JPH05117704A - Magnetic powder, its production and magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium excellent in electromagnetic conversion characteristic and durability. CONSTITUTION:A magnetic powder with a polymer obtained by polymerizing a monomer having a polymerizable unsaturated double bond deposited on its surface is used as the magnetic powder of a magnetic recording medium. This magnetic powder is produced by polymerizing a monomer having a polymerizable unsaturated double bond in the presence of a magnetic powder. Consequently, the magnetic powder is refined, its dispersibility is remarkably improved, and a magnetic recording medium excellent in electromagnetic conversion characteristic and durability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic powder suitable for magnetic recording media such as magnetic tapes, magnetic sheets and magnetic disks used in audio equipment, video equipment, computers and the like, a method for producing the same, and a magnetic recording medium.

[0002]

2. Description of the Related Art A magnetic recording medium such as a magnetic disk, a floppy disk or a magnetic tape is coated with a magnetic coating composed of magnetic powder and a binder on a surface of a non-magnetic support such as a polyester film and dried to form a magnetic recording layer. It is manufactured by

In recent years, in order to improve the recording density and the S / N ratio of a magnetic recording medium, the magnetic powder used for forming the magnetic recording layer is made finer or highly filled, and the coercive force, the saturation magnetization amount, etc. Methods such as raising it have been developed. With such technological development, it has become an extremely important requirement to improve the dispersibility of the finely divided magnetic powder.

Conventionally, as a method for improving the dispersibility of magnetic powder, a dispersant is used in the preparation of a magnetic paint or water is added, or the magnetic powder and a binder resin are kneaded by applying a high shearing force. Or a method of improving dispersibility by using a polyurethane resin having a sulfonic acid metal salt and a vinyl chloride resin as a binder resin and introducing a polar group into the binder resin.

[0005]

Although the above-mentioned conventional method can improve the dispersibility of the magnetic powder to some extent, the effect of improving the dispersibility is limited, and further improvement is currently desired. is there.

The present invention has been made in view of the above-mentioned conventional circumstances, and a magnetic recording medium excellent in electromagnetic conversion characteristics and excellent in durability, corresponding to high recording density, and magnetic powder used therefor, It is an object to provide a method for producing the magnetic powder.

[0007]

The magnetic powder according to claim 1 has a polymer obtained by polymerizing a monomer having a polymerizable unsaturated double bond on the surface of the magnetic powder.

The method for producing magnetic powder according to claim 2 is the method for producing magnetic powder according to claim 1, in which a monomer having a polymerizable unsaturated double bond is polymerized in the presence of the magnetic powder. Is characterized by.

A magnetic recording medium according to a third aspect is the above-mentioned first aspect.
It is characterized by using the magnetic powder of.

The present invention will be described in detail below.

The magnetic powder of the present invention is a magnetic powder having a polymer obtained by polymerizing a monomer having a polymerizable unsaturated double bond on the surface, and the magnetic powder is preferably a polymerizable unsaturated double bond. It is obtained by polymerizing a monomer having a bond in the presence of magnetic powder.

Examples of the monomer having a polymerizable unsaturated double bond include vinyl monomers, (meth) acrylic monomers, (meth) allyl monomers and the like. (In this specification, "(meth) acrylic" means "acrylic or methacrylic". The same applies to "(meth) allyl" and "(meth) acrylate".) Of the above monomers Examples of vinyl monomers include vinyl halides such as vinyl chloride and vinyl bromide, vinyl acetates such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate, vinyl sulfonic acids or salts thereof, N-vinyl. Examples include formamide, N-vinylacetamide, styrene, styrene derivatives such as styrenesulfonic acid or salts thereof, N-vinylpyrrolidone, vinylpyridine, vinylimidazole and the like.

Examples of the (meth) acrylic monomer include (meth) acrylic acid or a salt thereof, (meth) acrylamide, t-butylacrylamide, diacetoneacrylamide, 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof. , (Meth) acrylamide aminoalkyl derivatives such as, methylenebis (meth) acrylamide, dimethylaminomethyl (meth) acrylamide, dimethylaminoethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, or the like. Neutralized salt of, quaternary salt of alkyl halide, and (meth)
Examples thereof include acrylic acid esters.

Among the esters of (meth) acrylic acid,
Examples of the linear or branched alkyl ester having 1 to 22 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth).
Examples include n-butyl acrylate, isobutyl (meth) acrylate, and t-butyl (meth) acrylate. Further, aromatic esters such as phenyl (meth) acrylate and benzyl (meth) acrylate may be used. Further, a part of hydrogen may be replaced by a halogen atom such as 2-chloroethyl (meth) acrylate and methyl α-chloro (meth) acrylate. Aminoalkyl esters of (meth) acrylic acid include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, and the like. In addition, these neutralized salts and alkyl halides
Grade salt is also good. Further, hydroxyalkyl esters such as 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate, and further ethylene glycol di (meth) acrylate. , Diethylene glycol di (meth) acrylate, or di- or tri (meth) acrylate such as glycerin or trimethylolpropane can also be used.

As the (meth) allyl monomer, for example,
(Meth) allyl alcohol, (meth) allylsulfonic acid or a salt thereof, allylamine, monomethylallylamine,
Examples thereof include dimethylallylamine, diallylamine, n-methyldiallylamine and triallylamine. Further, neutralized salts of these amines or quaternary salts of alkyl halides may be used.

The types of salts of the above monomers include, for example:
There are salts of alkali metals such as sodium and potassium, salts of alkaline earth metals such as calcium and magnesium, ammonium salts, amine salts such as alkylamines having 1 to 22 carbon atoms and alkanolamines, but preferably alkali metal salts. Is.

These monomers may be used alone or in any combination of two or more.

Polymerization of these monomers in the presence of magnetic powder is carried out by adding the magnetic powder to an aqueous or organic medium and at the same time containing one or more polymerizable unsaturated double bonds. It is carried out by dissolving or dispersing a monomer, removing oxygen through an inert gas, and then radically polymerizing in the presence of an inert gas.

From the viewpoint of workability, the aqueous or organic medium used preferably has a boiling point in the range of 60 to 150 ° C., for example, water, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone. , Acetic acid esters such as ethyl acetate and butyl acetate, hexane,
Hydrocarbons such as heptane, and aromatic hydrocarbons such as benzene, toluene, and xylene. These media also
One kind may be used alone, or two or more kinds may be used in combination.

The concentration of the monomer having a polymerizable unsaturated double bond in the aqueous or organic medium is 5 to 90% by weight, preferably 10 to 60% by weight.

In the polymerization, a general radical polymerization initiator is used, and in the case of polymerization in an aqueous solution, for example,
Peroxides such as potassium persulfate and ammonium persulfate, or redox initiators using these, N, N'-azobis- (2-amidinopropane) dihydrochloride, 4,4
A water-soluble radical polymerization initiator such as -azobis- (4-cyanovaleric acid) -2-sodium is desirable. Also, for polymerization in an organic medium, for example, benzoyl peroxide, azobisisobutyronitrile, etc. are used.

The amount of these radical polymerization initiators used is
The amount is usually 0.005 to 5% by weight, preferably 0.05 to 2% by weight, based on the total weight of the copolymerizable polymerizable unsaturated double bond-containing monomer.

The polymerization temperature is usually 10 to 150 ° C.
Is selected according to the molecular weight of the target polymer, but is preferably in the range of 40 to 100 ° C.

The weight average molecular weight (Mw) of the polymer obtained by the polymerization is usually 1,000 to 1,000,
000, preferably 2,000 to 100,000.

Thus, a magnetic powder modified with the polymer (hereinafter sometimes referred to as "modified magnetic powder") is obtained. Depending on the purpose, the water content of the polymer attached to the modified magnetic powder may be further increased. A modification reaction such as decomposition or esterification may be performed.

As the magnetic powder used in the present invention, Fe, Ni, Co, Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Ni-Zn alloy, F
Fe such as e-Co-Ni-Cr alloy and Co-Ni alloy,
Ferromagnetic metals such as Ni and Co or alloy powders containing these as the main components, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Co-containing γ-
Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , iron oxide magnetic powder, C
Various ferromagnetic powders such as metal oxides such as rO ₂ , barium ferrite and strontium ferrite can be used.

The ratio of the polymer adhering to the surface to these ferromagnetic powders is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, with respect to 100 parts by weight of the ferromagnetic powder. Preferably.

In the magnetic recording medium of the present invention, a magnetic coating material is prepared using such a modified magnetic powder, whereby a magnetic recording layer (magnetic layer) containing the modified magnetic powder is non-magnetically supported. It is a magnetic recording medium formed on the body.

In the magnetic recording medium of the present invention, the amount of the modified magnetic powder used is such that the content of the ferromagnetic powder in the magnetic layer is 50 to 90% by weight, preferably 55 to 85% by weight. Is preferred. In the present invention, a normal magnetic powder having no polymer may be mixed with the modified magnetic powder.

As the binder resin used in the magnetic layer, one having excellent adhesion to the non-magnetic support and excellent abrasion resistance is appropriately used. For example, polyurethane resin, polyester resin, cellulose acetate butyrate, cellulose diacetate, cellulose derivative such as nitrocellulose, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Examples thereof include vinylidene chloride copolymers, vinyl chloride resins such as vinyl chloride-acrylic copolymers, various synthetic rubbers such as styrene-butadiene, epoxy resins, phenoxy resins, etc. These may be used alone or in combination of two or more. It can be mixed and used.

The content of the binder resin in the magnetic layer is 2
It is preferably used in an amount of 50 to 50% by weight, particularly 5 to 35% by weight.

In the magnetic recording medium of the present invention, a low-molecular polyisocyanate compound having a plurality of isocyanate groups is further contained in the magnetic coating material to form a three-dimensional network structure in the magnetic layer, and its mechanical strength. Can be improved. Examples of the low molecular weight polyisocyanate compound include trimethylolpropane adduct of tolylene diisocyanate. Such a low molecular weight polyisocyanate compound has a binder resin content of 5
It is preferably used in a proportion of ˜100% by weight.

Further, various additives such as a lubricant, an abrasive and an antistatic agent can be further used in the magnetic coating material forming the above magnetic layer.

Here, as the lubricant, an aliphatic type, a fluorine type, a silicone type or a hydrocarbon type lubricant can be used. Examples of the aliphatic lubricant include fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, and aliphatic alcohols. Preferable examples of the fatty acid include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid and behenic acid, and examples of the metal salt of fatty acid include Mg salt, Al salt, Na salt and Ca salt of these fatty acids. Are preferred. Preferable examples of the fatty acid ester include butyl, octyl ester and glyceride of the above fatty acids, and examples of the fatty acid amide and aliphatic alcohol include amides of the above acids, alcohols, linoleic acid amides and caproic acid amides. As the fluorine-based lubricant, perfluoropolyether, perfluoroalkylpolyether, perfluoroalkylcarboxylic acid, etc.
Also, as a silicone-based lubricant, silicone oil,
Modified silicone oil and the like and paraffin, squalane, wax and the like are preferable as the hydrocarbon lubricant. The content of the lubricant in the magnetic layer is usually 0.5 to 20% by weight, preferably 1 to 10% by weight. When two magnetic layers are laminated, the content of the lubricant may be different between the upper layer and the lower layer.

Examples of the abrasive include known materials such as alumina, silicon carbide, chromium oxide and silicon nitride, and the content in the magnetic layer is preferably in the range of 1 to 20% by weight.

As the antistatic agent, carbon black,
In addition to inorganic particles such as graphite, an organic antistatic agent can be used, and the content thereof is usually 1 to 15% by weight in the magnetic layer.

Kneading, dispersion of a magnetic coating material containing the above components,
As the solvent used at the time of coating, toluene, methyl ethyl ketone, methyl isobutyl ketone, ketone-based such as cyclohexanone, alcohol-based such as methanol, ethanol, propanol, isopropyl alcohol, ester-based such as methyl acetate, ethyl acetate, butyl acetate, An ether type such as diethyl ether and tetrahydrofuran, an aromatic type such as benzene, toluene and xylene, and a hydrocarbon type such as hexane can be used.

The method of kneading and dispersing, the order of addition of each component and the like are carried out by the usual methods applied to kneading and dispersing magnetic coating materials.

The magnetic coating material thus prepared is coated on a non-magnetic support and dried to obtain the magnetic recording medium of the present invention.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose acetate, plastics such as polycarbonate, polyamide and polyimide, and aluminum and glass. Can also be used.

As a method of applying the magnetic coating material to such a non-magnetic support, various methods such as air doctor coating, blade coating, reverse roll coating, gravure coating and the like which are usually applied are adopted. When a plurality of magnetic coating materials are applied, the lower layer coating solution and the upper layer coating solution may be applied simultaneously in a wet state, or each layer may be applied sequentially.

The thickness of the magnetic layer formed on the non-magnetic support is usually 0.1 to 10 μm, and preferably 0.3 to 2 μm after drying.

After the formation of the magnetic layer, an orientation treatment, a random treatment, a smoothing treatment, or the like may be further performed, if necessary.

[0044]

The modified magnetic powder in which the polymer is adhered to the surface by polymerizing a monomer having a polymerizable unsaturated double bond has a significantly improved dispersibility due to the polymer on the surface. .. Therefore, by using this modified magnetic powder, a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent durability is provided.

[0045]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

[0046] Examples 1-9 Aratameshitsu磁 soluble powder produced in Example 1 condenser and a thermometer, a nitrogen inlet tube, fitted with a stirrer 30
Co-γ-Fe ₂ O ₃ magnetic powder (Hc = 700 Oe, specific surface area (SSA) = 20 m ^{2 in a} 0 ml four-necked flask.
/ G) 100 g, 112.5 g of 20 wt% sodium acrylate aqueous solution prepared in advance, and 47.3 g of demineralized water
After adding, the mixture was stirred uniformly using a stirrer.

Nitrogen was introduced from the nitrogen introducing tube to sufficiently replace oxygen in the system, and then the temperature was raised to 60 ° C. Next, as a polymerization initiator, 2,2′-azobis (2-amidinopropane)
Polymerization was initiated by adding 0.795 g of a 5% by weight aqueous solution of dihydrochloride, and polymerization was carried out for 6 hours to obtain a magnetic powder-containing polymer solution.

By thoroughly washing the above magnetic powder-containing polymer solution with demineralized water to remove the polymer not attached to the magnetic powder, the polymer is dried at 60 ° C. to be surface-modified with the polymer. A modified magnetic powder was obtained.

The amount of the polymer adhering to the obtained modified magnetic powder measured by a differential thermogravimetric analyzer was 3.
It was 0% by weight. The molecular weight of the polymer that was not attached was measured and found to be Mw = 23,000.

Example 2 In Example 1, instead of sodium acrylate, the molar ratio of acrylic acid and methyl methacrylate was 90:10.
Polymerization and purification were carried out in the same manner as in Example 1 except that the above-mentioned monomer was used.
A modified magnetic powder having a weight% of polymer attached was obtained.

Example 3 Example 1 was repeated except that a monomer having a molar ratio of acrylic acid to 2-hydroxyethyl methacrylate of 50:50 was used in place of sodium acrylate in Example 1. Polymerization and purification were performed in the same manner as in 1. to obtain a modified magnetic powder having 3.8% by weight of the polymer attached to the magnetic powder.

Example 4 20% by weight of sodium acrylate in Example 1
Polymerization and purification were performed in the same manner as in Example 1 except that a 30% by weight aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate was used as a monomer instead of the aqueous solution, and the magnetic powder was obtained. A modified magnetic powder having 4.3% by weight of the polymer attached was obtained.

Example 5 Polymerization and purification were carried out in the same manner as in Example 1 except that ethyl trimethylammonium methacrylate chloride was used as a monomer instead of sodium acrylate in Example 1, to obtain a magnetic powder. On the other hand, a modified magnetic powder having 4.1% by weight of the polymer attached was obtained.

Example 6 20% by weight of sodium acrylate in Example 1
Instead of the aqueous solution, 5 parts of sodium methallyl sulfonate
Polymerization and purification were carried out in the same manner as in Example 1 except that a 0% by weight aqueous solution was used as a monomer to obtain a modified magnetic powder in which 4.9% by weight of the polymer was attached to the magnetic powder. It was

Example 7 30 equipped with a cooling pipe, a thermometer, a nitrogen introducing pipe, and a stirrer
After adding 100 g of the same magnetic powder as used in Example 1, 32.0 g of methyl methacrylate, and 121.6 g of acetone to a 0 ml four-necked flask, the mixture was uniformly stirred using a stirrer.

Nitrogen was introduced from the nitrogen introducing tube to sufficiently replace oxygen in the system, and then the temperature was raised to 50 ° C. Next, 6.4 g of a 5% by weight acetone solution of 2,2′-azobisisobutyronitrile was added as a polymerization initiator to start polymerization, and polymerization was performed for 6 hours to give a magnetic powder-containing polymer solution. Obtained.

The polymer solution containing the magnetic powder was thoroughly washed with acetone to remove the polymer not attached to the magnetic powder, followed by drying at 60 ° C. and surface modification with the polymer. A modified magnetic powder was obtained.

The amount of polymer adhering to the obtained modified magnetic powder measured by a differential thermogravimetric analyzer was 4.
It was 7% by weight. The molecular weight of the polymer that did not adhere was measured and found to be Mw = 8,500.

Example 8 30 equipped with a cooling pipe, a thermometer, a nitrogen introducing pipe, and a stirrer
In a 0 ml four-necked flask, 100 g of the same magnetic powder as used in Example 1, 27.68 g of vinyl acetate, 4.32 g of acrylonitrile, and 121.6 tetrahydrofuran.
After adding g, the mixture was stirred uniformly using a stirrer.

Nitrogen was introduced from the nitrogen introducing tube to sufficiently replace oxygen in the system, and then the temperature was raised to 60 ° C. Next, 6.4 g of a 5% by weight acetone solution of 2,2′-azobisisobutyronitrile was added as a polymerization initiator to start polymerization, and polymerization was performed for 6 hours to give a magnetic powder-containing polymer solution. Obtained.

By thoroughly washing the above magnetic powder-containing polymer solution with tetrahydrofuran (THF), the polymer not attached to the magnetic powder is removed and dried at 60 ° C., and the surface of the polymer is modified. Magnetic powder was obtained.

The amount of polymer adhering to the obtained modified magnetic powder measured by a differential thermogravimetric analyzer was 5.
It was 0% by weight. Example 9 30 equipped with a cooling pipe, a thermometer, a nitrogen introducing pipe, and a stirrer
100 g of the same magnetic powder as used in Example 1, 10.53 g of vinyl chloride, 1.61 g of vinyl acetate, and 121.6 g of THF were added to a 0 ml four-necked flask, and then uniformly stirred using a stirrer.

Nitrogen was introduced from the nitrogen introducing tube to sufficiently replace oxygen in the system, and then the temperature was raised to 60 ° C. Next, as a polymerization initiator, 6.4 g of a 5% by weight solution of 2,2'-azobisisobutyronitrile in dimethylsulfoxide was added to initiate polymerization, and the polymerization was continued for 8 hours to obtain a magnetic powder-containing polymer solution. Got

By thoroughly washing the above magnetic powder-containing polymer solution with THF to remove the polymer not attached to the magnetic powder and replacing it with acetone, drying was carried out at 100 ° C. and the surface of the polymer was removed. A modified magnetic powder was obtained.

The amount of polymer adhering to the obtained modified magnetic powder measured with a differential thermogravimetric analyzer was 4.
It was 9% by weight. Example 10-18 to prepare a magnetic paint manufacturing and Evaluation Example 10 The following formulation magnetic recording recording medium, so that the thickness of the magnetic layer after drying the polyethylene terephthalate on the film thickness of 75μm is 1.0μm Applied. Further, after carrying out a surface smoothing treatment, it was punched out into a 3.5 inch disk to manufacture a floppy disk.

Magnetic paint formulation (parts by weight) Modified magnetic powder obtained in Example 1: 100 Polyurethane (N2304 manufactured by Nippon Polyurethane Co.): 15 Vinyl chloride-vinyl acetate copolymer ("VAGH" manufactured by UUC) ): 15 carbon black (“# 3250B” manufactured by Mitsubishi Kasei Co., Ltd.): 8 α-alumina (“AKP-20” manufactured by Sumitomo Chemical Co., Ltd.): 6 butyl stearate: 8 Tolylene diisocyanate adduct of trimethylolpropane: 10 Methyl ethyl ketone: 195 Cyclohexanone: 195 The surface gloss, S / N ratio, and durability of the obtained floppy disk were evaluated by the following methods, and the results are shown in Table 1.

The S / N ratio was set to 2 by rotating at 300 rpm using a ferrite head having a head gap of 0.9 μm.
It was determined by recording a 50 KHz digital signal and measuring the ratio of the signal and noise during reproduction.

The durability test was conducted at a temperature of 45 ° C. and a relative humidity of 80.
% Environment for 7 hours, temperature 5 ° C relative humidity 50% over 5 hours, and this environment for 7 hours
Take a total of 24 hours to return to the initial environment
The test was conducted under cyclical environmental changes. The evaluation was represented by the number of cycles that could be repeatedly carried out without deterioration in output (80% or less of the initial value) or deterioration such as scratches on the medium.

For the gloss, the surface after the smoothing treatment has an incident angle of 60.
It was determined by measuring the total reflectance at 60 ° and a reflection angle of 60 ° using a standard gloss meter.

Example 11 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 2 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 12 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 3 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 13 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 4 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 14 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 5 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 15 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 6 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 16 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 7 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 17 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 8 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Example 18 A floppy disk was manufactured in the same manner as in Example 10 except that the modified magnetic powder obtained in Example 9 was used as the magnetic powder, and the evaluation results are shown in Table 1.

Comparative Example 1 A floppy disk was manufactured in the same manner as in Example 10 except that untreated magnetic powder (magnetic powder used as a raw material in Example 1) was used as the magnetic powder, and the evaluation results are shown. The results are shown in Table 1.

[0079]

[Table 1]

[0080]

As described above in detail, according to the magnetic recording medium of claim 3 which uses the modified magnetic powder of claim 1, a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent durability is provided. ..

Therefore, according to the method of claim 2, it is possible to easily and efficiently produce the modified magnetic powder of claim 1.

Claims (3)

[Claims] 1. A magnetic powder comprising a polymer obtained by polymerizing a monomer having a polymerizable unsaturated double bond on the surface of the magnetic powder. 2. A monomer having a polymerizable unsaturated double bond is polymerized in the presence of magnetic powder.
A method for producing the magnetic powder described above. 3. A magnetic recording medium using the magnetic powder according to claim 1.