JP2005126324A - Magnetite particle powder and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fine magnetite particle powder suitable for a black pigment for coating or an electrophotographic magnetic toner. <P>SOLUTION: Magnetite is generated by blowing air into a ferrous chloride aqueous solution in which an alkali hydroxide of 0.6-1.0 mol and an alkali carbonate of 0.1-0.5 mol per ferrous chloride of 1 mol are added. The pH value of slurry containing magnetite is controlled in the range of 10-13 and an Si compound and a ferric chloride aqueous solution are added to the slurry. The magnetite particle powder added with the Si compound of 0.60-2.39% per Fe in terms of Si is manufactured by the coprecipitation of Si and Fe on the surface of magnetite. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a black pigment for paint excellent in blackness, dispersibility, heat resistance and environmental properties, fine magnetite particle powder suitable for magnetic toner for electrophotography, and a method for producing the same.

  Conventionally, magnetite particle powder has been widely used as a black pigment. However, in order to reduce the cost, it is necessary to increase the blackness of the magnetite to improve dispersibility, and heat resistance is required to be about 230 ° C. As for the blackness, it is necessary to make the particle size finer, but as it becomes finer, the heat resistance and dispersibility decrease. When the average particle size is about 0.3 μm or less, the upper limit of heat resistance is about 180 ° C. When the temperature exceeds 180 ° C., the surface of the magnetite is oxidized and becomes reddish.

  On the other hand, although the magnetite particle powder is also used as a magnetic toner for electrophotography, as is well known, when magnetite particle powder is converted into a toner, magnetite has high dispersibility and fluidity, and has high blackness. It is necessary to have uniform chargeability. In addition, if the dispersibility of the magnetite particle powder at the time of toner formation is poor, the content of magnetite particles in the toner will not be constant, resulting in uneven blackness and variations in magnetic properties, resulting in unstable developability, fog and toner scattering. Will occur.

  Regarding the dispersibility of the magnetite itself, fine particles are always in an aggregated state to some extent, but each particle does not exist independently as a primary particle. As the specific surface area increases, that is, as the particles become finer, the aggregation action becomes stronger. However, in order to make a good toner, it is necessary to make magnetite particles finer and further highly dispersed. In addition, although the magnetite particles are different in degree, the blackness becomes higher and the blackness improves as the particle size is reduced. Therefore, in order to increase the image density, the particles can be made the same particle size as much as possible and the particle size distribution can be reduced. It is necessary to adjust to narrower and more uniform particles.

  An object of the present invention is to provide a magnetite particle powder that is suitable for black pigments for paints and magnetic toners and has excellent blackness, dispersibility, heat resistance, and environmental properties, and a method for producing the same.

  That is, the present invention adds 0.6 to 1.0 mol of alkali hydroxide and 0.1 to 0.5 mol of alkali carbonate to 1 mol of ferrous chloride in an aqueous ferrous chloride solution; Generate magnetite; adjust the pH of the slurry in which magnetite is generated to a range of 10 to 13; add Si compound and aqueous ferric chloride solution to the slurry, and co-precipitate Si and Fe on the surface of magnetite particles It is related with the magnetite particle powder which is manufactured by this, and the addition amount of Si compound is 0.60-2.39% with respect to Fe in Si conversion, and its manufacturing method. The magnetite particle powder of the present invention is produced by the method described below.

  First, an aqueous solution of alkali metal carbonate and alkali metal hydroxide is added to the ferrous salt aqueous solution, and while maintaining the reaction temperature at 70 to 100 ° C., an oxidizing gas is passed through to produce fine magnetite that exhibits a polyhedron. As a secondary reaction, an alkaline aqueous solution is added to make the pH in the range of 10 to 13, and then a mixture of Si and / or Al is added to the surface of the magnetite particles while dropping water-soluble Si and / or Al compound and ferric chloride aqueous solution. Is produced by co-precipitation on the surface of magnetite particles.

  The usual magnetite production method is to generate magnetite by adding an aqueous alkali hydroxide solution at least twice the equivalent to ferrous chloride aqueous solution and then blowing an oxidizing gas while maintaining the reaction temperature at 70 to 100 ° C. However, the particle size of the magnetite particle powder obtained by this method is about 0.5 to 1.0 μm, and the particle size distribution width is widened. Therefore, the present invention reduces the charged amount of the ferrous chloride aqueous solution at the time of charging to a low level of 2.5 mol or less, preferably 2 mol or less, compared with about 3 mol in the usual reaction slurry, The concentration of the alkali hydroxide and alkali carbonate to be added is 0.6 to 1.0 mol and 0.1 to 0.5 mol, respectively, with respect to 1 mol of ferrous chloride. The amount is increased, the reaction balance is improved, and a fine magnetite exhibiting a polyhedron can be produced. The average particle size at this time is about 0.05 to 0.2 μm. In this method, alkali is added dropwise to the slurry after the reaction to adjust the pH to a range of 10 to 13, and a Si mixture is coprecipitated by adding a soluble Si compound and a ferric chloride aqueous solution.

At this time, the average particle size is 0.15 to 0.24 μm, the specific surface area is 14.1 to 14.9 m ² / g, and the bulk density is 0.41 to 0.43 g / cm ³ . Furthermore, the addition amount of Si compound in magnetite is 0.60 to 2.39% with respect to Fe in terms of Si. If the addition amount of Si compound is too small, the effect on dispersibility and heat resistance is small, and if too much, Si content is too large. A single precipitate is formed. The heat resistance is evaluated by a change in color when heated at 200 ° C. for 3 hours.

The Si compound used in the present invention may be soluble or colloidal, such as silicates such as Na ₂ SiO ₃ and Na ₂ SiO ₅ , hydroxides such as “Si (OH) ₄ ”, “ For example, “SiO ₂ ” can be mentioned, and silicate is particularly preferable.

The reason for setting the pH at the time of addition of the Si compound to the range of 10 to 13 on the surface of the fine magnetite particle powder is to ensure the dissolution of the Si compound.
The addition rate of the Si compound and ferric chloride needs to be aged while adding an aqueous solution diluted to 1 to 5 mol / l at a rate of about 100 ml / min and stirring for 30 to 60 minutes after completion. If the dropping time is too short, the attached state is poor and fine single crystals are precipitated. If the dropping time is too slow, the reaction time becomes longer and the working efficiency becomes worse.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
(Examples 1 to 5) A predetermined amount of ferrous chloride aqueous solution (concentration 328 g / l) was charged into a reactor having a capacity of 4 l, and sodium hydroxide (concentration 328 g / l) and sodium carbonate (concentration 328 g / l) while stirring. ) Was added, and the temperature was raised to 90 ° C., and air was blown at a rate of 3 l / min to produce black fine particles. After adding sodium hydroxide solution to this suspension to adjust the pH to 13, water glass was added and stirred well, then an aqueous ferric chloride solution (concentration 328 g / l) was added, and the Si compound was added. It coprecipitated with iron on black fine particles, filtered and dried to obtain magnetite particle powder containing Si compound. The details and results are shown in [Table 1].

  (Comparative Examples 1-4) The liquid amount, stirring speed, and temperature of the reaction conditions in the examples were not changed, and the amounts of ferrous chloride, sodium hydroxide, sodium carbonate, and ferric chloride were changed, and the Si compound The details and results when the coprecipitation is appropriately omitted are shown in [Table 1].

  The fine magnetite particle powder according to the present invention is excellent in blackness, dispersibility, heat resistance, and environmental resistance, and has good suitability as a black pigment for paint and a magnetic toner for electrophotography.

Claims (4)

  Add 0.6 to 1.0 mol of alkali hydroxide and 0.1 to 0.5 mol of alkali carbonate to 1 mol of ferrous chloride to ferrous chloride aqueous solution; blow air to generate magnetite; The pH of the resulting slurry is adjusted to a range of 10 to 13; the Si compound and the aqueous ferric chloride solution are adjusted so that the amount of Si compound added is 0.60 to 2.39% of Fe in terms of Si. A magnetite particle powder having an average particle diameter of 0.15 to 0.24 μm, which is produced by adding Si and Fe to the surface of the magnetite to coprecipitate on the surface of the magnetite. Magnetite particle powder having a specific surface area of 14.1 to 14.9 m ² / g, a bulk density of 0.41 to 0.43 g / cm ³ and heat resistance at 200 ° C. The magnetite particle powder according to claim 1, wherein the Si compound is selected from Na ₂ SiO ₃ , Na ₂ SiO ₅ , Si (OH) ₄ , or SiO ₂ . Adding 0.6 to 1.0 mol of alkali hydroxide and 0.1 to 0.5 mol of alkali carbonate to 1 mol of ferrous chloride to the ferrous chloride aqueous solution; blowing air to produce magnetite; The pH of the slurry in which the magnetite is generated is adjusted to a range of 10 to 13; the Si compound and the aqueous ferric chloride solution are adjusted so that the addition amount of the Si compound is 0.60 to 2.39% with respect to Fe in terms of Si. Including co-precipitation of Si and Fe on the surface of the magnetite;
The manufacturing method of the magnetite particle powder whose average particle diameter is 0.15-0.24 micrometer.