JP2727187B2 - Method for producing plate-like hematite particle powder - Google Patents

Description

The present invention relates to a method for producing plate-like hematite particle powder. The plate-like hematite particle powder according to the present invention has a controlled particle size while maintaining a constant thickness, and is mainly used for paints, printing inks, cosmetics, coloring pigments for rubber and plastics, anticorrosion. Rust preventive pigments and raw material powders for magnetic materials. [Prior art] Hematite (petal) particle powder, which is the most typical iron oxide pigment, has a red color and is widely used as a red coloring pigment for paints, printing inks, cosmetics, rubber and plastics. I have. In particular, hematite particles having a plate-like morphology have a purple-red color.
It has a black-purple color and is used as a red-purple to black-purple color pigment, and has the property of being excellent in coatability because the plate-like particles resulting from the form are superposed and oriented, and have anticorrosion properties. Used as a rust-preventive pigment. Hematite particle powder is also widely used as a raw material powder for ferrite. That is, hard ferrite or soft ferrite is obtained by mixing a main material such as a hematite particle powder and a sub-material such as a Ba, Sr or Pb compound, or a Zn, Mn, Ni, Mg or Cu compound and heating and calcining. Being manufactured. In particular, when plate-like hematite particles are used as a main raw material, various ferrites having excellent anisotropy can be obtained. Further, hematite particle powder is expected to be used as a raw material powder of a magnetic material for magnetic recording. That is, the magnetic iron oxide particle powder, the hematite particles as a raw material powder, or heat reduction of the raw material powder into magnetite particles, or,
It is obtained by further oxidizing to maghemite particles as necessary.Especially, when plate-like hematite particles are used as a raw material powder, the particle morphology is maintained and inherited, so that plate-like magnetic oxidation having excellent orientation is obtained. An iron particle powder is obtained. As described above, hematite particle powder is used in various fields.Particularly, particles having a plate-like particle form have a better orientation than particles, cubic, and needle-like particles. Therefore, great demand is expected. However, the particle size of the plate-like hematite particles required according to the purpose of use varies, and is, for example, as follows. When using plate-like hematite particles as a coloring pigment,
In the production of paints, it is necessary to disperse the pigment uniformly and easily at the time of kneading in the production of rubber and plastics, and to disperse the pigments easily.
Particles as fine as possible are required. When plate-like hematite particles are used as anti-corrosion and rust-prevention pigments, relatively large particles are required to enhance the coating property. This fact is, for example, the Journal of the Society of Color Materials, Vol. 52, No. 5 (19
1979), p. 261 "The most suitable particle size for rust-preventive pigments is mainly those having a flake size of 5 to 105 µm". Next, sintered magnet, Ba, Sr or Pb ferrite particle powder used as a magnetic material for rubber and plastic magnets,
It is required that the residual magnetic flux density Br and the coercive force _I Hc be as high as possible. For this purpose, it is necessary that the grains have sufficient crystal growth and have a single magnetic domain structure. The Ba or Sr ferrite particles have a single magnetic domain structure when the crystal particles are about 1 μm or less, and therefore, the hematite particles as raw material particles are required to be about 1 μm or less. Furthermore, the particle size of the magnetic iron oxide particles for magnetic recording is closely related to the noise of the magnetic recording medium, and the smaller the particle size of the magnetic iron oxide particles, the lower the noise, the smaller the size of the magnetic iron oxide particles. In particular, it is required to be 0.3 μm or less. For this purpose, hematite, a starting material, is 0.3μ
m or less. Conventionally, the plate-like hematite particles include ferric salt or hydrated ferric oxide or FeOx · Fe ₂ O ₃ and (0 ≦ x ≦ 1) pH9.0
It is obtained by subjecting the above alkaline suspension to a hydrothermal treatment. As a method of controlling the particle size of the plate-like hematite particles to be generated, for example, Japanese Society of Color Materials, Vol. 60, No. 5, (1987)
Pp. 265-272, “The crystal size of the α-Fe ₂ O ₃ formed grows as the particle size of the raw material α-FeOOH increases and as the concentration of the aqueous alkali solution in the hydrothermally treated mother liquor increases.” As described, there is known a method of changing the particle size and the concentration of an aqueous alkaline solution of a ferric hydrate hydroxide as a raw material. [Problems to be Solved by the Invention] Plate-like hematite particles having various viscosities depending on the purpose of use are currently the most required, but when using the known method as described above, the particle size is large. At the same time, the particles grow in the thickness direction, so that it was difficult to independently control only the particle size irrespective of the particle thickness and plate ratio (average diameter of the particle plate surface: particle thickness). The thickness and the plate-like ratio of the plate-like hematite particles are important factors for specifying the particle morphology similarly to the above-described particle size, and it is strongly required that the plate-like hematite particles can be controlled separately from the particle size according to the purpose of use. That is, the plate ratio of the magnetic iron oxide particles for magnetic recording is preferably about 3: 1 to 20: 1 in consideration of the orientation, and accordingly, the plate ratio of the plate-like hematite particles as the raw material is also high. Something about 3: 1 to 20: 1 is required. On the other hand, the plate-like ratio of the plate-like hematite particles as the rust-preventive pigment is, for example, `` the most appropriate particle size as the rust-preventive pigment of the Journal of the Coloring Materials Association, the size of the flakes is within 5-105μ, ‥‥ Thickness is said to be 2-3 µm or less. ' Therefore, there is a strong demand for the establishment of technical means capable of independently controlling only the particle size of plate-like hematite particles obtained by hydrothermal treatment. [Means for Solving the Problem] The present inventors have conducted various studies on a method capable of independently controlling only the particle size of plate-like hematite particles obtained by hydrothermal treatment, and as a result, the present invention has been achieved. is there. That is, the present invention, the plate-like hematite by a pH9.0 more alkaline suspension containing ferric salt or hydrated ferric oxide or _{FeOx · Fe 2 O 3 (0} ≦ x ≦ 1) to hydrothermal treatment In the method for producing a particle powder, the alkali suspension is selected from the group consisting of sulfates, nitrates, chlorides, and acetates of alkali metals in a predetermined ratio in the range of 0.1 to 15.0 moles per mole of Fe in advance. The production of plate-like hematite particle powder comprising forming a plate-like hematite particle in which the particle size of the particle is controlled according to the abundance ratio of the water-soluble salt by leaving one or more kinds of water-soluble salts in existence Is the law. [Operation] First, the most important point in the present invention, a pH9.0 more alkaline suspension containing ferric salt or hydrated ferric oxide or _{FeOx · Fe 2 O 3 (0} ≦ x ≦ 1) In the method of producing plate-like hematite particles by hydrothermal treatment, the alkali suspension contains a predetermined ratio of alkali metal sulfates, nitrates, chlorides in a range of 0.1 to 15.0 moles per mole of Fe in advance. When one or more water-soluble salts selected from the group consisting of
This is a fact that plate-like hematite particles having a controlled particle size according to the abundance ratio of the water-soluble salt can be obtained while maintaining a constant thickness. Now, a description will be given of a part extracted from a number of experimental examples performed by the present inventors. FIGS. 1 and 2 show NaCl in Example 1 respectively.
1 shows the relationship between the thickness and particle size (plate surface diameter) of plate-like hematite particles obtained when 1 is present in the range of 0 to 15.0 mole ratio with respect to 1 mole of Fe and the abundance ratio of NaCl. As shown in FIGS. 1 and 2, the particle size of the plate-like hematite particles tends to increase as the abundance ratio of NaCl to Fe increases, while the thickness of the particles is almost equal to the abundance ratio of NaCl. Irrespective of the thickness, it maintains the same thickness. Next, conditions for implementing the present invention will be described. As the ferric salt in the present invention, ferric chloride, ferric sulfate and the like can be used. The hydrous ferric oxide particles in the present invention may be in the form of any of particles such as needles and spindles obtained by well-known various reactions, and the reaction mother liquor containing hydrous ferric oxide as it is or A wet cake in which the reaction mother liquor is washed with water and the by-product salt is removed to various degrees, a dried product of the wet cake, and the like can be used. The _{FeOx · Fe 2 O 3 (0} ≦ x ≦ 1) particles in the present invention, as the reaction mother liquor containing granular or cubic magnetite particles obtained by reacting a ferrous salt with an aqueous alkali solution, or the The reaction mother liquor is washed with water, and the wet cake obtained by removing various by-product salts to various degrees, the dried product of the wet cake and the like, and the above-mentioned needle-shaped or spindle-shaped hydrous ferric oxide particles are reduced, or further reduced if necessary. oxide can be used to FeOx · Fe ₂ O ₃ obtained acicular or spindle shape (0 ≦ x ≦ 1) particles or the like. The pH of the alkaline suspension in the present invention is 9 or more. If it is less than 9, acicular hydrous ferric oxide particles or FeOx · Fe ₂ O ₃ particles mixed in the plate-like hematite particles. The hydrothermal treatment in the present invention is usually performed in a temperature range of 150 to 330 ° C. using an autoclave device. Generally, as the alkali concentration becomes higher, the reaction temperature at which plate-like hematite particles are formed tends to be lower. When the temperature is lower than 150 ° C., the ferric salt or the ferric hydroxide or FeOx.Fe ₂ O ₃ remains as it is, and no plate-like hematite particles are generated. Although plate-like hematite particles can be generated even when the temperature exceeds 330 ° C., the upper limit of the temperature is 33
0 ° C. The water-soluble salts used in the present invention include alkali metal sulfates, nitrates, chlorides, acetates, and the like.
It includes both water-soluble salts which are by-produced by the reaction between the iron raw material and the aqueous alkali solution in the process of producing plate-like hematite particles, and water-soluble salts which are added separately. The content ratio of the water-soluble salt is selected within the range of 0.1 to 15.0 mol ratio with respect to 1 mol of Fe. If the molar ratio is less than 0.1, the object of the present invention cannot be achieved. When the molar ratio exceeds 15 mol, plate-like hematite particles aimed at by the present invention can be obtained, but there is no point in adding more than necessary. Practically 1
It is preferable to select within the range of 1010 molar ratio. The water-soluble salt in the present invention affects the particle morphology of the resulting plate-like hematite particles,
It must be present before the formation reaction of plate-like hematite particles is started. [Examples] Next, the present invention will be described with reference to Examples and Comparative Examples. The particle size of the particles in the above experimental examples and the following examples and comparative examples is indicated by an average value of numerical values measured from electron micrographs, and the thickness is calculated from the specific surface area value measured by the BET method and the particle size. It was shown by the calculated value. Example 1 α-FeOOH (Long axis: 1.0 μm, BET specific surface area: 50.2 m ^{2 /} g) 0.2
mol and 0.6 mol of NaCl (corresponding to 3 mol per mol of Fe)
And 1 mol of NaOH were mixed, and the alkaline suspension of pH 13.8 was heated to 280 ° C in an autoclave and kept at this temperature for at least 2 hours with mechanical stirring to produce a red-purple precipitate. I let it. After cooling to room temperature, the reddish purple precipitate was separated, washed thoroughly with water, and dried. The obtained magenta particles were hematite particles as a result of X-ray diffraction.
m, the BET specific surface area was 1.90 m ² / g, the thickness was 2590 °, and the plate ratio was 10.0: 1. Examples 2 to 7 Plates were prepared in the same manner as in Example 1 except that the type and concentration of the iron raw material, the amount of NaOH, the type and amount of the water-soluble salt, the pH of the suspension, and the temperature and time of the hydrothermal treatment were variously changed. Hematite particle powder was obtained. Table 1 shows the main manufacturing conditions and various characteristics at this time. FIGS. 3 and 4 show electron micrographs (× 10,000) of the plate-like hematite particles obtained in Example 2 and Example 6. FIG. Comparative Examples 1 to 3 Except that NaCl, Na ₂ SO _{4 and} NaNO ₃ were not added, plate-like hematite particles were obtained in the same manner as in Examples 1, 3 and 5. Table 1 shows the main manufacturing conditions and various characteristics at this time. An electron micrograph (× 10,000) of the plate-like hematite particles obtained in Comparative Example 1 is shown in FIG. [Effects of the Invention] According to the method for producing plate-like hematite particles according to the present invention, as shown in the above-mentioned experimental examples and examples, plate-like hematite particles whose particle size is controlled while maintaining a constant thickness are produced. Since it can be obtained, it is suitable as a coloring pigment for paints, cosmetics, rubber and plastics, an anticorrosive pigment, and a raw material powder for magnetic materials.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show the thickness and particle size (plate surface diameter) of plate-like hematite particles obtained when NaCl is present in the range of 0 to 15.0 mole ratio to 1 mole of Fe. It shows the relationship with the addition ratio of NaCl. 3 to 5 are electron micrographs (× 10,000).
And the plate-like hematite particles obtained in Example 2, Example 6, and Comparative Example 1, respectively.

Claims (1)

(57) [Claims] Ferric salt or hydrous ferric oxide or FeO _x・ Fe ₂ O ₃
A method for producing plate-like hematite particles by hydrothermally treating an alkaline suspension having a pH of 9.0 or more containing (0 ≦ x ≦ 1), wherein 0.1 to 15.0 parts by mass of Fe is added to the alkaline suspension in advance. Presence of one or more water-soluble salts selected from alkali metal sulfates, nitrates, chlorides, and acetates in a predetermined ratio within the range of the molar ratio allows the abundance ratio of the water-soluble salts to be present. A method for producing plate-like hematite particle powder, characterized in that plate-like hematite particles whose particle size is controlled according to the conditions are generated.