JP3437714B2 - 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 particularly, the amount of silicon component present on the surface (amount converted to silicon) is By controlling and heat-treating the obtained particles, various properties such as electric resistance, remanent magnetization and fluidity can be improved in a well-balanced manner, and especially environmental copying resistance material powder for electrostatic copying magnetic toner, black for paint The present invention relates to magnetite particles mainly used for pigment powder and a method for producing the same.

[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.

The present invention has been made to solve the problems of the prior arts, and has a low remanent magnetization, an electric resistance not lower than that of the current state, and excellent workability, fluidity and environment resistance. An object of the present invention is to provide magnetite particles and a method for producing the same.

[0012]

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 out that the above problems can be solved by exposing magnetite particles to obtain magnetite particles and heat-treating the particles in an inert gas.

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 in a proportion of 0.05 to 2.0% by weight in terms of silicon, and is high temperature. Under high humidity, assuming that the amount of silicon (% by weight) of the magnetite-containing silicon component converted to silicon is A, the magnetite-containing water content (% by weight) is shown by the following formula (1), and the moisture resistance is improved. And the resistance is 1 × 1
It is characterized in that it is 0 ³ Ω · cm or more. Moisture content (% by weight) ≦ 0.5 + A / 2 (1)

In the magnetite particles, B
The specific surface area (m ² / g) of magnetite particles by the ET method is
It is represented by the following formula (2), and when B is the abundance (% by weight) of the silicon component exposed on the surface converted to silicon with respect to the magnetite particles, the relationship of C / B ≧ 15 is satisfied. It is what BET (m ² / g) = 6 / (particle size (μm) × 5.2) + C (2)

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 carried out while maintaining at 10, and the magnetite particles obtained by this oxidation reaction are heated to 200 ° C. in an inert 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.

In the present invention, the magnetite has a silicon component both inside and on the surface thereof, and in particular, the amount of the silicon component exposed on the surface (amount converted to silicon) is controlled, and the obtained particles are heat treated to obtain magnetite. To get particles,
The obtained magnetite particles have various properties such as electric resistance, remanent magnetization and fluidity improved in a well-balanced manner, and have excellent environmental resistance. Especially, the material powder for electrostatic copying magnetic toner, the black pigment powder for paints. It is mainly used for and is suitable for.

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 an inert 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.

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 an inert 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.

Further, the magnetite particles of the present invention have a resistance ≧ 1.0 × 10 ³ (Ω · cm) and the specific surface area of the magnetite particles by the BET method is shown by the following formula (2). When the amount (% by weight) of the exposed silicon component converted to silicon is B, C / B ≧
It is necessary to satisfy 15 relationships. BET (m ² / g) = 6 / (particle size (mm) × 5.2) + C (2)

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.

Regarding the BET value, when the magnetite particles have a relationship of C / B <15, the resistance is not high and the resistance decreasing tendency at the time of heat treatment for environmental resistance cannot be endured 1.0 × 10. ³ (Ω · cm) or less, which is not preferable,
In addition, the liquidity also decreases.

Conventionally, particle powders having excellent dispersibility are
Generally, it has been necessary to have a small specific surface area with respect to the particle size and a low oil absorption amount. However, since the magnetite particles according to the present invention have a large unevenness coefficient of the particle surface, they have a large ratio to the particle size. It has a surface area and a high oil absorption. Since the magnetite particles of the present invention have silicon on the surface of the powder, they are easily wet with the resin, which seems to contribute to the improvement of the dispersibility.

The magnetite of the present invention is characterized by being heat-treated in an inert gas. In the past, magnetite particles having a silicon component were present on the inside and the surface part in order to have excellent dispersibility and fluidity, but due to the hygroscopicity of the silicon component, it absorbs moisture in the air and contains It had the drawback of becoming expensive. By conducting the heat treatment in an inert gas, the hygroscopic property is reduced, the above-mentioned drawbacks are solved, and the dispersibility is improved, for unknown reasons. It is considered that one of the reasons for this is that the —OH groups of the silicon components exposed inside and on the surface are removed by the heat treatment.

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)

Further, the use of an inert gas causes oxidation in an oxidizing gas as described in Japanese Patent Application Laid-Open No. 4-170325, resulting in a decrease in saturation magnetization. The inert gas is not limited as long as it is an inert gas such as N ₂ or Ar, 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. Further, the heat treatment in an inert gas improved the saturation magnetization and increased the negative charge amount value.

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 into the magnetite particles, and conversely when the pH is lowered, it is hard to be taken inside and the surface can be deposited.

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 BET 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 (3),
The particles of the magnetite particles of the present invention before heat treatment have a BET value obtained by adding C (C / B ≧ 15, B: abundance (wt%) in terms of silicon of surface-exposed silicon component) to the following formula (3). Because. BET (m ² / g) = 6 / (particle size (μm) × 5.2) (3)

In the present invention, the magnetite particles that have been produced and washed with water are granulated during or after drying to obtain magnetite particles that are more excellent in fluidity and workability. .

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. 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. After that, by cooling and granulating,
The magnetite particles having the above characteristics are obtained.

[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 silicon component exposed on the surface was measured by the above-mentioned analysis method, and the particle size, electric resistance and the like 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.
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) Remanent magnetization (σr) The residual magnetic field was measured using a vibrating sample magnetometer VSM-P7 type manufactured by Toei Industry Co., Ltd. with an applied magnetic field of 10 KOe. 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 carbonate was used as an 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.

[0078]

[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 diameter 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) Dispersible magnetite (1 g) and linseed oil (0.7 g) were kneaded with a Hoover-type Mahler, and then 4.5 g of clear lacquer was added to the mixture, which was further kneaded. 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 heat treatment is carried out in an inert gas, an embodiment using the inert gas treatment will be described below.

Example 10 2 kg of the magnetite particles obtained in Example 2 were placed in a cylindrical furnace having a diameter of 200 mm and a length of 790 mm, and the temperature was raised to 500 ° C. and kept for 30 minutes while flowing nitrogen gas at 20 liters / minute. It was cooled to room temperature and crushed.

Examples 11 and 12 The same processes as in Example 10 were carried out except that Examples 5 and 6 were used.

Example 13 The procedure of Example 10 was repeated except that Example 2 was used and the heat treatment temperature was 300 ° C.

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 13 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.

[0091]

[Table 2]

From the results of "Table 2", the heat treatment lowers the resistance as compared with the original value, but "Examples 10 to 13"
Was 1 × 10 ³ or more, and it was less than that in “Comparative Examples 6 and 7”. Moreover, the saturation magnetization and the amount of negative charge were increased compared to the original. Further, the heat treatment did not affect the fluidity. Furthermore, dispersibility was improved by heat treatment.

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 thermo-hygrostat, "LHL-111" (trade name) manufactured by TABAI ESPEC CORP was used, and the temperature was 35 ° C, 85%, and 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 ℃)

[0095]

[Table 3]

From the results of "Table 3", it was possible to greatly reduce the moisture content of magnetite even in an environment of high temperature and high humidity by heat treating magnetite particles in an inert gas.

[0097]

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.

─────────────────────────────────────────────────── --- Continuation of front page (56) Reference JP-A-7-267646 (JP, A) JP-A-62-278131 (JP, A) JP-A-5-213620 (JP, A) JP-A-7- 138023 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01G 49/00-49/08 G03G 9/00-9 / 10,9 / 16 H01F 1/00-1/375

Claims (3)

(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.
Of the magnetite-containing silicon component in the high-temperature and high-humidity condition in terms of silicon content (% by weight).
The moisture content (% by weight) of magnetite is expressed by the following equation (1), the moisture resistance is improved, and the resistance is 1 ×
Magnetite particles having a resistance of 10 ³ Ω · cm or more. Moisture content (% by weight) ≦ 0.5 + A / 2 (1) 2. The specific surface area (m ² / g) of the magnetite particles by the BET method is represented by the following formula (2), and the abundance (wt%) of the silicon component exposed on the surface with respect to the magnetite particles is calculated as silicon. ) Is B, C / B ≧
The magnetite particles according to claim 1, wherein the relationship of 15 is satisfied. BET value (m ² / g) = 6 / (particle size (μm) × 5.2) + C (2) 3. The pH is maintained at 7 to 10 after a silicon component is added to a solution containing a ferrous salt as a main component and further mixed 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 insufficient 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 an inert gas. A method for producing magnetite particles, which comprises performing heat treatment in the temperature range of 1.