JPH0581648A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the oxidation resistance and rust resistance of the recording medium and to suppress the deterioration of magnetic characteristics with lapse of time by subjecting a magnetic layer consisting of ferromagnetic metallic particles and a binder to a surface treatment with phosphoric acid or phosphate. CONSTITUTION:The ferromagnetic metallic particles are prepd. into a magnetic coating material together with a resin binder or org. solvent and the coating material is applied on a nonmagnetic base to form the magnetic layer. The magnetic layer is subjected to the surface treatment with the phosphoric acid or phosphate. The phosphoric acid or phosphate is used as the surface treating agent of the ferromagnetic metallic particles or is added to the coating material at the time of forming the coating material. The magnetic layer is subjected to the surface treatment with the phosphoric acid in such a manner, by which the micropores generated at the time of forming an oxide film on the surface are closed and the infiltration of oxygen, water or corrosive gases from these parts is prevented. The oxidation resistance and rust resistance of the recording medium are improved and the deterioration in the magnetic characteristics with lapse of time is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated magnetic recording medium and a method for manufacturing the same.

[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 coating material composed of magnetic powder and a binder resin on a support and drying. In recent years, in the field of magnetic recording, particularly in video tape recorders and the like, higher recording density is required in order to achieve high image quality. Along with this increase in density, iron or a metal material mainly containing iron has been used in place of the iron oxide-based material that has been conventionally used as magnetic powder for magnetic recording media and the like. These iron or ferromagnetic metal fine particles composed of iron are iron oxide or iron oxyhydroxide, or iron oxide or oxyhydroxide containing a metal other than iron such as Co, Ni, Mn, Cu, Zn, Ti and V. It is produced by reducing iron or the like with hydrogen gas. These ferromagnetic metal particles have magnetic recording characteristics superior to those of conventional iron oxide-based ferromagnetic fine particles.

However, the ferromagnetic metal fine particles have a high surface activity and are easily oxidized in the atmosphere, and they may be ignited in some cases. Such properties tend to become stronger as the magnetic powder becomes finer as the noise of the magnetic recording medium becomes lower. For this reason, when the ferromagnetic metal fine particles are used as a magnetic powder of a magnetic recording medium, during storage of the ferromagnetic metal fine particles, or during the process of forming a coating by combination with a resin, an organic solvent, or the like, polyester is further used. After coating on a support such as a film to form a sheet, a predetermined atmosphere and temperature,
During storage under conditions such as humidity, oxidation progresses mainly due to the effects of oxygen, certain gases, and moisture, which leads to deterioration of magnetic properties such as saturation magnetization over time, leading to storage stability problems. there were.

To solve this problem, 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 them. The method has been taken. Also, a method of covering the ferromagnetic metal fine particles with a certain metal element, a surfactant, or an organic substance such as resin has been used.

[0005]

However, in the method of forming the oxide film passivation and the method of covering with a certain kind of metal element or organic substance, the oxidation of the ferromagnetic metal fine particles is suppressed,
It is not always sufficient to prevent deterioration of magnetic recording characteristics over time. On the contrary, depending on the treatment method, there is a possibility that the surface treatment itself may cause deterioration of the magnetic recording characteristics, or that the dispersibility may be lowered when the coating material is formed.

Therefore, the present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a magnetic recording medium which enhances the temporal stability of the recording medium and is excellent in storage stability.

[0007]

Means for Solving the Problems As a result of intensive research aimed at achieving the above object, the present inventors have found that a magnetic layer mainly composed of a magnetic powder and a binder is formed on a non-magnetic support. In the magnetic recording medium of the present invention, it has been found that by including phosphoric acid or a phosphate in the magnetic layer, it is possible to improve the oxidation resistance and rust resistance of the medium and suppress the deterioration of the magnetic properties with time. The invention has been completed.

The ferromagnetic metal fine particles for magnetic recording media 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
F such as -B, Fe-Co-Cr-B, Fe-Co-V
Ferromagnetic metal fine particles composed of various ferromagnetic alloy materials containing e, Co, and Ni as main components, and further Al, Si, Ti, Cr, Mn, and C for the purpose of improving various characteristics.
It may be one to which an element such as u, Zn, Mg or P is added. Although the specific surface area of these ferromagnetic metal fine particles is arbitrary, it is highly effective when applied to a specific surface area of 25 m ² / g or more, particularly 30 m ² / g or more.

The ferromagnetic metal fine particles for magnetic recording media used in the present invention are characterized in that their surfaces are treated with phosphoric acid or a phosphate. The surface of ferromagnetic metal fine particles, which is generally called metal magnetic powder, has a thin oxide film for the purpose of storage stability, and this oxide film has an extremely irregular structure due to the expansion of volume accompanying oxidation. , Has a large specific surface area. It is thought that treating the surface with phosphoric acid has the effect of blocking the structural irregularities, that is, micropores, that occur during the process of such oxidation, and suppressing the entry of oxygen, water, certain corrosive gases, etc. from this site. Be done. This is also indicated by the fact that the high magnetization is maintained when treated with phosphoric acid. Further, generally, the surface of the oxide film of such ferromagnetic metal fine particles has chemically adsorbed water, and among them, the hydroxyl group of the chemically adsorbed water bonded to the hexacoordinate metal ion is basic. However, phosphoric acid is an acid, and it is considered that the phosphoric acid is dehydrated by the neutralization reaction with the basic hydroxyl group of the surface chemically adsorbed water to form a chemically stable film on the surface. This is 3690 cm in the infrared reflection absorption spectrum of a diluted sample of ferromagnetic metal particles.
It is also clear from the fact that the absorption band derived from the OH stretching vibration of the hydroxyl group of the chemically adsorbed water of ^-1 disappears by the treatment with phosphoric acid.

The phosphate as referred to in the present invention is
If the phosphate anion in the hydrated state is orthophosphate,
Lophosphate, metaphosphate, triphosphate,
Other polyphosphate ions and the like are included. Construct phosphate
NH as a cation _Four ⁺, Li⁺, Na⁺, K
⁺, Rb⁺, Cs⁺Monovalent cation, divalent or
Trivalent metal cations may be mentioned. Or proton
Hydrogen salt (eg Na₂HPO_Four)
Will also be good. These may be used alone or in
Depending on the case, a mixed solution of two or more kinds may be used.

The metal fine particles for a magnetic recording medium of the present invention can be made into a magnetic coating material together with a resin binder, an organic solvent, and various additives. By coating the magnetic coating material on a non-magnetic support, the magnetic recording medium can be obtained. Is created. 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 compounding ratio and the like are set in accordance with those for ordinary magnetic recording media.

In the present invention, in the coating type magnetic recording medium having the above-mentioned fine magnetic metal particles, the magnetic layer contains phosphoric acid or phosphate. These compounds may be previously treated in water or an organic solvent containing these compounds, or may be added at the time of forming a paint. Further, these compounds may be used alone or in combination of different kinds of compounds.

As a method of using the above-mentioned compound, in the case of surface deposition on ferromagnetic metal fine particles, a method of pretreating 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 magnetic paint preparation process. The most effective solvent to treat is water. The amount of the compound used is 0.03 to 30 parts by weight based on 100 parts by weight of the magnetic metal particles,
It is preferably 0.1 to 10 parts by weight. If the amount is out of the above range, a small amount of effective oxidation resistance cannot be obtained, and if the amount is out of the above range, the effect does not change, and the excess amount is wasted, resulting in the physical properties of the magnetic coating film of the magnetic recording medium. May have an adverse effect.

In the present invention, the ferromagnetic metal fine particles for magnetic recording medium and the 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 material and applying the coating material on a non-magnetic support. In this case, these phosphoric acid or phosphate may be separately used as a surface treatment agent for the ferromagnetic metal powder, or may be added at the time of forming a coating. Resin binders and organic solvents,
As the various additives, any of those used in ordinary magnetic recording media can be used. Further, in this case, the mixing ratio and the like are also set according to the case of an ordinary magnetic recording medium.

The binder that can be used in the magnetic layer is
The average molecular weight is preferably 10,000 to 200,000,
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, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea Resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, polyester polyol and poly Mixtures of isocyanate, urea-formaldehyde resin, mixture of low molecular weight glycol and a high molecular weight diol and isocyanate, and, mixtures thereof and the like. These _binders, -SO 3 _M, -CO
OM, hydrophilicity such as -PO (OM ') ₂ (where M is hydrogen or an alkali metal such as lithium, potassium and sodium, M'is hydrogen, an alkali metal such as lithium, potassium and sodium or a hydrocarbon residue) A resin containing a polar group is preferred. That is, such a resin improves the compatibility with the magnetic powder due to the polar group in the molecule, thereby suppressing the agglomeration of the magnetic powders from each other, thereby increasing the dispersion stability of the magnetic powder, and thus also the durability as a medium. Can improve.

Among the binder resins, the vinyl chloride-based copolymer is a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid and, if necessary, various other copolymerizable monomers. It can be easily obtained by copolymerizing monomers by vinyl polymerization. This makes it possible to arbitrarily control the polarity of the copolymer and achieve dispersion stability of the particles.

A dispersant is used in the magnetic coating material used to form the magnetic layer, and if necessary, additives such as a lubricant, an abrasive, a matting agent and an antistatic agent may be added. Examples of the dispersant used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid esters, known surfactants, and salts thereof. , A negative organic acid (for example, --CO
It is also possible to use salts of polymeric dispersants with OH). These dispersants may be used alone or in combination of two or more. Further, as a lubricant, silicone oil, graphite, carbon black graphite polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, carbon atoms 12 to 16
A fatty acid ester or the like composed of the above fatty acid and a monohydric alcohol having 21 to 23 carbon atoms in total with the number of carbon atoms of the fatty acid can be used. These lubricants are usually added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder. As the abrasive, generally used materials include various types of alumina such as fused alumina and α-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery. As these abrasives, those having an average particle diameter of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm. These abrasives are usually used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.
It is added in the range of parts by weight. As the matting agent, organic powders or inorganic powders are used individually or as a mixture. The organic powder used in the present invention is preferably acrylic styrene-based resin powder, benzoguanamine-based resin powder, melamine-based resin powder, phthalocyanine-based pigment, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder. Resin powder, polyfluorinated ethylene resin powder, etc. can also be used, and as inorganic powder, silicon oxide, titanium oxide, aluminum oxide,
Examples thereof include calcium carbonate, barium sulfate, zinc oxide, tin oxide, chromium oxide, silicon carbide, iron oxide, talc, kaolin, calcium sulfate, phosphorus nitride, zinc fluoride and molybdenum dioxide. Examples of the antistatic agent include carbon black, graphite, tin oxide antimony oxide-based compounds, conductive powders such as titanium oxide tin oxide monoxide-based antimony compounds, natural surfactants such as saponins, alkylene oxides, and glycerin. -Based, glycidol-based nonionic surfactants, higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acid, sulfates Examples thereof include anionic surfactants containing acidic groups such as groups, amino acids, aminosulfonic acids, amphoteric active agents such as sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

As the solvent to be blended in the paint or a diluent solvent when the paint is applied, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones, methanol, ethanol, propanol,
Alcohols such as butanol, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, esters such as ethylene glycol monoacetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, ethers such as tetrahydrofuran, benzene, toluene,
Aromatic hydrocarbons such as xylene, halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and 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, ceramics such as boron nitride and silicon carbide can 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, and in the case of disk or card, 30 μm to 1
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 adhesiveness may be provided between the support and the magnetic layer. As a coating method for forming the magnetic layer on the support, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray A coat, an extrusion coat, and the like can be used, but are not limited thereto. When the magnetic layer is formed on the support by these coating methods, there are a method of stacking coating and drying steps one by one and a method of successively coating the next layer on the undried layer in a wet state. However, any method can be adopted in manufacturing the magnetic recording medium of the present invention.

According to such a method, the magnetic layer coated on the support is subjected to a treatment for aligning 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 with alternating current or direct current.
Gauss, the drying temperature is about 50-120 ℃,
The drying time is about 0.1 to 10 minutes. The magnetic recording medium of the present invention is manufactured by subjecting it to planar smoothing or cutting it into a desired shape if necessary.

[0022]

[Function] 2, which is a typical compound that forms a complex with a metal
In the surface treatment of the ferromagnetic metal fine particles with 2′-bipyridyl or 9,10-phenanthroline, the retention ratio of the saturation magnetization is the same as that of the untreated case even though a large amount of these compounds are adsorbed on the surface of the metal fine particles. Almost the same level, and no effect of oxidation resistance is exhibited. On the other hand, it was confirmed that when the phosphoric acid or phosphate used in the present invention was used, water was produced in the treatment reaction. This is because the adsorption reaction between the treating agent and the surface of the ferromagnetic metal fine particles is a dehydration type, and these compounds as the treating agent and the surface of the ferromagnetic metal fine particles (for example, iron) are directly bonded by a kind of neutralization reaction. Suggest that you are taking This is as described above.

Therefore, the Fe-OH basic hydroxyl group present on the surface of the ferromagnetic metal fine particles and phosphoric acid or its salt as the 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.

[0024]

EXAMPLES The present invention will now be described with reference to examples, but needless to say, the present invention is not limited to these examples. Needle-shaped metallic iron magnetic particles for magnetic recording (specific surface area 5
The examination was carried out using 3.9 m ² / g, coercive force Hc = 1590 Oe, saturation magnetization σs = 120 emu / g, average major axis length 0.3 μm, and acicular ratio 8-10). To 10 parts by weight of a 1.0 × 10 ^-2 mol / l aqueous solution of the compound shown in Table 1,
The magnetic particles (5 parts by weight) were dispersed, irradiated with ultrasonic waves for about 30 minutes, and then allowed to stand for about 2 hours. The magnetic particles are filtered,
After repeatedly washing with a 20% aqueous ethanol solution, vacuum drying was performed to obtain treated magnetic particles. A magnetic medium was prepared using the magnetic particles.

100 parts by weight of the above-mentioned magnetic particles 10 parts by weight of vinyl chloride-vinyl acetate copolymer 10 parts by weight of polyurethane resin 10 parts by weight of carbon 3 parts by weight of carbon 2 parts by weight of aluminum oxide 100 parts by weight of methyl ethyl ketone 100 parts by weight of toluene 50 parts by weight of cyclohexanone Was prepared and coated on a polyester base film having a thickness of 9 μm to prepare a magnetic tape.

The magnetic recording medium thus obtained is
The sample was kept under the condition of humidity of 90% and temperature of 60 ° C. for 1 week, and the deterioration with time of magnetic properties was examined by comparison with initial values before storage. The results are shown in Table 2. For comparison, a magnetic tape was prepared by replacing the treated powder in the magnetic paint with the ferromagnetic metal fine particles similarly immersed in water and the untreated ferromagnetic metal fine particles, and the results are also shown.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As is apparent from Table 2, the magnetic tape using the ferromagnetic metal fine particles treated with phosphoric acid or the phosphate is compared with the magnetic tape using the magnetic powder which is treated with only water or is not treated. , The residual magnetic flux density and the coercive force are extremely small, and the squareness ratio is maintained at the initial value. Further, from Comparative Examples 1 and 2, although treating the ferromagnetic metal fine particles with the water solvent slightly lowers the magnetic characteristics at the initial value, the magnetic characteristics after the acceleration test are the metal fine particles treated with only water. It is clear that the treatment with a water solvent does not cause any problems. Therefore, in the magnetic recording medium of the present invention, the temporal stability of the magnetic characteristics and the storage stability are remarkably improved.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of ferromagnetic metal particles and a binder formed on a non-magnetic support, wherein the ferromagnetic metal particles are surface-treated with phosphoric acid or phosphate. A magnetic recording medium characterized by the above.