JPH0785452A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a high performance by using Co-containing 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. Co-containing oxide magnetic powder which is play and of which the axis of easy magnetization is within a platy face is used as magnetic powder of the magnetic layer. As for the aforesaid magnetic powder, hexagonal platy Co-containing FeOX (1.3<=x<=1.5) can be mentioned, for instance, and this is obtained by burning with Co or Co salt and hexagonal platy delta-FeOOH used as seeds, particularly by burning wherein the Co or the Co salt and the hexagonal platy delta-FeOOH on the surfaces of which an oxide of one or more elements selected from the group of Si, Al, Cr, Ru, Ca, Zr, P, Mo, Ti, and Mn (e.g. SiO2 or Al2O3) sticks as the sintering preventing agent are used as the seeds, and further 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. As the magnetic powder for such a magnetic recording medium, oxide-based acicular magnetic powder such as γ-Fe ₂ O ₃ and Fe ₃ O ₄ has been used in the early stage, but it is more densified. From the viewpoint, the coercive force Hc is high (500 to 1
000 Oe) Co-containing γ-Fe ₂ O ₃ and Co-containing F
Co-containing (deposition type or doping type) oxide acicular magnetic powder such as e ₃ O ₄ has come to be used.

However, even this type of magnetic powder is not satisfactory, and further research is being promoted.

[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 a Co-containing oxide magnetic powder having a plate shape and an easy axis of magnetization in the plate surface.

Examples of the magnetic powder (plate-shaped and Co-containing (adhesion type or doped type) oxide magnetic powder having its axis of easy magnetization in the plate-shaped surface) include, for example, hexagonal plate-shaped Co. There is a material containing FeO _x (1.3 ≦ x ≦ 1.5) as a main component, which is fired using Co or Co salt and hexagonal plate-shaped δ-FeOOH as seeds, and particularly Si, A
Oxide of one or more selected from the group consisting of 1, Cr, Ru, Ca, Zr, P, Mo, Ti and Mn (for example, S
iO ₂ or Al ₂ O ₃ ) can be obtained by firing with Co or Co salt attached to the surface as a sintering inhibitor and hexagonal plate-shaped δ-FeOOH, and reducing and oxidizing.

The hexagonal tabular Co-containing oxide magnetic powder used in the present invention, for example, hexagonal tabular Co-containing FeO _x, preferably has a Co content of about 0.5 to 10%. Further, such a magnetic powder has a larger size due to the plate-like shape than the acicular magnetic powder having the same length, and a high saturation magnetization σs (saturation magnetic flux density Bs) can be expected. Moreover, because of the plate shape, the packing density is high, the number of effective magnetic powders per unit volume is large, and S /
High N can also be expected. As a result, a high-performance magnetic recording medium having excellent reproduction characteristics is obtained.

Further, in the case where a ferrite head is used, it is reported that the sliding noise is smaller when the magnetic recording medium has an appropriate polishing property (the head is worn for 1 to 2 μm after running for 100 hours). Yes, this is also preferable because the magnetic powder is plate-shaped. Hereinafter, the present invention will be described in detail.

Oxidation of a Co-containing oxide magnetic powder which is plate-shaped and has an easy axis of magnetization in the plate-shaped plane, for example, hexagonal plate-shaped Co-containing FeO _x (1.3 ≦ x ≦ 1.5). The magnetic powder 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. As a result, hexagonal plate-shaped δ-FeOOH
Is obtained. Then, cobalt nitrate (cobalt ferrite or other Co salt may be added thereto.
It may be metallic Co. Also, Mn or its salt, C
r or a salt thereof, Ni or a salt thereof, Zn or a salt thereof, Sn or a salt thereof may be added).
Is added. Then water glass and aluminum chloride are added and the pH is brought to below 6 with acetic acid. After that, it is filtered, washed with water, and after firing washed in air at a temperature of 650 ° C. After calcination, it is obtained by reducing with hydrogen gas at a temperature of 480 ° C. and then reoxidizing in air at a temperature of about 70 to 300 ° C.

The hexagonal plate-shaped Co-containing oxide magnetic powder obtained as described above has a thickness of about 0.003 to.
The size is preferably 0.1 μm, the diameter is about 0.03 to 0.5 μm, and the plate ratio (diameter / thickness) is about 3 to 20. And the coercive force is about 500 to 1000 O
e, the saturation magnetization σs is preferably about 70 to 85 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 in combination. 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,
Examples thereof include urethane elastomers, vinylidene chloride-acrylonitrile copolymers, butadiene-acrylonitrile copolymers, polyamide resins, ceruce derivatives, styrene-butadiene copolymers and polyester resins.
As the thermosetting resin or the reactive resin, phenol-
Formalin-novolak resin, phenol-formalin-resole resin, urea resin, melamine resin, unsaturated polyester resin, terminal isocyanate polyester moisture curable resin, terminal isocyanate polyether moisture curable resin, polyisocyanate prepolymer and the like can be mentioned. These binder resin components are contained in an amount of about 5 to 100 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder.
Used in the range of parts by weight.

Dispersants, lubricants, abrasives, antistatic agents, rust preventives, anti-mold agents, etc. 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 in the production of 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 and the like are kneaded to form a magnetic coating material. At the time of kneading, the magnetic powder and the above-mentioned components are all charged into the kneading machine 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 applying a magnetic coating material prepared by kneading and dispersing the above-mentioned magnetic powder, binder and various additives in a solvent, orienting and drying it 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.

[0019]

【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. Next, pure water is added and sufficiently dispersed, and cobalt nitrate is added thereto in an amount of 5 wt% with respect to Fe.
%, Water glass is 1 wt% with respect to Fe, and aluminum chloride is 1 wt% with respect 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
It was calcined at 0 ° C. for 2 hours and then reduced with hydrogen gas at 380 ° C. using a batch kiln. After this reduction operation, the product was kept at 250 ° C. in air to be reoxidized.

Examining the magnetic powder thus obtained
And hexagonal plate-shaped Co-containing γ-Fe₂O ₃And the thickness
0.03 μm, diameter 0.25 μm, plate ratio 8
It was The coercive force Hc is 630 Oe and the saturation magnetization σs is 72.
emu / g, and the easy axis of magnetization is in the in-plane direction of the hexagonal plate.
It was. The Co content was 4%. Then like this
246 parts by weight of magnetic metal powder with unique characteristics, vinyl chloride resin 1
9 parts by weight, polyurethane resin 28 parts by weight, polyisocyanate
7 parts by weight of anate, 30 parts by weight of alumina having a particle size of 0.15 μm
Parts by weight, 8 parts by weight of fatty acid ester, 298 parts by weight of toluene
Parts, 298 parts by weight of methyl ethyl ketone, cyclohexano
66 parts by weight of the magnetic paint was used to prepare the magnetic paint.
Is 4.5μ after dried by direct gravure method
Polyethylene terephthalate with a thickness of 14.5 μm
A magnetic layer was provided by coating on a rate film.

The thus-obtained product was slit into a 1/2 inch width to obtain a VTR magnetic tape. Example 2 In Example 1, the temperature during the reoxidation treatment was performed at 150 ° C., and hexagonal plate-shaped Co-containing γ-FeO _x (x
= 1.45, thickness 0.02 μm, diameter 0.2 μm, plate ratio 10, coercive force Hc740Oe, saturation magnetization σs80em
A magnetic powder having u / g and Co content of 5%) was obtained, and the magnetic powder was used in the same manner as in Example 1 to obtain a VTR magnetic tape.

Example 3 In Example 1, the temperature during the reoxidation treatment was performed at 80 ° C., and hexagonal plate-shaped Co-containing γ-F was used.
eO _x (x = 1.33, thickness 0.015 μm, diameter 0.
Magnetic powder of 15 μm, plate ratio 10, coercive force Hc820Oe, saturation magnetization σs85 emu / g, Co content 6%) was obtained, and this was used in the same manner as in Example 1 to obtain a VTR magnetic tape.

Comparative Example 1 Instead of the magnetic powder used in Example 1, the major axis length was 0.26 μm, the needle ratio was 8, and the coercive force was Hc6.
40 Oe, Co-containing γ − with a saturation magnetization σs 78 emu / g
A magnetic tape was obtained by using Fe ₂ O 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 0.15 μm, a plate ratio 7, a coercive force Hc690Oe, and a saturation magnetization σs 51 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 each of the above examples were investigated, and the results are shown in Table 1 below. In addition, Y-S / N and C-S / N were measured using a noise meter obtained by modifying a commercially available VHS type video deck (the relative value is expressed in dB with reference to that of Comparative Example 1). The magnetic characteristics are measured by using VSM, and the head wear is measured by a microscope with respect to the amount of wear at the tip of the ferrite head after running for 100 hours.

Table-1 Hc Bs Y-S / N C-S / N (dB) Head wear amount Oe G dB AM PM PM μm Example 1 720 1800 +1.0 +0.5 +0.6 1.8 Example 2 790 1900 +1.4 +0.8 +1.4 1.3 Example 3 940 2050 +2.1 +2.0 +2.8 1.2 Comparative example 1 760 1800 000 0 0.8 0.8 Comparative example 2 890 1600 1.9 -4.5 -3.8 0 According to this, the magnetic recording medium according to the present invention, which has a plate-like shape and is formed using the Co-containing oxide magnetic powder having the easy axis of magnetization in the plate-like surface, has excellent electromagnetic conversion characteristics. And
Also, it can be seen that the amount of head wear is within an appropriate range.

[0026]

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

Front Page Continuation (72) Inventor Akira Shiga 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Company Information Science Laboratory

Claims (5)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer provided on the magnetic layer. The magnetic powder for the magnetic layer is plate-shaped, and its easy axis of magnetization is in a plate-shaped plane.
A magnetic recording medium comprising an o-containing oxide magnetic powder. 2. The magnetic powder is hexagonal plate-shaped Co-containing FeO _x.
The magnetic recording medium according to claim 1, wherein (1.3 ≦ x ≦ 1.5) is a main component. 3. The magnetic powder is obtained by burning, reducing and oxidizing Co or Co salt and hexagonal plate-shaped δ-FeOOH as seeds. Item 2. A magnetic recording medium of item 2. 4. A magnetic powder having a sintering inhibitor attached on its surface,
The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is obtained by firing, reducing and oxidizing a salt of o or Co and δ-FeOOH having a hexagonal plate shape as a seed. 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, Ti, and Mn.