JP2001106529A - Iron oxide particle and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce octahedral iron oxide particles which have high FeO content, do not injure heat resistance and tinge, are low in residual magnetization and are little in magnetic flocculation. SOLUTION: This iron oxide particles have an octahedral shape, an average grain size of 0.05-0.5 μm and FeO content of >=24 wt.%. Therein, the following equation (1) is satisfied between the residual magnetization σr (emu/g) at an external magnetic field of 10 kOe and the average grain size d (μm): σr<=-26d+16 (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to iron oxide particles suitable for a material powder for an electrostatic copying magnetic toner, a material powder for an electrostatic copying carrier, or a black pigment powder for a paint, and a method for producing the same.

[0002]

2. Description of the Related Art Iron oxide particles including magnetite particles produced by an aqueous solution reaction are used in various fields, in particular, material powders for magnetic toners for dry-type electronic copying machines and printers, and material powders for electrostatic copying carriers. Or, it is widely used as a raw material such as black pigment powder for paints. Among these applications, various general development characteristics are required for magnetic toner applications, and in recent years, with the development of electrophotography technology, in particular, copiers and printers using digital technology have rapidly developed, and the required characteristics have been increased. It has become more sophisticated.

Some copiers and printers have a capacity of more than 1200 dots per inch, and the latent image on the photoreceptor is becoming finer. It is one of the required characteristics.

[0004] JP-A-3-122658 and JP-A-6-130718 disclose that it is preferable that the magnetic aggregation of iron oxide particles is small in order to improve such image characteristics.

Various techniques for reducing the residual magnetization of iron oxide particles have been disclosed as means for reducing the magnetic cohesion.
As described in Japanese Patent No. 30718, there is a proposal of making the shape of iron oxide particles spherical.

According to the technique described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 6-130718, spherical particles certainly have advantages such as excellent fluidity, so that they are effective in improving magnetic aggregation. However, on the other hand, it also has disadvantages such as free powder falling off from the toner at the time of pulverization in the production of toner.

On the other hand, octahedral iron oxide particles have the property of compensating for such disadvantages. However, in the conventional product, magnetic cohesion is large due to the large residual magnetization, and the fine line reproducibility in the above-mentioned development is high. What could be improved could not be obtained.

Accordingly, an object of the present invention is to provide a high FeO content without impairing heat resistance and color, low remanence,
It is an object of the present invention to provide octahedral iron oxide particles having low magnetic cohesion and a method for producing the same.

[0009]

As described above, the octahedral iron oxide particles according to the prior art have a large magnetic cohesion due to a large remanent magnetization. In order to solve the problem, it was inferred that iron oxide particles in which the magnetism on the particle surface was weakened while maintaining the characteristics inside the particles would be suitable.

The present inventors have made intensive studies on such inferences and found that the above object was achieved by providing a specific double coating on the particle surface as a means for lowering the remanent magnetization without impairing the properties inside the particle. I knew that I could get it.

[0011] The present invention has been made based on the above findings, and has an octahedral particle shape and an average particle size of 0.05 to 0.05.
0.5 μm, FeO content is 24% by weight or more, and residual magnetization σr (emu / g) at an external magnetic field of 10 kOe
Satisfies the following expression (1) with respect to an average particle diameter d (μm). σr ≦ −26d + 16──── (1)

Further, as a preferred method for producing the iron oxide particles of the present invention, the pH of a slurry obtained by mixing an aqueous solution of ferrous salt containing an aqueous solution of silicate and an aqueous solution of alkali is adjusted to 10%.
While maintaining the above conditions, an oxygen-containing gas is passed to perform the first-stage oxidation reaction. After the oxidation reaction is completed, an aqueous ferrous salt solution containing zinc is added to the obtained slurry containing iron oxide particles, and p
The pH was adjusted to 6 to 9 to perform the second-stage oxidation reaction. Further, an aqueous ferrous salt solution containing silicate was added, and the pH was adjusted to 6 to 9 to perform the third-stage oxidation reaction. An object of the present invention is to provide a method for producing iron oxide particles, which comprises subjecting iron oxide particles to heat treatment in an oxidizing atmosphere.

[0013]

Embodiments of the present invention will be described below. The iron oxide particles of the present invention have an octahedral particle shape, an average particle size of 0.05 to 0.5 μm, and an FeO content in the iron oxide particles of 24% by weight or more.

When the average particle size of the iron oxide particles is less than 0.05 μm, it is difficult to reduce the residual magnetization, and when the average particle size exceeds 0.5 μm, the density of the toner decreases. If the FeO content is less than 24% by weight, the saturation magnetization is reduced and the blackness is also inferior.

Further, the iron oxide particles of the present invention have an external magnetic field of 1
It is necessary that the following expression (1) is satisfied between the residual magnetization σr (emu / g) at 0 kOe and the average particle diameter d (μm). σr ≦ −26d + 16──── (1)

In the conventional octahedral iron oxide particles, the residual magnetization is large as described above. This fact is also shown in FIG. 1 described later. In order to reduce the large remanent magnetization, it is effective to include an additive component other than iron oxide in the iron oxide particles, or to perform a dry treatment to adjust the magnetism of the particle surface. The addition of such means directly to the particles impairs other important properties.

For example, when a silicon component is contained or covered as a means for containing an additive component, heat resistance and fluidity are improved, but when the silicon component is excessive, the balance of magnetic properties is lost, This may lead to poor environmental resistance. In addition, when the treatment is performed under an inert gas as a means of the dry treatment, it is possible to suppress the decrease in the saturation magnetization and the blackness, but there is a problem that the cost is high, and the magnetization of the particle surface is large and magnetic aggregation is likely to occur. .

The iron oxide particles of the present invention are characterized by having a small residual magnetization without impairing the above-mentioned general characteristics.

Therefore, the iron oxide particles not satisfying the above formula (1) have a large remanent magnetization at the level of the conventional octahedral iron oxide particles, and the magnetic cohesion is not improved.

The iron oxide particles of the present invention can be used in air at 150
The reduction rate of FeO content (FeO degradation rate) before and after heat treatment at 2 ° C. for 2 hours is preferably 20% or less, more preferably 15% or less, and particularly preferably 10% or less. FeO
When the deterioration rate exceeds 20%, the color becomes poor and the heat resistance becomes poor. The FeO deterioration rate here is shown below.

FeO degradation rate = [(FeO content before heating−
FeO content after heating) / FeO content before heating] × 100

Further, the iron oxide particles of the present invention can be used in air in air.
The hue change ΔE shown below before and after the heat treatment at 50 ° C. for 2 hours is preferably 0.5 or less, more preferably 0.4 or less. If the change in hue ΔE exceeds 0.5, the heat resistance will be poor.

[0023]

(Equation 1)

The iron oxide particles of the present invention contain silicon inside the particles, and the content thereof is S with respect to the total amount of the iron oxide particles.
0.1 to 3% by weight in terms of i, and the surface layer of the particles has a lower coating composed of a compound of zinc and iron and an upper coating composed of a compound of silicon and iron.

The silicon content inside the particles is important for reducing the residual magnetization without deteriorating characteristics such as saturation magnetization, and is 0.1% in terms of Si with respect to the total amount of iron oxide particles.
If the amount is less than 3% by weight, the above effect cannot be obtained. If the amount exceeds 3% by weight, the saturation magnetization decreases.

If the lower layer coating composed of a compound of zinc and iron and the upper layer coating composed of a compound of silicon and iron do not exist on the surface of the particles, heat resistance is lacking. It is difficult to stabilize other characteristics such as blackness.

The content of zinc in the lower layer coating made of the compound of zinc and iron is preferably 0.1 to 1% by weight, calculated as Zn, based on the total amount of iron oxide particles.
More preferably, it is 0.7% by weight. Further, the proportion of zinc in the lower layer coating is preferably 7 to 50 mol%, more preferably 10 to 40 mol%, based on the iron in the lower layer coating.

Further, the content of silicon in the upper layer coating made of a compound of silicon and iron is expressed as S to the total amount of iron oxide particles.
It is preferably 0.05 to 0.5% by weight, and more preferably 0.1 to 0.4% by weight in terms of i.
Further, the ratio of silicon in the upper layer coating is preferably 10 to 80 mol% with respect to iron in the upper layer coating, and
More preferably, it is 0 mol%.

The form of the iron oxide particles of the present invention includes magnetite (Fe ₃ O ₄ ) and maghemite (γ-F
e ₂ O ₃ ) and a belt-ride compound (Fe
Ox.Fe ₂ O ₃ , 0 <X <1), and a single compound or a composite compound of these compounds with Al, Mn, N other than Fe, Si, and Zn.
Spinel ferrite particles containing at least one of i, Cu, Mg, Ti, Co, Zr, W, Mo, P and the like may be selected according to the required characteristics.

Further, in order to improve dispersibility, Al
Iron oxide particles containing components or the like, or having a surface treatment coating with an organic treatment agent or the like may be used.

The coating of the surface of the iron oxide particles in the present invention is considered to have a corresponding effect even if only a compound of zinc and iron and a compound of silicon and iron are present on the surface of the core particles. Needless to say, a coating layer is more preferable.

The above-described compounds of zinc and iron and the compounds of silicon and iron exhibit effects regardless of the form. However, when the iron component is oxidized in the presence of zinc and silicon, it takes in zinc and silicon, Alternatively, it is more preferable to be a bound iron oxide, a so-called composite iron oxide.

Next, a method for producing iron oxide particles of the present invention will be described. In the method for producing iron oxide particles of the present invention, an oxygen-containing gas is passed while maintaining the pH of a slurry obtained by mixing a ferrous salt aqueous solution containing a silicate aqueous solution and an alkaline aqueous solution at 10 or more. A one-stage oxidation reaction is performed, and after the oxidation reaction is completed, an aqueous ferrous salt solution containing zinc is added to the obtained slurry containing the iron oxide particles, and the pH is adjusted to 6 to 9 to perform the second-stage oxidation reaction. Further, an aqueous ferrous salt solution containing silicate is further added, and the pH is adjusted to 6 to 9 to perform a third-stage oxidation reaction, and the obtained iron oxide particles are heat-treated in an oxidizing atmosphere. And

The iron oxide particles of the present invention must contain a silicon component in order to reduce the residual magnetization. Further, since it must have an octahedral shape, the oxygen-containing gas is passed while maintaining the pH of the slurry obtained by mixing the aqueous ferrous salt solution containing the aqueous silicate solution and the aqueous alkali solution at 10 or more. It is important to carry out the first-stage oxidation reaction. Therefore, if this condition is not satisfied, iron oxide particles having an octahedral shape and low remanence cannot be produced.

Further, an aqueous solution of ferrous salt containing zinc is added to the slurry containing the core particles to adjust the pH to 6 to 9 to perform an oxidation reaction, and further, an aqueous solution of ferrous salt containing silicate is added. , PH 6 to 9, and the oxidation reaction is performed, whereby the iron oxide particles can be given heat resistance that can be used in combination with dry treatment in air.

Here, when the double coating is not performed or the order of coating is changed, the effect of lowering the residual magnetization is reduced, and the hue and fluidity of the iron oxide particles are deteriorated.

Further, by performing the heat treatment in an oxidizing atmosphere, the magnetization of the particle surface can be weakened, and as a result, it is possible to obtain iron oxide particles with small magnetic cohesion. The processing conditions at this time are as follows.
A method of treating at 0 to 300 ° C. for about 1 to 6 hours is also preferable from the viewpoint of manufacturing cost.

[0038]

The present invention will be specifically described below with reference to examples.

Example 1 A 50 liter aqueous solution containing 2.0 mol / l of Fe ²⁺ was mixed with water-soluble silicate as Si.
20 liter of an aqueous solution containing 0.288 mol / l of ⁴⁺ was added, and the mixture was stirred and mixed with 42 liter of an aqueous solution containing 5.0 mol / l of NaOH. The residual NaOH in the obtained slurry was 3.2 g / l. While maintaining the temperature of the slurry at 90 ° C., air was supplied at 65 liter / min.
Oxidation was performed by aeration to obtain magnetite core particles (first-stage oxidation reaction).

The obtained slurry was added with 0.28 mol of Fe ²⁺ .
0.11m of ferrous sulfate aqueous solution containing 1 / l and Zn ²⁺
ol / l mixed aqueous solution with zinc sulfate aqueous solution 2.2
Five liters were added, the mixture was oxidized by passing air while maintaining the pH of the mixed slurry at 8.5 and the temperature at 90 ° C., and the surface was coated with a compound of zinc and iron (second stage oxidation reaction).

Further, Fe was added to the slurry thus obtained.
Ferrous sulfate aqueous solution containing 1.01 mol / l of ²⁺
2.25 L of an aqueous solution mixed with an aqueous solution of sodium silicate containing 0.44 mol / l of i ⁴⁺ was added, and while maintaining the pH of the mixed slurry at 8.5 and the temperature at 90 ° C., air was passed to oxidize. Then, the surface was covered with a compound of silicon and iron (third stage oxidation reaction).

The thus obtained slurry of magnetite particles is filtered, washed and dried in a usual manner to obtain magnetite particles. Drying here means that water in the washed cake is blown off at 100 ° C. or less, and the water loss in the powder is 100
C., up to less than 0.5% by weight in 1 hour. After that, heat treatment was performed by keeping the film in the air at 150 ° C. for 2 hours, and then pulverization was performed.

With respect to the magnetite particles having the coating layer thus obtained, the average particle diameter, the inside of the particles relative to the total iron oxide particles and the total silicon quality were determined by the following method.
The FeO grade before and after the heat treatment with zinc, the FeO degradation rate, the magnetic properties, the hue of the powder, and the specular reflectance were evaluated, and the value of equation (1) was determined. The results are shown in Tables 2 and 3.
Shown in FIG. 1 is a graph showing the relationship between the average particle size and the residual magnetization. FIG. 2 shows the relationship between the heat treatment time (heat treatment temperature of 150 degrees) and the deterioration rate of FeO.

[Measurement Method] (1) Average Particle Size Obtained by observing with a scanning electron microscope and measuring the Feret diameter of 100 particles. (2) Silicon Grade Inside Particles Based on Total Magnetite Particles A 0.9 g sample is weighed, and 25 ml of a 1N NaOH solution is added. The liquid is heated to 45 ° C. with stirring to dissolve the silicon component on the particle surface. The undissolved matter obtained by filtration was sufficiently washed, dried, weighed, dissolved in a mixed solution of hydrochloric acid and hydrofluoric acid, and measured by ICP. (3) Total silicon quality The sample was dissolved in a mixed solution of hydrochloric acid and hydrofluoric acid and measured by ICP. (4) Zinc quality After dissolving the sample in acid, it was measured by ICP. (5) FeO quality The oxidation-reduction titration method using a potassium permanganate standard solution was performed. (6) Degradation rate of FeO FeO before and after heat treatment at 150 ° C for 2 hours in air
It was determined from the quality based on the following formula. FeO degradation rate = [(FeO grade before heating-FeO grade after heating) / FeO grade before heating] x 100 (7) Magnetic properties Using a vibration sample type magnetometer VSM-P7 manufactured by Toei Kogyo Co., Ltd., an external magnetic field of 10 kOe and 1 kOe The sample after the heat treatment was measured. (8) Value of Equation (1) Calculated from the average particle diameter and the residual magnetization value obtained in the evaluations of (1) and (7). (9) Color of powder 1.4 g of castor oil was added to 2.0 g of magnetite particles, and kneaded with a Hoover-type muller. 7.5 g of lacquer was added to 2.0 g of the kneaded sample, and further kneaded. This was applied onto a mirror-coated paper using a 4 mil applicator, dried, and measured with a color difference meter (color analyzer TC-1800, manufactured by Tokyo Denshoku Co., Ltd.). (10) Specular reflectance styrene acrylic resin (TB-100F)
60 g of the solution dissolved in toluene = 1: 2), 10 g of the sample after heat treatment, and 90 g of glass beads having a diameter of 1 mm were placed in a bottle having an internal volume of 140 ml, and the bottle was covered with a paint shaker (manufactured by Toyo Seiki). Mix for 30 minutes. This was applied to a glass plate using a 4 mil applicator, dried, and then measured for blackness and murakami GLOS using a color difference meter.
The reflectance at 60 degrees was measured with S METER (GM-3M).

Examples 2 to 4 and Comparative Examples 1 to 6 As shown in Table 1, magnetite particles were produced in the same manner as in Example 1 except that various production conditions were changed. Table 2 shows the results of evaluating various properties and characteristics in the same manner as in Example 1. The heat treatment time (heat treatment temperature 150 ° C.) and F
FIG. 2 shows the relationship between the eO deterioration rates.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

As shown in Tables 2 and 3 and FIG. 1, the magnetite particles of Examples 1 to 4 had a higher FeO content than the magnetite particles of Comparative Examples 1 to 5, and exhibited heat resistance and color. There is no loss and the residual magnetization corresponding to the particle size is low. Further, as shown in FIG. 2, the magnetite particles of Examples 1, 2, and 4 have a smaller FeO degradation rate with respect to the heat treatment time than the magnetite particles of Comparative Examples 1 to 3. Further, the magnetite particles of Examples 1 to 4 are comparative examples 1 to 4.
Compared with the magnetite particles of No. 5, the dispersibility due to the specular reflectance was improved, and it is presumed that the magnetic aggregation was improved.

[0050]

As described above, the iron oxide particles of the present invention are octahedral in shape, have a high FeO content, do not impair heat resistance and tint, have low residual magnetization, and have low magnetic cohesion. Further, the iron oxide particles can be easily obtained on an industrial scale by the production method of the present invention.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an average particle diameter and a residual magnetization (σr) in Examples and Comparative Examples.

FIG. 2 is a graph showing the relationship between the heat treatment time and the FeO degradation rate in the examples and comparative examples (heat treatment temperature of 150;
° C).

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Claims (4)

[Claims] The present invention has an octahedral particle shape, an average particle size of 0.05 to 0.5 μm, an FeO content of 24% by weight or more, and a residual magnetization σr (e) in an external magnetic field of 10 kOe.
mu / g) and the average particle diameter d (μm) are as follows:
Iron oxide particles characterized by satisfying the following. σr ≦ −26d + 16──── (1) 2. The reduction rate of the FeO content before and after the heat treatment at 150 ° C. for 2 hours in air is 20% or less;
And a change ΔE in hue of the powder is 0.5 or less.
The iron oxide particles according to the above. 3. Particles containing silicon, the content of which is 0.1 to 3% by weight in terms of Si with respect to the total amount of iron oxide particles, and a compound of zinc and iron in the surface layer of the particles. The iron oxide particles according to claim 1 or 2, having a lower coating and an upper coating made of a compound of silicon and iron. 4. A slurry obtained by mixing an aqueous ferrous salt solution containing an aqueous silicate solution and an aqueous alkaline solution has a pH of 1
A first-stage oxidation reaction is performed by passing an oxygen-containing gas while maintaining at 0 or more, and after the oxidation reaction is completed, a ferrous salt aqueous solution containing zinc is added to the obtained slurry containing iron oxide particles,
The pH was adjusted to 6 to 9, and the second-stage oxidation reaction was performed. Further, an aqueous ferrous salt solution containing silicate was added, and the pH was adjusted to 6 to 9 to perform the third-stage oxidation reaction. A method for producing iron oxide particles, comprising subjecting iron oxide particles to a heat treatment in an oxidizing atmosphere.