JPH08293119A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To produce a magnetic recording medium excellent in electromagnetic transducing characteristics such as output and C-N ratio and to produce a thin layer magnetic recording medium excellent in such characteristics, ensuring smooth contact with a head and having satisfactory shelf stability. CONSTITUTION: A thixotropic coating liq. for a non-recording layer contg. powder dispersed in a binder and a thixotropic coating liq. for a recording layer contg. ferromagnetic powder dispersed in a binder are separately prepd. The ratio of the shearing stress of each of the coating liqs. at 10<4> sec<-1> to that at 10sec<-1> is between 100 and 3. The coating liq. for a non-recording layer is applied on a substrate and dried and then the coating liq. for a recording layer is applied so as to attain <=1.0μm dry thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a very thin magnetic recording medium having a magnetic layer of 1.0 .mu. Or less. Magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media such as video tapes, audio tapes, magnetic disks, etc. have a magnetic layer in which ferromagnetic iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic alloy powder, etc. are dispersed in a binder. A non-magnetic support coated with is widely used. In recent years, the recording wavelength tends to become shorter as the recording density becomes higher, and the problem of thickness loss at the time of recording / reproducing such as a decrease in output when the thickness of the magnetic layer is large becomes more serious. For this reason, the magnetic layer has been thinned, but if the magnetic layer is thinned to about 2 μm or less, the surface property of the support is likely to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics tend to deteriorate. .

Therefore, by providing a nonmagnetic thick lower layer on the surface of the nonmagnetic support and then providing the magnetic layer on the upper layer,
Attempts have been made to eliminate the problem caused by the surface roughness of the support and to reduce the thickness demagnetization to achieve a high output by making the magnetic layer thin. For example, in JP-A-59-142741, an undercoat layer having a thickness of 0.03 to 0.3 μm is applied to the surface of a nonmagnetic support, and the average particle size in the undercoat layer is 0.8 μm or less. Of SnO ₂ -based powder to improve the conductivity of the undercoat layer and to improve the adhesion with the magnetic layer coated on the undercoat layer, thereby providing a coating type with good durability. A magnetic recording medium having a magnetic layer and good electromagnetic conversion characteristics is described. JP-A-59-
According to the description of the example, the magnetic layer of the magnetic recording medium described in Japanese Patent No. 142741 is 5 μm, the minor axis length of the magnetic powder is 0.05 μm, and Hc is 400 Oe.

Further, in Japanese Patent Laid-Open No. 61-204827, it is possible to prevent the occurrence of streaky scratches on the surface of the non-magnetic support during the manufacture of the magnetic recording medium, and to prevent the quality of the finished product, especially the dropout. On a flexible substrate to prevent
A magnetic recording comprising a coating layer containing a polymerizable binder and a fine particle pigment having an average particle size of 50 to 1500 angstroms, more preferably a lubricant and an antistatic agent added to the coating layer. It is described to provide a base film for media. This Japanese Patent Laid-Open No. 61-204
In the technique described in Japanese Patent No. 827, a magnetic film containing a magnetic powder having a thickness of 2 μm and a minor axis of the magnetic powder of 0.5 μm and a magnetic powder Hc of 1200 Oe is formed on the base film for a magnetic recording medium. A magnetic recording medium having a coating type magnetic layer having a layer and having good durability is described.

Further, Japanese Patent Laid-Open No. 2-257424 discloses that
In order to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and less sliding noise and dropout, a nonmagnetic layer is provided on a nonmagnetic support, and the average particle size of the nonmagnetic layer is 5 or less.
A magnetic recording medium is described in which a filler of 0 mμ or more is contained, a plurality of magnetic layers are provided on the non-magnetic layer, and the thickness of the uppermost magnetic layer is 1.5 μm or less. The magnetic layers described in the examples of the magnetic recording medium were two layers, the thickness of the magnetic layers other than the uppermost layer was 3.2 μm, and the thickness of the uppermost magnetic layer was 0.
8 μm, the magnetic material used for the uppermost magnetic layer is BET
It has a value of 50 m ² / g and Hc 1200 Oe. JP-A-59-142741, JP-A-61-204
The thickness of the magnetic layer of the magnetic recording medium described in JP-A No. 827 and JP-A-2-257424 is 2 μm or more, and good electromagnetic conversion characteristics cannot be obtained when used for high density recording with a short recording wavelength.

In JP-A-62-154225, in order to prevent the magnetic layer from having a thickness of 0.5 μm or less and the surface electric resistance of the magnetic layer from increasing, a conductive layer is formed between the magnetic layer and the substrate. A magnetic recording medium has been proposed in which an undercoat layer having a thickness including fine powder is equal to or larger than the thickness of the magnetic layer. JP-A-62-222427 discloses a support and an undercoat layer provided on the support and containing an abrasive having an average particle size of 0.5 to 3 μm, and an undercoat layer provided on the undercoat layer. A magnetic recording medium having a magnetic layer containing a magnetic powder and having a thickness of 1 μm or less has been proposed. However, since a part of the abrasive in the undercoat layer protrudes into the magnetic layer, a magnetic head of the magnetic recording medium has been proposed. The cleaning function is also provided.

In the prior art, in order to achieve high density recording by thinning the magnetic layer and at the same time to prevent static electricity in the lower non-magnetic layer, carbon black is included, and polishing is performed to improve the cleaning characteristics and durability. I am adding materials.
In JP-A-63-317926, in order to maintain sufficient durability even if the magnetic layer is made thin, the magnetic layer contains a lubricant such as higher fatty acid or its derivative, fluorine oil and silicone oil. In addition, a non-magnetic inorganic powder having a Mohs hardness of 7 or more is contained alone or in a mixed state, and the maximum particle size between the support and the magnetic layer of the magnetic recording medium does not exceed the film thickness. It has been proposed to provide an undercoat layer composed of a non-magnetic powder such as titanium oxide or carbon black, a nitrocellulose resin, a polyurethane resin having a solubility parameter of 9.0 to 9.5, and a low molecular weight isocyanate compound. The particle size of the non-magnetic powder such as titanium oxide or carbon black to be put in the undercoat layer is 0.25 μm, the thickness of the magnetic layer is 1 μm or less, and the Hc of the magnetic substance is 650 Oe. Further, in JP-A-63-187418, the thickness of the magnetic layer is made as thin as 0.5 μm or less, and an undercoat layer is provided to maintain sufficient durability even if the magnetic layer is made thin. Inorganic powder having a particle size of 0.001 to 1.0 μm (however,
The size of the inorganic powder is not mentioned in the examples. ) Is included, and a magnetic recording medium using Hc1200Oe as a magnetic material is described, but it is necessary to reduce tape edge damage in order to improve tape running durability, and the magnetic recording medium is insufficient. Is.

Further, in the conventional technique, the lower non-magnetic layer is first coated on the non-magnetic support, dried and then, depending on the case,
Since the upper magnetic layer is provided after calendering, the manufacturing process is complicated and there are the following problems. That is, in order to make the magnetic layer thinner, it is conceivable to reduce the coating amount or to add a large amount of solvent to the magnetic coating liquid to reduce the concentration. If you take the former,
When the coating amount is reduced, there is not enough time for leveling after coating, and drying starts, which causes a problem that coating defects such as streaks and marking patterns remain. When the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids, and it is not possible to obtain a sufficient degree of filling of the ferromagnetic powder. This causes various problems such as insufficient strength of the film. One means for solving these problems is disclosed in JP-A-63-1913.
As described in Japanese Patent Publication No. 15, a method has been proposed in which a non-magnetic layer is provided as a lower layer by using a simultaneous multi-layer coating method, and a high-concentration magnetic coating solution is applied thinly.

In the case of the simultaneous multi-layer coating method or the sequential wet coating method, that is, in the case of the so-called Wet on Wet coating method in which the upper layer is coated simultaneously or sequentially while the lower layer is in a wet state, various magnetic layers that have already been laminated are various. Are being studied. However, even if this technique was applied to the lower non-magnetic layer, similarly good results were not obtained. That is, when the lower non-magnetic layer and the upper magnetic layer were provided by Wet on Wet, disturbance occurred at the interface between the two, causing pinholes and repelling of the magnetic layer. Therefore, the inventors of the present invention have made earnest studies on the relationship between the composition of the lower non-magnetic layer and the coating method, and as a result, have found that there is a point in rheological properties, and have reached the present invention.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin layer magnetic recording medium having excellent electromagnetic conversion characteristics such as output and C / N ratio, and good head contact and storage stability. A thin-layer magnetic recording medium having good properties is provided.

[0011]

SUMMARY OF THE INVENTION The above-mentioned object is to realize the magnet of the present invention.
This is achieved by a method of manufacturing a gas recording medium. That is, (1) coating for lower non-recording layer in which powder is dispersed in a binder
Liquid and an upper recording layer in which ferromagnetic powder is dispersed in a binder
Prepare the coating solutions respectively and apply the above-mentioned lower non-recording layer on the support.
Coating solution for the upper recording layer, and then the coating solution for the upper recording layer.
In the method of manufacturing a magnetic recording medium to be coated, the powder is bound.
The coating liquid for the lower non-recording layer dispersed in the mixture is
Has a tropic property and a shear rate of 10^Foursec^-1Shearing on
Stress A10 ^FourAnd shear rate 10 sec^-1Shear stress at
Ratio with A10 A10^Four/ A10 is 100 ≧ A10^Four/ A
10 ≧ 3, and the lower non-recording layer on the support
After applying the coating solution for the coating, the lower non-recording layer obtained is dried.
After that, the dry thickness of the upper recording layer becomes 1.0 μm or less.
The coating liquid for the upper recording layer is applied so that
And a method for manufacturing a magnetic recording medium.

The preferred embodiment of the method of manufacturing the magnetic recording medium of the present invention is as follows. (2) The powder in the lower non-recording layer contains at least carbon black and an inorganic powder having an average primary particle diameter smaller than the dry thickness of the lower non-recording layer, and the coating liquid for the lower non-recording layer and the upper recording layer. 10. The method for producing a magnetic recording medium as described in (1) above, wherein the coating liquid contains a thermosetting polyisocyanate in a binder in an amount of 10 to 70% by weight. (3) The method for producing a magnetic recording medium as described in (1) above, wherein the powder of the coating liquid for the lower non-recording layer contains a non-metal inorganic powder having an average primary particle diameter of 0.08 μm or less. (4) The ferromagnetic powder of the coating liquid for 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, C.
r, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb,
Te, Ba, Ta, W, Re, Au, Pb, Bi, L
a, Ce, Pr, Nd, P, Co, Mn, Zn, Ni,
The method for producing a magnetic recording medium according to (1) above, which contains at least one atom selected from Sr and B. (5) The coating liquid for the lower non-recording layer contains an inorganic powder having a Mohs hardness of 4 or more as a powder.
A method of manufacturing a magnetic recording medium according to 1.

(6) As powder of the coating liquid for the lower non-recording layer, α-alumina, β-alumina having an α-conversion rate of 90% or more,
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, calcium carbonate, calcium sulfate. The method for producing a magnetic recording medium according to (1) above, which comprises at least one kind of inorganic powder selected from the group consisting of barium sulfate and molybdenum disulfide. (7) The method for producing a magnetic recording medium as described in (1) above, wherein the powder of the lower non-recording layer contains a magnetic powder incapable of magnetic recording. (8) The magnetic recording medium as described in (1) above, wherein the coating liquid for the lower non-recording layer contains magnetic powder, and Bm of the lower non-recording layer is 500 gauss or less. Method.

(9) The elastic modulus of the support is 100 to 20.
The method for producing a magnetic recording medium according to (1) above, wherein the magnetic recording medium is 00 Kg / mm ² . (10) The support is made of polyethylene terephthalate, polyethylene naphthalate polyesters, polyolefins, cellulose triacetate, polycarbonate.
The method for producing a magnetic recording medium according to (1) above, wherein the magnetic recording medium is at least one selected from the group consisting of the following:

That is, in the present invention, both the lower non-recording layer coating solution and the upper recording layer coating solution have the constitutions of the embodiments described in (1) above, and the preferred embodiments described in (2) to (8) above are provided. It has been found that, by virtue of having a constitution and having the same or similar thixotropic properties, the interface is not disturbed when applying both paints, pinholes and cissing are not generated, and both head contact can be improved. . That is, in the present invention, the lower non-recording layer after drying has appropriate elasticity and affinity, and the dry thickness of the upper recording layer is 1.0 μm.
It is easy to apply the coating layer having a thickness of m or less.

The thixotropy is also called thixotropy, which is a softening phenomenon of an object accompanied by a recovery and is accompanied by recovery, but it causes softening by increasing the number of strains of the object. The magnetic paint exhibits a typical thixotropic property, and when it is stirred, for example, the internal structure gradually breaks and softens to increase the fluidity. When a magnetic coating is applied on a non-magnetic support and oriented in a magnetic field, the ferromagnetic powder rotates, but at that time, the internal structure is destroyed and the fluidity is considerably increased. Does the conventional lower non-recording layer dispersion exhibit no thixotropy, or is it very small at all? Alternatively, a liquid having an extremely strong thixotropic property such as a liquid containing carbon black has been used. The present inventors have paid attention to the thixotropic properties of these two liquids, and surprisingly, no disturbance occurred at the interface when they were set to the same or similar values. That is, the thixotropy, that is, viscoelasticity of the lower non-recording layer has not been paid attention to in the past, and it has not been particularly controlled.

Here, the same or similar thixotropy means that both the dispersions of the lower non-recording layer and the magnetic coating material of the upper recording layer are not mixed at the interface when they are applied by the Wet on Wet method. It means that the thixotropic properties of liquids are similar. As described above, the basic idea of the present invention is that each of the lower non-recording layer and the upper recording layer has a rheological property specified for each coating solution, the lower non-recording layer has the dispersion, and the upper recording layer has the The magnetic paint is characterized by using the one prepared so as to have thixotropy which is the same or similar to each other at the time of coating, thereby eliminating coating defects, durability, The electromagnetic conversion characteristics such as output improvement can be improved.

Further, the dispersion for forming the lower non-recording layer has a rheological property, that is, a shear rate of 10 ⁴ sec ^-1.
Ratio A10 ⁴ / A10 between shear stress A10 ⁴ and shear stress A10 at a shear rate of 10 sec ⁻¹ is 100 ≧ A
It is adjusted to 10 ⁴ / A10 ≧ 3. Therefore, the rheological properties of the magnetic paint of the upper recording layer can be considered based on the above range. Here, the shear stress with respect to the shear rate is measured by a viscometer, for example, Rotovisc manufactured by HAAKE.
o It is measured with a coaxial cylindrical viscometer such as a viscometer RV-II, and the shear rate is determined by the diameter of the inner cylinder and the outer cylinder, the clearance and the rotation speed. The following relationship exists between the shear rate, apparent viscosity and shear stress.

[0019] A = η · D (A: shear stress, eta: Viscosity, D: shear rate) D = dv / dr (v : peripheral speed, r: radius) Accordingly, A10, A10 ⁴ each A = 10η , A = 1
0 ⁴ refers to eta, A10 ⁴ / A10 ratio represents the degree of thixotropy, the smaller the thixotropy large,
The smaller the ratio, the greater the thixotropic property. Conventionally, nonmagnetic dispersions have only weak thixotropic properties, and A10 ⁴ / A10 is about 200 to 500. When A10 ⁴ / A10 is large, the dispersion approaches a Newtonian fluid, making simultaneous multilayer coating difficult when the upper layer is a magnetic layer. If the viscosity is too low, the thixotropy is so strong that it is impossible to achieve both a viscosity that allows simultaneous multilayer coating and a viscosity that allows liquid feeding. There are the following three technologies (hereinafter referred to as “invention” for convenience, but different from the present invention) as specific technical means for imparting such thixotropy. The magnetic recording medium of the present invention is not limited to these three inventions, and the essence thereof is to make the thixotropic property of the dispersion liquid the same as or close to the thixotropic property of the magnetic paint. More specifically, the value is in the range of A10 ⁴ / A10, and these are merely exemplary inventions.

The lower non-recording layer powder contains at least carbon black and an inorganic powder having an average primary particle size smaller than the dry thickness of the lower non-recording layer, and the lower non-recording layer and the upper recording layer are thermoset poly A method for producing a magnetic recording medium, characterized in that the binder contains 10 to 70% by weight of the binder.

The dry thickness of the upper recording layer is 1.0 μm.
A method for producing a magnetic recording medium, characterized in that the powder of the lower non-recording layer contains a non-metal inorganic powder having an average primary particle diameter of 0.08 μm or less.

A method for manufacturing a magnetic recording medium, wherein the saturation maximum magnetic flux density Bm of the lower non-recording layer is 500 gauss or less, preferably 30 to 500 gauss.

That is, in the method for producing a magnetic recording medium described above, as the powder to be dispersed, carbon black which greatly imparts thixotropic properties and inorganic powder having a small thixotropic property are used and polyisocyanate is used. The dispersion liquid prepared according to 1. is used. As a result, the upper recording layer can be made thin, and by using polyisocyanate in the upper recording layer and the lower non-recording layer, the head contact is maintained well, the storage stability at high temperature and high humidity is ensured, and an appropriate rigidity is obtained. A flexible magnetic recording medium is obtained and durability is improved.

The method for producing the magnetic recording medium described above uses a dispersion prepared by reducing the particle size of the dispersed non-metallic inorganic powder and adjusting the thixotropy thereof. That is, in order to perform coating after drying, it is important to combine the rheological properties of the upper recording layer and the lower non-recording layer. The magnetic paint has a very strong thixotropic property because of the structural viscosity in the magnetic paint due to the magnetic attraction of the ferromagnetic powder. On the other hand, the dispersion liquid for the lower non-recording layer has no magnetic attraction force, and thus has only weak thixotropic property. When coating was performed in this state, the upper recording layer and the lower non-recording layer were significantly mixed in the vicinity of the interface, and severe agglomeration streaks were generated during orientation after coating, and sufficient surface properties could not be obtained. . In order to solve such a problem, the present invention uses a non-metal inorganic powder having an average primary particle diameter of 0.08 μm or less. In the present invention, a non-metallic inorganic powder can be mainly used and carbon black can be used in combination.

In the method of manufacturing the magnetic recording medium described above, the maximum saturation magnetic flux density Bm of the lower non-recording layer is set to 30 to 500 Gauss. Specifically, the magnetic recording medium satisfies A10 ⁴ / A10 and is magnetically recorded. Is used, and a dispersion liquid whose thixotropic property is adjusted by using a magnetic powder that does not adversely affect the upper recording layer is used. That is, in order to set the lower non-recording layer to 30 to 500 Gauss, use a magnetic substance having a low saturation magnetization (σ _S ) or prepare a dispersion liquid in which the filling ratio of the magnetic substance in the lower non-recording layer is reduced. Achieved by

The inventions of these, A10 ⁴ / A1
Although preferred means for adjusting 0 to the above-mentioned range are shown, for example, these have a relationship (including overlapping descriptions) with the following factors, and by variously selecting, the desired A10 A dispersion having ⁴ / A10 and a magnetic paint can be obtained, and a magnetic recording medium having desired characteristics can be produced.

Examples of the factor include (1) particle size (specific surface area, average primary particle diameter, etc.), (2) structure (oil absorption amount, particle morphology, etc.), for inorganic powder or magnetic powder to be dispersed. (3) Properties of the powder surface (pH, loss on heating, etc.), (4) Particle suction force (σ _S, etc.), and binders (1) Molecular weight, (2) Functional group type, solvent, etc. Regarding (1) type (polarity, etc.), (2) binder solubility, (3) solvent formulation amount, water content, etc.

That is, the ratio of A10 ⁴ / A10 is, for example,
Various parameters such as the molecular weight of the binder, the structure, the affinity with the solvent, the water content are involved, but the largest contribution is to the powder to be filled, the surface properties of the dispersed powder, the particle size,
The amount of oil absorption, affinity with the solvent, etc. are related. The smaller the particle size, the stronger the thixotropy. In addition, carbon black having a large oil absorption and rich in structure has a very strong thixotropy. In addition, magnetic particles exhibit 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 adjust the thixotropy of the coating liquid for the lower non-recording layer and the magnetic coating material for the upper recording layer within a predetermined range.

Next, preferred embodiments of the inventions 1 to 3 will be described below. First, the invention will be described. In addition, the average primary particle diameter means the average of the particle diameters determined from the distribution of single particles having no fusion or association.

The carbon black used in the dispersion has an average primary particle diameter of 30 mμ or less and a specific surface area of 15
0~400m ² / g, preferably 180~350m ² /
g, DBP oil absorption is 40 to 300 ml / 100 g, preferably 45 to 200 ml / 100 g. Particle size is 3
It is 0 mμ or less, preferably 5 to 27 mμ, and more preferably 10 to 22 mμ. The pH is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc. The blending ratio of carbon black and inorganic powder is preferably 10:90 to 80:20 by weight, more preferably 15:85 to 60:40. Further, it is preferable that the carbon black is previously dispersed with a binder having good dispersion and then mixed with an inorganic powder to be dispersed.

The particle size of the inorganic powder is preferably 0.01 to 1 μm. A particularly preferred range is from 0.02 to 0.5 μm, and a more preferred range is from 0.02 to 0.08 μm. Further, if necessary, particles having different particle diameters may be combined, or a single particle may have a wide particle diameter distribution to obtain the same effect. Tap density is 0.05-2g / c
c, preferably 0.2-1.5 g / cc. The moisture content is 0.
1-5%, preferably 0.2-3%. pH is 2-11.
Specific surface area is 1 to 100 m ² / g, preferably 5 to 50 m
² / g, and more preferably 7 to 40 m ² / g. The crystallite size is preferably 0.01 μ to 2 μ. Oil absorption using DBP is 5 to 100 ml / 100 g, preferably 10 to 100 ml / 100 g.
~ 80ml / 100g, more preferably 20-60ml
/ 100 g. Specific gravity is 1 to 12, preferably 2 to 8
Is. The shape may be any of a needle shape, a spherical shape, and a dice shape. The above-mentioned inorganic powder does not necessarily need to be 100% pure, and the surface may be treated with another compound according to the purpose. At that time, if the purity is 70% or more, the effect is not reduced. For example, when using titanium oxide,
It is commonly used to treat the surface with alumina. The ignition loss is preferably 20% or less. The Mohs hardness of the inorganic powder used in the present invention is preferably 4 or more. As the inorganic powder, in particular, titanium oxide,
Zinc oxide, tin oxide and aluminum oxide have given good results. In the present invention, in addition to the non-magnetic powder consisting of carbon black and inorganic powder, any other non-magnetic powder can be used if desired.

The non-magnetic powder is used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.2 with respect to the binder. The binder used in the lower non-magnetic layer of the present invention is preferably used in the range of 10 to 100% by weight, more preferably in the range of 13 to 50% by weight based on the non-magnetic powder.
It is preferable to use 5 to 25% when using a vinyl chloride resin, 1 to 25% when using a polyurethane resin, and 1 to 15% for polyisocyanate in combination. The amount of the polyisocyanate contained in the lower non-magnetic layer of the present invention is preferably in the range of 10 to 70% by weight, more preferably 20 to 50% by weight of the binder.

Regarding the invention of (1), it is preferable that the magnetic coating material and the dispersion liquid contain a polyisocyanate. Also,
Carbon black having an average primary particle diameter of 0.03 μm or less, and more preferably 0.023 μm or less, in a weight ratio to the inorganic powder, inorganic powder: carbon black = 99: 1 to
It can be used in the range of 70:30. Especially preferably, it is 95: 5 to 80:20. If the carbon black content is 1% by weight or less, it means that the carbon black content is not substantially contained, and the desired thixotropic property cannot be obtained. Also,
If the amount is 30% by weight or more, the surface properties of the obtained magnetic recording medium will be insufficient.

As the inorganic powder, especially Si0₂, Ti
O₂, Α-alumina, α-Fe₂O₃, Boron nitride, tin oxide
Is preferred. The average primary particle diameter of the inorganic powder is 0.08μ
m or less, but if necessary, inorganic powder other than this size
A wide range of particle sizes can be obtained by combining various powders or using a single inorganic powder.
You can also get the same effect. The inorganic powder
Has a tap density of 0.05 to 2 g / cc, preferably 0.
2 to 1.5 g / cc, water content is 0.1 to 5%, preferably
Is 0.2 to 3%, pH is 2 to 11, specific surface area is 1 to 10.
0m²/ G, preferably 5 to 50 m²/ G, more preferred
Kuha 7-40m ²/ G. Crystallite size is 0.01
μ to 2μ is preferable. The oil absorption using DBP is 5-10
0 ml / 100 g, preferably 10-80 ml / 100
g, more preferably 20 to 60 ml / 100 g.
The specific gravity is 2-8. The shapes are needle-shaped, spherical, dice-shaped,
Any of The above inorganic powder is not always 100%
It does not have to be pure, and the surface can be treated with other compounds depending on the purpose.
May be processed in. At that time, if the purity is 70% or more
It does not diminish the effect. For example, titanium oxide
When used, it is common to treat the surface with alumina.
It is used. Ignition loss is preferably 20% or less
Good. It is preferable that the inorganic powder has a Mohs hardness of 4 or more.
Good.

The specific surface area of carbon black which can be used in combination is 100 to 500, preferably 150 to 400 m ² / gD.
The BP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. Particle size is 5mμ ~
It is 30 mμ, preferably 10 to 50 mμ, more preferably 10 to 40 mμ. The pH is preferably 2 to 10, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc. These non-magnetic powders have a weight ratio to the binder of 20 to 0.1, preferably 10 to 0.5, more preferably 8 to 1, and a volume ratio of 10 to 0.2. Used.

With respect to the invention of 30, the lower non-recording layer is 30
The setting of ~ 500 gauss can be achieved by using a magnetic material having a low saturation magnetization ([sigma] _S ) or reducing the filling ratio of the magnetic material in the lower non-recording layer. In this case, the non-magnetic material is 100 to 500 parts by weight with respect to 100 parts by weight of the magnetic material.
It is preferably 0 part by weight. The non-magnetic material preferably contains a non-magnetic powder in addition to the binder, an inorganic powder,
Carbon black and the like are preferred. As the magnetic material, for example, a Co-γ-Fe ₂ O ₃ magnetic material is preferable, and the coercive force thereof is not particularly limited, but is preferably about 400 Oe to 1500 Oe. Also, hexagonal barium ferrite can be used for the lower non-recording layer. Organic powder H at that time
There is no limitation on c, but 800 O when BaFe is used.
e or more and 4500 Oe or less are preferable. The Hc of the upper recording layer is 1200 Oe to 3000 Oe, and the Bm is 200 to
It is preferably 4500 gauss.

When carbon black is used, the amount based on the magnetic material is 0.1 for both the lower non-recording layer and the upper recording layer.
Preferably, it is used at ３０30%. In addition to imparting thixotropy, carbon black has functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different characteristics, such as particle size, oil absorption, conductivity, pH, etc., in the lower non-recording layer and the upper recording layer by changing types, amounts and combinations. Of course, it is possible to use them properly according to the purpose. For example, carbon black having a high conductivity is used for the lower non-recording layer to prevent charging, and carbon black having a large particle size is used for the upper recording layer to lower the friction coefficient.

The physical properties of the inorganic powder are as follows. The particle diameter is preferably 0.01 to 2 .mu.m, but if necessary, various particles having different particle diameters may be combined, or a single particle may have a wide particle diameter distribution to obtain the same effect. The tap density is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. Water content is 0.1-5%, preferably 0.2-3%. pH is 2-11. Specific surface area is 1
100 m ² / g, preferably from 5 to 50 m ² / g, more preferably 7~40m ² / g. The crystallite size is 0.
01μ to 2μ is preferable. The oil absorption using DBP is 5
100 ml / 100 g, preferably 10-80 ml / 1
The amount is 00 g, more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 2 to 8. The shape may be any of a needle shape, a spherical shape, and a dice shape, but a needle shape is preferable for improving magnetic properties, and a size and a shape close to the shape of the ferromagnetic powder are particularly preferable. The ratio of the major axis length of the acicular inorganic powder to the length is 0.5 to 3
Is particularly preferred. The above inorganic powder is not necessarily 10
It need not be 0% pure, and the surface may be treated with other compounds depending on the purpose. At that time, if the purity is 70% or more, the effect is not reduced. For example, when using titanium oxide, it is generally used to treat the surface with alumina. The ignition loss is preferably 20% or less. The Mohs hardness of the inorganic powder used in the present invention is preferably 4 or more.

The physical properties of the carbon black that can be used are as follows. The specific surface area is 100 to 500, preferably 150 to 400 m ² / g, and the DBP oil absorption is 20 to 40.
0 ml / 100 g, preferably 30-200 ml / 10
0 g. The particle size is 5 to 80 mμ, preferably 1
It is 0 to 50 mμ, and more preferably 10 to 40 mμ. The pH is preferably 2 to 10, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc.

Other non-magnetic powders that can be used in the present invention include organic powders such as acrylic styrene resin powders, benzoguanamine resin powders, melamine resin powders and phthalocyanine pigments. Resin powder, polyamide resin powder, polyimide resin powder, and polyfluorinated ethylene resin are used. The production method is described in Japanese Patent Application Laid-Open No. 62-18564.
JP-A-60-255827 and JP-A-60-255
No. 827 can be used. These non-magnetic powders have a weight ratio of 0.
It is used in a range of 1 to 10 and a volume ratio of 10 to 0.2.

General items common to the present invention will be described below. As the inorganic powder that can be used in the present invention, specifically, metal oxides, metal carbonates, metal sulfates,
It is an inorganic compound powder such as metal nitride, metal carbide, metal sulfide, and the like. As the inorganic compound, for example, a pregelatinization rate of 90%
The above α-alumina, 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, calcium carbonate, calcium sulfate, barium sulfate, molybdenum sulfide and the like are used alone or in combination.

Specific examples of the inorganic powder used in the present invention include AKP-20, AKP-30 manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, HiT-100, manufactured by Nippon Chemical Industry: G5, G7, S-1, manufactured by Toda Kogyo: TF
-100, TF-120, TF-140, manufactured by Ishihara Sangyo:
TTO-55, FT-1000, FT-2000, FT
L-100, FTL-200, M-1, S-1, SN-
100, manufactured by Titanium Industry: ECT-52, STT-4D,
STT-30, STT-65C, Y-LOP, Y-LO
Α-hematite obtained from P, manufactured by Mitsubishi Metals: T-1,
Nippon Shokubai: NS-O, NS-3Y, NS-8Y and the like.

As the carbon black used in the present invention, a furnace for rubber, a thermal for rubber, a black for color, an acetylene black, etc. can be used.
Specific examples of the carbon black used in the present invention include: BLACKPEARLS 200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 880, 7
00, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo:
$ 3250B, $ 950, $ 650B, $ 970B, $
850B, manufactured by Columbian Carbon Co .: CONDUCT
EX SC, RAVEN 8800, 8000, 700
0, 5750, 5250, 3500, 2100, 200
0, 1800, 1500, 1255, 1250, manufactured by Akzo Ketjen Black EC. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by partially graphitizing the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

As the ferromagnetic powder used in the upper recording layer of the present invention, γ-FeOx (x = 1.33 to 1.5), Co
Known ferromagnetic powders such as modified γ-FeOx (x = 1.33 to 1.5), ferromagnetic alloy fine powder containing Fe or Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite are used. it can. These ferromagnetic powders include Al, Si, S, Sc,
Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag,
Sn, Sb, Te, Ba, Ta, W, Re, Au, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. These ferromagnetic fine powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before dispersion. Specifically,
-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 4
7-22062, JP-B 47-22513, JP-B 46-28466, JP-B 46-38755, JP-B 47-4286, JP-B 47-12422, JP-B 47-17284, JP-B 47 -18509, Japanese Patent Publication No. 47-18573, Japanese Patent Publication No. 39-10307,
JP-B-48-39639, U.S. Pat.
No. 3031341, No. 3100194, No. 32
No. 42005, No. 3389014 and the like.

Of the above-mentioned ferromagnetic powder, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of a ferromagnetic alloy fine powder can be used, and the following method can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, a metal carbonyl compound Pyrolysis method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, evaporation of the metal in a low pressure inert gas to produce a fine powder. How to get it. The ferromagnetic alloy powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it. Any of the method of forming the oxide film on the surface by adjusting the partial pressure of oxygen gas and the inert gas without using an organic solvent can be used.

The ferromagnetic powder of the upper recording layer of the present invention is BET
The specific surface area according to the method is 25 to 80 m ² / g,
It is preferably 35 to 60 m ² / g. When it is 25 or less, noise becomes high, and when it is 80 or more, surface properties are difficult to obtain, which is not preferable. The ferromagnetic powder of the upper recording layer of the present invention has a crystallite size of 450 to 100 angstroms, preferably 350 to 150 angstroms. Σ _{S of the} iron oxide magnetic powder is 50 emu / g or more, preferably 70 em
u / g or more, 100e in the case of ferromagnetic metal fine powder
mu / g or more is preferable.

The r1500 of the ferromagnetic powder is preferably 1.5 or less. More preferably r1500 is 1.
It is 0 or less. r1500 indicates the percentage of the amount of magnetization remaining without being reversed when a magnetic field of 1500 Oe is applied in the opposite direction after the magnetic recording medium is saturated.

The water content of the ferromagnetic powder is preferably 0.01 to 2%. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of binder. The tap density of γ iron oxide is preferably 0.5 g / cc or more, more preferably 0.8 g / cc or more. When using gamma iron oxide, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%. The amount of cobalt atom to iron atom is 0 to 15%, preferably 2 to 8%.

The pH of the ferromagnetic powder is preferably optimized by the combination with the binder used. The range is 4-1
2, but preferably 6 to 10. The ferromagnetic powder may be surface-treated with Al, Si, P or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and the surface treatment is preferable because the adsorption of the lubricant such as fatty acid becomes 100 mg / m ² or less. Soluble Na, Ca, Fe, Ni,
It may contain inorganic ions such as Sr, but 500pp
If it is m or less, the characteristics are not particularly affected.

Further, the ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the above-mentioned characteristics regarding the particle size are satisfied. In order to achieve an SFD of 0.6 or less for the ferromagnetic powder, it is necessary to reduce the Hc distribution of the ferromagnetic powder. For that purpose, there are methods such as improving the particle size distribution of goethite, preventing the sintering of γ-hematite, and slowing the deposition rate of cobalt for cobalt-modified iron oxide as compared with the conventional method.

The present invention also provides barium ferrite, strontium ferrite, and tabular hexagonal ferrite.
Hexagonal Co powder can be used. When barium ferrite is used, its particle size is 0.001 to 1 μm and the thickness is 1/2 to 1/20 of the diameter. Specific gravity is 4-6g
/ Cc, the specific surface area is 1 to 60 m ² / g.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 100.
0-200000, preferably 10,000-10000
0, the degree of polymerization is about 50 to 1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, and various rubber resins. Also,
Examples of the thermosetting resin or reactive resin are phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin and isocyanate. Examples thereof include a mixture of prepolymers, a mixture of polyester polyols and polyisocyanates, a mixture of polyurethanes and polyisocyanates, and the like.

These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the first layer or the second layer. These examples and the manufacturing method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but at least one selected from the group consisting of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer is preferred. Examples include a combination of a seed and a polyurethane resin, or a combination of these and a polyisocyanate.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all of the binders listed here, COO may be added as necessary to obtain better dispersibility and durability.
_{M, SO 3 M, OSO 3} M, P = O (OM) 2, O-P
═O (OM) ₂ (M is hydrogen atom or alkali metal base for the above), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group for the above), epoxy group, SH, CN, etc. It is preferable to use at least one polar group introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbide.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, manufactured by Denki Kagaku: 1000W, DX80,
DX81, DX82, DX83, manufactured by Zeon Corporation: MR
110, MR100, 400X110A, manufactured by Nippon Polyurethane Co., Ltd .: Nipporan N2301, N2302, N23
04, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105,
T-R3080, T-5201, Burnock D-40
0, D-210-80, Crisbon 6109, 720
9. Toyobo: Byron UR8200, UR830
0, RV530, RV280, manufactured by Dainichiseika Co., Ltd .: Daifureramine 4020, 5020, 5100, 5300, 90
20,9022,7020, Mitsubishi Kasei: MX500
4. Sanyo Kasei Co., Ltd .: Samprene SP-150; Asahi Kasei Co., Ltd .: Saran F310, F210.

The binder used in the upper magnetic layer of the present invention is used in the range of 5 to 50% by weight, preferably 10 to 30% by weight, based on the ferromagnetic powder. When using a vinyl chloride resin, it is preferable to use them in a combination of 5 to 30% by weight, in the case of using a polyurethane resin, 2 to 20% by weight, and for polyisocyanate in a range of 2 to 20% by weight.

In the present invention, when a polyurethane resin is used, the glass transition temperature is -50 to 100 ° C, the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10 kg.
/ Cm ² , and the yield point is preferably 0.05 to 10 Kg / cm ² . The magnetic recording medium of the present invention comprises two layers. Therefore,
Binder amount, vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, molecular weight of each resin forming the magnetic layer, polar group amount, or the physical properties of the resin described above. It is of course possible to change the characteristics and the like of the intermediate layer and the upper magnetic layer as needed.

The polyisocyanates used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
5-diisocyanate, o-toluenediisocyanate,
Isophorone diisocyanate, isocyanates such as triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and
A polyisocyanate produced by condensation of isocyanates can be used. Commercially available trade names of these isocyanates are: Nippon Polyurethane Co .: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Yakuhin: Takenate D-10.
2, Takenate D-110N, Takenate D-200,
Takenate D-202, manufactured by Sumitomo Bayer: Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, and the like. These may 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.

Carbon black used in the upper recording layer of the present invention, that is, in the magnetic layer, may be furnace for rubber, thermal for rubber, black for color, acetylene black or the like. Specific surface area is 5 to 500 m ² / g, D
BP oil absorption is 10-400ml / 100g, particle size is 5
mμ ~ 300mμ, pH 2 ~ 10, water content 0.1 ~
The tap density is preferably 10 to 1 g / cc.
Specific examples of the carbon black used in the present invention include BLACKPEARLS200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 700, V
ULCAN XC-72, manufactured by Asahi Carbon Co., Ltd .: 80,
60, 55, 50, 35, manufactured by Mitsubishi Kasei Kogyo:
2400B, 2300, 900, 1000, 3
0, 40, 10B, manufactured by Conlonvia Carbon Co .: C
ONDUCTEX SC, RAVEN 150, 50,
40, 15 and the like. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be graphitized on a part of the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint.
These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the ferromagnetic powder. Carbon black has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving film strength, etc.
These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention, the first layer, ie, the lower non-recording layer, the second layer, that is, the type, amount, change the combination in the upper recording layer, particle size, oil absorption, conductivity, Of course, it is possible to use differently according to the purpose based on the above-mentioned various properties such as pH. For example, carbon black having a high conductivity is used for the lower non-recording layer to prevent charging, and carbon black having a large particle size is used for the upper recording layer to lower the friction coefficient.
The carbon black that can be used in the upper recording layer of the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

As the abrasive used for the upper recording layer of the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond having an α conversion of 90% or more, Known materials having a Mohs hardness of 6 or more such as silicon nitride, silicon carbide titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 9
If it is 0% or more, the effect is the same. The particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution to obtain the same effect. . Tap density is 0.3 to 2 g / cc, water content is 0.1 to 5%, pH is 2 to 11, specific surface area is 1 to 30 m.
² / g is preferred. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness.

Specific examples of the abrasive used in the present invention and
Then, Sumitomo Chemical Co., Ltd .: AKP-20, AKP-30,
AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd .: G
5, G7, S-1, manufactured by Toda Kogyo: 100ED, 140
ED, etc. The abrasive used in the present invention is
Change the type, amount and combination of the first layer and the second layer
Of course, it is possible to use them properly. these
Abrasive is dispersed in binder beforehand and then magnetic paint
It does not matter if it is added inside. On the magnetic recording medium of the present invention
The abrasive present on the surface of the recording layer and on the end face of the upper recording layer
5 pieces / 100 μm ²The above is preferable.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, fluorinated graphite, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate ester and its alkali metal salt,
Alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt, monobasic fatty acid having 10 to 24 carbon atoms (may contain unsaturated bond or may be branched) ) And their metal salts (Li, Na,
K, Cu, etc.), or a monovalent, divalent, trivalent, tetravalent, pentavalent or hexavalent alcohol having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched), carbon Number 1
Alkoxy alcohols having 2 to 22 carbon atoms, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and monovalent, divalent, trivalent, having 2 to 12 carbon atoms; Mono-fatty acid ester, di-fatty acid ester or tri-fatty acid ester comprising any one of tetrahydric, pentahydric and hexahydric alcohols (which may contain an unsaturated bond or may be branched), alkylene oxide polymer Fatty acid esters of monoalkyl ethers of 8 to 2 carbon atoms
2 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms, and the like can be used. Specific examples of these are lauric acid,
Myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, ann Hydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol.

Further, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfonium, anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, and phosphoric acid ester group, amino acids, aminosulfonic acids, sulfuric acid of aminoalcohol, or the like. Amphoteric surfactants such as phosphoric acid esters and alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in the lower non-recording layer and the upper recording layer in different types and amounts according to need. For example, the lower non-recording layer and the upper recording layer control bleeding to the surface using fatty acids having different melting points, control bleeding to the surface using esters with different boiling points and polarities, and adjust the amount of surfactant. By doing so, it is conceivable to improve the stability of coating, to increase the amount of lubricant added in the lower non-recording layer to improve the lubricating effect, and of course, the present invention is not limited to the examples shown here.

All or part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. In some cases, it may be added in a kneading step using a binder and a solvent, in a dispersing step, after a dispersing step, or just before coating. Examples of commercial products of these lubricants used in the present invention are: NAA-102, NAA-415, NAA-31 manufactured by NOF CORPORATION.
2, NAA-160, NAA-180, NAA-17
4, NAA-175, NAA-222, NAA-34,
NAA-35, NAA-171, NAA-122, NA
A-142, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, Nymeen L-201, Nymeen L-202, Nymeen S-202. , Nonion E-208, Nonion P-20
8, nonion S-207, nonion K-204, nonion NS-202, nonion NS-210, nonion HS
-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP-60R, nonion O
P-80R, Nonion OP-85R, Nonion LT-2
21, nonion ST-221, nonion OT-221,
Monogly MB, Nonion DS-60, Anon BF, Anon LG, Butyl stearate, Butyl laurate, Erucic acid, Kanto Chemical Co., Ltd .: Oleic acid, Takemoto Yushi Co., Ltd .: FA
L-205, FAL-123, manufactured by Shin Nippon Rika Co., Ltd .: Engerb LO, Engerb IPM, Sanso Sizer E4
030, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, KF-96, KF-
96L, KF-96H, KF410, KF420, KF
965, KF54, KF50, KF56, KF-90
7, KF-851, X-22-819, X-22-82
2, KF-905, KF-700, KF-393, KF
-857, KF-860, KF-865, X-22-9
80, KF-101, KF-102, KF-103, X
-22-3710, X-22-3715, KF-91
0, KF-3935, Lion Armor Co., Ltd .: Armide P, Armide C, Armoslip CP, Lion Yushi Co., Ltd .: Duomin TDO, Nisshin Oil Co., Ltd .: BA-41
G, Sanyo Chemical Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, Ionette MO
-200, IONET DL-200, IONET DS-
300, Ionet DS-1000, Ionet DO-
For example, 200 is given.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene, etc. Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The kind and amount of the organic solvent used in the present invention may be changed between the upper recording layer and the lower non-recording layer if necessary. A solvent with high volatility is used for the lower non-recording layer to improve the surface property, a solvent with high surface tension (cyclohexanone, dioxane, etc.) is used for the upper recording layer to improve coating stability, and the solubility parameter of the upper recording layer As an example thereof, a high solvent may be used to increase the filling degree, but it goes without saying that the present invention is not limited to these examples.

The thickness of the magnetic recording medium of the present invention is 1-100 μm, preferably 4-80 μm for the non-magnetic support, and 0.5 μm-10 μm, preferably 1-5 for the lower non-recording layer.
μm, the upper recording layer is 0.05 μm or more and 1.0 μm or less,
The thickness is preferably 0.05 μm or more and 0.6 μm or less, more preferably 0.05 μm or more and 0.3 μm or less. The total thickness of the upper recording layer and the lower non-recording layer is 1/100 to 2 times the thickness of the nonmagnetic support. Also,
An undercoat layer may be provided between the non-magnetic support and the lower non-recording layer to improve adhesion. The thickness of these is 0.0
It is 1 to 2 μm, preferably 0.05 to 0.5 μm.
Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1-2 μm,
It is preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used.

The non-magnetic support used in the present invention is a known polyester such as polyethylene terephthalate, polyethylene naphthalate, etc., polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide and the like. The film can be used. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. In order to achieve the object of the present invention, the nonmagnetic support has a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less.
You need to use: Further, it is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support, if necessary. Examples of these fillers include Ca,
In addition to oxides and carbonates such as Si and Ti, organic fine powders such as acrylics can be used. The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 5 to 5.
0 Kg / mm ² , F-5 value in the tape width direction is preferably 3 to 30 Kg / mm ² , and F-5 value in the tape longitudinal direction.
The value is generally higher than the F-5 value in the tape width direction, but this is not the case when it is necessary to particularly increase the strength in the width direction.

The heat shrinkage ratio of the non-magnetic support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3.
% Or less, more preferably 1.5% or less, and the heat shrinkage percentage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5-100 in both directions
Kg / mm ^2, an elastic modulus 100~2000Kg / mm ²
Is preferred.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but a strong kneading force such as a continuous kneader or a pressure kneader is used in the kneading step. The high Br of the magnetic recording medium of the present invention can be obtained by using the material having the same. When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferable) and 100 parts of the ferromagnetic powder are mixed in the range of 15 to 500 parts. It is processed. For details of these kneading processes, see JP-A-1-106338,
It is described in JP-A-64-79274.

In the present invention, the following coating method can be used for more efficient production. The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. The lower non-recording layer is first coated by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for coating a magnetic coating, and after the lower non-recording layer is dried, Japanese Patent Publication No. 46186 / JP-A-6
The upper recording layer is coated by a support pressure type extrusion coating device disclosed in JP-A No. 0-238179 and JP-A-2-265672.

In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000G or more solenoid and 200
It is preferable to use a cobalt magnet of 0 G or more in combination, and it is preferable to further provide an appropriate drying step in advance before orientation so that the orientation after drying becomes the highest.

Further, a heat-resistant plastic roll of epoxy, polyimide, polyamide, polyimide amide or the like is used as the calendering roll. Further, it is also possible to perform processing by using metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the speed is 20 m / cm.
/ Min to 700 m / min.

The friction coefficient of the upper recording layer surface of the magnetic recording medium of the present invention and the opposite surface thereof to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ⁻⁵ to 10 ⁻¹² ohm. / Sq, the elastic modulus at 0.5% elongation of the upper recording layer is preferably 100 to 2000 Kg / mm ^{2 in} both the running direction and the width direction, the breaking strength is preferably 1 to 30 Kg / cm ² , and the elastic modulus of the magnetic recording medium. Is preferably 100-1500K in both the running and longitudinal directions
g / mm ² , residual spread is preferably 0.5% or less, 10
Heat shrinkage at any temperature below 0 ° C is preferably 1%
Or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The residual solvent contained in the upper recording layer is preferably 100 mg / m ² or less, more preferably 10 mg.
/ M ² or less, and the residual solvent contained in the upper recording layer is preferably smaller than the residual solvent contained in the lower non-recording layer.

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 5
When measured with KOe, the squareness ratio in the tape running direction is 0.
It is 70 or more, preferably 0.80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less.

The magnetic recording medium of the present invention has an upper recording layer and a lower non-recording layer, but it is easily presumed that the physical properties of the lower non-recording layer and the upper recording layer can be changed according to the purpose. That is. For example, the elastic modulus of the upper recording layer is increased to improve running durability, and at the same time, the elastic modulus of the lower non-recording layer is made lower than that of the upper recording layer to improve the contact of the magnetic recording medium with the head.

[0079]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. still,
"Parts" indicate parts by weight.

Examples described in the present invention will be described below. Example 1 Lower non-recording layer A Inorganic powder Fe ₂ O ₃ 80 parts Average particle size 0.27 μ BET specific surface area 18 m ² / g pH 5.5 Carbon black 20 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8 .0 BET method by a specific surface area of 250 meters ² / g volatiles 1.5% vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - polar groups of 5 × 10 ^-6 eq Composition ratio 86: 13: 1 Polymerization degree 400 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content Butyl stearate 1 part Stearic acid 1 part Copper oleate 1 part Methyl ethyl ketone 200 parts

Upper recording layer A Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe, specific surface area by BET method 60 m ² / g Crystallite size 195Å Particle size (major axis diameter) 0.20 μ, acicular ratio 10 σ _S : 130 emu / g vinyl chloride copolymer 12 parts —SO ₃ Na content: 1 × 10 ⁻⁴ eq / g degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone Polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-alumina (particle size 0.3 μm) 2 parts Carbon black (particle size 0.10 μm) 5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts

With respect to the coating material for the lower non-recording layer A, the respective components were kneaded with a continuous kneader and then dispersed using a sand mill. 5% of polyisocyanate was added to the obtained dispersion.
Parts, and 40 parts of butyl acetate to each part
The coating liquid for forming the lower non-recording layer was prepared by filtering using a filter having an average pore size of μm. The components of the above magnetic coating material for upper recording layer A were kneaded with a continuous kneader and then dispersed using a sand mill. To the resulting dispersion, 6 parts of polyisocyanate was added, and 40 parts of butyl acetate was added to each, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating liquid for forming an upper recording layer.

Example 1 was by sequential coating. That is, the coating liquid for forming the lower non-recording layer was applied on a polyethylene terephthalate support having a thickness of 7 μm and a center line surface roughness of 0.01 μ so that the thickness after drying was 2.7 μm. After drying, it was wound and calendered. afterwards,
After curing treatment at 80 ° C. for 24 hours, coating was performed so that the thickness of the recording layer of the upper magnetic layer was 0.5 μm, the same orientation and drying as in Example 1 were performed, and the film was wound. afterwards,
The sample was processed with a calendar at a temperature of 90 ° C. and slit into a width of 8 mm to manufacture an 8 mm video tape of sample #Example 1.

Comparative Example 1-1 A coating material for the lower non-recording layer A and a coating material for the upper recording layer A were prepared in the same manner as in the above-mentioned Example 1, and the obtained coating material for the lower non-recording layer A was mainly applied to a thickness of 7 μm. The thickness after drying is 3μ on a polyethylene terephthalate support with a line surface roughness of 0.01μ.
m, and immediately after that, the coating material for the upper recording layer A was applied simultaneously on the lower non-recording layer so that the thickness after drying was 0.2 μm, and both layers were still wet. And a cobalt magnet with a magnetic force of 3000G and 150
After being oriented by a solenoid having a magnetic force of 0 G and dried, a temperature of 90 is obtained with a 7-stage calender consisting of only metal rolls.
The sample was treated at a temperature of ℃ and slit into a width of 8 mm to manufacture an 8 mm video tape of Sample #Comparative Example 1-1. Comparative Examples 1-2 and 1-3 Only the coating material for the upper recording layer A was applied on a polyethylene terephthalate support having a thickness of 7 μm and a center line surface roughness of 0.01 μ so that the thickness after drying was 0.5 μm. It is applied to the above, and while being in a wet state, it is oriented by a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G, dried, and then treated at a temperature of 90 ° C. with a 7-stage calender consisting of only metal rolls. , 8 mm width, and 8 mm video tapes of sample #comparative examples 1-2 and 1-3 were manufactured.

The performance of the samples of Example 1 and Comparative Examples 1-1, 1-2 and 1-3 was evaluated as follows. Table 1 shows the results. In addition, A10 ⁴ / A1 of the coating liquid for the upper recording layer
The 0 ratio is also described. Evaluation method Storage stability evaluation method Samples were stored in an atmosphere of 60 ° C. and 90% RH for 48 hours, and then in an atmosphere of 23 ° C. and 70% RH, 8 mm video deck FUJIX8 manufactured by Fuji Photo Film Co., Ltd.
0 was run for 10p. During that time, the decrease in output was measured, and the dirt on each part in the deck after running was evaluated, and three grades of ◯, Δ, and × were performed according to the degree of dirt.

Electromagnetic conversion characteristics 7 MHz output A 7 MHz signal was recorded using a FUJIX8, 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. C / N ratio FUJIX8, 8mm VCR made by Fuji Photo Film Co., Ltd. was used to record a 7MHz signal, and the noise generated at 6MHz when this signal was reproduced was measured with a spectrum analyzer. The ratio was measured. Per head Recording a 7MHz signal using FUJIX8, 8mm video deck manufactured by Fuji Photo Film Co., Ltd., and observing the envelope waveform before demodulation when this signal was reproduced with an oscilloscope, the output was secured and the waveform was flat. If there is, ○, if there is a drop in output somewhere, △,
A three-level evaluation of × was performed. The yield is the yield of the product, and the ratio of non-defective products made from one jumbo roll is expressed as a percentage in terms of P6-120.

[0087]

[Table 1]

As is clear from the results in Table 1, the sample of Example 1 which falls within the scope of the present invention has a high output of 7 MHz, and good results were obtained in all items per head. On the other hand, in Comparative Example 1-1, the output of 7 MHz deteriorated when the thickness of the upper recording layer was thicker than 1 μm. Although Comparative Examples 1-2 and 1-3 are single layers, the output at 7 MHz was also low in this case.

Specific examples of the present invention will be described below. Example 2 Lower non-recording layer Inorganic powder TiO ₂ (TTO-55A manufactured by Ishihara Sangyo) 100 parts Average primary particle diameter 0.05 μ BET specific surface area 18 m ² / g pH7 carbon black 20 parts Average primary particle diameter 18 mμ DBP oil absorption 80 ml / 100 g pH 8.0 specific surface area by the BET method: 250 meters ² / g volatiles 1.5% vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 × polar group Including 10 ^-6 eq / g Composition ratio 86: 13: 1 Degree of polymerization 400 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 200 parts

Upper recording layer Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe, specific surface area by BET method 60 m ² / g Crystallite size 195Å Particle size (major axis diameter) 0. 20μ, acicular ratio 10 σ _S : 130 emu / g vinyl chloride copolymer 12 parts-SO ₃ Na content: 1 x 10 ^-4 eq / g degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-alumina (particle size 0.3 μm) 2 parts Carbon black (particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, after kneading the components with a continuous kneader, use a sand mill. Chiite was dispersed.
To the resulting dispersion, 1 part of the polyisocyanate was added to the lower non-recording layer coating solution and 3 parts to the upper recording layer coating solution, and 40 parts of butyl acetate was added to each. A filter having an average pore diameter of 1 μm was added. Then, a coating solution for forming a lower non-recording layer and a coating solution for forming an upper recording layer were respectively prepared.
Incidentally, it showed A10 ⁴ / A10 ratio of the lower non-recording layer coating solution in Table 2.

The obtained coating liquid for lower non-recording layer was applied to a thickness of 7 μm.
It was coated on a polyethylene terephthalate support having a center line surface roughness of 0.01 μm and a thickness after drying of 2.0 μm, followed by winding after drying and calendering. Then, after curing treatment at 80 ° C. for 24 hours, the upper magnetic layer recording layer was coated so as to have a thickness of 0.3 μm, oriented and dried in the same manner as in Example 1, and then wound. . After that, it was processed with a calender at a temperature of 90 ° C. and slit into a width of 8 mm to obtain a sample # 8 mm of Example 2.
Videotape manufactured.

Comparative Examples 2-1, 2-2 and 2-3 In Example 2, the kind of the inorganic powder, its average primary particle diameter, and the thickness of the upper recording layer and the lower non-recording layer when carbon black was used. The coating liquids for forming the lower non-recording layer and the upper recording layer were respectively prepared in the same manner as in Example 2 except that the conditions described in Table 2 were used. The liquid was dried to a thickness of 2 μm, and immediately after that, the coating liquid for the upper recording layer was applied thereon to a thickness of 7 μm.
Simultaneous multi-layer coating is performed on a polyethylene terephthalate support having a center line surface roughness of 0.01 μ in μm, and while both layers are still in a wet state, a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G are used for orientation. After drying and drying, treatment was performed at a temperature of 90 ° C. with a 7-stage calender consisting of only metal rolls, slitting to a width of 8 mm, and an 8 mm video tape (Sample #: Comparative Example 2-1,
2-2 and 2-3) were produced.

The performance of the samples of Example 2 and Comparative Examples 2-1, 2-2 and 2-3 was evaluated as follows. The results are shown in Table 2. In addition, A10 ⁴ / A1 of the coating liquid for the upper recording layer
The 0 ratio is also described. Evaluation method Electromagnetic conversion characteristics 7 MHz output A FUJIX8, 8 mm video deck manufactured by Fuji Photo Film Co., Ltd. was used to record a 7 MHz signal, and the 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope.

[0094]

[Table 2]

As is clear from the results in Table 2, the sample of Example 2 had a good output of 7 MHz. On the other hand, in Comparative Examples 2-1, 2-2 and 2-3 in which the thickness of the upper recording layer was thicker than 1 μm, the output at 7 MHz was low.

Specific examples of the present invention will be described below. Example 3 Lower non-recording layer Cobalt-modified iron oxide 0 or 100 parts Hc 9500 Oe, specific surface area 58 m ² / g crystallite size 250 Å particle size (major axis diameter) 0.20 μ, acicular ratio 8 vinyl chloride-vinyl acetate-vinyl Alcohol copolymer 13 parts Polyester polyurethane resin containing 5 × 10 ⁻⁶ eq / g of polar group of —N (CH ₃ ) ₃ ⁺ Cl ⁻ 11 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-iron oxide Needle-like See Table 3 Long axis length 0.3 μm, specific surface area by BET 45 m ² / g pH 3.5 α-alumina (particle size 0 .3μm) 5 parts carbon black 100 or 500 parts average primary particle size 16Emumyu DBP oil absorption of 80 ml / 100 g pH 8.0 specific surface area by the BET method: 250 meters ² / g volatiles 1. % Butyl stearate 1 part 2 parts Methyl ethyl ketone 400 parts of stearic acid

Upper recording layer Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe, specific surface area by BET method 60 m ² / g Crystallite size 195Å Particle size (major axis diameter) 0. 20μ, acicular ratio 10 σ _S : 130 emu / g vinyl chloride copolymer 12 parts -SO ₃ Na content: 1 x 10 ^-4 eq / g degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-alumina (particle size 0.3 μm) 2 parts Carbon black (particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, after kneading the components with a continuous kneader, use a sand mill. Chiite was dispersed.
To the resulting dispersion, 6 parts of polyisocyanate was added to the coating solution for the lower non-recording layer, 3 parts to the coating solution for the upper recording layer, 40 parts of butyl acetate was added, and a filter having an average pore diameter of 1 μm was added. Then, a coating solution for forming a lower non-recording layer and a coating solution for forming an upper recording layer were respectively prepared.
The A10 ⁴ / A10 ratio of the coating solution for the lower non-recording layer is also shown.

The obtained coating liquid for lower non-recording layer was applied to a thickness of 7
A polyethylene terephthalate support having a center line surface roughness of 0.01 μm and a thickness of 2.0 μm after drying was coated, dried, wound, and calendered. Then, after curing at 80 ° C. for 24 hours, coating was performed so that the thickness of the recording layer of the upper magnetic layer was 0.3 μm, the same orientation and drying as in Example 1 were performed, and the film was wound. .. After that, it was processed with a calender at a temperature of 90 ° C. and slit into a width of 8 mm to obtain a sample # 8 mm of Example 3.
Videotape manufactured.

Comparative Examples 3-1 to 3-2 In Example 3, the type of the inorganic powder, the average primary particle diameter thereof, and the thickness of the upper recording layer and the lower non-recording layer when carbon black was used are shown. The coating liquids for forming the lower non-recording layer and the upper recording layer were respectively prepared in the same manner as in Example 3 except that the coating liquids for forming the lower non-recording layer were dried. So that the subsequent thickness becomes 2 μm, and immediately after that, in the case of Comparative Example 3-1, the coating liquid for the upper recording layer has a thickness of 1.1 μm after drying.
On the other hand, in the case of Comparative Example 3-2, on the other hand, the thickness after drying the coating liquid for the upper recording layer was 0.3 μm, and the center line surface roughness was 0.01 μm. Simultaneous multi-layer coating is performed on a polyethylene terephthalate support, and while both layers are still in a wet state, a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G are used for orientation and drying. Treatment was performed at a temperature of 90 ° C. with a multi-stage calender, slit into a width of 8 mm, and an 8 mm video tape (Sample #: Comparative Example
1 and 3-2) were produced.

The performance of the samples of Example 3, Comparative Examples 3-1 and 3-2 was evaluated by the following. Table 3 shows the results. Evaluation method Electromagnetic conversion characteristics 7 MHz output A FUJIX8, 8 mm video deck manufactured by Fuji Photo Film Co., Ltd. was used to record a 7 MHz signal, and the 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope.

[0101]

[Table 3]

As is clear from the results shown in Table 3, the output of 7 MHz was good in Example 3 of the present invention. On the other hand, Comparative Examples the thickness of the upper recording layer is thicker than 1 [mu] m 3-1 and A10 ⁴
Comparative example 3-2 in which the value of / A10 ratio is out of the range of the present invention
Had a low output of 7 MHz.

[0103]

INDUSTRIAL APPLICABILITY The present invention defines the thixotropy properties of the lower non-recording layer coating liquid and the upper recording layer coating liquid, particularly the physical properties and composition of the non-magnetic or magnetic powder of the lower non-recording layer coating liquid. It is possible to easily provide a magnetic recording medium which can be thinned by a sequential coating method after being adjusted by the above method and which has excellent electromagnetic conversion characteristics.

Claims (10)

[Claims] 1. A coating liquid for a lower non-recording layer in which a powder is dispersed in a binder and a coating liquid for an upper recording layer in which a ferromagnetic powder is dispersed in a binder are prepared, and the coating liquid is prepared on a support. In the method for producing a magnetic recording medium in which the coating solution for the lower non-recording layer is applied, and subsequently the coating solution for the upper recording layer is applied, a coating solution for the lower non-recording layer obtained by dispersing the powder in a binder is used. , Thixotropic, shear rate 10 ⁴ sec
The ratio of the shear stress A10 ⁴ at ^-1 to the shear stress A10 at a shear rate of 10 sec ^-1 , A10 ⁴ / A10 is 100 ≥
A10 ⁴ / A10 ≧ 3, and after the lower non-recording layer obtained by coating the support with the lower non-recording layer coating solution, the dry thickness of the upper recording layer is 1. 0
A method of manufacturing a magnetic recording medium, characterized in that the coating liquid for upper recording layer is applied so as to have a thickness of not more than μm. 2. The lower non-recording layer powder contains at least carbon black and an inorganic powder having an average primary particle diameter smaller than the dry thickness of the lower non-recording layer, and the lower non-recording layer coating liquid and the upper recording layer. 2. The method for producing a magnetic recording medium according to claim 1, wherein the coating liquid contains a thermosetting polyisocyanate in a binder in an amount of 10 to 70% by weight. 3. The method for producing a magnetic recording medium according to claim 1, wherein the powder of the coating liquid for the lower non-recording layer contains a non-metal inorganic powder having an average primary particle diameter of 0.08 μm or less. 4. The ferromagnetic powder of the coating liquid for 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, B
i, La, Ce, Pr, Nd, P, Co, Mn, Zn,
The method for manufacturing a magnetic recording medium according to claim 1, wherein the method comprises at least one atom selected from Ni, Sr, and B. 5. The method for producing a magnetic recording medium according to claim 1, wherein the coating liquid for the lower non-recording layer contains, as powder, an inorganic powder having a Mohs hardness of 4 or more. 6. The powder of the coating liquid for the lower non-recording layer, which is an α-alumina, β-alumina, or γ-, having an α conversion of 90% or more.
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, corundum, silicon nitride, titanium carbide,
2. At least one inorganic powder selected from titanium oxide, silicon dioxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, and molybdenum sulfide is contained. A method of manufacturing a magnetic recording medium according to 1. 7. The method of manufacturing a magnetic recording medium according to claim 1, wherein the powder of the lower non-recording layer contains a magnetic powder that cannot be magnetically recorded. 8. A magnetic powder is contained as a powder of the coating liquid for the lower non-recording layer, and the Bm of the lower non-recording layer is 500.
The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is Gauss or less. 9. The elastic modulus of the support is 100 to 2000.
The method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium has a Kg / mm ² . 10. The support comprises polyethylene terephthalate, polyethylene naphthalate polyesters, polyolefins, cellulostriacetate, polycarbonate.
2. The method for producing a magnetic recording medium according to claim 1, wherein the method is at least one selected from the group consisting of bone, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide.