JPH066490B2 - 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 a production method in which at least one metal element compound selected from the group consisting of barium, strontium and calcium is mixed and blended with iron oxide in a predetermined molar ratio, followed by firing and crushing. Previously, it was mainly used as a permanent magnet material such as an exciting magnetic field magnet material for motors, generators, etc., but recently, after focusing on its high coercive force, particle size adjustment was performed. , 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, a method of using a cobalt-adhered iron oxide (Co-γ-Fe ₂ O ₃ ) or Fe ₃ O ₄ particle powder as a magnetic material to obtain a magnetic card with a reduced noise level 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 due to, for example, in Japanese Patent Laid-Open No. 56-118304, "In a magnetic card having a small coercive force ( _I Hc) such as the one currently used, the original characteristics of the magnetic card are lost due to magnetic disturbance. It is also clear from the statement "There is a drawback."

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, Technical Report of IEICE MR 81-11.
It is shown in “Fig 3” on page 27, 23-9. "Fig 3" is
It is a figure which shows the relationship between the specific surface area of particles in Co-adhered acicular maghemite particle powder, and a noise level, and a noise level linearly falls, 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,
Compounds of at least one metal element selected from the group consisting of strontium and calcium and acicular α-FeOOH particles, obtained by heating dehydration, reduction or reduction and reoxidation using the acicular α-FeOOH particles as a starting material α-Fe ₂ O ₃ particles, Fe
Water glass, water glass and Na ₂ CO ₃ , or water glass at the same time when mixing and mixing ₃ O ₄ particles or one iron raw material of γ-Fe ₂ O ₃ particles so as to have a predetermined molar ratio And Na ₂ CO ₃
And BaCl ₂ or SrCl ₂ water glass alone or a mixture of the above water glasses, the firing temperature can be increased.
Even if the temperature is lowered to 900 ° C or lower, the ferrite formation reaction occurs, grain growth of the particles themselves and strong sintering between particles are suppressed in the firing process, so the obtained particle powder has a large and narrow specific surface area. It was confirmed that the powder was a magnetoplumbite-type ferrite particle powder having a particle size distribution, 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. Compounds of elements and acicular α-FeOOH particles, heating dehydration of the acicular α-FeOOH particles as a starting material, α-Fe ₂ O ₃ particles obtained by reduction or reduction and reoxidation, Fe ₃ O ₄ particles,
Alternatively, water glass, water glass and Na ₂ CO ₃ , or water glass, Na ₂ CO ₃ and Ba may be used together with any one iron raw material of γ-Fe ₂ O ₃ particles.
After mixing in the presence of either Cl ₂ or SrCl ₂ , 75
A method for producing a magnetoplumbite-type ferrite fine particle powder, which is characterized by firing in a temperature range of 0 to 900 ° C.

[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 described. 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 _I Hc, become extremely low, which is not desirable for practical use.

The iron raw material in the present invention includes a wet synthesis method, that is, Fe ²⁺
Alternatively, needle-shaped α-FeOOH particles obtained by oxidation or polycondensation reaction from an aqueous solution containing Fe ³⁺ , or α-Fe ₂ obtained by heating dehydration, or reduction and oxidation of the needle-shaped α-FeOOH particles.
O ₃ particles, Fe ₃ O ₄ particles, and γ-Fe ₂ O ₃ particles having a BET specific surface area of 10 to 60 m ² / g can be used.

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
If it exceeds the above range, it is possible to obtain a ferrite particle powder having desired fine particles and a narrow particle size distribution, but if it is added excessively, the specific surface area of the ferrite particle 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. A DC BH tracer (Type 3257, Yokogawa Electric Co., Ltd.) was used for magnetic measurement, and the measured magnetic field was 10 KOe.
It was measured at.

Example 1 Needle-shaped α-FeOOH so that the molar ratio of Fe ₂ O ₃ / BaO was 5.85.
When 1230 g of particle powder (BET specific surface area 35.4 m ² / g) and 239 g of barium carbonate were mixed, 30 g of water glass (Fe ₂
0.76% by weight in terms of SiO ₂ was added to O ₃ and mixed sufficiently, the mixture was calcined at 830 ° C. for 3 hours, and the calcined product was pulverized with an atomizer. The obtained particles were magnetoplumbite type ferrite particles as a result of X-ray analysis, and Fe ₂ O ₃ /BaO=5.87 as a result of composition analysis.

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 characteristics of this material, the coercive force was _I Hc: 4400 Oe.

Examples 2 to 12 The 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 type and amount of additives, and the firing temperature were variously changed. 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 1230 g of α-FeOOH powder (BET specific surface area 35.4 m ² / g) and barium carbonate 23 so that the molar ratio of Fe ₂ O ₃ / BaO was 5.85.
9 g was thoroughly mixed, the mixture was calcined at 1200 ° C. for 3 hours, and then the calcined material was pulverized for 60 minutes by a vibration type ball mill, and the particles obtained were X-ray analysis results. Met.

The specific surface area of this particle powder measured by the BET method was 7.0 m ² / g. As a result of electron microscopic 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 properties of this product, coercive force _I Hc: 3
It was 300 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 Compound and acicular α-FeOOH particles, acicular α
-FeOOH particles as a starting material, and one of iron materials selected from α-Fe ₂ O ₃ particles, Fe ₃ O ₄ particles, and γ-Fe ₂ O ₃ particles obtained by heating dehydration, reduction or reduction and reoxidation, and Is mixed in the presence of water glass and then fired in a temperature range of 750 to 900 ° C., 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) = 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 Compound and acicular α-FeOOH particles, acicular α
-FeOOH particles as a starting material, and one of iron materials selected from α-Fe ₂ O ₃ particles, Fe ₃ O ₄ particles, and γ-Fe ₂ O ₃ particles obtained by heating dehydration, reduction or reduction and reoxidation, and Is mixed in the presence of water glass and Na ₂ CO _3, and then fired in the temperature range of 750 to 900 ℃, a method for producing a magnetoplumbite-type ferrite fine particle powder. 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 Compound and acicular α-FeOOH particles, acicular α
-Α-Fe ₂ O ₃ particles, Fe ₃ O ₄ particles, γ-obtained by heating dehydration, reduction or reduction and reoxidation using FeOOH particles as a starting material
Any one of Fe ₂ O ₃ particles as an iron raw material was mixed with water glass and Na ₂
After mixing in the presence of CO ₃ and BaCl ₂ or SrCl _2, seven hundred and fifty to ninety
A method for producing a magnetoplumbite-type ferrite fine particle powder, which comprises firing in a temperature range of 0 ° C. 7. 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 6, which is 0.05 to 1.45% by weight in terms of SiO ₂ . 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 wt% with respect to 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.