JPH0524869B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing plate-shaped Ba ferrite fine particle powder for magnetic recording.
Plate shape with zinc hydroxide deposited on the particle surface
The object of the present invention is to provide plate-shaped Ba ferrite fine particles having a large magnetization value by heating and firing Ba ferrite particles in the presence of a flux at a temperature equal to or higher than the melting point of the flux. [Prior Art] In recent years, for example, as described in JP-A-55-86103, ferromagnetic non-ferromagnetic materials having a large magnetization value, an appropriate coercive force, and an appropriate average particle size have been developed. Acicular particles are increasingly desired as magnetic materials for recording, especially magnetic materials for perpendicular magnetic recording. Generally, Ba ferrite particles are well known as ferromagnetic non-acicular particles. Conventionally, one of the methods for producing plate-shaped Ba ferrite is to hydrothermally treat an alkaline suspension containing Ba ions and Fe() using an autoclave as a reaction device (hereinafter referred to simply as hydrothermal synthesis). ) is known. First, regarding magnetic properties, it is necessary that the magnetization value of plate-shaped Ba ferrite particles for magnetic recording be as large as possible. The magnetoplumbite ferrite used as a media material is required to have as large a saturation magnetization as possible.'' In addition, a coercive force of about 300 to 1500 Oe is generally required, and in order to reduce the coercive force of the Ba ferrite fine particle powder produced in the above hydrothermal synthesis method and achieve an appropriate coercive force, the
It has been proposed to replace a part of the ions with Ti() and Co() or Co() and divalent metal ions M() such as Mn, Zn, Ni, etc. Next, regarding the particle size of the plate-shaped Ba ferrite fine particle powder for magnetic recording, it is necessary that the particles be as fine as possible, especially 0.3 μm or less. This fact can be seen, for example, in Japanese Patent Application Laid-open No. 125219/1983, which states, In order to perform sufficient recording and reproduction in this wavelength region, the crystal grain size of the ferrite is preferably about 0.3 μm or less.However,
If it is about 0.01 μm, the desired ferromagnetism will not be exhibited, so a suitable crystal grain size is required to be about 0.01 to 0.3 μm. ” is as stated. [Problems to be solved by the invention] Having a large magnetization value and appropriate coercive force, and
Plate-shaped Ba ferrite particles having an appropriate average particle size are currently most in demand, but in the hydrothermal synthesis method described above, various Ba ferrite particles can be precipitated by selecting reaction conditions. I'll come. These precipitated particles usually have a hexagonal plate shape, and their particle size distribution and average diameter vary depending on the production conditions, so their magnetic properties vary. The present inventor has been involved in the research and development of plate-shaped Ba ferrite particles using a hydrothermal synthesis method for many years. We have obtained knowledge that Ba ferrite fine particles can be obtained. However, when trying to control the coercive force to 1500 Oe or less, the plate-shaped Ba ferrite particles having the average diameter of 0.05 to 0.3 μm have a lower magnetization value.
It is difficult to maintain the concentration above 50 emu/g. Furthermore, a method is known in which the magnetization value is improved by heating and firing plate-shaped Ba ferrite fine particles produced from an aqueous solution by a hydrothermal synthesis method at a temperature of 800°C or higher (Japanese Patent Publication No. 12973/1983). . However, when using this method, the magnetization value tends to increase as the heating and firing temperature increases, and in order to obtain a large magnetization value, especially about 57 to 60 emu/g or more, a high temperature of 900°C or higher is required. In this case, sintering between particles and particles becomes significant, resulting in lumpy particles, which is not preferable as a magnetic particle powder for magnetic recording. In addition, in order to control the coercive force of the plate-shaped Ba ferrite fine particles obtained by heating and firing to 1500 Oe or less, it is necessary to add a large amount of the above-mentioned coercive force reducing agent, which reduces the magnetization value. Therefore, it was difficult to control the coercive force within the range of 300 to 1500 Oe while maintaining a large magnetization value, especially 57 to 60 emu/g or more. Therefore, it is strongly desired to establish a method for obtaining plate-shaped Ba ferrite particles having a large magnetization value, an appropriate coercive force, and an appropriate average particle size. [Means for solving the problem] In view of the above, the present inventor set the coercive force of plate-shaped Ba ferrite particles having an average diameter of 0.05 to 0.3 μm to 300 to 1500 Oe in a hydrothermal treatment method, and The present invention was achieved as a result of various studies aimed at further increasing the value. That is, the present invention uses plate-shaped Ba ferrite fine particles.
Suspended in an aqueous solution containing zinc with a pH of 4.0 to 12.0,
Plate shape with zinc hydroxide deposited on the particle surface
Ba ferrite fine particles are obtained, the particles are separated and dried, and then heated and calcined in the presence of a flux at a temperature range of 800 to 1000°C to dissolve zinc, and the heated and calcined product is washed. This is a method for producing plate-shaped Ba ferrite fine particle powder for magnetic recording, which involves removing a fluxing agent. [Function] First, the most important point in the present invention is that the plate-like
Ba ferrite particles are suspended in an aqueous solution containing zinc with a pH of 4.0 to 12.0 to obtain plate-shaped Ba ferrite fine particles with zinc hydroxide deposited on the particle surface.The particles are separated, dried, and then , in the presence of a fluxing agent,
When fired at a temperature range of 800 to 1000℃,
The point is that the magnetization value of the plate-shaped Ba ferrite particles can be effectively increased. The present inventor has discovered that when plate-shaped Ba ferrite particles with zinc hydroxide deposited on the particle surface are heated and fired at a temperature range of 600 to 900°C, zinc is solid-dissolved on the surface of the plate-shaped Ba ferrite particles. can be made,
As a result, it has already been found that plate-shaped Ba ferrite particles having a large magnetization value can be obtained (Japanese Patent Application No. 18834-1982). If you use this method,
The effect of increasing the magnetization value and lowering the coercive force can be obtained at the same time, but this effect is only achieved by dissolving zinc into the surface of the plate-shaped Ba ferrite particles. In the hydrothermal treatment method, zinc is added during the reaction for producing plate-shaped Ba ferrite particles (for example,
Japanese Patent Publication No. 46-3545, the aforementioned Japanese Patent Publication No. 60-12973), and the surface of plate-shaped Ba ferrite particles is coated with zinc oxide and/or hydroxide (Japanese Patent Publication No. 58-56232). ) is not expressed in either case. In the above method, as the amount of zinc dissolved in the particle surface of the plate-shaped Ba ferrite fine particles increases, the magnetization value can be effectively increased, and the amount of zinc dissolved in the particle surface increases. Control is performed by adjusting the pH and the amount of zinc added when depositing zinc hydroxide on the particle surface. In the above method, the present inventor has conducted various studies in order to further increase the magnetization value of the plate-shaped Ba ferrite particles, and has found that when heating and firing the plate-shaped Ba ferrite particles on which zinc hydroxide is deposited on the particle surface, They obtained a completely new finding that the magnetization value can be further increased in the presence of an agent. In the present invention, a plate-like material having a large magnetization value is used.
Regarding the reason why Ba ferrite particles are obtained,
Although it is not clear yet, the present inventor has found that when plate-shaped Ba ferrite particles with zinc hydroxide deposited on the particle surface are heated and fired to dissolve zinc as a solid solution, the plate-shaped Ba ferrite particles become a fluxing agent. Since a larger magnetization value was obtained compared to the case of heating and firing in the presence of , we believe that this is due to the synergistic effect of the zinc solid-solved on the particle surface and the flux. Conventionally, when heating and firing plate-shaped Ba ferrite particles, a fluxing agent is present, for example, in JP-A-60-151224 and JP-A-60-
There are methods described in Japanese Patent No. 161345, but the magnetization value of plate-shaped Ba ferrite particles obtained by these methods is at most 58 emu/g. Next, various conditions for implementing the present invention will be described. The plate-shaped Ba ferrite fine particles as the starting material in the present invention are plate-shaped BaO・nFe ₂ O ₃ (3.5≦n
≦6) Refers to fine particles and those to which the well-known coercive force reducing agent mentioned above is added, including plate-shaped Ba ferrite fine particles produced from an aqueous solution by a hydrothermal synthesis method, as well as those obtained by heating and calcining this, and those from an aqueous solution. A plate-shaped plate obtained by a so-called coprecipitation method in which Ba ions and Fe ions are precipitated and the precipitate is heated and fired.
Any of Ba ferrite fine particles and plate-shaped Ba ferrite fine particles obtained by a so-called glass melting method in which a component raw material of Ba ferrite and a glass-forming substance are mixed and melted and then the melt is rapidly cooled can be used. The deposition of zinc hydroxide in the present invention is plate-like.
Ba ferrite fine particles may be suspended in an aqueous solution containing zinc with a pH of 4.0 to 12.0. As the aqueous solution containing zinc, halides such as zinc chloride, zinc bromide, and zinc iodide, zinc nitrate, zinc sulfate, zinc acetate, and the like can be used. If the pH is less than 4 or more than 12, zinc deposition becomes difficult. The amount of zinc hydroxide deposited on the particle surface is PH8
The maximum value is around ~10, and it tends to increase as the pH increases. The flux in the present invention includes alkali metals,
One or more of alkaline earth metal halides and sulfates can be used, and in consideration of improving the magnetization value and economical efficiency, NaCl, BaCl ₂ ,
SrCl ₂ , KCl, etc. are preferred. The amount of flux in the present invention is 3 to 400% by weight based on the plate-shaped Ba ferrite particles. If it is less than 3% by weight, sintering occurs between particles and particles during heating and baking, which is not preferable. 400% by weight
Although the purpose of the present invention can be achieved even if the amount is exceeded, there is no point in adding more than necessary. The heating and firing temperature in the present invention is 800 to 1000°C.
It is. When the temperature is lower than 800℃, it is difficult to form a solid solution of zinc in the plate-shaped Ba ferrite particles.
If the temperature exceeds 1000°C, grain growth of the resulting plate-like Ba ferrite fine particles occurs, which is not preferable. The fluxing agent in the present invention can be washed using one or more of water and aqueous solutions such as hydrochloric acid, acetic acid, nitric acid, and hydrogen bromide. The solid solution amount of zinc in the plate-shaped Ba ferrite fine particles in the present invention is 0.2 to 5.0% by weight. If it is less than 0.2% by weight, the object of the present invention cannot be fully achieved. Although the purpose of the present invention can be achieved even if the amount exceeds 5.0% by weight, there is no point in adding more than necessary. [Example] Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the average diameter of particles in the following Examples and Comparative Examples is a value measured using an electron micrograph. In addition, the magnetization value and coercive force are 10KOe in powder form.
This was measured in a magnetic field of Example 1 By hydrothermal synthesis, 9.5 mol% Ba and
Plates containing 8.5 mol% Co and 2.8 mol% Ti
Ba ferrite fine particles were obtained. The obtained fine particles are
The average diameter was 0.07 μm, the coercive force Hc was 130 Oe, and the magnetization value was 10 emu/g. 100 g of the above particles were dispersed and mixed in a 0.07 mol zinc chloride aqueous solution, and after depositing zinc hydroxide on the surface of the particles at pH 6.0, they were separately dried. Next, 100 g of plate-shaped Ba ferrite fine particles powder with zinc hydroxide deposited on the particle surface was added.
An aqueous solution containing a flux consisting of NaCl (corresponding to 200% by weight based on the plate-shaped Ba ferrite fine particles) was added, and after evaporating water, the mixture was fired at 810° C. in the air for 1 hour. The fine particles obtained by heating and firing have an average diameter of 0.07μ.
m, and the magnetism has a coercive force Hc of 680 Oe and a magnetization value of
It was 65.8 emu/g. As a result of chemical analysis, zinc oxide and zinc hydroxide, which are heated and extracted in an alkaline solution, were not detected, so it was recognized that zinc was dissolved in solid solution. As a result of line analysis,
It was 2.5% by weight. Incidentally, the plate-shaped Ba ferrite fine particles containing Co and Ti obtained in the same manner as above except that heating and firing were carried out without the presence of a flux had an average diameter of 0.07 μm.
m, the coercive force is 740Oe, and the magnetization value is 61.0emu/
It was hot at g. Example 2 By hydrothermal synthesis, 10.0 mol% Ba and
Platy containing 7.0 mol% Co and 2.0 mol% Ti
Ba ferrite fine particles were obtained. The obtained fine particles are
The average diameter was 0.1 μm, the coercive force Hc was 140 Oe, and the magnetization value was 11.0 emu/g. 100 g of the above fine particles were dispersed and mixed in a 0.05 mol zinc nitrate aqueous solution, and after depositing zinc hydroxide on the surface of the particles at pH 10.0, they were separately dried. Next, 20 g of plate-shaped Ba ferrite fine particles powder with zinc hydroxide deposited on the surface of the particles was added.
An aqueous solution containing a flux consisting of SrCl ₂ and 10 g of NaCl (corresponding to 60% by weight based on the plate-shaped Ba ferrite fine particles) was added, and after evaporating the water, the mixture was fired at 900°C in the air for 2 hours. . The fine particles obtained by heating and firing have an average diameter of 0.1 μm.
The coercive force Hc is 900 Oe, and the magnetization value is
It was 65.7 emu/g. As a result of chemical analysis, zinc oxide and zinc hydroxide, which are heated and extracted in an alkaline solution, were not detected, so it was recognized that zinc was dissolved in solid solution. As a result of line analysis,
It was 2.9% by weight. Incidentally, the plate-shaped Ba ferrite fine particles containing Co and Ti obtained in the same manner as above except that heating and firing were carried out without the presence of a flux had an average diameter of 0.1 μm,
Regarding magnetism, the coercive force was 950 Oe and the magnetization value was 61.5 emu/g. Example 3 By hydrothermal synthesis, 10.0 mol% Ba was added to Fe.
Platy Ba ferrite fine particles containing . The obtained fine particles have an average diameter of 0.11 μm and a coercive magnetic field.
Hc was 480 Oe and magnetization value was 31.0 emu/g. 100 g of the above particles were dispersed and mixed in a 0.08 mol zinc acetate aqueous solution, and after depositing zinc hydroxide on the surface of the particles at pH 7.0, they were separately dried. Next, 200 g of plate-shaped Ba ferrite fine particles powder with zinc hydroxide deposited on the particle surface was added.
An aqueous solution containing a flux consisting of KCl (corresponding to 400% by weight based on the plate-shaped Ba ferrite fine particles) was added, and after evaporating water, the mixture was fired at 850° C. in the air for 1.5 hours. The fine particles obtained by heating and firing have an average diameter of 0.11μ.
m, and the magnetism is such that the coercive force Hc is 1080 Oe and the magnetization value is
It was 66.5 emu/g. In addition, as a result of chemical analysis, zinc oxide and zinc hydroxide, which are heated and extracted in an alkaline solution, were not detected, so it was recognized that zinc was dissolved in solid solution. As a result of optical X-ray analysis, it was 3.0% by weight. The plate-shaped Ba ferrite fine particles obtained in the same manner as above, except that they were heated and fired in the absence of a flux, had an average diameter of 0.11 μm and a coercive force.
The magnetization value was 1140 Oe and 60.5 emu/g. Example 4 Platy Ba ferrite fine particles containing 9.0 mol % of Ba based on Fe were obtained by a hydrothermal synthesis method. The obtained fine particles have an average diameter of 0.15 μm and a magnetic coercive force Hc.
was 450 Oe, and the magnetization value was 28.0 emu/g. 100 g of the above particles were dispersed and mixed in a 0.09 mol zinc chloride aqueous solution, zinc hydroxide was deposited on the particle surface at pH 9.0, and then separately dried. Next, 15 g of plate-shaped Ba ferrite fine particles powder with zinc hydroxide deposited on the surface of the particles was added.
An aqueous solution containing a flux consisting of BaCl ₂ and 5 g of KCl (corresponding to 40% by weight based on the plate-shaped Ba ferrite fine particles) was added, and after evaporating the water, the mixture was heated and calcined at 910°C in the air for 0.5 hours. . The fine particles obtained by heating and firing have an average diameter of 0.15μ.
m, and the magnetism has a coercive force Hc of 980 Oe and a magnetization value of
It was 67.1 emu/g. In addition, as a result of chemical analysis, zinc oxide and zinc hydroxide, which are heated and extracted in an alkaline solution, were not detected, so it was recognized that zinc was dissolved in solid solution. As a result of optical X-ray analysis, it was 4.0% by weight. In addition, the plate-shaped Ba ferrite fine particles obtained in the same manner as above except that heating and firing without the presence of a flux had an average diameter of 0.15 μm and a coercive force.
The magnetization value was 1030 Oe and 64.3 emu/g. Comparative Examples 1 to 14 Platy Ba ferrite particles were prepared in the same manner as in Example 1, except that the type of starting material, the type and amount of Zn added, the type and amount of flux, and the heat treatment temperature and time were varied. I got it. In addition, the starting material particles of Comparative Example 9 had an average diameter of
0.12μm, coercive force Hc is 110Oe, magnetization value is
Plates containing 12emu/g of Co, Ti and Zn
Ba ferrite particle powder (Co/Fe () = 8.0 at%, Ti/Fe () = 2.1 at% and Zn/Fe () =
4.0 at%) was used. Table 1 shows the main manufacturing conditions and various characteristics at this time. As a result of chemical analysis, the plate-shaped Ba ferrite particles obtained in Comparative Examples 13 and 14 detected zinc oxide and zinc hydroxide that were extracted by heating in an alkaline aqueous solution. It was confirmed that the zinc hydroxide existed as an oxide and zinc hydroxide and was not dissolved in solid solution. Further, as a result of electron microscopic observation, the plate-shaped Ba ferrite fine particle powders obtained in Comparative Examples 1, 2, 5, 7, 9, 11, and 12 were particles in which sintering occurred between the particles and between particles. .

【table】

〔effect〕

According to the method for producing plate-shaped Ba ferrite fine particle powder in the present invention, as shown in the previous example,
A plate-shaped plate with a large magnetization value in a magnetic field of 10 KOe, a coercive force of 300 to 1500 Oe, and an appropriate particle size.
Since Ba ferrite fine particles can be obtained,
It is most suitable as a magnetic material for magnetic recording, especially as a material for perpendicular magnetic recording.

Claims (1)

[Claims] 1 Platy Ba ferrite fine particles are suspended in an aqueous solution containing zinc with a pH of 4.0 to 12.0 to obtain plate-like Ba ferrite fine particles with zinc hydroxide deposited on the particle surface, and the particles are separated and dried. and then heating and firing in the presence of a flux at a temperature range of 800 to 1000°C to dissolve zinc in solid solution, and then washing the heated and fired product to remove the flux. plate shape
Manufacturing method of Ba ferrite fine particle powder.