JPS62154228A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease electrostatic noise and to permit good high-density recording by incorporating hexagonal ferrite powder contg. Fe<2+> ions in the powder particles into a magnetic layer. CONSTITUTION:The magnetic powder is preferably the planar hexagonal ferrite powder which contains the Fe<2+> ions in the powder particles and of which the axis of easy magnetization is in the direction perpendicular to the plane of the particle plate. The effect of improving electrical conductivity is hardly admitted if the content of Fe<2+> is lower than 0.01 in terms of Fe<2+>/Fe<3+> ratio and the magnetic characteristics are debased when the content is increased to 0.2 or above. The content of the Fe<2+> is, therefore, kept within a 0.02-0.10 range in terms of Fe<2+>/Fe<3+> ratio. The incorporation of the Fe<2+> ions into such hexagonal ferrite powder is usually executed by mixing an aq. metallic soln. of barium or the like and aq. caustic soda soln., bringing the co-deposit of the resulted hydroxide of the metallic salt into reaction with heating in an autoclave, heating the resulted planar crystal in air and reducing the hexagonal ferrite powder formed in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium using hexagonal ferrite powder as magnetic powder.

[Conventional technology]

Generally, magnetic recording media improve magnetic properties by orienting acicular magnetic powder in the magnetic layer in the longitudinal direction of the magnetic layer, but in the case of magnetic recording media that utilize such magnetization components in the longitudinal direction, As the magnetic recording density increases, the demagnetizing field within the magnetic layer increases, so there is a limit to how high the magnetic recording density can be achieved.

On the other hand, the perpendicular magnetic recording method, which uses magnetization components perpendicular to the magnetic layer surface, is known as a recording method suitable for high-density recording because the demagnetizing field decreases as the recording density increases.
As the magnetic powder most suitable for perpendicular magnetic recording, hexagonal ferrite powder is used which is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface.

[Problem that the invention seeks to solve]

However, although this type of hexagonal ferrite powder has excellent recording properties, it has extremely high electrical resistance, and the magnetic recording medium obtained by using it as a magnetic powder has the disadvantage of extremely large charging noise. Even if you try to improve the conductivity by using black together, since the powder particles are plate-shaped, this kind of plate-shaped hexagonal ferrite powder particles will be interposed between the carbon blank particles, preventing contact between the carbon blanks. conductivity is hardly improved.

[Means for solving problems]

The present invention has been made as a result of various studies in view of the current situation, and is based on the fact that F
By incorporating the hexagonal ferrite powder containing e2+ ions into the magnetic layer, the conductivity of the hexagonal ferrite powder and thus the conductivity of the magnetic layer can be improved, and charging noise can be reduced. It is designed to have a sufficiently small kussia and to be able to perform high-density recording well.

In this invention, the ferrite powder used is preferably a plate-shaped ferrite powder containing Fe2+ ions in the powder particles, with the axis of easy magnetization perpendicular to the particle plate surface. , the content of Fe2+ is Fe2+/
If the Fe3+ ratio is less than 0.01, little effect of improving conductivity will be observed, and if it is more than 0.2, the magnetic properties will deteriorate. Therefore, the Fe2+ content is Fe2
The ratio of +/Fe3+ is preferably within the range of 0.01 to 0.2, more preferably within the range of 0.02 to 0.10.

In order to incorporate Fe2+ ions into the plate-shaped hexagonal ferrite powder whose axis of easy magnetization is perpendicular to the particle plate surface, an aqueous solution of a metal salt such as barium or iron and an aqueous solution of caustic soda are usually used. 60,000-product ferrite is produced by heating the resulting co-precipitate of totally bent salt hydroxide in an autoclave, and then heating the plate-like crystals obtained in the autoclave in air. Either reduce the powder or
Alternatively, it can be easily carried out by surface treatment in a ferrous salt aqueous solution to contain Fe2+ ions. and Fe2
The content of + ions can be adjusted by adjusting the heating temperature and time when reducing hexagonal ferrite powder, or by adjusting the temperature and treatment temperature of the ferrous salt aqueous solution when surface treating it in a ferrous salt aqueous solution. This is done by adjusting the

In this way, F
When Fe2+ ions are contained in a ratio of 0.01 to 0.2 e ''/F e 3+ , Fe2+ ions and ['
The smooth movement of electrons between e 3+ ions improves the conductivity of the hexagonal ferrite powder particles, and also improves the conductivity of a magnetic layer using this type of hexagonal ferrite powder. Therefore, this type of Fe2+ ion is converted into Fe
Magnetic recording media obtained using 60,000 Feray I powder containing Fe 2+ / Fe 3+ ratio within the range of 0.01 to 0.2 have sufficiently small charging noise and high density. Good recording is possible.Also, when carbon black is used in combination, plate-shaped hexagonal ferrite powder particles are interposed between the carbon black particles, and even if contact between the carbon blanks is prevented, the plate-shaped hexagonal ferrite (powder) "Since the stand-up itself is conductive, there is no loss of conductivity, and since the excellent conductivity of carbon bra and glue is added, the conductivity of the magnetic layer is further improved, and charging noise is further reduced. As a result, high-density recording can be performed better.

The magnetic recording medium of the invention can be assembled using a conventional method. For example, the above-mentioned Fe2+ ion is
/Fe3+ ratio is 0. (A magnetic paint is prepared by mixing and dispersing 60,000 ferrite powder containing a concentration within the range of 11 to 0.2 with a binder resin, an organic solvent, etc., and applying this to a substrate such as a polyester film. roll coater
It may be applied by any coating means such as the like and dried.

As the binder resin used here, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymer, polyvinyl bunal resin, cellulose resin, polyurethane resin, polyester resin, and isocyanate compound are widely used. (Used.

As the R-containing agent, conventional organic solvents such as toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and ethyl acetate can be used alone or in combination of two or more.

Note that various commonly used additives such as dispersants, lubricants, 1iJF polishing agents, antistatic agents, etc. may be optionally added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Production of hexagonal Ba ferrite i powder> Ferric chloride (F
eCff3) 1 mol, barium chloride (BaC62) 1/
8 mol, cobalt chloride (Cocf2) 1/20 mol, and titanium chloride (1-i Ce+) 1/20
Dissolve 1 mole of H in water, add 5 moles of caustic soda to this mixed solution, and add 5 moles of caustic soda to I! ! The mixture was added to an aqueous solution of caustic soda dissolved in water and stirred. Next, after aging this suspension for one day, the precipitate was placed in an autoclave and incubated at 300°C for 2 days.
Ba ferrite particles were obtained by a heating reaction for a period of time. After the obtained [3a fluorite particles were washed with water and dried, they were further heat-treated in air at 800°C for 2 hours. After that, Ba was further reduced in hydrogen gas at 250°C for 2 hours.
Ferrite powder was obtained. The obtained Ba ferrite powder has an average particle diameter of 0.08 μm and a saturation magnetization of 58.3e.
mu/g, coercive force is 650 oersted, Fe 2
+/F e 3+ was 0.084.

<Preparation of magnetic recording medium> Using the hexagonal Ba ferrite powder obtained as described above, 800 parts by weight of hexagonal Ba ferrite powder VAG
H (manufactured by U, C, C, USA, 110 chloride-vinyl acetate-vinyl alcohol copolymer) Pandenox T-5250 (Dai 1170, manufactured by Hon Ink Kagaku Kogyo Co., Ltd., urethane elastomer) Coronate (Japan Polyurethane) 20. Trifunctional low molecular weight bone isocyanate compound) n-butyl stearate 8 methyl isobutyl 1 ton 500 toluene
A magnetic coating material was prepared by mixing and dispersing a composition having a composition of 500% in a ball mill for 72 hours. This magnetic ↑ material was applied onto a polyester film with a thickness of 12 μm and dried to form a magnetic layer with a dry thickness of 2 μIn. After surface treatment of the magnetic layer, the magnetic material was cut into a predetermined width and I made a tape.

Example 2 In the production of Ba ferrite powder in Example 1,
Reduction treatment in hydrogen gas at 250℃, 2 hours to 200℃
, except that the time was changed to 6 hours, in the same manner as in Example 1, the average particle diameter was 0.1 μm, and the saturation magnetization amount was 57.6 e/g.
, coercive force is 665 oersted, Fe2+/Fe3+
Ba ferrite powder with a diameter of 0.03') was produced and a magnetic tape was made.

Example 3 In the composition of the magnetic paint in Example 1, HS-50
0 (manufactured by Asahi Carbon Co., Ltd., carbon black), new 8
0! A magnetic tape was produced in the same manner as in Example 1 except that fi part was added.

Example 4 In the production of Ba ferrite powder in Example 1,
Instead of the reduction treatment in hydrogen gas, Ba ferrite powder is dispersed in an aqueous solution of 0.12 mol of ferrous sulfate dissolved in 0.51/8 water, and 1.2 mol of ferrous sulfate is added to this dispersion. The procedure was repeated in the same manner as in Example 1 except that a caustic soda aqueous solution prepared by dissolving caustic soda in 0.5p of water was added and treated at 60°C for 3 hours.The average particle diameter was 0.08 μm and the saturation magnetization was 57.
．． 8.: mu/g, coercive force is 620 oersted, F
A Ba ferrite powder with e 2-'/F e 3+ of 0.055 was produced 1 and a magnetic tape was made.

Comparative Example 1 In the production of Ba ferrite powder in Example 1,
Example 1 was carried out in the same manner as in Example 1, except that the reduction treatment in hydrogen gas was omitted, and the average particle diameter was 0.08 μm and the saturation magnetization amount was 5.
A hexagonal Ba ferrite powder with a coercivity of 7.4 emu/g and a coercive force of 690 oersted was produced, and a magnetic tape was made. The content of Fe2+ ions in the obtained Ba ferrite powder was 0.

Comparative Example 2 In the composition of the magnetic paint in Comparative Example 1, HS-50
0 (manufactured by Asahi Carbon Co., Ltd., carbon blank), new 8
A magnetic tape was produced in the same manner as in Comparative Example 1 except that 0 part by weight was added.

Regarding the magnetic tapes obtained in each example and comparative example,
Surface electrical resistance was measured.

The table below shows the results.

(Effects of the Invention) As is clear from the above table, the magnetic tapes obtained in Examples L-111 to 4 had significantly lower surface electrical resistance than the magnetic tapes obtained in Comparative Examples 1 and 2. This shows that the magnetic recording medium obtained according to the present invention has a low surface electrical resistance and is suitable for high-density recording.

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a magnetic layer contains hexagonal ferrite powder containing Fe^2^+ ions in the powder particles.