JP3181038B2 - Magnetic recording medium and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having a very thin magnetic layer having a thickness of 1.0 .mu.m or less. 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 specifically, the present invention relates to a magnetic recording medium having a lower layer, and more particularly to a magnetic recording medium having improved electromagnetic conversion characteristics, running properties and durability. Further, the present invention relates to a method of manufacturing the magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a video tape, an audio tape, a magnetic disk or the like, a magnetic layer in which a ferromagnetic iron oxide, a Co-modified iron oxide, CrO ₂ , a ferromagnetic alloy powder or the like is dispersed in a binder is used. Are coated on a non-magnetic support. In recent years, the recording wavelength tends to be shortened with the increase in recording density, and the problem of thickness loss at the time of recording / reproducing, such as a decrease in output when the thickness of the magnetic layer is large, is increasing. For this reason, the thickness of the magnetic layer has been reduced. However, when the thickness of the magnetic layer is reduced to about 2 μm or less, the influence of the surface properties of the support on the surface of the magnetic layer tends to appear, and the electromagnetic conversion characteristics tend to deteriorate. .

Therefore, by providing a nonmagnetic thick lower layer on the surface of the nonmagnetic support and then providing the magnetic layer on the upper layer, the problem caused by the surface roughness of the support is eliminated and the magnetic layer is made thin. Has proposed an attempt to reduce the thickness demagnetization and achieve a high output. For example, in Japanese Patent Application Laid-Open No. Sho 62-154225, the thickness of the magnetic layer is set to 0.5
μm or less to prevent the surface resistance of the magnetic layer from becoming high, and to provide an undercoat layer between the magnetic layer and the substrate, the thickness of the undercoat layer containing the conductive fine powder being equal to or greater than the thickness of the magnetic layer. Recording media have been proposed. Also, JP-A-62-222
No. 427 discloses a support and an undercoat layer provided on the support and containing an abrasive having an average particle size of 0.5 to 3 μm, and a film thickness containing a ferromagnetic powder provided on the undercoat layer. 1μ
A magnetic recording medium provided with a magnetic layer having a thickness of not more than m has been proposed. However, since a part of the abrasive in the undercoat layer protrudes into the magnetic layer, the magnetic recording medium also has a magnetic head cleaning action. It is. In this way, the magnetic layer is thinned to achieve high-density recording, and at the same time, carbon black is included in the lower non-magnetic layer to prevent electrification, and an abrasive is added to improve cleaning characteristics and durability. are doing.

However, in the prior art, the lower magnetic layer is first coated on a non-magnetic support, dried, and then, if necessary, calendered before providing the upper magnetic layer. It is complicated and has the following problems. That is, in order to make the magnetic layer thinner, it is conceivable to reduce the amount of coating or to add a large amount of a solvent to the magnetic coating solution to reduce the concentration. When taking the former,
When the amount of application is reduced, there is not enough time for leveling after application, and drying starts, so that a problem such as an application defect, for example, a stripe or engraved pattern remains, and the yield is extremely deteriorated. If the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids,
Various adverse effects are caused, such as insufficient filling of the ferromagnetic powder, and insufficient strength of the coating film due to the large number of voids. As one means for solving these problems, as described in JP-A-63-191315, a non-magnetic layer is provided as a lower layer using a simultaneous multilayer coating method, and a magnetic coating solution having a high concentration is provided. Thin coating methods have been proposed.

In the simultaneous multi-layer coating method or the sequential wet coating method, that is, in the case of the so-called wet-on-wet coating method in which the upper layer is simultaneously or sequentially coated while the lower layer is in a wet state, various magnetic layers have already been used. Has been studied. However, even when this technique was applied to the lower non-magnetic layer, similarly good results could not be obtained. In other words, when the lower non-magnetic layer and the upper magnetic layer were provided by wet on wet, disturbance occurred at the interface between the two, causing pinholes and cissing of the magnetic layer.

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

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

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

As a means for addressing such a problem, it has been proposed to include a non-magnetic granular abrasive or filler in the undercoat layer. However, the problem with these techniques is that when a magnetic layer and a non-magnetic layer are simultaneously coated and the upper magnetic layer is oriented, a magnetic field caused by a magnetic field is used. Mixing occurs at the interface between the upper and lower layers due to the rotational movement of not only does not 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 magnetic particles in the upper layer by forming a conductive intermediate layer using graphite as non-magnetic scaly particles.
(Japanese Patent Laid-Open No. 55548/55) However, although such materials can improve the orientation, the graphite itself has no effect of reinforcing the film and is insufficient in durability. Proposals have also been made for mixing powders. Further, it has been proposed to improve the orientation of magnetic particles in an upper layer by forming a reinforcing layer using acicular oxalate as non-magnetic acicular particles. . (Special Publication 58-51
No. 327).

[0011] Although these proposals improve the orientation and ensure durability, the scale-like particles are liable to stacking during the actual production of the medium, and substances such as oxalate are difficult to disperse in the binder. It was found that the smoothness of the magnetic surface was impaired due to poor quality. Further, the magnetic recording medium is required to have a very smooth surface to reduce the spacing loss with the head in order to increase the density and output.
For this reason, the lower non-magnetic layer which is not directly exposed on the surface also has a good dispersibility as much as possible, and the necessity for smooth surface properties when simultaneous multilayer coating is performed is increasing. Further, as described above, when the thickness of the magnetic layer is reduced, the proportion of the dispersibility of the lower non-magnetic layer which contributes to the surface property when the layers are simultaneously layered is increasing. As a result of intensive studies, even if the dispersibility of only the lower layer is simply improved,
As a result of simultaneous layering, it was found that the surface became rough.

When the coercive force of the magnetic layer is low, the self-demagnetization loss is large, and the magnetic layer is not suitable for short-wavelength recording. Means that can be used for such a purpose are 0.5 μm to 5 μm between the nonmagnetic support and the magnetic layer.
It has been proposed to provide an undercoat layer of 0 μm and make the Hc of the magnetic layer 1000 Oe. (Japanese Patent Laid-Open No. 57-19853)
6) However, conventionally known techniques have the following problems to achieve this object. JP-A-57-198 mentioned above.
In the technique disclosed in U.S. Pat. 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. As a technique for improving the orientation in the simultaneous multi-layer coating, Japanese Patent Application Laid-Open No. 3-490 is disclosed.
No. 32 discloses that a layer in which carbon black is dispersed is used as a lower layer to perform multi-stage alignment. Although the interface between the upper and lower layers was sometimes disturbed and the SQ measured in the in-plane direction was high, the improvement of the residual coercive force in the normal direction of the magnetic layer, which was the object of the present invention, was insufficient.

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

A magnetic substance having a short major axis length and a small acicular ratio is less likely to be flow-oriented, so that the orientation of the magnetic substance is further reduced and sufficient electromagnetic conversion characteristics cannot be obtained. In recent years, fine particles of a magnetic material included in a magnetic layer have been advanced for higher density. By making the particles fine, the strength of the magnetic layer becomes inferior. For example, when a high tension is applied in a manufacturing process or in a video deck, the tape is elongated, and the skew (SKEW) distortion becomes large. In order to cope with this, it has been attempted to reduce the heat shrinkage of the support or increase the strength thereof, but there is a limit. In addition, when the simultaneous multi-layer coating method is adopted, the heat shrinkage ratio increases and the Skew distortion increases as compared with the sequential multi-layer coating method. This is because, in the case of sequential multilayer coating, the lower layer is hardened by calendering or curing after the lower layer is applied, so that the medium is hard to stretch and shrink, but in the simultaneous multilayer coating method, the lower layer and the upper layer are applied at once. This is because the expansion and contraction of the medium cannot be suppressed by the lower layer. JP-A-63-187418 and JP-A-63-191315 disclose inventions based on the simultaneous multi-layer coating method, but have such disadvantages.

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

As shown in JP-A-63-191315, in order to improve the head contact, it was confirmed that the lower non-magnetic layer contained no polyisocyanate.
As a result, the storage stability at high temperature and high humidity is inferior. Therefore, this method is effective in a system that does not emphasize saving, but is difficult to use in a system that emphasizes saving such as business use or data saving. JP-A-63-18741
No. 8, it is disclosed that the magnetic layer is similarly thinned to improve the electromagnetic conversion characteristics. However, in this invention, there were still some electromagnetic conversion characteristics which were insufficient. JP-A-50-8
No. 03 also discloses an invention in which a fine-grained non-magnetic pigment having a Mohs hardness of 6 or more is provided between the magnetic layer and the support. The purpose is to increase the flatness of the base.

Further, it is difficult for these methods to respond to the recent demand for a thinner magnetic recording medium due to longer time and higher density, and these methods provide excellent electromagnetic conversion characteristics and running durability. Incompatibility was inadequate. In particular, in order to improve running durability with a thin tape, it is necessary to reduce tape edge damage.
15 and JP-A-63-187418 were insufficient.

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

Also, Japanese Patent Application Laid-Open No. 62-22922 (US Pat.
No. 4916024) discloses a magnetic recording medium in which a conductive layer (intermediate layer) contains 5% to 25% of ferromagnetic powder of carbon black. This is to improve the dispersibility of carbon black,
Since the ferromagnetic powder to be added to the intermediate layer is of the same order of magnitude as that in the magnetic layer, disturbance at the interface could not be successfully prevented. Japanese Patent Application Laid-Open No. Sho 62-214524 discloses that each coating solution composition is selected so as to have mutual solubility in a solvent and a solute of each coating solution composition of a plurality of adjacent layers.
A method for manufacturing a magnetic recording medium which is applied and dried by et on wet is disclosed. However, although there is an example of a combination of an upper magnetic layer and a lower non-magnetic layer, it is an example of only a binder and suggests that carbon black is also included in the intermediate layer, but based on such disclosure, The disturbance of the interface could not be eliminated. JP-A-62-241
No. 130 (US Pat. No. 4,839,225) discloses a magnetic recording medium in which the intermediate layer contains at least one binder containing a hydroxyl group and / or an amino group and the magnetic layer contains an isocyanate compound. It is disclosed that the adhesive strength between the intermediate layer and the magnetic layer is improved by performing the bonding. It is stated that carbon black may be added to the intermediate layer and that the intermediate layer may be applied by a wet-on-wet method. However, such a disclosure could not solve the interface fluctuation.

Further, Japanese Patent Application Laid-Open No. 63-88080 (US Pat.
No. 4,854,262) discloses a coating apparatus having an improved doctor edge. Among these, there is disclosure of viscosity at a high shear rate (10 ⁴ sec ^-1 ), but it merely shows the viscosities of the upper layer liquid and the lower layer liquid, and such a disclosure cannot sufficiently suppress interface fluctuation. Was. Also JP 6
JP-A-3-146210 discloses a magnetic recording medium in which a binder of a lower magnetic layer or a non-magnetic layer is a non-curable binder and a binder of an uppermost magnetic layer is an electron beam-curable resin. I have. However, the lower non-magnetic paint is only an example containing carbon black, and the disturbance at the interface could not be solved. Japanese Patent Application Laid-Open No. 63-164022 discloses a multi-layer extrusion coating method in which a non-magnetic liquid layer having a lower viscosity than the magnetic liquid layer is formed on the front and rear wall sides of the slot in the slot of the extrusion type head. There is disclosed a method of applying a magnetic liquid to perform the following. It has been invented that a high-viscosity magnetic layer liquid is wrapped with a low-viscosity non-magnetic layer binder solution to improve high-speed thin layer coating properties, and an object of the present invention is to reduce the gap between a magnetic layer coating liquid bead and a Gieser. Such disclosure alone could not sufficiently resolve interface disturbances. Also, JP-A-63-187418 (US4863)
No. 793) discloses a magnetic recording medium in which a ferromagnetic powder contained in an upper magnetic layer has an average major axis length of less than 0.30 μm by a transmission electron microscope and a crystallite size of less than 300 ° by an X-ray diffraction method. Have been. Lower nonmagnetic layer is carbon black, graphite, is disclosed and can include a titanium oxide, and specific examples alpha-Fe ₂
A combination of 100 parts by weight of O _{3 and} 10 parts of conductive carbon is disclosed. However, since the amount of carbon used is small and the particle size of α-Fe ₂ O ₃ is not described, the disclosure of these publications could not sufficiently solve the disorder of the interface.

Further, Japanese Patent Application Laid-Open No. 63-191315 (U.S. Pat.
In S4963433, the binder in the lower layer is a thermoplastic binder, and the thickness of the lower layer is 0.5 μm in dry thickness.
m or more. Specific examples of the non-magnetic powder contained in the lower non-magnetic layer include α-Fe ₂ O ₃ 10 as described in JP-A-63-187418.
A combination of 0 parts by weight and 10 parts of conductive carbon is disclosed. However, the low carbon usage and α
Since the particle size of -fe ₂ O ₃ is not described, it has not been possible to resolve the disturbance of the interface in the disclosure of these publications.

Japanese Unexamined Patent Publication (Kokai) No. 2-254621 discloses a non-magnetic layer containing carbon black as a main component, on which a magnetic layer containing an Fe-Al ferromagnetic powder is applied by a wet-on-wet multilayer coating method. A formed magnetic recording medium is disclosed. However, an example of the lower layer is only carbon black. With this, the structural viscosity is too strong, and the disturbance of the interface cannot be solved.

Further, Japanese Patent Application Laid-Open No. 2-257424 discloses a magnetic recording medium in which a nonmagnetic layer contains a filler having an average particle size of 50 μm or more. Examples of the filler include abrasives such as carbon black, Al ₂ O ₃ , and SiC. However, a specific example is the use of only carbon black, only Al ₂ O _{3, and} only SiC, and such a combination could not solve the disorder of the interface.

Next, Japanese Patent Application Laid-Open No. 2-257425 discloses that the coefficient of dynamic friction is 0.25 or less and the surface resistivity is 1.1.
A magnetic recording medium provided with a plurality of layers of 0 × 10 ⁹ Ω / sq or less is disclosed. However, examples of the non-magnetic powder in the lower layer are only SnO _{2 and} only carbon black,
Interface turbulence could not be resolved. Also Japanese Patent Laid-Open No. 2
Japanese Unexamined Patent Application Publication No. 2602601 discloses a magnetic recording system in which a first nonmagnetic layer, a first magnetic layer, a second nonmagnetic layer, and a second magnetic layer are laminated in this order on a nonmagnetic support. A medium is disclosed. This non-magnetic layer is an example of only the binder, and the disturbance of the interface could not be solved.

Further, Japanese Patent Application Laid-Open No. 3-49032 (US Pat.
No. 051291) has a magnetic layer thickness of 1.5 μm.
A magnetic recording medium is disclosed, wherein the magnetic recording medium has a squareness ratio of 0.85 or more. This is to improve the squareness ratio by multi-stage orientation, but the lower layer is a layer using only carbon black, and the structural viscosity is too strong to solve the interface disorder.

In recent years, Hi8 tapes have been studied, and the ultimate need is to satisfy both the advantages of ME (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, double coating technology has been applied to VTR
By focusing on the signal recording mechanism, that is, the recording depth of each signal, the performance has been improved by designing the upper and lower magnetic layers that are optimal for each. The VHS double coating has realized a high output and a low noise in all the bands of luminance, color, and sound by using a two-layer structure in which ferromagnetic powders having different sizes and magnetic characteristics are used for an upper layer and a lower layer, respectively.

In the Hi8MP multilayer tape, a metal magnetic material corresponding to high-density recording is used for the upper magnetic layer, and an iron oxide magnetic material excellent in medium and low frequency characteristics is used for the lower magnetic layer.
The so-called high-grid double coating using completely different types of magnetic materials was developed, and a great improvement in image quality was achieved, such as reproduction of 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 is a limit only by the conventional techniques and ideas. Therefore, the present inventors conducted analysis and research by stepping down to the principle and mechanism of magnetic recording itself, and made intensive studies to realize high-frequency characteristics higher than that of a vapor-deposited tape.

[0030]

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

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

A fifth object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics and good runnability. In particular, the simultaneous multi-layer coating method has good surface roughness and high electromagnetic conversion characteristics. To provide a magnetic recording medium having the same. A sixth object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics, and to provide a magnetic recording medium having a small heat shrinkage and excellent long-term storage characteristics. A seventh object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics, and to provide a magnetic recording medium which has little edge damage due to repeated running and has excellent running durability. An eighth object of the present invention is to provide a method for manufacturing the above magnetic recording medium.

[0033]

As a result of intensive studies, the present inventors have found that although the conventional simultaneous multi-layer coating technique is partially based, it exceeds the limit and becomes larger as the recording becomes shorter in wavelength. And the development of a new magnetic material and high-density packing are two important points to thoroughly reduce the thickness of the magnetic layer and to increase the magnetic energy of the magnetic layer as much as possible. Was. First, the signal loss was thoroughly reduced. In magnetic recording, various "losses" occur during the recording / reproducing process. However, the present inventors have reduced the "self-demagnetization loss" which has been considered inevitable with MP (metal) tapes. I found a completely new way of thinking about improving the region characteristics. That is, the present invention has the following constitutions, whereby the above object can be achieved. (1) A magnetic material having two or more layers in which at least a lower nonmagnetic layer in which nonmagnetic powder is dispersed in a binder is provided on a support, and an upper magnetic layer in which ferromagnetic powder is dispersed in a binder is provided thereon. In the recording medium, the average dry thickness (d) of the upper magnetic layer is 1.0 μm or less, and the average thickness change (Δd) of the thickness variation at the dried interface between the upper magnetic layer and the lower nonmagnetic layer is The ferromagnetic powder contained in the upper magnetic layer and / or the nonmagnetic powder contained in the lower nonmagnetic layer has a surface of Al ₂ O ₃ , SiO _2.
A magnetic recording medium comprising at least one selected from ZrO ₂ and ZrO ₂ . (2) The ferromagnetic powder has Al ₂ O ₃ , SiO _{2 on the} surface.
And a ferromagnetic metal powder having at least one selected from the group consisting of ZrO ₂ and ZrO ₂ . (3) The non-magnetic inorganic powder contained in the lower non-magnetic layer is a non-magnetic inorganic powder having a Mohs hardness of 3 or more having at least one selected from Al ₂ O ₃ , SiO ₂ and ZrO ₂ on the surface. The magnetic recording medium according to the above (1). (4) A coating solution for a lower non-magnetic layer containing a non-magnetic powder and a binder, and a coating solution for an upper magnetic layer containing a ferromagnetic powder and a binder are respectively prepared, and the coating for the lower non-magnetic layer is formed on a support. In the method for producing a magnetic recording medium in which a liquid and a coating liquid for an upper magnetic layer are coated, the ferromagnetic powder contained in the coating liquid for the upper magnetic layer and / or the nonmagnetic powder contained in the coating liquid for the lower nonmagnetic layer have a surface Having at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO _{2. The} coating solution for the lower non-magnetic layer is applied on the support, and the obtained lower non-magnetic layer is in a wet state. The magnetic recording medium according to any one of (1) to (3), wherein the coating liquid for the upper magnetic layer is applied simultaneously or sequentially with the application of the coating liquid for the lower nonmagnetic layer. A method for producing a magnetic recording medium, comprising:

According to the present invention, the average thickness (d) of the magnetic layer of the above magnetic layer is 1.0 μm or less, and the average value (Δ
d) of 0.001 to 0.5 μm, which is an unprecedented uniform thin magnetic layer, and the self-demagnetization loss in the short wavelength region is greatly reduced. To obtain the above d and Δd,
The thixotropy of the coating solution of each of the upper magnetic layer (hereinafter, also referred to as “upper layer”) and the lower non-magnetic layer (hereinafter, also referred to as “lower layer”) is made the same or similar, and the ferromagnetic property of the upper magnetic layer is increased. Adjusting the size and shape of the powder and the size and shape of the non-magnetic powder in the lower non-magnetic layer can be mentioned.
According to the present invention, the turbulence at the interface between the upper layer and the lower layer is kept extremely low by such means, and a more uniform interface with less fluctuation can be realized, and an ultra-smooth magnetic layer surface is completed. This smooth magnetic layer surface completely eliminated "space loss" and improved high-frequency output.

According to the present invention, a high magnetic energy and a high coercive force are achieved by using a ferromagnetic powder of fine particles having both high remanence coercive force (Hr) and coercive force (Hc) for the upper magnetic layer, and ME (deposition) ) High frequency output equal to or higher than that of tape can be exhibited. The ferromagnetic powder of the magnetic layer of the present invention is densely packed. In the conventional technology, when the magnetic layer is simply made thinner, the low-frequency output decreases and the color characteristics deteriorate, but in the present invention, the particulate inorganic powder having extremely high rigidity in the thickness direction greatly enhances the filling effect by calendering. Since the high-energy ferromagnetic powder is filled at a high density, excellent medium and low band characteristics can be realized.

Further, the present invention can secure excellent durability that cannot be achieved by ME (evaporation) tape,
Shows excellent properties such as adhesion strength, steel ball wear, residual solvent, and sol fraction. As described above, the present invention is an unprecedented new layer configuration, ultra-thin layer, ultra-smooth, ultra-high filling, and innovative high-frequency characteristics that were difficult with conventional single-layer coating technology, Excellent medium and low frequency characteristics are realized.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the principle of self-demagnetization. The smaller the cross-sectional area of a magnetic layer, the smaller the loss. Therefore, in order to increase the output of short-wavelength signals, it is essential to make the magnetic layer ultra-thin. It is found that it is. Moreover, 1 μm
With the above thickness, the effect is small, and generally １ ／ of the recording wavelength.
As the effective recording thickness is approached, that is, the saturation recording is approached, the effect becomes greater. Therefore, it is necessary to make an ultrathin layer in sub-micron units.

In the conventional single-layer coating technique, it is difficult to apply a thin layer in a 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, the conventional double coating technology has been innovated, and a nonmagnetic layer containing fine-particle inorganic powder is preferably provided as a lower layer by wet on wet, and the average value Δd of the thickness variation of the magnetic layer is 0.001 to 0.
By setting the thickness to 5 μm, the epoch-making ultra-thin magnetic layer, which is difficult with the conventional technology of 1/3 to 1/10 or less of the conventional general Hi8 MP tape, reduces the self-demagnetization loss and reduces the brightness. This is a large improvement in signal output.

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

The size depends on the shape of the magnet. That is, the demagnetizing field decreases as the cross-sectional area decreases and the distance between the magnetic poles increases, and self-demagnetization hardly occurs. Taking as an example a sewing needle and a pachinko ball that have completely different shapes, they are all made of iron and stick to a magnet, but the sewing needle has a small self-demagnetization, so it is easy to become a magnet, while a pachinko ball has a self- Because of the large magnetism, oneself has the property of not easily becoming a magnet.

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

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

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

Next, the ultra-smoothing of the magnetic layer surface in the present invention will be described. Originally, the double coating technology is a technology capable of realizing excellent smoothness. This is because the lower magnetic layer absorbs the irregularities on the surface of the base film and makes it difficult to transmit the influence of the irregularities to the upper layer. However, 0.5
The conventional technique alone has its limitations when aiming for further smoothness, with the problem of negligible space loss at shorter wavelengths of less than μm.

Due to the recording mechanism, it is necessary to use an ultrafine magnetic material having excellent high-frequency characteristics for the upper layer, and even a very small disturbance of the upper and lower layer interfaces in units of particle size caused by a relatively large lower nonmagnetic powder. It is necessary to pursue it thoroughly. In particular, as the upper layer becomes an ultra-thin layer, the influence of the smoothness of the interface on the smoothness of the surface of the magnetic layer becomes greater, and the solution of this problem was even more important.

In the present invention, in order to make the interface between the upper and lower layers ultra-smooth, the non-magnetic particles in the lower layer are made ultra-fine and their packing density is increased. However, on the other hand, it is difficult to fill uniformly and densely as it is because it is extremely fine particles.Therefore, special surface treatment is applied to each surface of ultrafine particles to improve dispersibility, so that high density filling is achieved And the smoothness of the interface between the upper and lower layers can be dramatically improved.

Further, since this nonmagnetic layer is a high-density filling layer, it has a high degree of freedom in the surface direction of the tape and has an extremely high flexibility in the thickness direction while having excellent flexibility. It exhibits rigidity and further enhances the smoothing effect of the calendar process. As a result, Hi8
20% smoother than MP-DC
The magnetic layer achieved a surface roughness of 2.5 nm or less. The super-smoothness achieved only by providing the non-magnetic layer in the lower layer significantly reduces the space loss in the short wavelength region and improves the high-frequency characteristics.

Next, the high output and low noise of the magnetic layer of the present invention will be described. Higher output and lower noise of the magnetic layer is the basis of the technology for improving the performance of magnetic tapes. In order to thoroughly pursue improvements in characteristics at short wavelengths, minimizing signal loss, as well as high output and low noise of the magnetic layer itself by "ultra-fine particles of magnetic material, high energy, and high density filling" Is essential.

That is, in the present invention, it is the lower non-magnetic layer that enables high-density packing of ferromagnetic powder. The non-magnetic layer that is smooth and extremely rigid in the thickness direction is formed of a super HDP (High Density Pa).
cking) The strong pressure of the calendar was firmly received, and an unprecedented breakthrough in high-density packing was realized.

Also, if the high-frequency characteristics are thoroughly pursued by making the magnetic layer ultra-thin, the mid- and low-frequency characteristics are reduced by the conventional technology,
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, a large improvement in the high-frequency output, and at the same time, secures a high middle / low-frequency characteristic and is excellent. Color output was realized.

That is, in the present invention, high-density recording comparable to a vapor-deposited tape, which was conventionally considered impossible with a coating-type magnetic recording medium, can be achieved. That the upper magnetic layer was formed in a wet state by a so-called Wet on Wet method, a uniform upper magnetic layer could be formed as a thin layer having a dry thickness of 1.0 μm or less, and an upper layer that had not been achieved conventionally. The average value d of the dry thickness of the magnetic layer is 1.0 μm or less, and the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer is 0.001 to 0.5 μm.
Thus, a coating-type high-density recording medium that is practically practical and comparable to a vapor-deposited tape was obtained for the first time. Conventionally, magnetic recording media having an upper magnetic layer and a lower non-magnetic layer having a dry thickness of 1.0 μm or less have been found only as patent applications, and no products that have been actually commercially available have been found. . The present invention is an epoch-making invention that breaks such conventional wisdom for the first time.

Here, the definitions and measuring methods of the above d and Δd are 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 the transmission electron microscope was used to cut out a magnification of 10,000 to 100.
Observation was performed at a magnification of 000 times, preferably 20,000 to 50,000 times, and the photograph was taken. Photo print size is A
4 to A5. Thereafter, the interface was visually determined by focusing on the difference in shape between the magnetic material and the non-magnetic powder of the upper magnetic layer and the lower non-magnetic layer, and the magnetic layer surface was similarly blackened. After that, Zeiss image processing device IBA
In S2, the length of the interval between the trimmed lines was measured. Thereby, d was obtained. The length of the interval is measured by segmenting an interval of 21 cm into 100 to 300 segments.

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

That is, Δd is obtained from the following equation. [Delta] d = The _{(Δd 1 + Δd 2 + ...} + Δd m) / m (m = 10~20), mountain curve interface forms - mountain distance (L) is preferably 1μm or more, and particularly preferably not less than 2μm preferable. Further, in the present invention, the standard deviation σ can be obtained by using exactly the same values as those used in the statistical processing for the thickness of each magnetic layer segmented into 100 to 300. This standard deviation σ is preferably 0.2 μm or less.

As a specific means for achieving the above-mentioned rule, first, the magnetic coating material for the magnetic layer and the respective dispersions of the lower non-magnetic layer have thixotropic properties. It is to control the thixotropic properties of each dispersion of the lower non-magnetic layer so as to be close to or the same as each other. Second, the size and shape of the powder contained in the lower non-magnetic layer and the magnetic layer are specified. It is to control mechanically so that a mixed region does not occur in the upper layer and the lower layer.

In order to impart a thixotropic property to a dispersion prepared by dispersing a nonmagnetic powder or a ferromagnetic powder in a binder, the shear stress A10 ⁴ at a shear rate of 10 ⁴ sec ^-1 and the shear stress A Shear stress at a speed of 10 sec ^-1 The ratio of A10 ⁴ / A10 to A10 is 100 ≧ A10
⁴ / A10 ≧ 3.

As the adjusting factor, for example,
Regarding inorganic powder or magnetic powder, (1) Particle size
(Specific surface area, average particle size, etc.), (2) structure (oil absorption,
(3) Powder surface properties (pH, loss on heating)
), (4) Attraction force of particles (σ _SEtc.)
(1) molecular weight, (2) type of functional group, etc.
(1) type (polarity etc.), (2) binder solubility,
(3) Solvent formulation amount, water content and the like.

Specific means for setting Δd to 0.001 to 0.5 μm include, for example, the following means (a) to (e). (A) the dry thickness of the lower nonmagnetic layer is 1 to 30 times d of the upper magnetic layer, and the difference between the powder volume ratio of the lower nonmagnetic layer and the powder volume ratio of the upper magnetic layer; But -5% ~
Be in the range of + 20%. (B) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and is composed of a polyhedral inorganic powder having a Mohs hardness of 6 or more and an average particle size of 0.15 μm or less, from spherical to cubic. thing. (C) The non-magnetic powder contained in the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size is １ ／ of the crystallite size of the acicular ferromagnetic powder contained in the upper magnetic layer.
~ 4 times. (D) The non-magnetic powder contained in the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle diameter is 1/1 / the average major axis length of the acicular ferromagnetic powder contained in the upper magnetic layer. 3 or less. (E) The coating solution for the lower non-magnetic layer contains a magnetic powder imparting thixotropic properties.

Hereinafter, (c) will be described. In order to apply the upper magnetic layer to an ultrathin layer of 1 μm or less, it is necessary to apply a wet multilayer coating. In this case, the particle size of the inorganic powder contained in the lower nonmagnetic layer and the ferromagnetic powder contained in the upper magnetic layer The fine surface roughness is determined in relation to the crystallite size of. The crystallite size generally corresponds to the average minor axis length in the case of acicular ferromagnetic powder. 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, if the average particle size of the lower inorganic powder exceeds four times the crystallite size of the ferromagnetic powder, the interparticle distance between the lower powder particles increases, so that the upper ferromagnetic powder has an effect on the surface properties of the lower layer. , It is not possible to obtain sufficient surface properties. As shown in the examples, in order to obtain a sufficient surface property, the size of the upper needle-like ferromagnetic powder crystallite size is ２〜 to 4 times,
More preferably, an inorganic powder having an average particle size of 2/3 to 2 times is preferable. As the shape of the inorganic powder,
A spherical shape and a dice shape are preferred. The Mohs hardness is 3 or more, preferably 4 or more, and more preferably 6 or more.

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

Next, (d) 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 (c). In order to reduce the disorder of the orientation, it is necessary to arrange fine non-magnetic powders in the longitudinal direction of the ferromagnetic powder so as to support the orientation of the ferromagnetic powder so that the orientation is not disturbed in the longitudinal direction. When the requirements for this purpose were experimentally confirmed, the squareness ratio becomes equivalent to that of the single-layer magnetic layer in the case of the acicular ferromagnetic powder, which is 1/3 or less of the average major axis length, more preferably 1/3 to 1%. The use of an inorganic powder of / 20 provides good surface properties and a good squareness ratio.

In (d), for the same reason as in (c), the volume filling ratio 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 average major axis length, the degree of filling by the calendar is remarkably improved.
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 in (c).

In the magnetic recording medium obtained according to the present invention, an extremely smooth magnetic layer is obtained as described above, and the average dry thickness d of the magnetic layer is λ / 4 ≦ d ≦ with respect to the shortest recording wavelength λ. 3
λ and the surface roughness Ra of the magnetic layer preferably satisfies the relationship of Ra ≦ λ / 50. A preferred powder composition for this is that the ferromagnetic powder in the magnetic layer has an average major axis length of 0.3 μm.
m or less needle-shaped ferromagnetic powder or 0.3 μm in average plate diameter
The following plate-like ferromagnetic powder, the non-magnetic powder in the lower non-magnetic layer is a granular particle having an average particle diameter of λ / 4 or less, or an acicular particle having an average major axis length of 0.05 to 0.2 μm. The ratio is 5-2
0 needle particles, or average plate diameter is 0.01 to 0.1 μm
And plate-like particles having a plate-like ratio (plate diameter / plate thickness) of 5 to 20 are preferable. According to the above aspect, the magnetic layer thickness d of the magnetic recording medium of the present invention and the thickness variation (ie, Δd) at the interface between the lower non-magnetic layer and the magnetic layer are achieved, and as a result, the optimum thickness of the magnetic layer according to the recording wavelength is obtained. It shows that the range and Ra can be defined. That is, in the present invention, since the thickness of the magnetic layer is made thin, uniform, and uniform, even if the recording wavelength is shortened, fluctuation in reproduction output and amplitude modulation noise are prevented, and high reproduction output and high C / N are realized. can do.

In other words, conventionally, when the magnetic layer becomes thinner, when the recording wavelength becomes shorter, all the layers of the magnetic layer contribute to recording / reproducing. Therefore, when the thickness of the magnetic layer fluctuates, fluctuations in reproduction output and amplitude modulation noise are observed. However, 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 d in the present invention is preferably λ / 4
≦ d ≦ 3λ, more preferably λ / 4 ≦ d ≦ 2λ (that is, 0.25 ≦ d / λ ≦ 2). D is usually 0.05 μm ≦ d ≦ 1.0 μm, preferably 0.05 μm.
μm ≦ d ≦ 0.8 μm.

The dry thickness average value d 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 calibrated. A line can be created, and then the thickness of the unknown sample can be determined from the intensity of the fluorescent X-ray. According to the present invention, the range of Δd is controlled to 0.001 to 0.5 μm, and when d is smaller than 0.5 μm, Δd / d is 0.5.
It is preferably 0 or less. In addition, thereby, the uniformity of the thickness of the magnetic layer is ensured and the surface roughness Ra is preferably Ra ≦ λ / 50, that is, λ / Ra is 50 or more, more preferably 75 or more, and particularly preferably 80 or more. Can be regulated. In the present invention, Ra indicates a value obtained by measuring a center line average roughness measured using a light interference roughness meter.

In order to obtain the magnetic recording medium of the present invention, it is preferable to coat the upper magnetic layer while the lower non-magnetic layer is in a wet state. It does not matter if it is in the state, but simultaneous multi-layer coating is preferred.

That is, by such a method, 1.0 μm
By coating the following magnetic layer on the lower non-magnetic layer, coating defects which are problematic when the magnetic layer is made thinner alone or when the lower non-magnetic layer is sequentially laminated in a dry state can be prevented.

In the magnetic recording medium obtained according to the present invention, the thickness of the magnetic layer cannot be simply reduced, and as described above, there is an optimum range for the shortest recording wavelength λ. That is, when the thickness of the magnetic layer becomes thinner than λ / 4, the magnetic flux contributing to reproduction decreases and the output decreases. In addition, since the short wavelength component is demagnetized by the deep recording magnetic field of the component having a longer recording wavelength and simultaneously recording exceeding 3λ, the output is reduced. Therefore, preferably, d ≦ 3λ, and more preferably, d ≦ 2λ.

The basic performance of the magnetic recording medium, C /
When N is captured, 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 magnetic layer, the thickness variation at the interface between the non-magnetic layer and the magnetic layer becomes a problem. This is because when d is in the range of λ / 4 ≦ d ≦ 3λ, the reproduction output is affected by the amount of magnetic flux of the entire magnetic layer, and this is not a problem in the conventional thick magnetic layer. The present invention has found out that this problem requires that the average value Δd of the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer be 0.001 to 0.5 μm. The surface roughness of the magnetic layer is required to be as smooth as the conventional thick magnetic layer, and the surface roughness Ra is Ra ≦ λ / 50.
It is preferable to satisfy the following relationship.

According to the present invention, processing in a vacuum is assumed.
The productivity and reliability of thin metal media that are vulnerable to corrosion.
No problem, the electromagnetic conversion characteristics are comparable to metal thin films, and
It is possible to obtain high performance coated magnetic recording media with excellent productivity.
Wear. The magnetic recording medium of the present invention has a scanning type surface on the magnetic layer.
Root mean square roughness R by tunneling microscope (STM) method_rmsBut
30 ≦ d / R between the dry thickness average value d of the magnetic layer
_rmsIt is preferable that the relationship

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

The glossiness of the surface of the magnetic layer is preferably from 250 to 400% after calendering. Further, in order to achieve high energy of the magnetic recording medium obtained by the present invention, it is necessary that the ferromagnetic powder contained in the upper magnetic layer has a needle having an average major axis length of 0.3 μm or less and an Hc of 1500 Oe or more. It is preferable that the ferromagnetic metal powder or the plate-shaped ferromagnetic powder having an average plate diameter of 0.3 μm or less and having a Hc of 1000 Oe or more.

As the ferromagnetic powder, a needle-shaped ferromagnetic metal powder, a plate-shaped hexagonal ferrite-based ferromagnetic material (Ba ferrite, Sr ferrite, etc.), and a plate-shaped Co alloy powder can be used. Hc and saturation magnetization (σ _s ) may be appropriately selected, but Hc is preferably 1500 (Oe) or more, especially for short-wavelength recording with a minimum recording wavelength of 1 μm or less.

In order to obtain a magnetic recording medium in which the magnetic layer is densely packed according to the present invention, the ratio of the stiffness SMD in the coating direction of the magnetic recording medium to the stiffness STD in the width direction with respect to the coating direction (longitudinal direction). SMD / STD is 1.0-1.
It is preferable to prepare each coating liquid so as to be 9. In order to set the stiffness to the above value, the nonmagnetic inorganic powder contained in the lower nonmagnetic layer has a polyhedral nonmagnetic inorganic powder having a Mohs hardness of 6 or more and an average particle diameter of 0.15 μm or less, from spherical to cubic. It is preferred to use.

The mechanism of operation regarding stiffness is as follows. In other words, by controlling the SMD / STD of the magnetic recording medium, the mechanical properties 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. is there.

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 stiffness tester manufactured by Toyo Seiki Co., Ltd., a manufactured magnetic recording medium is 8 mm wide and a 50 mm long sample is used for SMD measurement so that the sample length direction is the same as the coating direction of the magnetic recording medium. In order to measure the STD, the sample is cut out so that the length direction of the sample is the same as the width direction of the magnetic recording medium, and this is formed into a ring.
The SMD and STD can be defined as the force expressed in mg of the force required to give a displacement of 5 mm at a displacement speed of 3.5 mm / sec in the inner diameter direction.

Here, SMD / STD is preferably 1.
0 to 1.9, more preferably 1.1 to 1.85. In a magnetic recording medium having a total thickness of 13.5 ± 1 μm, SMD is preferably 50 to 200 mg, more preferably 50 to 150 mg, and STD is preferably 4 to 200 mg.
It is 0 to 150 mg, more 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 nonmagnetic inorganic powder contained in the lower layer. It is desirable to select a polyhedral nonmagnetic inorganic powder having a hardness of preferably 6 or more, more preferably 6.5 or more, and an average particle size of 0.15 μm or less, preferably 0.12 μm or less, from spherical to cubic. .

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

Particularly, the effect on the electromagnetic conversion characteristics is high because of S
TD is close to SMD, ie close to 1. When the nonmagnetic inorganic powder contained in the lower layer is made into a polyhedral shape from a sphere to a cube, the mechanical properties of the coating become isotropic.
It is convenient to improve TD. Here, the polyhedron shape specifically refers to a regular polyhedron or a non-regular polyhedron selected from one or more selected from a regular n-gon such as a sphere, a regular pentagon, and a regular hexagon, or a simple n-polygon. As an example, preferably, the arbitrarily selected two axis ratio is 0.6 to 0.6.
Those in the range of 1.4, preferably 0.7 to 1.3 are desirable.

As another mode for achieving a high density of the magnetic layer according to the present invention, the temperature of the magnetic recording medium at 70 ° C.
Each coating solution is prepared so that the heat shrinkage after 48 hours is 0.4% or less. Specifically, the dry thickness of the lower non-magnetic layer is 1 to 30 times d of the upper magnetic layer, and the powder volume ratio of the lower non-magnetic layer to the powder volume ratio of the upper magnetic layer. The difference is to be in the range of -5% to + 20%.

By controlling the heat shrinkage in this way, it is possible to provide a magnetic recording medium that improves and reduces skew distortion and has electromagnetic conversion characteristics comparable to a ferromagnetic metal thin film.

Here, the heat shrinkage ratio is 100 × (length of magnetic recording medium at room temperature before heating−70 ° C. environment)
This is a value represented by (length after holding the magnetic recording medium for 8 hours without applying tension) / (length of the magnetic recording medium at room temperature before heating).

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

As means for adjusting the film strength of the lower layer and the upper layer, the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is preferably -5% to +2.
0%, more preferably in the range of 0 to 15%. Here, if the content is less than -5%, the increase in the thermal shrinkage of the magnetic layer cannot be suppressed, and if the content is more than 20%, the medium itself becomes too hard, and the powder falls off, which is not preferable.

In the present invention, the powder volume ratio of the upper layer is preferably 10 to 50%, more preferably 2 to 50%.
The range of 0 to 45% is exemplified, and the powder volume ratio of the lower layer is:
Preferably, it is 20 to 60%, more preferably 25 to 5%.
A range of 0% is exemplified. The powder volume ratio of each layer is
The amounts of the powder and the binder to be added can be changed, and the particle size and shape of the powder in each layer can be controlled. When the amount of the binder is increased, the powder volume ratio relatively decreases. The finer the particle size of the powder, the more effective it is in reducing the heat shrinkage. However, if the particle size is too fine, dispersion becomes difficult.

For example, as for the particle size of the ferromagnetic powder, the crystallite size is 300 ° or less, preferably 100 to
250 °, the average major axis length is desirably in the range of 0.005 to 0.4 μm, preferably 0.1 to 0.3 μm, and the average major axis length / crystallite size is in the range of 3 to 25, preferably 5 to 20. Is mentioned. The specific surface area of the ferromagnetic powder by the BET method is 25 to 80 m ² / g, preferably 30 to 80 m ² / g.
７０70 m ² / g. If it is less than 25 m ² / g, the noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable.

The particle size and shape of the non-magnetic inorganic powder in the lower layer are as follows. / Needle-like ratio represented by average short axis length is 5
Needles, etc., which are -20 to 20 are exemplified. As the nonmagnetic inorganic powder, rutile-type titanium oxide, α-iron oxide, and goethite are preferable.

The powder used for the lower layer includes carbon black. The carbon black has an average particle size of preferably 5 to 80 nm, more preferably 30 nm or less, particularly preferably 5 to 28 nm, and a DBP oil absorption of usually 30 to 300 ml / 10.
0 g, preferably 50-250 ml / 100 g, BE
The specific surface area by the T method is usually 150 to 400 m ² / g,
Preferably it is 170 to 300 m ² / g, and the pH is 2 to
10, the water content is 0.1 to 10% by weight, and the tap density is 0.1.
1-1 g / cc is preferred.

The carbon black is preferably added to the lower layer in a proportion of preferably less than 50 parts by weight, more preferably 13 to 40 parts by weight, based on 100 parts by weight of the nonmagnetic inorganic powder. The carbon black is used to control the volume ratio of the powder in the lower layer by controlling the porosity, in addition to functions such as antistatic and enhancement of the film strength of the magnetic recording medium. That is, when the porosity is high, the powder volume ratio relatively decreases. As the carbon black for controlling the porosity, it is effective to use carbon black having a structure or hollow carbon black.

The porosity of the lower layer is preferably in the range of the porosity of the upper layer ± 10%. The porosity of the lower layer is preferably in the range of 10 to 30%. The magnetic recording medium produced by the present invention preferably exhibits the following properties,
The present invention provides a magnetic recording medium having excellent running durability.
The Young's modulus of the magnetic recording medium measured by a tensile tester is preferably 300 to 2000 kg / mm ² , more preferably 400 to 1500 kg / mm ² , and the Young's modulus of the magnetic layer is preferably 400 to 5000 kg. /
mm ² , more preferably 500-4000 Kg / mm
^{2. The} yield stress is preferably 3 to 20 kg / mm ² , more preferably 4 to 18 kg / mm ² , and the yield elongation is preferably 0.2 to 8%, more preferably 0.5 to 5%. Is desirable

This affects the durability because the ferromagnetic powder, binder, carbon black, non-magnetic inorganic powder, and support are involved. The bending rigidity (annular stiffness) of the magnetic recording medium 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 measured at 23 ° C. and 70% RH is preferably 20% or less. Further, the Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium measured using an X-ray photoelectron spectrometer is preferably 0.3 to 0.6,
N / Fe spectrum β is preferably 0.03 to 0.12
It is.

This is related to the ferromagnetic powder, the non-magnetic inorganic powder and the binder, and is important in obtaining durability. Further, the glass transition temperature Tg of the magnetic layer (the maximum point of the loss elastic modulus in the dynamic viscoelasticity measurement measured at 110 Hz) of the magnetic layer measured using a dynamic viscoelasticity measuring device is preferably 40 to 120 ° C. And a storage elastic modulus E ′ (50 ° C.) of preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / c.
m ² , and the loss 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, adhesion failure is likely to occur. These are related to binders, carbon black, and solvents, and are important properties related to durability.

Further, the distance between the support and the magnetic layer is
The 180 ° adhesion strength of the 8 mm wide tape at 70 ° C. and 70% RH is preferably 10 g or more. Also,
The wear of a steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ . This is a measure of the durability mainly related to ferromagnetic powder, which is a direct observation of the wear of the magnetic layer surface.

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

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

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

The coefficient of friction (μ) of the magnetic recording medium obtained by the present invention is preferably from 0.15 to 0.4 on the magnetic surface.
It is particularly preferably 0.2 to 0.35, and the back layer surface is preferably 0.15 to 0.4, and particularly preferably 0.1 to 0.4.
2 to 0.35. The contact angle of the magnetic recording medium obtained by the present invention is preferably 60 to 130 °, particularly preferably 80 to 120 ° in the case of water. In the case of methylene iodide, preferably 10 to 90 °,
Particularly preferably, it is 20 to 70 °.

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

Hereinafter, general items which can be selected by the present invention will be described.
I will describe. Non-magnetic inorganic powder that can be used in the present invention,
For example, metals, metal oxides, metal carbonates, metal sulfates,
Non-magnetic inorganic materials such as metal nitrides, metal carbides and metal sulfides
Powder. Specifically, TiO_Two (Rutile, ana
Tase), TiO_X, Cerium oxide, tin oxide, titanium oxide
Ngustene, ZnO, ZrO_Two , SiO_Two , Cr_Two O
_Three , Α-alumina, β-alumina, γ-a
Lumina, α iron oxide, goethite, corundum, silicon nitride
Element, titanium carbide, magnesium oxide, boron nitride,
Molybdenum disulfide, copper oxide, MgCO_Three , CaCO_Three ,
BaCO_Three , SrCO_Three , BaSO_Four , Silicon carbide, carbonized
Titanium or the like is used alone or in combination. this
The shape, size, etc. of the nonmagnetic inorganic powder are arbitrary.
They combine different non-magnetic inorganic powders as needed.
Or the particle size distribution etc. can be selected even for a single non-magnetic powder.
Can also be.

The particle shape and particle size of the nonmagnetic inorganic powder are preferably selected according to the specific embodiment of the present invention.

As the non-magnetic inorganic powder, the following are preferred.
Good. Tap density is 0.05 to 2 g / cc, preferably
Is 0.2 to 1.5 g / cc. Moisture content is 0.1-5 weight
%, Preferably 0.2-3% by weight. pH 2-11, special
Is preferably 4 to 10. Specific surface area is 1-100m^Two /
g, preferably 5 to 70 m^Two / G, more preferably 7 to
50m^Two / G. Crystallite size is 0.01 μm to 2
μm is preferred. The oil absorption using DBP is usually 5 to 1
00ml / 100g, preferably 10-80ml / 10
0 g, more preferably 20 to 60 ml / 100 g.
You. SA (stearic acid) adsorption amount is 1 to 20 μmol /
m^Two , More preferably 2 to 15 µmol / m ^Two It is.
The roughness factor of the powder surface is preferably 0.8 to 1.5.
And more preferably 2 to 15 μmol / m^Two It is.
Heat of wetting in water at 25 ° C. is 200 erg / cm^Two ~ 60
0 erg / cm^Two Is preferred. The range of this heat of wetting
Can be used. 100-400 ° C
The amount of water molecules on the surface at 1 to 10 / 100Å is appropriate
is there. The pH of the isoelectric point in water may be between 3 and 9.
preferable. The specific gravity is usually 1 to 12, preferably 3 to 6.
is there.

The above nonmagnetic inorganic powder is not necessarily 100
% Need not be pure and the surface may be coated with another compound, such as Al, Si, Ti, Zr, Sn, Sb, Z, depending on the purpose.
n, etc., to form oxides thereof on the surface. At this time, if the purity is 70% or more, the effect is not reduced. The ignition loss is preferably 20% or less. The nonmagnetic powder used in the lower layer of the present invention, a surface Al, treated with a compound of Si or Zr, a layer having one or more selected from Al ₂ O _3, SiO ₂ and ZrO ₂ on the surface A nonmagnetic inorganic powder having a Mohs hardness of 3 or more is preferred.

Specific examples of the nonmagnetic inorganic powder used in the present invention include UA5600 and UA5 manufactured by Showa Denko KK
605, AKP-20, AKP-30, A manufactured by Sumitomo Chemical Co., Ltd.
KP-50, HIT-55, HIT-100, ZA-G
1, G5, G7, S-1 manufactured by Nippon Chemical Industries, TF-100, TF-120, TF-140, R51 manufactured by Toda Kogyo
6, Ishihara Sangyo TTO-51B, TTO-55A, T
TO-55B, TTO-55C, TTO-55S, TT
O-55S, TTO-55D, FT-1000, FT-
2000, FTL-100, FTL-200, M-1,
S-1, SN-100, R-820, R-830, R-
930, R-550, CR-50, CR-80, R-6
80, TY-50, ECT-52, ST manufactured by Titanium Industry Co., Ltd.
T-4D, STT-30D, STT-30, STT-6
5C, 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 manufactured by Sakai Chemical Co.
NEX-25, BF-1, BF-10, BF-20, B
F-1L, BF-10P, DEFIC- manufactured by Dowa Kogyo
Y, DEFIC-R, Y-LOP manufactured by Titanium Industry Co., Ltd. and baked products thereof.

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

In the present invention, carbon black can be used for the lower layer, and the known effects such as R _S (surface electric resistance) can be reduced. As the carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used.

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, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050, # 3150, # 3250, #
3750, # 3950, # 2400B, # 2300, #
1000, # 970, # 950, # 900, # 850,
# 650, # 40, MA40, MA-600, manufactured by Columbian Carbon, CONDUCTEX SC, RAV
EN company 8800, 8000, 7000, 5750, 5
250, 3500, 2100, 2000, 1800, 1
500, 1255, 1250 and Ketjen Black EC manufactured by Akzo. Carbon black may be surface-treated with a dispersing agent or the like, or may be grafted with a resin, or may be used in which a part of the surface is graphitized. Before adding the carbon black to the non-magnetic paint, the carbon black may be dispersed in a binder in advance.
These carbon blacks can be used alone or in combination.

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

The carbon black and the organic powder of these nonmagnetic powders are usually added in a weight ratio of 2 to the binder.
It is used in a range of 0 to 0.1% and a volume ratio of 10 to 0.1%. In general magnetic recording media, it is performed to provide an undercoat layer, which is provided to improve the adhesion between the support and the magnetic layer,
The thickness is also 0.5 μm or less, which is different from the lower non-magnetic layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesion between the underlayer and the support.

As the ferromagnetic powder used in the coating solution for a magnetic layer of the present invention, magnetic iron oxide FeOx (x = 1.33 to 1.3.
5), Co-modified FeOx (x = 1.33 to 1.5), F
Known ferromagnetic powders such as simple substance and alloy ferromagnetic metal powder containing e or Ni or Co as a main component (75 atomic% or more), barium ferrite, and strontium ferrite can be used, but ferromagnetic metal powders are more preferable. These ferromagnetic powders include Al, Si, S, S
c, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, A
g, Sn, Sb, Te, Ba, Ta, W, Re, Au,
Hg, Pb, Bi, La, Ce, Pr, Nd, P, C
It may contain atoms such as o, Mn, Zn, Ni, Sr, and B. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513,
JP-B-46-28466, JP-B-46-38755
No., JP-B-47-4286, JP-B-47-12422
No., JP-B-47-17284, JP-B-47-1850
No. 9, JP-B-47-18573, JP-B-39-103
07, JP-B-48-39639, and U.S. Pat.
No. 6215, No. 3031341, No. 3100194
Nos. 3,242,005 and 3,389,014.

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

When the ferromagnetic powder of the upper magnetic layer is expressed by a specific surface area by the BET method, it is usually 25 to 80 m ² / g, preferably 30 to 70 m ² / g. If it is less than 25 m ² / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable. The σ _{S of the} iron oxide magnetic powder is usually at least 50 emu / g, preferably at least 70 emu / g, and the ferromagnetic metal powder is preferably at least 100 emu / g, more preferably from 110 emu / g to 17 emu / g.
0 emu / g. The coercive force is usually preferably 1100 Oe or more and 2500 Oe or less, more preferably 15 Oe or less.
It is not less than 00 Oe and not more than 2000 Oe. The needle ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.

The r1500 of the ferromagnetic powder is 1.5 or less.
Preferably. More preferably, r1500 is 1.
0 or less. r1500 is the saturation magnetization of the magnetic recording medium
After applying a magnetic field of 1500 Oe in the opposite direction,
It shows% of the amount of magnetization remaining without turning. Strong magnetism
The moisture content of the conductive powder is preferably 0.01 to 2% by weight.
No. Optimizing the moisture content of ferromagnetic powders depending on the type of binder
Is preferred. Tap density of gamma iron oxide is 0.5g /
cc or more, more preferably 0.8 g / cc or more.
New In the case of metal powder, 0.2 to 0.8 g / cc is preferable.
Especially, if you use higher than 0.8g / cc, strong magnetic
Oxidation easily proceeds during the compaction process of the conductive powder, and sufficient saturation magnetization
(σ _S) Is difficult to obtain. Less than 0.2cc / g
In this case, dispersion tends to be insufficient.

When γ iron oxide is used, trivalent iron
The ratio to iron is preferably 0-20%, more preferably
Preferably, it is 5 to 10%. Kovar for iron atom
The amount of atom is usually 0 to 15%, preferably 2 to 8%.
is there. The pH of the ferromagnetic powder depends on the combination with the binder used.
It is preferable to optimize it. The range is usually 4-1
2, but preferably 6 to 10. Ferromagnetic powder
If necessary, the surface can be treated to make Al, S
i, P or their oxides should be present on the surface.
Can be. The amount is 0.1 to 10 times the ferromagnetic powder
% By surface treatment and adsorption of lubricants such as fatty acids
Is 100 mg / m ^Two The following is preferred. Upper layer of the present invention
As the ferromagnetic powder used in the above, the surface is Al, Si or
Treated with a compound of Zr,_TwoO_Three, SiO_TwoAnd Zr
O_TwoForming a layer having at least one member selected from the group consisting of
Ferromagnetic metal powder is preferred. Soluble in ferromagnetic powder
Including inorganic ions such as Na, Ca, Fe, Ni, Sr
In some cases, if the concentration is 500 ppm or less, the characteristics are particularly affected.
Does not affect.

The ferromagnetic powder used in the present invention preferably has a small number of pores, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape is selected from acicular, granular, rice granular, plate-like, and the like so as to satisfy the conditions described above. SFD of ferromagnetic powder 0.6
To achieve the following, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For this purpose, there are methods such as improving the particle size distribution of goethite, preventing sintering of γ-hematite, and decreasing the deposition rate of cobalt on cobalt-modified iron oxide as compared with the conventional method.

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

When barium ferrite is used, the average plate diameter means the width of hexagonal plate-like particles, and is measured using an electron microscope. In the present invention, the average plate diameter is 0.001.
〜1 μm, and the average thickness is preferably １ ／ to 1/20 of the diameter. The specific surface area (S _BET ) is preferably from 1 to 60 m ² / g, and the specific gravity is preferably from 4 to 6. As the binder used in the lower nonmagnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1000 to 1000.
200,000, preferably 10,000-100,000,
The degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters,
Vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as a polymer or copolymer containing as a structural unit,
There are polyurethane resins and various rubber resins. As the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin And mixtures of isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates.

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

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

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

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

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

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

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

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

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

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

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

The 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
Monoolefins (eg, ethylene, propylene), acrylates (eg, (meth) acrylates containing a functional group such as methyl (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitriles (eg, , (Meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), and vinyl ester (eg, vinyl acetate, vinyl propionate, etc.).

Specific examples of these binders used in the present invention include: VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku: 100
0W, DX80, DX81, DX82, DX83, 10
0FD, manufactured by Zeon Corporation: MR105, MR110, M
R100, 400X110A, manufactured by Nippon Polyurethane Co .:
Nipporan N2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105, T-R30
80, T-5201, Barnock D-400, D-21
0-80, Chris Bon 6109, 7209, manufactured by Toyobo: Byron UR8200, UR8300, UR860
0, UR5500, UR4300, RV530, RV2
80, manufactured by Dainichi Seika Co., Ltd .: Daifelamin 4020, 502
0, 5100, 5300, 9020, 9022, 702
0, manufactured by Mitsubishi Kasei: MX5004, manufactured by Sanyo Kasei: Samprene SP-150, manufactured by Asahi Kasei: Saran F310, F
210 and the like.

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

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

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 non-magnetic powder, the resin other than the epoxy group-containing resin is usually added in an amount of 3 to 30% by weight. 30% by weight can be used. When a polyurethane resin is used, 3 to 30% by weight and polyisocyanate can be used at 0 to 20% by weight. ^{-5 to} 16
It is preferable to be contained in the range of × 10 ^-4 eq / g.

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

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

As the carbon black used in the upper magnetic layer of the present invention, furnace black for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, average particle size is 5 nm to 30
0 nm, the pH is preferably 2 to 10, the water content is preferably 0.1 to 10% by weight, and the tap density is preferably 0.1 to 1 g / cc. Specific examples of the carbon black used in the present invention include: BLACKPEARLS 2000, manufactured by Cabot Corporation;
1300, 1000, 900, 800, 700, VUL
CAN XC-72, manufactured by Asahi Carbon Co .: $ 80, $ 6
0, $ 55, $ 50, $ 35, manufactured by Mitsubishi Kasei Industries: $ 2
400B, $ 2300, $ 900, $ 1000, $ 3
0, $ 40, $ 10B, manufactured by Columbian Carbon Co .: C
ONDUTEXT SC, RAVE150, 50, 4
0, 15 and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by graphitizing a part of the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the ferromagnetic powder. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination in the lower layer and the upper layer, and the particle size,
Of course, it is possible to use differently according to the purpose based on the above-mentioned various characteristics such as oil absorption, conductivity, pH and the like. The carbon black that can be used in the upper layer of the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

The abrasive used for the upper magnetic layer and the lower layer of the present invention includes α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-alumina having an α conversion of 90% or more.
Iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide,
Known materials having a Mohs hardness of 6 or more, such as boron nitride, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 μm. However, if necessary, abrasives having different particle sizes can be combined, or even a single abrasive can have the same effect by widening the particle size distribution. . The tap density is 0.3 to 2 g / cc, the water content is 0.1 to 5% by weight, the pH is 2 to 11, and the specific surface area is 1
３０30 m ² / g is preferred. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness.

Specific examples of the abrasive used in the present invention include AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, manufactured by Nippon Chemical Industries: G
5, G7, S-1, manufactured by Toda Kogyo: TF-100, TF
-140, 100ED, 140ED and the like.
The abrasive used in the present invention can be of different types, amounts and combinations for the lower layer and the upper layer, and can be of course used properly according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

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

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group, and the like, amino acids, aminosulfonic acids, sulfuric acid of amino alcohol or Ampholytic surfactants such as phosphates and alkylbedynes can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

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

All or a part of the additives used in the present invention may be added in any step of producing a magnetic paint or a non-magnetic paint. For example, the additives are mixed with a ferromagnetic powder before the kneading step. In the case, when the ferromagnetic powder and the binder and the solvent are added in the kneading step, when the addition in the dispersion step,
There is a case where it is added after the dispersion or a case where it is added just before the application. Commercial products of these lubricants used in the present invention include those manufactured by NOF Corporation: NAA-102, NAA-415,
NAA-312, NAA-160, NAA-180, N
AA-174, NAA-175, NAA-222, NA
A-34, NAA-35, NAA-171, NAA-1
22, NAA-142, NAA-160, NAA-17
3K, castor hardened fatty acid, NAA-42, NAA-4
4, Cation SA, Cation MA, Cation AB, Cation BB, Nymeen L-201, Nymeen L-20
2, Nymeen S-202, Nonion E-208, Nonion P-208, Nonion S-207, Nonion K-2
04, 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-60
R, Nonion OP-80R, Nonion OP-85R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-60, Anone BF, Anone LG, Butyl stearate, Butyl laurate, Elka Acid, manufactured by Kanto Chemical Co., Ltd .: Oleic acid, manufactured by Takemoto Yushi Co., Ltd .: FAL-205, FAL-123, manufactured by Nippon Rika Co., Ltd .: Engelbu LO, Engelbu IPM, Sansocizer E4030, manufactured by Shin-Etsu Chemical: TA-3, KF
-96, KF-96L, KF-96H, KF410, K
F420, KF965, KF54, KF50, KF5
6, KF-907, KF-851, X-22-819,
X-22-822, KF-905, KF-700, KF
-393, KF-857, KF-860, KF-86
5, X-22-980, KF-101, KF-102,
KF-103, X-22-3710, X-22-371
5, KF-910, KF-3935, manufactured by Lion Armor Co .: Armid P, Armid C, Armoslip C
P, manufactured by Lion Yushi Co., Ltd .: Duomin TDO, manufactured by Nisshin Oil Co., Ltd .: BA-41G, manufactured by Sanyo Chemical Co., Ltd .: ProFan 2012
E, Newpole PE61, Ionnet MS-400,
Examples include ionet MO-200, ionet DL-200, ionet DS-300, ionet DS-1000, ionet DO-200, and the like.

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

The thickness of the magnetic recording medium obtained according to the present invention is generally 1 to 100 μm, preferably 4 to 8 μm.
0 μm, lower layer 0.5 to 10 μm, preferably 1 to 5 μm
m, the upper layer has a thickness of 1.0 μm or less, preferably 0.05 μm or more and 0.6 μm or less, and more preferably 0.05 μm or more and 0.3 μm or less. The upper magnetic layer is preferably thinner than the lower nonmagnetic layer. The total thickness of the upper layer and the lower layer is 1/100 to 2 times the thickness of the support. In addition, an undercoat layer for improving adhesion may be provided between the support and the lower layer. This thickness is usually 0.01
２2 μm, preferably 0.05-0.5 μm. Further, a back layer may be provided on the side of the support opposite to the magnetic layer side. This thickness is usually 0.1-2 μm, preferably 0.3-1.0 μm. Known undercoat layers and back layers can be used.

The support used in the present invention is preferably a flexible support. Examples of the support include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, and the like. Known films such as 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 support has a center line average surface roughness of usually 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less.
It is preferred to use: Further, it is preferable that these supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si and Ti, and organic fine powders such as acryl.

The F-5 value of the support in the tape running direction
Is preferably 5 to 50 kg / mm ^Two , Tape width direction
The F-5 value is preferably 3 to 30 kg / mm.^Two And
The F-5 value in the tape longitudinal direction is the same as the F-5 value in the tape width direction.
Generally, the strength is high in the width direction.
This is not the case when it is necessary to do so. Also, the support
Heat collection at 100 ° C for 30 minutes in tape running direction and width direction
The shrinkage ratio is preferably 3% or less, more preferably 1.5%.
Hereinafter, the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less.
Lower, more preferably 0.5% or less. The breaking strength is
5-100kg / mm in both directions^Two , Elastic modulus is 100 ~
2000Kg / mm^Two Is preferred.

In the present invention, the step of producing the coating solution for the upper magnetic layer 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. Ferromagnetic powder used in the present invention, a binder,
All raw materials such as carbon black, abrasives, antistatic agents, lubricants, and solvents may be added at the beginning or during any of the steps. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading step, a strong kneading force such as a continuous kneader or a pressure kneader is used. By using the magnetic recording medium, a high residual magnetic flux density (Br) of the magnetic recording medium of the present invention can be obtained. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, preferably 30% by weight or more of the total binder) and 15 to 500 parts by weight based on 100 parts by weight of the ferromagnetic powder. It is kneaded in the range. Details of these kneading processes are described in JP-A-1-106338 and JP-A-64-79274.
No. Further, when preparing the coating solution for the lower non-magnetic layer, the method for preparing the coating solution for the upper magnetic layer is applied, but it is preferable to use a dispersion medium having a high specific gravity, and zirconia beads and metal beads are preferable. is there. The present invention is to coat the lower non-magnetic layer coating solution on a support,
While the obtained lower non-magnetic layer is in a wet state, simultaneously or sequentially with the application of the lower non-magnetic layer coating solution, the so-called wet-on-wet coating method of applying the upper magnetic layer coating solution is supported. It is preferably manufactured by providing a lower layer and an upper layer on the body. The wet-on-wet coating method is a so-called sequential coating method in which one layer is first applied, and then the next layer is applied as soon as possible in a wet state, and a multi-layer simultaneous extrusion coating method is applied. Say. As a wet-on-wet coating method, a magnetic recording medium coating method disclosed in JP-A-61-139929 and JP-A-62-212933 can be used, and production can be performed more efficiently. Specifically, the following configuration can be proposed as applied to the present invention. 1. First, the lower layer is applied by a gravure coating, roll coating, blade coating, extrusion coating apparatus, etc., which are generally used for applying a magnetic paint, and the lower layer is wet while the lower layer is wet. -23
No. 8179 and Japanese Unexamined Patent Publication (Kokai) No. 2-265672, the upper layer is applied by a support pressure type extrusion coating apparatus. 2. JP-A-63-88080, JP-A-2-17921
The upper layer and the lower layer are coated almost simultaneously by one coating head having two built-in coating liquid passage slits as disclosed in JP-A-2-265672. 3. The upper layer and the lower layer are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in JP-A-2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of the ferromagnetic powder, Japanese Patent Application Laid-Open Nos.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in JP-A-6968. Furthermore, regarding the viscosity of the coating solution, Japanese Patent Application No. 1-312659.
It is preferable to satisfy the numerical range disclosed in the above item.

FIG. 2 is an explanatory view showing an example of a sequential coating method used for providing both layers. The coating apparatus (A) 3 applies a lower layer to a continuously running support 1 such as polyethylene terephthalate. The coating liquid (a) was pre-coated, and immediately thereafter, the coating surface was smoothed with a smoothing roll 4.
While the coating liquid 2 is in a wet state, the next upper layer coating liquid (b) is applied by another extrusion coating machine (B) 6.

FIG. 3 is an explanatory view showing an example of an extrusion type simultaneous coating system preferably used for providing both layers. This is to explain a state in which the coating liquid (a) 2 and the upper layer coating liquid (b) 5 are simultaneously coated. After applying both layers, the magnetic recording medium is obtained by applying a magnetic field orientation, drying and smoothing.

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

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

After the calendering treatment, a thermotreatment at 40 ° C. to 80 ° C. may be performed to accelerate the curing of the magnetic layer, the back layer and the nonmagnetic layer. The friction coefficient of the upper layer and the opposite surface of the magnetic recording medium obtained by the present invention with respect to SUS420J is preferably 0.5 or less, more preferably 0.3 or less.
Hereinafter, the magnetic layer surface resistivity is 10 ⁴ to 10 ¹¹ ohm / s.
q, the surface resistivity when the lower layer is applied alone is 10 ⁴
-10 ⁸ ohm / sq, surface electric resistance of back layer is 10
^{3-10 9} ohms / sq is preferred.

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

The magnetic properties of the magnetic recording medium obtained according to the present invention, when measured at a magnetic field of 5 KOe, usually have a squareness ratio in the tape running direction of 0.70 or more, preferably 0.80 or more.
It is 0 or more, more preferably 0.90 or more. The squareness ratio in two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction.

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

[0160]

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

A coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations. Example 1 A coating solution for an upper magnetic layer and a coating solution for a lower nonmagnetic layer were prepared according to the following formulation. Lower layer non-magnetic layer coating solution Inorganic powder TiO ₂ 90 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% by weight or more Surface treatment layer Al ₂ O ₃ BET specific surface area 35 to 45 m ² / g DBP oil absorption Amount 27-38 g / 100 g pH 6.5-8 8 carbon black 10 parts Average particle size 16 nm DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5 wt% Vinyl chloride-acetic acid vinyl - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts of neopentyl glycol / Caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group 1 × 10 ⁻⁴ eq / g Allate 1 part Stearic acid 1 part Methyl ethyl ketone 200 parts Cyclohexanone 80 parts Coating solution for upper magnetic layer Fine powder of ferromagnetic metal Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe Specific surface area by BET method 60 m ² / g Crystal Particle size 195 ° Average major axis length 0.20 μm, needle ratio 10 Saturated magnetization (σ _S ): 130 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ^-4 eq / g contained, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ⁻⁴ eq / g-containing α-alumina (average particle size 0.2 μm) 2 Part Carbon black (average particle size 0.10 μm) 8 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl For each ton 200 parts The two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. Add 1 part of polyisocyanate to the resulting dispersion and 1 part to the coating liquid of the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and further add 40 parts of butyl acetate to each, having an average pore diameter of 1 μm. The mixture was filtered 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 at a thickness of 7 μm so that the thickness after drying was 3 μm, and immediately thereafter, the thickness of the upper magnetic layer was 0.5 μm thereon. Simultaneous multi-layer coating is performed on a polyethylene naphthalate support having a center average surface roughness of 0.01 μm, and while both layers are still wet, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss are used. After orientation and drying, treatment was performed at a temperature of 90 ° C. using a seven-stage calender consisting of only metal rolls, slit to a width of 8 mm, and an 8 mm video tape of Example 1-1 was manufactured.

Similarly, by changing the factors described in Tables 1 and 2, the samples, Examples 1-2 to 1-9, and Comparative Examples 1-1 to 1--1
No. 3 was prepared, and the performance was evaluated as follows.
-2. 1. Volume ratio (filling ratio) of lower inorganic powder The medium was cut out to about 0.1 μm with a diamond cutter to prepare a test piece, which was observed with a transmission electron microscope. Counting the number of inorganic powder particles per 1 μm ² from this transmission electron microscope photograph image, taking into account the thickness of the cut test piece, measuring the number of inorganic powder particles contained per unit volume, and The volume per unit was determined from the particle size of the powder obtained from the same photograph and multiplied by the number of inorganic powder particles contained per unit volume to obtain the volume ratio of the inorganic powder. The calculation formula is as follows.

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

DM = Bm / 4πσ _S where Bm (Gauss): Maximum magnetic flux density of the magnetic layer dM (g / cc): Density of ferromagnetic powder σ _S (emu / g): Saturation magnetization strength of ferromagnetic powder The volume ratio in the upper layer of the magnetic powder is obtained by dividing the above density by the specific gravity of the ferromagnetic powder. Further, the density of the other powder components and the binder in the magnetic layer is calculated from the prescribed amount of the magnetic layer, and divided by the specific gravity of each powder component, the volume ratio of each powder component is obtained, and these are summed. By doing
The powder volume ratio of the upper layer is determined. 3. Average long axis length of ferromagnetic metal powder and average particle diameter of inorganic powder Obtained as an arithmetic average from a transmission electron microscope. 4. The crystallite size of the ferromagnetic metal powder was determined from the spread of the half width of the diffraction lines on the (1,1,0) plane and the (2,2,0) plane by X-ray diffraction. 5. Measurement of surface roughness R _rms scanning tunneling microscope (STM)
Tunnel current 10 using Nanoscope II manufactured by Strument
A, a range of 6 μm × 6 μm was scanned under the condition of a bias voltage of 400 mV, and was obtained from the following equation (1).

[0166]

(Equation 1)

6. d and Δd d of the magnetic layer: cross section of the tape by transmission electron microscope (TEM)
(Magnification: 20000 times) and determined according to the above definition. Average value of thickness variation (Δd): cross-section of the tape photographed with a transmission electron microscope (TEM) (magnification: 20,000 times), length 2
The displacement of the magnetic layer and the lower non-magnetic layer in 0 μm (actual length) was measured, and the average value of the displacement difference between the peaks and valleys was determined as Δd. 7.7 MHz output A 7 MHz signal was recorded using an FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The reference is an internal reference of Fuji Photo Film Co., Ltd. 8. Pinhole After coating the magnetic layer and before coating the back layer, the magnetic layer was visually observed with transmitted light to measure pinholes per 100 m ² . It is desirable that the number be one or less per 100 m ² .

[0168]

[Table 1]

[0169]

[Table 2]

As shown in Tables 1 and 2, the average particle size of the inorganic powder contained in the lower non-magnetic layer was 実 施 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer. 4
D ≦ 1.0 μm and 0.001 μm ≦
A [Delta] d ≦ 0.5 [mu] m, even when d is 0.5 [mu] m smaller than satisfy the [Delta] d ≦ 0.50D, further surface roughness R _{rm s}
Is small, d / R _rms is 30 or more, and σ is 0.2 μm.
This is an excellent magnetic recording medium in which a magnetic layer having the following uniform and excellent surface properties is formed, the reproduction output is high, and the pinhole is extremely small. On the other hand, in the comparative example, Δd ≦ 0.50d
Not satisfied. In Comparative Example 1-1, since the thickness d of the magnetic layer was as thick as 1.2 μm, the reproduction output was slightly inferior. Comparative Example 1
-2 is a single-layer magnetic recording medium having only a magnetic layer. In Comparative Example 1-3, application was impossible because the volume ratio of the inorganic powder was too large.

Example 2 A coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations. Coating solution for lower nonmagnetic layer: same as in Example 1-1 Coating solution for upper magnetic layer 100 parts of Co-modified γFe ₂ O ₃ Hc 700 Oe Specific surface area by BET method 42 m ² / g Crystallite size 300Å Saturation magnetization (σ _S ) 75 emu / g vinyl copolymer chloride polymer 9 parts -SO ₃ Na group 1 × 10 ^-5 eq / g containing, polymerization degree 300 particulate abrasive (Cr ₂ O _3, average particle size 0.3 [mu] m) 7 parts toluene 30 parts 30 parts of methyl ethyl ketone The above composition was kneaded in a kneader for about 1 hour, and then the following composition was added and dispersed in the kneader for about 2 hours.

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

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

6 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts of tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower nonmagnetic layer obtained as described above were polyethylene terephthalate having a thickness of 75 μm. First, the coating solution for the lower non-magnetic layer was applied, and then the coating solution for the upper magnetic layer was applied in a wet state, and the back surface was similarly treated. The thickness of the lower non-magnetic layer was 1.5 μm and the thickness of the magnetic layer was 0.5 μm in dry film thickness. Thereafter, a calendar process was performed to obtain a magnetic recording medium. Thereafter, the magnetic recording medium was punched into a 3.5-inch cartridge, placed in a 3.5-inch cartridge having a liner installed inside, and a predetermined mechanical component was added thereto. Got a disc. Table 3
The samples described in Examples 2-2 to 2-5, with the factors described in
Comparative Example 2-1 was prepared, and the performance was evaluated as follows. The results are shown in Table 3. 1. 1. Volume ratio (filling ratio) of lower inorganic powder; same as in Example 1 2. Average major axis length of ferromagnetic metal powder and average particle size of inorganic powder; same as in Example 1. Crystallite size of iron oxide magnetic powder;
It was determined from the spread of the diffraction lines on the (4.4.0) plane and the (2.2.0) plane. 4. _4. Surface roughness R _rms ; same as in Example 1 5. d and Δd; same as in Example 1 Inner circumference 2F output relative value (%); calculated assuming that the initial 2F output value of Example 2-1 is 100%. The drive used is PD211 (manufactured by Toshiba Corporation).

[0175]

[Table 3]

As is clear from Table 3, the samples of the examples are
0.001 μm ≦ Δd ≦ 0.5 μm, and Δd ≦
0.50d, and the average particle size of the inorganic powder contained in the lower non-magnetic layer is 〜 to 4 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer. R
_An excellent magnetic recording medium having a small _rms , a d / R _rms of 30 or less, a uniform magnetic layer having excellent surface properties, a high reproduction output, and extremely few pinholes. In Comparative Example 2-1, the reproduction output is slightly inferior because the thickness d of the magnetic layer is as thick as 1.2 μm.

Example 3 In the same coating solution composition for the upper magnetic layer and the lower non-magnetic layer as in Example 1-1, the factors described in Tables 4 and 5 (particularly the average particle diameter of the inorganic powder of the lower non-magnetic layer and the upper layer Various samples were prepared by changing the average long axis length of the ferromagnetic powder of the magnetic layer), and the performance was evaluated in the same manner as in Example 2. The results are shown in Table 4.

Squareness ratio: The application direction Br / Bm when measured with a vibration sample magnetometer (VSM; manufactured by Toei Kogyo Co., Ltd.) at 5 mOe was defined as the squareness ratio.

[0179]

[Table 4]

As is clear from the above table, the example samples were
d ≦ 1.0 μm and 0.001 μm ≦ Δd ≦ 0.5 μm
Where Δd ≦ 0.50d is satisfied, and the average particle size of the inorganic powder contained in the lower nonmagnetic layer is not more than １ ／ times the average major axis length of the ferromagnetic powder contained in the upper magnetic layer. _Therefore , d / R _rms is 30 or more, a uniform magnetic layer is formed, a reproducing output is high, and an excellent magnetic recording medium with few pinholes is provided. Comparative example 3-1
Has a poor reproduction output because the thickness d of the magnetic layer is as thick as 1.3 μm. Comparative Example 3-2 is an example of a single magnetic layer, in which there is no lower non-magnetic layer and d is thin, so that coatability and electromagnetic conversion characteristics are inferior.

Example 4 Example 2-1 Co-modified γ in the composition of the coating solution for the upper magnetic layer
The exception that the Fe ₂ O ₃ in the following ferromagnetic powder Example 2
The same coating solution as the coating solution for the upper magnetic layer and the coating solution for the lower non-magnetic layer in Example 1-1 were prepared, and a sample of Example 4-1 was prepared.

Ferromagnetic Powder (Hexagonal Barium Ferrite) Average Plate Diameter 0.05 μm, Plate Ratio 4 Specific Surface Area by BET Method 39 m ² / g Hc 1100 Oe Also, the factors shown in Table 5 (particularly, the inorganic property of the lower non-magnetic layer) The ratio of the average particle diameter of the powder to the average plate diameter of the ferromagnetic powder in the upper magnetic layer) was changed to prepare samples, Examples 4-2 to 4-3 and Comparative example 4-1. Evaluation was performed similarly, and the results are shown in Table 5.

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

[0184]

[Table 5]

From Table 5, it is found that the sample of the example has d ≦ 1.0 μm
0.001 μm ≦ Δd ≦ 0.5 μm, and Δd
≤0.50d, the average particle size of the inorganic powder contained in the lower non-magnetic layer is less than the average plate diameter of the plate-like ferromagnetic powder contained in the upper magnetic layer, so that the perpendicular squareness ratio is high,
A uniform magnetic layer is formed. Therefore, the sample of the example is an excellent magnetic recording medium having a high D50 and very few pinholes. On the other hand, the comparative example is 0.001μ.
m ≦ Δd ≦ 0.5 μm is not satisfied. Comparative Example 4-1 is
This is an example of a single magnetic layer without a lower nonmagnetic layer, and D50 is poor.

Example 5 A coating solution for the upper magnetic layer and a coating solution for the lower nonmagnetic layer were prepared according to the following formulations. Example 5-1 Coating solution for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% by weight Inorganic powder surface treatment layer Al ₂ O ₃ (10% by weight) BET method Specific surface area according to 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 carbon black 20 parts Average particle diameter 16 nm DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface according to BET method 250 m ² / g Volatile 1.5 weight % vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization of 400 polyester polyurethane resin 5 parts of neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group 1 × 10 ^-4 e / G containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Coating solution for upper magnetic layer Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET method Specific surface area of 60 m ² / g Crystallite size 195Å Average major axis length 0.20 μm, needle ratio 10 Saturation magnetization (σ _S ): 130 emu / g Surface treatment layer: Al ₂ O ₃ , SiO ₂ vinyl chloride copolymer 12 parts -SO ₃ Na group 1 × 10 ^-4 eq / g, degree of polymerization 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group 1 × Α-alumina containing 10 ⁻⁴ eq / g (average particle size 0.3 μm) 2 parts carbon black (average particle size 0.1 0 part) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 50 parts Toluene 60 parts For each of the above two paints, each component was kneaded with a continuous kneader and then dispersed using a sand mill. Add 1 part of polyisocyanate to the resulting dispersion and 1 part to the coating liquid of the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and further add 40 parts of butyl acetate to each, having an average pore diameter of 1 μm. The mixture was filtered using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The coating liquid for the lower non-magnetic layer obtained 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 multilayer coating is performed on a polyethylene terephthalate support having a center average surface roughness of 0.01 μm, and while both layers are still wet, oriented by a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss After drying, a treatment was performed at a temperature of 90 ° C. using a seven-stage calender composed of only metal rolls, slit to a width of 8 mm, and an 8 mm video tape of Example 5-1 was manufactured.

Similarly, the samples, Examples 5-2 to 5-12 and Comparative examples 5-1 to 5-5 were prepared by changing the factors described in Tables 6 and 7.
-3, and the performance was evaluated in the same manner as described above. The results are shown in Tables 6 and 7. The relative speed of 8mm video is 38
m / sec, and the 7 MHz recording wavelength is 0.54 μm. Therefore, λ / 50 is 10.8 nm. Center line average surface roughness (Ra): Area R of about 250 μm × 250 μm by MIRAU method using TOPO3D manufactured by WYKO.
a was measured. The measurement wavelength is spherical correction at about 650 nm.
Cylinder correction was added.

[0189]

[Table 6]

[0190]

[Table 7]

As is clear from the above table, the example samples were
d ≦ 1.0 μm and 0.001 μm ≦ Δd ≦ 0.5 μm
It satisfies Δd ≦ 0.50d, and includes a treatment layer of Al ₂ O ₃ , SiO ₂ , ZrO _2, etc. on the surface of the inorganic powder as shown in the above table, so that the dispersibility is improved, Ra is low, λ
/ 50 (10.8 nm) or less and good electromagnetic conversion characteristics. Comparative Example 5-1 has poor electromagnetic conversion characteristics because the magnetic layer is thick. In Comparative Example 5-2, a sample could not be prepared because of successive layers.

Example 6 A coating solution for the upper magnetic layer and a coating solution for the lower nonmagnetic layer were prepared according to the following formulations. Example 6-1 Coating solution for lower nonmagnetic layer; same as that for Example 5-1 Coating solution for upper magnetic layer 100 parts of Co-substituted barium ferrite Specific surface area by BET method 35 m ² / g Average particle size 0.06, plate shape The ratio 5 vinyl copolymer 9 parts -SO ₃ chloride Na group 1 × 10 ^-5 eq / g containing, polymerization degree 300 particulate abrasive (Cr ₂ O _3, average particle size 0.3 [mu] m) 7 parts toluene 30 parts Methyl ethyl ketone 30 parts The above composition was kneaded in a kneader for about 1 hour, and then the following composition was added and dispersed in the kneader for about 2 hours.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content Average molecular weight 35,000 Methyl ethyl ketone 200 parts Cyclohexanone 100 parts Toluene 80 parts Then, the following carbon black and coarse particle abrasive were added, and a dispersion treatment was performed at 2,000 rpm for about 2 hours with a sand grinder.

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

6 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts of tridecyl stearate 6 parts The coating solution for the upper magnetic layer and the coating solution for the lower non-magnetic layer obtained as described above were polyethylene terephthalate having a thickness of 75 μm. First, the coating solution for the lower non-magnetic layer was applied, and then the coating solution for the upper magnetic layer was applied in a wet state, and the back surface was similarly treated. The thickness of the lower non-magnetic layer was adjusted to 2.5 μm and the thickness of the magnetic layer was adjusted to 0.5 μm in dry film thickness. Thereafter, a calendar process was performed to obtain a magnetic recording medium. Thereafter, the magnetic recording medium was punched into a 3.5-inch cartridge, placed in a 3.5-inch cartridge having a liner installed inside, and a predetermined mechanical component was added thereto. Got a disc. Table 8
The samples described in Examples 6-2 to 6-7 were prepared by changing the factors described in the above, and the performance was evaluated. The results are shown in Table 8.

Initial innermost 2F output: A relative value was calculated with the sample of Example 6-1 taken as 100. The drive used is PD211 (manufactured by Toshiba Corporation). The recording wavelength is
1.428 μm. Therefore, λ / 50 is 28.5n
m. Surface roughness: Ra was measured in the same manner as in Example 5.

[0197]

[Table 8]

From the above table, it can be seen from the above table that the sample of the example was d ≦ 1.0 μm and 0.001 μm ≦ Δd ≦ 0.5 as in the case of the fifth example.
μm, and satisfies Δd ≦ 0.50d. In the embodiment, Al ₂ O ₃ , SiO ₂ , ZrO ₂
And so on, the dispersibility is improved, the Ra is low, and the electromagnetic conversion characteristics are good. Example 7 Polyethylene terephthalate (10 μm thick) was used as a support.
m, F5 value: MD direction 20 kg / mm ² , TD direction 1
4 kg / mm ² , Young's modulus: 750 kg / m in the MD direction
m ² , TD direction 470 Kg / mm ² ) or polyethylene terephthalate (thickness 7 μm, F5 value: MD direction 22 Kg / mm ² , TD direction 18 Kg / mm ² , Young's modulus: MD direction 750 Kg / mm ² , TD direction 7
50 kg / mm ² ), and the mixture was stirred with a disperser stirrer for 12 hours according to the following formulation to prepare an undercoat liquid.

Polyester resin (containing —SO ₃ Na group) 100 parts Tg 65 ° C. Na content 4600 ppm Cyclohexanone 9900 parts The obtained undercoat liquid was applied to the support at a dry thickness of 0.1 μm by bar coating using a bar coating.

On the other hand, a coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations. Formulation of coating solution for upper magnetic layer 100 parts of ferromagnetic powder: Fe alloy powder (Fe-Co-Ni); composition: Fe: Co: Ni = 92: 6: 2 Al ₂ O ₃ is used as a sintering inhibitor Hc 1600 Oe, σ _S 119 emu / g Average major axis length 0.13 μm, needle ratio 7 Crystallite size 172 °, water content 0.6% by weight Vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g, − OH, epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g content —OH 8 × 10 ^{− 5} eq / g containing Tg 38 ° C., Mw 50000 α-alumina (average particle size 0.15 μm) 12 parts Specific surface area (S _BET ) by BET method 8.7 m ² / g pH 8.2, water content 0.06% by weight Shiku After 6 hours mixed and dispersed in a sand mill hexanone 150 parts Methyl ethyl ketone 150 parts The above composition,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid, and 1.5 parts of butyl stearate were added to obtain a coating solution for an upper magnetic layer.

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

The above coating solution was applied in a wet state using two doctors having different gaps, and then applied to the permanent magnet 3.
After orientation treatment with 500 gauss and then 1600 gauss solenoid, it was dried. After that, a super calender treatment using a metal roll and a metal roll was performed at a temperature of 80 ° C. The thickness d of the magnetic layer was 0.3 μm and the thickness of the non-magnetic layer was 3.0 μm.

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

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

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

The average value d of the thickness of the magnetic layer was 0.3 μm. Practically 1.0 μm or less, particularly preferably 0.6 μm
m. The magnetic layer thickness variation Δd is
0.07 μm, 0.001 μm ≦ Δd ≦ 0.5 μm and Δd ≦ 0.50d, and the standard deviation σ of the thickness of the magnetic layer
Was 0.08 μm or less. In practice, σ is 0.2μ
m, particularly preferably 0.1 μm or less. According to the same measurement, in Example 1-4, σ was 0.06 μm.
m.

The magnetic tape was stretched so that the magnetic layer was floated from the support, and the magnetic layer was peeled off with a cutter blade. 500 mg of the separated magnetic layer is added to 1N-NaO
The mixture was refluxed in 100 ml of an H / methanol solution for 2 hours to hydrolyze the binder. Since the ferromagnetic powder sinks to the bottom due to its large specific gravity, the supernatant was removed. Then, it was washed with water three times by decantation, and then washed three times with THF. The obtained ferromagnetic powder was dried with a vacuum dryer at 50 ° C. Next, the obtained ferromagnetic powder was dispersed in collodion, and observed at 60,000 times using a TEM. As a result, the average major axis length of the ferromagnetic powder was 0.13 μm, and the acicular ratio was 10. Similarly, in Example 1-2, the average major axis length was 0.25 μm, and the acicular ratio was 15. It has been found that the average major axis length needs to be 0.4 μm or less in practical use, and preferably 0.3 μm or less. Further, it has been found that the needle ratio needs to be 2 to 20, and preferably 2 to 15 in practical use. (2) AFM (Atomic Force Micro)
Scope) The surface roughness R _rms was measured. Digita the magnetic layer surface
l Instrument's Nanoscope II
, Tunnel current 10 nA, bias voltage 400 m
V was scanned over a range of 6 μm × 6 μm. For surface roughness, R _rms in this range was determined.

As a result, R _rms was 6 nm. It has been found that a thickness of 20 nm or less is necessary for practical use, and it is preferably 10 nm or less. Similarly, the result of Example 1 can be referred to. (3) Surface roughness meter The surface roughness was measured using 3d-MIRAU. WYK
About 250μ by MIRAU method using TOPO3D manufactured by Company O
Ra, R _rms , Peak-Va of area of mx250 μm
The lley value was measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by light interference. Ra was 2.7 nm. Practically, Ra was found to be preferably 1 to 4 nm, more preferably 2 to 3.5 nm. R _rms
Was 3.5 nm. It was found that the thickness is preferably 1.3 to 6 nm in practical use, and more preferably 1.5 to 5 nm. The PV value was 20 to 30 nm. 8 for practical use
0 nm or less is preferable, and 10-60 nm is more preferable.
It turned out to be. (4) VSM (vibrating sample magnetometer) The magnetic characteristics of the magnetic layer of the magnetic tape obtained using the VSM were measured. It measured with Hm 5kOe using the vibration sample type magnetometer made by Toei Industry Co., Ltd.

As a result, Hc was 1620 Oe and Hr (9
0 °) is 1800 Oe, Br / Bm is 0.82, SFD
Was 0.583. In practice, Hc is 1500 to 25
00 Oe is required, preferably 1600 to 2000 Oe
It turned out to be. Hr (90 °) is practically 100
From 0 to 2800 Oe, preferably from 1200 to 25
It was found to be 00 Oe. It has been found that Br / Bm is practically 0.75 or more, preferably 0.8 or more. It has been found that the SFD needs to be 0.7 or less practically, and preferably 0.6 or less. Example 3 also obtained similar results for practicality with similar measurements. (5) X-ray diffraction X-ray diffraction was performed using the ferromagnetic powder extracted from the magnetic layer in the above (1). The magnetic tape was directly applied to an X-ray diffractometer, and determined from the spread of the half value width of the diffraction lines on the (1,1,0) plane and the (2,2,0) plane. As a result, the crystallite size was found to be 180 °. Practically preferably 400 ° or less, particularly preferably 100 to 300 °.
It turned out to be. Similarly, it was 280 ° when measured in Example 5-2. (6) Tensile test Young's modulus, yield stress and yield elongation of the magnetic tape obtained by the tensile tester were measured. Tensile tester (Toy Baldwin universal tensile tester STM-T-50B
P) was measured at an atmosphere of 23 ° C. and 70% RH at a pulling rate of 10% / min.

As a result, the Young's modulus of the magnetic tape was 700
Kg / mm ^2, yield stress 6~7Kg / mm ^2, yield elongation was 0.8%. Practically preferably, Young's modulus is 4
00 to 2000 kg / mm ² , particularly preferably 500 to 2000 kg / mm ²
It was found to be 1500 kg / mm ² . It has been found that the yield stress is practically preferably 3 to 20 kg / mm ² , particularly preferably 4 to 15. The yield elongation is practically preferably 0.2 to 8%, particularly preferably 0.1 to 8%.
It was found to be 4-5%. (7) Flexural rigidity, annular stiffness Using a loop stiffness tester, width 8 mm, length 5
A 0 mm sample is formed into a ring, and the force required to give a displacement of 5 mm at a displacement speed of about 3.5 mm / sec is expressed in mg.

As a result, the thickness of the 8-mm p6-120 tape was 10.5 μm, and the stiffness was 40 to 40 μm.
It was 60 mm. It has been found that, for practical use, the thickness is 10.5 ± 1 μm, the stiffness is preferably 20 to 90 mg, and particularly preferably 30 to 70 mg. When the thickness is more than 11.5 μm, it is preferably 4 in practice.
It was found to be 0-300 mg. 9.5μ thick
In the case of m or less, it turned out that it is practically preferably 10-70 mg. (8) Stretching fracture The crack generation elongation was measured at 23 ° C. and 70% RH.

The both ends of the test piece having a tape length of 10 cm were set to 0.
The surface of the magnetic layer is observed under a microscope at a magnification of 400 at a pulling speed of 1 mm / sec, and the elongation at which five or more obvious cracks are formed on the surface of the magnetic layer is measured. As a result, the generated elongation was 4%. It turned out that it is practically preferably 20% or less, particularly preferably 10% or less. (9) The ESCA Cl / Fe spectrum α and the N / Fe spectrum β were measured.

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

The N-1S spectrum and Fe-2P (3
/ 2) The integral intensity ratio with respect to the spectrum was calculated and set to β. As a result, α was 0.45 and β was 0.07. In addition, according to the measurement of Example 2-5, α was 0.32,
β was 0.10. In practice, α is preferably 0.3
０．６0.6, particularly preferably 0.4-0.5. In practice, β is preferably 0.03 to 0.3.
It was found that the value was particularly preferably 0.04 to 0.1. (11) Leo vibron The dynamic viscoelasticity at 110 Hz was measured.

The viscoelasticity of the tape was measured at a frequency of 110 Hz using a dynamic viscoelasticity measuring device (Leo Vibron manufactured by Toyo Baldwin). Tg was the peak temperature of E ''. This method applies vibration from one end of the tape and measures the vibration that propagates to the other end. As a result, Tg was 73 ° C. and E ′
(50 ° C.) is 4 × 10 ¹⁰ dyne / cm ² , E ″ (5
0 ° C.) was 1 × 10 ¹¹ . In practice, it has been found that Tg is preferably from 40 to 120 ° C, particularly preferably from 50 to 110 ° C. Practically E '(50 ° C) is 0.8 × 10
^{It was found to be 11 to} 11 × 10 ¹¹ dyne / cm ² , particularly preferably 1 × 10 ^{11 to} 9 × 10 ¹¹ dyne / cm ² . For practical purposes, E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² ,
Particularly preferably, 0.7 × 10 ^{11 to} 5 × 10 ¹¹ dyne /
cm ² . (12) Adhesion strength The adhesion strength between the support and the magnetic layer was measured by a 180 ° peeling method.

The tape slit to a width of 8 mm was attached to a 3M adhesive tape, and the 180 ° peel strength was measured at 23 ° C. and 70% RH. The obtained result was 50 g.
In addition, the measurement of Example 2-1 was 25 g in the same manner.
It has been found that the adhesion strength is preferably at least 10 g, particularly preferably at least 20 g, in practical use. (13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured.

A sample was fixed on a prepared glass by attaching both ends of the sample with an adhesive tape, and a steel ball of 6.25 mmφ was slid by applying a load of 50 g. At that time, after running once at a speed of 20 mm / sec over a distance of 20 mm, the same operation was repeated 20 times while moving the steel ball to a new magnetic surface. Then, observe the sliding surface of the steel ball with a microscope of 40 times,
The diameter was determined assuming that the surface was a circle, and the amount of wear was calculated from the diameter.

The obtained result was 0.7 × 10 ^{−5 to} 1.1.
× 10 ⁻⁵ mm ³ . The sample of Example 2-2 had a size of 4 × 10 ⁻⁵ mm ³ . Practically, it is preferably 0.
It was 1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ , particularly preferably 0.4 × 10 ⁻⁵ to 2 × 10 ⁻⁵ mm ³ . (14) SEM (Scanning Electron)
ic Microscope) The surface condition of the magnetic layer was observed by SEM.

Magnification of 50 with a Hitachi electron microscope S-900
Five images were taken at a magnification of 00 and the abrasive on the surface was measured. As a result, the number of abrasives was 0.2 / μm ² . Further, the measurement of Example 3-6 was 0.4 / mm ² . In practice, it was found that the number of abrasives was 0.1 / μm ² or more, and particularly preferably 0.12 / μm ^{2 to} 0.5 / μm ² . (15) GC (Gas Chromatography) The residual solvent of the magnetic tape was measured by GC.

Gas chromatography GC manufactured by Shimadzu Corporation
Using a -14A, a 20 cm ² sample was heated to 120 ° C., and the residual solvent in the medium was measured. As a result, the residual solvent was 8 mg / m ² . In practice, preferably 50
mg / m ² or less, particularly preferably 20 mg / m ²
It turned out that: (16) Sol fraction The ratio of the soluble solid extracted from the magnetic layer of the magnetic tape with THF to the weight of the magnetic layer was determined. As a result, the sol fraction was 7%. In practice, the sol fraction is preferably 15
%, Particularly preferably 10% or less. (17) Magnetic development pattern The obtained magnetic recording medium having a width of 8 mm was applied to a Sony VTR.
Using EVO-9500, short-wavelength recording of 1 MHz was performed, only the recorded portion was slit into a width of 5 mm, and a solution of ferricolloid (approximately 100 ° φ) (manufactured by Taiho Kogyo Co., Ltd.) was flowed and magnetically developed. The product subjected to the immersion treatment for 24 hours was photographed with a differential interference microscope manufactured by Nippon Kogaku Co., Ltd. at a magnification of 10 with the interference color being blue. When the photograph is visually observed, a black or white line does not appear in the sample having the average thickness of the magnetic layer, but a black or white line appears when the thickness variation of the magnetic layer becomes large. This line is a portion having an uneven thickness, and it is preferable that such a black or white line be within 5 lines within a width of 5 mm. Further, the density difference between the black and white lines measured by a microdensitometer on those lines is preferably 0.2 or less, particularly preferably 0.1 or less. (18) Coefficient of friction (μ) 8 mm wide tape and sus420J, 4 mmφ rod
The tape was brought into contact at a wrap angle of about 180 ° with a tension of 0 g (T1), and the tension (T2) required to run the tape at a speed of 14 mm / sec under these conditions was measured and determined by the following equation.

Μ = (1 / π) · ln (T1 / T2) As a result, μ of the magnetic surface was 0.3. Practically, it was found that μ of the magnetic surface is preferably 0.15 to 0.4, and particularly preferably 0.2 to 0.35. Μ of the back layer surface was 0.2. Practically, μ of the back layer surface is preferably 0.15 to 0.4, and particularly preferably 0.2 to 0.4.
It turned out to be 0.35.

The coefficient of friction is determined in relation to the magnetic substance, abrasive, carbon black, lubricant, dispersant and the like. (19) Contact Angle Drops of water and methylene iodide were dropped on the magnetic layer, and the contact angles were measured with a microscope. In the case of water, it was 90 °.
In practice, the angle is preferably 60 to 130 °, particularly 80 °.
１２０120 ° was found to be preferred.

In the case of methylene iodide, the contact angle is 20
°. In practice, preferably 10 to 90 °,
Particularly preferably, it was 10 to 70 °. These contact angles are values determined by a lubricant and a dispersant. (20) Surface free energy of magnetic layer and back layer JP-A-3-119513, DK 0wens, J. App
l. polymer Sci., 13 (1969) and J. Panzer J. Colloid &
Based on the method described in Interfacial Sci., 44, No1.

As a result, both the magnetic layer and the back layer were 40 d thick.
yne / cm. Practically 10-100 dyne /
cm has been found to be particularly preferred. The surface free energy is a value determined by a lubricant and a dispersant. (21) Surface electric resistance A sample having a width of 8 mm and a cross section of a quadrant having a radius of 10 mm is used.
It was passed over two electrodes placed at an interval of mm and measured with a digital surface electric resistance meter TR-8611A (manufactured by Takeda Riken).

As a result, both the surface of the magnetic layer and the surface of the back layer were 1 × 10 ⁶ Ω / sq. 1 × 10 ⁹ Ω /
It was found that sq or less was preferable, and 1 × 10 ⁸ Ω / sq or less was particularly preferable. This surface electric resistance is a value determined by the ferromagnetic powder, binder, carbon black and the like.

The 8 mm video tape samples 1 and 2 having the above properties were compared with currently available tapes and the results are shown in Table 9.

[0227]

[Table 9]

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

C: Clogging lasting 30 seconds or more. Scratch: Run for 10 minutes in still mode. ○ No scratch is visually observed. X: Scratches are visually observed.

[Brief description of the drawings]

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

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

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

[Description of sign]

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

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoru Hayakawa 2-2-1-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd. (56) References JP-A-63-187418 (JP, A) JP-A Sho 62-188017 (JP, A) JP-A-2-15415 (JP, A) JP-A-2-24822 (JP, A) JP-A-58-56232 (JP, A) JP-A-59-103310 (JP, A A) JP-A-1-294810 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/70 G11B 5/712 G11B 5/738 G11B 5/842

Claims (4)

(57) [Claims] 1. A support comprising a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder, and an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder. In the magnetic recording medium, the average dry thickness (d) of the upper magnetic layer is 1.0 μm or less, and the average thickness change (Δd) at the interface between the upper magnetic layer and the lower nonmagnetic layer after drying. ) Is 0.001 to 0.5 μm, and the ferromagnetic powder contained in the upper magnetic layer and / or the nonmagnetic powder contained in the lower nonmagnetic layer has Al on the surface.
A magnetic recording medium comprising at least one selected from ₂ O ₃ , SiO ₂ and ZrO ₂ . 2. The method according to claim 1, wherein the ferromagnetic powder has an Al surface._TwoO_Three,
SiO_TwoAnd ZrO _TwoStrength with at least one selected from
2. The magnetic material according to claim 1, wherein the magnetic material is a magnetic metal powder.
Mind recording medium. 3. A non-magnetic inorganic substance contained in the lower non-magnetic layer
Powder has Al on the surface _TwoO_Three, SiO_TwoAnd ZrO_TwoFrom
Non-magnetic non-magnetic material with Mohs hardness of 3 or more
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is powder.
Recording medium. 4. A coating solution for a lower non-magnetic layer containing a non-magnetic powder and a binder, and a coating solution for an upper magnetic layer containing a ferromagnetic powder and a binder are prepared, and the lower non-magnetic layer is formed on a support. In the method for producing a magnetic recording medium in which the coating liquid for the upper magnetic layer is coated with the coating liquid for the upper magnetic layer, the ferromagnetic powder contained in the coating liquid for the upper magnetic layer and / or the nonmagnetic powder contained in the coating liquid for the lower nonmagnetic layer are preferably Having at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO ₂ on the surface, and coating the lower non-magnetic layer coating solution on the support, and obtaining the lower non-magnetic layer. In a wet state, the magnetic recording medium according to any one of claims 1 to 3, by applying the upper magnetic layer coating liquid simultaneously or sequentially with the application of the lower nonmagnetic layer coating liquid. A method for manufacturing a magnetic recording medium, comprising: