JPH05120668A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a high-density magnetic recording medium excellent in magnetic recording characteristics by improving the dispersibility and dispersion stability of the ferromagnetic powder in a magnetic coating material. CONSTITUTION:The magnetic recording medium is constituted by providing the magnetic coating film incorporating at least the ferromagnetic powder and the binder on a nonmagnetic base and incorporates the soft magnetic powder having <=0.01mum average grain size in the relevant magnetic coating film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium, and more particularly to a magnetic recording medium comprising a non-magnetic support and a magnetic coating film containing at least a ferromagnetic powder, and more particularly hexagonal barium. It is suitable for a high-density recording medium having a high recording density using a ferromagnetic powder such as ferrite, Co-coated γ-iron oxide, and metal powder.

[0002]

2. Description of the Related Art In recent years, high density magnetic recording media have been studied, and as a ferromagnetic powder, Co-deposited γ-iron oxide having a small particle size,
Attention has been focused on metal magnetic powder having a small particle size and high coercive force, and hexagonal ferrite powder having a hexagonal plate shape and a minute particle size.

However, when these ferromagnetic powders are used as paints, the quality of the dispersion has always been a problem, and a sufficient solution has not yet been reached.

For example, since hexagonal ferrite powder has an axis of easy magnetization in the direction perpendicular to the plate surface, the powder particles are closely adhered to each other in the paint and form extremely strong agglomerates. In addition, metal magnetic powder is larger than oxide-based magnetic powder,
Since they have a magnetic moment, the powders strongly attract each other even in the paint to form extremely strong aggregates.

As a binder for the magnetic powder, vinyl chloride-vinyl acetate copolymer, fibrin resin, polyurethane resin, polyester resin, polyester-polyurethane resin, polycarbonate-polyurethane resin, polyvinyl butyral resin, etc. Various have been investigated to improve dispersibility. However, it cannot be said that sufficiently good results have been obtained.

Accordingly, in recent years, in particular, from the viewpoints of dispersibility and packing of magnetic powder, polar groups such as sulfonate group, sulfate ester group, phosphate ester group, phosphonate group, and carboxylate group are used as binders. Resins added to the skeleton or side chains have been widely used.

However, the above-mentioned metal magnetic powder and hexagonal ferrite powder have a very strong cohesive force, and it is difficult to finely disperse the agglomerates even if the binder is used, and only a paint having insufficient dispersibility can be obtained. However, it is difficult to obtain a satisfactory magnetic recording medium.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to improve the dispersibility and dispersion stability of ferromagnetic powder in a magnetic coating material so as to achieve further surface smoothness and high density of a magnetic coating film. It is an object of the present invention to provide a magnetic recording medium having excellent magnetic recording characteristics, particularly high density magnetic recording characteristics.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, co-existed with a ferromagnetic powder a soft magnetic magnetic powder having an average particle diameter of 0.1 μm or less in a magnetic coating material. When the magnetic powder is dispersed, the soft magnetic powder enters the gap where the aggregation of the ferromagnetic powder is loosened to promote the dispersion of the magnetic powder, and the loosened magnetic powder is re-aggregated in the paint. Is prevented (for example, even if the coating is left for a long time and then formed into a coating film, "bumping" due to re-aggregation hardly occurs), and therefore the surface smoothness of the magnetic layer (magnetic coating film) can be significantly improved. The present invention has been found.

That is, the present invention is a magnetic recording medium comprising a non-magnetic support and a coating film of a magnetic coating material containing a ferromagnetic powder, the magnetic coating material having an average particle diameter of 0.1 μm or less. The magnetic magnetic powder was added in an amount of 0.
The magnetic recording medium is characterized by containing 01 to 20 parts by weight.

The soft magnetic magnetic powder (hereinafter referred to as “A powder”) used in the present invention is a fine powder having an average particle size of 0.1 μm or less, and is written by Satoshi Konnozumi (published by Sokabo) in “ferromagnetic material”. Physical (lower) magnetic properties and applications "368 to 376, that is, a soft magnetic material, that is, a fine powder of metal or oxide having a high magnetic susceptibility and a low coercive force is preferably used.
Among these soft magnetic materials, the material used for the magnetic head material can be more preferably used than the material used for the magnetic core material of the high-voltage equipment.

Examples of such soft magnetic materials include the following. Alloy-based materials include iron silicon alloy, iron-aluminum alloy, iron-nickel alloy, iron-cobalt alloy,
Iron-cobalt-nickel alloys, nickel-cobalt alloys, etc., sendust, etc. as amorphous alloy materials, and Mn-Zn ferrites, Ni-Zn ferrites, Mg-Zn ferrites, Mg as oxide materials. —Mn-based ferrite and the like can be mentioned.

The powder A can be produced from these soft magnetic materials by a pulverization method or other known methods, in particular, various methods proposed for producing magnetic particles.

The powder A produced by such a method is preferably made to coexist with the ferromagnetic powder before the dispersion treatment step of the ferromagnetic powder for the purpose of use, but it can be added at the stage after the dispersion treatment step.

The powder A may be added in the form of a dispersion liquid in advance, or may be added in the form of powder.

The powder A may be used in an amount of 0.01 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder. In particular, in order to improve the dispersibility, it is preferable to add 0.1 to 20% by weight. Considering the filling property of the magnetic powder in the coating film,
A range of 2 to 15 parts by weight is preferably selected.

In the present invention, the non-magnetic support is not particularly limited, and those commonly used can be used.
Examples of materials forming the non-magnetic support include various synthetic resins such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polyethylene, polypropylene, polycarbonate, polyamide, polyamideimide, polyimide, polysulfone and polyethersulfone. Films and metal foils such as aluminum foil, stainless steel foil can be raised.

In the present invention, there is no limitation on the ferromagnetic powder, and those commonly used can be used, but especially C
O-coated γ-iron oxide powder, Fe-based metal powder, hexagonal barium ferrite powder and the like are preferable. Co-deposition γ
As the iron oxide powder, one having a saturation magnetization of more than 70 emu / g, a specific surface area of 20 to 60 m ² / g, an acicular ratio (axial ratio) of 5 to 15, and a coercive force of 400 to 1000 Oe (Oersted) is used. preferable. Further, as the metal powder mainly composed of Fe, one having a saturation magnetization of more than 100 emu / g, a specific surface area of 30 to 70 m ² / g, an acicular ratio of 5 to 15, and a coercive force of 500 to 3000 Oe. Is preferred. The hexagonal barium ferrite powder has a saturation magnetization of more than 50 emu / g and a specific surface area of 25 to 60.
m ² / g, plate ratio 2 to 10, coercive force 200 to 200
Those in the range of 0 Oe are preferable.

In the present invention, the magnetic paint is prepared by mixing and dispersing such a ferromagnetic powder and A powder, specifically a soft magnetic magnetic powder, with a binder, and this dispersion process is a known method or Methods accumulated in the art can be used.

In the present invention, the binder is not particularly limited, but those containing at least one of a sulfonate group and a sulfobetaine group are preferably applied.

The resin having at least one of sulfonate group and sulfobetaine group may be any resin having at least one of sulfonate group and sulfobetaine group in the molecule. Examples include urethane resins, polyester resins, vinyl chloride-based copolymers, vinylidene chloride-based copolymers, acrylic resins, butadiene-acrylonitrile-based polymers, and styrene-butadiene-based copolymers.

As the polar group-introduced binder, a commercially available binder may be used, and it can be produced according to the method of a known document or partially modified if desired. To give some examples of these, the production of polyester binders: JP-A-54-143117 and JP-A-54-15141.
No. 7, No. 54-157603, No. 56-74827
No. 59-132418, No. 59-172118
No. 60-55514, JP-A-1-95126, and the production of polyurethane binders: JP-A-57-9
No. 2423, No. 58-41436, No. 61-2023
No. 27, No. 62-28927, No. 62-66420
No. 1, JP-A 1-115920, Production of polyurethane and polyurea binders: JP-A-62-2892
No. 0, Production of vinyl polymerization binder: JP-A-58-1
08032, 60-121514, 61-32
No. 216, No. 61-39927, No. 62-20841
No. 9, the preparation of betaine (other) binders: JP-A-60-177427 and the like.

The content of the polar group in the resin is at least 1.
It is preferably × 10 ⁻⁶ equivalent / g (resin) or more,
Further, from the viewpoint of dispersion of magnetic powder and prevention of re-aggregation, more preferably 1 × 10 ⁻⁶ to 1 × 10 ⁻² equivalent / g (resin), particularly preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻² equivalent / It is in the range of g (resin).

The amount of the polar group-containing resin used is 0.1 to 50 parts by weight, and further 0.5 to 100 parts by weight of the ferromagnetic powder.
It is preferably 40 parts by weight, particularly preferably 1 to 30 parts by weight. Regarding the polar group-containing resin, considering not only the weight ratio but also the amount of polar groups in the resin, the amount of polar groups per 100 g of ferromagnetic powder is 1 × 10 ⁻⁶ to 1 × 10 ⁻² equivalent / 100 g of magnetic powder, 2 × 10 ⁻⁶ to 1 × 10 ⁻² equivalent / 100 g magnetic powder, especially 5
It is preferable to use x10 ^{-6 to} 5x10 ^-3 equivalent / 100 g of magnetic powder.

In addition to the above-mentioned ferromagnetic powder, A powder, and sulfonate-containing resin, the magnetic coating material of the present invention may contain components that have been known or used in the past. For example, a binder such as a thermoplastic resin, a thermosetting resin, or a reactive resin, an abrasive, an antistatic agent, a reinforcing agent,
Dispersants, lubricants and the like can be contained alone or in combination.

This thermoplastic resin has a softening temperature of 15
0 ° C. or less, average molecular weight 10,000 to 300,000
0, having a degree of polymerization of about 50 to 2,000, for example, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinylidene chloride copolymer, vinyl chloride / acrylonitrile copolymer, acrylic ester / acrylonitrile copolymer Coalescence, acrylic acid ester / vinylidene chloride copolymer, acrylic acid ester / styrene copolymer, methacrylic acid ester / acrylonitrile copolymer, methacrylic acid ester / vinylidene chloride copolymer, methacrylic acid ester / styrene copolymer, urethane Elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate Tate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene / butadiene copolymer, polyester resin, chlorovinyl ether / acrylic acid ester copolymer, amino resin, various synthetic rubber Thermoplastic resins and mixtures thereof are used.

The thermosetting resin or the reaction type resin has a molecular weight of 200,000 or less in the state of a coating solution, and by heating after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Become. Further, among these resins, those which are not softened or melted before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin and isocyanate prepolymer. Polymer mixture, methacrylate copolymer and diisocyanate prepolymer mixture, polyester polyol and polyisocyanate mixture, urea formaldehyde resin, low molecular weight glycol /
A mixture of a high molecular weight diol / triphenylmethane triisocyanate, a polyamine resin, a mixture thereof and the like can be used.

These binders may be used alone or in combination. The mixing ratio of the ferromagnetic fine powder and the binder in the magnetic layer is a weight ratio, and is based on 100 parts by weight of the ferromagnetic fine powder.
The binder is used in the range of 5 to 300 parts by weight.

As the polishing agent, generally used materials are fused alumina, silicon carbide and chromium oxide (Cr
₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main component:
Corundum and magnetite) are used. These abrasives have a Mohs hardness of 5 or more and an average particle size of 0.05 to
Those having a size of 5 μm are effective, and preferably 0.4
Is about 1.5 μm. These abrasives are added in the range of 7 to 15 parts by weight based on 100 parts by weight of the binder. When the amount is less than 7 parts by weight, sufficient durability cannot be obtained, and when the amount is more than 15 parts by weight, the filling degree is reduced and sufficient output cannot be obtained.

As the antistatic agent, carbon black,
Conductive fine powder such as carbon black graft polymer; natural surfactant such as saponin; nonionic surfactant such as alkylene oxide type, glycerin type, glycidol type; higher alkylamines, quaternary ammonium salts, pyridine and other complex Cationic surfactants such as rings, phosphoniums or sulfoniums; anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group; amino acids,
Amphoteric activators such as amino sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used.

The conductive fine powder is 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder, and the surfactant is 0.1 to 20 parts by weight.
It is added in the range of 10 parts by weight.

These surfactants are used alone or as a mixture, but sometimes they are used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity and coating aid. ..

As the dispersant (pigment wetting agent), the carbon number of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid, etc. 12-
22 fatty acids (R ₁ COOH, R ₁ has 11 to 22 carbon atoms
An alkyl or alkenyl group); a metal soap comprising an alkali metal (Li, Na, K, etc.) or alkaline earth metal (Mg, Ca, Ba) of the above fatty acid; a fluorine-containing compound of the above fatty acid ester; Amides of fatty acids; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy fourth
Quaternary ammonium salt (alkyl has 1 to 5 carbon atoms, olefin has ethylene, propylene, etc.); other coupling agents (for example, silane coupling agent, titanium coupling agent, etc.) and the like are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfuric acid ester and the like can be used. These dispersants are added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder.

As the lubricant, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms).
5. Alkoxy has 1 to 4 carbon atoms, silicon oil such as phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms), conductive fine powder such as graphite, molybdenum disulfide, tungsten disulfide, etc. Inorganic fine powder; polyethylene, polypropylene, polyethylene-vinyl chloride copolymer, polytetrafluoroethylene, and other plastic fine powder; α-olefin polymer; unsaturated aliphatic hydrocarbons that are liquid at room temperature (n-olefin double bond Compound bound to terminal carbon, carbon number about 20); monobasic fatty acid having 12 to 20 carbon atoms and 3 carbon atoms
Fatty acid esters consisting of ~ 12 monohydric alcohols,
Examples are fluorocarbons. These lubricants are added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder.

A low molecular weight isocyanate compound is preferably used as the curing agent. As the low molecular weight isocyanate compound, tolylene diisocyanate, 4,
4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate,
Isocyanates such as naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of the isocyanates and polyalcohols, and polyisocyanates formed by condensation of the isocyanates It can be illustrated. Commercially available trade names of these low molecular weight isocyanate compounds are Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL (manufactured by Nippon Polyurethane Co., Ltd.), Takenate D-102, Takenate D-110N. , Takenate D-200, Takenate D-202 (Takeda Pharmaceutical Co., Ltd.)
Made), Death Module L, Death Module 1L, Death Module N, Death Module HL (Sumitomo Bayer Ltd.)
Manufactured) and the like. These can be used alone or in combination of two or more by utilizing the difference in curing reactivity.

The magnetic coating material of the present invention can be manufactured by a conventionally known method.

An organic solvent is preferable as the solvent used for preparing the magnetic coating material. Examples of the organic solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran in any ratio; methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate,
Ester-based solvents such as ethyl lactate, glycol acetate and monoethyl ether; glycol ether-based solvents such as ether, glycol dimethyl ether and dioxane; tar-based solvents such as benzene, toluene, xylene, cresol, chlorobenzene and styrene (aromatic hydrocarbons) );
Chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde and hexane can be used.

In kneading and dispersing the ferromagnetic powder and the above-mentioned respective components, the ferromagnetic powder and the respective components are all charged into the disperser at the same time or individually. For example, there is a method in which magnetic powder is added to a solvent containing a dispersant and the dispersion is continued for a predetermined time to obtain a magnetic coating material. At that time, the magnetic powder is A
It is preferable to make the powder coexist with the powder in advance, and it is preferable to mix with other components in this coexisting state. This makes the action of the A powder more effective.

Various dispersers can be used for kneading and dispersing the magnetic paint. For example, two roll mill, three roll mill, ball mill, pebble mill, tron mill, sand glider, Szegvari attritor, high speed impeller disperser, high speed stone mill, high speed impact mill,
A disper, a kneader, a high speed mixer, a homogenizer, an ultrasonic disperser or the like can be used.

As a technique for kneading and dispersing, see D.C. Patton, "Paint Flow and Pigment Dispersion" (19
1975) can be used.

As a method of applying the magnetic coating material thus obtained onto a non-magnetic support, a conventionally known method can be used. For example, two or more magnetic layers may be simultaneously provided by a multi-layer simultaneous coating method.

According to such a method, the magnetic layer coated on the support is optionally subjected to the treatment for non-orienting the magnetic material in the layer as described above, and then the formed magnetic layer is dried.
If necessary, the surface is smoothed or punched into a desired shape to obtain a magnetic disk.

The magnetic layer has a dry thickness of about 0.2 to 12
It is applied so that it is in the range of μm, preferably 0.3 to 4 μm. In the case of multiple layers, the total is within the above range. The dry thickness may be determined depending on the use, shape, standard, etc. of the magnetic recording medium.

This magnetic layer has very few surface defects due to poor dispersion of ferromagnetic powder and re-aggregation, and has extremely excellent surface smoothness. For example, the center line average roughness (Ra) is 0.020 μm.
It is a magnetic layer which is extremely smooth as m or less, has little noise, has a good S / N ratio, and has remarkably improved recording characteristics at short wavelengths.

[0045]

EXAMPLES The present invention will be further described with reference to examples of flexible magnetic disks. The properties in the examples were obtained by the following methods.

1. Dispersion degree of coating material A magnetic coating material is applied on the surface of a polyethylene terephthalate film having a thickness of 75 μm so that the thickness after drying becomes 3.0 ± 1.0 μm, followed by drying and smoothing treatment. The obtained coating film is observed with a differential phase contrast microscope (magnification: 100 times), the number of irregularities having a diameter of 20 μm or more in the visual field is counted in one arbitrary visual field, and the number is defined as the paint dispersity.

2. Short wavelength recording characteristics Using a 3.5 inch floppy disk drive having a cap length of 0.3 μm and a ring type Mn—Zn ferrite head, recording wavelengths of 0.7 and 1.5 at optimum recording currents.
Measure the output in μm. This output is shown as the output of the reference disk being 0 dB.

3. S / N (signal / noise) ratio Recording wavelength 0.7 μm at the innermost part of the recording area of the disc
Was measured at.

[0049]

Examples 1 to 8 and Comparative Examples 1 and 2 The magnetic coating materials of Examples 1 to 5 were prepared as follows. That is, the following hexagonal barium ferrite 80 parts by weight (specific surface area: 50 m ² / g, coercive force: 800 Oe plate ratio: 7) A powder (see Table 1) See Table 1 Polyurethane 6 parts by weight (Kyowa Fermentation Industry ( Ltd .; Esten 5701 F1) Vinyl chloride / vinyl acetate resin 6 parts by weight (Nisshin Chemical Co., Ltd. TA-5C) α-alumina 5 parts by weight (Sumitomo Chemical Co., Ltd. AKP-20) Oleic acid oleyl ester 5 parts by weight Carbon Black 5 parts by weight (Mitsubishi Kasei Co., Ltd. # 3950) Garfac RE610 3 parts by weight (Toho Chemical Co., Ltd.) Cyclohexanone 400 parts by weight A composition consisting of 400 parts by weight was mixed and dispersed in a sand grinder, and then Coronate L 10 parts by weight (Japan Polyurethane Co., Ltd .: low molecular weight isocyanate) was added and further mixed in a high speed disperser to prepare a magnetic paint.

As the magnetic paints of Comparative Examples 1 and 2, α-Fe ₂ O ₃ shown in Table 1 was used instead of the powder A in Example 1.
Magnetic paints having the same composition except that (Comparative Example 1) and SiO ₂ (Comparative Example 2) were prepared in exactly the same manner.

Further, the magnetic paints of Examples 6 to 8 were applied to Examples 1 to 1.
It adjusted like 5th. That is, the following hexagonal barium ferrite 80 parts by weight (specific surface area: 50 m ² / g, coercive force: 800 Oe plate ratio: 7) A powder (see Table 1) See Table 1 Polyurethane 4 parts by weight (Kyowa Fermentation Industry ( Ltd .; Esten 5701 F1) 2 parts by weight of resin containing sulfonate group MR110 (Example 6), TP-249 (Examples 7 and 8) 4 parts by weight of vinyl chloride / vinyl acetate resin (Nisshin Chemical Co., Ltd. TA- 5C) α-alumina 5 parts by weight (Sumitomo Chemical Co., Ltd. AKP-20) Oleic acid oleyl ester 5 parts by weight Carbon black 5 parts by weight (Mitsubishi Kasei Corporation # 3950) Garfac RE610 3 parts by weight (Toho Chemical Co., Ltd. )) Cyclohexanone (400 parts by weight) was mixed and dispersed in a sand grinder, and then 10 parts by weight of Coronate L (Nippon Polyurethane Co., Ltd .: low molecular weight isocyanate) was added and mixed in a high-speed disper. , To prepare a magnetic paint.

Here, MR110 is a vinyl chloride / vinyl acetate containing sulfonate group of Nippon Zeon Co., Ltd., and TP-
249 is a sulfonate group-containing polyester polyurethane manufactured by Nippon Gosei Co., Ltd.

The obtained magnetic coating composition was aged at 15 ° C. for 24 hours, applied on one surface of polyethylene terephthalate having a thickness of 75 μm so that the thickness after drying was 2.5 μm, and after non-orientation treatment, dried. Then, the magnetic layer was calendered. Further, the same treatment was performed on the back surface.
After heat treatment at 60 ° C. for 100 hours, a disk-shaped magnetic disk was punched out. The characteristics of this magnetic disk are shown in Table 1.

By using the powder A, as shown in Table 1, the dispersibility of the coating material, particularly the dispersion stability, is remarkably improved. Furthermore, in industrial products, it is not desirable that the quality of the products at the beginning and the end of the production will vary, but the variation in quality is also minimal because the coating is stabilized by the use of powder A (short wavelength recording characteristics evaluation ).
Furthermore, the S / N ratio is greatly improved.

The S / N ratio and short wavelength recording characteristics in Table 1 are shown by using Comparative Example 1 as a reference disk.

[0056]

[Table 1]

[0057]

Examples 9 to 14 and Comparative Examples 3 and 4 The magnetic paints of Examples 9 to 11 were prepared as follows using Co-adhered gamma iron oxide. That is, the following Co-adhered γ iron oxide 70 parts by weight (specific surface area 50 m ² / g, coercive force 750 Oe, acicular ratio 10) A powder (see Table 2) 3 parts by weight Resin containing sulfonate group (Table 2 6 parts by weight Garfac RE610 (Toho Chemical Co., Ltd.) 3 parts by weight Polyurethane 6 parts by weight (Dainippon Ink and Chemicals, Inc .: Spandex T-5250) 8 parts by weight vinyl chloride / vinyl acetate resin (Nisshin Chemical Co., Ltd.) ) TA-5C) α-alumina 4 parts by weight (Sumitomo Chemical Co., Ltd. AKP-20) Carbon black 6 parts by weight (Mitsubishi Kasei Co. # 3950) Oleyl oleate 6 parts by weight Cyclohexanone 400 parts by weight After mixing and dispersing with a sand grinder, 10 parts by weight of Coronate L (Nippon Polyurethane Co., Ltd .: low molecular weight isocyanate) was added, and further mixed in a high speed disperser to prepare a magnetic paint.

As Comparative Example 3, A in Example 9 was used.
A magnetic paint prepared in exactly the same manner was prepared except that α-Fe ₂ O ₃ was used instead of the powder.

Further, magnetic iron magnetic powder was used as the magnetic coating material of Examples 12 to 14 to make the following adjustments. That is,
70 parts by weight of the following metallic iron magnetic powder (specific surface area 50 m ² / g, coercive force 1500 Oe needle ratio 10) A powder (see Table 2) 3 parts by weight Resin containing sulfonate group, etc. (see Table 2) 6 parts by weight Garfac RE610 (Toho Chemical Co., Ltd.) 3 parts by weight Polyurethane 6 parts by weight (Dainippon Ink and Chemicals Co., Ltd .: Spandex T-5250) 8 parts by weight vinyl chloride / vinyl acetate resin (Nisshin Chemical Co., Ltd. TA-5C) α-alumina 4 parts by weight (Sumitomo Chemical Co., Ltd. AKP-20) Carbon black 6 parts by weight (Mitsubishi Kasei Co. # 3950) Oleyl oleate 6 parts by weight Cyclohexanone 400 parts by weight A composition is mixed and dispersed by a sand grinder. After that, 10 parts by weight of Coronate L (Nippon Polyurethane Co., Ltd .: low molecular weight isocyanate) was added and further mixed in a high-speed disperser to prepare a magnetic paint.

As Comparative Example 4, a magnetic coating material prepared in exactly the same manner as in Example 12 except that SiO ₂ was used instead of the powder A in Example 12 was prepared.

The obtained magnetic coating composition was aged at 15 ° C. for 24 hours, and then dried on a polyethylene terephthalate film having a thickness of 75 μm, and the thickness after drying was 1.0 μm in the case of Co-adhered γ iron oxide. 2.7 for metallic iron-based ferromagnetic powder
It was coated so as to have a thickness of .mu.m, non-oriented and dried, and then the magnetic layer was calendered. Hereinafter, Examples 1 to 8
A magnetic disk was created in the same manner as in.

Table 2 shows the characteristics of this magnetic disk. In Table 2, the S / N ratio and the short wavelength recording characteristics are shown by using Comparative Example 3 as a reference disk in Examples 9 to 11 and Comparative Example 4 in Examples 12 to 14.
MR110 in the column of resin containing sulfonic acid group, etc. in the table,
TP-249 is the same as in Examples 6 to 8 above.

[0063]

[Table 2]

Claims (4)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic coating film containing at least a ferromagnetic powder and a binder, wherein the magnetic coating film has a soft magnetic particle size of 0.1 μm or less. Magnetic powder was added to 100 parts by weight of the ferromagnetic powder.
A magnetic recording medium containing 0.1 to 20 parts by weight. 2. The magnetic recording medium according to claim 1, wherein the content of the soft magnetic magnetic powder is 0.2 to 15 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. 3. The ferromagnetic powder 100, wherein the binder contains a polar group-containing resin containing at least one of a sulfonate group and a sulfobetaine group at 1 × 10 ⁻⁶ equivalent / g (resin) or more.
The magnetic recording medium according to claim 1 or 2, which is contained in an amount of 0.1 to 50 parts by weight with respect to parts by weight. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is hexagonal barium ferrite, Co-coated γ iron oxide, or metal powder.