JP4422530B2 - Magnetite particles - Google Patents

Description

  The present invention relates to a magnetite particle and a method for producing the same, and more particularly, a magnetite particle having a coating layer containing a compound of one or more elements other than iron on a magnetite core particle, particularly electrostatic copying The present invention relates to magnetite particles used for magnetic toner material powder, electrostatic latent image developing carrier material powder, paint black pigment powder and the like, and a method for producing the same.

  Recently, magnetite particles produced by an aqueous solution reaction have been widely used as materials for magnetic toners such as electronic copying machines and printers. Various general development characteristics are required for magnetic toners, but in recent years, due to the development of electrophotographic technology, especially copiers and printers using digital technology have rapidly developed, and the required characteristics have become more advanced. I came.

  That is, in addition to conventional characters, output of graphics and photographs is also required, and some copiers and printers have a capacity of 1200 dots or more per inch, and the latent image on the photoconductor is more precise. It is becoming. For this reason, there are strong demands for high reproducibility of fine lines in development, and that they can be used without problems even in various environments.

  In response to these requirements, improvements have been made such that magnetite particles contain compounds of various elements and, if necessary, part or all of the compounds of the elements are coated on or exposed to the particle surfaces. It was. These are applied to improve fluidity, magnetic properties, electrical properties, dispersibility, and environmental resistance.

  The present applicant has previously proposed magnetite particles (Patent Document 1) coated with a composite iron oxide layer of silica, aluminum, and iron.

  However, the technique disclosed in the above-mentioned patent document, in particular, the technique for coating the particle surface with the compound of the above-mentioned various elements, generally depends on the wet processing method only for the embodiment. The compound is difficult to complex with iron, and part of it adheres to the particle surface in a soluble form, so when melt-kneaded with a highly reactive resin such as polyester, the elemental component on the surface of the magnetite particle reacts with the resin, There was a problem that the characteristics of the resin were deteriorated.

  There is also a technique for improving various properties by attaching fine particles such as alumina to the surface of magnetite particles only by physical treatment (Patent Document 2). According to this technique, although the produced magnetite particles have low reactivity with the resin, silica and alumina fine particles may be peeled off during melt-kneading with the resin, which is not preferable.

  There is also a disclosure of a technique relating to magnetite particles containing elemental compounds other than iron from the relatively inside of the particles and biased to a high concentration in the outer shell (Patent Document 3). The magnetite particles disclosed in the patent document may cause a problem that the characteristics of the resin described above are deteriorated when a part of the additive element is exposed on the particle surface. On the other hand, when the above-mentioned elements are not exposed on the particle surface, the improvement of various target characteristic values cannot be sufficiently achieved.

  The present applicant has previously proposed a technique relating to magnetite particles coated with a composite iron oxide layer containing aluminum and magnesium (Patent Document 4). In this method, a slurry is aged at a specific pH and temperature for a long time to form a composite iron oxide layer containing aluminum, magnesium and iron, but the composite is insufficient. This is insufficient in terms of suppressing deterioration of the resin characteristics described above.

JP 2001-072425 A JP-A-8-183620 JP 2000-272923 A JP 2003-192350 A

  Accordingly, an object of the present invention is to provide magnetite particles that can eliminate the various drawbacks of the prior art described above.

  That is, even when a compound of an element other than iron is coated on the particle surface or exposed to improve various properties such as fluidity, magnetic properties, electrical properties, dispersibility, and environmental resistance, the resin and An object of the present invention is to provide magnetite particles in which the reactivity of is suppressed.

The present invention relates to a magnetite particle having a coating layer containing a compound of one or more elements other than iron on the surface of the magnetite core particle,
Surface of the core particles, to the particles coated with the compounds of elements other than the iron state, and are not subjected to dry mechanochemical treatment,
The element other than iron is one or more selected from Al, Mn, Zn, Ni, Co, Cr, Cu, and Cd,
Electrostatic copying magnetic toner material powder is obtained by achieving the above object by providing an electrostatic latent image developing carrier material powder, magnetite particles, wherein Rukoto used as paint black pigment powder.

  The magnetite particles of the present invention have a coating layer containing a compound of one or more elements other than iron, and the element forms a composite compound with the iron element. Thus, when melt-kneaded with a highly reactive resin, the properties of the resin are not impaired, and therefore, it is suitable for stably producing toner for copying machines and printers.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The magnetite particles of the present invention have a coating layer containing a compound of one or more elements other than iron on the surface of magnetite core particles (hereinafter also simply referred to as core particles). In the following description, when referring to magnetite particles or core particles, it means either individual particles or aggregates thereof.

  As the core particles, those produced by a wet method are usually used, but those produced by a dry method may be used. The core particle may be composed of magnetite itself, or may contain an element such as silica inside the particle. The particle diameter (ferret diameter) of the core particles depends on the thickness of the composite iron oxide layer, but is preferably 0.05 to 0.5 μm, particularly preferably about 0.1 to 0.3 μm. There is no restriction | limiting in particular in the shape of a core particle, For example, it can take a polyhedron, a hexahedron, and a spherical shape with more face numbers than it.

  In the present invention, the magnetite particles having a coating layer containing a compound of one or more elements other than iron on the surface of the magnetite core particles are coated on the particles coated with the compound of an element other than iron. It is important that the mechanochemical treatment is performed.

  That is, by first coating the surface of the magnetite core particle with a compound of an element other than iron by some method, and further performing a dry mechanochemical treatment, an element other than iron present in the coating of the surface of the magnetite particle This is a magnetite particle having a compound complexed with an element.

  In the present invention, the above-mentioned two-stage treatment is important. Details of the coating and the dry mechanochemical treatment will be described later.

  In the composite compound layer covering the surface of the core particle, 95% or more, preferably 97% or more, more preferably 99% or more of the compound of elements other than iron in the composite compound layer is complexed with the iron element. It is preferable. The higher the composite ratio, the more the resin properties are not impaired when kneaded with a highly reactive resin such as polyester. The term “composite” as used herein means that elements other than iron on the particle surface are not in the form of a single compound but in the form of a compound compound with iron or a compound compound containing iron and other elements other than iron. Whether the compounding ratio of elements other than iron in the composite compound layer is sufficient is determined by suspending magnetite particles in an acidic aqueous solution (for example, an aqueous potassium hydrogen phthalate solution having a pH of 4.01, which will be described later). It can be judged by whether or not elution occurs. Elements that are not complexed are dissolved in the acidic aqueous solution.

  When the composite ratio is 95% or more, the magnetite particles of the present invention do not impair the properties of the resin when producing toner for copying machines and printers. Impairing the properties of the resin means that the viscosity of the resin changes when the binder resin and magnetite particles are melt-kneaded, causing problems in toner production due to the inability to knead with appropriate torque, and the thermal properties of the obtained toner. It means that a problem occurs when toner is fixed due to a change. In order to prevent such problems, magnetite particles are formed by combining a compound of an iron element and an element other than iron by a dry mechanochemical treatment to form a strong composite compound layer.

  There is no restriction | limiting in particular in the upper limit of the composite ratio of a composite compound layer, and it is so preferable that it is high. Using the method described later, it is possible to achieve a high value of 98% or more. The method for obtaining the composite ratio of the composite compound layer is as follows.

  First, the core particles before formation of the composite compound layer commensurate with 20 g of the magnetite particles having the composite compound layer to be finally produced and the magnetite particles 20 g after formation of the composite compound are completely dissolved in the acid. The amount of elements other than iron in the solution is quantified by ICP, and the content of elements other than iron in the region other than the core particles is determined from the difference between the two (this amount is designated as A).

  On the other hand, 20 g of the magnetite particle powder after forming the composite compound layer is suspended in 100 ml of 0.01 mol / l potassium hydrogen phthalate aqueous solution (pH is 4.01 at 25 ° C.) and stirred at 25 ° C. for 3 hours. After stirring, the suspension is filtered with a membrane filter having an opening diameter of 0.1 μm, and the amount of elements other than iron in the filtrate is quantified by ICP. The amount of element eluted from the magnetite particles is determined from the product of the liquid volume and the concentration (this amount is designated as B). The element eluted from magnetite is an uncomplexed element, which means, for example, a portion attached in the form of a hydroxide. Elements that are not complexed can be detected by this method because they are dissolved in an aqueous potassium hydrogen phthalate solution having a pH of 4.01.

From the above A and B, the composite ratio of elements other than iron coated on the magnetite particles is obtained using the following formula (1).
Composite ratio (%) = [(A−B) / A] × 100 (1)

  As is apparent from this equation, the compounding ratio indicates the ratio of elements compounded among elements other than iron coated on the particle surface.

  Moreover, it is important that the elements coated on the magnetite particles of the present invention are one type or two or more types. Even in the case of one kind, the object of the present invention is achieved because the element and the iron element form a composite compound such as composite iron oxide, but when two or more kinds of elements are added in order to satisfy some functions at the same time. Even so, the compounding is promoted sufficiently. However, when no element other than iron is present on the surface of the magnetite particles, the energy given by the mechanochemical reaction oxidizes the divalent iron of the magnetite, resulting in maghemite and hematite, thereby causing redness. In addition, the magnetic properties are reduced.

  Moreover, the magnetite particle | grains of this invention are 0.1-2 weight% with respect to the magnetite particle | grains with respect to the magnetite particle | grains about the total content converted into each element about 1 type, or 2 or more types of elements other than iron in coating | cover. It is preferable. If it is less than 0.1%, there is not much difference from the state where there is no at all, so the energy given by the mechanochemical treatment tends to oxidize the divalent iron in the magnetite and promotes the formation of maghemite and hematite, thereby making the particles There is a risk of deterioration of hue or deterioration of magnetic properties. On the other hand, if it exceeds 2%, the energy required for compositing is not transmitted, and compositing is not completely promoted, so that the compositing ratio is low, and it is originally necessary for magnetite particles. This leads to a decrease in magnetic properties. The total amount is preferably 0.1 to 1% by weight in order to balance each characteristic. The total amount of elements other than the coated iron is a value obtained by subtracting the amount of elements contained in or contained in the particles. This is also shown by equation (1).

Further, magnetite particles of the present invention, as an element other than iron used in the complex compound coating layer formed, Al, Mn, Z n, Ni, Co, Cr, Cu be, and are those selected from Cd preferred . By including the compound of these elements in the coating layer, various properties such as fluidity, magnetic properties, electrical properties, dispersibility, and environmental resistance can be improved.

By the way, in recent years, magnetic toners tend to have smaller particle sizes for improving resolution. Therefore, it is preferable to reduce the particle size of the magnetite used in such toner. However, magnetite particles having a reduced particle size generally lack stability in various properties including magnetic properties. On the other hand, the magnetite particles of the present invention have a feature that is particularly excellent in stability of saturation magnetization while having a small particle size. As a scale indicating the size of the magnetite, there is a specific surface area by the BET method. The specific surface area of the magnetite particles of the present invention is preferably 7 to 15 m ² / g. At the same time, the particle size is preferably 0.05 to 0.5 μm, particularly preferably 0.1 to 0.3 μm.

  Moreover, the shape of the magnetite particles of the present invention is not limited. A shape that satisfies the required characteristics may be selected, and the shape of the core particles before the formation of the composite barrier layer may be arbitrarily selected.

  Next, the preferable manufacturing method of this invention is demonstrated. First, as described above, the core particle to be prepared is generally manufactured by a wet method, but may be manufactured by a dry method. However, in order to obtain magnetite particles having a small particle size and a good particle size distribution, a wet method is more preferable. As a wet reaction product, for example, a ferrous hydroxide slurry prepared by neutralization with a water-soluble Fe (II) compound (for example, ferrous sulfate) and an alkaline aqueous solution is prepared. Core particles can be obtained by blowing an oxygen-containing gas such as air under the condition of heating to a predetermined temperature. In order to impart functions, if necessary, a water-soluble salt (for example, zinc sulfate or sodium silicate) can be added at the beginning of synthesis or until the completion of core particle generation.

  As the core particles, the slurry after the reaction may be used as it is, or a slurry in which magnetite particles are dispersed in water may be used. A predetermined amount of a water-soluble salt of the necessary element is added to the slurry, and the pH is adjusted to 7 to 12, preferably 8 to 10, using an alkali such as sodium hydroxide or potassium hydroxide. At this time, iron ions may be added at the same time, or a part of ferrous hydroxide may be intentionally left in the slurry when the core particle generation is terminated. However, it is preferable that the iron component intentionally added or intentionally left does not exceed twice the weight ratio with respect to the element to be added. If it exceeds twice, the iron concentration on the particle surface becomes high, and oxidation is promoted by the energy of the mechanochemical treatment performed thereafter, which is not preferable. Moreover, you may perform oxygen-containing gas blowing operation at the time of core particle production | generation as needed. The thus obtained magnetite particles coated with a compound of an element other than iron are filtered off from the slurry by an ordinary method, washed and dried.

  Thus, the magnetite particle | grains by which the surface of the core particle was coat | covered with the compound of elements other than iron are obtained. However, the elements covered at this stage are not sufficiently complexed with iron elements and other elements, and the coverage is low. Hereinafter, the magnetite particles coated with a compound of an element other than iron at this stage are referred to as precursor particles.

  The magnetite particles of the present invention can be obtained by subjecting the precursor particles to a dry mechanochemical treatment. The mechanochemical treatment is performed using a device capable of exerting mechanochemical and mechanical alloying actions while pulverizing the whole particle while giving very high energy under a dry process. An example of such an apparatus is a dry crushing apparatus. Examples of the dry crushing device include a device that gives high energy to the particles by a shearing force and a device that gives high energy to the particles by a spatula. Specific examples of such a device include a sand mill and a planetary mill.

  It is known that when particles are pulverized using the above apparatus, the surface temperature of the particles becomes higher than the temperature of the whole particles due to the collision of the particles. As a result, the elements coated on the magnetite particles are highly complexed. In addition, even if the temperature is simply raised, diffusion and compounding of atoms occur, but in particular, high-temperature atmosphere firing etc., it is necessary to block oxygen, and depending on the temperature, sintering between particles is promoted and dispersed. The property deteriorates, which is not preferable. In contrast, the method for producing magnetite particles according to the present invention is such that the temperature of the whole powder is not so high while pulverizing the particles, but the same energy is given to the particle surface as high temperature is applied. Thus, the effect of the present invention can be obtained.

  When the compound of the element coated on the magnetite particles is compounded by mechanochemical treatment, the element that is not compounded can be reduced as much as possible. Non-complexed elemental compounds hydrate easily with water molecules and cause hygroscopicity. By reducing it as much as possible, magnetite particles with low hygroscopicity can be obtained. Magnetite particles with high hygroscopicity are not preferable because they absorb moisture in the air and have low electrical resistance.

Compounding by mechanochemical treatment also has the advantage of shortening the treatment time. In the magnetite particles described in Patent Document 4 described in the background section above, compositing takes a long time of approximately 10 hours by a wet method, and the particles tend to aggregate and are sufficiently composited. Not.
On the other hand, the magnetite particles of the present invention have a relatively short treatment time, the dispersibility of the obtained magnetite particles is good, and the composite state is higher than that of the wet method.
Here, the time required for the mechanochemical treatment may be 5 to 60 minutes, particularly 10 to 40 minutes, depending on the amount of energy applied.

  What is necessary is just to adjust suitably the magnitude | size of the energy given by a mechanochemical process so that sufficient mechanochemical process may be accelerated | stimulated, without destroying particle | grains itself. If too much energy is applied, the particle surface breaks down and irregularities are generated on the particle surface. In that case, since the specific surface area increases, the hygroscopicity of the obtained magnetite particles deteriorates. Therefore, it is preferable to control the energy according to operating conditions of a specific apparatus (for example, a sand mill or a planetary mill) that performs mechanochemical treatment. For example, when Yodomill (trade name) manufactured by Yodocasting Co. is used as a sand mill, the linear pressure is preferably 150 to 200 kgf / cm, particularly 160 to 180 kgf / cm. When p-7 (trade name) manufactured by Fritche is used as the planetary mill, the rotational speed is preferably 1000 to 2000 rpm, particularly 1500 to 2000 rpm.

  During the mechanochemical treatment, great energy is applied to the magnetite particles. At this time, if oxygen is present in the reaction system, the magnetite is remarkably oxidized by the energy and may be changed to maghemite or hematite. Therefore, it is preferable to perform the mechanochemical treatment in an inert gas atmosphere such as nitrogen gas or argon gas.

  In order to efficiently perform the mechanochemical treatment, it is preferable to heat the magnetite particles to a predetermined temperature during the treatment. A preferred temperature is 100 to 200 ° C. When the heating temperature is too low, the effect of heating is not observed. When the heating temperature is too high, the particles are easily sintered, and the dispersibility of the obtained magnetite particles may be lowered. When heating, for example, when using a sand mill, a jacket may be attached to the powder charging container and heated with steam, or heated with an electric heater.

  The magnetite particles thus obtained are suitably used for applications such as electrostatic copying magnetic toner material powder, electrostatic latent image developing magnetic carrier material powder, or paint black pigment powder.

  Hereinafter, the present invention will be specifically described with reference to examples and the like. However, the scope of the present invention is not limited to such examples.

[Comparative Example 1]
(A) Production of core particles 50 liters of an aqueous ferrous sulfate solution having an Fe ²⁺ concentration of 2.0 mol / l and 50 liters of an aqueous solution of 3.6N sodium hydroxide were mixed to obtain a ferrous hydroxide slurry. The resulting slurry had a pH of 6.5. The slurry was blown with 65 l / min air while adding an aqueous sodium hydroxide solution so as to maintain a pH of 6 to 9 at a temperature of 85 ° C. to promote oxidation, thereby producing core particles. When the ferrous hydroxide was completely consumed, the air blowing was stopped and the oxidation reaction was completed.

(B) Production of Precursor Particles 1 liter of an aluminum sulfate aqueous solution having an Al concentration of 1 mol / l was added to the slurry containing core particles, and the pH was adjusted to 8 using an aqueous sodium hydroxide solution. The slurry temperature was maintained at 85 ° C. The slurry was stirred and mixed for 2 hours, filtered, washed and dried to obtain precursor particles having an Al compound layer formed on the surface of the core particles. This precursor particle was used as the magnetite particle of Comparative Example 1.

[Comparative Examples 2 to 10]
Magnetite particles were obtained in the same manner as in Comparative Example 1 except for the conditions shown in Table 1.

[Comparative Example 11]
50 liters of Fe2 + 2.0 mol / l ferrous sulfate aqueous solution and 50 liters of 3.6N sodium hydroxide aqueous solution to which 1 liter of Mg0.9 mol / l magnesium sulfate aqueous solution was added were mixed and stirred. The pH at this time was 6.5. While maintaining the slurry at 85 ° C. and pH of 6 to 7, 65 l / min of air was blown to terminate the reaction once (generation of core particles).

  The slurry was adjusted to pH 8 by mixing 3 liters of an aluminum sulfate aqueous solution with an Al concentration of 0.6 mol / l, 5 liters of ferrous sulfate aqueous solution with an Fe 2+ concentration of 1.4 mol / l, and an aqueous sodium hydroxide solution. The slurry temperature was 80 ° C. Subsequently, 65 liter / min air was blown in and oxidized again to complete the reaction.

After completion, sodium hydroxide solution was added dropwise to adjust the pH to 10. At this point, the slurry temperature was 78 ° C. This state was maintained for 10 hours.
The resulting generated particles were subjected to normal filtration, washing, and drying to obtain magnetite particles.

[Example 1]
The total amount of magnetite particles obtained by the production method shown in Comparative Example 1 was mechanochemically charged at a 1 kg linear pressure of 170 kgf / cm for 30 minutes in a powder charging container of Yodomill (trade name MSPU-2) which is a sand mill manufactured by Yodocasting. Processed. The vessel was heated to 110 ° C. by steam. In this way, the Al component was combined with the iron component of the magnetite particles to obtain magnetite particles having a composite iron oxide layer.

[Examples 2 to 14]
Magnetite particles were obtained in the same manner as in Example 1 except for the conditions shown in Table 2.

  About the magnetite particle | grains of Examples 1-14 and Comparative Examples 1-11, the compounding ratio was calculated | required by the method described previously. Furthermore, various properties of the magnetite particles were measured and evaluated by the methods described below. The results are shown in Table 3.

<Evaluation method>
(A) BET specific surface area Measured with a 2200 type BET meter manufactured by Shimadzu Micromeritics.
(B) Electric resistance value 10 g of a sample was put in a holder, and a pressure of 600 kgf / cm ² was applied to form a 25 mmφ tablet mold, and then an electrode was attached and measured in a pressurized state of 150 kgf / cm ² . The electrical resistance value was calculated from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.
(C) Saturation magnetization Using a vibrating sample magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd., measurement was performed with a load magnetic field of 796 kA / m.
(D) 60 ° specular reflectance 60 ° on the coating film surface obtained by spreading a kneaded mixture of a dispersion paste prepared according to the Hoover Muller method of JIS K 5101 and nitrified cotton clear lacquer on a white paper using a 1 mil film applicator. The reflectance of was measured.
(E) Moisture absorption after exposure for 4 hours under an atmosphere of 35 ° C. and 85% RH A sample 3 g was dried in advance at 105 ° C. for 1 hour and the dry weight W ₁ was measured. Subsequently, the sample was exposed to an environment of 35 ° C. and 85% RH for 4 hours to absorb moisture. And measured the weight W ₂ after moisture absorption. The amount of moisture absorption (% by weight) was calculated by the following formula.
W: Moisture absorption (% by weight) = [(W ₂ −W ₁ ) / W ₁ ] × 100
(F) Moisture absorption with respect to BET specific surface area The moisture absorption after exposure for 4 hours in the 35 ° C. and 85% RH atmosphere determined above was gradually increased with the BET specific surface area to determine the moisture absorption with respect to the BET specific surface area.
(G) Presence or absence of thickening phenomenon 40 g of the sample and 40 g of the polyester resin were mixed well and kneaded at 140 ° C. for 30 minutes with a kneader (Plastic coder manufactured by Brabender). Meanwhile, the torque required for kneading was measured. Thickening phenomenon level 1 when this torque changed sharply after the 5th minute from the start of kneading, level 2 when the torque began to gradually increase after the 15th minute, level 0 when the torque did not increase at all It was.

As is apparent from the results shown in Table 3, the magnetite particles of each example have a remarkably high composite ratio as compared with the magnetite particles of the comparative example, and as a result, do not thicken when kneaded with the polyester resin. In addition, it is suitable for electrostatic copying magnetic toner material powder, electrostatic latent image developing carrier material powder, black pigment powder for paint, etc. It is suitable for applications produced by kneading with high resin.

Claims (3)

In the magnetite particle having a coating layer containing a compound of an element other than one or more kinds of iron on the surface of the magnetite core particle,
Surface of the core particles, to the particles coated with the compounds of elements other than the iron state, and are not subjected to dry mechanochemical treatment,
The element other than iron is one or more selected from Al, Mn, Zn, Ni, Co, Cr, Cu, and Cd,
Electrostatic copying magnetic toner material powder, an electrostatic latent image developing carrier material powder, magnetite particles, wherein Rukoto used as paint black pigment powder.   The magnetite particles according to claim 1, wherein 95% or more of the compound of an element other than iron is complexed with an iron element.   3. The magnetite particle according to claim 1, wherein the total content of each element other than iron is 0.1 to 2% by weight based on the magnetite particle. .