JP3433879B2 - Magnetite particles and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetite particles and a method for producing the same, and more specifically, it has a silicon component both inside and on the surface of the particle, and in particular, the amount of silicon component present on the surface (the amount converted to silicon) is determined. By controlling and heat-treating the obtained particles in a fluorine-based gas,
Magnetite particles that are used mainly for electrostatically copying magnetic toner material powders and black pigment powders for coatings, which have excellent balance of properties of remanent magnetization and fluidity and are excellent in environmental resistance, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art Recently, magnetite particles produced by an aqueous solution reaction have been widely used as a material for magnetic toners of dry type electronic copying machines, printers and the like. Although various general development characteristics are required for the magnetic toner, in recent years, due to the development of electrophotographic technology, particularly, copying machines and printers using digital technology have rapidly developed, and the required characteristics have become higher. Came.

That is, in addition to conventional characters, it is required to output graphics, photographs, etc. In particular, some printers have an ability of 400 dots or more per inch, and the latent image on the photoconductor is more precise. Is becoming. Therefore, high reproducibility of fine lines in development is strongly required.

In order to satisfy these requirements, it is necessary to provide magnetite having a good balance of residual magnetization and high resistance.

Further, for example, Japanese Patent Application Laid-Open No. 4-100474 discloses that magnetic iron oxide particles still have points to be improved in terms of environmental resistance. As described above, there is a demand for magnetic powders which satisfy various characteristics in the production of toner and are further excellent in environment resistance (moisture resistance).

[0006]

As magnetite particles that can meet these requirements, for example, JP-A-61-15 is available.
5223, JP-A-62-278131 and the like disclose magnetite particles containing a silicon component only inside the particle powder. Although these particles can provide image quality with improved fine line reproducibility, they are still insufficient.

Further, the magnetite particles according to these proposals have poor fluidity, and due to vibration during transportation and the like,
There is a problem that the packing density of the powder is excessively increased, and the workability at the time of forming a toner is significantly reduced.

Further, Japanese Patent Application Laid-Open No. 54-139544 proposes to deposit a silicon component on the surface of magnetite particles to improve electric resistance. However,
Although workability is improved by this, the balance of remanent magnetization is poor and it is insufficient to give fluidity.
Since there is a silicon component on the surface, there is a problem that hygroscopicity becomes particularly high.

Further, JP-A-5-213620 discloses magnetite particles in which a silicon component is divided into an inner portion and a surface portion, the residual magnetization is well balanced, the fluidity is good, and the resistance is high. However, although these particles provide an image quality with improved fine line reproducibility, there is a problem in that the surface silicon component absorbs moisture.

Further, in Japanese Patent Laid-Open No. 4-170325, particles containing Si and Al are heated and oxidized in an oxidizing atmosphere, and then heat-reduced in a reducing atmosphere, whereby magnetite having high coercive force and large residual magnetization is obtained. Particles have been proposed. However, this is because the particles are first oxidized and then reduced in order to obtain a high coercive force and a high remanent magnetization, which is different from the magnetic particles of the present purpose and a manufacturing method.

Further, Japanese Patent Application Laid-Open No. 61-124502 proposes a method of treating the surface with a fluoride in order to prevent oxidation of the metal powder. In this method, the metal powder is to be coated. That is, the purpose is to prevent oxidation, and the purpose thereof is different from that of the magnetic fine particles of the present invention.

The present invention has been made to solve these problems of the prior art. It has a low remanent magnetization, does not lower the electric resistance from the current level, and is excellent in workability, fluidity and environment resistance. An object of the present invention is to provide magnetite particles and a method for producing the same.

[0013]

Means for Solving the Problems The inventors of the present invention have made earnest studies to solve the above problems, and as a result, not only the magnetite particles contain a silicon component, but also the surface of the particle contains a silicon component, particularly a fine particle. The present invention has been completed by finding that magnetite particles can be obtained by exposing various silicon components and the particles can be heat-treated in a fluorine-based gas to solve the above problems.

The magnetite particles according to the present invention based on the above findings contain a silicon component inside and the silicon component is exposed on the surface at a ratio of 0.05 to 2.0% by weight in terms of silicon, and Fluorine (F) component is magnetite particles
Respect, the proportion of 0.01 to 1.0 wt% in terms of F
The surface of the magnetite is covered with, and the magnetite-containing water content (wt%) is expressed by the following formula (1), where A is the amount of silicon in the magnetite-containing silicon component converted to silicon (wt%) under high temperature and high humidity. , The moisture resistance is improved, and the resistance is 1 × 10 ³ Ω · cm or more. Moisture content (% by weight) ≦ 0.5 + A / 2 (1)

On the other hand, the method for producing magnetite particles is as follows. A silicon component is added to a solution containing a ferrous salt as a main component, and the mixture is further mixed with 1.0 to 1.1 equivalent of alkali with respect to iron. , The pH is maintained at 7 to 10 to carry out the oxidation reaction, and 0.9 to 1.
After adding 2 equivalents of deficient iron, continue to pH 6-
The oxidation reaction is performed while maintaining the temperature at 10, and the magnetite particles obtained by this oxidation reaction are heated to 200 ° C. in a fluorine-based gas.
The heat treatment is performed in a temperature range of up to 700 ° C.

The water content in the present invention is the water content of the magnetite at the Karl Fischer method of 200 ° C. The high temperature and high humidity means that the test was conducted under the conditions of 35 ° C., 85%, and 4 hours.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

The present invention has a silicon component both inside and on the surface of the particles, and in particular controls the amount of silicon components present on the surface (the amount converted to silicon), and obtains the particles in a fluorine-based gas. By heat treatment, magnetite particles further coated with a fluorine component are obtained. The obtained magnetite particles have a well-balanced improvement in various characteristics such as electric resistance, remanent magnetization and fluidity, and are environmentally resistant. It is excellent and is suitable for use mainly in the application of material powder for electrostatic copying magnetic toner and black pigment powder for paints.

That is, the magnetite particles of the present invention are
It is characterized in that it contains a silicon component inside, and a silicon component, especially a fine silicon component, is exposed on the surface and is heat-treated in a fluorine-based gas.

As described above, the magnetite particles of the present invention need to have a silicon component both inside and on the surface of the magnetite particles before heat treatment. Therefore, even if the silicon component is present inside the magnetite particles, if the silicon component is not exposed on the surface, the fluidity is poor. Further, when the silicon component is exposed only on the surface of the magnetite particles, the remanence becomes poor and the fluidity is not sufficient. In the present invention, the silicon component is a compound containing silicon or silicon oxide as a main component.

In the present invention, the amount of silicon component exposed on the surface (hereinafter, abbreviated as "surface-exposed silicon component") with respect to the magnetite particles is 0.05 to 2.0% by weight in terms of silicon. Is preferable (hereinafter, the amount of silicon component present is the amount converted to silicon). This is because when the amount of the surface-exposed silicon component is less than 0.05% by weight, the effect of improving the fluidity tends to be small, while the amount of the surface-exposed silicon component is 2.0% by weight.
If it exceeds, good characteristics can be obtained, but the workability is difficult, such that the filter cloth may be clogged during washing with water, which is not preferable.

That is, the magnetite particles are required to be washed with water in order to remove alkali salts such as sodium and potassium produced as by-products during the synthesis. However, if a large amount of surface-exposed silicon component is present on the filter cloth at this time, Clogging of
This causes a decrease in workability. Further, when the surface-exposed silicon component is present in an excessive amount, the amount of silicon consumed increases correspondingly, resulting in poor economic efficiency.

If the amount of the surface-coated fluorine component is 1% by weight or more, the saturation magnetization is lowered, which is not preferable. Further, if it is less than 0.01%, it may be adversely affected in dispersion after the improvement of the specific surface area, which is not preferable. Here, the improvement of the specific surface area has been one of the causes that the particles not heat-treated in the fluorine-based gas of the present invention have a high unevenness coefficient, so that the contact area with the outside is high and the hygroscopicity is large. .

The abundance of the surface-exposed silicon component referred to herein is a value obtained by the following analytical method. That is, 0.900 g of a sample is weighed, and 1N NaOH solution 2
Add 5 ml. The liquid is heated to 45 ° C. with stirring to dissolve the silicon on the particle surface.

After filtering the undissolved material, the eluate was purified with pure water.
It is quantified to 25 ml, and silicon contained in the eluate is quantified by plasma emission spectrometry (ICP). Surface-exposed silicon component (% by weight) = {[silicon contained in eluate (g / l) × 125 ÷ 1000] /0.900
(G)} × 100 The total SI amount is determined by plasma emission analysis (ICP) after dissolving the sample in a salt-hydrofluoric acid solution.

As described above, the magnetite particles of the present invention need to have a silicon component both inside and on the surface of the magnetite particles. As described above, the present applicant has technically established the above-mentioned analysis method for distinguishing the silicon component exposed on the surface of the magnetite particles from the silicon component present inside thereof (JP-A-5-213620).
No.), the magnetite particles obtained by this analysis method were heat-treated in a fluorine-based gas to complete the present invention.

Further, in the present invention, the ratio (B /) of the total content of silicon components (A: silicon equivalent) to the magnetite particles and the amount of surface-exposed silicon (B).
A) is 0.03 to 0.7, preferably 0.1 to 0.6
From the viewpoint of characteristics, it is desirable that the range be within the range. This selection needs to be made so as not to disturb the balance of fluidity while observing the desired particle size and residual magnetization.

The magnetite particles of the present invention have a resistance ≧ 1.0 × 10 ³ (Ω · cm).

Regarding resistance, magnetite particles are usually 1
Although it is around 10 ³ (Ω · cm), a higher magnetic toner is preferable, but when it is lower, it is difficult to maintain the charge amount required by the magnetic toner.

Conventionally, a particle powder having excellent dispersibility has generally been required to have a small specific surface area with respect to the particle diameter and a low oil absorption. Incidentally, JP-A-5-21362
No. 0 publication has a large specific surface area with a high unevenness coefficient of the particle surface and a high oil absorption amount, but since it has silicon on the powder surface, it contributes to the improvement of dispersibility and has a good balance of residual magnetization. Although particles with good fluidity and high resistance have been proposed, they also increase the contact area with the outside and deteriorate the moisture absorption resistance. The magnetite particles of the present invention eliminate the above-mentioned drawbacks by heat treatment coating in a fluorine-based gas.

Although the function and function thereof are not clear, it is considered that the OH groups of the silicon component exposed inside and the surface and the silicon component on the outermost surface are replaced and removed by the heat treatment using fluorine. However, the surface silicon component remained, and the fluidity was not lost due to the surface coating effect with the fluorine component. Also, by removing the silicon on the outermost surface,
The unevenness coefficient decreases, the specific surface area decreases, and the moisture absorption resistance
It contributed to the low specific surface area and low oil absorption for excellent dispersibility.

According to the above, the water content (% by weight) of the magnetite particles under high temperature and high humidity is reduced to less than half, and when the abundance (% by weight) converted to silicon of the magnetite-containing silicon component is A, The magnetite-containing water content (% by weight; 200 ° C. Karl Fischer method) has led to the finding that the moisture resistance is improved as shown in the following formula (1).
In addition, 0.5% by weight is a value obtained even without containing silicon. Moisture content (% by weight) ≦ 0.5 + A / 2 (1)

As the fluorine-based gas, fluorine gas or a mixed gas of fluorine gas and a non-oxidizing gas may be used, or magnetite particles may be mixed with a fluorine-based compound and heat-treated in a non-oxidizing gas. Absent. Fluorine-based compounds include hydrogen fluoride, hydrofluoric acid, NH ₄ F, NH ₄ HF ₂ , KHF ₂ , and NaHF.
Any hydrogen fluoride-containing compound such as ₂ and fluorinated compounds such as bromine fluoride, iodine fluoride and boron fluoride may be used.
Further, the non-oxidizing gas is used as the carrier gas because it is oxidized in the oxidizing gas as described in JP-A-4-170325, and the saturation magnetization is reduced accordingly. . The non-oxidizing gas is N ₂ , Ar,
The non-oxidizing gas such as ammonia is not limited in any way, and any gas may be used.

The heat treatment temperature is from 200 ° C to
700 ° C is preferred. This is because the effect of improving the moisture content is low at 200 ° C or lower, and industrially unfavorable at 700 ° C or higher.

Due to the above, the moisture content of the magnetic powder decreases,
Even in the high temperature and high humidity environment, the moisture content decreased obviously. This gives excellent fluidity and resistance of 1.0 x 1
The inventors have invented a magnetite having a good balance of remanent magnetization of 0 ³ Ω · cm or more and good environmental resistance. Moreover, the saturation magnetization was improved by performing the heat treatment in a fluorine-based gas.

Next, a preferred manufacturing method of the present invention will be described.

First, a silicon component is added to a solution whose main component is a ferrous salt. The ferrous salt used here is preferably ferrous sulfate, and the silicon component is preferably a solution containing a silicon colloid prepared from a silicic acid compound.

Next, 1.0 to 1.
Mix with 1 equivalent of alkali to produce ferrous hydroxide.

An oxygen-containing gas, preferably air, was blown into the ferrous hydroxide to obtain 60 to 100 ° C., preferably 8
Oxidation reaction is performed at 0 to 90 ° C. to generate seed crystals. The control of the oxidation reaction amount is performed by analyzing the unreacted ferrous hydroxide during the reaction, aeration, and adjusting the oxygen-containing gas amount. In this oxidation reaction, it is important to maintain the pH at 7-10.

During this oxidation reaction, when the amount of seed crystals produced is 1 to 30%, preferably 2 to 10% of the total amount of oxidation, 0.9 to 1.2 equivalents relative to the initial alkali. Insufficient iron, preferably 1.05 to 1.15 equivalents, is added. Examples of iron used here include ferrous sulfate such as ferrous sulfate.
Iron salt solutions are preferred.

Further, under the same conditions as above, a pH of 6 to 1 is obtained.
The oxidation reaction is continued while maintaining 0, preferably 6 to 9, particles are produced, and the particles are further washed, filtered, dried and pulverized by a conventional method to obtain magnetite particles.

In the present invention, the pH during the oxidation reaction is preferably adjusted to 6 to 10 as described above. The reason is that when the pH during the oxidation reaction is higher than the neutral range, silicon is taken inside the magnetite particles, and conversely when it is lowered, it is hard to be taken inside and can be deposited on the surface.

The present inventors observed the particle shape during the oxidation reaction, and found that the seed crystals formed in the first reaction were amorphous, but in the latter half neutral range, weak alkaline range (pH 6-9), magnetite was formed. The particles are covered with fine particles containing a silicon component and grow into particles with very large irregularities on the surface of the particles. Therefore, since fine particles containing a silicon component are present on the surface of the particles, it is possible to obtain particles having a high oil absorption and a high specific surface area.

That is, in the case of the original spherical shape, the BET (m ² / g) value should be obtained by the following equation (2),
This is because the magnetite particles generated as described above before the heat treatment have a BET value larger than that of the following formula (2). BET (m ² / g) = 6 / (particle size (μm) × 5.2) (2)

By subjecting the particles to a granulation treatment during or after drying, magnetite particles having more excellent fluidity and workability can be obtained.

Next, the obtained magnetite particles were put into a cylindrical furnace, and N ₂ gas was flown. The flow rate may be a positive pressure in the cylindrical furnace, that is, an amount that is more than the amount that prevents the inflow of air from outside. At this time, either the fluorine compound may be mixed in advance with the magnetite particles or a mixed gas of N ₂ gas and fluorine gas may be used. Next, the temperature was raised to a desired temperature (200 ° C. to 700 ° C.) and then maintained for a certain period of time. The holding time varies depending on the size of the apparatus, the capacity, and the amount added, but it is sufficient if the holding time is at least the time required to reach the desired temperature for all the added magnetite particles. Then, the mixture is cooled and granulated to obtain magnetite particles having the above characteristics.

[Examples] Preferred examples showing the effects of the present invention will be described below with reference to comparative examples.

[0048]Example 1 Fe²⁺Ferrous sulfate aqueous solution 5 containing 2.4 mol / liter 5
To 7 liters, SiO ₂28% grade sodium silicate 10
05 g was taken and added after adjusting the pH.

65 liters of 4.3 N NaOH aqueous solution and ferrous sulfate aqueous solution containing the above silicic acid component are mixed, and 40 liters / minute of air is blown while maintaining the temperature at 80 ° C., and 30 minutes is passed. Seed crystals were formed.

Next, 6.5 liters of an aqueous ferrous sulfate solution having the same composition as that at the time of seed crystal formation was added to the iron hydroxide slurry containing the seed crystal particles, and the amount of 40 liter / min was maintained while maintaining the temperature at 80 ° C. Air was blown in to promote the oxidation reaction. 12.5N NaOH from the time when pH drop was detected on the way
The reaction was terminated in 6 hours while adding an aqueous solution and maintaining the pH at 8 to 10. The produced particles were washed, filtered, dried and pulverized by a conventional method.

The amount of surface-exposed silicon component of the magnetite particles thus obtained (in terms of silicon), particle size,
The electrical resistance, residual magnetization, charge amount, fluidity, oil absorption amount, etc. were measured, and the results are shown in "Table 1". The amount of surface-exposed silicon component was measured by the above-described analysis method, and the particle size, electric resistance, etc. were measured by the following methods.

[Measurement Method] (1) Particle Size The particle size on the photograph was measured from a transmission electron micrograph (magnification: 30,000 times), and the average was taken as the particle size.

(2) 10 g of the electric resistance sample was put in a holder and a pressure of 600 kg / cm ² was applied to form a tablet shape of 25 mmφ, and then an electrode was attached to the holder.
It is measured under a pressure of 0 kg / cm ² . The electric resistance value of the magnetite particles was obtained by calculating from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.

(3) Residual Magnetization (σr) The residual magnetic field was measured with an applied magnetic field of 10 KOe using a vibrating sample magnetometer VSM-P7 manufactured by Toei Industry. And σr is 5-7
The range of Am ² / kg was designated as “medium”, those exceeding this range were designated as “high”, and those below this range were designated as “low”.

(4) Flowability The angle of repose and the degree of aggregation were measured using a powder tester made by Hosokawa Micron, and the angle of repose was 40 degrees or less as "small",
41 degrees or more was displayed as "large". Then, the smaller the angle of repose and the degree of aggregation were, the more excellent the fluidity was determined to be.

(5) Charge amount It was determined by a blow-off method using an iron powder carrier.

(6) Oil absorption It was measured according to JIS K 5101.

Examples 2 to 6 Magnetite particles were obtained in the same manner as in Example 1 except that the amount of sodium silicate added, the pH during the oxidative growth reaction, and the particle size were changed.

The properties and characteristics of these magnetite particles were measured in the same manner as in Example 1, and the results are shown in "Table 1".

Example 7 Magnetite particles were obtained in the same manner as in Example 2 except that sodium hexacarbonate was used as the alkali to form a pseudohexahedral particle shape.

The properties and characteristics of the magnetite particles are
The measurement was performed in the same manner as in "Example 1", and the results are shown in "Table 1".

Example 8 Magnetite particles were obtained in the same manner as in "Example 1" except that the pH during the oxidative growth reaction was changed to 10-12. No silicon component was present on the surface of the magnetite particles.

500 g of magnetite particles containing a silicon component only in the inside was made into a slurry of 100 g / liter, and stirring was continued while maintaining the temperature at 50 ° C. Next, 2.7 g of sodium silicate having a SiO ₂ quality of 28% was added, and after stirring for 30 minutes, 1 N H ₂ SO ₄ was gradually added to adjust the pH to 7 in 1 hour to coat the surface with a silicon component. The produced particles were washed, filtered, dried and pulverized by a conventional method.

The properties and characteristics of the magnetite particles thus obtained were measured in the same manner as in "Example 1", and the results are shown in "Table 1".

Example 9 Magnetite particles were obtained in the same manner as in "Example 8" except that the addition amount of sodium silicate was changed.

The properties and characteristics of these magnetite particles were measured in the same manner as in "Example 1", and the results are shown in "Table 1".

Comparative Example 1 Magnetite particles were obtained in the same manner as in "Example 2" except that sodium silicate was not added at all.

The properties and characteristics of the magnetite particles are
The measurement was performed in the same manner as in "Example 1", and the results are shown in "Table 1".

Comparative Example 2 Magnetite particles were obtained in the same manner as in "Example 1" except that the pH during the oxidative growth reaction was changed to 10-12. No silicon component was present on the surface of the magnetite particles.

The properties and characteristics of the magnetite particles are
The measurement was performed in the same manner as in "Example 1", and the results are shown in "Table 1".

Comparative Example 3 The surface of the magnetite particles obtained in Comparative Example 1 was coated with a silicon component according to the coating method of "Example 9".

The properties and characteristics of the magnetite particles are
The measurement was performed in the same manner as in "Example 1", and the results are shown in "Table 1".

Comparative Example 4 Magnetite particles having a surface coated with a silicon component were obtained according to the method described in JP-A-54-139544.

The properties and characteristics of the magnetite particles are
The measurement is performed in the same manner as in "Example 1", and the results are shown in "Table 1".

Comparative Example 5 According to the method described in JP-A-61-155223, magnetite particles containing a silicon component only inside the particle powder were obtained.

The properties and characteristics of the magnetite particles are
The measurement was performed in the same manner as in "Example 1", and the results are shown in "Table 1" below.

[0077]

[Table 1]

As shown in the results of "Table 1", the magnetite particles of "Examples 1 to 7" obtained by the production method of the present invention have good properties of remanence and fluidity.

In "Examples 8 and 9", the surface of magnetite particles containing silicon was coated with a silicon component by the dipping method. The electric resistance was increased as compared with "Examples 1 to 7". Although the fluidity was poor, it was within the acceptable range.

On the other hand, "Comparative Example 1" contained no silicon component at all, and therefore had a high residual magnetization relative to the particle size and was inferior in fluidity. In "Comparative Example 2", since the silicon component was contained only in the inside, the residual magnetization was low relative to the particle diameter, but the fluidity was poor. In "Comparative Examples 3 and 4", since silicon was present only on the surface, the residual magnetization was high relative to the particle diameter. "Comparative example 5" was inferior in fluidity. In addition, all the comparative examples were less effective in increasing the resistance.

As described above, since the silicon component is present both inside and on the surface, the fluidity and workability are good,
It was possible to manufacture magnetite particles having a low remanence and an increased resistance for the particle size.

Next, the reflectance was measured in order to examine the dispersibility.

(7) 1 g of dispersible magnetite and 0.7 g of linseed oil were kneaded with a Hoover type muller, 4.5 g of clear lacquer was added thereto, and they were kneaded further well. This is applied on a glass plate with a 4 mil applicator, dried and then used
The reflectance at 60 ° was measured with OSS METER (GM-3M).

Since the present invention is characterized in that the obtained magnetite is heat-treated in a fluorine-based gas, an example of the fluorine-based gas treatment will be described below.

Example 10 2 kg of magnetite particles obtained in Example 2 and NH ₄ H
39 g of F ₂ (1.3% of F with respect to magnetite) was mixed, and 2 kg of the mixed powder was put into a cylindrical furnace with a diameter of 200 mm and a length of 790 mm, and the temperature was raised to 500 ° C. while flowing nitrogen gas at 20 liters / minute. Then, it was kept for 30 minutes, cooled to room temperature and crushed.

Example 11 The procedure of Example 10 was repeated except that Example 6 was used.

Example 12 The same process as in Example 10 was performed except that Example 2 was used and the heat treatment temperature was 300 ° C.

Example 13 78 g of NH ₄ HF ₂ (F2.7 with respect to magnetite) was used.
%) And treated in the same manner as in Example 10.

Example 14 20 g of NH ₄ HF ₂ (F0.7 for magnetite) was used.
%) And treated in the same manner as in Example 10.

Comparative Examples 6 and 7 The same processes as in Example 10 were carried out except that Comparative Examples 3 and 4 were used.

The resistance value, saturation magnetization, charge amount and reflectance after heat treatment of Examples 10 to 14 and Comparative Examples 6 and 7 are shown in "Table 2" below. As a unit of saturation magnetization in the table
The "emu / g" used depends on the unit specified by the Measurement Law.
For example, "Am ² / kg" is displayed, and 1 emu / g is 1 Am ²
/ Kg is converted.

[0092]

[Table 2]

From the results of "Table 2", the heat treatment in the fluorine-containing gas lowers the resistance as compared with the original, but in "Examples 10 to 14", the resistance is 1 × 10 ³ or more, and "Comparative Example 6,"
7 ”was less than that. The specific surface area and oil absorption decreased due to removal of the outermost surface silicon. The saturation magnetization was higher than that before the heat treatment. Further, the heat treatment in the fluorine-based gas did not affect the fluidity. Furthermore, the dispersibility was improved by heat treatment in a fluorine-based gas.

Next, the moisture resistance was examined by the method shown below. Moisture content (% by weight); Karl Fischer method Mitsubishi Chemical lnd ltd WATER VAPORIZER VA
Moisture in magnetite particles at each temperature is evaporated at -05 and MOISTUR METER CA manufactured by MITSUBISHI KASEI Corpration
-03 to detect the water content in magnetite.

-Environmental conditions As the constant temperature and constant humidity machine, "LHL-111" (trade name) manufactured by TABAI ESPEC CORP was used, and the temperature was 35 ° C, 85%, 4 hours. For repeated test, the dryer "PS-222" (trade name) manufactured by TABAI ESPEC CORP was heated to 150 ° C under the following conditions. At the measurement, sampling was performed and the water content in the magnetite particles was measured by the above method. (Wt%) was measured. The results are shown in "Table 3" below. The measuring method was as follows. Sample → Dry (150 ℃) → High temperature and high humidity → Measurement (15
0 ℃ / 200 ℃) → Drying (150 ℃) → High temperature and high humidity → Measurement (150 ℃ / 200 ℃)

[0096]

[Table 3]

From the results shown in "Table 3", it was possible to greatly reduce the water content of magnetite even in an environment of high temperature and high humidity by heat-treating magnetite particles in a fluorine-based gas.

[0098]

As described above, the magnetite particles of the present invention have low remanence, good fluidity, and excellent resistance to environment while maintaining resistance above a certain level. It is suitable for copying magnetic toner.

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Claims (2)

(57) [Claims] 1. A silicon component is contained inside and the silicon component on the surface is 0.05 to 2.0% by weight in terms of silicon.
And the fluorine (F) component is magnetite.
To the particle, of 0.01 to 1.0% by weight in terms of F
The surface of the magnetite is coated in a proportion, and when the amount of silicon in the magnetite-containing silicon component converted to silicon (% by weight) under high temperature and high humidity is A, the magnetite-containing water content (% by weight) is as follows (1) Magnetite particles represented by the formula, having improved moisture resistance and having a resistance of 1 × 10 ³ Ω · cm or more. Moisture content (% by weight) ≦ 0.5 + A / 2 (1) 2. The pH is maintained at 7 to 10 after adding a silicon component to a solution containing a ferrous salt as a main component and further mixing with 1.0 to 1.1 equivalents of alkali with respect to iron. Then, the oxidation reaction is carried out, and in the middle of the reaction, it becomes 0.
After adding a deficiency of iron of 9 to 1.2 equivalents, the pH is kept at 6 to 10 to carry out an oxidation reaction, and the magnetite particles obtained by this oxidation reaction are heated to 200 ° C to 700 ° C in a fluorine-based gas. A method for producing magnetite particles, which comprises performing heat treatment in the temperature range of 1.