JP2552958C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION       [0001]     [Industrial applications]   The present invention relates to a magnetic recording medium, in particular, a high-density thin-layer magnetic recording medium having a magnetic layer thickness of less than 1.0 μm.
More specifically, the present invention relates to a magnetic recording medium having a non-magnetic layer as a lower layer
More particularly, the present invention relates to a magnetic recording medium having improved electromagnetic conversion characteristics, running properties and durability.       [0002]     [Prior art]   Conventionally, magnetic recording media such as video tapes, audio tapes, magnetic disks, etc.
Ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO_Two, Ferromagnetic alloy powder, etc.
A magnetic layer dispersed in a binder coated on a non-magnetic support is widely used
.   In recent years, the recording wavelength tends to be shorter with the increase in recording density, and the thickness of the magnetic layer If the thickness is too large, the problem of thickness loss at the time of recording / reproducing, such as a decrease in output, has become more serious.       [0003]   For this reason, the thickness of the magnetic layer is reduced, but the thickness of the magnetic layer is reduced to about 2 μm or less.
If the thickness is reduced, the effect of the surface properties of the non-magnetic support is likely to appear on the surface of the magnetic layer.
The conversion characteristics tend to deteriorate.   For this reason, a nonmagnetic thick lower layer is provided on the surface of the support, and then the magnetic layer is used as the upper layer.
The effect of the surface roughness of the support described above can be eliminated by providing the conductive layer.
However, there was a problem that the head wear and durability were not improved.   Conventionally, a thermosetting (curing) resin is used as a binder as a non-magnetic lower layer.
The lower layer is hardened, and the contact between the magnetic layer and the head and the contact with other members are not loose.
And the magnetic recording medium having such a lower layer becomes somewhat flexible.
It is thought to be due to poorness. In order to solve this,
It is conceivable to use a curable (thermoplastic) resin as a binder.
If the magnetic layer is applied as the upper layer after the lower layer is applied and dried, the lower layer
The magnetic layer swells with an organic solvent, causing turbulence in the upper coating solution, etc.
Problems such as deterioration of the surface properties and deterioration of the electromagnetic conversion characteristics.       [0004]   In recent years, short wavelength recording has been advanced in order to improve the recording density of magnetic recording media.
, 8 mm video tape, the recording wavelength has reached 0.54 μm. Corresponding magnetism
A recording medium using a ferromagnetic metal thin film has been put to practical use. Metal thin film magnetism
Since the recording medium has a very thin magnetic layer, the loss due to the thickness is small.
A medium with high output can be always obtained. However, these media make metals non-magnetic
Mass production compared to conventional coated magnetic recording media because it is manufactured by vapor deposition on a support
Inferior in storage properties, and because it is a metal thin film, it has problems with long-term storage, such as oxidation.
have. To solve these problems, the magnetic properties of conventional coated magnetic recording media
Attempts have been made to increase the output by making the layers thinner. For example
In U.S. Pat. No. 2,819,186, the upper magnetic layer is hard and brittle,
Is 85% by weight or more, and the lower non-magnetic layer is soft and excellent in flexibility.
It is known that the thickness of the lower non-magnetic layer is 0.25 mil or less and the thickness of the lower non-magnetic layer is not less than the thickness of the upper layer. You. In Japanese Patent Application Laid-Open No. 62-154225, the thickness of the magnetic layer is set to 0.5 .mu.
Use undercoat thicker than the thickness and use carbon black as conductive powder
Is described. In Japanese Patent Application Laid-Open No. 62-222427, the thickness of the magnetic layer is 1.0 μm or less.
It is described that an abrasive having an average particle size of 0.5 to 3 μm is used. Further Japanese Patent
In 1988-191315, the thickness of the lower layer was 0.5 μm or more by simultaneous coating.
Techniques containing no cyanate are described.   However, in order to apply the upper magnetic layer as a thin layer of 1.0 μ or less,
In addition, the magnetic liquid must be diluted with a large amount of a solvent, and the aggregation of the magnetic liquid is easily promoted. Also,
Since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder is easily disturbed,
For media that is not hand-recorded, such as magnetic disks, performance can be secured to some extent.
However, the orientation of the tape-shaped magnetic recording medium is poor.
It is difficult to secure sufficient electromagnetic conversion characteristics due to poor directivity and poor surface properties
. In addition, since many voids are generated during the drying process, the strength of the magnetic film is weak and the running resistance is low.
The results were also insufficient in terms of durability. Improves orientation and reduces voids in the coating.
In order to reduce the amount of the organic solvent to be diluted, the coating stability is poor.
There was a problem that a large amount of holes and the like were generated and the yield was deteriorated.       [0005]     [Problems to be solved by the invention]   The present invention provides a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability.
And Especially, the output in short wavelength recording is high, and the yield in production is high.
An object of the present invention is to provide a good magnetic recording medium. Conventionally, the recording wave
It is clear from magnetic recording theory that output can be improved by thinning to a long length.
You. However, as described above, reducing the diluting solvent in the magnetic coating solution reduces coating defects and other problems.
For this reason, the tape yield decreases. To improve the yield, apply coating liquid
It is necessary to dilute with a large amount of solvent, but this will deteriorate the orientation and strength of the coating
.       [0006]     [Means for Solving the Problems]   That is, the object of the present invention is to disperse a non-magnetic powder in a binder on a non-magnetic support. An upper magnetic layer in which a ferromagnetic powder is dispersed in a binder
In a magnetic recording medium having at least two or more layers provided with layers,
The upper magnetic layerLayer strengthMagnetic powder with a major axis length of 0.3μ or less and crystallite size of 300mm
The thickness of the upper magnetic layer (hereinafter sometimes simply referred to as the upper layer) is less than 1.0 μm.
The lower non-magnetic layer (hereinafter sometimes simply referred to as the lower layer).
And a non-magnetic metal oxide powder and a carbon bra having an average primary particle diameter of less than 20 nm.
In a ratio of 95/5 to 60/40, and at leastUnderlayerFor non-magnetic layer
Polyurethane having 3 or more OH groups in one molecule and polyisocyanate compound
And a magnetic recording medium characterized by including:       [0007]   That is, one of the features of the present invention is that while the lower non-magnetic layer is in a wet state,
Consists in forming a layer.   If an attempt is made to apply the magnetic layer as a thin layer of 1.0 μ or less,
As mentioned above, the magnetic liquid must be diluted with a large amount of solvent, which deteriorates the orientation.
In addition, the voids increase and the strength of the coating film decreases. Apply with less dilution solvent
Defects occur and yield decreases. To solve this, Japanese Patent Application Laid-Open No. 61-13 / 1986
No. 9929, a non-magnetic layer is disposed below the lower layer.
Then, a layer of the dispersion liquid containing the ferromagnetic powder was applied to the upper layer. Such a web
Even if the upper magnetic layer is applied as a thin layer of 1 μ or less,
Very few coating defects (pinholes, coating streaks, etc.) and good yield
I was able to. Even if the same layer configuration is adopted for the successive multilayers, coating defects are not reduced.   The second feature of the present invention is that the major axis length of the ferromagnetic powder in the upper magnetic layer is 0.3 μm or less.
The crystallite size is 300 ° or less.   Use fine-grained ferromagnetic powder as much as possible to satisfy output in short wavelength recording
Is preferred. In addition, a dispersion using a ferromagnetic powder of such a size is
Good matching of rheological properties with magnetic dispersion. If the long axis length is 0.3μ or more,
When the crystallite size is 300 mm or more, mixing with the non-magnetic dispersion liquid occurs, and 1.0 μ or less
Cannot be obtained.   The third feature of the present invention is that the powder constituting the lower non-magnetic layer is (non-magnetic metal oxide powder). Powder) / (carbon black having an average particle diameter of less than 20 nm) = 95/5 to 60/40
Is to meet.   If the average particle size of the carbon black is smaller than 20 nm, the carbon blacks
A weakly cohesive structure is formed in the dispersion, and a pseudoplastic dispersion can be obtained. Also, non
From 95/5 to 60/40 of magnetic metal oxide powder and such carbon black
Mixing can provide moderate rheological properties, especially at low shear
The rheological properties at speed can be adjusted.   If the amount of carbon black is less than 95/5, pseudoplasticity at a low shear rate can be secured.
The flaws cause a mixture of the magnetic layer and the lower non-magnetic layer. Carbon black from 60/40
When the amount is too large, pseudoplasticity proceeds too much, and the liquid sending property of the dispersion becomes a problem. In addition, the lower layer dispersion
The dispersibility is reduced, resulting in a medium having poor surface properties.   The fourth feature of the present invention is that the lower nonmagnetic layer has three or more OH groups in one molecule.
It is to contain urethane and a polyisocyanate compound.   A very thin upper magnetic layer was formed by the wet-on-wet coating method described above.
For this purpose, it is necessary to adjust the rheological properties of the upper magnetic liquid and the lower nonmagnetic liquid.
is there. For dispersions in which the upper and lower layers contain ferromagnetic powder, use the wet-on-wet coating method.
Although the range of rheological properties required for magnetic liquids that can be
When a dispersion containing only non-magnetic powder is prepared in the lower layer as in the invention, since there is no magnetism,
The rheological properties are very different from the layer magnetic liquid. Wet if the viscoelasticity of the dispersion is different
When applied on-wet, no film is formed, and the upper and lower layers
A match occurs. The rheological properties and dispersion properties of the dispersion using the magnetic material shown in the second feature
The rheological properties of the combined lower non-magnetic liquid combine the above third and fourth characteristics.
Attained.   It is known that polyisocyanate compounds react with OH groups to polymerize.
You. When three or more OHs are contained in one molecule, this also slightly polymerizes in the dispersion.
And can provide moderate rheological properties. Not more than 2 per molecule
In this case, the rheological characteristics are different from those of the upper magnetic liquid and cause mixing.   That is, the present invention provides a crystallographic substrate having a major axis length of 0.3 μ
A magnetic layer containing a fine particle ferromagnetic powder having a size of 300 ° or less is provided on the upper layer, and a non-magnetic layer is provided on the lower layer. Despite being a conductive powder, it exhibits thixotropic properties by being connected to beads.
This thixotropic feature uses carbon black of fine particles smaller than nm.
In order to maximize the property, at least three or more O atoms in one molecule are contained in the lower non-magnetic layer.
Having an H group, forms a network polymer by bonding with the polyisocyanate used in combination
And thereby synergistically enhance the thixotropic properties of carbon black described above.
By adopting such a method, wet-on-wet
There is no pinhole or coating streak, and a very thin magnetic layer is provided on the non-magnetic layer.
It can be broken.   In the present invention, the lower layer coating solution and the upper layer coating solution are applied in a superposed state in a wet state.
On a non-magnetic support by the so-called wet-on-wet coating method
You.   What is the wet-on-wet coating method used to provide the lower layer and the upper layer in the present invention
, First coat the next layer on the first layer in wet condition as soon as possible
So-called sequential coating method, and method of applying multiple layers simultaneously by extrusion coating method
Etc.   A wet-on-wet coating method is disclosed in JP-A-61-139929.
The magnetic recording medium coating method described above can be used.   FIG. 1 is an illustration showing an example of a sequential coating method used for providing both layers in the present invention.
Is applied to a flexible support 1 such as polyethylene terephthalate which runs continuously.
The lower layer coating solution (a) 2 is pre-coated with a cloth machine (A) 3 and immediately thereafter, a smoothing roll
4, the coating surface is smoothed, and another extrusion coating is performed while the coating liquid 2 is in a wet state.
The next upper layer coating solution (b) is applied by the cloth machine (B) 6.   FIG. 2 shows an extrusion type preferably used for providing both layers in the present invention.
FIG. 2 is an explanatory view showing an example of a time-layered coating method, in which simultaneous multilayer coating is performed on a flexible support 1.
A state in which the lower layer coating liquid (a) 2 and the upper layer coating liquid (b) 5 are simultaneously applied using the liquid injector 8.
This is to explain the state. After applying both layers, apply magnetic field orientation, drying and smoothing
This is applied to a magnetic recording medium.       [0008]   The non-magnetic metal powder used in the lower non-magnetic layer of the present invention has an α-conversion of 90% or more. Alumina, β-alumina, γ-alumina, chromium oxide, cerium oxide, α-oxidation
Iron, corundum, silicon nitride, titanium carbide, titanium oxide, ZnO, etc.
Used in Germany or in combination. The particle size of these nonmagnetic powders is 0.01 to 3
μ is preferred. Tap density is 0.3-2g / cc, water content is 0.1-5%, pH is
2-11, specific surface area is 1-30m^Two/ G is preferred. Needle-shaped nonmagnetic powder
The shape may be spherical, dice-like, or the like. Specific examples of non-magnetic powder include
AKP-20, AKP-30, AKP-50, HIT-50, Japan
Chemical Industries, G5, G7, S-1, Toda Kogyo, TF-100, TF-12
0, TF-140, and the like.   The carbon black used in the lower non-magnetic layer of the present invention is a furnace for rubber,
Thermal black, color black, acetylene black, etc.
You. Specific surface area is 100-600m^Two/ G, DBP oil absorption is 30-290ml / 10
0 g, the particle size is 20 nm or less, preferably 10 to 20 nm, more preferably 12 to
18 nm. pH 2-10, water content 0.1-10%, tap density 0.1
１1 g / cc is preferred. Specific examples of carbon black used in the present invention and
BLACKPEARLS 2000, 1300, 100 manufactured by Cabot Corporation
0, 900, 880, 800, 700, manufactured by Mitsubishi Kasei Kogyo Co., Ltd., # 950B, # 85
0B manufactured by Columbia Carbon, CONDUCTEX SC, RAVEN 880
0, 8000, 7000, 5750, 5250, 3500, 2100, 2000
, 1800, 1500, 1250, and the like. Carbon black as dispersant
Even if the surface is treated with, for example, or grafted with a resin, part of the surface can be graphed.
It is permissible to use one that has been converted to a program. In addition, carbon black is used as a magnetic paint
May be dispersed in a binder before being added to the mixture.       [0009]   The polyurethane used in the present invention is, for example, basically a polyol and a diisocyanate.
An anate and, if necessary, a chain extender are produced by a method known per se.
In this case, the above-mentioned polyol and / or the above-mentioned chain extender can be used.
Manufactured by using substances having different reactive hydroxyl groups
be able to. Alternatively, a polyurethane having an epoxy group (for example, In the method for producing urethane, a polyol having an epoxy group is used.
Can be synthesized. )) Can also be produced by the method of opening the epoxy group.
Wear. As the above polyol, if it has two or more OH groups,
The skeleton may be of any type, for example, polyether
Riol, polycarbonate polyol, polycaprolactone polyol, and
Any of these copolymerized polyols may be used. However, chain extension
When no agent is used, it is necessary to use a polyol having three or more hydroxyl groups.
It is important. A typical example of the above polyether polyol serving as a basic skeleton is polyether polyol.
Polyalkylene glycols such as ethylene glycol and polypropylene glycol
Can be mentioned. The polyester polyol serving as the basic skeleton is, for example,
Polycondensation of dihydric alcohol and dibasic acid, lactones, for example, caprolactone
Can be synthesized by ring-opening polymerization or the like. Typical dihydric alcohol
Is ethylene glycol, propylene glycol, butanediol, 1,6-
Examples of glycols such as xandiol and cyclohexanedimethanol
it can. Representative dibasic acids include adipic acid, pimelic acid and azelaic acid.
Acid, sebacic acid, phthalic acid, terephthalic acid and the like.   The polycarbonate polyol serving as a basic skeleton is, for example, a compound represented by the following general formula “1”
"       HO-R₁-OH "1" (Where R₁Is-(CH_Two)_n-(N = 3 to 14),       [0010]     Embedded image       [0011] Represents ) And phosgene, chloroformate, dialkyl carbonate
Synthesized by condensation or transesterification with a salt or diaryl carbonate
Polycarbonate polycarbonate having a molecular weight of 300 to 20,000 and a hydroxyl value of 20 to 300
Riol, or the polycarbonate polyol, and HOOC-
R_Two-COOH "2" (wherein MR_TwoIs an alkylene group having 3 to 6 carbon atoms, 1
, 4-1,3- or 1,2-phenylene or 1,4- 1,3- or
Represents a 1,2-cyclohexylene group).
Polycarbonate having a molecular weight of 400 to 30,000 and a hydroxyl value of 5 to 300
Polyester polyol.   Other polyols such as the above polyols, such as polyether polyols, poly
The polyester, which is an ester polyol, is blended up to 90% by weight of the above polyol.
May be used. The above-mentioned polyols include, in addition to a hydroxyl group, -SH group, -COSH group, -CS
SH group, -SO_ThreeM group, COOM group, -OPO (OM)_TwoGroup (where M is a hydrogen atom
Having polar functional groups such as epoxy groups, amino groups, etc. May be. Used to form polyurethane by reacting with the above polyol
There is no particular limitation on the diisocyanate used, and those commonly used are used.
be able to.   For example, tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate
, Hexamethylene diisocyanate, xylylene diisocyanate, naphthy
Len-1,5-diisocyanate, o-toluidine diisocyanate, isophoro
Isocyanates such as diisocyanate and triphenylmethane triisocyanate
It is a kind.   Further, as the chain extender, for example, the above-mentioned polyhydric alcohol, aliphatic polyamine,
Known ones such as alicyclic polyamines, aromatic polyamines, and the like;
Those having hydroxyl groups having different reactivities can be used.   These polyurethane resins are preferably used in an amount of 1 to 100 parts by weight based on the nonmagnetic oxide powder.
Preferably 3 to 50 parts by weight, more preferably 4 to 40 parts by weight are added. These ports
The glass transition temperature of the urethane is -50 to 100C, and the elongation at break is 100 to 2000.
%, Breaking stress is 0.05 to 10 kg / cm^Two, Yield point is 0.05-10kg / cm^TwoIs preferred
New   As the polyisocyanate to be added at the same time, tolylene diisocyanate
G, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate
, Xylylene diisocyanate, naphthylene-1,5-diisocyanate
, O-toluidine diisocyanate, isophorone diisocyanate, triphenyl
Isocyanates such as methane triisocyanate,
Products from polyalcohols and isocyanates
The polyisocyanate formed can be used. These isocyanates
Commercially available brand names include Nippon Polyurethane Co., Ltd., Coronate L,
Ronate HL, Coronate 2030, Coronate 2031, Millionate MR,
Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-102, Takenate D-1
10N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer
Death module L, Death module IL, Death module N, Death module HL
, Etc., either alone or two or more using the difference in curing reactivity Can also be used in combination. The addition amount of these polyisocyanates is
1 to 50% by weight, preferably 2 to 40% by weight, more preferably 4 to
30% by weight.   As a binder used in the present invention other than urethane, conventionally known thermoplastic resins,
Thermosetting resins, reactive resins and mixtures thereof are used. As a thermoplastic resin
Has a glass transition temperature of -100 to 150C and a number average molecular weight of 1,000 to 200.
10,000, preferably 10,000-100,000, with a degree of polymerization of about 50-100
It is about 0. Such examples include vinyl chloride, vinyl acetate, vinyl
Alcohol, maleic acid, acrylic acid, acrylate, vinylidene chloride,
Acrylonitrile, polyester, methacrylic acid, methacrylic acid ester, styrene
Len, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl
Polymers or copolymers containing polyester as a structural unit, and various rubber resins
.   In addition, phenol resins, epoxy resins, etc. are used as thermosetting resins or reactive resins.
, Urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde
Hydresin, silicone resin, epoxy-polyamide resin and the like can be mentioned.   For details on these resins, see "Plastic Handbook" published by Asakura Shoten.
It is described in. Especially, vinyl chloride resin, vinyl chloride vinyl acetate resin, salt
Combination with at least one selected from vinyl chloride vinyl acetate vinylidene chloride resin
A combination is preferred.       [0012]   Specific examples of these binders used in the present invention include Union Carbide
VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYE
S, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC
, PKFE, manufactured by Nissin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, electrochemical
1000W, DX80, DX81, DX82, DX83, manufactured by Zeon Corporation M
R110, MR100, 400X110A, Sanyo Chemical Co., Ltd., Samprene SP-1
50, manufactured by Asahi Kasei Corporation, Saran F310, F210 and the like.   When using a vinyl chloride resin as the binder used in the present invention,
1 to 50%, preferably 2 to 40%, preferably 4 to 30% by weight, more preferably
Or 5 to 25% by weight.   In the lower non-magnetic layer, the type and amount of lubricant used for the magnetic layer
Can be added to suit.       [0013]   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
Alloy fine powder containing barium as a main component (75% or more), barium ferrite,
Known ferromagnetic powders such as hexagonal ferrite such as nthium ferrite can be used. This
These ferromagnetic powders include Al, Si, S, SC, Ti, V, Cr
, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, R
e, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn
, Ni, Sr, B and the like.   25-80m if ferromagnetic powder size is expressed by specific surface area by BET method^Two/ G
, Preferably 35-60m^Two/ G. 25m^Two/ G or less, the noise increases,
80m^Two/ G or more is not preferable because it is difficult to obtain surface properties. Ferromagnetic powder of magnetic layer of the present invention
Has a crystallite size of 300 ° or less, preferably 250 to 100 °. Long
The axial length is 0.3 μm or less, preferably 0.25 μm or less, more preferably 0.2 μm or less.
0 μm or less.   The magnetic properties of the magnetic recording medium of the present invention were measured at a magnetic field of 5 KOe.
The squareness ratio in the direction is 0.70 or more, preferably 0.80 or more, more preferably
0.90 or more. The squareness ratio of the two directions perpendicular to the tape running direction is
It is preferable that it is 80% or less of the squareness ratio.   The SFD of the magnetic layer is preferably 0.6 or less. The magnetic layer can be two or more layers
No. For example, a first layer and a second layer thereon.   When using ferromagnetic iron oxide powder or hexagonal oxide as the ferromagnetic powder, σs is 50 emu
/ G or more, preferably 70 emu / g or more, and in the case of ferromagnetic metal powder, 10
0 emu / g or more is preferable.   R1500 of the uppermost ferromagnetic powder is preferably 1.5 or less. further
Preferably, r1500 is 1.0 or less. r1500 saturates the magnetic recording medium
After being magnetized, it remains without reversing when a magnetic field of 1500 Oe is applied in the opposite direction
% Of the magnetization amount.   The water content of the ferromagnetic powder is preferably 0.01 to 2%. Depending on the type of binder
Therefore, it is preferable to optimize the water content of the ferromagnetic powder.   The tap density of the ferromagnetic powder is 0.5 when using Co-modified iron oxide.
g / cc or more is preferable, and 0.8 g / cc or more is more preferable. Divalent iron trivalent
The ratio to iron is preferably 0-20%, more preferably 5-10%.
. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 3 to 8%.
You. When using metal powder, Fe, Ni, Al, Co, Zn, Sb, Mn, M
Alloys composed of g, Ca, Sr, Zr, Ba and the like are preferred. Also, these alloy powders
When the surface of is treated with Si, Al, Ti, B, etc., a more preferable result is obtained.
Bring. The tap density of the metal powder is preferably 0.2 g / cc or more.   It is preferable to optimize the pH of the ferromagnetic powder depending on the combination with the binder used.
. Its range is from 4 to 12, preferably from 6 to 10.   The ferromagnetic powder may be made of Al, Si, P, Ti, B, Co, Cu, Ni or
May be subjected to surface treatment with these oxides or the like. The amount is in ferromagnetic powder
On the other hand, when the surface treatment is performed, the adsorption of a lubricant such as a fatty acid is 100%.
mg / m^TwoThe following is preferred.   The ferromagnetic powder contains soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr.
However, if the content is 500 ppm or less, the characteristics are not particularly affected.   These ferromagnetic powders contain dispersants, lubricants, surfactants, antistatic
Before dispersing with an agent or the like, treatment may be performed in advance.   Among the above ferromagnetic powders, a small amount of hydroxide or oxide
Things may be included. Using a ferromagnetic alloy powder obtained by a known manufacturing method
And the following methods can be given. Complex organic acid salts (mainly
(Oxygenate) and reducing gas such as hydrogen, reducing iron oxide with reducing gas such as hydrogen
To obtain Fe or Fe-Co particles by reduction with Thermal decomposition of materials, sodium borohydride,
Reduction by adding a reducing agent such as acid salt or hydrazine;
For example, a method of evaporating in an active gas to obtain a fine powder. Obtained in this way
The ferromagnetic alloy powder is subjected to a known slow oxidation treatment, that is, immersion in an organic solvent, followed by drying.
Immersion in an organic solvent and then sending an oxygen-containing gas to form an oxide film on the surface
After drying, adjust the partial pressure of oxygen gas and inert gas without using organic solvent
Any of the methods of forming an oxide film on the surface can be used
You.   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.
In addition, if the shape satisfies the characteristics of the particle size shown above, the shape of needles
Shape, rice grain, plate shape.   In order to achieve the SFD of ferromagnetic powder of 0.6 or less, the distribution of Hc in the ferromagnetic powder must be adjusted.
Need to be smaller. For that purpose, γ-
Cobalt deposition for cobalt-modified iron oxide to prevent sintering of hematite
There are methods such as lowering the speed than before.       [0014]   As the binder used in the magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting
A system resin, a reactive resin, and a mixture thereof are used. As thermoplastic resin,
The lath transition temperature is -100 to 150 ° C, and the number average molecular weight is 1,000 to 200,00.
0, preferably 10,000 to 100,000, with a degree of polymerization of about 50 to 1,000
Of the degree.   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, phenol resins, epoxy resins, etc. are used as thermosetting resins or reactive resins. , Polyurethane curing resin, urea resin, melamine resin, alkyd resin, acrylic
Resin, formaldehyde resin, silicone resin, epoxy-polyamide resin
Fat, polyester resin and isocyanate prepolymer mixture, polyester resin
Mixture of riol and polyisocyanate, polyurethane and polyisocyanate
And mixtures thereof. About these resins, "Plastic
It is described in detail in the Handbook. In addition, a known electron beam-curable resin is
, Or an upper layer. About these examples and their manufacturing methods
Is described in detail in JP-A-62-256219. The above resins are used alone or
It can be used in combination, but preferred are vinyl chloride resin and vinyl chloride vinyl acetate.
Resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate
Maleic anhydride copolymer, at least one selected from the group consisting of a polyurethane resin
Combinations, or combinations of these with a polyisocyanate.   Polyurethane resin structure is polyester polyurethane, polyetherpolyuree
Tan, polyether polyester polyurethane, polycarbonate polyurethane
, Polyester polycarbonate polyurethane, polycaprolactone polyurethane
A known material such as a resin can be used. For all of the binders shown here,
In order to obtain excellent dispersibility and durability, COOM, SO_ThreeM, OSO_ThreeM
, P = O (OM)_Two, OP = O (OM)_Two, (Where M is a hydrogen atom, or
Alkali metal base), OH, NR^Two, N⁺R^Three(R is a hydrocarbon group) Epoxy group, S
Copolymerization or addition of at least one or more polar groups selected from H, CN, etc.
It is preferable to use those introduced by the reaction. The amount of such polar groups is 10^-1~
10^-8Mol / g, preferably 10^-2-10^-6Mol / g.   Specific examples of these binders used in the present invention include Union Carbide
VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES
, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC,
PKFE, manufactured by Nissin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL
, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, Electrochemical
1000W, DX80, DX81, DX82, DX83, ZEON MR 110, MR100, 400X110A, Nipporan N2 manufactured by Nippon Polyurethane Co.
301, N2302, N2304, Pandex T-5105 manufactured by Dainippon Ink and Chemicals, Inc.
, T-R3080, T-5201, Barnock D400, D-210-80,
Lisbon 6109, 7209, Toyobo U Byron R8200, UR8300
, RV530, RV280, manufactured by Dainichi Seika Co., Ltd., Diferamine 4020, 5020
MX5, 5100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Corporation
004, Sanyo Kasei Co., Ltd., Samprene SP-150, Asahi Kasei Corp., Saran F310
, F210 and the like.   The binder used in the present invention is preferably in the range of 5 to 50% with respect to the ferromagnetic powder of each layer.
Preferably, it is used in the range of 10 to 30%. 5 when vinyl chloride resin is used
~ 30%, 2-20% when using polyurethane resin, polyisocyanate
Is preferably used in combination in the range of 2 to 20%.   In the present invention, when polyurethane is used, the glass transition temperature is -50 to 10
0 ° C, elongation at break 100-2000%, stress at break 0.05-10 kg / cm^Two, Descending
0.05-10kg / cm^TwoIs preferred. At least the magnetic recording medium of the present invention
Consists of two layers. Therefore, the amount of binder, vinyl chloride resin and
Formation of magnetic layer, amount of urethane resin, polyisocyanate or other resin
Requires the molecular weight of each resin, the amount of polar groups, or the physical properties of the resin described above.
It is of course possible to change between the magnetic layer and the non-magnetic lower layer according to the conditions.       [0015]   Examples of the polyisocyanate used in the magnetic layer of the present invention include tolylene diisocyanate.
, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate
Anate, xylylene diisocyanate, naphthylene-1,5-diisocyanate
G, o-toluidine diisocyanate, isophorone diisocyanate, triphe
Isocyanates such as nylmethane triisocyanate,
By condensation of products of nates and polyalcohols and isocyanates
The generated polyisocyanate and the like can be used. These isocyanates
The commercially available trade names of the products include Coronate L, manufactured by Nippon Polyurethane Co., Ltd.
Coronate HL, Coronate 2030, Coronate 2031, Millionate MR , Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-102, Takenate D-
110N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer,
Death module L, Death module IL, Death module N, Death module H
L, etc., and these may be used alone or two or more by utilizing the difference in curing reactivity.
The lower layer and the upper layer can be used in the above combination.       [0016]   The carbon black used in the magnetic layer of the present invention is a furnace for rubber and a rubber for rubber.
Color, black for color, acetylene black and the like can be used. ratio
Surface area is 5-500m^Two/ G, DBP oil absorption 10-400ml / 100g, particle size
Is 5 nm to 300 nm, pH is 2 to 10, water content is 0.1 to 10%, and tap density is 0.1 to 1.0.
1-1 g / cc is preferred.   Specific examples of carbon black used in the present invention, manufactured by Cabot Corporation,
BLACKPEARLS2000, 1300, 1000, 900, 800, 70
0, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, #
50, # 35, manufactured by Mitsubishi Chemical Corporation, # 2400B, # 2300, # 900, # 1
000, # 30, # 40, # 10B, CONDUC, manufactured by Konlon Via Carbon
TEX SC, RAVEN 150, 50, 40, 15 and the like. Carb
Surface treatment with a dispersant or grafted with a resin,
A part of the surface may be graphitized.   Before adding carbon black to the magnetic paint, disperse it with a binder beforehand.
It doesn't matter.   These carbon blacks can be used alone or in combination with the lower and upper layers.
Can be. When using carbon black, the amount based on the ferromagnetic powder is the lower layer,
It is preferable to use 0.1 to 30% for both upper layers.   Carbon black is suitable for antistatic of magnetic layer, reduction of friction coefficient, light shielding property, and film strength.
They have the above functions, and they differ depending on the carbon black used. Therefore the book
These carbon blacks used in the present invention are used in the lower layer and the upper layer in the type, amount and combination.
And adjust the particle size, oil absorption, conductivity, pH, etc.
Of course, it is possible to use them properly according to the purpose. For example, the lower conductive layer The use of carbon black prevents charging, and the upper layer has a large particle size car.
Use of Bon Black to lower the coefficient of friction. Power that can be used in the present invention
For carbon black, for example, refer to the “Carbon Black Handbook” edited by the Carbon Black Association.
Can be considered.       [0017]   As an abrasive used in the magnetic layer of the present invention, α-alumina having an α conversion of 90% or more is used.
, Β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corane
Dam, synthetic diamond, silicon nitride, silicon carbide titanium carbide, titanium oxide,
Well-known materials such as silicon dioxide, boron nitride, mainly Mohs 6 or more alone or
Used in combination. In addition, a composite of these abrasives (the abrasive is
Surface-treated with an agent). These abrasives contain other than the main component
In some cases, a compound or an element may be contained.
No. The particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary,
Abrasives with different particle sizes can be combined, or the particle size distribution can be
The same effect can be obtained by widening. Tap density is 0.3-2g / cc,
Water content 0.1-5%, pH 2-11, specific surface area 1-30m^Two/ G is preferred
. The abrasive used in the present invention may have any of a needle shape, a spherical shape, and a die shape.
However, those having a corner in a part of the shape are preferable because of high abrasiveness. Used in the present invention
As specific examples of the polishing agent, AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, manufactured by Nippon Chemical Industry Co., Ltd., G5, G7, S-1, Toda mechanic
100ED, 140ED, etc., manufactured by Kogyosha. Polishing used in the present invention
The type, amount and combination of the agent can be changed between the lower layer and the upper layer, and can be used properly according to the purpose.
Of course it is possible. For example, to improve the durability of the magnetic layer surface,
Do not increase the amount of abrasive in the lower layer to improve the durability of the end face of the magnetic layer.
Any ingenuity can be done.   These abrasives are pre-dispersed with a binder and then added to the magnetic paint.
It doesn't matter.   Five abrasives are present on the surface of the magnetic layer and the end surface of the magnetic layer of the magnetic recording medium of the present invention.
/ 100μm^TwoThe above is preferred.       [0018]   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, graphite fluoride, silicone oil, polar group-containing silicon
Corn, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol
, Fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate ester
And its alkali metal salts, alkyl sulfates and their alkali metal salts
, Polyphenyl ether, fluorine-containing alkyl sulfate and its alkali
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), having 12 to 2 carbon atoms
2 alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (unsaturated bond
And may be branched), and monovalent, divalent, having 2 to 12 carbon atoms,
Any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohols (including unsaturated bonds,
Or a mono-fatty acid ester or di-fatty acid ester
Monoalkyl ethers of stele or trifatty acid esters and alkylene oxide polymers
Fatty acid ester of fatty acid, fatty acid amide having 8 to 22 carbon atoms, fat having 8 to 22 carbon atoms
Aliphatic amines can be used. Specific examples of these are lauric acid, myristic
Acid, palmitic acid, stearic acid, behenic acid, butyl stearate, olein
Acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, stearie
Amyl phosphate, isooctyl stearate, octyl myristate, stearic acid
Butoxyethyl, anhydrosorbitan monostearate, anhydrosorbita
Distearate, anhydrosorbitan tristearate, oleyl alcohol
And lauryl alcohol. In addition, alkylene oxides,
Serine, glycidol, alkylphenol ethylene oxide adducts, etc.
Nonionic surfactants, cyclic amines, ester amides, quaternary ammonium salts
, Hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc.
Thione surfactant, carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphoric acid Anionic surfactants containing acidic groups such as ester groups, amino acids, aminosulfates
Sulfonic acid or phosphoric acid esters of sulfonic acids, amino alcohols, alkylbedine type
, Etc. can also be used.   For these surfactants, see "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.)
) Is described in detail.   These lubricants and antistatic agents are not necessarily 100% pure,
May contain impurities such as isomers, unreacted products, by-products, decomposition products, oxides, etc.
I don't know. These impurities are preferably 30% or less, more preferably 10% or less.
Below.       [0019]   The type and amount of these lubricants and surfactants used in the present invention in the lower layer and the upper layer
Can be properly used as needed. For example, fats with different melting points in the lower and upper layers
Use esters with different boiling points and polarities to control oozing to the surface using fatty acids
Coating stability by controlling the amount of surfactant to control bleeding to a rough surface
Improve the lubrication effect by increasing the amount of lubricant to the powder in the lower layer
Of course, it is not limited to the example shown here.   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. The present invention
Examples of commercial products of these lubricants used in Nippon Yushi Co., Ltd., NAA-102,
NAA-415, NAA-312, NAA-160, NAA-180, NAA-
174, NAA-175, NAA-222, NAA-34, NAA-35, NA
A-171, NAA-122, NAA-142, NAA-160, NAA-17
3K, castor hardened fatty acid, NAA-42, NAA-44, cationic SA, Katio
MA, Cation AB, Cation BB, Nymeen L-201, Nymeen L-
202, Nymeen S-202, Nonion E-208, Nonion P-208,
Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS
-210, Nonion HS-206, Nonion L-2, Nonion S-2, Nonion S-4, nonionic O-2, nonionic LP-20R, nonionic PP-40R, nonionic
On SP-60R, Nonion OP-80R, Nonion OP-85R, Nonion L
T-221, Nonion ST-221, Nonion OT-221, Monogly MB, No
Neon DS-60, Anon BF, Anon LG, butyl stearate, butyl lau
Rate, erucic acid, manufactured by Kanto Chemical Co., Inc., oleic acid, manufactured by Takemoto Yushi Co., Ltd., FAL-205
, FAL-123, manufactured by Nippon Rika Co., Ltd., Njerbu LO, Njolbu IPM,
Sansocizer E4030, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-96, KF-96
L, KF96H, KF410, KF420, KF965, KF54, KF50,
KF56, KF907, KF851, X-22-819, X-22-822, K
F905, KF700, KF393, KF-857, KF-860, KF-86
5, X-22-980, KF-101, KF-102, KF-103, X-22
-3710, X-22-3715, KF-910, KF-3935, Liona
Armor P, Armide C, Armoslip CP, Lion Fat
, Duomin TDO, Nisshin Oil, BA-41G, Sanyo Chemical, Prof.
Fan 2012E, New Pole PE61, Ionnet MS-400, Ionnet
MO-200, IONET DL-200, IONET DS-300, IONET
DS-1000 and Ionnet DO-200.       [0020]   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.   These organic solvents are not necessarily 100% pure, and may contain isomers,
Impurities such as reaction products, by-products, decomposition products, oxides, and moisture may be included.
These impurities are preferably at most 30%, more preferably at most 10%.   The kind and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the intermediate layer if necessary.
It doesn't matter. Use a highly volatile solvent for the lower layer to improve the surface properties.
Use a high-tension solvent (cyclohexanone, dioxane, etc.) to improve coating stability.
For example, use a solvent with a high solubility parameter in the upper layer to increase the packing degree.
It goes without saying that it is not limited to these examples.       [0021]   The thickness configuration of the magnetic recording medium of the present invention is such that the nonmagnetic support is 1 to 100 μm, preferably
3-20 μm, the intermediate layer is 0.5 μ-10 μm, preferably 1-5 μm, and the magnetic layer is 0.0
5μ or more and 1.0μ or less, preferably 0.1μ or more and 0.7μ or less, more preferably
Is 0.15 μm or more and 0.4 μm or less. The thickness of the magnetic layer is the thickness of the non-magnetic support.
It is used in the range of 1/100 to 2 times. Adhesion between non-magnetic support and intermediate layer
An undercoat layer for improving the properties may be provided. Their thickness is 0.01 to 2
μ, preferably 0.05 to 0.5 μ. In addition, the nonmagnetic support is opposite to the magnetic layer side.
A back coat layer may be provided on the opposite side. This thickness is 0.1-2μ, preferably
Or 0.3 to 1.0 μm. Known intermediate and back coat layers are used.
Can be used.       [0022]   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
A known film such as sulfone can be used. These supports
Perform corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, etc.
May be. In order to achieve the object of the present invention, a center line average
Surface roughness is 0.03 μm or less, preferably 0.02 or less, more preferably 0.02 μm or less.
It is necessary to use one of 1 μm or less. The cutoff value is 0.25 mm. Also
These non-magnetic supports have not only low center line average surface roughness but also 1 μm. It is preferable that there are no such coarse protrusions. Also supports the surface roughness shape as required
It is freely controlled by the size and amount of filler added to the body.
You. Examples of these fillers include oxides such as Ca, Si, and Ti and charcoal.
In addition to acid salts, organic fine powders such as acrylics can be used. Non-magnetic used in the present invention
The F-5 value of the flexible support in the tape running direction is preferably 5 to 50 kg / mm.^Two, Tape width
The F-5 value in the direction is preferably 3 to 30 kg / mm^TwoAnd the tape long hand direction F-
In general, the quintuple value is higher than the F-5 value in the tape width direction.
If it is necessary to increase the value, this is not the case.   The heat shrinkage of the support in the tape running direction and the width direction at 100 ° C. for 30 minutes is as follows:
Preferably 3% or less, more preferably 1.5% or less, heat shrinkage at 80 ° C. for 30 minutes
The rate is preferably 1% or less, more preferably 0.5% or less. Both breaking strength
5-100kg / mm in both directions^Two, Elastic modulus is 100 ~ 2000kg / mm^TwoIs preferred.       [0023]   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.   In order to achieve the object of the present invention, a conventional known manufacturing technique is used as a part of the process.
Needless to say, it can be used in the kneading process.
The magnetic recording of the present invention is first achieved by using a material with a strong kneading force such as a kneader.
High Br of the medium could be obtained. When using a continuous or pressure kneader
Indicates that all or part of the ferromagnetic powder and binder (however, more than 30% of the total binder is
(Preferably) and 15 to 500 parts by mass with respect to 100 parts of the ferromagnetic powder.
It is. The details of these kneading processes are described in JP-A-1-106338 and JP-A-64-64. -79274. In the present invention, a method disclosed in JP-A-62-212933 is disclosed.
More efficient production by using the simultaneous multi-layer coating method.
come.   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.       [0024]   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
Is 300 kg / cm or more.   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 to
30kg / cm^TwoThe elastic modulus of the magnetic recording medium is preferably 10 in both the running direction and the long direction.
0-1500kg / mm^Two, The residual growth is preferably 0.5% or less, and 100 ° C or less.
The heat shrinkage at any temperature is preferably 1% or less, more preferably 0.5% or less.
, Most preferably 0.1% or less.   The residual solvent contained in the magnetic layer is preferably 100 mg / m^TwoThe following is more preferable
Is 10mg / m^TwoBelow, and the residual solvent contained in the upper magnetic layer is contained in the non-magnetic lower layer.
It is preferred that the amount is smaller than the residual solvent.   The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 10% by volume.
% Or less. It is preferable that the porosity of the nonmagnetic lower layer is larger than the porosity of the upper magnetic layer.
More preferably, the porosity of the lower layer may be small as long as it is 5% or more.   The magnetic recording medium of the present invention has a lower layer and an upper layer.
It is easily estimated that these physical properties can be changed. For example, Increase the elastic modulus of the upper layer to improve running durability, and at the same time increase the elastic modulus of the lower layer compared to the upper layer.
For example, the magnetic recording medium may be lowered to improve the contact with the head. Also, if necessary
Thus, the arrangement of two or more magnetic layers on the magnetic layer can be easily achieved.       [0025]     【Example】   The present invention will be specifically described with reference to examples.   In the examples, "parts" indicates "parts by weight".       [0026] Example 1 Non-magnetic lower layer formulation   Non-magnetic powder α-Fe_Two0_Three(Toda Kogyo TF-100) 80 parts           Average particle size 0.1μ           Specific surface area by BET method 11m^Two/ G           pH 5.6   20 parts of carbon black           Average primary particle size 16nm           DBP oil absorption 80ml / 100g           pH 8.0           Specific surface area 250m by BET method^Two/ G           Volatile content 1.5%   Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts           -N (CH_Three)_Three ⁺Cl^-5 × 10 polar groups^-6eq / g included           Composition ratio 86: 13: 1 Degree of polymerization 400   8 parts polyester polyurethane resin           Basic skeleton 1,4-BD (butanediol) / phthalic acid / HM                         DI (hexamethylene diisocyanate)           Molecular weight 10,200           Hydroxyl group 1.23 × 10^-3eq / g           -SO_ThreeNa group 1 × 10^-Foureq / g   1 part butyl stearate   1 part of stearic acid   200 parts of methyl ethyl ketone Formulation of upper magnetic layer   Ferromagnetic metal powder composition Fe / Zn / Ni = 92/4/4 100 parts           Hc 1600 Oe, BET specific surface area 60m^Two/ G           Crystallite size 200‖           Particle size (major axis diameter) 0.20μ, needle ratio 10           σs: 130 emu / g   12 parts of vinyl chloride copolymer           -SO_ThreeNa content: 1 * 10^-Foureq / g Degree of polymerization 300   Polyester polyurethane resin 3 parts           Neopentyl glycol / caprolactone polyol / MDI           Enylmethane diisocyanate) = 0.9 / 2.6 / 1           -SO_ThreeNa group 1 ×^-Foureq / g content   α-alumina (particle size 0.3 μm) 2 parts   0.5 parts of carbon black (particle size 100 nm)   1 part butyl stearate   2 parts of stearic acid   200 parts of methyl ethyl ketone   After kneading each component with a continuous kneader for each of the two paints,
It was dispersed using a domill. Non-magnetic lower layer with polyisocyanate in the resulting dispersion
Of the second layer and 6 parts of the coating solution for the second layer.
And the mixture was filtered through a filter having an average pore size of 1 μm,
Coating solutions for forming and forming the upper magnetic layer were respectively prepared.   Immediately after that, the obtained lower layer coating solution is further dried so that the thickness after drying becomes 2 μm.
A 7 μm thick center line surface on top of which the upper magnetic layer is 0.3 μm thick
Simultaneous multilayer coating is performed on a polyethylene terephthalate support having a roughness of 0.01μ.
No, a cobalt magnet with a magnetic force of 3000G while both layers are still wet After being oriented and dried by a solenoid having a magnetic force of 1500G, only from a metal roll
Perform processing at a temperature of 90 ° C with a 7-stage calender, and slit it to a width of 8 mm.
, 8 mm videotape.       [0027] Examples 2 to 6, Comparative Examples 1 to 5   In Example 1, the amounts of carbon black and petal were changed as shown in Table 1 (Examples 2 to 5).
3. Comparative Examples 1 and 2) and reduce the OH group content of urethane (Comparative Example 3).
The particle size of the magnetic layer was changed (Comparative Example 4), and the thickness of the upper magnetic layer was changed (Examples 5 to 6,
A video tape was manufactured in the same manner as in Example 1 except that Comparative Example 5) was performed.   In Example 4, the ferromagnetic powder used was changed as follows.   Ferromagnetic metal powder composition Fe / Zn / Ni = 92/4/4           Hc 1580 Oe, BET specific surface area 42m^Two/ G           Crystallite size 280Å           Particle size (major axis diameter) 0.30μ, needle ratio 10           σs: 140 emu / g       [0028] Reference example   Methyl ethyl ketone of the magnetic layer of Example 1 in order to reduce the thickness of the upper layer by sequential coating
Was added to lower the concentration of the coating solution for the upper magnetic layer. First, only the non-magnetic lower layer
After applying and curing this well, the dry thickness of the above magnetic layer becomes 0.3μ.
After applying, orienting and drying as described above, calendering is performed to create an 8 mm video tape.
Done.       [0029] Comparative Example 6   The ferromagnetic powder used in Example 1 was changed as follows.   Ferromagnetic metal powder composition Fe / Zn / Ni = 92/4/4           Hc 15800 Oe, BET specific surface area 35m^Two/ G           Crystallite size 330Å           Particle size (major axis diameter) 0.35μ, needle ratio 10           σs: 140 emu / g       [0030] Example 7   A video tape was prepared in the same manner as in Example 1 except that the formulation of the upper magnetic layer was as follows. .   Cobalt-modified iron oxide 100 parts           Hc 950 Oe, specific surface area 58m^Two/ G           Crystallite size 280Å           Particle size (major axis diameter) 0.25μ, needle ratio 8   13 parts of vinyl chloride-vinyl acetate-vinyl alcohol copolymer           -N (CH_Three)_Three ⁺Cl^-5 × 10 polar groups^-6eq / g included           Composition ratio 86: 13: 1 Degree of polymerization 400   Polyester polyurethane resin 3 parts           Neopentyl glycol / caprolactone polyol / MDI = 0.           9 / 2.6 / 1           -SO_ThreeNa group 1 ×^-Foureq / g content   α-alumina (particle size 0.3 μm) 2 parts   0.5 parts of carbon black (particle size 100 nm)   1 part butyl stearate   2 parts of stearic acid   200 parts of methyl ethyl ketone       [0031] Evaluation method Coating aptitude: Observed in an undried state during coating, the lower non-magnetic layer and upper magnetic layer             The case where no occurrence occurred was evaluated as ○, and the case where mixing occurred occurred was evaluated as ×. mixture             If this occurs, the process is not performed after that.             No MHz output evaluation or scratch test evaluation was performed. 7MHz output   FUJIX8 manufactured by Fuji Photo Film Co., Ltd. Signal, and reproduce the 7MHz signal output when this signal is reproduced with an oscilloscope.
It was measured. Tape scratch tester   8mm tape magnetic layer using stainless steel as a contact and pulling test with 15g load
Was done. Visually assess the damage status of the magnetic layer after scratching,
○ × × Long axis diameter of magnetic material   The average particle diameter of the major axis was determined by a transmission electron microscope. Crystallite size   Hiro of the half width of the diffraction lines of the (4,4,0) plane and the (2,2,0) plane by X-ray diffraction
It was determined from the amount of glue.       [0032] [Table 1]       [0033]   As is clear from the results in the table, the samples of the examples of the present invention have a coating suitability of ○,
There is no lower layer mixing, 7MHz signal output is high, and tape scratch test is also ○
Met. On the other hand, as Comparative Example 1 in which the ratio of carbon black to non-magnetic powder was off,
Is poor in application suitability, output is low, urethane OH is low
Comparative Examples 3 and 4 having a large particle size of carbon black had poor coating suitability. or
Even when the long axis length or crystallite size of the ferromagnetic powder is too large (Comparative Example 7), the coating suitability is poor.
Deteriorated.       [0034]     【The invention's effect】   The present invention has a major axis length of 0.3 μm or less and a crystallite size of 3 μm which satisfies the output of short wavelength recording.
A magnetic layer containing fine particle ferromagnetic powder of less than or equal to 00 ° is provided in the upper layer, and a non-magnetic powder is formed in the lower layer.
Despite being smaller than 20 nm, they are connected in beads and exhibit thixotropic properties.
Uses fine-grained carbon black to maximize this thixotropic property
At least 3 OH groups per molecule in at least the lower non-magnetic layer
Combined with the polyisocyanate used in combination to form a network polymer,
Synergistically enhances the thixotropic properties of carbon black described above.
Things. By adopting such a method, wet-on-wet
There is no pinhole or coating line, and a very thin magnetic layer is provided on the non-magnetic layer.
Video tape excellent in application suitability, 7MHz signal output tape scratch test
Is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing one example of a sequential coating method used for providing a lower layer and an upper layer by a wet-on-wet coating method in the present invention. It is explanatory drawing which shows an example. DESCRIPTION OF SYMBOLS 1 ... Flexible support, 2 ... Coating liquid (a), 3 ... Coating machine (A), 4 ... Smoothing roll, 5 ... Coating liquid (b), 6 ... Coating machine (B), 7 ... Backup roll, 8. Simultaneous multi-layer coating liquid injector.

Claims (1)

Claims: 1. An upper magnetic layer comprising a nonmagnetic support and a lower nonmagnetic layer in which a nonmagnetic powder is dispersed in a binder, and a ferromagnetic powder dispersed in the binder. In a magnetic recording medium having at least two or more layers provided with a layer,
The following ferromagnetic powder major axis length of the layer is 0.3 micron, the crystallite size is at 300Å or less,
The upper magnetic layer has a thickness of less than 1.0 μm, and the lower layer is composed of a nonmagnetic metal oxide powder and carbon black having an average primary particle diameter of less than 20 nm as the nonmagnetic powder.
5 to 60/40, and at least 3 in one molecule in the lower non-magnetic layer.
A magnetic recording medium comprising a polyurethane having at least two OH groups and a polyisocyanate compound. 2. The ferromagnetic powder used for the upper magnetic layer has a coercive force (Hc) of 15 or more.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a ferromagnetic powder having a length of 50 Oe or more, an average major axis length of 0.2 μm or less, a crystallite size of less than 200 °, and a saturation magnetization (σs) of 110 emu / g or more.