JPS6238532A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve orientation by incorporating specific hexagonal ferrite powder into a magnetic layer. CONSTITUTION:Hexagonal ferrite powder incorporated with 0.01-2.0wt% phosphorus near the surface of powder particles is used. The hexagonal ferrite powder is formed by bringing metallic salts such as Ba salt, Sr salt and Pb salt and iron salt into reaction in a flux to form a hexagonal ferrite crystal having 0.01-0.3mum average particle size, treating the same with a phosphorus treating agent to incorporate the phosphorus near the particle surface of the hexagonal ferrite powder, then subjecting the powder to a heating treatment. Such hexagonal ferrite powder is mixed and dispersed together with a binder resin, org. solvent, etc. to prepare a magnetic coating compd. Such compd. is coated on the substrate by an optional coating means such as roll coater and is dried. The dispersibility, packability and orientation of the hexagonal ferrite powder incorporated into the magnetic layer are thereby improved and the magnetic recording medium suitable for high-density recording is obtd.

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]

In general, 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 longitudinal magnetization components, 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, when this type of hexagonal ferrite powder is dispersed in a binder resin and then oriented in a magnetic field, since the particles are plate-shaped, the particles tend to overlap with each other, especially when the average particle diameter is 0. Hexagonal ferrite powder, which is fine with a diameter of 3 μm or less and is suitable for high-density recording, has this tendency, and it is difficult to separate the particles one by one, making it difficult to orient the particles so that their plate planes are parallel to the magnetic layer plane. There is.

[Means for solving problems]

This invention has been made as a result of various studies in view of the current situation, and includes surface treatment with a phosphoric acid-based treatment agent to inject 0.01 to 2.0% by weight of phosphorus near the surface of powder particles. By using the contained hexagonal ferrite powder, the dispersibility in the binder resin is improved, the orientation is improved, and high-density recording can be performed satisfactorily.

In this invention, the magnetic powder contained in the magnetic layer is
It is preferably a hexagonal ferrite powder containing 0.01 to 2.0% by weight of phosphorus near the surface of the powder particles,
When the phosphorus content is less than 0.01ffi%,
The effect of improving dispersibility was not so noticeable, and 2.
If the amount exceeds 0fflit%, there is a risk of deterioration of magnetic properties. In this way, the phosphorus content is reduced to 0.01
An effect is observed when the content is within the range of ~2.0 mm%, but it is most effective when the content is within the range of 0.05 to 1.5% by weight. Further, the average particle size is preferably within the range of 0.01 to 0.3 μm; if the average particle size is larger than 0.3 μm, high-density recording cannot be performed well;
If it is smaller than μm, it tends to exhibit superparamagnetism and the magnetic properties deteriorate.

In this way, 0.01 to 2 phosphorus is added near the surface of the powder particles.
．． Average particle size containing 0% by weight is 0.01 to 0.3 μm
The hexagonal ferrite powder is dissolved in an aqueous solvent or flux,
Metal salts such as Ba salt, Sr salt, and Pb salt are reacted with iron salt to produce hexagonal ferrite crystals with an average particle size of 0.01 to 0.3 μm, and then hexagonal ferrite crystals of the fine particles are produced. It can also be obtained by treating hexagonal ferrite powder obtained by heat-treating with a phosphoric acid-based treatment agent, but before heat-treating the hexagonal ferrite crystal, it is treated with a phosphoric acid-based treatment agent, It is most effective to contain phosphorus near the particle surface of hexagonal ferrite powder, and by treating it with a phosphoric acid-based treatment agent before heat treatment, it is possible to contain phosphorus near the particle surface of hexagonal ferrite powder. If this is done, the appropriate amount of phosphorus contained near the particle surface will effectively prevent plate-shaped powder particles from overlapping each other during heat treatment, resulting in effective heat treatment and crystallization of the particles. A hexagonal ferrite magnetic powder with improved properties, fine particles with an average particle size of 0.01 to 0.3 μm, a large amount of saturation magnetization, and excellent dispersibility and orientation can be obtained. As the phosphoric acid-based treatment agent for containing phosphorus, for example, sodium phosphate, sodium metaphosphate, sodium polyphosphate, sodium hydrogen phosphate, ammonium hydrogen phosphate, etc. are preferably used.

In this way, 0. O1~2.01
Average particle size containing it% phosphorus is 0.01 to 0.3
The μm hexagonal ferrite powder is fine and contains an appropriate amount of phosphorus near the particle surface, which improves dispersibility in the binder resin, improves orientation, and improves high-density recording characteristics. do.

The magnetic recording medium of the present invention may be manufactured according to a conventional method.
The average particle size containing 0.01 to 2.0% by weight of phosphorus is 0.01 to 2.0% by weight.
A magnetic paint is prepared by mixing and dispersing hexagonal ferrite powder with a diameter of 0.01 to 0.3 μm together with a binder resin, an organic solvent, etc., and this is applied onto a substrate such as a polyester film using any coating method such as a roll coater. Just apply it and let it dry.

As the binder resin used here, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin, polyurethane resin, polyester resin, and isocyanate compound are widely used. It will be done.

Further, as the organic solvent, conventionally widely used organic solvents such as toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and ethyl acetate are used alone or in a mixture of two or more.

Note that various commonly used additives such as dispersants, lubricants, abrasives, 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 powder> 1 mol of ferric chloride (FeCA3), barium chloride (Ba
Cj! 2) 1/10 mol, cobalt chloride (COCj!
2) 1/30 mol, titanium chloride (Ticfi+) 1/3
0 mol was dissolved in 11 mol of water. Next, to this mixed solution,
A caustic soda aqueous solution of IA in which 10 mol of caustic soda was dissolved was added and stirred. Next, after aging this suspension for one day, the precipitate was placed in an autoclave and heated at 300°C.
A heating reaction was carried out for 2 hours to obtain Ba ferrite particles. After washing the obtained Ba ferrite particles with water, an aqueous solution in which 2.0 g of sodium metaphosphate (Na PO3) n was dissolved was added and stirred for 30 minutes. After stirring, this was dehydrated and dried. Thereafter, it was heat-treated in air at 800° C. for 2 hours to obtain hexagonal Ba ferrite powder. The obtained hexagonal Ba
The ferrite powder has a phosphorus content of 0.3% by weight, a coercive force of 980 oersted, and a saturation magnetization of 56 emu/
g, the average particle diameter was 0.12 μm.

<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, chloride 110 vinyl-vinyl acetate-vinyl alcohol copolymer) Pandex T-5250 (Oguchi 70 manufactured by Hon-Ink Kagaku Kogyo Co., Ltd., urethane elastomer) Coronate Japan Polyurethane 20 Trifunctional low molecular weight incyanate compound (manufactured by N Kogyo Co., Ltd.) n-butyl stearate 8 Methyl isobutyl ketone 500 Toluene
A magnetic coating material was prepared by mixing and dispersing a composition having a composition of 500% in a ball mill for 48 hours. This magnetic coating material was applied onto a polyester film with a thickness of 12 μm, and the film was run through opposing magnetic fields with different polarities to perform a vertical alignment treatment, and dried to form a magnetic layer with a dry thickness of 3 μm. Next, the formed magnetic layer was subjected to surface treatment, and then cut to a predetermined width to produce a magnetic tape.

Example 2 In the production of hexagonal Ba ferrite powder in Example 1, the same procedure as in Example 1 was carried out, except that the amount of sodium metaphosphate used in the phosphoric acid treatment was changed from 2.0 g to 4.0 g. Phosphorus content is 0.52% by weight, coercive force is 1020 oersted, and saturation magnetization is 53 emu.
/g, hexagonal Ba ferrite powder with an average particle size of 0.12 μm was produced to make a magnetic tape.

Example 3 In the production of hexagonal Ba mitzerite Hansong in Example 1, 2.5 g of ammonium hydrogen phosphate (NH4H2P 04 ) was used instead of sodium metaphosphate.
The same procedure as in Example 1 was carried out except that the phosphoric acid treatment was performed using the same method as in Example 1. Hexagonal Ba ferrite powder is produced,
I made magnetic tape.

Comparative Example 1 The hexagonal Ba ferrite powder was produced in the same manner as in Example 1 except that the phosphoric acid treatment with sodium metaphosphate was omitted, and the coercive force was 920 oersted and the saturation magnetization was 57 emu/g. , the average particle diameter is 0.1
A 5 μm hexagonal Ba ferrite powder was produced and a magnetic tape was made.

Regarding the magnetic tapes obtained in each example and comparative example,
Vertical coercive force, saturation magnetic flux density, residual magnetic flux density, and squareness were measured. The vertical square shape has a demagnetizing field coefficient of 4
It is considered as π and expressed as the value after demagnetizing field correction.

The table below shows the results.

Table [Effects of the Invention] As is clear from the above table, the magnetic tapes obtained in Examples to 3 have higher coercive force, square shape, residual magnetic flux density, and Both have high saturation magnetic flux densities, and therefore, according to the present invention, the hexagonal ferrite powder contained in the magnetic layer has good dispersibility, filling properties, and orientation, and a magnetic recording medium that can be used for high-density recording. You can see what you can get.

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a magnetic layer contains hexagonal ferrite powder containing 0.01 to 2.0% by weight of phosphorus near the surface of the powder particles.