JPS6240293B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing fine iron oxide powder for pigments, which is suitable for coloring plastics, paints, etc. and gives a transparent yellow to red color tone. Conventionally, FeO(OH) or Fe ₂ O ₃ , so-called transparent iron oxide pigment, has been used as a pigment that gives yellow or red tones to plastics, paints, rubber, etc.
Iron oxide fine powders with the chemical formula xH ₂ O are known, but these iron oxide fine powders have long axes of 200~
600 nm, the short axis is about 20 to 100 nm, and the particle size distribution is wide, so it has disadvantages such as insufficient transparency, complicated synthesis operations, poor reproducibility, and uneven hue, so it is not practical. It was unsatisfactory as a pigment. In order to impart high transparency to iron oxide pigments,
The average particle size of iron oxide powder is determined by the wavelength of visible light (400n
m) It is naturally expected that it would be fine to make it as fine as possible, but conventionally industrially obtained iron oxide fine powders have a maximum length of 200 to 600 nm for the long axis and 25 to 100 nm for the short axis; The technology for producing iron oxide fine powder with the following particle sizes with good reproducibility remains an unresolved problem. For example, in the "method for producing transparent ferric oxide hydrate" described in Japanese Patent Publication No. 43-11661, sodium hexametaphosphate is added to an aqueous ferrous sulfate solution, and air and ammonia are supplied to produce the product. A crystal nucleus of ferric oxide hydrate is generated from a ferrous hydroxide suspension, and this is allowed to precipitate and grow to a width of 25 to 100 nm.
A method for producing a brown to yellow ferric oxide hydrate with a length of 250 to 600 nm and a method for controlling the crystal grain size within the above range by adjusting the amount of sodium hexametaphosphate added are disclosed. There is. In addition, in the "Production method for iron oxide" described in Japanese Patent Publication No. 55-40533, sulfuric acid is added to an aqueous solution of Na and K hydroxides and carbonates while keeping the pH at 12 or higher and the liquid temperature at 20 to 35°C. A ferrous hydroxide solution is added to form ferrous hydroxide, and an oxygen-containing gas is bubbled through the aqueous mixture to form a 15-40% portion of the ferrous hydroxide with a diameter of 6-18 nm and a length of 40-40 nm. A manufacturing method is disclosed in which Fe ₂ O ₃ xH ₂ O seeds of 80 nm are changed and the seeds are grown into hydrated ferric oxide with a diameter of about 20 nm and a length of about 200 nm. In any of the above methods, the particle size of the iron oxide particles finally obtained is 200 to 600 nm for the long axis and 200 to 600 nm for the short axis.
Growth to 20 to 100 nm is inevitable,
It was extremely difficult to stop grain growth when the long axis was 100 nm or less. As mentioned above, in the above-mentioned Japanese Patent Publication No. 55-40533, it is shown that Fe ₂ O ₃ xH ₂ O seeds with a length of 40 to 80 nm can be obtained, but the proportion thereof is determined by the starting material. Furthermore, there is no disclosure of a method for separating such fine particle precipitation from water while preventing particles from agglomerating together. In addition, in New Experimental Chemistry Course 8 "Synthesis of Inorganic Compounds", a method for producing ultrafine amorphous ferric hydroxide with primary particles of about 5 nm is shown, but this product has significant agglomeration. It is not suitable for pigments because it is impossible to maintain the particle size of the primary particles and disperse them in vehicles such as plastics and paints. Generally, even if the precipitation of iron hydroxide in an aqueous solution is in a fine state, it is necessary to avoid grain growth, agglomeration, and sintering during processes such as drying and heating. However, this tendency is more pronounced as the finer the precipitates become. The inventors of the present invention solved the problems of the above-mentioned conventional technology and conducted various studies to provide fine iron oxide powder for pigments with excellent dispersibility. By combining these methods, we have established a method for producing fine iron oxide powder with good dispersibility and a long axis of 100 nm or less and a short axis of 40 nm or less. It was discovered that the powder was well dispersed in a vehicle without agglomeration and was suitable for use as a transparent iron oxide pigment, and the present invention was achieved based on this finding. That is, the gist of the present invention is as follows. (1) 2 to 10 g per mole of ferrous salt in an aqueous solution containing at least twice the mole of alkali carbonate to the ferrous salt.
of metaphosphate is dissolved in the aqueous solution, and then added to the aqueous solution at a concentration such that the final amount of precipitated hydrated iron oxide is about 7 to 28 g as Fe per 1 liquid amount, while keeping the liquid temperature within a range of not exceeding 50°C. A precipitate generation step in which a ferrous salt aqueous solution is added to generate a ferrous precipitate, and a ferrous precipitate is added to the suspension containing the ferrous precipitate. A wet oxidation step in which 1 to 4 minutes of air is aerated to produce a hydrated iron oxide precipitate, and 0.1 to 2.5% by weight of Fe in the hydrated iron oxide precipitate is added to the suspension containing the generated hydrated iron oxide precipitate. A fine iron oxide powder for pigments, comprising an agglomeration prevention step of adding a nonionic surfactant, separating the hydrated iron oxide precipitate, washing, drying, and pulverizing it to obtain a yellow fine iron oxide powder. manufacturing method. The present invention further provides yellow fine iron oxide powder obtained by the above method for producing fine iron oxide powder for pigments.
A red fine iron oxide powder can be obtained by subjecting it to a heating dehydration step of heating in a temperature range of 250 to 500°C. As described above, the fine iron oxide powder for pigments produced by the method of the present invention is yellow to red in color and has a particle size of 50 to 100 nm on the long axis and 20 to 40 nm on the short axis, and can be easily dispersed without agglomerating in the vehicle. It is highly suitable for dispersing and transparent iron oxide pigments. As mentioned above, the method for producing this yellow fine iron oxide powder consists of a combination of a precipitation generation step, a wet oxidation step, and an agglomeration prevention step, and the method for producing the red fine iron oxide powder consists of the above three steps. It consists of a combination of processes in which a heating dehydration process is further added. Next, these steps in the present invention will be explained in detail. (1) Precipitation generation step The alkaline aqueous solution used in this step needs to be an alkali carbonate aqueous solution. Sodium carbonate is suitable as the alkali carbonate. If sodium hydroxide or a sodium carbonate aqueous solution mixed with sodium hydroxide is used instead of soda carbonate, not only will unintended magnetite be more likely to be produced as a by-product, but the long axis versus short axis of the final fine iron oxide powder will vary. The axial ratio, so-called acicular ratio, becomes extremely large, and when used as a pigment, problems of color unevenness due to orientation may occur. The amount of sodium carbonate used must be at least twice the mole of the ferrous salt. If the amount of sodium carbonate used is less than twice the mole, there is a tendency for the same problems as described above to occur. Since the generated ferric precipitate is required to be a fine precipitate, it is necessary to generate the precipitate in a diluted state of ferrous ions, that is,
It is necessary to add the aqueous ferrous salt solution to the sodium carbonate solution in which the metaphosphate is dissolved; reverse addition does not result in a fine precipitate with the required uniform particle size. Metaphosphoric acid dissolved in a sodium carbonate solution is presumed to have some effect on the surface of the ferrous precipitate and suppress the grain growth of the precipitate, so if the metaphosphate is too dilute when forming the precipitate, the effect will be small. Therefore, it is necessary to dissolve the required amount of metaphosphoric acid in a soda carbonate solution in advance. In the case of sodium hexametaphosphate, the amount of metaphosphate added is at least 2 g per mole of ferrous salt, and the larger the amount added, the finer the precipitate will be, but adding 10 g per mole of ferrous salt is not effective. Since a tendency towards saturation is observed, the amount added ranges from 2 to 10 g per mole of ferrous salt. On the other hand, as the ferrous salt, ferrous sulfate, ferrous chloride, and ferrous nitrate are used, with ferrous sulfate being preferred. As the amount of the added precipitate increases, the particles become coarser, so it is necessary to ensure that the final amount of hydrated iron oxide precipitate does not exceed 0.5 mol (approximately 28 g) of Fe per 1 liquid amount. Although it is possible to adjust the particle size by reducing the amount of precipitation, the effect of reducing the particle size is saturated at about 0.125 mol (about 7 g) of Fe per liquid amount. Furthermore, in this process, the liquid temperature is 50
If the temperature exceeds 50°C, magnetite will be produced as a by-product and will be mixed in, so the liquid temperature must be controlled so that it does not exceed 50°C. (2) Wet oxidation step This step is a step in which air is blown into the ferrous iron precipitate obtained in the previous step to wet oxidize it into hydrous iron oxide. The air blowing speed affects the particle size of the hydrous iron oxide produced, and the larger the blowing speed, the smaller the particle size of the hydrous iron oxide tends to be. Therefore,
In order to keep the particle size below the target, it is necessary to blow at a rate of at least 1 per minute per mole of Fe, and if the blowing rate exceeds 4, there will be no difference in effectiveness. In the above-mentioned precipitation generation step and this step, the reaction for producing a hydrous iron oxide precipitate from ferrous sulfate is as follows. 2FeSO ₄ +2Na ₂ CO ₃ +1/2O ₂ +H ₂ O →2FeO(OH) +2Na ₂ SO ₄ +2CO _2Also in this process, if the liquid temperature exceeds 50°C, magnetite will be produced as a by-product and mixed in, so the temperature will be lower than 50°C.
It is necessary to control the liquid temperature so that it does not exceed. (3) Agglomeration prevention step In this step, a nonionic surfactant is added to the suspension containing the hydrated iron oxide precipitate obtained in the previous step, and then the precipitate is separated, washed, dried, and pulverized according to a conventional method. Then, the X-ray diffraction image shows α-FeO
A yellow fine iron oxide powder corresponding to (OH) is obtained. In this case, the finer the precipitated particles in the suspension, the more significant the particles will agglomerate together during the removal of water from the precipitate, but by adding a nonionic surfactant as described above, Drying temperature 70°C with almost no agglomeration
It is now possible to remove adhering water at ~120°C, and the yellow fine iron oxide powder obtained through the normal grinding process has a particle size of 50 to 100 nm on the long axis and 20 nm on the short axis.
At ~40 nm, it disperses well in vehicles such as paints, plastics, etc., giving a transparent yellow hue. The above nonionic surfactant acts as an anti-aggregation agent for precipitated particles, and is based on polyethylene glycol (the structural formula is

[Formula]) is preferable, and the amount added is in the range of 0.1 to 2.5% by weight of Fe weight in the hydrous iron oxide precipitate. If the amount added is less than 0.1% by weight, the effect of addition cannot be obtained, and if it exceeds 2.5% by weight, no improvement in the effect can be observed, which is economically disadvantageous. (4) Heating dehydration step In this step, the yellow fine iron oxide powder obtained in the previous step is heated and dehydrated at a temperature range of 250 to 500°C, and then pulverized by a conventional method to obtain red fine iron oxide powder. . This red fine oxidized powder has a particle size of 50 to 100 nm on the major axis and 20 to 40 nm on the minor axis, and when dispersed in a vehicle such as paint or plastic, it is well dispersed and provides excellent transparency and a uniform color tone. If the above-mentioned nonionic surfactant is not added, agglomeration and sintering between particles during heat dehydration will be significant, and the resulting red iron oxide powder will be difficult to disperse in vehicles such as paints and plastics, resulting in poor transparency. Also inferior. The heating dehydration temperature of the above yellow fine iron oxide powder is
The range is 250~500℃, and the heating dehydration temperature is 500℃.
If it exceeds 250°C, the growth of primary particles and aggregation between particles will be significant, and if it is below 250°C, it will take a long time to obtain a stable color tone. The above-mentioned steps of the present invention are easy to operate and enable mass production of the required fine iron oxide powder for pigments, and have great industrial value. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 10g of sodium hexametaphosphate was dissolved.
While stirring 0.5 mol/10 of a sodium carbonate aqueous solution, 0.25 mol/10 of a ferrous sulfate aqueous solution was added, and then the temperature was raised to 45°C, and air was evaporated to 10/1.
After blowing at min for 60 minutes, a yellow precipitate was obtained. After adding 1.4 g of a nonionic surfactant (Nissan Nonion 04, manufactured by Nissan Chemical) to this suspension, the precipitate was separated, washed, dried, and crushed to obtain a yellow fine iron oxide powder. When this fine iron oxide powder was examined by powder X-ray diffraction, it was found that hydrated iron oxide α-FeO(OH)
When examined with an electron microscope, the long axis was 50n.
It was a granular fine particle with a minor axis of 20 nm. When this fine iron oxide powder was made into a paint using an acrylic resin varnish, a yellow coating with excellent transparency and good dispersion was obtained. Example 2 The yellow fine iron oxide powder obtained in Example 1 was
By heating and dehydrating at 500° C. for 30 minutes, red fine iron oxide powder α-Fe ₂ O ₃ consisting of particles of the same size as in Example 1 was obtained. When this α-Fe ₂ O ₃ was made into a paint, a red paint film with good dispersibility and excellent transparency was obtained. Example 3 20g of sodium hexametaphosphate was dissolved.
While stirring 10% of a 6mol/aqueous sodium carbonate solution, 10% of a 1mol/aqueous ferrous sulfate solution was added, then the temperature was raised to 45°C, and air was evaporated to 10%.
After blowing at min for 3 hours, a yellow precipitate was obtained. After adding nonionic surfactants (7 g each of Nitsusan Nonion 04 and Nitsusan Nonion L4) to this suspension, the precipitate was separated, washed, dried, and pulverized, and then dehydrated by heating at 350°C for 1 hour to give it a red color. α-Fe ₂ O ₃ powder was obtained. This red powder is the long axis
They are rice-grain-like fine particles with a diameter of 100 nm and a minor axis of 40 nm. When mixed with PET resin and the same amount of zinc stearate and injection molded, a colored resin piece with excellent transparency was obtained. Comparative Example 1 Red α- obtained by operating under the same conditions as Example 3 except that sodium hexametaphosphate was not added.
Fe ₂ O ₃ had a long axis of 250 nm and a short axis of 50 nm. When this α-Fe ₂ O ₃ was mixed with PS resin along with the same amount of zinc stearate and injection molded, a colored resin piece was obtained which was much inferior in transparency to the powder obtained in Example 3. . Comparative Example 2 The operation was carried out under the same conditions as in Example 3 except that no nonionic surfactant was added. The powder after heating and dehydration showed significant agglomeration of secondary particles, and under the same conditions as in Example 3, poor dispersion was observed. It was not possible to turn it into paint. Comparative example 3 0.25 mol/aqueous solution of soda 5
The operation was carried out under the same conditions as in Example 1 except that a mixed alkali of 0.25 mol/caustic soda aqueous solution 5 was used, and the obtained powder was α-Fe ₂ O ₃ .
It was not xH ₂ O but black Fe ₃ O ₄ powder.

Claims (1)

[Scope of Claims] 1. Dissolve 2 to 10 g of metaphosphate per mole of ferrous salt in an aqueous solution containing at least twice the mole of alkali carbonate per mole of ferrous salt, and then add to the aqueous solution at a temperature of The final amount of hydrated iron oxide precipitation is approximately 7 to 28 g as Fe per liquid volume while maintaining the temperature within a range of 50℃.
A precipitation generation step in which a ferrous salt aqueous solution with a concentration of A wet oxidation step in which 1 to 4 air per mol of Fe is aerated per minute while maintaining the Fe weight in the hydrated iron oxide precipitate is added to the suspension containing the hydrated iron oxide precipitate. After adding 0.1 to 2.5% by weight of a nonionic surfactant, the hydrated iron oxide precipitate is separated, washed, dried, and crushed to obtain a fine yellow iron oxide powder. A method for producing fine iron oxide powder for pigments. 2. Dissolve 2 to 10 g of metaphosphate per 1 mole of ferrous salt in an aqueous solution containing at least twice the mole of alkali carbonate relative to ferrous salt, and then add it to the aqueous solution at a temperature not exceeding 50°C. While maintaining within the range, the final amount of hydrated iron oxide precipitation is approximately 7 to 28 g as Fe per liquid volume.
A precipitation generation step in which a ferrous salt aqueous solution with a concentration of A wet oxidation step in which 1 to 4 air per mol of Fe is aerated per minute while maintaining the Fe weight in the hydrated iron oxide precipitate is added to the suspension containing the hydrated iron oxide precipitate. After adding 0.1 to 2.5% by weight of a nonionic surfactant, the hydrated iron oxide precipitate is separated, washed, dried, and crushed to obtain a fine yellow iron oxide powder. A method for producing fine iron oxide powder for pigments, comprising a heating dehydration step of heating the powder in a temperature range of 250 to 500°C to obtain red fine iron oxide powder.