JP2566070B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a magnetic recording medium .
Law, particularly preferably magnetic layer relates following very thin layer magnetic recording medium 1.0 micron, further details excellent electromagnetic conversion characteristics, and production yield of the magnetic recording medium excellent in good productivity characteristics Regarding the method .

[0002]

2. Description of the Related Art Conventional magnetic recording media such as video tapes, audio tapes and magnetic disks have a magnetic layer in which ferromagnetic iron oxide, Co- modified iron oxide, CrO ₂ , ferromagnetic alloy powder and the like are dispersed in a binder. A non-magnetic support coated with is widely used. In recent years, the recording wavelength tends to be shortened with the increase in recording density, 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, is increasing. 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, the problem due to the surface roughness of the support described above is eliminated and the magnetic layer is made a thin layer, Attempts to reduce thickness demagnetization and achieve high output have been proposed. For example, in Japanese Patent Application Laid-Open No. 62-154225, a conductive layer is provided between a magnetic layer and a substrate in order to reduce the thickness of the magnetic layer to 0.5 μm or less and to prevent the surface electric resistance of the magnetic layer from increasing. There has been proposed a magnetic recording medium provided with an undercoat layer having a thickness containing a powder equal to or greater 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 this way, the magnetic layer is made thin to achieve high density recording, and at the same time, carbon black is included in the lower non-magnetic layer to prevent static electricity, and an abrasive is added to improve the cleaning property and durability. are doing. However, in the conventional technology, the lower magnetic layer is first applied to the non-magnetic support, and then dried and, if necessary, calendered, and then the upper magnetic layer is provided. There were the following problems. That is, in order to reduce the thickness of the magnetic layer, it is conceivable to reduce the amount of coating or to add a large amount of a solvent to the magnetic coating solution to reduce the concentration. In the former case, if the amount of application is reduced, there is not enough time for leveling after application, and drying starts, so that a problem such as an application defect, for example, a stripe or engraved pattern remains, and the yield is extremely deteriorated. When the latter method is adopted, if the concentration of the magnetic coating liquid is low,
The resulting coating film has various harmful effects, such as that there are many voids and a sufficient degree of filling of the ferromagnetic powder cannot be obtained, and that there are many voids and the strength of the coating film is insufficient. One means for solving these problems is disclosed in JP-A-63-19 / 1988.
As described in Japanese Patent No. 1315, there has been proposed a method in which a non-magnetic layer is provided as a lower layer using a simultaneous multilayer coating method, and a high-concentration magnetic coating liquid is applied thinly. In the case of the simultaneous multilayer 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 simultaneously or sequentially coated while the lower layer is in a wet state, various studies have already been performed on the magnetic layer of the multilayer. Has been done. However, even when this technique was applied to the lower non-magnetic layer, similarly good results could not be obtained. In other words, Wet on We
When the lower non-magnetic layer and the upper magnetic layer were provided according to t, disturbance occurred at the interface between the two, causing pinholes and cissing of the magnetic layer. Then, the present inventors considered the composition of these lower nonmagnetic layers and the wet-on-wet.
As a result of extensive studies on the relationship between t and the coating method, the present invention was found to have points in rheological properties.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a thin-layer magnetic recording medium which has a good yield and ensures production efficiency and which is excellent in electromagnetic conversion characteristics such as output and C / N ratio. Another object of the present invention is to provide a method for manufacturing a thin-layer magnetic recording medium having good head contact and good storage stability.

[0004]

The above objects of the present invention are as follows.
(A) Coating liquid for forming lower non-recording layer containing powder and binder
And magnetic coating liquid for upper recording layer containing ferromagnetic powder and binder
Are prepared respectively, and the lower non-recording layer is formed on the non-magnetic support.
Apply the coating liquid for forming and the magnetic coating liquid for the upper recording layer
In the method of manufacturing a magnetic recording medium according to the above, the lower layer
The coating liquid for forming the non-recording layer has thixotropy and shear
Shear stress A10 ⁴ at shear rate 10 ⁴ sec ^-1 and shear rate 1
Ratio with shear stress A10 at 0 sec ^-1 A10 ⁴ / A10
Is 100 ≧ A10 ⁴ / A10 ≧ 3, and the non-magnetic
Coating the lower non-recording layer forming coating liquid on a permeable support,
While the obtained lower non-recording layer is in a wet state, the lower non-recording layer
Simultaneously or sequentially with the application of the coating liquid for forming the recording layer, the upper layer
For the upper recording layer, the dry thickness of the recording layer is 1.0 μm or less.
Of a magnetic recording medium characterized by applying a magnetic coating liquid
Manufacturing method, preferably, (b) the magnetic coating liquid for the upper recording layer is sheared.
Shear stress A10 ⁴ and shear rate at a shear rate of 10 ⁴ sec ^-1
Ratio to shear stress A10 at 10 sec ^-1 A10 ⁴ / A1
0 is a coating liquid adjusted to 100 ≧ A10 ⁴ / A10 ≧ 3
The magnetic recording medium according to claim 1, wherein
This can be achieved by the manufacturing method .

That is, according to the present invention, a dispersion liquid containing the powder as a binder in the lower non-recording layer and a magnetic coating material in which the ferromagnetic powder used in the upper recording layer are dispersed in a binder are mutually compatible. > by having a switch Kisotoropi of the stomach, Wet o
The inventors have found that when both coating materials are applied with n Wet, the interface is not disturbed, pinholes and craters do not occur, and both head contact can be improved.

[0006] The thixotropic property is also called thixotropy and refers to the phenomenon of softening of an object due to stress that involves recovery, but causes softening by increasing the strain 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, thereby increasing 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. As the conventional dispersion liquid for the lower non-recording layer, those having no thixotropy property, or very small if any , or liquids containing carbon black and having extremely strong thixotropy property have 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 the thixotropy of both liquids is such that when the dispersion of the lower non-recording layer and the magnetic paint of the upper recording layer are applied by the wet-on-wet method, mixing does not occur at the interface. It means that the sexes are similar.

[0007] In the present invention, a dispersion obtained by dispersing the pre-Symbol powder in the binder may have a thixotropic, shear rate 10
Shear stress A10 ⁴ at ⁴ sec ^-1 and shear rate 10se
the ratio A10 ⁴ / A10 between shear stress A10 at c ^-1 is 100 ≧ A10 ⁴ / A10 ≧ 3 is intended thixotropy that same or similar further specifically illustrated, of the dispersion By setting the ratio of A10 ⁴ / A10 within a certain range, it has a thixotropic property similar to that of the upper magnetic coating material, no disturbance at the interface occurs, and as a result, problems such as pinholes and cissing do not occur.

As described above, the basic idea of the present invention is that the lower non-recording layer and the upper recording layer are the coating solutions having the specified rheological properties, and the lower non-recording layer is the dispersion and the upper recording layer. The magnetic coating is characterized by using the one prepared to have thixotropic properties which are the same or similar to each other at the time of application, thereby eliminating coating defects. Improve yield,
The electromagnetic conversion characteristics such as durability and 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 using a viscometer, for example, a Rotovisco viscometer RV-II manufactured by HAAKE.
The shear rate is determined by the diameter of the inner cylinder and the outer cylinder, the clearance, and the number of revolutions. The following relationship exists between the shear rate, apparent viscosity and shear stress.

A = η · D (A: shear stress, η: 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 liquid approaches the Newtonian fluid, and it is difficult to perform simultaneous multi-layer coating 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 means as specific means for having such thixotropy. The method for producing the magnetic recording medium of the present invention is not limited to these three means, and the essential point is that the thixotropy of the dispersion is the same as or close to the thixotropy of the magnetic paint. More specifically, A10 ⁴ / A10 is set within the above-mentioned range of values, and these are merely exemplary means.

Formation of lower non-recording layer containing powder and binder
Coating liquid and magnetic material for the upper recording layer containing ferromagnetic powder and binder.
Of the above-mentioned lower layers on a non-magnetic support.
The non-recording layer forming coating solution and the upper recording layer magnetic coating solution
In the method of manufacturing a magnetic recording medium by coating,
At least the powder of the coating liquid for forming the lower non-recording layer is
Carbon black and smaller than the dry thickness of the lower non-recording layer
The lower layer contains no inorganic powder having an average primary particle size
Thermosetting to the layer forming coating liquid and the magnetic recording liquid for the upper recording layer
10 to 70% by weight of the polyisocyanate in the binder
No

Formation of lower non-recording layer containing powder and binder
Coating liquid and magnetic material for the upper recording layer containing ferromagnetic powder and binder.
Of the above-mentioned lower layers on a non-magnetic support.
The non-recording layer forming coating solution and the upper recording layer magnetic coating solution
In the method of manufacturing a magnetic recording medium by coating,
The powder of the coating liquid for forming the lower non-recording layer has an average primary particle diameter.
A non-magnetic inorganic powder of 0.08 μm or less is included. The non-magnetic inorganic powder or powder dispersed in the lower layer in the present invention does not contain carbon black.

Formation of lower non-recording layer containing powder and binder
Coating liquid and magnetic material for the upper recording layer containing ferromagnetic powder and binder.
Of the above-mentioned lower layers on a non-magnetic support.
The non-recording layer forming coating solution and the upper recording layer magnetic coating solution
In the method of manufacturing a magnetic recording medium by coating,
The saturation maximum magnetic flux density Bm of the lower non-recording layer is 500 gau
Be less than or equal to

That is, the means described is a dispersion prepared by using, as the powder to be dispersed, carbon black which greatly imparts thixotropic properties and an inorganic powder which has a small thixotropic property, and a polyisocyanate. Is used. As a result, the upper recording layer can be made thinner and the yield can be improved. By using polyisocyanate for the upper recording layer and the lower non-recording layer, the head contact can be maintained well, and the storage stability at high temperature and high humidity can be maintained. And a magnetic recording medium having appropriate rigidity and flexibility is obtained, and the durability is improved.

The means described is one in which the dispersion is prepared by reducing the particle size of the non-metal inorganic powder to be dispersed and the thixotropy thereof is adjusted. That is, in order to perform coating simultaneously or sequentially in a wet state, the combination of the rheological properties of the upper recording layer and the rheological properties of the lower non-recording layer is important. 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 simultaneous multi-layer coating is performed in this state, the upper recording layer and the lower non-recording layer are significantly mixed near the interface, or intense agglomeration lines are generated at the time of orientation after coating, and sufficient surface properties can be obtained. Did not. 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.

According to the means described, the saturation maximum magnetic flux density Bm of the lower non-recording layer is set to 30 to 500 Gauss. Specifically, A10 ⁴ / A10 is satisfied, and magnetic recording is impossible. In addition, a dispersion liquid is used whose thixotropic property is adjusted by using a magnetic powder that does not adversely affect the upper recording layer. That is, the lower non-recording layer is 30 to 5
In order to set it to 00 Gauss, it is achieved by using a magnetic substance having a low saturation magnetization (σ _S ) or preparing a dispersion liquid in which the filling ratio of the magnetic substance in the lower non-recording layer is reduced.

These means of ~ are 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, etc., water content etc. can be mentioned.

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.

[0021] Next will be described the preferred embodiments below in the means described in ~. First, the means 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 size 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 450 to 200 ml / 100 g. The particle size is 30 mμ or less, preferably 5 to 27 mμ, more preferably 10 to 22 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. 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. Also,
The carbon black is preferably dispersed in advance with a binder having good dispersion, and then mixed and dispersed with an inorganic powder.

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 be used to obtain a similar effect by broadening the particle diameter distribution. 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 μm to 2 μm. 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 this 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 above means , in addition to the non-magnetic powder consisting of carbon black and inorganic powder, other arbitrary non-magnetic powder can be used if desired.

The nonmagnetic 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.

With respect to the means (1), it is preferable that the magnetic paint and the dispersion contain 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. When the content of carbon black is 1% by weight or less, it is substantially the same as that when carbon black is not 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.

Examples of the inorganic powder include SiO ₂ and Ti.
O ₂ , α-alumina, α-Fe ₂ O ₃ , boron nitride and tin oxide are preferred. The average primary particle diameter of the inorganic powder is 0.08μ
m or less, but if necessary, various combinations of inorganic powders other than this size, or even a single inorganic powder, can have a similar particle size distribution to achieve the same effect. The tap density of the inorganic powder is 0.05 to 2 g / cc, preferably 0.
2 to 1.5 g / cc, water content 0.1 to 5%, preferably 0.2 to 3%, pH 2 to 11, specific surface area 1 to 10
0 m ² / g, preferably from 5 to 50 m ² / g, more preferably 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.
Specific gravity is 2-8. The shape is needle-like, spherical, dice-like,
Any of The above inorganic powder is not necessarily 100%
It need not be pure and the surface may be treated with other compounds depending on the purpose. At this 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 inorganic powder preferably has a Mohs hardness of 4 or more.

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 are
The weight ratio is 20 to 0.1, preferably 10 to 0.5, more preferably 8 to 1, and the volume ratio is used in the range of 10 to 0.2.

Regarding the means of, 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,
100 parts by weight or less of non-magnetic material with respect to 100 parts by weight of magnetic material
The above is preferable, and it may be 100 to 5000 parts by weight.
Preferred. The non-magnetic substance preferably contains non-magnetic powder in addition to the binder, and inorganic powder, carbon black and the like are preferable. Examples of the magnetic substance include Co-γ-
Fe ₂ O ₃ magnetic material is preferable, and its coercive force is not particularly limited, but is preferably about 400 Oe to 1500 Oe. Also,
Hexagonal barium ferrite may be used in the lower non-recording layer. There is no limitation on the organic powder Hc at that time,
When BaFe is used, it is preferably 800 Oe or more and 4500 Oe or less. Hc of the upper recording layer is 1200 Oe to 30 Oe.
00Oe and Bm are preferably 200 to 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. The carbon black to be used in accordance with <br/> is lower non-recording layer, the type of the upper layer recording layer, changing the amount, the combination, particle size, oil absorption, conductivity, indicated above such as pH Of course, it is possible to use properly according to the purpose based on various characteristics. For example, charging is prevented by using highly conductive carbon black for the lower non-recording layer, and the friction coefficient is reduced by using carbon black having a large particle diameter for the upper recording layer.

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 preferred. 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 this 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.

[0033] Oite, as the non-magnetic powder that can be used by others, organic powder include acrylic styrene resin powders, benzoguanamine resin powders, melamine resin powders, and phthalocyanine pigments, polyolefin resin, polyester 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 are used for the binder.
It is used in the range of 0.1 to 10 in weight ratio and 10 to 0.2 in volume ratio.

[0035] will be described below per general matter of the present invention. Specific examples of the inorganic powder that can be used in the present invention include inorganic compound powders such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.
As the inorganic compound, for example, α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide having an α conversion of 90% or more, Silicon dioxide, tin oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination.

Specific examples of the inorganic powder used in the present invention include AKP-20 and AKP-30 manufactured by Sumitomo Chemical.
AKP-50, HIT-50, HiT-100, Nippon Kagaku Kogyo KK: G5, G7, S-1, Toda Kogyo KK: DP
N-250BX , TF-100, TF-120, TF-
140, made by Ishihara Sangyo: TTO-55, FT-1000,
FT-2000, FTL-100, FTL-200, M
-1, S-1, SN-100, E-303, E-30
4, made by Titanium Industry: ECT-52, STT-4D, ST
Α-hematite obtained from T-30, STT-65C, Y-LOP, Y-LOP, Mitsubishi Metals: T-1, Nippon Shokubai: NS-O, NS-3Y, NS-8Y and the like.

As the carbon black used in the present invention, furnace for rubber, thermal for rubber, black for color, acetylene black and the like 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 Konlon Via Carbon: 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, H
g, Pb, Bi, La, Ce, Pr, Nd, P, Co,
It may contain atoms such as Mn, 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, Japanese Examined Patent Publication No. 44-14090, Japanese Examined Patent Publication No. 45-18372, Japanese Examined Patent Publication No. 47-22062, Japanese Examined Patent Publication No. 47-22513,
JP-B-46-28466, JP-B-46-38755
No. 4, Japanese Patent Publication No. 47-4286, Japanese Patent Publication No. 47-12422
No. 4, Japanese Patent Publication No. 47-17284, Japanese Patent Publication No. 47-1850
No. 9, JP-B 47-18573, JP-B 39-103
07, JP-B-48-39639, and U.S. Pat.
No. 6215, No. 3031341, No. 3100194
Nos. 3,242,005 and 3,389,014.

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

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% of the amount of magnetization remaining without being inverted 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 γ iron oxide is used, 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.

The ferromagnetic powder used in the present invention preferably has few voids, and the value thereof is 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 includes 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, and 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 , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ , R is a hydrocarbon group), an epoxy group, SH, CN, or the like, and at least one polar group selected by copolymerization or addition reaction is preferably used. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 1
It is 0 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include Union Carbide: VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries: 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 Dainichi Seika Co., Ltd .: Daifu eramine 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 a rubber furnace, thermal rubber, color black, 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, Asahi Carbon Co .: # 80, #
60, # 55, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo: #
2400B, # 2300, # 900, # 1000, # 3
0, $ 40, $ 10B, manufactured by Konlon Via Carbon: 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, charging is prevented by using highly conductive carbon black for the lower non-recording layer, and the friction coefficient is reduced by using carbon black having a large particle diameter for the upper recording layer.
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 in 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 polishing agent used in the present invention include: AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
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 can be of different types, amounts and combinations for the first layer and the second layer, and can be used properly according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. The abrasive present on the surface of the upper recording layer and the end face of the upper recording layer of the magnetic recording medium of the present invention is preferably 5/100 μm ² or more.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, 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, 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 as required. 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 a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with the ferromagnetic powder before the kneading step, the ferromagnetic powder is used. There are cases where it is added in a kneading step using a binder and a solvent, when it is added in a dispersion step, when it is added after dispersion, and when it is added immediately 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 .: NJ Erb LO, N Jorb 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, glycol ethers such as benzene, benzene, 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 such that the non-magnetic support has a thickness of 1 to 100 μm, preferably 4 to 80 μm, and the lower non-recording layer has a thickness of 0.5 μm to 10 μm, preferably 1 to 5 μm.
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,
Preferably it is 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 at 100 ° C. for 30 minutes in the tape running direction and the width direction 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, more efficient production can be achieved by using the simultaneous multi-layer coating method as disclosed in JP-A-62-212933. 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. First, a lower non-recording layer is applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like generally used in the application of a magnetic paint, and the lower non-recording layer is placed in a wet state while the coating is performed. JP-A-60-238179, JP-A-2-265672
The upper layer recording layer is coated by the support pressure type extrusion coating device disclosed in Japanese Patent No. 2. JP-A-63-88080, JP-A-2-17921
No. 2,265,672, the upper recording layer is coated almost simultaneously by one coating head having two slits for passing the coating liquid therein. 3. The upper recording layer is coated almost simultaneously by an extrusion coating device with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic powder, JP-A-62-95174 and JP-A-1-236 are used.
It is desirable to apply shear to the coating liquid inside the coating head by the method as disclosed in 968.

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 provide an appropriate drying step before orientation so that the orientation after drying is the highest.

Further, a heat-resistant plastic roll of epoxy, polyimide, polyamide, polyimide amide, etc. 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 , and the residual growth is preferably 0.5% or less.
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.
/ M ² or less, and it is preferable that the residual solvent contained in the upper recording layer is 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 a magnetic field of 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 estimated 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.

[0074]

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

Example 1 Lower non-recording layer A Inorganic powder α- 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 80ml / 100g 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}} - 5 a polar group × 10 ^-6 eq / g containing 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 Copper oleate 1 part Methyl ethyl ketone 200 parts Each component of the above paint is kneaded with a continuous kneader. After that, it was dispersed using a sand mill. 5 parts of polyisocyanate was added to the obtained dispersion liquid, 40 parts of butyl acetate was further added to each dispersion liquid, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating liquid for forming the lower non-recording layer. Lower Non-Recording Layer B The coating liquid was diluted by adding 5 parts of polyisocyanate and 350 parts of butyl acetate to the liquid after dispersion of the non-magnetic lower layer liquid A. Lower non-recording layer C, D, E, F The blending ratio of α-Fe ₂ O ₃ and carbon black of the lower non-recording layer A is 8/2 to C 9/1, D 5/5, F, respectively. Changed to 4/6. In E, carbon black was not added.

Lower Non-Recording Layer G Polyisocyanate was not added to the lower non-recording layer A formulation. The lower non-recording layer H was treated by previously dispersing carbon black as follows. (1) Carbon black is previously dispersed according to the following formulation. Carbon black 100 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 100 parts -N ( CH ₃ ) ₃ ⁺ Cl ⁻ polar group containing 5 × 10 ⁻⁶ eq / g 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-containing copper oleate 5 parts Phthalocyanine blue-based dispersant 5 parts Methyl ethyl ketone 200 parts After continuous kneader treatment with this formulation, dispersion was performed with a sand glider.

(2) Next, the following formulation was mixed and dispersed, and further dispersed by a sand glider. Inorganic powder α- Fe ₂ O ₃ 80 parts Average particle size 0.27 μ, specific surface area by BET 18 m ^{2 /} g, pH 5.5 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 5 parts-N (CH ₃ ) ₃ ⁺ Containing 5 × 10 ⁻⁶ eq / g of polar groups of Cl ⁻ Composition ratio 86: 13: 1 Polymerization degree 400 Polyester polyurethane resin 4 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group: 1 × 10 ⁻⁴ eq / g content Carbon black dispersion of the above (1) 83 parts Butyl stearate 1 part Stearic acid 1 part Copper oleate 1 part Methyl ethyl ketone 200 parts After dispersion, 6 weight parts of polyisocyanate In addition, a lower non-recording layer H was formed. 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 Crystal size 195Å Particle size (major axis diameter) 0.20 μ, Needle ratio 10 σ _S : 130 emu / g Vinyl chloride-based 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) 0.5 part Butyl steer rate 1 part stearic acid 2 parts Methyl ethyl ketone 200 parts upper recording layer B hexagonal barium ferrite 100 parts Hc 1250 Oe, a specific surface area of 47m ² / g particle Sa 'S 0.05 .mu.m, tabular ratio 5 vinyl chloride copolymer 13 parts -SO ₃ Na polar groups of 5 × 10 ^-6 eq / g containing composition ratio PVC: vinyl acetate: vinyl alcohol = 86: 13: 1 Polymerization degrees 400 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (particle size 0.3 [mu] m) 2 Parts carbon black (particle size 80 mμ) 0.5 parts butyl stearate 1 part stearic acid 2 parts methyl ethyl ketone 200 parts Example 1-1 The above magnetic coating material for upper recording layer A was kneaded with a continuous kneader and then sand milled. Dispersed using.
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.

The obtained coating liquid for lower non-recording layer A was
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 becomes 3 μm and immediately after that the thickness of the upper recording layer becomes 0.2 μm. Simultaneous multi-layer coating on the body, 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 to orient and dry the layer. At a temperature of 90 ° C. and slit into a width of 8 mm to manufacture an 8 mm video tape of sample #Example 1-1.

Examples 1-2 to 1-7, Comparative examples 1-1 to 1
-7 , Reference Examples 1-3 to 1-4 In the same manner as in Example 1-1, magnetic coating materials for upper recording layers A or B were prepared, and the magnetic coating materials for upper recording layers shown in Tables 1 and 2 were prepared. The lower non-recording layer B to H coating material, the upper recording layer thickness,
Each sample was prepared in the same manner as in Example 1-1, except that the lower non-recording layer thickness was used. However, Comparative Examples 1-2 and 1
-7 is a single layer having only the upper recording layer. Reference Examples 1-3, 1
-4 was applied sequentially after drying. That is, the lower non-recording layer coating liquid was prepared by the same liquid preparation method as in Example 1-1, and was applied so that the thickness after drying was 2.7 μm, and was wound after drying and calendered. I went. After that, 80 ℃ 2
After curing treatment for 4 hours, coating was performed so that the thickness of the recording layer of the upper magnetic layer was 0.5 μm, orientation and drying were performed in the same manner as in Example 1, and then winding. Then, calendar processing was performed. The performance of these samples was evaluated as follows. The results are shown in Tables 1 and 2. Incidentally, as described in conjunction with A10 ⁴ / A10 ratio of upper recording layer coating solution.

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., 10 units of P6-12.
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.

[0081]

[Table 1]

[0082]

[Table 2] As is clear from the results of Tables 1 and 2, the samples of Examples 1-1 to 1-7 within the scope of the present invention are all 7M.
Hz output is high, C / N is good, and the yield is
Good results were obtained over all items of storage stability and head. On the other hand, in Comparative Example 1-1, the output of 7 MHz and the C / N were deteriorated when the thickness of the upper recording layer was thicker than 1 μm. Comparative Example 1-2 is a single layer, but in this case also 7 MHz
Output and C / N were low. After further coated the lower non-recording layer, dried, calendered, performs subsequent curing process, then so-called sequential coating coating the upper recording layer (Wet on Dry) and the Reference Examples 1-3 Reference Example 1 C./N was low, and storage stability was poor. The yields of the samples of Comparative Examples 1-5 and Comparative Examples 1-6, which were out of the range of A10 ⁴ / A10, were extremely low .

Example 2-1 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 pH 7 carbon black 20 parts Average primary particle diameter 18Emumyu DBP oil absorption of 80ml / 100g 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}} - in Composition containing a polar group of 5 × 10 ^-6 eq / g 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 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 Crystal size 195Å Particle size (major axis diameter) 0.20 μ, acicular ratio 10 σ _S : 130 emu / g Chloride vinyl copolymer 12 parts -SO ₃ Na content: 1 × 10 ^-4 eq / g polymerization degree: 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group 1 × 10 ⁻⁴ eq / g content α-alumina (particle size 0.3 μm) 2 parts Carbon black (particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts Above The components of each of the two paints were kneaded with a continuous kneader and then dispersed using a sand mill.
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 3.

The coating liquid for the lower non-recording layer thus obtained was dried so that the thickness after drying was 2 μm, and immediately thereafter, the thickness of the upper recording layer was 0.3 μm. 7μ
Simultaneous multi-layer coating is performed on a polyethylene terephthalate support having a center line surface roughness of 0.01 μm at m, 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 being dried, it was processed at a temperature of 90 ° C. in a 7-stage calender composed of only metal rolls and slitted into a width of 8 mm to manufacture an 8 mm video tape (Sample #: Example 2-1).

Examples 2-2 to 2-5 and Comparative examples 2-1 to 2
-4, Reference Example 2-2 In Example 2-1, 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 is used are shown in Table 3. Each sample was prepared in the same manner as in Example 2-1 except that the conditions were as described. In Reference Example 2-2, multilayer coating was performed after drying. That is, the lower non-recording layer coating liquid was prepared by the same liquid preparation method as in Example 2, coated so that the thickness after drying was 2.0 μm, wound after drying, and calendered. It was Then, after curing treatment at 80 ° C. for 24 hours, coating is performed so that the thickness of the upper magnetic layer recording layer is 0.3 μm, orientation and drying are performed in the same manner as in Example 2-1, and then winding is performed. I took it. Then, calendar processing was performed . Evaluation method Running durability measurement method Samples were recorded at 23 ° C. and 70% RH in an atmosphere of Fuji Photo Film Co., Ltd., 8 mm video deck FUJIX8, 10 units, and P
6-120 was run 100p. During that time, the output decrease was measured, and the dirt on each part in the deck after running was evaluated.
、, △△, △, △ ×, × were evaluated on a 5-point scale. 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. Yield The percentage of non-defective products after slitting was completed. Usually, 97% or more is required.

[0086]

[Table 3]

As is clear from the results of Table 3, Example 2-
The samples of Examples 1 to 2-5 had good outputs of 7 MHz, running durability, and yield. On the other hand, the thickness of the upper recording layer is thicker than 1 μm, Comparative Example 2-1 has a low output of 7 MHz, and after the lower non-recording layer is provided, it is dried, calendered and cured, and then the upper recording layer is provided. Reference Example 2 by sequential application (so-called Wet on Dry)
-2 had a very low yield. Also, A10 ⁴ / A1
Comparative examples 2-3 and 2 in which the value of 0 is outside the range of the present invention
-4 had a low yield and a low output of 7 MHz. In addition, the running durability of Reference Example 2-2 and Comparative Example 2-4 significantly deteriorated.

Examples 3-1 to 3-6 and Comparative Examples 3-1 to 3-1
2, Reference Example 3-3, Comparative Example 3-4, the lower non-recording layer of cobalt denatured iron oxide 0 or 100 parts Hc 950Oe, a specific surface area of 58m ² / g crystal size 250Å particle size (major axis diameter) 0.20, Needle ratio 8 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 13 parts Polyester polyurethane resin containing 5 × 10 ^-6 eq / g 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 Refer to Table 3 Long axis length 0.3 μm, BET specific surface area 45 m ² / g pH 3.5 α-alumina (particle size 0.3 μm) 5 parts Carbon black 100 or 500 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 ² / g Volatile 2 parts Methyl ethyl ketone 400 parts upper recording layer content of 1.5% Butyl stearate 1 part Stearic acid ferromagnetic metal powder composition Fe / Zn / Ni = 92/ 4/4 100 parts Hc 1600 Oe, the ratio by BET method Surface area 60 m ² / g Crystal 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 polymerization degree: 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g 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 Above For each One of paint were kneaded with the components in a continuous kneader and then dispersed using a sand mill.
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 resulting coating liquid for the lower non-recording layer was adjusted to a thickness of 2 μm after drying, and immediately thereafter to a thickness of 0.3 μm on the upper recording layer. 7μ
Simultaneous multi-layer coating (note that in Reference Example 3-3 , sequential coating) was performed on a polyethylene terephthalate support having a center line surface roughness of 0.01 μm and a thickness of 3000 G while both layers were still in a wet state. Cobalt magnet with magnetic force and 1
After being oriented with a solenoid having a magnetic force of 500 G and dried, it was processed at a temperature of 90 ° C. in a 7-stage calender consisting of only metal rolls, and slit into a width of 8 mm.
mm video tape was manufactured. In Reference Example 3-3, multilayer coating was performed after drying. That is, the lower non-recording layer coating liquid was prepared by the same liquid preparation method as in Example 3-1, and the coating was performed so that the thickness after drying was 2.0 μm, and the film was wound after drying and calendered. I went. Then, after curing treatment at 80 ° C. for 24 hours, coating was performed so that the thickness of the upper magnetic layer recording layer was 0.3 μm, orientation and drying were performed in the same manner as in Example 3-1, and then winding. I took it. Then, calendar processing was performed. The performance of these samples was evaluated as follows. The results are shown in Tables 4 and 5.

Example 3-7 In the above example, the ferromagnetic powder of the upper recording layer was replaced with the following C.
except for changing the o denatured γ-Fe ₂ O ₃ creates a sample under the conditions described above as well as Table 5 described and evaluated in the same manner.

[0091] Co denatured _{γ-Fe 2 O 3: Hc} 1400Oe, specific surface area by the BET method: 45 m ² / g crystal size 290Å particle size (major axis diameter) 0.3 [mu] m, the acicular ratio 10 σ _S: 75emu / g Evaluation Method 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. Yield The percentage of non-defective products after slitting was completed. Usually, 97% or more is required.

[0092]

[Table 4]

[0093]

[Table 5]

[0094] Table 4 and Example 3-1 to Example 3-7 Results from clear as the present invention in Table 5 are improved both the output and yield of 7 MHz, comparison outside the scope of the present invention EXAMPLE 3 In Examples 1 to 3-3, the yield was not sufficient. Moreover, the output of 7 MHz was significantly inferior in Reference Example 3-4 .

[0095]

According to the present invention, the thixotropy of the coating solution for the lower non-recording layer and the coating solution for the upper recording layer are determined, particularly the physical properties and composition of the non-magnetic or magnetic powder of the coating solution for the lower non-recording layer. By doing so, it is possible to easily provide a magnetic recording medium having excellent yield, durability and excellent electromagnetic conversion characteristics, which can be thinned by a simultaneous multi-layer or sequential wet coating method.

Continuation of front page (56) Reference JP-A-4-325915 (JP, A) JP-A-5-12650 (JP, A) JP-A-5-182173 (JP, A) JP-A-5-182177 (JP , A) JP 5-182178 (JP, A) JP 5-197946 (JP, A) JP 5-217149 (JP, A) JP 5-298653 (JP, A) JP 7-311932 (JP, A) JP 7-326037 (JP, A) JP 7-326038 (JP, A) JP 8-50718 (JP, A) JP 4-238111 (JP, A) JP-A-4-283416 (JP, A) JP-A-4-321924 (JP, A)

Claims (7)

(57) [Claims] 1. For forming a lower non-recording layer containing a powder and a binder.
Coating liquid, magnetic for upper recording layer containing ferromagnetic powder and binder
Prepare each coating solution and apply the above-mentioned lower layer on the non-magnetic support.
Apply the coating liquid for forming the recording layer and the magnetic coating liquid for the upper recording layer.
In the method of manufacturing a magnetic recording medium by applying a cloth,
The coating liquid for forming the lower layer and the non-recording layer has thixotropy.
Chi, shear stress at a shear rate of 10 ⁴ sec ^-1 A10 ⁴ and pruning
Ratio of shear stress A10 at shear rate 10 sec ^-1 A10 ⁴
/ A10 is 100 ≧ A10 ⁴ / A10 ≧ 3, and
The coating liquid for forming the lower non-recording layer is formed on the non-magnetic support.
When the lower non-recording layer obtained by coating is wet,
Simultaneously or sequentially with the application of the coating liquid for forming the lower non-recording layer,
The upper recording layer has a dry thickness of 1.0 μm or less.
A magnetic recording method characterized by applying a magnetic coating liquid for a recording layer.
Recording medium manufacturing method. 2. The magnetic coating liquid for the upper recording layer is sheared at a high speed.
Shear stress A10 ⁴ at 10 ⁴ sec ^-1 and shear rate 10
The ratio A10 ⁴ / A10 to the shear stress A10 at sec ^-1 is
It is a coating liquid adjusted to 100 ≧ A10 ⁴ / A10 ≧ 3.
The manufacturing of the magnetic recording medium according to claim 1, wherein
Method. 3. A powder of a coating liquid for forming the lower non-recording layer.
Is at least carbon black and the dryness of the lower non-recording layer.
Contains an inorganic powder having an average primary particle size smaller than the dry thickness and
The lower non-recording layer forming coating liquid and the upper recording layer magnetic
A thermosetting polyisocyanate was added to the coating solution in a binder.
The porcelain according to claim 1, wherein the porcelain contains about 70 to 70% by weight.
Method of manufacturing a gas recording medium. 4. The powder of the coating liquid for forming the lower non-recording layer is
Non-magnetic inorganic powder having an average primary particle diameter of 0.08 μm or less
The magnetic recording medium according to claim 1, comprising:
Manufacturing method. 5. A saturation maximum magnetic flux density B of the lower non-recording layer
Claim m is equal to or is 500 gauss or less 1
A method of manufacturing a magnetic recording medium according to 1. 6. The coating liquid for forming the lower non-recording layer is magnetically recorded.
A magnetic powder that cannot be recorded is included.
1. The method for manufacturing a magnetic recording medium according to 1. 7. The coating liquid for forming the lower non-recording layer is a magnetic substance.
To 100 parts by weight In contrast, contains 100 parts by weight or more of non-magnetic material
A magnetic recording medium according to claim 1, characterized in that
Build method.