JPH11353635A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having significantly improved electromagnetic conversion characteristics, especially high-density recording characteristics, excellent durability, and especially having a significantly improved error rate, output and durability in a high-density recording area. SOLUTION: This magnetic record medium is produced by successively forming a base layer which is substantially nonmagnetic on a supporting body, and a magnetic layer where ferromagnetic powder consisting of ferromagnetic metal powder or ferromagnetic hexagonal ferrite powder is dispersed in a binder. In this case, signals with 0.17 to 2 Gbit/inch<2> recording density are recorded. The magnetic layer has 0.05 to 0.30 μm dry film thickness, 10.0×10<-3> to 1.0×10<-3> emu/cm<2> ϕm and >=1800 Oe coercive force. The surface layer of the supporting body contains 5×10<6> to 3×10<7> particles/mm<2> of filler having 0.05 to 0.3 μm average particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium having a high recording density. In particular, the present invention relates to a magnetic recording medium for high-density recording, which has a magnetic layer and a substantially nonmagnetic lower layer, and includes a ferromagnetic metal powder or a hexagonal ferrite powder in an upper layer.

[0002]

2. Description of the Related Art In the field of magnetic disks, 2 MB MF-2HD floppy disks using Co-modified iron oxide have been standardly mounted on personal computers. 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.

In the field of magnetic tapes, in recent years, with the spread of office computers such as minicomputers, personal computers, and workstations, magnetic tapes for recording computer data as external storage media (so-called backup tapes).
Research is being actively conducted. In practical use of magnetic tapes for such applications, especially with the downsizing of computers and the increase in information processing capacity, the increase in recording capacity,
In order to achieve miniaturization, improvement in recording capacity is strongly required.

[0004] Conventionally, magnetic recording media have widely been prepared by coating a support with a magnetic layer in which iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder are dispersed in a binder. Used. Among them, ferromagnetic metal powders and hexagonal ferrite powders are known to be excellent in high density recording characteristics. In the case of a disk, a large-capacity disk using a ferromagnetic metal powder excellent in high-density recording characteristics is 4 MB as a large-capacity disk using 10 MB MF-2TD, 21 MB MF-2SD or hexagonal ferrite.
There are MF-2ED of MB, 21MB floptical, etc., but it was not sufficient in capacity and performance. 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. It has been proposed to use a metal powder having a Hc of 1000 Oe (Oe) or more and a specific surface area of 25 to 70 m ² / g. Proposed.

In order to improve the durability of the disk-shaped magnetic recording medium, Japanese Patent Publication No. 7-85304 proposes to use a fatty acid ester having an ether bond with an unsaturated fatty acid ester, and Japanese Patent Publication No. 7-70045 discloses a branch. It has been proposed to use a fatty acid ester having a fatty acid ester and an ether bond, and JP-A-54-124716 proposes to include a non-magnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester. Has a volume and surface roughness of 0.005 to 0.025
μm is proposed in Japanese Patent Application Laid-Open No. 61-294637.
It is proposed to use a low melting point and a high melting point fatty acid ester in JP-B-7-36216.
It has been proposed to use an abrasive having a particle size of ４ to ／ and a fatty acid ester having a low melting point, and JP-A-3-203018 proposes to use a ferromagnetic metal powder containing Al and chromium oxide.

As a configuration of a disk-shaped magnetic recording medium having a nonmagnetic lower layer and an intermediate layer, JP-A-3-120613 proposes a configuration having a conductive layer and a magnetic layer containing metal powder, and JP-A-6-290446. Has proposed a structure having a magnetic layer and a non-magnetic layer of 1 μm or less.
337 proposes a configuration including a carbon intermediate layer and a magnetic layer containing a lubricant, and JP-A-5-290358 proposes a configuration having a nonmagnetic 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.
Has an Hc of 1400 Oe or more and a thickness of 0.5 μm
A configuration having the following magnetic layer and a non-magnetic layer containing conductive particles has been proposed. Japanese Patent Application Laid-Open No. 5-197946 has proposed a configuration containing an abrasive larger than the magnetic layer thickness.
Japanese Patent Application Laid-Open No. Hei 6-68453 discloses a configuration in which the thickness of the magnetic layer is 0.5 μm or less, the thickness variation of the magnetic layer is within ± 15%, and the surface electric resistance is specified. There has been proposed a configuration in which an abrasive is included and the amount of abrasive on the surface is regulated.

[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 to practical use, especially in connection with the miniaturization 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 miniaturization. In addition, the use environment of magnetic tapes is widespread, so it can be used under a wide range of environmental conditions (especially in the circumstance where temperature and humidity fluctuates rapidly). 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. And in any system, the magnetic tape used has a film thickness of 2.
A magnetic layer containing a ferromagnetic powder, a binder and an abrasive having a relatively thick single layer structure of 0 to 3.0 μm is provided. In order to maintain the condition, a back coat layer is provided. 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 decrease in reproduction output due to the thickness loss of the magnetic layer. Comprising a lower nonmagnetic layer dispersed in a binder and an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing ferromagnetic powder in the binder while the nonmagnetic layer is in a wet state. A recording medium is 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. In other words, there is a problem that the output decreases, the error rate increases, and the durability also decreases, particularly with the increase in capacity and density. It is becoming a difficult situation.

[0013]

SUMMARY OF THE INVENTION According to the present invention, electromagnetic conversion characteristics, especially high-density recording characteristics, are remarkably improved and have excellent durability. It is an object of the present invention to provide an improved magnetic recording medium. Especially the recording capacity is 0.17
２2 Gbit / inch ² , particularly preferably 0.35 to ² Gbit / inch ²
It is intended to provide a disk-shaped magnetic recording medium having a large capacity of ² inches.

[0014]

Means for Solving the Problems The inventors of the present invention aimed at obtaining a magnetic recording medium which has good electromagnetic conversion characteristics and durability, and in particular, an error rate, output and durability in a high-density recording area which are significantly improved. As a result of intensive studies, it has been found that by using the following medium, excellent high-density recording characteristics and excellent durability, which are the objects of the present invention, can be obtained, and the present invention has been accomplished.

That is, according to the present invention, a substantially nonmagnetic lower layer and a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder dispersed in a binder are dispersed on a support. In the magnetic recording medium provided in order, the magnetic recording medium has an areal recording density of 0.17 to ² Gbit / inch ^2.
Wherein the dry thickness of the magnetic layer is 0.05 to 0.30 μm and φm is 1
0.0 × 10 ^{−3 to} 1.0 × 10 ⁻³ emu / cm ² , the coercive force of the magnetic layer is 1800 Oe or more, and the surface layer of the support has an average particle diameter of 0.05 to 0.3μ
By providing a magnetic recording medium characterized by having 5 to 30 million fillers / mm ^{2 of} m, excellent high-density characteristics and excellent durability that could not be obtained by conventional techniques It has been found that a magnetic recording medium having a significantly improved error rate, output, and durability in a high-density recording area can be obtained.

Here, the substantially non-magnetic lower layer means that it may have a magnetic property to such an extent that it does not participate in recording, and is hereinafter simply referred to as the lower layer or the non-magnetic layer. The magnetic layer is also referred to as an upper layer or an upper magnetic layer. Also,
The areal recording density is obtained by multiplying the linear recording density by the track density.

Φm is defined by using a vibration sample type magnetometer (VSM: manufactured by Toei Kogyo Co., Ltd.) from the magnetic layer per unit area on one side,
Hm is the magnetic moment amount (emu / cm ² ) directly measurable with 10 kilooersted (kOe), and the magnetic flux density Bm (unit G = 4πemu / c) determined by VSM
m ³ ) times thickness (cm). Therefore φ
The unit of m is represented by emu / cm ² or G · cm.

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, in the present invention, in order to improve the areal recording density, the magnetic layer thickness, the magnetic layer Hc, and the center plane average surface roughness were improved in terms of linear recording density, and φm was optimized in terms of track density. Things.

In the present invention, a filler having a specific average particle size is present at a specific density in the surface layer of the support.
The average particle size and density of the filler present on the surface layer of the support were measured as follows. The support surface layer is subjected to oxygen plasma treatment for 40 to 50 minutes to expose the filler on the support surface layer. The surface of the support subjected to the plasma treatment is photographed with an electron microscope at a magnification of 30,000 times, and the size and the number of the filler are measured. The number of fillers is arbitrary 2
The filler in the electron micrograph of the field of view is Kon
The average particle diameter and the number are determined using an image analyzer KS400 manufactured by torn. The average particle size of the filler is the average value of the particle sizes of all the fillers that can be seen in an electron micrograph. The number of fillers is converted into the number per 1 mm ² of the surface layer of the support, and the value rounded off to the nearest ten thousand is defined as the density of the filler present in the surface layer of the support.

Preferred embodiments of the present invention are as follows. (1) The magnetic recording medium has a surface recording density of 0.35 to 0.35.
A magnetic recording medium for recording ² Gbit / inch ² signals,
And a lower layer containing an inorganic powder having a Mohs hardness of 4 or more. (2) The dry thickness of the magnetic layer is 0.05 to 0.20 μm
And a polishing agent having an average particle diameter of 0.4 μm or less in the magnetic layer. (3) The magnetic recording medium according to (1), wherein the surface roughness of the magnetic layer is 4.0 nm or less as a center plane average surface roughness according to a 3D-MIRAU method. (4) A magnetic recording medium, wherein the coercive force of the magnetic layer is 2000 Oe or more. (5) The filler present on the surface of the support has an average particle diameter of 0.05 to 0.25 μm and a number of 8,000,000 to 30.
A magnetic recording medium characterized in that the number is 100,000 pieces / mm ² . (6) The magnetic recording medium, wherein the magnetic recording medium is a disk. (7) The magnetic recording medium, wherein the magnetic recording medium is a computer tape.

According to the present invention, with the above configuration, the areal recording density of 0.17, which cannot be obtained by the conventional technique, is obtained.
２2 Gbit / inch ^{2 and} surface recording density of 0.35 to ² Gbi
A magnetic recording medium that is t / inch ² and has both excellent high-density characteristics and excellent durability, and in particular, an error rate in a high-density region, and a magnetic recording medium with significantly improved output and durability, particularly It has been found that a disk-shaped magnetic recording medium can be obtained.

That is, it has been known that it is preferable to use a smoother support than before, but there was a problem in achieving compatibility with the transportability of the magnetic recording medium. However, in the present invention, the surface layer of the support was used. Has an average particle size of 0.05-0.3μ
m, preferably 0.05 to 0.02 μm
Million to 30 million pieces / mm ² , preferably 1000
It has been found that the presence of up to 30 million pieces / mm ² can provide a smooth support, achieve compatibility with transportability, and particularly remarkably improve output and durability in a high-density region. It is.

In the present invention, the surface layer of the support refers to a region near the surface including the surface on which the lower layer is provided and the surface on the opposite side, usually a depth of 0.04 to 0.1 μm from the surface.
Say about the area. The density of the filler present in the surface layer is measured by the above-described method. However, the mode of the presence of the filler in the surface layer is not particularly limited as long as it is basically an element constituting the surface layer. It is not necessary to do so, and part of the filler may constitute the surface of the support. For example, a part of the filler may be exposed on the surface of the support without being coated with another component of the support, for example, a resin.

In the present invention, the density of the filler is controlled within the above range, but the means for producing such a support is not particularly limited as long as the above conditions are satisfied. Instead, any means can be employed. As a specific means, for example, after adding a filler to a dissolved polymer and / or monomer, a method of forming into a belt shape by a known method, a filler containing a polymer and / or a monomer is included, and the paint is mixed. A method of applying to an arbitrary substrate (including a rigid body such as aluminum and glass in addition to a resin or the like) may be used.

The filler material may be inorganic particles or organic particles. As inorganic particles, Ca, Si, Ti
And organic particles such as acrylic resin and silicone resin. Examples of the polymer serving as a main component other than the filler of the support used in the present invention include polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, and the like. Known films such as polyamide, polyimide, polyamideimide, polysulfone, polyaramid, aromatic polyamide, and polybenzoxazole can be used. It is preferable to use high strength materials such as polyethylene naphthalate and polyamide. If necessary, a laminated type as shown in JP-A-3-224127 can be used.

The support to be used in the present invention may be preliminarily subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment,
Dust removal processing may be performed.

The support used in the present invention has a center surface average surface roughness Ra measured by the Mirau method of a surface roughness meter TOPO-3D manufactured by WYKO, usually 7 nm or less, preferably 1 to 6 nm. More preferably, it can be adjusted to 2 to 5 nm. It is preferable that these supports not only have a small center plane average surface roughness but also have no coarse protrusions of 0.5 μm or more. The maximum height SRmax of the support is 1
μm or less, ten-point average roughness SRz is 0.5 μm or less, center plane peak height SRp is 0.5 μm or less, center plane valley depth SRv is 0.5 μm or less, center plane area ratio SSr is 10% or more, 9 μm or less.
0% or less, and the average wavelength Sλa is preferably 5 μm or more and 300 μm or less.

In the present invention, the surface projection distribution of the support can be arbitrarily controlled by a filler in order to obtain desired electromagnetic characteristics and durability. As the filler, only a filler having the above-mentioned size may be used, but a filler having an average particle diameter other than the above may also be used in combination. As fillers that can be used in combination, those having a particle size of less than 0.01 to 0.05 μm may preferably be included at the same level or less as in the present invention. Those having a size of more than 0.3 μm and 1 μm or less can be present on the support surface in an amount of 0 to 500,000 per 1 mm ² of the support surface. In the present invention, the number of fillers that form such surface protrusions (provided that the average particle diameter of the present invention is in the range) is as follows:
It shall be included in the number of the filler density of the surface layer.

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² ,
The heat shrinkage rate per minute is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. The breaking strength is 5-100 kg / mm ² , and the elastic modulus is 100-2000.
Kg / mm ² is preferred. The coefficient of thermal expansion is usually 10 ^-4 to 1
0 ⁻⁸ / ° C., preferably 10 ⁻⁵ to 10 ⁻⁶ / ° C. The coefficient of humidity expansion is usually 10 ⁻⁴ / RH% or less, preferably 10 ⁻⁵ / RH% or less. These thermal characteristics, dimensional characteristics and mechanical strength characteristics are 10% in each direction in the plane of the support.
It is preferable that the differences are approximately equal to each other.

According to the present invention, the excellent areal recording density is 0.1
7 to ² Gbit / inch ² , and a surface recording density of 0.35 to 2
With Gbit / inch ^2, a coating type magnetic recording medium has been obtained which has both high density characteristics and excellent durability, especially disk-shaped magnetic recording media, which have never been achieved with products known in the world. This is the result of combining the following points organically and integrating them.

The points of the present invention are high Hc, super smoothness,
Improved durability by improving composite lubricants, highly durable binders and ferromagnetic powders, ultra-thin magnetic layers and reduced fluctuations at the interface with the lower layer, high filling of powders (ferromagnetic powders and non-magnetic powders) ,
Ultra fine particles of powder (ferromagnetic powder, non-magnetic powder), stabilization of head touch, dimensional stability and servo, improvement of thermal shrinkage of magnetic layer and support, action of lubricant at high and low temperature, etc. These were combined, and as a result of the synthesis, the present invention was achieved.

In the field of personal computers, which are becoming increasingly multi-media, attention has been paid to large-capacity recording media in place of conventional floppy disks, and they 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 MO
(3.5 inches), and one newspaper article can fit in July or August. The transfer rate indicating data (information) write / read time is 2 MB or more per second, which is comparable to that of a hard disk.
20 times faster than MO and more than twice as fast as 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 price than MOs and hard disks.

The present inventors have conducted intensive studies based on the knowledge of such a medium, and as a result, have found that the ZIP disk and the MO
(3.5 inches), the areal recording density which is much larger than the recording capacity is 0.17 to ² Gbit / inch ^{2 and} preferably 0.2 to ² Gb.
it / inch ^{2 and} surface recording density of 0.35 to ² Gbit / inch
⁽²⁾ A magnetic recording medium that has both high density characteristics and excellent durability that have never been achieved with products known to the world, and especially improved error rate especially in high density recording area, 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 ultrafine ferromagnetic powder having high output and high dispersibility, and a lower layer containing spherical or acicular inorganic powder. By reducing the thickness, it is possible to reduce the magnetic force cancellation in the magnetic layer, greatly increase the output in the high frequency range, and further improve the overwriting characteristics. 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 0.05 to 0.30 μm, preferably 0.05 to 0.3 μm, so as to match the magnetic recording system for high density recording and the performance required from the magnetic head.
It is selected for a thin layer of 25 μm. Such an ultrathin magnetic layer, which is uniform and thin, achieves high packing by highly dispersing the ferromagnetic powder and nonmagnetic powder of fine particles by using a dispersant and a combination of a binder having high dispersibility. Was. The ferromagnetic powder used is a ferromagnetic powder excellent in high output, high dispersibility, and high randomization in order to maximize the suitability of a large-capacity FD or computer tape. That is, by using a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder that can achieve high output with very fine particles, particularly, the average major axis length is 0.1 μm or less, and the crystallite size is 80 ° or more.
By being 180 °, it further contains Co, and Al or Y is added to impart functions such as prevention of sintering and improvement of durability.
, High output and high durability can be achieved.
3 suitable for ultra-thin magnetic layer to achieve high transfer rate
Using a three-dimensional network binder system, the running stability and durability during high-speed rotation are secured. 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 the upper and lower layers. An appropriate amount of lubricant can always be supplied to the layer, the durability of the upper magnetic layer is increased, and the reliability is improved. Further, 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. Specifically, the rotation speed is preferably 1800 rpm or more, and
00 rpm or more is more preferable. Increased capacity of magnetic recording /
As the recording density increases, 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, it is preferable to use a support having improved isotropic dimensional stability as a support, and further stabilization of traceability can be achieved. By using an ultra-smooth support, the smoothness of the magnetic layer can be further improved.

To increase the density of magnetic recording in the form of a disk,
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, particularly the isotropy, is considered. Servo recording is an indispensable technique in recording and reproduction at a high track density, but this improvement can be achieved from the medium side by making the support 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 forming a thin magnetic layer structure (2) Improvement of durability by stable supply of lubricant (3) High output by smoothing upper magnetic layer (4) Separation of functions of magnetic layer Easy provision of required functions These functions cannot be achieved simply by stacking the magnetic layers. In order to configure a multilayer structure, a “sequential multilayer system” in which 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 slitting process, a punching process, a shell assembling process, and a certifying process.

By forming the magnetic layer into a thin layer structure, the following electromagnetic conversion characteristics can be greatly improved. (1) Improvement of output in high frequency region by improvement of recording demagnetization characteristic (2) Improvement of overwrite (overwrite) characteristic (3) Ensuring window margin Durability is an important factor for magnetic disks. Particularly, in order to achieve a high transfer rate, it is necessary to increase the number of rotations of the magnetic disk by one digit or more compared to the conventional FD system, and the medium durability when the medium in the magnetic head / cartridge and the medium slide at high speed. Is an important issue.
As means for improving the durability of the medium, there are 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 media of the present invention improves upon the 3D network binder system proven in current FD systems for binder formulations.

In the present invention, a lubricant is used in combination with a plurality of lubricants each exhibiting excellent effects under various temperature and humidity environments to be used.
Each lubricant exerts its function even under the environment (room temperature, high temperature) and humidity (low humidity, high humidity), and can maintain a comprehensively stable lubricating effect. Utilizing the structure of the upper and lower two layers,
By making the lower layer have a tank effect of a lubricant, an appropriate amount of lubricant is always supplied to the upper magnetic layer, and the durability of the upper magnetic layer can be improved. 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 surface electric resistance in addition to the function of holding the lubricant. Generally, for controlling 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 ferromagnetic powder 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 multi-media society, the need for image recording is increasing 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.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [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 on the lower layer after the lower layer is applied, either while the lower layer is wet (W / W) or after the lower layer is dried (W / D). From the viewpoint of production yield, simultaneous or 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) with 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 needs to be 1800 Oe or more, and it is preferable that the ferromagnetic metal powder has a Bm of 2000 to 5000 G and the barium ferrite powder has a Bm of 1000 to 3000 G.

[Ferromagnetic Metal Powder] The ferromagnetic metal powder used in the upper magnetic layer of the present invention is preferably a ferromagnetic alloy powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca,
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, and B. In particular, Al, Si, Ca, Y, Ba, La, N
Preferably, at least one of d, 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 to 40 at.%, More preferably from 15 to 35 at.%, More preferably from 20 to 35 at.% Based on Fe. The content of Y is preferably from 1.5 to 12 at%, more preferably from 3 to 10 at%, and still more preferably from 4 to 9 at%. Al is 1.5 atomic%
It is preferably at least 12 at% and more preferably at least 3 at% and at most 10 at%, more preferably at least 4 at% and at most 9 at%. These ferromagnetic metal powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion before the dispersion. Specifically, JP-B-44-14090, JP-B-45-18
No. 372, JP-B-47-22062, JP-B-47-2
No. 2513, JP-B-46-28466, JP-B-46-46-
No. 38755, No. 47-4286, No. 47-
No. 12422, JP-B-47-17284, JP-B-47
-18509, JP-B-47-18573, JP-B-3
Nos. 9-10307, JP-B-46-39639, U.S. Pat. Nos. 3,026,215, 3,303,341 and 310.
No. 0194, No. 3242005, and No. 3389014.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. A ferromagnetic metal 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, reducing iron oxide with a reducing gas such as hydrogen to reduce Fe or F
a method of obtaining e-Co particles or the like, a method of thermally decomposing a metal carbonyl compound, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal; A method of evaporating in a low-pressure inert gas to obtain a powder. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then sending an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

The ferromagnetic metal powder of the magnetic layer of the present invention was
When expressed in terms of specific surface area by the method, it is 45 to 80 m ² / g,
Preferably it is 50-70 m < ² > / g. If it is less than 45 m ² / g, noise increases, and if it is more than 80 m ² / g, it tends to be difficult to obtain surface properties, which is not preferable. The crystallite size of the ferromagnetic powder of the magnetic layer of the present invention is preferably 80 to
180 °, more preferably 100 to 180 °, particularly preferably 110 to 175 °. The average major axis length of the ferromagnetic metal powder is usually 0.01 μm or more and 0.25 μm or less, preferably 0.03 μm or more and 0.15 μm or less, and more preferably 0.03 μm or more and 0.12 μm or less. The needle ratio of the ferromagnetic metal powder is preferably 3 or more and 15 or less, and more preferably 5 or more and 12 or less. The saturation magnetization (σ _S ) of the ferromagnetic metal powder is usually 100 to 180 em
u / g, preferably 110 emu / g to 170 emu / g,
More preferably, it is 125 to 160 emu / g. The coercive force of the ferromagnetic metal powder is preferably 1700 Oe or more and 3500 Oe or less, more preferably 1,800 Oe.
It is not less than Oersted and not more than 3000 Oersted.

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 metal powder depending on the type of the binder. It is preferable that the pH of the ferromagnetic metal powder be optimized depending on the combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10. Ferromagnetic metal powder can be
Surface treatment may be performed with l, Si, P, or an oxide thereof. The amount is 0.1 to 10% by weight based on the ferromagnetic metal powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. Soluble Na, Ca, Fe, N
It may contain inorganic ions such as i and Sr. It is preferable that these inorganic ions are essentially absent, but 200 ppm
If it is below, there is little influence on the characteristics. The ferromagnetic metal powder used in the present invention preferably has a small number of vacancies, and its value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of a needle shape, a rice grain shape, and a spindle shape. The SFD of the ferromagnetic metal powder itself is preferably small, and is preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic metal 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, there are methods for improving the particle size distribution of goethite and preventing sintering in ferromagnetic metal powder.

[Ferromagnetic Hexagonal Ferrite Powder] The ferromagnetic hexagonal ferrite contained in the magnetic layer of the present invention includes a substituted body of barium ferrite, strontium ferrite, lead ferrite, and calcium ferrite, and a Co substituted body. Specifically, magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel,
Furthermore, magnetoplumbite-type barium ferrite and strontium ferrite containing a part of spinel phase are mentioned.
Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd,
Ag, Sn, Sb, Te, Ba, Ta, W, Re, A
u, Hg, Pb, Bi, La, Ce, Pr, Nd, P,
It may contain atoms such as Co, Mn, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Zn, Co
-Ti, Co-Ti-Zr, Co-Ti-Zn, Ni-
Ti-Zn, Nb-Zn-Co, Sb-Zn-Co, N
A substance to which an element such as b-Zn is added can be used. Some raw materials and production methods contain specific impurities.

The size of the ferromagnetic hexagonal ferrite powder is usually 10 to 200 nm, preferably 10 to 100 nm, as an average of the maximum major axis of the hexagonal plate (hereinafter referred to as “average plate diameter”).
nm, and particularly preferably 10 to 80 nm.

In particular, when reproducing with a magnetoresistive head in order to increase the track density, it is necessary to reduce the noise. The plate diameter is preferably 40 nm or less, but if it is less than 10 nm, stable magnetization cannot be expected due to thermal fluctuation. Above 200 nm, noise is high, and neither is suitable for high-density magnetic recording. The plate ratio (average plate diameter / average 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. 1
If it is larger than 5, noise increases due to stacking between particles. The specific surface area by the BET method in this particle size range usually shows 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, but when calculated and expressed as a standard deviation with respect to the average size (average plate diameter and average plate thickness), σ / average size = 0.1 to 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 with the ferromagnetic powder can be made up to about 500 Oersted to 5000 Oersted. A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, Hc is about 1700 Oersted to 4000 Oersted, but is preferably 1800 Oersted or more and 3500 Oersted or less. When the saturation magnetization of the head exceeds 1.4 Tesla, it is preferable that the saturation magnetization be 2000 Oe or more. Hc can be controlled by particle size (plate diameter / plate thickness), kind and amount of contained element, substitution site of element, particle generation reaction condition and the like. Saturation magnetization (σ _s ) is 40 emu / g to 80 emu
/ g. σ _S is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite in order to improve σ _S , 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 ferromagnetic powder, the surface of the ferromagnetic powder particles is sometimes treated with a substance suitable for the dispersion solvent 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 material is 0.1 to 10% by weight based on the ferromagnetic powder. The pH of the ferromagnetic powder is also important for dispersion. Normally, the pH is about 4 to 12, and there is an optimum value depending on the dispersion solvent and the polymer. The moisture contained in the ferromagnetic powder also influences the dispersion, and there is an optimum value depending on the dispersion solvent and the polymer. Hexagonal ferrite is produced by mixing barium oxide, iron oxide, and a metal oxide that replaces iron with boron oxide as a glass-forming substance to obtain the desired ferrite composition, then melting, quenching, and then crystallization. And then reheated, washed and pulverized to obtain a barium ferrite crystal powder, a glass crystallization method, a barium ferrite composition metal salt solution is neutralized with an alkali, and by-products are removed.
The liquid phase heating is followed by washing, drying and pulverization to obtain a barium ferrite crystal powder, a hydrothermal reaction method, a barium ferrite composition metal salt solution is neutralized with an alkali, by-products are removed and then dried and dried at 1100 ° C. There is a coprecipitation method or the like in which a barium ferrite crystal powder is obtained by treating and pulverizing as follows, but the present invention does not select a production method.

[Non-Magnetic Layer] The details of the lower layer will now be described. The inorganic powder used in the lower layer of the present invention is a non-magnetic powder, for example, selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Can be. 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 because of many means for imparting functions, and more preferred are titanium dioxide and α-iron oxide. The average particle diameter of these inorganic powders is preferably from 0.005 to 2 μm, but it is also possible to combine inorganic powders having different particle sizes as needed, or to obtain a similar effect by widening the particle size distribution even with a single inorganic powder. it can. Particularly preferably, the average particle size of the inorganic powder is from 0.01 μm to 0.2 μm. In particular, when the inorganic powder is a particulate metal oxide, the average particle size is 0.08.
μm or less, and in the case of a needle-shaped metal oxide, the average major axis length is preferably 0.3 μm or less, more preferably 0.2 μm or less. Tap density is usually 0.05-2g / m
l, preferably 0.2-1.5 g / ml. The water content of the inorganic 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 inorganic powder is usually 2 to 11, but the pH is 5.5 to 5.5.
Particularly preferred is between 10. The specific surface area of the inorganic powder is usually
It is 1 to 100 m ² / g, preferably 5 to 80 m ² / g, more preferably 10 to 70 m ² / g. The crystallite size of the inorganic powder is preferably 0.004 μm to 1 μm, and 0.04 μm to
0.1 μm is more preferred. The oil absorption using DBP (dibutyl phthalate) is usually 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, more preferably 20 to 60 m.
l / 100g. The specific gravity is usually 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. SA (stearic acid) adsorption amount of inorganic powder is 1-2
0 μmol / m ² , preferably ² to 15 μmol / m ² , more preferably 3 to 8 μmol / m ² . Preferably, the pH is between 3 and 6. The surface of these inorganic powders is subjected to a surface treatment, and Al ₂ O ₃ , SiO ₂ , TiO ₂ ,
ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ are preferably present. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ , and more preferred are Al ₂ O ₃ , SiO ₂ and ZrO ₂
It is. These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used according to the purpose, or a method in which alumina is first present and then silica is present in the surface layer, 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 inorganic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko and H
IT-100, ZA-G1, α hematite DPN-250, DPN-250BX, DPN-24 manufactured by Toda Kogyo Co., Ltd.
5, DPN-270BX, DPN-500BX, DBN
-SA1, DBN-SA3, Titanium oxide TT manufactured by Ishihara Sangyo
O-51B, TTO-55A, TTO-55B, TTO
-55C, TTO-55S, TTO-55D, SN-1
00, α hematite E270, E271, E300, E
303, titanium industrial titanium oxide 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 made by Sakai Chemical
NEX-25, BF-1, BF-10, BF-20, S
TM, Dowa Mining DEFIC-Y, DEFIC-R,
AS2BM and TiO2P25 manufactured by Nippon Aerosil, 100A and 500A manufactured by Ube Industries, and baked products thereof. Particularly preferred inorganic powders are titanium dioxide and α-
It is iron oxide.

By mixing carbon black in the lower layer, the surface electric resistance Rs, which is a known effect, can be reduced, the light transmittance can be reduced, and a desired micro-Vickers hardness can be obtained. 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 for rubber, thermal 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 usually 100 to 500 m ² / g, preferably 150 to 40 m ² / g.
0 m ² / g, DBP oil absorption is usually 20 to 400 ml / 100
g, preferably 30 to 400 ml / 100 g. The average particle size of the carbon black is usually 5 nm to 80 nm, preferably 10 to 50 nm, more preferably 10 to 40 nm. The pH of carbon black is usually 2 to 10, the water content is 0.1 to 10% by weight, and the tap density is 0.1 to 1 g /
ml is preferred. Specific examples of the carbon black used in the present invention include BLACKPEA manufactured by Cabot Corporation.
RLS 2000, 1300, 1000, 900, 80
0,880,700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050B, # 3150B, # 325
0B, # 3750B, # 3950B, # 950, # 65
0B, # 970B, # 850B, MA-600, MA-
230, # 4000, # 4010, CONDUCTEX SC, RAVEN 88 manufactured by Columbian Carbon Co., Ltd.
00,8000,7000,5750,5250,35
00, 2100, 2000, 1800, 1500, 12
55,1250, Akzo Ketjen Black EC
And so on. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used in which a part of the surface is graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in an amount generally not exceeding 50% by weight and not exceeding 40% by weight of the total weight of the nonmagnetic layer based on the inorganic powder. These carbon blacks alone,
Or they can be used 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
No. 18,564, and those described in JP-A-60-255827 can be used.

[Binder] The binder resin, lubricant, dispersant, additive, solvent, dispersing method, etc. of the lower layer can be the same as those of the magnetic layer described below. In particular, with respect to the amount and type of the binder resin, the amount of the additive and the type of the dispersant, and the type thereof, 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 a thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1.0.
00 to 200,000, preferably 10,000 to 10
000 and a degree of polymerization of about 50 to 1,000.

Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
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. In addition, as a thermosetting resin or a reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin,
Examples include epoxy-polyamide resins, mixtures of polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. 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 resins,
A combination of at least one selected from vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer and a polyurethane resin, or a combination of these with a polyisocyanate Is raised.

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

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, ZEON Corporation MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
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 Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Daiferamine 4020, 5020, 5 manufactured by Dainichi Seika
100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Co., Ltd., MX5004, Samprene S manufactured by Sanyo Kasei Co., Ltd.
P-150 and Saran F310, F210 manufactured by Asahi Kasei Corporation.

The binder used in the non-magnetic layer and the magnetic layer of the present invention is 5 to 50% for the non-magnetic layer in the non-magnetic layer and 5 to 50% in the magnetic layer for the ferromagnetic powder. weight%
, Preferably in the range of 10 to 30% by weight. 5 to 30% by weight when using a vinyl chloride resin,
When a polyurethane resin is used, it is preferable to use a combination of 2 to 20% by weight and a polyisocyanate in a range of 2 to 20% by weight. For example, when head corrosion occurs due to a slight amount of dechlorination, only polyurethane or It is also possible to use only polyurethanes and isocyanates. In the present invention, when polyurethane is used, the glass transition temperature is -50 to 150 ° C, preferably 0 ° C to 100 ° C, the breaking elongation is 100 to 2000%, the breaking stress is 0.05 to 10 kg / mm ² , and the yield point is 0.05 ~
10 kg / mm ² is preferred.

The magnetic recording medium of the present invention comprises two or more layers. Therefore, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the resin described above. It is of course possible to change the physical characteristics of the non-magnetic layer and the magnetic layer as needed, and 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 the binder in each layer, it is effective to increase the amount of the binder in the magnetic layer in order to reduce abrasion on the surface of the magnetic layer,
In order to improve the head touch with the head, the amount of the binder in the nonmagnetic layer can be increased to provide flexibility.

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

[Carbon Black, Abrasive] As the carbon black used in the magnetic layer of the present invention, furnace for rubber, 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, average particle size is 5 nm to 300 nm, pH is 2-1.
0, water content is 0.1-10% by weight, tap density is 0.1
１1 g / cc is preferred. Specific examples of the carbon black used in the present invention include BLA manufactured by Cabot Corporation.
CKPEARLS 2000, 1300, 1000, 9
00, 905, 800, 700, VULCAN XC-
72, manufactured by Asahi Carbon Co., # 80, # 60, # 55, # 5
0, # 35, manufactured by Mitsubishi Chemical Corporation, # 2400B, # 23
00, # 900, # 1000 # 30, # 40, # 10
B, CONDUCTEX manufactured by Columbian Carbon Co., Ltd.
SC, RAVE150, 50, 40, 15, RAVE
N-MT-P, manufactured by EC Japan, Ketjen Black E
C, and the like. Even if carbon black is surface-treated with a dispersant or grafted with resin,
A part of the surface may be 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% by weight based on the ferromagnetic powder. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are magnetic layers,
It is of course possible to change the type, amount, and combination in the lower layer, and use them according to the purpose based on the above-mentioned characteristics such as particle size, oil absorption, conductivity, and pH. Should be. 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 magnetic layer of the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, and nitride having an α conversion of 90% or more. Known materials having a Moh's hardness of 6 or more, such as silicon, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% by weight or more. The average particle size of these abrasives is preferably from 0.01 to 2 μm, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different average particle diameters as needed, or to use a single abrasive to broaden the particle diameter distribution to have the same effect. Tap density 0.3 ~ 2g / cc, water content 0.1 ~
5% by weight, pH 2-11, specific surface area 1-30 m ² / g,
Is preferred. The shape of the abrasive used in the present invention is acicular,
Any of a spherical shape and a dice shape may be used, but those having a corner in a part of the shape are preferable because of high abrasiveness. Specifically, AKP-12, AKP-15, and AKP-2 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-30, AKP-50, HIT20, HIT
-30, HIT-55, HIT60, HIT70, HI
T80, HIT100, manufactured by Reynolds, ERC-DB
M, HP-DBM, HPS-DBM, manufactured by Fujimi Abrasives, WA10000, manufactured by Uemura Kogyo Co., Ltd., UB20, manufactured by Nippon Chemical Industry Co., Ltd., G-5, Chromex U2, Chromex U1, manufactured by Toda Kogyo, TF100 TF140, manufactured by IBIDEN Co., Ltd., Beta Random Ultra Fine, manufactured by Showa Mining Co., Ltd., and B-3. 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 and amount of the abrasive added to the magnetic layer and the non-magnetic layer should of course be set to optimal values.

[Additives] As 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. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, Alkyl phosphates and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ether,
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 alkali metal salts thereof, having 10 to 10 carbon atoms
24 monobasic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (such as Li, Na, K, and Cu) or C12 to C2
2, monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols (which may contain an unsaturated bond or may be branched), alkoxy alcohols having 12 to 22 carbon atoms (It may contain unsaturated bonds or be branched),
A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and a carbon atom having 2 to 1 carbon atoms;
Mono-fatty acid ester comprising any one of monohydric, divalent, trivalent, tetravalent, pentavalent, and hexavalent alcohols (which may contain an unsaturated bond or may be branched) Or difatty acid ester or trifatty acid ester, monoalkyl ether fatty acid ester of alkylene oxide polymer, C8-C22 fatty acid amide, C8-C22
Can be used.

Specific examples of these fatty acids 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. Can be Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. 2-hexyl decyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol for alcohols , Stearyl alcohol, lauryl alcohol and the like.
Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Heterocycles, cationic surfactants such as phosphoniums or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acids,
Anionic surfactants containing an acidic group such as a sulfate group, a phosphate group, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphates of amino alcohol, and alkylbedine type can also be used. . These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are always 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight 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 by using fatty acids having different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface by using esters having 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 selected in the range of 0.1% by weight to 50% by weight, preferably 2% by weight to 25% by weight based on the ferromagnetic powder or nonmagnetic powder.

All or a part of the additives used in the present invention may be added at any step of the production of magnetic and non-magnetic paints. For example, when the additives are mixed with the ferromagnetic powder before the kneading step, There are a case where it is added in a kneading step using a ferromagnetic powder, 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 solvents can be used, and for example, solvents described in JP-A-6-68453 can be used. [Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the support has a thickness of 2 to 100 μm, preferably 2 to 80 μm. The support of the computer tape is 3.0 to 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0.
厚 5.5 μm). The support of the disk medium is usually 20 to 100 μm, preferably 30 to 80 μm.

An undercoat layer may be provided between the support and the nonmagnetic layer to improve the adhesion. The thickness of the undercoat layer is usually 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm.
5 μm. The present invention may be a double-sided magnetic disk medium having a nonmagnetic layer and a magnetic layer on both sides of the support, or a disk medium or tape medium having 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 usually 0.1-4 μm, preferably 0.3-2.0 μm. Known undercoat layers and backcoat layers can be used.

The thickness of the magnetic layer of the magnetic recording medium of the present invention is optimized by the saturation magnetization of the head used, the head gap length, and the band of the recording signal. 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. In that case, the dry thickness of the magnetic layer indicates the total of those magnetic layers.

The thickness of the non-magnetic layer as the lower layer of the medium according to the present invention is generally 0.2 μm or more and 5.0 μm or less, preferably 0.3 μm or more and 3.0 μm or less, and more preferably 1.
It is not less than 0 μm and not more than 2.5 μm. The lower layer of the medium of the present invention exerts its effect if it is substantially non-magnetic.For example, even if a small amount of a magnetic substance is included as an impurity or intentionally, it exhibits the effect of the present invention, It goes without saying that the configuration can be regarded as substantially the same as that of the present invention. Substantially non-magnetic means that the lower layer has a residual magnetic flux density of 100 G (Gauss) or less or a coercive force of 100 Oersted or less, and preferably has no residual magnetic flux density and coercive force.

[Backcoat layer] The backcoat layer includes:
It preferably contains carbon black and inorganic powder.

It is preferable to use two types of carbon black having different average particle diameters in combination.
In this case, it is preferable to use a combination of fine-particle carbon black having an average particle diameter of 10 to 20 nm and coarse-particle carbon black having an average particle diameter of 230 to 300 nm. In general, the surface electric resistance of the back coat layer can be set low and the light transmittance can be set low by the addition of the fine carbon black as described above. Some magnetic recording devices use the light transmittance of the tape and use it as an operation signal. In such a case, the addition of fine carbon black is particularly effective. In addition, fine carbon black is generally excellent in holding power of a liquid lubricant, and contributes to reduction of a friction coefficient when used in combination with a lubricant. On the other hand, coarse-grained carbon black having an average particle diameter of 230 to 300 nm has a function as a solid lubricant, and also forms fine projections on the surface of the back layer to reduce the contact area, thereby reducing the friction coefficient. Contributes to the reduction of However, coarse-grained carbon black is used in severe driving systems.
The sliding of the tape easily causes the tape to fall off from the back coat layer, which has a drawback of increasing the error ratio.

Specific examples of commercial products of the particulate carbon black include the following. RAVE
N2000B (18 nm), RAVEN 1500B (1
7 nm) (all manufactured by Columbia Carbon Co., Ltd.), BP80
0 (17 nm) (Cabot), PRINTENTEX
90 (14 nm), PRINTEX 95 (15 nm),
PRINTEX85 (16 nm), PRINTEX75
(17 nm) (all manufactured by Degussa), # 3950 (16
nm) (manufactured by Mitsubishi Chemical Corporation).

Specific examples of commercial products of coarse particle carbon black include thermal black (270 nm) (manufactured by Khancarb) and RAVEN MTP (275 nm).
(Made by Columbia Carbon Co., Ltd.).

In the case of using two types having different average particle diameters in the back coat layer, the content ratio (weight ratio) of the fine carbon black of 10 to 20 nm to the coarse carbon black of 230 to 300 nm is determined by the former. : The latter is preferably in the range of 98: 2 to 75:25, more preferably in the range of 95: 5 to 85:15.

The content of carbon black in the back coat layer (when two types are used, the total amount thereof) is usually in the range of 30 to 80 parts by weight with respect to 100 parts by weight of the binder. Preferably, it is in the range of 45 to 65 parts by weight.

It is preferable to use two kinds of inorganic powders having different hardnesses in combination. Specifically, Mohs hardness 3 ~
It is preferable to use a 4.5 soft inorganic powder and a 5 to 9 Mohs hardness hard inorganic powder. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, the friction coefficient can be stabilized by repeated running. Further, with the hardness in this range, the sliding guide pole is not cut off. The average particle diameter of the inorganic powder is 30 to 50 nm.
Is preferably within the range.

Examples of the soft inorganic powder having a Mohs' hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. They are,
They can be used alone or in combination of two or more. Among these, calcium carbonate is particularly preferred.

The content of the soft inorganic powder in the back coat layer is 10 to 14 parts by weight per 100 parts by weight of carbon black.
It is preferably in the range of 0 parts by weight, more preferably 35 to 100 parts by weight.

By adding a hard inorganic powder having a Mohs' hardness of 5 to 9, the strength of the back coat layer is enhanced and the running durability is improved. When these inorganic powders are used together with carbon black or the above-mentioned soft inorganic powders, they are less deteriorated even in repeated sliding and form a strong backcoat layer. In addition, the addition of the inorganic powder provides an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with a soft inorganic powder (among others, calcium carbonate), the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back coat layer can be stabilized.

The hard inorganic powder has an average particle diameter of 80 to
It is preferably in the range of 250 nm (more preferably, 100 to 210 nm).

Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Of these, α-iron oxide or α-alumina is preferred. The content of the hard inorganic powder is usually 3 to 30 parts by weight based on 100 parts by weight of carbon black,
Preferably, it is 3 to 20 parts by weight.

When the soft inorganic powder and the hard inorganic powder are used in combination in the back coat layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, particularly preferably It is preferable to select and use a soft inorganic powder and a hard inorganic powder as in (3).

It is preferable that the back coat layer contains the two types of inorganic powders having different specific Mohs hardness, each having the specific average particle size, and the two types of carbon black having different average particle sizes. In particular, in this combination, it is preferable that calcium carbonate is contained as the soft inorganic powder.

The back coat layer may contain a lubricant. The lubricant can be appropriately selected from the above-mentioned lubricants that can be used for the nonmagnetic layer or the magnetic layer. In the back coat layer, the lubricant is usually added in a range of 1 to 5 parts by weight based on 100 parts by weight of the binder. [Production Method] The step of producing the magnetic paint and the lower layer paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All raw materials such as ferromagnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic recording medium 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, all or a part of the ferromagnetic powder or non-magnetic powder and the binder (however, preferably 30% by weight or more of the total binder) and the ferromagnetic powder 100 are used.
The kneading treatment is performed in a range of 15 to 500 parts per part. The details of these kneading treatments are described in JP-A-1-10633.
8, JP-A-1-79274. 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 a magnetic recording medium having a multilayer structure is applied in the present invention, the following method is preferably used. First, a lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the application of a magnetic paint. Showa 60-238
179, Japanese Patent Application Laid-Open No. 2-265672, a method of coating an upper layer by a support pressure type extrusion coating apparatus.
No. 17971, Japanese Patent Application Laid-Open No. 2-265672, a method for applying the upper and lower layers almost simultaneously by one coating head having two built-in slits for passing a coating liquid, and a third method disclosed in Japanese Patent Application Laid-Open No. 2-174965. This is a method in which the upper and lower layers are applied almost simultaneously by an extrusion coating device with a backup roll. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of the magnetic particles, Japanese Patent Application Laid-Open Nos. 62-95174 and 1-236968 are known.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in US Pat. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the constitution of the present invention, it is of course possible to use a sequential multi-layer coating in which a lower layer is applied and dried, and then a magnetic layer is provided thereon, 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 may be obtained even without orientation, without using an orientation device. However, a cobalt magnet may be alternately arranged diagonally, or an alternating magnetic field may be applied by a solenoid. It is preferable to use a known random alignment device. In the case of ferromagnetic metal powder, isotropic orientation is generally preferably in-plane two-dimensional random, but may be three-dimensional random with a vertical component.
In the case of hexagonal ferrite, three-dimensional randomness in the in-plane and vertical directions generally tends to occur, but 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 making the magnets vertically oriented. In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

In the case of a magnetic tape, it is oriented in the longitudinal direction using a cobalt magnet or a solenoid. It is preferable that the drying position of the coating film can be controlled by controlling the temperature of the drying air, the flow rate, and the coating speed, and the coating speed is 20 m / min to 1 m.
The temperature of the drying air is preferably 60 ° C. or more at 000 m / min, and an appropriate preliminary drying can be carried out before entering the magnet zone.

As a calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll is used.
In particular, in the case of forming a double-sided magnetic layer, it is preferable to perform the treatment with metal rolls. The processing temperature is preferably 50 ° C. or higher,
More preferably, the temperature is 100 ° C. or higher. The linear pressure is preferably at least 200 kg / cm, more preferably at least 300 kg / cm.

[Physical Characteristics] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is as follows when a ferromagnetic metal powder is used.
Usually, it is 2000G or more and 5000G or less, and when using hexagonal ferrite, it is usually 1000G or more and 3000G or less. The coercive force Hc of the magnetic layer is 1800 Oe or more and usually 5000 Oe or less, but preferably 1900 Oe or more and 3000 Oe or less. The distribution of coercive force is preferably narrow, and SF
D and SFDr are preferably 0.6 or less. Squareness ratio is 2
In the case of dimension random, it is usually 0.55 or more and 0.67 or less, preferably 0.58 or more and 0.64 or less. In the case of three-dimensional random, it is usually 0.45 or more and 0.55 or less. In the case of orientation, it is usually 0.6 or more, preferably 0.7 or more in the vertical direction, and when demagnetization correction is performed, it is usually 0.7 or more, preferably 0.8 or more. The orientation ratio is preferably 0.8 or more for both two-dimensional random and three-dimensional random. In the case of two-dimensional randomness, the squareness ratio in the vertical direction, B
r, Hc and Hr are each 0.1 to 0.5 in the in-plane direction.
It is preferable to set it within twice.

In the case of a magnetic tape, the squareness ratio is 0.7 or more,
Preferably it is 0.8 or more. The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is 0.5 or less, preferably 0.3 or less, in the temperature range of -10 ° C. to 40 ° C. and the humidity of 0% to 95%. ^Four
-10 to ¹² ohms / sq, charged potential from -500V to + 500V
Is preferably within. Preferably 100 to 2,000 kg / mm ² in elastic modulus plane directions at 0.5% elongation of the magnetic layer, the breaking strength is preferably 10 to 70 kg / mm ^2, the modulus of elasticity of the magnetic recording medium is plane directions And preferably 100 to 1500 kg / mm
^{2. The} residual elongation is preferably 0.5% or less, and the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.
1% or less. The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus in the dynamic viscoelasticity measurement measured at 110 Hz) is 50.
0 ° C. or more and 120 ° C. or less, and that of the nonmagnetic layer is 0 ° C.
-100 ° C is preferred. Loss modulus is 1 × 10 ⁶ -8 ×
It is preferably in the range of 10 ⁹ dyne / 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 at most 100 mg / m ² , more preferably at most 10 mg / m ² . The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the lower layer and the magnetic layer. 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 surface of the magnetic layer was formed by using Mira of TOPO-3D.
The center plane surface roughness Ra measured by the u method is preferably 4.0.
nm or less, more preferably 3.8 nm or less, particularly preferably 3.5 nm or less. The maximum height SRmax of the magnetic layer is 0.
5 μm or less, ten-point average roughness SRz is 0.3 μm or less, center plane peak height SRp is 0.3 μm or less, center plane trough depth SRv is 0.3 μm or less, center plane area ratio SSr is 20% or more, 80
% Or less, and the average wavelength Sλa is preferably 5 μm or more and 300 μm or less. The surface protrusions of the magnetic layer can be arbitrarily set in the range of 0 to 2000 with a size of 0.01 μm to 1 μm, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. . 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. Curl is ± 3mm
It is preferable to be within.

In the present invention, it is easily presumed that the physical properties of the nonmagnetic layer and the magnetic layer can be changed 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.

[0098]

Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. In addition,
In the examples, "parts" indicates "parts by weight" unless otherwise specified. <Preparation of paint> Magnetic paint ML-1 (using acicular ferromagnetic powder) Ferromagnetic metal powder: 100 parts of M-1 Composition: Co / Fe atomic ratio 30% Hc2550 Oersted, specific surface area 55 m ² / g, σ _S 140 emu / g Crystallite size 120 °, average major axis length 0.048 μm, acicular ratio 4 Al compound (Al / Fe atomic ratio 8%) Y compound (Y / Fe atomic ratio 6%) Vinyl chloride copolymer MR110 (Nihon Zeon) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo) 3 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co.) 5 parts 3 parts phenylphosphonic acid 10 parts butyl stearate 10 parts butoxyethyl Stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 1 0 parts magnetic paint ML-2 (needle-like ferromagnetic powder used) ferromagnetic metal powder: M-2 100 parts Composition: Co / Fe atomic ratio 30% Hc2360 Oe, a specific surface area of 49m ² / g, σs146emu / g Crystallite size 170 °, average major axis length 0.100 μm, needle ratio 6, SFD 0.51 Al compound (Al / Fe atomic ratio 5%) Y compound (Y / Fe atomic ratio 5%) pH 9.4 vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin UR5500 (manufactured by Toyobo) 4 parts α-alumina HIT70 (manufactured by Sumitomo Chemical) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co.) 1 part Phenylphosphonic acid 3 parts oleic acid 1 Part Stearic acid 0.6 part Ethylene glycol dioleyl 12 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts Magnetic paint ML -3 (using acicular ferromagnetic powder: comparative example) Ferromagnetic metal powder: M-3 composition / Fe: Ni = 96: 4 100 parts Hc1600 oersted, specific surface area 45 m ² / g crystallite size 220 °, σs135 emu / g average Long axis length 0.20 μm, needle ratio 9 Vinyl chloride copolymer MR110 (Nippon Zeon) 12 parts Polyurethane resin UR-8600 (Toyobo) 5 parts α-alumina (average particle diameter 0.65 μm) 2 parts Oxidation Chromium (average particle diameter: 0.35 μm) 15 parts Carbon black (average particle diameter: 0.03 μm) 2 parts Carbon black (average particle diameter: 0.3 μm) 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 (plate-like strength Sex powder used) Barium ferrite powder: M-4 100 parts of pairs Ba molar ratio composition: Fe9.10, Co0.20, Zn0.77 Hc2500 Oersted, a specific surface area of _{^{50m 2 / g, σ S 58emu}} / g average plate diameter 35 nm, Tabular ratio 4 Vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo) 3 parts α-alumina HIT55 (manufactured by Sumitomo Chemical) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co., Ltd.) 5 Part Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts Magnetic paint ML-5 (using plate-like ferromagnetic powder) Barium ferrite powder : M-5 100 parts to Ba molar ratio composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 2500 Oersted, specific surface area 50 m ² / g, σ _S 58 emu / g average plate diameter 35 nm, plate ratio 2.5 vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 Part Polyurethane resin UR5500 (manufactured by Toyobo) 4 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co.) 1 part Phenylphosphonic acid 3 parts Oleic acid 1 part Stearic acid 0.6 part Ethylene glycol dioleil 16 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts Nonmagnetic paint NU-1 (using spherical inorganic powder) Inorganic powder TiO ₂ crystalline rutile 80 parts Average particle diameter 0.035 μm, specific surface area by BET method 40 m ² / g pH 7 TiO ₂ content of 90 wt% or more, DBP oil absorption of 27~38ml / 100g, 8% by weight of Al ₂ O _{3 on the} surface of the whole particles Carbon black Conductex SC-U (manufactured by Columbian Carbon) 20 parts Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 12 parts Polyurethane resin UR8200 (Toyobo) 5 parts 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 Nonmagnetic paint NU-2 (Use of spherical inorganic powder) Inorganic powder TiO ₂ crystalline rutile 100 parts Average particle diameter 0.035 μm, specific surface area by BET method 40 m ² / g pH 7 TiO ₂ content 90 wt% or more, DBP oil absorption 27-38 ml / 100 g Ketjen Black E with Al ₂ O ₃ and SiO _{2 on} the surface C (manufactured by AKUZO NOBEL) 13 parts Average particle diameter: 30 nm DBP oil absorption: 350 ml / 100 g pH: 9.5 Specific surface area by BET method: 950 m ² / g Volatile content: 1.0% by weight Vinyl chloride copolymer MR110 (Nippon Zeon) 16 parts Polyurethane resin UR8200 (Toyobo) 6 parts Phenylphosphonic acid 4 parts Ethylene glycol dioleyl 16 parts Oleic acid 1 part Stearic acid 0.8 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 Part Non-magnetic paint NU-3 (using spherical inorganic powder) Inorganic powder TiO ₂ crystalline rutile 75 parts Average particle diameter 0.035 μm, specific surface area 40 m ² / g pH 7 TiO ₂ content 90 wt% or more, DBP oil absorption 27 ~38ml / 100g, Al ₂ O ₃ on the surface, SiO ₂ is present carbon black Ketjen Black EC 10 parts α-alumina AKP-15 (Sumitomo Chemical Co., Ltd.) Average particle size: 0.65 μm 15 parts Vinyl chloride copolymer MR110 (Nippon Zeon) 12 parts Polyurethane resin UR8600 (Toyobo) 5 parts Iso Hexadecyl 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 Nonmagnetic paint NU-4 (using needle-like inorganic powder) inorganic powder α-Fe ₂ O ₃ hematite 80 parts Average major axis length 0.15 μm, specific surface area by BET method 50 m ² / g pH 9 Al ₂ O ₃ is present on the surface at 8% by weight based on the whole particles Carbon black Conductex SC-U (Columbian Carbon Co., Ltd.) 20 parts Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 12 parts Polyure Tan resin UR8200 (Toyobo) 5 parts 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) Inorganic powder α-Fe ₂ O ₃ hematite 100 parts Average major axis length 0.15 μm, BET specific surface area 50 m ² / g pH 9, Al ₂ O _{3 on the} surface 8% by weight based on the whole particles Carbon black # 3250B (Mitsubishi Kasei) 18 parts Vinyl chloride copolymer MR104 (Nippon Zeon) 15 parts Polyurethane resin UR5500 (Toyobo) 7 parts 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 For each of the above 10 paints, each component was kneaded with a kneader, and then dispersed using a sand mill. To the obtained dispersion, 10 parts of polyisocyanate was added to the coating liquid for the non-magnetic layer, 10 parts to the coating liquid for the magnetic layer, and 40 parts of cyclohexanone was added to each. A filter having an average pore diameter of 1 μm was added. And filtered to prepare coating liquids for forming a non-magnetic layer and for forming a magnetic layer, respectively.

Production Method 1 (W / W): Examples 1 to 19 Example 1 (Orientation: O-1) The coating liquid containing the nonmagnetic paint NU-1 was dried to a thickness of 1.5 μm. Immediately thereafter, a coating solution containing the magnetic coating material ML-2 is simultaneously and multi-layer coated on a support B-1 described later so that the thickness of the magnetic layer becomes 0.15 μm thereon. While the layer is still wet, frequency 50 Hz, magnetic field strength 250 gauss and frequency 50 Hz, 12
After passing through two alternating magnetic field generators of 0 gauss and performing random orientation treatment and drying, treatment is performed at a temperature of 90 ° C. and a linear pressure of 300 kg / cm using a seven-stage calendar.
After punching a 7-inch surface and subjecting it to polishing, a 3.7-inch cartridge with a liner installed inside (Iomega, USA)
Zip-disk cartridge), and a predetermined mechanical component was added thereto to obtain a 3.7-inch floppy disk.

Examples 2 to 16 and Comparative Examples 1 to 5 (Orientation: O
-1) A 3.7 inch floppy disk was obtained in the same manner as in Example 1 except that the factors described in Tables 1 and 2 were changed. Examples 17 and 18 (Orientation: O-2) Except that in Example 1, the factors described in Table 2 were changed, and longitudinal orientation was performed by a 4000 G homopolar opposing Co magnet before randomizing orientation treatment. A 3.7 inch floppy disk was obtained in the same manner as in Example 1.

Example 19 (Orientation: O-3) In Example 1, the factors described in Table 2 were changed, and instead of the randomizing orientation treatment, vertical orientation (using a different-pole opposed magnet) was performed. A 3.7 inch floppy disk was obtained in the same manner as in Example 1.

In the case of this production method 1 (O-1 and O-2),
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. In addition, if necessary, after punching into a disk shape, a high-temperature thermo-treatment (usually 50 ° C. to 90 ° C.) is performed to accelerate the curing treatment of the coating layer. Such post-processing may be performed.

Production Method 2 (W / D): Example 20 (Orientation: O
-1) A coating solution containing the non-magnetic paint NU-5 is applied on the support B-1 so that the thickness after drying becomes 1.5 μm, dried once, subjected to a calendar treatment, and then further applied. Except that a coating solution containing the magnetic coating material ML-2 was applied by a blade method so that the thickness of the magnetic layer became 0.15 μm,
Performed in the same manner as in Example 1.

Here, it is also possible to adopt a method in which the calendering of the nonmagnetic layer is not performed.

Production method 3 (spin coating): Examples 21 and 2
2 (Orientation: O-4) A coating solution containing the non-magnetic paint NU-5 was spin-coated on the support B-1 such that the thickness after drying became 1.5 μm, and dried once. Further, spin coating was performed thereon so that the thickness of the magnetic layer became 0.15 μm.
The magnetic layer described above was applied, and an orientation treatment was performed in the circumferential direction with a 6000 G same-pole opposed Co magnet. 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.

It is also possible to use 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. The use of the spin coating method not only increases the amount of remanent magnetization in the recording direction, but also reduces the perpendicular magnetization component of barium ferrite and ferromagnetic metal powder having a short needle ratio to improve the symmetry of the reproduced waveform. it can.

The supports used are as follows. Support B-1 Main polymer: Polyethylene terephthalate Filler of surface layer: Average particle size 0.10 μm Density 12 million / mm ² Center plane average surface roughness: 3.0 nm 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: Long axis 15 × 10 ⁻⁵ / ° C., short axis 18 × 10 ⁻⁵ / ° C. Support B-2 Main polymer: Polyethylene terephthalate Surface layer filler: Average particle size 0.29μm density 11.9 million pieces / mm ² central plane average surface roughness: 4.0 nm thickness: 62 .mu.m support B-3 base polymer: Triethylene terephthalate surface layer of filler: average particle size 0.05μm Density 12.3 million pieces / mm ² central plane average surface roughness: 2.0 nm thickness: 62 .mu.m support B-4 base polymer: polyethylene terephthalate surface of the filler: average particle diameter 0.10 μm Density 29.5 million / mm ² Center plane average surface roughness: 4.2 nm Thickness: 62 μm Support B-5 Main polymer: Polyethylene terephthalate Filler of surface layer: Average particle diameter 0.10 μm Density 5.1 million / mm ⁽²⁾ Center plane average surface roughness: 2.2 nm Thickness: 62 μm Support B-6 Main polymer: polyethylene naphthalate Filler of surface layer: Average particle diameter 0.10 μm Density 11.5 million / mm ² Center plane average surface roughness: 2.8 nm thickness: 55 μm heat shrinkage (80 ° C., 30 minutes): MD 0.02%, TD 0 0.3% thermal shrinkage rate (100 ° C., 30 minutes): MD 0.08%, TD 0.05 % Temperature expansion coefficient: major axis 10 × 10 ^-5 / ℃, minor axis 11 × 10 ^-5 / ℃ support B -7 (comparative example) Main polymer: polyethylene terephthalate Filler of surface layer: average particle diameter 0.45 μm density 12.2 million particles / mm ² center plane average surface roughness: 5.8 nm thickness: 62 μm Support B-8 (comparative example) ) Main polymer: Polyethylene terephthalate Filler of surface layer: Average particle size 0.01 μm Density 12.1 million / mm ² Center plane average surface roughness: 0.9 nm Thickness: 62 μm Support B-9 (Comparative example) Main polymer: Polyethylene terephthalate surface layer of filler: average particle diameter 0.10μm density 41 million pieces / mm ² central plane average surface roughness: 6.5 nm thickness: 62 .mu.m support B-10 (Comparative example Base polymer: polyethylene terephthalate surface of the filler: average particle diameter 0.10μm Density 2.2 million / mm ² central plane average surface roughness: 0.8 nm thickness: 62 .mu.m support B-11 base polymer: aramid surface layer of filler: Mean Particle size 0.08 μm Density 18.1 million / mm ² Center plane average surface roughness: 2.8 nm Thickness: 45 μm Heat shrinkage (80 ° C., 30 minutes): MD 0%, TD 0% Heat shrinkage (100 ° C.) , 30 minutes): MD 0.001%, TD 0.001% Thermal expansion coefficient: major axis 5 × 10 ⁻⁵ / ° C., minor axis 6 × 10 ⁻⁵ / ° C. The orientation method is as follows. Orientation: O-1 Randomized orientation is performed. Orientation: After orientation in the longitudinal direction with an O-2Co magnet, randomized orientation is performed. Orientation: Vertical orientation is performed with an O-3Co magnet. Orientation: Circumferential orientation is performed with an O-4Co magnet.

The magnetic properties, center plane average roughness, surface recording density and the like of the samples obtained as described above were measured. (1) Magnetic properties (Hc): Measured using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) with an Hm of 10 kOe (KOe). (2) Center plane average surface roughness (Ra): 3D-MIRAU
Surface roughness (Ra): Ra value of an area of about 250 μm × 250 μm was measured by MIRAU method using TOPO3D manufactured by WYKO. 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 was measured using a vibration sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at Hm 10 kOe. (7) The error rate of the disk was measured by recording the signal of the above linear recording density on the disk by the (2,7) RLL modulation method. (8) Thickness of magnetic layer A magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter over a longitudinal direction, and the transmission electron microscope was used to magnify 10,000 to 10,000 times.
Observation was performed at a magnification of 0, preferably 20,000 to 50,000, and the photograph was taken. Photo print size is A
4-A5. Thereafter, the interface was visually determined 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 magnetic layer surface was similarly blackened. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. Sample photo length is 2
In the case of 1 cm, the measurement was performed 85 to 300 times. The average of the measured values at that time was defined as the magnetic layer thickness. (10) The average particle diameter of the filler contained in the surface layer of the support was determined by the above method. (11) The number of fillers in the surface layer of the support was determined by the above method. (12) Durability is measured using a floppy disk drive (US I
OMEGA ZIP100: 2968 rpm)
The head was fixed at a position with a radius of 38 mm using, and after recording at a recording density of 34 kfci, the signal was reproduced to make it 100%. Thereafter, the vehicle was run for 1500 hours in a thermocycle environment in which the following flow (to) was defined as one cycle. The output was monitored every 24 hours of running, and the time when the output became 70% or less of the initial value (H: time) was regarded as NG.
The thermocycle flow is as follows. 25 ° C, 5
0% RH 1 hour → Temperature rise 2 hours → 60 ° C, 20% RH 7 hours → Temperature decrease 2 hours → 25 ° C, 50% RH 1 hour → Temperature decrease 2 hours → 5 ° C, 10% RH 7 hours → Temperature rise 2 hours

[0109]

[Table 1]

[0110]

[Table 2]

[0111]

[Table 3] In Examples 23 to 25 and Reference Example 1, the error rate was similarly measured using the disk of Example 19 while changing the linear recording density and the track density.

From the results shown in the above table, it can be seen that the magnetic recording medium of the present invention has an error rate of 10 ^-5 or less, particularly in a high-density recording area, and is much more durable than the conventional disk-shaped medium. . On the other hand, in the comparative example, it is difficult to achieve both the error rate and the durability, and it can be seen that at least one of them is inferior to the example.

[0113]

According to the present invention, a substantially nonmagnetic lower layer and a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder ferromagnetic powder dispersed in a binder are provided on a support. In the magnetic recording medium provided in order, the magnetic recording medium is a magnetic recording medium for recording a signal having a surface recording density of 0.17 to ² Gbit / inch ² , and the dry thickness of the magnetic layer is 0.05 to 0.30 μm. And φm is 10.0 ×
10 ^{−3 to} 1.0 × 10 ⁻³ emu / cm ² , the coercive force of the magnetic layer is 1800 Oe or more, and the surface layer of the support has an average particle diameter of 0.05 to 0.3 μm. By providing a magnetic recording medium characterized by having 5 to 30 million fillers / mm ² , excellent high-density characteristics which cannot be obtained by the conventional coating type magnetic recording medium technology A magnetic recording medium having a significantly improved error rate, output, and durability in a high-density recording area having both excellent and excellent durability can be obtained.

Claims (1)

[Claims] 1. A support in which a substantially non-magnetic lower layer and a magnetic layer in which a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder is dispersed in a binder are provided in this order on a support. In the magnetic recording medium, the magnetic recording medium is a magnetic recording medium for recording a signal having an areal recording density of 0.17 to ² Gbit / inch ² , and the dry thickness of the magnetic layer is 0.05.
0.30 μm, and φm is 10.0 × 10 ⁻³ .
1.0 × 10 ⁻³ emu / cm ² , a coercive force of the magnetic layer of 1800 Oe or more, and a filler having an average particle diameter of 0.05 to 0.3 μm on the surface of the support.
A magnetic recording medium characterized in that it is present in an amount of from 100,000 to 30,000,000 pieces / mm ² .