JP2001331931A - Floppy disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferromagnetic metallic thin film type floppy disk which has high running durability and in which generation of thermal asperity is suppressed. SOLUTION: In the magnetic recording medium with a magnetic layer consisting of a ferromagnetic metal thin film with fine projections on the surface on at least one face of a nonmagnetic substrate and a carbon protective layer and a lubricant on the magnetic layer, the area of projections of the height of >=15 nm from a reference surface determined by measuring the surface of the magnetic layer with an atomic force microscope is <=10 times the area of projections of the height of >=30 nm from the reference surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a floppy disk type magnetic recording medium having a ferromagnetic thin film having a high areal recording density.

[0002]

2. Description of the Related Art In recent years, demands for storing high-capacity data such as image data have been increasing year by year, and demands for higher recording densities have been increasing year by year. A tape type magnetic recording medium using a ferromagnetic metal thin film produced by a recording layer as a recording layer and a magnetic recording medium having a ferromagnetic metal thin film formed on a rigid base material have been put to practical use. In such a magnetic recording medium, high magnetic energy can be easily obtained, and smooth surface properties can be easily achieved by smoothing the surface of the non-magnetic substrate. Because of its characteristics, it is suitable for high-density recording materials.

On the other hand, floppy disk type magnetic recording media have been widely used mainly in the 2HD class because of their excellent impact resistance and low cost, but more recently Zip (Zip) using thin layer coating technology has been used. Iomega), HiFD
High-density magnetic recording media represented by (Sony Corporation) have also been put to practical use. These floppy disk systems rotate at a high speed of about 3000 rpm to perform recording and reproduction, and achieve a transfer speed comparable to that of a hard disk. However, the recording density is still less than 1/20 that of a hard disk. This is because floppy disks such as hard disks having a ferromagnetic metal thin film in the magnetic layer have not yet been put to practical use, and the use of MR heads composed of magnetoresistive elements effective for improving the recording density has A major factor is the technical difficulty with disks. There are various reasons for this. One of the reasons is that it is difficult to secure sufficient running durability and obtain practical reliability with a floppy disk having a ferromagnetic metal thin film.

[0004] The reason that it is more difficult to secure the durability of a floppy disk having a ferromagnetic metal thin film produced by a sputtering method than to a floppy disk produced by a coating method is that a floppy disk produced by a coating method is used. Magnetic particles whose magnetic film is wrapped with an organic binder,
It is excellent in wear resistance, impact resistance and lubricity due to inorganic particles etc., the outermost layer is an organic binder, there are voids between the particles, the lubricant is contained in the magnetic film, etc. On the other hand, in the case of a floppy disk manufactured by the sputtering method, the magnetic film is a metal thin film that is easily worn.

Therefore, studies have been made to improve running durability by providing a solid protective layer on a magnetic film as in a hard disk. Among them, it is known that carbon films have excellent durability. However, merely providing a carbon protective film similar to a hard disk on a floppy disk has the effect of improving running durability, but does not always provide sufficient practical reliability.

[0006] Regarding a lubricant, the running durability of a floppy disk having a ferromagnetic metal thin film cannot be sufficiently improved.

There are various reasons why it is difficult to use an MR head. One of the biggest reasons is the generation of so-called thermal asperity, which occurs when the disk and the MR head come into contact with each other. It is not kept as low as a hard disk. Thermal asperity is a phenomenon in which the temperature of the MR element changes due to the influence of frictional heat or the like generated when the disk and the head come into contact, and the output of the reproducing head varies regardless of the magnetic signal.
The output of this thermal asperity may reach several times the reproduction output of the magnetic recording signal. In such a case, saturation of the head amplifier is caused, signal cannot be read, and a reading error occurs.

In the case of a hard disk, when the number of revolutions of the disk is increased, the head floats due to the effect of a floating force acting on the head, and the head is used in a state where the hard disk does not come into contact with the disk. Even if the number of rotations of the disk is increased, the vibration of the disk (runout) is large, so that the head cannot float stably, and the head frequently comes into contact with the floppy disk even during high-speed rotation. This is a very serious problem in obtaining sufficient running durability and in using the MR head.

Therefore, in order to obtain sufficient running durability with a floppy disk having a ferromagnetic metal thin film and enable use of an MR head, it is necessary to: 1. Lubricating film with excellent lubricity 2. A protective film with excellent wear resistance. 3. Low runout to reduce the frequency of contact. 4. A controlled surface hardness that does not cause peeling or destruction even when the head and disk contact. 5. In addition to the conventionally required requirements such as controlled surface roughness for reducing the frequency of contact between the head and the disk, A controlled surface profile is required to minimize the friction that occurs when the head and disk come into contact.
In particular, unlike a hard disk which is basically supposed to run in a non-contact state, a medium design is required in consideration of the contact between the head and the disk during running.

[0010] The surface roughness, especially the height and density of the surface projections, as well as the shape and area, have been studied in the field of hard disks provided with textures and bumps.
For example, Japanese Unexamined Patent Publication No. 7-296375 discloses that the base angle of a cone having a base area equal to the cross section 16 angstroms below the apex of the projection is 0.60 to 1.40.
° has been proposed.
The publication proposes that the average value of the area of the figure 1 nm below the vertex of the protrusion be 2 μm ² or less. However, these are related to the shape of bumps etc. related to the improvement of characteristics at the time of CSS (contact start / stop).
The shape of the fine protrusions on the surface of the magnetic recording medium having the ferromagnetic metal thin film is not an appropriate shape. Also, Japanese Patent Application Laid-Open
Japanese Patent Laid-Open No. 0-302238 discloses a description of the height and area of a protrusion of a head-side slider. Optimization of the surface shape is being studied not only for a magnetic recording medium but also for a mechanical component.

Regarding the surface of a magnetic recording medium, see
JP-A-195217 discloses a load ratio (bearing ratio) of 3 to 60 below 45 nm from the apex of a projection.
% And a contact area of 5 mm ² or more have been proposed, and JP-A-11-232634 discloses that the measurement area is S
It is described that the interval between the height at which the cross-sectional area is 0.8S and the height at which the cross-sectional area is 0.2S is 5 to 8 nm. However, even with these conventional techniques, it has not been possible to realize a floppy disk having a ferromagnetic metal thin film satisfying the problems of securing sufficient running durability and using an MR head.

[0012]

SUMMARY OF THE INVENTION The present invention suppresses the occurrence of thermal asperity in a magnetic recording system having sufficient running durability and using a MR head to greatly improve the recording density. An object of the present invention is to provide a ferromagnetic metal thin film type floppy disk which has achieved sufficient practical reliability.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic layer comprising a ferromagnetic metal thin film having fine protrusions on at least one surface of a non-magnetic substrate, a carbon protective layer and a lubricant on the magnetic layer. When the surface of the magnetic recording medium is measured by an atomic force microscope (AFM), the surface where the volume of the convex portion and the volume of the concave portion are equal is set as a reference surface, and 15 n from the reference surface.
The problem can be solved by a floppy disk in which the protrusion area of m or more is 10 times or less the protrusion area of 30 nm or more from the reference plane. Moreover, said the number of projections of more than 15nm from a reference plane obtained by measuring the surface with AFM following 300 in 900 .mu.m ^2, and projection area of more than 15nm from the reference plane is 1 to 7 [mu] m ² during 900 .mu.m ² This is achieved by a magnetic recording medium.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method for recording / reproducing information on / from a magnetic recording medium using an MR head by making the surface of a floppy disk a specific surface property.
This makes it possible to run with stability and sufficient durability. The floppy disk of the present invention will be described. The floppy disk is obtained by laminating an undercoat film, a base film, a ferromagnetic metal thin film, a protective film, and a lubricating film on at least one surface of a flexible support. With regard to the minute projections provided on the floppy disk surface, the height will be considered on the assumption that the number of projections is the same.

When the height of the projections increases, the spacing loss between the recording / reproducing head and the medium increases and the electromagnetic conversion characteristics deteriorate. When the height of the projections decreases, the electromagnetic conversion characteristics are advantageous, but the sliding characteristics are improved. And jumping of the head and thermal asperity are easily generated. Therefore, a height that achieves both electromagnetic conversion characteristics and sliding characteristics is required. Further, it is preferable that the surface projections have no specifically high projections, and it is particularly preferable that the heights are uniform.
If there is a wide distribution of protrusion heights or locally high protrusions, only the tall protrusions will come into contact, resulting in deterioration of service life due to local wear and thermal asperity when using an MR head. Will occur.

When the number of microprojections is increased by adding a large amount of filler particles to increase the number of projections, the number of high projections due to an increase in agglomerated particles increases and the electromagnetic conversion characteristics deteriorate. When the number of projections is small, the effect of improving the sliding characteristics is reduced by simply reducing the amount of filler particles added, and head jumps and thermal asperity are likely to occur. If you are in a state where you can maintain enough, you can achieve that purpose.

It is considered that the sliding characteristics are improved by reducing the contact area between the disk and the head. That is, a protrusion on the disk surface is provided, and the disk is brought into contact with the head at a certain contact surface. At this time, if the area of the contact surface is too small, the force concentrates on the contact surface, and it is considered that the abrasion of the protrusion is likely to be promoted. Therefore, it is necessary to disperse the force applied to each projection when it comes into contact with the head. For that purpose, the purpose is achieved by increasing the surface area of the contacted projections, for example, by increasing the number of projections and dispersing the force, thereby dispersing the force, that is, by reducing the pressure at the time of contact. Is thought to be
It is important not only to set the number and height of the projections in a certain range but also to increase the surface area. Of course, in order to maintain the sliding characteristics and not to increase the thermal asperity when using the MR head, the contact area cannot be increased without limit, but the durability, the sliding characteristics, and the MR head It is presumed that there is an optimum projection area range for the magnetic recording medium having the ferromagnetic metal thin film that can satisfy the suitability.

Regarding the surface projections, not only the number, height and area, but also the shape are important. Comparing a conical projection with a hemispherical projection in terms of a model, it is thought that the conical projection has a sharp tip, so a large force is applied at the time of contact, and wear is easily promoted, and as a result, the tip is rounded. . Further, the head that has advanced from the lateral direction to the projection has a large impact when hitting the side surface, and is susceptible to damage such as cracking or breakage. In addition, there is a possibility that secondary abrasion or destruction such as abrasion due to broken fragments may be caused. On the other hand, a hemispherical projection is close to a flat surface when viewed in the vicinity of the tip, is advantageous for abrasion when compared to the tip of a cone, and has an impact on contact with a head that has advanced from the side. It is thought that it is easy to escape in the tangential direction of the spherical surface. Therefore, as the shape of the surface projection,
For example, it is considered that a hemispherical shape is more preferable than a shape such as a cone having a tapered and pointed tip.

As a characteristic of this shape, there is a change in the surface area in the height direction. The conical protrusion has a larger reduction rate of the surface area at a higher portion than the hemispherical protrusion. This can also be confirmed by calculating the surface area by integrating a cone and a hemisphere of the same height using a model function. For actual projections, certain heights a and b (a <b) are set, and the difference between the projection area at a height of a or more and the projection area at a height of b or more corresponds to the decrease in surface area. The larger the rate of decrease of this protrusion area,
This indicates a so-called sharp projection.

The number, height and surface area of the projections can be measured by an atomic force microscope. The projections are formed by applying fine particles to any of the support, the undercoat film, the magnetic film, and the protective film. At this time, the particle size of the fine particles, the amount added, the solvent composition, the dispersion conditions and the like are provided by optimizing, but in the present invention, the means for adjusting the surface projections is not limited to the above-described method, and is conventionally known. Means, such as texturing, can also be used.

With respect to the shape other than the minute projections on the surface, in order to achieve stable running as a floppy disk device, the disk runout should be 100 μm or less, preferably 50 μm or less when the head is not in contact with the floppy disk surface. There is a need to. Since this runout is mainly due to the static deformation of the floppy disk,
A floppy disk with a small curl is required, and the static curl amount is preferably 1 mm or less.

A material constituting a magnetic recording medium having the above features, having sufficient running durability, satisfying electromagnetic conversion characteristics, and suppressing the occurrence of thermal asperity when an MR head is used. Examples include the following.

The non-magnetic substrate includes a flexible substrate, and preferably includes a polymer substrate. Examples of the polymer substrate include polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide imide, and polybenzoxazole. Among them, preferred are polyimide and polyamide.
The thickness of these polymer substrates is usually 20 to 200 μm,
Preferably it is 30 to 90 μm. Generally, the thickness of the substrate is 30 to 50 μm when the disk diameter is relatively small such as 1.8 type, and 50 to 90 μm when the disk diameter is relatively large such as 3.5 type. The amount of curl also depends on the size of the disc, for example, 3.5
In the case of a type floppy disk, it is 2 mm or less, preferably 1 mm. In order to ensure high electromagnetic conversion characteristics, the surface roughness of the magnetic film surface is preferably 2 nm or less in Ra, and the maximum surface roughness Rmax is preferably 60 nm or less.

When the surface property of the magnetic film surface of the polyimide film or the polyamide film is not as smooth as that of a film such as polyethylene terephthalate or polyethylene naphthalate, an undercoat film for the purpose of smoothing is first prepared on the magnetic film surface of the film. May be. The thickness of the undercoat film is preferably 0.1 to 3 μm.

As the undercoating agent that can be used for the undercoating layer, a general undercoating agent such as polyester can be used. However, from the viewpoint of surface hardness, thermosetting resins and thermoplastic resins such as polyamide, polyimide, polyamideimide, and polysiloxane are used. preferable. The thermosetting resin can be prepared, for example, by applying a monomer having a terminal group capable of polymerizing with an imide structure in a molecule of a thermosetting imide resin, and polymerizing by heating to form a polyimide structure. Such compounds are disclosed in JP-A-59-80662 and JP-A-60-17886.
No. 2, JP-A-61-18761, JP-A-63
Known compounds synthesized by a known synthesis method described in JP-A-170358, JP-A-7-53516 and the like can be used. Such compounds are obtained from Maruzen Petrochemical's BANI series and ANI series. It is commercially available as Alternatively, a thermosetting silicone resin may be used by a method of applying a monomer containing a silane coupling agent having an epoxy group, followed by thermosetting.

On the thus obtained smooth non-magnetic support, undercoat film, magnetic film, or protective film,
It is preferable to provide fine projections having a uniform height and a low level, for example, by applying fine particles of SiO ₂ , Al ₂ O ₃ , TiO _2, or the like or an organic substance on a substrate or an undercoat layer together with the above resin binder. Protrusions can be provided.
Of these, a nonmagnetic support or an undercoat film is preferred.

As a method of producing such a fine projection structure, a method of applying spherical silica particles dispersed in a solvent, a method of forming an organic substance projection by applying an emulsion, and the like can be used. Silica particles are preferred to achieve a uniform particle size. Further, it is also possible to use a binder for adjusting the height and the shape in order to fix the projection to the surface. It is particularly preferable to use a thermosetting imide or a thermosetting silicone resin as such a material. The microprojections have a height from the reference plane of 1 when measured with an atomic force microscope (AFM) on the disk surface.
Although the number of protrusions of 5 nm or more is in a range of 300 or less per 900 μm ² , in order to form such protrusions, it is necessary to determine the particle size in consideration of the thickness of a magnetic film or a protective film formed thereon. is there. When a general underlayer, magnetic film, or protective film is formed, the particles are spherical particles of about 5 nm to 50 nm, and the density is 0.1 to 100 particles / μm ² , preferably 1 to 30 particles / μm ² . .

If the height of the fine projections is too high, the electromagnetic conversion characteristics are degraded due to the spacing loss between the recording / reproducing head and the medium. If the height of the fine projections is too low, the effect of improving the sliding characteristics is reduced. If the density of the fine projections is too low, the effect of improving the sliding characteristics is reduced, and if it is too high, the number of high projections increases due to the increase in aggregated particles, and the electromagnetic conversion characteristics deteriorate. The thickness of the coating film of the binder is preferably 20 nm or less. If the binder is too thick, it may adhere (block) to the back surface of the film after drying.

The ferromagnetic metal thin film to be a magnetic layer in the magnetic recording medium of the present invention can be a ferromagnetic metal thin film formed by vacuum film formation, and a film formed by a sputtering method is particularly preferable. . As the composition, an alloy mainly containing cobalt or a material obtained by adding a nonmagnetic substance such as silicon oxide to the alloy can be used. Specific examples of the alloy include Co-Cr, Co-Ni-Cr, Co-Cr-Ta, C
o-Cr-Pt, Co-Cr-Ta-Pt, Co-Cr
-Pt-Si, Co-Cr-Pt-B and the like can be used.
In particular, Co-Cr-Pt for improving the electromagnetic conversion characteristics,
Co-Cr-Pt-Ta is preferred. The thickness of the magnetic layer is 1
It is desirable to set it to 0 to 30 nm. Further, in this case, it is preferable to provide a base film for improving the magnetostatic characteristics of the magnetic film, and a known metal or alloy can be used as the composition of the base film. Specifically, Cr, V, Ti, T
a, W, Si and the like or alloys thereof can be used, and among them, Cr, Cr-Ti, and Cr-V are particularly preferable. The thickness of the underlayer is 5 nm to 50 nm, preferably 10 nm to 30 nm. Further, in order to control the crystal orientation of the underlayer, a seed layer may be used under the underlayer. Specifically, Ta, Mo, W, V, Zr, Cr, R
h, Hf, Nb, Mn, Ni, Al, Ru, Ti or an alloy thereof, particularly preferably Ta, Cr, Ti or an alloy thereof, and has a thickness of 15 to 60 nm. When a magnetic film is formed by a sputtering method, the film is preferably formed while the substrate is heated, and the temperature at that time is 20 ° C. to 300 ° C., and more preferably 15 ° C.
0 ° C to 250 ° C.

Further, the ferromagnetic metal thin film may have a multilayer structure for improving the electromagnetic conversion characteristics, a nonmagnetic underlayer, a seed layer for improving the crystallinity of the underlayer, and an intermediate layer thereof. Is also good. As a material for the nonmagnetic underlayer,
Cr, Co alloys, for example, alloys with the following metals, W, T
i, Mo, V, Ta, B, Si, Mo and alloys of Mo and the above elements are preferable. . The film thickness is usually from 5 nm to
The thickness is 500 nm, and particularly preferably 10 nm to 150 nm. However, the thickness of these nonmagnetic underlayers also affects the surface shape, so it is necessary to set the thickness to an optimum thickness.

In the magnetic recording medium of the present invention, a protective film is formed on the ferromagnetic metal thin film in order to improve running durability and corrosion resistance. Examples of the protective film include oxides such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitrides such as titanium nitride, silicon nitride, and boron nitride; carbides such as silicon carbide, chromium carbide, and boron carbide; graphite; Although a protective film made of carbon such as fixed carbon can be used, a hard carbon film called diamond-like carbon (DLC), which hardly causes seizure during sliding and has a stable and stable effect, is preferable.

The method for producing a diamond-like carbon film is CV
D (Chemical Vapor Deposition)
The n) method, for example, a method in which hydrocarbons are decomposed by generating plasma in an atmosphere in which a trace amount of hydrocarbons are present, and deposited on a substrate by applying a bias to the generated active species is effective. . Examples of the hydrocarbon as a raw material include alkanes such as methane, ethane, propane, and butane; alkenes such as ethylene and propylene; and alkynes such as acetylene. Among them, ethylene, methane, and ethane are preferable. It is preferable to introduce a rare gas such as argon, xenon, or helium as a carrier gas at the same time as the hydrocarbon gas.

As a method for generating plasma, a method using RF, a method using ECR, a method using a hot filament, and the like can be used. At this time, the magnetic layer on the film formation side is preferably -200 to -700 V, more preferably -40.
By forming a carbon film while applying a voltage of 0 to -600 V, a dense and high-hardness diamond-like carbon film can be produced.

The surface of the magnetic layer on which the protective layer is provided can be etched in advance by a reverse sputtering method or the like. In the etching, it is preferable to reduce the amount of the surface of the magnetic layer that is easily decomposed or separated by plasma.
As a gas used for etching, it is preferable to use an inert gas such as Ar or a reactive gas such as H ₂ or O ₂ .
Further, a silicon intermediate layer or the like can be formed on the surface of the magnetic film.

The structure of the diamond-like carbon film in the carbon protective layer obtained as described above is not particularly limited, but microscopically, clusters formed by SP ² bonds (graphite structure) and SP ³ bonds (graphite structure). (Diamond structure). The hardness of this diamond-like carbon film is 1000 kg in Vickers hardness.
/ Mm ² or more, preferably 2000 kg / m ² or more. When a diamond-like carbon film is measured by Raman spectroscopy, the so-called G (Gr) around 1550 cm ^-1 is measured.
aphite) main peak, called peak, 13
A broad left-right asymmetric peak consisting of a shoulder-like peak called a so-called D (Dis-order) peak near 90 cm ^-1 is obtained.

In order to modify the diamond-like carbon film, nitrogen or hydrogen can be introduced into the plasma. For example, when hydrogen is introduced, the etching effect during film formation is increased, so that a diamond-like carbon film having high hardness can be obtained. In addition, by introducing nitrogen gas into the reaction gas, nitrogen is contained in the protective film, whereby the coefficient of friction of the film can be reduced. In the case of a diamond-like carbon film containing nitrogen, when measured by the aforementioned Raman spectroscopy, 2
A peak of C≡N bond is found around 220 cm ^−1, and Kineti is measured by X-ray photoelectron spectroscopy (XPS).
An N1s peak is observed when c Energy is around 400 eV. When the thickness of the carbon protective layer is large, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is reduced, and when the thickness is small, the wear resistance is insufficient. Especially preferably, it is 5 to 20 nm. Also,
The adhesion with the lubricant provided on the carbon protective layer is further improved. For the purpose, the surface of the carbon protective layer may be treated with an oxidizing or inert gas.

In the magnetic recording medium of the present invention, it is preferable to form a lubricating film on the protective film in order to improve running durability and corrosion resistance. As the lubricant, a hydrocarbon-based lubricant, a fluorine-based lubricant, an extreme pressure additive and the like can be used. Examples of the hydrocarbon-based lubricant include carboxylic acids such as stearic acid and oleic acid, esters such as butyl stearate, sulfonic acids such as octadecylsulfonic acid, phosphoric esters such as monooctadecyl phosphate, stearyl alcohol, oleyl alcohol and the like. Alcohols, carboxylic acid amides such as stearic acid amide, and amines such as stearylamine.

Examples of the fluorine-based lubricant include lubricants in which part or all of the alkyl group of the hydrocarbon-based lubricant is replaced with a fluoroalkyl group or a perfluoropolyether group. 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. Further, a compound having a phosphazene ring into which a fluorine or fluorinated alkyl group is introduced can be used as a lubricant because it is thermally and chemically stable.

Examples of extreme pressure additives include phosphates such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphates 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 protective film, 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 the like, or is attached by a vacuum evaporation method. Good. The amount of lubricant to be applied is 1 to
30 mg / m ² is preferable, and 2 to 20 mg / m ² is particularly preferable.

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

When the magnetic recording medium of the present invention is used as a floppy disk, it is used with the disk incorporated in a shell. The shell is very important not only for preventing the attachment of dirt from the outside, but also for ensuring the rotational stability of the floppy disk. Further, it is preferable that a liner is provided on a surface of the shell that contacts the disk. The liner has the effect of removing dust from the surface of the floppy disk for cleaning, and also has the function of preventing adhesion of the floppy disk to the shell of the present invention. As the liner, a non-woven fabric containing polyester fibers and acrylic fibers, mainly cellulose fibers such as rayon fibers, polynosic fibers, cupra fibers, and acetate fibers can be used. In addition, the liner may contain rust inhibitors, lubricants, antistatic agents, fungicides, etc., which are applied to the surface of the floppy disk during use of the floppy disk, so that the floppy disk can be used for a long period of time can do.

[0042]

The present invention will be described below with reference to examples and comparative examples of the present invention. Example 1 A thermosetting imide resin (BANI-NB manufactured by Maruzen Petrochemical Co., Ltd.) was coated on both sides of a polyimide film having a maximum projection roughness of 200 nm and a thickness of 75 μm on both sides with isopropanol: ethanol: cyclohexanone (1: 1: 2 weight ratio). The solution dissolved in the mixed solvent was filtered through a membrane filter having a pore size of 0.1 μm, and then applied by a dip coating method.
Heating was performed at 0 ° C. for 12 hours to prepare an undercoat film having a thickness of 1.7 μm. On top of this, an organosilica sol having a particle size of 18 nm is dispersed in cyclohexanone so as to have a concentration of 0.15% by weight, and further a binder (thermosetting imide resin: manufactured by Maruzen Petrochemical Co., Ltd.) having a concentration of 0.75% by weight. BAN
The solution prepared by adding I-NB) was applied by a dip coating method, and then dried at 250 ° C. for 1 hour to prepare a support having fine projections formed on the surface. The particle size was measured with a scanning electron microscope, and the average value of 20 particles was obtained.

Next, this support was placed in a sputtering apparatus for forming a magnetic film while being sandwiched between holders, and the support was heated to 200 ° C., and then Cr—Ti, Ta, Cr—Ti was formed by DC magnetron sputtering. Underlayers were formed to a thickness of 30 nm, 20 nm, and 60 nm, respectively, and subsequently a Co—Cr—Pt magnetic film was formed to a thickness of 25 nm. The base film and the magnetic film were formed on both sides of the support. Further, after the surface of the magnetic film was cleaned by argon glow discharge, a bias voltage of -500 V was applied to the magnetic film, and a substrate bias voltage was further applied thereto by RF plasma CVD using ethylene 150 ccm and argon 150 ccm as source gases. -500V, RF
Under the condition of an output of 500 W, a diamond-like carbon protective film having a thickness of 20 nm was formed.

Next, the sample was taken out of the holder, and a phosphazene ring compound (X-1 manufactured by Dow Chemical Co.) in which a perfluoropolyether-based lubricant (FOMBLIN Z-DOL manufactured by Ausimont) and fluorine were introduced on the protective film.
P) with a fluorinated solvent (HFE-72 manufactured by Sumitomo 3M Limited)
00) (composition 9: 1) with a pore size of 0.1 μm
After filtration through a filter having a thickness of 1 m, the resultant was applied by a dip coating method to form a lubricating film having a thickness of 1 nm. Then, the number of surface protrusions, the height, and the area were evaluated by cutting out this sample. Further, this sample was punched into a 3.7-type magnetic disk shape, incorporated into a shell provided with a liner made of rayon fiber to produce a floppy disk, and a running durability test and an MR head test were performed.

Example 2 A device was produced in the same manner as in Example 1 except that the binder concentration when providing the fine projections was 0.5% by weight.

Example 3 The procedure of Example 2 was repeated, except that the particle size of the organosilica sol used for forming the fine projections was changed to 25 nm.

Example 4 In the same manner as in Example 2, except that the concentration of the organosilica sol used for providing the fine projections was 0.3% by weight and the fine projections were formed without adding a binder. Prepared.

Example 5 A device was produced in the same manner as in Example 1 except that the binder concentration when providing the fine projections was 1.5% by weight.

Example 6 Example 1 was the same as Example 1 except that the dispersion solvent of the organosilica sol was changed from cyclohexanone to isopropyl alcohol when forming the fine projections, and the fine projections were formed without adding a binder. Prepared.

Example 7 In Example 1, the undercoat layer was not provided, and when the fine protrusions were provided, the particle size of the organosilica sol was 12 nm.
It was produced in the same manner as in Example 1 except that the concentration was 0.5% by weight and the binder concentration was 0.5% by weight.

Example 8 In the same manner as in Example 1, except that the concentration of the organosilica sol used for providing the fine projections was 1.5% by weight, and the fine projections were produced without adding a binder. Prepared.

Comparative Example 1 The procedure of Example 1 was repeated, except that the particle size of the organosilica sol used for forming the fine projections was 25 nm and the binder concentration was 1.0% by weight.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the binder concentration when providing the fine projections was changed to 1.0% by weight.

Comparative Example 3 The same procedure as in Example 1 was carried out except that no fine projections were provided.

(Evaluation Method) Evaluation of protrusion area The prepared floppy disk was 30 μm × 30 μm.
Atomic force microscope (AFM) (DIGI
NANOSCO manufactured by TAL INSTRUMENTS
Scanning was performed in contact mode using PE3). In the detected image from which distortion and noise that are not related to the original surface shape caused by a measurement problem due to the filtering process have been removed, the volume of the convex and concave portions is equal using the roughness analysis command of the same atomic force microscope. Is the reference plane,
The surface area values attributable to the protrusions when sliced at a height of 30 nm and 15 nm from the reference plane were respectively calculated from the reference plane by 30 nm.
The results were shown in Table 1 with the protrusion area being not less than nm and not less than 15 nm. The probe used was a silicon nitride probe, NP type, manufactured by Nanosensors. 2. Evaluation of number of protrusions Similarly to the evaluation of the number of protrusions, an area of 30 μm × 30 μm was scanned by an atomic force microscope, and distortion and noise unrelated to the original surface shape, which were caused by a measurement problem due to filtering, were removed. In the detected image, using the roughness analysis command of the same atomic force microscope, the surface where the volume of the convex portion and the concave portion is equal is used as the reference surface, and the number of peaks when sliced at a height of 15 nm from the reference surface is calculated from the reference surface. Fifteen
The results are shown in Table 1 with the number of protrusions having a height of at least nm.

3. Running Durability Test The disc was inserted into a Zip drive (Zip-100, manufactured by Fuji Photo Film Co., Ltd.), the head was set to run repeatedly on the same track, and a signal having a frequency of 8 MHz was recorded and reproduced. The time required for the reproduced output to reach the initial -3 dB was measured, and the results are shown in Table 1. The measurement environment was 25 ° C. and RH 50%. 4. Test with MR head Track width: 2.2 μm, head gap: 0.26 μ
A negative pressure slider to which a m MR head was attached was attached to a transverse head arm to produce a pair of head assemblies. The floppy disk was sandwiched so that the head loads above and below the head arm were both 34.3 mN (3.5 gf). The center height of this head arm matches the height of the innermost circumference of the floppy disk,
Adjusted the head load position. In this state, insert 3 disks
Rotate at 600 rpm, use upper head, radius 3
Signal recording and reproduction were performed at a linear recording density of 100 kFCI at a position of 2 mm, and the C / N (signal / noise ratio) was measured.
Next, the head was scanned at intervals of 0.1 mm in a radius of 20 mm to 30 mm where no signal was recorded, and the head output was measured. In the head output, the same voltage as the output value at the time of the C / N measurement is set as a threshold level, and a portion where the output equal to or higher than the threshold level is observed is regarded as thermal asperity, and the number of occurrences is measured. The number is shown in Table 1 as "TA". The environment is 25 ° C,. 50%.

[0057]

Table 1 Durability of 30 nm or more, 15 nm or more, 15 nm or more TA projection area Projection area Number of projections (pieces) (time) Example 1 0.25 2.11 140 194 29 Example 2 0.43 1.26 180 221 11 Example 3 0.89 6.71 220 300 or more 38 Example 4 0.52 3.87 288 300 or more 15 Example 5 0.10 0.97 76 145 22 Example 6 1.08 7.09 198 294 91 Example 7 0.28 1.55 323 156 18 Example 8 2.71 16.99 775 300 or more 131 Comparative Example 1 0.31 3.56 165 116 161 Comparative Example 2 0.08 1.62 138 102 33 Comparative example 3 0.00 0.21 21 10 or less 372 However, Table projection area, the projection area occupied area per 900 .mu.m ² in [mu] m ² did. The number of projections was represented by the number of projections per 900 μm ² .

By using the floppy disk of the present invention, sufficient running durability is ensured, and even when running with an MR head, very little thermal asperity is generated and good results are obtained. You can see that.

[0059]

The present invention has sufficient running durability and suppresses the occurrence of thermal asperity due to collision between a disk and a head which occurs when an MR head is used. A floppy disk having a magnetic metal thin film is obtained.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a ferromagnetic metal thin film having fine projections on at least one surface of a non-magnetic substrate and a carbon protective layer and a lubricant on the magnetic layer. When measured by a force microscope (AFM), the surface where the volume of the convex portion and the concave portion is equal is defined as a reference surface, and the area of the projection 15 nm or more from the reference surface is 10 times or less the area of the projection 30 nm or more from the reference surface. A floppy disk characterized by that: 2. The number of protrusions of 15 nm or more from a reference plane measured by an atomic force microscope is 300/900 μm ^2.
And a protrusion area of 15 nm or more from the reference plane is 90
^2. The floppy disk according to claim 1, wherein 1 to 7 [mu] m < ² > in 0 [mu] m < ² >. 3. A magnetic recording system in which the front and back surfaces of a floppy disk are sandwiched between magnetic head arms each having a slider having an MR head at the end thereof, and the slider is run together with the floppy disk to perform recording and reproduction. Floppy disk.