JPH0785450A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium being excellent in a reproducing charac teristic and having a high performance by using metal magnetic powder obtained by reducing hexagonal platy ferrite magnetic powder, as magnetic powder of a magnetic layer. CONSTITUTION:The magnetic recording medium has a magnetic layer provided on a nonmagnetic substrate. Metal magnetic powder obtained by reducing hexogonal platy ferrite magnetic powder is used as magnetic powder of the magnetic layer. For instance, hexagonal-system ferrite magnetic powder expressed by BaO.6Fe2O3 or barium ferrite magnetic powder obtained by substituting a metal such as Ti, Cr, Co, Zn, In, Mn, Cu, Ge or Nb for a part of Ba or Fe in the above formula is used as the hexagonal-system platy ferrite magnetic powder. According to excellent in a reproducing 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 A magnetic recording medium prepared by coating a magnetic coating material prepared by dispersing magnetic powder or binder resin in an organic solvent on a non-magnetic support such as polyester resin and drying it is used for video tapes and floppy disks. Has been coming. The magnetic powder used in such a magnetic recording medium is Fe
Oxide-based acicular magnetic powder such as ₂ O _3, plate-like magnetic powder such as barium ferrite, or acicular metal magnetic powder are known, but acicular metal magnetic powder has been mainly used recently. That is, since the acicular metal magnetic powder has a high coercive force Hc and a large saturation magnetization σs, the residual magnetic flux density B is
This is because it is expected that r is high and the magnetic energy determined by Hc × Br is high.

In order to perform high density recording, it is necessary to reduce the particle size of magnetic powder. This is because the signal / noise (S / N) is proportional to (1 / Vp) ^1/2 (Vp is the volume of the particle). Needs to be small. When performing high-density recording with a recording wavelength of 0.7 μm or less, the particle size of the magnetic powder is 0.2 μm or less, particularly 0.1 μm or less.
It is said that it is preferably 2 μm or less.

By the way, the particle size of the magnetic metal powder is 0.12 μm.
When it becomes as small as m or less, the saturation magnetization σs becomes 1
It becomes 10 emu / g or less, which makes it difficult to deal with high density. In addition, there is a problem that the degree of orientation does not increase as the miniaturization progresses.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a high-performance magnetic recording medium having excellent reproduction characteristics. An object of the present invention is to provide a magnetic recording medium having a magnetic layer provided on a non-magnetic support, wherein a magnetic metal powder obtained by reducing hexagonal plate-shaped ferrite magnetic powder is used as the magnetic powder of the magnetic layer. It is achieved by a magnetic recording medium characterized in that

In a magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, hexagonal plate-shaped ferrite magnetic powder having a sintering inhibitor as a magnetic powder of the magnetic layer is reduced. This is achieved by a magnetic recording medium characterized by using metal magnetic powder. The hexagonal plate-shaped ferrite magnetic powder is, for example, a hexagonal ferrite magnetic powder represented by BaO.6Fe ₂ O ₃ or Ba or F represented by the above chemical formula.
Part of e is Ti, Cr, Co, Zn, In, Mn, C
Barium ferrite magnetic powder substituted with a metal such as u, Ge or Nb can be used.

Barium ferrite magnetic powder (hexagonal ferrite magnetic powder) is obtained by solid phase reaction method, coprecipitation-heating reaction method, hydrothermal synthesis method, oxide flux method, molten salt method, glass crystallization method, etc. To be Above all, a barium ferrite component is mixed with a glass-forming substance typified by B ₂ O ₃ ,
Melts at a temperature of 1300 ° C or higher, rapidly cools this to obtain glass (amorphous body), heats this glass again to a temperature of 700 ° C or higher to crystallize, and extra glass substances and acids are heated in hot water. What was obtained by the glass crystallization method, such as dissolving by, for example, washing with water and drying. Further, those obtained by an autoclave method in which α-FeOOH or Fe (OH) ₃ , NaOH, Ba (OH) _{2 and the} like are placed in an autoclave and heated at 200 to 300 ° C. for 5 to 10 hours are also preferable.

The hexagonal ferrite magnetic powder as described above, especially Si, Al, Cr, Ru, Ca, Zr,
A hexagonal ferrite magnetic powder having an oxide (for example, SiO ₂ or Al ₂ O ₃ ) selected from the group consisting of P, Mo, Mn, and Ti as a sintering inhibitor is heated. , Hexagonal plate-shaped metal magnetic powder is obtained by reduction with hydrogen gas. 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. Further, the axis of easy magnetization of the hexagonal ferrite magnetic powder is in the direction perpendicular to the plate surface, whereas the one according to the present invention is in the plane, so that the conventional ring-type magnetic head is used. Excellent recording and playback characteristics.

The hexagonal plate-shaped metal magnetic powder obtained as described above has a thickness of about 0.003 to 0.1 μm.
Diameter is about 0.03-0.5μm, plate ratio (diameter / thickness)
Is preferably about 3 to 20. The coercive force is about 800 to 1900 Oe, and the saturation magnetization σs is 1.
It is preferably about 10 to 160 emu / g. In the present invention, the magnetic metal powder obtained by reducing the hexagonal plate-shaped ferrite magnetic powder is mainly used. For example, Co, Ni, Fe-Co, Fe-Ni, Fe-Al, F
e-Ni-Al, Co-Ni, Fe-Co-Ni, Fe
A ferromagnetic metal powder such as -Ni-Al-Zn or Fe-Al-Si, an oxide-based acicular magnetic powder, or a hexagonal plate-shaped ferrite magnetic powder may be used together.

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 Thickness is 0.01 μm and diameter is 0.12 μm
A hexagonal barium ferrite magnetic powder (produced by an autoclave method) having a plate ratio of 12, a coercive force Hc of 1460 Oe and a saturation magnetization σs of 56 emu / g (produced by an autoclave method) was reduced with hydrogen gas at 450 ° C. using a batch kiln. It was When the reduction work was completed, the temperature was lowered to room temperature, air was passed through little by little, the atmosphere in the kiln was replaced with the atmosphere over 40 hours, and then the metal powder was taken out.

Examination of the thus-obtained metal magnetic powder revealed that it had a hexagonal plate shape, a thickness of 0.01 μm, a diameter of 0.09 μm, and a plate ratio of 9. Also, coercive force H
c was 1600 Oe, the saturation magnetization σs was 125 emu / g, and the easy axis of magnetization was in the in-plane direction of the hexagonal plate. next,
246 parts by weight of 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 size of 0.15 μm, 8 parts by weight of fatty acid ester, Toluene 29
A magnetic paint was prepared using 8 parts by weight, 298 parts by weight of methyl ethyl ketone, and 66 parts by weight of cyclohexanone, and the magnetic paint was dried by a direct gravure method on a polyethylene terephthalate film having a thickness of 10 μm so that the thickness after drying was 2.9 μm. To form a magnetic layer. Then, a coating containing carbon black was applied to the surface of the polyethylene terephthalate film opposite to the magnetic layer so that the thickness after drying was 0.5 μm to form a back coat layer.

Then, the thus obtained material was slit into a width of 8 mm to obtain a magnetic tape. Example 2 Thickness is 0.01 μm, Diameter is 0.12 μm
With a plate-like ratio of 12, a coercive force Hc of 1390 Oe, and a saturation magnetization σs of 58 emu / g with hexagonal barium ferrite magnetic powder having 1 wt% of SiO ₂ and Al ₂ O ₃ attached thereto in a batch kiln It was used and reduced with hydrogen gas at 450 ° C. After the reduction work was completed, the temperature was lowered to room temperature, air was passed little by little, the atmosphere in the kiln was replaced with the atmosphere over 40 hours, and then the metal powder was taken out.

Examination of the metal magnetic powder thus obtained revealed that it had a hexagonal plate shape, a thickness of 0.01 μm, a diameter of 0.09 μm and a plate ratio of 9. Also, coercive force H
c was 1570 Oe, saturation magnetization σs was 132 emu / g, and the easy axis of magnetization was in the in-plane direction of the hexagonal plate. Then, a magnetic tape was obtained in the same manner as in Example 1 using the magnetic metal powder having this feature.

Comparative Example 1 Instead of the magnetic powder used in Example 1, the major axis length was 0.1 μm, the acicular ratio was 8, and the coercive force was Hc1.
A magnetic tape was obtained in the same manner as above except that acicular metal magnetic powder having 560 Oe and saturation magnetization σs110 emu / g was used. [Comparative Example 2] Instead of the magnetic powder used in Example 1, a plate-like ratio 12 having a thickness of 0.01 μm and a diameter of 0.12 μm was used.
Coercive force Hc is 1460 Oe, saturation magnetization σs56 emu /
g hexagonal barium ferrite magnetic powder was used, and otherwise the same procedure was performed to obtain a magnetic tape.

[Characteristics] The magnetic tapes obtained in the above examples are
Since the Y-S / N, C-S / N, still durability, and corrosion resistance were examined by using a commercially available 8 mm VTR equipped with a ring type magnetic head and a noise meter, The results are shown in Table 1 below.
The corrosion resistance is expressed by the rate of decrease in the saturation magnetic flux density after standing at 60 ° C. and 90% RH for 1 week. or,
Y-S / N and C-S / N are based on a commercially available 8 mm reference tape, and their relative values are shown in dB.

Table-1 Hc Bs YS / N C-S / N Still durability Durability Corrosion resistance emu / g G dB AM PM dB% Example 1 1600 3300 +1.0 +1.5 +1.3 -0.4 4 Example 2 1630 3100 +1.3 +1.2 +1.1 -0.2 2 Comparative example 1 1600 2700 +0.8 -0.1 -0.3 -0.9 9 Comparative example 2 1580 1900 +0.4 -3.6 -5.1 -0.5 1 According to this, hexagon A magnetic recording medium composed of metal magnetic powder obtained by reducing plate-shaped ferrite magnetic powder has excellent recording / reproducing characteristics, still durability, and corrosion resistance. I understand.

[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 (4)

[Claims] 1. A magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, wherein metal magnetic powder obtained by reducing hexagonal plate-like ferrite magnetic powder is used as the magnetic powder of the magnetic layer. A magnetic recording medium characterized by: 2. A magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, wherein hexagonal plate-like ferrite magnetic powder having a sintering inhibitor as a magnetic powder of the magnetic layer is reduced. A magnetic recording medium comprising a magnetic metal powder. 3. The hexagonal plate-shaped ferrite magnetic powder is BaO.
6. Fe ₂ O ₃ (however, part of Ba or Fe may be replaced with another metal).
Alternatively, the magnetic recording medium according to claim 2. 4. The sintering inhibitor is Si, Al, Cr, Ru,
The magnetic recording medium according to claim 2, which is an oxide of one or more selected from the group of Ca, Zr, P, Mo, Mn, and Ti.