JPH08329460A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a producing method of such a high-density magnetic recording medium that although the medium is a coating type one, it not only gives a high frequency range output comparable to a vapor deposition tape but has traveling durability and storage property. CONSTITUTION: Each of a coating liquid for a lower nonmagnetic layer containing a nonmagnetic powder and a binder and a coating liquid for an upper magnetic layer containing a ferromagnetic powder and a binder is prepared, and the prepared liquids are applied on a flexible supporting body. The coating liquid for a lower nonmagnetic layer shows thixotropy and is first applied on a flexible supporting body. The coating liquid for an upper magnetic layer is applied while the lower nonmagnetic layer thus formed is in a wet state, or at the same time when the coating liquid for the lower nonmagnetic layer is applied, or successively after that. The average dry film thickness d of the upper magnetic layer is specified to <=1.0μm and the average thickness fluctuation Δd on the interface between the upper magnetic layer and the lower nonmagnetic layer after dried is in the relation of Δd<=0.50d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a very thin magnetic recording medium having a magnetic layer of 1.0 .mu. Or less. More specifically, it has excellent electromagnetic conversion characteristics. The present invention also relates to a method for manufacturing a magnetic recording medium having good yield and excellent production characteristics. In particular, the present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a high density thin layer magnetic recording medium having a magnetic layer thickness of 1.0 μ or less. The present invention relates to a method for manufacturing a magnetic recording medium having improved electromagnetic conversion characteristics, runnability and durability.

[0002]

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

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

However, in the conventional technique, the lower non-magnetic layer is first coated on the non-magnetic support, dried and then calendered, and then the upper magnetic layer is provided, so that the manufacturing process is It was complicated and had the following problems. That is, in order to thin the magnetic layer, it is conceivable to reduce the coating amount or to add a large amount of solvent to the magnetic coating liquid to reduce the concentration. If you take the former,
If the coating amount is reduced, there is not enough time for leveling after coating, and the drying starts, which causes a problem of coating defects such as streaks and marking patterns, resulting in a very low yield. When the latter method is adopted, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids,
There are various problems 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 Japanese Patent Laid-Open No. 63-191315, a non-magnetic layer is provided as a lower layer by using a simultaneous multi-layer coating method to prepare a magnetic coating solution having a high concentration. A method of thin coating has been proposed.

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

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

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

However, in order to apply the upper magnetic layer in a thin layer of 1.0 μm or less, the magnetic liquid must be diluted with a large amount of solvent, which easily promotes aggregation of the magnetic liquid.
Also, since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder is likely to be disturbed, and some performance can be secured in media that are not longitudinal recording, such as magnetic disks, but in tape-shaped magnetic recording media. 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. In addition, since the magnetic film was weak because the excessive drying caused many voids, the running durability was also insufficient. If it is attempted to improve the orientation and reduce the amount of the organic solvent to be diluted in order to reduce the voids in the coating film, the coating stability will deteriorate.

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

It has been proposed to improve the orientation of the upper magnetic particles by forming a conductive intermediate layer using graphite as the non-magnetic scaly particles.
(Japanese Patent Application Laid-Open No. 55-55438) However, although such a substance can improve the orientation, graphite itself does not have a reinforcing effect on the film and is insufficient in durability. Proposals to mix powders have also been made. (JP-A-60-125926) It has also been proposed to improve the orientation of the upper magnetic particles by forming a reinforcing layer using acicular oxalate as the non-magnetic acicular particles. . (Japanese Patent Publication Sho 58-51327
issue).

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

When the coercive force of the magnetic layer is low, self-demagnetization loss is large and it is not suitable for short wavelength recording. Therefore, it is necessary to have a considerable Hc. As means which can be used for such a purpose, the gap between the non-magnetic support and the magnetic layer is 0.5 μm to 5.
It has been proposed to provide an undercoat layer of 0 μm and Hc of the magnetic layer to 1000 Oe. (Japanese Patent Laid-Open No. 57-19853)
6) However, the conventionally known technique has the following problems in achieving this object. The above-mentioned JP-A-57-1
In the technique disclosed in Japanese Patent No. 98536, when the simultaneous multilayer coating of the upper and lower layers, which is a feature of the present invention, the upper and lower layers are mixed with each other, so that not only the surface property is bad but also the orientation is disturbed. Further, as a technique for improving the orientation in simultaneous multi-layer coating, Japanese Patent Laid-Open No. 3-4
Although it is disclosed that a layer in which carbon black is dispersed in 9032 is used as a lower layer and multi-stage orientation is performed, a filler having a small true specific gravity such as carbon black is used for simultaneous multi-layer coating due to the rotational movement of the magnetic substance during orientation. At some time, the interfaces between the upper and lower layers were disturbed, and the SQ measured in the in-plane direction was high, but the improvement of the residual coercive force in the direction normal to the magnetic layer, which is the purpose of this case, was insufficient.

As a known technique for such a technique, there is JP-A-62-1115. However, when this known technique is applied to simultaneous multi-layer coating as in the present application, there are the following problems. That is, in the case of simultaneous multilayer coating using a non-magnetic lower layer low specific gravity carbon black,
In the coating process or the orientation process, the non-magnetic lower layer and the magnetic layer are mixed with each other, or turbulence causes turbulence at the interface between the two layers. Such mixing and turbulence between the two layers extremely reduces the orientation of the magnetic material in the magnetic layer.

Further, since a magnetic material having a short major axis length and a small acicular ratio is less likely to be flow-oriented, the orientation of the magnetic material is further lowered, and sufficient electromagnetic conversion characteristics cannot be obtained. In recent years, the magnetic material contained in the magnetic layer has been made finer to increase the density. By using fine particles, the strength of the magnetic layer becomes inferior, and if a high tension is applied in the manufacturing process or in a video deck, for example, the tape will be elongated and skew (SKEW) distortion will increase. In order to prevent this, it has been attempted to reduce the heat shrinkage rate or increase the strength of the support, but there is a limit. Further, when the simultaneous multi-layer coating method is adopted, there is a problem that the heat shrinkage rate becomes larger and Skew strain increases as compared with the sequential multi-layer coating method. This is because in the case of sequential multilayer coating, the lower layer was hardened by calendering or curing treatment after coating the lower layer to make the medium hard to expand and contract, but in the simultaneous multilayer coating method, the lower layer and the upper layer are coated at the same time. This is because the expansion and contraction of the medium cannot be suppressed by the lower layer. JP-A-63-187418 and JP-A-63-191315 disclose inventions based on the simultaneous multi-layer coating method, but have such drawbacks.

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

As shown in JP-A-63-191315, it was confirmed that the lower non-magnetic layer did not contain polyisocyanate in order to improve the contact with the head.
Therefore, the result is that the storage stability at high temperature and high humidity is poor. For this reason, it is effective in a system that does not emphasize storage, but is difficult to use in a system that emphasizes storage such as business use or data storage. JP-A-63-18741
Regarding No. 8 as well, it is disclosed that the magnetic layer is thinned to improve the electromagnetic conversion characteristics in the same manner. However, in the present invention, there were still insufficient electromagnetic conversion characteristics. JP-A-50-8
No. 03 has an invention that a fine granular non-magnetic pigment having a Mohs hardness of 6 or more is provided between the magnetic layer and the support. The essence of this invention is to polish an aluminum substrate with a non-magnetic powder having a Mohs hardness of 6 or more. The purpose is to increase the flatness of the substrate.

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

Next, various patent applications have been filed for obtaining a magnetic recording medium in which the upper layer is a magnetic layer and the lower layer is non-magnetic, and the method is Wet on Wet. For example, in JP-A-50-104003, there is a description suggesting Wet on Wet, but the nonmagnetic layer is an example of only carbon black, and the structural viscosity is too strong, and the interface disorder is severe.

In addition, Japanese Patent Laid-Open No. 62-2122922 (US
Japanese Patent No. 4916024) discloses a magnetic recording medium containing 5% to 25% of ferromagnetic powder of carbon black in the conductive layer (intermediate layer). This is added to improve the dispersibility of carbon black,
Since the ferromagnetic powder to be added to the intermediate layer is the same as that in the magnetic layer, the disorder of the interface could not be satisfactorily prevented. Further, in JP-A-62-214524, each coating solution composition is selected so as to have mutual solubility in the solvent and solute of each coating solution composition of a plurality of adjacent layers.
A method of manufacturing a magnetic recording medium which is applied and dried by et on Wet is disclosed. However, although there is an example of the combination of the upper magnetic layer and the lower non-magnetic layer, it is an example of only the binder and suggests that carbon black is also contained in the intermediate layer, but based on such a disclosure, It was not possible to eliminate the disorder of the interface. In addition, JP-A-62-241
No. 130 (US Pat. No. 4,839,225) is 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. To improve the adhesion strength between the intermediate layer and the magnetic layer. Although it is stated that carbon black may be added to the intermediate layer and that it may be applied by the Wet on Wet method, such a disclosure could not solve the interface fluctuation.

Further, JP-A-63-88080 (US
No. 4,854,262) discloses a coating device having an improved doctor edge. Although there is a disclosure of viscosity at a high shear rate (10 ⁴ sec ^-1 ) in this, only the viscosity of the upper layer and lower layer liquids is shown, and such a disclosure cannot sufficiently suppress the interfacial fluctuation. It was In addition, JP-A-6
Japanese Unexamined Patent Publication No. 3-146210 discloses a magnetic recording medium in which the binder of the lower magnetic layer or the non-magnetic layer is a non-curable binder and the binder of the uppermost magnetic layer is an electron beam curable resin. There is. However, only the example in which the lower non-magnetic coating material contained carbon black was not able to solve the disorder of the interface. Further, in Japanese Patent Laid-Open No. 63-164022, a nonmagnetic liquid layer having a viscosity lower than that of the magnetic liquid layer is formed in the center of the slot of the extrusion type head on the front and rear wall surfaces of the slot, and extrusion coating of multiple layers is performed. A method of applying a magnetic liquid is disclosed. The inventors have 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 the purpose is to reduce the gap between the magnetic layer coating liquid bead and the Giessor. Disturbances at the interface could not be sufficiently solved only by such disclosure. Also, JP-A-63-187418 (US4863)
No. 793) discloses a magnetic recording medium in which the ferromagnetic powder contained in the 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 300Å by an X-ray diffraction method. Has been done. It is disclosed that the lower non-magnetic layer can contain carbon black, graphite, titanium oxide and the like, and specific examples include α-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 cannot sufficiently solve the disorder of the interface.

Further, JP-A-63-191315 (U
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.
A magnetic recording medium having a size of m or more is disclosed. Specific examples of the non-magnetic powder contained in the lower non-magnetic layer include α-Fe ₂ O ₃ 10 as in the above-mentioned JP-A-63-187418.
A combination of 0 parts by weight and 10 parts of conductive carbon is disclosed. However, the amount of carbon used is small α-
Since the particle size of Fe ₂ O ₃ is not described, the disclosure of these publications cannot solve the disorder of the interface.

Further, in Japanese Patent Laid-Open No. 2-254621, a non-magnetic layer containing carbon black as a main component is provided, and a magnetic layer containing Fe--Al based ferromagnetic powder is formed thereon by a wet-on-wet multi-layer coating method. A formed magnetic recording medium is disclosed. However, the lower layer is exemplified only by carbon black, and the structural viscosity was too strong to solve the disorder of the interface.

Further, JP-A-2-257424 discloses a magnetic recording medium containing a filler having an average particle diameter of 50 mμ or more in a non-magnetic layer. As the filler, abrasives such as carbon black, Al ₂ O ₃ and SiC are listed. However, the 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 interface disorder.

Next, in JP-A-2-257425, the dynamic friction coefficient is 0.25 or less and the surface specific resistance is 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 SnO ₂ only and carbon black only,
It was not possible to solve the disorder of the interface. In addition, JP-A-2
-260231 discloses a magnetic recording in which a first non-magnetic layer, a first magnetic layer, a second non-magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support. A medium is disclosed. This non-magnetic layer is only an example of the binder, and the disorder of the interface could not be resolved.

Further, JP-A-3-49032 (US5
No. 051291), the thickness of the magnetic layer is 1.5 μm.
A magnetic recording medium having the following ratio and a squareness ratio of the magnetic layer of 0.85 or more is disclosed. 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 was too strong to solve the interface disorder.

In recent years, research on Hi8 tapes has been made, and the ultimate need is to satisfy both the merits of ME (vapor deposition) tapes and MP (metal) tapes. The most important issue was how to achieve high C / N in the short wavelength region (luminance signal in the high frequency range) of vapor deposition tape while maintaining the running property, durability, and production suitability. .

Conventionally, the double coating technique is a VTR
Focusing on the signal recording mechanism, that is, the recording depth of each signal, the performance has been improved by designing the optimum upper and lower magnetic layers for each. The VHS double coating has a two-layer structure in which upper and lower layers are made of ferromagnetic powders having different sizes and magnetic characteristics, and high output and low noise have been realized in all bands of brightness, color and sound.

In the Hi8MP multilayer tape, the upper magnetic layer is made of a metal magnetic material suitable for high density recording, and the lower magnetic layer is made of an iron oxide magnetic material excellent in middle and low range characteristics.
The so-called high grid double coating, which uses a completely different kind of magnetic material, was developed, and the image quality was greatly improved by vividly reproducing images with high sharpness.

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

[0030]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a high density magnetic recording medium which, while being a coating type, exhibits a high frequency output comparable to that of a vapor deposition tape and has running durability and storage stability. It is to provide a manufacturing method. A second object of the present invention is to provide a method for manufacturing a thin-layer magnetic recording medium which has a high yield and ensures production efficiency and is excellent in output, C / N ratio, and other electromagnetic conversion characteristics. It is an object of the present invention to provide a method for manufacturing a thin-layer magnetic recording medium having good storage stability and good storage stability.

A third object of the present invention is to provide a method of manufacturing a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability. In particular, it is an object of the present invention to provide a method of manufacturing a magnetic recording medium which has a high output in short wavelength recording and a good yield in production. A fourth object of the present invention is to provide a method of manufacturing 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 method for producing a magnetic recording medium which has good electromagnetic conversion characteristics and good running properties, and in particular, the simultaneous multilayer coating method provides good surface roughness and high electromagnetic properties. A method of manufacturing a magnetic recording medium having conversion characteristics is provided. A sixth object of the present invention is to provide a method of manufacturing a magnetic recording medium having good electromagnetic conversion characteristics, and a method of manufacturing a magnetic recording medium having a small heat shrinkage ratio and excellent long-term storage stability. is there. A seventh object of the present invention is to provide a method for manufacturing a magnetic recording medium having good electromagnetic conversion characteristics, and to provide a method for manufacturing a magnetic recording medium excellent in running durability with little edge damage due to repeated running. Is.

[0033]

Means for Solving the Problems As a result of intensive investigations by the present inventors, although the conventional simultaneous multi-layer coating technique is partially based, it exceeds the frame and becomes larger as the wavelength becomes shorter. It was found that there are two important points: development of a new magnetic material and high density packing in order to make the magnetic layer thinner and the magnetic energy of the magnetic layer as high as possible. It was First, the signal loss was thoroughly reduced. In magnetic recording, various "losses" occur during the recording / reproducing process. However, the present inventors have found that by reducing the "self-demagnetization loss" which has been considered inevitable with MP (metal) tapes, a high level is achieved. I found a completely new way of thinking about improving the region characteristics. That is, the present invention has the following configurations. (1) A lower non-magnetic layer coating solution containing a non-magnetic powder and a binder and an upper magnetic layer coating solution containing a ferromagnetic powder and a binder were prepared, and the lower non-magnetic layer was formed on a flexible support. In the method for producing a magnetic recording medium, which comprises applying a coating liquid for a layer and a coating liquid for an upper magnetic layer, the coating liquid for the lower non-magnetic layer has thixotropy and is used for the lower non-magnetic layer on the flexible support. When the lower non-magnetic layer obtained by applying the coating solution is wet, the upper magnetic layer coating solution is applied simultaneously or sequentially with the application of the lower non-magnetic layer coating solution, and the upper magnetic layer is applied. Has an average dry thickness d of 1.0 μm or less, and the average thickness variation Δd at the interface between the upper magnetic layer and the lower non-magnetic layer after drying is Δd ≦ 0.50d. And a method for manufacturing a magnetic recording medium. (2) The dry thickness average value d of the upper magnetic layer is λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ, and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 50, and The method for producing a magnetic recording medium according to (1) above, wherein the shortest recording wavelength λ is 2 μm or less. (3) Scanning tunneling microscope of the surface of the upper magnetic layer (S
TM) method or atomic force microscope (AFM) method, the root mean square roughness R _rms has a relationship of 30 ≦ d / R _rms with the dry thickness average value d of the magnetic layer. The method for producing a magnetic recording medium according to (1) or (2).
(4) The magnetic recording medium according to any one of (1) to (3), wherein the magnetic recording medium has a heat shrinkage ratio of 0.4% or less after being stored at 70 ° C. for 48 hours. Recording medium manufacturing method. (5) The dry thickness of the lower non-magnetic layer is 1 to 30 times the d of the upper magnetic layer, and the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer. The difference is -5
% To + 20%, wherein (1)
(4) The method for manufacturing a magnetic recording medium according to any one of (4). (6) The ratio SMD / STD of the application direction (longitudinal direction) stiffness SMD of the magnetic recording medium to the width direction relative to the application direction SMD / STD is 1.0 to 1.9. The method for manufacturing a magnetic recording medium according to any one of 1) to (5). (7) The nonmagnetic powder contained in the coating liquid for the lower nonmagnetic layer contains an inorganic powder, and the inorganic powder has a Mohs hardness of 6 or more and an average primary particle diameter of 0.15 μm or less from spherical to cubic polyhedron. The method for producing a magnetic recording medium according to any one of (1) to (6) above, wherein the magnetic recording medium is made of a granular inorganic powder. (8) The non-magnetic powder contained in the coating liquid for the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size thereof is a needle-like ferromagnetic powder contained in the coating liquid for the upper magnetic layer. The method for producing a magnetic recording medium according to any one of (1) to (7) above, wherein the crystallite size is 1/2 to 4 times. (9) The non-magnetic powder contained in the coating liquid for the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle diameter thereof is a needle-like ferromagnetic powder contained in the coating liquid for the upper magnetic layer. The method for producing a magnetic recording medium according to any one of (1) to (8) above, wherein the major axis length is ⅓ or less. (10) The above-mentioned (1), wherein the coating liquid for the lower non-magnetic layer contains a magnetic powder imparting thixotropy.
(9) The method for manufacturing a magnetic recording medium according to any one of (9). (11) Any one of the above (1) to (10), wherein Bm of the lower non-magnetic layer is 500 gauss or less.
A method of manufacturing a magnetic recording medium according to item. (12) The lower non-magnetic layer coating liquid contains magnetic powder,
The method for producing a magnetic recording medium according to any one of (1) to (11) above, wherein the lower non-magnetic layer is a layer that does not participate in recording. (13) The support is polyethylene terephthalate, polyethylene naphthalate polyesters, polyolefins, cellulose triacetate, polycarbonate.
(1), which is at least one selected from the group consisting of polyamide, polyimide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide.
The method for manufacturing a magnetic recording medium according to any one of (12). (14) The bending rigidity (annular stiffness) of the magnetic recording medium is 40 to 30 when the total thickness is thicker than 11.5 μm.
0 mg, 20 to 90 when the total thickness is 10.5 ± 1 μm
10 mg when the total thickness is less than 9.5 μm.
70 mg, (1) to (13) above
The method for manufacturing a magnetic recording medium according to any one of 1. (15) The crack generation elongation of the magnetic layer of the magnetic recording medium measured at 23 ° C. and 70% RH is 20% or less, and the magnetic recording medium according to any one of (1) to (14) above. Manufacturing method of magnetic recording medium of. (16) The Cl / Fe spectrum α of the surface of the upper magnetic layer measured by an X-ray photoelectron spectrometer of the magnetic recording medium is 0.3 to 0.6, and the N / Fe spectrum β is 0.03 to. (1), characterized in that it is 0.12
(15) A method for manufacturing a magnetic recording medium according to any one of (15). (17) The wear of a steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ (1) to (16) The method for manufacturing a magnetic recording medium according to any one of 1. (18) The number of visually observed abrasives on the surface of the upper magnetic layer taken by SEM (electron microscope) at a magnification of 50,000 times for 5 sheets of the magnetic recording medium is 0.1 / μm 2 or more. The method for manufacturing a magnetic recording medium according to any one of (1) to (17) above. (19) Short wavelength recording of 1 MHz was performed on the upper magnetic layer of the magnetic recording medium, magnetic development was performed using a ferri colloid, and continuous black was observed in a 5 mm wide sample observed at 10 times using a differential interference microscope. Alternatively, the number of white lines is 5 or less, and the method for producing a magnetic recording medium according to any one of (1) to (18) above. (20) The in-plane squareness ratio in the coating direction (longitudinal direction) of the upper magnetic layer of the magnetic recording medium is 0.7 or more, and the squareness ratio in the vertical direction is 0.6 or more. 1)
(10) A method for manufacturing a magnetic recording medium according to any one of (10).

That is, the first point of the present invention is that the coating liquid for the upper magnetic layer and the lower non-magnetic layer have thixotropic properties, and preferably the thixotropic properties of the coating liquid for the upper magnetic layer and the lower non-magnetic layer are the same or By approximating the above values, it was possible to realize an unprecedented uniform thin magnetic layer in which the average dry thickness d of the magnetic layer was 1.0 μm or less and the average thickness variation Δd was 0.50 d or less. This is a significant reduction in self-demagnetization loss.

A second point of the present invention is to suppress the above-mentioned disturbance of the interface to a very low level and to determine the size and shape of the ferromagnetic powder of the coating liquid for the upper magnetic layer and the size of the non-magnetic powder of the coating liquid for the lower non-magnetic layer. By adjusting the shape, a more uniform interface with less fluctuation was realized and an ultra-smooth magnetic layer surface was completed. This smooth surface of the magnetic layer completely banished "space loss", improving high-frequency output.

The third point of the present invention is to increase the energy of the magnetic layer. It becomes possible to use fine particles of ferromagnetic powder with both Hr and Hc increased for the coating liquid for the upper magnetic layer, and it is possible to achieve high magnetic energy and high coercive force, and achieve a high frequency output equivalent to or higher than ME (vapor deposition) tape. I found that The fourth point of the present invention is dense packing. In the conventional technology, if the magnetic layer is simply thinned, the low-frequency output is lowered and the color characteristics are deteriorated.However, in the present invention, the fine particle inorganic powder having extremely high rigidity in the thickness direction greatly enhances the filling effect by the calendar treatment. It has been found that by improving and packing high-energy ferromagnetic powder at high density, excellent middle and low frequency characteristics can be realized.

The fifth point of the present invention lies in the properties such as viscoelasticity, adhesion strength, steel ball wear, residual solvent, and sol fraction, which ensure excellent durability that cannot be achieved by ME (vapor deposition) tape. As described above, the first to fifth points of the present invention act on each other in an organically complementary manner, in a complementary manner, and in a comprehensive manner, and a new layer structure that has never existed is an ultra-thin layer, an ultra-smooth layer,
It achieves super high filling and achieves epoch-making high frequency characteristics, which were difficult with conventional single layer coating technology, and excellent middle and low frequency characteristics.

First, the first point of the present invention will be described. The first point of the present invention is to realize an ultrathin magnetic layer. From the principle of self-demagnetization, the smaller the cross-sectional area of the magnetic layer, the smaller the loss. Therefore, it was discovered that it is essential to make the magnetic layer ultra-thin in order to increase the output of short wavelength signals. Moreover, if the thickness is 1 μm or more, the effect is small, and the effect increases as the effective recording thickness, which is generally called ¼ of the recording wavelength, is approached, that is, as the saturation recording is approached. is necessary.

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

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

The size depends on the shape of the magnet. That is, the smaller the cross-sectional area and the greater the distance between the magnetic poles, the smaller the demagnetizing field, and the less self-demagnetization occurs. Taking sewing needles and pachinko balls, which have completely different shapes, as examples, they are both made of iron and stick to magnets, but since the sewing needles have little self-demagnetization, it is easy for them to become magnets. Since the magnetism is large, it has the property that it is hard to become a magnet.

When this is replaced with a magnetic tape, the demagnetizing field is small in long wavelength (low range) recording, but short wavelength (high range).
As the recording is performed, the distance between the magnetic poles of the magnetization becomes smaller, the demagnetizing field increases, and the loss due to self-demagnetization increases. This is one of the major factors that deteriorate the high frequency characteristics of the tape. In order to reduce the self-demagnetization loss, it is effective to reduce the cross-sectional area, that is, reduce the thickness of the magnetic layer according to the principle of self-demagnetization. Moreover, the self-demagnetization loss becomes smaller as it approaches saturation recording and the output improves, so that it approaches the effective magnetic layer thickness which is said to be ¼ of the recording wavelength. An ultra-thin layer in the submicron region is required.

The shortest recording wavelength of Hi8 is 0.49 μm,
The wavelength is extremely short, and this is one of the reasons why it has excellent high-frequency characteristics similar to an extremely thin ME (evaporation) tape having a magnetic layer 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 the coating method used so far has to be considerably thicker than the recording wavelength. It was an inevitable large wall.

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

Next, the second point of the present invention will be described. The second point of the present invention is super smoothing of the magnetic layer surface. The double coating technology is originally a technology that can achieve 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, when the problem is a slight space loss of 0.5 μm or less at a shorter wavelength and further smoothness is aimed at, there is a limit only in the conventional technique.

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

In the present invention, in order to achieve ultra-smoothness of the interface between the upper and lower layers, the non-magnetic particles in the lower layer were made into ultrafine particles and the packing thereof was dense. On the other hand, however, since it is extremely fine particles, it is difficult to fill it uniformly and in high density as it is. Therefore, by applying a special surface treatment to each surface of the ultrafine particles to enhance the dispersibility, high-density filling is possible. And the smoothness of the interface between the upper and lower layers has been dramatically improved.

Since this non-magnetic layer is a high-density packing layer, it has a high degree of freedom in the surface direction of the tape and has excellent pliability, but it is well-suited to the force in the thickness direction. It exhibits high rigidity and further enhances the smoothing effect of calendering. As a result, Hi8
20% smoother than MP-DC,
The surface roughness of the magnetic layer was 2.5 nm. The ultra-smoothness, which can be realized only by Wet on Wet having the non-magnetic layer as the lower layer, can greatly reduce the space loss in the short wavelength region and improve the high frequency characteristics.

Next, the third point of the present invention will be described. The third point of the present invention is the high output and low noise of the magnetic layer, which is the basis of the technology for improving the performance of the magnetic tape.
In order to thoroughly pursue improvement of characteristics at short wavelengths, in addition to minimizing signal loss, the magnetic layer itself has high output and low noise due to "ultrafine particles of magnetic material, high energy and high density packing". Ization is essential. Next, the fourth point of the present invention will be described.

That is, the fourth point of the present invention is high-density packing, and it is the lower non-magnetic layer that enables high-density packing of ferromagnetic powder. The non-magnetic layer that is smooth and has extremely high rigidity in the thickness direction is super HDP (Hi
gh Density Packing) It firmly receives the strong pressure of the calendar and realizes an epoch-making high-density packing that has never been seen before.

Further, if the high-frequency characteristics are thoroughly pursued by making the magnetic layer ultra-thin, the conventional technology deteriorates the mid- and low-frequency characteristics.
Excellent color characteristics cannot be obtained. However, the lower non-magnetic layer of the present invention solves this problem and makes possible high packing of high energy magnetic material, which greatly improves the high frequency output and at the same time secures high middle and low frequency characteristics. It was possible to achieve excellent color output.

That is, according to the present invention, it is possible to achieve high-density recording comparable to vapor-deposited tape, which was conventionally considered impossible with a coating type magnetic recording medium. This is because the lower non-magnetic layer is in a wet state. By the so-called Wet on Wet method in which the upper magnetic layer is provided, a uniform upper magnetic layer can be formed as a thin layer having a dry thickness of 1.0 μm or less, and conventionally, such a Wet on Wet method was used.
The average value d of the dry thickness of the upper magnetic layer, which has not been achieved by the magnetic recording medium method according to the above method, is 1.0 μm or less,
Moreover, the high density recording medium of a coating type and comparable to a vapor deposition tape can be practically used only by setting the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer to be Δd ≦ 0.50d. Is obtained. 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.
Until now, no product was actually found on the market. The present invention is an epoch-making invention that breaks such conventional wisdom for the first time.

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

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

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

As a concrete means for achieving the above stipulation, firstly, the magnetic coating of the magnetic layer and each dispersion of the lower non-magnetic layer should have thixotropic properties, preferably the magnetic coating of the magnetic layer. It is to control the thixotropic properties of the respective dispersions of the lower non-magnetic layer so as to be similar or identical to each other. Secondly, the size and shape of the powder contained in the lower non-magnetic layer and the magnetic layer are specified. It is to control so that a mixed region does not occur dynamically in the upper and lower layers.

To impart thixotropic properties to dispersions prepared by dispersing non-magnetic powders or ferromagnetic powders in a binder, shear stress A10 ⁴ and shear stress at a shear rate of 10 ⁴ sec ^-1 are applied to each dispersion. Shear stress at a speed of 10 sec ^-1 Ratio of A10 ⁴ / A10 to 100 ≧ A10
^An example of adjustment is ⁴ / A10 ≧ 3.

Examples of the adjusting factors include (1) particle size (specific surface area, average primary particle diameter, etc.), and (2) structure (oil absorption amount, particle morphology, etc.) for the inorganic powder or magnetic powder to be dispersed. , (3) powder surface properties (pH, loss on heating, etc.), (4) particle suction force (σ _S, etc.), etc., for the binder, (1) molecular weight, (2) type of functional group, etc. Regarding the solvent, (1) type (polarity, etc.), (2) binder solubility, (3) solvent formulation amount, water content and the like can be mentioned.

Specific means for setting Δd ≦ 0.50d include, for example, the above-mentioned means (5) and (7) to (10). (5) The dry thickness of the lower non-magnetic layer is 1 to 30 times the d of the upper magnetic layer, and the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer. Is -5%
Within + 20% range. (7) The non-magnetic powder contained in the lower non-magnetic layer coating liquid contains an inorganic powder, and the Mohs hardness of the inorganic powder is 6 or more,
It is composed of spherical to cubic polyhedral inorganic powder having an average primary particle diameter of 0.15 μm or less. (8) The non-magnetic powder contained in the lower non-magnetic layer coating liquid is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size thereof is a needle-like ferromagnetic powder crystal contained in the upper magnetic layer coating liquid. 1/2 to 4 times the size of the child. (9) The non-magnetic powder contained in the lower non-magnetic layer coating liquid is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size of the non-magnetic powder is the length of the acicular ferromagnetic powder contained in the upper magnetic layer coating liquid. Must be 1/3 or less of the axial length. (10) The lower non-magnetic layer coating liquid contains a magnetic powder that imparts thixotropy.

The item (8) will be described below. In order to apply the upper magnetic layer to an ultrathin layer of 1 μm or less, wet multi-layer coating is required. At that time, the particle size of the inorganic powder contained in the lower non-magnetic layer coating solution and the upper magnetic layer coating solution are included. The fine surface roughness is determined in relation to the crystallite size of the ferromagnetic powder contained in. In the case of needle-like ferromagnetic powder, the crystallite size generally corresponds to the minor axis diameter. When the average particle size of the inorganic powder of the lower non-magnetic layer coating liquid is 1/2 or less of the crystallite size of the acicular ferromagnetic powder, dispersion itself becomes difficult,
Since a smooth lower layer surface cannot be obtained, the surface smoothness of the resulting magnetic recording medium is insufficient. Conversely, when the average particle size of the lower layer inorganic powder exceeds 4 times the crystallite size of the ferromagnetic powder, the interparticle distance between the lower layer powder particles increases, so the upper layer ferromagnetic powder affects the surface properties of the lower layer. Since it receives, it cannot obtain sufficient surface property. As shown in the examples, in order to obtain a sufficient surface property, an inorganic powder having an average particle diameter of 1/2 to 4 times, more preferably 2/3 to 2 times the crystallite size of the upper needle-like ferromagnetic powder is used. It is preferable. The shape of the inorganic powder is preferably spherical or dice. The Mohs hardness is 3 or more, preferably 4 or more, and more preferably 6 or more.

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

Next, (9) will be described below. It is necessary to increase the squareness ratio in order to maintain good electromagnetic conversion characteristics in wet multi-layer coating, but if the average particle size of the inorganic powder of the coating liquid for the lower non-magnetic layer is larger than that of the upper ferromagnetic powder, the lower layer particles The gap between them becomes large, and the orientation of the ferromagnetic powder is disturbed particularly at the interface between the upper layer and the lower layer, which deteriorates the surface property of the magnetic layer as in (8). 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 in the longitudinal direction. As a result of experimental confirmation of the requirements, it is found that the squareness ratio is equivalent to that of the single-layer magnetic layer in the case of needle-like ferromagnetic powder, 1/3 or less of the major axis length,
More preferably, 1/3 to 1/20 inorganic powder is used to obtain good surface property and squareness ratio.

In (9), the volume filling rate in the lower layer of the inorganic powder is preferably 20 to 60% for the same reason as in (8).

When the thickness of the magnetic layer is 5 times the major axis length or less, the filling degree by the calendar is remarkably improved, and a magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained. The preferred types and properties of the inorganic powder are the same as in (8).

The magnetic recording medium obtained by the manufacturing method of the present invention has an extremely smooth magnetic layer as described above, and the dry thickness average value d of the magnetic layer is λ / with respect to the shortest recording wavelength λ.
4 ≦ d ≦ 3λ and the surface roughness Ra of the magnetic layer is Ra ≦ λ
The relationship of / 50 is preferable. A preferred powder structure for this is that the ferromagnetic powder in the magnetic layer has a major axis length of 0.
Needle-like ferromagnetic powder of 3 μm or less or plate diameter of 0.3 μm
The following tabular ferromagnetic powder, the non-magnetic powder in the lower non-magnetic layer is granular particles having an average particle diameter of λ / 4 or less, or a major axis length of 0.05 to 0.2 μm and an acicular ratio. Is preferably 5 to 20, or plate particles having a plate diameter of 0.01 to 0.1 μm and a plate ratio (plate diameter / plate thickness) of 5 to 20. In the above aspect, in addition to the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer produced by the present invention (that is, the variation width in the thickness direction of the interface), the optimum thickness of the magnetic layer according to the recording wavelength is obtained. By defining the range, the surface roughness of the magnetic layer can be specified and improved, and the thickness of the magnetic layer can be made thin, uniform, and uniform, so that even if the recording wavelength becomes short, fluctuations in reproduction output and amplitude modulation noise will occur. It is possible to prevent this, and to realize high reproduction output and high C / N.

In other words, conventionally, when the recording wavelength becomes shorter when the magnetic layer becomes thinner, the entire magnetic layer contributes to recording and reproduction, so that when the thickness of the magnetic layer changes, reproduction output fluctuation and amplitude modulation noise are observed. However, the present invention solves this drawback.

In the present invention, the shortest recording wavelength λ varies depending on the type of magnetic recording medium.
5 μm and 0.67 μm for digital audio.

The range of d in the present invention is λ / 4 ≦ d ≦ 3λ,
Preferably, λ / 4 ≦ d ≦ 2λ (that is, 0.25 ≦ d /
λ ≦ 2). Further, d is usually 0.05 μm ≦ d ≦
The range is 1 μm, preferably 0.05 μm ≦ d ≦ 0.8 μm.

The dry thickness average value d of the magnetic layer is obtained by actual measurement as described above. For the element uniquely contained in the magnetic layer by fluorescent X-ray, a magnetic layer sample having a known thickness is measured and calibrated. It is also possible to create a line and then determine the thickness of the sample of unknown material from the intensity of the fluorescent X-ray. In the present invention, Δd is 0.50d or less, that is, Δd / d is 0.50.
Or less, preferably 0.30 or less, more preferably 0.
Control to 25 or less. The range of Δd is 0.001
To 0.5 μm, preferably 0.03 to 0.3 μm, and more preferably 0.05 to 0.25. Thereby, the uniformity of the magnetic layer thickness is ensured and the surface roughness Ra is set to Ra.
≦ λ / 50, that is, λ / Ra of 50 or more, preferably 75
As described above, more preferably 80 or more can be regulated. In the present invention, Ra represents a value obtained by measuring the center line average roughness measured using an optical interference roughness meter.

In the present invention, the upper magnetic layer is coated while the lower non-magnetic layer is in a wet state. In this case, the lower non-magnetic layer may be in the wet state in either simultaneous multi-layer coating or sequential coating. Application is preferred.

That is, according to the present invention, when the magnetic layer having a thickness of 1.0 μm or less is coated on the lower non-magnetic layer, the magnetic layer can be made thin alone, or the lower non-magnetic layer can be sequentially laminated in a dry state. In this case, a coating defect which is a problem can be prevented.

In the magnetic recording medium obtained by the present invention, it cannot be said that the thickness of the magnetic layer needs to 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 is smaller than λ / 4, the magnetic flux that contributes to reproduction is reduced and the output is reduced. In addition, since the short wavelength component is demagnetized by the deep recording magnetic field of the component having a long recording wavelength and simultaneously recorded when exceeding 3λ, the output is reduced. Therefore, d ≦ 3λ, preferably d ≦ 2λ
Is good.

C / which is the basic performance of the magnetic recording medium
When N is taken into consideration, in addition to the unevenness (so-called surface roughness) on the surface of the magnetic layer, which has been a problem in the conventional thick magnetic layer, there is a problem that the thickness variation at the interface between the non-magnetic layer and the magnetic layer becomes a problem. 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, which is not a problem in the conventional thick magnetic layer. In the present invention, the average value Δd of the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer is 0.
It was found that it is required to be 50 or less. The surface roughness of the magnetic layer is required to be smooth as in the conventional thick film magnetic layer, and the surface roughness Ra is
It is preferable to satisfy the relationship of Ra ≦ λ / 50.

According to the present invention, the treatment in a vacuum is a prerequisite, there is no problem of productivity and reliability of the metal thin film medium which is vulnerable to corrosion, the electromagnetic conversion characteristics are comparable to those of the metal thin film, and the productivity is excellent. A high performance coated magnetic recording medium can be obtained. In the magnetic recording medium manufactured according to the present invention, the root mean square roughness R _{rms of the} surface of the magnetic layer by the scanning tunneling microscope (STM) method is 30 ≦ d / between the mean value d of the dry thickness of the magnetic layer. It is preferable that there is a relationship of R _rms .

When the thickness of the magnetic layer becomes thin, self-demagnetization loss should be reduced and the output should be improved. The roughness increases. In order to improve output by reducing self-demagnetization loss, S that satisfies the relation of the above equation
Surface roughness by TM is preferred. R by AFM
_{The rms} is preferably 10 nm or less. It is preferable that the optical interference surface roughness Ra measured by 3d-MIRAU is 1 to 4 nm, and the PV value (Peak-Valley) value is 80 nm or less.

The glossiness of the surface of the magnetic layer is preferably 250 to 400% after calendering. In order to achieve high energy of the magnetic recording medium obtained by the present invention, the ferromagnetic powder contained in the coating liquid for the upper magnetic layer is
Needle-shaped ferromagnetic alloy powder having a major axis length of 0.3 μm or less and Hc of 1500 Oe or more, or a plate-shaped ferromagnetic powder having a plate diameter of 0.3 μm or less and Hc of 1000 Oe or more. Is preferred.

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

In order to obtain a magnetic recording medium in which a magnetic layer is densely packed according to the present invention, the ratio of the application direction stability SMD of the magnetic recording medium to the application direction (longitudinal direction) widthwise stability STD. SMD / STD is 1.0-1.
It is preferable to prepare each coating solution so as to be 9. In order to make the above-mentioned value of the stability, the inorganic powder contained in the coating liquid for the lower non-magnetic layer has a Mohs hardness of 6 or more and an average particle diameter of 0.15 μm or less from spherical to cubic polyhedral inorganic powder. Is preferably used.

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

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

Here, SMD / STD is 1.0 to 1.9,
It is preferably controlled to 1.1 to 1.85. In a magnetic recording medium having a total thickness of 13.5 ± 1 μm, SMD is
50-200 mg, preferably 50-150 mg, STD
Is 40 to 150 mg, preferably 50 to 130 mg. The means for controlling the value of SMD / STD is not particularly limited, but it is preferable to select the shape and the Mohs hardness of the inorganic powder contained in the lower layer. The inorganic powder contained in the lower layer has a Mohs hardness of 6 or more. It is desirable to select a spherical to cubic polyhedral inorganic powder having a particle size of preferably not less than 6.5 and an average particle size of not more than 0.15 μm, preferably not more than 0.12 μm.

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

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

Another embodiment for achieving a high density of the magnetic layer according to the present invention is as follows:
Each coating solution is prepared so that the heat shrinkage ratio after 48 hours is 0.4% or less. Specifically, the dry thickness of the lower non-magnetic layer is 1 to 30 times the d of the upper magnetic layer, and the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer. The difference is to be in the range of -5% to + 20%.

In this embodiment, a coating type magnetic recording medium having a magnetic layer having a d of 1.0 μm or less and improved self-demagnetization loss can be manufactured with high productivity without coating defects such as pinholes and stripes, and the magnetic recording medium can be manufactured. The heat shrinkage of is suppressed below a predetermined value. That is, in this embodiment, by controlling the heat shrinkage ratio after storage at 70 ° C. for 48 hours to 0.4% or less, the skew distortion is improved and reduced, and the magnetic conversion characteristics comparable to those of the ferromagnetic metal thin film are obtained. A method of manufacturing a recording medium is provided.

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

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

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

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

For example, as the particle size of the ferromagnetic powder, the crystallite size is 300 Å or less, preferably 100 to
250Å, the average major axis length is 0.005 to 0.4 μm, preferably 0.1 to 0.3 μm, and the average major axis length / crystallite size is 3 to 25, preferably 5 to 20. Is mentioned. The specific surface area of the ferromagnetic powder measured by the BET method is 25 to 80 m ² / g, preferably 30.
˜70 m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, surface properties are difficult to obtain, which is not preferable.

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

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

This carbon black is less than 50 parts by weight, preferably 13 parts by weight, based on 100 parts by weight of the above inorganic powder.
It is preferably added to the lower layer coating solution in a proportion of about 40 parts by weight. The carbon black is used for controlling the powder volume ratio of the lower layer by controlling the porosity, in addition to the functions of preventing static charge of the magnetic recording medium and strengthening the film strength. That is, when the porosity is high, the powder volume ratio is relatively reduced. It is effective to use carbon black having a structure or hollow carbon black as the carbon black for controlling the porosity.

The lower layer has a porosity of ± 10%.
Ranges are preferred. The porosity of the lower layer is 10 to 30%.
It is preferably in the range. Magnets produced by the present invention
The air recording medium preferably exhibits the following various characteristics,
The present invention provides a magnetic recording medium having excellent running durability.
Young's modulus of the magnetic recording medium measured by a tensile tester is 3
00-2000Kg / mm² , Preferably 400 to 1
500 kg / mm² And the Young's modulus of the magnetic layer is 4
00-5000Kg / mm² , Preferably 500-40
00 Kg / mm ² , Yield stress is 3 ~ 20Kg / mm² ,
Preferably 4-18 Kg / mm² , Yield elongation is 0.2 ~
8%, preferably 0.5-5%

This influences the durability because the ferromagnetic powder, the binder, the carbon black, the inorganic powder and the support are involved. The bending rigidity (annular stiffness) of the magnetic recording medium is preferably 40 to 300 mg when the total thickness is thicker than 11.5 μm, preferably 20 to 90 mg when the total thickness is 10.5 ± 1 μm, or 9. When it is thinner than 5 μm, it is preferably 10 to 70 mg.

This is mainly related to the support and is important for ensuring durability. The cracking elongation of the magnetic recording medium measured at 23 ° C. and 70% RH is preferably 20% or less. The Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium measured with an X-ray photoelectron spectrometer is preferably 0.3 to 0.6,
N / Fe spectrum β is preferably 0.03 to 0.12
Is.

This is related to the ferromagnetic powder, the inorganic powder and the binder, and is important in obtaining durability. Further, the glass transition temperature Tg of the magnetic layer measured on the magnetic recording medium using a dynamic viscoelasticity measuring device (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 40 to
120 ° C., the storage elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / cm ² , and the loss elastic modulus E ″ (50 ° C.) is preferably 0. 5x
It is preferably 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² . The loss tangent is preferably 0.2 or less. If the loss tangent is too large, sticking failure tends to occur. These are important properties associated with durability, associated with binders, carbon black, and solvents.

It is preferable that the 180 ° adhesive strength of the 8-mm wide tape at 23 ° C. and 70% RH between the flexible support and the magnetic layer is preferably 10 g or more. Further, the abrasion of the steel 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 that is directly related to the wear of the magnetic layer and is mainly associated with the ferromagnetic powder.

Further, five magnetic recording media of the present invention were photographed with an SEM (electron microscope) at a magnification of 50,000, and the number of abrasives on the surface of the magnetic layer was preferably 0.1 / μm ^2.
The above is desirable. The number of abrasives present on the end surface of the upper magnetic layer of the magnetic recording medium selected by the manufacturing method of the present invention is preferably 5 pieces / 100 μm ² or more. These are scales that are affected by the abrasive and binder in the magnetic layer and exert an effect on durability.

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

Further, it is desirable that the sol fraction, which is the ratio of the soluble solid content extracted with THF from the magnetic recording medium of the present invention to the magnetic layer weight, is 15% or less. This is influenced by the ferromagnetic powder and the binder,
It is a measure of durability. The magnetic recording medium selected by the manufacturing method of the present invention was recorded on the upper magnetic layer at a short wavelength of 1 MHz, magnetically developed using ferri colloid, and observed at 10 times magnification using a differential interference microscope. It is preferable that there are no more than 5 continuous black or white lines in the sample.

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

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

The general items that can be selected by the present invention will be described below.
I will describe. The non-magnetic inorganic powder that can be used in the present invention,
For example, metal, metal oxide, metal carbonate, metal sulfate,
Non-magnetic inorganic substances such as metal nitrides, metal carbides, and metal sulfides
A powder is mentioned. Specifically, TiO₂ (Rutile, Anna
Tase), TiO_X, Cerium oxide, tin oxide, oxide
Nungsten, ZnO, ZrO₂ , SiO₂ , Cr₂ O
₃ , Α-alumina, β-alumina, γ with α conversion rate of 90% or more
Alumina, α-iron oxide, goethite, corundum, silicon nitride
Element, titanium carbide, magnesium oxide, boron nitride,
Molybdenum disulfide, copper oxide, MgCO₃ , CaCO₃ ,
BaCO₃ , SrCO₃ , BaSO_Four , Silicon carbide, carbonized
Titanium or the like is used alone or in combination. this
Etc., the shape and size of the inorganic powder are arbitrary.
If necessary, combine different inorganic powders or individually
It is also possible to select the particle size distribution and the like of the non-magnetic powder.

The particle size is preferably based on the specific method of the above embodiment, but in the case of granular, spherical or polyhedral shape, it is generally from 0.01 to 0.7 μm, which is 1 at the shortest recording wavelength λ. It is preferably / 4 or less. In the case of needles or plates, the major axis length is 0.05 to 1.0 μm, preferably 0.05 to 0.5 and the needle ratio is 5 to 20, preferably 5 to 5.
15 or plate diameter 0.05 to 1.0 μm, preferably 0.05 to 0.5 μm, plate ratio (ratio between plate diameter and thickness)
5 to 20, preferably 10 to 20 are used.

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

The above inorganic powder does not necessarily have to be 100% pure, and its surface may be treated with other compounds such as Al, Si, Ti, Zr, Sn, Sb and Zn depending on the purpose. , Those oxides may be formed on the surface. At that time, if the purity is 70% or more, the effect is not reduced. The ignition loss is preferably 20% or less.

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

Examples of the inorganic powder used in the present invention include:
Particularly, titanium oxide (particularly titanium dioxide) is preferable. Hereinafter, the method for producing this titanium oxide will be described in detail. Titanium oxide is mainly produced by a sulfuric acid method and a chlorine method. In the sulfuric acid method, a raw ore of illuminite is distilled with sulfuric acid to extract Ti, Fe, etc. as sulfates. Iron sulfate is crystallized and removed, and the remaining titanyl sulfate solution is filtered and purified, and then thermally hydrolyzed to precipitate hydrous titanium oxide. After this is filtered and washed, foreign substances are washed and removed, and a particle size regulator and the like are added.
If it is fired at 1000 ° C., it becomes crude titanium oxide. The rutile type and the anatase type are classified according to the kind of core material added during hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. For the chlorine method, natural ore natural rutile and synthetic rutile are used. The ore is chlorinated in a high-temperature reduced state, Ti becomes TiCl ₄ and Fe becomes FeCl ₂ , and iron oxide that becomes solid by cooling is liquid TiCl ₄
And separated. The crude TiCl ₄ obtained is purified by rectification, then a nucleating agent is added, and the crude TiCl ₄ is instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher to obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

In the present invention, carbon black can be used in the lower layer, and R _S (surface electric resistance), which is a known effect, can be lowered. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the carbon black. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400, DBP oil absorption is 20-400 ml / 10
It is 0 g, preferably 30 to 200 ml / 100 g.
The average particle size is usually 5 to 80 mμ, preferably 10 to
It is 50 mμ, and more preferably 10 to 40 mμ. pH
Is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc.

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

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

These non-magnetic powders are usually used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.
Used in the range of 1. In general magnetic recording media, an undercoat layer is provided. This is provided to improve the adhesive strength between the support and the magnetic layer, and has a thickness of 0.5 μm. The following is different from the lower non-magnetic layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesiveness between the underlayer and the support.

As the ferromagnetic powder used in the coating liquid for the magnetic layer of the present invention, magnetic iron oxide FeOx (x = 1.33 to 1.
5), Co-modified FeOx (x = 1.33 to 1.5), F
Known ferromagnetic powders such as ferromagnetic alloy powders containing e, Ni or Co as a main component (75% or more), barium ferrite, strontium ferrite and the like can be used, but ferromagnetic alloy powders are more preferable. . These ferromagnetic powders include Al, Si, S, Sc, Ti, V, C in addition to the specified atoms.
r, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb,
Te, Ba, Ta, W, Re, Au, Hg, Pb, B
i, La, Ce, Pr, Nd, P, Co, Mn, Zn,
It may contain atoms such as Ni, Sr, and B. These ferromagnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before dispersion. Specifically, Japanese Patent Publication No. 44-1409
No. 0, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-220
No. 62, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28
466, Japanese Patent Publication No. 46-38755, Japanese Patent Publication No. 47-4
No. 286, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-1
No. 7284, Japanese Patent Publication No. 18-18509, Japanese Patent Publication No. 47-
No. 18573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48
-39639, U.S. Pat. Nos. 3,026,215 and 30,
No. 313341, No. 3100194, No. 3242005
No. 3,389,014 and the like.

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

[0116] Expressed ferromagnetic powder of the upper magnetic layer in the specific surface area by the BET method 25~80m was ² / g, preferably 40~70m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, surface properties are difficult to obtain, which is not preferable. The crystallite size of ferromagnetic powder is 450-
It is 100Å, preferably 350 to 100Å.
Σ _{S of} iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu / g or more, and in the case of ferromagnetic metal powder, 100 emu / g or more is preferable, and more preferably 11
It is 0 emu / g to 170 emu / g. Coercive force is 11
It is preferably 00 Oe or more and 2500 Oe or less, and more preferably 1400 Oe or more and 2000 Oe or less. The acicular ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.

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

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

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

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

When barium ferrite is used, the plate diameter means the plate width of hexagonal plate-like particles and is measured by using an electron microscope. In the present invention, this plate diameter is 0.001 to 1 μm.
Then, the plate thickness may be set to 1/2 to 1/20 of the diameter. The specific surface area (S _BET ) is preferably 1 to 60 m ² / g, and the specific gravity is preferably 4 to 6. Coating liquid for the lower non-magnetic layer of the present invention,
As the binder used in the coating liquid for the upper magnetic layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 100.
0-200000, preferably 10,000-10000
0, the degree of polymerization is about 50 to 1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, and various rubber resins. Also,
Examples of the thermosetting resin or reactive resin are phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin and isocyanate. Examples thereof include a mixture of prepolymers, a mixture of polyester polyols and polyisocyanates, a mixture of polyurethanes and polyisocyanates, and the like.

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

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

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

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

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

The content of the repeating unit having an epoxy group is lower than 1 mol%, or the repeating unit of vinyl chloride 1
The amount of the repeating unit having an epoxy group is 0.
If it is less than 01 mol, it may not be possible to effectively prevent the release of hydrochloric acid gas from the vinyl chloride-based copolymer, while on the other hand, it is higher than 30 mol% or has an epoxy group per 1 mol of vinyl chloride repeating units. When the amount of the repeating unit is more than 0.5 mol, the hardness of the vinyl chloride-based copolymer may decrease, and when this is used, the running durability of the magnetic layer may decrease.

Further, if the content of the repeating unit having a specific polar group is less than 0.01 mol%, the dispersibility of the ferromagnetic powder may be insufficient, and if it is more than 5.0 mol%, the co-weight will increase. The coalescence becomes hygroscopic and the weather resistance may deteriorate. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000.

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

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

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

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

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

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

The binder used in the coating liquid for the upper magnetic layer of the present invention is used in the range of 5 to 50% by weight, preferably 10 to 35% by weight, based on the ferromagnetic powder. When a vinyl chloride resin is used, it is preferably used in a range of 5 to 30% by weight, a polyurethane resin is used in a range of 2 to 20% by weight, and a polyisocyanate is used in a range of 2 to 20% by weight.

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

When the epoxy group-containing resin having a molecular weight of 30,000 or more is used in the present invention in an amount of 3 to 30% by weight based on the nonmagnetic powder, the resin other than the epoxy group-containing resin is added in an amount of 3 to 30% by weight based on the nonmagnetic powder. %, When using a polyurethane resin, 3 to 30% by weight and 0 to 20% by weight of polyisocyanate can be used, but the epoxy group is 4 × 10 ^{−5 with respect} to the total weight of the binder (including the curing agent). ~ 16x1
It is preferably contained in the range of 0 ⁻⁴ eq / g.

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

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

The carbon black used in the coating liquid for the upper magnetic layer of the present invention may be, for example, furnace for rubber, thermal for rubber, black for color or acetylene black. Specific surface area is 5-500 m ² / g, DB
P oil absorption is 10 ~ 400ml / 100g, particle size is 5m
μ-300 mμ, pH 2-10, water content 0.1-1
0% 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 200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 700, V
ULCAN XC-72, Asahi Carbon Co .: # 80, #
60, # 55, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo: #
2400B, # 2300, # 900, # 1000, # 3
0, # 40, # 10B, Colombian Carbon Co .: C
ONDUCTEX SC, RAVEN150, 50, 4
0, 15 and so on. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be graphitized on a part of the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the ferromagnetic powder. Carbon black has the functions of preventing electrification of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the lower layer and the upper layer, and can be used in accordance with the purpose based on the various characteristics shown above such as particle size, oil absorption, electric conductivity, and pH. Of course, it is possible to use them properly. The carbon black that can be used in the upper layer of the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

The abrasives used in the coating liquid for the upper magnetic layer of the present invention include α-alumina and β-alumina having an α conversion of 90% or more.
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, corundum, artificial diamond, silicon nitride,
Known materials having a Mohs hardness of 6 or more such as silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably 0.01 to 2 μm,
If necessary, combine abrasives with different particle sizes,
A single abrasive can also have a similar effect by broadening the particle size distribution. Tap density is 0.3-2 g / cc,
Moisture content 0.1-5%, pH 2-11, specific surface area 1
-30 m < ² > / g is preferable. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness.

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

As the additive used in the present invention, one having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. is used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, fluorinated graphite, silicone oil, polar group silicone, fatty acid modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Ester and its alkali metal salt, alkyl sulfate ester and its alkali metal salt,
Polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (it may contain an unsaturated bond or may be branched), and these metal salts ( Li, N
a, K, Cu, etc.) or monovalent with 12 to 22 carbon atoms,
Dihydric, trihydric, tetrahydric, pentahydric, hexahydric alcohol (may contain unsaturated bonds or may be branched), alkoxy alcohol having 12 to 22 carbon atoms, 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms,
Any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohol (may contain unsaturated bond or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, and a carbon number of 8 to
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid,
Linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol. , Lauryl alcohol.

Further, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfonium, anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, and phosphoric acid ester group, amino acids, aminosulfonic acids, sulfuric acid of aminoalcohol, or the like. Amphoteric surfactants such as phosphoric acid esters and alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

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

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

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

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

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

Further, the F of the flexible support in the tape running direction is
The -5 value is preferably 5 to 50 kg / mm.² , Tape width
F-5 value in the direction is preferably 3 to 30 Kg / mm² so
Yes, the F-5 value in the tape longitudinal direction is the F-5 value in the tape width direction.
It is generally higher than 5 values, but especially strength in the width direction
This is not the case when it needs to be raised. Also possible
100 ° C 3 in the tape running direction and width direction of the flexible support
The heat shrinkage at 0 minutes is preferably 3% or less, more preferably
Less than 1.5%, heat shrinkage at 80 ° C for 30 minutes is preferable
It is preferably 1% or less, more preferably 0.5% or less.
Breaking strength is 5 to 100 kg / mm in both directions² , Elastic modulus
Is 100 to 2000 kg / mm ² Is preferred.

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

In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but a strong kneading force such as a continuous kneader or a pressure kneader is used in the kneading step. The high Br of the magnetic recording medium of the present invention can be obtained by using the material having the same. In the case of using a continuous kneader or a pressure kneader, all or part of the ferromagnetic powder and the binder (however, 30% by weight or more of the total binder is preferable) and the ferromagnetic powder 100.
Kneading is performed in the range of 15 to 500 parts per part. For details of these kneading treatments, see JP-A-1-106338.
And JP-A-64-79274. Further, when preparing the 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 desirable to use a dispersion medium having a high specific gravity, zirconia beads,
Metal beads are preferred. The present invention applies the coating liquid for the lower non-magnetic layer onto a flexible support, and while the lower non-magnetic layer obtained is in a wet state, simultaneously with the coating of the coating liquid for the lower non-magnetic layer or The lower layer and the upper layer are provided on the flexible support by a so-called wet-on-wet coating method in which the coating solution for the upper magnetic layer is sequentially coated. The wet-on-wet coating method is a so-called sequential coating method in which a first layer is first coated and then the next layer is coated thereon in a wet state as quickly as possible, and a method in which multiple layers are simultaneously coated in an extrusion coating method. Say. A wet-on-wet coating method is disclosed in JP-A-61-13992.
The magnetic recording medium coating method disclosed in Japanese Patent Laid-Open No. 9-62,62-123933 can be used, and more efficient production is possible. The present invention can specifically propose the following configurations. 1. The lower layer is first coated by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for coating a magnetic coating, and when the lower layer is in a wet state, Japanese Examined Patent Publication No. 1-46186 or JP-A-60-46186. -23
The upper layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-A-8179 and JP-A-2-265672. 2. JP-A-63-88080, JP-A-2-17921
No. 2, JP-A-2-265672, the upper layer and the lower layer are coated almost simultaneously by one coating head having two slits for passing the coating liquid therein. 3. The upper layer and the lower layer are coated almost at the same time by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic powder, JP-A-62-95174 has been disclosed.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in JP-A No. 1-236968. Furthermore, it is preferable that the viscosity of the coating liquid satisfies the numerical range disclosed in Japanese Patent Application No. 1-312659.

FIG. 2 is an explanatory view showing an example of a sequential coating method used for providing both layers in the present invention, in which a flexible support 1 such as polyethylene terephthalate running on a coating machine ( A) 3 is precoated with the lower layer coating solution (a), and immediately thereafter, the smoothing roll 4 smoothes the coated surface, and another extrusion coating machine (B) is used while the coating solution 2 is in a wet state. The following upper layer coating solution (b) according to 6
Apply.

FIG. 3 is an explanatory view showing an example of the extrusion type simultaneous coating method preferably used for providing both layers in the present invention, in which the simultaneous multilayer coating device 8 is used on the flexible support 1. The state in which the lower layer coating liquid (a) 2 and the upper layer coating liquid (b) 5 are simultaneously coated will be described. After applying both layers, magnetic field orientation, drying and smoothing treatment are performed to obtain a magnetic recording medium.

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

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

After the calendar treatment, the magnetic layer, the back layer, and the
In order to accelerate the curing of the magnetic layer, the temperature of 40 ℃ ~ 80 ℃
It may be subjected to a moth treatment. According to the manufacturing method of the present invention
SUS4 on the upper layer of the selected magnetic recording medium and the opposite surface
The friction coefficient for 20 J is preferably 0.5 or less,
0.3 or less, the magnetic layer surface specific resistance is 10^Four -10¹¹Oh
Rms / sq, surface resistivity when the lower layer is applied alone
Is 10^Four -10⁸ Ohm / sq, surface electric resistance of BC layer
Is 10³ -10 ⁹ Is preferred.

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

The magnetic characteristics of the magnetic recording medium selected by the manufacturing method of the present invention, when measured in a magnetic field of 5 KOe, have a squareness ratio in the tape running direction of 0.70 or more, preferably 0.
It is 80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction.

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

[0161]

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

A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared according to the following formulations. Example 1 Formulation of coating liquid for upper magnetic layer Ferromagnetic powder: Fe alloy powder 100 parts Composition: 93% by weight of Fe, 3% by weight of Ni, 3% by weight of Co, other Zn, Cr, etc. Hc 1600 Oe, σ _S 135 emu / g Major axis length 0.18 μm, acicular ratio 9 vinyl chloride copolymer 10 parts —SO ₃ Na, epoxy group-containing polyurethane resin 5 parts —SO ₃ Na-containing, molecular weight 45000 α-alumina (average particle size 0.2 μm) 5 parts Cyclohexanone 150 parts Methyl ethyl ketone 200 parts After mixing and dispersing the above composition in a sand mill for 6 hours,
A polyisocyanate (Coronate L), 5 parts of stearic acid and 10 parts of butyl stearate were added to obtain a magnetic coating solution.

Coating liquid formulation for lower non-magnetic layer Granular TiO ₂ 100 parts Average particle size 0.09 μm Carbon black 5 parts Average particle size 20 mμ Vinyl chloride copolymer 8 parts —SO ₃ Na, epoxy group-containing molecular weight 50000 Polyurethane resin 5 part -SO ₃ Na content, after 4 hours mixed and dispersed in a sand mill molecular weight 45000 alpha-alumina (average particle size 0.2 [mu] m) 5 parts cyclohexanone 150 parts Methyl ethyl ketone 50 parts the above composition,
5 parts of polyisocyanate (Coronate L), 1 part of stearic acid and 1 part of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

The above coating solution was applied in a wet state by using two doctors having different gaps, and after orientation treatment with a permanent magnet, it was dried. A 9.8 μm polyethylene terephthalate film was used as the flexible support, and a back layer containing carbon black was provided on the surface of the support opposite to the magnetic layer. After that, a super calendar treatment was performed. Coating thickness is magnetic layer 0.3μm, non-magnetic layer 3.0μm
Met. The original fabric thus obtained was cut into 3.81 mm width and the digital audio tape of Example 1-1 (D
AT).

In other Examples and Comparative Examples, tapes were prepared by changing the factors shown in Table 1 with respect to Example 1-1. These tapes were evaluated by the following methods, and the results are shown in Table 2. Standard deviation σ of d and d of magnetic layer: Cross-section of tape was photographed with a transmission electron microscope (TEM) (magnification: 20,000 times)
And determined according to the above definition. Average thickness variation (Δ
d): The cross section of the tape was photographed with a transmission electron microscope (TEM) (magnification: 20000 times), the displacement between the magnetic layer and the lower non-magnetic layer in a length of 20 μm (actual length) was measured, and the displacement difference between the peak and the valley was measured. The average value of is calculated and set as Δd.

The sequential multi-layer of the comparative example means that the lower non-magnetic layer is applied, and after drying, the upper magnetic layer is applied. Electromagnetic conversion characteristics Deck used: Sony DTC-1000 reproduction output: A signal of 4.7 MHz single frequency was input, the reproduction signal was output to a spectrum analyzer, and the peak value of the signal was read.

C / N: A noise spectrum was taken at the time of reproducing output measurement, and the reproducing output and the center recording frequency (4.7 MH) were measured.
From the noise level ratio 0.1 MHz away from z), C /
I asked for N. The spectrum analyzer is HP-358
5A and 0 dB are the number of error flags in the tape BER (block error rate): 10,000 tracks of the magnetic layer of Comparative Example 1, which is expressed by the following formula.

BER = error flag / 10,000 × 128 blocks The DAT signal structure encodes an analog signal, one code is 8 bits, and one block is 32 symbols × 8 bits = 25.
Since it is 6 bits, one track is composed of 128 blocks. The signals of 2 tracks, that is, 128 × 2 blocks are taken into the memory, shuffled, and the error is detected. A DAT deck manufactured by Sony Corporation was used, and an HP5328A manufactured by Hewlett-Packard Co. was used as a counter, and the measurement was performed by connecting to a personal computer.

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

[0170]

[Table 1]

[0171]

[Table 2]

The shortest recording wavelength λ of the created DAT is 0.
67 μm. Therefore, from λ / 4 ≦ d ≦ 3λ, the thickness range of the magnetic layer is 0.17 μm ≦ d ≦ 2.01 μm, but the present invention is in the range of 0.17 μm ≦ d ≦ 1.0 μm. Further, there is a relationship of Δd / d ≦ 0.50.

In Examples 1-1 to 1-3, the lower non-magnetic layer thickness and the upper magnetic layer thickness were made constant, and the upper and lower layer thickness ratios were changed. Example 1
-2 is set to the middle of the same thickness, and Example 1-3 is set to almost the upper limit. Example 1-4 has a configuration in which the thickness of the lower non-magnetic layer is reduced to near the lower limit. Examples 1-5 to 1-7
Is an example in which the type of non-magnetic powder in the lower non-magnetic layer is changed, and it is understood that Ra is affected within the definition of the present invention. Examples 1-8 are examples in which barium ferrite was used as the ferromagnetic powder. Example 1-9 is an example in which the thickness of the upper magnetic layer is close to the upper limit, and this system is inferior in characteristics to other examples.

Comparative Example 1-1 is a magnetic recording medium having a single-layer thick magnetic layer. In Comparative Example 1-2, coarse red iron oxide (having an average particle size of 0.2 is used as the non-magnetic powder of the lower non-magnetic layer).
5), λ / 4 = greater than 0.1675), so that Δd is large and C / N is inferior. Comparative Example 1-3 uses needle-shaped red iron oxide with a long major axis length, and therefore has large Δd and poor Ra. Comparative Examples 1-4 are examples of successive multi-layering in which the lower layer is coated, then dried, and the upper layer is coated on the lower layer, which has many pinholes.

In Examples 1 to 8, the ranges of d and Δd / d were satisfied, and σ and Ra were also in the preferable ranges.
It can be seen that all of the reproduction output, C / N, BER, DO, and coating moldability are superior to the comparative example.

According to the present invention, by coating a thin magnetic layer (3 times or less of the shortest recording wavelength) with the lower non-magnetic layer at the same time, it is possible to prevent a coating defect which is a problem when the magnetic layer is thinned alone. At the same time, the reproduction output is improved by optimizing the thickness of the magnetic layer for the shortest recording wavelength according to the recording system, the thickness variation of the thinned magnetic layer is reduced, and the surface of the magnetic layer is smoothed. / N is improved.

According to the present invention, there is provided a coating type magnetic recording medium manufacturing method capable of obtaining electromagnetic conversion characteristics comparable to those of a metal thin film magnetic recording medium and solving the problems of productivity and storage reliability of the metal thin film magnetic recording medium. Can be supplied. Example 2 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 90 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ BET specific surface area 35-45 m ² / g DBP oil absorption 27 to 38 g / 100 g pH 6.5 to 8 carbon black 10 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate- vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 200 parts Cyclohexanone 80 parts Coating liquid for upper magnetic layer Ferromagnetic metal fine powder composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET specific surface area 60 m ² / g crystallite Size 195Å Average major axis length 0.20 μm, acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (average particle size 0.2 [mu] m) 2 parts Carbon black (average particle size 0.10 μm) 8 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 2 For each 0 parts The above two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 3 μm and immediately after that the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene naphthalate support having a central average surface roughness of 0.01 μm. While both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used. After being oriented and dried, it was treated at a temperature of 90 ° C. with a 7-stage calender consisting of only metal rolls and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 2-1.

Similarly, the factors shown in Tables 3 to 4 were changed to prepare samples, Examples 2-2 to 2-10, and Comparative examples 2-1 to 2-2.
-7 was prepared and the performance was evaluated by the following. The results are shown in Tables 3 to 4. 1. Volume Ratio (Filling Ratio) of Lower Layer Inorganic Powder A 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. From this transmission electron micrograph image, the number of inorganic powder particles per 1 μm ² was counted, the thickness of the cut out test piece was calculated, and the number of inorganic powder particles contained per unit volume was measured. The volume ratio of the inorganic powder was determined by determining the volume per particle from the powder particle diameter determined from the same photograph and multiplying it by the number of inorganic powder particles contained per unit volume. The calculation formula is as follows.

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

DM = Bm / 4πσ _S where Bm (Gauss): residual magnetic flux density dM (g / cc): ferromagnetic powder density σ _S (emu / g): magnetization amount of ferromagnetic powder of ferromagnetic powder The volume ratio in the upper layer can be obtained by dividing the above density by the specific gravity of the ferromagnetic powder. Also, the density of other powder components and binder in the magnetic layer is calculated from the magnetic layer prescription amount, and divided by the specific gravity of each powder component to obtain the volume ratio of each powder component, and sum these. By
The powder volume ratio of the upper layer is obtained. 3. Average particle size of inorganic powder The average particle size along the long axis was determined by a transmission electron microscope. 4. Crystallite size of ferromagnetic metal powder It was determined from the spread of the half-value widths of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane by X-ray diffraction. 5. Surface Roughness R _rms Scanning Tunneling Microscope (STM) is measured by Digital In
tunnel current 10 using Nanoscope II manufactured by strument
Scanning was performed in the range of 6 μm × 6 μm under the condition of A and bias voltage of 400 mV, and the value was obtained from the following formula 1.

[0182]

[Equation 1]

6. σ: Same method as in Example 1. 7.7 MHz Output A FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co. was used to record a 7 MHz signal, and the 7 MHz signal reproduction output when the signal was reproduced was measured with an oscilloscope. The reference is an internal reference of Fuji Photo Film Co., Ltd. 8. Pinholes After coating the magnetic layer and before coating the back layer, the magnetic layer was visually observed with transmitted light to measure pinholes per 100 m ² . It is desirable that the number is 1 or less per 100 m ² .

[0184]

[Table 3]

[0185]

[Table 4]

As shown in Tables 3 and 4, in the example samples, the average particle size of the inorganic powder contained in the lower non-magnetic layer was 1/2 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer. Four
The magnetic layer satisfies Δd ≦ 0.50d and has a small surface roughness R _rms and a uniform d / R _rms of 30 or more and σ of 0.2 μm or less and excellent surface property. It is an excellent magnetic recording medium which has a high reproduction output and has very few pinholes. On the other hand, in the comparative example, Δd ≦
0.50d is not satisfied. In Comparative Example 2-1, R _rms becomes large because (average particle diameter of inorganic powder / crystallite size of ferromagnetic powder) is larger than the predetermined range, and reproduction output is not improved. In Comparative Example 2-2, (average particle diameter of inorganic powder / crystallite size of ferromagnetic powder) is too small than the predetermined range, and thus R _rms becomes large and reproduction output is not improved. In Comparative Example 2-3, the thickness d of the magnetic layer is 1.2.
The playback output is slightly inferior because it is as thick as μm. Comparative Example 2-4
Is a single-layer magnetic recording medium having only a magnetic layer. Comparative Example 2-
In No. 5, since the added amount of the inorganic powder is small, R _rms becomes large and the electromagnetic conversion characteristics are not improved. Comparative Example 2-6
Since the volume ratio of the powder is too small, R _rms is large and the electromagnetic conversion characteristics are not improved. Comparative Example 2-7 could not be applied because the volume ratio of the inorganic powder was too large.

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

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

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

Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts Tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer obtained as described above were applied to polyethylene terephthalate having a thickness of 75 μm. First, the lower non-magnetic layer coating solution was applied first, and then the upper magnetic layer coating solution was applied in a wet state, and the back surface was treated in the same manner. The dry thickness was such that the thickness of the lower non-magnetic layer was 1.5 μm and the thickness of the magnetic layer was 0.5 μm. Then, calendar processing was performed to obtain a magnetic recording medium. Thereafter, this magnetic recording medium was punched out into 3.5 inch, put into a 3.5 inch cartridge having a liner installed inside, and a predetermined mechanical component was added to the 3.5 inch floppy disk of Example 3-1. I got a disc. Similarly, Table 5
Samples, Examples 3-2 to 3-5, by changing the factors described in 1.
Comparative Examples 3-1 to 3-3 were prepared, the performance was evaluated as follows, and the results are shown in Table 5. 1. Volume ratio (filling rate) of lower layer inorganic powder; same as in Example 2. Average particle size of inorganic powder; same as in Example 2. Crystallite size of iron oxide magnetic powder; by X-ray diffraction,
It was calculated from the spread of diffraction lines of the (4.4.0) plane and the (2.2.0) plane. 4. Surface roughness R _rms ; same as in Example 2. d and Δd; the same method as in Example 1. 6. Inner circumference 2F output relative value (%); calculated based on the initial 2F output value of Example 3-1 as 100%. The drive used is PD211 manufactured by Toshiba Corporation.

[0191]

[Table 5]

As is clear from Table 5, the example samples are
Since Δd ≦ 0.50d is satisfied and the average particle size of the inorganic powder contained in the lower non-magnetic layer is 1/2 to 4 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer, A magnetic layer having a small roughness R _rms and a uniform d / R _rms of 30 or less and excellent surface property is formed, the reproduction output is high,
Moreover, it is an excellent magnetic recording medium with very few pinholes. On the other hand, the comparative example does not satisfy Δd ≦ 0.50d.
In Comparative Example 3-1, since (average particle diameter of inorganic powder / crystallite size of ferromagnetic powder) was too large than the predetermined range, R
_rms becomes large and output is not improved. Comparative Example 3-2
In the case of (average particle diameter of inorganic powder / crystallite size of ferromagnetic powder) is too smaller than the predetermined range, R _rms becomes large and the output is not improved. In Comparative Example 3-3, since the thickness d of the magnetic layer was as large as 1.2 μm, the reproduction output was slightly inferior.

Example 4 In the same coating solution composition for the upper magnetic layer and the lower nonmagnetic layer as in Example 2-1, the factors shown in Tables 6 to 7 (particularly the average particle diameter of the inorganic powder of the lower nonmagnetic layer and the upper layer) were used. Various samples were prepared by changing the ratio of the major axis length of the ferromagnetic powder in the magnetic layer, and the performance was evaluated in the same manner as in Example 2, and the results are shown in Tables 6 to 7.

Squareness ratio: The coating direction Br / Bm when measured with a vibrating sample type magnetometer (VSM; manufactured by Toei Industry Co., Ltd.) at Hm 5 kOe was taken as the squareness ratio.

[0195]

[Table 6]

[0196]

[Table 7]

As is clear from the above table, the example samples are
Since Δd ≦ 0.50d is satisfied and the average particle size of the inorganic powder contained in the lower non-magnetic layer is 1/3 or less of the major axis length of the ferromagnetic powder contained in the upper magnetic layer, d / R _rms is 3
This is a method for producing an excellent magnetic recording medium in which a magnetic layer is 0 or more, a uniform magnetic layer is formed, reproduction output is high, and pinholes are extremely small. On the other hand, in the comparative example, Δd ≦ 0.50
Do not satisfy d. In Comparative Example 4-1, since (average particle diameter of inorganic powder / long axis length of ferromagnetic powder) is larger than the predetermined range, Δd becomes large and the output is not improved. In Comparative Example 4-2, the reproduction output is inferior because the thickness d of the magnetic layer is as thick as 1.3 μm. Comparative Example 4-3 is an example of a single magnetic layer, and since there is no lower non-magnetic layer and d is thin, the coatability and electromagnetic conversion characteristics are poor. In Comparative Example 4-4, the coating properties are not improved because the layers are successively laminated after drying the lower layer. Reference Example 4-1
Has a good coating property because the magnetic layer is a single layer and has a large d, but the electromagnetic conversion characteristics are not improved. In Comparative Example 4-5, since no inorganic powder was used in the lower layer, the interface fluctuation between the upper layer and the lower layer was large, and thus Δd was high and the electromagnetic conversion characteristics were poor.
In Comparative Example 4-6, since the volume ratio of the lower layer inorganic powder was low, Δd was also high and the electromagnetic conversion characteristics were poor.

Example 5 Co-modified γ in the coating solution composition for the upper magnetic layer of Example 3-1
Example 3 except that Fe ₂ O ₃ was changed to the following ferromagnetic powder
The same coating liquid as the coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer of Example 3-1 were prepared to prepare the sample of Example 5-1.

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 In addition, the factors described in Table 8 (particularly the inorganic material 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 of the upper magnetic layer) was changed to obtain samples, Examples 5-2 to 5-3, and Comparative examples 5-1 to 5-1.
5-2 was prepared, the performance was evaluated in the same manner as in Example 3, and the results are shown in Table 8.

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

[0201]

[Table 8]

From Table 8, the samples of the examples have Δd ≦ 0.50.
d is satisfied, and the average particle size of the inorganic powder contained in the lower non-magnetic layer is equal to or smaller than the average plate size of the plate-like ferromagnetic powder contained in the upper magnetic layer, the squareness ratio in the vertical direction is high and uniform. A magnetic layer is formed. Therefore, the example sample is an excellent magnetic recording medium having a high D50 and extremely few pinholes. On the other hand, the comparative example does not satisfy Δd ≦ 0.50d. In Comparative Example 5-1, since the average particle diameter of the inorganic powder is larger than the average plate diameter of the ferromagnetic powder, Δd becomes large, and D
50 is not improved. Comparative Example 5-2 is an example of a single magnetic layer without a lower non-magnetic layer, and has a poor D50.

Example 6 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared according to the following formulations. Example 6-1 Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% by weight Inorganic powder surface treatment layer Al ₂ O ₃ (10% by weight) BET method Specific surface area by 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - polar groups of 5 × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group 1 × 10 ^-4 eq / g Contains butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Coating liquid for upper magnetic layer Ferromagnetic metal fine powder composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET method ratio Surface area 60 m ² / g Crystallite size 195 Å Average major axis length 0.20 μm, acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Surface treatment agent: Al ₂ O ₃ , SiO ₂ vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, polymerization degree 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 —SO ₃ Na group 1 × 10 ^{− 4} eq / g containing α- alumina (average particle size 0.3 [mu] m) 2 parts carbon black (average particle size 0.10μ ) For each of 0.5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 50 parts Toluene 60 parts The two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 2 μm and immediately thereafter the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene terephthalate support having a center average surface roughness of 0.01 μm, and while both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used for orientation. Then, after drying, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 6-1.

Similarly, the factors shown in Tables 9 to 10 were changed, and samples, Examples 6-2 to 6-12, and Comparative examples 6-1 to
6-3 was prepared, the performance was evaluated in the same manner as described above, and the results are shown in Tables 9 to 10. The relative speed of the 8 mm video is 38 m / sec, and the recording wavelength of 7 MHz is 0.54 μ.
m. Therefore, λ / 50 is 10.8 nm. Centerline average surface roughness (Ra): TOYO3D manufactured by WYKO
Area of about 250 × 250 nm by MIRAU method using
a was measured. Spherical correction at measurement wavelength of about 650 nm.
Cylinder correction was added.

[0206]

[Table 9]

[0207]

[Table 10]

As is clear from the above table, the example samples are
Satisfying Δd ≦ 0.50d, Al ₂ O on the surface of the inorganic powder
_Since the treatment layers such as ₃ , SiO ₂ and ZrO ₂ are included as shown in the above table, the dispersibility is improved, Ra is low, and λ / 50 (1
0.8 nm) or less, and the electromagnetic conversion characteristics are good.
In Comparative Example 6-1, since Δd ≦ 0.50d is not satisfied and the inorganic powder does not include the treatment layer, dispersibility is poor, Ra and σ are high, and electromagnetic conversion characteristics are poor. Comparative Example 6-2
Has a poor magnetic conversion characteristic because the magnetic layer is thick. In Comparative Example 6-2, although Δd ≦ 0.50d, Δd is very large and d is larger than 1.0 μm, so it is meaningless. In Comparative Example 6-3, a sample could not be prepared because of the successive layers.

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

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content average molecular weight 35000 methyl ethyl ketone 200 parts cyclohexanone 100 parts toluene 80 parts Next, the following carbon black and a coarse particle abrasive were added, and the mixture was subjected to a dispersion treatment for 2000 hours with a sand grinder for about 2 hours.

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

Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts Tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer obtained as described above were applied to polyethylene terephthalate having a thickness of 75 μm. First, the lower non-magnetic layer coating solution was applied first, and then the upper magnetic layer coating solution was applied in a wet state, and the back surface was treated in the same manner. The dry thickness was such that the thickness of the lower non-magnetic layer was 2.5 μm and the thickness of the magnetic layer was 0.5 μm. Then, calendar processing was performed to obtain a magnetic recording medium. Then, this magnetic recording medium was punched out into 3.5 inch, put into a 3.5 inch cartridge with a liner installed inside, and a predetermined mechanical component was added to the 3.5 inch floppy disk of Example 7-1. I got a disc. Similarly, Table 1
Samples, Examples 7-2 to 7-, in which the factor described in 1 is changed.
7, Comparative Example 7-1 was prepared, the performance was evaluated, and the results are shown in Table 11.

Initial innermost 2F output: Calculated as a relative value with the sample of Example 7-1 as 100. The drive used is PD211 (made by Toshiba Corp.). The recording wavelength is
It is 1.428 μm. Therefore, λ / 50 is 28.5n
m. Surface roughness: Ra was measured by the same method as in Example 6.

[0214]

[Table 11]

From the above table, the sample of the example satisfies Δd ≦ 0.50d like the example 6. In the examples, since the treated layer of Al ₂ O ₃ , SiO ₂ , ZrO _{2 and the} like is included on the surface of the inorganic powder as shown in the above table, the dispersibility is improved, the Ra is low, and the electromagnetic conversion characteristics are good. In Comparative Example 7-1, since the inorganic powder does not include the treatment layer, the dispersibility is poor, and Ra
And σ and Δd are increased, and Δd ≦ 0.50d is not satisfied, resulting in poor electromagnetic conversion characteristics.

Example 8 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared according to the following formulations. Example 8-1 Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 Carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts -N (CH ₃ ) Containing 5 × 10 ⁻⁶ eq / g of polar group of ₃ ⁺ Cl ⁻ Composition ratio 86: 13: 1 Polymerization degree 400 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone Ton 200 parts Upper magnetic layer Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET specific surface area 60 m ² / g Crystallite size 195 Å Average major axis diameter 0.20 μm, acicular Ratio 7 Saturation magnetization (σ _S ): 128 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (average particle size 0.2 [mu] m) 2 parts carbon black (average particle size 0.10 .mu.m) 0. 5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, open kneader each component Kneaded and dispersed in a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were added to each to add 1 μm.
The coating liquids for the lower non-magnetic layer and the upper magnetic layer were prepared by filtering with a filter having an average pore size of.

The thickness of the obtained coating liquid for the lower non-magnetic layer was adjusted so that the thickness after drying was 2.5 μm, and immediately thereafter, the thickness of the upper magnetic layer was 0.5 μm. 7 μm
At the same time, multi-layer coating was performed on a polyethylene terephthalate support having a central average surface roughness of 0.01 μm. While both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used. After being oriented and dried, it is composed of only metal rolls 7
Treatment was carried out at a temperature of 90 ° C. with a step calender and slit into a width of 8 mm to produce an 8 mm video tape of Example 8-1.

Similarly, the factors shown in Tables 12 to 15 were changed to prepare samples, Examples 8-2 to 8-6, and Comparative examples 8-1 to 8-1.
8-4 was created. In addition, Example 8-4 and Comparative Example 8-1
A continuous kneader was used for kneading in the magnetic layer in order to increase the packing density of the ferromagnetic powder. The characteristics of the sample were evaluated, and the results are shown in Tables 16 and 17. Evaluation Method 7 MHz Output A 7 MHz signal was recorded using a FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when the signal was reproduced was measured with an oscilloscope. The contrast is 8 mm tape SAG made by Fuji Photo Film Co., Ltd.
It is P6-120.

C / N ratio A FUJIX8 8 mm VCR made by Fuji Photo Film Co. was used to record a 7 MHz signal, and the noise generated at 6 MHz when this signal was reproduced was measured with a spectrum analyzer. The ratio was measured. Tape heat shrinkage The sample tape was stored in a constant temperature bath at 70 ° C for 48 hours, and the change in length before and after that was taken as the heat shrinkage. The tape length was about 100 mm, and the length was measured with a comparator. No tension was applied during storage in a constant temperature bath.

Skew Distortion A color bar signal was recorded in advance and then stored in a constant temperature bath at 70 ° C. for 48 hours, after which it was confirmed that the temperature had sufficiently returned to room temperature, and then reproduced to display the color bar signal on the screen. Obtained from the change. One color bar is 7.48 μsec. Running Durability The sample was P6-in a 10mm 8mm VCR FUJIX8 made by Fuji Photo Film Co. in an atmosphere of 23 ° C and 70% RH.
The 120 was run 100 times. During that time, the output decrease was measured, and the dirt on each part in the deck after running was evaluated. ○
Indicates that there are less than 5 spots with stains, Δ indicates that there are 5 or more spots with stains, but there is no actual damage due to clogging, and × indicates that There are 5 or more areas where dirt is attached, indicating that there is a real damage due to clogging. In addition, ◯ Δ means a performance intermediate between ◯ and Δ.

[0221]

[Table 12]

[0222]

[Table 13]

[0223]

[Table 14]

[0224]

[Table 15]

[0225]

[Table 16]

[0226]

[Table 17]

From the above table, the magnetic recording medium selected by the manufacturing method of the present invention shown in each example has Δd ≦ 0.50d.
Is satisfied, the skew distortion is smaller than that of the comparative example, and σ,
Since Δd was also small, the reproduction output, C / N ratio, and running durability were also good. In Comparative Example 8-1, the upper layer thickness is 1.2 μm.
Since it is thick, the electromagnetic conversion characteristics are inferior.

In this example, the magnetic recording medium of 70 ° C. and 48 ° C. was used.
By controlling the heat shrinkage ratio in time to 0.4% or less, skew distortion is reduced and running durability, and C
/ N, it is a coating type magnetic recording medium having an extremely thin magnetic layer having excellent characteristics capable of ensuring a good reproduction output and can be manufactured in large quantities without coating defects. Example 9 A coating liquid for the lower non-magnetic layer and a coating liquid for the upper magnetic layer were prepared according to the following formulations. Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area by BET method 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 Carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts-N (CH ₃ ) Composition ratio 86: 13: 1 polymerization degree 400 polyester polyurethane resin 5 parts containing 5 × 10 ⁻⁶ eq / g of polar group of ₃ ⁺ Cl ⁻ neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g butyl stearate 1 part 1 part of methyl ethyl stearate Ton 200 parts the upper magnetic layer (a) a ferromagnetic metal powder composition Fe / Zn / Ni = 92/ 4/4 100 parts Hc 1600 Oe BET method specific by surface area 60 m ² / g Crystallite size 195Å average major axis length 0.20μm , Acicular ratio 10 saturation magnetization (σ _S ): 130 emu / g vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / Caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing α-alumina (average particle size 0.3 μm) 2 parts Carbon black (average particle size 0.10 μm ) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, each component is continuously kneaded. After kneading with a dough, it was dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating solution was adjusted to 2.5 μm after drying, and immediately after that, the thickness of the upper magnetic layer was adjusted to 0.5 μm. 7 μm
At the same time, multi-layer coating was performed on a polyethylene terephthalate support having a central average surface roughness of 0.01 μm. While both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used. After being oriented and dried, it is composed of only metal rolls 7
Treatment was carried out at a temperature of 90 ° C. with a step calender and slit into a width of 8 mm to produce an 8 mm video tape of Example 9-1.

Similarly, the factors shown in Tables 18 to 19 were changed, and the samples, Examples 9-2 to 9-6 and Comparative Examples 9-1 to 9-1.
9-4 was created. Further, the samples of Examples 9-7 were prepared by using the following paints as the upper magnetic layer. Upper magnetic layer (b) Ferromagnetic metal fine powder Composition BaFe (barium ferrite) 100 parts Hc: 2400 Oe Specific surface area by BET method: 45 m ² / g Plate diameter: 0.03 μm, Plate ratio: 5 Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content α-alumina (average particle size 0.3 μm) 5 parts Carbon black (average particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts The above sample was evaluated. The results are shown in Tables 18 to 19. SMD, STD, Stiffness ratio Using a loop stiffener tester manufactured by Toyo Seiki, a sample with a width of 8 mm and a length of 50 mm is cut out for SMD and STD, and this is used as a ring, and the displacement speed in the inner diameter direction is 3.5 mm /
Each force required to give a displacement of 5 mm in seconds is SMD in mg,
The stiffness ratio SMD / STD was determined by determining STD. Envelope flatness A FUJIX8 8mm VCR made by Fuji Photo Film Co. was used to record a 7MHz signal, and when this signal was reproduced, the 7MHz signal reproduction output was observed with an oscilloscope.
Expressed by the difference between the maximum output and the minimum output in the field. 7 MHz Output A 7 MHz signal was recorded using a FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The contrast is 8 mm tape SAG made by Fuji Photo Film Co., Ltd.
It is P6-120. C / N ratio A FUJIX8 8mm VCR made by Fuji Photo Film Co., Ltd. was used to record a 7MHz signal, the noise generated at 6MHz when this signal was reproduced was measured with a spectrum analyzer, and the ratio of the reproduced signal to this noise was measured. did. Running Durability Measurement Method A sample was used at 23 ° C. and 70% RH in an atmosphere of Fuji Photo Film Co., Ltd. 8 mm biodecks FUJIX8 10 units for P6-1.
20 was run 100 times. During that time, the output reduction was measured.

◯: Output decrease is within 2 dB Δ: Output decrease is 2-4 dB ×: Output decrease is 4 dB or more or clogging occurs Pinhole After applying the magnetic layer and before applying the back layer, the magnetic layer is irradiated with transmitted white light. Was visually observed to measure pinholes per 100 m ² . One or less is preferable per 100 m ² .

[0232]

[Table 18]

[0233]

[Table 19]

From the above table, in the embodiment of the present invention, Δd ≦ 0.
Since 50D is satisfied and SMD / STD is controlled to 1.0 to 1.9, the head contact is improved and the envelope flatness is small as compared with the comparative example. Further, in the examples, since there are no coating defects and σ is small, running durability, output, C /
It turns out that N is excellent. On the other hand, in the comparative example, Δd ≦ 0.
Do not satisfy 50d. In Comparative Example 9-1, STD is low and a predetermined SMD / STD cannot be obtained because the lower layer uses carbon having a Mohs hardness of 2 instead of inorganic powder, and envelope flatness, σ, and running durability are not improved. . Comparative Example 9-2
Since the inorganic powder having a large average particle size is used, the predetermined SMD / STD cannot be obtained, and the envelope flatness and σ cannot be improved. Comparative Example 9-3 is an example in which the lower layer is not provided, and a coating defect occurred in the magnetic layer, and an evaluation sample could not be obtained.
In Comparative Example 9-4, the thickness of the magnetic layer was as thick as 1.2, and thus the electromagnetic conversion characteristics were inferior to those of the other Examples.

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

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

On the other hand, a coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. The upper magnetic layer coating liquid formulation ferromagnetic powder: Fe alloy powder (Fe-Co-Ni) 100 parts Composition; Fe: Co: Ni = 92 : 6: a for Al ₂ O ₃ 2 sintered inhibitor used Hc 1600 Oe, σ _S 119 emu / g major axis length 0.13 μm, acicular ratio 7 crystallite size 172 Å, water content 0.6 wt% 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) 38,000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g included —OH 8 × 10 ⁻⁵ eq / g containing Tg 38 ℃, Mw 50000 α-alumina (average particle diameter 0.15 [mu] m) 12 parts ^{_{S BET 8.7m 2 / g, pH}} 8.2, water content 0.06 wt% cyclohexanone 150 parts methyl ethyl After 6 hours mixed and dispersed in a sand mill 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 liquid for the upper magnetic layer.

Coating liquid formulation for lower non-magnetic layer TiO ₂ 85 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 4. 1 pH 6.5-8.0 Carbon black 5 parts Average particle diameter 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 S _BET 250 m ² / g Coloring power 143% Vinyl chloride copolymer 13 parts-SO ₃ Na 8 × 10 ⁻⁵ eq / g, —OH, epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38,000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g containing -OH 8 × 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 cyclohexane 100 parts Methyl ethyl ketone 100 parts the above composition in a sand mill After 4 hours mixed and dispersed,
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 liquid for the lower non-magnetic layer.

After applying the above coating solution in a wet state using two doctors having different gaps, the permanent magnet 3
Alignment treatment was performed with 500 gauss and then with a solenoid 1600 gauss, followed by drying. Then, a metal roll and a super calender treatment with the metal roll were performed at a temperature of 80 ° C. The coating thickness is 0.3 μm for the magnetic layer and 3.0 for the non-magnetic layer.
μm.

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

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

The following measurements were performed on the obtained 8 mm video tape, and the measurement results were obtained. (1) TEM (Transmission Electron Microscope) An ultrathin section of the magnetic layer was observed. The medium was cut to a thickness of about 0.1 μm with a diamond cutter, which was observed with a transmission electron microscope and photographed. The interface between the upper and lower layers of the photographed image and the surface of the magnetic layer were removed, the thickness of the magnetic layer was measured by an IBASII image processing device, and the average value d and the standard deviation σ were obtained.

The average thickness d of the magnetic layer was 0.3 μm. Practically 1.0 μm or less, particularly preferably 0.6 μm
It was found to be m or less. Magnetic layer thickness variation Δd is
At 0.07 μm, Δd ≦ 0.50d was satisfied, and the standard deviation σ of the magnetic layer thickness was 0.08 μm or less. It was found that σ is practically 0.2 μm or less, particularly preferably 0.1 μm or less. In the same measurement, Example 2-4
σ was 0.06 μm.

The magnetic tape was stretched so that the magnetic layer floated from the support, and the magnetic layer was peeled off by squeezing with a cutter blade. 500 mg of the peeled magnetic layer was added to 1N-NaO.
The binder was hydrolyzed by refluxing in 100 ml of H / methanol solution for 2 hours. Since the ferromagnetic powder has a large specific gravity and sinks to the bottom, the supernatant liquid was removed. Then, it was washed with water 3 times by decantation and then 3 times with THF. The obtained ferromagnetic powder was dried in a vacuum dryer at 50 ° C. Next, the obtained ferromagnetic powder was dispersed in collodion and observed with a TEM at a magnification of 60,000. As a result, the particle major axis length of the ferromagnetic powder was 0.13 μm, and the acicular ratio was 10. Similarly, in Example 2-2, the major axis length was 0.25 μm, and the acicular ratio was 15. It has been found that the particle major axis length needs to be 0.4 μm or less for practical use, and is preferably 0.3 μm or less. Further, it has been found that the acicular 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. The surface of the magnetic layer is Digita
l Instrument Nanoscope II
With a tunnel current of 10 nA and a bias voltage of 400 m
The V was scanned over a range of 6 μm × 6 μm. For the surface roughness, R _rms in this range was obtained.

As a result, R _rms was 6 nm. It was found that 20 nm or less is necessary for practical use, and preferably 10 nm or less. Similarly, the results of Example 2 can be referred to. (3) Surface roughness meter The surface roughness was measured using 3d-MIRAU. WYK
Approximately 250 × by MIRAU method using TOPO3D manufactured by O company
Ra, R _rms , Peak-Vall of 250 mm area
The ey 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 optical interference. Ra was 2.7 nm. For practical use, it was found that Ra is preferably 1 to 4 nm, more preferably 2 to 3.5 nm. R _rms was 3.5 nm. It was found that 1.3 to 6 nm is preferable for practical use, and more preferably 1.5 to 5 nm. The PV value was 20 to 30 nm. 80 in practical use
It was found that the thickness is preferably equal to or less than nm, more preferably 10 to 60 nm. (4) VSM (Vibration Sample Type Magnetometer) The magnetic characteristics of the magnetic layer of the magnetic tape obtained by using VSM were measured. It was measured at Hm 5 kOe using a vibrating sample type magnetometer manufactured by Toei Industry Co., Ltd.

As a result, Hc is 1620 Oe and Hr (9
0 °) is 1800 Oe, Br / Bm is 0.82, SFD
Was 0.583. Practically Hc is 1500-25
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 was found that the SFD is practically required to be 0.7 or less, and preferably 0.6 or less. Regarding practicality, similar results were obtained in Example 4 by the same measurement. (5) X-ray Diffraction X-ray diffraction was performed using the ferromagnetic powder taken out from the magnetic layer in (1) above. The magnetic tape was directly applied to an X-ray diffractometer, and the half-width of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane was obtained. As a result, it was found that the crystallite size was 180Å. Practically preferably 400 Å or less, particularly preferably 100 to 300 Å
It turned out to be. Similarly, when Example 6-2 was measured, it was 280 Å. (6) Tensile test Young's modulus, yield stress, and yield elongation of the magnetic tape obtained by the tensile tester were measured. Tensile tester (Universal tensile tester STM-T-50B manufactured by Toyo Baldwin Co., Ltd.
P) was used in 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
00-2000 Kg / mm ² , particularly preferably 500-
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 , and particularly preferably 4 to 15. Practically, the yield elongation is preferably 0.2 to 8%, particularly preferably 0.
It was found to be 4-5%. (7) Bending rigidity, circular stiffness Using a loop stiffener tester, width 8 mm, length 5
The force required to give a displacement of 5 mm at a displacement rate of about 3.5 mm / sec is expressed in mg, using a 0 mm sample as a ring.

As a result, the 8 mm p6-120 tape had a thickness of 10.5 μm and a stiffness of 40 to 40.
It was 60 mm. It was found that when the thickness is practically 10.5 ± 1 μm, the stiffness is preferably 20 to 90 mg, particularly preferably 30 to 70 mg. When the thickness is 11.5 μm or more, it is practically preferably 40 to
It was found to be 200 mg. It was found that when the thickness is 9.5 μm or less, it is practically preferably 10 to 70 mg. (8) Stretching fracture 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.
It is pulled at a pulling speed of 1 mm / sec, and the surface of the magnetic layer is observed under a microscope at a magnification of 400 times to measure the elongation at which five or more obvious cracks are generated on the surface of the magnetic layer. Similarly, Example 8-4 was 12%. As a result, the elongation at occurrence was 4%. It was found that it is practically preferably 20% or less, and particularly preferably 10% or less. (9) ESCA Cl / Fe spectrum α and N / Fe spectrum β were measured.

An X-ray photoelectron spectrometer (manufactured by PERKIN-ELMER) was used for the measurement of α and β. The Mg anode was used as the X-ray source, and the measurement was performed at 300 W. First, the lubricant of the video tape was washed off with n-hexane and then set on the 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-
The 2P (3/2) spectrum was integrated for 10 minutes and measured.
The bath energy was constant at 100 eV. The integrated intensity ratio between the measured Cl-2P spectrum and the Fe-2P (3/2) spectrum was calculated and set 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. Further, when Example 3-5 is measured, α is 0.32,
β was 0.10. Practically α is preferably 0.3
It was found that it was ˜0.6, and particularly preferably 0.4 to 0.5. Practically, β is preferably 0.03 to 0.
12, especially preferably 0.04 to 0.1. (11) Rheovibron 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 (Rheovibron manufactured by Toyo Baldwin Co., Ltd.). Tg is the peak temperature of E ″. This method applies vibration from one end of the tape and measures the vibration propagating 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 . It has been found that the Tg is preferably 40 to 120 ° C, and particularly preferably 50 to 110 ° C for practical use. Practically E '(50 ℃) is 0.8 × 10
It was found that it was ^{11 to} 11 × 10 ¹¹ dyne / cm ² , and particularly preferably 1 × 10 ^{11 to} 9 × 10 ¹¹ dyne / cm ² . Practically, 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 /
It was found to be cm ² . (12) Adhesion Strength The adhesion strength between the support and the magnetic layer was measured by the 180 ° peeling method.

A tape having a width of 8 mm was attached to a 3M adhesive tape, and 180 peel strength was measured at 23 ° C. and 70% RH. The result obtained was 50 g. or,
It was 25 g when Example 3-1 was similarly measured. It has been found that the practically preferable adhesion strength is 10 g or more, and particularly preferably 20 g or more. (13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured.

The sample was fixed on the prepared glass by sticking both ends thereof with adhesive tape, and was slid by applying a load of 50 g to a 6.25 mmφ steel ball. At that time, after traveling once at a speed of 20 mm / sec for a distance of 20 mm, the steel ball was moved to a new magnetic surface and the same operation was repeated 20 times. After that, observe the sliding surface of the steel ball with a microscope of 40 times,
The diameter was calculated assuming that the surface was a circle, and the amount of wear was calculated from the diameter.

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

Magnification 50 with Hitachi electron microscope S-900
Five pieces were photographed at 00 times to measure the surface abrasive. As a result, the number of abrasives was 0.2 / μm ² . Moreover, when Example 4-6 was measured, it was 0.4 piece / mm < ² >. In practice, it was found that the number of abrasives was 0.1 / μm ² or more, 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 -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 . Moreover, it was 18 mg / m < ² > when Example 1-1 was similarly measured. Practically, it is preferably 50 mg / m ² or less, particularly preferably 20.
It was found to be below mg / m ² . (16) Sol Fraction The ratio of the soluble solids extracted with THF from the magnetic layer of the magnetic tape to the weight of the magnetic layer was determined. As a result, the sol fraction was 7%. Moreover, it was 5% when Example 1-1 was similarly measured. Practically, the sol fraction is preferably 15
It has been found that the content is not more than%, particularly preferably not more than 10%. (17) Magnetic development pattern The obtained 8 mm wide magnetic recording medium was used as a Sony VTR.
Using EVO-9500, short wavelength recording of 1 MHz was performed, and only the recorded portion was slit to a width of 5 mm, a ferri colloid (about 100 Åφ) (manufactured by Taiho Kogyo Co., Ltd.) liquid was flowed to perform magnetic development, and the resulting product was placed in the ligroin liquid. The one subjected to the immersion treatment for 24 hours was photographed at 10 times with a differential interference microscope manufactured by Nihon Kogaku Co., Ltd. with the interference color being blue. When the photograph is visually observed, black or white lines do not appear in the sample in which the thickness of the magnetic layer is averaged, but black or white lines appear as the thickness variation of the magnetic layer increases. This line is a portion having uneven thickness, and it is preferable that the number of such black or white lines is within 5 within a width of 5 mm. Further, the density difference between the black and white lines measured by a microdensitometer for these lines is preferably 0.2 or less, and particularly preferably 0.1 or less. (18) Friction coefficient (μ) 2 mm of 8 mm wide tape and sus420J, 4 mmφ rod
The tension (T2) required to make the tape run at a speed of 14 mm / sec under the conditions of contact with a wrap angle of about 180 ° with a tension of 0 g (T1) was measured and determined by the following formula.

Μ = (1 / π) ln (T1 / T2) As a result, μ of the magnetic surface was 0.3. In practice, it has been found that μ of the magnetic surface is preferably 0.15 to 0.4, particularly preferably 0.2 to 0.35. Further, μ of the back layer surface was 0.2. In practice, the back layer surface has a μ value of preferably 0.15 to 0.4, particularly preferably 0.2 to 0.4.
It was found to be 0.35.

The friction coefficient is determined in relation to the magnetic substance, abrasive, carbon black, lubricant, dispersant and the like. (19) Contact angle Water and methylene iodide droplets were dropped on the magnetic layer, and the contact angle was measured with a microscope. In the case of water, it was 90 °.
Practically, it is preferably 60 to 130 °, particularly 80.
It has been found that ~ 120 ° is preferred.

In the case of methylene iodide, the contact angle is 20.
It was °. Practically, it is preferably 10 to 90 °,
Particularly preferably, it was 10 to 70 °. These contact angles are values determined by the lubricant or 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 are 40d.
It was yne / cm. Practically 10-100 dyne /
It has been found that cm is particularly preferred. This surface free energy is a value that is particularly determined by the lubricant and dispersant. (21) Surface electric resistance A sample with a width of 8 mm has a quadrant cross section with a radius of 10 mm.
The measurement was performed with a digital surface electric resistance meter TR-8611A (manufactured by Takeda Riken) while passing it over two electrodes placed at an interval of mm.

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

8 mm videotape samples 1 and 2 having the above characteristics were compared to the currently commercially available tapes and the results are shown in Table 20.

[0264]

[Table 20]

The evaluation method was the above-mentioned method or a general method. The criteria for judgment 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 × Generation of rust after storage at 60 ° C, 90% RH for 10 days Durability: When running 50 passes on an 8mm VCR ○ No clogging that lasts for 30 seconds or longer.

Clogged for 30 seconds or longer. Scratch: Run in still mode for 10 minutes. ○ No scratches are visually observed. X: Scratches are visually observed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of measuring Δd of a magnetic recording medium obtained by a manufacturing method of 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 in a wet-on-wet coating method in the present invention.

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

[Description of sign]

 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 multi-layer coating device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C08J 7/04 CFD C08J 7/04 CFDV G11B 5/716 G11B 5/716 (72) Inventor Satoru Hayakawa 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (20)

[Claims] 1. A lower non-magnetic layer coating solution containing a non-magnetic powder and a binder and an upper magnetic layer coating solution containing a ferromagnetic powder and a binder are prepared, and the lower layer is formed on a flexible support. In the method for producing a magnetic recording medium, which comprises coating a coating liquid for a non-magnetic layer and a coating liquid for an upper magnetic layer, the coating liquid for the lower non-magnetic layer has thixotropic properties, and the lower non-magnetic layer is formed on the flexible support. When the lower non-magnetic layer obtained by applying the coating solution for the layer is wet, simultaneously or sequentially with the application of the lower non-magnetic layer coating solution, the upper magnetic layer coating solution is applied, and the upper layer The dry thickness average value d of the magnetic layer is 1.0 μm or less,
A method of manufacturing a magnetic recording medium, characterized in that the average thickness variation Δd at the interface between the upper magnetic layer and the lower non-magnetic layer after drying has a relation of Δd ≦ 0.50d. 2. The dry thickness average value d of the upper magnetic layer is λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ, and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 50. The method of manufacturing a magnetic recording medium according to claim 1, wherein the shortest recording wavelength λ is 2 μm or less. 3. The _root mean square roughness R _{rms of the} surface of the upper magnetic layer measured by a scanning tunneling microscope (STM) method or an atomic force microscope (AFM) method is a dry thickness average value d of the magnetic layer.
3. The method of manufacturing a magnetic recording medium according to claim 1, wherein there is a relationship of 30 ≦ d / R _rms between and. 4. The magnetic recording according to claim 1, wherein the thermal shrinkage of the magnetic recording medium after storage at 70 ° C. for 48 hours is 0.4% or less. Medium manufacturing method. 5. The dry thickness of the lower non-magnetic layer is 1 to 30 times the 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. 5. The method for producing a magnetic recording medium according to claim 1, wherein the difference between the magnetic recording medium and the magnetic recording medium is -5% to + 20%. 6. The ratio SMD / STD between the staying direction SMD of the magnetic recording medium in the coating direction (longitudinal direction) and the staying direction STD in the width direction with respect to the coating direction is 1.0 to 1.9. The method for manufacturing the magnetic recording medium according to claim 1. 7. The non-magnetic powder contained in the coating liquid for the lower non-magnetic layer contains an inorganic powder, and the inorganic powder has a Mohs hardness of 6 or more and an average primary particle diameter of 0.15 μm or less from a spherical shape to a cubic shape. 7. The method for producing a magnetic recording medium according to claim 1, wherein the polyhedral inorganic powder is used. 8. The non-magnetic powder contained in the coating liquid for the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size thereof is needle-like strong contained in the coating liquid for the upper magnetic layer. 8. The method for producing a magnetic recording medium according to claim 1, wherein the crystallite size is ½ to 4 times the crystallite size of the magnetic powder. 9. The non-magnetic powder contained in the coating liquid for the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size thereof is needle-like strong contained in the coating liquid for the upper magnetic layer. 9. The method for producing a magnetic recording medium according to claim 1, wherein the length is 1/3 or less of the major axis length of the magnetic powder. 10. The method for producing a magnetic recording medium according to claim 1, wherein the coating liquid for the lower non-magnetic layer contains a magnetic powder that imparts thixotropy. 11. The method for manufacturing a magnetic recording medium according to claim 1, wherein Bm of the lower non-magnetic layer is 500 Gauss or less. 12. The lower non-magnetic layer coating liquid contains magnetic powder, and the lower non-magnetic layer is a layer not involved in recording, according to any one of claims 1 to 11. Manufacturing method of magnetic recording medium. 13. The support is polyethylene terephthalate, polyethylene naphthalate polyesters, polyolefins, cellulose triacetate, polycarbonate.
13. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least one selected from the group consisting of bone, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide. Production method. 14. The bending rigidity (annular stiffness) of the magnetic recording medium is 4 when the total thickness is thicker than 11.5 μm.
0 to 300 mg, and 2 when the total thickness is 10.5 ± 1 μm
It is 0 to 90 mg, and when the total thickness is thinner than 9.5 μm, it is 10 to 70 mg.
4. The method for manufacturing a magnetic recording medium according to any one of 3 above. 15. The magnetic recording medium at 23 ° C. and 70% R
The method for producing a magnetic recording medium according to any one of claims 1 to 14, wherein the crack generation elongation of the magnetic layer measured by H is 20% or less. 16. The Cl / Fe spectrum α of the surface of the upper magnetic layer measured by an X-ray photoelectron spectrometer of the magnetic recording medium is 0.3 to 0.6, and the N / Fe spectrum β is 0. It is 03-0.12, The manufacturing method of the magnetic recording medium of any one of Claims 1-15 characterized by the above-mentioned. 17. The surface of the upper magnetic layer is 23 ° C. and 70%
The method of manufacturing a magnetic recording medium according to claim 1, wherein the wear of the steel ball of RH is 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ . 18. The magnetic recording medium is an SEM (electron microscope).
The upper magnetic layer was photographed with a mirror) at a magnification of 50,000 times.
Visual number of abrasive on the surface is 0.1 / μm ²And above
The method according to any one of claims 1 to 17, characterized in that
Manufacturing method of magnetic recording medium of. 19. The upper magnetic layer of the magnetic recording medium comprises 1M
Recorded at a short wavelength of Hz, magnetically developed with ferri colloid, and observed with a differential interference microscope at 10 times 5 mm.
The method for producing a magnetic recording medium according to claim 1, wherein the number of continuous black or white lines in the width sample is 5 or less. 20. The in-plane squareness ratio in the coating direction (longitudinal direction) of the upper magnetic layer of the magnetic recording medium is 0.7 or more, and the squareness ratio in the vertical direction is 0.6 or more. A method of manufacturing a magnetic recording medium according to claim 1.