JP2666823B2 - Magnetic recording medium and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly a magnetic recording medium having a very thin magnetic layer of 1.0 .mu. Manufacturing method. More particularly, the present invention relates to a magnetic recording medium having a non-magnetic layer as a lower layer, and more particularly to a magnetic recording medium having improved electromagnetic conversion characteristics, running properties and durability, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a video tape, an audio tape, a magnetic disk, etc., a magnetic layer in which a ferromagnetic iron oxide, a Co-modified iron oxide, CrO ₂ , a ferromagnetic alloy powder or the like is dispersed in a binder is used. Are coated on a non-magnetic support. 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 thickness of the magnetic layer has been reduced. However, when the thickness of the magnetic layer is reduced to about 2 μm or less, the effect of the surface properties of the support on the surface of the magnetic layer tends to appear, and the electromagnetic conversion characteristics tend to deteriorate. .

[0003] 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 above-mentioned problem caused by the surface roughness of the support is eliminated and the magnetic layer is made thin. Has proposed an attempt to reduce the thickness demagnetization and achieve a high output. For example, in Japanese Patent Application Laid-Open No. Sho 62-154225, the thickness of the magnetic layer is set to 0.5
μm or less to prevent the surface electric resistance of the magnetic layer from increasing. Recording media have been proposed. Also, JP-A-62-222
No. 427 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 a film thickness containing a ferromagnetic powder provided on the undercoat layer. 1μ
A magnetic recording medium having a magnetic layer of m or less has been proposed. However, since a part of the abrasive in the undercoat layer protrudes into the magnetic layer, the magnetic recording medium also has a magnetic head cleaning action. It is. In this way, the magnetic layer is thinned to achieve high-density recording, and at the same time, carbon black is included in the lower non-magnetic layer to prevent electrification, and an abrasive is added to improve cleaning characteristics and durability. doing.

However, in the prior art, the lower magnetic layer is first coated on a non-magnetic support, dried, and then, if necessary, calendered before providing the upper magnetic layer. It is complicated and has 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. When taking the former,
When 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 used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids,
Various adverse effects are caused, such as that a sufficient degree of filling of the ferromagnetic powder cannot be obtained, and that the strength of the coating film is insufficient due to many voids. As one means for solving these problems, as described in JP-A-63-191315, a non-magnetic layer is provided as a lower layer using a simultaneous multilayer coating method, and a magnetic coating solution having a high concentration is provided. Thin coating methods have been proposed.

In the simultaneous multi-layer coating method or the sequential wet coating method, that is, in 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 magnetic layers are already used in the multi-layer. Has been studied. However, even when this technique was applied to the lower non-magnetic layer, similarly good results could not be obtained. In other words, 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 cissing of the magnetic layer.

In the case where a nonmagnetic thick lower layer is provided on the surface of the support and the magnetic layer is provided with the magnetic layer as the upper layer, the influence of the surface roughness of the support can be eliminated.
There was a problem that head wear and durability were not improved. Conventionally, since a thermosetting (curing) resin is used as a binder as a non-magnetic lower layer, the lower layer is hardened, and the contact between the magnetic layer and the head and the contact with other members are unbuffered. This is considered to be caused by the fact that the magnetic recording medium having such a lower layer is somewhat less flexible. In order to solve this problem, it is conceivable to use a non-curable (thermoplastic) resin as a binder for the lower layer. However, in the conventional method, when the lower layer is coated and dried and then the magnetic layer is applied as the upper layer, the lower layer is used. Are swelled by the organic solvent in the upper layer coating solution, causing turbulence in the upper layer coating solution and the like, deteriorating the surface properties of the magnetic layer and deteriorating electromagnetic conversion characteristics.

In order to improve the recording density of a magnetic recording medium, short-wavelength recording has been advanced, and the recording wavelength of an 8-mm video tape has reached 0.54 μm. A magnetic recording medium using a ferromagnetic metal thin film has been put to practical use. Since the metal thin film magnetic recording medium has a very thin magnetic layer, the loss due to the thickness is small, and therefore, a medium having a very high output can be obtained. However, these media are manufactured by depositing a metal on a non-magnetic support, so that they are inferior in mass productivity as compared with conventional coated magnetic recording media. I have a problem with preservation. In order to solve these problems, it has been desired to reduce the thickness of the magnetic layer of the conventional coating type magnetic recording medium.

However, in order to apply the upper magnetic layer as a thin layer having a thickness of 1.0 μm or less, the magnetic liquid must be diluted with a large amount of a solvent, and aggregation of the magnetic liquid is easily promoted.
In addition, since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder is likely to be disturbed. Poor orientation,
Even if a thin layer is achieved, it is difficult to secure sufficient electromagnetic conversion characteristics due to deterioration of orientation and surface property. Further, since too much drying causes many voids, the strength of the magnetic film is weak, and the running durability is also insufficient. If an attempt is made to reduce the amount of the organic solvent to be diluted in order to improve the orientation and to reduce the voids in the coating film, the coating stability will deteriorate.

As a means for addressing such problems, it has been proposed to include a non-magnetic granular abrasive or filler in an undercoat layer (Japanese Patent Application Laid-Open No. 62-222427,
JP-A-2-257424). However, as a problem of these techniques, when the magnetic layer and the non-magnetic layer are simultaneously coated and the upper magnetic body is oriented, mixing occurs at the interface between the upper and lower layers due to the rotational movement of the magnetic body due to the magnetic field, Not only is it not possible to obtain sufficient surface properties, but also since the orientation is not sufficiently performed, sufficient electromagnetic conversion characteristics cannot be obtained.

It has been proposed to improve the orientation of magnetic particles in the upper layer by forming a conductive intermediate layer using graphite as non-magnetic scaly particles.
(Japanese Patent Application Laid-Open No. 55548/55) However, in such a substance, although the orientation is improved, graphite itself has no effect of reinforcing the film and is insufficient in durability. It has been proposed to mix inorganic powder. (JP-A-60-125926)
It has been proposed to improve the orientation of magnetic particles in the upper layer by forming a reinforcing layer using acicular oxalate as the non-magnetic acicular particles (Japanese Patent Publication No. 58-51327).
No.).

[0011] Although these proposals can improve the orientation and ensure the durability, at the stage of actually manufacturing the medium, the flaky particles are liable to stack, and substances such as oxalate are difficult to disperse in the binder. Was found to impair the smoothness of the magnetic surface. Further, the magnetic recording medium is required to have a very smooth surface property in order to reduce the spacing loss with the head for higher density and higher output.
For this reason, the lower non-magnetic layer which is not directly exposed on the surface also has a good dispersibility as much as possible, and the necessity for smooth surface properties in simultaneous multi-layer coating is increasing. As described above, when the thickness of the magnetic layer is reduced, the proportion of the dispersibility of the lower non-magnetic layer which contributes to the surface properties when the layers are simultaneously overlaid is increasing. As a result of intensive studies, even if the dispersibility of only the lower layer is simply improved,
As a result of simultaneous layering, it was found that the surface became rough.

If the coercive force of the magnetic layer is low, the self-demagnetization loss is large, and the magnetic layer is not suitable for short-wavelength recording. Means that can be used for such a purpose are 0.5 μm to 5 μm between the nonmagnetic support and the magnetic layer.
It has been proposed to provide an undercoat layer of 0 μm and make the Hc of the magnetic layer 1000 Oe (JP-A-57-198536).
No.). However, conventionally known techniques have the following problems to achieve this object. The aforementioned Japanese Patent Laid-Open No. 5
In the technique disclosed in Japanese Patent Application Laid-Open No. 7-198536, when the simultaneous multi-layer coating of the upper and lower layers, which is a feature of the present invention, is performed, mixing of the upper and lower layers occurs and not only the surface property is deteriorated, but also the orientation is disturbed.
As a technique for improving the orientation in the simultaneous multi-layer coating, Japanese Patent Application Laid-Open No. Hei 3-49032 discloses that a layer in which carbon black is dispersed is used as a lower layer to perform multi-stage orientation. Due to the rotational motion of the magnetic material during orientation, the interface between the upper and lower layers was disturbed during the simultaneous multilayer coating, and the small filler was measured in the in-plane direction.
Although Q was high, the improvement of the residual coercive force in the normal direction of the magnetic layer, which was the object of the present invention, was insufficient.

As a known technique for such a technique, there is Japanese Patent Application Laid-Open No. Sho 62-1115. However, when this known technique is applied to the simultaneous multi-layer coating as in the present application, there are the following problems. That is, in the case of simultaneous multi-layer coating using a non-magnetic lower-layer carbon black having a low specific gravity, mixing of the non-magnetic lower layer and the magnetic layer or turbulence of the two-layer interface due to turbulence is caused in the coating process or the alignment process. . Such mixing and turbulence between the two layers extremely lowers the orientation of the magnetic substance in the magnetic layer.

A magnetic substance having a short major axis length and a small acicular ratio is less likely to be flow-oriented, so that the orientation of the magnetic substance is further reduced and sufficient electromagnetic conversion characteristics cannot be obtained. In recent years, fine particles of a magnetic material included in a magnetic layer have been advanced for higher density. By making the particles fine, the strength of the magnetic layer becomes inferior. For example, when a high tension is applied in a manufacturing process or a video deck, the tape is elongated, and the skew (SKEW) distortion becomes large. In order to cope with this, it is attempted to reduce the heat shrinkage of the support or increase the strength, but there is a limit. Further, when the simultaneous multilayer coating method is employed, there is a problem that the heat shrinkage increases and the Skew distortion increases as compared with the sequential multilayer coating method. This is because, in the case of sequential multilayer coating, the lower layer was hardened by calendering and curing after the lower layer was applied to make the medium harder to stretch and shrink, but in the simultaneous multilayer coating method, the lower layer and the upper layer were applied at once. This is because expansion and contraction of the medium cannot be suppressed by the lower layer. JP-A-63-187418 and JP-A-63-191315
Japanese Patent Application Laid-Open Publication No. H11-163,086 discloses an invention based on a simultaneous multilayer coating method, but has such a drawback.

[0015] Similarly, there is a tendency that the tape thickness is reduced in order to increase the length of the tape. When the thickness of the tape is reduced, the tape stiffness is reduced, so that good contact with the head cannot be maintained, and the electromagnetic conversion characteristics are reduced. In particular, 8mm video tapes and VH
Since the total thickness of the long tape of S is as thin as 14 μm or less, it is difficult to secure head contact. Conventionally,
It was effective to lower the strength of the lower non-magnetic layer to maintain a smooth contact state in a medium with a large thickness,
In recent years, in a thin tape in a recording / reproducing apparatus using a rotating head, it is difficult to secure head contact unless the stiffness of the lower nonmagnetic layer is increased. There is a method of controlling the stiffness by a method of stretching the non-magnetic support, but the stiffness in the width direction is reduced, which is not preferable for running durability.

As disclosed in Japanese Patent Application Laid-Open No. 63-191315, the effect of not containing a polyisocyanate in the lower non-magnetic layer was confirmed to improve the head contact. The result is poor storage stability. Therefore, this method is effective in a system that does not emphasize saving, but is difficult to use in a system that emphasizes saving such as business use or data saving. JP-A-63-187
JP-A-418-418 also discloses that the magnetic layer is similarly thinned to improve the electromagnetic conversion characteristics, but there are still some of the inventions whose electromagnetic conversion characteristics are insufficient. Japanese Patent Application Laid-Open No. 50-803 also discloses an invention in which a fine-grained non-magnetic pigment having a Mohs' hardness of 6 or more is provided between a magnetic layer and a support. The purpose is to increase the flatness of the substrate by polishing with non-magnetic powder.

Further, it is difficult for these methods to respond to the recent demand for a thinner magnetic recording medium due to longer time and higher density, and these methods provide excellent electromagnetic conversion characteristics and running durability. Incompatibility was inadequate. Particularly, in order to improve running durability with a thin tape, it is necessary to reduce tape edge damage.
The inventions of JP-A No. 15 and JP-A-63-187418 are insufficient.

A magnetic recording medium using plate-shaped hexagonal ferrite has been proposed as a coating type magnetic recording medium capable of performing high-density recording. However, a magnetic recording medium using plate-shaped hexagonal ferrite has a low surface electric resistance. There was a problem that it became extremely high. In order to solve this drawback, a first magnetic powder made of carbon black and high magnetic permeability magnetic powder such as Cu-Zn ferrite is used.
A magnetic recording medium comprising a magnetic film and a second magnetic film comprising a plate-like hexagonal ferrite magnetic powder such as barium ferrite is described in JP-A-62-180523. In addition, carbon black and carbon black having a particle size of 5 are provided between the magnetic layer containing the plate-like hexagonal ferrite and the nonmagnetic support.
A magnetic recording medium provided with a conductive layer containing a nonmagnetic needle-like insulator having an axial ratio of 5 to 15 and an axial ratio of 5 to 15 is disclosed in Japanese Patent Laid-Open No. 1-30041.
No. 9 has been proposed. However, Japanese Patent Application Laid-Open No. 62-18 / 1987
The thickness of the second magnetic film of the magnetic recording medium described in Japanese Unexamined Patent Publication No. 0523 is 3 μm or less, and is as thick as 2 μm in the embodiment. The diameter of the non-magnetic needle-like insulator is large, and the smoothness of the interface with the magnetic layer is not sufficient, and the thickness of the first magnetic film is as thick as 3 μm. It is insufficient for obtaining excellent electromagnetic conversion characteristics.

As a magnetic recording medium having a thin second magnetic film, a magnetic recording medium having a thickness of 1 μm or less has already been described in JP-A-62-222427. The first layer of the recording medium merely contains an abrasive that sticks out to the magnetic layer, and has only a magnetic head cleaning action. In addition, Japanese Unexamined Patent Application Publication No.
In Japanese Patent No. 254621, a non-magnetic layer mainly composed of carbon black is provided on a non-magnetic support, and F
Including a plate-like hexagonal ferrite magnetic powder such as e-Al ferromagnetic powder or barium ferrite, the film thickness is 0.3 to
A magnetic recording medium in which a 4.0 μm magnetic layer is formed by a wet-on-wet multilayer coating method is disclosed. However, an example of the lower layer is only carbon black, which has too high a structural viscosity to solve the disorder of the interface.

Next, various patent applications have been filed for obtaining a magnetic recording medium by a wet-on-wet method in which the upper layer is a magnetic layer and the lower layer is nonmagnetic. For example, Japanese Patent Application Laid-Open No. Sho 50-104003 discloses that wet-on-wet is suggested, but the non-magnetic layer is an example of only carbon black, and the structural viscosity is too strong, and the interface disorder is severe.

Also, Japanese Patent Application Laid-Open No. 62-22922 (US Pat.
No. 4,916,024) discloses a magnetic recording medium in which a conductive layer (intermediate layer) contains 5% to 25% of ferromagnetic powder of carbon black. This is to improve the dispersibility of carbon black,
Since the ferromagnetic powder to be added to the intermediate layer is the same as that in the magnetic layer, disturbance at the interface could not be successfully prevented. Japanese Patent Application Laid-Open No. Sho 62-214524 discloses that each coating solution composition is selected so as to have mutual solubility with respect to the solvent and solute of each coating solution composition of a plurality of adjacent layers.
A method for manufacturing a magnetic recording medium that is applied and dried in et on Wet is disclosed. However, although there is an example of a combination of an upper magnetic layer and a lower non-magnetic layer, it is an example of only a binder and suggests that carbon black is also included in the intermediate layer, but based on such disclosure, The disturbance of the interface could not be eliminated. JP-A-62-24113
No. 0 (US Pat. No. 4,839,225) discloses that an intermediate layer contains at least one binder having a hydroxyl group and / or an amino group.
And a magnetic recording medium in which the magnetic layer contains an isocyanate compound, and discloses that the two are chemically bonded to each other to improve the adhesion strength between the intermediate layer and the magnetic layer. It is stated that carbon black may be added to the intermediate layer and that the intermediate layer may be applied by a wet-on-wet method. However, such a disclosure could not solve the interface fluctuation.

Further, Japanese Patent Application Laid-Open No. 63-88080 (US Pat.
No. 4,854,262) improves the doctor's edge.
An application device is disclosed. High shear rate in this
(10 ^Foursec^-1), The viscosity is disclosed.
Layer, only the viscosity of the underlayer liquid was shown
The interface fluctuation could not be sufficiently suppressed. Also JP 6
JP-A-3-146210 discloses a lower magnetic layer or a non-magnetic layer.
Of the uppermost magnetic layer
A magnetic recording medium in which the mixture is an electron beam-curable resin is disclosed.
ing. However, carbon black is used for the lower non-magnetic paint.
This is only an example that contains the
Could not. JP-A-63-164022
Liquid in the slot of the extrusion head
Slot a non-magnetic liquid layer with lower viscosity than the magnetic liquid layer at the center of the layer
A magnetic liquid that is formed on the front and rear wall surfaces and extruded in multiple layers
An application method is disclosed. Low magnetic layer liquid with high viscosity
Non-magnetic layer binder solution of high viscosity is wrapped, and high-speed thin layer coating is possible.
The magnetic layer coating solution beads and
The purpose is to reduce the gap between the lasers. Such an open
It is not possible to sufficiently solve interface turbulence by only showing
Was. Also, JP-A-63-187418 (US4863)
No. 793) describes a ferromagnetic powder contained in the upper magnetic layer.
The average major axis length by transmission electron microscope is less than 0.30 μm.
The crystallite size by X-ray diffraction is less than 300 °
A magnetic recording medium is disclosed. The lower non-magnetic layer
Contains carbon black, graphite, titanium oxide, etc.
And α-Fe as a specific example._Two
O_ThreeCombination of 100 parts by weight and 10 parts of conductive carbon
It is shown. However, low carbon usage
That, α-Fe_TwoO_ThreeParticle size is not listed
Therefore, the disclosures of these publications sufficiently resolve interface disturbances
I couldn't do that.

Further, JP-A-63-191315 (U.S. Pat.
In S4963433, the binder in the lower layer is a thermoplastic binder, and the thickness of the lower layer is 0.5 μm in dry thickness.
m or more. Specific examples of the non-magnetic powder contained in the lower non-magnetic layer include α-Fe ₂ O ₃ 10 as described in JP-A-63-187418.
A combination of 0 parts by weight and 10 parts of conductive carbon is disclosed. However, the small amount of carbon used α-
Since the particle size of Fe ₂ O ₃ is not described, the disclosure of these publications could not solve the disorder of the interface. Further, Japanese Patent Application Laid-Open No. 2-257424 discloses a magnetic recording medium in which a nonmagnetic layer contains a filler having an average particle size of 50 μm or more. Examples of the filler include abrasives such as carbon black, Al ₂ O ₃ and SiC. However, a specific example is the use of only carbon black, only Al ₂ O _{3, and} only SiC, and such a combination could not solve the disorder of the interface.

Next, JP-A-2-257425 discloses that the coefficient of kinetic friction is 0.25 or less and the surface resistivity is 1.25.
A magnetic recording medium provided with a plurality of layers of 0 × 10 ⁹ Ω / sq or less is disclosed. However, examples of the nonmagnetic powder in the lower layer are only SnO _{2 and} only carbon black,
Interface turbulence could not be resolved. Also Japanese Patent Laid-Open No. 2
JP-A-260231 discloses a magnetic recording system in which a first nonmagnetic layer, a first magnetic layer, a second nonmagnetic layer, and a second magnetic layer are laminated in this order on a nonmagnetic support. A medium is disclosed. This non-magnetic layer is an example of only the binder, and the disturbance of the interface could not be solved.

Further, Japanese Patent Application Laid-Open No. 3-49032 (US Pat.
No. 051291) has a magnetic layer thickness of 1.5 μm.
The magnetic recording medium is disclosed below, wherein the magnetic layer has a squareness ratio of 0.85 or more. This is to improve the squareness ratio by multi-stage orientation, but the lower layer is a layer using only carbon black, and the structural viscosity is too strong to solve the interface disorder. Further, Japanese Patent Laid-Open No. 5-
No. 12650 discloses that a nonmagnetic buffer layer is provided on a nonmagnetic support, and a magnetic layer composed of hexagonal ferrite plate-like magnetic powder is provided on the nonmagnetic buffer layer by simultaneous coating. Although a magnetic tape coated with is described,
With the formulation of the coating solution for the lower non-magnetic layer described, appropriate thixotropic properties cannot be obtained, and interface disturbance cannot be solved.

In recent years, Hi8 tapes have been studied, and the ultimate need is to satisfy both the advantages of ME (vapor deposition) tapes and MP (metal) tapes. The most important issue was how to maintain the runnability, durability, and suitability for production, and how to achieve a high C / N ratio in a short wavelength region (high-range luminance signal) like a vapor-deposited tape. .

Conventionally, double coating technology has been used in VTRs.
By focusing on the signal recording mechanism, that is, the recording depth of each signal, the performance has been improved by designing the upper and lower magnetic layers that are optimal for each. The VHS double coating has realized a high output and a low noise in all the bands of luminance, color, and sound by using a two-layer structure in which ferromagnetic powders having different sizes and magnetic characteristics are used for an upper layer and a lower layer, respectively.

In the Hi8MP multilayer tape, a metal magnetic material corresponding to high-density recording is used for the upper magnetic layer, and an iron oxide magnetic material excellent in medium and low-frequency characteristics is used for the lower magnetic layer.
The so-called high-grid double coating using completely different types of magnetic materials was developed, and a great improvement in image quality was achieved, such as reproduction of images with high sharpness and vivid colors.

However, in order to pursue further ultra-high-density recording with Hi8MP and to dramatically improve high-frequency characteristics, there has been a limit only by the conventional techniques and ideas. Therefore, the present inventors conducted analysis and research by stepping down to the principle and mechanism of magnetic recording itself, and made intensive studies to realize high-frequency characteristics higher than that of a vapor-deposited tape.

[0030]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a high-density magnetic recording medium which, while being of a coating type, exhibits a high-frequency output comparable to that of a vapor-deposited tape and has running durability and storage stability. To provide. A second object of the present invention is the first object of the present invention, which is a coating type, and provides output, C / N with good yield and high production efficiency.
An object of the present invention is to provide a thin-layer magnetic recording medium having excellent electromagnetic conversion characteristics such as a ratio, and to provide a thin-layer magnetic recording medium which has good head contact and good storage stability.

A third object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability. In particular, the output in short wavelength recording is high,
An object of the present invention is to provide a magnetic recording medium having a high production yield. A fourth object of the present invention is to provide a magnetic recording medium having high RF output, excellent running durability, low dropout, and low block error rate (BER).

A fifth object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics and good running properties. Particularly, the simultaneous multilayer coating method has good surface roughness and high electromagnetic conversion characteristics. It is to provide a magnetic recording medium. A sixth object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics, and a small heat shrinkage,
An object of the present invention is to provide a magnetic recording medium having excellent long-term storage characteristics. A seventh object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics and to provide a medium having little edge damage due to repeated running and excellent running durability.

[0033]

The above object of the present invention is achieved by the following magnetic recording medium of the present invention and a method of manufacturing the same. That is, the present invention provides a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder on a support,
In a magnetic recording medium having at least two or more layers in which an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder is provided, the dried magnetic layer has an average dry thickness (d) of 1 μm or less. And the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization perpendicular to the flat plate as the ferromagnetic powder, and the nonmagnetic powder of the lower nonmagnetic layer has a Mohs hardness of 3 or more. A magnetic recording medium, the average particle size of which is smaller than the plate diameter of the hexagonal plate-like ferromagnetic powder, and a lower non-magnetic layer coating solution in which the non-magnetic powder is dispersed in a binder; A method for preparing a magnetic recording medium in which a coating solution for an upper magnetic layer dispersed in a binder is prepared, and the coating solution for a lower nonmagnetic layer and the coating solution for an upper magnetic layer are coated on a support. The coating solution for the magnetic layer is The powder includes a hexagonal plate-shaped ferromagnetic powder having an axis of easy magnetization perpendicular to the flat plate, and the coating liquid for the lower non-magnetic layer has a Mohs hardness of 3 or more as the non-magnetic powder and has an average particle size of After containing the inorganic powder smaller than the average plate diameter of the hexagonal plate-like ferromagnetic powder and applying the lower non-magnetic layer coating solution on a support, while the lower non-magnetic layer is in a wet state, The magnetic recording medium according to claim 1, wherein the coating liquid for the upper magnetic layer is applied simultaneously or sequentially with the application of the coating liquid for the lower nonmagnetic layer so that the average dry thickness (d) of the upper magnetic layer is 1 μm or less. This can be achieved by a manufacturing method.

Further, preferred embodiments of the magnetic recording medium of the present invention are as follows. (1) AFM (Atmic Force Micr) on the surface of the upper magnetic layer
o Scope) or a magnetic recording medium having an Rrms of 20 nm or less as measured by a scanning tunneling microscope (STM) method. (2) A magnetic recording medium in which the lower nonmagnetic layer has a volume filling ratio of 20 to 60% in the lower nonmagnetic layer of the inorganic powder. (3) The hexagonal plate-like ferromagnetic powder has a plate diameter of 0.001 to 0.001.
A magnetic recording medium of 0.3 μm. (4) A magnetic recording medium in which the hexagonal plate-like ferromagnetic powder is a plate-like hexagonal ferrite of barium ferrite, strontium ferrite, lead ferrite, or calcium ferrite. (5) The hexagonal plate-like ferromagnetic powder has a plate diameter of 0.001 to 0.001.
0.09 μm, and the plate thickness is ２〜 to の of the plate diameter.
0 and a magnetic recording medium having a specific surface area of 1 to 60 m ² / g.

(6) The nonmagnetic powder of the lower nonmagnetic layer is T
iO_Two(Rutile, anatase), TiO_X, Cerium oxide
System, tin oxide, tungsten oxide, ZnO, ZrO_Two,
SiO _Two, Cr_TwoO_Three, Α aluminum with α conversion rate of 90% or more
Na, β alumina, γ alumina, α iron oxide, goethite,
Corundum, silicon nitride, titanium carbide, magnesia
Cium, boron nitride, molybdenum disulfide, copper oxide, MgC
O_Three, CaCO_Three, BaCO_Three, SrCO_Three, BaSO
_Four, At least one selected from silicon carbide and titanium carbide
A magnetic recording medium. (7) The flexible support is polyethylene terephthalate
Polyesters such as g, polyethylene naphthalate,
Polyolefins, cellulose triacetate, polycarbonate
-Carbonate, polyamide, polyimide, polyamideimi
, Polysulfone, aramid, aromatic polyamide
At least one selected magnetic recording medium. (8) The lower non-magnetic layer has a saturation maximum magnetic flux density Bm of 50.
A magnetic recording medium of 0 gauss or less. (9) The lower non-magnetic layer imparts thixotropy
A magnetic recording medium containing a magnetic powder. (10) The lower nonmagnetic layer contains a magnetic powder, and
The lower non-magnetic layer is a magnetic recording medium that is not involved in recording.
body. (11) The magnetic recording medium is for DAT or a magnetic disk.
Magnetic recording media for

In order to solve the above-mentioned problems of the present invention, the present inventors use a plate-like hexagonal ferrite ferromagnetic powder as the ferromagnetic powder and use a simultaneous multilayer coating technique. As a result of intensive study on the basis of that,
Thoroughly reduce the "signal loss" that increases as the recording becomes shorter, reduce the thickness of the magnetic layer, and develop a new magnetic material and increase the packing density to maximize the magnetic energy of the magnetic layer We found that two points were important.

The means for solving the above-mentioned problems of the present invention is based on using a plate-like hexagonal ferrite-based ferromagnetic powder as the ferromagnetic powder and using a simultaneous multilayer coating technique. It is constituted by means consisting of the following first to fifth points based on the above two points as a basic idea. First,
The thorough reduction of signal loss was carried out. Above all, until now M
Based on a completely new concept of the present inventors to improve the high-frequency characteristics by reducing the “self-demagnetization loss” that was considered inevitable with P (metal) tape, Was reduced. Also,
Along with self-demagnetization loss, space loss is another major cause of high-frequency characteristics degradation due to signal loss, and we have reduced it.

That is, the first point of the present invention is to make the coating liquid of the upper magnetic layer and the lower non-magnetic layer have the same or similar chicken tropism or to adjust the shape of the lower non-magnetic powder at the interface. By eliminating the mixed region, it is possible to realize an unprecedented uniform thin magnetic layer having a thickness of the magnetic layer of 1 μm or less, an average value of the thickness variation of １ ／ of the thickness or less, and a standard deviation of the measured thickness of 0.2 μm or less. In addition, the self-demagnetization loss in the short wavelength region is greatly reduced.

Further, a second point of the present invention is that the disturbance of the interface is suppressed to an extremely low level, and the size and shape of the ferromagnetic powder of the upper magnetic layer, the size of the nonmagnetic powder of the lower nonmagnetic layer,
By adjusting the shape and adding an invention to improve the dispersibility of the non-magnetic powder itself, a more uniform interface with less variation was realized and an ultra-smooth magnetic layer surface was completed. This smooth magnetic layer surface completely eliminated the "space loss" and improved high-frequency output.

The third point of the present invention is to increase the energy of the magnetic layer. It has been found that by using a ferromagnetic powder of fine particles with both high Hr and Hc in the upper magnetic layer, high magnetic energy and high coercive force can be achieved, and a high frequency output equal to or higher than that of a ME (evaporation) tape can be exhibited. Fourth Embodiment of the Present Invention
Is high density packing. In the conventional technology, when the magnetic layer is simply made thinner, the low-frequency output decreases and the color characteristics deteriorate, but in the present invention, the particulate inorganic powder having extremely high rigidity in the thickness direction greatly enhances the filling effect by calendering. It has been found that, by improving the density and filling the high-energy ferromagnetic powder at a high density, excellent mid- and low-frequency characteristics can be realized.

The fifth point of the present invention lies in characteristics such as viscoelasticity, adhesion strength, steel ball wear, residual solvent, and sol fraction which ensure excellent durability which cannot be achieved by ME (evaporation) tape. As described above, the first to fifth points of the present invention mutually act organically supplementally, additively and even comprehensively, and an unprecedented new layer constitution is an ultra-thin layer, an ultra-smooth layer,
It enables ultra-high filling and achieves revolutionary high-frequency characteristics and excellent mid- and low-frequency characteristics that were difficult with conventional single-layer coating technology.

First, the first point of the present invention will be described. That is, the object of the present invention is to provide a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder on a non-magnetic support, and bond the ferromagnetic powder while the lower non-magnetic layer is in a wet state. In a magnetic recording medium having at least two or more layers provided with an upper magnetic layer dispersed in an agent, an average dry thickness (d) of the upper magnetic layer is 1 μm or less, and the upper magnetic layer and the lower layer This can be achieved by a magnetic recording medium characterized in that the average value Δd of the thickness variation at the interface of the nonmagnetic layer satisfies the relationship Δd ≦ d / 2.

That is, the first point of the present invention is to realize an ultra-thin magnetic layer. From the principle of self-demagnetization, it has been found that the loss decreases as the cross-sectional area of the magnetic layer decreases, so that the ultra-thin magnetic layer is indispensable for increasing the output of a short-wavelength signal. In addition, the effect is small at a thickness of 1 μm or more, and the effect increases as the recording thickness approaches the effective recording thickness generally called い of the recording wavelength, that is, as the recording approaches the saturation recording. is required.

In the conventional single-layer coating technique, it is difficult to apply a thin layer in the submicron region itself, and the thinner the layer is, the more difficult it is to secure a uniform thickness and to achieve ultra-smoothness. It was extremely difficult to do. However, innovating the conventional double coating technology, a non-magnetic layer containing fine-particle inorganic powder is provided in the lower layer by wet-on-wet, and the average value of the thickness variation of the magnetic layer is less than 1/2 of the thickness, and the standard deviation of the thickness of the magnetic layer is reduced. By setting the thickness to 0.2 μm or less, an epoch-making ultra-thin magnetic layer, which is difficult with the conventional technology of 1/3 to 1/10 or less of the conventional general Hi8 MP tape, reduces self-demagnetization loss. Thus, the luminance signal output is greatly improved.

The principle of self-demagnetization is as follows. The poles of a magnetized magnet create a magnetic field not only outside the magnet but also inside it. The magnetic field inside the magnet is opposite to the direction of the magnetization and acts in a direction to decrease the magnetization. This internal magnetic field is called a "demagnetizing field", and the decrease in magnetization caused by this is "self-demagnetizing".

The size depends on the shape of the magnet. In other words, the demagnetizing field decreases as the cross-sectional area decreases and the distance between the magnetic poles increases, and self-demagnetization is less likely to occur. Taking as an example a sewing needle and a pachinko ball that have completely different shapes, they are all made of iron and stick to a magnet. Because of the large magnetism, oneself has the property of not easily becoming a magnet.

When this is replaced with a magnetic tape, the demagnetizing field is small in long-wavelength (low-band) recording, but short-wavelength (high-band).
As the recording is performed, the distance between the magnetic poles of the magnetization decreases, the demagnetizing field increases, and the loss due to self-demagnetization increases. This is one of the major factors that degrade the high frequency characteristics of the tape. In order to reduce the self-demagnetization loss, it is effective to reduce the cross-sectional area according to the principle of self-demagnetization, that is, to reduce the thickness of the magnetic layer. In addition, the self-demagnetization loss becomes smaller as the recording approaches the saturation recording and the output is improved, so that the effective magnetic layer thickness is close to １ ／ of the recording wavelength. Ultra-thin layers in the submicron region are required.

The shortest recording wavelength of Hi8 is 0.49 μm,
This is an extremely short wavelength, which is one of the reasons why the magnetic layer has an excellent high-frequency characteristic as well as an extremely thin ME (evaporation) tape having a thickness of about 0.2 μm. On the other hand, the thickness of the magnetic layer of the coating type MP tape is about 3 μm, and in the conventional coating method, it has to be considerably thicker than the recording wavelength, and deterioration of high-frequency characteristics due to self-demagnetization loss increases image quality. It was an inevitable big wall.

However, according to the present invention, such a wall was greatly broken. Space loss is also an important factor. Along with self-demagnetization, another major cause of high-frequency characteristic degradation is space loss. The shorter the wavelength, the weaker the magnetic flux that appears on the tape surface, so even the slightest spacing between the tape and the video head can result in large losses. The space loss includes a microscopic loss caused by the roughness of the magnetic layer surface and a macroscopic loss caused by the rigidity of the tape. The former has a problem how to secure stable running performance while realizing super smoothness.
As described above, the importance is extremely high in high-density recording in which the shortest recording wavelength is about 40% of VHS. The latter is what is called "head contact", and the problem is how to achieve both excellent tape strength and flexibility. This is not limited to short-wavelength recording, and greatly affects the image quality. The present invention has solved the problem of space loss at once.

Next, the second point of the present invention will be described. That is, according to the present invention, the dry thickness d of the upper magnetic layer is 1.0 μm or less, and the mean square roughness R of the surface of the upper magnetic layer by a scanning tunneling microscope (STM) is used.
_rms is 30 ≦ d / d between the dry thickness d of the upper magnetic layer.
Preferably, there is a relationship of R _rms .

The second point of the present invention is ultra-smoothing of the magnetic layer surface. Originally, the double coating technique is a technique that can realize excellent smoothness. This is because the lower magnetic layer absorbs the irregularities on the surface of the base film and makes it difficult to transmit the influence of the irregularities to the upper layer. However, 0.5
The problem with the very small space loss at shorter wavelengths of less than μm has been a problem, and there has been a limit to the prior art alone when aiming at further smoothness.

Due to the recording mechanism, it is necessary to use an ultra-fine particle magnetic material having excellent high-frequency characteristics for the upper layer. It is necessary to pursue it thoroughly. In particular, as the upper layer becomes an ultra-thin layer, the influence of the smoothness of the interface on the smoothness of the surface of the magnetic layer increases, and the solution of this problem has become even more important.

In the present invention, in order to make the interface between the upper and lower layers ultra-smooth, the non-magnetic particles in the lower layer are made ultra-fine and the density thereof is increased. However, on the other hand, it is difficult to fill uniformly and densely as it is because it is extremely fine particles. Is achieved, and the smoothness of the interface between the upper and lower layers is dramatically improved.

Since the non-magnetic layer is a high-density filling layer, the non-magnetic layer has a high degree of freedom in the surface direction of the tape, has excellent flexibility, and is intense against force in the thickness direction. It demonstrates high rigidity and further enhances the smoothing effect of the calendering process. As a result, Hi8
20% smoother than MP-DC
The magnetic layer achieved a surface roughness of 2.5 nm. The super-smoothness that can be realized only by the wet-on-wet in which the nonmagnetic layer is provided as the lower layer significantly reduces the space loss in the short wavelength region and improves the high-frequency characteristics.

Next, the third point of the present invention will be described. That is, according to the present invention, the ferromagnetic powder contained in the upper magnetic layer is a powder having a plate diameter of 0.3 μm or less, and
Is preferably a plate-like ferromagnetic powder of 1000 Oe or more. That is, the third point of the present invention is to reduce the output and noise of the magnetic layer, which is the basis of the technology for improving the performance of the magnetic tape. In order to thoroughly pursue improvements in characteristics at short wavelengths, minimizing signal loss, as well as high output and low noise of the magnetic layer itself by "ultra-fine particles of magnetic material, high energy, and high density filling" Is essential.

Next, a fourth point of the present invention will be described. That is, in the present invention, the ratio SMD / STD of the stiffness SMD in the application direction of the magnetic recording medium to the stiffness STD in the width direction with respect to the application direction is preferably 1.0 to 1.9. Specifically, the inorganic powder contained in the lower nonmagnetic layer has a Mohs hardness of 6 or more and an average particle size of 0.15 μm.
It is preferable to use the following polyhedral inorganic powder ranging from spherical to cubic.

The present invention also relates to the magnetic recording medium of the present invention.
The heat shrinkage at 30 ° C. for 30 minutes is preferably 0.4% or less, and specifically, the dry thickness of the lower non-magnetic layer is 1 to 30 times the dry thickness of the upper magnetic layer. Preferably, the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is in the range of -5% to + 20%.

That is, the fourth point of the present invention is the high-density filling, and the lower non-magnetic layer enables high-density filling of the magnetic material of the present invention. The non-magnetic layer that is smooth and extremely rigid in the thickness direction is made of Super HDP
(High Density Packing) The powerful pressure of the calendar was firmly received, and an unprecedented breakthrough in high density packing was realized. Further, if the high-frequency characteristics are thoroughly pursued by making the magnetic layer ultra-thin, the mid- and low-frequency characteristics are reduced by the conventional technology, and excellent color characteristics cannot be obtained. However, the lower non-magnetic layer of the present invention enables a revolutionary high filling of the high-energy magnetic material that solves this, and at the same time as significantly improving the high-frequency output, securing high mid / low-frequency characteristics and excellent Color output was realized.

That is, in the present invention, high-density recording comparable to a vapor-deposited tape, which was conventionally considered impossible with a coating type magnetic recording medium, was achieved. Among them, a uniform upper magnetic layer could be formed as a thin layer having a dry thickness of 1.0 μm or less by the so-called Wet on Wet method of providing the upper magnetic layer.
The average value of the dry thickness of the upper magnetic layer, which has not been achieved by the magnetic recording medium method according to the method, is 1 μm or less, and the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer is Δd ≦ d Thus, a magnetic recording medium having a relationship of / 2 was obtained, and as a result, a high-density recording medium practically practical and comparable to a vapor-deposited tape was obtained for the first time. Conventionally, a magnetic recording medium having an upper magnetic thin layer and a lower non-magnetic layer having a dry thickness of 1.0 μm or less has been found only as patent applications, and no product has ever been found that is actually commercially available. Was. The present invention is an epoch-making invention that breaks such conventional wisdom for the first time.

Here, the definition and measurement method of Δd are as follows. Here, the method of obtaining the thickness of the upper magnetic layer and the interface fluctuation Δd is as follows. That is, the magnetic recording medium was cut out to a thickness of about 0.1 μm in the longitudinal direction with a diamond cutter, and the transmission electron microscope was used to magnify 10,000 to 1 ×.
Observation was performed at a magnification of 0000 times, preferably 20000 to 50,000 times, and the photograph was taken. The print size of the photograph was A4 to A5. Thereafter, the interface was visually determined by focusing on the difference in shape between the magnetic material and the nonmagnetic powder of the upper magnetic layer and the lower nonmagnetic layer, and the surface of the magnetic layer was similarly blackened. Then, Zeiss image processing device IB
In AS2, the length of the interval between the trimmed lines was measured. Thereby, the average value of the thickness of the upper magnetic layer was obtained. The length of the interval was measured by segmenting the 21 cm length interval into 100 to 300 segments.

The average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower non-magnetic layer is the peak of the mountain formed by the bordered interface between the magnetic layer and the lower non-magnetic layer having a length of 20 μm (actual length). We distance in the thickness direction of the bottom of the valley ([Delta] d _i) from 10 to 20 locations (all in 20 [mu] m) obtained as an average of the sum. That is, in the present invention, it is the most preferable mode that the curve forming the interface is ideally a straight line having a constant d. It is preferable that a curve similar to a long smooth sine curve is formed, and the number of peaks and valleys is 2
It is preferable that the length is limited to about 10 to 20 at a maximum of 0 μm (see FIG. 1).

That is, Δd is obtained from the following equation. Δd = (Δd ₁ + Δd ₂ + ... + Δd _m ) / m
(M = 10-20) Further, the distance (L) between peaks of the curve formed by the interface is preferably 1 μm or more, particularly preferably 2 μm or more. Further, in the present invention, the standard deviation σ can be obtained by using the values of the thickness of each magnetic layer segmented into 100 to 300 exactly the same as those used in the statistical processing. This standard deviation σ is preferably 0.2 μm or less.

The first point of the present invention is that a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder is provided on a flexible support, and the lower non-magnetic layer is provided thereon while the lower non-magnetic layer is in a wet state. In a magnetic recording medium having at least two or more layers provided with an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder, the dry thickness average value (d) of the upper magnetic layer is 1
μm or less, and the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer has a relationship of Δd ≦ d / 2. The magnetic recording medium is characterized in that the standard deviation σ of the average value of the measured values of the dry thickness of the upper magnetic layer is 0.2 μm or less.

There are the following two specific means for achieving the above definition. The first aspect is to control the thixotropic properties of the magnetic coating material of the magnetic layer and the respective dispersions of the lower non-magnetic layer so as to approximate each other. That is, the size and shape of the powder to be formed are regulated so as to control mechanically so that a mixed region is not formed in the upper layer and the lower layer.

As a specific method of the first embodiment, a dispersion obtained by dispersing a nonmagnetic powder in a binder has a thixotropic property and a shear stress A at a shear rate of 10 ⁴ sec ^−1.
Shear stress at 10 ⁴ and shear rate 10 sec ^-1 A10
The ratio A10 ⁴ / A10 with 100 ≧ A10 ⁴ / A10 ≧
Adjust to 3. There are the following four specific means for having such thixotropic properties. The magnetic recording medium of the present invention is not limited to these four, and the essence thereof is to make the thixotropy of the dispersion the same or similar to the thixotropy of the magnetic paint, More specifically, it is in the range of A10 ⁴ / A10. (A) the powder of the lower non-magnetic 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-magnetic layer, and the lower non-magnetic layer and the upper magnetic layer contain a thermosetting polyisocyanate 10 in binder
To 70% by weight. (B) The powder of the lower non-recording layer has an average primary particle size of 0.08 μm
m or less. (C) a magnetic powder that imparts thixotropic properties such that the dry thickness of the upper magnetic layer is 1.0 μm or less and the saturation maximum magnetic flux density Bm of the lower nonmagnetic layer is 500 gauss or less, preferably 30 to 500 gauss. to use. However, the lower non-magnetic layer does not participate in recording. (D) The ferromagnetic magnetic powder in the upper magnetic layer has a plate diameter of 0.3 μm or less, and the lower layer contains non-magnetic metal oxide powder as non-magnetic powder and carbon black having an average particle size of less than 20 nm of 95 /
It is contained at a ratio of 5 to 60/40, and at least the lower layer contains a polyurethane having 3 OH groups in one molecule and a polyisocyanate compound.

These (A) to (D) correspond to A10 ⁴ / A
Although preferred means for adjusting 10 to the above range are shown, they are related to each other (including overlapping descriptions) with the following factors, and by variously selecting, the desired A10 ^{It is possible} to obtain a dispersion having ⁴ / A10 and a magnetic coating material, and to manufacture a magnetic recording medium having desired characteristics.

As the factors, for example, regarding the inorganic powder or magnetic powder to be dispersed, (1) particle size (specific surface area, average primary particle diameter, etc.), (2) structure (oil absorption, particle form, etc.), (3) the nature of the powder surface (pH, heating loss etc.), (4) the suction force of the particles (sigma _S, etc.) or the like, with respect to the binder, (1) molecular weight, (2) types of functional groups such as, solvent Examples of (1) include (1) the type (polarity, etc.), (2) the solubility of the binder, (3) the formulation amount of the solvent, and the water content.

Next, specific means of the second embodiment include the following (E) to (G), but the essential point thereof is essentially a mixed region between the lower non-magnetic layer and the upper magnetic layer. And these are merely examples. (E) The longest axial length r _{1 of the} nonmagnetic powder contained in the lower layer
That the ratio r ₁ / r ₂ of the shortest axial length r ₂ to 2.5 or more. (F) The needle ratio of the non-magnetic powder is 2.5 or more, and the average diameter of the longest axial length of the ferromagnetic powder is 0.3 μm or less. (G) The lower non-magnetic layer contains scale-like non-magnetic powder and a binder containing an epoxy group having a molecular weight of 30,000 or more, and the upper magnetic layer contains needle-like ferromagnetic powder or plate-like ferromagnetic powder. To make it.

In these, acicular non-magnetic powder or scaly non-magnetic powder is used for the lower non-magnetic layer in order to prevent a mixed region from being formed at the interface between the lower non-magnetic layer and the upper magnetic layer. Compared to conventional granular non-magnetic powders, if needle-shaped non-magnetic powders are present in a line, a strong coating film is formed even in an undried state, and even when the ferromagnetic powder in the upper magnetic layer rotates, the No mixing occurs. Another means for preventing the mixed region from occurring is to lay the tiles in a so-called tile form using scale-like non-magnetic powder for the lower non-magnetic layer. Even when the ferromagnetic powder rotates, no mixing occurs at the interface.

In order to improve the dispersibility, it is preferable to use a binder containing an epoxy group having a molecular weight of 30,000 or more to spread the tiles. By using non-magnetic powder having a characteristic shape in the lower non-magnetic layer and providing the upper magnetic layer on the lower non-magnetic layer, a mixed region does not occur at the interface, and therefore, an extremely thin and smooth magnetic layer is formed. A layer is obtained.

In the magnetic recording medium of the present invention, the dry thickness average value d of the magnetic layer is λ / 4 ≦ d with respect to the shortest recording wavelength λ.
≦ 3λ and the magnetic layer has a surface roughness Ra ≦ λ / 50.
It is preferable that the following relationship is satisfied. A preferable powder composition for this purpose is that the ferromagnetic powder in the magnetic layer is a plate-like ferromagnetic powder having a plate diameter of 0.3 μm or less, and the major axis of the non-magnetic powder in the lower non-magnetic layer. It is preferably smaller than the length or the plate diameter. Further, the non-magnetic powder in the lower non-magnetic layer is composed of granular particles having an average particle diameter of λ / 4 or less, or having a major axis length of 0.05 to
Needle-like particles having a needle ratio of 5 to 20 or 0.3 µm or plate-like particles having a plate diameter of 0.05 to 0.3 µm and a plate-like ratio of 5 to 20 are preferable.

The surface properties of the present invention can be achieved based on the invention in which the standard deviation of the average thickness of the upper magnetic layer is 0.2 μm or less, and the following (J) and (K). Can be achieved by means. (J) The ferromagnetic powder contained in the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization perpendicular to the flat plate,
In addition, the non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the average particle size thereof is equal to or less than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer. (K) The inorganic powder contained in the lower non-magnetic layer contains an inorganic non-magnetic powder having a surface layer coated with an inorganic oxide.

The respective functions and effects described above are as follows. First, (J) will be described. When the hexagonal plate-like ferromagnetic powder (J) is used, the powder is oriented in the vertical direction, the disturbance at the interface is reduced, and the squareness ratio can be increased. The inorganic powder used for the lower layer preferably has a plate diameter or less, more preferably a plate diameter or less and 1/5 or more of the plate diameter. When the thickness of the magnetic layer is five times or less the major axis length, the degree of filling by the calendar is remarkably improved, and a magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained. Preferred types and properties of the inorganic powder are as follows. The shape of the inorganic powder is preferably spherical or dice. The Mohs hardness is 3 or more, preferably 4 or more, and more preferably 6 or more.
That is all.

The volume filling ratio in the lower layer of the inorganic powder is preferably in the range of 20 to 60%, more preferably 25 to 55%. In order to reduce the surface roughness based on the relationship between the particle size of the lower nonmagnetic powder and the crystallite size of the upper ferromagnetic powder, there is a preferable range for the volume filling ratio of the lower powder. If the volume filling ratio is 20% or less, the distance between the lower powder particles increases, and the surface of the upper magnetic layer becomes affected by the roughness of the lower powder surface. It may be mixed and the surface becomes very severe. In addition, the squareness ratio is reduced. On the other hand, if the volume filling ratio is 60% or more, the viscosity of the dispersion becomes extremely high, making it substantially impossible to apply.
Even if it is applied, problems such as powder falling off in terms of running durability may occur. In addition, the inorganic powder is 60% by weight of the nonmagnetic powder.
% Or more, and the inorganic powder is preferably a metal oxide, an alkaline earth metal salt or the like.
A known effect (for example, reduction of surface electric resistance) can be expected by adding carbon black. Therefore, it is preferable to use in combination with the above-mentioned inorganic powder. ,
Carbon black alone cannot secure sufficient electromagnetic conversion characteristics. In order to obtain good dispersibility, it is necessary to select at least 60% by weight from metal oxides, metals and alkaline earth metal salts. If the inorganic powder is less than 60% by weight of the non-magnetic powder and the carbon black is more than 40% of the non-magnetic powder, the dispersibility becomes insufficient and the desired electromagnetic conversion characteristics cannot be obtained.

Next, (K) will be described. The inorganic oxide coated on the surface of the inorganic powder contained in the lower nonmagnetic layer is preferably Al ₂ O ₃ , SiO ₂ , TiO ₂ .
₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO and the like are more preferable, and Al ₂ O ₃ , SiO ₂ , ZrO are more preferable.
₂ These may be used in combination,
It can be used alone. Further, a co-precipitated surface treatment tank may be used according to the purpose, or a structure in which the surface layer is treated with silica and then the surface layer is treated with silica or vice versa may be employed. Further, the surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is uniform and dense.

For example, the surface treatment of the nonmagnetic inorganic powder
After the non-magnetic inorganic powder material is dry-pulverized, water and a dispersing agent are added, and coarse-particle classification is performed by wet pulverization and centrifugation. After that, the fine slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al,
An aqueous salt solution such as Si, Ti, Zr, Sb, Sn, or Zn is added, and an acid or alkali for neutralizing the solution is added.
The surface of the inorganic powder particles is coated with the generated hydrated oxide.
Water-soluble salts produced as by-products are removed by decantation, filtration and washing, and finally the slurry is filtered by adjusting the pH thereof.
Wash with pure water. The washed cake is dried with a spray drier or a band drier. Finally, the dried product is pulverized by a jet mill into a product. Also,
In addition to the aqueous system, the vapor of AlCl ₃ and SiCl ₄ is passed through the non-magnetic inorganic powder, and then the vapor is flowed into Al and S
It is also possible to perform i-surface treatment.

For other surface treatment methods, refer to “Cha
rectification ofPowder Su
rfaces ", Academic Press. In this embodiment, the surface roughness of the magnetic layer is determined by defining the optimum thickness range of the magnetic layer according to the recording wavelength and the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer (that is, the variation width in the thickness direction of the interface). Is defined and improved, and the thickness of the magnetic layer is made thinner and uniform and uniform. Therefore, even if the recording wavelength is shortened, fluctuations in reproduction output and amplitude modulation noise can be prevented, and high reproduction output and high C / N can be achieved. Can be realized. In other words, conventionally, when the magnetic layer becomes thinner, when the recording wavelength becomes shorter, all the layers of the magnetic layer contribute to recording / reproduction.
Although amplitude modulation noise was observed, the present invention has solved this drawback.

In the present invention, the shortest recording wavelength λ varies depending on the type of the magnetic recording medium. For example, it is 0.7 μm for an 8 mm metal video and 0.
5 μm, and 0.67 μm for digital audio. The range of the thickness d of the magnetic layer of the present invention is λ / 4 ≦ d ≦
3λ, preferably λ / 4 ≦ d ≦ 2λ (ie 0.25
≦ d / λ ≦ 2). The average thickness d of the magnetic layer of the present invention is generally in the range of 0.05 μm ≦ d ≦ 1 μm, preferably in the range of 0.05 μm ≦ d ≦ 0.8 μm.

The thickness of the magnetic layer can be obtained by actual measurement as described above. For elements specifically contained in the magnetic layer by X-ray fluorescence, a magnetic layer sample having a known thickness is measured, and a calibration curve is prepared. Next, the thickness of the sample of the unknown material can be determined from the intensity of the fluorescent X-ray. In the present invention, Δd is set to d /
2 or less, that is, Δd / d is 0.5 or less, preferably
It is controlled to 0.3 or less, more preferably 0.25 or less.
The range of Δd is 0.001 to 0.5 μm, preferably 0.03 to 0.3 μm, more preferably 0.05 to 0.5 μm.
0.25. Thereby, the uniformity of the thickness of the magnetic layer is ensured, and the surface roughness Ra is Ra ≦ λ / 50, that is, λ /
Ra can be regulated to 50 or more, preferably 75 or more, and more preferably 80 or more. Further, in the present invention, Ra means a value obtained by measuring a center line average roughness measured using an optical interference roughness meter.

The magnetic recording medium of the present invention is formed by coating the upper magnetic layer while the lower non-magnetic layer is in a wet state. It does not matter if it is provided, but simultaneous multi-layer coating is preferred.
That is, according to the present invention, for example, by simultaneously coating a magnetic layer of 1 μm or less with the lower non-magnetic layer, when the magnetic layer is made thinner alone, or when the lower non-magnetic layer is sequentially laminated in a dry state, there is a problem. Coating defects can be prevented.

In the present invention, the thickness of the magnetic layer cannot be simply reduced, and the present inventors have found that there is an optimum range for the shortest recording wavelength λ. That is, when the thickness of the magnetic layer becomes thinner than λ / 4, the magnetic flux contributing to reproduction decreases, and the output decreases. Further, since the short-wavelength component is demagnetized by the deep recording magnetic field of the component having the longer recording wavelength and simultaneously recording exceeding 3λ, the output is reduced. Therefore, d ≦ 3λ, preferably d ≦ 2λ is good.

When C / N, which is the basic performance of the medium, is obtained, in addition to the unevenness (so-called surface roughness) on the surface of the magnetic layer, which is a problem in the conventional thick magnetic layer, the non-magnetic layer And the thickness variation at the interface of the magnetic layer becomes a problem because, when the magnetic layer thickness d is in the range of λ / 4 ≦ d ≦ 3λ, the reproduction output is affected by the magnetic flux amount of the entire magnetic layer. This is not a problem with the conventional thick magnetic layer. The present invention has found out that this problem requires that the average value Δd of the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer is not more than の of the thickness d of the magnetic layer. Also,
The surface roughness of the magnetic layer is required to be as smooth as the conventional thick film magnetic layer, and the surface roughness Ra is Ra ≦ λ / 5.
It is preferable to satisfy the relation of 0.

According to the present invention, processing in a vacuum is premised, there is no problem of productivity and reliability of a metal thin film which is vulnerable to corrosion, the electromagnetic conversion characteristics are comparable to those of a metal thin film, and the productivity is excellent. A high performance coating type magnetic recording medium can be obtained. A second aspect of the present invention is that the magnetic layer surface has a root-mean-square roughness R _rms measured by a scanning tunneling microscope (STM) between the dry thickness average value d of the magnetic layer and 30 ≦ m. d / R _rms .

When the thickness of the magnetic layer is reduced, the self-demagnetization loss should be reduced and the output should be improved. However, the reduction in thickness due to the reduced thickness of the magnetic layer decreases the calendering property and deteriorates the calenderability. The roughness increases. In order to improve the output by reducing the self-demagnetization loss, S
Surface roughness by TM is preferred. R by AFM
_rms is preferably 10 nm or less. Preferably, the light interference surface roughness Ra measured by 3d-MIRAU is 1 to 4 nm, and the PV value (Peak-Valley) value is 80 nm or less.

The glossiness of the surface of the magnetic layer is preferably from 250 to 400% after calendering. In order to achieve the third point of the present invention, the ferromagnetic powder contained in the upper magnetic layer has a plate diameter of 0.3 μm or less, is a powder, and has a Hc of 1000 Oe or more. It is preferably a powder.

As the ferromagnetic powder, plate-like hexagonal ferrite ferromagnetic materials (Ba ferrite, Sr ferrite, etc.) and plate-like Co alloy powder can be used. Hc and saturation magnetization (σ _s ) may be appropriately selected. In particular, for short-wavelength recording with a minimum recording wavelength of 1 μm or less, Hc is 1500 (O
e) or more is preferred. The size of the magnetic material is generally in the form of a plate, and is suitable for high-density recording.
m or less.

To achieve the fourth point of the present invention, the stiffness SMD in the application direction of the magnetic recording medium and the stiffness STD in the width direction with respect to the application direction (longitudinal direction) are considered.
Is preferably 1.0 to 1.9. In order to set the stiffness to the above value, a polyhedral inorganic powder having a Mohs hardness of 6 or more and an average particle size of 0.15 μm or less from a sphere to a cubic, which is contained in the lower nonmagnetic layer, is used. Is preferred.

The working mechanism of the stiffness invention is as follows. This embodiment controls the mechanical characteristics of the magnetic recording medium by controlling the SMD / STD of the magnetic recording medium,
This is to improve the head contact of the magnetic recording medium and improve the electromagnetic conversion characteristics particularly in short wavelength recording. That is, this embodiment controls SMD / STD to 1.0 to 1.9.

The stiffness SMD in the coating direction and the stiffness STD in the width direction can both be measured using a commercially available stiffness tester. For example, using a loop stiffness tester manufactured by Toyo Seiki Co., Ltd., the manufactured magnetic recording medium is 8 mm in width, and a sample having a length of 50 mm is used for SMD measurement so that the sample length direction is the same as the coating direction of the magnetic recording medium. In addition, for the measurement of STD, the sample was cut out so that the length direction of the sample was the same as the width direction of the magnetic recording medium, and this was cut into an annular shape.
The SMD and STD can be defined as the force expressed in mg of the force required to give a displacement of 5 mm at a displacement speed of 3.5 mm / sec in the inner diameter direction.

Here, SMD / STD is 1.0 to 1.9,
Preferably, it is controlled to 1.1 to 1.85. In a magnetic recording medium having a total thickness of 13.5 ± 1 μm, SMD is
50-200 mg, preferably 50-150 mg, STD
Is 40 to 150 mg, preferably 50 to 130 mg. The means for controlling the value of SMD / STD is not particularly limited, but it is preferable to select the shape and Mohs hardness of the lower inorganic powder. It is desirable to select a polyhedral inorganic powder ranging from a spherical shape to a cubic shape having an average particle diameter of 0.5 or more and 0.15 μm or less, preferably 0.12 μm or less.

In order to improve the head contact of the magnetic recording medium, it is necessary to increase the stiffness of each tape to a certain degree. If the Mohs hardness is less than 6, each stiffness is low, and good head contact cannot be secured. Further, the smaller the average particle size is 0.15 μm or less,
Good head contact. This is because the contact interface with the binder is increased, so that it becomes resistant to deformation, and each stiffness S
It is thought that MD and STD are improved. In the present invention, this SMD / STD is adjusted to the above range.

Especially, the effect on the electromagnetic conversion characteristics is high because S
TD is close to SMD, ie close to 1. When the inorganic powder contained in the lower layer is formed into a polyhedral shape from spherical to cubic, the mechanical properties of the coating film become isotropic, which is convenient for improving the STD. Here, the polyhedron shape specifically refers to a regular polyhedron or a non-regular polyhedron selected from one or more selected from a regular n-sided shape such as a sphere, a regular pentagon, a regular hexagon, or a simple n-sided shape. Although it is possible to exemplify, it is desirable that two arbitrarily selected ratios are in the range of 0.6 to 1.4, preferably 0.7 to 1.3.

Another aspect for achieving the fourth point of the present invention is that the magnetic recording medium has a heat shrinkage of 0.4% or less at 80 ° C. for 30 minutes.
Specifically, the dry thickness of the lower nonmagnetic layer is 1 to 30 times the dry thickness of the upper magnetic layer, and the powder volume ratio of the lower nonmagnetic layer to the powder volume ratio of the upper magnetic layer. Is in the range of −5% to + 20%, the crystallite size of the ferromagnetic powder contained in the upper magnetic layer is 300 Å or less, and the average of the inorganic powder contained in the lower nonmagnetic layer is A particle having a particle size of less than 0.15 μm or a needle having an average major axis diameter of less than 0.6 μm, wherein the inorganic powder contained in the lower nonmagnetic layer is titanium oxide, barium sulfate, calcium carbonate, Being at least one selected from strontium sulfate, silica, alumina, zinc oxide, and α-iron oxide, the lower nonmagnetic layer has an average particle size of 30 mμ or less, and has a DBP oil absorption of 30 to 300. In l / 100 g, BET specific surface area is with respect to the inorganic powder 100 parts by weight of carbon black is 150 to 400 m ² / g as a second component, is that a proportion of less than 50 parts by weight.

According to this embodiment, a coating type magnetic recording medium having a magnetic layer thickness of 1 μm or less and having improved self-demagnetization loss can be manufactured with high productivity without coating defects such as pinholes and streaks, and the heat of the magnetic recording medium can be reduced. The shrinkage is suppressed below a predetermined value. That is, in this embodiment, by controlling the heat shrinkage after storage at 70 ° C. for 48 hours to 0.4% or less, the skew distortion is improved and reduced, and the magnetic properties having electromagnetic conversion characteristics comparable to a ferromagnetic metal thin film are obtained. A recording medium is provided.

In other words, the present embodiment has found that the magnetic recording medium having an extremely thin magnetic layer can be manufactured with high productivity, and the strength of an appropriate magnetic recording medium for reducing skew distortion can be defined by the above-mentioned heat shrinkage. It is. Here, the heat shrinkage ratio is 100 × (length of magnetic recording medium at room temperature before heating−length after holding magnetic recording medium without tension in an environment of 70 ° C. for 48 hours) ÷ (heating (Length of the magnetic recording medium at the previous room temperature).

In this embodiment, the means for controlling the heat shrinkage is not particularly limited, and any method can be applied. As the control means, specifically, the following examples are preferable. The dry thickness of the lower non-magnetic layer is controlled to 1 to 30 times, preferably 2 to 20 times the dry thickness of the upper magnetic layer, and the expansion and contraction of the magnetic recording medium is controlled by the film strength of the lower layer and the upper layer. Is mentioned. If the thickness ratio is less than 1, it is not possible to prevent an increase in the heat shrinkage due to the strength deterioration due to the magnetic layer being finely divided. On the other hand, when the thickness ratio is 30 times or more, the thickness of the applied film becomes thicker, so that the residual solvent increases and adverse effects such as plasticization of the film occur.

As means for adjusting the film strength of the lower layer and the upper layer, the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is -5% to + 20%, preferably Controlling to a range of 0 to 15% is mentioned. Here, if the content is less than -5%, the increase in the thermal shrinkage of the magnetic layer cannot be suppressed, and if the content is more than 20%, the medium itself becomes too hard and powder drop increases, which is not preferable.

In the present invention, the powder volume ratio of the upper layer is, for example, in the range of 10 to 50%, preferably 20 to 45%, and the powder volume ratio of the lower layer is 20 to 60%, preferably , 25 to 50%. The powder volume ratio of each layer can be controlled by changing the amounts of the powder and the binder to be added and the particle size and shape of the powder of each layer. When the amount of the binder is increased, the powder volume ratio relatively decreases. The finer the particle size of the powder, the more effective it is in reducing the heat shrinkage, but if it is too fine, dispersion becomes difficult.

The particle size and shape of the inorganic powder in the lower layer include a granular material having an average particle diameter of less than 0.15 μm, preferably 0.005 to 0.7 μm, and an average major axis diameter of less than 0.6 μm. Preferably, it is 0.1 to 0.3 μm, and the acicular ratio represented by average major axis diameter / minor axis length is 4 to 50,
Needle-like objects, preferably 5 to 30 are exemplified. As the inorganic powder, rutile-type titanium oxide, α-iron oxide, and goethite are preferable.

The powder used for the lower layer includes carbon black. The carbon black has an average particle size of 30 μm or less, preferably 5 to 28 μm.
mμ, and the DBP oil absorption is 30 to 300 ml / 1.
00g, preferably 50-250ml / 100g, B
The specific surface area by the ET method is 150 to 400 m ² / g, preferably 170 to 300 m ² / g, the pH is 2 to 10, the water content is 0.1 to 10%, and the tap density is 0.1 to 1 g / cc.
Is preferred.

This carbon black is less than 50 parts by weight, preferably 13 parts by weight, based on 100 parts by weight of the inorganic powder.
It is preferable to add to the lower layer in a proportion of ４０40 parts by weight. The carbon black is an antistatic material for a magnetic recording medium,
In addition to functions such as enhancement of film strength, it is also used to control the volume ratio of powder in the lower layer by controlling the porosity.
That is, when the porosity is high, the powder volume ratio relatively decreases. As the carbon black for controlling the porosity, it is effective to use a carbon black having a structure or a hollow carbon black.

The porosity of the lower layer is preferably in the range of the porosity of the upper layer ± 10%. The porosity of the lower layer is preferably in the range of 10 to 30%. The fifth point of the present invention relates to durability. The Young's modulus of the magnetic recording medium of the present invention measured by a tensile tester is 300 to 2000.
Kg / mm ² , preferably 400 to 1500 Kg / m
m ² , and the Young's modulus of the magnetic layer is 400 to 5000.
Kg / mm ² , preferably 500-4000 Kg / mm
^{2. The} yield stress is 3 to 20 kg / mm ² , preferably 4 to
It is desirable that the yield elongation is 18 kg / mm ² and the yield elongation is 0.2 to 8%, preferably 0.5 to 5%.

This affects the durability because the ferromagnetic powder, binder, carbon black, inorganic powder and support are involved. The bending rigidity (annular stiffness) of the magnetic recording medium of the present invention is preferably 40 to 300 mg when the total thickness is more than 11.5 μm, and the total thickness is 10.5 ± 1.
In the case of μm, preferably 20 to 90 mg and the total thickness is 9.5 μm
When it is thinner, it is preferably 10 to 70 mg.

This is mainly related to the support and is important for ensuring durability. The crack elongation of the magnetic recording medium of the present invention measured at 23 ° C. and 70% RH is preferably 20% or less. The Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium of the present invention measured with an X-ray photoelectron spectrometer is preferably 0.1.
3 to 0.6, the N / Fe spectrum β is preferably 0.0
3 to 0.12.

This is related to the ferromagnetic powder, the inorganic powder and the binder, and is important for obtaining durability. Further, the glass transition temperature Tg of the magnetic layer of the magnetic recording medium of the present invention measured by using a dynamic viscoelasticity measuring device (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 40 to 40. 120 ° C., and the storage elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / cm.
² , and the loss modulus E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² . Further, the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These are related to binders, carbon black, and solvents, and are important properties related to durability.

The 180 ° adhesive strength of the 8-mm wide tape at 23 ° C. and 70% RH between the flexible support and the magnetic layer is preferably 10 g or more. The wear of a steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.7 × 10 ^{−7 to} 5 × 10 ⁻⁷ m ³ . This is a measure of the durability mainly related to ferromagnetic powder, which is a direct observation of the wear of the magnetic layer surface.

The number of abrasives on the surface of the magnetic layer obtained by photographing five images of the magnetic recording medium of the present invention with a SEM (electron microscope) at a magnification of 50,000 times is preferably 0.1 / μm ^2.
It is desirable that this is the case. The abrasive present on the end face of the upper magnetic layer of the magnetic recording medium of the present invention is 5 abrasives / 100 μm.
^Two or more are preferred. These are measures that are affected by the abrasive and binder of the magnetic layer and exert an effect on durability.

The residual solvent of the magnetic recording medium of the present invention measured by gas chromatography is preferably 50 mg / m ² or less. The residual solvent contained in the upper layer is preferably 20 m
g / m ² or less, more preferably 10 mg / m ² or less, and it is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer.

The sol fraction, which is the ratio of the soluble solid extracted from the magnetic recording medium of the present invention with THF to the weight of the magnetic layer, is preferably 15% or less. This is affected by the ferromagnetic powder and binder,
It is a measure of durability. The magnetic recording medium of the present invention has a 1-MHz short-wavelength recording on the upper magnetic layer, is magnetically developed using a ferricolloid, and is continuous in a 5-mm-wide sample observed at a magnification of 10 using a differential interference microscope. Preferably, there are no more than five black or white lines.

The coefficient of friction (μ) of the magnetic recording medium of the present invention
Is preferably 0.15 to 0.4 on the magnetic surface, particularly preferably 0.2 to 0.35, and the back layer surface is 0.1 to 0.4.
5 to 0.4 is preferable, and particularly preferably 0.2 to 0.3.
5 The contact angle of the magnetic recording medium of the present invention is 60
To 130, and particularly preferably 80 to 120. In the case of methylene iodide, preferably 10 to
It is 90 °, particularly preferably 20-70 °.

These contact angles are values determined particularly by the lubricant and the dispersant. The surface free energy of the magnetic layer and the back layer of the magnetic recording medium of the present invention is 10 to 100 dyes.
n / cm is particularly preferred. The surface electric resistance of the magnetic recording medium of the present invention is 1 × 1 on both the magnetic layer surface and the back layer surface.
It is preferably at most ^{9 9} Ω / sq, particularly preferably at most 1 × 10 ⁸ Ω / sq.

[0112]

BEST MODE FOR CARRYING OUT THE INVENTION The following is a general description of the present invention.
Matters are described. Non-magnetic inorganic materials that can be used in the present invention
Powders include, for example, metals, metal oxides, metal carbonates, metals
Non-magnetic such as sulfate, metal nitride, metal carbide, metal sulfide
Inorganic powder. Specifically, TiO_Two(Luchi
Le, anatase), TiO_X, Cerium oxide, sulfur oxide
, Tungsten oxide, ZnO, ZrO_Two, SiO_Two,
Cr_TwoO _Three, Α-alumina, β-Al with 90% or more pregelatinization ratio
Mina, gamma alumina, alpha iron oxide, goethite, colander
System, silicon nitride, titanium carbide, magnesium oxide,
Boron nitride, molybdenum disulfide, copper oxide, MgCO_Three, C
aCO_Three, BaCO_Three, SrCO_Three, BaSO_Four, Carbonized
Silicon or titanium carbide used alone or in combination
It is. The shape, size, etc. of these inorganic powders are arbitrary.
These combine different inorganic powders as needed.
Or the particle size distribution etc. can be selected even for a single non-magnetic powder.
Can also be.

The particle size is preferably based on the specific methods (A) to (K) described above. , It is preferable to set it to １ ／ or less of the shortest recording wavelength λ. In the case of a plate, the plate diameter is 0.05 to 1.0 μm, preferably 0.05 to 0.5 μm, and the plate ratio (ratio of plate diameter to thickness) is 5 to 20, preferably 10 to 20. Is used.

As the inorganic powder, the following are preferable. The tap density is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. The water content is 0.1-5%, preferably 0.2-3%. The pH is preferably 2 to 11, particularly preferably 4 to 10. The specific surface area is 1 to 100 m ² / g, preferably 5 to 70 m ² / g, more preferably 7 to 50 m ² / g.
It is. The crystallite size is preferably from 0.01 μm to 2 μm. Oil absorption using DBP is 5-100ml / 100
g, preferably 10 to 80 ml / 100 g, more preferably 20 to 60 ml / 100 g. The SA (stearic acid) adsorption amount is 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The roughness factor of the powder surface is preferably 0.8 to 1.5, and more preferably ² to 15 μmol / m ² . The heat of wetting in water at 25 ° C. is preferably from 200 erg / cm ^{2 to} 600 erg / cm ² . Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is suitably 1 to 10/100 °. The pH of the isoelectric point in water is preferably between 3 and 9. Specific gravity is 1
-12, preferably 3-6.

The above-mentioned inorganic powder is not necessarily required to be 100% pure, and the surface is treated with another compound, for example, each compound such as Al, Si, Ti, Zr, Sn, Sb, Zn, etc., according to the purpose. And their oxides may be formed on the surface. At this time, if the purity is 70% or more, the effect is not reduced. The ignition loss is preferably 20% or less.

Specific examples of the inorganic powder used in the present invention include UA5600 and UA560 manufactured by Showa Denko KK
5. AKP-20, AKP-30, AKP manufactured by Sumitomo Chemical Co., Ltd.
-50, HIT-55, HIT-100, ZA-G1,
G5, G7, S-1 manufactured by Nippon Chemical Industry Co., Ltd., T manufactured by Toda Industry Co., Ltd.
F-100, TF-120, TF-140, R516,
Ishihara Sangyo TTO-51B, TTO-55A, TTO
-55B, TTO-55C, TTO-55S, TTO-
55S, TTO-55D, FT-1000, FT-20
00, FTL-100, FTL-200, M-1, S-
1, SN-100, R-820, R-830, R-93
0, R-550, CR-50, CR-80, R-68
0, TY-50, ECT-52, STT manufactured by Titanium Industry Co., Ltd.
-4D, STT-30D, STT-30, STT-65
C, T-1 manufactured by Mitsubishi Materials, NS- manufactured by Nippon Shokubai
O, NS-3Y, NS-8Y, MT-100 manufactured by Teika
S, MT-100T, MT-150W, MT-500
B, MT-600B, MT-100E, FI manufactured by Sakai Chemical Co.
NEX-25, BF-1, BF-10, BF-20, B
F-1L, BF-10P, DEFIC- manufactured by Dowa Kogyo
Y, DEFIC-R, Y-LOP manufactured by Titanium Industry Co., Ltd., and a fired product thereof.

The nonmagnetic inorganic powder used in the present invention is particularly preferably titanium oxide (particularly titanium dioxide). Hereinafter, the method for producing the titanium oxide will be described in detail. There are mainly a sulfuric acid method and a chlorine method for producing titanium oxide. In the sulfuric acid method, raw ore of illuminite is distilled with sulfuric acid, and Ti, Fe, and the like are extracted as sulfates. Iron sulfate is removed by crystallization separation, and the remaining titanyl sulfate solution is filtered and purified, and then thermally hydrolyzed to precipitate hydrous titanium oxide. After filtering and washing this,
After washing and removing contaminants and adding a particle size regulator, etc.,
If calcined at 80 to 1000 ° C., it becomes crude titanium oxide. The rutile type and the anatase type are classified according to the type of nucleus material added at the time of hydrolysis. The crude titanium oxide is prepared by pulverizing, sizing and surface treatment. In the chlorine method, natural rutile or synthetic rutile of the original ore is used. The ore is chlorinated in high-temperature reduced state, Ti is TiCl ₄ and Fe is FeCl ₂
And the iron oxide solidified by cooling becomes liquid TiC
It is separated from the l _4. After the obtained crude TiCl ₄ is purified by rectification, a nucleating agent is added and reacted with oxygen instantaneously at a temperature of 1000 ° C. or more to obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

In the present invention, carbon black can be used for the lower layer, and the known effects such as R _S (surface electric resistance) can be reduced. As the carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400, DBP oil absorption 20-400ml / 10
0 g, preferably 30 to 200 ml / 100 g.
The average particle size is 5 mμ to 80 mμ, preferably 10 to 50 m
μ, more preferably 10 to 40 μm. pH is 2
10, water content 0.1 ~ 10%, tap density 0.1 ~
1 g / cc is preferred.

Specific examples of the carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72, # 3050, # 3150, # 3250, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
# 3750, # 3950, # 2400B, # 2300,
# 1000, # 970, # 950, # 900, # 8
50, # 650, # 40, MA40, MA-600, manufactured by Columbia Carbon, CONDUCTEX SC, R
8800, 8000, 7000, 575 manufactured by AVEN
0, 5250, 3500, 2100, 2000, 180
0, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo Corporation, and the like. Carbon black may be surface-treated with a dispersing agent or the like, or may be grafted with a resin, or may be used in which a part of the surface is graphitized. Before adding the carbon black to the non-magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination.

The carbon black that can be used in the present invention is
For example, ("Carbon Black Handbook", edited by Carbon Black Association) can be referred to. Non-magnetic organic powder used in the present invention, acrylic styrene resin powder,
Benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are exemplified, and polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluoroethylene resin powder are used. The production method is disclosed in Japanese Patent Application Laid-Open No. 62-18564.
And JP-A-60-255827 can be used.

These non-magnetic powders are generally used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.1 to the binder.
It is used in the range of 1. In general magnetic recording media, an undercoat layer is provided. This is provided to improve the adhesive strength between the support and the magnetic layer, and has a thickness of 0.5 μm. The following is different from the lower non-magnetic layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesion between the underlayer and the support.

As the ferromagnetic powder used in the magnetic layer of the present invention, known ferromagnetic powders such as barium ferrite and strontium ferrite can be used. These ferromagnetic powders include Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Specifically,
No. 14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513.
JP, JP-B-46-28466, JP-B-46-28466
38755, JP-B-47-4286, JP-B-47-12422, JP-B-47-17284, JP-B-47-18509, and JP-B-47-1
No. 8573, JP-B-39-10307, JP-B-48-39639, U.S. Pat.
Nos. 3,301,341, 3,100,194, 3,242,005, 3,389,014 and the like.

In the present invention, plate-like hexagonal ferrite is exemplified as a hexagonal plate-like ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate. Hexagonal Co powders such as powders and Co-substitutes can be used.
Specific examples include barium ferrite and strontium ferrite of magnetobranbite type, barium ferrite and strontium ferrite of magnetobranbite type further containing a part of spinel phase, and particularly preferred are barium ferrite and strontium ferrite. Is a substitution. In order to control the coercive force, Co-Ti, Co-T
i-Zr, Co-Ti-Zn, Ni-Ti-Zn, Ir
A substance to which an element such as -Zn is added can be used.

When barium ferrite is used, the plate diameter means the width of the plate of hexagonal plate-like particles, and is measured using an electron microscope. In the present invention, the plate diameter is set to 0.001 to 1 μm.
In m, the plate thickness may be set to 1/2 to 1/20 of the diameter. The specific surface area (S _BET ) is preferably from 1 to 60 m ² / g, and the specific gravity is preferably from 4 to 6. As the binder used in the lower nonmagnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. As a thermoplastic resin, the glass transition temperature is -1.
00 to 150 ° C, number average molecular weight of 1,000 to 20,000
0, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins. In addition, as thermosetting resin or reactive resin, phenol resin, epoxy resin,
Polyurethane curing resin, urea resin, melamine resin, alkyd resin, acrylic-based reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer,
A mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like can be given.

These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Further, a known electron beam-curable resin can be used for the lower layer or the upper layer. These examples and the method for producing them are described in detail in JP-A-62-256219.

The above resins can be used alone or in combination. Preferred are selected from the group consisting of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin and vinyl chloride vinyl acetate maleic anhydride copolymer. And a combination of at least one of the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known materials 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 shown here, -COO is required to obtain better dispersibility and durability.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM 1)
(OM ₂ ), -OP = O (OM ₁ ) (OM ₂ ), -NR
₄ X (where M, M ₁ and M ₂ are H, Li, Na,
K, -NR _4, shows a -NHR _3, R represents an alkyl group or H, X is a halogen atom. ), OH, N
R ₂ , N ⁺ R ₃ , (R is a hydrocarbon group), epoxy group, S
It is preferable to use one obtained by introducing at least one or more polar groups selected from H, CN and the like 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.

The vinyl chloride copolymer is preferably an epoxy group-containing vinyl chloride copolymer.
Vinyl chloride repeating unit, a repeating unit having an epoxy group, optionally _{-SO 3 M, -OSO 3 M,} -COO
M and —PO (OM) ₂ (where M is a hydrogen atom,
Or a repeating unit having a polar group such as an alkali metal). In combination with the repeating unit having an epoxy group, an epoxy group-containing vinyl chloride copolymer preferably contains a repeating unit having an -SO ₃ Na.

The content of the repeating unit having a polar group in the copolymer is usually in the range of 0.01 to 5.0 mol% (preferably, 0.5 to 3.0 mol%). The content of the repeating unit having an epoxy group in the copolymer is usually in the range of 1.0 to 30 mol% (preferably 1 to 20 mol%). And the vinyl chloride polymer is
Usually 0.01 to 1 mol of vinyl chloride repeating unit
It contains a repeating unit having 0.5 mol (preferably 0.01 to 0.3 mol) of an epoxy group.

The content of the repeating unit having an epoxy group is lower than 1 mol%, or
The amount of the repeating unit having an epoxy group per mole is 0.
If the amount is less than 01 mol, the release of hydrochloric acid gas from the vinyl chloride-based copolymer may not be effectively prevented. On the other hand, it may be higher than 30 mol% or have an epoxy group per 1 mol of the vinyl chloride repeating unit. If the amount of the repeating unit is more than 0.5 mol, the hardness of the vinyl chloride-based copolymer may decrease, and if this is used, the running durability of the magnetic layer may decrease.

If the content of the repeating unit having a specific polar group is less than 0.01 mol%, the dispersibility of the ferromagnetic powder may be insufficient. The coalescing may become hygroscopic and the weather resistance may decrease. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000.

A vinyl chloride copolymer having such an epoxy group and a specific polar group can be produced, for example, as follows. For example, in the case of producing a vinyl chloride copolymer into which an epoxy group and -SO ₃ Na are introduced as a polar group, 2-vinyl having a reactive double bond and -SO ₃ Na as a polar group is used. Sodium (meth) acrylamide-2-methylpropanesulfonate (a monomer having a reactive double bond and a polar group) and diglycidyl acrylate are mixed at a low temperature, and this is mixed with vinyl chloride at 100 ° C. under pressure. It can be produced by polymerizing at the following temperature.

Examples of the monomer having a reactive double bond and a polar group used for introducing a polar group by the above method include the above-mentioned sodium 2- (meth) acrylamido-2-methylpropanesulfonate. And 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonic acid and its sodium or potassium salt, (anhydrous) maleic acid and Examples thereof include (meth) acrylic acid and (meth) acrylic acid-2-phosphate.

In introducing an epoxy group, glycidyl (meth) acrylate is generally used as a monomer having a reactive double bond and an epoxy group. In addition, in addition to the above-mentioned production method, for example, a vinyl chloride copolymer having polyfunctional OH is produced by a polymerization reaction of vinyl chloride and vinyl alcohol, and the copolymer and a polar solvent described below are produced. A method of reacting a compound containing a group and a chlorine atom (dehydrochlorination reaction) to introduce a polar group into the copolymer can be used.

ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ C
H ₂ OSO ₃ M, ClCH ₂ COOM, ClCH ₂ PO
(OM) _{2 In} addition, epichlorohydrin is usually used to introduce an epoxy group using this dehydrochlorination reaction.

The vinyl chloride copolymer may contain another monomer. Examples of other monomers include vinyl ether (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether), α
Monoolefins (eg, ethylene, propylene), acrylates (eg, (meth) acrylates containing a functional group such as methyl (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitriles (eg, , (Meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), and vinyl ester (eg, vinyl acetate, vinyl propionate, etc.).

Specific examples of these binders used in the present invention include: 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, MPR-TAO, manufactured by Denki Kagaku: 100
0W, DX80, DX81, DX82, DX83, 10
0FD, manufactured by Zeon Corporation: MR105, MR110, M
R100, 400X110A, manufactured by Nippon Polyurethane Co .:
Nipporan N2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105, T-R30
80, T-5201, Barnock D-400, D-21
0-80, Chris Bon 6109, 7209, manufactured by Toyobo: Byron UR8200, UR8300, UR860
0, UR5500, UR4300, RV530, RV2
80, manufactured by Dainichi Seika Co., Ltd .: Daifelamin 4020, 502
0, 5100, 5300, 9020, 9022, 702
0, manufactured by Mitsubishi Kasei: MX5004, manufactured by Sanyo Kasei: Samprene SP-150, manufactured by Asahi Kasei: Saran F310, F
210 and the like.

The binder used in the upper magnetic layer of the present invention is used in an amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the ferromagnetic powder. It is preferable to use 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, and 2 to 20% by weight for polyisocyanate in combination.

The binder used in the lower non-magnetic layer of the present invention is in a range of 5 to 50% by weight in total with respect to the non-magnetic powder.
Preferably, it is used in the range of 10 to 35% by weight. When using a vinyl chloride resin, 3 to 30% by weight, when using a polyurethane resin, 3 to 30% by weight,
The polyisocyanate is preferably used in combination in the range of 0 to 20% by weight.

In the present invention, when an epoxy group-containing resin having a molecular weight of 30,000 or more is used in an amount of 3 to 30% by weight based on the nonmagnetic powder, a resin other than the epoxy group-containing resin is used in an amount of 3 to 30% by weight based on the nonmagnetic powder. %, When a polyurethane resin is used, 3 to 30% by weight and polyisocyanate can be used at 0 to 20% by weight. However, the epoxy group accounts for 4 × 10 ^{−5 based on the} total weight of the binder (including the curing agent). ~ 16 × 1
It is preferably contained in the range of 0 ^-4 eq / g.

In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress 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 has two layers. Therefore,
Amount of binder, amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in binder, molecular weight of each resin forming magnetic layer, amount of polar group, or physical properties of resin described above It is of course possible to change characteristics and the like between the lower layer and the upper magnetic layer as needed.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Use of isocyanates such as 5-diisocyanate, o-toluidine isocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can do. Commercially available trade names of these isocyanates include Nippon Polyurethane Co .: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M
R, Millionate MTL, Takeda Pharmaceutical: Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, manufactured by Sumitomo Bayer: Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These are used alone or in combination of two or more using the difference in curing reactivity. Both the lower nonmagnetic layer and the upper magnetic layer can be used in combination.

As the carbon black used in the upper magnetic layer of the present invention, furnace black for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle size is 5 mμ to 300
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. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 130 manufactured by Cabot Corporation.
0, 1000, 900, 800, 700, VULCAN
XC-72, manufactured by Asahi Carbon: # 80, # 60, # 5
5, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo: # 2400
B, # 2300, # 900, # 1000, # 30, # 4
0, # 10B, manufactured by Konlon Via Carbon: CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5 and the like. 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 graphitizing a part of the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. 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 based on the ferromagnetic powder. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination in the lower layer and the upper layer, and according to the purpose, based on the above-mentioned properties such as particle size, oil absorption, conductivity, and pH. It is of course possible to use them properly. The carbon black that can be used in the upper layer of the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

Examples of the abrasive used in the upper magnetic layer of the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, and the like. Known materials mainly 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. Further, a composite of these abrasives (abrasive whose surface is 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 not changed. The particle size of these abrasives is preferably from 0.01 to 2 μm. However, if necessary, abrasives having different particle sizes can be combined, or even a single abrasive can have the same effect by widening the particle size distribution. . Tap density is 0.3-2 g / cc, water content is 0.1-5%, pH is 2-11, specific surface area is 1-30 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 include AKP-20, AKP-30, and Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, manufactured by Nippon Chemical Industries: G
5, G7, S-1, manufactured by Toda Kogyo: TF-100, TF
-140, 100ED, 140ED and the like.
The abrasive used in the present invention can be of different types, amounts and combinations for the lower layer and the upper layer, and can be of course used properly according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

As the additives used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Esters and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof,
Polyphenyl ethers, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched), and metal salts thereof ( Li, N
a, K, Cu etc.) or monovalent having 12 to 22 carbon atoms,
Divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols (which may contain an unsaturated bond or may be branched), alkoxy alcohols having 12 to 22 carbon atoms, 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent, divalent, 2 to 12 carbon atom,
One of trihydric, tetrahydric, pentahydric, and hexahydric alcohols (may contain unsaturated bonds or be branched)
A monofatty acid ester or difatty acid ester or trifatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer,
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used. Specific examples of these include 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, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol , Lauryl alcohol.

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums and Cationic surfactants such as sulfoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group, and the like, amino acids, aminosulfonic acids, sulfuric acid of amino alcohol or Ampholytic surfactants such as phosphates and alkylbedynes can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. 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 selectively used in the lower non-magnetic layer and the upper magnetic layer in their types and amounts as needed. For example, controlling the bleeding to the surface using fatty acids with different melting points in the lower non-magnetic layer and upper magnetic layer, controlling bleeding to the surface using esters with different boiling points and polarities, adjusting the amount of surfactant By doing so, it is conceivable to improve the stability of coating, to increase the amount of lubricant to be added in the lower non-magnetic layer to improve the lubricating effect, and of course, it is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added at any step in the production of the magnetic paint. For example, when mixing with the ferromagnetic powder before the kneading step, the ferromagnetic powder may be added. In a kneading step using a solvent and a binder and a solvent, there is a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. Examples of commercial products of these lubricants used in the present invention include NAA-102, NAA-415, and 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, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku: oleic acid, manufactured by Takemoto Yushi: FA
L-205, FAL-123, manufactured by Shin-Nippon Rika Co., Ltd .: Enjielb LO, Enjolbu IPM, Sansocizer 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, manufactured by Lion Armor: Armide P, Armide C, Armoslip CP, manufactured by Lion Yushi: Duomin TDO, manufactured by Nisshin Oil Co., Ltd .: BA-41
G, manufactured by Sanyo Kasei Co., Ltd .: Profan 2012E, Newpole PE61, Ionnet MS-400, Ionnet MO
-200, IONET DL-200, IONET DS-
300, IONET DS-1000, IONET DO-
200 and the like.

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, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene; Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
N-dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less. If necessary, the organic solvent used in the present invention is preferably of the same type in the upper layer and the lower layer. The amount added may be changed. It is important to improve the coating stability by using a solvent having a high surface tension (cyclohexanone, dioxane, etc.) for the lower layer. Specifically, it is important that the arithmetic average value of the upper solvent composition does not fall below the arithmetic average value of the lower solvent composition. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong. The solvent used for the coating liquid for the lower non-magnetic layer and the upper magnetic layer has a solubility parameter of 8 to 11, and the dielectric constant at 20 ° C. It is preferable that 15% or more of the solvent is contained in 15% or more.

The thickness of the magnetic recording medium of the present invention is 1 to 100 μm, preferably 4 to 80 μm for the flexible support, 0.5 to 10 μm for the lower layer, preferably 1 to 5 μm, and 0.05 to 1 μm for the upper layer. 0.0 μm or less, preferably 0.05
μm or more and 0.6 μm or less, more preferably 0.05 μm
m or more and 0.3 μm or less. The upper magnetic layer is preferably thinner than the lower nonmagnetic layer. The total thickness of the upper layer and the lower layer is used in a range of 1/100 to 2 times the thickness of the flexible support. In addition, an undercoat layer for improving adhesion may be provided between the flexible support and the lower layer. Their thickness is 0.01-2 μm, preferably 0.05-0.5 μm
m. Further, a back coat layer may be provided on the side of the flexible support opposite to the magnetic layer side. This thickness is 0.1
２2 μm, preferably 0.3-1.0 μm. Known undercoating layers and backcoat layers can be used.

The flexible support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfon, aramid, aromatic polyamide and the like. Known films 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 flexible 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: It is preferable that these flexible supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. Also,
The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include C
In addition to oxides and carbonates of a, Si, Ti, and the like, organic fine powders of an acryl system and the like can be given.

Further, F of the flexible support in the tape running direction is
The -5 value is preferably 5 to 50 kg / mm.^Two, Tape width
The F-5 value in the direction is preferably 3 to 30 kg / mm.^Twoso
Yes, F-5 value in the tape longitudinal direction is F-value in the tape width direction.
It is generally higher than 5 values, but especially in the width direction
This is not the case when it is necessary to raise it. Also possible
100 ° C.3 in the tape running direction and width direction of the flexible support
The heat shrinkage at 0 minutes is preferably 3% or less, more preferably.
1.5% or less, heat shrinkage at 80 ° C for 30 minutes is preferred
At most 1%, more preferably at most 0.5%.
The breaking strength is 5 to 100 kg / mm in both directions.^Two, Elastic modulus
Is 100 to 2000 kg / mm ^TwoIs preferred.

The step of producing the magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as 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 during 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 supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading step, a strong kneading force such as a continuous kneader or a pressure kneader is used. By using the magnetic recording medium, it is possible to obtain a high Br of the magnetic recording medium of the present invention. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, preferably 30% by weight or more of the total binder) and the ferromagnetic powder 100
The kneading treatment is performed in a range of 15 to 500 parts per part. The details of these kneading processes are described in JP-A-1-106338.
And JP-A-64-79274. When preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads and metal beads are suitable.

In the present invention, the production can be performed more efficiently by using the simultaneous multilayer coating method as disclosed in JP-A-62-212933. The following configuration can be proposed as an example of an apparatus and method for applying a magnetic recording medium having a multilayer configuration as in the present invention. 1. First, the lower layer is applied by a gravure coating, roll coating, blade coating, extrusion coating device, etc., which are generally used in the application of a magnetic paint, and the lower layer is wet while the lower layer is wet. -23
No. 8179 and Japanese Unexamined Patent Publication (Kokai) No. 2-265672, the upper layer is applied by a support pressure type extrusion coating apparatus. 2. JP-A-63-88080, JP-A-2-17921
The upper layer and the lower layer are coated almost simultaneously by one coating head having two built-in coating liquid passage slits as disclosed in JP-A-2-265672. 3. The upper layer and the lower layer are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in JP-A-2-174965. Note that, in order to prevent a decrease in electromagnetic conversion characteristics and the like of a magnetic recording medium due to agglomeration of ferromagnetic powder, Japanese Patent Application Laid-Open No. 62-95174 is disclosed.
It is desirable to apply a shear to the coating liquid inside the coating head by a method as disclosed in JP-A No. 236968/1990 or JP-A-1-236968. Further, the viscosity of the coating solution preferably satisfies the numerical range disclosed in Japanese Patent Application No. 1-312659.

In the present invention, the lower layer coating solution is provided on a flexible support by a so-called wet-on-wet coating method in which the lower layer coating solution is applied in a wet state. The wet-on-wet coating method used for providing the lower layer and the upper layer in the present invention is a so-called sequential coating method in which a first layer is first coated and the next layer is coated as soon as possible in a wet state, and a multilayer. At the same time, it refers to a method of applying by an extrusion coating method. As a wet-on-wet coating method, a magnetic recording medium coating method disclosed in JP-A-61-139929 can be used.

FIG. 1 is an explanatory view showing an example of a sequential coating system used for providing both layers in the present invention. The coating machine (applying machine) is applied to a continuously running flexible support 1 such as polyethylene terephthalate. A) The lower layer coating solution (a) is pre-coated in 3 and immediately after that, the coating surface is smoothed by a smoothing roll 4 and another extrusion coating machine (B) in a state where the coating solution 2 is in a wet state. 6. Next upper layer coating solution (b)
Is applied.

FIG. 2 is an explanatory view showing one example of an extrusion type simultaneous coating method preferably used for providing both layers in the present invention, wherein a simultaneous multilayer coating device 8 is used on a flexible support 1. This explains a state in which the lower layer coating liquid (a) 2 and the upper layer coating liquid (b) 5 are simultaneously applied. After applying both layers, the magnetic recording medium is obtained by applying a magnetic field orientation, drying and smoothing.

In order to obtain the medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1000 G (Gauss) or more and a cobalt magnet of 2000 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, when the present invention is applied to a disk medium, an orientation method for randomizing the orientation is required.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, the treatment can be performed between metal rolls. The processing 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 / min.
The range is 700 m / min. The effect of the present invention can be further enhanced at a temperature of 80 ° C. or more and a linear pressure of 300 kg / cm or more.

After the calendering treatment, a thermotreatment at 40 ° C. to 80 ° C. may be performed to accelerate the curing of the magnetic layer, the back layer and the nonmagnetic layer. The friction coefficient of the upper layer and the opposite surface of the magnetic recording medium of the present invention with respect to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, the magnetic layer surface resistivity is 10 ⁴ to 10 ¹¹ ohm / sq, and the lower layer is used alone. The surface specific resistance when coated is preferably 10 ⁴ to 10 ⁸ ohm / sq, and the surface electric resistance of the BC layer is preferably 10 ³ to 10 ⁹ .

The porosity of the upper and lower layers is preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording in which repetitive use is emphasized, a higher porosity is often preferable in running durability. It is easy to set these values in an appropriate range according to the purpose.

The magnetic characteristics of the magnetic recording medium of the present invention are as follows.
When measured by KOe, the squareness ratio in the tape running direction is 0.1.
70 or more, preferably 0.80 or more, and more preferably 0.90 or more. The squareness ratio in 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.

Although the magnetic recording medium of the present invention has a lower layer and an upper layer, it is easily presumed that these physical properties can be changed between the lower layer and the upper layer according to the purpose. The magnetic recording medium of the present invention basically comprises two layers of an upper magnetic layer and a lower nonmagnetic layer, but may have three or more layers. The configuration of three or more layers is that the upper magnetic layer is composed of two or more magnetic layers. In this case, an ordinary concept of a plurality of magnetic layers can be applied to the relationship between the uppermost magnetic layer and the lower magnetic layer. For example, the concept of using a ferromagnetic powder having a higher coercive force in the uppermost magnetic layer and a smaller average major axis length and a smaller crystallite size than the lower magnetic layer can be applied. Further, the lower non-magnetic layer may be formed of a plurality of non-magnetic layers.
However, when roughly classified, the structure is an upper magnetic layer and a lower nonmagnetic layer.

[0166]

Next, the present invention will be described more specifically with reference to examples and comparative examples. In each example, “parts” means “parts by weight” unless otherwise specified.

Example 1-1 A coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following prescriptions. Lower layer non-magnetic layer coating liquid Inorganic powder TiO ₂ 90 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ BET specific surface area 35 to 45 m ² / g DBP oil absorption 27-38 g / 100 g pH 6.5-8 carbon black 10 parts Average particle size 16 μm 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 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 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 butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 200 parts Cyclohexanone 80 parts Coating solution for upper magnetic layer Ferromagnetic powder (hexagonal barium ferrite) Average plate diameter 0.05 μm, plate ratio 4 Specific surface area by BET method 39 m ² / g Hc 1100 Oe chloride vinyl copolymer 9 parts -SO ₃ Na group 1 × 10 ^-5 eq / g containing, polymerization degree 300 particulate abrasive (Cr ₂ O, an average particle diameter of 0.3 [mu] m) 7 parts toluene 30 parts Methyl ethyl ketone 30 parts of the above After kneading the composition for about 1 hour with a kneader, the following composition was further added and dispersed for about 2 hours with a kneader.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ⁻⁴ eq / g average molecular weight 35000 toluene 200 parts methyl ethyl ketone 200 parts The following carbon black and coarse particle abrasive were added, and a dispersion treatment was performed with a sand grinder.

Carbon black (average particle diameter: 20 to 30 μm) 5 parts Lion Akzo Ketjen Black EC coarse particle abrasive 2 parts α-alumina (AKP-12 manufactured by Sumitomo Kagaku, average particle diameter 0.5 μm) The composition was added and dispersed again by a sand grinder to obtain a coating solution for the upper magnetic layer.

6 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co.) 6 parts of tridecyl stearate 6 parts The coating solution for the upper magnetic layer and the coating solution for the lower non-magnetic layer obtained as described above were polyethylene terephthalate having a thickness of 75 μm. First, the coating solution for the lower non-magnetic layer was applied, and then the coating solution for the upper magnetic layer was applied in a wet state, and the back surface was similarly treated. The thickness of the lower non-magnetic layer was 1.5 μm and the thickness of the magnetic layer was 0.5 μm in dry film thickness. Thereafter, a calendar process was performed to obtain a magnetic recording medium. Thereafter, the magnetic recording medium was punched into a 3.5-inch cartridge, placed in a 3.5-inch cartridge having a liner installed inside, and a predetermined mechanical component was added thereto. Got a disc. Further, the sample by changing the factor (especially the ratio of the average plate diameter of the ferromagnetic powder in the lower nonmagnetic layer inorganic powder having an average particle diameter and the upper magnetic layer of) described in Table 1
Examples 1-2 and 1-3, Comparative Examples 1-1 and 1-2
Was prepared and the performance was evaluated as follows. The results are shown in Table 1.

[0171] 1. Volume ratio (filling ratio) of lower layer inorganic powder The medium was cut out to about 0.1 μm with a diamond cutter to prepare a test piece, which was observed with a transmission electron microscope. Counting the number of inorganic powder particles per 1 μm ² from this transmission electron microscope photograph image, taking into account the thickness of the cut test piece, measuring the number of inorganic powder particles contained per unit volume, and The volume per unit was determined from the particle size of the powder obtained from the same photograph and multiplied by the number of inorganic powder particles contained per unit volume to obtain the volume ratio of the inorganic powder. The calculation formula is as follows.

The volume ratio of the lower inorganic powder = 4π / 3 (D
/ 2) ³ (n / t) × 100 (%) D: Particle size (μm) of powder determined from section photograph n: Number of powders contained per unit area determined from section photograph (pieces / μm) ² ) t: Thickness of section (μm) Powder Volume Ratio of Upper Magnetic Layer The ferromagnetic powder density can be obtained from the following equation.

DM = Bm / 4πσ _S where Bm (Gauss): residual magnetic flux density dM (g / cc): density of ferromagnetic powder σ _S (emu / g): magnetization amount of ferromagnetic powder The volume ratio in the upper layer is obtained by dividing the density by the specific gravity of the ferromagnetic powder. Further, the density of the other powder components and the binder in the magnetic layer is calculated from the prescribed amount of the magnetic layer, and divided by the specific gravity of each powder component, the volume ratio of each powder component is obtained, and these are summed. By doing
The powder volume ratio of the upper layer is determined. 3. Average Particle Size of Inorganic Powder The average particle size of the major axis was determined from a transmission electron microscope. 4. Crystallite size of ferromagnetic metal powder The crystallite size was determined by X-ray diffraction from the spread of the half width of the diffraction lines on the (4,4,0) plane and the (2,2,0) plane. 5. The surface roughness R _rms scanning tunneling microscope (STM) measurement is performed by Digit.
Nanoscope manufactured by al Instrumentum
Tunnel current 10A, bias voltage 400m using eII
Under the condition of V, a range of 6 μm × 6 μm was scanned and found by the following equation (1).

[0174]

(Equation 1)

6. d standard deviation σ; tape cross section photographed by transmission electron microscope (TEM) (magnification: 20000 times)
And determined according to the above definition. (2) AFM (Atomic Force Micro)
Scope) The surface roughness R _rms was measured. Digita the magnetic layer surface
l Instrument's Nanoscope II
, Tunnel current 10 nA, bias voltage 400 m
V was scanned over a range of 6 μm × 6 μm. For the surface roughness, R _rms in this range was determined.

As a result, R _rms was 8.7 nm.
Practically, it is required to be 20 nm or less, preferably 10 n
m . 7.7 MHz output A 7 MHz signal was recorded using an 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. The reference is an internal reference of Fuji Photo Film Co., Ltd. 8. Pinholes After coating the magnetic layer and before coating the back layer, the magnetic layer was visually observed with transmitted light to measure pinholes per 100 m ² . It is desirable that the number be one or less per 100 m ² . 9. Inner circumference 2F output relative value (%); calculated as initial 2F output value of Example 1-1 . Drive used is PD211
Made by Toshiba Corporation.

10. Vertical squareness ratio: Br / Bm in a direction perpendicular to the coated surface was measured using a vibrating sample magnetometer. D50 (kfci): output is 50 of long wavelength recording / reproducing output
% Recording density. This D50 is a measure of the maximum recording density that can be realized as an apparatus.

[0178]

[Table 1]

As shown in Table 1, the samples of Examples 1-1 to 1-3 have an average particle diameter of the inorganic powder contained in the lower non-magnetic layer of:
Since the average plate diameter of the plate-like ferromagnetic powder contained in the upper magnetic layer is equal to or less than the average, the squareness ratio in the vertical direction is high, and a uniform magnetic layer having Δd of d / 2 or less is formed. Therefore, the sample of the example is an excellent magnetic recording medium having a high D50 and very few pinholes. On the other hand, in Comparative Example 1-1, since the average particle diameter of the inorganic powder was larger than the average plate diameter of the ferromagnetic powder, Δd increased, and D50 was not improved. Comparative Example 1-2 is an example of a single magnetic layer without a lower nonmagnetic layer,
D50 is bad.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method for measuring Δd of a magnetic recording medium according to the present invention.

FIG. 2 is an explanatory view showing an example of a sequential coating method used for providing a lower layer and an upper layer by a wet-on-wet coating method in the present invention.

FIG. 3 is an explanatory diagram showing an example of a simultaneous multilayer coating method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flexible support 2 Coating liquid (a) 3 Coating machine (A) 4 Smoothing roll 5 Coating liquid (b) 6 Coating machine (B) 7 Backup roll 8 Simultaneous multilayer coating device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication G11B 5/842 G11B 5/842 Z H01F 1/11 H01F 1/11 Q (72) Inventor Satoru Hayakawa 2-12-1 Ogimachi, Odawara City, Kanagawa Prefecture Inside Fuji Photo Film Co., Ltd. (56) References JP-A-4-238111 (JP, A) JP-A-4-283416 (JP, A) JP-A-4-321924 (JP, A) JP-A-4-325915 (JP, A) JP-A-4-325917 (JP, A) JP-A-5-12650 (JP, A) JP-A-5-197946 (JP, A) JP-A-5-182173 (JP, A) JP-A-5-182177 (JP, A) JP-A-5-182178 (JP, A) JP-A-5-73883 (JP, A) JP-A-63-187418 (JP) JP, A)

Claims (13)

(57) [Claims] 1. A plurality of at least two or more layers in which a lower nonmagnetic layer in which at least nonmagnetic powder is dispersed in a binder is provided on a support, and an upper magnetic layer in which ferromagnetic powder is dispersed in a binder is provided thereon. Wherein the average thickness (d) of the dry thickness of the upper magnetic layer is 1 μm or less,
The ferromagnetic powder of the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization perpendicular to the flat plate, and the nonmagnetic powder of the lower nonmagnetic layer has a Mohs hardness of 3 or more. A magnetic recording medium having an average particle size smaller than the plate diameter of the hexagonal plate-shaped ferromagnetic powder. 2. An AFM (Atom) on the surface of the upper magnetic layer.
Rrms is 20 nm as measured by ic ForceScope) or scanning tunneling microscope (STM).
2. The magnetic recording medium according to claim 1, wherein: 3. The magnetic recording medium according to claim 1, wherein a volume filling ratio of the lower nonmagnetic layer in the lower nonmagnetic layer of the inorganic powder is 20 to 60%. 4. The hexagonal plate-shaped ferromagnetic powder has a plate diameter of 0.
2. The magnetic recording medium according to claim 1, wherein the thickness is from 001 to 0.3 [mu] m. 5. The hexagonal plate-like ferromagnetic powder is made of barium ferrite, strontium ferrite, lead ferrite,
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a plate-like hexagonal ferrite of calcium ferrite. 6. The hexagonal plate-shaped ferromagnetic powder has a plate diameter of 0.3 mm.
001 to 0.09 μm, and the plate thickness is の of the plate diameter.
^2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a specific surface area of 1 to 60 m ² / g. 7. The non-magnetic powder of the lower non-magnetic layer is made of TiO.
₂ (rutile, anatase), TiO _x , cerium oxide,
Tin oxide, tungsten oxide, ZnO, ZrO ₂ , Si
O ₂ , Cr ₂ O ₃ , α-alumina with α-rate of 90% or more, β
Alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgC
O ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO
_4. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least one selected from silicon carbide and titanium carbide. 8. The flexible support includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, and the like.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least one selected from polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide. 9. The method according to claim 1, wherein the lower nonmagnetic layer has a saturation maximum magnetic flux density B
2. The method according to claim 1, wherein m is equal to or less than 500 Gauss.
The magnetic recording medium according to the above. 10. The magnetic recording medium according to claim 1, wherein the lower non-magnetic layer contains a magnetic powder imparting thixotropic properties. 11. The lower non-magnetic layer contains a magnetic powder,
2. The magnetic recording medium according to claim 1, wherein the lower non-magnetic layer is a layer not involved in recording. 12. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is for a DAT or a magnetic disk. 13. A lower non-magnetic layer coating liquid in which a non-magnetic powder is dispersed in a binder and an upper magnetic layer coating liquid in which a ferromagnetic powder is dispersed in a binder are prepared, and the lower non-magnetic layer coating liquid is prepared. Liquid and the coating liquid for the upper magnetic layer are coated on a support, in the method for producing a magnetic recording medium, the coating liquid for the upper magnetic layer is a hexagonal plate having an easy axis of magnetization as the ferromagnetic powder in the vertical direction of a flat plate. The lower non-magnetic layer coating liquid containing the ferromagnetic powder of No. 3, the non-magnetic powder has a hardness of 3 or more and has an average particle size smaller than the average plate diameter of the hexagonal plate-like ferromagnetic powder. After coating the lower non-magnetic layer coating solution on a support containing the powder, while the lower non-magnetic layer is wet, the dry thickness average value (d) of the upper magnetic layer is reduced to 1 μm or less. Simultaneous or simultaneous application of the lower non-magnetic layer coating solution Method of manufacturing a magnetic recording medium, characterized by then coating the upper magnetic layer coating solution.