JP2002015414A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a disk like magnetic recording medium having improved electromagnetic transducing characteristics, especially high density recording characteristics, excellent durability, an improved error rate in a high density recording region and a large recording capacity of 0.031-0.31 Gbit/cm2. SOLUTION: The magnetic recording medium is formed by providing a lower layer which is esseentially non-magnetic and a magnetic layer formed by dispersing a ferromagnetic metal fine powder or a ferromagnetic hexagonal system ferrite fine powder in a bonding agent on a non-magnetic substrate in this order and has 0.031-0.31 Gbit/cm2 surface recording density. The magnetic layer has 0.05-0.25 μm dry thickness, 10.1-1.3 μTcm of Φm and >=142.2 kA/m coercive force. After the non-magnetic substrate is preserved for 1 Hr at 150 deg.C under dry condition, <=43,000/mm2 deposits are formed on the surface of the non- magnetic substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium having a high recording density, and more particularly to a coating type magnetic recording medium having a magnetic layer and a substantially nonmagnetic lower layer, and a ferromagnetic metal fine powder or a hexagonal ferrite on the uppermost layer. The present invention relates to a magnetic recording medium for high density recording containing fine powder.

[0002]

2. Description of the Related Art In the field of magnetic disks, a 2 MB MF-2HD floppy (registered trademark) disk using Co-modified iron oxide has been standardly mounted on a personal computer. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of floppy disks.

[0003] With the increase in capacity of magnetic recording media, the amount of data recorded on one medium is much larger than that of conventional media. For this reason, the effect when the recorded data cannot be reproduced is significantly increased. In particular, magnetic recording media used for computer use are often stored for a long period of time, and there is a strong demand for improved storage capacity as well as improved storage capacity.

Conventionally, a magnetic recording medium has a magnetic layer obtained by dispersing iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder in a binder on a non-magnetic support. Is widely used. Among them, ferromagnetic metal fine powder and hexagonal ferrite fine powder are known to be excellent in high density recording characteristics. In the case of a disk, a large-capacity disk using ferromagnetic metal fine powder excellent in high-density recording characteristics is 10 MB MF-2TD, a 21-MB MF-2SD or a 4-MB MF-SD is a large-capacity disk using hexagonal ferrite. There are 2ED, 21MB floptical, etc., but the capacity and performance were not sufficient. Under such circumstances, many attempts have been made to improve the high-density recording characteristics. An example is shown below.

In order to improve the characteristics of a disk-shaped magnetic recording medium, Japanese Patent Application Laid-Open No. 64-84418 proposes to use a vinyl chloride resin having an acidic group, an epoxy group and a hydroxyl group. No. Hc7
9.0 kA / m (1000 Oe, Oe) or more,
It has been proposed to use metal fine powder having a specific surface area of 25 to 70 m ² / g, and Japanese Patent Publication No. 6-28106 proposes to determine the specific surface area and the amount of magnetization of a magnetic substance and to include an abrasive. .

In order to improve the durability of a disk-shaped magnetic recording medium, Japanese Patent Publication No. 7-85304 proposes to use an unsaturated fatty acid ester and a fatty acid ester having an ether bond, and Japanese Patent Publication No. 7-70045. The publication proposes to use a fatty acid ester having an ether bond with a branched fatty acid ester, as disclosed in JP-A-54-1247.
No. 16 proposes to include a nonmagnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester.
No. 9407 proposes that the volume and surface roughness of pores containing a lubricant be 0.005 to 0.025 μm,
Japanese Patent Application Laid-Open No. 61-294637 proposes to use a fatty acid ester having a low melting point and a high melting point.
JP-A-6216 proposes to use an abrasive having a particle size of 1/4 to 3/4 of the thickness of the magnetic layer and a fatty acid ester having a low melting point, and JP-A-3-203018 discloses a metal magnet containing Al. It has been proposed to use body and chromium oxide.

As a configuration of a disk-shaped magnetic recording medium having a nonmagnetic lower layer and an intermediate layer, Japanese Patent Application Laid-Open No. 3-120613 has proposed a configuration having a conductive layer and a magnetic layer containing fine metal powder. Japanese Patent Application Laid-Open No.
The following configuration having a magnetic layer and a non-magnetic layer has been proposed. Japanese Patent Application Laid-Open No. 62-159337 has proposed a configuration including a carbon intermediate layer and a magnetic layer containing a lubricant.
Japanese Patent No. 90358 proposes a configuration having a non-magnetic layer having a defined carbon size.

On the other hand, a disk-shaped magnetic recording medium comprising a thin magnetic layer and a functional non-magnetic layer has recently been developed.
0MB class floppy disks have appeared. Japanese Patent Application Laid-Open No. 5-109061 shows these features.
In Japanese Patent Application Laid-Open No. H05-1993, there is proposed a configuration having a magnetic layer having a Hc of 110.6 kA / m (1400 Oe) or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing conductive particles.
Japanese Patent Application Laid-Open No. 197946 proposes a configuration containing an abrasive larger than the thickness of the magnetic layer.
Japanese Patent Application Laid-Open No. 6-68453 proposes a configuration in which the surface electrical resistance is set to 15% or less, and a configuration in which two types of abrasives having different particle sizes are included and the amount of the abrasive on the surface is defined. .

[0009] In recent years, with the spread of office computers such as minicomputers and personal computers, magnetic tapes (so-called backup tapes) for recording computer data as external storage media have been developed for tape-shaped magnetic recording media. Research is being actively conducted. When a magnetic tape for such a purpose is put into practical use, especially with the downsizing of computers and the increase in information processing capacity, an increase in recording capacity is strongly demanded in order to achieve large-capacity recording and downsizing. In addition, the use environment of magnetic tapes is widespread, so the use under a wide range of environmental conditions (especially in the rapidly fluctuating temperature and humidity conditions), the reliability of data storage, and the stable use of data in multiple runs by repeated use at high speed. Reliability for performance such as recording and reading is required more than before.

Conventionally, a magnetic tape used in a digital signal recording system is determined for each system, and a so-called DLT type, 3480, 3490, 3590,
Magnetic tapes compatible with QIC, D8 type, or DDS type are known. In any system, the magnetic tape used has a relatively thick monolayer ferromagnetic powder having a thickness of 2.0 to 3.0 μm, a binder, and a polishing agent on one side of the nonmagnetic support. A magnetic layer containing an agent is provided, and a back coat layer is provided on the other side to prevent winding disturbance and maintain good running durability.
However, in the magnetic layer having a relatively thick single-layer structure as described above, there is a problem of a loss in thickness that the output is reduced.

It is known that the magnetic layer is made thinner in order to improve the reduction of the reproduction output due to the thickness loss of the magnetic layer. A lower nonmagnetic layer containing an inorganic powder and dispersed in a binder, and an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing a ferromagnetic powder in the binder while the nonmagnetic layer is in a wet state. A magnetic recording medium has been disclosed.

However, with the rapid increase in capacity and density of magnetic recording media in the form of disks or tapes, it has become difficult to obtain satisfactory characteristics even with such techniques. Also, it is becoming difficult to achieve both durability and durability.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to significantly improve electromagnetic conversion characteristics, especially high-density recording characteristics, and have excellent durability, and to further improve the error rate in a high-density recording region. To provide a magnetic recording medium. A special object of the present invention is to provide a recording medium having excellent characteristics and a recording capacity of 0.031 to 0.31 Gbit / c.
m ² , preferably 0.054 to 0.31 Gbit / cm ²
And to provide a large-capacity disk-shaped magnetic recording medium.

[0014]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a magnetic recording medium having good electromagnetic conversion characteristics and durability and a particularly improved error rate in a high-density recording area. It has been found that by using the following medium, excellent high-density recording characteristics and excellent durability can be obtained, and the present invention has been accomplished. That is, according to the present invention, a magnetic recording medium having the following configuration is provided, and the above object of the present invention is achieved. 1. In a magnetic recording medium having a substantially non-magnetic lower layer and a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder dispersed in a binder on a non-magnetic support in this order, I) 0.031-0.31 Gbit /
It has a surface recording density of recording signals of cm ^2, a 0.05~0.25μm the dry thickness of (II) a magnetic layer, (II
I) When Φm is 10.1 to 1.3 μTcm (8.0 × 10 ⁻³⁾
IV1.0 × 10 ⁻³ emu / cm ² ), (IV) the coercive force of the magnetic layer is 142.2 kA / m (1800 Oersteds) or more, and (V) the nonmagnetic support is 150
A magnetic recording medium, wherein the number of precipitates deposited on the surface of the support after storage for 1 hour at a temperature of 4 ° C. is 43,000 / mm ² or less. 2. The magnetic recording medium as described in 1 above, wherein the magnetic recording medium has a surface recording density for recording a signal of 0.054 to 0.31 Gbit / cm ² and contains an inorganic powder having a Mohs hardness of 4 or more in a lower layer. 3. 3. The magnetic recording medium according to 1 or 2, wherein the dry thickness of the magnetic layer is 0.05 to 0.20 μm, and the magnetic layer contains an abrasive having an average particle size of 0.4 μm or less. 4. 4. The magnetic recording medium according to any one of the above items 1 to 3, wherein the surface roughness of the magnetic layer is 4 nm or less as a center plane average roughness measured by a light interference type surface roughness meter. 5. 5. The magnetic recording medium according to any one of items 1 to 4, wherein the coercive force of the magnetic layer is 158 kA / m (2000 Oersteds) or more. 6. The ferromagnetic metal fine powder is mainly composed of Fe and has a major axis of 0.
6. The magnetic recording medium according to any one of the above items 1 to 5, wherein the magnetic recording medium has a crystallite size of 12 μm or less and a crystallite size of 80 to 180 °. 7. 7. The magnetic recording medium according to any one of the above items 1 to 6, wherein the surface roughness of the nonmagnetic support is 8 nm or less as a center plane average surface roughness measured by a light interference type surface roughness meter. 8. 8. The magnetic recording medium according to any one of the above items 1 to 7, wherein the magnetic recording medium is a disk. 9. 8. The magnetic recording medium according to any one of the above items 1 to 7, wherein the magnetic recording medium is a computer tape.

The magnetic recording medium having the above-described structure has excellent high-density characteristics and excellent durability, which cannot be obtained by the prior art, has a remarkably improved error rate in a high-density recording area, and has a very high error rate. 054-0.31 Gbit / c
A disk-shaped magnetic recording medium having a large capacity of m ² can be obtained.

Here, the substantially non-magnetic lower layer means that it may have a magnetic property to the extent that it does not participate in recording, and is hereinafter simply referred to as the lower layer or the non-magnetic layer. The surface recording density is obtained by multiplying the linear recording density by the track density. Φm is the amount of magnetization per unit area of the magnetic recording medium (Bm (Gauss) multiplied by the thickness), which is a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.)
Is a value measured at a Hm of 790 kA / m (10000 Oersteds), which can be directly measured.

The linear recording density is the number of bits of a signal to be recorded per inch in the recording direction. These linear recording density, track density, and areal recording density are values determined by the system. That is, the present invention improves the surface recording density by improving the magnetic layer thickness, the magnetic layer Hc, and the center plane average surface roughness in terms of linear recording density, and optimizing Φm in terms of track density. It is intended.

In this way, the areal recording density of 0.031 to 0.31 Gb, which cannot be obtained by the conventional technique, is obtained.
it / cm ² , and further, the areal recording density is 0.054-0.
A magnetic recording medium having 31 Gbit / cm ² , which has both excellent high-density characteristics and excellent durability, and particularly has a remarkably improved error rate in a high-density region, particularly a disk-shaped magnetic recording medium. Can be obtained.
That is, it has been known that oligomers contained in a polyethylene terephthalate support precipitate on the surface of the coating layer due to long-term storage and cause actual harm such as DO. In order to prevent this, the undercoat layer is applied to shield the oligomer, and the applied layer is made thicker to some extent so that no substantial harm is caused. But,
As the magnetic layer becomes thinner with the increase in recording density, precipitation of a low molecular weight component contained in a nonmagnetic support represented by an oligomer on the surface of a coating layer has become a problem. In the present invention, the number of precipitates on the surface of the non-magnetic support after storage for 1 hour at 150 ° C. and under drying conditions is 43,000 / mm ² or less, whereby the magnetic properties of the thin magnetic layer are reduced. Even if the recording medium is stored for a long period of time, there is no actual harm caused by deposits on the coating layer due to the non-magnetic support, and the storage properties are excellent, and the output and durability especially in a high density region are remarkably improved.

According to the present invention, the excellent areal recording density is 0.0
High-density characteristics of 31 to 0.31 Gbit / cm ² , and surface recording densities of 0.054 to 0.31 Gbit / cm ² , which have never been achieved with a coating-type magnetic recording medium that has not been achieved by products known to the world The fact that a magnetic recording medium having both excellent and excellent durability, particularly a disk-shaped magnetic recording medium, was obtained is a result obtained by organically combining the following technical points and synthesizing them.

In the field of personal computers, which are becoming increasingly multi-media, large-capacity recording media replacing floppy disks have begun to attract attention, and have been sold as ZIP disks by IOMEGA (Iomega), USA. This is an ATOMM (Advanced S) developed by the present applicant.
upper Thin Layer & High Ou
input Metal Media Technology
gy), a recording medium having a lower layer and a thin magnetic layer, and a product having a recording capacity of 3.7 inches and a recording capacity of 100 MB or more is sold. 100-120MB capacity is M
The capacity is almost the same as O (3.5 inches), and one newspaper article can fit in July to August. Data (information)
The transfer rate indicating the writing / reading time of a hard disk is about 2 MB or more per second, which is comparable to that of a hard disk, and is 20 times faster than the conventional FD and 2 times faster than the MO. Further, this recording medium having a lower layer and a thin magnetic layer can be mass-produced with the same coating type medium as that of the current FD, and has the advantage of being lower in cost than MOs and hard disks.

The present inventors have conducted intensive studies based on the knowledge of such media, and as a result, have found that the ZIP disk and MO
(3.5 inches), the areal recording density which is much larger than the recording capacity is 0.054 to 0.31 Gbit / cm ² , and further, the areal recording density is 0.054 to 0.31 Gbit / cm ^2.
In other words, magnetic recording media that have high density characteristics and excellent durability that have never been achieved with products known to the world, and that have significantly improved error rates especially in high density recording areas, especially disk-shaped magnetic recording A medium has been obtained, which is an invention which can also be applied to magnetic tapes such as computer tapes.

The magnetic recording medium of the present invention contains an ultra-thin magnetic layer containing ultra-fine magnetic powder of high output and high dispersibility, and a spherical or needle-like inorganic powder in the lower layer. By reducing the thickness, the canceling of the magnetic force in the magnetic layer is reduced, the output in the high frequency range is greatly increased, and the overwriting characteristics are also improved. By improving the magnetic head, the effect of the ultra-thin magnetic layer can be further exhibited in combination with the narrow gap head, and the digital recording characteristics can be improved.

The thickness of the upper magnetic layer is selected to be as thin as 0.05 to 0.25 μm so as to match the performance required from the magnetic recording system for high density recording and the magnetic head. Such an ultra-thin magnetic layer, which is uniform and thin, highly disperses fine magnetic powder and non-magnetic powder by using a dispersant and a highly dispersible binder in combination to achieve high packing. . The magnetic material used is a magnetic material excellent in high output, high dispersion and high randomization in order to maximize the suitability of a large capacity FD or computer tape. That is, by using a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder which can achieve high output with very fine particles,
Particularly, the major axis length is 0.1 μm or less, and the crystallite size is 80 to
When the angle is 180 °, high output and high durability can be achieved by further containing Co and containing Al and Y as a sintering inhibitor. In order to achieve a high transfer rate, a three-dimensional network binder system suitable for an ultra-thin magnetic layer is used to ensure running stability and durability during high-speed rotation. In addition, a composite lubricant that can maintain its effectiveness even when used under a wide range of temperature and humidity conditions or when used at high speeds is arranged in two layers, the upper and lower layers. An appropriate amount of lubricant can always be supplied to the magnetic layer, the durability of the upper magnetic layer is increased, and the reliability is improved. In addition, the cushion effect of the lower layer can provide good head touch and stable running performance.

In a large-capacity recording system, a high transfer rate is required. For this purpose, it is necessary to increase the number of rotations of the magnetic disk by one digit or more compared to the conventional FD system. As the capacity and density of magnetic recording increase, the recording track density increases. In general, a servo recording area is provided on a medium to ensure traceability of a magnetic head with respect to a recording track. In the magnetic recording medium of the present invention, a base having improved isotropic dimensional stability is used as a support base to further stabilize traceability. The use of an ultra-smooth base can further improve the smoothness of the magnetic layer.

In order to increase the density of disk-shaped magnetic recording,
It is necessary to improve the linear recording density and the track density. Of these, the characteristics of the support are important for improving the track density. In the medium of the present invention, the dimensional stability of the support base, particularly the isotropy, is considered. Servo recording is an indispensable technique in recording / reproducing at a high track density, but this improvement can be achieved from the medium side by making the support base as isotropic as possible.

The advantages of the present invention in which the magnetic layer is changed from a single layer to an ATOMM structure are considered as follows. (1) Improvement of electromagnetic conversion characteristics by making the magnetic layer thinner, (2) Improvement of durability by stable supply of lubricant (3) High output by smoothing the upper magnetic layer (4) Function separation of the magnetic layer These functions cannot be achieved simply by increasing the number of magnetic layers. In order to configure a multilayer structure, a “sequential multilayer system” in which the layers are sequentially configured is generally used. In this method, first, a lower layer is applied, cured, or dried, and then an upper magnetic layer is similarly applied, cured, and surface-treated. The FD differs from the magnetic tape in that the same processing is performed on both sides. After the coating process, it is completed as a final product through a slit process, a punch process, a shell assembling process, and a certifying process.

The following electromagnetic conversion characteristics can be greatly improved by forming a thin magnetic layer. (1) Improvement of the output in the high frequency region by improving the characteristics at the time of recording demagnetization, (2) Improvement of the overwriting (overwrite) characteristics (3) Ensuring the window margin Durability is an important factor for the magnetic disk. Particularly, in order to realize a high transfer rate, it is necessary to increase the number of rotations of the magnetic disk by one digit or more compared with the conventional FD system, and the medium durability when the medium in the magnetic head / cartridge slides at high speed with the medium. Is an important issue.
Means for improving the durability of the medium include a binder formulation for increasing the film strength of the disk itself, and a lubricant formulation for maintaining the slipperiness with the magnetic head. The medium of the present invention improves the binder formulation from the three-dimensional network binder system that has been proven in current FD systems.

The lubricant is used in combination with a plurality of lubricants which exhibit excellent effects under various temperature and humidity environments used, and has a wide range of temperature (low temperature, room temperature, high temperature) and humidity (low humidity, high humidity). Even under a wet environment, each lubricant exerts its function and can maintain a totally stable lubricating effect. In addition, by utilizing the structure of the upper and lower two layers, the lower layer has a lubricant tank effect so that an appropriate amount of lubricant is always supplied to the upper magnetic layer, and the durability of the upper magnetic layer can be improved. Things. There is a limit to the amount of lubricant that can be included in the ultra-thin magnetic layer, and simply thinning the magnetic layer reduces the absolute amount of lubricant, leading to deterioration in running durability. In this case, it was difficult to obtain a balance between the two. The upper and lower layers are provided with different functions and complement each other to achieve both improved electromagnetic conversion characteristics and improved durability. This functional differentiation was particularly effective in a system in which a magnetic head and a medium slide at high speed.

The lower layer can have a function of controlling the surface electric resistance in addition to the function of holding the lubricant. Generally, to control the electric resistance, a solid conductive material such as carbon black is often added to the magnetic layer. These not only limit the packing density of the magnetic material but also affect the surface roughness as the magnetic layer becomes thinner. These disadvantages can be eliminated by adding a conductive material to the lower layer.

With the advent of the multimedia society, the need for image recording has become stronger not only in the industrial world but also in homes. It has the ability to sufficiently meet the demands for function / cost as a medium. The large-capacity medium of the present invention is based on a coated magnetic recording medium that has a proven track record, and has excellent long-term reliability and excellent cost performance.

The present invention is achieved for the first time by accumulating various factors as described above and acting synergistically and organically.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION [Magnetic Layer] In the magnetic recording medium of the present invention, a lower layer and an ultrathin magnetic layer may be provided on only one side or both sides of a support. The upper and lower layers can be provided with an upper magnetic layer either after the lower layer is applied and the lower layer is in a wet state (W / W) or after drying (W / D). Simultaneously in terms of production yield,
Alternatively, sequential wet coating is preferable, but in the case of a disk, coating after drying can be used sufficiently. The upper layer / lower layer can be formed simultaneously by simultaneous or sequential wet coating (W / W) in the multilayer structure of the present invention, so that surface treatment steps such as a calendering step can be effectively utilized, and even in the case of an ultrathin layer, the surface roughness of the upper magnetic layer can be improved. Can be improved. The coercive force Hc of the magnetic layer is 142.2 kA / m (18
Bm is 200 to 500 mT (2000 to 5 mT) for the metallic magnetic powder.
000 gauss), and 100 ~ for barium ferrite powder.
It is necessary to be 300 mT (1000 to 3000 Gauss).

[Ferromagnetic Metal Fine Powder] As the ferromagnetic powder used in the upper magnetic layer of the present invention, a ferromagnetic alloy powder containing α-Fe as a main component is preferable. These ferromagnetic powders include Al, Si, S, Sc, Ca, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. In particular, Al, Si, Ca, Y, Ba, La, Nd,
Preferably, at least one of Co, Ni, and B is contained other than α-Fe, and more preferably, at least one of Co, Y, and Al is contained. The content of Co is preferably from 0 at% to 40 at%, more preferably from 15 at% to 35 at%, more preferably from 20 at% to 35 at% with respect to Fe. The content of Y is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic% to 10 atomic%, more preferably 4 atomic%.
Not less than 9 atomic%. Al is 1.5 atomic% or more and 12
Atomic% or less, preferably 3 atomic% or more and 10 atomic% or less, more preferably 4 atomic% or more and 9 atomic% or less.
It is as follows. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513,
JP-B-46-28466, JP-B-46-38755
No., JP-B-47-4286, JP-B-47-12422
No., JP-B-47-17284, JP-B-47-1850
No. 9, JP-B-47-18573, JP-B-39-103
07, Japanese Patent Publication No. 46-39639, U.S. Pat.
No. 6215, No. 3031341, No. 3100194
Nos. 3,242,005, 3,389,014 and the like.

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

The ferromagnetic powder of the magnetic layer of the present invention is applied to the BET method.
45-80m in terms of specific surface area ^Two/ G, preferred
Or 50-70m^Two/ G. 40m^Two/ G or less
Noise rises, 80m^Two/ G or more gives good surface properties
Unfavorable. Crystal of ferromagnetic powder of magnetic layer of the present invention
The child size is 80-180Å, preferably 100-
180 °, more preferably 110 ° to 175 °.
The major axis diameter of the ferromagnetic powder is 0.01 μm or more and 0.25 μm or less
Below, preferably 0.03 μm or more and 0.15 μm or less
Lower, more preferably 0.03 μm or more and 0.12
μm or less. Needle ratio of ferromagnetic powder is 3 or more and 15 or less
And more preferably 5 or more and 12 or less. Magnetic
Σs of metal powder is 100 to 180 Am^Two/ Kg (10
0 to 180 emu / g), preferably 110 to 1
70A ・ m^Two/ Kg (110-170 emu / g)
More preferably 125 to 160 Am^Two/ Kg (125
１６０160 emu / g). The coercive force of the metal powder is 1
34.3 to 276.5 kA / m (1700 to 3500 d
Rusted), more preferably 142.2.
~ 237kA / m (1800-3000 Oersted)
It is as follows.

The water content of the ferromagnetic metal powder is 0.01 to 2%.
It is preferred that It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. PH of ferromagnetic powder
Is preferably optimized by the combination with the binder used. The range is from 4 to 12, preferably from 6 to
It is 10. The ferromagnetic powder can be made of Al, Si, P
Alternatively, a surface treatment with such an oxide may be performed. The amount is 0.1 to 10% based on the ferromagnetic powder.
g / m ² or less, which is preferable. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr in some cases. These are preferably essentially absent,
If it is 200 ppm or less, there is little influence on the characteristics. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less. The shape may be acicular, rice grain, or spindle shape as long as the particle size characteristics described above are satisfied. The SFD of the ferromagnetic powder itself is preferably small, and is preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, and the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, the particle size distribution of goethite is improved in the ferromagnetic metal powder.
There are methods such as preventing sintering.

[Hexagonal Ferrite Fine Powder] As the hexagonal ferrite contained in the uppermost layer of the present invention, there are barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and other Co-substituted products. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite in which the particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite that further contain a part of the spinel phase. Other than predetermined atoms, Al, Si, S, Sc,
Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag,
Sn, Sb, Te, Ba, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, Pr, Nd, P, Co,
It may contain atoms such as Mn, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Zn, Co-T
i, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti
-Zn, Nb-Zn-Co, Sb-Zn-Co, Nb-
A substance to which an element such as Zn is added can be used. Some raw materials and production methods contain specific impurities. The particle size is 10 to 200 nm, preferably 10 to 100 nm as a hexagonal plate diameter, particularly preferably 10 to 8 nm.
0 nm.

In particular, when reproducing with a magnetoresistive head in order to increase the track density, it is necessary to reduce noise, and the plate diameter is preferably 40 nm or less, but if it is 10 nm or less, stable magnetization cannot be expected due to thermal fluctuation. Above 200 nm, noise is high and none of them are suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is desirably 1 to 15. Preferably it is 1-7. When the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. Fifteen
If it is larger, noise increases due to stacking between particles. The specific surface area by the BET method in this particle size range is 10 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. Although it is difficult to make a numerical value, it can be compared by randomly measuring 500 particles from a particle TEM photograph. In many cases, the distribution is not a normal distribution.
Average size = 0.1-2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force Hc measured on the magnetic material is 39.5.
It can be made up to about 395 kA / m (500 to 5000 Oe). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, H
c is 134.3 to 316 kA / m (1700 to 4000)
Oersted), but preferably 142.2-
It is 276.5 kA / m (1800-3500 Oersteds). The saturation magnetization of the head is 1.4T (14000
Gauss) is preferably 158 kA / m (2000 Oe). Hc can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like. The saturation magnetization s is 40 to 80 A · m ² / kg (40 to 80 em
u / g). The higher the value of σs, the better, but the smaller the particles, the smaller the tendency. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic substance, the surface of the magnetic substance particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides of Si, Al, P, etc., various silane coupling agents, and various titanium coupling agents. The amount of the surface treatment agent is 0.1 to 10% based on the magnetic material. The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12, depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% is selected. As a method of producing hexagonal ferrite, a metal oxide that replaces barium oxide, iron oxide, and iron and a glass-forming substance such as boron oxide are mixed to a desired ferrite composition and then melted.
A glass crystallization method in which a barium ferrite crystal powder is obtained by quenching to obtain an amorphous body, followed by reheating treatment, and then washing and pulverizing. A hydrothermal reaction method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, heated in a liquid phase at 100 ° C. or higher, washed, dried, and pulverized to obtain barium ferrite crystal powder. The barium ferrite composition metal salt solution is neutralized with an alkali, and after removing by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder. We do not choose manufacturing method.

[Non-Magnetic Layer] Next, the details of the lower layer will be described. The inorganic powder used in the lower layer of the present invention is a non-magnetic powder, and may be selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. it can. As the inorganic compound, for example, α-alumina having an α conversion of 90% or more,
β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide , Tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred are small particle size distribution,
Titanium dioxide, zinc oxide, iron oxide, and barium sulfate are preferred, and titanium dioxide and α-iron oxide are more preferred. The particle size of these non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have a similar particle size distribution to achieve the same effect. You can also. Particularly preferred nonmagnetic powder has a particle size of 0.01 μm to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is preferably 0.08 μm or less, and when the nonmagnetic powder is a needle-shaped metal oxide, the major axis length is preferably 0.3 μm or less, and 0.2 μm or less.
μm or less is more preferable. Tap density is 0.05-2
g / ml, preferably 0.2 to 1.5 g / ml.
The water content of the nonmagnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic powder is 2 to 11, but p
H is particularly preferably between 5.5 and 10.

The specific surface area of the nonmagnetic powder is 1 to 100 m ² /
g, preferably 5 to 80 m ² / g, more preferably 1 to 80 m ² / g.
0 to 70 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 to 1 μm, and 0.04 to 0.1 μm.
μm is more preferred. DBP (dibutyl phthalate)
Is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 100 ml / 100 g.
It is 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The Mohs' hardness is preferably 4 or more and 10 or less. The non-magnetic powder has an SA (stearic acid) adsorption amount of 1 to 20 μmol / m ² , preferably ² to 15 μmo.
1 / m ² , more preferably 3 to 8 μmol / m ² . Preferably, the pH is between 3 and 6. Al ₂ O ₃ , SiO ₂ , TiO ₂ , Z
It is preferable to perform a surface treatment with rO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ . Particularly preferred for dispersibility is Al ₂
O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ are preferred, and Al ₂ O ₃ , SiO ₂ and ZrO ₂ are more preferred. These may be used in combination or may be used alone. In addition, a co-precipitated surface treatment layer may be used according to the purpose, or a method of treating the surface layer with silica and then treating the surface layer with silica, or vice versa, may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α-hematite DPN-250 and DPN-250BX manufactured by Toda Kogyo. , DPN-24
5, DPN-270BX, DPN-500BX, DBN
-SA1, DBN-SA3, Ishihara Sangyo Titanium Oxide TT
O-51B, TTO-55A, TTO-55B, TTO
-55C, TTO-55S, TTO-55D, SN-1
00, α hematite E270, E271, E300, E
303, titanium industrial STT-4D, STT
-30D, STT-30, STT-65C, α-hematite α-40, MT-100S, MT-100 manufactured by Teika
T, MT-150W, MT-500B, MT-600
B, MT-100F, MT-500HD, FI manufactured by Sakai Chemical
NEX-25, BF-1, BF-10, BF-20, S
TM, Dowa Mining DEFIC-Y, DEFIC-R,
Nippon Aerosil AS2BM, TiO2P25, Ube Industries, Ltd. 100A, 500A, and the thing which baked it are mentioned. Particularly preferred non-magnetic powders are titanium dioxide and α
-Iron oxide.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. As the type of carbon black, furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like can be used. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

The specific surface area of the lower carbon black is 10
0~500m ² / g, preferably 150~400m ² /
g, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 400 ml / 100 g. The particle size of the carbon black is 5 to 80 nm, preferably 10 to 50 n.
m, more preferably 10 to 40 nm. Carbon black has a pH of 2 to 10 and a water content of 0.1 to 10.
% And the tap density are preferably 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 880, 7
00, VULCAN XC-72; manufactured by Mitsubishi Kasei Kogyo
# 3050B, # 3150B, # 3250B, # 375
0B, # 3950B, # 950, # 650B, # 970
B, # 850B, MA-600, MA-230, # 40
00, # 4010; CON manufactured by Konlon Via Carbon
DUCTEXT SC, RAVEN 8800, 800
0, 7000, 5750, 5250, 3500, 210
0, 2000, 1800, 1500, 1255, 125
0; Ketjen Black EC manufactured by Akzo Corporation. Surface treatment of carbon black with a dispersant,
It may be used by grafting with a resin or by using a part of the surface graphitized. Also, the car
Before adding the bon black to the paint, it may be dispersed in a binder in advance. These carbon blacks can be used in an amount not exceeding 50% by weight and not exceeding 40% of the total weight of the nonmagnetic layer based on the inorganic powder. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

In the lower layer, an organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. The manufacturing method is disclosed in
Those described in JP-A-2-18564 and JP-A-60-255827 can be used.

For the binder resin, lubricant, dispersant, additive, solvent, dispersing method, etc. of the lower layer, those of the magnetic layer described below can be applied. In particular, binder resin amount, type, additives,
Known techniques for the magnetic layer can be applied to the amount and type of the dispersant. [Binder] The binder, lubricant, dispersant, additive, solvent, dispersing method, etc. of the magnetic layer, non-magnetic layer and back layer of the present invention can be applied to the magnetic layer, non-magnetic layer and back layer.
In particular, the amount of the binder, the type, the additive, the amount of the dispersant added,
As for the type, a known technique for the magnetic layer can be applied.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As the thermoplastic resin, the glass transition temperature is -100 to 150 ° C, and the number average molecular weight (GPC
(In terms of polystyrene measured by the method) is 1,000
~ 200,000, preferably 10,000-100,0
The degree of polymerization is about 50 to 1,000.

Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin,
Epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, polyester polyol
A mixture of toluene and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer, At least one selected from
Examples include a combination of a seed and a polyurethane resin, or a combination of these with a polyisocyanate.

The structure of the polyurethane resin is polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane,
Known materials such as polycaprolactone polyurethane can be used. For all the binders shown here, -CO is required to obtain better dispersibility and durability.
_{OM, -SO 3 M, -OSO 3} M, -P = O (OM) 2,
-O-P = O (OM) 2, ( wherein, M represents a hydrogen atom or an alkali _{metal,), - OH, -NR 2} , -N + R
₃ (where R represents a hydrocarbon group), an epoxy group,-
It is preferable to use one obtained by introducing at least one or more polar groups selected from SH, -CN, and the like by copolymerization or addition reaction. The amount of such a polar group is 1 × 10
^-1 to 1 × 10 ⁻⁸ mol / g, preferably 1 × 10 ⁻²
１1 × 10 ⁻⁶ mol / g.

Specific examples of these binders used in the present invention include VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE; manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO; 1000 manufactured by Denki Kagaku
W, DX80, DX81, DX82, DX83, 100
FD: MR-104, MR-105, M manufactured by Zeon Corporation
R110, MR100, MR555, 400X-110
A: Nipporan N2301, N2 manufactured by Nippon Polyurethane Co.
302, N2304; Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9, 7209: Toyobo Co., Ltd. Byron UR8200, UR
8300, UR-8700, RV530, RV280;
Diferamine 4020, 5020, 51 manufactured by Nissei Chemicals, Inc.
00, 5300, 9020, 9022, 7020; MX5004, manufactured by Mitsubishi Kasei Co., Ltd., Samprene SP manufactured by Sanyo Kasei Co., Ltd.
-150; Saran F310, F210 manufactured by Asahi Kasei Corporation and the like.

The binder used in the non-magnetic layer and the magnetic layer of the present invention is used in an amount of 5 to 50%, preferably 10 to 30%, based on the non-magnetic powder or magnetic material. 5 to 30% when using a vinyl chloride resin, 2 to 20% when using a polyurethane resin, polyisocyanate
It is preferable to use these in combination in the range of 2 to 20%. For example, when head corrosion occurs due to a small amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate.
In the present invention, when polyurethane is used, the glass transition temperature is -50 to 150C, preferably 0C to 100C.
° C, breaking elongation is 100 ~ 2000%, breaking stress is 0.4
9-98 MPa (0.05-10 kg / mm ² ), yield point 0.49-98 MPa (0.05-10 kg / mm ² )
² ) is preferred.

The magnetic recording medium of the present invention comprises two or more layers. Accordingly, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate, or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the amount described above. It is of course possible to change the physical properties of the resin between the non-magnetic layer and each magnetic layer, if necessary. Rather, it should be optimized for each layer, and a known technique for a multilayer magnetic layer can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. Can be made flexible by increasing the amount of binder.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-1. ,
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate and other isocyanates; products of these isocyanates and polyalcohols; and polyisocyanates formed by condensation of isocyanates. -And the like can be used. Commercially available trade names of these isocyanates include those manufactured by Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M
R, milliont MTL, Takeda D, manufactured by Takeda Pharmaceutical Co., Ltd.
-102, Takenet D-110N, Takenet D-2
00, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These can be used alone or by utilizing the difference in curing reactivity. Each layer can be used in a combination of two or more.

[Carbon Black and Abrasive] Carbon black used in the magnetic layer of the present invention is a rubber
Ness, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5-50
0 m ² / g, DBP oil absorption 10-400 ml / 100
g, particle diameter is 5 to 300 nm, pH is 2 to 10, water content is 0.1 to 10%, and 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-130, manufactured by Asahi Carbon Co., Ltd., $ 55, $ 50, $ 3
5, N660, manufactured by Mitsubishi Kasei Kogyo Co., Ltd., and RAVEN 410, 420, 500, 22 manufactured by Columbian Carbon Co., Ltd. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount based on the magnetic substance. Carbon black has functions such as preventing the magnetic layer from charging, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength. These functions differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are composed of an upper magnetic layer,
It is of course possible to change the type, amount and combination of the lower non-magnetic layer and use them according to the purpose based on the above-mentioned properties such as particle size, oil absorption, conductivity and pH. Should be optimized. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

Examples of the abrasive used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, and the like. Silicon carbide titanium car
Known materials having a Mohs hardness of 6 or more, such as a bite, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component in some cases, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 μm, and in particular, the particle size distribution is preferably narrow in order to enhance the electromagnetic conversion characteristics. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as needed, or to use a single abrasive to broaden the particle size distribution to achieve the same effect. Tap density is 0.3-2g / cc, water content is 0.1-5%,
The pH is preferably ^{2 to} 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive 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. Specifically, AKP-1 manufactured by Sumitomo Chemical Co., Ltd.
2, AKP-15, AKP-20, AKP-30, AK
P-50, HIT20, HIT-30, HIT-55,
HIT60, HIT70, HIT80, HIT100;
ERC-DBM, HP-DBM, HP manufactured by Reynolds
S-DBM; manufactured by Fujimi Abrasives Co., Ltd .; WA10000; manufactured by Uemura Kogyo Co., Ltd .; UB20; manufactured by Nippon Kagaku Kogyo Co., Ltd .;
100, TF140; manufactured by Ibiden Co., Ltd., Beta Random Ultra Fine; B-3 manufactured by Showa Mining Co., Ltd. These abrasives can be added to the nonmagnetic layer as needed. By adding to the non-magnetic layer, the surface shape can be controlled, and the projected state of the abrasive can be controlled. The particle size of the abrasive added to these magnetic layers and non-magnetic layers,
The amount should of course be set to the optimum value.

[Additives] As the additives used in the magnetic layer and the nonmagnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Specifically, molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil,
Silicones having polar groups, fatty acid-modified silicones, fluorine-containing silicones, fluorine-containing alcohols, fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and alkali metal salts thereof, alkyl sulfates and the like Alkali metal salt, polyphenyl ether
Ter, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and their alkali metals Salts, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched), and metal salts thereof (such as Li, Na, K, and Cu) or carbon atoms 12-22 monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols (which may contain unsaturated bonds or may be branched), alkoxy having 12 to 22 carbon atoms Alco-
A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and having 2 carbon atoms
~ 12 monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols
A monofatty acid ester or a difatty acid ester or a trifatty acid ester consisting of any one of the above (which may contain an unsaturated bond or may be branched), a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, C8-C22 fatty acid amide, C8-C
22 aliphatic amines and the like can be used.

The following are specific examples of the above fatty acids and esters. Examples of the fatty acid include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and isostearic acid. In esters, butyl stearate,
Octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate,
2-octyl dodecyl palmitate, 2-hexyldodecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl,
Alcohols include oleyl alcohol, stearyl alcohol, lauryl alcohol and the like.

Further, nonionic surfactants such as alkylene oxides, glycerins, glycidols, and alkylphenol ethylene oxide adducts, cyclic amines,
Including acid groups such as ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, cationic surfactants such as phosphonium or sulfoniums, and carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, phosphate groups, and the like. Anionic surfactants, amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohol, alkylbedine-type amphoteric surfactants, and the like can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
Not pure, but may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

Each of these lubricants and surfactants used in the present invention has a different physical action.
The type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose.
To control bleeding to the surface using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface using esters with different boiling points, melting points and polarities, and to adjust the amount of surfactant However, the lubrication effect can be improved by increasing the amount of the lubricant added in the intermediate layer, and it is a matter of course that the present invention is not limited to only the examples shown here. Generally, the total amount of the lubricant is from 0.1% to 50%, preferably from 2% to 2%, based on the magnetic substance or the non-magnetic powder.
It is selected in the range of 5%.

All or a part of the additives used in the present invention may be added at any step of the production of the magnetic and non-magnetic paints. There are a case where it is added in a kneading step using a body, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after slitting. As the organic solvent used in the present invention, known organic solvents can be used.
No. 453 can be used.

[Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the non-magnetic support is 20 to 100 μm, preferably 3 to 100 μm.
0 to 80 μm. An undercoat layer for improving adhesion may be provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer. The thickness of the undercoat layer is 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm. The present invention may be a double-sided magnetic layer disk-shaped medium in which a nonmagnetic layer and a magnetic layer are usually provided on both sides of a support, or may be provided on only one side.
In this case, a back coat layer may be provided on the side opposite to the non-magnetic layer and the magnetic layer in order to obtain effects such as antistatic and curl correction. This thickness is 0.1 to 4 μm, preferably 0.3 to 2 μm. These undercoat layers, backcoats
Known layers can be used for the layer.

The thickness of the magnetic layer of the medium of the present invention is optimized depending on the saturation magnetization of the head to be used, the head gap length, and the band of the recording signal.
0.25 μm, preferably 0.05 to 0.2 μm
It is. The magnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the nonmagnetic layer as the lower layer of the medium according to the present invention is 0.2 to 5 μm, preferably 0.3 to 3 μm, and more preferably 1 to 2.5 μm. The lower layer of the medium of the present invention exerts its effects as long as it is substantially a non-magnetic layer. For example, even if a small amount of a magnetic substance is included as an impurity or intentionally, the effects of the present invention are exhibited. Needless to say, the configuration can be regarded as substantially the same as the present invention. The substantially non-magnetic layer means that the lower layer has a residual magnetic flux density of 10 mT (100 Gauss) or less or a coercive force of 7.9 kA / m (100 Oersteds) or less, and preferably has no residual magnetic flux density and coercive force. Indicates that

[Support] The non-magnetic support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose acetoacetate, polycarbonate, polyamide, and polyimide. , Polyamide imide, polysulfone,
Known films such as polyaramid, aromatic polyamide and polybenzoxazole can be used. Among them, it is preferable to use a high-strength support such as polyethylene naphthalate or polyamide. In addition, if necessary, the surface roughness of the magnetic surface and the base surface can be changed by changing the surface roughness.
It is also possible to use a laminated type support as disclosed in JP-A-7. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

In order to achieve the object of the present invention, the center plane average surface roughness SR measured by a light interference type surface roughness meter (for example, TOPO-3D manufactured by WYKO, USA) as a nonmagnetic support is used.
It is preferable to use a having a of 8.0 nm or less, preferably 4.0 nm or less, and more preferably 2.0 nm or less. It is preferable that these nonmagnetic supports not only have a small center plane average surface roughness but also have no coarse protrusions of 0.5 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and organic fine powders such as acryl. The maximum height SRmax of the support is 1 μm or less, the ten-point average roughness SRz is 0.5 μm or less, and the height of the center plane peak is SRp.
Is 0.5 μm or less, the center plane valley depth SRv is 0.5 μm or less, the center plane area ratio SSr is 10 to 90%, and the average wavelength Sλ is
a is preferably from 5 to 300 μm. In order to obtain desired electromagnetic conversion characteristics and durability, the surface projection distribution of these supports can be arbitrarily controlled by a filler.
Each having a size of 01 μm to 1 μm is 0.1 mm ²
The control can be performed in a range of 0 to 2000 pieces.

F-5 of the non-magnetic support used in the present invention
The value is preferably 49 to 490 MPa (5 to 50 kg / m
m ² ), and the heat shrinkage of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less,
The heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 49-9
80 MPa (5-100 kg / mm ² ), elastic modulus 98
0 to 19600 MPa (100 to 2000 kg / m
m ² ) is preferred. The coefficient of thermal expansion is 10 ^-4 to 10 ^-8 / ° C.
And preferably 10 ^-5 to 10 ^-6 / ° C. The coefficient of humidity expansion is 10 ⁻⁴ / RH% or less, preferably 10 ⁻⁵ / RH.
/ RH% or less. It is preferable that these thermal characteristics, dimensional characteristics, and mechanical strength characteristics are substantially equal to each other in the in-plane direction of the support with a difference within 10%.

[Production Method] The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. Magnetic material, non-magnetic powder, binder, carbon black, abrasive, antistatic agent,
All raw materials such as a lubricant and a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example,
Polyurethane may be added separately 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, a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, and an extruder. When a kneader is used, the magnetic material or non-magnetic powder and all or a part of the binder (however, preferably 30% or more of the total binder) and 100 to 100 parts of the magnetic material are kneaded in a range of 15 to 500 parts. You. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-79.
274. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When applying a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. In the first method, a lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for applying a magnetic paint. In this method, the upper layer is coated by a support-pressing-type extrusion coating apparatus disclosed in JP-A-60-238179 and JP-A-2-265672. The second method is disclosed in JP-A-63-88080 and JP-A-2-179.
No. 71, Japanese Unexamined Patent Publication No. 2-265672 discloses a method in which upper and lower layers are coated almost simultaneously by a single coating head having two built-in coating liquid passage slits. The third method is a method in which the upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Note that, in order to prevent a decrease in electromagnetic conversion characteristics and the like of a magnetic recording medium due to agglomeration of magnetic particles, Japanese Patent Application Laid-Open No. Sho 62-9517 has been proposed.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in Japanese Patent Application Laid-open No. 4 and JP-A-1-236968. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in Japanese Patent Application Laid-Open No. 3-8471. In order to realize the layer constitution of the present invention, the lower layer is coated and dried, and then a magnetic layer is formed thereon, and a sequential multi-layer coating may be used, and the effect of the present invention is not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

In the case of a disk, a sufficient isotropic orientation can be obtained even without orientation, without using an orientation device. It is preferable to use a known random alignment device. In the case of ferromagnetic metal fine powder, isotropic orientation is generally preferred to be in-plane two-dimensional random,
It is also possible to add a vertical component to make it three-dimensional random. In the case of hexagonal ferrite, three-dimensional randomness in the in-plane and vertical directions generally tends to occur. However, in-plane two-dimensional randomness is also possible. In addition, isotropic magnetic characteristics can be imparted in the circumferential direction by using a known method such as a different polarity opposed magnet and performing vertical alignment. In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

The calendering is performed by using epoxy as a roll,
The treatment is performed using a heat-resistant plastic roll such as polyimide, polyamide or polyimide amide or a metal roll. In particular, in the case of forming a double-sided magnetic layer, it is preferable to perform the treatment between metal rolls. The processing temperature is preferably 5
The temperature is 0 ° C or higher, more preferably 100 ° C or higher. The linear pressure is preferably 1960 N / cm (200 kg / cm)
More preferably, 2940 N / cm (300 kg
/ Cm) or more.

[Physical Characteristics] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium of the present invention is 2 when the ferromagnetic metal fine powder is used.
00 to 500 mT (2000 to 5000 Gauss), and 100 to 300 mT (1
000-3000 Gauss). Coercive force Hc and H
r is 118.5 to 395 kA / m (1500 to 5000).
Oersted), preferably 134.3 to 237.
kA / m (1700-3000 Tesla). The distribution of coercive force is preferably narrow, and SFD and SFDr are preferably 0.6 or less. The squareness ratio is 0.55 or more and 0.67 or less in the case of two-dimensional random, preferably 0.58 or more and 0.64 or less. In the case of three-dimensional random, it is preferably 0.45 or more and 0.55 or less. The orientation is 0.6 or more, preferably 0.7 or more in the vertical direction, and 0.7 or more, preferably 0.8 or more when demagnetizing field correction is performed. 2
The orientation ratio is preferably 0.8 or more in both the three-dimensional random and the three-dimensional random. In the case of two-dimensional randomness, the squareness ratio in the vertical direction, Br, Hc and Hr are 0.1 to 0.5 in the in-plane direction.
It is preferable to set it within twice.

The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is -10 ° C. to 40 ° C., and the humidity is 0% to 95%.
In the range, preferably 0.5 or less, more preferably 0.3 or less, the surface resistivity preferably magnetic surface 10 ⁴
-10 ¹² ohms / sq, charged potential from -500V to +50
It is preferably within 0V. The elastic modulus of the magnetic layer at 0.5% elongation is preferably 980 to 19600 MPa in each direction in the plane.
(100-2000 kg / mm ² ), the breaking strength is preferably 98-686 MPa (10-70 kg / mm ² ),
The elastic modulus of the magnetic recording medium is preferably 980 in each in-plane direction.
~ 14700MPa (100 ~ 1500kg / m
m ² ), the residual elongation is preferably 0.5% or less, 100 ° C.
The thermal shrinkage at any of the following temperatures is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. Glass transition temperature of magnetic layer (11
The maximum point of the loss elastic modulus in the dynamic viscoelasticity measurement measured at 0 Hz) is preferably from 50 ° C to 120 ° C, and that of the lower nonmagnetic layer is preferably from 0 ° C to 100 ° C. The loss modulus is 1
× 10 ⁵ to 8 × 10 ⁸ Pa (1 × 10 ⁶ to 8 × 10 ⁹ dyn
e / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
It is as follows. The porosity of the coating layer is preferably 30% by volume or less for both the non-magnetic lower layer and the magnetic layer, and more preferably 2% by volume.
0% 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 disk medium in which repeated use is emphasized, a larger porosity is often preferable in running durability.

The center plane surface roughness Ra of the magnetic layer measured by an optical interference type surface roughness meter (for example, TOPO-3D manufactured by WYKO, USA) is 4 nm or less, preferably 3.8 nm or less, more preferably 3 nm or less. 0.5 nm or less. The maximum height SRmax of the magnetic layer is 0.5 μm or less, and the ten-point average roughness SRz
Is 0.3 μm or less, the height of the center plane peak SRp is 0.3 μm or less, the depth of the center plane valley SRv is 0.3 μm or less, the center plane area ratio SSr is 20 to 80%, and the average wavelength Sλa is 5 to 300 μm.
m is preferred. The surface protrusions of the magnetic layer can be arbitrarily set in a range of 0 to 2000 with a size of 0.01 μm to 1 μm, thereby optimizing the electromagnetic conversion characteristics and the friction coefficient. preferable. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder to be added to the magnetic layer, the roll surface shape of the calendar treatment, and the like. The curl is preferably within ± 3 mm.

When the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easy to change the physical properties of the non-magnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0076]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not construed as being limited to the examples.

<Preparation of Paint> Magnetic Paint ML-1 (using needle-shaped magnetic powder) Ferromagnetic metal fine powder: 100 parts of M-1 Composition: 70% Fe, 30% Co, Hc 201.5 kA / m (2550 Oe), specific surface area 55 m ² / g, σs140A · m ² / kg (140 emu / g) Crystal size 120 °, major axis length 0.048 μm, needle ratio 4 Sintering inhibitor Al compound (Al / Fe atomic ratio 8%) Y compound (Y / Fe atomic ratio 6%) Vinyl chloride copolymer 12 parts MR110 (manufactured by Zeon Corporation) Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 3 parts α-alumina 10 parts HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) Carbon black 5 parts # 50 (manufactured by Asahi Carbon Co., Ltd.) Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate Part 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts of stearic acid

Magnetic paint ML-2 (using needle-like magnetic powder) Ferromagnetic metal fine powder: 100 parts of M-2 Composition: 70% Fe, 30% Co, Hc 186.4 kA / m (2359 Oe), specific surface area 49 m ² / g, s146A · m ² / kg (146 emu / g), crystallite size 170 °, major axis length 0.100 μm, needle ratio 6, SFD 0.51 sintering inhibitor Al compound (Al / Fe atomic ratio 5%) pH 9 .4 Y compound (Y / Fe atomic ratio 5%) 10 parts of vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) 4 parts of polyurethane resin UR5500 (manufactured by Toyobo) α-alumina 10 parts HIT70 (manufactured by Sumitomo Chemical) -Bon Black 1 part # 50 (made by Asahi Carbon Co., Ltd.) Phenylphosphonic acid 3 parts Oleic acid 1 part Stearic acid 0.6 part Ethylene glycoldioleyl 12 parts Methi Ethyl ketone 180 parts Cyclohexanone 180 parts

Magnetic paint ML-3 (using acicular magnetic powder: Comparative example) Ferromagnetic metal powder: M-3 100 parts Composition / Fe: Ni = 96: 4 Hc 126.4 kA / m (1600 Oe), specific surface area 45 m ² / G Crystallite size 220 °, σs135A · m ² / kg (135 emu / g) Average major axis diameter 0.20 μm, needle ratio 9 Vinyl chloride copolymer 12 parts MR110 (manufactured by Zeon Corporation) Polyurethane resin 5 parts UR- 8600 (manufactured by Toyobo) α-alumina (particle size: 0.65 μm) 2 parts Chromium oxide (particle size: 0.35 μm) 15 parts Carbon black (particle size: 0.03 μm) 2 parts Carbon black (particles) 9 parts isohexadecyl stearate 4 parts n-butyl stearate 4 parts butoxyethyl stearate 4 parts oleic acid 1 part stearic acid 1 part Methyl ethyl ketone 300 parts

Magnetic paint ML-4 (using plate-like magnetic powder) Barium ferrite magnetic powder: 100 parts of M-4: Ba molar ratio composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 197.5 kA / m (2500 Oe) , Specific surface area 50 m ² / g, σs 58 Am ² / kg (58 emu / g) plate diameter 35 nm, plate ratio 4 vinyl chloride copolymer 12 parts MR110 (manufactured by Zeon Corporation) polyurethane resin 3 parts UR8200 (Toyobo Co., Ltd.) Α-alumina 10 parts HIT55 (Sumitomo Chemical Co., Ltd.) Carbon black 5 parts # 50 (manufactured by Asahi Carbon Co., Ltd.) Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 Part Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Magnetic coating material ML-5 (using plate-shaped magnetic powder) Barium ferrite magnetic powder: 100 parts of M-5 Mo: Ba molar ratio Composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 197.5 kA / m (2500 Oe) Specific surface area 50 m ² / g, σs 58 Am ² / kg (58 emu / g) Plate diameter 35 nm, Plate ratio 2.5 Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin UR5500 (Toyobo Co., Ltd.) 4 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 10 parts # 50 (manufactured by Asahi Carbon Co., Ltd.) 1 part phenylphosphonic acid 3 parts oleic acid 1 part stearic acid 0.6 part ethylene glycol-dioldioleyl 16 parts methyl ethyl ketone 180 parts Cyclohexanone 180 parts

Non-magnetic paint NU-1 (using spherical inorganic powder) Non-magnetic powder TiO ₂ crystalline rutile 80 parts Average primary particle diameter 0.035 μm, specific surface area by BET method 40 m ² / g pH 7, TiO ₂ content 90% or more, DBP oil absorption 27 to 38 g / 100 g, surface treatment agent Al ₂ O ₃ 8 wt% carbon black 20 parts Conductex SC-U (manufactured by Columbian Carbon Co.) vinyl chloride copolymer 12 parts MR110 ( Nippon Zeon Co., Ltd. Polyurethane resin 5 parts UR8200 (Toyobo Co., Ltd.) Phenylphosphonic acid 4 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixture) Solvent) 250 parts

Non-magnetic paint NU-2 (using spherical inorganic powder) Non-magnetic powder TiO ₂ crystalline rutile 100 parts Average primary particle diameter 0.035 μm, Specific surface area by BET method 40 m ² / g, pH 7, TiO ₂ content 90% or more, DBP oil absorption 27 to 38 g / 100 g, surface treatment agent Al ₂ O ₃ , SiO ₂ Ketjen Black EC (manufactured by AKUZO NOBEL) 13 parts Average primary particle diameter: 30 μm DBP oil absorption: 350 ml / 100 g pH : 9.5 BET specific surface area: 950m ² / g Volatile content: 1.0% Vinyl chloride copolymer 16 parts MR110 (manufactured by Zeon Corporation) Polyurethane resin 6 parts UR8200 (manufactured by Toyobo) 4 parts phenylphosphonic acid Ethylene glyco-lydioleyl 16 parts Oleic acid 1 part Stearic acid 0.8 parts Methyl ethyl ketone / cyclo Hexanone (8/2 mixed solvent) 250 parts

Non-magnetic paint NU-3 (using spherical inorganic powder) Non-magnetic powder TiO ₂ crystalline rutile 75 parts Average primary particle diameter 0.035 μm, specific surface area 40 m ² / g pH 7, TiO ₂ content 90% or more DBP oil absorption 27 to 38 g / 100 g, surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 10 parts Ketjenblack EC α-alumina 15 parts AKP-15 (manufactured by Sumitomo Chemical Co., Ltd.) Average particle diameter: 0 65 μm vinyl chloride copolymer 12 parts MR110 (manufactured by Zeon Corporation) polyurethane resin 5 parts UR8600 (manufactured by Toyobo Co., Ltd.) isohexadecyl stearate 4 parts n-butyl stearate 4 parts butoxyethyl stearate 4 parts oleic acid 1 part Stearic acid 1 part Methyl ethyl ketone 300 parts

Non-magnetic paint NU-4 (using acicular inorganic powder) Non-magnetic powder α-Fe ₂ O ₃ hematite 80 parts Long axis length 0.15 μm, BET specific surface area 50 m ² / g pH 9 Surface treatment agent Al ₂ O ₃ 8% by weight Carbon black 20 parts Conductex SC-U (manufactured by Columbian Carbon Co.) Vinyl chloride copolymer 12 parts MR110 (vinyl chloride copolymer) Polyurethane resin 5 parts UR8200 (manufactured by Toyobo Co., Ltd.) Phenylphosphonic acid 4 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

Non-magnetic paint NU-5 (using acicular inorganic powder) Non-magnetic powder α-Fe ₂ O ₃ hematite 100 parts Major axis length 0.15 μm, specific surface area by BET method 50 m ² / g, pH 9, surface Treatment agent Al ₂ O ₃ 8% by weight Carbon black 18 parts # 3250B (manufactured by Mitsubishi Kasei Co., Ltd.) Vinyl chloride copolymer 15 parts MR104 (manufactured by Zeon Corporation) Polyurethane resin 7 parts UR5500 (manufactured by Toyobo Co., Ltd.) Phenylphosphonic acid 4 parts Ethylene glycoldioleyl 16 parts Oleic acid 1.3 parts Stearic acid 0.8 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

Production Method 1 (Disk: W / W) For each of the above ten paints, each component was kneaded with a kneader and then dispersed using a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating solution for the non-magnetic layer, 10 parts to the coating solution for the magnetic layer, and 40 parts of cyclohexanone was added to each. And filtered to prepare coating solutions for forming a nonmagnetic layer and a magnetic layer, respectively.

The obtained non-magnetic layer coating solution was applied to a thickness of 62 μm so that the thickness after drying became 1.5 μm and immediately thereafter the thickness of the magnetic layer became 0.15 μm.
At the same time, a multi-layer coating is performed simultaneously on a polyethylene terephthalate support having a center plane average surface roughness of 3 nm.
T (250 gauss) and frequency 50 Hz, 12 mT (1
After passing through two AC magnetic field generators (20 gauss) for random orientation treatment and drying, the temperature is 90 ° C. and the linear pressure is 2940 N / cm (300 kg /
cm), punched into a 3.7-inch surface, polished, and then placed in a 3.7-inch cartridge (Zip-disk cartridge manufactured by Iomega, USA) with a liner installed inside. Add parts 3.7
An inch floppy disk was obtained. For some of the samples, 400 mT (400 mT) was applied before the randomizing alignment treatment.
(0 gauss) for the longitudinal orientation by the same pole opposing Co magnet.

In this case, it is preferable to increase the frequency and the magnetic field strength of the AC magnetic field generator so that sufficient randomization is finally performed, whereby an orientation ratio of 98% or more can be obtained. When a barium ferrite magnetic material is used, vertical alignment can be performed in addition to the above-described alignment method. Also, if necessary, after punching into a disk shape, heat treatment at high temperature (normally 50 ° C to 90 ° C)
May be performed to accelerate the curing treatment of the coating layer, to perform a burnishing treatment with a polishing tape, and to perform a post-treatment such as shaving projections on the surface.

Production Method 2 (Disk: W / D) For each of the above 10 paints, each component was kneaded with a kneader and dispersed using a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating solution for the non-magnetic layer, 10 parts to the coating solution for the magnetic layer, and 40 parts of cyclohexanone was added to each. And filtered to prepare coating solutions for forming a nonmagnetic layer and a magnetic layer, respectively.

The obtained coating solution for the nonmagnetic layer was coated on a polyethylene terephthalate support having a thickness of 62 μm and an average surface roughness of 3 nm so that the thickness after drying would be 1.5 μm. Once dried and calendered, a magnetic layer is further applied thereon by a blade method so that the thickness of the magnetic layer becomes 0.15 μm, frequency 50 Hz, magnetic field strength 25 mT (250 gauss) and frequency 50 Hz
Two magnetic field strengths of 12 mT (120 gauss) were passed through an AC magnetic field generator to perform random orientation processing. In addition, a method in which calendering of the non-magnetic layer is not performed may be adopted.

Production Method 3 (Disk: Spin Coating) For each of the above 10 paints, each component was kneaded with a kneader, and then dispersed using a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating solution for the non-magnetic layer, 10 parts to the coating solution for the magnetic layer, and 40 parts of cyclohexanone was added to each. And filtered to prepare coating solutions for forming a nonmagnetic layer and a magnetic layer, respectively.

The obtained coating solution of the non-magnetic layer was spin-coated on a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 3 nm so that the thickness after drying became 1.5 μm. After coating and drying once, a magnetic layer is further applied thereon by spin coating so that the magnetic layer has a thickness of 0.15 μm, and is oriented in the circumferential direction by a 600 mT (6000 gauss) homopolar opposing Co magnet. Processing was performed. This was subjected to a batch-type rolling treatment capable of obtaining the same pressure as in Production Method 1 to smooth the surface. The subsequent steps were performed in the same manner as in Production Method 1. Alternatively, a method of spin-coating the non-magnetic layer and spin-coating the magnetic layer on the non-magnetic layer while the non-magnetic layer is not dried may be used. By using the spin coating method, not only the amount of residual magnetization in the recording direction is increased, but also the perpendicular magnetization component of barium ferrite or a metal magnetic material having a short needle ratio can be reduced, and the symmetry of the reproduced waveform can be improved. .

(Supports Used in Examples and Comparative Examples) Support B-1: Polyethylene terephthalate Thickness: 62 μm, F-5 value: MD 114 MPa, TD 107 MPa Breaking strength: MD 276 MPa, TD 281 MPa Breaking Elongation: MD 174 MPa, TD 139 MPa Heat shrinkage (80 ° C., 30 minutes): MD 0.07%, TD 0.05% Heat shrinkage (100 ° C., 30 minutes): MD 0.2%, TD 0. 3% Thermal expansion coefficient: major axis 15 × 10 ⁻⁵ / ° C., minor axis 18 × 10 ⁻⁵ / ° C. Center plane average surface roughness 3 nm precipitates 38,000 particles / mm ² support B-2: polyethylene naphthalate Thickness: 55 μm, 40,400 precipitates / mm ² Other physical properties are the same as those of the support B-1.

Support B-3: Polyethylene terephthalate Thickness: 62 μm, 7,200 precipitates / mm ² Other physical properties are the same as those of Support B-1. Support B-4: Polyethylene terephthalate (Comparative Example) Thickness: 62 μm Deposits 43,200 / mm ² Other physical properties are the same as those of Support B-1. Support B-5: Polyethylene terephthalate (Comparative Example) Thickness: 62 μm Deposits 52,000 particles / mm ² Other physical properties are the same as those of Support B-1. Support B-6: Polyethylene terephthalate Thickness: 55 μm, Heat shrinkage (80 ° C., 30 minutes): MD 0.02%, TD 0.03% Heat shrinkage (100 ° C., 30 minutes): MD 0.08%, TD 0.05% Thermal expansion coefficient: major axis 10 × 10 ^-5 / ° C, minor axis 11 × 10 ^-5 / ° C center plane average surface roughness 5 nm precipitates 14,400 / mm ^{2 etc.} Has the same physical properties as Support B-1.

(Orientation Method) The following orientation method was appropriately used. O-1: Randomize orientation is performed. O-2: After orientation in the longitudinal direction with a Co magnet, random orientation is performed. O-3: Perform vertical orientation with a Co magnet. O-4: Circumferential orientation is performed with a Co magnet.

Examples 1 to 22 and Comparative Examples 1 to 2 obtained by appropriately combining the above methods as shown in Tables 1 and 2.
4. The samples of Reference Example 1 were measured for magnetic properties, center plane average roughness, surface recording density, and the like. Examples 20 to
22, in Reference Example 1, the disk of Example 19 was used to evaluate the error rate and the like while changing the linear recording density and the track density as shown in Table 2. These results are shown in Tables 1 and 2. (1) Magnetic properties (Hc): Measured using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) at Hm 790 kA / m (10 kOe). (2) Center surface average surface roughness (Ra): TO manufactured by WYKO
Using PO-3D, Ra, Rrms, and Peak-Valley values of an area of about 250 μm × 250 nm were measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by light interference. (3) The areal recording density is obtained by multiplying the linear recording density by the track density. (4) The linear recording density is the number of bits of a signal recorded per inch in the recording direction. (5) Track density is the number of tracks per inch. (6) φm is the amount of magnetization per unit area of the magnetic recording medium. Bm (Gauss) multiplied by the thickness, using a vibrating sample magnetometer (Toei Kogyo Co., Ltd.)
It is a value measured at Hm 790 kA / m (10 kOe) and can be directly measured. (7) The error rate of the disk was measured by recording the signal of the above-mentioned linear recording density on the disk by the (2, 7) RLL modulation method.

(8) Thickness of the magnetic layer The magnetic recording medium is cut along the longitudinal direction to a thickness of about 0.1 μm with a diamond cutter, and the magnification is 10,000 to 100,000 times, preferably, with a transmission electron microscope. 20,000 times to 50,
Observation was performed at a magnification of 000, and the photograph was taken. The print size of the photograph is A4 to A5. Thereafter, the interface was visually judged by paying attention to the shape difference between the ferromagnetic powder and the nonmagnetic powder of the magnetic layer and the lower nonmagnetic layer, and the surface of the magnetic layer was similarly blackened. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. When the length of the sample photograph was 21 cm, the measurement was performed 85 to 300 times. The arithmetic average of the measured values at that time was defined as d. (9) The number of precipitates was determined by differentiating the nonmagnetic support at a magnification of 1000 after the nonmagnetic support was heated to 150 ° C. and left in a dry oven for 1 hour, and the temperature of the nonmagnetic support removed from the oven was lowered to room temperature. A photograph of the surface of the nonmagnetic support was taken with an interference microscope, and the number of precipitates on the photograph (actual area: 6840 μm ² ) was counted and converted to per mm ² . (10) The storage stability was evaluated by the presence or absence of deposits on the surface of the coating layer after storage for 3 months in a room temperature environment.

[0099]

[Table 1]

[0100]

[Table 2]

From the results in the above table, it can be seen that the magnetic recording medium of the present invention has a particularly good error rate in the high-density recording area of 10 ^-5 or less, and also has a good error rate after storage. Understand. On the other hand, in Comparative Examples 1 and 2 in which the number of precipitates deposited on the surface exceeds 43,000 as the nonmagnetic support (Supports B-4 and B-5), the error rate after storage is low. It became worse and a precipitate was observed. In Comparative Example 3 in which the thickness of the magnetic layer exceeds 0.25 μm, the error rate is inferior. The coercive force of the magnetic layer is 14
In the case of Comparative Example 4 of less than 2.2 kA / m (1800 Oe), the error rate is remarkably inferior. Reference Example 1
Is an example in which the areal recording density is reduced.

[0102]

The magnetic recording medium of the present invention has significantly improved electromagnetic conversion characteristics, especially high-density recording characteristics, has excellent durability, and has significantly improved error rate in a high-density recording region. ing. The magnetic recording medium of the present invention has a recording capacity of 0.031 to 0.31 Gbit / c.
m ² , preferably 0.054 to 0.31 Gbit / cm ²
Large-capacity disk-shaped magnetic recording medium.

Continued on the front page (72) Inventor Jin Noguchi 2-12-1, Ogimachi, Odawara City, Kanagawa Prefecture Inside Photo Film Co., Ltd. (72) Inventor Junichi Nakamikawa 2-12-1, Ogimachi, Odawara City, Kanagawa Prefecture Fuji Photo F-term in Film Co., Ltd. (reference) 5D006 BA01 BA06 BA07 BA10 BA19 CA04 DA02 FA09

Claims (9)

[Claims] 1. A magnetic material comprising a substantially non-magnetic lower layer and a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder dispersed in a binder on a non-magnetic support in this order. In the recording medium, (I) 0.031 to 0.31
Having a surface recording density for recording a signal of Gbit / cm ² ,
(II) the dry thickness of the magnetic layer is 0.05 to 0.25 μm, (III) Φm is 10.1 to 1.3 μTcm,
(IV) the coercive force of the magnetic layer is 142.2 kA / m or more, and (V) the number of precipitates deposited on the surface of the non-magnetic support after storing the non-magnetic support at 150 ° C. for 1 hour under dry conditions. A magnetic recording medium, wherein the number is 43,000 pieces / mm ² or less. 2. 0.054 to 0.31 Gbit / cm ²
2. An inorganic powder having a surface recording density for recording a signal having a Mohs hardness of 4 or more in a lower layer.
3. The magnetic recording medium according to 1. 3. The dry thickness of the magnetic layer is 0.05 to 0.20.
μm, and the average particle size in the magnetic layer is 0.4 μm.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium contains an abrasive of m or less. 4. The magnetic recording according to claim 1, wherein the surface roughness of the magnetic layer is 4 nm or less as a center plane average roughness measured by a light interference type surface roughness meter. Medium. 5. The magnetic recording medium according to claim 1, wherein the coercive force of the magnetic layer is 158 kA / m or more. 6. A ferromagnetic metal fine powder mainly composed of Fe, having a major axis length of 0.12 μm or less and a crystallite size of 80 to 180.
The magnetic recording medium according to any one of claims 1 to 5, wherein? 7. The nonmagnetic support according to claim 1, wherein the surface roughness of the nonmagnetic support is 8 nm or less as a center plane average surface roughness measured by a light interference type surface roughness meter. Magnetic recording medium. 8. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a disk. 9. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a computer tape.