JP2607356C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION       [0001]     [Industrial applications]   The present invention relates to a magnetic recording medium, in particular, a magnetic layer.0.3μmVery thin magnetic recording of
Regarding media, more specifically, a production medium with very excellent electromagnetic conversion characteristics and good yield
The present invention relates to a magnetic recording medium having excellent production characteristics and a method for manufacturing the same.       [0002]     [Prior art]   Conventionally, magnetic recording media such as video tapes, audio tapes, magnetic disks, etc. Ferromagnetic iron oxide, Co-modified iron oxide, CrO_Two, Ferromagnetic alloy powder, etc. in binder
A magnetic layer dispersed on a non-magnetic support is widely used. In recent years, the recording wavelength tends to be shortened with the increase in recording density, and the thickness of the magnetic layer is increased.
The problem of thickness loss at the time of recording and reproduction, such as a decrease in output, is increasing. For this reason, the magnetic layer is thinned, but the magnetic layer is thinned to about 2 μm or less.
Then, the influence of the surface properties of the support on the surface of the magnetic layer is likely to appear, and the electromagnetic conversion characteristics deteriorate.
Tended to. Therefore, a nonmagnetic thick lower layer is provided on the surface of the nonmagnetic support, and then the magnetic layer is provided on the upper layer.
This solves the above-mentioned problem due to the surface roughness of the support, and the magnetic layer
Attempts to reduce the thickness demagnetization and achieve high output by making
was suggested. For example, in JP-A-62-154225, the thickness of the magnetic layer is set to 0.1.
In order to reduce the surface electric resistance of the magnetic layer to 5 μm or less,
An undercoat layer between the magnetic layer and the substrate, which contains the conductive fine powder and has a thickness equal to or greater than the thickness of the magnetic layer.
A provided magnetic recording medium has been proposed. Also, Japanese Patent Laid-Open No. 62-222427 discloses
Is provided on the support and the support and contains an abrasive having an average particle size of 0.5 to 3 μm.
An undercoat layer and a film having a thickness of 1 μm or less containing a ferromagnetic powder provided on the undercoat layer.
A magnetic recording medium having a magnetic layer has been proposed.
Part of the magnetic recording medium protrudes from the magnetic layer.
It also has the function of the horn. In this way, the magnetic layer is
Recording to prevent static electricity in the lower non-magnetic layer.
Or adding abrasives to improve the cleaning properties and durability.
You. However, in the conventional technique, a lower non-magnetic layer is first coated on a non-magnetic support and dried.
After that, depending on the case, the upper magnetic layer is provided after calendering
In addition, the manufacturing process is complicated and there are the following problems. That is, in order to make the magnetic layer thinner, it is necessary to reduce the amount of coating or to use a magnetic coating solution.
It is conceivable to add a large amount of a solvent to the mixture to reduce the concentration. If taking the former, apply
If the amount is reduced, there is not enough time for leveling after application and drying starts,
Problems such as cloth defects, for example, streaks and engraved patterns remain, Very bad. If the latter method is adopted, if the concentration of the magnetic coating solution is low,
There are many voids in the completed coating film, and sufficient filling degree of ferromagnetic powder cannot be obtained,
In addition, there are various adverse effects such as insufficient strength of the coating film due to many voids.
You. One means for solving these problems is disclosed in JP-A-63-191315.
As described, a non-magnetic layer was provided below using the simultaneous
A method of thinly applying a magnetic coating solution with high degree has been proposed. In the case of the simultaneous multilayer coating method or the sequential wet coating method, that is, the lower layer is in a wet state.
A so-called wet-on-wet coating method in which the upper layer is applied simultaneously or sequentially during a certain period
In the case of (1), various studies have already been made on the multilayer magnetic layer. However, below
Even if this technique was applied to the non-magnetic layer, good results could not be obtained. One
In other words, when the lower non-magnetic layer and the upper magnetic layer are provided by wet on wet,
Causes turbulence at the interface between them, causing pinholes and cissing of the magnetic layer.
I was frustrated. Therefore, the present inventors have studied the composition of these lower non-magnetic layers and the wet-on-wet coating.
As a result of intensive studies on the relationship with the cloth method, there is a point in the rheological properties.
And found the present invention.       [0003]     [Problems to be solved by the invention]   SUMMARY OF THE INVENTION It is an object of the present invention to provide an output, C / N ratio, etc.
The purpose of the present invention is to provide a thin-layer magnetic recording medium having excellent conversion characteristics and a good head contact.
To provide a thin-layer magnetic recording medium having good storage stability and good storage stability, and a method for producing the same.
And       [0004]     [Prior art] [0005] [Means for Solving the Problems]   An object of the present invention is to provide a lower non-recording layer in which a powder is dispersed in a binder on a support.
And a magnetic recording layer on which an upper recording layer in which ferromagnetic powder is dispersed in a binder is provided.
In the recording medium, the dry thickness of the upper recording layer is0.05μm or more, 0.3μmLess than Below, the crystallite size of the ferromagnetic powder of the upper recording layer is 450 to 100 Å
And the powder of the lower non-recording layer has an average primary particle size of 0.08 μm or less.
A magnetic recording medium, characterized by comprising a non-magnetic inorganic powder,
Is provided in the lower non-recording layer in which the ferromagnetic powder is dispersed in the binder.
In a magnetic recording medium provided with a dispersed upper recording layer, the dry thickness of the upper recording layer
Miga0.05 μm or more, 0.3μm or less, Hc of the upper recording layer is 1200
3000 Oe, and the powder of the lower non-recording layer has an average primary particle diameter of 0.08 μm.
m, and a magnetic recording medium comprising a nonmagnetic inorganic powder having a particle size of not more than m.
Coating solution for lower non-recording layer containing powder and binder, and upper layer recording containing ferromagnetic powder and binder
A magnetic recording medium in which a coating solution for a layer is prepared, and these coating solutions are coated on a support.
In the method of manufacturing, the crystallite size of the ferromagnetic powder of the coating solution for the upper recording layer
Is 450 to 100 angstroms, and the powder of the coating solution for the lower non-recording layer is
Powder having an average primary particle diameter of 0.08 μm or less, and the lower layer
The coating solution for the recording layer is applied, and the lower non-recording layer obtained is
SequentiallyUpper recording layerDry thickness0.05μm or more, 0.3μmSo that
A method for producing a magnetic recording medium, comprising applying the upper recording layer coating solution.
Thus it can be achieved.   Preferred embodiments of the present invention are as follows. (1) The dispersion of the lower non-recording layer in which the powder is dispersed in a binder is thixotropic.
A magnetic recording medium having properties. (2) The ferromagnetic powder of the upper recording layer mainly contains Fe, Ni or Co.
This is a ferromagnetic alloy powder that contains Al, Si, S, Sc, Ti, V, Cr,
Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re
, Au, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni,
A magnetic recording medium comprising at least one atom selected from Sr and B.
body. (3) The powder of the lower non-recording layer contains a nonmagnetic inorganic powder having a Mohs hardness of 4 or more.
A magnetic recording medium characterized by the above-mentioned. (4) The powder of the lower non-recording layer is α-alumina or β-alumina having an α conversion of 90% or more. Na, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, kora
, Silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tungsten oxide
Ten, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate
, Barium sulfate, and molybdenum disulfide.
A magnetic recording medium characterized by containing a mechanical powder.(5) The elastic modulus of the support is 100 to 2000 kg / mm.^TwoIs characterized by
Magnetic recording medium. (6) The support is made of polyethylene terephthalate or polyethylene naphthalate.
Polyesters, polyolefins, cellulose triacetate, polycarbonate
-, Polyamide, polyimide, polyamide-imide, polysulfone, aramid
Characterized in that it is at least one kind selected from aromatic polyamides.
Recording medium. [0006]   That is, according to the present invention, the powder used for the lower non-recording layer has the above configuration.
The dispersion liquid containing the powder in the binder and the ferromagnetic powder used in the upper recording layer are separated into binders.
The scattered magnetic paint has the same or similar thixotropy as each other,
When applying both paints in ton Wet, the interface is not disturbed and pinholes and cissing
It has been found that there is no occurrence and that the head contact can be improved. [0007]   The thixotropic property is also called thixotropy, and refers to the softening phenomenon of an object due to stress.
Among them, those with recovery, but softening by increasing the strain of the object
Is what causes it. Magnetic coatings exhibit typical thixotropic properties, such as stirring
When given, the internal structure gradually breaks down and softens, increasing the fluidity. Magnetic paint
Is applied on a non-magnetic support and the magnetic field orientation causes the ferromagnetic powder to rotate.
Occasionally, the internal structure is destroyed, resulting in a considerably increased fluidity. Conventional lower layer
Is the recording layer dispersion non-thixotropic or very small at all?
Or extremely strong thixotropy like liquid containing carbon black
Things were used. The present inventor paid attention to the thixotropic properties of these two solutions,
Surprisingly no disturbance at the interface when they were the same or similar . That is, the thixotropic property of the lower non-recording layer, that is, the viscoelasticity of the lower layer
It was not controlled and was not specifically controlled.
With this, the effect of the present invention is extremely effectively exhibited. Here, the same or similar thixotropy is defined as a wet-on-wet method.
When the dispersion liquid of the lower non-recording layer and the magnetic paint of the upper recording layer are applied,
Means that the thixotropic properties of both solutions are close enough to avoid mixing
. [0008]   In the present invention, the powder is preferably used as a binder
The lower layer dispersion liquid dispersed therein has a thixotropic property and a shear rate of 10^Four  s
ec^-1  Stress A10 at^Four  And shearing speed 10 sec^-1  A1 shear stress
Ratio A10 with 0^Four  / A10 is 100 ≧ A10^Four  / A10 ≧ 3
And A10 of the dispersion^Four  / A10 ratio within a certain range, the upper magnetic coating
It has a thixotropic property close to that of the material, and no disturbance occurs at the interface.
No problems such as unhole and cissing occurred. [0009]   As described above, the basic idea of the present invention is that the lower layer has a non-magnetic fine particle of 0.08 μm or less.
By using an organic powder, the lower non-recording layer and the upper recording layer
Each of the specified coating liquids, the dispersion liquid in the case of the lower non-recording layer, and the dispersion liquid in the case of the upper recording layer
The magnetic paint has the same or similar thixotropy when applied.
Can be prepared as follows. This eliminates coating defects, improves yield, improves durability,
Electromagnetic conversion characteristics such as output improvement can be improved. [0010]   Here, the shear stress with respect to the shear rate is measured by a viscometer, for example, Roto manufactured by HAAKE.
The shear rate is measured with a coaxial cylindrical viscometer such as visco viscometer RV-II.
It is determined by the diameter of the outer cylinder, the clearance and the number of revolutions. Shear rate, apparent viscosity and shear response
Power has the following relationship: [0011]   A = η · D (A: shear stress, η: viscosity, D: shear rate)   D = dv / dr (v: peripheral speed, r: radius)   Therefore, A10, A10^Four  Are A = 10η and A = 10, respectively.^Four  η, but A
10^Four  The ratio of / A10 indicates the degree of thixotropic, and the larger the ratio, the greater the thixotropic.
The smaller the ratio, the smaller the ratio, the greater the thixotropy. Conventionally, non
The magnetic dispersion has only weak thixotropic properties, and A10^Four  / A10 is 200 ~
It was about 500. A10^Four  When / A10 is large, the dispersion becomes Newtonian fluid
It becomes difficult to perform simultaneous multilayer coating when the upper layer is used as a magnetic layer. If too low, tiki
A balance between viscosity that allows for simultaneous multi-layer application and viscosity that allows for liquid transfer due to too strong sotropic properties
Is difficult to do. [0012]   That is, the magnetic recording medium of the present invention reduces the particle size of the dispersed non-magnetic inorganic powder.
This makes it possible to adjust the thixotropic property of the dispersion. That is, in a wet state,
Or, in order to perform coating sequentially, the rheological properties of the upper recording layer and the lower non-recording layer
The combination of rheological properties is important. Magnetic paints are magnetically absorbed by ferromagnetic powders.
Very strong thixotropy due to the structural viscosity in the magnetic paint due to the attractive force
It has properties. In contrast, the dispersion for the lower non-recording layer has no magnetic attraction.
Conventionally, it had only weak thixotropic properties. In this state, simultaneous multi-layer coating is performed.
When the upper recording layer and the lower non-recording layer are significantly mixed near the interface,
Intense aggregation streaks occurred during orientation, and sufficient surface properties could not be obtained
. Thus, the present invention solves such a problem by increasing the average primary particle size to 0.0.
A nonmagnetic inorganic powder specified to be 8 μm or less is used. In addition, the present invention
Non-magnetic inorganic powders can be mainly used and carbon black can be used in combination. [0013]   The magnetic recording medium of the present invention has a saturation maximum magnetic flux density Bm of the lower non-recording layer of 500 ga.
Or less, more preferably 30 to 500 gauss. Specifically, A
10^Four  / A10 or magnetic recording is not possible and the upper recording layer
Dispersion with thixotropic properties adjusted using magnetic powder that does not adversely affect
Can also be used. That is, the lower non-recording layer has a thickness of 500 gauss or less, preferably
0 To set the saturation magnetization (σ_S) Low magnetic material
By preparing a dispersion with a reduced magnetic material filling ratio in the non-recording layer
Is done. [0014]   The present invention relates to A10^Four  A preferred means for adjusting / A10 to the above range is shown.
These are, for example, also related to the following factors (repeated description)
), And by selecting variously, the desired A10^Four  / A10
Obtain dispersions and magnetic paints, and eventually manufacture magnetic recording media with the desired properties.
Can be. [0015]   Such factors include, for example, non-magnetic inorganic powder or magnetic powder to be dispersed.
(1) particle size (specific surface area, average primary particle size, etc.), (2) structure (oil absorption
, Particle morphology, etc.), (3) powder surface properties (pH, heat loss, etc.), (4) particle absorption
Attraction (σ_SAnd the like, (1) molecular weight, (2) type of functional group, etc.
Regarding the solvent, (1) type (polarity etc.), (2) binder solubility, (3) solvent formulation
And water content. [0016]   That is, A10^Four  The ratio of / A10 is, for example, the molecular weight of the binder, the structure,
Various parameters such as affinity and water content are involved, but the largest contribution is
Surface properties of dispersed powder, particle size, oil absorption, affinity with solvent
Which is relevant. The smaller the particle size, the stronger the thixotropy. Also, oil absorption
Large amounts of structure-rich carbon black are very thixotropic
Becomes stronger. In addition, magnetic particles have strong structural viscosity due to the magnetic attraction of the particles themselves.
And usually have strong thixotropic properties. That is, the present invention utilizes such properties.
To determine the thixotropic properties of the coating solution for the lower non-recording layer and the magnetic paint for the upper recording layer
Adjust to the range.       [0017]   Next, preferred embodiments of the present invention will be described below.       [0018]   In the context of the present invention, magnetic paints and dispersions may contain polyisocyanates.
preferable. Further, the average primary particle diameter is 0.03 μm or less, more preferably 0.02 μm or less.
Non-magnetic inorganic powder in a weight ratio of carbon black of 3 μm or less to non-magnetic inorganic powder
Powder: carbon black = 99: 1 to 70:30.
Especially preferably, it is 95: 5 to 80:20. 1% by weight or less of carbon black
Underneath is equivalent to substantially not including the desired thixotropic property.
It becomes difficult to be. Further, when the content is more than 30% by weight, the surface property of the obtained magnetic recording medium is improved.
Tends to be insufficient. [0019]   As the nonmagnetic inorganic powder, in particular, Si0_Two  , TiO_Two  , Α-alumina, α-F
e_Two  O_Three, Boron nitride and tin oxide are preferred. The average primary particle size of the nonmagnetic inorganic powder is
0.08 μm or less, but if necessary, a non-magnetic inorganic powder other than this size is seeded.
The same effect can be obtained by widening the particle size distribution even with various non-magnetic inorganic powders in combination.
It can also be done. The tap density of the non-magnetic inorganic powder is preferably 0.05 to 2 g / cc.
Preferably 0.2 to 1.5 g / cc, water content 0.1 to 5%, preferably 0.2 to 5
3%, pH 2-11, specific surface area 1-100m^Two  / G, preferably 5 to 50
m^Two  / G, more preferably 7 to 40 m^Two  / G. Crystallite size is 0.01
μ-2 μm is preferred. The oil absorption using DBP is 5-100ml / 100g, preferably
Or 10 to 80 ml / 100 g, more preferably 20 to 60 ml / 100 g.
is there. Specific gravity is 2-8. The shape may be any of needle shape, spherical shape, dice shape
. The above non-magnetic inorganic powder does not necessarily have to be 100% pure,
Alternatively, the surface may be treated with another compound. At that time, if the purity is 70% or more, it is effective
Is not reduced. For example, when using titanium oxide, the surface should be alumina
Is generally used. Ignition loss should be less than 20%
preferable. The non-magnetic inorganic powder preferably has a Mohs hardness of 4 or more. The present invention
Does not contain carbon black in non-magnetic inorganic powders, but can be used together
You. [0020]   The specific surface area of the carbon black that can be used in combination is 100 to 500, preferably 150.
~ 400m^Two  / G, DBP oil absorption is 20-400ml / 100g, preferably
3 It is 0 to 200 ml / 100 g. The particle size is preferably 5 μm to 130 μm,
0 to 50 mμ is more preferable, and 10 to 40 mμ is particularly preferable. pH 2-1
0, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc. [0021]   These non-magnetic powders are used in a weight ratio of 20 to 0.1, preferably with respect to the binder.
Is 10 to 0.5, more preferably 8 to 1, and a volume ratio of 10 to 0.2.
Used in [0022]   In the present invention, the lower non-recording layer is formed to have a thickness of 500 gauss or less, preferably 30 to 50
To set it to 0 Gauss, the saturation magnetization (σ_S) Low magnetic material,
This is achieved by reducing the filling ratio of the magnetic material in the recording layer. In this case, the magnetic
The nonmagnetic substance is preferably 100 parts by weight or more based on 100 parts by weight of the active substance, and 100 to 5 parts by weight.
More preferably, the amount is 000 parts by weight. As the non-magnetic material, in addition to the binder,
Nonmagnetic inorganic powder, preferably magnetic powder, carbon black, etc. are preferred.
. As the magnetic material, for example, Co-γ-Fe_Two  O_Three  Magnetic materials are preferred, and
The coercive force is not particularly limited, but is preferably 1500 Oe or less, and 400 Oe to 1500
Oe is more preferable. Hexagonal barium ferrite is used for the lower non-recording layer.
Can also be. There is no limitation on Hc at that time, but barium ferrite is used.
In this case, the content is preferably 800 Oe or more and 4500 Oe or less.   Hc of the upper recording layer is 1200 Oe to 3000 Oe, and Bm is 200 to 4500.
Preferably it is Gaussian. [0023]   In the present invention, other nonmagnetic powders that can be used include organic powders, for example,
Acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder
, Phthalocyanine pigments, but polyolefin resins, polyesters
Resin powder, polyamide resin powder, polyimide resin powder, polyethylene fluoride
Resin is used. Its production method is described in JP-A-62-18564 and JP-A-60-25.
No. 5827 and those described in JP-A-60-255827 can be used.
Wear. [0024]   These non-magnetic powders are 0.1 to 10 in weight ratio to the binder,
Is used in the range of 10 to 0.2. [0025]   Hereinafter, general items common to the present invention will be described.   Specific examples of the nonmagnetic inorganic powder that can be used in the present invention include metal oxides and metal charcoal.
Inorganic compound powders such as acid salts, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc.
It is the end. Examples of the inorganic compound include α-alumina and β-a having an α conversion of 90% or more.
Lumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide
, Tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate
, Calcium sulfate, barium sulfate, molybdenum sulfide, etc., alone or in combination
Used in. [0026]   Specific examples of the non-magnetic inorganic powder used in the present invention include: AK manufactured by Sumitomo Chemical Co., Ltd.
P-20, AKP-30, AKP-50, HIT-50, HiT-100, Japan
Chemical Industries: G5, G7, S-1, Toda Industries: DPN-250BX, TF
-100, TF-120, TF-140, manufactured by Ishihara Sangyo: TTO-55, FT-1
000, FT-2000, FTL-100, FTL-200, M-1, S-1,
SN-100, E-303, E-304, manufactured by Titanium Industry: ECT-52, STT
-4D, STT-30, STT-65C, Y-LOP, Y-LOP
α-Hematite, manufactured by Mitsubishi Metals: T-1, Nippon Shokubai: NS-O, NS-3Y, NS
-8Y and the like. [0027]   Examples of the carbon black used in the present invention include a furnace for rubber and a circuit for rubber.
Maru, black for color, acetylene black and the like can be used. Departure
Specific examples of carbon black used in the present invention include Cabot Corporation: BLA.
CKPEARLS 2000, 1300, 1000, 900, 800, 880,
700, VULCAN XC-72, manufactured by Mitsubishi Kasei Corporation: $ 3250B, $ 95 0, $ 650B, $ 970B, $ 850B, manufactured by Columbian Carbon: CON
DECTEX SC, RAVEN 8800, 8000, 7000, 5750,
5250, 3500, 2100, 2000, 1800, 1500, 1255, 1
250, manufactured by Akzo: Ketjen Black EC. Carbon fiber
Even if the rack is surface treated with a dispersant or grafted with resin,
A part of which may be made of graphite may be used. Also, carbon bra
Before adding the coating to the magnetic paint, the coating may be dispersed in a binder in advance. this
These carbon blacks can be used alone or in combination. In the present invention
Usable carbon black is, for example, "Carbon Black Handbook" (Carbon Black
Eds. Association).       [0028]   The ferromagnetic powder used in the upper recording layer of the present invention is γ-FeOx (x = 1.3).
3-1.5), Co-modified γ-FeOx (x = 1.33-1.5), Fe or N
Ferromagnetic alloy fine powder containing i or Co as a main component (75% or more), barium huera
Known ferromagnetic powders such as iron and strontium ferrite can be used. these
Al, Si, S, Sc, Ti, V, Cr, Cu
, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, A
u, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni
, Sr, B and the like. Later on these ferromagnetic fine powders
Pretreatment before dispersion with dispersants, lubricants, surfactants, antistatic agents, etc.
You can go. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-
No. 18372, No. 47-22062, No. 47-22513, No. Sho
46-28466, JP-B-46-38755, JP-B-47-4286,
JP-B-47-12422, JP-B-47-17284, JP-B-47-18509
No., JP-B-47-18573, JP-B-39-10307, JP-B-48-39
Nos. 639, U.S. Pat.
Nos. 4, 324,005 and 3,389,014.       [0029]   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. Complex organic acid salt (mainly
Oxalate) and a reducing gas such as hydrogen, reducing iron oxide with hydrogen
Method of obtaining Fe or Fe-Co particles by reduction with a neutral gas, metal carbonyl
How to thermally decompose a compound, sodium borohydride,
Reduction method by adding a reducing agent such as phosphate or hydrazine, low pressure metal
And evaporating in an inert gas to obtain 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 and drying.
After immersion in an organic solvent, an oxygen-containing gas is fed in to form an oxide film on the surface.
After forming, drying method, partial pressure of oxygen gas and inert gas without using organic solvent
Any of the methods of adjusting and forming an oxide film on the surface can be used.
it can. [0030]   When the ferromagnetic powder of the upper recording layer of the present invention is represented by the specific surface area by the BET method, it is 25 to 8
0m^Two  / G, preferably 35-60 m^Two  / G. 25m^Two/ G or less
In this case, the noise becomes high, and if it is 80 or more, it is difficult to obtain surface properties, which is not preferable. Of the present invention
The crystallite size of the ferromagnetic powder in the upper recording layer is 450 to 100 Å.
And preferably 350 to 150 angstroms. Σ of iron oxide magnetic powder_S
Is at least 50 emu / g, preferably at least 70 emu / g, and
In the latter case, it is preferably 100 emu / g or more. [0031]   R1500 of the ferromagnetic powder is preferably 1.5 or less. More preferred
R1500 is 1.0 or less. r1500 is the saturation magnetization of the magnetic recording medium
Then, when a magnetic field of 1500 Oe is applied in the opposite direction, the amount of magnetization remaining without reversal
%. [0032]   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. Tap density of gamma iron oxide is 0
. It is preferably at least 5 g / cc, more preferably at least 0.8 g / cc. [0033]   When using gamma iron oxide, the ratio of divalent iron to trivalent iron is preferably 0-20.
%, More preferably 5 to 10%. Also cobalt source for iron atom
The amount of offspring is 0-15%, preferably 2-8%. [0034]   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. Ferromagnetic powder required
May be subjected to a surface treatment with Al, Si, P or an oxide thereof.
Absent. The amount is 0.1 to 10% with respect to the ferromagnetic powder.
Adsorption of lubricants such as 100mg / m^Two  The following is preferred. For ferromagnetic powder
Although it may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr,
If it is 500 ppm or less, there is no particular effect on the characteristics. [0035]   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. As for the shape,
Needle, granular, rice granular, plate-like
It doesn't matter. In order to achieve the SFD of ferromagnetic powder of 0.6 or less,
It is necessary to reduce the distribution of Hc in the powder. To achieve this, goitite particle size
Improves fabric, prevents sintering of γ-hematite,
For example, there is a method in which the deposition speed of cobalt is made lower than before. [0036]   The present invention also includes barium ferrite and stron as platelet hexagonal ferrite.
Titanium ferrite and hexagonal Co powder can be used. Use barium ferrite
In the case, the particle size is 0.001-1 μm in diameter and the thickness is ２〜-２〜 of the diameter.
0. Specific gravity is 4-6g / cc, specific surface area is 1-60m^Two  / G. [0037]   As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins,
Reactive resins and mixtures thereof are used. Glass transition as thermoplastic resin
Temperature is -100 to 150 ° C, number average molecular weight is 1000 to 200,000, preferably Are from 10,000 to 100,000 and the degree of polymerization is about 50 to 1,000. This
Examples include vinyl chloride, vinyl acetate, vinyl alcohol, and maleic acid.
, Acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, meta
Crylic acid, methacrylate, styrene, butadiene, ethylene, vinyl
Polymer containing tylal, vinyl acetal, vinyl ether, etc. as constituent units
Alternatively, there are copolymers, polyurethane resins, and various rubber resins. In addition, thermosetting tree
Fat or reactive resin such as phenolic resin, epoxy resin, polyurethane cured
Mold resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, form
Aldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin
Mixture of fat and isocyanate prepolymer, polyester polyol and polyiso
A mixture of cyanate, a mixture of polyurethane and polyisocyanate, and the like.
You. [0038]   For details on these resins, see "Plastic Handbook" published by Asakura Shoten.
It is described in. A known electron beam-curable resin is used for the first layer or the second layer.
It is also possible to use. These examples and the manufacturing method thereof are described in JP-A-62-2.
No. 56219. These resins can be used alone or in combination
But preferably vinyl chloride resin, vinyl chloride vinyl acetate resin, chloride
Vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride
A combination of at least one selected from the group of copolymers and a polyurethane resin, or
Those obtained by combining these with a polyisocyanate are exemplified. [0039]   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_Three  M, OSO_Three
  M, 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) At least one polar group selected from a group consisting of
It is preferable to use those introduced by polymerization or addition reaction. Such a polar group
Amount of 10^-1-10^-8Mol / g, preferably 10^-2-10^-6Mol / g
You.       [0040]   Specific examples of these binders used in the present invention include Union Carbide
Company: VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYE
S, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC
, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, electrochemical
Company: 1000W, DX80, DX81, DX82, DX83, manufactured by Zeon Corporation
: MR110, MR100, 400X110A, manufactured by Nippon Polyurethanes: Nippo
Runs N2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd .: Pandex T
-5105, T-R3080, T-5201, Barnock D-400, D-21
0-80, Chris Bon 6109, 7209, manufactured by Toyobo: Byron UR8200
, UR8300, RV530, RV280, manufactured by DAINICHI SEIKA CO., LTD.
20, 5020, 5100, 5300, 9020, 9022, 7020, Mitsubishi
Manufactured by Seikosha: MX5004, manufactured by Sanyo Kasei: Samprene SP-150, manufactured by Asahi Kasei:
Saran F310, F210 and the like. [0041]   The binder used in the upper recording layer of the present invention is 5 to 50% by weight based on the ferromagnetic powder.
, Preferably in the range of 10 to 30% by weight. Vinyl chloride resin
5 to 30% by weight when used, 2 to 20 weights when using polyurethane resin
% Of the polyisocyanate in the range of 2 to 20% by weight.
Is preferred. [0042]   In the present invention, when a polyurethane resin is used, the glass transition temperature is -50 to
100 ° C, elongation at break 100-2000%, stress at break 0.05-10 kg / c
m^Two, Yield point is 0.05 to 10 kg / cm^Two  Is preferred. The magnetic recording medium of the present invention
Consists of two layers. Therefore, the amount of binder, vinyl chloride resin in binder,
The amount of urethane resin, polyisocyanate or other resin,
The molecular weight and polar group content of each resin to be formed, or the physical properties of the resin described above are required.
It is of course possible to change between the lower non-recording layer and the upper recording layer as necessary. [0043]   As the polyisocyanate used in the present invention, tolylene diisocyanate, 4
4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate
, Xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-
Toluidiisocyanate, isophorone diisocyanate, triphenylmethane
Isocyanates such as polyisocyanate, and these isocyanates and polyisocyanates.
With alcohols and polyisocyanates
Isocyanates and the like can be used. Commercial availability of these isocyanates
The trade names include those manufactured by Nippon Polyurethane Co .: Coronate L, Coronate H
L, Coronate 2030, Coronate 2031, Millionate MR, Milliony
To MTL, manufactured by Takeda Pharmaceutical Co., Ltd .: Takenate D-102, Takenate D-110N,
Kenate D-200, Takenate D-202, manufactured by Sumitomo Bayer Ltd .: Desmodu
L, death module IL, death module N, death module HL, etc.
These can be used alone or in combination of two or more using the difference in curing reactivity
Both the lower non-recording layer and the upper recording layer can be used. [0044]   The carbon black used in the upper recording layer of the present invention, that is, the magnetic layer, is a rubber filler.
Use thermal, rubber thermal, color black, acetylene black, etc.
be able to. Specific surface area is 5-500m^Two  / G, DBP oil absorption is 10-400
ml / 100 g, the particle size is 5 μm to 300 μm, the pH is 2 to 10, and the water content is 0.1 μm.
The tap density is preferably 0.1 to 1 g / cc. Used in the present invention
A specific example of carbon black is BLACKPEARL manufactured by Cabot Corporation.
S 2000, 1300, 1000, 900, 800, 700, VULCAN
XC-72, manufactured by Asahi Carbon Co .: $ 80, $ 60, $ 55, $ 50, $ 35, Mitsubishi
Kasei Kogyo Co., Ltd .: $ 2400B, $ 2300, $ 900, $ 1000, $ 30, $
40, $ 10B, manufactured by Columbian Carbon Co .: CONDUCTEX SC, RA
VEN 150, 50, 40, 15 and the like. Disperse carbon black
Even if the surface is treated with an agent or grafted with a resin, part of the surface
It is also possible to use phytoite. Also, apply carbon black with magnetic coating.
It may be dispersed in a binder before adding to the mixture. These carbon
Black can be used alone or in combination. Use carbon black
When used, it is preferable to use 0.1 to 30% of the amount based on the ferromagnetic powder.
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, which are used for the purpose of clarity, have a first layer, namely, a lower non-recording layer, a second layer.
Layer, that is, the type, amount and combination of the upper recording layer, particle size, oil absorption, conductivity
Depending on the purpose, it can be used based on the characteristics shown above, such as temperature and pH.
Is possible. For example, using a highly conductive carbon black for the lower non-recording layer
The use of carbon black with a large particle size for the upper recording layer
And lowering the coefficient of friction. Carbon usable in the upper recording layer of the present invention
For black, for example, refer to "Carbon Black Handbook" (edited by Carbon Black Association)
Can be [0045]   As the abrasive used in the upper recording layer of the present invention, α-Al Mina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Random, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide
Well-known materials with a Mohs hardness of 6 or more, such as tan, silicon dioxide, boron nitride, etc.
Used alone or in combination. In addition, a composite of these abrasives (abrasives)
Which has been surface-treated with another abrasive). Most of these abrasives
Compound or element other than the main component may be contained, but if the main component is 90% or more,
No change in effect. The particle size of these abrasives is preferably from 0.01 to 2 μm.
However, if necessary, it is possible to combine abrasives with different particle sizes,
The same effect can be obtained by widening the diameter distribution. Tap density is 0.3-2
g / cc, water content 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 is needle-like, spherical, dice-like
, But those having corners in a part of the shape are preferable because of high polishing properties. [0046]   Specific examples of the abrasive used in the present invention include AKP-2 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-30, AKP-50, HIT-50, manufactured by Nippon Chemical Industry: G5, G
7, S-1, manufactured by Toda Kogyo KK: 100ED, 140ED. Departure
The type of abrasive used for the first layer and the second layer can be changed by changing the type, amount and combination.
Of course, it is possible to use them properly. These abrasives are pre-bonded
It may be added to the magnetic paint after dispersion treatment with the agent. The magnetic recording medium of the present invention
5 abrasives / 100 μm on the surface of the upper recording layer and on the end face of the upper recording layer
^Two  The above is preferred. [0047]   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
Silicone, fatty acid modified silicone, fluorine-containing silicone, fluorine-containing alcohol
, Fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate
Ter and its alkali metal salts, alkyl sulfates and their alkali metals
Salts, polyphenyl ethers, fluorine-containing alkyl sulfates and their alka Metal salts, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds,
And metal salts thereof (Li, Na, K, Cu, etc.).
Or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms
(Which may contain an unsaturated bond or may be branched), and has 12 to 2 carbon atoms.
2 alkoxy alcohols, monobasic fatty acids having 10 to 24 carbon atoms (unsaturated
And may be branched), and C2-12 monovalent, divalent, trivalent
Any one of polyhydric, tetrahydric, pentahydric and hexahydric alcohols (including unsaturated bonds,
A mono-fatty acid ester or di-fatty acid ester consisting of
Teralkylates of tri- or tri-fatty acid esters and alkylene oxide polymers
Ter fatty acid ester, C8-C22 fatty acid amide, C8-C22 fat
Group amines and the like can be used. Specific examples of these are lauric acid, myristin
Acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid
, Linoleic acid, linolenic acid, elaidic acid, octyl stearate, stearin
Amyl acid, isooctyl stearate, octyl myristate, butyl stearate
Toxiethyl, anhydrosorbitan monostearate, anhydrosorbitan
Distearate, anhydrosorbitan tristearate, oleyl alcohol
, Lauryl alcohol. [0048]   In addition, alkylene oxide, glycerin, glycidol, alkyl
Nonionic surfactants such as enol ethylene oxide adducts, cyclic amines,
Steroids, quaternary ammonium salts, hydantoin derivatives, heterocycles, phos
Cationic surfactants such as phonium or sulfoniums, carboxylic acids, sulfonium
Anions containing acidic groups such as fonic acid, phosphoric acid, sulfate groups, phosphate groups, etc.
Surfactants, amino acids, aminosulfonic acids,
Can also be used amphoteric surfactants such as phosphates and alkylbedynes.
About these surfactants, "Handbook of Surfactants" (published by Sangyo Tosho Co., Ltd.)
In more detail. These lubricants and antistatic agents are not necessarily 100% pure
It is not pure, but isomers, unreacted materials, by-products, decomposition products, oxides, etc.
Impurities may be included. Preferably, these impurities are 30% or less. Is preferably 10% or less. [0049]   These lubricants and surfactants used in the present invention are a lower non-recording layer and an upper recording layer.
The type and amount can be properly used as needed. For example, the lower non-recording layer,
The upper recording layer uses fatty acids with different melting points to control bleeding to the surface,
Use surfactants with different polarities to control bleeding to the surface
The amount of lubricant added can be increased in the lower non-recording layer to improve coating stability by adjusting
To improve the lubrication effect. Of course, it is limited to only the examples shown here.
Not something. [0050]   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: 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,
Neon DS-60, Anone BF, Anone LG, butyl stearate, butyl lau
Rate, erucic acid, manufactured by Kanto Chemical Co., Ltd .: oleic acid, manufactured by Takemoto Yushi Co., Ltd .: FAL-205
, FAL-123, manufactured by Nippon Rika Co., Ltd .: Engelbu LO, Engelbu IPM, Sansocizer E4030, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, KF-96, KF-96
L, KF-96H, KF410, KF420, KF965, KF54, KF50
, KF56, KF-907, KF-851, X-22-819, X-22-82
2, KF-905, KF-700, KF-393, KF-857, KF-860
, KF-865, X-22-980, KF-101, KF-102, KF-10
3, X-22-3710, X-22-3715, KF-910, KF-3935
, Manufactured by Lion Armor Co .: Armid P, Armid C, Armoslip CP,
Lion Fat & Oil Company: Duomin TDO, Nisshin Oil Company: BA-41G, Sanyo Chemical
Made by: Profan 2012E, New Pole PE61, Ionet MS-400
, Ionet MO-200, Ionet DL-200, Ionet DS-300
, Ionnet DS-1000, Ionnet DO-200 and the like. [0051]   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.
Impurities such as substances, by-products, decomposition products, oxides, and moisture may be included. This
Their impurity content is preferably 30% or less, more preferably 10% or less. Book
If necessary, the type and amount of the organic solvent used in the
You can change it. Use a highly volatile solvent for the lower non-recording layer to improve the surface properties
Use a solvent with a high surface tension (such as cyclohexanone or dioxane) for the upper recording layer. Use a solvent with a high solubility parameter for the upper recording layer to improve the coating stability.
Examples include increasing the filling degree, but are not limited to these examples.
Of course it is.       [0052]   The thickness configuration of the magnetic recording medium of the present invention is such that the support is 1 to 100 μm, preferably 4 to 100 μm.
80 μm, lower non-recording layer 0.5 μm to 10 μm, preferably 1 to 5 μm, upper layer
Recording layerIs 0. It is not less than 05 μm and not more than 0.3 μm. Upper recording layer and lower non-recording layer
Is used in the range of 1/100 to 2 times the thickness of the support. Also,
An undercoat layer may be provided between the support and the lower non-recording layer to improve adhesion.
. Their thickness is 0.01 to 2 μm, preferably 0.05 to 0.5 μm.
Further, a back coat layer may be provided on the side of the support opposite to the magnetic layer side. this
The thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. These primers
Known layers and backcoat layers can be used. [0053]   The support used in the present invention is preferably non-magnetic,
Polyesters such as phthalate, polyethylene naphthalate, etc., polyolefin
, Cellulose triacetate, polycarbonate, polyamide, polyimide,
Known polyamideimide, polysulfone, aramid, aromatic polyamide and the like
Film can be used. These supports are previously treated with corona discharge,
It is also possible to carry out a baking treatment, an easy adhesion treatment, a heat treatment, a dust removal treatment and the like. Eye of the invention
In order to achieve the target, the support preferably has a center line average surface roughness of 0.03 μm or less.
Or 0.02 μm or less, more preferably 0.01 μm or less.
There is a need. In addition, these supports merely require a small center line average surface roughness.
It is preferable that there is no coarse protrusion of 1 μm or more. Also need surface roughness shape
Can be freely controlled by the size and amount of filler added to the support according to
It is what is done. Examples of these fillers include Ca, Si, Ti and the like.
In addition to oxides and carbonates, there may be mentioned organic fine powders such as acrylic. For use in the present invention
The F-5 value of the support in the tape running direction is preferably 5 to 50 kg / mm.^Two
The F-5 value in the tape width direction is preferably 3 to 30 kg / mm.^Two  And tape
Long Generally, the F-5 value in the hand direction is higher than the F-5 value in the tape width direction.
This does not apply when it is necessary to increase the strength in the width direction. [0054]   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
5-100 kg / mm in both directions^Two, Elastic modulus is 100-2000Kg / mm^Two  Is good
Good. [0055]   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. [0056]   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, but in the kneading process, a continuous kneader or a pressure kneader is used.
By using a material having a strong kneading force such as a
Br can be obtained. Ferromagnetic when using a continuous or pressure kneader
All or part of the powder and the binder (however, more than 30% of the total binder is preferred)
) And 100 parts of the ferromagnetic powder are kneaded in the range of 15 to 500 parts. This
Details of these kneading processes are described in JP-A-1-106338 and JP-A-64-79.
274. [0057]   In the present invention, a simultaneous multilayer coating method as disclosed in JP-A-62-212933 is used.
By using, it is possible to produce more efficiently. Multilayer as in the present invention The following configuration is proposed as an example of an apparatus and method for applying a magnetic recording medium having the following configuration.
Wear. 1. Gravure coating, roll coating, and blade commonly used for applying magnetic paint
First, apply the lower non-recording layer using a coating or extrusion coating device.
While the non-recording layer is in a wet state, Japanese Patent Publication No.
No. 179 and Japanese Patent Application Laid-Open No. 2-265672.
The upper recording layer is applied by a coating device. 2. JP-A-63-88080, JP-A-2-17921, JP-A-2-2656
No. 72, which has two slits for applying the coating solution,
The upper recording layer is applied almost simultaneously by a pad. 3. Extract with backup roll disclosed in JP-A-2-174965
The upper recording layer is applied almost at the same time by a extrusion coating device. In addition, it is possible to prevent a decrease in electromagnetic conversion characteristics and the like of the magnetic recording medium due to aggregation of the ferromagnetic powder.
Therefore, it is disclosed in JP-A-62-95174 and JP-A-1-236968.
It is desirable to apply shear to the coating liquid inside the coating head by such a method. [0058]   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. [0059]   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, and the speed is 20 m / min or more and 700 m / min or less.
The range is below. [0060]   For the upper recording layer surface of the magnetic recording medium of the present invention and SUS420J on the opposite surface, The friction coefficient is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferred.
Or 10^-Five-10^-12Ohm / sq, the elastic modulus at 0.5% elongation of the upper recording layer is
It is preferably 100 to 2000 kg / mm in both the running direction and the width direction.^TwoGood breaking strength
Preferably 1-30Kg / cm^TwoThe elastic modulus of the magnetic recording medium depends on the running direction and the longitudinal direction.
Also preferably 100 to 1500 kg / mm^Two, The residual growth is preferably 0.5% or less.
The heat shrinkage at any temperature below 100 ° C. is preferably 1% or less, more preferably
It is preferably at most 0.5%, most preferably at most 0.1%. [0061]   The residual solvent contained in the upper recording layer is preferably 100 mg / m^Two  Below
Preferably 10 mg / m^Two  Below, the residual solvent contained in the upper recording layer is lower
It is preferable that the amount is smaller than the residual solvent contained in the non-recording layer. [0062]   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 0.6 or less
Is preferred. [0063]   The magnetic recording medium of the present invention has an upper recording layer and a lower non-recording layer.
It is easy to say that these physical properties can be changed between the non-recording layer and the upper recording layer.
Is to be determined. For example, increase the elastic modulus of the upper recording layer to improve running durability
At the same time, the elastic modulus of the lower non-recording layer is lower than that of the upper recording layer,
For example, the contact with the head is improved. [0064]     【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. [0065]   Hereinafter, specific examples of the present invention will be described.   Example 1-1 Lower non-recording layer   Non-magnetic inorganic powder TiO_Two  (TTO-55A manufactured by Ishihara Sangyo) 100 parts     Average primary particle diameter 0.05μ BET specific surface area 18m^Two  / G pH7   20 parts of carbon black     Average primary particle size 18mμ     DBP oil absorption 80ml / 100g     pH 8.0     Specific surface area by BET method 250m^Two  / G     Volatile content 1.5%   Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts     −N (CH_Three)_Three ⁺Cl^-5 × 10 polar groups^-6eq / g included     Composition ratio 86: 13: 1 Degree of polymerization 400   5 parts of polyester polyurethane resin     Neopentyl glycol / caprolactone polyol / MDI             = 0.9 / 2.6 / 1       −SO_Three  Na group 1 × 10^-Foureq / g content   1 part butyl stearate   1 part of stearic acid   200 parts of methyl ethyl ketone Upper recording layer   Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts     Hc 1600Oe, BET specific surface area 60m^Two  / G     Crystallite size 195Å     Particle size (major axis diameter) 0.20μ, needle ratio 10     σs: 130 emu / g   12 parts of vinyl chloride copolymer     −SO_Three  Na content: 1 × 10^-Foureq / g Degree of polymerization 300   Polyester polyurethane resin 3 parts     Neopentyl glycol / caprolactone polyol / MDI         = 0.9 / 2.6 / 1       −SO_Three  Na group 1 × 10^-Foureq / g content   α-alumina (particle size 0.3 μm) 2 parts   0.5 parts of carbon black (particle size 0.10 μm)   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 above two paints,
And dispersed using a sand mill. A polyisocyanate is added to the resulting dispersion to form an underlayer.
Add 1 part to the recording layer coating solution and 3 parts to the upper recording layer coating solution.
40 parts of butyl acid was added, and filtered using a filter having an average pore size of 1 μm,
Coating solutions for forming the lower non-recording layer and for the upper recording layer were prepared. Table 1
A10 of the coating solution for the lower non-recording layer^Four  / A10 ratio was shown. [0066]   The obtained lower non-recording layer coating solution is further dried so that the thickness after drying is 2 μm.
Immediately thereafter, the thickness of the upper recording layer is set to 7 μm so that the thickness of the upper recording layer becomes 0.3 μm.
Simultaneous overlay on polyethylene terephthalate support with centerline surface roughness 0.01μ
After applying the coating, a cover with a magnetic force of 3000 G was applied while both layers were still wet.
After being oriented and dried by a tilt magnet and a solenoid having a magnetic force of 1500 G,
Process at a temperature of 90 ° C with a 7-stage calendar consisting of only
To produce an 8 mm video tape (Sample #: Example 1-1). [0067]   Example 1-21-3, 1-4, 1-5, Reference Example, Comparative Examples 1-1 to 1-4   In Example 1-1, the type of nonmagnetic inorganic powder, its average primary particle size,
Table 1 shows the thicknesses of the upper recording layer and the lower non-recording layer when
Each sample was prepared in the same manner as in Example 1-1, except that the test was performed under the described conditions.   Evaluation methods Zero-row durability measurement method   The sample was placed at 23 ° C. and 70% RH in an 8 mm video disk manufactured by Fuji Photo Film Co., Ltd.
FUJIX8, 10 P6-120s were run 100p. Meanwhile, output low
The lower part was measured, and dirt of each part in the deck after running was evaluated. ○ 、 ○ △ 、 △ 、 △ ×
, And × were evaluated. Electromagnetic conversion characteristics 7MHz output   FUJIX8 manufactured by Fuji Photo Film Co., Ltd.
The z signal is recorded, and the 7 MHz signal reproduction output when this signal is reproduced is output to an oscilloscope.
Measured in a loop. Yield   The non-defective rate after the end of the slit is shown. Usually, 97% or more is required. [0068] [Table 1] [0069]   As is clear from the results in Table 1, Examples 1-1 to Examples1-2 and 1-4,
The sample No. 1-5 was excellent in output of 7 MHz, running durability, and yield.   On the other hand, the thickness of the upper recording layer is larger than 1 μm, and Comparative Example 1-1 has an output of 7 MHz.
Low, and the average primary particle diameter of the nonmagnetic inorganic powder is larger than 0.08 μm;
0^Four  Comparative Example 1-2 in which the value of / A10 is out of the preferred range in the present invention and the lower layer
Comparative Examples 1-3 containing only carbon black had low yields,
The output was also low. In Comparative Examples 1-4, the lower non-recording layer was applied and dried, and then the upper recording layer was formed.
Coating method for forming an upper recording layer by applying a coating solution for the coating (sequential after drying)
The yield was low. [0070]     【The invention's effect】   The present invention provides a coating solution using a nonmagnetic inorganic powder of 0.08 μm or less for a lower non-recording layer.
And the thixotropic properties of the coating solution for the upper recording layer, especially for the lower non-recording layer.
Adjust thixotropy, specify physical properties, composition, etc. of non-magnetic or magnetic powder
The magnetic layer can be thinned by simultaneous coating or sequential wet coating method.
Magnetic recording media with excellent yield, durability, and electromagnetic characteristics.
Can be provided.

Claims (1)

Claims: 1. A lower non-recording layer in which a powder is dispersed in a binder is provided on a support,
In a magnetic recording medium provided with an upper recording layer in which a ferromagnetic powder is dispersed in a binder, a dry thickness of the upper recording layer is 0.05 μm or more and 0.3 μm or less, and the strength of the upper recording layer is A magnetic recording medium, wherein the magnetic powder has a crystallite size of 450 to 100 Å, and the powder of the lower non-recording layer contains a non-magnetic inorganic powder having an average primary particle diameter of 0.08 μm or less. 2. A lower non-recording layer in which a powder is dispersed in a binder is provided on a support,
In a magnetic recording medium provided with an upper recording layer in which a ferromagnetic powder is dispersed in a binder, a dry thickness of the upper recording layer is 0.05 μm or more and 0.3 μm or less , and the Hc of the upper recording layer is Is from 1200 to 3000 Oe, and the powder of the lower non-recording layer contains a nonmagnetic inorganic powder having an average primary particle size of 0.08 μm or less. 3. The magnetic recording medium according to claim 1, wherein the dispersion of the lower non-recording layer in which the powder is dispersed in a binder has thixotropic properties. 4. The ferromagnetic powder of the upper recording layer is a ferromagnetic alloy powder containing Fe, Ni or Co as a main component, and in addition to these atoms, Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta
, W, Re, Au, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Z
3. The magnetic recording medium according to claim 1, comprising at least one atom selected from n, Ni, Sr, and B. 5. The magnetic recording medium according to claim 1, wherein the powder of the lower non-recording layer contains a nonmagnetic inorganic powder having a Mohs hardness of 4 or more. 6. The powder of the lower non-recording layer is α-alumina having an α conversion of 90% or more,
β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, carbonic acid At least one selected from calcium, calcium sulfate, barium sulfate, and molybdenum sulfide
The magnetic recording medium according to claim 1, comprising a kind of nonmagnetic inorganic powder. 7. A magnetic recording medium according to claim 1 or 2, wherein the elastic modulus of the support is 100 to 2,000 kg / mm ^2. Wherein said support is a polyethylene terephthalate - DOO, polyethylene naphthalate - DOO polyesters, polyolefins, cellulose - Sutoriasete - DOO, polycarbonate - Bonnet - DOO, polyamide, polyimide, polyamideimide, polysulfone, aramid The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least one selected from aromatic polyamides. 9. A lower non-recording layer coating solution containing a powder and a binder, respectively to prepare an upper recording layer coating solution containing a ferromagnetic powder and a binder, applying these coating solutions on a support magnetic In the method for producing a recording medium, the ferromagnetic powder of the coating liquid for the upper recording layer has a crystallite size of 450 to 100 Å, and the powder of the coating liquid for the lower non-recording layer has an average primary particle size of 0. .08μm or less and the lower non-recording layer coating solution was coated on the support, while the resulting lower non-recording layer is wet, the dry thickness of simultaneously or sequentially upper recording layer 0 0.05μm or more, 0.3μ
m , wherein the coating liquid for the upper recording layer is applied so as to be not more than m .