JP3645124B2 - Iron oxide particles and method for producing the same - Google Patents

Description

【００４４】
表１の結果から明らかなように、実施例１〜５のマグネタイトを主成分とする酸化鉄粒子は、比較例１〜２のマグネタイト粒子に比較して、安定した黒色度を有し、かつ磁気凝集が小さい。また、図１に示されるように、実施例１は２θ＝３５°付近に現れるマグネタイトのメインピークの強度に対し、５％以上の強度を有する回折ピークが２θ＝３２°〜３３°に現れたが、図２に示される比較例１ではこのような回折ピークが現れなかった。図示しないが、実施例２〜５では実施例１と同様の回折ピークが現れたが、比較例２は比較例１と同様にこのような回折ピークは現れなかった。
【００４５】
【発明の効果】
以上説明したように、本発明の酸化鉄粒子は、各種環境中において安定した黒色度を有し、かつ磁気凝集が小さく、分散性に優れるため、特に静電複写磁性トナー用材料粉、静電潜像現像用キャリア用材料粉、塗料用黒色顔料粉等の用途に好適である。また、本発明の製造方法によって、上記酸化鉄粒子が、簡便に、かつ工業的規模で得られる。
【図面の簡単な説明】
【図１】図１は、実施例１におけるＸ線回折図。
【図２】図２は、比較例１におけるＸ線回折図。[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to iron oxide particles suitable for electrostatic copying magnetic toner material powder, electrostatic copying carrier material powder, or black pigment powder for paint, and a method for producing the same.
[0002]
[Prior art and problems to be solved by the invention]
Iron oxide particles such as magnetite particles produced by aqueous solution reaction are widely used as raw materials in various fields, especially magnetic toner material powders for dry electronic copying machines and printers, electrostatic copying carrier material powders, and black pigment powders for paints. It's being used. Among these applications, magnetic toners require various general development characteristics. In recent years, with the development of electrophotographic technology, copiers and printers using digital technology have developed rapidly, and the required characteristics. Has become more advanced.
[0003]
Among the above development characteristics, the factor that affects the image density and high image quality is the blackness of the iron oxide particles. Regarding the blackness, in “Powder and Powder Metallurgy”, Vol. 26, No. 7, pp. 239-240, the blackness of the black pigment depends on the Fe ²⁺ content and the particle size, and Fe ²⁺ There is a description that it is preferable to be above a specific level, and various proposals have been made to improve the blackness of iron oxide particles.
[0004]
For example, in JP-A-3-201509, JP-A-5-281778, JP-A-9-59024, etc., the blackness is increased by increasing the Fe ²⁺ content of the entire iron oxide particles or the specified part. There are proposals to improve this.
[0005]
However, it is known that Fe ^{2+ in} iron oxide particles is oxidatively deteriorated in various environments. With these means, although blackness immediately after production is high, if it is due to wet production, it is dried. It cannot be suppressed that the oxidation from Fe ²⁺ to Fe ³⁺ progresses gradually from the toner manufacturing process to after the toner production.
[0006]
Various proposals have also been made to improve the deterioration in the various environments. For example, in JP-A-6-100317, JP-A-6-310317, JP-A-6-310318, etc., the surface of the iron oxide particles is coated with a complex oxide of iron, cobalt, and zinc to achieve blackness. Proposals have been made to improve durability and moisture resistance.
[0007]
However, since these means use heavy metals other than iron, they are not preferable from the viewpoint of reducing environmentally hazardous substances, which has been considered a problem recently.
[0008]
On the other hand, as a characteristic required for pigment powder, particularly magnetic toner material powder, magnetic aggregation is small, and as a result, it has excellent dispersibility.
[0009]
As a means for reducing the magnetic aggregation, it is described in JP-A-6-130718 that the residual magnetization of the iron oxide particles needs to be reduced, but a representative means is described in the same publication. There are proposals for making the shape of the iron oxide particles spherical as described above, or for containing an additive such as zinc as described in JP-A-4-187523.
[0010]
However, even with these means, the prevention of magnetic aggregation is insufficient, and at the same time, if heavy metals other than iron are used, it is not preferable from the viewpoint of reduction of environmental load substances.
[0011]
Accordingly, an object of the present invention is to provide iron oxide particles mainly composed of iron oxide having stable blackness in various environments, small magnetic aggregation, and excellent dispersibility, and a method for producing the same. It is in.
[0012]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that in the iron oxide particles containing Fe ²⁺ , the above object can be achieved by making iron oxide in a nonmagnetic form exist on the surface of the core particles. did.
[0013]
The present invention has been made based on the above knowledge, and has iron oxide particles containing Fe ²⁺ having a coating layer mainly containing nonmagnetic iron oxide on the surface of core particles mainly containing magnetite. A diffraction peak having an intensity of 5% or more with respect to the intensity of the main peak of magnetite appearing in the vicinity of 2θ = 35 ° obtained by X-ray diffraction measurement using Cu Kα1 (λ = 1.54s0Å) as a target. Appears in 2θ = 32 ° to 33 °, and provides iron oxide particles.
[0014]
In addition, as a preferred method for producing iron oxide particles of the present invention, when producing iron oxide particles by a wet method, oxidation is performed while confirming the oxidation state of ferrous hydroxide in the reaction slurry with an oxidation-reduction potential (ORP). Iron oxide particles characterized in that the oxidation reaction is continued by a wet method until the rate of change of ORP reaches 10 mV / min after the reaction is performed and ORP enters the high stable region and ferrous hydroxide is completely consumed The manufacturing method of this is provided.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The iron oxide particles referred to in the present invention, there is provided a iron oxide particles containing Fe ^2+, are those core particles composed mainly of magnetite, berthollide compound of intermediate composition other magnetite and maghemite (Fex · Fe ₂ O ₃ , 0 <X <1) or the like may be used.
[0016]
Moreover, the shape of the iron oxide particles of the present invention may be octahedral, hexahedral, or spherical as long as it is granular.
[0017]
In consideration of the environmental load, Si, Al, Mg, Ti, P, Mn, Zn, Co, Ni, Cr, Cu, Zr, Sn, etc. inside the particle, that is, inside the core particle or on the surface of the core particle An element effective for improving the properties of the iron oxide particles may be contained, and those obtained by surface treatment can further reduce the amount of added elements 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 in enhancing the fluidity of the powder, and since light elements are used, they are less affected by the environmental load and are preferable.
[0018]
The iron oxide particles of the present invention are magnetite particles that appear in the vicinity of 2θ = 35 ° obtained by X-ray diffraction measurement using Cu Kα ₁ (λ = 1.540Å) as a target in iron oxide particles containing Fe ^2+. A diffraction peak having an intensity of 5% or more appears at 2θ = 32 ° to 33 ° with respect to the intensity of the main peak.
[0019]
In the iron oxide particles of the present invention, the non-magnetic iron oxide present in the main component and the core particles child table surface of the core particles are those that vary revealed forms. Usually, in the case of iron oxide particles mainly composed of magnetite, when X-ray diffraction measurement is performed using Cu Kα ₁ (λ = 1.540 mm) as a target, the main peak of magnetite is around 2θ = 35 °. appear. On the other hand, since the iron oxide particles of the present invention have a coating layer mainly composed of nonmagnetic iron oxide on the particle surface, peaks other than the main peak of magnetite, specifically an intensity of 5% or more of the main peak. It is a feature that a diffraction peak having a value appears at 2θ = 32 ° to 33 °.
[0020]
This peak is meant that the presence of iron oxide in the non-magnetic form core particles child table surface. In particular, it is preferable that the core particle surface is uniformly coated with a very thin nonmagnetic iron oxide coating.
[0021]
Further, if the intensity of this peak is 5% or more with respect to the main peak intensity of magnetite, it can be observed separately from noise during measurement. In addition to this peak, 2θ = 40 ° ± 0.5 °. Alternatively, it is preferable that another peak appears at 46.5 ° ± 0.5 °.
[0022]
Iron oxide particles that do not have the characteristics as described above, for example, iron oxide particles that are mainly composed of iron oxide containing Fe ²⁺ such as magnetite particles cannot prevent oxidation from the particle surface. On the other hand, since the iron oxide particles of the present invention already have a chemically stable coating in the form of Fe ^{3+ on} the particle surface, the core particles are shielded from the external environment and the deterioration of Fe ²⁺ does not easily proceed.
[0023]
Further, when iron oxide particles containing iron oxide containing Fe ²⁺ as a main component such as magnetite alone are oxidized from Fe ²⁺ to Fe ³⁺ during drying or in the air, γ-Fe ₂ O ₃ Although γ-Fe ₂ O ₃ is magnetic, the main component in the coating is non-magnetic α-Fe ₂ O ₃ according to the iron oxide particles of the present invention. It is presumed that the residual magnetization in the vicinity of the particle surface is lowered, and as a result, the magnetic aggregation is also reduced.
[0024]
Thus, since the role of α-Fe ₂ O ₃ is important, the iron oxide particles of the present invention are characterized by containing α-Fe ₂ O ₃ in the iron oxide particles. -Fe ₂ O ₃ is preferably present as a main component in the particle surface coating layer.
[0025]
The iron oxide particles of the present invention preferably contain FeO in an amount of 18% by weight or more, more preferably 20% by weight or more, and particularly preferably 25% by weight or more. When FeO is less than 18% by weight, the blackness of the iron oxide particles becomes low.
[0026]
The saturation magnetization value in an external magnetic field of 10 kOe is preferably 75 emu / g or more, and more preferably 80 emu / g or more. When the saturation magnetization value is less than 75 emu / g, the magnetization on the developing sleeve is insufficient when the toner is used.
[0027]
The degree of aggregation is preferably 50% or less, more preferably 40% or less. If the degree of aggregation exceeds 50%, poor dispersion in the resin at the time of toner formation will be caused.
[0028]
Next, the manufacturing method of the iron oxide particle of this invention is described.
The method for producing iron oxide particles of the present invention is characterized in that, when iron oxide particles are produced by a wet method, the oxidation reaction is continued by a wet method even after ferrous hydroxide in the reaction slurry is completely consumed. And
[0029]
As a method for producing iron oxide particles by a wet method, a ferrous salt slurry containing a ferrous hydroxide colloid obtained by neutralizing a ferrous salt aqueous solution containing Fe ²⁺ with an alkaline aqueous solution (hereinafter referred to as a ferrous hydroxide slurry) In general, a method of obtaining iron oxide particles by oxidizing an oxygen-containing gas through a reaction slurry). The standard of reaction completion in this method is possible by checking the remaining amount of Fe ²⁺ in the reaction slurry, but a method of measuring the oxidation-reduction potential (ORP) and determining when the reaction ends by using the change point is widely used. Yes.
[0030]
The ORP during production by the above production method is stable at a low level during the progress of the oxidation reaction, but rapidly increases when the residual amount of Fe ²⁺ in the reaction slurry becomes lower than 0.1 mol / l. Further, when the Fe ²⁺ residual amount in the reaction slurry becomes lower than 0.01 mol / l, this increase becomes gradual, and eventually reaches the high stability region and no change is observed.
[0031]
As for the determination of the completion of the reaction by ORP, as disclosed in Japanese Examined Patent Publication No. 51-11038, it is generally the time when a sudden change point is confirmed or the time when the high stability region is entered. It is.
[0032]
On the other hand, the present invention sets the reaction end point after ferrous hydroxide in the reaction slurry is completely consumed, that is, after the ORP exceeds the rapid change point and enters the high stability region, An iron oxide coating mainly composed of α-Fe ₂ O ₃ is formed on the surface of core particles mainly composed of iron oxide containing Fe ²⁺ such as magnetite. Specifically, the oxidation reaction is continued by a wet method until the rate of change of ORP reaches 10 mV / min. Of course, the amount of coating formed mainly of α-Fe ₂ O ₃ on the surface of the core particle can be arbitrarily controlled by adjusting the time during which the oxygen-containing gas is passed and the amount of gas.
[0033]
Further, as described above, when oxidation from Fe ²⁺ to Fe ³⁺ proceeds in drying or in the air, it is considered that the iron oxide particles as in the present invention are transformed into γ-Fe ₂ O _3. It is difficult to obtain a coating, and the method of forming a coating containing α-Fe ₂ O ₃ as a main component on the particle surface by dry means using iron oxide particles as a starting material is also a form change to α-Fe ₂ O ₃ . Since it requires heating at 500 ° C. or higher, the operation of oxidizing only the particle surface is impossible.
[0034]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples and the like.
[0035]
[Example 1]
50 liters of an aqueous solution containing 2.0 mol / l Fe ²⁺ and 53 liters of an aqueous sodium hydroxide solution containing 4.0 mol / l NaOH were mixed and stirred. While maintaining the reaction temperature at 80 ° C., the oxidation reaction was conducted by passing air at 65 liters / min while stirring the ferrous hydroxide slurry. At this time, an ORP meter (Model PH82 series manufactured by Yokogawa Electric Corporation, ORP electrode K9220YL) was placed in the reaction vessel, and the oxidation state of ferrous hydroxide was confirmed. After confirming that ferrous hydroxide was completely consumed, the ORP potential was higher than −200 mV, and that the rate of change was 10 mV / min or less, 65 liters / min of air was continuously passed through the reaction vessel, Peroxidation reaction was performed for a minute. The obtained slurry was subjected to normal filtration, washing, drying and pulverization to obtain iron oxide particles mainly composed of magnetite.
[0036]
The iron oxide particles were measured and evaluated by the following methods (particle shape, specific surface area, magnetic properties, FeO content, aggregation degree), and the results are shown in Table 1. Further, X-ray diffraction was measured, and the results are 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 vibrating magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd., measurement was performed with an external magnetic field of 10 kOe.
(4) FeO content sample was dissolved in sulfuric acid and measured by oxidation-reduction titration using a potassium permanganate standard solution. The deterioration test was evaluated by exposing a sample immediately after production in an environment of 60 ° C. and 90% RH for 28 days and measuring the FeO content in the sample.
(5) Aggregation degree The vibration time was measured at 65 sec using Powder Tester Type PT-E manufactured by Hosokawa Micron. The degree of aggregation was determined from the measurement result using a predetermined calculation formula.
(6) X-ray diffraction measurement The measurement was performed under the following measurement conditions.
X-ray generation: Cu K-α1 line / 40 kV / 26 mA
-Goniometer: RINT2000 vertical goniometer-Divergence slit, scattering slit: 1 deg
・ Reception slit: 0.15mm
・ Counter: Scintillation counter ・ Scanning speed: 2 ° / min
・ Scan step: 0.01 °
[0037]
[Example 2]
Except that the alkaline aqueous solution to be initially mixed was 45 liters, the pH during the oxidation reaction was maintained at 6.3, and after the ORP potential was confirmed, 20 liter / min of air was continuously passed through the reaction tank for 30 minutes. In the same manner as in Example 1, iron oxide particles mainly containing magnetite were obtained. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0038]
Example 3
50 liters of an aqueous solution containing 2.0 mol / l Fe ²⁺ and 52 liters of an alkaline aqueous solution containing 4.0 mol / l NaOH were mixed and stirred. The reaction temperature was maintained at 78 ° C., and the oxidation reaction was performed by passing air at 40 liters / min while stirring the ferrous hydroxide slurry. In the same manner as in Example 1, the state of oxidation of ferrous hydroxide was confirmed using an ORP meter, and air ventilation was stopped when the ORP potential was -300 mV. At this time, the unreacted Fe ²⁺ remaining in the slurry was 0.2 g / l. To this slurry was added 2.3 liters of an aqueous solution containing 1.02 mol / l Fe ²⁺ and 0.44 mol / l Si ⁴⁺ , and an oxidation reaction was performed by passing air at 20 liters / min while maintaining pH 8. It was. After confirming that the ORP potential of the slurry was higher than -200 mV and the rate of change was 10 mV / min or less, a peroxidation reaction was continued for 15 minutes by passing 20 liter / min of air through the reaction vessel. The obtained slurry was subjected to normal filtration, washing, drying and pulverization to obtain iron oxide particles mainly composed of magnetite. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0039]
Example 4
The aqueous solution to be added after the oxidation reaction has been temporarily stopped is composed mainly of magnetite in the same manner as in Example 3 except that the aqueous solution containing Fe ²⁺ is 1.01 mol / l and Al ³⁺ is 0.44 mol / l. Iron oxide particles were obtained. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0040]
Example 5
The air aeration rate 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 with an aqueous solution containing 0.5 mol / l Except that, iron oxide particles mainly containing magnetite were obtained in the same manner as in Example 3. Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0041]
[Comparative Example 1]
Magnetite particles were obtained in the same manner as in Example 1 except that the oxidation status of ferrous hydroxide was confirmed using an ORP meter, and the aeration was stopped when the ORP potential was -300 mV, and the reaction was terminated. . Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1. Further, X-ray diffraction was measured, and the results are shown in FIG.
[0042]
[Comparative Example 2]
Magnetite particles were obtained in the same manner as in Example 2 except that the oxidation status of ferrous hydroxide was confirmed using an ORP meter, and the aeration was stopped when the ORP potential was −300 mV, and the reaction was terminated. . Various characteristics were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0043]
[Table 1]

[0044]
As is clear from the results in Table 1, the iron oxide particles mainly composed of magnetite of Examples 1 to 5 have a stable blackness and magnetic properties compared to the magnetite particles of Comparative Examples 1 and 2. Aggregation is small. In addition, as shown in FIG. 1, in Example 1, a diffraction peak having an intensity of 5% or more appeared at 2θ = 32 ° to 33 ° with respect to the intensity of the main peak of magnetite appearing near 2θ = 35 °. However, such a diffraction peak did not appear in Comparative Example 1 shown in FIG. Although not shown, diffraction peaks similar to those in Example 1 appeared in Examples 2 to 5, but such diffraction peaks did not appear in Comparative Example 2 as in Comparative Example 1.
[0045]
【The invention's effect】
As described above, the iron oxide particles of the present invention have a stable black level during each seed environment and magnetic agglomeration is small, it is excellent in dispersibility, particularly electrostatic copying magnetic toner material powder, electrostatic Suitable for applications such as carrier powder for developing electrostatic latent image, black pigment powder for paint, and the like. In addition, the iron oxide particles can be obtained easily and on an industrial scale by the production method of the present invention.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern in Example 1. FIG.
2 is an X-ray diffraction pattern in Comparative Example 1. FIG.

Claims (4)

An iron oxide particle having a coating layer mainly composed of non-magnetic iron oxide on the surface of a core particle mainly composed of magnetite and containing Fe ²⁺ , and Cu Kα1 (λ = 1.54s0Å) A diffraction peak having an intensity of 5% or more appears at 2θ = 32 ° to 33 ° with respect to the intensity of the main peak of magnetite appearing in the vicinity of 2θ = 35 ° obtained by X-ray diffraction measurement using the target. Iron oxide particles. The coating layer is α-Fe ₂ O _Three The iron oxide particles according to claim 1 containing as a main component. The iron oxide particles according to claim 1 or 2, wherein FeO has a saturation magnetization value of 75 emu / g or more and an aggregation degree of 50% or less in an external magnetic field of 18 wt% or more and 10 kOe. When the iron oxide particles are produced by a wet method, an oxidation reaction is carried out while confirming the oxidation state of ferrous hydroxide in the reaction slurry with an oxidation-reduction potential (ORP), and the ORP enters the high stable region and is subjected to hydroxylation. A method for producing iron oxide particles, characterized in that the oxidation reaction is continued by a wet method until the rate of change of ORP reaches 10 mV / min even after complete consumption of ferrous iron.

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