio of 7 to 11. 3. A plurality of at least two layers comprising a non-magnetic flexible support, a lower layer containing mainly inorganic non-magnetic powder dispersed in a binder, and an upper layer containing ferromagnetic powder dispersed in the binder. In the magnetic recording medium having the above-mentioned layer, the average value d of the magnetic layer thickness of the upper layer is larger than 0.05 μm and is 0.1.
The magnetic recording medium according to claim 1, which has a thickness of 8 μm or less. 4. The magnetic material according to claim 3, wherein an upper layer having ferromagnetic powder dispersed in the binder is provided while the lower layer having the inorganic non-magnetic powder dispersed in the binder is in a wet state. recoding media. 5. The magnetic recording medium according to any one of claims 1 to 4, wherein the magnetic material is a ferromagnetic alloy powder containing Fe as a main component and obtained by reducing spindle-type goethite. . 6. The amount of soluble Na salt contained in the ferromagnetic alloy powder used in the magnetic layer farthest from the non-magnetic support is 5.
The magnetic recording medium according to claim 5, wherein the content is 0 ppm or more and 700 ppm or less. 7. The inorganic non-magnetic powder used in the lower layer is titanium oxide, rouge (α-hematite), barium sulfate,
One or more kinds selected from aluminum oxides, the average particle diameter is 0.08 μm or less in the case of granules, the major axis length is 0.05 to 0.3 μm, and the minor axis length is 5 m μ to 30 m in the case of needles.
4. The magnetic recording medium according to claim 3, wherein μ is μ.