JPS5847846B2 - Manufacturing method of hexagonal plate-shaped magnetoplumbite type ferrite particle powder for perpendicular magnetic recording - Google Patents

Description

Detailed Description of the Invention The present invention provides hexagonal plate-shaped magnetoplumbite-type Ba, Sr or pb ferrite particles or Ba, Sr
or composite ferrite particle powder consisting of two or more types selected from Pb (MO-nFe203n = 6, however, M
is Ba, Sr, Pb, or two or more selected from these)
The purpose of this invention is to easily and economically produce ferrite particles suitable for perpendicular magnetic recording.

More specifically, Ba ferrite particle powder, Sr.
The object of the present invention is to obtain a ferrite particle powder, a Pb'7 ferrite particle powder, or a composite ferrite particle powder containing two or more selected from Ba, Sr, or Pb as a composition.

As is well known, the conventional magnetic recording method is
A method is adopted in which recording is performed by magnetizing in a direction parallel to the base film of a magnetic tape (hereinafter referred to as the conventional method). Therefore, the magnetic particles used as the raw material for magnetic recording are needles with an axis of easy magnetization in the long axis direction. Magnetic iron oxide particles, acicular iron magnetic particles, or acicular alloy magnetic particles containing acicular maghemite particles, acicular magnetite particles, and different metals have been used.

However, when performing high-density recording using this conventional method, there is a limit to high-density recording because the reduction in magnetization due to the demagnetizing field becomes large.

In recent years, in response to the demand for high-density recording, perpendicular magnetic recording systems that are capable of recording at several times higher density than conventional systems have been proposed and are being put into practical use.

Here, the perpendicular magnetic recording method is a method in which recording is performed by magnetizing in the direction perpendicular to the base film of the fusion tape, and the higher the density, the smaller the demagnetization effect, and Since an attractive force acts between the particles, they have the property of mutually strengthening their magnetization, so it is possible to achieve a significant increase in recording density.

A magnetic recording medium used in the perpendicular magnetic recording system must have an axis of easy magnetization in a direction perpendicular to the base film of the magnetic tape.

In addition, rJAs journal 1 February issue (''
80), page 13, ``In order to be a perpendicularly magnetized film, Ku>2πMs2 or Hk>4π
Ms (Ku is the crystal anisotropy constant, Ms is the saturation magnetization, and Hk is the anisotropy magnetic field).

A cobalt-chromium thin film produced by sputtering has been announced as a magnetic recording medium for perpendicular magnetic recording.

Regarding the cobalt-to-chromium thin film, the above-mentioned rJAs
Journal 1, February issue ('80), p.
This alone does not result in perpendicular magnetization.

Therefore, Cr is added to reduce the saturation magnetization while maintaining a large magnetocrystalline anisotropy, and the JKu>2π
We make sure that the relationship Ms2 or Hk>4πMs holds true.

”. However, the cobalt-to-chromium thin film produced by the sputtering method requires special manufacturing equipment and the raw materials are expensive, so it cannot be said to be industrially or economically viable.

In recent years, magnetoplumbite-type ferrite particles having a hexagonal plate shape have been attracting attention as a raw material magnetic powder for perpendicular magnetic recording.

Now, regarding the case of a recording medium in which hexagonal plate-shaped Ba ferrite particles are used and coated on a base film with the plate-like surfaces arranged parallel to the film surface, the Ba ferrite has a Ku of 3.3 x 10'. erg/cc, M
Since s: 380 gauss, the above-mentioned relational expression Ku>2πMs2, which is a condition for a perpendicular magnetic recording medium, is satisfied.

Furthermore, since the axis of easy magnetization of the hexagonal plate-shaped Ba ferrite particles is perpendicular to the plate-like surface of the particles, it is possible to provide uniaxial anisotropy in the direction perpendicular to the coating film surface.

That is, Ba ferrite particles exhibiting a hexagonal plate shape are suitable as a raw material for perpendicular magnetic recording media.

In addition, not only magnetoplumbite-type Ba ferrite particles exhibiting a hexagonal plate shape, but also Sr ferrite particles, Pb ferrite particles, and composite ferrite particles consisting of two or more selected from Ba, Sr, and Pb are also suitable for perpendicular magnetic recording media. It is suitable as a raw material for industrial use.

On the other hand, magnetoplumbite-type ferrite particle powder exhibiting a hexagonal plate shape has been conventionally used as a raw material for sintered magnets and rubber and plastic magnets.

The characteristics of hexagonal plate-shaped magnetoplumbite-type ferrite particles, which are generally used as raw materials for sintered magnets, rubber, and plastic magnets, are that the particle size is generally several μm, especially 1 μm.
μm, and the coercive force IHc should be as high as possible (
In general, there has been a demand for a material with a diameter of 30,000e or higher) and a material with an energy product (BH) max as large as possible.

On the other hand, the characteristics of magnetoplumbite-type ferrite particle powder exhibiting a hexagonal plate shape used as raw material magnetic powder for perpendicular magnetic recording are as follows: the particle size is as fine as possible, especially around 0.01-0.5 μm. Yes, and coercive force HH
A material with a c of about 20,000e or less is required.

First, regarding particle size, for example, “Science 10
Vol. 1, No. 1 (1980), p. 52, ``In perpendicular recording, the minimum bit length is twice the domain wall (if the material has a domain wall) or the size of a crystal grain...
... Considering the recording material, 500 angstroms (0
．． 05 μm).

” in Japanese Patent Application Laid-open No. 55-86103, “...
... If it is less than 0.01 μm, it will not exhibit the required ferromagnetism, and if it exceeds 0.3 μm, perpendicular magnetization recording cannot be carried out advantageously.

” and “
Powder particle size is 0.01 to 0.5, ideal for magnetic recording powder
As is clear from the description "μ......", it must be as fine as possible. oi~0.5μm
It is said that something of the order of magnitude is preferable.

Next, regarding coercive force, the above-mentioned Japanese Patent Publication No. 55-861
No. 03, ``... High-density recording by perpendicular magnetization can be performed satisfactorily due to the fact that agglomeration is prevented by having a coercive force (Hc) of about 200 to 2000 oersteds.

As is clear from the statement "...", 20
0 0 0eJJ or lower is required.

Furthermore, the characteristics required of the hexagonal plate-shaped magnetoplumbite-type ferrite particle powder used as raw material magnetic powder for perpendicular magnetic recording are that the chemical composition is homogeneous and that it has a high saturation magnetization σS. This is required.

Regarding the chemical precepts, in the above-mentioned ``Science Vol. This means that it can be shortened to the size of the crystal grains of the material or the thickness of the domain wall inherent to the magnetic material.

As is clear from the description, since the recording unit is reduced to the size of a crystal grain, the chemical composition of each particle must be as homogeneous as possible.

Regarding the saturation magnetization σS of the raw material magnetic particles, σS is related to Ms of the recording medium, and as mentioned above, magnetoplumbite-type ferrite particles exhibiting a hexagonal plate shape satisfy the relational expression Ku>2πMs2. It is a thing,
Within this range, raw material magnetic particles for magnetic recording are required to have a large saturation magnetization σS in order to improve high-density recording, especially high-output characteristics.

By the way, as a manufacturing method of magnetoplumbite type ferrite particle powder for magnetic recording, for example, Japanese Patent Laid-Open No. 50-3
The methods described in JP-A No. 249'8 and JP-A-55-86103 mentioned above are known.

A mixture of iron oxide or an iron compound that becomes iron oxide upon heating, any one of Ba, Sr, or Pb oxides, or two or more selected from these, and a flux described in JP-A-50-32498. The hexagonal plate-shaped magnetoplumbite-type ferrite particle powder obtained by heating and burning is described as having "at least 90 crystals with a maximum dimension of 5 μm..." As described above, the particle size is extremely large, and it cannot be said that it satisfies the requirements for high-density recording.

Furthermore, the obtained powder particles do not have a homogeneous ferrite composition, but contain a large number of non-magnetic α-Fe203 particles.

For example, in "Example 8", 70% α-Fe 20s particles are mixed, and as a result, the saturation magnetization is 30.
It is extremely low at 1 emu/g.

The method described in the above-mentioned Japanese Patent Application Laid-Open No. 55-86103 is B
In a method for obtaining magnetoplumbite type ferrite particle powder by heat-treating a coprecipitate obtained by adding an alkaline aqueous solution to an aqueous solution of one or more of a, Sr, and Pb salts and an iron salt, In, Zn -Ge Zn-Nb
, Zn-V, Co-Ti, and Co-Ge, the average particle size is 0.01-0.3 μm and the coercive force IHc is 200-20.
000e magnetoplumbite round light particles, but it is difficult to obtain hexagonal plate-shaped ferrite particles with this method, and the addition of impurities lowers the saturation magnetization. According to Example 1, 50
It is about emu/g.

In view of the above, the present inventor has developed a hexagonal plate-shaped magnetoplan with a homogeneous structure, a grain size of 0.01 to 0.5 μm, a large saturation magnetization, and a coercive force IHc of 20000e or less. As a result of various studies to obtain bite-type ferrite particle powder, the present invention was completed.

That is, the present invention uses iron oxide particles or an iron compound that becomes iron oxide particles by heating and Ba, Sr as a starting material composition.
Alternatively, any one of Pb carbonates or oxides, or a mixture of two or more selected from these, is dispersed and mixed in an aqueous solution of a flux, and then 0% is added to the starting material composition.
．． The particles are granulated to have an average diameter of l1IIIl to an average particle size of 15, and after drying, the dried product is adjusted to contain a fluxing agent of 1 to 50% by weight. By heating and burning at a temperature above, fine and homogeneous hexagonal plate-shaped magnetoplumbite-type Ba, Sr or Pb ferrite or composite ferrite particles consisting of two or more selected from Ba, Sr and Pb are obtained. This is a method for producing hexagonal plate-shaped magnetoplumbite-type ferrite particle powder for perpendicular magnetic recording.

The principles and effects of the present invention will be explained as follows.

First, various findings on which the present invention is based will be described.

Conventionally, as a method for obtaining hexagonal plate-shaped magnetoplumbite-type ferrite particles, iron oxide particles or an iron compound that becomes iron oxide particles by heating and any one of Ba, Sr, or Pb carbonate or oxide have been used. Alternatively, a method is known in which a flux is added to a mixture of two or more selected from these and the mixture is heated and burned.

In order to obtain magnetoplumbite-type ferrite particle powder exhibiting a hexagonal plate shape that is optimal as a raw material magnetic powder for perpendicular magnetic recording in the above method, the present inventor has repeatedly investigated the chemical composition, particle size, saturation magnetization, and coercive force. , we obtained the following findings.

That is, in order to obtain a homogeneous chemical composition, it is necessary that the ferrite-forming reaction occur homogeneously, and in order to cause the ferrite-forming reaction to occur homogeneously, the raw material composition and the flux must be intimately mixed. In addition, it is necessary to control the ferritization reaction during firing.

In order to control the particle size, it is necessary to control the amount of flux mixed and the firing temperature, and as the amount of flux mixed increases, the ferritization reaction proceeds rapidly and the particle size tends to increase.

In addition, when the burning temperature increases, the ferrite reaction rapidly progresses, and coarse particles tend to grow and become irregular in shape.

In order to obtain a large saturation magnetization, ferrite formation must occur completely, and the presence of impurities such as unreacted substances causes a decrease in saturation magnetization.

The coercive force of a particle is deeply related to the particle morphology (size of the plate-like surface, plate-like thickness, plate-like ratio); the thinner the plate-like thickness, the smaller the coercive force, and the thicker the plate-like thickness, the smaller the coercive force. thing.

Control of particle morphology can be achieved by controlling the amount of flux mixed and the burning temperature.

The larger the amount of flux mixed and the higher the firing temperature, the faster the ferritization reaction rate, the coarser the particle size, and generally the thicker the particles tend to be.

Based on the above-mentioned findings, the inventors of the present invention have further investigated the method of accurately controlling the amount of flux mixed into the starting material composition in order to homogeneously cause the ferrite-forming reaction. The composition is dispersed and mixed in an aqueous solution of a flux, and then 0.1 to
Each F is adjusted to contain a flux of 50% by weight, and then granulated into granules with an average particle size of 1 to 15% by weight. After drying, the dried product is mixed with a flux. When heating and burning at a reduction degree higher than the eutectic point of As a result,
Coercive force IHc 200 having a homogeneous structure, a particle size of 0601 to 0.5 μm, and a large saturation magnetization
It was found that hexagonal plate-like magnetoplumbite-type ferrite particle powder of 00e or less can be obtained.

The method of the present invention will be described in more detail below.

First, in the method of the present invention, it is important to use an aqueous solution of a flux.

In order to cause the ferritization reaction to occur homogeneously, it is important to intimately mix the starting raw materials and the flux. To do this, the starting materials are slurried using an aqueous solution of the flux. It is extremely effective to mix the mixture in the same state.

If the starting material composition and the flux are mixed as they are, the mixture will be non-uniform because it is a mixture of solids.

Furthermore, when an aqueous solution of a flux is used, the amount of flux mixed into the starting material composition can be controlled with high precision.

Next, it is important to adjust each starting material composition so that it contains a flux of 0.1 to 50% by weight.

In this case, as mentioned above, since an aqueous solution of the flux is used, the amount of the flux to be mixed can be adjusted by adjusting the water content in the paste when separating the mixture from the mixed slurry. It is possible to control the amount with high precision.

Furthermore, in the present invention, an average particle size of 1 to 15
Since the ferrite is granulated to a certain degree of granulation, dried, and then heated and calcined, a homogeneous ferrite-forming reaction can be achieved.

Homogenization and completion of the ferrite-forming reaction are related to the size of the granules, and if the granules are too large, homogenization and completeness of the ferrite-forming reaction cannot be expected.

Conventionally, in the method of producing hexagonal plate-shaped magnetoplumbite type ferrite particle powder using a flux, dry mixing or a method using a non-aqueous solution was generally adopted for mixing the starting material composition and the flux. .

This can be explained, for example, in the above-mentioned Japanese Patent Application Laid-Open No. 50-32498, which states, ``Dry mixing . . . and placing it in an alumina crucible for firing cycle.

It is clear from the description that "...in other mixing steps...the entire mixture is dispersed in alcohol or xylene to form a slurry...".

In this case, the flux, for example BaCl2 used in "Example 2", is insoluble in alcohol or xylene, resulting in a mixture of solids and solids, resulting in a non-homogeneous mixture, and as a result, ferrite Homogenization and completion of the chemical reaction are difficult to occur, and the product contains a large amount of α-Fe203 particles.

In addition, in the method described in JP-A-50-121200, "...680 g of strontium chloride hexahydrate
Add and mix a solution dissolved in warm water, granulate to a size of 20 mm, and dry.

``...'' method is being adopted.

However, when using this method, it is the same as the method of granulating powder while adding water and mixing, which is the usual method of granulating powder. Since the method uses a liquid dissolved in the granules, it is impossible to adjust the mixing amount of the flux and the granulation size, and even worse, it is not possible to obtain granules made of a homogeneous composition as in the present invention.

Next, specific conditions for carrying out the method of the present invention will be described.

The starting material combination in the present invention is iron oxide particles or an iron compound that becomes iron oxide particles by heating, and one or more carbonates or oxides of Ba, Sr, or Pb, or two or more selected from these. A mixture of can be used.

Here, the iron oxide particles include hematite particles, magnetite particles, maghemite particles, and the like.

Iron compounds that become iron oxide particles when heated are α-, β-,
r - Refers to hydrated ferric oxide particles.

As the fluxing agent in the present invention, sulfates of Na, K1 or Li, chlorides, bromides, iodides or fluorides of Na, K, Li or Ca, and Ba
Alternatively, one or more selected from Sr chloride or fluoride or pb bromide, iodide, or oxide can be used, but from an industrial standpoint, Na2S
Sulfates and chlorides such as O4, NaC#, BaCA2, or SrCl2 are preferred.

When the flux in the present invention is used, the flux is dissolved in water or warm water and used as an aqueous solution of the flux.

If the flux is used in a solid state, it cannot be intimately mixed with the starting material composition, and therefore the ferritization reaction cannot be homogenized, making it difficult to control the mixing amount of the flux with high precision. Can not do it.

In the present invention, the mixing amount of the fluxing agent is o. i~50 weight section.

If the weight ratio is less than 0.1, particles having the desired particle form cannot be obtained.

Even when the weight ratio is 50% or more, the preferable ferrite-forming reaction proceeds and raw ferrite particles having the desired particle size and coercive force can be obtained, but excessive mixing will not affect the amount of evaporation of the flux. It is not economical because it only increases the amount of water.

When considering the particle size and coercive force of the desired product ferrite particles, a weight ratio of 1 to 30 is preferable.

In the present invention, granulation is carried out with an average particle diameter of IM to an average particle diameter of 15
Make a granulated product of about a size.

If it is less than 11g1 and more than 15M, the ferrite-forming reaction will not occur homogeneously, making it impossible to obtain raw ferrite particles with a uniform composition.

When considering productivity, the average particle size is 3M to 10W.
l1. It is particularly preferable that

The firing temperature in the present invention is above the eutectic point of the flux,
The upper limit is preferably 1400°C or less.

If the temperature is below the eutectic point of the flux, the object of the present invention cannot be fully achieved.

If the temperature is 1,400° C. or higher, the particle growth of the product ferrite particles is rapid, making it difficult to adjust the shape and particle size of the particles, and also being unfavorable in terms of equipment and environment.

The heat-burning product obtained by the present invention is in the form of a lump, but if it is washed with water or an acid aqueous solution in a conventional manner and then dried, each particle becomes a hexagonal plate-shaped Ba, Sr or Pb ferrite particle. , or a composite ferrite particle powder consisting of two or more types selected from these.

The present invention configured as described above has the following effects.

That is, according to the present invention, the group precepts are homogeneous and have a particle size of 0.01 to 0.01.
Ba, Sr or Pb having a hexagonal plate shape with a diameter of 0.5 μm, a large saturation magnetization, a coercive force IHc of 20000e or less, and an axis of easy magnetization perpendicular to the plate surface of the particle.
Since ferrite particles or a composite ferrite particle powder consisting of two or more types selected from Ba, Sr, and Pb can be obtained reliably, it is possible to provide an inexpensive raw material magnetic powder for perpendicular magnetic recording that is excellent in mass production.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Incidentally, the particle shape and particle size of the examples were observed and measured using a scanning electron microscope.

Example 1 α-Fe203 5 2 5 f! and BaCOa 1
20 g of BaCl2.2H20768 in advance
g was dispersed in an aqueous solution of a flux prepared by dissolving 1000 cc of water, and thoroughly mixed.

The amount of flux mixed is 23.8% by weight based on the starting material mixture.
The above mixed slurry was individually adjusted into a 20 wt % water-containing cake using a filter press, and then granulated to an average particle size of 3 mm and dried.

100.9 liters of the dried granulated material was calcined in a molten alumina crucible at 980° C. for 30 minutes in an electric furnace.

Next, the heated and calcined product was washed with water in a conventional manner to remove the flux, and then filtered and dried to obtain Ba ferrite particle powder.

As a result of scanning electron microscopy observation, the obtained Ba ferrite particles were found to be hexagonal plate-like particles, and the particle size (plate-like surface) was 0.
It had a thickness of 30 μm and a thickness of 0.025 μm.

A scanning electron micrograph (xsoooo) is shown in FIG.

Further, the magnetic properties were a coercive force IHc of 11800e and a saturation magnetization of 62.3 emu/g.

It is clear from the saturation magnetization value that the composition is homogeneous, and furthermore, as a result of X-ray diffraction, it was found to be 1001% Ba ferrite particles.

Examples 2 to 19 Type and amount of Sr or Ba carbonate or oxide,
Ba ferrite particle powder, Sr ferrite particle powder or Ba-Sr was prepared in the same manner as in Example 1 except that the type and amount of flux, the mixed amount of flux, granulation degree, heating and burning temperature and time were varied. A composite ferrite particle powder was obtained.

Table 1 shows the main manufacturing conditions of Examples 2 to 19 and the properties of the obtained ferrite particles.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph (X80,000) of the Ba ferrite particle powder obtained in Example 1.

Claims (1)

[Claims] 1 Starting material composition: iron oxide particles or an iron compound that becomes iron oxide particles upon heating, and Ba, Sr, or Pb.
Any one type of carbonate or oxide, or a mixture of two or more selected from these, is dispersed and mixed in an aqueous solution of a flux, and then o. i~50
Adjustments are made for each furnace to contain a flux in a range of weights, and further,
After granulating to an average particle size of 1wIl to 15wIl and drying, the dried product is heated and calcined at a temperature higher than the eutectic point of the flux to produce a fine and homogeneous hexagonal plate-like magnetoplumbite type. Ba, Sr or Pb ferrite or Ba,
A method for producing hexagonal plate-shaped magnetoplumbite type ferrite particle powder for perpendicular magnetic recording, characterized by obtaining composite ferrite particles consisting of two or more types selected from Sr and Pb. 2. The method for producing a hexagonal plate-shaped magnetoplumbite type ferrite particle powder for perpendicular magnetic recording according to claim 1, wherein the mixing amount of the flux is 1 to 30% by weight. 3 Granulation particle size is average particle size 37IgIl ~ average particle size i0M
A method for producing a hexagonal plate-shaped magnetoplumbite type ferrite particle powder for perpendicular magnetic recording according to claim 1.