JPH10143854A - Magnetic recording disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording disk with ferromagnetic metallic thin films as magnetic layers capable of ultrahigh density recording under high- speed rotation and excellent in running durability. SOLUTION: This magnetic recording disk has magnetic layers formed on both sides of the flexible polymer substrate by vacuum film formation, also has a solid protective layer and a lubricant on each of the magnetic layers and performs recording and reproduction at >=3,000r.p.m. rotational frequency. This medium has <=2mm curl and fine protrusions arranged in a direction perpendicular to the direction of the curl exist on the protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrahigh-density floppy disk (F) having a magnetic layer formed of a ferromagnetic metal thin film formed on a flexible polymer support by a vacuum film forming method such as evaporation or sputtering.
D).

[0002]

2. Description of the Related Art In a hard disk (HD), which is one of ultra-high-density magnetic recording disks, about 1 G is obtained by using a ferromagnetic metal thin film formed on a support such as glass or aluminum by a sputtering method as a recording layer. Magnetic recording disks capable of high-density recording have been put to practical use. In order to cope with low-speed rotation, the surface of the disk is roughened, a solid protective layer is provided, and a lubricant is provided to ensure running durability. By separating them, durability is ensured and practical use.

However, in order to further increase the density, the head must be brought into contact with the HD in order to efficiently pick up a minute magnetic signal, and the substrate cannot be largely roughened.
HD has a drawback in that a rigid substrate is used, and damage is likely to occur when a rigid head comes into contact with a smooth surface. That is, durability is a problem, and the above-mentioned practical use is hindered. Have been.

In addition, it is desired that the magnetic recording disk be replaceable, but in this case, the impact increases the chance of strong contact between the head and the medium, and a rigid substrate becomes an obstacle. Also, HD is expensive. On the other hand, since a floppy disk uses a flexible substrate, it has an advantage that damage is less likely to occur upon contact, which is advantageous in terms of durability.
The recording density can be attained by providing a ferromagnetic metal thin film instead of a film coated with magnetic powder. Manufacturing cost is also low.

[0005] In order to put into practical use a ferromagnetic metal thin film type FD which is advantageous in terms of mechanical properties of the substrate, the following studies have been made to ensure durability. One is to provide minute projections on the surface. However, since magnetic recording disks have so-called spacing loss, ultra-high density recording requires
Since the distance between the magnetic layer and the magnetic head must be kept short, the projection for ensuring running durability must be very small. Being small is
This means that the effect of increasing running durability is small. As a result, it was very difficult to solve this problem only by providing minute projections at a level that enables ultrahigh-density recording.

By providing a solid protective layer on a ferromagnetic metal thin film, running durability can be improved. The effect can be more strongly expressed by increasing the thickness. However, this thickness results in space loss and cannot be made too large in high-density recording. For this reason, there is a problem that the running durability of the ultra high density recording FD cannot be improved only by providing the solid protective layer.

Further, the running durability of ultra-high-density recording has not been sufficiently improved even with a lubricant. Furthermore, in order to secure a high transfer rate in an ultra-high-density recording disk, the number of rotations must be increased, which has made it more difficult to ensure durability.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording disk having a ferromagnetic metal thin-film magnetic layer having excellent running durability and capable of performing ultra-high density recording at high speed rotation.

[0009]

That is, the object of the present invention is to
A magnetic layer formed by vacuum film formation on both surfaces of a flexible polymer support, having a solid protective layer and a lubricant on the magnetic layer,
In a magnetic recording disk for a recording system that performs recording and reproduction at a rotation speed of 3000 rpm or more, the magnetic recording disk has a curl amount of 2 mm or less, and has fine projections on the protective layer. And a magnetic recording disk characterized by being arranged in a direction perpendicular to the direction.

The present inventors have made intensive studies and found that FD
Found that, unlike the HD, there was curl, the FD and the head did not float completely even at high speed rotation, and the FD was damaged from the curled portion, resulting in insufficient running durability. This is because if there is curl, FD
It is thought that this is because the contact with the head differs depending on the location, and the FD is damaged from that location in the long-term running durability test.

[0011] In order to eliminate curl, the present inventor first sets
The cause of the curl was examined. As a result, it was found that the largest cause of curling was caused by the step of forming a film while heating the flexible polymer support. this is,
For high-density recording, high output, low noise, and high resolution are required. To achieve this, it is necessary to increase the coercive force Hc of the magnetic layer and magnetically separate the magnetization units.
For this reason, a nonmagnetic element is present together with a ferromagnetic element as a ferromagnetic metal thin film, and the support is heated at the time of film formation to activate the movement of the element at the time of film formation, thereby causing the above-described segregation.

However, as described above, in the FD using a flexible polymer support, this heating results in deformation of the support and curl of the FD. Although an investigation was made to eliminate the curl amount, the curl amount was reduced but did not reach zero at all. Next, we investigated how to avoid damage from the head in the curled part.As a result, we obtained the result that no curling damage was caused by arranging the fine protrusions on the solid protective layer at right angles to the curl direction. This has led to the present invention.

The reason why this effect is not seen when the curl amount exceeds 2 mm is presumed to be that the effect of the curl is so large that the effect of the distribution of the fine projections does not appear. In the present invention, the microprojection means that the surface of the solid protective layer of the FD has an AFM (having a height of usually 1 to 50 nm observed with an atomic force microscope,
The protrusions are preferably 5 to 30 nm, and the bottom of the fine protrusions is preferably circular when viewed from the surface, but may be oval. However, the shape of the minute projection is not particularly limited. Further, the minute projections may be present on wider hill-shaped projections. The hill-shaped protrusion has a height of 50 nm or less, preferably 30 nm or less.

In the present invention, the direction of curl refers to a direction perpendicular to the contact line between the convex portion of the magnetic recording disk and the contact surface and on the contact surface. Here, the convex portion refers to an outer surface when the curl is assumed to be a gutter, and the surface of the water guide portion of the gutter is a concave portion of the magnetic recording disk (see FIG. 1). And that the microprojections are arranged in a direction perpendicular to the direction of the curl means that one arbitrary microprojection is selected and the direction of the curl and the direction perpendicular to the direction of the curl are centered on the microprojection. 15 degrees, ie a range n with a spread of 30 degrees
And p are selected, and in each of the ranges n and p, the 50 closest particles to the optional microprojection are selected, and the distance between each of the 50 closest particles to the optional microprojection in the range p is determined. By arranging the sum Lp of the squares of l _pi so as to always be smaller than the sum Ln of the squares of the distance l _ni in the range n, the following expression is satisfied (FIG. 2).
reference).

[0015]

(Equation 1) In the present invention, a row of microprojections arranged in a direction perpendicular to the direction of curl is hereinafter simply referred to as a “microprojection group in a perpendicular direction”, and a connection line of one array of the microprojections is referred to as Connection line ". In the group of microprojections in the perpendicular direction, the distance Δa between adjacent microprojections is usually
0.01 to 50 μm, preferably 0.05 to 1 μm, and the distance Δb between adjacent perpendicular connection lines is usually
It is 0.01 to 100 μm, preferably 0.1 to 2 μm. Here, the distance between the minute protrusions and the distance between the connection lines in the perpendicular direction refer to the distance between the centers of the minute protrusions (see FIG. 3). In FIG. 3, the minute projections are drawn apart for explanation, but the bottoms of the minute projections may be in contact with each other.

In the present invention, the means for adjusting the distribution of the fine projections on the solid protective layer within the scope of the present invention is not particularly limited. For example, the means for adjusting the surface properties of the flexible polymer support may be used. Is a preferred means. Specific methods for adjusting the surface properties of the flexible polymer support include inorganic powders such as SiO ₂ , Al ₂ O ₃ and TiO ₂ , and organic powders such as JP-A-53-116115. JP-A-59-84927, etc. Preferably, a coating material in which preferably spherical fine particles such as polyethylene described in JP-A-59-84927 are dispersed in a polymer is applied on a flexible polymer support substrate, dried, and then stretched in the width direction. There is a method of performing heat setting.

As the polymer used in the paint, it is preferable to use polyvinyl alcohol, methylcellulose and the like together with silicone. Water and various organic solvents can be used as appropriate as the solvent for the paint. The average particle size of the fine particles is usually 0.001 to 1 μm, preferably 0.1 to 1 μm.
It is in the range of 002 to 0.1 μm. Further, the coating thickness of the coating is preferably adjusted by the average particle size so that the height of the fine projections is in the above range, but usually the dry thickness,
0.001-0.2 μm, 0.01-0.1 μm
Is preferred. The stretching and heat fixing conditions in the width direction are usually stretched at 90 to 150 ° C. about 2 to 5 times,
The heat setting includes performing heat treatment at 180 to 250 ° C.

Here, the coating film provided on the flexible polymer support may be provided continuously over the entire surface or partially discontinuously. In the latter case, a plurality of fine particles of powder such as silica are provided at positions corresponding to the microprojections of the present invention through a polymer coating film of a coating material, preferably 2 to 3.
Three layers may be stacked and formed in a strip shape with a height and a width.

The layer for controlling the surface properties provided on the flexible polymer support is not limited to one layer, but may be several layers. This surface property control layer may be a layer having high heat resistance such as silica or polyimide by a sol-gel method. Examples of the flexible polymer support substrate include polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide imide, and polybenzoxazole. The thickness of these substrates is typically 2
The thickness is 0 to 200 μm, preferably 30 to 90 μm, and the curl amount is 2 mm or less, but preferably 1 mm.

The measurement of the curl amount is as follows (FIG. 4)
reference). After forming a ferromagnetic metal thin film on a flexible polymer support, punching it into a FD having the desired outer and inner diameters, insert the inner periphery into the protrusion, and fix the FD vertically The contact A between one of the parallel vertical surfaces and the most protruding part of the FD and the other vertical surface and F
The distance Δ between the contact portion B and the most retracted portion of D, Δ
C is measured by a micrometer and determined as a curl amount.

As the ferromagnetic metal thin film serving as the magnetic layer in the magnetic recording disk of the present invention, a conventionally known vacuum deposited film or sputtered film can be used. The thickness of the magnetic layer is preferably
It is 10 to 300 nm, particularly preferably 15 to 60 nm. In the magnetic recording disk of the present invention, a nonmagnetic underlayer can be provided below the magnetic layer. The underlayer and the magnetic layer are preferably provided by a vacuum film formation method. In particular, sputtering is preferable because a film can be formed without changing the composition of many elements.

When the magnetic layer is formed by a continuous winding type vacuum evaporation method capable of forming a film at a high speed, the composition may be a conventionally known metal or alloy mainly composed of cobalt.
Specifically, Co, CoNi, CoFe, or the like is deposited in an oxygen atmosphere, and a film containing oxygen can be used. In particular, in order to improve the electromagnetic conversion characteristics, 90% or more, more preferably 95% or more, of the metal atoms constituting the magnetic layer is cobalt Co-O or Co-F containing Co-O.
e and the like are preferable.

When the magnetic layer is formed by a sputtering method, the composition may be a conventionally known metal or alloy mainly composed of cobalt, and specifically, Co-Cr, Co-Ni
-Cr, Co-Cr-Ta, Co-Cr-Pt, Co-
Cr-Ta-Pt, Co-Cr-Pt-Si, Co-C
r-Pt-B or the like can be used. Particularly, Co-Cr-Ta and Co-Cr-Pt are preferable for improving the electromagnetic conversion characteristics.

Further, the ferromagnetic metal thin film may have a multilayer structure to improve electromagnetic conversion characteristics, or may have a nonmagnetic underlayer or an intermediate layer. As a material of the nonmagnetic underlayer, C
r, Cr alloys, for example, alloys with the following metals, W, Ti,
Mo, V, Ta, B, Si, Mo, or an alloy of Mo and the above elements is preferable. The film thickness is usually 5 to 500 n
m, particularly preferably 10 to 150 nm.

In the magnetic recording disk of the present invention, a solid protective layer is provided on the ferromagnetic metal thin film. As the solid protective layer, silica, alumina, titania, zirconia, cobalt oxide, oxides such as nickel oxide, titanium nitride, silicon nitride, nitrides such as boron nitride, silicon carbide, chromium carbide, carbides such as boron carbide, graphite, Examples of the protective layer include carbon such as amorphous carbon.

The protective layer is equivalent to the head material.
Or a hard film having a higher hardness is preferable.
Seizure hardly occurs during sliding, the effect is stable and lasts
Is most preferable, and such a protective layer is hard.
Carbon membrane. The carbon protective layer is made of plasma C
Amorphous produced by VD method, sputtering method, etc.
Graphite, diamond structure, or a mixture of these
Carbon film, particularly preferably
Hard carbon film called diamond-like carbon
It is. This hard carbon film has a Vickers hardness of 1000K.
g / mm ^Two Above, preferably 2000 kg / mm^Two that's all
Is a hard carbon film. Its crystal structure is Amorph
It has a ground structure and is non-conductive. And this application
Raman spectroscopy of diamond-like carbon film structure
1520-1560c as measured by analysis
m^-1Can be confirmed by detecting peaks
it can. Carbon film structure deviates from diamond-like structure
The peak detected by Raman spectroscopy
With the deviation from the range, the hardness of the carbon film also decreases.

This hard carbon protective layer comprises methane, ethane,
Plasma C made from a carbon-containing compound such as an alkane such as propane or butane, an alkene such as ethylene or propylene, or an alkyne such as acetylene.
It can be formed by VD, sputtering in a hydrogen or hydrocarbon atmosphere using carbon as a target, or the like.

The carbon protective layer may contain H, F, N and the like. When the thickness of the hard carbon protective layer is large, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is reduced. When the thickness is small, the abrasion resistance is insufficient.
Is preferably, and particularly preferably 5 to 10 nm. Further, the surface of the hard carbon protective layer may be surface-treated with an oxidizing or inert gas for the purpose of further improving the adhesion with the lubricant provided on the hard carbon protective layer.

In the magnetic recording disk of the present invention, a lubricant is applied in order to improve running durability and corrosion resistance. The lubricant can be applied on the solid protective layer or the magnetic layer. In the present invention, it is preferable to further provide a rust preventive. As the lubricant, known hydrocarbon-based lubricants, fluorine-based lubricants, extreme pressure additives and the like can be used.

As the hydrocarbon-based lubricant, stearic acid,
Carboxylic acids such as oleic acid, esters such as butyl stearate, sulfonic acids such as octadecylsulfonic acid, phosphoric esters such as monooctadecyl phosphate, alcohols such as stearyl alcohol and oleyl alcohol, and carboxylic acids such as stearamide. Examples thereof include acid amides and amines such as stearylamine.

Examples of the fluorine-based lubricant include lubricants in which part or all of the alkyl groups of the hydrocarbon-based lubricant are replaced with fluoroalkyl groups or perfluoropolyether groups. Examples of the perfluoropolyether group include a perfluoromethylene oxide polymer, a perfluoroethylene oxide polymer, a perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , and a perfluoroisopropylene oxide polymer (CF ( CF ₃ )
CF ₂ O) _n or a copolymer thereof.

Examples of extreme pressure additives include phosphoric esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphoric esters such as trilauryl trithiophosphite, and the like. And sulfur-based extreme pressure agents such as dibenzyl sulfide. The above lubricants are used alone or in combination of two or more. As a method of applying these lubricants on the magnetic layer or the solid protective layer, the lubricant is dissolved in an organic solvent and applied by a wire bar method, a gravure method, a spin coating method, a dip coating method, or a vacuum evaporation method. May be attached.

The amount of the lubricant to be applied is 1 to 30 mg / m
² is preferable, and 2 to 20 mg / m ² is particularly preferable.

The rust preventives usable in the present invention include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives having an alkyl side chain introduced into the mother nucleus, benzothiazole, 2-mercapto. Benzothiazole, tetrazaindene ring compound,
Nitrogen- and sulfur-containing heterocycles such as thiouracil compounds and derivatives thereof.

[0035]

Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. Example 1 After coating and drying an emulsion obtained by mixing silica having an average particle diameter of about 12 nm in methylcellulose on both surfaces of polyethylene naphthalate, performing horizontal stretching and heat fixing to form microprojections corresponding to the distribution of the microprojections of the present invention. Have thickness 60μm
Was obtained. The height of the microprojections was the largest and was about 20 nm.

The heat setting is a heat treatment at 180 ° C. for about 10 minutes. This support is cut, fixed to the convex substrate holder by applying tension in the longitudinal direction of the original support, set in a sputtering apparatus, and heated to 150 ° C. in a state of 3 × 10 ^−7. Exhaust to Torr, introduce Ar and sputter Cr-Ti at 3 × 10 ^-3 Torr to form a film with a thickness of 60 nm, and Co-Cr-Pt to form a film with a thickness of 30 nm under the same conditions. Layers. Further, carbon was formed to a thickness of 20 nm to form a solid protective layer.

A sample was taken out from the vacuum condition, set on the substrate holder, and placed on the opposite surface under the same conditions under the same conditions.
A magnetic layer and a protective layer were formed. The sample was taken out of the sputtering apparatus, and a fluoropolyether-based lubricant (FOMBLIN Z-DOL manufactured by Ausimont) was applied on the solid protective layer to form a 2 nm lubricant film.

This was punched out to 3.5 inches to prepare an FD sample. The curl amount was 0.6 mm, and an array of minute protrusions was obtained in a direction perpendicular to the curl direction. Furthermore, while rotating the FD at 3000 rpm using a spin stand, the tripad head is sandwiched from both sides of the FD, and the FD is run while monitoring the output. The number of passes until the output falls below the initial 6 dB is measured. The sex was evaluated. In the environment of 25 ° C., 60%, and 10 million passes, the output hardly changed.

The curl amount was measured by the method described above.
The reason why the FD is held vertically is to eliminate the influence of the attractive force. Example 2 A sample was prepared in the same manner as in Example 1 except that the heat treatment was not performed at 180 ° C. for 10 minutes.

Comparative Example 1 A direction perpendicular to the direction applied after cutting the flexible polymer support in Example 1 (ie, the width direction of the support).
A sample was prepared under the same conditions as in Example 1 except that tension was applied to the sample. Comparative Example 2 A sample was prepared in the same manner as in Example 1 except that a flexible polymer support in which microprojections were uniformly distributed was used.

Comparative Example 3 A sample was prepared in the same manner as in Comparative Example 1 except that the thickness of the underlayer on the opposite surface was changed to 150 nm. Comparative Example 4 A sample was prepared in the same manner as in Example 1 except that the thickness of the underlayer on the opposite surface was changed to 160 nm.

For each of the prepared FDs,
In the same manner as in Example 1, the curl amount, the direction of the arrangement of the fine projections with respect to the curl direction, and the running durability were evaluated. The results are shown in Table 1. Note that, when the direction of the arrangement of the minute projections is parallel to the direction of the curl, it means that Ln <Lp is satisfied in Expression 1, and that the uniformity means that Ln = Lp is satisfied.

[0043]

[Table 1] From the results shown in Table 1, the example in which the curl amount is 2 mm or less and the direction of the arrangement of the fine protrusions is perpendicular to the direction of the curl is extremely high in running durability, but the arrangement of the fine protrusions is small even when the curl amount is 2 mm or less. It can be seen that in the comparative examples in which the directions are parallel or uniform, and in the comparative examples in which the curl amount exceeds 2 mm even when the arrangement is perpendicular, the running durability is extremely inferior to the examples.

[0044]

According to the present invention, there is provided a magnetic recording device comprising a magnetic layer comprising a ferromagnetic metal thin film having a very large recording capacity and excellent running durability, which is an FD using a flexible polymer support having a small size and excellent usability. The disk can be provided by a simple method of adjusting the distribution of microprojections on the surface of the support.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a curl direction defined in the present invention.

FIG. 2 is a diagram illustrating an arrangement of minute projections according to the present invention.

FIG. 3 is a diagram specifically illustrating an arrangement of minute projections according to the present invention.

FIG. 4 is a diagram illustrating a method for measuring a curl amount in the present invention.

Claims (1)

[Claims] 1. A magnetic layer formed by vacuum film formation on both surfaces of a flexible polymer support, a solid protective layer and a lubricant on the magnetic layer, and recording / reproduction is performed at a rotation speed of 3000 rpm or more. In a magnetic recording disk for a recording system to be performed, the magnetic recording disk has a curl amount of 2 mm or less, has fine protrusions on the protective layer, and the fine protrusions are arranged in a direction perpendicular to the direction of the curl. A magnetic recording disk, comprising: