JPH0371380B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a metal iron magnetic powder on a board and a method for producing the same. The disk-shaped metal iron magnetic powder of the present invention can be used as a magnetic recording magnetic powder suitable for high output and high density, and as a material powder for magnetic toner for electrostatic copying. [Prior Art] Magnetic materials commonly used in magnetic recording media include magnetite (Fe ₃ O ₄ ) and maghemite (γ
-Fe ₂ O ₃ ), chromium dioxide (CrO ₂ ), etc., and these magnetic powders have a saturation magnetization σs70~
It has a coercive force of 85 emu/g and a coercive force Hc of 250 to 500 Oe. In particular, the σs of the above oxide magnetic powder is the maximum
It is about 85emu/g, and generally σs70~80emu/
g is the main factor that limits the reproduction output and recording density of magnetic recording media. In addition, Co-magnetite and Co-containing Co-containing
-Maghemite magnetic particles are also used in magnetic recording media, but these magnetic particle powders have a low coercive force.
Although it has the advantage of having a high Hc of 400 to 800 Oe, it has the disadvantage of having a low saturation magnetization σs of 60 to 80 emu/g. Furthermore, as a magnetic powder having a large saturation magnetization σs and a high coercive force, acicular crystal hydrated iron oxide particles,
There are acicular iron magnetic powders and acicular iron alloy magnetic powders obtained by heating and reducing acicular iron oxides or those containing different metals other than iron in a reducing gas at about 400°C. These acicular iron magnetic powders or acicular iron alloy magnetic powders have the characteristics of extremely large saturation magnetization σs and high coercive force Hc, but it is difficult to obtain particles with uniform particle size, and dendritic particles It is difficult to obtain a product with good dispersibility because these materials tend to be mixed together. [Problems to be Solved by the Invention] Magnetic recording media are required to have higher density and output, especially improved frequency characteristics and lower noise levels.
It is necessary to improve the coercive force (Hc), as well as improve dispersibility, filling properties, and tape surface smoothness.
Similar properties are required for electrostatographic toners. Today, in order to meet these demands, acicular iron magnetic powders or acicular alloy magnetic powders have come to be used in many magnetic recording media. Since it is generally obtained by reducing particles, it is difficult to obtain the starting material acicular α-FeOOH powder with uniform particle size and no dendritic particles, and it is difficult to obtain magnetic powder with uniform particle size. There is a drawback that there is no Furthermore, even if acicular α-FeOOH particles with uniform particle size and no dendritic particles are obtained and reduced to obtain acicular ferromagnetic powder, the magnetic powder is acicular. Therefore, it has the disadvantage of poor dispersibility and filling properties. Therefore, if disk-shaped metal magnetic powder can be obtained in place of these needle-shaped crystals, it is expected that the dispersibility and filling properties of the magnetic powder and the surface smoothness of the magnetic recording medium will be improved. An object of the present invention is to provide a disc-shaped metal magnetic powder and a method for producing the same. One possible method for obtaining disc-shaped alloy magnetic powder is to reduce it using a reducing gas such as hexagonal barium ferrite _H2 , but the hexagonal disc-shaped alloy magnetic powder obtained by this method is It has the disadvantage that it is diluted with Ba and its saturation magnetization decreases. [Means for solving the problem] As a result of continuing research on improving the particle morphology, particle size distribution, and dispersibility of α-FeOOH, the present inventors found that
A ferric salt and an alkali are reacted in an aqueous medium in the presence of an oxyalkylamine to produce ferric hydroxide, which is a precursor of α-FeOOH, and the ferric hydroxide is hydrothermally treated. Surprisingly, α-FeOOH particles with a disk-like particle shape, more specifically a hexagonal disk-like shape, or a shape similar to a hexagonal disk, which is completely different from conventional particles, were obtained, and if necessary, they were coated with Si or the like.
By heat treatment in a non-reducing atmosphere and further reduction in a reducing gas atmosphere, a plate-shaped metal iron magnetic powder with fine, uniform particle size and good dispersibility can be obtained, and plate-shaped α-FeOOH or Disc-shaped α−
The present inventors have discovered that when Fe ₂ O ₃ particles are coated with a Si compound, the deformation of the particle shape is significantly suppressed, and the present invention has been achieved. The present invention is a metallic iron magnetic powder with a plate-like particle shape, a particle diameter (disc diameter) of 0.03 to 1 μm, and a disc-like ratio (particle diameter/
A plate-shaped metallic iron magnetic powder characterized by having a thickness) in the range of 3 to 10, and a ferric hydroxide obtained by reacting a ferric salt and an alkali hydroxide in an aqueous medium in the presence of an oxyalkylamine. Iron is generated, and the resulting slurry of ferric hydroxide is hydrothermally treated to form a plate-shaped α-
The present invention relates to a method for producing a disc-shaped metal ferromagnetic powder, which is characterized in that a disc-shaped metal ferromagnetic powder is obtained by obtaining FeOOH and reducing the obtained α-FeOOH using a reducing gas. The plate-shaped metal iron magnetic powder of the present invention also includes the plate-shaped iron alloy magnetic powder described below. The disc-shaped metal iron magnetic powder of the present invention and the method for producing the same will be explained in more detail. First, a method for producing disc-shaped α-FeOOH particles will be explained. In the present invention, as the ferric salt, ferric sulfate, ferric chloride, ferric nitrate, etc. are generally used, and among these, ferric chloride is preferred.
As the alkali hydroxide, sodium hydroxide, potassium hydroxide, etc. are preferably used. As a method for reacting a ferric salt and an alkali hydroxide in an aqueous medium, it is generally preferable to carry out the reaction using an aqueous ferric salt solution and an aqueous alkali hydroxide solution. At this time, it is appropriate to prepare the aqueous solution so that the concentration of ferric salt is 0.1 to 1 mol/, and the concentration of alkali hydroxide is 0.3.
It is appropriate to adjust the amount to 5 mol/min. The amount of alkali hydroxide used is preferably about 1 to 5 times equivalent to the ferric salt. In obtaining plate-like goethite, which is one of the features of the method of the present invention, in particular, ferric salt and alkali hydroxide are reacted to produce ferric hydroxide, which is a precursor of goethite. In this case, it is advantageous for the oxyalkylamine to be present in an aqueous medium. The oxyalkylamine is dissolved in a solvent,
For example, the oxylalkylamine may be added dissolved in a solvent such as water, dissolved in an aqueous alkali hydroxide solution, or directly added to the system, but the amount of oxylalkylamine is usually 30-80 for iron salts
It is advisable to adjust the amount to twice the molar amount, preferably 35 to 75 times the molar amount. If the amount of oxyalkylamine is too small, it will tend to become granular or the particle size distribution will become wide, and if it is too large, it is not economical and α-Fe ₂ O ₃ is likely to be generated. Become. As the oxyalkylamine, those having an alkyl group of 2 to 6 carbon atoms are suitable, and representative examples thereof include monoethanolamine, γ-propanolamine, β-propanolamine, diethanolamine, triethanolamine, and isobutanolamine. Among them, ethanolamine is preferred. The reaction temperature for producing ferric hydroxide by reacting a ferric salt with an alkali hydroxide in the presence of an oxyalkylamine is 50°C or less, preferably 0°C.
A temperature of ~45°C is suitable for enhancing the effect of the oxyalkylamine and controlling the disc ratio, particle morphology, etc. of α-FeOOH particles. If the temperature is too high, the α-FeOOH particles will become longer,
It is easy for α-Fe ₂ O ₃ to coexist and the variation in α-FeOOH particle morphology becomes large, and there is no particular advantage in lowering the temperature too much. Further, the reaction time is not particularly limited, but is generally appropriately selected from the range of 1 to 20 hours. A slurry of ferric hydroxide obtained by the reaction of a ferric salt and an alkali hydroxide can produce plate-shaped goethite even if it is immediately treated with hydrothermal treatment. When ripened, it becomes easier to obtain disk-like particles with uniform morphology. As a maturing method, generally employed is a method of leaving the product at 0 to 80°C for about 5 to 30 hours with or without stirring. In addition, in order to enhance the hydrothermal treatment effect, it is necessary to
It is desirable to perform the hydrothermal treatment at a pH of 10 or more, preferably 10.5 to 14. To adjust the pH of the slurry to 10 or higher, for example, the slurry containing ferric hydroxide may be filtered, washed, or after removing the supernatant liquid, an alkali such as sodium hydroxide or potassium hydroxide may be added to the slurry. This method is convenient. Hydrothermal treatment temperature is 100~250℃, preferably 120~
230°C is preferred. If the hydrothermal treatment temperature is too low, it will take a long time to convert ferric hydroxide into goethite, and the goethite particles may become elongated or have a large variation in morphology, and the hydrothermal treatment temperature is too high. and α-Fe ₂ O ₃ are generated. Hydrothermal treatment time is not particularly limited, but generally
It takes about 0.5 to 5 hours. Further, an autoclave is generally suitably employed for the hydrothermal treatment. By hydrothermal treatment, the ferric hydroxide in the slurry is converted into highly dispersible platy goethite having an unprecedented particle morphology. As a method for recovering the platy goethite particles from the slurry after hydrothermal treatment, conventional methods such as washing with water, filtration, drying, etc. can be employed. In the present invention, the plate-shaped goethite particles recovered after hydrothermal treatment are found to have α
-It is confirmed that it is a crystal of FeOOH. Also, particle diameter (disc diameter), disc ratio (particle diameter/thickness)
etc. can be varied over a wide range depending on manufacturing conditions, but observation and measurement of disc-shaped goethite particles using a transmission electron microscope (TEM) reveals that the particle morphology is disc-shaped, more specifically hexagonal disc-shaped or They have a similar morphology, the particle diameter is in the range of 0.03 to 1 μm, especially 90% or more of the particles are in the range of 0.04 to 0.3 μm, and the plate ratio is in the range of 3 to 10, especially in the range of 3 to 6. It is in. In addition, in a hexagonal disk shape or a form similar to it, the ratio of the lengths of the short side and the long side of the six sides (long side/short side) is 4 or less, and most of the particles are 2 or less. Further, the average particle diameter and average platelet ratio (average value of arbitrarily measured 30 particles) are in the ranges of 0.05 to 0.5 μm and 3 to 6. Next, a case will be described in which a hexagonal disc-shaped metal iron magnetic powder is obtained by reducing the disc-shaped α-FeOOH particles obtained in this way. Prior to reduction, heat treatment is preferably performed at 500 to 900°C, preferably 500 to 800°C in a non-reducing atmosphere such as air or nitrogen. If the heat treatment temperature in a non-reducing atmosphere is too low, the plate-shaped α-Fe ₂ O ₃ particles may not become substantially dense particles with an increased degree of crystallinity; The deformation of the shape due to holes etc. becomes large, which causes a decrease in Hc. On the other hand, if the heating temperature is too high, it will cause deformation of the plate-like particles and sintering of the particles and each other. Moreover, it requires highly accurate equipment and advanced technology, and is not industrially economical. In addition, during this heat treatment, the plate-shaped α-
By pre-deposition treatment of FeOOH particles with a Si compound, the sintering prevention effect and shape retention effect are improved, the degree of crystallinity on the particle surface and inside the particle is increased, and the excellent hexagonal shape with no bond between particles is achieved. It is preferable to carry out the adhesion treatment with Si compound particles since this will result in a plate that retains and retains its disk shape. This Si
The following method is generally used for the deposition treatment using a compound. In other words, disc-shaped α−
FeOOH particles are suspended in water, the suspension is dispersed in an acidic or alkaline solution, and a disc-shaped α-
After adding 0.1 to 10.0% of water-soluble silicate such as sodium silicate in terms of SiO ₂ to FeOOH, by adjusting the pH value to 7 to 8, SiO ₂
A method of obtaining coated disc-shaped α-FeOOH particles is preferred. The deposition treatment with the Si compound may be performed on the disc-shaped α-Fe ₂ O ₃ particles after the heat treatment. The temperature range of thermal reduction in reducing gas is
A temperature of 350°C to 600°C, preferably 400 to 550°C is suitable. As the reducing gas, hydrogen, a mixed gas of hydrogen and nitrogen, etc. are generally used. If the reduction temperature is too low, the reduction reaction will proceed slowly and take a long time. On the other hand, if the temperature is too high, the reduction reaction proceeds rapidly, causing deformation of the plate-like particles and sintering of the particles and each other. The disc-shaped metallic iron magnetic powder of the present invention has a disc-shaped α-
It inherits the shape of FeOOH particles, preferably a hexagonal disc or a shape similar to it, and the particle diameter is 0.03.
~1 μm, and the platelet ratio is in the range of 3 to 10. In addition, we also control coercive force, stability, etc.
Depending on the purpose of using magnetic powder for plate-shaped metal iron
It is also easy to obtain disc-shaped iron alloy magnetic powder by coating disc-shaped α-FeOOH particles with metals such as Ni, Co, and Zn. In particular, even if Ni is added during the synthesis of α-FeOOH, it can be alloyed as is without changing the particle morphology. [Effects of the Invention] The present invention provides a disk-shaped metal iron magnetic powder with an unprecedented particle form and a method for producing the same. When disk-shaped metallic iron magnetic powder is used as magnetic powder for magnetic recording, it is possible to obtain a magnetic recording medium that has high coercive force and large saturation magnetization, and has high dispersion, high filling property, and good surface smoothness due to its shape. is possible. Next, the present invention will be explained with reference to Examples. [Example] Example 1 50 g of ferric chloride [FeCl ₃ 6H ₂ O] was added to 1 part of distilled water.
75g of sodium hydroxide and 500ml of monoethanolamine
(45 times the mole relative to ferric chloride) was dissolved in distilled water 2, and added dropwise to the solution kept at 10°C.
The mixture was sufficiently stirred and reacted while being maintained at a temperature of 0.degree. C. to obtain a ferric hydroxide slurry. After leaving this slurry at 30°C for about 20 hours to age, remove the supernatant liquid, wash with a 10% sodium hydroxide aqueous solution to adjust the pH of the slurry to 11, and place the slurry in an autoclave with a volume of 500 ml. Prepared for 150
Hydrothermal treatment was performed at ℃ for 1 hour to obtain a plate-shaped goethite slurry. The plate-shaped goethite slurry is washed with water, filtered,
After drying, a hexagonal disk-shaped goethite as shown in FIG. 1 was obtained in powder form. A transmission electron micrograph of the obtained platy goethite powder is shown in Fig. 1 at a magnification of 100,000 times (magnification of 50,000 times to 2 times). Moreover, analysis by X-ray diffraction confirmed that this disc-shaped goethite had an α-FeOOH structure. Platy-shaped goethite can be seen using a transmission electron microscope (TEM)
The particle size (disc diameter), disc ratio (particle diameter/thickness), etc. were measured. These results are shown in Table 1 together with the specific surface area measurement results. Note that the average particle diameter and average platelet ratio in Table 1 are average values for 30 particles. Examples 2 to 6 The amount of monoethanolamine used in Example 1 was changed from 45 times the mole to 55 times the amount of ferric chloride (Example 2), and when producing the ferric hydroxide of Example 1, Change the temperature from 10℃ to 20℃ (Example 3),
The hydrothermal treatment temperature in Example 1 was changed from 150°C to 180°C (Example 4), β-propanolamine was used in place of the monoethanolamine in Example 1 (Example 5), and the monoethanol in Example 1 was changed to Using diethanolamine instead of amine (Example 6),
Other conditions were the same as in Example 1 to obtain the same plate-like goethite as in Example 1. A transmission electron micrograph (100,000 times magnification) of the platy goethite powder obtained in Example 4 is shown in FIG. Table 1 shows the results measured in the same manner as in Example 1. Example 7 The filtered and water-washed disc-shaped α- obtained in Example 1
30 g of FeOOH particles were suspended in 3 ml of water. Next, acetic acid was added to the above suspension to adjust the pH to 3.5, and then
Sodium silicate (Na ₂ SiO ₃ ) 4.9g (disc-shaped α-
(equivalent to 8.0wt% as _SiO2 in FeOOH particles)
was dissolved in 200 ml of water and added. After stirring for 60 minutes, ammonia water (28wt%) was added so that the pH value of the suspension was 8.0, and after aging overnight,
By washing, filtering, and drying, hexagonal disc-shaped α-FeOOH particles coated with a Si compound were obtained. 20g of the particle powder
was dehydrated and heated in air at 650°C for 1 hour in a fluidized bed calcining furnace, and then _H2 gas was passed through at a rate of 5.0 per minute and reduced at a reduction temperature of 450°C for 3 hours, resulting in a plate-shaped α-FeOOH. We obtained a hexagonal disk-shaped metallic iron magnetic powder that inherited the above. Examples 8 to 12 Hexagonal disc-shaped α-FeOOH obtained in Examples 2 to 6
A hexagonal disc-shaped metal iron magnetic powder was obtained in the same manner as in Example 7 except that . Table 2 shows the properties of the obtained powder particles.

【table】

【table】 [Brief explanation of drawings]

FIGS. 1 and 2 are transmission electron micrographs magnified by 100,000 times of the particle morphology of the platy goethite obtained in Example 1 and Example 4 of the present invention.

Claims (1)

[Claims] 1. Particles have a disc shape and a particle diameter (disc diameter) of 0.03.
~1 μm, and a plate-like metal iron magnetic powder having a plate-like ratio (particle size/thickness) in the range of 3 to 10. 2 (a) Reacting a ferric salt with an alkali in an aqueous medium in the presence of an oxyalkylamine to form ferric hydroxide, and hydrothermally treating the resulting slurry of ferric hydroxide. (b) reducing the plate-like α-FeOOH obtained in the above step using a reducing gas to obtain a plate-shaped metallic iron magnetic powder; Characteristic method for manufacturing plate-shaped metallic iron magnetic powder.