JPH05326230A - Ferromagnetic metallic powder and magnetic recording medium composed thereof - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in weatherability and oxidation resistance by containing. a compound having a specified partial structure on the surface of ferromagnetic metallic powder. CONSTITUTION:Ferromagnetic metallic powder is immersed into toluene.ethyl alcohol mixture solution into which a compound shown by formula (where, X represents a bivalent group of CH2, O, NR, S, or Se, R represents H or alkyl or aryl group of 1-6C, and Y represents a bivalent group of CH2 or NH), e.g. benzoimidazoline-2-thione; is dissolved. Subsequently, it is filtered through a centrifugal filter and vacuum dried to obtain a ferromagnetic metallic powder subjected to surface treatment. This method produces a ferromagnetic metallic powder excellent in weatherability and a magnetic recording medium excellent in long term stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferromagnetic metal powder and a magnetic recording medium using the same, and more particularly to a magnetic recording medium having a ferromagnetic metal powder excellent in weather resistance and rust resistance. ..

[0002]

2. Description of the Related Art Conventionally, as a ferromagnetic material used for a magnetic recording medium such as a video tape, an audio tape, a memory tape, a floppy disk and a magnetic card, a metal oxide such as ferromagnetic iron oxide or chromium oxide has been mainly used. However, recently, in order to achieve higher recording density and shorter wavelength recording, ferromagnetic metal powders mainly composed of iron or the like have been widely used.

Ferromagnetic metal powders mainly composed of iron or the like are excellent in magnetic characteristics, but since this kind of ferromagnetic metal powder has a nature that it is easily oxidized, it is better than oxide-based ferromagnetic powders. Therefore, there is a drawback that the magnetic properties deteriorate with time. As a means for preventing this time-dependent oxidation, a method of gradually oxidizing the surface of the metal powder to form an oxide film is generally known. To improve oxidative stability, JP-A-56-
As described in Japanese Patent No. 30707, treatment with peroxide,
If the oxide film is further thickened, the magnetic characteristics, especially the saturation magnetic flux density will be lowered, and the superiority of the metal powder will be impaired.

Further, the deposition of a metal such as Cr, Mn or Zn or a metal oxide is disclosed in JP-A-50-4109.
7, the same 51-112465, JP-B-44-27942,
Also, as disclosed in JP-A-49-41899, the surface properties are changed, dispersion is deteriorated, magnetic properties are deteriorated, and they are insufficient. It is also possible to make the surface hydrophobic by treating with a silane coupling agent, silicone oil or the like, and JP-A-52-155398, 53-5798, and 56-
Although disclosed in Japanese Patent No. 169304, there is a problem that the lipophilicity of the surface becomes too large and the dispersion becomes poor.

As the most recent and improved surface treating agent for solving these problems, JP-A-4-6619 discloses an azino compound (--NH--N).
= N- in the cyclic structure), JP-A-4-6617 discloses a cyclohexane skeleton, a compound containing a hydroxyl group, and JP-A-3-292617 uses dihydroxynaphthalene or a derivative thereof. It describes that you do.

Further, there is a demand for a surface treating agent which is further excellent in weather resistance and oxidation resistance and which can disperse the surface-treated ferromagnetic metal powder in the binder resin more favorably.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is a ferromagnetic metal powder and a surface having a surface treating agent exhibiting excellent weather resistance and oxidation resistance. It is an object of the present invention to provide a magnetic recording medium which is suitable for high density recording in which the treated ferromagnetic metal powder has good dispersibility in a binder resin.

[0008]

The present invention is a ferromagnetic metal powder characterized by containing a compound having a partial structure of Chemical formula 3 on the particle surface of a ferromagnetic metal powder, which solves the above problems. it can.

[0009]

[Chemical 3]

However, X is CH ₂ , O, NR, S, Se
Divalent group (R is H or an alkyl group or aryl group having 1 to 6 carbon atoms), Y is CH ₂ or NH 2
It is a valence group. Further, the compound is preferably a compound represented by the following formula 4.

[0011]

[Chemical 4]

However, Ar represents a divalent aromatic ring which may be substituted with one or more substituents or an aliphatic group having a double bond, and X and Y have the same meanings as described above. Further, the present invention provides a magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly comprising a ferromagnetic metal powder and a binder resin,
A magnetic recording medium characterized in that the magnetic layer contains a compound having the partial structure of Chemical formula 3, preferably the compound of Chemical formula 4.

The ferromagnetic metal powder and the magnetic recording medium of the present invention define or select the chemical structure of the surface treatment agent (hereinafter also referred to as the compound of the present invention) contained on the surface of the ferromagnetic metal powder. .. That is, the compounds of the present invention are characterized in particular by the inclusion of = C = S groups. In the compound of the present invention, the ═C═S group has, as a soft acid, a surface of the ferromagnetic metal powder, usually an oxide film, and has an affinity for the weakly alkaline surface. Further, in the compound of the present invention, by using an atom such as nitrogen or oxygen as X, an affinity such as hydrogen bond acts on a metal,
Further, by selecting X and Y, keto-enol tautomerism occurs in the = C = S group, and therefore, it is possible to cope with various coordination structures of surface atoms of the ferromagnetic metal powder.

For example, in the compound of the present invention, X or Y adjacent to the ═C═S group is NH, and the ferromagnetic powder is Fe.
The interaction in the case of is briefly described according to the diagram shown in Chemical formula 5. The surface of the ferromagnetic metal powder usually has an oxide film of several tens of liters, and the surface of Fe is -O-Fe-O.
It is believed that the structure of H exists. And this -OF
As shown in (1) and (2), e-OH forms a hydrogen bond or a coordinate bond with the keto form (1) or the enol form (2) of the compound of the present invention, and the compound of the present invention and the ferromagnetic metal. It is considered to form a bond structure with powder surface atoms.

[0015]

[Chemical 5]

It is considered that the compound of the present invention binds to the ferromagnetic metal powder with a proper interaction as described above. Further, the chemical structure of the compound of the present invention is considered to control the interaction with the binder resin to a certain extent, thereby improving the dispersibility of the ferromagnetic metal powder. Y in the compounds of the invention is preferably NH.

Specific examples of the partial structure of compound 3 of the present invention are shown below.

[0018]

[Chemical 6]

Further, the compound of the present invention is preferably a compound having the structure shown in the chemical formula 4, wherein Ar is a divalent aromatic ring which may be substituted with one or more substituents or an aliphatic having a double bond. Represents a group. Here, examples of the divalent aromatic ring include a phenylene group, a naphthylene group, and an anthrene group, and examples of the divalent aliphatic group include vinylene and —CH═N.
-, -N = N- and the like.

Specific examples of the compound of the present invention are listed below, but the invention is not limited thereto. 2-pyrroline-5
-Thion, 4-oxazoline-2-thione, 4-imidazoline-2-thione, 1-phenyl-4-imidazoline-2-thione, 4-thiazoline-2-thione, 4-selenazoline-2-thione, benzopyrroline- 5-thion,
Benzoxazoline-2-thione, benzimidazoline-2-thione, 1-phenyl-benzimidazoline-2
-Thion, 1-methyl-benzimidazoline-2-thione, benzothiazoline-2-thione, benzoselenazoline-2-thione, α-naphthopyrroline-5-thione, α
-Naphthoxazoline-2-thione, α-naphthoimidazoline-2-thione, α-naphthothiazolin-2-thione, α-naphthoselenazoline-2-thione, β-naphthopyrrolyl-benzimidazoline-2-thione, benzothiazoline- 2-thione, benzoselenazoline-2-thione, α-naphthopyrroline-5-thione, α-naphthoxazoline-2-thione, α-naphthoimidazoline-2-
Thione, α-naphthothiazolin-2-thione, α-naphthoselenazoline-2-thione, β-naphthopyrroline-5
-Thion, β-naphthoxazoline-2-thione, β-
Naphthoimidazoline-2-thione, β-naphthothiazolin-2-thione, β-naphthoselenazoline-2-thione, 2-cyclopentene-5-thione, 2-oxolene-5-thione, 2-thiolen-5-thione, 2-selenolene-5-thione, indan-2-thione, benzooxolene-5-thione, benzothiolene-5-thione, benzoselenolene-5-thione and the like can be mentioned.

Further, these compounds may be substituted with one or more substituents, and examples of the substituents include those having a Hammett's substituent constant of -0.9 to 0.8,
Specific examples thereof include alkyl groups such as methyl group, ethyl group and t-butyl group, aryl groups such as phenyl group, Cl and B.
halogen such as r, amino group, amino group such as dimethylamino group, alkoxy group such as hydroxy group and methoxy group, acyloyl group such as acetyl group, alkoxycarbonyl group such as ethyloxycarbonyl group, cyano group, nitro group, trichloro Examples thereof include halogen-substituted alkyl groups such as methyl group. To obtain the ferromagnetic metal powder of the present invention, the compound of the present invention is dissolved or dispersed in an organic solvent having a low boiling point such as methanol, ethanol, acetone, and methyl ethyl ketone at a concentration of 0.1 to 10% by weight. Then, an appropriate amount of ferromagnetic metal powder, usually 5 to 30% by weight with respect to the solvent, is added to this solution and mixed, and then the organic solvent is filtered or distilled off.

The amount of the compound of the present invention contained in the ferromagnetic metal powder of the present invention is 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight based on 100 parts by weight of the total amount of the ferromagnetic metal powder before preparation.
The range is parts by weight. If the amount is less than 0.01 parts by weight, the effect of oxidation stability cannot be exerted, and if it is more than 10 parts by weight, the dispersion of the ferromagnetic metal powder is deteriorated and the magnetic properties are deteriorated, or the particles are blown to the surface of the magnetic layer. Is not preferable.

In the magnetic recording medium of the present invention, it is most preferable to use the ferromagnetic metal powder treated with the compound of the present invention, but the compound of the present invention is bound to the untreated ferromagnetic metal powder. Therefore, other methods may be used alone or in combination with the above methods. For example, when a magnetic coating material is prepared, the compound of the present invention is dissolved or dispersed in a part of a solvent for preparing a magnetic coating material and added together with a binder resin and an untreated or treated ferromagnetic metal powder to knead and disperse. The surface of the ferromagnetic metal powder can be treated and adhered with the compound of the present invention by utilizing the method of performing.

Therefore, the compound of the present invention can be present in the magnetic layer of the magnetic recording medium of the present invention so that the interaction with the ferromagnetic metal powder is sufficiently formed. The treatment amount is approximately the same as that of the magnetic metal powder, and may be appropriately selected according to the purpose. The ferromagnetic metal powder used in the present invention is not particularly limited, and examples thereof include various conventionally known ferromagnetic metal powders such as metal or alloy fine powder mainly composed of Fe, Co, Ni and the like. it can. For example, the metal content is 75% by weight or more, and the metal content 80% by weight or more is at least one ferromagnetic metal or alloy (eg, Fe, Co, Ni, Fe-C).
o, Fe-Ni, Co-Ni, Co-Ni-Fe, Co
-Ni-P, Co-Ni-Fe-B, Fe-Ni-Z
n, Fe-Co-Cr), and 20% by weight of the metal content.
Other components within the following range (for example, Al, Si, S, S
c, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
Examples thereof include alloys that may contain d, B, P).

The ferromagnetic alloy powder used in the present invention preferably has a particle size of 30 to 60 m ² / g by BET method and a crystallite size determined by X-ray diffraction method. Is 100 to 300Å. If the specific surface area is too small, it will not be possible to sufficiently support high density recording, and if it is too large, it will not be possible to disperse sufficiently and a magnetic layer with a smooth surface cannot be formed, and it will not be possible to support high density recording either. ..

As magnetic characteristics, the saturation magnetization is at least 110 emu / g or more, and preferably 120 emu / g.
That is all. The coercive force is 800 Oe or more, preferably 900 Oe or more. The acicular ratio (average particle length / average width) of the particles is preferably 5 or more. The method for producing the ferromagnetic metal powder used in the present invention is not particularly limited, but it can be produced, for example, by the following method. (1) A method of reducing an organic acid salt of a ferromagnetic metal, for example, a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen. (2) A method of reducing needle-shaped oxyhydroxides or those containing other metals, or needle-shaped iron oxides obtained from these oxyhydroxides. (3) A method of evaporating a ferromagnetic metal in a low pressure inert gas. (4) A method of thermally decomposing a metal carbonyl compound. (5) A method of depositing ferromagnetic metal powder using a mercury electrode and then separating mercury. (6) A method of obtaining a ferromagnetic metal powder by reducing with a reducing substance (borohydride compound, hypophosphite, hydrazine or the like) in an aqueous solution of a salt of a metal capable of forming a ferromagnetic metal.

The ferromagnetic metal powders produced by the above methods (2), (3) and (6) are easy to use, but among them, the ferromagnetic metal powders obtained by (2) are low in production cost and quality. Most desirable in. The surface of the ferromagnetic alloy powder thus obtained is preferably provided with an oxide film in order to improve chemical stability, and for example, any of the known slow oxidation treatments such as the following is performed. However, it can be used. -A method of immersing in an organic solvent and then drying. A method of immersing in an organic solvent, feeding an oxygen-containing gas to form an oxide film on the surface, and then drying. -A method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent.

As the binder resin used in the present invention, various known resins such as thermoplastic resins, thermosetting resins and reactive resins can be used without any particular limitation. Examples thereof include addition polymerization type copolymers such as vinyl chloride, vinyl ester, (meth) acrylic acid ester and styrene, and condensation polymerization type polymers such as polyester and polyurethane. Further, the binder of the present invention preferably has a polar group in order to improve the dispersion of the ferromagnetic metal powder.

Further, a curable resin or a curing agent may be contained in order to improve durability, and examples thereof include thermosetting resins such as polyisocyanate compounds and polyepoxy compounds, compounds and compounds. There are UV / electron beam curable resins and compounds containing saturated double bonds. Examples of the ultraviolet / electron beam curing resin and a method for producing the same are described in detail in JP-A-62-256219.

The thermoplastic resin used in the present invention has a softening temperature of 150 ° C. or lower and an average molecular weight of 10,000 to 3
00000, the degree of polymerization is about 50 to 2000,
For example, (meth) acrylic acid ester, styrene, (meth) acrylonitrile, butadiene, vinyl ester,
Polymers or copolymers of (meth) acrylamide, vinyl chloride, vinylidene chloride and the like, or polymers or copolymers of these derivatives, and copolymers with monomers copolymerizable therewith, for example, vinyl chloride vinyl acetate copolymer, Vinyl chloride copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer, acrylic ester vinylidene chloride copolymer, acrylic ester styrene copolymer, methacrylic ester acrylonitrile Copolymer,
Methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyfucca vinyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide Resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethyl cellulose, methyl cellulose, propyl cellulose, methyl ethyl cellulose, carboxymethyl cellulose,
(Acetyl cellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various synthetic rubber thermoplastic resins, and mixtures thereof.

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating solution.
By heating after drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Among these resins, those that do not soften or melt before the resin thermally decomposes are preferable. Specifically, for example, phenol resin, phenoxy 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 mixture, methacrylate copolymer and diisocyanate prepolymer mixture, polyester polyol and polyisocyanate mixture, urea formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixture, polyamine Resins, polyimine resins and mixtures thereof.

As these thermoplastic resins, thermosetting resins and reactive resins, it is desirable to use at least those having polar groups listed below in addition to the main functional groups. Examples of the polar group include a carboxylic acid group, a sulfinic acid group, a sulfenic acid group, a sulfonic acid group, a phosphoric acid group, a sulfuric acid group, a phosphon group, a phosphine group, a boric acid group, a sulfuric acid ester group, a phosphoric acid ester group, and alkyl esters thereof. Acidic groups such as groups (these acidic groups may be in the form of Na salts, etc.); amino acid groups; aminosulfonic acid groups, aminoalcohol sulfuric acid or phosphoric acid ester groups; alkylbetaine-type amphoteric groups, etc. Group; basic group such as amino group, imino group, imide group, amide group; usually one or more epoxy group, hydroxyl group, alkoxyl group, thiol group, halogen group, silyl group, siloxane group, etc. Up to 6 types can be included. Particularly preferred polar group epoxy _{group, -OH, -COOM, -SO 3 M} , -OSO 3
Examples thereof include M, —PO ₃ M ₂ and —OPO ₃ M ₂ groups (where M is H or an alkali metal such as Na or K, or an ammonium ion). These polar groups are copolymerized with monomers containing polar groups (cocondensation polymerization).
It is possible to introduce into the resin by or by utilizing a polymer reaction. It is preferable that the polar group is contained in an amount of 1 × 10 ⁻⁵ equivalent / g to 1 × 10 ⁻³ equivalent / g based on the weight of the resin.

In the present invention, as the polar group-containing resin,
Vinyl chloride resin and polyurethane resin are preferred. In particular,
Examples of the polar group, an epoxy group, -SO ₃ M, -OH group and the like. -SO ₃ Na-containing polyurethane (Toyobo Preferred examples of the polar group-containing resin Co. "UR
-8300 "), - SO ₃ Na-containing polyester polyurethane (Toyobo Co., Ltd.," Vylon 530 "), - SO
₃ Na-containing vinyl chloride / vinyl acetate copolymer (“MR-110” manufactured by Nippon Zeon Co., Ltd.) and the like.

These polar group-containing resins can be used alone or in combination of two or more kinds, and are used together with the usual thermoplastic resin, thermosetting resin, reactive resin or the like having no polar group. May be. In this case, the polar group content resin is 30% by weight or more, preferably 50 to 100.
It is preferably present in a weight percentage or more. In the present invention, the amount of the binder resin is preferably 8 to 25 parts by weight per 100 parts by weight of the ferromagnetic metal powder. When the amount of the binder resin is small, the dispersibility and durability are poor, and when the amount of the binder resin is large, the filling degree of the magnetic layer decreases, which is not desirable. However, the term "binder resin" as used herein includes a curing agent when used.

Examples of the curing agent include polyisocyanate compounds. Examples of the polyisocyanate compound include di, tri, and tetraisocyanates selected from aliphatic, aromatic, and alicyclic compounds having two or more -N = C = O groups in the molecule. Specifically, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and isophorone diisocyanate, products of the isocyanates with polyalcohols, and polyisocyanates produced by condensation of isocyanates. Can be used. Commercially available trade names of these polyisocyanates 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 (manufactured by Takeda Pharmaceutical Co., Ltd.), Death Module L, Death Module IL,
There are Desmodur N, Desmodur HL (manufactured by Sumitomo Bayer Co., Ltd.) and the like, and these can be used alone or in combination of two or more utilizing the difference in curing reactivity. For the purpose of accelerating the curing reaction, hydroxyl groups (butanediol, hexanediol, polyurethane having a molecular weight of 1,000 to 10,000, water, etc.),
A compound having an amino group (monomethylamine, dimethylamine, trimethylamine, etc.) or a metal oxide catalyst can be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanate compounds are used in an amount of 1 to 50% by weight based on the total amount of the binder resin,
It is preferable to use 10 to 30% by weight.

The magnetic layer of the present invention may contain a lubricant, a dispersant, an abrasive, an antistatic agent and the like as additives in addition to the above-mentioned ferromagnetic powder. As the lubricant, fatty acid esters composed of a monobasic fatty acid having 12 to 20 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms, dialkyl polysiloxane (where alkyl is 1 to 5 carbon atoms), dialkoxy Polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 carbon atom)
~ 5, alkoxy has 1 to 4 carbons), silicon oil such as phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbons); conductive fine powder such as graphite; molybdenum disulfide, two Inorganic powder such as tungsten sulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α-olefin polymer; unsaturated aliphatic hydrocarbon liquid (n-olefin double) at normal temperature A compound having a bond to a terminal carbon, a carbon number of about 20); fluorocarbons and the like can be used. These lubricants are usually used in an amount of 0.2 parts by weight based on 100 parts by weight of the binder.
-20 parts by weight may be added.

Examples of the dispersant (content wetting agent) used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid and linolenic acid. , Fatty acids with 12 to 18 carbon atoms such as stearolic acid (R ₁ CO
OH and R ₁ are an alkyl group or an alkenyl group having 11 to 17 carbon atoms); the alkali metal (Li, N
a, K, etc.) or alkaline earth metals (Mg, Ca, B)
a) a metal soap consisting of a); a compound containing a fluorine of the above fatty acid ester; an amide of the above fatty acid; a polyalkylene oxide alkyl phosphate ester; lecithin; a trialkylpolyolefinoxy quaternary ammonium salt (where alkyl is 1 to 5 carbon atoms) Individual, olefin is ethylene, propylene, etc.); In addition to these, higher alcohols having 12 or more carbon atoms, and sulfuric acid ester and the like can also 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.

Examples of the abrasive used in the present invention include non-magnetic inorganic fine powders which are commonly used materials and have a Mohs hardness of 5 or more, preferably 7 or more. Specifically, aluminum oxide (α-Al ₂ O) is used. ₃ , γ-Al ₂ O ₃ , fused alumina, corundum, etc.), chromium oxide (Cr ₂ O ₃ ),
Examples thereof include iron oxide (α-Fe ₂ O ₃ ), oxides such as silicon dioxide and titanium dioxide, carbides such as silicon carbide and titanium carbide, nitrides such as boron nitride, and fine powders such as diamond. The average particle size of these is 0.05 to 1.0 μ.
m is preferably 0.5, based on 100 parts by weight of the ferromagnetic powder.
It can be added in the range of ˜20 parts by weight.

As the antistatic agent, conductive fine powder such as carbon black (especially, one having an average particle diameter of 10 to 300 nm), carbon black graft polymer and the like; natural surfactant such as saponin; alkylene oxide type , Nonionic surfactants such as glycerin and glycidol; cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid Anionic surfactants containing an acidic group such as a sulfuric acid ester group and a phosphoric acid ester group are used.

The conductive fine powder is contained in an amount of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder, and 0.1% by weight of the surfactant.
It is added in the range of 10 to 10 parts by weight. These surfactants may be added alone or as a mixture. These are used as antistatic agents, but sometimes for other purposes, such as dispersion, improvement of magnetic properties, improvement of lubricity,
It may be applied as a coating aid.

The magnetic layer of the magnetic recording medium is usually formed by immersing a ferromagnetic metal powder, a binder and the like in a solvent, dissolving them, dispersing them by a known disperser, and then coating them on a non-magnetic support. .. As the solvent, an organic solvent is desirable, and they can be mixed and used in any ratio. Specific examples are shown below. Acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones; methanol, ethanol, propanol, butanol and other alcohols; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate mono. Ester type such as ethyl ether; glycol type such as ether, glycol dimethyl ether, glycol monoethyl ether, dioxane; tar type (aromatic hydrocarbon) such as benzene, toluene, xylene, cresol, chlorobenzene, styrene; methylene chloride, Chlorinated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde and hexane can be used.

The above ferromagnetic powder, binder resin, organic solvent,
The method of dispersion and mixing in the preparation of the magnetic coating material containing additives and the like is arbitrary, and conventionally known methods can be applied. For example, the magnetic coating can be divided into several compositions and mixed later. Various kneaders are used for kneading and dispersing. For example, two-roll mill, three-roll mill, ball mill, pebble mill, tron mill, sand grinder, Segvari, attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultra A sonic disperser or the like can be used.

As a method for forming the magnetic layer on the non-magnetic support, a conventionally known method can be used, and details are described in the textbooks such as "Coating Engineering" (Asakura Shoten, 1969). You can do it the way you are. As a coating method of the magnetic paint prepared as described above, any coating device, for example, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, Examples thereof include a method using cast coat, spray coat, bar coat, spin coat and the like.

Techniques relating to kneading dispersion and coating are described in T.W. C.
Two or more magnetic layers may be provided at the same time by the multi-layer simultaneous coating method as described in "Paint Flow and Pigment Dispersion" (1975) by Patton. The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of materials forming the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide,
Examples thereof include films of various synthetic resins such as polyamideimide, polyimide, polysulfone, and polyethersulfone, and metal foils such as aluminum foil and stainless steel foil. The non-magnetic support is generally 2.5-100 μm.
m, preferably 3 to 80 μm thick is used,
Used in the form of tapes, sheets, cards, discs, drums, etc.

As a method for forming the magnetic layer on the non-magnetic support, a conventionally known method can be used, and more specifically, the method described in "Coating Engineering" (1965, Asakura Shoten) is used. be able to. By such a method, the magnetic layer coated on the support is optionally subjected to a treatment for orienting the ferromagnetic powder in the layer, then dried and subjected to a surface treatment such as calendering treatment (pressure molding treatment). To be done.

Further, as the curing treatment, a heat treatment, an irradiation treatment with an electron beam or the like can be carried out if necessary. After that, the magnetic recording medium of the present invention is manufactured by cutting it into a desired shape. The thickness of the magnetic layer is not particularly limited, but usually,
It is 0.5 to 6, and further 2 to 4 μm. When the magnetic layer has a multi-layer structure such as a multi-layer structure, one layer may be as thin as 0.2 to 1 μm. The dry thickness is determined by the application, shape, standard, etc. of the magnetic recording medium.

Further, in the present invention, a magnetic layer can be formed on both sides of the non-magnetic support, or a back layer made of non-magnetic powder and resin can be formed on the side opposite to the magnetic layer. Known methods can be applied.

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. still,
"Part" means "part by weight".

(Ferromagnetic metal powder) Needle-shaped goethite particles having an oxide film containing Al and B formed on the surface thereof are heated and calcined in air at 400 ° C. to obtain 300 g of needle-shaped hematite particles in a volume of 3 liters. Was put into the retort container, and H ₂ gas was aerated at a rate of 35 l / min while rotating, and reduction was carried out at 450 ° C. for 6 hours. Then, the mixture was cooled to room temperature while flowing nitrogen gas into the retort container, and gradually oxidized while gradually increasing the oxygen concentration in nitrogen gas, and the ferromagnetic metal powder containing iron as a main component was taken out into the air. ..

The characteristics of the ferromagnetic metal powder are as follows: specific surface area: 5
1.9 m ² / g, saturation magnetization; 122.0 emu / g, H
c; 1610 Oe. Using this ferromagnetic metal powder, a magnetic coating composition was prepared, and a magnetic recording medium sample was prepared. The prepared ferromagnetic metal powder was immersed in a toluene / ethyl alcohol mixed (10: 1) solution in which the compounds of the present invention shown in Table 1 were dissolved, stirred for 20 hours, then filtered with a centrifugal filter and vacuum dried, A surface-treated ferromagnetic metal powder was obtained. The surface treatment amount was adjusted by the compound concentration in the solution and the treatment liquid amount, and the surface treatment amount was obtained from the change in the concentration of the compound in the treatment solution before and after the treatment.

These ferromagnetic metal powders were allowed to stand for 1 week under the conditions of 60 ° C. and 90% relative humidity, and the magnetic properties before and after were compared. Table 1 shows the characteristics of each surface-treated ferromagnetic metal powder and the characteristics after the weather resistance test.

[0051]

[Table 1]

The following coating composition was prepared using the above ferromagnetic metal powder. (Composition for magnetic coating) Ferromagnetic metal powder 100 parts (pretreated with the compound shown in Table 2 (pretreatment), or the compound was added to the coating in an amount converted per surface of ferromagnetic gold powder) (Addition.) Binder resin Sulfonic acid group-containing vinyl chloride resin 12 parts (Average degree of polymerization: 300, SO ₃ Na group content: 6 × 10 ⁻⁵ equivalent / g, epoxy group content: 4 × 10 ^-4 equivalent / g, OH group content; 2 × 10 ^-4 equivalent / g) Sulfonic acid group-containing polyurethane resin 8 parts (polyester polyurethane, average molecular weight: about 50,000, SO ₃ Na group content; 6 × 10 ^{- 5} eq / g) alpha-alumina (average particle diameter 0.2 [mu] m) 10 parts carbon black (average particle size 0.03 .mu.m) 1 part Methyl ethyl ketone 80 parts cyclohexanone 80 parts toluene 40 parts (Preparation of magnetic recording medium) above Sex coating composition using a sand mill, after sufficiently kneading and dispersing treatment, further, polyisocyanate (Bayer Desmodur L-
75 parts), 50 parts of a MEK solution in which 2 parts of stearic acid and 2 parts of butyl stearate were dissolved, and further subjected to high speed shear dispersion to obtain a magnetic coating material.

After this coating material was filtered, it was coated on a polyester film having a thickness of 10 μm so that the dry film thickness would be 3.5 μm, oriented in a magnetic field, and dried. Subsequently, pressure molding was performed with a calendar, and heat treatment was further performed at 60 ° C. for 24 hours to prepare a sample of a magnetic recording medium. The surface glossiness, the saturation magnetic flux density and the squareness ratio of the sample obtained as described above were measured under the following conditions, and the surface smoothness of the magnetic layer and the dispersion of the ferromagnetic metal powder in the magnetic recording medium of the present invention were measured. The magnetic property and the filling degree were evaluated, and the weather resistance of the ferromagnetic metal powder for the magnetic layer was evaluated.

Weather resistance test ... The sample was left for 1 week under the condition of 60 ° C. and 90% relative humidity to examine the change in magnetic properties. Surface gloss ... In accordance with JIS-Z-8741, incident angle 45
Measured in degrees. The glossiness of Comparative Example 2 was 100%. Saturation magnetic flux density (Bm) of magnetic layer and squareness ratio (B
r / Bm) ... Using a vibration test magnetometer manufactured by Toei Industry Co., Ltd., Bm, residual magnetic flux density (Br) and squareness ratio were determined when the magnetic field strength (Hm) was 5 kOe.

Specific surface area: It was determined from the amount of nitrogen adsorbed by the BET method using a fully automatic specific surface area measuring device 4-soap manufactured by Yuasa Ionics Co., Ltd. The results are shown in Table 2.

[0056]

[Table 2]

From the results shown in Tables 1 and 2, it is understood that the ferromagnetic metal powder of the present invention has improved oxidation resistance as compared with the surface-untreated ferromagnetic metal powder. Further, in the magnetic recording medium using the compound of the present invention, even if the compound of the present invention is allowed to act on the ferromagnetic metal powder before or during dispersion, the oxidation resistance and weather resistance are improved, and It can be seen that excellent surface properties can be secured.

[0058]

INDUSTRIAL APPLICABILITY The present invention provides a ferromagnetic metal powder having excellent weather resistance by depositing a compound having a partial structure of the present invention containing a = C = S group on the particle surface of the ferromagnetic metal powder. In addition, in a magnetic recording medium comprising a magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin on a non-magnetic support, the compound of the present invention is added or strongly added to the magnetic layer. A magnetic recording medium having excellent stability over time can be obtained by coating the magnetic metal powder and containing it.

Claims (4)

[Claims] 1. A ferromagnetic metal powder containing a compound having a partial structure of Chemical formula 1 on the surface of a particle of the ferromagnetic metal powder. [Chemical 1] However, X is a divalent group of CH ₂ , O, NR, S, and Se (R is H or an alkyl group or aryl group having 1 to 6 carbon atoms), and Y is a divalent group of CH ₂ or NH. It is a base. 2. The ferromagnetic metal powder according to claim 1, wherein the compound is a compound of Chemical formula 2. [Chemical 2] However, Ar represents a divalent aromatic ring which may be substituted with one or more substituents or an aliphatic group having a double bond, and X and Y have the same meanings as described above. 3. A magnetic recording medium comprising a magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin on a non-magnetic support in a magnetic recording medium, wherein the magnetic layer has a partial structure according to claim 1. A magnetic recording medium containing a compound having: 4. A magnetic recording medium comprising a magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin on a non-magnetic support, wherein the compound of the chemical formula 2 according to claim 2 is contained in the magnetic layer. A magnetic recording medium characterized by containing.