JPH11110742A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide satisfactory surface property to a magnetic layer, to set an electromagnetic conversion characteristic to be superior, to prevent head clogging and to set travel durability to be superior. SOLUTION: This medium is provided with the magnetic layer 3 to which magnetic coating where magnetic powder and abrasive are dispersed in bonding agent is applied. Abrasive is constituted of first particles whose Moh's hardness is not less than six and which have the average particle diameter that is larger than the thickness of the magnetic layer 3 and not more than 1 μm and second particles whose Moh's hardness is not less than six and which have the average particle diameter of not more than the thickness of the magnetic layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk and a method for manufacturing the same, and more particularly to a magnetic recording medium having a recording layer coated with a magnetic paint and a method for manufacturing the same.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
Video tape, backup data cartridge,
It is widely used as a recording medium for floppy disks and the like. In particular, recently, in this magnetic recording medium, high-density recording such as a shorter recording wavelength or a digital recording method has been actively studied, and an improvement in electromagnetic conversion characteristics has been demanded. As such a magnetic recording medium, a magnetic paint prepared by dispersing a ferromagnetic powder such as a ferromagnetic iron oxide, a Co-modified iron oxide, CrO ₂ , a ferromagnetic alloy powder in a binder is used as a non-magnetic support. A so-called coating type in which a magnetic layer is formed by coating on a body, may be used.

[0003] In a coating type magnetic recording medium, thinning of a magnetic layer has been studied in order to improve electromagnetic conversion characteristics. This is because by reducing the thickness of the magnetic layer, the self-demagnetization loss during recording can be reduced, and as a result,
The electromagnetic conversion characteristics can be improved.

However, when the thickness of the magnetic layer is reduced, the surface of the nonmagnetic support affects the surface of the magnetic layer.
For this reason, when the magnetic layer is thinned, there is a problem that the smoothness of the surface of the magnetic layer cannot be improved.

In order to solve this, various coating methods have been proposed in recent years. As a coating method that achieves both thinning of the magnetic layer and improvement of the smoothness of the magnetic layer surface, a so-called simultaneous multi-layer method in which the upper magnetic layer and the lower non-magnetic layer are simultaneously coated on a non-magnetic support by a die coater. Application methods have been proposed. According to this simultaneous multilayer coating method, the magnetic layer can be formed into a uniform coating film without coating defects or streaks, and the surface of the upper magnetic layer can be smoothed by the presence of the lower nonmagnetic layer. . As a result, it is possible to improve electromagnetic conversion characteristics and reduce noise in the magnetic recording medium. The simultaneous multi-layer coating method is also effective as a method for improving the adhesiveness of the interface between the upper and lower layers, and has become a central coating method in recent years.

In order to improve the electromagnetic conversion characteristics and reduce noise in the thinned magnetic layer, it is effective to improve the ferromagnetic powder contained in the magnetic layer. Specifically, (1) use of ferromagnetic alloy powder as ferromagnetic powder, (2) miniaturization of ferromagnetic powder, (3)
Increasing the coercive force of the ferromagnetic powder and making the coercive force distribution uniform can be mentioned. Regarding (1) and (2), as a result of aggressive progress in improving magnetic materials, ferromagnetic powders having a saturation magnetization of more than 140 Am ² / kg and a long axis length of 0.
Ferromagnetic powders of 1 μm or less have been developed. Also (3)
With respect to (1), remarkable developments have been seen, such as the appearance of ferromagnetic powder having a coercive force exceeding 160 kA / m, and a very uniform particle size distribution reflecting the coercive force distribution.

[0007]

Generally, in the above-described magnetic recording medium, an abrasive is added for the purpose of preventing head clogging or imparting running durability. This abrasive was generally added to the magnetic layer by kneading a non-magnetic material such as alumina oxide into the magnetic paint.

However, if a sufficient amount of abrasive is added to the magnetic recording medium to ensure running durability, the abrasive may protrude too much on the surface of the medium, and the smoothness of the surface of the magnetic layer may be reduced. Can not be good. As a result, the magnetic recording medium has significantly reduced electromagnetic conversion characteristics. In particular, when the simultaneous multilayer coating method as described above was used, the deterioration of the electromagnetic conversion characteristics was particularly remarkable.

If the smoothness of the magnetic layer is poor, a spacing loss during recording and reproduction may occur. In particular, when the recording wavelength is short and high-density recording is intended, the magnetic layer is easily affected by the roughness of the surface of the magnetic layer, and high smoothness is required.

For this reason, it is conceivable to improve the smoothness of the surface of the magnetic layer by reducing the amount of the abrasive added. However, simply reducing the amount of the abrasive added provides a desired surface property, but lowers the polishing power and frequently causes problems such as head clogging.

Therefore, the present invention has been proposed in view of such conventional circumstances, and the magnetic layer has good surface properties, excellent electromagnetic conversion characteristics, and prevents head clogging. An object of the present invention is to provide a magnetic recording medium having excellent running durability and a method for manufacturing the same.

[0012]

A magnetic recording medium according to the present invention, which has achieved the above-mentioned objects, comprises a non-magnetic layer formed by applying a non-magnetic paint in which a non-magnetic powder is dispersed in a binder. A magnetic layer obtained by applying a magnetic paint obtained by dispersing a magnetic powder and an abrasive in an agent, on the nonmagnetic layer, wherein the abrasive has a Mohs hardness of 6 or more, A first material having an average particle size larger than the thickness and not more than 1 μm;
And a second particle having an average particle diameter of not less than 6 and a thickness of not more than the thickness of the magnetic layer.

The magnetic recording medium according to the present invention having the above-described structure has a first particle having a predetermined average particle diameter and a second particle having a predetermined average particle diameter.
To provide a magnetic layer having an abrasive consisting of particles of
The surface properties of the magnetic layer can be improved, and a desired polishing force can be exhibited. Further, in this magnetic recording medium, since the magnetic layer is formed on the nonmagnetic layer, the surface of the magnetic layer can be smoothed and the thickness of the magnetic layer can be reduced.

In the method of manufacturing a magnetic recording medium according to the present invention, a non-magnetic layer is formed by applying a non-magnetic paint in which a non-magnetic powder is dispersed in a binder, and the non-magnetic layer is formed on the non-magnetic layer. In a method for manufacturing a magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint containing a binder, a magnetic powder, and an abrasive, the Mohs hardness is 6 or more, and the thickness is larger than the thickness of the magnetic layer. And an abrasive comprising first particles having an average particle diameter of 1 μm or less and second particles having an Mohs hardness of 6 or more and having an average particle diameter of not more than the thickness of the magnetic layer, together with a binder and a solvent. And a step of forming an abrasive slurry by dispersing the slurry, separately from this abrasive slurry,
Dispersing a binder and magnetic powder in a solvent to form a magnetic powder slurry; mixing the abrasive slurry and the magnetic powder slurry to form a magnetic paint; and applying the magnetic paint to form a magnetic paint Forming a layer.

In the method of manufacturing a magnetic recording medium according to the present invention having the above-described structure, an abrasive slurry and a magnetic powder slurry are separately prepared, and a magnetic paint is prepared by mixing the two. For this reason, the abrasive is well dispersed in the magnetic paint. According to this method, since the abrasive is well dispersed, the magnetic paint can be easily applied, and a magnetic recording medium having a desired flatness can be manufactured. Further, in this method, since the magnetic layer is formed on the non-magnetic layer, the surface of the magnetic layer can be smoothed and the thickness of the magnetic layer can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a magnetic recording medium and a method of manufacturing the same according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, a magnetic recording medium according to the present invention comprises a non-magnetic support 1, a lower non-magnetic layer 2 formed on the non-magnetic support 1, and a lower non-magnetic layer 2 formed on the non-magnetic support 1. And a magnetic layer 3 formed thereon.

In this magnetic recording medium, the nonmagnetic support 1 includes polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; celluloses such as cellulose triacetate and cellulose diacetate; Examples thereof include a polymer material represented by a base resin, polyimides, and polycarbonates, and a support formed of metal, glass, ceramics, or the like. In this magnetic recording medium, the non-magnetic support 1
Is not particularly limited, and may be any shape such as a tape shape, a disk shape, and a card shape.

As will be described in detail later, this magnetic recording medium is formed by forming a lower non-magnetic layer 2 and a magnetic layer 3 by a simultaneous multilayer coating method. At this time, the lower non-magnetic layer 2
Is formed by applying a non-magnetic paint, and the magnetic layer 3 is formed by applying a magnetic paint. The magnetic paint constituting the magnetic layer 3 is obtained mainly by kneading a ferromagnetic powder and an abrasive together with a binder in a solvent. The non-magnetic paint constituting the lower non-magnetic layer 2 is as follows.
It is mainly obtained by kneading a nonmagnetic powder together with a binder in a solvent.

Specifically, as the ferromagnetic powder, Fe, C
o, metals such as Ni, Fe-Co, Fe-Ni, Fe-A
1, Fe-Ni-Al, Fe-Al-P, Fe-Ni-
Si-Al, Fe-Ni-Si-Al-Mn, Fe-M
n-Zn, Fe-Ni-Zn, Co-Ni, Co-P,
Fe-Co-Ni, Fe-Co-Ni-Cr, Fe-C
o-Ni-P, Fe-Co-B, Fe-Co-Cr-
Alloys such as B, Mn-Bi, Mn-Al, and Fe-Co-V, iron nitride, iron carbide, and the like are included. Further, as the ferromagnetic powder, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and F
Belt compound with e ₃ O ₄ , Co-containing γ-Fe
₂ O ₃ , Co-containing Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃
A berthollide compound of Fe ₃ O _4, 1 or more metal elements CrO _2, for example Te, Sb, Fe,
An oxide containing B or the like can be used. Further, as the ferromagnetic powder, hexagonal plate-like ferrite can also be used, and M-type, W-type, Y-type, Z-type barium ferrite,
Strontium ferrite, calcium ferrite, lead ferrite, and, for the purpose of controlling the coercive force,
Co-Ti, Co-Ti-Zn, Co-Ti-Nb, C
Those to which o-Ti-Zn-Nb, Cu-Zr, Ni-Ti and the like are added can also be used. In addition, this ferromagnetic powder has A for the purpose of preventing sintering or maintaining its shape during reduction.
Even if a light metal element such as l, Si, P, or B is contained in an appropriate amount, the effects of the present invention are not prevented.

[0021] These ferromagnetic powders may be used alone or in combination of two or more. The specific surface area of the ferromagnetic powder is preferably 30~80m ² / g, more preferably 40~70m ² / g. Ferromagnetic powder, when its specific surface area is in this range,
It will be finely divided. Therefore, in this case, the magnetic recording medium can perform high-density recording and have excellent noise characteristics.

The ferromagnetic powder has a major axis length of 0.05 to
It is preferable that the diameter is 0.30 μm and the axial ratio is 5 to 15. When the major axis length is less than 0.05 μm, the ferromagnetic powder becomes difficult to disperse in the magnetic paint. If the major axis length exceeds 0.30 μm, noise characteristics may be degraded. If the axial ratio is less than 5, the orientation of the ferromagnetic powder is reduced and the output is reduced. If the axial ratio exceeds 15, the short-wavelength signal output may be reduced.

Further, when plate-like ferrite is used as the ferromagnetic powder, the plate diameter is preferably about 0.01 to 0.5 μm, and the plate thickness is preferably about 0.001 to 0.2 μm.
Here, the major axis length, the axial ratio, the plate diameter and the plate thickness are calculated as average values of 100 or more samples randomly selected from transmission electron micrographs.

On the other hand, the abrasive contained in the magnetic coating material forming the magnetic layer 3 has a Mohs hardness of 6 or more, a thickness greater than the thickness of the magnetic layer 3 and an average particle size of 1 μm or less. And second particles having an average particle size of 6 or more and a thickness of the magnetic layer 3 or less. Here, the average particle size is a value obtained by measuring the particle size of the primary particles of the abrasive for at least 100 samples randomly selected from transmission electron micrographs and calculating the average value thereof. It is.

At this time, abrasives having Mohs hardness of 6 or more include aluminum oxide (α, β, γ), chromium oxide (Cr ₂ O ₃ ), silicon carbide, diamond, garnet,
Emery, boron nitride, titanium carbide, silicon carbide,
Titanium carbide, titanium oxide (rutile, anatase), corundum and the like can be mentioned.

In this magnetic recording medium, the amount of the first particles added is 1 to 100 parts by weight of the above-mentioned ferromagnetic powder.
To 5 parts by weight, and the addition amount of the second particles is 3 parts per 100 parts by weight of the above-described ferromagnetic powder.
It is preferably from 10 to 10 parts by weight. If the first particles and the second particles are added in amounts larger than this range, the surface properties of the magnetic layer 3 may be deteriorated. Further, in this case, the magnetic layer 3 contains a relatively small amount of ferromagnetic powder, and the electromagnetic conversion characteristics are deteriorated. On the other hand, when the first particles and the second particles are added in a smaller amount than this range, the polishing power is reduced, and the polishing power for the head may be reduced. In this case, the wear resistance of the magnetic layer 3 also deteriorates, and it becomes difficult to secure the reliability as a magnetic recording medium. Therefore, by setting the addition amount of the first particles and the second particles within this range, the magnetic layer 3
Has excellent surface properties and a desired polishing force, and the magnetic recording medium has excellent electromagnetic conversion characteristics and can secure reliability.

As the nonmagnetic powder constituting the nonmagnetic paint, for example, nonmagnetic iron oxide such as α-Fe ₂ O ₃ ,
Goethite, rutile titanium oxide, anatase titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, B
N, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate and the like can be mentioned. These non-magnetic powders may be used alone or in combination of two or more. Further, the non-magnetic powder may be doped with an appropriate amount of impurities depending on the purpose, and may be a large amount. For the purpose of improving dispersibility, imparting conductivity, improving color tone, etc., Al, Si, Ti , Sn, Sb, Zr or the like.

Here, the nonmagnetic powder has a specific surface area of 30 to
80 m ² / g, preferably 40 to 70 m ² / g
Is more preferable. In addition, the non-magnetic powder includes a furnace for rubber, pyrolytic carbon,
Carbon black such as color black and acetylene black may be contained. This carbon black preferably has a specific surface area of 100 to 400 m ² / g, and has a DBP oil absorption of 20 to 200 m 2.
It is preferably 1/100 g. When the specific surface area of the non-magnetic powder and carbon black is in these ranges,
As a result, the lower non-magnetic layer 2 can be smoothed, and as a result, the magnetic layer 3 can be smoothed. For this reason, the magnetic recording medium has excellent modulation noise characteristics and is less affected by spacing loss. The non-magnetic powder has better dispersibility than the above-described ferromagnetic powder because it has no magnetic cohesive force,
If the specific surface area is larger than the above range, dispersion of the non-magnetic powder may be difficult. On the other hand, if the specific surface area of the non-magnetic powder is too small, the surface smoothness that can withstand high-density recording may not be secured.

As the binder contained in the magnetic paint and the non-magnetic paint, known thermoplastic resins, thermosetting resins, reactive resins and the like conventionally used as binders can be used. The binder used herein preferably has a number average molecular weight of 5,000 to 100,000.
Examples of the binder for the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and acrylate-acrylonitrile copolymer. Coalescence, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer,
Acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-arylonitrile Copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyurethane resin, Examples thereof include polyester resins, amino resins, and synthetic rubbers. 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.

These binders include -SO ₃ M, -OSO ₃ M, and -COO for the purpose of improving the dispersibility of the pigment.
Polar functional groups such as M and -PO (OM) ₂ may be introduced. Here, M in the formula is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium. Further, as the polar functional group, -NR ₁ R ₂ , -NR ₁ R ₂ R
₃ ⁺ X ^- as the side chain type having an end group ^{_{of,> NR 1 R 2 + X}} -
Main chain type. Where R ₁ , R ₂ , R
₃ is a hydrogen atom or a hydrocarbon group, X ^- is fluorine,
It is a halogen element ion such as chlorine, bromine and iodine or an inorganic / organic ion. Also, -OH, -SH, -C
It may have a polar functional group such as N or an epoxy group. The amount of these polar functional groups is 10 ^-1 to 10 ^-8 mol
/ G, preferably 10 ^-2 to 10 ^-6 mol / g. These binders may be used alone,
Two or more kinds may be used in combination.

This binder is preferably added in an amount of 1 to 200 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic powder or nonmagnetic powder. If the amount of the binder is too large, the ratio of the ferromagnetic powder in the magnetic layer 3 is relatively reduced and the output is reduced. On the other hand, if the amount of the binder is too small, the mechanical strength of the coating film is reduced. And the running durability decreases.

Further, the magnetic coating material may contain a polyisocyanate for crosslinking and curing the binder. Examples of the polyisocyanate include toluene diisocyanate and its adduct, alkylene diisocyanate, and its adduct. These polyisocyanates are preferably added in an amount of 5 to 80 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the binder. These polyisocyanates may be used for the lower non-magnetic layer 2. This polyisoyanate was used as the lower non-magnetic layer 2
Alternatively, it may be used for only one of the magnetic layers 3. When used in the lower non-magnetic layer 2 and the magnetic layer 3, the compounding amount may be added to each layer in an equal amount, or different amounts may be added at an arbitrary ratio.

Further, a lubricant and a surfactant may be added to the magnetic layer 3 and the lower non-magnetic layer 2 as necessary. As this lubricant, graphite, molybdenum disulfide,
Examples thereof include tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, and fatty acid esters of these and alcohols having 2 to 26 carbon atoms, terpene compounds, and oligomers thereof. These lubricants may be added only to the magnetic layer 3 or may be added to the magnetic layer 3 and the lower non-magnetic layer 2. Examples of the surfactant include nonionic, anionic, cationic, and amphoteric surfactants. These surfactants can be used in the magnetic layer 3 depending on the type and amount.
And the lower non-magnetic layer 2, or only one of the magnetic layer 3 and the lower non-magnetic layer 2.

In the lower non-magnetic layer 2, aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery,
Boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase) and the like may be contained. These nonmagnetic reinforcing particles are preferably added in an amount of 20 parts by weight or less based on 100 parts by weight of the nonmagnetic powder.
0 parts by weight or less is more preferable. The non-magnetic reinforcing particles preferably have a Mohs hardness of 4 or more, more preferably 5 or more. Furthermore, these nonmagnetic reinforcing particles preferably have a specific gravity of 2 to 6, and more preferably 3 to 5. Further, these nonmagnetic reinforcing particles preferably have an average particle size of 1.0 μm or less, more preferably 0.5 μm or less. In addition,
The average particle size of the non-magnetic reinforcing particles is also determined from a transmission electron microscope photograph and statistically processed in the same manner as the above-mentioned average particle size of the abrasive.

On the other hand, as a solvent used for forming a magnetic paint and a non-magnetic paint, for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol,
Alcohol solvents such as 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, methylene chloride, ethylene chloride,
Examples thereof include halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, and chlorobenzene.

It should be noted that the magnetic recording medium according to the present invention is not limited to the above-described structure, and the magnetic recording medium may be provided on the surface of the nonmagnetic support 1 opposite to the surface on which the magnetic layer 3 is provided. May be provided with a back coat layer for the purpose of improving the running property of the film and preventing charge and transfer. The magnetic recording medium according to the present invention has an undercoat layer provided between the lower non-magnetic layer 2 and the non-magnetic support 1 for the purpose of enhancing the adhesiveness of the lower non-magnetic layer 2. It may be.

By the way, in the method of manufacturing a magnetic recording medium according to the present invention, when producing the above-described magnetic paint, the average Mohs hardness is 6 or more, which is larger than the thickness of the magnetic layer 3 and 1 μm or less. An abrasive comprising first particles having a particle diameter and second particles having an Mohs hardness of 6 or more and having an average particle diameter equal to or less than the thickness of the magnetic layer 3 is dispersed in a solvent together with a binder and polished. A slurry is formed, and separately from the abrasive slurry, a binder and magnetic powder are dispersed in a solvent to form a magnetic powder slurry. Thereafter, the abrasive slurry and the magnetic powder slurry are mixed to form a magnetic powder slurry. Make a magnetic paint.

These abrasive slurry and magnetic powder slurry are produced through a kneading step, a mixing step and a dispersion step. At this time, a roll mill, a ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, an ultrasonic disperser, or the like is used in the dispersion step and the kneading step.

In this method, the magnetic paint is applied to the lower non-magnetic layer 2 formed by applying the above-described non-magnetic paint on the non-magnetic support 1 to thereby form the magnetic layer 3.
After the lower non-magnetic layer 2 and the magnetic layer 3 are dried, the surface is smoothed by calendering to form a magnetic recording medium.

When the non-magnetic paint and the magnetic paint are applied onto the non-magnetic support 1, a so-called wet
It is preferable that the magnetic paint is applied by the on-wet method (simultaneous multilayer coating method) when the nonmagnetic paint is in a wet state. At this time, a die coater is used as a coating device. As the lip configuration of the die coater, any of a two-lip system, a three-lip system, and a four-lip system can be used.

Specifically, in the wet-on-wet method, as shown in FIG. 2, a two-lip type die coater 5 is used. The die coater 5 includes a first liquid reservoir 6 to which a non-magnetic paint is supplied, and a second liquid reservoir 7 to which a magnetic paint is supplied. This die coater 5
The non-magnetic support 1 running in the direction indicated by the arrow A in FIG.

The die coater 5 configured as above is
When the nonmagnetic support 1 travels in the direction of arrow A, the first
The non-magnetic paint and the magnetic paint are extruded from the liquid reservoir 6 and the second liquid reservoir 7 to the non-magnetic support 1 side. As a result, the non-magnetic paint is applied on the non-magnetic support 1 and the magnetic paint is applied on the wet non-magnetic paint.

After the non-magnetic paint and the magnetic paint applied on the non-magnetic support 1 are dried, the surface is smoothed by calendering. Then, if necessary, a back coat layer is applied to the surface opposite to the surface on which the multi-layer coating is performed, and then slit, for example, to a width of 8 mm to produce a tape-shaped magnetic recording medium having a width of 8 mm.

According to the method of manufacturing a magnetic recording medium according to the present invention as described above, the abrasive and the magnetic powder are separately formed into a slurry when the magnetic paint is prepared, and they are mixed. Therefore, according to this method, the abrasive can be favorably dispersed in the magnetic paint. Therefore, according to this method, the abrasive is dispersed well without being present as a lump in the magnetic layer 3, and the surface property of the magnetic layer 3 is improved. That is, the manufactured magnetic recording medium has a highly smooth surface of the magnetic layer 3 and a desired polishing force.

In the method according to the present invention, the wet
Non-magnetic paint and magnetic paint are applied by an on-wet method. For this reason, the surface of the lower non-magnetic layer 2 becomes smooth, and as a result, the surface properties of the magnetic layer 3 are improved, and the adhesion between the lower non-magnetic layer 2 and the magnetic layer 3 is also improved.

Therefore, the magnetic recording medium satisfies the required performance as a magnetic recording medium that requires high output and low noise particularly for high-density recording, and film peeling is eliminated and film strength is improved. In addition, the manufactured magnetic recording medium can also reduce dropout and improve reliability.

[0047]

EXAMPLES Hereinafter, examples in which a magnetic recording medium according to the present invention is actually manufactured will be described, but it goes without saying that the present invention is not limited to this. Further, a magnetic recording medium of a comparative example was also manufactured for comparison with these examples, and characteristics of these examples and the comparative example were evaluated.

Example 1 In Example 1, a magnetic paint and a non-magnetic paint were prepared with the following compositions. At this time, the magnetic paint was obtained by separately preparing a magnetic powder slurry and an abrasive slurry, and mixing the magnetic powder slurry and the abrasive slurry at a predetermined ratio. The abrasive slurry was prepared by performing a dispersion treatment with a sand mill for 15 hours.

<Magnetic Layer Coating> (Magnetic Powder Slurry) 100 parts by weight of Fe-based metal ferromagnetic powder (coercive force = 160 kA / m, saturation magnetization = 145 Am ² / kg, specific surface area = 51 m ² / g, length Shaft length = 0.1 μm, needle ratio = 5) 14 parts by weight of polyvinyl chloride resin (MR-110, manufactured by Zeon Corporation) 3 parts by weight of polyester polyurethane resin (manufactured by Toyobo Co., Ltd.) 1 part by weight of stearic acid 1 part by weight of heptyl 1 part by weight of stearate ・ 150 parts by weight of methyl ethyl ketone ・ 150 parts by weight of cyclohexanone (abrasive slurry) ・ 100 parts by weight of abrasive (α-Al ₂ O ₃ ) ・ 14 parts by weight of polyester polyurethane (Nipporan N-2304) ・ 105 parts by weight of methyl ethyl ketone parts cyclohexanone 105 parts by weight <magnetic coating _{composition> · α-Fe 2 O 3} 100 weight parts ( Surface area = 53m ² / g, long axis length = 0.15 [mu] m, acicular ratio = 5) Polyvinyl chloride resin (manufactured by Nippon Zeon Co., Ltd. MR-110) 13 parts Polyester polyurethane resin (manufactured by Toyobo Co., Ltd.) 4 parts by weight -1 part by weight of stearic acid-1 part by weight of heptyl stearate-105 parts by weight of methyl ethyl ketone-105 parts by weight of cyclohexanone At this time, the abrasive slurry has an average primary particle diameter of 0.1 [mu] m. Two types having a thickness of 3 μm were prepared. The abrasive having an average particle diameter of 0.1 μm is 5 parts by weight based on 100 parts by weight of the magnetic powder, and the abrasive having an average particle diameter of 0.3 μm is 3 parts by weight based on 100 parts by weight of the magnetic powder. Thus, the magnetic powder slurry and the abrasive slurry were mixed. Thereafter, 3 parts by weight of polyisocyanate was added to the magnetic paint. Also, 2 parts by weight of polyisocyanate was added to the non-magnetic paint.

Then, the magnetic paint and the non-magnetic paint thus constituted are simultaneously coated on a non-magnetic support (polyethylene terephthalate) having a thickness of 7 μm using a die coater as shown in FIG. did. Then, a magnetic field orientation treatment is performed by a solenoid coil, and after drying each layer,
A calendering treatment and a curing treatment were performed. Further, a back paint having the following composition was applied to the surface of the non-magnetic support opposite to the surface on which the magnetic layer and the like were formed, and the non-magnetic support was 8 mm thick.
The tape was cut into a width to produce a tape-shaped magnetic recording medium.

<Back coating> 100 parts by weight of carbon black (Asahi # 50) 100 parts by weight of polyester polyurethane (Nipporan N-2304) 500 parts by weight of methyl ethyl ketone 500 parts by weight of toluene In this way, the thickness is 2.0 μm A tape-shaped magnetic recording medium having a lower non-magnetic layer and a magnetic layer having a thickness of 0.2 μm was formed.

Examples 2 to 9 Example 2 was repeated in the same manner as in Example 1 except that the type of abrasive, the average particle size of the primary particles, the amount of addition and the thickness of the magnetic layer were as shown in Table 1. -Example 9 was produced.

Comparative Examples 1 to 5 Comparative Example 1 was carried out in the same manner as in Example 1 except that the type of abrasive, the average particle size of the primary particles, the amount added, and the thickness of the magnetic layer were as shown in Table 1. Comparative Example 5 was prepared.

[0054]

[Table 1]

With respect to Examples 1 to 9 and Comparative Examples 1 to 5 manufactured as described above, the surface roughness, the electromagnetic conversion characteristics, and the durability were evaluated.

In this evaluation, the surface roughness was measured using an optical contact type surface roughness meter (device name: Maxim 3D5700, Zyg).
The evaluation was made by measuring the center line average roughness (Ra) using the product of O.

The electromagnetic conversion characteristics were evaluated by measuring the relative output using a fixed head type electromagnetic conversion characteristic measuring device and an 8 mm Hi8 tape manufactured by Sony Corporation as a reference. This fixed head type electromagnetic conversion characteristic measuring device comprises a rotating drum and a magnetic head in contact with the rotating drum, and records and reproduces a sample tape wound on the rotating drum by the magnetic head. At this time, a rectangular wave of 10 MHz was recorded on each sample tape, and a reproduction output level of 10 MHz was detected by a spectrum analyzer. At this time, the relative speed between the sample tape and the magnetic head was 3.33 m / s.

Further, the durability was evaluated by measuring the still durability. That is, each sample tape was loaded into a recording / reproducing apparatus to be in a temporary stop state, and the durability was evaluated by measuring the decay time until the output was attenuated by 3 dB in this state. In this evaluation, the output attenuation may be due to head clock and surface damage. At this time, as a recording / reproducing device, a product name: EV-S55 manufactured by Sony Corporation was used, and the temperature was -5 ° C and 40 ° C / 80%.
The measurement was performed in an environment of RH. This still durability evaluation was performed three times, and as a result, the average decay time was 1 unit.
20 minutes or more are marked as ◎, and the average decay time is 60 to 1
19 minutes were indicated by ○, averaging times of 10 to 59 minutes were indicated by Δ, and averaging times of less than 10 minutes were indicated by X.

Table 2 shows the evaluation results of the surface roughness, the electromagnetic conversion characteristics and the durability.

[0060]

[Table 2]

As is apparent from Table 2, the magnetic recording media shown in Examples 1 to 9 have excellent surface properties,
It has excellent electromagnetic conversion characteristics and excellent durability. Further, in the magnetic recording medium, the addition amount of the first particles is in the range of 1 to 5 parts by weight based on 100 parts by weight of the ferromagnetic powder, and the addition amount of the second particles is 100 parts by weight of the ferromagnetic powder. It can be seen that when the content is within the range of 3 to 10 parts by weight, a better output is exhibited.

On the other hand, as shown in Comparative Example 1, when only an abrasive having an average particle diameter smaller than the thickness of the magnetic layer is used, the surface properties of the magnetic layer are excellent, but the polishing power is high. Since there is no head clock, a head clock or the like is generated, resulting in poor durability. Further, as shown in Comparative Example 2, when an abrasive having an average particle diameter larger than the thickness of the magnetic layer is used, the durability is excellent, but the surface properties are poor and the output level is lowered. .

As shown in Comparative Examples 3 and 4, when the average particle diameter of the abrasive having an average particle diameter larger than the thickness of the magnetic layer exceeds 1.0 μm, the durability is deteriorated. It is excellent, but the surface properties are poor and the output is low. Further, as shown in Comparative Example 5, when graphite having a Mohs hardness of 6 or less was used as an abrasive, durability was poor due to lack of abrasive power, and output was low due to poor surface properties. I have.

[0064]

As is clear from the above description, the magnetic recording medium according to the present invention has a Mohs hardness of 6 or more,
Polishing comprising first particles having an average particle diameter larger than the thickness of the magnetic layer and 1 μm or less, and second particles having an average particle diameter of 6 or more and a Mohs hardness of 6 or more and not more than the thickness of the magnetic layer. By having the agent, the surface properties are excellent and the durability is excellent.

According to the method of manufacturing a magnetic recording medium of the present invention, an abrasive slurry and a magnetic powder slurry are separately prepared at the time of preparing a magnetic paint, and then the abrasive slurry and the magnetic powder slurry are prepared. Is mixed. Therefore, according to this method, the abrasive is well dispersed in the magnetic paint, and as a result, a magnetic recording medium having excellent flatness and excellent durability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic diagram illustrating an example of a coating apparatus of the coating film forming system.

[Explanation of symbols]

 1 non-magnetic support, 2 lower non-magnetic layers, 3 magnetic layers

Claims (6)

[Claims] 1. A non-magnetic layer formed by applying a non-magnetic paint having a non-magnetic powder dispersed in a binder, and a magnetic paint having a magnetic powder and an abrasive dispersed in a binder, A magnetic layer coated on a non-magnetic layer, wherein the abrasive has a Mohs hardness of 6 or more, is larger than the thickness of the magnetic layer, and has an average particle size of 1 μm or less. And a second particle having a Mohs' hardness of 6 or more and having an average particle size not more than the thickness of the magnetic layer. 2. The method according to claim 1, wherein the content of the first particles is 1%.
2. The magnetic recording according to claim 1, wherein the content of the second particles is 3 to 10 parts by weight based on 100 parts by weight of the magnetic powder. Medium. 3. The magnetic recording medium according to claim 1, wherein said magnetic layer has a thickness of 0.5 μm or less. 4. A non-magnetic layer is formed by applying a non-magnetic paint in which a non-magnetic powder is dispersed in a binder, and a binder, a magnetic powder and an abrasive are contained on the non-magnetic layer. A method for producing a magnetic recording medium, comprising forming a magnetic layer by applying a magnetic paint, comprising: a first layer having a Mohs hardness of 6 or more, a thickness greater than the thickness of the magnetic layer, and an average particle size of 1 μm or less. Particles,
Dispersing an abrasive comprising second particles having a Mohs hardness of 6 or more and having an average particle diameter of not more than the thickness of the magnetic layer in a solvent together with a binder to form an abrasive slurry; A step of forming a magnetic powder slurry by dispersing a binder and a magnetic powder in a solvent, separately from the slurry, and mixing the abrasive slurry and the magnetic powder slurry to form a magnetic paint; Forming a magnetic layer by applying a magnetic recording medium. 5. The magnetic recording medium according to claim 4, wherein the non-magnetic paint is applied on a non-magnetic support, and the magnetic paint is applied when the non-magnetic paint is in a wet state. Production method. 6. The method according to claim 4, wherein a calendering process is performed after the step of forming the magnetic layer.