JPH0485722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having a large output and low surface electric resistivity by using specific planar hexagonal ferrite powder. CONSTITUTION:A magnetic layer contg. magnetic powder and binder is provided on a nonmagnetic base body. The planar hexagonal ferrite powder which contains spinel ferrite and M phase magnetoplumbite type ferrite respectively at 3 to 50 wt.% and consists of the balance W phase magnetooplumbite type ferrite is used as the magnetic powder. The magnetic recording medium having the excellent reliability in terms of the output characteristics and electric resistance is then obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks.

[Conventional technology]

In order to improve the recording and reproducing characteristics of this type of magnetic recording medium, a perpendicular magnetic recording medium using plate-shaped hexagonal ferrite powder as the magnetic powder is being developed.

As the plate-shaped hexagonal ferrite powder, substitutional M-phase magnetoplumbite type 13a ferrite powder synthesized by a method such as a hydrothermal method has been commonly used.

[Problem to be solved by the invention]

However, since the known plate-shaped hexagonal ferrite powder has a low saturation magnetization (σS) of about 55 emu/g, magnetic recording media using this powder have the disadvantage that sufficient recording and reproducing output cannot be obtained. Ta.

In addition, since the above-mentioned magnetic powder has a high electrical resistance, in order to use it to create a magnetic recording medium, it is necessary to add a large amount of conductive filler to the magnetic layer or form a conductive undercoat layer. There were also drawbacks such as higher costs and more complicated manufacturing processes.

The present invention aims to eliminate the above-mentioned conventional drawbacks and to obtain a magnetic recording medium with excellent reliability in terms of output characteristics and electrical resistance.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the present inventors found that plate-shaped hexagonal ferrite powder having a specific crystal structure consisting of three types of ferrite compositions has high saturation magnetization and low electrical resistance. The present invention was completed based on the finding that this can bring about very good results in reducing the output characteristics and surface electrical resistance of magnetic recording media using this as a magnetic powder.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder is provided on a non-magnetic substrate, in which spinel ferrite and M-phase magnetoplumbite ferrite are each used in an amount of 3 to 50% by weight as the magnetic powder. % and the remainder is W-phase magnetoplumbite type ferrite.

[Structure and operation of the invention]

The plate-shaped hexagonal ferrite powder used in the present invention is mainly composed of W-phase magnetoplumbite ferrite, and this W-phase magnetoplumbite ferrite is expressed by the following general formula; In the formula, A is Ba*
At least one element selected from S r , p b , Ca, M is l';'e, Co, Ni, Z
At least one divalent metal ion selected from n, Cu, and Mg.

Such W-phase magnetoplumbite type ferrite is
Conventionally, attempts have been made to synthesize M-phase magnetoplumbite-type ferrite because it has higher saturation magnetization than that of magnetoplumbite-type ferrite, but the temperature at which W-phase is generated is 1,300 to 1,40℃.
Since the temperature was as high as about 0°C, particle growth was unavoidable, making it difficult to obtain fine particles.

In the present invention, in order to overcome the above-mentioned problems, we tried incorporating a small amount of M-phase magnetoplumbite ferrite into W-phase magnetoplumbite ferrite, and it became possible to synthesize it at a relatively low temperature and form fine particles. It has been discovered that magnetic powder with uniform particle size distribution can be obtained.

Here, the M phase magnetoplumbite type ferrite is W
Compared to the phase magnetoplumbite type ferrite, it has a common feature in that it has a spinel block S and a block R containing Ba (other metal A in the above formula), but
There is a clear difference in the crystal structure in that the arrangement is S RS'S'R' in the W phase, whereas it is S RS'R' in the M phase. Basic IJ
P192-193 (published by Kyoritsu Publishing Co., Ltd. in 1972;
(Refer to Keizo Ota).

On the other hand, both of these magnetoplumbite type ferrites have the drawback of high electrical resistance. Therefore, in the present invention, a small amount of spinel ferrite is added to both of these ferrites to avoid the above-mentioned drawbacks.

That is, this spinel ferrite is a cubic ferrite having a spinel crystal structure and a molecular formula represented by MO-Fez○3 (M is the same as above),
Since its electrical resistance is as low as about 103, its inclusion can greatly contribute to reducing the electrical resistance of the entire powder.

As described above, the plate-shaped hexagonal ferrite powder of the present invention is mainly composed of W-phase magnetoplumbite ferrite, and contains M-phase magnetoplumbite ferrite and spinel ferrite, so that the fine particles have no saturation magnetization. It has the characteristics of high magnetic powder and low electrical resistance, and particularly when spinel ferrite is localized on the surface of magnetic powder, a great effect can be obtained in reducing electrical resistance.

In such a plate-like hexagonal ferrite powder, the content of M-phase magnetoplumbite ferrite and spinel ferrite is 3 to 50% by weight, preferably 5% by weight, respectively.
It should be within the range of ~30% by weight. If each is less than 3% by weight, there is no effect, and if each exceeds 50% by weight, the saturation magnetization will be low. From the viewpoint of increasing the saturation magnetization, the total amount of M-phase magnetoplumbite ferrite and spinel ferrite is preferably 50% by weight or less, particularly 30% by weight or less.

In the plate-shaped hexagonal ferrite powder of the present invention having such a structure, the coercive force thereof is preferably in the range of 200 to 2.000 oersteds. If it is less than 200 oersted, high-density recording cannot be performed well, and if it exceeds 2,000 oersted, it is not suitable for magnetic recording media.

Moreover, the average particle diameter of this ferrite powder is 0.0
It is preferable that it is 2-0.5 micrometer. If it is less than 0.02 μm, sufficient magnetism cannot be obtained, and if it exceeds 0.5 μm, the surface smoothness of the magnetic layer cannot be sufficiently improved and high-density recording cannot be performed.

The above plate-shaped hexagonal ferrite powder used in the present invention can be synthesized, for example, as follows. First, an aqueous solution of a compound containing elements constituting a ferrite having the desired composition, such as Ba, Sr, Pb, and chlorides of Fe, Co, N+, etc., is added to an alkaline aqueous solution,
Obtain a precipitate.

Next, this precipitate is washed with water and filtered, and then Na
Add flux such as C1, 1.100~],,
Heat and bake at 400°C for several hours. After cooling, the above plate-shaped hexagonal ferrite powder is obtained by removing the flux.

In the synthesis of this ferrite powder, the content of spinel ferrite and M-phase magnetoplumbite type ferrite can be arbitrarily controlled by changing the charging composition, heating temperature, and heating time.

In addition to the methods described above, the following methods (1) and (2) are also particularly effective as methods for incorporating spinel ferrite.

■ After synthesizing W-phase magnetoplumbite-type ferrite powder containing M-phase magnetoplumbite-type ferrite by firing, the flux is removed and this is heated to 0.5-2. By heating for a period of time, only the surface layer is transformed into spinel ferrite.

■ After synthesizing W-phase magnetoplumbite-type ferrite powder containing M-phase magnetoplumbite-type ferrite by firing, the flux is removed and this is dispersed in an alkaline solution, and a spinel ferrite composition such as ``pe2+Co'' is added to this. After adding the ionic solution, at 40-90℃
The mixture is heated and stirred for 6 hours, and after the reaction is washed, filtered, and dried, spinel ferrite is formed on the surface.

In the methods (2) and (2) above, spinel ferrite exists on the surface of hexagonal ferrite powder, and it is possible to contain a large amount of Fe"+ that improves electrical conductivity.
Particularly favorable results are obtained for reducing electrical resistance.

In addition, in the hexagonal ferrite powder synthesized by the above method, the content of spinel ferrite and M-phase magnetoplumbite type ferrite can be determined by an X-ray diffraction method.

To manufacture magnetic recording media using such plate-shaped hexagonal ferrite powder, it is sufficient to follow conventional methods. The magnetic paint may be prepared, coated on a non-magnetic substrate such as a polyester film by any coating means, and dried.

In addition, when a magnetic paint containing such a plate-like hexagonal ferrite powder is applied on a non-magnetic substrate and then subjected to magnetic field orientation by applying a magnetic field perpendicular to the magnetic layer surface, the direction of easy magnetization becomes easier. It is preferable to carry out such magnetic field orientation because it provides good vertical orientation and good surface smoothness of the magnetic layer.

As the binder resin used here, conventional general-purpose binder resins such as vinyl chloride vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, isocyanate compounds, and radiation-curable resins are widely used.

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

Note that various commonly used additives such as dispersants, lubricants, antistatic agents, etc. may be optionally added to the magnetic coating material.

〔Effect of the invention〕

As described above, in the present invention, by using a specific plate-shaped hexagonal ferrite powder, it is possible to provide a magnetic recording medium that has a large output and a low surface electrical resistance.

〔Example〕

Next, examples of the present invention will be described in more detail. In addition, in the following, parts mean parts by weight.

Example I BaCj! 2 H2Hz O29g FeC/! z ・6H20503g ZnCl2 2.7g in water 5Il
This was mixed with 2N NaOH aqueous solution 51 to obtain a precipitate. After washing this precipitate with water, 1.5 times the weight of the precipitate was mixed with NaCf, and then heated in air at 1,280° C. for 8 hours. Further increase the temperature to 1,05
After heating at 0°C for 4 hours under flowing N2 gas, the mixture was taken out to room temperature, and the flux was removed to obtain magnetic powder.

As a result of X-ray diffraction, this magnetic powder contains 10% by weight of M-phase magnetoplumbite ferrite and 15% by weight of spinel ferrite, and the remainder is plate-shaped hexagonal Ba ferrite consisting of W-phase magnetoplumbite ferrite. It was powder.

Using the thus obtained magnetic powder, a magnetic disk (floppy disk) was produced in the following manner.

Magnetic powder 1,000 parts α-AI
lzOx powder 100 parts Methyl isobutyl ketone 800 parts Toluene
After partially dispersing 800 parts of the above composition in a ball mill for 3 days, 80 parts of oleyl oleate and 25 parts of a trifunctional isocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) were added, and the mixture was further mixed and dispersed for 2 hours. A magnetic paint was prepared.

This magnetic paint was applied to both sides of a 75 μm thick polyester film and dried to form a magnetic layer.

Then, after smoothing, a floppy disk was punched out into a disk shape with a predetermined diameter. The thickness of the magnetic layer after the smoothing treatment was 3 μm.

Example 2 In the synthesis of magnetic powder in Example 1, 1,050°C
First, plate-shaped hexagonal Ba ferrite powder containing 15% by weight of M-phase magnetoplumbite ferrite and the remainder consisting of W-phase magnetoplumbite ferrite was synthesized without performing only the step of heating in N2 gas for 4 hours.

Next, 10 g of this ferrite powder was dispersed in 200 cc of a 2N NaOH aqueous solution, and Fe50. -7Hz03
．． An aqueous solution of 200.6 g of Og and COSO4.7H dissolved in 20 g of water was added, and after heating at 60°C for 6 hours, washing,
The powder was filtered and dried to obtain a magnetic powder consisting of plate-shaped hexagonal Ba ferrite on the surface of which 9% by weight of spinel ferrite was formed.

Using this magnetic powder, a floppy disk was produced in the same manner as in Example 1.

Example 3 Contains 15% by weight of M-phase magnetoplumbite ferrite synthesized as intermediate magnetic powder in Example 2, with the balance being W.
A plate-shaped hexagonal Ba ferrite powder consisting of phase magnetoplumbite type ferrite was heated at 280°C for 2 hours in an H2 gas stream containing water vapor, and then taken out to room temperature.
A magnetic powder consisting of plate-shaped hexagonal f3a ferrite which was transformed into spinel ferrite by a weight percent was obtained.

Using this magnetic powder, a floppy disk was produced in the same manner as in Example 1.

Comparative Example 1 In the synthesis of magnetic powder in Example 1, FeCl2.
The amount of 6H20 used was 432g, and ZnCj! 2
Change the usage amount to 27g and further increase the heating temperature to 1,380g.
A single-phase plate-shaped hexagonal Ba ferrite powder consisting of only W-phase magnetoplumbite ferrite was obtained in the same manner as in Example 1, except that the temperature was changed to .degree.

Using this magnetic powder, a floppy disk was produced in the same manner as in Example 1.

Comparative Example 2 As magnetic powder, M which is CoT ii converted by hydrothermal method
Phase magnetoplumbite type Ba ferrite powder was synthesized. Using this magnetic powder, a floppy disk was produced in the same manner as in Example 1.

The characteristics of each magnetic powder according to the above Examples and Comparative Examples and the characteristics of a floppy disk manufactured using the same are shown in Table 1 below.

From the results in Table 1 above, the magnetic powders according to Examples 1 to 3 of the present invention have high saturation magnetization, small particle diameter, and low electrical resistance, so floppy disks using the magnetic powders are C/ It is clear that the N ratio is high and the surface electrical resistance is low.

On the other hand, since the magnetic powders of Comparative Examples 1 and 2 both have high electrical resistance, floppy disks using them have high surface electrical resistance and large charging noise.

In addition, although a high saturation magnetization was obtained especially with the magnetic powder of Comparative Example 1, due to the large particle size, the surface roughness of the floppy disk using this was poor and the C/N ratio was extremely poor. .

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder is provided on a non-magnetic substrate, as the magnetic powder,
A magnetic recording medium characterized by using plate-shaped hexagonal ferrite powder containing 3 to 50% by weight each of spinel ferrite and M-phase magnetoplumbite ferrite, with the balance being W-phase magnetoplumbite ferrite.