JP4351740B2 - Magnetite particles and method for producing the same - Google Patents

Description

【００４９】
表１から明らかなとおり、実施例１及び２のマグネタイト粒子は、高電気抵抗で（高Ｒ_ＮＮ）、分散性に優れ（低Ｌ）、かつ電気抵抗における耐環境性にも優れている（低Ｒ_ＬＬ／Ｒ_ＨＨ）ことがわかる。
【００５０】
これに対し、比較例１のマグネタイト粒子は、粒子中のナトリウム成分残存が多く、電気抵抗における耐環境性が劣るものだった。
また、比較例２及び比較例３のマグネタイト粒子は、ケイ素化合物やアルミニウム化合物の被覆がなされていない、あるいはケイ素化合物やアルミニウム化合物の含有量が少ないので、電気抵抗が低く、分散性にも劣るものだった。
また、比較例４のマグネタイト粒子は、ケイ素化合物やアルミニウム化合物の含有量が多いので、電気抵抗における耐環境性が著しく劣るものだった。
【００５１】
【発明の効果】
以上説明したように、本発明のマグネタイト粒子は、粒子表面のアルカリ金属残留量が抑制され、耐環境性、特に高温高湿下における電気抵抗等の安定性に優れており、高電気抵抗で、分散性や流動性も良好なので、静電複写磁性トナー用材料粉の用途に好適である。また、本発明のマグネタイト粒子の製造方法によれば、上記マグネタイト粒子を効率的に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetite particle and a method for producing the same. Specifically, the residual amount of alkali metal on the surface of the particle is suppressed, and the environment resistance, particularly excellent stability such as electrical resistance under high temperature and high humidity, is high. In particular, the present invention relates to a magnetite particle that is excellent in dispersibility and fluidity, and that is used mainly for use as a material powder for electrostatic copying magnetic toner, and a method for producing the same.
[0002]
[Prior art and problems to be solved by the invention]
Granular magnetite particles obtained by an aqueous solution reaction or the like are widely used in various fields, particularly for dry electronic copying machines, printers and the like. In this magnetic toner application, various general development characteristics are required, and in recent years, with the development of electrophotographic technology, copiers and printers using digital technology have developed rapidly, and the required characteristics have become more advanced. It has become.
[0003]
In other words, in addition to conventional characters, output of graphics, photographs, etc. is also required, and some copiers and printers have a capacity of 1200 dots or more per inch, and the latent image on the photoconductor is more precise. It is becoming. For this reason, there are strong demands for excellent reproducibility of fine lines in development and for obtaining stable images and for being usable without problems in various environments.
[0004]
Among the above-mentioned problems, in order to obtain a stable image with excellent fine line reproducibility in development, magnetite particles, which are magnetic toner material powders, are preferred to have high electrical resistance (patent) Reference 1). As means for increasing the electrical resistance of the magnetite particles, there is a disclosure relating to a magnetic material to which silicon or aluminum components are added or various compounds are coated (Patent Documents 2 and 3). For example, the effect of improving the dispersibility and fluidity of the magnetic material obtained by the additive component can also be expected.
[0005]
However, when a component other than magnetite is used as described above, the silicon component has high hygroscopicity, deteriorates the environmental resistance, and even when other methods such as using an aluminum component are adopted, the surface of the environmental resistance So we still haven't got a satisfactory one.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 3-1160 [Patent Document 2]
JP-A-5-213620 [Patent Document 3]
Japanese Patent Laid-Open No. 2000-239021
Accordingly, an object of the present invention is to provide magnetite particles having a sufficiently high electrical resistance, excellent dispersibility and fluidity, excellent environmental resistance, and particularly excellent stability such as electrical resistance, and a method for producing the same. is there.
[0008]
[Means for Solving the Problems]
As a result of intensive studies, the inventors of the present invention have prepared a slurry containing ferrous hydroxide salt obtained by neutralization with an alkali hydroxide using a wet reaction, particularly a ferrous salt aqueous solution as a starting material, such as air. Focusing on the alkali metal salt remaining in the magnetite particles produced by oxidation with an oxygen-containing gas, it has been found that the above object can be achieved.
[0009]
The magnetite particles of the present invention are made based on the above knowledge, and include one or more oxides, hydroxides, hydrated oxides, or a mixture thereof selected from silicon and aluminum on the particle surface. A magnetite particle having a coating, wherein the content of silicon and aluminum in the coating with respect to the entire magnetite particle is 0.05 to 1% by mass, and the residual amount of alkali metal on the particle surface is 10 It is characterized by being -50 ppm.
[0010]
Moreover, the method for producing magnetite particles of the present invention is obtained by a wet oxidation method of neutralized ferrous hydroxide with an alkali hydroxide, and one or a composite oxide selected from silicon and aluminum, a hydroxide, When the slurry containing magnetite particles subjected to the coating treatment containing either the hydrated oxide or the mixture thereof is subjected to solid-liquid separation and washing, an emulsion disperser treatment is performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
Magnetite particles obtained by an aqueous solution reaction, particularly a slurry containing ferrous hydroxide salt obtained by neutralization with alkali hydroxide using a ferrous salt aqueous solution as a starting material, in an oxygen-containing gas such as air The magnetite particles produced by oxidation are suitable as material powders for magnetic toners and are widely used as described above, but in such magnetite particles, alkali metal components derived from alkali hydroxide on the particle surface. Remains.
[0012]
The remaining alkali metal component, which is merely present on the particle surface, is removed to some extent by ordinary washing, but the magnetite particles, which are magnetic materials, tend to form aggregates such as magnetic agglomerates. Then, it is cleaned while holding the alkali metal component at the aggregation interface. In such a magnetite aggregate, it is difficult to remove the alkali metal component present at the aggregation interface by ordinary washing.
[0013]
In particular, in the case of magnetite particles that have been coated with silicon compounds or aluminum compounds for the purpose of increasing electrical resistance, improving dispersibility or fluidity, or exposed magnetite particles, the residual alkali metal component on the particle surface Is remarkable.
The magnetite particles inherently have magnetism, and thus have a property of easily causing magnetic aggregation, and the particles are magnetically aggregated even in the reaction slurry. In addition, when a silicon compound or an aluminum compound is coated on the particle surface or exposed, these components have a property of easily forming a network at the time of reaction, so that it is considered that a stronger aggregate is formed.
[0014]
And after washing | cleaning, when an aggregate is disintegrated by the mechanical dry-type grinding | pulverization which is the next process, an alkali metal component will be exposed to a particle | grain interface. This alkali metal component is often a sodium component or a potassium component derived from the alkali hydroxide to be used, but acts as an electrolyte and exhibits electrical conductivity, so that the electrical resistance value of the magnetite particles decreases particularly under high humidity. Presumed to be.
[0015]
The magnetite particles of the present invention are magnetite particles having a coating containing either one or a composite oxide selected from silicon and aluminum, a hydroxide, a hydrous oxide, or a mixture thereof on the particle surface, The content of silicon and aluminum in the coating with respect to the whole magnetite particles is 0.05 to 1% by mass, and the residual amount of alkali metal on the particle surface is 10 to 50 ppm with respect to the whole particles. .
[0016]
When the content of silicon and aluminum is less than 0.05% by mass, the effect of increasing the electrical resistance of the magnetite particles is low. When the content exceeds 1% by mass, the electrical resistance is sufficiently high but the environmental resistance is poor. .
Moreover, when the said alkali metal residual amount exceeds 50 ppm, it will lack the stability of environmental resistance. Moreover, setting it to less than 10 ppm is not only physically difficult but also uneconomical in terms of cost.
[0017]
In the magnetite particles of the present invention, the alkali metal is often derived from sodium hydroxide or potassium hydroxide, which is widely used as a neutralizing agent in production, so that the amount of sodium and / or potassium is 10 to 50 ppm. It is preferable.
[0018]
Magnetite particles preferable as a material powder for electrostatic copying magnetic toner have a sharp particle size distribution and a suitable level of particle average particle size (ferret diameter of about 0.1 to 0.3 μm by SEM observation). In the case of a magnetic toner obtained using such magnetite particles, the magnetite particles are uniformly dispersed in the toner particles, and various characteristics of the magnetic toner are also stabilized.
[0019]
Examples of the method for producing magnetite particles include a dry reduction method of FeOOH, an ion electrolytic separation method, and the like, and these methods can reduce alkali metal contamination.
However, in the dry method, sintering and agglomeration at the time of reduction are remarkable, and the particle size distribution tends to be broad. In the electrolysis method, etc., the particle size does not increase, and magnetite particles having the desired average particle size cannot be obtained. It is also uneconomical and not industrial.
Therefore, the magnetite particles of the present invention are more preferably used when they are obtained by wet oxidation of neutralized ferrous hydroxide with alkali hydroxide.
[0020]
In addition, when the volume electric resistance of the magnetite particles of the present invention is 1 × 10 ⁴ Ω · cm or more at a temperature of 23 ° C. and a humidity of 55% RH, excellent thin line reproducibility in development and a stable image can be obtained. It is suitable as a material powder for high-resistance magnetic toner for the purpose.
[0021]
Needless to say, the magnetite particles of the present invention preferably have a high volumetric electrical resistance and excellent environmental resistance. Specifically, the volume electrical resistance _{RNN at} a temperature of 23 ° C. and a humidity of 55% RH is 1 × 10 ⁴ Ω · cm or more, and each environment of a temperature of 10 ° C., a humidity of 20% RH, a temperature of 35 ° C., and a humidity of 85% RH. It is preferable that 1 ≦ R _LL / R _HH ≦ 6 is satisfied when the measured values (Ω · cm) of the volume electric resistance after being exposed for 24 hours are R _LL and R _HH , respectively.
[0022]
Regarding environmental resistance in electrical resistance, volume electrical resistance R _LL (temperature 10 ° C., humidity 20% RH) under low temperature and low humidity and volume electrical resistance R _HH (temperature 35 ° C., humidity 85%) under high temperature and humidity. The smaller the difference from (under RH), the better. Here, R _LL is a volume electric resistance in a state where the magnetite particles are hardly affected by moisture, and R _HH is a volume electric resistance in a state where the influence of moisture adhering to the surface of the magnetite particles is large. It is preferable that the ratio R _LL / R _HH is smaller.
[0023]
In the known magnetite particles whose surface is covered with a silicon compound or an aluminum compound, or just exposed, R _LL and R _NN are about 1 × 10 ⁴ to 1 × 10 ⁸ Ω · cm, R _LL / R _HH exceeds 7 and the environmental resistance is poor.
For this reason, the magnetite particles of the present invention preferably have a low alkali metal residue on the particle surface and R _LL / R _HH of 1 to 6.
[0024]
Also, if R _NN / R _HH, which is the ratio of volume electrical resistance R _NN under normal temperature and normal humidity, which is actually used environment, to volume electrical resistance R _HH under high temperature and high humidity, is about 1 to 5. For example, the degree of stability during normal use is high, which is preferable.
[0025]
It should be noted here that if the residual amount of alkali metal on the surface of the magnetite particles is small, R _LL / R _HH may show 1 to 6 even if the silicon compound or aluminum compound is not coated or exposed. Is to get. However, in that case, the absence of a silicon compound or an aluminum compound on the particle surface results in low electrical resistance and poor dispersibility and fluidity of the magnetic material.
[0026]
Moreover, the magnetite particles of the present invention contain elemental components such as Mn, Ti, Mg, Co, Ni, Cr, Cu, Zn, Zr, Sn, and P as required, and improve various properties according to demands. It is also possible to do.
[0027]
It is also known that the shape of the particles can be changed to octahedron, hexahedron, and sphere by changing the conditions during oxidation, but the magnetite particles of the present invention can be applied to any shapes.
[0028]
In addition, the magnetite particles of the present invention have an average particle diameter in the range of about 0.1 to 0.3 μm (ferret diameter by SEM observation), and the specific surface area is not necessarily relative to the average particle diameter. Is preferably about 5 to 15 m ² / g as a material powder for electrostatic copying magnetic toner.
[0029]
Next, the preferable manufacturing method of the magnetite particle | grains of this invention is described.
The method for producing magnetite particles of the present invention is obtained by a wet oxidation method of neutralized ferrous hydroxide with an alkali hydroxide, and is one or a composite oxide selected from silicon and aluminum, a hydroxide, and a hydrous hydroxide When the slurry containing the magnetite particles subjected to the coating treatment containing the product or any of these mixtures is subjected to solid-liquid separation and washing, an emulsifying disperser treatment is performed.
[0030]
What is important here is that when the slurry containing magnetite particles after the oxidation reaction is solid-liquid separated and washed, the slurry is always treated with an emulsifying disperser.
The above-mentioned emulsifying disperser is originally widely used for the production of emulsions and emulsions. However, in the present invention, in the state of a slurry, only agglomerates contained in the slurry are crushed and the particles are broken. In order to prevent deformation, the action of exposing the alkali metal component present in the aggregated particle interface to the slurry liquid is realized.
[0031]
Specifically, the slurry containing the magnetite particles after the completion of the oxidation reaction before the washing is subjected to an emulsifier-disperser treatment, and then solid-liquid separation and washing, or the slurry containing the magnetite particles after the completion of the oxidation reaction is performed at least once or more. What is necessary is just to carry out the emulsification disperser process of what was reslurried with water after washing | cleaning (This emulsification disperser process also serves as washing | cleaning, but it is more preferable if washing is performed further). The washing may be carried out by a conventional method using a filtration washing machine or the like, and the conditions are not limited at all. However, washing is preferably carried out until the wastewater conductivity after washing becomes 200 μS / cm or less.
[0032]
In any case, before performing the final washing step, the aggregate of the magnetite particles may be pulverized by an emulsifying disperser treatment, and the alkali metal component confined at the interface may be sufficiently washed.
[0033]
Specific names of emulsifiers and dispersers include homomixers (manufactured by Nippon Seiki Co., Ltd.), homogenizers (manufactured by Niro Soavi Co., Ltd., manufactured by Kokusai Seiko Co., Ltd.), Claremix (manufactured by Mtechnics), etc. Any structure can be used as long as it has a structure in which pulverization is performed in the gap portion in the small hole by the centrifugal force generated by the rotating rotor penetrating the small hole provided in the main body (stator). , Do not use grinding media).
In a wet disperser or a pulverizer other than the above emulsifying disperser, for example, a media mill (bead mill or ball mill), the mechanical load applied to the particles is too great and the particles are broken, which is unpleasant.
[0034]
In addition, the preferable operating conditions at the time of using an emulsification disperser, when using a homomixer by a batch type, although the processing time of about 1 to 10 minutes is preferable at the rotation speed of 5000-10000 rpm, It can also be used by a continuous type. . When using a homogenizer, it is good to process at a rotation speed of 3000-10000 rpm and the clearance gap width of 0.08-1 mm. Although the amount of liquid supply depends on the size of the apparatus, it is preferably 5 to 50 liters / minute in the case of the Harel homogenizer type 3 manufactured by Kokusan Seiko Co. Moreover, when using CLEARMIX, it is good to set the rotation speed of a rotor to 10,000-21000 rpm and the rotation speed of a screen to 3000-5700 rpm.
[0035]
If the solid-liquid separation and washing process combined with the above-described emulsifying disperser treatment is adopted, even if the silicon compound or aluminum compound is coated on the surface of the magnetite particles or exposed, the alkali metal is removed from these coated portions and exposed portions. The components can be greatly removed, and magnetite particles having high electrical resistance and excellent environmental resistance can be produced without impairing dispersibility and fluidity.
[0036]
That is, in the method for producing magnetite particles according to the present invention, the target to be processed by the above emulsifying disperser is obtained by a wet oxidation method of neutralized ferrous hydroxide with an alkali hydroxide and selected from silicon and aluminum. Or a magnetite particle having a coating containing any one of a composite oxide, a hydroxide, a hydrous oxide, or a mixture thereof, wherein the content of silicon and aluminum in the coating with respect to the entire magnetite particle is 0.05. A slurry containing ˜1% by mass of magnetite particles is used.
[0037]
For the slurry containing magnetite particles subjected to the above-described coating treatment, water-soluble silicate and aluminum salt are added to ferrous salt aqueous solution, reaction slurry during oxidation reaction, slurry containing magnetite particles after completion of oxidation reaction, etc. And the pH of the slurry is adjusted to a known pH range in which the additive element precipitates as an oxide, hydroxide, hydrated oxide or the like.
[0038]
At this time, sodium silicate, potassium silicate, or the like can be used as the water-soluble silicate to be added. As the water-soluble aluminum salt, aluminum sulfate, sodium aluminate, aluminum nitrate or the like can be used.
[0039]
【Example】
Hereinafter, the present invention will be specifically described based on examples and the like.
[0040]
(Example 1)
70 liters of Fe2 + 1.8 mol / liter iron sulfate aqueous solution, 546 g of sodium silicate with Si grade of 13.4%, 589 g of aluminum sulfate with 4.2 grade of Al grade and 10.6 kg of sodium hydroxide were mixed to make a total amount of 140 When the temperature was maintained at 90 ° C. and 20 liters / minute was blown in, 20% of the initial ferrous hydroxide was consumed, and seed crystal formation was confirmed. Next, 10 liters of ferrous sulfate aqueous solution having the same concentration as that used at the beginning of the reaction was added to the iron hydroxide slurry containing the seed crystal particles, and the total amount was 150 liters. Then, air was blown at 20 liters / minute at a pH of 6-9 and a temperature of 90 ° C. to complete the oxidation reaction.
[0041]
The slurry containing the magnetite particles was passed through a Harel homogenizer type 3 manufactured by Kokusan Seiko Co., Ltd. under the conditions of a rotational speed of 5000 rpm, a supply amount of 20 liters / minute, and a gap width of 0.22 mm. At this time, the temperature of the magnetite slurry was 70 ° C., the slurry concentration was 70 g / l, the slurry viscosity was 50 cP, and pH 6.0.
The slurry that had been treated with the emulsifier / disperser was subjected to conventional solid-liquid separation, washing, and drying to obtain magnetite particles.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated by the method shown below. The results are shown in Table 1.
[0042]
(Evaluation methods)
(1) Average Particle Size The particle shape was observed with a scanning electron microscope, a 30,000-fold photograph was taken, the ferret diameter of 200 particles was measured, and the average particle size was calculated.
(2) Specific surface area The surface area was measured with a Shimadzu-Micromeritics type 2200 BET meter.
(3) Sodium amount analysis sample of particle surface 25g is accurately weighed and dispersed in 250ml of pure water, boiled for 5 minutes, cooled to room temperature, and the liquid reduced by evaporation is added again with pure water. It was 250 ml, filtered through 5 C filter paper according to JIS P3801, the filtration was started, the first 50 ml was discarded, and the remaining filtrate was collected. The collected filtrate was subjected to ICP to measure the sodium ion concentration in the filtrate. From the measured sodium ion concentration, it was converted into the sodium ratio in magnetite.
(4) Silicon and aluminum content analysis samples were dissolved and measured by ICP.
{Circle around (5)} 0.9 g of silicon and aluminum content analysis samples in the particle surface coating with respect to the whole particles are weighed and 25 ml of 1N NaOH solution is added. The liquid is heated to 45 ° C. with stirring to dissolve silicon (aluminum) on the particle surface. After filtering the undissolved material, the eluate is quantified to 125 ml with pure water, and silicon (aluminum) contained in the eluate is quantified by plasma emission analysis (ICP).
Silicon (aluminum) content (% by weight) on the particle surface = {[amount contained in eluate (g / l) × 125 ÷ 1000] /0.9 (g)} × 100
(6) Volume electrical resistance temperature 23 ° C. and humidity 55% RH (referred to as normal temperature and normal humidity or NN), 10 ° C., 20% RH (referred to as low temperature and low humidity or LL), and 35 ° C., 85% RH in various environments Each sample is exposed for 24 hours in an environment adjusted to high temperature and high humidity (referred to as HH), and 10 g of each sample after exposure is put in a holder and a pressure of 600 kg / cm ² is applied to form a 25 mmφ tablet. Thereafter, an electrode is attached and measurement is performed under a pressure of 150 kg / cm ² . The electric resistance value of the magnetite particles was determined by calculating from the thickness, cross-sectional area and resistance value of the sample used for the measurement. The electrical resistance value in a normal temperature and humidity environment was R _NN , the electrical resistance value in a low temperature and low humidity was R _LL , and the electrical resistance value in a high temperature and high humidity was R _HH .
▲ 7 ▼ environmental dependency of the environmental dependence volume resistivity of volume electrical _{resistance, R LL} / R _HH, were determined _R NN _/ R _HH. The smaller this value, the better the environmental resistance.
(8) Coloring power Add 0.5 g of castor oil to 0.5 g of magnetite particles and 1.5 g of titanium oxide (R800 manufactured by Ishihara Sangyo Co., Ltd.), and knead with a Hoover-type Mahler. 0.5 g was added and further kneaded, and this was applied onto a mirror-coated paper using a 4 mil applicator, dried, and then measured with a color difference meter (color analyzer TC-1800 manufactured by Tokyo Denshoku Co., Ltd.).
[0043]
(Example 2)
The same reaction as in Example 1 was performed to obtain a slurry containing magnetite particles.
The slurry containing magnetite was washed by a usual method to obtain a magnetite cake containing 20 wt% of water.
Furthermore, 140 liters of water was added to 12,000 g of this cake, and the slurry containing the magnetite particles was subjected to conditions of a rotational speed of 5000 rpm, a liquid supply amount of 20 liters / minute, and a gap width of 0.22 mm using a Hallel homogenizer type 3 manufactured by Kokusan Seiko Co., Ltd. The slurry was passed through. At this time, the temperature of the magnetite slurry was 70 ° C., the slurry concentration was 70 g / l, the slurry viscosity was 50 cP, and pH 7.0.
The slurry that had been treated with the emulsifier / disperser was subjected to conventional solid-liquid separation, washing, and drying to obtain magnetite particles.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated by the method shown below. The results are shown in Table 1.
[0044]
(Comparative Example 1)
Magnetite particles were produced in the same manner as in the examples except that the treatment with the emulsifying disperser was not performed.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated similarly to Example 1. FIG. The results are shown in Table 1.
[0045]
(Comparative Example 2)
Magnetite particles were produced in the same manner as in the Examples except that sodium silicate and aluminum sulfate were not added.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated similarly to Example 1. FIG. The results are shown in Table 1.
[0046]
(Comparative Example 3)
Magnetite particles were produced in the same manner as in the Examples except that the amount of sodium silicate added was 28 g and the amount of aluminum sulfate added was 80 g.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated similarly to Example 1. FIG. The results are shown in Table 1.
[0047]
(Comparative Example 4)
Magnetite particles were produced in the same manner as in Example except that the addition amount of sodium silicate was 1300 g and the addition amount of aluminum sulfate was 1767 g.
About the obtained magnetite particle | grains, the property and various characteristics were evaluated similarly to Example 1. FIG. The results are shown in Table 1.
[0048]
[Table 1]

[0049]
As is apparent from Table 1, the magnetite particles of Examples 1 and 2 have high electrical resistance (high R _NN ), excellent dispersibility (low L), and excellent environmental resistance in electrical resistance (low R _LL / R _HH ).
[0050]
On the other hand, the magnetite particles of Comparative Example 1 had many sodium components remaining in the particles and were inferior in environmental resistance in terms of electrical resistance.
In addition, the magnetite particles of Comparative Examples 2 and 3 are not coated with a silicon compound or an aluminum compound, or have a low content of silicon compound or aluminum compound, and therefore have low electrical resistance and poor dispersibility. was.
Moreover, since the magnetite particles of Comparative Example 4 contained a large amount of silicon compound or aluminum compound, the environmental resistance in electrical resistance was remarkably inferior.
[0051]
【The invention's effect】
As described above, the magnetite particles of the present invention have a reduced amount of alkali metal remaining on the particle surface, and are excellent in environmental resistance, in particular, stability such as electrical resistance under high temperature and high humidity, with high electrical resistance, Since it has good dispersibility and fluidity, it is suitable for use as a material powder for electrostatic copying magnetic toner. Moreover, according to the method for producing magnetite particles of the present invention, the magnetite particles can be produced efficiently.

Claims (7)

  A magnetite particle having a coating containing any one or a composite oxide selected from silicon and aluminum, a hydroxide, a hydrous oxide, or a mixture thereof on the surface of the particle, wherein the entire magnetite particle is being coated Magnetite particles having a silicon and aluminum content of 0.05 to 1% by mass and an alkali metal residual amount on the particle surface of 10 to 50 ppm based on the entire particles.   The magnetite particle according to claim 1, wherein the alkali metal is sodium and / or potassium.   The magnetite particles according to claim 1 or 2, wherein those obtained by a wet oxidation method of neutralized ferrous hydroxide with an alkali hydroxide are used. Volume electrical resistance R _{NN at a} temperature of 23 ° C. and humidity of 55% RH is 1 × 10 ⁴ Ω · cm or more, and exposure is performed for 24 hours in each environment of temperature 10 ° C., humidity 20% RH, temperature 35 ° C., and humidity 85% RH. The magnetite according to any one of claims 1 to 3 , wherein 1 ≦ R _LL / R _HH ≦ 6 is satisfied when the measured values (Ω · cm) of the volume electric resistance after being set to R _LL and R _HH , respectively. particle. One of oxides, hydroxides, hydrated oxides, or a mixture thereof obtained by a wet oxidation method of neutralized ferrous hydroxide with an alkali hydroxide and selected from silicon and aluminum The method for producing magnetite particles according to any one of claims 1 to 4 , wherein an emulsification disperser treatment is performed when the slurry containing magnetite particles subjected to the coating treatment is subjected to solid-liquid separation and washing.   6. The method for producing magnetite particles according to claim 5, wherein the slurry containing the magnetite particles after completion of the oxidation reaction is treated with an emulsifying disperser, followed by solid-liquid separation and washing.   6. The method for producing magnetite particles according to claim 5, wherein the slurry containing the magnetite particles after completion of the oxidation reaction is washed at least once and then reslurried with water, and then treated with an emulsifying disperser.