JP2001052326A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve surface strength without degrading the electromagnetic conversion characteristics. SOLUTION: This medium has a nonmagnetic base 1, a magnetic layer 3 which is formed by applying magnetic paint obtained by kneading at least magnetic powder and a binding agent, a hard carbon protection film 4 formed on the magnetic layer 3, and a lubricant layer 5 formed of a lubricant on the hard carbon protection film 4. The magnetic recording medium has a superior surface strength by having the DLC protection film and lubricant layer formed, and its coefficient of friction is reduced. The medium, therefore, has superior wear resistance and electromagnetic conversion characteristics. Thus, the magnetic recording medium is suitable for high-density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium having a magnetic layer formed by applying a magnetic paint.

[0002]

2. Description of the Related Art Magnetic recording media using ferromagnetic powder include not only tape media for audio and video, but also disc-shaped media such as micro-flexible disks and high-density flexible disks. In particular,
2. Description of the Related Art A magnetic disk is used as a magnetic recording medium in computer peripheral devices because of its excellent random access and the like, and high-density recording is being promoted.

In a disk drive for recording / reproducing a magnetic disk such as the above-mentioned micro-flexible disk or high-density flexible disk, for example, a sliding head or a floating head is used as a head.

In a disk drive employing a sliding head, recording and reproduction are performed by sliding the sliding head against the surface of a rotating magnetic disk.
For a single-sided magnetic disk with a magnetic layer formed only on one side, a sliding head is placed on the magnetic layer side and felt-like pads are placed on the back side, sandwiched between both. Recording and reproduction are performed. For a double-sided magnetic disk having a magnetic layer formed on both sides, recording / reproduction is performed while being sandwiched between magnetic disks disposed on both sides of the disk.

In a disk drive employing a flying head, a CSS (Contact Start / S
Recording and reproduction are performed by the (top) method. This C
In the SS system, the floating head is pressed against the surface of the magnetic disk while the rotation of the magnetic disk is stopped. When the magnetic disk starts rotating, the flying head floats with a very small amount (several hundred nm) from the magnetic disk utilizing the air flow generated by the rotation of the magnetic disk, and recording and reproduction are performed in this state. When the magnetic disk stops rotating, the flying head is pressed against the surface of the magnetic disk due to the loss of airflow. This CSS
In the system, high-density recording is achieved by minimizing the distance between the magnetic disk and the flying head.

[0006]

However, when a sliding head is used, the magnetic head is rotated at a high speed for the purpose of high-speed signal transfer. I do. As a result, the surface of the magnetic disk is worn, and there are problems such as deterioration of electromagnetic conversion characteristics and damage of the magnetic disk. When a floating head is used, recording and reproduction are performed by the CSS method. Therefore, when the magnetic disk starts rotating and stops rotating, the floating head slides on the surface of the magnetic disk. Also, in order to achieve high-density recording, the distance between the flying head and the surface of the magnetic disk is extremely small, so that the flying head may come into contact with the magnetic disk during rotation of the magnetic disk. Had the problem of causing wear and damage.

As described above, when the magnetic disk is driven in the disk drive, the head slides and comes into contact with the magnetic disk, causing abrasion and damage of the magnetic disk, thereby deteriorating electromagnetic conversion characteristics and damaging the magnetic disk. There was a problem that occurs.

In order to solve this problem, it is conceivable to improve the surface strength of the magnetic disk by changing the type and amount of the binder in the magnetic paint.

However, in this case, the coating properties of the magnetic coating material may be significantly changed, and the coating properties may be degraded.
Also, as a method for improving the surface strength of the magnetic disk, by adjusting the size and amount of additive particles such as abrasives,
A method of controlling the surface property is conceivable. However, in this case, the magnetic disk has disadvantages such as deterioration of electromagnetic conversion characteristics.

As described above, conventionally, both improvement of the surface strength of the magnetic disk and prevention of deterioration of the electromagnetic conversion characteristics cannot be satisfied.

Accordingly, the present invention has been proposed in view of such a conventional situation, and has as its object to provide a magnetic recording medium having improved surface strength without deteriorating electromagnetic conversion characteristics. I do.

[0012]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention comprises a non-magnetic support, and a magnetic paint obtained by kneading at least a magnetic powder and a binder. And a hard carbon protective film formed on the magnetic layer, and a lubricant layer made of a lubricant on the hard carbon protective film.

In the magnetic recording medium according to the present invention configured as described above, since the hard carbon protective film is provided on the magnetic layer and the lubricant layer is provided on the hard carbon protective film, excellent surface strength is obtained. And a low coefficient of friction is realized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a magnetic recording medium to which the present invention is applied will be described in detail with reference to the drawings.

As shown in FIG. 1, a magnetic disk to which the present invention is applied includes a nonmagnetic support 1, a lower layer 2 on both main surfaces of the nonmagnetic support 1, an upper layer 3 which is a magnetic layer, and a hard disk. Carbon (Diamond Like Carbon: DLC)
The protective film 4 and the lubricant layer 5 formed by applying a lubricant are laminated in this order.

This magnetic disk has a disk shape, and recording and reproduction are performed in a disk drive.

In a magnetic disk drive using a sliding head, recording and reproduction are performed by sliding the sliding head on the surface of the magnetic disk. In a disk drive using a flying head, recording and reproduction are performed by a CSS method in which the flying head floats a very small amount (several hundred nm) on a rotating magnetic disk.

Hereinafter, the lower layer 2, the upper layer 3, the DLC protective film 4, and the lubricant layer 5 formed on one main surface of the nonmagnetic support 1 will be described.

The DLC protective film 4 formed on this magnetic disk is a film in which peaks are observed at positions corresponding to the diamond crystal structure in Raman spectroscopy. It is preferable that the thickness of the DLC protective film 4 is 1 to 20 nm.

The lubricant layer 5 is made of a lubricant and provided on the DLC protective film 4. The lubricant forming the lubricant layer 5 is obtained by mixing a fatty acid and a fatty acid ester and diluting the mixture with a solvent. The dilution ratio of the fatty acid and the fatty acid ester with the solvent is preferably 10 to 100 times.

The fatty acids used in the lubricant layer 5 include:
It may be a monobasic acid or a dibasic acid. The fatty acid preferably has 6 to 30 carbon atoms, and particularly preferably 12 to 22 carbon atoms. As specific fatty acids, lauric acid,
Myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, and the like.

Specific examples of the fatty acid ester used for the lubricant layer 5 include fatty acids having 12 to 22 carbon atoms and monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent Mono-fatty acid esters, di-fatty acid esters or tri-fatty acid esters composed of any one of the polyhydric alcohols are exemplified. Specific fatty acid esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, and the like.

The amount of the fatty acid and fatty acid ester forming the lubricant layer 5 is preferably 5 to 100 mg / m ² . If the application amount is less than 5 mg / m ² ,
If the effect of reducing the coefficient of friction on the surface of the magnetic disk is insufficient, and if it exceeds 100 mg / m ² , the fatty acids and fatty acid esters may become uneven on the upper layer 3 or lower the output level.

As the lubricant layer 5, a conventionally known lubricant may be used in combination with the fatty acid and the fatty acid ester. Specific examples of the lubricant used in combination include silicone oil, carbon fluoride, fatty acid amide, olefin oxide and the like.

Other lubricants include graphite, molybdenum disulfide, tungsten disulfide, terpene-based compounds, oligomers thereof, and fluorine-based lubricants.

As the nonmagnetic support 1 in the above-mentioned magnetic disk, a conventionally known material can be used. Specifically, polyethylene terephthalate, polyethylene-2,
Polyesters such as 6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, polymer substrates represented by vinyl resins, polyimides and polycarbonates, or metals, glasses and ceramics And the like.

The upper layer 3 is a layer in which an information signal is recorded as a magnetic signal, and is a magnetic layer mainly composed of a ferromagnetic metal powder and a binder. Specific ferromagnetic metal powders used for the upper layer 3 include, for example, metals such as Fe, Co, and Ni;
e-Co, Fe-Ni, Fe-Al, Fe-Ni-A
1, Fe-Al-P, Fe-Ni-Si-Al, Fe-
Ni-Si-Al-Mn, Fe-Mn-Zn, Fe-N
i-Zn, Co-Ni, Co-P, Fe-Co-Ni,
Fe-Co-Ni-Cr, Fe-Co-Ni-P, Fe
-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn
-Al, alloys such as Fe-Co-V, iron nitride, iron carbide and the like. To these ferromagnetic metal powders, an appropriate amount of a light metal element such as Al, Si, P, or B may be added to prevent sintering or maintain the shape during reduction. Most commonly, Fe or Fe-Co, Fe-Ni, Fe-C
An alloy obtained by adding Al and / or Si to an o-Ni alloy is used.

The specific surface area of these ferromagnetic metal powders is 2
0 to 90 m ² / g is preferred, and 25 to 70 m ² / g is particularly preferred. By setting the specific surface area of the ferromagnetic metal powder within the above range, excellent high-density recording characteristics and noise characteristics are imparted to the magnetic disk.

As the ferromagnetic metal powder, one of the above ferromagnetic metal powders can be used alone, but two or more may be used in combination. Further, hexagonal plate-like ferrite can also be used as the ferromagnetic metal powder. As specific hexagonal plate-like ferrite, M type, W
Type, Y type, Z type barium ferrite, strontium ferrite, calcium ferrite, lead ferrite and the like. Further, in order to control the coercive force of these hexagonal plate-like ferrites, Co-Ti, Co-Ti-Z
n, Co-Ti-Nb, Co-Ti-Zn-Nb, Cu
-Zr, Ni-Ti or the like may be added.

On the other hand, the lower layer 2 is a layer formed to prevent the surface shape of the nonmagnetic support 1 from affecting the surface of the upper layer 3 and to make it easier to apply a coating for the upper layer. . The lower layer 2 is a layer mainly composed of a nonmagnetic powder and a binder, but a magnetic powder having a small amount of magnetization and a small coercive force may be used instead of the nonmagnetic powder. Further, the lower layer 2 may be mixed with a non-magnetic powder and a magnetic powder having a small amount of magnetization and a small coercive force.

Specific examples of the nonmagnetic powder used for the lower layer 2 include α-iron oxide, goethite, and acicular titanium oxide. These non-magnetic powders have improved dispersibility,
Surface treatment may be performed for the purpose of imparting conductivity or adjusting light transmittance.

These non-magnetic powders have an average particle size (average long axis length) in order to ensure surface smoothness after coating.
It is preferably 0.3 μm or less, particularly preferably 0.2 μm or less. When the needle ratio (length: diameter) is 5 or more, an effect of suppressing curling is exhibited, and in particular, the needle ratio is 10%.
It is preferable that it is above. On the other hand, when the acicular ratio is 30 or more, dispersibility may be deteriorated, and surface roughness may be deteriorated.

As the magnetic powder used for the lower layer 2, the above-mentioned ferromagnetic powder used for the upper layer 2 can be used. However, in order to not adversely affect the electromagnetic conversion characteristics of the upper layer 3, which is the layer where the magnetic signal is recorded, the lower layer 2 includes
It is preferable to use a magnetic powder having a small amount of magnetization and a small coercive force. As a specific magnetic powder used for the lower layer 2, γ
Examples include iron oxide, cobalt-modified gamma iron oxide, magnetite, cobalt-modified magnetite, and chromium dioxide. The magnetic particles of these magnetic powders may be subjected to a surface treatment in consideration of the dispersion stability with the non-magnetic powder that is simultaneously dispersed.

These magnetic powders have an average particle size (average long axis length) in order to ensure surface smoothness after coating.
0.3 μm or less, especially 0.2 μm
The following is preferred. Further, in order to suppress the warpage, the needle ratio of the magnetic powder is preferably 5 or more and less than 30 and particularly preferably 10 or more and less than 30. When the acicular ratio of the magnetic powder is 30 or more, there is a possibility that the dispersibility may be deteriorated and the surface roughness may be deteriorated.

Further, carbon black,
In particular, carbon black, goethite, rutile type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide,
Chromium oxide, cerium oxide, titanium carbide, BN,
Pigments such as α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, and barium titanate can also be used in combination. When the pigment is used in combination, the average particle size (the average major axis length in the case of acicular particles) is preferably 0.3 μm or less, in order to ensure surface smoothness after coating. It is preferably 0.2 μm or less.

Further, the pigment may be doped with an appropriate amount of impurities according to the purpose. The pigment preferably has a specific surface area of 5 to 100 m ² / g,
It is particularly preferably ^{20 to} 70 m ² / g. By setting the specific surface area of the pigment within the above range, the shape of the pigment is made finer, and deterioration of the surface property exerted on the magnetic disk surface can be minimized.

Further, carbon black may be added to the lower layer 2 as an antistatic agent. The addition of conductive carbon black to the lower layer 2 lowers the electric resistance of the magnetic disk surface, prevents discharge noise and head sticking, and reduces dust adhesion to the magnetic disk surface due to static electricity. It is possible to prevent the resulting dropout. As the carbon black, it is preferable to use a carbon black having a structured structure having an oil absorption of 100 ml / 100 g or more. It is preferable that the amount of carbon black added be kept to the minimum necessary in order to maintain the surface properties of the lower layer 2.

As described above, the lower layer 2 is
By forming the upper layer 3 between the nonmagnetic support 1 and the upper layer 3 which is a magnetic layer, the adhesive strength between the nonmagnetic support 1 and the upper layer 3 is improved, and the upper layer 3 is formed thinner than directly formed on the nonmagnetic support 1. It becomes possible.

As the binder used in the upper layer 3 and the lower layer 2 described above, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like used as binders for magnetic recording media can be used. . The average molecular weight of the binder is 500
It is preferably from 0 to 100,000. As specific thermoplastic resins, vinyl chloride, vinyl chloride copolymer, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate- Acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-chloride Vinylidene copolymer, methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral , Cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like. Specific examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea formaldehyde resin.

All the above-mentioned binders include -SO ₃ M, -OSO ₃ M, and-for the purpose of improving the dispersibility of the pigment.
A polar functional group such as COOM and P = O (OM) ₂ may be introduced. In the formula, M represents a hydrogen atom or an alkali metal such as lithium, potassium, and sodium. Further, as the polar functional groups, -NR ₁ NR ₂ , -NR ₁
NR ₂ NR ₃ ⁺ X ^- as the side chain type having an end group, -NR
There is a main chain type of ₁ NR ₂ ⁺ X ⁻ . Where R ₁ ,
R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group, and X ⁻
Is a halogen element ion such as fluorine, chlorine, bromine and iodine, or an inorganic / organic ion. X ^- is -O
It may be a polar functional group such as H, -SH, -CN or an epoxy group. The amount of these polar functional groups is 10 ^-1 to 10 ^-8 mol / g.
Is preferred, and particularly preferably 10 ⁻² to 10 ⁻⁶ mol / g.
These binders can be used alone, or a plurality of binders can be mixed and used.

Examples of the solvent used for the upper layer 3 and the lower layer 2 include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohol solvents such as methanol, ethanol and propanol, methyl acetate and ethyl acetate. , Butyl acetate,
Ester solvents such as propyl acetate, ethyl lactate and ethylene glycol acetate; ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; methylene chloride; ethylene Halogenated hydrocarbon solvents such as chloride, carbon tetrachloride, chloroform, chlorobenzene and the like can be mentioned, and these are used by being appropriately mixed.

Further, a lubricant, non-magnetic reinforcing particles and the like can be internally added to the upper layer 3 and the lower layer 2 as necessary.

Specific lubricants include graphite, molybdenum disulfide, tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, fatty acids having 10 to 22 carbon atoms, and alcohols having 2 to 26 carbon atoms. A terpene compound, an oligomer of a terpene compound, a fluorine-based lubricant, and the like. However, DL
In consideration of the adhesion between the C protective film 4 and the upper layer 3, it is preferable to avoid adding a lubricant to the upper layer 3 and the lower layer 2. When a lubricant is added, the lubricant may seep out to the surface of the upper layer 3 and the adhesion between the DLC protective film 4 and the upper layer 3 may be reduced.

Specific non-magnetic reinforcing particles include aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide, titanium oxide (rutile, anatase). ) And the like.

The content of the nonmagnetic reinforcing particles is preferably 20 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the ferromagnetic metal powder. The Mohs hardness of the non-magnetic reinforcing particles is 4 or more, preferably 5 or more, and more preferably 6 or more. The specific gravity of the non-magnetic reinforcing particles is preferably 2 to 6 g / cm ³ , particularly ³ to 5 g / cm ^3.
cm ³ is preferred. The average primary particle size of the non-magnetic reinforcing particles is
It is 1.0 μm or less, preferably 0.5 μm or less, and more preferably 0.3 μm or less.

It is also possible to use a polyisocyanate for crosslinking and curing the above binder. Specific examples of the polyisocyanate include toluene diisocyanate and its adduct, and alkylene diisocyanate and its adduct. The content of these polyisocyanates is 5 parts by weight based on 100 parts by weight of the binder.
The amount is preferably from 80 to 80 parts by weight, particularly preferably from 10 to 50 parts by weight. These polyisocyanates are contained in the upper layer 3 and the lower layer 2.
Can be used for both, or can be used for only the upper layer 3. When the polyisocyanate is contained in both the upper layer 3 and the lower layer 2, the content can be arbitrarily changed.

Next, a method of manufacturing the magnetic disk configured as described above will be described.

First, an upper layer paint for forming the upper layer 3 and a lower layer paint for forming the lower layer 2 are prepared.
Upper layer paint, ferromagnetic metal powder, binder, solvent,
It can be obtained by mixing with various additives, kneading and then dispersing. The lower layer paint can be obtained by mixing a nonmagnetic powder, a binder, a solvent, and various additives, kneading and then dispersing.

Specific kneading apparatuses used in the above-described kneading step include a continuous twin-screw kneader, a continuous twin-screw kneader capable of multistage dilution, a kneader, a pressure kneader, a roll kneader and the like.

Specific dispersing apparatuses used in the above-mentioned dispersing step include a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a DCP, an agitator, a homogenizer, and an ultrasonic disperser. .

Next, a lower layer paint and an upper layer paint are applied on one main surface of the non-magnetic support 1 in a multi-layered manner by an application device, so that the lower layer 2 Is formed, and the upper layer 3 is formed on the lower layer 2.

As a coating apparatus for applying the upper layer coating and the lower layer coating on the nonmagnetic support 1 in a multi-layered manner, a gravure coater, a knife coater, a blade coater, a reverse roll coater, a die coater and the like can be mentioned. As a lip configuration of the die coater, there are a two-lip system, a three-lip system, a four-lip system, and the like.

As a method of applying the upper layer paint and the lower layer paint on the non-magnetic support 1 in a multi-layer manner, a method of applying and drying one layer at a time (so-called wet-on-dry coating method) may be applied. Alternatively, a method of applying the upper layer paint on the wet lower layer paint that has not been dried (so-called wet-on-wet coating method or simultaneous wet multilayer coating method) may be applied. However, considering the uniformity of coating film, adhesiveness of interface, and productivity, wet
It is preferable to apply an on-wet coating method.

A method of forming a lower layer 2 on one main surface of a nonmagnetic support 1 by applying a wet-on-wet method as a method of applying a multi-layer coating and further forming an upper layer 3 on the lower layer 2 will be described. I do. For example, in the wet-on-wet method, as shown in FIG. 2, a lower paint reservoir 11 for supplying a lower paint 10, an upper paint reservoir 13 for supplying an upper paint 12, and a lower paint 10 are provided. A die coater 16 having a slit 14 for discharging and a slit 15 for discharging the upper layer paint 12 is used.
A die coater 16 is arranged on one main surface of the non-magnetic support 11 running in the direction of arrow A so that the openings of the slits 14 and 15 face each other.
The lower layer paint 10 is discharged from the slit 12, and the upper layer paint 17 is simultaneously discharged from the slit 12 so as to overlap the discharged lower layer paint 10. Thereby, the lower layer 2 and the upper layer 3 are formed, and a laminate including the nonmagnetic support 1, the lower layer 2, and the upper layer 3 is formed.

The laminate is dried, introduced into a calender, smoothed on the surface, and taken up on a take-up roll.

In this wet-on-wet method, the upper layer paint 12 is applied on the lower layer 2 in a wet state, so that the surface of the lower layer 2 (that is, the surface in contact with the upper layer 3).
And the surface properties of the upper layer 3 are improved, and the adhesion between the lower layer 2 and the upper layer 3 is also improved. Therefore, by applying the lower layer 2 and the upper layer 3 in a multi-layer coating,
High output and low noise required for high density recording can be realized, film strength can be improved, and dropout can be reduced.
Further, compared with the application by the dry-on-wet method, the upper layer 3 can be made thinner.

On the other hand, when the lower layer 2 and the upper layer 3 are formed by a wet-on-dry method, it is necessary to use a lower layer paint having sufficient solvent resistance to the solvent of the upper layer paint.

When the lower layer 2 and the upper layer 3 are formed by the above wet-on-wet method, the interface between the lower layer 2 and the upper layer 3 is substantially replaced with the lower layer 2 and the upper layer 3. May be present as a boundary region in which the above components are mixed.

Next, the DLC protective film 4 is formed on the laminated body formed as described above, in which the lower layer 2 and the upper layer 3 are coated on the non-magnetic support 1 in multiple layers.

As a specific method of forming the DLC protective film 4, a sputtering method, a chemical vapor deposition method using a hydrocarbon-based gas (Chemical Vapor Depo) is used.
site: CVD method), a vacuum evaporation method, an ion plating method, and the like. Note that a specific sputtering method includes a magnetron sputtering method, a facing target method, and the like. Specific CVD methods include a plasma CVD method, an ECR plasma CVD method, and an arc jet plasma CVD method.

For example, as shown in FIG.
(ct Current) magnetron sputtering apparatus will be briefly described.

The DC magnetron sputtering device is
A vacuum chamber 32 provided with a gas inlet 30 and a vent 31
The cathode electrode 33 and the anode electrode 34 are arranged so as to face each other, and the target 3
5, and a magnet 36 for forming a magnetic field is arranged on the anode electrode 34 side.

Then, as described above, the winding roll 37
The laminate wound up is sent out in the direction of the arrow, and DLC is passed between the cathode electrode 33 and the anode electrode 34.
The protective film 4 is formed. The laminate on which the DLC protective film 4 is formed is taken up by a take-up roll 38.

Next, a lubricant layer 5 is formed on the DLC protective film 4 manufactured as described above to obtain a raw material. Lubricant layer 5
As a method for forming the lubricant, any method such as a method of applying a lubricant solution, a method of spraying a lubricant solution, and a method of impregnating the lubricant solution is possible.

The above is a description of the process of forming the lower layer 2, the upper layer 3, the DLC protective film 4, and the lubricant layer 5 on one main surface of the non-magnetic support 1. It goes without saying that the steps of forming the lower layer 2, the upper layer 3, the DLC protective film 4, and the lubricant layer 5 on the other main surface of the magnetic support 1 can be performed by the same steps.

Next, the raw material produced as described above is slit into a predetermined width, and is punched into a disk having a desired diameter.
It is to be noted that the order of forming the lubricant layer 5 after punching in a disk shape may be used instead of the above manufacturing order.

Finally, the magnetic disk manufactured in this manner is housed in a jacket or a case.

The magnetic disk manufactured in this manner is recorded and reproduced by a disk drive employing a sliding head and a flying head.

In a disk drive employing a sliding head, the head is always in contact with the surface of the magnetic disk. When performing recording and reproduction, the disk drive rotates the magnetic disk at a high speed and slides the head on the surface of the magnetic disk.

In a disk drive employing a floating head, the head attached to the slider is:
When the magnetic disk is stopped, it is pressed against the surface of the magnetic disk. When performing recording / reproduction, the disk drive rotates the magnetic disk at high speed, and the rotation of the magnetic disk generates a compressed air flow between the magnetic disk and the head, and the head floats using this air flow. Let it. The balance between the flying force of the head due to the rotation of the magnetic disk and the force of pressing the head against the surface of the magnetic disk keeps the distance between the head and the surface of the magnetic disk very small and achieves high-density recording. At the end of recording / reproduction, the disk drive stops the rotation of the magnetic disk, so that the floating force of the head is lost and the head is pressed against the surface of the magnetic disk.

The magnetic disk manufactured as described above has the DLC protective film 4 on the upper layer 3 and the lubricant layer 5 on the DLC protective film 4, so that the friction coefficient of the surface of the magnetic disk is reduced. Surface strength is improved. That is, the magnetic disk has abrasion resistance and running durability against sliding and contact with the head when recording and reproduction are performed in the disk drive, and wear and damage on the surface of the magnetic disk are reduced. Therefore, it has excellent electromagnetic conversion characteristics.

The thickness of the DLC protective film 4 is preferably 1 to 20 nm. If the thickness of the DLC protective film 4 is less than 1 nm, abrasion resistance, that is, the effect of protecting the upper layer 3 from abrasion and damage may not be sufficiently obtained. Also,
If the thickness of the DLC protective film 4 exceeds 20 nm, the electromagnetic conversion characteristics may be degraded due to spacing.

The lubricant forming the lubricant layer 5 is preferably a mixture of a fatty acid and a fatty acid ester and diluted with a solvent. In particular, the dilution ratio of the fatty acid and the fatty acid ester with the solvent is preferably 10%. Preferably it is 100 times. If the dilution ratio of the fatty acid and fatty acid ester used in the lubricant layer 5 with the solvent is less than 10 times, sticking may occur between the head and the magnetic disk, and running durability may be impaired. Further, the dilution ratio with the solvent is 10
If it exceeds 0 times, the effect of the lubricant such as reduction of the friction coefficient and running durability may not be sufficiently exhibited.

[0074]

EXAMPLE Next, using a magnetic disk actually produced by applying the present invention, the preferable thickness of the DLC protective film, the constitution of the lubricant layer, and the like were examined.

Sample 1 Materials shown below were stirred and homogenized by a continuous kneader according to a standard method, and were subjected to a dispersion treatment with a sand mill to prepare a lower layer paint and an upper layer paint. The processing time in the sand mill was 3 hours for the lower layer paint and 5 hours for the upper layer paint.

<Coating for lower layer> α-iron oxide: 100 parts by weight Carbon black: 11 parts by weight Polyvinyl chloride resin: 17 parts by weight Stearic acid: 1 part by weight Heptyl stearate: 1 part by weight Methyl ethyl ketone: 150 parts by weight Cyclohexanone: 150 parts by weight The α-iron oxide used had an average major axis length of 0.15 μm, an acicular ratio of 12, and a pH of 5.7. The polyvinyl chloride resin has a polymerization degree of 150, and potassium oxysulfonate is used as a polar functional group in an amount of 5 × 10 5
^One containing ^-5 mol / g was used.

<Coating for upper layer> Fe-based metal ferromagnetic powder: 100 parts by weight Polyvinyl chloride resin: 14 parts by weight Polyester polyurethane resin: 6 parts by weight Additive: 5 parts by weight Stearic acid: 3 parts by weight Heptyl stearate: 3 Parts by weight Methyl ethyl ketone: 150 parts by weight Cyclohexanone: 150 parts by weight The Fe-based metal ferromagnetic powder has an average major axis length of 0.2 μm, an acicular ratio of 9, and a saturation magnetization of 130 Am ² /. kg and a coercive force of 135 kA / m. As the polyvinyl chloride resin,
A polymer having a degree of polymerization of 150 and containing 5 × 10 ⁻⁵ mol / g of potassium oxysulfonate as a polar functional group was used. As the above-mentioned polyester polyurethane resin, sodium sulfonate as a polar functional group is 1 × 10 ^-4 m
ol / g was used. As the additive, Al ₂ O ₃ having a primary particle size of 0.20 μm was added as a slurry.

Next, 2 parts by weight of the polyisocyanate was added to the lower layer paint and 4 parts by weight of the upper layer paint prepared as described above.

The non-magnetic support has a thickness of 62 μm, a glass transition point of 69 ° C., and a surface roughness Ra of 8 n.
m, a polyethylene terephthalate film was used. Using a four-lip type die coater, a lower layer paint and an upper layer paint were overlaid on one main surface of the polyethylene terephthalate film, subjected to a non-orientation treatment by a solenoid coil, and dried. Next, on the other main surface side of the polyethylene terephthalate film, a lower layer coating material and an upper layer coating material were applied in multiple layers in the same manner as on the one main surface side, and then calendered to give a laminate. The thickness of the lower layer after drying is 2.0
μm, and the thickness of the upper layer 3 was set to 0.25 μm.

Next, a laminate having an upper layer and a lower layer formed on both main surfaces of the polyethylene terephthalate film as described above was punched into a disk having a diameter of 3.5 inches.

Next, the punched laminate was set in a constant temperature facility, left at a processing temperature of 60 ° C. for 48 hours, and cooled to room temperature to produce a magnetic disk.

Sample 2 A laminate in which a lower layer and an upper layer were formed on both main surfaces of a polyethylene terephthalate film was prepared in the same manner as in Sample 1, and a D layer was formed on both main surfaces of the laminate under the following conditions.
An LC protective film was formed. DLC protective film thickness is 0.5
nm. To form the DLC protective film, the DC shown in FIG.
A magnetron sputtering device was used.

<Film formation conditions> Apparatus: DC magnetron sputtering apparatus Target: Carbon sputter gas: Ar Vacuum degree at the time of film formation: 8 × 10 ^-1 Pa The above DLC protective film was formed on both sides of the laminate, and then sample 1 In the same manner as in the above, the disk was punched into a disk having a diameter of 3.5 inches, a magnetic disk was set in a constant temperature facility, left at a processing temperature of 60 ° C. for 48 hours, and then cooled to room temperature.

A lubricant layer was further formed on both main surfaces of the magnetic disk on which the DLC protective film was formed as described above.

The lubricant layer was formed by a spin coating method using a solution obtained by mixing a mixture of a fatty acid and a fatty acid ester at a ratio of 2: 1 and diluting 100 times with toluene.

Sample 3 Sample 2 was prepared except that the thickness of the DLC protective film was 1 nm.
A magnetic disk was produced in the same manner as described above.

Sample 4 Sample 2 was the same as Sample 2 except that the thickness of the DLC protective film was 3 nm.
A magnetic disk was produced in the same manner as described above.

Sample 5 Sample 2 was prepared except that the thickness of the DLC protective film was changed to 6 nm.
A magnetic disk was produced in the same manner as described above.

Sample 6 A magnetic disk was manufactured in the same manner as in Sample 2, except that the thickness of the DLC protective film was changed to 12 nm.

Sample 7 A magnetic disk was manufactured in the same manner as in Sample 2, except that the thickness of the DLC protective film was changed to 18 nm.

Sample 8 A magnetic disk was manufactured in the same manner as in Sample 2, except that the thickness of the DLC protective film was changed to 21 nm.

Sample 9 A magnetic disk was manufactured in the same manner as in Sample 2, except that the thickness of the DLC protective film was changed to 30 nm.

Sample 10 A magnetic disk was manufactured in the same manner as in Sample 7, except that the lubricant layer was not formed.

With respect to Samples 1 to 10, the coating film strength, running durability, and electromagnetic conversion characteristic output were examined.

The strength of the coating film was evaluated by an indentation test using a thin film scratch tester. The coating film strength was measured under the following measurement conditions, and the complete damage point, that is, the load (mN) at which the film was completely destroyed was measured.

<Measurement conditions> Indenter needle tip diameter: 15 μm Spring constant: 22.5 g / mm Load rate: 12 mN / m Sample tilt angle: 3 degrees Pushing speed: 10 μm / s Measurement environment: 25 ° C./40% rh For the test of running durability, a floppy disk drive (manufactured by Sony Corporation, trade name MPF-42B) was modified to use a thin film head having a disk rotation speed of 3600 rpm and a gap length of 0.2 μm as a head. It was used. With the above floppy disk drive, the head was run on the outermost track of the sample, and the time until the coating film of the sample was damaged at that time was measured.

The electromagnetic conversion characteristics were measured by using a modified floppy disk drive in the same manner as in the above running durability test, by running the sample on the outermost track of the sample, and measuring the reproduction output level of 25 MHz generated in the magnetic head at that time. The evaluation was performed by:

The evaluation of coating film strength, evaluation of running durability,
Table 1 shows the results of the evaluation of the electromagnetic conversion characteristics.

[0099]

[Table 1]

Samples 3 to 7 in which a lubricant layer was formed and the thickness of the DLC protective film was 1 to 20 nm
Had excellent coating film strength and running durability, and the reproduction output level was within -10 dBm. However, in Sample 1 in which the DLC protective film was not formed and in Sample 2 in which the thickness of the DLC protective film was 0.5 nm, the coating strength,
The running durability was poor. This means that sample 1 is D
Since no LC protective film was formed, no abrasion resistance was imparted at all, and it was considered that Sample 2 had a DLC protective film thickness of 0.5 nm and did not provide sufficient abrasion resistance. Can be In samples 8 and 9 in which the thickness of the DLC protective film exceeds 21 nm, the spacing loss between the head and the recording layer increases, and as a result, the reproduction output level falls below -10 dBm. The playback output level is-
If it is less than 10 dBm, short-wavelength output cannot be secured, and it may be difficult to deal with high-density floppy disks and the like. Therefore, the thickness of the DLC protective film is 1 to 20 n.
It is understood that m is preferable.

Further, in Sample 10 in which the lubricant layer was not formed, it was found that although the thickness of the DLC protective film was sufficient, the running durability was extremely poor due to lack of lubricity. Therefore, it is understood that the lubricant layer is preferably formed.

Next, the influence on the running durability was examined by changing the structure of the lubricant layer.

Sample 11 A magnetic disk was manufactured in the same manner as in Sample 5, except that the mixing ratio between the fatty acid and the fatty acid ester in the lubricant layer was 1: 0.

Sample 12 A magnetic disk was manufactured in the same manner as in Sample 5, except that the mixing ratio of the fatty acid and the fatty acid ester in the lubricant layer was set to 0: 1.

Sample 13 A magnetic disk was manufactured in the same manner as in Sample 5, except that the mixing ratio of the fatty acid and the fatty acid ester in the lubricant layer was 1: 1.

Sample 14 A magnetic disk was prepared in the same manner as in Sample 5, except that the mixing ratio of the fatty acid and the fatty acid ester in the lubricant layer was 1: 2.

Sample 15 A magnetic disk was manufactured in the same manner as in Sample 5, except that the lubricant layer was not formed.

Sample 16 Except that the dilution ratio of the mixture of fatty acid and fatty acid ester contained in the lubricant layer with toluene was 200 times,
A magnetic disk was manufactured in the same manner as in Sample 5.

Sample 17 A magnetic disk was prepared in the same manner as in Sample 5, except that the dilution ratio of the mixture of the fatty acid and the fatty acid ester contained in the lubricant layer with toluene was changed to 20 times.

Sample 18 A magnetic disk was prepared in the same manner as in Sample 5, except that the dilution ratio of the mixture of fatty acid and fatty acid ester contained in the lubricant layer with toluene was 10 times.

Sample 19 A magnetic disk was prepared in the same manner as in Sample 5, except that the dilution ratio of the mixture of fatty acid and fatty acid ester contained in the lubricant layer with toluene was 7 times.

The running durability of Samples 11 to 19 was evaluated. Table 2 shows the results.

[0113]

[Table 2]

In samples 11 to 15 in which the mixing ratio of the fatty acid and the fatty acid ester was changed, there was no significant change in running durability.
In Sample 19 which was doubled, remarkable deterioration in running durability was observed. This is presumably because in Sample 16, the toluene dilution was 200 times, and the fatty acid and fatty acid ester were excessively diluted, so that the effectiveness as a lubricant was impaired. Further, in Sample 19, the toluene dilution ratio was 7 times, and the surface properties of the magnetic disk were degraded, and it is considered that sticking occurred between the head and the magnetic disk. Therefore, the dilution ratio of the lubricant layer with toluene is 1
It is understood that the ratio is preferably 0 to 100 times.

[0115]

As is clear from the above description, according to the present invention, the magnetic recording medium has excellent surface strength due to the formation of the DLC protective film and the lubricant layer, and has a high friction coefficient. Is reduced. Thus, according to the present invention,
A magnetic recording medium having excellent wear resistance and electromagnetic conversion characteristics and suitable for high-density recording can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a basic configuration of a magnetic disk to which the present invention is applied.

FIG. 2 is a conceptual diagram for explaining a method for forming an upper layer and a lower layer on a nonmagnetic support by a die coater.

FIG. 3 is a conceptual diagram for explaining a DC magnetron sputtering device.

[Explanation of symbols]

1 Non-magnetic support, 2 Lower layer, 3 Upper layer, 4 DLC protective film, 5 Lubricant layer

Claims (5)

[Claims] A non-magnetic support, a magnetic layer formed by applying a magnetic paint obtained by kneading at least a magnetic powder and a binder, a hard carbon protective film formed on the magnetic layer, A magnetic recording medium comprising: a lubricant layer made of a lubricant on a carbon protective film. 2. The thickness of the hard carbon protective film is from 1 to
2. The magnetic recording medium according to claim 1, wherein the thickness is 20 nm. 3. The magnetic recording medium according to claim 1, further comprising a non-magnetic layer formed by applying a non-magnetic paint between the magnetic layer and the non-magnetic support. 4. The magnetic recording medium according to claim 1, wherein the lubricant is obtained by diluting a fatty acid and a fatty acid ester with a solvent. 5. The magnetic recording medium according to claim 4, wherein a dilution ratio of the fatty acid and the fatty acid ester in a solvent is 10 to 100 times.