JPH066491B2 - Method for producing magnetoplumbite-type fine ferrite powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a magnetoplumbite type ferrite particle powder, and more specifically, a large specific surface area of particles suitable as a magnetic material for a magnetic card. The present invention also relates to a method for producing a magnetoplumbite-type ferrite particle powder capable of obtaining a magnetoplumbite-type ferrite fine particle powder having a narrow particle size distribution.

[Prior art]

As is well known, in recent years, magnetic card application products such as various traffic tickets and credit cards have been remarkably spread, and demands for high recording density of magnetic card application products have been increasing more and more.

Conventionally, magnetoplumbite-type ferrite particle powder has been used as a magnetic material for magnetic cards. The magnetoplumbite type ferrite particle powder is said to be obtained by mixing and compounding at least a compound of at least one metal element selected from the group consisting of barium, strontium and calcium and iron oxide in a predetermined molar ratio, firing and crushing. It was obtained by the manufacturing method, and was used as a permanent magnet material such as a magnet material for exciting magnetic field of motors and generators in the past, but recently, grain size adjustment was performed focusing on its high coercive force. Above, it is used as a magnetic material for magnetic cards.

[Problems to be solved by the invention]

However, the magnetoplumbite-type ferrite particle powder obtained by the above-mentioned manufacturing method is fired at a high temperature of at least 900 ° C. or higher and usually 1100 ° C. or higher, and the particle size is adjusted by a pulverizer. In addition, since the particle powder has a BET specific surface area of at most 2-5 m ² / g and a wide particle size distribution, and the particles have distortion due to mechanical impact, the S / N ratio is poor as a magnetic recording material, and therefore the noise level is low. However, it is not suitable as a magnetic material for a magnetic card having a high recording density.

On the other hand, cobalt-coated iron oxide (Co-γ-Fe ₂ O ₃ ) and Fe ₃ O ₄ particle powders were used as magnetic materials to reduce the noise level.
-The way to get a do is also adopted. In this case, the coercive force is about 600 to 700 Oe at the most, and the magnetic card is easily affected by the external magnetic field, and there are many problems in using the magnetic card, which is a problem at present. This fact is
For example, in Japanese Patent Laid-Open No. 56-118304, "a magnetic card having a small coercive force ( _I Hc) such as the one currently used has a drawback that the original characteristics of the magnetic card are lost due to magnetic disturbance. It is also clear from the description "."

Therefore, a magnetic material having a high coercive force and a reduced noise level is required as a magnetic material suitable for high recording density for a magnetic card.

It is said that the decrease in noise level is affected by the particle size and particle size distribution of the magnetic material powder used, and in detail, the value of the specific surface area of the particle powder is often used as a method of expressing the particle size of the magnetic particle powder. Although used, it is said that the noise level due to the magnetic recording medium tends to decrease as the specific surface area of the magnetic particle powder increases.

This phenomenon is caused by, for example, IEICE Technical Research Report MR81-11.
It is shown in “Fig3” on page 27, 23-9. "Fig3" is Co
It is a figure which shows the relationship between the specific surface area of a particle | grain and the noise level in acicular needle-like crystal | crystallization maghemite particle powder, and a noise level falls linearly, so that the specific surface area of a particle becomes large.

The same applies to the magnetoplumbite type ferrite particle powder.

The present inventor has conducted extensive studies to make magnetoplumbite type ferrite particles that have been conventionally used as a magnetic material for a magnetic card a magnetic material suitable for a magnetic card having a high recording density.

The conventional magnetoplumbite ferrite powder is
As mentioned above, at least 900 ° C or higher, usually 110
Since it is fired at a high temperature of 0 ° C or higher, abnormal crystals occur during the firing process, grain growth of the particles themselves and strong sintering between particles occur, and coarse particles are generated, which results in a small specific surface area. However, even if a strong pulverization is performed in the subsequent step to make the particles finer, the powder becomes a particle powder having a wide particle size distribution.

However, when the firing temperature is lowered to 1000 ° C or lower, for example, to about 900 ° C, it is possible to prevent abnormal crystals from being generated during the firing process, grain growth of the grains themselves, and strong sintering between grains as much as possible. The particles are powders having a large specific surface area, but it is difficult to obtain magnetoplumbite type ferrite particles because the ferrite formation reaction is difficult.

[Means for solving problems]

The present inventor, when using the magnetoplumbite ferrite particle powder as a magnetic material for a magnetic card, has a larger specific surface area and a narrower particle size distribution in order to reduce the noise level. Over the years of exploring particle powders, many experimental studies have been conducted on the method of reducing the particle size of magnetoplumbite type ferrite particle powders and the effects of various additives. And as a result, barium,
Obtained by a wet synthesis method with a compound of at least one metal element selected from the group consisting of strontium and lead
Fe ₃ O ₄ particles, and any one iron raw material of γ-Fe ₂ O ₃ particles or α-Fe ₂ O ₃ particles obtained by heating and oxidizing the Fe ₃ O ₄ particles so as to have a predetermined molar ratio. Water glass at the same time when mixing and blending
If water glass and Na ₂ CO ₃ , or water glass and Na ₂ CO ₃ and BaCl ₂ or SrCl ₂ water glass alone or any one of a mixture of the above water glasses is added, the firing temperature is 900 ° C or less. Even if the temperature is lowered to the temperature, the ferrite formation reaction occurs, and the grain growth of the particles themselves and the strong sintering between the particles are suppressed in the firing process, so the obtained particle powder has a large specific surface area and a narrow particle size distribution. It was confirmed that the present invention was a magnetoplumbite type ferrite particle powder, and the present invention was achieved.

That is, the present invention provides a molar ratio Fe ₂ O ₃ / MO (M (M) which comprises a step of firing and pulverizing a mixture of iron oxide and a compound of at least one metal element selected from the group consisting of barium, strontium and calcium. : Ba, Sr, Ca, or two or more of them) = at least one metal selected from the group consisting of barium, strontium, and calcium in the method for producing a magnetoplumbite-type ferrite particle powder having a composition of 5.6 to 6.1. Fe ₃ O ₄ particles obtained by a wet synthesis method with a compound of an element, and γ-Fe ₂ obtained by heating and oxidizing the Fe ₃ O ₄ particles
An iron raw material of either O ₃ particles or α-Fe ₂ O ₃ particles,
After mixing in the presence of either water glass, water glass and Na ₂ CO ₃ , or water glass and Na ₂ CO ₃ and BaCl ₂ or SrCl ₂ , in the temperature range of 750-900 ° C. A method for producing a magnetoplumbite-type ferrite fine particle powder, which is characterized by firing.

[Work]

 Next, the present invention will be described in detail.

First, the composition of the magnetoplumbite type ferrite particle powder of the present invention will be explained. Fe ₂ O ₃ / Mo (M: Ba, S
The molar ratio of one or more of r and Ca) must be in the range of 5.6 to 6.1. Outside this range, the magnetic properties, especially the coercive force ₁ Hc, are extremely low, which is not desirable for practical use.

The iron raw material in the present invention includes a wet synthesis method, that is, F
e ²⁺ , or Fe ₃ O ₄ particles obtained by synthesizing from an aqueous solution containing Fe ²⁺ and Fe ³⁺ , or γ-Fe ₂ O ₃ particles produced by heating and oxidizing the Fe ₃ O ₄ particles, α -Fe ₂ O ₃ particles having a BET specific surface area of 5 to 15 m ² / g can be used.

A typical method for producing Fe ₃ O ₄ particles is Fe (OH) ₂ obtained by adding an equivalent amount or more of a basic substance (alkali) to an acid radical in an aqueous ferrous salt solution such as ferrous sulfate. PH 1 including colloid
An aqueous solution of 0 or more is kept in a temperature range of 60 to 100 ° C., a black precipitate is formed by carrying out an oxidation reaction while aerating an oxidizing gas and stirring, and then, a black precipitate is formed, which is washed with water, dried, and Fe ₃ A manufacturing method for obtaining O ₄ particles. There is also a method by a coprecipitation reaction of ferrous iron Fe ²⁺ and ferric ion Fe ³⁺ . This coprecipitation reaction method uses a ferrous sulfate aqueous solution such as ferrous sulfate and a ferric salt aqueous solution such as ferric sulfate to prepare a mixed aqueous solution in which Fe ²⁺ : Fe ³⁺ is 1: 2. There is a method of synthesizing Fe ₃ O ₄ particles by adjusting, adding an alkaline aqueous solution such as NaOH to the mixed aqueous solution in an amount of 1 equivalent or more, and heating at a temperature of 50 to 100 ° C.

As a raw material for barium, strontium and calcium, BaCO ₃ , SrCO ₃ , CaCO _3, etc. can be used, but when heated, Ba
Ba compounds, Sr compounds, and Ca compounds that become O, SrO, and CaO can also be used.

Next, the additives in the present invention will be described.

For the water glass in the present invention, a water-soluble silicate such as sodium silicate or potassium silicate can be used. Further, the addition amount (amount to be present) is effective in the range of 0.05 to 1.45% by weight in terms of SiO _{2 with} respect to iron oxide (in terms of Fe ₂ O ₃ ). 1.
Addition of an amount exceeding 45% by weight lowers the magnetization value of the product ferrite, which is not preferable as a magnetic material. Also 0.05
If it is less than wt%, the desired effect of the present invention cannot be obtained.

The amount of Na ₂ Co ₃ added in the present invention is iron oxide (Fe ₂ O 3
It is effective between 0.35 to 12.0 wt% relative to ₃ basis).
If it is less than 0.35% by weight, the effect of addition is small. 12.0% by weight
When it exceeds the above range, it is possible to obtain ferrite particle powder having desired fine particles and a narrow particle size distribution, but if excessively added, the specific surface area of the ferrite particles tends to be small, which is not desirable.

The addition amount of BaCl ₂ or SrCl _{2 in} the present invention is effective in the range of 1.5 to 7.0% by weight with respect to iron oxide (calculated as Fe ₂ O ₃ ). If it is less than 1.5% by weight, its effect is small, while if it exceeds 7.0% by weight, the specific surface area of the ferrite particles tends to be small, and it is not economical.
Considering the particle size and particle size distribution of the target ferrite particles, 1.5 to 7.0% by weight is preferable.

Incidentally, it is appropriate to add each additive in the present invention immediately before the firing step. That is, in each of the raw material blending step, the firing step, and the crushing step, it can be added at the time of raw material blending, which is the step immediately before the firing step.

The firing temperature range in the present invention may be between 750 and 900 ° C. If the temperature is lower than 750 ° C, it is insufficient to carry out the ferrite formation reaction, and if the temperature is higher than 900 ° C, due to the grain growth of the particles themselves during the firing process of the ferrite particles and strong sintering between the particles. However, it is not preferable because the subsequent pulverization becomes difficult.

In the case of the above-mentioned firing temperature, the pulverization after firing can be carried out under a relatively mild condition by using an ordinary pulverizer such as an atomizer or an attritor. Is not necessary.

〔Example〕

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

The specific surface area of the particles in Examples and Comparative Examples was measured by the BET method, and X-rays were used for the structural analysis of the products. For magnetic measurement, a DC BH tracer (Type 3257, Yokogawa Electric Co., Ltd.) was used, and the magnetic field was measured at 10 kOe.

Example 1 Fe ₃ O ₄ particle powder (BET specific surface area 8.7 m ² / g) obtained by a wet synthesis method such that the molar ratio of Fe ₂ O ₃ / BaO was 5.85 760
30 g of water glass (corresponding to 0.76% by weight in terms of SiO _{2 with} respect to Fe ₂ O ₃ ) when g and 239 g of barium carbonate are mixed
Was added and mixed well, the mixture was calcined at 830 g for 3 hours, and then the calcined product was pulverized with an atomizer. The obtained particles were magnetoplumbite-type barium ferrite particles as a result of X-ray analysis.
Was Fe ₂ O ₃ /BaO=5.86.

The specific surface area of the obtained magnetoplumbite-type barium ferrite fine particle powder was measured by the BET method.
It was m ² / g, and as a result of electron microscope observation, it was found to have a narrow particle size distribution width. As a result of measuring the magnetic properties of this material, the coercive force was _I Hc: 4360 Oe.

Examples 2 to 12 Same as Example 1 except that the type and amount of iron raw material, the type and amount of Ba or Sr carbonate or oxide, the salt and amount of additives, and the firing temperature were variously changed. As a result, a magnetoplumbite-type ferrite fine particle powder was obtained.

The magnetoplumbite-type ferrite fine particle powders obtained in Examples 2 to 12 were all observed to have a narrow particle size distribution width as a result of electron microscopic observation. Table 1 shows the specific surface area and magnetic characteristics of the obtained magnetoplumbite-type ferrite fine particle powder by the BET method.

Comparative Example 1 Fe ₃ O ₄ particle powder (BET specific surface area 8.7 m ² / g) obtained by a wet synthesis method so that the molar ratio of Fe ₂ O ₃ / BaO was 5.85.
760 g and 239 g of barium carbonate were thoroughly mixed, and the mixture was
Particles obtained by firing at 1200 ° C. for 3 hours and then pulverizing the fired product for 60 minutes with a vibrating ball mill were magnetoplumbite type barium ferrite particles as a result of X-ray analysis.

The specific surface area of this particle powder measured by the BET method was 6.5 m ² / g. As a result of electron microscope observation, it was found that the particle size distribution range was wide and coarse particles were mixed. In addition, as a result of measuring the magnetic characteristics of this product, the coercive force _I Hc: 30
It was 00 Oe.

[Effect] According to the method for producing a magnetoplumbite-type ferrite fine particle powder according to the present invention, as shown in the above Examples, the magnetoplumbite-type ferrite fine particle powder has a large specific surface area of particles and a narrow particle size distribution. Therefore, it can be suitably used as a magnetic material for a magnetic card having the highest recording density currently required.

Claims (9)

[Claims] 1. A molar ratio of Fe ₂ O ₃ / MO (M: M: M) comprising a step of firing and pulverizing a mixture of iron oxide and a compound of at least one metal element selected from the group consisting of barium, strontium and calcium. (1 or more of Ba, Sr, and Ca) = at least one metal element selected from the group consisting of barium, strontium, and calcium in the method for producing a magnetoplumbite-type ferrite particle powder having a composition of 5.6 to 6.1 Of Fe and Fe obtained by wet synthesis
₃ O ₄ particles, and any one iron raw material of γ-Fe ₂ O ₃ particles or α-Fe ₂ O ₃ particles obtained by heating and oxidizing the Fe ₃ O ₄ particles are mixed in the presence of water glass. And then firing in a temperature range of 750 to 900 ℃, a method for producing magnetoplumbite type ferrite fine particles. 2. The amount of water glass present is an iron raw material (calculated as Fe ₂ O ₃ ).
The method for producing a magnetoplumbite-type ferrite fine particle powder according to claim 1, wherein the amount is 0.05 to 1.45% by weight in terms of SiO ₂ . 3. A molar ratio of Fe ₂ O ₃ / MO (M: M: M) which comprises a step of firing and pulverizing a mixture of iron oxide and a compound of at least one metal element selected from the group consisting of barium, strontium and calcium. (1 or more of Ba, Sr and Ca) = 5.6 to 6.1, in the method for producing a magnetoplumbite ferrite particle powder, at least one metal element selected from the group consisting of barium, strontium and calcium Of Fe and Fe obtained by wet synthesis
₃ O ₄ particles, the Fe ₃ O ₄ and any one of the iron raw material to heating oxidation-obtained γ-Fe ₂ O ₃ particles or α-Fe ₂ O ₃ particles particles, water glass and Na ₂ CO ₃ A method for producing a magnetoplumbite-type ferrite fine particle powder, which comprises firing in the temperature range of 750 to 900 ° C. after mixing in the presence of. 4. The amount of water glass present is an iron raw material (calculated as Fe ₂ O ₃ ).
The method for producing a magnetoplumbite-type ferrite fine particle powder according to claim 3, wherein the amount is 0.05 to 1.45% by weight in terms of SiO ₂ . 5. The magnetoplumbite-type ferrite fine particles according to claim 3 or 4, wherein the amount of Na ₂ CO ₃ present is 0.35 to 12.0% by weight with respect to the iron raw material (calculated as Fe ₂ O ₃ ). Powder manufacturing method. 6. A molar ratio of Fe ₂ O ₃ / MO (M: M: M) comprising a step of firing and pulverizing a mixture of iron oxide and a compound of at least one metal element selected from the group consisting of barium, strontium and calcium. (1 or more of Ba, Sr, and Ca) = at least one metal element selected from the group consisting of barium, strontium, and calcium in the method for producing a magnetoplumbite-type ferrite particle powder having a composition of 5.6 to 6.1 Of Fe and Fe obtained by wet synthesis
₃ O ₄ particles, the Fe ₃ O ₄ and any one of the iron raw material to heating oxidation-obtained γ-Fe ₂ O ₃ particles or α-Fe ₂ O ₃ particles particles, water glass and Na ₂ CO ₃ And BaCl ₂ or SrCl ₂ in the presence of
A method for producing a magnetoplumbite-type ferrite fine particle powder, which comprises firing in a temperature range of 750 to 900 ° C. 7. The magnetoplumbite type ferrite fine particle powder according to claim 6, wherein the amount of water glass present is 0.05 to 1.45% by weight in terms of SiO _{2 with} respect to the iron raw material (in terms of Fe ₂ O ₃ ). Manufacturing method. 8. The magnetoplumbite-type ferrite fine particles according to claim 6 or 7, wherein the amount of Na ₂ CO ₃ present is 0.35 to 12.0% by weight based on the iron raw material (calculated as Fe ₂ O ₃ ). Powder manufacturing method. 9. The amount of BaCl ₂ or SrCl ₂ present in the iron raw material (Fe ₂ O ₃
The method for producing a magnetoplumbite type ferrite fine particle powder according to any one of claims 6 to 8, wherein the amount is 1.5 to 7.0% by weight based on the calculated value.