JP2000351628A - Iron oxide particles and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a particle having stable degree of black in various environments, slight magnetic flocculation and excellent dispersibility, comprising Fe2+-containing iron oxide particle showing a diffraction peak having a specific strength at a specified position to a main peak of magnetite obtained by X-ray diffraction measurement. SOLUTION: This iron oxide particle comprises iron oxide in a nonmagnetic form in the interior and/or on the surface of core particle. The iron oxide particle shows a diffraction peak having >=5% strength at 2θ=32-35 deg. to the strength of the main peak of a magnetite appearing in the vicinity of 2θ=35 deg. obtained by the measurement of X-ray diffraction using CuKα1 (λ=1.540Å) as a target. The iron oxide particle contains >=18 wt.% FeO and the main component in the coated layer is α-Fe2O3. The saturation magnetization value in an external magnetic field of 10 kOe is >=75 emu/g and the degree of aggregation is <=50%. The particle is obtained by introducing an oxygen-containing gas to a Fe2+-containing ferrous salt slurry to carry out an oxidation reaction.

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, particularly, powders of magnetic toners for dry-type electronic copying machines and printers, and materials for electrostatic copying carriers. It is widely used as a raw material such as powder or black pigment powder for paint.
Among these uses, various general development characteristics are required in the use of magnetic toner, and in recent years, with the development of electrophotography technology, in particular, copiers and printers using digital technology have rapidly developed, Has become more sophisticated.

Among the above-mentioned development characteristics, a factor that affects image density and high image quality includes blackness of iron oxide particles. This blackness is "Powder and Powder Metallurgy", Vol. 26, No. 7, blackness of the black pigment in pages 239-240 can be affected by Fe ²⁺ content and particle size, Fe ²⁺ Is preferred to be at least a specific level, and various proposals have hitherto been made to improve the blackness of iron oxide particles.

[0004] For example, Japanese Patent Application Laid-Open No. Hei 3-201509,
JP-A-5-281778, JP-A-9-59024
Publications and the like include the iron oxide particles as a whole and the Fe
Proposals have been made to improve blackness by increasing the ²⁺ content.

[0005] However, it is known that Fe ^{2+ in} iron oxide particles is oxidatively degraded in various environments. With these means, although blackness immediately after production is high, it is due to wet production. If so, it is not possible to suppress the gradual oxidation of Fe ²⁺ to Fe ³⁺ from the start of the drying process to the end of the process from the toner manufacturing process to the toner formation.

Various proposals have been made to improve the deterioration in the above-mentioned various environments. For example, Japanese Patent Application Laid-Open No. 6-1
JP-A-00317, JP-A-6-310317 and JP-A-6-310318 disclose that the surface of iron oxide particles is coated with a composite oxide of iron, cobalt and zinc to improve the durability of blackness and the moisture resistance. Suggestions for improvement have been made.

[0007] However, since these means use heavy metals other than iron and the like, it is not preferable from the viewpoint of reducing environmentally hazardous substances, which has recently become a problem.

On the other hand, pigment powders, especially powders for magnetic toner, are required to have low magnetic cohesion and consequently to have excellent dispersibility.

Japanese Patent Application Laid-Open No. 6-130718 discloses that as a means for reducing the magnetic cohesion, it is necessary to reduce the residual magnetization of the iron oxide particles. As described in the official gazette, the shape of iron oxide particles is made spherical,
As described in Japanese Patent Publication No. 23, a proposal for adding an additive such as zinc has been made.

However, even with these means, the prevention of magnetic aggregation is not sufficient, and at the same time, if heavy metals other than iron are used, it is not preferable from the viewpoint of reducing environmental load substances.

Accordingly, an object of the present invention is to provide an iron oxide particle containing iron oxide as a main component, which has stable blackness in various environments, has low magnetic cohesion, and is excellent in dispersibility, and a method for producing the same. To provide.

[0012]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in iron oxide particles containing Fe ²⁺ , iron oxide in a non-magnetic form is present inside and / or on the surface of the core particles. As a result, it has been found that the above object can be achieved.

The present invention has been made based on the above findings, and is an iron oxide particle containing Fe ²⁺ , wherein Cu Kα
₁ (λ = 1.540 °) as a target, a diffraction peak having an intensity of 5% or more of 2θ = 32 with respect to the intensity of the main peak of magnetite appearing around 2θ = 35 ° obtained by X-ray diffraction measurement. The present invention provides iron oxide particles characterized by appearing at an angle of ° to 33 °.

Further, as a preferred method for producing the iron oxide particles of the present invention, when the iron oxide particles are produced by a wet method, the oxidation reaction is carried out even after the ferrous hydroxide in the reaction slurry is completely consumed. And a method for producing iron oxide particles.

[0015]

Embodiments of the present invention will be described below. The iron oxide particles referred to in the present invention are iron oxide particles containing Fe ^2+, whose core particles are preferably composed mainly of magnetite, and a beltride compound having an intermediate composition between magnetite and maghemite (Fex. Fe ₂ O
₃ , 0 <X <1) or the like.

The shape of the iron oxide particles of the present invention may be any of octahedral, hexahedral, and spherical as long as they are granular.

In consideration of the environmental load, Si, Al, M are formed inside the particles, that is, inside the core particles and on the surface of the core particles.
g, Ti, P, Mn, Zn, Co, Ni, Cr, Cu,
An element effective for improving the properties of the iron oxide particles such as Zr and Sn may be contained, and the one obtained by the surface treatment can reduce the amount of the added element while further improving the effect. . In particular, those in which a silicon component or an aluminum component is present on the surface of the core particles are effective for enhancing the fluidity of the powder, and since light elements are used, they are less likely to be affected by the environmental load, and thus are suitable.

The iron oxide particles of the present invention are the same as the iron oxide particles containing Fe ²⁺ , except that Cu Kα ₁ (λ = 1.540) is used.
2) obtained by X-ray diffraction measurement using Å) as a target
= Diffraction peak having an intensity of 5% or more with respect to the intensity of the main peak of magnetite appearing around 35 ° is 2θ =
Appears between 32 ° and 33 °.

In the iron oxide particles of the present invention, the form of the main component of the core particles and the non-magnetic iron oxide present inside and / or on the surface of the core particles are clearly different. Usually, if it is iron oxide particles containing magnetite as a main component, Cu
When X-ray diffraction measurement is performed using Kα ₁ (λ = 1.540 °) as a target, a main peak of magnetite appears around 2θ = 35 °. On the other hand, since the iron oxide particles of the present invention have a coating layer containing nonmagnetic iron oxide as a main component on the particle surface, a peak other than the main peak of magnetite, specifically, an intensity of 5% or more of the main peak. The characteristic feature is that a diffraction peak having the following expression appears at 2θ = 32 ° to 33 °.

Regarding this peak, the inside of the core particle and / or
Alternatively, it means that non-magnetic iron oxide is present on the surface. In particular, those in which a very thin nonmagnetic iron oxide coating is uniformly applied to the surface of the core particles are preferable.

If the intensity of this peak is 5% or more of the main peak intensity of magnetite, it can be observed separately from noise at the time of measurement. In addition to this peak, 2θ = 40 ° ± 0 0.5 ° or 46.5
It is preferred that another peak appears at ° ± 0.5 °.

In the case of iron oxide particles not having the above-described characteristics, for example, iron oxide particles mainly containing iron oxide containing Fe ²⁺ such as magnetite particles, it is necessary to prevent oxidation from the particle surface. In contrast, the iron oxide particles of the present invention already have a chemically stable coating in the form of Fe ^{3+ on} the particle surface, so that the core particles are shielded from the external environment and the deterioration of Fe ²⁺ progresses. Hard to do.

Also, Fe such as magnetite²⁺including
The iron oxide particles containing iron oxide as the main component alone are drying or in the air.
Fe inside²⁺From Fe³⁺When the oxidation to
_TwoO _ThreeΓ-Fe_TwoO_ThreeIs magnetic
On the other hand, according to the iron oxide particles of the present invention,
The main component in the coating is non-magnetic α-Fe_TwoO_ThreeIs that
As a result, the residual magnetization near the particle surface becomes lower,
It is presumed that gas coagulation is also reduced.

As described above, since the role of α-Fe ₂ O ₃ is important, the iron oxide particles of the present invention are composed of α-Fe ₂ O ₃
Is contained in the iron oxide particles,
-Fe ₂ O ₃ is preferably present as a major component in the particle surface coating layer.

In the iron oxide particles of the present invention, FeO is preferably at least 18% by weight, more preferably at least 20% by weight, particularly preferably at least 25% by weight. FeO is 1
If it is less than 8% by weight, the blackness of the iron oxide particles will be low.

The saturation magnetization in an external magnetic field of 10 kOe is preferably at least 75 emu / g, more preferably at least 80 emu / g. Saturation magnetization value is 75 em
If it is less than u / g, the magnetization on the developing sleeve when the toner is used becomes insufficient.

The degree of agglomeration is preferably at most 50%, more preferably at most 40%. If the agglomeration degree exceeds 50%, poor dispersion in resin at the time of conversion to toner is caused.

Next, the method for producing iron oxide particles of the present invention will be described. The method for producing iron oxide particles of the present invention is characterized in that, when producing iron oxide particles by a wet method, the oxidation reaction is continued by the wet method even after ferrous hydroxide in the reaction slurry is completely consumed. And

As a method for producing iron oxide particles by a wet method, a ferrous salt containing a ferrous hydroxide colloid obtained by neutralizing an aqueous ferrous salt solution containing Fe ²⁺ with an aqueous alkaline solution is used. In general, a method of obtaining iron oxide particles by oxidizing a slurry (hereinafter, referred to as a reaction slurry) by passing an oxygen-containing gas through the slurry is generally used. The end of the reaction in this method can be estimated by checking the amount of Fe ²⁺ remaining in the reaction slurry. However, a method of measuring the oxidation-reduction potential (ORP) and determining the end of the reaction based on the change point has been widely used. I have.

The ORP at the time of production by the above-mentioned production method is low and stable during the progress of the oxidation reaction, but rapidly increases when the residual amount of Fe ²⁺ in the reaction slurry is lower than 0.1 mol / l. Further, when the residual amount of Fe ²⁺ in the reaction slurry becomes lower than 0.01 mol / l, the increase becomes gentle, and eventually reaches the high-order stable region, and no change is observed.

The termination of the reaction by the ORP is determined at a time when a sharp change point is confirmed or at a time when the ORP enters a high stability region, as disclosed in JP-B-51-11038. Is common.

On the other hand, according to the present invention, the reaction end point is set after the ferrous hydroxide in the reaction slurry is completely consumed, that is, after the ORP exceeds the sharp change point and enters the high stability region. This is characterized in that an iron oxide coating mainly composed of α-Fe ₂ O ₃ is formed on the surface of a core particle mainly composed of iron oxide containing Fe ²⁺ such as magnetite. Of course, α-Fe ₂ on the core particle surface
The amount of coating containing O ₃ as a main component can be arbitrarily controlled by adjusting the time during which the oxygen-containing gas is passed or the amount of gas.

Further, as described above, the F
When the oxidation of e ²⁺ to Fe ³⁺ proceeds, γ-Fe ₂ O
It is considered to be transformed to _3, to it is difficult to obtain the iron oxide particles as in the present invention, the coating composed mainly of alpha-Fe ₂ O ₃ on the particle surfaces by dry means the iron oxide particles as a starting material Also, in the method of forming the particles, since heating at 500 ° C. or more is required to change the form into α-Fe ₂ O ₃ , the operation of oxidizing only the particle surface is impossible.

[0034]

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

Example 1 50 L of an aqueous solution containing 2.0 mol / l of Fe ²⁺ and 4.0 mol / l of NaOH
and 53 liters of an aqueous sodium hydroxide solution containing 1 liter. While maintaining the reaction temperature at 80 ° C., the oxidation reaction was performed by passing air at 65 L / min while stirring the ferrous hydroxide slurry. At this time, an ORP meter (Model PH82 series manufactured by Yokogawa Electric Corporation, OR
A P electrode (K9220YL) was inserted to check the oxidation state of ferrous hydroxide. Ferrous hydroxide is completely consumed and O
After confirming that the RP potential was higher than -200 mV and that the rate of change was 10 mV / min or less, air was continuously passed through the reaction vessel at 65 L / min, and
A peroxidation reaction was performed for 0 minutes. The obtained slurry was subjected to ordinary filtration, washing, drying, and pulverization to obtain iron oxide particles containing magnetite as a main component.

The iron oxide particles were measured and evaluated (particle shape, specific surface area, magnetic properties, FeO content, agglomeration degree) by the following methods, and the results are shown in Table 1. In addition, X-ray diffraction was measured,
The result is shown in FIG. (1) Particle shape The particle shape was observed with a scanning electron microscope. (2) Specific surface area Measured with a 2200 type BET meter manufactured by Shimadzu-Micromeritex. (3) Magnetic properties Using a vibration type magnetometer VSM-P7 manufactured by Toei Kogyo Co., the magnetic properties were measured at an external magnetic field of 10 kOe. (4) FeO content The sample was dissolved in sulfuric acid, and measured by redox titration using a potassium permanganate standard solution. The deterioration test was performed by exposing a sample immediately after production to an environment of 60 ° C. and 90% RH for 28 days, and measuring the FeO content in the sample. (5) Agglomeration degree Powder T manufactured by Hosokawa Micron
Oscillation time was set to 6 using ester TypePT-E.
It was measured at 5 seconds. The measurement results were used to determine the degree of agglomeration using a predetermined formula. (6) X-ray diffraction measurement It was measured under the following measurement conditions.・ X-ray generation: Cu K-α1 line / 40 kV / 26 mA ・ Goniometer: RINT2000 vertical goniometer ・ Diverging slit, scattering slit: 1 deg ・ Receiving slit: 0.15 mm ・ Counter: scintillation counter ・ Scan speed: 2 ° / min ・Scan step: 0.01 °

[Example 2] The alkaline aqueous solution to be initially mixed was 45 liters, the pH during the oxidation reaction was maintained at 6.3, and after confirming the ORP potential, air was continuously passed through the reactor at 20 liters / min for 30 minutes. Iron oxide particles containing magnetite as a main component were obtained in the same manner as in Example 1 except that the peroxidation reaction was performed. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 50 L of an aqueous solution containing 2.0 mol / l of Fe ²⁺ and 4.0 mol / l of NaOH
52 liters of an aqueous alkaline solution containing 1 liter were mixed and stirred. The reaction temperature was maintained at 78 ° C., and the oxidation reaction was carried out by passing air at a rate of 40 L / min while stirring the ferrous hydroxide slurry. The oxidation state of ferrous hydroxide was confirmed using an ORP meter in the same manner as in Example 1, and the ORP potential was -300.
Air ventilation was stopped at the time of mV. At this point, unreacted Fe ²⁺ remaining in the slurry was 0.2 g / l. 2.3 liters of an aqueous solution containing 1.01 mol / l of Fe ²⁺ and 0.44 mol / l of Si ⁴⁺ was added to this slurry, and an oxidation reaction was carried out at 20 liters / min while maintaining pH 8 by passing air through. Was. The ORP potential of this slurry was higher than -200 mV, and the rate of change was 1
After confirming that the pressure was 0 mV / min or less, a peroxidation reaction was continuously performed for 15 minutes by passing air at 20 L / min through the reaction tank. The obtained slurry is subjected to ordinary filtration,
Washing, drying and grinding were performed to obtain iron oxide particles containing magnetite as a main component. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 An aqueous solution to be added after the oxidation reaction was once stopped was changed to 1.01 mol / l of Fe ²⁺ and Al
Iron oxide particles containing magnetite as a main component were obtained in the same manner as in Example 3 except that an aqueous solution containing 0.44 mol / l of ³⁺ was used. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0040] Example 5 air aeration during the initial oxidation reaction and 70 l / min, a 1.27 mol / l and Zn ²⁺ aqueous solution of Fe ²⁺ to be added after stopping the oxidation reaction once 0 Iron oxide particles containing magnetite as a main component were obtained in the same manner as in Example 3 except that the aqueous solution contained 0.5 mol / l. Various characteristics were evaluated in the same manner as in Example 1,
Table 1 shows the results.

[Comparative Example 1] The oxidation state of ferrous hydroxide was confirmed using an ORP meter, and when the ORP potential was -300 mV, the ventilation of air was stopped and the reaction was terminated. Similarly, magnetite particles were obtained. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1. Also,
X-ray diffraction was measured, and the results are shown in FIG.

[Comparative Example 2] The oxidation state of ferrous hydroxide was confirmed using an ORP meter, and when the ORP potential was -300 mV, the ventilation of air was stopped and the reaction was terminated. Similarly, magnetite particles were obtained. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0043]

[Table 1]

As is clear from the results in Table 1, Example 1
The iron oxide particles mainly composed of magnetite of No. 5 to No. 5 have stable blackness and small magnetic aggregation as compared with the magnetite particles of Comparative Examples 1 and 2. Further, as shown in FIG. 1, in Example 1, a diffraction peak having an intensity of 5% or more with respect to the intensity of the main peak of magnetite appearing around 2θ = 35 ° appeared at 2θ = 32 ° to 33 °. But,
In Comparative Example 1 shown in FIG. 2, such a diffraction peak did not appear. Although not shown, in Examples 2 to 5,
However, Comparative Example 2 did not show such diffraction peaks as in Comparative Example 1.

[0045]

As described above, the iron oxide particles of the present invention have a stable blackness in a seed environment, have low magnetic cohesion, and are excellent in dispersibility. Material powder, carrier material powder for electrostatic latent image development,
It is suitable for applications such as black pigment powder for paints. 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 an X-ray diffraction chart in Example 1.

FIG. 2 is an X-ray diffraction diagram in Comparative Example 1.

Claims (6)

[Claims] 1. An iron oxide particle containing Fe ²⁺ ,
A diffraction peak having an intensity of 5% or more with respect to the intensity of the main peak of magnetite appearing around 2θ = 35 ° obtained by X-ray diffraction measurement using Cu Kα ₁ (λ = 1.540 °) as a target was 2θ. = Iron oxide particles characterized by appearing at 32 ° to 33 °. 2. The iron oxide particles according to claim 1, comprising magnetite as a main component. 3. The iron oxide particles according to claim 1, comprising α-Fe ₂ O ₃ . 4. The iron oxide particles according to claim 1, which has a coating layer mainly composed of α-Fe ₂ O ₃ on the surface. 5. The iron oxide particles according to claim 1, wherein the FeO particles have a saturation magnetization of not less than 75 emu / g and an agglomeration degree of not more than 50% in an external magnetic field of 10 wt. 6. The method of producing an iron oxide particle according to claim 1, wherein when the iron oxide particles are produced by a wet method, the oxidation reaction is continued by the wet method even after the ferrous hydroxide in the reaction slurry is completely consumed. Production method.