Ferrite particles, carrier core material for electrophotographic developer, carrier for electrophotographic developer, and electrophotographic developer

Abstract

Provided are: ferrite particles that can suppress the generation of carrier scatter in high temperature, high humidity environments, and have good developability; an electrophotographic developer carrier core material; an electrophotographic developer carrier; and an electrophotographic developer. The ferrite particles are characterized by containing a crystal-phase component comprising perovskite crystals represented by the composition formula of RZrO3 (wherein R is an alkaline earth metal element), by having a surface roughness Rz of 2.0 μm to 4.5 μm, inclusive, and satisfying a prescribed formula. The ferrite particles are used as an electrophotographic developer carrier core material. Using the same, an electrophotographic developer carrier and an electrophotographic developer are obtained.

Description

[Technical Field]

[0001] The present invention relates to ferrite particles, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer. [Background technology]

[0002] Electrophotographic development is a method of developing an electrostatic latent image formed on a photoreceptor by attaching the toner in the developer to the electrostatic latent image. The developers used in this method are divided into two-component developers consisting of toner and carrier, and one-component developers that use only toner. In the past, the cascade method was used as a development method using two-component developers, but now the magnetic brush method using a magnet roll is the mainstream.

[0003] In the magnetic brush method, the carrier and toner are stirred and mixed in a developing box filled with developer, giving the toner an electric charge. The carrier is then transported to the surface of the photoconductor by a developing roll holding a magnet. At that time, the carrier transports the charged toner to the surface of the photoconductor. After a toner image is formed on the photoconductor by electrostatic action, the carrier remaining on the developing roll is collected back into the developing box, stirred and mixed with new toner, and reused over a certain period of time.

[0004] Unlike single-component developers, two-component developers allow the magnetic and electrical properties of the carrier itself to be designed separately from the toner, providing good controllability when designing the developer. Therefore, two-component developers are suitable for full-color developing devices that require high image quality and high-speed printing devices that require reliable image maintenance and durability.

[0005] In recent years, efforts have been made to reduce the particle size of toner in order to develop electrostatic latent images with high resolution. This reduction in toner particle size has also led to a reduction in the particle size of carriers. By reducing the particle size of carriers, mechanical stress during agitation and mixing of the carrier and toner is reduced, suppressing the occurrence of toner-spent and other problems, resulting in a longer developer life than before. Carriers generally consist of a magnetic core material, such as ferrite particles, coated with a resin. Over long-term use of a developer, the resin coating on the carrier surface can peel off, exposing the core material. Because the core material has low resistance, exposing the surface of the core material reduces the surface resistance of the carrier, leading to carrier scattering due to charge injection and increasing the likelihood of image defects.

[0006] To address these issues, various proposals have been made, for example, to use highly resistive ferrite particles as a core material. Patent Document 1 proposes such highly resistive ferrite particles, including a ferrite component represented by the formula (MnO)x(MgO)y(Fe2O3)z, where the amounts of x, y, and z are within a predetermined range, and a predetermined amount of ZrO2 that is not dissolved in the ferrite component. By using the ferrite particles described in Patent Document 1 as a core material, a highly resistive carrier can be obtained and carrier scattering can be suppressed. Furthermore, even when the resin coating layer peels off, the high resistance of the core material itself can suppress carrier scattering due to charge injection. These factors make it possible to suppress carrier scattering over a long period of time and reduce image defects associated with carrier scattering. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3872025 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional carriers using ferrite particles as the core material tend to have low resistance under high temperature and high humidity conditions, making it difficult to sufficiently suppress carrier scattering under high temperature and high humidity conditions.Furthermore, leakage of counter charge after development is difficult to occur, which makes it difficult to obtain good image density, particularly during high-speed image printing or high-density printing.

[0009] Therefore, an object of the present invention is to provide ferrite particles, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer that can suppress the occurrence of carrier scattering under high temperature and high humidity conditions and have good developability. [Means for solving the problem]

[0010] In order to solve the above problems, the ferrite particles according to the present invention contain a crystalline phase component made of a perovskite-type crystal represented by the composition formula RZrO3 (where R is an alkaline earth metal element), Contains 0.1 mol% or more and 3.0 mol% or less of zirconium, The surface roughness Rz is 2.0 μm or more and 4.5 μm or less, and is characterized by satisfying the following formula: 6.5 ≦ logH 1000 ≦ 8.5 0.80 ≦ logH 1000 / logH 100 ≦ 1.00 however, logH 1000 : Resistance value H of the ferrite particles when an applied voltage of 1000 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) 1000 Logarithm of (Ω) (logΩ) logH 100 : Resistance value H of the ferrite particles when an applied voltage of 100 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) 100 Logarithm of (Ω) (logΩ)

[0011] In the ferrite particles according to the present invention, the surface roughness Rz is preferably 2.5 μm or more and 4.2 μm or less.

[0012] The ferrite particles according to the present invention preferably satisfy the following formula: 6.7 ≦ logH 1000 ≦ 8.2 0.85 ≦ logH 1000 / logH 100 ≦1.00

[0013] In the ferrite particles according to the present invention, the R is preferably at least one element selected from the group consisting of Sr, Ca, and Ba.

[0014] In the ferrite particles according to the present invention, when a phase composition analysis of the crystalline phase constituting the ferrite particles is performed by Rietveld analysis of an X-ray diffraction pattern, it is preferable that the crystalline phase component consisting of the perovskite-type crystals is contained in an amount of 0.05 mass % or more and 4.00 mass % or less.

[0015] The ferrite particles according to the present invention are preferably spinel ferrite particles mainly composed of a crystalline phase component made of spinel crystals represented by the composition formula (MnO)(MgO)(FeO) (where 15≦x≦50, 2≦y≦35, 45≦z≦60, and x+y+z=100 (mol%)).

[0016] In order to solve the above problems, the carrier core material for an electrophotographic developer according to the present invention is characterized by containing the above ferrite particles.

[0017] In order to solve the above problems, the carrier for electrophotographic developer according to the present invention is characterized by comprising the above ferrite particles and a resin coating layer provided on the surface of the ferrite particles.

[0018] In order to solve the above problems, the electrophotographic developer according to the present invention is characterized by containing the above-mentioned carrier for electrophotographic developer and toner.

[0019] The electrophotographic developer according to the present invention may be used as a replenishment developer. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide ferrite particles, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer that can suppress the occurrence of carrier scattering under high temperature and high humidity conditions and have good developability. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a diagram schematically showing a cross section of a ferrite particle, and is a diagram for explaining a method for determining the degree of dispersion of Zr in the ferrite particle. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the ferrite particles, carrier core material for electrophotographic developer, carrier for electrophotographic developer, and electrophotographic developer according to the present invention will be described. In this specification, unless otherwise specified, the terms ferrite particles, carrier core material for electrophotographic developer, carrier for electrophotographic developer, and electrophotographic developer each refer to an aggregate of individual particles, i.e., powder. First, embodiments of the ferrite particles will be described. Hereinafter, the ferrite particles according to the present invention will be described as being primarily used as a carrier core material for electrophotographic developer. However, the ferrite particles according to the present invention can also be used in various applications, such as magnetic inks, magnetic fluids, magnetic fillers, various functional fillers such as fillers for bonded magnets and fillers for electromagnetic wave shielding materials, and electronic component materials, and the use of the ferrite particles is not limited to carrier core materials for electrophotographic developers.

[0023] 1. Ferrite particles and carrier core materials for electrophotographic developers First, an embodiment of the ferrite particles according to the present invention will be described. The ferrite particles according to the present invention are characterized by containing a crystalline phase component consisting of perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element), having a surface roughness Rz within a predetermined range, and having a resistance value that satisfies a predetermined condition.

[0024] 1-1. Perovskite-type crystal phase components, surface properties, and resistance (1) Crystal phase component consisting of perovskite-type crystals First, the crystalline phase component made of perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element) will be described.

[0025] Resin-coated carriers, which have magnetic particles as core materials and whose surfaces are coated with resin, are used as carriers for two-component electrophotographic developers suitable for the magnetic brush method. Ferrite particles, which are magnetic oxides primarily composed of ferric oxide (Fe2O3), are commonly used as core magnetic particles. To suppress carrier scattering, it is necessary to use ferrite particles with high magnetization and high resistance as the core material.

[0026] In recent years, multi-element ferrite particles containing metal elements such as Mg, Mn, Sr, and Ca in addition to Fe have been widely used as core materials. When manufacturing ferrite, metal oxides, metal hydroxides, etc. containing the metal elements of the desired composition are used as raw materials. To obtain highly magnetized ferrite particles, it is necessary to sufficiently advance the ferritization reaction of the raw materials so that unreacted raw materials that do not exhibit magnetism (hereinafter referred to as "unreacted raw materials") do not remain in the ferrite particles. However, in the case of multi-element ferrite, the ferrite formation temperature and formation rate vary depending on the combination of elements, and the ferrite reaction only proceeds at the contact surface between the raw materials. Therefore, it is difficult to completely ferrite the raw materials under typical sintering conditions. As a result, unreacted raw materials remain in the ferrite particles.

[0027] Furthermore, ferrite raw materials contain unavoidable impurities, such as metals or metal compounds that are not involved in the ferrite reaction, such as sodium and potassium. These unavoidable impurities are not magnetic. Therefore, to obtain highly magnetized ferrite particles, it is necessary to reduce the amount of unavoidable impurities. However, no matter how pure the raw materials used are, trace amounts of unavoidable impurities will exist in the raw materials, and it is not practical to completely remove the unavoidable impurities.

[0028] Furthermore, defects in the structure of ferrite particles reduce the magnetization of the ferrite particles. Structural defects that reduce magnetization include defects within ferrite particles (e.g., lattice defects). In the case of multi-element ferrites, the ferrite reaction is more complex than in single-element ferrites, making structural defects more likely to occur.

[0029] On the other hand, ferrite particles are made of metal oxides and therefore generally have high resistance. However, resistance decreases when moisture adheres to the surface. In addition, unavoidable impurities, including alkali metals such as Na and K, contained in the raw materials are easily ionized in the presence of moisture in the atmosphere. Therefore, as the amount of unavoidable impurities in ferrite particles increases, the resistance of the ferrite particles decreases. Furthermore, as the amount of unavoidable impurities increases, resistance becomes more susceptible to fluctuations due to changes in atmospheric humidity.

[0030] For these reasons, in order to obtain ferrite particles with high resistance and low environmental dependency of resistance, it is necessary to reduce the amount of unavoidable impurities in the ferrite particles. However, as mentioned above, it is not realistic to completely remove the unavoidable impurities. Note that, since the unreacted raw materials (excluding the unavoidable impurities) are metal oxides, the presence of unreacted raw materials does not cause the resistance of the ferrite particles to decrease.

[0031] Ferrite particles are often polycrystalline, which is an aggregate of single crystals. Even if the composition of ferrite particles is the same, the magnetic and electrical properties of the ferrite particles vary depending on the microstructural structure of the ferrite particles. Therefore, the present inventors focused on the microstructural structure of ferrite particles and discovered that in order to obtain ferrite with high magnetization and high resistivity and low environmental dependency of resistivity, it is important to include a crystalline phase component consisting of a perovskite-type crystal represented by the composition formula RZrO3 (where R is an alkaline earth metal element), which led to the present invention.

[0032] The reason why the above problem can be solved by including a crystalline phase component consisting of a perovskite-type crystal represented by the composition formula RZrO3 (where R is an alkaline earth metal element) is not clear, but the inventors of the present invention speculate as follows.

[0033] The grain boundaries of ferrite particles contain components that are not dissolved in ferrite, such as unreacted raw materials and unavoidable impurities. Furthermore, these components are extruded to the grain boundaries as the crystal grains grow and are also present on the surface of the ferrite particles. When the crystal grains constituting the ferrite particles are large, the grain boundaries are continuously formed within the ferrite particles, like channels connecting one point to another on the surface of the ferrite particles. Unavoidable impurities present on the surface and grain boundaries of ferrite particles are easily ionized. Therefore, if unavoidable impurities such as Na are continuously distributed along the continuously formed grain boundaries within the ferrite particles, when moisture adheres to the surface of the ferrite particles, the grain boundaries become conductive, reducing the resistance of the ferrite particles. Furthermore, ferrite particles with this structure are thought to exhibit significant fluctuations in resistance due to changes in atmospheric humidity. Furthermore, as mentioned above, it is difficult to completely remove the unreacted raw materials and unavoidable impurities from the ferrite particles.

[0034] On the other hand, crystalline phase components consisting of perovskite-type crystals represented by the formula RZrO3 (where R is an alkaline-earth metal element) do not form a solid solution with ferrite, and therefore the crystalline phase components are dispersed at the grain boundaries of ferrite particles. Therefore, ferrite particles containing the crystalline phase components have a relatively larger grain boundary volume than ferrite particles without the crystalline phase components. For a given amount of unavoidable impurities contained in ferrite particles, a relative increase in the grain boundary volume of the ferrite particles results in a relative decrease in the distribution density of the unavoidable impurities at the grain boundaries. In addition to the unavoidable impurities, the crystalline phase components, which are insulating materials, are present at the grain boundaries. In the ferrite particles of the present invention, the grain boundaries are distributed in a complex manner within the particles, and the unavoidable impurities and insulating materials such as the crystalline phase components are distributed discontinuously within the grain boundaries, thereby preventing the grain boundaries from functioning as conductive paths. Therefore, the ferrite particles of the present invention are believed to be able to reduce the environmental dependency of resistance.

[0035] Furthermore, when the grain boundary volume of a ferrite particle is relatively small, unavoidable impurities are pushed from the grain boundary to the surface, resulting in a relatively large amount of unavoidable impurities present on the ferrite particle surface. On the other hand, when the grain boundary volume of a ferrite particle is relatively large, the amount of unavoidable impurities present on the ferrite particle surface can be relatively reduced. Therefore, the resistance of the ferrite particle can be increased, and the environmental dependency of the resistance due to unavoidable impurities on the ferrite particle surface can be reduced. Furthermore, since the resistance of ordinary ferrite particles decreases as the atmospheric humidity increases, carriers using ferrite particles as a core material are prone to carrier scattering due to charge injection. On the other hand, the ferrite particles can maintain high resistance even at high atmospheric humidity, thereby suppressing carrier scattering due to charge injection.

[0036] Furthermore, the crystalline phase component consisting of perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element) has high insulating properties, and the presence of this crystalline phase component at the grain boundaries and particle surfaces can increase the resistance of ferrite particles. Furthermore, to obtain ferrite particles containing this crystalline phase component, a compound containing Zr (e.g., ZrO2) is used as a raw material. For example, when a multi-element ferrite has a composition containing R, the raw material containing R and the compound containing Zr undergo a solid-state reaction, thereby reducing the content of the unreacted raw material in the ferrite particles. Therefore, the occurrence of structural defects can be suppressed, and ferrite particles with relatively high magnetization can be obtained.

[0037] In the ferrite particles, "containing a crystalline phase component consisting of a perovskite-type crystal represented by the composition formula RzO3 (where R is an alkaline earth metal element)" means that the crystalline phase component is contained at least inside the ferrite particles. It is preferable that the crystalline phase component is well dispersed inside the ferrite particles, and it is more preferable that the crystalline phase component is uniformly dispersed on the surface and inside the ferrite particles. When the degree of dispersion of Zr element in the ferrite particles, which will be described later, is used as an indicator of uniform dispersion of the crystalline phase component on the surface and inside the ferrite particles, it is preferable that the degree of dispersion of Zr element is 1.1 or less and 1.0 or more. A preferred composition of the ferrite particles will be described later.

[0038] (2) Surface condition (surface roughness Rz) Next, the surface properties of the ferrite particles will be described. The ferrite particles are characterized by a surface roughness Rz of 2.0 μm or more and 4.5 μm or less. As a result of extensive research, the present inventors have found that by controlling the manufacturing conditions of the ferrite particles, such as the amount of zirconium dioxide and alkaline earth metal elements added, the firing temperature, and the atmospheric oxygen concentration during firing, the surface roughness Rz of the ferrite particles can be controlled within the above-mentioned range, and at the same time, the resistance can be controlled within the range described below. This effectively suppresses carrier scattering, particularly in high-temperature, high-humidity environments, while allowing the protrusions of the ferrite particles to function as leak points, particularly in low-temperature, low-humidity environments, thereby achieving good developability. This will be described in detail below.

[0039] Generally, when a carrier for electrophotographic developer is formed by using magnetic particles such as ferrite particles as a core material and providing a resin coating layer on the surface thereof, if the resistance of the core material is low, when the resin coating layer peels off and the core material is exposed, the resistance of the carrier decreases, making it more likely for carrier scattering due to charge injection. On the other hand, if the resistance of the core material is high, leakage of countercharge after development is less likely to occur, making it difficult to develop the next image satisfactorily. In other words, developability deteriorates.

[0040] Conventionally, in order to suppress carrier scattering and maintain good developability, ferrite particles that have been subjected to a surface oxidation treatment have been used as core materials to increase the resistance of the core material surface. However, it is difficult to uniformly oxidize the surfaces of ferrite particles. Therefore, the surfaces of ferrite particles locally have portions that are not sufficiently oxidized and exhibit low resistance, and portions that are oxidized to an excessively high resistance, and the effect of this method has been limited.

[0041] In addition, it has been attempted to increase the resistance of the core surface while adding conductive fine particles such as carbon black to the resin coating layer to maintain a high overall surface resistance of the carrier, and to quickly release the countercharge after development using the conductive fine particles, thereby suppressing carrier scattering and maintaining good developability. However, because carbon black is black, if it is detached from the resin coating layer due to mechanical stress, the toner may be printed with the carbon black mixed in, causing color turbidity. Therefore, it is preferable to achieve the desired leak resistance without adding conductive fine particles such as carbon black, or by adding a smaller amount than conventionally.

[0042] The present inventors discovered that controlling the surface roughness of ferrite particles increases the resistance of the carrier surface, while distributing low-resistance portions on the carrier surface, thereby suppressing carrier scattering and enabling rapid countercharge leakage after development, leading to the present invention. This is due to the following reasons: By providing surface roughness on ferrite particles, when a resin coating layer is formed on the surface of the ferrite particles as a core material, the thickness of the resin coating layer is relatively thinner on the convex portions than on the concave portions. Since the ferrite particles according to the present invention have high resistance even in high-humidity environments, controlling the surface roughness makes it possible to maintain high overall surface resistance of the carrier when used as a carrier, while substantially uniformly distributing low-resistance portions resulting from the convex portions of the ferrite particles on the carrier surface. As a result, it is possible to effectively suppress carrier scattering, rapidly leak countercharge after development, and maintain developability, particularly in high-humidity environments.

[0043] The surface roughness Rz of the ferrite particles is 2.0 μm or more and 4.5 μm or less. Here, the surface roughness Rz is more preferably 2.5 or more, and more preferably 4.0 μm or less. When the surface roughness Rz of the ferrite particles is within these ranges, the unevenness of the surface of the ferrite particles is within a moderate range, so that when a resin coating layer is provided to form a carrier, the protruding portions of the ferrite particles become leak points, thereby improving developability, particularly in low-humidity environments.

[0044] (3) Resistance value The ferrite particles have a surface roughness Rz within the above range, and their resistance value satisfies the following formula.

[0045] 6.5 ≦ logH 1000 ≦ 8.5 (1) 0.80 ≦ logH 1000 / logH 100 ≦1.00 (2) logH 1000 : Resistance value H of the ferrite particles when an applied voltage of 1000 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) 1000 Logarithm of (Ω) (logΩ) logH 100 : Resistance value H of the ferrite particles when an applied voltage of 100 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) 100 Logarithm of (Ω) (logΩ)

[0046] The resistance value (H 1000 When the logarithm of (V) is within the range of the formula (1), the ferrite particles have high resistance even in a high-temperature, high-humidity environment, and therefore, carrier scattering due to the charge injection can be suppressed. Furthermore, when a resin coating layer is provided on the surface of the ferrite particles to form a carrier, the convex portions can serve as leak points to maintain developability.

[0047] In order to obtain the above effects, the lower limit of the above formula (1) is preferably 6.7, and the upper limit is preferably 8.2.

[0048] Furthermore, when the ferrite particles satisfy the relationship represented by the above formula (2), the resistance value of the ferrite particles has low electric field dependency, so that even when the development electric field differs depending on the developing device, etc., carrier scattering can be suppressed while maintaining developability.

[0049] In order to obtain the above effect, the lower limit of the above formula (2) is preferably 6.7, and the upper limit is preferably 8.2.

[0050] Furthermore, when the ferrite particles were measured at an electrode distance of 2 mm and an applied voltage of 1000 V, the resistance value H 1000 It is preferable that the logarithm of (Ω) logH is 6.5 or more and 8.5 or less. In a high temperature and high humidity environment, the resistance value H 1000 Since ferrite particles exhibiting the above characteristic have high resistance even in a high-temperature, high-humidity environment, it is easy to suppress carrier scattering due to charge injection.

[0051] 1-2. Constituent elements and composition 1-2-1. Constituent elements Next, preferred embodiments of the constituent elements and composition of the ferrite particles according to the present invention will be described. First, matters relating to the crystalline phase component made of perovskite crystals having the composition formula RZrO3 will be described.

[0052] (1) Zirconium content The ferrite particles preferably contain zirconium in an amount of 0.1 mol% to 3.0 mol%. By containing zirconium within this range, the content of the crystalline phase component consisting of perovskite-type crystals represented by the composition formula RZrO3 is approximately within the above range, resulting in ferrite particles with high magnetization, high resistivity, and low environmental dependency of resistivity. The zirconium content in the ferrite particles is more preferably 1.0 mol% or less, and even more preferably 0.5 mol% or less.

[0053] (2) R (alkaline earth metal element) content In the present invention, R is at least one element selected from the group consisting of Ca, Sr, Ba, and Ra, i.e., an alkaline earth metal element. Alkaline earth metal elements have an ionic radius sufficiently larger than that of zirconium and form a zirconate perovskite compound having a perovskite-type crystal structure. In the present invention, R is more preferably at least one element selected from the group consisting of Sr, Ca, and Ba. These elements undergo a solid-phase reaction with zirconium under predetermined temperature conditions to form the zirconate perovskite compound. Therefore, the ferrite particles of the present invention can be obtained by controlling the firing temperature within a predetermined temperature range in the ferrite particle production process.

[0054] The alkaline earth metal element (R) content is more preferably 0.1 mol% or more and 3.0 mol% or less. By including the alkaline earth metal element (R) within this range, the content of the crystalline phase component consisting of the perovskite-type crystal represented by the composition formula RZrO3 will be approximately within the above range, and ferrite particles can be obtained that have high magnetization, high resistance, and little environmental dependency of resistance. The alkaline earth metal element (R) content in the ferrite particles is more preferably 1.0 mol% or less, and even more preferably 1.5 mol% or less.

[0055] Alkaline earth metal elements react with iron in a solid state to form ferrites with magnetoplumbite-type crystal structures and their precursors. When alkaline earth metal elements are contained within the above ranges, the ferrite particles contain various components with different crystal structures, such as ferrites with magnetoplumbite-type crystal structures, as minor components, along with zirconium dioxide and perovskite zirconate compounds derived from the zirconium raw material. For example, when a crystalline phase with a different crystal structure, such as a spinel-type crystal structure, is the main component, if a minor component with a different crystal structure from the main component is present inside the particle, the main component will grow in the direction of the particle surface, where it is relatively easy to grow, resulting in appropriate particle surface irregularities. Furthermore, by uniformly incorporating these minor components inside the particle, the particle surface irregularities can be controlled to a uniform state, and the surface roughness Rz can be kept within the above range.

[0056] (3) Alkaline earth metal element and zirconium content Furthermore, the total amount of alkaline earth metal element and zirconium is preferably 0.2 mol% to 1.5 mol%. When both elements are contained within such a range, it becomes easier to keep the surface roughness Rz and resistivity of the ferrite particles within the range of the present invention.

[0057] (4) Crystalline phase component content When the phase composition of the crystalline phase constituting the ferrite particles is analyzed by Rietveld analysis of the X-ray diffraction pattern, the crystalline phase component consisting of the perovskite-type crystal represented by the composition formula RZrO3 is preferably contained in an amount of 0.05 mass % to 4.00 mass %.

[0058] When the content ratio of the crystalline phase component consisting of perovskite-type crystals represented by the composition formula RZrO3 is within the above range, it becomes easy to uniformly disperse the crystalline phase component inside the ferrite particles, and ferrite particles having high magnetization and high resistivity and good environmental dependency of resistivity can be obtained.

[0059] To achieve these effects, the ferrite particles preferably contain 0.10% by mass or more of the crystalline phase component, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more. The ferrite particles may contain 3.50% by mass or less of the crystalline phase component, or 3.00% by mass or less, and even if the content is 1.50% by mass or less, the effects of the present invention can be obtained.

[0060] 1-2-2. Composition (composition of main components) The composition of the ferrite particles is not particularly limited as long as they contain a crystalline phase component made of perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element). However, from the viewpoint of obtaining ferrite particles having resistance and magnetization suitable for use as a core material for a carrier in a two-component electrophotographic developer, it is preferable that the ferrite particles contain, as a main component, a crystalline phase component made of spinel-type crystals represented by the composition formula (MO)a(Fe2O3)b (where M is at least one metal element selected from the group consisting of Fe, Mg, Mn, Cu, Zn, and Ni, and a+b=100 (mol%)).

[0061] Ferrite has a crystal structure such as a spinel crystal structure, a magnetoplumbite crystal structure, or a garnet crystal structure, and ferrite with a spinel crystal structure exhibits soft magnetic properties and is easy to adjust electrical properties such as resistance, making it suitable as a carrier core material for electrophotographic developers. The term "main component" refers to the fact that, when the ferrite contains multiple crystal phase components (including a crystal phase component consisting of a perovskite crystal represented by the above-mentioned RZrO3 composition formula (where R is an alkaline earth metal element)), the spinel crystal phase accounts for the largest proportion of these crystal phase components. In particular, the spinel crystal phase component preferably accounts for 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. The ferrite particles are preferably spinel ferrite particles, excluding the perovskite crystal phase component and inevitable impurities. The content of the spinel phase crystalline phase component can be determined by the composition of the metal elements, and can be the mass fraction obtained when the phase composition of the crystalline phase constituting the ferrite particles is analyzed by Rietveld analysis of the X-ray diffraction pattern described below.

[0062] Furthermore, it is more preferable that the ferrite particles have a main composition consisting of a crystalline phase component made of a spinel-type crystal represented by the composition formula (MnO)x(MgO)y(Fe2O3)z (where 15≦x≦50, 2≦y≦35, 45≦z≦60, and x+y+z=100 (mol%)). By combining the above-mentioned composition with a conventional ferrite production method, it is possible to obtain ferrite containing 50 mass% or more of the spinel-type crystalline phase component. In the ferrite particles according to the present invention, the content of the spinel-type crystalline phase component is preferably 75 mass% or more, more preferably 85 mass% or more, even more preferably 95 mass% or more, even more preferably 96 mass% or more, and even more preferably 98 mass% or more.

[0063] By using a composition containing Mn, the magnetization on the low magnetic field side can be increased. Also, by using a composition containing Mn, re-oxidation of ferrite during furnace discharge after main firing can be prevented. In particular, by setting the content of Mn to 15 mol% or more, an increase in the content of Fe can be relatively suppressed, and an increase in the content ratio of the magnetite component in the ferrite particles can be suppressed. Therefore, a decrease in magnetization on the low magnetic field side can be suppressed, and the occurrence of carrier adhesion can be suppressed. Also, since it becomes easy to adjust to a good resistance value in electrophotographic printing, the occurrence of image defects such as fogging, deterioration of gradation, and white spots can be suppressed. Furthermore, the toner consumption can be kept appropriate. By setting the content of Mn to 50 mol% or less, it is possible to suppress the occurrence of image defects such as white spots due to excessive increase in resistance.

[0064] By using a composition containing Mg, high-resistance ferrite particles can be obtained. Also, by setting the content of Mg to 2 mol% or more, the content of Mn becomes appropriate with respect to the content of Fe, and it becomes easy to adjust the magnetization and resistance of the ferrite particles within a good range for electrophotographic printing. Therefore, the occurrence of image defects such as fogging, deterioration of gradation, occurrence of streaks, and carrier scattering can be suppressed. Furthermore, when magnesium hydroxide is used as the Mg raw material, if the firing temperature during the production of the ferrite particles is low, hydroxyl groups may remain in the ferrite particles. By setting the content of Mg to 35 mol% or less, the amount of residual hydroxyl groups present due to the raw materials can be reduced. Therefore, it is possible to suppress the electrical properties such as the charge amount and resistance of the ferrite particles from being affected by the ambient humidity and fluctuating, and to make the environmental dependence of the electrical properties of the ferrite particles better.

[0065] The ferrite particles are magnetic oxides mainly composed of ferric oxide. Therefore, it is premised that x < z is satisfied. By setting the content of Fe to 45 mol% or more and 60 mol% or less, it becomes easy to adjust the magnetization and resistance of the ferrite particles within a good range for electrophotographic printing.

[0066] 1-3.Magnetic properties Next, we will discuss the magnetic properties of the ferrite particles. When using these ferrite particles as the core material of a carrier for electrophotographic developers, it is preferable that the saturation magnetization measured by VSM in a magnetic field of 1K·1000 / 4π·A / m be between 50 emu / g and 65 emu / g. A saturation magnetization of 50 emu / g or higher provides a high magnetic force for the core material, effectively suppressing carrier scattering due to low magnetization. Furthermore, while saturation magnetization and electrical resistance are in a trade-off relationship, a ferrite particle with a saturation magnetization within this range achieves a good balance between the two, resulting in an electrophotographic developer capable of producing high-quality electrophotographic prints. Furthermore, high magnetization but low resistance can cause carrier scattering due to low resistance. A saturation magnetization of 65 emu / g or lower effectively suppresses carrier scattering due to low resistance.

[0067] 1-4.Physical properties (1) Volume average particle size (D 50 ) When the ferrite particles are used as a core material of a carrier for an electrophotographic developer, the volume average particle diameter (D 50 ) is preferably 24 μm or more and 40 μm or less. However, the volume average particle diameter referred to here refers to a value measured by a laser diffraction / scattering method in accordance with JIS Z 8825:2013. When the volume average particle diameter is within this range, the charge imparting ability to the toner is high and the charge imparting ability can be maintained for a long period of time. Therefore, the life of the electrophotographic developer can be extended.

[0068] In contrast, the volume average particle size (D 50 If the volume average particle diameter (D ) of the ferrite particles is less than 24 μm, the particle diameter is small and the carrier scattering is likely to occur. 50If the particle diameter is less than 24 μm, the ferrite particles are prone to agglomeration due to their small particle size. When the ferrite particles are used as a core material and their surfaces are coated with a resin to form a carrier, if the ferrite particles are agglomerated, the surfaces of the individual ferrite particles cannot be adequately coated with the resin. If the ferrite particles subsequently disaggregate during the production or use of the developer, the developer will have a high content of carrier particles with large areas not coated with resin. Therefore, producing a developer using a carrier with such ferrite particles as a core material is not preferable because it may not be possible to obtain sufficient charge imparting properties to the toner.

[0069] On the other hand, the volume average particle size (D 50 When the volume average particle diameter (D ) exceeds 40 μm, the particle diameter of each particle constituting the powder becomes large. 50 Compared with ferrite particles with a small particle size, the surface area of ​​the carrier that contributes to frictional charging with the toner is smaller when viewed as a whole powder. As a result, sufficient charge imparting properties to the toner may not be obtained. To remedy this, the surface area of ​​the carrier that contributes to frictional charging with the toner can be increased by imparting irregularities to the surface of each ferrite particle, thereby increasing the surface area of ​​the carrier. In this case, although the charge imparting properties to the toner are improved, mechanical stress is applied to the protrusions on the carrier surface when mixing with the toner, which is undesirable because it makes the carrier more susceptible to cracking and chipping. In other words, the strength of the carrier may not be maintained when used in a developer, which is undesirable.

[0070] (2) Shape factor SF-1 (circularity) The ferrite particles preferably have a shape factor SF-1 calculated based on the following formula of 100 or more and less than 120. The closer the value of the formula is to 100, the closer the shape of the ferrite particles is to a perfect sphere. When the shape factor SF-1 of the ferrite particles is within the above range, it means that the ferrite particles are approximately spherical and have an approximately circular cross section.

[0071] SF-1 = (R2 / S)×(π / 4)×100 however, R: Feret diameter (maximum), S: Area (projected area)

[0072] 2. Carrier for electrophotographic developer Next, the electrophotographic developer carrier according to the present invention will be described. The electrophotographic developer carrier according to the present invention is characterized by comprising the above-mentioned ferrite particles and a resin coating layer provided on the surface of the ferrite particles. That is, the above-mentioned ferrite particles are characterized by being used as a core material of the electrophotographic developer carrier. Since the ferrite particles have been described above, the resin coating layer will be mainly described here.

[0073] (1) Types of coating resin The type of resin (coating resin) constituting the resin coating layer is not particularly limited. Examples include fluororesins, acrylic resins, epoxy resins, polyamide resins, polyamideimide resins, polyester resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, phenolic resins, fluoroacrylic resins, acrylic-styrene resins, and silicone resins. Modified silicone resins, such as silicone resins modified with acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins, may also be used. For example, from the viewpoint of suppressing resin peeling due to mechanical stress during stirring and mixing with the toner, the coating resin is preferably a thermosetting resin. Suitable thermosetting resins for the coating resin include epoxy resins, phenolic resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, and resins containing these. However, as mentioned above, the type of coating resin is not particularly limited, and an appropriate resin can be selected depending on the type of toner to be combined, the usage environment, and the like.

[0074] The resin coating layer may be formed using one type of resin, or two or more types of resins. When two or more types of resins are used, two or more types of resins may be mixed to form one resin coating layer, or multiple resin coating layers. For example, it is preferable to provide a first resin coating layer having good adhesion to the ferrite particles on the surface of the ferrite particles, and then provide a second resin coating layer on the surface of the first resin coating layer to impart the desired charging performance to the carrier.

[0075] (2) Resin coating amount The amount of resin coating the surface of the ferrite particles (resin coating amount) is preferably 0.1% by mass or more and 10% by mass or less of the ferrite particles used as the core material. If the resin coating amount is less than 0.1% by mass, it becomes difficult to sufficiently coat the surface of the ferrite particles with resin, making it difficult to obtain the desired charge-imparting ability. Furthermore, if the resin coating amount exceeds 10% by mass, aggregation of carrier particles occurs during production, resulting in reduced productivity such as a decrease in yield, and also in fluctuations in developer properties such as developer fluidity in the actual machine and developer charge-imparting ability to toner, which is undesirable.

[0076] (3) Additives The resin coating layer may contain additives such as conductive agents and charge control agents for the purpose of controlling the carrier's electrical resistance, charge amount, and charging speed. Examples of conductive agents include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents. However, because the electrical resistance of conductive agents is low, adding too much conductive agent can easily cause charge leakage. In particular, the ferrite particles control the surface irregularities, making the convex portions leak points when a resin coating layer is applied. This allows the amount of conductive agent added to be reduced compared to conventional methods. For example, the content of the conductive agent is preferably 0.1% to 12.0% by mass, more preferably 0.1% to 10.0% by mass, and even more preferably 0.1% to 8.0% by mass, based on the solid content of the coating resin.

[0077] Examples of charge control agents include various charge control agents commonly used for toners and silane coupling agents. While the types of these charge control agents and coupling agents are not particularly limited, preferred examples include nigrosine dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, as well as aminosilane coupling agents and fluorine-based silane coupling agents. The content of the charge control agent is preferably 0.25% by mass or more and 20.0% by mass or less, more preferably 0.5% by mass or more and 15.0% by mass or less, and even more preferably 1.0% by mass or more and 10.0% by mass or less, based on the solid content of the coating resin.

[0078] 3. Electrophotographic Developer Next, an embodiment of the electrophotographic developer according to the present invention will be described. The electrophotographic developer contains the above-mentioned carrier for electrophotographic developer and toner.

[0079] As the toner constituting the electrophotographic developer, for example, either a polymerized toner produced by a polymerization method or a pulverized toner produced by a pulverization method can be preferably used. These toners may contain various additives and may be any toner as long as they can be used as an electrophotographic developer in combination with the above-mentioned carrier.

[0080] Volume average particle size of toner (D 50 The volume average particle diameter (D) of the toner is preferably 2 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less. 50 ) is within the above range, an electrophotographic developer capable of performing high-quality electrophotographic printing can be obtained.

[0081] The mixture ratio of the carrier to the toner, i.e., the toner concentration, is preferably 3% by mass or more and 15% by mass or less. An electrophotographic developer containing toner at this concentration can easily obtain a desired image density and can more effectively suppress fogging and toner scattering.

[0082] On the other hand, when the electrophotographic developer is used as a replenishment developer, the amount of toner is preferably 2 parts by mass or more and 50 parts by mass or less per part by mass of carrier.

[0083] The electrophotographic developer can be suitably used in various electrophotographic developing devices that employ a magnetic brush development method in which a carrier is attracted and attached to a magnetic drum or the like by magnetic force to form a brush-like toner, and a visible image is formed by attaching the toner to an electrostatic latent image formed on a photosensitive member or the like while applying a bias electric field.The electrophotographic developer can be used not only in electrophotographic developing devices that use a DC bias electric field when applying a bias electric field, but also in electrophotographic developing devices that use an AC bias electric field in which an AC bias electric field is superimposed on a DC bias electric field.

[0084] 4. Manufacturing method Hereinafter, methods for producing the ferrite powder, the carrier core material for an electrophotographic developer, the carrier for an electrophotographic developer, and the electrophotographic developer according to the present invention will be described.

[0085] 4-1. Ferrite powder and carrier core material for electrophotographic developers The ferrite powder and the carrier core material for an electrophotographic developer according to the present invention can be produced as follows.

[0086] First, raw materials are weighed in appropriate amounts to obtain the desired ferrite composition, and then pulverized and mixed in a ball mill or vibration mill for 0.5 hours or more, preferably 1 hour to 20 hours, and then calcined.

[0087] For example, to produce ferrite particles (spinel-type ferrite particles) whose main component is a crystalline phase component made of a spinel-type crystal represented by the composition formula (MnO)x(MgO)y(Fe2O3)z (where 15≦x≦50, 2≦y≦35, 45≦z≦60, and x+y+z=100 (mol%)), raw materials are weighed and pulverized and mixed so that x, y, and z have desired values. As raw materials, it is preferable to use, for example, Fe2O3, Mg(OH)2 and / or MgCO3, and one or more manganese compounds selected from the group consisting of MnO2, Mn2O3, Mn3O4, and MnCO3.

[0088] The ferrite particles according to the present invention contain a crystalline phase component consisting of a perovskite-type crystal represented by the formula RZrO3 (where R is an alkaline earth metal element). Therefore, for the alkaline earth metal element (R), an oxide of the alkaline earth metal element (R) is used as a raw material, weighed out to the desired amount, and pulverized and mixed with other raw materials. For Zr, ZrO2 can be used as a raw material.

[0089] When producing ferrite particles containing 0.05% by mass to 4.00% by mass of the perovskite-type crystal phase component (this is the mass fraction obtained by analyzing the phase composition of the crystalline phase constituting the ferrite particles by Rietveld analysis of the X-ray diffraction pattern), the molar ratio of ZrO2 to 100 of the main component raw material is preferably 0.1 to 3.0, and more preferably 0.2 to 1.5. Furthermore, the molar ratio of ZrO2 to 100 of the main component raw material is preferably 0.1 to 3.0, and more preferably 0.2 to 1.5. The perovskite-type crystal phase component is generated by a solid-phase reaction between the oxide of the alkaline earth metal element (R) and ZrO2. Therefore, by appropriately changing the amounts and ratios of the oxide of the alkaline earth metal element (R) and ZrO2 added within the above-mentioned preferred blending ranges, it is possible to adjust the amount of the crystalline phase component consisting of the perovskite-type crystal produced.

[0090] Furthermore, in order to control the Rz of the ferrite particles within the range of the present invention, it is preferable to add an alkaline earth metal element and zirconium dioxide in a total amount ranging from 0.2 mol% to 1.5 mol%. If the total amount of alkaline earth metal element and zirconium is less than 0.2 mol%, the surface roughness Rz of the ferrite particles tends to increase, and the standard deviation Rzσ also tends to increase. On the other hand, if the total amount of both elements is more than 1.5 mol%, Rz tends to decrease. Therefore, from the viewpoint of easily controlling the surface roughness Rz within the range of the present invention, it is preferable to add both elements in a total amount within the above-mentioned range.

[0091] When producing the ferrite particles of the present invention, ZrO2 is weighed out to the desired amount and pulverized and mixed with other raw materials. To uniformly disperse zirconium dioxide inside the particles, it is desirable to add zirconium dioxide when pulverizing and mixing the raw materials. It is also preferable to pulverize and mix the raw materials other than ZrO2, calcinate them in the atmosphere, add ZrO2, and then pulverize and mix them further. In this case, the pulverized mixture of the raw materials other than ZrO2 is pelletized using a press or other molding machine, calcined in the atmosphere at a temperature of 700°C to 1200°C, and then ZrO2 is added.

[0092] After all raw materials including ZrO2 are pulverized and mixed, or after raw materials other than ZrO2 are pulverized and mixed and calcined, a predetermined amount of ZrO2 is added to the calcined product, which is then pulverized using a ball mill or vibration mill. In either case, water is added to the pulverized mixture and finely pulverized using a bead mill or the like to obtain a slurry. The degree of pulverization can be controlled by adjusting the diameter, composition, and pulverization time of the beads used as media. To uniformly disperse the raw materials, it is preferable to use fine beads with a particle size of 1 mm or less as media. Furthermore, to uniformly disperse the raw materials, the volume average particle size (D 50 ) is preferably pulverized to 2.5 μm or less, and more preferably 2.0 μm or less.

[0093] In addition to this, in order to obtain the ferrite particles according to the present invention, the BET specific surface area is 20 to 150 m 2 / g, and the volume average particle size (D 50 It is desirable to use ZrO2 having a particle size (D ) of 0.5 μm to 2.5 μm as the raw material. By using a raw material with such properties, ZrO2 can be well dispersed within the particles, while the growth of the crystalline phase components consisting of perovskite-type crystals can be uniformly promoted. Segregation of the crystalline phase components within the particles and abnormal grain growth of each crystalline phase component can be suppressed, making it easy to control the surface roughness Rz within the range of the present invention. Therefore, even when mechanical stress is applied, cracks and chips can be suppressed at the interface between different crystalline phases that are not solid-soluble with each other, and the strength of the ferrite particles can be improved. Furthermore, in order to suppress abnormal grain growth, it is preferable to use a particle size (D ) on the coarse side of the particle size distribution. 90 ) is preferably pulverized to 3.5 μm or less. By adjusting these, the crystalline phase components made of perovskite crystals can be dispersed more uniformly from the surface to the interior of the particles.

[0094] Next, it is preferable to add a dispersant, a binder, etc. to the slurry obtained in this way as needed to adjust the viscosity to 2 to 4 poises. In this case, polyvinyl alcohol or polyvinylpyrrolidone can be used as the binder.

[0095] The slurry prepared as described above is sprayed and dried using a spray dryer to obtain granules. The granulation conditions are preferably a discharge rate of 20 Hz to 50 Hz, an atomizer disk rotation speed of 11,000 rpm to 20,000 rpm, and a drying temperature of 100°C to 500°C. For example, to obtain ferrite particles having an apparent density within the above range, the atomizer disk rotation speed is preferably 11,000 rpm to 16,000 rpm, and a drying temperature of 150°C to 300°C.

[0096] Next, it is preferable to classify the granulated material before firing it to remove fine particles contained in the granulated material in order to obtain ferrite powder with a uniform particle size. The classification of the granulated material can be carried out using a known air classification or a sieve.

[0097] Next, the classified granules are fired. The granules are preferably fired primarily in a firing furnace such as a rotary kiln, in which the granules (material to be fired) are passed through a hot section while being fluidized, and then fired.

[0098] By performing the primary firing in a firing furnace such as a rotary kiln, in which the granulated material is passed through a hot section while flowing, it is possible to remove organic substances such as binders used during granulation from the granulated material in a relatively short time and uniformly, compared to performing the primary firing while the granulated material is left stationary in a kiln, etc. At the same time, it is possible to advance part of the ferrite reaction during the primary firing, thereby suppressing variations in the surface Rz during the subsequent main firing.

[0099] Furthermore, when primary firing is performed using the above-described type of firing furnace, the temperature is preferably, for example, 850°C or higher and 1050°C or lower. By performing primary firing within this temperature range, organic matter removal and ferrite reaction are efficiently performed while suppressing abnormal grain growth, making it easier to suppress the occurrence of variations in surface roughness Rz as described above. Furthermore, in order to more efficiently remove organic matter and perform ferrite reaction, the primary firing temperature is preferably higher than 850°C, and more preferably higher than 900°C or higher. Furthermore, in order to suppress abnormal grain growth, the primary firing temperature is more preferably lower than 1050°C, and even more preferably lower than 1000°C or lower, for example, 980°C or lower.

[0100] To produce ferrite particles with low electric field dependence of resistance that satisfies the above formula (2), the main sintering is preferably carried out in a weakly oxidizing atmosphere at a temperature of 850°C or higher for 4 to 24 hours. The main sintering is preferably carried out at a temperature higher than that of the primary sintering. However, the main sintering temperature is not particularly limited as long as the ferrite particles according to the present invention are obtained. Here, a weakly oxidizing atmosphere refers to a nitrogen and oxygen mixed gas atmosphere in which the oxygen concentration is 0.1% by volume (1000 ppm) to 5% by volume (50,000 ppm), more preferably 0.2% by volume (2000 ppm) to 3.5% by volume (35,000 ppm), and even more preferably 0.3% by volume (3000 ppm) to 2.5% by volume (25,000 ppm). To prevent reoxidation of the particle surface after the main sintering, it is preferable to cool the particles to 300°C or lower in the weakly oxidizing atmosphere.

[0101] For example, in the present invention, in order to produce ferrite particles (spinel ferrite particles) having as a main component a crystal phase component made of spinel crystals represented by the composition formula (MnO)x(MgO)y(Fe2O3)z (where 15≦x≦50, 2≦y≦35, 45≦z≦60, x+y+z=100 (mol %)), it is more preferable to carry out the main sintering by holding the temperature in a temperature range suitable for generating ferrite components made of spinel crystals (850°C or higher and 1150°C or lower) for 5 hours or longer and shorter than 10 hours before reaching the sintering temperature, in order to sufficiently grow the ferrite crystal grains made of spinel crystals and disperse the zirconium component at the grain boundaries, and then holding the temperature for 1 hour or longer at a temperature suitable for generating a crystal phase component made of perovskite crystals represented by the composition formula RZrO3, such as strontium zirconate. Slow firing for a long period of time at a temperature suitable for generating a ferrite component consisting of spinel crystals, the main component, can promote grain growth and increase the surface roughness Rz. However, when holding for 5 hours or more but less than 10 hours at a temperature range suitable for generating a ferrite component consisting of spinel crystals (850°C or more but 1150°C or less), it is also possible to hold at a predetermined temperature (e.g., 1000°C, 1100°C, etc.) within the range of 850°C or more but 1150°C or less. For example, by setting the heating rate within this temperature range to 60°C / hour or less, the heat load time at 850°C or more but 1150°C or less can be adjusted to 5 hours or more but less than 10 hours. In short, firing for 5 hours or more but less than 10 hours is sufficient in a firing furnace at 850°C or more but 1150°C or less. Then, the mixture is held at a temperature (main firing temperature) suitable for generating a crystalline phase component consisting of perovskite-type crystals represented by the composition formula RZrO3, such as strontium zirconate, for one hour or more, thereby obtaining the ferrite particles of the present invention.

[0102] For example, in the case of strontium zirconate (SrZrO3), in order to sufficiently generate a crystalline phase component consisting of perovskite crystals while keeping the apparent density within the range of the present invention, the sintering temperature is preferably 1170°C to 1400°C, more preferably 1180°C to 1350°C, and even more preferably 1200°C to 1330°C, and it is preferable to hold the sintering temperature at this temperature for one hour or more. In this case, the amount of zirconium oxide (ZrO2) blended is preferably 0.2 mol to 3.00 mol.

[0103] For example, in the case of calcium zirconate (CaZrO) or barium zirconate (BaZrO), it is preferable to pulverize the raw materials, add a reaction accelerator, and then sinter them at a predetermined temperature. To generate a crystalline phase component consisting of perovskite crystals of calcium zirconate (CaZrO) or barium zirconate (BaZrO), sintering at a high temperature of 2000°C or higher is required without adding a reaction accelerator. On the other hand, by pulverizing the raw materials to a primary particle size of several tens of nanometers and adding an aluminum compound (e.g., alumina (AlO)) as a reaction accelerator, it is possible to generate a crystalline phase component consisting of these perovskite crystals even at a sintering temperature of 1500°C or lower. Thus, the ferrite particles of the present invention can be obtained by maintaining the temperature appropriate for generating a crystalline phase component consisting of perovskite crystals according to the desired composition and adjusting other conditions as necessary.

[0104] Unlike the primary firing, the main firing is preferably performed in a firing furnace such as a tunnel kiln or elevator kiln, in which the granulated material (material to be fired) is placed in a container or the like and passed through the hot section while remaining stationary, rather than in a firing furnace such as a rotary kiln, in which the granulated material passes through the hot section while flowing. In firing furnaces such as a rotary kiln, in which the granulated material passes through the hot section while flowing, if the oxygen concentration in the firing atmosphere is low, the granulated material may adhere to the inner surface of the furnace as it passes through the hot section, preventing sufficient heat from being applied to the granulated material as it flows through the hot section. In such cases, the granulated material passes through the hot section without being fully sintered, and the resulting fired material often has sufficient surface sintering but insufficient internal sintering. Such fired products not only lack the strength required for a carrier core material for electrophotographic developers, but also lack the magnetic and electrical properties required for a carrier core material for electrophotographic developers due to insufficient internal ferrite reaction. Furthermore, if the sintering inside the fired product is insufficient, the crystalline phase component consisting of perovskite crystals represented by the composition formula RZrO3 cannot be sufficiently generated during the firing process, making it difficult to obtain the ferrite particles according to the present invention.

[0105] On the other hand, if the granulated material is placed in a kiln or the like and left stationary while being fired in a firing furnace that passes through a hot section, the interior of the fired material can be sufficiently sintered, making it easier to obtain ferrite particles that have high magnetization and high resistivity and in which a sufficient amount of crystalline phase components consisting of perovskite crystals represented by the composition formula RZrO3 are produced. For these reasons, it is preferable to use a tunnel kiln, elevator kiln, or the like when performing the main firing step.

[0106] The fired product is then crushed and classified to obtain ferrite particles. The particle size is adjusted to the desired size using conventional classification methods such as air classification, mesh filtration, and sedimentation. When dry recovery is performed, recovery can also be performed using a cyclone or the like. When adjusting the particle size, two or more of the above-mentioned classification methods may be selected and used, or the conditions for one classification method may be changed to remove coarse and fine particles.

[0107] 4-2. Carrier for electrophotographic developer The electrophotographic developer carrier according to the present invention comprises the above-described ferrite particles as a core material, and a resin coating layer provided on the surface of the ferrite particles. The resin constituting the resin coating layer is as described above. When forming the resin coating layer on the surface of the ferrite particles, known methods such as brush coating, spray drying using a fluidized bed, rotary drying, and immersion drying using a universal mixer can be used. To improve the ratio of the resin coating area to the surface of the ferrite particles (resin coverage), it is preferable to use a spray drying method using a fluidized bed. Regardless of which method is used, the ferrite particles can be subjected to a resin coating treatment once or multiple times. The resin coating liquid used to form the resin coating layer may contain the above-described additives. Furthermore, the amount of resin coating on the surface of the ferrite particles is as described above, and therefore will not be described here.

[0108] After applying the resin coating liquid to the surface of the ferrite particles, baking may be performed by external heating or internal heating, as necessary. For external heating, a fixed or fluidized type electric furnace, a rotary electric furnace, a burner furnace, or the like can be used. For internal heating, a microwave furnace can be used. If a UV-curable resin is used as the coating resin, a UV heater is used. Baking must be performed at a temperature above the melting point or glass transition point of the coating resin. If a thermosetting resin or a condensation cross-linking resin is used as the coating resin, baking must be performed at a temperature at which the resin is sufficiently cured.

[0109] 4-3. Electrophotographic developer Next, a method for producing an electrophotographic developer according to the present invention will be described. The electrophotographic developer according to the present invention contains the above-mentioned carrier for electrophotographic developer and a toner. As the toner, either a polymerized toner or a pulverized toner can be preferably used, as described above.

[0110] Polymerized toner can be produced by known methods such as suspension polymerization, emulsion polymerization, emulsion aggregation, ester elongation polymerization, and phase inversion emulsification. For example, a colored dispersion in which a colorant is dispersed in water using a surfactant is mixed and stirred with a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium to emulsify and disperse the polymerizable monomer in the aqueous medium. Polymerization is then carried out while stirring and mixing, and a salting-out agent is added to salt out the polymer particles. The particles obtained by salting out are filtered, washed, and dried to obtain a polymerized toner. Thereafter, an external additive may be added to the dried toner particles, if necessary.

[0111] Furthermore, when producing the polymerized toner particles, a toner composition containing a polymerizable monomer, a surfactant, a polymerization initiator, a colorant, etc. The toner composition may also contain a fixation improver and a charge control agent.

[0112] The pulverized toner is prepared by thoroughly mixing, for example, a binder resin, a colorant, a charge control agent, etc., in a mixer such as a Henschel mixer, then melt-kneading and uniformly dispersing the mixture in a twin-screw extruder or the like, cooling the mixture, finely pulverizing it in a jet mill or the like, and classifying it using, for example, an air classifier to obtain a toner of the desired particle size. If necessary, wax, magnetic powder, a viscosity modifier, and other additives may be added. Furthermore, external additives may be added after classification.

[0113] Next, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples. [Example]

[0114] (1) Ferrite particles In Example 1, ferrite particles containing a crystalline phase component consisting of a spinel-type crystal represented by the composition formula (MnO)x(MgO)y(Fe2O3)z as the main component and a crystalline phase component consisting of a perovskite-type crystal represented by the composition formula SrZrO3 (R = Sr) were produced as follows. First, as the main component raw materials, MnO raw material, MgO raw material, and Fe2O3 raw material were weighed out so that the molar ratios were 46.0 (MnO equivalent), 3.0 (MgO equivalent), and 51.0 (Fe2O3). Furthermore, SrO raw material was weighed out so that the molar ratio was 100 (main component raw material) to 0.30 (SrO). Here, trimanganese tetroxide was used as the MnO raw material, magnesium oxide as the MgO raw material, ferric oxide as the Fe2O3 raw material, and strontium carbonate as the SrO raw material.

[0115] The weighed raw materials were then pulverized for 5 hours in a dry media mill (vibration mill, 1 / 8-inch diameter stainless steel beads), and the resulting pulverized material was then made into pellets of approximately 1 mm square using a roller compactor. The resulting pellets were passed through a vibrating sieve with 3 mm openings to remove coarse particles, and then through a vibrating sieve with 0.5 mm openings to remove fine particles. The pellets were then heated at 800°C for 3 hours in a continuous electric furnace for pre-firing. The mixture was then pulverized using a dry media mill (vibration mill, 1 / 8-inch diameter stainless steel beads) until the average particle size was approximately 5 μm. The pulverization time was 6 hours.

[0116] The resulting pulverized material was mixed with water and a ZrO2 raw material with a BET specific surface area of ​​30 m 2 Zirconium dioxide with an average particle size of 2 μm was added and ground for 6 hours using a wet media mill (horizontal bead mill, zirconia beads with a diameter of 1 mm). Zirconium dioxide was added to the ground material so that the molar ratio of the main component raw material was 100 to ZrO2:0.25. The particle size of the resulting slurry (primary particle size of the ground material) was measured using a laser diffraction particle size distribution analyzer (LA-950, Horiba, Ltd.). 50 is approximately 1.9 μm, D 90 was 3.4 μm.

[0117] An appropriate amount of dispersant was added to the slurry prepared as described above, and 0.4% by mass of PVA (polyvinyl alcohol) was added as a binder based on the solid content (the amount of pre-calcined material in the slurry), followed by granulation and drying using a spray dryer. The particle size of the resulting granules was adjusted, and then the mixture was heated in a rotary electric furnace at 900°C for 2 hours in an air atmosphere for primary firing to remove organic components such as the dispersant and binder.

[0118] The granulated material was then sintered in a tunnel electric furnace at a sintering temperature (holding temperature) of 1215°C in an atmosphere with an oxygen concentration of 1.2% by volume for 3 hours. The heating rate to 850°C was 100°C / hour, and the heating rate from 850°C to the sintering temperature of 1215°C was 50°C / hour, with a cooling rate of 110°C / hour. The resulting sintered material was crushed using a hammer crusher, and further classified using a gyro sifter (vibrating sieve) and a turbo classifier (air classifier) ​​to adjust particle size. Low magnetic particles were separated by magnetic separation to obtain ferrite particles. The main production conditions for the ferrite particles of Example 1 are shown in Table 1.

[0119] (2) Carrier for electrophotographic developer The above ferrite particles were used as core materials, and the ferrite particles were coated with silicone resin as follows to obtain a carrier of Example 1.

[0120] First, a silicone resin solution (resin solid content 10% by mass) was prepared by mixing silicone resin (KR-350, manufactured by Shin-Etsu Silicones Co., Ltd.) and toluene. This resin solution was mixed with the ferrite particles of Example 1 using a universal stirrer, thereby coating the surfaces of the ferrite particles with the resin solution. An amount of resin solution was used such that the resin solid content relative to the ferrite particles was 1.0% by mass. The ferrite particles with the resin solution attached were then heated at 250°C for 3 hours while stirring using a heat exchange stirring / heating device, volatilizing the volatile components contained in the resin solution and drying the ferrite particles. This resulted in the electrophotographic developer carrier of Example 1, which had a resin coating layer on the surfaces of the ferrite particles.

[0121] (3) Electrophotographic developer The electrophotographic developer carrier and toner were mixed by stirring for 30 minutes using a Turbula mixer to obtain 50 g of developer (toner concentration 7.5 wt %). The toner used was a commercially available negative toner (cyan toner, manufactured by Fuji Xerox Co., Ltd., for DocuPrint C3530; average particle size approximately 5.8 μm) used in full-color printers. [Example]

[0122] In this example, the ferrite particles of Example 2 were produced in the same manner as in Example 1, except that the ZrO raw material was weighed out so that the molar ratio of ZrO to the main component raw material was 100:0.75, the SrO raw material was weighed out so that the SrO:0.75, and the firing temperature was set to 1245°C and the heating rate from 850°C to the firing temperature of 1245°C was set to 60°C / hour. The main production conditions of Example 2 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer. [Example]

[0123] In this example, the ferrite particles of Example 3 were produced in the same manner as in Example 1, except that the ZrO raw material was weighed out so that the molar ratio of ZrO to the main component raw material was 100 to 0.15, the SrO raw material was weighed out so that the SrO molar ratio was 0.15, and the firing temperature was set to 1205°C and the heating rate from 850°C to the firing temperature of 1205°C was set to 40°C / hour. The main production conditions of Example 3 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer. [Example]

[0124] In this example, ferrite particles of Example 4 were produced in the same manner as in Example 1, except that the atmospheric oxygen concentration during main firing was set to 0.7% by volume. The main production conditions for Example 4 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer. [Example]

[0125] In this example, ferrite particles of Example 5 were produced in the same manner as in Example 1, except that the atmospheric oxygen concentration during main firing was set to 1.8% by volume. The main production conditions for Example 5 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer. [Example]

[0126] In this example, the ferrite particles of Example 6 were produced in the same manner as in Example 1, except that the atmospheric oxygen concentration during the main firing was set to 0.4% by volume, the SrO raw material was weighed so that the SrO:0.15 ratio was achieved, and after the ferrite particles were obtained, they were subjected to a surface oxidation treatment (hot section in an air atmosphere, 450°C) in a rotary electric furnace equipped with a hot section and a cooling section subsequent to the hot section, followed by cooling, thereby carrying out the surface oxidation treatment. The main production conditions of Example 6 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer. Comparative Example

[0127] [Comparative Example 1] In this comparative example, the ferrite particles of comparative example 1 were produced in the same manner as in example 1, except that the ZrO raw material was weighed out so that the molar ratio of ZrO to the main component raw material was 100 to 0.90, the SrO raw material was weighed out so that the SrO molar ratio was 0.90, and the firing temperature was set to 1235°C and the heating rate from 850°C to the firing temperature of 1235°C was set to 100°C / hour. The main production conditions of comparative example 1 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer.

[0128] Comparative Example 2 In this comparative example, the ferrite particles of comparative example 2 were produced in the same manner as in example 1, except that the ZrO2 raw material was weighed out so that the molar ratio of ZrO2 to the main component raw material was 100 to 0.15, the SrO raw material was weighed out so that the SrO:0.15 molar ratio, and the firing temperature was set to 1230°C and the heating rate from 850°C to the firing temperature of 1230°C was set to 30°C / hour. The main production conditions of comparative example 2 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer.

[0129] Comparative Example 3 In this comparative example, ferrite particles were produced in the same manner as in Example 1, except that ZrO was not weighed, the SrO raw material was weighed so that the SrO:0.05 ratio was achieved, the atmospheric oxygen concentration during the main firing was set to 0% by volume, the main firing temperature was set to 1180°C, and the heating rate from 850°C to the main firing temperature of 1180°C was set to 100°C / hour. The ferrite particles of Comparative Example 3 were then produced by subjecting them to a surface oxidation treatment in the same manner as in Example 6 (except that the oxidation treatment temperature in the hot zone was 600°C). The main production conditions for Comparative Example 3 are shown in Table 1. Furthermore, a carrier for an electrophotographic developer was produced in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was produced using the carrier for an electrophotographic developer.

[0130] <evaluation> The ferrite particles of each Example and Comparative Example obtained as described above were measured for (1) the content of perovskite-type crystalline phase components, (2) the degree of dispersion of Zr element, (3) the volume average particle size, (4) the saturation magnetization, (5) the electrical properties, (6) SF-1, and (7) the surface roughness Rz. In addition, the electrophotographic developers of each Example and Comparative Example obtained as described above were used to evaluate (8) the image density and (9) the carrier scattering. The evaluation methods / measurement methods and evaluation results are described below.

[0131] 1. Evaluation method / measurement method (1) Perovskite crystal phase component content (mass%) The ferrite particles produced in each example and comparative example were used as samples, and the content of the perovskite-type crystalline phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element) in each ferrite particle was determined by Rietveld analysis of the powder X-ray diffraction pattern. Although it can be difficult to identify and quantify each crystalline phase by waveform separation of the powder X-ray diffraction pattern, Rietveld analysis based on a crystal structure model makes it possible to identify and quantify each phase.

[0132] The X-ray diffraction device used was the "X'PertPRO MPD" manufactured by PANalytical. A Co tube (CoKα rays) was used as the X-ray source. A focused optical system and a high-speed detector "X'Celarator" were used as the optical system. The measurement conditions were as follows: Scan speed: 0.08° / sec Divergence slit: 1.0° Scattering slit: 1.0° Receiving slit: 0.15 mm Voltage and current of the sealed tube: 40kV / 40mA Measurement range: 2θ=15°~90° Accumulation count: 5 times

[0133] Based on the measurement results obtained, the crystal structure was identified as follows from the structure disclosed in "National Institute for Materials Science, AtomWork (URL: http: / / crystdb.nims.go.jp / )". Phase A: A crystalline phase consisting of manganese ferrite (spinel-type crystals) Crystal structure: space group F d -3 m (No. 227) Phase B: A crystalline phase consisting of perovskite-type crystals represented by the composition formula RZrO3 Crystal structure: Space group P nma (No. 62) Phase C: Zirconium dioxide (zirconia) Crystal structure: Space group P -4 2 m (No. 111) However, in the space group Fd-3m assigned to the A phase, the Wyckoff positions of each atom were set as follows: 8b for the Mn atom, 16c for the Fe atom, and 32e for the O atom.

[0134] Next, the identified crystal structure was refined using the analytical software "RIETAN-FP v2.83 (http: / / fujioizumi.verse.jp / download / download.html)" to calculate the abundance ratio of each crystal phase in terms of mass as the phase composition ratio. The profile function was a pseudo-Voigt function of Thompson, Cox, and Hastings, and was asymmetrized by Howard's method. After confirming that the Rwp and S values, which indicate the accuracy of the fitting, were less than 2% and less than 1.5, respectively, and that the main peaks of phases B and C were fitted at 2θ = 35–37°, each parameter was optimized.

[0135] Based on the results of Rietveld analysis of the X-ray diffraction patterns obtained as described above, the content (mass%) of the crystalline phase component (phase B) consisting of perovskite-type crystals was determined when the phase composition of the crystalline phases constituting the ferrite particles was analyzed. The content (mass%) of the crystalline phase component (phase A) consisting of spinel-type crystals was also determined.

[0136] (2) Dispersion degree of Zr element The degree of dispersion of Zr element defined by the following formula was measured for the ferrite particles produced in each of the examples and comparative examples. Dispersion degree of Zr = Zr(s) / Zr(c) however, Zr(s): Zr content (mass%) in the surface area of ​​the particle cross section measured by energy dispersive X-ray analysis Zr(c): Zr content (mass%) at the center of the particle cross section measured by energy dispersive X-ray analysis

[0137] Here, an explanation will be given with reference to FIG. 1. The center of the cross section (particle cross section) of a ferrite particle is defined as follows: When the maximum diameter in the particle cross section (for example, in an SEM image) is defined as a line segment Dx, the midpoint of the line segment Dx is defined as the center C of the particle cross section, and the end points of the line segment Dx are defined as points P. Then, the center C is defined as the center position, and a square whose side length is 35% of the length of the line segment Dx is defined as square S. The area surrounded by this square S is defined as the center.

[0138] The surface portion of the cross section of the particle is defined as follows: Point P' is a point on the line segment Dx, located 15% of the length of the line segment Dx from point P toward the center C. Rectangle R1 is a rectangle whose long side is a line segment having a length of 35% of the length of the line segment Dx, perpendicular to the line segment Dx, and having point P or point P' as its midpoint, and whose short side is a line segment having a length of 15% of the length of the line segment Dx. In the present invention, the area enclosed by rectangle R1 in the cross section of the ferrite particle is defined as the surface portion. Note that FIG. 1 shows the cross-sectional shape of the ferrite particle 100 as a simplified circular shape for the purpose of explanation, and does not show the actual cross-sectional shape of the ferrite particle according to the present invention.

[0139] The central and surface regions of the particle cross section thus defined are subjected to energy dispersive X-ray analysis (EDX analysis) to measure the content of Zr element in each region. The specific measurement method is as follows.

[0140] (a) Ferrite particles are embedded in resin and cross-sections are processed by ion milling to prepare cross-section samples for measurement. Ion milling is performed using an IM4000PLUS manufactured by Hitachi High-Technogies Corporation, with the ion beam acceleration voltage set to 6.0 kV in an argon atmosphere. Here, the ferrite single particles to be analyzed are those whose volume average particle diameter is D 50 When the maximum diameter Dx is D 50 ×0.8≦Dx≦D 50 The particles are in the range of ×1.2.

[0141] (b) The cross section of the ferrite particle to be analyzed is observed using a scanning electron microscope (SEM, Hitachi High-Technogies SU8020) with an acceleration voltage of 15 kV and a working distance of 15 mm. The magnification is set so that only one ferrite particle to be analyzed is present in the field of view and the entire particle fits within the field of view.

[0142] (c) Then, EDX analysis is performed on the center and surface regions (the regions defined above) of the ferrite particle cross section. In the EDX analysis, mapping collection is performed on Fe, Mn, Mg, Sr, and Zr using an energy dispersive X-ray analyzer (Horiba, Ltd. EMax X-Max50), and the amount of each element (mass%) is calculated from the obtained X-ray spectrum peaks. The amount of Zr in the center of the obtained particle cross section is designated "Zr(c)," and the amount of Zr in the surface region of the particle cross section is designated "Zr(s)."

[0143] The Zr content in the center of the particle cross section (Zr(c)) and the Zr content in the surface of the particle cross section (Zr(s)) obtained by EDX analysis can be substituted into the above-mentioned formula (1) to obtain the degree of dispersion of Zr in the ferrite particles being analyzed.

[0144] The amount of Zr in the surface region of the particle cross section was defined as four regions enclosed by rectangle R2, which was defined similarly to rectangle R1, and rectangles R3 and R4, which were defined based on points Q and Q', which were determined similarly to points P and P' above, on a line Dy that passes through the center C of the particle cross section and is perpendicular to line Dx. The surface region was defined as the average amount of Zr in each region. Rectangles R1, R2, R3, and R4 were arranged at approximately equal intervals along the contour of the particle cross section.

[0145] Here, when there are multiple line segments Dx representing the maximum diameter for one ferrite particle, the line segments Dy (line segment QQ') that have a length of 0.5 or more relative to the line segment Dx are defined as Sx and Dy. As will be described later, the ferrite particles produced in each example are roughly granular (see SF-1 value). Therefore, if the length of the line segment Dy (line segment QQ') relative to the line segment Dx is less than 0.5, such particles are likely to be particles with cracks or chips. Therefore, the ferrite single particle to be analyzed is one in which the length of the line segment Dy (line segment QQ') relative to the line segment Dx is 0.5 or more.

[0146] (3) Volume average particle size (D 50 ) Volume average particle size (D 50 ) was measured as follows using a Microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd. The ferrite particles produced in each example and comparative example were used as samples, and 10 g of each sample and 80 ml of water were placed in a 100 ml beaker, and 2 to 3 drops of a dispersant (sodium hexametaphosphate) were added. Using an ultrasonic homogenizer (UH-150 model manufactured by SMT.Co.LTD.) at an output level of 4, dispersion was carried out for 20 seconds, and bubbles formed on the surface of the beaker were removed to prepare a sample, and the volume average particle size of the sample was measured using the Microtrac particle size analyzer.

[0147] (4) Saturation magnetization The saturation magnetization was measured using a vibrating sample magnetometer (model: VSM-C7-10A (manufactured by Toei Kogyo Co., Ltd.)). The specific measurement procedure is as follows. First, the ferrite particles produced in each example and comparative example were used as samples, and the samples were filled into a cell with an inner diameter of 5 mm and a height of 2 mm and set in the above-mentioned apparatus. A magnetic field was then applied and swept up to 1 K·1000 / 4π·A / m (=1 kOe). Next, the applied magnetic field was reduced, and a hysteresis curve was created on recording paper. From the data of this curve, the magnetization at an applied magnetic field of 1 K·1000 / 4π·A / m was read and taken as the saturation magnetization.

[0148] (5) Resistance The ferrite particles produced in each example and comparative example were used as samples, and the resistance value H 1000 (Ω), H 100 The resistance (Ω) of each electrode was measured. First, non-magnetic parallel plate electrodes (10 mm x 40 mm) were placed facing each other with an inter-electrode distance of 2.0 mm, and 200 mg of sample was filled between them. The sample was held between the parallel plate electrodes by a magnet (surface magnetic flux density: 1500 Gauss, area of ​​magnet in contact with the electrode: 10 mm x 30 mm) attached to the parallel plate electrodes. Then, a predetermined voltage (H 1000 For 1000V, H 100 A voltage of 100 V was applied and the resistance was measured using an electrometer (KEITHLEY insulation resistance meter model 16517A). 1000 , resistance value H 100 is the resistance value measured in the above-mentioned high-temperature, high-humidity environment by the above-mentioned method after exposing the sample to the above-mentioned high-temperature, high-humidity environment for 12 hours or more in a constant temperature and humidity chamber in which the atmospheric temperature and humidity are adjusted.

[0149] Also, the resistance value H measured in this way 1000 and resistance value H 100 Based on the logarithm of 100 / logH 1000 ) were calculated. The values ​​are shown in Table 1.

[0150] (6) SF-1 (Circularity) A sample solution was prepared using the ferrite particles produced in each example and comparative example, and 3,000 particles in the sample solution were observed using a particle size and shape distribution analyzer PITA-1 manufactured by Seishin Enterprise Co., Ltd. Next, the area (projected area) and Feret's diameter (maximum) were determined using the ImageAnalysis software provided with the device, and the shape index SF-1 value was calculated for each particle according to the above formula. The average value of the 3,000 particles observed was then taken as the shape index SF-1 of each ferrite particle.

[0151] The sample liquid was prepared by dispersing 0.1 g of each ferrite particle in 30 cc of xanthan gum solution with a viscosity of 0.5 Pa·s as the dispersion medium. By properly adjusting the viscosity of the dispersion medium in this way, the ferrite particles remained dispersed in the dispersion medium, allowing for smooth measurement. The measurement conditions were a 10x objective lens magnification, an ND4x2 filter, a xanthan gum solution with a viscosity of 0.5 Pa·s used to prepare the sample liquid, and the flow rates for both were 10 μl / sec, with the sample liquid flow rate being 0.08 μl / sec.

[0152] (7) Surface roughness Rz The ferrite particles produced in each of the examples and comparative examples were used as samples, and the surface roughness Rz was measured by the following method.

[0153] First, the 3D shape of the particle surface to be measured was obtained using a Lasertec Corporation hybrid laser microscope mc2000. To pretreat the sample, double-sided tape was attached to a glass slide, and ferrite particles were sprinkled on the adhesive surface to fix the ferrite particles to the glass slide. A xenon lamp was used as the light source, and the objective lens magnification was set to 100x. The ferrite particles to be measured (target particles) were selected, and the 3D shape of their surface was obtained using the auto-photography function of the LMeye7 software provided with the instrument.

[0154] Twenty-one 15.0 μm line segments were drawn at 0.75 μm intervals on the 3D image of the target particle obtained as described above, and a measured profile curve on each line segment was extracted. Each of the obtained measured profile curves was corrected using a profile filter to extract a roughness curve. The cutoff values ​​of the profile filter were λs, which separates the roughness component from shorter wavelength components, and λc, which separates the roughness component from the waviness component. The respective cutoff values ​​were set to λs = 0.0025 mm and λc = 0.0800 mm, and the surface roughness Rz was calculated from the obtained roughness curve. The average value of the values ​​obtained based on the 21 line segments was used as the Rz of each target particle. Then, 30 particles were measured using the same procedure, and the average of the surface roughness Rz values ​​of the 30 target particles was used as the surface Rz of the ferrite particles in each Example and Comparative Example.

[0155] (8) Image density The image density was evaluated as follows using the electrophotographic developers produced in each Example and Comparative Example. Image density was measured using a full-color electrophotographic developing machine (Ricoh Corporation's imagio MP C2500) in a constant temperature and humidity room where the atmospheric temperature and humidity were adjusted in a low-temperature, low-humidity environment (10°C, relative humidity 20%). A 1000 (1k) test image was printed under appropriate exposure conditions, followed by a solid image. The image density of the solid image was then measured using a spectrophotometric densitometer (X-Rite Corporation's "Model 938") and evaluated according to the following criteria. The evaluation was made according to the following criteria and judged as either ◯, △ or ×.

[0156] "○": 1.2 or higher "△": 1.0 or more and less than 1.2 "×": Less than 1.0

[0157] (9) Amount of carrier scattering The amount of carrier scattering was evaluated using the electrophotographic developers produced in each Example and Comparative Example as follows. A full-color electrophotographic developing machine (Ricoh Corporation's Imagio MP C2500) was used in a constant temperature and humidity room where the atmospheric temperature and humidity were adjusted to a high temperature and high humidity environment (30°C, 80% relative humidity). 1000 (1k) test images were printed under appropriate exposure conditions, and then three solid images were printed. The total amount of carrier scattering in the solid images was visually counted and evaluated as ○, △, or × according to the following criteria.

[0158] "○": 0 to 5 pieces "△": 6 to 10 pieces "×": 11 or more

[0159] 2. Evaluation Results Table 2 shows the measurement results for each of the above evaluation items. In Table 2, the XRD analysis values ​​indicate the content (mass%) of the perovskite-type crystalline phase component obtained by Rietveld analysis of the powder X-ray diffraction pattern. 1000 , resistance value H 100 The logarithm of each is shown.

[0160] (1) Perovskite-type crystalline phase component content and Zr element dispersion As shown in Table 2, it was confirmed that the ferrite particles of Examples 1 to 6 were obtained by using an oxide containing an alkaline earth metal element (R) and zirconium dioxide as raw materials, thereby obtaining ferrite particles containing 0.22 mass % to 0.64 mass % of a perovskite-type crystalline phase component represented by the composition formula RZrO3. Furthermore, the Zr dispersion degree in the ferrite particles of Examples 1 to 6 was small, ranging from 1.0 to 1.1, confirming that the perovskite-type crystalline phase component was well dispersed within the ferrite particles. The ferrite particles of Example 3, which used a lower total amount of zirconium dioxide and an alkaline earth metal element (R) as raw materials compared to the other Examples, had a lower content of the perovskite-type crystalline phase component compared to the other Examples. Furthermore, while the Zr dispersion degree in the other Examples was 1.0, only the ferrite particles of Example 3 showed a slightly larger Zr dispersion degree of 1.1. Although a simple comparison cannot be made between Example 2 and Example 3 because the firing conditions were different, it was confirmed that the content of the perovskite-type crystalline phase component in the ferrite particles can be adjusted by controlling the total amount of zirconium dioxide and alkaline earth metal element (R) used as raw materials and the firing conditions.

[0161] On the other hand, ferrite particles containing a perovskite-type crystalline phase component were not obtained from the ferrite particles of Comparative Example 3, in which ZrO2 was not added as a raw material. In contrast, ferrite particles containing a perovskite-type crystalline phase component were obtained from Comparative Examples 1 and 2, in which ZrO2 and SrO2 were used as raw materials in amounts equal to or greater than those of the respective Examples.

[0162] Furthermore, the ferrite particles of each of the examples and comparative examples contained 98 mass % or more of the spinel crystal phase component, and were confirmed to be spinel ferrite particles.

[0163] (2) Surface roughness Rz As shown in Table 2, the surface roughness Rz of the ferrite particles of Examples 1 to 6 was 2.1 μm or more and 4.3 μm or less. On the other hand, the ferrite particles of Comparative Example 1 had a small surface roughness Rz of 1.8 μm, and the ferrite particles of Comparative Example 2 had a large surface roughness Rz of 4.7 μm, both of which were outside the range specified in the present invention. Although the ferrite particles of Comparative Example 1 all contained perovskite-type crystalline phase components within the range specified in the present invention, the heating rate in the temperature range of 850°C to 1150°C was 100°C / hour or 30°C / hour, which was less than 5 hours or more than 10 hours, resulting in a surface roughness Rz that was either too small or too large. Furthermore, this confirmed that the surface roughness Rz can be adjusted by controlling the heating rate in the temperature range of 850°C to 1150°C.

[0164] (3) Other The volume average particle size, saturation magnetization, and SF-1 of each of the examples and comparative examples are shown in Table 2.

[0165] (4) Electrical characteristics Next, the electrical properties of each ferrite particle will be described with reference to Table 2. The ferrite particles of Examples 1 to 6 have a resistance value H 1000 Logarithm of logH 1000 , resistance value H 100 Logarithm of logH 100 The values ​​of the resistances were 6.6 to 7.9 and 7.1 to 8.2, respectively, and it was confirmed that the film had high resistance values ​​under high temperature and high humidity conditions. 1000 / logH 1000 ) is in the range of 0.83 to 0.96, and it is recognized that the electric field dependency is low and that there is little fluctuation in resistance even when the development electric field differs depending on the developing device. Furthermore, the ferrite particles of Comparative Examples 1 and 2 have the same electric field dependency as the Examples. On the other hand, the ferrite particles of Comparative Example 3 have a resistance value H 1000 could not be measured.

[0166] (5) Image density and carrier scattering amount Table 3 confirms that when carriers having ferrite particles of Examples 1 to 6 as core materials are used, good or acceptable image densities can be maintained even in low-temperature, low-humidity environments. Furthermore, when carriers having ferrite particles of Examples 1 to 6 as core materials are used, carrier scattering can be sufficiently suppressed even in high-temperature, high-humidity environments. Therefore, according to the ferrite particles of the present invention, by controlling the surface irregularities of the ferrite particles, when a resin coating layer is formed on the surface of the ferrite particles as core materials, the thickness of the resin coating layer on the convex portions is relatively thinner than that on the concave portions. Since the ferrite particles of the present invention have high resistance even in high-humidity environments, controlling the surface irregularities makes it possible to maintain high overall surface resistance of the carrier when used as a carrier, while substantially uniformly distributing low-resistance portions due to the convex portions of the ferrite particles on the carrier surface. As a result, particularly in high-humidity environments, carrier scattering is effectively suppressed, and countercharge is rapidly released after development, thereby maintaining developability.

[0167] On the other hand, when the ferrite particles of Comparative Examples 1 to 3 were used, either or both of the image density and the amount of carrier scattering were evaluated as "x." Specifically, for example, the ferrite particles of Comparative Example 1 had a resistance value within the range of the present invention, but a small surface roughness Rz. Although carrier scattering could be suppressed in a high-temperature, high-humidity environment, image density decreased in a low-temperature, low-humidity environment, and good developability could not be obtained. The ferrite particles of Comparative Example 2 had a resistance value within the range of the present invention, but a large surface roughness Rz. Although good image density was obtained in a low-temperature, low-humidity environment, carrier scattering could not be suppressed in a high-temperature, high-humidity environment. The ferrite particles of Comparative Example 3 did not contain a perovskite crystalline phase, but the effect of increasing surface resistance was achieved by subjecting them to surface oxidation treatment. However, as described above, it was recognized that the surfaces of the ferrite particles locally contained portions that were not sufficiently oxidized and exhibited low resistance, and portions that were oxidized to an excessively high resistance. As a result, the effect of reducing image density and suppressing carrier scattering could not be obtained.

[0168] [Table 1]

[0169] [Table 2]

[0170] [Table 3] [Industrial Applicability]

[0171] According to the present invention, it is possible to provide ferrite particles, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer that can suppress the occurrence of carrier scattering under high temperature and high humidity conditions and have good developability.

Claims

1. RZrO ３ (wherein R is an alkaline earth metal element), Contains 0.1 mol% or more and 3.0 mol% or less of zirconium, Ferrite particles having a surface roughness Rz of 2.0 μm or more and 4.5 μm or less, and satisfying the following formula: 6.5 ≦ logH １０００ ≦ 8.5 0.80 ≦ logH １０００ / logH １００ ≦ 1.000 logH １０００ : Resistance value H of the ferrite particles when an applied voltage of 1000 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) １０００ Logarithm of Ω (logΩ) logH １００ : Resistance value H of the ferrite particles when an applied voltage of 100 V is applied at an electrode distance of 2 mm in a high temperature and high humidity environment (30°C, relative humidity 80%) １００ Logarithm of Ω (logΩ)

2. 2. The ferrite particles according to claim 1, wherein the surface roughness Rz is 2.5 μm or more and 4.2 μm or less.

3. The ferrite particles according to claim 1 or 2, which satisfy the following formula: 6.7 ≦ logH １０００ ≦ 8.2 0.85 ≦ logH １０００ / logH １００ ≦ 1.000

4. 4. The ferrite particles according to claim 1, wherein the R is at least one element selected from the group consisting of Sr, Ca, and Ba.

5. The ferrite particles according to any one of claims 1 to 4, wherein when a phase composition analysis of the crystalline phase constituting the ferrite particles is performed by Rietveld analysis of an X-ray diffraction pattern, the ferrite particles contain 0.05 mass% or more and 4.00 mass% or less of a crystalline phase component consisting of the perovskite-type crystal.

6. The ferrite particles are (MnO)x(MgO)y(Fe ２ O ３ 6. The ferrite particles according to claim 1, wherein the ferrite particles are spinel ferrite particles mainly composed of a crystalline phase component consisting of a spinel crystal represented by a composition formula of 15≦x≦50, 2≦y≦35, 45≦z≦60, x+y+z=100 (mol %).

7. A carrier core material for an electrophotographic developer, comprising the ferrite particles according to any one of claims 1 to 6.

8. 7. A carrier for electrophotographic developer, comprising: the ferrite particles according to claim 1; and a resin coating layer provided on the surface of the ferrite particles.

9. An electrophotographic developer comprising the carrier for electrophotographic developer according to claim 8 and a toner.

10. The electrophotographic developer according to claim 9, which is used as a replenishment developer.

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