JP2871978B2 - Ferromagnetic metal powder and magnetic recording medium using the same - Google Patents

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 is mainly used. In recent years, ferromagnetic metal powders mainly composed of iron or the like have been widely used for higher recording density and shorter wavelength recording.

[0003] Ferromagnetic metal powder mainly composed of iron or the like has excellent magnetic properties, but since this type of ferromagnetic metal powder is inherently susceptible to oxidation, it is compared with oxide-based ferromagnetic powder. Therefore, there is a disadvantage that the magnetic characteristics deteriorate with time.

[0004] As a means for preventing the oxidation over time, a method of gradually oxidizing the surface of a metal powder to form an oxide film is generally known. However, if the oxide film is further thickened by a treatment with a peroxide as disclosed in JP-A-56-30707 to improve the oxidation stability, the magnetic properties, especially the saturation magnetic flux density, decrease, The advantage of the powder will be lost.

Further, it is disclosed in Japanese Patent Application Laid-Open No. 50-4109 that a metal such as Cr, Mn and Zn or a metal oxide is deposited.
7, Ibid. 51-112465, JP-B-44-27942,
And Japanese Patent Application Laid-Open No. 49-41899, but the surface properties are changed, the dispersion is deteriorated, the magnetic properties are deteriorated, and the results are insufficient. Treatment with a silane coupling agent, silicone oil, or the like to make the surface hydrophobic is also described in JP-A-52-155398, JP-A-53-5798 and JP-A-56-5798.
Although disclosed in Japanese Patent No. 169304, there is a problem that the lipophilicity of the surface is too large and the dispersion is poor.

[0006] Japanese Patent Application Laid-Open No. 61-223064 and 6
1-223065, 61-22066, 61
No.-223067, No.61-223068, No.61-
Nos. 223069 and 61-223070 use a 2-thiouracil derivative, thiosalicylic acid, dithiouracil, 6-mercaptopurine, 2-mercaptobenzothiazole and 6-amino-2-thiouracil, respectively. It is proposed to perform surface treatment. Further, as the newest and improved surface treatment agent for solving these problems, Japanese Patent Application Laid-Open No. 4-6619 discloses an azino compound (-NH-N).
= N- in a cyclic structure), quinones, naphthols, and oximes are disclosed. JP-A-4-6617 discloses a cyclohexane skeleton and a hydroxyl group-containing compound, and JP-A-3-292617 discloses , Dihydroxynaphthalene or its derivatives.

In particular, in a magnetic recording medium using ferromagnetic metal powder as a ferromagnetic metal powder, there is a problem that the surface of the magnetic head becomes dirty during running and the output is reduced. This phenomenon of magnetic head contamination is also called burn-in because it looks like burn-in of metal.
And this problem was remarkable especially when used under low humidity. The above-mentioned compounds disclosed in the above-mentioned prior art mainly have a dispersibility of magnetic powder as a main effect, and do not describe an effect of preventing contamination of a magnetic head under a condition of low humidity.

Therefore, the ferromagnetic metal powder which is more excellent in weather resistance and oxidation resistance, and at the same time, the surface-treated ferromagnetic metal powder is more well dispersed in the binder resin, and furthermore, even under low humidity conditions, the magnetic head becomes dirty. There is a demand for a surface treatment agent without any.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has been developed in view of the above problems, and a ferromagnetic metal powder and a surface having a surface treating agent exhibiting excellent performance in weather resistance and oxidation resistance. Provided is a magnetic recording medium that has a good dispersibility of the treated ferromagnetic metal powder in a binder resin, has no magnetic head contamination even under low humidity conditions, has little output fluctuation, and is optimal for high-density recording. It is intended to be.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is attained by a ferromagnetic metal powder characterized in that a compound represented by the general formula (1) is contained on the particle surface of the ferromagnetic metal powder. it can.

[0011]

Embedded image

(Wherein R ₁ and R ₂ represent H or a substituted or unsubstituted alkyl group or aryl group, provided that R ₁ and R ₂ are not both H at the same time.)
Another object of the present invention is to provide a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin on a non-magnetic support, wherein the magnetic layer is represented by the general formula (1). This can be achieved by a magnetic recording medium characterized by containing a compound to be prepared.

The ferromagnetic metal powder and magnetic recording medium of the present invention are those in which the chemical structure of a surface treating agent (hereinafter, also referred to as the compound of the present invention) contained on the surface of the ferromagnetic metal powder is defined or selected. . The surface of the ferromagnetic metal powder is usually
An oxide film of about several tens of degrees exists, and the surface of Fe
It is considered that the structure of O-Fe-OH exists. This —O—Fe—OH is considered to form a bond structure between the compound of the present invention and a surface atom of the ferromagnetic metal powder by forming a hydrogen bond or a coordinate bond with the compound of the present invention. That is,
It is considered that the compound of the present invention acts more chelately by the SH group and the OH group in the molecule and adheres more firmly to the surface of the ferromagnetic metal powder particles. It is considered that the compound of the present invention binds to the ferromagnetic metal powder with an appropriate interaction as described above.

Further, since at least _one of the substituents R ₁ and R ₂ in the molecule of the compound of the present invention is an alkyl group or an aryl group, the compound has an excellent water repellent effect. It is believed that the corrosion resistance will be higher. It is also considered that the magnetic layer has a high affinity for the binder resin in the magnetic layer, so that the mechanical properties of the magnetic layer are improved. As a result, the magnetic head is less likely to be stained even under low humidity conditions, and the output fluctuation is reduced. Further, it is considered that the compound of the present invention controls the interaction with the binder resin appropriately from its chemical structure, and improves the dispersibility of the ferromagnetic metal powder. The compound of the general formula (1) is, for example, R ₂ —CO—CH (R ₁ ) —
It can be synthesized from the reaction between COOH and thiourea.

In the general formula (1), when R ₁ or R ₂ is an unsubstituted alkyl group, it preferably has 1 to 20, more preferably 1 to 12, carbon atoms. Examples thereof include a carbonylalkyl group, an aryloxycarbonylalkyl group, an N-aryl or an aralkylcarbamoylalkyl group. The carbon number of the substituent substituted by the unsubstituted alkyl group in the substituted alkyl group is selected from the range of 1 to 20, preferably 1 to 12.

When R ₁ or R ₂ is an aryl group, examples of the aryl group include a phenyl group and a naphthyl group. The aryl group may have a substituent, if desired.
Specific examples of the compound of the present invention are listed below, but are not limited thereto. (1) 2-mercapto-4-hydroxy-6-methylpyrimidine (2) 2-mercapto-4-hydroxy-6-ethylpyrimidine (3) 2-mercapto-4-hydroxy-6-propylpyrimidine (4) 2- Mercapto-4-hydroxy-6-butylpyrimidine (5) 2-mercapto-4-hydroxy-6-pentylpyrimidine (6) 2-mercapto-4-hydroxy-6-hexylpyrimidine (7) 2-mercapto-4-hydroxy -6-heptylpyrimidine (8) 2-mercapto-4-hydroxy-6-octylpyrimidine (9) 2-mercapto-4-hydroxy-6-nonylpyrimidine (10) 2-mercapto-4-hydroxy-6-decylpyrimidine (11) 2-mercapto-4-hydroxy-6-undecyl pirimi (12) 2-mercapto-4-hydroxy-6-dodecylpyrimidine (13) 2-mercapto-4-hydroxy-6-tridecylpyrimidine (14) 2-mercapto-4-hydroxy-6-tetradecylpyrimidine (15) ) 2-mercapto-4-hydroxy-6-pentadecylpyrimidine (16) 2-mercapto-4-hydroxy-6-hexadecylpyrimidine (17) 2-mercapto-4-hydroxy-6-heptadecylpyrimidine (18) 2 -Mercapto-4-hydroxy-6-octadecylpyrimidine (19) 2-mercapto-4-hydroxy-6-phenylpyrimidine (20) 2-mercapto-4-hydroxy-6-naphthylpyrimidine (21) 2-mercapto-4- Hydroxy-5- (N
-Methyl-piperazinylmethyl) -6-phenylpyrimidine (22) 2-mercapto-4-hydroxy-5,6,
7,8-tetrahydroquinazoline

These compounds may be substituted with one or more substituents. Examples of the substituent include those having a Hammett's substituent constant of -0.9 to 0.8.
Specific examples thereof include an alkyl group such as a methyl group, an ethyl group and a t-butyl group, an aryl group such as a phenyl group, Cl, B
halogen such as r, amino group, amino group such as dimethylamino group, hydroxy group, alkoxy group such as methoxy group, acyloyl group such as acetyl group, alkoxycarbonyl group such as ethyloxycarbonyl group, cyano group, nitro group, trichloro Examples include a halogen-substituted alkyl group such as a methyl group.

In order to obtain the ferromagnetic metal powder of the present invention, the compound of the present invention is mixed with a low-boiling organic solvent such as methanol,
0.1% in ethanol, acetone, methyl ethyl ketone, etc.
After dissolving or dispersing so as to have a concentration of 1 to 10% by weight, ferromagnetic metal powder is added to this solution in an appropriate amount, usually 5 to 30% by weight based on the solvent and mixed, and then the organic solvent is filtered or It can be prepared by distillation.

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 whole ferromagnetic metal powder before preparation.
It is in the range of parts by weight. If the amount is less than 0.01 part by weight, the effect of oxidation stability cannot be exhibited. Is not preferred.

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. However, the compound of the present invention is bonded to the untreated ferromagnetic metal powder. For this purpose, other methods may be used alone or in combination with the above methods. For example, when preparing a magnetic paint, the compound of the present invention is dissolved or dispersed in a part of a solvent for preparing a magnetic paint, and is charged 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 the present invention.

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. It is about the same as the treatment amount 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 is mainly composed of Fe, Co, Ni
And various conventionally known ferromagnetic metal powders such as metal or alloy fine powders. For example, the metal content is at least 75% by weight and the metal content is at least 80% by weight with at least one ferromagnetic metal or alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni, C
o-Ni, Co-Ni-Fe, Co-Ni-P, Co-
Ni-Fe-B, Fe-Ni-Zn, Fe-Co-Cr
), And other components (for example, Al, Si, S, Sc, Ti, V, and C) within a range of 20% by weight or less of the metal content.
r, Mn, Cu, Zn, Y, Mo, Rh, Pd, Ag,
Sn, Sb, Te, Ba, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, Pr, Nd, B, and P).

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

As for the magnetic properties, the saturation magnetization is at least 110 emu / g or more, preferably 120 emu / g.
That is all. The coercive force is 800 Oe or more, preferably 900 Oe or more. The needle ratio (average particle length / average width) of the particles is desirably 5 or more. The method for producing the ferromagnetic metal powder used in the present invention is not particularly limited. For example, it can be produced by the following method. (1) A method of reducing with 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 acicular oxyhydroxides, those containing other metals therein, or acicular 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 separating mercury after depositing a ferromagnetic metal powder using a mercury electrode. (6) A method of obtaining a ferromagnetic metal powder by reducing a reducing substance (such as a borohydride compound, hypophosphite, or hydrazine) in an aqueous solution of a metal salt capable of forming a ferromagnetic metal.

The ferromagnetic metal powders produced by the methods (2), (3) and (6) are easy to use, but the ferromagnetic metal powders obtained by the method (2) are particularly expensive in terms of production cost and quality. Most desirable. The surface of the ferromagnetic alloy powder obtained in this manner is preferably provided with an oxide film in order to improve chemical stability, for example, those subjected to any of the known gradual oxidation treatments described below. However, it can be used. -A method of drying after dipping in an organic solvent. A method of immersing in an organic solvent, sending 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, conventionally known various resins such as a thermoplastic resin, a thermosetting resin, and a reactive resin can be used without any particular limitation. For example, addition polymerization copolymers such as vinyl chloride, vinyl ester, (meth) acrylic acid ester, and styrene, and condensation polymerization polymers such as polyester and polyurethane are exemplified. Further, the binder of the present invention preferably has a polar group in order to improve the dispersion of the ferromagnetic metal powder.

Further, it is possible to include a curable resin or a curing agent in order to improve the durability. Examples thereof include thermosetting resins such as polyisocyanate compounds and polyepoxy compounds, compounds and non-curable resins. There are ultraviolet ray / electron beam curable resins and compounds containing saturated double bonds. Examples of the ultraviolet / electron beam curable resin and the production method thereof 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 less and an average molecular weight of 10,000 to 3
00000, the degree of polymerization is about 50-2000,
For example, (meth) acrylic acid ester, styrene, (meth) acrylonitrile, butadiene, vinyl ester,
Polymers 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, acrylate acrylonitrile copolymer, acrylate vinylidene chloride copolymer, acrylate styrene copolymer, methacrylate acrylonitrile Copolymer,
Methacrylate vinylidene chloride copolymer, methacrylate styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide Resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethyl cellulose, methyl cellulose, propyl cellulose, methyl ethyl cellulose, carboxymethyl cellulose,
Acetylcellulose), styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various synthetic rubber-based 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 which do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic-based reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin Mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, 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 the following polar groups 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 sulfate group, a phosphon group, a phosphine group, a boric acid group, a sulfate group, a phosphate group, and an alkyl ester thereof. Acidic groups such as groups (these acidic groups may be in the form of Na salt or the like); amino acid groups; aminosulfonic acid groups; sulfuric acid or phosphoric acid ester groups of amino alcohol; amphoteric groups such as alkyl betaine type; A basic group such as an amino group, an imino group, an imide group, or an 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
M, -PO ₃ M _2, can be exemplified -OPO ₃ M ₂ group (where, M is H or Na, an alkali metal, an ammonium ion of K, and the like.). These polar groups are copolymerized with monomers containing polar groups (co-condensation polymerization).
It is possible to introduce the resin into the resin by using a polymer reaction. The polar group preferably contains 1 × 10 ⁻⁵ equivalents / g to 1 × 10 ⁻³ equivalents / g based on the weight of the resin.

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

These polar group-containing resins can be used alone or as a combination of two or more kinds, and are used together with a typical thermoplastic resin having no polar group, thermosetting resin, or reactive resin. You may. In this case, the content of the polar group-containing resin is 30% by weight or more, preferably 50 to 100%.
Preferably, it is present in an amount of at least% by weight. 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. If the amount of the binder resin is small, the dispersibility and durability are poor, and if the amount of the binder resin is large, the degree of filling of the magnetic layer is undesirably reduced. However, the term “binder resin” used herein includes a curing agent when used.

As the curing agent, for example, a polyisocyanate compound is exemplified. 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, isophorone diisocyanate, products of the isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates Can be used. Commercially available trade names of these polyisocyanates include 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.), Desmodur L, Desmodur 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 by utilizing the difference in curing reactivity. In order to accelerate 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 also be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanate compounds are 1 to 50% by weight of the total amount of the binder resin,
Preferably, it is used in an amount of 10 to 30% by weight.

The magnetic layer of the present invention may contain, as additives, a lubricant, a dispersant, an abrasive, an antistatic agent and the like in addition to the ferromagnetic powder. Examples of the lubricant include higher fatty acids having 12 to 22 carbon atoms, fatty acid esters composed of monobasic fatty acids having 12 to 20 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms, dialkyl polysiloxane (alkyl Is 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy is 1 to 4 carbon atoms), monoalkylmonoalkoxypolysiloxane (alkyl is 1 to 5 carbon atoms, alkoxy is 1 to 4 carbon atoms), Phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1 to 5 carbon atoms)
Conductive oil such as graphite; inorganic powder such as molybdenum disulfide, tungsten disulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α- Olefin polymers; unsaturated aliphatic hydrocarbons which are liquid at room temperature (compounds having an n-olefin double bond bonded to a terminal carbon, having about 20 carbon atoms); fluorocarbons and the like can be used. These lubricants can be added usually in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

The dispersants (content wetting agents) 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. , A fatty acid having 12 to 18 carbon atoms such as stearic acid (R ₁ CO
OH and R ₁ are an alkyl group or alkenyl group having 11 to 17 carbon atoms); alkali metals (Li, N
a, K, etc.) or alkaline earth metals (Mg, Ca, B)
a) a metal soap comprising a) a fluorine-containing compound of the above fatty acid ester; an amide of the above fatty acid; a polyalkylene oxide alkyl phosphate; a lecithin; And olefins such as ethylene and propylene); and the like. In addition, higher alcohols having 12 or more carbon atoms, and sulfate esters and the like can also be used. These dispersants are added in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the binder.

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

As the antistatic agent, conductive fine powders such as carbon black (especially those having an average particle diameter of 10 to 300 nm), carbon black graft polymer, etc .; natural surfactants such as saponin; alkylene oxides , Glycerin-based, glycidol-based, nonionic surfactants; cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids, and phosphoric acids Anionic surfactants containing an acidic group such as a sulfuric acid ester group and a phosphoric ester group are used.

The conductive fine powder is used in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder, and the surfactant is used in an amount of 0.1 to 0.1 parts by weight.
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, improved magnetic properties, improved lubricity,
It may be applied as a coating aid.

The formation of the magnetic layer of the magnetic recording medium is usually carried out by immersing and dissolving a ferromagnetic metal powder, a binder and the like in a solvent, dispersing the powder with a known dispersing machine, and applying the dispersion to a nonmagnetic support. . As the solvent, an organic solvent is desirable, and can be mixed and used at an arbitrary ratio. Specific examples are as follows: ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol acetate mono. Ester systems such as ethyl ether; glycol ether systems such as ether, glycol dimethyl ether, glycol monoethyl ether and dioxane; tar systems (aromatic hydrocarbons) such as benzene, toluene, xylene, cresol, chlorobenzene, and styrene; methylene chloride; Chlorinated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde, hexane and the like can be used.

The above ferromagnetic powder, binder resin, organic solvent,
The method of dispersion and mixing in the preparation of the magnetic paint composed of additives and the like is arbitrary, and conventionally known methods can be applied. For example, the magnetic paint 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 sound disperser or the like can be used.

As a method for forming a magnetic layer on a non-magnetic support, a conventionally known method can be used, and details thereof are described in books such as "Coating Engineering" (Asakura Shoten, 1971). The way you can do it. As a method of applying the magnetic paint prepared as described above, any coating apparatus, 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 include a method using a cast coat, a spray coat, a bar coat, a spin coat, and the like.

Techniques relating to kneading, dispersion and coating are described in T.A. C.
Two or more magnetic layers may be provided simultaneously by a multilayer simultaneous coating method as described in "Paint Flow and Pigment Dispersion" by TA Patton (TC Patton) (1975). The non-magnetic support used in the present invention is not particularly limited, and a commonly used non-magnetic support can be used. Examples of the material forming the nonmagnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide,
Examples include films of various synthetic resins such as polyamideimide, polyimide, polysulfone, and polyethersulfone, and metal foils such as aluminum foil and stainless steel foil. Non-magnetic supports are generally 2.5-100 μm
m, preferably 3 to 80 μm thick,
Used in the form of tapes, sheets, cards, disks, drums, etc. According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting the ferromagnetic powder in the layer if necessary, dried, and subjected to a surface treatment such as a calendering treatment (pressure molding treatment). Is done.

Further, as a curing treatment, a heat treatment, an irradiation treatment with an electron beam or the like can be performed as required. Thereafter, the magnetic recording medium of the present invention is manufactured by cutting into a desired shape. The thickness of the magnetic layer is not particularly limited, but usually,
0.5 to 6, furthermore 2 to 4 μm. When the magnetic layer has a multilayer structure such as a multi-layer structure, it may be as thin as 0.2 to 1 μm. The dry thickness is determined according to the use, shape, and standard of the magnetic recording medium.

In the present invention, a magnetic layer can be formed on both sides of a nonmagnetic support, or a back layer made of nonmagnetic powder and resin can be formed on the opposite side of the magnetic layer. Known methods can be applied.

[0045]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. still,
“Parts” indicates “parts by weight”. (Ferromagnetic Metal Powder A) 300 g of acicular hematite particles obtained by heating and calcining acicular goethite particles containing Al and B at 400 ° C. in the air are charged into a 3 liter retort container, and rotated while rotating. 35 liters of ₂ gas
And reduced at 450 ° C. for 6 hours. Then, cooled to room temperature while flowing nitrogen gas in the retort container,
The gradual oxidation treatment was performed while gradually increasing the oxygen concentration in the nitrogen gas, and the ferromagnetic metal powder containing iron as a main component was taken out into the air.

The properties of the ferromagnetic metal powder are as follows: specific surface area;
1.9 m ² / g, saturation magnetization: 122.0 emu / g, H
c: 1610 Oe. (Ferromagnetic metal powder B) 300 g of acicular hematite particles obtained by heating and calcining acicular goethite particles containing Al and B in air at 400 ° C. are charged into a 3 liter retort container, and H _{2 is} rotated while rotating. Gas was passed at 35 liters / min and reduced at 450 ° C. for 6 hours. Then, toluene was introduced and immersed in the retort container, and toluene was distilled off while flowing air at room temperature, and a gradual oxidation treatment was performed, and a ferromagnetic metal powder containing iron as a main component was taken out into the air.

The properties of the ferromagnetic metal powder are as follows: specific surface area;
3.0 m ² / g, saturation magnetization; 133.0 emu / g, H
c: 1600 Oe. The prepared ferromagnetic metal powder is immersed in a mixed solution (1: 1) of methyl ethyl ketone / ethyl alcohol in which the compound of the present invention shown in Table 1 is dissolved, stirred for 20 hours, and then filtered by a centrifugal filter and dried under vacuum. Thus, a surface-treated ferromagnetic metal powder was obtained. The surface treatment amount was adjusted by the concentration of the compound in the solution and the amount of the treatment solution, and the surface treatment amount was determined from the change in the concentration of the compound in the treatment solution before and after the treatment.

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

[0049]

[Table 1]

Using the above ferromagnetic metal powder, the following coating composition was prepared. (Composition for magnetic paint) 100 parts of ferromagnetic metal powder (pre-treated with the compound of the present invention shown in Table 2 or the like) (pre-treatment) or the amount of the compound converted to the surface of the ferromagnetic metal powder 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 contained) 4 × 10 ⁻⁴ equivalents / g, OH group content: 2 × 10 ⁻⁴ equivalents / 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 (magnetic recording Medium Formed) using a sand mill of the above magnetic coating composition, after sufficiently kneading and dispersing treatment, further, polyisocyanate (Bayer Desmodur L-
75), 50 parts of an MEK solution in which 2 parts of stearic acid and 2 parts of butyl stearate were dissolved, and further subjected to high-speed shearing dispersion to obtain a magnetic paint.

After this coating material was filtered, it was applied on a 10 μm-thick polyester film so as to have a dry film thickness of 3.5 μm, oriented in a magnetic field, and dried. Subsequently, the resultant was subjected to pressure molding with a calender, heat-treated at 60 ° C. for further 24 hours, and slit to a width of 8 mm to prepare a sample of a magnetic recording medium. The surface glossiness, saturation magnetic flux density, and 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 properties and the degree of filling were evaluated, and the weather resistance of the magnetic layer ferromagnetic metal powder was evaluated.

Weather resistance test: The sample was left standing for one week under the conditions of 60 ° C. and 90% relative humidity, and the change in magnetic properties was examined. Surface glossiness: Incident angle 45 according to JIS-Z-8741
Measured in degrees. In addition, the glossiness of the comparative example without the compound using the ferromagnetic metal powder A was set to 100%. The saturation magnetic flux density (Bm) of the magnetic layer and the squareness ratio (B
r / Bm): Using a vibration test magnetometer manufactured by Toei Kogyo Co., Ltd., Bm, residual magnetic flux density (Br), and squareness when the magnetic field strength (Hm) was 5 kOe were determined.

Specific surface area: 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. Table 2 shows the results.

[0054]

[Table 2]

Further, a change in output during repeated reproduction was examined for a sample of a magnetic recording medium prepared in the same manner.
Measurement of repetitive output: Using a 900 deck made by Sony V, at a temperature of 23 ° C. and a relative humidity of 10%, a tape having a length of 120 minutes was repeatedly reproduced 10 times. The ratio of the RF output was determined.

[0056]

[Table 3]

From the results shown in Tables 1, 2 and 3, the ferromagnetic metal powder of the present invention has improved oxidation resistance as compared with the non-surface-treated, 2-thiouracil-treated or benzotriazole-treated ferromagnetic metal powder. Further, the magnetic recording medium using the compound of the present invention has improved oxidation resistance and weather resistance in any case even if the compound of the present invention is allowed to act on the ferromagnetic metal powder before or during dispersion, It can be seen that excellent surface properties and output during repeated use can be secured.

[0058]

According to the present invention, a ferromagnetic metal powder having excellent weather resistance can be provided by applying the compound represented by the general formula (1) on the particle surface of the ferromagnetic metal powder. Further, in a magnetic recording medium having 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 to the magnetic layer or the ferromagnetic metal powder is coated. By wearing and containing
A magnetic recording medium having excellent stability over time can be obtained.

Claims (2)

(57) [Claims] 1. A ferromagnetic metal powder comprising a compound represented by the general formula (1) of Chemical Formula 1 on the particle surface of the ferromagnetic metal powder. Embedded image (Wherein R ₁ and R ₂ represent H or a substituted or unsubstituted alkyl or aryl group, provided that R ₁ and R ₂ are
Do not both R ₂ is H at the same time. ) 2. A magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin, wherein the magnetic layer has a general formula (1) according to claim 1. A magnetic recording medium comprising a compound represented by the formula: