JP2000285434A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a magnetic layer surface hard to damage and superior in durability by setting a scratch resistance of the surface of the magnetic layer as an upper layer applied to a non-magnetic body to a specific value or larger, and setting a surface roughness of the surface to a specific value or smaller. SOLUTION: In the magnetic recording medium in which at least an upper layer is a magnetic layer, a surface scratch resistance of the magnetic layer is made 10 gf or larger and a surface roughness (Ra) of the magnetic layer is made 7.0 nm or smaller. The upper layer is preferably formed by applying a magnetic paint obtained by kneading a binder by 8-20 pts.wt. to 100 pts.wt. of a pigment essentially consisting of a magnetic powder and a non-magnetic powder, and a lower layer is preferably formed by applying a magnetic paint obtained by kneading a binder by 16-50 pts.wt. to 100 pts.wt. of a pigment essentially consisting of a non-magnetic powder. When a Young's modulus of the upper layer is E1 and a Young's modulus of the lower layer is E2, E1/E2 is preferably 0.2-3. The magnetic powder is a ferromagnetic alloy powder or the like, and the binder can be a thermoplastic resin, a thermosetting resin or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium in which at least a lower layer and an upper layer are formed in this order on a non-magnetic support. More specifically, the present invention relates to a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent magnetic characteristics. The present invention relates to a magnetic recording medium having both durability and durability.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, there is a magnetic disk in which a magnetic layer formed on a non-magnetic support is punched into a disk shape and formed into a disk shape. In this magnetic disk, it is desired to improve the recording capacity. In order to increase the capacity of the magnetic disk, it is conceivable to use a signal in a short wavelength region. Therefore, when the capacity of the magnetic disk is increased, it is necessary to improve the output of the signal in the short wavelength region. In order to meet these requirements, it is conceivable to reduce the thickness of the magnetic layer of the magnetic disk.

[0003] That is, by making the magnetic layer thin, signals in the short wavelength region can be recorded and reproduced. However, when the thickness of the magnetic layer is 0.5 μm or less, it is difficult to achieve uniform film quality and to achieve excellent productivity. For this reason, as a magnetic disk, a lower nonmagnetic layer formed by applying a nonmagnetic paint in which a nonmagnetic powder is dispersed in a binder is formed on a nonmagnetic support, and a ferromagnetic metal powder is formed thereon. There has been proposed a method of forming an upper magnetic layer by applying a magnetic paint dispersed in a binder.

On the other hand, a magnetic disk is mounted on a disk drive device, and recording and reproduction are performed by a magnetic head device while being rotated at a predetermined rotation speed. That is, in this disk drive device, the magnetic disk is rotated at a predetermined rotation speed. The above-described magnetic disk having a large capacity is rotated at a high speed to increase the data transfer speed in the disk drive device. In other words, the rotation speed of the magnetic disk increases as the capacity increases.

In some disk drive devices, a so-called near-contact method is employed in order to increase the data transfer speed. That is, according to the near-contact method, recording and reproduction can be reliably performed on a magnetic disk rotating at high speed.

[0006]

As described above, when the capacity of a magnetic disk is increased, the magnetic head device and the magnetic disk often come into contact with each other. When the magnetic disk comes into contact with the magnetic head device, the surface of the magnetic layer may be damaged. Conventionally, in order to prevent such damage, a lubricant has been added to the magnetic layer and the non-magnetic layer, or applied to the surface of the magnetic layer to reduce the frictional resistance of the surface of the magnetic layer, thereby improving durability and resistance. Attempts have been made to improve the impact properties. However, such a method has not been able to say that durability and impact resistance have been sufficiently improved.

The durability of a magnetic disk has been improved by adding an abrasive which is hard particles to the magnetic layer. However, in this method, the impact resistance of the magnetic disk is improved by adding a considerable amount of abrasive, but the surface roughness is deteriorated and the number of times of contact with the magnetic head is increased. In addition, it may cause damage to the magnetic head, thereby deteriorating the durability of the magnetic head.

As described above, the conventional magnetic disk has a problem that the surface of the magnetic layer is easily damaged and its durability is deteriorated as the capacity is increased.

In view of the foregoing, the present invention has been made in view of the above-described problems, and provides a magnetic recording medium which is hardly damaged on the surface of the magnetic layer, has excellent durability, and has excellent electromagnetic conversion characteristics. The purpose is to provide.

[0010]

A magnetic recording medium according to the present invention, which has achieved the above-mentioned object, comprises a non-magnetic support having at least a lower layer and an upper layer coated thereon, wherein at least the upper layer is a magnetic layer. Wherein the surface scratch strength of the magnetic layer is 10 gf or more, and the surface roughness (Ra) of the magnetic layer is 7.0 nm or less.

In the magnetic recording medium according to the present invention configured as described above, the surface scratch strength of the magnetic layer is specified to a predetermined value, and the surface roughness (Ra) of the magnetic layer is specified to a predetermined value. By doing so, the strength of the magnetic layer surface is improved,
Moreover, it has excellent surface properties. Here, the surface scratch strength is a value measured as follows.
First, at a temperature of 20 ° C., a sapphire indenter of 0.05 mmR is pressed against a magnetic recording medium, and a sliding speed of 60 mm /
The magnetic recording medium is run for min. Then, when a load is continuously applied from 0 to 50 g at a sliding distance of 10 mm, the frictional resistance generated on the surface of the magnetic recording medium is measured. At this time, if a curve showing the relationship between the load and the frictional resistance is taken, a portion where a large change in inclination appears is found. That is,
There is a load point at which the frictional resistance greatly changes, and the value of this load is defined as the scratch strength.

[0012]

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

In this embodiment, a magnetic disk 1 formed in a disk shape as shown in FIG. 1 will be described. The magnetic disk 1 has a configuration in which a lower nonmagnetic layer 3 and an upper magnetic layer 4 are formed in this order on both main surfaces 2a and 2b of a disc-shaped nonmagnetic support 2. The present invention is not limited to the magnetic disk 1 having the configuration shown in this embodiment. For example, the lower non-magnetic layer 3 and the upper magnetic layer 3 are provided only on one main surface 2a of the non-magnetic support 2. A configuration having a layer 4 or a configuration having a lower magnetic layer instead of the lower nonmagnetic layer 3 may be employed.

First, the upper magnetic layer 4 will be described.

The upper magnetic layer 4 contains a ferromagnetic powder. The ferromagnetic powder is not particularly limited, but, for example, ferromagnetic alloy powder, ferromagnetic hexagonal ferrite powder, ferromagnetic iron oxide particles, ferromagnetic CrO 2, ferromagnetic cobalt ferrite (CoO—Fe 2 O 3) , Cobalt-adsorbed oxide, and fine particles such as iron nitride. As the ferromagnetic alloy powder, Fe alloy powder, Co alloy powder,
Ni alloy powder, Fe-Co, Fe-Ni, Fe
-Co-Ni, Co-Ni, Fe-Co-B, Fe-C
Alloy powders such as o-B, Mn-Bi, Mn-Al, and Fe-Co-V, or alloy powders that are compounds of these alloys and other elements can be used. Further, in order to improve the magnetic properties of the ferromagnetic alloy powder, Al, S
Non-metals such as i, P, B, and C may be added. Usually, an oxide layer is formed on the particle surface of the ferromagnetic alloy powder for chemical stability. As a method for forming an oxide, a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, a method of immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying, A method of forming an oxide film on the surface by adjusting the partial pressure of an oxygen gas and an inert gas without using a solvent, and the like, may be used. Ferromagnetic hexagonal ferrite powder is a ferromagnetic powder having a flat plate shape and an easy axis of magnetization in a direction perpendicular to the flat plate surface, such as barium ferrite, strontium ferrite,
There are lead ferrite, calcium ferrite and their cobalt-substituted products, and among them, a cobalt-substituted product of barium ferrite and a cobalt-substituted product of strontium ferrite are particularly preferable. Further, if necessary, to improve the magnetic properties of the ferromagnetic hexagonal ferrite powder,
Elements such as n, Zn, Ge, Nb, and V may be added.
Ferromagnetic hexagonal ferrite powder, for long wavelength recording,
Although the output is lower in proportion to the other ferromagnetic powder, the recording wavelength in the high frequency band is 1.5 μm or less, preferably 1.0 μm or less.
In the case of short-wavelength recording of μm or less, high output is obtained rather than other ferromagnetic powders.

The shape of the ferromagnetic powder is not particularly limited, and examples thereof include a needle shape, a granular shape, a die shape, and the like.
Examples thereof include rice grains and plate-like ones. In the case of acicular, the acicular ratio is 3/1 to 30/1, especially 4/1.
The above is preferred. As the specific surface area of this ferromagnetic powder,
In order to achieve excellent electromagnetic conversion characteristics, 40 m2 / g
Or more, and more preferably 45 m2 / g or more. The coercive force of the ferromagnetic powder is 1300 Oe
It is preferable that it is above.

Further, as the binder to be contained in the upper magnetic layer 4, a conventionally known thermoplastic resin, thermosetting resin, radiation cross-linkable resin using an electron beam or the like, or a mixture thereof can be used.

As the thermoplastic resin, the softening point temperature is 15
Those having a temperature of 0 ° C. or lower, an average molecular weight of 5,000 to 50,000, and a degree of polymerization of about 50 to 500 are preferred. For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylate acrylonitrile copolymer, acrylate vinylidene chloride copolymer, acrylate styrene copolymer Polymer, methacrylate acrylonitrile copolymer, methacrylate vinylidene chloride, methacrylate styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl resin Butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate,
Cellulose propionate, nitrocellulose, etc.),
Examples include styrene-butadiene copolymer, polyester resin, various synthetic rubber-based thermoplastic resins (polybutadiene, polychloroprene, polyisoprene, styrene-butadiene copolymer, etc.), and mixtures thereof.

As the thermosetting resin, a phenol resin,
Epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, urea formaldehyde resins, and the like can be given.

The molecules of the resin used as a binder as described above include -SO3H, -OSO3H,-
Acidic groups such as PO3H, -OPO3H2 and -COOH or salts thereof, or hydroxyl groups, epoxy groups,
Those having a polar group such as an amino group provide more excellent dispersibility and coating film durability. Among them, -SO3Na, -COO
Those having H, -OPO3Na2 and -NH2 groups are preferred.

Furthermore, polyisocyanate may be added to the upper magnetic layer 4 as a curing agent in order to form a crosslinked structure in the above-mentioned binder. Examples of the polyisocyanate include isocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, and isophorone diisocyanate, and adducts of these isocyanates with polyhydric alcohols such as trimellilol propane or Condensation products of isocyanates can be used. Furthermore, the upper magnetic layer 4
Preferably contains inorganic particles having a Mohs hardness of 5 or more. By including inorganic particles having a Mohs hardness of 5 or more in the upper magnetic layer 4, the surface of the magnetic disk can be made to have a desired roughness, and a cleaning effect of polishing the magnetic head of the drive device can be provided.

The inorganic particles used are not particularly limited as long as they have a Mohs hardness of 5 or more. Inorganic particles having a Mohs hardness of 5 or more include Al2O3 (Mohs hardness 9), TiO (Mohs hardness 6), TiO2 (Mohs hardness 6.5), SiO2 (Mohs hardness 7), SnO2 (Mohs hardness 6.5), Cr2O3 (Mohs hardness 9) and α-
Fe2O3 (Mohs hardness 5.5),
These can be used alone or in combination. It is particularly preferable to use inorganic particles having a Mohs hardness of 8 or more.

When inorganic particles having a Mohs hardness lower than 5 are used, the inorganic particles are likely to fall off from the upper magnetic layer, and the magnetic head has almost no polishing effect. And the running durability is poor. The content of such inorganic particles is usually 0.1 to 2 parts by weight per 100 parts by weight of the ferromagnetic powder.
It is in the range of 0 parts by weight, preferably in the range of 1 to 10 parts by weight.

Further, in addition to the ferromagnetic powder, non-magnetic powder, binder and the like, a dispersant, an antistatic agent, a lubricant and the like may be added to the upper magnetic layer 4 if necessary. Examples of the dispersing agent include fatty acids having 5 to 25 carbon atoms, and metal soaps thereof composed of alkali metals or alkaline earth metals, fatty acid esters, fatty acid amides, amines, quaternary ammonium salts, phosphate esters, borate esters and the like. Known dispersants can be used.

As an antistatic agent, carbon black,
Known antistatic agents such as natural surfactants, nonionic surfactants, and cationic surfactants can be used. Specific examples of the antistatic agent include conductive fine powders such as carbon black and carbon black graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin and glycidol; Cationic surfactants such as alkylamines, quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, phosphonium or sulfoniums;
Anionic surfactants containing acidic groups such as carboxylic acids, phosphoric acids, sulfate groups, and phosphate groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphate esters of amino alcohols; it can.

Further, a lubricant may be added to the upper magnetic layer 4. As the lubricant, the following can be used. As the lubricant, a fatty acid having 8 to 22 carbon atoms, a fatty acid amide, an aliphatic alcohol, or the like can be used. Also, silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide wax, etc.), alkyl phosphate, polyphenyl ether, Tungsten sulfide can also be used. Specific examples of these organic compound-based lubricants include myristic acid, oleic acid, stearic acid, oleyl alcohol, lauryl alcohol, and the like.

Next, the lower nonmagnetic layer 3 will be described.

The lower non-magnetic layer 3 contains a non-magnetic powder. As the non-magnetic powder, for example, α-Fe 2 O
3, TiO2, carbon black, graphite, barium sulfate, ZnS, MgCO3, CaCO3, ZnO,
CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO2, Cr2O3, α-Al2O
3, α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica, silicon nitride, boron nitride, silicon carbide,
Molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, triboli, diatomaceous earth, dolomite and the like can be mentioned.

Among them, α-Fe 2 O is preferable.
3, TiO2, carbon black, CaCO3, barium sulfate, α-Al2O3, α-FeOOH, Cr2O3
And polymer powders such as polyethylene.

The binder contained in the lower non-magnetic layer 3 includes a surface property of the lower non-magnetic layer 3, that is, a dispersing ability of the pigment contained in the lower non-magnetic layer 3 and an interface between the lower non-magnetic layer 3 and the upper magnetic layer 4. It is preferable that the selection be made with primary consideration of satisfying the uniformity. As such a binder, similarly to the binder used in the upper magnetic layer 4 described above, a conventionally known thermoplastic resin, thermosetting resin, radiation cross-linkable resin using an electron beam or the like, or a mixture thereof is used. can do.

Further, for the lower non-magnetic layer 3, the following lubricants can be used. Usable lubricants include fatty acids or fatty acid amides having 8 to 22 carbon atoms,
Aliphatic alcohols and the like can be used. Examples of the lubricant include silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin (eg, polyethylene wax), polyglycol (eg, polyethylene oxide wax), alkyl phosphate, Polyphenyl ether, tungsten disulfide can also be used. Specific examples of these organic compound-based lubricants include myristic acid, oleic acid, stearic acid, oleyl alcohol, lauryl alcohol, and the like.

Further, an antistatic agent may be added to the lower non-magnetic layer 3. Examples of the antistatic agent include conductive fine powders such as carbon black and carbon black graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin and glycidol; higher alkylamines; Cationic surfactants such as quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, phosphoniums and sulfoniums; anionic surfactants containing acidic groups such as carboxylic acid, phosphoric acid, sulfate group and phosphate group An amphoteric surfactant such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of aminoalcohols. When the above-mentioned conductive fine powder is used as the antistatic agent, for example, the non-magnetic powder 10
Used in the range of 1 to 15 parts by weight relative to 0 parts by weight, even when using the above-described surfactant as an antistatic agent,
Similarly, it is used in the range of 1 to 15 parts by weight.

Further, the lower non-magnetic layer 3 may contain inorganic particles having a Mohs hardness of 5 or more, as in the upper magnetic layer 4. As inorganic particles having a Mohs hardness of 5 or more, A
l2O3 (Mohs hardness 9), TiO (Mohs hardness 6),
TiO2 (Mohs hardness 6.5), SiO2 (Mohs hardness 7), SnO2 (Mohs hardness 6.5), Cr2O3 (Mohs hardness 9) and α-Fe2O3 (Mohs hardness 5.5)
These can be used alone or in combination.

Next, an example of a method for manufacturing the magnetic disk 1 will be described.

First, a non-magnetic paint for the lower non-magnetic layer 3 and a magnetic paint for the upper magnetic layer 4 are prepared. These non-magnetic paints and magnetic paints are prepared by dispersing a non-magnetic powder or a ferromagnetic powder in a binder and kneading the above-mentioned lubricant and other fillers and additives as necessary with a solvent. You.

As the solvent used for kneading, for both non-magnetic paint and magnetic paint, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohol solvents such as methanol, ethanol and propanol, methyl acetate, Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ester solvents such as ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, ether solvents such as dioxane, benzene,
Aromatic hydrocarbon solvents such as toluene and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene can be used. can do.

The method of kneading is not particularly limited, and the order of addition of each component can be appropriately set. In particular,
For the preparation of the magnetic paint, a usual kneading machine, for example, sand mill, dyno mill, double cylinder pearl mill, two roll mill, three roll mill, ball mill, high speed impeller disperser, high speed stone mill, high speed impact mill, extruder , A disper kneader, a high-speed mixer, a homogenizer, and an ultrasonic disperser.

The thus prepared non-magnetic paint is applied on the non-magnetic support 2 with a predetermined thickness. At this time, the thickness of the nonmagnetic support 2 may be appropriately determined according to the purpose of use of the magnetic disk 1, and in many cases, 1 to 100 μm.
m, and more preferably 40 to 80 μm.

Examples of the material of the nonmagnetic support 2 include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and vinyl resins such as polyvinyl chloride. In addition to plastics such as polycarbonate, polyamide, and polysulfone, ceramics such as aluminum and copper as well as metals and glass can be used. These non-magnetic supports 2 may be subjected to corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, dust removal treatment, metal deposition treatment, or alkali treatment prior to coating.

The application of the non-magnetic paint can be performed directly on the non-magnetic support 2, but can also be applied on the non-magnetic support 2 via an adhesive layer or the like.
Examples of the coating method on the nonmagnetic support 2 include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, Cast coating, spray coating, spin coating and the like can be mentioned. In particular, a so-called wet-on-wet coating method in which the magnetic paint is superimposedly applied while the non-magnetic paint is wet may be used.

Then, on the non-magnetic support 2, a non-magnetic paint,
Further, after applying the magnetic paint on the non-magnetic paint, a random orientation treatment using a magnetic field is performed to remove the direction dependency of the magnetic properties. Thereafter, the binder in the non-magnetic paint and the magnetic paint is cured and dried. The curing reaction of the binder is performed by heating the non-magnetic paint and the magnetic paint at a predetermined temperature. Thus, the lower non-magnetic layer 3 and the upper magnetic layer 4 are formed on the non-magnetic support 2 in this order.

Finally, if necessary, a surface smoothing treatment by a calender treatment is performed, and a heat treatment, if necessary,
After performing a radiation treatment or the like, the magnetic disk 1 is cut into a disk shape.

In the above description, the magnetic disk 1, which is a disk-shaped magnetic recording medium, has been described. However, when used as a tape-shaped magnetic recording medium, the ferromagnetic powder in the magnetic layer is oriented. And then dried.

In the magnetic disk 1 manufactured as described above, in order to control the surface scratch strength of the upper magnetic layer 4, for example, the ratio between the ferromagnetic powder and the non-magnetic powder and the binder is adjusted or used. Change the size and shape of the ferromagnetic powder and the non-magnetic pigment, or adjust the polar group and the degree of polymerization of the binder used, or adjust the ratio of the binder when using two or more binders. Change,
Alternatively, a method such as changing the type and amount of the inorganic hard material is used. Further, in order to control the surface scratch strength, it can be performed by adjusting the temperature, pressure, and curing treatment during the above-described calendering treatment.

Here, the scratch strength is a value measured as follows. First, at a temperature of 20 ° C,
A 0.05 mmR sapphire indenter is pressed against the magnetic recording medium, and the magnetic recording medium is run at a sliding speed of 60 mm / min. Then, when a load is continuously applied from 0 to 50 g at a sliding distance of 10 mm, the frictional resistance generated on the surface of the magnetic recording medium is measured. At this time, if a curve showing the relationship between the load and the frictional resistance is taken, as shown in FIG. 2, a portion where a large change in inclination appears is found. That is, there is a load point (indicated by point A in FIG. 2) at which the frictional resistance greatly changes, and the value of this load is defined as the scratch strength.

On the other hand, in order to control the surface roughness (Ra) of the upper magnetic layer 4, for example, the size and shape of the ferromagnetic powder and the non-magnetic pigment to be used are changed. When two or more binders are used, a method of changing the ratio of the binder, or changing the size, shape, and amount of the inorganic hard material may be used. Further, the surface roughness (Ra) of the upper magnetic layer 4 can be controlled by changing the temperature, the pressure, and the curing treatment during the calendering treatment. However, since these methods also change the surface scratch strength of the upper magnetic layer 4 described above, a thorough combination of the above methods is required.

Incidentally, the magnetic disk 1 manufactured as described above is preferably used for a disk drive device in which the magnetic disk 1 is mounted and rotated at a relatively high speed. In other words, the magnetic disk 1 as described above is suitable for a high-speed disk drive.

Such a disk drive device has a pair of magnetic head devices arranged so as to sandwich both main surfaces of the magnetic disk 1, and the magnetic disk 1 is sandwiched by the pair of magnetic head devices. Rotate at a predetermined rotational speed. The magnetic disk 1 is stably rotated by being sandwiched between a pair of magnetic head devices, thereby suppressing surface shake and the like.

Here, as the magnetic head device, in addition to the inductive head, a magnetoresistive magnetic head or the like can be used. Further, the magnetic head device may be such that an air film is formed between the magnetic disk device 1 and the rotating magnetic disk 1 so that the air film slightly floats from the main surface of the magnetic disk 1. Further, the magnetic head device may be of a sliding type which is always in contact with the rotating magnetic disk 1.

In the magnetic disk 1 described above, the surface scratch strength of the upper magnetic layer 4 is 10 gf or more, and
Since the surface roughness (Ra) of the upper magnetic layer 4 is 7.0 nm or less, recording and reproduction can be suitably performed with such a disk drive device. That is, this magnetic disk 1
In this case, even when rotated at a high speed, the upper magnetic layer 4
Has a surface roughness (Ra) of 7.0 nm or less, the number of collisions with the magnetic head device is greatly reduced.
Further, in the magnetic disk 1, since the surface scratch strength of the upper magnetic layer 4 is 10 gf or more, the magnetic disk 1 is excellent in impact resistance even when the magnetic head device collides.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

Example 1 In Example 1, a magnetic disk in which a lower non-magnetic layer was formed on a non-magnetic support and a single upper magnetic layer was formed on the lower magnetic layer was prepared as a sample. did. First, a magnetic paint for forming the upper magnetic layer and a non-magnetic paint for forming the lower non-magnetic layer were prepared. These non-magnetic paints and magnetic paints are to be applied according to a normal production method. In both cases, first, a pigment (ferromagnetic powder or non-magnetic powder), a binder, an additive, a solvent, etc. are mixed, The mixture was kneaded with a kneader so that the nonvolatile content was 85% by weight. Then, after that, the magnetic paint is sand-milled for 5 hours, and the non-magnetic paint is sand-milled for 3 hours.
Time was dispersed to obtain each paint. The composition of each paint is shown below.

<Magnetic paint formulation> Ferromagnetic powder: Fe-based metal ferromagnetic powder (specific surface area: 51 m 2 / g) 100 parts by weight Binder: polyvinyl chloride resin 10 parts by weight Inorganic particles: α-Al 2 O 3 5 parts by weight Solvent: methyl ethyl ketone 150 parts by weight Solvent: cyclohexanone 150 parts by weight <Non-magnetic paint compounding> Non-magnetic pigment: α-iron oxide (needle ratio 8, major axis length 0.18 μm) 100 parts by weight Binder: polyvinyl chloride resin 20 parts by weight Charge Inhibitor: carbon 10 parts by weight Solvent: methyl ethyl ketone 105 parts by weight Solvent: cyclohexanone 105 parts by weight Next, these magnetic paints and non-magnetic paints are passed through a 2 μm filter, and then these magnetic paints and non-magnetic paints are coated with a 4-lip Daiko. Non-magnetic paint is a lower layer on a polyethylene terephthalate base having a thickness of 60 μm using a The magnetic paint was applied simultaneously as an upper layer so as to form an upper layer, followed by drying and calendering.

At this time, the thickness of the upper magnetic layer after drying was 0.2 μm, and the thickness of the lower nonmagnetic layer after drying was 2.0 μm.
It was set to be. Thereafter, the disk was punched out into a 3.5-inch floppy disk and placed in a thermostat at 65 ° C. for 48 hours to obtain a magnetic disk. This magnetic disk was used in Example 1
Called.

Examples 2 to 4 and Comparative Examples 1 to
Example 4 In Examples 2 to 4 and Comparative Examples 1 to 4, the amounts of the binder contained in the magnetic paint and the amounts of the binder contained in the non-magnetic paint were as shown in Table 1. A magnetic disk was manufactured in the same manner as in Example 11 except for the above.

[0056]

[Table 1]

The scratch strength and the surface roughness of the thus-prepared Examples 1 to 4 and Comparative Examples 1 to 4 were measured as described above. Further, as compared with Examples 1 to 4 and Comparative Examples 1 to 4, the Young's modulus when the lower non-magnetic layer is a single layer and the upper magnetic layer is a single layer as shown below. The Young's modulus of each case was measured.

<Young's modulus> The Young's modulus was measured in the “tensile test”.
Was measured.

Test machine name: “AG-100D” manufactured by Shimazu Co., Ltd. Tensile test speed: 10 mm / min Sample: total length 30 mm, width 6.25 mm Further, regarding these Examples 1 to 4 and Comparative Examples 1 to 4, Then, running durability characteristics and electromagnetic conversion characteristics as shown below were measured.

<Running Durability> Using a HiFD drive (manufactured by Sony, trade name: HiFD200), the samples of the respective magnetic disks were continuously run at 3600 rpm, and the output of the track 35 mm from the center was an initial value of 80.
%. The measurement result is
It was calculated as the average value of five HiFD drives.

<Electromagnetic Conversion Characteristics> Using a HiFD drive (manufactured by Sony, trade name: HiFD200), the samples of each magnetic disk were continuously run at 3600 rpm, and 3 mm from the center.
The output of the track at 5 mm was evaluated based on the magnetic disk of Example 1.

Table 1 shows the evaluation results. As for the above-mentioned Young's modulus, the ratio (E1 / E2) between the Young's modulus (E1) of the upper magnetic layer and the Young's modulus (E2) of the lower non-magnetic layer.
As shown.

[0063]

[Table 2]

As is clear from the results shown in Table 2,
Examples 1 to 4 in which the scratch strength is 10 gf or more and the surface roughness (Ra) is 7.0 nm or less.
It can be seen that the sample No. shows excellent running durability and excellent electromagnetic conversion characteristics. On the other hand, in Comparative Examples 1 to 4, since the scratch strength is less than 10 gf or the surface roughness (Ra) exceeds 7.0 nm, the running durability or the electromagnetic conversion characteristics are deteriorated. . In particular, when the scratch strength is less than 10 gf, the running durability is not excellent, and there is a possibility that it may become a practical problem. If the surface roughness (Ra) exceeds 7.0 nm, the electromagnetic conversion characteristics deteriorate, which is a problem.

As is apparent from Table 2, the ratio of the Young's modulus (E1 / E1 / E1) in the upper magnetic layer and the lower nonmagnetic layer.
The samples having E2) of 0.2 to 3 have a high coating film strength, and thus have a scratch strength of 10 gf or more. Therefore, as one method for increasing the scratch strength to 10 gf or more, the ratio of the Young's modulus (E1 / E2) in the upper magnetic layer and the lower nonmagnetic layer is 0.2 to 3
To be specified.

[0066]

As described above in detail, the magnetic recording medium according to the present invention has a magnetic layer having a surface scratch strength of 10%.
gf or more, and the surface roughness (Ra) of the magnetic layer
Is specified to be 7.0 nm or less, excellent electromagnetic conversion characteristics can be exhibited and excellent running durability can be exhibited.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a magnetic disk shown as an example of a magnetic recording medium according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a load of a sapphire indenter and a frictional resistance force on a surface of an upper magnetic layer.

[Explanation of symbols]

1 magnetic disk, 2 non-magnetic support, 3 lower non-magnetic layer, 4 upper magnetic layer

Claims (4)

[Claims] 1. A magnetic recording medium comprising at least a lower layer and an upper layer coated on a non-magnetic support, wherein at least the upper layer is a magnetic layer, wherein the magnetic layer has a surface scratch strength of 10 gf or more, and Surface roughness (Ra) of the layer is 7.0 nm
A magnetic recording medium characterized by the following. 2. The upper layer is formed by applying a magnetic paint which is kneaded so that the binder is 8 to 20 parts by weight with respect to 100 parts by weight of a pigment mainly composed of a magnetic powder and a non-magnetic powder. 2. The magnetic recording medium according to claim 1, wherein: 3. The method according to claim 1, wherein the lower layer is formed by applying a magnetic coating material which is kneaded so as to be 16 to 50 parts by weight of a binder with respect to 100 parts by weight of a pigment mainly composed of a nonmagnetic powder. The magnetic recording medium according to claim 1, wherein: 4. When the Young's modulus of the upper layer is E1 and the Young's modulus of the lower layer is E2, E1 / E2 is 0.2.
2. The magnetic recording medium according to claim 1, wherein