JPH0785451A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium being excellent in an electromagnetic transducing characteristic by using oxide magnetic powder which is platy and of which the axis of easy magnetization is within a platy face, as magnetic powder of a magnetic layer. CONSTITUTION:The magnetic recording medium has a magnetic layer provided on a nonmagnetic substrate. Oxide magnetic powder which is platy and of which the axis of easy magnetization is with in a platy face is used as magnetic powder of the magnetic layer. This magnetic powder contains hexogonal platy FeOx (1.3<=x<=1.5), for instance, as the main constituent, and this is obtained by burning wherein delta-FeOOH, particularly the delta-FeOOH on the surface of which an oxide of one or more elements selected from the group of Si, Al, Cr, Ru, Ca, Zr, P, Mo, Mn and Ti (SiO2 or Al2O3, for instance) sticks as the sintering preventing agent is used as a seed, and by reduction and oxidation. Thereby, the magnetic recording medium being excellent in electromagnetic transducing characteristic and having a high performance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium.

[0002]

BACKGROUND OF THE INVENTION Magnetic recording media have been used in which a magnetic coating material prepared by dispersing magnetic powder or a binder resin in an organic solvent is coated on a non-magnetic support such as polyester resin and dried. Known magnetic powders used in such magnetic recording media are acicular magnetic powders of oxides such as γ-Fe ₂ O ₃ and Fe ₃ O ₄ , barium ferrite magnetic powders, or acicular metal magnetic powders. ing. By the way, in the case of audio equipment, the coercive force Hc is 350 to 450 Oe.
Magnetic powder of a certain degree has been mainly used, and the magnetic head of a recording / reproducing apparatus is also adapted to this. Therefore, when the metal magnetic powder having a high coercive force Hc is used, it cannot be said that the metal magnetic powder is better than the oxide magnetic powder because the magnetic head cannot handle it. Rather, it can be said that oxide-based magnetic powder such as γ-Fe ₂ O ₃ and Fe ₃ O ₄ is preferable as the magnetic powder of the magnetic recording medium used in the low frequency region.

However, conventional γ-Fe
It is also true that the use of oxide-based acicular magnetic powders such as ₂ O ₃ and Fe ₃ O ₄ is not satisfactory.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a high-performance magnetic recording medium excellent in electromagnetic conversion characteristics. An object of the present invention is to provide a magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, as magnetic powder for the magnetic layer,
This is achieved by a magnetic recording medium characterized by using an oxide magnetic powder which is plate-shaped and whose easy axis of magnetization is in the plate-shaped surface.

An oxide magnetic powder having a plate shape and an axis of easy magnetization in the plate surface is, for example, hexagonal plate F
There is one containing eO _x (1.3 ≦ x ≦ 1.5) as a main component, which is a hexagonal plate-shaped δ-FeOOH, especially Si,
Al, Cr, Ru, Ca, Zr, P, Mo, Mn, Ti
Oxides of one or more selected from the group of
Hexagonal plate-like δ-FeOOH having SiO ₂ or Al ₂ O ₃ ) as a sintering inhibitor attached to the surface is used as a seed for reduction,
Obtained by oxidation.

[0006] Such magnetic powder is large in size because it is plate-shaped and can be expected to have a high saturation magnetization σs, as compared with the acicular magnetic powder having the same length. Moreover, since it is plate-shaped, it can be expected that the packing density is high, the number of effective magnetic powders per unit volume is large, and the S / N is high. As a result, a high-performance magnetic recording medium having excellent reproduction characteristics is obtained.

The present invention will be described in detail below. In the form of a plate,
And, the oxide magnetic powder whose easy axis of magnetization is in the plate-like plane,
For example, a hexagonal plate-shaped oxide magnetic powder made of FeO _x (1.3 ≦ x ≦ 1.5) can be obtained as follows. While stirring, an aqueous solution of ferrous sulfate (part of Fe may be replaced with Co, Ni, Zn, Sn, etc.) is added with caustic soda in an equivalent amount or more to make it alkaline. This causes iron hydroxide to precipitate. Then, hydrogen peroxide solution is added with stirring to forcefully oxidize. Then water glass and aluminum chloride are added and the pH is brought to below 6 with acetic acid. Then, it is filtered, washed with water, and after washing with water 65
Bake in air at a temperature of 0 ° C. 420 ° C after firing
Reduction with hydrogen gas at a temperature of 70 to 30
Obtained by reoxidation in air at a temperature of about 0 ° C.

The hexagonal plate-shaped oxide magnetic powder obtained as described above has a thickness of about 0.003 to 0.1 μm.
m, the diameter is about 0.03 to 0.5 μm, and the plate ratio (diameter / thickness) is about 3 to 20.
Further, its coercive force is about 300 to 550 Oe, and saturation magnetization σs.
Is preferably about 70 to 90 emu / g. As the binder used in the magnetic paint for forming the magnetic recording medium, a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof can be used together. For example, as the thermoplastic resin, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester -Vinylidene chloride copolymer, urethane elastomer, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin,
Examples thereof include ceruce derivatives, styrene-butadiene copolymers, polyester resins and the like. Examples of the thermosetting resin or reactive resin include phenol-formalin-novolak resin, phenol-formalin-resole resin, urea resin, melamine resin, unsaturated polyester resin, terminal isocyanate polyester moisture-curing resin, terminal isocyanate polyether moisture-curing resin. Examples include mold resins and polyisocyanate prepolymers. These binder resin components are contained in an amount of about 5 to 10 with respect to 100 parts by weight of the magnetic powder.
It is used in an amount of 0 part by weight, preferably 10 to 30 parts by weight.

Dispersants, lubricants, abrasives, antistatic agents, rust preventives, mildew proofing agents and the like may be added as other components added to the magnetic paint for constituting the magnetic recording medium. As the dispersant, a fatty acid having 12 to 18 carbon atoms, a metal soap consisting of an alkali metal or an alkaline earth metal of the above fatty acid, an amide of the above fatty acid, a polyalkylene oxide alkyl phosphate ester, lecithin, a trialkyl polyolefinoxy. Examples thereof include quaternary ammonium salts. In addition to these, there are higher alcohols having 12 or more carbon atoms, sulfuric acid esters and the like. These dispersants may be added in an amount of 10 parts by weight or less based on 100 parts by weight of the magnetic powder.

Although the above-mentioned dispersants are also effective as lubricants, silicone oils such as dialkyl polysiloxanes, dialkoxy polysiloxanes and monoalkyl monoalkoxy polysiloxanes, conductive fine powders such as graphite,
Inorganic fine powders such as molybdenum disulfide and tungsten disulfide, plastic fine powders such as polyethylene and polypropylene, and fatty acid esters can be used. These lubricants are added in the range of 0.1 to 15 parts by weight with respect to 100 parts by weight of the magnetic powder.

As the polishing agent, alumina, α-iron oxide,
Examples thereof include titanium oxide, silicon carbide and chromium oxide. As these abrasives, those having a Mohs hardness of 5 or more and an average particle diameter of 0.05 to 5 μm are used. Then, these abrasives are added in the range of 0.5 to 15 parts by weight with respect to 100 parts by weight of the magnetic powder. Examples of the antistatic agent include conductive fine powder such as carbon black. Such conductive fine powder is magnetic powder 100.
It is added in the range of 0.01 to 10 parts by weight with respect to parts by weight.

As the rust preventive agent, if a vaporizable rust preventive agent such as dicyclohexylamine nitrite, cyclohexylamine chromate or diisopropylamine nitrite is used, the rust preventive effect is improved. These rust preventives are used in the range of 20 parts by weight or less based on 100 parts by weight of the ferromagnetic fine powder. Examples of the fungicide include copper naphthenate, zinc naphthenate, mercury naphthenate, pentachlorophenol, trichlorophenol, p-dinitrophenol, sorbic acid, butyl p-oxybenzoate, and dihydroaceto acid. It is used in the range of 5 parts by weight or less with respect to parts by weight.

As the solvent used for producing the magnetic paint, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol monoethyl ether acetate are used. Solvent, ether, glycol dimethyl ether, glycol monoethyl ether, glycol ether solvent such as dioxane, tar (aromatic hydrocarbon) solvent such as benzene, toluene, xylene, methylene chloride, ethylene chloride, tetrachloride A chlorinated hydrocarbon solvent such as carbon, chloroform, ethylene chlorohydrin or dichlorobenzene can be appropriately selected and used.

Magnetic powder, binder, etc. are kneaded to form a magnetic coating material. At the time of kneading, the magnetic powder and the above-mentioned components are all introduced into the kneader at the same time or individually. In kneading and dispersing this magnetic coating material, various kneading machines such as a two-roll mill, a three-roll mill, a ball mill, a sand glider, a high-speed impeller dispersing machine,
High speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultrasonic disperser, etc.

Materials for the non-magnetic support used in the magnetic recording medium include polyesters such as polyeletin terephthalate, polyolefins such as polyethylene and polypropylene, and cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate. Vinyl resins such as polyvinyl chloride and polyvinylidene chloride are used. Of course, it is not limited to these.

A magnetic coating medium is obtained by coating a magnetic coating material prepared by kneading and dispersing the above-mentioned magnetic powder, binder and various additives in a solvent, orienting and drying if necessary. To be Also, a magnetic recording medium can be obtained by subjecting it to a surface smoothing treatment or cutting it into a desired shape if necessary.

[0017]

【Example】

Example 1 A 5% ferrous sulfate aqueous solution was placed in a container equipped with a stirrer, and 10% caustic soda aqueous solution was added little by little while operating the stirrer to adjust the pH to 10. This causes white iron hydroxide to precipitate. Then, a 20 wt% hydrogen peroxide aqueous solution was added until it became dark black.
As a result, iron hydroxide is forcibly oxidized to form hexagonal plate-shaped δ-FeOOH. And it filters using a filter press and wash | cleans with water. Then, deionized water is added and sufficiently dispersed, and water glass is added to this in an amount of 1 wt% relative to Fe, and aluminum chloride is added to 1 wt% relative to Fe.
% Was added. Then, acetic acid is added to adjust the pH to 4, and the mixture is filtered using a filter press and washed with water. After this, the precipitate is removed in a muffle furnace in air at 65
The mixture was calcined at 0 ° C. for 2 hours and then reduced at 380 ° C. using a batch kiln with a mixed gas of hydrogen gas and nitrogen gas. After this reduction operation, the temperature was kept at 300 ° C. in air to perform reoxidation.

Examination of the magnetic powder thus obtained revealed that it was hexagonal plate-like γ-Fe ₂ O ₃ and had a thickness of 0.04 μm.
m, the diameter was 0.3 μm, and the plate ratio was 7.5. Further, the coercive force Hc is 340 Oe, and the saturation magnetization σs is 72 emu / g.
And the easy axis of magnetization was in the in-plane direction of the hexagonal plate. Next, 246 parts by weight of the metal magnetic powder having such characteristics, 19 parts by weight of vinyl chloride resin, 28 parts by weight of polyurethane resin, 7 parts by weight of polyisocyanate, 30 parts by weight of alumina having a particle diameter of 0.15 μm, and fatty acid ester 8 A magnetic paint was prepared by using 1 part by weight, 298 parts by weight of toluene, 298 parts by weight of methyl ethyl ketone, and 66 parts by weight of cyclohexanone,
This magnetic paint was applied by a direct gravure method onto a polyethylene terephthalate film having a thickness of 10 μm so as to have a thickness after drying of 5.0 μm to form a magnetic layer.

The thus obtained tape was slit into a width of 3.8 mm to obtain an audio magnetic tape. [Example 2] In Example 1, the temperature during the reoxidation treatment was performed at 250 ° C, and hexagonal plate-shaped γ-FeO _x (x = 1.4) was used.
1, thickness 0.03 μm, diameter 0.25 μm, plate ratio 8,
(Coercive force Hc360Oe, saturation magnetization σs80emu / g)
The magnetic powder of No. 1 was obtained and the magnetic powder for audio was obtained in the same manner as in Example 1.

[Embodiment 3] In Embodiment 1, the reoxidation treatment is performed.
Hexagonal plate-shaped γ-Fe is used at a physical temperature of 80 ° C. ₃O_Four
(Thickness 0.02 μm, diameter 0.2 μm, plate ratio 10,
Magnetic force Hc420Oe, saturation magnetization σs86emu / g)
Magnetic powder was obtained, and using this, the same procedure as in Example 1 was performed.
I got a magnetic tape for Dio.

Comparative Example 1 Instead of the magnetic powder used in Example 1, the major axis length was 0.3 μm, the acicular ratio was 10, and the coercive force was Hc3.
Γ-Fe ₂ O with 20 Oe and saturation magnetization σs 71 emu / g
_A magnetic tape was obtained by using ₃ in the same manner as above. Comparative Example 2 Instead of the magnetic powder used in Example 1, hexagonal plate-shaped barium ferrite magnetic powder having a diameter of 0.3 μm, plate ratio 5, coercive force Hc680 Oe, and saturation magnetization σs 50 emu / g was used. I went to and got a magnetic tape.

[Characteristics] The magnetic characteristics and the electromagnetic conversion characteristics of the magnetic tapes obtained in the above examples were examined, and the results are shown in Table 1 below. The electromagnetic conversion characteristics are based on the tape of Comparative Example 1. Table-1 Hc Bs MOL (dB) Sensitivity (dB) emu / g G 333Hz 10kHz 333Hz 3kHz 10kHz Example 1 370 2000 +1.5 0 +0.5 +0.6 +1.1 Example 2 380 2100 +2.4 0 +1.3 +1.4 +2.1 Example 3 430 2400 +4.0 +0.5 +1.4 +2.0 +2.8 Comparative Example 1 370 1900 0 0 0 0 0 Comparative Example 2 740 1700 -4.5 -2.7 -6.5 -5.4 -5.3 * MOL = Maximum Output Level It can be seen that the magnetic recording medium according to the present invention, which is formed in a plate-like shape and has an easy axis of magnetization in the plate-like plane, is excellent in electromagnetic conversion characteristics.

[0023]

According to the present invention, a high performance magnetic recording medium can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Shiga 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Co., Ltd.

Claims (5)

[Claims] 1. A magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, wherein the magnetic powder of the magnetic layer is plate-shaped and its easy axis of magnetization lies in a plate-shaped surface. A magnetic recording medium characterized by using a magnetic powder. 2. The hexagonal plate-shaped FeO oxide magnetic powder
The magnetic recording medium according to claim 1, wherein _x (1.3 ≦ x ≦ 1.5) is a main component. 3. The magnetic oxide powder is hexagonal plate-shaped δ-FeO.
The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is obtained by firing, reducing and oxidizing OH as a seed. 4. The oxide magnetic powder is obtained by firing, reducing and oxidizing hexagonal plate-shaped δ-FeOOH having a sintering inhibitor on the surface as a seed. The magnetic recording medium according to claim 1 or 2. 5. The sintering inhibitor is Si, Al, Cr, Ru,
The magnetic recording medium according to claim 4, which is an oxide of one or more selected from the group of Ca, Zr, P, Mo, Mn, and Ti.