JP3158300B2 - Ferromagnetic metal fine particles for magnetic recording medium and magnetic recording medium using the metal fine particles - 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 fine particle used as a magnetic recording material of a coating type magnetic recording medium, and a coating type magnetic recording medium using the metal fine particle.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic tape is
It is manufactured by applying a magnetic paint composed of a magnetic powder and a binder resin on a support and drying it. In recent years, in the field of magnetic recording, particularly in video tape recorders and the like, higher recording density has been demanded in order to achieve higher image quality. With this increase in density, iron or a metal material mainly composed of iron has been used instead of an iron oxide-based material conventionally used as ferromagnetic metal fine particles for a magnetic recording medium or the like. In recent years, to meet such demands, those having extremely fine particle shapes have been supplied, and by using them as ferromagnetic metal fine particles for magnetic recording media, higher recording densities have been achieved. And excellent electromagnetic conversion characteristics in high frequency bands. These ferromagnetic metal particles composed of iron or iron include iron oxide or iron oxyhydroxide, or Co, Ni, Mn, Cu,
It is produced by reducing iron oxide or iron oxyhydroxide containing metals other than iron such as Zn, Ti and V with hydrogen gas. These magnetic metal particles have better magnetic recording characteristics than conventional iron oxide-based magnetic fine particles.

However, the ferromagnetic metal fine particles have a high surface activity and are easily oxidized in the air, and may be ignited in some cases. Such a property is
As the size of the ferromagnetic metal fine particles is reduced with the reduction in noise of the magnetic recording medium, the magnetic recording medium tends to be more and more strong. For this reason, when the above ferromagnetic metal fine particles are used as ferromagnetic metal fine particles of a magnetic recording medium, during the storage of the ferromagnetic metal fine particles, or during the process of coating with a resin or an organic solvent, etc., furthermore, After being coated on a support such as a polyester film and made into a sheet, oxidation proceeds mainly due to the effects of oxygen, certain gases, moisture, etc. during storage under conditions such as the specified atmosphere, temperature, and humidity. As a result, the magnetic properties such as the saturation magnetization deteriorate over time,
There was a problem with storage stability.

In order to stabilize the surface of the ferromagnetic metal fine particles, an oxide film is generally formed on the surface of the particles by a liquid layer method or a gas layer method to passivate the particles. The method has been taken. In addition, a method of covering the ferromagnetic metal fine particles with an organic substance such as a certain metal element, a surfactant, and a resin has been adopted.

[0005]

However, in the above-mentioned method of forming an oxide film passivation or a method of covering with a certain metal element or an organic substance, the oxidation of the ferromagnetic metal fine particles is suppressed.
It is not always sufficient to prevent the deterioration of the magnetic recording characteristics over time. On the other hand, depending on the treatment method, the surface treatment may cause deterioration of the magnetic recording characteristics, or may cause a decrease in dispersibility in the case of coating.

Accordingly, the present invention has been proposed in view of such a situation. By treating the surface of ferromagnetic metal fine particles for a magnetic recording medium, the magnetic recording is excellent in oxidation resistance and has little deterioration over time. It is an object of the present invention to provide ferromagnetic metal fine particles for a medium, and to provide a magnetic recording medium having improved storage stability over time and excellent storage stability.

[0007]

Means for Solving the Problems The present inventors have intensively studied to achieve the above object and found that the surface of the ferromagnetic metal fine particles for a magnetic recording medium has a benzene skeleton or a catalyzed and peri-condensed ring skeleton. It was found that remarkable storage stability can be realized by treating with a heterocyclic aromatic organic acid having a nitrogen atom. Further, in a magnetic recording medium having a magnetic layer mainly composed of ferromagnetic metal fine particles and a binder formed on a non-magnetic support, a benzene skeleton or a catalyte and a peri-condensed ring skeleton have a nitrogen atom on the magnetic layer. It has been found that by containing a heterocyclic aromatic organic acid into which is introduced, it is possible to improve oxidation resistance and rust resistance as a medium and to suppress deterioration over time of magnetic properties, and to complete the present invention. It is a thing.

The ferromagnetic metal fine particles for a magnetic recording medium in the present invention include ferromagnetic metal materials such as Fe, Co, and Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, and Co.
-Ni, Fe-Mn-Zn, Fe-Ni-Zn, Fe-
Co-Ni-Cr, Fe-Co-Ni-P, Fe-Co
-B, F-Co-Cr-B, F-Co-V, etc.
e, Co, and Ni are ferromagnetic metal fine particles composed of various ferromagnetic alloy materials mainly containing Ni, Al, Si, Ti, Cr, Mn, and the like for the purpose of improving these various characteristics.
Elements to which elements such as Cu, Zn, Mg, and P are added may be used. Although the specific surface area of these ferromagnetic metal fine particles is arbitrary, the specific surface area is 25 m ² / g or more, particularly 30 m ² / g.
The effectiveness when applied to the above is large.

In general, the acidity of an organic acid is often represented by the degree of dissociation of its proton as an acid. However, the degree of acid dissociation increases uncertain factors such as a problem of ionic strength, a problem when a solvent is changed, and a multi-step acid dissociation constant associated with sequential dissociation of a polyfunctional acid. Therefore, in the present invention, a π charge by the simple LCAO method is employed as a parameter indicating the acidity of the aromatic organic acid. This molecular orbital method is generally called the Huckel approximation, and we have already added the π charge of the heteroatom directly bonded to the metal ion of the surface oxide layer of the ferromagnetic metal fine particles to the anti-rust performance of the rust preventive agent by this molecular orbital calculation. They find that there is a close correlation.

The surface oxidized layer of the ferromagnetic metal fine particles generally has a surface hydroxyl group derived from chemically adsorbed water, and it is known that the chemically adsorbed water adsorbed on six-coordinate metal ions is particularly basic. I have. The organic acid is chemically adsorbed to the basic hydroxyl group by a dehydration reaction. This means that before and after the treatment with the organic acid, the 3690 cm ⁻¹ OH stretching vibration derived from the hydroxyl group of the surface chemically adsorbed water, which is observed in the infrared reflection absorption spectrum of the KBr diluted sample of the magnetic metal fine particles. It is also evident from the disappearance of. Accordingly, the reaction between the organic acid and the oxide film on the surface of the ferromagnetic metal fine particles is as shown in the following chemical formula 1.

[0011]

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Here, the organic acid which effectively exhibits rust-preventive ability is desirably bifunctional and present at the ortho position when the functional group is an aromatic hydroxyl group. This means that, as can be seen in the case of catechol shown above, the distance between two oxygen atoms of catechol is almost equal to the distance between iron atoms of the oxide film lattice of ferromagnetic metal fine particles, and the valence state is reasonable. Derived from the chemisorption reaction in the form.

When an organic acid treatment is applied to the ferromagnetic metal fine particles for a magnetic recording medium, it is desirable that the organic acid has a functional group of an ortho type even when the functional group is an aromatic carboxyl group. Is flexible in the reaction, and this structure is not an essential factor.

The organic acid used in the present invention is an organic acid having one or more nitrogen atoms introduced into a benzene skeleton or a cata- and peri-condensed ring skeleton and having an acid functional group such as a hydroxyl group or a carboxyl group. It is. Specific examples of the heterocyclic aromatic organic acid having a nitrogen atom in the benzene skeleton include a combination of a heterocyclic ring and an acid functional group as shown in Table 1.

[0015]

[Table 1]

An ortho-type organic acid in which one or more acid functional groups are present as substituents on these skeletons and two acid functional groups are adjacent to each other is preferred. Therefore, Table 2 can be given as an example of an ideal compound.

[0017]

[Table 2]

Examples of the heterocyclic aromatic organic acids having a nitrogen atom in the catalyzed and peri-condensed ring skeleton include a combination of a heterocyclic ring and an acid functional group as shown in Table 3.

[0019]

[Table 3]

Of course, the acid functional groups such as thiol and carboxyl groups are those capable of dehydration reaction with basic chemically adsorbed water on the surface of the oxide film of ferromagnetic metal fine particles. These compounds also have methyl, ethyl, other alkyl, nitro,
The proton may be substituted by a substituent such as a methoxy group or an amino group, or a halide such as chlorine, fluorine, chlorine or iodine, or a metal salt.

On the other hand, in a magnetic recording medium containing a heterocyclic aromatic organic acid in the magnetic layer, when the functional group of the organic acid is an aromatic carboxyl group, for example, when the organic group has a naphthalene skeleton, 2,3 -Ortho-type bifunctional compounds such as naphthalic acid, or carbon atoms of crosslink bonds may be sandwiched like 1,8-naphthalic acid. This is because the carboxyl group has a more flexible structure than the hydroxyl group.

As described above, an oxide film for stabilization is generally formed on the surface of the ferromagnetic metal fine particles.
However, the formation of the oxide film involves expansion of the volume, and the oxide film differs from a regular oxide lattice in that the structure is significantly irregular. Therefore, it is easily presumed that a hydroxyl group derived from chemically adsorbed water present on the surface of the oxide film of the ferromagnetic metal fine particles should have a distribution in acidity and basicity due to the structural irregularity.

In view of the above, in the present invention, the surface of the above-described ferromagnetic metal fine particles is coated with a heterocyclic aromatic organic acid having a benzene skeleton or a catalyte and peri-condensed ring skeleton into which a nitrogen atom is introduced. The present inventors have found that an organic acid is efficiently reacted with a hydroxyl group derived from chemically adsorbed water on the surface of the oxide film of the ferromagnetic metal fine particles after the treatment, whereby more effective oxidation resistance can be realized.

Organic acids having a benzene skeleton of an azaheterocycle include a hydroxyl group, a carboxyl group, and a basic skeleton as shown in Table 1.
Examples include compounds in which an acid functional group such as a thiol group, an imino group, or a hydrazide group is bonded as a substituent. Further, the organic acid having a azaheterocycle as the cata- and peri-condensed ring skeleton is obtained by bonding an acid functional group such as a hydroxyl group, a carboxyl group, a thiol group, an imino group or a hydrazide group to a basic skeleton as shown in Table 3. Compounds which have been mentioned. Other, pyrene,
Also included are aza heterocycles of peri-fused cyclic aromatic compounds such as perylene and those in which three or more nitrogen atoms have been introduced into the above skeleton.

In general, a nitrogen atom introduced into a heterocyclic ring is
Increase the acidity of the acid function of the substituent. In the simple LCAO method, when dealing with a heterocyclic aromatic organic acid, the difference between the resonance integral (α) of the nitrogen atom, which is a heterocyclic ring constituent atom, and the carbon atom is calculated as Δα = 0.6β using the resonance integral β. It is common to regard By using this value to evaluate the π charge on the heteroatom such as oxygen or sulfur of the acid functional group, for example, when an aromatic organic acid such as pyrogallol becomes a heterocyclic aromatic organic acid, the acidity of the hydroxyl group is changed. Is improved, and it is predicted that the resin has effective oxidation resistance and rust resistance even when judged from the correlation diagram as shown in (Japanese Patent Application No. 2-217226).

As a method of treating the surface of the ferromagnetic metal fine particles with the organic acid, for example, a method of immersing the ferromagnetic metal fine particles in a processing solution dissolved in an organic solvent may be mentioned. In this case, the solvent for the organic acid is not particularly limited, but any of an alcohol solvent such as water and ethanol, a ketone solvent such as acetone, and an aromatic solvent such as toluene can be used.

The amount of the organic acid to be applied to the metal fine particles is 0.1 to 100 parts by weight of the ferromagnetic metal fine particles.
The amount is preferably from 30 to 30 parts by weight, and from 0.1 to 10 parts by weight.
More preferably, it is part by weight. Even if the organic acid is present in excess beyond the above range, the effect does not change and the excess is wasted. Also, if you attach too much,
The physical properties of the magnetic coating film of the magnetic recording medium may be adversely affected. Conversely, if it is less than the above range, that is, if it is 0.03 parts by weight or less, the effect is insufficient and sufficient temporal stability cannot be obtained.

The metal fine particles for a magnetic recording medium of the present invention can be made into a magnetic paint together with a resin binder, an organic solvent and various additives, and the magnetic paint is applied to a non-magnetic support by applying the magnetic paint to a non-magnetic support. Is produced. In this case, as the resin binder, the organic solvent, and various additives, any of those used for ordinary magnetic recording media can be used, and the mixing ratio and the like are set according to the case of ordinary magnetic recording media.

In the coating type magnetic recording medium of the present invention comprising the ferromagnetic metal fine particles as described above, the magnetic layer has a benzene skeleton or a heterocyclic aromatic compound having a catalyte and peri-condensed ring skeleton into which a nitrogen atom is introduced. Contains organic acids. These compounds are added at the time of coating, but of course ferromagnetic metal fine particles previously treated in water or an organic solvent containing these compounds may be used. Further, these compounds may be used alone or in combination of different kinds of compounds.

As a method of using the above compound, in the case of surface deposition on ferromagnetic metal fine particles, a method of pre-treating the metal fine particles in water and an alcohol, ketone or aromatic organic solvent, or There is a method of adding to the magnetic paint during the process of preparing the magnetic paint. The amount of the compound used is 0.1 to 100 parts by weight of the ferromagnetic metal fine particles.
03 to 30 parts by weight, preferably 0.1 to 10 parts by weight. When the amount is outside the above range, effective oxidation resistance cannot be obtained, and when the amount is outside the above range, the effect does not change, the excess is wasted, and the physical properties of the magnetic coating film of the magnetic recording medium are reduced. There is a risk of adverse effects.

In the present invention, a ferromagnetic metal fine particle for a magnetic recording medium and the above compound are mixed with a resin binder, an organic solvent,
A magnetic recording medium can be obtained by kneading with various additives to form a coating and applying it on a non-magnetic support. In this case, these organic acids may be separately used as a surface treatment agent for the ferromagnetic metal fine particles, or may be added at the time of coating. As the resin binder, the organic solvent, and the various additives, any of those used for ordinary magnetic recording media can be used. Also, in this case, the mixing ratio and the like are set according to the case of a normal magnetic recording medium.

The binder usable in the magnetic layer includes:
Those having an average molecular weight of 10,000 to 200,000 are good,
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-vinyl acetate-
Polyvinyl alcohol copolymer, vinyl chloride-acrylonitrile copolymer, polyurethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, Nitrocellulose), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, high molecular weight polyester resin and isocyanate resin Mixture of polymers, mixture of polyester polyol and polyisocyanate, urea-formaldehyde resin, low molecular weight glycol, high molecular weight diol and isocyanate Mixtures of bets, and, mixtures thereof and the like. These binders, -SO ₃ M, -
COOM, -PO (OM ') ₂ (where M is hydrogen or an alkali metal such as lithium, potassium, and sodium; M' is an alkali metal such as hydrogen, lithium, potassium, and sodium or a hydrocarbon residue); Desirably, the resin contains a hydrophilic polar group. In other words, such a resin improves the compatibility with the magnetic powder due to the polar group in the molecule, thereby suppressing the aggregation of the magnetic powder, thereby increasing the dispersion stability of the magnetic powder, and consequently the durability as a medium. Can also be improved.

Of the above-mentioned binder resins, vinyl chloride copolymers include vinyl chloride monomers, copolymerizable monomers containing sulfonic acid or alkali phosphate and, if necessary, other various copolymerizable monomers. It can be easily obtained by copolymerizing the monomer by vinyl polymerization. This makes it possible to arbitrarily control the polarity of the copolymer and to improve the dispersion stability of the particles.

A dispersant is used in the magnetic paint used for forming the magnetic layer, and a lubricant, if necessary,
Additives such as abrasives, matting agents and antistatic agents may be included. Examples of the dispersant used in the present invention include a phosphoric acid ester, an amine compound, an alkyl sulfate, a fatty acid amide, a higher alcohol, a polyethylene oxide, a sulfosuccinic acid, a sulfosuccinate, a known surfactant and the like, and salts thereof. , And also negative organic acids (eg-
It is also possible to use a salt of a polymer dispersant having (COOH). These dispersants may be used alone or in combination of two or more. In addition, as a lubricant,
Silicone oil, graphite, carbon black graphite polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, 12 to 1 carbon atoms
Fatty acid esters comprising a fatty acid of 6 and a monohydric alcohol having 21 to 23 carbon atoms in total with the number of carbon atoms of the fatty acid can also be used. These lubricants are binder 100
Usually, it is added in the range of 0.2 to 20 parts by weight with respect to parts by weight. As abrasives, commonly used materials are fused alumina, various aluminas such as α-alumina, silicon carbide,
Chromium oxide, corundum, artificial corundum, artificial diamond, garnet, emery and the like are used. These abrasives have an average particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm. These abrasives are usually used in an amount of 1 to 2 parts by weight based on 100 parts by weight of the binder.
It is added in a range of 0 parts by weight. As the matting agent, an organic powder or an inorganic powder is used individually or as a mixture. As the organic powder used in the present invention, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferable. Resin powder, polyfluoroethylene resin powder, etc. can also be used. As inorganic powder, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, chromium oxide, silicon carbide, iron oxide, talc, Examples include kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide. Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponins, alkylene oxides, and glycerin. Surfactants, nonionic surfactants such as glycidols, higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acids, sulfates Examples include anionic surfactants containing an acidic group such as a group, amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohol.

Examples of the solvent to be mixed with the above paint or a diluting solvent at the time of applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as methanol, ethanol, propanol and butanol, and acetic acid. Esters such as methyl, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene and xylene, methylene chloride , Ethylene chloride, carbon tetrachloride, chloroform,
Halogenated hydrocarbons such as dichlorobenzene can be used.

Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. However, metals such as copper, aluminum, and zinc, glass, boron nitride, and ceramics such as silicon carbide can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
μm, and 30 μm to 1 in the case of a disk or card.
It is about 0 mm, and in the case of a drum shape, it is used in a cylindrical shape, and its type is determined according to the recorder used. An intermediate layer for improving adhesion may be provided between the support and the magnetic layer. Coating methods for forming the magnetic layer on a support include air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, and spray. A coat, an extrusion coat, and the like can be used, but are not limited thereto. When a magnetic layer is formed on a support by these coating methods, there are a system in which coating and drying steps are stacked one by one, and a system in which the next layer is successively stacked on a layer in a wet state that has not been dried. However, in producing the magnetic recording medium of the present invention, any method can be adopted.

According to such a method, the magnetic layer coated on the support is subjected to a treatment for orienting the ferromagnetic metal fine particles in the layer if necessary, and then the formed magnetic layer is dried. In this case, the orientation magnetic field is about 500 to 5000 in AC or DC.
It is about Gauss, the drying temperature is about 50-120 ° C,
The drying time is about 0.1 to 10 minutes. Further, the magnetic recording medium of the present invention is manufactured by performing a flattening process or cutting it into a desired shape as required.

[0039]

A typical compound that forms a complex with a metal is 2,
In the surface treatment of the ferromagnetic metal fine particles with 2′-bipyridyl or 9,10-phenanthroline, the retention of the saturation magnetization is the same as in the case of untreated, despite the fact that a large amount of these compounds are adsorbed on the surface of the metal fine particles. It is almost the same, and the effect of oxidation resistance is not exhibited at all. On the other hand, the heterocyclic organic acid having a nitrogen atom in the benzene skeleton or the aza heteroaromatic organic acid having a nitrogen atom in the catalyzed and peri-condensed ring skeleton used in the present invention generates water in the treatment reaction. It was confirmed that. This is because the adsorption reaction between the treating agent and the surface of the ferromagnetic metal fine particles is of a dehydration type, and the hetero atom of the acid functional group of the organic acid as the treating agent is directly bonded to the surface of the ferromagnetic metal fine particles (eg, iron). It suggests that it has a structure that does. This is as described above.

Therefore, in the surface treatment using a heterocyclic organic acid having a nitrogen atom in the benzene skeleton or an azaheteroaromatic organic acid having a nitrogen atom in the catalyzed or peri-condensed ring skeleton, the water repellency of the surface treatment results in oxidation resistance. Property is not obtained, and F
It is considered that e-OH and an organic acid as a treating agent form a strong ionic bond, and the potential of this bond formation affects the internal structure and contributes to the improvement of oxidation resistance.

That is, when the ferromagnetic metal fine particles are surface-treated with a heterocyclic organic acid having a nitrogen atom in a benzene skeleton or an azaheteroaromatic organic acid having a nitrogen atom in a catalyzed or peri-condensed ring skeleton, A dehydration reaction occurs between the acid and the surface of the ferromagnetic metal fine particles, and a film of the organic acid is formed on the surface of the ferromagnetic metal fine particles. The coating of the organic acid prevents an oxidation reaction on the surface of the ferromagnetic metal fine particles that proceeds during storage of the ferromagnetic metal fine particles, preparation of a magnetic paint containing the ferromagnetic metal fine particles, and storage of the magnetic recording medium.

Further, in the present invention, the organic acid used is a mixture of acids having different acidities, respectively, and effectively forms hydroxyl groups derived from chemically adsorbed water having different basicities due to structural irregularities on the surface of the ferromagnetic metal fine particles. As a result, the formation of the organic acid film on the surface of the ferromagnetic metal fine particles proceeds more effectively, thereby realizing high oxidation resistance. Further, the organic acid used in the present invention is a heterocyclic ring, and a nitrogen atom of the heterocyclic ring and a carboxyl group form a hydrogen bond. In general, a polymer having a carboxyl group in a side chain is often used when forming ferromagnetic metal fine particles into a paint. The use of such a polymer has the advantage of improving the dispersibility of the ferromagnetic metal fine particles.

[0043]

Next, the present invention will be described with reference to examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 The following Tables 4 to 6 show the compounds used in the examples and the compounds used in the comparative examples. The concentration of these compounds in an ethanol solution was 1.0 × 10 ⁻² mol / l.

1 g of ferromagnetic metal fine particles was added to 50 ml of this solution.
Was added and left for 2 hours. Thereafter, the mixture was filtered using a membrane filter, and washed repeatedly with methanol to remove organic acids in a physically adsorbed state. The obtained ferromagnetic metal fine particles were vacuum-dried for 8 hours while maintaining the temperature at 30 ° C. to obtain a treated powder.

With respect to the obtained treated powder, the coercive force Hc immediately after drying and the saturation magnetization σs were measured. After that, the humidity 90
%, And left for 2 weeks in a thermo-hygrostat maintained at a temperature of 60 ° C., and the same measurement was performed again to evaluate the amount of decrease with time. As a comparative example, the magnetic properties of the ferromagnetic metal fine particles, which were not subjected to the surface treatment but were washed with methanol and then dried, were examined for the change over time in the magnetic properties by the above-described method. Here, Δσs and ΔHc are used as indices indicating the decrease in the saturation magnetization and the coercive force during the two-week storage period. Here, these values are all evaluated by the following formula in% units.

[0047]

Table 7 shows the results of the evaluation.

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

[Table 6]

[0052]

[Table 7]

Example 2 Needle-like metallic iron magnetic particles for magnetic recording (specific surface area: 53.9 m 2
/ G, coercive force Hc = 1590 Oe, saturation magnetization s = 12
0 emu / g, average major axis length 0.3 μm, needle ratio 8 to 1
0). 5 parts by weight of the above magnetic particles were dispersed in 10 parts by weight of a 1.0 × 10 ⁻² mol / l ethanol solution of the compounds shown in Tables 4 to 6, and after irradiating ultrasonic waves for about 30 minutes, about 2 hours It was left still. The magnetic particles were filtered, washed repeatedly with ethanol, and then dried under vacuum to obtain treated magnetic particles. A magnetic medium was manufactured using the magnetic particles.

The above magnetic particles 100 parts by weight Vinyl chloride vinyl acetate copolymer 10 parts by weight Polyurethane resin 10 parts by weight Carbon 3 parts by weight Aluminum oxide 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

A magnetic paint having the above composition was prepared, and this was coated with 9 μm.
m was applied on a polyester base film to prepare a magnetic tape. The magnetic recording medium thus obtained was held for one week under the condition of a relative humidity of 90% and a temperature of 60 ° C., and the deterioration with time of the magnetic characteristics was examined by comparing with the initial value before storage. Table 8 shows the results. For comparison, a magnetic tape was prepared by replacing the treated powder in the magnetic paint with untreated ferromagnetic metal fine particles, and the results are also shown.

[0056]

[Table 8]

Example 3 In Example 2, metal fine particles which had been subjected to a surface treatment in advance were used. However, compounds having the compositions shown in Tables 4 to 6 were mixed and directly added to the magnetic paint without performing the surface treatment. The composition is as follows.

Organic acid mixture 3 parts by weight Untreated magnetic particles 100 parts by weight Vinyl chloride / vinyl acetate copolymer 10 parts by weight Polyurethane resin 10 parts by weight Carbon 3 parts by weight Aluminum oxide 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 Part by weight Similarly, the deterioration with time was examined, and the results are shown in Table 9.

[0059]

[Table 9]

[0060]

As is evident from the above examples, the treated ferromagnetic metal fine particles show a remarkable reduction in the deterioration of the saturation magnetization with time, as compared with the case of using the non-added ferromagnetic metal fine particles. At the same time, the coercive force was kept stable. In addition, the magnetic tape using metal fine particles treated with an organic acid or mixing an organic acid when forming a paint has a very small decrease in residual magnetic flux density and coercive force, and the squareness ratio is maintained at an initial value. Was. Therefore, in the ferromagnetic metal fine particles for a magnetic recording medium according to the present invention and the magnetic recording medium using the ferromagnetic metal fine particles, the temporal stability and storage stability of the magnetic properties are remarkably improved.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-6619 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22F 1/02

Claims (4)

(57) [Claims] 1. Ferromagnetic metal fine particles for a magnetic recording medium, the surface of which is treated with a heterocyclic aromatic organic acid having a nitrogen atom in a benzene skeleton. 2. The method according to claim 1, wherein the surface is a cata- and peri-fused ring skeleton (only
Excluding the naphthalene skeleton. (1) ferromagnetic metal fine particles for a magnetic recording medium, wherein the fine particles are treated with a heterocyclic aromatic organic acid having a nitrogen atom. 3. A magnetic recording medium comprising a magnetic layer mainly composed of ferromagnetic metal fine particles and a binder formed on a non-magnetic support, wherein a heterocyclic ring having a nitrogen atom in a benzene skeleton in the magnetic layer is provided. A magnetic recording medium comprising an aromatic organic acid. 4. A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic metal fine particles and a binder is formed on a non-magnetic support, wherein a kata and peri-fused ring skeleton are provided in the magnetic layer.
(However, a naphthalene skeleton is excluded.) A magnetic recording medium characterized by containing a heterocyclic aromatic organic acid having a nitrogen atom.