JP2614154C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001]     [Industrial applications]   The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer,
More specifically, a magnetic recording medium having at least two layers and having excellent electromagnetic characteristics is provided.
It is about. [0002]     [Prior art]   The magnetic recording medium is audio tape, video tape or floppy disk
Widely used as. Recent magnetic recording media are capable of high-density recording and
It is required to have excellent electromagnetic conversion characteristics that can provide image quality and high sound quality.
Various attempts have been made to obtain magnetic conversion characteristics. In addition, a large amount of magnetic recording media
And are consumed in large quantities as media and become cheaper.
It must be able to be manufactured at a reasonable price. Its technology is high filling, high coercive force,
Mainly smoothing, etc., but more effective recording in the depth direction of the magnetic layer
In order to achieve this, a multi-layer structure has been actively used. It is a high-quality
In order to provide high sound quality in the lower layer, appropriate ferromagnetic powder can be used. Because it can. In addition, multi-layering is inexpensive because appropriate materials can be used depending on the layer.
It also has features that can be manufactured at a low cost. On the other hand, to achieve high image quality and high sound quality
It is necessary to improve the S / N by increasing the reproduction output and lowering the modulation noise.
Therefore, it is necessary to increase the filling degree and smoothness of the magnetic recording medium. [0003]   For example, Japanese Patent Application Laid-Open Nos. Sho 59-172144 and 61-214
No. 223 and JP-A-57-69528, the upper layer has a high coercive force and the lower layer has a high coercive force.
By reducing the power, a high output can be obtained in a wide frequency band.
JP-A-58-56230, JP-A-58-56231, JP-A-58-7042
9, JP-A-1-106333 and JP-A-58-17539 disclose fine particles in the upper layer.
It has been shown that the use of the ferromagnetic powder of (1) reduces noise. JP-A-58-53
In No. 024, a high output is obtained by highly filling the upper layer. JP-A-57-9
No. 8135, JP-A-63-187419, JP-A-64-19524, JP-A-Hei.
JP-A-2-192019 and JP-A-2-254626 disclose the size of the upper ferromagnetic powder.
Attempts have been made focusing on shapes and shapes. In this way, layering improves electromagnetic conversion characteristics
It has a great effect in making the recording medium
Is becoming inadequate. [0004]   For example, to reduce the size of ferromagnetic powder to reduce noise
And has been done. To reduce noise, the long axis length of the ferromagnetic powder should be 0.3μ.
m or less. Such an example is disclosed in the above-mentioned JP-A-63-187419.
As disclosed in JP-A-64-19524, the dispersion and distribution of
Orientation was difficult, and it was very difficult to increase the degree of filling. Because of that
Even if the size was reduced, the output was reduced, and sufficient characteristics could not be obtained. [0005]     [Problems to be solved by the invention]   An object of the present invention is to provide an audio tape, a video tape, etc. having excellent electromagnetic conversion characteristics.
An object of the present invention is to provide a magnetic recording medium. [0006]     [Means for Solving the Problems]   The present inventors have conducted intensive studies on such a situation, and as a result, have found that a multilayer magnetic recording medium can be used.
When the thickness of the upper layer and the shape of the ferromagnetic powder have a certain relation,
It has been found that the exchange characteristics are improved, and the present invention has been achieved. [0007]   That is, the present invention provides a method for producing a lower magnetic layer comprising a ferromagnetic powder and a binder on the surface of a nonmagnetic support.
And a magnetic recording medium having a plurality of magnetic layers comprising an upper magnetic layer provided thereon.
And included in the upper magnetic layer.Oriented in the longitudinal directionThe major axis length of the ferromagnetic powder is 0.
30 μm or less, crystallite size is 400 ° or less, ratio of major axis length to crystallite size
Is 3 or more and 7 or less, and the dry thickness of the upper magnetic layer is
Powder crystallite size25 times or lessAnd a center line average surface of the surface of the upper magnetic layer.
A magnetic recording medium having a roughness (Ra) of 6 nm or less. [0008] [0009] [0010]   The magnetic recording medium according to the present invention basically has a shape of an upper magnetic layer-containing ferromagnetic powder,
The filling degree is improved by defining the size and the center average surface roughness (ie, Ra).
Thus, the output is improved and the noise is reduced. [0011] [0012]   In the present invention, the long axis length means the average particle diameter of the long axis measured by a transmission electron microscope.
The crystallite size was determined by X-ray diffraction from the (4,4,0) plane to the (2,2,2) plane.
It is a value obtained from the spread of the half value width of the diffraction line on the 0) plane. Also, the center line average surface
The roughness was measured using a three-dimensional surface roughness meter (for example, manufactured by Kosaka Laboratories), with a cutoff of 0.
It is a value measured at 08 mm. [0013]   Hereinafter, the present invention will be described. In order to simplify the description, the upper magnetic layer and the lower
The magnetic layer may simply be referred to as an upper layer or a lower layer.   According to the study results of the present inventors, the major axis length of the ferromagnetic powder was 0.3 μm or less, 400 ° or less, especially the ratio of the major axis length to the crystallite size is 3 or more and 7 or less.
It has been found that sufficient filling degree can be obtained by doing so. The reason is that the needle ratio is
If it is too high, voids will form when trying to fill the ferromagnetic powder in the longitudinal direction due to the shape effect.
On the other hand, when the needle ratio is low, the effect of the shape is reduced, so that voids are not easily generated.
And is presumed to be related. Such a ferromagnetic powder with a small axial ratio is
The use of an upper layer is conventionally known in, for example, the above-mentioned JP-A-2-254626.
However, the filling degree is low and Ra is large probably because the upper layer thickness is as thick as 1.5 μm.
Therefore, sufficient output and S / N have not been obtained. We consider this reason.
As a result of the investigation, the relationship between the crystallite size and the upper layer thickness, that is,
The upper layer thickness25 times or lessIn the case of conventional magnetic recording media,
They have found that they can achieve significantly higher output than they could. [0014]   The reason why the magnetic recording medium of the present invention has such a high output is not clear, but is as follows.
It is estimated as follows. The arrangement of the ferromagnetic powder in the layer is determined by various factors.
However, considering the effect of the thickness of the magnetic layer, the thinner one is arranged in the longitudinal direction.
It is thought that it becomes easy to do. This is because the arrangement of the upper ferromagnetic powder is
The surface of the conductive layer is smoothed in the longitudinal direction by calendering, etc.)
(In the case of a support, a lower layer in the case of a multilayer), it is easy to line up in the longitudinal direction due to external restrictions.
On the other hand, the middle part is likely to be arranged in a relatively disorderly direction. Therefore, on
The thinner the layer, the more the proportion of the ferromagnetic powder is easy to arrange in the longitudinal direction and the better the filling degree.
It is thought to be up. It is extremely difficult to predict the degree, but the cross section of the tape
The present inventors have experimentally confirmed by observation and the like that the length of the major axis length and the thickness of the upper layer
And the ratio of the major axis to the crystallite size is 3
Above, 7 or less, the upper layer thickness is the crystallite size25 times or lessEffectively high when
It was found to be packed. Such an example is disclosed in the aforementioned Japanese Patent Laid-Open No. 2-201919.
Although shown, the output was high but the S / N ratio was not always sufficient. [0015]   The present inventors have studied to further improve these, and as a result, Ra was set to 6 nm or less.
, The S / N ratio was remarkably improved. Ferromagnetic powder with small axial length Even if high output and low noise are measured by improving the filling degree using powder, the surface
If the roughness is rough, it is difficult to improve the output due to spacing loss. That's not all
Modulation noise due to roughness adds to the effect of reducing noise. Ferromagnetic powder
Both noise reduction by fine powder and noise reduction by surface smoothing are achieved.
S / N is improved for the first time by making the ferromagnetic powder finer,
By setting the relative relationship between the major axis length of the powder and the surface roughness to the value shown in the present application, it is extremely large
It has been found that it becomes. [0016]   The major axis length of the ferromagnetic powder used in the present invention is 0.3 μm or less, preferably
Is 0.2 μm or less. The major axis length of the ferromagnetic powder contained in the upper layer is
The length of the ferromagnetic powder is preferably smaller than the major axis length. Upper layer used in the present invention
The ratio of the major axis length to the crystallite size of the ferromagnetic powder is 3 or more and 7 or less
However, both are preferably 4 or more and 6 or less. If it is less than 3, the orientation deteriorates.
Not preferred. 25-80m if ferromagnetic powder particles are expressed by specific surface area by BET method
^Two/ G, preferably 35-60 m^Two/ G. Noise is high below 25
If it is 80 or more, it is difficult to obtain surface properties, which is not preferable. Also the ferromagnetism contained in the upper layer
The specific surface area of the powder is preferably larger than the specific surface area of the ferromagnetic powder contained in the lower layer.
No. The upper ferromagnetic powder used in the present invention has a crystallite size of 400 ° or less.
, Preferably 350 to 150 °. The crystallite of the ferromagnetic powder contained in the upper layer
The size is preferably smaller than the crystallite size of the ferromagnetic powder contained in the lower layer.
Hc of the ferromagnetic powder used in the present invention is 200 to 2000 Oe, preferably
It is 350-1600 Oe. The upper layer Hc is preferably higher than the lower layer Hc. [0017] [0018] [0019] [0020] [0021] [0022]   Hereinafter, general matters relating to the present invention will be described.   The upper layer preferably has a ferromagnetic powder content of 70% or more. 70% ferromagnetic powder content
If it is less than 1, the degree of filling is reduced and the electromagnetic conversion characteristics are degraded. Ferromagnetic powder
Percentage is defined as (ferromagnetic powder) / (ferromagnetic powder + binder + additive contained in the magnetic layer)
%). [0023]   When the magnetic properties of the magnetic recording medium of the present invention were measured at a magnetic field of 5 KOe, the squareness ratio was different for each layer.
Both are preferably 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more.
No. [0024]   Σ of the ferromagnetic powder used in the present invention_sIs at least 50 emu / g, preferably 70
emu / g or more, and preferably 100 emu / g or more in the case of fine metal powder.
Further, the water content is preferably set to 0.01 to 2%. Strong magnetic depending on the type of binder
It is preferable to optimize the water content of the conductive powder. [0025]   When a cobalt-modified iron oxide is used as the ferromagnetic powder of the present invention, trivalent iron
The ratio of valence to iron is preferably from 0 to 33.3%, more preferably from 5 to 1%.
0%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 3 to 15%.
~ 8%. [0026]   It is preferable to optimize the pH of the ferromagnetic powder depending on the combination with the binder used.
. Its range is 4-12.   Even if the ferromagnetic powder is subjected to surface treatment with Al, Si, P or an oxide thereof,
I don't care. The amount is 0.1 to 10% based on the ferromagnetic powder. [0027]   Both lower and upper ferromagnetic powders are soluble in inorganic materials such as Na, Ca, Fe, Ni, and Sr.
There may be a case where ions are contained, but if it is 500 ppm or less, there is no particular effect.   As the ferromagnetic powder used in the present invention, γ-FeOx (x = 1.33 to 1.5)
, Co-modified γ-FeOx (x = 1.33 to 1.5), Fe or Ni or Co Well-known ferromagnetic powders such as ferromagnetic alloy fine powders whose main component is (75% or more)
Wear. These ferromagnetic powders include Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta
, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It may contain atoms such as n, Zn, Ni, Sr, and B. These ferromagnetic fine powders contain dispersants, lubricants, surfactants,
Before dispersing with an agent or the like, treatment may be performed in advance. [0028]   Among the above ferromagnetic powders, a small amount of hydroxide or acid
May also be included. Ferromagnetic alloy fine powder obtained by a known manufacturing method
The following methods can be used. A method of reducing with a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen,
Fe or Fe-Co particles are obtained by reducing iron oxide with a reducing gas such as hydrogen.
Method, thermal decomposition of metal carbonyl compound, hydrogenation to aqueous solution of ferromagnetic metal
Add a reducing agent such as sodium boron, hypophosphite or hydrazine to reduce
To obtain a fine powder by evaporating the metal in a low-pressure inert gas.
You. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, an organic method.
Drying after immersion in a solvent, sending oxygen-containing gas after immersion in an organic solvent
To form an oxide film on the surface and then dry it.
Any method of forming an oxide film on the surface by adjusting the partial pressure of the gas and inert gas.
Can be used. [0029]   Further, the ferromagnetic powder used in the present invention preferably has a smaller number of vacancies, and the value is preferably
It is 20% by volume or less, more preferably 5% by volume or less.   The ferromagnetic powder used in the present invention can be produced according to a known method. [0030]   As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins,
Reactive resins and mixtures thereof are used. As a thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1000 to 200,000, preferably 10,000 to 100,000, and a degree of polymerization of about 5
It is about 0 to 1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic
Acid, acrylic acid, acrylate, vinylidene chloride, acrylonitrile,
Tacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl
Polymerization containing butyral, vinyl acetal, vinyl ether, etc. as constituent units
There are polymers or copolymers, polyurethane resins and various rubber resins. In addition, as thermosetting resin or reactive resin, phenol resin, epoxy resin,
Polyurethane curing resin, urea resin, melamine resin, alkyd resin, acrylic
Reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin
, A mixture of polyester resin and isocyanate prepolymer, polyester poly
Mixture of all and polyisocyanate, mixture of polyurethane and polyisocyanate
Compounds and the like. These resins are described in detail in the Plastic Handbook published by Asakura Shoten.
Are listed. It is also possible to use a known electron beam-curable resin. These examples and their
The production method is described in detail in JP-A-62-256219. that's all
Resins can be used alone or in combination.
, Vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, salt
Vinyl acetate vinyl acetate maleic anhydride copolymer, at least one selected from the group consisting of:
Combinations of polyurethane resins or combinations of these with polyisocyanates
Is raised. Polyurethane resin structure is polyester polyurethane, polyether polyurethane
Polyether polyester polyurethane, polycarbonate polyurethane,
Polyester polycarbonate polyurethane, polycaprolactone polyurethane
For example, known materials can be used. For all the binders shown here, for better dispersibility and durability
May be COOM, SO as required_ThreeM, OSO_ThreeM, P = O (OM)_Two, OP = O
(OM)_Two, (Where M is a hydrogen atom or an alkali metal base), OH, NR^Two, N⁺R^Three, R is a hydrocarbon group) selected from epoxy groups, SH, CN, etc.
Use at least one polar group introduced by copolymerization or addition reaction.
Is preferred. The amount of such polar groups is 10^-1-10^-8Mol / g, preferred
H10^-2-10^-6Mol / g. Specific examples of these binders used in the present invention include Union Carbide
Made: VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES
, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC,
PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TAL
, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, Electrochemical
Manufactured by: 1000W, DX80, DX81, DX82, DX83, manufactured by Zeon Corporation:
MR110, MR100, 400X110A, manufactured by Nippon Polyurethanes: Nippola
N2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd .: Pandex T-
5105, T-R3080, T-5201, Barnock D-400, D-210
-80, Chris Bon 6109, 7209, manufactured by Toyobo: Byron UR8200,
UR8300, RV530, RV280, manufactured by Dainichi Seika: Daifuramin 402
0, 5020, 5100, 5300, 9020, 9022, 7020, Mitsubishi Kasei
Manufactured by: MX5004, manufactured by Sanyo Kasei: Samprene SP-150, manufactured by Asahi Kasei: sa
Runs F310, F210, and the like. The binder used in the present invention is used in an amount of 5 to 50 with respect to the ferromagnetic powder in each of the upper and lower layers.
%, Preferably in the range of 10 to 30%. Vinyl chloride resin
Is used, 5 to 30% by weight, and when polyurethane resin is used, 2 to 20% by weight.
% By weight and polyisocyanate in a range of 2 to 20% by weight.
Is preferred. In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100.
° C, breaking elongation is 100 to 2000%, and breaking stress is 0.05 to 10 kg / cm.^Two,
The yield point is 0.05-10Kg / cm^TwoIs preferred. As the polyisocyanate used in the present invention, tolylene diisocyanate, 4-
4'-diphenylmethane diisocyanate, hexamethylene diisocyanate,
Xylylene diisocyanate, naphthylene-1,5-diisocyanate, o- Louis diisocyanate, isophorone diisocyanate, triphenyl methane tri
Isocyanates such as isocyanates, and these isocyanates and polyisocyanates
Products with alcohols and polyisocyanates produced by condensation of isocyanates
Socyanates and the like can be used. Commercially available of these isocyanates
Brand names are those manufactured by Nippon Polyurethane Co .: Coronate L, Coronate HL
, Coronate 2030, Coronate 2031, Millionate MR, Millionate
MTL, manufactured by Takeda Pharmaceutical: Takenate D-102, Takenate D-110N, Take
Nate D-200, Takenate D-202, manufactured by Sumitomo Bayer: Desmodur
L, death module IL, death module N, death module HL, etc.
These may be used alone or in combination of two or more using the difference in curing reactivity.
Both the layer and the upper layer can be used. [0031]   The carbon black used in the magnetic layer of the present invention may be a furnace black for rubber or a rubber black.
Color, black for color, acetylene black and the like can be used. Specific surface area is 5-500m^Two/ G, DBP oil absorption is 10-400ml / 100g,
The particle size is 5 μm to 300 μm, pH is 2 to 10, water content is 0.1 to 10%,
The packing density is preferably from 0.1 to 1 g / cc. Specific examples of the carbon black used in the present invention include Cabot Corporation: B
LACKPEARLS 2000, 1300, 1000, 900, 800, 70
0, VULCAN XC-72, manufactured by Asahi Carbon: $ 80, $ 60, $ 55, $
50, 35, manufactured by Mitsubishi Chemical Corporation: 2400B, 2300, 900, 1
000, $ 30, $ 40, $ 10B, made by Konlon Via Carbon: CONDUC
TEX SC, RAVEN 150, 50, 40, 15 and the like. car
Even if Bon Black is surface-treated with a dispersant or grafted with resin
Alternatively, a part of the surface may be graphitized. Also carb
The black may be dispersed with a binder before adding it to the magnetic paint.
. These carbon blacks can be used alone or in combination. Mosquito
When using carbon black, it should be 0.1 to 30% of the amount based on the ferromagnetic powder.
Is preferred. Carbon black prevents static in the magnetic layer, reduces friction coefficient, imparts light-shielding properties, and improves film strength
These functions differ depending on the carbon black used. Therefore
These carbon blacks are used in the lower layer and upper layer in their types, amounts and combinations.
Of the particle size, oil absorption, conductivity, pH, etc.
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 described in, for example,
(Edited by the Carbon Black Association). [0032]   Examples of the abrasive used in the present invention include α-alumina and β-a having an α conversion of 90% or more.
Lumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, human
Diamond, silicon nitride, silicon carbide titanium carbide, titanium oxide, silicon dioxide
Well-known materials with a Mohs of 6 or more such as silicon, boron nitride, alone or in combination
used. In addition, a composite of these abrasives (the abrasive is surfaced with another abrasive)
Processed) may be used. These abrasives contain compounds other than the main component or
May contain an element, but the effect is not changed if the main component is 90% or more.
. The particle size of these abrasives is preferably from 0.01 to 2 μm,
The same can be achieved by combining abrasives of different sizes or broadening the particle size distribution with a single abrasive
The effect of can also be provided. Tap density is 0.3-2 g / cc, water content is 0
. 1-5%, pH 2-11, specific surface area 1-30m^Two/ G is preferred. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape.
However, those having a corner in a part of the shape are preferable because of high abrasiveness. Specific examples of the abrasive used in the present invention include AKP-20 manufactured by Sumitomo Chemical Co., Ltd.
, AKP-30, AKP-50, HIT-50, manufactured by Nippon Chemical Industry: G5, G7
, S-1, manufactured by Toda Kogyo KK: 100ED, 140ED. These abrasives can be dispersed in a binder before being added to the magnetic paint.
I don't care. [0033]   The additives used in the present invention include a lubricating effect, an antistatic effect, a dispersing effect,
Those having a plastic effect and the like are used. Molybdenum disulfide, tungsten disulfide Graphite, boron nitride, fluorinated graphite, silicone oil, silicone with polar groups
Corn, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol
, Fluorine-containing esters, polyolefins, polyglycols, alkyl phosphate esters
And its alkali metal salts, alkyl sulfates and their alkali metal salts
, Polyphenyl ethers, fluorine-containing alkyl sulfates and their alkalis
Metal salts, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds,
And metal salts thereof (Li, Na, K, Cu, etc.)
) 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), and has 12 to 22 carbon atoms.
Alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds)
Or it may be branched) and C2-12 monovalent, divalent, trivalent
, Tetrahydric, pentahydric or hexahydric alcohols (including unsaturated bonds,
Mono-fatty acid ester or di-fatty acid ester consisting of
Or trifatty acid esters, monoalkyl ethers of alkylene oxide polymers
Fatty acid esters, fatty acid amides having 8 to 22 carbon atoms, aliphatics having 8 to 22 carbon atoms
Amines and the like can be used. Examples of these are Lauric acid, myristic acid, palmitic acid, stearic acid, hebenic acid, steariic acid
Butyl phosphate, oleic acid, linoleic acid, linolenic acid, elaidic acid, stearin
Octyl acid, amyl stearate, isooctyl stearate, o myristate
Cutyl, butoxyethyl stearate, anhydrosorbitan monostearate
, Anhydrosorbitan distearate, anhydrosorbitan tristearate
And oleyl alcohol and lauryl alcohol. In addition, alkylene oxide, glycerin, glycidol,
Nonionic surfactants such as ethylene oxide adducts, cyclic amines,
Teramides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phospho
Surfactants such as chromium or sulfonium, carboxylic acid, sulf
Anions containing acidic groups such as phosphoric acid, phosphoric acid, sulfate groups, phosphate groups, etc.
Surfactants, amino acids, amino sulfonic acids, amino alcohol sulfuric acid or
Ampholytic surfactants such as phosphates and alkylbedynes can also be used. This For more information about these surfactants, see "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.).
It is described in detail. These lubricants, antistatic agents, etc. are not necessarily 100% pure.
It may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc.
Absent. These impurities are preferably 30% or less, more preferably 10% or less.
is there. [0034]   These lubricants and surfactants used in the present invention require their types and amounts in each layer.
Can be used properly. [0035]   All or some of the additives used in the present invention may be used in the production of magnetic paints.
May be added in the step of, for example, mixing with ferromagnetic powder before the kneading step.
When adding in the kneading process using ferromagnetic powder, binder and solvent,
In some cases, it is added after dispersion, or it is added just before coating. [0036]   The organic solvent used in the present invention is acetone in any ratio, methyl ethyl ketone,
Methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone
, Tetrahydrofuran, and other ketones, methanol, ethanol, propanol
, Butanol, isobutyl alcohol, isopropyl alcohol, methylcyclo
Alcohols such as hexanol, methyl acetate, butyl acetate, isobutyl acetate
, Isopropyl acetate, ethyl lactate, glycols such as glycol acetate, glycols
Glyco such as dimethyl ether, glycol monoethyl ether, dioxane, etc.
Ether, benzene, toluene, xylene, cresol, chlorobenzene
, Such as aromatic hydrocarbons, methylene chloride, ethylene chloride, tetrachloride
Chlorination of carbon, chloroform, ethylene chlorohydrin, dichlorobenzene, etc.
Hydrocarbons, N, N-dimethylformamide, hexane and the like can be used. [0037]   The thickness configuration of the magnetic recording medium of the present invention is such that the nonmagnetic support is 1 to 100 μm, preferably
6-20 μm, lower magnetic layer 0.5 μ-10 μm, preferably 1-5 μm, upper magnetic layer Is preferably not more than 20 times the crystallite size. Magnetic layer thickness is non-magnetic
It is used in a range of 1/100 to 2 times the thickness of the support. Further, an undercoat layer for improving adhesion between the nonmagnetic flexible support and the intermediate layer, or
An intermediate layer such as a layer containing carbon black for antistatic may be provided.
Their thickness is 0.01 to 2μ, preferably 0.05 to 0.5μ. Also,
A back coat layer may be provided on the side opposite to the magnetic layer side of the non-magnetic support. This
Has a thickness of 0.1 to 2 μ, preferably 0.3 to 1.0 μ. These intermediate layers,
A known backcoat layer can be used. [0038]   The non-magnetic support used in the present invention is polyethylene terephthalate or polyethylene.
Polyesters such as nannaphthalate, polyolefins, cellulose triacetate
Tate, polycarbonate, polyamide, polyimide, polyamideimide, poly
Known films such as sulfon, aramid, and aromatic polyamide can be used.
These supports are treated in advance with corona discharge treatment, plasma treatment, easy adhesion treatment, and heat treatment.
Processing, dust removal processing, and the like may be performed. To achieve the object of the present invention, a non-magnetic
The support has a center line average surface roughness of preferably 0.02 or less, more preferably
In other words, it is necessary to use one having a size of 0.01 μm or less. Also, these non-magnetic supports
Means that not only the center line average surface roughness is small but also that there are no coarse protrusions of 1μ or more.
Is preferred. The surface roughness shape can be adjusted by adding a filler to the support if necessary.
Is freely controlled by the size and amount of With these fillers
For example, in addition to oxides and carbonates such as Ca, Si and Ti, acrylic
Any organic fine powder can be mentioned. [0039]   The step of producing the magnetic paint of the magnetic recording medium of the present invention includes at least a kneading step,
It consists of a dispersing step and a mixing step optionally provided before and after these steps. Individual
Each process may be divided into two or more steps. Used in the present invention
Ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent
Any of the raw materials may be added at the beginning or during any of the steps. Also, individual
Each raw material may be divided and added in two or more steps. For example, Polyure Divided into the kneading step, dispersion step, and mixing step for adjusting viscosity after dispersion
May be. [0040]   In order to achieve the object of the present invention, a conventionally known manufacturing technique is used as a part of the steps.
Of course, it can be used.
A material having a strong kneading power such as a die can be used. Continuous kneader or pressurized
When using a ferromagnetic powder, all or part of the ferromagnetic powder and binder (but not all
And more preferably 15 to 500 parts per 100 parts of ferromagnetic powder.
It is kneaded in the range. The details of these kneading processes are described in JP-A-1-1063.
No. 38, JP-A-1-79274. According to the present invention,
By using the simultaneous multilayer coating method as shown in Japanese Patent No.
It can be produced efficiently. [0041]   In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000G or more
It is preferable to use a combination of a solenoid and a cobalt magnet of 2000 G or more.
It is necessary to provide an appropriate drying step before orientation so that the orientation after drying is the highest.
Is preferred. [0042]   Epoxy, polyimide, polyamide, poly
Use a heat-resistant plastic roll such as imidoamide. Also, metal low
They can be processed by each other. The processing temperature is preferably 70 ° C. or more, more preferably
Preferably, it is 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably
Or 300 kg / cm or more. [0043]   With respect to SUS420J on the magnetic layer surface and the opposite surface of the magnetic recording medium of the present invention.
The coefficient of friction is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably
Is 10^-Five-10^-12Ohm / sq, the elastic modulus at 0.5% elongation of the magnetic layer is the running direction
, Preferably in the width direction of 100 to 2000 kg / mm^Two, The breaking strength is preferably
1-30 kg / cm^Two, The elastic modulus of the magnetic recording medium is preferable in the running direction and the longitudinal direction. 100 to 1500 kg / mm^Two, The residual growth is preferably 0.5% or less,
The heat shrinkage at any temperature below 0 ° C. is preferably 1% or less, more preferably
It is at most 0.5%, most preferably at most 0.1%. [0044]   The residual solvent contained in the magnetic layer is preferably 100 mg / m^TwoLess preferred
Or 10mg / m^TwoBelow, the residual solvent contained in the upper layer
It is preferable that the amount is smaller than the distillation solvent. [0045]   The porosity of the magnetic layer is preferably 30% by volume or less for both the lower layer and the upper layer, and more preferably.
More preferably, it is 10% by volume or less. The porosity of the lower layer is larger than the porosity of the upper layer
Although preferred, the porosity of the lower layer may be as small as 5% or more. Of the present invention
The magnetic characteristics of the magnetic recording medium are, when measured at a magnetic field of 5 KOe, square in the tape running direction.
The ratio is at least 0.70, preferably at least 0.80, more preferably at least 0.90.
Above. The squareness ratio in two directions perpendicular to the tape running direction is 8 which is the squareness ratio in the running direction.
It is preferably 0% or less. The SFD of the magnetic layer is preferably 0.6 or less.
New [0046]     【Example】   Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.
Not. Note that “parts” indicates parts by weight. [0047]   Example 1 Lower magnetic layer   Cobalt-modified iron oxide 100 parts     Hc 700 Oe, specific surface area 60m^Two/ G     Crystallite size 400Å     Particle size (long axis length) 0.30μ,     Long axis length / crystallite size 7.5   Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts       Composition ratio 86: 13: 1 Degree of polymerization 400   5 parts of polyester polyurethane resin   Carbon black (particle size 0.05μm) 3 parts   1 part butyl stearate   2 parts of stearic acid   200 parts of butyl acetate Upper magnetic layer   Cobalt-modified iron oxide 100 parts     Hc 900 Oe, specific surface area 50m^Two/ G     Crystallite size 300Å     Particle size (long axis length) 0.18μ,     Long axis length / crystallite size 6   Sodium sulfonate-containing vinyl chloride copolymer 12 parts     Sodium sulfonate content 5 × 10^-FiveMol / g polymerization degree 300   6 parts of polyester polyurethane resin     Carboxyl group 10^-FourMol / g content   α-alumina (particle size 0.3 μm) 3 parts   3 parts carbon black (particle size 0.10 μm)   1 part butyl stearate   2 parts of stearic acid   200 parts of butyl acetate   For each of the above two paints, after kneading each component with a kneader,
Dispersed using a mill. The resulting dispersion is coated with a polyisocyanate for the lower magnetic layer.
Add 5 parts to the cloth liquid and 6 parts to the coating liquid for the upper magnetic layer.
40 parts, and filtered using a filter having an average pore size of 1 μm.
Coating solutions for forming the conductive layer and for forming the upper magnetic layer were respectively prepared. [0048]   The obtained coating solution for the lower magnetic layer is further coated so that the thickness after drying becomes 3.0 μm. Immediately thereafter, the thickness of the upper magnetic layer is set to 15 μm so that the thickness of the upper magnetic layer is 0.5 μm.
m on a polyethylene terephthalate support with a centerline surface roughness of 0.01μ
Perform a multilayer coating and have a magnetic force of 3000G while both layers are still wet
After being oriented and dried by a cobalt magnet and a solenoid having a magnetic force of 1500 G, the metal
The treatment is performed at a temperature of 90 ° C. with a seven-stage calendar composed of only rolls,
Video tapes were made by slitting to inch width. Obtained in this way
Table 1 shows the characteristics of the tape A2. [0049]   Example 1-2   The major axis length of the ferromagnetic powder of the upper magnetic layer is 0.21 μm, 0.12 μm, 0.09 μm.
Samples obtained in the same manner as in Example 1 except that m was used as A1, A3, and A4.
Was. [0050]   Example 1-3   The ferromagnetic powder of the upper magnetic layer has a crystallite size of 400 ° and a major axis length of 0.28 μm.
And a sample obtained in the same manner as in Example 1 except that
, A6. [0051]   Example 1-4   Same as Example 1 except that the thickness of the upper magnetic layer was set to 0.7 μm and 0.2 μm.
The samples obtained were A7 and A8. [0052]   Example 1-5   Same as Example 1 except that the center line average surface roughness of the support was set to 0.005 μm.
The sample obtained was designated as A10. [0053]   Example 1-6   As the ferromagnetic powder of the upper magnetic layer, the major axis length is 0.14 μm, the crystallite size is 200 °,
Specific surface area 55m^Two/ G, Hc 1600 Oe Example except that ferromagnetic metal powder was used A sample obtained in the same manner as 1 was designated as A10. [0054]   Example 1-7   As the ferromagnetic powder of the upper magnetic layer, the major axis length is 0.10 μm, the crystallite size is 200 °,
Same as Example 2 except that a ferromagnetic metal powder having a specific surface area of 55 and Hc of 1600 Oe was used.
The sample obtained in this manner was designated as A11. [0055]   Comparative Example 1   Same as Example 1 except that the major axis length of the ferromagnetic powder in the upper magnetic layer was 0.30 μm.
The sample obtained in this manner was designated as B1. [0056]   Comparative Example 2   The major axis length of the ferromagnetic powder in the upper magnetic layer is 0.36 μm, and the crystallite size is 450 °.
A sample obtained in the same manner as in Example 1 except for the above was designated as B2. [0057]   Comparative Example 3   The major axis length of the ferromagnetic powder in the upper magnetic layer is 0.30 μm, and the crystallite size is 400 °.
The same procedure was followed as in Example 1 except that the thickness of the upper magnetic layer was 1.5 μm.
The sample was designated as B3. [0058]   Comparative Example 4   A sample obtained in the same manner as in Example 1 except that the thickness of the upper magnetic layer was set to 1.0 μm.
The sample was designated as B4. [0059]   Comparative Example 5   Except that the center line average surface roughness of the support was set to 0.02 μm and 0.015 μm
Samples obtained in the same manner as in Example 5 were designated as B5 and B6.   Comparative Example 6   The major axis length of the ferromagnetic powder in the upper magnetic layer is 0.28 μm, and the crystallite size is 350 °. A sample obtained in the same manner as in Example 1 except for the above was designated as B7.   Comparative Example 7   The major axis length of the ferromagnetic powder in the upper magnetic layer is 0.09 μm, and the crystallite size is 150 °.
A sample obtained in the same manner as in Example 1 except for the above was designated as B7. [0060]   Evaluation methods RF output   The video signal of the image signal 50IRE was recorded at the reference recording current. This playback RF output
The average value of the envelope was measured by an oscilloscope and calculated by the following equation. [0061]   RF output (dB) = 20log_Ten(V / V₀) (V: average value, V₀= Reference value) S
/ N   Using a noise meter (925R) made by Shibasoku and using Comparative Example B1 as a reference tape
To determine the difference in S / N ratio. The used VTR is Matsushita NV-8300. Hc   Using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.), measurement was performed with Hm2KOe. Center line average surface roughness   Using a three-dimensional surface roughness meter (manufactured by Kosaka Laboratories) and measuring at a cutoff of 0.08 mm
Was. Long axis length of ferromagnetic powder   The average particle diameter of the major axis was determined by a transmission electron microscope. Crystallite size of ferromagnetic powder   X-ray diffraction increases the half-value width of the diffraction lines on the (4,4,0) plane and the (2,2,0) plane.
It was calculated from the minutes. [0062] [Table 1] [0063] [0064] [0065] [0066] [0067] [0068] [0069] [0070] [0071] [0072] [0073] [0074] [0075] [0076]     【The invention's effect】   The present invention relates to a lower magnetic layer containing a ferromagnetic powder and a binder on the surface of a nonmagnetic support,
In a magnetic recording medium having a plurality of magnetic layers composed of an upper magnetic layer provided thereon,
The major axis length of the ferromagnetic powder contained in the upper magnetic layer is 0.30 μm or less, and the crystallite size is
Is 400 ° or less, and the ratio of the major axis length to the crystallite size is 3 or more and 7 or less,
The dry thickness of the upper magnetic layer is smaller than the crystallite size of the ferromagnetic powder of the upper magnetic layer.25 times
Less thanAnd the center line average surface roughness (Ra) of the surface of the upper magnetic layer is 6 nm or less.
According to the magnetic recording medium, the filling degree of the ferromagnetic powder in the upper magnetic layer is
And the electromagnetic conversion characteristics are significantly improved.

Claims (1)

Claims: 1. A magnetic recording medium having a plurality of magnetic layers comprising a lower magnetic layer containing a ferromagnetic powder and a binder on a surface of a nonmagnetic support and an upper magnetic layer provided thereon. The longitudinal axis of the ferromagnetic powder contained in the upper magnetic layer and oriented in the longitudinal direction is 0.3
0 μm or less, the crystallite size is 400 ° or less, the ratio of the major axis length to the crystallite size is 3 or more and 7 or less, and the dry thickness of the upper magnetic layer is the crystallite size of the ferromagnetic powder of the upper magnetic layer. of is 25 times or less, the magnetic recording medium, wherein the center line average surface roughness of the upper magnetic layer (Ra) of the surface is 6nm or less. 2. The magnetic recording medium according to claim 1, wherein the content of the ferromagnetic powder in the upper magnetic layer is 70% or more.