JPH08335310A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium having wide reproduction output comparable to that of a vapor-deposited tape in spite of a coating type medium, excellent in C-N ratio, improving contact with a head, excellent in shelf stability and running durability and less liable to edge damage. CONSTITUTION: A nonmagnetic layer as a lower layer contg. at least nonmagnetic powder and a binder is formed on a flexible substrate and a magnetic layer as an upper layer contg. ferromagnetic powder and a binder is formed on the nonmagnetic layer to obtain the objective magnetic recording medium with two or more layers. The average dry thickness (d) of the magnetic layer is <=1.0μm, the ratio (SMD/STD) of the stiffness SMD of the magnetic recording medium in the coating direction to the stiffness STD in the transverse direction is 1.0-1.9 and the nonmagnetic powder is inorg. powder having a Mohs hardness of >=3.

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 particularly to a very thin magnetic recording medium having a magnetic layer of 1.0 .mu.m or less. More specifically, it has very good electromagnetic conversion characteristics and good yield. The present invention relates to a magnetic recording medium having excellent production characteristics. In particular, the present invention relates to a magnetic recording medium, in particular, a magnetic layer having a thickness of 1.
More particularly, the present invention relates to a magnetic recording medium having a non-magnetic layer as a lower layer, and more particularly to a magnetic recording medium having improved electromagnetic conversion characteristics, running properties and durability.

[0002]

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

Therefore, by providing a nonmagnetic thick lower layer on the surface of the nonmagnetic support and then providing the magnetic layer on the upper layer, the problems due to the surface roughness of the support described above are solved and the magnetic layer is made thin. Proposed an attempt to reduce thickness demagnetization and achieve high output. For example, in JP-A-62-154225, the thickness of the magnetic layer is 0.5.
In order to prevent the surface electric resistance of the magnetic layer from becoming high as well as the thickness of the magnetic layer is less than or equal to μm, a magnetic underlayer is provided between the magnetic layer and the substrate, the undercoat layer containing conductive fine powder having a thickness equal to or larger than the thickness of the magnetic layer. Recording media have been proposed. Also, JP-A-62-222
No. 427, a support and a subbing layer provided on the support and containing an abrasive having an average particle diameter of 0.5 to 3 μm; and a film thickness containing a ferromagnetic powder provided on the subbing layer. 1μ
A magnetic recording medium provided with a magnetic layer of m or less has been proposed, but this has a function of cleaning the magnetic head of the magnetic recording medium because part of the abrasive in the undercoat layer protrudes into the magnetic layer. Is. In this way, the magnetic layer is made thin to achieve high-density recording, and at the same time, carbon black is included in the lower non-magnetic layer to prevent electrification, and an abrasive is added to improve cleaning characteristics and durability. are doing.

However, in the conventional technique, the lower non-magnetic layer is first coated on the non-magnetic support, dried and then calendered, and then the upper magnetic layer is provided, so that the manufacturing process is It was complicated and had the following problems. That is, in order to thin the magnetic layer, it is conceivable to reduce the coating amount or to add a large amount of solvent to the magnetic coating liquid to reduce the concentration. In the former case, if the amount of application is reduced, there is not enough time for leveling after application, and drying starts, so that a problem such as an application defect, for example, a stripe or engraved pattern remains, and the yield is extremely deteriorated. When the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids, and it is not possible to obtain a sufficient degree of filling of the ferromagnetic powder. This causes various problems such as insufficient strength of the film. As one means for solving these problems, as described in Japanese Patent Laid-Open No. 63-191315, a non-magnetic layer is provided as a lower layer by using a simultaneous multi-layer coating method to prepare a magnetic coating solution having a high concentration. A method of thin coating has been proposed.

In the case of the simultaneous multi-layer coating method or the sequential wet coating method, that is, the so-called Wet on Wet coating method in which the upper layer is coated simultaneously or sequentially while the lower layer is in a wet state, various magnetic layers already formed in the multi-layer structure. Are being studied. However, even if this technique was applied to the lower non-magnetic layer, similarly good results were not obtained. That is, when the lower non-magnetic layer and the upper magnetic layer were provided by wet-on-wet, disturbance occurred at the interface between them, and the surface roughness was greatly deteriorated.

Further, when the nonmagnetic thick lower layer is provided on the surface of the support and then the magnetic layer is provided as the upper layer, the influence of the surface roughness of the support can be eliminated.
There was a problem that head wear and durability were not improved. This is because a non-magnetic lower layer has conventionally used a thermosetting (curing) resin as a binder, so the lower layer is cured and contact between the magnetic layer and the head and other members is unbuffered. It is thought that this is because the magnetic recording medium having such a lower layer is somewhat inflexible. In order to solve this, it is considered to use a non-curable (thermoplastic) resin as a binder in the lower layer, but in the conventional method, when the lower layer is applied and dried and then the magnetic layer is applied as the upper layer, the lower layer is used. Swells with the organic solvent of the upper layer coating solution, causing turbulent flow in the upper layer coating solution, deteriorating the surface properties of the magnetic layer, and deteriorating electromagnetic conversion characteristics.

Further, in order to improve the recording density of the magnetic recording medium, short wavelength recording has been advanced, and the recording wavelength of 8 mm video tape has reached 0.54 μm. As a magnetic recording medium corresponding to this, one using a ferromagnetic metal thin film has been put into practical use. Since the metal thin film magnetic recording medium has a very thin magnetic layer, the loss due to the thickness is small, and thus a medium having a very high output can be obtained. However, these media are inferior in mass productivity as compared with the conventional coating type magnetic recording media because they are manufactured by vapor-depositing a metal on a non-magnetic support, and because they are metal thin films, they are oxidized for a long time. There is a problem in terms of storability. In order to solve these problems, it has been desired to thin the magnetic layer of the conventional coating type magnetic recording medium.

However, in order to apply the upper magnetic layer in a thin layer of 1.0 μm or less, the magnetic liquid must be diluted with a large amount of solvent, which easily promotes aggregation of the magnetic liquid.
Also, since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder tends to be disturbed, and the orientation is poor in magnetic recording media. It is difficult to secure sufficient electromagnetic conversion characteristics. In addition, since the magnetic film was weak because the excessive drying caused many voids, the running durability was also insufficient. If it is attempted to improve the orientation and reduce the amount of the organic solvent to be diluted in order to reduce the voids in the coating film, the coating stability will deteriorate.

As a means for coping with such a problem, it has been proposed to include a non-magnetic granular abrasive or a filler in the undercoat layer. (JP-A-62-222427, JP-A-2-257424) However, a problem with these techniques is that when a magnetic layer and a non-magnetic layer are simultaneously coated to orient the magnetic material in the upper layer, a magnetic material with a magnetic field is applied. Due to the rotational movement of the above, mixing occurs at the interface between the upper and lower layers, and not only does it have sufficient surface properties,
Since the orientation is not performed sufficiently, sufficient electromagnetic conversion characteristics cannot be obtained.

It has been proposed to improve the orientation of the upper magnetic particles by forming a conductive intermediate layer using graphite as the non-magnetic scaly particles.
(Japanese Patent Application Laid-Open No. 55-55438) However, although such a substance can improve the orientation, graphite itself does not have a reinforcing effect on the film and is insufficient in durability. Proposals to mix powders have also been made. (JP-A-60-125926) Further, it has been proposed to improve the orientation of the upper magnetic particles by forming a reinforcing layer using acicular oxalate as the non-magnetic acicular particles. . (Japanese Patent Publication Sho 58-51
327).

Although these proposals improve the orientation and ensure the durability, scale-like particles are likely to cause stacking at the stage of actually producing the medium, and substances such as oxalate are dispersible in the binder. It was found that the smoothness impairs the smoothness of the magnetic surface because of the poor value. 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.
Therefore, the lower non-magnetic layer that is not directly exposed on the surface has excellent dispersibility as much as possible, and the necessity for smooth surface properties when simultaneous multilayer coating is increasing. Further, as described above, when the magnetic layer is made thin, the dispersibility of the lower non-magnetic layer further contributes to the surface property in the case of simultaneous superposition. As a result of earnest study, even if the dispersibility of only the lower layer is improved,
As a result of simultaneous layering, it was found that the surface became rough.

When the coercive force of the magnetic layer is low, self-demagnetization loss is large and it is not suitable for short wavelength recording. Therefore, it is necessary to have a considerable Hc. As means which can be used for such a purpose, the gap between the non-magnetic support and the magnetic layer is 0.5 μm to 5.
It has been proposed to provide an undercoat layer of 0 μm and Hc of the magnetic layer to 1000 Oe. (Japanese Patent Laid-Open No. 57-19853)
No. 6) However, the conventionally known technique has the following problems in achieving this object. The above-mentioned JP-A-57-198.
In the technique disclosed in Japanese Patent No. 536, when the simultaneous multi-layer coating of the upper and lower layers, which is a feature of the present invention, is performed, mixing of the upper and lower layers occurs, resulting in poor surface properties and disordered orientation. Further, as a technique for improving the orientation in simultaneous multi-layer coating, JP-A-3-49
No. 032 discloses that a layer in which carbon black is dispersed is used as a lower layer for multi-stage orientation. However, a filler having a small true specific gravity, such as carbon black, is applied at the same time by the rotational movement of a magnetic substance during orientation. At that time, the interfaces between the upper and lower layers were disturbed, and the SQ measured in the in-plane direction was high, but the improvement of the residual coercive force in the direction normal to the magnetic layer, which is the object of the present invention, was insufficient.

[0013] Since a magnetic material having a short major axis length and a small acicular ratio is less likely to be flow-oriented, the orientation of the magnetic material is further reduced and sufficient electromagnetic conversion characteristics cannot be obtained. In recent years, the magnetic material contained in the magnetic layer has been made finer to increase the density. By using fine particles, the strength of the magnetic layer becomes inferior, and if a high tension is applied in the manufacturing process or in a video deck, for example, the tape will be elongated and skew (SKEW) distortion will increase. In order to prevent this, it has been attempted to reduce the heat shrinkage rate or increase the strength of the support, but there is a limit. Further, when the simultaneous multi-layer coating method is adopted, there is a problem that the heat shrinkage rate becomes larger and Skew strain increases as compared with the sequential multi-layer coating method. This is because in the case of sequential multilayer coating, the lower layer was hardened by calendering or curing treatment after coating the lower layer to make the medium hard to expand and contract, but in the simultaneous multilayer coating method, the lower layer and the upper layer are coated at the same time. This is because the expansion and contraction of the medium cannot be suppressed by the lower layer.

Similarly, there is a tendency that the tape thickness is reduced in order to prolong the time. When the tape thickness is reduced, the tape stiffness is reduced, and good contact with the head cannot be maintained, resulting in deterioration of electromagnetic conversion characteristics. In particular, 8mm video tapes and VHs that have become popular in recent years
Since the total length of the long-time tape of S is as thin as 14 μm or less, it is difficult to secure the head contact. Conventionally,
For thick media, it was effective to lower the strength of the lower non-magnetic layer and maintain a smooth contact state.
In a thin tape used in a recording / reproducing apparatus using a rotary head in recent years, it is difficult to secure head contact unless the stiffness of the lower non-magnetic layer is increased. There is also a method of controlling this stiffness by a stretching method of the non-magnetic support, but the stiffness in the width direction is reduced, which is not preferable for running durability.

As shown in JP-A-63-191315, it was confirmed that the lower non-magnetic layer did not contain polyisocyanate in order to improve head contact. The results are inferior. For this reason, it is effective in a system that does not emphasize storage, but is difficult to use in a system that emphasizes storage such as business use or data storage. JP-A-63-187
No. 418 also discloses that the magnetic layer is similarly thinned to improve the electromagnetic conversion characteristics, but there are still some of the inventions whose electromagnetic conversion characteristics are insufficient. JP 5
No. 0-803 also has an invention of providing a fine granular non-magnetic pigment having a Mohs hardness of 6 or more between a magnetic layer and a support.
The gist of the present invention is to increase the flatness of the aluminum substrate by polishing the aluminum substrate with a nonmagnetic powder having a Mohs hardness of 6 or more.

Further, it is difficult for these methods to meet the demand for thinning of the magnetic recording medium due to the recent increase in time and density, and these methods provide excellent electromagnetic conversion characteristics and running durability. There was insufficient compatibility. In particular, in order to improve running durability with thin tape, it is necessary to reduce tape edge damage.
The inventions of No. 15 and JP-A No. 63-187418 were insufficient.

In recent years, Hi8 tapes have been studied, and the ultimate need is to satisfy both the advantages of ME (evaporation) 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 double coating technique is the VTR
Focusing on the signal recording mechanism, that is, the recording depth of each signal, the performance has been improved by designing the optimum upper and lower magnetic layers for each. The VHS double coating has a two-layer structure in which upper and lower layers are made of ferromagnetic powders having different sizes and magnetic characteristics, and high output and low noise have been realized in all bands of brightness, color and sound. And H
The i8MP multilayer tape uses a metal magnetic material for high-density recording in the upper magnetic layer, uses an iron oxide magnetic material with excellent medium and low-frequency characteristics in the lower magnetic layer, and uses completely different types of magnetic materials. The so-called high-grid double coating was developed, and a large improvement in image quality was achieved, such as reproduction of sharp images and vivid colors.

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

[0020]

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-density magnetic recording medium which is a coating type of the present invention and has good electromagnetic conversion characteristics such as output and C / N ratio, particularly, good head contact and high output in short wavelength recording. It is to be.

A third object of the present invention is to provide a magnetic recording medium which has good electromagnetic conversion characteristics, a small heat shrinkage and a good storage stability. A fourth object of the present invention is to
An object of the present invention is to provide an excellent thin-layer magnetic recording medium having good electromagnetic conversion characteristics, excellent running durability, and high production yield while securing production efficiency.

A fifth object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics. The magnetic recording medium has a small edge damage due to repeated running, has excellent running durability, and has excellent long-term storage characteristics. Is to provide a medium. In particular, the object of the present invention is to be able to exhibit a high-frequency output comparable to that of a vapor-deposited tape while being a coating type, to have a good head contact, to have good electromagnetic conversion characteristics in short-wavelength recording, and to have a small heat shrinkage and storage stability. Is to provide a coating-type high-density magnetic recording medium which is excellent.

[0023]

The above-mentioned problems can be solved by the magnetic recording media according to the present invention listed below. (1) A plurality of at least two layers in which a lower non-magnetic layer containing at least non-magnetic powder and a binder is provided on a flexible support, and an upper magnetic layer containing ferromagnetic powder and a binder is provided thereon. In the magnetic recording medium having a layer, the dry thickness average value (d) of the upper magnetic layer is 1 μm or less, the application direction (longitudinal direction) stiffness SMD of the magnetic recording medium, and the width direction stiffness STD with respect to the application direction. Ratio to SM
A magnetic recording medium, wherein D / STD is 1.0 to 1.9, and the non-magnetic powder is an inorganic powder having a Mohs hardness of 3 or more. (2) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the inorganic powder has a Mohs hardness of 6 or more and an average particle size of 0.15 μm or less from spherical to cubic polyhedral inorganic powder. The magnetic recording medium according to (1) above. (3) The magnetic recording medium according to (1) above, wherein the ferromagnetic powder has a crystallite size of 300 Å or less. (4) The magnetic recording medium according to (1), wherein the non-magnetic powder is rutile type titanium oxide. (5) The magnetic recording medium according to (1), wherein the upper magnetic layer is provided while the lower nonmagnetic layer is in a wet state. (6) The inorganic powder of the lower non-magnetic layer has a spherical or dice-like shape.
(7) The magnetic recording medium described in (1) above, wherein the ferromagnetic powder is a needle-like ferromagnetic alloy powder containing Fe, Ni or Co. (8) The support is at least one selected from polyesters, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide. The magnetic recording medium according to 1). (9) The magnetic recording medium as described in (1) above, wherein the lower non-magnetic layer contains a magnetic powder imparting thixotropy. (10) The magnetic recording medium according to (1), wherein the lower nonmagnetic layer has a Bm of 500 Gauss or less. (11) The magnetic recording medium according to (1), wherein the lower nonmagnetic layer contains a magnetic powder and is not involved in recording.

In order to control the mechanical characteristics of the magnetic recording medium and improve the head contact of the magnetic recording medium by setting the stiffness to the above value, it is necessary to reduce the morphology of the inorganic powder contained in the lower non-magnetic layer as described below. The hardness is 3 or more, preferably 6 or more, more preferably 6.5 or more, and the average particle size is 0.1 or more.
It is preferable to use spherical to cubic polyhedral inorganic powder having a particle size of 15 μm or less, preferably 0.12 μm or less.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The action mechanism of the present invention for controlling the value of the stiffness SMD in the coating direction, the value of the stiffness STD in the width direction, and the value of the ratio SMD / STD thereof will be described below. That is, although the space loss is a major cause of the deterioration of the high-frequency characteristics, the shorter the wavelength is, the weaker the magnetic flux that appears on the tape surface is. Even a very small spacing between the tape and the video head causes a large loss. Space loss includes microscopic ones due to the roughness of the magnetic layer surface and macroscopic ones due to the rigidity of the tape. The former is an issue of how to ensure stable running performance while realizing ultra-smoothness, and the latter is what is called so-called "head contact", and how to achieve both excellent tape strength and flexibility Is the issue. This is not limited to short-wavelength recording, and the image quality is greatly affected. As a result of intensive studies, the present inventors have solved this problem of space loss at once.

The value of the stiffness SMD of the magnetic recording medium,
The value of the stiffness STD in the width direction and their ratio S
By controlling the MD / STD value, 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. An aspect of the present invention is to control SMD / STD to 1.0 to 1.9.

Both the stiffness SMD in the coating direction and the stiffness STD in the width direction can be measured using a commercially available stiffness tester. For example, using a loop stiffener tester manufactured by Toyo Seiki Co., Ltd., a magnetic recording medium manufactured with a width of 8 mm and a length of 50 mm is used for SMD measurement so that the sample length direction is the same as the magnetic recording medium coating direction. For STD measurement, the sample was cut out so that the length direction of the sample was the same as the width direction of the magnetic recording medium, and this was used as a ring.
The values required to give a displacement of 5 mm at a displacement rate of 3.5 mm / sec in the inner diameter direction expressed in mg can be used as SMD and STD.

Here, SMD / STD is 1.0 to 1.9,
It is preferably controlled to 1.1 to 1.85. In a magnetic recording medium having a total thickness of 13.5 ± 1 μm, SMD is
50-200 mg, preferably 50-150 mg, STD
Is 40 to 150 mg, preferably 50 to 130 mg. The means for controlling the value of SMD / STD is not particularly limited, but it is preferable to select the shape and Mohs hardness of the lower layer inorganic powder, and the inorganic powder contained in the lower layer has a Mohs hardness of 6 or more, preferably 6 or less. It is desirable to select a spherical to cubic polyhedral inorganic powder having a particle size of 0.5 or more and an average particle size of 0.15 μm or less, preferably 0.12 μm or less.

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

In particular, S has a great effect on electromagnetic conversion characteristics.
TD is close to SMD, that is, close to 1. When the inorganic powder contained in the lower layer has a polyhedral shape from spherical to cubic, the mechanical properties of the coating film become isotropic, which is convenient for improving STD. Here, specifically, the polyhedron shape means a regular polyhedron or a non-regular polyhedron selected from one or more kinds of regular n-gons such as a sphere, one side of a square, regular pentagon, regular hexagon and the like, or simple n-gons. Although it can be illustrated, it is preferable that the two axial ratios selected arbitrarily are in the range of 0.6 to 1.4, preferably 0.7 to 1.3.

In order to achieve the object of the present invention better and to provide an excellent magnetic recording medium, a preferable main technique of the present invention described below is applied to impart excellent characteristics to the magnetic recording medium. It is desirable to do. The following describes a number of preferred key technologies to be introduced for this purpose, and a number of preferred properties provided thereby. In the present invention, these preferable main techniques and characteristics act on each other in an organically complementary, additive and even comprehensive manner to form an ultra-thin layer in the magnetic recording medium of the present invention.
It enables an unprecedented new layer configuration consisting of ultra-smooth and ultra-highly filled layers, and offers innovative high-frequency characteristics and excellent middle and low-frequency characteristics that were difficult with conventional single-layer coating technology. This is realized by the magnetic recording medium of the present invention. The following is a description of some, but not essential, preferred key techniques and characteristics. That is, the application of the coating layer of the magnetic recording medium has conventionally been based on the simultaneous multi-layer coating technique. In the process for achieving the present invention, the simultaneous multi-layer coating technique is partially basic, but the frame is limited. Beyond that, the "signal loss" that increases as the recording becomes shorter will be drastically reduced, the thickness of the magnetic layer shall be reduced, and the development of a new magnetic material to increase the magnetic energy of the magnetic layer as much as possible and its new magnetism It has been found that two points of high density filling of the body coating layer are important technologies and characteristics. 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 the "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 of the preferred main technologies of the present invention.
Is the same as or similar to the thixotropy of the coating liquid for the upper magnetic layer and the lower non-magnetic layer, or the shape of the lower non-magnetic powder is adjusted so that the thickness of the magnetic layer is 1 μm or less and the average thickness variation is It realizes an unprecedented uniform thin magnetic layer with a value of ½ or less of the thickness and a standard deviation of the thickness measurement value of 0.2 μm or less, and significantly reduces self-demagnetization loss in the short wavelength region. is there.

The second of the preferred main technologies of the present invention is to adjust the size and shape of the ferromagnetic powder in the upper magnetic layer and the size and shape of the nonmagnetic powder in the lower nonmagnetic layer, and to disperse the nonmagnetic powder itself. This technology realizes a more uniform interface with less fluctuation, completes a super smooth magnetic layer surface, thoroughly eliminates "space loss", and improves high-frequency output. To make it happen.

A third preferred preferred technique and characteristic of the present invention
Is to increase the energy of the magnetic layer. H for the upper magnetic layer
High magnetic energy and high coercive force are achieved by using fine ferromagnetic powders with high r and Hc.
(Evaporation) High-frequency output equivalent to or higher than tape can be exhibited. The fourth of the main technologies and characteristics of the present invention is the high density filling of the magnetic layer described above. In the prior art, if the magnetic layer is simply made thinner, the low-frequency output decreases and the color characteristics deteriorate, but in the present invention, by providing a fine particle inorganic powder layer (lower layer) having extremely high rigidity in the thickness direction, the magnetic layer becomes thinner. When calendering is performed from the top of the layer, the magnetic layer can be densely packed, and high-density filling of high-energy ferromagnetic powder can significantly improve high-frequency output and at the same time have high mid- and low-frequency characteristics , And high output and low noise can be realized in all bands of luminance, color, and sound.

Fifth of the preferred main technologies and characteristics of the present invention, the magnetic layer of the present invention has excellent viscoelasticity, adhesion strength and steel ball wear characteristics, and the residual solvent and sol fraction of the magnetic layer are reduced. As a result, an excellent durability that cannot be achieved by a conventional ME (evaporation) tape can be obtained.

The following is a detailed description of the first preferred main technology and characteristics of the present invention. That is, the preferred magnetic recording medium of the present invention is one in which a lower non-magnetic layer containing at least non-magnetic powder and a binder is provided on a flexible support, and the lower non-magnetic layer is ferromagnetic on the lower non-magnetic layer in a wet state. In a magnetic recording medium having a plurality of layers of at least two layers provided with an upper magnetic layer containing a powder and a binder, the dry thickness average value (d) of the upper magnetic layer is 1 μm or less. It is a recording medium.

From the principle of self-demagnetization, it has been found that the smaller the cross-sectional area of the magnetic layer, the smaller the loss. Therefore, in order to increase the output of a short-wavelength signal, it has been found that the magnetic layer must be made ultra-thin. is there. Moreover, if the thickness is 1 μm or more, the effect is small, and the effect increases as the effective recording thickness, which is generally called ¼ of the recording wavelength, is approached, that is, as the saturation recording is approached. is necessary. The specific means for realizing the ultra-thin magnetic layer is the first of the preferable main techniques of the present invention, that is, the chicken tropic property of the coating liquid for the upper magnetic layer and the lower non-magnetic layer. They are to make the same or similar, and to eliminate the mixed region at the interface by adjusting the shape of the lower non-magnetic powder. According to the first of the above-mentioned preferred main techniques of the present invention, the thickness of the magnetic layer is 1 μm or less, the average value of the thickness variation is 以下 or less of the thickness, and the standard deviation of the measured thickness is 0.1 μm or less.
An unprecedented uniform thin magnetic layer of 2 μm or less is realized, and self-demagnetization loss in the short wavelength region is significantly reduced.

With 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. However, innovating the conventional coating technology, a non-magnetic layer containing fine-particle inorganic powder is provided as a lower layer, and a magnetic layer is provided thereon. The average value of the thickness fluctuation of the magnetic layer is １ ／ of the thickness or less, By setting the standard deviation to 0.2 μm or less, the conventional general H
i8 MP tape realizes an epoch-making ultra-thin magnetic layer with a coating type magnetic recording medium, which was difficult with the conventional technology of 1/3 to 1/10 or less the thickness of the magnetic layer. In this case, the luminance signal output is greatly improved.

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

The size of the magnet depends on the shape of the magnet. That is, the smaller the cross-sectional area and the greater the distance between the magnetic poles, the smaller the demagnetizing field, and the less self-demagnetization occurs. Taking the case of sewing needles and pachinko balls with completely different shapes as an example, they are all made of iron and stick to magnets. Due to the large demagnetization, it has the property of not becoming a magnet itself.

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 becomes smaller, the demagnetizing field increases, and the loss due to self-demagnetization increases. This is one of the major factors that deteriorate the high frequency characteristics of the tape. In order to reduce the self-demagnetization loss, it is effective to reduce the cross-sectional area, that is, reduce the thickness of the magnetic layer according to the principle of self-demagnetization. Moreover, the self-demagnetization loss becomes smaller as it approaches saturation recording and the output improves, so that it approaches the effective magnetic layer thickness which is said to be ¼ of the recording wavelength. An ultra-thin layer in the submicron region is required.

The shortest recording wavelength of Hi8 is 0.49 μm,
It has an extremely short wavelength. The magnetic layer of the magnetic recording medium of the present invention has a thickness of 1 of the conventional general Hi8 MP tape magnetic layer thickness.
The reason is that the magnetic recording medium of the present invention has excellent high frequency characteristics as in the case of an ME (evaporation) tape having an extremely thin magnetic layer thickness of about 0.2 μm. It is one. On the other hand, the thickness of the magnetic layer of the coating type MP tape is about 3 μm, and the coating method used so far has to be considerably thicker than the recording wavelength. It was an inevitable large wall. However, according to the present invention, such a wall was greatly broken.

Along with self-demagnetization, another major cause of deterioration of high frequency characteristics is space loss.
The shorter the wavelength, the weaker the magnetic flux on the surface of the tape, so even the slightest spacing between the tape and the video head causes a large loss. Space loss includes microscopic ones due to the roughness of the magnetic layer surface and macroscopic ones due to the rigidity of the tape. The former has a problem how to secure stable running performance while realizing super smoothness.
The importance becomes extremely high in high-density recording in which the shortest recording wavelength is about 40% of VHS, such as i8. The latter is so-called "head contact", and the issue is how to achieve both excellent tape strength and flexibility. This is not limited to short-wavelength recording, and the image quality is greatly affected. The present invention solves this space loss problem all at once.

Next, the second preferable main characteristic of the present invention will be described. That is, in the present invention, the dry thickness d of the upper magnetic layer is 1.0 μm or less, and the _root- mean-square roughness R _{rms of the} surface of the upper magnetic layer by a scanning tunneling microscope (STM) method is the same as that of the upper magnetic layer. 30 between dry thickness d
It is preferable that there is a relationship of ≦ d / R _rms .

The second of the preferred main technologies of the present invention is a technology for ultra-smoothing the magnetic layer surface. Originally, the double coating technique is a technique that can realize excellent smoothness of the magnetic layer surface. This is because the lower magnetic layer absorbs the irregularities on the surface of the base film and makes it difficult to transmit the influence of the irregularities to the upper layer. However, when the problem is a slight space loss of 0.5 μm or less at a shorter wavelength and further smoothness is aimed at, there is a limit only in the conventional technique.

Because of the recording mechanism, it is necessary to use an ultra-fine particle magnetic material having excellent high-frequency characteristics for the upper layer. This is because even interface disturbances need to be thoroughly pursued. In particular, the smoother the upper layer, the greater the influence of the smoothness of the interface on the smoothness of the surface of the magnetic layer, and the solution of this problem was more important.

In the present invention, in order to achieve ultra-smoothness of the interface between the upper and lower layers, the non-magnetic particles in the lower layer were made into ultrafine particles and the packing thereof was dense. However, on the other hand, the particles in the upper magnetic layer are extremely fine particles, so it is difficult to fill them uniformly and at a high density as it is. By increasing the density, high-density filling is realized, and the smoothness of the interface between the upper and lower layers is dramatically improved.

Further, since the lower non-magnetic layer of the present invention is a high-density filling layer, it has a high degree of freedom in the surface direction of the tape, has excellent flexibility, and can withstand a force in the thickness direction. Has a very high rigidity and further enhances the smoothing effect of the magnetic layer by calendering.
As a result, as compared with Hi8 MP-DC, smoothing of the magnetic layer of 20% was realized. The ultra-smooth surface of the magnetic layer significantly reduced the space loss in the short wavelength region and improved high-frequency characteristics.

Next, a third preferred main technique and characteristic of the present invention will be described. That is, in the present invention, the ferromagnetic powder contained in the upper magnetic layer is a needle-like ferromagnetic alloy powder having a major axis length of 0.3 μm or less and Hc of 1500 Oe or more or a plate diameter of 0.3 μm or less. It is preferable that the plate-like ferromagnetic powder has Hc of 1000 Oe or more.

The third of the preferable main characteristics of the present invention is that the magnetic layer has high output and low noise characteristics as a basis for improving the performance of the magnetic tape. In particular,
In order to thoroughly pursue the improvement in characteristics at short wavelengths, the third of the preferable main technologies of the present invention is to “ultrafine magnetic material, increase energy,
The technology of high output and low noise of the magnetic layer itself by "high density filling" is indispensable.

Next, a fourth preferred main technique and characteristic of the present invention will be described. In the present invention, the heat shrinkage of the magnetic recording medium at 80 ° C. for 30 minutes is 0.4% or less,
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 -5%. ~ + 20%
It is preferably in the range of. This means that the inorganic powder contained in the lower nonmagnetic layer of the present invention has a Mohs hardness of 6
As described above, the polyhedral inorganic powder from spherical to cubic having an average particle size of 0.15 μm or less and high-density filling of the inorganic powder contained in the lower non-magnetic layer were enabled.

That is, the fourth point of the present invention is the high-density filling of the magnetic substance, and the lower non-magnetic layer enables the high-density filling of the magnetic substance. The lower non-magnetic layer that is smooth and extremely rigid in the thickness direction is super HD
The strong pressure of the P (High Density Packing) calendar was firmly received, and an unprecedented breakthrough high density packing of the upper magnetic material was realized.

Further, if the high frequency characteristics are thoroughly pursued by making the magnetic layer ultra-thin, the middle and low frequency characteristics are deteriorated in the conventional technology.
Excellent color characteristics cannot be obtained. However, the lower non-magnetic layer of the present invention enables a revolutionary high filling of the high-energy magnetic material that solves this, and at the same time as significantly improving the high-frequency output, ensuring high mid / low-frequency characteristics, It achieved high output and low noise in all bands of luminance, color, and sound, and also achieved excellent color output. Conventional dry thickness 1.0
Magnetic recording media having an upper magnetic thin layer and a lower non-magnetic layer having a thickness of μm or less are only occasionally found as patent applications, and no product that has ever been actually put on the market has been found. The present invention is an epoch-making invention that breaks such conventional wisdom for the first time.

As described above, in the preferred magnetic recording medium of the present invention, a lower non-magnetic layer containing at least a non-magnetic powder and a binder is provided on a flexible support, and a lower ferromagnetic powder is bonded to the lower non-magnetic layer. In a magnetic recording medium having at least two or more layers provided with an upper magnetic layer containing an agent, the average dry thickness (d) of the upper magnetic layer is 1 μm or less, and the dry thickness of the upper magnetic layer is A magnetic recording medium characterized in that the standard deviation σ of the average of the measured taste values is 0.2 μm or less. In the present invention, the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower non-magnetic layer is expressed as Δd ≦ d
The relationship of / 2 is preferable, whereby a more practical, high density recording medium of the coating type and comparable to the vapor deposition tape can be obtained.

Here, the definition of Δd and the measuring method are as follows. Here, the method for obtaining the thickness of the upper magnetic layer and the interface variation Δd is as follows. That is, the magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter in the longitudinal direction, and a magnification of 10,000 to 1 was obtained with a transmission electron microscope.
Observation was performed at a magnification of 0000 times, preferably 20000 to 50,000 times, and the photograph was taken. The print size of the photograph was A4 to A5. After that, the interface was visually judged by observing the shape difference between the magnetic substance and the non-magnetic powder in the upper magnetic layer and the lower non-magnetic layer, and the surface of the magnetic layer was also black. After that, Zeiss image processing device IB
The length of the space between the trimmed lines was measured by AS2. Thereby, the average value of the thickness of the upper magnetic layer was obtained. The length of the space was measured by segmenting a space having a length of 21 cm into 100 to 300.

The average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower non-magnetic layer is the peak formed by the bordered interface between the magnetic layer and the lower non-magnetic layer having a length of 20 μm (actual length). The distance (Δd _i ) in the thickness direction of the bottoms of the ridges and valleys was determined at 10 to 20 places (all in 20 μm), and the average value of the sums was obtained. That is, in the present invention, it is the most preferable mode that the curve forming the interface is ideally a straight line having a constant d. It is preferable that a curve similar to a long smooth sine curve is formed, and the number of peaks and valleys is 2
It is preferable to limit the length to 0 μm to a maximum of 10 to 20 pieces (see FIG. 1).

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

As a specific means for achieving the above rules,
First of the preferred main technologies of the present invention already described above
Will be specifically described in detail. Preferred first of the present invention
One major technology has two aspects. The first aspect is
Thixoto of magnetic dispersion of magnetic layer and dispersion of lower non-magnetic layer
This is to control the ropiness to approximate each other.
The specific method is to disperse the non-magnetic powder in the binder.
Has a thixotropic property and a shear rate of 10
^Foursec^-1Shear stress A10^FourAnd shearing speed 10sec
c^-1Ratio of shear stress A10 to A10^Four/ A10
100 ≧ A10 ^Four/ A10 ≧ 3.
Specific measures to have such thixotropic properties
There are the following four steps. The magnetic recording medium of the present invention is
The book is not limited to these four
Quality refers to the thixotropic properties of the dispersion.
The value is the same as or close to the thixotropic property of the magnetic paint.
And more specifically, A10 ^FourValue of / A10
In the range.

(A) The powder of the lower non-magnetic layer contains at least carbon black and inorganic powder having an average primary particle diameter smaller than the dry thickness of the lower non-magnetic layer, and the lower non-magnetic layer and the upper magnetic layer are heated. Including 10 to 70% by weight of a curable polyisocyanate in the binder. (B) The powder of the lower non-recording layer has an average primary particle diameter of 0.08 μm
Including a non-metallic inorganic powder that is m or less. (C) A magnetic powder that imparts thixotropy so that the dry thickness of the upper magnetic layer is 1.0 μm or less, and the maximum saturation magnetic flux density Bm of the lower nonmagnetic layer is 500 gauss or less, preferably 30 to 500 gauss. to use. However, the lower non-magnetic layer does not participate in recording. (D) The ferromagnetic powder in the upper magnetic layer has a major axis length of 0.3 μm or less and a crystallite size of 300 μm or less, and the lower layer is made of nonmagnetic metal oxide powder as nonmagnetic powder and has an average particle size of 20 n.
containing carbon black of less than m in a ratio of 95/5 to 60/40, and at least 3 OH in one molecule in the lower layer.
Including a polyurethane having a group and a polyisocyanate compound.

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

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

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

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

In order to spread the scaly non-magnetic powder in a tile form, it is necessary to improve the dispersibility of the powder to be applied by the coating solution and to improve the arrangement thereof when applying the epoxy group by using an epoxy group having a molecular weight of 30,000 or more. It is preferred to use a binder that contains
In this way, by using a non-magnetic powder having a characteristic shape in the lower non-magnetic layer and providing the upper magnetic layer on it, no mixed region is generated at the interface, and therefore, an extremely thin and smooth magnetic layer is obtained. A layer is obtained.

In the magnetic recording medium of the present invention, the dry thickness average value d of the magnetic layer is λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ.
Further, it is preferable that the surface roughness Ra of the magnetic layer has a relationship of Ra ≦ λ / 50. The preferred powder composition for this is
The ferromagnetic powder in the magnetic layer is a needle-like ferromagnetic powder having a major axis length of 0.3 μm or less or a plate-like ferromagnetic powder having a plate diameter of 0.3 μm or less; But,
Granular particles having an average particle size of λ / 4 or less, or needle-shaped particles having a major axis length of 0.05 to 1.0 μm and an acicular ratio of 5 to 20,
Or the plate diameter is 0.05 to 1.0 μm and the plate ratio is 5
It is preferably 20 plate-like particles.

The surface properties of the present invention can be achieved based on the invention in which the standard deviation of the average thickness of the upper magnetic layer is 0.2 μm or less, and the following (H) to (H).
This can be achieved by the four means (J). (H) The non-magnetic powder contained in the lower non-magnetic 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-like ferromagnetic powder, and the average particle diameter of the inorganic powder is 1/2 to 4 of the crystallite size of needle-like ferromagnetic powder
Be double. (I) 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, and the average particle size of the inorganic powder Is 1/3 or less of the major axis length of the acicular ferromagnetic powder. (J) The ferromagnetic powder contained in the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate,
In addition, the non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the average particle size thereof is equal to or less than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer. (K) The inorganic powder contained in the lower non-magnetic layer contains the inorganic non-magnetic powder having the surface layer coated with the inorganic oxide.

The respective operational effects described above are as follows. First, (H) will be described. 1 upper magnetic layer
In order to apply to an ultra-thin layer of μm or less, wet multilayer coating is necessary. The fine surface roughness is determined in relation to. In the case of needle-like ferromagnetic powder, the crystallite size generally corresponds to the minor axis diameter. If the average particle size of the inorganic powder in the lower nonmagnetic layer is less than half the crystallite size of the acicular ferromagnetic powder, the dispersion itself becomes difficult, and a smooth lower layer surface cannot be obtained. The surface smoothness of the recording medium also becomes insufficient. Conversely, when the average particle size of the lower layer inorganic powder exceeds 4 times the crystallite size of the ferromagnetic powder, the interparticle distance between the lower layer powder particles increases, so the upper layer ferromagnetic powder affects the surface properties of the lower layer. Since it receives, it cannot obtain sufficient surface property.
As shown in the examples, in order to obtain a sufficient surface property, an inorganic powder having an average particle diameter of 1/2 to 4 times, more preferably 2/3 to 2 times the crystallite size of the upper needle-like ferromagnetic powder is used. It is preferable. The shape of the inorganic powder is preferably spherical or dice. The Mohs hardness is 3 or more, preferably 4 or more, and more preferably 6 or more.

The volume filling rate of the lower layer of the inorganic powder is preferably 20 to 60%, more preferably 25 to 55%. In order to reduce the surface roughness due to the relationship between the particle size of the lower non-magnetic powder and the crystallite size of the upper ferromagnetic powder, the volume packing ratio of the lower powder has a preferable range. If the 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 upper layer ferromagnetic powder is present in the lower layer. It will also be mixed in and the surface will become very rough. In addition, the squareness ratio is also reduced. Further, when the volume filling rate is 60% or more, the viscosity of the dispersion becomes extremely high, and it becomes substantially impossible to apply the dispersion.
Even if it is applied, it causes problems such as powder falling in terms of running durability. Further, 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.
Further, since it is possible to expect a known effect (for example, to reduce the surface electric resistance) by adding carbon black, it is preferable to use it in combination with the above inorganic powder, but carbon black has very poor dispersibility. ,
Carbon black alone cannot secure sufficient electromagnetic conversion characteristics. In order to obtain good dispersibility, it is necessary to select 60% by weight or more from metal oxides, metals and alkaline earth metal salts. When the inorganic powder is less than 60% by weight of the non-magnetic powder and the carbon black is 40% or more of the non-magnetic powder, the dispersibility becomes insufficient and desired electromagnetic conversion characteristics cannot be obtained.

Next, (I) will be described below. In order to maintain good electromagnetic characteristics in wet multilayer coating, it is necessary to increase the squareness ratio.However, if the average particle size of the inorganic powder in the lower nonmagnetic layer is larger than that of the upper ferromagnetic powder, the gap between the lower particles is large. And the orientation of the ferromagnetic powder is disturbed particularly at the interface between the upper layer and the lower layer, thereby deteriorating the surface properties of the magnetic layer as in (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 orientation of the ferromagnetic powder so that the orientation is not disturbed. As a result of confirming experimentally the requirements therefor, it is found that the squareness ratio becomes equivalent to that of the single-layer magnetic layer in the case of needle-like ferromagnetic powder, 1/3 or less of the major axis length, more preferably 1/3 to 1 / When 20 inorganic powders are used, good surface property and squareness ratio can be obtained.

In (J), when hexagonal plate-shaped ferromagnetic powder is used in the same way as above instead of the needle-shaped ferromagnetic powder, the powder is oriented in the vertical direction, the disturbance at the interface is reduced, and the squareness ratio is increased. be able to. The inorganic powder used for the lower layer is
The plate diameter or less, more preferably from the plate diameter or less to 1 / the plate diameter
It is preferably 5 or more. In (I) and (J),
For the same reason as in (H), the volume filling rate in the lower layer of the inorganic powder is preferably 20 to 60%.

When the thickness of the magnetic layer is 5 times or less the major axis length, the filling degree 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 (H).

Next, (K) will be described. Lower layer non-magnetic
Oxidation on the surface of the inorganic powder contained in the layer
Preferably, the material is Al₂O₃, SiO₂, TiO
₂, ZrO₂, SnO₂, Sb₂O ₃, ZnO, etc. are preferred
And more preferably Al₂O₃, SiO₂, ZrO
₂Is. These may be used in combination,
It can be used alone. Also, coprecipitate according to the purpose.
Surface treatment tank may be used.
After that, its surface is treated with silica, and vice versa
You can also take Also, the surface treatment layer can be used according to the purpose.
It may be a porous layer, but it is better if it is homogeneous and dense.
Generally preferred.

For example, the surface treatment of the non-magnetic inorganic powder is
After the dry pulverization of the non-magnetic inorganic powder material, water and a dispersant are added, wet pulverization and centrifugation are performed for coarse particle classification. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al,
An aqueous salt solution of Si, Ti, Zr, Sb, Sn, Zn or the like is added, and an acid or alkali for neutralizing the same is added,
The surface of the inorganic powder particles is coated with the produced hydrous oxide.
By-produced water-soluble salts are removed by decantation, filtration and washing, and finally the slurry pH is adjusted and filtered,
Wash with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product. Also,
Not only water-based but also AlCl ₃ and SiCl ₄ vapors are passed through the non-magnetic inorganic powder, and then steam is introduced to feed Al, S
It is also possible to perform i surface treatment.

For other surface treatment methods, see “Charac
terization of Powder Surfaces ", Academic Press can be referred to. In this embodiment, the magnetic layer surface roughness is defined by defining the optimum thickness range of the magnetic layer according to the recording wavelength and the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer (that is, the variation width in the thickness direction of the interface). Is defined and improved, and the thickness of the magnetic layer is made thin, uniform, and uniform, so that even if the recording wavelength becomes short, reproduction output fluctuation and amplitude modulation noise can be prevented, and high reproduction output and high C / N can be achieved. Can be realized. In other words, conventionally, when the magnetic layer becomes thinner, when the recording wavelength becomes shorter, the entire layer of the magnetic layer contributes to recording / reproduction. Therefore, when the thickness of the magnetic layer fluctuates, fluctuations in reproduction output and amplitude modulation noise were observed. The present invention has solved this drawback.

In the present invention, the shortest recording wavelength λ varies depending on the type of the magnetic recording medium.
5 μm and 0.67 μm for digital audio. The range of the thickness d of the magnetic layer of the present invention is λ / 4 ≦ d ≦
3λ, preferably λ / 4 ≦ d ≦ 2λ (ie, 0.25
≦ d / λ ≦ 2). The average thickness d of the magnetic layer of the present invention is usually in the range of 0.05 μm ≦ d ≦ 1 μm, preferably 0.05 μm ≦ d ≦ 0.8 μm.

The thickness of the magnetic layer can be determined by actual measurement as described above. For elements specifically contained in the magnetic layer by X-ray fluorescence, a magnetic layer sample having a known thickness is measured, and a calibration curve is prepared. Next, the thickness of the sample of the unknown material can be determined from the intensity of the fluorescent X-ray. According to the present invention, the uniformity of the magnetic layer thickness is ensured and the surface roughness Ra is Ra ≦ λ / 5.
0, that is, λ / Ra can be regulated to 50 or more, preferably 75 or more, and more preferably 80 or more. Also,
In the present invention, Ra indicates a value obtained by measuring the center line average roughness measured using an optical interference roughness meter.

In the present invention, it cannot be said that the thickness of the magnetic layer needs to be simply reduced, and the present inventors have found that there is an optimum range for the shortest recording wavelength λ. That is, when the thickness of the magnetic layer is smaller than λ / 4, the magnetic flux that contributes to reproduction is reduced and the output is reduced. In addition, since the short wavelength component is demagnetized by the deep recording magnetic field of the component having a long recording wavelength and simultaneously recorded when exceeding 3λ, the output is reduced. Therefore, d ≦ 3λ, and preferably d ≦ 2λ.

When the C / N, which is the basic performance of the medium, is taken into consideration, in addition to the unevenness (so-called surface roughness) on the surface of the magnetic layer which has been a problem in the conventional thick film magnetic layer, the non-magnetic layer is used. And the thickness variation at the interface of the magnetic layer becomes a problem. This is because when the magnetic layer thickness d is in the range of λ / 4 ≦ d ≦ 3λ, the reproduction output is influenced by the magnetic flux amount of the entire magnetic layer. That is, it was not a problem in the conventional thick magnetic layer. The present invention has found that, with respect to this problem, the average value Δd of the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer is required to be 1/2 or less of the magnetic layer thickness d. Also,
The surface roughness of the magnetic layer is required to be as smooth as the conventional thick film magnetic layer, and the surface roughness Ra is Ra ≦ λ / 5.
It is necessary to satisfy the relationship of 0. According to the present invention, processing in a vacuum is premised, there is no problem of productivity and reliability of the metal thin film medium which is vulnerable to corrosion, and the electromagnetic conversion characteristics are comparable to those of the metal thin film, and the high performance coating which is excellent in productivity. Type magnetic recording medium can be obtained.

The second preferred main technique and characteristic of the present invention will be described in more detail. That is, there is a relation of 30 ≦ d / R _rms between the root-mean-square roughness R _{rms of the} surface of the magnetic layer by the scanning tunneling microscope (STM) method and the dry thickness average value d of the magnetic layer. . If the thickness of the magnetic layer becomes thinner, the self-demagnetization loss should be reduced and the output should be improved. growing. In order to improve the output by reducing the self-demagnetization loss, it is preferable to use the surface roughness by STM which satisfies the above equation. R _rms by AFM is preferably 10 nm or less. It is preferable that the optical 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 250 to 400% after calendering.

The third preferred main technique and characteristic of the present invention will be described in more detail. That is,
The ferromagnetic powder contained in the upper magnetic layer has a major axis length of 0.
Preferably, it is a needle-like ferromagnetic alloy powder having a thickness of 3 μm or less and Hc of 1500 Oe or more, or a plate-like ferromagnetic powder having a plate diameter of 0.3 μm or less and having a Hc of 1000 Oe or more.

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

As described above, the present invention relates to the main technique of the present invention and the fourth characteristic (filling ratio of upper and lower coating layers and film strength), which improves the head contact of the magnetic recording medium and particularly in short wavelength recording. In order to improve the electromagnetic conversion characteristics, the ratio SMD / STD of the application direction stayness SMD of the magnetic recording medium to the application direction (longitudinal direction) widthwise direction STD of the magnetic recording medium is 1.0 to 1.9 as described above.
It is related to the characteristic of being. In order to set the stiffness to the above value, the inorganic powder contained in the lower nonmagnetic layer has a Mohs hardness of 6 or more and an average particle size of 0.1 or less.
This is a technique of using a polyhedral inorganic powder having a spherical shape and a cubic shape of 5 μm or less.

Further, the preferred main technique and fourth characteristic of the present invention will be further supplemented and described. The thermal shrinkage of the magnetic recording medium at 80 ° C. for 30 minutes is 0.4% or less. Specifically, the dry thickness of the lower non-magnetic layer is 1% of the dry thickness of the upper magnetic layer And a 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%.

A granular material in which the ferromagnetic powder contained in the upper magnetic layer has a crystallite size of 300 angstroms or less and the average particle size of the inorganic powder contained in the lower nonmagnetic layer is less than 0.15 μm, or Needle-like material having an average major axis diameter of less than 0.6 μm, and the inorganic powder contained in the lower nonmagnetic layer is titanium oxide, barium sulfate, calcium carbonate, strontium sulfate, silica, alumina, zinc oxide, α-iron oxide At least one selected from
The lower non-magnetic layer has an average particle size of 30 μm or less and a DBP oil absorption of 30 to 300 ml / 10
0 g, specific surface area by BET method is 150-400 m ²
/ G of carbon black is contained as a second component in a ratio of less than 50 parts by weight with respect to 100 parts by weight of the inorganic powder.

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

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

In 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 controlled to be 1 to 30 times, preferably 2 to 20 times the dry thickness of the upper magnetic layer, and the expansion / contraction of the magnetic recording medium is controlled by the film strength of the lower and upper layers. Is mentioned. If the thickness ratio is 1 or less, it is not possible to prevent an increase in the heat shrinkage ratio due to strength deterioration due to making the magnetic layer fine particles. On the other hand, if the thickness ratio is 30 times or more, the coating thickness becomes thicker, so that the residual solvent increases and the film is plasticized.

As means for adjusting the film strength of the lower layer and the upper layer, the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is -5% to + 20%, preferably Controlling in the range of 0 to 15% can be mentioned. Here, if it is -5% or less, it is not possible to suppress an increase in the heat shrinkage rate of the magnetic layer, and if it is increased by 20% or more, the medium itself becomes too hard and powder is often dropped, which is not preferable.

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

In this embodiment, as a preferable embodiment, for example, as a particle size of the ferromagnetic powder, the crystallite size is 300 Å or less, preferably 100 to 250 Å,
The average major axis diameter is 0.005 to 0.4 μm, preferably 0.1.
The average major axis diameter / crystallite size is in the range of 3 to 25, preferably 5 to 20. It expressed a ferromagnetic powder in the specific surface area by the BET method was 25~80m ² / g, preferably 30 to 70 m ²
/ G. Below 25 m ² / g, the noise increases,
If it is 80 m ² / g or more, it is difficult to obtain surface properties, which is not preferable.

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

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

This carbon black is less than 50 parts by weight, preferably 13 parts by weight, based on 100 parts by weight of the above inorganic powder.
It is preferably added to the lower layer in a proportion of about 40 parts by weight. The carbon black is an antistatic agent for magnetic recording media,
It is also used for controlling the powder volume ratio of the lower layer by controlling the porosity, in addition to the function of strengthening the film strength.
That is, when the porosity is high, the powder volume ratio is relatively reduced. It is effective to use carbon black having a structure or hollow carbon black as the carbon black for controlling the porosity. The porosity of the lower layer is preferably within the range of the porosity of the upper layer ± 10%.
The porosity of the lower layer is preferably in the range of 10 to 30%.

Further, the fifth preferred main technology and characteristics of the present invention will be described in more detail. That is,
The fifth of the preferred main technologies and characteristics of the present invention relates to durability. The Young's modulus of the magnetic recording medium of the present invention measured by a tensile tester is 300 to 2000 Kg / m.
m ² , preferably 400 to 1500 Kg / mm ² , and the Young's modulus of the magnetic layer is 400 to 5000 Kg / m 2.
m ² , preferably 500 to 4000 Kg / mm ² , yield stress 3 to 20 Kg / mm ² , preferably 4 to 18 Kg
/ Mm ² , yield elongation 0.2 to 8%, preferably 0.5
It is desirable to be ˜5%.

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

This is mainly related to the support and is important for ensuring durability. The crack elongation of the magnetic recording medium of the present invention measured at 23 ° C. and 70% RH is preferably 20% or less. The Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium of the present invention measured using an X-ray photoelectron spectrometer is preferably 0.3 to 0.6, and the N / Fe spectrum β is preferably 0.1 to 0.6. 03 to 0.12.

This is related to the ferromagnetic powder, the inorganic powder and the binder, and is important in obtaining durability. Further, the glass transition temperature Tg of the magnetic layer of the magnetic recording medium of the present invention measured by using a dynamic viscoelasticity measuring device (the maximum point of the loss elastic modulus of the dynamic viscoelasticity measured at 110 Hz) is preferably 40. １２０120 ° C., and the storage elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / c.
m ² and the loss elastic modulus E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² . The loss tangent is preferably 0.2 or less. If the loss tangent is too large, sticking failure tends to occur. These are important properties associated with durability, associated with binders, carbon black, and solvents.

It is preferable that the 180 ° adhesive strength of the 8-mm wide tape at 23 ° C. and 70% RH between the flexible support and the magnetic layer is preferably 10 g or more. Further, the abrasion of the steel balls at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.7 × 10 ^{−7 to} 5 × 10 ⁻⁷ m ³ . This is a measure of the durability that is directly related to the wear of the magnetic layer and is mainly associated with the ferromagnetic powder.

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

The residual solvent of the magnetic recording medium of the present invention measured by gas chromatography is preferably 50 mg / m ² or less. The residual solvent contained in the upper layer is preferably 2
It is 0 mg / m ² or less, more preferably 10 mg / m ² or less, and it is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer.

The sol fraction, which is the ratio of the soluble solid content extracted from the magnetic recording medium of the present invention using THF to the weight of the magnetic layer, is preferably 15% or less.
It is influenced by the ferromagnetic powder and the binder and is a measure of durability. In the magnetic recording medium of the present invention, short-wavelength recording of 1 MHz is performed on the upper magnetic layer, magnetically developed using a ferricolloid, and recorded using a differential interference microscope.
It is preferable that there are no more than 5 continuous black or white lines in the sample having a width of 5 mm observed at double magnification.

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

These contact angles are values particularly determined by the lubricant and dispersant. The surface free energy of the magnetic layer and the back layer of the magnetic recording medium of the present invention is 10 to 100 dyes.
n / cm is particularly preferred. The surface electric resistance of the magnetic recording medium of the present invention is 1 × 1 on both the magnetic layer surface and the back layer surface.
It is preferably 0 ⁹ Ω / sq or less, particularly preferably 1 × 10 ⁸ Ω / sq or less.

The general items that can be selected by the present invention will be described below.
I will describe. The non-magnetic inorganic powder that can be used in the present invention,
For example, metal, metal oxide, metal carbonate, metal sulfate,
Non-magnetic inorganic substances such as metal nitrides, metal carbides, and metal sulfides
A powder is mentioned. Specifically, TiO₂(Rutile, Anna
Tase), TiO_X, Cerium oxide, tin oxide, oxide
Nungsten, ZnO, ZrO₂, SiO₂, Cr
₂O ₃, Α-alumina, β-aluminum with α conversion rate of 90% or more
Na, γ-alumina, α-iron oxide, goethite, corundum,
Silicon nitride, titanium carbide, magnesium oxide, nitriding
Boron, molybdenum sulfide, copper oxide, MgCO₃, CaC
O₃, BaCO₃, SrCO₃, BaSO_Four, Silicon carbide
Element, titanium carbide, etc. are used alone or in combination.
It The shape and size of these inorganic powders are arbitrary,
These were combined with different inorganic powders as needed
It is also possible to select the particle size distribution etc. even with a single non-magnetic powder.
it can.

The particle size is preferably based on the specific methods (A) to (K) above, but is generally 0.01 to 0.7 μm in the case of granular, spherical or polyhedral. , It is preferable to set it to １ ／ or less of the shortest recording wavelength λ. In the case of needles or plates, the major axis length is 0.05 to 1.0
μm, preferably 0.05 to 0.5 and an acicular ratio of 5 to 2
0, preferably 5 to 15, or a plate diameter of 0.05 to 1.
0 μm, preferably 0.05 to 0.5 μm, and a plate ratio (ratio between plate diameter and thickness) of 5 to 20, preferably 10 to 20.
What 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. Water content is 0.1-5%, preferably 0.2-3%. The pH is preferably 2 to 11, more preferably 4 to 10. The specific surface area is 1 to 100 m ² / g, preferably 5 to 70 m ² / g, and more preferably 7 to 50 m ² / g.
Is. The crystallite size is preferably 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 amount of SA (stearic acid) adsorbed is 1 to 20 μmol / m ² , and more preferably ² to 15 μmol / m ² . The roughness factor of the powder surface is preferably 0.8 to 1.5, more preferably ² to 15 μmol / m ² . The heat of wetting with water at 25 ° C. is preferably 200 erg / cm ^{2 to} 600 erg / cm ² . In addition, a solvent having a heat of wetting in this range can be used. The amount of water molecules on the surface at 100 to 400 ° C is appropriately 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. Specific gravity is 1
-12, preferably 3-6.

The above inorganic powder does not necessarily have to be 100% pure, and its surface may be treated with other compounds such as Al, Si, Ti, Zr, Sn, Sb and Zn depending on the purpose. , Those oxides may be formed on the surface. At that 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, Sumitomo Chemical Co., Ltd. AKP-20, AKP-30, AKP
-50, HIT-55, HIT-100, ZA-G1,
Nippon Kagaku Kogyo G5, G7, S-1, Toda Kogyo T
F-100, TF-120, TF-140, R516,
Ishihara Sangyo Co., Ltd. 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, Titanium Industry Co., Ltd. ECT-52, STT
-4D, STT-30D, STT-30, STT-65
C, Mitsubishi Materials T-1 and Nippon Shokubai NS-
O, NS-3Y, NS-8Y, MT-100 manufactured by Teika
S, MT-100T, MT-150W, MT-500
B, MT-600B, MT-100E, FI made by Sakai Chemical Co., Ltd.
NEX-25, BF-1, BF-10, BF-20, B
F-1L, BF-10P, Dowa Kogyo DEFIC-
Y, DEFIC-R, Y-LOP manufactured by Titanium Industry Co., Ltd. and a product obtained by firing the same.

The nonmagnetic inorganic powder used in the present invention is particularly preferably titanium oxide (particularly titanium dioxide). Hereinafter, the method for producing this titanium oxide will be described in detail. Titanium oxide is mainly produced by a sulfuric acid method and a chlorine method. In the sulfuric acid method, a raw ore of illuminite is distilled with sulfuric acid to extract Ti, Fe, etc. as sulfates. Iron sulfate is crystallized and removed, and the remaining titanyl sulfate solution is filtered and purified, and then thermally hydrolyzed to precipitate hydrous titanium oxide. After filtering and washing this,
After removing contaminants by washing and adding a particle size regulator etc.,
If it is fired at 80 to 1000 ° C., it becomes crude titanium oxide. The rutile type and the anatase type are classified according to the kind of core material added during hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. For the chlorine method, natural ore natural rutile and synthetic rutile are used. Ore is chlorinated in a high temperature reduced state, Ti for TiCl ₄ and Fe for FeCl ₂
And the iron oxide that became solid by cooling is liquid TiC.
Separated from l ₄ . The crude TiCl ₄ obtained is purified by rectification, then a nucleating agent is added, and the crude TiCl ₄ is instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher 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 R _S (surface electric resistance), which is a known effect, can be lowered. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the carbon black. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400, DBP oil absorption is 20-400 ml / 10
It is 0 g, preferably 30 to 200 ml / 100 g.
The average particle size is 5 m-80 m, preferably 10-50 m
μ, and more preferably 10 to 40 mμ. pH is 2
10, water content 0.1 ~ 10%, tap density 0.1 ~
1 g / cc is preferred.

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

The carbon black that can be used in the present invention is
For example, (“Carbon Black Handbook”, edited by Carbon Black Association) can be referred to. The non-magnetic organic powder used in the present invention is an acrylic styrene resin powder,
Examples thereof include benzoguanamine resin powder, melamine-based resin powder, and phthalocyanine-based pigment, and polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluorinated ethylene resin powder are used. The manufacturing method is disclosed in JP-A-62-18564.
Nos. 60-255827 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.
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 adhesiveness between the underlayer and the support.

The ferromagnetic powder used in the magnetic layer of the present invention includes magnetic iron oxide FeOx (x = 1.33 to 1.5), C
Known ferromagnetic powders such as o-modified FeOx (x = 1.33 to 1.5), ferromagnetic alloy powder containing Fe or Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used. Further, ferromagnetic alloy powder is more preferable. These ferromagnetic powders include Al, Si, S, Sc, Ti, V, Cr, Cu,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hg, Pb, Bi, La,
Ce, Pr, Nd, P, Co, Mn, Zn, Ni, S
It may contain atoms such as r and B. These ferromagnetic powders include the dispersant, lubricant, surfactant, and
Treatment with an antistatic agent or the like may be performed before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062,
Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466
No., JP-B-46-38755, JP-B-47-4286
No. 4, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-1728
No. 4, JP-B-47-18509, JP-B-47-185
No. 73, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-39
Nos. 639 and 3032615 and 30313.
No. 41, No. 3100194, No. 3242005, No. 3389014.

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

The ferromagnetic powder of the upper magnetic layer of the present invention was
The specific surface area according to the method is 25 to 80 m ² / g,
It is preferably 40 to 70 m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, surface properties are 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 100Å, preferably 350 to 100Å. Σ _{S of the} iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu / g or more, and in the case of the ferromagnetic metal powder, 100 emu / g or more is preferable, and 110 emu / g to 170 e is more preferable.
mu / g. Coercive force is 1100 Oe or more, 2500
It is preferably Oe or less, and more preferably 1400 Oe or more and 2000 Oe or less. The acicular ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.

The r1500 of the ferromagnetic powder is preferably 1.5 or less. More preferably r1500 is 1.
It is 0 or less. The r1500 indicates the percentage of the amount of magnetization remaining without being reversed when a magnetic field of 1500 Oe is applied in the opposite direction after saturation magnetization of the magnetic recording medium. The water content of the ferromagnetic powder is preferably 0.01 to 2%.
It is preferable to optimize the water content of the ferromagnetic powder depending on the type of binder. The tap density of γ-iron oxide is 0.5g / cc
The above is preferable, and 0.8 g / cc or more is more preferable. In the case of alloy powder, 0.2 to 0.8 g / cc is preferable, and if it is used at 0.8 g / cc or more, oxidation easily proceeds in the consolidation process of the ferromagnetic powder, and sufficient saturation magnetization (σ _S ) can be obtained. Becomes difficult. If it is 0.2 cc / g or less, the dispersion tends to be insufficient.

When γ iron oxide is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, and more preferably 5 to 10%. The amount of cobalt atom to iron atom is 0 to 15%, preferably 2 to 8%.
The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4-12,
It is preferably 6 to 10. Ferromagnetic powder, if necessary,
The surface treatment may be performed with Al, Si, P or an oxide thereof. The amount is 0.1 with respect to the ferromagnetic powder.
It is preferably 10%, and when the surface treatment is performed, adsorption of a lubricant such as fatty acid is 100 mg / m ² or less, which is preferable. The ferromagnetic powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 500 ppm or less, the characteristics are not particularly affected.

The ferromagnetic powder used in the present invention preferably has few voids, and the value is 20% by volume or less, more preferably 5% by volume or less. The shape is selected from needle-like, granular, rice-like, plate-like or the like so as to satisfy the above-mentioned conditions. SFD of ferromagnetic powder 0.6
In order to achieve the following, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For that purpose, there are methods such as improving the particle size distribution of goethite, preventing the sintering of γ-hematite, and slowing the deposition rate of cobalt for cobalt-modified iron oxide as compared with the conventional method.

In the present invention, a hexagonal plate-like ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate is exemplified by plate-like hexagonal ferrite, and barium ferrite, strontium ferrite, lead ferrite, calcium ferrite Hexagonal Co powder such as each substitution product and Co substitution product can be used. Specific examples include magnetobranbite-type barium ferrite and strontium ferrite, and magnetobranvite-type barium ferrite and strontium ferrite containing a part of a spinel phase.
Particularly preferred are barium ferrite and strontium ferrite substitutes. In addition, in order to control the coercive force, Co--Ti, C is added to the hexagonal ferrite.
o-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
A material to which an element such as n or Ir-Zn is added can be used.

When barium ferrite is used, the plate diameter means the plate width of hexagonal plate-like particles and is measured by using an electron microscope. In the present invention, the plate diameter is 0.001 to 1 μm.
In m, the plate thickness may be ½ to 1/20 of the diameter. The specific surface area (S _BET ) is preferably 1 to 60 m ² / g, and the specific gravity is preferably 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 -1.
00 to 150 ° C, number average molecular weight of 1000 to 20000
0, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, a phenol resin, an epoxy resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer,
Examples thereof include a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like.

[0122] These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the lower layer or the upper layer. These examples and the manufacturing method thereof are described in detail in JP-A-62-256219.

The above resins may be used alone or in combination, but are preferably selected from the group of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. Examples thereof include a combination of at least one of the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all of the binders shown here, in order to obtain better dispersibility and durability, -COO is added as necessary.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM 1)
(OM ₂ ), -OP = O (OM ₁ ) (OM ₂ ), -NR
₄ X (where M, M ₁ and M ₂ are H, Li, Na,
K, -NR _4, shows a -NHR _3, R represents an alkyl group or H, X is a halogen atom. ), OH, N
R ₂ , N ⁺ R ₃ , (R is a hydrocarbon group), epoxy group, S
It is preferable to use one obtained by introducing at least one or more polar groups selected from H, CN and the like by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

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

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

The content of the repeating unit having an epoxy group is lower than 1 mol%, or the repeating unit of vinyl chloride 1
The amount of the repeating unit having an epoxy group is 0.
If it is less than 01 mol, it may not be possible to effectively prevent the release of hydrochloric acid gas from the vinyl chloride-based copolymer, while on the other hand, it is higher than 30 mol% or has an epoxy group per 1 mol of vinyl chloride repeating units. When the amount of the repeating unit is more than 0.5 mol, the hardness of the vinyl chloride-based copolymer may decrease, and when 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 coalescence becomes hygroscopic and the weather resistance may deteriorate. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000.

The vinyl chloride copolymer having such an epoxy group and a specific polar group can be produced, for example, as follows. E.g., having an epoxy group, in the production of -SO ₃ Na and is introduced in which vinyl copolymer chloride polymer as the polar group, a reactive double bond, and -SO ₃ Na as a polar group 2 Sodium (meth) acrylamido-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 under pressure at 100 ° C. 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. In addition to 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonic acid and sodium or potassium salt, (anhydrous) maleic acid and Examples thereof include (meth) acrylic acid and (meth) acrylic acid-2-phosphate ester.

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

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

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

Specific examples of these binders used in the present invention are Union Carbide: VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku: 100
0W, DX80, DX81, DX82, DX83, 10
0FD, manufactured by Zeon Corporation: MR105, MR110, M
R100, 400X110A, made by Nippon Polyurethane Company:
Nipporan N2301, N2302, N2304, Dainippon Ink and Chemicals: Pandex T-5105, T-R30
80, T-5201, Burnock D-400, D-21
0-80, Crisbon 6109, 7209, Toyobo Co., Ltd .: 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, Mitsubishi Kasei: MX5004, Sanyo Kasei: Sampren SP-150, 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. When a vinyl chloride resin is used, it is preferably used in a range of 5 to 30% by weight, a polyurethane resin is used in a range of 2 to 20% by weight, and a polyisocyanate is used in a range of 2 to 20% by weight.

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

When the epoxy group-containing resin having a molecular weight of 30,000 or more is used in the present invention in an amount of 3 to 30% by weight based on the nonmagnetic powder, the resin other than the epoxy group-containing resin is added in an amount of 3 to 30% by weight based on the nonmagnetic powder. %, When using a polyurethane resin, 3 to 30% by weight and 0 to 20% by weight of polyisocyanate can be used, but the epoxy group is 4 × 10 ^{−5 with respect} to the total weight of the binder (including the curing agent). ~ 16x1
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 elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10 kg.
/ Cm ² , and the yield point is preferably 0.05 to 10 Kg / cm ² . The magnetic recording medium of the present invention comprises two layers. Therefore,
Binder amount, vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, molecular weight of each resin forming the magnetic layer, polar group amount, or the physical properties of the resin described above. Of course, it is possible to change the characteristics and the like between the lower magnetic layer and the upper magnetic layer as required.

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

As the carbon black used in the upper magnetic layer of the present invention, furnace black for rubber, thermal for rubber, black for color, acetylene black, and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, and particle diameter is 5 mμ to 300.
It is preferable that mμ, pH is 2 to 10, water content is 0.1 to 10%, and tap density is 0.1 to 1 g / cc. Specific examples of the carbon black used in the present invention include: BLACKPEARLS 2000, 130 manufactured by Cabot Corporation.
0, 1000, 900, 800, 700, VULCAN
XC-72, Asahi Carbon Co., Ltd .: # 80, # 60, # 5
5, # 50, # 35, manufactured by Mitsubishi Chemical Industries: # 2400
B, # 2300, # 900, # 1000, # 30, # 4
0, # 10B, manufactured by Conlon Via Carbon Co .: CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5 and so on. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be graphitized on a part of the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the ferromagnetic powder. Carbon black has the functions of preventing electrification of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the lower layer and the upper layer, and can be used in accordance with the purpose based on the various characteristics shown above such as particle size, oil absorption, electric conductivity, and pH. Of course, it is 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).

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

Specific examples of the polishing agent used in the present invention include: AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd .: G
5, G7, S-1, manufactured by Toda Kogyo: TF-100, TF
Examples include −140, 100ED, 140ED and the like.
It is of course possible to use the abrasives used in the present invention by changing the type, amount and combination of the lower layer and the upper layer, and selectively using them according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

As the additive used in the present invention, one having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. is used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, fluorinated graphite, silicone oil, polar group silicone, fatty acid modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Ester and its alkali metal salt, alkyl sulfate ester and its alkali metal salt,
Polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (it may contain an unsaturated bond or may be branched), and these metal salts ( Li, N
a, K, Cu, etc.) or monovalent with 12 to 22 carbon atoms,
Dihydric, trihydric, tetrahydric, pentahydric, hexahydric alcohol (may contain unsaturated bonds or may be branched), alkoxy alcohol 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 or divalent one having 2 to 12 carbon atoms,
Any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohol (may contain unsaturated bond or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, and a carbon number of 8 to
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 oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfonium, anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, and phosphoric acid ester group, amino acids, aminosulfonic acids, sulfuric acid of aminoalcohol, or the like. Amphoteric surfactants such as phosphoric acid esters and alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in the lower non-magnetic layer and the upper magnetic layer in different types and amounts according to need. For example, fatty acids with different melting points are used in the lower non-magnetic layer and upper magnetic layer to control bleeding to the surface, esters with different boiling points and polarities are used to control bleeding to the surface, and the amount of surfactant is adjusted. By doing so, it is considered that the stability of the coating is improved, the amount of the lubricant added is increased in the lower non-magnetic layer, and the lubricating effect is improved. Of course, the present invention is not limited to the examples shown here.

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

The organic solvent used in the present invention is any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, glycol ethers such as benzene, benzene, Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. These impurities are preferably 30% 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 addition amount may be changed. It is important to use a solvent having a high surface tension (cyclohexanone, dioxane, etc.) for the lower layer to improve the stability of the coating. Specifically, it is important that the arithmetic average value of the upper layer solvent composition does not fall below the arithmetic average value of the lower layer solvent composition. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and the solvents used for the coating liquids of the lower non-magnetic layer and the upper magnetic layer both have a solubility parameter of 8 to 11 and a dielectric constant at 20 ° C. It is preferable that 15% or more of the solvent is contained in 15% or more.

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

The flexible support used in the present invention is preferably non-magnetic, and polyethylene terephthalate,
Known films such as polyesters such as polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone, aramid, and aromatic polyamide can be used. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. In order to achieve the object of the present invention, the flexible support has a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less,
More preferably, it is necessary to use one having a size of 0.01 μm or less. Further, it is preferable that these flexible supports have not only a small center line average surface roughness but also no large protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates of Ca, Si, Ti, and the like, as well as organic fine powders of acrylic and the like.

Further, the F of the flexible support in the tape running direction is
The -5 value is preferably 5 to 50 kg / mm.², Tape width
F-5 value in the direction is preferably 3 to 30 Kg / mm²so
Yes, the F-5 value in the tape longitudinal direction is the F-5 value in the tape width direction.
It is generally higher than 5 values, but especially strength in the width direction
This is not the case when it needs to be raised. Also possible
100 ° C 3 in the tape running direction and width direction of the flexible support
The heat shrinkage at 0 minutes is preferably 3% or less, more preferably
Less than 1.5%, heat shrinkage at 80 ° C for 30 minutes is preferable
It is preferably 1% or less, more preferably 0.5% or less.
Breaking strength is 5 to 100 kg / mm in both directions², Elastic modulus
Is 100 to 2000 kg / mm ²Is preferred.

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

In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but a strong kneading force such as a continuous kneader or a pressure kneader is used in the kneading step. The high Br of the magnetic recording medium of the present invention can be obtained by using the material having the same. In the case of using a continuous kneader or a pressure kneader, all or part of the ferromagnetic powder and the binder (however, 30% by weight or more of the total binder is preferable) and the ferromagnetic powder 100.
Kneading is performed in the range of 15 to 500 parts per part. For details of these kneading treatments, see JP-A-1-106338.
And JP-A-64-79274. Further, when preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads and metal beads are suitable.

In the present invention, the production can be performed more efficiently by using the simultaneous multilayer coating method as disclosed in JP-A-62-212933. The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. The lower layer is first coated by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for coating a magnetic coating, and when the lower layer is in a wet state, Japanese Examined Patent Publication No. 1-46186 or JP-A-60-46186. -23
The upper layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-A-8179 and JP-A-2-265672. 2. JP-A-63-88080, JP-A-2-17921
No. 2, JP-A-2-265672, the upper layer and the lower layer are coated almost simultaneously by one coating head having two slits for passing the coating liquid therein. 3. The upper layer and the lower layer are coated almost at the same time by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to aggregation of the ferromagnetic powder, JP-A-62-95174 and JP-A-1-23
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in No. 6968. Further, regarding the viscosity of the coating liquid, Japanese Patent Application No. 1-312659
It is preferable to satisfy the numerical range disclosed in the publication.

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

FIG. 2 is an explanatory view showing an example of a sequential coating method used for coating both the upper and lower layers according to an embodiment of the present invention, and shows the flexibility of a continuously running polyethylene terephthalate or the like. The lower layer coating liquid 2 is applied to the support 1 by a roller coating type coating machine 3, and immediately thereafter, the coating surface is smoothed by a smoothing roll 4.
While the lower coating film composed of is in a wet state, an upper coating liquid 5 is applied by an extrusion coating machine 6 disposed further downstream to form an upper coating layer.

FIG. 3 is an explanatory view showing one example of an extrusion type simultaneous multiple coating method preferably used for coating both upper and lower layers according to another embodiment of the present invention. The running direction is reversed,
The lower layer coating liquid 2 is formed on the supported flexible support 1 by using an extrusion type simultaneous multiple coating machine 8.
And the coating solution 5 for the upper layer are simultaneously applied to form both upper and lower layers. After applying both layers, magnetic field orientation, drying and smoothing treatment are performed to obtain a magnetic recording medium.

In order to obtain the medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1000 G (Gauss) or more and a cobalt magnet of 2000 G or more in combination, and it is preferable to further provide an appropriate drying step in advance before orientation so that the orientation after drying becomes the highest.
Further, when the present invention is applied to the disk medium, an alignment method that randomizes the alignment is required.

Furthermore, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, it is also possible to perform processing by using metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the speed is 20 m / min.
The range is 700 m / min. The effects of the present invention can be further enhanced with a linear pressure of 300 kg / cm 2 or more at a temperature of 80 ° C. or more.

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

The porosity of the upper and lower layers is preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, the running durability is often preferable when the porosity is large. 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 with KOe, the squareness ratio in the tape running direction is 0.
It is 70 or more, preferably 0.80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less.

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

[0163]

EXAMPLES Next, the present invention will be described more specifically by showing Examples and Comparative Examples. In each example, "part" means "part by weight" unless otherwise specified.

Example 1 A coating solution for the lower non-magnetic layer and a coating solution for the upper magnetic layer were prepared according to the following formulation. Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area by BET method 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 Carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts-N (CH ₃ ) Composition ratio 86: 13: 1 polymerization degree 400 polyester polyurethane resin 5 parts containing 5 × 10 ⁻⁶ eq / g of polar group of ₃ ⁺ Cl ⁻ neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g butyl stearate 1 part 1 part of methyl ethyl stearate Ton 200 parts the upper magnetic layer (a) a ferromagnetic metal powder composition Fe / Zn / Ni = 92/ 4/4 100 parts Hc 1600 Oe BET method specific by surface area 60 m ² / g Crystallite size 195Å average major axis length 0.20μm , Acicular ratio 10 saturation magnetization (σ _S ): 130 emu / g vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, 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 0.3 μm) 2 parts Carbon black (average particle size 0.10 μm ) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, each component is continuously kneaded. After kneading with a dough, it was dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The resulting lower non-magnetic layer coating solution was dried to a thickness of 2 μm, and immediately thereafter, a 7 μm-thick layer was formed thereon so that the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multi-layer coating on a polyethylene terephthalate support with a center average surface roughness of 0.01 μm, orientation with a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss while both layers are still wet After drying, the treatment was performed at a temperature of 90 ° C. using a seven-stage calender composed of only metal rolls, and slit to a width of 8 mm to produce an 8-mm video tape of Example 1-1.

Similarly, by changing the factors described in Tables 1 and 2, the samples, Examples 1-2 to 1-7 and Comparative Examples 1-1 to 1--1
Created 4. In addition, samples of Examples 1 to 8 were prepared using the following coating materials as the upper magnetic layer. Upper magnetic layer (b) Ferromagnetic metal fine powder composition BaFe (barium ferrite) 100 parts Hc 2400 Oe BET specific surface area 45 m ² / g particle size 0.030 μm, plate ratio 5 vinyl chloride copolymer 12 parts -SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ⁻⁴ eq / G content α-alumina (average particle size 0.3 μm) 5 parts Carbon black (average particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts The above sample was evaluated, and the results are shown. Are shown in Tables 1 and 2. SMD, STD, Stiffness ratio Using a loop stiffener tester manufactured by Toyo Seiki, a sample with a width of 8 mm and a length of 50 mm is cut out for SMD and STD, and this is used as a ring, and the displacement speed in the inner diameter direction is 3.5 mm /
Each force required to give a displacement of 5 mm in seconds is SMD in mg,
The stiffness ratio SMD / STD was determined by determining STD. Envelope flatness A FUJIX8 8mm VCR made by Fuji Photo Film Co. was used to record a 7MHz signal, and when this signal was reproduced, the 7MHz signal reproduction output was observed with an oscilloscope.
Expressed by the difference between the maximum output and the minimum output in the field. 7 MHz Output A 7 MHz signal was recorded using a FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The contrast is 8 mm tape SAG made by Fuji Photo Film Co., Ltd.
It is P6-120. C / N ratio A FUJIX8 8mm VCR made by Fuji Photo Film Co., Ltd. was used to record a 7MHz signal, the noise generated at 6MHz when this signal was reproduced was measured with a spectrum analyzer, and the ratio of the reproduced signal to this noise was measured. did. Running Durability Measurement Method A sample was used at 23 ° C. and 70% RH in an atmosphere of Fuji Photo Film Co., Ltd. 8 mm biodecks FUJIX8 10 units for P6-1.
20 was run 100 times. During that time, the output reduction was measured.

○: Output drop within 2 dB Δ: Output drop: 2 to 4 dB ×: Output drop of 4 dB or more or clogging pinhole After coating the magnetic layer and before coating the back layer, transmit the white light to the magnetic layer. Was visually observed to measure pinholes per 100 m ² . One or less is preferable per 100 m ² .

[0168]

[Table 1]

[0169]

[Table 2]

From the above table, according to the embodiment of the present invention, SMD / STD
Is controlled to 1.0 to 1.9, the head contact is improved and the envelope flatness is small as compared with the comparative example. In addition, it can be seen that the example has no coating defect and has a small σ, and thus has excellent running durability, output, and C / N. Comparative Example 1-1 has a low STD and a low SMD /
No STD is obtained, and the envelope flatness, σ, and running durability are not improved. In Comparative Example 1-2, since the inorganic powder having a large average particle size was used, a predetermined SMD / STD was not obtained, and the envelope flatness and σ were not improved. Comparative Example 1
-3 is an example in which no lower layer was provided, and a coating defect occurred on the magnetic layer, and an evaluation sample could not be obtained. In Comparative Example 1-4, since the thickness of the magnetic layer was as thick as 1.2, the electromagnetic conversion characteristics were inferior to those of the other Examples, but the envelope flatness and running durability were improved.

[0171]

INDUSTRIAL APPLICABILITY According to the present invention, a high frequency output comparable to a vapor deposition tape is obtained while being a coating type, a high output is obtained even in a short wavelength region, and excellent electromagnetic conversion characteristics are obtained.
It has remarkable effects such as excellent magnetic conversion characteristics such as reduced dropout and BER, excellent running durability and storage stability, and a magnetic recording medium with excellent productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of both upper and lower layers for explaining a method of measuring Δd of a magnetic recording medium of the present invention.

FIG. 2 is an explanatory diagram showing an example of a sequential coating method for layering 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]

 REFERENCE SIGNS LIST 1 flexible support 2 coating liquid 3 coating machine 4 smoothing roll 5 coating liquid 6 coating machine 7 backup roll 8 simultaneous multilayer coating machine

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Satoru Hayakawa 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (11)

[Claims] An at least two or more layers in which a lower nonmagnetic layer containing at least a nonmagnetic powder and a binder is provided on a flexible support, and an upper magnetic layer containing a ferromagnetic powder and a binder is provided thereon. In a magnetic recording medium having a plurality of layers, an average dry thickness (d) of the upper magnetic layer is 1.0 μm or less, and a stiffness SMD in a coating direction (longitudinal direction) of the magnetic recording medium and a width with respect to the coating direction. Stiffness S in direction
A magnetic recording medium, wherein the ratio of SMD / STD to TD is 1.0 to 1.9, and the nonmagnetic powder is an inorganic powder having a Mohs hardness of 3 or more. 2. The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the inorganic powder has a Mohs hardness of 6 or more and an average particle diameter of 0.15 μm or less from spherical to cubic polyhedral inorganic material. The magnetic recording medium according to claim 1, which is made of powder. 3. The ferromagnetic powder has a crystallite size of 300.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is Å or less. 4. The magnetic recording medium according to claim 1, wherein said nonmagnetic powder is rutile type titanium oxide. 5. The magnetic recording medium according to claim 1, wherein the upper magnetic layer is provided while the lower non-magnetic layer is in a wet state. 6. The inorganic powder of the lower non-magnetic layer,
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a spherical shape or a dice shape. 7. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is an acicular ferromagnetic alloy powder containing Fe, Ni, or Co. 8. The support according to claim 1, wherein the support is at least one selected from polyesters, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide. The magnetic recording medium according to claim 1. 9. The magnetic recording medium according to claim 1, wherein the lower non-magnetic layer contains a magnetic powder imparting thixotropic properties. 10. The Bm of said lower non-magnetic layer is 500
The magnetic recording medium according to claim 1, which has a Gaussian density or less. 11. The magnetic recording medium according to claim 1, wherein the lower nonmagnetic layer contains a magnetic powder and is not involved in recording.