JPS58159238A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with small noise and satisfactory frequency characteristics and sensitivity in a wide band, by forming a magnetic layer having a specified 2-layered structure including an upper layer contg. magnetic iron oxide powder contg. solubilized Co. CONSTITUTION:The 1st magnetic layer contg. needlelike Co-contg. magnetic iron oxide powder having a surface Co layer on magnetic iron oxide powder as nuclear crystals and the 2nd magnetic layer contg. magnetic iron oxide powder contg. solubilized Co and having <=0.1mum particle size are successively laminated on a substrate to form a magnetic recording medium suitable for high density recording. The 1st layer has 400-600Oe coercive force, and the coercive force of the 2nd layer is >=100Oe higher than that of the 1st layer. The thickness of the 2nd layer is >=1mum, and the ratio of (the thickness of the 2nd layer)/(the thickness of the 1st layer) is adjusted to 1/0.5-1/9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a two-layered magnetic layer structure, and its purpose is to reduce noise and improve frequency characteristics and sensitivity in low and high frequency bands.
The object of the present invention is to provide a magnetic recording medium particularly suitable for high-density recording.

In a magnetic recording medium with a two-layer magnetic layer structure,
It is known that frequency characteristics and sensitivity in low and high frequency bands can be improved by lowering the coercive force of the layer and increasing the coercive force of the upper layer. First, a magnetic paint containing cobalt-containing iron oxide magnetic powder with a relatively low coercive force is applied onto the substrate and dried to form a lower magnetic layer, and then a cobalt-containing powder with a relatively high coercive force is applied on the lower magnetic layer. It is made by applying and drying magnetic paint containing iron oxide magnetic powder.

However, the cobalt-containing iron oxide magnetic powder conventionally used as the magnetic powder for the upper magnetic layer has a large particle size of about 0.4μ, so it is difficult to improve the surface smoothness of the magnetic layer to reduce noise. As a result, the sensitivity and frequency characteristics in the high frequency band are still not sufficiently good, making it difficult to perform high-density recording.

In view of the current situation, the inventors conducted IIIj1 studies and found that the particle size of iron oxide magnetic powder in which cobalt is solid-dissolved inside the particles is 0.1 as the magnetic powder of the upper magnetic layer.
A granular magnetic powder of less than μ is used, and the upper magnetic layer containing this magnetic powder is placed on the lower magnetic layer containing acicular cobalt-containing iron oxide magnetic powder and having a coercive force of 400 to 600 oersted on the substrate. The coercive force of the upper magnetic layer is made to be 100 Oe or more higher than the coercive force of the magnetic layer of the underwear by forming a heavy N1 layer, and the thickness of the upper magnetic layer is made to be 1 μ or more, and the thickness of the upper magnetic layer and the lower magnetic layer are The ratio (thickness of the upper magnetic layer/thickness of the lower magnetic layer) to the thickness is 110.5 to 1.
When it is within the range of /9, the surface smoothness of the magnetic layer becomes good, noise is sufficiently reduced, and sensitivity and frequency characteristics in low and high frequency bands are further improved, making magnetic recording especially suitable for high-density recording. They discovered that a medium could be obtained and came up with this invention.

In this invention, the cobalt-containing iron oxide magnetic powder used in the upper magnetic layer is a granular magnetic powder with a particle size of 0.1μ or more, in which cobalt is solidly dissolved inside the iron oxide magnetic powder. It is preferable that the particle size is 0.1
Cobalt solid solution granular iron oxide magnetic powder with a particle size of less than μ is produced by mixing a metal salt aqueous solution in which a ferrous salt and a cobaltous salt are dissolved in water and an alkaline aqueous solution, and simultaneously blowing an oxygen-containing gas into the powder at a temperature of 40°C or less. The reaction is carried out while maintaining the pH at a temperature of 7 to 12, and the resulting powder is washed with water, dehydrated, and dried.
It is made by heating in air. Since the thus obtained cobalt solid-dissolved iron oxide magnetic powder with a particle size of 0.1μ or less is granular, it has a component suitable for perpendicular magnetic recording. The surface smoothness of the upper magnetic layer contained as a magnetic layer is sufficiently improved, noise is sufficiently reduced, and as a result, high-density recording characteristics are further improved.

In addition, as for the cobalt-containing iron oxide magnetic powder used in the lower magnetic layer, the iron oxide magnetic powder is used as a core crystal and a cobalt-containing acicular powder having a surface layer in which cobalt is mainly contained in the core crystal. Iron oxide magnetic powders are preferably used, preferably those having a coercive force Fi in the range of 400 to 600 Oersteds.

The coercive force of both the upper and lower magnetic layers is set such that the coercive force of the lower magnetic layer is within the range of 400 to 600 oersteds, and the coercive force of the upper magnetic layer is set to this range in order to improve the sensitivity and frequency characteristics in low frequency and high frequency bands. 1 from the coercive force of the lower magnetic layer
It is preferable to set it higher than 00 Oe F, because if the difference between the coercive force of the upper magnetic layer and the coercive force of the lower magnetic layer is too large, a sagging phenomenon (lowering of the middle range) in the frequency characteristics will occur. Preferably, it is 500 Oersted or less.

The thickness of both the upper and lower magnetic layers is 1 μm thicker than that of the upper magnetic layer.
In addition to the above, it is preferable that the ratio of the upper magnetic layer thickness to the lower magnetic layer thickness be within the range of 1:0.5 to 1:9. The characteristics cannot be sufficiently improved, and if it is too thin, the characteristics in the high frequency band and noise cannot be sufficiently improved.

The formation of the l-downward magnetic layer may be performed according to a conventional method,
For example, first, on a bridge body such as polyester film,
A magnetic paint containing acicular cobalt-containing iron oxide magnetic powder, a binder resin, an organic solvent and other additives is applied by conventional means and dried to form a lower magnetic layer, which is then coated on top of this lower magnetic layer. granular magnetic powder with a particle size of 0.1μ or less, in which cobalt is dissolved inside the particles of iron oxide magnetic powder;
The upper magnetic layer may be formed by applying a magnetic paint containing a binder resin, an organic solvent, and other additives by conventional means and drying.

The binder resin used to form both the upper and lower magnetic layers is not particularly limited, and may include vinyl chloride-vinyl acetate copolymer, polyvinyl ptylar/l resin, polyurethane resin, cellulose resin, Any conventionally used binder resin such as an isocyanate compound may be suitably used.

Furthermore, the organic solvent is not particularly limited, and may include those commonly used as solvents suitable for dissolving the binder resin used, such as toluene, methyl isobutyl ketone,
Methyl ethyl ketone, dichlorohexanone, tetrahydrofuran, and ethyl are used alone or in combination.

When the L upper magnetic layer is multilayered on the substrate as described above, the cobalt solid-dissolved iron oxide magnetic powder used in the upper magnetic layer is granular and fine particles with a particle size of 0.1 μ or less; The surface smoothness of the magnetic layer has been sufficiently improved, noise has been sufficiently reduced, and as a result, high-density recording characteristics have been improved.As a result of this various upper magnetic layer, sensitivity and frequency characteristics in high frequency bands have been improved. A magnetic recording medium having better sensitivity and frequency characteristics in low frequency and high frequency bands and particularly suitable for high-density recording can be obtained. .

Next, embodiments of the invention will be described.

Example 1 <Preparation of magnetic paint for lower layer> Co-containing r-Fe20. Magnetic powder 1 part soo (particle size (long axis) 0.4 tone, axial ratio (horizontal axis/furnace axis) 8, coercive force 550 oersted) VAGH (manufactured by U, C, C, USA, salt 80 parts by weight) (vinyl-vinyl acetate-vinyl alcohol copolymer) Takelac E-551 (trial drug 90 1 item 1-manufactured by Kogyo, urethane breporin) Silonate Nippon Polyurethane 30 trifunctional low molecular weight f-socyanate, manufactured by Lin Kogyo Co., Ltd. Compound) Methyl isobutyl ketone 500 Toluene
500 liters of this composition was mixed and dispersed in a ball mill for about 72 hours to prepare a magnetic paint for the second layer.

Preparation of magnetic paint for one layer> 4J! Cobalt acid 13009 and ferrous sulfate 210
009 was dissolved in 100j of water, and a solution of caustic soda 63509 dissolved in 100j of water was added thereto with stirring until the pH of the reaction solution reached 10. The reaction temperature was then maintained at 35°C and 100/min/min. The reaction was carried out for 5 hours while blowing in air, and the PH4-
1 It was controlled within the range of 8 to 10 by adding an appropriate alkali. After the reaction was completed, the temperature was raised to 100°C.
After heating for 4 hours at
It was dried at C.

Next, the magnetic powder thus obtained was heated in air for 400 min.
°C17) 71! Particle size: 040 after heat treatment for 3 hours at
A 4μ granular cobalt solid solution iron oxide magnetic powder was obtained.

The cobalt solid solution iron oxide magnetic powder obtained has a coercivity of 700
It was Ersted. Using cobalt solid solution iron oxide magnetic powder obtained by
03rjB powder* 75 (1m part VAGH125
& Bandex T-5250f large 100 1 Nippon Ink Chemical Industries, Ltd., urethane elastomer) Coronate L 25 #n-butyl stearate 15 N methyl ethyl ketone 600 #toluene
A magnetic paint for the upper layer was prepared by mixing and dispersing 600 parts by weight of a composition in a ball mill for 96 hours.

<Manufacture of double-layer magnetic tape> After coating the above-mentioned ten-layer magnetic paint on a 12-μ thick polyester film, drying it, and performing surface treatment, it is further heated at 60°C for 24 hours without curing for about 3 μm. A lower magnetic layer was formed. Next, the above-mentioned magnetic paint for the upper layer is roughly coated on this magnetic layer, dried, and subjected to surface treatment to form an upper magnetic layer with a thickness of approximately 2 μm.Then, the upper magnetic layer is cut to a predetermined width to form a 2-ton layer magnetic tape. I made it.

Example 2 Production of cobalt solid solution iron oxide magnetic powder in Example 1 In one rod, the reaction temperature of the metal salt aqueous solution and the alkaline aqueous solution was
Granular baltic solid solution iron oxide magnetic powder with a particle size of 0.025 μm was obtained in the same manner as in Example 1 except that the temperature was changed from 5° C. to 20° C. The coercive force of the obtained co-curd solid solution iron oxide magnetic powder was 800 Els T. The thus obtained cobalt solid solution iron oxide magnetic powder was used in the upper layer magnetic paint in Example 1.
A double layer magnetic tape was produced in the same manner as in Example 1 except that ferrochloride magnetic powder was used instead.

Comparative Example 1 In the magnetic paint for the upper layer in Example 1, the particle size was 0.0.
4μ, coercive cuff 00 Oersted Co solid 7f11-F
e20. Instead of magnetic powder, use Co with a particle size (long axis) of 0°4μ, an axial ratio (long axis/furnace axis) of 8, and a coercive cuff of 00 oersted.
A multilayer magnetic tape was prepared in the same manner as in Example 1 except that the same amounts of solid solution r -Fe2O and magnetic powder were used.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the formation of the lower magnetic layer was omitted.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that the curing after forming the lower magnetic layer was omitted and the formation of the upper magnetic layer was omitted.

Magnetic tape 1/(1
Then, the coercive force, AC noise, frequency characteristics, and sensitivity at 315 Hz of both the upper and lower magnetic layers were measured.

Table F shows the results.

As is clear from Table 11, the double-layer magnetic tapes obtained in each Example 1 had better frequency characteristics in the high frequency band, especially in the low frequency and high frequency bands, compared to the magnetic tapes obtained in the comparative examples. In addition, the sensitivity is high and the noise is small, which means that the magnetic layer strength obtained by this invention is a magnetic recording medium with a 2@ structure.The frequency characteristics and sensitivity in the low frequency and high frequency bands are even better, especially for high density magnetic recording media. It can be seen that it is suitable for recording and that noise is sufficiently reduced.

Claims (1)

[Claims] 1. A first magnetic layer containing acicular cobalt-containing iron oxide magnetic powder with a coercive force of 400 to 600 oersteds is formed on the substrate, and furthermore, cobalt is solid-dissolved inside the particles of U cobalt-containing iron oxide magnetic powder. The coercive force containing granular magnetic powder with a particle size of 0.1μ or less is 100% lower than that of the lower first magnetic layer.
A second magnetic layer with a higher Oersted is formed as a magnetic layer and becomes the upper layer #! When the thickness of the second magnetic layer is set to 1μ or more, the thickness of the second magnetic layer, which is the upper layer, and the first, which is the lower layer, are
A magnetic recording medium characterized in that the ratio (thickness of the upper magnetic layer/thickness of the magnetic layer of the F layer) to the thickness of the magnetic layer is within the range of 1/0.5 to 1/9.