JP2666820B2 - Magnetic recording media - 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, and more particularly to an ultra-thin layer magnetic recording medium in which the dry thickness of a magnetic layer is 1.0 .mu.m or less. The present invention also relates to a magnetic recording medium with good yield and good production characteristics. In particular, the present invention relates to a magnetic recording medium, particularly a high-density thin-layer magnetic recording medium having a magnetic layer thickness of 1.0 μm or less, and more specifically, the present invention relates to a magnetic recording medium having a nonmagnetic layer as a lower layer, The present invention relates to a magnetic recording medium with improved running properties and durability.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a video tape, an audio tape, a magnetic disk or the like, a magnetic coating medium in which ferromagnetic iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic alloy powder or the like is dispersed in a binder is used. A recording medium in which a liquid is layered on a flexible support is widely used. In recent years, the recording wavelength tends to be shortened with the increase in recording density, and as a result, the problem of thickness loss at the time of recording / reproduction 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 influence of the surface properties of the support on the surface of the magnetic layer tends to appear, and the electromagnetic conversion characteristics deteriorate. There was a tendency.

[0003] Therefore, by providing a nonmagnetic thick lower layer on the surface of a flexible support and then providing a magnetic layer as an upper layer, the above-mentioned problem caused by the surface roughness of the support is solved and the magnetic layer is formed as a thin layer. Attempts to reduce the thickness demagnetization and achieve high output have been proposed. For example, in Japanese Patent Application Laid-Open No. 62-154225, in order to reduce the thickness of the magnetic layer to 0.5 μm or less and to prevent the surface electric resistance of the magnetic layer from increasing,
There has been proposed a magnetic recording medium provided with an undercoat layer containing a conductive fine powder having a thickness not less than the thickness of the magnetic layer. or,
JP-A-62-222427 discloses a support, an undercoat layer provided on the support and containing an abrasive having an average particle size of 0.5 to 3 μm, and an undercoat layer provided on the undercoat layer. A magnetic recording medium provided with a magnetic layer containing a ferromagnetic powder and having a thickness of 1 μm or less has been proposed. This is achieved by projecting a part of an abrasive in an undercoat layer onto the magnetic layer to thereby reduce the magnetic property of the magnetic recording medium. The head cleaning function is also provided. In this way, the magnetic layer is thinned to achieve high-density recording, and at the same time, the lower non-magnetic layer contains carbon black for antistatic, and an abrasive is used to improve cleaning characteristics and durability. Or have been added.

However, in the prior art, a lower non-magnetic layer is first coated on a flexible support, dried and then subjected to a calender treatment as needed, and then an upper magnetic layer is provided. The manufacturing process is complicated and there are the following problems. That is, in order to reduce the thickness of the magnetic layer, it is conceivable to reduce the amount of coating or to add a large amount of a solvent to the magnetic coating solution to reduce the concentration. In the former case, if the amount of application is reduced, there is not enough time for leveling after application, and drying starts, so that an application defect, for example, a streak or engraved pattern remains, resulting in a very poor yield. In the latter case, when the concentration of the magnetic coating solution is low, a large amount of voids composed of a large number of micropores are formed in the dried film, and a sufficient degree of filling of the ferromagnetic powder cannot be obtained. For this reason, various adverse effects such as insufficient strength of the coating film are caused. 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.

The simultaneous multi-layer coating method or the sequential wet coating method, that is, a 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, has already been subjected to various studies in the multi-layer coating of the magnetic layer. Has been done. However, even when this technique was applied to the lower non-magnetic layer, similarly good results could not be obtained. In other words, Wet on
When the lower non-magnetic layer and the upper magnetic layer were provided by the Wet method, the interface between these two layers was disturbed, and the surface roughness was significantly deteriorated.

If a magnetic layer is provided as an upper layer after a nonmagnetic thick lower layer is provided on the surface of the support, the influence of the surface roughness of the support can be eliminated, but head wear and durability are reduced. There was a problem that it was not improved. The reason is that the thermosetting (curing) resin is used as the binder for the non-magnetic lower layer, so the lower layer is excessively hardened, and as a result, the contact between the magnetic layer and the head or other members is unbuffered. Or the flexibility of the entire magnetic recording medium having such a lower layer may be somewhat low. In order to solve this, it is conceivable to use a non-curable (thermoplastic) resin as a binder for the lower layer. However, in the conventional method, when the magnetic layer is applied as the upper layer after the lower layer is applied and dried, the lower layer becomes the upper layer. It swells due to the organic solvent of the coating liquid and causes turbulence in the upper coating liquid, thereby 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 thickness of the magnetic layer of the metal thin-film magnetic recording medium is very small, the loss due to the thickness is small, so that a medium having a very high output can be obtained. However, since these media are manufactured by depositing a metal on a flexible support, they are inferior in mass productivity as compared with conventional coated magnetic recording media, and are easily oxidized because they are thin metal films. Has a problem with long-term storage. In order to avoid these problems, it has been desired to reduce the thickness of the magnetic layer of the conventional coating type magnetic recording medium.

However, the thickness of the upper magnetic layer is set to 1.
If it is attempted to apply and dry a thin layer having a thickness of 0 μm or less, the magnetic liquid must be diluted with a large amount of a solvent, and as a result, the magnetic liquid tends to aggregate. In addition, since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder is easily disturbed, and the orientation is poor in a magnetic recording medium. It is difficult to ensure sufficient electromagnetic conversion characteristics. In addition, since excessive drying generates voids composed of many micropores, the strength of the magnetic film is weak, and good results in running durability cannot be obtained. If the amount of diluting organic solvent is reduced in order to improve the orientation and reduce the voids in the dried film, the coating stability deteriorates.

As a means for addressing such problems, it has been proposed to include a non-magnetic granular abrasive or filler in the undercoat layer. However, a problem with these techniques is that when a magnetic layer and a non-magnetic layer are simultaneously coated and subjected to an orientation treatment, the magnetic material is rotated by an orientation magnetic field. Mixing occurs at the interface between the two layers. As a result, the surface properties are reduced and the orientation is insufficient, and 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 scale-like particles.
However, this intermediate layer has improved orientation, but graphite itself has no effect of reinforcing the film and has insufficient durability, so that it has a Mohs hardness of 5 or more. It has been proposed to mix inorganic powder. Further, 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).

[0011] Although these proposals improve the orientation and ensure durability, in the actual production of a medium, flaky particles are liable to cause stacking, and acicular particles such as oxalate are dispersed in a binder. It has been found that the magnetic properties are low and the smoothness of the magnetic surface is impaired. 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,
It is desired that the lower non-magnetic layer that is not directly exposed on the surface be improved in dispersibility as much as possible. The rate of contribution is increasing further. As a result of intensive studies, it has been found that the surface is roughened even when the dispersibility of only the lower layer is simply improved in the simultaneous multilayer.

If the coercive force of the magnetic layer is low, the self-demagnetization loss is large, and it is not suitable for short-wavelength recording. Means that can be adapted to such a purpose include a thickness of 0.5 mm between the flexible support and the magnetic layer.
A subbing layer having a thickness of 5.0 μm to 5.0 μm
It is proposed to be 00 Oe. (Japanese Unexamined Patent Publication No.
However, with the conventionally known technology, there are the following problems to achieve this object. When the upper and lower layers are simultaneously coated as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-198536, the two layers are mixed to deteriorate the surface properties and disturb the orientation. Japanese Patent Application Laid-Open No. 3-490 discloses a technique for improving orientation in simultaneous multilayer coating.
No. 32 discloses that a layer in which carbon black is dispersed is used as a lower layer to perform multi-stage orientation, but a filler having a small true specific gravity, such as carbon black, is rotated immediately after the simultaneous multilayer coating due to the rotational motion of the magnetic material during orientation. Although the interface between the two layers was disturbed by the orientation treatment, the squareness ratio measured in the in-plane direction was high, but 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. 62-1115. However, when applying this known technique in simultaneous multilayer coating, there are the following problems. In other words, when simultaneous non-magnetic lower-layer carbon black is applied to the lower layer using low specific gravity, during the coating process or orientation process, mixing of the non-magnetic lower layer and the upper magnetic layer, or turbulence at the interface between the two layers due to turbulent flow. cause. Such mixing and turbulence between the two layers extremely reduces 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 in a video deck, the tape expands, and skew distortion increases. In order to prevent this skew distortion, attempts have been made to reduce the heat shrinkage of the support and to increase the strength, but there are limits to this. Also,
When the simultaneous multilayer coating method is adopted, there is a problem that the heat shrinkage rate 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 is hardened by applying a calender or curing treatment after the lower layer is applied to suppress the expansion and contraction of the medium. This is because expansion and contraction cannot be suppressed. JP-A-63-187418 and JP-A-63-191315 disclose inventions based on the simultaneous multi-layer coating method, but have such disadvantages.

[0015] Similarly, the tape thickness tends to be reduced in order to record and / or reproduce for a long time. When the tape thickness 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, the total thickness is 14 μm for 8 mm video tapes and VHS long-time tapes that have become popular in recent years.
It is difficult to secure the head contact because of the following thinness. Conventionally, when the medium thickness is large, it has been effective to lower the strength of the lower non-magnetic layer to maintain a smooth contact state. However, thin tapes used in recent recording / reproducing apparatuses have a lower non-magnetic layer. If the stiffness of the magnetic layer is not increased, it is difficult to secure a so-called head contact with the rotating head. Although there is a method of controlling the stiffness by a method of stretching the flexible support, the stiffness in the width direction is reduced, which is not preferable for running durability.

As shown in Japanese Patent Application Laid-Open No. 63-191315, it has been confirmed that the lower non-magnetic layer is free of polyisocyanate in order to improve head contact. The result is poor storage stability. Therefore, this method is effective in a system that does not place importance on storability, but is difficult to use in a system that places importance on storability such as business use or data storage. JP-A-63-187
418 also discloses that the magnetic layer is similarly thinned to improve the electromagnetic conversion characteristics. However, in the present invention, there are still some electromagnetic conversion characteristics that are insufficient. JP-A-50-
803 also has an invention in which a fine-grained non-magnetic pigment having a Mohs hardness of 6 or more is provided between the magnetic layer and the support. The gist of the present invention is to grind an aluminum base with a non-magnetic powder having a Mohs hardness of 6 or more. The purpose is to increase the flatness of the base.

In addition, these methods are difficult to meet the recent demands for thinner magnetic recording media due to longer recording times and higher densities of magnetic recording, and have excellent electromagnetic conversion characteristics and running durability. It was insufficient to balance the properties. In particular, in order to improve running durability with a thin tape, it is necessary to reduce tape edge damage.
The inventions of 91315 and JP-A-63-187418 were insufficient.

Next, various patent applications have been filed for obtaining a magnetic recording medium by a wet-on-wet coating method in which the upper layer is a magnetic layer and the lower layer is a nonmagnetic layer. For example, in Japanese Patent Application Laid-Open No. 50-104003, Wet on W
Although there is a description suggesting the et coating method, the nonmagnetic 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 added to improve the dispersibility of the carbon black, but the ferromagnetic powder to be added to the intermediate layer uses the same ferromagnetic powder as that in the magnetic layer. Could not be prevented. JP-A-62-214524
Japanese Patent Application Publication No. JP-A-2005-17764 discloses a method of manufacturing a magnetic recording medium in which each coating solution composition is selected so as to have mutual solubility with respect to a solvent and a solute of each coating solution composition of a plurality of adjacent layers, and the coating and drying are performed by a wet-on-wet coating method. A method is disclosed. However, although there is an example of a combination of a magnetic layer as an upper layer and a non-magnetic layer as a lower layer, it is an example of only a binder, and suggests that carbon black is also included in the intermediate layer. Based on this, it was not possible to eliminate interface turbulence.
Also, Japanese Patent Application Laid-Open No. 62-241130 (US48392)
No. 25) describes a magnetic recording medium in which the intermediate layer contains at least one binder containing a hydroxyl group and / or an amino group, and the magnetic layer contains an isocyanate compound. It discloses that the bonding is performed to improve the adhesion strength between the intermediate layer and the magnetic layer. Carbon black may be added to the intermediate layer, and the wet-on-we
It is stated that the coating may be performed by the t-coating method, but such a disclosure cannot 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)), But the upper layer
Only the viscosity of the liquid and the underlayer liquid are shown.
Then, the interface fluctuation could not be sufficiently suppressed. Also JP
JP-A-63-146210 discloses a lower magnetic layer or a non-magnetic layer.
The binder in the conductive layer is an uncured binder, and the magnetic layer in the top layer
Discloses a magnetic recording medium in which the binder is an electron beam-curable resin
Have been. However, carbon is used for the lower non-magnetic paint.
Solving interface turbulence with only examples containing black
I couldn't do that. JP-A-63-164022
The gazette states that the extrusion type coating head
A non-magnetic liquid layer with lower viscosity than the magnetic liquid layer
Extrusion coating of multiple layers by forming on the wall surface before and after the slot
A method for applying a magnetic liquid is disclosed. High viscosity magnetic layer
Wrap the solution with a binder solution of a low-viscosity nonmagnetic layer,
The aim is to improve the suitability for thin layer coating,
The purpose is to reduce the gap between the bead and the coating head.
Such disclosure alone is sufficient to solve interface turbulence
Could not. JP-A-63-187418
(U.S. Pat. No. 4,863,793) includes an upper magnetic layer.
The average long axis length of the ferromagnetic powders
Less than 0.30 μm, crystallite size by X-ray diffraction method is 3
A magnetic recording medium less than 00 ° is disclosed. Underlayer
Non-magnetic layer of carbon black, graphite, oxidized
It is disclosed that titanium can be included, and as a specific example
Α-Fe_TwoO_Three100 parts by weight and conductive carbon 10
A combination of parts is disclosed. However, carbon
Low usage, α-Fe_TwoO_ThreeOf the particle size
Are not listed in the publications,
Could not be solved enough.

Further, Japanese Patent Application Laid-Open No. 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 low carbon usage and α
Since the particle size of -fe ₂ O ₃ is not described, it has not been possible to resolve the disturbance of the interface in the disclosure of these publications.

Japanese Unexamined Patent Publication (Kokai) No. 2-254621 discloses a non-magnetic layer containing carbon black as a main component, and a magnetic layer containing an Fe-Al-based ferromagnetic powder on the non-magnetic layer.
A magnetic recording medium formed by a Wet 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.

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
Japanese Unexamined Patent Publication No. 260260/1990 discloses that a magnetic layer 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 flexible support. A recording 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.

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, the multi-layer coating technique has focused on the signal recording mechanism of the VTR, that is, the recording depth of each signal, and has attempted to improve the performance by designing an optimum upper and lower magnetic layer for each signal. The VHS multi-layer coating has achieved a high output and a low noise in all the luminance, color and sound bands by a two-layer structure in which the upper layer and the lower layer employ ferromagnetic powders having different sizes and magnetic characteristics respectively.

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

However, in order to pursue further ultra-high-density recording with Hi8MP tape 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 to provide a high output, C / C
It is an object of the present invention to provide a thin-layer magnetic recording medium having excellent electromagnetic conversion characteristics such as N, and to provide a thin-layer magnetic recording medium having good head contact and excellent 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 bit 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.

[0033]

As a result of intensive studies, the present inventors have found that although the conventional simultaneous multi-layer coating technique is partially based, it exceeds the limit and becomes larger as the recording becomes shorter in wavelength. And the development of a new magnetic material and high-density packing are two important points to thoroughly reduce the thickness of the magnetic layer and to increase the magnetic energy of the magnetic layer as much as possible. Was. First, the signal loss was thoroughly reduced. In magnetic recording, various “losses” occur during the recording / reproducing process. However, the present inventors have found that by reducing “self-demagnetization loss” which has been considered inevitable with MP (metal) tapes, a high level is achieved. I found a completely new way of thinking about improving the region characteristics.

That is, the first point of the present invention is to make the thixotropic properties of the coating solutions of the upper magnetic layer and the lower non-magnetic layer the same or similar, or to adjust the shape of the non-magnetic powder for the lower layer. By eliminating the mixed region at the interface, the average dry thickness (d) of the upper magnetic layer is 1 μm or less, and the average dry thickness (d) is λ / 4 ≦ d ≦ with respect to the shortest recording wavelength λ. 3λ and before
250 μm × 25 using 3D-MIRAU of the magnetic layer
The surface roughness Ra measured at an area of 0 μm is Ra ≦ λ / 50
This realizes an unprecedented uniform and ultra-thin magnetic layer, and significantly reduces self-demagnetization loss in a short wavelength region.
In the following description, “surface roughness Ra” refers to 3D-
Measured over an area of 250 μm × 250 μm using MIRAU
The surface roughness is shown.

Further, the second point, which can be said to be a preferable condition to be adopted in carrying out the present invention, is to suppress the disturbance of the interface to an extremely low level and to determine the size and shape of the ferromagnetic powder of the upper magnetic layer and the non-magnetic property of the lower layer. By adjusting the size and shape of the non-magnetic powder for the magnetic layer and adding an invention to improve the dispersibility of the non-magnetic powder itself, a more uniform interface with less fluctuation can be realized and the super-smooth magnetic layer surface can be realized. completed. This smooth magnetic layer surface completely eliminated the "space loss" and improved high-frequency output.

A third point, which can be said to be a preferable condition employed in carrying out the present invention, is to increase the energy of the magnetic layer. H is applied to the upper magnetic layer.
Higher magnetic energy and higher coercive force can be achieved by using a ferromagnetic powder of fine particles in which both r and Hc are increased.
(Evaporation) It has been found that a high-frequency output equal to or higher than that of a tape is exhibited. The fourth point of a similar preferred condition of the present invention is high density packing. In the prior art, simply reducing the thickness of the magnetic layer reduces the low-frequency output and degrades the color characteristics. And
By filling high-energy ferromagnetic powder with high density,
It has been found that excellent mid and low frequency characteristics can be realized.

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 flexible support, and an upper magnetic layer containing the ferromagnetic powder and the binder thereon. In the provided magnetic recording medium having at least two or more layers, the upper magnetic layer has an average dry thickness (d) of 1 μm or less, and has a λ with respect to the shortest recording wavelength λ.
/ 4 ≦ d ≦ 3λ and the surface roughness Ra is Ra ≦ λ /
50, the non-magnetic powder is an inorganic powder having a Mohs hardness of 3 or more, and the shortest recording wavelength λ
Is 4 μm or less.

That is, the first point of the present invention is to realize an ultra-thin magnetic layer. It is known from the principle of self-demagnetization that the smaller the cross-sectional area of the magnetic layer, the smaller the loss.Therefore, in order to increase the output of short-wavelength signals, it is essential to make the magnetic layer ultra-thin. It was found. Moreover, the effect is small at a thickness of 1 μm or more,
The effect becomes larger as the effective recording thickness approaches １ ／ of the recording wavelength, that is, as the recording approaches the saturation recording. Therefore, the ultra-thin layer in sub-micron units is required.

In the conventional single-layer coating technique, it is difficult to apply a thin layer in the submicron region, and the thinner the layer, the more difficult it is to secure a uniform thickness and to achieve ultra-smoothness. It was extremely difficult to do. Therefore, the conventional multi-layer coating technology was renovated to provide an upper magnetic layer with respect to the lower non-magnetic layer containing the fine particle inorganic powder, and the average dry thickness (d) of the magnetic layer was 1 μm or less, The average value (d) has a relationship of λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ, and the surface roughness Ra of the magnetic layer is Ra ≦ λ /
50, the self-demagnetization loss is reduced by using an epoch-making ultra-thin magnetic layer of 1/3 to 1/10 or less of the conventional general Hi8MP tape, and the luminance is reduced. A large improvement in signal output is realized. Further, at this time, by setting the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower magnetic layer in a relation of Δd ≦ d / 2, the effect can be further improved. it can. Further, when the upper magnetic layer is provided on the lower non-magnetic layer by a wet-on-wet coating method, the effect can be 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 of the magnet 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, both are made of iron and are attracted to a magnet. Since the self-demagnetization is large, it has the property that it is difficult to become 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, since the self-demagnetization loss becomes smaller as the recording approaches the saturation recording and the output is improved, it is necessary to make the sub-micron region ultra-thin to approach the effective magnetic layer thickness, which is said to be 1/4 of the recording wavelength.

The shortest recording wavelength on the Hi8MP tape is 0.
This is an extremely short wavelength of 49 μm, which is one of the reasons why the magnetic layer has excellent high-frequency characteristics 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 conventional coating type MP tape is about 3 μm, and the conventional coating method has to be considerably thicker than the recording wavelength. Was.

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 that even a very small spacing between the tape and the video head results in a large output loss. 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 with the i8MP tape, the shortest recording wavelength is about 4
The importance is extremely high in high-density recording of 0%. The latter is what is called "head contact", and it is an issue 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.

The second point of the present invention is ultra-smoothing of the magnetic layer surface. Originally, the multilayer coating technique is a technique capable of realizing 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 magnetic layer. But,
Conventionally, the multilayer coating technique alone has had a limit in aiming for further smoothness even with a slight space loss at a shorter wavelength of 0.5 μm or less.

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. Even 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 in the upper 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 contained in the lower layer were made into ultra-fine particles and the high-density non-magnetic particles were pursued. However, because it is ultrafine particles, it is difficult to fill it uniformly and at high density if it is used as it is. Therefore, a special surface treatment is applied to the surface of the ultrafine particles to improve the dispersibility, thereby realizing high density filling. And the smoothness of the interface between the upper and lower layers is dramatically improved.

Further, since this non-magnetic layer is a high-density filling layer, it has high flexibility in the surface direction of the tape, has excellent flexibility, and is extremely resistant to force in the thickness direction. It exhibits high rigidity and further enhances the smoothing effect by calendering. As a result, as compared with the conventional multilayer Hi8MP tape, the smoothness was further improved by 20%, and the surface roughness Ra of the magnetic layer achieved 2.7 nm. The super-smoothness achieved by using a wet-on-wet coating method in which a nonmagnetic layer is provided as a lower layer significantly reduces space loss in a short wavelength region and improves high-frequency characteristics. .

Next, the third point of the present invention will be described. That is, according to the present invention, the major axis length of the ferromagnetic powder contained in the upper magnetic layer is 0.3 μm or less, and the coercive force H
It is preferable that c is a needle-like ferromagnetic alloy powder of 1500 Oe or more, or a powder having a plate diameter of 0.3 μm or less and a coercive force Hc of 1000 Oe or more. A third point of the present invention is to increase the output and lower the noise of the magnetic layer, which is the basis of the technology for improving the performance of a magnetic tape. In order to thoroughly pursue improvements in characteristics at short wavelengths, minimizing signal loss and making the magnetic material ultra-fine,
It is indispensable to increase the output and lower the noise of the magnetic layer itself by increasing the energy and filling it with high density.

Next, a fourth point of the present invention will be described. The medium of the present invention has a ratio SMD of a longitudinal stiffness SMD and a stiffness STD in a width direction of the magnetic recording medium.
/ STD is preferably from 1.0 to 1.9. Specifically, it is preferable that the inorganic powder contained in the lower non-magnetic layer is a polyhedral inorganic powder having a Mohs hardness of 6 or more and an average particle diameter of 0.15 μm or less, from spherical to cubic. In the medium of the present invention, the thermal shrinkage of the magnetic recording medium at 70 ° C. for 30 minutes is preferably 0.4% or less. Specifically, the dry thickness of the lower nonmagnetic layer is preferably not more than 0.4%. The dry thickness of the upper magnetic layer is 1 to 30 times, and the difference between the powder volume ratio of the lower nonmagnetic layer and the powder volume ratio of the upper magnetic layer is -5% to + 20%. Is preferably within the range. The fourth point of the present invention lies in the high density packing, and it is the lower non-magnetic layer that enables the high density packing of the magnetic material of the present invention. Smooth,
The non-magnetic layer, which is extremely rigid in the thickness direction,
Super HDP (High DensityPacki
ng) An extremely high-pressure nip pressure provided by a calendar was effectively received, and an unprecedented breakthrough in high-density packing was realized.

On the other hand, 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 the high-energy magnetic material to be remarkably filled to solve this problem. The low frequency characteristics were ensured, and an excellent color output was obtained.

Here, the method of obtaining the average thickness d of the upper magnetic layer is as follows. First, a magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter in the longitudinal direction, and the transmission electron microscope was used to magnify 10,000 to 100 magnifications.
Observe at 000 times, preferably 20,000 to 50,000 times, and take a photograph. The photo print size is A4
To A5. Thereafter, while paying attention to the difference in shape between the magnetic material and the non-magnetic powder contained in the upper magnetic layer and the lower non-magnetic layer, the interface is visually checked and blackened, and the surface of the magnetic layer is similarly blacked out. Then, the length of the interval between the bordered lines is measured by an image processing device IBAS2 manufactured by Zeiss. Thus, the average value of the thickness of the upper magnetic layer is obtained. The length of the interval is 100-300 for an interval of 21 cm in length.
And measure its length.

Incidentally, by quantitatively grasping the fluctuation of the interface between the lower layer and the upper layer, it is possible to control the disturbance phenomenon at the interface well. As a method of obtaining the interface variation value, the average value of the thickness variation Δ
taken as d, the length 20 [mu] m (actual length) the magnetic layer and the thickness direction of the bottom portion of the top and the valley of the edge peaks of the surface that is formed up of the non-magnetic layer distance in the ([Delta] d _i). 10 to 20
Locations (all within 20 μm) were determined, and the average value of the sum was obtained. That is, in the present invention, the curve forming the interface is ideally preferably a straight line having a constant d. Preferably, a curve similar to a smooth sine curve with a long interval is formed, and the number of peaks and valleys is 20
It is preferable that the length is limited to about 10 to 20 μm each. (See FIG. 1) That is, Δd = (Δd ₁ + Δd ₂ +... + Δd _m ) / m
(M = 10 to 20) Further, a distance (L) between peaks of a curve formed by the interface.
Is preferably 1 μm or more, particularly preferably 2 μm or more. In addition, the standard deviation σ can be obtained from the values of the thickness of each magnetic layer segmented into 100 to 300 as in the statistical processing. This standard deviation σ is preferably 0.2 μm or less. Incidentally, the thickness average value d of the magnetic layer
And the average value Δd of the thickness variation at the interface is
Δd ≦ d / 2 is preferred.

The first point of the present invention is that a lower nonmagnetic layer in which at least a nonmagnetic powder is dispersed in a binder is provided on a flexible support, and an upper layer containing a ferromagnetic powder and a binder is provided thereon. In the magnetic recording medium having at least two or more layers provided with the above magnetic layer, the upper magnetic layer has an average dry thickness (d) of 1 μm or less, and has a λ / λ with respect to the shortest recording wavelength λ. 4 ≦ d ≦ 3λ and surface roughness Ra
Have a relationship of Ra ≦ λ / 50, the nonmagnetic powder is an inorganic powder having a Mohs hardness of 3 or more, and the shortest recording wavelength λ is 4 μm or less. The specific means are as follows. The first embodiment is to control the thixotropic properties of the respective dispersions of the magnetic coating for the upper magnetic layer and the coating for the lower non-magnetic layer so as to be close to each other. The purpose is to regulate the size and shape of each powder contained in the magnetic layer and the upper magnetic layer 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 has a shear stress A10 ⁴ at a shear rate of 10 ⁴ sec ⁻¹ and a Shear stress at a shear rate of 10 sec ^-1 A
The ratio A10 ⁴ / A10 to 10 is calculated as follows: 100 ≧ A10 ⁴ / A
That is, it is adjusted to 10 ≧ 3. Specific means for having such thixotropic properties include the following items (A) to (D). The magnetic recording medium of the present invention is not limited to each of the above items, and the essential point is to make the thixotropic properties of the respective dispersion liquids to be the same or approximate values. Is in the range of A10 ⁴ / A10. (A) the powder contained in 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 layer The binder contains a thermosetting polyisocyanate in the binder in an amount of 10 to 70% by weight. (B) The lower non-recording layer contains a non-metallic inorganic powder having an average primary particle diameter of 0.08 μm or less. (C) Thixotropic properties are imparted 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. Use magnetic powder. However, the lower non-magnetic layer does not participate in recording. (D) a ferromagnetic powder contained in the upper magnetic layer has a major axis length of 0.3 μm or less and a crystallite size of 300 nm or less, and the lower layer has a nonmagnetic metal oxide powder as a nonmagnetic powder and an average particle size of Is less than 95 nm carbon black
5 to 60/40, and at least the lower layer contains a polyurethane having three OH groups per molecule and a polyisocyanate compound.

These items (A) to (D) correspond to A10^Four/ A
The preferred means for adjusting 10 within the ranges described above are shown.
These are, for example, also the following factors:
There is a mutual relationship (including duplicated descriptions)
By doing so, the desired A10 ^FourDispersion with / A10
Liquid, magnetic paint is obtained, as a result, with the desired properties
A magnetic recording medium can be manufactured.

The factors mentioned above include, for example, (1) particle size (specific surface area, average primary particle size, etc.), (2) structure (oil absorption, particle form, etc.) for the inorganic or magnetic powder to be dispersed. (3) Properties of the powder surface (pH, loss on heating, etc.), (4) Attraction of particles (σ _S, etc.), and the like. On the other hand, regarding the binder, (1) molecular weight, (2)
For the type of functional group, etc., and for the solvent, (1) type (polarity etc.), (2) binder solubility, (3) solvent formulation amount,
(4) water content and the like.

Next, as specific means of the second embodiment, the following items (E) to (G) can be mentioned, but the essential points thereof are essentially the above-mentioned lower non-magnetic layer and upper magnetic layer. To eliminate the mixing zone between them, which are merely examples. (E) The ratio r ₁ / r ₂ of the longest axis length r ₁ and the shortest axis length r ₂ of the nonmagnetic powder contained in the lower layer is 2.5 or more. (F) The needle ratio of the nonmagnetic powder is 2.5 or more, and the average diameter of the longest axial length of the ferromagnetic powder is 0.3 μm.
Do the following. (G) The lower nonmagnetic layer contains a scale-like nonmagnetic powder and a binder containing an epoxy group having a molecular weight of 30,000 or more, and the upper magnetic layer has a needle-like ferromagnetic powder or a plate-like ferromagnetic powder. Include magnetic powder.

These items (E) to (G) include a needle-shaped nonmagnetic layer in the lower nonmagnetic layer in order to prevent a mixed region from being formed at the interface between the lower nonmagnetic layer and the upper magnetic layer. Powder or scaly non-magnetic powder is used. Compared to conventional granular non-magnetic powder, if the needle-shaped non-magnetic powder is present in alignment, a strong coating film is formed even in an undried state, and even if the ferromagnetic powder of the upper magnetic layer rotates, the No mixing occurs at the interface. Another means for preventing the mixed region from occurring is to use a scale-like non-magnetic powder for the lower non-magnetic layer and to lay it in a tile-like manner, so as to form the upper layer as described above. Even when the ferromagnetic powder of the magnetic layer rotates, no mixing occurs at the interface.

In order to improve the dispersibility by laying tiles as described above, it is preferable to use a binder containing an epoxy group having a molecular weight of 30,000 or more. By using a 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. Magnetic layer can be obtained.

In the magnetic recording medium of the present invention, the average dry thickness d of the magnetic layer is λ / 4 ≦ d with respect to the shortest recording wavelength λ.
≦ 3λ, and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 5.
It is necessary that they have a relationship of 0. As a preferable powder structure for this purpose, the ferromagnetic powder in the magnetic layer has a needle-like ferromagnetic powder having a major axis length of 0.3 μm or less or a plate diameter of 0.3 μm.
3 μm or less of a plate-like ferromagnetic powder, and the non-magnetic powder in the lower non-magnetic layer is a granular particle having an average particle diameter of λ / 4 or less, or a major axis length of 0.05 to 1.0 μm. , Needle-like particles having a needle-like ratio of 5 to 20 or a plate diameter of 0.05 to 1.
It is preferable that the particles are 0 μm and have a plate-like ratio of 5 to 20.

In order to achieve such a surface property of the medium of the present invention, the following means (H) to (K) also contribute. (H) the non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more; the ferromagnetic powder contained in the upper magnetic layer is a needle-shaped ferromagnetic powder; Has an average particle size of 1/2 to 4 times the crystallite size of the acicular ferromagnetic powder. (I) the nonmagnetic powder contained in the lower nonmagnetic layer contains an inorganic powder having a Mohs hardness of 3 or more, and the ferromagnetic powder contained in the upper magnetic layer is a needle-shaped ferromagnetic powder; Has an average particle diameter of 1 / of the major axis length of the acicular ferromagnetic powder.
3 or less. (J) The ferromagnetic powder contained in the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder whose easy axis of magnetization is perpendicular to the flat plate, and the nonmagnetic powder contained in the lower nonmagnetic layer is made of an inorganic material. Powder, and the average particle size is not more than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer. (K) The inorganic powder contained in the lower nonmagnetic layer contains an inorganic nonmagnetic powder having a surface layer coated with an inorganic oxide.

The functions and effects of the above items (H) to (K) are as follows. First, (H) will be described. In order to apply and dry the upper magnetic layer to an ultrathin layer of 1 μm or less, the particle size of the inorganic powder contained in the lower nonmagnetic layer and the crystal size of the ferromagnetic powder contained in the upper magnetic layer are required. Fine surface roughness is determined in relation to the size of the element. The crystallite size generally corresponds to the minor axis diameter in the case of acicular ferromagnetic powder. When the average particle size of the inorganic powder of the lower nonmagnetic layer is less than or equal to 1/2 of the crystallite size of the acicular ferromagnetic powder, the dispersion itself becomes difficult, and a smooth lower layer surface cannot be obtained. The smoothness of the final film surface of the magnetic recording medium also becomes insufficient. Conversely, if the average particle size of the lower inorganic powder exceeds four times the crystallite size of the ferromagnetic powder, the distance between the lower powder particles increases, so that the upper ferromagnetic powder is Sufficient surface properties cannot be obtained because of the influence of surface properties. As shown in the examples, in order to obtain sufficient surface properties, the average particle size of the needle-like ferromagnetic powder crystallite in the upper layer should be 1/2 to 4 times, more preferably 2/3 to 2 times. Inorganic powders are preferred. The shape of the inorganic powder is preferably spherical or dice. Also,
The Mohs hardness is 3 or more, preferably 4 or more, and more preferably 6 or more. Preferred inorganic powder and To illustrate the Mohs hardness, TiO ₂ (5.5~6), α hematite _{(5~6), BaSO 4 (3~3.5} ), ZnO (4)
It is.

The volume filling ratio of the inorganic powder in the lower layer is preferably in the range of 20 to 60%, more preferably 25 to 55%. Due to the relationship between the particle size of the nonmagnetic powder in the lower layer and the crystallite size of the ferromagnetic powder in the upper layer as described above, there is a preferable range for the volume filling ratio of the lower layer powder in order to reduce the surface roughness. Volume filling rate is 20
% Or less, the distance between the lower layer powder particles becomes large, the surface of the upper magnetic layer is affected by the roughness of the surface of the lower layer powder, and the lower layer contains the ferromagnetic powder of the upper layer. 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, (I) will be described below. In the magnetic recording medium of the multilayer coating method, in order to maintain good electromagnetic conversion characteristics, it is necessary to increase the squareness ratio. However, the average of the lower nonmagnetic powder inorganic powder relative to the upper ferromagnetic powder is required. If the particle size is large, the distance between the lower layer particles increases, and particularly the orientation of the ferromagnetic powder is disturbed at the interface between the upper and lower layers, thereby deteriorating the surface properties of the magnetic layer as in the above item (H). In order to reduce the disorder of the orientation, it is necessary to arrange fine non-magnetic powder along the major axis direction of the ferromagnetic powder and to support the ferromagnetic powder so that the orientation is not disturbed in the longitudinal direction. When the requirements for this are experimentally confirmed, the squareness ratio becomes equivalent to that of the single-layer magnetic layer in the case of the acicular ferromagnetic powder, in the case of a long axis length of 1/3 or less, more preferably 1/3 to 1 / l. It was found that when the inorganic powder of No. 20 was used, good surface property and squareness ratio could be obtained.

In the above-mentioned item (J), if hexagonal plate-like ferromagnetic powder is used in the same way instead of the needle-like ferromagnetic powder in the same way, the orientation is vertical and the disturbance of the interface is reduced,
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 to 1/5 or more of the plate diameter. (I)
In (J) and (J), for the same reason as in (H), the volume filling rate of the inorganic powder in the lower layer is 20 to 60%.
Is preferred. When the thickness of the magnetic layer is 5 times or less the major axis of the ferromagnetic material, 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 the same as those in the above (H).

Next, the item (K) will be described. As the inorganic oxide coated on the surface of the inorganic powder contained in the lower nonmagnetic layer, Al ₂ O ₃ , S
iO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ ,
ZnO and the like are preferable, and more preferable are Al ₂ O ₃ and S
iO ₂ and ZrO ₂ . These may be used in combination or may 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, in the surface treatment of the non-magnetic inorganic powder, after the non-magnetic inorganic powder material is dry-pulverized, water and a dispersant are added thereto, and the coarse particles are classified 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 an aqueous solution of a salt such as Al, Si, Ti, Zr, Sb, Sn, or Zn is added, and an acid or alkali for neutralizing the solution is added, and the surface of the inorganic powder particles is coated with the generated hydrated oxide. I do. Water-soluble salts produced as by-products are decanted, filtered,
It is removed by washing, and finally the slurry pH is adjusted, filtered, and washed 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.
In addition, it is also possible to pass AlCl ₃ and SiCl ₄ vapors through the non-magnetic inorganic powder, and then to introduce water vapor to perform Al and Si surface treatments.

For other surface treatment methods, see “Charac
terization of Powder Surfaces ", Academic Press. In this embodiment, 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 upper magnetic layer (that is, the variation width in the thickness direction of the interface) are specified. By doing so, the surface roughness of the magnetic layer is specified and improved, and furthermore, since the thickness of the magnetic layer is made thin and uniform, fluctuations in reproduction output and amplitude modulation noise can be prevented even when the recording wavelength is shortened. , High reproduction output and high C / N can be realized.

Looking at the effect of the medium of the present invention from another viewpoint,
Conventionally, when a magnetic layer is made thinner and short-wavelength recording is performed, all the layers of the magnetic layer contribute to recording and reproduction. Therefore, when the thickness of the magnetic layer changes, the reproduction output directly changes, and amplitude modulation noise is observed. However, the present invention has solved this drawback.

In the present invention, the shortest recording wavelength λ is 4 μm
And more preferably variously depending on the type of the magnetic recording medium.
μm, 0.5 μm for digital video, and 0.67 μm for digital audio.

The range of the average thickness d of the magnetic layer of the present invention is as follows.
λ / 4 ≦ d ≦ 3λ, preferably λ / 4 ≦ d ≦ 2λ (that is, 0.25 ≦ d / λ ≦ 2). The average thickness d of the magnetic layer of the present invention is usually 0.05 μm ≦ d ≦ 1 μm.
m, preferably in the range of 0.05 μm ≦ d ≦ 0.8 μm.

The average value d of the magnetic layer thickness is 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 obtained. Then, the thickness of the sample of the unknown material can be determined from the intensity of the fluorescent X-ray. In the present invention, the surface roughness Ra is Ra ≦ λ / 50, that is, λ / Ra is 5
It can be specified as 0 or more, preferably 75 or more, and more preferably 80 or more. Further, the surface roughness Ra in the present invention refers to a center line average roughness measured using an optical interference roughness meter.

The magnetic recording medium of the present invention is not limited to the method of applying the upper magnetic layer while the lower non-magnetic layer is in a wet state, but may be a simultaneous multi-layer coating or a sequential multi-layer coating. .

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 average value d of the thickness of the magnetic layer is smaller than λ / 4, the magnetic flux contributing to reproduction decreases and the output decreases. On the other hand, if the average value d exceeds 3λ, the short wavelength component is demagnetized by the deep recording magnetic field of the component having a long recording wavelength to be simultaneously recorded, so that the output decreases. Therefore, the magnetic layer thickness average value d is preferably d ≦ 3λ, and more preferably d ≦ 2λ.

When the C / N, which is the basic performance of the medium, is taken, in addition to the unevenness (so-called surface roughness) of the surface of the magnetic layer, which has been a problem in the conventional relatively thick magnetic layer, The thickness variation at the interface between the nonmagnetic layer and the magnetic layer becomes a problem. This is because when the average thickness d of the magnetic layer 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. In order to solve this problem, the present invention is required to be smoother than a conventional thick magnetic layer, and the surface roughness Ra needs to satisfy the relationship of Ra ≦ λ / 50.

According to the present invention, processing in a vacuum is premised, there is no problem regarding productivity and reliability as in a metal thin film medium which is vulnerable to corrosion, and electromagnetic conversion characteristics are comparable to those of the metal thin film. Thus, a high-performance coated magnetic recording medium having excellent performance can be obtained. A preferred embodiment for achieving the second point of the present invention is that the _root- mean-square roughness R _rms of the magnetic layer surface measured by a scanning tunneling microscope (STM) is different from the average dry thickness d of the magnetic layer. 30 ≦ d / R
There is a relationship of _rms .

When the thickness of the magnetic layer becomes thinner, the self-demagnetization loss should be reduced and the output could be improved. Surface 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. Further, in order to achieve the third point of the present invention, it is necessary that the long axis length of the ferromagnetic powder contained in the upper magnetic layer is 0.3 μm or less and the coercive force Hc thereof is 1500 Oe or more. It is preferable to use an alloy powder or a plate-shaped ferromagnetic powder having a plate diameter of 0.3 μm or less and a coercive force Hc of 1000 Oe or more.

As the ferromagnetic powder, a needle-shaped ferromagnetic alloy powder, a plate-shaped hexagonal ferrite-based ferromagnetic material (Ba ferrite, Sr ferrite, etc.), and a plate-shaped Co alloy powder can be used. Hc and saturation magnetization (σ _s ) may be appropriately selected, but particularly for short-wavelength recording with a minimum recording wavelength of 1 μm or less, coercive force Hc is preferably 1500 (Oe) or more.
The size of the magnetic material is generally a needle-like one having a major axis length of 0.3 μm or less and a plate-like one having a plate diameter of 0.3 μm or less, which is suitable for high-density recording.

In order to achieve the fourth point of the present invention, the ratio SMD / STD of the stiffness SMD in the longitudinal direction to the stiffness STD in the width direction of the magnetic recording medium is 1.0 to 1.0.
It is preferably 1.9. In order to set the stiffness ratio to the above-described value, 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.
It is preferable to use a polyhedral inorganic powder having a spherical shape of not more than μm and a cubic shape.

The operation and effect of the stayiness of the present invention are as follows. As described above, SMD / S of magnetic recording media
By controlling the TD, the mechanical characteristics of the magnetic recording medium are controlled to improve the head contact of the magnetic recording medium and to improve the electromagnetic conversion characteristics particularly in short-wavelength recording. That is, in the present embodiment, SMD / STD is set to 1.
It is controlled to 0 to 1.9.

The stiffness SMD in the longitudinal 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., a sample obtained by cutting a manufactured magnetic recording medium into a width of 8 mm and a length of 50 mm is used. In order to measure the STD, the sample is cut out so that the length direction of the sample is the same as the width direction of the magnetic recording medium so as to be in the same direction as the application direction.
A value expressed in mg of a force required to give a displacement of 5 mm per second can be used as each SMD and STD.

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. 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 layer inorganic powder. 6.5 or more, average particle size of 0.15 μm or less, preferably 0.12
It is desirable to select a polyhedral inorganic powder from a spherical shape to a cubic shape of μm or less.

In order to improve the head contact of the magnetic recording medium, it is necessary to increase the stiffness of the tape to some extent. To this end, it is preferable that the hardness of each powder to be blended is hard. If the Mohs hardness is less than 6, each stiffness is low, and good head contact cannot be secured. The smaller the average particle size is 0.15 μm or less, the better the head contact. This is considered to be because the contact interface with the binder is increased, so that the deformation becomes strong and the stiffness SMD, STD is improved. In the present invention, this SMD / STD is adjusted to the above range.

In particular, 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.
It is convenient to improve. 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-gon such as a sphere, a regular pentagon, and a regular hexagon, or a simple n-polygon. As an example, preferably, the arbitrarily selected two axis ratio is 0.6 to 0.6.
Those in the range of 1.4, preferably 0.7 to 1.3 are desirable.

As another embodiment for achieving the fourth point of the present invention, the temperature of the magnetic recording medium at 80 ° C. and 3 ° C.
The heat shrinkage in 0 minutes is 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. And 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%, and ferromagnetic contained in the upper magnetic layer. A needle whose powder has a crystallite size of 300 angstroms or less and an average particle size of the inorganic powder contained in the lower nonmagnetic layer of less than 0.15 μm, or an average major axis diameter of less than 0.6 μm; The inorganic powder contained in the lower non-magnetic layer is at least one selected from titanium oxide, barium sulfate, calcium carbonate, strontium sulfate, silica, alumina, zinc oxide, and α-iron oxide.
The lower non-magnetic layer has an average particle size of 30 μm.
And the DBP oil absorption is 30 to 300 ml / 1
00g, specific surface area by BET method is 150-400m
² / g of carbon black as a second component in a proportion of less than 50 parts by weight based on 100 parts by weight of the inorganic powder.

In this embodiment, the average value of the magnetic layer thickness d is 1 μm.
m to produce coated magnetic recording media with improved self-demagnetization loss without pinholes, streaks, etc. It was done. That is, the present embodiment has a
By controlling the heat shrinkage after storage for 8 hours to 0.4% or less, it is possible to provide a magnetic recording medium which improves and reduces skew distortion and has electromagnetic conversion characteristics comparable to a ferromagnetic metal thin film. .

In other words, the present embodiment has found that a 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 specified by the above-mentioned thermal shrinkage. It is a thing.
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) ÷
(Length of magnetic recording medium at room temperature before heating).

In the present 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 1 to 30 times, preferably 2 to 20 times, the dry thickness of the upper magnetic layer.
And controlling the expansion and contraction of the magnetic recording medium by the film strength of the lower and upper layers. If the thickness ratio is less than 1, it is not possible to prevent an increase in the thermal shrinkage due to the deterioration in strength due to the micronization of the magnetic layer. Also,
If the thickness ratio is 30 times or more, the thickness of the applied film becomes large, so that the residual solvent increases, which causes adverse effects such as plasticization of the film.

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 + 2%.
0%, preferably in the range of 0 to 15%. 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 the powder falls off.

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 6%.
0%, preferably in the range of 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 is, the more effective the reduction of the heat shrinkage is. However, if the particle size is too fine, dispersion becomes difficult.

In the present embodiment, the preferred particle size range is, for example, as the particle size of the ferromagnetic powder, the crystallite size is 300 Å or less, preferably 100 to 250 Å, and the average major axis diameter is 0.005. ~ 0.4μ
m, preferably in the range of 0.1 to 0.3 μm,
Average major axis diameter / crystallite size is 3 to 25, preferably 5
To 20. The specific surface area of the ferromagnetic powder by the BET method is 25 to 80 m ² / g, preferably 30 to 70 m ² / g. If it is less than 25 m ² / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable.

The particle size and shape of the inorganic powder of the lower layer may be 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 0.1 to 0.3 μm, and the acicular ratio represented by average long axis diameter / short axis length is 4 to 5
Needles such as 0, preferably 5 to 30 are exemplified.
As the inorganic powder, rutile type titanium oxide, α iron oxide,
Goethite is preferred.

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

The 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 ratio of ４０40 parts by weight. The carbon black is used to control the powder volume ratio of the lower layer by controlling the porosity, in addition to functions such as antistatic and strengthening of the film strength of the magnetic recording medium. 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 ± 10% of the porosity of the upper layer.
% Is preferred. The porosity of the lower layer is 10 to
Preferably it is in the range of 30%.

Hereinafter, general items that can be selected by the present invention will be described.
I will describe. The nonmagnetic inorganic powder that can be used in the present invention
Is, for example, metal, metal oxide, metal carbonate, metal sulfuric acid
Non-magnetic material such as salt, metal nitride, metal carbide, metal sulfide
Powder. Specifically, TiO_Two(Rutile,
Anatase), TiO_X, Cerium oxide, tin oxide, acid
Tungsten oxide, ZnO, ZrO_Two, SiO_Two, Cr _Two
O_ThreeΑ-alumina, β-alumina having an α-rate of 90% or more,
gamma alumina, alpha iron oxide, goethite, corundum, nitriding
Silicon, titanium carbide, magnesium oxide, boron nitride
Element, molybdenum disulfide, copper oxide, MgCO_Three, CaCO
_Three, BaCO_Three, SrCO_Three, BaSO_Four, Silicon carbide,
Titanium carbide or the like is used alone or in combination.
The shape, size, etc., of these inorganic powders are arbitrary.
Can combine different inorganic powders as needed,
It is possible to select the particle size distribution with a single non-magnetic powder.
You.

The particle size is preferably based on the specific method described in the above items (A) to (K). In general, when the particle size is spherical, spherical or polyhedral, the particle size is 0.01 to 0.7 μm.
m, and is preferably not more than ４ of the shortest recording wavelength λ. In the case of needle or plate, the major axis length is 0.05 to
1.0 μm, preferably 0.05 to 0.5 and a needle ratio of 5
~ 20, preferably 5 ~ 15, or plate diameter 0.05 ~
1.0 μm, preferably 0.05 to 0.5 μm, plate-like ratio (ratio of plate diameter to thickness) of 5 to 20, preferably 10 to 2
0 is used.

The following are preferred as the inorganic powder. 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 its 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.

As the non-magnetic inorganic powder used in the present invention, titanium oxide (particularly titanium dioxide) is particularly preferable. 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. The sulfuric acid method is
The raw illuminite ore is distilled with sulfuric acid to extract Ti, Fe, etc. as sulfates. Crystallize and remove iron sulfate,
After filtering and purifying the remaining titanyl sulfate solution, thermal hydrolysis is performed to precipitate hydrous titanium oxide. After filtration and washing, impurities are washed and removed, a particle size regulator and the like are added, and the mixture is calcined at 80 to 1000 ° C. to obtain 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 reduction state, Ti is TiCl ₄ and Fe is Fe
The iron oxide which becomes Cl _{2 and} becomes solid by cooling is separated from the liquid TiCl 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 in 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 150 to 400, and the DBP oil absorption is 20 to 400 ml / g.
100 g, preferably 30 to 200 ml / 100 g. The average particle size is 5 μm to 80 μm, preferably 10 to 5 μm.
0 μm, more preferably 10 to 40 μm. The pH is 2 to 10, the moisture content is 0.1 to 10%, and the tap density is 0.1.
1-1 g / cc is preferred.

Specific examples of the carbon black used in the present invention include BLACKP manufactured by Cabot Corporation.
EARLS 2000, 1300, 1000, 900,
800, 880, 700, VULCAN XC-7
2. # 3050, # 3150, # 32 manufactured by Mitsubishi Chemical Corporation
50, # 3750, # 3950, # 2400B, # 23
00, # 1000, # 970, # 950, # 900, #
850, # 650, # 40, MA40, MA-600,
CONDUCTEXSC, R, manufactured by Columbia Carbon
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 can be referred to, for example, “Carbon Black Handbook” edited by The Carbon Black Association. Non-magnetic organic powder used in the present invention, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder,
Phthalocyanine pigments are exemplified, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluoroethylene resin powder are used. The production method is described in Japanese Patent Application Laid-Open No. 62-185.
Nos. 64 and 60-255827 can be used.

These non-magnetic powders are usually 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, a magnetic iron oxide FeOx (x = 1.33 to
1.5), Co-modified FeOx (x = 1.33-1.
5) A known ferromagnetic powder such as a ferromagnetic alloy powder containing Fe, Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used, but a ferromagnetic alloy powder is more preferable. These ferromagnetic powders include Al, Si, S, Sc, T
i, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It may contain atoms such as n, 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,
-14090, JP-B-45-18372, JP-B-4
7-22062, JP-B-47-22513, JP-B-46-28466, JP-B-46-38755, JP-B-47-4286, JP-B-47-12422, JP-B-47-17284, JP-B-47 -18509, JP-B-47-18573, JP-B-39-10307,
JP-B-48-39639, U.S. Pat.
No. 3031341, No. 3100194, No. 32
No. 42005, No. 3389014 and the like.

Among the above ferromagnetic powders, the ferromagnetic alloy powder may contain a small amount of hydroxide or oxide.
A ferromagnetic alloy powder obtained by a known production method can be used, and the following method can be used.
A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

The specific surface area of the ferromagnetic powder of the upper magnetic layer according to the present invention by BET method is 25 to 80 m ² / g, preferably 40 to 70 m ² / g. 25m ²
If it is less than 80 m ² / g, the surface property is difficult to obtain, which is not preferable. The crystallite size of the ferromagnetic powder of the upper magnetic layer of the present invention is 450 to 100 °.
, Preferably 350 to 100 °. Σ _{S of the} iron oxide magnetic powder is 50 emu / g or more, preferably 7 emu / g or more.
0 emu / g or more, and 10 for ferromagnetic metal powder.
0 emu / g or more is preferable, and 110 emu / g or more is more preferable.
mu / g to 170 emu / g. The coercive force is 1100
It is preferably from Oe to 2500 Oe, more preferably from 1400 Oe to 2000 Oe. The needle ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.
It is as follows.

It is preferable that r1500 of the ferromagnetic powder is 1.5 or less. More preferably, r1500 is 1.0 or less. r1500 indicates the% of the amount of magnetization remaining without being inverted when a magnetic field of 1500 Oe is applied in the opposite direction after the magnetic recording medium is saturated.
The water content of the ferromagnetic powder is preferably 0.01 to 2%. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. Tap density of gamma iron oxide is 0.5
g / cc or more is preferable, and 0.8 g / cc or more is more preferable. 0.2-0.8 g / cc for alloy powder
When it is used at 0.8 g / cc or more, oxidation easily proceeds in the process of compacting the ferromagnetic powder, and a sufficient saturation magnetization (σ
_S ) becomes difficult to obtain. At 0.2 cc / g or less, dispersion tends to be insufficient.

When using γ-iron oxide, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 2 to 8%.
The pH of the ferromagnetic powder is preferably optimized by combining with the binder used. Its range is from 4 to 12, preferably from 6 to 10. The ferromagnetic powder may be surface-treated with Al, Si, P or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and it is preferable that the surface treatment is performed so that the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less.
The ferromagnetic powder contains soluble Na, Ca, Fe, Ni,
May contain inorganic ions such as Sr.
If it is less than m, the characteristics are not particularly affected.

The ferromagnetic powder used in the present invention preferably has a small number of pores, and its value is 20% by volume or less, more preferably 5% by volume or less. In addition, the shape is acicular, granular, so as to satisfy the conditions shown above.
It is selected from rice grain, plate shape, and the like. SF of the ferromagnetic powder
In order to achieve D0.6 or less, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For this purpose, there are a method of improving the particle size distribution of goethite, a method of preventing sintering of γ-hematite, and a method of lowering the deposition rate of cobalt with respect to cobalt-modified iron oxide.

The present invention also exemplifies plate-like hexagonal ferrite as a hexagonal plate-like ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate, such as barium ferrite, strontium ferrite, lead ferrite and calcium ferrite. Hexagonal Co powders such as each substituted body and Co substituted body can be used. Specifically, magneto-brumbite-type barium ferrite and strontium ferrite, and further include magneto-brambite-type barium ferrite and strontium ferrite containing a part of the spinel phase,
Particularly preferred are substituted bodies of barium ferrite and strontium ferrite. Further, in order to control the coercive force, Co-Ti, C
o-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
A substance to which an element such as n or Ir-Zn is added can be used.

When the 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 0.001 to
It is preferable that the thickness is 1 μm and the thickness is 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 non-magnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,000 to 200,000, preferably 1,000.
0-100,000 and a degree of polymerization of about 50-1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester Examples of the mixture include a mixture of a resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate.

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-mentioned resins can be used alone or in combination. Preferred are those 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 these and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all binders shown here, to obtain better dispersibility and durability,-
_{COOM, -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, N
a, K, —NR ₄ , and —NHR ₃ , R represents an alkyl group or H, and X represents a halogen atom. ), O
It is preferable to use one in which at least one or more polar groups selected from H, NR ₂ , N ⁺ R ₃ , (R is a hydrocarbon group), an epoxy group, SH, CN and the like are introduced by a 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
It is.

The vinyl chloride copolymer is preferably
Or an epoxy group-containing vinyl chloride copolymer.
And a vinyl chloride repeating unit and a repeating unit having an epoxy group.
And optionally -SO_ThreeM, -OSO_ThreeM, -C
OOM and -PO (OM) _Two(M is a hydrogen source
Repeating unit having a polar group such as
And a vinyl chloride-based copolymer containing Epoki
When used in combination with a repeating unit having a di group, -SO_ThreeNa
Epoxy group-containing vinyl chloride containing repeating units
Polymers are preferred.

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%). The vinyl chloride polymer is usually used in an amount of 0.01 mol per mol of the vinyl chloride repeating unit.
０．５0.5 mol (preferably 0.01 to 0.3 mol) of a repeating unit having an epoxy group.

If the content of the repeating unit having an epoxy group is less than 1 mol%, or if the amount of the repeating unit having an epoxy group is less than 0.01 mol per 1 mol of the vinyl chloride repeating unit, the vinyl chloride copolymer may be used. In some cases, the release of hydrochloric acid gas from the coalescence cannot be effectively prevented, while the amount of the repeating unit having an epoxy group is higher than 30 mol% or 0.5 mol per 1 mol of the vinyl chloride repeating unit. If the amount is too large, the hardness of the vinyl chloride-based copolymer may decrease, and if this is used, the running durability of the magnetic layer may decrease.

Further, 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, and if it is more than 5.0 mol%, the co-weight will increase. 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) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonic acid and its sodium or potassium salt, (anhydride) maleic acid and Examples thereof include (meth) acrylic acid and (meth) acrylic acid-2-phosphate ester.

For the introduction of 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 above-mentioned vinyl chloride copolymer may contain another monomer. Examples of other monomers include vinyl ethers (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether),
α-monoolefin (eg, ethylene, propylene), acrylate (eg, (meth) acrylate containing a functional group such as methyl (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitrile ( Examples include (meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), and vinyl esters (eg, vinyl acetate, vinyl propionate, etc.).

Specific examples of these binders used in the present invention include: VAGH, manufactured by Union Carbide Co., Ltd.
VYHH, VMCH, VAGF, VAGD, VROH,
VYES, VYNC, VMCC, XYHL, XYSG,
PKHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, 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 of polyisocyanate in combination.

The binder used in the lower nonmagnetic layer of the present invention is used in a total amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the nonmagnetic powder. When a vinyl chloride resin is used, 3 to 30
% By weight, 3 to 30% by weight when a polyurethane resin is used, and 0 to 20% by weight of a polyisocyanate in combination.

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 at least two layers. Therefore, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the resin described above. It is, of course, possible to change the physical characteristics and the like of the lower non-magnetic layer and the upper magnetic layer as necessary.

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-isocyanate.
Isocyanates such as 1,5-diisocyanate, o-toluidine isocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, and products of these isocyanates and polyalcohols;
Further, a polyisocyanate or the like generated by condensation of isocyanates can be used. 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. 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, D
BP oil absorption is 10-400ml / 100g, particle size is 5
mμ ~ 300mμ, pH 2 ~ 10, water content 0.1 ~
The tap density is preferably 10 to 1 g / cc.
Specific examples of the carbon black used in the present invention include BLACKPEARLS200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 700, V
ULCAN XC-72, manufactured by Asahi Carbon: {80,}
60, $ 55, $ 50, $ 35, manufactured by Mitsubishi Kasei Kogyo:
2400B, $ 2300, $ 900, $ 1000, $ 3
0, $ 40, $ 10B, manufactured by Konlon Via Carbon: C
ONDUCTEX SC, RAVEN 150, 50,
40, 15 and the like. 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 the functions of preventing static charge of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, and the like.
These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount, and combination between 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).

The abrasive used in the upper magnetic layer of the present invention includes α-alumina having an α conversion of 90% or more,
β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride, etc. Mainly known with a Mohs hardness of 6 or more. 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 effect remains unchanged if the main component is 90% or more. 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 0.3-2g / c
c, the water content is preferably 0.1 to 5%, the pH is preferably ^{2 to} 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any one 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 and AKP-3 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-50, HIT-50, manufactured by Nippon Chemical Industry Co., Ltd .:
G5, G7, S-1, manufactured by Toda Kogyo: TF-100, T
F-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 of course can be properly used according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

The additives used in the present invention include:
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.

Further, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, etc., cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or 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 the kind and amount as required. For example,
The lower non-magnetic layer and the upper magnetic layer control bleeding to the surface using fatty acids having different melting points, control bleeding to the surface using esters having different boiling points and polarities, and the amount of surfactant. It is considered that the stability of the coating is improved by adjusting the amount of the lubricant, the lubrication effect is improved by increasing the amount of the lubricant added to the lower non-magnetic layer, and of course, only those shown here are limited. is not.

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 the additives are mixed with the ferromagnetic powder before the kneading step, There are a case where it is added in a kneading process using a powder, a binder and a solvent, a case where it is added in a dispersion process, 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-3 manufactured by NOF Corporation.
12, 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 acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,
Ketones such as isophorone, tetrahydrofuran, etc., alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate,
Esters such as butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; and aromatics such as benzene, toluene, xylene, cresol, and chlorobenzene. Chlorinated hydrocarbons such as hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc.
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, and 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 at 20 ° C. It is preferable that 15% or more of a solvent having a dielectric constant of 15 or more is contained.

The thickness structure of the magnetic recording medium of the present invention is such that the flexible support has a thickness of 1 to 100 μm, preferably 4 to 80 μm.
The lower layer is 0.5 to 10 μm, preferably 1 to 5 μm, and the upper layer is 0.05 μm or more and 1.0 μm or less, preferably 0.0 μm or less.
5 μm or more and 0.6 μm or less, more preferably 0.05
It is not less than μm and not more than 0.3 μm. The upper magnetic layer is preferably thinner than the lower nonmagnetic layer. The total thickness of the upper layer and the lower layer is 1 / th of the thickness of the flexible support.
It is used in the range of 100 to 2 times. Further, an undercoat layer for improving adhesion may be provided between the flexible support and the lower layer. Their thickness is 0.01 to 2 μm, preferably 0.05 to 0.5 μm. Further, a back coat layer may be provided on the side of the flexible support opposite to the magnetic layer side. This thickness is 0.1 to 2 μm, preferably 0.1 to 2 μm.
3 to 1.0 μm. Known undercoating layers and backcoat layers can be used.

The flexible support used in the present invention is preferably non-magnetic, and includes polyesters such as polyethylene terephthalate and polyethylene naphthalate;
Known films such as polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone, aramid, and aromatic polyamide can be used. These supports have a corona discharge treatment, a plasma treatment, an easy adhesion treatment,
Heat treatment, dust removal treatment, and the like may be performed. In order to achieve the object of the present invention, it is necessary to use a flexible support having 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. . 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 is
It can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates of Ca, Si, Ti and the like, and organic fine powders of an acryl system and the like.

The F-5 value of the flexible support in the tape running direction is preferably 5 to 50 kg / mm ² , and the F-5 value in the tape width direction is preferably 3 to 30 kg / mm 2.
^{In general} , the F-5 value in the longitudinal direction of the tape is higher than the F-5 value in the width direction of the tape, but this is not the case particularly when the strength in the width direction needs to be increased. The heat shrinkage of the flexible support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less,
More preferably 1.5% or less, the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less.
% Or less. Its breaking strength is 5-100K in both directions
g / mm ^2, the elastic modulus is preferably from 100 to 2,000 kg / mm ^2.

The step of producing the magnetic coating material 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 needless to say 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, a magnetic recording medium having a high residual magnetic flux density Br as in the present invention can be obtained. When the continuous kneader or the 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 15 to 500 parts with respect to 100 parts of the ferromagnetic powder. Is kneaded. 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. However, the medium of the present invention is a coating method other than these simultaneous multilayer coating methods, for example, a conventional sequential wet on dry coating method, a sequential wet coating method.
Regardless of the on-dry coating method or the almost simultaneous wet-on-wet coating method, the material, shape, size, etc. of the above-described ferromagnetic material, non-magnetic powder, binder, flexible support, etc. It will be easily understood that by selecting and combining, it is possible to provide a tape maintaining the quality as a multi-layer coated product even though the productivity is slightly inferior. The following configuration can be proposed as a specific example of an apparatus and a method for applying a magnetic recording medium having the above-described multilayer configuration. 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-2-1792
No. 1 and Japanese Patent Application Laid-Open No. 2-265672, the upper layer and the lower layer are applied almost simultaneously by one coating head having two built-in slits. 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.

As one embodiment of the present invention, a so-called wet-on-wet method in which the above-mentioned lower layer coating solution is applied in a wet state.
It is provided on a flexible support by a coating method. Wet on wet coating method used to provide the lower layer and the upper layer in the present invention,
It refers to a so-called sequential coating method in which the lower layer is first applied, and then the next upper layer is coated as soon as possible on the wet lower layer, or a simultaneous application method using an extrusion coating method. This coating method is disclosed in JP-A-61-13.
The method for coating a magnetic recording medium disclosed in Japanese Patent Application No. 9929 can be used.

FIG. 2 is an explanatory view showing an example of a sequential coating method used for coating both upper and lower layers according to an embodiment of the present invention. The lower layer coating liquid A is applied to the support 1 by the first coating device 2 of a roller coating method, and immediately after that, the coating surface is smoothed by the smoothing roll 3 to form a lower coating film composed of the coating liquid A. While in the wet state, the upper-layer coating liquid B is applied by the second coating device 4 of the extrusion system disposed further downstream to form an upper-layer coating film.

FIG. 3 is an explanatory view showing an example of an extrusion simultaneous coating method preferably used for coating both upper and lower layers according to another embodiment of the present invention. The lower-layer coating liquid A and the upper-layer coating liquid B are simultaneously coated on the upper layer using an extrusion-type simultaneous multi-layer coating apparatus 5 to form both upper and lower layers. 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. For that, 1000G (Gauss)
It is preferable to use the above-mentioned solenoid in combination with a cobalt magnet of 2000 G or more, and it is preferable to provide an appropriate drying step before orientation so that the orientation after drying is the highest. When the present invention is applied to a disk medium, a method of randomizing the orientation is adopted.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide and a metal roll, or a calendering roll,
The treatment is performed with a combination of a metal roll and a metal roll. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure on the processing roll is preferably 200 kg / cm, more preferably 300 kg / cm.
/ Cm or more, and the speed ranges from 20 m / min to 700 m / min. The calendering effect of the present invention can be further improved at a temperature of 80 ° C. or more and a linear pressure of 300 kg / cm or more.

After the above-described calendering, the magnetic layer and the battery
40 ° C. to accelerate the hardening of the magnetic layer and the non-magnetic layer.
In some cases, a thermo-treatment at -80 ° C is performed. The magnetism of the present invention
The upper surface of the recording medium and the opposite surface (tape back)
Coefficient of friction against stainless steel (SUS420J) is preferable
Is 0.5 or less, further 0.3 or less, the magnetic layer surface resistivity
Is 10^Four-10¹¹Ω / sq, when the lower layer is applied alone
Has a surface resistivity of 10^Four-10⁸Ω / sq, BC layer table
Area resistance is 10^Three-10 ⁹Ω / sq is preferred.

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 to achieve high output,
Although a smaller value is preferable, 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 repeated use is emphasized, the larger the porosity, the better the running durability in many cases. 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.
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 the lower layer and the upper layer, it is easily assumed that the physical properties of the upper layer and the lower layer can be changed according to the purpose.
The magnetic recording medium of the present invention basically comprises two layers of the upper magnetic layer and the lower nonmagnetic layer, but may have three or more layers. As a configuration of three or more layers, the upper magnetic layer is a plurality 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, it is possible to apply a concept that the uppermost magnetic layer has a higher coercive force than the lower magnetic layer and uses a ferromagnetic powder having a small average major axis length and a small crystallite size. Further, the lower nonmagnetic layer may be formed of a plurality of nonmagnetic layers. But,
Broadly speaking, the structure includes the upper magnetic layer and the lower nonmagnetic layer.

[0156]

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.

The coating solution for the upper magnetic layer and the coating solution for the lower nonmagnetic layer were prepared according to the following formulations. Example 1 Formulation of Coating Solution for Upper Magnetic Layer Ferromagnetic powder: 100 parts of Fe alloy powder Composition: Fe 93% by weight, Ni 3% by weight, Co 3% by weight, other Zn, Cr, etc. Hc 1600 Oe, σ _S 135 emu / g Long axis length 0.18 μm, needle ratio 9 Vinyl chloride copolymer 10 parts —SO ₃ Na, epoxy group-containing polyurethane resin 5 parts —SO ₃ Na content, molecular weight 45000 α-alumina (average particle size 0.2 μm) 5 Part cyclohexanone 150 parts methyl ethyl ketone 200 parts After the above composition was mixed and dispersed in a sand mill for 6 hours,
Polyisocyanate (Coronate L), 5 parts each of stearic acid and 10 parts of butyl stearate were added to obtain a magnetic coating solution.

Formulation of Coating Solution for Lower Non-Magnetic Layer 100 parts of granular TiO ₂ Average particle size 0.09 μm Carbon black 5 parts Average particle size 20 μm Vinyl chloride copolymer 8 parts —SO ₃ Na, epoxy group-containing molecular weight 50,000 polyurethane resin 5 parts -SO ₃ Na content, molecular weight 45000 α-alumina (average particle size 0.2 μm) 5 parts Cyclohexanone 150 parts Methyl ethyl ketone 50 parts After mixing and dispersing the above composition in a sand mill for 4 hours,
5 parts of polyisocyanate (Coronate L), 1 part of stearic acid and 1 part of butyl stearate were added to obtain a coating solution for a lower nonmagnetic layer.

The above two coating solutions were applied in a wet state using two doctors having different gaps, and then subjected to an orientation treatment with a permanent magnet and then dried. 9.8 μm flexible support
And a back layer containing carbon black was provided on the surface of the support opposite to the magnetic layer. Thereafter, a super calendar treatment was performed. The coating thickness is 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer.
Met. The raw material thus obtained was cut into a 3.81 mm width, and the digital audio tape (D
AT).

In other Examples and Comparative Examples, tapes were prepared by changing the factors shown in Table 1 with respect to Example 1-1. These tapes were evaluated by the following methods, and the results are shown in Table 2. Average value d of magnetic layer, standard deviation σ of d: photograph of tape cross section by transmission electron microscope (TEM) (magnification: 20)
000) and determined according to the above definition. Average value (Δd) of thickness fluctuation at the interface between the two layers: photographing a cross section of the tape with a transmission electron microscope (TEM) (magnification: 20,000 times), length 2
The displacement of the upper magnetic layer and the lower non-magnetic layer in 0 μm (actual length) was measured, and the average value of the displacement difference between the peak and the valley was determined as Δd.

The sequential multilayer in the comparative example means that the lower nonmagnetic layer is applied, dried, and then the upper magnetic layer is applied. Electromagnetic conversion characteristics Deck used: DTC-1000 manufactured by SONY Reproduction output: A signal of a single frequency of 4.7 MHz was input, a reproduction signal was output to a spectrum analyzer, and a peak value of the signal was read.

C / N: The noise spectrum is measured at the time of measuring the reproduction output, and the reproduction output and the center recording frequency (4.7 MH)
z) from the noise level ratio 0.1 MHz away from C /
N was determined. The spectrum analyzer is HP-358
5A and 0 dB are tapes of a single magnetic layer of Comparative Example 1. BER (block error rate): 1000
It refers to the number of error flags in track 0 and is expressed by the following equation. BER = error flag / 10000 × 128 blocks

The DAT signal configuration encodes an analog signal, one code is 8 bits, and one block is 32 symbols × 8.
Since bits = 256 bits, one track is 128 bits.
Consists of blocks. 2 tracks, ie 128 × 2
The block signal is fetched into the memory, shuffled, and errors are detected. Using a DAT deck manufactured by Sony Corporation, and using a Hewlett-Packard H counter as a counter.
The measurement was performed using P5328A connected to a personal computer.

Dropout: A signal having a single frequency of 4.7 MHz was input, and a threshold (DO) was measured with a dropout counter having a level of −10 dB and a length of 0.5 μSEC.

[0165]

[Table 1]

[0166]

[Table 2]

The shortest recording wavelength λ of the created DAT is 0.
67 μm. Accordingly, from λ / 4 ≦ d ≦ 3λ, the thickness range of the magnetic layer is 0.17 μm ≦ d ≦ 2.01 μm, but in the present invention, the thickness range is 0.17 μm ≦ d ≦ 1 μm. Further, there is a relationship of Δd / d ≦ 0.5 from Δd ≦ d / 2.

In Examples 1-1 to 1-3, the total thickness of the lower non-magnetic layer and the upper magnetic layer was made substantially constant and the thickness ratio between the upper and lower layers was changed. 1
Indicates a total thickness of 3.30 μm (thickness ratio 1/10) , and Example 1-2 indicates a total thickness of 3.20 μm (thickness ratio 1/3.
6) In Example 1-3, the total thickness was 3.10 μm (thickness ratio).
1 / 2.1) . Example 1-4
In this configuration, the thickness of the lower nonmagnetic layer is reduced to a value close to the lower limit. Examples 1-5 to 1-7 are examples in which the type of the non-magnetic powder of the lower non-magnetic layer is changed, and it can be seen that Ra affects Ra within the range of the present invention. Examples 1-8
This is an example in which barium ferrite is used as a ferromagnetic powder. Example 1-9 is an example in which the thickness of the upper magnetic layer was close to the upper limit, and the characteristics of this system were inferior to those of the other examples.

Comparative Example 1-1 is a magnetic recording medium having a single-layer, relatively thick magnetic layer. Comparative Example 1-2 is a case where the thickness of the lower nonmagnetic layer was reduced,
Ra is inferior. In Comparative Example 1-3, coarse non-magnetic powder (average particle diameter of 0.25
Λ / 4 = greater than 0.1675).
Δd is large and C / N is inferior. Comparative Example 1-4 uses a long needle-shaped bengal with a long major axis, so that Δd is large.
Ra is inferior. Comparative Example 1-5 is an example in which the thickness of the magnetic layer is below the lower limit, and various properties are inferior.

In Examples 1-1 to 1-8, d, Δd, σ,
And Ra satisfy the respective ranges, so that
It can be seen that the reproduction output, C / N, BER, DO, and coating moldability are all excellent.

According to the present invention, by applying a thin magnetic layer (three times or less of the shortest recording wavelength) simultaneously with the lower non-magnetic layer, coating defects which are a problem when the magnetic layer is thinned alone can be prevented. . At the same time, the reproduction output is improved by optimizing the thickness of the magnetic layer for the shortest recording wavelength according to the recording system, and the thickness fluctuation of the thinned magnetic layer is reduced,
Moreover, C / N is improved by smoothing the surface of the magnetic layer.

According to the present invention, it is possible to provide a coating type magnetic recording medium capable of obtaining electromagnetic conversion characteristics comparable to a metal thin film magnetic recording medium and solving the problems of productivity and storage reliability of the metal thin film magnetic recording medium. Can be.

Example 2 A coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations. 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 metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe Specific surface area by BET method 60 m ² / g crystallite Size 195Å Average long axis length 0.20 μm, needle ratio 10 Saturation magnetization (σ _S ): 130 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ^-4 eq / g contained, degree of polymerization 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing α-alumina (average particle size 0.2 μm) 2 parts Carbon black (average particle size 0.10 μm) 8 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 2 For each 0 parts The above two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. One part of the resulting dispersion was mixed with polyisocyanate in the coating solution for the lower non-magnetic layer, and 3 parts in the coating solution for the upper magnetic layer.
Parts, and further add 40 parts of butyl acetate to each,
Filtration using a filter having an average pore size of 1 μm,
Coating solutions for the lower non-magnetic layer and the upper magnetic layer were respectively prepared.

The lower non-magnetic layer coating solution was dried to a thickness of 2 μm, and immediately thereafter, the upper magnetic layer was 0.5 μm thick thereon. Simultaneous multi-layer coating is performed on a polyethylene terephthalate support having a thickness of 7 μm and a center average surface roughness of 0.01 μm, and while both layers are still wet, a cobalt magnet having a magnetic force of 3000 Gauss and a magnetic force of 1500 Gauss are applied. Oriented by a solenoid having, after drying, treated at a temperature of 90 ° C. with a seven-stage calender consisting only of metal rolls,
It was slit to a width of 8 mm to produce an 8 mm video tape of Example 2-1.

Similarly, by changing the factors described in Tables 3 and 4, the samples, Examples 2-2 to 2-12 and Comparative Examples 2-1 to 2
-3, and the performance was evaluated in the same manner as described above. The results are shown in Tables 3 and 4. The relative speed of 8mm video is 38
m / sec, and the 7 MHz recording wavelength is 0.54 μm. Therefore, λ / 50 is 10.8 nm. Center line average surface roughness (Ra): Area Ra of about 250 × 250 nm by MIRAU method using TOYO3D manufactured by WYKO.
Was measured. The measurement wavelength is spherical correction at about 650 nm. Cylinder correction was added.

[0176]

[Table 3]

[0177]

[Table 4]

As is clear from the above table, the samples of the examples have improved dispersibility because the surface of the inorganic powder contains a treatment layer of Al ₂ O ₃ , SiO ₂ , ZrO ₂ or the like as shown in the above table.
a is low, λ / 50 (10.8 nm) or less, and the electromagnetic conversion characteristics are good. In Comparative Example 2-1, since the inorganic powder does not contain the treatment layer, the dispersibility is poor, Ra, σ, and Δd are high, and the electromagnetic conversion characteristics are poor. Comparative Example 2-
No. 2 has poor electromagnetic conversion characteristics because the magnetic layer is thick.

Example 3 The coating solution for the upper magnetic layer and the coating solution for the lower nonmagnetic layer were prepared according to the following formulations. Example 3-1 Coating solution for lower non-magnetic layer; same as Example 2-1 Coating solution for upper magnetic layer Co-substituted barium ferrite 100 parts Specific surface area by BET method 35 m ² / g Average particle size 0.06, plate Shape ratio 5 Vinyl chloride copolymer 9 parts -SO ₃ Na group 1 × 10 ^-5 eq / g contained, degree of polymerization 300 Fine particle abrasive (Cr ₂ O, average particle diameter 0.3 μm) 7 parts Toluene 30 parts Methyl ethyl ketone 30 parts The above composition was kneaded in a kneader for about 1 hour, and then the following composition was added and dispersed in the kneader for about 2 hours.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content Average molecular weight 35000 Methyl ethyl ketone 200 parts Cyclohexanone 100 parts Toluene 80 parts Then, the following carbon black and coarse particle abrasive were added, and a dispersion treatment was performed at 2,000 rpm for about 2 hours by 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 Chemical Co., average particle diameter 0.5 μm) The composition was added and dispersed again by a sand grinder to obtain the above-mentioned coating solution for the upper magnetic layer.

6 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts of tridecyl stearate 6 parts of the coating solution for the upper magnetic layer and the coating solution for the lower nonmagnetic layer obtained as above First, the lower layer non-magnetic layer coating solution was applied onto 75 μm polyethylene terephthalate, and then the upper layer magnetic layer coating solution was applied while it was still wet, and the back surface was treated in the same manner. The thickness of the lower non-magnetic layer was set to 2.5 μm and the thickness of the magnetic layer was set to 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. Similarly, samples were prepared by changing the factors described in Table 5.
Examples 3-2 to 3-7 and Comparative Example 3-1 were prepared, the performance was evaluated, and the results are shown in Table 5.

Initial innermost circumference 2F output: The sample of Example 3-1 was set to 100 and calculated as a relative value. The drive used is PD211 (manufactured by Toshiba Corporation). The recording wavelength is
1.428 μm. Therefore, λ / 50 is 28.5n
m. Surface roughness: Ra was measured in the same manner as in Example 2.

[0184]

[Table 5]

From the above table, it can be seen from the above table that, similarly to Example 2, the sample of Example ₂ had Al ₂ O ₃ , SiO ₂ , ZrO ₂
And so on, the dispersibility is improved, the Ra is low, and the electromagnetic conversion characteristics are good. Comparative Example 3
In the case of -1, since the treatment layer is not contained in the inorganic powder, the dispersibility is poor, Ra, σ, and Δd are high, and the electromagnetic conversion characteristics are poor.

Example 4 Polyethylene terephthalate (thickness: 10 μm, F5 value: 20 kg / mm ^{2 in} MD direction, TD) as a flexible support
Direction 14Kg / mm ² , Young's modulus: MD direction 750K
g / mm ² , 470 Kg / mm ^{2 in} TD direction) or polyethylene terephthalate (thickness 7 μm, F5 value: M)
22 kg / mm ^{2 in the} D direction, 18 kg / m in the TD direction
m ² , Young's modulus: 750 Kg / mm ^{2 in the} MD direction, TD
Using a direction of 750 Kg / mm ² ), the mixture was stirred with a disperser stirrer for 12 hours according to the following formulation to prepare an undercoat liquid.

Polyester resin (containing —SO ₃ Na group) 100 parts Tg 65 ° C. Na content 4600 ppm Cyclohexanone 9900 parts The obtained undercoat liquid was dried on the flexible support by bar coating with a thickness of 0.1 μm. Applied.

On the other hand, the coating solution for the upper magnetic layer and the coating solution for the lower nonmagnetic layer were prepared according to the following formulations. Formulation of Coating Solution for Upper Magnetic Layer 100 parts of ferromagnetic powder: Fe alloy powder (Fe-Co-Ni); composition: Fe: Co: No: Ni = 92: 6: 2 Al ₂ O ₃ was used as a sintering inhibitor Hc 1600 Oe, σ _S 119 emu / g Long axis length 0.13 μm, needle ratio 7 Crystallite size 172 °, water content 0.6% by weight Vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g , -OH, epoxy group-containing Tg 71 ° C, degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38000 polyurethane resin 5 parts -SO ₃ Na 8 × 10 ^-5 eq / g content -OH 8 × 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 α-alumina (average particle diameter 0.15 [mu] m) 12 parts ^{_{S BET 8.7m 2 / g, pH}} 8.2, water content 0.06 wt% cyclohexanone 150 parts After 6 hours mixed and dispersed in a sand mill methyl ethyl ketone 150 parts The above composition,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid, and 1.5 parts of butyl stearate were added to obtain a coating solution for an upper magnetic layer.

Formulation of Coating Solution for Lower Nonmagnetic Layer 85 parts of TiO ₂ Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 4 1.1 pH 6.5 to 8.0 Carbon black 5 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 S _BET 250 m ² / g Coloring power 143% Vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g, —OH, epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g containing -OH 8 × 10 ^-5 eq / g containing Tg 38 ° C., sand mill Mw 50000 cyclohexane 100 parts Methyl ethyl ketone 100 parts the above composition In After 4 hours mixing dispersion,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid, and 1.5 parts of butyl stearate were added to obtain a coating solution for the lower nonmagnetic layer.

The above-mentioned coating solution was applied in a wet state using two doctors having different gaps.
After orientation treatment with 500 gauss and then 1600 gauss solenoid, it was dried. After that, a super calender treatment using a metal roll and a metal roll was performed at a temperature of 80 ° C. The coating thickness is 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer.
Met.

Next, a coating solution was prepared according to the following formulation. BC layer formulation Carbon black 100 parts S _BET 220 m ² / g Average particle size 17 μm DBP oil absorption 75 ml / 100 g Volatile content 1.5% pH 8.0 Bulk density 15 lbs / ft ³ Nitrocellulose RS1 / 2 100 parts Polyester polyurethane 30 Part Nipporan (manufactured by Nippon Polyurethane Co., Ltd.) Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation property) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts The above composition was pre-kneaded and kneaded by a roll mill. Next, based on 100 parts by weight of the above dispersion, 100 parts of carbon black S _BET 200 m ² / g Average particle diameter 200 μm DBP oil absorption 36 ml / 100 g pH 8.5 α-Al ₂ O ₃ (average particle diameter 0.2 μm) Disperse with a sand grinder with the composition containing 0.1 part,
After filtration, the following composition was added to 100 parts by weight of the dispersion to prepare a coating solution.

120 parts of methyl ethyl ketone 5 parts of polyisocyanate The obtained coating solution was applied by a bar coater on the opposite side of the flexible support provided with the magnetic layer to a dry thickness of 0.5 μm. The raw material thus obtained was cut into an 8 mm width to prepare 8 mm video tapes of Sample 1 (PET support) and Sample 2 (PEN support).

The following measurement was performed on the obtained 8 mm video tape, and the measurement results were obtained. (1) TEM (transmission electron microscope) Ultrathin sections of the magnetic layer were observed. The medium was cut out to a thickness of about 0.1 μm with a diamond cutter, observed with a transmission electron microscope, and photographed. The interface between the upper and lower layers of the photograph and the surface of the magnetic layer were shaded, the thickness of the magnetic layer was measured with an IBASII image processor, and the average d and standard deviation σ were obtained.

The average value d of the thickness of the magnetic layer was 0.45 μm. Practically 1 μm or less, particularly preferably 0.6 μm
It turned out that: The standard deviation σ of the magnetic layer thickness variation was 0.08 μm or less. In practice, σ is 0.2
It was found that it was not more than μm, particularly preferably not more than 0.1 μm.

The magnetic tape was stretched to make the magnetic layer float above the support, and the magnetic layer was peeled off by squeezing with a cutter blade. 500 mg of the separated magnetic layer is added to 1N-NaO
The mixture was refluxed in 100 ml of an H / methanol solution for 2 hours to hydrolyze the binder. Since the ferromagnetic powder sinks to the bottom due to its large specific gravity, the supernatant was removed. Then, it was washed with water three times by decantation, and then washed three times with THF. The obtained ferromagnetic powder was dried with a vacuum dryer at 50 ° C. Next, the obtained ferromagnetic powder was dispersed in collodion, and observed at 60,000 times using a TEM. As a result, the particle major axis length of the ferromagnetic powder was 0.13 μm, and the acicular ratio was 10. Practically, it has been found that the major axis length of the particles needs to be 0.4 μm or less, and preferably 0.3 μm or less. In practice, the needle ratio needs to be 2 to 20, preferably 2 to 1.
It turned out to be 5.

(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 6 nm. It has been found that a thickness of 20 nm or less is necessary for practical use, and it is preferably 10 nm or less. The measurement of the surface roughness R _rms here was measured using a scanning tunneling microscope. Scanning tunneling microscope (STM) measurement
6μm × 6 with a tunnel current of 10A and a bias voltage of 400mV using a Nanoscope II manufactured by gital Instrument.
The range of μm was scanned and found from the following equation (1).

[0197]

(Equation 1)

[0198] (3) The surface roughness meter 3 surface roughness using D -MIRAU was measured. WYK
About 250 μM by MIRAU method using TOPO3D manufactured by Company O
m × 250 mu of the area of _{m Ra, R rms, Peak-} Va
The lley value was measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by light interference. Ra was 2.7 nm. Practically, Ra was found to be preferably 1 to 4 nm, more preferably 2 to 3.5 nm. R _rms
Was 3.5 nm. It was found that the thickness is preferably 1.3 to 6 nm in practical use, and more preferably 1.5 to 5 nm. The PV value was 20 to 30 nm. 8 for practical use
0 nm or less is preferable, and 10-60 nm is more preferable.
It turned out to be.

(4) VSM (vibrating sample magnetometer) The magnetic characteristics of the magnetic layer of the magnetic tape obtained by using the VSM were measured. It measured with Hm 5kOe using the vibration sample type magnetometer made by Toei Industry Co., Ltd. As a result, Hc was 1620
Oe and Hr (90 °) were 1800 Oe, Br / Bm was 0.82, and SFD was 0.583. Hc for practical use
Needs 1500 to 2500 Oe, preferably 160
It turned out to be 0-2000 Oe. Hr (90 °)
Practically, it was found that 1000 to 2800 Oe was necessary, and preferably 1200 to 2500 Oe. Br
It has been found that / Bm is practically required to be 0.75 or more, preferably 0.8 or more. SFD is practically 0.
It was found that it was 7 or less, and preferably 0.6 or less.

(5) X-ray Diffraction X-ray diffraction was performed using the ferromagnetic powder extracted from the magnetic layer in the above (1). The magnetic tape was directly applied to an X-ray diffractometer, and determined from the spread of the half value width of the diffraction lines on the (1,1,0) plane and the (2,2,0) plane. As a result, the crystallite size was found to be 180 °. Practically preferably 400 ° or less, particularly preferably 100 to 300 °.
It turned out to be. Similarly, it was 280 ° when measured in Example 2-2.

(6) Tensile Test The Young's modulus, yield stress and yield elongation of the magnetic tape obtained by the tensile tester were measured. Tensile tester (Toy Baldwin universal tensile tester STM-T-50B
P) was measured at an atmosphere of 23 ° C. and 70% RH at a pulling rate of 10% / min. As a result, the Young's modulus of the magnetic tape was 700 kg / mm ² , and the yield stress was 6 to 7 kg / mm.
^{2. The} yield elongation was 0.8%. It has been found that the Young's modulus is preferably 400 to 2000 kg / mm ² , particularly preferably 500 to 1500 kg / mm ² for practical use. The yield stress is practically preferably 3 to 20 kg / mm.
² and particularly preferably 4 to 15. It has been found that the yield elongation is practically preferably 0.2 to 8%, particularly preferably 0.4 to 5%.

(7) Flexural rigidity, annular stiffness Using a loop stiffness tester, width 8 mm, length 5
A 0 mm sample is formed into a ring, and the force required to give a displacement of 5 mm at a displacement speed of 3.5 mm / sec is expressed in mg. As a result, in the case of an 8-mm p6-120 tape, the thickness is 10.
5 μm, and the stiffness was 40 to 60 mm. Practically, when the thickness is 10.5 ± 1 μm, the stiffness is preferably 20 to 90 mg, particularly preferably 3 to 90 mg.
It was found to be 0-70 mg. 11.5μ thick
In the case of m or more, it turned out that it is practically preferably 40 to 200 mg. It was found that when the thickness is 9.5 μm or less, the amount is practically preferably 10 to 70 mg.

(8) Stretching fracture The crack elongation was measured at 23 ° C. and 70% RH. The both ends of the test piece having a tape length of 10 cm were pulled at a pulling speed of 0.1 mm / sec, and the surface of the magnetic layer was observed under a microscope at 400 times to determine the elongation at which five or more cracks were formed on the surface of the magnetic layer. Measure. Similarly, Example 8-4 is 12%
Met. As a result, the generated elongation was 4%. It turned out that it is practically preferably 20% or less, particularly preferably 10% or less.

(9) ESCA Cl / Fe spectrum α and N / Fe spectrum β were measured. For measurement of α and β, an X-ray photoelectron spectrometer (PE
RKIN-FLMER) was used. The measurement was performed at 300 W using an Mg anode as an X-ray source. First, the lubricant of the video tape was washed away using n-hexane, and then set on an X-ray photoelectron spectrometer. The distance between the X-ray source and the sample was 1 cm. The sample was evacuated to vacuum and after 5 minutes Cl-
2P spectrum, N-1S spectrum and Fe-2P (3
/ 2) The spectrum was integrated for 10 minutes and measured. The bus energy was kept constant at 100 eV. Measured Cl
The integrated intensity ratio between the -2P spectrum and the Fe-2P (3/2) spectrum was calculated and defined as α.

The N-1S spectrum and Fe-2P (3
/ 2) The integral intensity ratio with respect to the spectrum was calculated and set to β. As a result, α was 0.45 and β was 0.07. In addition, when measuring Example 3-5, α was 0.32,
β was 0.10. In practice, α is preferably 0.3
-0.6, particularly preferably 0.4-0.5. In practice, β is preferably 0.03 to 0.3.
12, especially preferably 0.04 to 0.1.

(11) The dynamic viscoelasticity of Leovibron at 110 Hz was measured. Using a dynamic viscoelasticity measuring device (Toyo Baldwin's Leo Vibron)
The viscoelasticity of the tape was measured at a frequency of 110 Hz. Tg was the peak temperature of E ''. This method applies vibration from one end of the tape and measures the vibration that propagates to the other end. As a result, Tg was 73 ° C. and E ′ (50 ° C.) was 4 × 10 ¹⁰ dyn.
e / cm ² and E ″ (50 ° C.) were 1 × 10 ¹¹ .
In practice, it has been found that Tg is preferably from 40 to 120 ° C, particularly preferably from 50 to 110 ° C. E 'for practical use
(50 ° C.) is 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne /
cm ² , particularly preferably 1 × 10 ^{11 to} 9 × 10
It was found to be ¹¹ dyne / cm ² . For practical use, E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 1.
0 ¹¹ dyne / cm ² , particularly preferably 0.7 ×
It was found to be 10 ^{11 to} 5 × 10 ¹¹ dyne / cm ² .

(12) Adhesion Strength The adhesion strength between the support and the magnetic layer was measured by a 180 ° peeling method. A tape slit to a width of 8 mm was attached to a 3M adhesive tape, and the 180 peel strength was measured at 23 ° C. and 70% RH. The obtained result was 50 g. In addition, the same measurement as in Example 3-1 yielded 25 g. It has been found that the adhesion strength is preferably at least 10 g, particularly preferably at least 20 g, in practical use.

(13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured. A sample was fixed on a prepared glass by attaching both ends of the sample with an adhesive tape, and a load of 5 mm was applied to a steel ball of 6.25 mmφ.
0 g was added and slid. At that time, after traveling once at a speed of 20 mm / sec over a distance of 20 mm, the same operation was repeated 20 times while moving the steel ball to a new magnetic surface. Thereafter, the sliding surface of the steel ball was observed with a microscope of 40 ×, the diameter was determined assuming that the surface was a circle, and the amount of wear was calculated from the diameter.

The obtained result was 0.7 × 10 ^{−5 to} 1.1.
× 10 ⁻⁵ mm ³ . Example 3-2 is 4 ×
It was 10 ^-5 mm ³ . Practically preferably 0.1 to 10
^-5 to (14) SEM (Scanning Electron)
ic Microscope) The surface condition of the magnetic layer was observed by SEM. Five images were taken with a Hitachi electron microscope S-900 at a magnification of 5000 times, and the abrasive on the surface was measured. As a result, the number of abrasives was 0.2 / μ.
m ² . In practice, the number of abrasives is 0.1 / μm ²
And more preferably 0.12 / μm ^{2 to} 0.
It was found to be 5 / μm ² .

(15) GC (Gas Chromatography) The residual solvent of the magnetic tape was measured by GC. Using gas chromatography GC-14A manufactured by Shimadzu Corporation, 20c
The m ³ sample was heated to 120 ° C. and the residual solvent in the medium was measured. As a result, the residual solvent was 8 mg / m ² . In addition, when Example 1-1 was measured in the same manner, 18 mg /
m ² . Practically, it was found to be preferably 50 mg / m ² or less, particularly preferably 20 mg / m ² or less. (16) Sol fraction The ratio of the soluble solid extracted from the magnetic layer of the magnetic tape with THF to the weight of the magnetic layer was determined. As a result, the sol fraction was 7%. Moreover, it was 5% when Example 1-1 was measured similarly. In practice, the sol fraction is preferably 15
%, Particularly preferably 10% or less.

(17) Magnetic Developing Pattern The obtained magnetic recording medium having a width of 8 mm was applied to a Sony VTR.
Using EVO-9500, short-wavelength recording of 1 MHz was performed, only the recorded portion was slit into a width of 5 mm, and a solution of ferricolloid (approximately 100 ° φ) (manufactured by Taiho Kogyo Co., Ltd.) was flowed and magnetically developed. The product subjected to the immersion treatment for 24 hours was photographed with a differential interference microscope manufactured by Nippon Kogaku Co., Ltd. at 10 times with the interference color being blue. When the photograph is visually observed, a black or white line does not appear in the sample having the average thickness of the magnetic layer, but a black or white line appears when the thickness variation of the magnetic layer becomes large. This line is a portion having an uneven thickness, and it is preferable that such a black or white line be within 5 lines within a width of 5 mm. Further, the density difference between the black and white lines measured by a microdensitometer on those lines is preferably 0.2 or less, particularly preferably 0.1 or less.

(18) Coefficient of friction (μ) An 8 mm wide tape and a sus420J, 4 mm
The tape was brought into contact at a wrap angle of about 180 ° with a tension of 0 g (T1), and the tension (T2) required to run the tape at a speed of 14 mm / sec under these conditions was measured and determined by the following equation. μ = (1 / π) · ln (T1 / T2) As a result, μ of the magnetic surface was 0.3. Practically, it was found that μ of the magnetic surface is preferably 0.15 to 0.4, and particularly preferably 0.2 to 0.35. Μ of the back layer surface was 0.2. Practically, μ of the back layer surface is preferably 0.15 to 0.4, and particularly preferably 0.2 to 0.4.
It turned out to be 0.35. This coefficient of friction is determined in relation to the magnetic material, abrasive, carbon black, lubricant, dispersant, and the like.

(19) Contact Angle Drops of water and methylene iodide were dropped on the magnetic layer, and the contact angles were measured with a microscope. In the case of water, it was 90 °.
In practice, the angle is preferably 60 to 130 °, particularly 80 °.
１２０120 ° was found to be preferred. In the case of methylene iodide, the contact angle was 20 °. In practice, it is preferably 10 to 90 °, particularly preferably 10 to 70 °.
Met. These contact angles are values determined by a lubricant and a dispersant.

(20) Surface Free Energy of Magnetic Layer and Back Layer JP-A-3-119513, DK 0wens, J. App.
l. polymer Sci., 13 (1969) and J. Panzer J. Colloid &
Based on the method described in Interfacial Sci., 44, No1. As a result, 40 dyne for both the magnetic layer and the back layer
/ Cm. Practically 10 to 100 dynes / cm
Was found to be particularly preferred. The surface free energy is a value determined by a lubricant and a dispersant.

(21) Surface Electric Resistance A sample having a width of 8 mm and having a cross section of a quadrant having a radius of 10 mm was used.
It was passed over two electrodes placed at an interval of mm and measured with a digital surface electric resistance meter TR-8611A (manufactured by Takeda Riken). As a result, both the magnetic layer surface and the back layer surface were 1 ×
It was 10 ⁶ Ω / sq. It has been found that practically, it is preferably 1 × 10 9 Ω / sq or less, and particularly preferably 1 × 10 8 Ω / sq or less. This surface electric resistance is a value determined by the ferromagnetic powder, binder, carbon black and the like. An 8 mm video tape having the above-described method and characteristics was compared with a tape currently on the market, and the results are shown in Table 6.

[0216]

[Table 6]

The evaluation method was the same as the above method or a general method. The criteria are as follows. Jitter: ○ Less than 0.2 μsec × 0.2 μsec or more Storage stability: ○ No rust after storage at 60 ° C., 90% RH for 10 days × Rust generation after storage at 60 ° C., 90% RH for 10 days There is running durability: (when running 50 passes on an 8 mm VCR) ○ No clogging lasting more than 30 seconds. C: Clogging lasting 30 seconds or more. Scratch: (Driving in the still mode for 10 minutes.) ○ No damage is visually observed. X: Scratches are visually observed.

[0218]

According to the present invention, excellent electromagnetic conversion characteristics can be obtained, such as high output in a high frequency range comparable to that of a vapor deposition tape and high output even in a short wavelength region even though it is a coating type. A magnetic recording medium with few holes, good running durability, good storage stability, and excellent productivity.
In particular, it has a remarkable effect of being a recording medium in that the simultaneous multilayer coating method has good surface roughness and high electromagnetic conversion characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of upper and lower layers 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 for forming 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 1st coating device 3 Smoothing roll 4 2nd coating device 5 Simultaneous multi-layer coating device A Lower layer coating liquid B Upper layer coating liquid

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C08J 7/04 CFD C08J 7/04 CFDV G11B 5/708 G11B 5/708 (72) Inventor Satoru Hayakawa 2-12-1, Ogimachi, Odawara, Kanagawa Prefecture, 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) Kaihei 5-182173 (JP, A) JP 5-182177 (JP, A) JP 5-182178 (JP, A) JP 5-73883 (JP, A) JP 63-187418 ( JP, A) JP-A-1-109518 (JP, A)

Claims (10)

(57) [Claims] 1. A non-magnetic support comprising: a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder; and an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder. In a magnetic recording medium having a plurality of layers or more, the dry thickness average value (d) of the upper magnetic layer is 1 μm or less, and λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ.
250 μm using 3D-MIRAU of the magnetic layer
The surface roughness Ra measured in an area of × 250 μm is Ra ≦ λ.
/ 50, and the non-magnetic powder has a Mohs hardness of 3 or more and an average particle size of
Granular particles of λ / 4 or less, or a major axis length of 0.05 to
1.0 μm, needle-like particles having a needle-like ratio of less than 20,
Has a plate diameter of 0.05 to 1.0 μm and a plate ratio of 5 to 20.
A magnetic recording medium comprising an inorganic powder composed of plate-like particles of the above , wherein the shortest recording wavelength λ is 4 μm or less. 2. The ferromagnetic powder in the upper magnetic layer has a major axis length of 0.3 μm or less and a crystallite size of 300 n.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a ferromagnetic powder of m or less. 3. The magnetic recording according to claim 1, wherein the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer has a relation of Δd ≦ d / 2. Medium. 4. The magnetic recording medium according to claim 1, wherein said upper magnetic layer is provided thereon while said lower nonmagnetic layer is in a wet state. 5. The inorganic powder of the lower non-magnetic layer
2. The magnetic recording medium according to claim 1, wherein the granular particles are spherical or dice-shaped. 6. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is an acicular ferromagnetic alloy powder containing Fe, Ni, or Co. 7. The flexible support includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate,
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. 8. The magnetic recording medium according to claim 1, wherein the lower non-magnetic layer contains a magnetic powder imparting thixotropic properties. 9. The magnetic recording medium according to claim 1, wherein Bm of the lower nonmagnetic layer is 500 gauss or less. 10. The magnetic recording medium according to claim 1, wherein the lower nonmagnetic layer contains a magnetic powder and does not participate in recording.