JPH02271925A - Production of transparent spheroidal fine iron oxide particles - Google Patents

Abstract

PURPOSE:To narrow particle size distribution by adding an alkali to an aq. soln. of a ferric salt to adjust the pH, bringing them into a reaction to form an Fe(OH)3 precipitate and a salt, drying the resulting slurry, washing and drying formed Fe2O3. CONSTITUTION:An aq. soln. of an alkali such as NaOH, Na2CO3 or NH4OH at <=50 deg.C is added to an aq. soln. of a ferric salt such as FeCl3 to adjust the pH to 6-10 and they are brought into a reaction to form an Fe(OH)3 precipitate and a salt. The resulting slurry is sucked, filtered and dried at <=300 deg.C. This salt-contg. dried product is washed to remove the salt contained by 20-60wt.% (expressed in terms of dry powder) and the washed product is dried to obtain transparent spheroidal fine Fe2O3 powder having hematite structure, 0.01-0.1mum particle size and >=0.7 ratio of minor to major axis size.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing transparent iron oxide fine particles useful for various metallic coatings, film coloring pigments, and food packaging films or containers that utilize the ultraviolet absorption ability of iron oxide.

[Prior art] Iron oxide fine particle powder is widely used as a pigment powder for paints, and when the purpose is to improve hiding power or coloring power, the optimum particle size as a pigment is in the range of 0.2 to 0.4 μI. However, when the average particle size becomes 0.1 μm or less, the hiding power decreases rapidly and becomes transparent, which means that one particle is % of the wavelength of light.
This is said to be due to the following scattering and diffraction phenomena occurring. Iron oxide pigments that use this phenomenon to impart transparency are being researched. Until now, there have been many methods for producing fine iron oxide particles (for example, 1) a method of producing fine hydrated iron oxide and heating and dehydrating it to obtain iron oxide fine particles (Japanese Patent Publication No. 51-1989).
21640. Special Publication No. 52-13528, Special Publication No. 62-4
0293, Japanese Patent Publication No. 61-163121), 2) Method of producing fine magnetite and heating it to obtain iron oxide fine particles (Japanese Patent Publication No. 54-7280, Japanese Patent Publication No. 61-2322)
25), 3) Hydrous iron oxide (mainly a -Fe00H1β-
Fe00H) was heat-treated in an autoclave. A method for obtaining iron oxide fine particles (JP-A-58-20733, JP-A-63-162535); 4) A method for obtaining iron oxide fine particles by neutralizing an aqueous solution of a ferric salt compound and then heat-treating it in an autoclave ( Special Publication No. 45-18372, Special Publication No. 6
2-216919), 5) A method for obtaining acicular iron oxide fine particles by adding an alkali to ferric salt to precipitate it, and drying it after washing the mouth (Japanese Unexamined Patent Publication No. 63-79726)
, 6) Add an anion exchange resin to a ferric salt solution to obtain a hydrated iron oxide sol, add an anionic surfactant to this to coagulate it, disperse it in an organic solvent, and then evaporate and reflux. There is a method for obtaining iron oxide fine particles (Japanese Patent Publication No. 59-4452). [Problems to be Solved by the Invention 1] In the conventional iron oxide fine particles as described above, when iron oxide fine particles are obtained by heating and dehydrating hydrous iron oxide, the temperature is at least 250°C.
The above heat treatment is necessary, and when heat-treating magnetite to obtain iron oxide fine particles, a temperature of 400°C or higher is required, and in manufacturing methods that include such a firing step, agglomeration occurs during firing, which can cause damage to plastics, paints, etc. It is difficult to disperse primary particles in a vehicle while maintaining their particle size. In addition, in the production method using an autoclave, it is difficult to reduce the average particle size of iron oxide fine particles to 0.1 gm or less,
It is difficult to produce transparent iron oxide fine particles. In addition, particles obtained in JP-A No. 63-79726 and hydrated iron oxide are used as raw materials (the shape of iron oxide fine particles is acicular, but acicular particles have a high oil absorption capacity). Dispersibility is poor and transparency is not sufficient. Also, in Japanese Patent Publication No. 51-12318, major axis: minor axis = 5 = 1
Although the following method for producing fine iron oxide pigments with spindle-shaped particles is described, the transparency is not necessarily satisfactory. [Means for Solving the Problems 1] The present invention has investigated a method for producing transparent iron oxide fine particles that are spherical in shape, have a narrow particle size distribution, and have extremely excellent transparency and dispersibility. Found a manufacturing method. That is, at least one species among alkali hydroxide, alkali carbonate, and ammonia is added to an aqueous solution of ferric salt so that the pH value becomes 6 to 10, and the reaction is carried out at 50°C or less to form ferric hydroxide. This is a method for producing transparent spherical iron oxide fine particles, which is characterized in that after a precipitate and a salt are generated, they are dried in a state containing the generated salt, and after iron oxide is generated, they are washed and dried. The transparent spherical iron oxide fine particles produced by this method have an average particle diameter of 0. Old ~ 0. Iu+m, the particle has a spherical shape with a length-to-width ratio of 0.7 or more. Ferric salts used in the present invention include nitrates, sulfates, chlorides, etc., but chlorides are particularly desirable in order to obtain iron oxide fine particles with extremely excellent dispersibility. Examples of alkaline solutions for adjusting the pH of this ferric salt solution include NaOII, KOJI, NagCOx, and 2C.
Mouth 3, N) 1.0) 1. Although NH3 can be used, alkali carbonate, aqueous ammonia or gas are preferred in order to obtain iron oxide particles with good crystallinity. The temperature at which the alkaline solution is added and reacted should be 50°C or lower in order to obtain transparent fine particles with a particle size of 0.111 m or less, because the higher the temperature, the coarser the particle size, and the lower the reaction temperature, the finer the particle size. Must. A more preferable reaction temperature is 30°C or lower, and the alkaline solution is NagC
In the case of Ox, the temperature is more preferably 10°C or less. The lower limit of the reaction temperature is the freezing point because it is a solution reaction. In this way, the pl+ of the solution is adjusted to 6-IO. When the pH exceeds IO, the final product contains hydrated iron oxide, and when pn is less than 6, the particle size of the produced iron oxide is 0.
．． If it exceeds 3μ, the particle size distribution becomes broad, and the transparency is poor, making it undesirable as a transparent pigment. Further, the reaction may be carried out by adding a ferric salt solution to an alkaline solution, or by adding an alkaline solution to a ferric salt solution. At this time, it is desirable to stir the solution to homogenize the solution and form a precipitate. Further, the ferric salt solution may contain an organic solvent such as a lower alcohol that is soluble in water. The pH value is adjusted to 6 to 10, and the resulting ferric hydroxide precipitate is passed through the mouth by a sweat connoisseur. This precipitate is dried in the presence of the formed salt. This is the most important point in the present invention, and is
Unlike the prior art of -79726, spherical iron oxide is not produced unless the produced salt is present. Since the precipitate is dried in the presence of the formed salt, the precipitate is washed and passed through the mouth as it is. The filtration may be carried out by any known method (for example, suction filtration), but depending on the raw material concentration and the filtration method, the resulting cake may have a dry powder content of 2.
Contains 0 to 60 wt% of produced salt. Then, by drying the cake containing the produced salt as it is, iron oxide fine particles are produced. When the salt content of the pass cake in terms of dry powder is less than 20 wt%, iron oxide is less likely to be produced, so in that case salt may be added later. Usually, it is preferable that the content is 30 wt% or more. The type of salt at this time is NaCl, KCI, NaNOs, KNO, NaCl, KCI, NaNOs, KNO, Na
2COs, K, S04, NH, C1, fNH41tsO
,,NH4N0. , Na2COs, (N)+41 *c
oz, etc., but NH, CI, Na (:l. MCI is preferred. The salt produced and the salt added to increase the salt content do not need to be the same. After forming a precipitate, pass through the mouth. (The purpose of the present invention can be achieved even by drying in a slurry state. There are no particular restrictions on the drying method, but the drying temperature is preferably 300°C or less to prevent agglomeration. After that, impurities such as formed salts are removed. The dry powder is washed for this purpose.Any washing method may be used as long as the salt can be removed.The transparent iron oxide fine particle powder obtained by the present invention has excellent transparency and is spherical, so although it is fine, it has good dispersibility. Because of its excellent properties, it can be dispersed in resins such as PET and acrylonitrile and used in resin bottles for beverages, pharmaceuticals, and cosmetics, food packaging films, metallic coatings, etc. It is also used in cosmetics, catalysts, adsorbents, etc. [Example] The present invention will be explained below with reference to Examples. Example 1 A 25% ammonia aqueous solution was added to 60 [1 ml] of a 0.5 mo1/ff aqueous FeC15 solution. The reaction temperature was 10°C, and the pn of the slurry was adjusted with a pH meter, and the slurry was added so that the pH of the slurry was 7.0.The slurry was stirred at 10°C for 1 hour, passed through a suction port, and
It was dried at 0°C. Thereafter, it was washed to remove ammonium chloride and dried again. As a result of X-ray diffraction measurement, the obtained dry powder had a hematite structure. As a result of SEM observation, the shape of hematite is spherical and the particle size is 0.05μ.
The particle size distribution was extremely sharp. Comparative Example 1 0.5 mol/I2 FeC11 aqueous solution 600ml
A 25% ammonia aqueous solution was added to the solution. The reaction temperature at this time was 10° C., and the pII of the slurry was adjusted using a pi meter, and the slurry was added so that the pII of the slurry was 7.0. This slurry was stirred at 10°C for 1 hour, washed with water, passed through a suction port, and dried at 120°C. As a result of X-ray diffraction, the obtained dry powder was amorphous and did not have a hematite structure. Comparative Example 2 0.5 mol/12 Fe(:Is aqueous solution 600 m
1.0 mol/I2 aqueous sodium carbonate solution was added to 1. The reaction temperature at this time was 80°C, and the pH of the slurry was adjusted using a pH meter.
Add this slurry so that it becomes 7゛0.
After stirring at 0°C for 1 hour, the mixture was filtered through a suction port and dried at 120°C. As a result of X-ray diffraction, the obtained dry powder was found to be β-Fe00
It had 11 structures. Comparative Example 3 0.5 mol/g FeC15 aqueous solution 600a+1
A 25% aqueous ammonia solution was added at 10°C. At this time, the pH of the slurry was adjusted using a 9H meter, and the slurry was added so that its pi was 11.0. This slurry was stirred at 10°C for 1 hour, then exposed to a suction port and heated to 12G'c.
It was dried. As a result of Xa diffraction, the obtained dry powder contained a mixture of hematite and α-Fe00H structures. Effects of the Invention According to the method for producing transparent iron oxide fine particles of the present invention, iron oxide having a narrow particle size distribution of 0.1 μm or less can be easily produced, and since the iron oxide fine particles are spherical, The structure of the paint allows for good dispersion in the vehicle, making it possible to obtain a coating film with excellent transparency.

Claims (1)

[Claims] At least one of alkali hydroxide, alkali carbonate, and ammonia is added to the ferric salt aqueous solution so that the pH value becomes 6 to 10, and the mixture is reacted at 50°C or lower to form a precipitate of ferric hydroxide and salt. 1. A method for producing transparent spherical iron oxide fine particles, which comprises: producing iron oxide, followed by drying in a state containing the produced salt, producing iron oxide, washing and drying.