JP2001184621A - Magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-density magnetic disk, particularly a high-density magnetic disk having servo signals with high track density and high line recording density and having high resolution and S/N and excellent traveling durability. SOLUTION: The magnetic disk is produced by forming at least a base coating layer and a magnetic layer in this order on a nonmagnetic supporting body. The magnetic layer is formed to <=0.2 μm thickness, and the magnetic powder incorporated into the magnetic layer consists of ferromagnetic iron-based alloy powder containing Co and rare earth elements and having <=0.15 μm major axial length (L) satisfying the relation of L/λ<=1/3, wherein λ is the shortest recording wavelength. The particle diameter of the carbon black incorporated into the magnetic layer is larger than the thickness of the magnetic layer. The minimum and maximum values of the coefficient of thermal expansion of the magnetic recording disk having the aforementioned materials satisfy the relation of maximum/minimum<=2.0. Further, the magnetic disk contains servo signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density magnetic disk, and more particularly to a magnetic disk having a servo signal and excellent in electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art Magnetic recording media have various uses such as audio tapes, video tapes, computer tapes, disks, and the like. As a magnetic disk having a higher density, there has been proposed a magnetic disk having a capacity of 100 MB or more, which is greatly increased from the capacity of 1 MB using the conventional oxide magnetic powder. Drives have also been reduced in size and weight, and have been used in various environments.

In a drive using such a high-density magnetic disk, the disk rotation speed is increased from the conventional 300 rpm to 72 in order to record and reproduce a large amount of data in a short time.
It is necessary to make the rotation speed twice as high as 0 rpm or to rotate at a high speed of 3,000 rpm or more.
In order to increase the capacity, developments are being made to increase the rotation speed and increase the track density and the linear recording density. Further, in order to ensure stable recording / reproducing characteristics and reliability during high-speed rotation, development of an optimal contact mechanism of a head with a medium has been promoted.

As a magnetic disk corresponding to such a high density and a change in environment, means for improving the magnetic properties of ferromagnetic powder, uniform distribution of ferromagnetic powder, and a spacing loss between a medium and a head are required. Means to reduce track circularity deterioration (difference in dimensional change in the circumferential direction) due to temperature change or humidity change of a high-density magnetic disk, that is, to reduce the anisotropy of the temperature expansion coefficient or the humidity expansion coefficient. There is a need for means to do so.

In order to improve the magnetic characteristics of the ferromagnetic powder, it is desirable to increase the degree of magnetization remaining on the magnetic disk to increase the output. Therefore, as the magnetic powder, conventional oxide magnetic powder or cobalt-containing iron oxide is used. Instead of magnetic powder, ferromagnetic iron-based alloy powder is becoming mainstream, and ferromagnetic iron-based alloy powder having a coercive force of 1,500 Oe or more has been proposed. For example, it is disclosed in JP-A-5-234064, JP-A-6-25702, JP-A-6-139553.

As means for improving the dispersibility of the ferromagnetic powder, a binder having a polar functional group such as a sulfonic acid group, a phosphoric acid group or an alkali metal salt thereof, or a low molecular weight compound together with the binder is used. Means have been proposed, such as using the above dispersant in combination, continuously performing the kneading and dispersing step of the magnetic paint, and adding a lubricant after dispersion. For example, Japanese Patent Application Laid-Open Nos. 62-23226 and 2-1
No. 01624, JP-A-3-216812, JP-A-3-17827, JP-A-4-47586, JP-A-8-235566, and the like.

Further, as means for reducing the spacing loss between the medium and the head, in addition to the above-mentioned means for increasing the dispersibility of the magnetic powder, a smoothing treatment of the magnetic layer under high temperature and high pressure conditions in the calendar step is performed. Means have been proposed in which a nonmagnetic undercoat layer is provided below the magnetic layer to suppress the influence of the surface properties of the nonmagnetic support on the surface of the magnetic layer. For example, it is disclosed in JP-B-64-1297, JP-B-7-60504, and JP-A-4-19815.

However, the conventional magnetic disk manufactured by the above means cannot satisfy the electromagnetic conversion characteristics and the running durability with a drive corresponding to a capacity of 100 MB or more. In the case of a high-density magnetic disk, in order to increase both the track density and the linear recording density, an output of only about a fraction is obtained with the saturation magnetization and coercive force of conventional magnetic powder, and an extremely short recording wavelength is used. Therefore, the effects of self-demagnetization loss during recording and reproduction and the thickness loss due to the thickness of the magnetic layer, which have not been a problem in the past, become large, and sufficient resolution cannot be obtained.

On the other hand, for example, Japanese Patent Laid-Open No.
No. 9061 and the like, coercive force of 1,000
A ferromagnetic iron-based alloy powder of 0 Oe or more is used, and a non-magnetic layer is provided between the non-magnetic support and the magnetic layer to reduce space loss and thickness loss due to surface properties. It has been proposed that the thickness of the layer be less than 0.5 μm. However, in a high-density magnetic disk having a track width of 10 μm or less and a shortest recording wavelength of 1.0 μm or less, the saturation magnetization and coercive force of the magnetic powder can be further increased, and the above space loss and thickness loss can be further reduced. There is a need to.

Moreover, in such a high-density disc,
Since the track width is narrowed by the improvement of the track density, expansion and contraction of the magnetic disk due to a change in temperature or humidity causes data errors due to a decrease in the S / N ratio due to off-track of the magnetic head. easy. This is because the off-track is likely to occur due to the dimensional change due to the temperature expansion coefficient or humidity expansion coefficient of the magnetic disk especially when the temperature and humidity environment when data is recorded and when the data is reproduced are different. It is necessary to provide a servo track having a servo signal for detecting a data track position on the magnetic layer separately from the data track. Therefore, suppression of off-track by a servo signal is becoming indispensable for improving track density. However, even with a medium having such a servo signal, it has become apparent that the data error increases when the data track width is extremely narrow as 10 μm or less as described above. . That is, even if the absolute value of the deviation amount from the data track due to the off-track of the magnetic head is the same, the data track width is narrowed, and the ratio of the minimum on-track width to the data track width is reduced.
Further, when the anisotropy of the temperature expansion coefficient or the humidity expansion coefficient is not appropriate, the head cannot follow the servo signal, and as a result, the S / N ratio is largely reduced by off-track,
It has the problem of inducing data errors. It is also possible to perform error correction on such an off-track data error on the device side, and such a correction circuit is actually used, but the S / N ratio is also improved on the medium side. Therefore, even when a certain amount of head off-track occurs, it is necessary to reduce the data error with respect to off-track by maintaining the required minimum S / N ratio.

On the other hand, the running durability of a high-density magnetic disk also has a problem that the running durability, which was not a problem at the conventional low-speed rotation, is extremely poor at the high-speed rotation. In recent years, in particular, in order to improve the reliability of a magnetic disk, it is necessary to satisfy seek durability in which the magnetic head is moved for several tracks while keeping the magnetic head in contact. The magnetic layer using
Compared with a magnetic layer using an oxide magnetic powder, sliding scratches are more likely to occur during high-speed rotation, which causes a reduction in output or dropout, and lowers the reliability of the disk.

Furthermore, with the spread of personal computers, the number of drives built into personal computers is increasing, and media are used in various environments. Accordingly, the cycle environment from low temperature and low humidity to high temperature and high humidity is used. In the durability and reliability tests under the following conditions, it is necessary that the output does not deteriorate and the dropout does not occur, so that further running durability and reliability under such severe conditions are desired. .

In view of the above circumstances, the present invention provides a high-density magnetic disk, particularly a high-density magnetic disk having a high track density and a high linear recording density servo signal, as well as high resolution and S / N ratio. It is intended to provide improved running durability.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above objects, and as a result, have provided an undercoat layer between a nonmagnetic support and a magnetic layer, and have a specific composition and length as a magnetic powder. Using a ferromagnetic iron-based alloy powder with an axial length, specify the thickness of the magnetic layer, the particle size of the carbon black contained in the magnetic layer, and the coefficient of thermal expansion or humidity expansion of the high-density magnetic disk composed of these. When the relationship between the maximum value and the minimum value of the anisotropy of the disk, that is, the temperature expansion coefficient or the humidity expansion coefficient in each direction in the disk surface, is specified, high electromagnetic conversion characteristics and excellent running durability can be obtained. Thus, the present invention has been completed.

That is, in the present invention, an undercoat layer and a magnetic layer are formed in this order on a non-magnetic support, the thickness of the magnetic layer is 0.2 μm or less, and the magnetic powder contained in the magnetic layer has a long axis length (L A) a magnetic layer made of a ferromagnetic iron-based alloy powder containing Co and a rare earth element having a relationship between the major axis length (L) and the shortest recording wavelength (λ) satisfying L / λ ≦ １ ／, which is 0.15 μm or less; Is larger than the thickness of the magnetic layer, and the coefficient of thermal expansion of the magnetic recording disk made of these is such that the relationship between the minimum value and the maximum value is the maximum value / minimum value ≦ 2.0.
Or a magnetic recording disk comprising the magnetic recording disk, wherein the relationship between the minimum value and the maximum value of the magnetic recording disk satisfies a maximum value / minimum value ≦ 2.0.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a high-density magnetic disk, in particular, a high-density magnetic disk and high linear recording density
For the purpose of improving the electromagnetic conversion characteristics by off-track, the relationship between the minimum value and the maximum value of the thermal expansion coefficient satisfies the maximum value / minimum value ≦ 2.0, or A magnetic disk is used which has been subjected to processing so that the relationship between the minimum value and the maximum value of the humidity expansion coefficient of the magnetic recording disk satisfies the maximum value / minimum value ≦ 2.0.

As a magnetic disk satisfying such conditions, it is preferable to use a non-magnetic support in which the relationship between the minimum value and the maximum value of the temperature expansion coefficient or the humidity expansion coefficient satisfies a maximum value / minimum value ≦ 2.0. However, even if a magnetic disk manufactured using a non-magnetic support that does not satisfy this condition is used, the crystal structure of the non-magnetic support and the magnetic disk composed of the undercoat layer and the magnetic layer becomes somewhat random. By performing the above, a magnetic disk satisfying the conditions of the present invention can be manufactured.

A magnetic disk satisfying such conditions is:
It can be manufactured by performing a calendaring process and an aging process. In the calendering step at this time, it is preferable to raise the roll temperature at a higher linear pressure, and the aging processing is to keep the magnetic disk in a tension-free state for a longer time under a higher temperature environment, for example, a 3.5-inch disk. It is preferable to perform an aging treatment in a state of punching.

In order to improve the electromagnetic conversion characteristics and durability in the present invention, the magnetic powder to be contained in the magnetic layer is preferably a long axis (L) among ferromagnetic iron-based alloy magnetic powders.
A ferromagnetic iron-based alloy magnetic powder containing 0.15 μm or less and containing Co and a rare earth element satisfying a relation of a long axis length (L) and a shortest recording wavelength (λ) satisfying L / λ ≦ １ ／ is used.

That is, as described later, in the present invention, the thickness of the magnetic layer must be set to 0.2 μm or less in order to obtain a high resolution. Since the filling amount is reduced, the magnetic characteristics are degraded, and a high output cannot be obtained. For this reason, the present invention uses the ultrafine ferromagnetic iron-based alloy magnetic powder having a major axis length (L) of 0.15 μm or less, more preferably 0.10 μm or less, so that the filling property of the magnetic powder in the magnetic layer is improved. To improve remanence and obtain high remanent magnetization,
By containing o, the magnetic properties of the magnetic powder itself, such as the saturation magnetization and coercive force, are improved, and high output is obtained even in high-density recording with a magnetic layer thickness of 0.2 μm or less and a shortest recording wavelength of 1.0 μm or less. Can be achieved.

On the other hand, in the magnetic disk having a servo signal as described above, even if a predetermined S / N ratio is obtained during on-track, the S / N of the medium is prevented to prevent data error due to off-track. It is necessary to improve the N ratio. Therefore, even when a medium having a high output is obtained by simply improving the magnetic properties of the magnetic layer using the magnetic powder as described above, if the noise is also high, the relative S / N ratio decreases and the off-track It became clear that sufficient S / N could not be obtained.

The inventors of the present invention have studied the reduction of the noise. As a result, the ferromagnetic iron-based alloy magnetic powder of the present invention having a diameter of 0.15 μm or less has a major axis length (L) and a shortest recording wavelength (λ). It has been found that the relationship has a relationship of L / λ ≦ １ ／ and can be solved by using a magnetic powder containing a rare earth element.

That is, the noise generated from the medium is one of the factors due to the particulate noise caused by the magnetic powder.
It is considered that the particle noise is caused by unevenness of the size and the particle size of the magnetic powder. Therefore, first, it is necessary to reduce the size of the particles. According to the study of the present inventors, the major axis length (L) of the magnetic powder and the shortest recording wavelength (λ)
When the relationship L / λ ≦≦, the number of magnetic particles in a fixed area contributing to the head output is increased, and the variation in the amount of magnetization in the fixed area due to the difference in the data recording location is prevented. It has been found that noise based on the size of the particles can be reduced. In addition, by using magnetic powder of fine particles that are 1/3 or less of the shortest recording wavelength as described above, noise due to the size of the particle can be reduced, but the particle property due to unevenness of the particle size can be reduced. Noise cannot be reduced. In other words, if there is a variation in the size of each magnetic powder, even if the data is in an unrecorded state, the magnetic flux generated from the magnetic particles existing in a certain area contributing to the head output varies, and the head output is generated. Is zero, that is, the total of the magnetic flux is hard to be zero. For this reason, an output difference occurs due to a difference in data recording location, which causes an increase in noise. This is because the noise based on the output fluctuation is also superimposed in the state where the signal is recorded, so that the noise further increases and the relative S / N ratio is reduced.

For this reason, the present invention provides a ferromagnetic iron-based alloy powder having the above-mentioned particle size, wherein a magnetic powder containing a rare earth element together with Co is used, so that the particle size distribution of the magnetic powder becomes uniform. Noise can be reduced, and S / N
It has been found that the ratio can be improved. Moreover, the inclusion of such a rare earth element is also preferable in that the scratch resistance of the magnetic powder can be improved.

In the present invention, the Co-containing ferromagnetic iron-based alloy powder is obtained by calcining a Gasite powder into a magnetite powder, which is ion-exchanged with divalent iron ions and cobalt ions in a cobalt ion-containing aqueous solution. A method of heat-reducing, a method of heat-reducing a cobalt-containing acicular gausite powder obtained from an aqueous suspension of an alkali of an iron salt and a cobalt salt, and a method of obtaining from an iron salt and a cobalt salt added to an aqueous oxalic acid solution. A method of reducing coprecipitates, a method of heating and reducing iron oxide powder having cobalt deposited on the surface, a method of adding a reducing agent to a solution containing iron salts and cobalt salts, and evaporating metals in an inert gas. Can be produced by colliding with gas molecules to obtain alloy magnetic powder, reducing iron to cobalt in a mixed gas of hydrogen, nitrogen and argon while flowing vapor of iron or cobalt chloride. . Among these,
It is preferable to use a method capable of forming a solid solution with a high cobalt content and having excellent corrosion resistance.

In the Co-containing ferromagnetic iron alloy powder, the higher the amount of cobalt, the higher the saturation magnetization and the higher the coercive force can be achieved. However, if the amount is too large, alloying with the magnetic iron metal cannot be performed, and the excess Is an oxide, so that the above characteristics cannot be achieved. Therefore, the amount of cobalt is Co /
A range in which the weight ratio of Fe is 0.1 to 0.5 is preferable,
In particular, the range of 0.2 to 0.4 is more preferable.

In order to make the particle size distribution of the magnetic powder uniform, the rare earth element is introduced into the ferromagnetic iron-based alloy powder containing Co by co-precipitating the rare earth element at the same time as the cobalt during the production of the goethite. And a method of suspending the raw material iron oxide powder of the alloy magnetic powder in a rare earth compound aqueous solution.

Here, the rare earth elements used in the present invention include Nd, Y, La, Ce, Pr, Sm, Gd, Y
b, Tb, etc., among which Y, La, C
e is preferred.

The larger the amount of the rare earth element contained in the ferromagnetic iron-based alloy powder of the present invention, the more uniform the particle size distribution of the magnetic powder becomes.
In addition, the adhesive strength with the binder can be increased, and a strong coating structure can be obtained, so that the ferromagnetic iron-based alloy powder can be prevented from falling off at the time of high-speed sliding. In order to reduce the saturation magnetization of the magnetic iron-based alloy powder,
The rare earth element / Fe weight ratio is preferably in the range of 0.01 to 0.1, more preferably 0.02 to 0.07. Further, by setting the content within the above range, the particle size distribution of the ferromagnetic iron-based alloy powder can be further improved, the particle noise can be reduced, and a high S / N ratio can be achieved. By further setting the above range,
The wear resistance of the ferromagnetic iron alloy powder itself can be increased,
Since magnetic powder damage during the coating kneading and dispersing step can be prevented, it is advantageous not only in electromagnetic conversion characteristics but also in durability.

In such a ferromagnetic iron-based alloy powder containing Co and a rare earth element, other elements such as
Transition metals such as Zn, Sn, Ni, Mn, Ti, Cr, and Cu can also be added. However, when an alkali metal, particularly Ca, is present in the ferromagnetic alloy magnetic powder, it reacts with a fatty acid in the magnetic layer to form a fatty acid salt on the surface of the magnetic layer. It is preferred to avoid contamination.

The ferromagnetic iron-based alloy powder containing Co and the rare earth element is coated with an inorganic oxide to prevent sintering during heat reduction and to improve dispersibility in a magnetic paint. Is desirable. Examples of the inorganic oxide include aluminum oxide and silicon oxide. Aluminum oxide is particularly preferable because it has excellent hardness and can improve the wear resistance of the ferromagnetic iron-based alloy powder. In order to carry out the coating, a method is used in which water is applied to an alcohol solution of aluminum, silicon or the like in advance on the raw iron oxide powder, and these compounds are adhered and formed on the particle surface by hydrolysis. The coating amount is F to prevent sintering and improve dispersibility.
The weight ratio to e is preferably 0.001 or more, and if it is too large, the saturation magnetization of the magnetic powder is reduced. That is, when the particle surface is coated with aluminum oxide, the weight ratio of Al / Fe is preferably in the range of 0.001 to 0.06.

Further, such a ferromagnetic iron-based alloy powder containing Co and a rare earth element is included in a magnetic paint because magnetic aggregation is likely to occur due to high saturation magnetization and the particle surface becomes very active. The pH is preferably less than 10, especially less than 8, because it acts as a catalyst that causes the denaturation of the solvent and the denaturation of the isocyanate component in the crosslinking agent used as the binder. By setting the pH value of the ferromagnetic iron-based alloy powder containing Co and the rare earth element to be less than 10, generation of denatured products in the magnetic paint can be suppressed, and sliding at the time of high-speed rotation when forming the magnetic layer can be suppressed. It can be a durable coating film.

The average major axis length is obtained by actually measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and obtaining the average value of 100 particles. For the same reason as described above, the ferromagnetic iron-based alloy powder B
ET specific surface area is preferably at least 35m ² / g, 40m ² /
g or more, and most preferably 50 m ² / g or more.

The coercive force of such a ferromagnetic iron-based alloy powder containing Co and a rare earth element is set to 1,7 in order to obtain high output and high resolution in short wavelength recording at a high linear recording density.
00-3,500 Oe, especially 2,000-2,800 Oe
e is preferred. The saturation magnetization is 120 to 200 emu / g, particularly 1 to obtain a good reproduction output at a high track density and maintain the corrosion resistance of the magnetic powder.
It is preferably from 30 to 160 emu / g. As the squareness ratio, σr / σs is preferably 0.46 or more, particularly 0.48 or more, and more preferably 0.49 or more.

In the present invention, the magnetic properties of the magnetic layer using the ferromagnetic iron-based alloy powder containing Co and the rare earth element are as follows.
e, particularly preferably 2,000 to 3,000 Oe. Further, the residual magnetic flux density is 1,800 G or more,
It is preferably from 000 to 4,000 G. The magnetic characteristics of this magnetic layer and the magnetic characteristics of the ferromagnetic iron-based alloy powder containing Co and the rare earth element both refer to values measured with an external magnetic field of 10 kOe using a sample vibrating magnetometer. .

In the present invention, the use of the ferromagnetic iron-based alloy powder containing Co and the rare earth element improves the magnetic properties of the magnetic layer, and a high output can be obtained even at the shortest recording wavelength of 1.0 μm or less. In addition, noise generated from the magnetic powder itself can be reduced, and a high S / N ratio can be obtained.
On the other hand, when the thickness of the magnetic layer is large at a high linear recording density of the shortest recording wavelength of 1.0 μm or less, the long-wavelength output increases with the thickness, but the short-wavelength output changes little due to the thickness loss. do not do. For this reason, when the short wavelength output is relatively lower than the long wavelength output, the resolution is remarkably reduced, and the improvement by the effect of reducing the self-demagnetization loss by increasing the coercive force is not sufficient.

In order to solve such a problem of resolution,
As a result of the study, at a high linear recording density of 1.0 μm or less in the shortest recording wavelength, when the thickness of the magnetic layer is set to 0.2 μm or less, which is 1/5 or less of the conventional magnetic disk, a high-resolution magnetic I found that I could get a disc. That is, in the present invention, a high residual magnetic flux density and a high coercive force of the magnetic layer are achieved by using the above-described ferromagnetic iron-based alloy powder containing Co and setting the thickness of the magnetic layer to 0.2 μm or less. Thus, the self-demagnetization loss at a high track density can be reduced, and the thickness loss can be reduced even at a high linear recording density of the shortest recording wavelength of 1.0 μm or less, and good electromagnetic conversion characteristics can be achieved.

From the above viewpoint, the thickness of the magnetic layer in the present invention needs to be 0.2 μm or less. However, if the thickness is too small, the uniformity of the coating film thickness during the formation of the magnetic layer is reduced. It becomes difficult to maintain, and the amount of magnetic powder that can be filled in the magnetic layer is reduced, and the magnetic properties of the magnetic layer are reduced. For this reason, the thickness of the magnetic layer is desirably 0.03 μm or more, particularly preferably 0.1 to 0.2 μm.

On the other hand, a high-density magnetic disk needs to perform high-speed data transfer in order to record and reproduce a large amount of data in a short time.
720 rpm which is twice or more than 00 rpm or 3,
A high-speed drive of a head contact type or a near contact type of 000 rpm or more is used. However, in the magnetic disk using the ferromagnetic iron-based alloy powder containing Co and the rare earth element described above, although the fall of the magnetic powder during running was improved, the magnetic layer was easily damaged during sliding, and the drop-out occurred. And output fluctuations are likely to occur, and sufficient running durability cannot be obtained.

On the other hand, in the present invention, an undercoat layer is provided between the nonmagnetic support and the magnetic layer, and the particle size of the carbon black contained in the magnetic layer is set to be equal to or larger than the thickness of the magnetic layer. It has been found that the running durability of the magnetic disk at the high speed rotation can be improved. That is, since the magnetic disk of the present invention is used in a drive rotating at a high speed, by providing an undercoat layer below the magnetic layer, the load from the magnetic head during sliding can be dispersed and the thickness of the magnetic layer can be reduced. Can compensate for the decrease in lubricant due to the thinner layer.

In the case where the magnetic layer was made thinner as in the present invention, it was confirmed that a large number of dropouts and a decrease in running durability due to falling off of carbon black occurred at high speed rotation. This is because carbon black added to the magnetic layer is present on the surface of the magnetic layer in order to reduce friction caused by sliding contact with the magnetic head. When only the carbon black is applied to the high-density magnetic disk of the present invention, it is necessary to increase the filling ratio of the magnetic powder in the magnetic layer and to reduce the thickness of the magnetic layer to 0.2 μm or less to reduce thickness loss. Therefore, in the present invention, since the active ferromagnetic iron-based alloy magnetic powder is used, the amount of the binder adsorbed on the carbon black and the amount of coating are reduced, and the magnetic layer It is considered that carbon black is detached at the time of high-speed sliding contact with the magnetic head. Furthermore, in the ultrafine ferromagnetic iron-based alloy magnetic powder of the present invention, the amount of binder adsorbed on the surface of the magnetic powder increases, so that the amount of free binder present on the surface of the magnetic layer decreases, and Such a load cannot be reduced, and the running durability is further degraded. Therefore, a large particle size
By using carbon black, especially carbon black having a thickness greater than the thickness of the magnetic layer, the carbon black is firmly fixed in the magnetic layer and is present on the surface of the magnetic layer. By suppressing the sliding contact between the sticky magnetic powder and the magnetic head, the friction at the time of sliding contact with the magnetic head can be reduced even during high-speed rotation, and stable running durability can be obtained. Conceivable. Further, since carbon black having such a large particle size is present on the surface of the magnetic layer, the function as a head support at the time of contact with the magnetic head can be sufficiently exerted. Is greatly reduced, and it is considered that running durability can be remarkably improved. Regarding the particle size of the carbon black having a large particle size according to the present invention, if the particle size is too large, the surface smoothness of the coating film is impaired and the electromagnetic conversion characteristics are reduced.
It is preferably 0 times or less, more preferably 1.1 times or more and 2.0 times or less. Specific examples of the large particle size carbon black of the present invention include "SEVACARB MTCI" manufactured by Columbian Carbon Co., Ltd. and "Termax Powder N-991" manufactured by Kancarb Co., Ltd. The addition amount is usually 0.1 to 100 parts by weight of the ferromagnetic iron-based alloy powder containing Co and the rare earth.
It is preferably 5 to 5 parts by weight, particularly preferably 1 to 3 parts by weight.

In the present invention, carbon black having a large bulk specific gravity and a small particle size of 0.01 to 0.03 μm is used in combination with the large particle size carbon black to impart conductivity. Is preferred. For carbon black with a small particle size, "BLACK PEARLS" manufactured by Cabot
800 ”,“ Mogul-L ”,“ VULCANXC ”
-72 "," Regal 660R ", Colombian
"Raven 1255", "Cond
octex SC ".

When carbon black having a small particle size as described above is used in combination, the ratio of the carbon black having a small particle size to the carbon black having a large particle size is 10/90 to 80/20 by weight.
Is preferred, and 20/80 to 50/50 is more preferred. By setting the above range, it is possible to leave a certain amount of holes in the magnetic layer, and to smoothly supply the lubricant to the surface of the magnetic layer, thereby friction with the magnetic head, and a disk such as a nonwoven fabric. The friction with the jacket component can be reduced, and the running durability can be further improved.

In the present invention, the thickness of the undercoat layer is 0.5 to 5 μm in order to obtain the above effects.
In particular, it is preferably 1 to 3 μm. By providing such an undercoat layer, the surface properties of the magnetic layer at the time of calendaring can be improved, which can contribute to an improvement in output. In addition, the thickness of the undercoat layer and the thickness of the magnetic layer are defined as the five cross-sections obtained by measuring 10 cross-sectional photographs of the coating film with a transmission electron microscope (50,000 times) at 1 cm intervals. It is obtained from the average value.

It is preferable that the amount of the lubricant extracted with n-hexane from the magnetic layer and the undercoat layer be 30 mg / cm ³ or more, because the running durability can be further improved. That is, with the above configuration, the presence of the sufficient lubricant in the magnetic layer and the undercoat layer assists the lack of lubricant on the surface of the magnetic layer, and is combined with the presence of carbon black having a large particle size. In addition, friction on the surface of the magnetic layer, which causes a decrease in running durability, can be reduced, and a cushion effect can be further obtained. In addition, even if the pores in the magnetic layer are reduced by performing a calendering process for smoothing the magnetic layer surface and increasing the filling of the magnetic powder, the lubricant easily oozes out to the magnetic layer surface, which is favorable. Durability is obtained.

It should be noted that the more the amount of the lubricant extracted, the more the friction coefficient at high speed can be reduced. However, if the amount of the lubricant is too large, the filling property of the magnetic powder is reduced so that the electromagnetic conversion characteristics are deteriorated. 250mg / g
It is preferably not more than cm ³ . Further, as the lubricant in the present invention, as described later, it is preferable to use a fatty acid having 10 or more carbon atoms and a fatty acid ester having a melting point of 35 ° C. or less, but the extraction weight ratio of the lubricant extracted with n-hexane is as follows. 0.3 / 9 of the above fatty acid and the above fatty acid ester
9.7 to 10/90, preferably 0.5 / 99.5 to 6
/ 94 is preferable. By setting such a range, the friction coefficient can be reduced and the running durability can be improved while maintaining the oil film strength on the surface of the magnetic layer.

In the present invention, the amount of the lubricant extracted by n-hexane means that the operation of cutting out a magnetic disk of 600 cm ² and immersing it in one liter of n-hexane for 10 minutes is repeated twice, and dried at 60 ° C. After that, it is a value obtained by dividing the value obtained from the weight difference before and after immersion by the total volume of the magnetic layer and the undercoat layer. Further, the composition ratio of the extracted lubricant is determined by gas chromatography from a temperature of 150 ° C. to 2 ° C.
A value obtained by measuring the temperature up to 00 ° C at a heating rate of 10 ° C / min by a calibration curve method.

Further, in the present invention, when the magnetic head and the magnetic disk are in sliding contact with each other, if the hardness of the magnetic layer is too weak with respect to the magnetic head, the magnetic layer is scraped, which causes a decrease in running durability. The present invention, when the thickness of the magnetic layer is 0.2μm or less, as a result of studying the self-polishing ability to improve running durability at high speed rotation, the steel ball wear volume of the magnetic layer to a specific range When specified, excellent running durability was obtained in terms of seek durability.

That is, in a high-density magnetic disk, if the steel ball wear volume of the magnetic layer is less than 0.5 × 10 ⁻⁴ mm ³ , the conventional low-speed rotation of about 300 rpm does not cause a problem. Damage is significant at high speeds, which can result in reduced output and increased dropout immediately after rotation. Therefore, the steel ball wear volume of the magnetic layer is set to 0.5
By setting the thickness to at least × 10 ⁻⁴ mm ³ , preferably at least 1.0 × 10 ⁻⁴ mm ³ , it is possible to reduce abrasion of the magnetic layer due to sliding contact with the magnetic head even during high-speed rotation. On the other hand, if the steel ball wear volume is larger than 5.0 × 10 ⁻⁴ mm ³ , the self-polishing ability of the magnetic layer becomes too high, damaging the magnetic head,
The output will be reduced. For this reason, the steel ball wear volume is 5.0 × 10 ⁻⁴ mm ³ or less, preferably 3.0 × 10 ⁻⁴ m 3.
By setting it to m ³ or less, magnetic head wear and head clogging can be reduced even after running for a long time.

The wear volume of the steel ball in the present invention is measured by a rotary sliding test while moving the position of the sliding surface as described below. This is different from the value measured by the method and reflects the self-polishing ability of the entire magnetic disk. That is,
As shown in FIG. 1, the wear volume of the steel ball of the magnetic layer was measured by removing the upper carriage of the drive 1 and replacing the upper head with a steel ball 3 [made of high carbon chromium bearing steel, having a diameter of 6.35 mm.
(JISB-1501)] is fixed, and a SUS metal plate 5 having a thickness of about 0.2 mm is attached to the head surface of the lower carriage 2 to form a receiving surface for steel balls.
In an environment of 0 ° C. and 50% RH, set the sample disk incorporated in the cartridge, place a weight on the balance so that a load of 10 g is applied to the steel ball, and in this state, at a position of a radius of 30 mm for 10 seconds. The disk is rotated at 720 rpm.

Next, the steel ball is moved to the outer peripheral portion of 1 mm while applying a load and rotated for 10 seconds, and the steel ball is further moved to the outer peripheral portion of 1 mm and rotated for 10 seconds. Repeat and spin for a total of 60 seconds to stop the disc. Thereafter, the steel ball is removed and observed with an optical microscope (100 times). From the radius (r) of the circular wear surface generated by sliding and the radius (R) of the steel ball, the following equation is obtained. Accordingly, the steel ball wear volume (V) of the magnetic layer is calculated. In FIG. 1, 6 is a drive board, 7 is a drive controller,
8 is a spindle and 9 is a statuser.

[0052]

(Equation 1)

The structure of the magnetic disk of the present invention will be described below in the order of a magnetic layer, an undercoat layer and a non-magnetic support. First, the constituent components of the magnetic layer include the above-described ferromagnetic iron-based alloy powder containing Co and a rare earth element, carbon black,
In addition to lubricants, there are binders and abrasives for this alloy powder, and other dispersants such as alcohols, fatty acids, aliphatic amines, and surfactants to enhance the dispersibility of the alloy powder. Used.

The binder used in the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, nitrocellulose. -There is a combination of at least one kind selected from polyurethane and a polyurethane resin. Among them, it is preferable to use a vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin and a polyurethane resin in combination. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and the like.

These binders preferably have a functional group in order to improve the dispersibility of the ferromagnetic iron-based alloy powder containing Co and the rare earth element and to enhance the filling property. As the functional group, COOM, SO ₃ M, OSO ₃ M, P = O (O
_{M) 3, O-P =} O (OM) 2, (M is a hydrogen atom or an alkali metal _{salt,), OH, NR 2,} N + R 3 (R is like a hydrocarbon group), epoxy group. When two or more resins are used in combination, it is preferable that the functional groups are the same, and among them, a —SO ₃ M group is preferable.

These binders are used in an amount of 5 to 5 parts by weight based on 100 parts by weight of a ferromagnetic iron alloy powder containing Co and a rare earth element.
0 parts by weight, preferably 10 to 35 parts by weight. In particular, when using a vinyl chloride resin as a binder, the range is from 5 to 30 parts by weight, and when using a polyurethane resin, the range is from 2 to 20 parts by weight. preferable.

It is desirable to use together with these binders a thermosetting crosslinking agent that bonds to a functional group or the like contained in the binder to form a crosslink. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate
, Methylene diisocyanate, etc., the reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and various polyisocyanates such as condensation products of the above isocyanates. Is preferred. These crosslinking agents are based on 100 parts by weight of the binder.
Usually, it is used in a proportion of 15 to 70 parts by weight.

As the lubricant used in the magnetic layer, conventionally known fatty acids, fatty acid esters, hydrocarbons and the like are used alone or in combination of two or more. Among them, it is preferable to use a fatty acid having 10 or more carbon atoms, preferably 12 to 30 carbon atoms, and a fatty acid ester having a melting point of 35 ° C. or less, preferably 10 ° C. or less. Some of these lubricants adsorb to ferromagnetic iron alloy powder to help disperse the magnetic powder, and also reduce the contact between the medium and the head during initial wear, reduce the wear coefficient and reduce head contamination. To contribute.

The fatty acids having 10 or more carbon atoms include straight-chain,
Any of isomers such as branched and cis-trans may be used, but a linear type having excellent lubricating performance is preferred. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

Fatty acid esters having a melting point of 35 ° C. or lower include n-butyl oleate, hexyl oleate, n-octyl oleate, 2-ethylhexyl oleate, oleyl oleate, n-butyl laurate, heptyl laurate, myristine N-butyl acid, n-butoxyethyl oleate, trimethylolpropane trioleate, n-butyl stearate, s-butyl stearate, isoamyl stearate, butyl cellosolve stearate and the like. These fatty acid esters can control the oil film strength and the amount of oil output depending on the difference in molecular weight, structure, and melting point, and may be optimized by combination. By having the above melting point, even when exposed to low temperature and low humidity, the magnetic layer easily oozes and migrates to the surface of the magnetic layer at the time of high-speed sliding contact between the magnetic layer and the magnetic head, and effectively exerts its excellent lubricating action. it can.

In order to incorporate these lubricants into the magnetic layer, when mixing the magnetic powder and the binder, they are added together with the two components, before or after the mixing, or A lubricant solution or the like may be applied or sprayed on the surface of the formed magnetic layer. At that time, the amount of the lubricant used is 1 to 15 parts by weight, preferably 2 to 12 parts by weight, more preferably 4 to 10 parts by weight, based on 100 parts by weight of the ferromagnetic iron alloy powder containing Co. Good to do.
When a fatty acid having 10 or more carbon atoms and a fatty acid ester having a melting point of 35 ° C. or less are used in combination, the addition ratio of both is 10% by weight.
/ 90-80 / 20, preferably 20 / 80-60 / 4
It is better to set to 0.

The abrasive used for the magnetic layer is preferably used for adjusting the wear volume of the steel ball of the magnetic layer. Examples of the abrasive include granular, angular, and needle-like α-alumina (Al ₂ O ₃ ) having an α conversion of 90% or more, β-alumina, γ-alumina, chromium, α-iron oxide, silicon carbide, and titanium oxide. , Cerium oxide, silicon dioxide, diamond and the like. Among them, α-alumina, which has a high hardness and exists on the surface of the magnetic layer and has a large effect of reducing the wear coefficient, is particularly preferable. The particle size of the abrasive is 0.3 μm in order to reduce the spacing between the medium and the head and to keep the steel ball wear volume within the range of the present invention.
m or less, particularly preferably 0.2 μm or less. However, if it is too small, the coefficient of wear with the magnetic head increases, and the running durability decreases. Therefore, it is preferably at least 0.02 μm, particularly preferably at least 0.1 μm.

In order to include the abrasive in the magnetic layer, the magnetic powder and the binder are added in a step of kneading with a kneader or the like or in a preliminary stirring step, or an abrasive dispersion is prepared in advance, and May be added to the magnetic paint. In terms of productivity, the former, which does not require a separate step, is more preferable. The amount of the abrasive added is 5 to 25 parts by weight, preferably 10 to 20 parts by weight, based on 100 parts by weight of the ferromagnetic iron alloy powder containing Co and the rare earth element, from the viewpoints of electromagnetic conversion characteristics and head contamination. Good to do.

In the formation of the magnetic layer, any of the conventionally used solvents can be used as a solvent for preparing a magnetic paint, a lubricant solution and the like. For example, aromatic solvents such as benzene, toluene and xylene; ketone solvents such as acetone, cyclohexanone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as ethanol and isopropanol. And hexane, tetrahydrofuran, dimethylformamide and the like.

The constituent components of the undercoat layer include inorganic powder, binder, lubricant, carbon black and the like. Both non-magnetic powder and magnetic powder can be used as the inorganic powder. Examples of the nonmagnetic powder include α-alumina, β-alumina, γ-alumina, α-iron oxide, TiO ₂ (rutile, anatase), TiO _X , cerium oxide, tin oxide having an α-conversion ratio of 90% or more. Tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , C
r ₂ O ₃ , gateite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , S
rCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination. As magnetic powder, γ
_{-Fe 2 O 3, Co-γ} -Fe 2 O 3, magnetic powder coercive force 300Oe following low coercivity such as Ba ferrite is used.

These inorganic powders may be in any of spherical, needle-like, and plate-like shapes. If the particle size of the inorganic powder is too large, the surface property of the undercoat layer is reduced, which affects the surface of the magnetic layer. Therefore, the particle size is preferably 0.5 μm or less. On the other hand, if it is too small, the filling property of the undercoat layer with the inorganic powder increases, the number of pores capable of holding the lubricant decreases, and the cushioning effect decreases.
It is preferably at least 5 μm. The amount of inorganic powder used is
For the same reason as the above particle size, 60 to 90 of the entire undercoat layer
It is preferred that the amount be from 70% to 80% by weight.

As the binder used for the undercoat layer, the same resin as the above-mentioned binder constituting the magnetic layer is used, and preferably, the same resin as the binder of the magnetic layer is used. In particular, when they are matched with each other in the combination system of the vinyl chloride resin and the polyurethane resin, the elasticity of the undercoat layer and the magnetic layer becomes close, and the load from the magnetic head can be dispersed well.
The binder of the undercoat layer preferably has the same type of functional group as the binder of the magnetic layer. In particular, when the functional groups of the undercoat layer and the magnetic layer are matched to each other in a combined system of a vinyl chloride resin and a polyurethane resin, the adhesion between the two layers is improved, and the leaching of the lubricant from the undercoat layer to the magnetic layer is smooth. Is preferable.

The amount of the binder used in the undercoat layer is determined based on the amount of the inorganic powder 1
20 to 45 parts by weight, especially 25 to 4 parts by weight, per 100 parts by weight
It is preferably 0 parts by weight. In addition, in order to increase the strength of the undercoat layer, in the same manner as in the case of the magnetic layer, together with the binder, a thermosetting crosslinking agent that is combined with the functional group contained in the binder and crosslinked is used. Is also desirable. The amount of the crosslinking agent used is preferably 15 to 70 parts by weight based on 100 parts by weight of the binder.

As the lubricant used for the undercoat layer, the same lubricant as that for the magnetic layer can be used. However, since fatty acids are less leaching to the upper layer than fatty acid esters, fatty acid esters are used alone or when fatty acid esters are added. It is desirable to use a larger ratio. The amount of lubricant added to the undercoat layer is
The amount is usually 4 to 18 parts by weight, preferably 5 to 16 parts by weight, more preferably 6 to 14 parts by weight based on 100 parts by weight of the inorganic powder. The weight ratio of the fatty acid and the fatty acid ester to the undercoat layer is preferably 0/100 to 40/60, particularly preferably 0/100 to 30/70. The lubricant may be contained in the undercoat layer by adding it at the time of kneading the undercoat layer paint with a kneader or the like, before or after the above-mentioned mixing, or by adding the surface of the previously formed undercoat layer. , A lubricant solution or the like may be applied or sprayed.

As the carbon black used in the undercoat layer, it is preferable to use a carbon black having a particle size of 0.01 to 0.03 μm and a carbon black having a particle size of 0.05 to 0.3 μm. The former carbon black is used to secure pores for holding the lubricant, as in the case of the magnetic layer. The latter carbon black improves the coating strength of the undercoat layer and improves the cushioning effect. It is to balance the two. The amount of carbon black added to the undercoat layer is 5 to 70 parts by weight, especially 15 to 4 parts by weight, based on 100 parts by weight of the inorganic powder, inclusive of both carbon blacks.
It is preferably 0 parts by weight. In addition, particle diameter 0.01-0.
For the carbon black of 03 μm, “BLACK PEARLS 800” and “Mogul” manufactured by Cabot
-L "," VULCAN XC-72 "," Regal
660R "and" Rav "manufactured by Columbian Carbon Co., Ltd.
en 1255 "and" Conductex SC ". For carbon black having a particle size of 0.05 to 0.3 μm, “BLACK PEARLS” manufactured by Cabot Corporation is used.
130 "," Monarch 120 "," Raven 450 "," Rave "manufactured by Columbian Carbon Co., Ltd.
n 410 "and" TermaxPow "manufactured by Kancarb Corporation
der. N-991 ".

In forming the undercoat layer, the same aromatic solvent, ketone-based solvent, ester-based solvent, alcohol-based solvent, etc. as in the case of the magnetic layer may be used as a solvent for preparing the undercoat-layer paint or the lubricant solution. Solvents such as hexane and tetrahydrofuran are used.

As the non-magnetic support, any conventional non-magnetic support for magnetic recording media can be used. Specifically, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate
A film having a thickness of usually 30 to 100 [mu] m is used, which is made of, for example, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide and the like.

The tracking servo mechanism used to achieve a high track density on a high-density magnetic disk is designed to follow the use environment, especially when the anisotropy of shrinkage of the non-magnetic support which occurs in a test in a high temperature environment is large. And tracking errors easily occur. For this reason, the nonmagnetic support has a heat shrinkage of 105 ° C. for 30 minutes, that is, a heat shrinkage of 1.5% or less in the vertical direction and 1% in the horizontal direction after heat treatment at 105 ° C. for 30 minutes and cooling. It is preferably at most 0.0%. The above thermal shrinkage rate was determined by taking six test pieces of 10 mm in width and 300 mm in length of the non-magnetic support from MD / TD, respectively.
After heat treatment for 30 minutes in hot air of 05 ° C. and cooling, the length is measured and [(original length−length after shrinkage) / original length] ×
It is obtained as an average value of 100 (%).

The magnetic disk having a servo signal according to the present invention is a medium in which servo tracks are provided in a fixed area on the magnetic disk. A form using an optical servo signal in addition to the negative servo signal may be used. The magnetic disk of the present invention is particularly suitable for a system in which the area occupied by such servo signals is 7% or less of the total area of the magnetic layer of the medium. Outside the range, although the tracking accuracy is improved, the ratio of the data area to the effective recording surface is reduced, and it is difficult to secure the recording capacity. As a general method of providing sector servo signals in magnetic servo signals, use a dedicated drive for servo write that has been modified so that the magnetic head can be tracked with high accuracy, and shift the position by half a track to the beginning of each sector The servo signal A is further shifted from the servo signal A by a half track in the reverse direction following the servo signal A, and the servo signal B is recorded. The servo signal A and the servo signal B use different frequencies so that discrimination is easy in the servo signal processing circuit. The number of bits of each servo signal is determined according to the ratio of the servo signal area to the recording surface, the relative speed between the head and the medium, the configuration of the servo circuit, and the like. Further, in a system in which an off-track extending over a plurality of tracks is assumed, for example, servo signals A,
A technique has been adopted that makes it easier to detect a correct track position by using four servo signals, a servo signal B, a servo signal C, and a servo signal D. On the other hand, as a method of providing the optical servo signal, for example, a method of forming a broken line groove with a duty ratio of 50:50 between tracks and detecting the position of this groove with an optical sensor to position the head is adopted. The width of the groove at this time is determined according to the ratio of the servo signal area to the recording surface, the required S / N ratio of the servo signal, and the like. As a method of forming such a groove, there are a method of stamping with a stamp method, a method of burning off a part of the surface of the magnetic layer using a laser beam, and the like. The latter has higher tracking accuracy.

In the production of the magnetic disk of the present invention, a conventionally known coating production process can be used for forming the magnetic layer and the undercoat layer. Particularly, a kneading process using a kneader or the like and a primary dispersion process are preferably used together. preferable. In the primary dispersion step, the use of a sand mill is preferable because the dispersibility of the magnetic powder can be improved and the strength of the coating film can be adjusted, whereby the wear volume of the steel ball of the magnetic layer can be set.

In the coating step, gravure coating and ro
Conventional coating methods such as metal coating, blade coating, and extrusion coating can be used. At that time, the method of applying the undercoat layer and the magnetic layer is to apply the magnetic layer after coating and drying the undercoat layer on the non-magnetic support, or to sequentially coat the undercoat layer and the magnetic layer, Any of the simultaneous multilayer coating methods may be employed.

In manufacturing the magnetic disk of the present invention,
After coating and drying, it is desirable to perform a surface treatment with a calendar using a plastic roll or a metal roll. By performing the calendering process, the surface of the magnetic layer can be smoothed, the filling degree of the ferromagnetic iron-based alloy powder can be improved, the residual magnetic flux density can be improved, and the anisotropy of the thermal expansion coefficient or the humidity expansion coefficient can be improved. Can be improved.

Since the wear volume of the steel ball varies depending on the surface roughness of the magnetic layer, it can be appropriately adjusted by the dispersibility of the magnetic paint in the primary dispersion step, the calendering treatment, and the coating film surface polishing treatment.
The surface roughness of the magnetic layer is such that the average surface roughness (Ra) in the three-dimensional surface roughness of the optical interferometer is 1 to 8.5 nm, preferably 3 to 8.5 nm.
It is preferable to perform a mirror finishing treatment and a final coating film surface polishing treatment by adjusting the pressure and temperature of the roll in the calendaring step so that the thickness becomes about 7 nm. It is preferable that the surface of the coating film is polished with a polishing wheel or a tape such as alumina or chromium oxide having an average surface roughness of 0.4 μm or less. If the Ra is less than 1 nm, the magnetic layer becomes too smooth, the friction coefficient becomes high, and sticking to the magnetic head occurs, and the decrease in temperature cycle durability is remarkable due to an increase in the real contact area with the magnetic head. Become. Ra
Is larger than 8.5 nm, the unevenness on the surface of the magnetic layer becomes conspicuous, so that the magnetic layer is similarly abraded to powder, resulting in a decrease in seek durability and a decrease in C / N ratio.
Also deteriorates.

[0079]

The present invention will now be described more specifically with reference to examples. In each example, “parts” means “parts by weight”.

(Example 1) <Coating composition for undercoat layer> 65 parts of α-iron oxide (major axis length: 0.14 μm, needle ratio: 7) 10 parts of granular α-alumina (particle diameter: 0.4 μm) Carbon black (particle size: 0.024 μm) 18 parts Carbon black (particle size: 0.075 μm) 7 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin 16 parts (contains -SO ₃ Na group: 0.1 part) 7 × 10 ^{- 4} equivalents / g) polyurethane resin (containing -SO ₃ Na group: 1 × 10 ^{- 4} equivalents / g) 7 parts n- butyl oleyl oleate 6 parts of stearic acid (melting point: 28 ° C.) 2 parts cyclohexanone 200 Part: Methyl ethyl ketone: 200 parts <Magnetic paint component> Ferromagnetic alloy powder containing Co and rare earth elements: 100 parts (Co / Fe: 0.2, Y / Fe: 0.03 Al / Fe: 0.02, pH: 7. Long axis : 0.12μm, Hc: 2,000Oe, BET specific surface ^{area: 50m 2 / g, σs:} 140emu / g) Ca - Bonburatsuku (particle diameter: 0.02 [mu] m) 1 part Ca - Bonburatsuku (particle size: 0.35 .mu.m) 2.5 parts Granular α-alumina (particle size: 0.3 μm) 15 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin 13 parts (contained -SO Na group: 0.7 × 10 ^-4 equivalent / g) polyurethane resin (containing -SO ₃ Na group: 1 × 10 ^{- 4} equivalents / g) 4 parts myristic acid (carbon number: 15), 1 part oleyl oleate (mp: 0 ° C. or less) 5 parts cyclohexanone 250 parts Methyl ethyl ketone 250 parts the above After kneading the undercoat layer coating components with a kneader, the mixture is dispersed in a sand mill for 10 hours.
6 parts were added to prepare a paint for an undercoat layer. Separately, after kneading the above magnetic paint components with a kneader, the mixture is dispersed in a sand mill for 10 hours.
Then, 7 parts were added to prepare a magnetic paint. The above-mentioned undercoat layer paint was coated on a support made of polyethylene terephthalate film (105 ° C., 30 min.
8%, 0.6% in the horizontal direction) and the thickness after drying is 1
It was applied on both sides to a thickness of μm and dried.

After the undercoat layers were formed on both sides of the support in this manner, the magnetic coating was calendered on the undercoat layer to a thickness of 0.2 μm on one side.
m and applied to both sides and dried. Then, the magnetic sheet was placed in a five-stage calendar (temperature 80 ° C., linear pressure 150
(Kg / cm), and aged at 60 ° C. for 24 hours. afterwards,
A surface polishing treatment (air pressure: 0.25 MPa, polishing time: 1 second, disk rotation speed: 2,000 rpm) by an alumina polishing tape (WA-6000: alumina average particle diameter: 2 μm, surface roughness: 0.4 μm) Further, aging treatment was performed at 70 ° C. for 24 hours to produce a magnetic disk. After sticking the obtained magnetic disk to a 3.5-inch floppy hub, a groove width of 2.2 μm was formed on the Side 0 surface of the disk by a laser cut method, and the number of grooves per circumference was 1
500, duty 50:50, servo track pitch 20.4 μm, track radius 23 mm to 39.5
A groove for optical servo was provided at 5.4% of the surface of the magnetic layer in the range of mm, and further stored in a 3.5-inch floppy cartridge to obtain a final magnetic disk.

(Example 2) In the magnetic paint component, the magnetic powder was
Ferromagnetic iron-based alloy powder containing Co and Y (Co / Fe:
0.2, Y / Fe: 0.03, Al / Fe: 0.03,
pH: 7, major axis length: 0.07 μm, Hc: 2,000 O
e, BET specific surface area: 50 m ² / g, σs: 135 em
u / g) was changed to 100 parts and granular α-alumina (particle size:
0.3 μm) 15 parts of granular α-alumina (particle size: 0.1
5 μm) to 15 parts, and the thickness of the magnetic layer after the calendering treatment was changed to 0.14 μm on one side, and the surface polishing treatment was changed to an alumina polishing tape (WA-6000) instead of an alumina polishing tape. A magnetic disk was produced in the same manner as in Example 1 except that the magnetic recording was performed using a wafer (WA-8000: alumina average particle diameter 1.2 μm, surface roughness 0.07 μm).

(Example 3) Particle size of 0.3 in the magnetic paint component
Particle size 0.2 instead of 2.5 parts of 5 μm carbon black
Using 2.5 parts of 7 μm carbon black, changing the amount of oleyl oleate in the undercoat layer coating composition from 6 parts to 13 parts, and dispersing the undercoat layer coating composition by a sand mill for 10 hours. A magnetic disk was manufactured in the same manner as in Example 1 except that the time was changed to 8 hours.

(Example 4) A magnetic powder in a magnetic paint component was
Ferromagnetic iron-based alloy powder containing Co and Ce (Co / Fe:
0.2, Ce / Fe: 0.04, Al / Fe: 0.0
3, pH: 7, major axis length: 0.14 μm, Hc: 1,95
0 Oe, BET specific surface area: 50 m ² / g, σs: 130
emu / g) was changed to 100 parts, the conditions for dispersing the undercoat layer coating component and the magnetic coating component by a sand mill were changed from 10 hours to 6 hours, and the mirror finishing treatment was performed at 70 ° C. 120kg / cm
A magnetic disk was manufactured in the same manner as in Example 1 except that the above procedure was performed.

(Example 5) In a magnetic paint component, a magnetic powder was
Ferromagnetic iron alloy powder containing Co and La (Co / Fe:
0.3, La / Fe: 0.03, Al / Fe: 0.0
2, pH: 9, major axis length: 0.12 μm, Hc: 2, 20
0 Oe, BET specific surface area: 55 m ² / g, σs: 150
emu / g) was changed to 100 parts, the conditions for dispersing the undercoat layer coating component and the magnetic coating component by a sand mill were changed from 10 hours to 15 hours, respectively, and the mirror finishing treatment was performed at a temperature of 90 ° C. using a five-stage calendar. , Linear pressure 250Kg
/ Cm in the same manner as in Example 1,
A magnetic disk was manufactured.

(Example 6) In the magnetic paint component, the magnetic powder was
Ferromagnetic iron-based alloy powder containing Co and Nd (Co / Fe:
0.4, Nd / Fe: 0.03, Al / Fe: 0.0
5, pH: 7, major axis length: 0.1 μm, Hc: 2,200
Oe, BET specific surface area: 55 m ² / g, σs: 145 e
mu / g) was changed to 100 parts, the amount of oleyl oleate in the undercoat layer coating composition was changed from 6 parts to 3 parts, and 1 part of myristic acid was replaced with stearic acid (carbon number: 18) in the magnetic coating composition. 1) 5 parts of oleyl oleate and 2 parts of 2-ethylhexyl oleate (melting point: 0 ° C. or lower)
A magnetic disk was manufactured in the same manner as in Example 1 except that the respective parts were changed.

(Example 7) In the magnetic paint component, the magnetic powder was
Ferromagnetic iron-based alloy powder containing Co and Tb (Co / Fe:
0.3, Tb / Fe: 0.05, Al / Fe: 0.0
3, pH: 7, major axis length: 0.10 μm, Hc: 2, 10
0 Oe, BET specific surface area: 55 m ² / g, σs: 150
emu / g) changed to 100 parts, and
Instead of 65 parts of α-iron oxide, γ-Fe ₂ O ₃ magnetic powder (particle size: 0.12 μm Hc: 300 Oe, σs: 75 em)
u / g, BET specific surface area 25 m ² / g) 65 parts, and as a non-magnetic support, the heat shrinkage at 105 ° C. for 30 minutes is 0.3% in the vertical direction and 0.1% in the horizontal direction. A magnetic disk was manufactured in the same manner as in Example 1, except that the polyethylene terephthalate film was used.

Comparative Example 1 A magnetic disk was produced in the same manner as in Example 1 except that no undercoat layer was provided.

(Comparative Example 2) A particle diameter of 0.3 in the magnetic paint component
Particle size 0.2 instead of 2.5 parts of 5 μm carbon black
The carbon black was changed to 2.5 parts of 7 μm, the thickness of the magnetic layer was set to 0.3 μm, and 105 μm was used as the nonmagnetic support.
A magnetic disk was produced in the same manner as in Example 1 except that a polyethylene terephthalate film having a heat shrinkage of 2.0% in the vertical direction and 1.2% in the horizontal direction at 30 ° C. for 30 minutes was used.

(Comparative Example 3) In the magnetic paint component, the magnetic powder was
Ferromagnetic iron-based alloy powder containing Co and Y (Co / Fe:
0.2, Y / Fe: 0.01, Al / Fe: 0.02,
pH: 7, major axis length: 0.35 μm, Hc: 1650O
e, BET specific surface area: 45 m ² / g, σs: 125 emu
/ G) Changed to 100 parts, and in the coating component for the undercoat layer, the vinyl chloride-vinyl alcohol copolymer resin and the polyurethane resin were changed from those having -SO ₃ Na groups as functional groups to those having only -OH groups. In addition, 3.0 parts of a carbon black having a particle size of 0.075 μm were used instead of 2.5 parts of a carbon black having a particle size of 0.35 μm in the magnetic coating component. The same procedure as in Example 1 was carried out except that the dispersion conditions of the paint components by a sand mill were changed from 10 hours to 5 hours, respectively, and the mirror finishing treatment by a 5-stage calendar was performed at a temperature of 70 ° C. and a linear pressure of 120 kg / cm. Thus, a magnetic disk was manufactured.

Comparative Example 4 6 parts of oleyl oleate in the undercoat layer coating composition was replaced with cetyl stearate (melting point: 40
° C) was changed to 18 parts, and carbon black having a particle size of 0.35 µm was not used in the magnetic paint component.
The addition amount of carbon black of 02 μm was changed from 1.0 part to 5.0 parts, the addition amount of granular α-alumina was changed from 15 parts to 30 parts, and 5 parts of oleyl oleate was changed to methyl oleate (melting point A magnetic disk was manufactured in the same manner as in Example 1, except that the temperature was changed to 8 parts at 20 ° C.). A magnetic disk was manufactured in the same manner as in Example 1.

Comparative Example 5 The amount of oleyl oleate was changed from 6 parts to 0.5 part and the amount of n-butyl stearate was changed from 2 parts to 1 part in the undercoat layer coating composition. At the same time, the magnetic powder in the magnetic paint component was replaced with a ferromagnetic Fe—Ni alloy powder (pH: 11, major axis length: 0.25 μm).
m, Hc: 1550 Oe, BET specific surface area: 55 m ² /
g, σs: 120 emu / g) In the same manner as in Example 1 except that the amount of oleyl oleate was changed from 5 parts to 0.5 part and myristic acid was not added, while changing to 100 parts. Thus, a magnetic disk was manufactured.

For each of the magnetic disks of Examples 1 to 7 and Comparative Examples 1 to 5, the wear volume of the steel ball of the magnetic layer was measured by the method described in the text. In measuring the steel ball wear volume, a drive (LKM-F434-1) manufactured by Matsushita Hisashi Electronics Co., Ltd. (a 3.5 inch cartridge was used) was used as a drive. These results were as shown in Table 1.

[0094]

[Table 1]

Next, for each of the magnetic disks of Examples 1 to 7 and Comparative Examples 1 to 5, the reproduction output, S / N
The ratio, resolution, temperature cycle durability and seek durability were measured by the following methods. These results are shown in Table 2.
The results were as shown in FIG.

<Reproduction Output> Spindle motor SPU-MUX158GV3 manufactured by NTN Corporation for disk rotation and precision stage MM-40XY, M manufactured by Chuo Seiki for head position adjustment
A MIG type head having a track width of 8 μm and a gap length of 0.3 μm was attached to an electromagnetic conversion characteristic evaluation device composed of M-40Z, MM-40GU and MM-40GL, a rotation speed of 1,000 rpm, a recording frequency of 7,215 kHz and a radius of 35 mm. After recording at the position (recording wavelength 1μ
m), the peak-to-peak value of the output of the reproduction amplifier is changed to an oscilloscope 54504 manufactured by Hewlett-Packard Co., Ltd.
A. The measured value was 1 for the magnetic disk of Comparative Example 2.
The relative values are shown as 00%. <Resolution> The measured absolute value of the reproduction output is set to the HF output,
The measured absolute value when the recording frequency is set to 1,804 kHz is defined as the LF output. The ratio of the HF output to the LF output (H
F output / LF output) was taken as the resolution. The measured values are shown as relative values with the magnetic disk of Comparative Example 2 taken as 100%. <S / N ratio> The above HF output signal was input to a spectrum analyzer 3588A manufactured by Hewlett-Packard Company, and a spectrum was displayed with a frequency span of 0 to 7 MHz, RBW of 4.6 kHz, and averaging 64 times. At this time, the peak level value (dBm) of 3608 kHz is converted to the signal level S.
And the noise floor level around 2.5 MHz and 4.5
The average value (dBm) of the noise floor level near MHz is measured as the noise level N, and the S / N ratio (dB) = S (dBm) −
Calculated as N (dBm). The measured values are shown as relative values with the magnetic disk of Comparative Example 2 set to 0 dB. <Temperature cycling durability> Using the above-described apparatus for measuring the regenerative output, the battery was continuously run at a radius of 35 mm in a temperature cycle environment of 5 ° C., 20% RH and 50 ° C., 80% RH. The total running time until the value dropped to 85% of the value was examined. <Seek durability> Using the apparatus for measuring the reproduction output described above,
Under an environment of 20 ° C. and 65%, a seek operation is performed in a range of r = 30 to 40 mm at a speed of 10 reciprocations / minute until the output voltage at a position of r = 35 mm drops to 85% of the initial value. I checked the time.

[0097]

[Table 2]

<Temperature Expansion Coefficient> Using a thermal stress strain measuring device manufactured by Seiko Denshi Kogyo, the magnetic disk
After sampling at 60 ° and processing into a width of 4 mm x a length of 20 mm (excluding the chuck grip portion), the load was measured at 4.0 g and the measurement temperature environment was changed from 25 ° C to 60 ° C. Further, the ratio between the maximum value and the minimum value of the thermal expansion coefficient was calculated from the measurement result as a maximum value / minimum value.

<Humidity Expansion Coefficient> Using the above-described measuring apparatus, a magnetic disk was sampled at 360 ° every 5 °, processed into a width of 4 mm × a length of 20 mm (excluding the chuck grip portion), and then loaded with a load of 4.0 g. , Measurement humidity environment 25% RH
From 60% to 60% RH. From the measurement results, the ratio of the maximum value and the minimum value of the humidity expansion coefficient was calculated as the maximum value / minimum value. Table 3 shows the results.

[0100]

[Table 3]

As is clear from Tables 2 and 3, each of the magnetic disks of Examples 1 to 7 of the present invention has a high reproduction output, a high resolution and a high signal-to-noise ratio, and has a high temperature cycle durability and a high shear rate. It also satisfies the ratio of the maximum value to the minimum value due to the anisotropy of the coefficient of thermal expansion or the coefficient of humidity expansion, as well as high electromagnetic conversion characteristics and excellent running durability. You can see that. On the other hand, in each of the magnetic disks of Comparative Examples 1 to 7, the ratio between the maximum value and the minimum value due to the anisotropy of the temperature expansion coefficient and the humidity expansion coefficient was not satisfied, and the electromagnetic conversion characteristics or the running durability were not satisfied. Is clearly inferior to any of the properties.

[0102]

As described above, in the present invention, the undercoat layer is provided between the nonmagnetic support and the magnetic layer, and a specific ferromagnetic iron-based alloy powder is used as the magnetic powder. The thickness of the magnetic layer, the particle size of the carbon black contained in the magnetic layer, and the wear volume of the steel ball of the magnetic layer are specified, and the minimum and maximum values of the thermal expansion coefficient or the humidity expansion coefficient of the magnetic disk manufactured in this manner are determined. By specifying the ratio of
To provide a high-density magnetic disk having high electromagnetic conversion characteristics and excellent running durability, particularly satisfactory seek durability and temperature cycle durability, particularly a high-density magnetic disk having a high track density and a high linear recording density. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an apparatus for measuring a steel ball wear volume of a magnetic layer.

[Explanation of symbols]

 1 Drive 2 Lower Carriage 3 Steel Ball 4 Balance 5 Metal Plate

 ──────────────────────────────────────────────────の Continued on the front page (72) Kazuhiko Nagiri, 1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Teruhisa Miyata 1-188 Ushitora, Ibaraki City, Osaka Prefecture F-term in Hitachi Maxell, Ltd. (reference) 5D006 BA05 BA08 BA09 BA10 BA11 BA19 CA01 CB07 DA02 FA02 FA09

Claims (20)

[Claims] At least an undercoat layer and a magnetic layer are formed in this order on a nonmagnetic support, and the thickness of the magnetic layer is 0.2 μm.
m or less, the magnetic powder contained in the magnetic layer has a major axis length (L) of 0.1
5 μm or less, made of a ferromagnetic iron-based alloy powder containing Co and a rare earth element that satisfies L / λ ≦ １ ／, the relationship between the long axis length (L) and the shortest recording wavelength (λ), and is included in the magnetic layer. The particle size of the carbon black is equal to or larger than the thickness of the magnetic layer, and the relationship between the minimum value and the maximum value of the coefficient of thermal expansion of the magnetic recording disk comprising them satisfies the maximum value / minimum value ≦ 2.0 and further has a servo signal. A magnetic disk characterized by the above-mentioned. 2. The ferromagnetic iron-based alloy powder containing Co and a rare earth element has a Co / Fe weight ratio of 0.1 to 0.5 and a rare earth element / Fe weight ratio of 0.01 to 0.1. Certain claim 1
The magnetic disk as described. 3. A ferromagnetic iron-based alloy powder containing Co and a rare earth element contains aluminum oxide as another material.
2. The magnetic disk according to claim 1, wherein the weight ratio of Fe / Fe is 0.001 to 0.06. 4. The magnetic disk according to claim 1, wherein the ferromagnetic iron-based alloy powder containing Co and the rare earth element has a pH of less than 10. 5. The magnetic disk according to claim 1, wherein the amount of the lubricant extracted from the magnetic layer and the undercoat layer with n-hexane is 30 mg / cm ³ or more. 6. The lubricant extracted from the magnetic layer and the undercoat layer with n-hexane contains a fatty acid having 10 or more carbon atoms and a fatty acid ester having a melting point of 35 ° C. or less, and the extraction weight ratio of both components is 0%. 2. The magnetic disk according to claim 1, wherein the ratio is from 3 / 99.7 to 10/90. 7. The magnetic disk according to claim 1, wherein the binder contained in the undercoat layer and the binder contained in the magnetic layer are made of the same resin. 8. The magnetic disk according to claim 1, wherein the binder contained in the undercoat layer and the binder contained in the magnetic layer have the same kind of functional groups. 9. The steel ball wear volume of the magnetic layer is 0.5 × 10 ^−4.
2. The magnetic disk according to claim 1, wherein the thickness is from 5.0 * 10 < ^-4 > mm < ³ >. 10. The non-magnetic support has a heat shrinkage of 1.5% or less in the vertical direction and 1.0% or less in the horizontal direction after being heat-treated at 105 ° C. for 30 minutes and allowed to cool. The magnetic disk as described. 11. At least an undercoat layer and a magnetic layer are formed in this order on a nonmagnetic support, and the thickness of the magnetic layer is 0.2
μm or less, the magnetic powder contained in the magnetic layer has a long axis length (L) of 0.
It is composed of a ferromagnetic iron-based alloy powder containing Co and a rare earth element having a relationship between the long axis length (L) and the shortest recording wavelength (λ) that satisfies L / λ ≦ １ ／, and is contained in the magnetic layer. The particle size of the carbon black is equal to or greater than the thickness of the magnetic layer, the relationship between the minimum value and the maximum value of the humidity expansion coefficient of the magnetic recording disk made of these satisfies the maximum value / minimum value ≦ 2.0, and the servo signal A magnetic disk comprising: 12. The ferromagnetic iron-based alloy powder containing Co and a rare earth element has a Co / Fe weight ratio of 0.1 to 0.5 and a rare earth element / Fe weight ratio of 0.01 to 0.1. The magnetic disk according to claim 11. 13. A ferromagnetic iron-based alloy powder containing Co and a rare earth element contains aluminum oxide as an additional component.
12. The magnetic disk according to claim 11, wherein the weight ratio of 1 / Fe is 0.001 to 0.06. 14. The magnetic disk according to claim 11, wherein the ferromagnetic iron-based alloy powder containing Co and the rare earth element has a pH of less than 10. 15. The magnetic disk according to claim 11, wherein the amount of the lubricant extracted with n-hexane from the magnetic layer and the undercoat layer is 30 mg / cm ³ or more. 16. The lubricant extracted from the magnetic layer and the undercoat layer with n-hexane contains a fatty acid having 10 or more carbon atoms and a fatty acid ester having a melting point of 35 ° C. or less, and the extraction weight ratio of both components is 0%. The magnetic disk according to claim 11, wherein the ratio is from 3 / 99.7 to 10/90. 17. The magnetic disk according to claim 11, wherein the binder contained in the undercoat layer and the binder contained in the magnetic layer are made of the same resin. 18. The binder according to claim 11, wherein the binder contained in the undercoat layer and the binder contained in the magnetic layer have the same kind of functional group.
The magnetic disk as described. 19. The steel ball wear volume of the magnetic layer is 0.5 × 10
^-4 to 5.0 × 10 ^- magnetic disk according to claim 11, wherein a ⁴ mm ^3. 20. The nonmagnetic support has a heat shrinkage of 1.5% in the longitudinal direction after being heat-treated at 105 ° C. for 30 minutes and allowed to cool.
The magnetic disk according to claim 11, wherein the magnetic disk content is 1.0% or less in the horizontal direction.