JPH0314783B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing magnetoplumbite-type ferrite particles, and specifically, particles having a large specific surface area and a narrow particle size distribution, suitable as a magnetic material for magnetic cards. The present invention relates to a method for producing magnetoplumbite-type ferrite particles that can produce magnetoplumbite-type ferrite fine particles. [Prior Art] As is well known, magnetic card application products such as various traffic tickets and credit cards have recently become widespread, and the demand for higher recording densities for magnetic card application products is increasing. Conventionally, magnetoplumbite-type ferrite particles have been used as a magnetic material for magnetic cards. Magnetoplumbite-type ferrite particles are produced by mixing and blending a compound of at least one metal element selected from the group consisting of barium, strontium, and lead with iron oxide to a predetermined molar ratio, followed by firing and pulverizing. It is obtained by a manufacturing method, and was previously used mainly as a permanent magnet material such as excitation field magnet material for motors, generators, etc., but recently, with attention to its high coercive force, particle size adjustment has been carried out. After that, 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 production method has at least
Since the firing is performed at a high temperature of 900℃ or higher, usually 1100℃, and the particle size is adjusted using a crusher, there is a limit to the fineness of the particles, and BET of 2 to 5 m ² /g at most.
It is a particle powder with a specific surface area and has a wide particle size distribution, and since the particles have distortion due to mechanical impact, they have a poor S/N ratio as a magnetic recording material, resulting in a high noise level. It was not suitable as a magnetic material for magnetic cards. On the other hand, cobalt-coated iron oxide (Co-γ-
There is also a method of using Fe ₂ O ₃ ), Fe ₃ O ₄ particle powder as a magnetic material to obtain a magnetic card with a reduced noise level. In this case, the coercive force is at most
At present, the magnetic card is about 600 to 700 Oe and easily affected by external magnetic fields, causing many troubles when using the magnetic card. This fact is true, for example, in JP-A-56-118304.
This is clear from the statement in the publication that ``Magnetic cards with low coercive force ( _I Hc), such as those currently in use, have the disadvantage that the original characteristics of the magnetic card are lost due to magnetic disturbance.'' be. Therefore, there is a need for a magnetic material suitable for high recording density for magnetic cards that has a high coercive force and a reduced noise level. The reduction in noise level is said to be influenced by the particle size and particle size distribution of the magnetic material powder used. Specifically, the value of the specific surface area of the magnetic powder is often used as a way to express the particle size of the magnetic powder. However, it is said that the noise level caused by the magnetic recording medium tends to decrease as the specific surface area of the magnetic particles increases. This phenomenon can be seen, for example, in the Technical Research Report of the Institute of Electronics and Communication Engineers.
This is shown in "Fig 3" on page 27, 23-9 of MR81-11. "Fig. 3" is a diagram showing the relationship between the specific surface area of the particles and the noise level in Co-coated acicular maghemite particle powder, and the noise level decreases linearly as the specific surface area of the particles increases. This relationship also applies to the magnetoplumbite type ferrite particle powder. The present inventor has repeatedly studied magnetoplumbite-type ferrite particles, which have been conventionally used as a magnetic material for magnetic cards, in order to make them a magnetic material suitable for magnetic cards with high recording density. As mentioned above, conventional magnetoplumbite type ferrite particle powder has a temperature of at least 900℃ or higher,
Normally, firing is carried out at a high temperature of 1100°C or higher, and during the firing process abnormal crystals occur, grain growth of the particles themselves, and strong sintering between particles occur, producing coarse particles that reduce the specific surface area. The particles become small, and even if the particles are made finer by powerful crushing in a post-process, the resulting particles will have a wide particle size distribution. However, the firing temperature should be lower than 1000℃, for example 900℃.
If the temperature is lowered to about ℃, the generation of abnormal crystals during the firing process, grain growth of the particles themselves, and strong sintering between particles can be prevented as much as possible, and the resulting particles will be powder particles with a large specific surface area. Magnetoplumbite type ferrite particles are difficult to obtain because the ferrite reaction is difficult. [Means for Solving the Problems] In order to reduce the noise level when using magnetoplumbite-type ferrite particle powder as a magnetic material for magnetic cards, the inventors have proposed the following:
We have been searching for magnetoplumbite-type ferrite particles having a larger specific surface area and narrower particle size distribution. In the process of researching this, we have repeatedly studied methods for reducing particle size and the effects of various additives, and have developed a technology that allows us to obtain magnetoplumbite-type ferrite particles with a large specific surface area and a narrow particle size distribution. has already been established. That is, magnetoplumbite-type ferrite particles having a large specific surface area and a narrow particle size distribution are made by combining iron oxide with a compound of at least one metal element selected from the group consisting of barium, strontium, and lead. In the process of firing and pulverizing the mixture, a compound of at least one metal element selected from the group consisting of barium, strontium, and lead is mixed with iron oxide in the presence of water glass, and then heated at 750 to 900°C. It can be obtained by firing at a temperature range (Japanese Patent Application No. 59-19241). In order to obtain a magnetoplumbite-type ferrite particle powder having a large specific surface area and a narrow particle size distribution, the present inventor has proposed that at least one selected from the group consisting of barium, strontium, and lead be used in the previously filed invention. Water glass has been used as an additive when mixing a compound of one type of metal element and iron oxide, but the effects of other additives that can be used together with water glass have been studied. When stacked, water glass and Na ₂ CO ₃ or water glass and Na ₂ CO ₃
When using BaCl ₂ or SrCl ₂ in combination, the ferritization reaction occurs even if the firing temperature is lowered to 900°C or lower, resulting in grain growth of the particles themselves and strong sintering between the particles during the firing process. As a result, the obtained particles have a large specific surface area and a narrow particle size distribution, and the authors found that the effect is equivalent to or greater than that of magnetoplumbite-type ferrite particles obtained when water glass is used alone. He completed his invention. That is, the present invention provides a molar ratio Fe ₂ O ₃ /MO (M :Ba,
A compound of at least one metal element selected from the group consisting of barium, strontium, and lead, in a method for producing magnetoplumbite type ferrite particle powder having a composition of Sr, Pb (one or more types) = 5.6 to 6.1. and iron oxide in the presence of water glass Na ₂ CO ₃ or water glass Na ₂ CO ₃ and BaCl ₂ or SrCl ₂ , and then firing at a temperature range of 750 to 900 ° C. This is a method for producing magnetoplumbite type ferrite fine particle powder. [Function] Next, the present invention will be explained 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: One or two of Ba, Sr, Pb
The molar ratio of (more than one species) should be in the range of 5.6 to 6.1. Outside this range, the magnetic properties, especially the coercive force, _I
Hc becomes extremely low, which is not desirable for practical purposes. Any of α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ or Fe ₃ O ₄ can be used as the iron oxide raw material. Also,
Raw materials for barium, strontium and lead
BaCO ₃ , SrCO ₃ , PbO, etc. can be used, but Ba compounds, Sr compounds, and Pb compounds that become BaO, SrO, and PbO when heated can also be used. Next, the additives in the present invention will be explained. As the water glass in the present invention, water-soluble silicates such as sodium silicate and potassium silicate can be used.
The amount added (the amount present) is 0.05 to 1.45 in terms of SiO ₂ to iron oxide (in terms of Fe ₂ O ₃ ).
Valid between % by weight. If 1.45% by weight or more is added, the magnetization value of the product ferrite decreases, making it undesirable as a magnetic material. Further, if it is less than 0.05% by weight, the desired effect of the present invention cannot be obtained. In the present invention, the effective amount of Na ₂ CO ₃ added is between 0.35 and 12.0% by weight based on iron oxide (Fe ₂ O ₃ equivalent). If the amount is less than 0.35% by weight, the effect of addition is small. If the amount is 12.0% by weight or more, it is possible to obtain the desired ferrite particles with fine particles and a narrow particle size distribution, but if it is added in excess, the specific surface area of the ferrite particles tends to become small, which is not desirable. In the present invention, the effective amount of BaCl ₂ or SrCl ₂ to be added is between 1.5 and 7.0% by weight based on iron oxide (Fe ₂ O ₃ equivalent). When the amount is less than 1.5% by weight, the effect of addition is small, while when it is more than 7.0% by weight, the specific surface area of the ferrite particles tends to become small, and it is not economical. When considering the particle size and particle size distribution of the target ferrite particles, the content is preferably 1.5 to 7.0% by weight. In addition, the appropriate time to add each additive in the present invention is immediately before the firing process. That is, in each process of raw material blending process, baking process, and crushing process,
It can be added at the time of raw material blending, which is a step immediately before the firing step. The firing temperature range in the present invention may range from 750 to 900°C. If the temperature is below 750℃, it is insufficient to carry out the ferritization reaction, and if the temperature is lower than 900℃.
In the case of a temperature higher than that, grain growth of the ferrite particles themselves during the firing process and strong sintering between the particles make subsequent pulverization difficult, which is not preferable. In addition, in the case of the above firing temperature, pulverization after firing can be carried out under relatively mild conditions using, for example, an ordinary pulverizer such as an atomizer or an attritor, or a special pulverizer or a powerful pulverizer. is not necessary. [Example] Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the specific surface area of particles in Examples and Comparative Examples is
It was measured by the BET method, and X-rays were used to analyze the structure of the product. Magnetic measurements were performed using a DC BH tracer (Yokogawa Electric Manufacturing Co., Ltd. Type 3257) at a measurement magnetic field of 10 KOe. Example 1 1100 g of iron oxide (α-Fe ₂ O ₃ ) powder and barium carbonate were mixed so that the molar ratio of Fe ₂ O ₃ /BaO was 5.85.
When mixing 239g with 30g of water glass
(Equivalent to 0.76% by weight of SiO ₂ based on Fe ₂ O ₃ )
and 63 g of Na ₂ CO ₃ (equivalent to 5.7% by weight based on Fe ₂ O ₃ ) and after thorough mixing, the mixture was
It was fired at 850°C for 3 hours, and then the fired product was pulverized with an atomizer. As a result of X-ray analysis, the obtained particles were found to be magnetoplumbite type barium ferrite particles, and as a result of compositional analysis, Fe ₂ O ₃ /BaO=
It was 5.84. The specific surface area of the resulting magnetoplumbite-type barium ferrite fine particles measured by the BET method was 20.2 m ² /g, and the particle size distribution was narrow as observed by electron microscopy. In addition, as a result of measuring the magnetic properties of this material, the coercive force _I Hc:
It was 3760 Oe. Examples 2 to 7 Magnetoplan was produced in the same manner as in Example 1, except that the type and amount of Ba or Sr carbonate or oxide, the amount of water glass, the amount of Na ₂ CO ₃ , and the firing temperature were varied. A bite-type barium ferrite fine particle powder, a magnetoplumbite-type strontium ferrite fine particle powder, or a magnetoplumbite-type barium-strontium composite ferrite fine particle powder were obtained. As a result of electron microscopic observation, the magnetoplumbite type ferrite fine particle powders obtained in Examples 2 to 7 all had narrow particle size distribution widths. Further, Table 1 shows the specific surface area and magnetic properties of the obtained magnetoplumbite type ferrite fine particle powder by BET method. Example 8 1100 g of iron oxide (α-Fe ₂ O ₃ ) powder and barium carbonate were mixed so that the molar ratio of Fe ₂ O ₃ /BaO was 5.85.
When mixing 239g with 30g of water glass
(Equivalent to 0.76% by weight of SiO ₂ based on Fe ₂ O ₃ )
and 20 g of Na ₂ CO ₃ (equivalent to 1.8% by weight based on Fe ₂ O ₃ ) and 22 g of BaCl ₂ (equivalent to 2.0% by weight based on Fe ₂ O ₃ ) and mixed thoroughly. The mixture was calcined at 850°C for 3 hours, and then the calcined product was pulverized with an atomizer. As a result of X-ray analysis, the obtained particles were found to be magnetoplumbite type barium ferrite particles, and as a result of compositional analysis, Fe ₂ O ₃ /BaO=
It was 5.84. The specific surface area of the obtained magnetoplumbite-type barium ferrite fine particles was measured by the BET method to be 22.6 m ² /g, and the particle size distribution was narrow as observed by electron microscopy. In addition, as a result of measuring the magnetic properties of this material, the coercive force _I Hc:
It was 3520Oe. Examples 9 to 11 The same procedure was carried out except that the type and amount of Ba or Sr carbonate or oxide, the amount of water glass, the amount of Na ₂ CO ₃ , the amount of BaCl ₂ or SrCl ₂ , and the firing temperature were varied. A magnetoplumbite type barium ferrite fine particle powder or a magnetoplumbite type strontium ferrite fine particle powder was obtained in the same manner as in Example 8. As a result of electron microscopic observation, the magnetoplumbite type ferrite fine particle powders obtained in Examples 9 to 11 all had narrow particle size distribution widths. Further, Table 1 shows the specific surface area and magnetic properties of the obtained magnetoplumbite type ferrite fine particle powder by BET method. Comparative Example 1 1100 g of iron oxide (α-Fe ₂ O ₃ ) powder was added to barium carbonate so that the molar ratio of Fe ₂ O ₃ /BaO was 5.85.
The mixture was fired at 1250°C for 3 hours, and the fired product was pulverized in a vibrating ball mill for 60 minutes. X-ray analysis revealed that the particles were magnetoplumbite-type barium ferrite particles. It was hot. Further, the specific surface area of this particle powder was measured by BET method and was found to be 5.0 m ² /g, and as a result of electron microscopy observation, it was found that the particle size distribution was wide and coarse particles were mixed therein. Moreover, as a result of measuring the magnetic properties of this material, the coercive force _I Hc was 3200 Oe.

【table】

〔effect〕

According to the method for producing a magnetoplumbite type ferrite fine particle powder according to the present invention, as shown in the above example, it is possible to obtain a magnetoplumbite type ferrite fine particle powder having a large specific surface area and a narrow particle size distribution. Therefore, it can be suitably used as a magnetic material for magnetic cards with high recording density, which is the most demanded at present.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph (×30,000) showing the particle structure of magnetoplumbite-type barium ferrite fine particles obtained in Example 1.

Claims (1)

[Scope of Claims] 1. A method with a molar ratio of Fe ₂ O ₃ /MO ( M: one or more of Ba, Sr, Pb) = 5.6 to 6.1 in the method for producing magnetoplumbite type ferrite particle powder with a composition of at least one selected from the group consisting of barium, strontium, and lead. Production of magnetoplumbite type ferrite fine particle powder characterized by mixing a compound of a metal element and iron oxide in the presence of water glass and Na ₂ CO ₃ and then firing at a temperature range of 750 to 900°C. Law. 2. The method for producing a magnetoplumbite-type ferrite fine particle powder according to claim 1, wherein the amount of water glass present is 0.05 to 1.45% by weight in terms of SiO ₂ based on iron oxide (in terms of Fe ₂ O ₃ ). 3. The method for producing magnetoplumbite-type ferrite fine particle powder according to claim 1 or 2, wherein the amount of Na ₂ CO ₃ is 0.35 to 12.0% by weight based on iron oxide (Fe ₂ O ₃ equivalent). . 4 Molar ratio Fe ₂ O ₃ /MO (M: Ba, Sr, A method for producing magnetoplumbite-type ferrite particles having a composition of Pb (one or more Pb) = 5.6 to 6.1, in which a compound of at least one metal element selected from the group consisting of barium, strontium, and lead is oxidized. iron, water glass, Na ₂ CO ₃ and BaCl ₂ or
A method for producing magnetoplumbite-type ferrite fine particle powder, which comprises mixing in the presence of SrCl ₂ and then firing at a temperature range of 750 to 900°C. 5. The method for producing a magnetoplumbite-type ferrite fine particle powder according to claim 4, wherein the amount of water glass present is 0.05 to 1.45% by weight in terms of SiO ₂ based on iron oxide (in terms of Fe ₂ O ₃ ). 6. The method for producing magnetoplumbite-type ferrite fine particle powder according to claim 4 or 5, wherein the amount of Na ₂ CO ₃ is 0.35 to 12.0% by weight based on iron oxide (Fe ₂ O ₃ equivalent). . 7. The magnetoplumbite-type ferrite according to any one of claims 4 to 6, wherein the amount of BaCl ₂ or SrCl ₂ is 1.5 to 7.0% by weight based on iron oxide (Fe ₂ O ₃ equivalent). Method for producing fine particle powder.