JPS6238531A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease noise by incorporating specific hexagonal ferrite powder into a magnetic layer. CONSTITUTION:The hexagonal ferrite powder having 70-120m<2>/g specific surface area by a BET method, 0.01-0.2mum average particle size, >=30emu/g satd. magnetization quantity and 500-1,500 oersted coercive force is used. The hexagonal ferrite powder is prepd. by adding an aq. caustic soda soln. to an aq. metallic salt soln. of barium and iron to prepare the precipitate of the fine hydroxide of such metallic salts, bringing the co-precipitate into heating reaction in an autoclave to form the fine planar crystal and heating the crystal in air. The magnetic recording medium is formed by mixing and dispersing such hexagonal ferrite powder together with a binder resin, org. solvent, etc. to prepare a magnetic coating compd., coating the compd. by an optional coating means on a substrate and drying the coating. The S/N is thereby improved and the magnetic recording medium which is small in noise and is 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, since the particles of this type of hexagonal ferrite powder are plate-shaped, for example, when compared with conventionally used needle-shaped magnetic powder, even if the specific surface area is the same according to the BET method, this type of hexagonal ferrite powder has a plate-like shape. The volume of the particles is large, such that the volume of the plate-shaped powder is more than twice the volume of the needle-shaped powder, and as a result, the magnetic recording obtained using this type of hexagonal ferrite powder The medium has the problem of high noise.

[Means for solving problems]

The present invention has been made as a result of various studies in view of the current situation, and has a specific surface area of 70 to 1 by the BET method.
20m/g, average particle diameter of o, ol~0.2μm, saturation magnetization of 30 emu/g or more, coercive force of 500~1
By using 500 Oe hexagonal ferrite powder, noise is sufficiently reduced, and high S/N and high density recording can be performed satisfactorily.

In this invention, the magnetic powder used has a specific surface area of 70 to 120 rrf/g by the BET method, an average particle diameter of 0.01 to 0.2 μm, a saturation magnetization of 30 emu/g or more, and a coercive force of 500 to 150 o. It is preferable to use Elstend's hexagonal ferrite powder, which has a specific surface area of 101T? according to the BET method. If you do not use more than /g,
A magnetic recording medium with a sufficiently high S/N ratio cannot be obtained. However, if the specific surface area determined by the BET method is larger than 120 m/g, the saturation magnetization tends to decrease, and the output of the magnetic recording medium obtained using this type of hexagonal ferrite powder decreases. A hexagonal ferrite powder having a particle size of 100 m/g or less, more preferably 100 m/g or less, is used. Such hexagonal ferrite powder usually has a plate shape, so even if the particle size (particle diameter) is the same, if the thickness of the plate-shaped powder differs, the volume will differ greatly. Therefore, the specific surface area determined by the BET method is suitable as a means of determining the volume of hexagonal ferrite powder, and the average particle size does not matter much, but it is usually 0.02 to 0.2 μm.
Those within the range of are preferably used. In addition, the saturation magnetization and coercive force are adjusted to ensure good high-density recording.
Saturation magnetization is 30 emu/g or more, coercive force is 500
It is preferable to use a magnet in the range of ~1500 oersteds, and a saturation magnetization lower than 3 emu/g.
If the coercive force is lower than 500 Oe, sufficient high-density recording cannot be performed, and if the coercive force is higher than 1500 Oe, it becomes difficult to record with a normal magnetic head.

Such hexagonal ferrite powder is produced by adding an aqueous solution of caustic soda to an aqueous solution of metal salts such as barium or iron to form fine hydroxide precipitates of these metal salts, and then heating this coprecipitate in an autoclave. The reaction is caused to form fine plate-like crystals, which are further heated in air to obtain fine barium ferrite particle crystals having the desired properties.

In this way, the specific surface area by BET method is 70~b, the sum magnetization is 30 emu/g or more, and the coercive force is 5oo~
1500 Oe hexagonal ferrite powder has an extremely small volume and is fine, and its saturation magnetization and coercive force are within suitable ranges as magnetic powder for high-density recording magnetic recording media. A magnetic recording medium obtained using powder can perform high-density recording without increasing noise.

The magnetic recording medium of the present invention may be manufactured according to a conventional method, for example, the specific surface area determined by the BET method described above is 70 to 120 d/g, and the average particle diameter is 0.01 to 0.2.
μm, a saturation magnetization of 30 emu/g or more, and a coercive force of 500 to 1500 Oe, hexagonal ferrite powder is mixed and dispersed with a binder resin, an organic solvent, etc. to prepare a magnetic paint, and this is applied to polyester films, etc. It may be applied onto the substrate using any coating means such as a roll coater and dried.

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 (FeC63), barium chloride (Ba
CJ2) 1z8 mol, cobalt chloride (Coc7!2)
1z20 mol, and titanium chloride (TICf+) 1z2
0 mol was dissolved in 1z water.

Next, a caustic soda aqueous solution prepared by dissolving 6 mol of caustic soda in 1β water was added to this mixed solution and stirred. Next, after aging this suspension for one day, the precipitate was placed in an autoclave and reacted by heating at 300°C for 4 hours to obtain Ba.
Ferrite particles were obtained. The obtained Ba ferrite particles were washed with water, dried, and then heat-treated in air at 700° C. for 3 hours to obtain a powder. The obtained powder was analyzed by X-ray analysis.
It was confirmed that it was magnetic brambite type hexagonal Ba ferrite. Hexagonal crystal B obtained in this way
The specific surface area of a ferrite powder according to the BET method is 72 m/
g, the average particle diameter is 0.08 μm, and the saturation magnetization is 51
emu/g, and the coercive force was 830 Oe.

<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
F ((manufactured by U, C, C, USA, chloride 110 vinyl-vinyl acetate-vinyl alcohol copolymer) Pandesox T-5250 (Oguchi 7o manufactured by Hon-Ink Kagaku Kogyo Co., Ltd., urethane elastomer) Coronate (Japan Polyurethane 20 〃N-Kogyo Co., Ltd., trifunctional low molecular weight isocyanate compound) 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 paint was applied onto a polyester film having a thickness of 65 μm, and was run through opposing magnetic fields with different polarities to perform a vertical alignment treatment, and then dried to form a magnetic layer having a dry thickness of 3 μm. Next, the formed magnetic layer was subjected to surface treatment, and then punched into a disk shape of 3 inches in diameter to produce a magnetic disk.

Example 2 In the production of Ba ferrite powder in Example 1,
The amount of cobalt chloride and titanium chloride used is 1
The specific surface area by the BET method was 94 m / g in the same manner as in Example 1, except that 20 mol of z was changed to 10 mol of 1z, and the heat treatment in air was changed from 700 ° C. for 3 hours to 800 ° C. for 2 hours. % average particle size is 0.05μm
, hexagonal Ba ferrite powder with a saturation magnetization of 43 emu/g and a coercive force of 650 Oe was produced, and a magnetic disk was manufactured.

Example 3 In the production of Ba ferrite powder in Example 2,
Heat treatment in air at 800℃, 2 hours to 650℃,
BET in the same manner as in Example 2 except that the time was changed to 3 hours.
The specific surface area by law is 110n? /g, average particle size is 0.
05 μm, saturation magnetization 32 emu/g, coercive force 5
A 90 Oe hexagonal Ba ferrite powder was produced and a magnetic disk was made.

Comparative Example 1 In the production of Ba ferrite powder in Example 1,
The amount of barium chloride added was increased from 1z8 mol to 1z10 mol, and the amounts of cobalt chloride and titanium chloride were increased to 1 each.
The specific surface area by the BET method was 64rd/
g, average particle diameter is 0.1 μm, saturation magnetization is 53 em
u/g, orthogonal Ba with a coercive force of 1020 oersteds
We produced ferrite powder and made magnetic disks.

Comparative Example 2 In the production of Ba ferrite powder in Example 1,
The amount of barium chloride added was increased from 1z8 mol to 1z10 mol, and the amounts of cobalt chloride and titanium chloride were increased to 1 each.
z from 20 moles to 1730 moles, the amount of water dissolved is 11
to 21, and instead of the aqueous solution of 6 mol of caustic soda dissolved in 1 liter of water, an aqueous solution of 15 mol of caustic soda dissolved in water from 21 was used, and further heat treatment was performed in air at 700°C for 3 hours. The procedure was the same as in Example 1 except that the temperature was changed to 800°C for 3 hours, and the specific surface area measured by the BET method was 38 m/g, the average particle diameter was 0.2 μm, the saturation magnetization was 58 emu/g, and the coercive force was 1160 Oe. Hexagonal Ba ferrite powder was produced and a magnetic disk was manufactured.

For the magnetic disks obtained in each example and comparative example, the playback output (
S) and the noise level (N) after DC cancellation were measured. The measured values are expressed as relative values, with the reproduction output and noise level of the magnetic disk of Comparative Example 1 expressed as OdB.

The table below shows the results.

〔Effect of the invention〕

As is clear from the above table, the noise level of the magnetic disks obtained in Examples 1 to 3 is significantly lower than that of the magnetic disks obtained in Comparative Examples 1 and 2, and the playback output is lower than that of BET. Even if it is made into fine particles of 70m'/g or more, there is almost no change when the BET is less than Loom/g,
When the BET exceeds 100d/g, there is a slight decrease in the playback output, but the noise level decreases more than the decrease in the playback output, so the S/N clearly improves. It can be seen that the magnetic recording media produced by this study have sufficiently low noise and are suitable for high-density recording.

Claims (1)

[Claims] 1. Specific surface area by BET method is 70 to 120 m^2/g
, the average particle diameter is 0.01 to 0.2 μm, and the saturation magnetization is 3
A magnetic recording medium characterized in that a magnetic layer contains hexagonal ferrite powder having a coercive force of 0 emu/g or more and a coercive force of 500 to 1,500 oersteds.